Surface Permanent Magnet Research Articles

A New Perspective on the PM Vernier Machine Mechanism

Permanent magnet vernier (PMV) machines have attracted more and more attention for their merits of high torque density and simple structure. Also, the principle of electromechanical energy conversion is the most common way to investigate the PMV machine by calculating back electromotive force and electromagnetic torque. In this paper, a new perspective on the mechanism of PMV machines based on the Maxwell stress tensor method is presented to deepen the insight into the reason why the force on the rotor of a PMV machine is larger than that of an surface permanent magnet (SPM) machine. Based on the finite element analysis (FEA) method, three machines with exactly the same rotor are analyzed and compared, namely 24-slot/20-pole SPM, 12-slot/20-pole surface PMV, and 6-slot/20-pole split-tooth PMV machines. The radial and tangential flux densities and force distributions along the airgap are illustrated. The influence of pole ratio on the performance of PMV machines is also investigated. It is shown that the improvement of tangential flux density in the PMV machine plays a primary role in the higher torque density, which shows a promising way to improve the torque density of machines.

Analysis and design of surface permanent magnet synchronous motor and generator

This paper presents an analytical method to design the high-efficiency surface permanent magnet synchronous motor (SPMSM) or generator (SPMSG). The air-gap and permanent magnet size can be approximately determined based on our mathematics model, which is the most important part of SPMSM design. From our method, we can know that motor's power out torque is related to the torque angle that we selected in our design and it affects the air-gap and permanent magnet size. If we choose a low torque angle, the motor or generator's overload power handing capability will increase. The embrace value has a vital place in designing a motor or generator due to its effects on air gap flux density, cogging torque, efficiency and so on. In order to avoid the knee effect, the working point of the permanent magnet we selected in the design should be bigger than 0.5. The developed 36 slots, 4 poles, surface mound permanent generator is proposed. The corresponding finite element analysis (FEA) model is built based on our design method. Structure optimization includes stator and rotor structure size, permanent magnet size, magnetic bridge and air gap length which are analyzed and simulated by ANSYS Maxwell 2D FEA. Thermal analysis is conducted, and the housing of the alternator is designed. The alternator prototype is fabricated and tested based on our design.

Investigation of the transient and steady state operations of two Line Start Permanent Magnet Motors (LSPMMS) with different rotor configurations

This paper investigates the transient and steady state operations of two Line Start Permanent Magnet Motors (LSPMMs) with different rotor types. The calculations showed that both designs can reach a higher efficiency than comparable induction motorsof the same size. The loading capability of the Surface Permanent Magnet (SPM) rotor is better than the Interior Permanent Magnet (IPM) rotor on asynchronous rotation as it has lesser torque ripples. However, IPM rotor had less flux leakage and copper losses at the synchronous operation under the same loading conditions.The results of the investigation also show that IPM motor attains a higher speed responses than SPM motor but SPM motor synchronizes faster than the IPM motor under the same loading conditions. During the asynchronous period, the chracteristics of both machines display similar features at a lower load torque less than 50N-m. The ripple contents of IPM is greater than that of SPM as can be observed in the run-up speed characteristics where IPM shows spontaneous overshoot. The pull out torque for SPM and IPM occurred at the time of 6 and 10 second respectively with same load increments. Keywords: synchronous, asynchronous, motor, permanent magnet, torque

Implementation Issues of Flux Linkage Estimation on Permanent Magnet Machine Position Sensorless Drive at Low Speed

This paper improves the surface permanent magnet (PM) machine position sensorless drive at low speed. Considering the surface PM machine (SPM) drive, EMF voltage or flux linkage should be estimated for the sensorless drive. Different from EMF voltage, the flux linkage based on the voltage integration is theoretically independent to speed which is suited for the low speed position estimation. In this paper, several improvements on the flux-based sensorless drive are proposed to enhance the low speed dynamic performance. First, a modified voltage integration is develop to remove the flux estimation drift caused by voltage or current offset. This integration contains a high-pass filter (HPF) for the DC drift elimination. In addtion, the filter delay is compensated to maintain the flux phase. Second, inverter deadtime harmonics are decoupled with the knowledge of actual machine phase voltages. It is shown that the position estimation error is decreased for the better low speed performance. According to experimental results, SPM machine sensorless drive is enhanced at 4%~6% speed region from many aspects. They include position signal SNR, position error and drive dynamic response. More importantly, the overall current regulation bandwidth can increase to 1kHz at low speed. It is compatible to standard encoder-based field oriented control (FOC) drives.

${H_\infty}$ Robust Control of Permanent Magnet Synchronous Motor Based on PCHD

The surface permanent magnet synchronous motor (SPMSM) speed regulation system is easily affected by the inner parameter perturbation and the external load disturbance at run time. To solve this problem, the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> robust control strategy is proposed in this paper. First, given the systematic uncertainties, the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> robust current controller based on the Hamilton-Jacobi Inequality is designed to ensure the robustness of current control under the SPMSM nominal mathematical model. This model is expressed as the port-controlled Hamiltonian with the dissipation form; second, the linear matrix inequality-based H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> sliding surface and the sliding control law are designed under the extended state space expression of the SPMSM motion equation. Thereby, the robust H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> sliding mode speed controller is acquired, thus realizing the robustness of speed control and improving the dynamic characteristics of the system. Finally, the effectiveness and availability of the proposed control strategy are verified by the hardware-in-the-loop simulation experiment.

Investigation of the End Leakage Flux in Fractional Slot Concentrated-Winding Surface Permanent Magnet Machines

When the end leakage flux or end leakage inductance cannot be ignored in a permanent magnet (PM) machine (e.g., a PM machine with a short axial length), the analysis of the machine is a time-consuming three-dimensional (3-D) issue. Existing research has made the end leakage inductance no longer to hinder that the performance calculation of fractional slot concentrated-winding surface permanent magnet (FSCWSPM) machines is simplified into a time-saving 2-D issue. However, no such mature research exists for end leakage flux. This paper proposes a novel end leakage flux function that can be used to accurately quantify the end leakage flux of FSCWSPM machines. Then, based on sensitivity research and regression analysis, a parametric model is established to quickly construct the end leakage flux function. Thus, even for FSCWSPM machines with nonnegligible end leakage flux, the results comparable to those from the 3-D finite element method (FEM) can be easily obtained using the proposed end leakage flux function and parametric model to revise the results from 2-D FEM. Moreover, the application of the above function and model is briefly described. Finally, FEM and experimental results are used to verify the calculation precision, adaptability, and timeliness of the proposed methodology.

Finite Element Approach of Interior Permanent Magnet Motor Acoustics Noise

IPM (Interior Permanent Magnet) motors produce torque based on two different mechanisms. The first of them is permanent-magnet torque, which is generated by the flux linkage between the PM (Permanent Magnet) rotor field and the electro-magnetic field of the stator. It is the same torque as produced by SPM (Surface Permanent Magnet) motors, however, IPM designs produce another force known as reluctance torque. The second one, the shape and location of the slots in the rotor laminations are designed to channel magnetic flux so that even if the slots were left as air gaps, the rotor would experience a force to align the magnetic flux lines with those generated by the stator coils. IPM motors are now very popular in industrial and military applications by providing high power density and high efficiency compared to other types of motors. This paper presents the use of finite element method harmonic analysis for investigation of IPM motor acoustics noise. This method is useful for DC (Direct Current) motor designs in many industrial and military applications.

Assessing PM2.5 concentrations in Tehran, Iran, from space using MAIAC, deep blue, and dark target AOD and machine learning algorithms

This study aims to explore the spatial estimation of fine particulate matter (PM2.5) using 10-km merged dark target and deep blue (DB_DT) Aerosol Optical Depth (AOD) and 1-km Multi-Angle Implementation of Atmospheric Correction (MAIAC) AOD over Tehran. The ability of four Machine Learning Algorithms (MLAs) to predict PM2.5 concentrations is also investigated. Results show that the association of satellite AOD with surface PM significantly increases after considering the contribution of relative humidity in PM mass concentration and normalization of AOD to Planetary boundary layer height (PBLH). The examination of derived aerosol layer height (ALH) from 159 Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) profiles shows that PBLH could successfully represent the top of aerosol-laden layers. Surprisingly, the highest correlation was found between normalized 10-km DB_DT AOD and corrected PM2.5 measurements. Consequently, random forest (RF) fed by this AOD product has yielded the best performance (R2 = 0.68, RMSE = 17.52 and MRE = 27.46%). Importance analysis of variables reveals that DB_DT and meteorological fields are of highest and least importance among selected variables, respectively. The RF performance is less satisfactory during summer which is assumed to be caused by the omission of unknown features representing the formation of secondary aerosols. The inferior accuracy of estimation in the north and east of Tehran is also linked to lacking features which could feed the transportation of PM2.5 from west to the east of the study area into MLAs.

Guest Editorial Emerging Electric Machines and Drives for Smart Energy Conversion

Energy conversion is one of the key steps for human utilizing the energy. In particular, as the key component for electromechanical energy conversion, electric machines play a significant role and greatly promote the development of modern civilization. Actually, the conventional types of electric machines, namely DC machines, induction machines, and synchronous machines, as well as surface permanent-magnet (SPM) machines and inserted-PM (IPM) machines, have been widely applied for various aspects in human lives. In recent years, emerging electric machines, including the double-salient type, hybrid-excitation type, PM memory type, magnetic-gearing type, PM vernier type, advanced magnetless type, multiport type, and some newly developing types, are proposed for new application occasions such as electric vehicles (EVs), electric ships, electric aircraft, electric robotics, wind power generation, unmanned propulsion systems, and so on. In addition, the corresponding advanced control strategies have presented for electric drives, which include the direct torque control (DTC), field oriented control (FOC), finite control set model predictive control (FCS-MPC), fault-tolerant control, and sensorless control. Thus, emerging electric machines and drives take active roles for applications with more electric or full electric. This special section brings new findings of electric machines and drives on their topologies, structures, analysis approaches, advanced control strategies, and new applications.

Comparison of Surface Permanent Magnet Axial and Radial Flux Coaxial Magnetic Gears

This paper provides a thorough, parametric comparison of axial and radial flux coaxial magnetic gears with surface-mounted permanent magnets. While both topologies share similar operating principles and can achieve comparable shear stresses, they exhibit different scaling trends with respect to key design parameters. Both topologies’ volumetric torque densities (VTDs) increase with the outer radius, but the axial flux topology's VTD increases with the radius at a much faster rate than the radial flux topology's VTD. Another difference between the topologies involves their cross-sectional scaling parameters. The stack length axially scales radial flux gear cross sections, and, as it increases, the impact of end-effects decreases, which improves the performance. For axial flux gears, the radii ratio scales the cross section's radial width between different radii. This fundamentally changes optimal parameter values and design performance tradeoffs. Finally, axial flux rotors experience significant axial forces, but the radial forces on radial flux rotors can be balanced out. Based on these trends, radial flux gears are superior to axial flux gears for most applications; however, axial flux gears have a significant advantage when a large radius and a small axial length are permissible or when mechanical power needs to be transmitted across a flat barrier.

Short-Circuit Fault Detection Observer Design in a PMSM

This paper explores detecting interturn short-circuit (ITSC) faults in surface permanent magnet synchronous machines (SPMSM) while simultaneously estimating the (typically large) fault current to determine if operation is within thermal limits. ITSC faults are caused by electrical insulation failures in the stator windings and can lead to shorts to ground resulting in oscillations in torque, localized heating, and even fires. This paper proposes a moving horizon observer methodology for detecting such faults, the level of fault, the motor state, and a thermally sensitive parameter in SPMSM. Theoretical verification of the observability and detection of fault levels and currents is also set forth. Fault detection, fault current estimation, and parameter estimation are verified via simulation for a set of ITSC faults using noisy measurements.

Modeling of Surface Permanent Magnet Motors With Cogging and Saturation Effects Included

A method for modeling permanent magnet motors including saturation effects on cogging and motive torque is described. This method rivals the accuracy of finite element analyses but solves 4–5 orders of magnitude faster, depending on several factors. Simulation results match well with laboratory measurements.

An Analytical Subdomain Model of Torque Dense Halbach Array Motors

A two-dimensional mathematical model estimating the torque of a Halbach Array surface permanent magnet (SPM) motor with a non-overlapping winding layout is developed. The magnetic field domain for the two-dimensional (2-D) motor model is divided into five regions: slots, slot openings, air gap, rotor magnets and rotor back iron. Applying the separation of variable method, an expression of magnetic vector potential distribution can be represented as Fourier series. By considering the interface and boundary conditions connecting the proposed regions, the Fourier series constants are determined. The proposed model offers a computationally efficient approach to analyze SPM motor designs including those having a Halbach Array. Since the tooth-tip and slots parameters are included in the model, the electromagnetic performance of an SPM motor, described using the cogging torque, back-EMF and electromagnetic torque, can be calculated as function of the slots and tooth-tips effects. The proposed analytical predictions are compared with results obtained from finite-element analysis. Finally, a performance comparison between a conventional and Halbach Array SPM motor is performed.

Low-Field Alignment of Anisotropic Bonded Magnets for Additive Manufacturing of Permanent Magnet Motors

Additive manufacturing techniques for fabricating bonded magnets have the potential to reduce manufacturing cost and time-to-market of products and address the criticality of rare-earth elements (REEs), which is a concern for economic design of dependent applications such as permanent magnet machines. We investigated the magnetic alignment of anisotropic bonded magnet material comprising 65 vol.% Nd-Fe-B in nylon-12 produced by extrusion in a 20-W brushless direct current surface permanent magnet motor for submersible water pump application using finite element analysis. The results predict that sufficient alignment for this application could be obtained at low alignment fields (μ0H ≤ 1 T) with a reduction in the volume of critical materials by up to 40% compared with isotropic permanent magnets. This demonstrates the economic feasibility of incorporating a magnetic alignment field source into additive manufacturing systems for bonded magnets, and the potential of aligned anisotropic bonded magnets to address REE criticality.

Rotor Design Optimization of a New Flux-Assisted Consequent Pole Spoke-Type Permanent Magnet Torque Motor for Low-Speed Applications

A new flux-assisted consequent pole spoke-type permanent magnet (PM) synchronous torque motor is proposed in this paper. The proposed motor has fractional slot structure with a spoke-type rotor geometry and flux-assisted magnets. Initial design, rotor design optimization, detailed 2-D and 3-D finite-element analyses (FEAs), and structural and thermal simulations are all carried out. A prototype motor is built and tested. The optimized design is validated by 2-D/3-D FEA and experiments and compared with the reference conventional surface PM (SPM)-type torque motor. The results indicate that the proposed new motor has higher torque-to-magnet-weight ratio and wider constant power region than the conventional SPM synchronous torque motor.

Design and Experimental Validation of a High-Speed Electric Turbocharger Motor Considering Variation of the &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${\boldsymbol{L}}/{\boldsymbol{D}}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Ratio

The commercialized electric turbocharger (ETC) made by Valeo includes a high-speed switched reluctance motor (SRM), ball bearings, impeller, and controller. SRMs are generally very noisy and have low efficiency (70%) at high speed. No ETC has yet been commercialized that includes a permanent magnet (PM) motor. The Korea Electrotechnology Research Institute, Changwon, South Korea, is developing a high-speed surface PM type of synchronous motor and a pulse width modulation-driven inverter. This system operates at a power density of 3 kW/kg at 100000 r/min and is intended to fit 1600 cc diesel vehicles to reduce turbolag to within 0.5 s. The design and analysis of the PM synchronous motor (PMSM) for the ETC have been successful by considering the electric and mechanical performance using multiphysics analysis. Validation by experiment was performed and matched within 1% error in terms of the efficiency. Design, analysis, and experiments with the PMSM for ETC applications were conducted successfully by utilizing an action–reaction torque sensor and the resistance load test method.

A Clamping Force Performance Evaluation of the Electro Mechanical Brake Using PMSM

This paper deals with clamping force simulation and experimental result of the Electro Mechanical Brake (EMB) for the High-Speed-Train (HST). Three phase Surface Permanent Magnet Synchronous Motor (SPMSM) is applied to the clamping force control of EMB. At the initial development stage, Proportional Integral (PI) current control under synchronous d-q axis frame was applied to the SPMSM torque control. In addition, an anti-windup controller, which is advantageous for fast current tracking, is proposed to improve the torque output. Matlab/Simulink simulation results were compared with the experimental results measured by the clamping force sensors of the EMB test rig. The experimental results were verified compared to the brake design specification of the High-Speed Electric Multiple Unit-430 Experimental (HEMU-430X) train.

Modular Spoke-Type Permanent-Magnet Machine for In-Wheel Traction Applications

This paper proposes a novel modular spoke-type permanent-magnet machine for in-wheel traction applications. First, the topology and the operating principle are briefly introduced. Then, an analytical model of the proposed machine is deduced based on conformal mapping. A three-phase 48-slot 52-pole modular spoke-type permanent-magnet (PM) machine is designed based on the deduced mathematical model where the dimensions and power source are constrained the same as those of a commercial three-phase surface PM machine in electric motorcycles. Electromagnetic performance comparisons among the proposed machine, the commercial machine, and a conventional spoke-type PM machine are conducted based on finite-element analysis (FEA) with respect to magnetic field, back electromotive force (EMF), flux-weakening capability, torque capability, machine efficiency, etc. The results indicate that the proposed machine has an improved torque, a higher efficiency, and an extremely better flux-weakening capability than the conventional in-wheel machine. Finally, a prototype machine is manufactured and tested to verify both the analytically and FEA predicted results.

Design of a Stator for a High-Speed Turbo-Generator With Fixed Permanent Magnet Rotor Radius and Volt–Ampere Constraints

This paper investigates high-speed surface PM machine design for portable turbo-generator applications. The rotor radius is fixed to achieve certain optimal characteristics of the magnet retention mechanism. The objective of this paper is to design and select the stator. The stator designs are populated by different slot/pole combinations, winding arrangements, and over a range of possible stack lengths. However, the design is constrained by physical diameter, stack length, and electrical volt–ampere constraints. A large number of preliminary machine designs do not satisfy the specified turbo-generator torque/speed requirements under the given volt–ampere constraints and therefore it is ineffective to perform finite element analysis on all preliminary design variations. In order to establish the feasibility of a machine design to fulfill the specified turbo-generator torque/speed requirements, the concept of inductance-limits is presented and then linked with stator design parameters. By application of this analysis strategy, a confined optimal set of stator designs are obtained and are subjected to detailed finite element simulations. A final machine design is selected and fabricated. Experimental results are presented for the validation of the final machine design.

On-Load Analysis of Saturated Surface Permanent Magnet Machines Using Conformal Mapping and Magnetic Equivalent Circuits

This paper presents an iterative method based on conformal mapping and magnetic equivalent circuits for on-load analysis of saturated surface permanent magnet machines with integer slot and fractional slot windings. Magnetic saturation is taken into account by defining additional point wires in the stator slots and interpolar region between the magnets. The added point wires create magnetomotive force equal to the magnetic voltage drops across iron core flux tubes that are calculated using magnetic equivalent circuit. An improved stator tooth model has been introduced that enables more accurate field calculations for tooth geometries with highly saturated tooth tips. The model also takes into account variation of permanent magnet magnetization due to external magnetic field. The proposed method has been implemented on a saturated 12 slot, 10 pole surface permanent magnet machine with nonoverlapping concentrated winding and shows a very good agreement with finite element calculations in terms of flux density, back electromotive force, and torque waveforms as well as $d$ - and $q$ -axis inductances, cross-saturation inductance, and permanent magnet flux linkage in both axes.