Mutual Magnetic Flux Research Articles

Effect of Mutual Magnetic Flux Linkage Between Stages of an Induction Coilgun on Its Performance

In a multistage electromagnetic induction coilgun (EIC), the time-varying magnetic flux generated by the first stage (or coil) links with the coils in the subsequent stages and induces EMF across their terminals. The magnetic flux linkage and the induced EMFs depend on the distance between the stages (or coils). This induced EMF circulates a current through the coils in the subsequent stages, if allowed to flow by such means of the pulsed power source (PPS) connection with these coils, i.e., it depends on the winding direction (clockwise or anticlockwise) of the coils and the connection of the crowbar diode (CD) in the PPS circuit. If CD is connected in parallel to the capacitor bank, then the main series switch averts this induced current flow through the coil, but if CD is connected in parallel to the coil following its winding direction, then induced current flows through the coil. In this article, the effect of this induced current on the projectile motion inside a multistage EIC is analyzed using hollow projectiles of different lengths but of fixed mass and outer diameter. Computational analysis is performed using a finite element method (FEM)-based software, Ansoft Maxwell, with excitation given only to the first stage. The results are then experimentally validated with a two-stage EIC facility developed. Only two stages are considered since farther stages will have insignificant magnetic flux linkage with the first stage and the projectile. For each projectile, the distance between the two stages (or coils) is varied, starting from 2.8 to 14.8 cm with a linear step of 1 cm. The results indicate that the projectile motion is affected in a multistage system, depending on the distance between the stages and the projectile length. The analysis will be beneficial for maintaining a suitable distance between the stages in a multistage type of EIC.

A High-Power Multiphase Wireless Dynamic Charging System With Low Output Power Pulsation for Electric Vehicles

Wireless dynamic charging (WDC) of electric vehicles (EVs) is a new initiative aimed to increase EV uptake. However, pulsating output power along the driving direction is a major problem with this technology. Moreover, in order to deliver enough driving power for EVs, WDC systems must operate at high power. This article proposes a WDC system that has the capability of providing a low pulsating and high output power to EVs. The proposed WDC utilizes multiple primary windings that guarantee a homogeneous mutual magnetic flux for the receiver along the driving direction. This results in a constant induced voltage across the receiver, and hence, constant output power to charge the EV battery. High output power is realized by using multiple transmitter windings, which have been arranged in a novel winding method. The structure layout of the proposed WDC, including ferrite cores, windings, and resonant tanks, is presented. Furthermore, a theoretical analysis is conducted to determine the conditions of each winding’s current phase and amplitude for achieving constant output power. The crossing mutual inductances between the different transmitter’s phases are compensated by adding small capacitors in series with each transmitter winding. An optimization analysis using Maxwell 3-D simulation for both transmitter and receiver is carried out to achieve the highest coupling factor by using minimum ferrite material. The effectiveness of the proposed system is analytically demonstrated and experimentally verified using a 3-kW laboratory prototype. Finally, the performance of the proposed method is compared with similar systems presented in the literature. The comparison shows that the proposed system has the advantages of using simple control, it also eliminates communications between the primary and secondary side and delivers a normalized power of 2.25, which is 125% higher compared to conventional single-phase systems.

Proton-decoupled carbon magnetic resonance spectroscopy in human calf muscles at 7 T using a multi-channel radiofrequency coil

13C magnetic resonance spectroscopy is a viable, non-invasive method to study cell metabolism in skeletal muscles. However, MR sensitivity of 13C is inherently low, which can be overcome by applying a higher static magnetic field strength together with radiofrequency coil arrays instead of single loop coils or large volume coils, and 1H decoupling, which leads to a simplified spectral pattern. 1H-decoupled 13C-MRS requires RF coils which support both, 1H and 13C, Larmor frequencies with sufficient electromagnetic isolation between the pathways of the two frequencies. We present the development, evaluation, and first in vivo measurement with a 7 T 3-channel 13C and 4-channel 1H transceiver array optimized for 1H-decoupled 13C-MRS in the posterior human calf muscles. To ensure minimal cross-coupling between 13C and 1H arrays, several strategies were combined: mutual magnetic flux was minimized by coil geometry, two LCC traps were inserted into each 13C element, and band-pass and low-pass filters were integrated along the signal pathways. The developed coil array was successfully tested in phantom and in vivo MR experiments, showing a simplified spectral pattern and increase in signal-to-noise ratio of approximately a factor 2 between non-decoupled and 1H-decoupled spectra in a glucose phantom and the human calf muscle.

Poynting Vector in High-Temperature Superconducting Transformers with a Separate Excitation Winding

The HTSC transformer with a separate winding for excitation of the mutual magnetic flux is considered; the windings of the transformer are performed of first- or second-generation HTSC wires. The article presents the design and the electrical circuit of the transformer, the equations of electromagnetic balance, and the total resistance of the primary and secondary power windings and the separate excitation winding. The transfer of the electromagnetic field energy is considered in a single-phase HTSC transformer with the separate excitation winding using the Poynting vector. The temporal change in the reactive and active components of the Poynting vector and the decrease in the leakage energy flux of the separate excitation winding are shown, which causes an increase in the critical current density of the HTSC power windings, a decrease in the energy losses in the latter, and an increase the in the specific power of the HTSC transformer.

Analysis and Control of Electromagnetic Coupling Effect of Levitation and Guidance Systems for Semi-High-Speed Maglev Train Considering Current Direction

A semi-high-speed magnetic levitation (maglev) train with a maximum speed of 200 km/h is being developed in Korea. It utilizes linear induction motors for propulsion and adopts electromagnetic suspension for levitation. For high-speed operation, guidance systems should be adopted to stabilize the train especially on curved tracks. For compatibility of the rail with previously developed urban maglev trains, the installation of the guidance electromagnet has to be restricted to be placed near the levitation electromagnet. Owing to the spatial closeness, mutual magnetic flux by the levitation and guidance electromagnets is produced at an overlapping portion of the rail. For stable control of the two systems, the coupling effects must be analyzed, because the levitation and guidance electromagnets are not operated independently. This paper aims to analyze the coupling effects by considering the magnetic field and a magnetic equivalent circuit. This paper suggests levitation and guidance systems for the semi-high-speed maglev train by considering each electromagnetic characteristic depending on the current direction.

High-speed synchronous machines: A computer system for the study of the effect of rotor radial eccentricity on electromagnetic forces

The problem of the development of modern bearings (magnetic, gas, etc.) for high-speed machines with a wide range of capacities (from tens of kilowatts to megawatts) and rotational speeds (from 6000 to 60000 rpm) used in oil and gas production, robotics, space technology, and mini gas-turbine power plants is considered. The distribution of forces applied to the rotor shaft in different modes of operation is investigated including the case of shaft eccentricity. In operation, the eccentricity should not exceed 5%. A computer system is designed on the basis of the numerical method for field (2D) computation in the active part of the machine. The distribution of forces is analyzed taking into account the saturation of the magnetic circuit of the machine and the harmonic content of the mutual magnetic flux (flux in the gap). When calculating these forces in the no-load mode of operation, it was assumed that, in machines with permanent magnets, the mutual magnetic flux on the rotor is about 10–15% higher than under the rated load because of the demagnetization effect of the armature reaction. The mutual magnetic flux was specified depending on the type of rotor magnets. The computer system takes into account the relative position of the rotor poles relative to the stator field reaction under load (load angle Θ). It is also taken into account that, during use, the resulting mutual magnetic flux is distorted (compared to the no-load mode). As a result, a number of additional high harmonics appear in the gap, which affect the forces applied to the rotor shaft. Load angle Θ is calculated using graphical options of the simulation package by the iteration method. An algorithm for the implementation of this method is described. The distribution of the radial forces along the rotor shaft surface (differential parameter) and the total radial attraction force applied to the rotor shaft (integral parameter) are calculated for different values of eccentricity and different modes of operation of high-speed machines.

A Floquet theory of the general linear rotating machine

As is well-known, the fundamental assumption underlying Park's decisive analysis of the ideal linear three-phase rotating machine is that all windings on the (nonsalient) stator are in effect sinnsoidally spacially distributed as far as concerns the calculation of any self or mutual magnetic flux linkage. As Park has shown, there exists a suitable reference frame in which such an "ideal" machine admits an internal constant-coefficient differential equation description under the condition of constant rotor angular velocity. On the other hand, if the machine is not Ideal, the various mmf's are no longer sinusoldally distributed and it is not at all obvious that stationarity can be achieved by any choice of frame. Nevertheless, it is shown in this paper that such a "Floquet" frame does Indeed exist and that it may be possible to devise experimental procedures for its determination. This new Park-like theory of the general linear rotating machine subsumes the Ideal case and is based squarely on the obvious geometric periodicity of the machine structure.