新型直流输电系统改善谐波不稳定的机理分析

将三相不对称的交流电源用正序和负序电压表示,用傅里叶分析方法计算了正序和负序电压传递到直流侧的谐波电压的规律,将这一理论应用到基于感应滤波的直流输电系统,计算在交流系统故障时,直流侧电压谐波的数学表达式,比较在同样的交流系统故障条件下,基于感应滤波的直流输电系统在抑制直流侧谐波幅值方面优于传统的直流输电系统,最后参考实验室基于感应滤波的直流输电系统模型,对输电系统在交流系统故障下的直流电压谐波进行了动模实验.结果表明,由于在感应滤波换流变压器的第三绕组接入2,11,13次LC滤波器,使直流电压中含量高的低次谐波大大减少,直流输电系统谐波不稳定得到一定的抑制。

Harmonic Instability Improving Mechanism in a New DC Transmission System

The transfer of harmonic between the AC and the DC system was investigated on the basis of the Fourier analysis of the voltages at both converter sides.Unbalanced AC voltages at AC side were represented by their positive and negative sequence components.The above method was used in the inductive filtering based HVDC system to analyze the voltage on the DC side of an HVDC converter bridge under unbalanced conditions.A comparison of the inductive filtering based HVDC system with the traditional DC transmission system in the same AC system fault conditions has shown that the former is superior to the latter for DC side harmonic amplitude suppression.In the end,referring to the parameters of the inductive filtering based HVDC system in the lab,a dynamic simulation was executed.The results obtained by switching the 2,11 and 13 harmonics LC filters on the valve side of inductive filtering transformer have shown that the contents of non-characteristic harmonic voltage in DC voltage are suppressed significantly and the harmonic instability is suppressed effectively in the inductive filtering based HVDC system.