Axial flux motor mass reduction with improved cooling.
The aim of the paper is the comparison of the axial flux motors structures versus the conventional radial flux (RF) structures for PM synchronous motors. The comparison procedure is based on simple thermal considerations. Two motor typologies are chosen and compared in terms of delivered electromagnetic torque. The comparison is developed for different motor dimensions and the pole number influence is put into evidence. The paper reports the complete comparison procedure and the related results analysis. The obtained results show that, when the axial length is very short and the pole number is high, axial flux motors can be an attractive alternative to conventional radial flux solutions.
Methods and apparatus are provided for an axial flux motors. The apparatus comprises, a stator having coils thereon for producing a magnetic field, a rotor rotated by the magnetic field, and an output shaft coupled to the rotor. The rotor includes a magnetic and non-magnetic component. The non-magnetic component has a lower density than the magnetic component. One or both of the rotor components have apertures therein for ventilation and weight reduction. Permanent magnets are desirably mounted on the magnetic component of the rotor facing the stator and portions of the rotor behind the permanent magnets are hollowed out to be thinner than portions of the rotor between the permanent magnets. This reduces rotor weight without significantly affecting magnetic axial flux motors density in the rotor or motor torque.
An axial flux electric motor comprising a rotor and a first and second stator. The first and second stators have a first and second air gap located between the first and second stators and the rotor, respectively, and the second air gap is greater than the first gap. In one embodiment, the coils of the first stator and the coils of the second stator are in parallel. The motor further comprises switches which alternatingly energize the coils of the first stator and of the second stator based upon required torque and required speed of the motor. In a second embodiment, the coils of the first stator and the coils of the second stator are in series and the motor further comprises switches which selectively bypass the coils of the second stator in order to reduce the back EMF of the motor and increase the maximum speed of the motor at a given input voltage.
We present dedicated designs of optimal current waveforms for disk-type axial flux motors wheel motors. The four-phase dedicated wheel motor has been designed and installed directly inside the wheel of electrical vehicles without mechanical differentials and reduction gears. We performed a torque-oriented optimization to obtain the optimal current waveform subject to various constraints for the independent winding structure. We found that the best optimal waveform with maximized torque and confined ohmic loss is proportional to the magnetic flux variation in the air gap between the stator and the rotor and has the same shape as the back-electromotive force (EMF). This finding is confirmed by both theoretical and numerical analyses. As expected, the current control waveform of the back-EMF extracted by experiments renders the best performance in terms of maximum torque and motor efficiency.
Because Axial Flux Induction Motors (AFIMs) have many advantages over radial flux (conventional) ones, they are increasingly used in industrial applications. So, their performance prediction is an important issue. On the other hand, parameter estimation is an inseparable part of performance prediction. In this paper, a new method, based on the discharge current of stator windings, is presented. In the proposed method, theoretical and practical discharge currents are compared to calculate coefficients, time constants and parameters. Then, calculated parameters are employed in the d-q model of the AFIM. Finally, 3-D finite element analysis and experimental tests are used to verify the proposed method.
Two design-and-analysis cases of a line-start axial-flux permanent-magnet motor: with solid rotor and with composite rotor. For a novel structure of the motor, two concentric unilevel spaced raised rings are added to the inner and outer radii of its rotors to enable auto-start capability. The composite rotor was coated by a thin (0.05 mm) layer of copper. The basic equations for the solid rotor ring were extracted. The motor's lack of symmetry necessitated 3D time-stepping finite element analysis, conducted via Vector Field Opera 14.0, which evaluated the design parameters and predicted the motor's transient performance. Results of the FEA show the composite rotor significantly improving both starting torque and synchronization capability over solid rotor.
The magnetic field distribution for a three-phase, disc-type, permanent-magnet, brushless DC motor with co-axial flux in the stator. Calculations are carried out using the 3-D finite element method (FEM). The electromagnetic torque is determined from the Maxwell stress tensor. For comparison, various dimensions of permanent magnets, pole shoes and air gap are analysed. It is shown that the ripple-cogging torque can be effectively reduced by an appropriate permanent magnet width and air-gap length. The simulation results are in good agreement with experimental data obtained from the prototype motor.
Axial flux hysteresis motor (AFHM) is self-starting synchronous motor that uses the hysteresis characteristics of magnetic materials. It is known that the magnetic characteristics of hysteresis motor could be easily affected by air gap and structure dimensions variation. Air gap length plays an important role in flux distribution in hysteresis ring and influences the output torque, terminal current, efficiency and even optimal value of other structural parameters of AFHM. Regarding this issue, in this study effect of air gap variation on performance characteristics of an axial flux hysteresis motor and effect of air gap length on hysteresis ring thickness and stator winding turns is investigated. Effect of air gap length on electrical circuit model is perused. Finally, simulation of AFHM in order to extract the output values of motor and sensitivity analysis on air gap variation is done using 3D-Finite Element Model. Hysteresis loop in the shape of an inclined ellipse is adopted. This study can help designers in design approach of such motors.
Low-cost double rotor axial flux motor (DRAFM) with low cost soft magnetic composite (SMC) core and ferrite permanent magnets (PMs). The topology and operating principle of DRAFM and design considerations for best use of magnetic materials are presented. A 905W 4800rpm DRAFM is designed for replacing the high cost NdFeB permanent magnet synchronous motor (PMSM) in a refrigerator compressor. By using the finite element method, the electromagnetic parameters and performance of the DRAFM operated under the field oriented control scheme are calculated. Through the analysis, it is shown that that the SMC and ferrite PM materials can be good candidates for low-cost electric motor applications.
Axial Flux Interior PM (AFIPM) synchronous motors, as candidates for small electric city cars drives, are presented in this work. The motor parameters effects on the motor torque performance are examined by the analysis of the stator current trajectories in the (id-iq) plane. The AFIPM motor parameters are designed by this analysis to make the motor power capability matching the torque requirements, considering the inverter current and the DC voltage limits.Furthermore, the voltage-limited optimum Torque per Ampere trajectory is drawn in the (id-iq) plane. It is shown that the proper choice of the motor parameters is a trade off between the parameters to get the ideal operating characteristic for the optimum control over a wide speed range and the parameters to get the high operating torque at low speed. Finally, some design considerations and the simulation results for a 180V (DC bus voltage), 10kW AFIPM synchronous motor drive for electric vehicles are presented.
The traction of an electrical vehicle (EV). The power unit is a Permanent Magnet Synchronous Motor (PMSM) piloted by the trapezoidal control, strategy. The models of the electrical vehicle, of the motor based on finite element identification and the drive, are implemented under Matlab/Simulink 7.1. The control is ensured by four closed loops, one for speed and three other for currents regulation. The results of the simulation show the effectiveness of the trapezoidal control for the electric traction systems.
An axial flux induction motor containing both laminates and soft magnetic composite materials is described. By combining these two materials, the axial flux induction motor obtains a limited volumetric space, including a limited height, and smooth torque output, including a limited ripple. The axial flux induction motor also contains rotors bars that are skewed. These skewed bars smooth the torque pulsations of the induction motor, enhancing an efficient operation of the motor.
The development of a "weight-power trade-off" applicable to high-performance, power limited vehicles. The theory is then applied to the electric vehicle case to justify the pursuit of an "in the wheel" motor design. The singular benefits of axial flux geometry are discussed with reference to the particular requirements of electric motors for vehicular applications. The basic design process, construction, and test results for a motor fitted in a 26 inch wheel to drive a 260 kg all up weight vehicle are presented. At an output power of 1 kW, the attainable vehicle speed is 72 km/h, corresponding to a motor/wheel speed of 578 r/min and torque of 16.5 Nm, at an estimated motor efficiency of 94%.
We have applied multiobjective optimal design to a brushless dc wheel motor. The resulting axial-flux permanent-magnet motor has high torque-to-weight ratio and motor efficiency and is suitable for direct-driven wheel applications. Because the disk-type wheel motor is built into the hub of the wheel, no transmission gears or mechanical differentials are necessary and overall efficiency is thereby increased and weight is reduced. The dedicated motor was modeled in magnetic circuits and designed to meet the specifications of an optimization scheme, subject to constraints such as limited space, current density, flux saturation, and driving voltage. In this paper, two different motor configurations of three and four phases are illustrated. Finite-element analyses are then carried out to obtain the electromagnetic, thermal, and modal characteristics of the motor for modification and verification of the preliminary design. The back-electromotive forces of prototypes are examined for control strategies of current driving waveforms.
Original features such as compactness and lightness make slotless axial-flux permanent-magnet machines (AFPMs) eligible for application in large power motor drives devoted to the direct drive of ship propellers. This paper discusses characteristics of AFPMs designed for application in marine propulsion, and machine performances such as efficiency, weight and torque density are evaluated for a comparison with those of conventional synchronous machines. A newly-conceived modular arrangement of the machine stator winding is proposed and experimental results taken from a small-size machine prototype are finally shown.
In electric vehicle (EV) motor drives, the use of a low-speed motor coupled directly to the wheel axle allows a reduction of the vehicle weight and an improvement in the drive efficiency. Slotless axial-flux PM motors are particularly suited for such an application, since they can be designed for high torque-to-weight ratio and efficiency. This paper deals with a 16 poles axial-flux PM motor prototype which is used in the propulsion drive of an electrical scooter. The motor prototype has 45 Nm peak torque, 6.8 kg active materials weight, and is coupled directly to the scooter rear wheel. The paper discusses design and construction of the motor prototype, and reports experimental results achieved from laboratory tests. Finally, details concerning the arrangement of the scooter motor drive are given.
Development of all-electric aircraft would enable more efficient, quieter and environmentally friendly vehicles and would contribute to the global reduction of greenhouse gas emissions. However, conventional electric motors do not achieve a power density high enough to be considered in airborne applications. Bulk high temperature superconducting (HTS) materials, such as YBCO pellets, have the capacity of trapping magnetic flux thus behaving as permanent magnets. Experimental data show that one single domain YBCO pellets could trap up to 17 T at 29 K, which enables the design of very high power density motors that could be used in aircraft propulsion. We designed a superconducting motor based on an axial flux configuration and composed of six YBCO plates magnetized by a superconducting coil wound on the outside of the motor. The six-pole homopolar machine uses a conventional air-gap resistive armature. Axial-flux configuration allows several rotors and stators to be stacked together and therefore enables the use of one or several conventional permanent magnet.
Construction of two twin prototypes of slotless axial-flux permanent-magnet motor drives jointly developed by SIMINOR Ascenseurs and the University of Rome for application in direct-drive elevator systems without a machine room. Each prototype of pulley-direct-drive motor is rated 5 kW, 95 rev/min, and has a shaft height of 380 mm and overall axial thickness of about 80 mm. Machine design based on unusual specification and original manufacturing solutions adopted for the proposed direct-drive elevator arrangement are discussed throughout the paper, including the leading dimensions and characteristics of the prototype motors. Finally, experimental results taken from the machine prototypes are reported.
A power unit assembly which has a pair of mirrored axial flux electric motors having a common axis of rotation, each axial flux motor including a rotor disposed on a rotor shaft and at least one stator disposed in operative relationship to said rotor. A common end plate is disposed between each of the pair of axial flux electric motors to provide a common mounting structure, while an output hub is operatively coupled to each rotor shaft of the pair of mirrored axial flux electric motors. Each of the pair of mirrored axial flux electric motors is operatively configured to provide independent speed and torque to each associated output hub.
Original features such as compactness and lightness make slotless axial-flux permanent-magnet machines (AFPMs) eligible for application in large power motor drives devoted to the direct drive of ship propellers. The paper discusses characteristics of AFPMs designed for the marine propulsion application. A newly-conceived modular arrangement of the machine stator winding is proposed and experimental results taken from a small-size machine prototype are finally given.
Analysis and experiment of an axial flux permanent magnet (AFPM) brushless direct current (BLDC) motor with minimized cogging torque. Recently, many optimal designs for the AFPM motor have been done by finite-element (FE) analysis, but such analysis generally is time-consuming. In this study, the equation of magnetic flux lines existing between PMs and cores is assumed mathematically and the minimum cogging torque is calculated theoretically and geometrically without FE analysis. The form of equation is assumed to be a second-order polynomial in this paper. The skew angle that makes the cogging torque minimized is calculated theoretically, and the value of minimum cogging torque is confirmed by FE analyses and experiments. In the theoretical analysis, the maximum cogging torque of a proposed AFPM motor has the smallest value approximately at a skew angle of 4and that value is about the same as those of FE analysis and experiments. Compared with the nonskewed motor, the cogging torque of the skewed motor can be decreased.
A multi-objective optimal design of a brushless dc disc-type axial-flux wheel motor and its optimal current waveforms are presented in this paper. This dedicated motor is modeled in magnetic circuits, and designed to meet the specifications of an optimization scheme, subject to constraints, such as limited space, current density, flux saturation and driving voltage. The torque-oriented optimization is then performed to obtain the optimal current waveform subject to various constraints for the independent winding structure. The best optimal waveform with maximized torque and confined ohmic loss is found to be proportional to the magnetic flux variation in the air-gap between the stator and the rotor, which is verified the same shape.
A variety of techniques exist for reducing the cogging torque of conventional radial flux PM machines. Even though some of these techniques can be applied to axial flux machines, manufacturing cost is especially high due to the unique construction of the axial flux machine stator. Consequently, new low cost techniques are desirable for use with axial flux PM machines. This paper introduces a new cogging torque minimization technique for axial flux multiple rotor surface magnet PM motors. First, basic principles of the new technique are explored in this paper. A 3-kW, 8-pole axial flux surface-magnet disc type machine with double-rotor-single-stator is then designed and optimized in order to apply the proposed new method. Optimization of the adjacent magnet pole-arc which results in minimum cogging torque as well as assessment of the effect on the maximum available torque using 3D finite element analysis (FEA) is investigated. The minimized cogging torque is compared with several existing actual machine data and some important conclusions are drawn.
Minimizing cogging torque in designing axial-flux permanent-magnet (AFPM) motors is one of the main issues which must be considered during the design process. This paper presents several cost-effective magnet-skewing techniques to minimize cogging torque components in double-rotor AFPM motors. Rotor-side cogging torque minimization methods are examined in detail with major focus on magnet-skewing approach, and several cost-effective alternative skewing techniques are proposed. A detailed comparison of magnet-skewing approaches is provided. A prototype AFPM motor with different rotor structures is built based on the analyses. Analyses are then validated with experimental results, and the influence of cogging torque component on torque quality of AFPM motors is explored. The results confirm that the proposed magnet-skewing approaches can significantly reduce the cogging component as opposed to reference AFPM motor with unskewed magnets and help to improve the torque quality of the disk motors.
Different measurement and identification approaches applied to a nonconventional permanent-magnet (PM) synchronous machine, namely, the novel axial flux interior PM (AFIPM) synchronous motor. The nonconventional geometry of the AFIPM motor requires a dedicated discussion on the parameter identification subject. In the paper, the standstill frequency-response test and the standstill time-response test on the AFIPM prototype are presented. On the basis of these tests, the d- and q-axes circuit parameters are chosen. To confirm the validity of the standstill tests, the load tests have also been performed. Furthermore, the load tests provide some preliminary AFIPM machine performance results and additional information on the saturation phenomena. The d- and q-axes equivalent circuits parameters obtained by the performed measurements are analyzed and compared. Finally, the most appropriate AFIPM machine model is selected.
A novel axial flux interior PM (AFIPM) synchronous motor for wheel-motor applications is presented. Due to the new anisotropic rotor structure, the AFIPM motor can deliver constant power with flux weakening operation. The rotor construction is feasible only using powdered soft magnetic materials. The proposed design procedure uses the finite element method (FEM) in addition to the classical electric motor design rules. Complete design data of the prototype under study are presented and the manufacturing stage of the prototype is described too. The computed values of the machine parameters are compared to the values determined on the basis of experimental measurements. Finally the prototype motor characteristics are determined and presented.
As aircraft technology is moving towards more electric architecture, use of electric motors in aircraft is increasing. Axial flux BLDC motors (brushless DC motors) are becoming popular in aero application because of their ability to meet the demand of light weight, high power density, high efficiency and high reliability. Axial flux BLDC motors, in general, and ironless axial flux BLDC motors, in particular, come with very low inductance Owing to this, they need special care to limit the magnitude of ripple current in motor winding. In most of the new more electric aircraft applications, BLDC motor needs to be driven from 300 or 600 Vdc bus. In such cases, particularly for operation from 600 Vdc bus, insulated-gate bipolar transistor (IGBT)-based inverters are used for BLDC motor drive. IGBT-based inverters have limitation on increasing the switching frequency, and hence they are not very suitable for driving BLDC motors with low winding inductance. In this study, a three-level neutral point clamped (NPC) inverter is proposed to drive axial flux BLDC motors.
Size reduction has become one of the most important aspects of motor design. This paper presents a miniature axial-flux spindle motor with a rhomboidal printed circuit board (PCB) winding. The design of its mechanical structure aims to eliminate any unnecessary space. Prior to prototyping, the motor geometry is calculated using an approximate analytical model, which helps speed up the design process. The flexible PCB winding represents an ultrathin electromagnetic exciting source where coils are wound in a rhomboidal shape in order to reduce the end-winding length and minimize the copper loss. The design process also incorporates finite-element analysis for further performance evaluation and refinement. The proposed motor is prototyped, and excellent agreement is found between simulation and measurement.
Optimal current waveforms for disk-type axial-flux wheel motors. The four-phase dedicated wheel motor has been designed and installed directly inside the wheel of electrical vehicles without mechanical differentials and reduction gears. We performed a torque-oriented optimization to obtain the optimal current waveform subject to various constraints for the independent winding structure. We found that the best optimal waveform with maximized torque and confined ohmic loss is proportional to the magnetic flux variation in the air gap between the stator and the rotor and has the same shape as the back-electromotive force (EMF). This finding is confirmed by both theoretical and numerical analyses. As expected, the current control waveform of the back-EMF extracted by experiments renders the best performance in terms of maximum torque and motor efficiency.
