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Robust primary frequency control in a system dominated by hydropower
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Concerns about deteriorating quality of the Nordic grid frequency, including frequently occurring oscillations with a period of 40-90~s, has called for improved primary frequency control of the Nordic hydropower. In this paper, the parameters of the currently used PI controller with droop are optimised using a robust control approach. The trade-off between performance, actuator work and robustness is analysed in frequency domain and time domain, and the sensitivity to disturbances and model errors is discussed. It is found that the low-frequency oscillation of the system can be reduced by almost half if the parameters of the primary control are retuned.

Keyword [en]
Load frequency control, primary frequency control, hydraulic turbine, robust control, PID control
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-237795OAI: oai:DiVA.org:uu-237795DiVA: diva2:768925
Available from: 2014-12-05 Created: 2014-12-05 Last updated: 2015-10-08
In thesis
1. A hydropower perspective on flexibility demand and grid frequency control
Open this publication in new window or tab >>A hydropower perspective on flexibility demand and grid frequency control
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The production and consumption of electricity on the power grid has to balance at all times. Slow balancing, over days and weeks, is governed by the electricity market and carried out through production planning.  Fast balancing, within the operational hour, is carried out by hydropower plants operating in frequency control mode. The need of balancing power is expected to increase as more varying renewable energy production is connected to the grid, and the deregulated electricity market presents a challenge to the frequency control of the grid.

The first part of this thesis suggests a method to quantify the need for balancing or energy storage induced by varying renewable energy sources. It is found that for high shares of wind and solar power in the system, the energy storage need over a two-week horizon is almost 20% of the production.

The second and third part of the thesis focus on frequency control. In the second part, measurements from three Swedish hydropower plants are compared with the behaviour expected from commonly used power system analysis hydropower models. It is found that backlash in the guide vane and runner regulating mechanisms has a large impact on the frequency control performance of the plants.

In the third part of the thesis, the parameters of the primary frequency control in the Nordic grid are optimised with respect to performance, robustness and actuator work. It is found that retuning of the controller parameters can improve the performance and robustness, with a reasonable increase of the actuator work. A floating deadband in the controller is also discussed as a means to improve performance without increasing the actuator work.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2014. 57 p.
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352 ; 339-14L
Keyword
hydropower, frequency control, balancing
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-237798 (URN)
Presentation
2014-12-01, ITC1211, Uppsala, 14:00 (English)
Opponent
Supervisors
Available from: 2014-12-11 Created: 2014-12-05 Last updated: 2015-10-08Bibliographically approved

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