Improved performance of a novel SMC-fuzzy controller for DTC brushless DC motor drive for precise speed regulation

The direct torque control (DTC) mechanism is the well popularly used technique as the control strategy for motor drive system. This paper presents a novel sliding mode control Fuzzy speed controller for the direct torque controlled (DTC) Permanent magnet brushless DC (PMBLDC) motor for instantaneous torque control, reduced torque ripple and precise speed control under parameter variations and dynamic load disturbances. The proposed controller employs only the signal of speed error, avoiding the sensitivity to the noise of the acceleration signal as in the conventional sliding mode controller (SMC). It is composed of an equivalent control term, a switching term and a fuzzy control term. The sliding mode controller that is made up of the former two terms ensures the system's stability. The SMC's chattering phenomenon is eliminated by varying its control continuously according to the distance of the system states from the sliding surface. The fuzzy control term improves dynamic response and reduces the steady-state error in the boundary layer. Equation based Matlab/Simulink simulation results for no-load operation, load perturbation and step change in reference speed show the proposed controller has the advantages of fast response and less steady-state error when compared to that of the conventional SMC controller with a boundary layer.