Ac-dc converter

An AC-DC converter that converts an AC power supply voltage to a DC output voltage of a prescribed magnitude with power factor regulation, comprising:

• a rectifying circuit that rectifies the AC power supply voltage to output a rectified voltage;
• a reactor that receives the rectified voltage;
• a semiconductor switching device connected in series to the reactor;
• a current detector that detects a rectified current flowing through the reactor;
• a proportional controller that multiplies the detected value of the rectified current by a prescribed gain;
• a voltage regulation unit that receives a detected value of the DC output voltage and a command value and that outputs an amplitude command that represents a difference between the command value and the detected value of the DC output voltage;
• an output voltage command calculator that calculates an output voltage command for the semiconductor switching device on the basis of an output of the proportional controller and the amplitude command outputted from the voltage regulation unit;
• and
• a drive signal generator that compares the output voltage command to a carrier signal so as to generate a drive signal for switching the semiconductor switching device ON and OFF,
• wherein the voltage regulation unit and the output voltage command calculator together function as a gain controlling unit that adjusts the prescribed gain on the basis of the difference between the command value and the detected value of the DC output voltage.