BESS Assisted Off-Grid Wind Energy Conversion System Operated Under Adverse Battery-SoC Conditions

Wind Energy Conversion systems (WECS), supplying islanded microgrids, often incorporate a Battery Energy Storage System (BESS) as an energy-buffer. To ensure safety and long life, the battery-bank (BB) in such systems must not be overcharged or deep-discharged. This paper proposes a reconfigurable operational strategy for a doubly-fed induction generator (DFIG) based islanded WECS integrated with a BESS. When the State-of-Charge (SoC) of the BB approaches the maximum limit, the rotor side converter regulates the DC bus voltage using a modified voltage controller while operating the DFIG away from the Maximum Power Point. When the BB-SoC approaches the minimum limit, a minimum consumer-discomfort factor based load-shedding strategy is proposed so that the BESS can regulate the DC-bus voltage without deep discharging the BB. The DFIG-BESS system supplying the benchmark CIGRE residential distribution network has been simulated in an Opal-RT real-time simulation environment. The proposed voltage controller shows 69.44% and 46.66% lower undershoot in the DFIG-stator active-power and 3.45% and 99.83% lower DC-voltage deviation compared to a PI-controller and latest literature, respectively, while transiting from the BESS to RSC based DC-bus voltage regulation. The proposed load-shedding strategy also reduces the DC-bus voltage dip significantly compared to a similar strategy proposed in the literature.