Patent ID: 7859209

Claim:
A control device for a synchronous motor comprising: a synchronous motor; a load device connected to the synchronous motor; an inverter for applying a voltage with modulated pulse width to the synchronous motor and driving the synchronous motor with an alternating current; a power supply for supplying power to the inverter; and a controller including a detector unit that detects at least one of current flowing to the synchronous motor or current supplied to the inverter and adjusting voltage output from the inverter based on a detected current value, wherein the controller comprises a proportional-integral controller having an integral gain Ki, wherein ω 1 is a driving electric angular frequency of the synchronous motor, N is an arbitrary integer, and the integral gain Ki is adjusted as functions of ω 1 and N in accordance with Ki=(ω 1 ·N) 2 ·L, where L is an inductance of the synchronous motor, wherein the controller has a phase property in which a disturbance response property of the controller is within ±45 degrees.