Efficiency Increase in a Wind System with Doubly Fed Induction Generator

In this paper, an improved efficiency control strategy for a Wind Energy Conversion System (WECS) with Doubly Fed Induction Generator (DFIG) is presented. The developed control strategy minimizes the electric loss in the DFIG and provides maximum power point tracking (MPPT) control in the wind turbine. The power loss in the DFIG can be decreased by applying flux weakening control at the low wind speeds while it is transferred to nominal flux operation in high wind speeds. The magnetic flux is regulated through control conditions which also govern the transition process from the flux weakening to nominal flux operation and viseversa. Therefore, increase of the generated electric energy by the wind system is attained and also expansion of the exploitable wind speed range towards the lower wind speed region is accomplished. The proposed control technique is implemented with a system of lower rated power converters and thus, the advantage of DFIG for lower requirements in the power converter capacity against other types of electrical generators (i.e. permanent magnet synchronous generators and squirrel cage induction generators) still holds. Selective simulation results are presented for demonstrating the efficiency increases in a WECS with the suggested control system.