| 摘要 |
A PWM inverter includes triangular-wave generating comprising a setting device (6) for setting a fundamental carrier frequency (FC_SET) (Hz) so that an electromagnetic sound produced by a motor is in the audio-frequency range, a factor-data table (7; 7A) including a plurality of data on factors, and a factor selector circuit (8; 8A) for selecting one factor from the factor-data table (7; 7A) periodically and at predetermined time intervals (Tc) (sec) in accordance with operating conditions of the inverter and the motor. The one factor and the fundamental carrier frequency (FC_SET) (Hz) are multiplied together to obtain a carrier frequency (1, 2, 3; 1, 2a, 2b, 3). <IMAGE> |
