Interactions analysis and quadrature voltage compensation control for stabilizing LCC-HVDC system with multiple STATCOMs

Abstract

Instability may occur in LCC-HVDC system when multiple STATCOMs operate simultaneously at the inverter station. To deeply investigate this problem, firstly a structured linear model of LCC-HVDC system with STATCOMs is presented. Then, a single-input single-output (SISO) form of the model is obtained. Based on the movement of dominant poles (MODPs) of the SISO model, the interactions at the receiving end of the system are investigated. The results reveal that the interactions between LCC and STATCOMs mainly affect the high-frequency (HF) characteristics of the system. With the increase in the number of online STATCOMs, the negative effects of the interactions on the system HF stability gradually increase, while that on low-frequency (LF) stability become weaker. In order to improve such negative interactions, a quadrature voltage compensation control (QVCC) of STATCOM is proposed in this paper. This method introduces the q-axis AC voltage into the constant AC voltage control (CAVC). The theoretical analysis indicates that the QVCC can enhance the stability of the LCC-HVDC system with multiple STATCOMs, which is verified by the simulation results conducted in PSCAD/EMTDC. Finally, the intuitive and physical explanations on the mechanism of instability caused by increasing number of online STATCOMs are given from two perspectives.