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  • 1. Bladh, Johan
    et al.
    Sundqvist, Per
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Torsional stability of hydropower units under influence of subsynchronous oscillations2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 4, p. 3826-3833Article in journal (Refereed)
    Abstract [en]

    Hydropower units are known to be comparatively insensitive to subsynchronous power oscillations. During a startup test of an electrical island in the Nordic power system, a series capacitor tripped due to a subsynchronous oscillation within the normal frequency range of hydropower unit torsional modes. Since no thermal units were connected, it is motivated to question the traditional view. In this paper, the small-signal and transient torsional mode stability of hydropower units is assessed through time-domain simulations. The model is based on the first IEEE benchmark model for subsynchronous resonance which has been tuned to fit one of the blackstart test system units for which detailed measurements are available. The stability conditions are investigated for several load conditions and machine configurations. It is found that the damping in the startup test system is sufficient to prevent growing oscillations. A fault however could expose the machines to high transient torques.

  • 2.
    Brandén, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Holmgren, Sverker
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Discrete Fundamental Solution Preconditioning for Hyperbolic Systems of PDE2003Report (Other academic)
  • 3.
    Brandén, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Holmgren, Sverker
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Discrete fundamental solution preconditioning for hyperbolic systems of PDE2007In: Journal of Scientific Computing, ISSN 0885-7474, E-ISSN 1573-7691, Vol. 30, p. 35-60Article in journal (Refereed)
  • 4.
    Brandén, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    An algorithm for computing fundamental solutions of difference operators2004In: Numerical Algorithms, ISSN 1017-1398, E-ISSN 1572-9265, Vol. 36, p. 331-343Article in journal (Refereed)
  • 5.
    Brandén, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    An Algorithm for Computing Fundamental Solutions of Difference Operators2003Report (Other academic)
  • 6.
    Brandén, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Preconditioners Based on Fundamental Solutions2005Report (Other academic)
  • 7.
    Brandén, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Preconditioners based on fundamental solutions2005In: BIT Numerical Mathematics, ISSN 0006-3835, E-ISSN 1572-9125, Vol. 45, p. 481-494Article in journal (Refereed)
  • 8. Dahlbäck, Niklas
    et al.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Examples of Benefits from Efficiency Evaluation Using Comparative Tests2014In: 10th International Conference on Hydraulic Efficiency Measurements 2014-09-16 - 19, Itajubá, Brazil, 2014Conference paper (Refereed)
    Abstract [en]

    Traditionally, most field efficiency measurements are made to verify guarantees for a new project, which have led to that this issue is well covered by standardization guidelines. There are however several other situations where information from field efficiency measurements contributes with value. Depending on issue and site characteristics, there are several feasible options, that are not described in current standards of primary methods.

    A comparative test is here defined as a test where efficiency is evaluated at the same flow conditions but with modified or changed turbine or water conduits. At an efficiency evaluation of a comparative test, many systematic uncertainties will cancel, and the overall evaluation of uncertainty will be at a very useful level. 

    This paper presents experiences of the hydropower producer Vattenfall, from several efficiency tests, where different types of comparative tests settings have been used.

  • 9.
    Holmgren, Sverker
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Serra-Capizzano, Stefano
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Can one hear the composition of a drum?2006In: Mediterranean Journal of Mathematics, ISSN 1660-5446, E-ISSN 1660-5454, Vol. 3, p. 227-249Article in journal (Refereed)
  • 10.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Field Measurements and System Identification of Three Frequency Controlling Hydropower Plants2015In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 30, no 3, p. 1061-1068Article in journal (Refereed)
    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.

  • 11.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Agneholm, Evert
    Gothia Power, Gothenburg, Sweden..
    Westberg, Andreas
    Svenska Kraftnat, Sundbyberg, Sweden..
    Full-scale test and modelling of the frequency control dynamics of the Nordic power system2016In: 2016 IEEE POWER AND ENERGY SOCIETY GENERAL MEETING (PESGM), New York: IEEE, 2016Conference 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.

  • 12.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall Hydropower AB, SE-81470 Alvkarleby, Sweden.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Alvkarlebylaboratoriet, Vattenfall Res & Dev, SE-81426 Alvkarleby, Sweden.
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Allocation of Frequency Control Reserves and its Impact on Wear and Tear on a Hydropower Fleet2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 1, p. 430-439Article in journal (Refereed)
    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.

  • 13.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall Hydropower AB, Älvkarleby, Sweden..
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Älvkarlebylaboratoriet, Vattenfall Res & Dev, Älvkarleby, Sweden..
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China..
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Linear synthetic inertia for improved frequency quality and reduced hydropower wear and tear2018In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 98, p. 488-495Article in journal (Refereed)
    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.

  • 14. Serra-Capizzano, Stefano
    et al.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Stability of the notion of approximating class of sequences and applications2008In: Journal of Computational and Applied Mathematics, ISSN 0377-0427, E-ISSN 1879-1778, Vol. 219, p. 518-536Article in journal (Refereed)
  • 15.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Boundary Summation Equations2004Report (Other academic)
  • 16.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Numerical Computations with Fundamental Solutions2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Two solution strategies for large, sparse, and structured algebraic systems of equations are considered. The first strategy is to construct efficient preconditioners for iterative solvers. The second is to reduce the sparse algebraic system to a smaller, dense system of equations, which are called the boundary summation equations.

    The proposed preconditioners perform well when applied to equations that are discretizations of linear first order partial differential equations. Analysis shows that also very simple iterative methods converge in a number of iterations that is independent of the number of unknowns, if our preconditioners are applied to certain scalar model problems. Numerical experiments indicate that this property holds also for more complicated cases, and a flow problem modeled by the nonlinear Euler equations is treated successfully.

    The reduction process is applicable to a large class of difference equations. There is no approximation involved in the reduction, so the solution of the original algebraic equations is determined exactly if the reduced system is solved exactly. The reduced system is well suited for iterative solution, especially if the original system of equations is a discretization of a first order differential equation. The technique is used for several problems, ranging from scalar model problems to a semi-implicit discretization of the compressible Navier-Stokes equations.

    Both strategies use the concept of fundamental solutions, either of differential or difference operators. An algorithm for computing fundamental solutions of difference operators is also presented.

    List of papers
    1. Preconditioners based on fundamental solutions
    Open this publication in new window or tab >>Preconditioners based on fundamental solutions
    2005 (English)In: BIT Numerical Mathematics, ISSN 0006-3835, E-ISSN 1572-9125, Vol. 45, p. 481-494Article in journal (Refereed) Published
    National Category
    Computational Mathematics Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-78887 (URN)10.1007/s10543-005-0010-7 (DOI)
    Available from: 2007-03-11 Created: 2007-03-11 Last updated: 2018-01-13Bibliographically approved
    2. An algorithm for computing fundamental solutions of difference operators
    Open this publication in new window or tab >>An algorithm for computing fundamental solutions of difference operators
    2004 (English)In: Numerical Algorithms, ISSN 1017-1398, E-ISSN 1572-9265, Vol. 36, p. 331-343Article in journal (Refereed) Published
    National Category
    Computational Mathematics Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-67772 (URN)10.1007/s11075-004-2879-7 (DOI)
    Available from: 2006-05-20 Created: 2006-05-20 Last updated: 2018-01-10Bibliographically approved
    3. Discrete fundamental solution preconditioning for hyperbolic systems of PDE
    Open this publication in new window or tab >>Discrete fundamental solution preconditioning for hyperbolic systems of PDE
    2007 (English)In: Journal of Scientific Computing, ISSN 0885-7474, E-ISSN 1573-7691, Vol. 30, p. 35-60Article in journal (Refereed) Published
    National Category
    Computational Mathematics Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-84009 (URN)10.1007/s10915-005-9018-z (DOI)000243906800002 ()
    Available from: 2007-01-31 Created: 2007-01-31 Last updated: 2018-01-13Bibliographically approved
    4. Boundary Summation Equations
    Open this publication in new window or tab >>Boundary Summation Equations
    2004 (English)Report (Other academic)
    Series
    Technical report / Department of Information Technology, Uppsala University, ISSN 1404-3203 ; 2004-042
    National Category
    Computational Mathematics
    Identifiers
    urn:nbn:se:uu:diva-68483 (URN)
    Available from: 2008-02-21 Created: 2008-02-21 Last updated: 2014-09-03Bibliographically approved
    5. Navier-Stokes equations for low Mach number flows solved by boundary summation
    Open this publication in new window or tab >>Navier-Stokes equations for low Mach number flows solved by boundary summation
    2005 (English)Manuscript (preprint) (Other academic)
    National Category
    Computational Mathematics Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-92953 (URN)
    Available from: 2005-04-21 Created: 2005-04-21 Last updated: 2018-01-13Bibliographically approved
  • 17.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Preconditioners and fundamental solutions2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    New preconditioning techniques for the iterative solution of systems of equations arising from discretizations of partial differential equations are considered. Fundamental solutions, both of differential and difference operators, are used as kernels in discrete, truncated convolution operators. The intention is to approximate inverses of difference operators that arise when discretizing the differential equations. The approximate inverses are used as preconditioners.

    The technique using fundamental solutions of differential operators is applied to scalar problems in two dimensions, and grid independent convergence is obtained for a first order differential equation.

    The problem of computing fundamental solutions of difference operators is considered, and we propose a new algorithm. It can be used also when the symbol of the difference operator is not invertible everywhere, and it is applicable in two or more dimensions.

    Fundamental solutions of difference operators are used to construct preconditioners for non-linear systems of difference equations in two dimensions. Grid independent convergence is observed for two standard finite difference discretizations of the Euler equations in a non-axisymmetric duct.

  • 18.
    Sundqvist, Per
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Holmgren, Sverker
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Navier-Stokes equations for low Mach number flows solved by boundary summation2005Manuscript (preprint) (Other academic)
  • 19.
    Vidholm, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Centre for Image Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing.
    Nyström, Ingela
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Centre for Image Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis.
    Accelerating the Computation of 3D Gradient Vector Flow Fields2006In: Proc, IEEE , 2006, p. 677-680Conference paper (Refereed)
  • 20.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China..
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall R&D, SE-81426 Älvkarleby, Sweden..
    Chung, Chi Yung
    Univ Saskatchewan, Dept Elect & Comp Engn, Saskatoon, SK S7N 5A9, Canada..
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China..
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plant2018In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 115, p. 1014-1025Article in journal (Refereed)
    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.

  • 21.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saarinen, Linn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yang, Jiandong
    Guo, Wencheng
    Zeng, Wei
    Wear and tear on hydro power turbines: influence from primary frequency control2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 87, p. 88-95Article in journal (Refereed)
    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.

  • 22.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China..
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall R&D, SE-81426 Alvkarleby, Sweden..
    Saarinen, Linn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall R&D, SE-81426 Alvkarleby, Sweden..
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China..
    Zeng, Wei
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China..
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wear reduction for hydro power turbines considering frequency quality of power systems: a study on controller filters2017In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 32, no 2, p. 1191-1201Article in journal (Refereed)
    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.

  • 23.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. The State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, 430072, China.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall R&D, Älvkarleby, SE-814 26, Sweden.
    Yang, Jiandong
    The State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, 430072, China.
    Analysis on regulation strategies for extending service life of hydropower turbines2016Conference 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.

  • 24.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan, Hubei, Peoples R China.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall R&D, SE-81426 Älvkarleby, Sweden..
    Lidenholm, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall R&D, SE-81426 Älvkarleby, Sweden..
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China..
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hydraulic damping mechanism of low frequency oscillations in power systems: Quantitative analysis using a nonlinear model of hydropower plants2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 212, p. 1138-1152Article in journal (Refereed)
    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.

  • 25.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan, Hubei, Peoples R China; Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan, Hubei, Peoples R China; Oak Ridge Natl Lab, Div Environm Sci, Oak Ridge, TN USA.
    Sundqvist, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall R&D, Älvkarleby, Sweden.
    Saarinen, Linn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall R&D, Älvkarleby, Sweden.
    Witt, Adam
    Oak Ridge Natl Lab, Div Environm Sci, Oak Ridge, TN USA.
    Smith, Brennan
    Oak Ridge Natl Lab, Div Environm Sci, Oak Ridge, TN USA.
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan, Hubei, Peoples R China.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Burden on hydropower units for short-term balancing of renewable power systems2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 2633Article in journal (Refereed)
    Abstract [en]

    There is a general need to change hydropower operational regimes to balance the growing contribution of variable renewable energy sources in power systems. Quantifying the burden on generation equipment is increasingly uncertain and difficult. Here, we propose a framework combining technical and economic indicators to analyze primary frequency control (PFC) on a timescale of seconds. We develop a model integrating hydraulic, mechanical, and electrical subsystems to characterize efficiency loss, wear and fatigue, regulation mileage, and frequency quality. We evaluate burden relief strategies under three idealized remuneration schemes for PFC, inspired by those used in Sweden, the USA, and China, respectively. We show how burden and compensation vary under future scenarios of renewable power systems. Our framework can be used by producers to develop favorable operation strategies that reduce burden and increase economic value, and by transmission system operators to provide insights on the relation between incentive structures and regulating performance.

  • 26.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yang, Jiandong
    Guo, Wencheng
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Frequency Stability of Isolated Hydropower Plant with Surge Tank Under Different Turbine Control Modes2015In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 43, no 15, p. 1707-1716Article in journal (Refereed)
    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.

  • 27.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yang, Jiandong
    Guo, Wencheng
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Response time for primary frequency control of hydroelectric generating unit2016In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 74, p. 16-24Article in journal (Refereed)
    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.

  • 28.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yang, Jiandong
    Guo, Wencheng
    Zeng, Wei
    Wang, Chao
    Saarinen, Linn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions2015In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 9, p. 10260-10275Article in journal (Refereed)
    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.

1 - 28 of 28
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