Importance

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Abstract

A pulse width modulation type invertor device for an AC power unit. In one form of the invention, a waveform detecting circuit detects an waveform of an output alternating current in an output circuit of the invertor device, and a correcting circuit forms a feedback signal indicative of portions of the waveform of the output alternating current which are outside a predetermined range of amplitude, and compares the feedback signal with a sine wave reference signal to amplify a difference between the feedback signal and the sine wave reference signal. A pulse width modulating circuit is responsive to an output from the correcting circuit for forming a pulse width modulated signal. In another form of the invention, a correcting circuit superposes a pair of signals which are indicative of electric current detected via a pair of current-detecting resistances interposed in a pair of electric current passages in a bridge invertor of the invertor device and reverse in phase to each other to form a signal indicative of a waveform of output current, forms a feedback signal indicative of portions of the signal indicative of the waveform of the output current which are outside a predetermined range of amplitude, and corrects a sine wave reference signal based on the feedback signal.

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First Claim