| 摘要 |
PURPOSE:To facilitate a stable and highly efficient operation by a method wherein a line current phase detecting circuit is especially provided and upper and lower short circuit avoiding periods are predetermined and the inversion timing of the phase of a three-phase AC current to control the on-off timings of switching devices properly during electrification. CONSTITUTION:A switching device part 3 which generates a three-phase artificial AC from a DC power supply, an upper and lower short circuit avoiding period predetermining means 6 which predetermines required upper and lower short circuit avoiding periods on pulse width modulation(PWM) signals, a line current phase detecting circuit 7 which functions as a phase inversion detecting means which detects the inversion timing of the phase of a three-phase AC current and a PWM signal changing means which changes the time width of the PWM signal and the upper and lower short circuit avoiding periods are provided. Thus the on-off timings of switching devices can be controlled properly and efficiently during electrification. |
