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This paper reports on the feasibility study performed to investigate the possibilities of connecting the 640-MW off-shore wind power farm, planned for Kriegers Flak 30km south of Trelleborg, to the E.ON 130-ky subtransmission system. The Kriegers Flak commissioning is planned for 2010. The aim of this study is to answer the question if such a connection is possible, and under what conditions; it is not meant as a design project. Following a general connection design discussion, the study comprises of three major parts: fault current calculations, load flow calculations, and dynamic simulations. The study shows that it is possible to connect such a large off-shore wind power farm to the 130-ky subtransmission system, but reinforcement concerning load currents during normal operation and fault currents have to be made. [ABSTRACT FROM AUTHOR]

Previous results concerning instability of the dc link in inverter drives fed from a dc grid or via a rectifier are extended. It is shown that rectifier-inverter drives equipped with small (film) dc-link capacitors may need active stabilization. The impact of limited bandwidth and switching frequency in the inverter-motor current control loop is considered, and recommendations for selection of the dc-link capacitor, the switching frequency, and the dc-link stabilization control law in relation to each other are given. This control law is incorporated in a field-weakening (to enhance voltage sag ride-through) current controller for which design recommendations are presented. [ABSTRACT FROM AUTHOR]

The response of the doubly fed induction generator (DFIG) wind turbine system to grid disturbances is simulated and verified experimentally. The results are compared to the response that a fixed-speed wind turbine would have given. A voltage sag to 80% (80% remaining voltage) is handled very well, which is not the case for a fixed-speed wind turbine. A second-order model for prediction of the response of DFIG wind turbines is derived, and its simulated performance is successfully verified experimentally. The power quality impact by the DFIG wind turbine system is measured and evaluated. Steady-state impact, such as flicker emission, reactive power, and harmonic emission, is measured and analyzed. It is found that the flicker emission is very low, the reactive power is close to zero in the whole operating range, and the current THD is always lower than 5%. [ABSTRACT FROM AUTHOR]

In this paper, different rotor current control methods are investigated with the objective of eliminating the influence of the back electromotive force (EMF), which is that of, in control terminology, a load disturbance, on the rotor current. It is found that the method that utilizes both feed-forward of the back EMF and so-called "active resistance" manages best to suppress the influence of the back EMF on the rotor current, particularly when voltage sags occur, of the investigated methods. This method also has the best stability properties. In addition it is found that this method also has the best robustness to parameter deviations. [ABSTRACT FROM AUTHOR]