Interbar currents and axial fluxes in healthy and faulty induction motors

Nearly 10% of all failures in cage induction motors occur on the rotor. In previous works, it has been shown that the interbar currents exist in healthy and faulty squirrel-cage induction motors. The majority of techniques detecting bar failures depend on detecting twice the slip-frequency modulation harmonic in the speed, torque, or stator current by analyzing the appropriate frequency spectrum and neglecting the interbar currents. However, the interbar currents create axial fluxes through the rotor shaft. In this paper, a three-dimensional magnetic equivalent circuit method is presented for the analysis of this phenomenon. Effects of the interbar currents on the broken rotor bar currents, and transient behavior of induction motor are also presented. Theoretical findings have been verified through experiments.     

Sensorless-Oriented Design of PM Motors

This paper deals with the design of a permanent-magnet (PM) motor for zero-speed sensorless rotor position detection, by means of injection of a high-frequency signal. Various aspects are investigated: influence of the rotor structure, stator and rotor saturation, reliability of finite-element analysis to predict the motor performance, and influence of rotor iron bridges and of rotor eddy currents induced. The results presented in this paper give the key rules to designing a PM motor suitable for sensorless rotor position detection.     

基于矢量控制的定子笼型十二相感应电机极对数切换策略

针对传统感应电机(IM)恒功率调速区间有限,额定点外效率降低以及受使用场景约束的问题,为了拓宽调速和高效率工作区间以及适应多种环境运行需求,采用定子鼠笼型十二相IM替代传统分布式绕组三相IM。经过转子磁场定向矢量控制解耦出不同平面的谐波电流从而驱动电机旋转,通过控制函数对所有平面的谐波电流进行调控,能方便快捷地实现电机的极对数切换。对所提出的控制函数调控矢量解耦平面实现极对数切换的方法进行仿真验证,仿真结果表明所提极对数切换技术能够实现十二相IM在不同转速下的极对数切换,拓宽了转速调节区间,满足了不同工况工作时的高效率运转。     

等距笼型转子无刷双馈电机的有限元分析

针对笼型无刷双馈电机的效率较低的问题进行研究,电机效率与转子磁场极数转换效率和转子漏阻抗参数相关,对转子结构进行优化设计是提高电机性能的根本途径。在分析现有笼型转子的特性基础上,提出等距笼型的新转子结构。新转子具有公共端环和独立叠式转子导体回路,每个转子导体回路的节距相等。利用ANSYS软件对不同笼型转子结构的磁场进行有限元分析,计算出转子磁动势谐波含量和转子漏阻抗参数。结果表明,新转子结构无刷双馈电机的转子电阻和漏电抗小,与定子功率绕组和控制绕组极数相对应的转子谐波磁场含量高,其他高次谐波磁场含量低。     

Stray load loss analysis of induction motor-comparison of measurement due to IEEE standard 112 and direct calculation by finite-element method

The purpose of this paper is to specify the main components of the stray load loss of induction motors from both results of measurement and analysis. The IEEE standard 112 Method B is applied to the cage induction motor for the measurement of the stray load loss. On the other hand, the losses generated at the stator core, the rotor core, and the rotor cage are calculated directly by the finite-element method considering the magnetic saturation and the harmonic fields, which vary due to the load condition. The measured and the calculated torque, losses, and efficiency agree well. It is clarified that the main parts of the stray load loss in the case of the analyzed motor are the increase of harmonic losses due to load, which are the harmonic Joule losses of the rotor cage and the harmonic core losses of the stator and the rotor. The relationships between the losses separated by the measurement and the losses calculated directly by the finite-element method are also clarified.     

Performance of a High-Speed Motor Drive System Using a Novel Multilevel Inverter Topology

The performance of a novel multilevel six-switch (SS) three-phase inverter drive is examined for low-voltage high-speed motor applications. The switching losses of hard-switched voltage-source-inverter topologies place limits on the maximum feasible switching frequency. When operating at higher fundamental frequencies, this results in low-frequency modulation ratios and either high load harmonic currents that cause excessive rotor heating or larger than desired output reactors with a large fundamental voltage drop. The multilevel inverter structure examined offers an increased number of output pulsewidth-modulated (PWM) voltage levels, higher frequency PWM output waveforms, reduced dead-time effects, and a significant reduction in harmonic content. These features reduce the total losses in the motor load when compared to the standard SS three-phase inverter. The harmonic reduction provided by the multilevel topology relative to the standard inverter is experimentally demonstrated with a 15-hp 18 000-r/min induction machine.     

Impact of inter-bar currents on the performance of the brushlessdoubly fed motor

The brushless doubly fed machine has been proposed as an alternative adjustable-speed drive because of its potential for reducing the size of the necessary power electronic converter. The motor's economic viability may depend upon the ability to die cast the rotor, bringing the cost of production in line with that of an induction machine. Recent industrial experience has shown that when the rotor is die cast, without any special precautions for insulating the bars from the rotor iron, the performance is degraded with respect to a fabricated rotor with insulated bars. This performance degradation is shown to be caused by the presence of inter-bar rotor currents. This paper presents a coupled-circuit model which is able to simulate the performance of the motor, including the presence of the inter-bar currents. The model describes the physical structure of the windings and the rotor in terms of complex harmonic impedances. Both measured results and predicted results are presented. In addition, this model enables investigation of the decreased performance obtained with varying values of inter-bar resistance     

无刷双馈电机笼型转子磁场调制能力分析

笼型转子无刷双馈电机(BDFM)由于其简单且特殊的转子结构,使得转子磁场谐波含量大,直接影响转子的磁场调制能力。从电机内部磁场入手,提出了一种快速计算BDFM转子磁场的方法,分析了转子磁场与转子短路环个数及短路环分布的关系。以短路环个数及短路环分布跨距为参数,建立MATLAB计算程序对转子磁场调制能力进行分析,研究了转子的极限调制能力。最后,通过Flux电磁场有限元分析软件建立电机模型并对所提方法进行了验证。研究结果有助于优化转子结构设计。     

Using Current Signature Analysis Technology to Reliably Detect Cage Winding Defects in Squirrel-Cage Induction Motors

This paper will demonstrate, through industrial case histories, the application of current signature analysis (CSA) technology to reliably diagnose rotor winding problems in squirrel-cage motors. Many traditional CSA methods result in false alarms and/or misdiagnosis of healthy machines due to the presence of current components in the broken cage winding frequency domain, which are not the result of such defects. Such components can result from operating conditions, motor design, and drive components such as mechanical load fluctuations, speed-reducing gearboxes, etc. Due to theoretical advancements, it is now possible to predict many of these current components, thus making CSA testing less error prone and therefore a much more reliable technology. Reliable detection of the inception of broken cage winding problems, or broken rotor bars, prior to failure allows for remedial actions to be taken to avoid significant costs associated with consequential motor component damage and unplanned downtime associated with such in-service failures     

考虑谐波影响后交流励磁电动机电磁转矩的分析与计算

虽然已有不少文章研究了交流励磁电机的运行性能 ,但是很少有文章在研究其性能时考虑了谐波电流的影响 ,特别是谐波对电机电磁转矩的影响。本文从该类电机的基本电磁关系出发 ,分析研究了基波电磁转矩及谐波转矩的特点 ,提出了基波谐波的等效电路 ,给出了谐波电路中参数的计算方法。导出了基波电磁转矩、稳定谐波电磁转矩及脉动谐波电磁转矩的计算公式。文章最后以一个实际的绕线型异步电机用交 直 交电压型逆变器供给励磁的交流励磁电动机为例 ,计算了主要谐波的稳定和脉动的电磁转矩以及电机总的电磁转矩。计算结果对进一步研究系统的驱动性能及电机与励磁系统的设计是十分有益的。     

An induction machine model including interbar currents for studying performances during transients and steady state

This paper presents a mathematical model of a three-phase induction motor taking into consideration the interbar contacts. Several models have been available in the references. However, they consider the rotor of the induction motor as being constituted either a three-phase or a squirrel cage even if it operates under stator and/or rotor faults condition. Nonetheless, the contact between a bar and the iron core for the machine has to be considered, especially when a rotor fault occurs. It is obvious that rotor currents are under the influence of rotor constitution materials. So, the paper aim’s concerns a transient model of the induction motors which can consider the rotor broken bars defect. Despite its increasing complexity, it could be able to provide with useful indications for diagnostic purposes. This model is advocated for the simulation of motors behavior under rotor defect which takes into account the interbar currents. The proposed technique is based on the mesh model analysis of the squirrel cage. As low power induction motors are prevalent in industrial plants, we pay a special attention on them. Notwithstanding, additional currents are due to the contact between the non-insulated bar constituting the squirrel cage to the rotor iron core. The monitoring of induction motors is predominantly made through the stator current analysis of the motor when it operates at nominal condition. Moreover, this one is observed in steady state operating system, knowing that the motor is generally fed by a sinusoidal supply. Consequently, simulation results showed in this paper prove the effectiveness of the proposed approach, and the impact of interbar resistance both on the model and the line current spectrum for the diagnostic. An experimental test proves the effectiveness of this model.     

笼型无刷双馈电机转子导条优化设计

针对笼型无刷双馈电机转子设计方法不完善的问题,从分析笼型无刷双馈电机的内部磁场入手,推导了无刷双馈电机在稳态运行时转子电流的解析表达式,利用迭代法在考虑转子电阻的情况下选择最合适的转子导条截面积,为笼型无刷双馈电机的转子设计提供了理论依据。通过有限元仿真,验证了理论推导的正确性。研究结果不仅有助于在设计时快速计算笼型无刷双馈电机转子电流,也有助于优化转子结构设计。     

Application of the Integrated Diode Synchronous Motor to Traction Drive Motors

In this study, a traction drive electric motor was designed with a new magnet‐free motor design technique where electromagnets are generated on a rotor by utilizing changes in the spatial second harmonic of the magnetic fields. To apply the proposed technique to electric motor design, balancing the rotor and stator magnetomotive force is important. This paper presents design methods for adjusting the rotor and stator magnetomotive forces. A test motor was designed with these design methods and evaluated using a motor bench. The analytical and measurement data indicated that the proposed motor performed comparably to magnet motors.     

Mechanical-sensorless permanent-magnet motor drive using relative phase information of harmonic currents caused by frequency-modulated three-phase PWM carriers

This paper proposes a novel control strategy of a permanent-magnet motor drive without a rotor position sensor. The strategy is based on use of relative phase information of harmonic currents caused by frequency-modulated three-phase pulsewidth-modulation (PWM) carriers. In this system, the PWM carrier source is placed on an estimated rotor reference frame, and coordinate transformation is applied to the carrier source to generate the frequency-modulated three-phase PWM carriers on a stator reference frame. By modulating voltage references with the transformed carriers, a locus of the corresponding harmonic currents on the estimated rotor reference frame is observed as a stationary ellipse because of a rotor saliency. Since a long-diameter direction of the harmonic-current ellipse indicates a true d-axis direction, orienting the estimated d axis to the long-diameter direction makes the sensorless operation possible. The paper describes a theoretical aspect of the proposed method and, then, presents experimental results as well as computer simulation results. Consequently, not only excellent controllability over a wide speed range including zero speed has been verified, but also robustness to the motor parameter variations has been confirmed.     

Analysis of transients at startup of cage induction motor: Acceleration stage

For the in-depth analysis of transients in a rotating induction motor the method of constant velocity is proposed, which allowed us to obtain analytical expressions for the currents and electromagnetic torque of the motor when selecting the d-q model as a starting point. The results of the theoretical analysis of transient currents and electromagnetic torque at the startup of the induction motor with a cage rotor are shown and the influence of the motor rotational frequency on them is determined. The results of the computer simulation of the induction motor startup confirm the validity of the analysis using the method of constant velocity.     

微机在线监测鼠笼型异步电动机转子的故障

本文研究鼠笼型异步电动机转子断条故障的在线检测方法。对定子电流和轴磁通信号的谱分析表明,定子电流中的某一谐波分量可做为转子静态偏心的特征分量,轴磁通信号中的3sf_1分量可做为转子断条故障的特征分量。实验结果表明,转子静态偏心对转子断条的特征分量没有影响。     

关于300MW火电机组辅机—5500KW锅炉给水泵用电动机的设计

本文叙述了根据西屋公司技术生产的4极5500kW锅炉给水泵用笼型异步电动机。与以往的相比,电动机设计采用较高的电和磁负载,从而将机座号从900mm中心高降至710mm。它节省了结构材料、降低了电机的重量,取得了较好的经济效果。文中还进一步阐述了机座结构、定子铁芯、绕组、转子装配、通风系统、轴承、噪声阻尼等新的结构细节。电机制造使用了国产材料,电机的性能得到用户的认可,和进口电机一样。     

Novel high-speed induction motor for a commercial centrifugalcompressor

This paper describes the electrical, mechanical and metallurgical design, construction, and testing of a novel low-cost high-speed high-efficiency induction motor to drive a new type of small centrifugal compressor in industrial cooling applications. The 28-shaft-hp 50-kr/min motor features a unique laminated rotor with a multifunction high-strength copper-alloy cage brazed with a novel process. Relatively thin high-silicon steel laminations were used to achieve low losses and high mechanical strength at low cost, Different heat treatments for the stator and rotor laminations were used to optimize the mechanical and magnetic properties, The preprototype motors achieved about 94% (electromagnetic) efficiency at the rated point, including inverter harmonics, while meeting cost (less than one-tenth of aerospace practice) and produceability goals     

车用永磁同步电机的电磁噪声分析与抑制

电机模态的准确分析是实现电机低噪声驱动设计的重要环节。当电机模态频率与对应阶次径向电磁力波频率接近时,会产生共振。以一台6极36槽的70 kW商务车主驱动永磁同步电机(PMSM)为研究对象,对比分析转子开辅助槽和针对一阶齿谐波的转子分段斜极方法对电磁力波的影响。采用转子开辅助槽和转子分段斜极的优化方法后,0阶12倍频径向电磁力波幅值可减小79%。建立电机三维有限元模态仿真模型,分析电机结构部件对模态的影响,结合常用车载驱动电机的安装固定方式对外壳进行约束,分析不同约束方式下电机的模态特性。结果表明,在峰值功率8 000 r/min的工况下,优化设计方案下的0阶12倍频的径向电磁力波幅值较大,但由于频率为4 800 Hz,远离电机模态的固有频率,因此不会发生共振,降低了电磁噪声。     

基于VPVM永磁同步电机无传感器控制策略的研究

贴面式永磁同步电机的无传感器控制在低速和静止时一直存在着转子位置难以检测和估算的问题,本文针对该情况提出了一种新的无传感器控制策略。转子初始位置检测是根据定子铁心的非线性磁化特性,采用电压脉冲矢量注入法（VPVM）。这种方法不需要电机参数和额外的硬件设施.电机开始运行时,由闭环自适应磁通观测器估算转子位置、速度.通过MATLAB仿真,从理论上验证了该方法的有效性。