A Coordinated Droop Controls and Power Management Scheme for Hybrid Energy Storage Systems in DC Microgrids

This paper proposes a coordinated droop controls for multiple hybrid energy storage systems (HESSs) including the batteries and supercapacitors (SCs) to achieve the slow- and fast-dynamic power-sharing as well as dc bus voltage restoration in a dc microgrid. A V-dP/dt droop scheme is proposed to control the output power of battery converters with a slow dynamic response. The traditional power droop is employed to regulate the SC converters to give a fast response. The dc bus voltage is maintained in a safe range by the SC converter control so that no voltage recovery loop is required. Hence, the order of the overall control system and the complexity of parameter design can be reduced. In addition, a power management scheme (PMS) is proposed to ensure the system power balance and protect the batteries from over-charge/over-discharge under different operating modes. A state of charge (SoC) balancing method is proposed to solve the issue of SoC imbalance among batteries with different capacities. Then, the SoC restoration of the SCs is considered. The output impedance characteristics and control system design are elaborated in detail. The processor in the loop (PIL) simulation results verified the effectiveness and feasibility of the proposed control method.