多端柔性直流输电系统谐波特性及交互机理分析

Analysis of Harmonic Characteristics and Interaction Mechanism of MMC-MTDC

为分析基于模块化多电平换流器的多端柔性直流输电系统(MMC-MTDC)的谐波特性及交互机理,首先引入平均开关函数的概念,建立了MMC详细时域模型,忽略内部动态特性得到MMC简化模型,从而得到MMC-MTDC的等值电路以及各换流器直流侧谐波电流对各换流器直流端口电压谐波的传递函数。随后,定义MMC交流侧电流和直流侧电压电流的各阶动态相量为状态变量,将MMC时域模型转化为序分量动态相量谐波分析模型,得到MMC特征谐波分布特性及交直流侧谐波传递机理。通过描绘换流器直流侧谐波电流对各换流器直流端口电压谐波传递函数的频率特性曲线,分析了MMC-MTDC的谐振特性以及谐波在不同换流器间的交互机理。最后,在MATLAB/Simulink中的仿真验证了谐波特性及交互机理分析的正确性,分析结果可为谐波抑制策略的提出提供理论支撑。

To analyze the harmonic characteristics and interaction mechanism of modular multilevel converter based multi-terminal HVDC system(MMC-MTDC),firstly,the concept of average switching function is introduced,and the detailed time domain model of MMC is established.The simplified model of MMC is obtained by neglecting the internal dynamics,thus the equivalent circuit of MMC-MTDC is obtained,and the transfer function of DC side harmonic current to DC side harmonic voltage on each converter is deduced.Secondly,by defining the dynamic phasors of each order of AC side current and DC side voltage as state variables,the time domain model of MMC is transformed into harmonic analysis model with dynamic phasor sequence components,which is used to analyze and obtain the harmonic distribution characteristics and harmonic transmission mechanism at AC/DC side of MMC.By describing the frequency characteristics of the transfer function of DC side harmonic current to DC side harmonic voltage on each converters,the resonant characteristics of MMC-MTDC and the interaction mechanism of harmonics between different converters are analyzed.Finally,the correctness of the analysis of harmonic characteristics and interaction mechanism are verified by simulation on MATLAB/Simulink.The analysis results can provide theoretical support for proposing harmonic suppression strategy.