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  • 1.
    Bao, Haiyan
    et al.
    Changsha Univ Sci & Technol, Sch Hydraul Engn, Changsha.; Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan.
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan.
    Zhao, Guilian
    PowerChina Chengdu Engn Corp Ltd, Chengdu.
    Zeng, Wei
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China..
    Liu, Yanna
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan.
    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.
    Condition of setting surge tanks in hydropower plants - A review2018In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 81, p. 2059-2070Article, review/survey (Refereed)
    Abstract [en]

    Hydropower plays an important role in the safe, stable and efficient operation of power systems, especially with current trends toward renewable energy systems. The total global potential of gross, technical, economic, and exploitable hydropower are still enormous in the future, and the developments of new hydropower stations (HPSs) are of great importance. For constructions of new HPSs, the condition of setting surge tanks (CSST) is crucial for various perspectives, e.g. safety, stability and economy of HPSs. In this review, the CSST are summarized and analyzed from the three aspects: regulation assurance, operation stability, and the regulation quality, with an aim of providing a reference and guidance for research and engineering applications regarding surge tanks. Upstream and downstream surge tanks in conventional HPSs and pumped storage power stations are all included. Moreover, a comprehensive comparison of CSST under different conditions is conducted. One of the main focuses of this review is on Chinese studies, for introducing many meaningful results written in Chinese to more readers all over the world.

  • 2. Guo, Wencheng
    et al.
    Yang, Jiandong
    Chen, Jieping
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yi, Teng
    Wei, Zeng
    Time response of the frequency of hydroelectric generator unit with surge tank under isolated operation based on turbine regulating modes2015In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 43, no 20, p. 2341-2355Article in journal (Refereed)
    Abstract [en]

    Aiming at studying the regulation quality of isolated turbine regulating systems under load disturbance and different regulation modes, the complete mathematical model of a turbine regulating system under three regulation modes is established. Then, based on dominant poles and null points, the method of order reduction for a high-order system of time response of the frequency is proposed. By this method, the complete high-order systems are solved and the regulation quality for time response of the frequency is studied. The results indicate that (1) the tail wave, which is the main body of time response of the frequency and the principal factor that determines the regulation quality, is mainly determined by the dominant poles; (2) for the three regulation modes, by deleting the high-order terms, the three equivalent overall transfer functions are fourth order, third order, and third order, respectively, and can be solved; (3) the analytical fluctuation equations of time response of the frequency solved from low-order equivalent overall transfer functions accurately simulate the fluctuation characteristics of time response; and (4) based on damped vibrations decomposed from analytical fluctuation equations, the regulation qualities of three regulation modes are analyzed.

  • 3. Guo, Wencheng
    et al.
    Yang, Jiandong
    Wuhan University.
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Modeling and stability analysis of turbine governing system of hydro power plant2017In: Modeling and Dynamic Behavior of Hydro Power Plants, Institution of Engineering and Technology, 2017Chapter in book (Refereed)
  • 4. Guo, Wencheng
    et al.
    Yang, Jiandong
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chen, Jieping
    Teng, Yi
    Regulation quality for frequency response of turbine regulating system of isolated hydroelectric power plant with surge tank2015In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 73, p. 528-538Article in journal (Refereed)
    Abstract [en]

    Aiming at the isolated hydroelectric power plant (HPP) with surge tank, this paper studies the regulation quality for frequency response of turbine regulating system under load disturbance. Firstly, the complete mathematical model of turbine regulating system is established and a fifth order frequency response under step load disturbance is derived. Then, the method of primary order reduction and secondary order reduction, for this complete fifth order system of frequency response, is proposed based on dominant poles. By this method, the complete fifth order system is solved and the regulation quality for frequency response is studied. The results indicate that the complete fifth order system always has a pair of dominant conjugate complex poles and three non-dominant poles. The primary fourth order equivalent system, which is obtained by primary order reduction, keeps the dominant poles almost unchanged, therefore it can represent and replace the complete fifth order system and it is obviously superior to other fourth order systems. The primary fourth order equivalent system is superimposed by two second-order subsystems, one of them is corresponding to two non-dominant real poles (i.e. head wave) and the other one is corresponding to a pair of dominant conjugate complex poles (i.e. tail wave), respectively. In the fluctuation process of frequency response, head wave decays very fast and works mainly in the beginning period while tail wave decays very slowly, fluctuates periodically and works throughout the period. The secondary order reduction of complete fifth order system can be conducted by using the second order system of tail wave, which is the main body of frequency response, to represent the fluctuation characteristics. The most important dynamic performance index that evaluates the regulation quality, i.e. settling time, is derived from the fluctuation equation of tail wave. The different characteristic parameters of turbine regulating system have different influences on the change rules of head wave, tail wave and settling time.

  • 5.
    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.

  • 6.
    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.

  • 7.
    Tang, Renbo
    et al.
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China;Zhongnan Engn Corp Ltd, Power Construct Corp China, Changsha 410014, Hunan, Peoples R China.
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China.
    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.
    Zou, Jin
    China Southern Power Grid, EPRI, Guangzhou 510663, Guangdong, Peoples R China.
    Lai, Xu
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China.
    Dynamic regulation characteristics of pumped-storage plants with two generating units sharing common conduits and busbar for balancing variable renewable energy2019In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 135, p. 1064-1077Article in journal (Refereed)
    Abstract [en]

    Pumped-storage plants (PSPs) are becoming increasingly important for balancing variable renewable energy (VRE) in power systems. A large portion of PSPs consist of multiple generating units (GUs) with shared water conduits and busbar. In this paper, an integrated transfer function (ITF) model for such PSPs in generation mode under primary frequency control (PFC) is proposed. Based on a real PSP in China, this ITF model is validated with both simulation results using the method of characteristics (MOC) as well as data from on-site measurements. For a series of governor parameter (K-p and K-i) settings under different governor control modes, stability limits expressed by gain and phase margins are evaluated and time domain simulations for balancing wind power variations are carried out to assess the quality of regulation. The results reveal that the dynamic regulation characteristics of the studied PSP system is clearly effected by the governor control mode. Besides, due to its complexity, a general range of the gain and phase margins is not viable for the studied PSP system under different governor control modes. Therefore, a thorough time domain sensitivity analysis using both step and realistic load disturbance as inputs is required for the studied PSPs for balancing VRE.

  • 8.
    Yang, Jiandong
    et al.
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China..
    Wang, Huang
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China.;Design & Res Co Ltd, Changjiang Inst Survey, Planning, Wuhan 430010, Peoples R China..
    Guo, Wencheng
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China.;Purdue Univ, Dept Agr & Biol Engn, Maha Fluid Power Res Ctr, W Lafayette, IN 47907 USA..
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Zeng, Wei
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China..
    Simulation of Wind Speed in the Ventilation Tunnel for Surge Tanks in Transient Processes2016In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 2, article id UNSP 95Article in journal (Refereed)
    Abstract [en]

    Hydroelectric power plants' open-type surge tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the surge tank. There is a great relationship between the wind speed and the safe use and project investment of ventilation tunnels. To obtain the wind speed in a ventilation tunnel for a surge tank during transient processes, this article adopts the one-dimensional numerical simulation method and establishes a mathematical model of a wind speed by assuming the boundary conditions of air discharge for a surge tank. Thereafter, the simulation of wind speed in a ventilation tunnel, for the case of a surge tank during transient processes, is successfully realized. Finally, the effective mechanism of water-level fluctuation in a surge tank and the shape of the ventilation tunnel (including length, sectional area and dip angle) for the wind speed distribution and the change process are discovered. On the basis of comparison between the simulation results of 1D and 3D computational fluid dynamics (CFD), the results indicate that the one-dimensional simulation method as proposed in this article can be used to accurately simulate the wind speed in the ventilation tunnel of a surge tank during transient processes. The wind speed fluctuations can be superimposed by using the low frequency mass wave (i.e., fundamental wave) and the high frequency elastic wave (i.e., harmonic wave). The water-level fluctuation in a surge tank and the sectional area of the ventilation tunnel mainly affect the amplitude of fundamental and harmonic waves. The period of a fundamental wave can be determined from the water-level fluctuations. The length of the ventilation tunnel has an effect on the period and amplitude of harmonic waves, whereas the dip angle influences the amplitude of harmonic waves.

  • 9.
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dynamic Processes and Active Power Control of Hydropower Plants2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

    List of papers
    1. Response time for primary frequency control of hydroelectric generating unit
    Open this publication in new window or tab >>Response time for primary frequency control of hydroelectric generating unit
    2016 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 74, 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
    2. Frequency Stability of Isolated Hydropower Plant with Surge Tank Under Different Turbine Control Modes
    Open this publication in new window or tab >>Frequency Stability of Isolated Hydropower Plant with Surge Tank Under Different Turbine Control Modes
    2015 (English)In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 43, no 15, p. 1707-1716Article in journal (Refereed) Published
    Abstract [en]

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

    National Category
    Other Engineering and Technologies
    Identifiers
    urn:nbn:se:uu:diva-260774 (URN)10.1080/15325008.2015.1049722 (DOI)000359869100003 ()
    Available from: 2015-08-24 Created: 2015-08-24 Last updated: 2017-12-04Bibliographically approved
    3. A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
    Open this publication in new window or tab >>A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
    Show others...
    2015 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 9, 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
    4. Wear and tear on hydro power turbines: influence from primary frequency control
    Open this publication in new window or tab >>Wear and tear on hydro power turbines: influence from primary frequency control
    Show others...
    2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 87, 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
    5. Wear reduction for hydro power turbines considering frequency quality of power systems: a study on controller filters
    Open this publication in new window or tab >>Wear reduction for hydro power turbines considering frequency quality of power systems: a study on controller filters
    Show others...
    2017 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 32, no 2, 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
  • 10.
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hydropower plants and power systems: Dynamic processes and control for stable and efficient operation2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    As the largest global renewable source, hydropower shoulders a large portion of the regulation duty in many power systems. New challenges are emerging from variable renewable energy (VRE) sources, the increasing scale and complexity of hydropower plants (HPPs) and power grid. Stable and efficient operation of HPPs and their interaction with power systems is of great importance.

    Theoretical analysis, numerical simulation and on-site measurement are adopted as main study methods in this thesis. Various numerical models of HPPs are established, with different degrees of complexity for different purposes. The majority of the analysis and results are based on eight HPPs in Sweden and China.

    Stable operation (frequency stability and rotor angle stability) and efficient operation are two important goals. Regarding the stable operation, various operating conditions are analysed; the response time of primary frequency control (PFC) and the system stability of isolated operation are investigated. A fundamental study on hydraulic-mechanical-electrical coupling mechanisms for small signal stability of HPPs is conducted. A methodology is proposed to quantify the contribution to the damping of low frequency oscillations from hydraulic turbines. The oscillations, with periods ranging from less than one up to hundreds of seconds, are analysed.

    Regarding the efficient operation, a description and an initial analysis of wear and tear of turbines are presented; a controller filter is proposed as a solution for wear reduction of turbines and maintaining the frequency quality of power systems; then the study is further extended by proposing a framework that combines technical plant operation with economic indicators, to obtain relative values of regulation burden and performance of PFC.

    The results show that the coupling between the hydraulic-mechanical subsystem and the electrical subsystem can be considerable and should be considered with higher attention. Effectiveness and applicability of different numerical models are shown, supplying suggestions for further model optimization. For the influence from power systems on HPPs, the dynamic processes and corresponding control strategies of HPPs under diverse disturbances and requirements from power systems are addressed. For the influence from HPPs on power systems, quantifications of frequency quality and the hydraulic damping are conducted utilising proposed methodologies.

    List of papers
    1. A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
    Open this publication in new window or tab >>A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
    Show others...
    2015 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 9, 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
    2. Response time for primary frequency control of hydroelectric generating unit
    Open this publication in new window or tab >>Response time for primary frequency control of hydroelectric generating unit
    2016 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 74, 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
    3. Frequency Stability of Isolated Hydropower Plant with Surge Tank Under Different Turbine Control Modes
    Open this publication in new window or tab >>Frequency Stability of Isolated Hydropower Plant with Surge Tank Under Different Turbine Control Modes
    2015 (English)In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 43, no 15, p. 1707-1716Article in journal (Refereed) Published
    Abstract [en]

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

    National Category
    Other Engineering and Technologies
    Identifiers
    urn:nbn:se:uu:diva-260774 (URN)10.1080/15325008.2015.1049722 (DOI)000359869100003 ()
    Available from: 2015-08-24 Created: 2015-08-24 Last updated: 2017-12-04Bibliographically approved
    4. Regulation quality for frequency response of turbine regulating system of isolated hydroelectric power plant with surge tank
    Open this publication in new window or tab >>Regulation quality for frequency response of turbine regulating system of isolated hydroelectric power plant with surge tank
    Show others...
    2015 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 73, p. 528-538Article in journal (Refereed) Published
    Abstract [en]

    Aiming at the isolated hydroelectric power plant (HPP) with surge tank, this paper studies the regulation quality for frequency response of turbine regulating system under load disturbance. Firstly, the complete mathematical model of turbine regulating system is established and a fifth order frequency response under step load disturbance is derived. Then, the method of primary order reduction and secondary order reduction, for this complete fifth order system of frequency response, is proposed based on dominant poles. By this method, the complete fifth order system is solved and the regulation quality for frequency response is studied. The results indicate that the complete fifth order system always has a pair of dominant conjugate complex poles and three non-dominant poles. The primary fourth order equivalent system, which is obtained by primary order reduction, keeps the dominant poles almost unchanged, therefore it can represent and replace the complete fifth order system and it is obviously superior to other fourth order systems. The primary fourth order equivalent system is superimposed by two second-order subsystems, one of them is corresponding to two non-dominant real poles (i.e. head wave) and the other one is corresponding to a pair of dominant conjugate complex poles (i.e. tail wave), respectively. In the fluctuation process of frequency response, head wave decays very fast and works mainly in the beginning period while tail wave decays very slowly, fluctuates periodically and works throughout the period. The secondary order reduction of complete fifth order system can be conducted by using the second order system of tail wave, which is the main body of frequency response, to represent the fluctuation characteristics. The most important dynamic performance index that evaluates the regulation quality, i.e. settling time, is derived from the fluctuation equation of tail wave. The different characteristic parameters of turbine regulating system have different influences on the change rules of head wave, tail wave and settling time.

    National Category
    Other Engineering and Technologies
    Identifiers
    urn:nbn:se:uu:diva-260775 (URN)10.1016/j.ijepes.2015.05.043 (DOI)000360771800057 ()
    Available from: 2015-08-24 Created: 2015-08-24 Last updated: 2017-12-04Bibliographically approved
    5. Time response of the frequency of hydroelectric generator unit with surge tank under isolated operation based on turbine regulating modes
    Open this publication in new window or tab >>Time response of the frequency of hydroelectric generator unit with surge tank under isolated operation based on turbine regulating modes
    Show others...
    2015 (English)In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 43, no 20, p. 2341-2355Article in journal (Refereed) Published
    Abstract [en]

    Aiming at studying the regulation quality of isolated turbine regulating systems under load disturbance and different regulation modes, the complete mathematical model of a turbine regulating system under three regulation modes is established. Then, based on dominant poles and null points, the method of order reduction for a high-order system of time response of the frequency is proposed. By this method, the complete high-order systems are solved and the regulation quality for time response of the frequency is studied. The results indicate that (1) the tail wave, which is the main body of time response of the frequency and the principal factor that determines the regulation quality, is mainly determined by the dominant poles; (2) for the three regulation modes, by deleting the high-order terms, the three equivalent overall transfer functions are fourth order, third order, and third order, respectively, and can be solved; (3) the analytical fluctuation equations of time response of the frequency solved from low-order equivalent overall transfer functions accurately simulate the fluctuation characteristics of time response; and (4) based on damped vibrations decomposed from analytical fluctuation equations, the regulation qualities of three regulation modes are analyzed.

    Keywords
    hydroelectric generator unit; surge tank; isolated operation; turbine regulating system; time response of the frequency; regulation quality; regulating mode; dominant pole
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-265426 (URN)10.1080/15325008.2015.1082681 (DOI)000364312000009 ()
    Available from: 2015-10-28 Created: 2015-10-28 Last updated: 2017-12-01
    6. Instability analysis of pumped-storage stations under no-load conditions using a parameter-varying model
    Open this publication in new window or tab >>Instability analysis of pumped-storage stations under no-load conditions using a parameter-varying model
    2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 90, p. 420-429Article in journal (Refereed) Published
    Abstract [en]

    The S-shaped characteristics of a pump turbine make its rotational speed unstable when it starts up under no-load conditions with low head, affecting its ability to connect to the grid. Although advanced strategies for controlling the speed governor can alleviate this problem, they cannot fundamentally resolve the internal mechanisms that cause difficulties with a grid connection. Therefore, this study set out to theoretically explore the root cause of the instability and the dominant factors influencing it. A correlation fitting process was used to simplify the transcendental function for the pipe flow in elastic mode into a high-precision and low-order linear equation. Next, a detailed study of the two key factors affecting system stability (pump turbine S-shaped characteristics and water elasticity) was carried out based on the system model, and a comprehensive parameter that reflects the no-load characteristics was extracted. Furthermore, the Laplace transform and inverse transform decomposition were used to obtain a mathematical expression for the no-load oscillation in order to analyze the oscillation characteristics. Finally, simulations of no-load oscillations under various heads were performed to further validate the accuracy of the extracted comprehensive parameter for the no-load stability.

    Keywords
    Pumped-storage station, Pump turbine, No-load instability, Water elasticity, S-shaped characteristics
    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-280219 (URN)10.1016/j.renene.2016.01.024 (DOI)000370102400038 ()
    Available from: 2016-03-10 Created: 2016-03-09 Last updated: 2017-11-30
    7. Extreme water-hammer pressure during one-after-another load shedding in pumped-storage stations
    Open this publication in new window or tab >>Extreme water-hammer pressure during one-after-another load shedding in pumped-storage stations
    2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 99, p. 35-44Article in journal (Refereed) Published
    Abstract [en]

    The intermittent and unpredictable wind and solar power leads to the frequent transient processing of pumped-storage stations, increasing the probability of load shedding. When one turbine sheds its load, the other turbines in the same hydraulic unit become overloaded and may shed their loads, which is referred to as a "one-after-another (OAA)" load-shedding process. An extremely high water-hammer pressure (WHP), namely, high spiral case pressure (SCP) or low draft tube pressure (DTP), may arise in this case, directly threatening the safety of the PSS. The objective of this study was to theoretically determine the hydraulic connections between the turbines and reveal the mechanism of the rapid rise in the WHP under the OAA load-shedding conditions. Theoretical derivations inferred that the drastic pressure changes in a trail shedding turbine (TST) are caused by the hydraulic connection with the lead shedding turbine (LST) in the S region. Furthermore, numerical simulations and model experiments were performed for the OAA load-shedding process, which confirmed the validity of the theoretical analysis. Finally, an analysis was conducted on the distribution of the water inertia in the upstream and downstream branch pipes, and engineering measures were proposed to guarantee the safe operation of PSS systems.

    Keywords
    Pumped-storage station, Pump-turbine, OAA load shedding, Transient pressure, Hydraulic connection, Model test
    National Category
    Environmental Engineering
    Identifiers
    urn:nbn:se:uu:diva-305290 (URN)10.1016/j.renene.2016.06.030 (DOI)000383811000004 ()
    Available from: 2016-10-18 Created: 2016-10-14 Last updated: 2017-11-29
    8. Simulation of Wind Speed in the Ventilation Tunnel for Surge Tanks in Transient Processes
    Open this publication in new window or tab >>Simulation of Wind Speed in the Ventilation Tunnel for Surge Tanks in Transient Processes
    Show others...
    2016 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 2, article id UNSP 95Article in journal (Refereed) Published
    Abstract [en]

    Hydroelectric power plants' open-type surge tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the surge tank. There is a great relationship between the wind speed and the safe use and project investment of ventilation tunnels. To obtain the wind speed in a ventilation tunnel for a surge tank during transient processes, this article adopts the one-dimensional numerical simulation method and establishes a mathematical model of a wind speed by assuming the boundary conditions of air discharge for a surge tank. Thereafter, the simulation of wind speed in a ventilation tunnel, for the case of a surge tank during transient processes, is successfully realized. Finally, the effective mechanism of water-level fluctuation in a surge tank and the shape of the ventilation tunnel (including length, sectional area and dip angle) for the wind speed distribution and the change process are discovered. On the basis of comparison between the simulation results of 1D and 3D computational fluid dynamics (CFD), the results indicate that the one-dimensional simulation method as proposed in this article can be used to accurately simulate the wind speed in the ventilation tunnel of a surge tank during transient processes. The wind speed fluctuations can be superimposed by using the low frequency mass wave (i.e., fundamental wave) and the high frequency elastic wave (i.e., harmonic wave). The water-level fluctuation in a surge tank and the sectional area of the ventilation tunnel mainly affect the amplitude of fundamental and harmonic waves. The period of a fundamental wave can be determined from the water-level fluctuations. The length of the ventilation tunnel has an effect on the period and amplitude of harmonic waves, whereas the dip angle influences the amplitude of harmonic waves.

    Keywords
    hydroelectric power plants, surge tank, ventilation tunnel, transient process, wind speed, numerical simulation, wave superposition
    National Category
    Ocean and River Engineering
    Identifiers
    urn:nbn:se:uu:diva-283792 (URN)10.3390/en9020095 (DOI)000371831900020 ()
    Available from: 2016-04-14 Created: 2016-04-14 Last updated: 2017-11-30Bibliographically approved
    9. Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plant
    Open this publication in new window or tab >>Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plant
    Show others...
    (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed) Submitted
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-318427 (URN)
    Available from: 2017-03-24 Created: 2017-03-24 Last updated: 2017-11-29
    10. Hydraulic damping on rotor angle oscillations: quantification using a numerical hydropower plant model
    Open this publication in new window or tab >>Hydraulic damping on rotor angle oscillations: quantification using a numerical hydropower plant model
    Show others...
    (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059Article in journal (Refereed) Submitted
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-318440 (URN)
    Available from: 2017-03-24 Created: 2017-03-24 Last updated: 2017-11-29
    11. Wear and tear on hydro power turbines: influence from primary frequency control
    Open this publication in new window or tab >>Wear and tear on hydro power turbines: influence from primary frequency control
    Show others...
    2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 87, 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
    12. Wear reduction for hydro power turbines considering frequency quality of power systems: a study on controller filters
    Open this publication in new window or tab >>Wear reduction for hydro power turbines considering frequency quality of power systems: a study on controller filters
    Show others...
    2017 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 32, no 2, 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
    13. Analysis on regulation strategies for extending service life of hydropower turbines
    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
    14. Burden on hydropower units for balancing renewable power systems
    Open this publication in new window or tab >>Burden on hydropower units for balancing renewable power systems
    Show others...
    (English)Article in journal (Refereed) Submitted
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-318444 (URN)
    Available from: 2017-03-24 Created: 2017-03-24 Last updated: 2017-03-24
    15. Allocation of Frequency Control Reserves and its Impact on Wear and Tear on a Hydropower Fleet
    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
    16. Linear Synthetic Inertia for Improved Frequency Quality and Reduced Hydropower Wear and Tear
    Open this publication in new window or tab >>Linear Synthetic Inertia for Improved Frequency Quality and Reduced Hydropower Wear and Tear
    (English)In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037Article in journal (Refereed) Submitted
    Keywords
    frequency control, hydropower, inertia, synthetic inertia, damping, power system stability, wear and tear
    National Category
    Engineering and Technology Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-308440 (URN)
    Available from: 2016-11-25 Created: 2016-11-25 Last updated: 2017-11-29
  • 11.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Bladh, Johan
    Yang, Jiandong
    Lundin, Urban
    Hydraulic damping on rotor angle oscillations: quantification using a numerical hydropower plant modelIn: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059Article in journal (Refereed)
  • 12.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Chung, Chi Yung
    Yang, Jiandong
    Wuhan University.
    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 plant2017In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed)
  • 13.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Chung, Chi Yung
    University of Saskatchewan.
    Yang, Jiandong
    Lundin, Urban
    Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plantIn: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed)
  • 14.
    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.

  • 15.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Saarinen, Linn
    Witt, Adam
    Oak Ridge National Laboratory.
    Smith, Brennan
    Oak Ridge National Laboratory.
    Yang, Jiandong
    Wuhan University.
    Lundin, Urban
    Burden on hydropower units for balancing renewable power systemsArticle in journal (Refereed)
  • 16.
    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.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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.

  • 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, 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.

  • 21.
    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.
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China.
    Advantage of variable-speed pumped storage plants for mitigating wind power variations: Integrated modelling and performance assessment2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 237, p. 720-732Article in journal (Refereed)
    Abstract [en]

    Developing the joint operation of hydro and variable renewable energy has emerged as a research trend, for handling the power variability. In recent years, variable-speed pumped storage plants (VSPSPs) have been proposed as an alternative to fixed-speed pumped storage plants, but VSPSPs require a higher investment cost for equipment. Hence, evaluating the advantages and demonstrating the value of VSPSPs are meaningful topics that have seldom been studied by quantitative analysis with a small timescale. In this paper, a performance assessment of VSPSPs in terms of power regulation for mitigating wind power variations is undertaken based on a timescale of seconds, and the assessment combines the analysis of physical features and the economic indicators regarding ancillary service markets. First, a numerical model integrating hydraulic-mechanical-electrical subsystems of VSPSPs with doubly fed induction machines is built with MATLAB/Simulink, and it is validated by on-site measurements of a Japanese VSPSP. Then, based on a Chinese VSPSP, a quantitative comparison between variable-speed units (VSUs) and fixed-speed units (FSUs) is conducted through four indicators based on ancillary service compensation in electricity markets in China and the USA. Twelve scenarios are investigated, including rasp studies based on measured wind power variations. The results show that the VSU outperforms the FSU by one order of magnitude in the aspect of power regulation performance: the maximum ratios between the VSU and the FSU of the four indicators (average of power difference, standard deviation of power difference, penalty energy, and power delay) are 3.92%, 7.85%, 3.92%, and 5.56%. VSUs not only stand out for contributing to power system stability but can also obtain a significantly higher assessment in the ancillary service of the electricity market from an economic perspective. These results could be an important source of support for the investment and development of variable-speed pumped storage technology.

  • 22.
    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.

  • 23.
    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.

  • 24.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yang, Jiandong
    Wuhan University.
    Guo, Wencheng
    Norrlund, Per
    Time-domain modeling and a case study on regulation and operation of hydropower plants2017In: Modeling and Dynamic Behavior of Hydro Power Plants, Institution of Engineering and Technology, 2017Chapter in book (Refereed)
  • 25.
    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.

  • 26.
    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.
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China.
    Zeng, Wei
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China;Univ Adelaide, Sch Civil Environm & Min Engn, Adelaide, SA 5005, Australia.
    Tang, Renbo
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China;Zhongnan Engn Corp Ltd, Power Construct Corp China, Changsha 410014, Hunan, Peoples R China.
    Hou, Liangyu
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China.
    Ma, Anting
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China.
    Zhao, Zhigao
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Hubei, Peoples R China.
    Peng, Yumin
    China Southern Power Grid Power Generat Co, Guangzhou 510630, Guangdong, Peoples R China.
    Experimental investigation of theoretical stability regions for ultra-low frequency oscillations of hydropower generating systems2019In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 186, article id UNSP 115816Article in journal (Refereed)
    Abstract [en]

    With the increasing momentum towards flexible power systems based on renewables, the role of hydropower has great importance, especially for providing balancing power. In this paper, a fundamental study on the operating stability of hydropower generating systems is conducted to reveal the practical characteristics for the newly emergent issue of ultra-low frequency oscillations. A unique study methodology is adapted by combing the theoretical analysis and the physical model experiment. In this paper, first, the set-up of the integral experiment platform for the transient processes of the pumped storage plants is presented. Second, a mathematical model of hydropower generating systems is built, and the theoretical stability analysis is conducted based on the Routh-Hurwitz criterion and the stability margin region. The model experiments related to the frequency stability of hydropower generating systems were conducted with reference to the stability region from theoretical analysis. The results demonstrate the sustained ultra-low frequency oscillations and frequency instability of hydropower units in experiments for the first time. Attenuation characteristics of the oscillations are theoretically derived based on the stability margin region, and then quantitatively identified by experiments. The experiment accorded with theoretical stability region within a reasonable tolerance that corresponded to the +/- 0.1 stability margin. (C) 2019 Elsevier Ltd. All rights reserved.

  • 27.
    Zeng, Wei
    et al.
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China..
    Yang, Jiandong
    Wuhan Univ, State Key Lab Water Resources & Hydropower Engn S, Wuhan 430072, Peoples R China..
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Instability analysis of pumped-storage stations under no-load conditions using a parameter-varying model2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 90, p. 420-429Article in journal (Refereed)
    Abstract [en]

    The S-shaped characteristics of a pump turbine make its rotational speed unstable when it starts up under no-load conditions with low head, affecting its ability to connect to the grid. Although advanced strategies for controlling the speed governor can alleviate this problem, they cannot fundamentally resolve the internal mechanisms that cause difficulties with a grid connection. Therefore, this study set out to theoretically explore the root cause of the instability and the dominant factors influencing it. A correlation fitting process was used to simplify the transcendental function for the pipe flow in elastic mode into a high-precision and low-order linear equation. Next, a detailed study of the two key factors affecting system stability (pump turbine S-shaped characteristics and water elasticity) was carried out based on the system model, and a comprehensive parameter that reflects the no-load characteristics was extracted. Furthermore, the Laplace transform and inverse transform decomposition were used to obtain a mathematical expression for the no-load oscillation in order to analyze the oscillation characteristics. Finally, simulations of no-load oscillations under various heads were performed to further validate the accuracy of the extracted comprehensive parameter for the no-load stability.

1 - 27 of 27
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