Virtual resistance-based fractional-order PI control strategy for sub-synchronous oscillation in doubly-fed wind turbines

Abstract

Aiming at the ineffective suppression results of sub-synchronous oscillation under grid connection of doubly-fed wind turbines process with traditional method,a virtual resistance-based fractional-order proportional integral (FOPI) control strategy is proposed. Firstly,the sub-synchronous oscillation mechanism of wind power systems is analyzed,and the grid-connected current of the wind turbine is selected as the input signal to design the sub-synchronous broadband current filter. To improve the electrical damping of the wind turbine system,a virtual resistance controller is constructed. After that,the influence of the integral order on the dynamic characteristics of current tracking is analyzed. Where the fractional integral operator is improved by employing Oustaloup algorithm,and the FOPI current control loop is reconstructed by choosing the grid-side converter's control equation as the bottom model. Then,the non-linear iterative weights and learning factors are introduced to improve the traditional gray wolf algorithm,as well as optimize the parameters of control policy. Finally,the simulation verification is carried out under Matlab/Simulink platform. The results show that the proposed strategy can suppress the sub-synchronous oscillation effectively under different compensation levels and exhibit strong robust stability.

Keywords

• virtual resistance
• doubly-fed wind farms
• sub-synchronous oscillation
• improved grey wolf optimizer algorithm
• fractional-order proportional integral (fopi)
• parameter optimization