Stator Axial Flux Permanent Magnet Research Articles

Multiple Operating Mode Based Magnetic-Pole Partitioned Design and Optimization for a Dual Stator Axial Flux Permanent Magnet Motor

Multiple Operating Mode Based Magnetic-Pole Partitioned Design and Optimization for a Dual Stator Axial Flux Permanent Magnet Motor

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.

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

Design and Optimization Analysis of Coreless Stator Axial-Flux Permanent Magnet In-Wheel Motor for Unmanned Ground Vehicle

In this article, a coreless stator axial-flux permanent magnet (CSAFPM) indirect drive (ID) in-wheel motor is proposed and researched taking into consideration the multiphysics constraints, including electromagnetic performance and mechanical strength for unmanned ground vehicles (UGVs). At first, two 12-slot-14-pole CSAFPM motors with different rotor structures are designed to meet the vehicle rim space and driving system demand. In addition, the rotor parameters are optimized to obtain higher torque density based on the response surface method (RSM) and finite element model (FEM). Meanwhile, the electromagnetic performance of optimized motors with different rotors is compared, including back electromotive force (EMF), output torque capability, and efficiency characteristics. The results indicate that the Halbach-array PM rotor has higher torque and efficiency than the spoke-type PM rotor. On that basis, the thermal stress and deformation of the stator support are analyzed and optimized, considering material property and temperature distribution. In addition, the stress of PM rotor, annular gear, and gear reducer are analyzed and optimized to achieve higher torque density. Finally, a 35-kW prototype is manufactured and tested to verify the performance of the design.

Analysis and Experimental Verification of a Conventional Inverter With Output LC Filter to Drive Ironless Stator Axial-Flux PM Motor

Ironless stator axial-flux permanent magnet (PM) machines are becoming a promising choice in aerospace and automotive applications. However, they come with the characteristic of extremely small armature inductance, which will result in a challenging difficulty to drive with the conventional inverter. Considering the limitation on increasing the switching frequency of high-power devices, a practical and cost-effective power circuit for driving an axial-flux ironless stator PM motor is developed for the application with high dc-link voltage, high-power level, and high fundamental frequency. A new and simple control strategy of the inverter with output inductor–capacitor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> ) filter is studied to achieve a well steady and dynamic performance for driving ironless stator PM motors. The dual closed loop of the phase current of the motor and the branch current of capacitors ensures the stability and torque control of the system. Due to the dual-loop current regulator, the maximum torque per ampere control is achieved. Meanwhile, the sinusoidal current with low harmonic content injected into the armature winding is of great significance for improving the performance of ironless stator AFPM motor. It proves that the development of the power circuit topology and effective control method provides an available solution for ironless stator motors or high-speed motors with small inductance.

Electromagnetic Analysis and Efficiency Improvement of Axial-Flux Permanent Magnet Motor With Yokeless Stator by Using Grain-Oriented Silicon Steel

This article employs grain-oriented (GO) silicon steel in an axial-flux permanent magnet (AFPM) machine to improve its torque and efficiency. Rolling direction of the GO material have been studied to ensure the machine&#x2019;s main magnetic flux passes through the easy magnetization direction. Based on the study of the electromagnetic characteristics of AFPM machine, GO silicon steel is laminated to form a stator according to a certain lamination direction. The torque and efficiency of the proposed machine with GO material shows an increase in comparison with that of the conventional non-oriented (NO) silicon steel machine under identical conditions. In addition, an equivalent magnetic circuit model is established to illustrate little difference of electromagnetic property under no-load condition for the yokeless stator AFPM using two kinds of silicon steel sheet. Furthermore, a AFPM machine with stator yoke is also established to highlight the superiority of GO in the application of the AFPM machine with yokeless stator.

Reduction of Cogging Torque in AFPM Machine Using Elliptical-Trapezoidal-Shaped Permanent Magnet

The reduction in cogging torque enables smooth operation and an increase in the torque density of the machine. This research aims to minimize cogging torque in dual rotor single stator axial flux permanent magnet (AFPM) machine. Reduction in cogging torque makes the back EMF sinusoidal and reduces the torque ripples in AFPM machine. In this paper, an elliptical trapezoidal-shaped permanent magnet (PM) is proposed to minimize torque ripples of the AFPM machine. The 3D finite element analysis (FEA) is used for the analysis of AFPM machine. The optimization of AFPM machine is done by employing the asymmetric magnet-overhang along with the parameters of elliptical-shaped PM using Genetic algorithm (GA).

Comparison of PCB winding topologies for axial‐flux permanent magnet synchronous machines

Although axial-flux permanent magnet machines have high torque densities, challenges regarding mass production of stators make them a less appealing choice. Printed circuit board (PCB) axial-flux machine is a type of machine with a stator that is made of layers of PCB. Given the precise, fast, and cheap mass production capabilities of PCB manufacturers, PCB axial-flux machines stand as a viable alternative for conventional round-wire winding machines. In this study, five different winding topologies are compared. Their induced phase voltages and torque are calculated using the developed magnetic scalar potential method and finite element analysis (FEA). Proposed windings are tested on a 16-pole, 2000-RPM, double rotor-single stator axial-flux permanent magnet synchronous machine. Results showed that the parallel winding had the smallest resistance and loss. Moreover, radial and concentric winding had the highest induced voltage and torque while the radial winding had 20% less phase resistance than concentric. Also, the induced voltage of radial winding had the smallest total harmonic distortion in comparison with other winding types. A novel unequal width parallel winding is proposed and it is compared with parallel winding separately. It is found that by simply increasing the cross-section area of wave windings, it is possible to decrease copper loss by 17%.

Design and Analysis of Oil-Immersed Cooling Stator With Nonoverlapping Concentrated Winding for High-Power Ironless Stator Axial-Flux Permanent Magnet Machines

Ironless stator axial-flux permanent magnet (AFPM) machines provide many attractive electromagnetic performances such as high efficiency in high-frequency mode and strong short-term overload ability, which make them more competitive in flywheel energy storage applications. However, designing high-torque-density AFPM machines, particularly their ironless stators, is with significant challenges and needs great efforts. In this article, a high-strength oil-immersed cooling stator with nonoverlapping concentrated winding is proposed for high-power ironless stator AFPM machine applications. This article explains in detail the design, analysis, and manufacturing process of the proposed oil-immersed cooling stator. With the three-dimensional finite-element analysis (3-D FEA), a 9000-r/m/50-kW 12-slot/10-pole prototype for a flywheel energy storage system is successfully designed and developed using the proposed high-strength oil-immersed cooling ironless stator. The experimental test results demonstrate the effectiveness of the cooling design and mechanical strength.

Effect of Slot-Pole Combination on the Electromagnetic Performance of Ironless Stator AFPM Machine With Concentrated Windings

Due to the elimination of the magnetic core on the stator, the design of coils is more flexible and more sensitive to the number of rotor poles for ironless stator axial flux permanent magnet (AFPM) machine. The slot-pole combination is a vital aspect of optimization design for the improvement of torque and power density. This article is mainly aimed at investigating the influence of slot-pole combination on the comprehensive performance of ironless stator AFPM machine with non-overlapping concentrated windings. Firstly, the space utilization of coils and winding factor of non-overlapping concentrated winding are deduced in formula form to compare the output capacity. And the copper mass and utilization are analyzed with different numbers of slots and stator diameter. Then, field utilization ratio is defined and derived to analyze magnetic flux leakage of Halbach-array PM dual-rotor for different numbers of poles. The performance comparison of the optimized prototypes is carried out using three-dimensional finite element analysis (3-D FEA). The back-EMF, torque and winding loss are also highlighted. Finally, a 50 kW prototype with 12-slot and 10-pole is designed and manufactured for experimental validations. This paper provides a valuable reference to select the basic configuration for the ironless stator AFPM machine application.

Load characteristic analysis of a double-side internal coreless stator axial flux PMG

The main issue of using a permanent magnet in electric machines is the presence of cogging torque. Several methods have been introduced to eliminate it, one of which is by employing a coreless stator. In this paper, the load characteristic analysis of the double-side internal coreless stator axial flux permanent magnet generator with the specification of 1 kW, 220 V, 50 Hz, 300 rpm and 1 phase is discussed. The purpose is to learn the effect of the load to the generator performance, particularly the output power, efficiency and voltage regulation. The design and analysis are conducted analytically and numerically with two types of simulated loads, pure resistive and resistive-inductive in series. Each type of load provides power factor 1 and 0.85 respectively. The simulation results show that when loaded with resistive load, the generator gives a better performance at the output power (1,241 W) and efficiency (91 %), whereas a better voltage regulator (5.86 %) is achieved when it is loaded with impedance. Since the difference in the value of each parameter being compared is relatively small, it can be concluded that the generator represents good performance in both loads.

Analysis of end effect in ironless stator AFPM machine via MEC model

The Halbach-array permanent magnet (PM) rotors can achieve higher air-gap flux density due to magnetic flux gathering effect, which contributes to the higher-torque density improvement of the ironless stator axial flux PM (AFPM) machine. However, the end leakage fluxes of the ironless stator AFPM machine are serious due to the large magnetic resistance of the main flux loop in ironless stator machines. Circular arc straight line permeance model is adopted to calculate magnet-to-magnet and magnet-to-rotor end leakage fluxes based on the analysis of the relationship between end leakage fluxes and coils. A magnetic equivalent circuit (MEC) model is established considering end leakage fluxes. The leakage coefficients representing the ratio of end leakage fluxes to main flux and radial coefficients representing effective radial lengths of end leakage fluxes are analysed via the MEC model. The coefficients vary with machine parameters including PM thickness, rotor yoke thickness and air-gap length. On the basis of the analysis results, the influence factors of end leakage fluxes are summarised and the 50 kW ironless stator AFPM machine is optimised. Finally, a 50 kW ironless stator AFPM machine with Halbach-array PM rotors is prototyped to verify the results of the finite element analysis and MEC model.

Design and Optimization of Halbach-Array PM Rotor for High-Speed Axial-Flux Permanent Magnet Machine With Ironless Stator

In this article, a high-speed Halbach-array permanent magnet (PM) rotor for ironless stator axial-flux permanent magnet (AFPM) machine is proposed and researched with consideration of the multiphysics constraints, including the electromagnetic characteristics, mechanical strength, and rotor dynamics. Considering the severity of attractive force between twin rotors, the complex repulsive force among PM segments of Halbach-array and centrifugal force, the new hybrid sleeve, and PM fixation method are proposed to improve the rotor mechanical strength. Then, the rotor stress is analyzed by numerical analysis and three-dimensional (3-D) finite-element analysis (FEA). Furtherly, the sleeve thickness and interference fit are optimized by 3-D FEA. The rotor dynamics and bearing arrangement are analyzed to validate the effectiveness of the high-speed Halbach-array PM rotor. A 50-kW, 9000 r/min ironless stator AFPM machine prototype with Halbach-array PM rotor is manufactured and tested. The measured results show that the output power is up to 53.8 kW at 9000 r/min. The feasibility of high-speed Halbach-array PM rotor and accuracy of analysis method are validated by both simulated and measured results.

Feasibility of a new ironless-stator axial flux permanent magnet machine for aircraft electric propulsion application

With the development of aviation electrification, higher demands for electrical machines are put forward in aircraft electric propulsion systems. The aircraft electric propulsion requirements and propulsion motor features are analyzed in this paper. Comparing with conventional PM machines, ironless stator axial flux permanent magnet (AFPM) machine topologies with Litz wire windings allow designs with higher compactness, lightness and efficiency, which are suitable for high-frequency and high-power density applications. Based on the motor requirements and constraints of aircraft electric propulsion systems, this paper investigates a high-power 1 MW multi-stack ironless stator AFPM machine, which is composed of four 250kW modular motors by stacking in axial. The design guidelines and special attentions are presented, in term of electromagnetic, thermal, and mechanical performance for the high-frequency coils and Halbach-array PM rotor. Finally, an ironless stator AFPM motor is manufactured, tested and evaluated with the consideration of cost and processing cycle. The results show that the output power is up to 53.8kW with 95% efficiency at 9000r/min at this stage. The proposed ironless stator AFPM machine with oil immersed forced cooling proves to be a favorable candidate for application in electric aircraft as propulsion motors.

Design of a PCB stator coreless axial flux permanent magnet synchronous motor based on a novel topology Halbach array

A novel topology Halbach permanent magnet array is proposed and applied to the design of a printed circuit board (PCB) axial flux permanent magnet (AFPM) motor. Compared with the traditional coreless AFPM motor, this novel topology for a Halbach permanent magnet array PCB stator AFPM motor has larger air-gap magnetic flux density and air-gap flux per pole. The magnetic flux leakage is effectively reduced, and the air-gap magnetic density is close to the sine wave. Results of the finite element analysis and prototype experiments verify the feasibility and effectiveness of the novel Halbach permanent magnet array PCB stator motor. A reference basis and practical value for the design of the PCB AFPM motor are provided.

Analysis and Implementation of New Ironless Stator Axial-Flux Permanent Magnet Machine With Concentrated Nonoverlapping Windings

This paper presents the integrated design and analysis of a new axial-flux permanent magnet (AFPM) machine, which consists of an ironless stator with double-layer concentrated nonoverlapping windings and twin external rotors with Halbach-array PMs. A general sizing equation based on fundamental theory, easily adjustable for ironless stator AFPM machine with concentrated windings, is derived to obtain preliminary parameters. Then, by using three-dimensional (3-D) finite element analysis (FEA), the optimization of a primary machine is implemented. A precise and fast calculation method based on a 3-D FEA model is proposed to confirm the eddy-current loss for ironless stator winding. By making a tradeoff between dc current loss and eddy-current loss of Litz wire for winding, the efficiency is further improved for a high frequency operation. Despite using Halbach-array PMs, a certain thickness of a rotor yoke is recommended to increase air-gap flux density. Finally, a prototype machine is developed, experimented, and evaluated. The test results reveal the strong overload and heat dispersal capacity of the proposed stator ironless AFPM machine with the maximum efficiency of 98.5%. Measured performances of the manufactured prototype verify the validity of the proposed analysis method and FEA results.

Design procedure of coreless stator PM axial field synchronous machine for small-scale wind applications

Axial field machines are available in a wide range of configurations. It has flexible design restrictions. Several research efforts were performed to discover machine performance and design horizons. However, the common design process of axial field machines depends on numerical field analysis, due to the lack of trusted and generalized analytical and/or empirical formulas especially for field distribution. This paper aims to present the essential analytic formulation for dimension selection. In addition, it provides the normalized relations between dimensions and airgap flux density using 3D-FEM as an alternative for empirical formulas. The paper describes a design procedure for coreless stator axial flux permanent magnet synchronous machine. Definite equations are derived to help the designer select the proper number of PM poles and concentrated coils to get balanced multi-phase voltage out of the generator. Moreover, the paper defines the necessary limitations of the span of the concentrated coil for a certain pole pitch to reduce the harmonic content of the output voltage waveform. The paper proposes a new approach for selecting the dimensions of the magnetic circuit using proposed data curves instead of struggling with the 3D-FEM along with its high time consumption and the need for high computational power. The loss calculations and the armature reaction are also investigated as a performance analysis criteria for the designed generator. The paper investigates the design for small-scale wind applications. The design procedure is validated using both 3D-FEM simulations and experimental results. The results show the consistency of the proposed procedure. The procedure is described and applied for a certain configuration and materials. However, it is solely extendable to several other configurations.

Design and Performance Analysis of Double Stator Axial Flux PM Generator for Rim Driven Marine Current Turbines

This paper presents the design and performance analysis of double stator axial flux permanent magnet generators for rim-driven marine current turbines (MCT). In submarine applications, drive train reliability is a key feature for reducing maintenance requirements. Rim-driven, direct-drive, multistator generators can therefore be an interesting solution to improve reliability. In this context, the work presented here focuses on the design of a double-stator, axial flux, permanent magnet (PM) generator as a rim-driven, direct-drive, multistator generator. The models, specifications and an optimization procedure that facilitate the preliminary design of these kinds of generators for rim-driven marine turbines are presented. Validation with finite element computations and a performance analysis for a particular design of rim driven generators are conducted. The results obtained highlight some designs issues associated with PM generators for rim driven marine turbines. To assess the effectiveness of the double stator axial flux PM generator, a comparison with a surface mounted radial flux PM generator design for rim marine turbines is carried out. The comparison shows that the double stator axial flux generator has a better cooling characteristic and a reduced active parts cost and mass than the radial flux PM generator.

Comparative Study on Novel Dual Stator Radial Flux and Axial Flux Permanent Magnet Motors With Ferrite Magnets for Traction Application

This paper proposes two novel traction motors with ferrite magnets for hybrid electric vehicles (HEVs), which have competitive torque density and efficiency as well as operating range with respect to a referenced rare earth magnet motor employed in the third-generation Toyota Prius, a commercialized HEV. The two proposed traction motors, named as dual stator radial flux permanent magnet motor (DSRFPMM) and dual stator axial flux permanent magnet motor (DSAFPMM), adopt the same design concept, which incorporates the unaligned arrangement of two stators together with the use of spoke-type magnet array and phase-group concentrated-coil windings for the purpose of increasing torque density and reducing torque ripple. A finite element method is utilized for predicting the main characteristics, such as back electromotive force, cogging torque, electromagnetic torque, iron loss, and efficiency in both of the proposed motors. Moreover, a comparative study between the proposed DSRFPMM and DSAFPMM is performed under the same operating condition. As a result, it is demonstrated that both of the proposed ferrite permanent magnet motors could be good alternatives for traction application, replacing the rare earth magnet motors.

A Comparative Analysis of Three-Phase, Multi-Phase and Dual Stator Axial Flux Permanent Magnet Synchronous Generator for Vertical Axis Wind Turbine

In this paper, the performances of all the three kinds of Axial type Multi-Pole Permanent Magnet Synchronous Generators (PMSG) namely Three-phase, Multi-phase or Five Phase and Double Stator fixed in Vertical Axis Wind Turbine (VAWT) were investigated and compared in order to get an optimal system. MATLAB/Simulink had been used to model and simulate the wind turbine system together with all the three types Permanent Magnet Generators. It was observed from the result that with the increasing number of pole in both low and high wind speed, the five phase generator produced more power than the other two generators. In general, it was observed that the responses of the Multi-phase generator at both high and low speed wind showed promising aspect towards the system followed by Dual Stator. But with the change of the variables such as wind velocity, turbine height, radius, area together with the generator pole pairs and stator resistance, the optimum system should be chosen by considering the trade-off between different configurations which were firmly analyzed and described in this paper.