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目录一、概述1、电机概述2、变频器概述3、三相异步牵引电机变频调速原理及其种类 3.1变频调速原理及其机械特性3.2.基频以下变频调速3.3.基频以上变频调速二、异步电动机在两相静止坐标系下的数学模型三、 异步电动机的仿真模型四、S-function程序五、电机系统模型六、仿真过程及其结果七、总结参考文献摘 要由于变频运行下三相异步电动机调速系统具有节能的重要优点,已在国内外工业生产和日常生活许多领域得到越来越广泛地应用。目前在变频调速系统中,随着电力电子技术及变频调速技术的迅速发展,交流调速技术日新月异，新的控制策略不断涌现，这也使得交流调速开始全面取代直流调速。在交流调速技术中，交流变频调速以其优异的调速性能，高效节能和广泛的应用范围等特点而被国内外人为是最有前途的调速方式。关键词：变频；三相异步电动机；调速ABSTRACTWith the important merit of saving energy for the timing system of three-phase induction motor under the supply of frequency converter, it has been widely used in more and more fields. Now, with the rapid development of power electronics and frequency-conversion technology.the technology of adjusting speed of AC induction electromotor changes quickly and new control method appears ceaselessly. DC electromotor by the AC induction electromotor is replaced by the AC induction electromotor in wide range. The AC variable frequency speed regulation is generally acknowledged by the home and abroad that it has a great future with excellent speed regulation, high efficiency saving energy, extensive scope of application and other merit. Keywords: frequency converter; three-phase induction motor;change speed一、概述在变频调速系统中异步电机是一个非线性、强耦合、高阶次的控制对象，如果忽略其非线性、强耦合、高阶次的条件，近似求出线性单变量动态结构，得到的控制系统的动态性能往往不高。要设计具有优良动态性能的异步电机调速系统，必须要深入分析异步电机的动态数学模型。本文在分析异步电机数学模型的基础上，利用MATLAB软件中的SIMULINK对异步电动机进行建模，通过给出异步电动机正弦脉宽调制(SPWMSinusoidal Pulse Width Modulation)变频调速系统的仿真结果来验证利用这三种方法对异步电机进行建模的可行性。1电机概述1电机作为一种机电能量转换装置，在电力工业各类工矿企业，农业国防，交通运输，日常生活各方面都占有重要地位。随着科学技术的发展和社会化大生产的需要，三相基本的电机形式：直流电机，感应电机，同步电机在工业生产和日常生活中获得了广泛的应用。异步电动机的转速根据负载的要求，人为的或自动的进行调节，称为调速。但出于不同的使用目的，往往对电动机的速度提出不同的要求，如电动车辆，电梯，机床等要求有良好的速度调节性能；调速也是风机，水泵类负载节能运行的需要。一般笼型异步电动机的转速略低于同步转速，且在负载变化时变化不大，是一种接近于恒速的驱动装置，其本身的调速性能不佳。因此电动机的调速控制一直是电气专家学者致力于解决的问题。近年来，直流调速，交流变频调速随着技术的进步，性能在不断改善。直流电动机具有优良的调速性能，但它有一个根本的缺点，就是有机械式的整流器整流子和电刷，因此它的维护工作量较大；而且由于机械式整流器的限制，制造大功率高电压的直流电机比较困难。由于这些原因，限制了直流可调速拖动系统的使用范围。我们知道，交流异步电动机的转速n与定子旋转磁场的速度、转子的转差率s有以下关系：式中电源效率，Hz，p电动机极对数；改变电源的频率，电动机可以调速。变频调速既适用于同步电动机，又适用异步电动机，是一种高效率的调速方案。2变频器概述 变频器是异步电动机调速系统中的关键设备。变频器是利用电力半导体器件的通断作用将工频电源变换为另一频率的电能控制装置。我们现在使用的变频器主要采用交直交方式（VVVF变频或矢量控制变频），先把工频交流电源通过整流器转换成直流电源，然后再把直流电源转换成频率、电压均可控制的交流电源以供给电动机。变频器的电路一般由整流、中间直流环节、逆变和控制4个部分组成。整流部分为三相桥式不可控整流器，逆变部分为IGBT三相桥式逆变器，且输出为PWM波形，中间直流环节为滤波、直流储能和缓冲无功功率。7变频器实际上就是一个逆变器.它首先是将交流电变为直流电.然后用电子元件对直流电进行开关.变为交流电.一般功率较大的变频器用可控硅.并设一个可调频率的装置.使频率在一定范围内可调.用来控制电机的转数.使转数在一定的范围内可调.变频器广泛用于交流电机的调速中.变频调速技术是现代电力传动技术重要发展的方向，随着电力电子技术的发展，交流变频技术从理论到实际逐渐走向成熟。变频器不仅调速平滑，范围大，效率高，启动电流小，运行平稳，而且节能效果明显。因此，交流变频调速已逐渐取代了过去的传统滑差调速、变极调速、直流调速等调速系统，越来越广泛的应用于冶金、纺织、印染、烟机生产线及楼宇、供水空调等领域。3三相异步电动机变频调速原理及其种类三相异步电动机的调速开始于上世纪50年代末。在电气传动领域中，原来只用于恒速传动的交流电动机实现了调速控制，以取代制造复杂，价格昂贵，维护麻烦的直流电动机。以后，随着电力电子技术和微型计算机的发展，再加上现代控制理论向电气传动领域的渗透，使得交流调速技术得到了迅速发展，其设备容量不断扩大，性能指标及可靠性不断提高，高性能交流调速系统应用的比例逐年上升，在各工业部门中，使得交流调速系统逐步取代直流调速系统，以达到节能，缩小体积、降低成本的目的。根据三相异步电动机的转速公式为 式中为异步电动机的定子电压供电频率；为异步电动机的极对数；为异步电动机的转差率。所以调节三相异步电动机的转速有三种方案。异步电动机的变压变频调速系统一般简称变频调速系统，由于调速时转差功率不变，在各种异步电动机调速系统中效率最高，同时性能最好，是交流调速系统的主要研究和发展方向。3.1变频调速原理及其机械特性改变异步电动机定子绕组供电电源的频率，可以改变同步转速，从而改变转速。如果频率连续可调，则可平滑的调节转速，此为变频调速原理。三相异步电动机运行时，忽略定子阻抗压降时，定子每相电压为 式中为气隙磁通在定子每相中的感应电动势；为定子电源频率；为定子每相绕组匝数；为基波绕组系数，为每极气隙磁通量。如果改变频率，且保持定子电源电压不变，则气隙每极磁通将增大，会引起电动机铁芯磁路饱和，从而导致过大的励磁电流，严重时会因绕组过热而损坏电机，这是不允许的。因此，降低电源频率时，必须同时降低电源电压，已达到控制磁通的目的。对此，需要考虑基频（额定频率）以下的调速和基频以上调速两种情况。3.2.基频以下变频调速18为了防止磁路的饱和，当降低定子电源频率时，保持为常数，使气每极磁通为常数，应使电压和频率按比例的配合调节。这时，电动机的电磁转矩为上式对求导，即 ，有最大转矩和临界转差率为由上式可知：当常数时，在较高时，即接近额定频率时，随着的降低，减少的不多；当较低时，较小；相对变大，则随着的降低，就减小了。显然，当降低时，最大转矩不等于常数。保持常数，降低频率调速时的机械特征如图1所示。这相当于他励直流电机的降压调速。图1 变频调速的机械特性（a） 基频以下调速（常数）（b）基频以上调速（=常数）3.3.基频以上变频调速在基频以上变频调速时，也按比例身高电源电压时不允许的，只能保持电压为不变，频率越高，磁通越低，是一种降低磁通升速的方法，这相当于它励电动机弱磁调速。保持=常数,升高频率时，电动机的电磁转矩为 上式求，得最大转矩和临界转差率为 由于较高，、和比大的多，则上式变为 因此，频率越高时，越小，也越小。保持 为常数，升高频率调速时的机械特性如图1（b）所示。二、异步电动机在两相静止坐标系下的数学模型在研究异步电动机的数学模型时，在文中作如下的假设：(1)忽略空间谐波。设三相绕组对称(在空间上互差120。电角度)，所产生的磁动势沿气隙圆周按正弦规律分布；(2)忽略磁路饱和，各绕组的自感和互感都是恒定的；(3)忽略铁芯损耗；(4)不考虑频率和温度变化对绕组电阻的影响。异步电动机在静止坐标系、上的数学模型为：(1)电压方程为：(2)磁链方程为：(3)转矩方程为：T (3) e=N p(i11-i11) (3)(4)运动方程为：T e-T l =J*dw/(dt*N p)(4) 式中R 1、R 2、L 1、L 2为定子、转子电阻和自感，L m为定子、转子间互感， 为电机转子角速度；u1、u1为、轴定子电压，i1、i1、1、1为、轴定子电流及磁链，T e为电磁转矩；T l为负载转矩；N p为电机极对数；J 为电机转动惯量。把静止轴系下三相/二相变换公式代入上述表达式，得到：将(6)式代入(5)式作非奇异变换，得到以定子电流及定子磁链为状态的异步电机状态方程为：三、 异步电动机的仿真模型基于MATLAB/SIMULINK的异步电机系统仿真可以利用SIMULINK模块搭建，但是，并非所有的数学模型都能利用模块轻易地搭建起来，有的模型更适合于MATLAB/SIMULINK支持的S一函数(_)格式，MATLAB语言或着C等语言格式来描述，构成S一函数模块，像标淮的SIMULINK模块直接调用。上述经过3/2变换的三相异步电机的数学模型仍是一个高阶、非线性、强祸合的多变量系统，用框图搭建非常烦杂，而且易于出错。本文的方法是利用MATLAB格式编写异步电机的S一函数来实现电机的建模，其模型简洁明了、不易出错。在 MA TL AB/SIMULINK软件平台中提供了一个sfuntmpl. m的模板文件，可以利用这个模板文件邀行修改，按自己的需要来构建自己的S一函数。根据 数 学 模型之(5)式，输人是静止a,8轴上的定子电压、,u,以及转子电角速度.，输出是静止a,a轴上的定、转子电流i,ii,0。根据MATLAB语言设计一个名为acmotor_sfun的S-函数，模型见图l。当仿真的时候，SFunction模块直接调用SIMULINK 中自己编写的acmotor_sfun.m二文件，即可完成M文件所要求的运行功能。M文件的具体程序如下:%两相静止坐标系下的电机模型(IM) %状态变量: x(1)=Wr; x(2)=phi_a; x(3)=phi_b; x(4)=i_a; x(5)=i_b; %输入变量为 u(1)=Ua; u(2)=Ub; u(3)=Uc; 三相输入电压; u(4)=T_L 负载转矩%输出变量 sys(1)=Wr; sys(2)=i_a; sys(3)=i_b; sys(4)=i_c; sys(5)=Te function sys,x0,str,ts = MOTOR(t, x, u,flag, Rs, Rr, Ls, Lr, Lm, J, np) switch flag, case 0, sys, x0, str, ts=mdlInitializeSizes; case 1, sys=mdlDerivatives(t, x, u, Rs, Ls, Rr, Lr, Lm, J, np); case 2, 9, sys= ; case 3, sys=mdlOutputs(t,x,Rs, Ls, Rr, Lr, Lm, J, np); case 4, sys=mdlGetTimeOfNextVarHit(t,x,u); otherwise error(Unhandled flag = ,num2str(flag); end % 初始化 function sys,x0,str,ts=mdlInitializeSizes sizes = simsizes; sizes.NumContStates = 5; sizes.NumDiscStates = 0; sizes.NumOutputs = 5; sizes.NumInputs = 3; sizes.DirFeedthrough = 1; sizes.NumSampleTimes = 1; sys = simsizes(sizes); x0 = 0; str = ; ts = 0 0; % 微分 function sys=mdlDerivatives(t,x,u,Rs,Ls,Rr,Lr,Lm,J,np) delta=1-Lm*Lm/(Ls*Lr); %状态方程(x(1)=Wr,x(2)=phi_a,x(3)=phi_b,x(4)=i_a,x(5)=i_b) dx(1)=(np2*Lm/(J*Lr)*(x(2)*x(5)-x(3)*x(4)-np*u(3)/J; dx(2)=-(Rr/Lr)*x(2)-x(1)*x(3)+(Rr/Lr)*Lm*x(4); dx(3)=-(Rr/Lr)*x(3)+x(1)*x(2)+(Rr/Lr)*Lm*x(5); dx(4)=Lm*Rr/(delta*Ls*Lr*Lr)*x(2)+Lm/(delta*Ls*Lr)*x(1)*x(3)-(Lm*Lm*Rr+Lr*Lr*Rs)/(delta*Ls*Lr*Lr)*x(4)+u(1)/(delta*Ls); dx(5)=Lm*Rr/(delta*Ls*Lr*Lr)*x(3)-Lm/(delta*Ls*Lr)*x(1)*x(2)-(Lm*Lm*Rr+Lr*Lr*Rs)/(delta*Ls*Lr*Lr)*x(5)+u(2)/(delta*Ls); sys=dx;%sys(1)=(np*np*Lm/(J*Lr)*(sys(2)*sys(5)-sys(3)*sys(4)-u(4)/J; % 微分结束 % 输出 function sys=mdlOutputs(t,x,Rs, Ls, Rr, Lr, Lm, J, np)sys(1)=x(1); %Wr sys(2)=sqrt(2/3)*x(4); %i_a sys(3)=-sqrt(1/6)*x(4)+sqrt(1/2)*x(5); %i_b sys(4)=-sqrt(1/6)*x(4)-sqrt(1/2)*x(5); %i_csys(5)=np*(Lm/Lr)*(x(2)*x(5)-x(3)*x(4); %Te % 输出结束 % 终止 function sys=mdlTerminate(t, x, u) sys = ; function sys=mdlGetTimeOfNextVarHit(t,x,u) sampleTime = 200; % Example, set the next hit to be one second later. sys = t + sampleTime; % end mdlGetTimeOfNextVarHit 四、S-function程序function A,B,C,D,K,X0 = motor(par,ts,aux)%MOTOR ODE file representing the dynamics of a motor.% A,B,C,D,K,X0 = MOTOR(Tau,Ts,G)% returns the State Space matrices of the DC-motor with% time-constant Tau (Tau = par) and known static gain G. The sample% time is Ts.% This file returns continuous-time representation if input argument Ts% is zero. If Ts0, a discrete-time representation is returned. To make% the IDGREY model that uses this file aware of this flexibility, set the% value of Structure.FcnType property to cd. This flexibility is useful% for conversion between continuous and discrete domains required for% estimation and simulation.% See also IDGREY, IDDEMO7. % L. Ljung% Copyright 1986-2011 The MathWorks, Inc.% $Revision: 1.1.10.1.2.1 $ $Date: 2011/12/27 15:42:57 $ t = par(1);G = aux(1); A = 0 1;0 -1/t;B = 0;G/t;C = eye(2);D = 0;0;K = zeros(2);X0 = 0;0;if ts0 % Sample the model with sample time Ts s = expm(A B*ts; zeros(1,3); A = s(1:2,1:2); B = s(1:2,3);end五、电机系统模型六、仿真过程及其结果（1）20HZ电流20HZ电流整体20HZ电压设置20HZ转速（2）50HZ电流50HZ电流整体50HZ转速50HZ电压设置六、总结本文讨论了基于两相静止坐标系下的三相异步交流电机在MATLAB/SIMULINK环境下的仿真，介绍了S一Function建模的方法，其特点是编程容易，模型直观，没有烦琐的框图。然后以转动惯量的大小变化对电机启动时的影响为例，进行电机模型的仿真，从仿真结果可以看出所建模型符含实际异步电机的运行特性，验证了设计模型的正确性，为进一步基于DSP的矢量控制变频调速系统的研究奠定基础。参考文献1陈建业，电力电子电路的计算机仿真，北京：清华大学出版社，20052陈刚，软开关双向DC/DC变换器的研究，浙江大学博士学位论文，20013张国安，朱忠尼，新型推挽式移相式软开关拓扑研究，电工技术杂志，1998（1）4伊林林，软开关PWM 双向D C / D C 变换器的研5百度g an employment tribunal claimEmployment tribunals sort out disagreements between employers and employees.You may need to make a claim to an employment tribunal if: you dont agree with the disciplinary action your employer has taken against you your employer dismisses you and you think that you have been dismissed unfairly.For more information about dismissal and unfair dismissal, seeDismissal.You can make a claim to an employment tribunal, even if you haventappealedagainst the disciplinary action your employer has taken against you. However, if you win your case, the tribunal may reduce any compensation awarded to you as a result of your failure to appeal.Remember that in most cases you must make an application to an employment tribunal within three months of the date when the event you are complaining about happened. If your application is received after this time limit, the tribunal will not usually accept it.If you are worried about how the time limits apply to you, take advice from one of the organisations listed underFurther help.Employment tribunals are less formal than some other courts, but it is still a legal process and you will need to give evidence under an oath or affirmation.Most people find making a claim to an employment tribunal challenging. If you are thinking about making a claim to an employment tribunal, you should get help straight away from one of the organisations listed underFurther help.If you are being represented by a solicitor at the tribunal, they may ask you to sign an agreement where you pay their fee out of your compensation if you win the case. This is known as adamages-based agreement. In England and Wales, your solicitor cant charge you more than 35% of your compensation if you win the case.If you are thinking about signing up for a damages-based agreement, you should make sure youre clear about the terms of the agreement. It might be best to get advice from an experienced adviser, for example, at a Citizens Advice Bureau. To find your nearest CAB, including those that give advice by e-mail, click onnearest CAB.For more information about making a claim to an employment tribunal, seeEmployment tribunals.The (lack of) air up there Watch mCayman Islands-based Webb, the head of Fifas anti-racism taskforce, is in London for the Football Associations 150th anniversary celebrations and will attend Citys Premier League match at Chelsea on Sunday.I am going to be at the match tomorrow and I have asked to meet Yaya Toure, he told BBC Sport.For me its about how he felt and I would like to speak to him first to find out what his experience was.Uefa hasopened disciplinary proceedings against CSKAfor the racist behaviour of their fans duringCitys 2-1 win.Michel Platini, president of European footballs governing body, has also ordered an immediate investigation into the referees actions.CSKA said they were surprised and disappointed by Toures complaint. In a statement the Russian side added: We found no racist insults from fans of CSKA.Age has reached the end of the beginning of a word. May be guilty in his seems to passing a lot of different life became the appearance of the same day; May be back in the past, to oneself the paranoid weird belief disillusionment, these days, my mind has been very messy, in my mind constantly. Always feel oneself should go to do something, or write something. Twenty years of life trajectory deeply shallow, suddenly feel something, do it.一字开头的年龄已经到了尾声。或许是愧疚于自己似乎把转瞬即逝的很多个不同的日子过成了同一天的样子；或许是追溯过去，对自己那些近乎偏执的怪异信念的醒悟，这些天以来，思绪一直很凌乱，在脑海中不断纠缠。总觉得自己自己似乎应该去做点什么，或者写点什么。二十年的人生轨迹深深浅浅，突然就感觉到有些事情，非做不可了。The end of our life, and can meet many things really do?而穷尽我们的一生，又能遇到多少事情是真正地非做不可？During my childhood, think lucky money and new clothes are necessary for New Year, but as the advance of the age, will be more and more found that those things are optional; Junior high school, thought to have a crush on just means that the real growth, but over the past three years later, his writing of alumni in peace, suddenly found that isnt really grow up, it seems is not so important; Then in high school, think dont want to give vent to out your inner voice can be in the high school children of the feelings in a period, but was eventually infarction when graduation party in the throat, later again stood on the pitch he has sweat profusely, looked at his thrown a basketball hoops, suddenly found himself has already cant remember his appearance.童年时，觉得压岁钱和新衣服是过年必备，但是随着年龄的推进，会越来越发现，那些东西根本就可有可无；初中时，以为要有一场暗恋才意味着真正的成长，但三年过去后，自己心平气和的写同学录的时候，突然就发现是不是真正的成长了，好像并没有那么重要了；然后到了高中，觉得非要吐露出自己的心声才能为高中生涯里的懵懂情愫划上一个句点，但毕业晚会的时候最终还是被梗塞在了咽喉，后来再次站在他曾经挥汗如雨的球场，看着他投过篮球的球框时，突然间发现自己已经想不起他的容颜。Originally, this world, can produce a chemical reaction to an event, in addition to resolutely, have to do, and time.原来，这个世界上，对某个事件能产生化学反应的，除了非做不可的坚决，还有，时间。A persons time, your ideas are always special to clear. Want, want, line is clear, as if nothing could shake his. Also once seemed to be determined to do something, but more often is he backed out at last. Dislike his cowardice, finally found that there are a lot of love, there are a lot of miss, like shadow really have been doomed. Those who do, just green years oneself give oneself an arm injection, or is a self-righteous spiritual.一个人的时候，自己的想法总是特别地清晰。想要的，不想要的，界限明确，好像没有什么可以撼动自己。也曾经好像已经下定了决心去做某件事，但更多的时候是最后又打起了退堂鼓。嫌恶过自己的怯懦，最终却发现有很多缘分，有很多错过，好像冥冥之中真的已经注定。那些曾经所谓的非做不可，只是青葱年华里自己给自己注射的一支强心剂，或者说，是自以为是的精神寄托罢了。At the moment, the sky is dark, the air is fresh factor after just rained. Suddenly thought of blue plaid shirt; Those were broken into various shapes of stationery; From the corner at the beginning of deep friendship; Have declared the end of the encounter that havent start planning. Those years, those days of do, finally, like youth, will end in our life.此刻，天空是阴暗的，空气里有着刚下过雨之后的清新因子。突然想到那件蓝格子衬衫；那些被折成各种各样形状的信纸；那段从街角深巷伊始的友谊；还有那场还没有开始就宣告了终结的邂逅计划那些年那些天的非做不可，终于和青春一样，都将在我们的人生中谢幕。Baumgartner the disappointing news: Mission aborted. r plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.The supersonic descent could happen as early as Sunda.The weatheThe balloon will slowly drift to the edge of space at 120,000 feet ( Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end. Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).cause there
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