Digital Simulation of Variable Frequency Transformers for Asynchronous Interconnection in Power System

Variable Frequency Transformers (VFT) is a new technology for asynchronous power system interconnection, which is functionally like back-to-back HVDC device. A digital simulation model of VFT and its control system are formed with Electromagnetic Transient Program (EMTP), and a series of studies on VFT had been accomplished with these models, including VFT energization, speed regulation of rotor, synchronizing, ramp power control, step power control, voltage dependent power limit control, power supply for an isolated passive system, reactive power balance and fault analysis. The response characteristics of VFT under various conditions are discussed, and its advantages are also proved.