Patent ID: 8018746

Claim:
A parallel inverter system comprising a plurality of inverter units which are connected in parallel and operating in parallel to supply electric power to a load, the inverter units each comprising: an inverter circuit including a plurality of semiconductor switching elements; a voltage detector which detects an output voltage of the inverter circuit; a current detector which detects an output current of the inverter circuit; and an inverter control circuit which outputs a PWM control signal for PWM controlling the semiconductor switching elements of the inverter circuit, the inverter control circuit including: a sinusoidal signal generating circuit which generates a sinusoidal signal of frequency in accordance with a commanded value for reference frequency when the commanded value is inputted; a PWM control signal generating circuit which receives an addition result signal and outputs the PWM control signal, wherein the addition result signal is obtained by adding a reference sinusoidal signal obtained by multiplying the sinusoidal signal by a predetermined coefficient and a gain-multiplied difference signal obtained by multiplying a difference signal between the reference sinusoidal signal and a detected voltage signal outputted from the voltage detector by a predetermined gain; a phase difference detecting circuit which obtains a phase difference between the detected voltage signal outputted from the voltage detector and the reference sinusoidal signal; and a feedback circuit which inputs to the sinusoidal signal generating circuit an addition result value obtained by adding to the commanded value for reference frequency a gain-multiplied phase difference value obtained by multiplying the phase difference value by a predetermined gain.