Sensorless control of three phase BLDC motor drive with improved flux observer

A Flux linkage observer (FLO) based sensorless estimation method for permanent magnet BLDC motor based on the integration of back EMF, with a simple start-up method, is proposed here. The rotor position is extracted from the rotor flux information using system equations. The estimated rotor position is improved using a phase locked loop structure which also uses a PI controller for speed estimation. Since the initial rotor position is not known, a simple start up strategy is also introduced. Using a ramp speed reference, an initial rotor position is used for motor control during starting. As the machine picks up speed, control is transferred to flux observer. The control method is validated using simulation results done in MATLAB/Simulink on a 24V, 4000rpm PMBLDC motor.