Patent ID: 7408312

Claim:
A control device for a permanent magnet synchronous motor, comprising: an inverter for converting input DC voltage into alternating current of variable voltage and variable frequency, and for driving the motor with the alternating current; a q-axis current instructing means for generating, in accordance with a speed instruction signal, an instruction signal for a q-axis component of the current, orthogonal to the magnetic field of the motor; a loss calculating means for calculating a loss that is the sum of the motor's copper loss and iron loss; a d-axis current generating means for generating, in accordance with the motor's rated loss decreased by the loss, an instruction signal for a d-axis current that is passed through the motor; a controlling means for judging, from the DC voltage, whether or not the motor is operating in a recovery state, and for activating the d-axis current generating means if the motor is in the recovery state.