HVDC换流器采样—数据模型的改进

Improvement on Sample-data Model of HVDC Converter

在研究高压直流(HVDC)系统的次同步振荡时通常采用换流器的准稳态模型,但其适用性尚存在争议。HVDC换流器的采样—数据模型能够反映开关电路的动态特性,但现有采样—数据模型中尚未对触发控制系统和触发小扰动延迟进行详细建模,为此文中建立了12脉冲换流器的改进采样—数据模型。基于等间隔触发方式和锁相环触发相位控制,给出了HVDC系统模型的具体形式。在小扰动分析时,触发控制系统输出的小扰动变化不能立刻作用于换流桥,而存在一定的延时,文中对此进行了详细分析,并由此改进了采样—数据模型。基于EPRI直流系统,分别采用特征值分析法和复转矩系数法将HVDC换流器的准稳态模型、采样—数据模型与PSCAD时域仿真进行了对比验证。结果表明,改进后的采样—数据模型更为准确,其计算结果与PSCAD仿真结果非常接近,适用于HVDC系统的次同步振荡研究。

Quasi-steady model of the HVDC system is usually used in the studies on Sub-Synchronous Oscillation （SSO）, even its suitability is still arguable. The sample-data model of HVDC converter can represent the dynamic response of switching circuits, however, the firing control scheme and phase-locked loop （PLL） are not modeled in details. An improved sample-data model of 12-pulse HVDC converter is presented. Based on the generally used equidistant firing control scheme and PLL control, a new model of HVDC system is presented. Under small disturbances, the output of firing controller will not act on the converter immediately because of the igniting delay. The process of igniting is considered in detail, such that the sample- data model is improved. The model is validated on the EPRI HVDC system by eigenvalue analysis and complex torque coefficient method. The studies show that the improved model is more accurate in studying the SSO of HVDC systems.