Abstract: An adder adds a phase ?plus, which is n times a size of 60 degrees, to a phase output from a phase switching unit and outputs the phase as a voltage command phase ?. A voltage generation unit generates voltage command value based on the voltage command phase output by the adder and outputs the command value. A drive-signal generation unit, based on an output from the voltage generation unit generates drive signals corresponding to respective switching elements of an inverter, and outputs respective generated drive signals to the corresponding switching elements of the inverter, and generates a high-frequency AC voltage in the inverter.

Abstract: The air-conditioning apparatus includes a coolant circuit configured by sequentially connecting a compressor, an indoor heat exchanger, an expansion valve, and an outdoor heat exchanger; a motor that operates a compressor mechanism disposed inside the compressor; an inverter for driving the motor; and a control unit that controls the inverter. The control unit includes a liquefaction detecting unit that detects coolant liquefaction in the compressor; includes a first PWM signal generating unit that generates an inverter control signal for driving the motor; includes a second PWM signal generating unit that generates an inverter control signal for making the motor perform a preheating operation; and includes a switching unit that performs switching in such a way that the first PWM signal generating unit or the second PWM signal generating unit outputs the corresponding inverter control signal to the inverter.