Feedback Control Systems ( FCS )
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Transcript of Feedback Control Systems ( FCS )
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Feedback Control Systems (FCS)
Dr. Imtiaz Hussainemail: [email protected]
URL :http://imtiazhussainkalwar.weebly.com/
Lecture-8-9Block Diagram Representation of Control Systems
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Introduction• A Block Diagram is a shorthand pictorial representation of
the cause-and-effect relationship of a system.
• The interior of the rectangle representing the block usually contains a description of or the name of the element, gain, or the symbol for the mathematical operation to be performed on the input to yield the output.
• The arrows represent the direction of information or signal flow.
dtd
x y
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Introduction• The operations of addition and subtraction have a special
representation.
• The block becomes a small circle, called a summing point, with the appropriate plus or minus sign associated with the arrows entering the circle.
• The output is the algebraic sum of the inputs.
• Any number of inputs may enter a summing point.
• Some books put a cross in the circle.
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Introduction• In order to have the same signal or variable be an input
to more than one block or summing point, a takeoff (or pickoff) point is used.
• This permits the signal to proceed unaltered along several different paths to several destinations.
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Example-1• Consider the following equations in which , , , are variables, and ,
are general coefficients or mathematical operators.
522113 xaxax
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Example-1
522113 xaxax
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Example-2• Draw the Block Diagrams of the following equations.
11
22
2
13
11
12
32
11
bxdtdx
dtxd
ax
dtxbdt
dxax
)(
)(
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Canonical Form of A Feedback Control System
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Characteristic Equation• The control ratio is the closed loop transfer function of the system.
• The denominator of closed loop transfer function determines the characteristic equation of the system.
• Which is usually determined as:
)()()(
)()(
sHsGsG
sRsC
1
01 )()( sHsG
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Example-31. Open loop transfer function
2. Feed Forward Transfer function
3. control ratio
4. feedback ratio
5. error ratio
6. closed loop transfer function
7. characteristic equation
8. Open loop poles and zeros if 9. closed loop poles and zeros if K=10.
)()()()( sHsGsEsB
)()()( sGsEsC
)()()(
)()(
sHsGsG
sRsC
1
)()()()(
)()(
sHsGsHsG
sRsB
1
)()()()(
sHsGsRsE
1
1
)()()(
)()(
sHsGsG
sRsC
1
01 )()( sHsG
)(sG
)(sH
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Reduction techniques
2G1G 21GG
1. Combining blocks in cascade
1G
2G21 GG
2. Combining blocks in parallel
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3. Eliminating a feedback loop
G
HGHG
1
G
1H
GG1
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Example-4: Reduce the Block Diagram to Canonical Form.
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Example-4: Continue.
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Example-5• For the system represented by the following block diagram
determine:1. Open loop transfer function2. Feed Forward Transfer function3. control ratio4. feedback ratio5. error ratio6. closed loop transfer function7. characteristic equation 8. closed loop poles and zeros if K=10.
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Example-5– First we will reduce the given block diagram to canonical form
1sK
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Example-5
1sK
ssK
sK
GHG
11
11
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Example-5 (see example-3)1. Open loop transfer function
2. Feed Forward Transfer function
3. control ratio
4. feedback ratio
5. error ratio
6. closed loop transfer function
7. characteristic equation
8. closed loop poles and zeros if K=10.
)()()()( sHsGsEsB
)()()(
sGsEsC
)()()(
)()(
sHsGsG
sRsC
1
)()()()(
)()(
sHsGsHsG
sRsB
1
)()()()(
sHsGsRsE
1
1
)()()(
)()(
sHsGsG
sRsC
1
01 )()( sHsG
)(sG
)(sH
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Example-6• For the system represented by the following block diagram
determine:1. Open loop transfer function2. Feed Forward Transfer function3. control ratio4. feedback ratio5. error ratio6. closed loop transfer function7. characteristic equation 8. closed loop poles and zeros if K=100.
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Reduction techniques
4. Moving a summing point behind a block
G G
G
G G
G1
5. Moving a summing point ahead a block
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7. Moving a pickoff point ahead of a block
G G
G G
G1
G
6. Moving a pickoff point behind a block
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8. Swap with two neighboring summing points
A B AB
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Example-7
R_+
_+1G 2G 3G
1H
2H
+ +
C
• Reduce the following block diagram to canonical form.
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Example-7
R_+
_+
1G 2G 3G
1H
1
2
GH
+ +
C
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Example-7
R_+
_+
21GG 3G
1H
1
2
GH
+ +
C
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Example-7
R_+
_+ 21GG 3G
1H
1
2
GH
+ +
C
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R_+
_+
121
21
1 HGGGG
3G
1
2
GH
C
Example-7
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R_+
_+
121
321
1 HGGGGG
1
2
GH
C
Example-7
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R_+
232121
321
1 HGGHGGGGG
C
Example-7
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Example 8
Find the transfer function of the following block diagram
2G 3G1G
4G
1H
2H
)(sY)(sR
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1. Moving pickoff point A ahead of block2G
2. Eliminate loop I & simplify
324 GGG B
1G
2H
)(sY4G
2G
1H
AB3G
2G
)(sR
I
Solution:
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3. Moving pickoff point B behind block324 GGG
1GB)(sR
21GH 2H
)(sY
)/(1 324 GGG
II
1GB)(sR C
324 GGG
2H
)(sY
21GH
4G
2GA
3G 324 GGG
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4. Eliminate loop III
)(sR)(1
)(
3242121
3241
GGGHHGGGGGG
)(sY
)()()(
)()(
32413242121
3241
1 GGGGGGGHHGGGGGG
sRsY
)(sR1G
C
324
12
GGGHG
)(sY324 GGG
2H
C
)(1 3242
324
GGGHGGG
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2G 4G1G
4H
2H
3H
)(sY)(sR
3G
1H
Example 9
Find the transfer function of the following block diagrams
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Solution:
2G 4G1G
4H)(sY
3G
1H
2H
)(sRA B
3H4
1G
4
1G
I1. Moving pickoff point A behind block
4G
4
3
GH
4
2
GH
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2. Eliminate loop I and Simplify
II
III
443
432
1 HGGGGG
1G)(sY
1H
B
4
2
GH
)(sR
4
3
GH
II
332443
432
1 HGGHGGGGG
III
4
142
GHGH
Not feedbackfeedback
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)(sR )(sY
4
142
GHGH
332443
4321
1 HGGHGGGGGG
3. Eliminate loop II & IIII
143212321443332
4321
1 HGGGGHGGGHGGHGGGGGG
sRsY
)(
)(
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Example-10: Reduce the Block Diagram.
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Example-10: Continue.
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Example-11: Simplify the block diagram then obtain the close-loop transfer function C(S)/R(S). (from Ogata: Page-47)
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Example-11: Continue.
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Superposition of Multiple Inputs
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Example-12: Multiple Input System. Determine the output C due to inputs R and U using the Superposition Method.
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Example-12: Continue.
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Example-12: Continue.
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Example-13: Multiple-Input System. Determine the output C due to inputs R, U1 and U2 using the Superposition Method.
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Example-13: Continue.
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Example-13: Continue.
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Example-14: Multi-Input Multi-Output System. Determine C1 and C2 due to R1 and R2.
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Example-14: Continue.
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Example-14: Continue.
When R1 = 0,
When R2 = 0,
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Block Diagram of Armature Controlled D.C Motor
Va
iaT
Ra La
J
c
eb
V f=constant
(s)IK(s)cJs
(s)V(s)K(s)IRsL
am
abaaa
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Block Diagram of Armature Controlled D.C Motor
(s)V(s)K(s)IRsL abaaa
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Block Diagram of Armature Controlled D.C Motor
(s)IK(s)cJs ama
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Block Diagram of Armature Controlled D.C Motor
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END OF LECTURES-8-9
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