Abstract

This paper describes a modeling and control of a variable speed squirrel-cage induction generator with back to back power electronics converters used in variable speed wind energy conversion system. The power electronics is composed of the generator side converter (GSC) coupling to the grid connected converter (GCC) together via DC bus capacitor. The generator side converter (GSC) is controlled by direct torque control (DTC).The control objectives of the generator side converter (GSC) are to optimize the energy capture from the wind turbine and supply the magnetic flux to the squirrel cage induction generator (SCIG). The GCC converter delivering the energy from the machine side to the utility grid regulated the DC link voltage and the power flows to the grid. The basic idea of P-Q control method used is based on voltage vector oriented control and decoupling in the d-q axis reference frame. The complete control system has been developed; analyzed and validated by Matlab simulation. The two operating modes of GCC converter and the performance under active and reactive power variations are also presented. The low voltage ride-through (LVRT) performances of the variable speed wind turbine (VSWT) is tested, when the grid voltage has dropped to a very low value. Simulation results confirmed the effectiveness of the proposed control strategies and their capability under different case study.

Key words: Variable speed wind turbine, converter control, power quality, back to back converters, vector oriented control.