Nonlinear Control for Grid Connected Wind Energy System with Multilevel Inverter

This paper deals with the problem of interfacing a wind turbine generator with an electrical three phase grid in the presence of nonlinear loads. Wind systems are generally connected to the grid through an AC/DC inverter in the generator side, followed by a DC/AC converter in the grid side. In this work, the considered DC/AC converter is based on multilevel neutral point clamped topology, and will operates simultaneously as an interfacing system and as an active power filter. The control objective is threefold: (i) transferring the extracted active power from the wind turbine generator to the power grid; (ii) cancelling harmonic currents and reactive power absorbed by the nonlinear load; (iii) balancing capacitor voltages and regulating the DC link voltage. The first and second control aims will be achieved using the backstepping design technique. The third objective dealing with the DC link voltage regulator will be achieved with a sliding mode technical design. The performances of the proposed control system are formally analyzed using tools from Lyapunov's stability. Simulations show that the proposed controller achieved the listed objectives under widely varying load and wind speed profiles.