利用复数储能设备以强健电力系统.doc

Autonomous Dispersed Control to Energy Storage Facilities for the Enhancement of System Stability1Autonomous Dispersed Control toEnergy Storage Facilities forthe Enhancement of System Stability利用複數儲能設備以強健電力系統穩定度之自律分散型控制Chung-Neng Huang黃崇能國立台北科技大學車輛工程系AbstractIn recent years, owing too highly meshed network and the increasing interest in wholesale wheeling alternatives open to third-party generations, the problem of system instability grows into a serious matter. This paper proposes an autonomous dispersed control conception of multiple energy storage facilities (ESFs) to alleviate the short-term disturbance for stability enhancement. In the proposal, each individual ESF is only subjected to a simple rule to determine the charge/discharge actions. Here, the area control error (ACE) is taken into account the control in a multi-machine system. Additionally, the automatic generation control (AGC) as speed governor is also considered. Consequently, the control results are consistent with reality. Since the scenario is particular interesting to the case in the loop networks, the WSCC three-machine nine-bus system is taken as a study example to confirm the appropriateness of the proposal. Keywords:System Stability, Autonomous Dispersed Control, and Energy Storage Facility.2臺北科技大學學報第三十七之一期摘要由於電力產業的開放競爭及輸電網路之高度密集化的結果，造成近年來系統穩定性問題日驅嚴重。為有效解除此一問題，故本文提出一儲能設備群之自律分散控制法來消除系統因不平衡所產生之干擾以增強系統穩定。在此控制規則下，各個分佈在系統中的儲能設備僅須依其區域性資訊亦即檢測連接線路潮流的大小來決定充放電的動作即可。此外,自動發電控制如調速機等控制功能亦納入在多機系統的控制過程中以維持控制結果的客觀性。因為在開放性的輸電環境中將更能彰顯出此控制概念的效果，故本文將透過WSCC之3機9匯流排的輸電系統來驗證其有效性。關鍵詞：電力系統穩定度、自律分散型控制、儲能設備投稿受理時間: 92 年 10 月 15 日 審查通過時間: 93 年 1 月 2 日241I. IntroductionFor the reasons of system restructuring and open transmission access, the regional power transfers vary over a wide range. Consequently, there are more and more power transactions are dealt via the transmission system. However, the capacity of system security is constrained by physical limits and reliability requirements 1-2. Nonetheless, many concerning utilities of electric power devote multitude of effort and capital to enhance power system in a sufficient robust for surviving a cascading disturbance in a heavy demand, the interconnected network still suffer from widespread and lengthy blackouts 3-5.As well known as above lesson, the impacts of a power disturbance occurring in anywhere of the system, not only causes internal frequency of the system in perturbation but also possibly influence neighboring systems to be instable via tie lines 6. In order to alleviate such a propagating disturbance from one system to another, this paper presents a possible solution to this problem by introducing an autonomous dispersed control conception on multiple ESFs to alleviate the short-term disturbance for the enhancement of system stability 7-8. However, a large number of system data and heavy computations are always needed for carrying out the above proposals. Moreover, such the patterns of central control are lack of flexibility for the extension from the local areas to interconnected system.Autonomous Dispersed Control to Energy Storage Facilities for the Enhancement of System Stability3System iSiSjXijPDSystem jSystem kXikXjkSkPijPjkPkiSi, Sj ,Sk : Energy Storage FacilityPD : Injection Power DisturbanceFig. 1. Imagination of ESF Control SystemIn this paper, the imagination of proposed conception is shown in Fig.1. Each tie line which connects with two systems is installed an ESF in its both terminals. The function of each ESF can be considered as a power buffer to absorb the flow deviation of the tie line as ACE resulting from a disturbance in a system. By the proposed control, ACE of each system can be subsided to be minimum and stabilize system oscillation. Furthermore, since the proposed control is only based on the local information of an area, it is possible to extend the control scale to an interconnected system. In order to perform the particular interesting of proposed conception to the case in the loop networks, the WSCC three-machine nine-bus system is taken as a study example to confirm the appropriateness and effectiveness of the control.II. Proposed Control SchemeThose roles such as ACE, tie-line bias control (TBC), and speed governors as well as AGC which play in the proposed control are described as following:2.1 AGC Control 9For supplementary control of interconnected system, at the fist observing the performance of speed control only. Since the internal generation of a power system is responsible to match its internal load requirements, the control function is considered to be independent from adjacent systems. An interesting observation on power and speed correlation of a speed governor so far as known as the feature of droop R which makes the system self regulate to some extent. The droop is defined as;Droop (1)Note that, the sloping nature of Ri an increasing Pm accelerates the rotor of generator and attempts to raise the system frequency f. The quantity droop is a speed droop expressed in Hz/per-unit megawatts. Now, considering the dynamics of rotor inertia with speed governor control, the correlation between a prime mover power and the output power of a generator can be expressed as4臺北科技大學學報第三十七之一期 (2.a) (2.b) (2.c)Pmi : mechanical output power of unit i in pu. Pei : generator output power of unit i in pu.Hi : inertia constant for unit i in S. t = time in S.where, frequency deviation of unit i.Consequently, for a control area where n generators exist, Eq. (1) may be rewritten as (3) : total prime mover output in an area.: total electric output in an area.: total inertia constant of an area. : total droop of an area.The required condition for power balance of the system is (4)Here, the right side terms of equation (4) present total load, system losses and tie-line power, respectively. 2.2 ACE Control 10Considering a power system i intercon- nected with the neighboring systems via t tie lines with reactance Xij (j=1,t) , the net interchanged power in/out the system can be expressed as (5)from Eq. (4) and (5) imply that the basic objective of ACE control is to restore power balance between each area. It is matching when the control action maintainssystem frequency fixed at scheduled interchange power with neighboring area maintained scheduled value.Consequently, under the fundamental mode of system operation, each control area should contribute its assigned share of generation to hold ACE on zero. That is, if there is a power disturbance occurring in a certain area, it should be supplemented only within the area but from other areas.The ACE for each area is defined as (6)wherePi(t): the deviation of net area interchange (MW).Autonomous Dispersed Control to Energy Storage Facilities for the Enhancement of System Stability5r :bias coefficient , where (MW/Hz)f(t) :deviation of interconnection frequencyWhen the balance of all power injections in a control area is losing, the frequency support will cause all other control areas to compensate the unbalance deviation by power flow via tie lines for maintaining their ACE close to zero. That is, it may unduly stress certain transmission corridors and causes unscheduled tie-line flows. Consequently, the major objective of the proposal contribution is to limit the unscheduled power flows occurring in the interconnection by ESFs.III. Autonomous ESF ControllerIn order to fix system frequency f in a flat rated, the control objective is by holding ACE down to zero as mentioned above. By introducing the ACE control of ESF, equation (6) can be represented as (7)where,S(t) : charge/discharge power of ESFs in area i.for the control objective to (8.a) (8.b)Practically, the mechanical delay of system control should be considered, thenif (9)In other words, if the deviation of net interchanged power Pi(t) can be completely supplemented by ESFs, then the perturbation of system frequencyf(t) can be subsided to zero. Thus, the system stability can be enhanced.In the proposal, the supplemental value Si(t) of ESFs is determined by the controllers which subject to following simple rules:Pi (net power)Integral Controlcharge/dischargePi (t)Si (t)PS (scheduled flow)+ACEi (t)Fig. 2. Alleviation of ACE by the Control of ESFs 1.if the net interchanged power Pi(t) is positive, then ESF begins to charge power.2.if the net interchanged powerPi(t) is negative, then ESF begins to discharge power.Through such rules of ESFs, the deviation of net interchanged powerPi (t) can be supplemented. Here, the supplemental value of ESF can be determined and implemented by the control of Fig. 2. In order to enhance the stability of ESF charge/discharge actions, an integral control is added to govern the response of ESF.6臺北科技大學學報第三十七之一期. Numerical StudiesFor the confirmation to the proposed control of ESFs, a simulation study is held in this chapter. In Fig. 3, the WSCC three-machine nine-bus system with 3 ESFs is shown. Noticeably, the connection of those transmission lines forms a loop-interconnected network is a particular feature of the test system. Where, Bus #1 is considered as a very large system as slack bus, Bus#2 and Bus#3 are the generation buses. All of the concerning parameters of those generators, controllers and transmission lines are shown in Table 1 and 2. Moreover, since the bus #5, #6 and #8 are assigned to be the load centers in the system, ESFs are only installed in these buses for the control effectiveness. Where, the capacity of each ESF is set on 0.1 pu. with the maximum output power of 0.05 pu. All of the simulation results are obtained through the AC power flow calculations. Fig. 3. WSCC Three-machine Nine-bus System with Three ESFsTable 1. The Parameters of Generators and Controllers in the System of Fig. 3.generatorunitG1G2G3capacity pu.23.6406.40003.0100inertia constantH S150.002.00001.0000speed droopR Hz/pu.100.004.00002.0000Power Share %0.00000.75000.2500Xd”pu.0.06080.11980.1813XT pu.0.05760.06250.0586Table 2. The Line Reactances of the System Autonomous Dispersed Control to Energy Storage Facilities for the Enhancement of System Stability7unitlineReactancepu.L10.0100 + j0.0850L20.0170+ j0.0920L30.0320+ j0.1610L40.0085+ j0.0720L50.0390+ j0.1700L60.0119+ j0.1008Table 2. The Results of Bus Voltages,Angle Corresponding to theInjection Power in Fig. 3unitBus Voltagepu.Angledeg.Ppu.Qpu.#11.0400000.000000.7160.270#21.0250009.300001.6300.067#31.0250004.700000.850-0.109#41.026000-2.2000000.0000.000#50.982854-4.297867-1.250-0.500#61.007676-3.161691-0.900-0.300#71.0260002.5934580.0000.000#81.002014-0.676657-1.000-0.350#91.0320000.5361450.0000.000Table 3. Load-Flow Results of WSCC SystemVolumeFlow DirectionPQBus #4 Bus #50.489710.47113Bus #4 Bus #60.219180.16543Bus #5 Bus #7-0.78419-0.16434Bus #6 Bus #9-0.68772- 0.18932Bus #7 Bus #80.845810.26519Bus #8 Bus #9-0.16228-0.14616All Above Results are Obtained Via AC Load-Flow Calculations Based on 100 MVA.As shown in Table 3, the bus voltages and phase angles without control are calculated. By above results, the flows of each line in the system can be found and shown in Table 4.The scenario of ESFs control in the simulation study is, under the fundamental mode of system operation, each control area should contribute its assigned share of generation to hold ACE on zero. On 2nd second, an increased power of 0.05 pu. is impacted on Bus #8. Fig. 4 shows the oscillations of each generator where system without ESFs controls. On the other hand, Fig. 5 is the controlled result on system stability by ESFs. Through the comparison of Fig. 4 and Fig. 5 knows that under the control of ESFs, system oscillation results from disturbance power can be substantially suppressed not only to its amplitude but also shorten oscillation time. Moreover, for the implementation of control objectives, the output and charging situation of each ESFs are shown in Fig. 8 and 9.Fig. 4. Frequency Deviation without ESF Control 8臺北科技大學學報第三十七之一期Fig. 5. ESF Control in Frequency Performance Fig. 6. Flow Deviation without ESF ControlFig. 7. ESF Control in Tie-Line Flow Performance Fig. 8. Action of ESFsFig. 9. ESF States of ChargingFig. 8 and 9 imply that for supplement the impact on Bus #8, all ESFs as S1, S2 and S3 are on the situation of discharging and exert the maximum output power 0.005 pu.V. ConclusionsFor the enhancement on power system stability to prevent from a widespread oscillation propagating through the interconnected system results from an impacted disturbance, an autonomous dispersed control conception by ESFs is proposed in this paper. In the proposal, since the control action of each ESFs is only based on the local information of its adjacent lines, it is possible to extend the control scale in an interconnected system. In order to perform the particular interesting of proposed conception to the case in the loop networks, a three-machine seven-bus with two-loop test system is taken as a study example to confirm the appropriateness and effectiveness of the control.Autonomous Dispersed Control to Energy Storage Facilities for the Enhancement of System Stability9AcknowledgementThis work was supported in part by the National Science Council of the R.O.C. under Grant NSC92-2213-E-027-046Conferences1Enrico De Tuglie, Maria Dicorato, Massimo La Scala and Pierangelo Scarpellini, “ A Static Optimization Approach to Assess Dynamic Available Transfer Capability”, IEEE Transactions on Power System, Vol. 15, No. 3, Aug. 2000, pp. 1069-1076.2Goran Strbac, Daniel Kirschen and Syed Ahmed, “ Allocating Transmission System Usage on the Basis of Traceable Contribu- tions of Generators and Loads to Flows”, IEEE Transactions on Power System, Vol. 13, No. 2, May 1998, pp. 527-534.3W. R. Lachs, “Controlling Grid Integrity after Power System Emergencies,” IEEE Transactions on Power System, Vol.