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1、摘 要锅炉是典型的复杂热工系统，目前，中国各种类型的锅炉有几十万台，由于设备分散、管理不善或技术原因，使多数锅炉难以处于良好工况，增加了锅炉的燃料消耗，降低了效率。锅炉的建模与控制问题一直是人们关注的焦点，而汽包水位是工锅炉安全、稳定运行的重要指标，保证水位控制在给定范围内，对于高蒸汽品质、减少设备损耗和运行损耗、确保整个网络安全运行具有要意义。锅炉汽包水位高度，是确保安全生产和提供优质蒸汽的重要参数，对现代工业生产来说尤其是这样。因为现代锅炉的特点之一就是蒸发量显著提高，汽包容积相对变小，水位变化速度很快，稍不注意就容易造成汽包满水或者烧成干锅。在现代锅炉操作中，即使是缺水事故，也是非常危险
2、的，这是因为水位过低，就会影响自然循环的正常进行，严重时会使个别上水管形成自由水面，产生流动停滞，致使金属管壁局部过热而爆管。无论满水或缺水都会造成事故，因此，必须严格控制水位在规定范围之内。维持汽包水位在给定范围内是保证锅护和汽轮机安全运行的必要条件，也是锅炉正常运行的主要指标之一。水位过高，会影响汽包内汽水分离效果，使汽包出口的饱和蒸汽带水增多，蒸汽带水会使汽轮机产生水冲击，引起轴封破损、叶片断裂等事故。同时会使饱和蒸汽中含盐量增高，降低过热蒸汽品质，增加在过热器管壁和汽轮机叶片上的结垢。水位过低，则可能破坏自然循环锅炉汽水循环系统中某些薄弱环节，以致局部水冷管壁被烧坏，严重时会造成爆炸事
3、故。这些后果都是十分严重的。随着锅炉容量的增加，水位变化速度愈来愈快，人工操作愈来愈繁重，因此对汽包水位实现自动调节提出了迫切的要求。汽包水位的控制是锅炉控制的一个难点，目前，对汽包水位控制大多采用常规PID控制方式，传统的常规PID控制方式是根据控制对象的数学模型建立，由于锅炉水位系统存在非线性、不确定性时滞和负荷干扰、非最小相位特征等，其精确的数学模型往往无法获得而且常规PID控制的参数是固定不变的，难以适应各种扰动及对象变化，其控制效果往往难以满足要求，控制效果不理想。模糊控制是建立在人工经验基础之上的，它能将熟练操作员的实经验加以总结和描述，并用语言表达出来，得到定性的、不精确的控规则
4、，不需要被控对象的数学模型。模糊控制易于被人们接受，构造容易，鲁棒性和适应性好。锅炉是工业过程中不可缺少的动力设备，为确保安全，稳定生产，对锅炉的自动控制十分重要，其中汽包水位是一个非常重要的被控变量。由于锅炉的水位调节过程难以建立数学模型，具有非线性、不稳定性、时滞等特点。给水控制的任务是维持汽包中水位在工艺允许范围内。由于影响汽包水位的几个因素中，燃料量的扰动影响较小，因此，汽包水位的控制中，主要的目的是以汽包水位为被控变量，以调节给水流量为控制手段。同时，由于汽包水位不仅受锅炉侧的影响，也受到汽轮机侧的影响，当锅炉负荷变化或汽轮机用汽量变化时，给水控制都应能限制汽包水位只在给定的范围内变
5、化。常用的汽包水位控制方式有单冲量、双冲量及三冲量控制。传统的锅炉水位三冲量控制系统大都采用PID控制，其控制效果还可以进一步提高。而模糊控制不要求知道被控对象的精确数学模型，只需要操作人员的经验知识及操作数据，鲁棒性强，非常适合用于非线性、滞后系统的控制。模糊控制器一般采用二维结构形式，即以误差及误差变化作用模糊控制器的输入信号，根据二者模糊化的结果查询模糊控制表，得到控制量的模糊量，再经去模糊化处理转化为精确量去控制执行机构。基于锅炉水位控制及模糊控制的特点，本文将模糊控制引入锅炉汽包水位的三冲量控制中，作了以下一些试探性工作,对现有的模糊控制器的构成方式进行归纳总结。对汽包水位的模糊控制
6、方式进行结构及性能上的分析和比较，并利用Simulink分别在设定值及在干扰作用下对控制系统进行仿真。关键词:汽包水位；模糊控制；三冲量VAbstractBoiler is typical complex thermal system, China, at present, various types of boiler, scores have pale because of a device or dispersion, poor management and technical reasons that most boiler is in good condition, increase
7、 the boiler efficiency, reduce the fuel consumption. The modeling and control problems of boiler is always the focus of attention and drum water level is secure and stable operation of the boiler work, guarantees the important index of water control in a given range, high quality steam for loss and
8、operation, reducing equipment, insure the whole network security is to run. Boiler drum water level elevation, is to ensure safety in production, and provide quality of important parameters for steam, especially that for modern manufacturing industry. Because of the characteristics of modern boiler
9、drum is improved markedly, evaporation capacity, water relatively less change quickly, a bit not paying attention to drum with water or burn into dry pot. In modern boiler operation, even if is the shortage of accident, is very dangerous, because the water is too low, it will affect the normal, natu
10、ral cycle will make serious on individual freedom, produce water pipe forming causes metal pipe flow stagnation, local overheating and tube. Whatever is full of water or water can cause an accident, therefore, must be strictly controlled within the scope stipulated in water.Maintain drum water level
11、 in a given range is to guarantee the safe operation of the boiler and steam turbine protects the necessary conditions for the normal operation of the boiler, and is also one of main index. High level within the drum, will affect the effect, make the separation of saturated steam drum exports increa
12、sed with water, steam turbines with water will produce shock, cause damage shaft seals, etc. The fault accident Also makes higher content of saturated steam, lower overheated steam quality, increase in superheater wall and turbine blade on the scale. Low water may destroy the natural cycles of boile
13、r steaming-water circulation system, some weaknesses, and that local water-cooled wall was burnt out, causing severe explosion accidents. The consequences are very serious. With the increasing capacity, water boiler changes are increasingly fast, the more strenuous manual operation, thus to realize
14、automatic adjusting drum water level forward urgently demands.Drum water level control is one of the boiler control, at present, the difficulty of drum water level control most of the conventional PID control mode, the traditional conventional PID control method is based on the established mathemati
15、cal model control object, due to the boiler water system, the uncertainty of nonlinear delay and load disturbance and non-minimum-phase characteristics, the accurate mathematical model often unavailable and conventional PID control parameters are fixed, difficult to adapt to all kinds of disturbance
16、s and object changes, the control effect is often difficult to meet the requirements, the control effect is not ideal.The fuzzy control is established on the basis of artificial experience, it can be skilled operators and the real experience summarized, and language expression comes out, get a qualitative, not accurate control rules, need not be charged object mathematical model. Fuzzy control is easy to be accepted by people, easily, robustness and adaptabi
