Design and implementation of the main controller of a solid-state transformer

[摘要] ENGLISH ABSTRACT: The Solid-State Transformer (SST) is presented as an alternative to the traditional Line-FrequencyTransformer (LFT) used for voltage-level transformation in distribution grids. The LFT technologyis highly matured which results in low costs and high efficiency. The SST however, introducesseveral advantages compared to the LFT, some of which are input unity power-factor,near perfect output-voltage regulation, frequency variation as well as harmonic filtering.The SST consists of three power-electronic converter stages: The input stage, the isolationstage and the output stage. The input and isolation stages are implemented with a multilevelconvertertopology incorporating a converter-stack for each phase. Each stack consists of Nconverter building blocks, called cells. In this thesis the design and implementation of the maincontroller is presented. The main controller, together with N cell controllers, is responsible forthe control of the cells within the respective stack. Three main controllers are thus implementedwithin the SST.Each cell consists of an Active Rectifier (AR) and a DC-DC Converter (DC-DC). The SSTcontrol design thus starts with the AR control which is subsequently expanded to CascadedActive-Rectifier (CAR) control. Design is completed with the addition of the DC-DC control.Time domain simulations of the AR- and CAR-control are presented and discussed. Test measurements,verifying functionality of each control design-phase, are presented and discussed.

[发布机构] Stellenbosch University