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Dynamic Processes and Active Power Control of Hydropower Plants
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)ORCID iD: 0000-0003-1638-0792
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Hydro-electricity plays an important role in the safe, stable and efficient operation of electric power systems. Frequency stability of power systems refers to the ability to maintain steady frequency following a severe system upset resulting in a significant imbalance between generation and load. In order to suppress power grid frequency fluctuations, generating units change their power output automatically according to the change of grid frequency, to make the active power balanced again. This is the primary frequency control (PFC). PFC of electrical power grids is commonly performed by units in hydropower plants (HPPs), because of the great rapidity and amplitude of their power regulation.

A hydropower generation system is a complex nonlinear power system including hydraulic, mechanical, electrical and magnetic subsystems. Nowadays, the size of HPPs and the structure complexity of systems have been increasing, especially in China. The proportion of electricity generated by intermittent renewable energy sources have also been growing. Therefore, the performance of HPPs in terms of frequency control is more and more important. The research on control strategies and dynamic processes of HPPs is of great importance. The frequency stability of hydropower units is a critical factor of power system security and power quality. The power response time for evaluating the frequency regulation quality, is also a key indicator.

In recent years, there is a tendency that the new turbines experience fatigue to a greater extent than what seem to be the case for new runners decades ago, due to more regulation movements caused by increasingly more integration of intermittent renewable energy sources. In some countries, as in Sweden, PFC is a service that the transmission system operator buys from the power producers. In other countries, as in Norway and China, there is also an obligation for the producers to deliver this service, free of charge. However, there are costs related to this, e.g. due to design constraints and auxiliary equipment when purchasing a new unit or system, and due to wear and tear which affects the expected life time and maintenance intervals. Hence the specific research on wear and tear of hydro units due to PFC is exceedingly necessary. 

Place, publisher, year, edition, pages
Uppsala: Institutionen för teknikvetenskaper; Elektricitetslära , 2015. , 53 p.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-262768OAI: oai:DiVA.org:uu-262768DiVA: diva2:855346
Presentation
2015-10-19, Polhemsalen, Ångströmlaboratoriet (Ång/10134), Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2015-10-14 Created: 2015-09-20 Last updated: 2015-10-14Bibliographically approved
List of papers
1. Response time for primary frequency control of hydroelectric generating unit
Open this publication in new window or tab >>Response time for primary frequency control of hydroelectric generating unit
2016 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 74, 16-24 p.Article in journal (Refereed) Published
Abstract [en]

For evaluating the power quality in primary frequency control for hydroelectric generating units, the power response time is an indicator which is of main concern to the power grid. The aim of this paper is to build a suitable model for conducting reliable simulation and to investigate the general rules for controlling the power response time. Two huge hydropower plants with surge tank from China and Sweden are applied in the simulation of a step test of primary frequency control, and the result is validated with data from full scale measurements. From the analytical aspect, this paper deduces a time domain solution for guide vane opening response and a response time formula, of which the main variables are governor parameters. Then the factors which cause the time difference, between the power response time and the analytical response time of opening, are investigated from aspects of both regulation and water way system. It is demonstrated that the formula can help to predict the power response and supply a flexible guidance of parameter tuning, especially for a hydropower plant without surge tank.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-259529 (URN)10.1016/j.ijepes.2015.07.003 (DOI)000362309100003 ()
Funder
StandUp
Available from: 2015-08-07 Created: 2015-08-07 Last updated: 2017-12-04Bibliographically approved
2. Frequency Stability of Isolated Hydropower Plant with Surge Tank Under Different Turbine Control Modes
Open this publication in new window or tab >>Frequency Stability of Isolated Hydropower Plant with Surge Tank Under Different Turbine Control Modes
2015 (English)In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 43, no 15, 1707-1716 p.Article in journal (Refereed) Published
Abstract [en]

Currently, the Thoma criterion is often violated to diminish the cross-section of the surge tank; therefore, the surge fluctuation is aggravated and the frequency stability becomes more deteriorative. The focus of this article is on stabilizing the low-frequency oscillation of an isolated hydropower plant caused by surge fluctuation. From a new perspective of hydropower plant operation mode, frequency stability under power control is investigated and compared with frequency control by adopting the Hurwitz criterion and numerical simulation. In a theoretical derivation, the governor equations of frequency control and power control are introduced to the mathematical model. For numerical simulation, a governor model with a control mode switch-over function is built. The frequency oscillations under frequency control, power control, and control mode switch-over are simulated and investigated, respectively, with different governor parameters and operation cases. The result shows that the power control has a better performance on frequency stability at the expense of rapidity compared with the frequency control. Other recommendations regarding worst operation cases and choice of control modes are also developed.

National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-260774 (URN)10.1080/15325008.2015.1049722 (DOI)000359869100003 ()
Available from: 2015-08-24 Created: 2015-08-24 Last updated: 2017-12-04Bibliographically approved
3. A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
Open this publication in new window or tab >>A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
Show others...
2015 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 9, 10260-10275 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a mathematical model of hydro power units, especially the governor system model for different operating conditions, based on the basic version of the software TOPSYS. The mathematical model consists of eight turbine equations, one generator equation, and one governor equation, which are solved for ten unknown variables. The generator and governor equations, which are different under various operating conditions, are presented and discussed in detail. All the essential non-linear factors in the governor system (dead-zone, saturation, rate limiting, and backlash) are also considered. Case studies are conducted based on one Swedish hydro power plant (HPP) and three Chinese plants. The simulation and on-site measurements are compared for start-up, no-load operation, normal operation, and load rejection in different control modes (frequency, opening, and power feedback). The main error in each simulation is also discussed in detail. As a result, the model application is proved trustworthy for simulating different physical quantities of the unit (e.g., guide vane opening, active power, rotation speed, and pressures at volute and draft tube). The model has already been applied effectively in consultant analyses and scientific studies.

National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-262746 (URN)10.3390/en80910260 (DOI)000362553000064 ()
Note

Correction in: Energies 9(6) Article number: 477 DOI: 10.3390/en9060477

Available from: 2015-09-18 Created: 2015-09-18 Last updated: 2017-12-05Bibliographically approved
4. Wear and tear on hydro power turbines: influence from primary frequency control
Open this publication in new window or tab >>Wear and tear on hydro power turbines: influence from primary frequency control
Show others...
2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 87, 88-95 p.Article in journal (Refereed) Published
Abstract [en]

Nowadays the importance and need of primary frequency control of hydro power units are significantly increasing, because of the greater proportion of intermittent renewable energy sources and more complex structure of power systems. It brings a problem of increasing wear and tear of turbines. This paper studies this problem by applying numerical simulation and concise theoretical derivation, from the point view of regulation and control. Governor models under opening and power feedback mode are built and validated by measurement data. The core index, guide vane movement, is analyzed based on ideal sinusoidal frequency input and real frequency records. The results show the influences on wear and tear of different factors, e.g. governor parameters, power feedback mode and nonlinear governor factors.

National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-262747 (URN)10.1016/j.renene.2015.10.009 (DOI)000367759500008 ()
Available from: 2015-09-18 Created: 2015-09-18 Last updated: 2017-12-04Bibliographically approved
5. Wear reduction for hydro power turbines considering frequency quality of power systems: a study on controller filters
Open this publication in new window or tab >>Wear reduction for hydro power turbines considering frequency quality of power systems: a study on controller filters
Show others...
2017 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 32, no 2, 1191-1201 p.Article in journal (Refereed) Published
Abstract [en]

Nowadays, the wear and tear of hydropower turbines is increasing, due to more regulation movements caused by the increasing integration of intermittent renewable energy sources. In this paper, a controller filter is proposed as a solution to the tradeoff between reducing the wear of turbines and maintaining the regulation performance and thereby the frequency quality of the power systems. The widely used dead zone is compared with a floating dead zone and a linear filter, by time-domain simulation and frequency-domain analysis. Simulink models are built and compared with onsite measurement. Then, the time-domain simulation is used to investigate the guide vane movement, the load disturbance and the power system frequency, based on a one-day grid frequency datameasured in this study. In the theoretical analysis, the describing functions method and the Nyquist criterion are adopted to examine the stability of the system with different filters. The results show that the floating dead zone, especially the one after the controller, has a better performance than the dead zone on both the wear reduction and frequency quality. The linear filter has a relatively weak impact on both guide vane movements and the frequency quality. Other related conclusion and understandings are also obtained.

National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-262748 (URN)10.1109/TPWRS.2016.2590504 (DOI)000395865900033 ()
Available from: 2015-09-18 Created: 2015-09-18 Last updated: 2017-04-27Bibliographically approved

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