当前位置:文档之家› Real-time reconfiguration of distribution network with distributed generation

Real-time reconfiguration of distribution network with distributed generation

Real-time reconfiguration of distribution network with distributed generation
Real-time reconfiguration of distribution network with distributed generation

Electric Power Systems Research 107 (2014) 59–67

Contents lists available at ScienceDirect

Electric Power Systems

Research

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e p s

r

Real-time recon?guration of distribution network with distributed generation

D.P.Bernardon ?,A.P.C.Mello,L.L.P?tscher,L.N.Canha,A.R.Abaide,A.A.B.Ferreira

UFSM –Federal University of Santa Maria,RS,Brazil

a r t i c l e

i n f o

Article history:

Received 30July 2013Received in revised form 18September 2013

Accepted 18September 2013

Keywords:AHP

Automatic recon?guration Distribution network Distributed generation

Remote controlled switches Smart grid

a b s t r a c t

This paper presents a new methodology to perform the automatic recon?guration of distribution net-works incorporating distributed generation in normal operation.The power generation availability of wind turbines,solar photovoltaic panels and small hydropower are considered in the recon?guration process.The real-time recon?guration methodology is based on a heuristic method to determine the best settings.The method assumes that only remote controlled switches are considered in the analysis.The multicriteria analysis AHP (Analytic Hierarchy Process)method is employed to determine the best sequence of switching.The developed algorithms are integrated into a supervisory system,which allows real-time measurements and commands to the equipment.The proposed methodology is tested in a real network of a power utility and results are presented and discussed.To evaluate the performance and ef?-ciency of the proposed method,different network recon?guration scenarios with distributed generation were tested.

? 2013 Elsevier B.V. All rights reserved.

1.Introduction

The need to improve the quality and reliability of power sys-tems,as well as environmental needs with the quest for reducing greenhouse gas emissions and replacing fossil fuels in power gener-ation,insert Distributed Generation (DG)using renewable energy sources in discussions about the future of distribution of electric power systems.

New methodologies and analysis tools for distribution sys-tems with distributed generators are necessary and have been receiving great attention from researches of Smart Grids and Micro-grids.Smart grids are characterized by a number of technologies,methodologies and integrated procedures,including the ability for self-recon?guration under changing operating conditions [1].

The recon?guration of the network can be responsible for pro-moting more ef?cient use of distributed generators of renewable primary sources,such as solar radiation and wind energy,by ana-lyzing the availability of each source for injecting energy into the system.As a result,it is possible to obtain a signi?cant reduction of losses and to improve the reliability of power supply.

Several researches are related to the recon?guration of distribu-tion network with distributed generators,based on mathematical methods,heuristics and arti?cial intelligence techniques [2].

?Corresponding author.Tel.:+555532208344;fax:+555532208030.E-mail addresses:dpbernardon@ufsm.br ,dpbernardon@https://www.doczj.com/doc/8014654951.html, (D.P.Bernardon).

In recent years,new methodologies of recon?guration of dis-tribution network have been presented,exploring the greater capacity and speed of computer systems,the increased availability of information and the advancement of automation,particularly,the SCADA (Supervisory Control and Data Acquisition).With the increased use of SCADA and distribution automation through remote controlled equipment,the recon?guration of distribution network became more viable as a tool for planning and control in real-time.Most of recent researches [3–5],however,do not take into account recon?guration in real-time.The works of Wang et al.[6]and López et al.[7]present an online recon?guration approach,the ?rst with emphasis on the reduction of load ?ow calculation time and the last on the demand characterization.The work of Vargas and Samper [8]presents fast algorithms for a smart distribu-tion management system,which include load estimation,load ?ow calculation and optimal feeder recon?guration considering DG.

Rao et al.[9]present a meta-heuristic algorithm to reduce losses of distribution networks and the allocation of DG units simultane-ously.In these works,however,the optimization approach is for monocriterial analysis,and some feasibility aspects for real-time application are not taken into account,such as a proper de?nition of the frequency of recon?guration and the coordination of protection devices.

A multicriteria analysis is discussed in the work of Martins and Borges [10],using the recon?guration of network as an alternative to system expansion.In general,the vast majority of works which involve DG,focuses on the planning of distribution systems and allocation of DG,and does not apply to the recon?guration under normal operation and real-time.

0378-7796/$–see front matter ? 2013 Elsevier B.V. All rights reserved.https://www.doczj.com/doc/8014654951.html,/10.1016/j.epsr.2013.09.011

60 D.P.Bernardon et al./Electric Power Systems Research 107 (2014) 59–67

The work of Celli et al.[11]considers the short-term varia-tions in generation due to meteorological conditions.In real-time applications it is necessary consider this information because the generation pro?les can change signi?cantly.

In this work,a methodology and a computational tool for auto-matic recon?guration of distribution network considering DG in real-time are developed from the standpoint of Smart Grid.The methodology uses the information and functionality of remote con-trolled equipment installed in distribution systems,applying them in a computer system that allows the recon?guration of the net-work in normal operation.The analysis consider the demand curves of feeders and generation curves based on Wind,Solar Photovoltaic and Small Hydropower energies,highlighting that these systems are interconnected to the distribution network.

The developed methodology is an evolution of the works [12,13],but with signi?cant contributions:

(i)analysis of generation pro?les related to distributed generators of different technologies;

(ii)speci?c constraints for distributed generation;

(iii)heuristic technique for selecting con?gurations incorporating

DG;

(iv)case studies considering real data of power utilities;

(v)integration of the developed tool with SCADA system,allowing

the automatic network recon?guration.

The proposed methodology is tested in a real distribution network,ensuring the practical applicability of the heuristic opti-mization algorithm employed.

2.Problem formulation

The recon?guration of distribution network can be character-ized as an optimization problem.To improve network performance,one or more objectives (e.g.reduce losses and improve reliability)are established,and then one veri?es which con?guration produces

the best result,without violating constraints on proper and safe operation of the network.This con?guration is de?ned as the opti-mal solution for the system.When more than one objective is set,the analysis should incorporate methods for multicriteria decision making,which may include expert opinion on the de?nition of a preference for one objective over another.

The main problem is that optimization of real networks allows a number of con?gurations quite high due to the number of switching devices on the network.In general,it may be unfeasible to test all possible combinations and perform,for each one,the necessary cal-culations –such as load ?ow –in order to identify the con?guration that results in best performance.To solve this problem,optimiza-tion methods that reduce the search space of the optimal solution are commonly used.

In this work,the developed optimization algorithm is based on a heuristic method and on the AHP multicriteria decision making method to identify the best network con?guration.In the sequence,some fundamental considerations are prede?ned to perform auto-matic recon?guration in real-time.

2.1.Real-time characteristics and requirements

Recon?guration of distribution network in normal operation usually has as main objective the reduction of energy losses.When considering automatic recon?guration in real-time,some aspects have to be included in the study:

a)it is necessary to establish a cost-bene?t relationship to deter-mine the necessity and the effectiveness of the recon?guration;b)the network must be ?exible to allow the recon?guration;

c)the technical feasibility of the switching should be studied in real-time,considering the availability of current measurements of the network.

The diagram in Fig.1shows the architecture employed in this work to meet these

premises.

Fig.1.Architecture of the proposed system.

D.P.Bernardon et al./Electric Power Systems Research 107 (2014) 59–67

61

123456

a b

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

W i n d S p e e d (m /s )

Month

0,10,20,30,4

0,5

0,60

100200300400500600700

8009001 2 3 4 5678 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

25

P o w e r C o e f f i c i e n t (C p )

P o w e r (k W )

Wind Speed (m/s)

P(kW)Cp

Fig.2.(a)Wind resource (b)power curve for wind turbine Enercon E53.

The real-time information access is needed to implement the methodology,such as the data and communication status of the devices controlled remotely,which is obtained from SCADA.The recon?guration software evaluates the load rates and generation scenarios of DG,and it performs the optimization method con-sidering the heuristic search and multicriteria analysis based on AHP.The proposed system also sends commands to open and close the switches by SCADA.The steps of the presented architecture are discussed in Section 3.

3.Methodology for automatic recon?guration in real-time

3.1.Demand rate evaluation

The ?rst step on the proposed methodology is to determine when a change in network con?guration is actually needed.This avoids frequent switching which may cause equipment degrada-tion.The strategy employed in this work is based on demand rates and load forecasting using typical curves for residential,industrial,commercial and rural consumers.

In order to obtain a good discretization of the demand curve and to avoid frequent recon?gurations in the network,it is employed a set of six demand rates,as presented in work [13].

3.2.Pro?le of distributed generation

The DG incorporation considered in this paper refers to a mod-erate insertion of midrange DG with installed power of a few MW from renewable sources.The DG is assumed to be connected to the medium voltage of the distribution feeders.During the recon-?guration occurs the simultaneous analysis of the demand and generation curves.The program veri?es the availability of DG power for injection into the system.

3.2.1.Wind power (W)

In this work,it was considered a small wind farm and a typi-cal generation scenario from historical data of average wind speed obtained by database of a weather station located in the South region of Brazil,with hourly measurements.

Fig.2(a)shows the monthly incidence of wind during the study period.The wind turbine model used was the Enercon E53,with rated power of 800kW,as shown in the power curve in Fig.2(b).

From the meteorological parameters and the power curve of the turbine,it is possible to obtain the daily curve of the potential for wind power generation.Fig.3illustrates the wind power curve for a typical day with good wind incidence,normalized to the maximum generation value (800kW).

3.2.2.Photovoltaic power systems

The pro?le of photovoltaic generation was de?ned based on indices of sunshine and solar radiation incidence in the South region of Brazil.Fig.

4illustrates the typical pro?le throughout the year.

It was considered a set of PV modules with a total power of 0.5MW.Fig.5shows the photovoltaic generation curve for a typical day with clear sky normalized to maximum generation (0.5MW).

Fig.3.Wind generation curve.

12345

678Jan

Feb

Mar

Apr May Jun Jul Aug

Sep Oct Nov De c

D a i l y R a d i a t i o n (k W h /m 2/d )

Daily Radiation

Fig.4.Monthly radiation pro?le throughout the year.

Fig.5.Photovoltaic generation for a typical day with clear sky.

62 D.P.Bernardon et al./Electric Power Systems Research 107 (2014) 59–67

0,20,40,60,8100:0001:0002:0003:0004:0005:0006:0007:0008:0009:0010:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

S m a l l H y d r o e l e t r i c P o w e r (p .u )

Period (hour)

Fig.6.SHP curve generation.

3.2.3.Small hydroelectric power plant (SHP)

The power plant operation depends on the river ?ow and on the reservoirs capacity,so there is also considerable uncertainty regarding this type of generation and the share that can be consid-ered in the studies.The ?ow data were extracted from the database of an SHP,in the South region of Brazil.From the knowledge of the generation characteristics such as local water availability and SHP machines availability,it was possible to obtain the hydraulic power curve generated by the SHP.Fig.6illustrates the generation curve normalized to the maximum generation value (1MW),for a typical day.

Several researches that analyze DG interconnected with distri-bution networks consider that the DG unit is able to keep generating throughout of the peak demand period.However,this does not always happen because there are some uncertainty factors,such as changes in radiation and wind speed levels,hydrological risks and possibility of machines breakdowns due to the mechanical problems,causing the unavailability of generation.

This work considers the behavior of generation sources,using the expected values for each period of analysis.In the worst-case scenarios with low rate of DGs generation availability (for example,solar energy in the period of light load)these ones do not participate in the recon?guration process.

3.3.Heuristic recon?guration technique using the potential generation of DG

3.3.1.Objective functions and constraints

The objective function (OF)used in this work includes the minimization of three distinct functions:(i)Normalized Expected Loss of Energy in the primary network (ELosses i *)(ii)Normalized Expected System Average Interruption Frequency Index in the sys-tem (ESAIFI i *)and (iii)Normalized Expected value of Energy Not Supplied (EENS i *).The total gain obtained in each con?guration combines the three functions and it is presented in (1):

OF =min(ELosses i ?·w 1+ESAIFI i ?·w 2+EENS i ?·w 3)

(1)

Subject to

|I i |≤I i max

V j min ≤V j ≤V j max

P min ≤P DGn ≤P max

(2)

where i corresponds to the period of analysis:1...6,w 1...w 3are weights of the criteria in multicriteria method,I i is current magni-tude of each element must lie within its permissible limits (A),V j is voltage magnitude of each node must lie within its permissible ranges (kV)and P DGn is active power delivered by the distributed generator n .The values of P min and P max depend on the DG tech-nology considered (kW).

In addition to these constraints the system should always keep radiality after recon?guration of feeders and should not allow islanded operation of DG units.To calculate the load ?ow values in the distribution system,the proposed algorithm implements the backward/forward sweep method with DG [14,15],which is suit-able for calculation of reverse ?ows from distributed generation.With load ?ow values,the energy losses for the distribution sys-tem are obtained.The calculation of reliability indicators ESAIFI and EENS is obtained from the equations of reliability for these indicators during the process of load ?ow [16].

3.3.2.Weights of criteria

The indicators of the OF are judged according to the deci-sion making method AHP developed by Saaty [17].The method is premised on the trial and the conversion of the criteria weights,so one can adjust the priority that each criterion has over the others.In [13]is presented the methodology in more details and calculations for setting the weights of the criteria and judgment matrices used in this work.The following results are assumed:w 1(ELosses )=0.64;w 2(ESAIFI )=0.26and w 3(EENS )=0.10.

3.3.3.Heuristic technique for selecting con?gurations

The optimization technique employed in this work is based on the Branch Exchange adaptation proposed by [12].This step is based on the analysis of the interconnections between the feeders,which are performed by normally open (NO)switches.For each inter-connection,the best network con?guration between two feeders is searched,by changing the status of a pair of switches.

The method has the following advantages over other techniques from the literature:

?it highly limits the search space of solutions,reducing calculation and computational processing time;

?it does not require adjustments of optimization parameters due to changes in the network (such as grid expansion or installation of new equipment);

?the radial network is guaranteed,without the need to verify if the combination of switches that comprise the topology tested is valid.

The recon?guration methodology was divided into two mod-ules:(A)analysis of connection between feeders without

DG

Fig.7.Distribution network:(a)Original con?guration.(b)Switching status changed.

D.P.Bernardon et al./Electric Power Systems Research 107 (2014) 59–67

63

Fig.8.Switching status

changed.

Fig.9.Switching status changed on the opposite direction.

connected to the network and (B)analysis of connection between feeders with DG.

3.3.3.1.Recon?guration without DG on feeders.1st Stage :Choose determined remotely controlled NO (normally opened)tie-switch at random,starting from the original con?guration of the network (Fig.7(a)).Go to the 2nd stage;

2nd Stage :Change the network con?guration,closing an NO tie-switch and opening an NC (normally closed)switch of any of the two feeders involved.However,it should be the ?rst switch upstream from the NO tie-switch (TS1),as shown in Fig.7(b).Go to the 3rd stage;

3rd Stage :Perform the load ?ow and reliability calculation for this new con?guration and check if there was a reduction of OF without violating the constraints.If OF is improved,proceed to the 4rd stage.Otherwise,go to the 5th stage.

4th Stage :Change the network con?guration,closing the actual NO switch (S6)and opening the ?rst NC switch upstream (S7),but in the same direction (feeder)of the previous iteration (Fig.8).Go to the 6th stage.

5th Stage :Re-establish the initial con?guration and change the network topology,closing the NO tie-switch and opening the NC switch of the other feeder upstream from the tie-switch (Fig.9).Go to the 6th stage.

6th Stage :Change the network con?guration in the same direc-tion (feeder)while the OF is improved without violating the de?ned constraints.The process is ?nished when the OF does not improve or if any constraint violation occurs.In this case,the topology found in the previous iteration is the ?nal solution.

The same process must be repeated when another tie-switch is analyzed,always beginning from the initial con?guration.The pro-cess is repeated until all remote controlled NO tie-switches without DG on feeders are analyzed.

3.3.3.2.Recon?guration with DG on feeders.Assuming that dis-tributed generation injects power into the grid,it is necessary to evaluate the gain of its connection to each feeder.Initially starts with the original con?guration with DG,as shown in Fig.10

.

Fig.10.Original con?guration with distributed

generation.

Fig.11.DG connected in feeder

FD3.

Fig.12.DG connected in feeder FD4.

1st Stage :Test the gain of DG connection on the current feeder (FD3),closing the remotely controlled NO tie-switch (TS2)and opening the next NC switch (S14)downstream of tie-switch,as illustrated in Fig.11.Go to the 2nd stage;

2nd Stage :Perform the load ?ow and reliability calculation for this new con?guration and check if there was a reduction of OF without violating the constraints.If OF is improved,proceed to the 3rd stage.Otherwise,go to the 4th stage;

3rd Stage :Change the network con?guration in the same direc-tion (feeder)while the OF is improved without violating the de?ned constraints.Go to the 4th stage;

4th Stage :Test the connection of GD on the other feeder (FD4).From the original con?guration with DG (Fig.),open the ?rst NC switch (S13)upstream of DG and close the NO tie-switch (TS2),as illustrated in Fig.12.Go to the 5th stage;

5th Stage :Perform the load ?ow and reliability calculation for this new con?guration and check if there was a reduction of OF without violating the constraints.If the OF is improved,go to the 6th stage.Otherwise,the process of recon?guration is ?nished,go to the 7th stage.

6th Stage :Change the network con?guration in the same direc-tion (feeder)while the OF is improved without violating the de?ned constraints (Fig.13).The process of recon?guration is ?nished when the OF does not improve or if any constraint violation occurs.Go to the 7th stage;

7th Stage :The con?guration with the greatest reduction in the OF is chosen as best topology,comparing the results obtained in the connection of DG on feeder FD3(3th Stage)and FD4(6th Stage).

The same process must be repeated when another source of DG is analyzed,always beginning from the initial con?guration.

The methodologies presented assume that only the remote con-trolled switches are analyzed and it consists in applying the branch exchange algorithm twice:?rst,to determine the individual result of each con?guration test from the initial network topology and second,to determine the ?nal sequence of con?gurations.In

the

Fig.13.Switching status changed.

64 D.P.Bernardon et al./Electric Power Systems Research 107 (2014) 59–

67

https://www.doczj.com/doc/8014654951.html,work distribution with DG.

?rst case,the procedure is repeated for each normally open tie-switch starting from the initial network topology.At the end of this process it is applied the multicriteria decision method described in the previous section,to de?ne the best sequence of switching.The procedure of optimization is then applied for the second time,but for each tie-switch tested,the analysis is made without returning to the initial con?guration.

4.Results and discussion

4.1.Validation of the methodology

An exhaustive search procedure was implemented in a simpli-?ed distribution network (Fig.15),in order to assess the robustness of proposed method.The best solution for this network was pre-viously obtained considering only the power losses minimization and compared with the proposed methodology,as shown in Table 1.Fig.15demonstrates a network with seven switches which leads to a total of 128(27)possible combinations,and it is used to validate the proposed method.

In actual networks is not feasible to apply the method of exhaus-tive search due to combinatorial explosion caused by the number of switching devices in the network.

4.2.Practical implementation of the methodology

The proposed methodology was veri?ed through several tests on the concession area of a power utility of Brazil.The real

Table 1

Recon?guration results for exhaustive search compared with the methodology.

Parameter

Exhaustive search

Proposed method

Initial solution loss (kW)37.74Optimal solution loss (kW)34.72

Obtained loss (kW)

34.7234.72Processing time (3.33GHz)

32s

8s

distribution network model presented in Fig.14is used as a case study.This network has 2substations 69/13.8kV,5feeders,3points of distributed generation,15tie-switches,99normally closed switches and over 21,000consumers.The switches are remote con-trolled.The dotted lines represent the presence of normally open tie-switches (TS).The DG is composed of a SHP of 1MW located at node 6,two wind turbines (E53)of 800kW at node 33and a photovoltaic park of 500kW located at node 37.Data genera-tion from these sources is updated for each load rate,in order to consider the power injection of DG on its current condition gener-ation.

Table 2illustrates the test condition considered for each level of demand and each consumer class and generation scenario during the recon?guration of distribution network.

The recon?guration algorithm is applied considering the individual analysis of each switch interconnection shown in Fig.14.It evaluates the power injection of DG for each feeder involved based on the conditions of generation scenarios in Table 2.

The individual analysis of the tie-switches leads to the results shown in Table 3from original con?guration of networks,com-paring the results with and without DG for the period of 6:00to 12:00.Only the cases where the objective functions analyzed presented positive evolution are shown.Note that in normal situ-ations,the number of consumers of a feeder does not vary during the day,which suggests the same ESAIFI value in all the simula-tions.

Each result in Table 3is normalized by the maximum value found in the tests (C n base )as follows:

C ?n o pm

=C n o pm

C n base

(3)

After normalization,the individual results are multiplied by the weight vector and summed as in (1).The results are sorted by a global index (GI),from lowest to highest.This result indicates the sequence of switching for the best combination of results from

D.P.Bernardon et al./Electric Power Systems Research107 (2014) 59–67

65

Fig.15.Simpli?ed distribution network with DG.

Table2

Discretization curve of demand for consumer class and generation scenario of DG.

Period–initial hour

0:006:0012:0013:0017:0021:00 Feeder class(demand)Residential Low Medium Low Medium Heavy Medium Industrial Low Heavy Medium Heavy Medium Low

Commercial Low Heavy Low Low Heavy Low

Rural Low Medium Low Medium Heavy Medium DG(generation)Photovoltaic–Medium Heavy Medium Low–

Windpower Low Medium Heavy Heavy Medium Low

SHP Medium Medium Medium Medium Medium Medium

Table3

Results for the individual analysis of tie-switches.

Options:close/open Con?guration without DG Con?guration with DG

Losses(kWh)EENS(MWh)ESAIFI(fail./year)Losses(kWh)EENS(MWh)ESAIFI(fail./year)

Rate06:00–12:00hour

Initial con?guration2263.32603.2011.782094.85562.8011.78

Option1:TS-1/S32243.94590.9011.302079.20551.5011.30

Option2:TS-2/S182265.89596.3011.462094.32556.2011.46

Option3:TS-3/S122143.5554.409.932010.91520.809.93

Option4:TS-5/S222266.98603.5011.742037.14580.4011.74

Option5:TS-7/S592242.57577.7011.661983.50532.6011.66

Option6:TS-8/S842037.01569.8011.751752.88520.3011.75

Option7:TS-9/S632153.80581.2011.621928.56538.4011.62

Option8:TS-10/S912011.90567.1011.671759.74519.3011.67

the individual switches interconnection analysis.Table4illustrates this procedure for the period of6:00to12:00with DG the sys-tem.

The Branch Exchange algorithm is reapplied,following the sequence of operations from the GI ranking of Table4.The difference from the previous analysis is that the best con?guration obtained with one tie-switch is maintained as the initial con?gu-ration to the following tie-switch to be tested.The?nal result of the optimization of the network to the rate demand analyzed is shown in Table5.

Table4

Normalized results,sequence and global index with AHP method.

Options Energy losses×0.64ESAIFI×0.26EENS×0.10Global index(GI)Sequence

Rate06:00–12:00hour

Option1:TS-1/S30.990.950.950.97966

Option2:TS-2/S18 1.000.970.950.98868

Option3:TS-3/S120.960.840.890.92323

Option4:TS-5/S590.970.99 1.000.98147

Option5:TS-7/S590.940.990.910.95515

Option6:TS-8/S840.830.990.890.88451

Option7:TS-9/S630.920.980.920.93834

Option8:TS-10/S910.840.990.890.88462

66 D.P.Bernardon et al./Electric Power Systems Research107 (2014) 59–67

Table5

Final results of recon?guration analysis with DG.

Sequence of test Switching with best result Energy losses(kWh)ESAIFI(failures/year)EENS(MWh) Rate06:00–12:00hour

Initial con?guration–2094.8511.78632.90 Option6Close TS-8/Open S841752.8810.75520.30 Option8Close TS-10/Open S911756.5411.67520.4 Option3Close TS-3/Open S121672.609.90478.30

Final reduction(%)20.15%15.95%15.01%

All procedures of the main program have been successful and the?nal topology of the network determined by the program improved the indicators of the objective functions of the opti-mization method,with no constraints in relation to the necessary switching.One way to con?rm if the solution presented is the opti-mal solution is using the?nal con?guration obtained by proposed methodology as input to a new test sequence.If there is no change in the topology,there is a strong indication that the con?gura-tion obtained is the optimal solution or very close to the optimal solution.

The tests were performed in about3min in a PC with Intel Core 3.33GHz and24GB RAM.The scale of few minutes is acceptable for the proposed application,since the recon?guration is analyzed at the beginning of each demand rate transition and the demand rate interval is in the range of one or few hours.

5.Conclusions

This paper presented a new methodology for automatic recon?guration of power distribution networks incorporating dis-tributed generation.The main contributions of the proposed system are:real-time recon?guration based on load rate analysis,modeling and generation pro?le of DG from different sources(wind,solar and SHP);application of the AHP method for multicriteria decision mak-ing and integration of computational analysis with a Supervisory Control and Data Acquisition of remote controlled switches to allow performing automatic recon?guration in real-time.The switching are performed automatically,in the sequence determined by the program.

The results stand out the contribution of DG for signi?cant improvement on network performance indicators,reducing losses and increasing reliability in the process of recon?guration of dis-tribution systems in which they are connected.

For a real evaluation of the system performance,case studies were performed with real data from a power utility in different operating scenarios.The results indicate the feasibility of the pro-posed methodology,which can be adapted to other real systems with DG.

With the advent of the Smart Grid,the pro?le of load curves of distribution feeders will be subject to a different dynamic behav-ior than currently occurs.Some features,such as greater use of distributed generation,demand response and charging of electric vehicles will require a rapid response of the network to the new generation and load scenarios.The automatic recon?guration in real-time will help to improve network performance and to pro-mote more ef?cient use of its resources in this new context. Acknowledgments

The authors would like to thank the technical and?nancial support of AES Sul Distribuidora Gaúcha de Energia SA,Conselho Nacional de Desenvolvimento Cientí?co e Tecnológico(CNPq), Fundac??o de AmparoàPesquisa do Estado do Rio Grande do Sul (FAPERGS)and Coordenac??o de Aperfeic?oamento de Pessoal de Nível Superior(CAPES).

Appendix A.Nomenclature

AHP Analytic Hierarchy Process

ELosses i Expected Loss of Energy in the primary network

ESAIFI i Expected System Average Interruption Frequency INDEX EENS i Expected Energy Not Supplied

i corresponds to the period of analysis:1 (6)

I i current magnitude of each element must lie within its

permissible limits(A)

NC normally closed

NO normally opened

OF objective function

P DGn active power delivered by the distributed generator n SCADA Supervisory Control and Data Acquisition

w1...w3weights of the criteria in multicriteria method

V j voltage magnitude of each node(kV)

References

[1]R.E.Brown,Impact of smart grid on distribution system design,IEEE Power and

Energy Society General Meeting–Conversion and Delivery of Electrical Energy in the21st Century(2008)1–4.

[2]T.Thakur,Jaswanti,Study and characterization of power distribution network

recon?guration,in:IEEE Transmission&Distribution Conference and Exposi-tion,Latin America,2006,pp.1–6.

[3]M.S.Thomas,S.Arora,V.K.Chandna,Distribution automation lead-

ing to a smarter grid,IEEE Innovative Smart Grid Technologies(2011) 211–216.

[4]D.Haughton,G.T.Heydt,Smart distribution system design:automatic recon-

?guration for improved reliability,IEEE Power and Energy Society General Meeting(2010)1–8.

[5]M.Merdan,W.Lepuschitz,T.Strasser,F.Andren,Multi-agent system for

self-optimizing power distribution grids,IEEE International Conference on Automation,Robotics and Applications(2011)312–317.

[6]J.-C.Wang,H.-D.Chiang,G.R.Darling,An ef?cient algorithm for real-time

network recon?guration in large scale unbalanced distribution systems,IEEE Transactions on Power Systems11(1996)511–517.

[7]E.López,H.Opazo,L.Garcia,P.Bastard,Online recon?guration considering

variability demand:applications to real networks,IEEE Transactions on Power Systems19(2004)549–553.

[8]A.Vargas,M.E.Samper,Real-time monitoring and economic dispatch of smart

distribution grids:high performance algorithms for DMS applications,IEEE Transactions on Smart Grid3(2)(2012)866–877.

[9]R.S.Rao,K.Ravindra,K.Satish,S.V.L.Narasimham,Power loss minimiza-

tion in distribution system using network recon?guration in the presence of distributed generation,IEEE Transactions on Power Systems28(1)(2013) 317–325.

[10]V.F.Martins,C.L.T.Borges,Active distribution network integrated planning

incorporating distributed generation and load response uncertainties,IEEE Transactions on Power Systems26(4)(2011)2164–2172.

[11]G.Celli,E.Ghiani,F.Pilo,G.G.Soma,Reliability assessment in smart distribution

networks,Electric Power Systems Research104(2013)164–175.

[12]D.P.Bernardon,V.J.Garcia,A.S.Q.Ferreira,L.N.Canha,Multicriteria distribution

network recon?guration considering subtransmission analysis,IEEE Transac-tions on Power Delivery25(4)(2010)2684–2691.

[13]L.L.P?tscher, D.P.Bernardon,L.N.Canha,V.F.Montagner,V.J.Garcia,

A.R.Abaide,Intelligent system for automatic recon?guration of distribu-

tion network in real time,Electric Power Systems Research97(2013) 84–92.

D.P.Bernardon et al./Electric Power Systems Research107 (2014) 59–6767

[14]W.H.Kersting,D.L.Mendive,An application of ladder network theory to the

solution of three-phase radial load-?ow problems,IEEE Power Engineering Society Winter Meeting A76044-8(1976)1–6.

[15]L.Zhang,W.Tang,H.Guan,L.Zhang,The back/forward sweep-based power?ow

method for distribution networks with DGs,IEEE International Conference on Power Electronics and Intelligent Transportation System(2009)145–149.[16]R.E.Brown,Electric Power Distribution Reliability,second ed.,CRC Press,New

York,2009,ISBN978-0-8493-7567-5.

[17]T.L.Saaty,The Analytic Hierarchy Process:Planning,Priority Setting,Resource

Allocation,McGraw-Hill,New York,1980.

RealTimeRTPCR常见问题分析

Real-Time RT-PCR常见问题分析 1.某一孔荧光信号特别强 问题:同一批样品,其中某一个荧光信号特别强? 原因:①试剂配制时反应液没完全溶化,导致探针量在一管中增多;②试剂配制时没有充分混匀致各管中各成分的量不同;③也可能是PCR仪热槽被荧光物质污染,这 时就要清除热槽中的污染; 2. 扩增曲线有一向上或向下的尖峰 问题:扩增曲线有一向上或向下的尖峰? 原因:①反应过程中电压不稳定;②可能在20循环左右仪器有停下或者仪器有开盖,使得光线突然增强;③如果尖峰向下,也可能是卤素灯老化所致,这时应更换;

3. 部分样本扩增效率过低 问题:部分样本扩增效率过低? 原因:①提取液残留,一定程度抑制了PCR反应;②反应液未严格取量混匀或分装不均匀;③试剂失效; 4.阴性对照或空白对照翘尾,可能原因:1、模板提取环境有污染。2、模板提取操作有 污染。3、配液过程存在污染。 问题:阴性对照或空白对照翘尾? 原因:①模板提取环境有污染;②模板提取操作有污染;③试剂配制过程存在污染;

5. 直线型扩增曲线 问题:直线型扩增曲线? 原因:①探针部分降解(探针降解原因:a.探针反复冻融――稀释的探针可在4℃保存至少3个月,应避免反复冻融;b.探针在光线下暴露时间太长);②反应液中有PCR抑 制物; 6.没有扩增曲线 问题:没有扩增曲线? 原因:①PCR参数设置错误,在设计循环参数时将荧光信号读取时间设在反应的第一步,即stage 1阶段;②电脑设定了自动休眠;

7.基线下滑 问题:扩增曲线有一个下滑阶段? 原因:基线选取范围不对,可试着将基线范围改大一些,这一问题常因试剂质量所致;8.扩增曲线断裂 问题:扩增曲线断裂? 原因:基线选取范围不对,基线终点大于Ct值,这通常是由于模板DNA浓度过高所致,因Ct值<15,而基线范围仍取3-15,其中包含部分扩增信号,导致标准差偏大, 阈值过高,解决办法:减少基线终点至Ct值前4个循环,重新分析数据 9.样品浓度跨度过大 样品浓度过高,至阳性样品扩增曲线在后面循环中呈一向下的直线,原因及解决办法同“扩增曲线断裂”。

关于时间管理的英语作文 manage time

How to manage time Time treats everyone fairly that we all have 24 hours per day. Some of us are capable to make good use of time while some find it hard to do so. Knowing how to manage them is essential in our life. Take myself as an example. When I was still a senior high student, I was fully occupied with my studies. Therefore, I hardly had spare time to have fun or develop my hobbies. But things were changed after I entered university. I got more free time than ever before. But ironically, I found it difficult to adjust this kind of brand-new school life and there was no such thing called time management on my mind. It was not until the second year that I realized I had wasted my whole year doing nothing. I could have taken up a Spanish course. I could have read ten books about the stories of successful people. I could have applied for a part-time job to earn some working experiences. B ut I didn’t spend my time on any of them. I felt guilty whenever I looked back to the moments that I just sat around doing nothing. It’s said that better late than never. At least I had the consciousness that I should stop wasting my time. Making up my mind is the first step for me to learn to manage my time. Next, I wrote a timetable, setting some targets that I had to finish each day. For instance, on Monday, I must read two pieces of news and review all the lessons that I have learnt on that day. By the way, the daily plan that I made was flexible. If there’s something unexpected that I had to finish first, I would reduce the time for resting or delay my target to the next day. Also, I would try to achieve those targets ahead of time that I planed so that I could reserve some more time to relax or do something out of my plan. At the beginning, it’s kind of difficult to s tick to the plan. But as time went by, having a plan for time in advance became a part of my life. At the same time, I gradually became a well-organized person. Now I’ve grasped the time management skill and I’m able to use my time efficiently.

英语演讲稿:未来的工作

英语演讲稿:未来的工作 这篇《英语演讲稿范文:未来的工作》,是特地,希望对大家有所帮助! 热门演讲推荐:竞聘演讲稿 | 国旗下演讲稿 | 英语演讲稿 | 师德师风演讲稿 | 年会主持词 | 领导致辞 everybody good afternoon:. first of all thank the teacher gave me a story in my own future ideal job. everyone has a dream job. my dream is to bee a boss, own a pany. in order to achieve my dreams, i need to find a good job, to accumulate some experience and wealth, it is the necessary things of course, in the school good achievement and rich knowledge is also very important. good achievement and rich experience can let me work to make the right choice, have more opportunities and achievements. at the same time, munication is very important, because it determines whether my pany has a good future development. so i need to exercise their municative ability. i need to use all of the free time to learn

关于坚持的英语演讲稿

关于坚持的英语演讲稿 Results are not important, but they can persist for many years as a commemoration of. Many years ago, as a result of habits and overeating formed one of obesity, as well as indicators of overall physical disorders, so that affects my work and life. In friends to encourage and supervise, the participated in the team Now considered to have been more than three years, neither the fine rain, regardless of winter heat, a day out with 5:00 time. The beginning, have been discouraged, suffering, and disappointment, but in the end of the urging of friends, to re-get up, stand on the playground. 成绩并不重要,但可以作为坚持多年晨跑的一个纪念。多年前,由于庸懒习惯和暴饮暴食,形成了一身的肥胖,以及体检指标的全盘失常,以致于影响到了我的工作和生活。在好友的鼓励和督促下,参加了晨跑队伍。现在算来,已经三年多了,无论天晴下雨,不管寒冬酷暑,每天五点准时起来出门晨跑。开始时,也曾气馁过、痛苦过、失望过,但最后都在好友们的催促下,重新爬起来,站到了操场上。 In fact, I did not build big, nor strong muscles, not a sport-born people. Over the past few years to adhere to it, because I have a team behind, the strength of a strongteam here, very grateful to our team, for a long time, we encourage each other, and with sweat, enjoying common health happy. For example, Friends of the several run in order to maintain order and unable to attend the 10,000 meters race, and they are always concerned about the brothers and promptly inform the place and time, gives us confidence and courage. At the same time, also came on their own inner desire and pursuit for a good health, who wrote many of their own log in order to refuel for their own, and inspiring. 其实我没有高大身材,也没健壮肌肉,天生不属于运动型的人。几年来能够坚持下来,因为我的背后有一个团队,有着强大团队的力量,在这里,非常感谢我们的晨跑队,长期以来,我们相互鼓励着,一起流汗,共同享受着健康带来的快

引物设计原则(含Realtime引物)

1.引物最好在模板cDNA的保守区内设计。 DNA序列的保守区是通过物种间相似序列的比较确定的。在NCBI上搜索不同物种的同一基因,通过序列分析软件(比如DNAman)比对(Alignment),各基因相同的序列就是该基因的保守区。 2.引物长度一般在15~30碱基之间。 引物长度(primer length)常用的是18-27 bp,但不应大于38,因为过长会导致其延伸温度大于74℃,不适于Taq DNA 聚合酶进行反应。 3.引物GC含量在40%~60%之间,Tm值最好接近72℃。 GC含量(composition)过高或过低都不利于引发反应。上下游引物的GC含量不能相差太大。另外,上下游引物的Tm值(melting temperature)是寡核苷酸的解链温度,即在一定盐浓度条件下,50%寡核苷酸双链解链的温度。有效启动温度,一般高于Tm值5~10℃。若按公式Tm= 4(G+C)+2(A+T)估计引物的Tm值,则有效引物的Tm为55~80℃,其Tm 值最好接近72℃以使复性条件最佳。 4.引物3′端要避开密码子的第3位。 如扩增编码区域,引物3′端不要终止于密码子的第3位,因密码子的第3位易发生简并,会影响扩增的特异性与效率。 5.引物3′端不能选择A,最好选择T。 引物3′端错配时,不同碱基引发效率存在着很大的差异,当末位的碱基为A时,即使在错配的情况下,也能有引发链的合成,而当末位链为T时,错配的引发效率大大降低,G、C 错配的引发效率介于A、T之间,所以3′端最好选择T。 6. 碱基要随机分布。 引物序列在模板内应当没有相似性较高,尤其是3’端相似性较高的序列,否则容易导致错误引发(False priming)。降低引物与模板相似性的一种方法是,引物中四种碱基的分布最好是随机的,不要有聚嘌呤或聚嘧啶的存在。尤其3′端不应超过3个连续的G或C,因这样会使引物在GC富集序列区错误引发。 7. 引物自身及引物之间不应存在互补序列。 引物自身不应存在互补序列,否则引物自身会折叠成发夹结构(Hairpin)使引物本身复性。这种二级结构会因空间位阻而影响引物与模板的复性结合。引物自身不能有连续4个碱基的互补。 两引物之间也不应具有互补性,尤其应避免3′ 端的互补重叠以防止引物二聚体(Dimer与Cross dimer)的形成。引物之间不能有连续4个碱基的互补。 引物二聚体及发夹结构如果不可避免的话,应尽量使其△G值不要过高(应小于4.5kcal/mol)。否则易导致产生引物二聚体带,并且降低引物有效浓度而使PCR 反应不能正常进行。 8. 引物5′ 端和中间△G值应该相对较高,而3′ 端△G值较低。 △G值是指DNA 双链形成所需的自由能,它反映了双链结构内部碱基对的相对稳定性,△G 值越大,则双链越稳定。应当选用5′ 端和中间△G值相对较高,而3′ 端△G值较低(绝对值不超过9)的引物。引物3′ 端的△G 值过高,容易在错配位点形成双链结构并引发DNA 聚合反应。(不同位置的△G值可以用Oligo 6软件进行分析) 9.引物的5′端可以修饰,而3′端不可修饰。 引物的5′ 端决定着PCR产物的长度,它对扩增特异性影响不大。因此,可以被修饰而不影响扩增的特异性。引物5′ 端修饰包括:加酶切位点;标记生物素、荧光、地高辛、Eu3+等;引入蛋白质结合DNA序列;引入点突变、插入突变、缺失突变序列;引入启动子序列等。引物的延伸是从3′ 端开始的,不能进行任何修饰。3′ 端也不能有形成任何二级结构可能。 10. 扩增产物的单链不能形成二级结构。

关于管理的英语演讲

1.How to build a business that lasts100years 0:11Imagine that you are a product designer.And you've designed a product,a new type of product,called the human immune system.You're pitching this product to a skeptical,strictly no-nonsense manager.Let's call him Bob.I think we all know at least one Bob,right?How would that go? 0:34Bob,I've got this incredible idea for a completely new type of personal health product.It's called the human immune system.I can see from your face that you're having some problems with this.Don't worry.I know it's very complicated.I don't want to take you through the gory details,I just want to tell you about some of the amazing features of this product.First of all,it cleverly uses redundancy by having millions of copies of each component--leukocytes,white blood cells--before they're actually needed,to create a massive buffer against the unexpected.And it cleverly leverages diversity by having not just leukocytes but B cells,T cells,natural killer cells,antibodies.The components don't really matter.The point is that together,this diversity of different approaches can cope with more or less anything that evolution has been able to throw up.And the design is completely modular.You have the surface barrier of the human skin,you have the very rapidly reacting innate immune system and then you have the highly targeted adaptive immune system.The point is,that if one system fails,another can take over,creating a virtually foolproof system. 1:54I can see I'm losing you,Bob,but stay with me,because here is the really killer feature.The product is completely adaptive.It's able to actually develop targeted antibodies to threats that it's never even met before.It actually also does this with incredible prudence,detecting and reacting to every tiny threat,and furthermore, remembering every previous threat,in case they are ever encountered again.What I'm pitching you today is actually not a stand-alone product.The product is embedded in the larger system of the human body,and it works in complete harmony with that system,to create this unprecedented level of biological protection.So Bob,just tell me honestly,what do you think of my product? 2:47And Bob may say something like,I sincerely appreciate the effort and passion that have gone into your presentation,blah blah blah-- 2:56(Laughter) 2:58But honestly,it's total nonsense.You seem to be saying that the key selling points of your product are that it is inefficient and complex.Didn't they teach you 80-20?And furthermore,you're saying that this product is siloed.It overreacts, makes things up as it goes along and is actually designed for somebody else's benefit. I'm sorry to break it to you,but I don't think this one is a winner.

关于工作的优秀英语演讲稿

关于工作的优秀英语演讲稿 Different people have various ambitions. Some want to be engineers or doctors in the future. Some want to be scientists or businessmen. Still some wish to be teachers or lawers when they grow up in the days to come. Unlike other people, I prefer to be a farmer. However, it is not easy to be a farmer for Iwill be looked upon by others. Anyway,what I am trying to do is to make great contributions to agriculture. It is well known that farming is the basic of the country. Above all, farming is not only a challenge but also a good opportunity for the young. We can also make a big profit by growing vegetables and food in a scientific way. Besides we can apply what we have learned in school to farming. Thus our countryside will become more and more properous. I believe that any man with knowledge can do whatever they can so long as this job can meet his or her interest. All the working position can provide him with a good chance to become a talent. 1 ————来源网络整理,仅供供参考

自我管理演讲稿英语翻译

尊敬的领导,老师,亲爱的同学们, 大家好!我是5班的梁浩东。今天早上我坐车来学校的路上,我仔细观察了路上形形色色的人,有开着小车衣着精致的叔叔阿姨,有市场带着倦容的卖各种早点的阿姨,还有偶尔穿梭于人群中衣衫褴褛的乞丐。于是我问自己,十几年后我会成为怎样的自己,想成为社会成功人士还是碌碌无为的人呢,答案肯定是前者。那么十几年后我怎样才能如愿以偿呢,成为一个受人尊重,有价值的人呢?正如我今天演讲的题目是:自主管理。 大家都知道爱玩是我们孩子的天性,学习也是我们的责任和义务。要怎样处理好这些矛盾,提高自主管理呢? 首先,我们要有小主人翁思想,自己做自己的主人,要认识到我们学习,生活这一切都是我们自己走自己的人生路,并不是为了报答父母,更不是为了敷衍老师。 我认为自主管理又可以理解为自我管理,在学习和生活中无处不在,比如通过老师,小组长来管理约束行为和同学们对自身行为的管理都属于自我管理。比如我们到一个旅游景点,看到一块大石头,有的同学特别兴奋,会想在上面刻上:某某某到此一游话。这时你就需要自我管理,你需要提醒自己,这样做会破坏景点,而且是一种素质低下的表现。你设想一下,如果别人家小孩去你家墙上乱涂乱画,你是何种感受。同样我们把自主管理放到学习上,在我们想偷懒,想逃避,想放弃的时候,我们可以通过自主管理来避免这些,通过他人或者自己的力量来完成。例如我会制定作息时间计划表,里面包括学习,运动,玩耍等内容的完成时间。那些学校学习尖子,他们学习好是智商高于我们吗,其实不然,在我所了解的哪些优秀的学霸传授经验里,就提到要能够自我管理,规范好学习时间的分分秒秒,只有辛勤的付出,才能取得优异成绩。 在现实生活中,无数成功人士告诉我们自主管理的重要性。十几年后我想成为一位优秀的,为国家多做贡献的人。亲爱的同学们,你们们?让我们从现在开始重视和执行自主管理,十几年后成为那个你想成为的人。 谢谢大家!

关于工作的英语演讲稿

关于工作的英语演讲稿 【篇一:关于工作的英语演讲稿】 关于工作的英语演讲稿 different people have various ambitions. some want to be engineers or doctors in the future. some want to be scientists or businessmen. still some wish to be teachers or lawers when they grow up in the days to come. unlike other people, i prefer to be a farmer. however, it is not easy to be a farmer for iwill be looked upon by others. anyway,what i am trying to do is to make great contributions to agriculture. it is well known that farming is the basic of the country. above all, farming is not only a challenge but also a good opportunity for the young. we can also make a big profit by growing vegetables and food in a scientific way. besides we can apply what we have learned in school to farming. thus our countryside will become more and more properous. i believe that any man with knowledge can do whatever they can so long as this job can meet his or her interest. all the working position can provide him with a good chance to become a talent. 【篇二:关于责任感的英语演讲稿】 im grateful that ive been given this opportunity to stand here as a spokesman. facing all of you on the stage, i have the exciting feeling of participating in this speech competition. the topic today is what we cannot afford to lose. if you ask me this question, i must tell you that i think the answer is a word---- responsibility. in my elementary years, there was a little girl in the class who worked very hard, however she could never do satisfactorily in her lessons. the teacher asked me to help her, and it was obvious that she expected a lot from me. but as a young boy, i was so restless and thoughtless, i always tried to get more time to play and enjoy myself. so she was always slighted over by me. one day before the final exam, she came up to me and said, could you please explain this to me? i can not understand it. i

关于时间管理的英语演讲

Dear teacher and colleagues: my topic is on “spare time”. It is a huge blessing that we can work 996. Jack Ma said at an Ali's internal communication activity, That means we should work at 9am to 9pm, 6 days a week .I question the entire premise of this piece. but I'm always interested in hearing what successful and especially rich people come up with time .So I finally found out Jack Ma also had said :”i f you don’t put out more time and energy than others ,how can you achieve the success you want? If you do not do 996 when you are young ,when will you ?”I quite agree with the idea that young people should fight for success .But there are a lot of survival activities to do in a day ,I want to focus on how much time they take from us and what can we do with the rest of the time. As all we known ,There are 168 hours in a week .We sleep roughly seven-and-a-half and eight hours a day .so around 56 hours a week . maybe it is slightly different for someone . We do our personal things like eating and bathing and maybe looking after kids -about three hours a day .so around 21 hours a week .And if you are working a full time job ,so 40 hours a week , Oh! Maybe it is impossible for us at

关于人英语演讲稿(精选多篇)

关于人英语演讲稿(精选多篇) 关于人的优美句子 1、“黑皮小子”是我对在公交车上偶遇两次的一个男孩的称呼代号。一听这个外号,你也定会知道他极黑了。他的脸总是黑黑的;裸露在短袖外的胳膊也是黑黑的;就连两只有厚厚耳垂的耳朵也那么黑黑的,时不时像黑色的猎犬竖起来倾听着什么;黑黑的扁鼻子时不时地深呼吸着,像是在警觉地嗅着什么异样的味道。 2、我不知道,如何诠释我的母亲,因为母亲淡淡的生活中却常常跳动着不一样的间最无私、最伟大、最崇高的爱,莫过于母爱。无私,因为她的爱只有付出,无需回报;伟大,因为她的爱寓于

普通、平凡和简单之中;崇高,是因为她的爱是用生命化作乳汁,哺育着我,使我的生命得以延续,得以蓬勃,得以灿烂。 3、我的左撇子伙伴是用左手写字的,就像我们的右手一样挥洒自如。在日常生活中,曾见过用左手拿筷子的,也有像超级林丹用左手打羽毛球的,但很少碰见用左手写字的。中国汉字笔画笔顺是左起右收,适合用右手写字。但我的左撇子伙伴写字是右起左收的,像鸡爪一样迈出田字格,左看右看,上看下看,每一个字都很难看。平时考试时间终了,他总是做不完试卷。于是老师就跟家长商量,决定让他左改右写。经过老师引导,家长配合,他自己刻苦练字,考试能够提前完成了。现在他的字像他本人一样阳光、帅气。 4、老师,他们是辛勤的园丁,帮助着那些幼苗茁壮成长。他们不怕辛苦地给我们改厚厚一叠的作业,给我们上课。一步一步一点一点地给我们知识。虽然

他们有时也会批评一些人,但是他们的批评是对我们有帮助的,我们也要理解他们。那些学习差的同学,老师会逐一地耐心教导,使他们的学习突飞猛进。使他们的耐心教导培养出了一批批优秀的人才。他们不怕辛苦、不怕劳累地教育着我们这些幼苗,难道不是美吗? 5、我有一个表妹,还不到十岁,她那圆圆的小脸蛋儿,粉白中透着粉红,她的头发很浓密,而且好像马鬓毛一样的粗硬,但还是保留着孩子一样的蓬乱的美,卷曲的环绕着她那小小的耳朵。说起她,她可是一个古灵精怪的小女孩。 6、黑皮小子是一个善良的人,他要跟所有见过的人成为最好的朋友!这样人人都是他的好朋友,那么人人都是好友一样坦诚、关爱相交,这样人与人自然会和谐起来,少了许多争执了。 7、有人说,老师是土壤,把知识化作养分,传授给祖国的花朵,让他们茁壮成长。亦有人说,老师是一座知识的桥梁,把我们带进奇妙的科学世界,让

关于时间的英语演讲稿范文_演讲稿.doc

关于时间的英语演讲稿范文_演讲稿 and organizing people to learn from advanced areas to broaden their horizons in order to understand the team of cadres working conditions in schools, the ministry of education has traveled a number of primary and secondary schools to conduct research, listen to the views of the school party and government leaders to make school leadership cadres receive attention and guidance of the ministry of education to carry out a variety of practical activities to actively lead the majority of young teachers work hard to become qualified personnel and for them to put up the cast talent stage, a single sail swaying, after numerous twists and turns arrived in port, if there is wind, a hand, and naturally smooth arrival and guide students to strive to e xcel, need to nazhen “wind” - teacher. teachers should be ideological and moral education, culture education and the needs of students organically combining various activities for the students or students to carry out their own. for example: school quiz competitions, essay contests, ke benju performances and other activities to enable students to give full play to their talents. teachers rush toil, in order to that will enable students to continue to draw nutrients, to help them grow up healthily and become pillars of the country before. for all students in general education, the government departments have also not forget those who cared about the

关于机会的英语演讲稿

good afternoon everybody! I’m very glad to stand here and give you a short speech about challenge and opportunity,双手交握微笑 So, what’s an opportunity? It’s a great chance to achieve dreams, it’s a platform to show ourselves.Just as now,I’m standing here showing myself,it's one of my dreams,also my opportunity. Then, what about challenge? Challenge is a new or difficult task which test our ability and skill. it is a fighter, a sense of courage, the fearless spirit towards all difficulties, Many people are afraid of being challenged, worrying about change and failure.I used to be a member of them,but now,I find that sth we haven’t done isn’t as difficult as it seems, fear always hindered our courage. Said so much,此刻我最想与你们分享的一句话就是: we should welcome being challenged,and try to enjoy it.它很可能是你进步的机会 Cruel competition isn 't the excuse for failure. No one is regularly on a winner or a loser. To the strong willed, competition is the spring of hope; To the weak minded, it means the winter of despair. So turning into opportunities means taking advantage of these challenges and benefiting from them.In this way,you can be the boss of your life.这句语法有没有错误?指着他,手势 That’s all, thank you!

关于坚持的英语演讲稿

---------------------------------------------------------------范文最新推荐------------------------------------------------------ 1 / 9 关于坚持的英语演讲稿 results are not important, but they can persist for many years as a commemoration of . many years ago, as a result of habits and overeating formed one of obesity, as well as indicators of overall physical disorders, so that affects my work and life. in friends to encourage and supervise, the participated in the team now considered to have been more than three years, neither the fine rain, regardless of winter heat, a day out with 5:00 time. the beginning, have been discouraged, suffering, and disappointment, but in the end of the urging of friends, to re-get up, stand on the playground. in fact, i did not build big, nor strong muscles, not a sport-born people. over the past few years to adhere to it, because i have a team behind, the strength of a strong team here, very grateful to our team, for a long time, we encourage each other, and with sweat, enjoying common health happy. for example, friends of the several run in order to maintain order and unable to attend the 10,000 meters race, and they are always concerned about the brothers and promptly inform the place and

相关主题
相关文档 最新文档