MMC-HVDC输电系统中高频阻抗建模及谐振机理分析

Medium-& High-frequency Impedance Modeling and Resonance Mechanism Analysis of MMC-HVDC Transmission System

目前对基于模块化多电平换流器的高压直流(modular multilevel converter based high voltage direct current,MMC-HVDC)输电系统的中高频谐振机理尚缺乏系统性的研究,因此,基于分块化阻抗建模方法和谐波阻抗分析法系统地揭示了MMC-HVDC输电系统的中高频谐振机理。首先,基于分块化阻抗建模方法,将MMC-HVDC输电系统进行分块,通过对交直流系统电路及MMC控制系统的分析,分别建立了MMC交、直流侧等效阻抗模型,同时根据线路的分布参数特性建立了输电线路阻抗模型,形成了MMC-HVDC输电系统等效模型;其次,通过研究控制环节和参数对MMC等效阻抗的影响,获得了主要的影响因素;然后将谐振分为有源谐振和无源谐振,从而系统地揭示了MMC-HVDC输电系统的谐振机理;最后,通过仿真验证了所建模型及谐振分析方法的有效性和正确性。分析及仿真结果表明:在中高频段,MMC直流侧系统仅可发生有源谐振,谐振频率主要与直流线路参数有关;MMC交流侧系统可发生无源和有源谐振,无源谐振主要受MMC交流侧阻抗负阻尼特性的影响,而有源谐振与MMC和电网参数均相关。

At present,there is still a lack of systematic research on the medium-& high-frequency resonance mechanism of the modular multilevel converter based high voltage direct current(MMC-HVDC) transmission system.Therefore,based on the partitioning impedance modeling and the harmonic impedance analysis method,this paper systematically reveals the medium-& high-frequency resonance mechanism of an MMC-HVDC transmission system.Firstly,based on the partitioning impedance modeling,the MMC-HVDC transmission system is divided into blocks.Through the analysis of the AC and DC system circuits and the MMC control system,the equivalent impedance models on the MMC AC and DC sides are established respectively.Meanwhile,the impedance model of the transmission line is established according to the line distributed parameter characteristics.Thus,the equivalent model of the MMC-HVDC transmission system is formed.Secondly,by studying the influence of the control links and the parameters on the MMC equivalent impedance,the main influencing factors are obtained.Then the resonance is divided into active resonance and passive resonance,and the resonance mechanism of the MMC-HVDC transmission system is systematically revealed.Finally,the effectiveness and correctness of the proposed model and resonance analysis are verified by simulation.The analysis and simulation results show that only active resonance occurs in the MMC DC-side system at middle-& high-frequency bands,and that the resonance frequency is mainly related to the DC line parameters.Both the passive and the active resonances may occur in the MMC AC-side system,and the passive resonance is mainly affected by the negative damping characteristics of the MMC AC-side impedance,while the active resonance is related to both the MMC and power grid parameters.