Abstract
In this thesis it is shown that in the case of an automotive electric power steering system, critical pulse power loads can be decoupled from the power net with a storage element and a multifunctional converter. A multifunctional converter system is proposed because it uses the motor drive system as a dc-dc converter and hence no additional front-end dc-dc converter is required. The influence of a multifunctional converter to the torque and losses in induction and PM synchronous machines were analyzed and design guidelines developed. This was necessary because of the fixed star-point connection and the superimposed dc phase currents in a multifunctional converter system. It was shown with analytical models and FEM simulations verified with measurements on induction and PM synchronous machines that the winding scheme has to be carefully selected to avoid partial saturation, braking torque and increased torque ripple. With the presented design improvements, consisting of interleaved pulse-width modulation and winding arrangements, the high-frequency ripple currents were significantly reduced. A further benefit of a multifunctional converter is that three-phase electrical machines can be operated with only two active phases to increase the reliability.
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