Nicole Lancereau-Forster

Josiane Martinez
email: josiane3.martinez@gmail.com

Nicole Lancereau

Keywords: linguistic insecurity, interlinguistic insecurity, foreign working language, English in the workplace, oral communication, higher education, foreign language anxiety

Due to globalization and the spread in the use of foreign languages in the workplace, language needs have been regularly and increasingly researched, whether from linguistic, psychological or socio-economic perspectives. The use of these languages, far from being neutral, gives rise to a whole set of attitudes, feelings, behaviours and representations from the speakers of these languages. It may also induce for employees situations of stress, work-related suffering and compromised promotion. This article deals with the interlinguistic insecurity of French employees using English as a foreign working language in oral communication. A quantitative research enquiry involving 642 French employees from various fields of activity was carried out. It explored attitudes, feelings (for example foreign language anxiety or feelings of inferiority), behaviours (such as withdrawal) and representations (like awareness of shortcomings and desire for improvement) linked to interlinguistic insecurity in the workplace. The above attitudes and feelings were analysed in the light of three variables: gender, age and education level. The effects of these variables and their relevance were investigated. The results showed that education level was the prevalent variable and that interlinguistic insecurity is a real issue for higher and continuous education. Possible approaches to alleviate insecurity in the workplace were then considered on linguistic and cultural grounds.

Introduction

Since the 1990s and the early years of the 21 st century, language needs in the workplace have been regularly and increasingly researched, whether from linguistic, psychological or socioeconomic perspectives. Indeed in a global world, the spread of the use of foreign languages in the workplace rarely runs smoothly. The frequent belief that a foreign language could be a mere tool or an "instrument of communication" may imply, as [START_REF] Calvet | CEFR. Common European Framework of Reference for Languages[END_REF] writes, that the relation between the speaker and the language used is "neutral". Yet the use of languages gives rise to a whole set of attitudes and feelings from the speakers of these languages, and linguistic attitudes undoubtedly have repercussions on linguistic behaviours. Among these attitudes, one emerged as a key issue from the research carried out at the LAIRDIL1 laboratory in its programme called OULis (Observatory of the use of languages in the workplace [START_REF] Lancereau-Forster | La gestion linguistique des entreprises[END_REF], namely linguistic insecurity. Although a crucial issue, linguistic insecurity in the workplace has been the focus of little research so far and our study tries to reduce this gap, more particularly with regard to language learning in higher education. Our research was conducted in the light of three variables deemed important by industrial partners in our OULis programme: gender, age and education level. Our overall aim is to alleviate linguistic insecurity in the workplace through the design of new language courses.

After defining the theoretical framework of linguistic insecurity, or rather interlinguistic insecurity, in the workplace, this article deals with a quantitative research study carried out among French employees in 2016. It explores the attitudes, feelings, behaviours and representations linked to interlinguistic insecurity in oral communication.

Theoretical framework

Language needs in the workplace

In the late 1990s, several European studies dealing with language needs in the workplace were published [START_REF] Huhta | Language/Communication Skills in Industry and Business -Report for Prolang/Finland[END_REF][START_REF] Hagen | Business communication across borders: a study of language use and practice in European companies[END_REF]. Some years later, the ELAN report (2006) (Effects on the European Economy of Shortages of Foreign Language Skills in Enterprise) stressed the effects of the lack of language skills in SMEs on the European economy, citing for example a loss of export contracts. In 2011, based on ELAN's findings, the PIMLICO report (Promoting, Implementing, Mapping Language and Intercultural Communication Strategies) presented forty case studies of companies and their "good practice in the use of language management strategies" (PIMLICO 2011: 8). This study was followed in 2013 by the CELAN report (CELAN 2013) (Language Strategies for Competitiveness and Employability).

In 2015, a Languages and Employability (LEMP) project focused on the link between foreign languages and employability in French businesses. It showed both a quantitative and qualitative increase in the use of English in the French workplace. The prevalence of the English language in the workplace was highlighted: English is top of the list of languages used in the workplace, with German, Spanish and Italian just behind. The need for greater linguistic diversity is clear as 21 foreign languages are cited by businesses. 22 languages are included by employers in the vacancies advertised by the public employment services.

(LEMP 2015: 2) Secondly, the importance of the use of foreign languages, whatever the position of the employees in the company, was also stressed:

Although executives and senior managers use foreign languages in all of their written and spoken forms, technicians, white and blue-collar workers all make use of written and verbal skills too. (LEMP 2015: 3) The summary of the report declared that, in order to alleviate the difficulties met by employees using a foreign language, some companies offered language courses to their staff and more particularly laid emphasis on "promoting personal skills development (increasing range of skills, helping staff to feel more at ease with a foreign language etc.)" (LEMP 2015: 4).

In parallel to these reports, international management researchers have also studied communication and language skills in the workplace and aim at making "the development of language in international business […] a research stream" (Brannen et al. 2014: 498). This is illustrated by increasing research into feelings and attitudes, social identity and emotions [START_REF] Klitmøller | When global virtual teams share knowledge: Media richness, cultural difference and language commonality[END_REF], career prospects [START_REF] Piekkari | Languages and careers in multinational corporations[END_REF], cultural awareness and intercultural skills (Neeley 2012).

Linguistic insecurity

The notion of linguistic insecurity (LI) was first developed by the sociolinguist William [START_REF] Labov | The social stratification of English in New York City[END_REF] 2006), as he investigated speech in New York City and studied the social stratification of English. He found a gap between the use of English by some speakers as observed by the linguist and the speaker's own perception of a more "prestigious" language.

In fact, Labov concluded that lower middle class speakers were more prone to experience LI since they hoped to emulate socially dominant groups. Women also showed higher LI than men. Labov noted that LI could have particular effects such as "superficial stigmata of insecurityhesitation, nervousness, self-correction and extreme style-shifting" [START_REF] Labov | The social stratification of English in New York City[END_REF] 2006: 322).

Labov devised what he called an index of linguistic insecurity to measure LI; [START_REF] Owens | Linguistic insecurity in Winnipeg: Validation of a Canadian index of linguistic insecurity[END_REF] later created a Canadian version of Labov's index to study LI in Winnipeg and validate the index. Differences between socioeconomic categories and between males and females were found as in Labov's initial study. LI was subsequently regarded as an intralinguistic issue, particularly by Frenchspeaking researchers (Guenier 1994;[START_REF] Bretegnier | L'insécurité linguistique: objet insécurisé? Essai de synthèse et perspectives[END_REF]Bretegnier & Ledegen 2002;[START_REF] Francard | L'insécurité linguistique dans les communautés francophones périphériques[END_REF][START_REF] Francard | L'insécurité linguistique dans les communautés francophones périphériques[END_REF]. Francard, in Belgium, defined linguistic insecurity as "the manifestation of a quest for linguistic legitimacy" (1997) and referred to Bourdieu's concept of "marché linguistique" ("linguistic marketplace") with dominated groups striving to ascend the social ladder (1982). Calvet went a step further and suggested extending the notion of LI to interlinguistic contexts and particularly language contact situations: L'insécurité peut aussi résulter de rapports que j'appellerai interlinguistiques, entre des langues différentes, et elle est alors le produit du plurilinguisme.

[Insecurity may also come from relations which I would call interlinguistic, between different languages. It is therefore the product of plurilingualism. [Our translation] (1999: 160) We can assume with Neeley (2017) that, when using a foreign language, "everyone is at least slightly uncomfortable detaching from a native language and culture". This form of interlinguistic discomfort or insecurity may be particularly crippling in the workplace when a foreign working language (FWL) has to be used. [START_REF] Neeley | Language matters: Status loss and achieved Status distinctions in global organizations[END_REF] stresses the fact that language performance anxiety is so important that it may affect everyday behaviour of non-native English-speaking employees in the workplace. Other researchers carried out studies on the use of a FWL. [START_REF] Holmes | Talking English from 9 to 5: challenges for ESL learners at work[END_REF] studied the challenges of using English in the workplace, particularly with regard to workplace small talk and social talk. Using a sociolinguistic approach, [START_REF] Deneire | English in the French workplace: realism and anxieties[END_REF] considered the anxiety caused by using English in French workplaces. More recently, [START_REF] Guntzviller | The Foreign Language Anxiety in a Medical Office Scale: Developing and Validating a Measurement Tool for Spanish-Speaking Individuals[END_REF] investigated the medical context and devised a scale to measure "foreign language anxiety in a medical office" (FLAMOS). [START_REF] Tenzer | Leading across language barriers: managing language-induced emotions in multilingual teams[END_REF] considered the business area and specifically studied "self-directed anxiety triggered by language barriers" (p. 17). [START_REF] Gargalianou | Foreign Language Anxiety in Professional Contexts. A Short Scale and Evidence of Personality and Gender Differences[END_REF] also explored foreign language anxiety (FLA) in professional Dutch environments. They concentrated on studying employees' emotions when working in English as a foreign language and created a short scale to measure FLA in formal contexts. They also examined its link to gender and general personality traits. They concluded that women tended to experience more FLA than men in the workplace and suggested that this may be more the result of personality variables than of gender differences.

In our article, a wider scope was chosen and consisted in the study of linguistic insecurity as a whole including foreign language anxiety, among other feelings, attitudes and behaviours. Moreover, English being a FWL in French multinationals, we will use the more appropriate term interlinguistic insecurity to refer to this kind of insecurity. Thus, following [START_REF] Francard | L'insécurité linguistique dans les communautés francophones périphériques[END_REF][START_REF] Francard | L'insécurité linguistique dans les communautés francophones périphériques[END_REF][START_REF] Francard | Sociolinguistique. Concepts de base[END_REF] and [START_REF] Calvet | Pour une écologie des langues du monde[END_REF][START_REF] Calvet | CEFR. Common European Framework of Reference for Languages[END_REF], we can adopt the following working definition of interlinguistic insecurity (ILI) as being the attitude derived from the selfperception by an individual or a group of individuals of a gap or a distance between the foreign language they make use of and the foreign language as taught or used according to the existing norm.

In this article, the focus was on the attitudes, feelings and behaviours linked to ILI as regards oral communication in the workplace. Three variables were applied: gender, age and education level. The first two variables were chosen after discussions with a number of human resource managers. They had noticed differences in the levels of discomfort experienced by the different genders and age groups when using a FWL. We then added a third variable, that of education level as it directly affects employability and is of particular interest to university research laboratories. The research questions in this article investigated the way these variables applied, as well as the relevance of each one.

Methodology

Quantitative survey

In order to explore ILI, a questionnaire was devised and sent to French employees in a national and international context who use a foreign working language (FWL). In all cases, English was reported as the most often used FWL (by 99.07% of the respondents) and our research then focused on English. The first part of the questionnaire included social characteristics such as gender, age, number of years at university, socio-professional category and field of activity. The second part of the questionnaire consisted in a list of 10 different feelings/attitudes, behaviours and representations linked to the use of English as a FWL (Appendix). The respondents were asked to rate each item on a Likert-type scale, from 1 to 5

(1 strongly disagree to 5 strongly agree), according to the feelings/ attitudes, behaviours or representations they were most likely to adopt when using English as a FWL.

The questionnaires were sent electronically to associations of former students and to companies. An important factor in order to avoid useless stress and ensure true and free answers were given was the fact that this questionnaire was anonymous. Only after the last question was a choice of leaving an electronic address and being contacted again given.

Respondents

A total of 642 people responded, 72% males and 28% females. The age groups of the respondents fell into 3 categories, shown in Table 1.

[Please insert Table 1 about here]

Respondents fell into two groups differing both in the duration of their studies and their academic qualifications. The first group was made up of former students of French universities (e.g. Institutes of Technology) who had studied for a Bachelor's degree with, at the most, 3 years in higher education and were aiming at the job of technician. The second group consisted of former students of French universities or engineering schools who had passed at least a Master's degree (4 or 5 years in higher education) and were aiming at a professional engineering or managerial position. For the students in this group, the universities would generally have made a selection after 4 years of study and only the top students would have entered the 5 th year. In the case of engineering schools, the students would have undergone a selective entry process accepting only top students. In addition, these students would have undergone a period of internship abroad to acquire practical skills. To investigate the differences in interlinguistic insecurity between these two groups, the respondents were classified into two categories: up to three years of HE, more than three years of HE. As Table 2 shows, a large majority of respondents had a higher level of studies (about four fifths of the total corpus).

[Please insert Table 2 about here]

As far as socio-professional category is concerned (Figure 1), a total of 84% of the respondents were chartered engineers, executives, managers, researchers and lecturers (> 3 years of HE). Conversely, the respondents with shorter studies (≤ 3 years of HE) were either technicians or intermediate staff (clerical, sales, service and administrative). This situation reflects the French reality in which a diploma or degree often paves the way to a job category.

[Please insert Figure 1 about here]

Our respondents reported a wide range of fields of activity. Figure 2 represents the variety of the fields (15) having a minimum of 10 occurrences. This variety had the advantage of providing us with a broad cross-section of the working world.

[Please insert Figure 2 about here]

Analysis

As the distribution of responses could not be assumed to be normally distributed, nonparametric tests were used: Wilcoxon rank sum test (also known as the Mann-Whitney test) for two independent samples, and the Kruskal-Wallis test for multiple independent samples. [START_REF] Hinton | Statistics Explained[END_REF] 2008).

Results

Horwitz et al. defined FLA (Foreign Language Anxiety) as a "distinct complex of selfperceptions, beliefs, feelings and behaviors related to classroom language learning" (1991: 31). In our study, we chose to use these categories as a starting point. These were adapted so as to explore the possible markers of interlinguistic insecurity: feelings/attitudes (including self-perceptions and beliefs) and behaviours. Finally, the category of representations/expectations was added in order to capture any positive aspects counterbalancing interlinguistic insecurity.

Feelings/ Attitudes

Feelings when using English as a FWL were first studied, following a Likert-type scale of 1 to 5 (1 strongly disagree to 5 strongly agree). Charts were drawn to show the influences of three variables, namely gender, age and education level.

Fear of being ridiculed if making mistakes

As is mentioned in the CEFR (2001: 155), a distinction is to be made between errors and mistakes:

Errors are due to an 'interlanguage', a simplified or distorted representation of the target competence. When the learner makes errors, his performance truly accords with his competence, which has developed characteristics different from those of L2 norms. Mistakes, on the other hand, occur in performance when a user/learner (as might be the case with a native speaker) does not bring his competences properly into action.

Yet even though this dichotomy does exist, our respondents gave a general answer to this question.

The following figure depicts the fear of being ridiculed if making mistakes. The y-axis represents the mean scores of the answers (1-5). The x-axis represents the different variables that are: F/M for gender, L/H for lower or higher education level and 1, 2 and 3 for the different age groups.

[Please insert Figure 3]

The results of the combination of these three variables will be presented in the graphs of the article so as to stress the different interactions.

With this combination, we can see that less well-qualified younger women (FL1) experience the most fear of being ridiculed if making mistakes. Women seem to be more aware of the negative effects of language mistakes and may be more concerned with linguistic standards and rules. Conversely, highly qualified older men (MH3) feel the least fear. Higher qualified males, whatever their ages, appear more constant and self-confident. This may correspond to the fact that they will occupy a higher position in the company, keeping in mind that, as discussed above, socio-professional categories in France are usually linked to the education level.

We conjecture that a higher education level implies a better mastery of the language, hence fewer mistakes made.

Awareness of French accent

The item of the questionnaire was: "I am aware that I have a French accent and that bothers me". In Labov's work, although one single language was considered, linguistic insecurity appeared in the variation of the pronunciation. After the study of the fear of making mistakes, we wanted to know the part occupied by the difficulties due to pronunciation, intonation and foreign accent.

[Please insert Figure 4]

Apart from less well-qualified younger women (FL1), the answers are quite homogeneous. The respondents do not seem very affected by their foreign accent, even if they are aware of it. A previous study showed that only 16% of the French technicians surveyed regarded pronunciation and intonation as problematical (Lancereau-Forster 2014). Awareness of the importance of the accent tends to remain stable with professional experience.

Feeling of inferiority

The awareness of the existence of people who communicate better in English can create a feeling of inferiority. They may be native speakers or colleagues with a higher mastery of English. The feeling of inferiority may also come from a mental comparison of the discourse they would hold in their mother tongue with the discourse held in a foreign language, simpler, more limited and lacking nuances, as summed up in the "Keep it short and simple" formula often used in the workplace. [START_REF] Neeley | Language Investments Pay Big Dividends for Global Companies[END_REF] makes this point in an interview: I've written about this for years, where you have these incredibly competent employees who are experts in their various areas of work. They say they feel "childlike" when they have to switch to the working language. It affects how they contribute.

[Please insert Figure 5 about here]

The highest scores are for lower-educated, middle-aged women and men. We conjecture that they are likely to feel inferior because of their short studies, their professional pressure and responsibilities linked to a career peak. For all those reasons, they may become more aware of their linguistic lacks and needs.

Foreign language anxiety (FLA)

MacIntyre and Gardner described FLA as "[t]he feeling of tension and apprehension specifically associated with second language (L2) contexts, including speaking, listening and learning " (1994: 284). MacIntyre later mentions "the worry and negative emotional reaction aroused when learning or using a second language" (MacIntyre 1999: 27). We wanted to observe if this feeling existed in the working world.

[Please insert Figure 6 about here]

Lower-educated women feel the most FLA, whatever their ages. Higher-educated women in the three age groups appear to experience practically the same level of FLA as higher-educated men in the three age groups. [START_REF] Gargalianou | Foreign Language Anxiety in Professional Contexts. A Short Scale and Evidence of Personality and Gender Differences[END_REF] noted that women tended to experience more FLA than men in the workplace. Yet by adding the variable of education to our study, we can see that highereducated women experience the same level of FLA as higher-educated men, which is particularly noteworthy.

Two reasons could explain this situation. First, longer study and different syllabuses could give a better command of the foreign language and hence alleviate FLA. Second, the motivation of higher-educated women who want to be regarded as equal to their male colleagues could play a part in the decrease in FLA. Trudgill pointed to this change in society for language as a whole:

If the social roles of men and women change, moreover, as they seem to be doing currently in many societies, then it is likely that gender differences in language will change or diminish also. (2000: 79-80)

Behaviours

These feelings give rise to varied behaviours. We studied 3 examples of these behaviours, which are withdrawal, incapacity to improvise and awareness of inadequate cultural behaviours.

Withdrawal

Some human resources managers told us in preliminary studies [START_REF] Lancereau-Forster | L'anglais comme langue de formation en IUT et langue de travail dans le domaine aéronautique industriel[END_REF][START_REF] Lancereau-Forster | La gestion linguistique des entreprises[END_REF] that the main problem faced by French employees having to use English as a FWL was "mental block", with difficulties or incapacity to express himself or herself in the foreign language. This may lead to partial or total silence with hardly any willingness to communicate but a will to escape from speaking the foreign language.

[Please insert Figure 7 about here]

Our results regarding mental block and withdrawal show that lower-educated women are more affected than any other group, whatever their ages. By contrast, higher-educated women feel no more hindered than men (or even less so), with the exception of older highereducated women.

Lower-educated men and women in age group 1 appear to have a high level of mental block, which could be linked to a "school-like" attitude, in which silence is a solution. Yet in the workplace the employee is expected to be involved and active.

Avoiding improvisation

To escape from this "silent way", the employees may have to resort to improvisation. This latter term was defined by [START_REF] Hodgson | Improvisation[END_REF] as "spontaneous response to the unfolding of an unexpected situation". [START_REF] Landy | Handbook of Educational drama and theater[END_REF] also referred to improvisation as "an unscripted, unrehearsed, spontaneous set of actions". Improvisation may then be a source of stress, all the more as a quick response is usually expected. Employees may or may not be ready to improvise.

Figure 8 shows capacity/incapacity to cope with improvisation.

[Please insert Figure 8 about here]

We can observe that the profile of the answers for resorting to improvisation is quite similar to the previous one, that of the mental block. Mental block could explain the difficulties encountered by individuals in improvising.

The averages are clearly higher for lower-educated women (whatever their age groups) having to improvise. This might suggest that the faculty of improvising increases with the practise of the foreign language and a better mastery of it.

Awareness of inadequate cultural behaviours linked to language use

Some employees lacking the knowledge of appropriate cultural behaviours may choose to transfer their usual cultural behaviours (linked to their mother tongue) over a particular communication context, even though they are aware of their inadequacy. Others may also choose wrong behaviours or refrain from acting.

[Please insert Figure 9 about here]

The scores are generally homogeneous and fairly high. The employees are aware that problems may exist both on the linguistic level and the cultural one. This could be the case of socializing in the professional context ("small talk", for example) or working in an international team. Nevertheless, group FL2 scores the highest. These women may have a better position than when they were FL1 and may be more aware of the importance of specific cultural behaviours.

Representations and expectations

As a third part, we tried to discover if, in spite of this linguistic insecurity, the employees could see some positive aspects in the use of a FL in the workplace.

Linguistic enjoyment

The employees were asked if they enjoyed using a FL in the workplace.

[Please insert Figure 10 about here]

The response values are generally quite high and stand in contrast with the previous answers. This implies that most employees, although being faced with hurdles, are able to overcome them and adopt a positive attitude. However, younger lower-educated women and older lower-educated men report feeling less enjoyment. For the second category, the use of a FL in the workplace has been a relatively recent phenomenon in France and older lowereducated people may resent it and feel it has been imposed on them (Lancereau-Forster 2013: 385-387).

Cultural enjoyment

The employees were asked whether they were eager to discover another culture.

[Please insert Figure 11 about here]

The results obtained reach the highest scores for everyone, especially for age groups 1 and 2. In this case, the gender variable is not relevant, men and women feeling the same desire to explore new cultural horizons.

We saw earlier that some employees admitted lacking appropriate cultural behaviours regarding the use of a FWL. Nevertheless, they are able to keep a positive representation of the foreign culture. Despite their awareness of linguistic and cultural insecurity and the suffering the employees may experience as a result of them, they are able to foresee solutions or remediation.

Desire for improvement

Finally, the employees were asked if their desire for improvement kept increasing.

[Please insert Figure 12 about here]

This graph shows that most employees display quite a high desire for progress. Here again, the gender variable appears irrelevant.

Middle-aged lower-educated employees have a greater desire for progress. This is probably due to maximum work stress related to the use of English and often linked to new career prospects. Secondly, older employees, whatever their education level, are not statistically different (p = 0.162). They may show more resistance to, or less adhesion to, the fact of having to use a foreign language in the workplace. They may regard English as a mandatory tool (Lancereau-Forster 2013: 225).

These last three graphs demonstrate that the "game is not over". Indeed, linguistic and cultural enjoyment as well as a desire for progress reveal an existing motivation which can be built upon in educational targets at the university.

Synthesis and discussion

From the previous analysis and observations, we can present a composite chart to synthesize the results obtained both regarding the relevance of each of the three variables and all the items of the questionnaire (Items 1, 5 and 9, being positive scale items, had to be reversed in our analysis).

[Please insert Figure 13 about here] [Please insert Table 3 about here]

Table 3 Statistical analysis of composite data with different variables In the composite chart, the obvious differences correspond to the FL group, whatever the age group, with the highest level of ILI. This is corroborated by the comparison in which groups FH and MH are the same (p=0.668) and groups FL and FH are different (p=0.00002).

In other words, the composite chart shows that the level of ILI is the same for higher-educated women as for higher-educated men. The gender variable is not relevant, whereas the education level is a key factor. Another major result is that ILI is higher for lower-educated women than for higher-educated women. In this context, the education level variable is also relevant.

As a comparison, the following results have to be highlighted: groups ML and MH are different (p=0.008) and groups FL and ML are different (p=0.002). ILI is higher for lowereducated men than for higher-educated men. The education level variable is relevant. Then, with the same education level (low), women experience more ILI than men. The gender variable plays a part in this case. To sum up, in 3 cases out of 4, the education level variable comes first. We can add that the age variable does not affect the general pattern in the chart.

The main conclusion that can be drawn from these results is that, according to our findings, the education level is the most relevant variable accounting for interlinguistic insecurity in the workplace, followed by the gender and age variables.

The grid of our questionnaire can also be adapted as a scale to measure ILI in the workplace. The answers to all items, except items 1, 5 and 9, can give rise to an individual profile regarding ILI. The answers to 1, 5 and 9 have to be processed inversely as they are positive items (1= maximum ILI and 5 =minimum ILI). The latter indicate a more or less positive attitude from the employees. A higher level of motivation would increase the capacity for improvement. The composite scale we obtained could be used for further research, adapting the items to various countries as appropriate.

Interlinguistic insecurity in the workplace appears as a real issue for higher education This study of the three variables, gender, age and education level, demonstrates that solutions to ILI in the workplace could come from higher education courses and continuous learning.

Teachers could be informed of this type of research on the use of English in the workplace and consequently become more aware of the expectations of the working world. Taking into consideration feelings, attitudes, behaviours and representations like the ones presented in our study could support the creation of new syllabuses targeting psycholinguistic factors, among others, to alleviate ILI. For example, in order to improve the pronunciation issue, syllables and lexical stress patterns could be focused on, as suggested by Stenton's research (2013) which calls for annotated, sound-synchronised on-screen text for better cognition. New directions to follow could be an innovative emphasis on the development of improvisation skills and debating to fight inhibition and reinforce self-confidence. The practice of "small talk" or role plays in simulated job environments (serious games) could also be motivating to develop instinctive reactions and gain spontaneity. Some of these activities could take place in Language Centres just as activities like videoconferences, teleconferences and telephone conversations so as to train the students for these usual forms of communication in the workplace.

The connections between higher education and the working world have to become close-knit so that the needs of both parties may be known and acknowledged. Some forms of cooperation could be defined, such as that of creating "shadow" employees with student trainees observing the linguistic difficulties faced by their fellow employees carrying out their daily tasks. Video CVs or videos of business meetings could be used to correct mistakes. This knowledge could then be collected by research organizations like OULis, the observatory, to set up resources for both universities and the working world.

Conclusion

This study dealt with the issue of the interlinguistic insecurity (ILI) in the oral communication of French employees using English as a foreign working language. First, the existence of ILI in the workplace was confirmed, as shown by the feelings, attitudes, behaviours and representations explored. This research, however, was based on self-declared assertions. The employees may have under-reported the level of their difficulties because the fear of making mistakes in the use of FWL may have hidden the fear of being judged by the management.

Nevertheless, the employees are both aware of the management expectations in favour of a very good command of the FL and of their own shortcomings and weaknesses.

Yet, even though employees declare their difficulties and the effects of their ILI, they do not reject the use of a FWL and show willingness to adapt and improve their command of the FWL. This fact could give food for thought to universities and language teachers and encourage the design of new courses. Further, with knowledge of appropriate sociocultural behaviours linked to languages, the learner might feel more at ease with the foreign language and better prepared for its use in his or her future workplace.

Our research examined the French context. For comparison, similar studies could be carried out as regards ILI variations in other countries. Other foreign languages could be also researched, either instead of English or as well as English, comparing the levels of ILI in the workplace.

Tables and figures

  and requires means for alleviation in order to reach what MacIntyre et al. (1998) regard as the ultimate goal of the learning process [which] should be to engender in language education students' willingness to seek out communication opportunities and the willingness actually to communicate in them" (p. 547).

Fig 1 Fig 2 Figure 3 Figure

 123 Fig 1

Table 1 :

 1 Age groups

		Age groups of respondents	Percentages
	1	≤ 25-30 years-old	36%
	2	31-45 years-old	39%
	3	46-≥ 61 years-old	25%

Table 1 :

 1 Education level

	Higher education level	Percentages
	≤ 3 years of HE	19%
	> 3 years of HE	81%

Table 3 :

 3 Statistical analysis of composite data with different variables

		Variable		Mean	SD	No Samples	Test	w	p
	Composite FH v MH	F		22,733 6,858	135 Wilcoxon	26700	0,668	Same
		M		22,262 6,112	386
	Composite F v M	F		24,16 7,437	181 Wilcoxon	46392	0,027	Different
		M		22,564 6,146	461
	Composite H v L	H		22,384	6,31	521 Wilcoxon	22480 8,466E-07 Different
		L		25,727 6,987	121
	Composite MH v ML	H		22,262 6,112	386 Wilcoxon	11676	0,008	Different
		L		24,12 6,125	75
	Composite FH v FL	H		22,733 6,858	135 Wilcoxon	1802,5	2,16E-05	Different
		L		28,348 7,561	46
		Age Group Median Mean	SD	No Samples	Test		p
	Composite/ Age	1	22	22,91	6,22	230 Kruskal-Wallis		0,968	Same
		2	22	23,1	6,72	248
		3	22,5	23,03 6,855	164
	Composite L / Age	1	25	25,82	6,853	67 Kruskal-Wallis		0,795	Same
		2	28	25,9 6,981	29
		3	25	25,28 7,602	25
	Composite H / Age	1	21	21,71	5,53	163 Kruskal-Wallis		0,506	Same
		2	22	22,73	6,61	219
		3	22	22,63	6,66	139
	Composite M/ Age	1	22	22,4	5,81	151 Kruskal-Wallis		0,873	Same
		2	22	22,76	6,32	185
		3	22	22,48	6,32	125
	Composite F/ Age	1	23	23,89	6,86	79 Kruskal-Wallis		0,925	Same
		2	23	24,11	7,73	63
		3	24	24,79	8,2	39

LAIRDIL: Laboratoire Inter-universitaire de Recherche en Didactique LANSAD, Toulouse, Université Paul Sabatier.

Appendix

Questionnairepart 2 (English translation from the French original) Rate each item, from 1 to 5 (1= minimum to 5= maximum), according to the feelings or behaviours you are most likely to adopt.

Complete the sentence: "when I have to use a foreign working language", …


Shan-Qi Zhao

Dominique Planson
email: planson@cegely.insa-lyon.fr

Jean-Pierre Chante

An effective simulation system with TSUPREM-4 TM and MEDICI TM simulators has been set up in this paper to simulate structures and electrical characteristics, and further to give an optimum design of a power insulated gate bipolar transistor. The latch-up effect of the device is also simulated and analyzed in different practical cases.

INTRODUCTION

The insulated gate bipolar transistor (IGBT) is a new power switching device developed as a monolithic integration of a MOSFET and a wide base bipolar transistor. The devices have the advantages of operating at much higher current density and higher blocking capability than power MOSFET and bipolar transistors, and are now widely used in the power electronic industry. TSUPREM-4 is a computer software that simulates the processing steps used in the manufacture of silicon integrated circuits and discrete devices, and MEDICI is a powerful device simulation program that can be used to simulate the distributions of potential and carrier concentrations in both MOS and bipolar devices and to predict its electrical characteristics for any bias condition. The results reported in this paper were obtained with these two simulators used to simulate the processing steps structure, and further electrical characteristics of an IGBT. Otherwise, we can define a certain structure and manufacturing TM TSUPREM-4 and MEDICI are trademarks of TMA, Inc., Palo Alto, CA 94303-4605, USA processes according to the specifications given by the device users.

MODEL AND STRUCTURE

A TSUPREM-4 simulator can present a twodimensional cross-section of a portion of a semiconductor wafer. We define the substrate region as an initial structure with certain width and depth, and the top of the surface is exposed. All the manufacturing processes occur at the top surface. Each region of the structure is divided into mesh of non-overlapping triangular elements. The grid lines are controlled to be fine in the channel region and junction regions and to be coarse in another regions. The choice of simulation models in TSUPREM-4 should be considered before performing any processing steps. The speed and accuracy of the simulation depend strongly on the choice of models. The most fundamental process simulated by TSUPREM-4 is diffusion. In addition to simulating the diffusion of the usual impurities, it can also result in oxidation when performed in an oxidizing ambient. The compress oxidation model is used for the entire process, which simulates viscous flow of the oxide during oxidation. In accordance with the practical processes, the fabrication steps, such as epitaxy, oxidation, ion implantation, diffusion, deposition, etching, photolithography etc., are simulated by using of relative models in the TSUPREM-4 (TMA 1995). A practical IGBT structure is obtained, which includes some information like concentrations of impurities in every region, contours of p-n junctions, channel length, gate length, configurations of the gate, emitter, and collector, and thicknesses of the gate oxide and the gate polysilicon. Fig. 1 presents cross section view and doping profile in a half cell of an IGBT. The p + is collector, n + b is buffer layer, n is epitaxy layer, p is p-type well, p + e is enhancement layer, n + is emitter. The simulations and analyses below are based on this structure. All the information about the practical structure from TSUPREM-4 are successfully transported into MEDICI program by means of two special joint commands.

∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼

ELECTRICAL CHARACTERISTICS

Because the IGBT is a high current and high voltage device controlled by a MOS gate, the effects of the impurity concentration, the temperature, the high field in the silicon bulk, and especially the surface scattering should be taken into account when mobility models are chosen [START_REF] Tma | Two-Dimensional Device Simulation Program TMA[END_REF]. The

Shokley-Read-Hall recombination, Auger recombination, and the band-gap narrowing effect are also considered. In addition, the models chosen should be used in cases where the grid spacing at the interface is smaller than the inversion layer width. The electrical characteristics are obtained by solving Poisson's equation and both continuity equations for electrons and holes using the iterative method of incomplete cholesky conjugate gradients [START_REF] Tma | Two-Dimensional Device Simulation Program TMA[END_REF]. Fig. 2 and Fig. 3 show gate characteristic and output characteristic of the device at T c = 25°C respectively.

Gate voltage Vg (V)

Vce = 3 V Temp = 25°C
Ic 45 A V CE =3V, V GE =15V Collector-emitter breakdown voltage BV CES 1000V V GE =0V, I C =2.0mA Gate threshold voltage V GE(th) 3∼6V V CE =V GE , I C =1.0mA Forward voltage drop V f(ON) 2.5∼3.2V V GE =15V, I CE =I C

LATCH-UP EFFECT

The presence of the parasitic four-layer thyristor structure in IGBT creates the possibility of the device latching up by regenerative action. The latchup phenomenon is highly undesirable because it can lead to loss of control of the collector current by the applied gate voltage.

Collector-emitter voltage Vce (V) These simulation results were supported by the theoretical analyses [START_REF] Baliga | Suppressing Latch-up in Insulated Gate Transistors[END_REF][START_REF] Baliga | Modern Power Devices[END_REF]. Fig. 6 and Fig. 7 show the latch-up phenomena at different temperatures and different minority lifetimes in the n-epitaxy layer. It is clear that the latch-up phenomena easily occur at high temperature and large lifetime as theoretical and experimental results [START_REF] Baliga | Modern Power Devices[END_REF][START_REF] Koh | Two-Dimensional Analysis of Latch-up Phenomena in Latch-up-Free Self-Aligned IGBT Structure[END_REF][START_REF] Baliga | Temperature Behavior of Insulated Gate Transistor Characteristics[END_REF]. The distribution of current flowlines before and after latch-up in the device are shown in Fig. 8.

CONCLUSION

The manufacturing processes, structures and electrical characteristics of an IGBT were simulated with both TSUPREM-4 and MEDICI simulators.

The simulation results agree with the experimental ones. Using the simulation system, processes and structure can be easily adjusted to obtain optimum design satisfying with user's specifications.

The latch-up effects with different structures, different temperatures and different lifetimes were simulated and analyzed, and some suppression methods for latch-up phenomenon were proposed.

Fig. 1 :

 1 Fig. 1 : Part-sectioned view (a) and doping slice (b) of an IGBT

FigFig. 3 :

 3 Fig. 2 : Simulated gate characteristic

Fig. 5

 5 Fig. 5 Simulated latch-up effects with different structures

Fig. 6 :

 6 Fig. 6 : Simulated latch-up effects with different temperatures

Table 1 :

 1 Principal electrical characteristics (measured valu es) at T c = 25°.

ACKNOWLEDGMENT

The authors would like to thank Advanced Power Technology (APT -Bend, Oregon 97702-1035, USA) for providing information on device structure for our simulation work and for providing devices to confirm the simulation.

A SIMULATION SYSTEM FOR A POWER INSULATED GATE BIPOLAR TRANSISTOR (IGBT) WITH TSUPREM-4 AND MEDICI SIMULATORS

Before latch-up, the main part of current flows through the n-channel like n-MOSFET. Only about 30% current run under the n + emitter in the p-well. However, more than 60% current does not pass through the n-channel after latch-up. In this case, the MOS-gate is out of control, and the IGBT has become latched into a thyristor-like conducting state. Therefore, in order to avoid latch-up in an IGBT, a buffer layer and p-enhancement layer should be adopted in the device structure, and operating temperature and minority lifetime in the nepitaxy layer should be decreased with most possibility.

DEVICE DESIGN

The electrical characteristics with different parameters from the techniques can be easily obtained with above simulation system. Fig. 9 and Fig. 10 show gate characteristics with different channel lengths and different gate lengths respectively. The current decreases with an increase of channel length, and increases with gate length because forward voltage drop decreases. In order to get a high current capability, some parts of surface area are enhanced by high doping concentration in simulation. The forward voltage drop decreases with increasing implant dose, as shown in figure 11. A high current value can be obtained when V f is fixed. However, the breakdown voltage decreases obviously with implant doses as shown in figure 12.

Gate voltage Vg (V)

There is a trade-off between breakdown voltage and forward voltage drop. For example, for a device with high switching speed and low voltage capability, a high implant dose could be chosen to get a low forward voltage drop.


Camille Birou

Xavier Roboam

Hugo Radet

Fabien

Fabien Lacressonnière
email: fabien.lacressonniere@laplace.univ-tlse.fr

Techno-economic analysis of second-life lithium-ion batteries integration in

Keywords: Microgrid», «Modelling», «Batteries», «Renewable energy systems», «Energy system management»

published or not. The documents may come

Introduction

Balancing electric power production vs demand becomes more and more complex due to the huge growth of alternative intermittent energies (solar and wind farms) and the increase of electric vehicles connected on the grid. In this context, grid services such as self-consumption, peak shaving and grid erasure become a prime necessity, which should lead to the emergence of smart microgrids, more performant if a storage device is used in order to guarantee a better autonomy and to limit power grid exchanges. Facing the constraints in the automotive industry, it is considered that batteries are no longer usable and must be replaced when it has reached 65% of its initial capacity. Instead of directly recycling batteries that still possess capacity, it is interesting to extend their lifespan with "a second life" on stationary applications, reducing the recycling cost for car manufacturers and lowering storage costs. The objective of this work is to design a techno-economic model of a microgrid composed of a second life battery in order to study the ageing of second life batteries for different solicitation profiles, but also to get an overview of the profitability of the storage device for the customers.

A) One case study for second life battery integration for microgrid analysis

Several applications for second-life batteries are conceivable. The aim is to extend the life of batteries from electric vehicles, which still have capacity in less restrictive applications such as in microgrids to limit the use on the grid via production-consumption balancing or to carry out grid services (peak shaving, clipping, etc.). In our case, we will focus on stationary applications in microgrids. These applications provide the advantage of being less constraining for batteries than in automotive applications because low current rates are typically required, and therefore a lower operating battery temperature, which slows down the ageing process. The installation of storage devices in a microgrid microgrids EPE'20 ECCE Europe ISBN: 978-9-0758-1536-8 -IEEE: CFP20850-ART P.1

Assigned jointly to the European Power Electronics and Drives Association & the Institute of Electrical and Electronics Engineers (IEEE) will make it possible to increase the self-consumed energy but also to mitigate the power variability on the grid due to the intermittent of renewable energies. In our case, an eco-district in Toulouse was considered, composed of twenty houses of 100 m 2 heated by heat pumps and equipped with roofmounted PV system and second life batteries. This microgrid is plugged into the electricity grid. The production and consumption data are normalized from the Homer software (synthetic data): production data for 1 kWp of photovoltaic panels in Toulouse and consumption data for a normalized residential type profile for an average daily consumption of 1 kWh. On the consumption profile, a peak in the evening is observed, when the solar panels no longer produce. Hence, in order to reduce the peak energy consumption on the grid, a storage is coupled on the microgrid (Fig. 1).

Fig. 1: Global synoptic of the microgrid

The grid service applied to the microgrid is related to the self-consumption with resale of the energy surplus as proposed in French policies for small producers (36 kWp<Pp<100 kWp). It is here possible to obtain a total 5-year photovoltaic investment bonus of 0.09 €/Wp paid annually over five years and to sell the surplus energy produced at a rate set at 0.06 €/kWh [START_REF] Edf Enr | Une prime pour encourager l'autoconsommation solaire[END_REF]. The energy purchased on the electricity grid will be invoiced at the standard Electricity of France (EDF) price of 0.147 €/kWh. 𝐶𝑜𝑠𝑡 = 𝐸 𝑜𝑢𝑡 ⋅ € 𝑜𝑢𝑡 -𝐸 𝑖𝑛 ⋅ € 𝑖𝑛 (1) With:

 Eout energy injected into the electrical grid (kWh).  €out grid injection price of energy at 0.06 €/kWh.  Ein energy extracted from the electrical grid (kWh).  €in purchase energy price at 0.147 €/kWh.

The objective of the microgrid is firstly to satisfy the needs of energy consumers by limiting grid impact. The Energy Management Strategy (EMS) is built on simple heuristic. The issue is to use the energy produced as much as possible to avoid buying it at more expensive price or to sell it at a low price. The battery is used as soon as consumption is different from production in order to readjust the productionconsumption balance. In case of underproduction, the battery provides the missing energy until it reaches its minimum of State Of Charge (SOC), in which case it is necessary to buy energy from the electricity grid. In a case of overproduction, firstly, the battery is charged and when it reaches the maximum SOC, energy will be injected into the grid. Given photovoltaic production data (PPV) and consumption data (Pload) seen as the program inputs, the EMS will allocate power flows in the different devices of the microgrid while monitoring the state of the battery [i.e. both (SOC) and state of health (SOH)] to estimate the power (Preal) that it can actually deliver. In order to do this, it is necessary to have a battery model, which is presented in the next section. The objective of the techno-economic model developed on Matlab from previous works [START_REF]Rapport de synthèse des activités de recherche au sein du Laboratoire LAPLACE dans le cadre du lot 3.5 : Optimisation technico économique[END_REF][START_REF] Rigo-Mariani | Méthodes de conception intégrée[END_REF][START_REF] Varais | Modèles à échelle réduite en similitude pour l'ingénierie système et l'expérimentation simulée "temps compacté": application à un micro-réseau incluant un stockage électrochimique[END_REF] is to simulate a microgrid, including a second life lithium-ion (Li-ion) battery over a long period of time (typically the microgrid lifecycle) to get technical and economic data. In order to do that, the tool proceeds in four steps: simulation data entry, technical simulation, economic simulation and results display. Table I presents the values of parameters set during the simulations.

𝑃 𝑔𝑟𝑖𝑑 = 𝑃 𝑙𝑜𝑎𝑑 -𝑃 𝑃𝑉 -𝑃 𝑏𝑎𝑡𝑡𝑒𝑟𝑦 (2) 𝑃 𝑏𝑎𝑡𝑡𝑒𝑟𝑦 = 𝑀(𝑃 𝑙𝑜𝑎𝑑 -𝑃 𝑃𝑉 ; 𝑃 𝑟𝑒𝑎𝑙 ) (3)

B) Lithium-ion battery model

Storage elements are characterized by their energy density (Wh/kg) and power density (W/kg). Li-ion batteries have the advantage to have a higher energy density and power density than lead or nickel-based batteries. Li-ion technology has developed strongly since the 1980s with the first commercialization in 1991 by Sony Energitech. In this part, the modelling of Li-ion battery will be discussed. Two models [START_REF] Delacourt | Vieillissement des accumulateurs lithium-ion dans l'automobile[END_REF] are used (Fig. 2) to design the battery as well as possible:  A behavioural model. It simulates the electrical behaviour of battery in order to calculate its SOC and its voltage. Hence, with these values, the EMS can control the battery level before allocating the power flows in the microgrid.  An ageing model, which allows estimating the degradation of the battery in order to get its SOH.

B.1) Characteristics of the tested battery

As part of this study, we focused on second-life Carbon -Lithium Manganese Oxide (C-LMO) Li-ion batteries from electric vehicles. It is composed of a negative carbon electrode (graphite) and a positive electrode based on spinel structures: lithium manganese oxide (LMO) using mainly manganese, which has the advantage of being available in large quantities [START_REF] Eddahech | Modélisation du vieillissement et détermination de l'état de santé de batteries lithium-ion pour application véhicule électrique et hybride[END_REF]. The Aging model is based on the cycle to failure curve for a temperature at 25°C and a C/2 discharge regime. It allows to know, for a given depth of discharge (DOD), the maximum number of equivalent maximum cycles. To obtain the parameters of the behaviour model, C/2 discharge characteristics (Fig. 3) was used for three SOH: 86%, 80%, 69%. As the electric vehicle market is particularly recent, many batteries are now arriving for recycling at high SOH levels (between 80 and 90%) due to accidents or manufacturer returns. Therefore, in this study, a high initial SOHini in second life was taken at 90%. In the future, this SOH before recycling will drop to the expected 65%.

B.2) The behaviour model

There are several types of battery models in the literature [START_REF] Rigo-Mariani | Méthodes de conception intégrée[END_REF] [6]:  Mathematical models (neural networks, fuzzy logic).  Electrochemical models.  Equivalent electrical circuit models.

For our application with a systemic vision of a microgrid, electrical circuit models seem to be the most suitable because they offer a good compromise between computation time and accuracy [START_REF]Rapport de synthèse des activités de recherche au sein du Laboratoire LAPLACE dans le cadre du lot 3.5 : Optimisation technico économique[END_REF].

B.2.1) Description of the Tremblay-Dessaint model

The In the case of our study, the calculation time step is large enough Δt=10 min, it is possible to neglect the filtering effect modelled by C2 [START_REF]Rapport de synthèse des activités de recherche au sein du Laboratoire LAPLACE dans le cadre du lot 3.5 : Optimisation technico économique[END_REF], so we take i instead of i*. The expressions of the Tremblay-Dessaint model can be written according to the SOC where the OCV is the open circuit voltage of the cell battery and R the resistive terms [START_REF] Cabello | Battery dynamic model improvement with parameters estimation and experimental validation[END_REF]:

OCV (SOC) = 𝐸 0 + 𝐴𝑒 -𝐵𝑄 𝑛𝑜𝑚 (1-𝑆𝑂𝐶) -𝐾𝑄 𝑛𝑜𝑚 ( 1 𝑆𝑂𝐶 -1) (4)
𝑉 𝑏𝑎𝑡 𝑖𝑛 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 = 𝑂𝐶𝑉(𝑆𝑂𝐶) -𝑅 1 𝑖 -𝑅 2 𝑖 ( 1 𝑆𝑂𝐶 ) (5)
𝑉 𝑏𝑎𝑡 𝑖𝑛 𝑐ℎ𝑎𝑟𝑔𝑒 = 𝑂𝐶𝑉(𝑆𝑂𝐶) -𝑅 1 𝑖 -𝑅 2 𝑖 ( 1 1.1-𝑆𝑂𝐶 ) (6)
It is necessary to identify the Tremblay-Dessaint parameters model [E0, A, B, K, R1, R2] from a cell characteristics.

B.2.2) Evolution of parameters with ageing

It is important to investigate the evolution of the parameters of this model with ageing in order to modify the parameters of the Tremblay-Dessaint model. In the literature [START_REF] Zhang | A Generalized SOC-OCV Model for Lithium-Ion Batteries and the SOC Estimations for LNMCO Battery[END_REF], OCV characteristics according to the SOC for (C-LMO) cells for different SOH are presented in Fig. 5.

Fig. 5: OCV evolution with ageing [START_REF] Zhang | A Generalized SOC-OCV Model for Lithium-Ion Batteries and the SOC Estimations for LNMCO Battery[END_REF] It can be noted from Fig. 5 that, for a given SOC, the value of the OCV remains almost identical regardless of the SOH of the cell. Therefore, in the OCV equation, it is assumed that the parameters [E0, A, B, K] remain constant despite ageing.

However, ageing mainly affects two factors: a decrease in capacity and an increase of the internal resistance of the battery as shown in Fig. 6 [START_REF] Eddahech | Modélisation du vieillissement et détermination de l'état de santé de batteries lithium-ion pour application véhicule électrique et hybride[END_REF]. Hence, the SOC takes into account the ageing of the battery cell with the value Q deg which represents the real capacity of the cell at a given instant tk:

𝑆𝑂𝐶 𝑘+1 = 𝑆𝑂𝐶 𝑘 - ∫ 𝑖 𝑑𝑡 𝑡 𝑘+1 𝑡 𝑘
𝑄 𝑑𝑒𝑔 𝑘 [START_REF] Tremblay | Experimental Validation of a Battery Dynamic Model for EV Applications[END_REF] Fig. 6: Evolution of capacity and internal resistance with ageing [START_REF] Eddahech | Modélisation du vieillissement et détermination de l'état de santé de batteries lithium-ion pour application véhicule électrique et hybride[END_REF] In order to take into account the increase on internal resistance with ageing, it will then be necessary to modify the value of the internal resistance R 1 in the Tremblay-Dessaint model. From the observations of the work carried out by Akram Eddahech [START_REF] Eddahech | Modélisation du vieillissement et détermination de l'état de santé de batteries lithium-ion pour application véhicule électrique et hybride[END_REF], a linear evolution of the internal resistance seems more suitable for low temperatures.

B.2.3) Method for identifying parameters

In order to identify the parameters of the Tremblay-Dessaint model [E0, A, B, K, R1, R2] of the cell, an optimization algorithm is required: the non-linear least squares method was used. It consists in minimizing the error between the experimental data (yi) and the model (f). For the identification process, we decided to use the following method. First, the OCV parameters were obtained from OCV characteristic (Fig. 5). Then R1 (with an ageing law) and R2 parameters were determined from discharge curves (Fig. 3).

S(θ) = ∑ (𝑦

B.3) The ageing model: "exchangeable energy model"

The ageing model allows to estimate the SOH of the battery cell. For batteries oriented energy, the SOH can be calculated as the ratio between the actual capacity of the battery and its maximal capacity. There are two types of ageing that occur in the battery operation [START_REF] Eddahech | Modélisation du vieillissement et détermination de l'état de santé de batteries lithium-ion pour application véhicule électrique et hybride[END_REF]  Calendar ageing which corresponds to the cell performance degradation over time when the battery not operates.  Ageing in cycling which refers to the cell performance degradation when a battery current circulate in the battery.

In the literature, there are three types of ageing models: physical, mathematical or fatigue models. In our case, with a systemic approach of a microgrid, the fatigue models seem to be the most adapted because they present a good compromise between calculation time/accuracy. Hence, the issue was simplified by considering the "exchangeable energy model" which consists in calculating the battery degradation as a function of the amount of energy (in charge and discharge) that the battery can exchange with the system throughout its life (between SOHini and SOHlim [START_REF]Rapport de synthèse des activités de recherche au sein du Laboratoire LAPLACE dans le cadre du lot 3.5 : Optimisation technico économique[END_REF][START_REF] Rigo-Mariani | Méthodes de conception intégrée[END_REF]. This maximum amount of exchangeable energy is estimated [START_REF]Rapport de synthèse des activités de recherche au sein du Laboratoire LAPLACE dans le cadre du lot 3.5 : Optimisation technico économique[END_REF][START_REF] Rigo-Mariani | Méthodes de conception intégrée[END_REF] from the "cycle to failure" curve where it is possible to read the maximum number of cycles according to the chosen discharge depth: 𝐸 𝑒𝑥𝑐ℎ 𝑚𝑎𝑥 = 2. 𝑁 𝑐𝑦𝑐𝑙𝑒𝑠 𝑚𝑎𝑥 (𝐷𝑂𝐷 𝑐ℎ𝑜𝑠𝑒𝑛 ). 𝐷𝑂𝐷 𝑐ℎ𝑜𝑠𝑒𝑛 . 𝐸 𝑖𝑟𝑎𝑡𝑒𝑑 (9) With:

 Erated: rated energy of the battery for SOH ini .  DODchosen desired depth of discharge for the battery cycle (between 0 and 1).  Ncycles max: maximum number of cycles for a DOD set to DOD chosen .  Eexch max: maximum amount of energy that can be exchanged by the battery during a certain period of its life (between SOH ini and SOH lim ).

Finally, the SOH is determined at the next step from the energy exchanged during a time step according to the formula below:

𝑆𝑂𝐻 𝑘+1 = 𝑆𝑂𝐻 𝑖𝑛𝑖 + 𝑆𝑂𝐻 𝑙𝑖𝑚 -𝑆𝑂𝐻 𝑖𝑛𝑖 𝐸 𝑒𝑥𝑐ℎ 𝑚𝑎𝑥 * ∑ |𝐸 𝑒𝑥𝑐ℎ (𝑖)| 𝑘+1 𝑖=1 (10)
With |𝐸 𝑒𝑥𝑐ℎ | = ∫ |𝑃 𝑏𝑎𝑡 (𝑡)| 𝑡+𝛥𝑡 𝑡 𝑑𝑡 (11)

C) Economic Model

In order to assess a techno economic analysis, it is necessary to calculate economic indicators to estimate the whole cost of the microgrid over its life cycle (i.e. the NPV, for Net Present Value is defined below). This latter is based on cash flows, noted Fm for the year m. Cash flows take into account the incomes due to the chosen self-consumption strategy (𝑐𝑓𝑔𝑟𝑖𝑑 𝑚 ) with resale of the power surplus for small producers (see part II in the case of French policies), to which the operating and maintenance costs (OPEX) must be deducted. To adjust the elements to the current value of costs for the year under consideration, it is required to multiply by (1+e) m with e the inflation rate.

𝐹 𝑚 = 𝑐𝑓𝑔𝑟𝑖𝑑 𝑚 -𝑂𝑃𝐸𝑋 𝑚 (12) 𝑐𝑓𝑔𝑟𝑖𝑑 𝑚 = (𝐸 𝑜𝑢𝑡 ⋅ € 𝑜𝑢𝑡 -𝐸 𝑖𝑛 ⋅ € 𝑖𝑛 ) ⋅ (1 + 𝑒) 𝑚 (13) 𝑂𝑃𝐸𝑋 𝑚 = (1 + 𝑒) 𝑚 ⋅ 𝑂𝑃𝐸𝑋 (14)
In our case, the CAPital Expenditure (CAPEX) takes into account the investment related to the photovoltaic production source CAPEXPV (development costs, purchase and delivery of equipment (solar panels, inverters, etc.), installation and connection) and that concerning the means of storage CAPEXBAT. The investment is considered to be fully paid the first year (no loan). To stay in a simple economic vision, investment costs were estimated in €/kWp for the photovoltaic production source and in €/kWh for the battery system. Regarding the OPEX, there are estimated as percentage rOM each year of the initial CAPEX investment. However, to be more precise, the OPEX of the battery is divided into two parts: a fixed part which will be a percentage of the CAPEX each year of the battery life and a variable part to take into account the extra cost when replacing the battery. The variable part is expressed as the cost (CAPEXbat -rRep . nbmodule €) by replacing of all the batteries with rRep the cost (€) that can be saved per module compared to the initial price of the battery (recovery of certain elements, in particular electronic devices such as BMS).

In a project, the net present value (NPV) is used to account for the overall cost of the microgrid over its lifetime by integrating its energy management strategy and its environment (solar irradiation, grid policies and rates). To do this, year by year, the cash flow is discounted to current value using the actual discount rate d [START_REF]Rapport de synthèse des activités de recherche au sein du Laboratoire LAPLACE dans le cadre du lot 3.5 : Optimisation technico économique[END_REF]. In the economic model implemented to analyse the microgrid performance, the objective is to selfconsume as much energy as possible (self-consumption case). That is why the microgrid does not allow to earn money. It is more convenient to compare the case of the microgrid with a "reference case" for which 100% of consumed energy is purchased from the electricity grid at a fixed price. The interest is to analyse if it is economically more profitable to create your microgrid (with corresponding investments and to self-consume your own energy as much possible) than to purchase energy from the grid at fixed price. In our analysis, the first key indicator will be the "relative NPV" (ΔNPV) which is the difference between the microgrid NPV (including a certain sizing of both the solar array and the storage device) and a reference system NPVref, which will obviously be negative, which would include neither storage device nor PhotoVoltaic (PV) source and which would lead to purchase the total consumed energy to the grid by considering the actual purchase rates €in. Thus, the microgrid is profitable if:

𝑁𝑃𝑉 = -𝐶𝐴𝑃𝐸𝑋 + ∑ 𝐹 𝑚 (1+𝑑) 𝑦𝑒𝑎𝑟 𝑁 𝑦𝑒𝑎𝑟=1 (15)
𝛥𝑁𝑃𝑉 = 𝑁𝑃𝑉 -𝑁𝑃𝑉 𝑟𝑒𝑓 > 0 (16) 𝑊𝑖𝑡ℎ 𝑁𝑃𝑉 𝑅𝐸𝐹 = ∑ -𝐸 𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑 . € 𝑖𝑛 (1+𝑑) 𝑦𝑒𝑎𝑟 𝑁 𝑦𝑒𝑎𝑟=1 (17)
To take account for the profitability of the microgrid in relation to the reference case, two typical economic indicators are calculated: the return on investment time (ROIT) and the profitability index (PI). The ROIT (years) represents the time from which the invested capital is recovered, i.e. when the cumulative NPV of the microgrid becomes higher than that of cumulative reference NPVref. The PI is the ratio between the financial gain at the end of the migrogrid lifetime and the CAPital Expenditure (CAPEX):

𝑃𝐼 𝑟𝑒𝑓 = 𝛥𝑁𝑃𝑉 𝐶𝐴𝑃𝐸𝑋 (18)

D) Some analysis results and discussion

With the emerging smart grids integrating intermittent renewable power sources, new pricing policies would appear to encourage renewable energy plants (solar, wind) coupled with storage to limit the use of the grid. As energy indicator, we know the "degree of autonomy" defined as the ratio between the energy produced and the energy consumed. But this latter indicator does not differ depending if the consumption takes place during production or outside production phases, thus neglecting the constraints of the grid (line congestion, etc). To quantify more conveniently the level of grid constraint, a new indicator called "degree of grid usage" (DGU) is defined as the ratio at each time step between the average grid energy (whatever if it is injected or extracted) and the energy consumed (excluding battery consumption):

DGU (in %) = 100*𝑀𝑒𝑎𝑛 𝑘=1 𝑁 ( 𝐺𝑟𝑖𝑑 𝑒𝑛𝑒𝑟𝑔𝑦 𝑘 𝐶𝑜𝑛𝑠𝑢𝑚𝑒𝑑 𝑒𝑛𝑒𝑟𝑔𝑦 𝑘 ) ( 19
)
with k the step time and N the number of points.

The issue about this indicator is linked with the fact that grid power must be balanced in both ways, over production as well as over consumption A first interesting analysis aims at assessing both the peak power of the photovoltaic installation and the total stored energy for the Li-ion battery with respect to the policies and grid services with that microgrid. It is necessary to look for the best configuration in order to maximize the ΔNPV or to minimize the DGU. To do this, the mapping of figure 7 allows having a trend on the profitability and the grid usage according to the investments (sizing of devices). The following maps are obtained with Enom (battery sizing) on the x-axis and PPV (solar panels sizing) on the y-axis. The scale color represents the value of ΔNPV on the left and DGU on the right with in yellow the highest values and in blue the lowest values. It can be noted that the pairs with the best ΔNPV (yellow part) are located at high installed peak power and with a storage capacity of less than 400 kWh with assumptions made in the model. Indeed, with this strategy, the optimal point to maximize ΔNPV is: ΔNPV=199k€ for PPV=100kWp and Enom=198kWh. With this sizing of photovoltaic panels and based on the assumptions taken from the model, a case with storage is more profitable than a case without storage. Thus, with such grid policies and economic assessments, there is a benefit with storage by using the energy produced during the day and by postponing it to the evening to avoid buying expensive energy from the electrical grid. Even if the DGU (equal to 71.3% for the techno economic optimum point) is smaller than if the consumers would buy all the energy needs, this parameter may be improved with other battery sizing making the microgrid more and more autonomous. Looking at the Degree of Grid Usage (DGU) map (on the right), we notice that the optimal point in terms of DGU is: DGU=37%, obtained for PPV=68kWp and with the maximal storage capacity Enom on this map: Enom=798kWh. But the ΔNPV= -4 227 € is here really negative with such a storage device: we can have here an "idea of the cost for full autonomy with stand alone microgrids". With this funding strategy, both indicators (ΔNPV and DGU) are not compatible (the yellow area on the left does not overlap the blue area on the right).

D.1) Analysis at the maximum ΔNPV point D.1.1) Analysis of the battery performance degradation over the life cycle

Thereafter, the techno-economic analysis is carried out for the optimal sizing in terms of ΔNPV (i.e. PPV = 100kWp and Enom=198kWh). For this simulation, the battery model parameters change with the battery ageing (R1 and Q). Looking at the evolution on the battery State Of Health (SOH) over the full lifetime of the microgrid (in our case 30 years), it appears that it is not necessary to change the battery as the SOH reaches 59% after 30 years. From an economic point of view, the microgrid costs more money each year than it brings us (Net Present Value (NPV)= -333.3k€<0). However, analysing the relative evolution of the cumulative ΔNPV observed by comparing the net present value of the microgrid with that of the reference case (with neither PV nor storage), the obtained Return On Investment Time is less than 12 years meaning that the microgrid costs less than buying all energy from the grid. Compared to this reference, the microgrid investments will be profitable and will save 199k€ after 30 years.

D.1.2) Comparison of analysis with and without battery performance degradation

With the same optimal sizing, it is possible to compare the previous results with the ones obtained without taking into account the degradation of battery performance due to the ageing (capacity and power losses), i.e there is no loopback of SOH on behavioural model parameters (R and SOC). In this latter case, the ageing model only allows to estimate the State Of Health (SOH) in order to calculate the cashflow (taking into account the cost of battery changes when they take place). The comparative analysis between the two cases are below. 12 After 30 years, without considering the degradation of battery performance, it can be observed that more ampere hours (Qth cell) are exchanged with the storage device. Indeed, the battery without accounting the degradation (with a constant capacity) is able to maintain the exchanged energy during cycle as in its initial conditions. This will result in a lower SOH than if the degradation is taken account. The relative error between both cases (with and without accounting the degradation) is significant on technical data: 6% on SOH and 12% on Qth (Ampere-hour exchanged by the battery). However, at the economic level, the error is decreasing with only 3% on NPV and 5% on ΔNPV. Setting the simulation time at 20 years, the error on NPV is reduced by half. Let notice that taking into account ageing on the battery's behaviour improves accuracy of analysis but increases the computation time.

D.2) Discussion

The previous results show a favorable trend towards the development of renewable sources (solar PV) and the implementation of storage devices in microgrids. This trend exists not only from an economic point of view (i.e. the ΔNPV is more important than without storage at the optimal sizing point) but also from a technical point of view (limitation of grid usage with a smart energy management, etc.). However, these results should be taken with some caution because we have placed ourselves in a very particular case study, dealing with an eco-neighbourhood with an Electricity of France (EDF) contract for the resale of the power surplus. The techno-economic model is built from hypotheses and simple models. In our case study, it is assumed that the contract for reselling the surplus with EDF remains valid for the entire life (30-years) of the microgrid (roughly corresponding with the solar panel life time), whereas it is a 20-year contract. In our model, the parameter set at the beginning of the simulation will remain the same during the 30 years, being just subject to the inflation rate (set here at 2%). However, it is obvious that certain parameters, such as the purchase price of energy, are likely to increase significantly in the next thirty years. It is thus difficult to predict economic parameters over a long period of time. For this reason, a sensitivity analysis was carried out to determine the parameters that have the greatest impact on the final ΔNPV. The sensitivity analysis revealed that the parameters which have a strong influence on ΔNPV are the inflation rate, the discount rate and the purchase price of energy from the grid. In addition, the cell temperature is considered constant around 25°C because of the low current regimes (C/2) recommendation to limit battery heating and therefore ageing. It is not necessary here to change the batteries for 30 years because the second life of the batteries was here started at high initial State Of Health (SOHini = 90%). Moreover, in our model, the efficiency of power electronic devices are not taken into account and it is assumed that a perfect balancing of the cells was performed (SOH of a cell = SOH of the battery pack) thanks to the balancing system of the Battery Management System (BMS). However, in reality, there can be a significant dispersion of the capacity of the different cells constituting the battery, all the more for second life batteries (with different first lifes).

In this work, the exchangeable energy model has been retained to take into account the battery ageing during cycling by neglecting the calendar ageing. Two different approaches were discussed: the first one was to consider that the ageing model has an impact only on economic indicators via the estimation of the battery SOH without considering the degradation of battery performance. Reasoning on global systems, the objective here was to estimate the qualitative trends of ageing in order to know which parameters were the most sensitive with the greatest impact on life expectancy. The second approach has considered that the ageing model has an impact, not only on economic indicators via the SOH, but also on technical performance (by coupling ageing effects on certain battery model parameters: R1 and Q). This approach allows to have a better accuracy on analysis but the calculation time is much more important because it is necessary to carry out the technical simulation on all years of the microgrid life. On the contrary, with the first approach, it is possible to simulate the behavior of the battery over one typical year and to consider that this year is repeated on the life time. This first qualitative analysis allows to save in computing time by going from a few minutes to a few seconds.

Conclusion

This study was essentially based on the modelling of a battery within a microgrid especially in the case of second life batteries. It provides a first simplified version of a techno-economic tool for microgrid analysis which will be developed further in the future. Such tools are needed to better understand how to improve the device sizing in microgrids, the competitiveness of battery technologies and to predict their ageing in a global system. In the particular case of second life batteries, the techno economic analysis is of prime necessity. The advantage of this tool is that it is easily scalable and allows adding quickly new features or testing different case studies.

Through this first study and with the hypotheses considered, an eco-neighbourhood composed of 20 houses was analysed and showed that it was possible to take advantage of the installation of a secondlife battery both from a technical point of view to reduce grid dependence and also from an economic point of view to improve profitability. In addition, the sensitivity analysis revealed that the economic parameters having a strong influence on the profitability of the microgrid ΔNPV are the inflation rate, the discount rate and the purchase price of energy from the grid. The modeling of the second life battery includes two models: a Tremblay-Dessaint behavioral model whose parameters were identified on discharge curves of second life batteries at different SOH and an exchangeable energy ageing model (taking into account the ageing in cycling and not calendar ageing). In this work, two different approaches were with and without taking into account the battery degradation on model parameters. Between the two cases, it is a compromise between precision (increase of 12% for certain technical data such as Ah exchanged) and calculation time (switch from few minutes to few seconds) that needs to be made.

For the future, the challenge is to include more complex energy management strategies, but most of all to improve the accuracy of the tool by refining hypothesis for example by taking into account the losses due to power electronics, the ageing of the various components of the microgrid (production sources, power electronics, etc.), the performance losses of batteries due to the dispersion of the cells' capacity in a module over time, but also the uncertainty of the evolution of the economic parameters over the years. To improve these studies, it will be also necessary in the future to develop more complex and precise ageing models (e. g. electrochemical) to better take into account the phenomena occurring within second life batteries (impact on second-lifetime of SOH and resistance values at the end-of-first-life, related to first-life use).

  With:  Pload and PPV >0.  Pgrid and Pbattery can be positive or negative : <0 in charge et >0 in discharge.  M=max in charge Pload -PPV < 0 and M=min in discharge Pload -PPV > 0. microgrids EPE'20 ECCE Europe ISBN: 978-9-0758-1536-8 -IEEE: CFP20850-ART P.1 Assigned jointly to the European Power Electronics and Drives Association & the Institute of Electrical and Electronics Engineers (IEEE)

Fig. 2 :

 2 Fig. 2: The battery model.

Fig. 3 :

 3 Fig. 3: Discharge curves at C/2 for different SOH

  Tremblay-Dessaint [2-4] [7-8] model (Fig. 4) is a quasi-static model where voltage and current are separated. It comes from Shepherd's work in 1965 and describes the battery operation from the discharge curve (taking into account the evolution of the voltage depending on the SOC) knowing the current and the SOC.

Fig. 4 :

 4 Fig. 4: Equivalent electrical circuit.

  𝑖 -𝑓(𝑥 𝑖 ; 𝜃)) 2 𝑁 𝑖=1 (8) With in our case:  N: number of cell voltage measurement points.  xi: inputs of the Tremblay-Dessaint model at point i, namely the current and the SOC.  : unknowns of the Tremblay-Dessaint [E0, A, B, K, R1, R2].

Fig. 7 :

 7 Fig. 7: Maps of the ΔNPV and the DGU versus both device sizing

Table I : Parameters set

 I

	Simulation time	Step time for technical simulation	Step time for economic simulation	PV investment bonus	Purchase energy price	Redemption price of energy
	30 years	10 minutes	1 year	0.09 €/Wp	0.147 €/kWh	0.06 €/kWh

Table II : Battery parameters set

 II

	SOCmin	SOCmax	SOHini	SOHlim	Vmin	Vmax	C-ratemax	Qnom
	10 %	90 %	90 %	45 %	2.5 V	4.1 V	C/2	50 Ah

Table

  III presents the accuracy performance of the model for the discharge curves studied (SOH=86%, 80% and 69%).

Table III : Errors between model and data

 III

		SOH=86%	SOH=80%	SOH=69%
	Mean-squared error	0.60 mV	0.79 mV	0.86 mV
	Average relative error	0.52 %	0.45 %	0.5 %

Table IV : set of economic parameters

 IV

	Inflation	Discount	PV	OPEX for PV	Battery	OPEX for Battery
	rate	rate	CAPEX		CAPEX
	e = 2 %	d = 3 %	Cinv PV =	rOM PV = 2.5 %	cinv bat =	Fixed part : rOM bat = 2% of
			1.2 €/Wp	of CAPEX PV	200€/kWh	CAPEX battery / year
				/ year		Variable part : rRep = 70€
						saved / module replaced

Table V : comparative analysis with and without degradation of battery performance microgrids

 V Assigned jointly to the European Power Electronics and Drives Association & the Institute of Electrical and Electronics Engineers (IEEE)

		ΔNPV (k€)	NPV (k€)	SOH end (%)	Qth cell (kAh)
	Without degradation	208.9	-323.3	55.5	534
	With degradation	198.9	-333.3	59.2	477.6
	Error (%)	5	3	6

EPE'20 ECCE Europe ISBN: 978-9-0758-1536-8 -IEEE: CFP20850-ART P.1