基于摄动法的表贴式永磁电机转子偏心空载气隙磁场计算

采用摄动法解析计算表贴式永磁电机转子偏心空载气隙磁场,以无量纲的偏心扰动量作为摄动变量,可解决表贴式永磁电机内转子结构和外转子结构的转子偏心磁场解析问题。根据气隙区域及永磁体区域的边界条件求解拉普拉斯方程和泊松方程,通过矢量磁位推导出气隙磁通密度的解析表达式,进而应用麦克斯韦应力张量法计算不平衡磁拉力,并将解析法结果与有限元法结果进行比较,发现二者一致性较好,验证了该方法的正确性和有效性。     

Octagonal Halbach Magnet Array Design for a Magnetic Refrigerator

An effective magnet array design for magnetic refrigeration systems is crucial given the space limitations and need for maintaining the required cooling capacity. Here, Halbach permanent magnet arrays (HPMA) in an octagonal orientation are studied using NdFeB permanent magnets. Gadolinium is selected as the magnetocaloric material (MCM) for the aperture inside the octagonal HPMA. The optimum outer-to-inner radii ratio for the octagonal HPMA and MCM system is found to be 2, at which the cooling energy per volume of magnet has a peak. For this ratio, the effect of using soft magnetic material, which in this study is FeVCo, inside and outside the HPMA is evaluated over a range of material thicknesses. The optimum soft magnetic material thickness outside the HPMA is obtained to be 3% of the external radius. At this thickness, soft magnetic material is also placed inside the array as a concentrator. It is found that although using soft magnetic material inside the magnet array increases the average flux, cooling energy is decreased due to using less MCM inside the aperture because of the space occupied by the soft magnetic material.     

Asynchronous Performance Prediction of AC Permanent Magnet Motor

many permanent magnet synchronous motors are run up from standstill by a sudden connection with an ac supply. The cage windings in rotor slots produce induction motor torque to run up the rotor, but two torque dips are produced in the torque-slip curve of the permanent magnet motor; one is caused by the rotating permanent magnet, and the other by the magnetic and the electric asymmetry between the direct and quadrature axes. Therefore, the prediction of the asynchronous performance is very important, as motors cannot be run up, unless the minimum values of the torque dips exceed the load torques at the slips. In this paper, ``harmonic permeance coefficient' is newly introduced, which is used to combine the finite element field solution with the calculation of air gap inductance, and equations for the calculation of asynchronous performance of permanent magnet motors are also expressed. The calculated value by these equations agreed well with the experimental results.     

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.     

Design criteria for high-efficiency SPM synchronous motors

This paper deals with the design criteria for a high-efficiency permanent magnet synchronous motor. The goal is not pursued by a trivial reduction of the electric and magnetic loadings (which decrease motor losses) but optimizing a set of motor design variables, without increasing the overall dimensions, which are typically imposed as design constraints. The effect of the number of slots and of the inner-to-outer diameter ratio on motor losses is investigated. The possibility of designing a stator with a tooth length lower than the total core length, using soft magnetic composites, is studied. Finally, a criterion is proposed to evaluate the convenience of using a nonoverlapping winding. An analytical approach is adopted so as to allows the obtained results to be useful for a wide variety of permanent magnet machines.     

Analytical model for permanent magnet motors with surface mounted magnets

This paper presents an analytical method of modeling permanent magnet (PM) motors. The model is dependent only on geometrical and materials data which makes it suitable for insertion into design programs, avoiding long finite element analysis (FEA) calculations. The modeling procedure is based on the calculation of the air gap field density waveform at every time instant. The waveform is the solution of the Laplacian/quasi-Poissonian field equations in polar coordinates in the air gap and takes into account slotting. The model allows the rated performance calculation but also such effects as cogging torque, ripple torque, back-EMF form prediction, some of which are neglected in commonly used analytical models.     

Magnet shaping to reduce induced voltage harmonics in PM machineswith surface mounted magnets

A simple methodology for reducing induced voltage harmonics in permanent magnet (PM) machines by selecting the appropriate magnet shape and dimensions is presented. The method, which uses a simplified analytical model of the magnetic circuit, is applied to three basic magnet shapes (rectangular, stepped, and trapezoidal), and can be extended to more complex geometries. The results of the analytical models are compared with results obtained from finite element analysis and with test results     

A finite element technique for calculating the magnet sizes andinductances of permanent magnet machines

A method for calculating the magnet size, and the direct and quadrature axis reactances of permanent magnet synchronous machines, using the finite-element method is presented. In this method the machine is modeled by its equivalent d-q representation of armature MMF and the appropriate reactances are calculated from the magnetic energy in the magnetic field. This is in contrast to the conventional approach of using an abc phase current model, solving the model and then converting the resulting quantities to respective d -q-o quantities. The method is applied to a permanent magnet motor design     

Design analysis of permanent magnet DC motors with differingarmature, magnet and yoke lengths

A modified magnetic circuit method and a 2-D finite element procedure are presented here for the analysis of DC permanent magnet motors with differing armature, magnet and yoke lengths including nonlinear material behavior of steel and permanent magnet. A 12 V, 120 W motor is analyzed through these methods and compared with experimental results of a prototype sample. In case of finite element analysis, commutation effects and short chording of the armature winding are treated appropriately, and cogging torque and voltage ripple are predicted     

Performance analysis of single-phase line-start permanent-magnet synchronous motor

Single-phase line-start permanent magnet (LSPM) synchronous motors have always been far less amenable to detailed computer-aided performance analysis compared with three-phase LSPM synchronous motors. The main reason is the lack of an accurate mathematical model of the motor characteristics arising from the unbalanced stator field and the rotor saliency. However, there is great potential for these types of motors to replace conventional single-phase induction motors in many domestic applications on account of their higher efficiencies when properly designed. In this paper, a new model that is applicable to both synchronous and asynchronous operation of the motor is proposed in which the parameters can be readily obtained by the two-dimensional (2-D) static finite-element method (FEM). It includes both the forward and backward rotating magnetic fields. It can be used to analyze the torque versus slip characteristics and predict the steady-state performances of the motor quickly with reasonable accuracy. The model has also been extended to simulate the transient start-up process and other dynamic performances. The models are suitable for the initial design and optimization of the motor geometry because of its low run-time overheads. Experimental results have verified the practicability of the models.     

Introduction to motors and controllers of flywheel energy storage systems

简述了飞轮储能系统的基本组成,介绍了飞轮储能系统常用的永磁无刷直流电机、永磁同步电机、感应电机和开关磁阻电机的工作原理和特点,讨论了四种电机的控制策略,分析了各种控制策略的优缺点及其应用。     

Control-based reduction of pulsating torque for PMAC machines

Control methods in torque pulsating reduction for surface-mounted permanent magnet motors are discussed in this paper. The pulsating torque is a consequence of the nonsinusoidal flux-density distribution caused by the interaction of the rotor's permanent magnets with the changing stator reluctance. The proposed control method is estimator based. To assure parameter convergence, Lyapunov's direct method is used in estimator design for the flux Fourier's coefficients. A novel nonlinear torque controller based on flux/torque estimate is introduced to reduce the influence of the flux harmonics. The influence of the cogging torque is considerably reduced at lower motor speed using the internal model principle and adaptive feedforward compensation technique. The overall control scheme and experimental results are also presented     

Starting characteristics of direct current motors powered by solarcells

The authors deal with the calculation of the starting to rated current ratio and starting to rated torque ratio of the permanent magnet, separately, series and shunt excited motors when powered by solar cells for the two cases where the system includes a maximum-power-point-tracker (MPPT), and without an MPPT. Comparing these two cases, one gets a torque magnification of about three for the permanent magnet motor and about seven for other motor types at rated design insolation. The calculation of the torques may assist the photovoltaic system designer to determine the advantage of including an MPPT in the system as far as the starting characteristics of the DC motors are concerned     

Structural integrity of a direct-drive generator for a floating wind turbine

In this work, the suitability of a direct-drive radial flux permanent magnet generator is examined as a probable drive-train candidate for a stepped-spar floating wind turbine system that supports a 2 MW downwind turbine. The suitability of the generator is assessed based on the structural integrity of its design (i.e., the stability of the air-gap between the rotor and stator) in response to the nacelle motions and its possible design implications on the overall system. Air gap deflections due to structural deflection and bearing tolerances were examined independently. The nacelle motions are obtained from experimental and numerical investigations on a 1:100 scale model. ANSYS suite is used to estimate the structural deformations of the generator and the changes in the air-gap distribution. Also, a simplified analytical model is used to compute the resulting changes in flux density and force distribution along the rotor periphery. The analytical model is also validated by 2D magneto-static simulations by utilising Finite Element Methods Magnetics software (FEMM).Preliminary results suggest that, if the nacelle accelerations are limited to 0.3 times the acceleration due to gravity (g) and the motion response cycles are below the fatigue limit, the air-gap stability of the generator is more sensitive to magnetic forces. Contributions to air-gap eccentricity from shaft displacements can be limited if the bearing supports can be designed for high stiffness. This also confirmed the adequacy of the platform design. The results also emphasise the need for air-gap management when designing direct-drive generators for floating wind turbines. Two methods are investigated as potential solutions to limit the maximum air-gap deflection to 10% level. The method of increasing structural stiffness led to a structurally unfavourable design that could potentially affect the stability and resonance properties of the system. The method of increasing the design air-gap led to a structurally more favourable design, although this meant an increase in magnetic material and hence the costs. Thus, implementing direct-drive radial flux permanent magnet generators for floating wind turbines is challenged by the difficulty in achieving optimal weight and costs at acceptable performance without compromising the air-gap tolerances. There is a need for an amendment to design standards to recognise the design challenges of Floating wind turbines.     

The available matching of solar arrays to DC motors having both constant and series-excited field components

This paper presents a procedure for increasing the daily output mechanical energy supplied by DC motors directly connected to solar cell arrays (SCA). The technique is based on the use of DC motors with two components of magnetic field: a constant component that can be provided by a permanent magnet (or a separately excited winding) and a second one produced by a series field winding. It will be shown that through properly selecting the parameters of the motor's magnetic circuit, (i.e., the value of the constant field and the mutual inductance as well as their relative directions), an improved matching between the PV-array and the dc motor can be achieved. Based on assessing and minimizing an expression used to quantify the power mismatch between the SCA and the dc motor, the optimal parameters will be identified. A comparison will then be made between this suggested motor design and tooth the separately excited and series motors.     

An improved control method of buried-type IPM bearingless motors considering magnetic saturation and magnetic pull variation

An improved control method of the buried-type interior permanent magnet (IPM) bearingless motors has been presented. It is shown that the conventional method is not applicable to this type of IPM bearingless motor for loaded conditions. In IPM bearingless motors, the armature reaction flux is present due to high magnetic permeance with thin permanent magnets and small airgap length. An increase in d-axis flux linkage is caused by armature reaction as a torque-component flux is increased. Thus, it is likely that magnetic saturation occurs in the stator teeth. In addition, a magnetic attractive force caused by the displacement force factor is dependent on the armature reaction flux. A new decoupling controller for the IPM bearingless motor considering magnetic saturation is proposed in this paper. It also considers the influence of magnetic attractive force variations. In addition, a new parameter identification method for the decoupling controller is also proposed. The new controller is found quite suitable to realize successful stable operation of the experimental IPM bearingless motor.     

Alnico Permanent Magnet Generator Pole Shape Evaluation using Finite Element Analysis

Complex demagnetization characteristics of Alnico permanent magnet material forces pole design procedure to rely upon empirical methods. The Alnico material adopts several B-H (flux density-coercive force) curves due to nonhomogenous demagnetization, thereby causing hand calculations for magnet working conditions and generator voltage to be nebulous. A method is presented which yields the magnetic operating characteristics of the Alnico pole and corresponding generator terminal voltage for a given load current. The finite element modeling of the pole is based on a field solution of the magnet's severest previous demagnetization.     

不同磁场布置对空气自然对流的影响

为研究顺磁性气体介质在外磁场作用下自然对流换热的规律，进一步揭示热磁对流的实质，该文用数值方法模拟了两种钕铁硼永磁系统产生的磁场作用下二维封闭方腔内空气的自然对流换热，得到了工作空间内磁场强度和磁加速度的分布，获得了两种梯度磁场作用下空气自然对流的流场和温度场以及壁面局部对流换热系数。研究表明，不同的永磁系统布置可在工作空间形成不同的磁加速度分布，产生不同的磁场力，从而影响空气自然对流换热的强弱。     

A novel high power density permanent magnet variable-speed motor

A novel polyphase, multipole, permanent magnet (PM) motor which possesses high power density, high efficiency and excellent controllability, yet can be produced by conventional fabrication techniques, is proposed. The basic operating principles, design features, performance analysis and control system are described. The experimental results for a 5 kW, 1500 RPM prototype PM motor and its comparison with other types of motors such as switched reluctance motors and induction motors are given. This motor also has superior dynamic performance     

一种新型永磁磁力耦合器导风散热片的仿真研究

本研究针对一款新型永磁磁力耦合器导风散热装置的导风散热片进行仿真分析。首先设计单因素实验,对其部分几何参数进行研究,利用Fluent软件进行流固耦合模拟,得出几何参数对最高温升及阻力距的影响关系,为正交实验提供合理的参数范围。然后设计正交实验,利用极差分析得出合理的参数组合。最后利用上文参数组合建模,模拟安装不同导风散热片个数的散热效果,寻找合适个数。并与未安装导风散热片的模型进行对比,得出此新型导风散热片设计合理,具有一定的实用价值。