Second-order sliding mode control of wind turbines to enhance the fault-ride through capability under unbalanced grid faults

• Main Authors: Tahir, Khalfallah, Allaoui, Tayeb, Denai, Mouloud, Mekhilef, Saad, Belfedal, Cheikh, Doumi, M'hamed
• Format: Article
• Published: John Wiley & Sons 2021
• Subjects: TK Electrical engineering. Electronics Nuclear engineering
• Online Access: http://eprints.um.edu.my/28514/

The integration of wind generation to the grid is growing rapidly across the world. As a result, grid operators have introduced the so-called grid codes (GC), which nowadays include a range of technical conditions and requirements, which wind generators must fulfill. Among these, the low-voltage ride through (LVRT) is a requirement for wind turbines to stay connected to the grid and continue to operate during the disturbance. In this study, a control structure, combining inertial kinetic energy storage with a crowbar circuit, is proposed to enhance the ride through capability of a wind turbine generator (WTG) based on a wound-field synchronous generator (WFSG) under unsymmetrical voltage dips. For the grid-side converter (GSC), a decoupled double synchronous reference frame (DDSRF) d-q current controller is used. Furthermore, a second-order sliding mode controller (SOSMC) with super-twisting (ST) algorithm is proposed for the GSC and the machine-side converter (MSC) to improve the response speed and achieve an accurate regulation of the dq-axis current components simultaneously. The main objectives of the GSC are to achieve a balanced, sinusoidal current and smooth the real and reactive powers to reduce the influence of the negative-sequence voltage. A series of simulations are presented to demonstrate the effectiveness of the proposed control scheme in improving the LVRT capability of the WFSG-driven wind turbine and the power quality of the system under unbalanced grid voltage conditions.