Control

1. Chapter 5
Reduction of Multiple
Subsystems

2. Chapter Learning Outcomes: the student will be able to:
• Reduce a block diagram of multiple subsystems to a single
block representing the transfer function from input to output
(Sections 5.1-5.2)
• Analyze and design transient response for a system
consisting of multiple subsystems (Section 5.3)
• Convert block diagrams to signal-flow diagrams (Section 5.4)
• Find the transfer function of multiple subsystems using
Mason's rule (Section 5.5)
• Represent state equations as signal-flow graphs (Section 5.6)
• Represent multiple subsystems in state space in cascade,
parallel, controller canonical, and observer canonical forms
(Section 5.7)
• Perform transformations between similar systems using
transformation matrices and diagonalize a system matrix
(Section 5.8)

3. =
G1(s)
G3(s)
+
-
G2(s) -
x(s)
x(s)
G1(s)
-G2(s)
-G3(s) x(s)
x(s)
FIGURE 5.2 Components of a block
diagram for a linear, time-invariant system
5.2 Block Diagrams

4. G(s)
X1(s) X2(s)
X2(s)=G(s)X1(s)
X2(s)
X3(s)
X4(s)
X1(s)
X5(s)
+
+
-
-
X5(s) = X1(s)-X2(s)+X3(s)-X4(s)
X(s)
X(s)
X(s)
X(s)
Summer (comparator)
5.2 Block Diagrams

5. 5.2 Block Diagrams
FIGURE 5.3 a. Cascaded subsystems; b. equivalent T/Function
Cascade (Series)

6. Cascade (Series)
G2(s)
G1(s)
X(s) G1(s)X(s) G1(s)G2(s)X(s)
a
S
a
 b
S
b

)
)(
( b
S
a
S
ab


5.2 Block Diagrams

7. The network of Figure 5.4(a) demonstrates this concept.
Its transfer function is

8. Tandem (Parallel)
5.2 Block Diagrams
FIGURE 5.5 a. Parallel subsystems; b. equivalent T/Function

9. Tandem (Parallel)
X(s)
G1(s)X(s)
G1(s) ± G2(s)
G1(s)
G2(s)
+
±
G2(s)X(s)
a
S
a

b
S
b

X(s)
T1(s) ± T2(s)
+
±
)
b
S
(
b
)
a
S
(
a
T
T
T





 2
1
5.2 Block Diagrams

10. Feedback Form
FIGURE 5.6 a. Feedback control system; b. simplified model;
c. equivalent T/Function

11. Figure:1.34 (page 74) Block diagram of a temperature control system
a
S
a
 b
S
b

E(s)
+
-
X(s) Y(s)
R(s)
Temperature
Heat
r(t) e(t) x(t) y(t)
a
S
a
s
E
s
X
T



)
(
)
(
1
b
S
b
s
X
s
Y
T



)
(
)
(
2
)
)(
(
)
(
)
(
2
1
b
S
a
S
ab
s
E
s
Y
T
T
T





)
)(
( b
S
a
S
ab


E(s)
+
-
Y(s)
R(s)
Temperature
e(t)
r(t) y(t)

12. E(s)
+
Y(s)
R(s)
B(s)=H(s)Y(s)
G(s)
H(s)
Y(s)
B(s)
Feedback
Configuration
Y(s)= G(s)E(s)
E(s)= R(s)B(s) =R(s)H(s)Y(s)
Y(s)= G(s) [R(s)H(s)Y(s)] =G(s)R(s)G(s)H(s)Y(s)
Y(s)=G(s)R(s)G(s)H(s)Y(s) Y(s) G(s)H(s)Y(s) =G(s)R(s)
Y(s)[1 G(s)H(s)]=G(s)R(s)
)
s
(
H
)
s
(
G
)
s
(
G
)
s
(
R
)
s
(
Y
)
s
(
T



1
Always
remember
Figure: 2.12
)
(
)
(
)
(
s
H
s
G
s
G

1
Y(s)
R(s)
r(t) y(t)

13. E(s)
+
Y(s)
R(s)
B(s)=H(s)Y(s)
G(s)
H(s)
Y(s)
B(s)
Y = G E
E = R B =R H Y
Y = G [R  H Y] =G R  G H Y
Y = G R  G H Y Y  G H Y = G R
Y [1 G H ] = G R
H
G
G
R
Y
TF



1
Always
remember
GH
G

1
Y
R
r y
Figure2.12 Feedback
Configuration
(Repeated)

14. FIG 5.7 Block diagram algebra for summing junctions-equivalent forms for
moving a block a. to the left past a summing junction; b. to the right past a
summing junction
Moving Blocks to Create Familiar Forms
C=G(R-X)
C=GR-GX
eqaul
C=G(R-X)

15. FIGURE 5.8 Block diagram algebra for pickoff points equivalent
forms for moving a block a. to the left past a pickoff point; b. to
the right past a pickoff point

16. Other Useful Block Diagram Equivalence
G2(s)
G1(s)
X(s)
G1(s)X(s)
G2(s)
G1(s)
X(s)
G1(s)X(s)
G1(s)
G2(s)
G1(s)
X(s)
G1(s)X(s)
G2(s)
G1(s)
X(s)
G1(s)X(s)
)
s
(
G2
1

17. Block Diagram Transformation Theorems - Block Diagram Equivalence

19. Example 5.1

20. Example 5.2

21. Example 5.2 cont…..

22. Example 5.2 cont…..

23. Skill-Assessment Exercise 5.1 Page:245
ANSWER: