Multiphe hydrogen injection at anode side of PEMFC
The alternating feeding architecture (known as Ping-Pong) was developed by the CEA. This architecture emerged in 2013 and has been implemented in several fuel cell systems. Following the latest tests on this architecture, questions remained unanswered. First, it is a question of understanding how species (hydrogen, nitrogen, liquid and gaseous water) move in cells operating with alternating feeding. Control laws influences these movements, it will be necessary to identify the levers to make the most out of it and then to propose methods to promote the evacuation of water and nitrogen while avoiding the evacuation of hydrogen.
The thesis work will aim to optimize the anode architecture with alternating feeding and to bring this architecture to maturity. The key points are the search for an optimum control of this architecture, the achievement of a hydrogen rejection rate of less than 1%. Finally, this optimization will also have to maximize the durability of the stack.
The doctoral student will have to model the movements of species at different time scales (10ms to 10 minutes), understand the mechanisms, adapt the control laws and validate the new control laws on a test bench.
This work will identify solutions to efficiently evacuate liquid water and nitrogen and minimize H2 rejection and then obtain superior performance compared to conventional architectures.
High-isolation power supply
With the rapid evolution of technologies and the growing challenges of miniaturization and resource management, power converters are facing ever more stringent performance requirements. To meet these needs, the use of wide-bandgap semiconductors such as SiC (silicon carbide) and GaN (gallium nitride) is becoming increasingly common. These materials significantly increase the switching speed of converters, reducing losses and improving efficiency.
However, this switching speed brings additional challenges: the steepness of the switching edges can cause stray currents that interfere with switch controls. To counter these undesirable effects, it is necessary to use switch drivers offering a high level of insulation. The traditional solution is based on high-frequency magnetic transformers, but these devices are expensive, take up a lot of space and offer limited insulation.
Thesis objective: the aim of this thesis is to design a new solution for powering wide-gap component drivers, by replacing magnetic transformers with piezoelectric transformers. This innovative approach aims to reduce costs, space requirements and improve the overall efficiency of power conversion systems.
Supervision and ressources: the selected candidate will work as part of a leading-edge research team, renowned for its expertise in the field of power conversion using piezoelectric resonators. The team has the resources and know-how to support the development and validation of this innovative technology.
Advanced functions for monitoring power transistors (towards greater reliability and increased lifespan of power converters for energy)
In order to increase the power of electronic systems, a common approach is to parallelize components within modules. However, this parallelization is complicated by the dispersion of transistor parameters, both initial and post-aging. Fast switching of Wide Bandgap (WBG) semiconductors components often requires slowdowns to avoid over-oscillation and destruction.
An intelligent driving scheme, including adjusted control, control of internal parameters of circuits and devices, as well as a feedback loop, could improve reliability, service life and reduce the risk of breakage.
The objectives of the thesis will be to develop, study and analyze the performance of control and piloting functions of power components, in silicon carbide (SiC) or gallium nitride (GaN), which could ultimately be implemented in a dedicated integrated circuit (ASIC type).
This thesis subject aims to solve critical problems in the parallelization of power components, thus contributing to eco-innovation by increasing the lifespan of power modules.
Impact of the Pulse Width Modulation strategy on the semiconductor ageing
The Pulse Witdh Modulation strategy (PWM) is a fundamental technique in power electronics. It is used to control the Energy transfer by modifying the pulse width of the control signals in a power converter. In an automotive traction inverter, this PWM strategy applied to a transistor phase leg allows to convert the DC current from the battery to an AC current adapted to the motor windings. The impact of the PWM on the performances and the reliability of the engine have been widely studied in the litterature. However, the impact of the PWM strategy on the reliability and the ageing of the semiconductor devices inside the power modules has not been adressed. This is particularly true for the power modules intagrating wide bandgap semiconductors (eg: SiC) which are widely used for 10 years. The main objective of this thesis is to understand and model the impact of several PWM strategies on the ageing of SiC power semiconductor devices.
The thesis targets to define a link between the stress on the semicondcutor devices and the shift of its key parameters offering the possibility to define a PWM strategy able to maximize the long term performances and the lifetime of the power electronics system. By combining experimental and theroretical approaches, this thesis will contribute to improve the PWM strategies in power electronics systems.