SYNCHRONOUS MOTOR DRIVING DEVICE AND SYNCHRONOUS MOTOR DRIVING METHOD

A synchronous motor driving device which accurately estimates and limits direct current (DC), without a dedicated current detection sensor. The device includes a first DC calculation unit that calculates a first DC based on a first voltage command value, a current value of a winding of a synchronous motor, and a battery voltage; a second DC calculation unit that calculates a second DC based on a current value of the winding of the synchronous motor, a rotation speed of the synchronous motor, and a predetermined motor characteristic; a model error extraction unit calculating inverter efficiency based on the first and second DC; a DC correction unit that calculates an estimated DC on the basis of the first and second DC, and the inverter efficiency; and a DC limiting unit that corrects a current command value of the winding based on the estimated DC and a predetermined DC limit value.