| 摘要 |
PURPOSE: To eliminate the need of a resistor and a control circuit for processing the energy by normally setting carriers for three phases in-phase and switching them to three-phase at the time of braking thereby increasing the current ripples of the carrier frequency component. CONSTITUTION: A PWM inverter comprises carrier oscillators 2, 3 for oscillating signals having phase lags of 120 deg. and 240 deg. behind the oscillating position of 0⊥ of a carrier generator 1 generating a reference carrier signal. At the time of acceleration or steady operation, switches 7, 8 are turned to side A in order to modulate three phases with a reference carrier. At the time of deceleration, the switches 7, 8 are turned to side B in order to modulate phases V and W with a carrier signal having phase lags of 120 deg. and 240 deg. behind phase U. Consequently, the three-phase voltage of carrier frequency component is fed to comparators 4, 5, 6 and a motor is applied with an output signal operated by comparing voltage command signals eu , ev , ew with three triangular carrier signals ec having different phases. This method can eliminate the need of a resistor to be inserted into a DC bus and a control circuit therefor. |
