基于三相桥式逆变电路的恒频调制技术对比分析

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为了验证逆变电路中不同调制技术的输出特性,基于三相桥式逆变电路,对几种恒频调制技术进行对比分析。针对基本三相桥式逆变电路和三相桥式模块化多电平换流器(Modular Multilevel Converter,MMC),采用PWM、SVPWM、载波移相、载波层叠及最近电平逼近调制(Nearest Level Modulation,NLM)等恒频调制技术对其进行控制,搭建Matlab/Simulink仿真,仿真分析不同调制方法下输出线电压波形,对直流电压利用率、总谐波畸变率(Total Harmonics Distortion,THD)和功率损耗进行分析比较。仿真结果表明,当拓扑为基本三相桥式逆变电路时,除NLM外,各调制方法均能满足电能质量国家标准THD规定,但直流电压利用率相差较大;当拓扑为三相桥式MMC电路时,分别采用载波移相、载波层叠及NLM实现了七电平MMC的调制。

In order to verify the output characteristics of different modulation techniques in the inverter circuit,several kinds of constant frequency modulation techniques are compared and analyzed based on the three-phase bridge inverter circuit.Constant frequency modulation techniques such as PWM,SVPWM,carrier phase shift,carrier disposition and nearest level modulation(NLM)were used to control basic three-phase bridge inverter circuit and three-phase bridge Modular Multilevel Converter(MMC)circuit.The DC voltage utilization,total harmonic distortion(THD)and power loss under different modulation methods were analyzed and compared according to the output line voltage waveforms obtained by Matlab/Simulink.The simulation results show that all modulation modes except NLM can meet the requirements of THD in the three-phase bridge inverter circuit,but their respective DC voltage utilization ratios are quite different.The modulation of MMC in seven level is realized by carrier phase shifting,carrier disposition and NLM in the three-phase bridge MMC circuit.