Advanced simulation of windmills in the electric power supply

An advanced model of a grid-connected windmill is set up where the windmill is a complex electro-mechanical system. The windmill model is implemented as a standardised component in the dynamic simulation tool, PSS/E, which makes it possible to investigate dynamic behaviour of grid-connected windmills as a part of realistic electrical grid models. This means an arbitrary number of wind farms or single windmills within an arbitrary network configuration. The windmill model may be applied to the study of electric power system stability and of power quality as well. It is found that a grid-connected windmill operates as a low-pass filter, whereby the two following observations are made: (1) interaction between the electrical grid and the mechanical systems of grid-connected windmills is given by a low frequency oscillation as the result of disturbances in the electric grid; (2) flicker, which is commonly explained by the dynamic wind variation, may also be caused by mechanical eigenswings in the windmill mechanical construction.