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To solve the problems mechanically caused by parallel direct‐drive permanent magnet motors (DD‐PMSM). This paper proposes a concave‐core stator direct‐drive permanent magnet motor (CCSDD‐PMSM) structure. In this study, an auxiliary yoke structure is proposed to optimise the magnetic circuit and analyse the cogging torque to achieve the minimum detent force. Based on the unit motor and combined with the magnetomotive force to analyse the symmetry of different winding distributions, the stability characteristics of the motor are studied. The magnetic field distribution of the motor load air gap is calculated using the finite element method. The contribution of different spatial order harmonics to the motor output torque is calculated using the Maxwell tensor method. The torque calculation expression of the CCSDD‐PMSM is given. Finally, an experimental prototype is made to verify the accuracy of the analysis in this paper. [ABSTRACT FROM AUTHOR]

Fractional slot concentrated winding (FSCW) permanent magnet (PM) machines are gaining more attention for low‐speed applications because of their great advantages. This paper proposes a new structure for an FSCW double rotor axial flux PM synchronous machine (DRAFPMSM) with counter‐rotating rotors. In addition, an analytical formula for the Back EMF waveform of the proposed structure is presented. The accuracy of the formula is investigated by designing a 40 W sample machine. The rotors of this machine rotate with speeds of 600 and 428 rpm in opposite directions. The Back EMF of the sample machine is calculated using the suggested formula. In addition, the finite element method (FEM) is used to determine the Back EMF waveform. Comparison of the obtained results confirms that the new formula yields the Back EMF precisely such that the results well match to those of FEM. The effect of the relative position of two rotors on the Back EMF waveform is investigated using the proposed formula. In addition, the optimum relative position of two rotors for minimizing the Back EMF THD of the case study machine is determined. [ABSTRACT FROM AUTHOR]

This article has conducted a comprehensive study on the stator and rotor vibration characteristics of the doubly‐fed induction generator (DFIG) in the case of radial air gap eccentricity (RAGE). Differently from other previous studies, this paper not only investigates the vibration characteristics of stator and rotor in radial static air gap eccentricity (RSAGE) and radial dynamic air‐gap eccentricity (RDAGE) fault but also takes the radial hybrid air gap eccentricity (RHAGE) into account. Through theoretical derivation, the detailed expressions of stator magnetic pull per unit area (MPPUA) and rotor unbalanced magnetic pull (UMP) are obtained. The finite element analysis (FEA) and experiment based on a two pairs of poles DFIG, and the results are consistent with theoretical calculations. It is shown that RAGE will enlarge the magnitude of stator MPPUA/vibration and rotor UMP/vibration. Specifically, RSAGE will not change the frequency components of stator MPPUA/vibration but will bring new frequency components to rotor UMP/vibration. However, both stator MPPUA/vibration and rotor UMP/vibration will generate new frequency components during RDAGE fault. In addition, the effect of RHAGE is the superposition of RSAGE and RDAGE. The research conclusions obtained in this paper can be used as a supplementary criterion for diagnosing the eccentricity of DFIG. [ABSTRACT FROM AUTHOR]

Compared with the single‐stator permanent magnet synchronous motor(SS‐PMSM), the double‐stator permanent magnet synchronous motor(DS‐PMSM) can make full use of the space in the motor cavity to make it have higher torque density, so it is more suitable for direct‐drive occasions with low‐speed and high‐torque. This paper aims to design and compare the parameters and performances of DS‐PMSMs with four different rotor structures: 1)Series magnetic circuit of radial magnetised single‐layer permanent magnet(type Ⅰ), 2)Series magnetic circuit of radial magnetised double‐layer permanent magnet(type Ⅱ), 3)Parallel magnetic circuit of radial magnetised double‐layer permanent magnet(type Ⅲ), 4)Parallel magnetic circuit of tangential magnetised permanent magnet(type Ⅳ). Firstly, the equivalent magnetic circuit method is used to analyse the magnetic circuits of the four DS‐PMSMs. Next, the finite element analysis tool is used to compare the performances of the four DS‐PMSMs with the same volume. Their air‐gap flux density, no‐load back‐EMF, cogging torque, torque characteristics, moment of inertia, rotor loss and efficiency are quantitatively analysed and compared. Finally, this paper provides guidance and suggestions for the selection of the rotor structure of DS‐PMSM. [ABSTRACT FROM AUTHOR]

The doubly fed induction generator is commonly used in commercial wind turbines because of its simplicity and robustness; it is a wound rotor induction machine. It has a relatively small airgap which makes it more vulnerable to unbalanced magnetic pull. This paper presents a simulation model to investigate the ability of extra stator windings with pm ± 1 pole‐pairs to control the unbalanced magnetic pull (UMP). These auxiliary windings are inserted in the stator slots and they are used to produce counteracting flux that reduces the UMP. In the theory section, an UMP control matrix is fully developed that involves additional winding currents for obtaining active UMP control. The algorithm for controlling the UMP is then introduced. This uses vector control with stator flux orientation. Several simulations are carried out using MATLAB and Altair Flux 2D finite element analysis. These show a good reduction of UMP under open circuit and locked rotor tests. These models allow the study of the combined effects of radial forces with changes in the machine design. It was found that the average power absorbed by the auxiliary windings equals 13% of the total power losses in normal operation conditions. [ABSTRACT FROM AUTHOR]

In this study, a fault diagnosis model based on magnetic density is proposed to analyse the current characteristics of synchronous generator rotor inter‐turn short circuit and air gap eccentric single fault and composite fault. The model considers the influence of rotor inter‐turn short circuit and air gap eccentricity on air gap magnetic density. According to two main factors, the short circuit turns and eccentric distance, are used to reflect the short circuit and eccentricity of the generator. The detailed parameter input model of the generator can easily and quickly predict the development trend of these current parameters based on the air gap magnetic density. And the phase current is selected as the current parameter. The validity of the proposed model is verified by two‐dimensional finite element analysis and experimental research. [ABSTRACT FROM AUTHOR]

A modified non‐linear magnetic equivalent circuit (MEC) model is presented for double‐stator single‐rotor axial flux permanent magnet (AFPM) (DSSR‐AFPM) machine considering stator radial‐end flux‐leakage, which is severer under a heavier load. Compared to the conventional MEC model for DSSR‐AFPM machine, the proposed model can predict the electromagnetic performance more accurately when the machine operates under a heavy load. The proposed MEC model is verified by the finite element analysis (FEA) on a 24‐slot/20‐pole DSSR‐AFPM machine. The comparison results show that the relative error between the proposed MEC model and FEA is <4% for back electromotive force and <5% for average electromagnetic torque, respectively. Specifically, the relative error of the average torque for the modified MEC model is 4.92% at 28.30 Arms/mm2 slot current density, which is lower than the conventional MEC model, that is, 7.75%. [ABSTRACT FROM AUTHOR]

Magnetic‐geared double‐rotor machines are recognized as a promising power‐splitting component in hybrid electric aircrafts (HEAs). However, the high fuel efficiency speed of the turbine engine in HEAs is about 10,000 rpm, whereas conventional topologies suffer from low efficiency at high speed due to its specific operation principle—the magnetic field modulating principle. A coreless stator magnetic‐geared double‐rotor machine (CS‐MGDRM) is proposed to enhance high‐speed efficiency and thus comply with the operation condition of HEAs. First, the machine structure and hybrid propulsion system configuration are introduced, and power‐flow analysis of three basic operation modes is presented. Second, the operation principle of the machine is illustrated, and investigation of electromagnetic performances is carried out by finite element analysis. Third, an analytical model of the machine is developed, based on which the design optimization towards the maximum torque capacity is investigated. Furthermore, the loss distribution law and transmission efficiency are analysed and compared with conventional scheme, and the power factor characteristic is investigated as well. Finally, the overall performance of the proposed machine is evaluated. [ABSTRACT FROM AUTHOR]

A multi‐phase permanent magnet synchronous motor (PMSM) with fractional‐slot windings is proposed to reduce electromagnetic vibration and improve torque performance. Firstly, the analytical expression of electromagnetic force is derived, and the stator teeth modulation effect of electromagnetic force is introduced. The spatial order of the electromagnetic force and the stator teeth modulation are closely related to the slot‐pole combination of the PMSM. Then, three PMSMs with different slot‐pole combinations are presented, and they represent fractional‐slot concentrated winding, integral‐slot distributed winding and fractional‐slot distributed winding, respectively. Their torque performance and electromagnetic vibration performance are studied and compared considering stator teeth modulation. In addition, the multi‐phase winding technology is adopted to further improve the torque performance of the proposed PMSM. Finally, a 90s20p PMSM is manufactured, and the finite element method and experimental method are used to verify the proposed low vibration design method. [ABSTRACT FROM AUTHOR]

The motive of this study is to analyse the characteristics of a novel dual‐stator embedded‐pole six‐phase permanent magnet synchronous motor for the application of electric vehicles. A comparative analysis of two separate motor topologies, namely, dual stator embedded‐pole six‐phase permanent magnet synchronous motor and single stator single rotor surface‐mounted permanent magnet synchronous motor, is accomplished to illustrate the performance superiority of the proposed motor. Furthermore, for optimal designing of the proposed motor, a design methodology has also been presented. For the above application, the motor should retain high torque density (HTD) and high reliability. In this regard, a novel H‐Shaped flux barrier is introduced in the rotor portion, which fulfils the requirement of HTD. Moreover, the availability of two sets of the stator winding enhances the performance efficiency and ensures the proposed motor's more significant fault‐tolerating ability of the motor. For performance evaluation, the Finite Element Method analysis is chosen, as it gives appropriate and precise results. From the above analysis, it is concluded that the HTD and the proposed motor's dynamic performance are better than the above‐mentioned conventional motor. [ABSTRACT FROM AUTHOR]

Shaft voltage often exists in synchronous generators due to the assembly error or various faults after the long‐term performance. The article investigates the shaft voltage characteristic under the stator interturn short circuit (SISC) condition. Different from other studies, this article mainly considers the mapping relationship between the amplitude–frequency characteristics of the shaft voltage and the SISC degrees. The detailed shaft voltage expressions are first derived based on the magnetic flux density under the normal condition and SISC condition. Then the finite element analysis and the experiment is studied on a CS‐5 prototype synchronous generator with two poles in order to validate the theoretical formula. The result shows that there is no shaft voltage in the normal condition, while the shaft voltage is generated obviously under the SISC condition. Meanwhile, the frequency component of the shaft voltage is mainly composed of odd harmonics including the first, third and fifth harmonics. [ABSTRACT FROM AUTHOR]

Transposition of stator windings for large turbo generators is a key technology. At present, the stator windings with four‐row strands for large turbo generators are usually transposed on both sides of the slot centreline and connected at the end by the joint sleeve. The different transposition methods of strands have an important effect on strand currents, circulating currents, and circulating current losses. A new four‐row integral transposition method is proposed in this study. Several transposition methods based on the four‐row integral transposition method are compared with the double Roebel transposition methods using 3‐D time‐harmonic field. The 3‐D model without the end and with the end are both calculated. The results show that the four‐row integral transposition method has an obvious advantage in reducing circulating current loss. Finally, a 2‐D finite element model of transient magnetic field is calculated and its calculation results further support for the effectiveness of the proposed transposition method. The proposed transposition method has a great application value, which can reduce additional loss, avoid partial overheating and short circuit fault of stator windings in large turbo generators. [ABSTRACT FROM AUTHOR]

The large permanent magnet synchronous machine (PMSM) usually adopts a modular technique to facilitate manufacture and maintenance. The rated power of large mechanical equipment is selected according to the limit capacity, and the motor efficiency is low at a low load. A kind of unwinding stator module combined permanent magnet synchronous machine (SMCPMSM) is proposed. Each module is mechanically and electrically decoupled. It can operate independently. The number of input modules can be flexibly selected according to the torque requirements in direct drive SMCPMSM to realise the optimum efficiency control of the ball mill. The work presents the loss model of the SMCPMSM and analyzes the torque distribution ratio of the modules. The mathematical model of torque distribution with optimum efficiency is established by using the genetic algorithm. The optimum efficiency control under different loads is determined. The motor performance of four operation modes is simulated by the finite element. An 80 kW prototype is developed, and its experiments are carried out. The experimental results verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

The 0‐order natural frequency resonance is the main cause of electromagnetic vibration noise in integer slot multi‐pole pair permanent magnet synchronous motors (PMSMs) for electric vehicles. To study this phenomenon, this study proposes a finite element (FE) model of the stator system based on a 48‐slot 8‐pole permanent magnet synchronous motor for electric vehicles. Based on this model, the effects of winding, frame end cover and temperature on the natural frequencies of a stator system are analysed by using the equivalent stiffness method (ESM). The simulation results show that the 0‐order natural frequency of the stator core system decreases after considering the winding varnished, and the 0‐order natural frequency is almost unaffected after considering the frame and end cover. However, the other natural frequencies increase in different degrees. In addition, the natural frequencies of the stator core decrease with the increase of temperature. The accuracy of the finite element model is verified by the modal experiment of the hammer method (HM). [ABSTRACT FROM AUTHOR]

High power‐generation efficiency can be achieved by optimising the shape of the claw pole used as automobile generators. The working process of the stator and rotor in the claw pole generator was simulated using the finite‐element method. First, one of the eight typical claw pole types commonly used in industry was selected. Then, orthogonal optimisation was performed based on the simulation results, yielding an optimal claw shape design. To examine the adaptability of the designed claw pole to shape change, the non‐destructive test for evaluating the magnetic properties of claw pole (NDTEM) was employed. Finally, a claw pole with an optimal shape was forged, and its magnetic induction intensity was assessed using the NDTEM. The results indicated that compared with the unoptimised claw pole, the magnetic induction intensity of the optimised claw pole increased by a maximum of 8.11% and its weight reduced by 4.86%. This optimisation effectively improved the efficiency of power generation and achieved the lightweight of the claw pole. [ABSTRACT FROM AUTHOR]