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Regulation quality for frequency response of turbine regulating system of isolated hydroelectric power plant with surge tank
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)
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2015 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 73, 528-538 p.Article 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.

Place, publisher, year, edition, pages
2015. Vol. 73, 528-538 p.
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:uu:diva-260775DOI: 10.1016/j.ijepes.2015.05.043ISI: 000360771800057OAI: oai:DiVA.org:uu-260775DiVA: diva2:848390
Available from: 2015-08-24 Created: 2015-08-24 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Hydropower plants and power systems: Dynamic processes and control for stable and efficient operation
Open this publication in new window or tab >>Hydropower plants and power systems: Dynamic processes and control for stable and efficient operation
2017 (English)Doctoral 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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 140 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1494
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-318470 (URN)978-91-554-9871-9 (ISBN)
Public defence
2017-05-19, Polhemsalen, Ångtröm 10134, Lägerhyddsvägen 1, Ångströmlaboratoriet, Uppsala, 13:15 (English)
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Available from: 2017-04-28 Created: 2017-03-24 Last updated: 2017-05-05

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Yang, Weijia

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