Modeling and Control of a Solid State Transformer and verification with Controller Hardware in the Loop

Climate change is driving the evolving energy mix in the world. The amount of renewables are rising to avoid the detrimental effects of fossil fuels to the environment. Solar and wind power are the major players in the rising renewable energy mix. Most of these power generation sources are interfaced through power electronic converters. In the future, it is foreseen that the amount of renewables in the distribution shall increase. The power system is designed to handle the unidirectional flow of power. However, with the increased renewables, the power flow becomes bidirectional. This leads to stability issues in the power system. Solid State Transformers (SST) are envisaged to mitigate these issues by providing advanced functionalities like reactive power support, DC power generators and storage integration among others.FLEXstation project is a Dutch government subsidized project which deals with building an SST. The SST shall be installed the distribution grid. In this thesis, the model and control algorithm for the transformer are discussed. Also, a controller hardware in the loop setup is made using two renowned makes of real time simulators namely OPAL-RT and dSpace. The setup between the two controllers is also discussed in detail.The topology of the SST is made using a multilevel Cascaded H-Bridge (CHB) converter as the grid interface and Dual Active Bridge (DAB) converters as high frequency links between the MV and LV side converters. The balancing of the capacitor voltage of the multilevel converter is discussed. It is shown that due to the difference in the properties of DAB high frequency transformer, the capacitor voltages do not get perfectly balanced through the conventional method used in the literature. The issue is solved using DABs for balancing the capacitor voltages. The capability of the DABs are further utilized to decouple the active power flowing through the capacitors. The method can be used to significantly reduce the capacitor sizes thus reducing the cost and size of the converter