This paper proposes a novel virtual inertia control (VIC) method based on a feedforward decoupling strategy to address the low inertia issue of power-converter-interfaced microgrids. The feedforward control scheme is employed to eliminate the coupling between active and reactive power caused by line impedance. The active power-voltage droop can be applied to the battery converter in the hybrid energy storage system (HESS). A novel VIC method is developed for the supercapacitor (SC) converter of HESS to increase the inertia of the microgrid. Detailed small-signal modeling of the SC converter with the proposed VIC was conducted, and the transfer function model was obtained. Parameter analysis of the virtual inertia and virtual damping was carried out with the pole-zero map method, and the step response characteristic of output voltage amplitude with power variation was analyzed in detail, deriving the parameter design principle. The simulation study verifies the effectiveness and validity of the proposed control strategy. The proposed feedforward decoupling method and VIC can be widely applied in microgrids to enhance inertia and improve their power quality.

For a new distribution network with energy storage and a flexible multi-state switch (FMSS), several problems of multi-mode operation and switching, such as the unbalance of feeder loads and feeder faults, among others, should be considered. This paper forwards a coordination control strategy to address the above challenges faced by the FMSS under grid-connected operations. To tackle the multi-mode operation problem, the system’s operational state is divided into multiple working modes according to the operation states of the system, the positions and number of fault feeders, the working states of the transformers, and the battery’s state of charge. To boost the system’s operational reliability and load balance and extend the power supply time for the fault load, the appropriate control objectives in the coordination control layer and control strategies in the equipment layer for different working modes are established for realizing the above multi-directional control objectives. To resolve the phase asynchrony issue among the fault load and other normal working loads caused by the feeder fault, the off-grid phase-locked control based on the V/f control strategy is applied. To mitigate the bus voltage fluctuation caused by the feeder fault switching, the switching control sequence for the planned off-grid is designed, and the power feed-forward control strategy of the battery is proposed for the unplanned off-grid. The simulation results show that the proposed control strategy can ensure the system’s power balance and yield a high-quality flexible power supply during the grid-connected operational state.