ACTIVE AND REACTIVE POWER CONTROL OF DOUBLY FED INDUCTION MACHINE

Abstract

The statistical data conveys that Doubly Fed Induction Machine (DFIM) is the most j common machine used now-a-days in the emergent renewable energy market. The DFIM is an induction machine with a wound rotor where stator and rotor both are connected to electrical sources, hence the term given as "doubly-fed". Usually, the stator circuit is directly connected to the grid while the rotor winding is connected via slip-rings to the three phase converter. Now-a-days DFIM is an integrated part of generation as well as automation system. Therefore, any abnormalities associates with grid are going to affect the system performance considerably. Taking into this in account, the basic concept behind the total system (DFIM with back-to-back converters) is that the machine-side converter controls the active and reactive power by controlling the d-q components of rotor current (i.e. i, and i,,), while the grid-side converter controls the dc link voltage and ensures the operation at unity power factor by making the reactive power drawn by the system from the utility grid to zero. Due to bidirectional converter in the rotor circuit the DFIM is able to work as a generator and motor in both super synchronous and sub synchronous modes with a rotor speed range around synchronous speed. In this thesis, the theory of operation and simulation for the control technique is presented. A mathematical model for DFIM is proposed. Afterwards the vector control or stator flux oriented control practice is established for active and reactive power control for utility grid. The simulation models of DFIM as well as vector control are developed in MATLAB/SIMULINK. The results are analyzed and discussed for the control technique presented.