计及转速和励磁电流变化的主动补偿脉冲发电机数学模型

建立了主动补偿脉冲发电机 (ACPA)放电过程的数学模型 ,模型中同时考虑了转速和励磁电流变化的作用。通过仿真计算 ,分析了励磁电流和转速在放电过程中的变化情况 ,讨论了励磁电流对电流脉冲波形的影响     

液态金属磁流体发电机电枢反应分析

为研究液态金属磁流体(LMMHD)发电机内部感生电流产生的感应磁场对外部永磁磁路的影响,采用3D有限元法分析了不同感生电流下LMMHD发电机的磁路分布特点、永磁体工作点磁密及工作气隙磁密分布规律,得到了LMMHD发电机电枢反应特性。结果表明,LMMHD发电机内电枢电流产生的感应磁场使工作气隙磁场发生畸变,永磁体产生去磁效应,铁磁部件磁通密度增大、甚至达到磁饱和,磁路漏磁增大;当外磁路已达到磁饱和,电枢反应磁场减小工作气隙有效磁场分量、增大工作气隙端部漏磁,且在工作气隙中间区域产生Y方向磁场分量(电枢电流为X方向)。     

基于电枢反应补偿原理的新型永磁同步电机

在永磁同步电机调速系统中,电机中电枢反应将引起铁心磁饱和,并进而导致电机的输出转矩随转矩电流增长明显钝化。分析表明造成该现象的主要原因是永磁电机的磁动势平衡机制存在缺陷。本文提出在永磁同步电机转子上增设一套电流可控的交轴励磁绕组,用以补偿电枢反应磁动势的作用,保证负载变化时电机气隙磁场基本维持恒定。这种基于电枢反应补偿原理的新型永磁同步电机突破了磁饱和对电磁转矩的限制,为提高永磁同步电机转矩密度开辟了新途径。文中给出了一台新型电机样机的设计方案。通过有限元仿真,验证了通过补偿电枢反应磁动势提高电机转矩密度的有效性,并分析了该电机带不同负载运行时的转矩、效率特性及其与传统电机的区别。     

基于交叉饱和主磁路的同步发电机数学模型

在同步发电机派克方程的基础上,利用同步发电机的空载特性曲线,建立用电压、电流、磁链表示的考虑主磁路交叉饱和的同步发电机数学模型.通过仿真研究论证该模型的正确性,该模型适用于研究同步发电机处于非正常工况等主磁路饱和程度变化较大时的运行行为,能够比较准确地分析主磁路饱和程度变化对于同步发电机运行行为的影响,相比线性模型具有准确性高和适用范围广的优点.     

汽轮发电机的定子铁芯设计

1 定子铁芯的作用发电机转子的旋转主磁通在定子绕组中感应电势,产生发电机的负载电流。而定子绕组的电流产生电枢磁势和转子的磁势合成的总磁势,在定子铁芯、气隙和转子构成的磁回路中形成合成磁通,建立起发电机电压。两极汽轮发电机磁路如图7所示。定子铁芯的作用是使发电机总磁通获得低磁阻的磁路,同时起着固定定子绕组的作     

磁路互补型横向磁通切换直线电机电磁推力计算与特性分析

有铁心永磁直线电机由于齿槽、边端效应及电枢电流谐波等,不可避免地会产生较高的电磁推力波动,电磁推力波动直接影响直线电机运行精度和平稳性。该文对具有磁路互补特征的横向磁通切换直线电机展开电磁推力特性研究,通过等效磁路法分析其磁场分布规律,得出该电机次级具有等磁位的电磁特性;基于气隙磁动势-磁导分析方法,揭示互补磁路条件下,该有铁心电机消除齿槽推力波动,实现有铁心电机无齿槽效果的机理;基于该电机磁场分布特征,建立其许-克变换气隙磁场计算模型,提出定位力、电枢绕组磁阻力及永磁推力等电磁推力快速准确的计算方法,获得该电机各电磁推力特性;对样机进行了空载感应电动势和电磁推力的测试实验,对比实验和仿真结果,验证了理论分析模型及计算方法的有效性和准确性。     

采用统一磁路及空载试验的变压器饱和模型

为了精确地对变压器饱和进行仿真并建立变压器饱和模型,提出了一种基于统一磁路(UMEC)模型及空载试验的变压器饱和新模型.该模型利用UMEC来表示磁路中各个磁导之间的关系,并采用变压器空载试验获得电压、电流有效值曲线和功率损耗曲线,通过分段线性化方法得到变压器励磁磁导与电流之间的关系而近似表示磁路的饱和.该模型充分利用了...     

无刷直流电动机电枢反应对转矩脉动的影响与分析

采用简化等效磁路图,分析了无刷直流电动机电枢反应作用在永磁体两端面的磁动势影响,进而分析了"三相星接六状态"运行的无刷直流电动机电枢反应磁动势对转子永磁体产生增磁和去磁作用的特征和过程。在此基础上,考虑电动机在负载情况下,通过永磁体工作曲线图,求出工作气隙内由电枢反应作用的磁通变化数值。以一台8槽、18极无刷直流电动机为例,采用上述方法,分析并计算了电枢反应引起的转矩脉动百分比,为无刷直流电动机结构设计和抑制转矩脉动提供了可靠的理论依据。     

同步发电机带脉冲负载的磁饱和问题研究

介绍了电机内部的磁饱和现象和脉冲负载下磁饱和现象产生的原理,搭建了同步电机的有限元仿真模型,并根据此模型分析励磁磁场和电枢电流分别增大时对定子铁心磁饱和程度的影响,用于模拟脉冲负载波动下电机内部的运行情况。结果表明励磁磁场和电枢电流的增加对定子铁心的磁饱和都有不同程度的加剧作用进而影响电机的输出电压,因此提出了通过减小磁饱和来抑制脉冲负载系统中柴油发电机组输出电压减小的方法。     

一种三维磁路永磁电机的集中参数磁路模型

为了研究一种定子采用类爪极磁极铁心形状及环形集中绕组的三维磁路结构的磁通切换型永磁电机,在对空载静磁场及电枢反应磁场进行三维有限元磁场计算的基础上,根据电机在不同定、转子相对位置时的磁场分布情况,对三维磁路结构进行集中参数磁路模型建模,并推导出节点磁动势矩阵,通过对矩阵进行解析计算以及对计算结果的分析,推导出电机各主要电磁参数的解析表达式并进行计算和分析,通过与三维磁场计算结果相对比,验证了该磁路模型计算方法的正确性。由于可采用集中参数磁路模型计算可以节省大量计算时间,可以更方便地进行三维磁路结构电机的各种参数优化,对其他三维磁路和分析工作也具有参考意义。     

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     

Improvement of saturation property of iron powder core by flux homogenizing structure

A new core structure is proposed to improve the saturation property of an inductor made of iron powder core. In the conventional structure made of a single core material, converging flux lines cause local magnetic saturation at the inner side of the corners of the magnetic path. Therefore, the conventional inductor shows worse saturation property than expected from its core material. This degradation mechanism is solved in the proposed core structure through homogenization of the flux distribution at the corners. Experiments are performed to evaluate the flux homogenization and improvement of the saturation property. Results show a homogenized flux distribution in the proposed core structure. Furthermore, the flux level improved by 28% while the inductance decreased by 40% of its initial value. Both these results are consistent with theoretical expectations, except that a larger improvement is found in the experiment compared to the 16% improvement predicted by numerical calculation. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

ROTOR FLUX COMPUTATION IN SATURATED FIELD-ORIENTED INDUCTION MACHINES

ABSTRACT

The paper discusses effects of main flux saturation in field–oriented induction machines and proposes improved schemes for rotor flux space vector calculation. Field–oriented control with rotor flux computation out of the measured quantities is elaborated. Two rotor flux computer structures are analyzed. The first one is based on stator voltages and currents as measured variables, while the second scheme carries out calculations on the basis of sensed stator currents and rotor speed (position). The sensitivity of the constant parameter rotor flux computers to saturation degree variation is investigated in detail. Modified structures of the computing schemes are then proposed, which account for change in saturation level in the machine. The modified rotor flux calculators are derived from flux state–space model of a saturated induction machine. Accurate computation of rotor flux space vector is enabled in this way, irrespective of the actual saturation level in the machine. Verification of the developed modified rotor flux computers, which account for main flux saturation, is provided by the aid of digital simulation.     

Improved cage rotor models for vector controlled induction motors

Variations in motor model parameters lead to the detuning of vector controllers which, in turn, cause a deterioration in performance, particularly during transient and field weakening operation. Parameter adaptation schemes seek to change the model parameters based on observed performance, but are still based around a simple model for the machine which is not adequately representative. Improved motor models, based on deeper phenomenological understanding of the machine offer a viable alternative. In this paper, the authors present a model which enables rotor leakage and main flux path saturation and deep-bar effects to be taken into account. The model is verified experimentally using a 7.5-kW 4-pole motor, mounted on a piezoelectric force table which enables transient torques to be measured     

Effects of main and leakage flux saturation on the transient performances of doubly-fed wind driven induction generator

Doubly-fed induction generators are gaining more attention especially in the field of wind power generation due to their many advantages and the rapid development in both power electronics and control strategies. In this paper, a new saturated doubly-fed induction generator model is proposed. This model takes into account both main flux saturation and leakage flux saturation. The effect of the main flux saturation and the leakage flux saturation on the determination of the transient performances of doubly-fed induction generator under different transient conditions such as step change in input power, voltage sag and short-circuit at the terminals is the main objective of this paper. It has been demonstrated that although the inclusion of the main flux saturation in the generator modelling is important, the effect of the leakage flux saturation is the most dominant in the determination of the transient performances in the first few cycles following the transient.     

Leakage flux saturation effects on the transient performance of wound-rotor induction motors

The prediction of induction machine performance has traditionally been based on the constant parameter models. This approach was later replaced by considering saturation in the main flux paths. However, such models have not been sufficiently accurate for certain transient conditions such as on-line starting and short-circuit. So, an accurate study of their performance should necessarily consider the magnetic saturation effect both in the main and leakage flux paths. In this paper, an experimental procedure to determine the machine parameters and saturation characteristics is adopted. The adopted experimental procedure facilitates the measurement of both stator and rotor leakage reactance saturation characteristics. Two models of saturated induction motors are developed to predict the transient performance of a laboratory wound-rotor induction motor. The results calculated by the proposed models considering and ignoring the leakage flux saturation are compared with the experimental results. The model that considers saturation in the leakage flux paths produces more accurate transient responses.     

A sensor for balancing flux in converters with a high-frequencytransformer link

A method is introduced for measuring a selected flux threshold below saturation, by means of a pickup winding. The method is illustrated using a block-wave oscillator and involves placing a pickup winding in a square indentation in the center leg of an E-core. Incorporating an air gap, a high-reluctance path is created at the area of the indentation. The remaining area saturates first and forces flux through the high-reluctance path, which induces a voltage on the pickup winding. The method was tested experimentally, and a proposed mathematical model was used to simulate the magnetic behavior of the sensor. Experimental and simulated results are presented and compared to verify the discussed operation. Although similar strategies have been reported previously, the significance of the sensor introduced in this paper is that detection takes place before saturation occurs and the sensor is integrated in the core     

汽轮发电机内部非线性特征的定量表述

为了建立汽轮发电机的精确的非线性模型，以有限元方法为工具，系统研究了汽轮发电机的3种非线性因素，即主磁通饱和效应、励磁电流漏磁通导致的转子轭部附加饱和效应及磁场畸变非线性。采用定、转子齿部磁压降及转子轭部磁压降在总的磁势中所占比例表示相关部分磁路饱和非线性，进而研究磁场畸变非线性的定量表示方法。提出用等效气隙长度相对于气隙设计长度的变化来描述磁场畸变非线性。在额定点附近，等效气隙长度达到设计值的1.4倍，而在临界失稳工况下，等效气隙长度达到后者的2倍以上。通过300 MW发电机实测数据与有限元计算结果对比，说明结果可信。该方法与传统方法相比，可以更准确地描述汽轮发电机非正常运行条件下的非线性程度。     

考虑主磁路饱和与铁损的异步电机模型

通过推导任意同步旋转坐标系下考虑主磁路饱和与铁损的异步电机状态方程,研究互感与铁损等效电阻随压频比的变化规律,提出了一种互感曲线的工程辨识方法。采用多项式拟合互感与铁损等效电阻曲线描述主磁路饱和与铁损变化,建立了考虑主磁路饱和与铁损的异步电机仿真模型。仿真及实验的动态及稳态结果验证了仿真模型的正确性、有效性与精确性,为异步电机的高性能控制提供了一个更接近电机真实物理行为的实用模型。     

Modeling of saturated AC machines including air gap flux harmoniccomponents

A new saturation model for induction machines that can be easily extended to other types of AC machines is presented. It is shown that saturation is responsible for the generation of flux space harmonic components traveling in the air gap with the same synchronous speed as the fundamental flux component, with the third being the dominant harmonic component. Superposition of the effects of the fundamental and third harmonic components of the air gap flux is utilized in order to model the saturation of the ferromagnetic parts of the machine. The concept of winding functions is used to derive the inductance terms relating to both stator and rotor winding components. In this approach, the air gap length is assumed to be variable, being a function of the position and level of the air gap flux. Terminal and torque values for steady and transient states are obtainable from the proposed model, with experimental results showing that the model proposed predicts spatial saturation effects with good accuracy