Triple-branch structure design and parameter optimization for supplementary damping controller of DFIG to suppress angular oscillation and reduce phase-locking error of PLL

The supplementary damping controller (SDC) in the doubly fed induction generator (DFIG) is to suppress the angular oscillations among synchronous generators (SGs). Due to the phase-locking error, the coupling between the SDC and the phase-locked loop (PLL) weakens the suppression effect. This paper proposes a novel triple-branch SDC (TB-SDC) and two-stage optimization to reduce the phase locking error and suppress the angular oscillation. The originalities are, (1) An analytical model to describe the coupling between the SDC and the PLL considering the phase locking error is newly proposed. (2) A triple-branch SDC with an additional input from the PLL is newly proposed to suppress the angular oscillation while reducing the phase-locking error. (3) Based on 2-norm of the trajectory sensitivities, two evaluation indices are newly defined to quantify the impact of the TB-SDC parameters on the oscillation and the phase locking error, and select the critical parameters. (4) A two-stage optimization model is proposed to adjust the parameters of the TB-SDC, where the 1st step is to reduce the phase locking error and decide the input signals of the SDC-P and the SDC-Q, and the 2nd step is to improve the suppression effect and reduce the phase locking error. The simulation results verify the impact of the coupling, and validate the effectiveness and adaptability of the TB-SDC and optimization. © 2017 Elsevier Inc. All rights reserved.