Harmonic Magnetic Flux Research Articles

High-Performance Vernier Machines with Halbach Array Permanent Magnets for Direct Drive Applications

This paper investigates the performance enhancements of permanent magnet Vernier machines (PMVMs) that can be achieved using a new structure of Halbach array permanent magnets (HAPMs) for a direct-drive motorcycle application. To start with, size and design specifications of the electric machine are determined based on the assumed acceleration and drive cycle performance of a motorcycle. Then, five-segment Halbach array permanent magnet Vernier machines (HAPMVMs) with two different slot/pole combinations (24 s/44 p and 12 s/20 p) are suggested and optimized to achieve a high torque density with an acceptable power factor while maintaining a low torque ripple. Two selected designs from optimizations are investigated in the full speed range considering power factor and efficiency maps. Consequently, in order to demonstrate the effectiveness of the proposed five-HAPM structure, the same optimization methods are repeated with three-segment HAPMs as well as with single-piece PMs. The comparisons show a great enhancement in torque and power factor achieved with the use of five HAPMs. For instance, for 22 s/44 p topology, generated torque doubles with the use of five-segment PMs compared to single-segment PMs. Finally, the harmonics of magnetic flux density in the airgap of PMVMs and HAPMVMs are compared and investigated to reveal the reasons behind the superiority of VMs with HAPMs.

Design and Optimization of the Low-Frequency Metasurface Shield for Wireless Power Transfer System

This article presents an optimized kilohertz (kHz) shielding metasurface (MTS) for wireless power transfer (WPT) system. Recently, the working frequencies of reported MTSs are concentrated in the megahertz range, which limits its application in low-frequency WPT system. Accordingly, the model of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times 3$ </tex-math></inline-formula> matrix MTS shield (M-MTSS) with resonance frequencies of 65 and 190 kHz is proposed to eliminate the influence of fundamental (85 kHz) and harmonic (255 kHz) leakage magnetic flux density on the human body, respectively. A circuit model is established to consider all coupling of the system structure. Meanwhile, an exhaustive fitting analysis is carried out on the electromagnetic parameters of the application model. The winding of the M-MTSS is optimized to achieve a tradeoff between the efficiency and the magnetic field. Moreover, the calculated magnetic flux density distribution and the principle of the M-MTSS are illustrated. Finally, a test platform is set up to evaluate the performance of suppressing the emission of magnetic flux density. The experimental results showed that the magnetic flux of the fundamental and harmonic is reduced in the entire plane. These results verify the feasibility of the proposed method.

Calculation of Magnetic Flux Density Harmonics in the Vicinity of Overhead Lines

This paper considers the method for the calculation of magnetic flux density in the vicinity of overhead distribution lines which takes into account the higher current harmonics. This method is based on the Biot–Savart law and the complex image method. The considered method calculates the values of the magnetic flux density for each harmonic component of the current separately at all points of interest (usually lateral profile). In this way, it is possible to determine the contributions of individual harmonic components of the current intensity to the total value of magnetic flux density. Based on the contributions of individual harmonic components, the total (resultant) value of the magnetic flux density at points of interest is determined. Validation of the computational method is carried out by comparison of the results obtained by the considered calculation method with measurement results. Furthermore, the application of the calculation method was demonstrated by calculating magnetic flux density harmonics in the vicinity of two overhead distribution lines of typical phase conductor arrangements.

Modeling anisotropic magnetic hysteresis properties with vector stop model by using finite element method

PurposeThis paper aims to use a history-dependent vector stop hysteresis model incorporated into a two dimensional finite elements (FE) simulation environment to solve the magnetic field problems in electrical machines. The vector stop hysteresis model is valid for representing the anisotropic magnetization characteristics of electrical steel sheets. Comparisons of the simulated results with measurements show that the model is well appropriate for the simulation of electrical machines with alternating, rotating and harmonic magnetic flux densities.Design/methodology/approachThe anisotropy of the permeability of an electrical steel sheet can be represented by integrating anhysteretic surfaces into the elastic element of a vector hysteresis stop model. The parameters of the vector stop hysteresis model were identified by minimizing the errors between the simulated results and measurements. In this paper, a damped Newton method is applied to solve the nonlinear problem, which ensures a robust convergence of the finite elements simulation with vector stop hysteresis model.FindingsAnalyzing the measurements of the electrical steel sheets sample obtained from a rotational single sheet tester shows the importance to consider the anisotropic and saturation behavior of the material. Comparing the calculated and measured data corroborates the hypothesis that the presented energy-based vector stop hysteresis model is able to represent these magnetic properties appropriately. To ensure a unique way of hysteresis loops during finite elements simulation, the memory of the vector stop hysteresis model from last time step is kept unchanged during the Newton iterations.Originality/valueThe results of this work demonstrates that the presented vector hysteresis stop model allows simulation of vector hysteresis effects of electrical steel sheets in electrical machines with a limited amount of measurements. The essential properties of the electrical steel sheets, such as phase shifts, the anisotropy of magnetizations and the magnetization characteristics by alternating, rotating, harmonic magnetization types, can be accurately represented.

Study for Influence of Harmonic Magnetic Fields on Vibration Properties of Core of Anode Saturable Reactor in HVDC Converter Valve System

The cores of anode saturated reactor (ASR) are the main vibration source of the HVDC converter valve system. The ASR is excited with an impulse voltage, which contains many harmonic components, and the magnetostriction of cores is usually the main reason of the ASR vibration. Therefore it is significant to study the influence of the harmonic on the vibration of core of ASR. In this paper, the magneto-mechanical coupling model is established based on the magnetostriction theory and the expression of vibration acceleration in the presence of third harmonic is derived. The vibration test platform is built to test the core's vibration acceleration. The magnetic and magnetostrictive properties of silicon steel sheet under different working conditions are measured. The three-dimensional simulation model of the core is established, and the vibration acceleration under different magnetic flux density is calculated. The comparison of the experiment and simulation results shows the rationality of the magneto-mechanical coupling model. The influence of third harmonic magnetic flux density on vibration is studied by changing the phase of the third harmonic magnetic flux density and the ratio of the third harmonic magnetic flux density to the fundamental magnetic flux density. Both the calculated and measured results show that the third harmonic magnetic flux density affects the vibration acceleration according to the double-frequency components of the third harmonic, as well the sum-frequency and difference-frequency components of the third harmonic and fundamental frequency.

Experimental and Comparative Study of Rotor Vibrations of Permanent Magnet Machines with Two Different Fractional Pole/Slot Combinations

This study deals with the noise, vibration, and harshness (NVH) characteristic analysis of permanent magnet synchronous motors (PMSMs) for electrical machines, such as electrically driven tools that are used in industries. An improved NVH design is needed for application to industrial tools. In general, the electromagnetic NVH characteristics of PMSMs are classified into electromagnetic excitation sources, such as total harmonic distortion of EMF, torque pulsation, magnetic pull force, and unbalanced magnetic force (UMF). This study compares the vibration and noise generated by fractional pole/slot combinations. In PMSMs with fractional pole/slot combinations, UMF is an important NVH source. PMSMs generate UMF because of armature reaction fields based on the pole/slot combinations and harmonics of magnetic flux density. UMF was derived using the finite element method, and the rotor vibration analysis was performed using electromagnetic mechanical coupling analysis. The analysis results and the effect of electromagnetic excitation characteristics on the rotor vibration of the PMSMs were compared and analyzed.

Controlling airgap magnetic flux density harmonics in synchronous machines using field current injection

In this paper, a method to control the harmonic content of the magnetic flux density in the airgap of a synchronous machine is presented. Voltage harmonics in one phase as well as the exciting magnetic forces can be affected. Switched power electronics were used to provide the field current to a synchronous machine, the control added specific current harmonics to the DC field current in order to minimize either voltage harmonics or magnetic forces. The method is verified and compared with simulations and experiments on an existing electrical machine.

Development of spoke-type IPM magnetic gear

Magnetic gears can change output-torque and -speed without any mechanical contacts. Therefore, they have a low acoustic noise and vibration, and their maintainability and reliability are high. Especially, a flux-modulated type magnetic gear is expected to be put into practical use because its torque density is higher than that of other magnetic gears. For the practical use, further improvement of torque and losses is important, especially, reduction of eddy current loss in permanent magnets (PMs) due to asynchronous harmonic magnetic fluxes is necessary. This paper investigates an interior permanent magnet (IPM) structure to improve the efficiency by reducing the eddy current loss in PMs. In addition, this paper presents a method for increasing torque of the IPM magnetic gear by changing a position of magnetic-bridge.

A controllable inductive power filtering system: modeling, analysis and control design

This paper presents a controllable inductive power filtering (CIPF) system with the novel filtering mechanism. Due to the zero-impedance design of the power transformer, the harmonic magnetic flux between the secondary load winding and the customized filtering winding can be balanced each other. Hence, the contaminated area of harmonics is reduced. The addition of the active filter contributes to further improve the filtering performance with the task of harmonic isolation between the power grid and the load. First, the three-phase unified equivalent circuit model and the mathematical model are given out at the harmonic domain. Based on the deduced transfer matrix, the filtering evaluation criterion of CIPF system is established, and the filtering principle is revealed, as well. According to the special operational law, an improved virtual impedance control strategy is designed to prevent the potential harmonic amplification, and the relationship between the phase/magnitude of the virtual impedance and the filtering performance is discussed. Finally, the experimental results based on the laboratory scaled prototype show the validity of the CIPF system with improved virtual impedance control.

Improved series active power filter with fundamental and harmonic magnetic flux hybrid compensation

The filtering performance of series hybrid active power filter (SHAPF) based on fundamental magnetic flux compensation positively correlates with the magnetising impedance of the transformer. However, excessive magnetising impedance will decrease reliability while increasing capacity and costs of the whole system. In order to reduce the magnetising impedance while ensuring the same filtering performance of SHAPF, an improved series active power filter (ISAPF) with fundamental and harmonics magnetic flux hybrid control is presented here. The equivalent impedances to fundamental and harmonics in ISAPF are firstly analysed to explain the principle of ‘harmonic isolation’. Then the range of compensation coefficients is investigated in detail based on the complete control block diagram and the open-loop function of ISAPF. Moreover, stability conditions of an overall system with non-linear loads are deduced. Finally, a set of single-phase prototype with two kinds of special transformer has been constructed; the related experiments results showed that ISAPF can ensure the filtering performance while applying a transformer with smaller capacity, thus resulting in the reduction in capacity and the costs while increasing the reliability.

Vibration and noise characteristics of the inductive filtering converter transformer

Harmonic magnetic fluxes in transformer's core and harmonic currents in grid-side winding can be restrained via the inductive filtering technology. Vibration and abating noise of the core caused by the harmonic magnetic fluxes are controlled at the source, and has a good effect in reducing vibration and abating noise of the grid-side winding. Vibration and noise characteristics of the inductive filtering converter transformer are tested under load. The experimental results verify this theory.

Noise characteristics of the new converter transformer under DC bias

Harmonic magnetic fluxes in transformer's core and harmonic currents in grid-side winding can be restrained via the inductive filtering technology, and running noise of the transformer is reduced at the source. The A-weighted sound levels of the measuring points are measured under DC bias. The noise test results verify this theory. When the fully-tuned filters matched with the new converter transformer are inputted and not inputted, the noise response curves of the measured points are compared. The fitting coefficients of the noise values at 1250 and 1600 Hz with the unbalance degrees of the trigger angle are obtained.

Investigation Into Loss Reduced Rotor Slot Structure by Analyzing Local Behaviors of Harmonic Magnetic Fluxes in Inverter-Fed Induction Motor

We analyzed the local behaviors of both time and space harmonic magnetic fluxes in this research to improve the efficiency of inverter-fed induction motors. As a result, we clarified that: the magnetic flux of time harmonics passes in parallel through rotor bars and the magnetic flux of space harmonics passes radially through the rotor bars from the delay side in the direction of rotation. We propose a new rotor slot structure to reduce harmonic losses by taking these results into consideration. We also manufactured a prototype that was applied to the proposed structure of rotor slots, and measured motor losses. Consequently, although the current was increased by 2%, the total loss under inverter driven condition in induction motor was reduced by 20% with the proposed structure under the equal output power of 1.1 MW.

A new approach for modeling of magnetorheological elastomers

This article presents a novel model to portray the behavior of magnetorheological elastomer in oscillatory shear test. The dynamic behavior of an isotropic magnetorheological elastomer is experimentally investigated at different input conditions. A modified Kelvin–Voigt viscoelastic model is developed to describe relationships between shear stress and shear strain of magnetorheological elastomers based on input frequency, shear strain, and magnetic flux density. Unlike the previous models of magnetorheological elastomers, the coefficients of this model, calculated by nonlinear regression method, are constant at various harmonic shear loads and different magnetic flux densities. The results show that the new phenomenological model can effectively predict the viscoelastic behavior of magnetorheological elastomers. Also, the results demonstrate that the trend of shear storage modulus of magnetorheological elastomer based on the frequency is nonlinear from 0.1 to 8 Hz, which is predicted by the present model. The proposed model is beneficial to simulate vibration control strategies in magnetorheological elastomer base devices under harmonic shear loadings.

An Industrial DC Power Supply System Based on an Inductive Filtering Method

This paper proposes a new direct current (dc) power supply system based on an inductive filtering method for one industrial dc load. The operating mechanism of the new inductive filtering method is analyzed, and then, the harmonic model and the equivalent model are established. Moreover, the impedance conditions for the implementation of the inductive filtering method are presented, and the influence of the filtering loop's impedance on the filtering performance is clarified. Both the simulation and the experimental study on one practical inductive-filtering-based industrial dc supply system for chemical electrolysis are used to validate the theoretical analysis. The research results show that the inductive filtering method not only greatly reduces the harmonic magnetic flux in the rectifier transformer but also prevents harmonic currents from flowing into the primary (grid) winding of the rectifier transformer. It presents good filtering and reactive power compensating performances to public networks and also increases the operating efficiency of the industrial dc power supply system itself.

表面磁石型磁気減速機の伝達トルク特性に関する研究

Magnetic gears have some advantages such as low mechanical loss and maintenance-free operation that are not observed in conventional mechanical gears. In addition, magnetic gears have inherent overload protection. Therefore, magnetic gears are expected to be used in special applications; for example, they can be used in a joint of a humanoid robot. Recently, various types of new magnetic gears have been proposed. Among these new gears, a surface-permanent-magnet-type (SPM-type) magnetic gear employing harmonic magnetic flux has gained attention because of its high transmission torque density, though it has a complex structure with multipole magnets. Some studies on an SPM-type magnetic gear have been carried out, but there are few papers on cogging torque. This paper describes the transmission torque characteristics of an SPM-type magnetic gear. The operating principle and the transmission torque under synchronous operation are formulated in accordance with the gear ratio. High orders of the cogging torque are computed by employing the 3-D finite element method, and the validity of the analysis is verified by carrying out measurements on a prototype. Furthermore, a method for reducing the cogging torque is discussed.

2D harmonic analysis of the cogging torque in synchronous permanent magnet machines

Presents an approach to determine sources of cogging torque harmonics in permanent magnet electrical machines on the basis of variations of air‐gap magnetic flux density with time and space. The magnetic flux density is determined from the two‐dimensional (2D) finite element model and decomposed into the double Fourier series through the 2D fast Fourier transform (FFT). The real trigonometric form of the Fourier series is used for the purpose to identify those space and time harmonics of magnetic flux density whose involvement in the cogging torque is the greatest relative contribution. Carries out calculations for a symmetric permanent magnet brushless machine for several rotor eccentricities and imbalances.

Brushless DC Motor without Stator Slots

The authors propose the new brushless DC motor without stator slots as a servo motor. The conventional motor has a lots of stator slots, and the stator coils are placed in the slots. In the new motor, the stator has no slots. Accordingly, the stator coils are fixed along the inside of the stator cores, and the coils are molded by a thermosetting resin. Therefore, the magnetic airgap is very large. Generally, as leakage fluxes increase in response to the size of the airgap, output torque decreases. But the new motor improves characteristics of torque by using a new magnet having high magnetic energy. And the new motor without slot does not produce cogging torque and electromagnetic noise and torque ripples of harmonic magnetic fluxes caused by stator slots. In this paper, calculated characteristics analyzed by flux density using FEM and experimental result is described. It is confirmed that the analyzed results agreed with experimental results with good accuracy. In the experimental results using a 4-pole 0.4kW test motor and high-efficiency drive inverter with power factor control, the motor efficiency is about 83.7%, the motor power factor is about 96.9%, and cogging torque is zero.

Considerations on Large Turbine Generator Electromagnetic Characteristics for an SFC Start.

This paper describes large turbine generator electromagnetic characteristics, considering harmonic components of the armature current, for a static frequency converter (SFC) start. Namely, the magnetomotive force for an SFC start is calculated, and frequency characteristics of higher harmonic magnetic flux and currents in a field circuit and a damper circuit are considered. Then the pulsating torque is analyzed, and the effects of the damper circuit toward the pulsating torque are considered. The results are as follows.(1) When the fundamental frequency is more than about one hertz, the higher harmonic magnetic flux decrease, and vibration due to the electromagnetic force is insignificant.(2) The eddy currents in each damper bar differ with each slot position and each angle between the armature fundamental magnetomotive force and the field fundamental magnetomotive force.(3) The torque waveforms differ for each fundamental frequency.

Quantitative Study on the Electromagnetic Vibration in a Squirrel-Cage Induction Motor.

1.Introduction Squirrel-cage induction motors have been widely used as constant-speed motors in many industrial applications for a long time. However, high performance speed control technology has advanced in recent times, with the result that vector-controlled squirrel-cage induction motors have been widely applied to variable speed driving systems (1),(2). Together with this increase in the use of induction motors have come increased requirements for much lower vibration and acoustic noise levels. As a result, a great deal of research on methods of reduction for both acoustic noise and vibration has been published (3)-(5). In squirrel-cage induction motors, the airgap magnetic flux density includes many harmonic components (other than fundamental component) due to harmonic magnetomotive force caused by winding and harmonic airgap permeance caused by slot opening. Harmonic torque, loss(6) and radially-directed electromagnetic forces (mentioned in this paper) are generated due to interaction of the airgap with the harmonic magnetic flux density. It is not the probability of harm, but rather the scale of the harm potentially due to these harmonics that makes them worthy of study. Therefore, it is necessary to quantitatively determine the factors which affect these harmonics (and their associated vibration and acoustic noise levels) with which to base design improvements for lower-noise squirrel-cage induction motors. In this paper, concept for quantitative study of the radially-directed electromagnetic forces which cause both vibration and acoustic noise will be offered and quantitative analytical expression will be shown. We will show the main factors causing the generation of these radially-directed electromagnetic forces, at the same time we shall describe how to perform quantitative calculations with respect to electromagnetic forces, vibration levels, and flexural vibration of the stator core. Then, the utility of the theoretical models will be evaluated by comparing calculated theoretical values against actual measured values. These include: variations in amplitude of vibrations in the stator core vibrations due to variations in, for example, supply frequency and supply voltage.