Direct Torque and Indirect Flux Control of Brushless DC Motor with Non-sinusoidal Back-EMF without position sensor

In this paper, the position sensorless direct torque and indirect flux control (DTIFC) of BLDC motor with nonsinusoidal (non-ideal trapezoidal) Back-EMF has been extensively investigated using three-phase conduction scheme with six-switch inverter. In the literature, several methods have been proposed to eliminate the low-frequency torque pulsations for BLDC motor drives such as Fourier series analysis of current waveforms and either iterative or least-mean-square minimization techniques. Most methods do not consider the stator flux linkage control, therefore possible high-speed operations are not feasible. In this work,by using sliding mode observer the mechanical rotor position is removed. The proposed sensorless DTC method controls the torque directly and stator flux amplitude indirectly using d–axis current. Since stator flux is controllable, flux-weakening operation is possible. Moreover, this method also permits to regulate the varyingsignals. Simple voltage vector selection look-up table is designed to obtain fast torque and flux control. Furthermore, to eliminate the low-frequency torque oscillations, the new method has been used to estimate the electromagnetic torque. Simulation results confirm that the proposed three-phase conduction DTC of BLDC motor drive with six-switch inverter scheme.

Keywords:

Brushless dc (BLDC) motor , sliding mode observer , direct torque control (DTC) , stator flux control , fast torque response