Speed and Torque Estimation of BLDC using DTC and Sliding Mode Observer

Abstract

This paper presents speed and torque estimation for Brushless DC (BLDC) motors with non-sinusoidal back electromotive force using six switch inverter and DTC technique. The 180 conduction mode is the more popular method used for three-phase drives but here we use two-phase conduction mode. A simple approach is discussed n how to reduce ripples in the estimated torque at low frequency operation. A simple look-up table at a pre-defined sampling time is used to select the inverter voltage space vectors and the quasi-wave current is obtained. Estimation of electromagnetic torque for BLDC drives is the key issue and so sensor-less control method are used. The sliding mode observer estimates the back-EMF and generates torque, as under sliding mode observer error equation is reduced and it makes stability easier. Only the measurements of the stator currents is used in the estimation of back-EMF waveform. The electromagnetic torque and the rotor speed is estimated using values from Sliding Mode Observer. Fuzzy Gain Scheduling method is used to tune the parameters because this scheme uses human expertise on PID gain scheduling can be represented in fuzzy rules. Furthermore, better control performance can be expected in the proposed method than that of the PID controllers with fixed parameters and the gains of the sliding mode observer are tuned manually. The effectiveness of the proposed scheme is verified by using simulation results.

Keywords: BLDC, DTC, Sliding Mode Observer(SMO), PID Controller, Fuzzy Gain Scheduling, Estimated Rotor speed, Estimated Torque, Estimated Back-EMF.