Industrial PhD programme
by Thyge Knüppel
Study# s021711
Period
October 2008 to June 2012
Supervisors
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
The key objective is the development of a generic-level aggregated wind turbine small-signal stability model of the Siemens Wind Power (SWP) Variable Speed wind turbine, e.g. the wind turbine using a full-rating power-electronics converter. The transfer functions of the wind turbine controllers are examined and evaluated for their purpose for small-signal stability analyses as well as a generic-level representation. 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. It is desired that the developed model is implemented into and work with the small-signal stability module of Siemens PTI PSS/E or DIgSILENT PowerFactory. The developed generic-level model will be evaluated against validated, transient reduced order models of the wind turbines of SWP.
The developed generic-level model will be applied on realistic power system models of the National Grid UK (NGT) for evaluation of the model performance and for determination of the eigenvalues and eigenvectors of the simplified NGT power system including wind farms 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 exposed, appropriate solutions to reduce or eliminate the undesired oscillatory behavior should be suggested and evaluated within the generic-level modeling technique.
Methods
The three methods, which primarily will be applied in this project, are theoretical calculations, computer modeling, and power system simulations. Theoretical calculations are a suitable method during the study of the wind turbines and wind farms due to identify the needed and sufficiently control systems for small-signal stability models. When the required control systems are defined and described, the theoretical calculations will be transferred and implemented in computer models. The proposed simulation models are then implemented in the simulation tool of the project and validated by simulations against SWP validated time-domain models of the wind turbines and large wind farms. The generated simulation models of the wind turbines and wind farm system will then be applied in the simulations of complex power systems with heavy generation from large wind farms and different operation conditions of the conventional power plants, PSSs, consumption centers, grid conditions etc. The power system simulations are needed to include all significant small signal stability phenomena in the power systems and in particular the interaction between the large wind farms and the power system.
2008-10-21 tk |