| 摘要 |
The present invention makes it difficult that an overcurrent is generated in low arm switching devices (Qx, Qy, Qz) even when a voltage is generated on a polyphase load (6) by an external cause, in a precharge period. When any of U-phase current, V-phase current and W-phase current (iu, iv, iw) is smaller than a negative predetermined value (when an absolute value is larger), it is judged which is the largest value. The low arm switching device is turned on only for a phase corresponding to the current of the largest value and the low arm switching devices of other phases are turned off. |
