Conceptualization and theoretical evaluation of modified energy management strategy enabling EIS and adaptive BoP control in PEMFC

Kurzfassung

Automotive proton exchange membrane fuel cells (PEMFC) operate under highly dynamic load conditions, which accelerate degradation and limit long-term durability. Although Electrochemical Impedance Spectroscopy (EIS) is a promising diagnostic technique for monitoring internal electrochemical processes, its application during vehicle operation is limited by the requirement for quasi-stationary operating conditions, which are not provided by conventional energy management strategies (EMS). Therefore, this thesis develops and evaluates a modified EMS capable of enabling quasi-stationary operating conditions suitable for EIS execution in automotive PEMFC. In addition, the work investigates the prospects of utilizing EIS-based diagnostic information for adaptive control of balance-of-plant (BoP) components.

To achieve this, recorded roller test and on-road driving data of a Hyundai NEXO are analyzed together with an existing vehicle powertrain simulation model developed at DLR. Based on the observed EMS behavior and the requirements for EIS-compatible operation, a modified rule-based EMS with eleven operating modes is developed and implemented in Dymola 2025x. One dedicated operating mode maintains the fuel cell stack at a nearly constant power level through controlled power distribution between the fuel cell stack and the high-voltage battery. Simulation-based evaluations demonstrate that the developed EMS can generate quasi-stationary operating phases without significantly affecting vehicle drivability. During the WLTC simulation, the modified EMS maintains a constant fuel cell power output for approximately 462 s, corresponding to 25.72 % of the driving cycle. Compared to the existing EMS, the modified EMS reduces the maximum fuel cell power peak and the average absolute ramp rate, indicating smoother and less transient fuel cell operation. Although hydrogen consumption increases, the overall tank-to-wheel efficiency remains competitive and improves by 4.21 %. Finally, the thesis discusses the prospects of adaptive BoP control using impedance-based diagnostic information. Overall, the presented work demonstrates that EMS modification is a feasible approach for enabling EIS-compatible operation and provides a foundation for future impedance-based diagnostics and adaptive control in automotive PEMFC systems.