| 摘要 |
The command signal processing unit outputs, when a first PWM frequency command signal is received, a high-PWM frequency command signal such that an asynchronous PWM control is performed at a PWM frequency of a predetermined constant frequency. The command signal processing unit outputs, when a second PWM frequency command signal is received, a low-PWM frequency command signal such that an asynchronous or synchronous PWM control is performed at a frequency lower than the above-described frequency. The PWM frequency control unit controls the PWM frequency such that an asynchronous PWM control is performed if a motor has a rotational speed less than a predetermined rotational speed and that a synchronous PWM control is performed if the motor has a rotational speed greater than or equal to the predetermined rotational speed, when a low-PWM frequency command signal is input.
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