Direct torque control in electric power assisted steering systems

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Supervisor:
Dr. Veszprémi Károly
Department of Electric Power Engineering

Nowadays hydraulic power assisted steering systems in vehicles are being supplanted by more flexible and energy-efficient electric solutions, due to the development of power electronics, electrical machines, and motion controls. Here, the power assist is implemented by a servomotor directly connected to mechanical parts. The motor is mostly a permanent magnet synchronous machine due to the special requirements. The most important requirements are minimal torque ripple and generated noise, small parameter sensitivity, high dynamics and wide speed range. These should be realized with limited hardware and software resources because of high price sensitivity and high volume manufacturing.

ThyssenKrupp Presta Hungary Kft. in Budapest is dealing with hardware and software development of electric steering systems. The topic of this thesis is the development, testing and implementation of an alternative motion control algorithm related to the corporate developments.

Besides the commonly used field-oriented control, direct regulations are more and more widely distributed in the recent decades thanks to very robust and parameter-independent structure, and high dynamical behaviour. One group is direct torque and flux control, where the control of the two physical quantities is made independently, thus making the system more safe and flexible. Depending on structure it is possible to implement either continuous or discrete controller, even without rotor position measurement.

My thesis first examines a variety of direct torque control solutions in simulation and presents other calculations, followed by hardware implementation and comparative measurements with the company’s currently used motor control. Finally, I examine the designs without rotor position measurement, and based on these results I draw the conclusions of the paper.

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