High frequency stability constraints based MMC controller design applying NSGA-III algorithm
Ke Ji, Weiming Chen, Xueguang Wu, Hui Pang, Jingxuan Hu, Shan Liu, Fan Cheng, Guangfu Tang
Abstract
High frequency resonances (HFRs) have been observed many times in MMC-HVDC projects. In order to avoid HFRs, the controller design of an MMC should satisfy two requirements: 1)controller is stable in high frequency range, and 2)MMC impedance does not have negative real part in high frequency range. So far, there requirements have not been well addressed in MMC controller design by the literatures. This paper first describes the simplified high frequency impedance model of the MMC developed by the authors. Then, it describes the mechanisms of two kinds of HFRs are revealed by the developed model, including 1)MMC controller instability and 2)interaction instability between MMC and AC cables. Furthermore, the mathematical expressions of controller stability constraint and positive damping constraint are proposed. More-over, NSGA-III based multi-objective optimization algorithm is applied to find out the applicable region of the MMC controller parameters for satisfying the proposed stability constraints. The proposed controller design method can effectively avoid the HFRs brought by inappropriate MMC. The detailed time-domain simulations in PSCAD/EMTDC verify the proposed designed method and comfirm the improved results.