Survey on Advanced Control Techniques in Thermal Process of
Boiler
Abstract: Boiler is a complicated control object with multi variable, strong coupling and uncertain time delay. It is hard to get ideal control effect with normal controller. This paper presents the overview of advanced control techniques in therma l process control of boiler, such as PID multiplex control system, intelligent c ontrol system and decoupling control system. The future of advance control resea rch and application is also discussed.
Key words: boiler; intelligent control; decoupling control; thermal process control
One foreword
The main importation of the boiler equipments changes the quantity is a burden, boiler water supply, fuel quantity, reduce WEN SHUI3 and send the breeze and lead the amount of breeze;Main output to change the quantity to include the vapor to wrap the water level and lead the hot steam temperature and pressures, smokes to annoy the oxygen to measure to take to press etc. with a Boiler .Owing to the complexity of the boiler, exist while carrying out the control to the boiler following a few a little bit difficult:1)The system exists the serious to match, for example the variety of the fuel quantity not only affects the steam pressure and vapors to wrap the water level, but also wills affect the hot steam temperature and smoke to annoy amount of oxygen etc.;2)Exist the indetermination , if the variety of the fuel quantity after wrapping to the steam temperature, pressure, vapor the water level influence of etc. contain different reduces WEN SHUI3 LIANG2 's variety to change towards leading the hot machine to export the steam temperature of after influence have the bigger , the size of the of these hours return along with the change of carry the condition but.Therefore, the boiler is a to input much and output and change the quantity much mutually complicated control object of the for the merger to have indetermination.
Because the boiler changes to measure the relation more complicated, but operate the worker's experience opposite more abundant.Therefore, in recent years boiler automation research main concentration at following three aspect:While ising in the
traditional PID control realm, make use of other methods and the PID control to combine together to improve the control result of PID;Two is the latest technique of the applied artificial intelligence and the calculator science, develop the expert the control system, the artificial nerve network control the system and faintnesses control system etc.;Three is a strong that aims at the boiler to match sex, the development solution control system.
2 the boilers hot work process forerunner the control strategy research present condition
2.1 new progresses of the PID controls
The PID control has the structure because of it simple, easy realization, the stick is strong and can carry out and did not differ the characteristics for regulate, getting the extensive application in traditional boiler control system.However, the controller of PID of the normal regulations is line, after being applicable to the small inertial and small of process, be to apply the PID control under the condition of not line, big , parameter indetermination, can hardly acquire the satisfied control result.Therefore, in recent years, a lot of scholars control other methods and PIDs the knot put together, on-line regulate the parameter of PID to handle various indetermination, not line and big hour , this is a good development direction that the hot work automation control.
For resolving the big and inertial and big behind the control problem of the process but again did not need the establishment to is control the mathematics model of the process, can adopt a kind of faintness to estimate the PID control method, established a faintness to estimate the machine before the normal regulations PID controller, estimated the machine through a faintness to the process the output's will estimate the function in the future to compensated to is control process of inertial and after to control the influence of the system function.Lead the hot vapor faintness estimates the PID control system, among them, the FE estimates the machine ( the fuzzy estimator) for the faintness, the z1 calculates the son behind for the .The faintness estimates the function of the machine according to the system appearance estimate k of the current time+ the exportation of the L time process, and send the k+ the L the time the process output's estimate value output the deviation of the value with process into the controller of PID carries on the control, thus and effectively prevent°fromed being to be control the pure of the process compares behind big, PID control the system appear severity of super the concordance flaps the vibration, being advantageous to repressing the move to
move.What demand point out is, the faintness here estimate that the machine and general Smiths estimate the machine dissimilarity, don't need the mathematics model that builds up the precision to the object, it carries out to the k according to a misty rule+ the L time outputs the estimate of.
2.2intelligence controls
The power station boiler is a have the high to match of change to measure the importation exportation much not hot work system of line, its dynamic state characteristic along with circulate variety but big scope varieties of the work condition, the dynamic state characteristic difference of each link is very big, still having the noise and the burden interferences, hour etc..Therefore want to build up the accurate mathematics model of the boiler more difficult, but the rough model can be distributed the parameter system description by a series only, the complicated characteristic of the boiler make is hard to obtain the ideal control result according to the normal regulations controller of the accurate mathematics model, this give do not need to build up the accurate model of the application that intelligences such as expert system, the artificial nerve a network and misty control etc. controls the method provided the vast space.Therefore, apply these intelligences control method in the hot work of boiler control the process has the stronger theories and practices the meaning.
Since the professor of E.H.Mamdani of England was successful in 1974 misty the control applied to control in the boiler and the steam machines, the misty control controled the realm to get the extensive application in the hot work.Studied the misty control system in lead the hot vapor control process of https://www.doczj.com/doc/5e7551925.html,bine with the estimate technique misty control, put forward the faintness to prepare to measure to control the method, misty control method that overcame the normal regulations can't in time the shortage of the feedback.Is divided into the theory area of the control quantity first some son area, and order to be the reference control quantity with the boundary, predict each reference control quantity later on at is control the process model function under of exportation, with estimate of the variety of the deviation and deviation measure two change the quantity for importation, build up the misty function rule database, reason logically a control function diagraph index sign, evaluate the control result of each reference control quantity.The end is certain that a the best control measures to measure the place son area to really control the exportation certainly with the best control.Lead into the misty controller in string class control system, according to circulate the personnel's operation experience, the adoption compound misty string class
control system, control to compare with the PID, have to respond to sooner and the stronger feedbackstick.Construct of added the misty control system of power to draw lessons from traditional three advantages of the blunt quantity water supply systems, copy the experience of operate the personnel, from three mutually independently of misty exportation the amount of exportation of the logic controller adds the power to decide the lord to control into the valve of water to open the degree.These three misty controllers investigate the vapor to wrap the equilibrium and actual exportation power of water level, discharge respectively.Aim at the automatic control system of the fire power station water supply and flow to turn the bed bed control circularly, design the misty controller, really imitate as a result good.The variety rate of the deviation and its deviation that the main vapor press for the importation that the main vapor press the misty controller, in order to increase the control signal of measure the form, the exportation of the misty controller plus the ex- signal of feedback , constitute the importation value of the vice- back track, then turn for the coal machine soon, can remove to measure move for coal to move quickly.The actual control that the best breeze coal that the misty controller applies to the power station 300 MW machine set to burn the system compare up, circulate steady, got the good control result.
Control the knot to the nerve network and faintness to put together to constitute the misty nerve network( FNN) controller also is to handle the boiler combustion process to match the indetermination and valid means.Synthesized to consider the steam pressure, the steam burden and calculate way with amount of oxygen etc., put forward the industry stove combustion system from study FNN control strategy, FNN adoption off-line study and in the line study combine togethers of the boiler, acquire many layer networks of a basic reflection system request, then add this network to the system in go to, adopt the on-line calculate way in system circulate, the deviation of that at any time revise the actual exportation of the system and hope to output.Put forward a kind of from adjust the misty control system, adopt to analyze the method to describe the misty control rule, lead the intelligence power function into the design of the misty controller, adopt a misty son to gather to belong to one degree function to carry out the misty control from https://www.doczj.com/doc/5e7551925.html,bine to control the method to this kind of to applies to the unit machine set to lead the hot vapor WEN CHUAN4 JI2's controller up, imitate to really as a result express that it controls the good result.
2.3 solution control
The boiler is a to change quantity more the close to match of is control object,
according to change to measure the area control theories much, overcome to solve the the most valid inside the move realization the path is an adoption solution to control the method.Among them, the precise advantage turns the method is a more practical and effectively square method that adapts the industry the spot environment.It solves the design of the controller D11, D12, D21, D22 is a key, usually take the D11 for the simplification= D22=1, the only design D12 and D21s are all right, at sent to lead the breeze object to adopt the above-mentioned controller to the boiler, solution after of object characteristic is constant and easy engineering realization.The cultural heritage aims at to flow to turn the bed( CFB) to anticipate the bed to undulate the bigger circumstance circularly on the foundation of the above-mentioned controller, putting forward and designing the in expiation of type solution control system, direct use the bed body temperature degree this undulates the bigger signal to compensate and regulate to measure for coal, overcoming because the CFB gives a degree of coal variety of bed that distributes the asymmetry to cause.
3boilers research of the hot work controls and the application foreground
In recent years the boiler hot work process research work of the advanced control theories is already for the theories foundation that the application that it is in give or get an electric shock stand establishes and should have.Control the universality and exaltations of the calculator also for advanced control of application provided the powerful hardware and the software terraces.Take a wide view these researches result, still exist some shortage, from now on hot work automation of research direction should notice following research and the development of severals:
1) in the actual control engineering, request the controller simple, compute time short, but the forerunner who study currently control strategy usually structure complications, compute time long, and big part research the result still is placed in the laboratory to imitate the true stage, how push it controls the actual application toward the hot work is an aftertime of diligent direction.
2) current forerunner control the strategy sets out from the some hot work process mostly, satisfying the special control request of this process, did not consider as to it's his process, is to the influence of the overall situation.So the power station unit machine set control further whole turn, the intelligence turns the research very important.How enter the foundation of control the strategy previously up, will produce to adjust the degree, plan, excellent turn to conduct the contentses such as management and decision etc. to join the control with excellent turn in the system, is the research direction of the
aftertime.
3) excellent turn to supervise and control the system with the appearance compute, analysis and examine a patient for foundation, safe and economic two aspectses that involve the power station, include a deviation of machine ability 损analysis, excellent turn the combustion, boiler, the vapor machine and it assists the machine breakdown diagnosis etc., should aggressive development forerunner of excellent turn to supervise and control the software and systems.
4) aim at the characteristics of the boiler equipments and hot work process, the development boiler becomes an appropriation control software and equips, having the market capacity that the good industry turns the foreground and amplitude, automating one of the high and technical development directions at home and abroad.
5) forerunner the control strategy can apply to successfully physically, the key lies in the thorough understanding to the spot circulates the circumstance and promotes theoretically.Therefore, should strengthen the electricity station boiler to circulate the process theories to set up the mold and set up the mold according to the movement database non- parameter, make expert's experience and the knowledge application control the strategy in the forerunner.
锅炉热工过程先进控制策略研究综述
摘要:锅炉是一个多输入输出、强耦合、不确定时滞的复杂控制对象，常规的控制器很难取得理想的控制效果。综述了近年来国内外在锅炉热工过程控制领域的主要研究成果，其中包括PID混合控制系统、智能控制系统、解耦控制系统以及它们在锅炉热工过程中的应用。指出了当前研究的不足，并探讨了今后国内热工自动化控制研究及应用的几个方向。
关键词:锅炉; 智能控制; 解耦控制; 热工自动化
1 前言
锅炉设备的主要输入变量是负荷、锅炉给水、燃料量、减温水、送风和引风量；主要输出变量包括汽包水位、过热蒸汽温度及压力、烟气氧量和炉膛负压等。鉴于锅炉本身的复杂性，对锅炉实施控制时存在以下几个难点：1)系统存在严重耦合，例如燃料量的变化不仅影响蒸汽压力和汽包水位，还会影响过热蒸汽温度和烟气氧量等；2)存在不确定时滞，如燃料量的变化对蒸汽温度、压力、汽包水位等的影响有不同的滞后，减温水量的变化对过热器出口蒸汽温度的影响有较大的滞后，这些时滞的大小还随着负荷状况的改变而改变。因此，锅炉是一个多输入、多输出且变量相互耦合并具有不确定时滞的复杂控制对象。
由于锅炉变量关系较为复杂，而操作工人的经验相对较丰富。因此，近年来锅炉自动化研究主要集中在以下三个方面：一是在传统PID控制领域，利用其他方法和PID控制相结合来改善PID控制效果；二是应用人工智能和计算机科学的最新技术，开发专家控制系统、人工神经网络控制系统和模糊控制系统等；三是针对锅炉的强耦合性，开发解耦控制系统。
2 锅炉热工过程先进控制策略研究现状
2.1 PID控制的新进展
PID控制因其具有结构简单、容易实现、鲁棒性强和能够实现无差调节的特点，在传统的锅炉控制系统中得到了广泛的应用。然而，常规的PID控制器是线性的，适用于小惯性小滞后的过程，当把PID控制应用在非线性、大时滞、参数不确定的情况下时，很难获得满意的控制效果。因此，近年来，很多学者将其他方法和PID 控制结合起来，在线调节PID参数来处理各种不确定性、非线性以及大时滞，这是热工自动化控制的一个很好的发展方向。
为了解决大惯性大滞后过程的控制问题而又无需建立被控过程的数学模型，可以采用一种模糊预估PID控制方法，即在常规PID控制器前串联一个模糊预估器，通过模糊预估器对过程未来输出的预估作用来补偿被控过程的惯性和滞后对控制系统性能的影响。如图1所示的过热汽温模糊预估PID控制系统，其中，FE为模糊预估器 (fuzzy estimator)，z1为滞后算子。模糊预估器的作用是根据系统当前时刻的状态预测k+L时刻过程的输出，并将k+L时刻过程输出的估计值y(k+L)与过程
输出值的偏差e(k+L)送入PID控制器进行控制，从而有效防止了当被控过程的纯滞后较大时，PID控制系统出现严重的超调和振荡，有利于抑制扰动。需要指出的是，这里的模糊预估器和一般的Smith预估器不同，不需要对对象建立精确的数学模型，它是根据一组模糊规则来实现对k+L时刻输出预估值的。
2.2 智能控制
电厂锅炉是个具有高度耦合的多变量输入输出非线性热工系统，其动态特性随着运行工况的变化而大范围变化，各环节的动态特性差异很大，还有噪音和负荷干扰、时滞等。因此要建立锅炉的精确数学模型较困难，而粗略模型只能由一系列分布参数系统描述，锅炉的复杂特性使得基于精确数学模型的常规控制器难以取得理想的控制效果，这就给不需要建立精确模型的专家系统、人工神经元网络以及模糊控制等智能控制方法的应用提供了广阔的空间。因此，将这些智能控制方法应用于锅炉热工控制过程具有较强的理论与实践意义。
自从1974年英国的E.H.Mamdani教授成功的把模糊控制应用于锅炉和蒸汽机控制以来，模糊控制在热工控制领域得到了广泛的应用。研究了模糊控制系统在过热汽温控制过程中的应用。将模糊控制和预测技术结合，提出了模糊预测控制方法，克服了常规的模糊控制方法不能及时反馈的不足。首先将控制量的论域分为若干子域，并且以分界点作为参考控制量，随后预测各参考控制量在被控过程模型作用下的输出，以预测的偏差和偏差的变化量两个变量为输入，建立模糊性能规则库，推理出控制性能测量指标，来评价各参考控制量的控制效果。最后确定出最佳控制量和最佳控制量所在子域的确定控制输出。在串级控制系统中引入模糊控制器，根据运行人员的操作经验，采用复合模糊串级控制系统，与PID控制相比，具有更快的响应和更强的鲁棒性。构造的加权模糊控制系统借鉴了传统的三冲量给水系统的优点，模仿操作人员的经验，由三个相互独立的模糊输出逻辑控制器的输出量加权来决定主控入水阀的开度。这三个模糊控制器分别考察汽包水位、流量平衡和实际输出功率。针对火电厂给水自动控制系统和循环流化床床温控制，设计了模糊控制器，仿真结果良好。把主汽压的偏差及其偏差的变化率为主汽压模糊控制器的输入，模糊控制器的输出为增量形式的控制信号，加上前馈信号，构成副回路的输入值，即给煤机转速，可快速消除给煤量扰动。文献把模糊控制器应用到电厂300MW机组燃烧系统的最佳风煤比的实际控制上，运行平稳，得到了良好的控制效果。
把神经网络和模糊控制结合起来构成模糊神经网络（FNN）控制器也是处理锅炉燃烧过程耦合不确定性的有效手段。综合考虑了锅炉的蒸汽压力、蒸汽负荷和含氧量等，提出了工业炉燃烧系统自学习FNN控制策略，如图5。FNN采用离线学习和在线学习相结合的算法，获得一个基本反映系统要求的多层网络，然后再将这一网络加到系统中去，在系统运行中采用在线算法，随时修正系统的实际输出和希望输出之间的偏差。文献提出了一种自调整模糊控制系统，采用解析法描述模糊控制规则，将智能权函数引入模糊控制器的设计，采用一组模糊子集隶属度函数实现模糊控制自调节。并把这种控制方法应用到单元机组过热汽温串级控制器上，仿真结果表明其控制效果良好。
2.3 解耦控制
锅炉是一个多变量紧密耦合的被控对象，根据多变量频域控制理论，克服内扰实现解耦的最有效途径是采用解耦控制方法。其中准优势化法是适应工业现场环境
的较为实用和有效的方。其解耦控制器D
11、D
12
、D
21
、D
22
的设计是关键，为简化通常
取D
11=D
22
=1，仅设计D
12
和D
21
就可以了，对锅炉送引风对象采用了上述控制器，解耦
后的对象特性不变而且容易工程实现。文献在上述控制器的基础上针对循环流化床（CFB）料床温波动较大的情况，提出和设计了补偿式解耦控制系统，直接用床体温度这一波动较大的信号去补偿和调节给煤量，克服了由于CFB给煤粒度分布不均匀引起的床温的变化。
神经网络具有的学习、泛化、非线性映射等多种能力使得多变量系统的解耦控制成为可能。基于神经网络α阶逆系统方法提出了一种锅炉主汽压非线性控制系统的设计方法。针对锅炉和汽轮机之间的非线性耦合关系，对锅炉对象，可以写成输入输出微分方程描述的形式
3 锅炉热工控制的研究及应用前景
近年来锅炉热工过程先进控制理论的研究工作已经为其在电站中的应用奠定了应有的理论基础。控制计算机的普及与提高也为先进控制的应用提供了强有力的硬件和软件平台。纵观这些研究成果，仍然存在一些不足，今后热工自动化的研究方向应该注意以下几个方面的研究与开发：
1)实际控制工程中，要求控制器简单，计算时间短，而目前研究的先进控制策略往往结构复杂，计算时间长，且大部分研究成果仍处于实验室仿真阶段，如何将其推向热工控制实际应用是今后的努力方向。
2)目前的先进控制策略大都是从某一热工过程出发，满足这一过程的特殊控制要求，没有考虑对其他过程，乃至全局的影响。因此电厂单元机组控制的进一步整体化、智能化研究十分重要。如何在先进控制策略的基础上，将生产调度、计划、优化经营管理与决策等内容加入到控制与优化系统中，是今后的研究方向。
3)优化监控系统以状态计算、分析和诊断为基础，涉及电厂的安全和经济两个方面，包括机组偏差能损分析，优化燃烧，锅炉、汽机及其辅机故障诊断等，应积极开发先进的优化监控软件和系统。
4)针对锅炉设备和热工过程的特点，开发锅炉成套专用控制软件和装置，具有良好的产业化前景和广阔的市场容量，是国内外自动化高技术的发展方向之一。
5)先进控制策略能否成功地应用到实际，关键在于对现场运行情况的深入了解及在理论上的提升。因此，应加强电站锅炉运行过程理论建模以及基于运行数据库的非参数建模，把专家经验和知识应用于先进控制策略。