The Effect of Variable Speed Wind Turbines on the Operation of Weak Distribution Networks

This paper analyses the repercussions from the connection of wind parks (WP) on the operation of weak electric distribution systems, based on simulation results. The effects on the voltage profile caused by variable-speed (VS) wind turbines (WT) are compared to the effects caused by fixed speed (FS) WTs. Both types of WT are assumed to be equipped with asynchronous machines. In the VS mode of operation, a voltage source converter cascade is used employing field-oriented control for the generator-side converter and three independent hysteresis controllers for the grid-side converter. The distribution system studied is an actual feeder located in a rural area at the southeastern part of mainland Greece. For the simulation of the WP and the grid, a library of WTs and electrical grid components was developed. Using the developed simulation tool, two cases concerning high and low wind speed are studied. General conclusions are drawn concerning the voltage fluctuations, harmonic content, and the penetration of harmonics through the network The advantages of the studied VS operation scheme are confirmed, and the possible increase in the installed capacity of the WP over the FS mode, maintaining the same power quality standards, is estimated.