Three dimensional magnetic field computation by a coupledvector-scalar potential method in brushless DC motors with skewedpermanent magnet mounts-the formulation and FE grids

A three dimensional finite element (3D-FE) method for the computation of global distributions of 3D magnetic fields in electric machines containing permanent magnets is presented. The formulation of this 3D-FE method including 3D permanent magnet modeling, which is based on a coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) approach, is given. The development of the necessary 3D-FE grids and algorithms for the application of the method to an example brushless DC motor, whose field is three dimensional due to the skewed permanent magnet mounts on its rotor, is also given here. A complete set of results of application of the method to the computation of the global 3D field distributions and associated motor parameters under no-load and load conditions are detailed in a companion paper     

Analytical calculation of air-gap magnetic field distribution and instantaneous characteristics of brushless DC motors

This paper derives the relative air-gap-specific permeance distribution function by Schwarz-Christoffel transformation, considering the effect of slotting. Neglecting the iron saturation, and employing the analytical algorithm for partial differential equations, efficient and effective analytical calculations of no-load air-gap magnetic field distribution, armature field distribution, and phase electromotive force (EMF), are demonstrated, considering the stator slots. Subsequently, based on the main circuit topology of a brushless DC motor (BLDCM), the field-circuit coupling model is constructed for the motor, and then the phase current waveforms and load air-gap magnetic field distribution at any time are determined. Consequently, the instantaneous electromagnetic torque is computed, which underpins the quantitative analysis of torque ripple and the pulsation induced by commutation. Hence, the present work paves the way to precise prediction of the motor's performance and acoustic noise. It is a powerful tool for the design of surface permanent magnet brushless DC motors.     

Modeling and experimental verification of the performance of a skewmounted permanent magnet brushless DC motor drive with parameterscomputed from 3D-FE magnetic field solutions

This paper contains a comparison between actual laboratory-measured performance of a brushless DC motor drive system, with skewed permanent magnet mounts on its rotor, and two computer-simulated motor drive system performance characteristics. These simulated motor drive system performance results were once obtained using motor parameters computed from rigorous three dimensional-finite element (3D-FE) magnetic field solutions detailed in two companion papers and once obtained using motor parameters from more conventional 2D-FE magnetic field solutions. The comparison demonstrates that 3D-FE based motor parameters lead to drive system performance simulations which are much closer to test results for this type of brushless DC drives with skewed permanent magnet mounts. Torque ripples computed from 3D-FE based and 2D-FE based motor parameters are also included. The results clearly show advantages to basing the drive system simulations on 3D-FE computed motor parameters     

The operation of permanent magnet DC motors powered by a commonsource of solar cells

In a photovoltaic water-pumping system, the solar cell array is usually designed to power a single motor-load pump. Several water-pumping systems of the same or different types that are in close proximity to each other can be powered by separate solar cell arrays (sources) for each one, or, alternatively, by a common solar cell source for all the water pumping systems. The authors introduce a procedure for comparing the performances of these two setups. One system includes a permanent magnet DC motor and a volumetric pump, and the other a permanent magnet DC motor and a centrifugal pump. The comparison was also done for the same systems when a maximum-power point tracker (MPPT) was included for both the separate and the common solar cell source. It is shown, for example, that in systems not including MPPTs the total performance of the two motor-pumps in the common source system is improved as compared to the performance of the two motor-pumps when they are powered separately by individual sources     

Determination of magnetic field constant of DC permanent magnet motor powered by photovoltaic for maximum mechanical energy output

The DC permanent magnet motor coupled with centrifugal pump has the better matching when directly powered by photovoltaic (PV) array. The important parameter of DC permanent magnet (DC PM) motor is magnetic field constant. The method for the determination of optimum magnetic field constant of DC PM motor, when powered by PV, has been obtained, and its analysis has been carried out for different magnetic field constants. It has been found that the maximum output is available at the output-energy-weighted average value of magnetic field constant. The parameter, magnetic field constant, should be properly selected during the design of DC PM motor in order to extract the maximum power from PV array.     

A neuro-fuzzy approach to automatic diagnosis and location of stator inter-turn faults in CSI-fed PM brushless DC motors

The paper presents a neuro-fuzzy-based perspective to the automation of diagnosis and location of stator-winding interturn short circuits in CSI-fed brushless dc motors. Performance of the drive under normal and short-circuit conditions are obtained through classical lumped-parameter network models. Waveforms of the electromagnetic torque and summation of phase voltages are monitored to develop two independent diagnostic algorithms. Diagnostic indices derived from the characteristic waveforms using discrete Fourier transform (DFT) lead to identifying the number of shorted turns. Fault location is achieved through a different set of indices extracted by the short-time Fourier transform (STFT). Adaptive neuro-fuzzy inference systems (ANFIS) are trained based on simulation results to automate the diagnostic process. ANFIS testing along with the good agreement between simulated and measured waveforms show the effectiveness of the proposed techniques.     

Three dimensional magnetic fields in extra high speed modifiedLundell alternators computed by a combined vector-scalar magneticpotential finite element method

A three-dimensional (3-D) finite-element (FE) approach was developed and implemented for computation of global magnetic fields in a 14.3 kVA modified Lundell alternator. The essence of the method is the combined use of magnetic vector and scalar potential formulations in 3-D FEs. This approach makes it practical, using state-of-the-art supercomputer resources, to globally analyze magnetic fields and operating performances of rotating machines which have 3-D magnetic flux patterns. The 3-D FE computed fields and machine inductances as well as various machine performance simulations of the 14.3-kVA machine are presented     

Numerical computation for Rayleigh-Benard convection of water in a magnetic field

The derivation process for the model equation is shown for the natural convection of water (diamagnetic) under both gravity and magnetizing force fields and numerically solved for the Rayleigh-Benard convection in a shallow cylinder heated from below and cooled from above. The cylindrical enclosure was located at two levels in the bore of a super-conducting magnet, where the radial component of the magnetizing force is minimal and its axial component prevails. The cylindrical enclosure was assumed to be located coaxially with the bore of the magnet, and a two-dimensional model equation was presumed. Sample computations were carried out without or with a gravity force for various strengths of Rayleigh number and magnetic induction. When the enclosure was placed above the coil center, where the magnetizing force is opposed to the gravitational force, the average Nusselt number decreased with increasing strength of the magnetic field. When the enclosure was placed below the coil center, where the magnetizing force is parallel to gravity, the average Nusselt number increased above unity even at Ra=1000 and 1500. All of the data agreed favorably with the classical experimental data of Silveston when plotted against the magnetic Rayleigh number proposed by Braithwaite et al.     

Three dimensional lattice Boltzmann simulation for mixed convection of nanofluids in the presence of magnetic field

In the present study, a three dimensional thermal lattice Boltzmann model was developed to investigate the flow dynamics and mixed convection heat transfer of Al₂O₃/water nanofluid in a cubic cavity in the presence of magnetic field. The model was first validated with previous numerical and experimental results. Satisfactory agreement was obtained. Then the effects of Rayleigh number, nanoparticle volume fraction, Hartmann number and Richardson number on nanofluid flow dynamics and heat transfer were examined. Numerical results indicate that adding nanoparticles to pure water leads to heat transfer enhancement for low Rayleigh numbers. However, this enhancement might be weakened and even reversed for high Rayleigh numbers. In addition, the results show the external applied magnetic field has an effect of suppressing the convective heat transfer in the cavity. Moreover, the results demonstrate that the Richardson number in mixed convection has significant influences on both streamlines and temperature field.     

Field distribution and iron loss computation in reluctanceaugmented shaded-pole motors using finite element method

A detailed field distribution in a reluctance augmented shaded-pole motor using the finite-element method is presented. No-load and loaded cases are considered separately. The effect of the shading coil on the spatial distribution of the air-gap flux density is examined, and it is found that the demagnetizing effect of the shading rings contributes to a more uniform distribution of the air-gap flux. Correct paths of various flux linkages and saturating regions are identified. The iron losses are computed using the flux density distribution obtained over the cross section of the machine     

Evaluation of stray load loss in induction motors with a comparison of input-output and calorimetric methods

This paper investigates the input-output and the calorimetric methods of evaluating stray load loss in induction motors. It highlights the difficulties of accurately measuring stray load loss experimentally and thereby declaring the correct machine efficiency. The standard experimental approach of input-output power measurement with loss segregation is widely used but has some limitations. Fifteen induction motors ranging between 11 kW (15 hp) and 200 hp have been carefully studied in this paper mainly using IEEE 112 Method B. Additional results obtained by calorimetric methods have been used to validate the standard test methods. The objectives of this paper are to quantify the stray load loss, to identify possible sources of error in such a process, and to provide indications of how some of these errors may be mitigated. The conclusion drawn confirms that the only valid way is to evaluate stray load loss directly and any arbitrary allowance for stray load loss is unfounded. The importance of this work is in improving measurement techniques and instrumentation accuracy.     

An investigation of compressible forced convection in a three dimensional tapered chimney by CUDA computation platform

Compressible forced convection in a three dimensional tapered chimney is investigated numerically. Schemes of Roe and preconditioning are adopted to resolve compressible flow problem under a low speed velocity situation. Coordinates transformation of algebraic grid generation and non-reflecting boundary condition is used to execute the coordinated transformation of the tapered duct and decrease the computation domain, respectively. Computing procedures are performed on the CUDA computation platform which is developed recently and is a very effective tool. Due to the variation of the geometry of three dimensional tapered chimney, the flow velocity increases in the central region and decreases near the corner region. Therefore, heat transfer rates are enhanced remarkably in the central region and become inferior abruptly near the corner region. The efficiency of CUDA computation platform is marvelous, and the possibility of capability of super computation of individualization may be realized by using the CUDA computation platform.     

Effect of magnetic field on radial dopant segregation in crystal growth by traveling heater method

A three dimensional time dependent computational model is developed to simulate the melt flow, heat transfer and the dopant transport during the growth of Si_1?xGe_x semiconductor crystals by traveling heater method. The effect of static magnetic fields of different orientations on the radial and axial segregation of dopant is analyzed. It is observed that the flow oscillations are damped and flow becomes steady for both horizontal and vertical applied magnetic fields as the Hartmann number increases. It is found that there is an optimum value of Hartmann number beyond which little improvement in uniformity of concentration can be obtained at the growth interface.     

Solutocapillary convection in the float-zone process with a strong magnetic field

This paper treats the steady axisymmetric flow and mass transport in a cylindrical liquid bridge between the melting end of a feed rod and the solidifying end of an alloyed semiconductor crystal. There is a strong, uniform, steady, axial magnetic field. The surface tension depends on the temperature and the concentration of the species, while variations of the concentration occur because one species is rejected into the liquid during solidification. The thermocapillary and solutocapillary convections tend to cancel over part of the liquid bridge. For certain parameter ranges, there are two different stable solutions: one where the concentration gradient along the free surface leads to dominance by the solutocapillary convection and one where the mass transport due to the thermocapillary convection makes the concentration gradient along the free surface small, so that the thermocapillary convection is dominant.     

某16缸柴油机冷却系统一维与三维联合仿真

标定工况下,对某16缸机车用柴油机进行联合仿真。利用GT—cool软件对柴油机整体进行一维仿真,得到冷却系统各个管路和机体的流量、温度和压力等数据,然后将一维仿真的结果作为边界条件,采用ANSYSCFX软件对冷却效果最差的第8缸进行冷却水三维仿真,得到此缸冷却水的内部流场、温度场和压力场,最后得出结论：排气管冷却水道两侧棱角处温度过高,存在流动死区,需进行冷却优化。实例表明,联合仿真可用于工程计算,能满足精度要求。     

Effect of static magnetic field on thermal conductivity measurement of a molten Si droplet by an EML technique: Comparison between numerical and experimental results

In order to investigate quantitatively the effect of melt convection in an electromagnetically levitated molten droplet on the thermal conductivity of liquid silicon measured by the electromagnetic levitation (EML) technique superimposed with a static magnetic field, the numerical simulations for melt convection in the droplet and additionally, for the measurement of thermal conductivity were carried out. In addition, the thermal conductivity of molten silicon was measured by the EML technique, and then compared with those obtained numerically. In the numerical simulations of melt convection, the buoyancy force, thermocapillary force due to the temperature dependence of the surface tension on the melt surface, and electromagnetic force in the droplet were considered as the driving forces of convection. As a result, the numerical simulations could sufficiently explain the measurement of thermal conductivity by the EML technique under a static magnetic field. Also, it was suggested that a magnetic field of more than 4 T should be applied to measure the real thermal conductivity of molten silicon by the EML technique.     

Numerical solution of power law fluids flow and heat transfer with a magnetic field in a rectangular duct

The steady laminar flow and heat transfer of an incompressible, electrically conducting, power law non-Newtonian fluids in a rectangular duct are studied in the presence of an external uniform magnetic field. The momentum and energy equations are solved iteratively using a finite difference method. Two cases of the thermal boundary conditions are considered; (1) T thermal boundary condition “constant temperature at the wall” and (2) H2 thermal boundary condition “constant heat flux at the wall”. The viscous and Joule dissipations are taken into consideration in the energy equation. A numerical solution for the governing partial differential equations is developed and the influence of the magnetic field on the velocity distribution, the friction factor and the average Nusselt number are discussed.     

Three Dimensional Separation with Spiral—Focus in a Decelerating Duct Flow （Effect of Asymmetric Inlet Boundary Layer Thickness）

An experimental apparatus was developed to study the three dimensional separated flow with spiral-foci. The internal decelerating flow was generated by the air suction from a side wall to produce the separation on an opposite-side wall. The relation between the upstream boundary layer and the generation of spiral-foci in the separation region was observed by a tuft method. As a result, it was clarified that the spiral-focus type separation could be produced on the side wall and its behavior was closely related to the vortices supplied into the separation region from the boundary layer developing along top wall or bottom one.     

Cogging torque reduction in axial-flux permanent magnet wind generators with yokeless and segmented armature by radially segmented and peripherally shifted magnet pieces

The inherent cogging torque component of the PM generators can cause problems at the start-up of wind turbines. To improve the operation of wind turbines, especially at low starting speeds, the wind generator cogging torque should be minimized. In this paper, an effective and practical approach is proposed for cogging torque reduction in the AFPM generators with yokeless and segmented armature (YASA). The proposed approach is based on the dividing magnets radially and shifting the magnet pieces peripherally with an appropriate shifting angle. Using a series of 3-D FEA simulations, the proposed approach is compared with the two conventional approaches, i.e. the magnet skewing approach and the selecting an appropriate magnet pole arc to pole pitch ratio, according to the cogging torque reduction and the negative impacts on the generator loadability. It is shown that using the proposed approach, the generator cogging torque can be greatly reduced (about 87%). Also, it is shown that compared with the other studied cogging torque reduction techniques, the proposed approach has less negative impact on the generator loadability. Some of the simulation results are verified using the experimental tests.     

Buoyancy and surface tension driven flows in float zone crystal growth with a strong axial magnetic field

The buoyancy driven flow due to the temperature gradient in the melt of a float zone and the surface tension driven flow due to the non-uniform temperature distribution along the free surface of the zone are studied in the presence of a strong axial magnetic field. The non-cylindrical shape of the zone is found to have a profound effect on the melt motion. The results indicate that the regions near the free surface are controlled mainly by the thermocapillarity, while the inner region is dominated by the buoyancy driven flow. Some implications for the mass transport of dopants in the molten float zone are discussed.