Modelling and Control of Doubly Fed Induction Generator Based Stand-Alone Wind Energy Conversion System

Abstract

The application of wound rotor induction machine is widely spread in wind energy generating stations because of its adaptability for variable speed wind turbines through which maximum possible extraction of wind energy is possible. Also among all the induction generator configurations for wind power systems the use of Doubly Fed Induction Generator (DFIG) configuration with back to back pulse width modulated voltage source converters (VSC) is one of the best topologies available and it is suitable for both grid connected systems as well as stand-alone systems. Here only stand-alone application of DFIG is considered. In this thesis mathematical modelling of doubly fed induction machine is presented. The control strategies for both stator side converter and rotor side converter are developed in stator flux oriented reference frame. The dynamics of dc link voltage build-up phase is also included. The stator side converter is used to control the output voltage in direct voltage control manner and the rotor side converter is current controlled where the power imbalance of the system is nullified using dc link voltage controller which modifies the quadrature axis rotor current reference value according to the changes in the wind speed as well as the load. Two control algorithms are presented out of which one gives the best performance for all kinds of loads (balance, unbalance, linear and non-linear) and the other gives poor load regulation and unwanted distortions in the output voltage for non-linear and unbalanced loads