Patent ID: 8754601

Claim:
A controller of a synchronous motor comprising: an allowable energy value acquisition unit which acquires an allowable energy value until which a dynamic brake resistor can bear, the dynamic brake resistor being for short-circuiting an input terminal of the synchronous motor at a time of failure; an inertia estimation unit which estimates inertia of a driven object based on a speed value which is fed back from the synchronous motor while the synchronous motor is driving the driven object and an electric current value which is fed back from an amplifier and input to the synchronous motor; an allowable maximum speed calculation unit which calculates an allowable maximum speed value of the synchronous motor from the inertia and the allowable energy value; and a speed control unit which controls the amplifier for operating the synchronous motor at a predetermined commanded speed, wherein the speed control unit acquires the allowable maximum speed value from the allowable maximum speed calculation unit, and limits the commanded speed to the allowable maximum speed value or lower.