Poul Ejnar Sørensen

Wind farm modelling for power quality

In this paper, the power quality impact of wind farms on the power system is investigated. A model is established for the wind farm Hagesholm (Denmark). This wind farm consists of six active stall controlled wind turbines from NEG-Micon with 2 MW rated power. The wind turbines are connected through two feeders to the 10kV busbar in a 50/10kV substation. The simulation model, implemented in the dedicated power system simulation tool DIgSILENT, is used in the first place to simulate the behaviour of the wind farm during normal operation of the wind farm. The model comprises a grid model, six almost identical wind turbine models, where electric, mechanic and aerodynamic aspects are included, and a model for the wind speed. The described model can be used for assessment of power quality, control strategies and behaviour in the event of grid faults. In this paper, the ability of the model to predict power quality is investigated. The simulations are used to compute power quality characteristics of a wind turbine, i.e. maximum power, reactive power consumption and flicker emission. The applied computation methods are reflecting the international power quality standards of wind turbine IEC 61400-21. The computed power quality characteristics are compared to measured power quality characteristics, determined by the same computation methods.

Power Quality Issues on Wind Power Installations in Denmark

This paper introduces the power quality issues of wind power installations in a historic perspective, as the development from a few small wind turbines connected directly to the low voltage grid, to the present system with high penetration on the medium voltage distribution grids and two large offshore wind farms connected at transmission level. In this perspective, the power quality issues are divided into local issues particularly related to the voltage quality in the distribution systems and global issues related to the power system control and stability. Power quality characteristics of wind turbines and wind farms are described according to national and international standards, and measurements from wind farms are presented.

Grid connection of active stall wind farms using a VSC based DC transmission system

Currently, there is an increasing trend to connect large MW wind farms to the transmission system. Requirements that focus on the influence of the farms on the grid stability and power quality, and on the control capabilities of wind farms have already been established. The main trends of modern wind turbines/farms are clearly the variable speed operation and a grid connection through a power electronic interface, especially using doubly fed induction generators. Using power electronics the control capabilities of these wind turbines/farms are extended and thus the grid requirements are fulfilled. However, the traditional squirrel-cage generators based wind turbines/wind farms directly connected to the grid have less control capabilities. These wind turbines/farms cannot regulate their production and contribute to power system stability. A DC transmission system for connection of the active stall wind farms to the grid can provide these features and also maximize the produced power especially at low wind speeds by using variable voltage/frequency for the wind farm. The focus in this paper is in studying the operation for the active stall wind farms using a voltage source converter based DC transmission system as well as the power quality issues of the generated power

Large-scale wind generation simulations: From the analysis of current installations to modelling the future

Modelling and understanding variability in wind generation will be increasingly important in the future with growing shares of wind power in energy systems. Crucially, the modelling needs to be extended to future scenarios, also considering the expected technological development of installations. Reanalysis data is often used in large-scale simulations to model the variability in wind. Wind power plant (WPP) data is also required, but may be only partially available. In this paper, a methodology for estimating missing hub height data is presented, using multiple regression models and large WPP and turbine datasets. The resulting estimated hub heights are presented on a pan-European level, and a scenario with capacity factor development until 2050 for two example countries is shown in detail.