Power conversion apparatus

A power conversion apparatus to perform power conversion between an AC power supply and a load,

• the power conversion apparatus comprising:
• an inverter circuit including a first leg, a second leg, a third leg, and a DC capacitor connected in parallel,
• the first leg having a first semiconductor device and a second semiconductor device connected in series, in which a first AC end that is a connection point between the first semiconductor device and the second semiconductor device is connected to one end of the AC power supply,
• the second leg having a third semiconductor device and a fourth semiconductor device connected in series,
• the third leg having a fifth semiconductor device and a sixth semiconductor device connected in series, in which a connection point between the fifth semiconductor device and the sixth semiconductor device is connected to another end of the AC power supply,
• the first semiconductor device, the third semiconductor device, and the fifth semiconductor device being connected, and the second semiconductor device, the fourth semiconductor device, and the sixth semiconductor device being connected;
• the power conversion apparatus further comprising:
• a transformer having a primary-side winding and a secondary-side winding, the primary-side winding having one end connected to the first AC end and another end connected to a second AC end that is a connection point between the third semiconductor device and the fourth semiconductor device, the secondary-side winding being magnetically coupled to the primary-side winding;
• a parallel resonance reactor connected in parallel with the primary-side winding of the transformer;
• a secondary-side rectifying circuit to rectify AC output from the secondary-side winding of the transformer;
• an output smoothing circuit disposed between the secondary-side rectifying circuit and the load and including at least one smoothing capacitor;
• and
• a control circuit to control the inverter circuit, wherein
• the control circuit performs at least pulse width modulation control on the first leg and selects to perform pulse width modulation control and pulse frequency modulation control, to perform pulse width modulation control and phase shift modulation control, or to perform pulse width modulation control, pulse frequency modulation control, and phase shift modulation control on the second leg, based on comparison of a voltage conversion ratio between DC voltage of the DC capacitor and output voltage to the load with at least one threshold.