Natural flux minimization technique for DFIG with grid unbalance

Natural flux minimisation technique for enhanced operation of doubly-fed induction generator

Abstract: This paper presents a robust reference current generation technique for rotor side converter (RSC) control of a grid connected doubly-fed induction generator (DFIG) to eliminate the natural flux revolving in air gap implemented in the positive d–q reference frame. The objective of the scheme is to enhance the performance of the generator under grid unbalance by eliminating the double frequency content in the d–q axes stator flux without using double vector control. RSC is employed to minimise the oscillations in stator flux and consequently in power and torque while grid side converter minimises the dc-link voltage ripples and maintains zero grid reactive power. It is revealed that, minimising the stator flux pulsations as a single control target enables minimisation of unbalance in stator and grid currents and pulsations in torque, power and dc-link voltage. Further, the simplicity in implementation and computation of reference currents and rotor flux, and robustness under parameter variations render the scheme attractive. The performance of DFIG is investigated through numerical simulations in PSCAD/EMTDC for a 250 kW DFIG system and further, through experimental results for a 2.3 kW DFIG test setup. The results show the enhanced performance of DFIG with the proposed scheme.