Axial Flux Permanent Magnet Research Articles

Power density improvement of axial flux permanent magnet synchronous motor by using different magnetic materials

PurposeThe purpose of this paper is to exploit the optimal performances of each magnetic material in terms of low iron losses and high saturation flux density to improve the efficiency and the power density of the selected motor.Design/methodology/approachThis paper presents a study to improve the power density and efficiency of e-motors for electric traction applications with high operating speed. The studied machine is a yokeless-stator axial flux permanent magnet synchronous motor with a dual rotor. The methodology consists in using different magnetic materials for an optimal design of the stator and rotor magnetic circuits to improve the motor performance. The candidate magnetic materials, adapted to the constraints of e-mobility, are made of thin laminations of Si-Fe nonoriented grain electrical steel, Si-Fe grain-oriented electrical steel (GOES) and iron-cobalt Permendur electrical steel (Co-Fe).FindingsThe mixed GOES-Co-Fe structure allows to reach 10 kW/kg in rated power density and a high efficiency in city driving conditions. This structure allows to make the powertrain less energy consuming in the battery electric vehicles and to reduce CO2 emissions in hybrid electric vehicles.Originality/valueThe originality of this study lies in the improvement of both power density and efficiency of the electric motor in automotive application by using different magnetic materials through a multiobjective optimization.

Mechanical and Thermal Design of an Optimized PCB Motor for an Integrated Motor Drive System With GaNFETs

PCB motors are a viable alternative to commercial electric motors as they are easy to mass-produce and have low manufacturing costs. Moreover, integrated motor drives have gained popularity thanks to their high power density and ease of installation. However, the mechanical and thermal aspects are challenging due to reduced volume. In this paper, a GaNFET switched integrated motor drive axial-flux permanent magnet synchronous machine with a printed circuit board (PCB) stator is designed. The machine is optimized using a multi-objective, non-dominated sorting genetic algorithm (NSGA-II). Two stator types are designed and manufactured to compare the effect of eddy losses. A method for measuring eddy current losses on PCB stators is proposed and used. A mechanical and thermal solution is proposed and tested. Integrated motor drive with sinusoidal pulsed width modulation (SPWM) is used to drive the motor up to 5000 RPM at a 1 MHz switching frequency. The overall system‘s efficiency is 82% at 0.36 N.m and 90% at 0.18 N.m torque. The system has an output power of 270 W of output power with 59 °C stator temperature that proved the effectiveness of the proposed passive cooling method.

Introducing Analytical Formulas for Calculating Back EMF of the Contra-Rotating Double-Rotor Axial Flux Permanent Magnet Synchronous Machine

Back electromagnetic force (back EMF) is one of the most significant performance characteristics of the machine which significantly affects the machine current, efficiency, power factor, and power angle. Studies showed that the precise analytical formulas to calculate the back EMF of Counter-rotating dual rotor axial flux permanent magnet synchronous machines (CRDR-AFPMSMs) were not presented so far. While by helping the analytical formulas, back EMF is calculated faster than the finite element method (FEM). Therefore, the novelty of this article is calculating the back EMF of CRDR-AFPMSMs considering its harmonic components. To fulfill this goal, Maxwell’s equations are used. The back EMF waveform obtained from the proposed formulas is compared with the results of FEM. Comparing the results confirms that the obtained results from the finite element (FE) simulation and analytical formulas are in good accordance. Besides, the shifting technique is used to reduce harmonic components of the back EMF. By helping proposed formulas and shifting techniques, the Total Harmonic Distortion (THD) of back EMF has decreased from 12.12 to 4.88%.

Magnetic equivalent circuit and finite element modelling of anisotropic rotor axial flux permanent magnet synchronous motors with fractional slot distributed winding

AbstractAxial flux motors have been in the focus of many research work due to their promising properties when compared to conventional radial flux machines. Axial flux permanent magnet synchronous motors (AFPMSM) studied in the literature were mostly limited to surface‐mounted permanent magnet machines (SPMSM), excluding only a few studies about axial flux internal permanent magnet (AFIPM) or permanent magnet‐assisted synchronous reluctance (AFPMaSynRM) machines. Since numerous rotor topologies have been proposed and investigated in case of radial flux motors, analogous design methodologies can be developed in case of axial flux motors with rotor saliency. The parametrisation and modelling of a magnetically anisotropic rotor axial flux motor are presented. This approach is described generally and the method is applied to an example motor geometry. The results were validated by FEA (Finite Element Analysis), using the 2D multi‐slice and 3D modelling approaches. The modelling error was calculated and the analytical and numerical methods were compared. It was found that the proposed model was suitable for calculating important parameters of the anisotropic rotor axial flux permanent magnet synchronous motor (AnR‐AFPMSM) during the design process.

Comparative Study of Dual-Rotor Slotless Axial-Flux Permanent Magnet Machines With Equidirectional Toroidal and Conventional Concentrated Windings

Axial-flux permanent magnet (AFPM) machines are gaining popularity in low-speed and high torque applications due to their high torque density, high efficiency, and compact structure. In this article, a dual-rotor slotless AFPM (DRSAFPM) machine equipped with equidirectional toroidal winding (EDTW) is proposed and compared with that equipped with conventional single-layer and double-layer concentrated windings (CWs). First, the differences between the DRSAFPM machine with EDTW and that with conventional CWs in coil layout, electromotive force (EMF), and winding magnetomotive force are revealed. Considering the special coil layout of the EDTW, the coil factor and size equations of the DRSAFPM machines with EDTW and conventional CWs are presented. Second, the electromagnetic performance including air-gap field, back-EMF, torque, and efficiency of the DRSAFPM machines with EDTW and conventional CWs are analyzed based on the three-dimensional finite-element method. The simulation results validate the correctness of the coil factor and size equations and indicate the EDTW–DRSAFPM machine has superiority in back-EMF amplitude and torque density. Finally, a prototype of the EDTW–DRSAFPM machine is manufactured and tested, which validates the feasibility of the EDTW–DRSAFPM machine and the correctness of the analysis.

Multiagent Control in Modular Motor Drives by Means of Deterministic Consensus

A modular motor drive (MMD) is composed of multiple identical pole drive units (PDUs), which consist of a concentrated stator winding fed by a dedicated power electronic converter module. To exploit the full flexibility and reliability of these MMDs, they are equipped with multiple controllers, operating as synchronized peers, and each driving only a limited set of PDUs. An MMD can hence be considered as a multiagent system, in which all the agents cooperate to deliver a certain torque demand. The goal of this work is to distribute this torque demand among the agents of a modular drive in a completely decentralized way, in order to comply with the flexibility and reliability of the hardware, while still taking into account the present condition of each agent. A deterministic consensus algorithm is used for this purpose, in combination with decentralized proportional integral (PI) current controllers. Communication is only allowed between neighboring agents, to limit the communication load. It is shown in this article that the total torque demand is delivered, under healthy conditions as well as during agent malfunctions and with nonidentical agents. The concept is demonstrated on a modular axial-flux permanent magnet synchronous machine with 15 PDUs that are assigned to five agents.

Hybrid Weighted Least Square Multi-Verse Optimizer (WLS–MVO) Framework for Real-Time Estimation of Harmonics in Non-Linear Loads

The electric power quality has become a serious concern for electric utilities and end users owing to its undesirable effects on system capabilities and performance. Harmonic levels on power systems have been pronounced to a greater extent with the continuous growth in the application of solid-state and reactive power compensatory devices. Harmonics are the key constituents that are mainly responsible for power quality deterioration. Power system harmonics need to be correctly estimated and filtered to increase power quality. This research work focuses on accurate estimation of power system harmonics with the proposed hybrid weighted least-square multi-verse optimizer (WLS–MVO) based framework. Multi-verse optimizer replicates the phenomenon of the formation of new universes as described by multi-verse theory to solve complex real-world optimization problems. The proposed WLS–MVO framework is tested and validated by estimating the harmonics present in multiple test signals with different noise levels. Amplitudes and phases of harmonics present in the polluted signal were estimated, and the framework computational time was compared with the previously developed technique’s results which are reported in the literature. There was 80% reduction in computational time and 82% improvement in terms of accuracy in estimating harmonics using WLS–MVO as compared to previously developed techniques. The performance of the developed framework is further validated by estimating the harmonics present in the real-time voltage and current waveforms obtained from axial flux permanent magnet generator (AFPMSG), uninterruptible power supply (UPS), and light-emitting diode (LED). The purposed technique technique outperforms the already-developed techniques, in terms of accuracy and computational time.

Comparative Study of Yokeless Stator Axial-Flux PM Machines Having Fractional Slot Concentrated and Integral Slot Distributed Windings for Electric Vehicle Traction Applications

Due to the high-power density and compact structure, axial-flux permanent magnet (AFPM) machines have gradually received much attention with a view to researching breakthroughs in the next generation electric drive technology for electric vehicles in the recent decades. The AFPM machines with factional slot concentrated winding (FSCW) and yokeless stator, namely yokeless, and segmented armature (YASA) motors, have drawn much attention for its high-power density and potential manufacturability due to the concentrated winding and modular stator core configuration. However, the significant rotor loss resulting from the abundant armature reaction harmonics in FSCW machines imposes a great challenge to the rotor heat dissipation, especially when the pursuit of higher speed has become the trend for electric vehicle applications. On the other hand, distributed winding is widely used in high speed radial flux permanent magnet (PM) machines due to its low armature reaction harmonics. In order to figure out the advantages and disadvantages of various winding arrangement and rotor configuration of AFPM for electric vehicle applications, the comparative study of four AFPM machines with various winding configurations and rotor PM arrangements are comprehensively conducted in this article. First, the design and primary optimization of the four AFPM machines are conducted for the electric vehicle requirement specifications. Then, a comprehensive three-dimensional finite-element analysis (FEA) is employed to compare the electromagnetic performance including torque/power density, efficiency, and flux-weakening capacity. Furthermore, the guideline of winding selection of AFPM machines for electrical vehicle is given. Finally, a yokeless stator AFPM prototype with ISDW configuration is manufactured and tested to verify the validity of the FEA results, as well as confirm the comparison conclusion.

Rotor Air-Friction Loss and Thermal Analysis of IPM Rotors for High Speed Axial-Flux Machine

This paper focuses on the temperature rise of high-speed disc rotor considering the air-friction loss for an axial flux permanent magnet (AFPM) motor with double rotors and sandwiched stator. The air-friction loss and the heat transfer coefficient on the rotor surface at different speed are obtained based on the formula method and Fluid-Thermal coupling analysis. The rotor temperature distribution based on the coupling analysis of temperature and fluid field is obtained considering various losses and the impact of heat dissipation of air flowing in the motor cavity. Finally, the temperature variation of rotor disc considering the rotating speed is presented for the AFPM motor in this paper. The heat dissipation mechanism of rotor disc for the AFPM motor are revealed. It provides a significant guideline for the cooling design and the efficiency enhancement of high speed AFPM motor.

3-D Analytical Model of Axial-Flux Permanent Magnet Machine With Segmented Multipole-Halbach Array

This paper presents a 3-D analytical model of an axial-flux permanent magnet (AFPM) machine with a segmented multipole-Halbach PM array. Closed-form solutions are self-consistently derived in terms of modified Bessel functions of the first- and the second-kind by solving analytically Laplace and Poisson equations by the method of magnetic scalar potential subject to the appropriate boundary conditions. In the preceding studies, their formulations are based on a 2-D or quasi 3-D geometry, and their discussions are often limited to the magnetic fields with low-poles of the regular PM. The proposed model successfully provides more rigorous and widely applicable expressions for magnetic fields, back-electromotive force, Lorentz torque and torque constant without limitations on the number of poles and the arrangements of the PM. Behavior of the torque constant is then shown against the number of poles ranging widely from low-poles to high-poles of the regular PM, the standard-Halbach PM and the multipole-Halbach PM for changeable geometrical parameters. The obtained results are of much use in understanding intrinsically the performance characteristics of the AFPM.

An effective Hilbert-Huang transform-based approach for dynamic eccentricity fault diagnosis in double-rotor double-sided stator structure axial flux permanent magnet generator under various load and speed conditions

Eccentricity fault in double-sided axial flux permanent magnet generator is very difficult to be detected as the fault generated variations in terminal electrical parameters are very weak and chaotic, especially at the initial stages of the fault occurrence. In addition, one of the most important problems in any fault diagnosis approach is the investigation of load and speed variation on the proposed indices. To overcome the aforementioned difficulty and problems, this paper adopts a novelty detection algorithm based on Hilbert-Huang transform (HHT) which is a time-frequency signal analysis approach based on empirical mode decomposition and the Hilbert transform. It is well suited for reliable fault diagnosis since it is unaffected by transient conditions which make the diagnosis process incur into false alarms. The HHT-based methods has been demonstrated in recent years for rotor and bearing faults detection of induction machine and also for stator faults identification in PM synchronous machines with radial flux structure. This study explores the possibility of applying the technique to the detection of dynamic eccentricity faults in double-rotor double-sided stator structure axial flux permanent magnet generator under variable load and speed conditions. This approach relies on two steps: estimating the intrinsic mode functions (IMFs) by the empirical mode decomposition (EMD) and computing the instantaneous amplitude (IA) and instantaneous frequency (IF) of IMFs using the Hilbert transform. The more significant IMFs are determined by means of Hilbert spectrum, which is applied for accurate eccentricity fault diagnosis. The eccentricity severity can be evaluated based on the IMFs energy value. The theoretical basis of the proposed method is presented. The effectiveness of the proposed method is verified by a series of simulation and experimental tests under different conditions. The results show that the presented approach in this paper is robust against load and speed variations.

Review on Thermal Behavior and Cooling Aspects of Axial Flux Permanent Magnet Motors–A Mechanical Approach

With the increasing demand for high-energy density motors for applications such as electric vehicles and aircraft propulsion, axial flux permanent magnet motors are promising. However, utmost care should be taken when designing an axial flux permanent magnet motor with a higher torque density because of thermal effects. To enhance the reliability and overall performance of a motor, efficient thermal management is important, because the torque density is restricted by maximum temperature. Therefore, this study comprehensively reviews different techniques used for the thermal modeling of motors. Computational fluid dynamics, the lumped parameter method, and finite element analysis were used to calculate the total heat transfer inside the motor. Various heat enhancement techniques for an axial flux permanent magnet motor have been presented, including core cooling (water jacket cooling, air cooling, and oil cooling) and winding cooling (direct slot cooling, end winding cooling, and fins). Finally, two case studies of an 8kW AFPM motor and a 65kW AFPM motor with a cooling arrangement are discussed.

Design and Analysis of Novel Modular Stator Axial-Flux Permanent Magnet Vernier Machine With Improved Power Factor

Design and Analysis of Novel Modular Stator Axial-Flux Permanent Magnet Vernier Machine With Improved Power Factor

Three-Dimensional Analytical Modeling of Axial-Flux Permanent Magnet Drivers

In this paper, the axial-flux permanent magnet driver is modeled and analyzed in a simple and novel way under three-dimensional cylindrical coordinates. The inherent three-dimensional characteristics of the device are comprehensively considered, and the governing equations are solved by simplifying the boundary conditions. The axial magnetization of the sector-shaped permanent magnets is accurately described in an algebraic form by the parameters, which makes the physical meaning more explicit than the purely mathematical expression in general series forms. The parameters of the Bessel function are determined simply and the magnetic field distribution of permanent magnets and the air-gap is solved. Furthermore, the field solutions are completely analytical, which provides convenience and satisfactory accuracy for modeling a series of electromagnetic performance parameters, such as the axial electromagnetic force density, axial electromagnetic force, and electromagnetic torque. The correctness and accuracy of the analytical models are fully verified by three-dimensional finite element simulations and a 15 kW prototype and the results of calculations, simulations, and experiments under three methods are highly consistent. The influence of several design parameters on magnetic field distribution and performance is studied and discussed. The results indicate that the modeling method proposed in this paper can calculate the magnetic field distribution and performance accurately and rapidly, which affords an important reference for the design and optimization of axial-flux permanent magnet drivers.

A Proposal of an Axial-Flux Permanent-Magnet Machine Employing SMC Core With Tooth-Tips Constructed by One-Pressing Process: Improving Torque and Manufacturability

A Proposal of an Axial-Flux Permanent-Magnet Machine Employing SMC Core With Tooth-Tips Constructed by One-Pressing Process: Improving Torque and Manufacturability

Research on Modeling Method for Eccentric Axial Force of Axial Flux Permanent Magnet Motor with Single-Rotor–Single-Stator Structure

Research on Modeling Method for Eccentric Axial Force of Axial Flux Permanent Magnet Motor with Single-Rotor–Single-Stator Structure

A Review of Axial-Flux Permanent-Magnet Motors: Topological Structures, Design, Optimization and Control Techniques

Axial-flux permanent-magnet (AFPM) motors are a kind of important motor with compact structure, high power density and high torque density. In this review, the progress of AFPM motors and their key technologies are analyzed and described, with emphasis on the topological structures, design and optimization methods and control techniques. Based on these analyses, the main findings of the review are the following: (1) the yokeless and segment armature (YASA)-type motors have great potential for development; (2) the multi-objective optimization design theories can be integrated and applied to optimize the design of AFPM motors; and (3) optimal control and sensorless control have important value in improving system reliability and reducing cost. Finally, highlights and prospects are provided for further advancing AFPM motors.

Direct torque control of non-salient pole AFPMSMs with SVPWM inverter

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Analytical Performance Prediction of a New-Structured Solid-Rotor Line-Start Axial Flux Permanent Magnet Motor

The Axial Flux Permanent Magnet (AFPM) motors have recently attracted more attention in various applications due to their special outstanding potentials. However, two major problems have already restricted their usage, which are the lack of starting torque and their probable instability. These problems have caused the AFPM motors to be energized so far necessarily via expensive and complicated power-electronic drives, even when are desired to operate in the constant-speed condition. Alternatively, the better and less expensive solution to these problems is to provide the Line-starting capability through modifying the motor structures. Therefore, this paper studies a Line-start Non-slotted AFPM motor with a new proposed structure. The parameters of the electrical equivalent circuit and the principal performance characteristics of the motor are extracted through establishing a detailed analytical model. Finally, the performance of the newly developed structure and the validity of the established analytical model have been successfully verified through implementing the model in MATLAB and comparing the results with those of Finite Element Analysis (FEA) and experiment on a fabricated prototype. The results demonstrate the accuracy of the analytical model and appropriate performance of the motor in terms of direct start-up and synchronization.

Study on AC Copper Losses in an Air-Cored Axial Flux Permanent Magnet Electrical Machine With Flat Wires

In this article, we propose the calculation method of ac copper losses of air-cored axial flux permanent magnet (AFPM) electrical machine with flat wires fed by pulsewidth modulation (PWM) inverters. The ac copper loss due to armature currents in air-cored electrical machines is significant when these machines are driven by PWM inverters. Besides, the exposure of windings to the inhomogeneous alternating rotor magnetic field causes ac copper loss. Analytical formulas are efficient tools to evaluate these losses but few pieces of literature have reported the derivation in such machines. To address this issue, the formulas of aforementioned ac copper losses are derived based on Maxwell's equations and Poynting theorem. As for end windings, the ac copper loss caused by armature current is calculated analytically, while the rotor-induced ac copper loss is calculated by aid of static three-dimensional finite-element analysis (FEA). The interaction of load current and rotor-induced eddy current is also studied. A 12-slot-16-pole air-cored AFPM machine is analyzed with the proposed method, and the analysis is validated by time-transient FEA simulations and prototype experiments. The influence of modulation ratio on ac copper loss due to armature current of the AFPM machine is also discussed.