Bi-directional Position and Speed Estimation Algorithm for Sensorless Control of BLDC Motor

Abstract

The observer design for estimation of back EMF to control the Brushless DC (BLDC) motor is described in this paper. Using the sequence of estimated back EMF, rotor position is estimated. During negative rotation, the actual and estimated values of speed fail to track the reference speed and if corrective action is not taken by the observer, the motor goes into the unstable region. To overcome this problem, the speed estimation algorithm is proposed to control the behavior of motor during negative rotation. Infinite Impulse Response (IIR) Butterworth first order low-pass filters are used in observer for smoothing the estimated back EMFs of BLDC motor. A new controller scheme based on Modified Hybrid Fuzzy PI (MHFPI) controller is proposed to control the speed of BLDC motor. Simulations have been carried out for different disturbances such as step changes in the reference speed and load torque of the motor. Comparison of the proposed scheme with the existing schemes clearly depicts that the effect of disturbance on actual and estimated responses are very less.