| 1. |
- Ackermann, Thomas
(författare)
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Distributed Resources in a Re-Regulated Market Environment
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis analyses the value that distributed resources(DR) can contribute to an economically effcient operation of are-regulated electricity market and discusses the relevantchanges in the regulatory framework to allow the appropriatedevelopment of DR whenever DR may increase the economiceffciency of the electricity market. Distributed resources thereby combine two aspects:Distributed generation and demand-side resources. Distributedgeneration is defined as generation within the distributionsystem or on the customer side of the meter. Demand-sideresources are those load resources on the customer-side thatcan be used to shift electricity demand from peak to off-peakperiods, or to reduce the overall electricity demand. To gain a better understanding of the value that DR mayprovide in a re-regulated market, an analysis of there-regulation approaches in England andWales, Scandinavia,Australia, New Zealand as well as in two regions in the USA isperformed. The key findings of this analysis are that non ofthe re-regulation approaches put special emphasis on DR. Thecomparison also shows that despite very different approachesused in the various markets, the remaining re-regulationproblems are very similar. These key problems are mainlyrelated to market power in the various markets and littlecompetition in network services. The thesis shows that DR has the potential to improveoverall economic market effciency by reducing market powerissues and increasing competition in network services. Forinstance, many DR business schemes have no incentive toexercise market power, because withholding generation may havea negative impact on the complex revenue stream from differentincome sources. While this may not allow the general conclusionthat DR will always provide benefits to market operation, it isimportant to consider that not all DR need to provide suchbenefits, as it was also shown that already comparatively smallamounts of demand resources or distributed generation cansignificantlyreduce market power issues. In addition, it wasalso shown that DR can introduce competition into networkservices and therefore can provide incentives for distributionand transmission network companies to operate more costeffectively. It was also demonstrated that the potential of DR to improveoverall economic market effciency will only be realized if: 1. DR is developed in the correct size, i.e. DR should fitinto an existing distribution network and may increase networkutilization rate,2. DR is developed at the correct location in thenetwork, e.g. in areas with congestion problems,3. DR is in operation during the correct times, whenbeneficial to the market, e.g. during times when market powerissues may arise, and4. independent ownership of DR projects isencouraged. Market regulations therefore must provide the correctincentives for the correct siting and operation of DR as wellas for independent ownership. The thesis uses examples andempirical data to explain the relevant regulatory aspects indetail and provides suggestions for a regulatory framework thatconsiders the potential of DR to improve overall economiceffciency in an electricity market.
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| 2. |
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| 3. |
- Amelin, Mikael, 1972-
(författare)
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On Monte Carlo simulation and analysis of electricity markets
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation is about how Monte Carlo simulation can be used to analyse electricity markets. There are a wide range of applications for simulation; for example, players in the electricity market can use simulation to decide whether or not an investment can be expected to be profitable, and authorities can by means of simulation find out which consequences a certain market design can be expected to have on electricity prices, environmental impact, etc. In the first part of the dissertation, the focus is which electricity market models are suitable for Monte Carlo simulation. The starting point is a definition of an ideal electricity market. Such an electricity market is partly practical from a mathematical point of view (it is simple to formulate and does not require too complex calculations) and partly it is a representation of the best possible resource utilisation. The definition of the ideal electricity market is followed by analysis how the reality differs from the ideal model, what consequences the differences have on the rules of the electricity market and the strategies of the players, as well as how non-ideal properties can be included in a mathematical model. Particularly, questions about environmental impact, forecast uncertainty and grid costs are studied. The second part of the dissertation treats the Monte Carlo technique itself. To reduce the number of samples necessary to obtain accurate results, variance reduction techniques can be used. Here, six different variance reduction techniques are studied and possible applications are pointed out. The conclusions of these studies are turned into a method for efficient simulation of basic electricity markets. The method is applied to some test systems and the results show that the chosen variance reduction techniques can produce equal or better results using 99% fewer samples compared to when the same system is simulated without any variance reduction technique. More complex electricity market models cannot directly be simulated using the same method. However, in the dissertation it is shown that there are parallels and that the results from simulation of basic electricity markets can form a foundation for future simulation methods. Keywords: Electricity market, Monte Carlo simulation, variance reduction techniques, operation cost, reliability.
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| 4. |
- Arshad, Waqas, 1973-
(författare)
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A Low-Leakage Linear Transverse-Flux Machine for a Free-Piston Generator
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The presented work is about a new low-leakage lineartransverse-flux electrical machine.The machine is dimensionedfor a free-piston generator. The intended application is inseries-hybrid vehicles. The free-piston generator is anintegration of a free-piston combustion engine with a linearelectrical machine. It provides benefits in e±ciency,emissions and multi-fuel capabilities, to name a few. Thesecombustion benefits are only possible if the total mover massis kept quite low (e.g.≤ 4 kg for a 50 kW unit). Thelimited mover mass and competitiveness demands result in a verystringent set of specifications for the electrical machine.Most existing electrical machine topologies arepreliminarily investigated. Of these only a transverse-fluxmachine (TFM) is found to be promising. Even for the case ofthe TFM, a factor 2 improvement in the performance indices ofthe existing TFMs is required. Different surface-mounted TFMsare investigated for improvement. It is found that theanalytically acceptable solutions fail during thethree-dimensional finite-element analysis (3D-FEM). Thesedesigns suffer from a very significant pole-to-pole armatureleakage flux in the stator. Similar design improvements for theburied-magnets TFMs are also investigated. Fortunately, in thiscase a promising design is derived. This design exhibits lowleakage and is verified with FEM analysis. A down-scaledone-phase 1.7 kW proof-of-concept TFM of this design isdimensioned. It is analysed thoroughly, both analytically aswell as by 3D-FEM computations. It is found that for thisparticular prototype the design suffered from saturation. It isshown how this design can be modified to yield the desiredforce with the allowed mover mass. The efficiency is found tobe only slightly lower than the demands but a poor power factoris noted.The prototype is built. Unfortunately, all the desiredmeasurements could not be carried out. This is because thebuilt-machine sufferedwith two major manufacturing defects.The magnets are found to be demagnetised to about 50% of theirmanufactured value. It is also found that the translator poleson the average are 7% longer (in the axial direction) than thestator poles. Low values of no-load induced voltage and forceare thus measured. The correlation between the manufacturingdefects and the measurements is established. Due toinsufficient measurement data, this relationship is mainly ofan indicative nature only. A more correct picture requiresconstruction of a new prototype. Still, the results do pointtowards a near fulfillment of the objectives. Other addressedtopics include, an investigation into a separate free-pistongenerator project with reduced specifications, application ofthe presented work to renewable energy sources like wind- andwave-energy and a brief introduction to the free-pistonapplication aspects.Keywords:Free-Piston Generators, Linear Machines,Transverse-Flux Machines, Hybrid Vehicles, Electrical MachinesDesign.
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| 6. |
- Carlsson, Fredrik, 1974-
(författare)
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On impacts and ride-through of voltage sags exposing line-operated AC-machines and metal processes
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the last decade, power quality has been recognised asa global problem. Among different types of power qualityproblems, voltage sags have been identified to be one of themost severe problems for different process industries. The mostcommon reason to voltage sags is lightning strikes in powerlines. Protection equipment, usually located at switchyards,disconnect faulted power lines as soon as possible, which isapproximately 100 ms. Thus, the duration of voltage sags areapproximately 100 ms. The sensitivity to voltage sags ofelectrical equipment in process industries can be observed asfor instance malfunction, automatic turnoff or damages.This thesis gives an overview of three metals processes withfocus on the sensitivity to voltage sags and interruptions. Theinherent energy in the process is used to find the sensitivity.This energy may also be used to obtain "ride-through" for theprocesses. The three metals processes are a blast furnaceprocess, a hot rolling mill process and a cold rolling millprocess. The main attention in this thesis is paid to the blastfurnace process, which is powered by a line-operatedsynchronous machine.The thesis shows that the protection equipment forelectrical machines can be adjusted to avoid unnecessaryshutdowns. It is also explained why there are high torque andcurrents during voltage sags as well as after voltage sags. Itis shown that the first peak torque and current during thevoltage sags is almost proportional to the voltage change, thatis the voltage magnitude before the voltage sag minus thevoltage magnitude during the voltage sag. The first peak torqueand current after the voltage sag depends sinusoidal-like onthe duration of the voltage sag and almost proportional to thevoltage change during the voltage sag. There is no fluxsaturation during voltage sags, however after voltage sagssaturation is very likely to occur. The thesis explains why andalso how the flux is changed during and after voltage sags.The duration of voltage sags is in many cases set by theprotection equipment located in switchyards. It is shown thatthe durations of voltage sags can be changed to durations thatwill cause less peak torque and current after voltage sags forline-operated AC-machines. It is also shown how this istheoretically achieved.Keywords:Rolling mill, Blast furnace, Power Quality,Synchronous machine, Asynchronous machine, Voltage sag, Voltageinterruption, Ride-through, Process disturbances, Simulation,Modelling
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| 7. |
- Chatelet, Sylvain
(författare)
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Dynamic analysis of a novel electromagnetic transducer for hybrid vehicle and experimental verification
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the results of the work carried out on the dynamic analysis and experimental performance measurements of a novel concept of electromagnetic system for hybrid vehicle powertrains. The main focus of this work is to present how this novel electromagnetic system can be operated in a hybrid vehicle and to show how a prototype of this system has succesfully been operated in a laboratory set-up. Research on hybrid vehicle powertrains is encouraged by the increasing popularity of these vehicles. There is a large variety of solutions for hybrid vehicle powertrains. At the Royal Institute of Technology (KTH), Stockholm, Sweden, a novel machine concept intended for hybrid vehicle powertrains has been developed. It consists of two electrical machines built together in one unit. It is called the Four Quadrant energy Transducer (4QT) and is intended to link a combustion engine to the transmission in a hybrid vehicle, and by an apropriate control to improve the vehicle efficiency in comparison to a conventional vehicle of similar size and performance. The research project on the 4QT system has been carried out by a research team, since 1995. It evolved from early machine study and vehicle simulation, to prototype design and manufacturing. The work presented in this thesis completes the previously published works on the 4QT, with dynamic simulations of a 4QT equipped vehicle and the experimental testing of the prototype machines. An experimental setup has been built in order to test the performance of the prototype machines. The control of the machines and its experimental implementation are presented. The experimental setup is controlled to simulate drive cycle conditions, in order to measure efficiency of the prototype machines. Dynamic simulations of a vehicle equipped with a 4QT have been carried out to analyse the powertrain behaviour under transient conditions. It is shown that it is possible to control the 4QT prototype and operate it within its full operating range. Results of the efficiency measurements show that the efficiencies are slightly lower than expected, probably due to an underestimation of the stray load losses. This gives room for further research and improvements in the design of the prototype machines. Transient simulations underline the importance of the control strategy and dimensioning of the powertrain elements to avoid excessive stress on the vehicle.
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| 8. |
- Chin, Yung-Kang
(författare)
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A permanent magnet synchronous motor for an electric vehicle - design analysis
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the study and the design analysis of apermanent magnet synchronous motor (PMSM) for the tractionapplication of an electric vehicle. An existing inductiontraction motor for an electric forklift benchmarks the expectedperformances of the proposed PMSM design. Further, thepossibility of using the identical stator as the one used inthe induction motor is explored for the fast prototyping. Theprototype motor is expected to be field-weakened and to have aconstant power speed range (CPSR) of 2.5 to 3.A design approach based on the CPSR contour plot in aninterior permanent magnet (IPM) parameter plane is derived toobtain the possible designs that meet all the designspecifications and the targeted CPSR. This study provides thepossible alternative designs for the subsequent futureprototype motors.An analytical approach to estimate the iron loss in PMsynchronous machines is developed and included in the designprocedure. The proposed technique is based on predicting theflux density waveforms in the various regions of the machine.The model can be applied at any specified load condition,including the field-weakening operation region. This model canbe ultimately embedded in the design process for a routine usein loss estimations.The first prototype motor with an inset permanent magnetrotor has been built and the available measurements are used tovalidate the design performance. In particular, the thermalanalyses based both on the lumped-circuit approach and thenumerical method are compared with the measured results. Asecond and possibly a third prototype motor targeting a widerand higher performance will be carried out in the continuingphase of the project.Keywords:Constant Power Speed Range, Electric Vehicles,Field-weakening, Reference Flux Linkage, Iron Loss, PermanentMagnet Synchronous Motor, Thermal Analysis
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| 9. |
- Cirani, Maddalena
(författare)
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Analysis of an innovative design of an axial flux Torus-machine
- 2002
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The high compactness of axialflux permanent magnet (AFPM) machines compared with theconventional induction, DC and radial flux permanent magnet(RFPM) machines, renders this machine-topology particularlysuitable to be integrated in a system for hybrid electricvehicles (HEVs). Indeed, due to the limited space inside thevehicle, the considerable reduction in volume and weightoffered by AFPM machines is of major importance. In particular,the limited axial length of AFPM machines is an important issuefor HEVs. Furthermore, AFPM machines present high efficiencydue to the absence of rotor currents. However, in order to besuitable for traction applications, the AFPM machine has tooperate at high-torque and high-speeds.A particular type of AFPMmachine, the so-called Torus-machine, has been investigated andan innovative design has been analyzed in order to fulfill thehigh-speed requirements. In fact, the machine has been designedto work in field-weakening operations and, to this purpose, themachine stator is provided with teeth and slots so as toincrease the field-weakening capability. A further improvementof the field weakening capability of the machine is obtained bythe addition of rotor saliency.A general analysis of theequations, which describe the machine parameters, is presented.Next the design of a 30kW, 4000 r/min Torus-machine has beeninvestigated on the basis of volume and performancerequirements. Furthermore, the performance of a machine havingthe previously calculated parameters but without rotor saliencyhas been investigated and the results have been compared. FEMcalculations based on the software programs Flux-2D and Flux-3Dhave been examined and most of the results present satisfactoryagreement with the analytical calculations. Moreover, asimplified thermal model of the machine has been developed inorder to predict the temperature rise in the winding atdifferent operating conditions.ABB Corporate Research,Västerås, Sweden, has manufactured a prototype of themachine. The measurements performed on the parameters of theprototype validate the analytical results. Furthermore, themachine thermal test agrees satisfactorily with the thermalmodel for the no load condition.
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| 10. |
- Demetriades, Georgios D., 1967-
(författare)
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On small-signal analysis and control of the single- and the dual-active bridge topologies
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-frequency dc-dc converters are nowadays widely used in a diversity of power electronic applications. High operating frequencies entail a reduction in size of the passive components, such as inductors, capacitors and power transformers. By operating the converter at higher frequencies with conventional hard-switching topologies, the transistor switching losses increase at both turn-on and turn-off. High-voltage converters in the power range of 1-10MW will therefore have excessive switching losses if the switching frequency is higher than 4 kHz. In order to achieve a high-frequency operation with moderate switching losses a number of soft-switched topologies have been studied in [Dem1]. The favourable DC-DC converter was found to be the Dual-Active Bridge when a bi-directional power flow is demanded. Additionally, the Single-Active Bridge (SAB) topology was introduced for the first time. In this thesis the two topologies are thoroughly studied. The dynamic small-signal models are presented and the dynamic behaviour of the converters is discussed in deep. Different control strategies are presented concerning the two converters and the advantages and the disadvantages of the different control strategies are stated. Critical issues as efficiency and stability are presented separately for the two converters.
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