Performance Analysis of Variable Frequency Transformer for Power Flow In-between Synchronous Network Under Varying Voltage Conditions

The Variable Frequency Transformer (VFT) is a controllable and bidirectional transmission device which integrates the principles of both rotatory transformer and phase shifting transformer, in order to regulate the power flow between two power grids. As most of the research work is focused on operating VFT at constant voltages; the analysis of VFT operating under varying voltage conditions remains unexamined. Keeping this gap in view, the paper presents detailed working of a VFT system used to control the power flow in-between synchronous grids operating under variable voltage conditions. For this, the two independent synchronous networks, under consideration, are connected to the stator and rotor winding of VFT, respectively. The power flow in-between the connected networks is first analysed under constant voltage conditions. The analysis shows that the power flow in-between the two synchronous connected networks, varies linearly with the applied torque and reverses as the direction of torque is reversed. The power flow is then analysed under variable voltage conditions, the obtained results show that reducing the voltage of either of the synchronous networks, increases the power flow towards that network while decreasing the power flow towards the other network. Further, the simulation results obtained using MATLAB/Simulink are validated using the real-time Typhoon HIL emulator.