| 摘要 |
PROBLEM TO BE SOLVED: To lower the level of electromagnetic noise by switching the drive of a drive means to drive the switching element constituting an inverter circuit from the one by a current waveform control means to the one by a thinning-out drive means, when it has detected the impossibility of the zero-crossing switching of a inverter circuit. SOLUTION: A control means 8 is so arranged as to detect the waveform of the current outputted by a frequency converting circuit 5, when it detects the disturbance of the waveform in the vicinity of zero, it switches the drive of a drive means 3b from the one by a current waveform control means 6 over to the one by a thinning-out drive means 7. In short, when it detects the impossibility of the zero-crossing switching of an inverter circuit 3, it switches the drive of the drive means 3b from the one by the current waveform control means 6 to the one by the thinning-out drive means 7. The thinning-out drive means 7 is so arranged as to perform the control of PWM, etc., at low voltage in the vicinity of zero. Hereby, the waveform with little distortion can be outputted, accordingly the generation level of the electromagnetic noise can be lowered. |
