Torque estimator for a permanent magnet brushless DC motor drive

Estimation of motor torque requires information of motor parameters and becomes crucial to the cases where phase inductance varies with the rotor position. Present paper proposes a simple instantaneous torque estimator for a permanent-magnet brushless dc (PM BLDC) motor drive. Proposed estimator requires information of phase currents from the current sensors and duty ratio applied to the individual phase legs of the VSI. Information of phase inductance is not required. Negligence of phase resistance reduces this estimator to a simplified one with considerable error. Applicability of this estimator even for the sinusoidal phase current supply makes it a general strategy for the estimation of instantaneous motor torque for a PM BLDC motor drive. For the validation of the estimator, torque from the Simulink model of PMSM motor with trapezoidal back-emf is considered as a reference.