| 摘要 |
PURPOSE:To suppress magnetic noise while suppressing the heating value of converter main circuit subjected to PWM control. CONSTITUTION:When a motor 3 is driven through a PWM control circuit 2 based on comparison results between 6 carrier signal fed from a carrier generator 1 and a control signal, magnetic noise decreases as the frequency of carrier signal increases but heating value of a switching element 21 in converter main circuit increases. In the invention, the converter is normally operated while selecting the frequency of carrier signal such that the heating value of the switching element 21 does not exceed an allowable value although some level of magnetic noise is allowed and when an overload detector 4 detects an overload state, the converter is operated while lowering the frequency of carrier signal thus satisfying both suppression of heating value and reduction of magnetic noise simultaneously. |
