Member, IEEE Walter Lhomme

Philippe Delarue

Tiago José

Santos Moraes

Ky Ngac

Eric Nguyen

Keyu Semail

Benedicte Chen

Silvestre

Member, IEEE K Chen

B Silvestre

T J Dos

Member, IEEE, É. Semail N K Nguyen

Integrated Traction/Charge/Air Compression Supply using 3-Phase Split-windings Motor for Electric Vehicle

Keywords: Battery charger, Multiphase drive, Air-compressor, Automotive, Electric vehicle

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

I. INTRODUCTION

Increasing pure electric driving range, decreasing the battery charge time and reducing vehicle costs are the three main challenges that automotive industry has to face for developing W. Lhomme, P. Delarue, T. J. Dos Santos Moraes, N. K. Nguyen and E. Semail are with the Univ. Lille, Centrale Lille, Arts et Métiers Paris Tech, HEI, EA 2697 L2EP -Laboratoire d'Electrotechnique et d'Electronique de Puissance F-59000 Lille, France (e-mail: walter.lhomme@univ-lille1.fr; philippe.delarue@univ-lille1.fr; tiago.dossantosmoraes@ensam.eu; eric.semail@ensam.eu; ngacky.nguyen@ensam.eu).

Electric Vehicle (EV). To meet the challenges, the key components are battery chargers, electrical machines and their power electronics. In most of the cases, the charger is installed in the vehicle, allowing the battery to be recharged anywhere a power outlet is available. However, in order to restrict the on-board charger size and weight, its power is limited. To turn vehicle components more compacted with higher power, many different integrated motor drive / battery charger solutions have been studied [START_REF] Haghbin | Gridconnected integrated battery chargers in vehicle applications: review and new solution[END_REF]- [START_REF] Kolli | Space-vector PWM control synthesis for an H-bridge drive in electric vehicles[END_REF].

These integrated motor drive / battery charger solutions can be classified by single-phase or 3-phase AC supply [START_REF] Haghbin | Gridconnected integrated battery chargers in vehicle applications: review and new solution[END_REF]- [START_REF] Khaligh | Comprehensive topological analysis of conductive and inductive charging solutions for plug-in electric vehicles[END_REF]. The integrated charger using single-phase AC supply is, however, generally limited to low power charge ability. For integrated charger using 3-phase AC supply, several solutions have been proposed. In [START_REF] Cocconi | Combined motor drive and battery recharge system[END_REF] Cocconi has presented an integrated motor drive / battery charger based induction or brushless DC motor with a set of relays. In [START_REF] Lacressonniere | Converter used as a battery charger and a motor speed controller in an industrial truck[END_REF] the authors have proposed an integrated motor drive / battery charger based on a wound-rotor induction motor. Recently a split-stator winding IPMSM has been proposed for an isolated high-power integrated charger [START_REF] Haghbin | An isolated high-power integrated charger in electrified-vehicle applications[END_REF]. Nevertheless, all of the above reference solutions generate motor torque during the charging and need a set of relays to reconfigure the motor between the traction and the charging modes. For safety reasons the generation of torque needs the use of a clutch or a mechanical rotor lock. To avoid rotating field into the motor a multiphase machine has to be used [START_REF] Levi | Advances in converter control and innovative exploitation of additional degrees of freedom for multiphase machines[END_REF]. Subotic et al. have proposed to connect the 3-phase AC supply to the neutral points of isolated 3-phase windings of an N-leg inverter. N is a multiple of 3 with at least 9 phases [START_REF] Subotic | On-board integrated battery charger for EVs using an asymmetrical nine-phase machine[END_REF]. Some solutions based on 6-phase drives have also been proposed. In [START_REF] Subotic | Isolated Chargers for EVs Incorporating Six-Phase Machines[END_REF] two topologies of an isolated charger are proposed according to the stator windings, asymmetrical or symmetrical, of the 6-phase induction machine. The case with an asymmetric 6-phase requires a transformer with dual secondary that creates a 6-phase voltage supply. The machine is supposed to have a sinusoidal magnetomotive force (MMF) and the torque is only created by the 1 st harmonic of currents: a sinusoidal rotating field in the αβ frame. In this work a phase transposition between the output of grid, with or without the transformer, and the 6-phase machine is required to impose a zero torque during the charging/vehicle to grid modes and a hardware reconfiguration is required to switch between the traction and the charging mode. In [START_REF] Diab | A Nine-Switch-Converter-Based Integrated Motor Drive and Battery Charger System for EVs Using Symmetrical Six-Phase Machines[END_REF], a topology for 3-phase charging and 6-phase traction modes has been proposed for a 6-phase symmetrical machine by using only a 9 switch inverter, instead of 12. During the charging mode, controlling the middle switch of the 9-switch inverter and an additional hardware reconfiguration, composed of 9 switches, leads the 6-phase symmetrical machine become a classical 3-phase machine.

According to Levi [START_REF] Levi | Advances in converter control and innovative exploitation of additional degrees of freedom for multiphase machines[END_REF], the most developed integrated motor drive / battery charger is based on the concept of [START_REF] De-Sousa | Combined electric device for powering and charging[END_REF]- [START_REF] Sousa | A combined multiphase electric drive and fast battery charger for electric vehicles[END_REF] with associated optimized controls using numerous degrees of freedom of the structure [START_REF] Bruyere | Rotary drive system, method for controlling an inverter and associated computer program[END_REF]- [START_REF] Sandulescu | Control strategies for open-end winding drives operating in the flux-weakening region[END_REF]. [START_REF] De-Sousa | Combined electric device for powering and charging[END_REF] and [START_REF] De-Sousa | Method and electric combined device for powering and charging with compensation means[END_REF] are the first patents of this concept to present the invention of the automotive supplier Valeo, which describes an integrated 3-phase split-winding electrical machine and on-board battery charger system without static relays. In [START_REF] Sousa | A combined multiphase electric drive and fast battery charger for electric vehicles[END_REF] De Sousa et al. presents, in terms of performances and efficiencies, the comparison of this integrated system with the classical solution using a 3-leg inverter with its 3-phase electrical machine and a battery charger. The concept uses a split-windings AC motor with just a 6-leg inverter instead of at least 9 in [START_REF] Subotic | On-board integrated battery charger for EVs using an asymmetrical nine-phase machine[END_REF]. The middle point of each phase windings is connected to the 3-phase supply to achieve charging mode. This technology ensures that, during charging mode, the rotor of the electrical machine does not vibrate or rotate, because the winding configuration allows decoupling magnetically the rotor and the stator of the electrical machine. No motor reconfiguration and no supplementary static relays are necessary. It may be noted that the traction mode has already been studied in the flux-weakening region [START_REF] Sandulescu | Control strategies for open-end winding drives operating in the flux-weakening region[END_REF] and in degraded mode [START_REF] Béthoux | Real-time optimal control of a 3-phase PMSM in 2-phase degraded mode[END_REF]. A space-vector pulse width modulation (SVPWM) of the 6-leg inverter has furthermore been proposed in [START_REF] Kolli | Space-vector PWM control synthesis for an H-bridge drive in electric vehicles[END_REF].

In this paper, based on the concept of [START_REF] De-Sousa | Combined electric device for powering and charging[END_REF]- [START_REF] Sousa | A combined multiphase electric drive and fast battery charger for electric vehicles[END_REF], a further advancement is proposed to not only combine in a unique system the traction and charging, but also to provide an auxiliary system supply in traction mode: the air-compressor supply of the air-conditioning. It has been demonstrated that several electrical machines could be connected in series with an appropriate connection using a single inverter, with which an independent control for each motor can be implemented [START_REF] Levi | Even-phase multi-motor vector controlled drive with single inverter supply and series connection of stator windings[END_REF]. The middle point of the split-windings of each phase can then be connected to another electrical machine, in this paper, an air compressor during the traction mode. All in all, the 6-leg inverter achieves the functions of propulsion, charging and air-conditioning. As the number of the inverter legs is reduced, the cost, volume and weight are potentially reduced.

The objective of this paper is to show the feasibility of this integrated system that combines the traction / charge / air-compression supply modes by experimental results. Prior to this paper, it is the first time to show the three modes experimental results of this innovative system. To deal with the complexity of the multi-phase system the Energetic Macroscopic Representation (EMR) will be used [START_REF] Bouscayrol | Graphic formalisms for the control of multi-physical energetic systems: COG and EMR[END_REF]- [START_REF] Martinez | Practical control structure and energy management of a testbed hybrid electric vehicle[END_REF]. A unified control scheme is deduced from this EMR to achieve the three operation modes.

Section 2 presents the electrical architecture of the vehicle with the combined electrical drive / battery charger / air-compression supply. The modeling, the description and the overall control of the system are dealt with in section 3. Finally, experimental results with discussions are presented in section 4.

II. ELECTRICAL ARCHITECTURE OF THE INTEGRATED 3-PHASE SPLIT-WINDINGS MOTOR OF THE VEHICLE

A. Studied system

The original concept in [START_REF] De-Sousa | Combined electric device for powering and charging[END_REF]- [START_REF] Sousa | A combined multiphase electric drive and fast battery charger for electric vehicles[END_REF] uses a common power electronic converter to propel the vehicle or charge the battery at a standstill. A 6-leg inverter supplies a 3-phase open-end winding motor with an accessible central point per phase. Six of the connection points (a, a', b, b', c and c' in Fig. 1) are connected to the inverter legs, in order to supply the three phases. The other three connection points (1, 2 and 3) are connected to the 3-phase AC system.

During charge mode, the motor windings compose the charger system. As the charger windings' cost and weight are directly related to its charging power, this sharing of the motor windings results in a considerable gain of weight and cost in comparison to other proposed structures, in which the charger has its own windings. Moreover, the windings of the system present in this paper are sized to ensure the traction function of the electric motor, whose power is equivalent of a standard high power charger: 22 kW. As a conclusion, no supplementary cost or volume is needed in order to ensure its traction and charging functions. A buck-boost converter is set between the battery and the 6-leg inverter. A constant DC bus voltage is then ensured. The constraint of the battery charger is then satisfied with a high value on the voltage whatever the depth of discharge level of the battery. Compared to other charging systems, the concept proposed is an economic and compact on-board solution, compatible with any type of grids, whatever the way of energy flow: battery charger mode or vehicle-to-grid mode.

The 6-leg inverter is used either for the traction mode or for the charging mode, never at the same time. The 6-leg inverter can be seen as 3 independent 2-leg inverter. Each 2-leg inverter is used to supply one of the 3 phases of the electrical machine. A classical 3-leg inverter has 8 (=2 3 ) different states. A 6-leg inverter presents then 64 (=2 6 ) different states, which leads to more degrees of freedom to be used to optimize the modulation or to control the zero sequence current inside the machine. More information regarding fundamental principles of a 6-leg inverter can be found in [START_REF] Sandulescu | FPGA implementation of a general space vector approach on a 6-leg voltage source inverter[END_REF]. Levi et al. [START_REF] Levi | Even-phase multi-motor vector controlled drive with single inverter supply and series connection of stator windings[END_REF] has nevertheless demonstrated that it was possible to decouple the control of two series-connected multi-phase machines, even though they are supplied by the same inverter. During the propulsion mode the mid-points of the windings can then be used to supply another electrical machine. In this paper, the electrical machine will be the air compressor of the air conditioning. A switch element is required to switch between charging and air compression mode. Both used electrical machines are considered as Permanent Magnet Synchronous Machine (PMSM).

B. Operating modes

Depending on the switching element state, different operating modes can be done. Table 1 summarizes all the operating modes for the currents of the mid-point of the winding 1 and the phase-to-phase voltages. In traction mode, the 3-phase openend winding PMSM is used by controlling its currents. Since a source or a load can be connected to the mid-points of the 3phase, the machine currents im of the traction mode are not directly given. In traction mode we have chosen, imposed by the control, to set the machine current im as half of the difference of

{ 𝑖 𝑚 = 1 2 𝑇 1 𝑖 ℎ 𝑣 𝑚 = 𝑇 1 𝑣 𝑐𝑜𝑛𝑣 with 𝑇 1 = [ -1 1 0 0 0 -1 0 0 0 0 0 0 1 0 0 0 -1 1 ] { 𝑖 ℎ = [𝑖 ℎ𝑎 𝑖 ℎ𝑎 ′ 𝑖 ℎ𝑏 𝑖 ℎ𝑏 ′ 𝑖 ℎ𝑐 𝑖 ℎ𝑐 ′ ] 𝑡 𝑣 𝑐𝑜𝑛𝑣 = [𝑣𝑎𝑂 𝑣 𝑎 ′ 𝑂 𝑣 𝑏𝑂 𝑣 𝑏 ′ 𝑂 𝑣 𝑐𝑂 𝑣 𝑐 ′ 𝑂 ] 𝑡 and { 𝑖 𝑚 = [𝑖 𝑚𝑎 𝑖 𝑚𝑏 𝑖 𝑚𝑐 ] 𝑡 𝑣 𝑚 = [𝑣𝑚𝑎 𝑣 𝑚𝑏 𝑣 𝑚𝑐] 𝑡 (1)
When the system is in traction mode, the machine's phase currents imX are equal to the currents of the leg:

imX = ihX = -ihX' with X [a, b, c].

III. MODELING AND CONTROL: SYSTEMIC APPROACH

A. Modeling

Change of variables -The aim of the change of variables is to decompose the 3-phase open-end winding machine in two fictitious machines (Fig. 3). The first fictitious machine is a 3phase 4-wire machine used to create the torque Tm in the traction mode. The second fictitious machine does not create torque (T1=0). It is then equivalent to three inductors.

The first change of variables (1) leads to calculate, from the six actual currents ih and voltages vconv, the three independent fictitious currents im and voltages vm of the fictitious 3-phase 4wire machine. The second change of variables (2) allows writing the relationships of the mid-points of the windings:

{ 𝑖 𝑝123 = -𝑇 2 𝑖 ℎ 𝑣 𝑝 = 1 2 𝑇 2 𝑣 𝑐𝑜𝑛𝑣 with 𝑇 2 = [ 1 1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 1 ] and { 𝑖 𝑝123 = [𝑖 𝑝1 𝑖 𝑝2 𝑖 𝑝3 ] 𝑡 𝑣 𝑝 = [ 𝑣 𝑝1 𝑣 𝑝2 𝑣 𝑝3] 𝑡 (2)

Mode Currents Voltages

Charging Due to the architecture, the open-end winding electrical machine is not electrically coupled. The three currents ima, imb and imc then have to be controlled to produce the torque Tm. Since the mid-point connection has three wires, only two control currents are sufficient for control purpose: ip1 and ip3. The relationship (2) then has to be rewritten with these currents and the phase-to-phase voltages up:

𝑖 𝑐𝑟1 = 0 𝑖 𝑚𝑎 = 0 𝑖 𝑔1 = 𝑖 𝑝1 = -2𝑖 ℎ𝑎 = -2𝑖 ℎ𝑎 ′ { 𝑢 𝑔12 = 𝑢 𝑝12 𝑢 𝑔32 = 𝑢 𝑝32 { 𝑢 𝑐𝑟12 = 0 𝑢 𝑐𝑟32 = 0 Traction 𝑖 𝑐𝑟1 = 𝑖 𝑝1 = 0 𝑖 𝑚𝑎 = 𝑖 ℎ𝑎′ = -𝑖 ℎ𝑎 𝑖 𝑔1 = 0 { 𝑢 𝑔12 = 0 𝑢 𝑔32 = 0 { 𝑢 𝑐𝑟12 = 𝑢 𝑝12 𝑢 𝑐𝑟32 = 𝑢 𝑝32 Air Compression 𝑖 𝑐𝑟1 = 𝑖 𝑝1 = -2𝑖 ℎ𝑎 = -2𝑖 ℎ𝑎 ′ 𝑖 𝑚𝑎 = 0 𝑖 𝑔1 = 0 { 𝑢 𝑔12 = 0 𝑢 𝑔32 = 0 { 𝑢 𝑐𝑟12 = 𝑢 𝑝12 𝑢 𝑐𝑟32 = 𝑢 𝑝32 Traction + Air Compression 𝑖 𝑐𝑟1 = 𝑖 𝑝1 = -𝑖 ℎ𝑎 -𝑖 ℎ𝑎′ 𝑖 𝑚𝑎 = (𝑖 ℎ𝑎′ -𝑖 ℎ𝑎 )/2 𝑖 𝑔1 = 0 { 𝑢 𝑔12 = 0 𝑢 𝑔32 = 0 { 𝑢 𝑐𝑟12 = 𝑢 𝑝12 𝑢 𝑐𝑟32 = 𝑢 𝑝32 1 i ha i ha' i hb i hb' i hc' i hc 2 3 u p12 i p1 i p3 i p2 u p32 v ma v mc v mc Tm tract T m  tract i ma i mb i mc i mF v mb v mc u p12 u p32 i p1 i p3 v ma T l = 0  tract
{ 𝑖 𝑝123 = 𝑇 3 𝑡 𝑖 𝑝13 𝑢 𝑝 = 𝑇 3 𝑣 𝑝 with 𝑇 3 = [ 1 -1 0 0 -1 1 ] and { 𝑖 𝑝13 = [𝑖 𝑝1 𝑖 𝑝3 ] 𝑡 𝑢 𝑝 = [ 𝑢 𝑝12 𝑢 𝑝32] 𝑡 (3)
Electrical windings -The design of the electrical machine leads to a strong magnetic coupling between each of the halfphases. Considering six identical windings and neglecting saliency effects, the inductor matrix LEM of the electrical machine can be written such as:

𝐿 𝐸𝑀 = [ 𝐿 + 𝑙 𝑙 -𝐿 𝑀 -𝐿 𝐿 + 𝑙 𝑙 -𝑀 𝑀 -𝑀 𝐿 + 𝑙 𝑙 -𝑀 𝑀 -𝑀 𝑀 -𝑀 𝑀 -𝐿 𝑀 -𝑀 -𝑀 𝑀 -𝐿 𝑀 -𝑀 𝑀 -𝑀 𝑀 -𝑀 𝐿 + 𝑙 𝑙 -𝑀 𝑀 -𝑀 𝐿 + 𝑙 𝑙 -𝐿 𝑀 -𝐿 𝐿 + 𝑙 𝑙 ] (4)
In relation (4), L is the half-winding's inductance, ll represents the leakage inductance and the mutual inductance between halfwindings is noted M. The change of variables ( 1) and ( 2) leads to write ( 5) and ( 6) for the two fictitious machines:

𝑣 𝑚 -𝑒 𝑚 = 𝑑 𝑑𝑡 [
Relations ( 5) and ( 6) form a five-order system of differential equations. Nevertheless the equations between both fictitious machines are totally decoupled.

Energy sources -The paper is focused on the PMSM control of the different operating modes: traction, charging and air compression. An electrical source connected to the DC bus is considered to represent the battery and the associated chopper. An equivalent mechanical load represents the traction subsystem. The torque Tm of the electrical machine acts on this load, the reaction is the speed tract. The 6-leg converter is supplied by the DC bus with a voltage Vbus, the reaction is the current itot. The system is supplied by the grid voltages ug and reacts by circulating currents ig.

6-leg power converter -

The switch orders are mathematically represented by switching functions sij. These functions are equal to 0 when switches are open and equal to 1 when switches are closed. The DC bus Vbus and switching functions sij lead to determine the rectifier voltages vconv. As well as, converter current ih and and switching functions sij leads to determine the DC bus current iconv and then itot.

𝑖 𝑡𝑜𝑡 =
Electromechanical conversion -The electrical machine leads to the torque Tm and the back EMF em. The currents of the machine are noted im and the rotation speed Ωtract. The modeling of the machine can be found in [START_REF] Sandulescu | Control strategies for open-end winding drives operating in the flux-weakening region[END_REF].

B. Energetic Macroscopic Representation

EMR is a functional description of energetic systems for control purpose [START_REF] Bouscayrol | Graphic formalisms for the control of multi-physical energetic systems: COG and EMR[END_REF]- [START_REF] Martinez | Practical control structure and energy management of a testbed hybrid electric vehicle[END_REF]. The system is split into elementary subsystems in interaction. According to the action and reaction principle all subsystems are interconnected. The instantaneous power flow between two subsystems is the product of the action and reaction variables. In EMR, only the integral causality must be used: outputs are integral functions of inputs. This property is described with accumulation elements. Other elements are defined using equations without time dependence. The EMR of the studied architecture, without the air compressor, has been proposed in [START_REF] Lhomme | Control of a combined multiphase electric drive and battery charger for electric vehicle[END_REF] (upper part in Fig. 2). For better clarity all variables are defined as vectors. The DC bus and the grid are considered as electrical sources (green oval pictograms). The air compression and the traction subsystems are considered as mechanical sources. The inverter performs mono-domain conversions (orange square pictograms). The parallel connection couples each leg of the 6-leg inverter and the change of variables is represented by a mono-domain distribution element (overlapping squares). The inductors are accumulation elements (orange rectangle pictograms with diagonal line). The currents of the machine im and the mid-points of the windings ip are the five state variables of the studied system.

C. Inversion-based control scheme

From inversion rules, EMR can deduce an inversion-based control scheme. Two kinds of levels are organized: local and global controls. The local control level controls the different subsystems. It is described by light blue parallelograms in Fig. 2. The global control level is the EMS, which stands for Energy Management Strategy. The EMS coordinates the local control to manage the whole system. It is described by dark blue parallelograms in Fig. 2. In this study, there are two main control objectives. The first objective is to impose the torque of the machine Tm through the currents im. The second objective is to impose the currents of the grid ig for the charging mode, or the torque of the air compressor Tcp for the air compressor mode, through the currents ip. Six tuning variables, the switching functions sconv, are managed to reach this aim. From the objectives to the switching functions, the local control can then be deduced by inverting the EMR. The accumulation elements is inverted with the crossed blue parallelograms, which correspond to closed-loop controls. The conversion elements with the blue parallelograms, which correspond to an open-loop control. The energetic coupling is inverted with the overlapped blue parallelograms.

The control of the three currents of the electrical machine im allows controlling the torque Tm and the magnetic flux m (EMS traction). To simplify the calculations of the control direct-quadrature-zero transformation is used. Comparing to wyeconnected structures, this topology has one more degree of freedom (DoF) consisting in the possibility to have the zero sequence current im-o-ref.

Based on this DoF, different studies have been proposed. Indeed, in [START_REF] Sandulescu | Control strategies for open-end winding drives operating in the flux-weakening region[END_REF] the homopolar current is used to extend the range of speed with a higher torque for a 3-phase PMSM during flux weakening operation. In case of open-phase fault, having the homopolar component reduces torque ripples [START_REF] Zhao | Remedial Injected-Harmonic-Current Operation of Redundant Flux-Switching Permanent-Magnet Motor Drives[END_REF]- [START_REF] Bolognani | Experimental faulttolerant control of a PMSM drive[END_REF]. In [START_REF] Flieller | A self-learning solution for torque ripple reduction for nonsinusoidal permanent-magnet motor drives based on artificial neural networks[END_REF], using im-o-ref leads to minimum copper losses for a given torque in case where the back-EMF contains harmonics k*n (n: the number of phases, k=1, 2,…). The work presented in [START_REF] Flieller | A self-learning solution for torque ripple reduction for nonsinusoidal permanent-magnet motor drives based on artificial neural networks[END_REF] is available not only for 3-phase drives but also for multiphase drives.

Currents in rotating frame are controlled by PI controllers 𝐶 𝑚-𝑜𝑑𝑞 since their references are constant. The machine voltages are thus determined as shown in [START_REF] Diab | A Nine-Switch-Converter-Based Integrated Motor Drive and Battery Charger System for EVs Using Symmetrical Six-Phase Machines[END_REF].

𝑣 𝑚-𝑜𝑑𝑞-𝑟𝑒𝑓 = 𝐶 𝑚-𝑜𝑑𝑞 (𝑖 𝑚-𝑜𝑑𝑞-𝑟𝑒𝑓 -𝑖 𝑚-𝑜𝑑𝑞-𝑒𝑠𝑡 ) + 𝑒 𝑚-𝑜𝑑𝑞-𝑒𝑠𝑡 𝑣 𝑚-𝑟𝑒𝑓 = 𝑃(𝜃) -1 𝑣 𝑚-𝑜𝑑𝑞-𝑟𝑒𝑓 𝑖 𝑚-𝑜𝑑𝑞-𝑒𝑠𝑡 = 𝑃(𝜃)𝑖 𝑚-𝑚𝑒𝑎 𝑃(𝜃) = √ 2 3 [ cos(𝜃) cos (𝜃 - 2𝜋 3 ) cos (𝜃 + 2𝜋 3 ) -sin(𝜃) -sin (𝜃 - 2𝜋 3 ) -sin (𝜃 + 2𝜋 3 ) √2 2 √2 2 √2 2 ] (10)
The control of the mid-points currents ip13 depends of the chosen operating mode through the input switch kS.

𝑖 𝑝-𝑑𝑞-𝑟𝑒𝑓 = 𝑘 𝑆 𝑖 𝑔-𝑑𝑞-𝑟𝑒𝑓 + (1 -𝑘 𝑆 )𝑖 𝑐𝑝-𝑑𝑞-𝑟𝑒𝑓 [START_REF] De-Sousa | Combined electric device for powering and charging[END_REF] In the charging mode, when kS = 1, the objective of the control is to manage the charge of the battery from the grid. Two grid currents ig-dq-ref leads to control active and reactive power on the grid. A classical Power Factor Correction is used in this purpose inside of the "EMS charge". The grid current references are calculated, according to the power of charging, from the grid voltages. Because PI controllers are used for tracking the currents, it should be better to have constant references of current by using a Phase-Locked Loop (PLL) for frame rotation. The grid currents are only used in case of charging. The voltage references are thus determined as given in [START_REF] De-Sousa | Method and electric combined device for powering and charging with compensation means[END_REF].

𝑢 𝑝-𝑑𝑞-𝑟𝑒𝑓 = -𝐶 𝑝-𝑑𝑞 (𝑖 𝑝-𝑑𝑞-𝑟𝑒𝑓 -𝑖 𝑝-𝑑𝑞-𝑒𝑠𝑡 ) + 𝑢 𝑆-𝑒𝑠𝑡 𝑢 𝑝-𝑟𝑒𝑓 = 𝑃(𝜃) -1 𝑢 𝑝-𝑑𝑞-𝑟𝑒𝑓 [START_REF] De-Sousa | Method and electric combined device for powering and charging with compensation means[END_REF] The second coupling element of the EMR, "change of variables" in Fig. 2, deduces the two phase-to-phase voltages of the mid-points of the windings up from the three single phase voltages of the mid-points vp. This change of variable that is nonbijective, leads to the homopolar voltage vM:

𝑣 𝑝-𝑟𝑒𝑓 = 𝑣 𝐾-𝑟𝑒𝑓 + 𝑣 𝑀 with 𝑣 𝐾-𝑟𝑒𝑓 = 𝑇 4 𝑢 𝑝-𝑟𝑒𝑓 where 𝑇 4 = 1 3 [ 2 -1 -1 -1 -1 2 ] 𝑣 1𝐾-𝑟𝑒𝑓 + 𝑣 2𝐾-𝑟𝑒𝑓 + 𝑣 3𝐾-𝑟𝑒𝑓 = 0 and 𝑣 𝐾-𝑟𝑒𝑓 = [ 𝑣 1𝐾-𝑟𝑒𝑓 𝑣 2𝐾-𝑟𝑒𝑓 𝑣 3𝐾-𝑟𝑒𝑓] 𝑡 (13) 𝑣 𝑐𝑜𝑛𝑣-𝑟𝑒𝑓 = [ 𝑇 1 1 2 𝑇 2 ] -1 [ 𝑣 𝑚-𝑟𝑒𝑓 𝑣 𝑝-𝑟𝑒𝑓 ] (14)
The homopolar voltage vM can be considered as a DoF to increase the modulation index of the converter using over-modulation techniques in case of wye-connection since there is no path for zero sequence of current. In this paper, choosing The proposed control of the entire system in Fig. 2 can seem complicated but, in fact, it is no more complex than a classical control of a 3-phase electrical machine for the traction mode and a classical control of a 3-phase PWM converter for the battery charger or for supplying the compressor. Current controllers in rotating frames have been used in the control scheme. The current references are obtained from the torque in traction mode and from the required power for air compressor / charging. Regular PI controllers are used since all currents in rotating frames are constant. The only differences are inversions of coupling relations implemented by relations [START_REF] De-Sousa | Combined electric device for powering and charging[END_REF] and ( 14) that are not so complicated to implement and which do not consume lots of execution time.

IV. RESULTS AND DISCUSSION

To test the system, the studied structure is presented in Fig. 4. The grid and the air compressor are represented by an electrical drive, which will work as a generator in charging mode and as motor in compression mode. A test bench built for this experiment is reported in Fig. 5. It is composed of:  two isolated DC-sources;  an industrial drive to simulate the load for both emulators;  a current measurement box and a dSPACE MicroLabBox to carry out the proposed control. The MicroLabBox is an equipment of dSPACE with a high calculation capacity up to 2GHz for real-time processor. During the tests, the fixedstep calculation has been set up at 100 µs in Simulink control scheme. The switching frequency has been fixed at 10 kHz;  a mechanical load of 10 kW to emulate the grid and the air compressor;  a 3-phase open-end winding PMSM of 15 kW with its 6-leg inverter connected mechanically to a load drive to emulate the traction subsystem, and connected electrically at the mid-points of the windings to a 3-phase PMSM. A profile test has been carried out to examine the different operating modes (Table II). Fig. 6 reports the experimental results for example functioning cycle having three modes: charging (I), traction (II) and traction plus compression (III).

The speeds of both machines and the DC bus current are shown in Fig. 6a. The emulated grid currents and references of voltage are reported in Fig. 6b and Fig. 6e. The currents and voltage references of the 3-phase open-end machine are given in Fig. 6c and Fig. 6d.

During the charging mode, the torque Tm is controlled to zero, then the speed is also zero. The speed of the machine emulating the 3-phase grid is setting to 80 rad/s. The measured DC bus current ibus, similar to the battery power, is negative showing that the battery is in charging mode; at this time the grid currents are sinusoidal. It can be seen that the relation given in Table I for charging mode is verified by observing the currents of the two machines. Indeed, for example, ip1 = -2 iha = -2 iha' leads to the current ima = 0 and as a consequence, the torque Tm generated by the 3-phase open-end winding machine is equal to zero. The emulated grid voltages are however not perfectly sinusoidal (Fig. 6e left side) due to some harmonics of the back-EMF, mainly the 3 rd one, existing in the 3-phase machine used for the emulation of the grid.

In traction mode (mode II), only the 3-phase open-end winding machine is controlled to track a reference speed, which is fixed at 50 rad/s. The DC bus current ibus becomes positive in this mode (Fig. 6a). During the traction mode, the currents of the 3-phase open-end winding machine are balanced with a phase-shifted of 60 degrees. This means that iha =iha', ihb =ihb' and ihc =ihc' (Fig. 6c right side) and ip1 = ip2 = ip3 = 0 (Fig. 6b middle). The voltage references of the traction machine are given in Fig. 6. These voltages are determined by PI current controllers and considered as voltages of a symmetric 6-phase wye-connected machine.

In mode III, i.e when the air compressor is started at 5.56s during the traction mode, the currents crossing the 3-phase open-end machine are unbalanced due to the different speeds of both machines. The change of torque for the 3-phase PMSM emulating air compressor at 7.05 s can be seen with the value of the currents in Fig. 6b right side. The above presented results confirm the validity of the proposed structure for automotive applications by offering three operating modes by control strategies. The results given in Fig. 6 confirm that all the calculation are finished in time into the MicroLabBox. To prove the feasibility of the proposed control scheme the grid and the air compressor have been emulated with a versatile scaled-down prototype using a same PMSM. To better emulate the characteristics of the grid, a large PMSM with a small synchronous reactance and low total harmonic distortion (THD) would be preferable. Nevertheless the balanced 3-phase currents during the charging mode prove the feasibility even if the voltage of the grid contains harmonics. For the future, the real grid and a PMSM with a smaller power rating of the air compressor would be necessary to check the effectiveness of the control in real-world application scenarios. V. CONCLUSION Using a split-windings AC motor, an integrated motor drive/battery charger/air-compressor supply system has been introduced and shown its feasibility by real-time experimentation. This paper describes the unique control, in a same structure, to achieve the three operating modes: charging, traction and air-compressor supply. The integrated system proposed in this paper is expected to increase the vehicle component compactness and power, therefore potentially reduces the cost and battery charging time. In future prospects, more potentialities of this integrated system will be studied, discussed and tested.

Fig. 1 .Fig. 2 .

 12 Fig. 1. The studied 3-phase open-end winding system

Fig. 3 .

 3 Fig. 3. Equivalence between the 3-phase open-end winding machine and two 3-phase machines

  vM = 0 is necessary to eliminate im-o-ref because of the sinusoidal back-EMF. The coupling inversion element leads then to the six converter reference voltages vconv-ref from the two grid reference voltages ul-ref, the three motor reference voltages vm-ref and the homopolar voltage uh-ref. The duty cycle of the switching function conv-ref are obtained by an inversion of (8): Modulation (PWM) is then classically used to define the switching function references sconv-ref from this duty cycle.

Fig. 5 .

 5 Fig. 4. Experimental set-up scheme

Fig. 6 .

 6 Fig. 6. Experimental results: a) Measured speeds of two machines (left) and the measured current of the DC bus (right); b) Grid currents; c) 6 currents of the 3-phase open-end winding machine; d) 6 references of voltage for the 3-phase open-end machine; e) Grid voltages (emulated by the back-EMF of a 3-phase PMSM).

TABLE I .

 I CURRENTS AND VOLTAGES ACCORDING TO THE OPERATING MODES

  𝐿 𝑚 𝑖 𝑚 ] + 𝑟 𝑚 𝑖 𝑚

				𝐿 + 𝑙 𝑙 /2		𝑀	𝑀
	with 𝐿 𝑚 = 4 [	𝑀 𝑀			𝐿 + 𝑙 𝑙 /2 𝑀	𝑀 𝐿 + 𝑙 𝑙 /2	]	(5)
					1 0 0
	and 𝑟 𝑚 = 2 𝑟 𝑠 [	0 1 0	]
					0 0 1
		𝑢 𝑆 -𝑢 𝑝 =	𝑑 𝑑𝑡	[𝐿 𝑝 𝑖 𝑝13 ] + 𝑟 𝑝 𝑖 𝑝13
	with 𝐿 𝑝 =	𝑙 𝑙 2	[	2 1 1 2	] and 𝑟 𝑝 =	𝑟 𝑠 2	[	2 1 1 2	]

  𝐼 𝑖 𝑐𝑜𝑛𝑣 with I the unitary matrix of size 1 X 6 and 𝑖 𝑐𝑜𝑛𝑣 = [𝑖 11 𝑖 21 𝑖 31 𝑖 41 𝑖 51 𝑖 61 ] 𝑡

			(7)
	𝑣 𝑐𝑜𝑛𝑣 = (𝑠 𝑐𝑜𝑛𝑣 -{ 𝑖 𝑐𝑜𝑛𝑣 = 𝑠 𝑐𝑜𝑛𝑣 𝑖 ℎ 1 2 ) 𝑉 𝑏𝑢𝑠
	with 𝑠 𝑐𝑜𝑛𝑣 = [𝑠11 𝑠 21 𝑠 31 𝑠 41 𝑠 51 𝑠 61] 𝑡	(8)
	where 𝑠 𝑖𝑗 ∈ {0; 1} with 𝑖 ∈ {1; 2; 3; 4; 5; 6} the number of
	the legs
	and 𝑗 ∈ {1; 2} the number of the switch in the leg
	Switch element -The switch element commutes through the
	grid currents or the air compressor currents based on the value
	of the switch input kS:
	{ 𝑖 𝑝13 = 𝑘 𝑆 𝑖 𝑔 + (1 -𝑘 𝑆 )𝑖 𝑐𝑝 𝑢 𝑆 = 𝑘 𝑆 𝑢 𝑔 + (1 -𝑘 𝑆 )𝑒 𝑐𝑝	with 𝑘 𝑆 ∈ {0; 1}

TABLE II .

 II PROFILE TEST

	Mode	3-phase open-end winding machine	3-phase machine (grid/air compres-sor)
	Charging (Mode I)	Speed and torque null	Generator with constant speed and
			torque
	Traction (Mode II)	Acceleration then constant speed	Speed and torque null
	Traction + Compression (Mode III)	Speed constant then deceleration	Motor with constant speed and 2 steps of torque


Hussein Zahr
email: hussein.zahr@ensam.eu

Franck Scuiller
email: franck.scuiller@ecole-navale.fr

Eric Semail
email: eric.semail@ensam.eu

Five-phase SPM machine with electronic pole changing effect for marine propulsion

In this paper, the possibility of designing a fivephase Surface-mounted Permanent Magnet (SPM) machine with 20 slots and 8 poles for a low power marine propulsion system is examined. Due to its particular winding and surface magnet design, the machine inherently offers an electronic pole changing effect from 3×4 pole pairs at low speed to 4 pole pairs at high speed. At high speed, in the constant power range, according to Finite Element Analysis, the Maximum Torque Per Ampere strategy appears not to be the right solution to minimize the whole machine losses (copper, iron and magnets). In particular, a strategy that favors the 4-pole rotating field at high speed allows to mitigate the magnet losses, thus limiting the risk of magnet overheating.

I. NOMENCLATURE

SPM Surface-mounted Permanent Magnet FEA Finite Elements Analysis CPR Constant Power Range MM Main Machine (1st harmonic dq-subspace) SM Secondary Machine (3rd harmonic dq-subspace) Ω 𝑚 Mechanical speed (rad/s) 𝑝 Pole pair number 𝑅 Armature resistance 𝜖 1 , 𝜖 3 MM and SM no load back-emf at 1 rad/s 𝐿 1 , 𝐿 3 MM and SM cyclic inductances 𝜃 1 , 𝜃 3 MM and SM back-emf to current angles 𝐼 1 , 𝐼 3 MM and SM currents 𝑉 𝑏 , 𝐼 𝑏 Base RMS voltage and current Ω 𝑏 , 𝑇 𝑏 Base speed and torque

II. INTRODUCTION

Multi-phase motors are widely used in electrical marine propulsion for reasons such as reliability, smooth torque and distribution of power [START_REF] Levi | Multiphase electric machines for variable-speed applications[END_REF]. For low power propulsion system (less than 10kW), the power partition constraint results from the low DC voltage (less than 60V) that supplies the drive. Hence increasing the phase number allows to limit the rating of the power electronic components. In addition, compactness objective can be more easily achieved if the phase number is considered as a design parameter. For instance, with five-phase machine, third harmonic current injection can be performed to boost the torque [START_REF] Semail | Right harmonic spectrum for the back-electromotive force of an n-phase synchronous motor[END_REF], [START_REF] Wang | Torque improvement of fivephase surface-mounted permanent magnet machine using third-order harmonic[END_REF]. Regarding the rotor, Permanent Magnet (PM) structure contribute to enhance the power density [START_REF]Oceanvolt website[END_REF], [START_REF]Torqeedo website[END_REF]. In case of Surfacemounted Permanent Magnet (SPM) rotor, the ripple torque mitigation is facilitated. Furthermore, with five-phase SPM machine, third harmonic current injection can be used to eliminate the pulsating torque [START_REF] Scuiller | Third harmonic current injection to reduce the pulsating torque of a five-phase spm machine[END_REF]. If fractional-slot windings facilitate the reduction of cogging torque for SPM machine [START_REF] Zhu | Influence of design parameters on cogging torque in permanent magnet machines[END_REF], they also generate magnetomotive force harmonics that could result in excessive magnet losses. Machine with 0.5 slots per phase and per pole (𝑠 𝑝𝑝 = 0.5) are known to limit this effect [START_REF] Aslan | General analytical model of magnet average eddy-current volume losses for comparison of multiphase pm machines with concentrated winding[END_REF]. In addition, the slot filling can also be improved with this solution [START_REF] El-Refaie | Fractional-slot concentrated-windings synchronous permanent magnet machines: Opportunities and challenges[END_REF]. Therefore the machine here considered is a five-phase machine with 20 slots and 8 poles (20-8-5 configuration) for a marine propeller.

The 3-phase counterpart of this 20-8-5 machine has 8 poles and 12 slots (12-8-3 configuration). With reference to this 12-8-3 machine, the benefits of the 20-8-5 machine are examined in [START_REF] Zahr | Five-phase version of 12slots/8poles three-phase synchronous machine for marinepropulsion[END_REF] for the same design specifications: rated torque, power and external diameters are identical. With numerical computations of the two machines, this study shows that the 5-phase configuration allows a significant reduction of the magnet losses. In addition, the 5-phase machine facilitates the reduction of the ripple torques (cogging and pulsating) that is of critical importance at low speed.

This paper focuses on another property of the 20-8-5 machine. Due to its particular winding distribution, this machine inherently owns 3×4 pairs of pole and 4 pairs of pole. Hence an electronic pole changing effect can be obtained if the machine is designed to operate at low speed with 3×4 pole pairs or at high speed with 4 pole pairs. More generally the appropriate polarity has to be selected regarding the load demand in transient or steady state, taking into account the inverter rating and the efficiency or torque quality requirements. Pole changing methods by winding switching are well known for induction machine [START_REF] Osama | A new inverter control scheme for induction motor drives requiring wide speed range[END_REF]. For multiphase induction machine, pole phase modulation strategy can be applied [START_REF] Gautam | Variable speed multiphase induction machine using pole phase modulation principle[END_REF]. In [START_REF] Sadeghi | Wide operational speed range of five-phase permanent magnet machines by using different stator winding configurations[END_REF], the speed range of a five-phase PM machine is extended by switching between different stator configurations. A similar procedure is achieved in [START_REF] Nguyen | Different virtual stator winding configurations of open-end winding five-phase pm machines for wide speed range without flux weakening operation[END_REF] but with electronic switching. In this paper, the pole changing effect is electronically ensured by the inverter, depending of the levels of first and third harmonics of current.

The paper is divided into two parts. In the first part, the 20-8-5 machine design is introduced. The magnet layer to obtain the double polarity property is introduced. To master the sizing, numerical field calculations are reported and the torque/speed characteristic is estimated. The second part focuses on the control strategy in the constant power range that corresponds to the steady state operation of the propeller. Two strategies are described and compared regarding the copper, magnet and iron losses (estimated with FEA).

III. MACHINE DESIGN

A. Five-phase machine modeling

If the magnetic saturation and the demagnetization issue are not considered, it can be shown that a star-connected five-phase SPM machine behaves as two two-phase virtual machines that are magnetically independent but electrically and mechanically coupled [START_REF] Semail | Vectorial formalism for analysis and design of polyphase synchronous machines[END_REF]. Furthermore, as the rotor saliency can be neglected with SPM machines, the space harmonics are distributed among the two virtual machines: the virtual machine sensitive to the fundamental is called Main Machine (MM) whereas the other sensitive to the third harmonic is called Secondary Machine (SM). Actually the virtual machine is a physical reading of the mathematical subspace build on the linear application that describes the phase-to-phase magnetic couplings: this two-dimension subspace is usually represented with 𝛼𝛽-axis circuit in stationary frame or with 𝑑𝑞-axis circuit in rotating frame. As there is no saliency effect, no distinction has to be made between d-axis and q-axis inductance.

B. Design specifications

The machine is intended to be integrated in a pod for an electrical outboard. The propeller is driven by the electrical machine with a mechanical gear that reduces the electrical rotating speed by five. The main machine parameters are listed in table I. The electromagnetic circuit is sketched out in Fig. 1 (over a pole pair): the five-phase winding distribution with the corresponding first and third harmonic winding factors (𝑘 𝑤,1 and 𝑘 𝑤,3 ) can be observed. The magnet layer shape is arranged to make the two virtual machines enable to produce the same torque level. To reach this goal, the rotor pole consists of two radially magnetized magnets, each magnet covering one third of the pole arc, as illustrated by Fig. 1.

Winding Factor k w,1 =0.5878 k w,3 =0.9811

C. Field analysis

In this subsection, the electromagnetic behaviour of the machine is estimated with FEA software FEMM [START_REF] Meeker | Finite element method magnetics, version 4.2, users manual[END_REF] under magnetostatic hypothesis. In addition, saturation effects are not taken into account (linear assumption for the materials).

Fig. 2 shows the no-load back-emf waveform and spectrum. The double polarity of the machine can be inferred. The spectrum confirms that first and third harmonic terms are of the same order. The inductance values 𝐿 1 for the MM and 𝐿 3 for the SM are calculated by loading the machine with the rated current:

• 𝐿 1 = 3.1𝑚𝐻 for the MM (4 pole pairs)

• 𝐿 3 = 4.0𝑚𝐻 for the SM (3 × 4 pole pairs). Fig. 3 shows the flux lines when loading the machine with fundamental rated current (for a given rotor position). The field intensity values allow to control the right sizing of the electromagnetic circuit: in the yokes and in the stator teeth, the field intensity is lower than 1.4T. Fig. 4 focuses on the cogging torque estimation. As previous, the cogging torque is negligible: its amplitude is less than 0.25Nm, that is less than 1% the rated torque.

Density Plot: |B|, Tesla 1.900e+000 : >2.000e+000 1.800e+000 : 1.900e+000 1.700e+000 : 1.800e+000 1.600e+000 : 1.700e+000 1.500e+000 : 1.600e+000 1.400e+000 : 1.500e+000 1.300e+000 : 1.400e+000 1.200e+000 : 1.300e+000 1.100e+000 : 1.200e+000 1.000e+000 : 1.100e+000 9.000e-001 : 1.000e+000 8.000e-001 : 9.000e-001 7.000e-001 : 8.000e-001 6.000e-001 : 7.000e-001 5.000e-001 : 6.000e-001 4.000e-001 : 5.000e-001 3.000e-001 : 4.000e-001 2.000e-001 : 3.000e-001 1.000e-001 : 2.000e-001 <0.000e+000 : 1.000e-001

D. Maximum reachable torque for finite Volt-Ampere rating

In this subsection, the torque/speed characteristic of the machine is calculated: for a given mechanical speed Ω 𝑚 (i.e. for a given electrical speed 𝜔), taking into account the maximum DC voltage and the maximum copper losses (driven by base current 𝐼 𝑏 ), the goal consists in finding the MM and SM current distribution that maximizes the electromagnetic torque [START_REF] Scuiller | Maximum reachable torque, power and speed for five-phase spm machine with low armature reaction[END_REF]. To solve this problem is equivalent to find the optimal d-axis and q-axis references for each virtual machine. The Maximum Torque Per Ampere (MTPA) for a given speed is then obtained. The optimization variable is defined as follows:

𝑧 = [ 𝐼 1 𝜃 1 𝐼 3 𝜃 3 ] 𝑇 (1)
The optimization variable is lower and upper bounded according to the following relations:

𝑍 𝑙𝑜𝑤 = ⎡ ⎢ ⎢ ⎣ 0 -𝜋 0 -𝜋 ⎤ ⎥ ⎥ ⎦ ≤ 𝑧 ≤ ⎡ ⎢ ⎢ ⎣ 𝐼 𝑏 𝜋 𝐼 𝑏 𝜋 ⎤ ⎥ ⎥ ⎦ = 𝑍 𝑢𝑝 (2)
The objective is to maximize the electromagnetic torque. This goal is expressed in the following relation where 𝑇 is the average electromagnetic torque:

𝑧 * = 𝑎𝑟𝑔𝑚𝑖𝑛(-𝑇 (𝑧)) (3)
The average electromagnetic torque is the sum of the torque of each virtual machine. The MM torque (due to the fundamental of current) is denoted 𝑇 1 and the SM torque (due to the third harmonic of current) is denoted 𝑇 3 :

𝑇 1 = 5𝜖 1 𝐼 1 cos 𝜃 1 ( 4
)
𝑇 3 = 5𝜖 3 𝐼 3 cos 𝜃 3 (5)
The five-phase machine torque is then expressed as follows:

𝑇 = 5𝜖 1 𝐼 1 cos 𝜃 1 + 5𝜖 3 𝐼 3 cos 𝜃 3 (6)
Equation ( 6) is used in relation (3) to track the optimal current repartition 𝑧 * . The non linear constraint regarding the peak phase voltage is written in the following relation:

𝑓 𝑉 (𝑧) = max {𝑣(𝑝Ω 𝑚 𝑡, 𝑧), 𝑝Ω 𝑚 𝑡 ∈ [0..2𝜋]} -𝑉 𝑝𝑒𝑎𝑘 (7)
In equation [START_REF] Zhu | Influence of design parameters on cogging torque in permanent magnet machines[END_REF], 𝑣(𝑝Ω 𝑚 𝑡, 𝑧) is the machine phase-to-neutral voltage for the current determined by 𝑧 at Ω 𝑚 speed. It should be noted that the considered voltage contains all the harmonics (i.e. not only the first and the third harmonics). The maximum allowable peak voltage is chosen to be half the bus voltage (thus meaning that linear modulation operation is targeted):

𝑉 𝑝𝑒𝑎𝑘 = 𝑉 𝑑𝑐 2 (8)
The constraint relative to the maximum RMS current is defined by the following equation:

𝑓 𝐼 (𝑧) = 𝑧(1) 2 + 𝑧(3) 2 -𝐼 2 𝑏 ( 9
)
The following expression summarizes the optimization problem under consideration:

𝑧 * = 𝑎𝑟𝑔𝑚𝑖𝑛(-𝑇 (𝑧)) with ⎧ ⎨ ⎩ 𝑍 𝑙𝑜𝑤 ≤ 𝑧 ≤ 𝑍 𝑢𝑝 𝑓 𝑉 (𝑧) ≤ 0 𝑓 𝐼 (𝑧) ≤ 0 (10)
Fig. 5 shows the resulting torque/speed characteristic corresponding to the resolution of optimization problem [START_REF] Zahr | Five-phase version of 12slots/8poles three-phase synchronous machine for marinepropulsion[END_REF]. It can be observed that the rated torque (about 34Nm) is obtained by using the virtual MM and the virtual SM in the same time, thus meaning that the five-phase machine here considered is designed to operate with first and third harmonic of current. In addition, the electronic pole changing effect is obtained since, at low speed, the MM (3 × 4 poles) mainly contributes to the torque whereas, at high speed, the SM (4 poles) torque becomes higher. The isopower line (7.7kW) drawn in fig. 5 allows to determine the constant power range that is between 2250rpm and 4500rpm (as specified in table I).

IV. CONTROL STRATEGIES IN THE CONSTANT POWER RANGE

This section focuses on the machine operation in the CPR. At low speed (below 2250rpm), the machine is supposed being in transient states and the MTPA strategy previously introduced is performed. At high speeds (between 2250rpm and 4500rpm), the constant power control is used: in this mode, since the torque is not maximized, the constant power can be obtained with different current distributions, depending on the considered objective. Therefore, two objectives will be examined: one that aims to reduce the copper losses and another that aims to maximize the MM torque contribution. These two strategies will be compared regarding the machine losses with FEA.

A. Constant Power Control with minimizing copper losses

For the control here described, the goal consists in minimizing the copper losses for a given electromagnetic power accounting the maximum allowable peak voltage. For a given torque, as the copper losses are minimized, this strategy is actually a MTPA one and is called CPR-MTPA in the following. The optimization problem can be written as follows:

𝑧 * = 𝑎𝑟𝑔𝑚𝑖𝑛(𝑧(1) 2 + 𝑧(3) 2 ) with ⎧ ⎨ ⎩ 𝑍 𝑙𝑜𝑤 ≤ 𝑧 ≤ 𝑍 𝑢𝑝 𝑓 𝑉 (𝑧) ≤ 0 𝑓 𝑇 (𝑧) = 0 (11)
In relation [START_REF] Osama | A new inverter control scheme for induction motor drives requiring wide speed range[END_REF], 𝑓 𝑇 (𝑧) is the constraint relative to the torque, simply obtained by dividing the required constant electromagnetic power 𝑃 𝑒𝑚 by mechanical speed Ω 𝑚 :

𝑓 𝑇 (𝑧) = 𝑇 (𝑧) - 𝑃 𝑒𝑚 Ω 𝑚 ( 12
)
The speeds where the CPR can be achieved are deduced from the maximum torque/speed characteristic estimated in the previous subsection (2250rpm -4500rpm). Fig. 6a shows the obtained torque/speed characteristics: at low speed (below 2250rpm), the reported characteristic is the one according to the MTPA strategy (10) whereas, at high speed, the reported characteristic is the one corresponding to the resolution of the CPR problem [START_REF] Osama | A new inverter control scheme for induction motor drives requiring wide speed range[END_REF] introduced in this subsection. Again the torque repartition between the two virtual machines confirms the electronic pole changing effect: at low speed, the SM is mainly used whereas, at high speed, the MM becomes predominant. Fig. 6b gives the corresponding power/speed characteristics. As specified, the CPR is actually obtained between 2250rpm and 4500rpm and the electronic pole changing effect already observed when, looking at Fig. 6a, is confirmed.

B. Constant Power Control with favoring Main Machine

In order to reinforce the pole changing effect at high speed, the constant power control (between 2250rpm and 4500rpm) is calculated so that the Main Machine torque contribution is maximized (always accounting the maximum allowable peak voltage). With this strategy, a limitation of the magnet eddy current losses is expected because the Main Machine owns 0.5 slot per pole and per phase [START_REF] Aslan | General analytical model of magnet average eddy-current volume losses for comparison of multiphase pm machines with concentrated winding[END_REF]. This strategy is called CPR-h1 and is obtained by solving the following optimization problem:

𝑧 * = 𝑎𝑟𝑔𝑚𝑖𝑛(-𝑇 1 (𝑧)) with ⎧ ⎨ ⎩ 𝑍 𝑙𝑜𝑤 ≤ 𝑧 ≤ 𝑍 𝑢𝑝 𝑓 𝑉 (𝑧) ≤ 0 𝑓 𝑇 (𝑧) = 0 (13)
In [START_REF] Sadeghi | Wide operational speed range of five-phase permanent magnet machines by using different stator winding configurations[END_REF], 𝑇 1 denotes the torque produced by the Main Machine defined by (4). Fig. 7a and Fig. 7b show respectively the resulting torque/speed and power/speed characteristics when solving optimization problem [START_REF] Sadeghi | Wide operational speed range of five-phase permanent magnet machines by using different stator winding configurations[END_REF] at high speed (at low speed, below 2250rpm, the MTPA characteristic is given). As aimed for, the torque produced by the Main Machine is maximized in the Constant Power Range. One can observe that, between 3200 and 4200rpm, the Secondary Machine operates in generator mode to facilitate the Main Machine power increase.

C. Losses analysis

Copper, magnet and iron (stator and rotor) losses are now considered with FE software Ansys Maxwell. Magnet and iron losses are estimated from the time variation of the flux density. The method to calculate the hysteresis, eddy current and excess losses is close to the one detailed in [START_REF] Lin | A dynamic core loss model for soft ferromagnetic and power ferrite materials in transient finite element analysis[END_REF]. For speed belonging to the CPR, the five-phase machine is simulated for the optimized currents corresponding to the CPR-MTPA and CPR-h1 strategies.

Fig. 8a and Fig. 8b give the copper, magnet and iron losses according to the speed for the CPR-MTPA and the CPR-h1 strategies respectively. With the CPR-MTPA strategy, as aimed for, the copper losses are minimized but, in Fig. 8a, it can be observed that copper losses do not represent the major losses. This trend is all the truer as the speed increases. Referring to the CPR-MTPA strategy that allows the lowest copper losses, the CPR-h1 strategy allows to reduce the whole losses up to 3200rpm as shown by Fig. 8b. This advantage is based on the significant decrease of the magnet losses. This result complies with the analysis carried out in [START_REF] Zahr | Five-phase version of 12slots/8poles three-phase synchronous machine for marinepropulsion[END_REF] where it is shown that the asynchronous space harmonics due the third harmonic generate eddy currents in the magnet layer. For SPM machine, magnet losses mitigation is critical because the magnet layer can not be cooled as easily as the stator winding. In steady state, the magnet losses should be carefully controlled to prevent from demagnetization due to overheating.

Fig. 9 gives another insight of the possible losses reduction with the CPR-h1 strategy: the efficiency versus speed for the two strategies are represented. Thus the efficiency enhancement up to 3200rpm with the CPR-h1 strategy is illustrated. Finally, for the SPM 20-8-5 machine, the MTPA strategy is not the right solution to maximize the efficiency and to limit the heating of the magnets.

V. CONCLUSION

In this paper, the estimations of the 20-8-5 machine performances are obtained without considering magnetic saturation and demagnetization issue. With a particular but quite simple design of the magnet layer, the 20-8-5 machine inherently owns 3×4 pole pairs and 4 pole pairs. With a single stator and single rotor structure, a magnetic gear behavior is then obtained by controlling two rotating fields. The torque/speed characteristic calculated by considering the current and voltage limitations imposed by the inverter confirms the electronic pole changing effect: at low speed, the SM (3×4 poles) mainly contributes to the torque whereas, at high speed, the MM (4 poles) torque becomes higher. As the propeller is specified to operate in the constant power range at steady state (between 2250rpm and 4500rpm), the machine losses are numerically estimated for two CPR control strategies: the CPR-MTPA that minimizes the copper losses and the CPR-h1 that favors the MM torque contribution. A better efficiency is obtained with CPR-h1 control up to 3200rpm, with a significant reduction of the magnet losses for the whole speed range. Finally, for the 20-8-5 machine here considered, the existence of an optimal Maximum Torque Per Losses (MTPL) strategy is then demonstrated and have to be explored in further studies.

Fig. 1 .

 1 Fig. 1. Electromagnetic circuit of the 5-phase machine

Fig. 2 .

 2 Fig. 2. No load back-emf at 2250rpm mechanical speed (FEA)

Fig. 3 .Fig. 4 .

 34 Fig. 3. Flux density (for fundamental rated current)

Fig. 5 .

 5 Fig. 5. Maximum reachable torque for the five-phase machine

Fig. 6 .

 6 Fig. 6. Torque and power with CPR-MTPA strategy

Fig. 7 .

 7 Fig. 7. Torque and power with CPR-h1 strategy

Fig. 8 .Fig. 9 .

 89 Fig. 8. Losses according to the speed in the CPR


The ethical approval is delivered by a Research Ethics Committee (REC) and it must be applied for using the guidance provided by National Research Ethics Service (NRES) at the Health Research Authority2 Tissue banks that have been approved by a REC can provide human tissues to researchers, whom do not need to store them under a Human Tissue Authority licence during the period of the research project, subject to certain requirements. However, specific project approval by a recognised REC will be required, or the samples will need to be stored under a Human Tissue Authority licence, if the research is not carried out in accordance with these requirements.

A Human Tissue Authority establishment licence for human tissue stored outside a specific research project An establishment licence delivered by the Human Tissue Authority is required to remove and store human material for research in England, Wales and Northern Ireland.

The Human Tissue Authority provides a detailed list of what is to be considered as 'relevant material' under the Human Tissue Act 2004, and as such regulated by the Human Tissue Authority for research notably: https://www.hta.gov.uk/policies/list-materials-considered-be-%E2%80%98relevant-material%E2%80%99-under-human-tissue-act-2004

The Human Tissue Authority's licensing role covers licensing premises to store tissue from the living and licensed establishments for tissue to be removed from the deceased for research. However, exceptions exist and the Human Tissue Authority licensing is not required where the relevant material is: -From a person who died prior to 1st September 2006 and at least one hundred years have elapsed since their death -Being held 'incidental to transportation' for a period no longer than a week -Being held whilst it is processed with the intention to extract DNA or RNA, or other subcellular components that are not relevant material (i.e. rendering the tissue acellular) for a period no longer than a week -If research is undertaken under REC approval from a recognised REC at an establishment that does not operate as a research tissue bank -And other cases (See Part 2. 16 of the Human Tissue Act 20043 and point 84 of the Human Tissue Authority, Code E: research4 ) A Designated Individual (DI) has to be appointed in each licensed establishment. The DI has a statutory responsibility under the HT Act to supervise activities taking place under the licence. The HTA's licensing Standards are grouped under four headings: -Consent (C); -Governance and quality systems (GQ); -Traceability (T); -and Premises, facilities and equipment (PFE) Complementarity between the Human Tissue Authority establishment licence and ethical approval Specific research ethics committees (RECs) can give broad ethics approval for research tissue banks. The latter will consequently be required to work under NRES standard operating procedures (SOPs). In that case, there is no need for further individual project specific approvals as long as a broad specified remit of work is permitted. But Human Tissue Authority licensed premises/establishments are always required for tissues to be stored in these research-based tissue banks.

2) Tissues and cells for research to be transplanted into humans

As long as tissues and cells, including cell lines, may be transplanted into humans, they must be licensed by the Human Tissue Authority under the Human Tissue (Quality and Safety for Human Application) Regulations 2007 (Q&S Regulations)5 .

The Human Tissue Authority regulates the following activities: procurement, testing, processing, storage, distribution and import/export of tissues and cells, including cell lines, which may be transplanted into humans, even where it is for research. These activities, apart from storage, can also be carried out under a third party agreement when: -The establishment carrying out the activity is acting on behalf of a licensed establishment; and -The third party agreement meets the standards set out in the Guide to Quality and Safety Assurance of Human Tissues and Cells for Patient Treatments . 6 When a cell therapy is deemed to be a Medicinal Product (MP), including an Advanced Therapy Medicinal Product (ATMP) or Investigational Medicinal Product (IMP), the Q&S regulations will apply for the donation, procurement and testing of tissues and cells. The Medicines and Healthcare products Regulatory Agency (MHRA) [START_REF]Tissues%20and%20Cells%20for%20Patient %20Treatment.pdf Human Tissue Authority, Code A: Guiding principles and the fundamental principle of consent[END_REF] will regulate the subsequent stages, including manufacture, storage and distribution. Moreover, a clinical trial authorisation and a positive opinion from an ethics committee are required for research. For further information, see: https://www.gov.uk/government/collections/clinical-trialsfor-medicines

B) Ethical and regulatory oversight

The Human Tissue Authority8 regulates under the Human Tissue Act the removal and storage of human tissues for a range of activities (scheduled purposes), including research (establishments/premises licensing in the Research sector). The Human Tissue Authority also regulates under the Q&S Regulations the procurement, testing, processing, storage, distribution and import/export of tissues and cells, including cell lines, intended for human application: which may be transplanted into humans, even where it is for clinical research (establishments/premises licensing in the Human Application sector). The Medicines and Healthcare products Regulatory Agency (MHRA)9 regulates when a cell therapy is deemed to be a Medicinal Product (MP) or Investigational Medicinal Product (IMP). Research Ethics Committees (RECs) deliver approvals for research projects and guidance for applications are provided by National Research Ethics Service (NRES) at the Health Research Authority. 10 The West London and Gene Therapy Advisory Committee 11 and its equivalent in Oxford, York and Edinburgh provides ethical opinions for clinical trials authorisation regarding gene therapy and cell therapy using stem cell lines.

II-Research on human embryonic stem cells

The Human Fertilisation and Embryology Authority (HFEA) 12 regulates the creation and use of human embryos in the derivation of human embryonic stem cell lines. However, its remit ceases at the point the embryo is dissociated. After that, the Human Tissue Authority's remit begins (see above).

A) Current legal position

Research on embryo and human embryonic stem cells is authorised by the Human Fertilisation and Embryology Act 1990, Schedule 2. 13 The Human Fertilisation and Embryology Authority (HFEA) 14 regulates the storage of gametes (eggs and sperm) and embryos. It also grants licences for research projects involving human embryos where the following conditions are met: -The research project is carried out in suitable premises -The use of human embryos is necessary and the research fulfils at least one of the purposes set out in the Act:

• Increasing knowledge about serious disease or other serious conditions.

• Developing treatments for serious diseases or other serious medical conditions. • Increasing knowledge about the causes of congenital diseases.

• Promoting the advances in the treatment of infertility.

• Increasing knowledge about the causes of miscarriages.

• Developing more efficient techniques of contraception.

• Developing methods for detecting gene, chromosome or mitochondrion abnormalities in embryos before implantation. • Increasing knowledge about the development of embryos.

-The people donating their eggs, sperm or embryos for research provided consent to do so -The embryos must not be allowed to develop in the laboratory beyond 14 days after fertilisation -No embryo created or used in research can be transferred to a woman -When a derived human embryonic stem cell line is fully characterised and cultured to ensure uniform characteristics it is a condition of all Human Fertilisation and Embryology Authority research licences that the cell line is deposited in the UK Stem Cell Bank. 15 The majority of embryos used in research projects are donated by patients undergoing fertility treatment. But embryos can also be created for research

  , CNRS-Aix-Marseille Université-Université de Pau et des Pays de l'Adour-Université de Toulon et du Var, Aix-en-Provence, France Regulatory Overview, July 2017, published on EuroStemCell website: http://www.eurostemcell.org/regulation-stem-cell-research-united-kingdom To be cited as: A. MAHALATCHIMY, Regulation of stem cell research in the United Kingdom, Site internet EuroStemCell, 18 Juillet 2017 : http://www.eurostemcell.org/regulation-stem-cell-research-united-kingdom I-Research on human stem cells A) Current legal position 1) Tissues and cells for research not to be transplanted into humans An ethical approval for specific research projects Human tissue held for a specific research project approved by a recognised Research Ethics Committee (REC) (or where approval is pending). (Section 1 (9) of the Human Tissue Act 2004 1 )

http://www.legislation.gov.uk/ukpga/2004/30/contents

http://www.hra.nhs.uk/

http://www.legislation.gov.uk/ukpga/2004/30/contents

https://www.hta.gov.uk/sites/default/files/Code%20E%20-%20Research%20Final_0.pdf

https://www.hta.gov.uk/sites/default/files/Q&S_Human_Application_Regs_2007.pdf

https://www.hta.gov.uk/sites/default/files/Guide%20to%20Quality%20and%20Safety%20As surance%20for%20Tissues%20and%20Cells%20for%20Patient%20Treatment.pdf

https://www.gov.uk/government/organisations/medicines-and-healthcare-productsregulatory-agency

8 https://www.hta.gov.uk

/ 9 https://www.gov.uk/government/organisations/medicines-and-healthcare-productsregulatory-

agency 10 http://www.hra.nhs.uk/

Acknowledgement: I would like to deeply thank Professor Andrew Webster and the Human Tissue Authority for their useful comments.


Ge ´rard Pergent

Vanina Pasqualini

Christine Pergent-Martini

Lila Ferrat

Catherine Fernandez
email: catherine.fernandez@up.univ-mrs.fr

Variability of Ruppia cirrhosa in two coastal lagoons with differing anthropogenic stresses

Keywords: aquatic Magnoliophyta, Mediterranean Sea, monitoring, population dynamics, seagrasses, wetland

The dynamics of Ruppia cirrhosa were studied over two years in two coastal lagoons on the Corsican coast (France, Mediterranean Sea). The lagoons differed in type of eutrophication: (1) Biguglia lagoon (urban and industrial effluent, agriculture, runoff from catchment area) and (2) Santa Giulia lagoon (tourist pressure in summer). Spatio-temporal variability of R. cirrhosa occurrence was monitored on permanent transects. We also monitored temporal changes in density, aboveground/belowground biomass and organic matter. Most of the parameters studied along the transects show variations with season and site. Density and aboveground biomass of R. cirrhosa in Biguglia lagoon were lower when Ulva species were present. This may be related to differences in nutrient availability. During the first year of the study, rainfall was greater with concomitantly higher nutrient inputs, which may account for the higher values of measured parameters in the first year. The results suggest that environmental parameter variations affect the functioning of R. cirrhosa meadows.

Introduction

Aquatic macrophytes, and especially aquatic Magnoliophyta, are prominent components of numerous lagoon habitats [START_REF] Millet | Relationships between benthic communities and physical environment in a lagoon ecosystem[END_REF][START_REF] Sfriso | Seasonal variation in biomass, morphometric parameters and production of seagrasses in the lagoon of Venice[END_REF][START_REF] Mene ´ndez | Net production of Ruppia cirrhosa in the Ebro Delta[END_REF], Sfriso et al. 2002). These plants have essential ecological roles [START_REF] Tamisier | Aquatic bird populations as possible indicators of seasonal nutrient flow at Ichkeul lake, Tunisia[END_REF], and also have economic importance [START_REF] Pearce | Caracte ´ristiques ge ´ne ´rales des zones humides me ´diterrane ´ennes[END_REF]Crivelli 1994, Skinner and[START_REF] Skinner | Fonctions et valeurs des zones humides me ´diterrane ´ennes[END_REF]. They contribute to sedimentary balance and constitute a bioindicator of water quality (Succow and Reinhold 1978[START_REF] Meriaux | Les ve ´ge ´tations aquatiques et subaquatiques. Relations avec la qualite ´des eaux[END_REF][START_REF] Blandin | Bioindicateurs et diagnostic des syste `mes e ´cologiques[END_REF][START_REF] Guilizzoni | The role of heavy metals and toxic materials in the physiological ecology of submersed macrophytes[END_REF]. For many years, strong anthropogenic pressures (e.g., fishing, fish and shellfarming, industrialisation and urbanisation) have disturbed Mediterranean lagoon eco-systems and strongly jeopardise their future survival [START_REF] Bacher | Modelling the impact of a cultivated oyster population on the nitrogen dynamics: the Thau lagoon case (France)[END_REF][START_REF] Bettinetti | Application of an integrated management approach to the restoration project of the lagoon of Venice[END_REF][START_REF] De Casabianca | Impact of shellfish farming eutrophication on benthic macrophyte communities in the Thau lagoon, France[END_REF][START_REF] Deslous-Paoli | Relationship between environment and resources: impact of shellfish farming on a Mediterranean lagoon (Thau, France)[END_REF][START_REF] Kjerfve | Coastal lagoon processes[END_REF]. Many studies highlight the degradation of aquatic Magnoliophyta in response to these disturbances, especially Cymodocea nodosa (Ucria) Ascherson, Zostera marina Linneaus and Zostera noltii Hornemann (Pe ´rez-Llorens and Niell 1993, [START_REF] Perez | Growth dynamics, production, and nutrient status of the seagrass Cymodocea nodosa in a Mediterranean semi-estuarine environment[END_REF][START_REF] Philippart | Seasonal variation in growth and biomass of an intertidal Zostera noltii stand in the Dutch Wadden Sea[END_REF][START_REF] Auby | Seasonal dynamics of Zostera noltii Hornem. in the bay of Arcachon (France)[END_REF][START_REF] Vermaat | Seasonal variation in the intertidal seagrass Zostera noltii Hornem.: coupling demographic and physiological patterns[END_REF][START_REF] De Casabianca | Impact of shellfish farming eutrophication on benthic macrophyte communities in the Thau lagoon, France[END_REF][START_REF] Sfriso | Seasonal variation in biomass, morphometric parameters and production of seagrasses in the lagoon of Venice[END_REF][START_REF] Laugier | Seasonal dynamics in mixed eelgrass beds, Zostera marina L. and Z. noltii Hornem., in a Mediterranean coastal lagoon (Thau lagoon, France)[END_REF][START_REF] Plus | Factors influencing primary production of seagrass beds (Zostera noltii Hornem.) in the Thau lagoon (French Mediterranean coast)[END_REF]). However, very few surveys deal with Ruppia cirrhosa (Petagna) Grande, an aquatic magnoliophyte of widespread occurrence in European coastal lagoon waters [START_REF] Verhoeven | The ecology of Ruppia-dominated communities in western Europe. III. Aspects of production, consumption and decomposition[END_REF][START_REF] Viarioli | Relationship between benthic fluxes and macrophyte cover in a shallow brackish lagoon[END_REF][START_REF] Bachelet | Seasonal changes in macrophyte and macrozoobenthos assemblages in three coastal lagoons under varying degrees of eutrophication[END_REF], especially in Mediterranean lagoons [START_REF] Verhoeven | Ruppia communities in the Camargue, France. Distribution and structure in relation to salinity and salinity fluctuations[END_REF][START_REF] Verhoeven | Structure of macrophyte dominated communities in two brackish lagoons on the island of Corsica, France[END_REF][START_REF] Baroli | Ricerche ecologiche nella laguna di s'ena arrubia (sardegna occidentale), variazioni stagionali della composizione delle principali associazioni vegetali e della biomassa delle specie dominanti[END_REF][START_REF] Pergent-Martini | Localisation et e ´volution des peuplements de phane ´rogames aquatiques de l'e ´tang de Berre (Bouches du Rho ˆne, France)[END_REF][START_REF] Ribera | Phytobenthic assemblages of Addaia Bay (Menerca, western Mediterranean): composition and distribution[END_REF][START_REF] Mene ´ndez | Net production of Ruppia cirrhosa in the Ebro Delta[END_REF][START_REF] Agostini | Distribution and estimation of basal area coverage of subtidal seagrass meadows in a Mediterranean coastal lagoon[END_REF][START_REF] Marzano | Distribution, persistence and change in the macrobenthos of the lagoon of Lesina (Apulia, southern Adriatic Sea)[END_REF]. R. cirrhosa is common in large permanent water bodies, in which it is one of the rare macrophytes that survives and exhibits healthy growth in salinities above 20 psu [START_REF] Verhoeven | The ecology of Ruppia-dominated communities in western Europe. I. Distribution of Ruppia representatives in relation to their autoecology[END_REF]. This climax species has extremely high resistance to variations in environmental conditions. We monitored seasonal variations of this species in two lagoons with different types of anthropogenic stress.

Materials and methods

The two lagoons chosen (Biguglia and Santa Giulia) are located along the eastern coast of Corsica (Mediterranean Sea; Figure 1). The environmental conditions vary between the lagoons: there is greater heterogeneity and human pressure in the Biguglia lagoon than in the Santa Giulia lagoon (Table 1). The Biguglia lagoon has been included in the Ramsar list (wetlands of international importance) since 1990, and has been listed as a natural reserve since 1994 (Decree no. 94-688 of August 9, 1994). It lies parallel to the sea over a distance of about 10 km, and is separated from the sea by a lido (recreational beach) not more than 1 km wide (Figure 1). This mesohaline lagoon [START_REF] Sacchi | Le sel de La Palice: re ´flexion sur le paralin me ´diterrane ´en[END_REF], Table 1) communicates with the sea through channels at the north and south ends. There are strong inputs of fresh water in the northern part of the lagoon (e.g., 23-53=10 6 m 3 y -1 of surface waters; [START_REF] Frisoni | L'e ´tang de Biguglia -diagnostic e ´cologique 1991-1992[END_REF]. In the centre of the lagoon and on the landward shore, the substratum is a fine sediment, rich in organic silt. On the seaward shore, the substratum is more sandy, sometimes with shells [START_REF] Agenc | Etang de Biguglia, Haute Corse. Dossier scientifique, propositions pour la cre ´ation d'une re ´serve naturelle[END_REF]. There is fish farming in the lagoon, with an annual mean production of 180 t [START_REF] Boulmer | Plan de gestion de la re ´serve naturelle de Biguglia[END_REF]. Nutrient concentrations in this lagoon are higher than in most other Mediterranean lagoons (e.g., total nitrogen, ammonium; [START_REF] Orsoni | Caracte ´risation de l'e ´tat d'eutrophisation des trois principaux e ´tangs corses (Biguglia, Diana et Urbino), et proposition de renforcement et leur surveillance[END_REF]).

The Santa Giulia lagoon (Figure 1) is located on an estate owned by the ''Conservatoire de l'espace littoral et des rivages lacustres''. This irregularly shaped lagoon is separated from the sea by a narrow sandy strand exposed to strong erosion since 1986 (Gauthier 1992). It is a mesohaline lagoon [START_REF] Sacchi | Le sel de La Palice: re ´flexion sur le paralin me ´diterrane ´en[END_REF], Table 1) with a temporary channel located to the south of the sandy beach. The bottom is constituted mainly of silty sediments [START_REF] Lorenzoni | Description phytosociologique et cartographique de la ve ´ge ´tation de l'e ´tang de Santa Giulia (Corse du Sud)[END_REF]). This lagoon is subjected to tourist pressures in summer.

Monitoring of the vegetation was carried out using the transect technique [START_REF] Corre | La me ´thode des transects dans l'e ´tude de la ve ´ge ´tation littorale[END_REF], with fixed markers set up in July 1997, and checked regularly thereafter. After preliminary studies, the transects (each 100 m long; Figure 1) were set up in the two lagoons in areas where seagrass beds were representatives (coverage, distribution, species; Figure 1). Spatio-temporal changes in seagrasses were investigated by recording the plant populations 1 m on either side of these markers for microcartography (precision 20 cm). Presence/absence, cover and health estimation (dead, alive) of populations were recorded along transects. Cover was estimated in four classes: 0-25, 25-50, 50-75 and 75-100%. In parallel, from July 1997 to July 1999, a systematic sampling was done at each sampling station parallel to the transect (5 replicates, every 20 m). A cylindrical corer (15 cm diameter = 50 cm long) was pushed up to 20 cm into the sediment in monospecific stands (5 replicates), in order to follow seasonal variations of Ruppia cirrhosa. For each core, shoots of R. cirrhosa were counted (density per m 2 ), and the aboveground biomass (foliar shoots) and the belowground biomass (rhizomes and roots) were weighed after oven drying (48 h at 608C). Organic matter content of the sediment was measured in the surface layer (0-10 cm) by weighing the ash after combustion in a muffle furnace (3 h at 5008C). Also, at the Biguglia lagoon, when presence of Ulvophyceae was observed, its cover and biomass were estimated by sampling the species in a 0.4 m 2 quadrat near each sampling station of R. cirrhosa.

Comparisons of parameters as a function of site or season were processed by paired t-tests or Kruskal-Wallis tests, coupled with a Student-Newmann-Keuls test, in order to detect significant differences [START_REF] Zar | Biostatistical analysis[END_REF]. The relation between two parameters was analysed using a simple linear regression [START_REF] Zar | Biostatistical analysis[END_REF]. The software Statgraphics plus (v 2.1) for Windows was used.

Results

Vegetation distribution along the transects differed according to season and site. In winter, Ruppia cirrhosa was dormant as short quiescent leaf-bearing stolons, which prevented monitoring the transects. At Biguglia, a healthy continuous and rather dense meadow of R. cirrhosa was observed (about 50 m off shore) in July 1997 and in April 1998, with presence of Ulva specimens (Figure 2). In July, R. cirrhosa was replaced by members of the Ulvophyceae that can, locally, constitute very dense formations that form detached free-floating mats near the bottom, with heights up to 20-30 cm (continuous beds of Ulva species, from 35 m to 75 m from shore; 1324 to 2983 g m -2 ; Figure 2). This continuous meadow of R. cirrhosa disappeared almost entirely during this period, with mortalities of R. cirrhosa and Ulva species. Later, R. cirrhosa appeared again with high cover in spring 1999 and Ulva species decreased drastically (2 to 162 g m -2 ; Figure 2). Seagrass was then much more developed than the previous year and it occupied almost the whole transect. At Santa Giulia in April 1998, a sparse meadow of R. cirrhosa was observed on silt, and this meadow became continuous 45 m off shore (Figure 2). Over the whole study period, the only variations were in meadow cover (Figure 2).

Shoot density of Ruppia cirrhosa meadows varied, on average, from 3316"1112 shoots m -2 (Biguglia, July 1998) to 16401"3657 shoots m -2 (Santa Giulia, October 1997; Figure 3A). Density variations occurred over the study period at both sites (Kruskal-Wallis test, p-0.05). Maximal densities for Biguglia were recorded in April 1998 and for Santa Giulia in July 1997 (SNK test, p-0.05). However, no seasonal pattern was observed. For each site, the average density was higher in the first year (July 1997-July 1998) than in the second year (July 1998-July 1999; SNK test, p-0.05). Comparison between sites shows that R. cirrhosa densities were generally significantly higher in the Santa Giulia lagoon (paired t-test, p-0.05; Figure 3A).

Ruppia cirrhosa aboveground biomass varied from 8"4 g DW m -2 (Biguglia, October 1998) to 343"70 g DW m -2 (Biguglia, July 1999; Figure 3B). For the two sites studied, significant seasonal variations were observed (Kruskal-Wallis test, p-0.05), with an increase of biomass in spring and summer, and a decrease in autumn and winter (SNK test, p-0.05). Significant differences between years were observed in April (higher in 1998) and July (higher in 1997 and 1999) for the two sites studied. Comparison of the two sites shows significant variations with a greater aboveground biomass at Santa Giulia than at Biguglia, except in July 1997 and 1999 when the reverse pattern was observed (paired t-test, p-0.05).

The belowground biomass varied from 4"2 g DW m -2 (Biguglia, October 1998) to 87"15 g DW m -2 (Santa Giulia, October 1997; Figure 3C). The variations observed for the study period were significant (Kruskal-Wallis test, p-0.05), even though no seasonal pattern was observed. Biomass was higher in the period July 1997-April 1998 than in the period July 1998-July 1999. In the same way, no significant difference was recorded between the two sites (paired t-test, p)0.05). The aboveground: belowground biomass ratio (AB:BB ratio, Figure 3D) confirms the seasonal trends observed for both lagoons, but highlights an important difference in biomass allocation in July 1998 between the sites. The AB:BB ratio was significantly higher in Santa Giulia (26.21) than in Biguglia (11.39).

Organic matter content in the Ruppia cirrhosa meadows sediment varied from 1.6% (Biguglia, January 1998) to 4.6% (Santa Giulia, July 1999; Figure 4) and differed among sampling times. At Santa Giulia, the organic matter content increased significantly from the beginning of 1998 to the end of the study; thus it was higher in the second year than in the first year (Kruskal-Wallis and SNK tests, p-0.05). On the other hand, at Biguglia the organic matter content remained steady over the whole period of study, except in April 1998 which showed a significantly higher content than the other months (Kruskal-Wallis and SNK tests, p-0.01). Statistical analysis of the results shows that, except in April 1998, the organic matter content was lower in Biguglia than in Santa Giulia (paired t-test, p-0.05). No correlation between the organic matter content in the sediment and the total biomass or the belowground biomass was observed (correlation test, 0.07-r-0.37; p)0.05).

Discussion

Our results on density, aboveground and belowground biomasses are concordant with those reported in the literature [START_REF] Verhoeven | The ecology of Ruppia-dominated communities in western Europe. III. Aspects of production, consumption and decomposition[END_REF][START_REF] Bachelet | Seasonal changes in macrophyte and macrozoobenthos assemblages in three coastal lagoons under varying degrees of eutrophication[END_REF], Calado and Duarte 2000[START_REF] Azzoni | Iron, sulphur and phosphorus cycling in the rhizosphere sediments of a eutrophic Ruppia cirrhosa meadow (Valle Smarlacca, Italy)[END_REF][START_REF] Mene ´ndez | Net production of Ruppia cirrhosa in the Ebro Delta[END_REF]. In particular, the total biomass values at both sites (Biguglia and Urbino) are higher than values observed in the Ebro Delta (Spain; Mene ´ndez 2002) and comparable with those recorded for the Santo Andre ´lagoon (Portugal;Calado and Duarte 2000).

The biotic parameters of the two populations of Ruppia cirrhosa showed seasonal variations. Higher aboveground biomass (attributable to larger leaves) in summer is well known for this species [START_REF] Verhoeven | The ecology of Ruppia-dominated communities in western Europe. III. Aspects of production, consumption and decomposition[END_REF][START_REF] Bachelet | Seasonal changes in macrophyte and macrozoobenthos assemblages in three coastal lagoons under varying degrees of eutrophication[END_REF][START_REF] Azzoni | Iron, sulphur and phosphorus cycling in the rhizosphere sediments of a eutrophic Ruppia cirrhosa meadow (Valle Smarlacca, Italy)[END_REF][START_REF] Mene ´ndez | Net production of Ruppia cirrhosa in the Ebro Delta[END_REF]. These variations in biomass of magnoliophytes seem to be linked to the strong variations in temperature and light over the year [START_REF] Duarte | Temporal biomass variability and production/ biomass relationships of seagrass communities[END_REF], Perez-Llorens and Niell, 1993[START_REF] Laugier | Seasonal dynamics in mixed eelgrass beds, Zostera marina L. and Z. noltii Hornem., in a Mediterranean coastal lagoon (Thau lagoon, France)[END_REF]. Biguglia and Santa Giulia lagoons have strong variations in temperature (Figure 5A), and a significant correlation between aboveground biomass and temperature was observed (rs0.69, p-0.05).

Comparison between the two populations of Ruppia cirrhosa (Biguglia and Santa Giulia) reveals the following differences: (i) a smaller density and aboveground biomass at Biguglia and (ii) more variation in cover at Biguglia. These results could be related to differences in nutrient availability due to inputs of nutrients in each lagoon (Figure 5B-E). The correlation matrix shows a significant correlation between aboveground biomass and ammonium, nitrates (correlation test, rs-0.57 and -0.54, respectively, p-0.05), and between density and phosphates (correlation test rs0.52, p-0.05). Important https://payment.sips-atos.com/cgis-payment/prod/callresource?rsc=creditcard 1/1 inputs in nutrients could cause negative indirect effects on the magnoliophytes through proliferation of plankton or macroalgal blooms [START_REF] Sfriso | Temporal and spatial changes of macroalgae and phytoplankton in a Mediterranean coastal area: the Venice lagoon as a case study[END_REF]. In Biguglia, observations of the green macroalgal bloom (Ulva species) in spring and summer 1998 reveal environmental modifications in the sampling site with a probable increase in nutrients in the water column, and an increase in organic matter in the sediment which could be related to significant rainfall at this site in March and April 1998 (compared to Santa Giulia and to 1999). These modifications seem to allow the development of macroalgae and to limit magnoliophyte development at this location. Macroalgae, such as members of the Ulvophyceae, are able to absorb large quantities of nutrients, eventually producing sudden blooms. These species are primarily nitrogen-limited and stimulated by the loading provided by waste discharge (Giusti and Marsilli-Libelli 2005). These data seem to describe a dystrophic crisis in the Biguglia lagoon in spring-summer 1998, as described by [START_REF] Viaroli | Macrophyte communities and their impact on benthic fluxes of oxygen, sulphide and nutrients in shallow eutrophic environments[END_REF]. These crises are often caused by the combination of nutrient input, high temperature, high oxygen consumption, long periods of calm winds and subsequent reduction in water exchange [START_REF] Orsoni | Caracte ´risation de l'e ´tat d'eutrophisation des trois principaux e ´tangs corses (Biguglia, Diana et Urbino), et proposition de renforcement et leur surveillance[END_REF], which generate a proliferation of opportunistic macroalgae [START_REF] Bachelet | Seasonal changes in macrophyte and macrozoobenthos assemblages in three coastal lagoons under varying degrees of eutrophication[END_REF]. This proliferation leads to a decrease in light intensity received by the magnoliophytes (Da Silva and Asmus 2001). The Biguglia lagoon is eutrophic because of agricultural runoff and wastewater discharge. The environmental modifications observed at the sampling site of this lagoon during spring-summer 1998 were confirmed by the mortality of R. cirrhosa. Algal decomposition may also generate an anoxic phenomenon harmful to the development of the magnoliophytes [START_REF] Giusti | Modelling the interactions between nutrients and the submersed vegetation in the Orbetello Lagoon[END_REF]. Light attenuation and decomposition of macroalgae following collapse of the bloom have strong effects on R. cirrhosa meadows (drop in biomass and densities). The phenomenon of macroalgal proliferation, which led to the regression of R. cirrhosa, has been observed in other Mediterranean lagoons (Viaroli et al. 1996, Bachelet et al. Data for water temperature, phosphates, ammonium, nitrites and nitrates were obtained from September 1998 to September 1999 for Biguglia lagoon [START_REF] Orsoni | Caracte ´risation de l'e ´tat d'eutrophisation des trois principaux e ´tangs corses (Biguglia, Diana et Urbino), et proposition de renforcement et leur surveillance[END_REF]) and from September 1994 to September 1995 for Santa Giulia lagoon [START_REF] Canovas | Diagnostic hydrologique et hydrobiologique de l'e ´tang de Palo, Corse. Rapport IARE[END_REF].

The data for Santa Giulia come from a nearby lagoon with similar characteristics (personal com. G.F. Frisoni). Rainfall data were collected between July 1997 and August 1999 (Me ´te ´oFrance ᮋ ) for the two lagoons.

2000, [START_REF] Mistri | Variability in macrobenthos communities in the Valli di Comacchio, Northern Italy, a hypereutrophized lagoonal ecosystem[END_REF]. Indeed, the differing physiological requirements of the algae and magnoliophytes tend to produce a mutual exclusion [START_REF] Giusti | Modelling the interactions between nutrients and the submersed vegetation in the Orbetello Lagoon[END_REF]. This phenomenon was reported for other magnoliophytes (e.g., Zostera marina; [START_REF] Coffaro | Resources competition between Ulva rigida and Zostera marina: a quantitative approach applied to the Lagoon of Venice[END_REF].

Comparison of the AB:BB ratio between the sites (Figure 3D) in July 1998 highlights the fact that R. cirrhosa meadows at Biguglia are not able to develop as much aboveground tissues as populations of Santa Giulia. Indeed, the presence of high densities of macroalgae in Biguglia leads R. cirrhosa to invest its biomass in subterranean tissues at the expense of photosynthetic tissues. These density and biomass results could be also related to differences in nutrient availability in the sediment. The high concentrations of organic matter at the sampling site in Santa Giulia lagoon seem to constitute an important source of nutrients, which may improve Ruppia cirrhosa growth. Sediment composition appears to have a primary influence on establishment and development of Ruppia meadows (Guisti and Marsili-Libelli 2005). The amount of nutrients being supplied by organic matter is a positive factor supporting plant growth, as has already been shown for Zostera marina [START_REF] Kenworthy | The use of fertilizer to enhance growth and transplanted seagrass Zostera marina L. and Halodule wrightii Aschers[END_REF][START_REF] Van Lent | Comparative study on populations of Zostera marina L. (seagrass): in situ nitrogen enrichment and light manipulation[END_REF][START_REF] Peralta | On the use of sediment fertilization for seagrass restoration: a mesocosm study on Zostera marina L[END_REF]. These organic matter concentrations must be carefully measured and considered with care, because an excess of organic matter can cause anoxic events in the sediment by mineralisation, and release of hydrogen sulphide with consequent negative effects on plants [START_REF] Tagliapietra | Macrobenthic community changes related to eutrophication in Palude della Rosa (Venetian Lagoon, Italy)[END_REF].

Annual comparisons (1997)(1998)(1998)(1999) for both sites (Biguglia and Santa Giulia) show higher values in 1997-1998 for the whole set of parameters measured, together with the development of macroalgae in the sam-pling site of Biguglia. The available rainfall data (Meteo France ᮋ data; Figure 5F) indicate that both lagoons benefited from higher inputs of fresh water, which came from their catchment areas in 1997-1998. This could have led to a better mixing of the water and to an enrichment in nutrients able to support the development of Ruppia cirrhosa plants (high density and biomass values for that period) and, in some cases, of macroalgae.

Presence of anthropogenic stresses causing environmental parameter variations in some Corsican lagoons affects the functioning Ruppia cirrhosa meadows. Even if this species shows a high resistance to variations in environmental conditions and resilience capacity (sensu [START_REF] Connell | On the evidence needed to judge ecological stability or persistence[END_REF], nutrient input by human activities could jeopardise the future survival of the meadows by facilitating the development of other more opportunistic species.

Figure 1

 1 Figure 1 Ruppia cirrhosa: location of Biguglia and Santa Giulia lagoons in Corsica (France) and sampling sites.

Figure 3

 3 Figure 3 Ruppia cirrhosa: seasonal variations of density (A), aboveground biomass (B), belowground biomass (C), and ratio aboveground:belowground biomass (D) in Biguglia and Santa Giulia lagoons (mean and 95% confidence interval).

Figure 4

 4 Figure 4Ruppia cirrhosa: seasonal variations of sediment organic matter in Biguglia and Santa Giulia lagoons (mean and 95% confidence interval).

Figure 5

 5 Figure5Ruppia cirrhosa: seasonal variations of water temperature (A), phosphates (B), ammonium (C), nitrites (D), nitrates (E), and rainfall (F) in Biguglia and Santa Giulia lagoons. Data for water temperature, phosphates, ammonium, nitrites and nitrates were obtained from September 1998 to September 1999 for Biguglia lagoon[START_REF] Orsoni | Caracte ´risation de l'e ´tat d'eutrophisation des trois principaux e ´tangs corses (Biguglia, Diana et Urbino), et proposition de renforcement et leur surveillance[END_REF]) and from September 1994 to September 1995 for Santa Giulia lagoon[START_REF] Canovas | Diagnostic hydrologique et hydrobiologique de l'e ´tang de Palo, Corse. Rapport IARE[END_REF]. The data for Santa Giulia come from a nearby lagoon with similar characteristics (personal com. G.F. Frisoni). Rainfall data were collected between July 1997 and August 1999 (Me ´te ´oFrance ᮋ ) for the two lagoons.

Table 1 Ruppia cirrhosa: main characteristics of the Biguglia and Santa Giulia lagoons.

		Biguglia	Santa Giulia
	Abiotic parameters
	Geographical coordinates	428379 N, 98279 E	4 1 8319 N, 98159 E
	Surface area (ha)	1500	26
	Maximum depth (m)	1.8	1.0
	Mean depth (m)	1.5	0.5
	Catchment area (km 2 )	180	15.5
	Water residence time (month)	1-2	1
	Temperature (8C)	5-26	12-25
	Salinity (psu)	4-26	12-37
	Human pressure sources
	Population of catchment area (ha)	18 528	712
	Industrial and touristic activities in	Effluent, wine making, airport, oil tanks,	None
	the catchment area	boilerworks, hotels and restaurants, transport
	Agricultural activities in the	Orchards, vineyards, pumpkins and squashes, stock	None
	catchment area	rearing
	Activities at the lido	Built-up area, holiday village, hotels and restaurants	Holiday village,
			hotels and restaurants
	Fishing and aquaculture	Fishing: 180 t/y of fish	None
	(Data from Pergent-Martini et al. 1997, Orsoni et al. 2001).

https://payment.sips-atos.com/cgis-payment/prod/callresource?rsc=creditcard

https://payment.sips-atos.com/cgis-payment/prod/callresource?rsc=creditcard 1/1 https://payment.sips-atos.com/cgis-payment/prod/callresource?rsc=creditcard 1/1

https://payment.sips-atos.com/cgis-payment/prod/callresource?rsc=creditcard 1/1 https://payment.sips-atos.com/cgis-payment/prod/callresource?rsc=creditcard 1/1

Acknowledgements

This work was carried out under, and funded by, the Programme National d'Oce ´anologie Co ˆtie `re (PNOC) in partnership with IFREMER and the French Ministry of the Environment, for the valorisation of Mediterranean lagoons. Some of the results were acquired from the European Life and Interreg programmes. The authors would like to thank O. Dumay, J.E. Tomaszewski and C. Segui for their participation in field missions and M. Paul for help with the English translation. The authors also greatly appreciate comments provided by the editor and the reviewers.

https://payment.sips-atos.com/cgis-payment/prod/