Risk Of Demagnetization Research Articles

Magnetic stability of low corrective force PM in series hybrid magnet memory machine under inverter open-circuit fault

Variable flux memory machine (VFMM) can dynamically adjust its air-gap magnetic field by changing the magnetization states of the employed low corrective force (LCF) permanent magnets (PMs). Due to the demagnetization risk of LCF PMs under armature current, it is necessary to analyze their magnetic stability in various operation states. The magnetic stability of LCF PMs in series hybrid magnet VFMM (SHM-VFMM) under inverter open-circuit (IOC) fault is studied in this article. Firstly, the topology of the investigated SHM-VFMM is introduced, and the field-circuit coupled model of the machine under IOC fault is established. Then, the magnetic stabilities of LCF PMs during the normal and fault operations are analyzed and compared by using the finite element method. The effects of LCF PM demagnetization and fault current on torque are also studied. Afterward, the influence mechanism of the fault armature magnetomotive force (MMF) on LCF PM demagnetization is revealed by using the synthetic MMF graphic method. Finally, the main factor affecting the LCF PM demagnetization under IOC fault is highlighted and an effective method for recovering the magnetic stability of LCF PM is proposed.

Optimal Designs of Wound Field Switched Flux Machines with Different DC Windings Configurations

Wound field switched flux (WFSF) machines exhibits characteristics of the simple robust rotor, flexible flux-adjustable capability, and no risk of demagnetization. However, they suffer from a poor torque density compared with permanent magnet machines due to the saturation. Therefore, in this paper, two WFSF machines with single- and double-layer DC windings, respectively, are optimized for the maximum torque. The end-winding (EW) lengths differ in these two machines, which can affect the optimal design. Design parameters including the DC to armature winding copper loss ratio, slot area ratio and split ratio are optimized when two machines have the same copper loss and overall sizes. In addition, the influence of the flux density ratio, total copper loss, air-gap length and aspect ratio on the optimal split ratio is investigated using the finite element method and results are explained through the analytical model accounting for the saturation. It is discovered that the EWs have no effect on the optimal copper loss ratio, which is unity. In terms of the slot area ratio, the machine with single-layer DC windings prefers smaller DC slot areas than armature slot areas. In the WFSF machine with longer EWs, the optimal split ratio becomes smaller. Moreover, compared with other parameters, the flux density ratio can significantly affect the optimal split ratio.

A Review of Permanent Magnet Models Used for Designing Electrical Machines

This article serves as an overview of existing models of permanent magnets (PMs) for electrical machines. The review study starts with the linear recoil model, which is commonly used to describe the reversible part of the demagnetizing curve. It is a simple model, especially useful for representing materials with high anisotropy, such as ferrite, NdFeB, and SmCo. The model is harder to apply for nonlinear materials, such as Alnico, but still possible since their recoil curves are linear. The study shows how the linear recoil model could be extended to include irreversible demagnetization, temperature dependence, and angular dependence. All such models have their advantages and disadvantages, which will be discussed further. Both the magnetization and the risk of demagnetization are temperature-dependent. It could be noted that NdFeB has an increased risk of demagnetization at high temperatures, while ferrite has it at very low temperatures. The temperature dependence is described and compared for several materials, also including simplifying models. There are different methods to include the inclination angle of an applied magnetic field when studying the demagnetization of PMs. Several models describe different phenomena associated with the underlying dynamics of magnetism. Such models could then consider coercivity mechanisms and coherent rotation of magnetization, both with the Stoner–Wohlfarth model and models of domain wall motions.

Solar PV-Fed Reverse Saliency Spoke-Type PMSM With Hybrid ANF-Based Self-Sensing for Water Pump System

In this work, a reverse saliency (RS) spoke-type permanent magnet (PM) synchronous motor (PMSM) besides its hybrid adaptive notch filter (HANF)-based self-sensing for driving a solar photovoltaic water pump system (WPS) is presented. The conventional spoke-PMSM-driven WPS experiences two types of problems. First, the motor is operated with a flux-weakening current to produce positive reluctance torque, thereby increasing the PM demagnetization risk. Second, an encoder is used to sense the rotor angle, which, in turn, affects the cost and reliability. To solve the first problem, the RS-PMSM is presented, which operates with a flux-intensifying current to produce positive reluctance torque, while the second issue is resolved by using the HANF-based rotor angle estimation. Although conventional methods give an estimate of rotor angle, they do not eliminate both the dc offset and dominant harmonics. The superiority of both the RS-PMSM and HANF over existing solutions is shown, respectively, by using finite-element methods and MATLAB-/Simulink-based performances. Besides, a prototype motor is also manufactured. The performance of the RS-PMSM prototype along with its HANF-based self-sensing is obtained in the laboratory, and various test results are reported. Meanwhile, a comparison of the HANF with available self-sensing techniques is also performed.

Non-Conventional, Non-Permanent Magnet Wind Generator Candidates

Global industrialization, population explosion and the advent of a technology-enabled society have placed dire constraints on energy resources. Furthermore, evident climatic concerns have placed boundaries on deployable energy options, compounding an already regrettable situation. It becomes apparent for modern renewable energy technologies, including wind generators, to possess qualities of robustness, high efficiency, and cost effectiveness. To this end, direct-drive permanent magnet (PM) wind generators, which eliminate the need for gearboxes and improve wind turbine drivetrain reliability, are trending. Though rare-earth PM-based wind generators possess the highly sought qualities of high-power density and high efficiency for direct-drive wind systems, the limited supply chain and expensive pricing of the vital raw materials, as well as existent demagnetization risks, make them unsustainable. This paper is used to provide an overview on alternative and viable non-conventional wind generators based on the so-called non-PM (wound-field) stator-mounted flux modulation machines, with prospects for competing with PM machine variants currently being used in the niche direct-drive wind power generation industry.

Investigation of an Intensifying-flux Variable Flux-leakage Interior Permanent Magnet Machine for Wide Speed Range

In this paper, a novel intensifying-flux variable flux-leakage interior permanent magnet (IFVF-IPM) machine is proposed, in which flux barriers were designed deliberately between the adjacent poles to obtain intensifying-flux effect and variable flux-leakage property. The rotor topology and design principles of the proposed machine are also introduced. Then, a multi-objective optimization method is adopted based on the sensitivity analysis, and some design variables of IFVF-IPM machine with strong sensitivity are selected to optimization progress by using the non-dominated sorting genetic algorithm-II (NSGA-II). Moreover, the electromagnetic characteristics of conventional IPM machine, conventional IFVF-IPM machine (CIFVF-IPM) and the novel IFVF-IPM machine are compared based on the finite element analysis (FEA) method which includes flux linkage, inductances characteristic, torque-speed envelops and power characteristic, as well as evaluation of the risk of irreversible demagnetization. Finally, the experiment results show that the IFVF- IPM machine has a better performance in flux weakening capability for wide speed range and a lower risk of irreversible demagnetization, which indicates the validity and feasibility of the proposed machine.

Comparison of Interior Permanent Magnet and Synchronous Homopolar Motors for a Mining Dump Truck Traction Drive Operated in Wide Constant Power Speed Range

Synchronous homopolar motors (SHMs) with an excitation winding located at the stator and a toothed salient pole rotor are a good alternative to motors traditionally used in traction applications such as induction motors or interior permanent magnet synchronous motors (IPMSM). This study presents the results of a theoretical comparison between an IPMSM and an SHM in a traction application with a constant power speed range of 1:10, which is specific to the mining truck drives, and with a rated power of 370 kW. The considered IPMSM and SHM have the same number of phases, poles and stator slots, and the same outer diameter of the stator lamination. The IPMSM design is optimized using the Nelder–Mead method. The main objectives of optimization are to minimize the average losses in the operating cycle and to limit the required power of the semiconductor inverter. The performance of the optimized IPMSM is compared with the previously obtained performance of the SHM optimized by the same method. Although the average losses in the operating cycle in the compared motors are approximately equal, the losses at high speed for the IPMSM are about two times greater than at low speed with maximum torque, which means that there is a need to intensify the IPMSM cooling system and there is deterioration of reliability. The advantage of the IPMSM is the reduction in the length of the active part by 30%. The advantage of the SHM is that there is 4.6 times lower cost of active materials. In addition, the SHM is more reliable than the IPMSM, as there is no risk of overheating, demagnetization or degradation of permanent magnets over time.

Comparative Study of Permanent-Magnet Synchronous Machines with Different Rotor Topologies for High-Speed Applications

High-speed permanent-magnet synchronous machines (HSPMSMs) are an attractive option for proton-exchange membrane fuel-cell systems. Various HSPMSMs have been developed in the past few years. However, it is difficult to judge which the best candidate is. In this paper, aimed at driving a fuel cell vehicle air compressor, four permanent-magnet machines with different rotor topologies were designed and are compared in terms of electromagnetic, mechanical, rotor-dynamics, and thermal performance. The main topologies of these HSPMSMs are introduced and explained. Then, the electromagnetic and mechanical performance of these HSPMSMs was obtained by using a finite-element method (FEM). To reduce PM demagnetization risk, the temperature increase distributed on the HSPMSMs was also obtained. Lastly, some important conclusions were obtained.

Design and Control of a New Compound Double-Rotor Electric Machine for Hybrid Propulsion System

In this article, a new compound consequent-pole double-rotor electric machine (CCPDRM) is proposed for hybrid propulsion system application. First, the operating principle and harmonic components in CCPDRMs are elucidated. The winding factor theory for conventional permanent magnet (PM) electric machines is further extended and applied in CCPDRMs. Then, this improved theory is adopted to investigate the structure and winding scheme requirement of the proposed CCPDRMs. In addition, the control strategy for the proposed CCPDRM is established. By utilizing a parameter sweep method, the variation trends of CCPDRMs’ torque density with respect to various geometrical parameters are revealed. Based on this, the structure of CCPDRMs is optimized to acquire a better electromagnetic performance. Next, the proposed CCPDRM is compared with a conventional compound bipolar double-rotor electric machine (CBDRM). It is found that the improved topology has a similar torque density but a much higher PM utilization factor and a lower PM demagnetization risk when compared with the CBDRM. Finally, a prototype is manufactured and tested in different operating modes. Furthermore, various mode-switching processes are performed to emulate the practical driving cycle of hybrid transportation. Both steady-state and dynamic mode-switching experimental results prove the effectiveness of CCPDRMs.

Comparative Design and Performance Analysis of 10 kW Rare-Earth and Non-Rare Earth Flux Reversal Wind Generators

Generators are a key technological element of the wind energy generation system. Currently, there is an increasing interest in adopting non-conventional stator-mounted permanent magnet generators, e.g., flux reversal generators (FRGs), which is a good alternative to conventional synchronous generators for medium-speed wind turbine generator applications. The usage of FRG with rare-earth (RE) permanent magnets (PMs) is increasing due to their high efficiency and high power density factors. However, RE PMs are unattractive to wind generators in terms of their cost and unpredictable market supply. In this paper, an attempt is made to study the potential of FRG with non-rare earths (ferrite PMs) for wind generators. The three-phase, 6/8 pole FRG is designed and compared with RE and NRE PMs for wind generator application at 375 r/min, 10 kW. Using 2D FEA, both the generators are compared in terms of their power generating performance with excellent overload capability. It shows that the average efficiency of the generators is approximately similar, but the torque density of NRE-FRG is only 51% that of RE-FRG. The NRE-FRG design is heavier, with the total active mass being 2.6 times higher than the RE-FRG, but with the estimated total active material cost of both generators almost the same. Moreover, the toque ripple for RE-FRG is 64% higher than for NRE-FRG. The demagnetization risk analysis was performed, and it is found that at higher temperatures, RE-FRG structures are prone to higher demagnetization risks, while it is much lower in NRE-FRGs. In summary, it is found that NRE-FRG is a suitable alternative to RE-FRG for medium-speed wind turbine generator applications in the 10-kW power range.

Comparative study of dual 3‐phase permanent magnet machines with coil span of two slot‐pitches

In this study, the electromagnetic performances of dual 3-phase permanent magnet (PM) machines with coil span of two slot-pitches are comparatively investigated. It mainly focuses on two PM machines with different slot/pole number combinations (Ns/2p), that is, the 24-slot/10-pole and 24-slot/14-pole machines (2p = Ns/2 ± 2). First, winding configurations are illustrated for these two dual 3-phase machines with 30° angle displacement. Then, the winding factor, back electromotive force, average torque, torque ripple, iron and PM losses, short-circuit (SC) current, and PM irreversible demagnetisation are analysed and compared for both machines on the conditions of healthy operation and one set of three-phase fault, that is, SC or open circuit (OC), respectively. The comparative results show that on healthy condition the 14-pole PM machine has a slightly larger torque output. Besides, on 3-phase OC condition, the 14-pole machine also performs better over-rating torque capability. In terms of iron and PM losses, the 10-pole machine has smaller iron losses but larger PM losses than the 14-pole machine. Moreover, on 3-phase SC condition, the 14-pole machine has a significantly lower risk of PM irreversible demagnetisation than the 10-pole machine, although both machines have very similar SC currents. Finally, the 24-slot/10- and 14-pole dual 3-phase PM machines are both prototyped and some tests are carried out for validation.

Experimental Validations of Hybrid Excited Linear Flux Switching Machine

Linear Flux Switching Machines (LFSMs) possess the capability to generate adhesive thrust force, thus problems associated with conventional rotatory electric machines and mechanical conversion assemblies can be eliminated. Additionally, the unique features of high force/power density, efficiency, and a robust secondary structure make LFSMs a suitable candidate for linear motion applications. However, deficiency of controllable air-gap flux, risk of PM demagnetization, and increasing cost of rare earth PM materials in case of PMLFSMs, and inherent low thrust force capability of Field Excited LFSMs compels researchers to investigate new hybrid topologies. In this paper, a novel Double-Sided Hybrid Excited LFSM (DSHELFSM) with all three excitation sources, i.e., PMs, DC, and AC windings confined to short moving primary and segmented secondary providing short flux paths is designed, investigated, and optimized. Secondly, unequal primary tooth width optimization and additional end-teeth at all four corners of the primary equip proposed design with balanced magnetic circuit and reduced end-effect and thrust force ripples. Thirdly, the measured experimental results of the manufactured proposed machine prototype are compared with corresponding simulated model results and shows good agreements, thus validating the theoretical study.

A New Field Modulation Machine With Hybrid Magnetic Sources

A new hybrid magnetic source field modulation machine (HMS-FMM) is proposed in this paper, which can work in a wide speed range and guarantee high quality torque output. Due to the bidirectional flux modulation effect applied in HMS-FMM, a large number of working harmonics can be used to generate torque. Direct current excitation is employed to regulate airgap flux density at stator yoke for wide speed range and low harmonic distortion rate at flux weakening state. In order to improve the air gap flux density, the auxiliary tooth is introduced to connect ferrite and stator tooth for providing parallel magnetic circuit. The proposed topology, operating principle and key design parameters are described. Then, the electromagnetic performances are analyzed using finite element analysis (FEA) including magnetic field distribution, back electromotive force, torque characteristics and irreversible demagnetization assessment for magnets. The FEA-predicted results show that the proposed HMS-FMM is an appealing choice for electric vehicle application, which has the merit of high torque production with low torque ripple and safe operation without demagnetization risk in wide operation range.

Analysis of a Hybrid Permanent Magnet Variable-Flux Machine for Electric Vehicle Tractions Considering Magnetizing and Demagnetizing Current

The overall driving cycle efficiency of conventional permanent magnet synchronous machines (PMSMs) for electric vehicle tractions in a wide speed range is constrained due to the large field weakening current and high iron loss in high speed. The series hybrid permanent magnet variable flux machines (HPM-VFMs) which employ both low coercive force (LCF) magnets and high coercive force magnets are proposed to obtain high torque density and flexible air-gap flux density simultaneously. The key of HPM-VFMs design is the accuracy of hysteresis model of LCF magnets and operating principle analysis. This article contributes to clarify operating principle based on hysteresis model of AlNiCo magnets and propose a novel design consideration to reduce magnetizing and demagnetizing current. Based on the theoretical analysis, this article proposes a novel series HPM-VFM, in which the NdFeB and AlNiCo magnets are arranged separately. Furthermore, flux paths are designed to achieve appropriate interaction between two kinds of magnets. The proposed machine has features of wide magnetization state (MS) variation range, low magnetizing and demagnetizing current, and low risk of unintentional demagnetization. By manipulating the MS of the proposed machine, the losses of a wide speed range operation could be reduced. The comparison of efficiency maps and the worldwide-harmonized light vehicles test cycle driving cycle losses between the proposed machine and a conventional interior PMSM proves that the proposed machine achieves higher efficiency for electric vehicle.

Influence of a Winding Short-Circuit Fault on Demagnetization Risk and Local Magnetic Forces in V-Shaped Interior PMSM with Distributed and Concentrated Winding

This paper presents a comparison of 30/8 and 12/8 AC permanent magnet motors with distributed (DW) and concentrated winding (CW) designed for electric vehicle traction. Both prototypes are based on an interior permanent magnet (IPM) motor topology and contain V-shape magnets. The radial flux AC IPM motors were designed for an 80 kW propulsion system to achieve 125 N·m. Finite element models (FEM) used to design the geometry of IPM motors and the required useful parameters of electric motors are widely investigated. The accuracy of finite element models is verified and validated on the basis of test data. Numerical simulations of healthy and faulty operation states, and studies of winding faults based on the FEM offer a deeper understanding of the associated phenomena. Therefore, in this paper, a short-circuit fault in a stator winding was simulated to investigate the transient currents under an external load collapse, for all winding phases. These simulations were used to define other important machine parameters to improve mechanical reliability of the motors and to assess the potential risk of permanent magnet (PM) demagnetization. Furthermore, the analysis of local magnetic forces affecting the PMs in the rotor and their possible displacement in a short-circuit situation were performed, also taking into account the centrifugal force. Lastly, it is demonstrated that the choice of winding configuration has a significant impact on the uncontrolled displacement of magnets in the rotor.

Design and optimization of reverse salient permanent magnet synchronous motor based on controllable leakage flux

In this paper, a controllable leakage flux reverse salient permanent magnet synchronous motor (CLF-RSPMSM) is designed, which has the advantages of wide speed range and low irreversible demagnetization risk. Firstly, the principle of controllable leakage flux and reverse saliency effect is introduced, and the design of the rotor flux barrier is emphatically discussed. Secondly, multiple design variables are stratified by the comprehensive sensitivity method, and the main variables are screened out. Then the relationship between the main variables and the optimization goal is discussed according to the response surface diagram. Thirdly, a sequential nonlinear programming algorithm (SNP) is used to optimize the three optimization objectives comprehensively. Finally, the electromagnetic performance of the proposed motor is compared with the initial IPM motor, the mechanical strength of the proposed rotor is analyzed, and the results verify the effectiveness of the design and optimization method of the proposed motor.

Investigation of PM Demagnetization Characteristics for Axial Split Phase PM Machine With Short-Circuit Fault

PM machine suffers high risk of demagnetization in terminal short-circuit (SC) fault and such fault will degrade the torque production capability and raise repair costs. Thus, reducing the risk of PM demagnetization is a key problem in the design of the PM machine used for safety critical applications. An axial split phase PM machine with optimized SC current limitation capability has been proposed. In this paper, the influence of structure parameters on PM demagnetization characteristics is investigated by analytical method and verified by finite element (FE) method. It is proved that the high pole numbers and turn numbers in series per phase of the axial split phase PM machine is benefit in improving PM demagnetization withstand capability. Based on the combination of analytical and FE methods, the axial split phase PM machine is optimally designed, and the risk of PM demagnetization in transient state SC fault is comprehensively assessed by FE method, which further proved that the axial split phase machine has competitive capability of PM demagnetization withstand.

ВИЗНАЧЕННЯ КООРДИНАТ ТОЧОК ПЕРЕМИКАНЬ ОПТИМАЛЬНИХ СТРАТЕГІЙ КЕРУВАННЯ ЯВНОПОЛЮСНИМИ СИНХРОННИМИ ДВИГУНАМИ З ПОСТІЙНИМИ МАГНІТАМИ

In this paper, a detailed analysis of the control algorithms for a permanent magnet synchronous motor in a wide range of speeds is carried out using the optimal strategies: "Maximum torque per ampere" (first zone), "Field weakening mode" (second zone) and "Maximum torque per volt" (third zone). A method for determining the boundaries of the first and second zones, as well as a method for determining the maximum static moment with which the motor can operate without the risk of irreversible demagnetization of permanent magnets, was proposed. It allows determining the maximum possible operating speed of the motor at a given load, the maximum motor load at a given speed, as well as the advisability of using the third control zone to achieve the maximum motor speed. References 19, figures 4.

Design and Analysis of Hybrid-Excited Flux Modulated Linear Machines With Zero-Sequence Current Excitation

This article investigates a hybrid-excited flux modulated linear machine (HEFMLM) with zero-sequence current excitation. With the adoption of integrated open winding, zero-sequence current can be utilized to provide the dc excitation and further improve the thrust force density. First, the machine topology, drive circuit, and operation principle are described. Then, the magnetomotive force (MMF)-permeance model is built to analytically calculate the air-gap hybrid-excited field harmonics and further verified by finite element (FE) analysis. Moreover, the electromagnetic performances including open circuit characteristics, flux regulation capability, thrust force characteristics, and demagnetization risk are comparatively studied. Due to the improved exciting field and armature MMFs with integrated winding, the thrust force capability can be significantly enhanced by 22.6% on the premise of rated copper loss. Besides, the proposed HEFMLM exhibits high thrust force density compared with the other three types of HEFMLM, benefitting from a high pole-pair number of permanent magnets (PMs) along with a more obvious magnetic gearing effect. Finally, a prototype of the HEFMLM is carried out for experimental validation.

Topology Exploration and Analysis of a Novel Winding Factor Modulation-Based Hybrid- Excited Biased Flux Machine

This article presents a novel permanent magnet (PM)-assisted flux-controllable machine, namely, the hybrid-excited biased flux machine (HEBFM). The proposed machine can implement flexible flux regulations (i.e., either field weakening or strengthening) by integrating the field current winding with the half consequence PM poles in the stator. The topology of the HEBFM can be explored in multipole cases, which contributes to improved flexibility for flux control and winding regulation. Compared with the conventional flux-controllable machines, the proposed machine gains the merits of owning: 1) extended flux control range via the modulation of winding factor (i.e., winding factor modulation); 2) stable and compact structure; 3) reduced demagnetization risk of PMs; and 4) capability of topology exploration. In this article, the operation principle and electromagnetic performance of the proposed machine are analyzed using the finite-element method (FEM). Besides, the torque and torque ripple are optimized based on multiobjective differential evolution (DE) coupled with FEM. Finally, a prototype is manufactured and tested to validate the effectiveness and feasibility of the proposed machine designs.