Low Voltage Multi-level Converters using Split-wound Coupled Inductors

• Author / Creator

  Ewanchuk, Jeffrey

• In low-voltage applications, an alternative approach to multi-level capacitorbased converters can be obtained by interleaving the switching of two converters across split-wound coupled inductors. When compared to traditional capacitor-based multi-level converters, using split-wound coupled inductors can double the effective switching frequency while eliminating the problem of voltage balancing inherent to split-capacitor connections. Furthermore, the number of voltage levels, relative to the number of devices, can be maximized by using an asymmetrical half-bridge topology with the splitwound coupled inductor. This thesis focuses on the topological attributes of asymmetrical half-bridge converters that use split-wound coupled inductors as a basis for low-cost, low voltage, multi-level converters. In three-phase dc/ac applications, the use of coupled inductors and asymmetric bridges is examined for a three-level converter. To reduce converter weight and costs, the three-phase coupled inductors can be integrated into a single three-limb coupled inductor by eliminating the common mode winding voltages present in traditional interleaved pulse-width modulation schemes. Reduced conversion quality and increased device switching frequency are identified as the challenges in the elimination of these windings voltages. These challenges are experimentally examined with a modification to the modulation of the three-level converter. A three-phase, five-level coupled inductor dc/ac converter is then presented, and space vector based analysis is used to overcome the challenges inherent to three-limb coupled inductor operation. Thus, a compact five-level dc/ac converter is enabled as a low-cost solution to loss sensitive applications, such as low-inductance electric drive systems. Automatic voltage balancing is also identified as a topological attribute of asymmetric half-bridges employing split-wound coupled inductors. With this attribute, a modular balancing converter is presented for the automatic balancing of serially connected voltage sources, e.g. lithium ion batteries in electric vehicles. Two modes of voltage balancing are identified, and the circuit parameters that influence the balancing currents for each mode are described. The circuit parameters are then used to size commercial transformers, and the practical considerations of the power electronics are discussed for the experimental prototype. Therefore, a balancing converter that uses modular components is enabled for low-cost, non-dissipative, voltage balancing which does not require voltage feedback for operation.

• Subjects / Keywords

  • Multi-level
  • Converters
  • DC/AC

• Graduation date

  Spring 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3MS4W

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.