Electromagnetic Performance Analysis of Variable Flux Memory Machines with Series-magnetic-circuit and Different Rotor Topologies

In this paper,the electromagnetic performance of variable flux memory(VFM)machines with series-magnetic-circuit is investigated and compared for different rotor topologies.Based on a V-type VFM machine,five topologies with different interior permanent magnet(IPM)arrangements are evolved and optimized under same constrains.Based on two-dimensional(2-D)finite element(FE)method,their electromagnetic performance at magnetization and demagnetization states is evaluated.It reveals that the iron bridge and rotor lamination region between constant PM(CPM)and variable PM(VPM)play an important role in torque density and flux regulation(FR)capabilities.Besides,the global efficiency can be improved in VFM machines by adjusting magnetization state(MS)under different operating conditions.

Comparative Study of Linear Variable Flux Reluctance Machine with Linear Wound Field Flux Reversal Machine

As members of doubly salient magnetless linear machines,linear variable flux reluctance(LVFR)and wound field flux reversal(LWFFR)machines inherit the merits of conventional magnetless linear machines such as low cost,high flux adjustment capability and high reliability.Furthermore,like linear switched reluctance machine,they have a very simple and compact long secondary,which are very attractive for long stroke applications.However,low force capability is their major defect.To solve this issue,new LVFR and LWFFR machine topologies were proposed in recent work,while lacking studies on their force improvement mechanism and further force evaluation.In this paper,LVFR and LWFFR machines with improved force performance are comparatively studied with the emphasis on their force capabilities.The operation principle of the two machines is analyzed based on magnetic field harmonics produced by flux modulation.Contributions of air-gap flux density harmonic components to no-load back electromagnetic forces of the two machines are analyzed and the average force equation is derived.Moreover,force capabilities of the both machines are investigated by means of the time-stepping finite-element analysis to verify the theoretical analysis.

Recent Advances in Variable Flux Memory Machines for Traction Applications: A Review

This paper overviews the recent advances in variable flux memory machines(VFMMs)for traction applications with particular reference to newly emerged machine topologies and related control strategies.Due to the use of flux memorable low coercive force(LCF)magnets,the air-gap flux of VFMM can be flexibly varied via a magnetizing current pulse.Thus,the copper loss associated with the flux weakening current and high-speed iron loss can be significantly reduced,and hence high efficiency can be achieved over a wide speed and torque/power operation.These merits make VFMM potentially attractive for electric vehicle(EV)applications.Various novel VFMMs are reviewed with particular reference to their topologies,working principle,characteristics and related control techniques.In order to tackle the drawbacks in the existing VFMMs,some new designs are introduced for performance improvement.Then,the electromagnetic characteristics of an exemplified EV-scaled switched flux memory machine and various benchmark traction machine choices,such as induction machine,synchronous reluctance machines,as well as commercially available Prius 2010 interior permanent magnet(IPM)machine are compared.Finally,the key challenges and development trends of VFMM are highlighted,respectively.

Research on DTC System with Variable Flux for Switched Reluctance Motor

When switched reluctance motor(SRM)is in the status of the traditional direct torque control(DTC)system,due to the high saturation nonlinearity of the electromagnetic relationships of switched reluctance motors,the torque ripple and the stator phase current are larger.In order to resolve the above problems,through the analysis and deduction for SRM flux model and the influence of characteristics of flux and speed on torque ripple,this paper presents a variable-flux control strategy with the three closed-loop structure based on the critical flux supersaturated speed.And a DTC system of SRM with variable flux and three closed-loop is built up in Matlab/simulink.Moreover,the DSP hardware experiment platform based on the TMS320F2812 is established to validate the performance of the improved algorithm.The simulation and experimental results show that the new scheme has an obvious effect on torque ripple reduction,and the three-phase stator current is obviously reduced,which greatly reduces the stator winding copper consumption during the operation of SRM.Moreover,the improved system has good system stability.

Analysis of a Novel Mechanically Adjusted Variable Flux Permanent Magnet Homopolar Inductor Machine with Rotating Magnetic Poles for Flywheel Energy Storage System

Permanent magnet homopolar inductor machine(PMHIM) has attracted much attention in the field of flywheel energy storage system(FESS) due to its merits of simple structure,brushless excitation, and rotor flywheel integration. However, the air-gap flux generated by the PM cannot be adjusted, which would cause large electromagnetic losses in the standby operation state of FESS. To solve this problem, a novel mechanically adjusted variable flux permanent magnet homopolar inductor machine with rotating magnetic poles(RMP-PMHIM) is proposed in this paper. The permanent magnet poles are rotated by an auxiliary rotating device and the purpose of changing the air-gap flux is achieved. First, the structure and operation principle of the proposed RMP-PMHIM are explained. Second,the flux weakening principle of the RMP-PMHIM is analyzed and the equivalent magnetic circuit models under different flux weakening states are built. Third, the parameters of the PM and its fixed structure are optimized to obtain the good electromagnetic performance. Fourth, the electromagnetic performance, including the air-gap flux density, back-EMF, flux weakening ability, loss, etc. of the proposed RMP-PMHIM are investigated and compared. Compared with the non-rotating state of the PM of RPM-PMHIM, the air-gap flux density amplitude can be weakened by 99.95% when the PM rotation angle is 90 degrees, and the no-load core loss can be suppressed by 99.98%,which shows that the proposed RPM-PMHIM is a good candidate for the application of FESS.

Fast Design Method of Variable Flux Reluctance Machines

In this paper,a fast design method is developed based on a combination of analytical and finite element(FE)methods for variable flux reluctance machines(VFRMs).Firstly,the feasibility of using analytical method in optimization under unsaturated condition is confirmed.Then,by applying the FE method,the influence of magnetic saturation is considered.Compared with the unsaturated case,the optimal split ratio for magnetically saturated case is increased by 1~1.2 times,the optimal rotor pole arc ratio varies within 0.33~0.44,and the stator pole arc ratio remains the same.Based on this,the optimal structural parameters can be initially set by analytical method and then refined by the FE method.Due to the fast speed of analytical method,less variable counts and narrowed variation ranges,the proposed method is significantly faster than the conventional pure FE based global optimization.Finally,the proposed method is used for optimizing the 6-stator-slots VFRMs having different numbers of rotor poles.The 6-stator-slot/7-rotor-pole(6s/7r)VFRM is found to have the highest torque density.It is prototyped and tested to verify the analyses.

Design and Analysis of Wide Speed Regulation of Variable Leakage Flux Reverse Salient-pole Motor

In this article, a new variable leakage flux reverse salient-pole motor(VLF-RSPM) is raised to widen the speed range. The innovation is to realize both reverse salient-pole characteristics and variable leakage flux characteristics by using a method of adding magnetic bridges and magnetic barriers. Firstly, the evolution of the topological structure and working principle of the motor are introduced. Secondly, based on 2D Finite Element Analysis(FEA), the electromagnetic properties and noise of the motor are analyzed in detail, and the electromagnetic properties are contrasted with that of the conventional V-type synchronous motor(CVTSM). The results show that VLF-RSPM has the advantages of small torque ripple, strong magnetic weakening ability, low noise, high efficiency, and low risk of permanent magnet demagnetization under different conditions. In addition, it is verified that the proposed motor extends the speed range.

Variable fluid properties and variable heat flux effects on the flow and heat transfer in a non-Newtonian Maxwell fluid over an unsteady stretching sheet with slip velocity

The effects of variable fluid properties and variable heat flux on the flow and heat transfer of a non-Newtonian Maxwell fluid over an unsteady stretching sheet in the presence of slip velocity have been studied. The governing differential equations are transformed into a set of coupled non-linear ordinary differential equations and then solved with a numerical technique using appropriate boundary conditions for various physical parameters. The numerical solution for the governing non-linear boundary value problem is based on applying the fourth-order Runge-Kutta method coupled with the shooting technique over the entire range of physical parameters. The effects of various parameters like the viscosity parameter, thermal conductivity parameter, unsteadiness parameter, slip velocity parameter, the Deborah number, and the Prandtl number on the flow and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed. Comparison of numerical results is made with the earlier published results under limiting cases.

Effect of slip velocity on Casson thin film flow and heat transfer due to unsteady stretching sheet in presence of variable heat flux and viscous dissipation

The aim of the present paper is to study flow and heat transfer charac- teristics of a viscous Casson thin film flow over an unsteady stretching sheet subject to variable heat flux in the presence of slip velocity condition and viscous dissipation. The governing equations are partial differential equations. They are reduced to a set of highly nonlinear ordinary differential equations by suitable similarity transformations. The re- sulting similarity equations are solved numerically with a shooting method. Comparisons with previous works are macle, and the results are found to be in excellent agreement. In the present work, the effects of the unsteadiness parameter, the Casson parameter, the Eckert number, the slip velocity parameter, and the Prandtl number on flow and heat transfer characteristics are discussed. Also, the local skin-friction coefficient and the local Nusselt number at the stretching sheet are computed and discussed.

Numerical Study by Imposing the Finite Difference Method for Unsteady Casson Fluid Flow with Heat Flux

This article presents an investigation into the flow and heat transfer characteristics of an impermeable stretching sheet subjected to Magnetohydrodynamic Casson fluid. The study considers the influence of slip velocity, thermal radiation conditions, and heat flux. The investigation is conducted employing a robust numerical method that accounts for the impact of thermal radiation. This category of fluid is apt for characterizing the movement of blood within an industrial artery, where the flow can be regulated by a material designed to manage it. The resolution of the ensuing system of ordinary differential equations (ODEs), representing the described problem, is accomplished through the application of the finite difference method. The examination of flow and heat transfer characteristics, including aspects such as unsteadiness, radiation parameter, slip velocity, Casson parameter, and Prandtl number, is explored and visually presented through tables and graphs to illustrate their impact. On the stretching sheet, calculations, and descriptions of the local skin-friction coefficient and the local Nusselt number are conducted. In conclusion, the findings indicate that the proposed method serves as a straightforward and efficient tool for exploring the solutions of fluid models of this kind.

Hybrid Excitation Flux Switching Motor with Permanent Magnet Placed at Middle of Field Coil Slots and High Filling Factor Windings

Design and experimental studies on a hybrid excitation flux switching motor as a traction motor for hybrid electric vehicles drive are presented.A stator body of the motor consists of not only laminated silicon-iron electromagnetic steel and three-phase armature windings,but also both of field excitation coils and permanent magnets working together as a variable field magnetomotive force source.On the other hand,a rotor is composed of just laminated silicon-iron electromagnetic steel with salient poles like switched reluctance motor.To bring out the best in drive performances of the hybrid excitation flux switching motor as a variable flux motor for the application,each material adopted for the stator and rotor body should be designed properly in terms of motor efficiency,maximum torque and power densities and so forth.As some of them,in this paper,thinner silicon-iron electromagnetic steel sheet and permanent magnets with high remanent and low amount of Dysprosium used are applied for achieving higher motor efficiency.Moreover,all coils wound flatwise and edgewise using rectangular wires are introduced to realizing high filling factor for reduced copper losses.Experimental tests using a 60kW prototype of the motor demonstrates the designed motor has good motor efficiency under frequent operating points expected for the target vehicle drive.

Investigation and Regulation of High-efficiency Region Boundary of Variable Magnetic Flux Permanent Magnet Motor

With the increasing complexity of electrical vehicles(EVs),the wide-speed-range high-efficiency characteristics of EV drive motors are in strict demand.In this study,the variable magnetic flux effect is introduced into a permanent magnet(PM)motor,and a variable magnetic flux permanent magnetic(VMF-PM)motor is proposed.First,the flux is adjusted flexibly to synchronously broaden the speed regulation range and high-efficiency region.Subsequently,an efficiency analytical model is developed considering the motor speed,current,and flux variations.It is indicated that by the purposeful design of the variable flux leakage topology,the efficiency under high speed can be improved based on a theoretical investigation of the high-efficiency boundary.In addition,based on finite element analysis,the performances before and after optimization of the key parameters of the VMF-PM motor are investigated,including the flux variable characteristics and efficiency characteristics.Finally,a prototype motor is built and tested.Both theoretical analysis and experimental results confirm that based on the assistance of the variable magnetic flux effect,the motor high-efficiency region is broadened effectively,providing a potential research path for designing a wide-speed-range high-efficiency motor.

Variability in Latent Heat Flux over the Tropical Pacific in Association with Recent Two ENSO Events

This paper analyzed the variations of latent heat flux (LHF) over the tropical Pacific in the period 1978-1988 by using COADS (Comprehensive Ocean and Atmospheric Data Set). It has been founded that the interannual variabili ty of LHF exhibits strong ENSO signal, with the significant increasing LHF during the recent two warm events, i.e., 1982 / 83 and 1986 / 87 and decreasing LHF in the cold episodes. However the longitudinal distribution of the LHF departures varies from event to event. In the eastern Pacific, the specific humidity difference at air-sea interface (qs -qa) makes a dominant contribution to the interannual variability of LHF ( r = 0.73 ), while in the western Pacific the surface wind speed, W and the qs - qa make nearly equal contribution to that of LHF.

Hydromagnetic Nanofluid Film Flow over a Stretching Sheet with Prescribed Heat Flux and Viscous Dissipation

Thermal radiative heat transfer through a thin horizontal liquid film of a Newtonian nanofluid subjected to a magnetic field is considered.The physical boundary conditions are a variable surface heat flux and a uniform concentration along the sheet.Moreover,viscous dissipation is present and concentration is assumed to be influenced by both thermophoresis and Brownian motion effects.Using a similarity method to turn the underlying Partial differential equations into a set of ordinary differential equations(ODEs)and a shooting technique to solve these equations,the skin-friction coefficient,the Nusselt number,and the Sherwood number are determined.Among other things,it is shown that large values of the thermal radiation heat transfer rate,thermal conductivity parameter,and the Brownian motion parameter can enhance the cooling of the sheet.

Variable-Flux Outer-Rotor Permanent Magnet Synchronous Motor for In-Wheel Direct-Drive Applications

In-wheel direct-drive is the most efficient driving mode for electric vehicles,and it is the trend for applications in the future.In this paper,a novel variable-flux outer-rotor permanent magnet synchronous motor with a hybrid magnetic structure design is developed.Due to the hybrid magnetic pole with Nd-Fe-B and Al-Ni-Co permanent magnet(PM),the air-gap flux can be adjusted by changing the magnetization states of Al-Ni-Co PM,which is beneficial to realize a wide range of speeds and loads from the electromagnetic structure design.Firstly,basic structure features of the motor and the flux-adjusting principle are introduced.The design and calculation method of the PM dimensions is derived based on magnetic circuit analysis.Then the Preisach hysteresis model of Al-Ni-Co PM is described and is adopted to analyze the motor performance with the coupling of the time step finite element method(FEM),and the magnetization are investigated.Finally,the operational performance of the proposed motor is obtained by simulation,which verifies the design.

Quantitative Comparison of Electromagnetic Performance of Electrical Machines for HEVs/EVs

In this paper,various types of sinusoidal-fed electrical machines,i.e.induction machines(IMs),permanent magnet(PM)machines,synchronous reluctance machines,variable flux machines,wound field machines,are comprehensively reviewed in terms of basic features,merits and demerits,and compared for HEV/EV traction applications.Their latest developments are highlighted while their electromagnetic performance are quantitatively compared based on the same specification as the Prius 2010 interior PM(IPM)machine,including the torque/power-speed characteristics,power factor,efficiency map,and drive cycle based overall efficiency.It is found that PM-assisted synchronous reluctance machines are the most promising alternatives to IPM machines with lower cost and potentially higher overall efficiency.Although IMs are cheaper and have better overload capability,they exhibit lower efficiency and power factor.Other electrical machines,such as synchronous reluctance machines,wound field machines,as well as many other newly developed machines,are currently less attractive due to lower torque density and efficiency.

Effects Viscous Dissipation on the Asymptotic Behaviour of Laminar Forced Convection for HerscheI-Bulkley Fluid in a Circular Duct

The asymptotic behaviour of laminar forced convection in a circular duct, for a Herschel-Bulkley fluid with constant properties, is analysed by taking into account the viscous dissipation effects. The axial heat conduction in the fluid is neglected. The asymptotic temperature field and the asymptotic value of the Nusselt number are determined for every boundary condition that allows a fully developed region. Comparisons with other existing solutions for Newtonian and non-Newtonian cases are presented.

Seasonally evolving dominant interannual variability mode of air-sea CO2 flux over the western North Pacific simulated by CESM1-BGC

We applied a season-reliant empirical orthogonal function(S-EOF) analysis based on the results of the Community Earth System Model, version 1-Biogeochemistry, to seasonal mean air-sea CO_2 flux over the western North Pacific(WNP)(0°–35°N, 110°E–150°E). The first leading mode accounts for 29% of the total interannual variance, corresponding to the evolution of the El Ni-Southern Oscillation(ENSO) from its developing to decaying phases. During the ENSO developing phase in the summer and fall, the contribution of surface seawater CO_2 partial pressure anomalies is greater than that of gas transfer/solubility anomalies, which contribute to increasing oceanic CO_2 uptake over the WNP. During the ENSO mature phase in the winter, the anomalous southwesterly northwest of the western North Pacific anticyclone(WNPAC) reduces the surface wind speed in the China marginal sea and thus decreases oceanic CO_2 uptake by reducing the gas transfer coefficient. In the subsequent spring, the WNPAC maintains with an eastward shift in position. The anomalous southwesterly warms sea surface temperatures in the China marginal sea by reducing evaporation and thus decreases oceanic CO_2 uptake by enhancing surface seawater CO_2 partial pressure. This process, rather than the effect of decreasing gas transfer coefficient, dominates CO_2 flux anomalies in the spring.

Analysis on capabilities of density-based solvers within OpenFOAM to distinguish aerothermal variables in difusion boundary layer

Open source feld operation and manipulation（OpenFOAM）is one of the most prevalent open source computational fluid dynamics（CFD）software.It is very convenient for researchers to develop their own codes based on the class library toolbox within OpenFOAM.In recent years,several density-based solvers within OpenFOAM for supersonic/hypersonic compressible flow are coming up.Although the capabilities of these solvers to capture shock wave have already been verifed by some researchers,these solvers still need to be validated comprehensively as commercial CFD software.In boundary layer where diffusion is the dominant transportation manner,the convective discrete schemes＇capability to capture aerothermal variables,such as temperature and heat flux,is different from each other due to their own numerical dissipative characteristics and from viewpoint of this capability,these compressible solvers within OpenFOAM can be validated further.In this paper,frstly,the organizational architecture of density-based solvers within OpenFOAM is analyzed.Then,from the viewpoint of the capability to capture aerothermal variables,the numerical results of several typical geometrical felds predicted by these solvers are compared with both the outcome obtained from the commercial software Fastran and the experimental data.During the computing process,the Roe,AUSM＋（Advection Upstream Splitting Method）,and HLLC（Harten-Lax-van Leer-Contact）convective discrete schemes of which the spatial accuracy is 1st and 2nd order are utilized,respectively.The compared results show that the aerothermal variables are in agreement with results generated by Fastran and the experimental data even if the1st order spatial precision is implemented.Overall,the accuracy of these density-based solvers can meet the requirement of engineering and scientifc problems to capture aerothermal variables in diffusion boundary layer.