感应电动机的电源快速软投入技术及其初始瞬态解析

感应电动机在短时间断电后,对于转速仍然保持在同步速附近的情况,其重新投入电源的过渡过程表现为短暂的电磁瞬态,该文提出基于电力电子开关控制的电源快速软投入技术,可以在0.1 s内快速投入电源而不产生瞬态电流冲击,其控制策略不同于针对较长机电动态过程的软起动控制。为实现软投入控制的快速性,采用解析方法推导出瞬态电流与触发角等控制参数之间的关系。对于软投入控制中所出现的感应电机两相和三相交替的瞬态过程,分别建立基于ab 0坐标系降阶的不对称瞬态数学模型和与之相关联的基于空间向量复数变量的对称瞬态数学模型,使解析求解得以简化,从而快速求出初始触发角,进而构成触发角序列,最终得到完整的软投入控制策略,通过仿真和实验予以验证。     

感应电动机定子缺相故障动态过程仿真研究

缺相故障是三相感应电动机的典型故障之一，本文采用三相感应电动机在αβ0坐标系下的数学模型，根据具体故障情况下定子绕组的接线，推导出电机定子端电压的约束条件，编写了一个适合于感应电动机对称和定子不对称运行情况的实用仿真计算程序，通过对定子三角形接法的三相感应电动机的两种故障状态，即电源一相断开和定子绕组一相开路的运行过程进行仿真计算，并对仿真结果进行分析，得出了一些有用的结论。     

三绕组单相感应电动机的性能分析与实验研究

针对三相感应电动机可以替代单相电动机接于单相电网运行,提出将三相感应电动机的一相绕组与电容器串联后再与另外一相绕组并联,然后与第三相绕组串联,构成Y接法三绕组单相感应电动机。基于等效电流法,对三绕组单相感应电动机的运行性能进行研究,建立三绕组对称运行的条件,分析匹配电容对电机性能的影响。结果表明由于电容器的影响,无法实现严格对称运行,提出依据额定负载下电磁转矩最大为目标函数的电容器优化方法。采用该联结方式在一台2.2 kW电机上进行了实验,结果表明选择适当的电容将提高电机的效率,与三相对称电机在三相对称电源上的运行相比较,该接法的电机具有较高的功率因数,且效率接近三相对称运行时的效率。     

三相感应电动机单相SemihexTM运行瞬态过程仿真

为了得到三相感应电动机Semihex^TM接法单相运行时的瞬态特性，根据三相感应电动机在A、B、C相坐标系下的动态数学模型及三相感应电动机采用Semihex^TM接法时的边界方程，编制计算机仿真程序，对三相感应电动机单相Semihex^TM运行的瞬态过程进行仿真研究，对仿真结果进行分析：用对称分量法分析三相感应电动机Semihex^TM接法时的不对称系统，确定电容的数值。试验证明了分析方法的正确性。     

中性点不接地系统非对称短路故障分析

为提高分布式电源接入配电网的可靠性,以对称分量法为基础,重点分析了中性点不接地系统各种短路故障特性。给出了单相接地短路、两相相间短路、两相接地短路以及各种经过渡阻抗短路时故障点系统电压、电流的变化特性。得出中性点不接地系统两相相间短路与中性点接地系统一致,且不发生中性点漂移。而中性点不接地系统两相接地短路与中性点接地系统两相相间短路一致,但发生中性点漂移。所得结论能够为分布式电源接入配电网后的短路故障分析以及继电保护整定提供理论参考。     

六相感应电动机电源反接制动瞬态仿真研究

对六相感应电动机电源反接制动的瞬态过程进行了仿真分析。为了得到瞬态特性,建立了六相感应电动机在静止dq0坐标系下的混合磁链瞬态数学模型。编写计算机仿真程序,通过实例对六相感应电动机的电源反接制动的瞬态过程进行仿真计算,对仿真结果进行分析,得出了一些有用的结论。     

三绕组新型接法单相电动机的研究

普通单相感应电动机在单相供电系统中,当电动机额定功率比较大时是不经济的。该文提出了一种新型连接方式的三绕组单相感应电动机,对感应电动机的三相绕组进行了改接,并与电容器相连,改变了绕组中电流的相位,使三相电机在单相供电系统中实现接近对称运行。采用合成电流法研究了该连接方式下电机对称运行应满足的条件,讨论了对称运行条件下电容的选择及其对电机性能的影响。对该连接方式进行了试验研究,并与三相对称运行进行了比较,证明了新型接法三绕组电机的效率接近在三相电源上对称运行的效率,并且具有更高的功率因数。     

感应电机电源切换中残压和电压差的研究及最优切换策略

为了在不同备用电源下均能够尽可能地抑制感应电机电源切换中的冲击问题,有必要寻求最优电源切换方式,并在考虑开关动作时间下确定最有利切换时刻,为此,需要对断电后定子残压及其与不同备用电源间的电压差和相角差进行更加准确的定量研究。本文首先根据感应电机断电后的定子电流实测波形,发现电机断电后依次进入两个阶段——定子两相不对称瞬态和转子自由运动阶段,这种考虑必然提高定子残压的准确定量计算;然后,基于感应电机对称、不对称空间矢量模型,对断电过程两个阶段分别进行深入的解析推导,求得定子残压解析表达式;最后,重点研究定子残压及其与不同备用电源间的电压差和相角差特性,据此确定最优电源切换策略和最有利切换时刻,并通过感应电机电源切换实测结果验证了所得结论的正确性和可行性。     

新型接法的三绕组单相电动机

在单相供电系统中,当电动机额定功率大于0.5 kW时,采用普通单相感应电动机是不经济的,为此提出一种新型连接方式的三绕组单相感应电动机,该接法对Y接法三相感应电动机的6个出线头进行改接,并与2个电容器相连接,改变了绕组中电流的相位,使三相电机在单相供电系统中实现接近对称运行。采用对称分量法研究该连接方式下电机对称运行需要满足的条件,讨论对称运行条件下电容的选择及其对电机性能的影响,推导了该电机性能计算的具体方法。针对该连接方式进行试验研究,并与三相对称运行进行比较。样机试验证明,新型接法三绕组电机的效率接近三相电动机在三相电源上对称运行的效率,且具有更高的功率因数,可替代普通单相感应电动机。     

基于Ansoft感应电机不对称短路瞬态

首先简述感应电机不对称短路的瞬态理论基础，然后利用Ansoft对三相感应电动机带恒转矩负载和通风机负载稳定运行时突然发生定子一相绕组对中点短路故障的运行过程进行仿真计算，并对仿真结果进行分析。     

Transient stability simulation of wind generator expressed by two‐mass model

Recently, wind power generation is increasing worldwide. In wind power stations, induction machines are mostly used as generators. Since induction generators have a stability problem similar to the transient stability of synchronous machines, it is important to analyze the transient stability of power systems including wind generators. Although there have been some reports analyzing the transient stability problem, wind turbine and wind generator are, in most cases, modeled as a one‐mass shaft system having total inertia constant. This paper presents simulation analyses of transient stability of power system including induction generator which is expressed by a two‐mass shaft model and analyzes an effect of shaft system modeling on the transient stability characteristics. Simulations are performed by PSCAD/EMTDC in this study. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(3): 27–37, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20394     

基于暂态能量流的双馈风电机组强迫振荡源定位

暂态能量流法是一种新型的振荡源定位方法。首先,根据暂态能量流的计算公式,结合双馈风电机组的轴系模型、网侧变换器模型及双馈感应电机的三阶简化模型,推导适用于双馈风电机组的暂态能量流,并定义能流功率作为判断能量流向的指标。然后,对双馈风电机组加入强迫振荡源后的频率特性进行分析。最后,基于PSCAD/EMTDC电磁暂态仿真平台搭建包含强迫振荡源的单机无穷大系统和多台风电机组经串补并网系统进行时域仿真。利用采集的数据计算暂态能量流和能流功率,验证了暂态能量流法对双馈风电机组强迫振荡源定位的有效性。     

Evaluation of losses in DC machines-a statistical approach

The power ratings of the drive systems used in cyclic duty applications such as flying-die and cut-to-length shears are dictated by the thermal considerations associated with the losses produced by the machine during an operation cycle and the specified production rate. Since speed and torque are both transient functions with no steady-state operating point for such systems, a study was conducted to determine an expression that would describe these losses for a DC machine as a function of its operating speed and torque. A multiple regression technique was applied to the data collected from a set of sample machines for this purpose. Starting with the analysis of individual expressions for each of the components of losses in a DC machine, two regression models are presented. The first, based on a sample size of ten machines, provides an expression for the determination of operating point losses at any specified speed and torque per unit of rated machine losses (at rated speed and torque). The second model, based on data on 64 machines, provides an expression for the determination of rated losses in percent of machine power rating as a function of rated motor speed in r/min, armature volume in cubic units (DSQL), and percent armature droop. Mean estimates are also presented for the determination of percent droop and armature volume for a range of power ratings from 50 hp to 800 hp machines     

故障位置对交直流外送系统暂态功角稳定性的影响分析

分析电源中心交直流外送系统中故障位置对暂态功角稳定性的影响.以三机系统为例建立数学模型,其中2台等值机位于电源中心内部.简化模型后,给出2台相互耦合的等值机转子运动方程.根据转子运动方程中各项的物理意义,分情况讨论了不同位置发生故障后系统的暂态功角稳定性,并结合实际系统运行特点进行概括,得到结论如下:当电源中心内部交流联络线潮流较轻时,电源中心的交流外送通道发生故障,系统更易发生功角失稳;反之,电源中心内部发生故障,系统更易发生功角失稳,并对内部故障位置进行区分.最后,通过基于陕西电网陕北交直流外送系统的算例验证了结论的正确性.     

On-line switched control of a six-phase induction generator in faulted mode

The operation of multiphase machines in open-phase fault conditions is always associated with undesirable ripples in torque and power, even in steady state conditions. In the literature, several methods have been proposed to reduce these oscillations considering a fixed-fault situation without taking into account the transient behavior during the modification. In this way, this paper deals with the design and implementation of a multi-control system for all possible open-phase situations of a symmetrical squirrel cage six-phase induction generator (SC6PIG) up to three opened phases in such a way to extract a qualified electrical power. For this, a general model of the SC6PIG in healthy and open-phase fault situations is employed to design the multi-control system. The control systems are re-arranged regarding the situation of the generator in different open-phase fault conditions to provide the output power as close as in healthy mode. A simple detection system is associated to define the state of the generator (number and type of opened phases in faulty operation) and to switch to the appropriate control system. Furthermore, in order to minimize the transient problems during the switching process between the different control systems, an on-line initial condition setting is imposed to the control systems during the motion. An experimental set up including a SC6PIG driven by a permanent magnet dc motor has been built to prove the capacities of the proposed on-line switched control system in different cases such as healthy, one opened phase and two opened phases situations with smooth switching.     

Transient current analysis of induction generators for wind power generating system

In this paper we present a transient current analysis of induction generators used in a wind power system before and after three‐phase fault conditions. First, the basic equations of an induction generator connected to an infinite bus are developed and then transient current analysis formulas are derived for a three‐phase fault before and after fault clearance. We also determine the initial phase angle for the three‐phase fault or the restoration phase angle of the power supply voltages and the time at which the maximum or minimum transient currents flow in the system. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(1): 38–45, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10319     

Closed solution of the transient skin effect in induction machines

The transient skin effect is solved for the rectangular open and semi closed slots containing a massive conductor. The solution is applied to the Joule losses and to the analytical calculation of the air gap torque and the stator currents of the induction machine exposed to the three-phase short circuit. The calculation of the Joule power losses under transient conditions has been accomplished, especially, for induction machines of the middle- and high-power range. This becomes important in dynamically controlled induction machines, especially when torque cycles of approximately 100 ms or less occur. Never before have the copper losses been evaluated completely under these transient conditions. For the calculation of the losses, the direct proportionality of the losses between torque and rotor bar current can be used. Furthermore, the results of the transient skin effect can find application in the operational behavior of the induction machine. The consideration of the transient skin effect of the rotor is necessary for calculating currents and torques. Until now, state of the art has only provided an analytical solving of the skin effect free model. Aiming to apply the given rotor geometry, this paper derives an approach which includes the transient skin effect, applying it on the three-phase short circuit of the idle running induction machine.     

Dynamic single machine equivalent techniques for on-line transient stability assessment

According to the post-fault trajectory duration characteristics, power system disturbances, which may cause transient stability problems, are classified into three types: short, long and extremely long duration ones. An improved method using dynamic single machine equivalent system (SMES) model for on-line first swing critical clearing time (CCT) estimation for both short and long duration disturbances on multi-machine power systems is developed in this paper. This dynamic SMES model substitutes for a large power system to provide fast, on-line transient stability assessment (TSA). Techniques such as assessment of energy margin, identification of a group of machines called the ‘dominant critical machines’ and an interpolation formula for CCT evaluation are proposed in this method to achieve high speed and accuracy in TSA. Test results on real size power systems are reported to show that the method is reliable for CCT assessment of both short and long post-fault duration disturbances.     

Analysis and application of three-phase induction motor voltagecontroller with improved transient performance

An improved transient performance of three-phase inductance machines with controlled thyristor triggering is presented. A recently developed dynamic function for the thyristor triggering angle is utilized. The triggering angle function influences the phase modulation of the machine-supplied voltage such that the normal transient problems are avoided. Simulation of transients, based on the analytical solution of the machine differential equations, for all modes of operation is provided. The simulation model results show that a smooth switching process for an induction machine, running at any speed, for both motor and generator operation, is achievable. The beneficial effect of the suggested function is smoothing the transient flux, currents and torque is illustrated. Application of the function to different switching conditions is performed with actual laboratory tests