Low-speed Direct-drive Applications Research Articles

Analysis of a Complementary Dual-Stator Vernier Machine With Reduced Non-Working Harmonics for Low-Speed Direct-Drive Applications

Analysis of a Complementary Dual-Stator Vernier Machine With Reduced Non-Working Harmonics for Low-Speed Direct-Drive Applications

Demagnetization Modeling and Analysis for a Six-Phase Surface-Mounted Field-Modulated Permanent-Magnet Machine Based on Equivalent Magnetic Network

Demagnetization Modeling and Analysis for a Six-Phase Surface-Mounted Field-Modulated Permanent-Magnet Machine Based on Equivalent Magnetic Network

Design of a Dual-Permanent-Magnet Vernier Machine to Replace Conventional Surface-Mounted Permanent Magnet Motor for Direct-Drive Industrial Turbine Application

Surface-mounted permanent magnet motors (SMPMMs) have been widely used in industrial fields. However, when it comes to direct-drive low-speed large-torque fields, SMPMMs have several problems, such as lower slot filling factor, complicated fabrication, low efficiency, and bulky size. Recently, dual-permanent-magnet Vernier motors (DPMVMs) have been investigated due to their high torque density for low-speed direct-drive applications. However, so far, there is little research that demonstrates the application of the DPMVM for real industrial fields and quantitatively compares the performances of the DPMVM and the SMPMM. This paper studies the application of a DPMVM to the direct-drive industrial turbine as a replacement for conventional SMPMM. Rectangular and trapezoidal PMs are first applied to DPMVM in this paper. The performances of the DPMVM are quantitively compared with two typical SMPMMs. One is the design that has the same stator slots as the DPMVM, while the other has the same rotor pole pairs as the DPMVM. Economic costs are considered to form a thorough comparison between DPMVM and SMPMMs. It is revealed that with rectangular and trapezoidal PMs adopted in the DPMVM, the cost of PMs is significantly reduced with little sacrifice of performance. The efficiency of DPMVM is around 12% higher, and the material cost is reduced by 6.87% compared with the SMPMM.

Design and Optimization of a High-Torque-Density Low-Torque-Ripple Vernier Machine Using Ferrite Magnets for Direct-Drive Applications

In recent years, Vernier permanent magnet machines (VPMs) have gained much interest in academia. However, due to the large leakage flux, the power factor of Vernier machines is too low to be applied in real industry. In this article, a novel split-tooth, concentrated-winding Vernier machine using ferrite magnets is proposed for high-torque, low-speed direct-drive applications in home appliance industry. It uses consequent-pole magnets in the rotor, as well as additional assisted magnets in the stator teeth, in order to reduce the leakage flux and boost the torque density. A systematic way of reducing the torque ripple from 40% to 4% is proposed by carefully choosing the right combination of stator/rotor pole-pair numbers. A comprehensive design optimization is conducted to achieve the optimal performance. Finally, the ac loading is carefully reduced to meet the torque, saturation, power factor and space requirements. The test results of a prototyped machine show that the proposed design can achieve 34% more torque and 20% less loss with a reasonable power factor of 0.63, compared with an optimized PM synchronous machine under the same volume. It is found that the significant torque boost is attributed to the multiple working harmonics of the air-gap flux density.

AC Losses in Form-Wound Coils of Surface Mounted Permanent Magnet Vernier Machines

Surface mounted permanent magnet Vernier (SPM-V) machines, because of their high torque density and multi-pole structure, are promising candidates for low-speed direct-drive applications. To achieve high torque density, the SPM-V machines are generally designed with high gear ratios. Therefore, their operating frequencies can be much higher than those of the conventional SPM machines. This potentially increases the alternating current (AC) winding losses, especially those with form-wound coils proposed for high-power applications. This article investigates the AC losses (including skin effect, proximity effect, rotor PM induced, and circulating current losses) in form-wound stator coils of a 3 MW direct-drive SPM-V machine with different slot/pole number combinations. The study reveals that the SPM-V machines have significantly higher AC winding losses than their conventional SPM counterparts for similar operating conditions. To reduce the AC winding losses in SPM-V machines, a novel flux shunt concept is proposed along with other conventional techniques such as increasing the number of turns/coil (with terminal voltage being kept constant) and parallel strands/turn, providing extra clearance at slot opening. With the loss reduction techniques implemented, the SPM-V machines can achieve comparable efficiency but much higher torque density than their conventional counterparts. Moreover, the proposed flux shunt was also found to be very effective in reducing the potential risk of permanent magnet (PM) irreversible demagnetization, a key issue for SPM-V machines at high power ratings.

Optimal Design and Analysis of the Novel Low Cogging Torque Axial Flux-Switching Permanent-Magnet Motor

The axial field flux-switching permanent-magnet machine (AFFSPM) is one of the most efficient machines which is appropriate for high torque and low-speed direct-drive applications. In this paper, the novel axial field flux switching machine with sandwiched permanent magnet (AFFSSPM) is proposed in order to increase torque density and decrease cogging torque. The proposed model equipped with an advanced phase-group concentrated-coil winding to obtain a unity displacement winding factor. Two three-phase 6-stator-slot (S)/10-rotor-pole (P) and 12(S)/19(P) configurations of the proposed model are investigated. Some specific design issues, including the sandwiching pole angle, the stator tooth angle, and the rotor pole angle have been optimized to obtain the maximum torque density and minimum cogging torque by artificial neural network and non-sorting genetic algorithm II. Moreover, the static electromagnetic characteristics are investigated. Compared with the conventional AFFSPM and 6(S)/10(P) AFFSSPM, the 12(S)/19(P) proposed machine shows higher torque density, lower cogging torque, and higher level of fault-tolerant capability. In order to improve the dynamic performance of the AFFSSPM motor, a space vector modulation-direct torque and flux control (SVM-DTFC) scheme is proposed. The AFFSSPM motor exhibits excellent dynamic performance with proposed scheme.

Design and prototyping of the novel axial flux-switching permanent-magnet motor

PurposeThe purpose of this paper is to propose a novel axial field flux-switching machine with sandwiched permanent magnets. It is one of the most efficient machines which is appropriate for high-torque and low-speed direct-drive applications. The proposed model is equipped with an advanced phase-group concentrated-coil winding to obtain a unity displacement winding factor. Two configurations of the proposed motors with 6-stator-slot (S)/10-rotor-pole (P) and 12S/19P are investigated. These two structures are compared with optimized a conventional axial-field flux-switching permanent-magnet (CAFFSPM) machine. Unity displacement winding factor increases the back-EMF and electromagnetic torque. Moreover, the prototype 12S/19P motor is built to verify the design.Design/methodology/approachThe torque equation is obtained and the dimensions of the two proposed motors are determined. Some specific design issues, including the stator/rotor pole sandwiching pole angle, the stator tooth angle and the rotor pole angle have been optimized to minimize the cogging torque while maintaining the high torque density by means of response surface methodology (RSM) and 3-D finite element model of the machine.FindingsTo improve the performance, especially at high torque density, low cogging torque and high level of fault-tolerant capability, the 12S/19P axial field flux-switching sandwiched permanent-magnet (AFFSSPM) motor is proposed. Based on the optimized design, a prototype of the 12S/19P AFFSSPM motor is fabricated and tested. It is found that the experimental results validate the 3-D finite element method (FEM) simulation results.Originality/valueThe AFFSSPM motor is one of the most efficient motors, but the 12S/19P AFFSSPM motor with sandwiched permanent magnet and unity displacement winding factor has not been specially reported to date. Thus, in this paper, the authors report on optimal design of a novel axial flux-switching sandwiched permanent-magnet machine for electric vehicles and fabricate a prototype of the 12S/19P AFFSSPM motor.

A Novel Linear Permanent Magnet Vernier Machine With Consequent-Pole Permanent Magnets and Halbach Permanent Magnet Arrays

The linear permanent magnet (PM) vernier machine (LPMVM) can reach a higher thrust density at low speed compared to the regular linear PM machines due to the utilization of the magnetic gear effect, which makes it a good solution for low-speed direct-drive applications. In order to further improve the machine thrust density, a novel LPMVM with consequent-pole and Halbach PM array is proposed and optimized in this paper. Then, in order to show the superior thrust performance of the proposed LPMVM, it is compared to two conventional LPMVMs in terms of back electric motive force (back EMF), thrust force, and power factor. It is found that machine no-load back EMF can be improved by 72.5% and its thrust density is 46% higher than that of the conventional LPMVM.

Application of Phase Shifting Technique for Reducing the Magnetomotive Force Space Harmonics of Tooth Concentrated Windings

Permanent magnet machines with fractional slot concentrated windings are very attractive for low-speed direct-drive applications due to their compactness, cost effectiveness, and high efficiency. However, one of the key challenges of using concentrated winding configurations is the high content of space harmonics in the air-gap magnetomotive force distribution, which can lead to undesirable effects such as high rotor losses, vibrations, and noise. In this article, the phase shifting technique is investigated to deal with the harmonic content of such windings. An example of application is given for a three-phase winding with a number of slots per pole per phase = 2/5. It is shown that by using this simple technique, one can cancel some of the harmful magnetomotive force space harmonics without decreasing the winding factor of the torque producing harmonic. Further, calculations revealed a significant improvement in machine performances when compared to the conventional design.

Comparison and analysis of dual stator permanent magnet vernier machines with different pole/slot combinations for low speed direct drive applications

Permanent magnet vernier machine (PMVM) based on flux modulation principle has attracted increasing attention in low-speed direct-drive applications due to its high torque capability. A dual-stator PMVM topology with sandwiched spokearray PM rotor is presented to produce higher air-gap flux density and larger torque in this paper, and the space utilization and the energy conversion efficiency are improved significantly. Two representative dual-stator PMVMs (DS-PMVMs) are designed with this topology, the pole/slot combinations and gear ratios of which are 18 slots/30 poles and 18 slots/28 poles, 5 and 3.5, respectively. In order to reveal the advantages of the proposed topology and assess the torque characteristics of the proposed machines with different pole/slot combinations, the electromagnetic characteristics of these two machines are quantitatively compared and analyzed by using finite element method (FEM). The results demonstrate that the 18 slots/28 poles DS-PMVM can offer higher output torque, lower torque ripples, lower cogging torque and higher power factor owing to its optimal pole/slot combination. In addition, the unbalanced magnetic pulls (UMPs) of the two machines are also investigated, and the UMP of the 18 slots/30 poles DS-PMVM is smaller than that of its counterpart due to its symmetrical winding.

Nonlinear Equivalent Magnetic Circuit Analysis for Linear Flux-Switching Permanent Magnet Machines

A double slot-pitch and multitooth linear flux-switching permanent magnet (FSPM) machine, which is appropriate for high thrust force and low speed direct-drive applications, is proposed. Moreover, a nonlinear equivalent magnetic circuit (NEMC) model is developed for the analysis of the linear FSPM machine. The permeance of the repetition-unit (RU) in the NEMC model, of which the magnetic saturation as well as the field interaction is taken into account, is calculated by finite element (FE) analysis. Finally, the NEMC method is applied to the linear FSPM machine for calculations of the static characteristics, and the method is verified by FE analysis and experiment.

Eddy-Current Analysis of Double-Stator Inset-Type Permanent Magnet Brushless Machines

In this paper, a new multi-pole double-stator inset-type permanent magnet (PM) machine is proposed for low-speed direct-drive applications. In the outer stator, a fractional-slot concentrated winding is adopted to reduce the slot number and stator yoke height, hence saving the space and improving the torque density. In the inner stator, a vernier structure is used to reduce the winding slots and enlarge the slot area to accommodate more conductors, hence fully utilizing the inner stator space. Consequently, the torque density is improved, and the cogging torque is reduced. Since the machine structure is so unique while its operating principle is so distinct, a nodal method based network-field coupled time-stepping finite element method (NF-TS-FEM) is newly developed. The corresponding modeling and analysis are simpler and more convenient than its loop method based counterpart. The analysis of eddy-current loss in both of the PMs is conducted. The performance of the proposed machine is verified by the proposed NF-TS-FEM.