Grid-connected Wide-band Oscillation Analysis of DFIG-based Wind Turbine Based on Polynomial Approximation of All Eigenvalue Trajectories

Power systems with high penetration of renewable energy oscillate in a wide range of frequencies, and the damping and oscillation frequencies are notably affected by system parameters. To avoid the system instability caused by the change of operation parameters and the improper setting of controller parameters, it is urgent to quantify the relationship between the system oscillation modes and parameters and analyze the hidden mechanism behind them. A method for calculating the all eigenvalue trajectories based on polynomial approximation is proposed. Through a series of linear combinations of polynomial basis functions, the complex implicit functional relationship between all eigenvalues and multiple parameters of the system is accurately described, and the explicit expression of the changing eigenvalue trajectories is obtained. The detailed electromagnetic transient modeling of the doubly-fed induction generator (DFIG)-based wind turbine grid-connected system is carried out, and the accuracy of the proposed method is verified by taking the single-machine infinite system and the wind-thermal-bundled system as examples. The influence of the important parameters, such as series-compensated capacitor, rotor-side controller proportion and integral coefficient, on the key modes of the DFIG-based wind turbine grid-connected system, such as sub-synchronous oscillation and low-frequency oscillation, is analyzed by using the explicit expression of eigenvalue trajectories. © 2023 Automation of Electric Power Systems Press. All rights reserved.