Torque Performance Research Articles

Safety-overrunning clutch elastic torque operation characteristic study

Safety-overrunning clutch elastic torque operation characteristic study

Analysis of Stator-Slot and Rotor-Pole Combinations of Axial Modular-Flux Reversal Permanent Magnet Machine

This paper investigates the influence of stator-slot and rotor-pole combinations on torque performances in axial modular-flux reversal permanent magnet (AM-FRPM) machines. Based on the slot-conductor back-EMF star vector theory, the winding factors of all stator-slot and rotor-pole combinations are improved by adopting toroidal windings. In addition, based on a magnetomotive-force and permeance model, the candidates of stator-slot and rotor-pole combinations with higher torque capacity can be determined by analyzing the harmonic combinations between the PM and armature reaction field. Besides, the cogging torque is suppressed by selecting the corresponding angle between rotor modules for different stator- slot and rotor-pole combinations. Finally, an electromagnetic performance comparison between a conventional FRPM machine and three AM-FRPM machines candidates with attractive torque performances is conducted, and the experiments are constructed to verify the theoretical analysis.

Development of a Novel Radial-Flux Machine With Enhanced Torque Profile Employing Quasi-Cylindrical PM Pattern

This article presents a novel radial-flux surface-mounted PM (SPM) machine with quasi-cylindrical pole pattern (QCPP). With the proposed configuration, the cogging torque and torque ripple of surface-mounted machines could be greatly decreased due to the adoption of large eccentric distance and the reduction of high-order airgap flux density harmonics. Moreover, the increase of fundamental flux component helps to improve torque generation well. Additionally, the magnet poles are semi-embedded into the rotor, and thus the sleeve in conventional SPM machines is no longer necessary, which helps to reduce the airgap size and improve the torque output further. Besides, the quasi-cylindrical magnet could offer lower rotor eddy loss and higher anti-demagnetization capability than conventional radial and eccentric pole patterns. Studies have been conducted on the novel structure to validate its advantages. Firstly, the topological structure and working principle of the QCPP machine are presented. Then, the influence of the QCPP structural parameters on the torque performance is investigated. Next, an electrical machine with quasi-cylindrical pole pattern is designed. Subsequently, the electromagnetic characteristics, such as flux density distribution, back EMF, average torque, cogging torque, torque ripple, eddy loss in sleeve, rotor stress and anti-demagnetization capability, of the proposed machine are analyzed and compared with those of conventional SPM machine with eccentric magnetic poles and skewing slots. Finally, one research prototype is developed, and experiments are carried out to evaluate the design concept and performance of the proposed QCPP machine.

Asymmetric flapping of a multi-segmented elastic structure

Motivated by the propulsion of animals using articulated bodies, this study experimentally investigates the deformation and torque generation of a multi-segmented structure undergoing flapping motion. The segmented structure consists of multiple rigid segments connected in a line through elastic sheets functioning as elastic hinges. To enhance the asymmetry in the deflection of the segmented structure between the power and recovery strokes, the elastic hinges are designed to bend only one way from their original position. To characterize the deflection profile of the segmented structure, new definitions are proposed for the effective bending stiffness of the entire structure and the dimensionless speed representing the relative magnitude of the fluid force acting on the structure to its internal bending force. These two quantities are used to determine the tip deflection adjusted by the discrete profile. Two typical deflection responses during the recovery stroke are identified, namely, an in-phase response and a delayed response. The difference in these deflection responses causes substantial changes in torque and thrust generation, particularly during the early stage of the subsequent power stroke. An evaluation of the torque and thrust generation performance, in terms of the net cyclic value and the degree of asymmetry between the two strokes, reveals the optimal model design and operation conditions of the segmented structure.

Demagnetization effects of surface-mounted permanent magnet synchronous wind generator

To prevent fossil resources from being depleted and protect the natural balance, renewable resources come to the forefront as an alternative to fossil resources. Wind energy resources, among the renewable energy resources, are important in terms of ensuring the reliability of energy and the use of their resources. Generators are the most important components for the conversion of wind power. Permanent magnet synchronous generators (PMSGs) are preferred in wind turbines since they have high efficiency and high volume/torque densities, thereby optimization of the PMSGs is an important topic for the wind energy community. On the one hand, these machines can cause problems due to overheating and mechanical friction during their long-time operation. To identify the performance lack of the machines due to the de-magnetization faults, systematic work has been performed. When a magnet of a PMSG is de-magnetized at different rates (i.e. 33%, 50%, and 100%), we have explored the artifacts in the electric generation. Besides, the torque performances of the generator at rated load are examined and the flux density distributions are revealed. The rated torque decreased substantially when the demagnetization rate of the magnet increased.

The Effects of the Unequal Rotor Slot Arc on Cogging Torque for Flux Switching Permanent Magnet Machines

Many of the electric machine researchers are studying the Flux switching permanent magnet (FSPM) machines. The cogging torque is one of the most unwanted parameter for highly sensitive electric machine applications. In this study, the configuration of the unequal rotor slot arc (URSA) to see the effects of the asymmetry for three phase FSPM machine has been studied. The proposed asymmetry contains of presenting different arc angled rotor poles and analyzing the torque performance of them by using 2D finite element analysis (2D-FEA). 12-stator pole/ 10-rotor pole (12s/10p) FSPM machine topology has been chosen for the design. Results proved that unequal rotor slot arc proposition demonstrate good performance in comparison to the symmetric design. Inequality on the rotor slots were simulated by using parametric analysis to minimize the cogging torque. The suggested design indicates a substantial reduction in cogging torque, achieving a conspicuous minimization. Consequently, the suggested using unequal rotor slot arc for FSPM machine has reasonable outcomes.

Hybrid energy storage system and management strategy for motor drive with high torque overload

The demand for small-size motors with large output torque in fields such as mobile robotics is increasing, necessitating mobile power systems with greater output power and current within a specific volume and weight. However, conventional mobile power sources like lithium batteries face challenges in surpassing the dual limitations of weight and output power due to constraints imposed by materials and other factors. Therefore, this paper references the approach of high-power hybrid energy systems in automobiles and proposes a battery–supercapacitor hybrid energy storage system (BSHESS) and energy management strategy. The motor is powered by the battery during low torque operating conditions, while the additional output power of the battery is used to charge the supercapacitor. In cases of torque overload, the rapid discharge of the supercapacitor provides the motor with a high current, ensuring instantaneous high output power. Furthermore, the proposed energy management strategy is used to control the charging and discharging processes of the supercapacitor, guaranteeing that the charging process of the supercapacitor does not interfere with the battery’s power supply to the motor, as well as maintaining controllability and stability of the current in the discharge process. The feasibility of the principle is verified through simulations, and we also design a complete prototype of the proposed BSHESS and conduct experiments on the motor. The results demonstrate that the maximum output current to the motor is increased by 150% compared to the original level, and the weight is reduced by 64.7% compared to a pure battery-powered system with same maximum current output. Additionally, the energy management strategy enables a more stable charging and discharging process compared to the unmanaged state.

Torque Performance Enhancement for Hybrid PM Motor Considering Magnet Characteristic Difference and Variation

In this paper, for the hybrid permanent magnet (HPM) motor using multi PM materials as excitation sources, considering the characteristic difference and coupling effect between magnet materials, a preliminary design of the hybrid PMs is presented to improve the PM utilization and the superposition rate of torque components. Besides, according to the magnet characteristic variation under different operation conditions of the motor, a multi-objective variable condition weighted optimization design method is carried out to further improve the torque performance, efficiency and anti-demagnetization capability of HPM motor.

PM Eddy-Current Loss Reduction of Axial Flux PM Wheel Motor With Arc Incompletion Segmentation

The high permanent magnet (PM) eddy-current loss will inevitably cause the risk of irreversible demagnetization, and the PM complete segmentation (CS) method is a common method to reduce the PM eddy-current loss. However, PM CS design will increase the cost and difficulty of assembly process, especially for axial flux PM (AFPM) machines. To address this issue, a new arc incompletion segmentation (AIS) method is proposed to reduce the PM eddy current loss and cost, including double-side AIS and single-side AIS designs. Then, some of the key parameters are optimized. In addition, the PM eddy current loss, cost, and torque performance are studied and compared with different segmentation methods under different conditions based on 3-D finite element method (FEM). Finally, two different 25kW prototypes are manufactured and tested to validate the proposed method and analysis.

Novel Stator Slot Opening to Reduce Electrical Machine Bearing Currents

Ball bearings are largely used in electrical machines, where the high frequency common mode currents affect their lifetime. This document presents a novel Zig-Zag stator slot opening geometry to reduce the winding-to-rotor capacitance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_wr</i> with the consequent reduction of Bearing Voltage Ratio and electrical discharge machining bearing currents. An improved analytical model to permit the calculation of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_wr</i> for unusual slot opening geometries is implemented. Electrostatic and electromagnetic Finite Element Analysis comparisons between the Zig-Zag, oblique and original (classical slot opening configuration) machines are performed. These comparisons suggest that the Zig-Zag model presents the best performance in terms of Bearing Voltage Ratio reduction, while keeping torque performance close to the original machine. An additional comparison between the novel Zig-Zag model and the classical one with reduced slot opening to have the same <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_wr</i> values is proposed, showing an higher degradation in terms of torque performance for the latter. The study shows that the Zig-Zag model could be a good candidate to reduce effectively electrical machine bearing currents. A validation test is proposed on two motorette prototypes having classical and Zig-Zag slot opening configurations, respectively. Moreover, the improved analytical method can be helpful for engineers and researchers to calculate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_wr</i> with a good accuracy for unusual slot opening geometries.

Novel Dual Inverter Sub-Harmonic Synchronous Machines

Sub-harmonic synchronous machines are a relatively new bread of brushless wound field synchronous machines considered alternatives to many electric machines in transportation electrification applications. This paper presents two dual inverter sub-harmonic synchronous machines having unique two-layer and three-layer stator winding topologies. The two inverters provide the stator windings with two sets of balanced three-phase currents. These two and three-layer windings are arranged in such a way that they can generate both fundamental and sub-harmonic magnetomotive force. Furthermore, the fundamental MMF component of this machine is four times the sub-harmonic MMF component used for the brushless operation. In contrast, the sub-harmonic magnetomotive force is used for field excitation, which leads to brushless operation. Two 8-pole, 48-slot, 2-inverter, 2-layer and 3-layer sub-harmonic machines are designed to validate the concept through a 2-D finite element analysis of these new topologies, showing a better overall torque profile and performance as compared with the other sub-harmonic and brushless wound field synchronous machines.

Additional Magneto Motive Force of Spoke-Type Vernier Permanent-Magnet Machines

The traditional permanent magnet (PM) magneto motive force (MMF) / specific permeance model has been widely applied to analytically predict the magnetic field of vernier permanent-magnet machines (VPMs). However, it fails to accurately predict the performances of spoke-type VPMs. This paper clarifies the intrinsic reason, i.e. the spoke-type VPMs have a large additional PM MMF introduced by the stator slotting, while the traditional model ignores it. In this paper, the additional PM MMF is analytically calculated and its influence on electromagnetic performance is comprehensively investigated. It shows that the additional PM MMF leads to reductions in the airgap flux density, back-EMF, and torque performances of spoke-type VPMs. Especially when the pole ratio is high, the reductions due to the additional PM MMF are more obvious. Finally, a spoke-type VPM prototype is built and tested to verify the theoretical analysis.

On winding reconstruction method for six-phase motor with single-phase winding open-circuit faults

Single-phase winding fault in six-phase permanent magnet synchronous motor (PMSM) will cause problems with reduced torque performance. For this problem, this paper analyses the reasons for the increase of torque ripple under single-phase winding open-circuit fault condition taking an 18-slot/10-pole (18S10P) six-phase surface mounted permanent magnet synchronous motor (SPMSM) as an example. Then, a torque performance improvement method by redistributing healthy phase windings to reconstruct the stator magnetic field is proposed in this paper. The proposed method not only can significantly reduce torque ripple caused by winding open-circuit faults but also can maintain a high average torque value. Moreover, this method is suitable for lots of six-phase motors with different pole-slot combinations. At last, considering the significant impact of harmonic contents in stator magnetic field on torque performance, an optimization method for armature current is proposed, which can decrease the torque ripple further. The simulation results by finite element analysis (FEA) show that the proposed method has significant superiority in motor fault operation.

Investigation of a Flux-Switching Machine With U-V-Array Permanent Magnet Arrangement for Traction Applications

This paper investigates a flux-switching (FS) machine with U-V-array permanent magnet (PM) arrangement, termed UV-FSPM. The key design is to construct parallel magnetic circuit by adopting U-V-array PMs. Based on the parallel magnetic circuit, the operating principle of the UV-FSPM is illustrated. To provide a deeper insight into the torque enhancement mechanism, the analytical model of the UV-FSPM is built by using the general air-gap field modulation theory. It is found that the U-V-array PMs can significantly enhance the dominant working harmonic which effectively contributes to torque enhancement of the investigated UV-FSPM. To reveal the impact of key parameters on torque performances, the parametric optimization of the UV-FSPM is conducted. The electromagnetic performances of three FSPMs are comparatively studied by finite element analysis (FEA). It is proved that the investigated UV-FSPM exhibits the highest torque density and highest PM utilization ratio within the pool. Finally, a prototype of the UV-FSPM is fabricated and tested for verification of the investigated concepts.

Equivalent circuit modeling and optimization design for a novel double‐stator linear‐rotary switched reluctance motor

SummaryThe energy coupling behavior is propagated through the magnetic field and would seriously affect the operation performance of two‐degree‐of‐freedom motion system based on linear‐rotary motor. This paper proposes a novel double‐stator linear‐rotary switched reluctance motor (DSLR‐SRM) to suppress the energy coupling behavior. First, the structure and operation principles of DSLR‐SRM are presented. The two stators of DSLR‐SRM are radially arranged to perform the independent magnetic circuit and suppress the energy coupling behavior through the magnetic field. Then, an equivalent circuit model is established to shorten the modeling and calculation time. It could be found that the energy coupling behavior directly affects the torque and force performance. Next, the sensitivity of the DSLR‐SRM dimensions is developed. Meanwhile, the dimensions of DSLR‐SRM are optimized to enhance the torque and force output via TOPSIS decision‐making. Finally, the validity of equivalent circuit modeling analysis and optimization results are verified through three‐dimensional finite element model.

A comparison study of loss generation between twin-entry and double-entry volutes of nozzled mixed-flow turbines

Turbochargers whose turbines contain two-entry volutes are advantageous as they help to improve the low-end torque and transient performance of internal combustion engines. Two types of two-entry turbines are applied currently in turbocharging, which are the twin-entry turbine (TE) and the double-entry turbine (DE). To develop more efficient turbocharged engines, a further understanding of the performance characteristics and loss mechanisms of two types of two-entry turbines is needed. However, few investigations have been carried out to directly compare these two types of turbines. Through an experimentally validated numerical method, this paper compares the performance and detailed flow mechanism of twin/double-entry turbines with the same nozzled mixed-flow rotor. The 3D simulation is validated against the measured performance as well as the flow field carried out on test rigs. Results show that the performance of the double-entry turbine is notably superior over that of the twin-entry counterpart although their peak swallowing capacities and efficiencies are at a similar level. In particular, the efficiency and swallowing capacity deteriorate more gently for the double-entry turbine as operational condition deviates from full admission. It was revealed via the loss breakdown of turbine components that, the volute and the nozzle are the main contributors to the performance discrepancy between the two turbines. Specifically, the loss in the twin-entry volute is higher than that of the double-entry one, especially in the case of partial admissions. Flow analysis shows that the flow is mixed strongly in the vicinity of the limb divider of the twin-entry volute in the whole circumference, while it only concentrates in the vicinity of the tongues for the double-entry turbine. Therefore, a higher entropy-rise is generated in the twin-entry volute. Moreover, the mixing flow attenuates the flow distortion in the nozzle and produces more uniform entropy rise in the nozzle for the twin-entry configuration. On the other hand, flow distortion is well preserved in nozzle for the double-entry turbine, thus regions with high entropy-rise appear in a portion of nozzle passages. Consequently, a higher loss is produced in the volute and the nozzle for the twin-entry turbine. This paper provides knowledge of performance characteristics of two two-entry turbines and sheds light on the performance improvement of two-entry turbines.

Analysis of an Axial-Flux Slotted Limited-Angle Torque Motor with Quasi-Halbach Array for Torque Performance Improvement

Better torque performance and higher reliability have long been the focus of research for slotted limited-angle torque motors (LATMs), which are primarily used to position first-stage valves in electrohydraulic servosystems. This paper presents a high reliability axial-flux slotted LATM with quasi-Halbach array for torque performance improvement including constant torque range (CTR) and output torque. Firstly, the structure with two sets of windings and the operation principle of the proposed slotted LATM is analyzed. Secondly, a brief design procedure is presented, the structure selections of open slot and double-stator single-rotor (DSSR) interior rotor with surface mounted quasi-Halbach permanent magnet (PM) array are illustrated, and the geometric parameters are optimized to obtain the optimal design of the proposed slotted LATM. Then, 3-D finite-element method (FEM) is employed to compare the proposed slotted LATM with the conventional surface mounted PM slotted LATM in terms of cogging torque, no-load back EMF, and output torque, and the results show that the proposed LATM with quasi-Halbach array has a 10% improvement in output torque and a 25% improvement in CTR. Meanwhile, the flux linkages and torque performance of the two sets of windings under various conditions verify good magnetic isolation. Finally, prototypes of two different rotor types are manufactured and a series of experiments are performed to validate the analysis.

A Multi-Mode High-Efficiency Fault-Tolerant Permanent Magnet Machine

This article proposes a new multi-mode high-efficiency fault-tolerant permanent magnet machine with an inner stator to place AC field windings. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current in the field windings enables the proposed machine to be driven individually or together with the armature windings. On the other hand, the flux can be regulated by applying the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current to the field windings. As a result, multiple operation modes are realized. The proposed machine can run in different modes at different torque and speed operating conditions, implementing the multi-zone high-efficiency operation. Meanwhile, a new fault-tolerant control method can be applied in the proposed machine by combining the mode switching and compensation current in the healthy windings, thus improving the efficiency under fault-tolerant operation. Moreover, the multi-zone high-efficiency regions of the proposed and conventional machines are investigated. The proposed and traditional fault-tolerant methods for the proposed machine are compared. The results reveal that the proposed machine offers a larger high-efficiency region and is capable of stronger fault tolerance. Furthermore, since the double stators in the proposed machine need to operate individually, a swallow-shaped rotor with auxiliary salient poles is adopted to reduce outer torque ripple and inner torque ripple. Finally, the experiments are performed to verify the predicted performances.

Topology Optimization of Synchronous Reluctance Motors Considering the Optimal Current Reference in the Field-Weakening and Maximum-Torque-Per-Voltage Regions

The torque performance of the synchronous reluctance motors (SynRMs) is primarily determined by the geometric design and current control. The motor structure needs to be designed to yield the maximum output torque under the given current and voltage limitations. The current reference supplied to the stator coils also needs to be determined to maximize the output torque while suppressing the back electromotive force (EMF) to protect a power supply system. However, in the field of design optimization, it has been challenging to simultaneously consider the geometric design and current control due to their complicated relationships. To solve the aforementioned issue, this study proposes a new topology optimization that can cover the maximum-torque-per-ampere (MTPA), field weakening (FW), and maximum-torque-per-voltage (MTPV) controls under both the current and voltage limitations, thereby maximizing the output torque in an entire rotational speed range. To effectively investigate the coupling effects between the geometric design and current reference, this study proposes the design parameterization for the FW and MTPV operation by performing the electromagnetic finite element (FE) analysis and then expresses the optimal current reference in terms of design variables. At every iteration, the structural FE analysis is also performed under the design-dependent loads to obtain a structurally meaningful design. By doing so, both the optimal design and the corresponding optimal current reference can be simultaneously determined. The optimized SynRM is manufactured and experimentally validated to demonstrate the effectiveness of the proposed optimization framework.

Sizing, Modeling, and Performance Comparison of Squirrel-Cage Induction and Wound-Field Flux Switching Motors

In this study, the analytical design and electromagnetic performance comparison of a squirrel-cage induction motor (SCIM) and a wound-field flux switching motor (WFFSM) for high-speed brushless industrial motor drives is undertaken for the first time. The study uses analytical sizing techniques and finite element analysis (FEA) to model and predict the performance of both motors at a 7.5 kW output power. This study includes detailed equations and algorithms for sizing and modeling of both types of motors, as well as performance calculations that aid in motor selection, design optimization, and system integration. The main findings show that the SCIM has superior torque performance for starting and overload conditions, while the WFFSM offers advantages in power factor, efficiency over a wide operating range, and potential for higher peak power output. To this end, the WFFSM is capable of high-speed and high-efficiency operation while the SCIM is suitable for applications requiring variable speed operation. The validation study shows good agreement between analytical and FEA calculations for both motors. The results provide insights into the design and performance characteristics of both motors, enabling researchers to explore innovative approaches for improving their efficiency, reliability, and overall performance.