Patent ID: 7906933

Claim:
An induction motor driving apparatus, the apparatus comprising: a plurality of inverters each including an inverter main circuit and an inverter controller to control the inverter main circuit; a changeover switch to change over outputs of the plurality of inverters to be supplied to one induction motor; a changeover controller to control the changeover switch on the basis of a failure detection signal of one inverter of said plurality of inverters to change over from the one inverter to another inverter of said plurality of inverters to start said another inverter so that the induction motor is driven; and a plurality of DC circuits, each of the plurality of DC circuits is connected to each of the plurality of inverters and includes a rectifier and a smoothing capacitor connected to an input of the inverter main circuit; wherein the changeover controller includes a frequency/phase detector to detect a frequency and a phase of a terminal voltage of the induction motor and controls a frequency and a phase at starting of said another inverter in accordance with detected values of the frequency and the phase of the terminal voltage detected by the frequency/phase detector when the failure detection signal is inputted; and each of the plurality of inverters includes an initial charging circuit to charge the smoothing capacitor connected to the inverter main circuit of said another inverter when a circuit breaker, connected between an AC power supply and said another inverter, is opened to provide an initial charge of the smoothing capacitor connected to the inverter main circuit of said another inverter before changing over from said one inverter to said another inverter; wherein said initial charging circuit provided separately from said another inverter for charging the smoothing capacitor connected to the inverter main circuit of said another inverter during a waiting period thereof before changing over from said one inverter to said another inverter, so that the charged smoothing capacitor causes said another inverter to start immediately after the changing over from said one inverter to said another inverter.