Control of a cascaded STATCOM with battery energy storage system under unbalanced and distorted grid voltage conditions

Abstract

This paper proposes a novel control strategy of a star-connected cascaded static synchronous compensator with a battery energy storage system (STATCOM/BESS) under unbalanced and distorted grid voltage conditions. Cascaded second-order generalized integrators are utilized to effectively extract the fundamental positive- and negative-sequence components from the adverse grid voltage. Moreover, proportional multi-complex integral current controllers are adopted to improve the harmonic characteristic of the grid-connected current with zero steady-state error and rapid dynamic response in the stationary αβ reference frame. However, unbalanced grid voltage along with the control target of obtaining the fundamental positive-sequence grid-connected current leads to unbalanced active powers among the three phase clusters. This issue will result in an unbalanced clustered state of charge of battery units and seriously affect the battery life and system performance. Accordingly, clustered active-power-balancing control is presented to solve this issue by injecting an appropriate zero-sequence voltage. Simulation results show the good operational performance of the cascaded STATCOM/BESS and verify the validity and effectiveness of the proposed control strategy.