四桥臂三相逆变器的PWM控制

PWM Control of a Four-Leg Three-Phase Inverter

四桥臂三相逆变器的结构 ,其三相负载可以是平衡的或不平衡的、线性的或非线性的。由于第四桥臂的加入 ,控制变得非常复杂。本文分析了三相逆变器的调制信号与输入直流电压的关系 ,讨论了中点电压这个关键量 ,分析了该技术电压利用率不高的缺点 ,提出谐波注入法解决了该缺点 ,谐波注入法可以输出幅值更高的基波 ,同时谐波不会影响输出电流。文中提出了一种新的 PWM控制方案 ,该方案电压利用率高 ,并能带任意负载。仿真和实验结果证实了该方案的可行性。

The structure of a four leg three phase inverter is introduced, its load is an arbitrary load: unbalanced and/or balanced load, linear and/or nonlinear load. With an additional neutral leg, the system control becomes very complex. Then the relationship between the modulated signal and source voltage is analyzed, the neutral voltage under both three leg and four leg conditions is discussed and the sine pulse width modulation (SPWM) method is introduced. A closer inspection reveals that the method does not fully utilize the available dc bus voltage. Harmonic injection is used to improve the utilization of dc bus voltage, the method has a higher fundamental content than SPWM method, and the harmonic content is not transferred to the load currents. Finally a new kind of PWM control strategy is presented, it has high utilization of dc bus voltage and can work under arbitrary load condition. Simulational and experimental results confirm its validity.