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Sundqvist, Per
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Publications (10 of 27) Show all publications
Saarinen, L., Norrlund, P., Yang, W. & Lundin, U. (2018). Allocation of Frequency Control Reserves and its Impact on Wear and Tear on a Hydropower Fleet. IEEE Transactions on Power Systems, 33(1), 430-439
Open this publication in new window or tab >>Allocation of Frequency Control Reserves and its Impact on Wear and Tear on a Hydropower Fleet
2018 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 1, p. 430-439Article in journal (Refereed) Published
Abstract [en]

Power systems are making a transition from purely technical, centrally planned systems to market based, decentralized systems. The need for balancing power and frequency control reserves are increasing, partially due to variable renewable production, which gives an opportunity for new incomes but also a challenge in terms of changed modes of operation with risk for reduced lifetime for controllable power plants. This paper investigates how the allocation of a sold volume of frequency control reserves within a large hydropower production fleet can affect the costs of providing primary and secondary reserves, in terms of its impact on wear and fatigue, production losses, and the quality of the delivered frequency control. The results show that for primary control, low static gain in the governors results in poor quality and a large amount of load cycles of the units. High static gain, on the other hand, increases the production losses. The control work of the fleet can be reduced by using a proper balance of primary and secondary control gain on each unit, although the intuitive results from linear models exaggerate this effect. Automatic secondary control improves the system frequency quality but also increases the wear.

Keywords
hydropower, frequency control, primary control, reserve allocation, wear and tear
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-308437 (URN)10.1109/TPWRS.2017.2702280 (DOI)000418776400038 ()
Note

Title of this article in dissertation reference lists: Allocation of Frequency Control Reserves and its Impact on Wear on a Hydropower Fleet

Available from: 2016-11-25 Created: 2016-11-25 Last updated: 2018-02-07Bibliographically approved
Yang, W., Norrlund, P., Chung, C. Y., Yang, J. & Lundin, U. (2018). Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plant. Renewable energy, 115, 1014-1025
Open this publication in new window or tab >>Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plant
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2018 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 115, p. 1014-1025Article in journal (Refereed) Published
Abstract [en]

Hydropower shoulders important responsibility for regulation and control of power systems with intermittent renewable energy sources. The quality of regulation required for hydropower units has been increasing, and the interaction between hydropower plants (HPPs) and power systems is of great importance. This work aims to conduct a fundamental study on hydraulic-mechanical-electrical coupling mechanism for small signal stability of HPPs. The main focus is the impact of hydraulic-mechanical factors on the local mode oscillation in a Single-Machine-Infinite-Bus system. A twelfth-order state matrix is established for theoretical eigen-analysis as the core approach. Meanwhile, a simulation model based on Simulink/SimPowerSystems is built for validation. The influencing mechanisms of water column elasticity, governor mechanical component, and water inertia are studied under different control modes of the turbine governor. The results show considerable influence from hydraulic-mechanical factors, and the effect of turbine governor actions is no longer ignorable; also, the damping performance under power system stabilizers can be considerably affected. Insights into interactions among physical quantities in various conditions are obtained as well.

Keywords
Small signal stability, Hydropower plant, Turbine governor, Eigenvalue, Power system stabilizer
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-340668 (URN)10.1016/j.renene.2017.08.005 (DOI)000413615500092 ()
Available from: 2018-02-05 Created: 2018-02-05 Last updated: 2018-02-05Bibliographically approved
Yang, W., Sundqvist, P., Lidenholm, J., Yang, J. & Lundin, U. (2018). Hydraulic damping mechanism of low frequency oscillations in power systems: Quantitative analysis using a nonlinear model of hydropower plants. Applied Energy, 212, 1138-1152
Open this publication in new window or tab >>Hydraulic damping mechanism of low frequency oscillations in power systems: Quantitative analysis using a nonlinear model of hydropower plants
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2018 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 212, p. 1138-1152Article in journal (Refereed) Published
Abstract [en]

As power systems grow reliant on an increasing mix of intermittent renewables, hydropower units are being called upon to provide more aggressive power-frequency control. This dynamic is enlarging the significance of interaction between hydraulic and electrical subsystems in hydropower plants (HPPs). The influence from HPPs on power system stability is of great importance, especially for hydro-dominant power systems like the Nordic power system and the China Southern Power Grid. This paper aims to quantify and reveal the influencing mechanism of the hydraulic damping of low frequency oscillations in power systems. An equivalent hydraulic turbine damping coefficient is introduced, and a nonlinear HPP model that combines electrical subsystems with a refined hydraulic-mechanical subsystem is established and verified. A novel quantifying methodology is proposed through simulations by two different models based on case studies on a Swedish HPP. Then, the quantification results of the damping coefficient are presented and the influencing mechanism behind is revealed, by studying three representative factors from the hydraulic-mechanical system: the delay in turbine governor systems, governor parameter and penstock length. Observations and discussions of on-site measurements are included to support the analysis. The results show that the damping effect from hydraulic turbines can be considerable. Based on the limited cases in the HPP, the damping coefficient can vary from + 3.0 to -2.3, while previously the contribution has been unclear and normally assumed to be positive. The phase shift in the mechanical power response with respect to the rotational speed deviation is an important reason for the different damping performance. Furthermore, the effect and significance of implementing the damping coefficient on cases with power system stabilizer (PSS) are demonstrated.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Hydraulic damping, Hydro-dominant power systems, Rotor angle stability, Low frequency oscillation, Nonlinear model, Numerical simulation
National Category
Environmental Engineering
Identifiers
urn:nbn:se:uu:diva-348101 (URN)10.1016/j.apenergy.2018.01.002 (DOI)000425200700085 ()
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-04-11Bibliographically approved
Saarinen, L., Norrlund, P., Yang, W. & Lundin, U. (2018). Linear synthetic inertia for improved frequency quality and reduced hydropower wear and tear. International Journal of Electrical Power & Energy Systems, 98, 488-495
Open this publication in new window or tab >>Linear synthetic inertia for improved frequency quality and reduced hydropower wear and tear
2018 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 98, p. 488-495Article in journal (Refereed) Published
Abstract [en]

The power system inertia is decreasing in many electrical grids as the share of production from directly connected synchronous generators decreases. Lower inertia increases the frequency deviations in normal operation, which leads to increased wear and tear in hydropower turbines and other units providing frequency control to the system. The predominant concepts for synthetic inertia from for example wind power does not address the frequency quality in normal operation, only the acute problem of frequency stability during large disturbances. This paper investigates how the frequency quality and frequency controlling hydropower units are affected by decreasing inertia and damping, using the Nordic power system as a case study. A new type of synthetic inertia (SI), which is linear and continuously active, is suggested as a means to mitigate the impacts on these units. It is shown that the suggested linear SI controller can effectively replace synchronous inertia and damping, improving frequency quality and reducing hydropower wear and tear. The controller includes an energy recovery feedback loop, to avoid depletion of the energy source behind the controller. The power and energy needed to provide linear SI is quantified, and the impact of the SI energy recovery integration time constant is investigated.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Synthetic inertia, Hydropower, Frequency control, Virtual synchronous machine, Wear and tear
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-350482 (URN)10.1016/j.ijepes.2017.12.007 (DOI)000425568100045 ()
Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-06-05Bibliographically approved
Yang, W., Norrlund, P., Saarinen, L., Yang, J., Zeng, W. & Lundin, U. (2017). Wear reduction for hydro power turbines considering frequency quality of power systems: a study on controller filters. IEEE Transactions on Power Systems, 32(2), 1191-1201
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
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2017 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 32, no 2, p. 1191-1201Article 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
Yang, W., Norrlund, P. & Yang, J. (2016). Analysis on regulation strategies for extending service life of hydropower turbines. In: : . Paper presented at 28th IAHR symposium on Hydraulic Machinery and Systems (IAHR2016). , Article ID 052013.
Open this publication in new window or tab >>Analysis on regulation strategies for extending service life of hydropower turbines
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Since a few years, there has been a tendency that hydropower turbines experience fatigue to a greater extent, due to increasingly more regulation movements of governor actuators. The aim of this paper is to extend the service life of hydropower turbines, by reasonably decreasing the guide vane (GV) movements with appropriate regulation strategies, e.g. settings of PI (proportional-integral) governor parameters and controller filters. The accumulated distance and number of GV movements are the two main indicators of this study. The core method is to simulate the long-term GV opening of Francis turbines with MATLAB/Simulink, based on a sequence of one-month measurements of the Nordic grid frequency. Basic theoretical formulas are also discussed and compared to the simulation results, showing reasonable correspondence. Firstly, a model of a turbine governor is discussed and verified, based on on-site measurements of a Swedish hydropower plant. Then, the influence of governor parameters is discussed. Effects of different settings of controller filters (e.g. dead zone, floating dead zone and linear filter) are also examined. Moreover, a change in GV movement might affect the quality of the frequency control. This is also monitored via frequency deviation characteristics, determined by elementary simulations of the Nordic power system. The results show how the regulation settings affect the GV movements and frequency quality, supplying suggestions for optimizing the hydropower turbine operation for decreasing the wear and tear.

Series
IOP Conference Series: Earth and Environmental Science, ISSN 1755-1307, E-ISSN 1755-1315 ; 49
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-310651 (URN)10.1088/1755-1315/49/5/052013 (DOI)000400156200054 ()
Conference
28th IAHR symposium on Hydraulic Machinery and Systems (IAHR2016)
Available from: 2016-12-17 Created: 2016-12-17 Last updated: 2018-04-04Bibliographically approved
Saarinen, L., Norrlund, P., Lundin, U., Agneholm, E. & Westberg, A. (2016). Full-scale test and modelling of the frequency control dynamics of the Nordic power system. In: 2016 IEEE POWER AND ENERGY SOCIETY GENERAL MEETING (PESGM): . Paper presented at IEEE-Power-and-Energy-Society General Meeting (PESGM), JUL 17-21, 2016, Boston, MA. New York: IEEE
Open this publication in new window or tab >>Full-scale test and modelling of the frequency control dynamics of the Nordic power system
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2016 (English)In: 2016 IEEE POWER AND ENERGY SOCIETY GENERAL MEETING (PESGM), New York: IEEE, 2016Conference paper, Published paper (Refereed)
Abstract [en]

The grid frequency quality in the Nordic power system has been deteriorating during the last decade. To improve the situation, a better understanding of the system is needed. In this paper, a model of the Nordic power system dynamics with respect to normal operation frequency control is set up and compared with full-scale measurements on the system. The "60 s oscillation" of the grid frequency is measured and explained by the system model.

Place, publisher, year, edition, pages
New York: IEEE, 2016
Series
IEEE Power and Energy Society General Meeting PESGM, ISSN 1944-9925
National Category
Energy Systems
Identifiers
urn:nbn:se:uu:diva-332914 (URN)10.1109/PESGM.2016.7741711 (DOI)000399937902105 ()978-1-5090-4168-8 (ISBN)
Conference
IEEE-Power-and-Energy-Society General Meeting (PESGM), JUL 17-21, 2016, Boston, MA
Available from: 2017-11-03 Created: 2017-11-03 Last updated: 2017-11-03Bibliographically approved
Yang, W., Yang, J., Guo, W. & Norrlund, P. (2016). Response time for primary frequency control of hydroelectric generating unit. International Journal of Electrical Power & Energy Systems, 74, 16-24
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, p. 16-24Article 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
Yang, W., Norrlund, P., Saarinen, L., Yang, J., Guo, W. & Zeng, W. (2016). Wear and tear on hydro power turbines: influence from primary frequency control. Renewable energy, 87, 88-95
Open this publication in new window or tab >>Wear and tear on hydro power turbines: influence from primary frequency control
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2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 87, p. 88-95Article 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
Yang, W., Yang, J., Guo, W., Zeng, W., Wang, C., Saarinen, L. & Norrlund, P. (2015). A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions. Energies, 8(9), 10260-10275
Open this publication in new window or tab >>A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
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2015 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 9, p. 10260-10275Article 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
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