| 摘要 |
PROBLEM TO BE SOLVED: To properly set the timing of the control operation of a switching element provided with the short circuit prevention period of an inverter without depending on a change in the characteristic of a phase voltage detector used to detect the timing. SOLUTION: The phase voltage of the output of an inverter part 18A is set in such a way that the output signal 11a of a phase voltage detector 14A used to detect the phase voltage becomes L at a phase voltage V0 corresponding to a preset reference voltage value VTH0 , and the phase voltage V0 corresponding to the reference voltage value VTH0 is measured actually. Then, a PWM circuit 29 equipped with a pulse-width correction function measures the time required to reach the voltage Vc of a converter part 21 from a phase voltage of 0, and the time required to reach a voltage Vc/2 from the phase voltage V0 corresponding to the reference voltage value VTH0 is computed as the correction time ΔT. Then, the time which elapses by the correction time ΔT from a point of time in which the output signal becomes L is set as a threshold value which turns on and off switching elements 4, 5 at an upper arm and a lower arm. |
