Permanent Magnet Volume Research Articles

Comparative Analysis of Different Permanent Magnet Arrangements in a Novel Flux Modulated Electric Machine

A novel dual permanent magnet (PM) machine with Halbach segmentation flux modulation is proposed in this paper, which is evolved from a flux switching PM machine (FSPM). In order to improve the performance of the FSPM, several PM arrangement methods have been adopted and three new different structures have been investigated. To achieve a fair comparison, all the structures are under the same size and rotate at the same speed. The performances of output torque and back EMF are compared. The analysis results show that the dual PM with Halbach segmentation has the highest torque density and power efficiency. The torque is improved by 100.3% from the FSPM while the PM volume does not increase too much. The unique of this best structure is that it not only combines the vernier machine and FSPM machine together, but also reduces the torque ripple. The performance of the motor is verified by the simulation using finite-element analysis (FEA).

Analysis on EMF characteristics for torque ripple reduction in BLAC motor intended for HVLS fan application

This paper analyzes the harmonic characteristics of electromagnetic force (EMF) in Brushless Alternating Current (BLAC) motor for High Volume Low Speed (HVLS) fan application. Vibration and noise are one of the main crucial things in HVLS fan application. It comes from torque ripples which can be detected by harmonics of Electro Magnetic Force (EMF). Commonly, there are a few methods to eliminate the noise and vibrations issue, but most literatures only focus on small motor and not intended for HVLS fan application. Thus, the objective of this paper is to eliminate the harmonics content in EMF at early stage design. Through EMF harmonics the expected torque produced could be used to select proper slot-pole number in order to eliminate the noise and vibrations issue. In here, the analysis involves three different slot-pole numbers which are 18s/20p, 12s/10p and 9s/8p BLAC model, respectively. All models have similar volume of permanent magnet. The analysis is carried out using FLUX 2D Finite Element Analysis (FEA) for EMF computational and transient torque computation. Later, Fast Fourier Transform (FFT) analysis is used to calculate the harmonics of EMF. The analysis stage includes the EMF parameter analysis, harmonics and torque ripples analysis. It was found that 18s/20p has higher output torque with the lowest 5% torque ripple value. As a conclusion, this paper presents low torque ripple in point of view of the EMF characteristics in designing HVLS fan.

Simplified Design of Magnetic Gear by Considering the Maximum Transmission Torque Line

Magnetic gears (MGs) technology is studied widely among research institutions, with several improvements being documented. This development attracts a high amount of attention due to the demand in the development of magnetic gears towards higher performance than the conventional mechanical counterpart. In general, the design is complicated and there is a lack in detailed references for designing an MG for specific transmission torque as required by its application. Trial-and-error approaches have been the norm in achieving the desired torque by referring the existing MGs for the desired value of torque. This paper presents a new simplified approach towards designing an MG for the required torque and size by referring through a Maximum Transmission Torque Line (MTTL) reference. Finite element method (FEM) is used in analyzing randomly designed magnetic gears with various parameters towards the desired values of the MTTL. The proposed approach of MTTL is a new approach to estimate the total volume of permanent magnets (PMs) required for the MG to achieve the desired transmission torque. The reference line is used to generate equation relating the specific parameters of MG to develop the simplified design of MG based on the estimated total volume of PMs. This simplified way details to 8.5% of error in targeting the desired transmission torque, a means and way for the first stage of the MG design approach to reduce the conventional approaches.

Analysis of Split-Tooth Stator Slot PM Machine

In this article, split-tooth stator slot permanent magnet (PM) machines, which have high fault-tolerant capability, are proposed. Compared with the existing 12-slot 10-pole (12S10P) stator slot PM machine, the torque can be improved by 66% by properly choosing the split tooth number and other geometric parameters. It is found that two split teeth stator slot PM machine (ST2) shows the best torque characteristics among the stator slot PM machines with different split tooth number. To further illustrate the merits and demerits of ST2, a conventional 6S4P surface mounted PM machine (SPMM) and a 6S4P variable flux reluctance machine serve as the benchmarks to compare with the 6S11P ST2, at both open circuit condition and load condition. The 6S11P ST2 shows 68% higher torque over the 6S4P VFRM. Although the torque of the 6S11P ST2 is around half of the 6S4P SPMM, the former has 70% higher torque per PM volume than the latter. Furthermore, demagnetization analyses under three-phase short-circuit and pure d-axis currents show that the 6S11P ST2 has much better demagnetization withstand capability over the 6S4P SPMM. A Prototype is manufactured and tested to validate the theoretical analyses.

Torque Performance Enhancement in Consequent Pole PMSM Based on Magnet Pole Shape Optimization for Direct-Drive EV

Developing a permanent magnet synchronous machine (PMSM) for direct-drive electric vehicle (EV) has challenges such as obtaining high torque density and low torque ripple. The PMSM should have high pole numbers owing to low-speed operation, thereby increasing the use of rare earth magnets and cost. Therefore, in this article a consequent pole (CP) rotor topology is proposed in which the permanent magnet (PM) volume is reduced when compared with conventional surface PMSM (SPMSM). However, replacing south poles in an SPMSM with induced steel poles can increase torque ripple and reduce torque density. In order to improve torque density in a CP PMSM, structural modifications such as multilayer windings and non-ferromagnetic barriers have been proposed in the literature. These modifications increased the torque density while increasing the torque ripple. Therefore, this article proposes a novel two-level optimization method based on gradient descent algorithm, to address the challenges of improving torque density and reducing torque ripple simultaneously in a CP PMSM. Initially, an expression for the magnet pole arc angle is derived for CP PMSM based on magnetic equivalent circuit. A two-level optimization is performed on a baseline CP PMSM to determine the optimal magnet pole arc. The torque production and torque ripples of the optimized design are validated by simulation and experimental results.

Design and optimization of segmented PM consequent pole hybrid excited flux switching machine for EV/HEV application

Hybrid Excited Flux Switching Machines (HEFSMs) unique feature of high torque density (T den ) of Permanent Magnet (PM) machines and flux regulation capability of wound field excitation machines. Due to aforesaid unique features, stator active HEFSMs are preferred for EV/HEV applications. In this paper a new Segmented PM Consequent Pole HE-FSM (sPMCPHEFSM) with flux bridge is proposed for EV/HEV. The developed SPMCPHEFSM exhibits improved flux modulation and flux regulation capability at reduced PM usage (suppressed PM volume by 46.52% and PM cost by 46.48%) and eliminating stator leakage flux. First, SPMCPHEFSM is geometric optimized (GO) for investigating influence of leading design with key performance indicators such as flux linkage (Φ pp ), average torque (T avg ), cogging torque (T cog ), T den , average power (P avg ) and power density (P den ) and then proceeded optimized model to structure modification for optimal stator design and position of field excitation coils (FEC). Comprehensive performance analysis reveals that the developed SPMCPHEFSM show improved Φ pp maximum up to 9.11%, improved T avg maximum up to 23.63%, truncate T cog up to 18.9% whereas T den and P den are boost up to 23.55% and 89.72% respectively.

Analysis of a New Flux Switching Permanent Magnet Linear Motor

A novel flux switching permanent magnet linear motor (FSPMLM), which has the advantages of high thrust density [the ratio of average thrust to permanent magnet (PM) volume] and low cost for long-stroke application, is proposed and investigated in this article. The topology of the novel FSPMLM with 12 slots is introduced and the basic operating principle is analyzed first. The optimal geometric parameters are selected by using the layered orthogonal optimization method. Then the electromagnetic performance of the motor is investigated by the analytical method based on the equivalent magnetic network model (MNM). Finally, a scheme of setting auxiliary teeth in the primary component is adopted to suppress the unbalance of the three phase flux linkages.

Investigation of New IPM Linear Machine Configuration with Low Permanent Magnet Used

Permanent magnet (PM) machines have received numerous attentions, since they are distinguished by many desirable features including simple construction and high efficiency. However, high price of the permanent magnet material may be considered as the main problems of such machines. Hence, the demand of PM machine with high efficient PM materials used is increased. In this study a new configuration of PM linear machine with high efficient PM material utilization, named as V-shape interior PM linear machine is investigated. The mentioned machine has been compared to the conventional I-shape counterpart. In order to perform sensible comparison, I-shape and V-shape machines have been designed with identical main design specifications. It has been observed that the V-shape topology shows better PM material utilization. It should be noted that about 43% higher efficient PM used is obtained by the V-shape machine compared to the conventional I-shape corresponding. It should be noted that the V-shape machine has been designed with about 51.6% less total permanent magnet volume compared to I-shape machine. Moreover, the introduced machine offers less cogging force as well as thrust force ripple than that of the conventional machine.

Multi-Objective Robust Optimization of a Dual-Flux-Modulator Magnetic Geared Machine With Hybrid Uncertainties

In order to improve the robustness and torque performance of a dual-flux-modulator magnetic-geared machine (DFM-MGM) considering simultaneously both random and interval uncertainties of design parameters, a multi-objective robust optimization (MORO) method with multiple Monte Carlo simulations (MCSs) is proposed. In this method, the multiple MCSs are adopted to evaluate the effects of parametric hybrid uncertainties on the robustness of optimization results. To build a MORO model of the DFM-MGM, the three-dimensional finite element model is established firstly and then validated by the experiment. Through a parametric study, it is found that five dimensional parameters of the permanent magnets (PMs) and stator have more significant effects on the stall torque (ST) and ST per PM volume (STPPV). Finally, a multi-objective particle swarm optimization algorithm with surrogate models, sigma criteria design and multiple MCSs method is implemented to solve the MORO problem. Both the average standard deviations and standard deviation differences of the ST and STPPV are used to deal with hybrid uncertainties during MORO. The optimized DFM-MGM by MORO has a STPPV 6.3% higher than that of the initial design under the same ST constraint. Moreover, the average standard deviations and standard deviation differences obtained by MORO are much smaller than those achieved by the deterministic optimization, indicating that the robustness of optimal results can also be significantly improved by the MORO.

Torque characteristics of high torque density partitioned PM consequent pole flux switching machines with flux barriers

Unique double salient structure of Permanent Magnet Flux Switching Machines (PMFSM) with both Concentrated Armature Winding (CAW) and Permanent Magnet (PM) on stator attract researcher's interest for high speed brushless application when high torque density (T den ) and power density (P den ) are the primal requirements. However, despite of stator leakage flux, high rare-earth PM usage, PMFSM is subjected to slot effects due to presence of both PM and CAW in stator and partial saturation due to double salient structure which generates cogging torque (T cog ), torque ripples (T rip ) and lower average torque (T avg ). To overcome aforesaid demerits, this paper presents Partitioned PM (PPM) Consequent Pole Flux Switching Machine (PPM-CPFSM) with flux barriers to enhance flux modulation, curtail PM usage and diminish stator leakage flux which reduces slotting effects and partial saturation to ultimately reduces T cog and T rlp . In comparison with the existing state of the art, proposed PPM-CPFSM reduces 46.53% of the total PM volume and offer T avg higher up to 88.8%, suppress T rlp maximum up to 24.8%, diminish T cog up to 22.74% and offer 2.45 times T den and P den . Furthermore, torque characteristics of proposed PPM-CPFSM is investigated utilizing space harmonics injection i.e. inverse cosine, inverse cosine with 3 rd harmonics and rotor pole shaping techniques i.e., eccentric circle, chamfering and notching. Detailed electromagnetic performance analysis reveals that harmonics injection suppressed T cog maximum up to 83.5%, T rip up to 40.72% at the cost of 4.71% T avg . Finally, rotor mechanical stress analysis is utilized for rotor withstand capability and 3D-FEA based Coupled Electromagnetic-Thermal Analysis (CETA) for thermal behavior of the developed PPM-CPFSM. CETA reveals that open space along PPM act as cooling duct that improve heat dissipation.

Sub‐domain modelling and multi‐variable optimisation of partitioned PM consequent pole flux switching machines

Permanent Magnet Flux Switching Machines (PMFSMs) enclose unique features of permanent magnet (PM) synchronous machine, direct current machine, and switch reluctance machine therefore, applicable for high speed brushless AC applications. However, conventional PMFSMs exhibits demerits of high PM volume V PM , high torque ripples T rip , low average torque T avg , lower torque density T den , power density P den and leakage flux. In this paper, a new topology of 12S-13P and 6S-13P E-Core PM Consequent Pole Flux Switching Machines (PMCPFSM) with flux barrier and partitioned PM is proposed that eliminate leakage flux, enhanced flux modulation effects through flux barriers and reduces the PM volume up to 46.53%. Moreover, due to non-linear behaviour of PM and complex stator structure alternate analytical sub-domain model is utilized for initial design and Multi-Variable Geometric Optimization (MVGO) is opted to investigate influence of design parameters on electromagnetic performances such as T avg , T rip , T den and P den . Analysis and comparison with the existing 12S-10P E-Core PMFSM, 6S-10P E-Core PMFSM, 6S-10P C-Core PMFSM and 12S-14P C-Core PMCPFSM reveals that proposed 6S-13P PMCPFSM produced T avg higher up to 88.8%, suppress T rip maximum up to 14.72% and offer 2.45 times T den and P den capabilities, when compared with the aforesaid state of the art.

Dual-Pole Line Start Synchronous Machine With Consequent-Magnetic Poles

This paper presents a new design of dual-pole (4-pole and 8-pole) Line Start Synchronous Motor (LSSM) with consequent magnetic pole structure. The proposed structure reduces the Permanent Magnet (PM) volume in the rotor core by 67 percent with respect to the reference dual-pole machine. Given the direct impact of the PM magnetic field on producing negative torque components such as braking torque and pulsating torque, lower PM volume can potentially limit the production of such negative torques. Therefore, in addition to cost saving benefits, the proposed structure contributes to a smooth start-up process. Meanwhile, different geometrical structures of PMs and flux barriers are discussed, their impacts on the overall motor performance are highlighted, and general design guidelines are provided. In particular, six different rotor structures with different PM arrangement and/or flux barrier arc angle are analyzed in Finite Element (FE) and their steady-state and transient performance metrics are compared. Finally, the best motor candidate is selected for further analyses, and prototyping.

Analytical validation of novel consequent pole E‐core stator permanent magnet flux switching machine

Flux switching machines (FSMs) encompass unique features of conventional direct current machine, permanent magnet (PM) synchronous machine and switch reluctance machine. Permanent magnet FSM (PMFSM) is capable of high torque density and applicable for high-speed application, however conventional PMFSM exhibits demerits of high PM volume, high torque ripples and significant stator flux leakage. In this paper, a novel consequent pole E-core stator PMFSM is proposed and compared with conventional topology utilising 2D finite-element analysis (2D-FEA). Finite-element analysis revealed that proposed design enhanced flux modulation effects by introducing flux bridges and flux barriers as a result reduced cogging torque by reducing 46.53% of the total PM volume, reduce torque ripples by reducing PM slot effects and reduce flux leakage utilising flux bridges in the stator. Furthermore, analytical model for flux linkages, cogging torque, mechanical torque, no load and on-load magnetic flux density (MFD) is developed for initial design of conventional and proposed model. 2D analytical methodologies resolve equivalent magnetic circuits for open-circuit flux linkages, Fourier analysis for cogging torque, Laplace equations for MFD and Maxwell stress tensor for mechanical torque. Finally, results obtained from 2D-FEA and analytical methodologies are validated and compared.

Optimal Design and Static Performance Analysis of Permanent Magnet Coupling for Chemical Pump Application

Magnetic couplings are considered suitable for many industrial applications where a separation is required between the driver and the driven. Utilizing magnetic couplings allows the transmission of torque without any mechanical contact. Generally, permanent magnets (PMs) are utilized in magnetic couplings instead of electromagnets to avoid extra circuitry. Accurate design and analysis of magnetic coupling are essential to reduce the PM volume for the required output performance. 3D finite element method (FEM) is considered the most accurate as it takes into account the end effects, which arises due to a shorter stack length as compared to the diameter of the coupling. In this paper, a permanent magnet coupling (PMC) is designed and optimized to be installed in a chemical pump that is handling high-temperature fluid. A prototype was also manufactured and tested in the laboratory to verify the analysis.

Linear Vernier actuator with two movers

Background: Linear motion devices for industrial machines and robots are expected to realize their high efficiency drive and simple structure. Usually, a feed screw mechanism composed of a rotary motor and a ball-screw or slide-screw is employed. However, it has some problems such as the decrease of the drive efficiency, flexibility against external forces, noise, etc. Various linear actuators and motors have been developed utilizing the feature of a direct drive.
 Aim: In this paper, we propose a novel linear actuator which 2 movers can be independently controlled using 3-phase and 6-phase superimposed currents for decreasing the size and weight of the system. The proposed linear actuator is driven by the operating principle of a vernier motor which is expected to achieve a high thrust force density per permanent magnet volume.
 Methods: The operating principle and the static thrust force characteristics of the proposed linear actuator are verified by an electromagnetic field analysis using 3-D finite element method, and the back electromotive force characteristics are also analyzed. In addition, the dynamic characteristics under position feedback control are analyzed. The control system uses a vector control using PID controller, and the control input is given by the 3-phase and 6-phase superimposed currents.
 Results: The static force characteristics were investigated. From the analyzed results, the force interference between the two movers was small. Moreover, the interference of the back electromotive force of the 3-phase and 6-phase movers were not observed. The movers could be independently driven under position feedback control using 3-phase and 6-phase superimposed currents. The dynamic characteristics analyses showed that the mover well followed a target position. From a step response, the time constant and the response of the position feedback system were investigated.
 Conclusion: This paper presents a linear vernier actuator with two movers. The basic structure and operating principle of the actuator were described. Moreover, the static characteristics and the dynamic characteristics under position feedback control were analyzed. It was found that the movers can be independently driven.

Analysis, fabrication and detailed comparative study of surface and interior rotor PMSM prototypes of identical nominal ratings and stators

This paper presents an in-depth analysis, performance evaluation and comparative study of two 5-kW, 8-pole, 750-rpm laboratory prototypes of a permanent magnet synchronous motor (PMSM) of identical nominal ratings with surface and interior permanent magnet (PM) rotor structures having same stator and armature winding (fractional slot distributed winding). The key electrical (such as rated voltage, current, power, speed, number of poles, etc.) and mechanical variables (such as overall volume, air-gap length, rotor diameter, shaft dimensions and magnetic material) of the fabricated prototypes have also been kept same to pin-point the direct influence of the two different rotor configurations (surface and interior PMSM) on the parameters, performance and operation of these PMSMs. For the two machines, a detailed comparison of air-gap flux density distribution, THD in induced voltage, torque ripple, losses, efficiency, torque–speed characteristics, field weakening capability, steady-state parameters at different operating conditions, etc. has been conducted. The salient observations from this comparative study have been duly highlighted. This paper also includes an in-depth comparison of volume and cost of PM used in the two types of PMSMs. The short-time performance figures of the said motors have also been presented. The possibility of demagnetisation of PMs, during a sudden fault, has also been investigated for both PMSMs. Challenges of making of both rotors have been discussed. The theoretically determined parameters and analytically evaluated performance figures have been verified through standard FEM packages and then validated experimentally on the prototypes.

Robust Optimization of a Permanent-Magnet Synchronous Machine Considering Uncertain Driving Cycles

This work focuses on the robust optimization of a permanent magnet (PM) synchronous machine while considering a driving cycle. The robustification is obtained by considering uncertainties of different origins. Firstly, there are geometrical uncertainties caused by manufacturing inaccuracies. Secondly, there are uncertainties linked to different driving styles. The final set of uncertainties is linked to ambient parameters such as traffic and weather conditions. The optimization goal is to minimize the PM's volume while maintaining a desired machine performance measured by the energy efficiency over the driving cycle and the machine's maximal torque. The magnetic behavior of the machine is described by a partial differential equation (PDE) and is simulated by the finite-element method employing an affine decomposition to avoid reassembling of the system of equations due to the changing PM geometry. The Sequential Quadratic Programming algorithm is used for the optimization. Stochastic collocation is applied to compute moments of stochastic quantities. The robustness of the optimized configurations is validated by a Monte Carlo sampling. It is found that the uncertainties in driving style and road conditions have significant influence on the optimal PM configuration.

Analysis and modeling of tooth-tip leakage fluxes in a radial-flux dual-stator machine with diametrically magnetized cylindrical permanent magnets

Tooth-tip Leakage flux (TLF) has a major effect on the prediction of air-gap flux distribution and electromagnetic torque in the permanent magnet (PM) machines. Therefore, deriving a model for TLF is necessary for machine design and optimization. Accurate modeling of TLF can lead to fast and precise solutions, which ease the analysis of electromagnetic devices. It also provides the opportunity to increase torque density by more efficient utilization of PM's volume and prevent saturation in machine optimization. This paper presents a method for modeling and analyzing TLFs in a radial-flux dual-stator permanent magnet (DSPM) machine with diametrically magnetized cylindrical permanent magnets (DMCPM) in series and parallel magnetic circuit structures. In this model, some expressions in terms of machine dimensions are derived for the TLF analysis. Finite element method (FEM) is applied to validate the proposed model. Results indicate that the maximum error between the proposed model and FEM is insignificant (less than 6%). Finally, by a prototyped machine the validity of the proposed model was investigated with the experimental tests.

Experimental Analysis and Optimization of a Contactless Eddy-Current-Based Speed Sensor for Smooth Conductive Surfaces

Speed sensing is an essential part in all closed-loop systems. There exist some situations in industry where the speed has to be measured without touching the target object, for example, the accurate speed measurement of the solid metal wheels with smooth surfaces of freight wagons. In this article, a contactless, eddy-current-based speed sensor is proposed for applications where the speed of a smooth conductive surface is to be measured; but contact to or modification of this target surface is prohibited. The proposed speed sensor is composed of a permanent magnet (PM) rotor that is free to rotate above the target surface. The relative motion of the surface with respect to the PM field induces eddy currents in the surface, which leads to a torque being applied on the rotor. Consequently, the PM rotor speeds up until it reaches a steady rotational speed that is proportional to the speed of the target surface. Three models are proposed. They are a two-dimensional (2-D) finite-element model, a 2-D analytical model, and a three-dimensional (3-D) combined numerical/analytical model. Measurements are taken on multiple hardware prototypes to validate the analysis. Finally, a multiobjective (PM volume vs. dynamic performance) Pareto optimization is conducted for the proposed speed sensing system. The results show that smaller rotors with lower pole-pair numbers generally have better dynamic performance as well as lower costs.

Comparison of magnetic field distributions generated by various permanent magnets for transcranial static magnetic stimulation: A simulation study

Recent experimental studies have shown that static magnetic field can be effective in modulating human brain functions. Following this discovery, a new noninvasive brain stimulation technique was developed: the transcranial static magnetic stimulation (tSMS). Various types of permanent magnets have been used in previous experimental studies, with the aim of validating the effectiveness of tSMS; nevertheless, the spatial distributions of magnetic field generated by these permanent magnets have not been fully investigated. In this study, we compared the distributions of magnetic field on the human cortical surface generated by five different cylindrical magnets (of various dimensions), using the finite element method. Our simulation results demonstrated that the magnitude of magnetic flux density induced in the cortical grey matter of the human brain is proportional to the volume of permanent magnets used, while the magnetic field gradient is not necessarily proportional to the volume of the magnets. Additionally, we showed that the use of magnets with internal holes might not be advantageous. The differences in magnetic field properties induced by various types of permanent magnets suggested that their careful selection, based on magnetic field simulations, might be necessary to increase the effectiveness of tSMS.