Permanent Magnet Shape Research Articles

Torque ripple reduction by optimizing magnet shape using GA in axial gap motor

This paper proposes a method to reduce torque ripple in axial gap motors by multi objective optimization of permanent magnets (PMs) shape using genetic algorithm (GA). Torque ripple is a problem because it causes vibration and noise. Conventionally, torque ripple has been reduced by quantitatively designing the PMs in the shape of multiplicative wave. However, it is difficult to optimize the objective function only by quantitative evaluation through sensitivity analysis. Therefore, in this study, the functions constituting the PMs interface shape are expressed as a Fourier-based series. The PMs is optimized by optimizing combination of their coefficients with GA. As a result, the proposed model is almost equal to the average torque of the basic model and the torque ripple is significantly reduced. Furthermore, fillets are applied and the effect on each characteristic is verified.

Numerical Analysis of Outer-Rotor Synchronous Motors for In-Wheel E-Bikes: Impact of Number of Windings, Slot, and Permanent Magnet Shapes

This study investigates the design an electric motor propelling hubless wheel mounted on an electric bicycle (e-bike) by numerical analysis. The motor is part of an in-wheel system that uses a permanent magnet synchronous motor (PMSM) to drive the hubless wheel. This paper presents an optimized PMSM design and compares various torque-related parameters, such as cogging torque, cogging torque total harmonic distortion (THD), and ripple torque. The comparison is based on a motor design that examines the effect of different factors, including the number of windings, slot openings, permanent magnet span, and magnet thickness. The motor was modeled and analyzed with variations in the number of windings (21, 23, 25), slot openings (2.4 mm, 3.0 mm, 3.6 mm), permanent magnet span (23 mm, 25 mm, 27 mm), and permanent magnet thickness (3.5 mm, 4.0 mm, 4.5 mm). Our findings suggest that increasing the permanent magnet’s thickness leads to a higher magnetic flux density. Additionally, when the permanent magnet span exceeds 25 mm, there is a sharp increase in cogging torque THD. Based on these results, a slot opening of 3.0 mm and the use of 25 windings are considered suitable for a hubless e-bike.

Research on Cogging Torque Reduction of Direct-Drive Type Dual-Rotor Radial Flux Permanent Magnet Synchronous Motor for Electric Propulsion Aircraft

The direct-drive type high-torque-density motor is one of the most promising solutions of electric propulsion for aircraft. The cogging torque of the direct-drive motor causes torque ripple, vibration, and noise, which seriously affect the stability and reliability of the electric propulsion system for aircraft. In this paper, a novel direct-drive type high-torque-density dual-rotor radial flux permanent magnet synchronous motor (DRPMSM) is proposed, and its cogging torque is weakened by permanent magnet shape design and pole-arc coefficient combination. An eccentric and chamfered permanent magnet shape is proposed, and the influence of eccentric distance and chamfer angle on cogging torque is clarified. Through the pole-arc coefficient combination design of the inner and outer rotors of the DRPMSM, the cogging torques of the inner and outer rotor are phase reversed, thus further reducing the total cogging torque of the DRPMSM. By employing the response surface method, a mathematical model is established for the cogging torque of the DRPMSM in relation to the pole-arc coefficients, chamfer angle, and eccentric distance of the permanent magnets. The parameters that minimize the cogging torque of the DRPMSM are obtained using a genetic algorithm. A prototype is manufactured according to the optimized parameters, and experimental results validate the correctness of the theoretical analysis and the effectiveness of the optimization design method.

Surface magnetic flux density optimization considering effect of aligned magnetic field molding conditions of ring-shaped multi-pole anisotropic ferrite permanent magnet for DC motors

The ring-shaped anisotropic ferrite magnet with multiple poles boasts significant benefits for brushless DC motors (BDCMs). However, the prevalent production method involves dry magnetic field molding, making it challenging to enhance the magnetic properties. Herein, ferrite powder made from iron oxide, a by-product of the steel industry, is used as the starting material of magnets, and the differences between dry and wet molding approaches on the surface magnetic flux density of a ring-shaped multi-pole anisotropic ferrite magnet are first investigated. ANSYS MAXWELL conducted an initial simulation to achieve the design specifications of the wet molding mold. Following this, the mold was prepared for the fabrication of ring magnets. Compared to magnets prepared via dry molding, those produced through wet molding exhibit a peak surface magnetic flux density of approximately 15.9% higher, demonstrating significant potential for industrial applications and substantial enhancement of the key magnetic properties of wet molded ferrite ring magnets. To achieve increased surface flux density of ring magnets, it is common practice to utilize magnetic powders with greater magnetic properties when molding the magnets. However, this requires a costly mold redesign. In this study, higher surface magnetic flux densities can be achieved for ring magnets by simply adjusting the shape, size and magnetization direction of NdFeB permanent magnets that provide a constant aligned magnetic field in the mold without requiring any alterations to the existing mold's dimensions. The findings of this study could improve the effectiveness of existing motor designs. The usage of ring-shaped multi-pole anisotropic ferrite magnets is anticipated to witness a surge in the coming years, driven by the growth of energy-efficient motors in diverse sectors.

Comparative Study of Mechanical and Electrical Characteristics of High-Strength and Conventional Electrical Steel for EV Traction High-Speed Multilayer IPMSM Using Rare-Earth Free PM

In this article, the electrical and mechanical characteristics of multilayer interior permanent magnet synchronous motors (ML-IPMSMs) using ferrite permanent magnets (PMs) are compared when driven at high speeds with respect to the type of electrical steel. In high-speed operation, the mechanical and electrical characteristics of ML-IPMSMs vary depending on the number of PM layers, PM shape, number of bridges, and bridge thickness. Additionally, ferrite PMs have a lower coercive force than neodymium (Nd) PMs; therefore, irreversible demagnetization (ID) must be considered, and it is affected by the number of PM layers and PM shape of ML-IPMSMs. Thus, when designing a multilayer IPMSM using ferrite PMs for electric vehicle (EV) traction, all characteristics should be considered. Compared to conventional electrical steel (CES), high-strength electrical steel (HSES) offers advantages in mechanical properties, allowing for greater flexibility in ML shape. Consequently, it is possible to design a shape with improved electrical performance when compared to CES by adjusting the ML shape. In this article, all characteristics of each ML-IPMSM using HSES and CES are reviewed via finite element analysis (FEA), and the benefits of HSES applied motors for high-speed driving motors are presented. To verify the validity of the review content in this article, experiments are conducted on the manufactured motor, and FEA results are compared with the test results.

Determination of the optimal shape of permanent magnets of a given volume providing maximum strength of their magnetic coupling

The ponderomotive force of the adhesion of two permanent magnets depends on their shape. We present the results of determining the optimal shape of ellipsoidal magnets providing maximum magnetic adhesion between them. The interaction of two halves of a magnet, which is an ellipsoid of revolution, and a magnet in the form of a long rod with an elliptical cross section, is analyzed. Analytical formulas for the cohesion forces in these cases are obtained. For a fixed mass or volume of magnets, the problem of optimizing the adhesion force is solved and a geometric shape which provide the maximum adhesion force is determined. It is shown that in the case of a magnet in the form of an ellipsoid of revolution, the maximum adhesion force of its halves (ignoring the magnetic tension on the side surfaces) is achieved at an eccentricity of 0.625958. The magnitude of the maximum adhesion force exceeds the adhesion force of the halves of a uniformly magnetized spherical magnet of the same volume by 1.7%. In this case, the adhesion area of the ellipsoidal magnet will be less than the adhesion area of the spherical magnet by 28%. The optimal form of a bar magnet with an elliptical section with the maximum force of adhesion of its halves at a fixed volume of the magnet is determined. A formula is derived for the ponderomotive magnetostatic force of the interaction between the halves of a bar magnet with an elliptical section and the maximum force of interaction. Numerical estimates for a sintered NdFeB bar magnet showed that the ponderomotive force of interaction with a cross-sectional radius of 5 cm can reach 2 tons per 1 m of length. The results obtained can be used to improve the efficiency of devices based on permanent magnets.

Design and Cogging Torque Reduction of Radial Flux Brushless DC Motors with Varied Permanent Magnet Pole Shapes for Electric Vehicle Application

Brushless direct current motors have more attractive features, making them a promising solution for electric vehicle applications. A 1 kW, 510 rpm, 24-slots and 8-pole inner runner type surface permanent magnet mounted radial flux brushless DC motor with seven different permanent magnet pole shape rotor is investigated. Motors with different permanent magnet shape rotors were designed, and finite element modelling and simulation were carried out. For performance comparison, the initial design with a radial-type pole shape was regarded as a reference design. Cogging torque is detrimental to the overall performance of the motor, typically in low-speed applications like electric vehicles. The primary aim of this paper is to reduce the cogging torque & study its effect on the overall performance of the motor and minimize torque ripples with reduced permanent magnet requirements. The proposed designs are analyzed in terms of cogging torque, flux density, torque, efficiency, flux linkage and back-EMF. The comparative analysis shows that the motor with bump-shaped permanent magnet rotor poles has betterperformance than the others.

Cold-Spray Additive Manufacturing of a Petal-Shaped Surface Permanent Magnet Traction Motor

Several applications require low torque pulsations as they can lead to mechanical vibrations and acoustic noise in the electric motor. Optimization of the rotor permanent magnet (PM) shape is one of the effective methods for reducing torque pulsations. Unfortunately, the low versatility of the magnet fabrication technologies limits the development of new motor geometries. Cold spray additive manufacturing can be used for shaping permanent magnets for the direct fabrication of motor parts without the need for additional assembly steps. This fabrication technique allows an increase in the design flexibility of electric machine geometries targeting improved performance. This paper investigates the performance of permanent magnet rotors fabricated using a cold spray additive manufacturing technique for radial flux surface permanent magnet synchronous machines (SPMSM). The permanent magnet rotors considered are conventional rectangular-shaped with unskewed magnets (Model A), skewed magnets (Model B), and sinusoidal-petal shaped magnets (Model C) along the axial direction. The magnitude of magnetization current pulse required to magnetize these rotors is calculated and an impulse magnetizer setup is designed for in-situ magnetization. The performance of the shaped cold sprayed permanent magnet rotors and their effects on back EMF, electromagnetic torque, and cogging torque are analyzed experimentally and comparisons are made between the different rotor designs.

A Study on the Improvement of Cogging Torque of Small Wind Turbines by Permanent Magnet Shape

A Study on the Improvement of Cogging Torque of Small Wind Turbines by Permanent Magnet Shape

Magnetic Liquid Metal Droplet Robot with Multifunction and High Output Force in Milli-Newton.

Magnetically actuated miniature robots have immeasurable potential in lab-on-a-chip and biomedical due to their ability to navigate in constrained space. However, current soft robots made by elastomers have limited functionalities and are prevented from very narrow environments such as channel much smaller than their size because of their non- or limited deformability. In this study, a soft and multifunctional robot based on liquid metal (magnetic liquid-metal droplet robot [MLDR]) with high output force is reported. It is fabricated by engulfing iron particles into a Galinstan droplet. By changing the shape and motion of permanent magnets, the MLDR can be reshaped and moved. The MLDR can also be split in batches and merged efficiently. It shows good softness and flexibility when navigating freely in a narrow channel, and thus can pass through a confined space smaller than its size easily. Furthermore, the MLDR can also push and spread the accumulated liquid in a desired path, and manipulate the motions of small objects well. Benefiting from the solidification-like phenomenon, an MLDR can output milli-Newton-level force much higher than the output force of ferrofluid droplet robots in micro-Newton level. The demonstrated capabilities of the MLDR are promising for the applications in lab-on-a-chip or biomedical devices.

Parameter-topology hybrid optimization of electric motor with multiple permanent magnets

A hybrid optimization method that combines parameter optimization (PO) with topology optimization (TO) is proposed for the design of a permanent magnet (PM) motor. The PM shape, configuration, and flux barrier topology were simultaneously optimized using the proposed method. The conventional hybrid method that deals with a single PM is effectively extended to deal with multiple PMs parameterized by several geometrical parameters. The use of this extension makes it possible to search for the optimal rotor structure of the multiple-PM motor, which is widely used in electric vehicles. The results obtained by the proposed method are shown superior over those obtained by conventional method. The rotor structure with double-U shaped PMs with small flux barriers near the airgap was obtained by the optimization.

Design and analysis of in-wheel motor with sinusoidal permanent magnet shape for electrical vehicles

This paper deals with the design and analysis of a surface-mounted outer rotor in-wheel motor (IWM) with the aim of reducing cogging torque and torque ripple for electric vehicles. The proposed IWM is equipped with axial sinusoidal surface-mounted permanent magnets (PMs), with the purpose of producing sinusoidal air gap flux density distribution, thus to realize sinusoidal back electromotive force (EMF) and smooth electromagnetic torque. To highlight the advantage of the proposed IWM, the conventional IWM with tile-shaped PMs and the IWM with stepwise-shaped PMs are also studied for comparison. The finite element method in the commercial software package is utilized to analyze the performance of the three motors, including the radial flux density of air gap, back EMF, cogging torque, and electromagnetic torque. Through the quantitative comparison, it is found that the proposed IWM greatly reduces the cogging torque, highly improves the sinusoidality of back EMF, and nearly eliminates the torque ripple.

Detailed Design and Prototyping of a High Power Density Slotless PMSM

This article describes the detailed design and development of a 300 kW permanent magnet (PM) synchronous motor for electric aircraft propulsion, taking into consideration manufacturability, balancing ease, and cost of high-volume production with motor performance. The motor consists of a slotless stator structure with custom litz wire and an outer rotor with a Halbach PM array. The design of the proposed motor is based on multi-physics performance including electromagnetic field, thermal and mechanical analysis. For ease of manufacturing and economies of scale, the detailed design is refined by altering the PM segment number, PM shape and litz wire construction. The impacts of changing these parameters are evaluated in detail using analytical and finite element methods. The simulation results are compared with experimental results in terms of torque production, back electromotive force, and current level.

Analytical and FEM Methods for Line Start Permanent Magnet Synchronous Motor of 2.2kW

This paper has developed electromagnetic equations based an analytical model to design a three-phase line start permanent magnet synchronous motor (LSPMSM) of 2.2 kW. In order to enhance the torque and efficiency of this machine, an optimized slot shape of rotor permanent magnet is proposed. The analytical model is first presented to evaluate the magnetic characteristics, and then analytical expressions are derived under the open circuit condition. The influence of the magnet size variables on the analytical model is considered to investigate the magnetic leakage flux and flux density distribution in air gaps. Moreover, the variation of design has a significant impact on the steady-state performance characteristics of this motor. In addition, in order to check the output results from the analytical model, a finite element method is developed to evaluate these solutions. Finally, experimental and simulation results have been compared and analyzed to validate the development of method.

Design and Analysis of Three Phase Axial Flux Permanent Magnet Machine with Different PM Shapes for Electric Vehicles

Axial flux permanent magnet (AFPM) machines are good candidates for electric vehicle applications due to their high torque density, improved efficiency, and better flux distribution; thus, they are often used. A dual-rotor single-stator AFPM machine with four differently shaped permanent magnet (PM) rotors is investigated. The main aim of this paper is to enhance the average torque while minimizing the cogging torque and torque ripples at the expense of low PM volume. The proposed machines are analyzed in terms of flux linkage, back-EMF, cogging torque, average torque, and torque ripples. The analysis reveals that the machine with an arc-shaped PM rotor performs better than the others. In addition, the trapozoidal arc-shaped PM used in the AFPM machine outperforms the hexagonal, skew arc, and traditional trapezoidal PMs. The torque density of the trapezoidal-shaped PM machine is 40.23 (KNm/m3), while that of the hexagonal shape is 32.46 (KNm/m3), that of the skew arc shape is 39.78 (KNm/m3), and that of the arc shape is 50.38 (KNm/m3).

Analysis of Air-Gap Magnetic Field and Structure Optimization Design of Hollow-Cup Motor

Hollow-cup motors are usually used in spacecraft because of their low power consumption and high control accuracy. However, because the air-gap between the permanent magnets (PMs) and the rotor of the hollow-cup motor is uniform, the sinusoidal characteristic of the air-gap magnetic field waveform is inferior and the total harmonic distortion (THD) is large, resulting in torque ripple. For the large air-gap hollow-cup motor, the existing methods for optimizing the sinusoidal characteristics of the air gap magnetic field change the shape of PMs, but the changed PMs are difficult to manufacture and magnetize, resulting in the methods being limited and not being able to achieve the ideal optimization effect for the hollow-cup motor. Based on the characteristics of the inner rotor and outer rotor rotating synchronously during operation, a new structure design of the hollow-cup motor with an eccentric inner rotor is proposed instead of changing the PMs’ shape. Firstly, the mathematical model of the hollow-cup motor is established. Then, the FEM shows that the inner rotor’s eccentricity can bring the air-gap magnetic field waveform closer to the ideal sinusoidal waveform and can effectively reduce the THD. Finally, a prototype with the optimal eccentricity value is made for experimental verification.

Zeroth-Mode Vibration Suppression Through Adjustment on Phases Difference of Concentrated Force Harmonics for PMSMs

Zeroth-mode vibration is the dominant noise source in permanent magnet synchronous machines (PMSMs). In conventional approaches, the zeroth-mode vibration is reduced by lowering the amplitudes of concentrated forces. Different from conventional approaches, this article proposes a zeroth-mode vibration suppression method through adjustment on phase difference of concentrated forces. First, the characteristics of concentrated forces are analyzed considering the effect of slotted structure on air-gap electromagnetic force wave (EMFW), and the relationship between phase difference of concentrated force harmonics (CFHs) and the mode of vibration is obtained. Subsequently, the effects of both permanent magnet (PM) and harmonic currents on air-gap EMFW are analyzed. It is found that the phase differences of CFHs can be adjusted by combining PM shape optimization and harmonic current injection. Finally, a 12-pole 36-slot PMSM and a 16-pole 48-slot PMSM are carried out to calculate the concentrated forces and vibrations by finite element method (FEM). It is proven that the proposed method can adjust the phase difference from zero to two tooth pitches, and the zeroth-mode vibration is significantly suppressed.

Simulation and Investigation of the Change of Geometric Parameters on Voltage Induced in the Energy Harvesting System with Magnetic Spring

The aim of this paper is to establish mathematical modelling and simulation for the voltage induced during movement of the moveable magnet in a double-sided magnetic spring, being part of the energy harvesting system. For various configurations of the set of permanent magnets, the repulsive forces of magnetic spring and induced voltage in energy harvester winding will be calculated. Changing the geometrical dimensions and shape of permanent magnets allows one to control the stiffness of the so-called double-sided magnetic spring, and furthermore, allows one to change the natural frequency of the energy harvester system. Properly chosen stiffness in the energy harvester system is the crucial issue for high efficiency in energy recovery. In a given case, the energy harvester consists of three permanent magnets inserted into a tube with coils wound on it. To calculate the force between the magnets and the magnetic flux in the coils, the ANSYS program was used. The voltages induced in coils for various configurations of the magnets were simulated in the MATLAB program.

Effect of Pole Shaping on Torque Characteristics of Consequent Pole PM Machines

Consequent pole (CP) permanent magnet (PM) machines offer scope for reducing the quantity of PM material and hence cost compared to more conventional PM machine topologies of the same rating. In this type of machine, the rotor pole arc is usually optimized to realize the largest output torque with pole shaping methods used to reduce torque ripple. However, such approaches tend to be limited by constraints imposed on the pole shapes. It is a common practice to adopt similar PM and iron pole shapes, an approach that does not fully account for the different characteristics of PM and iron poles in CPPM machines, often leading to large even order harmonics in the airgap flux density. This article proposes a shaping method with a variable rotor profile and pole arc span being established by means of optimization by Genetic Algorithm. It is demonstrated that for a fixed quantity of PM material, different PM and iron pole shapes in combination with optimal PM and iron pole arc spans are essential for ensuring both maximum output torque and lower torque ripple when the due account is taken of flux leakage. It also demonstrates that since the flux density in the region under a PM pole is governed by the magnetic potential produced by magnets while it is governed by magnetic reluctance under iron pole, different PM pole and iron pole shapes are necessary to reduce the even-order harmonics in a CPPM machine and consequently to reduce torque ripple. The performances of optimized and more conventional CP machines are compared by finite-element method on 12-slot/8-pole prototype motors.

Refine design parameters for permanent magnet shape modification of the direct-drive generator

The high cost associated with operation has promoted the progress of wave energy conversion and has higher power output and larger size. However, many countries are bordered by the sea, and the possible area for using wave energy is very small which can generate peak power generation systems with a power output of less than 100 W. The purpose of this article is to introduce the refined parameters of new design of the permanent magnet shape of with tubular longitudinal direct-drive generator. Three designs proposed, which different shapes of permanent magnets with same topology. The parameter optimization process was analysed using finite element analysis to determine the best main parameters of the design, namely the length of the stator length to translation ratio (𝐿𝑠/𝐿𝑟), pitch ratio (𝜏𝑚𝑟/𝜏𝑝.), and split ratio (𝑅𝑚/𝑅𝑒). To evaluate design performance, electrical losses from the proposed design were also evaluated. The optimization results show these designs generator can produce 100 W of peak level output power with higher efficiency at rated current and optimal load.