Advanced simulation of hydroelectric transient process with Comsol/Simulink

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1 IOP Confeence Seies: Eath and Envionmental Science Advanced simulation of hydoelectic tansient pocess with Comsol/Simulink To cite this aticle: L Li and J D Yang 2010 IOP Conf. Se.: Eath Envion. Sci View the aticle online fo updates and enhancements. Related content - Study on the stability of watepowe-speed contol system fo hydopowe station with upsteam and downsteam suge chambes based on egulation modes J P Chen, J D Yang, W C Guo et al. - 3D numeical simulation of tansient pocesses in hydaulic tubines S Cheny, D Chikov, D Bannikov et al. - Tansitoy flow in a complex hydoelectic scheme with multiple intakes and wate tanks D M Bucu, C M Ghegu, N O Tnase et al. This content was downloaded fom IP addess on 24/11/2017 at 11:56

2 25th IAHR Symposium on Hydaulic Machiney and Systems Advanced simulation of hydoelectic tansient pocess with Comsol/Simulink 1. Intoduction L Li 1 and J D Yang 1 1 State Key Laboatoy of Wate Resouces and Hydopowe Engineeing science, Wuhan Univesity, Wuhan, , China belli2008@sina.com Abstact. In the study of hydoelectic system, the eseach of its tansient pocess and the impovement of its simulation accuacy ae esticted mainly by the pecision mismatch among the hydaulic and powe system models. Simulink povides a vey ich contol and automation model libay system, thus electical and mechanical conditioning contol systems can be accuately simulated. Howeve, it can only solve time but spatial integal poblem. Due to that cause, the hydaulic system model often needs to be simplified in couse of the simulation of hydoelectic tansient pocess. Comsol, a patial diffeential equation (PDEs)-based multiphysics finite element analysis softwae, can pecisely simulate the hydaulic system model. Being developed in the Matlab envionment, it also can seamlessly integate with Simulink. In this pape, based on the individual component model, an integal hydaulic-mechanical-electic system model is established by implementing Comsol code into the Simulink S-Function. This model helps to study the inteaction between the hydaulic system and the electic system, and analyze the tansients of a hydo plant. Meanwhile the calculation esults ae compaed and analyzed with the geneal simulation system only by using Simulink. With the apid constuction and development of China lage-scale hydopowe stations, the associated secuity and stability issues among hydaulic, mechanical and electical systems becomes inceasingly pominent. In the past eseach, the thee systems ae often studied espectively by expets of each field. Among those eseaches,the coupled inteaction is usually not consideed and the model accuacy always can not meet the demand of eseach, which leads to simplification of the impacts among hydaulic, mechanical and electical system. Unde such condition, this pape takes a single-machine infinite-bus powe system as an example by using Comsol/Simulink. Based on this model, the inteaction between systems is studied and simulation esults ae given and analyzed. The hydaulic-mechanical-electic coupled system is shown in Fig. 1. Fig. 1 Hydaulic-mechanical-electic coupled system 2. How Comsol woks Comsol (fomely FemLab) is a finite element analysis, solve and Simulation softwae package fo vaious physics and engineeing applications. It also offes an extensive inteface to MATLAB and allows fo enteing coupled systems of patial diffeential equations (PDEs), 1-D, 2-D o 3-D, nonlinea and time dependent. The specified PDEs and bounday conditions can be epesented by the geneal fom: c 2010 Ltd 1

3 25th IAHR Symposium on Hydaulic Machiney and Systems 2 u u e + d + Γ = F in Ω (1) a 2 a t t T R n Γ = G+ u μ on Ω (2) R = 0 on Ω (3) Whee eq. (1) is satisfied inside the domain Ω, eq. (2) (genealized Neumann bounday) and eq. (3) (Diichlet bounday) ae both on the bounday of Ω. 2.1 Hydaulic system model In the study of tansient pocess in a hydopowe station, the hydaulic system is geneally calculated as one dimensional compessible unsteady flow. Consideing head loss and compessibility of wate and pipe wall, the basic equations of the wate hamme pessue (including motion and continuity equations of unsteady flow) ae as follows: 2 H Q Q fq Q ga + Q + A + l l t 2D = 0 (4) 2 H H a Q Q + A + = 0 l t g l (5) To be consistent with the tansfe function in Simulink, eq. (4) ~ (5) should be into dimensionless fom: gah h Q q q fq + ( q+ q ) + + q+ q ( q+ q ) = (6) LQ x AL x t 2DA 2 Q h h a Q q ( q+ q ) + + = 0 0 AL x t galh x (7) H H Q Q l 0 0 h =, q =, x = H Q L (8) In this case, the PDE model fo the inside of the domain is given by eq. (6) ~ (7). The geneal fom is hee used fo this type of non-linea poblem. In Appendix 6.1 the coesponding pat of Comsol code is povided. 2.2 Implement Comsol code into S-Function Comsol has standad facilities to expot models to Simulink. Being a non-linea model which can not be simulated efficiently by Simulink, a standad expot of the hydaulic system model to Simulink is not vey pactical. A possible solution to this poblem is to implement the Comsol code in the Simulink S-function. The S-function solves each time step the hydaulic system model using the FemLab solve. Depending on the input value of q fom Simulink, afte each time step the value of h fom Comsol is expoted. Appendix 6.2 shows details of how an S-function can be pogammed fo the use with this Comsol model and solve. 3. Models unde Simulink envionment Simulink, developed by The MathWoks, is widely used fo modeling, simulating and analyzing multidomain dynamic systems. Its pimay inteface is a gaphical block diagamming tool and a customizable set of block libaies. Simulink povides a vey ich contol and automation model libay system, thus electical and mechanical conditioning contol systems can be accuately simulated. 3.1 Hydo tubine model The chaacteistic of tubine is too complex to be accuately expessed by a mathematical expession due to 2

4 25th IAHR Symposium on Hydaulic Machiney and Systems the complexity of flow movement. In this pape, tubine chaacteistic cuve is used and descibed by two tables, namely: 1) table of the elationship between unit speed, guide vane opening and unit dischage; 2) table of the elationship between unit speed, guide vane opening and unit toque. Look-up Table (2-D) in Fig. 2 is a twodimensional look-up table module. Accoding to the known unit speed, head and opening, the unit dischage and toque can be deived though intepolation calculation by this module. 3.2 Tubine goveno model The paallel PID goveno is used in this pape, shown in Fig. 3. 1/b t x 1 1 b t T d s T y 1s y T ns/ b t b p Fig. 2 Hydo tubine model Fig. 3 Tubine goveno model 3.3 Unit geneato, Excitation system and PSS models The thee models ae diectly selected fom the SimPoweSystems in Matlab. The electical pat of the Unit geneato model is sixth-ode state-space and takes into account the dynamics of the stato, field, and dampe windings. And the excitation system block implements a DC excite, without the excite's satuation function. The basic elements that fom the excitation system block ae the voltage egulato and the excite. PSS can add damping to the oto oscillations of the synchonous machine by contolling its excitation. The output signal of the PSS is used as an additional input (vstab) to the Excitation System block, and the input signal in this pape is the machine speed deviation. 4. Simulation of hydaulic-mechanical-electic coupled system Fig. 4 Model of hydaulic-mechanical-electic integal coupled system By combining each pat of above models, the model of hydaulic-mechanical-electic integal coupled system is built, as shown in Fig Application example Accoding to the established coupling system model, an actual Hydopowe plant is simulated. The calculatio n data of the plant ae as follows: L=780m, D=14.5m, a=1000m/s, f=0.02, D 1 =8.15m, H =106m, Q =624.5 m 3 /s, P m =605MW; b t =0.4, T d =7s, Ty=0.02s. The paametes of excitation and PSS model can be found in efeence 4. 3

5 25th IAHR Symposium on Hydaulic Machiney and Systems Calculation conditions: 1) Thee-phase shot cicuit: T=5.0s, it suddenly happens thee-phase shot-cicuit at the teminal outlet of geneato with nominal output, the fault is emoved at T= 5.1s. 2) Load ejections: The plant with nominal output ejects 80% load at T=5.0s. 4.2 Results analysis Figue 5 and 6 shows the calculation esults of above two calculation conditions and compaison with the system of simplified elastic wate hamme model: hs () Ts w G () s = = ( T = LQ / gh A, T = 2 L/ a ) h w (9) qs () Ts 2 2 Fig. 5a Relative change of dischage (condition 1) Fig. 6a Relative change of dischage (condition 2) Fig. 5b Relative change of head (condition 1) Fig. 6b Relative change of head (condition 2) 4

6 25th IAHR Symposium on Hydaulic Machiney and Systems Fig. 5c Electomagnetic powe/p.u. (condition 1) Fig. 6c Electomagnetic powe/p.u. (condition 2) Fig. 5d Load angle/deg (condition 1) Fig. 6d Load angle/deg (condition 2) 1) As can be see fom Fig. 5c, d and 6c, d, by using Comsol and simplified models, the esults of electomagnetic powe and load angle unde two conditions ae nealy the same. Howeve, these two models did obvious impacts on the esult of dischage and head. The maximum diffeences of dischage and head between two models ae about 3%. 2) When it had a lage distubance at electical system side (condition 1), the changes of tubine dischage and head ae vey small. The biggest changes ae only and espectively. On the contay, the electomagnetic powe of geneato and the load angle had geat changes. Paticulaly, the change of the electomagnetic powe had amounted to 2 afte the distubance. Fom the simulation esults, we can see that effects of electical system distubance on itself ae elatively lage than hydaulic system. In theoy, the eason is that in the tansient pocess shot-cicuit ecovey of the electic powe system takes quickly while the tubine goveno is too late to espond in such a shot peiod, which leads to little change to hydaulic system. 3) When it occu a lage distubance at hydaulic system side (condition 2), the changes of tubine dischage and head ae vey apid and geat. Fom Fig. 6c and 6d it can be seen that the distubance to the electical system is also vey lage and the electomagnetic powe of geneato had a significant oscillation. We can say that the impact of hydaulic system distubance on the electical system is elatively lage. 5

7 25th IAHR Symposium on Hydaulic Machiney and Systems 5. Conclusions Accoding to the electomechanical components of Hydopowe Station, hydaulic-mechanical-electic integal coupled system model of single-machine infinite-bus powe system is built in this pape. The model consides a moe compehensive inteaction between hydaulic and electical system. With the help, we can analysis many kinds of hydaulic-mechanical-electic tansition pocess and get the main conclusions as follows: 1) The accuacy of hydaulic model has little impact on the electical system in a singlemachine infinite-bus powe system. But it did obvious diffeence to the hydaulic system. The Comsol model is moe desiable in the study of hydaulic tansient pocess. 2) The impact of hydaulic system and electical system on each side will be diffeent. The distubance fom hydaulic system side makes a bigge effect on electical side. In shot, the hydaulic system distubance will make significant changes of head and dischage, which finally leads to the apid and geat vibation of the geneato mechanical toque. Howeve, the inte-coupling elations of hydaulic system, mechanical system and electical system ae vey complex. Only a simple machine infinite-bus system had been studied in this pape. In tems of the station with moe than one machine and a suge tank, isolated powe netwok, the inteactions ae so complicated that a futhe study is still needed. 6. Appendix 6.1 Main coesponding Comsol code 6

8 25th IAHR Symposium on Hydaulic Machiney and Systems 6.2 Implementation of a Comsol model in S-function 7

9 25th IAHR Symposium on Hydaulic Machiney and Systems e a, d a Γ,F,G,R L A D a f H, Q H 0,Q 0 H,Q D Nomenclatue Mass and damping coefficients in Comsol Comsol coefficients Length of penstock [m] Coss section aea of penstock [m 2 ] Coss section diamete of penstock [m] Wave speed[m/s] Head loss coefficient Pessue[m] and dischage[m 3 /s] at section l and time t Initial values of Pessue[m] and dischage [m 3 /s] Unit nominal Pessue[m] and dischage[ m 3 /s] Nominal diamete of tubine [m] P m h q y p e delta b t b p T d T n T y Nominal mechanical powe [MW] Relative change of head Relative change of dischage Guide vane elative opening electomagnetic powe [p.u.] Load angle [deg] Tempoay speed doop Pemanent speed doop Time constant of damping device [s] Deivative time constant Sevomoto esponse time constant [s] Refeences [1] Comsolab Comsol Multiphysics Vesion 3.5a 2008 [2] The Mathwoks Inc Using Simulink 2001 [3] MathWoks SimPoweSystem 4 use Guide 2004 [4] IEEE Standad [5] Wylie E B and Steete V L 1978 Fluid Tansients (New Yok, USA: McGaw-Hill) [6] Kundu P 1994 Powe system Stability and Contol (New Yok, USA: McGaw-Hill) [7] Wu R and Chen J 1997Hydaulic Tansients of Hydopowe Station (Beijing: China Wate Powe Pess) [8] Shen Z 1997 Tubine Regulation (Beijing: China Wate Powe Pess) [9] Shen Z and Zhang Y 1988 Stability and Contol of Hydoelectic Plant (Wuhan: Huazhong Univesity of science and technology Pess) [10] van Schijndel A W M 2005 Implementation of FemLab in S-Functions Poc. of the COMSOL Multiphysics Use's Confeence (Fankfut, Gemany) [11] Su H and Zhang J 2008 Study on the Hydaulic-mechanical-electic Coupled System and Its tansient Automation of Electic Powe Systems 32(13) [12] Wei Z, Chen J and Pan X 2000 Study of the inteactions among hydaulic, mechanical and powe system Automation of Electic Powe Systems 24(24)