Power converter and power conditioner

A power conditioner that converts a DC power from a DC power source into an AC power interconnected to a system of a commercial power source, the power conditioner comprising:

• first means for chopping a DC voltage at a first frequency that is a system frequency to produce a first square-wave voltage string comprising a plurality of square-wave voltages,
• wherein a voltage level of the square-wave voltage changes onto a positive side with respect to a first reference potential,
• the first means comprising a first switch circuit in which first and second switch elements are connected in series,
• wherein the first switch circuit is connected in parallel to a first capacitor connected between positive and negative electrodes of a DC power source;
• second means for chopping an output of the first means at a second frequency higher than the first frequency by a predetermined number of times to produce a second square-wave voltage string comprising a plurality of square-wave voltages,
• wherein a voltage level of the square-wave voltage is lower than that of the first square-wave voltage string on the positive side and changing onto a negative side with respect to a second reference potential,
• wherein a potential at the first square-wave voltage string is set to the second reference potential,
• wherein the second means produces a third square-wave voltage string by adding the first square-wave voltage string and the second square-wave voltage string,
• wherein the first square-wave voltage string and the second square-wave voltage string alternately change in a sine-wave manner on positive and negative sides with respect to the first reference potential in the third square-wave voltage string,
• the second means comprising a parallel-connected circuit in which a second capacitor and a second switch circuit are connected in parallel,
• wherein one side of the parallel-connected circuit is connected to a series-connected portion of the first and second switch elements,
• wherein the second switch circuit comprises third and fourth switch elements connected in series;
• third means for chopping the third square-wave voltage string at a third frequency to perform charge and discharge,
• wherein the third frequency is fixed by timing according to a positive or a negative of a difference between the third square-wave voltage string and a sine-wave voltage,
• the third means comprises a parallel-connected circuit in which a third capacitor and a third switch circuit are connected in parallel,
• wherein the third switch circuit comprises fifth and sixth switch elements connected in series,
• wherein a series-connected portion of the fifth and sixth switch elements is connected to a series-connected portion of the third and fourth switch elements;
• fourth means for performing PWM control to outputs of the charge and discharge of the third square-wave voltage string means at a PWM frequency higher than the third frequency so as to correct the difference between the third square-wave voltage string and the sine-wave voltage,
• wherein the fourth means obtains a sine-wave voltage that continuously changes on the positive and negative sides with respect to the first reference potential by the third square-wave voltage string and the PWM output,
• the fourth means comprising a fourth switch circuit that is connected in parallel to the parallel-connected circuit of the third means,
• wherein the fourth switch circuit comprises including seventh and eighth switch elements connected in series;
• a plurality of measuring circuits each of which measures a voltage between both ends of each of the first capacitor, the second capacitor, and the third capacitor;
• control means for controlling each of the first to eighth switch elements based on a measured value of each measuring circuit;
• and
• gain calibration means for calibrating a gain of each measuring circuit.

A power converter comprising:

• a first switch circuit comprising first and second switch elements connected in series,
• wherein the first switch circuit is connected in parallel to a first capacitor connected between positive and negative electrodes of a DC power source,
• wherein the first switch circuit chops a DC voltage at a first frequency to produce a first square-wave voltage string comprising a plurality of square-wave voltages, wherein a voltage level of the square-wave voltage changes onto a positive side with respect to a first reference potential;
• a first parallel-connected circuit comprising a second capacitor and a second switch circuit connected in parallel,
• wherein one side of the parallel-connected circuit is connected to a series-connected portion of the first and second switch elements, wherein the second switch circuit comprises third and fourth switch elements connected in series,
• wherein the first parallel-connected circuit chops an output of the first switch circuit at a second frequency higher than the first frequency to produce a second square-wave voltage string comprising a plurality of square-wave voltages,
• wherein a voltage level of the square-wave voltage is lower than that of the first square-wave voltage string on the positive side and changing onto a negative side with respect to a second reference potential,
• wherein a potential at the first square-wave voltage string is set to the second reference potential,
• wherein the parallel-connected circuit produces a third square-wave voltage string by adding the first square-wave voltage string and the second square-wave voltage string,
• wherein the first square-wave voltage string and the second square-wave voltage string alternately change in a sine-wave manner on positive and negative sides with respect to the first reference potential in the third square-wave voltage string;
• a second parallel-connected circuit in which a third capacitor and a third switch circuit are connected in parallel,
• wherein the third switch circuit comprises fifth and sixth switch elements connected in series, wherein a series-connected portion of the fifth and sixth switch elements is connected to a series-connected portion of the third and fourth switch elements,
• wherein the second parallel-connected circuit chops the third square-wave voltage string at a third frequency to perform charge and discharge,
• wherein the third frequency is fixed by timing according to a positive or a negative of a difference between the third square-wave voltage string and a sine-wave voltage;
• a fourth switch circuit that is connected in parallel to the parallel-connected circuit of the second parallel-connected circuit, the fourth switch circuit including seventh and eighth switch elements connected in series,
• wherein the fourth switch circuit performs PWM control to outputs of the charge and discharge of the third square-wave voltage string at a PWM frequency higher than the third frequency so as to correct the difference between the third square-wave voltage string and the sine-wave voltage,
• wherein the fourth switch circuit obtains a sine-wave voltage that continuously changes on the positive and negative sides with respect to the first reference potential by the third square-wave voltage string and the PWM output;
• a plurality of measuring circuits each of which measures a voltage between both ends of each of the first capacitor, the second capacitor, and the third capacitor;
• a control circuit for controlling each of the first to eighth switch elements based on a measured value of each measuring circuit;
• and
• a gain calibration circuit for calibrating a gain of each measuring circuit.