Direct torque control for BLDCM based on optimized sliding mode observer

Direct torque control for brushless DC motor is a kind of control strategy with fast dynamic response and small torque ripple. The key issue of torque calculation is the estimation of back EMF. For that this paper proposes an optimized back electromotive force (back-EMF) sliding mode observer (SMO), a continuous smooth arc-tangent function is introduced into the observer in order to weaken chattering phenomenon, then the sliding and convergence condition is proved. Flux observation of conventional DTC could be omitted by three-phase Hall position sensor. Space voltage vector is selected by the output of cascade control of rotor speed and torque. Simulation results show that the suggested method can accurately estimate back EMF, the direct torque control for BLDCM can be satisfactorily realized.