Patent ID: 7294988

Claim:
A synchronous motor drive unit comprising a synchronous motor, an inverter for supplying variable-voltage and variable-frequency DC to the motor, a current sensor for sensing the current through the motor, a rotary sensor for sensing the rotating angle of the motor rotor, vector computing means for controlling the motor torque based on the current sensed by the current sensor and rotating angle signal sensed by the rotary sensor, and a PWM controller for controlling the inverter by PWM according to the computation result, a rotary sensor that generates a rotary output analog signal with multiple periods within one period of the electrical angle or absolute angle of the motor, means that energizes the motor at each position for a specified length of time upon its startup, by using multiple electrical angles of the motor corresponding to the multiple angles, including an absolute angle of magnetic pole position of the motor, sensed by the rotary sensor as the initial position of the motor, and an initial position determining means that determines the electrical angle at which the motor acceleration becomes maximum among the respective angles of energization as the absolute angle of the motor.