Fuzzy Controller for Energy Management and SoC Equalization in DC Microgrids Powered by Fuel Cell and Energy Storage Units

This article proposes a coordinated and decentralized control structure for a dc microgrid (MG) powered by fuel cells (FCs) and energy storage units (ESUs). With the employment of ESUs in the dc MG, the balancing among their states of charge (SoCs) increases their lifetimes and improves the dc MG reliability. Assuming the FC as the main source, fast transients of load on the dc link can damage its membrane. In this context, the FC and ESUs show a complementary behavior during the transitory, while the possibility to change the energy shared between the sources at a steady state promotes the energy management system. The SoCs of all ESUs connected to the MG are balanced using a fuzzy controller. Furthermore, a low-pass filter in association with a droop controller can mitigate the stress caused by the fast transients on the FC terminals. The main benefits of using the fuzzy controllers are related to the practical simplicity of implementation and the fact that a high-speed link of communication between the FC and the ESUs is not needed. Additionally, Lyapunov's indirect method performs the stability analysis of the dc MG. Finally, a laboratory-scale prototype evaluates the effectiveness of the proposed approach.