This paper studies the applicability of second order sliding mode control strategies to a wind energy conversion system aiming to optimise its power conversion efficiency. Four different controllers are designed and analysed, based on the "sub-optimal", "twisting", "super-twisting" and "with a prescribed law of variation" algorithms, which present finite-time convergence, robustness, chattering and mechanical stress reduction, and are of quite simple online operation and implementation. Representative simulation results are shown, using a complete model of the system under realistic operating conditions, where the performance of the controlled system can be appreciated for each of the controllers and some comparisons can be made. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.