Battery System Modeling and Cross-Cultural Engineering Experience in France
By WANG Mindong
This internship at OPmobility in France represented an important stage in my master’s studies and research, as well as a valuable opportunity to combine theoretical knowledge with engineering practice. Focusing on NMC battery performance modeling and IMD/IMR integrated verification for the optimization of railway BEMU battery systems, the internship enabled me to make substantial progress in professional expertise while also deepening my understanding of cross-cultural communication, personal development, and future career planning.
The internship took place at the OPmobility Alphatech Research Centre in Compiègne, a historic city located approximately 60 kilometers from Paris. The city is known for the Palace of Napoleon III and for having served as the headquarters of the Allied Powers during the First World War, where the armistice agreement ending the war was signed.
Internship Responsibilities and Technical Work
My primary responsibility was to develop an electro-thermal coupling model of a battery pack using MATLAB/Simulink and Simscape. The objective of this model was to predict key operating parameters of the BEMU (Battery Electric Multiple Unit) battery system under real operating conditions, including temperature distribution, State of Charge (SOC), and terminal voltage.
Furthermore, I integrated this model with the company’s existing IMD/IMR (Instantaneous Maximum Discharge/Charge Current) estimation model in order to improve the overall safety and operational reliability of the battery system.
The main tasks included:
Battery Structure and Cooling System Modeling
I developed a complete battery pack structure based on the 460 NMC prismatic cells used in the Alstom BEMU system, organized into modules and strings. In parallel, I established a liquid cooling plate system model to accurately represent the thermal management process.
Equivalent Circuit Model Development and Parameterization
I implemented a zero-order equivalent circuit model based on Lookup Tables to dynamically calculate SOC, terminal voltage, and temperature.
Electro-Thermal Coupling Simulation
The electrical and thermal models were coupled through bidirectional interfaces to achieve dynamic temperature distribution prediction across twelve subregions.
Integration with the IMD/IMR Model
Simulated SOC and temperature data were used as inputs for real-time calculation of safe current limits, allowing evaluation of battery operational safety under complex working conditions.
Simulation Validation
The model was validated using real BEMU operational power data at ambient temperatures of 10°C and 25°C. The results demonstrated high accuracy, with a maximum temperature prediction error of approximately 3.3°C, a voltage error within 4.3 mV, and an SOC error below 0.51%, confirming the model’s ability to effectively reproduce real battery behavior.
Full-Day Operating Simulation
A 13-hour operational cycle simulation was conducted using real power profiles and a multi-stage charging strategy. The results showed that temperatures remained within the range of 25–34°C, while temperature differences between subregions remained below 0.8°C. Operating currents consistently stayed within IMD/IMR safety thresholds, demonstrating the engineering feasibility and reliability of the model.
Professional Development and Engineering Skills
This internship significantly strengthened my professional skills in several aspects.
Through the construction of multi-level battery pack models using Simscape Battery Builder and coupling them with cooling systems, I considerably improved my modeling and simulation capabilities for battery systems.
I also learned how to use measured train operational data to validate model accuracy and perform error analysis, making the simulation results more applicable to real engineering scenarios.
During the model integration process, I needed to continuously balance computational efficiency and simulation accuracy. This experience helped me develop stronger systems engineering thinking and improved my ability to make engineering judgments and optimization decisions.
Moreover, by integrating concepts from thermodynamics, control theory, and electrochemistry, I strengthened my interdisciplinary problem-solving abilities and developed a more comprehensive understanding of complex energy systems.
Cross-Cultural Working Experience
The internship took place in a French research and development center, where I participated in engineering projects within an international and multicultural environment. Working alongside engineers from France and other countries allowed me to observe significant differences in communication styles and professional approaches across cultures.
For example, French engineers tended to focus more on the overall project logic and practical feasibility, whereas I had previously concentrated more on technical details. Through continuous adaptation and learning, I gradually learned how to combine macro-level thinking with detailed technical verification, which greatly improved communication efficiency and teamwork.
Personal Growth and Reflections
This internship made me realize that technical skills alone are not sufficient for the development of complex engineering systems. Communication abilities, teamwork, and time management are equally essential.
When facing cross-departmental requirements, I learned how to quickly understand project needs, clarify boundary conditions, and propose effective solutions. During periods of high workload and pressure, I also developed the ability to break complex challenges into manageable tasks, allowing me to address problems more calmly and efficiently.
Understanding the Company and French Work Culture
As a global leader in sustainable mobility technologies, OPmobility maintains strong investment in emerging sectors such as battery technologies and hydrogen energy. The company emphasizes innovation-driven development and interdisciplinary collaboration, while its research center provides advanced experimental platforms and an open working atmosphere for young engineers.
Living and working in France also allowed me to experience the local balance between professional efficiency and quality of life. While work environments emphasize rigor and teamwork, equal importance is given to leisure, well-being, and personal life outside working hours. This culture helped me realize that professional development should not focus solely on speed and performance, but also on long-term sustainability and personal well-being.
Challenges and Solutions
Several important challenges arose during the internship.
The first involved difficulties in model integration. The IMD/IMR model and the thermal battery model used different solvers and time-step configurations, which initially caused unstable coupling behavior. By adjusting simulation configurations and optimizing interface variables, I ultimately achieved stable collaborative operation between the models.
The second challenge involved balancing computational accuracy and efficiency. Increasing the number of subregions significantly increased computational costs. Through comparative analysis, I identified twelve subregions as the optimal balance between precision and efficiency.
The third challenge concerned language barriers. Since many colleagues, like myself, were non-native English speakers, misunderstandings occasionally occurred during daily communication. To overcome this, we learned to express ideas more clearly and precisely. Although effective communication required additional time and effort, active interaction ultimately led to successful collaboration.
Future Perspectives
This internship helped me clarify my future professional direction. Electrification and low-carbon development represent inevitable trends in the transportation sector, and the safety, reliability, and optimization of battery systems constitute key foundations for this transition.
In the future, I hope to continue specializing in battery modeling and energy system optimization, combining both theoretical research and practical engineering applications.
At the same time, this experience of international collaboration made me realize that becoming an engineer with a truly global perspective requires continuous improvement not only in technical expertise, but also in language proficiency, communication abilities, and interdisciplinary integration skills.
