System modeling and cascaded passivity based control for distribution transformer integrated with static synchronous compensator

Abstract In order to improve the quality of the reactive power compensation current injected via winding taps on the primary windings of the transformer, this paper presents an improved winding tap injection distribution transformer with LCL-type static synchronous compensator (DT-STATCOM) and its control strategy. The winding tap injection method can make full use of the leakage inductance and spare capacity of the distribution transformer and reduce the voltage stress. Based on the winding tap connection, the system mathematical modeling is analyzed to build the equivalent circuit of DT-STATCOM. In consideration of the frequent changes in operating point, a Cascaded Passivity Based Control (CPBC) with additional integral action is developed for LCL-type DT-STATCOM. The step-by-step stability analysis and the principles for selecting injection dampings of the CPBC controller are presented. Under the proposed CPBC, the coupling terms in d -axis and q -axis of LCL filter can be attenuated significantly, and a fast dynamic response is achieved with low-current overshoot. Moreover, the method has a strong robustness against DT-STATCOM parameters deviation. Finally, a laboratory prototype of 800V DT-STATCOM with LCL filter is used to test the feasibility and effectiveness of the proposed structure and CPBC control strategy.