Axial Field Flux-switching Permanent Magnet Machine Research Articles

Performance analysis and comparison for two topologies of flux-switching permanent magnet machine

Flux-switching permanent magnet (FSPM) machine is a kind of stator-typed permanent magnet machine, which is suitable for driving electric vehicles and hybrid electric vehicles because of their large power/torque density and high efficiency. The axial field flux-switching permanent magnet machine (AFFSPMM) and radial field flux-switching permanent magnet machine (RFFSPMM) with H-typed iron cores are reached and compared in this paper. On the condition of the same outer diameters and total volumes, the electromagnetic performances of the two machines are analyzed and compared by the three-dimensional finite element method, including the air gap flux density, inductance, back electromotive force (EMF), electromagnetic torque and loss. The finite element results show that the copper loss of AFFSPMM is higher than that of RFFSPMM at the rated load, however, the total loss of AFFSPMM is lower than that of the RFFSPMM. Meanwhile, AFFSPMM has greater torque than RFFSPMM in the constant power range. The related experiments are done to validate the finite element results, which are basically consistent with experiment results.

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.

Analysis and Comparison of Axial Field Flux-Switching Permanent Magnet Machines With Three Different Stator Cores

Axial field flux-switching permanent magnet machine (AFFSPMM) is a novel brushless AC machine, which incorporates the advantages of flux-switching permanent magnet machine and axial field permanent magnet machine. It is suitable to be applied in the field of direct drive electric vehicles due to short axial size and large torque density. In the paper, the different stator core structures such as U-, C-, and E-shape are researched on basis of a three-phase 600 W conventional AFFSPMM. These parameters including rotor pole numbers, stator tooth shape, and the deflection angle of rotor pole are optimized for obtaining sinusoidal back electromotive force and small cogging torque. The electromagnetic performances are analyzed and compared by 3-D finite element method. It is found that C-core AFFSPMM can get higher output torque in comparison with U-core machine, and E-core machine can improve fault-tolerant capability and reduce the torque ripple.

Cogging Torque Reduction of a Hybrid Axial Field Flux-Switching Permanent-Magnet Machine With Three Methods

The hybrid axial field flux-switching permanent-magnet machine (HAFFSPMM) is a novel hybrid excited machine with short axial length and high torque density, which is suitable for electrical vehicle drive. However, the HAFFSPMM exhibits a higher cogging torque than traditional permanent-magnet machines due to the doubly salient structure and the high flux density. To reduce the cogging torque, three cogging torque reduction methods by tangential displacement of stators, asymmetric rotor pole shape, and segment-twisted rotor are investigated in this paper. The influences of the asymmetric angle of the three methods on the cogging torque and the output torque are analytically investigated and numerically verified by a three-dimensional finite-element method. The results show that the cogging torque can be greatly reduced, whereas the output torque decreases slightly even increases. In no terms of output torque, the cogging torque with segment-twisted rotor is less than the other two methods; in terms of output torque, the cogging torque reduction with an asymmetric rotor pole shape is better than the others.

Influence of design parameters on inductances of e-core axial field flux-switching permanent magnet machines

Purpose – Axial field flux-switching permanent magnet machine (AFFSPMM) can be applied in the field of electric and hybrid electric vehicles because of short axial size, large torque density, and high-power density. The purpose of this paper is to improve the reliability of AFFSPMM itself, the design parameters have to be considered for attaining high self-inductances and reduced mutual-inductances. Design/methodology/approach – The original parameters of E-core AFFSPMM are designed with reference to a 600 W prototype, on the basis of which the 3-D model of the original AFFSPMM is established, and the inductances are calculated by finite element method. The influence of these parameters on the inductances, including combinations of stator and rotor pole numbers, spilt ratio, stator side tooth width, magnet thickness, and rotor pole width etc., are respectively investigated and analyzed under the constant copper loss. Findings – The relationships of rotor pole numbers and inductances are deduced on the condition of the fixed stator poles. It is found that the rotor pole numbers has significant effects on the ratio of mutual-inductance to self-inductance, and the self-inductance is mainly affected by the rotor pole numbers, the split ratio, the stator tooth width, and the rotor pole width. The asymmetry of back-EMF can be largely reduced by optimizing the rotor tooth width. In this paper, the static characteristics are compared and analyzed for the original and optimal 6/14-pole AFFSPMM. Meanwhile, the open-circuit and short-circuit fault are investigated by transient analysis. The results show that the optimized E-core AFFSPMM has good fault tolerance. Originality/value – The research of inductance characteristics for E-core AFFSPMM is valuable to design the fault-tolerant machine, by which the cost of control and manufacture can be largely saved.

ANALYSIS OF COGGING TORQUE REDUCTION TECHNIQUES IN AXIAL FIELD FLUX-SWITCHING PERMANENT MAGNET MACHINE

An axial-field flux-switching permanent-magnet machine (AFFSPMM) is suitable to be used in wind power generation and electric vehicles. However, the cogging torque (Tcog) is large. To obtain high-performance AFFSPMM, the reduction of Tcog in AFFSPMM is investigated. The theoretical Tcog expression is deduced. Based on a 3-D finite-element method, the influences of the design parameters on the Tcog and the reduction methods of Tcog, such as rotor tooth skewing (RTS), rotor tooth circumferential pairing (RTCP), and rotor tooth notching (RTN), are analyzed. The design parameters, except the axial length of rotor, have influences on Tcog, and optimizing the design parameters can decrease Tcog. Tcog can be greatly reduced by RTS for AFFSPMM with a parallel stator tooth and fan-shape permanent-magnet structure. However, RTS is not effective in reducing Tcog for AFFSPMM with a fan-shape stator tooth and parallel PM (FSST-PPM) structure. Tcog greatly decreases by RTN and RTCP for an FSST-PPM stator structure. Moreover, the reduction effect of Tcog with RTN is better than that with RTCP.

Design and Analysis of Novel Hybrid-Excited Axial Field Flux-Switching Permanent Magnet Machines

The axial field flux-switching permanent magnet machine (AFFSPMM) is a novel brushless AC machine. The magnets and concentrated windings are both in the stator instead of the rotor. The short axial length is beneficial to save the place of electric vehicles (EVs). Furthermore, the AFFSPMM exhibits the advantages of high power density and torque density. However, it is difficult to regulate the air-gap field since the field is produced by magnets alone. The fault-tolerant capability needs to be enhanced in the application of a direct-drive EV. Hence, a novel hybrid-excited AFFSPMM is proposed, in which the air-gap field can be easily regulated and the mutual inductance is largely reduced. In this paper, the design parameters of the novel machine, such as the split ratio, the rotor pole numbers, the rotor pole width, etc., are optimized in order to attain a sinusoidal back-EMF waveform and low cogging torque. Moreover, the static performance including each phase flux-linkage, inductance, and torque is analyzed on the basis of the 3-D finite-element method (FEM).

Cogging Torque Reduction of Axial-Field Flux-Switching Permanent Magnet Machine by Rotor Tooth Notching

Axial-field flux-switching permanent magnet machine (AFFSPMM) is a novel PM machine with high power density and efficiency. However, the cogging torque in AFFSPMM is larger than that in the traditional PM machine because of the double salient structure. In order to reduce the cogging torque, the cogging torque reduction method by rotor tooth notching is investigated in this paper. Three different tooth-notching structures are proposed, and the influence of the dummy slot width, slot depth, and slot shape angle on the cogging torque is analyzed based on the 3-D finite-element method (FEM). The optimized tooth-notching structure with the minimum cogging torque is obtained by the response surface method and verified by an FEM. The results show that the cogging torque can be reduced greatly, while the output torque decreases slightly by rotor tooth notching in AFFSPMM. The cogging torque reduction effect by adding two dummy slots in the rotor pole is better than that by adding one dummy slot.

Vector Control of a Hybrid Axial Field Flux-Switching Permanent Magnet Machine Based on Particle Swarm Optimization

A hybrid axial-field flux-switching permanent magnet machine (HAFFSPMM) is a novel hybrid excited flux-switching permanent magnet motor, which combines the advantages of the axial-field flux-switching permanent magnet machine and hybrid excited synchronous machine. In this paper, based on the vector control method, the mathematical model of the HAFFSPMM is deduced and the operating performance of the HAFFSPMM in the entire operating region is investigated. A novel control scheme for the HAFFSPMM drive system, including the $i_{d }=0$ and flux-weakening strategy, is proposed. To improve the robustness of the control system, the parameters of the proportional-integral (PI) controller are optimized using the particle swarm optimization (PSO) algorithm. The experimental results demonstrate that the proposed control strategy can maximize the output torque and speed range of the drive system, and the PSO-PI controller can reduce the torque ripple and improve the stability of the control system. Moreover, the strong flux-weakening ability, large load capacity, high power, and torque density of the HAFFSPMM are validated.

Cogging Torque Reduction of Axial Field Flux-Switching Permanent Magnet Machine by Adding Magnetic Bridge in Stator Tooth

Axial field flux-switching permanent magnet machine (AFFSPMM) is a novel stator PM machine with high torque density and efficiency. The cogging torque in AFFSPMM is larger than that in the traditional PM machine because of the double salient structure. In order to decrease the cogging torque, the analytical expression of the cogging torque is deduced and a cogging torque reduction method by adding magnetic bridge in adjacent stator tooth is proposed. Based on the 3-D finite-element (FE) method, the influence of the magnetic bridge thickness on the cogging torque and the output torque is analyzed and compared with the rotor skewing and notching methods. The influence of the stator tooth and rotor pole width on the output torque is studied. The 3-D FE analysis is compared with the experimental results. The research results show that the proposed method is effective in the reduction of cogging torque for all kinds of stator structures. Moreover, the cogging torque can decrease greatly and the average output torque decreases slightly when combined with the optimization of the stator tooth width and rotor pole width.

Static Characteristics of a Novel Axial Field Flux-Switching Permanent Magnet Motor with Three Stator Structures

A three-phase 12/10-pole axial field flux-switching permanent magnet machine (AFFSPMM) with three different stator structures, including parallel permanent magnet and parallel slot (PPPS), parallel tooth and parallel slot (PTPS), and parallel permanent magnet and parallel tooth (PPPT), is analyzed. Based on a 3-D finite element (FE) method, the static characteristics, such as the flux density, PM flux linkage, back-EMF, cogging torque, and electromagnetic torque for the three stator structures are investigated. The influence of the design parameters on the electromagnetic torque is analyzed. The AFFSPMM with PPPS topology has the larger torque, lower cogging torque, and more sinusoidal back-EMF. The prototype with PPPS structure is built and tested. The experimental results are in agreement with the 3-D FE analysis.

Design and Analysis of a Novel E-Core Axial Field Flux-Switching Permanent Magnet Machine

A simple analytical method is developed to design novel axial field flux-switching permanent magnet (AFFSPM) machines in terms of back electromotive force (back-EMF) and cogging torque. The machine is proposed with E-shaped laminated segments in the stator. Some major parameters are originally designed with reference to those of a 12/10-pole U-core AFFSPM machine, including the rotor tooth width, the split radio of the inner diameter to outer diameter of the stator and the stator parameters. In this paper, they are investigated and optimized for attaining essentially sinusoidal back-EMF and low cogging torque by 3-D finite element method (FEM). Compared with 12/10-pole AFFSPM machine, it is shown that the volumes of magnets are almost reduced by 30%, while the similar output torque at the rated current can be obtained, and the ratio of the mutual-to self-inductance is largely reduced, which indicates the proposed motor has better fault-tolerant capability.

Static Characteristics Analysis and Experimental Study of a Novel Axial Field Flux-Switching Permanent Magnet Generator

A novel axial field flux-switching permanent magnet (AFFSPM) machine with a doubly-salient structure is developed as a wind power generator. The electromagnetic characteristics of a 0.6 kW, 3-phase 12/10-pole AFFSPM machine, including the air-gap flux density distribution, open-circuit flux linkage, EMF, and winding inductances, etc., are investigated based on 3-D finite element (FE) analysis. A prototype is built to test the characteristics under both open-circuit and load conditions. The theoretical analysis is validated experimentally. It shows that the phase EMF is essentially sinusoidal, and the machine can not only be used as a wind power generator, but also as a permanent magnet brushless AC motor.