| 摘要 |
PURPOSE:To suppress a magnetic noise by varying the frequency of a modulation carrier signal of a PWM inverter proportionally to the amplitude of its output current, and preventing upper and lower limit values from exceeding predetermined ranges. CONSTITUTION:A DC power from a DC power source 2 is converted by a PWM inverter 3 into an AC power of desired voltage and frequency to drive an induction motor 4 at a variable speed. The inverter 3 is pulse-width modulated by a command value from a frequency setter 11 through a calculator 12, etc., to control ON, OFF transistors. In this case, in order to vary a carrier signal input to a comparator 13 corresponding to the output current of the inverter 3, carrier frequency varying means which has an upper/lower limiter 23, a voltage/frequency converter 24, an integrator 25, etc., is provided. Thus, the switching losses of the transistors can be reduced.
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