Since the mid eighties, a large number of wind turbines and distributed combined heat and power plants (CHPs) have been connected to the Danish power system. Especially in the Western part, comprising Jutland and Funen, the penetration is high compared to the load demand. In some periods the wind power alone can cover the entire load demand. The objective of the work is to investigate the influence of wind power and distributed combined heat and power production on the operation of the distribution systems. Where other projects have focused on the modeling and control of the generators and prime movers, the focus of this project is on the operation of an entire distribution system with several wind farms and CHPs. Firstly, the subject of allocation of power system losses in a distribution system with distributed generation is treated. A new approach to loss allocation based on current injections and an impedance matrix is presented. The formulation can be used for statistical analysis of the losses based on linear regression or estimates of covariances between production and load. Secondly, the problem of short term voltage stability in networks with high penetration of DG is assessed. The focus is on the representation of the network during and after a fault as a Thevenin equivalent voltage and impedance. The influence of adjacent synchronous generators, Danish concept wind turbines, SVCs and STATCOMs on the Thevenin parameters have been investigated. Thirdly, the problem of voltage and reactive power control is investigated. Special focus is on the constraints for active and reactive power injection which are imposed by the voltage magnitude limits. Finally, a case study of the distribution system of Brønderslev in Northern Jutland is presented. A supervisory control and data acquisition (SCADA) system with the possibility of logging measurements and a steady state load flow model are available for the system. The measurements have been integrated with the load flow model, and a series of load flow simulations with 15 minutes time steps has been performed for a 10 months period.
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Sørensen, Poul Ejnar, Lund, Per, Nielsen, Arne Hejde
Technical University of Denmark, Department of Electrical Engineering, 2008