基于多电平随机脉宽调制技术的共模电压和谐波抑制方法

在PWM电机驱动系统中,多电平逆变技术可以降低系统中的共模电压和谐波含量,但是由于开关频率是固定的,在开关频率处的谐波仍很大。随机开关频率空间矢量调制技术可以通过对零矢量的控制,实现对共模电压的抑制,并且开关频率的随机化,使得开关频率处的幅值较大的谐波分散为一定带宽的幅值较小的谐波,降低了谐波的幅值。给出了混合型七电平逆变器的拓扑结构及控制方法,将高压单元的低频输出和低压单元的高频输出进行叠加,实现七电平的电压输出。分析了不同的开关状态对共模电压的影响,提出了用于共模电压抑制的矢量选择方法和用于降低谐波的开关频率随机化方法,仿真和实验结果显示,多电平逆变技术和随机脉宽调制技术的结合使用,大大降低了系统的共模电压和开关频率处的谐波分量。

Common Mode Voltage and Harmonic Reduction Method Based on Multilevel Random PWM Technique

Applications of multilevel inverter can reduction of the common mode voltage and harmonic components in PWM motor drive systems.However,the harmonic component on switching frequency is still very high because of the fixed switching frequency.By controlling the zero vectors,random switching frequency space vector modulation technique can reduce the common mode voltage.Moreover,randomization of the switching frequency cause the harmonic components with high magnitude on switching frequency extend as low magnitude harmonic components with a bandwidth.The magnitude of harmonic components can be reduced.The topology and control method of a hybrid seven level inverter are given.The seven level output voltage is realized by adding the low frequency output of high voltage units to the high frequency output of the low voltage units.The effect of different switching state on common mode voltage is analyzed.The vector choose method used to mitigate the common mode voltage and the switching frequency randomize method used to reduce the harmonic component are given.It has been demonstrated that the common mode voltage and the harmonic components on switching frequency can be mitigated dramatically when the multilevel inverter technique and random PWM technique are used synchronously.