| 1. |
- Bao, Haiyan, et al.
(författare)
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Condition of setting surge tanks in hydropower plants - A review
- 2018
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 81, s. 2059-2070
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Forskningsöversikt (refereegranskat)abstract
- 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.
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| 2. |
- Tang, Renbo, et al.
(författare)
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Dynamic regulation characteristics of pumped-storage plants with two generating units sharing common conduits and busbar for balancing variable renewable energy
- 2019
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 135, s. 1064-1077
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Yang, Weijia, 1989-, et al.
(författare)
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Advantage of variable-speed pumped storage plants for mitigating wind power variations : Integrated modelling and performance assessment
- 2019
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 237, s. 720-732
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Yang, Weijia, 1989-, et al.
(författare)
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Burden on hydropower units for short-term balancing of renewable power systems
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Yang, Weijia, 1989-, et al.
(författare)
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Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plant
- 2018
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 115, s. 1014-1025
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Yang, Weijia, 1989-, et al.
(författare)
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Experimental investigation of theoretical stability regions for ultra-low frequency oscillations of hydropower generating systems
- 2019
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Ingår i: Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0360-5442 .- 1873-6785. ; 186
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Yang, Weijia, 1989-, et al.
(författare)
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Hydraulic damping mechanism of low frequency oscillations in power systems : Quantitative analysis using a nonlinear model of hydropower plants
- 2018
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Ingår i: Applied Energy. - : ELSEVIER SCI LTD. - 0306-2619 .- 1872-9118. ; 212, s. 1138-1152
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Yang, Weijia, 1989-, et al.
(författare)
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Model experiments and study on regulating stability of isolated hydropower plants
- 2019
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Ingår i: 29th IAHR symposium on hydraulic machinery and systems. - : IOP Publishing.
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Konferensbidrag (refereegranskat)abstract
- Hydropower shoulders a large portion of the regulation and balancing duty in many power systems all over the world. The stable regulation of hydropower plants (HPPs) is a conventional and crucial research topic, and many meaningful studies have been carried out by theoretical analysis and numerical simulations; however seldom experimental works on this issue are reported. This paper investigates stability of isolated HPPs based on model experiments on an integral experiment platform for transient processes of pumped storage plants in Wuhan University. Theoretical stability analysis is conducted based on Routh Hurwitz stability criterion, and the stability region of the model power plant is obtained. The experiment results validate the theoretical analysis on the system stability, and the instability of the hydropower system due to poor settings of speed governor parameters are captured and demonstrated. This work presents initial results of experimental study on oscillation characteristics and regulation performance of HPPs for power system stability.
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| 9. |
- Yang, Weijia, 1989-, et al.
(författare)
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Wear reduction for hydro power turbines considering frequency quality of power systems : a study on controller filters
- 2017
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Ingår i: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 32:2, s. 1191-1201
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Saarinen, Linn, 1980-, et al.
(författare)
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Allocation of Frequency Control Reserves and its Impact on Wear and Tear on a Hydropower Fleet
- 2018
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Ingår i: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 33:1, s. 430-439
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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