Acceleration tests to determine salient pole synchronous motorinrush currents and torques

Determining torque and current at locked rotor and various slips during the acceleration test on a synchronous machine is very tedious and time consuming. Induction and synchronous machines behave similarly during acceleration except that synchronous machine acceleration can include a pulsation torque. Because of the salient poles, conditions exist where the synchronous motor has minimum torque at quadrature axis and maximum torque at direct axis during locked rotor or stall. Since synchronous machines do not have large numbers of rotor bars in the amortisseur winding, like the induction motor has in the squirrel cage, their stall times tend to be shorter. Due to the shorter stall time and large starting torque, locked-rotor torque and current are generally determined from acceleration tests conducted at reduced voltage rather than by tests at stand-still. Data showing that saturation effects impact both torque and current are presented in this paper. The data shows that the voltage index that has to be applied to the torque and current measured at reduced voltage varies with speed and can be obtained from a series of acceleration tests     

新型同步电机的结构、原理及空载特性研究

针对现有同步电机存在的问题,提出一种新型同步电机。该电机省去了滑环和电刷,通过调节励磁电流的大小和方向使发电机的输出电压可调。描述了电机的结构及原理,计算了发电机的空载特性。结果表明,电机的空载电势可以通过励磁电流方便地调节,电机的可靠性增加,但体积也有所增大。     

Optimum torque control of permanent-magnet AC Machines in the field-weakened region

This paper presents a novel current regulation algorithm for permanent-magnet ac (PMAC) machines that provides maximum torque-per-ampere capability in the entire field-weakened region. The algorithm provides robust current regulation with maximum efficiency and torque capability for PMAC machines despite significant changes in the voltage source and machine parameters. The algorithm identifies when the current regulator starts to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined from the torque command and d-axis current feedback. When the voltage angle reaches the maximum angle, the current magnitude is decreased to provide maximum torque per ampere. Experimental results from a machine prototype show that the algorithm provides good overall dynamic response and smooth transitions into the field-weakened region with maximum torque-per-ampere capability in all four quadrants of operation.     

Stator-flux-based vector control of induction machines in magneticsaturation

In many variable-torque applications of induction machines, it is desirable to operate the machine at high flux levels, thus allowing the machine to produce higher torques. This can lead to saturation of the main flux path, introducing cross-coupling effects which can severely disrupt the performance of controllers dependent on knowledge of the machine's magnetic parameters. Stator flux-oriented torque-control schemes need not depend on the magnetic parameters of the machine and, hence, are potentially more robust and easier to implement in magnetic saturation than rotor-flux-oriented control. In this paper, the authors present and analyze a stator-flux-oriented torque-control scheme. This controller only requires knowledge of the stator voltage, stator current, and stator resistance. An analytical expression for the maximum achievable torque output of the machine using a linear magnetics model is compared with values calculated using a nonlinear magnetics model incorporating saturation of the main flux path and is shown to be a good approximation at high flux levels, when the main flux path is heavily saturated. Experiments carried out on a 3 hp 1800 RPM wound-rotor induction machine show smooth operation of the control scheme at torque levels up to at least four times rated torque     

能自起动的抽水蓄能电站用双速同步发电─电动机，第一部分──原理

本文提出一种能自行起动的抽水蓄能电站用变极双速凸极同步发电─电动机，其机械结构和单速凸极同步电机一样，但转子极靴上不装阻尼笼，制造十分容易。作电动机运行时，不需要任何附加的起动装置，便能全电压直接起动，起动电流小，起动转矩大，容易牵入同步。该新型电机并有消除励磁绕组过电压，提高机组动态稳定性，显著改进作发电机运行时的电压波形等突出优点，用于抽水蓄能电站将获得巨大的经济效益和社会效益。     

Design Tradeoffs Between Stator Core Loss and Torque Ripple in IPM Machines

High stator core losses can pose a significant problem in interior permanent-magnet (IPM) machines operating over wide constant-power speed ranges. At lower speeds, the torque ripple can be undesirably large in some IPM machine designs, contributing to acoustic noise and vibration. While previous work has addressed these two problems independently, this paper shows that the conditions for reducing stator core losses during flux-weakening operation, dominated by harmonic eddy-current losses in the stator teeth, can conflict with the conditions for reducing the torque ripple of IPM machines. It is also shown that the resulting design tradeoffs depend on the details of the IPM machine topologies that are under consideration. The appropriate IPM machine topologies that offer more favorable tradeoffs are identified to achieve the best possible compromise of high-speed stator core losses and torque ripple characteristics.      

An egg‐shaped diagram and its discrepancies in switched reluctance machines

Recently, switched reluctance motors have attracted attention from industries. It is a common practice to develop several test machines for performance evaluation. One way to make a comparison among several test machines is to draw an efficiency map in a speed and torque plane, but this is rather complicated. For an easy comparison, a machine parameter measurement with an egg‐shaped diagram has been proposed by the authors. In this method, it is possible to measure an inductance ratio, which indicates the saliency of switched reluctance machines. In this paper, a calculation of tolerance between theoretical egg‐shaped curves and measured powers is proposed. It is found that the tolerances are within 4% as a result of several test machines. Although discrepancies in instantaneous current waveforms and voltage phase angles are seen, the obtained machine parameters indicate an exact relation between input power and required apparent power. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(1): 61–71, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10286     

Before and during voltage sags

The relationship between the voltages and the tripping level for line-operated synchronous machines is discussed. Voltage sags may cause tripping and large torque peaks in electrical machines. Tripping is caused by undervoltage protection or overcurrent protection. The ability to keep synchronism for the synchronous machines is mostly related to the loading of the machine and not very related to the voltage before and after the voltage sag.     

Torque-ripple minimization in modular permanent-magnet brushless machines

This paper discusses the suitability of four-phase, five-phase, and six-phase modular machines, for use in applications where servo characteristics and fault tolerance are key requirements. It is shown that an optimum slot number and pole number combination exists, for which excellent servo characteristics could be achieved, under healthy operating conditions, with minimum effects on the power density of the machine. To eliminate torque ripple due to residual cogging and various fault conditions, the paper describes a novel optimal torque control strategy for the modular permanent-magnet machines operating in both constant torque and constant power modes. The proposed control strategy enables ripple-free torque operation to be achieved, while minimizing the copper loss under voltage and current constraints. The utility of the proposed strategy is demonstrated by computer simulations on a four-phase fault-tolerant drive system.     

复合绝缘子两种污秽试验方法的对比

通过对比复合绝缘子的两种污秽试验结果,提出了复合绝缘子污秽试验中所存在的一些问题,说明了这些问题对试验结果的影响情况,给出了解决这些问题的一些方法,并探讨了复合绝缘子憎水性恢复对污闪电压的影响。     

同步发电机的动态阻尼力矩分析

根据由李亚普诺夫定理导出的综合阻尼系数的原理，统一定义了同步发电机的动态阻尼力矩系数和动态同步力矩系数。对同步发电机的阻尼力矩产生的机理进行了分析，并指出了使电力系统稳定装置产生阻尼力矩的同时，不致减少动态同步力矩的理论方向。     

Determination of Synchronous Reactance and No‐Load Saturation Curve of Synchronous Machines by dc Test Considering Magnetic Saturation Effect

dc Tests can accurately determine the unsaturated synchronous machine‐equivalent circuit constants by a simple standstill test. This paper presents two improved dc tests that account for the magnetic saturation of the stator iron core by the main flux. These tests are tentatively named Step Response Test (I) and Step Response Test (II). The former can predict the incremental d‐axis synchronous reactance by performing a Fourier transform of the voltage and current measured when a small step voltage is applied to the two armature terminals as a field current flows. The latter can determine the incremental d‐ and q‐axes synchronous reactances by the same Fourier transform of the voltage and current measured when a small step voltage is applied to the two armature terminals as an armature current flows. In addition, this paper introduces a new method to calculate not only the static d‐ and q‐axes synchronous reactances but also the no‐load saturation and short‐circuit characteristic curves. This new method does not require the results from any additional tests including the rotational driving tests and dimensional information, which can only be obtained from the manufacturer. To demonstrate the validity of the proposed method, results of an experiment using 10‐kVA laminated synchronous machines with damper winding are presented.     

Encoderless direct torque controller for limited speed range applications of brushless doubly fed reluctance motors

The paper proposes a direct torque control (DTC) algorithm suitable for low-variable-frequency operation of the brushless doubly fed reluctance machine (BDFRM) and considers aspects of its practical implementation. The simulation and experimental results show that a small BDFRM prototype can successfully operate down to zero supply frequency of the inverter-fed (secondary) winding, unlike cage induction or many other alternating current machines with DTC. This BDFRM advantage is a consequence of using a flux estimation technique not relying on the secondary voltage integration and therefore avoiding the well-known problems at low secondary frequencies, being typical for the BDFRM normal operation. The developed algorithm also offers the prospect for optimizing the machine performance in a manner similar to conventional vector controllers but with control actions executed in a stationary reference frame as usual for all traditional DTC methods. The maximum torque per inverter ampere control strategy has been chosen as a case study.     

Direct torque control for brushless doubly-fed machines

Work has illustrated the potential benefits of brushless doubly-fed machines in adjustable speed drive applications. While it has been shown that the drive is open-loop stable over a wide speed range, the resultant steady-state and dynamic performance characteristics are far from optimum. Thus, a closed-loop controller is desirable to achieve competitive drive performance. The controller proposed here is applicable for general purpose industrial drives in the medium to high power range. The nature of the doubly-fed machine, with two separate sources of excitation, only one of which is controllable, rules out field-oriented control strategies applied to conventional induction machines. However, the concept of direct torque control based on instantaneous error shows promise for this machine geometry. The present paper extends the concept of predictive torque control for induction machines to the doubly-fed machine. The controller calculates the value of converter voltage which leads to desired changes of flux and torque. Once the voltage is determined, conventional algorithms, such as space vector pulsewidth modulation (PWM), can be used to generate the inverter switching function     

冻结磁导率先进技术及其在高性能电机研发中的应用

如何考虑磁场饱和的影响是当前电机设计中一个亟待解决的重要问题。近年来提出的冻结磁导率技术越来越多地被应用到电机负载电磁性能和参数计算中。本文详细阐述了冻结磁导率的原理及其在各种电机中的应用现状。研究表明,冻结磁导率技术可以用来精确分离各种电机负载状态下的电磁分量,如磁场、磁链、电感、转矩、转矩波动、反电势和端电压、弱磁性能以及径向力等均可以用冻结磁导率技术预测,并用来辅助电机及其驱动控制系统的设计。因此,冻结磁导率技术为高性能电机的研发提供了一个全新的方法。     

Developing measuring inductance strategies on a direct current machine using a DC source with magnetic saturation

This article describes a novel measuring inductance strategy on direct current (DC) machines. Measuring self‐inductance and mutual‐inductance in rotating machines is always a very challenging task over a few decades. A significant challenge in modeling electric machines is to obtain their variables and parameters as accurate as possible. The method developed in this paper using a DC source for measuring the inductance in a DC machine overcomes some problems associated with traditional methods by using an alternating current source. In particular, it enables the field winding to carry its rated DC. This approach has demonstrated the feasibility of taking measurements for inductance in a DC machine and providing its field current that is sufficient to lead magnetic saturation, such that the flux can be kept the same as the supplied flux to the running DC machine. The proposed method for measuring both self‐inductance and mutual inductance of the DC machine armature winding coils has played a main role in modeling DC machines under a wide range of operating conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Current and flux regulation in field-weakening operation [ofinduction motors]

Field-weakening techniques have been developed which provide maximum torque capability above rated speed. Unfortunately, most of these techniques are valid only for steady-state operation and show significant sensitivity to DC-bus voltage and machine parameters. This paper analyzes the requirements of dynamically providing maximum torque under field-weakening operation. Three major issues are addressed: current regulator design; saturation techniques for current regulators in order to ensure best performance under voltage constraints; and flux regulator design to minimize transient errors when varying flux. Maximum DC-bus utilization through the proper use of saturation techniques, dynamic response and reduced sensitivity are the advantages of the proposed solution     

PERFORMANCE CALCULATIONS FOR INDUCTION MACHINES WITH A SOLID STEEL ROTOR

ABSTRACT

A method of calculating the performance characteristics for induction machines having solid steel rotors is presented. An equivalent circuit is derived in which the expressions for the circuit elements include the effects of rotor steel saturation, the finite length of the rotor, and the effect of induced rotor currents on the air gap flux density distribution. The analysis may be applied, with equal facility, to machines operating under conditions of constant voltage supply, or constant current supply. The accuracy of the method is demonstrated by comparison of torque/slip, power factor/slip, and current/slip curves that have been obtained by calculation and from practical tests. Results for three solid rotor machines of different rating, and pole number, are presented.     

Effect of manufacturer, winding age and insulation type on stator winding partial discharge levels

With thousands of machines monitored for as long as 25 years with the same method, on-line partial discharge (PD) testing has become a recognized, proven tool to help maintenance engineers identify which stator windings need off-line testing, inspections and/or repairs. With over 63,000 test results acquired with the same test method, what constitutes a winding with low, moderate or high PD has been identified. This paper presents tables that enable test users to easily identify with some certainty which stators are likely to suffer from groundwall insulation deterioration, with only a single measurement on a machine. The practical importance of these tables is that if one applies PD sensors to a machine and, in the first measurement, one obtains a Qm that exceeds the 90 percentile of the relevant Qm distribution, then one should be concerned enough at the PD level to take action, such as more frequent testing and/or off-line tests and inspections at the next convenient machine shutdown. Within the statistical accuracy possible with several thousands of independent results, it seems that critical PD levels only depend on operating voltage, hydrogen pressure, manufacturer, and the specific type of PD sensor and instrumentation used.     

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。