| 摘要 |
PROBLEM TO BE SOLVED: To reduce the switching losses of an inverter when it is PWM- controlled, and to reduce harmonic currents too, when a compressor is controlled. SOLUTION: An AC power supply is converted into a DC voltage by a rectifier unit, and the DC voltage is filtered into a specified DC voltage through the use of an active filter and is supplied to the inverter. The DC voltage is converted into an arbitrary AC voltage and is applied to the motor of the compressor to operate the motor. When the motor is operated, its input AC current which flows when PWM control is performed is detected. The rate of increase of a set output DC voltage for the active filter is set to 10 V, when the detected input AC current is smaller than a first set value. The rate of increase is set to 5 V, when the input AC current is not lower than the first set value and is smaller than a second set value. Moreover, the rate of increase is set to 3 V respectively, when the input AC current is not lower than the second set value. These values 10 V, 5 V, and 3 V are added to a presently set output DC voltage, and the active filter is controlled. Operation of the switching means of the active filter is stopped near the peaks of the input AC current, and the operation range of the active filter is varied. |
