Flux Linkage Self-control Based Direct Torque Control of Brushless DC Motor

Based on analysis of the characteristics of brushless DC motor (BLDCM) and the traditional pulse width modulation (PWM) current control, a novel BLDCM flux linkage self-control based direct torque control (DTC) scheme was proposed to overcome difficulties of flux linkage estimation and reference. A single hysteresis-controlled torque loop was adopted and flux linkage self-control was achieved by means of throwing the voltage vectors decided by both the torque loop output and position of magnetic poles. The presented scheme simplified the control system by eliminating the flux linkage loop. Additionally, torque ripples produced by both the nonideal back electromotive force (back-EMF) and low-speed current commutation could be restrained. In order to estimate torque accurately, a sliding mode observer was used to obtain the back-EMF in the two-phase stationary reference frame. Perfect dynamic and steady performances of torque control in the flux linkage self-control based DTC system were validated by simulation and experimental results.