Improved virtual capacitive droop control for hybridization of energy storages in DC microgrid

Hybrid energy storage system (HESS) facilitates the integration of various energy storages (ESs) with different ramp rate. Virtual capacitive control (VCC) is used to ensure the idle condition of supercapacitors (SCs) when HESS is in steady state and dynamic power sharing in transion. Improved virtual capacitive droop (IVCD) is proposed in this paper by introducing DC bus voltage regulation for batteries. Compared with VCC, HESS under IVCD eliminates redundant SCs SOC regulation controller and realizes SOC recovery by automatically transferring power from the battery to SCs in transient state. Therefore, both SCs SOC recovery and DC bus voltage regulation are concurrently achieved. System stability is also studied with parameters variation under IVCD control scheme. The effectiveness and feasibility of the proposed IVCD are verified in Matlab simulations. Advantages of IVCD are demonstrated by exhaustive analysis of simulation results.