A novel starting method of sensorless salient-pole brushless motor

Brushless DC motors are receiving much attention for drive application because of their high efficiency, high torque to current ratio and high power density. Among various types of brushless DC motors, the salient-pole brushless motor is attractive from two standpoints: torque/current ratio; and feasibilities of sensorless drive and stable starting without a position sensor. Unlike the conventional cylindrical rotor motor, the salient-pole brushless motor produces additional reluctance torque, which improves the torque/current ratio. In addition to that, the winding inductance is a function of rotor position and a novel approach to rotor position estimation is possible without using a position sensor. The paper presents a sensorless drive of a 2.2 kW salient-pole brushless DC motor and emphasis is placed on stable starting by estimating initial rotor position before starting. To estimate initial rotor position, two types of pilot voltages from an inverter are provided. The pilot voltages are rectangular pulsewise DC voltages with different duties and the resultant current peaks are used to estimate the initial rotor position before starting. The proposed algorithm for initial rotor position identification is verified by simulations and experiments