| 摘要 |
A drive device for an AC motor (54) has a comparator (68) by means of which both output signals of a current detector (56) can be compared with one another to determine the output current of an invertor (200) and of a current command circuit (100) for controlling the waveform of the output current from the invertor (200), in order to control the main switching elements (31, 32, 34, 36, 38, 40) of the invertor (200) with a hysteresis width corresponding to the PWM control signal produced by the comparison, the comparator (68) having a command circuit (801, 802, 803, 804) for changing the hysteresis width of the comparator (68) by determining the speed of rotation of the AC motor (54), the output frequency of the invertor (200) or the induced electromotive force in the AC motor (54) and a modification circuit (821, 822, 823) by means of which the hysteresis width of the comparator (68) can be varied in accordance with the command from the control circuit (801, 802, 803, 804) for the hysteresis width, as a result of which it is possible to suppress the fluctuation in the switching frequency of the main switching elements of the invertor. <IMAGE>
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