Performance Evaluation of DFIG During Asymmetrical Grid Disturbances Using Internal Model Controller and Resonant Controller

In this paper, grid disturbances like asymmetrical sag and swell faults in phase-A are analyzed for the grid connected DFIG. The dynamic behavior of DFIG is compared and tabulated with results using state error compensators like PI, PI with resonant (PIR) and internal model control (IMC) on rotor side converter (RSC). The RSC is designed analytically with enhanced field oriented control (EFOC) technique for better performance during such grid disturbances. In this technique, rotor flux reference changes from synchronous speed to some smaller speed or zero during the fault for injecting current at the rotor slip frequency. In this process, DC-Offset component of flux is controlled in not decomposing into a lower value of faults and maintaining it. This offset decomposition of flux will be oscillatory in conventional FOC, whereas in EFOC with internal model controller, flux can damp quickly not only for single fault but multiple faults. This strategy can regulate stator and rotor current waveform to sinusoidal without much distortion during and after fault. It has better damped torque oscillations, control in rotor speed and generator flux during and after fault. The fluctuations in DC bus voltage across capacitor are also controlled using proposed EFOC technique. The system performance with phase-A over voltage and under-voltage with above controllers and EFOC technique are analyzed using simulation studies.