A Planar Generator for a Wave Energy Converter

This article presents a permanent magnet planar translational generator which is able to exploit multiple modes of sea wave energy extraction. Linear electrical generators have recently been studied for the exploitation of sea wave energy, but, to the best of our knowledge, no synchronous planar translational generator has been proposed. In this article, to maximize the energy extraction, we have considered all the potential modes of motion due to wave excitation and included them within the mathematical model of the proposed system. The principle of operation of the generator can be summarized as follows: the moving part (translator) of the generator is driven from the sea waves and induces and electromotive force (EMF) on the windings mounted to the armature. The movement of the translator is 2-D and, therefore, all the movement modes of the wave, except heave, can be exploited. The proposed mathematical model includes the dynamic equations of the translator and the electric equations of the windings. The coupling parameters (inductances and fluxes) have been determined by finite element method analysis. Optimization of the device has been performed by considering both, the parameters of the electromagnetic circuit, and, the parameters associated with the stochastic features of the wave

Production-oriented design of electric traction drives with hairpin winding

In recent years, the manufacturing of stators by hairpin technology has proven its ability to fulfill the requirements on quality, productivity and robustness of traction drive applications in automotive industry. However, the uncertainty and necessity of rapid product development despite fuzzy target systems still cause that processes, machines and equipment – as well as the electric design – are often in an imperfect prototype stage at the start of production ramp-up. Due to the complex interdependencies between the stator components in combination with a high sensitivity of the overall process reliability to minor adjustments of stator design features, possible production-related weaknesses in design are often recognized first in the prototype stage of the production system. In order to reduce the economic risk resulting from these volatile technological conditions, production-oriented design based on numerical simulation methods can be applied from the beginning of product development. Therefore, several techniques for numerical process modeling are presented in this paper as possibilities to consider manufacturing constraints in an early stage of product development. For this purpose, the influence of wire dimensions on the forming process of hairpin coils is investigated using the example of rotary bending as well as the twisting process of a full stator by finite element simulations. Furthermore, a numerical approach to investigate the influence of heat input during laser welding of hairpin coils on the required stripping length is introduced

Weight Reduction in Electric Motors: Aluminum vs Copper Wires

Environmental concerns driven by climate change have resulted in increased market demand for lightweight and inexpensive electric vehicles. This study examines the feasibility of replacing copper conductors with aluminum conductors in automotive scale electric motors to address this demand. A comprehensive review of the literature contrasting aluminum and copper conductors is included to create a unified source for future research. This study also contains a two-part formability and windability analysis of square cross section electrical conductor aluminum and rectangular electrolytic tough pitch copper. The first part of the analysis applies standardized testing from ASTM D1676 to characterize the formability and windability of both conductors. Aluminum saw formability and windability advantages over copper, especially regarding springback, accommodation of elongation during high speed winding, and repeated absorption of bends and twists during winding; however, insulation adhesion and delamination issues occurred for elongation beyond 10% due to incompatibility of properties between the polymer coating and aluminum wire. The second part of the analysis compares forming behaviour of aluminum to known results for copper using a novel wire bending simulator machine. The effects of normal load, wire travel speed, and forming angle on coefficient of friction (COF) are analyzed to determine the feasibility of using aluminum for hairpin windings. The analysis finds that COF increases with both wire travel speed and forming angle. COF versus normal load shows a spike in COF followed by a sharp decrease indicative of a deformation mechanism that copper did not experience. Macroscopic analysis reveals aluminum to be more susceptible to damage from the forming equipment when compared to copper. Microscopic analysis reveals shingles and a suspected near-surface deformed layer at the aluminum/insulation interface. Detachment of these imperfections was found to occur at peak COF loads and higher from crack propagation and insulation flow into said cracks. Overall, this study shows aluminum is a viable conductor that provides significant cost and weight savings in electric machines with similar performance to copper; however, further improvement to aluminum surface quality and insulation properties is required to effectively replace copper

Characterization of rectangular copper wire forming properties and derivation of control concepts for the kinematic bending of hairpin coils

As a result of the continuously growing demand for electric vehicles, innovative production technologies must be developed to fulfill the high automotive requirements for productivity and quality in the manufacturing of electric drives. By providing advantages regarding the degree of automation, the productivity as well as the attainable filling factors in comparison to established round wire winding technologies, the hairpin technology shows a high potential for meeting the requested specifications but also technological weaknesses, especially concerning the process reliability. The referring production process of stators is normally based on the spatial forming of open, hairpin-shaped coils of enameled flat copper wire as well as subsequent joining and contacting processes. Consequently, the hairpin coils represent the elementary components of the process chain and can be either shaped by robust tool-bound or flexible kinematic bending processes that enable the shaping of different contours at moderate tool costs. In this paper, the essential mechanical forming and product properties of flat copper wires with different dimensions and insulation coatings are characterized by means of uniaxial tensile tests as well as metallographic analyses of the material structure, at first. Subsequently, the identified forming properties are correlated to the applied manufacturing processes drawing, rolling as well as continuous extruding and considered as limits of possible material variations. To evaluate the effect of fluctuating wire qualities on the robustness of kinematic hairpin bending processes, the fabrication tolerances are analyzed by finite element simulations, using the example of elementary kinematic bending operations and modeled changes of the material properties. Based on the knowledge of material-based process tolerances, different control concepts for the kinematic bending of hairpin coils are derived and compared based on technical as well as economic aspects

Design and Status of the Dipole Spectrometer Magnet for the ALICE Experiment

Proposal of abstract for MT16, Tallahesse, Florida, 26th September to 2nd October 1999.A large Dipole Magnet is required for the Muon Arm Spectrometer of the ALICE experiment at the LHC.The absence of strong requirements on the symmetry and homogeneity of the magnetic field has lead to a design dominated by economic and feasibility considerations.In March 1997 the decision was taken to build a resistive dipole magnet for the muon spectrometer of the ALICE experiment. Since then, design work has been pursued in JINR/Russia and at CERN. While a common concept has been adopted for the construction of the steel core, two different proposals have been made for the manufacturing technology of the excitation coils. In both cases, however, the conductor material will be Aluminium.The general concept of the dipole magnet is based on a window frame return yoke, fabricated from low carbon steel sheets. The flat vertical poles follow the defined acceptance angle of 9 degrees. The excitation coils are of saddle type. The coils are wound from large hollow Aluminium profiles. They are cooled by pressurized demineralised water. The coil ends are located to both sides of the magnet yoke and determine the overall length of the magnet. The main flux direction in the gap is horizontal and perpendicular to the LHC beam axis.Both coil concepts and the underlying manufacturing technology are compared and the present status of the development of the magnet is described

Cure Behavior Study and Elastic Modulus Characterization of Resin System of a Quasi Poloidal Stellarator Modular Coil

Composites materials are increasingly becoming choice materials because of their tremendous strength-to-weight properties and impressive design flexibility. A more recent application of composites is in nuclear fusion reactors. One such reactor is the Quasi-Poloidal Stellarator (QPS) being developed by Oak Ridge National laboratory. QPS, with a non-axisymmetric, near-poloidally symmetric magnetic configuration, has stranded copper/epoxy composite coils, used for magnetic confinement of plasma. CTD- 404 and CTD-101K are the resins under consideration for the modular coils with copper fiber as reinforcement. Structural integrity of the modular coils over wide range of temperatures, including liquid nitrogen temperature, is of vital importance and appropriate resin with optimal cure cycle has to be used for this purpose. In this regard, a study of the stresses induced on the fibers during cure of CTD-404 and CTD-101K was performed using the Cure Induced Stress Test (CIST) setup at UT composites laboratory. Carbon fiber was used for comparison purposes. It was observed that both CTD-404 and CTD-101K induced low cure stresses and high cool down stresses. Later in this study a new method was developed to calculate the elastic modulus of a resin during cure. The knowledge of elastic modulus development of a resin during cure is vital in minimizing the residual stresses by appropriately changing the parameters of cure cycle. The method was developed based on difference in the displacements of the resin sample during cure, with fiber and without fiber. The method was developed for 3501-6 as the volume change data for CTD-101K and CTD-404 were not available. The volume change data for 3501-6, obtained by using volumetric dilatometer previously, was used and the load data of the reinforced fiber was obtained from cure-induced stress test. The curve for elastic modulus was developed for two isothermal cure cycles. Results obtained were compared with available experimental data and the data available in literature from three-point bend tests of cured samples at different cure times. The values of modulus obtained with this approach compared well with the available data. Also, a study of the effect of liquid nitrogen temperature on the elastic modulus of the modular coil composite was performed. A fixture was designed to perform a cantilever bend test in liquid nitrogen on a MTS machine. It was observed that the liquid nitrogen temperature did not affect the modulus

Switched Flux Permanent Magnet Brushless Machines for Electric Vehicles

This thesis investigates different topologies of switched flux permanent magnet (SFPM) machines and variable flux (VF) methods for high speed applications. Although several novel topologies of SFPM machines have been proposed and investigated recently, their torque-speed capability has not been studied systematically. Therefore, the torque-speed capability as well as the open circuit and electromagnetic performance of conventional SFPM machines with three different stator/rotor pole combinations, i.e. 12/10, 12/13 and 12/14, and three novel SFPM machine topologies, i.e. multi-tooth, E-core and C-core are analysed and investigated by the finite element (FE) method and experiments. Moreover, in order to improve the flux-weakening capability of these machines a variable flux method using flux adjusters (FAs) is employed and the corresponding electromagnetic performance of the machines are investigated, analysed and compared. Both FE and measured results show when the FAs are used the torque-speed capability of the three conventional machines can be improved significantly, while no improvement is shown in the three novel topologies primarily due to the large winding inductances. The technique of using flux adjusters has been improved by reducing the number of FAs. Thus, a new mechanical variable-flux machine topology, which uses only half of FAs outside the stator at alternative stator poles, is proposed, developed and analysed. Open circuit results, electromagnetic performance and torque- and power-speed curves of the 12/10, 12/13 and 12/14 stator/rotor pole SFPM machines with alternative FAs are predicted and compared by 2D and 3D-FE, and experimentally validated. Furthermore, a novel SFPM machine topology with radial and circumferential PMs is proposed, investigated and optimized. This topology reduces the stator flux leakage and offers high magnetic utilization. Moreover, this topology can also be developed as a mechanical variable flux machine. Finally, three SFPM machines with variable flux techniques, i.e. mechanically movable flux adjusters (MMFA), mechanically rotatable permanent magnet set (MRMS) and hybrid excitation with backside DC coils (HEBC) are analysed. Their open circuit results and electromagnetic performance with emphasis on torque-speed characteristic are investigated and compared. Additionally, the required power to switch between flux weakening and strengthening states, flux weakening capability and permanent magnet demagnetization withstand capability are predicted, analysed and compared. The influence of end-effect on the torque-speed capability in the conventional, multi-tooth, E-core and C-core SFPM machines is investigated. Measurements and 3D-FE are performed to obtain the torque-speed curve in order to validate the findings of the research. The 3D-FE predicted results match well with the measured results, while the 2D-FE predicted results are lower due to the high end-effect in the SFPM machines

Development and Coil Fabrication Test of the Nb3Sn Dipole Magnet PRESCA2

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