故障状态下同步电机永磁体磁性能的有限元分析

对于永磁电机而言,故障状态下的外部退磁磁场对永磁体磁性能的影响,一直是影响永磁电机设计的关键之一.利用场路耦合时步有限元法,建立合理有效的数学模型来模拟故障状态下永磁电机的运行,并且计算额定状态到故障状态过程中,永磁体内部单元的最小径向磁密的变化情况,通过最小径向磁密的大小来判定该故障状态下永磁体能否出现不可逆退磁,以此来指导电机设计.     

永磁体预偏磁功率电感永磁结构分析

磁元件在各种功率变换器中一直有着不可替代的作用,如电感在电路中起到储能、滤波等作用,并且其体积占据的比重也较大,因此磁元件的优化设计备受关注,永磁体偏磁技术的出现为其开辟了一条新的途径。永磁体偏磁技术不仅可以提高磁元件的抗饱和能力,也有助于减小磁元件的体积。针对现有偏磁方案的不足,以Boost电感为例,建立电感的磁路模型进行分析,得到电感各个磁路上的参数设计要求,防止磁芯退磁,提高电感元件工作的稳定性,最终设计出新型的偏磁方案模型。对比几种优化结构,采用钕铁硼作为永磁体材料,用高饱和磁密的磁芯材料把永磁体和电感磁芯隔离开,避免局部饱和,并且当支路磁芯体积较大、永磁体夹在两个支路磁芯中间时,该结构的效果较好。同时还对引入短路环进行损耗分析。当下功率变换器不断朝着轻量化、小型化、高功率密度化方向发展,永磁体预偏磁技术为其增加了更多的可能性。     

一种具有抑制匝间短路失磁能力的永磁同步发电机

绕组匝间短路故障是永磁同步发电机(PMSG)最为常见的故障之一,容易造成永磁体的不可逆失磁。为了解决失磁问题,提出了一种具有抑制匝间短路下不可逆失磁能力的特种PMSG。首先介绍了发电机的特殊结构,紧接着通过数学模型推导出抑制失磁的原理。利用Flux软件建立发电机的模型,对发电机在运行过程中突然发生的匝间短路故障进行仿真。以永磁体各点在短路过程中出现的最小磁密值是否低于相应温度下退磁曲线的膝点磁密值为判断依据,分析得到发电机在不同短路故障下永磁体的失磁情况,从而验证了抑制失磁的可行性。     

Alnico magnet‐based cost‐efficient design of a permanent magnet reluctance generator for wind energy conversion systems

In this work, a 6/4 permanent magnet reluctance generator (PMRG) with Alnico magnets is designed for small‐scale wind energy conversion systems and its performance is analyzed by finite element analysis. A simple converter topology is proposed to protect the Alnico magnets from demagnetization. Thus, NdFeB magnets, which are predominantly used in electric machines, can be directly replaced by Alnico magnets without changing the size or location. Since Alnico magnets are very cheap, the design cost can be significantly reduced without losing much from the generator performance. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

双三相永磁同步发电机多目标优化设计

为实现双三相永磁同步发电机(PMSG)的低固有电压调整率、高发电效率和低成本的特性,研究了侧重于降低固有电压调整率的多目标优化设计方案。采用解析法建立单元电机磁链模型,以永磁体磁化方向长度、永磁体所跨弧长和单元电机相绕组匝数为设计变量,分析上述参数对固有电压调整率、发电效率等评价指标的影响,并提出了基于权重系数的多目标优化函数。分别用标准遗传算法(SGA)、差分进化算法(DE)和基于以上2种算法的混合遗传算法(HGA)优化设计参数并进行对比。试验结果表明,HGA优化效果与设计目标具有良好的一致性,与初始设计参数相比,优化后的电机输出能力以及稳压能力均有所改善。     

混合动力汽车ISG用混合永磁同步电机转子研究

设计了一款混合动力汽车集成式起动发电机(ISG),用钕铁硼和铁氧体混合永磁的永磁同步电机(PMSM)。分析了两种永磁体的结构参数对电机磁路的影响规律,推导了钕铁硼和铁氧体并联磁路的约束条件;以铁氧体的不可逆退磁量和电机的基本性能为优化目标,通过场-路结合的方法,确定了钕铁硼和铁氧体的结构参数;并与传统的钕铁硼PMSM在电机性能和永磁体成本等方面进行了比较分析。研究结果表明,所提出的ISG混合永磁电机能有效地减少永磁体材料成本和铁氧体退磁风险,电机性能达到了设计要求。     

Optimal design method with thermomagnetic field coupling analysis for miniaturization of permanent magnet synchronous motor

A straightforward solution for minimizing the cost of major materials used in motors, such as permanent magnets and silicon steel sheets, is to reduce the motor size as far as possible. However, there is a trade‐off between the motor size and temperature rise in the motor that should be taken into account while reducing the motor size. For achieving this, we have been developing an optimal design method based on a combination of a thermomagnetic field coupling analysis and a direct search algorithm. This paper reports the details of this design method. A multipole permanent magnet synchronous motor of an outer rotor is the test motor. The results of the torque‐density‐maximization problem involving constraints on the terminal voltage, coil‐temperature rise, and demagnetization of the permanent magnet are shown. The usefulness of our method is also demonstrated. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(2): 29–38, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22346     

Analytical study of optimal layout of permanent magnet in IPMSM for generating sinusoidal flux‐density distribution in air gap

This paper demonstrates an analytical optimization method for rotor designs of interior permanent magnet synchronous machines with multiple flux‐barriers. In particular, this study focuses on the optimal layout of permanent magnets for generating a sinusoidal flux density distribution in the air gap. In addition, practical design methods for realizing the optimal layout are proposed, and the designs are verified through finite‐element analyses. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(2): 39–46, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22344     

异步起动永磁同步电动机起动过程中永磁体平均工作点的解析计算

针对采用时步有限元法研究异步起动永磁同步电动机起动过程中永磁体工作点的变化时存在计算时间长、不适合电机设计阶段的快速计算的问题,通过将异步起动永磁同步电动机的动态数学模型和磁路计算模型结合,建立了异步起动永磁同步电动机起动过程中永磁体平均工作点的解析计算模型。利用该解析计算模型计算了3台样机起动过程中永磁体平均工作点的变化,分别得到了电机起动过程中最大退磁磁场出现时的永磁体平均工作点和电机稳定运行时的永磁体平均工作点。通过与有限元法的计算结果作比较,验证了该解析计算模型的准确性,可为该类电机的快速设计提供参考。     

永磁同步电机永磁体状况在线监测

提出一种基于卡尔曼滤波器的永磁同步电机永磁体磁场状况在线监测方法。通过选择磁场同步旋转坐标系下定子电流和永磁体磁链为状态变量，构建估算转子永磁体磁链幅值和方向的卡尔曼滤波器。该方法能准确跟踪永磁体真实状况，对电机参数不敏感，鲁棒性强。基于动态估算的电机永磁体磁链，可为永磁同步电机控制系统实时提供准确的转子磁链信息，提高系统控制性能和效率。同时，基于永磁体磁场状况的动态监测，可防止永磁电机失磁状况的恶化，降低不可逆失磁程度，提高系统可靠性。实验结果验证了方法的正确性和有效性。     

Cumulative current‐magnetizing method for a capacitor‐discharged impulse magnetizer

This paper presents a cumulative current‐magnetizing method for magnetization of permanent magnet, aimed at alleviating the bulky capacitor problem of traditional capacitor‐discharged impulse magnetizers. The method employs circuit resonance to boost the output voltage. The resonant alternative current (ac) voltage is then directly discharged to the magnetizing coil without using any rectifier. The proposed resonant ac discharge repeats a number of times over several milliseconds. This allows the magnetizing current to increase incrementally until it reaches the peak that is sufficient to fully magnetize the permanent magnet. With this design, the energy for magnetization is accumulated by small steps, and each increment would require much lower energy. This results in smaller capacitors needed compared to traditional designs. To validate the effectiveness of the proposed scheme, several pieces of ferrite magnet without being pre‐magnetized were tested using the developed magnetizer. The test results support the feasibility and practicability of the scheme for potential applications. Copyright © 2017 John Wiley & Sons, Ltd.     

一种基于波形等效原则的永磁电机空载反电动势在线测量方法研究

永磁电机的空载反电动势是电机设计的重要指标,综合反映了电机的电磁性能。一台永磁电机在设计完成时,其额定转速下的空载反电动势的大小是确定的。但随着电机投入运行,由于工作环境的温度、机械或是化学变化,可能会使得永磁体发生退磁问题,进而影响电机的工作性能。传统的反电动势测量方法均为离线测量,具有诸多不便性。本文根据实际的工程需要,提出一种在线测量永磁电机反电动势的方法,并设计样机验证了理论的有效性。通过捕获电机在任意转速断电后一个电周期内的反电动势波形,利用波形等效思想得到等效正弦波,并进一步推算出永磁电机在额定转速下的反电动势。将其与空载反电动势设计值进行对比,即可对当下永磁体的磁性能做出快速评估,为电机的故障维护和长期稳定运行提供技术保障。     

Five‐phase modular stator surface‐mounted permanent magnet machine with reduced space sub‐harmonics

Multiphase modular stator surface‐mounted permanent magnet machines (MSPMs) feature short end connection, unity winding factor, and low cost. However, they also exhibit rich space harmonics. A five‐phase MSPM with reduced space sub‐harmonics is proposed in this paper. The phase‐shifting method and magnetic flux barriers are adopted to reduce the slot harmonic and lowest order harmonic, respectively. A modified MSPM used for phase shifting is specially proposed. Further, the phase‐shifted MSPMs without and with magnetic flux barriers are both studied to show the separate effectiveness of the phase‐shifting method and magnetic flux barriers. The phase‐shifting angle is determined based on winding function method and the optimal angle is fixed considering the minimal tooth width. A double‐layer MSPM with 20 slots and 22 poles is exemplified, and two single‐layer 40‐slot 22‐pole MSPMs, which are respectively equipped without and with magnetic flux barriers, are proposed. Finite element analysis is performed, and the comparison results show that the space sub‐harmonics, permanent magnet eddy current loss, and the lowest mode of vibration are largely reduced in the phase‐shifted MSPM with magnetic flux barriers. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

New Dynamic Self‐Consistent Mathematical Model and Torque Characteristics of Permanent‐Magnet Synchronous Motors with Magnetic Cross‐Coupling

This paper proposes a new dynamic mathematical model of permanent‐magnet synchronous motors (PMSMs) with magnetic cross‐coupling and presents a new analysis of the torque characteristics of the motors. Generally speaking, dynamic mathematical models used for the design and analysis of PMSM control systems must consist of three basic equations that describe the main motor characteristics as an electrical circuit, torque generator, and electromechanical energy converter. In order to obtain reasonably compact models, some characteristics have to be approximated. However, in the case where the approximations used in the three basic equations are different from each other, the dynamic mathematical model often loses self‐consistency and becomes self‐contradictory. The proposed model, which takes the magnetic cross‐coupling into account, is self‐consistent and compact, and its effectiveness is validated by experimental data. Using the self‐consistency and compactness, this study presents a new analysis of the torque characteristics of PMSMs, focusing on efficient torque generation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(1): 42–55, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22382     

An application of reference point‐based NSGA‐II for power system congestion management ensuring system stability

In this paper, we formulate the power transmission congestion problem as a multiobjective optimization problem and solve it using the reference point NSGA‐II (R‐NSGA‐II) technique. Restructuring of the electric power industry has led to intensified use of the transmission grid, thereby causing more frequent power transmission congestion. Congestion threatens the power system security and reliability and is therefore a crucial issue in the unbundled power system scenario, which is usually managed by rescheduling the generators and the demand. Stability considerations should also be incorporated within the congestion management (CM) methodology so as to ensure secure stability margins post CM. In this paper, we formulate the CM problem in a pool model as a true multiobjective optimization problem with the three conflicting objectives of minimizing CM cost and maximizing the voltage stability margin and the transient stability margin. The multiobjective CM problem is solved using the R‐NSGA‐II method, which is a modification of the well‐known non‐dominated sorting genetic algorithm II (NSGA‐II) optimization algorithm. R‐NSGA‐II makes use of decision maker (DM)‐supplied preference information to guide the search for better solutions corresponding to the DM's preferences. The R‐NSGA‐II‐based CM approach is tested and verified on the IEEE‐39 bus system model, and its performance is compared with those of NSGA‐II and other reported method. The results obtained demonstrate that the proposed method is capable of obtaining Pareto‐optimal solutions as per the user's choice with fewer iterations, and therefore could be effectively used for solving the multiobjective CM problem. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于超螺旋滑模观测器的六相永磁同步电机失磁故障重构

针对六相永磁同步电机在复杂运行工况下永磁体容易发生失磁故障的问题,提出一种基于超螺旋算法的永磁体失磁故 障重构方法。 首先,利用矢量空间解耦坐标变换(VSD)进行降阶和解耦,构建了六相永磁同步电机失磁故障数学模型。 其次, 以定子电流为状态变量,设计基于超螺旋算法的滑模观测器(STA-SMO),根据滑模等值原理实现转子磁链的实时重构,并采用 一种类二次型 Lyapunov 函数证明了所设计 STA-SMO 的稳定性。 最后通过仿真与实验验证了该方法的有效性,与传统滑模观 测器(SMO)相比,所设计的 STA-SMO 准确地实现了对失磁故障的重构,有效抑制了抖振,且鲁棒性更强。     

新型直驱永磁风力发电机电磁场数值分析

以新型直驱永磁风力发电机为研究对象,在完成采用XLPE高压电缆作为定子绕组的1.5 MW/10.5kV内转子新型直驱永磁风力发电机电磁设计的基础上,在Ansoft Maxwell环境下建立发电机二维模型,对发电机各个工况下的电磁场进行有限元仿真与分析,包括静态空载、额定负载、不对称短路故障情况,对发电机永磁体在出线端突然三相短路时受冲击电流影响是否会发生局部失磁进行分析,验证新型永磁风力发电机电磁设计的可行性。结果表明,新型风力发电机与传统永磁风力发电机电磁场分布规律一致,且其额定电压高,绕组电流密度较小,额定负载与单相短路情况下永磁体磁场受电枢磁场影响较小,铜耗和铁耗也较小,同时在极端短路情况下永磁体局部不会出现永久性退磁,设计方案可行。     

Analytical Modeling of an Eddy-current Adjustable-speed Coupling System with a Three-segment Halbach Magnet Array

This article presents a two-dimensional analytical model to predict the magnetic field distributions and torque characteristics in an axial-flux eddy-current adjustable-speed coupling system with a three-segment Halbach magnet array. The main contribution of this article is the analytical evaluation of a moving-conductor eddy-current problem based on a three-segment Halbach magnet array by considering the influence of the eddy currents on the magnetic field. Based on the layer model method, the three-dimensional eddy-current problem is linearized to a two-dimensional problem, and the field equations derived from Maxwell's equations in each layer (iron core, magnet, air gap, and conductor) are solved by using the variable separation method and Cramer's rule. The proposed analytical model is validated by the three-dimensional finite-element method in terms of both magnetic field prediction and parameter analysis. Because the analytical methods take less computational time than numerical methods, they are an effective tool for the first step of design optimization.     

Anti‐windup synthesis for a model predictive control system

In this paper, an anti‐windup design problem for a model predictive control system is studied. The plant is assumed to be stable. First, we propose the structure of an output feedback model predictive controller with an anti‐windup compensator. Then we show a design method of the anti‐windup compensator that guarantees closed‐loop stability and improves the transient response. The design problem of the anti‐windup compensator is reduced to a linear matrix inequality (LMI) optimization problem. Further, it is shown that there always exists an anti‐windup compensator that ensures global asymptotic stability. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Basic Design Method for SPMSM Based on Air‐Gap Magnetic Flux Density Distribution Focusing on Image Magnetic Pole

This paper presents a basic design method for the surface‐mounted permanent magnet synchronous motor (SPMSM) for both distributed and concentrated windings. The design is based on the air‐gap magnetic flux density distribution focusing on the image magnetic pole. The calculus equation of the air‐gap magnetic flux density distribution is analytically derived by supposing the magnetic pole is located on the magnet surface and image planes. In this study, a three‐phase and double‐layer stator winding SPMSM that has a linear demagnetizing characteristic magnet, such as a ferrite or rare‐earth magnet is considered. From the required specifications and design conditions, the design target values of the parameters that appear in the voltages equations of the d–q axis coordinate system are calculated. Then, the relational equations for the torque constant, d‐axis inductance, copper loss, and the maximum current density are presented as a function of three design parameters under i_d = 0 control. They are the stator stack length, the number of coil turns in series in a phase, and the slot bottom length. Hence, this approach reduces the SPMSM basic design to the problem with these design parameters has to be solved. The proposed method makes it possible to address the concentrated winding as a special case of the distributed winding. The FEA results confirm the validity of the proposed basic design method for both distributed and concentrated windings.