Analysis of variable frequency transformer used in power transfer between asynchronous grids

The continued existence of geographical disparity between the generation and load centers forces us to go for grid inter connections, especially with the increase in load demand. Conventional grid inter-connection solutions include phase shifting transformers (PST) and back-back HVDC. The former cannot cater to asynchronous grids and can only give step wise variation, while the latter has restrictions to be used in weak grids. Variable frequency transformer (VFT) which is a new grid interconnection solution has been developed by General Electric, which can cater to inter connection of asynchronous grids and also provide continuously controllable power transfer between them. The VFT is being considered by many utilities as an alternative to back-back HVDC in certain installations or as a redundant system in parallel to HVDC to provide additional stability and damping. This work thoroughly analyzes the VFT, its operation, and principles of asynchronous power transfer by using MATLAB SIMULINK^®.