US Patent 9713244 Power-supply apparatus

A power supply apparatus includes a controller that performs the following action and resonance means for creating a resonance state between the power supply apparatus and a plasma generator. That is, the controller changes, when a value of electric power input equal to 100% (or a value of electric power input equal to or more than a threshold % and equal to or less than 100%) of a rated power is instructed, an inverter frequency and obtains an inverter output power factor for each of a plurality of inverter frequencies. Then, the controller determines, as a driving frequency of the inverter, one of the plurality of inverter frequencies at which the inverter output power factor is maximized.