Electrical motors with permanent magnets in field systems

Main characteristics of hard magnetic materials are considered from the standpoint of their use in low-power electric motors. The basic designs of micromotors with excitation by permanent magnets are presented both by commutator DC motors and induction motors, with indications given of their advantages and disadvantages and the technical specifications of universal (both single-phase and three-phase), three-phase, and variable-frequency controlled synchronous electrical motors developed by the Department of Electrical Mechanics of Moscow Power Engineering Institute (MEI); the electrical engineering enterprises of Russia in various years are also presented.     

Optimization of the magnetic system of a brushless DC motor with rare-earth permanent magnets

This article discusses the causes of cogging torque pulsations in a deenergized brushless dc motor (BLDC) with a tooth stator and magnetoelectricity stimulation. Based on the causes that we identify, we propose a method of reducing cogging torque pulsations in order to improve the rotation speed uniformity of a BLDC. The method is based on optimization of the number of stator slots, which determines the type of stator winding for a given number of poles in magneto-electric machines. For the maximum possible reduction of cogging torque pulsations, it is proposed to bevel the stator slots at an angle divisible by the main tooth harmonic period. All analytical calculations were performed with the use of numerical methods for mathematical modeling of the magnetic field in the magneto-electric machines with the use of Elcut specialized software. Based on the calculation results, recommendations for the design of a BLDC with a minimum level of cogging torque pulsations were elaborated. Our theoretical studies have been checked by experimental investigations of a DBM 142-18-3 motor and applied to the design of the BLDC (DBM series) manufactured by JSC Electroprivod, Kirov. Electric motors of DBM series are used as precision electric drives for metalworking equipment, where a high uniformity of rotation speed is a major requirement.     

Application of optimization techniques in the design of brushless dc electric motors with permanent magnets for special electric drives

The characteristics of special electric drives with brushless electric motors are represented, and the influence of dynamics, energy, and the weight and size parameters of motors on their characteristics is shown. The results of application of optimization algorithms in the form of a comparison table of parameters of electric motors developed without the use of optimization and using optimization algorithms. The results of tests of special electric drives are presented.     

Analysis of characteristics of half-wave rectified brushless synchronous motor with permanent magnets

Previously, the authors proposed a “half-wave rectified brushless synchronous motor” as a novel servomotor. The rotor winding emf of the motor is induced by the stator current mmf which rotates at synchronous speed and pulsates at bias frequency. The field excitation is produced by the field current obtained from rectifying the emf with a diode inserted into the field winding. To improve the power factor and the efficiency, they also proposed a new-type half-wave rectified brushless synchronous motor with permanent magnets. This paper analyzes the flux distribution and the torque characteristics of the new half-wave rectified brushless synchronous motor using the finite element method. The computed torque characteristics are confirmed with the experimental results. Furthermore, the steady-state characteristic equations are derived and the effect of the modulation function waveforms on the motor performance is investigated. The theory also is confirmed by the experiments.     

混合动力汽车牵引电机永磁体温度建模

建立了两个不同永磁体温度预测模型:模型一是从温度与永磁体性能的关系出发,由实时检测的电压、电流、转速和绕组温度通过运算而求得永磁体温度;模型二是从电机的损耗出发,建立了电机的热路,该热路包含连接点,热阻和热源,体现了整个电机内的热循环过程,求解热路而得到永磁体温度.另外,考虑永磁体涡流损耗,进一步提高计算精确性.在三相正弦电压供电下,对以给定电机进行计算,结果由实验验证.对PWM电源供电的情况下,由于PWM波中含有大量的高次谐波,因此永磁体温升明显.此外,通过有限元仿真进一步验证了本文所提的两种温度预测模型的正确性.     

Analytical approach to cogging torque calculation of PM brushless motors

This paper discusses the approach to analytical calculation of the cogging torque in permanent-magnet (PM) brushless motors. Magnetic field energy in the air gap has been used to obtain the cogging torque equations. Two equations have been derived: with the PM circumferential width taken into account, and a simplified equation, i.e., without the effect of the finite width of the PM. The effect of eccentricity has also been included. Calculation results have been compared with laboratory test results.     

自起动永磁电机在转子表层结构不对称条件下的堵转电流

为了研究转子表层磁路结构不对称对永磁电机堵转电流的影响,以一台22kW电机为例,利用时步有限元法,系统分析了计及表层磁路结构不对称及磁路附加饱和条件下的堵转电流特点.分析发现:当转子磁极d轴与某相绕组轴线重合时,该相电流有效值比其他两相高10%左右,且正负半波幅值相差接近10%.进一步揭示了转子表层结构不对称是导致三相堵转电流不对称的主要原因,而永磁体存在引起的附加饱和是导致堵转电流正负半波幅值不等的主要原因.通过堵转电流实测验证了分析的正确性.     

定子开槽表贴式永磁电机转子偏心空载气隙磁场全局解析法

针对表贴式永磁电机定子开槽后的转子偏心空载气隙磁场解析问题,结合正则摄动理论建立其全局解析模型.将解析区域划分为永磁体、气隙和槽区域,通过各子区域之间的边界条件,求解拉普拉斯方程或泊松方程.叠加气隙磁密的零阶分量和一阶分量,得到偏心气隙磁场分布.解析解与有限元解的比较结果表明,气隙磁密、齿槽转矩和不平衡磁拉力计算准确,验证了解析模型的可靠性.所述解析方法计算快速准确,便于分析表贴式永磁电机转子偏心磁场.     

Optimum values for magnet and armature winding thickness foraxial-field permanent magnet brushless DC motors

When the motor thickness and the required starting torque are set for an axial-field permanent magnet brushless DC motor, the optimal ratio of the permanent magnet thickness to armature winding thickness is 2:1 because the copper loss of the armature windings is kept to a minimum. This conclusion is based on a new method presented by the authors in which factors such as loop resistance, a radial air gap magnetic flux density approximated by curves of second order, and an experimental formula for the leakage coefficient are incorporated. The demagnetization curves of the magnets are assumed to be linear. The new method is also applicable to estimating torque, current, and input power at the start. These items can be more promptly estimated without a computer program, and the physical insight is more easily gained by the aid of the new method than a 3-D finite element method     

基于改进子域模型的双绕组无轴承磁通切换电机磁场解析计算

针对双绕组无轴承磁通切换永磁电机的复杂结构,通过建立一种改进的子域模型来分析电机电磁特性.对于悬浮绕组采用分布式双层绕组嵌放方式,提出了一种等效电流分析方法,将上、下层绕组电流等效为同一电流元.与传统子域模型中分布式双层绕组分析法相比,所提改进子域模型法可减少求解变量的个数,将未知参数矩阵从22阶简化到18阶,降低了磁...     

Cogging torque investigation of PM motors resulting from asymmetry property of magnetic poles: Influence of performance variation between permanent magnets

This paper examines the cogging torque of a permanent magnet (PM) motor resulting from the asymmetry property of magnetic poles, which comes from the performance variation between magnets. A PM motor with 32 poles (= 16 pole pairs) and 36 slots is selected for verification, because the motor whose pole/slot ratio is 8/9 is sensitive to the performance variation between permanent magnets. Assuming that two different magnetization levels of magnets are mixed together in one rotor, the amplitude of the 2.25th and 4.5th components of cogging torque, which show 36 (= 2.25 × 16) and 72 (= 4.5 × 16) times of pulsation per rotation respectively and both of which result from the asymmetry property of the magnetic poles, are evaluated. As a result, it is clarified that the cogging torque characteristics depend on the alignment pattern of the two kinds of magnets. The amplitudes of the 2.25th and 4.5th components of cogging torque are proportional respectively to the amplitude of the 36th and 72nd order harmonics of the squared magnetic flux density around the rotor which is set in the space without stator. Using the proportional constants found from the finite element analyses in some alignment patterns, the cogging torque amplitudes of the motors with other alignment patterns can be predicted by calculating the squared magnetic flux density around the rotor only. The predicted cogging torque amplitudes correspond to the actually calculated results. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(3): 57– 67, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20669     

Monitoring of defects in induction motors through air-gap torqueobservation

This paper suggests a method to monitor defects such as cracked rotor bars and the shorted stator coils in induction motors. Air-gap torque can be calculated while the motor is running. No special down time for measurement is required. Data of the air-gap torque for a motor should be periodically kept for comparison purposes. Since more data than just a line current are taken, this method offers other potential possibilities that cannot be handled by examining only a line current. The theoretical foundation for this proposed method is presented. Experiments conducted on a 5-hp motor show the validity and potential of this approach. Further studies are planned to extend the proposed method in detail and to monitor defects developed in other types of rotating machines     

表面式永磁电机气隙磁场分析

针对表面式永磁电机齿槽结构复杂,应用传统许克变换法很难精确计算电机磁场分布的问题,将表面式永磁电机气隙磁场分为定子绕组和永磁体产生的气隙磁场两部分.应用许克变换工具箱将电机不规则空气间隙转化为几何上简单区域,分析电机定子绕组产生的气隙磁场.将永磁体等效为线电流,借助许克变换工具箱分析永磁体产生的气隙磁场.将定子绕组和永...     

基于锁相环和双模速度双重控制的永磁无刷直流电机的研究

无刷直流电机系统具有转矩电流比高、转速高、动态性能好、可靠性高和易于控制等优点,在中小功率驱动场合应用广泛;但其缺点是转矩脉动大并易造成速度波动,目前普遍采用速度-电流双闭环PI控制。在无刷直流电机用于某些负载变化率大及大惯量的速度控制模式下时,可能因速度不稳带来震动、谐振、噪声等问题。研究讨论了一种基于锁相环和双模的速度控制法,利用锁相环加上速度环的方法,有效改善了传统速度电流PI调节器在无刷直流电机大惯量负载中存在的转速波动问题,在实际应用中具有良好的速度控制精度和稳定性。     

盘式永磁Halbach悬浮装置的磁场和力特性分析

针对电磁式(EMS)磁悬浮实现稳定悬浮需要复杂的闭环控制和悬浮气隙较小等问题,提出的盘式永磁Halbach悬浮装置是一种电动式(EDS)磁悬浮系统,具有悬浮气隙大和不需要复杂的闭环控制即可实现稳定的悬浮等优点.盘式永磁Halbach悬浮装置通过永磁体和导体板上感应出的涡流相互作用产生悬浮力和转矩.从电磁场理论出发建立悬浮装置的分环电磁模型,采用拉普拉斯分离变量方法进行磁场分布求解,并直接利用磁场分析所得的磁场分布结果求解次级悬浮力和水平转矩,给出磁悬浮装置的力特性与其参数的关系,证明在一定的相对速度下,装置可以输出足够大的悬浮力.建立有限元模型,通过分析得出系统的磁场分布以及电磁力等的分析结果;搭建实验平台对永磁电动式系统的基本特性进行研究,主要是悬浮力和转矩的测试;利用有限元计算和样机实验验证理论分析和计算结果的正确性.     

（23期已送排）表面式永磁同步电动机新型转矩控制

永磁同步电动机的反推控制通常采用电流作为虚拟变量,不适用于转矩需要精确跟踪的场合。本文介绍了一种以转矩和磁链为虚拟变量的反推算法,可以使永磁同步电动机输出转矩和负载转矩的差值在全局范围内快速收敛于零,并且在忽略粘滞摩擦的情况下,控制变量将不受负载的转动惯量变化的影响。该方法适用于负载转矩和转动惯量经常变化的场合,具有一定的参考价值。     

Study of the magnetic force delivered by an actuator with nonlinear ferrofluid and permanent magnets

The main purpose of the paper is to calculate the magnetic force delivered by actuators with a nonmagnetic body levitated in a ferrofluid that is magnetized by permanent magnets. A linear algebraic formula is proposed for this purpose, which is then validated experimentally. The nonlinear magnetization curve for the ferrofluid, known in detail, was used in computations. Satisfactory agreement between the results obtained with the linear formula for the force and the experimental results was obtained. The expression for the force is very simple, having only three independent variables, and can be used as a “guideline” in the analysis and design of the mentioned actuators. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.