A controller 40 performs a control operation in a cycle based on a carrier frequency fc of a carrier, specifically, at timings corresponding to the peaks and troughs of the carrier signal. Moreover, in the case where the carrier frequency fc is switched, a disturbance estimation part forming the controller 40 updates control constants that are used for disturbance estimation and are dependent on the control operation cycle, in a control operation performed one cycle after a control operation immediately after the switching of the carrier frequency fc.