Axial Field Flux-switching Permanent Magnet Research Articles

Design and Optimization of the Dual-Stator Axial-Field Flux-Switching Permanent Magnet Motor with High-Torque Density and Low-cost

Design and Optimization of the Dual-Stator Axial-Field Flux-Switching Permanent Magnet Motor with High-Torque Density and Low-cost

Optimal design of a yoke-less axial flux switching PM motor based on multi-objective PSO

PurposeIn this paper, an improved multiobjective particle swarm optimization (PSO) algorithm is proposed to optimize a three-phase, 12-slot, 19-pole, yokeless axial-field flux-switching permanent magnet (YASA-AFFSPM) motor.Design/methodology/approachBased on the structural characteristics of the YASA-AFFSPM, a mathematical model is established to calculate the main size of the YASA-AFFSPM motor. The split ratio, stator axial length, sandwiching pole angle, rotor pole angle, PM arc and number of conductors per slot are selected as optimization variables. Also, the efficiency, power factor, cogging torque and average torque are considered as the optimization objectives. The objectives are optimized by combining the improved multiobjective PSO algorithm with electromagnetic calculation.FindingsBased on the proposed algorithm, the investigated motor is optimized. The on-load efficiency, power factor and average torque of the motor performance have increased by 0.87%, 3.13% and 10.39%, respectively. Moreover, the cogging torque and slot fill factor have undergone decreases of 8.57% and 3.34%, respectively. Finally, the effectiveness of the algorithm is verified using experiment results.Originality/valueSo far, no comprehensive report has been observed on the optimization of the YASA-AFFSPM motor using evolutionary algorithms and the study of the effect of the motor parameters. Therefore, in this paper, the authors decided to investigate the effect of YASA-AFFSPM motor parameters and improve motor performance with the improved PSO method.

Investigation on the field regulation capacity in a hybrid excited axial field flux-switching permanent magnet machine for EV application

In this paper, a novel hybrid excited axial field flux-switching permanent magnet (HEAFFSPM) machine is presented, of which the high torque capability and flexible flux regulation make it suitable for EV application. The field regulation principle of the machine is investigated, and the analogical saturation effect at pro-magnetized condition is revealed. Then the influence of the machine design parameters on the field regulation capacity and output torque of a 3-phase 6/10 stator/rotor-pole HEAFFSPM machine are analyzed by 3-D finite element analysis (FEA) method under univariate optimization condition. With the slight decrease of the electromagnetic torque, both the analogical saturation effect under pro-magnetized condition and the high flux regulation capacity are effectively improved with multivariable optimization via design of experiments (DOE) method. Finally, a prototype has been manufactured and the analysis result is validated with the experiment result.

Lumped parameter thermal network for thermal analysis of a rotor-excited axial flux switching machine with electromagnetic-thermal design

In this paper, a three-dimensional (3-D) lumped parameter thermal network (LPTN) model is presented for the first time for a rotor-excited axial-field flux-switching permanent magnet (RE-AFFSPM) machine. The 3-D LPTN predicts the steady-state temperature of different parts in various operating conditions. To enhance the LPTN accuracy and comprehensiveness, (i) the convection heat transfer in the internal and external areas, as well as radiation from the end-windings, (ii) core material anisotropic thermal conductivity, (iii) the equal thermal conductivity of the winding in the slot, and (iv) contact thermal resistances are all considered. Heat transfer coefficients are obtained mathematically to be applicable for the RE-AFFSPM machines with different parameters. A 3-D finite element method (FEM) is established to calculate the electromagnetic losses and thermal analysis with high accuracy. Eddy current losses in the stator core, rotor core, permanent magnets (PMs), and carriers, along with hysteresis losses in the stator and rotor cores, are calculated by 3-D FEM then coupled to the thermal analysis to predict the temperature distribution. By comparing the temperature results of the 3-D LPTN and 3-D FEM at various speeds, air–gap lengths, loading levels, and simultaneous variation of the current density and speed, the performance of the proposed 3-D LPTN is further investigated and verified. Results indicate that by the proposed 3-D LPTN, components temperature can be approximated with high accuracy in a lesser time than the 3-D FEM.

Investigation of the Torque Production Mechanism of Dual-Stator Axial-Field Flux-Switching Permanent Magnet Motors

This paper studies the torque production mechanism of the dual-stator axial-field flux-switching permanent magnet (DSAFFSPM) machine. Due to the double-sided slotting design of such topology, more resultant air-gap working harmonics in the air-gap flux density are responsible for the torque production and the stator air-gap permeance is especially considered in the investigation. Based on the magnetic force (MMF)-permeance model, the composition and difference of the air-gap working harmonics are demonstrated. The DSAFFSPM machine torque contributions of the main working harmonics are analyzed theoretically and quantified by finite element analysis (FEA). The influence laws of the parameters on the working harmonics are shown and this effectively improves the motor operation performance. Finally, some experiments on the DSAFFSPM machine are carried out to validate the analytical and FEA results.

Comparative Study of E- and U-core Modular Dual-Stator Axial-Field Flux-Switching Permanent Magnet Motors With Different Stator/Rotor-Pole Combinations Based on Flux Modulation Principle

In this paper, the dual-stator axial-field flux-switching permanent magnet (DSAFFSPM) motors with E- and U-core stator modular segments, as well as different stator/rotor-pole combinations are compared. The operation performance of the DSAFFSPM machines are explored by using the MMF-permeance model method. A more comprehensive theoretical analysis, no more limited to numerical calculation, is presented. This reveals directly the relations between the operation performance and design parameters of the machine. The performance comparisons between the E-shaped and U-shaped teeth DSAFFSPM machines are given, including the effects of the structural parameters on the electromagnetic torque, different stator/rotor-pole combinations on the winding factor and gear ratio, the differences of the average torque and the torque density and the efficiency in the 12/10 U-core and 6/10 E-core topology. These are the basis of the DSAFFSPM machine design and optimization. Finally, the experiments on the two prototype, 6/10 E-core and 12/10 U-core DSAFFSPM machines are carried out. The results show that the average torque of the 12/10 U-core prototype is higher than that of the 6/10 E-core prototype, while the torque density and the efficiency of 6/10 E-core DSAFFSPM machines are much higher.

Investigation of cogging torque reduction for a 6/10 hybrid axial field flux‐switching permanent magnet machine by harmonic field current injection

Hybrid axial field flux-switching permanent magnet (HAFFSPM) machine exhibits a high-cogging torque due to its doubly salient structure and flux focusing effect. In consideration of the armature and field windings are both equipped in the HAFFSPM machine, a cogging torque reduction method by the harmonic field current injection is proposed in this study. Initially, the mathematical model of the HAFFSPM machine is analysed. Moreover, the theoretical principle of the proposed method is investigated based on the analytical model of the machine. The amplitude and phase angle of the injected current are calculated according to the harmonic component of the cogging torque. The feasibility of the proposed method is analysed and validated by both the finite-element analysis method and experiments on the prototype. Finally, the comparison between the proposed method and several topology optimisation methods of the HAFFSPM machine is given to indicate the priority of the harmonic field current injection method on cogging torque reduction.

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.

Model Predictive Torque Control of a Hybrid Excited Axial Field Flux-Switching Permanent Magnet Machine

Hybrid excited axial field flux-switching permanent magnet (HEAFFSPM) machine is a novel stator excitation hybrid excited synchronous machine, which combines the advantages of the axial field flux-switching permanent magnet machine and wound field machine. In this paper, two model predictive torque control (MPTC) methods with flux-adjusting strategy implementation for the HEAFFSPM machine, including the MPTC and MPTC with duty cycle control (MPTC-DCC) by optimizing the active voltage vector duration to reduce the torque and flux ripples, are proposed and comparatively investigated. Based on the theoretical analysis, a discrete-time model of the HEAFFSPM machine is established. Considering the flux-enhancing/-weakening strategies, the different multi-objective cost functions are designed. The multiple right weight coefficients are analyzed and chosen to optimize the operating performance of the drive system. The results indicate that the proposed MPTC-DCC method reduces the torque and flux ripples significantly compared with MPTC method, and the drive system has better steady performance. Meanwhile, the load capability in the whole speed region is improved and the constant power operating range is broadened by using the proposed flux-adjusting strategy.

Speed Sensorless Control of Hybrid Excitation Axial Field Flux-Switching Permanent-Magnet Machine Based on Model Reference Adaptive System

A novel 6/13-pole hybrid excitation axial field flux-switching permanent magnet machine (HEAFFSPMM) exhibits strong fault tolerance capability, high efficiency, and large torque density. However, merely few research on speed sensorless control in HEAFFSPMM exists. The speed sensorless control methods based on model reference adaptive system (MRAS) are studied and compared for the machine to improve the stability and reliability of the system and consequently improve the application of machine in control system. Based on the field-oriented control strategy, the MRAS observer of speed is designed and built by applying stator currents, stator flux linkages, and simplified stator currents. The three speed sensorless control algorithms of MRAS are compared and analyzed by using MATLAB/Simulink simulation and dSPACE1104 experimental platform. Results show that the speed sensorless control algorithm based on simplified stator currents has good control performance and high control accuracy.

Fault-Tolerant Control of Hybrid Excitation Axial Field Flux-Switching Permanent Magnet Machines

With the development of electric vehicles (EVs), the reliability and security of the motor drive system have been in high demand in recent years. EVs can still work reliably even when the motor drive system encounters some failures. Therefore, fault-tolerant motors have become the focus of research all over the world. The hybrid excitation axial field flux-switching permanent magnet machine (HEAFFSPMM) is a novel stator excitation brushless PM machine. It combines the advantages of AFFSPMM and hybrid excitation PM machine. Based on a 600 W prototype of three-phase 12/10 stator/rotor pole AFFSPMM, these parameters of HEAFFSPMM are optimized by 3-D finite element method in order to obtain the high self-inductance and low ratio of mutual and self-inductances, including the number of rotor poles, the split ratio, the width of permanent magnet, and the width of stator middle teeth. Then, the fault-tolerant control method of the space vector pulse width modulation based on minimum copper loss is proposed in this paper with the combination of adjusting the field current. The control methods of the HEAFFSPMM are simulated and investigated at healthy and one-phase open-circuit operation. Finally, the experiments are done to validate the proposed fault-tolerant control method. The results indicate that the HEAFFSPMM has good fault tolerance under the proposed control method.

Dynamic performance of the novel axial flux-switching permanent magnet motor

PurposeThe purpose of this paper is to investigate a novel axial flux-switching motor with sandwiched permanent magnet for direct drive electric vehicles (EVs), in which the torque density is increased and the cogging torque is decreased. For reducing the back-electromotive force (EMF) harmonics and cogging torque, a twisted structure is employed. To improve the dynamic performance of the axial field flux-switching sandwiched permanent magnet (AFFSSPM) motor a space vector modulation-direct torque and flux control scheme is proposed.Design/methodology/approachA multi-objective optimization is performed by means of artificial neural network and non-sorting genetic algorithm II to minimize the cogging torque while preserving the average torque.FindingsA comparative study between two proposed machines and the conventional flux-switching permanent magnet (FSPM) machine is accomplished and the static electromagnetic characteristics are analyzed. It is demonstrated that the proposed model with twisted structure has significantly improved performance over the conventional FSPM machine in back-EMF and efficiency. The proposed controller has a speed loop only and contains neither the current loop nor hysteresis control. The AFFSSPM motor exhibits excellent dynamic performance with this scheme.Originality valueThe axial flux-switching permanent-magnet machine is one of the most efficient machines but the AFFSSPM with sandwiched permanent magnet has not been specially reported to date. Thus in this paper, the authors report on optimal design of an axial flux-switching sandwiched permanent magnet machine for electric vehicles and investigate its dynamic performance.

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.

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.

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.

Novel Fault-Tolerant Design of Axial Field Flux-Switching Permanent Magnet Machine

Axial field flux-switching permanent magnet machine (AFFSPMM) has significant advantages, such as the short axial size and high torque density. It is suitable for the direct drive in-wheel applications for the electric and hybrid electric vehicles. For improving the reliability, a novel fault-tolerant structure is applied in the AFFSPMM. The stator is composed of E-shaped laminated segments. The phase windings are physically isolated to each other by the middle teeth of E-shaped cores. The field windings wounded around the middle teeth are used to regulate air-gap flux in the proposed machine. The electromagnetic performances are investigated and analyzed by three-dimensional finite element method (FEM), including the inductance, the back-EMF, and the torque capability, etc. It is shown that the fault tolerance is improved in the novel AFFSPMM, and a wide speed range of operation can be attained by a small DC field current.

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.