Analysis of Dynamic Behaviour of Electric Power Systems with Large Amount of Wind Power

Vladislav Akhmatov

Research output: Book/ReportPh.D. thesis

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The Industrial Ph.D. project "Analysis of dynamic behaviour of electric power systems with large amount of wind power" has been started by the Danish power distribution company NESA because wind power penetration into the Danish power grid has rapidly increased. The project was started ultimo 199 e.g. four year before commissioning of the large offshore windfarm ad Rødsand/Nysted should take place in eastern Denmark. The project should build-up the know-how about (i) representation of existing wind turbine concepts in the dynamic simulation tools, (ii) grid-connection of a large amount of wind power and (iii) maintaining of short-term (transient) voltage stability. The main goal of this project has been to answer the following question: what would happen in the power grid with a large amount of wind power when a three-phase, short-circuit fault has occured in the transmission power network? The project has been a pioneering work in the area of dynamic modelling of wind turbines in electric power supply. At the project start, the fixed-speed wind turbines equipped with conventional asynchronous generators were the most common wind turbine concept in Denmark. During the last three years, the wind turbines equipped with frequency converters and power electronics have become represented in a number of large wind turbine sites in Denmark and abroad. At the project start, the existing dynamic simulation tools did not contain models of wind turbines of sufficient complexity and accuracy to be used in investigations of short-term coltage stability. Therefore this project has focused on representation of the four main concepts in dynamic simulation tools:

1) Fixed-speed wind turbines equipped with no-load compensated induction generators, which is the so-called Danish concept. Those can be either fixed-pitch or with blade-angle control.
2) Pitch-controlled wind turbines equipped with doubly-outage induction generators and variable rotor resistance control.
3) Variable-speed, pitch-controlled wind turbines equipped with doubly-fed induction generators abd partial-load frequency converters.
4) Variable-speed, pitch-controlled wind turbines equipped with direct-driven, multi-pole synchronous generators and frequency converters. Here, the model is described in case of permanent magnet generators.

The dynamic wind turbine models of all the four wind turbine concepts have been applied to investigate transient voltage stabilityand suggest uninterrupted operation (ride-through) features. The main investigations have been carried out with use of the model of a large (offshore) wind farm consisting of eighty wind turbines. Especially, it has focused on the Dansih concept since this has still been the most common concept in Denmark. Consequences of the incorporation of a large amount of wind power and local combined heat-power units have been investigated with use of a detailed and sufficiently realistic model of a large power network. Here, it has been distinguished between (i) local sites feeding into the local distribution networks and (ii) large wind farms connected to the transmission power networks and assigned to the technical specifications of the transmission system operator. Considerations of representing the local generation units and their protection have been explained. The investigations have been carried out with respect to the following issues.

1) When the wind turbines in the large wind farms have been (i) fixed-speed active-stall controlled and equipped with induction generators or (ii) variable-speed pitch-controlled and equipped with doubly-fed induction generators and partial-load frequency converters.
2) Access of the connection point of the large wind farm to (i) a strong power network or (ii) a weak power network.

Accessing a connection point in a strong power netowrk has been found favourable to maintain (i) short-term voltage stability and (ii) uninterrupted operation of the large wind farms. Operation of the large wind farms, especially the frequency converters of variable-speed wind turbines, could be affected by weak power grids and dynamic behaviour of local generation units at transient events.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages270
ISBN (Print)87-91184-18-5
Publication statusPublished - 2003

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