Modeling and Practical Evaluation of AC-DC Solid-State Transformer With Electric Spring Functions

Power electronics (PE) devices have become ubiquitous in the modern power system. Their potential in participation in grid supporting has been gathering growing attention. PE-based electric spring (ES) technology has recently evolved from the low-voltage ac mains to the medium-voltage distribution network. When equipped with ES functions, solid-state transformers (SSTs) can be associated with energy storage and smart loads to absorb power fluctuations arising from renewable energy sources. Unlike previous studies in which PE systems are generally simplified as V,theta,P,Q , or represented by the simplest power converter topology, this paper implements and examines the grid-supporting functionality of a practical ES enabled-SST (ES-SST) system. The dynamic model of the ES-SST is presented and simulated, including both the circuit and control loops. Experimental results obtained from a scaled-down power system are also included to confirm the validity of the dynamic model in a microgrid environment. This dynamic model will facilitate smart-grid researchers to evaluate the use of a large group of distributed ES-SSTs in large power systems in future studies.