Cooperative Control to Enhance the Frequency Stability of Islanded Microgrids with DFIG-SMES

The issue of frequency stability of microgrids under islanded operation mode and mode transfer has attracted particular attention recently. In this paper, a cooperative frequency control method, which consists of a microgrid central control (MGCC) and microgrid local control (MGLC), is proposed to achieve a seamless transfer from grid-connected to islanded mode, and hence increase the frequency stability of islanded microgrids during both primary and secondary frequency control. A power deficiency prediction and distribution method is proposed in MGCC to effectively distribute and utilize the power and loads, and accomplish the cooperative control of all microgrid units. With regards to MGLC, a Hopfield fuzzy neural network control (HFNNC) is applied to make the corresponding frequency control of DFIG-SMES more adaptive. Meanwhile a state of capacity (SOC) control is utilized in battery energy storage (BES) to extend battery life. Simulation results indicate that the proposed frequency control approach can maintain the frequency stability of islanded microgrids even in emergency conditions.