A Decentralized Power Coordination Strategy for Battery/Supercapacitor in DC Microgrids

The battery-supercapacitor (SC) based hybrid energy storage system (HESS) is widely used in DC microgrid to suppress the power fluctuation. Many coordination strategies have been proposed for HESS, but most of them rely on communication system. This paper proposes an enhanced dual virtual impedance droop strategy without communication for HESS. A high-pass filter-based virtual resistance droop control is used for battery converter to solve the issues of DC bus deviation state-of-charge (SoC) violation. An adjustable virtual impedance droop control applied to a SC converter can realize the constant current charge or discharge of the SC in the steady state to prevent the SC's SoC from exceeding the critical value. With the proposed control strategy, SC's SoC can be automatically recovery while considering boundary conditions, thus improving the service life. Moreover, the approach can realize the high and low frequency power sharing between the SC and the battery, and the bus voltage can be restored to the nominal value. Simulations are conducted to verify the effectiveness of the proposed control strategy.