Rotor Current Oriented Control with Efficiency Investigation of a Standalone DFIG with Diode-Reactified DC Output

This paper presents a novel rotor current-oriented control concept and simulation results for a small-scale 7.5 kW DFIG system used in standalone applications. The system incorporates a specialized transformer with star and delta connections on the secondary side connected to a 12-pulse rectifier. The primary side of the transformer is connected to the DFIG stator windings. For DFIG rotor-side converter a Rotor Current-Oriented Control strategy is employed, where the dq- axis reference frame rotates with the rotor current's speed (rotor field speed in steady state). By choosing the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{qr}=0$</tex> the cross-coupling effect is minimized for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{dr}$</tex>. This strategy requires only rotor current measurements, dc-link voltage, and rotor speed for implementation. The system's performance is analyzed during start-up, steady-state, and dynamic conditions under various loading scenarios. Furthermore, a comprehensive investigation into system efficiency is conducted, considering different rotor (wind) speeds, load conditions, and stator frequencies of the DFIG.