Industrial PhD programme
by Thyge Knüppel
Study no s021711
PhD defence
Date & time: Monday, 3 December 2012, at 13:00
Location: DTU, Building 308, Auditorium 11
Examiners:
Associate Professor Arne Hejde Nielsen, DTU Elektro
Professor Göran Andersson, ETH, Zürich
Dr. Markus Pöller, M.P.E.GmbH
Chairperson at defence:
Associate Professor Bogi Bech Jensen, DTU Elektro
Period
October 2008-10-01 to December 2012
Supervisors
Professor Jacob Østergaard, CEE, DTU Electrical Engineering
PhD Kim Høj Jensen, Siemens Wind Power
PhD Jørgen Nygård Nielsen, Siemens Wind Power
Dr. Andrew Dixon, National Grid, UK
In cooperation with
Siemens Wind Power
Technical University of Denmark
Danish Agency for Science Technology and Innovation
National Grid, UK
Background of the project
In weakly connected large power systems with synchronous generators, there is an inherent risk of power system oscillations and oscillatory instability. To reduce and control the power system oscillations, Power System Stabilizers (PSS) are applied as part of the dynamic control of the conventional power plants. The control settings are determined from small-signal stability analyses using well-described routines and modules of commercially available simulation programs.
Large wind farms equipped with power-electronics-converter-based wind turbines and Wind Farm Controllers (WFC) make these power park modules comply with the same grid code requirements as large power plants based on synchronous generators. However, as opposed to the central power plants, the wind farms are often commissioned in remote, weak areas of the power systems. The present and scheduled extension of renewable energy sources will entail a gradual outsourcing of the conventional power plants and PSSs and such maybe introduce an enhanced risk of power system oscillations and oscillatory instability. Such oscillations may also be started between the remaining conventional power plants in-service and the large wind farms due to lack of damping in the system.
At present, there are no models of WFC or the wind turbines using power-electronics converters as can be applied with the small-signal stability modules of commercially available simulation programs. The interaction of the wind farms and their WFC with large power systems in terms of small-signal stability has so far remained an unexplored area, although the issue has been discussed by Transmission System Operators due to the rapid grid-integration of wind power in many countries. Therefore, it is of utmost importance to initiate the development of small signal stability models for the wind turbine and its control for small-signal stability analyses and get these new models tested and evaluated with results on realistic power systems.
Project contents
A key objective is the analysis of the properties of the WFC and the Siemens Wind Power Variable Speed wind turbine with respect to small-signal stability. The transfer functions of the wind turbine controllers and WFC are examined, and evaluated for their purpose for small-signal stability analyses. The generic-level small-signal stability properties are described and documented in block diagrams, such that a client user model can be implemented in commercially available power systems simulation tools, and preferably work with the small-signal stability module of Siemens PTI PSS/E or DIgSILENT PowerFactory.
The investigation of the impact on the small-signal stability properties will be applied on realistic power system models from the National Grid UK for evaluation of model performance. The analysis includes determination of the eigenvalues and eigenvectors of the simplified NGT power system including wind farms with WFCs and conventional power plants with PSSs. The investigations will be carried out for different operation scenarios of the power system with respect to consumption, and power generation units in service.
If the risk of power system oscillations or oscillatory instability is identified, appropriate solutions to reduce or eliminate the undesired oscillatory behavior should be suggested and evaluated. It is investigated if and how the wind farms can be controlled to actively contribute to the small-signal stability of the power system through modulation of the active and/or reactive power output of the wind turbines. When such stabilizing control is studied, it is essential to consider the distributed and modular characteristics of a wind farm. A stabilizing control is fundamentally different from the functions in the WFCs of today, and the mutual interaction between the wind turbines and between the wind turbine controllers need to be thoroughly investigated.
The key focus in this project is the technical aspects of the wind farm control and grid simulations, whereas all the legal aspects are left to the TSO and wind farm operators.
Links
ORBIT database