Reduced Model and Control of Diode-Interfaced Offshore Wind Farms with DC Power Systems

This paper deals with dynamic modelling and control of wind power units in an offshore wind farm with a dc system, consisting of permanent magnet synchronous generators, diode-bridge rectifiers and dc/dc converters. Such an integration offers a robust structure well-suited for offshore wind power applications. A simplified yet accurate model for a wind power unit is proposed and validated for the design of controller to capture the maximum wind power of the unit. The model is developed based on singular perturbation theory in which only slow dynamics of the system are considered and the fast dynamics are represented with a static model. A control design procedure for wind farm using the reduced model is also presented. The performance of the controller has been investigated based on sensitivity analysis and time-domain simulation of a study system including series connected units and a dc system that are modelled with full dynamics. The results of analysis show an accurate tracking performance with less than 1% error when the wind speed varies about 25% of its rated value.