Performance of solid state transformers under imbalanced loads in distribution systems

This paper will compare the performance of two solid state transformer (SST) topologies in terms of their ability to deal with load imbalance in a four wire power distribution system. The topologies studied consist of an SST with a basic three phase output stage with three separate decoupled phases, and a topology with a four leg inverter output stage. Experimental validation of the control approach for the four leg inverter has been performed. It is shown that both topologies can maintain output voltage balance in the face of significant load imbalance, although the SST with three decoupled phases is best at maintaining output voltage balance. However because of the larger number of switches used it has lower efficiency than the other topologies. The four leg inverter topology is also shown to maintain good output voltage balance while having a lower number of switches and lower loss. Hence this topology presents a better a compromise between performance and efficiency.