一种模块化多电平直流输电线路单端保护原理

A protection principle of direct current transmission lines based on modular multilevel converter using one-end converter data

应用故障网络分析法,研究了模块化多电平高压直流输电线路可能发生的各种短路故障类型,并对其故障特性进行分析。分析结果表明:当发生正极故障时,两侧换流站正极、负极串联小电感电压的故障分量的极性均为负;当发生负极故障时,串联小电感处电压的故障分量的极性均为正;当发生双极故障时,正极、负极串联小电感处电压的故障分量的极性为一负一正,二者极性是相异。根据此特征,可以实现故障极的判别。另外,当发生单极区内故障时,正、负极串联小电感处,电压故障分量的变化速率不同;当发生单极区外故障时,上述位置处,电压故障分量的变化速率都比较慢,几乎相同。若单极故障是正极区内故障,正极电压故障分量变化率要远大于负极的;若是负极区内故障,则正极电压故障分量变化率要远小于负极的。当发生双极区内故障时,正、负极的电压故障分量的变化速率均很快,其极性为正极为负,负极为正,二者的极性是不同的。因此,根据一端换流站正、负极小电感电压的故障分量变化速率的快慢,可实现区内、外故障的识别。最后,用PSCAD搭建双端模块化多电平高压直流输电系统仿真模型。基于该模型,进行各种故障的仿真,用以产生故障数据,并用MATLAB对故障数据进行处理,对保护算法进行验证。仿真结果表明故障分析及保护原理的正确性和有效性。

By using the fault network analysis method,various types of short circuit faults in modular multilevel HVDC transmission lines are studied,and the fault characteristics are analyzed.Analysis results show that when a positive pole fault occurs,the polarities of the series of small inductance voltage fault components on the positive and negative pole are negative at both converter stations;when a negative pole fault occurs,the polarities of them are positive;When a bipolar fault occurs,the polarities of the series of small inductance voltage fault components on the positive and negative pole are different at both converter stations,and the polarity of the series of small inductance voltage fault components on the positive line is negative,and the polarity of the series of small inductance voltage fault components on the negative line is positive.According to this fault feature,the fault pole can be distinguished.In addition,when an internal fault occurs on a polar line,the change rates of the series inductance voltage fault component of the positive and negative pole are different;when an external fault occurs beyond a polar pole line,the change rates of the series inductance voltage fault component of the positive and negative pole are slow and almost the same.If an internal fault occurs on the positive pole line,the change rate of the positive voltage fault component is greater than that of the negative voltage fault component;If an internal fault occurs on the negative pole line,the change rate of the positive voltage fault component is smaller than that of the negative voltage fault component.When an internal fault occurs on the positive and negative pole line at the same time,the change rates of the series inductance voltage fault component of the positive and negative pole are rapid,and the polarities of them are negative and positive respectively and the polarities of them are different.According to the fault characteristics,the internal or external fault identification can be realized by using the change rate of the positive and negative inductance voltage fault component of the series inductance on the positive and negative pole at one end of converter station.Finally,a two-end high voltage direct current transmission system based on modular multilevel converter is built in PSCAD.Based on the model,different faults type are simulated,and fault data can be obtained.And the fault data was processed by Matlab to verify the protection algorithm.Simulation results showed that the proposed protection principle was correct and effective.