直流输电谐波不稳定抑制新方法

Suppression of harmonic instability in HVDC

针对传统直流输电系统中谐波不稳定现象,研究了一种新型换流变压器及其滤波系统。其阀侧绕组采用延边三角形接线,为3倍数次谐波电流提供通路;通过匝比配合,实现12脉波换流;延边绕组与公共绕组构成自耦变压器接线,在公共绕组上连接滤波支路,并调至谐振点,配之以变压器零阻抗设计,在阀侧实现谐波抑制兼无功补偿功能。对拟建立的直流输电开发研究平台在设计参数的基础上,进行了计算机仿真研究,仿真结果表明:新型换流变压器及其滤波系统可大幅降低交流网侧中2、3次非特征谐波与11、13次特征谐波电流含量,很好地抑制直流输电系统的谐波不稳定,同时新系统中的滤波器阻抗在基频下呈容性,其对换流器可进行无功功率补偿,改善了系统的动态稳定性。

A type of converter transformer and its filtering system are researched to suppress the harmonic instability in HVDC system. The winding at the valve side adopts prolonged delta connection,providing circuit for third harmonic currents. 12-pluse converter is implemented through fit ratio. The autotransformer connection is formed by prolonged windings and the common windings, the filter branch is connected with the common windings,L and C are adjusted to the resonant point, the zero equivalent impedance of common windings is designed,and the reactive power compensation and harmonic current suppression are thus realized at the valve side. A DC transmission system exploitation platform is simulated with designed parameters and results show that,the contents of 2nd and 3rd noncharacteristic harmonic currents and 11th and 13th characteristic harmonic currents at AC net side are suppressed significantly and the harmonic instability is suppressed effectively. As the filter impedances appear capacitive,it may provide reactive power compensation to the converter and improve the system dynamic stability.