Patent ID: 8716965

Claim:
A synchronous motor control device for controlling a synchronous motor to carry out a power regenerative operation to return regenerative energy, which is generated during speed reduction of a synchronous motor and stop the synchronous motor when an alternating-current power source fails, comprising: a q-axis current and d-axis current detection unit configured to detect a q-axis current, which corresponds to a torque current of the synchronous motor, and a d-axis current, which corresponds to a magnetic excitation current of the synchronous motor, based on at least two of a first phase current, a second phase current and a third phase current, which flow through the synchronous motor, and a position of the synchronous motor; a q-axis current command value setting unit configured to set a first q-axis current command value of the synchronous motor, based on a difference between a speed of the synchronous motor and a speed command value for the synchronous motor when the alternating-current power source does not fail at the time of driving of the synchronous motor, and to set a second q-axis current command value of the synchronous motor when the alternating-current power source fails at the time of the driving of the synchronous motor; a d-axis current command value setting unit configured to set a first d-axis current command value of the synchronous motor to zero value when the alternating-current power source does not fail at the time of the driving of the synchronous motor, and to set a second d-axis current command value of the synchronous motor to a value larger than zero when the alternating-current power source fails at the time of the driving of the synchronous motor; and a drive unit configured to drive the synchronous motor based on the q-axis current, the d-axis current, the first or second q-axis current command value, and the first or second d-axis current command value, wherein the second q-axis current command value and the second d-axis current command value are set so that an absolute value of power per unit time of the synchronous motor is equal to loss per unit time of the synchronous motor.