Device for controlling power conversion apparatus

The present invention pertains to a device for controlling a direct-type power conversion apparatus, which is capable of highly efficiently driving a motor. According to the present invention, a rectified voltage obtained through full-wave rectification of single-phase AC voltage is applied between first and second DC power supply lines. A discharge switch and a capacitor are mutually connected in series between the first and second DC power supply lines. A voltage step-up circuit steps up the rectified voltage and charges the capacitor. The rectified voltage is inputted to an inverter as DC voltage when the discharge switch is in a non-conductive state, and the voltage between both ends of the capacitor is inputted to the inverter as DC voltage when the discharge switch enters a conductive state, whereby the inverter converts the inputted DC voltage to AC voltage and outputs the AC voltage to the motor. A switch control unit keeps the discharge switch in a non-conductive state over a first period, and switches the discharge switch between a conductive state and a non-conductive state during a second period different from the first period. A charge/discharge period setting unit sets a first period, during which the rotation speed of the motor is higher than a speed threshold value, to be shorter than a first period during which the rotation speed of the motor is lower than the speed threshold value.