Showing papers on "Magnetic circuit published in 1994"

Brushless permanent-magnet motor design

Abstract: Written for electrical, electronics, and mechanical engineers responsible for designing and specifying motors, the book provides details of brushless DC and synchronous motors, as well as both radial and axial motor topologies. Beginning with a discussion of the fundamentals of generic motor design, it logically progresses to a set of more advanced, yet easily understandable, concepts for designing brushless permanent-magnet motors. In addition, the author fully explains techniques for magnetic modelling and circuit analysis, shows how magnetic circuit analysis applies to motor design, describes all major aspects of motor operation and design in simple mathematical terms, develops rigorous design equations for radial flux and axial flux motors, and illustrates basic motor drive schemes. All common motor design terms are clearly defined and a wealth of charts, tables and equations are included.

Permanent Magnet Materials and their Application

Abstract: 1 Fundamentals of magnetism 2 Permanent magnet processes 3 Thermal stability 4 Magnetic circuit design 5 Magnetic field analysis 6 Magnetizing and testing 7 Applications

Reconfigurable mobile vehicle with magnetic tracks

Abstract: A reconfigurable mobile vehicle having at least one endless driven member and a motor for driving the endless member on a surface capable of supporting a magnetic circuit The vehicle is equipped with a magnetic system that comprises a magnet, a fixed magnetic circuit member, and a movable magnetic circuit member for establishing first and second magnetic circuits A clutch is provided to selectively connect the movable magnetic circuit member to the motor to move the movable magnetic circuit member between a first position wherein the first magnetic circuit is established such that the endless driven member can magnetically engage the surface and a second position wherein the second magnetic circuit is established such that the endless member does not magnetically engage the surface The vehicle is equipped with sensing apparatuses for analyzing the structural integrity of the surface upon which the vehicle is riding and is also equipped with acoustical positioning apparatus for assisting the operating personnel and computer in locating and controlling the vehicle's position within an enclosed environment The vehicle is also equipped with a tether line that is used to facilitate the transfer of control power/data between the vehicle and the various operating components attached thereto and a control console located remote from the vehicle The tether line is also used to deploy and retrieve the vehicle

Calculation of leakage inductance in transformer windings

Abstract: A formula is presented to calculate mutual impedance between transformer windings on ferromagnetic cores. The formula is based on the solution of Maxwell's equations for coils on ferromagnetic cores and as such offers the ultimate in accuracy. The formula is frequency dependent, taking into account the effect of eddy currents in the core on the flux distribution as well as representing the eddy current core loss as an equivalent resistance. Experimental results are presented for leakage inductance and an illustrative example is presented showing how leakage inductance affects the operation of a typical switching mode power supply. Approximations for the formula are also presented to simplify the calculations under certain operating conditions. >

A new approach to calculating core losses in the SRM

Abstract: In the switched reluctance motor, the flux waveforms are nonsinusoidal and different parts of the magnetic circuit have different waveforms. This paper presents a new approach to taking into account these flux waveforms in the calculation of core losses. Relations between the fluxes of different parts of the magnetic circuits are given in the form of matrix equations, where the fluxes are expressed in terms of normalized flux pulses. Rewriting the eddy-current loss term in the Steinmetz equation in terms of the square of dB/dt and combining it with the matrix equations, eddy-current losses for the complicated flux waveforms of the stator and rotor yokes are calculated. The effect of PWM is taken into account by considering the PWM voltage waveform as dB/dt. From the matrices, it is easy to count how many times the full and minor hysteresis loops occur at each pole and yoke segment. The effect of the minor loop is taken into account based on experimental results. The proposed approach gives a systematic procedure for the core loss calculation. The derived equations are simple and useful for the design of the SRM. >

Normal conducting bending electromagnet

Abstract: A normal conducting bending electromagnet having: a pair of pole pieces having respective pole piece faces, said pole pieces being; disposed with the pole piece faces thereof facing each other with a substantially constant gap therebetween; a magnetic field for forming a charged particle beam arc orbit, being generated in the gap between the pole pieces. A yoke coupled to the pole pieces for forming a closed magnetic circuit with the gap, and a pair of coils is provided for generating a magnetomotive force and generating magnetic fluxes in the magnetic circuit. At least one side wall of each of the pole pieces is slanted or stepped along a virtual slanted plane; along the magnetic path of the pole piece so as to gradually broaden the cross sectional area of the pole piece at the plane perpendicular to the magnetic path from the gap toward the yoke, the slanted side wall or the virtual slanted plane; having a slant angle in the range from 30° or smaller relative to the pole piece faces, the width of the pole piece face being in the range from 4 cm or wider to 20 cm and the height of the gap along the magnetic path being in the range from 1 cm or higher to 6 cm. The normal conducting bending electromagnet can generate a strong magnetic field and reduce the orbit radius of an electron storage ring.

A fully integrated planar toroidal inductor with a micromachined nickel-iron magnetic bar

Abstract: A fully integrated toroidal inductor is realized on a silicon wafer by using a multilevel metallization technique to fabricate a wrapped coil wound around a micromachined bar of high-permeability magnetic material. In particular, efforts are made to minimize the coil resistance by using thick conductor lines and electroplated vias. In this structure, a 30 /spl mu/m thick nickel-iron permalloy magnetic core is wrapped with 40 /spl mu/m thick multilevel copper conductor lines, constructing a conventional toroidal inductor in planar shape. A closed magnetic circuit (i.e., toroidal) in this inductive component is adopted, where magnetic core bar and wrapped conductor lines are tightly interlinked, so that leakage flux and electromagnetic interference are minimized. For an inductor size of 4 mm/spl times/1 mm/spl times/130 /spl mu/m thickness having 33 turns of multilevel coils, the achieved inductance is approximately 0.4-0.1 /spl mu/H at 1 kHz-1 MHz, corresponding to a core permeability of approximately 800. The measured dc resistance of the conductor lines is approximately 0.3 /spl Omega/. Since this inductive component shows favorable magnetic characteristics as well as electrical properties, it is potentially very useful as a basic inductive component in applications for magnetic microsensors, microactuators, and micromagnetic power devices such as a dc/dc converter. >

Thin-film magnetic sensor using high frequency magneto-impedance (HFMI) effect

Abstract: This study reports on the performance of a thin-film magnetic sensor which uses the high frequency magneto-impedance (HFMI) effect. In order to obtain a high sensitivity and a large voltage change ratio (/spl Delta/Vpp/Vpp(0): corresponds to the MR ratio), a strip pattern, a closed magnetic circuit, and a NiFe/SIO/sub 2/ multilayer film structure are adopted for the magnetic films of the sensor. A /spl Delta/Vpp/Vpp(0) of 60-70% is achieved by applying an external magnetic field of several Oe. Moreover there is no hysteresis or no Barkhausen noise in this sensor, which has a magnetic film width of 10 /spl mu/m. In terms of linearity, the sensor exhibits modulation degree (m) of 12% and a total harmonic distortion (THD) of 0.8%. >

Calculation of UMP in induction motors with series or parallel winding connections

Abstract: This paper presents a general analytical method for determining the unbalanced magnetic pull (UMP) produced in three-phase induction motors with an eccentric rotor. The model uses the conformal transformation technique coupled to a winding impedance approach that is capable of accommodating any stator winding connection. The paper examines the influence of using parallel stator winding paths as a means of reducing the resultant UMP (static and pulsating). The results clearly demonstrate the significant reduction of static UMP of a typical stator winding with parallel paths together with the unbalanced winding currents that are produced. >

Charger for hand-held rechargeable electric apparatus with switch for reduced magnetic field

Abstract: A system transfers electric power between two devices using a magnetic coupling and no electrical connections. Each device incorporates a magnetic core surrounded by a coil. When properly aligned the cores form a closed magnetic circuit whereby stray magnetic fluxes are substantially reduced. In the preferred embodiment, a base unit incorporates a substantially `C` shaped magnetic core surrounded by its respective coil. A portable detachable device, such as an electric toothbrush, incorporates a substantially linear shaped magnetic core surrounded by its coil. The linear shaped magnetic core and the portable device are configured to fit within a gap formed in the `C` shaped magnetic core forming a substantially closed magnetic circuit thereby. Stray magnetic fluxes are thus significantly reduced. Additionally, an apparatus deactivates the power to the coil in the base unit when the portable device is removed from the base unit or when the battery within the portable device is charged to a predetermined level.

Flat linear motor

Abstract: A flat linear motor has a single row of permanent magnets mounted upon backplate and an armature having non-overlapping flat coils encapsulated in a block of epoxy resin mounted upon an armature backplate comprised of a magnetic material and having anchoring recesses or protrusions. The armature backplate serves to provide magnetic circuits of low magnetic resistance in the flat linear motor thereby increasing a force generated by the linear motor. A length of the armature backplate is a non-integral number of a pitch length of the permanent magnets so as to reduce cogging. The three non-overlapping flat coils are comprised of square wire windings which provide increased thermal conduction. An embodiment of the invention employs software commutation wherein a position sensing device is used by a controller to determine a position of the armature from which a field polarity is found by means of a formula or a look-up table. Further embodiments of the invention have a cooling manifold, magnetic flux focusing armature backplates, and a modified Halbach magnet array.

Leakage inductance and termination effects in a high-power planar magnetic structure

Abstract: The leakage inductance of planar magnetic structures designed for high-frequency power electronics applications is a critical performance parameter that significantly effects circuit operation. This paper presents numerical models for a particular high power (100-500 W) transformer designed for low-profile applications. The impact that secondary winding terminations have on the leakage characteristics of the device is examined using a set of laboratory measurements. It is shown that the effective inductance the transformer presents to the circuit can be several times the inductance calculated or measured based on an ideal short-circuited winding. These results point toward some general design guidelines that are useful for minimizing leakage inductance for planar structures. >

Position sensor with improved magnetic circuit

Abstract: A rotary position sensor connected to the butterfly valve of an internal combustion engine, the sensor having a dual magnet structure interconnected by a pole piece having a generally C-shaped cross section forming a varying dimension air gap. The magnets, the pole piece and the air gap define a closed magnetic circuit. A Hall effect sensor is fixedly mounted in the air gap and is exposed to a well defined but varying magnetic field. Through the use of specific magnetic materials and sloping, curved surfaces, a precise yet tolerance friendly magnetic circuit is produced so that the sensor produces signals as a function of the angular positions of the magnets.

Motor-generator using permanent magnets

Abstract: An electric motor-generator has a rotor (1), a stator including soft ferromagnetic cores (3, 5) and coils (4, 6), permanent magnets (2) having pole axes in a plane radial to an axis of rotation of the rotor, means for mounting the magnets, the cores and coils to the rotor and stator, and means for energizing the coils. The rotor is caused to rotate by attraction of the magnets to the cores (5) as the magnets and cores approach one another, an opposite attraction force between the magnets and the cores being neutralizeable by energizing the coils (6) as the magnets and cores move apart. The cores are C-shaped and a magnetic circuit is formed when the magnets and cores are in proximate alignment.

Numerical simulation of a power transformer using 3D finite element method coupled to circuit equation

Abstract: Most of the electromagnetic devices work connected to an electric circuit and their numerical simulation in 3D leads to a large number of unknowns. To deal with these problems we propose to use the T/sub 0//spl Omega/ formulation and describe the way of coupling magnetic and electric circuit equations. The coupling is obtained by expressing the electric vector potential T/sub 0/ from the current and the flux of induction and from the magnetic scalar potential /spl Omega/. To consider the magnetic nonlinearity we use the Newton-Raphson procedure. This formulation is used to model a 100 MVA power transformer short circuit test in the transient state. The same device is studied at no-load. >

A strong coupled model for analysing dynamic behaviours of non-linear electromechanical systems

Abstract: A strong coupled model solving simultaneously electric circuit, magnetic field and mechanical motion equations is presented. The magnetic field is solved by a formulation in terms of magnetic vector potential. The working variable in the mechanical equation can be either the displacement or the velocity. The magnetic force is calculated by the virtual work method associated with the edge element. The non-linear system is solved by the Newton-Raphson method. The final matrix equation is symmetrized. A numerical example shows that, compared with a conventional sequential coupling model, the convergence of the present method is less dependent on time step values. >

Magnetic system and method for uniformly scanning heavy ion beams

Abstract: A magnetic system for uniformly scanning an ion beam comprising a magnetic structure having poles with associated scanning coils and respective pole faces that define therebetween a gap through which the ion beam passes; and a magnetic circuit for producing in the gap a magnetic field of sufficient magnitude to prevent the occurrence of a recently observed plasma effect in which the transverse cross-section of the ion beam substantially fluctuates in size while the ion beam is being scanned across the selected surface.

Core losses estimation in a multiple teeth per stator pole switched reluctance motor

Abstract: This paper presents a suitable approach to loss prediction in a multiple-teeth-per-stator-pole switched reluctance motor based upon the conventional core losses equation and taking into account the complicated flux variations in the magnetic circuit. Flux waveform in a part of the stator yoke is measured and used to predict the flux waveforms of the other parts of the magnetic circuit of the motor. These flux waveforms are then used to predict the core losses in the motor. Comparison between the predicted and measured values shows a 25.8% discrepancy. >

Magnetic disc unit having a plurality of magnetic heads which include multilayer magnetic films

Abstract: A magnetic disc unit has a thin film magnetic head in which a lower magnetic core and an upper magnetic core form a magnetic circuit. The upper magnetic core is constructed by magnetic films having at least two layers. A saturation magnetic flux density of the inside magnetic film, of the magnetic films having at least two layers, facing a magnetic gap of the magnetic circuit is larger than that of the outside magnetic films of the upper magnetic core and the lower magnetic core.

Displacement sensors using soft magnetostrictive alloys

Abstract: We report results on the response of a family of displacement sensors, which are based on the magnetostrictive delay line (MDL) technique, using current conductors orthogonal to the MDL. Such sensing technique is based on the change of the magnetic circuit at the acoustic stress point of origin due to the displacement of a soft magnetic material above it. Integrated arrays of sensors can be obtained due to the acoustic delay line technique and they can be used as tactile arrays, digitizers or devices for medical applications (gait analysis etc.), while absence of hysteresis and low cost of manufacturing make them competent in this sector of sensor market. >

Effect of end core flux on the performance of the switched reluctance motor

Abstract: The aim of the paper is to bridge the gap between two-dimensional and three-dimensional finite-element modelling of the switched reluctance motor. The flux linkage/current diagram and static torque profile of a four phase 8/6 machine are computed with the aid of two-dimensional and three-dimensional models. Comparison of the predicted values with measurements on the motor demonstrates the superiority of three-dimensional modelling. Three-dimensional effects in the switched reluctance motor are examined and a suitable procedure for estimating the end-core flux at a range of rotor positions and excitations is proposed. The sensitivity of the end-core flux value to magnetic circuit parameters such as applied MMF, magnetic saturation and path reluctance is presented.

Optimized reduction of the magnetic field near Swedish 400 KV lines by advanced control of shield wire currents. Test results and economic evaluation

Abstract: The design of existing Swedish 400 kV lines is described, especially as regards parameters influencing the characteristics of the magnetic field. Field reduction possibilities by introducing controlled shield wire currents on the relatively new delta configuration are analyzed together with results from tests on a line in operation. The use of a regulator to optimize each shield wire current separately in order to compensate for asymmetry is demonstrated. >

Magnetic and gas dynamic effects on arc motion in miniature circuit breakers

Abstract: This paper presents new results on the magnetic and atmospheric environment in the arc chamber of a miniature circuit breaker under short circuit conditions. Finite element magnetic field calculations provide data on the flux density in the arc chamber and the effects of steel plates placed around the arc chamber. The magnetic calculations are used with a one-dimensional flow model to assess the influence of the magnetic environment on the arc dynamics. The results are compared with new experimental data on arc dynamics obtained using an an optical fiber imaging system in a production miniature circuit breaker. Additional information on the environment within the arc chamber is supplied by pressure and conductance measurements. Results show that the presence of steel in the sides of the arc chamber has a large effect on the magnetic field and the arc dynamics. Plasma jet and pressure wave formation have a significant effect on atmospheric conditions in the arc chamber. >

Plasma accelerator with closed electron drift

Abstract: The proposed accelerator comprises: a magnet system (2) with an outer magnetic pole (10) and an inner magnetic pole (9), both connected to one another by a magnetic circuit (8); an outer magnetic screen (13); an inner magnetic screen (12); a central magnetization coil (5) and outer magnetization coils (7) In addition, the proposed accelerator has a discharge chamber (3) containing a concave anode (18) enclosing magnetic force planes (25) of an ionization zone (22); a sectional gas distributor (26); an inner side plate (15) and an outer side plate (16) whose inner surfaces (20) in the ionization zone (22) are at an angle to the accelerator's longitudinal axis (A-A)

3D finite element models and external circuits using the A/spl psi/ scheme with cuts

Abstract: Many devices can only be accurately modelled using a combined circuit and finite element model (FEM), This paper describes the coupling of massive conductor circuits modelled using 3D finite elements and the A/spl psi/ scheme with an external circuit model. The massive conductor circuits by their nature lead to the fact that the magnetic scalar region becomes multiply connected. The cuts which are introduced to deal with the multiply connected magnetic scaler regions lead naturally to the current and voltage variables required to couple the field model and lumped circuit model. >

Study of 3D formulations to model electromagnetic devices

Abstract: For simulation of electromagnetic devices it is necessary to solve simultaneously the electromagnetic and electric circuit equations. Then the difficulties are in the choice of magnetic formulations to take into account the electric circuit equations with a limited number of unknowns. In this communication, we present and discuss several electromagnetic formulations. The cases of stranded and solid conductors are considered and three applications are treated. >

Flat rotating machine

Abstract: PURPOSE: To improve the efficiency of a core-less flat rotating machine while reducing the generation of its eddy current, by so configuring its disk-form stator coil that a plurality of coils formed out of a Ritz wire each of which is wound in the form of a nearly triangular one are provided in the form of a circle. CONSTITUTION: In each air-gap formed out of two flat type rotors of a flat rotating machine, a disk-form stator coil 10 shaped in the form of a flat type is provided. In the stator coil 10, coils 11 of respective phases U, V, W each of which is wound in the form of a nearly triangular one with a Ritz wire of an insulating wire stranded out of tens to several tens of fine enamel wires, etc., are provided in the form of a circle. Therefore, the area of the conductor of the coil 11 which is projected on a plane in the direction of the magnetic flux of the flat rotating machine is made small. Also, since the stator coil 10 is a core-less one, the iron loss comprising a hysteresis loss caused by the fact that the magnetic flux is changed with time in a magnetic circuit and an eddy current loss is eliminated, and as a result, the heat generation quantity of the stator coil 10 is reduced. Thereby, the generation of the eddy current loss of the core-less flat rotating machine can be reduced, and its efficiency can be improved. COPYRIGHT: (C)1996,JPO

Numerical optimization of the electromagnetic field by stochastic search and MEC-model

Abstract: The increase of output power of an electromagnetic device by the raise of flux density is limited by the nonlinear behaviour of the iron parts of the electromagnetic circuit. An improved power output can be achieved by optimizing the nonlinear magnetic circuit. A combination of evolution strategy and simulated annealing leads to a robust numerical optimization method. Evaluation of the objective function is done by a nonlinear flux tube model called magnetic equivalent circuit (MEC). Results from field calculations and optimizations will be presented for an example of automated optimal design of an electromagnetic device. >

Toward functional magnetic stimulation (FMS) theory and experiment

Abstract: Examines the use of magnetic fields to functionally stimulate peripheral nerves. All electric fields are induced via a changing magnetic field whose flux is entirely confined within a closed magnetic circuit. Induced electric fields are simulated using a nonlinear boundary element solver. The induced fields are solved using duality theory. The accuracy of these predictions is verified by saline bath experiments. Next, the theory is applied to the stimulation of nerves using small, partially occluded ferrite and laminated vanadium permendur cores. Experiments demonstrate the successful stimulation of peripheral nerves in the African bullfrog with 11 mA, 153 mV excitations. These results offer a new vista of possibilities in the area of functional nerve stimulation. Unlike functional electric stimulation (FES), FMS does not involve any half cell reactions, and thus would not have the commensurate FES restrictions regarding balanced biphasic stimulation, strength duration balances, and oxidation issues, always exercising care that the electrodes remain in the reversible operating regime. >

Magnetic field analysis by finite element method taking rotational hysteresis into account

Abstract: In the conventional magnetic field analyses that are applied to such things as rotating machines, the magnetic properties of the arbitrary direction have been modelled by using the magnetic properties of the easy axis and its perpendicular direction. Such kind of numerical modeling can not exactly show the phase difference between the magnetic flux density B and the magnetic field strength H in the case of a rotating magnetic flux excitation. In this paper, the B- and H-values are measured as vector quantities under the rotating magnetic flux excitation. The magnetic properties of the material are expressed by the magnetic reluctivity tensor based on the measured results. This new expression is applied to the rotating magnetic field problem. As a result, it is shown that our new method is applicable to the problem in the case of the rotating magnetic flux excitation. >