Circuit Reluctance Research Articles

Modeling and optimization of a modified iron-yoked electromagnetic propulsion system using the gravitational search algorithm

Potential uses for electromagnetic launchers in defense systems, space exploration, and transportation have recently emerged. In addition, this accelerator has many applications, such as deploying small satellites into low-earth orbit and accelerating high-speed trains (e.g., bullet trains and Hyperloop) with a low-cost propulsion system instead of expensive linear motors, particularly in space applications. Therefore, the full capability and optimization of these launchers’ efficiency are still required. Therefore, this paper focuses on presenting a new design to decrease the coil’s magnetic circuit reluctance and boost the magnetic flux lines by adding a laminated iron yoke surrounding the coil. This design makes the inductance value of the iron-yoked accelerator twice the inductance in case of the absence of the iron-yoke at its peak. Additionally, the initial inductance of the iron-yoked accelerator is approximately 65% higher than that of the coil without the iron yoke. Consequently, the modified design proposed an efficiency of 17.5%, which represents a 60% improvement over the efficiency of the regular accelerator. In addition, the introduced design eliminates the suck-back force using a fast-switching device (IGBT) to switch the coil off when the projectile reaches half of the coil. Moreover, a mathematical model for the iron-yoked accelerator is built on MATLAB Simulink and validated experimentally. An artificial intelligence optimization technique, the gravitational search algorithm (GSA), is used to optimize the accelerator parameters, such as the number of turns, capacitor value, and capacitor voltage. Finally, the experimental evaluation of the GSA-optimized system demonstrated an additional 15% enhancement in efficiency, bringing the total efficiency to 20%.

Improved design-oriented analytical modelling of flux switching PM machines

Purpose This paper aims at the analytical formulation of the electromagnetic features of flux switching permanent magnet (PM) machines with emphasis on the PM air gap flux density and armature magnetic reaction. Design/methodology/approach The PM air gap flux density is formulated considering three different analytical models. These differ by the incorporation of the air gap magnetic saliency level from the stator side. In addition, the armature magnetic reaction is investigated based on a simplified magnetic reluctance circuit that considers the flux switching permanent magnet machines magnetic circuit geometry specification. Then, the no- and on-load torque is predicted based on the two air gap flux densities. Findings It has been found that the PM air gap flux density considering the stator saliencies with trapezoidal magnetomotive force waveform presents the highest accuracy. Despite the simplicity of the magnetic equivalent circuit-based approach, the predicted air gap armature magnetic reaction is in good agreement with the finite element analysis (FEA) one. These lead to the analytical predictions of the no- and on-load torque which is characterized by an acceptable accuracy. Research limitations/implications This work should be extended to experimental validation of the FEA results regarding the torque production generation. Originality/value The paper proposes an improved design-oriented analytical approach with emphasis on the PM air gap flux density and the armature magnetic reaction of flux switching PM machines.

Modeling of Dual-Phase Composite Magnetic Material and Its Application in Transformers

Dual-phase composite magnetic materials have magnetic and permanent magnetic properties. They can realize the dual-phase conversion of soft magnetic and permanent magnetic composites with a small amount of excitation energy. They have the advantages of good control and conversion characteristics and save energy, and they have a wide range of application scenarios in regard to power equipment. In this paper, the magnetization modeling of dual-phase composite magnetic materials is carried out based on micromagnetic theory, and a specific mathematical expression is given. Secondly, the preparation process of the dual-phase composite magnetic material is studied, the dual-phase composite magnetic material is prepared, and the demagnetization curve of the dual-phase composite magnetic material is measured. Finally, the application of dual-phase composite magnetic materials in power equipment is carried out. Using the soft magnetic and permanent magnetic characteristics of dual-phase composite magnetic materials, their impact on DC bias suppression in transformers is assessed. Magnetic circuit reluctance theory is used to develop the structure and electromagnetic design of a transformer. A transformer prototype with DC bias suppression ability based on dual-phase composite magnetic materials is manufactured, and simulation and experimental research are carried out. The simulation and experimental results verify the correctness of the proposed scheme. Although this scheme requires a more complex core structure, the energy-saving effect is remarkable without changing the transformer’s neutral grounding. The indicators meet the actual requirements of the project.

Analytical Performance Estimation of a Fall-Back Inner-Rotor Transverse-Flux Permanent Magnet Generator using Magnetic Equivalent Reluctance Circuit

The potential of wind energy resources is propelled fast and power extraction is increasing considerably due to the development of reliable and cost-effective wind turbine generators. Various permanent magnet (PM) wind generators have been implemented for wind power generation, among which, the conventional transverse-flux permanent magnet generator (TFPMG) is popular due to their higher torque density and simple coil design, but it has some disadvantages in comparison with radial flux PM generator, i.e., higher flux leakages and complex 3D flux pattern. In this article, a fall-back inner rotor transverse-flux PM wind generator FB-TFPMG has been investigated to override the disadvantages of conventional TFPMG. It employs half of the total PMs on the rotor and U-shaped stator cores. An analytical model of the proposed FB-TFPMG has derived using magnetic equivalent reluctance circuit (MERC) to predict the performance of the generator, i.e., flux densities in the air-gap, under aligned and unaligned conditions of rotor PMs with U-shaped stator cores. The results of the MERC model is verified with the results obtained through 3D finite element analysis.

Overview of Hybrid Excitation in Electrical Machines

Hybrid excitation is a technology that combines the advantages of field windings and permanent magnets for inducing magnetic flux. This article studies the benefits of hybrid excitation and provides an outlook on their possible applications, such as wind power generators and electric vehicle motors. Compared to permanent magnet-based machines, hybrid excitation gives a variable flux while still using the advantage of the permanent magnets for a portion of the flux. This article also looks into some different categories of machines developed for hybrid excitation. The categories are based on the reluctance circuit, the relative geometrical location of the field windings relative to the permanent magnets, or the placement of the excitation system.

양극성 자기장 커플러 구조를 가지는 무선전력전송 시스템의 누설 자기장 저감을 위한 페라이트 격벽 구조 설계

In this study, ferrite wall structures are proposed for reducing leakage magnetic field in a wireless power transfer system with a bipolar magnetic coupler structure in the form of a ferrite core inductor. In the proposed framework, the magnetic field of the transmitting coil remains on the ferrite wall, and the leakage magnetic field is minimized. However, when the magnetic field of the transmitting coil is induced in the ferrite wall, the mutual inductance and coupling coefficient decrease. Therefore, in this paper, the height of the ferrite wall structure is adjusted to minimize the decrease through simulations based on the reluctance circuit model. The performance of the proposed structure was verified through simulations and experiments. The simulation results indicated that the magnetic field leakage effectively decreased with an increase in the height of the ferrite wall structure. The results of experiments demonstrated that although the power transfer efficiency of the framework with the proposed ferrite wall was 3.6 % lower than that of the framework without the ferrite wall, the corresponding leakage magnetic field was reduced by more than 60 %.

Prediction of Power Generation Performance of Wound Rotor Synchronous Generator Using Nonlinear Magnetic Equivalent Circuit Method

This paper presents a nonlinear magnetic equivalent circuit method and an electromagnetic characteristic analysis and verification of a wound rotor synchronous generator (WRSG). The reluctance generated by the stator, rotor, and air gap is subdivided to form a reluctance construction. A nonlinear magnetic equivalent circuit (MEC) for the WRSG is constructed and solved by an iteration method. Moreover, to calculate the inductance of the generator, the reluctance circuit of the d−qaxis is constructed, and the inductance of the generator is obtained using the initial relative permeability of the material. Using the electromagnetic parameters obtained via the MEC method, the power generation characteristics of the generator are predicted. The results of this MEC method are also verified by comparing them with the finite element analysis (FEA) results and experimental results.

Design of a Transverse Flux Permanent Magnet Generator Using a Reluctance Circuit

This work presents an analytical methodology to design a permanent magnet transverse flux generator using a reluctance circuit. Unlike other research, it fully indicates the details to design the rotor, stator, and the air gap of the machine, with all its geometry. In the design section, special considerations to determine the outer diameter of the rotor, and the accompanying pole pitch for the U-cores and I-cores are presented. The proposal of an iterative algorithm using a reluctance circuit to calculate the turns of the armature winding and curved trajectories of flux tubes to model the leakage flux that will allow the synchronous inductance calculation also is presented. The proposed methodology allows determining the performance and the lumped parameters of the generator. Furthermore, it provides evidence that with this design it is possible to select the values of standard voltage for electric generators of this topology. The analytical results of the magnetic flux densities, magnetic flux, lumped parameters, electromotive force, terminal voltage, armature current, power factor, and efficiency are compared with 3D finite element method. Analyzing these results, it is possible to verify the good agreement between them.

Equivalent Magnetic Circuit Reluctance Optimization for Rotor Loss Reduction in Permanent Magnet Synchronous Motor for UPS-FESS

Due to poor heat dissipation of rotor, especially in flywheel energy storage system (FESS) for uninterruptible power supply (UPS), there is a higher risk of irreversible demagnetization by rotor temperature rising. Irreversible demagnetization of permanent magnets by rotor loss always is a critical problem of high-speed permanent magnet synchronous machine (PMSM). The stabilization and efficiency can be increased by reduction of rotor loss. By Finite Element Method simulations with experiment date, the rotor temperature rising of the prototype PMSM mainly comes from rotor loss induced by time harmonic. The distribution and components of prototype rotor loss are given. Rotor loss is analyzed by equivalent magnetic circuit with considering time harmonic magnetomotive force in this paper. According to analysis of rotor loss, this paper presents a method to reduce rotor loss without changing stator structure and winding current. This rotor structure optimization will not affect output performance of PMSM. The method has been proved to be available by the no-load experiment finally. It can greatly reduce the rotor loss in no-load operation when PMSM is driven in high-speed operation zone.

Performance comparison of a spoke‐type PM motor with different permanent magnet shapes and the same magnet volume

This study investigates the characteristics of a spoke-type permanent magnet (PM) motor with one of three magnet shapes, rectangular magnet (RM), trapezoidal magnet (TM), or inverted TM (ITM) in order to compare motor performance for the same magnet volume. The three magnet shapes vary in terms of upper thickness, lower thickness, and width of the magnet. Two-dimensional (2D) finite element method is performed to analyse torque, inductance, core loss, efficiency, and demagnetisation reliability. Advantages and disadvantages of each magnet shape are presented based on the analysis results. The ITM motor shows higher efficiency at its rated load due to the reduced core loss resulting from the decreased armature reaction field coupled with the increased magnetic reluctance circuit of the rotor near the airgap. However, the ITM motor shows lower maximum torque due to the reduced reluctance torque and demagnetisation reliability with a heavy over-current. ITM is thus suitable for applications that require low core loss with small starting torque, e.g. fans, TM is helpful for increasing maximum torque, and RM is appropriate for low-cost applications that require high demagnetisation reliability. Therefore, magnet shape should be carefully considered based on the required specifications of the motor application.

Characterization of a variable reluctance harvester

In our last year's PowerMEMS contribution we presented a proof-of-concept of a variable reluctance harvester for the application in a railroad surveillance system. It was shown that intermittently closing a magnetic circuit could supply power output in the range of mW's. The test setup used showed unwanted energy pickup from the electro motor used. In this paper we present thorough measurements of the reluctance circuit with a compressed air motor to exclude the effects of the above mentioned magnetic stray fields. The effects of eddy currents and moment of inertia on the output power, the optimal coil position on the stators, and effects of different magnetic field strengths are studied. The gap width is set to a fixed value of 14 mm, representing a realistic scenario.

Influence of Rotor-Sleeve Electromagnetic Characteristics on High-Speed Permanent-Magnet Generator

Alloy rotor sleeves are used extensively in high-speed permanent-magnet machines since they could fasten the permanent magnets availably. However, it is inevitable that eddy-current losses will be generated in the sleeve, which may make the permanent magnets overheated. In order to reduce the rotor eddy-current losses, this paper focuses on the influence of the rotor-sleeve electromagnetic characteristics. Taking a high-speed permanent-magnet generator (HSPMG) as an example, the variations of output performance and rotor eddy-current losses were analyzed when the generator adopts the steel sleeve and the copper-iron alloy sleeve, respectively, and therewith, the principles of the variations were exposed. Then, the rotor eddy-current losses were further analyzed when the generator sleeve conductivity was changed. The worst range of the sleeve conductivity was also given, in which the rotor eddy-current losses were the largest. Additionally, the increase of the sleeve permeability could reduce the main magnetic circuit reluctance and improve the operating point of permanent magnets. On the other hand, it can increase the pole-to-pole flux leakage dramatically. So, the generator performance should be analyzed by considering the two factors when the rotor-sleeve permeability was different.

Variable reluctance harvester for applications in railroad monitoring

We present the design, realization, and testing of a variable reluctance energy harvester for the detection of moving ferromagnetic parts, e.g. the wheels of a train while passing over a train passage detector. Measurements were done to determine the output voltage, the energy output per event and the power output with the frequency of the moving ferromagnetic body. Results are compared with finite element analysis (FEA) to estimate the change in magnetic flux and the output voltages. A maximum energy output of 131 μJ per pulse was measured for a simulated condition of a train wheel passing with a speed of 81.5 km/h, which results in a mean output power of 5.9 mW, with a spacing of 10 mm between wheel and the reluctance circuit. This shows that the variable reluctance principle, a well-known method used for numerous sensor applications, is also a comfortable, energy-autonomous and reliable method to detect passing train wheels or other moving ferromagnetic parts, with a simple setup and fairly high useable output power.

Research on the Computational Algorithms for Layer Wound Linear Variable Differential Transformers

According to the algorithms of traditional Linear Variable Differential Transformers (LVDTs) could not represent the performances of the Layer Wound Linear Variable Differential Transformers (Layer Wound LVDTs), new computational algorithms were presented in this paper. Based on magnetic circuit theory, the calculations for the Layer Wound LVDT’s magnetic circuit reluctance, self-inductance, mutual inductance, output voltage and sensitivity are provided. Simulation analysis and experimental tests were used to verify the calculations. The results show that the calculations and equations can accurately express the performance of the Layer Wound LVDTs.

Measurement of the surface field on open magnetic samples by the extrapolation method

Determination of the magnetic field in open magnetic samples is a very difficult problem. Two basic approaches exist—to calculate the field from the applied current or to measure it near the sample surface. Both depend on the quality of sample-yoke contacts that affect the circuit reluctance and the field gradient above the sample. In this work, a method of the surface field determination by extrapolation from the field measurements at different distances from the surface is investigated. The field behavior above the sample is studied for a single C-yoke system numerically and experimentally on magnetically different samples. The influence of the driving coil position, yoke size, air gap, and the sample material on the field gradient is determined. The main factors affecting the resulting accuracy are discussed. The applicability of the method was checked by comparing derivatives of the results, i.e., differential permeability curves measured for different air gaps.

A Wideband Lumped Circuit Model of the Terminal and Internal Electromagnetic Response of Rotating Machine Windings with a Coaxial Insulation System

The polyphase model can be used to simulate the terminal and internal electromagnetic response of, for example, Powerformer/spl trade/: a new power generator. The circuit parameters are based on geometrical and material data. The slot leakage is modeled by means of a reluctance circuit, which is coupled to the electric circuit by means of winding templates. The capacitive current and its losses in the outer semiconducting layer of the cable are modeled with a simplified version of an RC model that has been used previously for other coaxially insulated windings. The eddy current losses were neglected; however, it is presented how they can be included in the model. The simulated frequency and transient response of the lumped circuit is compared with measurements on an 11-MVA/45-kV, 600-r/min hydro Powerformer. With exception of the damping, the agreement is good, qualitatively, up to 100 kHz.

Analysis of skewed slots in induction machines by using 2D finite element method

Electrical machine slots cause an undesirable effect on the m.m.f. wave in the airgap. This effect consists of the occurrence of high frequency harmonics. When the rotor turns, the movement of rotor slots in relation to the stator slots produces cycle variations in the magnetic circuit reluctance. This effect results in high frequency harmonics in the current wave spectrum. Simultaneously high frequency harmonics torques appear. These are known as slot harmonics. To avoid slot harmonics, both in the rotor and in the stator slots, the slots are skewed. When this technique is used, the simplified hypothesis of the finite element model (FEM) in 2D cannot be employed, as it is based on the concept that the magnetic field possesses translational symmetry along the machine shaft. In this paper a method for analysing electrical machines with skewed slots is presented without using the 3D analysis.

Computational algorithms for linear variable differential transformers (LVDTs)

The authors present an equivalent magnetic circuit for a solenoid linear variable differential transformer. Using magnetic circuit theory, the calculations for its magnetic circuit reluctance, mutual inductance, output voltage and sensitivity are provided. Experimental tests are used to verify the calculations.

Eddy current damping due to a linear periodic array of magnetic poles

Eddy currents induced in a conductor moving in a magnetic field produce a retarding force proportional to the heat generated in the material. This principle is utilized in the design of magnetic damping or systems for various applications. The problem considered here is that of a conducting sheet adjacent to a periodic array of magnetic poles. Quasistatic magnetic field solutions are derived for a sheet of arbitrary permeability and thickness moving uniformly at a fixed distance from the poles. The fields inside and outside the conducting sheet are computed over the complete range of dynamic conditions in terms of a relative magnetic penetration length. The field solutions are then employed to calculate the induced current density in the case where the conductor thickness is large in comparison with the axial pole length. The resulting braking power is computed for the purpose of establishing design principles for effective damping. The derived results are applied to two possible situations: a high reluctance magnetic circuit which utilizes a nonpermeable conducting sheet, and a low reluctance circuit which requires a highly permeable conductor. Differences in these two approaches are analyzed with respect to braking power and preferred type of permanent magnets for optimum performance.

Magnetic Shunt for Three Phase Reactors

For three phase shunt reactors to function effectively in EHV power systems the behavior of the circuit reluctance must be known under all operating conditions. Difficulties have occurred in effectively designing electromagnetic circuits with multiple air gaps in shunt reactors. This paper describes design techniques for magnetic shunts which can be applied to three phase shunt reactors resulting in size and weight reduction. Performance characteristics of shunt reactors under imbalanced system conditions are presented and magnetic shunt performance for a 345 kV, 100 MVAR three phase shunt reactor is given.