Date of Award

12-2017

Degree Type

Thesis

Degree Name

Master of Science in Electrical and Computer Engineering (MSECE)

Department

Electrical and Computer Engineering

Committee Chair

Steven Pekarek

Committee Member 1

Oleg Wasynczuk

Committee Member 2

Scott Sudhoff

Committee Member 3

Saeed Mohammadi

Abstract

Modeling techniques to predict common-mode (CM) current in an electric drive intended for a hybrid vehicle are examined. A particular focus is on the derivation of a common-mode equivalent circuit (CMEC) in which machines, cables, and passives are represented by their passive coupling paths to ground and power electronic devices are replaced by equivalent voltage sources. The interconnection of components is accomplished using a judicious selection of a reference point used to define CM voltage. Circuit-based simulation results are presented for a system consisting of a permanent magnet generator coupled to an active rectifier that is providing power to an inverter/permanent magnet motor. The simulation results are compared to those obtained from a detailed system model in which the switching behavior of all semiconductor devices is represented. It is shown that the CM current predicted using the CM equivalent circuit closely matches that obtained using the detailed system model. Finally, several switching strategies are presented for three-phase, three-leg converters with the intent of reducing the CM voltage at a single or multitude of frequencies. The CM equivalent circuit is used to explore the impact that these strategies have on CM current in modern power electronics systems as well as future systems that will be dominated by wide-bandgap semiconductor devices.

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