Abstract
This paper presents a new position sensorless scheme in which a smoothing filter algorithm is proposed to improve the results obtained through Extended Kalman Filter (EKF) algorithm in tracking the rotor position for sensorless control of brushless DC motors. The rotor position and speed are estimated from the input voltage and current using the Extended Kalman Filter. States obtained through filtering in each sampling instant are refined, using the new smoothing algorithm, giving much better results. In the proposed method, the estimated state in previous instant is enhanced using the present measurement sample by the smoothing algorithm which is then used to improve the present estimated state variables. The complete system is modelled and simulated in MATLAB to verify the merit of the proposed smoothing algorithm. A comparison with conventional EKF is done for various load torque and speed conditions to establish the performance of the new sensorless algorithm. Simulation results show that the proposed smoothing technique offers better estimation accuracy. The peak error in the estimated speed and rotor position is considerably reduced when compared with EKF. The improved state estimate can be used as feedback for speed control of brushless DC motors in variable speed drives.
Highlights
Varying energy price always demands for variable speed motor drive which is highly efficient for energy saving [1]
Stable operation and control of Brushless DC (BLDC) motor necessitate the current commutation in windings to be synchronized with instantaneous rotor position
Many position sensorless schemes have been reported in literature for trapezoidal back EMF type of Permanent magnet (PM) motors
Summary
Varying energy price always demands for variable speed motor drive which is highly efficient for energy saving [1]. The position information for phase commutation is obtained by integrating back EMF wave of unexcited phase in [7, 8] This approach is less sensitive to noise but has inferior performance during low speed due to integration error. A method of sensing zero crossing of back EMF wave by detecting the current through the freewheeling diode in unexcited phase is presented in [9]. This method works in all speed ranges but needs more circuitry for current detection. Rotor position and speed estimation of permanent magnet synchronous motors using EKF was established in [14] in which the measured signal is filtered for eliminating higher order harmonics.
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