Fractional order PI controller for grid connected wind energy conversion system

This paper proposes control of a grid connected variable speed wind energy conversion using factional calculus. The global system contains a wind turbine emulator and PMSG connected to the grid via two back-to-back converters. The control system under study is composed of two parts, a current vector control with fractional order PI controller (FOPI) on the speed loop to ensure maximum power extraction and a direct power control (DPC) to guarantee a unity power factor. The fractional order PI controllers are designed using the isodamping feature, which desensitizes the phase frequency variations, by means a flat phase around a gain crossover frequency. This increases the robustness of a fractional order control system against uncertainties. The proposed control scheme improves the tracking performance and system robustness. To investigate the efficiency and the accuracy of the proposed controller, an experimental bench is built. The experimental results demonstrate the superiority of the proposed controller over integer order controllers by realizing maximum power extraction and improving the grid-side power factor for a wide range of wind speeds.