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A hydropower perspective on flexibility demand and grid frequency control
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)
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 [en]
hydropower, frequency control, balancing
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-237798OAI: oai:DiVA.org:uu-237798DiVA: diva2:768935
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
List of papers
1. Power system flexibility need induced by wind and solar power intermittency on time scales of 1-14 days
Open this publication in new window or tab >>Power system flexibility need induced by wind and solar power intermittency on time scales of 1-14 days
2015 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 83, 339-344 p.Article in journal (Refereed) Published
Abstract [en]

This article describes a method to assess the needed production flexibility to adapt the power system to the production from variable renewable energy sources such as wind power and photovoltaics over time horizons of 1-14 days. Load and production data from the German power system is used to quantify the flexibility need in terms of power and energy storage requirement due to higher shares of renewable energy (20-80%). It is found that with an 80% variable renewable energy share in the German system, the average power need from flexible sources decreases by 31 GW (59%) while the peak power need only decreases by 3 GW (4%). In terms of energy, the storage need over a two week horizon increases by 2.6 TWh, which is 14% of the average load per day. If the European plans for 100 GW wind power in the North Sea region are realised, this would mean an increase of the energy storage need in the region with 2.2 TWh over a two week horizon.

Keyword
Energy storage, wind power, solar power, dispatching, 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-237789 (URN)10.1016/j.renene.2015.04.048 (DOI)000358455100031 ()
Available from: 2014-12-05 Created: 2014-12-05 Last updated: 2017-12-05
2. Field Measurements and System Identification of Three Frequency Controlling Hydropower Plants
Open this publication in new window or tab >>Field Measurements and System Identification of Three Frequency Controlling Hydropower Plants
2015 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 30, no 3, 1061-1068 p.Article in journal (Refereed) Published
Abstract [en]

The dynamic behaviour of hydropower plants participating in primary frequency control is investigated in this paper through frequency response, step response and setpoint change tests on three Swedish hydropower plants. Grey-box system identification is used to estimate the parameters of simple linear models suitable for power system analysis and the major shortcomings of the linear models are discussed. It is found that frequency response tests with sinusoidal input signals give more reliable information about the dynamics of the plants than step response tests. It is also shown that backlash in the runner and guide vane regulating mechanisms are of great importance for the dynamic behaviour of the plants, and that the incremental gain from guide vane opening to power varies considerably with the operation point.

Keyword
hydropower, system identification, frequency control, field measurements
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-237793 (URN)10.1109/TEC.2015.2425915 (DOI)000360439300026 ()
Available from: 2014-12-05 Created: 2014-12-05 Last updated: 2017-12-05Bibliographically approved
3. Robust primary frequency control in a system dominated by hydropower
Open this publication in new window or tab >>Robust primary frequency control in a system dominated by 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
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:nbn:se:uu:diva-237795 (URN)
Available from: 2014-12-05 Created: 2014-12-05 Last updated: 2015-10-08

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