一种抑制HVDC换相失败的STATCOM补偿方案

摘要

针对高压直流输电(High Voltage Direct Current, HVDC)系统中的换相失败问题,提出一种STATCOM补偿方案.该方案将星型级联H桥STATCOM中性点直接接地,并入HVDC系统逆变端,从而具备三点优势:保留星型级联H桥STATCOM经济性高的优点;三相独立,可视为三个单相STATCOM,各相换流链独立控制,克服了传统星型级联H桥STATCOM在电网电压不平衡情况下的控制问题;利用HVDC所接入的交流电网的中性点接地的特点构成零序电流通道,不仅可以补偿谐波、正序、负序无功电流,也可以补偿零序无功电流,补偿性能较传统拓扑更为优良.详细分析了该补偿方案在HVDC中的可行性,并推导了电网电压不平衡情况下,换流链电流指令中的零序电流分量.给出了控制策略并通过PSCAD/EMTDC对所提补偿方案用于抑制HVDC换相失败的性能进行验证.%This paper proposes a STATCOM compensation scheme for suppressing commutation failure in HVDC. In this scheme, the neutral-point of CHB-STATCOM with star configuration which is connected to power grid is grounded. The scheme possesses three advantages. Firstly, it reserves high economy as 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 using of 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. The feasibility of the proposed scheme in HVDC is analyzed in detail. Zero-sequence current is calculated in detail under unbalanced grid condition. The control strategy is given and the simulations based on PSCAD/EMTDC are carried out to illustrate the effectiveness to suppress communication failure in HVDC.