三电平变频调速系统SVPWM和SHEPWM混合调制方法的研究

三电平中点钳位逆变器在高压大容量变频调速中得到了广泛的研究和应用。该文在三电平高压变频器中同时应用SVPWM和SHEPWM，即低频时采用异步SVPWM，高频时采用SHEPWM，避免了高频时SVPWM谐波特性变差和SHEPWM在低频时存储量大的缺点，充分发挥了二者的优点，使变频器在整个工作范围内都可以有效抑制低次谐波，得到较好的输出波形。混合调制的难点在于衔接问题，文中分析了影响二者之间平滑切换的原因并提出了具体的解决方法，保证了切换过程中电压和电流没有跳变。采用PSIM软件对三电平SVPWM和SHEPWM进行了仿真研究，并在实际三电平变频器控制平台上进行了实验。仿真和实验结果证实了该文的混合调制方法在低频和高频都有较好的谐波特性，二者间的平滑过渡保证了混合调制的实用性，并已用于实际三电平变频器之中。

Study on a Hybrid Method of SVPWM and SHEPWM Applied to Three-level Adjustable Speed Drive System

Three-level NPC inverter has been widely applied and investigated in high voltage high power adjustable speed drive systems.A novel hybrid PWM method is proposed,which uses asynchronous SVPWM at low frequency and SHEPWM at high frequency,thus in the whole output frequency range the low order harmonic is suppressed effectively and high quality output waveforms are obtained. One of the key problems of hybrid PWM is that when switching between SVPWM and SHEPWM,there may be voltage jumping even oscillation. This paper studies the cause of jumping and gives the corresponding solution,which assures the smooth switching between SVPWM and SHEPWM. The proposed PWM method is simulated with PSIM software and experimentally verified through the three-level NPC inverter ASD systems. Simulation and experimental results prove that the hybrid PWM has high quality of output waveforms both in low and high frequency,and the switching between SVPWM and SHEPWM is smooth.