Yokeless And Segmented Armature Research Articles

Multi-Objective Optimization of Yokeless and Segmented Armature Machine for In-Wheel Traction Applications Based on the Taguchi Method

For electrical machines with complex structures, the design space of parameters can be large with high dimensions during optimization. Considering the calculation cost and time consumption, it is hard to optimize all the design parameters at the same time. Therefore, in that situation, sensitivity analysis of these design parameters is usually used to sort out crucial parameters. In this paper, the sensitivity analysis-based Taguchi method is applied to optimize the axial-flux permanent magnet (AFPM) machine with yokeless and segmented armature (YASA) topology for an in-wheel traction system. According to the key parameters and their sensitivity analysis, the optimal machine scheme to meet the performance requirements can be formed. In this case study, the machine performance is improved significantly after optimization. Lastly, the experimental results verify the accuracy of the model used in this study.

Study on the Influence of a Combined-Halbach Array for the Axial Flux Permanent Magnet Electrical Machine With Yokeless and Segmented Armature

To increase torque density, a combined-Halbach array for the axial flux permanent magnet machine (AFPMM) with yokeless and segmented armature (YASA) is presented in this paper. Firstly, the YASA machine models with conventional axial magnets and combined-Halbach array magnets are established by using 3-D finite-element method (FEM). Then, the torque, torque per magnet-volume and no-load back electromotive force (back-EMF) are calculated, and the performance of two machines are analyzed and compared. It is demonstrated that the combined-Halbach array can improve the torque density of the machine and the utilization rate of the magnets. Finally, the combined-Halbach array rotor is optimized, where the rotor with unequal-thickness magnets is established, and its torque density is calculated under different thickness. The results show that the combined-Halbach array with unequal-thickness magnets can decrease the amount of permanent magnet materials, thus improve the utilization of magnets and reduce the costs.

Axial Flux Permanent Magnet Motor Topologies Magnetic Performance Comparison

Axial flux permanent magnet motors have attracted increasing attention due to their compact topology and high torque density. Many topological variations have arisen over time; however, limited research has directly compared the differences in magnetic performance of these topologies. This paper carries out a comprehensive investigation, employing both analytical and 3D finite element analyses, to compare the magnetic performance of three topologies: yokeless and segmented armature (YASA), axial flux internal rotor (AFIR), and offset AFIR. The findings reveal that each topology offers specific advantages for different applications. The YASA topology excels in minimizing core losses; the AFIR configuration achieves the highest torque density; and the offset AFIR topology shows the highest efficiency. The offset AFIR topology appears to offer advantages for a wide array of applications due to its higher power factor and lower permanent magnet loss, leading to reduced costs for converter design and cooling system design.

Comprehensive Analysis of Dual-Rotor Yokeless Axial-Flux Motor with Surface-Mounted and Halbach Permanent Magnet Array for Urban Air Mobility

A dual-rotor yokeless and segmented armature (YASA)-type axial-flux permanent magnet (AFPM) motor with a surface-mounted permanent magnet (SPM) array type was developed for urban air mobility (UAM) aircraft in this work. The proposed AFPM motor had rated and peak output powers of 75.5 and 104 kW, respectively, with rated and peak rotational speeds of 1800 rpm. To achieve a high torque, a cobalt–iron alloy core material was used for the stator core. The prototype AFPM motor, developed by KSEP in the Republic of Korea, was successfully manufactured and verified through experimentation. Additionally, the thermal stability of the winding and permanent magnets (PMs) was confirmed with a water-cooling system. A structure analysis of the proposed AFPM motor was conducted due to the detachment of an uneven air-gap length in the prototype AFPM motor. An output performance comparison based on core materials for the stator and rotor was carried out to explore the material cost reduction. Subsequently, the design for performance improvement by applying a Halbach permanent magnet (HPM) array type was investigated for further research.

Pole shape design of ring winding axial flux permanent magnet used in a direct‐drive electric boat for cost‐efficient cogging torque alleviation

AbstractThe recently introduced Ring Winding Axial Flux Permanent magnet Motor (RW‐AFPM) is inspired by the yokeless structure of Yokeless and Segmented Armature (YASA) AFPMs and the partitioned‐phases configuration of transverse flux motors. Its potential application for rim‐driven electric ships propulsion has been examined in the previous studies and, here, it will be studied for ultra‐light direct‐drive electric boats. Owing to their specific structural features, the relatively large cogging torque of RW‐AFPMs seems to be a significant challenge for such applications. On the other hand, as investigated in previous studies, cogging torque reduction methods, such as conventional skewing, seem unsuitable for this type of machine. Thus, this paper will address the cogging torque issue via a comprehensive pole shape analysis. The results will be useful for all kinds of partitioned‐phases topologies that have high specific torque capability but suffer from large cogging effects. All analyses are performed via 3D‐FE models, the accuracy of which is pre‐verified through experiments.

Torque Assessment of Multiphase AFPM Machines With Experimental Validation for YASA Topology

This work presents a theoretical and experimental study on the electromagnetic torque of multiphase axial-flux permanent-magnet (AFPM) machines. Initially, a torque equation is obtained through four different methods. The first method follows the definition of electromagnetic power, the second uses the magnetic shear stress, the third is based on the concept of co-energy, and the fourth applies the principle of Lorentz force. Although these methods are based on different assumptions, they lead to the same generalized torque equation, which depends on four parameters: i) the fundamental air gap induction; ii) the electrical loading defined for an arbitrary rotor radius; iii) the ratio of inner and outer rotor radius; iv) the cubic power of the outer rotor diameter. The torque equation is then validated using finite element (FE) analyses and experimental results obtained with a 32-pole/30-slot yokeless and segmented armature (YASA) machine. For this machine, the coils can be connected according to different arrangements so that the phase number can be chosen as three, five, or fifteen. The results show that the torque equation derived here provides sufficient accuracy in practical cases and that it can be applied to machines with phase numbers higher than three.

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.

Thermal Model Approach to the YASA Machine for In-Wheel Traction Applications

The axial-flux permanent magnet (AFPM) machines with yokeless and segmented armature (YASA) topology are suitable for in-wheel traction systems due to the high power density and efficiency. To guarantee the reliable operation of the YASA machines, an accurate thermal analysis should be undertaken in detail during the electrical machine design phase. The technical contribution of this paper is to establish a detailed thermal analysis model of the YASA machine by the lumped parameter thermal network (LPTN) method. Compared with the computational fluid dynamics (CFD) method and the finite element (FE) method, the LPTN method can obtain an accurate temperature distribution with low time consumption. Firstly, the LPTN model of each component of the YASA machine is constructed with technical details. Secondly, the losses of the YASA machine are obtained by the electromagnetic FE analysis. Then, the temperature distribution of the machine can be calculated by the LPTN model and loss information. Finally, a prototype of the YASA machine is manufactured and its temperature distribution under different operating conditions is tested by TT-K-30 thermocouple temperature sensors. The experimental data matches the LPTN results well.

Design and Development of a Multiphase Inverter for Automotive Applications

This work describes the development of a multiphase inverter that can operate as a platform for driving and testing electrical machines with up to 15 phases, in addition, it can operate with a fundamental frequency of up to 1 kHz and a switching frequency of 100 kHz. Therefore, a multiphase voltage source inverter (VSI) topology using SiC MOSFETs and approved components for automotive applications was designed and constructed. The developed platform is composed of independent power modules and a control module with technology that uses only a single microcontroller capable of generating all signals with pulse width modulation (PWM). To validate the inverter, experimental tests were carried out with a YASA (Yokeless and Segmented Armature) machine that can operate with 3, 5, or 15 phases and also with multi-star connections, one with three independent systems of five phases and another with five independent three-phase systems. Experimental results show that the inverter is capable of driving and testing multiphase machines with a wide variety of electrical connections using high fundamental and carrier frequencies. Therefore, the developed platform is an important tool that allows the testing of multiphase and multi-star electrical machines operating under the most diverse configurations and operating conditions.

A Comparative Study of Yokeless and Segmented Armature Versus Single Sided Axial Flux PM Machine Topologies for Electric Traction

This article systematically compares two axial flux permanent magnet machines designed for a university student racing car application: a double-rotor single-stator yokeless and segmented armature (YASA) structure, and a single-stator single-rotor configuration. Both machines are optimized for minimum loss and active weight using three-dimensional finite element analysis and the highest performing candidate designs are compared in more detail. The studies indicate that the benefits offered by the YASA configuration over the single-stator single-rotor machine are achieved only for specific designs that are heavier. For the design space with lower mass, albeit with increased losses, the Pareto front designs overlap. In this envelope, the YASA configuration demonstrates higher efficiencies at higher speeds, whilst the single-stator single-rotor is more efficient in high torque duty cycles. This shows the performance of the two machines is very similar and the choice is application specific. To validate the finite element analysis used in the optimization, a prototype was built and tested. Results showed good alignment between simulation and experimental data.

Development and Investigation of Novel Axial-Field Dual-Rotor Segmented Switched Reluctance Machine

This article presents a new type of axial-field switched reluctance machine (AFSRM) and axial-field dual-rotor segmented switched reluctance machine (ADS-SRM), along with its design methodology. The proposed ADS-SRM is featured by the segmental stator and rotor poles, the auxiliary flux-conductive rings, and the concentrated windings. The yokeless topology reduces the active length of the motor. Besides, the adopted short-end winding layout increases the slot-fill factor and the motor's reliability. First, the basic topology of ADS-SRM is introduced along with its operating principle and various stator/rotor pole combinations. The three-phase 12/8 configuration of ADS-SRM is chosen for further analysis. Then, the design methodology considering the fringing and leakage field effects through the magnetic equivalent circuit (MEC) method is developed, and the flowchart detailing the design procedure is presented. Through the comparison with the conventional yokeless and segmented armature (YASA) topology, ADS-SRM exhibits excellent performance at overload conditions. The prototype is designed and fabricated, and the experimental results verify the motor performance.

An Air-Cooled YASA Motor for in-Wheel Electric Vehicle Applications

In-wheel motors present a range of opportunities for innovation in electric vehicle design as the torque produced at each of two or four wheels can be controlled individually. A high-aspect ratio (large radius, short axial length) motor is required to fit within the wheel. Due to its location, liquid cooling of the in-wheel motor is difficult and undesirable, but a high power density is required to reduce the mass—which is particularly important as it is unsprung—and fit the space envelope. Furthermore, a high-torque density is required to eliminate the need for a gearbox. These constraints create a real challenge for the design of a machine for this application. An axial field machine using a yokeless and segmented armature (YASA) topology is designed to fit these requirements as such a machine has clear advantages when considering the high-aspect ratio. A soft magnetic composite material is utilized to carry the flux in its nonplanar path without incurring excessive losses or requiring a lamination design, which is difficult and expensive to manufacture. A novel cooling arrangement involving heat-spreading elements on each armature segment is employed to improve heat dissipation and, hence, power density. The design, analysis, manufacturing, and testing of the motor is described in this article to verify the concept against the requirements outlined earlier.

Comparison and Analysis of Stator Plate Holder on Yokeless and Segmented Armature Machine

This paper deals with comparison and analysis of stator plate holder on Yokeless and segmented armature (YASA) machine. YASA topology consists of two rotors and one inner stator comprised of many independent segments. Core for stator uses Soft Magnetic Composite (SMC) to conduct the three-dimensional magnetic flux. All stator segments and concentrated winding are fixed with the aid of two annular plates. There are cavities on both plates which have the same shape as the shoe of the stator segment. Moreover, the deformation of the plates must be kept as low as possible and have very high yield strength because of stress from the bearing. A complex structure, high durability, and high electrical resistance are the challenges. Polyetheretherketone (PEEK) is usually used as the plates, however high price and manufacturing cost remain an issue. Some other materials have a possibility and approach to PEEK capability. In this paper, candidate materials will be developed as a specimen and tested on the BH - Curve meter. The BH-Curve data provide simulation on Finite Element Magnetic Method (FEMM). The advantages and disadvantages are discussed in this paper. The analysis result demonstrates that other materials possess a similar capability as PEEK related to YASA stator plate holder.

Dual-Skew Magnet for Cogging Torque Minimization of Axial Flux PMSM With Segmented Stator

Reduction of the cogging torque is preferred during the design process of a permanent magnet (PM) synchronous machine (PMSM), especially in the low-speed traction applications. This article presents a dual-skew magnet technique to minimize the cogging torque in the axial-flux permanent-magnet (AFPM) motor with a yokeless and segmented armature (YASA). The theoretical expression of the cogging torque of the AFPM machine is deduced, and the advantages of the dual-skew magnet are verified by comparing with a sector shape magnet and a conventional skew magnet using the 3-D finite-element method (FEM). The simulation results show that, compared with the other two magnet topologies, the machine equipped with the dual-skew magnet shows its advantages in the reduction of cogging torque, torque ripple, and magnet eddy current loss.

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.

Multiphysics Analysis of an Axial-Flux In-Wheel Motor With an Amorphous Alloy Stator

This paper presents a novel yokeless and segmented armature (YASA) axial-flux in-wheel motor with amorphous magnetic material (AMM) stator cores for a solar-powered electric vehicle. Although this new axial-flux in-wheel motor has many advantages such as high efficiency, shorter axial length, and high power density, its working condition is complicated. In-wheel motors are usually operated in electromagnetic, thermal, and other multiphysics environments. Increasing the performance requirements of in-wheel motors, such as power density, efficiency, and reliability, requires a multiphysics design approach. The focus of this paper is on the analysis of electromagnetic characteristics, losses, temperature distribution, mechanical behavior and other characteristics of the axial-flux in-wheel motor. The back electromotive force (EMF) and electromagnetic torque of the motor with harmonic current are obtained by the 3-D finite element method (FEM). The permanent magnet (PM) eddy-current losses when using different PM shapes are studied. The equivalent thermal model of the tape-wound AMM stator segments and the windings are established, and the temperature distribution of the motor is obtained. The mechanical behavior of the stator segments and the rotor disks when the motor is eccentric and axially offset is analyzed, and the structural strength of the motor is evaluated. Finally, a prototype of the motor is fabricated, and the electromagnetic performance and temperature of the motor are tested to verify the accuracy of the multiphysics design approach.

Parametric Studies for Combined Convective and Conductive Heat Transfer for YASA Axial Flux Permanent Magnet Synchronous Machines

In this paper, the effect of some geometrical parameters on the steady state average temperature of the stator core, the winding and the permanent magnets of the yokeless and segmented armature (YASA) axial flux permanent magnet synchronous machine (AFPMSM) is studied. The geometrical parameters selected for the study are the air gap length, the inward heat extraction fin thickness and the permanent magnet thickness. These parametric studies make it possible to obtain a better trade-off between power density and efficiency. These investigations are very helpful in correlating the values of the geometrical parameters to some specific desired performance criteria like not going below some desired minimum efficiency, limiting the temperature of specific part to some maximum value for maximization of lifetime and also determination of the allowed speed range to limit the temperatures lower than the critical values. This is important specifically for the synchronous machines due to the fact that the speed value affects both the losses and the heat transfer convection coefficients. The air gap length has a direct effect on the overall machine losses and the air gap convection coefficient and hence on the temperature of the machine. As the fins are between the stator windings, a thicker fin reduces the space for copper windings and hence increases the losses, but at the same time improves heat evacuation. In addition, the effect on the temperature is studied of the speed variation, which influences both the losses and the convection coefficients of the machine. Every study is made based on coupled electromagnetic and thermal models. The results are obtained from analytical electromagnetic and thermal models verified by finite element simulations and validated experimentally on a 4 kW yokeless and segmented armature axial flux machine.

A 3D Dynamic Lumped Parameter Thermal Network of Air-Cooled YASA Axial Flux Permanent Magnet Synchronous Machine

To find the temperature rise for high power density yokeless and segmented armature (YASA) axial flux permanent magnet synchronous (AFPMSM) machines quickly and accurately, a 3D lumped parameter thermal model is developed and validated experimentally and by finite element (FE) simulations on a 4 kW YASA machine. Additionally, to get insight in the thermal transient response of the machine, the model accounts for the thermal capacitance of different machine components. The model considers the stator, bearing, and windage losses, as well as eddy current losses in the magnets on the rotors. The new contribution of this work is that the thermal model takes cooling via air channels between the magnets on the rotor discs into account. The model is parametrized with respect to the permanent magnet (PM) angle ratio, the PM thickness ratio, the air gap length, and the rotor speed. The effect of the channels is incorporated via convection equations based on many computational fluid dynamics (CFD) computations. The model accuracy is validated at different values of parameters by FE simulations in both transient and steady state. The model takes less than 1 s to solve for the temperature distribution.

Analysis and selection of harmonics sensitive to demagnetisation faults intended for condition monitoring of double rotor axial flux permanent magnet synchronous machines

Yokeless and segmented armature (YASA) axial flux permanent magnet synchronous machines may have asymmetrical demagnetisation defects in their two rotors. Condition monitoring, therefore, becomes more complicated than in conventional single rotor machines. To develop a real-time condition monitoring algorithm for demagnetisation faults in YASA machines – which requires solving an inverse problem – a fast forward model is necessary. A frequency-based analytical model is used to calculate the three-phase terminal voltages based on the three-phase current waveforms and the demagnetisation defects including asymmetrical defects in the two rotors. To reduce the computational time of the forward model, this study focuses on the sensitivity of different voltage harmonics on several demagnetisation faults. To this end, the Cramer–Rao lower bound technique is used to analyse the harmonics sensitivity to the demagnetisation faults. The goal of the sensitivity analysis is to select an appropriate set of harmonics that gives maximal information about the defects. It becomes much faster and useful for real-time condition monitoring. The results of the analysis show that the subharmonics around and including the fundamental are the most sensitive harmonics to the demagnetisation defects. The analytical model is validated with experimental data and finite element simulations.

Air inlet/outlet arrangement for rotor cooling application of axial flux PM machines

The maximum power and torque of a Permanent Magnet (PM) machine may be limited by its magnets’ temperature. An operational temperature above the magnets’ threshold may cause demagnetization, particularly under abnormal conditions. For Axial Flux Permanent Magnet (AFPM) machines, the PMs are mounted on its rotor, therefore, one way to regulate the PM temperature is via an appropriate rotor cooling method. Selective designs of air inlet and outlet arrangement have been studied by the Computational Fluid Dynamics (CFD) analysis to assess and compare their flow and cooling capabilities. The new cooling designs were then implemented on a Yokeless and Segmented Armature (YASA) machine for flow experimental validation. Additionally, the cooling performance after the design implementation is analysed via CFD. This paper’s proposed cooling method is expected to lead to lower magnet temperatures, thus increased reliability, output power and efficiency.