重庆大学-过程控制-process-control-中文-翻译-第十章(1)

FT: flow transducer TC: temperature controller FC: fuel gas controller
Two measured variables
fluctuation波动
disturbance is now in slave loop 6 副回路
Multiloop Systems
16
Multiloop Systems
Cascade Control
Example 1. the furnace temperature control
Problem (d): Choose the proper integral time constant among the given values of 0.05, 0.5, and 5 s, such that 1. guaranteeing保证 the system stable,
Problem (e): determine 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 is
S-loop control solution单环开环控制
1. measure T by TT, 2. compute p by TC,
TT TC
Tsp
3. send the p to the valve
4
Multiloop Systems
Cascade Control
Motivation of动机 Cascade Control
2. allowing a slightly稍微的 underdamped response
3. making system response as fast as possible
17
Multiloop Systems
Cascade Control
Example 1. the furnace temperature control
to ensure that the proper amount of数量的 fuel is delivered.
7
Multiloop Systems
Cascade Control
Cascade Design Criteria设计标准
Cascade is desired when
1. single-loop performance unacceptable 2. a measured variable is available 测量值可用
8
Multiloop Systems
Cascade Control
Cascade Control Solution Reducing the block diagram方块图
Setting Gm1=Gm2=1
where
9
Multiloop Systems
Cascade Control
Reducing the block diagram
System is stable if and only if Kc<7.5
19
Multiloop Systems
Cascade Control
Example 1 (cont.) the furnace temperature control
Solution of problem (e): compared with与……相比较 cascade control ➢ cascade control is always stable when I =0.5, from (d)
3 *v smaller, faster response of the regulating valve调节阀
14
KL*
1
KL Kc2 KL
* v
1
v
Kc2
Kv
Multiloop Systems
Cascade Control
Example 1. the furnace temperature control
Problem (b): find Kc2 while *v = 0.1v
Solution
参考方程
➢with Kv=0.5, v=1 s, and *v=0.1 s, we have
➢thus
slave loop has a 10% offset with respective to the desired set point changes in the
2
Multiloop Systems
Improving the DR Performance
Cascade Control
Control of a furnace temperature；炉温
DR: Disturbance Rejection
3
Multiloop Systems
Improving the DR干扰抑制 performance
5
Multiloop Systems
Cascade Control
Cascade control solution
It consisting of包含:
➢ master (primary) loop ➢ slave (secondary) loop
TT: temperature transducer 温度传感器
secondary controller.次循环在二级控制器的设定点有10％的偏移变化
15
Multiloop Systems
Cascade Control
Example 1. the furnace temperature control
Problem (c): Now that既然 certainly an offset偏移 in the inner loop, why do we stay with继续做 p-control here?
Solution of解决 problem (d): with PI master controller, the entire closed-loop system is
18
Multiloop Systems
Cascade Control
Example 1. the furnace temperature control
减少来自被控变量的干扰.
2. accomplish a faster response in the valve, 3. make the system more stab11le
Multiloop Systems
Cascade Control
Example 1: the furnace temperature control
the system is stable by Routh-Hurwitz劳氏判据
analysis
20
Multiloop Systems
Process Control
陈刚 College of Automation Chongqing University
1
Multiloop Systems Outline
Improving （disturbance rejection干扰抑制)performance
cascade control级联控制 feedforward control,前馈控制 ratio control, and 比例控制 time delay compensation时间延迟补偿with Smith predictor. smith 预估补偿
Cascade Control
Cascade control solution
TC in master-loop sends its signal to slave-loop副回路,
▪ in terms of依据 the desired flow rate (casual relation) ▪ the signal is the set point of the secondary flow controller (FC).
the master loop uses a PI controller,
the slave loop uses a p-controller, with the first order functions
12
Multiloop Systems
Cascaபைடு நூலகம்e Control
Example 1. the furnace temperature control
13
Multiloop Systems
Cascade Control
Example 1. the furnace temperature control
Problem (a): choosing Kc2 properly for better performance
as the proportional gain Kc2 becomes larger
1. K*v 1, more effective change in manipulated variable,
Kv*
Kc2 Kv 1 Kc2 Kv
2 K*L 0, manipulated variable is less sensitive to changes in load,操纵变量对负载的变化敏感度降低
Solution 1. slave loop with 10% offset is acceptable in most cases 2. master loop has integral action积分作用,
a) TC adjust调整 its output to ensure that b) there is no steady state error in the controlled variable 受控变量
Problem (a): choosing Kc2 properly for better performance Solution: ➢Substituting取代 Gc2 = Kc2 and Gv = Kv/(vs+1) into G*v
where
➢substituting GL = KL/(Ls+1) into G*L
A secondary variable 次要变量must
3. Indicate指出 the occurrence of发生的 an important disturbance 4. have a causal relationship因果关系 from primary to secondary
(cause → effect) 5. have a faster response than the primary
From the reduced block diagram
E=R-C
10
Multiloop Systems
Cascade Control
Cascade control solution The closed-loop characteristic polynomial特征多项式
Comments on the slave-loop 1. reducing disturbance in the manipulated variable被控变量
If fluctuation波动 in the fuel gas flow rate燃气流速,
the system will not counter计数 the disturbance until
the controller senses that感知 the temperature has deviated From偏离 the set point (Tsp)
FC in slave loop adjusts the regulating valve调节阀
▪ FC compares the desired and measured fuel gas flow rates
▪ responding immediately to fluctuations in the fuel gas flow 立即对波动的燃气速率做出反应