In a power conversion apparatus that boosts a solar light voltage, converts it to AC and supplies AC power to a load or system, power loss is reduced and efficiency is improved. An inverter unit, in which AC sides of three single-phase inverters receive DC power from respective sources with a voltage ratio of 1:3:9 as respective inputs are connected in series. Gradational output voltage control of an output voltage is carried out using the sum of the respective generated AC voltages. Also, a solar light voltage is boosted by a chopper circuit to generate the highest voltage DC power source. When the solar light voltage exceeds a predetermined voltage, the boosting of the chopper circuit is stopped, thereby reducing power loss due to the boosting.