Showing papers on "Maximum power transfer theorem published in 2006"

Efficiency of energy conversion for a piezoelectric power harvesting system

Abstract: This paper studies the energy conversion efficiency for a rectified piezoelectric power harvester. An analytical model is proposed, and an expression of efficiency is derived under steady-state operation. In addition, the relationship among the conversion efficiency, electrically induced damping and ac–dc power output is established explicitly. It is shown that the optimization criteria are different depending on the relative strength of the coupling. For the weak electromechanical coupling system, the optimal power transfer is attained when the efficiency and induced damping achieve their maximum values. This result is consistent with that observed in the recent literature. However, a new finding shows that they are not simultaneously maximized in the strongly coupled electromechanical system.

Methods and apparatus for high power factor controlled power delivery using a single switching stage per load

Abstract: Methods and apparatus for high power factor power transfer to a load using a single switching stage. In exemplary implementations, a controllable variable power may be delivered to a load using a single switching stage while maintaining high power factor, in some cases without requiring any feedback information relating to the load conditions (i.e., without monitoring load voltage and/or current) to control normal switching operations in the single switching stage, and without requiring regulation of load voltage and/or load current. In one example, a single stage high power factor driver is used to control power delivery to an LED-based light source.

A system and method for contact free transfer of power

Abstract: A system and method is provided for the inductive transfer of electric power between a substantially flat primary surface and a multitude of secondary devices in such a way that the power transfer is localized to the vicinities of individual device coils. The contact free power transfer does not require precise physical alignment between the primary surface and the secondary device and can allow the secondary device or devices to be placed anywhere and in arbitrary orientation with respect to the primary surface. Such power transfer is realized without the need of complex high frequency power switching network to turn the individual primary coils on or off and is completely scalable to almost arbitrary size. The local anti-resonance architecture of the primary device will block primary current from flowing when no secondary device or devices are in proximity to the local RF power network. The presence of a tuned secondary device detunes the local anti-resonance on the primary surface; thereby enable the RF power to be transferred from the local primary coils to the secondary device. The uniformity of the inductive coupling between the active primary surface and the secondary devices is improved with a novel multi-pole driving technique which produces an apparent traveling wave pattern across the primary surface.

Design of loosely coupled inductive power transfer systems

Abstract: The model of inductive power system is set up,and how to choose the compensation topology and resonant frequency is analyzed.According to the analysis result,the model of inductive power system is set up,and the impact of the power transfer due to the variety of load is analyzed.

A New Concept: Asymmetrical Pick-Ups for Inductively Coupled Power Transfer Monorail Systems

Abstract: Inductively coupled power transfer systems have recently proven to be popular in moving vehicle monorail systems situated in difficult environments such as clean rooms. In such applications the magnetic design is critical if low weight high power pick-ups are to be realized. Early designs were largely experimental and used magnetic shapes that easily fit the existing structure. Modern finite-element-modeling packages are now being used to achieve significant alterations to the pick-up shape under the assumption that the monorail structures can be changed. This paper introduces several important magnetic design metrics that must be considered in such a design process, and applies these to various newly proposed and unconventional asymmetrical pick-up shapes. These new pick-ups are shown to be capable of achieving comparable power output with lower ferrite volume/length of the pick-up structure, or significant increases in output power for identical volume/length, to a conventional E-shaped pick-up

A distributed optical fiber sensor for temperature detection in power cables

Abstract: The power transfer capacity of an underground power cable is limited by high-temperature regions that occur along the cable. It is very difficult to determine and control these ‘hot spots’. Optimum use and temperature profile control of power cables before and during load transmission can be achieved with real-time processing of temperature data. There are various methods developed for this purpose such as conventional point temperature measurement method, where a large number of sensors and connectors are required, and methods based on mathematical models which can only approach real values by approximation. In this study, temperature detection in an XLPE insulated 154 kV power cable is performed using a distributed sensing method where the optical fiber itself behaves as a sensor. Therefore, there is no need for the devices of conventional method. Moreover, contrary to methods based on mathematical models, where it is difficult to predict environmental variations, this method considers the variations with a temperature resolution of ±1 °C. Distributed temperature sensing (DTS) method, detection system configuration and required system parameters are explained in the paper. Experimental results obtained for 126 and 412 m cables show a temperature resolution of ±1 °C and a spatial resolution of 1.22 m. Simulations for a 10 km cable are also given. Results show that DTS is a reliable method for both short and long range cable systems.

Capacitive Inter-Chip Data and Power Transfer for 3-D VLSI

Abstract: We report on inter-chip bidirectional communication and power transfer between two stacked chips. The experimental prototype system components were fabricated in a 0.5-mum silicon-on-sapphire CMOS technology. Bi-directional communication between the two chips is experimentally measured at 1Hz-15 MHz. The circuits on the floating top chip are powered with capacitively coupled energy using a charge pump. This is the first demonstration of simultaneous nongalvanic power and data transfer between chips in a stack. The potential use in 3-D VLSI is aimed at reducing costs and complexity that are associated with galvanic inter-chip vias in 3-D integration

A Multilevel Inverter Topology for Inductively Coupled Power Transfer

Abstract: This paper describes a multilevel inverter that can synthesize quantized approximations of arbitrary ac waveforms. This converter could be used to deliver power over multiple frequencies simultaneously. Unlike traditional multilevel inverters, this topology does not require an external voltage balancing circuit, a complicated control scheme, or isolated dc sources to maintain its voltage levels while delivering sustained real power. In this paper, we use this circuit for heating frequency selectable induction targets designed to stimulate temperature sensitive polymer gel actuators. For this application our multilevel inverter offers higher efficiency than a pulse width modulated full-bridge inverter (a more conventional power supply solution) at comparable levels of total harmonic distortion

Allocation of fixed costs in distribution networks with distributed generation

Abstract: In this paper, we propose a method for the allocation of fixed (capital and nonvariable operation and maintenance) costs at the medium voltage (MV) distribution level. The method is derived from the philosophy behind the widely used MW-mile methodology for transmission networks that bases fixed cost allocations on the "extent of use" that is derived from load flows. We calculate the "extent of use" by multiplying the total consumption or generation at a busbar by the marginal current variations, or power to current distribution factors (PIDFs) that an increment of active and reactive power consumed, or generated in the case of distributed generation, at each busbar, produces in each circuit. These PIDFs are analogous to power transfer distribution factors (PTDFs). Unlike traditional tariff designs that average fixed costs on a per kWh basis across all customers, the proposed method provides more cost-reflective price signals and helps eliminate possible cross-subsidies that deter profitable (in the case of competition) or cost-effective (in the case of a fully regulated industry) deployment of DG by directly accounting for use and location in the allocation of fixed costs. An application of this method for a rural radial distribution network is presented.

Studies of acoustic-electric feed-throughs for power transmission through structures

Abstract: There are numerous engineering design problems where the use of wires to transfer power and communicate data thru the walls of a structure is prohibitive or significantly difficult that it may require a complex design. Using physical feedthroughs in such systems may make them susceptible to leakage of chemicals or gasses, loss of pressure or vacuum, as well as difficulties in providing adequate thermal or electrical insulation. Moreover, feeding wires thru a wall of a structure reduces the strength of the structure and makes the structure prone to cracking due to fatigue that can result from cyclic loading and stress concentrations. One area that has already been identified to require a wireless alternative to electrical feedthroughs is the container of the Mars Sample Return Mission, which will need wireless sensors to sense a pressure leak and to avoid potential contamination. The idea of using elastic or acoustic waves to transfer power was suggested recently by [Y. Hu, et al., July 2003]. This system allows for the avoidance of cabling or wiring. The technology is applicable to the transfer of power for actuation, sensing and other tasks inside any sealed container or vacuum/pressure vessel. An alternative approach to the modeling presented previously [Sherrit et a., 2005] used network analysis to solve the same problem in a clear and expandable manner. Experimental tests on three different designs of these devices were performed. The three designs used different methods of coupling the piezoelectric element to the wall. In the first test the piezoelectric material was bolted using a backing structure. In the second test the piezoelectric was clamped after the application of grease and finally the piezoelectric element was attached using a conductive epoxy. The mechanical clamp with grease produced the highest measured efficiency of 53% however this design was the least practical from a fabrication viewpoint. The power transfer efficiency of conductive epoxy joint was 40% and the stress bolts (12%).

Aerialwind power generation system and method

Abstract: An aerial power generation system includes a guide line supported by a support body. Wind driven elements are configured and shaped to provide maximum force from both lift and drag during the downwind phase of operation and minimum force during the upwind phase. The guide lines add stability to the system and provide better control over angular orientation and direction of motion. Power transfer is through one or more tow lines connected from the driven elements to power generation devices on the ground. Another embodiment of the aerial power generation system includes a revolving apparatus and two or more wind powered driven elements connected by tow lines to the revolving apparatus. The method includes changing the driven elements between high and low force configurations for downwind and upwind operation, and flying the driven elements in a selected pattern perpendicular to the tow line.

Wireless Powering of Implanted Sensors using RF Inductive Coupling

Abstract: Radio frequency inductive links are becoming extensively used for telemetry and wireless powering of implanted devices such as biomedical sensors and RFID implants. The design of RF coils for such links is often empirical and non-optimal. Based on loop antenna theory, this paper presents an analytical model for near-field magnetic coupling incorporating misalignment of the RF coil system. Formulae are derived for the magnetic field at the receiver coil when it is laterally and angularly misaligned from the transmitter. For the first time a near-field power transfer formula is suggested incorporating coil characteristics and misalignments. This novel power transfer function allows a comparison between different coil structures such short solenoids, with air or ferromagnetic core, and spirals with respect to the power delivered at the implant. It is also possible to define the maximum degree of misalignment permissible in a given application. This analysis allows a formal design procedure to be established in order to optimise wireless power transfer for a given application.

Switching Frequency Analysis of Dynamically Detuned ICPT Power Pick-ups

Abstract: Dynamic detuning methods have been used in inductive contactless power transfer (ICPT) systems for power flow control However, the highly variable switching frequency involved in the detuning operation will contribute to electromagnetic interference (EMI) and power losses It is difficult to determine the detuning frequency precisely due to nonlinear features of power pick-ups Uncertainty in the operating frequency can result in difficulties in designing filters with suitable bandwidths and choosing suitable switching devices Based on detailed analytical analysis in four segments of the detuning process, a numerical method is developed in this paper to determine the boundaries of the switching frequencies An iterative algorithm is presented using a flow chart to illustrate the process taken in the numerical analysis Simulation and practical experiments are conducted to verify the algorithm so as to ensure the calculated results are sufficiently accurate for designing EMI filters and choosing suitable switching devices

Research of LCL Resonant Inverter in Wireless Power Transfer System

Abstract: The LCL type MCWPT system in continuous current mode is analyzed in detail. The iterative model for numerical analysis of transient dynamic response is built up with discrete time mapping modeling method. It is found that when the control frequency is equal to the inherent resonant frequency of secondary side, the inverter output current has large distortion and the switches are working in hard-switching mode. Then an effective way to find out the ideal operation frequency with the impedance analysis is proposed. A parameter optimizing process is applied to the system to realize its ideal operation mode where it has the maximum power transfer capability and efficiency. Simulation results from PSpice have verified the theoretical results.

Multi-objective VAr Planning with SVC for a Large Power System Using PSO and GA

Abstract: Particle swarm optimization (PSO) algorithm is used for planning the static VAr compensator (SVC) in a large-scale power system. The primary function of an SVC is to improve transmission system voltage, thereby enhancing the maximum power transfer limit. To enhance voltage stability, the planning problem is formulated as a multiobjective optimization problem for maximizing fuzzy performance indices. The multi-objective VAr planning problem in a large-scale power system is solved by the fuzzy PSO with very encouraging results, and the results are compared with those obtained by the genetic algorithm (GA)

A new contactiess power pick-up with continuous variable inductor control using magnetic amplifier

Abstract: This paper proposes a new contactless power pick-up with a LCL tuning circuit which utilizes the magnetic amplifier as a variable inductor. The tuning circuit of the power pick-up is based on the LCL configuration and provides a simple relationship between the open circuit voltage of the pick-up coil and the output voltage regardless of the load variation. The use of magnetic amplifier as a variable inductor offers significant advantages where the inductance is dynamically varied using a controller and BJT to deliver power under a variety of load conditions. The proposed method can significantly improve the overall performance of the ICPT (Inductively Coupled Power transfer) system by producing continuous waveforms within the system at all times. Simulations based on PLECS (a Simulink toolbox) demonstrate that the new method can successfully control the output voltage resulting in satisfactory steady state performance.

A genetic algorithm-based procedure to optimize system topology against parallel flows

Abstract: Parallel (or loop) flows consist in the undesired circulation of power flows through certain interconnection corridors. Remedial actions available to transmission system operators or system planners include installation and operation of phase-shifting transformers and of dc transmission systems. Moreover, the invaluable experience of transmission system operators has shown that the network can be operated so as to reduce parallel flows also by properly selecting the topology of the system. In the present paper, a genetic algorithm-based procedure is designed for the topological optimization of the network against parallel flows. The control variables considered are the status of substation breakers and the location (and angle) of phase-shifting transformers. The problem is formulated as a multiobjective optimization. The main objective is that of reducing the power transfer distribution factor of an assigned transaction with reference to a set of lines; N and N-1 security levels are accounted for by means of subsidiary objective functions. The procedure is tested on a small CIGRE sample system and on a 4500-bus network representative of the European electric system (UCTE).

On the maximum power transfer theorem within electromechanical systems

Abstract: Conditions for maximum power transfer are considered within electrical, mechanical and electromechanical systems. The familiar concept of resistance load matching within an electrical system is extended to a mechanical system, and is 50% efficient. For electromechanical systems, the transfer of maximum power from one domain (say, the electrical) to the other (say, mechanical) is also 50% efficient. However, when losses occur in both the electrical and mechanical domains, the concept of load matching must be applied within the domain to which power is being delivered; efficiency is now less than 50%, which is most easily seen from the source domain.

Application of Power Flow Sensitivity Analysis and PTDF for Determination of ATC

Abstract: Power system restructuring throughout the world is undergoing various reforms in the power business. One of the objectives of restructuring process is to allow open access of transmission network to the market participants thereby creating a competitive power market. However it may cause the congestion and further threaten the security of the network. This situation may be avoided by providing the information about available transfer capability of the network to the market players (buyers and sellers). Available transfer capability (ATC) of transmission network is the additional amount of power transfer that can be effected between the buyer bus and seller bus without loss of security. For proper system operations under the various transactions, ATC calculations must be reasonably accurate and fast enough. This paper describes a novel approach of application of sensitivity analysis and power transfer distribution factor for the determination of ATC. Advantages of the proposed approach are also discussed.

Hybrid electric vehicle and powertrain

Abstract: A hybrid electric vehicle and powertrain include an engine operable to output torque in only one direction, and further includes a power transfer arrangement configured to provide output torque in two rotational directions. In one embodiment, the power transfer arrangement includes three gears and a single clutch, the configuration of which provides a simple mechanism for driving the vehicle in reverse using torque produced by the engine.

Design, Implementation and Characterisation of a Contactless Power Transfer System for Rotating Applications

Abstract: This paper describes the design, implementation and characterisation of a contactless power transfer system for rotating applications. The power transfer system is based upon a zero-voltage-switched, full-bridge, dc-dc converter, but utilises a non-standard transformer. This transformer allows power transfer between its primary and secondary windings while also allowing free rotation between these windings. The aim of this research is to develop a solution that could replace mechanical slip-rings in certain applications where a non-contacting system would be advantageous. Based upon the design method presented in this paper, a 2 kW prototype system is constructed. Results obtained from testing the 2 kW prototype are presented and discussed. This discussion considers how the performance of the transformer varies with rotation and also the overall efficiency of the system.

Technical and Economic Aspects of Tripole HVDC

Abstract: This paper shows how, with simple modifications using either conventional or bidirectional valves, bipole and monopole systems can be connected in parallel and operated as a three pole configuration in which no earth return current flows in either normal or pole-out conditions. While slightly less efficient in terms of equipment utilization, the system reduces line losses for a given MW transfer and has better overload and internal redundancy; both of which enhance (n-1)-constrained loading of the parallel ac system. Because it makes full thermal use of three conductors, the tripole system improves both the technical and economic cases for converting existing three-phase ac lines to dc. Doing so increases power transfer much more than is possible with compensation or phase shifting transformers. The paper reviews the basic principles inherent in the tripole HVDC system and compares characteristics of both bipole and tripole alternatives in the context of an ac network.

Applications of security-constrained optimal power flows

Abstract: This paper deals with the SecurityConstrained Optimal Power Flow (SCOPF) problem. We first revisit both preventive and corrective variants of the SCOPF problem. Then we present the nonlinear Interior-Point Method (IPM) which we use for the solution of the SCOPF problem. Next, we provide numerical results, on a 60-bus test system, for three main SCOPF applications, namely: minimum overall cost of generation, minimum cost of removing congestion and maximum power transfer computation. We finally discuss some critical issues related to the SCOPF problem.

Tuning methods and apparatus for inductively coupled power transfer (ICPT) systems

Abstract: A method is provided for controlling a resonant circuit (1) of an ICPT system. The resonant circuit has a controlled variable reactance (2), and a predetermined perturbation is introduced in the magnitude of variable reactance. The change in a property of the resonant circuit in response to the perturbation is sensed, and the variable reactance is varied to alter the resonant frequency of the circuit in response to the sensed change.

A new high frequency current generation method for inductive power transfer applications

Abstract: This paper proposes a new method to generate high frequency currents for inductive power transfer systems where AC-DC-AC or DC-AC converters are being used There are a lot of circuit and controller design issues associated with these traditional converters A DC link has to be used as a middle stage for high frequency current generation even when a low frequency AC source is available, which causes large system cost, size, as well as power losses and maintenance associated Unlike matrix converters having complicated switching topologies and control, the new converter proposed in this paper is based on simply free oscillation and energy injection control It can achieve DC to AC inversion, or direct AC to AC conversion without using any DC links, thus a low frequency utility power source at 50/60Hz can be converted to a high frequency current source along a track loop directly Furthermore, soft switching techniques are applied to minimize the power losses and EMI, and the track current magnitude can be controlled easily without any overshoots Theoretical analysis, simulation and experimental results have demonstrated the new converting method is valid for high frequency currents generation for most inductive power transfer systems

A Three-Phase Inductively Coupled Power Transfer System

Abstract: This paper discusses the development of a new three phase bipolar Inductively Coupled Power Transfer (ICPT) system for improving the power profile across the width of a roadway surface for automatic guided vehicles (AGVs) and people mover systems. A prototype system was constructed that supplies 40 Amperes per phase into a thirteen meter long track to supply power to a number of moving vehicles (toy cars). Flat pick-ups are used on the underside of the vehicle and FEM software was successfully used to determine a suitable geometrical position for the cables in the track resulting in a considerably wider power delivery zone than possible using a single-phase track layout. Mutual coupling effects between the various track phases, requires additional compensation to be added to ensure balanced three-phase currents. Experimental tests verified simulation results with a high degree of accuracy.

High Efficiency Energy Storage System Design for Hybrid Electric Vehicle with Motor Drive Integration

Abstract: This paper proposes a new energy storage system (ESS) design including both batteries and ultracapacitors (UC) in hybrid electric vehicle (HEV) and electric vehicle (EV) applications. The conventional designs require a dc-dc converter to interface the UC unit. Herein, the UC can be directly switched across the motor drive dc-link during the peak power demands. The resulting wide voltage variation due to UC power transfer is addressed by the simple modulator introduced in this paper, so that the motor drive performance is not disrupted. Based on this new methodology, the paper further introduces two ESS schemes with different topologies, UC rating and energy flow control. They are applicable to both lightly and heavily hybridized HEVs. Both schemes have the benefits of high efficiency (without a dc-dc link) and low cost. The simulation and experimental results validate the new methodology.

A new method for SSSC optimal location to improve power system Available Transfer Capability

Abstract: In recent years, an increased interest was devoted to the problem of flexible AC transmission system devices location. In literature, most of proposals consist in iterative analyses, exhaustively looking for the branch that maximizes or minimizes an objective, such as least transmission losses or best power transfer capability. In this paper, attention is particularly focused on the static synchronous series compensator and a method is proposed to determine the device best location that maximizes the power system available transfer capability measured as the maximum system load increase before any operating limit is reached. The proposed method always performs an exhaustive analysis although conducted by modelling the transmission network by means of the simplified DC load flow equations embedded within an opportune optimisation model. Tests carried on networks modelled also by means of the AC load flow representation have demonstrated the validity of the proposed DC load flow based method

Variable Frequency Transformer - FACTS Technology for Asynchronous Power Transfer

Abstract: A new power transmission technology has been developed. The variable frequency transformer (VFT) is a controllable, bi-directional transmission device that can transfer power between asynchronous networks. Functionally, the VFT is similar to a back-to-back HVDC converter. The core technology of the VFT is a rotary transformer with three-phase windings on both rotor and stator. A motor and drive system are used to adjust the rotational position of the rotor relative to the stator, thereby controlling the magnitude and direction of the power flowing through the VFT. The worlds first VFT was recently installed in Hydro-Quebec's Langlois substation, where it will be used to exchange up to 100 MW of power between the asynchronous power grids of Quebec (Canada) and New York (USA). This paper describes the VFT technology and provides an overview of the VFT equipment installed at Langlois substation. Results of commissioning tests are also included