Implementation of variable frequency transformer for integration of stand alone wind energy conversion system with battery energy storage

The conventional power electronics interface used for integration of wind energy conversion system (WECS) with load produces harmonics which deteriorates the quality of power supplied. To overcome this drawback, a variable frequency transformer (VFT) has been used as a link between WECS and load. For this, first a detailed steady-state modeling of VFT has been carried out. The derived model is then used for the analysis of the steadystate performance of VFT which acts as a link between WECS with battery energy storage and load for standalone operation. For this purpose, an equivalent circuit of VFT for standalone operation is developed. A set of equations for the output voltage and power delivered by VFT is derived from its equivalent circuit. The analytical solution of these equations helps in assessing the behavior of VFT. To validate the analytical results obtained from equivalent circuit, an experimental study is also carried out. The experimental study is conducted on a 3 phase, 400 V (L -L), 50 Hz, 2.2 kW, 1440 rpm, 4 pole, wound rotor induction machine. On comparison between analytical and experimental results, it is evident that both results are in good agreement. Further, the analysis is extended for variable load under various values of wind turbine generator speed and load power factor.