| 摘要 |
PURPOSE:To eliminate a rotational irregularity of an induction motor by sensing a phase voltage generated through the ON-OFF operations of switching devices, and by giving an input signal to a means for insulating signals electrically, when the phase voltage reaches about half the value of an input DC voltage, and further, by making the means output the electrically insulated signal corresponding to its input signal, and furthermore, by correcting the distortions of current waveform in a low frequency region. CONSTITUTION:A sensing circuit 14A senses a phase voltage VU generated through the ON-OFF operations of switching devices 4, 5. When the phase voltage VU reaches about half the value of an input DC voltage, by switching a shunt regulator 13 on, the sensing circuit 14A gives an input signal to a photo-coupler 11. Also, the sensing circuit 14A feeds back, the output signal of the photo-coupler 11 for insulating signals electrically, to a control part 20 of an inverter. In this manner, when the phase voltage VU is sensed at half the valve of the input DC voltage value, voltage fluctuations in a duration Td for preventing a short-circuit are so sensed as to average them, and no deviated signal is outputted from the sensing circuit 14A. Thereby, the distortions of current waveform in a low frequency region are corrected and the rotationl irregularity of an induction motor can be eliminated. |
