Two-axis torque control of BLDC motors for electric vehicle applications.
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Date
2014
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Abstract
This thesis begins with a literature review focusing on electric vehicle (EV) applications. Systems
used for steering, braking and energy storage are investigated, with specific concentration on
torque control in various DC and AC motors commonly used in EVs. A final solution for a low range
personal transportation EV in the form of a wheelchair is proposed.
The theme for this thesis is motion control, focusing on a two axis (or two wheel drive) brushless
DC hub motor (BLDCHM) EV, with torque and direction control tracking a user reference. The
operation principle for a BLDCHM is documented and the dynamic and electrical equations
derived. Simulation results for motor response under different load and speed conditions are
compared to practical measurements. Current and torque control loops are designed, implemented
and tuned on a single-axis test-bed with an induction motor (IM) load coupled via a torque
transducer. A Texas Instrument DSP development kit is used for the control algorithm bench
testing.
The final control algorithm is then duplicated and expanded in simulation to form a dynamic two axis
system for an electric wheelchair. It incorporates both motor drive and regenerative
capabilities. After demonstrating two axis controls for BLDCHMs, a control algorithm is designed
simulated and compared to traditional systems. The final solution focuses specifically on an
intuitive response to the driver input whilst maintaining direction tracking, even when there is a
difference in smoothness of the individual terrains traversed by the left and right wheels. In
addition the motor drives are equipped with controllers that ensure regenerative braking in order to
recover as much energy as possible when the wheelchair is commanded to decelerate.
Description
M. Sc. Eng. University of KwaZulu-Natal, Durban 2014.
Keywords
Brushless direct current electric motors., Torque., Electric vehicles., Digital control systems., Theses--Electrical engineering.