Showing papers on "Magnetic circuit published in 1998"

Micromachined planar inductors on silicon wafers for MEMS applications

Abstract: This paper describes three micromachined planar inductors (a spiral type, a solenoid type, and a toroidal meander type) with electroplated nickel-iron permalloy cores which have been realized on a silicon wafer using micromachining techniques. The electrical properties among the fabricated inductors are compared and the related fabrication issues are discussed, with emphasis on the low-temperature CMOS-compatible process, the high current-carrying capacity, the high magnetic flux density, the closed magnetic circuits, and the low product cost. The micromachined on-chip inductors can be applied for magnetic microelectromechanical systems devices, such as micromotors, microactuators, microsensors, and integrated power converters, which envisages new micropower magnetics on a chip with integrated circuits.

Magnetic models of saturated interior permanent magnet motors based on finite element analysis

Abstract: This paper deals with the magnetic model of an interior permanent magnet synchronous motor, whose parameters are computed using finite element analysis. As known, in unsaturated conditions the motor inductive parameters and flux linkage call be univocally determined. Conversely, under saturated operation, different choices may be adopted to define them. Various models are examined, with the purpose to individuate the most effective for a prediction of the motor and speed capability. Attention is devoted to the performance at base speed as well as in the flux-weakening region. Comparison with tests confirms the good agreement with the results obtained by finite element analysis.

Complex vector model of the squirrel cage induction machine including instantaneous rotor bar currents

Abstract: In this paper a new detailed mathematical derivation of the squirrel cage induction machine d-q model is introduced. The model is based on coupled magnetic circuit theory and complex space vector notation and takes into account the actual nonsinusoidal rotor bar distribution. It is shown for the first time that, given the structural symmetry of the induction machine, both stator and rotor circuits can be modeled by the simple set of only four coupled differential equations. More important, the number of equations does not depend on the number of rotor bars and the model is valid even if the number of bars per pole is not an integer number. This enormous simplification is achieved without loss of generality nor loss of any information contained in the full set of equations and it is valid for any operating condition. The actual n rotor bars and end-ring currents are fully included in the model and they are obtained directly by using a simple vector transformation. In addition, the three-phase rotor equivalent parameters are obtained. Second order effects, such as skin effect in the rotor bars, can be taken into account by simply modifying the bar and end ring resistance values. An equivalent circuit based on the model is also derived. Since the number of equations needed is only four (the same as in the equivalent dq model) the computation effort required to solve the full system is drastically reduced.

An improved magnetic equivalent circuit method for predicting the characteristics of highly saturated electromagnetic devices

Abstract: The magnetic equivalent circuit (MEC) method has been used to model the nonlinear magnetic field in electromagnetic devices for steady-state and dynamic conditions. However, for highly saturated electromagnetic devices, the conventional MEC method is inaccurate in predicting device characteristics. With experience gained from the finite element (FE) method, the MEC method can be modified to provide significant accuracy improvement in the field solution results. The main modification is done in the modeling of the highly saturated regions. The improved magnetic equivalent circuit (IMEC) is used to predict the characteristics of a switched reluctance motor (SRM). The results from IMEC are compared with those obtained by conventional MEC, FE methods and measurements.

Passive magnetorheological fluid device with excursion dependent characteristic

Abstract: A magnetorheological fluid device which exhibits excursion (stroke or rotation) dependent resistance (force or torque) which is obtained passively. Linear and rotary embodiments are described. The devices described herein include various ways for passively varying magnetic circuit reluctance to accomplish the stroke or rotation dependent characteristic. The devices include a first component with an internal cavity, a second component received in the cavity and moveable relative to the first component, a working zone created between the first and second component, a magnetorheological fluid contained therein, at least one permanent magnet for producing a magnetic field, a magnetic circuit for directing a magnetic flux created by the permanent magnet toward the magnetorheological fluid in the working zone, and passively varying a magnetic circuit reluctance (such as by changing a thickness of a magnetic return, by changing a gap thickness, by changing the material reluctance, by interacting multiple magnetic fields, or combinations thereof) as a function of excursion. This changes the magnetic field strength acting upon the MR fluid in the working zone and produces a force/torque which varies as a function of excursion (x or θ).

Reduction of inrush current in single-phase transformer using virtual air gap technique

Abstract: In this paper the authors present a technique based on the use of a virtual air gap in which equivalent thickness varies as a function of controllable parameters adapted to the configuration of the magnetic circuit and the associated control system. The principle is presented using a magnetic circuit similar to the transformer one. Among the numerous applications, this technique can be applied to reduce inrush current in single-phase transformers.

Magnetic thin film memory element utilizing GMR effect, and recording/reproduction method using such memory element

Abstract: It provides a magnetic thin film memory element utilizing the GMR effect. The memory element comprising a first magnetic layer with a closed magnetic circuit structure, a second magnetic layer with a closed magnetic circuit structure having a coercive force higher than that of the first magnetic layer, and a non-magnetic layer disposed between the first and second magnetic layers, at least a part of which is made of an insulating material. It also discloses methods for recording and reproducing information in and from such memory element.

A new basic technology for magnetic micro-actuators

Abstract: This paper presents a new technology for the fabrication of electromagnetic micro-actuators. This technology allows "U-core" electromagnets to be built on ferromagnetic substrates. The electromagnets consist of multi-level copper coils and electroplated NiFe poles. Combined with a NiFe "keeper", an electromagnetic actuator is obtained, which can generate a magnetic force up to several tens of mN. The actuator can be implemented in several applications, such as valves, motors and relays. In this paper, an electromagnetic microrelay, to be used, for instance, in the automatic test equipment (ATE) market, is described. First experimental results of the relay, using a driving coil of 127 turns and having gold contacts, have shown an on-resistance of less than 0.4 /spl Omega/ for an input (driving) current of 8 mA, corresponding to a driving power of 14 mW. These data compare favorably well with previous results of electromagnetic microrelays as presented in the literature.

Vibration actuator for pager

Abstract: A vibration actuator for pager in which a vibrating section (13) of an electroacoustic transducer is driven using low frequencies to collide it against a fixed section (14), and the vibration generated from the collision is taken out as external vibration. The vibrating section (13) of a coil (15) and the fixed section (14) are bonded via an elastic member (19) provided therebetween. The vibration generated at the time of collision can be effectively increased by flexibly supporting a magnetic circuit composed of a magnet, a yoke, etc. and driving it with alternating current which has a polarity. To permit easier assembly and to prevent damage or deterioration in characteristics, it is preferable to provide an annular molded member (21), which has hook-like projections, around the magnetic circuit (18) and to support the magnetic circuit by a rubber member attached to the hook-like projections.

Airgap armature coils and electric machines using same

Abstract: A flywheel energy conversion device provides highly efficient conversion between kinetic and electrical energy. The flywheel produces increased output by providing armature coils in an air gap formed about the flywheel (both radial and axial embodiments are described). In preferred embodiments, field coils of a magnetic circuit are energized with DC drive current that creates homopolar flux within a rotating solid rotor having teeth cut from a flat disk. The total reluctance of the magnetic circuit and total flux remain substantially constant as the rotor rotates. The flux may travel radially outward and exit the flat disk through the teeth passing across an armature air gap. Airgap armature coils are preferably utilized in which the changing flux density (due to the rotating teeth) induces an output voltage in the coils. The flux is diffused before returning to the rotor in one of several ways such that core losses are effectively reduced, thereby enabling the flywheel to operate efficiently at high frequencies.

Fault indicator providing contact closure and light indication on fault detection

Abstract: A fault indicator for detecting the occurrence of a fault current in a monitored conductor and providing a contact closure and a light indication indicative thereof includes a rotatably mounted indicator flag. The flag is positioned in either a reset indicating or a fault indicating state by a four-pole magnetic pole piece, which is magnetized to an appropriate magnetic orientation by momentary application of a current to an actuator winding on the pole piece. A first magnetically actuated reed switch in an auxiliary magnetic circuit associated with a first pole of the magnetic pole piece and including the actuator winding and a first bias magnet closes upon occurrence of the fault current to connect an internal lithium battery to an LED visible from the exterior of the fault indicator housing. A second magnetically actuated reed switch associated with a second pole of the magnetic pole piece and including the actuator winding and a second bias magnet closes upon occurrence of the fault current for external signaling or control purposes.

Three-dimensional analytical optimization of permanent magnets alternated structure

Abstract: The paper presents the analytical study of an alternated structure of permanent magnets. These structures are used to construct position sensors, for example. Such devices need to be optimized, and only through analytical expressions can this be done. The paper presents these analytical expressions and their use in optimization of the magnetic circuit with regard to such constraints as mechanical airgap and resolution.

Permanently excited transverse flux machine

Abstract: The invention concerns a permanently excited transverse flux machine which requires only one permanent magnet segment per phase and per magnetic circuit. The magnetic flux generated by a permanent magnet segment (3) flows alternately through the soft magnetic body on two conductor rings (7) of this transverse flux machine. The conductor rings (7) are arranged on different sides of the permanent magnet segment, the direction of flux in the permanent magnet segments corresponding to the direction of magnetic flux in the two air gaps through which said flux passes. Preferably, the permanent magnet segments are arranged between two U-shaped halves of a square wound C-core constituting the rotor bodies (5). The stator bodies (6) are also prefabricated from grain-oriented materials as U-shaped C-cores.

Characterization of induction motors in adjustable speed drives using a time-stepping coupled finite element state space method including experimental validation

Abstract: This paper describes how a comprehensive time-stepping coupled finite element phase flux linkage-based state-space modeling approach can be used for the characterization of induction motors in adjustable-speed drives. The model implemented the faster indirect and iterative coupling approach based on the curl-curl nondiffusion equation rather than the direct coupling approach, which is based on the curl-curl diffusion equation. The model presented in this paper is capable of rigorously modeling the effects of magnetic nonlinearities and space harmonics due to the machine magnetic circuits' topology and winding layouts, time harmonics resulting from electronic switching of inverters, as well as the synergistic interaction between these time and space harmonics. This includes the presentation of a unique approach for the calculation of electromagnetic torque by means of a concept of energy balance computed from instantaneous magnetic field solutions calculated at each time sample in an at cycle. This approach reveals higher content of torque ripples than given by more conventional approaches to torque calculations. The results of motor drive performance simulations and corresponding test results are shown to correlate well here with current waveforms and torque averages. This includes sinusoidal excitation and six-switch inverter excitation with pulsewidth modulation switching pattern, respectively.

Non-contact position sensor

Abstract: A core of semi-permeable material forms a magnetic circuit having air gaps. A movable magnet provides flux in a first portion and a second portion of the magnetic circuit with the location of the magnet determining the portion. Magnetoresistive sensors in the air gaps provide signals related to the position of the magnet.

Reluctance network formed by means of edge element method

Abstract: Equivalence between the equations of the reluctance network method and the equations of the edge element method has been presented. The edge values of magnetic vector potential represent the loop fluxes in reluctance network Magnetomotive forces in the branches of the reluctance network are defined by the edge values of current vector potential. The magnetic scalar potential is determined in the centre of gravity of the element. The reluctance network formed by the edge element method contains mutual reluctances.

A method and device for controlling the magnetic flux in a rotating high voltage electric alternating current machine with permanent magnet rotor

Abstract: A rotating electric machine for direct connection to high-voltage networks, in which the magnetic circuit adapted for high voltage comprises a permanent magnetic rotor, stator and main and auxiliary flux control windings in operative relation. At least one of the windings is a conductor surrounded by a magnetically permeable, field confining insulation system.

Flux control for high power static electromagnetic devices

Abstract: A high power static electromagnetic device with variable inductance has a magnetic circuit with a flux bearing region. A main winding and at least one control winding surrounds the portions of the flux bearing region. A control device is coupled to the control winding for varying the distribution of flux. The winding is formed of a magnetically permeable, field-confining insulating cable.

Electrical machine magnetic circuit structure in which pole-to-rotor air clearances vary asymmetrically to provide a more uniform flux distribution

Abstract: An electrical machine structure includes a plurality of magnetic circuit units, each including at least two magnetic poles interconnected by a magnetic circuit structure. The magnetic circuit units are stacked or intercrossed in such a way that ventilation openings are formed between the magnetic circuit units. Clearances between the magnetic poles and an interactive electrical machine structure or rotor are arranged to vary asymmetrically across the lengths of the poles to provide a more uniform flux distribution. The use of relatively small magnetic circuit units arranged to form ventilation openings, and the manner in which the clearance between the magnetic poles is varied, enables the use of smaller pole structures than is possible with a conventional more integral magnetic circuit structure.

High voltage rotating electric machines

Abstract: A rotating electric machine for direct connection to all types of high-voltage networks, in which the magnetic circuit adapted for high voltage comprises a rotor (7), stator (6) and at least one winding. The winding, or at least one of the windings, comprises cooled conductor means (3), preferably cooled superconducting means, surrounded by a solid insulation system (4).

Apparatus and method for evaluation a condition of a magnetic circuit of an electric machine

Abstract: The method consists in positioning a probe in front of a pair of teeth provided on the face of the magnetic circuit of an electric machine. The probe has spaced apart magnetic prong portions having respective end faces adapted to match the teeth of the pair with the end faces in registry with the teeth. The prong portions are respectively provided with an excitation winding and a measurement winding. The excitation winding is excited to induce a magnetic flux in a test zone formed of the teeth in front of the probe and a portion of the magnetic circuit extending therebetween. The current flowing in the excitation winding and the voltage across the measurement winding are measured for calculating a resulting power which is indicative of the condition of the test zone. The apparatus is formed of the probe and electronics carrying out the above functions.

Method and device for controlling the magnetic flux with an auxiliary winding in a rotating high voltage electric alternating current machine

Abstract: A rotating electric machine for direct connection to high-voltage networks, in which the magnetic circuit adapted for high voltage comprises a rotor, stator and main and auxiliary windings in operative relation. At least one of the windings is a conductor surrounded by a magnetically permeable, field confining insulation system.

Soft magnetic thin film having Co, Ni and Fe as main ingredients, method of manufacturing the same and magnetic head and magnetic storage unit using the soft magnetic thin film

Abstract: A soft magnetic thin film for magnetic head has high saturation magnetization and at the same time high resistivity. There are provided a method of manufacturing the soft magnetic thin film and a magnetic head and a magnetic storage unit which use the soft magnetic thin film. At least one of lower and upper soft magnetic layers of magnetic head which define a magnetic circuit is formed of a soft magnetic thin film having as a main constituent a Co--Ni--Fe alloy consisting of 30 to 90 at % Co, less than 40 at % Ni and less than 40 at % Fe and containing at least S by 0.5 to 4 at %. The soft magnetic thin film is formed from a Co--Ni--Fe alloy plating solution containing metal salts of Co, Ni and Fe and additionally containing a sulfur system organic compound through electrodeposition process.

Simple models for dynamic hysteresis which add frequency-dependent losses to static models

Abstract: The broadening of magnetic hysteresis with increasing frequency of excitation may be represented in an electrical equivalent circuit by placing a resistor in parallel with an inductor whose core is the magnetic material represented by a static hysteresis model. This broadening can be controlled as an arbitrary function of frequency by changing the resistance with frequency. This, in turn, may be accomplished by using a parallel set of linear resistors, each placed in series with a bandpass filter, in place of a single resistor. This technique is illustrated by a simulation of both fast pulse excitations and moderate frequency sinusoidal excitations for 3C81 ferrite material using an equivalent circuit containing just three resistive parallel branches along with the static hysteresis model of Jiles and Atherton.

A method for reduction of cogging torque in brushless DC motor considering the distribution of magnetization by 3DEMCN

Abstract: A method of reducing cogging torque and improving average torque has been studied by changing the dead zone angle of trapezoidal magnetization distribution of the ring type rotor magnet in a brushless DC motor (BLDCM). Because the BLDCM has a 3-D shape of its overhang, 3-D analysis should be used for exact computation of its magnetic field. A 3-D equivalent magnetic circuit network method (3-D EMCN) which can analyze an accurate 3-D magnetic field has been introduced. The analysis results of cogging torque using this 3-D EMCN are compared with those of the 3-D finite element method (3-D FEM) and experimental data.

Electromagnetic core-energy actuator

Abstract: An electromagnetic actuator device converts electrical energy to mechanical energy by the interaction of two types of closed magnetic circuits (11, 13). A first closed magnetic circuit functions to generate high magnetic intensity in a portion of a ferromagnetic core (11, 13). A second substantially-closed magnetic circuit (13) contains a movable permanent magnet (21) which injects flux into the high-end region of the first magnetic circuit (23). Interaction of these two fields, in closed magnetic circuits, results in efficient and controllable electromechanical energy conversion.

Comprehensive salient-pole synchronous machine parametric design analysis using time-step finite element-state space modeling techniques

Abstract: This paper details the application of a time-stepping coupled finite element-state space (CFE-SS) model to predict a salient-pole synchronous generator's parameters and performance, including damper bar current profiles and bar losses as well as iron core (including pole face) losses, under various operating conditions. The CFE-SS modeling environment is based on the natural ABC flux linkage frame of reference, which is coupled to a time/rotor stepping FE magnetic field and machine winding inductance profile computation model. This allows one to rigorously include the synergism between the space harmonics generated by magnetic saturation and machine magnetic circuit as well as winding layout topologies, and the time harmonics generated by the nonsinusoidal phase currents, ripple rich field excitation and damper bar currents. The impact of such synergism between these space and time harmonics on damper bar current profiles and losses, iron core losses, various machine winding current, voltage and torque profiles/waveforms is studied here for a 10-pole, 44.9 kVA, 17,143 RPM, 1428.6 Hz, 82 V (L-N), wound-pole aircraft generator.

Design and FE analysis of an outer-rotor PM generator for directly-coupled wind turbine applications

Abstract: This paper presents the design and finite element (FE) analysis of a permanent magnet (PM) generator using neodymium-iron-boron magnets for directly-coupled wind turbine applications To accomplish the goal of small size and light weight with an extra-low speed for direct coupling, the outer rotor structure is applied The simple magnetic equivalent circuit approach is used for initial design iteration, and the finite element method applied to analyze the detailed characteristics Comprehensive experimental tests were conducted to verify the theoretical predictions A good agreement between the theoretical work and testing results was achieved

Influence of the permanent magnet overhang on the performance of the brushless dc motor

Abstract: Axial overhang of the permanent magnets has been used to enhance the performance of radial flux brushless dc motors, but its precise contribution to performance is not well known. This article aims at the investigation of the overhang effects by finite element and lumped parameter modeling. An empirical formula which allows two-dimensional analysis to account for overhang effects is proposed. A three-dimensional equivalent magnetic circuit model is developed and its ability to accurately predict overhang effects is assessed. Results of finite element and lumped parameter models are compared and a design methodology is forwarded.

3D edge element based formulation coupled to electric circuits

Abstract: This paper describes a new approach for 3-D magnetic field analysis of electromagnetic devices, taking into account electric circuit equations. The approach is based on the ungauged magnetic vector potential with edge elements and it is particularly useful for end-coils effects analysis. To ensure the continuity of the current density, a new wire density vector is introduced. The electric circuit is analysed using the time-integrated electric potential as a nodal unknown. The whole system is solved step by step with respect to time. To validate the proposed approach, some numerical examples are treated.