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Design tool for prediction of flicker from wind turbines


Four generator models of increasing levels of precision were developed for fixed speed turbines and incorporated in the code. A model for variable speed generators was also incorporated. Since active and reactive power can be rapidly controlled with modern variable speed drives, a relatively simple model of the dynamics is sufficient in this case. A simple network model has been incorporated into the software package, allowing the characteristics of the distribution network connecting the turbines on a wind farm to be specified as well as the connection to the wider network. A detailed dynamic load flow model was used to study the effect of various network configurations with embedded static and dynamic loads on the flicker effects of a wind turbine or wind farm. This has shown that the flicker effect is generally reduced by the presence of consumer loads. The reduction is small for static loads, and rather more significant in the case of dynamic loads. It is safe to ignore consumer loads, as this will produce a conservative estimate of the flicker. Flicker measurements on two commercial 1 MW turbines were undertaken, and then used to carry out a validation of the models. The results showed that the flicker generated by the turbines was well predicted, for a range of different network angles. Furthermore, it was found that the flicker during normal operation was dominated by relatively low frequency power variations, mainly at blade passing frequency, and that the more detailed dynamic models of the generator were little better than the simple models. The wind turbine design tool, Bladed, now extended to allow flicker evaluation at the design stage, is of particular value to wind turbine designers and manufacturers. However, the need was also recognised for a simpler software tool aimed at utilities and wind farm developers, which they can use to assess the flicker implications of installing one or more wind turbines with known flicker characteristics onto a particular network. This project has defined the scope of such a software tool, and developed this into a complete functional specification. The specification also includes provision for evaluating the effect of turbine starts and stops. Although the software itself was not written during the course of the project, the specification is sufficiently detailed, including all the necessary equations, to allow such a software package to be written.