Showing papers on "Magnetic circuit published in 1999"

Linear Synchronous Motors : Transportation and Automation Systems

Abstract: Topology and Selection Definitions, Geometry, and Thrust Generation Linear Synchronous Motor Topologies Calculation of Forces Linear Motion Selection of Linear Motors Materials and Construction Materials Laminated Ferromagnetic Cores Permanent Magnets Conductors Principles of Superconductivity Laminated Stacks Armature Windings of Slotted Cores Slotless Armature Systems Electromagnetic Excitation Systems Superconducting Excitation Systems Hybrid Linear Stepping Motors Theory of Linear Synchronous Motors Permanent Magnet Synchronous Motors Motors with Superconducting Excitation Coils Variable Reluctance Motors Permanent Magnet Hybrid Motors Motion Control Control of AC Motors EMF and Thrust of PM Synchronous and Brushless Motors Dynamic Model of a PM Motor Thrust and Speed Control of PM Motors Control of Hybrid Stepping Motors Precision Linear Positioning Sensors Linear Optical Sensors Linear magnetic Encoders High Speed Maglev Transport Electromagnetic and Electrodynamic Levitation Transrapid System (Germany) Yamanashi Maglev Test Line in Japan Swissmetro Marine Express Building and Factory Transportation Systems Elevator Hoisting Machines Ropeless Elevators Assessment of Hoist Performance Horizontal Transportation systems Industrial Automation Systems Automation of Manufacturing Processes Casting Processes Machining Processes Welding and Thermal Cutting Surface Treatment and Finishing Material Handling Testing Industrial Laser Applications Appendix A Magnetic Circuits with Permanent Magnets Appendix B Permeances for Magnetic Fluxes Appendix C Performance Calculations for PM LSMs Symbols and Abbreviations References

Modeling and simulation, and their validation of three-phase transformers with three legs under DC bias

Abstract: This paper proposes a new model for three-phase transformers with three legs with and without task under DC bias based on electric and magnetic circuit theory. For the calculation of the nonsinusoidal no-load currents, a combination of time and frequency domains is used. The analysis shows that (1) asymmetric three-phase transformers with three legs generate magnetizing currents with triplen harmonics not being of the zero-sequence type. (2) The wave shapes of the three magnetizing currents of (asymmetric) transformers are dependent on the phase sequence. (3) The magnetic history of transformer magnetization-due to residual magnetization and hysteresis of the tank-cannot be ignored if a DC bias is present and the magnetic influence of the tank is relatively strong, e.g., for oil-cooled transformers. (4) Symmetric three-phase transformers with three legs generate no-load currents without triplen harmonics. (5) The effects of DC bias currents (e.g., reactive power demand, harmonic distortion) can be suppressed employing symmetric three-phase transformers with three legs including tank. Measurements corroborate computational results; thus this nonlinear model is valid and accurate.

Electromagnetic flowmeter having low power consumption

Abstract: An electromagnetic flow meter and method of operating the same. There is provided a flow measurement duct, a magnetic circuit including pole pieces for generating a magnetic field in fluid flowing in a direction in the duct across the direction of flow, and an electrical circuit including at least one sensing electrode for measuring a voltage thereby induced in the fluid to provide an output indicative of the flow. The method comprises measuring a series of pairs of outputs of the electrical circuit, each pair of outputs comprising an output when the magnetic field is present and an output when the magnetic field is absent, and determining from the measured series of pairs of outputs whether fluid is present or absent in the duct.

Radial force characteristics of a switched reluctance machine

Abstract: The operation of a switched reluctance machine with eccentric rotor positions creates asymmetrical airgap flux distributions and results in unbalanced magnetic pull. This paper comprehensively investigates the static and dynamic radial force characteristics of an 18/12 switched reluctance machine with unbalanced operation. A powerful magnetic equivalent circuit (MEC) modelling approach is developed and allow fast and accurate force predictions with arbitrary excitation and position. The model calculates the instantaneous radial and tangential forces on the individual poles as well as the net forces on the rotor. The method is validated with finite element analysis (FEA) and against experimental results from a 12/8 machine. Static radial force characteristics are first developed. The MEC is then coupled with a time stepping algorithm to calculate the simultaneously varying electrical, mechanical, and magnetic variables for dynamic operation of the complete SR motor drive. Dynamic radial force behavior is examined, where parallel connected windings are found to naturally and significantly reduce the unbalanced magnetic pull. Variations of radial force with torque-speed operating point are also examined.

Analysis and performance of an ironless stator axial flux PM machine

Abstract: This paper presents the analysis, design and performance of an axial flux permanent magnet (AFPM) machine with an ironless stator. The topology has a large airgap length and zero core losses. A machine model that uses both lumped magnetic circuit and finite element method results is used with a multi-variable optimization algorithm to obtain the optimum machine dimensions. Special attention is given to the magnet interpolar gap to ensure a certain minimum plateau width for brushless DC operation. The large airgap length allows several approximations to be made that simplifies the machine model. A prototype machine is constructed and evaluated. Measured results of the armature reaction effect in the large airgap are given and discussed.

Electrical machine with double excitation, especially a motor vehicle alternator

Abstract: A rotary electrical machine such as a motor vehicle alternator comprises a stator and a rotor. The stator has at least one armature winding in at least one pair of stator slots. The rotor includes means for selectively establishing closed magnetic circuits which pass around the turns of the armature winding or windings. The means for setting up closed magnetic circuits comprise at least two permanent excitation magnets which set up two magnetic fluxes having components in opposite directions according to the direction of displacement of the rotor; and, between each pair of successive magnets, at least one excitation winding having two wires and being arranged to produce in an adjustably way two flux components which are such as to oppose the fluxes set up in the magnets of the pair. The wires of the excitation windings are located in rotor slots, each of which lies between two successive rotor poles.

Derivation, calculation and measurement of parameters for a multi-winding transformer electrical model

Abstract: The conventional model for multiwinding transformers is difficult to relate to its physical construction, and the measurement of the model parameters is difficult and unreliable. In this paper a physically-based electrical model of a high voltage multi-winding transformer is presented. Each component in the electrical model corresponds to a physical quantity of the transformer. A method is also presented to calculate the leakage inductance for nonuniformly spaced windings, which store significant energy in the flux in the radial field. Also, the parameters can be directly measured on experimental prototypes. The experimental results closely match the predicted results.

Electric machinery parameters and torques by current and energy perturbations from field computations. I. Theory and formulation

Abstract: In this first of a two-part article, the well-established energy/current (E/C) perturbation method of computation of machine winding inductances is reviewed. The method's efficacy in machine performance calculations is delineated and verified in a companion paper by comparison to experimental results. The critical role that winding inductance parameters have in modeling and simulation of the nonsinusoidal steady state time-domain (forced response) performance of electric machinery is demonstrated using state models in both the winding flux linkage and current-based frames of reference. The computed machine performance characteristics include profiles of winding inductances, induced terminal voltage waveforms, and instantaneous torque profiles that contain all the ripples due to the significant space harmonics in a machine. The method and associated formulations and techniques are shown to be very effective in both 2D-FE and 3D-FE electric machinery field solutions involving substantial degrees of saturation and complexity of construction. The machines analyzed in the comparison paper include a 15-HP permanent magnet brushless DC motor, a 1.2-HP three-phase induction motor, and a 14.3 kVA three-phase modified Lundell alternator possessing very complex magnetic circuit geometries. The well-posedness of the method held true for all these cases, as well as many other case-studies briefly reviewed here.

Consideration of contactless power station with selective excitation to moving robot

Abstract: A new method of contactless energy transmission to a moving machine is proposed. This system is useful for application with moving robots, including electric vehicles such as an electric wheelchair, an automatic guided vehicle, and so on. A moving robot was used as a model experimental system with these loads. The primary coils, an arrangement of spiral coils used with the selective excitation system, are located on the floor. A secondary spiral coil is attached to the bottom of the robot. The robot receives the magnetic flux radiating from the primary coils, which serves as the power source for the robot. In terms of electric power, in this experimental system the robot needs at least 2 W to start moving. As the robot moves, the excitation follows its movement. We have studied the characteristics of power transmission when the robot moves from one primary coil to another. This selective excitation system was found to be very effective for the overall efficiency of electric power transmission. We also examined the efficiency of the coil system used herein. Based on a comparison of the closed magnetic loop circuit and the open magnetic loop circuit, the efficiency of the former determined to be 70 [%] and that of the latter was determined to be 9 [%]. A monitoring system was constructed to ascertain which coil was excited. Based on our results, it would be possible to apply this contactless power transmission system to larger systems.

Development of passive fault current limiter in parallel biasing mode

Abstract: So far literature reports on the magnetic fault current limiter (FCL) are based on the series biasing mode in which the flux due to line current flows through the permanent magnet. As a result there is a high possibility of demagnetization of the permanent magnet. A passive fault current limiter is a combination of passive elements such as permanent magnet and saturable core. The permanent magnet is used to bias the core. In order to avoid severe demagnetization of the permanent magnet, we have investigated the performance of passive fault current limiters based on permanent magnet and saturable core in parallel biasing mode. The functional characteristics have been analyzed by Tableau approach and the simulation results are presented, The experimental results for a small scale prototype model are also presented for verification.

Improvements of single sheet testers for measurement of 2-D magnetic properties up to high flux density

Abstract: Due to structural limitation, the currently proposed apparatus based on a single sheet tester (SST) cannot measure magnetic properties along arbitrary directions (so-called 2-D magnetic properties) of silicon steel at high flux densities. In this paper, significant improvements are carried out on magnetizing windings and auxiliary yokes of a double excitation type of SST. Furthermore, crosswise overlapped H-coils are introduced so that even an ordinary single-excitation type of SST can be applicable to the measurements of 2-D properties. It is demonstrated that 2-D magnetization property up to 1.9 T can be measured by using the newly developed SST's.

High-efficiency inductor-alternator

Abstract: An inductor-alternator provides highly efficient conversion between mechanical and electrical energy The inductor-alternator produces increased output by providing armature coils in a single air gap formed between two halves of a toothed rotor In preferred embodiments, field coils of a magnetic circuit are energized with DC drive current that creates homopolar flux within the rotating rotor Airgap armature coils are mounted with the field coils to form a stationary assembly that is placed within the single air gap in the rotor so that the changing flux density (due to the rotating teeth) induces an output voltage in the armature coils The rotor and stationary assembly are mounted in a housing by bolts that may also be used as terminals for the armature coils to reduce assembly complexity and production cost The combined assembly provides high energy and power density because tip speed of the rotor is maximized and the use of air gaps is minimized

Estimation of magnetic loss in an induction motor fed with sinusoidal supply using a finite element software and a new approach to dynamic hysteresis

Abstract: A method to estimate precise iron loss in an electrical machine is presented. This method implements a 2D finite element simulation of moving structure including the non-linear magnetic behaviour and a new dynamical hysteresis model of the magnetic circuit. The 2D finite element simulation is used to evaluate the induction evolution with time in any point of the motor structure. The time evolution induction signal is then used as the input of the dynamical hysteresis model to estimate the hysteresis cycle and therefore local iron loss. Results on a 4 kW, 4-pole, 3-phase sine fed induction motor show a good agreement between theoretical estimation and measurement. For the first time, it is shown that rotor loss represents 30% of the motor iron loss.

Rotational vibration detection using a velocity sense coil

Abstract: An apparatus and method for detecting rotational vibration applied to a disc drive having a rotary actuator adjacent a rotatable disc. The actuator supports a head adjacent a recording surface of the disc and an actuator coil in a magnetic field of a magnetic circuit of a voice coil motor. A second, velocity sense coil is further coupled to the actuator and immersed in the magnetic field of the magnetic circuit, with the velocity sense coil being electrically isolated from the actuator coil. Rotational vibration is detected in relation to a sense voltage induced across the velocity sense coil as the magnetic circuit is moved relative to the velocity sense coil. A data transfer operation between the head and a host device is interrupted when the magnitude of the rotational vibration exceeds a specified magnitude. A servo circuit applies current to the actuator coil to position the head relative to the disc recording surface in relation to servo information transduced by the head, as well as in relation to the sensed voltage from the velocity sense coil.

3-D analysis of permanent magnet linear synchronous motor with magnet arrangement using equivalent magnetic circuit network method

Abstract: In this paper, the fields and forces of permanent magnet linear synchronous motors (PMLSM) with segmented or skewed magnet arrangement are analyzed according to length of segment or skew. And, the effects according to the lateral overhang of magnet are investigated. For the analysis, 3-dimensional equivalent magnetic circuit network (3-D EMCN) method is used. The analysis results are compared with the experimental ones and show a reasonable agreement.

Apparatus and method for electronically reducing the impact of an armature in a fuel injector

Abstract: A method is provided to control velocity of an armature of a fuel injector as the armature moves from a first position towards a second position. The fuel injector includes a stator core at the second position and a coil is associated with the stator core. The coil, the stator core and the armature define a magnetic circuit. The coil generates a magnetic force to cause the armature to move towards and impact the stator core. The method includes energizing the coil to permit the armature to move towards the stator core. A rate of change of magnetic flux of the magnetic circuit is determined. Closed loop feedback control of the determined rate of change of magnetic flux is used to regulate a rate of magnetic flux by controlling current to the coil so as to control a velocity of the armature upon impact with the stator core.

Differential solenoidal magnetic field sensing device and method for manufacturing the same

Abstract: A differential solenoidal magnetic field sensing device is a magnetic field sensor fabricated on a microscopic scale and is constructed by two soft magnetic film cores laminated on a semiconductor substrate, an excitation of the soft magnetic film cores, and a magnetic flux variation detecting coil formed of a spirally wound metal film pattern. Since two soft magnetic film cores constitutes closed magnetic paths, leakage of magnetic flux can be minimized. Also, the magnetic sensing device is a differential type sensor, the combination of driving signals can be offset. That is to say, the magnetic field sensing device is constructed such that two soft magnetic film cores are laminated and are formed lengthwise in the direction of a detection axis to reduce anti-magnetic field components, and the excitation coil wound around the two soft magnetic film cores and the magnetic flux variation detecting coil for obtaining the sum of magnetic flux variations generated in the soft magnetic film cores are alternately wound turn by turn around the soft magnetic film cores.

Fault indicator providing light indication on fault detection

Abstract: A fault indicator for detecting the occurrence of a fault current in a monitored conductor and providing a light indication thereof includes a rotatably mounted indicator flag. The flag is positioned in either a reset indicating or a fault indicating state by a magnetic pole piece, which is magnetized in one magnetic direction or the other by momentary application of a current in one direction or the other to an actuator winding on the pole piece. A magnetically actuated reed switch in an auxiliary magnetic circuit comprising an auxiliary pole piece magnetized by the actuator winding and a bias magnet magnetically aligned to oppose the reset magnetic orientation and reenforce the trip magnetic orientation of the magnetic pole piece 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.

Magnetic bearing system

Abstract: A magnetic bearing system includes a rotor shaft 1, stationary electromagnetic pole, a radial displacement sensor 5 for detecting the position of the rotor shaft 1 with respect to the electromagnetic polarity, and a control circuit 220 which supplies a control current in accordance with an output from the radial displacement sensor 5. A permanent magnet 20 is disposed in the magnetic bearing so as to constitute a portion of a magnetic member 10 which forms a magnetic circuit between the rotor shaft 1 and the electromagnetic pole. The position where a balance exists between an attraction force developed in the permanent magnet 20 and static force, which acts on the rotor shaft 1 when no load is imposed on the rotor shaft 1, is set as a target position for the rotor shaft 1.

A magnet type electric motor and generator

Abstract: To obtain the magnetic flux increase of the air gap, a radial slit for inserting a magnet is provided in a respective pole iron core, and the length of the magnet is adjusted to a radial direction and to an axial direction. In particular, when the magnetic flux is tried to strengthen, a strong magnetic flux magnet and a magnet which is inserted fully into the slit are used. Further, forming an attachment and detachment structure, it is possible to carry out easily the alternation and the adjustment of the characteristics of a magnet type electric motor and the generator. Next, in a single magnet, since there are limit in the structure and the magnetic force, further when the magnetic force of the air gap is tried to strengthen, plural magnets are combined effectively every pole. Further, in a case of a weak magnetic flux magnet, the adjustment of the length of the axial direction and the arrangement of an empty space of the magnet iron core and a three-dimensional face of the magnetic pole are utilized fully and the characteristic same to the strong magnetic flux magnet can be obtained further. The performance and the efficiency of the magnet type electric motor and generator can be improved, in accordance with the devices in the structure, the size and the arrangement of an iron core for aiming the magnetic flux increase in an air gap portion an aimed magnetic type electric machine can be obtained.

Differential spiral magnetic field sensing device and magnetic field detection module using the same

Abstract: A differential spiral magnetic field sensing device is constructed such that two soft magnetic film cores are arranged parallel to each other, each soft magnetic film core is divided into several parts in a detection axial direction to reduce anti-magnetic field components, the differential excitation coil, the magnetic flux variation detecting coil and the zero magnetic field detecting coil are laminated and wound turn by turn around the soft magnetic film cores, and there is no induced voltage waveform to the magnetic flux variation detecting coil without external magnetic field. Also, in order to minimize the leaked magnetic field components of the soft magnetic film cores, the soft magnetic film cores are sandwiched to form closed magnetic paths, and the differential excitation coil, the magnetic flux variation detecting coil and the zero magnetic field detecting coil are spirally laminated around the sandwiched soft magnetic film cores. Further, in the magnetic field detection module, a differential spiral magnetic field sensing device and a signal process for driving the same are integrated on the substrate of a monolithic semiconductor device.

Optimization of integrated magnetic sensor by mixed signal processing

Abstract: An array of integrated Hall elements is presented to maximize signal to noise ratio and to minimize the offset. Novel magnetic sensor bias circuits and signal amplification circuit suitable for sensor arrays are shown. The positioning of sensor array elements on the ASIC, to precisely determine the spatial distribution of the magnetic field for various physical quantity measurement applications, is discussed. On board sensor calibration together with controlled temperature behavior to compensate for the non-ideal temperature behavior of the applied magnetic field is demonstrated to allow for a robust design suitable for volume ASIC production.

Closed electron drift plasma thruster adapted to high thermal loads

Abstract: The closed electron drift plasma thruster uses a magnetic circuit to create a magnetic field in a main annular channel (124) for ionization and acceleration, said magnetic circuit comprises: an essentially radial first outer pole piece (134); a conical second outer pole piece (311); an essentially radial first inner pole piece (135); a conical second inner pole piece (351); a plurality of outer magnetic cores (137) surrounded by outer coils (131) to interconnect the first and second outer pole pieces (134, 311); an axial magnetic core (138) surrounded by a first inner coil (133) and connected to the first inner pole piece (135); and a second inner coil (132) placed upstream from the outer coils (131). The thruster also comprises a plurality of radial arms (352, 136) included in the magnetic circuit, and a structural base (175) which is separate from the magnetic circuit and which serves, amongst other things, to cool the coils (131, 132, 133).

Synthesis study of magnetic torque sensors

Abstract: There exist numerous solutions to measure the torque applied to a structure or a shaft, and we first present the available devices. They fall into two groups; some measure the torsion angle resulting from the applied torque, others use the shaft material property changes due to the induced stresses, We then present our contribution in this area: a synthesis study of torque sensors with variable-reluctance magnetic circuits excited by permanent magnets or coils. Among these sensors are new structures not only for stationary devices, but also for fully rotating devices. The advantages of structures of these types lie in their great design and implementation simplicity. The structures' study shows how to choose the different parameters of the sensors to meet specifications, It also demonstrates the advantages of some new designs in terms of performance-the ones using "overlapping" teeth for example.

Compact cylindrical radial gap type motor

Abstract: An iron core type cylindrical radial gap type motor structure, by having field magnetic poles generated by permanent magnets and, in opposition to these, salient poles generating a rotational magnetic field and arranged with their emission direction along the rotational axis, the shape of salient poles being approximately T-shaped in cross-section along the rotational axis direction, and I-shaped in cross-section at right angles to the rotational axis direction, the upper end of said T-shaped opposing the axial direction of the rotor magnets and the lower end being mechanically coupled and fixed to the stator ring, thus constructing the magnetic circuit of the armature, and where the relationship between the length L 1 of the said salient pole in the axial direction opposed to the field magnetic pole, and the length L 2 in the axial direction of the coil core section about which the coil is wrapped, satisfies the conditions 0.3*L 1 ≦L 2 ≦0.6*L 1 , and, furthermore, where the relationship between the thickness A 1 of the said salient pole in the circumferential direction, and the pitch P of the field magnetic pole, satisfies the conditions 0.4*P≦A 1 ≦0.8*P.

Dual excitation electrical machine, and especially motor vehicle alternator

Abstract: A flux commutating electrical machine includes a stator and a rotor. The rotor selectively establishes closed magnetic circuits around sections of the armature coils. Excitation permanent magnets establish a magnetic flux closing on itself in a circumferential direction and excitation coils establish a localized variable magnetic flux in an opposite direction to that of the flux produced by the magnets. Each magnet is housed in a first rotor part defining a first pair of rotor poles, and the coils are disposed around a second rotor part ends of which define a second pair of poles. The rotor has between the adjacent first and second rotor parts third rotor parts forming with the first and second parts a circumferential magnetic conduction path.

Magnet device with double fixing positions for changing the magnetic circuit

Abstract: A magnet device with double fixing positions for changing the magnetic circuit is provided, and includes an external housing whose inner edge is fitted with a coil The inside of the external housing includes a space for the axial movement of an iron core. The external housing and a positioning cover at the opening end of the housing are made of metal with excellent magnetic conductivity. The iron core is connected to a permanent magnet which is fixed at the inner side of the positioning cover. A drive circuit is provided whereby a positive impulse voltage will be output and the electrical energy is saved in a capacitor when the power is switched on. A discharge current is created to output a negative impulse voltage after the power is switched off, and the positive and the negative impulse voltages serve to make the coil change the direction of the magnetic force by the excitation process, so that a push force or a pull force on the iron core will be created for movement thereof. The permanent magnet will be forced to change the magnetic circuit and the iron core under ordinary circumstances will be kept at the pre-arranged position without continuous waste of electricity. Not only can this save electric energy, but it will avoid creating an over-heated state or a short circuit, so that a dangerous situation is prevented and the useful life of the device is extended.

1D magnetic component model for planar structures

Abstract: 1D magnetic component models are very useful to study particular cases in which 1D approximations can be assumed. The field distribution can be considered as 1D when the magnetic field (H) shows negligible values in two of the three dimensions, and the magnitude of the nonzero coordinate keeps constant along this 1D direction. Therefore, 1D models should be modified in order to be used with planar transformers, because their magnetic field vector has a constant direction, but its magnitude is not constant along that direction. This work presents a 1D model for planar magnetic transformers. Since those components are widely applied this procedure can become a useful analysis tool. Some comparisons between 2D approaches and the proposed 1D model have been carried out in order to show the accuracy of the proposed method.

Performance and torque-ripple characterization in induction motor adjustable-speed drives using time-stepping coupled finite-element state-space techniques

Abstract: In this paper, the time-stepping coupled finite-element state-space (TSCFE-SS) model developed in an earlier companion paper is applied here for assessments of effects of machine geometry and magnetic circuit design modifications, and effects of pulsewidth modulation (PWM) carrier frequency on performance characteristics of induction motor drives. Namely, this has been accomplished through analysis of developed torque profile ripples and harmonic spectra of mid-air-gap radial flux density waveforms of the case-study motor. Furthermore, consequent effects of design modifications pertaining to geometry and/or magnetic circuit modifications and PWM carrier frequency on ohmic and iron core losses are investigated. The investigation has been performed on a case-study motor, which is a Y-connected single-layer three-phase two-pole 1.2-hp 208-V squirrel-cage induction motor with 24 stator slots and a cage with 34 rotor bars.