High Torque Capability Research Articles

Performance Comparison of AFDS PMSG During Voltage Regulation by Mechanical Field-weakening in Extended-speed-range

Background: Axial-flux permanent magnet synchronous generators (AFDS PMSG) have been found suitable in wind energy conversion system and electric vehicle owing to its compactness, high torque capability at low speed, high torque to inertia ratio, modular geometry, and high magnet usability index. Such applications require the generator to operate in Extended Speed Range (ESR). In ESR, voltage regulation is achieved by generator field-weakening. Usually, negative daxis current is injected in the armature winding of the generator to achieve field-weakening. However, in the axial-flux machine field-weakening by current injection is not substantial due to the low inductance of the machine and use of permanent magnets with high coercivity. We have revised all patents related to field-weakening methods applied to axial-flux permanent magnet generators. Methods: Therefore, this paper emphasizes field-weakening using mechanical methods. This paper compares the performance of AFDS PMSG topologies based on its mechanical-field-weakeningbased voltage regulation capability. In this paper, generator field-weakening is achieved by angularly displacing, one of the stators with respect to the other via a mechanical actuator. Results: The experimental results show that during voltage regulation of the DS PMSG with perfectsinusoidal back-emf characteristic, least amount of harmonics is injected in the generated output power. Conclusion: Thus, the same is best suited to design an automotive generator based on MFW method for wind energy conversion system and electric vehicle running in ESR.

Efficient Gear Ratio Selection of a Single-Speed Drivetrain for Improved Electric Vehicle Energy Consumption

The electric vehicle (EV) market has grown over the last few years and even though electric vehicles do not currently possess a high market segment, it is projected that they will do so by 2030. Currently, the electric vehicle industry is looking to resolve the issue of vehicle range, using higher battery capacities and fast charging. Energy consumption is a key issue which heavily effects charging frequency and infrastructure and, therefore, the widespread use of EVs. Although several factors that influence energy consumption of EVs have been identified, a key technology that can make electric vehicles more energy efficient is drivetrain design and development. Based on electric motors’ high torque capabilities, single-speed transmissions are preferred on many light and urban vehicles. In the context of this paper, a prototype electric vehicle is used as a test bed to evaluate energy consumption related to different gear ratio usage on single-speed transmission. For this purpose, real-time data are recorded from experimental road tests and a dynamic model of the vehicle is created and fine-tuned using dedicated software. Dynamic simulations are performed to compare and evaluate different gear ratio set-ups, providing valuable insights into their effect on energy consumption. The correlation of experimental and simulation data is used for the validation of the dynamic model and the evaluation of the results towards the selection of the optimal gear ratio. Based on the aforementioned data, we provide useful information from numerous experimental and simulation results that can be used to evaluate gear ratio effects on electric vehicles’ energy consumption and, at the same time, help to formulate evolving concepts of smart grid and EV integration.

Analysis of cogging torque in dual-stage magnetically geared devices considering magnetic flux coupling

The dual-stage magnetically geared machine (DSMGM) has a high gear ratio. The first stage is a Vernier machine (VM), and the second stage is a coaxial magnetic gear (CMG). These two components share a common rotor (CR), and they are partially flux coupled. Two DSMGMs with different PM arrangements are fabricated and tested. The DSMGM-I with gear ratio 34 can work smoothly, while the DSMGM-II with gear ratio 14.875 is hard to be started up. The purpose of this paper is to reveal the failure of the DSMGM-II. Due to the magnetic flux coupling, there is a recessive CMG in DSMGM structure. The recessive CMG in DSMGM-II prototype is activated and results in high cogging torque and high torque ripple. The thickness of CR yoke controls the portion of flux penetrating through stator. When the thickness of CR yoke is large enough, the cogging torque of the DSMGM-II can be improved. Moreover, another effective method to improve the cogging torque is designing a flux barrier to magnetically decouple the VM and CMG components. For direct-drive robotic application, a DSMGM with Halbach-PM-array is presented. It has a high gear ratio, high torque capability and low cogging torque.

Control of an over-actuated spacecraft using a combination of a fluid actuator and reaction wheels

In 2017, Technische Universität Berlin (TU Berlin) has launched the first space-rated fluid-dynamic actuator (FDA) on the TechnoSat mission. This type of actuator is unique with respect to its dynamic properties, as it offers a very high torque but limited angular momentum storage capabilities in comparison to reaction wheels (RWs). In combination with the tetrahedron RW assembly featured on the spacecraft, a unique combination of attitude control actuators has been formed. The spacecraft axis parallel to the FDA is over-actuated, featuring control actuators of contrasting nature which offers novel options in terms of spacecraft operations. However, with the camera axis on TechnoSat being aligned parallel to the actuator’s axis of rotation, there is limited operational use to this setup.In July 2019, TU Berlin launched Berlin Experimental and Educational Satellite 9 (BEESAT-9) – the first CubeSat featuring a set of three orthogonal RWs and a single picosatellite fluid-dynamic actuator (pFDA) for attitude control. The camera axis of BEESAT-9 is perpendicular to the actuator axis, and therefore allows the demonstration of the proposed novel modes of operation. Among the proposed modes is an artificial increase of the swath and the acquisition of stereo images of multiple, successive targets on the ground. Crucial to these operation scenarios is the control allocation between the RW assembly and the single pFDA.This paper first introduces the spacecraft and describes the proposed novel modes of operation that are enabled by the actuator combination realized on BEESAT-9, followed by a review of the state of the art of control allocation for over-actuated spacecraft. The main part of the paper comprises a description of the implementation of the dynamics models of the attitude control actuators and spacecraft, followed by a description of the implemented high-level control laws and control allocation methods. Finally, simulation results for the artificial swath increase and the single spacecraft stereo imaging mode are appended and discussed.

48 V Starter-Generator Induction Machine With Pole-Changing Windings

An electronic pole-changing winding induction machine with eight and four poles for a 48-V starter-generator application is studied in this article. Starter-generators require high torque capability for short durations at low speed for cranking, a wide flux weakening region for regeneration, as well as high torque density, so that the machine may be integrated into a drive train with minimum change to the existing system. In this article, it is shown that when pole-changing windings are used, the axial length of the machine can be reduced compared to the baseline induction machine design, resulting in a more compact machine. The effects of shorter stack length and pole-changing windings on the performance of the induction machine are studied. Efficiency, loss, and power factor maps are calculated with analytical and finite-element methods and experimentally validated to compare the performance of the pole-changing winding induction machine with a baseline design under various operating conditions.

Six-Phase Pole-Changing Winding Induction Machines With Improved Performance

Automotive starter-generator applications require a high peak torque for cranking and a wide speed flux weakening region for generation. In such applications, the pole-changing winding induction machine offers a wide speed flux weakening region with a low pole number and a high peak torque capability when operated with a higher number of poles. In this article, a 6-phase, electronic pole-changing winding induction machine with improved performance over the existing 3-phase pole-changing is discussed. Compared to the 3-phase 120o phase belt winding, the proposed 6-phase pole-changing winding induction machine shows a 15 % increase in peak torque due to improved winding factor. Finite element analysis is used to predict the torque capability, losses and efficiency of the 6-phase and 3-phase pole-changing winding induction machines. A 1kW induction machine is prototyped and the improved torque capability of the 6-phase pole-changing machines over 3-phase counterparts is experimentally validated under various operating conditions.

A New Exterior-Rotor Multiple Teeth Switched Reluctance Motor With Embedded Permanent Magnets for Torque Enhancement

In this article, a novel exterior-rotor multiple teeth enhanced-torque switched reluctance motor (SRM) is proposed, which exploits permanent magnets (PMs) inside the end teeth of the neighboring stator poles. First, the topology of the proposed motor, namely PM-SRM, is introduced and its working principle is illustrated. Then, based on the magnetic equivalent circuit (MEC) of the motor, it is proven that the PMs contribute to increase the air-gap flux density and regulate the stator poles flux density. As a result, the output torque of the motor is increased as well. The electromagnetic analyses of the proposed PM-SRM are performed using 3-D finite-element analysis. To validate the improved performance of the proposed PM-SRM, it is compared with its PMless counterpart and a classical 12/10-pole SRM in terms of the output torque and power, losses, and efficiency. It is shown that the proposed motor outperforms the two compared motors in terms of the output power and torque, and efficiency. Finally, a prototype of the motor is fabricated and tested to evaluate the predicted results. Both simulation and experimental results demonstrate the high torque and power production capability of the proposed PM-SRM.

Dynamic modelling and torque ripple minimization of a lightweight ultra-high transmission ratio harmonic drive

Harmonic drives have been of significant importance in many industrial and high-end applications including robotics, aerospace and manufacturing. Their unique characteristics combine high torque capabilities, high to ultra-high transmission per stage and low backlash performance in compact designs, suited for limited space applications. However, apart from the eminent merits of the technology, this type of gearboxes is associated with complex dynamic performance. Since their operations is associated with high compliance and friction a non – linear behavior is imposed to the system. This is also intensified due to torque ripples which in many cases apart from adding up to the overall complexity of the system, can also interfere with components of similar resonance frequency. In the frame of this paper a novel concept for a low-cost lightweight plastic harmonic drive used in positioning of telecommunication antennas is presented. Due to the tight dynamic specifications of the application (settling time, positioning error etc.) the torque ripple of the transmission was modelled and minimized. Design changes were also incorporated in various features in order to improve the overall dynamic performance.

Scale-up of NiTiHf shape memory alloy tubes with high torque capability

High-torque, NiTiHf high-temperature shape memory alloy tubes were examined by means of constant-torque thermal cycling experiments. The alloy, with a Ni-rich composition of Ni50.3Ti29.7Hf20 (at%), was hot worked via extrusion from large ingots to produce final rods with an outer diameter of 25.4 mm. After aging at 550 °C for 3 h and air-cooling, the manufactured torque tubes were subjected to shear stresses from 0 to 500 MPa (torques of 0–1400 N m) and thermally cycled 20 times under stress, and twice after stress removal to evaluate the two-way shape memory effect. A transformation shear strain of 6% was obtained, and a maximum work output of 27.5 J cm−3. Two-way shear strains approached 3% strain without any extended training or cycling. The strain values obtained for the first time in this large-diameter, high-torque tube consistently matched smaller diameter tubes previously reported. This highlights the successful production and scale-up of both the material and the component level in torque tubes without degrading the actuation response, while providing much higher torque capability.

Analysis of Stator Slots and Rotor Pole Pairs Combinations of Rotor-Permanent Magnet Flux-Switching Machines

This paper investigates the influence of stator slots and rotor pole pairs combinations on torque performances in rotor permanent magnet flux switching (RPM-FS) machines. Based on a magnetomotive force (MMF) permeance model, the candidates of stator slots and rotor pole pairs combinations with higher torque capability can be determined by analyzing the PM-MMF and winding factor. Meanwhile, the candidates with a lower torque ripple can be obtained by referring to the cogging torque, which is related to the greatest common divisor of stator slots and rotor pole pairs. In addition, from the field modulation principle, the RPM-FS machines with the same fundamental magnetic loadings and winding factors exhibit identical fundamental harmonic torque, but different modulation harmonic components. Finally, four candidates with attractive torque performance are chosen, and the characteristics are verified by finite-element analysis and experiments.

Particle swarm optimization approach to optimal design of an AFPM tractionmachine for different driving conditions

Axial flux permanent magnet (AFPM) machines can be employed as the traction motor of electric vehicles due to their high torque capability, high efficiency, modular and compact construction, and capability of integration with other mechanical components in integrated systems. Besides, the system efficiency can be further improved by optimal design of the selected electric machine. In this paper, an AFPM machine is optimized against two well-known driving cycles called the New European Drive Cycle (NEDC) and US06 and the influence of the driving cycle on the obtained machine parameters is evaluated. US06 is the more demanding driving cycle and thus the machine designed for this driving cycle demands more electrical loading compared to the machine designed for NEDC. Therefore, the copper loss minimization becomes more important for the US06-optimized machine compared to the NEDC-optimized machine. Consequently, the machine design parameters optimized for different driving cycles would be quite different. Compared to the NEDC-optimized machine, the US06-optimized machine has a lower number of coil turns, lower height of teeth, and lower diameter ratio to limit the copper losses. Furthermore, fewer magnets are needed for the motor optimized for the NEDC compared to the motor optimized for US06. A quasi-3D approach and particle swarm optimization algorithm are used in the semianalytical design optimization process. Additionally, computationally efficient 3D finite-element analysis and measurements made for the prototype AFPM machine are carried out to validate the accuracy of the quasi-3D approach.

Fault-Tolerant Control of Modular Permanent Magnet Synchronous Motor Under Open-Circuit Faults

The paper studies a novel fault-tolerant strategy of the modular permanent magnet synchronous motor under open-circuit faults, which is called as the extended open-circuit fault-tolerant control (EOCFTC) strategy. The faulty modular motor based on the EOCFTC strategy can achieve the high fault-tolerance and maximum output torque capability by making the most of the remaining healthy phases. First, the mathematical model of the modular motor with n modules is described. Then based on the characteristics of the modular motor, a novel winding reconstruction strategy is proposed to deal with multiphase open-circuit faults in different modules. All remaining healthy phases are reasonably reconstructed according to the maximum output torque principle. Then these new modules can operate well by employing the armature magnetomotive force (MMF) compensation and the field-orientated control (FOC) strategy. Finally, all cases of open-circuit faults and the corresponding processing methods are discussed. The extreme case of open-circuit faults is described in detail, which shows the high fault-tolerance of the modular motor with the EOCFTC strategy. The experimental results verify the rationality and feasibility of the EOCFTC strategy on a two-module modular motor.

Detailed description and analysis of the cross‐coupling magnetic saturation on permanent magnet synchronous motor

Permanent-magnet synchronous motor (PMSM) has obtained more attention, acquired more applications, and received great reputation due to its high torque density and simple structure. While exploiting its high torque capability, PMSM's control strategy faces great challenge at high overload scenario due to core-saturation effect. This study presents a detailed physical description and analysis on the effect of cross-coupling magnetic saturation in PMSM. Applying the conventional i d = 0 control strategy on a 1.5 MW surface mounted permanent-magnet synchronous generator, this study discusses the cause and influence of cross-coupling effect, presents the unbalanced magnetic permeance between direct -(d -) and quadrature-(q -)axis magnetic circuit. Either d - or q -axis electromotive force (mmf) would generate both d - and q -axis flux, especially those induced by permanent magnets. Then a permeance-fixed finite-element analysis is applied to separate the influence between permanent magnets and armature current. Finally, this study proposes a revised maximum-torque-per-ampere trajectory for surface-PMSM at high overload situation.

A Novel Dual-Flux-Modulator Coaxial Magnetic Gear for High Torque Capability

This paper presents a novel dual-flux-modulator coaxial magnetic gear (DFM-CMG) characterized by high torque capability and high permanent-magnet (PM) utilization efficiency. The DFM-CMG adopts spoke-type outer PM rotor and introduces an auxiliary flux modulator placed in the outermost layer. The harmonic analysis with detailed theoretical derivation is performed to reveal that the ferromagnetic pole shoes on the spoke-type outer PM rotor could modulate the flux density distribution as well and realize a nested magnetic-gearing effect. More effective magnetic harmonics are, thus, led into the air gaps to make contribution to the torque production. The effect of the auxiliary flux modulator on the flux density distribution is also studied by the finite-element (FE) analysis. Due to the presence of the auxiliary flux modulator, the flux leakage is suppressed and the useful harmonics are amplified. A quantitative comparison among the surface-mounted CMG (SM-CMG), spoke-type CMG (ST-CMG), and DFM-CMG is made to verify the performance improvement of the proposed CMG. With the same amount of consumed PMs, the torque capability and PM utilization efficiency of the DFM-CMG shows a 73% growth over the SM-CMG and a 44% growth over the ST-CMG. The ST-CMG and DFM-CMG are finally prototyped and tested to verify the FE analysis.

2D-FEA Based Design and Performance Analysis of Low Weight Segmented Rotor HE-FSM for Light Weight Aircrafts

All electric aircraft (AEA), is one of the main intentions of the aerospace industry for future. Where electrical machines are capable to provide high torque density and are dominant for the feasibility of direct drive electrical driving force for aircraft applications. Besides, low weight and high torque capabilities, the best candidate solution should also inherently fault tolerant for aircraft applications. For these reasons, a new sort of machine has been familiarized and published in last decade know as flux switching machine (FSM). FSMs contain all excitation sources on stator side with robust rotor structure. According to the type of excitation, FSMs are characterized into three types such as permanent magnet PM FSM, field excitation FE FSM and hybrid excitation HE FSM. PM FSM and FE FSM use PM and FE coil for their excitation sources respectively, whereas both PM and FE coil is used in HE-FSM for excitation. Subsequently, these machines have shown high torque to weight ratios and high efficiency during research in the last decade. Therefore in this paper, a new structure of 12S-8P HE-FSM with segmental rotor has been proposed and analyzed. The proposed segmented HE-FSM has the simple structure using only three PMs and three FECs. The proposed structure is analyzed using commercial 2D FEA package, JMAG-designer ver. 14.0. This paper presents the coil test analysis of segmented HE-FSM to confirm the working principle. Besides, cogging torque, flux strengthening, torque vs current densities and power vs current densities have been analyzed and presented.

Characteristics Assessment and Comparative Study of a Segmented-Stator Permanent-Magnet Hybrid-Excitation SRM Drive With High-Torque Capability

Hybrid-excitation switched reluctance motors (HESRMs) have attracted considerable attention for various drive applications due to their simple structure, low cost, and high-torque/power capabilities. This paper comprehensively evaluates and compares a high-torque segmented-stator HESRM drive with a conventional SRM drive in terms of static magnetic and dynamic performances. The stator of the segmented HESRM consists of six individual U-shaped segments; each one has two teeth associated with a permanent magnet (PM) installed between them. The static magnetic characteristics of a segmented HESRM and a conventional SRM, including flux distribution, phase flux linkage, electromagnetic torque, are analyzed and compared. The total fluxes created by the PM and by the excited current are strongly coupled. The details of mathematical model as well as dynamic performances of the segmented HESRM is derived and compared with the conventional SRM. Finally, a segmented HESRM and a conventional SRM of the same size are prototyped for experimental verification. From the comparative study, it is indicated that the segmented HESRM has better characteristics than the conventional SRM, such as less iron consumption, higher static and dynamic average torque production, lower torque ripple, higher power and torque densities, higher efficiency, and stronger starting capability. The measured results of static magnetic characteristic, steady-state and transient performances, and torque–speed characteristic of two SRM drives verify the finite-element analysis, modeling, and corresponding predictions.

High Torque Flux Switching Permanent Magnet Machine in Segmented Outer Rotor using Appropriate Split Ratio for Electric Scooter Propulsion

<span>Recently, permanent magnet synchronous machine (PMSM) having the diameter of 11inches was successfully developed and installed in electric scooter vehicle (ESV) for propulsion. It consists of segmented stators of 24 armature slots and 100 pieces of permanent magnet of 2 kg weight mounted on rotating rotor. Upon the huge amount of materials and permanent magnet used, PMSM produced 110Nm only. Looking at the size, this torque is low and could not sustain acceleration for long distance travels. To overcome the challenge of low torque, this paper presents a new machine type, flux switching motor (FSM) with 1 kg weight of permanent magnet flux source employing segmented outer rotor. Six ranges of split ratio of 0.80-0.85 for outer rotor 24slot-14pole FSPM motor configurations were designed and compared. The 2D-FEA by JMAG software version 14 is used to examine its performance in term of flux linkage, cogging torque, back-emf and average torque which the structure with split ratio of 0.85 took lead by securing highest torque profile of 209Nm. It also achieved low cogging torque to operate in safe region. In conclusion, appropriate split ratio significantly enhances high torque capability of permanent magnet flux switching motor for electric scooter propulsion.</span>

High‐torque‐density pseudo‐direct‐drive permanent‐magnet machine with less magnet

Magnetic gears, an alternative to conventional mechanical gearboxes, have been extensively studied in the last decade. By combining a magnetic gear and a conventional permanent-magnet machine into one frame, different magnetic-gear-integrated permanent-magnet machines with a high-torque density are obtained, among which the pseudo-direct-drive permanent-magnet machine features both a high-torque capability and a good power factor with an acceptable structural complexity. However, the stator PM array in the conventional pseudo-direct-drive permanent-magnet machine obstructs the magnetic path and reduces the excitation torque due to the coils. Another problem is the large permanent-magnet amount which increases the overall cost. The authors propose a novel topology which has an improved torque capability under the same excitation current with a reduced permanent-magnet amount. The working principles of the proposed machine are analysed theoretically using the linear-material assumption to decouple the permanent-magnet-machine part and the magnetic-gear part. Its performance is then validated by the finite-element method. A comparison study with the conventional topology is conducted to show its merits.

Design and Analysis of a Stator HTS Field-Modulated Machine for Direct-Drive Applications

This paper proposes a new stator high-temperature superconducting (HTS) field-modulated machine with the merit of high torque density for direct-drive applications, which incorporates the attractive features of both stator excitation HTS machine and field-modulated machine. The key is to artfully place the HTS windings on the stator to implement static seals as well as utilizing the “magnetic gearing effect” to achieve high torque capability. Based on the geometry of the fabricated double-layer Dewar assembly for cooling the HTS excitation coil, the proposed machine is initially designed. By using the finite element analysis (FEA), the machine performances are analyzed, and its validity is verified

Flux Switching Permanent Magnet Motor using Segmented Outer Rotor Structure for Electric Scooter

Flux switching motor is a type of electric machine that locates both flux source and armature windings on the stator leaving its rotor a simple piece of iron. This machine was developed by combining the toothed stator structure of induction machine and the toothed rotor structure of switched reluctance machine together. Furthermore, it has three types of flux sources which include permanent magnet. Conventionally, the toothed kind of rotor has dominated machines rotor design and has been known for high manufacturing cost and iron loss, resulting to low performance. This calls for worry and the need to overcome it and also reduce the manufacturing cost while securing high torque. This paper presents flux switching permanent magnet motor employing segmented outer rotor for high torque capability. 2D-FEA using JMAG to investigate the motor characteristics in terms of flux linkage, Induce back-emf, cogging torque, maximum average torque and efficiency. Finally, preliminary results and comparison revealed that motors employing segmented rotor are capable of higher torque than conventional toothed rotor.