串联混合型直流输电系统的小信号模型及其稳定性研究

Small Signal Model and Stability Analysis for Series Connected Hybrid HVDC System

针对高压端采用电网换相换流器(line commutated converter,LCC)、低压端采用模块化多电平换流器(modular multilevel converter,MMC)串联构成的串联混合型直流输电系统,该文建立了其状态空间及小信号模型。推导LCC与MMC在交、直流侧的数学模型,换流站间及换流站与交直流系统间的接口模型,建立包含LCC、考虑详细内部动态特性的MMC、直流输电线路、交流系统的串联混合型直流输电系统状态空间模型及对应的小信号模型,并与电磁暂态仿真模型的动态响应特性进行对比,验证所提建模方法的准确性。研究了受端交流系统强度对串联混合型直流输电系统小信号稳定性的影响,结果表明高压端LCC和低压端MMC之间的耦合作用在一定程度上降低了弱交流系统下串联混合系统的稳定裕度。

Based on a series hybrid high voltage direct current(HVDC)system composed of a line commutated converter(LCC)on the high voltage side and a modular multilevel converter(MMC)on the low voltage side,this paper developed the state-space and small-signal model.By combing the electrical and control signal transfer relationship between the AC and DC sides of the LCC and MMC,deriving the interface models between converters,AC and DC systems,a small-signal model was developed.The entire system contained LCC,MMC with detailed internal dynamic characteristics,DC transmission line and AC system.The dynamic performance comparisons between small-signal model and detailed electromagnetic transient simulation in PSCAD/EMTDC were conducted.The results validated the accuracy of the derived small-signal model.Then,based on this model,this paper studied the influence of the strength of receiving AC system on the small signal stability of the series hybrid DC transmission system.The results show that the coupling between LCC and MMC reduces the stability margin of the series hybrid HVDC system under a weak AC system to a certain extent.