Study on the Optimal Allocation and Capacity of Energy Storage to Improve the Three-Phase Unbalance in Distribution Systems

Three-phase unbalance occurs in the distribution network due to unbalanced loads, uneven power equipment parameters, system faults, and improper maintenance, integration of renewable generation, etc. Distributed Energy Storage System (DESS) is one of the effective means to solve this problem due to its flexible power regulation function. Through proper setting of DESS, the three-phase unbalance can be reduced. In this paper, a three-phase power flow model for unbalanced distribution systems is proposed considering the PV-type DG and energy storage device. And the zero-sequence voltage unbalance is defined to evaluate the system unbalance. A modified particle swarm optimization algorithm is employed to find the optimal allocation and capacity of energy storage devices connected to the distribution system. Case studies show that the three-phase unbalance of the distribution system can be effectively improved by the optimal allocation of energy storage devices.