PURPOSE: To obtain a power conversion device which consumes a less amount of power and generates less noise by providing a carrier distributing rate changing means which changes the occupying rates of a plurality of carriers to be compared with a modulated wave given to a PWM circuit in a prescribed period of time by means of a control signal.
CONSTITUTION: Of a plurality of carriers, the carrier 7 which can reduce noise is set at a frequency near the upper limit of the audible frequency range of human beings and the carrier 8 which can reduce the power consumption of a power converter is set at a carrier frequency nearly equivalent to that of the power converter. A carrier distributing rate changing means 9 outputs the occupying rates of the carriers 7 and 8 by changing the rates in accordance with the magnitude of the output signal 10 of a load current detecting means and a PWM circuit 5 outputs a pulse-like gate signal to a gate circuit 4 by performing PWM-control and drives an induction motor 3 at a prescribed voltage and prescribed frequency by switching the self-extincting element of an inverter 2. As a result, low noise can be attained while the emphasis is laid upon at the saving of the power consumption when the load current is large and saving of power consumption can be attained while the emphasis is laid upon the low noise when the load current is small.
ANDO TAKEYOSHI
INABA HIROMI
MITSUNE SHUNSUKE
HITACHI BUILDING SYST ENG
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