Rotor Structure Research Articles

Rotor Strength Analysis of FeCo-Based Permanent Magnet High Speed Motor

To solve the problem of tension stress caused by centrifugal force and caused by high-speed operation of permanent magnet (PM) rotor, a FeCo-based PM rotor structure model is proposed. Based on the thick-walled cylinder theory, the uniform analytical calculation formulas of strain field, displacement field, and stress field of high-speed permanent magnet rotor are derived, and the stresses of FeCo-based PM and sleeve are obtained. The correctness of analytical calculation method (ACM) is verified by finite element method (FEM). Based on the derived analytical formula, the influence of static interference, sleeve thickness, rotating shaft, and PM thermal expansion coefficient on the strength of high-speed permanent magnet rotor is analyzed, and the mechanical design law of high-speed permanent magnet rotor is summarized. Alloy sleeves are usually fitted outside the high-speed permanent magnet rotor to protect the PM from damage. In order to ensure safe operation of PM rotor under hot rotating conditions, strength calculation and check of sleeve and PM must be carried out. Based on the characteristics of slender structure of high-speed rotor, a high-speed permanent magnet motor (HSPMM) with a rated power of 100 kW and a rated speed of 18,000 r/min was produced, and a continuous operation test was carried out to verify the validity of the above theoretical analysis.

Numerical investigations on unsteady vortical flows and separation-induced transition over a cycloidal rotor at low Reynolds number

The unsteady vortical flows and separation-induced transition over a 2-bladed cycloidal rotor are investigated numerically at two advance coefficients, with special emphasis on the influence of two different turbulence models, namely the original SST k-ω model and SST γ-Reθt transition model. Firstly, the applicability of the transition model in predicting the transitional flows over a single airfoil at different incidences is evaluated, and the main results show a good agreement with the experiments, in terms of the mean pressure coefficients and transition locations. Then, the global performance and detailed internal flow structures of the cycloidal rotor are also used to compare with the existing numerical and experimental data. The primary results show that increasing the advanced coefficient can’t change the transition location of the performance of the single blade, but the magnitudes of these variables (vertical force, propulsive force and power coefficients). Then, combining the forces (lift and drag) acting on two blades, the blade loadings and the detailed near-wall flows, the difference of the vertical force and propulsive force of the rotating system and single blade are clarified clearly for two turbulence models. Finally, at advancing side, the transition and its evolution on a single blade is elaborated. It shows that the SST γ-Reθt transition model is superior in predicting the overall performance, but is highly subjected to the disturbances, characterized by the large-scale vortex structures and massive flow separation, compared with SST k-ω model. Simultaneously, it has the capability to capture the transition process, from growing waves of the laminar boundary layer induced by the roll-up vortices to the fully generation of the separation bubble. It believes that this work can deepen the understandings of underlying flow physics inside the cycloidal rotor at low Reynolds number.

A Slotless PM Variable Reluctance Resolver With Axial Magnetic Field

The stator-PM machine concept has been practiced on the recently proposed stator-PM variable reluctance (VR) resolver. When inheriting the simple and sturdy rotor structure of the conventional VR resolver, the novel stator-PM VR resolver provides a chance to avoid the high-frequency excitation by the unique PM back electromotive force decoding solution. This article extends this stator-PM VR resolver category with the axial magnetic field technology. The axial slotless structure makes the VR resolver compact and much smaller than the radial field prototypes. The thin and light leaf-style rotor is suitable for the super-high-speed applications, as the additional inertia due to a sensor is not welcome in those scenarios. Additionally, the printed circuit board replaces the winding coils in the regular VR resolvers, significantly simplifying the manufacturing. The design with even and odd poles cannot share the same principle, so they are discussed separately. The prototypes with 4-X and 5-X configurations are tested in the experiment setup respectively to validate the analysis of the proposed structure. Moreover, the 4-X resolver is integrated with a permanent magnet synchronous machine, and a motor driver with the space vector modulation on the basis of the specific resolver decoder is built.

A Modified Permanent Magnet-Assisted Synchronous Reluctance Motor Design for Torque Characteristics Improvement

A modified configuration for Permanent Magnet Assisted Synchronous Reluctance Motors (PMaSyRM) is studied in this paper. Conventionally, the PM materials are inserted in the flux barriers region of the rotor. Consequently, the PMs sizing parameters will be restricted to the available space that may limit the efficient use of PMs benefits. In this study, a portion of the rotor structure is replaced with an Interior PM (IPM) rotor so that an axially segmented integration of IPM and SyRM is obtained. Thus, the PMs design is performed specifically in the IPM segment independent of the SyRM scheme, while the SyRM segment remains PM-less. The main motivation of this concept is to improve the contribution of the PM material in the total torque as well as utilizing the special property of the proposed rotor configuration for pulsating torque reduction. A computationally cost-effective algorithm is proposed for the optimal design of IPM-SyRM motor by which a low-power design is carried out for a lightweight electric vehicle. The results for torque profile characteristics, PM volume, power-factor, and efficiency are compared with a conventional PMaSyRM that has been optimally designed as the reference case. Finally, a prototype is constructed to verify the theoretical analysis.

Static Characteristics Analysis of Shaft Rotor of Vertical Long-Shaft Fire Pump Under the Connection of Different Shaft Lengths

In this paper, a vertical long-shaft fire pump XBC18-178-240LC3 was taken as the research object to study the static characteristics of the pump rotor-shaft system under different shaft length connection. To analyse the influence of the length and number of the intermediate shaft section of the pump shaft on the deformation and equivalent stress of the shafting rotor, three shafting rotor models Z4(modified model), Z5(original model) and Z6(modified model) were designed, and then the static characteristics of them were analysed and compared under four operating conditions of 0.65Q d(0.65 times design flow),1.0Q d, 1.2Q d and 1.4Q d by numerical simulation. The results suggested that the changed rules of the three models' deformation and equivalent stress were basically the same. After the rated operating condition, the maximum deformation of the impeller of Z5 model was smaller than that of the Z4 and Z6 models. Under the four operating conditions, the maximum equivalent stress of the impeller of Z5 model was the smallest. This showed that the length and number of the intermediate shaft section affected the deformation and equivalent stress of the shaft rotor. Therefore, Z5 model was selected as the best rotor structure design scheme.

Analytical Modeling for Rotor Eddy Current Loss of a Surface-Mounted PMSM With Both Non-Ferromagnetic Conductive Retaining Sleeve and Shielding Cylinder

It is recognized that the rotor with shielding cylinder (SC) is one of the effective measures to restrain the rotor eddy current loss (RECL) for high-speed surface-mounted permanent magnet synchronous motors (PMSMs). At present, the RECL of PMSMs with multilayer composite rotor structure is mainly analyzed by the finite element method (FEM), which has obvious shortcomings in time-consumption and the mesh generation of thin SC. In this paper, a multi-layer subdomain analytical model for calculating the RECL of high-speed PMSMs with both non-ferromagnetic retaining sleeve and SC is proposed by taking the effects of eddy current reaction, stator slotting and current harmonics into account. Moreover, the 3-D distribution coefficient of eddy current in the SC is derived by the equivalent impedance method and the effects of temperature on the conductivity of the SC and RECL are obtained through equivalent thermal network (ETN) model. Based on the analytical model, the SC parameters are calculated to obtain the variation ranges when the RECL is minimum. Finally, the C-shape core experiment was built up to verify the correctness of the multilayer analytical model under different shielding layer conductivities and thicknesses.

Design and Optimization of a Magnetic-Geared Direct-Drive Machine With V-Shaped Permanent Magnets for Ship Propulsion

This article presents a novel magnetic-geared direct-drive machine (MGDM) with V-shaped permanent magnets (PMs) installed on its rotor. By extending the inner rotor shaft and connecting it to a prime motor, the torque and power density of the proposed MGDM are boosted. In addition, compared with the conventional MGDM with surface-mounted PMs (SPMs), the proposed MGDM with V-shaped PMs has a more robust rotor structure to cope with extreme operating conditions. The operating principle and structure requirement of this MGDM are first derived. Then, the geometrical parameters are optimized via a three-stage multiobjective optimization method to maximize output torque and efficiency and minimize torque ripple via the genetic algorithm (GA) and finite element analysis (FEA) combined optimization strategy. Furthermore, the proposed MGDM is artfully integrated into hybrid electric ships (HESs) to construct an onboard integrated power system (OB-IPS). Since the proposed system possesses various operating modes to cope with practical operating conditions, it enjoys a high systematic efficiency and good dynamic performance. Finally, a prototype is fabricated and tested with various operating modes by referring to the practical navigation cycle of an HES. The experimental results validate the feasibility of the proposed MGDM for being applied in HESs.

Analytical modelling for magnetic field of interior permanent magnet synchronous motors accounting for bridge saturation

Most of the motors used in industrial fields are interior permanent magnet synchronous motors (IPMSMs). The rotor structure of IPMSM is complex, and the rotor bridge region is affected by non-linear saturation, which increases the difficulty of modelling and calculation. The accuracy of traditional methods for the magnetic field prediction needs to be improved. An analytical model for IPMSM that accounts for the bridge saturation and the complex rotor structure is presented. This method transformed the structure of IPMSM equivalently, which makes it easier to use modelling in the polar coordinate system. Meanwhile, the bridge subdomain and the bridge saturation overflow subdomain are established separately based on the different saturation levels, and the relative permeability value of each subdomain is solved by the iterative permeability method. The magnetic field and electromagnetic performance obtained using the analytical method are compared with those of the finite element method. Finally, the analytical predictions are compared with the measured data to confirm the validity of the methods proposed.

Investigation of the Effect of Design Parameters of Small Brushless DC Motors on Motor Performance by Finite Element Method

Direct Current (DC) motors are widely used in industrial applications. The limited use of brushed models in some areas has brought Brushless Direct Current Motors (BLDC) to the fore. The constant need for maintenance of brushed type motors creates a disadvantage in variable conditions and in areas that are used continuously. For this reason, brushless DC motors have a wide range of uses. Brushless DC motors stand out with their high-performance values. Brushless DC motors with outer rotor type are used in applications that require high torque and inertia. The fact that electrical machines have moving parts and the computational complexity created by these parts have led electrical machine designers to alternative ways such as software and simulation programs where the results can be predicted. In this paper, a Brusgless Permanent Magnet Direct Current motor (BLPMDC) was designed and analyzed. The obtained speed, efficiency, torque, and air gap flux distributions were examined and the results were compared with literature for the motor type. In this study, applications were made to examine the effects of design parameters such as rotor structure, rotor position, magnet arrangement and materials used in the structures on the efficiency and output power of the motor. Efficiency-speed and power-speed values were obtained for different structures and features of the engine. The results obtained are compared with each other and presented in the article in the form of graphs and tables.

Design and Research on High Power Density Motor of Integrated Motor Drive System for Electric Vehicles

Although many PMSMs are used as the driving source for electric vehicle motor drive systems, there is still a gap compared with the power density index in the DOE roadmap. Considering that the motor occupies a large space in the motor drive system, it is of great significance for the system to increase the motor power density and thus reach the system power density index. This article starts with electrical machine basic design theory and finds the motor power density influence factors. Guided by the theory and considering motor driver influence, this article proposes a high power density motor for electric vehicle integrated motor drive system. The motor for the system is a five-phase interior permanent magnet synchronous motor (IPMSM) with a double-layer rotor structure and fractional slot distributed winding. Compared with Ver1.0 motor, Ver2.0 motor power density improves significantly. In order to prevent damage from excessive temperature, a temperature field solution model is established in this article to compare the cooling effect and pressure loss of the spiral, dial, and axial water jackets. The temperature is checked at motor main operating conditions using an optimal cooling structure. Finally, the power density of the designed Ver2.0 motor reaches 3.12 kW/kg in mass and 15.19 kW/L in volume.

Study on the bistable vibration behaviour of a rod-fastened rotor-bearing system.

Gas turbine generator sets are widely used in IGCC system, gas-steam combine cycle, distributed energy system et al. for its advantages of low pollution, high efficiency, quick start and stop. The structure of gas turbine rotor can be divided into integral rotor and rod-fastened rotor. Experimental study shows that the vibration signal, especially the displacement signal, of the rod-fastened rotor will increase/decrease greatly in a small interval of rotating speed. The reason for this phenomenon is the unique structure of the rod-fastened rotor, namely the interfaces between discs. In this paper, based on the Lagrange equation, the equation of motion of a rod-fastened rotor-bearing system considering the damping of the contact interface is established. The bistable behaviour and hysteretic cycle, also called the jumping phenomenon in engineering, are revealed. In addition, a test bench of the rod-fastened rotor-bearing system is built. The bistable behaviour and hysteretic cycle are experimentally proven, and the effect of the eccentric distance of the rotor on the bistable behaviour is experimentally explored.

Rainbow gyroscopic disk metastructures for broadband vibration attenuation in rotors

In the last decade, the study of metastructures has gained increasing attention and its engineering applications for vibration control have been gaining maturity for industrial applications. Remarkably, there is a gap on the application of the former approach for rotating machines yet to be bridged. In this work, we present an investigation on the use of locally resonant metastructures for vibration attenuation on rotating machines. A simple rotor structure with periodically attached, compliantly mounted disk resonators is modelled and its dynamical behaviour is investigated. Both forced harmonic response and modal analyses are explored and a thorough evaluation on the interactions between the resonators and main structure is presented for varying conditions of rotating speed and forward and backward excitations. Periodic and rainbow type of resonators with a gradient spatial profile are considered for translational and rotational resonators. It is shown that the former does not present any gyroscopic effect while the attenuation performance of latter depends on the interaction of the forward and backward resonating modes with the excitation. In addition, the rainbow disk metastructure presented attenuation bands up to 60% larger than the periodic case with the same added mass. The results suggest that the proposed gyroscopic periodic structures can be effectively applied for new alternatives for vibration attenuation in rotors paving the way for further innovative engineering solutions on vibration control in lightweight and high speed hermetic rotating machinery.

Investigation of the effect of demagnetization fault at Line Start AF-PMSM with FEM

In motors containing magnets, irreversible demagnetization failure is one of the factors that negatively affect motor performance. In this study, the traditional Axial Flux Permanent Magnet Synchronous Motor (AF-PMSM) rotor structure was changed and the structure that gained the feature of starting from the line was used. Line Start AF-PMSM with 5.5 kW shaft power has 4 poles and each pole consists of 5 magnets. Demagnetization failure was obtained by the flux values of the magnets in any pole are drawn to zero and virtual demagnetization failure is created at certain rates (20%, 40% and 60%). With FEM, the data of the healthy and faulty motor were obtained. The data are then presented comparatively. Obtained data showed that demagnetization fault in Line Start AF-PMSM negatively affects motor performance, and the results are given in detail in the article. The original aspect of the study is that the demagnetization fault in Line Start AF-PMSM was investigated for the first time with FEM.

A Novel Dual-Stator Vernier Permanent Magnet Machine With Improved Power Factor

A dual-stator Vernier permanent magnet (DSVPM) machine is proposed in this article for improving the power factor. Compared with the conventional single-stator Vernier permanent magnet (SSVPM) machine with the surface-mounted permanent magnet rotor, the proposed DSVPM machine has the higher power factor and the overload capacity. The reason for the higher power factor and the overload capacity in DSVPM machines is explained theoretically in this article by air gap permeance theory, and the advantages of the power factor and overload capacity of DSVPM machine are verified by the finite element analysis (FEA) through 18-slots and 34-poles SSVPM and DSVPM FEA model. The rotor eddy current losses, core losses and magnet demagnetization ratio of the DSVPM and SSVPM machines are also studied in this article, the FEA results reveal eddy current and core losses and magnet demagnetization ratio are all lower in the proposed DSVPM machine. The power factor of DSVPM machine variation with the magnet thickness and pole ratio (the ratio of the rotor pole pair number to the stator pole pair number) is also researched by the theoretical and FEA methods. In this article, a surface-mounted permanent magnet machine with fractional-slot concentrated-winding is designed to compare the torque density and cost with DSVPM machine. The sandwiched rotor structure of the proposed DSVPM machine is discussed and the structural analysis by three-dimensional FEA is carried out to prove the feasibility of rotor support, the result reveal that the rotor structure has the sufficient strength.

SMC Development Guidelines for Axial Flux PM Machines Employing Coreless Rotor Structure for Enhancing Efficiency Based on Experimental Results

In recent years, there has been growing demand for flat electrical machines in order to minimize system size while also maintaining high efficiency. In general, axial flux machines (AFMs) are more suitable for flat form than radial flux machines (RFMs). AFMs usually employ a soft magnetic composite (SMC) for the stator core, and their efficiency can be improved by employing an SMC that has low iron loss. However, this reduces the average torque because there is generally a tradeoff relationship between iron loss and magnetic permeability in SMCs. This article, therefore, proposes an AFM with a coreless rotor structure in which the torque performance is not easily affected by the permeability of the SMC. This article aims to reveal the ideal SMC characteristics for high efficiency in AFMs. First, many virtual SMC materials with different iron loss and permeability are used for simulations of AFMs in order to investigate sensitivity to material properties. The simulations by virtual SMCs take into account the experimental increase in the iron loss. As a result, guidelines for developing SMCs are constructed based on the experimental results. Finally, prototype AFMs employing new SMCs developed by following the guidelines are shown, and it is found that they offer higher efficiency in all operating area than conventional AFMs. In particular, one prototype achieves an extremely high efficiency of over 96% at 6000 r/min, 0.8 Nm in experiments.

Hybrid-Excited Permanent Magnet-Assisted Synchronous Reluctance Machine

This paper presents the results of simulation tests of a unique hybrid-excited permanent magnet machine operating in in different working regimes. The common feature of analyzed machine is a presence of magnetic barriers in the rotor structure. Structurally, this machine combines the advantages of the PMa-SynRM machine (Permanent Magnet-assisted Synchronous Machine) and a wound synchronous machine. The paper presents, among other results, the voltage and torque characteristics as a function of the current in the stator and the additional DC control coil. Selected results of experimental studies are also shown.

Flux-Barrier Design and Torque Performance Analysis of Synchronous Reluctance Motor with Low Torque Ripple

In this paper, an improved rotor structure with cross-shaped flux-barriers was proposed to improve the torque output capacity and reduce the torque ripple of the synchronous reluctance motor (SynRM). Firstly, an improved rotor structure of synchronous reluctance motor with cross-shaped flux-barriers, which can be described by two main parameters, is presented. Second, the improved motor is qualitatively analyzed by using magnetic equivalent circuit (MEC), and then the effects of the main parameters of the improved flux-barriers on the distribution of air-gap flux density, average torque, and torque ripple were analyzed by using the finite element method. Based on the above analysis, the rotor structure parameters of the proposed cross-shaped flux-barriers were obtained, and the performance was compared with that of the initial motor. The results show that the proposed rotor structure with cross-shaped flux-barriers can significantly reduce the torque ripple and increase the average torque.

R-D-A and R-D-π-A Structured AIEgens: Relationship between Electronic, Conformational Characteristics and Photophysical Properties.

The design of new aggregation-induced emission luminogens (AIEgens) has aroused continuous attention. The relationship between structure and performance plays an important role in guiding such efforts. In this contribution, two R-D-A- and R-D-π-A-type AIEgens were facilely designed and synthesized, that is, DPE-PTZ-CN and DPE-PTZ-PCN, with diphenylethylene as the twisted rotor structure (R), phenothiazine as electron-donor (D), and the (aryl) cyano group as electron-acceptor (A) fragments. Both luminophores were endowed with typical AIE properties, while their αAIE (PL intensity ratio of AIEgen in a mixed solution with water fraction (fw) = 90 vol % to that with fw = 0) were quite different. The αAIE for DPE-PTZ-CN was as high as 41, but it was only 3 for DPE-PTZ-PCN, in which the π-bridge (aryl linker) was introduced between its D and A groups. In addition, the push-pull electronic effect endowed both molecules with the feature of intramolecular charge transfer (ICT). The solvatochromism effect observed in solutions with different polarities confirmed the existence of the ICT process. The theoretical calculation and single crystal structure analysis revealed that the electronic structure and molecular conformation characteristics had a decisive influence on the differences in photophysical behaviors.

Comparative Study of Non-Rare-Earth and Rare-Earth PM Motors for EV Applications

Recently, non-rare-earth motors are attracting more and more attention due to the booming of the electric vehicle (EV) market and, more importantly, the increasing price of the rare-earth magnet material. This paper focuses on the performance comparison among a commercial interior permanent magnet (IPM) motor and two non-rare-earth motors, including a synchronous reluctance motor (SynRM) and a permanent-magnet-assisted synchronous reluctance motor (PMaSynRM). The design procedure to develop a high-torque-density, low-torque-ripple and high-efficiency SynRM is presented. Combined with a developed automatic modeling and simulation procedure, the finite element analysis (FEA)-based differential evolution (DE) algorithm is introduced for the SynRM rotor optimization. In order to fully inspire the potential of the SynRM, a novel method to optimize the motor split ratio is proposed under the constraint of the copper loss. In addition, different slot–pole combinations are investigated to maximize the motor torque, and the rotor structure is also dealt with towards the centrifugal stress at the maximum operating speed. Finally, the motor performance comparison is carried out, and the results show that although the SynRM achieves almost 61% cost savings, its poor torque capability, power factor and flux weakening (FW) capability are non-negligible defects. On the contrary, the PMaSynRM exhibits excellent features for the EV applications in terms of cost, torque density, efficiency and FW capability. This paper presents a novel split ratio optimization method for the optimal SynRM/PMaSynRM design and demonstrates the characteristics of the IPM motors, SynRMs and PMaSynRMs for EV applications.

Design optimization with improved torque performance of a new flux-intensifying PMSM using multilayer barriers for solar water pumps

A novel flux-intensifying interior (FII) permanent magnet synchronous motor (PMSM) based on multilayer barriers in rotor structure with improved torque performance for solar water pump system is proposed here. The conventional interior (CI) PMSM generates maximum total torque on application of negative current along d-axis, resulting in an increment of demagnetization possibility of permanent magnets (PMs). Although flux-intensifying PMSMs solve this issue, their reluctance torque is lower due to the reduced saliency difference. This problem is solved by the presented FII-PMSM, which produces higher reluctance torque through specially designed barriers. Two types of barriers namely, inner and outer cutoff barriers are designed in rotor along quadrature axis. The inner barriers realize flux-intensifying effect while the outer cutoff barriers increase the saliency difference and hence the reluctance torque. Besides, the dimensions of barriers are optimized by using parametric optimization to maximize saliency difference and minimize torque ripples. The finite element methods based electromagnetic performances of FII-PMSM like inductance curves, torque profiles, airgap gap flux density, back electromotive force plots, efficiency map, output power map and PM flux density are obtained and compared with the CI-PMSM to show the superiority of presented motor.