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

the block diagram
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
2. allowing a slightly稍微的 underdamped response
3. making system response as fast as possible
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Multiloop Systems
Cascade Control
Example
1. the furnace temperature control
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
thus
slave loop has a 10% offset with respective to the desired set point changes in the 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
where
substituting GL = KL/(Ls+1) into G*L
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Multiloop Systems
Cascade Control
Example
1. the furnace temperature control
Problem (a): choosing Kc2 properly for better performance
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 control,前馈控制
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
as the proportional gain Kc2 becomes larger
1. K*v 1, more effective change in
manipulated variable,
2 K*L 0, manipulated variable is less sensitive to
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 to ensure that the proper amount of数量的 fuel is delivered.
Two measured variables
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disturbance is now in slave loop 副回路
Multiloop Systems
Cascade Control
Cascade
TC
control solution
in master-loop sends its signal to slave-loop副回路,
TT
TC
Tsp
4
Multiloop Systems
Cascade Control
Motivation
If
of动机 Cascade Control
fluctuation波动 in the fuel gas flow rate燃气流速, system will not counter计数 the disturbance until
feedforward ratio time
control, and 比例控制
delay compensation时间延迟补偿with Smith
predictor. smith 预估补偿
2
Multiloop Systems
Improving the DR Performance
Cascade
the
the
controller senses that感知 the temperature has deviated From偏离 the set point (Tsp)
5
Multiloop Systems
Cascade Control
Cascade
control solution
It consisting of包含:
Control
Control
of a furnace temperature；炉温
DR: Disturbance Rejection
3
Multiloop Systems
Improving the DR干扰抑制 performance
S-loop control solution单环开环控制
1. measure T by TT, 2. compute p by TC, 3. send the p to the valve
in terms of依据 the desired flow rate (casual relation) the signal is the set point of the secondary flow controller (FC).
FC
in slave loop adjusts the regulating valve调节阀
master (primary) loop
slave (secondary) loop
TT: temperature transducer 温度传感器
fluctuation波动
FT: flow transducer
TC: temperature controller FC: fuel gas controller
with
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Multiloop Systems
Cascade Control
Example
1. the furnace temperature control
Problem (a): choosing Kc2 properly for better performance Solution: Substituting取代 Gc2 = Kc2 and Gv = Kv/(vs+1) into G*v
System is stable if and only if Kc<7.5
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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)
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 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
Kv
*
Kc Kv
2
1 K c2 K v
KL 1 Kc KL
2
changes in load,操纵变量对负载的变化敏感度降低
KL
*
3 *v smaller, faster response of the regulating valve调节阀
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v
*
v
1 Kc Kv
2
Multiloop Systems
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
受控变量
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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,
Multiloop Systems
Cascade Control
Example
the
the
1: the furnace temperature control
master loop uses a PI controller,
slave loop uses a p-controller, the first order functions
8
Multiloop Systems
Cascade Control
Cascade
Control Solution
Reducing the block diagram方块图
Setting Gm1=Gm2=1
where
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Multiloop Systems
Cascade Control
Reducing
Comments on the slave-loop 1. reducing disturbance in the manipulated variable被控变量
减少来自被控变量的干扰.
2. accomplish aFra Baidu bibliotekfaster response in the valve, 3. make the system more stable 11
Solution of解决 problem (d): with PI master controller, the entire closed-loop system is
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Multiloop Systems
Cascade Control
Example
1. the furnace temperature control
the system is stable by Routh-Hurwitz劳氏判据
Cascade Control
Example
1. the furnace temperature control
Problem (b): find Kc2 while *v = 0.1v
参考方程 Solution with Kv=0.5, v=1 s, and *v=0.1 s, we have