Design and Implementation of Nonlinear Observer and Controller for BLDC Motor

Abstract

In this work, three different linear observer schemes are proposed to estimate the speed of the BLDC motor. A sensorless control method is proposed in first scheme, on the basis of unidentified input observer. In this scheme, the BLDC motor line to line back EMF is continuously estimated from the existing voltages and currents. This back EMF is further converted to a dq back EMF that can be used to determine the position of the rotor. In second scheme, the position of the rotor is determined by the sequence of estimated back EMF rather than by the dq component of the back EMF. The performance of the BLDC motor drive can be affected by disturbance torque which acts on the motor shaft. The information on the disturbance torque is therefore important and necessary. Hence, in third scheme, the disturbance torque is estimated using a disturbance torque observer which is further useful to estimate the speed of the BLDC motor. This estimated disturbance torque is the sum of the proportional and the time integral of the estimation error of current. But all these three schemes do not work satisfactorily during parameter variations of the BLDC motor. Hence, nonlinear observer i.e. Immersion and Invariance (II) observer is designed to estimate the speed and load torque of the motor. This observer gives the satisfactory response for parameter variation of the motor. newlineMotor performance can be controlled using different controllers i.e. PI controller, Fuzzy controller and nonlinear controller. The PI and Fuzzy controller do not work satisfactorily during parameter variation with the linear observer and sustain oscillations are observed in motor performance during steady state. Lyapunov s direct method-based controller has been discussed but this controller also gives the error during load variations as well as during parameter variations. Hence, new controller based on Interconnection and Damping newlineiv newlineAssignment Passivity based Control (IDA-PBC) is designed which is suitable for normal as well as parameter variations of BLDC moto