High Torque Density Research Articles

Optimal Split Ratio for High Torque Density PM Machines Based on Analytical Determination

Optimal Split Ratio for High Torque Density PM Machines Based on Analytical Determination

D-Q-axis magnetic field design and investigation of asymmetrical multi-layer flux barriers PM motor for speed regulation enhancement

In this paper, an asymmetrical multi-layer flux barriers permanent magnet (AMFB-PM) motor is proposed. The key of this study is to design the d-q-axis magnetic field reasonably. Firstly, the influence of d-axis inductance on the constant power speed range is analyzed. To optimize the constant power speed regulation performance, an asymmetric flux barrier is employed to adjust the saturation degree of the d-axis magnetic circuit under flux-weakening state. Additionally, the introduction of the asymmetrical flux barrier enables directional deflection of reluctance torque, thereby enhancing the output torque. The analysis results verify the effectiveness of the asymmetrical flux barrier design, which provide a wide speed regulation with constant power operation and high torque density for PM motors.

Design and Optimization of an Interior Permanent-Magnet Synchronous Motor for Aircraft Drive Application

The torque performance of the interior permanent-magnet synchronous motor (IPMSM) must be further improved to satisfy the growing demand of aircraft drive application. To this end, this article focuses on the design optimization of the IPMSM structure in the aircraft drive systems to improve the torque density and reduce the torque ripple. A special fractional-slot winding and ∇-type magnetic-pole rotor topology are proposed as the optimized IPMSM structure compared with the structure of an existing motor. The simulations of the original and optimized structures at different current values reveal the variance of the torque in the average and ripple, mechanical and external characteristics, efficiency and steady-state temperature. The performance of an optimized prototype is analyzed by experimental testing, and the results show that an optimized motor has a higher torque density and lower torque ripple than the original one at the same speed and rated power, but it also has a higher temperature rise. However, the temperature rise value is acceptable in the experimental testing condition, so the validity of the design optimization method for the proposed structure is verified.

A modified approach for efficient cogging torque suppression in a flux switching permanent magnet generator used in micro‐scale wind turbines

AbstractIn recent years, Flux Switching Permanent Magnet (FSPM) machines have attracted notable attention in direct drive, low speed, and high torque density applications such as wind turbines. However, their relatively high cogging torque has been identified as a significant challenge for such applications primarily because of its effects on both starting and running performance of the wind turbines. The authors, therefore, aim to present a modified approach that can improve the cogging torque issue and eliminate the weaknesses of the previously introduced designs. To reach this goal, first, an operating point is chosen for the studied machine regarding the available small‐scale turbines in the market. Then, the potential benefits of combining different cogging torque reduction schemes are investigated thorough the proposed method. This is intended to be done on the rotor teeth without imposing any complications or extra costs. The results show that a simultaneous improvement in the cogging torque and the energy conversion capability of the machine could be achieved through this cost‐effective approach. To end with, the sensitivity of the best cases to the expected manufacturing tolerances is investigated. All analyses are performed via two‐dimensional finite‐element (2D‐FE) models, the accuracy of which has been pre‐certified through experimental measurement.

Reduced-Order Observer-Based Position Control of a Magnetic-Geared Servo Drive

Magnetic gears (MGs) emerged as an interesting alternative to conventional mechanical gears, owing mainly to their high torque densities and contactless operation. This paper presents a novel observer-based position control system for a magnetic-geared servo drive. The presented control system is based on two well established control strategies—field-oriented control (FOC) and state feedback control. The former is used to achieve effective torque control of a permanent magnet synchronous motor (PMSM) which is considered as an actuator that drives the high-speed rotor, whereas the latter is used to control the position of the low-speed rotor. A reduced-order extended state observer is used to estimate the position and speed of the low-speed rotor, thereby reducing the number of sensors required for the implementation of the controller. The whole control system is implemented on a microcontroller and tested on an existing prototype with a gear ratio of 18:1. The experimental results show that the presented control system guarantees precise positioning within a short amount of time and excellent disturbance rejection.

A single current sensor based adaptive step size MPPT control of a small scale variable speed wind energy conversion system

Due to the limited size and lower environmental impact, a small-scale wind energy conversion system (WECS) is a promising alternative for remote locations and residential areas where installing large wind turbines is not feasible. This system employs a permanent magnet synchronous generator (PMSG) as a variable speed wind generator due to its advantages such as high torque density, gearless, and require no external excitation, etc. This article proposes a single load current sensor-based adaptive step size (LCAS) maximum power point extraction (MPPT) method which utilizes the load current information to track the maximum power. This method does not require rotor speed information and knowledge of the turbine parameters. Also, this article uses a simple and cost-effective switch mode rectifier topology (AC–DC and DC–DC boost converters) for the PMSG-based variable speed WECS. The proposed method is validated in a 1.5 kW test rig using an OPAL-RT digital signal controller and also compared with various fixed step size (FSS) MPPT algorithms at various operating conditions. Extensive experimental work has been carried out for the LCAS MPPT method that confirms the tracking efficiency is better and tracking speed is faster along with the improved steady state as well as transient performance.

Characterization of an Axial Flux Machine With an Additively Manufactured Stator

Axial flux machines (AFM) are promising alternatives to radial flux machines for applications that benefit from high torque density and a large diameter to axial length ratio, such as in-wheel traction motors. However, the 3D flux paths in AFM present unique challenges to manufacturing laminated stator cores. This paper positions metal additive manufacturing (AM) technology as a potential solution to manufacture unconventional electric machine components such as AFM stators by investigating novel lamination emulating geometric structures and material silicon composition as design handles. In this paper, techniques to additively manufacture soft magnetic components for rotating electric machines are reviewed, and the Hilbert pattern is identified as a promising candidate to reduce eddy-current losses in these components. To further reduce the eddy current losses, this paper investigates the use of 6.5% silicon steel, which has higher resistivity compared to conventional steel laminations. The results in this paper show that the Hilbert structure is effective in reducing the eddy current losses by 50% compared to a solid structure with 3% silicon steel, and using 6.5% silicon steel further reduces the eddy current losses by 24%. Finally, a candidate AFM stator is designed with the Hilbert pattern and fabricated additively using 6.5% silicon steel. This machine is characterized and experimentally compared with an identical axial flux machine that uses a laminated stator. The results demonstrate the potential of metal AM technology to fabricate electric machine components with eddy current losses comparable to ultra-thin gauge laminations at frequencies up to 200Hz and conventional 29Ga laminations up to 480Hz.

Performance analysis of sandwich switched flux switching permanent magnet motor using modular rotor

Conventional flux-switching permanent magnet brushless machines (PMFSM) gained a lot of attraction due to their high torque densities, simple and robust rotor structure, and the permanent magnets and coils on the stator. The sandwich PMFSM machine has been proposed to improve the torque density of the machine in which two PM pieces are sandwiched in one stator pole to enhance the PMs usage efficiency. 2D finite element analysis (2DFEA) method is employed to compare the performance of sandwich PMFSM with salient rotor topology with that of sandwich PMFSM with modular rotor, in terms of flux linkage, flux distribution, flux strengthening, induced back EMF, cogging torque and average torque. From the results it is shown that the salient sandwich PMFSM and sandwich PMFSM modular rotor produces 9.28Nm and 6.7Nm, respectively.

Design of 6 slots/10 poles modular rotor sandwich switched flux switching permanent magnet motor

Conventional flux-switching permanent magnet brushless machines (PMFSM) gained a lot of attraction due to their high torque densities, simple and robust rotor structure, and the permanent magnets and coils on the stator. The sandwich PMFSM machine has been proposed to improve the torque density of the machine in which two PM pieces are sandwiched in one stator pole to enhance the PMs usage efficiency. 2D finite element analysis (2DFEA) method is employed to compare the performance of sandwich PMFSM with salient rotor topology with that of sandwich PMFSM with modular rotor, in terms of flux linkage, flux distribution, flux strengthening, induced back EMF, cogging torque and average torque. From the results it is shown that the salient sandwich PMFSM and sandwich PMFSM modular rotor produces 9.28Nm and 6.7Nm, respectively.

A Novel Series Magnetic Circuit Variable Flux Memory Machine With Self-Flux Leakage Paths

Variable flux memory machine (VFMM) applying low coercivity force (LCF) permanent magnets (PMs) is suitable for electric vehicles (EVs) since its air-gap flux can be adjusted easily. In this article, a novel series magnetic circuit VFMM with self-flux leakage paths (SMC-VFMM-SLP) is proposed, in which the design concept of self-flux leakage is introduced to enhance air-gap flux regulation (FR) range and keep high torque density simultaneously. The self-flux leakage paths can control the self-flux leakages based on the magnetization states (MSs) of the employed LCF PMs. The machine can thus keep a high torque density under the positive MS and achieve excellent flux-weakening ability under the negative MS when it is loaded. First, the topology and the FR range expansion principle of SMC-VFMM-SLP are interpreted in detail, in which the magnetic circuits under different MSs are qualitatively analyzed. The electromagnetic performance of SMC-VFMM-SLP under the positive and negative MSs is subsequently investigated by the finite element method, including no-load characteristics, torque abilities, and efficiency maps. Finally, an SMC-VFMM-SLP prototype is manufactured and measured, which confirms the feasibility of the proposed self-flux leakage paths design for the air-gap FR range improvement.

Comparative Analysis of Novel Asymmetric Consequent-Pole and Conventional Flux Reversal Permanent Magnet Machines

Torque density is a critical performance index for flux reversal permanent magnet (FRPM) machines. In this paper, a novel asymmetric consequent-pole (ACP) FRPM machine with alternate teeth wound is proposed. Different from the conventional consequent-pole FRPM machine with uniform “Fe/N-Fe/N-Fe/N” structure, the proposed ACP FRPM machine adopts “Fe/N/Fe-N-Fe/N/Fe” topology. With the novel topology, torque capability of the proposed machine is significantly improved due to the newly produced lower working harmonics of air-gap flux density. The operating principle of the proposed ACP FRPM machine is analyzed based on the magnetomotive force (MMF)-permeance model with variable winding factors and validated by finite element analysis (FEA). The effects of geometric parameters such as magnet, main tooth-tip and rotor tooth width on average torque and torque ripple are also investigated. Finally, a prototype has been manufactured to validate the theoretical results. With experimental test results, it is demonstrated that the proposed topology can achieve 109.1% higher back EMF and 55.7% higher torque density despite the stator current is reduced by 25.4% compared with the conventional consequent-pole FRPM machines.

Design and Optimization of a Pole Changing Flux Switching Permanent Magnet Motor

A flux switching permanent magnet (FSPM) motor is designed and optimized in this paper to achieve high torque density and expanded speed regulation range from a design viewpoint of pole-changing (PC). Based on the field modulation theory, the PM field in the FSPM motor is modulated by the stator and rotor teeth, generating rich harmonics with different pole-pair numbers in the air-gap flux density. By adopting an appropriate slot pole combination, working harmonics with different slot pitch angles are obtained to establish a basis of the PC-FSPM motor. Then, different working harmonics can be used to achieve different energy conversions with different winding configurations, so the PC operation can be performed to realize the high torque and wide speed regulation range by switching the working modes. Based on the field modulation theory, the operation principle of conventional and PC-FSPM motors are analyzed and compared. Then, according to the design principle of the PC-FSPM motor, a 24/22-pole PC-FSPM motor with the E-core is designed and optimized by a multi-level optimization method. Finally, the electromagnetic performances are analyzed by finite element analysis and the test results of the prototype have verified the feasibility of the motor.

Research on speed regulation method of high power magnetic gear

Magnetic gears have attracted the attention of many scholars due to their advantages of low noise, maintenance free, high torque density and inherent overload protection. In this paper, three speed regulation methods of high power magnetic gear transmission system are summarized and proposed, and the finite element analysis of the three speed regulation methods is carried out by COMSOL Multiphysics simulation software. The results show that when the sizes of the three magnetic gears are similar, the output torque and load power of the speed regulation method of the magnetic gear using the magnetic field modulated type is the largest. On the contrary, the axial magnetic gear with air gap length regulation method has the lowest output torque and load capacity. Compared with the other two methods, the coupling length regulation method has the minimum eddy current loss and the simple speed regulation structure, which is the most suitable for high power magnetic gear.

Analytical Model of Air‐Gap Magnetic Field for Eccentric Harmonic Magnetic Gear with Halbach Array

The eccentric harmonic magnetic gear (EHMG) has the characteristics of high torque density, high transmission ratio and high efficiency. The EHMG with Halbach array has better performance than the EHMG with traditional radial magnetization. Accurate calculation of its air‐gap magnetic field is of great significance for design and optimization. Based on the boundary perturbation method, a 2D analytical model of the air‐gap magnetic field of EHMG with Halbach array is established in this paper. The eccentric air‐gap magnetic field is calculated due to the permanent magnets of the eccentric rotor and the stator acting alone, and then the air‐gap magnetic field of the EHMG is obtained according to the superposition principle. The results of the air‐gap magnetic field are compared and evaluated by the regression evaluation indexes. The analytical results are consistent with the finite element results, which verifies the validity and accuracy of the analytical model. Comparing the EHMG with Halbach array and radial magnetization, the maximum static and dynamic electromagnetic torques of EHMG with Halbach array are increased by 59.1% and 55.6% compared with the EHMG with radial magnetization, which verifies the superior performance of EHMG with Halbach array. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Investigation of self-adjusting cooling system for the autonomous underwater vehicle propulsion motor

Permanent magnet (PM) motors are widely employed in the autonomous underwater vehicle (AUV) propulsion because of their high efficiency and torque density. Since the AUV housings are sealed and narrow, motors are vulnerable to the risk of overheating, leading to dissolution of the winding insulation and demagnetization of the permanent magnets. In this study, a self-adjusting cooling scheme was proposed, which uses the hydrodynamic pressure to pump seawater into the cooling channel automatically. Firstly, the mathematical model of the flow field and heat transfer was established using equation derivations. Subsequently, to clarify the characteristics of the self-adjusting cooling system, the effect of the AUV speed on the thermal and fluid characteristics was investigated using computational fluid dynamics. Results show that the flow rate in the channel increases from 2 to 8.1 L/min as the AUV speed increases from 15 to 50 kn, resulting in the improvement of the heat transfer coefficient from 41 to 764 W/(m2∙K). Subsequently, the influences of inlet and outlet on the thermal characteristics were studied and found to be beneficial for improving the cooling performance. To investigate the spiral flow channels, the distribution coefficient kC and shape factor Rf were defined. Compared to the closed-cycle cooling system for the AUV propulsion motor, the proposed cooling system eliminated auxiliary devices such as pumps and heat exchangers, which makes it more compact and efficient for AUVs. However, introducing seawater into the AUV housing poses a risk of liquid leakage.

Simultaneous improvement of cogging torque and torque density in axial flux‐switching permanent magnet motor

AbstractAxial Flux‐Switching Permanent Magnet motors are broadly used in various industrial applications due to their high torque density and low rotor inertia. However, one major drawback of these motors is their cogging torque, which results in torque ripple and vibration. Existing methods for reducing cogging torque have often led to a decrease in useful electromagnetic torque, thereby compromising motor efficiency. To address this issue, a novel hybrid structure for the simultaneous improvement of cogging torque and electromagnetic torque in Axial Flux‐Switching Permanent Magnet motors is presented. The proposed structure combines the optimal arc coefficient of the rotor pole technique with the notching rotor technique, resulting in a new motor configuration that exhibits both reduced cogging torque and increased torque density. Analytical equations for calculating cogging torque are derived, and 3D finite element analysis is conducted to evaluate the effectiveness of the proposed structure design. Furthermore, the optimal values of the arc coefficient and forming angle of the rotor pole are determined using the Taguchi analysis. Comparing the results of the optimal motor structure with the previous design shows that the new structure can improve the cogging torque, average electromagnetic torque, torque ripple, torque density, and peak torque output of the motor, which confirms the effectiveness of the proposed structure.

High Torque Density and Lightweight Design of Permanent Magnet In-Wheel Motor Based on Magnetic Field Modulation Effect

High Torque Density and Lightweight Design of Permanent Magnet In-Wheel Motor Based on Magnetic Field Modulation Effect

A Modified Brush-Less DC Motor Having High Torque Density and Its Simplified Current Control Technique

A Modified Brush-Less DC Motor Having High Torque Density and Its Simplified Current Control Technique

A Novel Magnetic-Geared Motor Combining Magnetic Gear and SR Motor

A direct-drive permanent magnet (PM) motor and a magnetic-geared PM motor have the advantage of high torque density. Therefore, these motors are expected to be applied as in-wheel motors for electric vehicles (EVs). However, they have a problem that it is difficult to achieve the wide speed-torque characteristics required for EVs. This paper presents a novel magnetic-geared motor that consists of a flux-modulated type magnetic gear and a switched reluctance (SR) motor. In this paper, the SR motor part and the magnetic gear part are designed, and both parts are combined into a magnetic-geared motor. The proposed magnetic-geared motor has the wide speed-torque characteristic, which direct-drive PM motors or SR motors cannot achieve.

Comparison of Permanent Magnet Vernier Motors With Evenly and Unevenly Distributed Modulation Teeth

Permanent magnet vernier motor (PMVM) possesses the advantage of high torque density. In split-tooth PMVMs, the modulation teeth can be evenly or unevenly distributed on each stator tooth, which leads to the corresponding evenly and unevenly distributed slot vector diagrams. So, by selecting closer slot vectors into one phase, the winding factor can be improved, so the torque of PMVMs can be increased further by using the unevenly distributed modulation tooth structure. In this paper, two split-tooth PMVMs with evenly and unevenly distributed modulation teeth are compared. The simulation and the test results verify the correctness.