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

Abstract

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.