8,816 research outputs found
Design metrics for evaluating the propulsive efficiency of future ships
No full textThere is an increasing need for the ship design process to take account of environmental issues such as the emission of greenhouse gases and the likely extension of a carbon dioxide charging mechanism to international shipping. These issues, together with the need for economic viability, provide further incentives to improve the efficiency of propulsion of ships. The main components of powering are firstly reviewed. Individual components and other power saving devices are identified which should contribute to improvements in the overall efficiency of propulsion. Suitable design metrics and procedures, taking into account economic and environmental factors, are recommended for the design of future ships
Parameterized Fast Decoupled Power Flow Methods For Obtaining The Maximum Loading Point Of Power Systems: Part I. Mathematical Modeling
No full textThe conventional Newton and fast decoupled power flow (FDPF) methods have been considered inadequate to obtain the maximum loading point of power systems due to ill-conditioning problems at and near this critical point. It is well known that the PV and Q-θ decoupling assumptions of the fast decoupled power flow formulation no longer hold in the vicinity of the critical point. Moreover, the Jacobian matrix of the Newton method becomes singular at this point. However, the maximum loading point can be efficiently computed through parameterization techniques of continuation methods. In this paper it is shown that by using either θ or V as a parameter, the new fast decoupled power flow versions (XB and BX) become adequate for the computation of the maximum loading point only with a few small modifications. The possible use of reactive power injection in a selected PV bus (QPV) as continuation parameter (μ) for the computation of the maximum loading point is also shown. A trivial secant predictor, the modified zero-order polynomial which uses the current solution and a fixed increment in the parameter (V, θ, or μ) as an estimate for the next solution, is used in predictor step. These new versions are compared to each other with the purpose of pointing out their features, as well as the influence of reactive power and transformer tap limits. The results obtained with the new approach for the IEEE test systems (14, 30, 57 and 118 buses) are presented and discussed in the companion paper. The results show that the characteristics of the conventional method are enhanced and the region of convergence around the singular solution is enlarged. In addition, it is shown that parameters can be switched during the tracing process in order to efficiently determine all the PV curve points with few iterations. © 2003 Elsevier B.V. All rights reserved.69193104Voltage Stability Criteria, Undervoltage Load Shedding Strategy, and Reactive Power Reserve Monitoring Methodology (1999) Final Report, p. 154. , MayLesieutre, B.C., Sauer, P.W., Pai, M.A., Existence of solutions for the network/load equations in power systems (1999) IEEE Trans. Circuits Syst. I: Fundam. Theory Applic., CAS-I-46, pp. 1003-1011Cañizares, C.A., Alvarado, F.L., Point of collapse and continuation methods for large ac/dc systems (1993) IEEE Trans. Power Syst., PS-8, pp. 1-8Hiskens, I.A., Analysis tools for power systems - Contending with nonlinearities (1995) Proc. IEEE, 83 (11), pp. 1573-1587Gao, B., Morison, G.K., Kundur, P., Towards the development of a systematic approach for voltage stability assessment of large-scale power systems (1996) IEEE Trans. Power Syst., PS-11, pp. 1314-1324Chao, X.Y., Practical determination of operating transfer limits (1995) Proceedings of the PICA Conference, pp. 271-277Iwamoto, S., Tamura, Y., A load flow calculation method for ill-conditioned power systems (1981) IEEE Trans. Power Apparatus Syst., PAS-100, pp. 1736-1743Mansour, Y., Suggested Techniques for Voltage Stability Analysis (1993) IEEE Power Engineering Subcommittee Report, 93 TH0620-5-PWRSeydel, R., (1994) From Equilibrium to Chaos: Practical Bifurcation and Stability Analysis, Second Ed., , Springer, New YorkAjjarapu, V., Christy, C., The continuation power flow: A tool for steady state voltage stability analysis (1992) IEEE Trans. Power Syst., PS-7, pp. 416-423Bijwe, P.R., Tare, R.S., An efficient continuation power flow method for voltage stability analysis (1997) Electric Machines Power Syst., 25, pp. 927-938Arya, L.D., Verma, H.K., A method for tracing P-V curve for voltage stability analysis with voltage dependent loads (1996) Electric Machines Power Syst., 24, pp. 583-596Chiang, H.D., Flueck, A.J., Shah, K.S., Balu, N., CPFLOW: A practical tool for tracing power systems steady-state stationary behaviour due to load and generation variations (1995) IEEE Trans. Power Syst., PS-10, pp. 623-633Taylor, C.W., (1994) Power System Voltage Stability, , McGraw-Hill, New YorkChiang, H.D., Li, H., Yoshida, H., Fukuyama, Y., Nakanishi, Y., The generation of ZIP-V curves for tracing power system steady state stationary behavior due to load and generation variations (1999) Proceedings of IEEE PES Summer Meeting, pp. 647-651. , Edmonton, Alberta, Canada, JulyFlatabø, N., Ognedal, R., Carlsen, T., Voltage stability condition in a power transmission system calculated by sensitivity methods (1990) IEEE Trans. Power Syst., PS-5, pp. 1286-1293Alves, D.A., Da Silva, L.C.P., Castro, C.A., Da Costa, V.F., New parameterization schemes for the continuation load flow method (2000) Proceedings of the International Conference on Electric Utility Deregulation and Restructuring, and Power Technologies, DRPT2000, , City University, London, UK, AprilStott, B., Alsac, O., Fast decoupled load flow (1974) IEEE Trans. PAS, PAS-93, pp. 859-869Van Amerongen, R.A.M., A general-purpose version of the fast decoupled load flow (1989) IEEE Trans. PAS, PAS-4, pp. 760-770Monticelli, A., Garcia, A., Saavedra, O.R., Fast decoupled load flow: Hypothesis, derivations and testing (1990) IEEE Trans. Power Systems, PS-5, pp. 1425-143
Technical and economic value of utility-scale wind-storage hybrid power plants
No full textThe potential technical benefits of wind-storage hybrids, mainly arbitrage, imbalance reduction, and frequency support, are convincing enough to launch demonstration projects. However, a quantitative analysis of these benefits, including economic considerations, is lacking. The aim of this study is to establish at what costs such technical benefits can be achieved, and whether developers reap sufficient economic advantage to make the development of such hybrid plants attractive. A wind-storage power plant is simulated for arbitrage, imbalance revenue maximization, and secondary frequency support using the Internal Rate of Return as a parameter to measure the economic performance. It is found that, for a wind-farm developer, deploying batteries just for arbitrage and/or imbalance revenue maximization does not improve profitability at current levels of battery costs. However, there is a strong economic incentive for a wind farm developer to deploy batteries to participate in the secondary frequency market.Wind Energ
Wideband High Power Amplifier Design
No full textThis thesis aims for high power wideband amplifiers suitable for base station instrumentation purposes. A power combing topology is introduced, not only to achieve high power but also good input and output matching. Two kinds of broadband 3-dB quadrature couplers, which are important components in the power combing topology, are designed and implemented. In order to reduce the cost, broadband Wilkinson dividers are designed to replace some of the 3-dB quadrature couplers in the topology. Both NXP LDMOS die and Cree GaN packaged transistors are reviewed for the wideband PA. Two bandwidth extension design methods are studied and developed within this thesis. The design using the Cree GaN packaged transistors was implemented and measured. Beside the high power wideband amplifier design, additional investigation on adaptive matching using duty-cycle control in Class-E power amplifier is presented.MicroelectronicsMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Ship resistance and propulsion: practical estimation of ship propulsive power
No full textShip Resistance and Propulsion is dedicated to providing a comprehensive and modern scientific approach to evaluating ship resistance and propulsion. This book, written by experts in the field, includes the latest developments from applied research, including those in experimental and CFD techniques, and provides guidance for the practical estimation of ship propulsive power for a range of ship types. A large number of fully worked examples are included to illustrate applications of the data and powering methodologies; these include cargo and container ships, tankers and bulk carriers, ferries, warships, patrol craft, work boats, planing craft and yachts. The book is aimed at a broad readership including practising naval architects and marine engineers, seagoing officers, small craft designers, undergraduate and postgraduate degree students. It should also appeal to others involved in transportation, transport efficiency and eco-logistics who need to carry out reliable estimates of ship power requirements.Contents1. Introduction; 2. Propulsive power; 3. Components of ship resistance; 4. Model-ship extrapolation; 5. Model-ship correlation; 6. Restricted water depth and breadth; 7. Measurements of resistance components; 8. Wake and thrust deduction; 9. Numerical estimation of ship resistance; 10. Resistance design data; 11. Propulsor types; 12. Propeller characteristics; 13. Powering process; 14. Hull from design; 15. Numerical methods for propeller analysis; 16. Propulsor design data; 17. Applications.<br/
Wideband Class B Power Amplifier Topologies
No full textWireless communication has encountered a tremendous growth over the past few decades. The increased plurality in communication standards, characterized by the use of different operating frequencies and data rates, has translated into very tough specifications for the broadcasting base station power amplifier, in terms of efficiency, bandwidth and linearity. For this reason, currently many high efficiency power amplifier concepts are investigated for their suitability to handle the upcoming generations of wireless communication standards. At this moment the Doherty power amplifier (DPA) is a popular concept, which gives good effciency in the power back-off, making it a suitable choice when dealing with signals that have a high peak-to-average power ratio. To be efficient in power back-off operation, the Doherty power amplifier is composed out of two linear amplifiers with an impedance inverter as an output power combiner. Due to its high complexity, the traditional Doherty amplifier is limited for its RF bandwidth. In view of this, the objective of this thesis is to design a linear wideband class-B power amplifier cell which allows incorporation in the DPA. For this purpose an LDMOS based push-pull topology together with baluns (implemented by bondwires) at the input and output of the transistors has been adapted. The described topology helps to achieve an orthogonal relation between the fundamental path and its second harmonic, resulting in wideband high efficiency operation. The resulting amplifier provides an output power of 60 W with a power added efficiency greater than 48% over a relative bandwidth of 40% centered around 1:8GHz.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
Wideband High Power Doherty Amplifiers
No full textCurrently the Doherty Power Amplifier (DPA) is replacing the traditional Class B amplifier in base-station and broadcast applications, as such becoming the preferred choice of industry due to its simplicity and high efficiency performance. In spite of its success, so far practical DPA implementations can provide only a very limited RF bandwidth, which tends to narrow down even more at higher power levels. This narrowband behavior of the DPA is mostly caused by the use of traditional operating classes for the active devices and bandwidth restrictions related to use of a conventional impedance inverter. In this work, the bandwidth of different DPA topologies has been analyzed, followed by a discussion of recent techniques that can help to improve the DPA bandwidth. To overcome the remaining bandwidth limitations in a DPA design, a novel differential configuration was proposed. In this approach, transmission line based baluns are used to implement the desired wideband 2nd harmonic terminations of the active devices. By combining this technique with a novel wideband impedance inverter, excellent DPA wideband performance can be achieved. Unfortunately, when going to practical balun implementations, various imperfections come to light, which trouble the achievable DPA bandwidth performance. For this reason, three practical balun structures are investigated in detail, namely, the coaxial cable based balun, the vertically installed planar balun and suspended planar stripline balun. To explore the proposed DPA concept when using practical baluns, two DPAs featuring mixed-signal driven inputs are presented. A dedicated design procedure for these DPAs is also given. The first prototype is implemented using NXP GaN devices and coaxial cable based baluns. Simulation results show a maximum output power of 52dBm, but in 6dB power back-off we only reach 40% efficiency from 530MHz to 700MHz, which is significantly less than the intend bandwidth (450MHz-810MHz). Using the lessons learned of this first amplifier, a second design with NXP LDMOS devices and suspended planar stripline balun has been developed. According to simulation this later design provides a maximum output power of 59dBm with the efficiency above 55% at both full power and 6dB power back-off. According the simulations this second design can even achieve 50% efficiency at 8dB back-off. The related center frequency is 650MHz with a high-efficiency bandwidth at 6dB power back-off (efficiency within 10% of its maximum) from 460MHz to 790MHz.Microwave groupMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
The effect of swimsuit resistance on freestyle swimming race time.
No full textIt is known that swimming equipment (suit, cap and goggles) can affect the total resistance of a swimmer, and therefore impact the resulting swimming speed and race time. After the 2009 swimming world championships (WC) the international swimming federation (FINA) banned a specific type of full body suit, which resulted in an increase in race times for subsequent WC events. This study proposes that the 2009 suits provided a reduction in swimming resistance and aims to quantify this resistance reduction for male and female freestyle events. Due to the practical difficulties of testing a large sample of swimmers a simulation approach is adopted. To quantify the race time improvement that the 2009 suits provided, an equivalent 2009 “no-suit” dataset is created, incorporating the general trend of improving swimming performance over time, and compared to the actual 2009 times. A full race simulation is developed where the start, turn, underwater and surface swimming phases are captured. Independent resistance models are used for surface and underwater swimming; coupled with a leg propulsion model for underwater undulatory swimming and freestyle flutter kick, and a single element arm model to simulate freestyle arm propulsion. A validation is performed to ensure the simulation captures the change in swimming speed with changes to resistance and is found to be within 5% of reality. Race times for an equivalent “no-suit” 2009 situation are simulated and the total resistance reduced to achieve the actual 2009 race times. An average resistance reduction of 4.8% provided by the 2009 suits is identified. A factor of 0.47 ± 10%, to convert resistance changes to freestyle race time changes is determine
A 60W Compact Highly Efficient Wideband Class-E Power Amplifier
No full textWith the rapid growth of wireless communication systems, there is more and more demand for radio frequency power amplifiers (RFPAs) in base stations to be power-efficient so as to reduce the cooling and electrical power cost. Besides the efficient requirement, wide-band working frequency and compact PCB size are also attractive for cutting more cost. This thesis deals with a switch-mode Class E power amplifier which provides wide-band, highly efficient and compact size performance, with a 60W GaN HEMT device. A mathematical model for Class E amplifier is presented and analyzed. Based on the model, a novel design procedure for wide-band power amplifier design is proposed. The input/output matching networks in the amplifier are built by bondwires and pre-matching capacitors so as to give an extremely compact size. The 60W compact wide-band power amplifier is then implemented with PCB to verify the concept. A wide-band measured output power performance is observed over 1.7GHz - 2.3GHz in the range of 40-65W and the measured drain efficiency is between 66% and 74%; measured PAE is between 61% and 70%. Transducer power gain is 12dB ± 1dB over the frequency range. Besides the amplifier, additional work is about large signal device modeling with PolyHarmonic Distortion model which is based on acquiring X-parameters of a device.MicroelectronicsMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Energy Efficient and Compact RF High-Power Amplifiers
No full textThe main objectives of this thesis are to improve the energy efficiency and physical form-factor of high-power amplifiers in base station applications. As such, the focus of this dissertation is placed on the outphasing amplifier concept, which can offer high-efficiency, good linearity and excellent opportunities for system integration. With this mind set, various outphasing concepts have been studied at different levels of abstraction, starting from their fundamental operation, to very detailed efficiency and bandwidth considerations. In order to enable the future package integration of complete RF high-power amplifiers and transmitter lineups, dedicated design techniques for very compact and high-power magnetic components have been developed utilizing low-cost wire bonding techniques. Using these techniques, a very low-loss, high-current RF transformer concept was introduced that allows straight forward power scaling in RF amplifiers. Next, to demonstrate the practical use of these low-loss magnetic components with their related design flow, two very compact high-power class-E branch amplifiers were realized and tested. Expanding on these initial works, one of the key demonstrators of this thesis was a "70W fully packaged-integrated GaN outphasing amplifier", which represents a remarkable combination of high-efficiency, high-output power with a very small form factor. Finally, to facilitate the future integration of advanced switchmode outphasing systems in a single package, the design of high-voltage CMOS drivers was discussed and demonstrated. These devices can provide the essential physical link between the final PA stages with the intelligence of the forgoing TX chain, which is typically implemented in standard low-voltage CMOS technologies.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
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