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  • 1.
    Bladh, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wallin, Mattias
    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.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements2016In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 1, p. 46-56Article in journal (Refereed)
    Abstract [en]

    Standstill Frequency Response (SSFR) test data from a salient-pole synchronous machine with reconfigurable damper winding is presented. In addition to the regular measurements, the damper bar currents are measured and used to obtain the stator-to-damper transfer functions. The test is performed three times with physically different damper winding configurations. An extension to the standard SSFR test analysis scheme is suggested where the stator-to-damper transfer functions are included. The validity of the identified models is substantiated by comparison of the simulated and measured machine response to a drive torque step disturbance. It is found that the damper winding measurements can be incorporated in the analysis scheme to isolate the effect of the damper circuits. However, for a machine of the type studied, also the standard SSFR test produce yields models that are accurate enough for power system studies.

  • 2.
    Saarinen, Linn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A hydropower perspective on flexibility demand and grid frequency control2014Licentiate 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.

    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, p. 339-344Article 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.

    Keywords
    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, p. 1061-1068Article 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.

    Keywords
    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.

    Keywords
    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
  • 3.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall AB, Älvkarlebylaboratoriet, Älvkarleby, Sweden.
    Dahlbäck, Niklas
    Vattenfall AB, Älvkarlebylaboratoriet, Älvkarleby, Sweden.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Power system flexibility need induced by wind and solar power intermittency on time scales of 1-14 days2015In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 83, p. 339-344Article in journal (Refereed)
    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.

  • 4.
    Saarinen, Linn
    et al.
    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.
    Robust primary frequency control in a system dominated by hydropowerManuscript (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.

  • 5.
    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.

  • 6.
    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.

  • 7.
    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.

  • 8.
    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.

  • 9.
    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.

  • 10.
    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.

  • 11.
    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.

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