Control Method for Grid-Connected/Islanding Switching of Hybrid AC/DC Microgrid

For hybrid AC/DC microgrid (HMG) under master-slave control strategy, DGs usually adopt constant power control (P control) in gird-connected mode and at least one DG adopts constant voltage control (V control) in islanding mode. However, when unplanned islanding happens, the voltage and current of the HMG will experience remarkable fluctuations, which affects the system's stability. This paper presents a control method to achieve smooth switching from grid-connected to islanding mode by introducing state tracking control between P control and V control. The state tracking control can make the current reference signal of the V control track that of the P control in grid-connected mode. When unplanned islanding happens, the mutation of the current reference signal can be tuned into a smooth transition by the voltage loop's PI controller, and the transient oscillations can be eliminated to realize smooth switching. The effectiveness of the proposed control method is verified by simulation results using MATLAB/Simulink.