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Hall sensor-based locking electric differential system for BLDC motor driven electric vehicle with independent wheel drives

University of British Columbia

It is generally known that stability of vehicles under certain driving conditions may be improved by forcing the wheels to turn at the same speed and angle regardless of the available traction under individual wheels. For conventional all-terrain vehicles or sport-utility vehicles, this function can be achieved by locking the mechanical differential system. In this thesis, we propose an innovative approach for locking the electrical differential system (EDS) of electric vehicles (EV) with independent brushless DC (BLDC) machine-based wheel drives. The proposed method locks the active wheels of the vehicle as if they were operating on a common “virtual” shaft. The locking algorithm is implemented by processing the Hall sensor signals of the considered motors and driving them with a single set of “averaged” Hall signals, thereby operating the motors at the same speed and angle. A detailed switch-level model of EDS embedded with the proposed Sync-Lock Control (SLC) along with the BLDC propulsion motors has been developed and compared against measurements for the considered BLDC propulsion motors. The proposed technique is shown to achieve better results compared to a conventional speed control loop as the considered motors are locked directly through the corresponding magnetic fields. An efficient realization of the proposed controller is presented that makes it possible to be potentially programmed inside existing motor controllers or implemented in a stand-alone microcontroller which can be packaged into a dongle circuit. The proposed SLC is implemented digitally using a programmable integrated circuit microcontroller. First, the Hall signals undergo a layer of filtering to mitigate the errors that are common due to Hall sensor misalignment in low-cost BLDC motors. Then, the locking algorithm is implemented by averaging the filtered Hall sensor signals. The SLC prototype is implemented in form of a standalone dongle-circuit that can be easily placed between the original Hall-sensors and the BLDC motor driver. Operation of typical industrial BLDC motors with the proposed controller is shown to outperform conventional controllers and lock both speed and angle of the motors.

Text

2012-04-20

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/42168

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/