一种平滑式调制切换策略

A Smooth Modulation Switching Strategy

在交流牵引系统中,逆变器的输出频率范围广,输出的最高频率通常可达到近200 Hz。在这种模式下,低频时采用异步调制可以保证牵引电机启动平滑无冲击,高频时采用同步调制可以保证能有效控制转矩,不会因电压波形的畸变产生危害性的转矩波动。但是调制模式切换时,由于电压相位突变,导致交流异步电动机定子电流发生畸变,影响其正常运行。为了解决这个问题,提出一种平滑切换策略,利用输出电压相位与同步角度的差来调整载波周期,最终使输出电压定位到同步角度上。仿真结果表明,该方法能有效消除畸变,调制方式切换时平滑无冲击。

In the ac traction system,the inverter output frequency range is wide,the maximum output frequency can reach nearly 200 Hz.In this mode,the asynchronous modulation at low frequency can ensure that the traction motor starts smoothly without impact,and the synchronous modulation at high frequency can ensure that the torque can be effectively controlled,and the harmful torque fluctuation will not be caused by the distortion of the voltage waveform.However,due to the sudden change of voltage phase during modulation mode switching,the stator current of ac induction motor is distorted,which affects its normal operation.To solve this problem,a smooth switching strategy is proposed.The carrier cycle is adjusted by using the difference between the output voltage phase and the synchronization Angle,and the output voltage is finally positioned at the synchronization Angle.Simulation results show that this method can effectively eliminate the distortion,and the modulation mode switching is smooth without impact.