SETTING U A GRID SIMULATOR A. Notholt, D. CollMayor 2, A. Engler Intitut für Solare Energieverorgungtechnik (ISET). Königtor 9. D349 Kael anotholt@iet.unikael.de 2 Department of hyic. Univerity of Balearic Iland Ctra. Valldemoa, km 7. / E722 Balearic Iland The tet and validation of prototype in the area of Ditributed Generation i often related to the effect of thee device on the electrical grid. However, due to the cale of the mentioned equipment it i difficult to oberve thi effect when the device interact with the main grid. A firt approximation to thi behavior can be imulated uing a model which interact with a imulated environment, with a oftware tool. When the oftware model i well defined, the prototyping phae tart and new teting will be required. The purpoe of thi work i to develop a tet tand for uch device which would mimic ome of the mot important parameter of a grid. The impact of the teted device in the grid can therefore be adjuted. Thi grid imulator will be ued for tability tudie in the introduction of Ditributed Generation Device a well a Renewable Energy Source in the grid and it can be een a a caled model of the real grid. Thi work wa implemented in the DeMoTeC laboratory in the Intitut für Solare Energieverorgungtechnik (ISET) in Kael (Germany) and it ha been ued for teting minigrid connected with the main grid. Keyword: Ditributed generation; ower Grid Simulator; Renewable Energy Source Integration; Energy infratructure.. Introduction Simulation tool bring, in general, a coniderable reduction in development time of conumer product a well a tet phae. In the cae of power ytem, they permit to viualize complex cae uch a tability problem, power flow or electromagnetical tranient in a fat, relatively inexpenive way. Example of uch tool are the ower Sytem Simulator for Engineering SS/E [] and the Alternative Tranient rogram ATEMT [2], Thee tool are widely ued in tability tudie of power tranmiion and ditribution grid among other. Although initially thought for largercale power ytem, thee tool have been alo applied in tudie in the area of Ditributed Generation and Demand Side Management with ucceful reult [3]. However, depite the clear advantage of pure ComputerAited imulation, there i the neceity of, at ome point, conduct tet of prototype under more real condition. Thee experiment normally require interacting with the grid to etimate their effect into the power ytem. The impact of the prototype in the local energy grid i mot of the time regarded a inignificant. Therefore the need for having a tet tand in which new configuration, equipment or control technique in the area of Ditributed Generation could be teted. The work preented propoe a imple, effective way of etting up and configuring a Grid Simulator for it ue a a tet tand of Ditributed Generation (DG) and Demand Side Management (DSM) technique, uing exiting hardware of the DeMoTeC laboratory in Germany. 2. Main Requirement In order to build up a laboratory imulator for analyzing the impact of DG and DMS in the power grid, ome requirement were identified. Firt, the Simulator had to be able to repreent a tiny to mall grid (eak ower in the range of GW) and be calable. The parameter of thi imulated grid had to be eaily changeable. Since the primer objective of the Simulator wa to be ue for analyzing the effect of DG and DMS, it had to be affectable by mall load. The lat requirement wa to ue commercial hardware. 3. Hardware decription The hardware ued comprie a 8 kw ynchronou machine with automatic voltage compenation (field control) mechanically coupled to a huntconnected DC machine. The DC link current i electronically controlled and the terminal of the ynchronou machine are connected to an interconnection board where the equipment will be teted. DCMachine Synchronou Machine Figure : Current Hardware Additionally, a torque a well a a peed and current enor are intalled. The block diagram of the equipment ued i hown in Figure. The original control of the DC machine i done through a Matlab interface which i depicted in figure 2. The frequency i et to a fixed value of uually Hz. When the torque demanded by the ynchronou generator I T, ω
grow up, the DC machine rapidly increae the power output in order to compenate the demanded power and maintain the peed contant. An additional torque limiter i implemented for ecurity. In thi control the effect of the control curve of different generator and other component in the imulated network are not contemplated. Analog Input Realtime Block Realtime em h Digital Input 94 K Ki Kn Ki Diplay Temp M2 Temp A2 Feldtrom A2 Betriebbereit A2 Diplay Real n_it(rpm) I_it(%) RTErr() Tettand Ein/Au /94. n_oll Reglerfreigabe. MA_oll. MB_oll 24 +/ 8 rpm 36 rozent von MA_max 67 rozent von MB_max Digital Output. Matrix ( ) Contant Figure 2: Matlab Control tool of the DC generator 4. General rinciple Analog Output The control technique propoed in thi paper conit in incorporating the frequency repone component into the current control; thi i, by meauring the output power and the current peed, the ytem hould be able to generate the uitable peed etpoint that would repreent the theoretical grid frequency. Since the deviation of power and frequency relevant for the tet cae are relatively mall, a linearized model (mall diturbance model) of a power grid will be ued. However, thi tet cae i ued for tatic power flow calculation and therefore lack of the dynamical parameter of the generator. Thee parameter can be found in everal tudie and reference uch a []. B. Generator In the propoed grid, five different generation facilitie were conidered, three tandard thermal power tation and two combined cycle. Figure 4, repreent the general form of the model ued to imulate the different generation plant. Thi comprie: The primary control of the plant; And the general tranfer function of the aggregated plant and involved control. ref + R a) etp + G H b) out Figure 4: General linearized model for a generation plant The frequency or primary control ha been adjuted adequately to each generator ize baed on the power flow reported in the IEEE Tet Cae. The tranfer function G H, depend on the type of generator; for thi cae, typical value obtained from have been ued and the inertia value of the generator machine have been baed on reference [6]. The repreentation of the control with the five generator i given in figure. G Stotal= 29.39MVA Selector Level : A. Grid Model In order to provide a imple, but tandard tet cae, an IEEE tandard tet cae ha been ued. Thi Tet Cae repreent a portion of the American Electric ower Sytem (in the Midwetern US) a of February, 962 [4], ee figure 3. Thi 4 node tet cae provide enough node to repreent a mall iolated power ytem, while keeping the model imple. G2 G3 G4 FREC MINIGRID Selector Level 2: Selector Level 3: Selector Level 4: Selector Level : Step function: 9%of Stotal= 26.9MVA G Generator L L2 L3 L4 Figure : Model of the control of the minigrid coupled to the IEEE 4 Node Tet The limitation of the primary control are an important characteritic of the implemented model. Thee limitation are related to the fact that at any given time lot (of uually minute) the primary control i able to vary the generator output in the range of +/ %. Figure 3: Simulation of the IEEE 4 Node Tet Cae C. Load and Line The conuming component of the ytem uch a line and load have a repone to udden unbalance between the generated and the conumed power of the type:
f yt K = + T n equation (), K S and T S are defined a the delay of the ytem repone to a power unbalance between generation and production. Knowing that K S = /D, D i defined a the repone in term of conumed power of the ytem to a change in the ytem frequency. Conidering all linear model for line and load, the reulting contant D wa found to be.3 pumw/hz, power bae of MVA. Thi value of the D parameter wa accepted ince the value of D for a GW grid would be around.2pumw/hz and for a GW would be.pumw/hz [7].. Control Implementation A jutified above, the control tak i to give a peed etpoint to the machine, which would repreent the current power conumption on the demand load. Since a mall diturbance model i being ued, a teady tate mut be reached before the experiment can run and the imulated model can be ued. Once thi tate i reached, the value of power and frequency are et up a contant and have the function of converting the actual value of power and frequency into deviation from the teady tate. Figure 6 illutrate thi converion. () Once the data i converted to the required format, the grid i imulated with the block called ubytem. Thi block contain the above mentioned equation which are repreenting the grid, ee figure 8. delta G G delta G2 G2 delta G3 G3 delta G4 G4 delta G G Add delta_ 33.333 37.797+ Repone of the ytem D [MWpu/Hz] Figure 8: IEEE 4bu block ubytem The grid i built up with generator, the different generator have pecific characteritic, which can be een opening the repective block. The power repone of the grid for a varying frequency (D) i given a tranfer function. Analog Input Realtime Block Realtime em h Digital Input 94 K Ki Kn Ki Diplay Switch 2.9 nref Temp M2 Temp A2 Feldtrom A2 Betriebbereit A2 f_ref IEEE4Bu Diplay f 3 f2n Real n_it(rpm) I_it(%) RTErr() Tettand Ein/Au /94. n_oll Reglerfreigabe roduct. MA_oll. MB_oll 24 +/ 8 rpm Speed 36 rozent von MA_max 67 rozent von MB_max Limit Frequency Switch Digital Output Frequency Setp. Matrix ( ) Contant Analog Output.2 control.3+ ervomechanim.3+ turbine.3 control + turbine2.3 control2.4+ turbine3 Figure 9: Generator.4 control3 Saturation delta G A an example, the generator (G) i depicted in figure 9. Thi generator i a combined cycle plant with three turbine of high and low preure. 6. Example of Experiment performed with the Grid Simulator Add Figure 6: Matlab Control block of the grid imulator An analogue converion from the frequency hould be done in order to provide the peed etpoint to the further control algorithm. The control block i therefore compounded by 3 input: Actual demanded power, teady tate peed and teady tate power conumption and give the etpoint frequency a output. The block called IEEE 4bu in figure 7 repreent the grid behaviour. The grid model i developed in a perunit ytem, allowing an eay caling of the model to uit different experiment configuration. 2 /4 delta_ Subytem Figure 7: IEEE 4bu block 3 f_ref f The experiment performed conited in teting the repone of the grid in front of a power input which detabilize the ytem [8], and conduct the grid frequency out of the margin accepted by the ytem. Thi experiment wa imulated uing a tandard oftware tool and comparing the reult with the reult obtained by uing the imulator decribed in thi paper. A. Software imulation The imulation wa done by uing a oftware tool. In the decribed power grid a tep of power i imulated; thi tep i enough for, knowing the characteritic of the generator and the contant D of the ytem, to drive the whole ytem out of the frequency acceptable margin. Figure repreent the repone of the grid uing a oftware tool in front of a.26pumva tep function. Thi repone of the main grid i a decreae in the
frequency that achieve a new equilibrium point at 49.4Hz, thi new equilibrium i out of acceptable range., f [Hz] ( file IEEEGRID2 pl4; t: XX2 2 2 [ 3 Figure : Repone of the grid to a.26pumva tep Adding load hedding repone for the ytem, after a while the frequency tart to recover, ee on figure. Figure 2: Output of the frequency in the grid while uing the DC motor control before modification,,,2,3,4,,6 2 2 3 3 [] 4 (f ile IEEEGRID2.pl4; xv ar t) t: FREC Figure : Frequency Repone of the ytem to a.26pumva and load hedding The intabilitie that can be een in figure are provoked by the reconnection of the line when the frequency et point i achieved. In the real model thi intability ha been corrected by uing a time delay in the reconnection proce. B. Grid Simulator Repreenting the ame ituation with the grid imulator uing the tandard control, before the modification propoed in thi paper, the reult of the frequency behavior of the power grid i hown in figure 2. The matlab control tool ued for controlling the DC motor keep the frequency almot contant at Hz for mall diturbance. If the modified control for the grid imulator i ued the reult i a variation in the frequency of the grid, thi variation can be een in figure 3. Adding alo the different line of load in the load hedding chema the reult of the grid imulator behavior i given in figure 3. Figure 2: Output of the frequency in the grid while uing the propoed DC motor control ower [VA] 3 27 24 2 8 2 9 6 3 : : :2 :3 :4 : : : :2 :3 :4 : 2: 2: 2:2 2:3 2:4 2: 3: Time [min:] ower frequency Figure 3: Frequency recovering in the grid while uing the propoed DC motor control and 3lineload hedding technologie,2, 49,9 49,8 49,7 49,6 49, 49,4 49,3 49,2 49, Frequency [Hz]
The reaction of the grid imulator repreent the real reaction of a mall power grid ubjected to mall diturbance. Thi reaction i conitent with the one imulated by uing oftware tool. 7. Concluion The grid imulator ha been ued in repreenting the behavior of the power grid when introducing DG and RES unit. The grid imulated i a caled model of the real grid and can be eaily adapted for repreenting different kind of grid and at different cale. Thi ability make of it a ueful tool in order to etimate the effect of large integration of DG device in different kind of power grid, a well a the analyi of Demand Side Management technique when diconnecting load by underfrequency. 8. Reference [] SS/E TM verion 3. Comprehenive analyi oftware for ue in tranmiion ytem tudie. Siemen, 2. [2] Information downloable from: http://www.emtp.org/ [3] Strau,. and Engler, A. AC coupled V hybrid ytem and microgridtate of the art and future trend. roceeding of 3rd World Conference on hotovoltaic Energy Converion. Volume 3, 26 May 23 age():229 234. Oaka 23. Japan. [4] IEEE Working Group on a Common Format for the Exchange of Solved Load Flow Data. Common Data Format for the Exchange of Solved Load Flow Data. IEEE Tranaction on ower Apparatu and Sytem, Vol. AS 92, No. 6, November/December 973, pp. 9692. []. M. Anderon and A. A. Fouad, ower Sytem Control and Stability. ISBN: 47238627. Willey IEEE re. [6] Kodi, S.K.M. and Claudio A. Cañizare, C.A. Modeling and imulation of IEEE 4 Bu Sytem with FACS Controller. Technical Report 233. Univerity of Waterloo, Waterloo March 23. [7] Gómez Expóito, A., Análii y operación de itema de energía eléctrica. Ed. McGrawHill. ISBN 9448392X. Madrid 22. [8] D. CollMayor. hd thei: The minigrid a a Grid Supporting element. Kael, 2. In Review proce.