Sliding mode control and simulation of a hybrid Fuel-Cell Ultracapacitor power system

This paper deals with a robust control strategy for modern distributed generation systems made up of hybrid PEM (proton exchange membrane) Fuel Cell (FC) and Ultracapacitors (UCs) power system. Particularly, for future fuel cell a vehicle application is presented. Given the constraint of the FC dynamics and the complexity of the energy management, a second order sliding mode control (SMC) strategy is designed to improve the robustness and the performance of the system. This control strategy, based on frequency decomposition of the load specifications, uses a cascaded closed loop control. It takes into account the slow dynamics of FC and the state of charge (SOC) of the UCs. FC output power is determined according to the low frequency (LF) load requirement and the UC SOC. UCs value is determined according to the high frequency (HF) load requirement. Therefore, two voltage control loops are designed. The DC bus voltage is regulated by the UCs source using a classical proportional integrator (PI) controller. The UCs SOC voltage is regulated by the FC source using a sliding mode (SM) controller, which improves the global performance of the controlled system. An analysis of the simulation results is conducted using Matlab/Simulink software in order to verify the effectiveness of the proposed control strategy. It confirms that the developed model and its control strategy exhibit excellent performance.