| 摘要 |
PURPOSE:To generate a control pulse whose width is not smaller than a required minimum pulse width without declining a maximum output voltage by a method wherein a carrier signal is modulated to generate a PWM signal by an instruction signal which is obtained by substitutiong a sine wave with a rectangular wave having a predetermined crest value in predetermined periods in the ranges 60 deg.-120 deg. and 240-300 deg. of the electric angle of a sine wave. CONSTITUTION:A three-phase AC sine wave is outputted by the sine wave generator 5 of an instruction signal generator 2 and a rectangular wave is generated by the rectangular wave generator 6 of the instruction signal generator 2. A switching circuit 7 switches an instruction signal between the sine wave and the rectangular wave so as to output the rectangular wave while the electric angle of the sine wave is in the ranges 60 deg.-120 deg. and 240 deg.-300 deg. and output the sine wave while the electric angle of the sine wave is in the other ranges. A triangle wave outputted by a carrier signal generator 4 is modulated by the instruction signal to generate a PWM signal which controls a three-phase inverter 3. The amplitude of the sine wave and the crest value of the rectangular wave are changed between the values in the state of a modulation rate of 1 and the values with which the pulse width of the PWM signal is a required minimum pulse width is obtained to maintain a minimum pulse width when a GTO is employed as a switching device. |
