A Control Method to Minimize Negative-Sequence Grid Voltage Considering Battery Lifespan in Battery Energy Storage Systems

This paper proposes a novel control method to compensate grid voltage imbalance by minimizing negative-sequence voltage while improving the battery lifespan in the battery energy storage system. When the negative-sequence current is injected to compensate for the grid voltage imbalance, an AC ripple of 120 Hz, which is the second harmonic of the grid's fundamental frequency of 60 Hz, appears in the battery input current. If an AC ripple current of 120 Hz is applied to the battery input above a certain value, it accelerates battery aging more than when only DC current is applied, thereby reducing the battery lifespan. Therefore, this paper aims to control the 120 Hz ripple current at a threshold that can prevent battery aging while maximizing the effect of the grid imbalance compensation. In the proposed method, the relationship between the negative-sequence current and the 120 Hz ripple current input to the battery is analyzed, and a negative-sequence current reference which meets the threshold of 120 Hz in the battery side is derived mathematically. The effectiveness of the proposed control method is verified by experimental results.