| 摘要 |
PROBLEM TO BE SOLVED: To reduce noise of air-conditioner by switching the carrier frequency at an interval shorter than one period of output voltage from a PWM control circuit thereby suppressing the carrier noise. SOLUTION: Upon receiving a timing signal T, a carrier frequency selecting section 6e selects a carrier frequency data among carrier frequency data fe1-fe4 according to a data select signal N and delivers the selected carrier frequency data to a carrier generating section 6c. The carrier generating section 6c delivers a carrier signal fc to a PWM waveform generating section 6d where the carrier signal fc is compared with a basic wave signal (f) based on a frequency command signal to and delivers a signal to a PWM control inverter circuit 3 through a transistor drive circuit 5. In this regard, the period of timing signal T being fed to the carrier frequency selecting section 6e is set at an appropriate value shorter than the period of output power from a current PWM control inverter circuit 3. |
