注入3次谐波控制的共模电压分析

由于功率器件仅有2个开关状态,输出电压只能离散变化,造成中性点存在共模电压,对电机的运行产生负面效应。以传统两电平变频器和级联型高压变频器为例,分析了共模电压产生机理和3次谐波注入理论,在此基础上,分析注入3次谐波在提高直流电压利用率的同时,对输出共模电压造成的影响。经对比发现,共模电压新增加了3次谐波电压成分,当调制比取最大值时,共模电压中3次谐波电压幅值达到最大,加剧了共模电压对电机可靠运行的影响。通过Matlab仿真,验证了理论分析的正确性,并进一步说明了,对采用同相调制算法的变频器,注入3次谐波将导致共模电压增加。

Research on common-mode voltage with third-order harmonic injection

Power devices have only two states,their output voltage is discontinuous and the common-mode voltage exists in the neutral point,which will cause negative effect on motor opera-tion.With traditional two-level inverter and cascade high-voltage inverter as examples,the mechanism of common-mode voltage generation and the theory of third-order harmonic injection are studied.When the third-order harmonic is injected to raise the usage factor of DC voltage,its influence on common-mode voltage is analyzed.There is third-order harmonic component added in common-mode voltage.When maximal modulation ratio is selected,the amplitude of the third-order harmonic voltage in common-mode voltage also reaches the maximum,which may further affect the reliable operation of generators.Simulations with Matlab prove the correctness of theoretic analysis and illuminate that the third-order harmonic injection into inverter controlled by in-phase modulation will increase common-mode voltage.