SOC Balancing Strategy for Parallel-connected Power Conversion System based on PQ decoupling Control

Nowadays the battery energy storage system (BESS) plays a significant role in power grid due to its excellent function in energy regulation. In most cases, BESS connects to the power grid through Power Conversion System(PCS). However, the state of charge (SOC) of different battery modules tend to be different during the working process. The difference between SOC would intensify buckets effect, and the performance of BESS would be degraded due to the abnormal feature (low SOC) of single battery cell. To avoid such shortcoming, it is necessary to eliminate the difference of SOC though control strategy. In this paper, we propose a SOC balancing strategy for parallel-connected power conversion system based on PQ decoupling control, which can also adjust the active power output of each battery module converge to optimization solution. Simulation and experimental results from a 2u 700V, parallel-connected power converter system are presented in order to validate the method.