Axial Air Gap Research Articles

Influence of Dual Air Gaps on Flux–Torque Regulation Hybrid Excitation Machine with Axial–Radial Magnetic Circuit

In this paper, a flux–torque regulation hybrid excitation machine (FTRHEM) with axial–radial dual air gaps, which can increase torque and regulate magnetic flux by changing the exciting current, is studied. Dual air gaps have a huge impact on the magnetic flux and additional torque. The effect of the air gap reluctances on the magnetic flux of the machine is obtained by establishing equivalent magnetic network models, which show that the dual air gaps are the key component in the axial–radial magnetic circuit. This study examines the flux regulation ability and the enhanced torque performance of an FTRHEM with dual air gaps. The mechanism by which the dual air gaps affect the machine’s magnetic field is clarified, and the constraints and relationships between the dual air gaps are explained, offering a theoretical foundation for future machine optimization. As the axial air gap decreases from 0.95 mm to 0.35 mm, the flux regulation capability improves from 15.44% to 26.51%, while the additional torque increases by 40.77%. Ultimately, prototypes are manufactured for experimental testing to validate the viability of the structure and the accuracy of the FEA for the FTRHEM featuring an axial–radial magnetic circuit.

Analysis of Disc Motor with Asymmetrical Conducting Rotor

The homogenous disc rotor construction allows higher rotational speeds and relatively higher power densities. This paper deals with a two-phase induction motor with homogenous disc rotor construction. The field analysis of an axial flux disk motor with a conducting disc rotor is carried out, using a new application of the Maxwell's field equations. A Suggested model is introduced to establish the geometry of motor construction and to enable the derivation of the field system differential equations. A new strategy is applied for the boundary conditions to complete the field solution. This is carried out by determining the complex integration constants. The current density is completely derived with it is components (the radial, the tangential current density and the axial air gap flux density). The performance of the flux density, rotor current components and the torque-slip characteristics are determined with and without disk rotor ends. The effects of the disk rotor design data and the rotor asymmetry on the motor performance are investigated.

Impact of 3D air gap eccentricity on winding insulation temperature characteristic in PMSG

The static air gap eccentricity is one of the prevalent faults in permanent magnet synchronous generators. In previous studies, the variation of magnetic flux density, stator current and vibration have been studied mostly. However, the temperature characteristic of winding insulation under 3D static air gap eccentricity fault is rarely investigated. As a supplement, this paper comprehensively analyzes the influence of radial static air gap eccentricity, axial static air gap eccentricity and the combined static air gap eccentricity (radial static air gap eccentricity and axial static air gap eccentricity) fault on the winding insulation thermal response. The whole work is based on not only the loss of core and windings but also the temperature rise of the winding insulation, which is carried out through theoretical analysis, finite element calculation, and experiment verification. It is shown that radial static air gap eccentricity will increase the winding insulation temperature whatever in singe radial static air gap eccentricity or combined static air gap eccentricity, while axial static air gap eccentricity has the opposite effect. Specifically, the winding insulation temperature in radial static air gap eccentricity 0.1 mm, 0.2 mm and 0.3 mm cases are 57.18℃, 59.10℃ and 61.04℃, respectively, which is 3.29℃, 5.21℃ and 7.15℃ higher than that under normal condition. However, under axial static air gap eccentricity, winding insulation temperature will decrease by 1.84℃, 4.11℃ and 5.9℃, respectively. When axial static air gap eccentricity is unchanged and radial static air gap eccentricity is increased, the winding insulation temperature will increase by 1.5℃ and 3.23℃, respectively. On the contrary, when radial static air gap eccentricity is unchanged and axial static air gap eccentricity increases, the winding insulation temperature decreases by 2.54℃ and 5.66℃, respectively. The end part and the join between the end and line parts of the winding insulation are the most dangerous positions to suffer from static thermal wear.

Numerical analysis of a flywheel energy storage system for low carbon powertrain applications

Flywheel energy storage has emerged as a viable energy storage technology in recent years due to its large instantaneous power and high energy density. Flywheel offers an onboard energy recovery and storage system which is durable, efficient, and environmentally friendly. The flywheel and the housing surface temperatures can be considerably influenced by the friction induced windage losses associated with non-vented airflows in the air-gap of a high-speed rotating flywheel. Many engineering applications have been interested in the features of radial and axial air-gap flows. The flow within the annulus of a flywheel is extremely complicated. This study has developed a numerical technique using ANSYS Fluent solver to model turbulent Taylor vortices formation and oscillation for thermal performance evaluation, and windage loss prediction of high-speed flywheel storage systems, operating under atmospheric and partial vacuum conditions. The numerical model has been experimentally validated with good accuracy. Several rotational speeds and pressures were investigated experimentally and numerically. The results demonstrated that a 40 % reduction in the operating pressure can reduce the flywheel surface temperature and windage loss by 20 % and 30 %, respectively. Consequently, a partial vacuum environment can achieve better energy conversion efficiencies provided an appropriate bearing seal is achieved to maintain the pressure inside the housing. The investigated flywheel energy storage system can reduce the fuel consumption of an average light-duty vehicle in the UK by 22 % and decrease CO2 emission by 390 kg annually.

A novel axial air‐gap transverse flux switching PM generator: Design, simulation and prototyping

AbstractWind energy as the cleanest source of renewable energy requires a highly efficient lightweight generator that provides maximum power density while having the least vibration noise and maintenance. In this study, an axial air gap transverse flux machine is presented, and all excitation sources are located in the stator. This structure provides lower core loss, weight and cost due to the full utilisation of the permanent magnets, SMC‐free structure and short magnetic flux path. In fact, by combining the features of a flux‐switching machine into a transverse flux generator with an axial air gap, it is possible to improve the performance of a direct‐drive wind turbine generator by overcoming traditional structures' challenges. To analyse the axial transverse flux switching permanent magnet generator performance characteristics, 3D finite element simulations have been performed, which have been validated by comparing them to the practical results of a single‐phase prototype. The results are in agreement with an acceptable error that is caused by manufacturing uncertainties.

Multi-Parameter Optimization of Heat Dissipation Structure of Double Disk Magnetic Coupler Based on Orthogonal Experimental Design

The existing heat dissipation research on double disk magnetic couplers ignores the coupling influence of electromagnetic temperature–stress and other multiphysics fields, and the error between the calculation and analysis results and the measured values is large. Therefore, a multi-parameter optimization method for heat dissipation structures of double disk magnetic couplers based on orthogonal experimental design is proposed. Based on the double disk magnetic coupler model, a three-dimensional finite element model based on fluid–solid–heat coupling is established, with the axial air gap length, input motor speed, the thickness of the permanent magnet in the magnetizing direction, the thickness of the copper plate, the number of fins of the heat dissipation plate and the length of the fins of the heat dissipation plate as design variables. Six-factor and three-level simulation experiments are designed with the minimum temperature of the heat dissipation plate as the objective function, and additionally, orthogonal experiments were designed according to the actual working conditions by selecting the optimal combination of parameters and modifying the model to perform physical tests. The results show that the variables that have the most significant impact on heat dissipation performance from high to low are as follows: axial air gap length, input motor speed, the length of the fins of the heat dissipation plate, the thickness of the permanent magnet in the magnetizing direction, the number of fins of the heat dissipation plate and the thickness of the copper plate. The increase in axial air gap length can effectively reduce the temperature rise, and the maximum decrease can reach 9.76%. Under the same conditions, the input motor speeds are set to 300 r/min, 400 r/min, 500 r/min, 600 r/min and 700 r/min, respectively, and the simulation results are in good agreement with the physical test results, with a maximum error of 4.8%. The error between the simulation result and the physical test result is only 1.9% under the optimal combination of parameters obtained by the orthogonal experiment, which verifies the correctness of the optimization model. In conclusion, the study is of reference significance for the parameter optimization of the heat dissipation structure of the double disk magnetic coupler.

A Simple Method to Calculate the Torque of Magnet-Rotating-Type Axial Magnetic Coupler Using a New Magnetic Equivalent Circuit Model

A magnet-rotating-type axial magnetic coupler (MAMC), namely, a novel axial magnetic coupler with rotatable monopole permanent magnets (PMs), is proposed. The speed of the MAMC can be adjusted by rotating the rotatable PMs mounted on the PM disk, or changing the axial air gap length between the PM disk and the conductor sheet (CS), or combining these methods. In order to analyze the torque performance, the magnetic circuit model of MAMC is established when the rotatable PMs are not parallel to the CS. Specifically, the influence of the induced eddy current is introduced into a new magnetic equivalent circuit (MEC) model. Combined with Kirchhoff’s law, the calculation formula of torque is derived. Moreover, according to Ampere’s law, the formula for calculating the induced eddy current is derived when the rotatable PMs after rotating are not parallel to the CS. Finally, the effectiveness of the proposed model is verified by the finite element method (FEM). The results obtained by the new MEC model proposed are consistent with those obtained by the FEM, and the formula derived is effective in the case of small rotational speed differences, small air gap lengths, and small thicknesses of the CS.

An Axial Airgap Eddy Current Speed Sensor

This article presents a novel configuration of the eddy current speed sensor to measure the rotating speed of iron rods and shafts up to 3000 r/min. The proposed eddy current speed sensor has an axial airgap structure with one excitation coil and two antiserially connected pick up coils. The speed sensor is mounted in the end shaft part region. Different solid iron materials for rotating shaft are considered in the measurements and calculations to evaluate solid iron material effect on the eddy current speed sensor performance. Two-dimensional (2-D) and 3-D finite element method is utilized for the performance analysis of the speed sensor. Also, a 2-D analytical method is developed for parametric analysis. A copper rod is also used to compare the speed sensor with the rotating iron shaft and copper shaft. Finally, two thin copper discs with different diameters are mounted on the solid iron shaft and their influences on the eddy current speed sensor were evaluated and measured to increase sensitivity and decrease sensor dependency on the permeability of the solid iron shaft. The achieved nonlinearity errors are about ±0.2%.

Computational Modeling of an Axial Airgap Induction Motor With a Solid Rotor

This article presents analytical calculations of an axial airgap or disk induction machine with a solid rotor. A quasi-3-D analytical analysis for the eddy current estimation in the solid disk rotor and 1-D and 2-D analytical analyses for the torque calculation are performed. The third-dimension effect in 1-D and 2-D analytical analyses is estimated by quasi-3-D analytical calculations of the eddy currents in the solid disk rotor. The analytical calculations are compared with the 3-D finite element method (FEM) and experimental results of a solid-rotor axial airgap induction motor. The analytical calculations are also used for the optimization of the axial airgap machine to improve torque characteristics at higher speeds.

Design of a Combined Magnetic and Gas Dynamic Bearing for High-Speed Micro-Gas Turbine Power Plants with an Axial Gap Brushless Generator

The development of modern energy is moving towards distributed generation, in which numerous sources of different capacities are connected into a single network. This makes it possible to increase the reliability of the entire system, since the probability of the failure of several energy sources at the same time is small. One of the major possibilities of distributed generation is the generation of electric energy based on high-speed gas turbines. The main advantage of these sources are high specific energy indicators, which improve with increasing rotation speed. However, it is technically difficult to realize the advantages of high-speed devices. It is necessary to abandon the step-down gearbox for the generator and directly connect it to a high-speed turbine, use high-strength materials that can withstand the load from centrifugal forces, abandon traditional plain bearings, and use special supports. Installations with generators that have a radial rotor design are the most widespread. The main problem with generators of this type is that the rotor diameter is limited by the mechanical strength from centrifugal forces and the power can be increased only by increasing the axial length. At the same time, only two supports can be used for a radial structure; this leads to a decrease in the rigidity of the shaft and the occurrence of resonant frequencies during acceleration. In addition, radial generators have unreasonably large losses in the stator magnetic circuit, which increase with increasing speed and are difficult to remove from a limited volume. For this reason, radial structures have exhausted their reserves and cannot develop further in the direction of increasing the speed of rotation. This article proposes the design of a high-speed gas turbine installation based on a generator of a fundamentally different design. This is a multi-section generator with an axial air gap. The electric machine has a diamagnetic armature, which eliminates magnetic losses and allows for increased efficiency and simplification of the design. A large number of rotor sections can be used as supports for a gas-dynamic bearing, which greatly increases the rigidity of the structure and eliminates resonant frequencies during acceleration. The main structural difference from existing designs is the use of two types of bearings at the same time: magnetic bearings and gas-dynamic bearings. Magnetic bearings ensure operation at low speeds during acceleration, and gas-dynamic bearings ensure the rotation of the rotor and its rigidity at high speeds. Analysis of developments in this area shows that this solution is innovative. The proposed design required study of both the power part, including the axial inductor and the diamagnetic armature, and the combined support. This article shows the results of the development of a combined suspension and provides calculations of magnetic and gas-dynamic bearings for a gas turbine installation of 100 kW and 70,000 rpm. The results of the study can be applied to a number of gas turbine installations from 10 kW to 500 kW. The authors consider this concept to be competitive with modern analogues that have a radial generator design.

Optimization of Air Gap for Axial Flux Machine

The analyses the axial flux permanent magnet generator (AFPMG) dual stator single rotor structure. For the valuation of analytical results, the electromagnetic design of AFPMG is done and compared with various air gaps to flux density and power density. In the axial flux design air gap to flux density is improvement for different air gap are analyzed. This machine is gauge with certain criteria such as the cost, the copper loss, the eddy current losses and the flux density.

A Passive Permanent Magnetic Bearing With Increased Axial Lift Relative to Radial Stiffness

Four different magnet bearing configurations, with varying number of combined radially and axially magnetized rings, are studied both experimentally and using the modeling framework MagTense. First, the optimal vertical position of the radially magnetized ring is determined using the numerical model. Then, the model is validated using experimental data. Finally, we show that a bearing where the rotor and the stator each consist of a single ring of axially magnetized magnets and a single ring of radially magnetized magnets has the smallest radial force per axial lift force at an axial air gap of 1 mm. For this bearing, the ratio of the radial force per axial lift here is 0.383 times that of the same bearing without the radially magnetized ring.

Performance Analysis of a Coreless Axial-Flux PMSM by an Improved Magnetic Equivalent Circuit Model

In this paper, an improved magnetic equivalent circuit (MEC) model of a coreless axial-flux permanent-magnet synchronous machine (AFPMSM) with printed circuit board (PCB) winding is presented, which considers the curvature effect, fringing effect, leakage flux, and rotor yoke's magnetic saturation. The axial air-gap flux density distribution, no-load back electromotive force, winding inductances, and electromagnetic torque are predicted by the proposed MEC model. The steady-state performances of the machine under heavy load, as well as the dynamic response of the machine with a connected voltage source and mechanical load, are calculated. All the results obtained from the proposed model are in good agreement with those issued from the 3D finite element method (FEM). The computation time of the proposed model is greatly reduced compared to 3D FEM. Finally, a coreless AFPMSM prototype with a PCB stator is manufactured, and experiments are carried out to verify the predicted results.

Regulation Method for Torque\u2013Angle Characteristics of Rotary Electric\u2013Mechanical Converter Based on Hybrid Air Gap

The torque–angle characteristics of electric–mechanical converters are important determinants of the quality of electrohydraulic proportional control systems. It is far more difficult for a rotary electric–mechanical converter (REMC) to obtain flat torque–angle characteristics than traditional proportional solenoid, greatly influencing the promotion and application of rotary valves for electrohydraulic proportional control systems. A simple and feasible regulation method for the torque–angle characteristics of REMCs based on a hybrid air gap is proposed. The regulation is performed by paralleling an additional axial air gap with the original radial air gap to obtain a flat torque–angle characteristic and increase output torque. For comparison, prototypes of REMCs based on hybrid and radial air gaps were manufactured, and a special test rig was built. The torque–angle characteristics under different excitation currents and step responses were studied by magnetic circuit analysis, finite element simulation, and experimental research. The experimental results were consistent with the theoretical analysis. It was shown that REMCs based on a hybrid air gap can obtain a flat torque–angle characteristic with further optimizing of key structural parameters and also increase output torque. This regulation method provides a new approach for the design of proportional rotary electromechanical converters.

Open Circuit Performance of Axial Air Gap Flux Switching Permanent Magnet Synchronous Machine for Wind Energy Conversion: Modeling and Experimental Study

The aim of this paper is to present the design and modeling of a machine that possesses some advantageous characteristics for wind energy conversion applications. The studied machine is a double stator inner rotor axial airgap flux switching permanent magnet machine (AFSPM). The paper will start by presenting this type of machine and its points of interest. Then, it will continue by introducing the constructed prototype and its specifications and structure. This prototype has been designed based on a reference specification used at GREAH to develop different prototypes and compare their performances. The second part will introduce the reluctance network model specifically constructed for this type of machine. The constructed model was validated by comparing its results to the results from the finite element method model. Finally, the experimental results will be presented and compared to the reluctance network (RN) model results where satisfying agreement between both results was obtained.

Evaluating the Effects of Electric and Magnetic Loading on the Performance of Single and Double Rotor Axial Flux PM Machines

Axial-flux permanent-magnet machines are used particularly in applications requiring a compact structure. Their disc-shaped topology and axial airgap have led to a variety of configurations including two popular ones: the yokeless and segmented armature (YASA), and the single-stator single-rotor or single-sided machine. In this study, a comprehensive comparative analysis of these configurations is conducted at different magnetic and electric loadings. It is found that at lower loadings, typically employed for air-cooled machines, the torque/ampere characteristics of the YASA machine are almost identical to those of a single-sided machine constructed with half the magnet volume. On the other hand, the single-sided machine outperforms the YASA machine when the magnet volumes in both machines are maintained equal. However, for higher electric loadings, the torque/ampere characteristics of the YASA machine droop significantly less than those of the single-sided machine. This article includes analytical estimations, which are verified with experimentally validated finite element analysis (FEA) simulations. In addition, the impacts of the armature reaction on saturation and the magnetic flux linkage, the magnet losses, and eddy current losses in both machines are also explored.

OPTIMUM DESIGN METHODOLOGY FOR AXIALLY POLARIZED MULTI-RING RADIAL AND THRUST PERMANENT MAGNET BEARINGS

—This article deals with the generalized procedure of designing and optimizing multi-ring radial and thrust permanent magnet bearings (PMBs) with an axial air gap for maximum force and stiffness per volume of the magnet. Initially, the procedure of determining optimized design variables in both the configurations is presented using the MATLAB codes written for solving the three dimensional (3D) equations of force and stiffness in PMB having ‘n’ number of rings on the stator and rotor. The maximized results of the forces in both radial and thrust multi-ring PMBs are validated with the values obtained using finite element analysis (FEA). Then, the correlation between the optimized parameters and the air gap is obtained, and curve fit equations for the same are proposed in terms of stator outer diameter. Further, curve fit equations establishing the relationship between the maximized bearing features, and the aspect ratio (L/D4) of the bearing are expressed for different values of air gap in both the radial and thrust bearings. Finally, the generalized method of designing and optimizing the multi-ring PMB is demonstrated with a specific application. A designer can use the presented curve fit equations for optimizing design variables and calculating maximized bearing features in multi-ring radial and thrust PMBs easily just by knowing the bearing features for a single ring pair.

Analysis of a PM Linear Generator with Double Translators for Complementary Energy Generation Platform

This paper presents a tubular permanent magnet (PM) linear generator (TPMLG) with one single stator and double translators for complementary energy generation platform. Moreover, groups of Halbach PM magnetized structure for double translators is applied to increase the radial air gap flux density and to decrease the axial air gap flux density in the TPMLG. Based on the linear generator model and finite element method (FEM), the radial air gap flux density and axial air gap flux density in the two translator of the TPMLG is calculated and analyzed comparatively. Magnet field distribution of the TPMLG with groups of Halbach PM magnetized structure is illustrated, no-load performance at constant velocity and at sine velocity is analyzed, respectively, and comparing with the radial magnetization PM, the detent force is analyzed contrastively. Finally, this study proposed an experiment system consisting of a TPMLG with a single translator, a cylindrical float and wave flume to verify the analysis results. Through comparative analyses, the proposed TPMLG with double translators and groups of Halbach PM magnetized structure fulfill the requirements of complementary energy generation platform systems.

Investigation on high-power-density design of small PM motors focusing on air gap configuration

This paper describes a case study of high-power-density design of small permanent magnet (PM) motors focusing on their air gap configurations. Two types of the PM motors, i.e., a radial air gap type and an axial air gap type, are comparatively discussed. Comparison between the two types has been conducted from the viewpoints of I-T characteristics, N-T characteristics, efficiency maps, torque ripple characteristics, and so forth. It has been clarified that the axial air gap type has significant advantages to achieve the high-power-density under some limited condition.

Direct Calculation Method of Fringing Field Reluctance in MEC Analysis for An Axisymmetric Solenoid Actuator

In this paper, a method is introduced to directly calculate the reluctances of fringing fields in analyzing a magnetic equivalent circuit model for an axisymmetric solenoid actuator including radial air gaps as well as axial air gaps. The introduced method was motivated by the possibility to calculate the cross section area depending on the radial position of an infinitesimal element when the infinitesimal element is defined to be integrated in the flux flow direction in a circular-arc straight-line model of an axisymmetric model. In this method, the reluctance of fringing field near an air gap can be calculated directly. For an objective model, the MEC analysis was performed using the introduced method and an iterative method. In the iterative method, the nonlinearity of the ferromagnetic material parts is resolved. In order to validate the introduced method, MEC analysis and FEA results are compared. And for validating the method in a view of computation also, an optimized design satisfying pre-defined constraints was searched using MEC analysis, and then the results of the MEC analysis using the introduced method and FEA results are compared for the searched design and the initial design.