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AssigneeHitachi, Ltd.
InventorsNobuyoshi Mutoh, Keijiro Sakai, Akiteru Ueda, Akira Ishibashi, Ikuo Okajima
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An AC motor such as an induction motor or a synchronous motor is driven by a PWM inverter circuit. Power switching elements of the inverter circuit are ignited by PWM pulses resulting from comparison of a carrier wave signal with a sine wave modulation signal at a frequency proportional to a frequency setting signal so as to control the inverter circuit. A current polarity detector detects positive and negative components of a DC current flowing in the input side of the inverter circuit. The frequency setting signal is so corrected as to be decreased when only the positive current component flows in excess of one period of the carrier wave signal or increased when only the negative current component flows in excess of the one period.
A method for controlling a PWM inverter circuit responsive to a pulse width modulated signal resulting from comparison of a carrier wave signal with a sine wave modulation signal having a frequency proportional to a frequency setting signal to drive an AC motor, said method comprising the steps of:
An apparatus for controlling a PWM inverter circuit adapted to drive an AC motor comprising:
Dependencies are inferred from the claim text.