Application of Fractional Calculus Theory to Robust Controller Design for Wind Turbine Generators

This paper presents a robust controller design method for wind turbine generators using the concepts of fractional calculus. It also compares features of fractional order control systems with those of classic integer order controllers. The proposed method uses isodamping feature, which desensitizes the phase-frequency variations about a gain crossover frequency. This increases the robustness of a fractional order control system against uncertainties. In conventional integer order control systems, realization of isodamping feature requires a controller with very high-order transfer function whereas a fractional order system can readily realize this feature in a compact form. The proposed method is applied to a study system consisting of a permanent magnet wind turbine generator. The test system investigates the tracking performance of the control system considering the backlash and aging phenomenon within the dynamic model of the wind turbine generator. The study results based on a time-domain simulation show the superior capabilities of fractional order controller compared with classic controllers in the presence of model uncertainties. It has been shown that the concept of fractional calculus can be used as a promising robust control approach for the future high performance feedback control systems with application to wind energy systems.