Modeling and simulation of variable frequency transformer for power transfer in-between power system networks

Recently a variable frequency transformer (VFT) has been used as a flexible ac link between two power systems. It avoids both HVDC link and FACTS based power transmission control system. Basically, it is a rotating transformer whose torque and speed are adjusted to control the power transmission. In this paper, a simulated model of VFT is used as a controllable bidirectional power transmission device that can transfer power in-between power system networks. A digital simulation model of VFT and its control system models are developed with MATLAB and a series of studies on power transmission between power system networks are carried out with this model. The response characteristics of power transfer under various torque conditions are discussed. The voltage, current, torque and speed plots are also obtained. Thus, the VFT concept and its advantages are verified by simulation results. It has distinct advantages in terms of controllability over conventional phase angle regulating transformers and does not inherently produce harmonics in case of many HVDC and FACTS technologies.