An Improved Virtual Impedance Droop Control of Three-Port Converter Interfaced Hybrid Energy Storage Systems

The power allocation of hybrid energy storage system (HESS) is crucial for the development of hydrogen fuel cell vehicles (HFCVs). To improve the operational efficiency, a triple active bridge (TAB) converter is designed as the interface circuit, which can transfer power bi-directionally and isolate the voltage in a wide range of transient conditions. This paper proposes a droop control strategy based on adjustable virtual impedance for HESS. The fuel cell (FC) side converter adopts the virtual resistance and inductance droop (VRID) control, while the Lithium battery side converter uses the virtual capacitance droop (VCD) control. The Lithium battery can quickly absorb the high-frequency component of the system power fluctuation, which improves the dynamic response of the system. Moreover, the value of the virtual resistance is adjusted according to the operating state of the circuit, which helps to enhance the power quality and eliminate the voltage deviations caused by conventional droop control. The proposed control strategy and analytical results are validated by both simulations and experiments.