Design and application of enhanced extended state observer for improving bus voltage stability during EIS testing of multi-stack proton exchange membrane fuel cells

Introduction Proton exchange membrane fuel cells (PEMFCs) are highly efficient and environmentally friendly energy conversion devices. Their modular multi-stack FC (MSFC) provides enhanced operational stability and power output. However, during online electrochemical impedance spectroscopy (EIS) testing, multi-frequency sinusoidal current disturbances injected by the DC/DC converter can cause periodic fluctuations in the common DC bus voltage, threatening system stability and measurement accuracy. Existing approaches, such as hardware filtering or improved topology, suffer from high cost and complexity. While the traditional extended state observer (ESO) can estimate the disturbance, it struggles to suppress the fluctuations during multi-frequency co-detection. Methods This paper proposes an enhanced ESO design, namely the multi-resonant ESO (MRESO), for MSFC hybrid systems. By embedding multiple resonant units, the MRESO accurately tracks the EIS disturbance frequency and combines feedforward compensation with battery-assisted control to achieve robust bus voltage stability. The system modeling is based on the principle of energy conservation, and the control scheme adopts a dual-loop structure consisting of an inner current loop and an outer voltage loop. The voltage loop integrates the MRESO to improve interference rejection capability. Results Simulation results show that under load current disturbances and EIS measurement interference, MRESO can reduce voltage fluctuations by over 70% and achieve stability within 0.08 s, outperforming both PI control and traditional ESO, validating its effectiveness in suppressing multi-frequency disturbances. Discussion This study provides a feasible voltage stabilization solution for online EIS monitoring of MSFC, contributing to improve the power quality and reliability of the hybrid system.