PM Demagnetization Research Articles

Robust model-free super-twisting sliding-mode control method based on extended sliding-mode disturbance observer for PMSM drive system

Unknown disturbances such as parameter perturbations, PM demagnetization fault, and external disturbances degrade the control performance of a permanent magnet synchronous motor (PMSM) drive system. This paper presents a novel model-free super-twisting sliding-mode control (MFSTSMC) method based on an extended sliding-mode disturbance observer (ESMDO) for a PMSM drive system. First, a novel model-free ultra-local model (ULM) is presented for PMSM with unknown disturbances. Next, the speed loop and d−q axis current loops controllers are designed by using the MFSTSMC method. This control strategy drives the system state quickly converges to the reference value in finite time. Then, an ESMDO is constructed to estimate the unknown parts of the novel model-free ULM. The estimated unknown part is fed back to the MFSTSMC controller to perform feedforward compensation, which effectively eliminates the influence caused by unknown disturbances. Moreover, the stability of the designed observer-based controller is discussed using a quasi-quadratic Lyapunov approach. Finally, comparisons with other methods demonstrate that the presented method improves the dynamic response, anti-disturbance, and robustness of the PMSM drive system.

Permanent Magnet Assisted Synchronous Reluctance Motor with Asymmetric Rotor for High Torque Performance

Permanent magnet assisted synchronous reluctance motor (PMA-SynRM) is a kind of high torque density energy conversion device widely used in modern industry. In this paper, based on the basic topology of PMA-SynRM, a novel PMA-SynRM of asymmetric rotor with position-biased magnet is proposed. The asymmetric rotor design with position-biased magnet realizes the concentration of magnetic field lines in the motor air gap to obtain higher electromagnetic torque, and makes both of magnetic and reluctance torque obtain the peak value at the same current phase angle. The asymmetric rotor configuration is theoretically illustrated by space vector diagram, and the feasibility of high torque performance of the motor is verified. Through the finite element simulation, the effect of the side barrier on output torque and the Mises stress under the rotor asymmetrical design are analyzed. Then the motor characteristics including airgap flux density, back EMF, magnetic torque, reluctance torque, torque ripple, losses, and efficiency are calculated for both the basic and proposed PMA-SynRMs. The results show that the proposed PMA-SynRM has higher torque and efficiency than the basic topology. Moreover, the torque ripple of the proposed PMA-SynRM is reduced by the method with harmonic current injection, and the torque characteristics in the whole current cycle are analyzed. Finally, the endurance to avoid PM demagnetization is confirmed based on the PM remanence calculation.

Design Criterion and Analysis of Hybrid-Excited Vernier Reluctance Linear Machine With Slot Halbach PM Arrays

This paper proposes a hybrid-excited vernier reluctance linear machine (HEVRLM) with slot halbach PM arrays. By utilizing halbach PM arrays, leakage flux that existing in the consequent pole structure can be greatly reduced. Besides, the dc excitation can enhance both the flux regulation capability and force density. First, the machine topology and working principle are introduced. Then, magnetomotive force (MMF)-permeance model is established to analytically calculate the air gap flux density under hybrid excitation. Moreover, the flux regulation capability, thrust force characteristic and PM demagnetization risk of the proposed machine are comparatively studied based on finite element method (FEM). It shows that halbach PM arrays can effectively reduce the leakage flux and further significantly improve the thrust force density by more than 30%. In addition, hybrid excitation is a feasible approach to further improve the thrust force density by distributing the optimal dc and ac currents. Moreover, the proposed HEVRLM exhibits high thrust force density compared with other three types of hybrid-excited linear machines. Finally, a prototype of HEVRLM is manufactured and tested for experimental validation.

Accurate SM Disturbance Observer-Based Demagnetization Fault Diagnosis With Parameter Mismatch Impacts Eliminated for IPM Motors

This paper proposes a novel sliding mode (SM) disturbance observer-based technique to diagnose demagnetization fault of interior permanent magnet (IPM) motors with stator parameter mismatch impacts eliminated. First, the IPM motor model incorporating the disturbances caused by the PM demagnetization and stator parameter mismatch is established. Then, an SM disturbance observer is constructed to identify the overall disturbance caused by all parameters, with its stability discussed by using the Lyapunov function. Third, a current-analysis-based method is developed to extract the disturbance only caused by flux linkage mismatch from the overall disturbance. Third, the extracted disturbance is adopted to calculate the real flux linkage, achieving demagnetization fault judgment and demagnetization degree calculation. Finally, experiment is conducted on two IPM motors to validate the proposed flux linkage estimation and fault diagnosis methods.

Thrust Ripple Reduction of Dual-Side Toroidal-Winding Linear Permanent Magnet Vernier Machine by Unequal End-Teeth Width

The linear permanent magnet vernier machines have attracted more and more attention last several years due to its high thrust density at low speed, which is very suitable for the direct-drive applications. A dual-side toroidal-winding linear permanent magnet vernier machine (DSTWLPMVM) with the unequal end-teeth width is proposed in this paper to reduce the detent force and thrust ripple. The low detent force in DSTWLPMVM is achieved by combination of two single-side detent forces with the opposite phase angle, which is obtained by optimizing the unequal end-teeth width of the primary two-sides. In the proposed machine, the symmetry three-phase flux linkage of the toroidal winding also can be obtained by optimizing the unequal end-teeth width. Therefore, the low thrust ripple of DSTWLPMVM is achieved by optimizing the unequal end-teeth width for obtaining the low detent force and symmetry three-phase flux linkage. The vertical magnetic force in the proposed LPMVM is also considered by finite element analysis (FEA) in this paper. Via optimizing the unequal end-teeth width, the detent force is reduced by 90% while the peak-to-peak thrust ripple is reduced by 69% than that of DSTWLPMVM with the equal end-teeth width, respectively. In this paper, the thermal and PM demagnetization behavior of the proposed machine are also analyzed by FEA.

Design and Optimization of an Asymmetric Rotor IPM Motor with High Demagnetization Prevention Capability and Robust Torque Performance

In this paper, an asymmetric rotor interior permanent magnet (ARIPM) motor with high demagnetization prevention capability and robust torque performance is proposed. The key contribution of this paper lies in two aspects. On the one hand, a novel asymmetric rotor with a shifted magnet axis is proposed to improve the demagnetization prevention capability and torque density. In order to obtain a proper asymmetric rotor topology of the ARIPM motor, the multi-physical performances, especially the PM demagnetization characteristics of five types of PM arrangements, are analyzed. Furthermore, an asymmetric rotor with V- and VV-type PM arrangement is preliminarily designed, considering the multi-physical performance balance and the potentially high anti-demagnetization ability. On the other hand, it is found that the asymmetric rotor structure can not only improve the nominal value of motor performance but also can enhance the resistance to the influence of manufacturing uncertainties. Therefore, multi-objective optimization of the ARIPM motor with rotor notch design is carried out to obtain an optimal motor structure with both high nominal value and robustness of motor performances. By comparing the simulation results with those of a benchmark motor, the superiority and validity of the proposed ARIPM motor are confirmed. Experimental tests will be carried out in the future to further verify the effectiveness of the proposed motor.

Analysis and Experiment of a Dual Stator/Rotor PM and Winding Flux Modulated PM Machine

In this article, a high torque density flux modulated permanent magnet machine topology with dual permanent magnets and dual armature windings (DMDA-FMPM) is proposed. The most notable feature of DMDA-FMPM is that both stator and rotor parts consist of PMs and armature windings so that a single air gap and a simple structure are kept. Moreover, both the PMs can interact with both the windings to produce four torque components, and the output torque on the shaft is the superposition of these four torque components. Consequently, extremely high torque is expected. This paper firstly introduces the topology and main drive circuit of DMDA-FMPMs. Then the basic operation principle and slot/pole combination equation are illustrated, taking the proposed topology as an example. Afterward, the electromagnetic performance, including flux line distribution, flux density, back electromotive force (EMF), torque quality, and power factor, is analyzed by finite element analysis (FEA). Besides, the fault-tolerance of windings failure and PM demagnetization is discussed. A prototype is designed and tested to verify the proposed DMDA-FMPM. The experimental results match well with the FEA and theoretical analysis. DMDA-FMPM has excellent torque performance and fault-tolerant capability. Finally, the possible applications, operating modes, advantages, and drawbacks are discussed comprehensively.

Composite PM Rotor Design and Alternating Flux Density Harmonic Component Analysis of a 200 kW High-Speed PMSM Used in FESS

The flywheel energy storage system (FESS) is a short-time high-power energy storage technology widely used in various fields. To improve speed and reduce air friction loss, the rotor of the high-speed permanent magnet synchronous machine (HSPMSM) used in FESS operates at a magnetic suspension state in vacuum. It is very difficult for the rotor to dissipate heat, which may even lead to PM demagnetization. In this paper, a 200 kW 20000 r/min HSPMSM is designed for FESS of an uninterruptible power supply (UPS), and a composite PM rotor with multilayer sleeves is proposed. Distinct from the previously proposed retaining sleeve design of the HSPMSM rotor, a silicon steel sleeve is added in the composite PM rotor, which can provide a bypass for alternating flux density harmonic components in the rotor and prevent them from entering the alloy sleeve and PM. Moreover, a post-processing method of finite-element analysis (FEA) results is proposed to obtain the alternating harmonic components in the rotor and further analyze the suppression effect of the silicon steel sleeve on them. As the silicon steel sleeve is introduced, the amplitudes of alternating harmonic components are effectively suppressed, which can mitigate the eddy current loss and heat generation of the HSPMSM rotor from the source.

Novel Mechanical Flux-Weakening Design of a Spoke-Type Permanent Magnet Generator for Stand-Alone Power Supply

In this paper, a novel mechanical flux-weakening design of a spoke-type permanent magnet generator for a stand-alone power supply is proposed. By controlling the position of the adjustable modulator ring mechanically, the total induced voltage, i.e., the amplitude of the back EMF vector sum can be effectively adjusted accordingly by the modulation effect. Consequently, the variable-speed constant-amplitude voltage control (VSCAVC) with a large speed range can be achieved. Compared to the electrical flux-weakening method, the mechanical flux-weakening method is easier to operate without the risk of PM demagnetization. The analytical model is presented, and the operation principles are illustrated. To analyze the performance of different combinations of stator/rotor pole pairs, four cases are optimized and analyzed using the finite element method for comparison. The characteristics of VSCAVC are analyzed.

Design and Analysis of 15 MW SPM Vernier Generator for Direct-Drive Wind Turbine Applications

This paper presents the design and an analysis of a surface PM vernier generator (SPMVG) for MW-scale direct-drive (DD) wind turbine application. An SPMVG has the advantage of higher torque density; however, especially at higher power ratings with increased electrical loadings, the power factor worsens and there are some serious concerns including magnetic saturation of cores and PM demagnetization. These issues are directly related to machine design parameters such as PM dimensions, applied electrical loading, slot geometry and the choice of slot–pole combination. It is determined that depending on the PM thickness and a few other design variables, each slot–pole combination has an optimal value of specific electrical loading. The use of the optimal value of specific electrical loading ensures that the machine is not saturated, the performance is optimum and the power factor is not unnecessarily degraded. Moreover, under certain design constraints, design criteria are developed that ensure the proper choice of various entailed design variables. By using the developed design criteria, the trends of various electromagnetic performances with variation in the slot–pole combination are discussed. The obtained trends clearly show that each slot–pole combination offers a certain torque density and power factor; thus, it serves as a guide for the selection of the slot–pole combination considering the required torque density and/or certain power factor limit. Finally, by using the developed design approach, an SPMVG for rated power of 15 MW is designed; the design objectives are to maximize torque per volume with a power factor limit of 0.4. Moreover, the various aspects of the performances of the designed SPMVG are comprehensively compared against a conventional PM DD 15 MW generator.

A Simple Method for Identifying Mass Unbalance Using Vibration Measurement in Permanent Magnet Synchronous Motors

There has been active research in fault diagnosis of permanent magnet synchronous motors (PMSMs) with the recent increase in reliability-critical PMSM applications. Most of the research efforts are focused on the motor current signature analysis (MCSA), as it allows remote online detection of the rotor and load defects using the current measurement available in the drive. A critical limitation of MCSA or vibration analysis is their inability to distinguish the type of rotor or load defect. It is crucial for the maintenance engineer to identify the type of defect since the course of action for continued operation differs depending on the fault. In this letter, a simple automated test method for identifying mass unbalance using vibration measurement commonly available in motor drive systems is proposed. The effectiveness of the proposed method is verified on a PMSM under emulated PM demagnetization, dynamic eccentricity, and mass unbalance conditions.

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.

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.

Comparative Analysis of Dual-Rotor Modular Stator Axial-Flux Permanent Magnet Machines With Different Rotor Topologies

In this paper, the influence of rotor topology on the electromagnetic performances of dual-rotor axial-flux permanent magnet (DRAFPM) machines with modular stator (MS) and fractional slot non-overlapping winding (FSNW) is investigated by comparing four different rotor structures, including surface-mounted PM (SPM), consequent-pole PM (CPM), Halbach CPM (HCPM) and interior PM rotor (IPM) structures. In order to reduce the PM flux leakage in CPM rotor, the air-barrier introduced beside the PM is optimized by the three-dimensional finite-element method. Then, the main electromagnetic characteristics of the investigated machines, such as open-circuit airgap flux density, back-EMF, average torque, torque ripple, PM eddy-current loss and PM demagnetization are compared quantitatively. Consequently, the machine with SPM rotor accommodates the highest back-EMF and output torque; meanwhile, the CPM machine possesses the highest torque per PM volume and inductance of d-axis. Moreover, both CPM and IPM machine generate reluctance torque, and the IPM machine features larger salient pole ratio and stronger resistance to irreversible demagnetization, as well as the highest machine efficiency.

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.

Analysis of Split-Tooth Stator-Slot Permanent-Magnet Machines With Different PM Arrangements

In this paper, the split-tooth stator-slot permanent-magnet (ST-SSPM) machines with different PM arrangements are comprehensively analyzed. Four types of ST-SSPM machines are first introduced and classified by the positions and polarities of PMs. Then, the operation principles are elaborated and the slot-pole combinations are derived from the view of field modulation theory. Besides, four types of ST-SSPM machines with different slots and rotor poles are globally optimized to achieve maximum torque and minimum torque ripple. Furthermore, the electromagnetic performances of the optimal designs are thoroughly analyzed by using the finite-element analysis (FEA), including the cogging torque, back-EMF, steady torque, PM utilization ratio, loss, efficiency, and PM demagnetization. Finally, some conclusions are drawn based on the optimal designs and analyzed results.

Optimal Design of Spoke-Type IPM Motor Allowing Irreversible Demagnetization to Minimize PM Weight

In this study, we introduce an optimal design for a spoke-type interior permanent magnet (IPM) motor that can minimize PM weight by allowing irreversible demagnetization, unlike the conventional motor design method that does not allow irreversible demagnetization. The spoke-type rotor structure has the advantage of concentrating the magnetic flux around the rotor core. However, part of the PM near the surface of the stator tooth becomes sensitive to the armature reaction and external magnetic factors. Therefore, typical spoke-type rotor construction follows a limited design process that does not allow irreversible demagnetization. Although the manufacturing process allows tolerance for the demagnetization rate, motor design without considering the demagnetization rate in all the design stages becomes a design constraint and limits the performance area. In this study, the performance improvement is examined, when irreversible PM demagnetization is allowed up to −3%, and is not zero. For optimal design, Latin hypercube sampling (LHS), the kriging model, and genetic algorithm (GA) are utilized. With the proposed design process, motors are effectively designed to reduce the PM weight by 23.7%, compared to the initial design model while maintaining an efficiency almost similar to that of the initial design model.

Analytical Airgap Field Model and Experimental Validation of Double Sided Hybrid Excited Linear Flux Switching Machine

Linear Flux Switching Machines (LFSMs) are suitable candidates for long stroke applications as they confines all excitation sources to primary thus leaving completely passive, robust, and low cost secondary. Permanent Magnet LFSMs (PMLFSMs) enables high thrust force density and efficiency. However, deficiency of controllable air-gap flux, risk of PM demagnetization, and increasing cost of rare earth PM materials diverted researchers towards Field Excited LFSMs (FELFSMs). FELFSMs wiped out aforementioned PMLFSM’s shortcomings at the cost of low thrust force density. In this paper, merits of PMLFSM and FELFSM are combined by proposing a novel Hybrid Excited LFSM (HELFSM). Proposed machine is excited by PMs, Field Excitation Coils (FECs), and Armature Windings (AWs). However, complex magnetic circuit of poly-excited HELFSM compels designers to adopt FE Analysis (FEA) for design, analysis, and optimization. To decrease dependency on computationally complex and time consuming FEA, an analytical model combining lumped parameter magnetic equivalent circuit, Fourier analysis, Laplace equation, and Maxwell Stress Tensor method is proposed to predict open-circuit flux linkage, B-EMF, normal and tangential components of no-load and on-load magnetic flux density, detent, and thrust force performance. Finally, predictions of the developed analytical model are validated with corresponding FEA and experimental results.

Detection of magnetization loss in a PMSM with Hilbert Huang transform applied to non-invasive search coil voltage

This paper presents a novel method for demagnetization fault detection in permanent magnet synchronous machine (PMSM). Demagnetization fault is a common problem existing in PMSM which deteriorates the machine performance and can lead to serious subsequential machine damages. Unlike the most popular method based on the analysis of the machine currents for detecting this type of fault, the approach proposed in this paper analyzes the voltage signal of a non-invasive search coil by means of Hilbert Huang transform. Simulations are carried out with a two dimensional finite element analysis (FEA) for different demagnetization levels to test the capability of the proposed method to detect PM demagnetization faults.

Failure Diagnosis of Demagnetization in Interior Permanent Magnet Synchronous Motors Using Vibration Characteristics

The detection of a precursor to the demagnetization of permanent magnets is very important because a high degree of reliability is necessary in permanent magnet synchronous motors (PMSMs). This paper investigated the diagnosis of very slight PM demagnetization. A part of the permanent magnet was altered to non-magnetic material so as to mimic the effect of demagnetization. The vibration characteristics were clarified for low demagnetization in PMSMs driven under vector control by experiments and 3D finite element (FE) analysis. We found that the amplitude of some components of the vibration was approximately proportional to the demagnetization level of the PM and the load torque. Therefore, the measurement of vibration and torque is very useful for the estimation of the magnetization level of PMSMs under vector control except for under very light load.