Controlling The Power Balance In An ‘empty M. Reza A. O .

2y ago
108 Views
2 Downloads
470.74 KB
19 Pages
Last View : Today
Last Download : 2m ago
Upload by : Jamie Paz
Transcription

Controlling the power balance in an ‘emptynetwork’M. Reza1, ,A. O. Dominguez2 ,P. H. Schavemaker1,3 ,A. Asmara4 ,F. A. Viawan5 andW. L. Kling1,31Electrical Power System Laboratory,Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology,Mekelweg 4, 2628 CD, Delft, the NetherlandsFax: 31 15 278 1182E-mail: m.reza@tudelft.nl Corresponding author2Electrical Engineering Department,University of Vigo,36310 Vigo (Pontevedra), Spain3TenneT TSO,TenneT B.V.,Utrechtseweg 310, 6812 AR, Arnhem, the Netherlands4Ship Production,Marine and Transport Technology, Delft University of Technology,Mekelweg 2, 2628 CD, Delft, the Netherlands5Division of Electric Power Engineering,Chalmers University of Technology,Gothenburg, Sweden, S-412 96 Gothenburg, SwedenAbstract: This paper presents the concept of an “empty network”and shows how the power balance can be controlled in such a system.In this study, an “empty network” is defined as a transmission system inwhich no rotating mass is present. All generators are connected to distributed systems and ’hidden’ behind power electronic interfaces. Onegenerator creates a neat 50 Hz voltage that serves as a frequency reference for the other generators. Consequently, a power imbalance cannotbe detected in the classical way, as an altered system frequency.Therefore, a novel control system to maintain the power balance isneeded. In this paper, voltage deviations are used to detect power imbalances, and remedies to eliminate the negative consequences of using

2M. Reza et al.the voltage deviations to detect the power imbalances are proposed anddiscussed.Keywords:‘empty network’, power balance control, distributed generationReference to this paper should be made as follows: Reza, M., DominguezA. O., Schavemaker P. H., Asmara A., Viawan F. A. and Kling W. L.(xxxx) ‘Controlling the power balance in an ‘empty network’, Int. J. ofEnergy Technology and Policy, Vol. x, No. x, pp.xxx–xxx.Biographical Notes: Muhamad Reza obtained his B.Sc. from Bandung Institute of Technology (ITB), Indonesia in 1997 and M.Sc. fromDelft University of Technology (TU Delft) in 2000, the Netherlands,both in Electrical Engineering. He is currently pursuing Ph.D. in theElectrical Power System (EPS) laboratory, TU Delft, in the main framework of Intelligent Power Systems.Alejandro O. Dominguez is a MSc student in the Electrical Engineering Department, University of Vigo, Spain. Within Socrates-ErasmusProgram, he spent 1 semester in the Electrical Power System (EPS)laboratory, Delft University of Technology (TU Delft) for performingresearch on the topic of “Empty Network”.Pieter H. Schavemaker obtained his M.Sc. in Electrical Engineeringfrom the Delft University of Technology in 1994 and he obtained hisPh.D. in Electrical Engineering from the Delft University of Technologyin 2002. Since 1996 he has been with the Power Systems Laboratorywhere he is currently Assistant Professor. His main research interestsinclude power system transients and power system calculations.Andi Asmara received the B.Sc. and M.Sc. degrees from BandungInstitute of Technology, Indonesia in 1996, and Dortmund University,Germany in 2005, respectively. He worked as an Automation ProductEngineer at Schneider Electric Indonesia from 1996 to 1999 and from1999-2002 he worked at Klockner-ROH Joint Operation. Since 2005, heis a PhD Student at the Ship Production, Delft University of Technology,Delft, The Netherlands.Ferry A. Viawan received the B.Sc. and M.Sc. degrees from BandungInstitute of Technology, Indonesia in 1996, and Chalmers University ofTechnology, Sweden in 2003, respectively. He worked as a Power SystemEngineer at PT Caltex Pacific Indonesia from 1996 to 2003, where heworked on operation, planning and protection of a transmission anddistribution system. Since 2004, he is a PhD Student at the Division ofElectric Power Engineering, Department of Energy and Environment,Chalmers University of Technology, Gothenburg, Sweden.Wil L. Kling received his M.Sc. in electrical engineering from theTechnical University of Eindhoven in 1978. Since 1993 he has been(part-time) professor at the faculty of Electrical Engineering in the fieldof power system engineering and in addition he has been with the Operations department of TenneT (a Dutch Transmission System Operator).Since 1999 he has also been a part-time professor at the TU Eindhoven.His area of interset is related to planning and operation of power systems.

Controlling the power balance in an ‘empty network’13BackgroundNowadays, natural and artificial constraints limit the expansion of centralizedlarge power plants and a shift towards an extensive use of distributed generation(DG) - small, decentralized/distributed power generators that are connected todistribution network - appears.The implementation of DG turns the current passive distribution network intoan active one. This active distribution network does not only consume power, butit also generates power and supplies it to the transmission system [1-3]. In thisway, power can be transferred from one distribution network to another. Whenwe reflect further on this issue to the extreme, we could imagine that at a certaintime, all centralized power plants are shut down and the electrical power generatedby the DG in distribution networks is sufficient to meet the total demand of thegrid. In other extreme, we can also imagine that the three-phase ac transmissionsystems are no longer used and those distribution networks are interconnected bydc transmission systems instead [4].In conventional large power plants, the generators, i.e. synchronous generators, operate at fixed speed and thereby with a fixed grid frequency. DG, however,presents a quite different characteristic. For example, the voltage generated byvariable speed wind power generator, photovoltaic generator and fuel cells can notbe directly connected to the grid. The power electronic converters play an important role to match the characteristic of DG units and requirements of the gridconnections [5].For a stable operation of a power grid, there should always be a balance betweengenerated power on one side and consumed power (plus losses) on the other. Forexample, in an isolated grid with power generated by a synchronous generator, thepower imbalance causes the generator to accelerate (or decelerate) and alter thegrid frequency. The increasing (or decreasing) power generated by the generatoras a response of the altered system frequency will balance the power and bringthe frequency back to the reference frequency. Many researchers try to adopt theclassical synchronous generator control to an isolated grid supplied from powerelectronic interfaced DGs. For example, in [6], a control scheme based on droopfrequency concept (of a synchronous generator) to operate inverters feeding anisolated system is presented. This concept is further explored in different modes ofoperation in [7].One of DG control method that does not adopt the classical the synchronousgenerator control is presented in [8]. The paper proposes to detect the powerimbalance from the voltage, instead of the frequency that has been widely used inclassical power systems. The paper starts from the assumption that in an ’emptynetwork’, the system frequency is fixed as it is created by a power electronic device,and therefore the power imbalance cannot be detected in the classical way, as analtered system frequency. The empty network is defined as the network withoutconventional rotating mass, where all generators are connected via power electronicconverters and the distributed systems are connected to the transmission systemvia power electronic interfaces, as it is illustrated in Figure 1. Further, the rotatingmasses of the generators (or the motors, if any) within the distribution networksare ’hidden’ from the transmission system. It is shown in the paper that the powerbalance in the empty network can be maintained by using the proposed method.

4M. Reza et al.Figure 1The illustration of an ’empty network’ model333In this paper, the usage of the voltages to detect a power imbalance in theempty network is further explored by using different control schemes. While in [8],the power balance is maintained by using one generator that can compensate thewhole system, which is uncommon in practice; in this paper, controlling the powerbalance in the system by using multi generators, where each generator has theirown controller, is presented. Three different control schemes are developed andtested to examine whether or not the power balance in the empty network can becontrolled.2Power BalanceClassically, a power system is characterized by a relatively small number ofcentralized power plants that are based on large synchronous generators. Thesegenerators are connected directly to the grid so that there is a coupling betweenthe generator rotor speed and the power balance in the system.The fundamental equation that governs the rotational dynamics of the synchronous generator is the swing equation [9]:2H d2 δ Pa Pm Pe .ωs dt2([pu])(1)where, ωs s is the synchronous speed in electrical units [rad/s], H is the inertiaconstant (the stored kinetic energy in MJ at synchronous speed per machine rating(Smach ) in MVA) [s], δ is the angular displacement of the rotor [rad], Pm is theshaft power input minus rotational losses [pu], Pe is the electrical power crossingthe air gap [pu], Pa is the accelerating power [pu], and t is the time [s].It can be seen from equation (1) that any imbalance in active power (Pe 6 Pm )will result in non-zero accelerating power (Pa 6 0), i.e. the rotor of the synchronous22generators will either accelerate ( ddt2δ 0) or decelerate ( ddt2δ 0).When there is a power imbalance, the kinetic energy of the rotation will beeither added to or taken from the generators. As a result, the frequency throughout

Controlling the power balance in an ‘empty network’5the power system varies. To maintain the power balance in a power system, thegenerators are equipped with turbine speed governor that monitors the turbinegenerator speed and adjusts the input from the prime mover in response to changesin this frequency.33.1‘Empty Network’ ModelBasic assumptionsTo decouple the changes of the voltages with the changes of the reactive powerin an empty network, several assumptions are applied on the model of the emptynetwork as the following: The distribution networks are equipped with reactive power sources. Thereactive power source is sufficient to fulfill the reactive power load within thedistribution networks. A reactive power control system is assumed to be applied within each distribution network, locally. This control system is responsible to absorb thereactive power load changes within the distribution network. The (active) distribution networks are connected to the transmission systemvia power electronic interfaces. The power electronic interface is assumed topermit only active power to flow (bi-directional). The reactances of the transmission lines are compensated, in such a way thatthey behave like resistive lines.3.2Active Distribution Network ModelThis paper focuses on the controlling of power balance in an empty network,on the transmission system level. Therefore, by taking the previously-mentionedassumptions (see section 3.1), the active distribution networks are considered asthe following: the (distributed) generators are connected via power electronic converters andthey generate only active power. The generators are initially set to balancethe active power demand. the loads demand active and reactive power. They are modeled as constantimpedance and constant power. Electrical motors (and the correspondinginertias) are hidden behind power electronic interfaces from the transmissionsystem; therefore, electrical motors, if any, are assumed to be included in theconstant power model of the loads. the reactive power is supplied by the dedicated reactive power sources. Thereactive power sources are preset to balance the reactive power demand. a power imbalance is simulated by changing the active power demand of theload. The distributed generators should respond to this change. However, a

6M. Reza et al.Figure 2balanceThe ‘empty network’ model used in the simulation of controlling the power33'*'*3'*reactive power imbalance is not simulated. The consequences to the activedistribution network model are:– only active power will flow between the distribution networks and thetransmission system. The power electronic interfaces that connect thedistribution networks to the transmission network are then not included,and– reactive power control systems that are responsible to balance the reactive power changes locally within the distribution networks are notincluded. The reactive power sources are then modeled as shunt devices.Thus, in the simulation of controlling the power balance, the empty networkcan be modeled as shown in figure 2.3.3(Distributed) Generator ModelIn the empty network, three converter connected generator models are used toperform different function, i.e.: a constant voltage source. This model is used to represent one generatorthat provides the voltage and frequency reference for the other generators inthe system. Figure 3 shows the representation of this generator, where Usis the constant (reference) voltage with a fixed frequency, and Zs is a sourceimpedance. a constant current source ig that generates a current that is in phase withthe terminal voltages Ut of the generator (a Phase Locked Loop, PLL, is usedfor this purpose). This model is used to represent generators that operate asactive power sources. Figure 4 shows the representation of this generator.

Controlling the power balance in an ‘empty network’Figure 37Constant voltage source model Figure 4Constant current source modelUtigFigure 5ZsControlled current source modelUtControlleric a controlled current source ic . This model is used to represent one or (more)generator that serves as the ’slack’ generator. The slack generator that willeither supply or absorb any deficit or surplus of active power in the system.This generator is assumed to have no current limiter and to be equipped withsufficient (energy) storage. The representation of this generator is shown infigure 5.A remark should be given that power electronic interfaces that drive the outputof converter connected (distributed generator) basically represent a voltage sourceconverter, the mostly used converter nowadays [5,10]. Yet, the use of constantcurrent sources to represent converter-connected generators in this simulation issupported by the following assumptions: a converter is actually a voltage source converter, but it behaves like a currentsource, so that current source models can substitute voltage source converterswhen simulations are made in large systems [11]. It is usual to model the sources as P Q-sources in studies on large systems [12].

8M. Reza et al.A constant current source that generates a current in phase with the (terminal) voltage represents a P Q-source that generates constant active power (P )and zero reactive power (Q 0), as long as the terminal voltage of the generator is constant. In practice, a converter is equipped with a current limiter. When the terminalvoltage drops, the converter will supply less active power. Thus, the use of aconstant current source corresponds to a converter whose current is limitedto the nominal value (in practice, 100% up to 120% of the nominal value).4Basic Controller ModelThe basic functionality of the controller-block in figure 5 is highlighted hereunder: In figure 6, three types of converter-connected generators are implemented. In steady state, the current of the voltage source should be zero (is 0), sothat there is no voltage drop across the impedance Zs . Any power imbalance should be eliminated by controlling the current ic thatis generated by the controlled current source. This controlled current sourcerepresents the ’slack’ generator. When, for example, the active power consumption of the load Pload increases, the current flowing to the load (iload )will rise. Both generators that are modeled as current sources do not react(yet), and the voltage source will start to supply active power in order tobalance the power. Thus is increases and causes a voltage drop over Z, sothat Ut decreases. This voltage drop will be detected by the controller of thecontrolled current source. As a result, the controlled current source will supply more active power (i.e. it injects more current ic ) until the power balanceis restored.The controller that is used in the basic controller model is a proportional-integralcontroller (PI controller) that is a common feedback loop component in industrialcontrol applications.To verify the basic controller model, a load jump will be simulated to cause apower unbalance in the system shown in figure 6. The system voltage is set at 10kV. The load demands 60 MW of active power (Pload ) initially. The load is equallydivided in constant impedance and constant power. The constant current sourcesupplies all the initial power demand. The currents generated by the constantvoltage source (is ) and the controlled current source (ic ) are thus equal zero. Aload jump is applied by increasing the load modeled as the constant impedancewith 30 MW.Figures 7, 8 and 9 show transitories of the voltages, currents and active powerwhen the load jump occurs. Note that the Pconstantcurrentsource , P‘slack0 , andP‘master0 in figure 9 represent the active power supplied by the constant currentsource, controlled current source and constant voltage source of the system in figure 6 respectively. The simulations are performed on a Real Time Digital Simulator(RTDS). A time step of 50 µs is used in the simulations.

Controlling the power balance in an ‘empty network’Figure 69Basic controller idea applied at a 1-bus test systemUtZUS1isigiciloadigControllericPloadFigure 7The transitories of the voltages when a 30 MW load jump is applied atbus-1 of the system shown in figure 612Us10Voltage (kV)8Ut ( bus 1)64200246Time (s)810

10M. Reza et al.Figure 8The transitories of the currents when a 30 MW load jump is applied atbus-1 of the system shown in figure 61098iloadCurrent (kA)76ig54ic32is100246810Time (s)Figure 9The transitories of the active power when a 30 MW load jump is applied atbus-1 of the system shown in figure 6

Controlling the power balance in an ‘empty network’11It can be seen in these figures that, following the load jump, the power balanceis restored when the ’extra’ power demand is supplied by the ’slack’ generator (seethe increasing current ic and active power P‘slack0 in figures 8 and 9). The busvoltage is also restored to a steady-state value that lies within a /-5% margin ofthe nominal voltage.5Empty Network ControlsPractically, a power system consists of more than one bus. In this case, thesystem is decoupled and no longer linear, due to the dependency of one bus withanother. In addition of that, the voltages at the buses throughout the system arepractically not the same (see Section 2). Consequently, applying the basic controlmodel of Section 4 for each bus gives potential difficulties, since the basic controlmodel is a linear control system.In this section, three control systems are proposed. These control systems aredefined as:1 Stand-alone master controller2 Decentralized-controller with single reference3 Decentralized controller with hysteresisTo verify these control systems, a simple test system that consists of 3 busesis defined as shown in figure 10. Tables 1 and 2 show respectively the componentparameters used and the load flow settings and computed results in the 3-bus testsystem. Note that Gref refers to the reference (‘master’) generator. Gj refers tothe constant-power generator (at bus-j). Loadj refers to the load (at bus-j) and Cjrefers to the reactive power source (at bus-j). Tj refers to the transformer (at bus-j)and TLjk refers to the transmission line (between bus-j and bus-k). In table 1, Sbasedenotes M V Abase of the test system [MVA]. UHV and UM V denote the system highand medium voltage levels [kV]. R, XL and B denote the resistance [pu], reactance[pu] and susceptance [pu] of the transmission lines. XT denotes the transformerreactance and Z denotes the impedance between the reference ’master’ generatorand bus-1.Table 1Component parameters used in the 3-bus test systemDescriptionSystem baseSystem voltageTransmission lines: TL12 , TL13 , TL23Transformer: T1 , T2 , T3Impedance:ParameterSbaseUHVUM kVpupupupupu

12M. Reza et al.Figure 10A simple 3-bus test system (empty network) 5.1Stand-alone master controllerThe most simple way to overcome the non-linearity problem is by using a standalone master controller. In this approach only one basic controller is applied andconnected to one of the bus of the system. In this case, the controller only regulates the voltage of one bus and let the system comes to balance using its ownconnectivity.Figure 11 shows the implementation of the stand-alone master controller in thetest system (empty network). The ‘slack’ generator (that is represented by theTable 2Load flow settings and computed results in the 3-bus test 1Load2Load3C1C2C3LoadShunt .3Note that the transmission lines introduce quite some capacitance in the system;each transmission line generates around 16 MVAr

Controlling the power balance in an ‘empty network’13Figure 11The implementation of the stand-alone master controller in the test system(empty network) controlled current source) is implemented at bus-1. In this controller scheme, onlyone ‘slack’ generator is implemented in the test system. The generator shouldhandle the active power imbalance occurs in the system. Note that GCj refers tothe controlled-power/‘slack’ generator (at bus-j).A load jump is applied by increasing the constant power load at bus-2 (the loadis modeled as constant power) with 30 MW. Figure 12 shows the transitories ofthe active power where all the 30 MW power (of the load jump) is supplied by the‘slack’ generator. The power balance is restored and all system parameters are backto stable steady state values.When the stand-alone master controller scheme is implemented, the problem of‘different signal’ of voltages for the control input is eliminated by only using onecontroller at bus-1. In this way, the controller uses only one voltage point as itsreference signal. However, challenge will be that one generator should compensatefor the power balance in the whole system. In the following Sections, some otherproposals concentrate on dividing the ‘slack’ generators.5.2Decentralized-controller with single referenceIn practice, it is uncommon to use one generator to compensate the wholesystem. Because of that, three generators with their own controllers should beapplied. However, if these three controllers are applied ’as is’ in the test system,even though the voltage can be regulated, the power balance of the generatorswill not be achieved. It is already expected that the system is decoupled and thevoltage for each bus is not exactly the same. Therefore, decentralized-controllers

14M. Reza et al.Figure 12The transitories of the active power when a 30 MW load jump is appliedat bus-2 of the system (empty network) shown in figure 11100Load90280Active Power [MW]70G ,G ,G1236050Load1 , Load34030GC120Gref100 100246810Time [s]with single reference is proposed here. In this approach, the ‘slack’ generator ineach bus has its own controller but the reference signal is common for all of them,and it can be taken from any voltage point.Figure 13 shows the implementation of the decentralized-controller with singlereference in the test system (empty network). Each of the ‘slack’ generators (represented by the controlled current source) is implemented at bus-1, -2 and -3. Thegenerators (altogether) should take care the active power imbalance occurs in thesystem. One control signal is used by all generators, that is the voltage at bus-1(U1 ). Note that GCj refers to the controlled-power/‘slack’ generator (at bus-j).A load jump is applied by increasing the constant power load at bus-2 (the loadis modelled as constant power) with 30 MW . Figure 14 shows the transitories ofthe active power. The 30 MW power (of the load jump) is supplied by the three‘slack’ generators at bus-1, -2 and -3. Each generator supplies the requirementpower in balance, 10 MW. Also, all system parameters are back to stable steadystate values.In the same manners with the first approach, by implementing the decentralizedcontroller with single reference, the problem of ‘different signal’ of voltages for thecontrol input is eliminated by only using one controller at bus-1. The differenceis that this control signal is used for all three controllers. With this approach thecontrol generator is no longer centralized, however there is one aspect that shouldbe considered. This approach needs a communication link between each controllerto transfer the reference data signal. It might happened that not all system hasthis luxury.The next section describes the third method that can be applied for the systemwithout communication link between each controller.

Controlling the power balance in an ‘empty network’15Figure 13The implementation of the decentralized-controller with single referencein the test system (empty network) Figure 14The transitories of the active power when a 30 MW load jump is appliedat bus-2 of the system (empty network) shown in figure 139080Load2Active Power [MW]70G1, G2, G3605040Load , Load133020Gref100 100G,GC12,GC2C346Time [s]810

165.3M. Reza et al.Decentralized controller with hysteresisThe third proposed approach uses three decentralized controllers; one controlleris applied at each bus. As already described above, the linear controller cannotworks perfectly on the non-linear decoupled system. The symptom that happensby applying the basic controller over the test system is that on the steady-stateregion the controller oscillates. This is due to the system that is decoupled and thereference signal that is not exactly the same.To prevent this symptom, hysteresis on the controller input is applied. It meansthat the controller stops regulating the system whenever the value of the voltagelies within the hysteresis boundary. The used of hysteresis is allowed as long as thewidth of it is less or equal than the tolerance of the voltage, which is 1% of thenominal value.Figure 15 shows the implementation of the decentralized controller with hysteresis in the test system (empty network). The ‘slack’ generators represented bythe controlled current sources) are implemented at bus-1, -2 and -3. One ‘slack’generator is implemented in each bus. In this controller scheme, each ‘slack’ generator uses the voltage of where the generator is implemented. The generators(altogether) should take care the active power imbalance occurs in the system. Thegenerator GCj is infed by the control signal the voltage of bus-j (Uj ).A load jump is applied by increasing the load at bus-2 (the load is modeled asconstant power) with 30 MW. Figure 16 shows the transitories of the active power.The 30 MW power (of the load jump) is supplied by the three ‘slack’ generatorsat bus-1, -2 and -3. Each generator supplies the power requirement in balance, 10MW. All system parameters are also restored to stable steady state values.By applying this approach, the power balance of the system can be achieved.The effect of hysteresis is that there is a steady state error on the voltage, but whilethe steady state value is smaller than the tolerance of the voltage value, it can beaccepted. Thus, the voltage regulation is maintained. It might be not the optimalsolution, but the system still operates on the specification. The main advantageusing this approach is that the requirement of the communication link betweencontrollers is eliminated.5.4RemarksIt is possible to improve the performance of the system by tuning the controlparameters of the controllers. However, parameter tuning is mostly practical, thatis, the tuned parameters can be used only for that particular system. Thereforethat is not done in this paper.Each control approach that is proposed in this paper has its own advantagesand disadvantages among each other. The stand-alone master controller is themost simple one, it is easy to implement and its performance is good. The maindisadvantage of this approach is that it uses a single generator to supply the requiredpower.The second approach, the decentralized-controller with single reference can overcome the single generator problem, with the price that it requires the availabilityof a communication link between controllers to transfer the reference signal data.The most realistic approach to be implemented is the third approach, the de-

Controlling the power balance in an ‘empty network’Figure 15network)17The implementation of the robust controller in the test system (empty Figure 16The transitories of the active power when a 30 MW load jump is appliedat bus-2 of the system (empty network) shown in figure 159080Load2Active Power [MW]70G1, G2, G36050Load1, Load34030G20refGC1, GC2, GC3100 100246Time [s]810

18M. Reza et al.centralized controller with hysteresis, since this a

Pieter H. Schavemaker obtained his M.Sc. in Electrical Engineering from the Delft University of Technology in 1994 and he obtained his Ph.D. in Electrical Engineering from the Delft University of Technology in 2002. Since 1996 he has been with the Power Systems Laboratory where he is c

Related Documents:

May 02, 2018 · D. Program Evaluation ͟The organization has provided a description of the framework for how each program will be evaluated. The framework should include all the elements below: ͟The evaluation methods are cost-effective for the organization ͟Quantitative and qualitative data is being collected (at Basics tier, data collection must have begun)

Silat is a combative art of self-defense and survival rooted from Matay archipelago. It was traced at thé early of Langkasuka Kingdom (2nd century CE) till thé reign of Melaka (Malaysia) Sultanate era (13th century). Silat has now evolved to become part of social culture and tradition with thé appearance of a fine physical and spiritual .

On an exceptional basis, Member States may request UNESCO to provide thé candidates with access to thé platform so they can complète thé form by themselves. Thèse requests must be addressed to esd rize unesco. or by 15 A ril 2021 UNESCO will provide thé nomineewith accessto thé platform via their émail address.

̶The leading indicator of employee engagement is based on the quality of the relationship between employee and supervisor Empower your managers! ̶Help them understand the impact on the organization ̶Share important changes, plan options, tasks, and deadlines ̶Provide key messages and talking points ̶Prepare them to answer employee questions

Dr. Sunita Bharatwal** Dr. Pawan Garga*** Abstract Customer satisfaction is derived from thè functionalities and values, a product or Service can provide. The current study aims to segregate thè dimensions of ordine Service quality and gather insights on its impact on web shopping. The trends of purchases have

Chính Văn.- Còn đức Thế tôn thì tuệ giác cực kỳ trong sạch 8: hiện hành bất nhị 9, đạt đến vô tướng 10, đứng vào chỗ đứng của các đức Thế tôn 11, thể hiện tính bình đẳng của các Ngài, đến chỗ không còn chướng ngại 12, giáo pháp không thể khuynh đảo, tâm thức không bị cản trở, cái được

Le genou de Lucy. Odile Jacob. 1999. Coppens Y. Pré-textes. L’homme préhistorique en morceaux. Eds Odile Jacob. 2011. Costentin J., Delaveau P. Café, thé, chocolat, les bons effets sur le cerveau et pour le corps. Editions Odile Jacob. 2010. Crawford M., Marsh D. The driving force : food in human evolution and the future.

Le genou de Lucy. Odile Jacob. 1999. Coppens Y. Pré-textes. L’homme préhistorique en morceaux. Eds Odile Jacob. 2011. Costentin J., Delaveau P. Café, thé, chocolat, les bons effets sur le cerveau et pour le corps. Editions Odile Jacob. 2010. 3 Crawford M., Marsh D. The driving force : food in human evolution and the future.