| 摘要 |
PURPOSE:To smoothly switch a synchronous control and an asynchronous control and to smoothly operate without impact by outputting a signal for switching the output voltage phase of an inverter at times of 0, 120 or 240 deg. to a control pulse selector when a synchronous modulation is switched to an asynchronous modulation. CONSTITUTION:A synchronous/asynchronous switching time setter 4 is provided. Phase signals of carrier and modulation wave from a synchronous PWM control pulse generator 1, and phase signals of carrier and modulation wave from an asynchronous PWM control pulse generator 1 are input to the setter 4, and synchronous control and asynchronous control switching signal is output at the times of 0, 120 and 240 deg. of the output voltage of an inverter. Since the values of triangular carrier waves have the same gradient at 0 deg. at the time, the synchronous control and the asynchronous control are switched at this time. Thus, it is not necessary to forcibly synchronize triangular carrier waves, but can be smoothly switched. |
