A fractional order sliding mode control-based topology to improve the transient stability of wind energy systems

Abstract

This paper proposes a control topology that integrates the robust performance of fractional order sliding mode control with the high charging/discharging rate and low maintenance requirements of super-capacitors to improve the transient stability of wind energy systems. The observer-based fractional-order sliding mode control (FOSMC) approach is designed to regulate the dc-link voltage and mitigate dynamic instabilities resulting from grid faults, matched and mismatched uncertainties and parameter variations. The super-capacitor, on the other hand, serves as an additional energy storage element that prevents dangerous current surges thereby stabilizing the power delivered to the grid. The proposed approach was validated using a DFIG-based wind energy system installed in a small-scale standalone power supply network. The obtained results confirmed the approach’s ability to effectively reduce current fault induced ripples and properly regulate the dc link voltage. They also revealed a remarkable reduction in the thermal stress of semiconductor junctions in the presence of grid faults and disturbances. A further comparison with a standard sliding mode control (SSMC) approach showed that the use of fractional calculus to formulate the FOSMC resulted in smoother control actions and reduced chattering effects compared to SSMC.