| 摘要 |
PURPOSE:To improve controlling characteristic at the time of voltage drop by so controlling that a motor terminal voltage becomes constant even if an AC input voltage is high or low. CONSTITUTION:A voltage control range of a PWM circuit 12 is generally specified by a control ratio determined by the amplitude ratio (A/B) of a triangular wave of a carrier signal to a control voltage signal. Then, the level of a 3-phase power supplied to a power source 1 is detected, and the control rate of the circuit 12 is altered at the time of turning ON the power source. Thus, the amplitude ratio (A/B) of the triangular wave to the control voltage signal is controlled inversely proportionally to the power source voltage. For example, in a low voltage range, the ratio (A/B) of the triangular wave to the control voltage signal is set to 1 or more, and the controlling characteristic at the time of voltage drop is improved. |
