Air-gap Magnetic Field Research Articles

Dosimetry in MRgPT: Impact of magnetic fields on TLD dose response during proton irradiation.

Proton beam therapy, when integrated with MRI guidance, presents complex dosimetric challenges due to interactions with magnetic fields. Prior research has emphasized the nuanced impact of magnetic fields on dosimetry. For thermoluminescent dosimeters (TLDs) the electron-return effect, alongside small air cavities surrounding the pellets, can lead to nonuniform dose distributions. Future MR-guided proton therapy will require reliable methods for end-to-end tests and dosimetric audits, which so far are often performed using TLDs equipped with phantoms. This implicates the necessity of accounting for theseinteractions. This study investigates the influence of magnetic fields on TLDs at two proton energies, using magnetic field strengths of 0, 0.25, and , aiming to clarify their impact on dose measurementaccuracy. The study was conducted at a synchrotron-based ion beam therapy beam line, enhanced by a resistive dipole magnet for creating magnetic fields up to to simulate MR-guided proton therapy. Individual correction factors were applied for TLD measurements. The impact of air gaps on the TLD signal was evaluated using three dedicated TLD holders with air gaps of 0.1, 0.25, and 0.5 mm surrounding the TLD pellets using the highest available proton energy of . Additionally, the influence of the magnetic field strength on the TLD response was evaluated for two proton energies of and . The study found no statistically significant variation in TLD dose response attributable to changes in the air gap or the presence of magnetic fields. A power analysis indicated an upper limit on a potential change in dose-response as small as 1.5%. The findings suggested that the impact of air gap variations and magnetic field strengths on the TLD response was below the detection threshold of TLD sensitivity. This emphasizes the suitability of TLDs for dose measurement in MR-guided proton therapy, indicating that additional correction factors may not be necessary despite the influence of magneticfields.

Analysis of rotor vibration characteristics of surface mounted permanent magnet synchronous motor under air gap eccentricity fault

Taking a permanent magnet synchronous motor as the research object, the effect of air gap eccentricity fault on the vibration response characteristics of the motor rotor is analyzed through theoretical calculations, numerical simulation and finite element simulation. First, the change of air gap magnetic field under air gap eccentricity fault is analyzed, and then further calculated to obtain the unbalanced magnetic force under air gap fault by the expression of air gap magnetic field, at last, the rotor’s vibration response characteristics under the action of unbalanced electromagnetic force are obtained by the Newmark- β calculation method. Detailed analysis of the effects of eccentricity distance, eccentricity angle and motor pole-pair number on motor rotor vibration. Finally, the synchronous motor eccentricity fault model is built in ANSYS Maxwell electromagnetic simulation software, and the change characteristics of rotor unbalanced magnetic force after eccentricity fault are calculated and the results are consistent with the theoretical calculations.

Thrust ripple suppression analysis of moving-magnet-type linear synchronous motor based on independent coil

In this paper, a novel thrust ripple suppression method for multi-secondary permanent magnet synchronous linear motor based on independent coil structure is proposed. Independent coil structure can realize independent power supply for each coil by changing the driving mode of the coils. Combined with the new power supply strategy, the detent and electromagnetic force fluctuation can be suppressed. Firstly, the cogging and end force of moving-magnet-type linear motor are separated by periodic and vector boundary conditions and harmonic analysis is carried out. An analytical model of air gap magnetic field based on virtual magnetic poles is established to solve the back EMF and electromagnetic force fluctuation of the motor. The generation mechanism and harmonic of electromagnetic force fluctuation are analyzed. A multi-secondary PMLSM based on independent coil is proposed, the principle of suppressing motor thrust ripple is expounded, and the coupling effect between modules is analyzed. Finally, a zero-crossing power supply strategy is proposed. The simulation and experimental results show that multi-secondary independent coil PMLSM can effectively suppress the detent and electromagnetic force fluctuation.

Torque improvement investigation of a double rotor permanent magnet motor based on effective utilization of magnetic field coupling

AbstractIn this paper, a torque improvement method is presented for a double rotor (DR) permanent magnet motor, where the key is to conduct the study based on effective utilization of magnetic field coupling. To facilitate systematic analysis, the magnetomotive force (MMF) and airgap flux density considering magnetic coupling effect are deduced and analysed. It contributes to building the relationships between the output torque caused by magnetic coupling and magnetic field harmonics. By introducing the coupling sensitivity coefficient, the coupling harmonics in the inner and outer airgap magnetic fields are obtained. Then, two coupling harmonic groups are further determined in terms of phase difference and torque contribution, where one of them is required to be enhanced and the other is needed to be reduced. On the basis of this, a comprehensive coupling factor is defined purposely to realise the design and evaluation of the characteristics of coupling harmonic groups. Some motor performances are analysed in details, including the torque, torque ripple, overload capability, and so on. Finally, a prototype motor is manufactured to verify the feasibility of the presented studies of the DR motor.

Multiple resonance of the ferromagnetic thin plate with axial velocity subjected to a harmonic excitation in an air-gap magnetic field

Multiple resonance of the ferromagnetic thin plate with axial velocity subjected to a harmonic excitation in an air-gap magnetic field

Investigation of a novel intensifying-flux hybrid excited permanent magnet machine for electric vehicles

PurposeTo address the issues of the insufficient output torque associated with the application of intensifying-flux permanent magnet (PM) machines in electric vehicles, this paper aims to propose an intensifying-flux hybrid excitation PM machine. It is possible to adjust the air gap magnetic field by adjusting the field current in the excitation winding, thereby increasing the torque output capability and speed range of the machine.Design/methodology/approachFirst, a novel intensifying-flux hybrid excited permanent magnet synchronous machine (IF-HEPMSM) is proposed on the basis of intensifying-flux permanent magnet synchronous machine (IF-PMSM) and an equivalent magnetic circuit model is established. Second, the tooth width and yoke thickness of the machine stator are optimized to ensure the overload capacity of the machine while effectively improving the wide flux regulation range. Furthermore, the electromagnetic characteristics of the IF-HEPMSM are investigated and compared with the IF-PMSM and conventional permanent magnet synchronous machine (PMSM) by using finite element simulations.FindingsThe id of IF-HEPMSM and IF-PMSM is greater than zero low-speed magnetizing current. And the flux-weakening current of the IF-HEPMSM is 18% and 3% smaller than of the conventional PMSM and IF-PMSM.Practical implicationsAiming at the problems of IF-PMSM applied to electric vehicles, this paper proposes an IF-HEPMSM. The air gap magnetic field is adjusted by controlling the current of the excitation winding to improve the reliability of the machine. Therefore, the IF-HEPMSM combines the advantages of high-power density and high efficiency of the PMSM and the controllable magnetic field of the electro-excitation machine, which is of great engineering value when applied in the field of electric vehicles.Originality/valueThe proposed IF-HEPMSM offers better flux regulation capability with electromagnetic characteristics analysis and maps of dq-axis current as compared to IF-PMSM and conventional PMSM. Moreover, the improvement of the torque can make up for the shortcomings of the insufficient torque output capability of the IF-PMSM.

Analytical Calculation of the No-Load Magnetic Field of a Hybrid Excitation Generator

Hybrid excitation generators combine the advantages of electric excitation motors and permanent magnet generators. Focusing on a permanent magnet generator as the object of study, an auxiliary excitation winding is introduced for voltage regulation. The main magnetic field is established by the permanent magnet, and the auxiliary excitation winding provides the magnetic potential required to regulate the air-gap magnetic field. While improving the voltage regulation performance of permanent magnet generators, it also reduces the loss of excitation windings in electrically excited generators. Based on a hybrid excitation generator with dual excitation windings, in the following article, we present a hybrid excitation generator equivalent to a full permanent magnet motor with the minimum output voltage, and an accurate subdomain model of the full permanent magnet motor is established considering the influence of slot opening. By establishing a matrix, the distribution curve of air-gap magnetic density was solved and ultimately verified using finite element analysis. The results of the present study lay a solid foundation for solving the air-gap magnetic density distribution of various parts of the hybrid excitation generator and studying its performance in the future.

Electromagnetic field coupled circuits and open‐loop control of fast starting processes in induction motors

AbstractTo solve the problems of difficulty in speed measurement and low accuracy of speed measurement of induction motor (IM) during fast starting, the electromagnetic field coupling circuit (EFCC) and open‐loop control of IM considering rapid speed change are proposed. First, the EFCC of IM is established through the stator circuit, air gap magnetic field circuit and rotor circuit, and the stator voltage and electromagnetic torque of the fast starting process are deduced from the air gap magnetic density on the basis of constant slip angular velocity, and then the open‐loop control method based on the EFCC is given. Finally, compared with the open‐loop control based on the TEC, the results of simulation and experiment show that the open‐loop control based on the EFCC can follow the acceleration starting more quickly and the starting current is smaller, which is conducive to reducing the cost of the drive.

Improved linear/nonlinear active disturbance rejection switching control for bearingless induction motor

ABSTRACT To achieve high-performance operation control for bearingless induction motor (BIM) systems, an improved linear/nonlinear active disturbance rejection switching control strategy is proposed (SADRC). The key innovation lies in the automatic switching between linear and nonlinear control modes based on system stability and disturbance magnitude. First of all, based on the principle of air-gap magnetic field directional control of the BIM, the first-order and second-order ADRC are designed for the rotating and suspending parts of the BIM, respectively. In addition, the nonlinear active disturbance rejection control (NLADRC) has the shortcoming of tracking performance degradation when the disturbance amplitude is large. Then, an active disturbance rejection controller that can automatically switch between linear and nonlinear based on the stability of the system and the magnitude of the disturbance is designed with the introduction of linear active disturbance rejection control (LADRC). The trigonometric function is introduced to improve the fal function to optimise the abrupt change at the linear interval and the high-frequency chattering phenomenon at the origin. The unknown parameters are rectified using the bandwidth method and the particle swarm algorithm, respectively, to ensure the robustness and adaptiveness of the control strategy. Finally, both simulation and experimental results show that the proposed SADRC strategy not only combines the advantages of linear and nonlinear self-anti-disturbance control but also improves the BIM rotor suspension performance and anti-disturbance capability.

Investigation of Torque and Reduction of Torque Ripples through Assisted-Poles in Low-Speed, High-Torque Density Spoke-Type PMSMs

In this article, rotor designs utilizing assisted-poles are investigated for a high-torque density spoke-type permanent magnet synchronous machine (PMSM) with fractional slot concentrated winding (FSCW) to explore the rich air-gap magnetic field harmonics and torque generation mechanism. Due to their higher average torque output, spoke-type PMSMs with FSCW are increasingly used in high-torque density applications. However, slot harmonics generate torque ripples that are difficult to eliminate in FSCW spoke-type PMSMs. Removing slot harmonics from the stator or winding results in a large drop in torque since their winding factors are identical to those of the main harmonic. Therefore, rotor designs having assisted-poles (symmetrical and asymmetrical) are investigated in this work to mitigate slot harmonics and minimize torque ripples. Firstly, the air-gap flux density is analyzed for the machines having assisted-poles, and a model of interaction between the stator and rotor-MMF harmonics is created and validated through Finite element analysis (FEA) to analyze the torque production mechanism. In addition, an analytical relationship between the assisted-poles’ dimensions and the generated torque harmonics is proposed. Furthermore, a generalized torque ripple reduction concept for the FSCW spoke-type PMSM having asymmetrically designed assisted-poles is presented. The proposed design and optimization method are validated through analytical calculations and FEA simulations, and a brief comparative analysis is presented for the analyzed machine prototypes. It has been established that the machine designed by applying the proposed asymmetrical assisted-poles can achieve a reduction in torque ripples while also significantly lowering cogging torque in comparison to the conventional spoke-type PMSMs and other spoke-type PMSMs with rotor having symmetrical assisted-poles.

Analysis and Optimization Design of U-Shaped Ironless Permanent Magnet Linear Synchronous Motor

The working speed of the U-shaped ironless permanent magnet linear synchronous motor is determined by the frequency and pole pitch. When the motor’s working speed is required to be constant, different combinations of frequency and pole pitch can be chosen. This article mainly discusses the influence of the pole pitch on the motor performance when other parameters are kept constant. First, the magnetic field of the motor permanent magnet is analyzed using the equivalent magnetizing current method to discuss the relationship between the pole pitch and the motor air gap magnetic field. Then, the finite element method is used to analyze the influence of the pole pitch on the motor air gap magnetic field, transverse edge effect, and electromagnetic thrust considering the saturation effect of the magnetic yoke. The research shows that under the conditions of constant motor basic structural parameters and speed, and the same amount of permanent magnet material, both the air gap magnetic density and the motor thrust line density have maximum values as the pole pitch changes. The research results have certain guiding significance for the design of this type of motor.

The influence of ITSF on vibration of high voltage Line-Start permanent magnet synchronous motor

PurposeThe purpose of this paper is to present the influence of inter-turn short circuit faults (ITSF) on electromagnetic vibration in high-voltage line-starting permanent magnet synchronous motor (HVLSPMSMS).Design/methodology/approachIn this paper, the ampere–conductor wave model of HVLSPMSM after ITSF is established. Second, a mathematical model of the magnetic field after ITSF is established, and the influence law of the ITSF on the air-gap magnetic field is analyzed. Further, the mathematical expression of the electromagnetic force density is established based on the Maxwell tensor method. The impact of HVLSPMSM torque ripple frequency, radial electromagnetic force spatial–temporal distribution and rotor unbalanced magnetic tension force by ITSF is revealed. Finally, the electromagnetic–mechanical coupling model of HVLSPMSM is established, and the vibration spectra of the motor with different degrees of ITSF are solved by numerical calculation.FindingsIn this study, it is found that the 2np order flux density harmonics and (2 N + 1) p order electromagnetic forces are not generated when ITSF occurs in HVLSPMSM.Originality/valueBy analyzing the multi-harmonics of HVLSPMSM after ITSF, this paper provides a reliable method for troubleshooting from the perspective of vibration and torque fluctuation and rotor unbalanced electromagnetic force.

Magnetic Field Distortion Analysis and Suppression for the Minimum Unit Winding Segmented Moving-Magnet Linear Motor

Segmented power supply is frequently utilized for long-stroke moving-magnet linear synchronous motors to lessen the issue of large loss and heating brought on by long-stroke power supply. However, the driving mode of partial excitation in segmented power supply brings some problems, such as unbalanced parameters of three-phase, the transient inductance of winding changing with secondary position, and distortion of armature reaction magnetic field. This paper proposes a new topology with the minimum unit winding segmented to solve the problems of unbalanced inductance parameters and distortion of armature reaction magnetic field in winding segmented permanent magnet linear synchronous motors (WS-PMLSM). An analytical model of inductance distortion in the end coils of a moving-magnet PMLSM is established and compared with the non-end coil inductance to summarize the mechanism of inductance unbalance in WS-PMLSM. Based on the model of winding transient inductance changing with secondary position, the changing law of transient inductance is expounded. An analytical method of the air gap magnetic field based on virtual winding is proposed, and the formation mechanism of magnetic field distortion caused by partial excitation is revealed. Aiming at the topology of the minimum unit winding segmented moving-magnet PMLSM, an optimized drive strategy of n+3 is proposed.

Air gap flux density measurement of PMSLM based on TMR sensing external stray magnetic field and CNN-LSTM

This paper presents a new non-invasive air gap flux density measurement method for permanent magnet synchronous linear motor (PMSLM) using tunneling magnetoresistance (TMR) sensor and convolutional neural networks-long short-term memory (CNN-LSTM) regression modeling. First, the analytical and finite element models of the air gap magnetic field of PMSLM are established as the data basis. Second, TMR sensor is used to measure the external stray magnetic density. Gramian Angular Field method combined with image similarity matching technology are used to obtain the optimal measurement position of the TMR sensor. Then, a new deep learning regression method as CNN-LSTM is introduced to establish a high-precision mapping model to realize non-invasive high-precision measurement of the air gap magnetic density by “substituting external to internal.” Finally, PMSLM prototype experimental platform with TMR sensor hardware acquisition circuit is built. Comparison confirmatory experiments with Gauss meter can verify the effectiveness and superiority of the proposed method.

Optimization design of a new hybrid magnetic circuit motor

The combination of permanent magnets and electrically excited windings creates an air gap magnetic field. The development of a hybrid magnetic circuit motor with an adjustable magnetic field is of great significance. This article introduces a hybrid magnetic circuit motor design that combines salient pole electromagnetic and permanent magnets. A tubular magnetic barrier has been designed to reduce inter-pole leakage and enhance the usage rate of permanent magnets in the hybrid magnetic circuit motor. The optimum eccentricity of the rotor has been accurately designed, resulting in an improved sinusoidal distribution of the air gap magnetic density waveform. An analysis of the static composite magnetic field under various excitation currents has been conducted, showcasing the capability of the hybrid magnetic circuit motor to stably adjust the air gap flux density level and output torque. A prototype has undergone comprehensive trial production and testing, conclusively confirming the machine’s superior output performance.

Five-phase space vector carrier-based PWM for third harmonic injection

Five-phase AC drives allow a third harmonic voltage to be fed into the stator winding – in addition to the fundamental voltage – to generate a third harmonic magnetic air gap field. This allows the generation of an additional small constant torque. Furthermore, the undesirable saturation harmonics that occur with saturated iron can be compensated. The desired third harmonic voltage is commonly generated via time-consuming space vector PWM algorithms, which are not well-suited for real-time application, or via look-up tables, which require an increased storage capacity. In our case, the desired third harmonic voltage is generated in the five-phase voltages by adding a non-sinusoidal zero-sequence voltage with five times the fundamental frequency to the fundamental voltage reference signals in carrier-based pulse width modulation (PWM) with a constant switching frequency. This is equivalent to a space vector PWM method (SVPWM) and avoids a significantly high calculation effort. The PWM algorithm programmed in MATLAB in real time allows the fast generation of a third harmonic voltage per phase with freely definable amplitude and phase shift without requiring a lot of storage capacity.

Nonlinear Dynamical Modeling and Free Vibration of Functionally Graded Cylindrical Shell in Air-gap Magnetic and Thermal Fields

Nonlinear dynamical modeling and free vibration of ferromagnetic functionally graded (FG) cylindrical shell in air-gap magnetic and thermal fields are investigated in this work. The shell is surrounded by an armature, and the air-gap layer generated by physical isolation exists between the two structures. The air-gap magnetic field in this space is generated by the armature, which induces the nonlinear magnetization of ferromagnetic materials. The nonlinear heat conduction characteristics along the shell thickness are considered. Under the theory framework for dual-nonlinear magneto-thermal effect, the magneto-thermoelastic dynamical model is established using Hamilton principle. The discrete governing equations and the natural frequency expression separately are derived by Galerkin and Krylov-Bogoliubov-Mitropolski (KBM) methods. Subsequently, the natural frequency characteristics under different parameter conditions are systematically analyzed. The results indicate that magnetic potential, initial air-gap thickness, and volume fraction index have a significant impact on natural frequencies. Temperature has a complex effect on natural frequencies corresponding to different circumferential wave numbers.

Design and harmonic analysis of single winding bearingless PM synchronous motor with high winding coefficient

Compared with double-winding bearingless permanent magnet synchronous motor, single-winding bearingless permanent magnet synchronous motor (SBPMSM) has the advantages of low copper loss and low failure rate. However, if the slot-pole combination of SBPMSM is not reasonably selected, the winding coefficient will be reduced, and even many advantages of the single-winding structure will be offset. In this paper, a single-winding design method based on magnetomotive force (MMF) star diagram is proposed, which can ensure high winding coefficient. The design process of the proposed single winding structure is introduced. This method can match the appropriate number of stator slots according to the number of rotor poles, and the winding phase separation design can be realized by reversing the slot number transposition. The mathematical models of the suspension force and torque of the bearingless permanent magnet synchronous motor are derived considering the magnetic field harmonics, and the 6-slot/2-pole SBPMSM and 18-slot/8-pole SBPMSM are taken as examples to analyze the magnetic field. The finite element simulation models of 6-slot/2-pole SBPMSM and 18-slot/8-pole SBPMSM are built and analyzed. Through the analysis of electromagnetic torque, suspension force and air-gap magnetic field under different magnetic fields, the general rules of main torque fluctuation and suspension force fluctuation are summarized.

Winding-MMF-based design and investigation of dual-winding hybrid-tooth vernier permanent magnet motor with reduced torque ripple and improved power factor

In this paper, in order to further reduce torque ripple and improve power factor, a new vernier permanent magnet motor is proposed, in which the design concept of dual-winding hybrid-tooth configuration is incorporated. In order to clarify motor torque ripple and power factor, the winding-magnetomotive-force-based design and analysis method is proposed, in which harmonic characteristics are considered as key factors during the magnetic field modulation process. The relationship between harmonics generated by winding MMF, torque ripple, and power factor are investigated. In addition, the split-tooth vernier permanent magnet motor is also investigated as a referenced motor. Detailed comparisons between the DWHT-VPM motor and ST-VPM motor are carried out, including air gap magnetic field, torque, and power factor. Both theoretical and simulation results verify the reasonability of the proposed DWHT-VPM motor, and the effectiveness of the proposed winding-MMF-based analysis method, which provide a new potential research path for the design and analysis of flux modulation motors.

Characterization of linear motor flux pump using H-formulation

H-formulation is an effective method for electromagnetic simulation analysis of superconductors. This paper innovatively uses H-formulation to simulate and analyze the operation characteristics of magnetic flux pump operating in linear-motor pattern. Via COMSOL Multiphysics, this paper establishes a two-dimensional electrical equipment simulation model that comprehensively compares excitation conditions of triangular and trapezoidal current waves to investigate the effects of the working excitation waveforms’ frequency and amplitude on the operating features of the equipment. The following operation control laws are revealed: the current amplitude has a linear control effect on the mean value of superconductor surface electric field and the average amount of air-slot density of magnetic flux, the current frequency has no effect on the air-gap magnetic field waveform, and the regulation effect of the excitation frequency on the average value of superconductor surface strength of electric field is related to the waveforms. Finally, the equivalent circuit of the pumping model is established, and two interrelated L-R equivalent circuits are designed by quadratic substitution, and the final pumping current reaches 43A.