Flux-switching Permanent Magnet Machine Research Articles

A Linear Hybrid Model for Analytical Magnetic Field Analysis in Flux-Switching Permanent-Magnet Machine

A hybrid model for the flux-switching permanent-magnet (FSPM) machine is proposed in this paper. In this hybrid model, the air-gap magnetic field in FSPM machine is investigated from the perspective of the stator modulation effect and rotor modulation effect. The stator modulation is discussed from the perspective of equivalent air-gap in the stator slots and permanent-magnets (PMs). The rotor modulation effect is divided to two aspects, namely the effect on the magnetomotive force (MMF) and the effect on stator modulation effect. Different from the conventional model where the stator modulation effect and the rotor modulation are independent of each other, stator modulation effect in the proposed model is coupled with the rotor modulation effect by the minimal reluctance principle. Therefore, MMF and the stator modulation effect in FSPM machine become susceptible to rotor positions with the influence of the rotor modulation effect. Air-gap flux density in FSPM machine is calculated by this hybrid model and compared with those by conventional model and finite element analysis (FEA). Finally, the effectiveness of the proposed hybrid model is validated by comparison of the electromotive force with FEA and experimental results.

Performance Comparison of Tubular Flux-Switching Permanent Magnet Machines Using Soft Magnetic Composite Material and Hybrid Material Magnetic Cores

The magnetic core of a conventional tubular flux-switching permanent magnet machine (TFSPMM) is made of axially laminated silicon steel sheets. The laminated direction is consistent with the motion direction of the mover. According to the flux-switching principle, a large amount of eddy current loss will be generated when the alternating flux passes through the silicon steel sheets vertically. The soft magnetic composite (SMC) material is magneto-thermal isotropy and has low eddy current loss, which can be used in TFSPMM. However, the permeability of SMC is much lower than that of silicon steel sheets, and the hysteresis loss is large at low frequency. When the two materials are used as the hybrid material magnetic core in the machine, their respective advantages can be used to improve the thrust force of the machine and reduce core loss. In order to study the effect of SMC core and hybrid material magnetic core on the machine, the performances of TFSPMM with different kinds of cores are calculated and compared by finite element method (FEM), including magnetic density distribution, permanent magnet (PM) flux linkage, back-electromotive force (EMF), inductance, detent force, thrust force and core loss. Finally, a prototype machine with hybrid material magnetic core is made and experimental verification is carried out.

Performance Improvement of Flux Switching Permanent Magnet Wind Generator Using Magnetic Flux Barrier Design

Flux-switching permanent magnet (FSPM) machines have attracted significant research attention in the field of wind power generation. In this study, the utilization of a magnetic flux barrier to improve the performance of the nine-phase FSPM generator designed for low-speed wind power applications is conducted. The proposed approach involves introducing magnetic flux barriers of different topologies to the conventional FSPM generator and analyzing their performance using 2D finite element simulations. Results suggested that |-shaped magnetic flux barriers exhibited the highest performance among other topologies, making them the appropriate choice for this generator. The geometry of the |-shaped flux barriers was further optimized using response surface methodology to maximize the generator’s performance. The proposed generator exhibits a significant decrease in cogging torque, achieving a remarkable reduction of up to 23.7%, while maintaining electromotive force. Moreover, it shows a significant decrease in permanent magnet eddy-current loss, with a noteworthy reduction of up to 51%. Additionally, significant improvements were demonstrated in terms of electromagnetic torque, torque ripple, output power, and efficiency. Details on the physical reasoning behind these improvements have been provided. Overall, the proposed FSPM generator with inserted flux barriers has the potential to meet the demands of low-speed wind power generation effectively.

Performance Evaluation of Stator/Rotor-PM Flux-Switching Machines and Interior Rotor-PM Machine for Hybrid Electric Vehicles

A three-phase interior permanent magnet (IPM) machine with 18-stator-slots/12-rotor-poles and concentrated armature winding is commercially employed as a 10 kW integrated-starter-generator in a commercial hybrid electric vehicle. For comprehensive and fair evaluation, a pair of flux-switching permanent magnet (FSPM) brushless machines, namely one stator permanent magnet flux-switching (SPM-FS) machine, and one rotor permanent magnet flux-switching (RPM-FS) machine, are designed and compared under the same DC-link voltage and armature current density. Firstly, a SPM-FS machine is designed and compared with an IPM machine under the same torque requirement, and the performance indicates that they exhibit similar torque density; however, the former suffers from magnetic saturation and low utilization of permanent magnets (PMs). Thus, to eliminate significant stator iron saturation and improve the ratio of torque per PM mass, an RPM-machine is designed with the same overall volume of the IPM machine, where the PMs are moved from stator to rotor and a multi-objective optimization algorithm is applied in the machine optimization. Then, the electromagnetic performance of the three machines, considering end-effect, is compared, including air-gap flux density, torque ripple, overload capacity and flux-weakening ability. The predicted results indicate that the RPM-FS machine exhibits the best performance as a promising candidate for hybrid electric vehicles. Experimental results of both the IPM and SPM-FS machines are provided for validation.

Thermal Analysis of a Flux-Switching Permanent Magnet Machine for Hybrid Electric Vehicles

This paper investigates the loss and thermal characteristics of a three-phase 10 kW flux-switching permanent magnet (FSPM) machine, which is used as an integrated starter generator (ISG) for hybrid electric vehicles (HEVs). In this paper, an improved method considering both DC-bias component and minor hysteresis loops in iron flux-density distribution is proposed to calculate core loss more precisely. Then, a lumped parameter thermal network (LPTN) model is constructed to predict transient thermal behavior of the FSPM machine, which takes into consideration various losses as heat sources determined from predictions and experiments. Meanwhile, a simplified one-dimensional (1D) steady heat conduction (1D-SHC) model with two heat sources in cylindrical coordinates is also proposed to predict the thermal behavior. To verify the two methods above, transient and steady thermal analyses of the FSPM machine were performed by computational fluid dynamics (CFD) based on the losses mentioned above. Finally, the predicted results from both LPTN and 1D-SHC were verified by the experiments on a prototyped FSPM machine.

Combined methods for torque variation reduction of high-speed FSPM

Flux switching permanent magnet machine (FSPM) with six slots and four poles (6/4) shows great potential for high-speed operation. However, the 6/4 FSPM suffers from high cogging torque at no load and loaded torque variation. In this paper, improved analytical model for 6/4 FSPM is derived by means of magnetomotive force and permeance, based on which various methods for cogging torque reduction are analyzed respectively. The two chosen effective methods are combined and a Kriging surrogate model is developed. NSGA-II is adopted to optimize the rotor parameters globally. With combined methods and optimal parameters, the cogging torque of 6/4 FSPM can be largely reduced and the results are verified by finite element analysis (FEA).

Analytical Investigation of Magnetic Scalar Potentials Oscillation in Spoke PM Flux Modulation Machines

In this paper, the oscillation phenomena of the scalar magnetic potential of iron pieces of spoke permanent magnet (PM) machines are analyzed and the effects of the oscillation on the air gap flux and back electro-motive force (EMF) are deeply investigated, especially for flux modulation machines such as vernier and flux switching PM (FSPM) machines. To these ends, the formula of the scalar magnetic potential is derived for a generalized spoke PM structure. It reveals that the oscillation phenomena depend on the slot/pole combination, consequently resulting in different behavior according to the machine types such as vernier and FSPM machines. Next, each core’s potential given as a discrete function is developed into a continuous function of an air gap magneto-motive force (MMF) rotating and oscillating through Fourier series expansion. Making use of the developed MMF and the specific permeance of air gap, the equations of air gap flux density and back EMF are derived, which enable accurately estimating the suppression of the modulation flux and the back EMF due to the potential oscillation for different types of spoke PM machines. For validation, various magnetic characteristics are quantitatively examined for different type of spoke PM structures, including PM vernier and FSPM machines, and verified by comparing with FEM simulation results.

High-Frequency Signal Injection-Based Sensorless Control for Dual-Armature Flux-Switching Permanent Magnet Machine

The new topology of the dual-armature flux-switching permanent magnet machine (DA-FSPM) leads to new characteristics and issues in the control of the machine, of which the mutual inductance of the two sets of armature windings is the most important one. This paper proposes a novel position–sensorless control method based on high-frequency injection (HFI) for DA-FSPM. The high-frequency model of the machine is derived, and the theory of the position estimation method is proposed. Different from the conventional HFI-based position estimation method, the proposed method utilizes the mutual inductance of the DA-FSPM rather than the machine saliency. Meanwhile, because the extracted position information based on the mutual inductance is more obvious, the proposed method also has better steady and dynamic performance. Then, the position observer based on the phase lock loop and the initial position detection method for the DA-FSPM is proposed. The experiments are executed on a DA-FSPM prototype with three-phase stator windings and five-phase rotor windings to prove the effectiveness and superiority of the proposed method.

Subdomain method for brushless double-rotor flux-switching permanent magnet machines with yokeless stator

Subdomain method for brushless double-rotor flux-switching permanent magnet machines with yokeless stator

Novel Partitioned Stator Flux-Switching Permanent Magnet Linear Machine: Design, Analysis, and Optimization

Over the past few decades, flux-switching permanent magnet (FSPM) machines have gained more attention. A novel flux-switching permanent magnet linear machine with a partitioned stator (FSPMLM-PS), which has the advantages of high thrust force density and high cost efficiency for short-stroke applications, is presented and analyzed in this article. Firstly, the twelve mover slots and seven stator poles (12s/7p) structure of FSPMLM-PS is introduced, and the fundamental principle of operation is investigated. The partitioned stator helps with the reduction in iron losses and the overall cost of the proposed FSPMLM-PS. One of the frequent issues in linear machines is the end effect, which is compensated for by setting assistant teeth at both ends of the mover. The proposed machine’s main design specifications are globally optimized through a multiobjective genetic optimization algorithm using JMAG software ver. 16.1, although the volumes of the PM and the magnetic and electric loadings are kept the same. The peak-to-peak flux linkage, thrust force, thrust ripples, and detent force are improved by 26.98%, 27.98%, 22.03%, and 68.33%, respectively, after optimization. The comparison results show that the proposed FSPMLM-PS is preferable to the conventional FSPMLM given in the literature. Under the same PM volume, the proposed machine provides 27.95% higher thrust force density.

Fault operation analysis of a novel dual-three-phase dual-rotor flux-switching permanent magnet machine

In this paper, based on the conventional flux-switching permanent magnet (PM) (FSPM) machine, a novel dual-three-phase dual-rotor FSPM machine with PMs of NS layout (NS-DRFSPM) is proposed. The stator of the proposed NS-DRFSPM machine is equipped with dual PMs and dual armature windings to operate in a variety of operating modes and to handle the case of PMs or armature windings failure. Firstly, the topological structure and eight fault operating states of the NS-DRFSPM machine are introduced, and the key design parameters of the NS-DRFSPM machine are optimized by genetic algorithm (GA) optimization and finite element analysis (FEA). Then, the operation principle of the NS-DRFSPM machine is analyzed in detail. Finally, the finite element method is used to analyze the performances of the NS-DRFSPM machine under eight fault operating states, which is mainly analyzed from two aspects: no-load performance and torque performance. The results show that the NS-DRFSPM machine has good electromagnetic performance under different fault conditions, including large back-electromotive force (EMF) amplitude, sinusoidal EMF waveform, high average torque, small torque ripple, and strong anti-saturation ability.

A Novel Six-Phase V-Shaped Flux-Switching Permanent Magnet Generator for Wind Power Generation

Flux-switching permanent magnet (FSPM) machines have attracted wide attention in many rotating applications that require high-power density. In this research, we propose for the first time a novel six-phase FSPM generator with a stator featuring a V-shaped flux-focusing magnet arrangement. The design is targeted for low-speed wind power generation. To achieve the design objectives as a wind generator, the highly comprehensive structural parameters, including the number of rotor poles, split ratio, and rotor pole width, are designed and optimized using 2D finite-element analysis. From findings, the optimal stator/rotor pole combination is discovered to be 12/19 for the considered power and speed requirements. When compared to the initial structure, the optimized structure of the V-shaped FSPM generator is found to produce a significant improvement in EMF, cogging torque, electromagnetic torque, power, and efficiency. The power-generating performance of the proposed FSPM generator is found to be outstanding when compared to the radial-flux PM generators described in the literature. Therefore, the proposed V-shaped FSPM generator is capable of being used for low-speed wind power generation. The machine configuration adjustment approach presented in this work can also be utilized for the design of permanent magnet wind generators.

Inductance Characteristics of Flux-Switching Permanent Magnet Machine Based on General Air-Gap Filed Modulation Theory

Winding inductance is a crucial parameter of machines, which plays an essential role in flux-weakening capability, reluctance torque, power factor, etc. In this article, winding inductance characteristics of flux-switching permanent magnet (FSPM) machines are investigated from the perspective of air-gap modulation magnetic field. With the aid of the general air-gap field modulation theory, the air-gap magnetic field contributed by an arbitrary energized winding of FSPM machines is modeled and analyzed. Then, an analytical expression of winding inductance is derived based on winding function and single-phase magnetic field, through which the relationship between winding inductance and single-phase magnetic field harmonics is unveiled. It is found that the direct current (dc) and 2nd harmonic components of winding inductances in FSPM machines are caused by the dc and 2nd time-harmonic components of primitive harmonics, respectively, which are essentially different from that of traditional interior permanent magnet or reluctance machines. Finally, experiments on a prototype three-phase 12/10 FSPM machine are conducted to verify the theoretical analysis.

Analysis of Synergistic Stator Permanent Magnet Machine With the Synergies of Flux-Switching and Flux-Reversal Effects

Dual permanent magnet (PM) machines have attracted numerous interests due to the high torque density and compact volume <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.</i> This article investigates a synergistic PM machines with the synergies of flux switching and flux reversal effects. The flux-reversal and flux-switching PM (FSPM) flux paths circulate from two sides of the split teeth separately, which avoid the over-saturation with dual PM excitations. The preferred stator and rotor pole number is derived from a simplified analytical model and the influence of leading parameters is analyzed as design guidelines. Furthermore, the synergistic stator PM machine is optimized and compared with FSPM machines. It is revealed that the synergistic stator PM machine exhibits ∼20%, ∼10%, and ∼17% higher torque density than conventional FSPM machine, C-core FSPM machine, and E-core FSPM machine, respectively. Besides, good flux weakening capability is achieved with a larger inductance than conventional FSPM machine, and higher efficiency is obtained at both low-speed and high-speed operations. Finally, an experimental prototype is fabricated to validate the proposed concepts.

Iron Loss Calculation for FSPM Machine With the PWM Inverter Supply Based on General Airgap Field Modulation Theory

In this article, an iron loss for the flux switching permanent magnet machine with the pulsewidth modulation (PWM) inverter supply is calculated based on the general airgap field modulation theory (GAFMT). First, the amplitudes and rotation speeds of the main space harmonics of the airgap magnetic flux density with the supply of PWM harmonics are calculated based on the GAFMT. When calculating the source magnetizing magnetomotive force based on the GAFMT, the equivalent magnetic circuit is applied to calculate the working point of the permanent magnet. Second, each spatial harmonic in the airgap magnetic field is synthesized by an equivalent current layer in the airgap and then is substituted into the 2-D finite element analysis models to calculate the iron losses. Finally, the iron losses calculated by the proposed method with different speeds, loads, and control strategies are compared with the experimental results.

Research on Magnetic Coupling Characteristic of a Double Rotor Flux-Switching PM Machine From the Perspective of Air-Gap Harmonic Groups

The magnetic coupling phenomenon widely exists in the type of double rotor motor, which is difficult to be eliminated completely due to the interactions between two layers of air-gap magnetic fields in a compact geometry structure. This article studies magnetic coupling in the perspective of air-gap harmonic groups, where the novelty is to propose the concept of positive coupling harmonics and the negative one. And, a double rotor flux-switching PM machine is chosen as the research subject. Then, the article begins with the analytical investigation of the modulation principle considering magnetic coupling, where the coupling harmonic group factor is defined. According to this factor, the coupling harmonics are analyzed and selected, and the positive and negative coupling harmonic groups are further determined. Next, the influence of coupling harmonic group on the machine performance is investigated in detail, including the back-EMF, torque performances, overload capability, and so on. The results show that the raise of positive coupling harmonic group factor brings the improvement of machine performances. In addition, a prototype machine is manufactured for experimental testing. Overall, theoretical analysis, simulation and test results verify the validation of the whole investigation to a large extent.

Torque Ripple Suppression of Flux-Switching Permanent Magnet Machine Based on General Air-Gap Field Modulation Theory

Compared with the conventional permanent magnet (PM) machines, the flux-switching permanent magnet (FSPM) machine exhibits higher torque ripple due to its special doubly salient structure and high air-gap flux density, leading to the deterioration of smooth operation. In this article, the output torque ripple suppression methods of FSPM machines from both rotor and stator sides are proposed with the aid of general air-gap field modulation theory. According to harmonic modulation mechanism, air-gap PM field can be modified by revising harmonic content of rotor and stator modulation functions and, consequently, three concepts, including cos-shaped edge rotor (CSER), cos-shaped edge stator, and double cos-shaped edge, are proposed and implemented to suppress the output torque ripple due to the cogging torque and electromagnetic torque ripple of FSPM machines. Finally, finite-element analysis and experiments are conducted to verify the proposed approaches. The results reveal that the CSER method exhibits the most effective suppression effect.

Analysis of the Flux Density and Back EMF in Eccentric Permanent Magnet Machines Based on 2-D Air-Gap Modulation Theory

In this article, the unified 2-D air-gap field modulation (AFM) model is established to analyze the flux density and back electromagnetic force (EMF) in both rotor-permanent magnet (PM) and stator-PM machines under eccentricity. For the temporal distribution of flux density, the static eccentricity (SE) causes amplitude unbalance, while the dynamic eccentricity (DE) leads to sideband harmonic components. The sideband harmonic is commonly regarded as a double-sideband (DSB) modulation effect, but it may be a single sideband (SSB) modulation effect in some specific cases, which is analytically and experimentally proved in this article. More importantly, a quantitative description of how eccentricity influences the phase back EMF is provided, which is only qualitatively expressed in the existing literature. A standardized analysis process is also given, which can be used for different machine topologies. The aforementioned conclusions are validated by the simulations and experiments on two prototyped machines, namely, an 18-slot 20-pole (18s/20p) surface-mounted PM (SPM) machine and a 12s/10p flux-switching PM (FSPM) machine.

Modeling of Fault-tolerant Flux-switching Permanent-magnet Machines for Predicting Magnetic and Armature Reaction Fields

The paper develops accurate analytical subdomain models for predicting the magnetic and armature reaction fields in fault-tolerant flux-switching permanent-magnet machines. The entire region is divided into five subdomains, followed by rotor slots, air-gap, stator slots, PM, and external air-gap imported to account for flux leakage. The coil turns and the remanence of magnets are adjusted by keeping the magnetic and electrical loading on the motor constant. The distance between the centers of two adjacent stator slots varies due to the introduction of fault-tolerant teeth. According to the variable separation method, the general solution expression of each region can be determined by solving the partial differential systems of equations. The magnetic field distributions of subdomains are obtained by applying the continuity conditions between adjacent regions. Some analytical field expressions are represented as new forms under armature reaction field condition compared to those under no-load condition. Based on the developed analytical models, the flux density distribution and the electromagnetic performance can be calculated under no-load or armature reaction field condition separately. The finite element analysis is carried out to verify the validity of the proposed analytical model.

Modeling and Optimal Configuration Design of Flux-Barrier for Torque Improvement of Rotor Flux Switching Permanent Magnet Machine

The rotor permanent magnet flux-switching (RPM-FS) machine is a promising candidate for electric vehicle (EV) and hybrid electric vehicle (HEV) applications. In this paper, we propose the magnetic flux barrier design to improve the torque capability of the RPM-FS machine. The response surface optimization method was used to design and optimize the topology of flux barriers. The 2D finite element analysis shows that the proposed RPM-FS machine has a higher electromotive force than the conventional structure, with only a slight increase in cogging torque. Notably, an insertion of flux barriers could yield a reduction of magnetic flux leakage, an improvement of magnetic saturation capability, and an enhancement of working harmonics of the air-gap flux density. As a result, a significant improvement in torque capability, eddy current losses, and efficiency was obtained. Hence, the RPM-FS machine proposed in this work is capable of being used in EV and HEV applications.