Sliding mode observer based position self-sensing control of a direct-drive PMSG wind turbine system fed by NPC converters

Information of rotor position and speed plays an crucial role in variable-speed wind energy conversion systems. Traditional sensors based position detection methods not only increase hardware complexity and system cost, but also face severe challenges on reliability caused by the disturbances from the varying weather and harsh operating conditions in wind energy generation sites. Thus, with the aim of eliminating position sensors and developing a reliable position self-sensing technique, this paper proposes a position self-sensing control method based on sliding mode observer for a 2 MW permanent magnet synchronous generator (PMSG) wind turbine system. In addition, a three-level neutral-point-clamped (NPC) back-to-back converter with space vector pulse width modulation (SVPWM) is developed for the full-scale power conversion, which has lower voltage stress on the switching devices and less harmonic distortion in the output voltage compared with those in traditional two-level power converters. Simulation analysis is carried out to verify the effectiveness of the proposed self-sensing method and the three-level SVPWM based back-to-back NPC converter. The simulation results soundly justified the feasibility of the proposed control scheme and power conversion strategy.