Robust control of the variable speed wind turbines in the presence of uncertainties: A comparison between H∞ and PID controllers

Abstract

To achieve a cost-effective and reliable use of wind power generation, advanced control techniques are required. In this paper, the application of two control strategies for the improvement of wind turbine power output is investigated in the presence of model/environmental uncertainties. Rotational speed of the wind turbine and consequently its power output are controlled via manipulation of blades pitch angle (at a constant generator torque). First, the classical PID controller is designed based on root locus analysis while in the second scheme, an H∞-robust controller is designed via μ-synthesis based on DK-iteration algorithm. Performance of the two controllers in tracking of the desired power outputs (including the step, sequence of steps, ramp and sinusoidal signals) is compared. Results are presented for various profiles of the wind speed. It is shown that H∞ controller guarantees the robust stability and performance of the uncertain systems. Moreover, when H∞ controller is implemented, less oscillatory behaviour is observed for both of the output power and pitch angles (which are desired for the electric grid and actuating systems, respectively).