A STATCOM Compensation Scheme for Suppressing Commutation Failure in HVDC

This paper proposes a STATCOM compensation scheme for suppressing commutation failure (CF) in HVDC. In this scheme, the neutral-point of CHB-STATCOM with star configuration is grounded and thus possesses three advantages. Firstly, it keeps the high economy of CHB-STATCOM with star configuration. Secondly, three phases are independent of each other, which can be considered as three single-phase STATCOMs, leading to a simple and flexible control strategy and overcoming the control problem when CHB-STATCOM with star configuration operations under unbalance grid. Thirdly, it forms zero sequence current channel by taking the characteristic of HVDC, which is the neutral-point of the AC grid connected by HVDC is directly grounded, thus it can compensate not only harmonics, positive and negative-sequence reactive power, but also zero sequence reactive power, resulting in excellent compensatory capacity. In this paper, first of all, feasibility of the proposed scheme in HVDC is analyzed in detail. Then, zero-sequence current is calculated in detail under unbalance power grid condition. Finally, simulations based on PSCAD/EMTDC are carried out to illustrate the effectiveness to suppress CF in HVDC.