Slotless Permanent Magnet Synchronous Motor Operation without a High Resolution Rotor Angle Sensor

An implementation for sinusoidal current control of a slotless Permanent Magnet Synchronous Motor (PMSM) with discrete Hall sensor position feedback is presented. To estimate the rotor position of the slotless PMSM, a flux estimation technique is used that takes advantage of the slotless machine’s characteristically low inductance to limit flux estimation error. The rotor position is estimated using a reference model and the measured phase currents and voltages. At startup and very low speeds, discrete Hall sensors are used to limit the position estimation error to approximately 30 electrical degrees and to prevent the flux estimators from drifting due to measurement noise and offset. The proposed sinusoidal control method reduces the torque pulsations present when Hall sensor position feedback alone is used and eliminates the need for high-resolution rotor angle sensors. The proposed control strategy is applied to a slotless PMSM drive system and implemented using a digital signal processor (DSP). Experiments are carried out for the system and the results demonstrate the effectiveness of the control.