Patent ID: 8373380

Claim:
A device for controlling an alternating-current motor, comprising: a sensor for detecting a rotational position of said alternating-current motor; and a control unit for performing control based on an output of said sensor to provide a rectangular wave voltage to each phase of said alternating-current motor, said control unit causing an amount of change in a voltage phase of the rectangular wave voltage of said each phase from a switching reference phase of said each phase to increase/decrease such that said amount of change is equivalent at each switching in one cycle of electrical angle determined from the output of said sensor, said control unit calculates a total amount of change in the voltage phase of the rectangular wave voltage for each said one cycle of electrical angle, and divides said total amount by the number of times said switching is performed in said one cycle, so as to set an amount of increase/decrease of said amount of change in the voltage phase of the rectangular wave voltage of said each phase, said control unit sets a difference in phase at an n-th switching from said switching reference phase of said each phase in said one cycle, to a value n times larger than said amount of increase/decrease, where n is an integer.