Design and implementation of a modular converter with application to a solid state transformer

[摘要] ENGLISH ABSTRACT: The purpose of a solid state transformer (SST) is to use power electronic converters to mimicthe operation of the conventional distribution transformer. These power electronic convertersare proposed to overcome the disadvantages of the conventional distribution transformer. Theadvantages of a SST include near perfect voltage regulation and harmonic isolation between theprimary and secondary windings of the transformer.This thesis discusses the design and development of the different converters in a solid statetransformer (SST). A prototype modular back-to-back converter is developed for the input andisolation stage of the SST. The isolation stage consists of a high voltage DC-DC converter, whichtransfers power across the isolation barrier of the SST. This stage is evaluated in the laboratorywith special attention being paid to the efficiency of the converter.The second aspect that this thesis addresses is the output stage of the SST, namely a threephase inverter. The discussion of the output stage focuses on the losses occurring in the inverter.The switching device losses are calculated by means of an adapted numerical method as opposedto using conventional analytical methods. The presented numerical method is compared to theexisting analytical method and the findings are discussed.A double loop control strategy is implemented for the output stage inverter. The innercurrent loop utilizes a predictive control strategy. The control analysis of the double loopcontroller is discussed and evaluated in the laboratory. All the converters that are discussed inthis thesis are evaluated in the laboratory and the relevant measurements are included.

[发布机构] Stellenbosch University