| 摘要 |
PROBLEM TO BE SOLVED: To reduce power loss, which is caused by a semiconductor device for power, by maintaining a switching element corresponding to one phase in the conductive condition during the predetermined switching period and moreover controlling a switching element corresponding to the other two phases to execute the switching operation. SOLUTION: A converter 20 converts a 3-phase AC current to a DC current and a converter 30 converts again the DC current to the 3-phase AC current. Here, three switching elements 30-1 of the inverter 30 are provided to conduct the switching operation with a current command signal and a voltage command signal outputted from a second pulse width modulation signal generator 40B. Therefore, during the switching period for the excitation, a controller 50 outputs the voltage command signal to the second pulse width modulation signal generator 40B, so that the switching element 30-1 corresponding to any one phase of the switching element 30-1 is maintained in the conductive condition and the switching element 30-1 corresponding to the other two phases performs the switching operation.
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