Patent ID: 8184461

Claim:
A non-insulated type power conditioner provided between a direct current power source and a commercial power source for converting a direct current input from the direct current power source into an alternating current output for utility interconnection with the commercial power source and outputting the converted alternating current output, comprising, a circuit for retaining a potential on a negative-electrode side of the direct current output at a potential level equivalent to or higher than a ground potential of the alternating current output, wherein the circuit comprises: a first circuit for chopping a direct current voltage from the direct current power source at a first frequency as a system frequency and thereby generating a first sequence of square wave voltages including a plurality of square wave voltages having a voltage level that changes to a positive side relative to a first reference potential as a potential on the negative-electrode side of the direct current power source; a second circuit for using a potential of the first sequence of square wave voltages as a second reference potential, the second circuit chopping an output of the first circuit at a second frequency of a predetermined number of times as high as the first frequency and thereby generating a second sequence of square wave voltages including a plurality of square wave voltages having a voltage level lower than the voltage level of the first sequence of square wave voltages on the positive side that changes to a negative side relative to the second reference potential, the second circuit further summing the first and second sequences of square wave voltages and thereby generating a third sequence of square wave voltages including a plurality of square wave voltages having a voltage level that changes to the positive and negative sides in turns in the manner of sinusoidal wave relative to the first reference potential; and a third circuit for chopping the third sequence of square wave voltages at a third frequency determined by a timing that depends on if a voltage difference thereof to a sinusoidal wave voltage results in a positive value or a negative value and outputting the chopped third sequence of square wave voltages as a charge/discharge output, the third circuit further PWM-controlling the charge/discharge output at a PWM frequency higher than the third frequency so that the voltage difference between the third sequence of square wave voltages and the sinusoidal wave voltage is corrected and thereby generating a sinusoidal wave voltage that continuously changes to the positive and negative sides relative to the first reference potential using the third sequence of square wave voltages and the PWM-controlled output, and outputting the generated sinusoidal wave voltage to a load.