A Position Sensorless Brushless DC Motor Drive with Inherent Torque Control for EV Application

This paper presents a new position sensorless approach to permanent magnet brushless DC (PMBLDC) motor drive based on torque control for electric vehicle (EV) application. This method introduces a sector defined voltage vector-based switching logic in a constant torque region compared to conventional six-step trapezoidal control. The selection of voltage vectors, depends on the rotor position and the torque error, which eventually reduces the torque ripple. Position information is obtained using stator flux linkage function, which shows superior dynamic performance at low speeds than the traditional back-EMF based method. Due to frequent commutation in the PMBLDC motor drive, the Lissajous pattern (locus) of the stator flux linkage deviates from ideal circle as in the case of a permanent magnet synchronous motor (PMSM), affecting rotor position estimation. Stator flux is kept constant while focusing only on the torque makes the controller computation simpler and faster. This approach keeps the stator flux linkage amplitude close to sinusoid and the position estimation tends to be more accurate. Low frequency oscillation in torque is minimized with this control, which is an advantage to EV or traction drive. The concept is well proved using detailed simulation analysis