Torque Ripple Mitigation in Sensorless PMBLDC Motor Drive With Adaptive Observer for LEV
Biswajit Saha, Bhim Singh
Abstract
This article presents a method for driving permanent magnet brushless dc (PMBLDC) motor in light electric vehicles that eliminates a need for position sensors. The method prioritizes torque control and employs sector-based predefined voltage vectors for switching in a constant torque mode, surpassing traditional 120° square-wave control. This technique reduces torque ripple by selecting appropriate switching vectors based on rotor position estimation and torque dynamics, elevating drive performance. Stator flux information is utilized to obtain rotor angular positions, resulting in position sensorless drive for variable speed. To address brushless DC (BLDC) motors with high current harmonics affecting commutation process and causing current and torque ripple, a modified flux observer incorporating an adaptive frequency synchronous reference frame phase-locked loop is employed for position estimation. This method filters current harmonics without introducing phase delay, with filter cutoff frequency being variable and adaptive to speed changes, facilitating sensorless operation over a broad speed range suitable for electric vehicle (EV) applications. The controller is streamlined by maintaining constant stator flux while concentrating solely on torque, resulting in a simple and fast process. This approach ensures that stator flux linkage amplitude closely resembles a sinusoid, contributing to more accurate position estimation. Control strategy effectively minimizes low-frequency oscillations in torque, presenting a distinct advantage for EV drive. The viability of proposed concept is substantiated through detailed experimental validation.