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1、第 31 卷 第 20 期 电 网 技 术 Vol.31 No.20 2007 年 10 月 Power System Technology Oct.2007 文章编号：1000-3673（2007）20-0109-12 中图分类号：TM917 文献标识码：A 学科代码：48040 电力系统低频振荡和储能系统 杜文娟1，高 山1，王海风2，Dunn Rod 3，程时杰4（1东南大学 电气工程学院，江苏省 南京市 210096；2贝尔法斯特女王大学，英国 贝尔法斯特；3 巴斯大学，英国 巴斯；4 电力安全与高效湖北省重点实验室(华中科技大学)，湖北省 武汉市 430074）Power Syste
2、m Oscillations and Energy Storage Systems W DU 1，GAO Shan1，WANG Hai-feng2，R DUNN 3，CHENG Shi-jie4（1 School of Electrical Engineering，Southeast University，Nanjing 210096，Jiangsu Province，China；2 The Queens University of Belfast，Belfast，UK；3University of Bath，Bath，UK；4Electric Power Security and High
3、Efficiency Lab (Huazhong University of Science and Technology)，Wuhan 430074，Hubei Province，China）ABSTRACT：This paper discusses the potential of applying energy storage systems to enhance power system oscillation stability.Firstly it briefly reviews the development of research and applications in the
4、 field of power system oscillation stability in the past four decades.That includes the analysis and control of power system oscillation stability.Then the paper addresses various issues in the applications of energy storage systems in power systems.The focus of discussions in the third part of the
5、paper is about applying energy storage systems to improve power system oscillation stability.The paper is concluded with several suggestions from the authors.KEY WORDS：power system oscillation stability；energy storage systems；FACTS；PSS 摘要：研究了将能量储存系统用于提高电力系统振荡稳定性的潜力。首先简要回顾了过去 40 年中在电力系统振荡稳定性领域的研究和应用的
6、发展情况，包括电力系统振荡稳定性的分析和控制；然后论述了在电力系统中应用能量储存系统的不同课题；第 3 部分重点讨论了用能量储存系统改善电力系统振荡稳定性问题；最后提出了一些建议。关键词：电力系统振荡稳定性；能量储存系统；灵活输电；电力系统稳定器 0 INTRODUCTION Power system oscillations are the electromechanical oscillations occurring in power systems with oscillation frequency in the range from 0.2 Hz to 2.0 Hz.Hence t
7、hey are also called power system low-frequency oscillations 1-4.Power system oscillations are the consequence of the development of interconnection of large power systems.Once started,the oscillations will continue for a while and then disappear,or continue to grow,causing system separation.Therefor
8、e this problem of power system oscillations is also refereed as power system oscillation stability.Power system low-frequency oscillations were first observed in Northern American power network in 1960s during a trial interconnection of the Northwest Power Pool and the Southwest Power Pool 2.Later,t
9、hey were reported in many countries,including the UK in 1980s.A low-frequency oscillation in a power system constrains the capability of power transmission,threatens system security and damages the efficient operation of the power system.It could occur in power system normal operation or fault condi
10、tions.Once it starts,it may grow to cause system to lose stability or to demand the level of power transfer to be reduced.Therefore,this problem has caused wide concerns and attracted the interests of many researchers.Generally,if the low-frequency oscillation is of a constant or increasing magnitud
11、e,it is called that the power system loses its oscillation stability.If the low-frequency oscillation subsides quickly,it is believed that the oscillation stability of the power system is maintained.If the low-frequency oscillation sustains for a certain period of time(several to tens of seconds)and
12、 sets eventually,it is said that the oscillation stability of the power system is maintained but needs improvement.Alternatively,the case that the oscillation does not subside quickly is also referred as that the 110 杜文娟等：电力系统低频振荡和储能系统 Vol.31 No.20 damping of the system oscillation is poor and requi
13、red more positive damping to be supplied.The causes of occurrence of the low-frequency oscillations or lacking of system oscillation damping vary among different power systems.It has been found that:The topological structure of a power system;The type and dynamic characteristics of the excitation sy
14、stem of generators;The load condition and type,are among the key factors affecting the damping of power system oscillations.Power system oscillations are classified mainly into three types,local oscillation,inter-area oscillation and intra-area oscillation.A local oscillation in a power system is th
15、at along a transmission corridor from a remote power plant to a large power network or load center.It is the oscillation of the power plant against the rest of the power system.Oscillation frequency is typically around 1 Hz to 2 Hz.An inter-area oscillation is that along a tie line connecting two la
16、rge networks in the power system.It is that one sub-system oscillates against the other and the oscillation frequency is usually between 0.5 Hz and 1 Hz.An intra-area power oscillation usually is of even lower oscillation frequency of around 0.2 Hz to 0.5 Hz.It often involves several sub-systems in
17、the power system to oscillate against each other and is the most complicated case of power system oscillations.To increase the damping of power system oscillations and improve system oscillation stability,the installation of supplementary excitation control,Power System Stabilizer(PSS),is a simple a
18、nd economical method.Through the effort of and experience accumulated by power engineers and researchers in the past three decades,this conclusion has been well accepted.To date,most major electric power plants in many countries are equipped with PSS.For example,in the UK it is compulsory that every
19、 generator must have a PSS installed.However,PSS does not solve the problem of power system oscillations completely.Usually it is more effective to damp local power oscillations as PSSs are installed in power plants.However,for suppressing inter-area or intra-area power oscillations,it has been foun
20、d that a new type of controllers,FACTS stabilizers,are more effective,which are associated with the new technology of Flexible AC Transmission Systems(FACTS)occurred at the beginning of 1990s 5.The advent and development of FACTS technology is the direct result of the fast advance in high-power elec
21、tronics made in 1980s and 1990s.With the application of controllers based on high-power electronics,the on-line control of line impedance,phase and magnitude of line voltage in power systems become possible.Thus the power transmission and distribution can achieve a great flexibility 6-7.Installation
22、 of FACTS devices is at key network nodes for voltage support or/and on transmission lines to regulate power flow.Usually they are classified into two types,thyristor-based FACTS devices and converter-based FACTS devices.For example,the following is three main thyristor-based FACTS devices:（1）Thyris
23、tor-Controlled Static Var Compensator(SVC),which controls the magnitude of line voltage.（2）Thyristor-Control Series Compensator(TCSC),which changes line impedance.（3）Thyristor-Control Phase Shifter(TCPS),which shifts the phase of line voltage.Those thyristor-based FACTS devices had been applied in p
24、ower systems even before the concept of FACTS was proposed formally by Prof.Hingarani in 1988 5.That is because the core of FACTS technology is the development of a so-called Unified Power Flow Controller(UPFC),the representative of new generation of converter-based FACTS devices 8.A UPFC has a shun
25、t part and a series part and can control line impedance,magnitude and phase of line voltage simultaneously in the range from the steady state to the transient of power systems.In fact the shunt and series part of the UPFC can operate separately or can be an individual converter-based FACTS device,ST
26、ATCOM(Static Synchronous Compensator,shunt part of the UPFC)and SSSC(Static Series Synchronous Compensator,series part of UPFC).They are the counterparts of thyristor-based FACTS devices,SVC and TCSC respectively.A FACTS stabilizer is a damping controller superimposed on a normal control function of
27、 a FACTS device,just like the case that PSS is superimposed on that of an AVR(Automatic Voltage Regulator).Since usually the FACTS device is installed at a key location in a power network,FACTS stabilizer is supposed to be more influential.In fact,it has been found that some of FACTS stabilizers are
28、 more effective in damping inter-area low-frequency 第 31 卷 第 20 期 电 网 技 术 111 power oscillations.Especially in a de-regulated power system,FACTS stabilizers have provided the network companies a new option of improving power system oscillation stability instead of having to rely entirely on PSSs bel
29、onging to generation companies.Over the next 15 years the UK government is committed to meet targets for renewable generation that will demand many changes to the infrastructure of various power supply systems within the UK.This will lead to fundamental changes in the near future with a fairly large
30、 percentage of renewable power generation penetrating the existing power systems.The increasing number of renewable generation units will have no means of regulation and control,adding uncertainty to power system operation and control.Hence high penetration of renewable generation imposes new burden
31、 and threat on the safe operation of existing power systems.One typical such example is the recent incident of blackout in Germany involving 8 countries in Europe on the 4th November 2006 9.In order to meet the challenges from the integration of renewable generation with existing power systems,Energ
32、y Storage Systems(ESS)are considered to be one of the future technologies that can bring about many benefits to improve the safety and efficient operation of existing power systems.There are four types of ESS that are reckoned to have great potential to be applied in power systems 10-11.They are Sup
33、erconducting Magnetic Energy Storage(SMES),Battery Energy Storage Systems(BESS),Advanced Capacitors(AC)and Flywheel Energy Storage(FES).Their applications in power systems cover a wide range of system operation,from steady-state,dynamic to transient in generation,transmission and distribution.One of
34、 typical examples is the utilization of ESS as the fast generation sources to solve the problem associated with the intermittence of renewable generation,such as wind 12-15.From the point of view of power system operation and control,essentially,an ESS device installed in a power system provides an
35、extra way of regulation and control.Hence as far as the improvement of power system oscillation stability is concerned,ESS offers the new option to the conventional PSS and the more recent FACTS stabilizers.In addition,ESS can be installed in the power network or/and power generation sites.They can
36、function by exchanging both active and reactive power with the power system.Hence technologically ESS should be more flexible,more effective and more efficient in enhancing power system oscillation stability.This paper intends to address the issue of applying the technology of energy storage systems
37、 in improving power system oscillation stability.It will review briefly in the next section the research on the analysis and control of power system oscillation stability.In the third section,it will give an introduction on the applications of energy storage systems in power systems.In the fourth se
38、ction,a survey is presented on the energy storage systems to improve power system oscillation stability,followed by conclusions of the paper.1 ANALYSIS AND CONTROL OF POWER SYSTEM OSCILLATION STABILITY Analysis and control of power system oscillation stability is mainly based on the linearized model
39、 of a power system.Although a power system oscillation could start at a normal or a fault operating condition,analysis and control based on non-linear model of the power system has been proved not realistic in order to cover the operation under the fault condition.Hence it has become the mainstream
40、of methodology in studying power system oscillation stability that linearized models are use to consider the case of the power oscillations at the normal operating condition.Conclusions obtained from linearized models then are examined through power system simulation under the fault condition 1-3.Fo
41、r the analysis of power system oscillation stability,damping torque analysis is a simple and effective method.It was firstly introduced in 16 to study the damping effect of AVR on power system oscillations based on the linearized Philips-Heffron model of a single-machine infinite-bus power system 17
42、.It was later used to design PSS,resulting in the proposal of famous phase compensation method 18.Both the damping torque analysis and phase compensation method are based on classical control theory in the frequency domain.They are easy to be understood and used as well as proved very successful for
43、 single-machine infinite-bus power systems.It is worthwhile to point out that the Phillips-Heffron model,damping torque analysis and phase compensation method have been later used for the analysis and design of FACTS stabilizers 19-22 with 112 杜文娟等：电力系统低频振荡和储能系统 Vol.31 No.20 many constructive result
44、s provided.However,the biggest challenge regarding to them is their extension to the case of a multi-machine power system.Several attempts have been made 23-25 but proved not very straightforward.They have turned out that either the model of damping torque analysis is very complicated with all gener
45、ators in the system involved 23 or the analytical calculation becomes meaningless when damping torque coefficients are immeasurable matrices 24-25.In the study of oscillation stability of a power system,the mostly-commonly used method is modal analysis or eigensolution.Basically,the method is based
46、on the linearized state-space representation of the power system(the so-called ABCD model).By using certain numerical techniques,such as the QR decomposition method,eigenvalues of system state matrix are calculated.Those eigenvalues associated with the electromechanical power oscillations are identi
47、fied as the oscillation modes of the power system.Hence local oscillation modes calculated are related to the local low-frequency oscillations.Inter-area oscillations are determined by the inter-area oscillation modes and so are the intra-area oscillations.In a single-machine infinite-bus power syst
48、em,there is only one local oscillation mode with a single oscillation frequency.Hence it is applicable in using the classical control theory in the frequency domain for the analysis of oscillation stability.That is why the damping torque analysis and phase compensation method are successful in the s
49、ingle-machine infinite-bus power system.In a multi-machine power system,there could be many oscillation modes being excited in power oscillations.Machines in the power system are related to oscillation modes differently.To investigate the degree of each machine involving in power oscillations relate
50、d to different oscillation modes,there are two commonly-used methods,computation of residue index and participation factor 26-27.The residue index is derived from the basic theory of modal control.According to modal control theory,an observability index and controllability index can be calculated fo