计及汇流母线行波特性的三端混合直流系统行波解析方法

三端混合直流输电系统区别于两端直流系统,由于两段参数各异的线路通过汇流母线连接换流站,因此当故障行波经过汇流母线时将产生复杂的折反射而出现畸变,而现有的两端直流系统行波解析方法因未计及该特性而不适用。文中计及汇流母线的行波特性,搭建了三端混合直流输电系统的行波解析等值模型;在此基础上推导出故障初始行波、线路传播衰减与畸变系数以及汇流母线和换流站的行波折射系数的复域表达式,从而构建各换流站测点故障行波的复域模型。提出了三端混合直流输电系统的复域与时域、模量与极线量的行波解析计算方法。然后,基于所提方法对三端混合直流线路的行波保护进行定值整定计算与灵敏度分析。最后,采用PSCAD构建三端混合直流系统的电磁暂态仿真模型,通过大量电磁暂态仿真验证了所提方法的正确性与高计算效率。

Analytical Calculation Method of Travelling Wave for Three-terminal Hybrid DC System Considering Characteristics of T-connect Bus

The three-terminal hybrid DC transmission system is different from the two-terminal DC system. Because two lines with different parameters are connected to the converter station through the T-connect bus, when the fault traveling wave passes through the T-connect bus, it will produce complex refraction and distortion. However, the existing analytical calculation methods for solving the traveling wave of the two-terminal DC system are not applicable because they do not take the above characteristic into account. Considering the traveling wave characteristics of the T-connect bus, an analytic equivalent model of the three-terminal hybrid DC transmission system is built. Based on this model, the complex expressions of the initial traveling wave, the attenuation and distortion coefficient of the line propagation, and the refraction coefficients of the T-connect bus and the converter station are derived, so as to build the complex domain model of the fault traveling wave of each converter station. The analytical calculation method of traveling wave for complex and time domains, the modulus and the polar line quantity of the three-terminal hybrid DC transmission system are calculated. Then, based on the proposed method, the setting calculation and sensitivity analysis of traveling wave protection for three-terminal hybrid DC lines are carried out. Finally, PSCAD is used to build the electromagnetic transient simulation model of three-terminal hybrid DC system, and the correctness and high efficiency of the proposed method are verified by a large number of electromagnetic transient simulations.