Robust control scheme for the braking chopper of PMSG-based wind turbines–A comparative assessment

Abstract

Despite the grid-integration of permanent magnet synchronous generator (PMSG) wind energy conversion systems (WECS), utilities are facing challenges that are hindering wind penetration growth. Grid-side voltage sags at the point of common coupling (PCC) are considered as one of such uncontested issues. Due to imbalance in back-to-back (BTB) converter’s dc-link input-output powers, its capacitor and power electronics are highly susceptible to PCC voltage sags. Hence, provision of wind farm grid-codes (GC) for supporting grid operations is imperative and development of strategies for realizing low-voltage ride-through capability in WECSs have emerged as an integral GC requirement. One strategy is to install a braking chopper (BC) across the dc-link. This study presents (a) an overview of conventional BC control methods, (b) design of a robust BC controller for PMSG-based WECSs, and (c) comparative performance assessment of (b) with (a) for PMSG-based WECS operations during normal and grid fault conditions. The robust BC controller takes advantage of the sliding mode method to control BC and to determine the grid-side converter active power reference set-point. This nonlinear control scheme ensures proper execution of GCs and offers reliable protection to the dc-link. Chattering phenomenon and reaching-time is reduced significantly, by further adoption of exponential reaching law. In addition to its robustness, a prominent feature of this BC controller is its applicability to present BTB control structures. The simulation results reflect on effectuality and robustness of the proposed BC controller in comparison to conventional BC control strategies.