To provide an inverter device for a three-phase AC motor driving capable of continuing operation of the three-phase AC motor even if failure occurs at a semiconductor switching device which constitutes an inverter circuit.
A failed device deciding means 9 is provided for detecting the failure of the plurality of semiconductor switching devices Q1 to Q6 which are included in the inverter circuit 4. When the failed device deciding means 9 decides the presence of the failed semiconductor switching device, a neutral connection switch driving circuit 8 outputs a driving signal for connecting an output point V of an arm circuit 4B including the failed semiconductor switching device Q3 to a neutral point N of DC side to a neutral connection switch circuit 7. Receiving the driving signal, the neutral connection switch circuit 7 closes a normally opened contact SW2 and V-connects an exciting winding of a motor. A PWM controller 10 drives four semiconductor switching devices of two arm circuits which do not include the failed semiconductor switching device by PWM control, thus obtaining three-phase balanced current.
YAMATO MASANORI
ARMAN JAYA
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