| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem where the an element service life to become short since the switching loss of a partial main circuit element increases, when an electric motor is driven at a speed closer to zero. SOLUTION: When an inverter 2 is to be controlled by a PWM waveform generation part 5, a judgment part 6B judges that the output frequency of the inverter is lower than a setting value, and a judgment part 6C judges that an output current is higher than the setting value. A switching part 6A switches the carrier frequency of PWM control from a normal frequency to a low one, when both the judgment conditions are established, An adjustment for gradually changing the carrier frequency to a low frequency according to the continuation time of both the judgment outputs, and an adjustment where a main circuit temperature is included in parameters are included. |
