Stator‐core structure and winding technology for EPS motors

Electric power steering (EPS) motors must have the performance characteristics of precision machines. They should be compact and produce high power. Moreover, the loss torque and the change of loss torque should be as low as possible. In this study, dividing the stator core into small blocks and winding the coils densely on the blocks are shown to be effective techniques for achieving compact high‐power motors. We examined whether I‐shaped divided cores or T‐shaped divided cores were more suitable for EPS motors in terms of motor performance and production cost. We built two experimental motors, one with I‐shaped divided cores and the other with T‐shaped divided cores, and measured three important characteristics of EPS motors: output torque, loss torque, and loss torque change. The T‐type motor proved to have better performance for all three characteristics. Moreover, the productivity of the T‐type motor was shown to be higher than that of the I‐type motor, indicating that overall, T‐shaped divided cores are advantageous for the stators of EPS motors. Next, we considered a new winding method for the continuous winding of two T‐shaped cores in order to achieve a compact terminal connection board. The extending lines made by the new winding method do not extend beyond the coil end. Therefore, this method will contribute to reduction of the axial dimension of EPS motors. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(1): 35–42, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21085     

变频牵引电机定子绕组绝缘老化特性研究

对比测量了不同运行年限的变频牵引电机的定子绕组绝缘诊断参数,包括绝缘电阻、介质损耗因数、局部放电起始电压(PDIV)、剩余击穿电压等特征参数,以及沿绕组不同部位的绝缘材料取样进行了热失重分析(TGA)来研究绝缘老化特征。介电性能测量结果表明,与新电机相比,运行后定子绕组的绝缘介电性能有不同程度的下降,出槽口附近绝缘的老化程度高于槽内。TGA分析结果表明,使用了长达10年的牵引电机定子绕组绝缘性能略有下降,且线圈下层边的绝缘老化比上层边明显。     

Diagnosis of Short‐Circuit Faults in Stator Winding Inside Low‐Voltage Induction Motor Using Impulse Voltage Test

Short‐circuit faults in windings due to the deterioration of insulation is among the most common faults in motor drive systems. An easy and effective fault diagnosis method is urgently required to ensure highly reliable operation. This paper proposes a novel method for the diagnosis of short‐circuit faults in stator winding inside a low‐voltage induction motor without removing the rotor, by performing an impulse voltage test. As the rotor does not need to be removed from the motor in this novel diagnosis method, the method can be put to practical use. In this study, first, several impulse voltage tests are carried out on the stator windings of motors. Second, the values of two features that represent the characteristics corresponding to the condition of the motor are calculated, and it is found that the shape of the feature distribution does not depend on the rotor position but on the condition of the winding. Third, the distance between the feature distribution for the healthy motor and features obtained from a target motor is calculated. On the basis of this distance, the condition of the stator winding inside the induction motor is determined. The effectiveness of the proposed diagnosis method is verified by performing experiments that involve several motors with healthy and faulty windings.     

New specs for ASD motors

The two main issues in pulse-width modulated ASD motors namely: stress concentration at slot exits and at junctions between stress grading and corona protection materials, and winding insulation aging due to partial discharge and/or dielectric heating, often intensified between turns as well as across the main-wall of the stator coils. This paper explores the IEC-60034-18-41 and IEC-60034-18-42 technical specifications for inverter duty motor insulation. These specifications describe the qualification and acceptance tests for both low and medium voltage motor windings in order to ensure reliability     

基于电流与最高温度检测的异步电动机保护研究

通过构建异步电动机定子温度分布的测试系统,对典型运行状态下的异步电动机定子绕组的温度分布进行实际测试,在实测温度分布数据的基础上分析了电动机定子温度分布的特点,得出定子绕组最高温度区域位于接线盒区域传动侧绕组端部结论.基于异步电动机热理论建立了定子三维温度场仿真模型,对更多运行状态下的温度分布进行研究,验证了实验确定的...     

A sensorless drive system for brushless DC motors using a digital phase‐locked loop

This paper proposes a sensorless drive system for Brushless DC (BLDC) motors using a Digital Phase‐Locked Loop (DPLL). The Back Electromotive Force (BEMF) voltage is measured from the motor winding to determine the permanent magnet rotor position using the DPLL, and Pulse Width Modulation (PWM) limits the motor current to control the speed of BLDC motors. The proposed method can drive BLDC motors using an open‐loop control without stepping out. Also, the proposed method is compared experimentally with a control method that uses Hall sensors. Experimental results for the BLDC motor show the effectiveness of the proposed method. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 57–66, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10074     

Transient characteristics of a tapped‐winding capacitor motor

Tapped‐winding capacitor motors are widely used for fans in air conditioners as speed adjusting motors. In tapped‐winding capacitor motors, the burnout accidents of phase‐shifting capacitors have been seen on occasion. The cause of such accidents is considered to be the transient capacitor current. In this paper, equations for calculating transient characteristics are derived for three types of tapped‐winding capacitor motors. Based on these equations, transient characteristics are clarified in high‐ and low‐speed winding connections. Further, from the design viewpoint, the effects of the turn ratio and capacitance of the capacitor on the transient characteristics are examined and a procedure for choosing the winding ratio and capacitance of the capacitor is suggested. Using this method, the transient current is shown to decrease by about 40%. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 69–77, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10063     

Analysis of steep-fronted voltage distribution and turn insulationfailure in inverter-fed form-wound AC motor

As a potential source of turn insulation failure, the steep-fronted voltage at the motor terminal generated by pulsewidth modulation drive switching or cable ringing is not uniformly distributed among the coils of the windings and among the turns of the coils. This paper presents a detailed electromagnetic analysis of the parameters of a transient model of coil and coil group which includes iron loss, skin, and proximity effects. The finite-difference method is applied to solve the model for the interturn and intercoil voltage distributions. The simulation is compared to a simplified lattice diagram analysis and to test results. A turn insulation surge-withstanding capability study is then presented with a flexible insulation test system that models the repetitive steep-fronted voltage stress and temperature stress     

Steep fronted surges applied to large AC motors-effect of surgecapacitor value and lead length

The line end coil of large AC motors is known to suffer increased inter-turn voltage stress under steep fronted surge conditions. Surge capacitors can be used to slow down the surge rise-time. The effects of capacitor value and lead length on the line end coil voltage are examined. The theoretical and measured waveforms for the line end coil of a 3.3 kV, 1 MW, four-pole induction motor are compared. The results show clearly that when the capacitor lead length approaches 1, even a relatively large capacitor value has little effect     

A low‐loss snubber for reducing motor terminal surge voltage

The development of an advanced Insulated Gate Bipolar Transistor (IGBT) has enabled high‐frequency switching operation and has improved the performance of PWM inverters for motor drive. However, the IGBT's high rate of dv/dt has adverse effects on motor insulation stress. In many motor drive applications, the inverter and motor are separated, requiring long motor feeds. The long cable contributes high‐frequency ringing at the motor terminal and results in high surge voltage which stresses the motor insulation. The inverter output filter and RDC snubber are the conventional method for reducing the surge voltage. In this paper, we propose a new low‐loss snubber to reduce the motor terminal surge voltage. The snubber consists of the series connection of chraging/discharging capacitor and the voltage‐clamped capacitor. At IGBT turn‐off, the snubber starts to operate when the IGBT voltage reaches the voltage‐clamped level. Since dv/dt is decreased by snubber operating, the peak level of the surge voltage can be reduced. Also the snubber operates at the IGBT voltage above the voltage‐clamped level, and the snubber loss is largely reduced compared with the RDC snubber. The proposed snubber enables reduction of the motor terminal surge voltage with low loss. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 64–72, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10378     

Effect of surge voltage risetime on the insulation of low-voltagemachines fed by PWM converters

This paper investigates the repetitive surge-voltage withstand of low-voltage mush-wound machines operated on adjustable-speed drives (ASDs) using insulated gate bipolar transistor (IGBT) semiconductor technology. Historical work on surge testing of motor insulation has focused on one or more of the following aspects: (1) large horsepower motors; (2) medium-voltage form-wound motors; (3) single-shot impulse-type transients; or (4) low-voltage machines with surge risetimes >200 ns. IGBT drives can have risetimes of 50-200 ns. Thus, a new study on electrical stress of insulation systems due to the nonlinear voltage distribution of mush-wound motors when subjected to repetitive steep dV/dt square-pulse waveforms (rather than impulse wave testing) is presented. Magnitude and risetime of the repetitive ASD surge-voltage transient induced on the machine terminals is reviewed first. Next, surge propagation into the winding was investigated to identify maximum voltage stress points on the conductor insulation. Potential failure mechanisms observed at these points are then discussed. The significance of decreasing surge risetime and increasing cable lengths on internal nonlinear voltage distribution is studied with experimental results from a 7.5-hp motor with a tapped stator winding     

Identification of plant model of linear induction motors for a traction system intended for use in a high‐performance controller

A linear induction motor (LIM) is suitable for use in trains. The motor can be used in both wheel‐suspended and contact‐less types such as the Linear Metro and HSST trains in Japan. The LIM has end winding as well as asymmetrical winding. The end effect is a major problem in the LIM, and it makes the analysis, design, and control of motors difficult. This paper describes a method that combines numerical analysis and the equivalent circuit for the LIM in order to design a high‐performance controller for the LIM that includes the end effect. A sample basic field‐oriented control scheme that is based on the plant model is applied to the LIM in order to check the control performance. The theory of rotary induction motors is used for verification. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 44–54, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21171     

Sensor Retrofitting of Motors For Protection Against Overtemperature

Low-cost fast-response thermal sensors are making it possible to add overtemperature protection to industrial motors on a retrofit basis. Easily applied by regular maintenance personnel, this protection system offers industrial plants, large and small, the opportunity for longer, trouble-free motor life, The application of sensors to existing induction motors to prevent thermal damage resulting from abnormal running overload or locked rotor conditions is also described here. Basic considerations for proper application are discussed, including motor winding configurations, insulation classes, and other design characteristics. Motor rewind shops provide a basic area of application where the sensors can be integrally installed in the stator winding at the time of repair. Examples and experiences are discussed where applications have been made.     

变频牵引电机定子绕组内部电压分布特性的研究

分析PWM逆变器驱动的变频牵引电机定子绕组内部电压分布特性,对研究定子绕组绝缘失效和进行绝缘结构设计有重要意义。文章依据变频牵引电机定子绕组结构形式,建立绕组的分布参数电路模型,采用有限差分方法求解得出绕组内部电压分布情况,然后用实际测试结果验证模型的有效性,基于该模型讨论脉冲上升沿时间和电缆对绕组内部电压分布特性的影响。研究结果表明:上升沿时间越短,绕组内部电压分布越不均匀,线圈和匝电压幅值越大,而电缆长度对绕组内部电压分布影响较小,但绕组内部电压幅值增加了约40%。     

A simplified equivalent thermal circuit for the substitution of a stator in an induction motor

Based on a review of investigations of the thermal behavior of induction motors, it has been established that the stator winding of an induction motor is subject to very high values of temperature in most applications and work regimes. The analysis of techniques to determine the temperatures of different units of an induction motor helped us to propose the use of equivalent thermal circuits, in particular, a simplified substitution circuit for the determination of winding and a magnetic conductor of a stator. The thermal equilibrium equations were found. A technique to calculate the thermal resistances of a stator by means of a laboratory setup was developed. The setup considers the features of cooling specific types of motors; thus, it is unnecessary to observe an induction motor as an aerodynamic system. The technique was tested using a setup containing a 14-kW short-circuited induction motor. The temperatures in different units of a motor were measured using chromel–copel thermocouples, and its load simulated the load of a traction electric drive of transport vehicles. The results of the experimental investigation are presented to show the influence of the rotor speed and the cooling air flow on the thermal resistances.     

Strains on Motor Endwindings

Stator winding failures are second in frequency of occurrence only to bearing problems in the categories of ac motor troubles and can lead to operational losses many times the cost of the complete motor. There are a number of causes of failure, but one of the more likely is inadequate bracing of the stator endwinding to withstand the high electromagnetic forces experienced during starting. The use of a finite element technique to predict stator endwinding forces and endwinding movement of large induction motors is described. The determination of the mechanical properties of the coils and bracing system components is discussed, as is the life testing of the insulation with mechanical vibration and electrical checks. The use of lasers to determine endwinding movement during the starting of several large 13.8-kV motors is also described.     

高频供电条件下的PCB定子盘式永磁电机绕组优化设计

PCB定子盘式永磁无铁心电机的定子采用印制电路板(printed circuit board,PCB)结构,其电机的损耗主要来源于绕组上的交流附加铜耗和直流铜耗,因此定子绕组的设计直接影响电机整体性能。针对应用在较高频率且工况稳定的PCB电机,该文提出一种新型分布式绕组。首先建立反电势、直流铜耗、交流附加铜耗和电阻的解析表达式,分析PCB电机的空载特性。其次,以提高电机的效率为目的,提出在绕组有效导体部分加入绝缘材料。对新型绕组进行优化找到最合适的导体线宽,然后根据有限元理论对比分析新型分布式绕组和已有绕组负载特性。结果表明新型绕组不仅可以降低总铜耗,提高电机效率,有效降低定子稳定温升,并且新型结构也不会影响电机输出性能。最后制作一台16极600W样机进行验证,对PCB定子盘式永磁电机设计具有一定的参考价值。     

The results do mesh

This article considers the effects of open-circuited phase windings and of shorted coil turns of the stator winding on the operation of the induction machine. The analysis and comparison of faulted modes of operation is achieved by simulation, using the dynamic mesh reluctance model (DMRM) approach. The DMRM approach gives valuable insight of induction motor detection of the faulted windings. Clearly, five-phase motors with third harmonic control give the best performance for machines with one-phase open circuit, and careful machine design can minimize adverse effects of torque ripple     

Using corona inception voltage for motor evaluation

Failures of the interturn insulation system of induction motors fed by PWM variable speed controllers have plagued the industry since the introduction of fast-switching, IGBT-based drives. The majority of these failures are attributed to high voltage stresses imposed upon the motor by the drive. Here, the author describes how the corona inception voltage can be used for evaluating the state of variable speed induction motor drive insulation     

基于探测线圈的无轴承异步电机气隙磁场测量方法研究

无轴承异步电机悬浮机理决定了转矩绕组和悬浮绕组两种气隙磁场的强耦合关系，而转矩绕组气隙磁场幅值和相位的准确识别又是实现径向悬浮控制的必要条件。文中提出采用探测线圈同时测量两套绕组的气隙磁场幅值和相位，从而避免了因电机参数测量误差或参数变化对悬浮控制性能带来的影响，而且使无轴承异步电机在超高速下运转成为可能。针对探测线圈安装位置的不同，分别详细论述了均匀分布角位置法、典型角位置法和解析法三种气隙磁密测量方法，并作了比较。实验结果验证了所述方法的有效性。