电气工程外文文献原文与译文---应用于独立运行微电网的潮流计算方法

1、 毕 业 设 计（论 文）外 文 文 献 译 文 及 原 文学 生： 王帅 学 号： 200806010123 院 （系）： 电气于信息工程学 专 业： 电气工程及其自动化 指导教师： 宋玲芳 2012 年 月 日application of the power flow calculation method to islanding micro gridsy.h. liu. z.q. wu, s.j lin, n. p. brandonabstract:most existing power flow calculation methods use a swing bus as a refe

2、rence node for the whole system increasingly. new distributed generation resources (dgrs) are being added to the grid. sometimes, local demand or failure of the grid can result in independent micro-grids forming, which are known as islanding systems howcver. current dgrs are often limited such that

3、there is no single dgr which can balance the power demand and stabilize the frequency of the micro-grid, meaning that there is no swing bus from which the microgrid can bemanaged. according to existing research. a dgr coupled with a dcdicated cnergy storage .system and suitable control stratcgy (her

4、e termed a distributcd generation (dg system) has the ability to adjust its output. this means that a dg system can respond dynamically to grid events. this means that a dg .system can rcspond dynamically to grid events. in this paper. a new power flow calculation method (based on newton-raphson pow

5、er flow solution) with good convergence is proposed that can accommodate the lack of a swing bus in an islanding system. this addresses power flow results and the frequency ofthe whole system. the method proposed is discussed in detail with cxamples of diffcrent dg systems with various adjustment co

6、efficients and load models.the results arc compared with those of a traditional power flow calculation mcthod based around the use of a swing bus. in conclusion, this paper shows that the improved method is more apprpriate for islanding systems with mesh topology and for micro-grid management wihtno

7、 swing bus.index terms-distributed generation; islanding; micro grid; power flow calculation; power system.nomenclaturea. indexesi,j numbef of node ;b. constantsn number of nods of the system;m number of non-power-source nodes in the system;ai percentage coefficient of constant impedance load in a c

8、ompound load modebi percentage coefficient ofconstant current load in a compound load model;ci percentage coefficient of constant power load in a compound load model;kg,p equivalent regulation coefficient of active power of dg;kgi,q equivalent regulation coefficient of reactive power of dg;li,pk equ

9、ivalent regulation coefficient of active power of load;li,qk equivalent regulation coefficient of reactive power of load;c. variablesp active power;pi active power node i; voltage phase angle.ij voltage phase angle differcnce between node i and j;q reactive power;pi active power injects to node i;qi

10、 rcactive power injects to node i;u voltage magnitude;ui voltage magnitude of node iuj voltage magnitude of node j;p derivative value of active power;q derivative value ofreactive power;u derivative value ofvoltage amplitude:f system frequency; f derivative value of system frequency;d. subscriptg ge

11、nerator;l load;p active power;q reactive power;0 initial value.introductionas the basis of analyzing and controlling power systems, power flow calculations have been cxtensively rescarched and widely used. most traditional powcr flow calculation mcthods need to set a swing bus for the system before

12、calculating.incrcasingly, new distributed generation resources (dgrs) are being added to the grid. these can include internal combustion cngines, micro-gas turbines, fuel cells, photo-voltaics, wind turbines, wave and tidal generators. the output of a distributed gencrator (dg) is often not as large

13、 as that of a traditional generator . often, there is no independent frequency adjustor in an islanding micro grid compared to a traditional system because of cost. however, the loads of the powcr system always vary with time. therefore, in an islanding micro grid. there is no single generator that

14、can keep the balance of the increasing demand of the whole system. this means there is no swinging bus in the power flow calculation of an islanding micro grid system, which is essentially different from the traditional power flow calculation of large power systems. there has been a lot of rescarch

15、about the interface design of distributed generation sources (dgrs) which show that active power, reactive power and output voltage of dgrs can be adjusted. lopes and co-workers discussed that distributed generation via control of both energy storage and inverter, can achieve similar charactcristics

16、 of powcr-frequency and voltage-reactive power as those of micro-turbines and traditional synchronous gencrators. k. de brabandere, etal.,discussed a control strategy of parallel invcrters for an islanding syste with falling charactcristics of voltage and frequency. the voltage and power adjusting a

17、bility ofdgrs wcre considered in the paper. almost all dgrs cxcept one have been processcd as a slack pq bus. but a swing bus is still needed in the power flow calculation. a traditional distribution system has radial, chain or other simple structure. using cmbedded gencrators, a flexible structure

18、can cnsure power supply to customers. however, flexible structures can also cause a complex topology of the nerwork. bccause of its quadratic convcrgcnee, the newton-raphson method is widely used in power flow solution of networks with complex topology. in this paper, a ncw power flow calculation me

19、thod based on the newton-raphson mehod is proposed to solve the power flow ofislanding micro grids. there is no swing bus to be set, while the voltage and power adjusting ability of the dgrs is considered. based on the ieee 5-node system with ring structure, a series of comparisons are made. such as

20、: different locations of the dgs, dgs with different charactcristics, and loads with different characteristics.islanding micro gridgenerally, the output power of one dg ranges from several kw t0 50 mw. while the usual capacity of hydro generators and coal fired generators is about 300mw to iooomw. t

21、hus, the capacity of a dg is much smaller than the traditional generator. through some interface (commonly an inverter), dg can supply power to acloads. by controlling the inverter,the output of the dg can bc controlled.lslanding systems are sometimes a result of the failure of the large system. to

22、maintain local power supply, the dg and its local loads become an islanding system instead of keeping its link with main grid. another case is to satisfy the demand of some remote customers or some large customers.power suppliers and their local loads naturally form a micro grid, called an islanding

23、 system. locally supplying power using dgs can save both energy and cost. islanding means that the micro electrical network is completely independent, isolated from the large-scale systcm, and has no clectrical or magnetic conneetion with it. the whole system must be kept in balance and the frequenc

24、y and voltage level of the whole systcm must remain in an acccptablc range. because the dg output is too limited to undertake frequeney adjustment, dgs must work together. power flow calculationcompared with traditional power flow computation, this paper reports the power flow and frequency computat

25、ion analysis ofislanding systcms with dgs.a. node typein traditional powcr flow computation. one of the first steps i.s to classify the nodes of the system. buses of the system can usually be divided into three main types: pq node. pv node and swing bus (ve node). the swing bus, also called slack bu

26、s, undertakes the frequency adjustment of the whole system. usually this is a largc-scale hydroclcctric power plant which has the ability to quickly produce large output.loads change with time in a real system, outputs of generators correspondingly change along with loads. the whole system is then k

27、ept in dynamic equilibrium, with its frequency maintaincd within an acccptablc range. in this paper, output is automatically allocatcd among dgs to dynamically balance loads changing across the whole system. thereis only slack pq nodes rather than any other type of bus, for example a swing bus. b. n

28、odal powcr equation each dg has a differcnt power regulation ability, shown by their equivalent different regulation coefficients:pgi=pgi01-kgi,p(f-f0) qgi=qgi01-kgi,p(u-ugi,0) (1)the load model in this paper is a combination model constructed with three kinds of separate models. considering static

29、characteristics, the power equation any load node is given in equation (2):pli=pli0ai,p(uiui0)2+bi,puiui0+ci,p1+kli,p(f-f0)qli=qli0ai,p(uiui0)2+bi,puiui0+ci,q1+kli,q(f-f0) (2) where, ai+bi+ci=l. c. jacobian matrixthe key issue when using the newton-raphson power flow solution is the jacobian matrix

30、and its inversion.the above node power balance equations consider the power source and the load adjustment effect. according ly. except sub-matrices l (n术n order), m (n*n-l order),n (n*n order)and h (n*n-l order) arc similar with those in traditional jacobin matrix, there are additional sub-matrices

31、 e (n* i order).f (n* 1 order) respectively stand for the relationship between the deviation of active power and reactive power with that of frequency: qp=- lmenhf uuf (3)the detailed elements of each sub-matrix are as the follows:where gij and bij respectively are the real partand imaginary part of

32、 conductancelvi and nvi respectively are the coefficient of effects of static adjustment of activepower source and the load:.examplegenerally, the network topology of a traditional distributed power system is radical the topology of a distributed network with dgs might be more complex. based on newt

33、on-raphson method, the method proposed in this paper adapts to power flow calculation for the network of both radical and circle topology. a. system and parametersin an example the ieee-5 node high voltage system (transmission system) is transformed into a micro grid (fig.l). besides reducing the sy

34、stem base capacity to 100kva, we removed acceptance of the sub branches which arc not considered in a low voltage level system. the other paramcters are the same as those given in the literature. b. assumptionresistance and reactance in distributed systems are different from those inransmission syst

35、ems. the real topology of a distributed system is more likely to becomplicated than the example in this paper. discussions focus on the power flowcalculation method ofan islanding system with the coopcration of cach dg off limits of output of power/voltage for each dg were not taken into account. we

36、 assume the system frequency is kept in an acccptable range. the equivalent regulation coefficients of the power source and the load are assumed values to make sense of the calculation cases and discussion. for example, if a dg has poor rcactive power regulation ability, then its value of reactive p

37、ower regulation coefficients set as zcro.in this model, we only discuss symmetrical three-phase power flow. the complexthree-phase asymmctrical situation will be discussed in further work.c. calculation cases and refcrcnce databased on the ieef. 5-node system with ring structure (fig. 1), a series o

38、fcomparisons are made.table i shows different locations of dgs, and differentdgswith different characteristics via given different coefflcients. the regulation ability ofloads has been considered.tablesummary of different regulation coefficientsk1k2k3k4k5k6nkv1kf1kv2kf2kv3kf3kv4kf4kv5kf5kv6kf61-22-2

39、2-22-2200-222-22-22-22-2200-223-22-22-22-2200-22420200202040002020101052040204020200020401020kf (frequency regulation coefficient) - for dg: kgbp ; for load: kl,p.kv (voltage regulation coefficient) - for dg is k(jq ; for load: kl,q.in table i, k2 has different dgs from kl; k3 exchanges the position

40、s of dgs with those shown by kl; k4 shows neither of dgs has regulation ability; k5 does not consider the regulation ability of each load; k6 means each dcj has half of regulation ability as shown by kl. different load models are considered via given different pcrecntage coefficicnts of the compound

41、ed load.table contrast of different load models percentl1:combined nodell2:pure resistancel3:pure currentl4:pure powera1b1c1a2b2c2a3b3c3a4b4c4pl100010001ql100010001thirteen cases (c) are compared (see table iii). the first two, co and cl are the cases u.qing the traditional power f

42、low calculation method (mi); others are the cases using the improved method (m2) put forward in this paper. node 5 is set to be the swing bus in ml. with m2,c2 to c9 consider different dgs wich different regulation cocffieients and their positions (shown in table i),different loads with different re

43、gulation coefficients (shown in table i), and different load models (shown in table ii).table comparison of different calculate casesdescription of different casem1:constant power load,basic loadm1:constant power load,each load increase by 10%m2:k1 regulation coefficient,l1 load ,basic loadm2:k1 reg

44、ulation confficient,l1 load,each increase by 10%m2:k2 regulation coefficient ,l1 basic loadm2: k3 regulation coefficient,l1 basic loadm2: k4 regulation coefficient,l1 basic loadm2:k4 regulation confficient,l1 load,each increase by 2%m2:k5 regulation coefficient ,l1 basic loadm2:k6 regulation coeffic

45、ient ,l1 basic load0m2:k6 regulation coefficient ,l2 basic loadm2:k6 regulation coefficient ,l3 basic load12m2:k6 regulation coefficient ,l4 basic loadc: case, different calculate cases; m: power flow calculation method, ml traditional method, m2-improved method; kl-k6: dirferent groups ofgeneration

46、 coefficients - see table i; ll-l4: different load models - see table ii. basic load with table iv shows the initial data of the power at each node. the initial value of voltage magnitude of each node is l.0; that ofvoltage phase ofeach node is zero.node12345pq1.62.03.75.0052.680.81.01.31.812.2d.res

47、ultsiterative error of results is less than 10-5in m1,the frequency is always taken as 50 hz.system frequencies calculated with m2 in different cases are shown in table v:c23456789101112f5049.88449.89549.99647.21349.1075049.98349.7459.96850.121fig 2,3and4separalely shows (in unit value) how the actv

48、e power, reactive power and voltage varies with different cases. to enable comparison, data are in unit values. in addition the base line ofeach data has been shifted in figs 2 and 3 to find the actual value for the data shown in fig. 2, the following steps are necessary. for node l: deduct l; node

49、2: deduce2; node 3: add 3; node 4: add 5; node 5: add 2. similarly, for the reactive power of nodes 4 and 5 in fig. 3, the original value can be obtained by adding l to the data shown. real unit values of voltage are shown in fig.4.e. discussion1. comparison of case o with case l shows that in the t

50、raditional power flow calculation, node 5 alonc undertakes the task to satisfy increasing active power demand, and together with node 4, to balance increasing reactive power demand. it causes the weakest voltage level at node l. while maintaining voltage levels at othcr nodes. the comparison of case

51、 2 with case 3 shows that. when using the proposed method, all dgs share the loads, and that increasing load demand results in an acceptable reduction ofvoltage levels at each node.2. comparison of case 2 with cases 4 and 5 shows that different types of power source. and different position of dg cau

52、se the power flow to change.3. comparison of case 2 with case 6 and 7 shows that system voltage and frequency are out of acceptable range because dgs lack of regulation ability. comparison of casc 2 with case 8 shows that the regulation ability of the load has little effect on system frequency and p

53、ower flow.4. contrasting case 9 with the cases 10, 11, 12 shows that different load models and their combination can greatly affect the system frequency and the power flow.5. from discussion 3 and 4 we know that the effect of load adjustment on the frequency and power flow in a simple system depends

54、 on whether the control ability of load is stronger than that of the power source or not.vi. conclusionscompared with the traditional power flow calculation, the improved power flow calculation method proposed in this paper reflects the rules of runnjng and controlling an islanding micro grid. it ca

55、n analyze both the power flow and the system frequency of an islanding system.in an islanding system, the active power-frequency and rcactive power-voltage regulation ability of the various dg are positive to system stability. succcssfully coordinated control of cach dgs output to balance changing l

56、oad and maintain the system frequency and voltage level, is the key to a stable islanding system. further research on regulating control of dg is recommended.viii. referencesperiodicals:1 lin c e ,huang y w, huang c l. disrribution system load flow calculation with microcomputer implementation. electrical power system research, vol. 13,pp 139-145,1987.2 10 k. l, zhang c. decomposed three phase power flow solution using the sequence component frame, proc lee, vol. 140,jouma