Robustness evaluation of SMO in sensorless control of BLDC motor under DTC scheme

Direct Torque Control (DTC) is a method to control the torque in variable frequency drives. This paper describes sensorless DTC of brushless dc (BLDC) motor drive operating in constant torque region under two phase conduction mode to get instantaneous torque control. Sliding Mode Observer (SMO) which is low sensitive to parameter variation is proposed to estimate the phase-to-phase trapezoidal back-EMF for the sensorless operation. This estimated back-EMF is used to deduce the rotor position and the angular velocity of the rotor. And instantaneous electromagnetic torque can be calculated by the product of back-EMF and current. The paper focuses the robustness evaluation of the Sliding Mode Observer to the variation of motor parameters and the effectiveness is also investigated with signum and saturation functions for DTC scheme.