A Structured Approach for Design of an SST Control Architecture Based on CAFCR Framework

Solid-State Transformers (SSTs) are a promising alternative to conventional oil-cooled copper-and-iron based power transformers in the electricity grid. They offer opportunities to make secondary (MV/LV) substations flexible, intelligent and modular. This work proposes to use a generic design tool from Systems Engineering - the CAFCR framework - for the SST control system to unlock its full potential. The framework provides a structured and thorough approach for collaboration and design, connecting what is desired with what is possible. The advantages are as follows: 1) Many research on SSTs has already been done and the framework can help to collect and aggregate the performed research; 2) It also helps to ensure important aspects are not overlooked and designs meet the necessary requirements; 3) Furthermore, it can identify new areas of research and facilitate new ideas. In the paper, we apply the CAFCR framework to SST by starting with the perspective of the Distribution System Operator (DSO) as the customer and an exploration of the application surroundings (substation housing, grid embedding). We then continue to examine the functionalities that are required and desired for an SST from a black-box perspective. These functionalities are presented in a table where the functionalities are divided into a) ‘additional features’ vs ‘mimicking a regular transformer’, and b) ‘normal operation’ vs. ‘fault conditions’. Based on this, four areas of research have been indicated to obtain a flexible, future-proof control architecture. To see how these areas could work together, a task division is proposed as well as applying distributed control to the MV side.