Microgrid Load Management Control Application

Transcription

1 Microgrid Load Management Control Application T. Madiba Dept. Electrical, Electronic and Computer Engineering Univerity of Pretoria Pretoria, Republic of South Africa Abtract Thi paper preent load management trategy for a microgrid (MG) compriing of wind,, micro-hydro, dieel, energy torage ytem to increae penetration from renewable energy reource (RER). The main objective of thi wor i to olve power hortage problem in MG by increaing the penetration from RER. The reult preented in the paper how that microgrid i able to maintain balance between the generation and demand with ignificant contribution form RER. Microgrid can alo upply meet additional current or future load requirement if microgrid ite i rich with the availability of natural reource and avoid load hedding and blacout problem. Index Term Load management technique, microgrid ytem, critical and future load, RER. I. INTRODUCTION Electric power ha haped and contributed to the progre and advance of humanind over the pat century. Power hould be available to the cutomer upon demand [], []. The power companie trive to eep the reerve capacity to meet the udden demand to a imum. Load management technique help the power companie to rehape the electric utility load curve and to reduce the pea demand [3]-[5]. The United State Government ha filed lawuit againt 3 electrical utility plant charging the releae of maive amount of air pollutant throughout the Midwet and Eat coat [6], [7]. A microgrid (MG) i a group of interconnected load and ditributed energy reource (DER) which clearly define electrical boundarie that act a a ingle controllable entity with repect to the grid. The mall capacity hydro-unit, bioga, wind, photovoltaic () ytem are the variou energy reource in MG. The MG ait in reducing the line loe, networ congetion, and line cot by higher energy efficiency [8]. Incorrect operation of protective ytem, epecially ditance relay have been the main caue of recently blacout [9], [0]. Over the lat decade, in the world everal evere blacout have happened and thee action caue the economy lo and ocial impact []. Generally, the MG operate in two mode which are ilanded and grid-connected. In grid-connected mode, the MG i interconnected with a power ytem and can exchange it power with the main grid. There i in ilanded mode, the MG operate with it only energy reource and no interconnection with the grid ytem and parameter uch a frequency, voltage control and R. C. anal Dept. Electrical, Electronic and Computer Engineering Univerity of Pretoria Pretoria, Republic of South Africa rcbanal@ieee.org intability are main iue [], [3]. Other apect for ilanded mode are the inefficient deign or lac of Under Frequency Load Shedding ytem (UFLS) [4], lac of under voltage load hedding ytem, and inefficient vegetation management trategie. In addition, mart MG face ome policy and regulatory barrier here that are being challenged a the reliability, quality and environmental benefit. The conequence of uch difficultie mae their offer become clearer [5]. MG may be very good in conception, depending on maret egment, ize and location. Some of exiting type of MG are lited and well nown a Remote MG, Cutomer MG, Utility and Virtual MG. Load hedding i the lat expected protection poibility againt cacading outage [6]. eide the introduction, thi paper i organied in three ection. The econd ection preent the problem formulation of the typical MG ytem, where the MG ytem i preented and decribed with an appropriated tructure. The third ection explain the imulation reult of the applied mathematical modelling of the power ditribution ytem and the fourth ection preent the concluion of the completed wor. II. PROLEM FORMULATION Thi ection i characteried by three ub-ection which are the ytem decription of the MG, the multi-objective function of the problem and the contraint equation of the MG power ytem. A. Sytem decription The typical MG tructure ued in thi wor i preented in Figure. The ytem i compoed of two main part, namely the upply and the demand ide. The upply ide i characteried by five ource of energy uch a dieel generator () unit, micro hydropower (), wind turbine generation (G), photovoltaic () and battery ban ytem which one operate under normal and abnormal condition of the MG ytem. The demand ide i characteried by active load (P L ), (P L ), (P L3 ), (P L4 ) and future load (P L5 ), (P L6 ). The micro hydropower ytem come into force, to balance the ytem, in cae of additional load and to increae the total power produced by the RER in MG

2 ytem. P P SOC SOC Dieel Generator P m P e Pm attery an (SOC) t t Pe Micro - Hydropower R Charge Controller ch I I idirectional Converter c P P P u Load Figure. Typical model of microgrid ytem Additionally, the rating of parameter of the other data to be applied into the imulation of the hybrid ytem are given in Table [7]. Table : Rating of parameter of the data of MG ytem No Parameter Rating Priority output power 3 W, g=0.8 Dieel fuel price.$/litre 3 parameter a = 0.46, b = 0.085, c = Sampling time and priority factor hour ; w = 0.5 and w = Noal capacity of the Wh or 0.5W attery or 85Ah Maximum SOC 95% Minimum SOC 40% Dicharging efficiency 95% Charging efficiency 80% 6 Accepted MG ytem frequency Accepted MG ytem voltage 7 RER Micro-hydropower G ytem ytem unit 8 Maximum load capacitie: active load: (PL),..,(PL4) and future load (PL5), (PL6) (50 ±.5) Hz (± 0.05) pu 4 W, Hg= 0.9 W, g = 0.85 W, g = 0% W, W, W, W and.8w,.8 W P L P L P L 3 P L 4 P L 5 P L 6!! Active load Future load. Multi-objective function The application of the will preferably be running only for a hort period in uch a way the RER ytem have been prioritized at the tandard level to eep the operating cot of the ytem lower, a long a the MG i operating. The main purpoe of thi tudy i to reduce the fuel cot of the and to imize the output power from RER with the objective to atify the load management problem in MG. The firt objective function i given by expreion () a follow: N ì i N ü Obj = Cf åw [ ap (i) + bp (i) + c], () í ý i= îw = 0. 5þ Where, where C f i the cot of the fuel ued to run the ; a, b and c are factor applied to the fuel propertie; P i the output power from unit to the hybrid ytem; i i the time horizon and N i the number of time period conidered for the optimization tudy of MG ytem, w i the priority factor taen into account for the ue of fuel applied to the conidered into the MG ytem. To imize the RER output power, the econd objective function i characteried by expreion () a: Obj N ì i N ü = -å w [ PRER( i) ], í ý i= îw = 0. 75þ Where, where w i the priority factor taen into account for the ue the RER conidered into the MG ytem, P RER i the output power from RER ytem. The combination of both () and (), will olve the load management iue in MG and the multi-objective function i conidered a the um of both equation () and () given by (3): Obj + Obj = C N å f i= - [ w [ ap N å i= w P (i) + bp RER ( i)] (i) + c] C. Microgrid contraint The MG contraint are characteried by power balance, frequency equation of the ytem. The power balance of MG i given in dicrete form by expreion (4) a: 3 ì P ³ å PLj + PL 5,6 ì N ü (4) l = í, íl =,..., 6 m 3 ý + + ± ³ + î = å P P P P å PLj PL 5,6 m þ î j= l= where P Lj () i the index of active load; P L5,6 () i the index of future load in the MG ytem, P () i the power from the dieel generator ytem P () and P () are the power from the and G ytem, P () i the power delivered by the battery ban ytem (S). The dynamic in time and dicrete domain of the, the micro hydropower and the battery ytem are given by the ytem of equation (5) a follow: (3) ()

3 ì dwt Pa, = M = Pm, - Pe, dt Dt w = + - d w(0) [ å Pm, ( t ) å Pe, ( t )(5) M, t = t = íw d wd wd Dt SOC( ) = SOC(0) - å P ( t ) Cn t = SOC SOC( ) SOC î where P a, () i the accelerated power of and micro hydropower; P m, () i the mechanical power of and micro hydropower; P e, () i the electrical power of and micro hydropower; SOC () i the tate of charge of the battery ytem, P () i the power from the dieel generator ytem, M, i the moment of inertia in MJ/MJ/rad/, SOC and SOC are the upper and lower limit of the SOC, ω d and ω d are upper and lower limit of angular peed ω d (), Δt i the variation of time. The boundary contraint of the conidered variable parameter into the MG ytem are preented by the ytem of equation a follow: vector X contain the feeder peed for all ampling interval. The linear inequality contraint are integrated into A and b. The lower and upper boundary contraint (5) and (6) are included into L b and U b.. Variation of wind, irradiation and load capacity The variation for a typical houehold for wind, output power due to irradiation and load capacity have been collected in ummer period [8]. Thee graph have been plotted with the implementation of Matlab programg tool a given in Figure - 4 a [8]: Figure. Variation of output power from G ìp P íp P P î, ( N ) (6) III. SIMULATION AND RESULTS OF MICROGRID To verify the performance of the propoed control ytem applied in thi tudy, the availability of accurate load data i an important factor. Moreover, the deign of RER mut be done according to the predefined objective, which mean that it i neceary to meet the load capacitie requirement. A. Algorithm applied for thi cae tudy The fcon function of MATLA R05 Optimiation Toolbox i implemented to olve all element of thi problem. The equation can be olved by thi function expreed a follow: f (X) (7) Subject to ìax b(linearinequalitycontraint), AeqX = beq (linearequalitycontraint), íc(x) 0(nonlinearinequalitycontraint), Ceq ( X ) 0(nonlinearequalitycontraint), î Lb X Ub (lowerand upper bound). The fcon function defined by equation (7) and (8) i more efficient to be applied to typical model of MG ytem with regard in taing into account all neceary parameter a per decribed Table. For the optimal control equation, the (8) Figure 3. Output power from Figure 4. Load profile of the Houehold The tudy of the typical MG ytem i principally baed on the conumption of the houehold ytem. The imiation of power from RER unit i cog into force to the power ditribution ytem with the objective to reduce unnecearily operating delay due to power hortage caued by upply ide of MG. The conequence of power hortage are the main factor reducing the balance performance of the MG. From the graph preented earlier by Figure - 4, load management control will be made with the objective to eep upplied the houehold permanently with energy from the generation ide of MG power ytem. Load management will be completed with the application of RER and the focu will

4 be on the variation of power balance variable of MG. Thi variable will confirm either the action of load management ha been achieved or not. C. Load management with total load capacity connected At thi tage, only the i upplying the demand ide of the MG ytem. A reult, the Figure 5-7 how that the i facing a eriou problem and the power balance of the ditribution ytem i not good, the olution to be applied for thi cae, i to hed all future connected load. A impact, the ytem i balanced and everything ha become too normal. RER, there i no need to prevent the failure of the entire ytem when the demand train the capacity of the ytem. There i no worry to thin about origin of load-hedding a the demand ide management (DSM) problem ha been completed with additional renewable reource. Figure 8. Power from the upplying the Houehold Figure 5. Power from the upplying the Houehold Figure 9. Power from upplying the Houehold Figure 6. Power balance for the MG ytem Figure 0. Power from the G upplying the Houehold Figure 7. Variation of SOC for the Houehold The implication of RER ytem ha been applied to the MG configuration, full load capacity ha been conidered and Figure 8 have proven that load management of the MG ytem ha been completed by RER and the power balance of the ditribution ytem i in acceptable limit according to the tandard. Additionally, no need of hedding all future load to be connected into the houehold. The olution for thi cae i no need of action to reduce the load on demand ide of MG ytem, epecially the interruption of an electricity upply to avoid exceive load on the generating ytem. Additionally, no deliberate hutdown of electric power in a part or part of a power-ditribution ytem, generally with the contribution of Figure. Power balance for the Houehold A thi can be een from the comparion between Figure 6 and, load management of the MG ytem i ecured with the application of RER a the power balance eem to be poitive a hown in Figure.

5 Additionally for thi tudy, the reult have proven that load management, alo nown a DSM, i the proce of balancing the upply of electricity on the networ with the electrical load by adjuting or controlling the load rather than the upply ide output. Figure prove that load management allow utilitie to reduce demand for electricity during pea uage time, which can, in turn, reduce cot by eliating the need for peaing power from. In addition, Figure 5 and 7 how that ome peaing ource of power can tae more than an hour to bring on-line which mae load management even more critical hould the and battery output power go off-line unexpectedly according to the high demand of the houehold. According to Figure, it i confirmed that load management performance can alo help reduce harmful emiion, ince peaing plant or bacup generator i often dirtier and le efficient than bae load power plant. IV. CONCLUSION Thi paper ha dicued the neceity of the ue of load management olution into the MG power ditribution ytem. The main objective of uch application i to mae ure that the upply ide of MG ytem i able to upply future additional load with the impact of RER ytem. RER are environmental friendly and need to be conidered for the development in rural community. A recommendation, it i important to tae the opportunity of RER for the aurance of the future of manufacturing companie and indutrie. REFERENCES [] A. F. Zobaa and R.C. anal (Ed.), Handboo of renewable energy technology, World Scientific Publiher Singapore, 0. [] A. H. Etemadi, E. J. Davion and R. Iravani, "A generalized decentralized robut control of ilanded microgrid," IEEE Tran. Power Sytem, vol. 9, no. 6, pp , 04. [3] R. Shah, N. Mithulananthan, R.C. anal, and V. K. Ramachandaramurthy, A review of ey power ytem tability challenge for large-cale integration, Renewable and Sutainable Energy Review, vol. 4, pp , 05. [4] A. Nagliero, R. A. Matromauro, V. G. Monopoli, M. Lierre and A. Dell Aquila, Analyi of a univeral inverter woring in grid-connect, tand alone and microgrid, IEEE Int. Sympoium on Indutrial Electronic, ari, pp , 00. [5] H. S. Mazheruddin, H. H. Zeineldin and M. S. El Mouri, Grid code violation during fault triggered ilanding of hybrid micro-grid, IEEE PES International Innovative Smart Grid Technologie Conf., Wahington DC, pp. -6, 03. [6] L. Qiang, Z. Lin and G. Ke, Review on the dynamic characteritic of micro grid ytem, IEEE Indutrial Electronic and Application, Singapore Conf., pp , 0. [7] Q. K. Pan, L. Wang and. Qian. Review on operation of micro grid and virtual power plant in the power maret, IEEE Int. Adaptive Science and Technology Conf., Ghana, pp , 009. [8] J. Wang, Z. Wang, L. Xu and Z. Wang, A ummary of application of D-FACTS on microgrid, IEEE Aia Pacific Power and Energy Engineering, Shanghai, pp. - 6, 0. [9] L. Gidwani, H. Tiwari, and R. C. anal, Improving power quality of wind energy converion ytem with unconventional power electronic interface, Int. Journal of Electrical Power and Energy Sytem, vol. 44, no., pp , 03. [0] L. Ji, D. X. Niu, M. Xu, G. H. Huang, An optimiation model for regional microgrid ytem management baed on hybrid inexact tochatic-fuzzi chance-contrained programg, Int. Journal of Electrical Power and Energy Sytem, vol. 64, pp , 05. [] J. A. Laghari, H. Mohli, A. H. A. aar and H. Mohamad, Application of computational intelligence technique for load hedding in power ytem: Review, Energy Converion and Management, vol. 75, pp , 03. [] P. Mahat, C. Zhe and. a-jenen, Under frequency load hedding for ilanded ditribution ytem with ditributed generator, IEEE Tran. Power Delivery, vol. 0, no. 5, pp. 9-98, 00. [3] U. Rudez and R. Mihalic, Analyi of under frequency load hedding uing a frequency gradient, IEEE Tran. Power Delivery, vol. 6, no., pp , 009. [4] M. Emmanuel, R. Rayudu, The impact of ingle-phae grid-connected ditributed ytem on the ditribution networ uing P-Q and P-V model, Int. Journal of Electrical Power and Energy Sytem, vol. 9, pp. 0-33, 07. [5] A. Pariio, E. Rio and L. Glielmo, A model predictive control approach to microgrid operation optimization, IEEE Tran. Control Sytem Technology, vol., no. 5, pp , 04. [6] Y. Levron, J. M. Guerrero and Y. ec, Optimal power flow in microgrid with energy torage, IEEE Tran. Power Sytem, vol. 8, no. 3, pp , 03. [7] L. Sigrit, I. Egido and L. Rouco, "Principle of a centralized UFLS cheme for mall iolated power ytem", IEEE Tran. Power Sytem, vol. 8, no., pp , 03. [8] Z. Song, J. Liu, Y. Liu and M. azargan, A method for the deign of UFLS cheme with dynamic correction, Energy and Power Engineering, vol. 5, pp , 03.