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STABILITY ANALYSIS OF VARIABLE FREQUENCY TRANSFORMER PARK USING ADVANCED CONTROLLING SCHEME

When HVDC link is used for interconnection, it requires a very costly converter plant at sending end and an inverter plant at receiving end. So a new technology known as Variable Frequency Transformer (VFT) has been developed for transmission interconnections. A VFT is a controllable, bidirectional transmission device that can transfer power between asynchronous networks. VFT park model proposed in this paper allows the simulation of multi unit VFT for increasing power transfer between two electric networks. Each VFT unit consists of round rotor synchronous machine, DC motor and a control system. In order to determine the stability of a VFT, a new approach based on Sequential Continuation Scheme and the Limit Cycle Method are presented. The computation of stability regions of VFT control system provides information for tuning ANFIC. Here PSO based ANFIC and ACO based ANFIC are used for power regulation and speed regulation of VFT control system. Stability diagram are reported for changes of power transfer and frequency on both sides of the asynchronous link. Sequential continuation Scheme determines how solutions vary with a certain parameter and Limit Cycle Method finds the steady state operating point. This will help to carry out the analysis more effectively. The effectiveness of this model is verified by the simulation results concerning the standard IEEE 17 bus system and 118 bus systems. The comparative results will be also shown for variations in power and frequency when PSO based ANFIC and ACO based ANFIC is incorporated in VFT control system.