中文论文文摘

    制浆造纸过程是一个复杂的化工过程，其中涉及到的设备，不论数量还是种类，都是其它多数工业过程所不能比拟的。而在整个生产流程中涉及到的数量庞大的控制回路中，相当一部分具有高度的非线性、多干扰、强耦合、大滞后等特点。尽管如此，这其中绝大部分采用的还是传统PID控制算法，或者是各个PLC制造商集成的PID功能块（例如西门子的FB41、42等）。FB42是西门子Step 7编程平台中集成的非连续PID功能块，主要用于以电动阀为代表的数字量控制回路。数字量控制回路，就是一类执行机构仅接受数字量控制信号的特殊回路。这类回路在制浆造纸过程中广泛存在，其显著特点就是其中的数字式执行机构，执行机构的特性也给这类回路的控制带来了新问题。
    本论文在简要介绍造纸流程的基础上，讨论了数字量回路在造纸过程中的使用特点，重点研究了西门子PID功能块FB42的内部构成，以及它在实际应用过程中存在的若干问题。针对这些问题，结合模糊控制理论的相关知识提出解决方案，并加以仿真验证。在此基础上，将新的控制方案编程实现并投入实际造纸过程应用。根据这条主线，本文从以下几方面展开了讨论。
    首先，论文论述了本课题的研究背景。介绍了制浆造纸过程的典型工艺流程，引出了数字量回路在制浆造纸过程中应用的广泛性及其研究意义。同时对回路中最常用的执行机构——电动阀的特性进行了总结，据此建立了电动阀的仿真模型，并分析了造纸工业中应用电动阀的几类典型数字量回路。
    在简单介绍模糊控制相关基础知识之后，对西门子功能块FB42及其内部各部分工作流程进行详细分析，通过试验和源代码的解读发现其内部的工作过程大致可以分为PID运算和脉冲输出两大块。其中，PID运算主要完成了比例和积分运算。积分参数不固定是FB42的特色之一，它与运算周期、阀门的行程时间和偏差有关。这种考虑回路偏差的参数选择过程，无疑有利于平衡系统的稳定性和响应快速这对矛盾。PID运算得到的控制信号是不能直接输出给数字式执行机构的，所以，把PID的控制输出通过一个三步元件转换成一个或多个脉冲输出，也是FB42区别于其它PID算法的一个重要特征。在这些分析结果的基础上，建立了西门子PID功能块的仿真模型。
    其次，根据已建立的电动阀和功能块模型，结合它们在实际工程中的应用情况，总结其中存在的几点主要问题。
    数字量回路中存在的问题归根结底是其非线性和对集成功能块结构不清楚所导致的。为此，结合前面的相关介绍，给出了用回路偏差值来动态修改功能块中相关参数的思想，这些参数除了传统的比例积分参数外还包括脉冲产生环节中的高电平最小持续时间和低电平最小持续时间参数等。为了避免非线性带来的负面影响，从实际工程实践经验出发，提出了将模糊控制理论与FB42相结合来解决问题的新策略。
    模糊控制理论与FB42的结合体现在模糊规则的制定上。综合对现有控制器的分析成果，立足于已有的参数调节经验，制定相关规则表，以此为依据建立模糊控制器仿真模型。这个模型和前文已建立的电动阀模型、功能块模型通过相互信号传递构成一个完整的仿真回路。
    最后，对这个回路进行仿真，得到的响应曲线对比于西门子PID功能块控制下的曲线，回路响应速度变快，调节周期缩短。同时，从两种算法下阀门开度的变化情况可以看出新算法中的阀门动作迅速而且准确，整个调节过程中，开关阀次数有所减少。这个仿真结果验证了新控制方案的确能弥补PID功能块控制下的数字量回路的不足。
    将新算法通过PLC编程在现场数字量回路中加以应用，回路的控制效果提升显著，这进一步说明该方案是切实可行的，具有广泛的推广应用价值。

外文论文文摘

    Paper-making process is a very complex chemical process, which involves equipment, both the quantitatively and types could not be compared with other industrial projects. And the production processes involves the numerous monitoring point, further more, a majority of which takes on the characteristics of highly nonlinear, multi-interference, strong coupling, pure lag etc. Nevertheless, mostly loops are controlled by the traditional or integrated PID algorithms (such as the Siemens’ FB41, FB42). Siemens Step 7 FB42 is the integrated non-continuous PID functional modules, primarily for represented electric devices figured control loop, which is a special one that the implementing agencies only accept digital signals from the controller transmissions in the control loop. This kind of loop is widely used in the present paper-making process, its remarkable characteristic is the digital implementing agency, and the characteristic brings new question to this kind of loop.
    The thesis discussed the handling characteristics of the digital loop in paper-making based on the brief introduction of paper-making flow, has studied Siemens PID function block FB42 and its internal constitution, and its certain questions in the application process. In view of these questions, fuzzy control theory related knowledge is proposed to the solution, and performs the simulation confirmation. In this foundation, the new control plan is invested the actual paper-making process through programmed. According to this master line, this article has launched the discussion from following several aspects.
    First, the dissertation elaborated the research background of this topic, introduced the typical process of pulp & paper-making, and has drawn out the application widespread and research significance of the digital loop in pulp & paper-making. Meanwhile, the characteristic of electric valve is summarized, which is the most commonly used implementing agency in control loop, then the simulation model of electric valve has established, and several kind of typical digital loop applying the electric valve is analyzed in paper-making industry.
    After simple introduction fuzzy control elementary knowledge, the thesis analyzed the interior each part of work flow of Siemens function block FB42, through experimental and read the source code discovered its internal work process approximately may divide into the PID operation and the pulse outputs two bulks. Among them, the PID operation has mainly completed the proportion and the integral action. The integral parameter unfixed is one of FB42 characteristics, which is connected with the operation cycle, the valve travel time and the error. This kind of parameter choice process considerate loop error is without doubt advantageous to balance the contradiction of system stability and response fast. The control signal of PID operation is not directly input for the digital implementing agency, therefore, transforms the PID control output through a three-step component into one or more pulses outputs, which is an important characteristic of distinguishing from other PID algorithms. In these analysis results foundations, the simulation model of Siemens PID function block has established.
Second, according to the model of the electric valve and function block, linking the actual project application, several main questions has summarized.
    In the final analysis, the reason that the digital loop existed the questions is its non-linearity and making little of the function block structure. Therefore, the thesis produced the idea of revising dynamically FB42 parameters with the loop error. In order to avoid the negative influence which the non-linearity brings, embarked from the actual project experience, proposed the new strategy that combining fuzzy control theory and FB42 to solve the questions.
    The union of fuzzy control theory and FB42 bodies in the formulation of fuzzy rules. According the analysis achievement of existing controller and the adjustment experience, the rules table is framed and the simulation model is established. This model and the mentioned that of electric valve and function block constitutes a complete simulation loop through the mutual signal transmission.
    Finally, the response curves obtained from simulating loop contrast to the one under the PID function block, the loop speed of response changes quickly and the adjustment cycle reduce. At the same time, the changes of valve open degree under the two algorithms indicated that the valve quick moving and accurate and the switch times decrease ender the new algorithm. This simulation result confirmed the new control plan indeed to be able to make up the insufficiency of the digital loop under the PID function block controlling.
    Performs the new algorithm through the PLC programming in the scene digital loop to apply, the loop control effect promotion is remarkable, which further explained this plan is practical and feasible, has the widespread promotion application value.