Integrated supervisory backstepping control and proportional harmonic compensation for DFIG-based wind farms under grid pollution

This paper proposes a supervisory control framework for a 6-MW wind farm (WF) comprising four 1.5-MW doubly fed induction generator (DFIG)-based wind turbines (WTs) to improve power quality and mitigate electrical and mechanical stresses under grid-pollution conditions. A backstepping control (BC) strategy is implemented at each WT to regulate active and reactive power while enabling active harmonic compensation through the existing power-electronic converters. A proportional allocation algorithm coordinates the compensation effort among the available WTs according to the load-current magnitude, thereby allowing partial or full-WF harmonic compensation depending on the operating condition. MATLAB/Simulink simulations under variable wind speeds, with an average wind speed of approximately 8.2 m/s, demonstrate accurate tracking of the WF-level active and reactive power references, with steady-state errors below 1.4%. Under nonlinear-load conditions, the proposed compensation strategy reduces the grid-current total harmonic distortion (THD) from 43.02% to 1.37% and from 33.16% to 1.33%, corresponding to reductions of approximately 96.8154% and 95.9891%, while improving the power factor from 0.78 lagging to 0.998. In addition, the rotor-circuit current ripple and electromagnetic torque ripple are reduced by 42% and 37%, respectively, indicating reduced electrical and mechanical stress on the DFIG-based WTs. These results demonstrate that the proposed supervisory and BC-based compensation framework can simultaneously achieve effective power regulation, harmonic mitigation, and stress reduction without requiring dedicated additional active-filter converters.