Optimal allocation and PQ output ratio of NAS batteries for improving voltage stability in distribution systems

In recent years, many studies have been made on allocating Na-S batteries in distribution substations to make good use of power facilities and improve the load factor. Besides, it has also been a hope to utilize Na-S batteries for controls such as AFC (automatic frequency control) or VQC (voltage reactive-power control), because Na-S batteries can respond faster than existing generator units and can control active and reactive power outputs independently by the function of AC-DC converter systems. In this paper, the authors propose a method for determining the optimal allocation and PQ output ratio of Na-S batteries in order to improve voltage stability. The proposed method combines a sensitivity method with an optimal power flow calculation method to determine the allocation and PQ output ratio efficiently and optimally. Simulations are carried out for a 73-bus distribution system to illustrate and verify the proposed method.