重慶大學(xué)-過(guò)程控制-process-control-中文-翻譯-第十章(1)

1、1Process Control陳剛College of AutomationChongqing University2Multiloop SystemsOutlineImproving （disturbance rejection干擾抑制)performance pcascade control級(jí)聯(lián)控制pfeedforward control,前饋控制pratio control, and 比例控制ptime delay compensation時(shí)間延遲補(bǔ)償with Smith predictor. smith 預(yù)估補(bǔ)償3Multiloop SystemsImproving the DR P

2、erformancenCascade ControlpControl of a furnace temperature；爐溫DR: Disturbance Rejection4TTTCTspMultiloop SystemsImproving the DR干擾抑制 performancen S-loop control solution單環(huán)開(kāi)環(huán)控制開(kāi)環(huán)控制1. measure T by TT,2. compute p by TC,3. send the p to the valve5Multiloop SystemsCascade ControlnMotivation of動(dòng)機(jī) Cascade

3、 Control pIf fluctuation波動(dòng) in the fuel gas flow rate燃?xì)饬魉? pthe system will not counter計(jì)數(shù) the disturbance untilpthe controller senses that感知 the temperature has deviated From偏離 the set point (Tsp)6Multiloop SystemsCascade ControlnCascade control solutionIt consisting of包含: master (primary) loop slave

4、 (secondary) loopTT: temperature transducer 溫度傳感器FT: flow transducerTC: temperature controllerFC: fuel gas controllerTwo measured variablesdisturbance is now in slave loop副回路fluctuation波動(dòng)7Multiloop SystemsCascade ControlnCascade control solution pTC in master-loop sends its signal to slave-loop副回路,

5、in terms of依據(jù) the desired flow rate (casual relation) the signal is the set point of the secondary flow controller (FC).pFC in slave loop adjusts the regulating valve調(diào)節(jié)閥 FC compares the desired and measured fuel gas flow rates responding immediately to fluctuations in the fuel gas flow 立即對(duì)波動(dòng)的燃?xì)馑俾首龀龇?/p>

6、應(yīng) to ensure that the proper amount of數(shù)量的 fuel is delivered.8Multiloop SystemsCascade ControlnCascade Design Criteria設(shè)計(jì)標(biāo)準(zhǔn)Cascade is desired when1. single-loop performance unacceptable2. a measured variable is available 測(cè)量值可用A secondary variable 次要變量次要變量must3. Indicate指出 the occurrence of發(fā)生的 an import

7、ant disturbance4. have a causal relationship因果關(guān)系 from primary to secondary (cause effect)5. have a faster response than the primary9Multiloop SystemsCascade ControlnCascade Control Solution Reducing the block diagram方塊圖Setting Gm1=Gm2=1where10Multiloop SystemsCascade ControlnReducing the block diagr

8、amFrom the reduced block diagramE=R-C11Multiloop SystemsCascade ControlnCascade control solutionThe closed-loop characteristic polynomial特征多項(xiàng)式Comments on the slave-loop1. reducing disturbance in the manipulated variable被控變量 減少來(lái)自被控變量的干擾.2. accomplish a faster response in the valve, 3. make the system

9、 more stable12Multiloop SystemsCascade ControlnExample 1: the furnace temperature controlpthe master loop uses a PI controller,pthe slave loop uses a p-controller,pwith the first order functions 13Problem (a): choosing Kc2 properly for better performanceMultiloop SystemsCascade ControlnExample 1. th

10、e furnace temperature controlSubstituting取代 Gc2 = Kc2 and Gv = Kv/(vs+1) into G*v wheresubstituting GL = KL/(Ls+1) into G*LSolution:14Multiloop SystemsCascade ControlnExample 1. the furnace temperature controlas the proportional gain Kc2 becomes larger1. K*v 1, more effective change in manipulated v

11、ariable, 2K*L 0, manipulated variable is less sensitive to changes in load,操縱變量對(duì)負(fù)載的變化敏感度降低3 *v smaller, faster response of the regulating valve調(diào)節(jié)閥Problem (a): choosing Kc2 properly for better performancevcvcvKKKKK221*vcvvKK21*LcLLKKKK21*15Multiloop SystemsCascade ControlnExample 1. the furnace tempe

12、rature controlProblem (b): find Kc2 while *v = 0.1v with Kv=0.5, v=1 s, and *v=0.1 s, we havethus slave loop has a 10% offset with respective to the desired set point changes in the secondary controller.次循環(huán)在二級(jí)控制器的設(shè)定點(diǎn)有10的偏移變化Solution參考方程16Multiloop SystemsCascade ControlnExample 1. the furnace temper

13、ature controlProblem (c): Now that既然 certainly an offset偏移 in the inner loop, why do we stay with繼續(xù)做 p-control here?Solution 1. slave loop with 10% offset is acceptable in most cases 2. master loop has integral action積分作用, a) TC adjust調(diào)整 its output to ensure that b) there is no steady state error in

14、 the controlled variable受控變量17Multiloop SystemsCascade ControlnExample 1. the furnace temperature controlProblem (d): Choose the proper integral time constant among the given values of 0.05, 0.5, and 5 s, such that 1. guaranteeing保證 the system stable, 2. allowing a slightly稍微的 underdamped response3.

15、 making system response as fast as possible18Multiloop SystemsCascade ControlnExample 1. the furnace temperature controlSolution of解決 problem (d): with PI master controller, the entire closed-loop system is 19Multiloop SystemsCascade ControlnExample 1. the furnace temperature controlProblem (e): det

16、ermine Kc of PI controller that guarantees system stable when I=0.5 without cascade Solution: system is a single-loop system when no cascade characteristic equation of its closed-loop equation isSystem is stable if and only if Kc7.520Multiloop SystemsCascade ControlnExample 1 (cont.) the furnace tem

17、perature controlSolution of problem (e): compared with與相比較 cascade control cascade control is always stable when I =0.5, from (d) the system is stable by Routh-Hurwitz勞氏判據(jù)analysis21Multiloop SystemsCascade ControlnSummary of總結(jié) cascade control based on基于 example 11. the system becomes more stable, an

18、d 2. allowing to use a larger Kc in master controller3. much faster response of the actuator in the inner loopSingle loop controlCascade control22Multiloop SystemsImproving the DR PerformancenFeedforward ControlpControl of a furnace temperature againDR: Disturbance Rejection23Multiloop SystemsImprov

19、ing the DR PerformancenMotivation of feedforward (FF) control前饋控制的動(dòng)機(jī)Temperature T can also be effected by the cold process stream flow rate FsFsOur ideas are 1. Measure the disturbance in Fs 測(cè)量Fs中的干擾2. Adjust the valve before the change of Fs has no chance to affect T Reminder: the stream temperatur

20、e are presumed being假定為 constant24Multiloop SystemsFeedforward ControlnDerive導(dǎo)出 process modelusing heat-mass balance熱質(zhì)量平衡 to track R precisely,為了精確地跟蹤R we ideally理想的 set R=Cwhere C: the controlled variable, (i.e., T)GL: the heat transfer function, Gp: the mass transfer functions25Multiloop SystemsFe

21、edforward ControlnDynamic feedforward control model1. Tells how to adjust the manipulated variable (a)when changing R, thus 1/Gp called setpoint tracking設(shè)定追蹤(b)when changing L, thus -GL/Gp called the FF controller2. Is dynamical because C=GLL+GpM is derived in源至于 a time-domain (a transient瞬態(tài) model)2

22、61. GmL is load measurement function2. GFF is the FF controller3. feedback loop is omitted4. If there are two more load variables, the FF controller can be added on each one (theoretically)Multiloop SystemsFeedforward ControlnImplementing實(shí)現(xiàn) the FF controller, -GL/GpThe elements基本原理 in the FF systeml

23、oad負(fù)載，omitted省略， be added on被添加在27Multiloop SystemsFeedforward ControlnImplementing實(shí)現(xiàn)the FF controller, GL/Gpsupposing the set point R has no changes, thus the FF loop is of regulating problem調(diào)節(jié)supposing that FF controller can perfectly reject很好的抑制 the load change, thus C=0C=028Multiloop SystemsFeed

24、forward ControlnImplementing the FF controller, GL/Gpsupposing 1seKGpsLLL 1*sKeGGGspvML and Substitute代替 them into the follow Further implement above以上進(jìn)一步實(shí)現(xiàn) as is called steady state compensator穩(wěn)態(tài)補(bǔ)償器 FLD= and FLG=p is called dynamic compensator動(dòng)態(tài)補(bǔ)償器 29Multiloop SystemsFeedforward ControlnTuning the

25、FF Controller Parametersbest practice最優(yōu)方法(1) FLD = m+ *v , (2) FLG = 0.1 FLD, (3) Gm=KmLif small m(4) GFF = KFF if small *v with cascade control a = 0, b =0.5, c = 1.0, d= 1.5, e= 2.030Multiloop SystemsImproving the DR PerformanceFeedforward-Feedback（FB） Control順饋控制 ncombine FF with FB Control Feedb

26、ack trim反饋微調(diào)nthe feedback loop in FF-FB system handlesthe measurement errorserrors in the feedforward functionchanges in unmeasured load variablesset point changes31Multiloop SystemsFeedforward-Feedback (FF-FB) ControlnFinding the closed-loop transfer functionmove G*vGp to form Fig. bwrite down the

27、final resultwhererearrange the equation above the FF control doesnt affect the system stability32Multiloop SystemsFeedforward-Feedback (FF-FB) ControlnExample 2. the furnace temperature controlSuppose that the probable disturbances includeprocess stream flow rate蒸汽流速 (major disturbance)process strea

28、m temperature蒸汽溫度 (secondary disturbance)the fuel gas flow rate燃?xì)饬魉?(manipulated variable) The task are:pdraw the schematic diagram原理圖 of the control system pcombine FF, FB and cascade controls for load changes負(fù)載變化33Multiloop SystemsFeedforward-Feedback (FF-FB) ControlnExample 2.(1) the cascade cont

29、rolUsing a flow controller (FC) in a slave loop次環(huán) to handle the fuel gas flow disturbance FC has the transfer function Gc2Slave loopSolution: Entire transfer function34Multiloop SystemsFeedforward-Feedback (FF-FB) ControlnExample 2(cont.):Solution:(2) The FF ControlFT sends the signals to FFC A summ

30、er () combines signals from FFC and TC its output becomes the set point for FC35Multiloop SystemsFeedforward-Feedback (FF-FB) ControlnExample 2(cont.):Solution:(3) The master looptemperature T is measured by (TT)T is sent to TC TT acts to reduce the deviation偏差 in the furnace temperature36Multiloop

31、SystemsImproving the DR PerformanceRatio Control比例控制DR: Disturbance RejectionAir flowFuel gas37Multiloop SystemsRatio ControlnConsidering air flow rate in the furnace controlMotivation動(dòng)機(jī): pmaintaining FFG at a defined proportion R relative to FA, Benefit:好處pEnsuring sufficient air flow for efficient

32、 combustion有效燃燒pRegulating air flow for the reduction of air pollutant污染Application of interests:pgases, liquids, powders, slurries or meltsp氣體、液體、粉劑、漿液或熔化物p 38Multiloop SystemsRatio ControlnConsidering air flow rate in the furnace controlSimple implementation實(shí)現(xiàn) 1.measuring the fuel gas flow rate FF

33、G 2.multiplying the value by R in ratio station FFG 在比值操作器中值增大R倍1. send the signal as the set point to the air flow controller. NoticeComputation計(jì)算 conducts on actual variable rather than deviation variable39Multiloop SystemsRatio ControlnConsidering air flow rate in the furnace controlFull metering

34、計(jì)量 implementation1. Sending the signals from the fuel gas FC and air FT to the ratio controller (RC)2. RC takes the desired R as set point and calculate the proper air rate FA.sp3. Taking FA.sp as the set point for air FC and calculate the control signal 40Multiloop SystemsImproving the DR Performan

35、ceSmith predictor for time delay compensationSmith預(yù)估的時(shí)間延遲補(bǔ)償DR: Disturbance Rejection41Multiloop SystemsTime Delay Compensation: Smith PredictornSuppose A feedback system with time delayTime lag causes the deficits不足:1.Introducing引入 extra phase lag相位滯后, 2. reducing the gain margin增益裕度, 3. a significa

36、nt source of instability. 不穩(wěn)定的一個(gè)重要來(lái)源The characteristic equationMotivation動(dòng)機(jī): How to cancel the impacts of the time lag of a process?42Multiloop SystemsTime Delay Compensation: Smith PredictornInterpretation of闡釋 the transfer function assuming that the process model is known, Construct構(gòu)造 the block di

37、agram （as follow依下列各項(xiàng)）.PredictorActual time delay prediction loopExponential terms are canceled out!指數(shù)部分被抵消43Multiloop SystemsTime Delay Compensation: Smith PredictornInterpretation of闡釋the transfer function The time delay effect is canceled out due to system with Smith predicatorsystem without Smith predicator44Multiloop SystemsTime Delay Compensation: Smith PredictornBenefits好處 of S