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A pulse train pulse-width modulated by PWM control using a sine-wave signal and a carrier signal is inverted alternately in positive-negative polarity. With a high-frequency AC signal obtained by the inversion, a primary side of a transformer for insulating input and output from each other is excite

A pulse train pulse-width modulated by PWM control using a sine-wave signal and a carrier signal is inverted alternately in positive-negative polarity. With a high-frequency AC signal obtained by the inversion, a primary side of a transformer for insulating input and output from each other is excited. This arrangement makes it possible to employ a high-frequency transformer which has a capacity ratio of about 1/30and a weight ratio of about 1/20relative to a commercial-frequency transformer, instead of using it. Thus, an inverter apparatus can be reduced in size and weight as compared with the system using the power-frequency transformer. A sine-wave AC waveform with substantially less distortion similar to the waveform output by the conventional PWM control can be obtained with a simple construction.

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A method for controlling an inverter apparatus which converts DC power generated by a DC power supply into AC power and then supplies the AC power to loads or an existing commercial power supply, the method comprising steps of: alternately inverting positive/negative polarity of a pulse train pulse-

A method for controlling an inverter apparatus which converts DC power generated by a DC power supply into AC power and then supplies the AC power to loads or an existing commercial power supply, the method comprising steps of: alternately inverting positive/negative polarity of a pulse train pulse-width modulated by PWM (Pulse Width Modulation) control using a sine-wave signal of a first frequency and a carrier signal of a second frequency; wherein said PWM control includes the steps of, generating a first pulse train signal by comparing the sine-wave signal and the carrier signal with each other and by outputting a first level when the sine-wave signal is greater than the carrier signal; outputting a second level when the sine-wave signal is less than the carrier signal; generating a second pulse train signal by inverting the first pulse train signal; generating a third pulse train signal by comparing an inverted carrier signal, which is an inversion of the carrier signal, and the sine-wave signal with each other and outputting the first level when the inverted carrier signal is greater than the sine-wave signal, or outputting the second level when the inverted carrier signal is smaller than the sine-wave signal; generating a fourth pulse train signal by inverting the third pulse train signal; generating a rectangular-wave signal equal in frequency to said second frequency of the carrier signal and shifted in phase by a 1/4period of the carrier signal; generating four separate pulse train signals by exclusive-ORing the rectangular-wave signal with each of the first to fourth pulse train signals; generating an AC signal also equal in frequency to that of the carrier signal by inputting the four pulse train signals to four switching devices of an inverter bridge and by performing on-off control on the switching devices, and exciting a primary side of a transformer, insulating a DC power input from an AC power output, with said AC signal.