| 摘要 |
PURPOSE:To miniaturize a device and reduce cost by controlling the duty ratio of ON-OFF of a switching element so as to control the quantity of electricity based on the quantity of electricity varying in response to the fluctuation of output currents. CONSTITUTION:A full-wave rectifier circuit 4 is connected to an AC power 1, and a smoothing capacitor 6 is connected between output terminals for the circuit 4 through a diode 5. A switching element 7 such as a power transistor is inserted, and a converter section A converting AC into DC is constituted of these circuit, diode, capacitor and switching element. An inverter section B is organized of switching elements S1-S4, etc., and a three-phase induction motor 8 as load is driven. A control circuit is constructed of a supply-voltage waveform detector 9, an input current detector 11 with a current transformer CT, an output voltage detector 12 and a CPU 18 with a modulation-factor arithmetic means 15, etc. Accordingly, the duty ratios of ON-OFF of the switching elements are controlled so as to inhibit the quantity of electricity based on the varying quantity of electricity.
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