Small‐signal model of vector current‐controlled MMC‐UPFC

Abstract

Modular multilevel converter based unified power flow controller (MMC-UPFC) projects are different from earlier UPFC projects in control methods and system structures. Characteristics of these MMC-UPFC projects have not been fully researched in the existing literature, so it is difficult to effectively analyse the small-signal stability and low-frequency oscillation characteristics of power system containing these UPFCs. To solve this problem, the small-signal model of vector current-controlled MMC-UPFC is studied. Firstly, the equivalent model of the general structure UPFC is given in this study. Secondly, the dynamic model and small-signal model of UPFC are derived. Thirdly, the method of combining the UPFC model and the rest of the system is presented, so that the linearised model of the whole system can be established. At last, the small-signal model is verified in two test systems by time-domain simulations and modal analysis. Results show that the method proposed in this study is applicable for both the novel structure UPFC and the traditional structure UPFC, and that the small-signal model obtained can accurately reflect system characteristics.