Grid-forming assisted based power management of AC microgrid system comprising multiple battery energy storage units, DFIG-based wind turbines and inverter-based resources

This paper deals with the decentralized control and power management of the under-study AC microgrid system comprising multiple battery-energy-storage (BES) units, DFIG-based wind turbines (WTs) and droop-controlled inverter-based dispatchable sources. The control structures of all sources are designed in a decentralized and coordinated manner to meet the balance between the generation and consumption and to keep the batteries state of charge (SOC) in the allowable ranges. To do this, all generation and storage sources are controlled in the gridforming mode as voltage-controlled sources to follow a unified power-frequency ( P- omega) droop curve. This P- omega droop curve is based on the microgrid frequency as an indicator index and adjusted locally in real time according to the available wind power, load demand, and SOC of the BESs. The study system based on the defined P- omega droop curve contains three regions: (a) Power curtailment mode of DFIGs with battery charging, (b) MPPT mode of DFIGs with battery charging, and (c) MPPT mode of DFIGs with battery discharging. Depending on the system frequency value, the operating point is placed in one of the three regions of the defined droop curve, and thus, decentralized power management and SOC control of BES units are realized without communication facility. Small signal models of the proposed control loops are presented, and the capability of the proposed unified control strategy is verified by simulation results.