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The field modulation magnetic gear is a kind of transmission device with broad development prospects. It has the advantages of no friction， no pollution， less maintenance and easy installation. The magnetic gear models with different transmission ratio are established. The input and output torque waveforms of different models are compared. The influences of the number of pole pairs of inner rotor （P1） and the number of pole pairs of outer rotor （P2） on torque ripple are analyzed. According to the principle of magnetic field modulation and spatial magnetic field harmonic distribution， the torque ripple of magnetic gear is greatly affected by P1 and P2. The research results show that the torque ripple can be effectively reduced by selecting the magnetic gear with P1=4， P1:P2=1:n+0.25 or 1:n+0.75 （n is a natural number）.

In the transmission process of coaxial magnetic gear, aiming at the problems of large torque ripple and high magnetic density in air-gap, a magnetic gear with thin metal sheet is studied. The structure fixates a layer of conductive and non-magnetic metal material respectively on the internal and external permanent magnets of the rotor in the magnetic gear. A magnetic gear model with 4 opposite poles for inner rotor and 21 opposite poles for outer rotor is established via finite element method. The internal and external air-gap magnetic field and torque of the magnetic gear are calculated. Meanwhile, high magnetic density and torque ripple are analyzed. The results demonstrate that the magnetic gear with metal sheet can not only reduce the high-order harmonic components of magnetic density but also reduce the torque ripple. A reference for the improvement of the stability in the magnetic gear transmission is provided.

The magnetic gear has the advantages of no friction between the rotor,simple manufacturing and installation,low cost and so on,it is an excellent transmission mechanism. The development history of magnetic gears from time to time is briefly described,and the research status of magnetic gears at home and abroad is compared. The topological structure of several kinds of common magnetic gears are introduced,and the advantages and disadvantages of these kinds of magnetic gears are compared. Its future development direction and research questions are summarized.

Comparing with the mechanical gear contact transmission,magnetic gear is a new transmission device with a novel structure and a broad development prospect. The large torque transmission is achieved by using the magnetic field modulation principle. On the basis of the traditional magnetic gear structure,the inner and outer rotor permanent magnets are improved,which the inner permanent magnets are triangular-fan-shaped phase and the inner and outer permanent magnets are Halbach arrays. The two dimensional（ 2 D） finite element（ FE） method is used to simulate the modified magnetic gear model,and the electromagnetic field and electromagnetic torque of the magnetic gear are calculated. At the same time,the magnetic field and torque are compared with the conventional magnetic gear. The simulation results show that the output torque of the improved magnetic gear is greatly than the traditional magnetic gear,which can effectively enhance the air gap magnetic density and reduce the air gap harmonic content. It is a great significance to study and apply the torque density of concentric magnetic gear.

For tackling the problem of large errors in simulating the static inner symmetrical minor hysteresis loops through the Simplified Landau-Lifshitz-Gilbert (S-LLG) equation, a modification by improving the grain structure arrangement and introducing additional hysteresis energy function is proposed. With the proposed model, only a unified set of parameters identified by four static hysteresis loops is needed to predict hysteresis loops under arbitrarily different magnetic flux density levels. To verify the global simulation capability of the proposed model, the simulation results of hysteresis loops are compared with the measured data of a grain-oriented (GO) steel. The obtained results show that the model has good simulation ability for hysteresis loops under different magnetic flux densities for both sinusoidal and harmonic excitation conditions. [ABSTRACT FROM AUTHOR]

The concentric magnetic gear is a transmission gear with a novel structure and a promising prospect,by using the magnetic field modulation principle,the large torque transmission is realized. On the basis of concentric magnetic gear structure,the modulation magnet ring is improved,the silicon steel is added on the inside of the modulation magnet ring to constitute a mechanical bridge. The model of the improved magnetic gear is simulated by using two dimensional（2D） finite element（FE） method,and the magnetic field and electromagnetic torque are calculated. At the same time,the magnetic field and torque are compared with the common gear. The results show that improved magnetic gear magnetic field is higher than normal- type magnetic gear,lower harmonic content,and torque is also improved. It is significant for the research and application of the concentric magnetic gear.

An eccentric harmonic magnetic gear (EHMG) is better suited for situations requiring larger transmission ratios than magnetic-field-modulated magnetic gears. In the meantime, to increase the torque density even further, a new structure for EHMGs is presented in this paper. The stator's permanent magnets (PMs) are irregularly distributed, while the rotor's PMs are applied to a fan-shaped structure. Moreover, a Halbach array is adopted in both the rotor and the stator. A two-dimensional finite element (FE) model of the proposed EHMG is developed, and the flux density distribution and torque of the EHMG are calculated and verified via FE analysis. When compared to a conventional EHMG, the presented model's torque increases from 38.04 Nm to 50.41 Nm. In addition, for the sake of avoiding the oscillation and noise caused by resonance, a modal analysis of the proposed model is conducted and the consequences show that it has better antivibration properties. Finally, a prototype is made, a test bench is established, and the correctness and effectiveness of the proposed model are verified. [ABSTRACT FROM AUTHOR]

To clarify the mechanism of the magnetic properties deterioration and the increasing loss of the Grain-Oriented (GO) electrical steel wound cores under serving conditions, the effect of the bending stress in a wide frequency range should be thoroughly investigated. In this paper, a magnetic properties measuring system for GO electrical steel under different bending stress from 50 Hz to 1000 Hz is proposed. To ensure the accuracy and reproductivity of the measurements, the waveform of magnetic flux densities should be controlled to be sinusoidal. However, the bending stress aggravates the material's nonlinear properties, making waveform control very difficult. To solve this problem, a frequency-domain adaptive dual-loop feedback control algorithm is developed. Obtained results show that the proposed method has a good effect on waveform control under bending stress, and the loss of the material under different magnetizing conditions is then analyzed. [ABSTRACT FROM AUTHOR]

Based on the consideration of the magnetic domain motion under different magnetization levels, an improved J-A model with variable parameters is proposed to solve the problem of significant errors in the process of calculating the inner symmetric small loops. The proposed method introduces a variable scale parameter v(B) to correct the irreversible magnetization component of the J-A model. Meanwhile, based on the magnetic domain theory, a method with variable pinning parameter k(B) and a variable domain wall bending parameter c(B) is proposed. By comparing the measured data of B30P105 Grain-Oriented (GO) silicon steel, the calculation error for each magnetization level of the model is within 7%, which means that the global hysteresis properties of GO silicon steel can be well reproduced. [ABSTRACT FROM AUTHOR]

As a typical representative of the stator permanent magnet (PM) machines, the flux reversal machines (FRMs) have a simple structure, high availability of PMs, and high efficiency, making them suitable for direct drive applications. However, the PMs of the FRMs are mounted on the surface of the stator tooth, and its equivalent length of air gap is relatively large, which limits the torque increase. To improve the torque density, a novel FRM with auxiliary teeth is proposed in this paper. Half of the stator teeth are replaced by auxiliary teeth without PMs to reduce magnetic flux leakage, the number of PMs on each stator tooth is also changed. To improve the torque, the genetic algorithm is used to optimize the key design parameters to determine the optimal parameters of the machine. Finally, a finite element model is established to verify the analysis results. Compared with the conventional FRM, the torque of the proposed FRM is increased by 25.1%, the torque ripple is reduced by 24.1%, and the consumption of PMs is reduced by 24.1%. Therefore, the proposed FRM has a broader application prospect. [ABSTRACT FROM AUTHOR]

Spoke structure can increase the torque density of coaxial magnetic gear (CMG). However, the outer rotor can produce a large number of magnetic leakages. To improve the utility of PMs, a novel magnetic gear was proposed in this paper. The structure of the auxiliary flux modulator is a slotted iron yoke, and the slot angle is same as the stationary ring. Among, the permanent magnets (PMs) of inner rotor are adopted uneven block structure to improve air gap flux density. At the same time, the stationary ring adopts high-temperature superconducting (HTS) bulks, replacing the epoxy resin. In addition, Genetic algorithm (GA) is applied to calculate the optimal parameters of the proposed CMG. Finally, the air gap flux density and output torque of the magnetic gear a compared by the finite element method. The results show that the output torque of the proposed magnetic gear is effectively improved. [ABSTRACT FROM AUTHOR]

In this study, an analytical model is proposed to calculate the magnetic field and electromagnetic torque (including cogging torque) in the surface‐mounted permanent‐magnet (SMPM) machines with Halbach arrays accounting for semi‐closed slots. The analytical model can be used to calculate both no load and load air gap magnetic field of SMPM. The permanent magnets (PMs) on the rotor are arranged Halbach array and each pole is divided into four segments. Additionally, in order to improve the performance of the SMPM, the analytical model is combined with genetic algorithm to optimise some parameters of the motor. The analytical results from the proposed model have been compared with those issued from finite‐element method. Finally, the 12‐slot/8‐pole motor is manufactured and the back‐electromotive force, iron loss and load characteristics are validated by experiments. [ABSTRACT FROM AUTHOR]

This article proposes a novel hybrid-excited magnetic gear (HEMG) with eccentric magnet structure. The novel HEMG has a higher electromagnetic torque when compared to its conventional counterpart. This study looks into the magnetic field of coaxial magnetic gear during overload, and investigates the cause of demagnetization of permanent magnets (PMs) on rotor. The PMs are attached to the inner and outer rotor; PMs of inner rotor are eccentric structure and magnetized along the radial direction, PMs of outer rotor are the radial magnetized, and the outer rotor yoke is slotted and injected with current. The proposed HEMG topology with 4 inner and 23 outer pole pairs is established; the corresponding magnetic flux density distributions, electromagnetic torque, and torque ripples are assessed and verified by finite element analysis. Finally, the HEMG is built and tested; the test results show that its transmission efficiency is up to 92.6%, and the effective length of the prototype corresponds to the torque density that is 135.15 kN·m/m3. [ABSTRACT FROM AUTHOR]

In this paper, a novel flux switching permanent- magnet machine (FSPM) with consequent-pole magnets and flux bridges in the stator core is proposed to improve the torque capability of FSPMs with high pole ratios. The stator yoke and flux bridges adjacent to the magnets can provide magnetic paths for the main working harmonic field, thus the magnetic reluctance of the working harmonic field is reduced, and the flux modulation effect, winding back-electromotive force (EMF), and output torque of the proposed FSPM can be significantly improved compared to the regular FSPM with high pole ratios. The operation principles and stator–slot/rotor–slot combinations of the proposed FSPM are introduced. Then, the influences of pole ratio, split ratio, slot opening ratio, and PM width on the torque density of the proposed FSPM is investigated using finite element analysis. Moreover, after the investigations, a proposed FSPM is compared to a regular FSPM in terms of back-EMF, rated torque, power factor, etc. Finally, to verify the theoretical analysis, a 12-stator–slot/14-rotor–slot FSPM is built and tested. [ABSTRACT FROM AUTHOR]

A novel interior permanent magnet linear vernier machine (IPM-LVM) is proposed and analyzed in this paper. Compared to the existing surface-mounted permanent magnet linear vernier machine (SPM-LVM) and the SPM-LVM with Halbach arrays, the proposed machine can offer higher flux density in both the air-gap and armature iron core, which lead to a higher back electric motive force (back EMF) and higher thrust density under the same mover volume and heat capacity. Besides, it is proven that the proposed IPM-LVM also has a lower demagnetization risk compared to the SPM-LVM. Furthermore, in order to reduce the thrust ripple of the proposed machine, the three-sectional structure is adopted in this paper, which makes the proposed IPM-LVM exhibit high thrust density and low thrust ripple at the same time. [ABSTRACT FROM AUTHOR]

This paper investigates a novel harmonic current injection method to optimize air-gap and yoke flux density distribution for multiphase motor simultaneously. The effect of harmonic currents on air-gap flux density and yoke flux density is analyzed as a whole, while the traditional method focuses on air-gap flux density optimization only. The proposed method fully makes use of multiple control freedoms and the optimal coefficients for corresponding harmonic current are derived. The theoretical analysis and experimental results indicate that novel harmonic current injection method is suitable for heavy load condition. Maintaining the same stator current density, a nine-phase induction motor improves torque density up to 8.47% with the proposed method. A three-phase induction motor is designed to verify the effectiveness of multiphase motor with concentrated full-pitched winding. Furthermore, the torque density and efficiency for two motors are compared under various load condition. Finally, a multiphase variable speed drive system is constructed and the proposed method is validated by experiments. [ABSTRACT FROM PUBLISHER]