Instantaneous Torque Estimation in Sensorless Direct-Torque-Controlled Brushless DC Motors

A key issue in the direct torque control of permanent-magnet brushless dc motors is the estimation of the instantaneous electromagnetic torque, while sensorless control is often advantageous. A sliding-mode observer is employed to estimate the nonsinusoidal back-electromotive-force waveform, and a simplified extended Kalman filter is used to estimate the rotor speed. Both are combined to calculate the instantaneous electromagnetic torque. The effectiveness of this approach is validated by simulations and measurements