ANALYSIS OF DOUBLY-FED INDUCTION GENERATOR

Abstract

The present work covers the steady-state analysis of a Doubly-fed induction generator operated at varying shaft speeds in the subsynchronous and supersynchronous regions. A modified equivalent circuit is used in the analyses in which core losses and harmonics are ignored. The operation of the doubly fed induction generator (DFIG) system is explained. The power control by rotor current injection is explained by the phasor diagrams. The controlling scheme is explained and the modeling of the complete system is done in MATLAB-SIMULINK. Direct power control which is a rotor side control of a doubly fed induction generator by which decoupled control of stator active and reactive power can be obtained is presented. It is based on the measurement of active and reactive power on the grid side where voltages and currents are alternating at fixed frequency. The active and reactive powers are made to track references using hysteresis controllers. The measurements are taken on stator side and the control is made on rotor side. This control system eliminates the need for rotor position sensing and gives an excellent dynamic performance as shown by simulation results. The dynamic performance of the system is observed and compared with vector control scheme. The response of the stator and rotor currents, power factor, stator and rotor powers for different values of reference active and reactive powers are shown in the simulation results