Simulation model and characteristics of variable frequency transformers used for grid interconnection

This paper constructs a PSCAD-based simulation model of the variable frequency transformer (VFT). The model verification is then performed on a one-machine infinite-bus system. The verification simulations show that the model is fairly accurate to represent VFT´s dynamic characteristics under different frequency control, phase angle control, and start-up control strategies. Based on this model, some further simulations are conducted to study VFT´s characteristics under fault conditions and its roles in preventing the spread of faults into the other area on Kundur´s well known four-machine two-area system. The simulation studies show that, while compared with a conventional power transformer, the VFT can effectively suppress power oscillations between the two interconnected power systems and thus prevent the faults from spreading.