锅炉水位模糊PID控制外文资料

1、唐 山 学 院 毕 业 设 计外文资料Research on Fuzzy Control for Steam Generator Water LevelWei Peng Da-fa ZhangI. INTRODUCTIONThe steam generator is one of the main devices in PWR nuclear power plant, in order to ensure the safety of nuclear power plant during operation; the steam generators water level must be co

2、ntrolled in a certain range. When the nuclear power plant is running, as the steam flow or the water flow changing, the amount of boiling bubbles in the steam generator will change due to local pressure or temperature change, the instantaneous water level showed “false water level” phenomenon . The

3、existence of “false water level” made it difficult to control the water level. The introduction of feed-forward control to the traditional single-loop PID control can, in a certain extent, overcome the false water level phenomenon. But the conventional PID control method in the process of steam gene

4、rator water level control has some shortcomings. To the steam generator that has highly complex, large time-delay and nonlinear time-varying characteristics, the PID parameters tuning is a tedious job and the control effect is very poor. Furthermore, to achieve good control performance still as cond

5、itions changing, it often needs to change the PID controller parameters. But the analog PID controller parameters are difficult to regulate online. Fuzzy control is a kind of nonlinear control strategy based on fuzzy reasoning, which express operating experience of skilled manipulation men and commo

6、n sense rules of inference through vague language. Fuzzy control do not need to know precise mathematical model of controlled object, is not sensitive to the change of process parameters, is highly robust and can overcome non-linear factors, so, fuzzy control has faster response and smaller ultra- t

7、one, can get better control effect. Based on understanding above, this paper design a steam generator water level fuzzy controller, the simulation shows that the controller has good control performance and practical value.II. DYNAMIC CHARACTERISTICS OF STEAM GENERATORThe transfer function of PWR ste

8、am generators mathematical model of the general form shows below:y(s)=GW(s)QW(s)+GS(s)QS(s) （1）where y is the steam generator water level; QW for the water flow; QS for the steam flow; GW (s) for the impact of the water flow to the steam generator water level; GS (s) for the effect of the steam flow

9、 (load) to the steam generator water level.The balance of the steam generator water level is maintained through the match between the water flow and steam flow. The process that water level changes with the steam flow or water flow changing can be regarded as a simple integration process, but impact

10、 of the water flow and steam flow s change on water level is different.A. Dynamics Characteristics under Water Flow DisturbanceSuppose steam flow GS remains unchanged, and water flow GW step increases, on the one hand because the temperature of feed water is much lower than the temperature of satura

11、ted water in the steam generator, so that , when feed water entering, it will absorb a lot of extra heat, the vapor phase bubble contents will reduce, resulting in water level decreasing; on the other hand, the increase in water flow GW made it greater than steam load, and cause water level increase

12、s linearly. Comprehensive two factors, after the step increase of the water flow, the water level rise has a time delay process, showing a down then up.B. Dynamic Characteristics under Steam Load DisturbanceSuppose feed water flow GW remains unchanged, and steam load GS step increases, on the one ha

13、nd the water level will flow down because the steam flow rate is greater than the water flow rate. On the other hand, as the steam load increased, vapor pressure is reduced; the bubble volume on the liquid surface increases, causing the water level increased. Comprehensive two factors, after the ste

14、p increase of the steam flow rate, the water level down has a time delay process, showing a up then down. The impact on the water level of water flow or steam flow stepping decreased has similar principle as above.As analysis can be seen as above, when the water flow or steam load change, the water

15、level did not follow the change immediately, but there is an opposite process at first. This phenomenon is called false water level phenomenon.III. DESIGN OF WATER LEVEL FUZZY CONTROLLERThe conventional PID controller has a poor control performance to the steam generator that exist “false water leve

16、l” characteristics, showing a greater overshoot in the tracking time. But a well-designed fuzzy controller is able to overcome the false water level phenomenon, and has good control performance. A. Sstructure of Fuzzy ControllerThe structure showed in Figure 1.FuzzycontrollerK1valveGW(s)dx/dtK2GS(s)

17、expected water leverStream flowWater leverwater floweec+-+-+Figure 1. Structure of steam generator water level fuzzy controllerChoose the water level error (e) and change rate of error (ec) as input of the fuzzy controller, the output of the fuzzy controller is the added value of the valve opening s

18、ignal u. Meanwhile, use the steam flow feed-forward to overcome the false water level phenomenon, use water flow feedback to overcome fluctuations in water supply side . k1, k2 were water flow and steam flow transmitter conversion factor. To ensure the water flow to match the steam flow, k1 and k2 v

19、alues should be equal to.B. Fuzzy theory, fuzzy subset and Membership FunctionThe fuzzy Analects of e, ec and u are -6, 6, both with seven fuzzy sets NB (negative big), NM (negative middle), NS (negative small), ZO (zero), PS (positive small), PM (positive middle) and PB (positive big) to describe.

20、e, ec and, u are all using triangular membership function (see Figure 2).Figure 2. Input and output variable membership functionC. Fuzzy control rule tableThe establishment principle of fuzzy control rules are: when the error is large, the output control volume should give priority to eliminate erro

21、r as soon as possible; when the error is small, the output control volume should givepriority to prevent overshoot. Where ec is negative ,it shows that water level has a rising trend, if the water level is high at this time, then we should reduce the valve opening signal; whereas, we should open the

22、 valve more. Through a comprehensive analysis of expertise, the establishment of rule table shown in Table 1.Table 1. Fuzzy control rule table eecNBNMNSZOPSPMPBNBNBNBNMNMNSNSZONMNBNMNMNSNSNSZONSNMNMNSNSZOPSPSZONMNSNSZOPSPSPMPSNSNSZOPSPSPMPMPMNSNSZOPSPSPMPMPBZOPSPSPMPMPBPBD. Fuzzy Reasoning and Solut

23、ionThis fuzzy inference system uses Mamdani. The basic properties of fuzzy inference system set to: and operation with a very small operation; or operation uses the maximum operation. Using a very small operation fuzzy implication, fuzzy rules integrated with great operations center Defuzzification

24、method used. IV. SIMULATION EXAMPLESA pressurized water reactor steam generator in Chinese Qinshan nuclear power station has empirical model G1 (s), G2 (s) below:where Ps denote the rated load. When load at 15% 90% Ps, use (6) and (8); when load less than 15% Ps, use (7) and (8).Figure 3. Expected w

25、ater level step response diagramThe coefficients in Control system are k1=k2=0.5. Water control valve is a king of linear valve, its gain is 4. The quantitative coefficients of e and ec are 6 and 60 respectively; the scale factor of u is 0.5. We limit water flow the range of 0 kg / s to the rated fl

26、ow 258kg / s when simulation. Consider the expected level step from the initial 0m to 10m, water level response is shown use the solid line in Figure 3. For contrasting the increase effect of fuzzy controller, we also carried out using the traditional PID control simulation. We can see, compared wit

27、h traditional PID control, fuzzy controller has reported significant improvements in overshoot, settling time, steady degrees.V. CONCLUSIONThis paper designed a water level fuzzy control system aimed at steam generators characteristics of large time delay and model uncertainty. We also gave a simula

28、tion to the steam generator of Qinshan nuclear power plant, and achieved satisfactory results. The method can also be used for other large time -delay and time-varying process control model, and has broad application prospects.蒸汽发生器水位模糊控制研究彭威 张达发1.导论蒸汽发生器是压水反应堆式核电厂里的一个重要的设备。为了保证核电厂运行的安全性，蒸汽发生器的水位必须控

29、制在一定的范围内。核电厂的运行中，因为蒸汽流量和给水流量的改变，蒸汽发生器里沸水中的气泡数量会随着局部气压和温度的变化而改变，瞬时水位呈现“虚假液位”现象。正是由于“虚假液位”的存在使得水位控制变得困难。将前馈控制引入到传统的单回路PID控制中，可以在一定程度上克服“虚假液位”的问题。但是蒸汽发生器的传统PID控制仍然存在着一些不足。对于具有高度复杂，大滞后，非线性特征的蒸汽发生系统，不仅PID参数的调整单调乏味，控制效果也很差。并且当条件改变时，为了获得好的控制性能，通常需要改变PID控制器的参数，但是模拟量的PID控制器参数的在线调整是很难的。模糊控制是一种基于模糊推理的非线性的控制方法，

30、它体现了熟练操作人员的实际经验和模糊语言推理的一般规则。模糊控制不需要知道被控对象的精确的数学模型，它对过程参数的变化并不敏感，鲁棒性很强，能够克服非线性因素，因此，模糊控制有更快的响应速度，更小的超调，更好的控制效果。基于以上了解，本文设计了一个蒸汽发生器水位的模糊控制器，仿真结果表明这个控制器有更好的控制效果和实用价值。2.蒸汽发生器的动态特性压水堆蒸汽发生器一般形式的数学模型的传递函数如下所示:y(s)=GW(s)QW(s)+GS(s)QS(s) （1）其中，y代表蒸汽发生器的水位；QW代表给水流量；QS代表蒸汽流量；GW代表给水流量对蒸汽发生器水位的作用；GS代表蒸汽流量对蒸汽发生器的

31、水位的作用。蒸汽发生器水位的平衡是靠蒸汽流量和给水流量的匹配来维持的。可以将水位随蒸汽流量或者给水流量变化而变化看作一个简单的一体化过程，蒸汽流量变化和给水流量变化对水位的影响又是不同的。(1) 给水流量扰动下的动态特性假设蒸汽流量保持不变，而给水流量阶跃增加，一方面，由于新增给水的温度要比蒸汽发生器中的饱和水的温度低很多，因此，当新水进入后就会吸收大量的额外热量，水中的气泡含量大大减少，从而导致水位下降；另一方面，给水流量大于蒸汽负荷，引起水位线性增加。综合以上两点，当给水阶跃增加，水位增长会有一个延迟的过程，表现为先下降后上升。(2) 蒸汽负荷扰动下的动态特性假设给水流量保持不变，蒸汽负荷

32、阶跃增加，一方面，由于蒸汽流速比给水流速大，水位会下降；另一方面，随着蒸汽负荷的增加，内部蒸汽压力降低，液面的气泡容积增加，从而引起水位增加。综合以上两个因素，当蒸汽流量阶跃增加以后，水位下降会有一个延迟的过程，表现为先上升后下降。给水流量或者蒸汽流量阶跃减少对水位的影响与上述有相似的原理。综上所述，当给水流量或者蒸汽负荷变化，水位不会立即跟随变化，开始会出现一个相反的过程。这个现象就称为“虚假液位”现象。3.水位模糊控制器的设计传统PID控制器对于蒸汽发生器水位的控制效果不佳，存在“虚假液位”的现象，表现为跟踪设定值时有较大的超调。但是，一个设计合理的模糊控制器能够克服“虚假液位”的现象，有较好的控制效果。(1) 模糊控制器的结构模糊控制器的结构如图1所示。FuzzycontrollerK1valveGW(s)dx/dtK2GS(s)expected water leverStream flowWater leverwater floweec+-+-+图1 蒸汽发生器水位模糊控制器