Sensorless operation of current controlled BLDC drive with phase lag compensation

This paper presents a method for sensorless rotor position detection of BLDC drive based on Back EMF which is indirectly obtained from motor terminal voltages along with PWM switching noise. Low pass filter is used to eliminate high frequency noise. The low pass filter used in position detection circuit also produces phase lag on back EMF signal which deteriorates the accuracy. This phase lag problem is compensated in real time in the method presented in this paper. During the starting stage of machine back EMF is low and due to poor signal to noise ratio, open loop acceleration is followed. Logarithmically decreasing commutation time steps is used for faithful acceleration even in high inertia conditions. I/f control scheme is used to control the speed of motor and it is use full in the starting and acceleration of motor at maximum torque. The simulation is conducted to validate the method.