Download presentation
Presentation is loading. Please wait.
1
Chapter 1: Introduction to Control Systems
In this chapter we describe a general process for designing a control system. A control system consisting of interconnected components is designed to achieve a desired purpose. To understand the purpose of a control system, it is useful to examine examples of control systems through the course of history. These early systems incorporated many of the same ideas of feedback that are in use today. Modern control engineering practice includes the use of control design strategies for improving manufacturing processes, the efficiency of energy use, advanced automobile control, including rapid transit, among others. We also discuss the notion of a design gap. The gap exists between the complex physical system under investigation and the model used in the control system synthesis. The iterative nature of design allows us to handle the design gap effectively while accomplishing necessary tradeoffs in complexity, performance, and cost in order to meet the design specifications.
2
Introduction System – An interconnection of elements and devices for a desired purpose. Control System – An interconnection of components forming a system configuration that will provide a desired response. Process – The device, plant, or system under control. The input and output relationship represents the cause-and-effect relationship of the process.
3
Introduction Open-Loop Control Systems utilize a controller or control actuator to obtain the desired response. Closed-Loop Control Systems utilizes feedback to compare the actual output to the desired output response. Multivariable Control System
4
History Greece (BC) – Float regulator mechanism
Holland (16th Century)– Temperature regulator Watt’s Flyball Governor (18th century)
5
History
6
History 18th Century James Watt’s centrifugal governor for the speed control of a steam engine. 1920s Minorsky worked on automatic controllers for steering ships. 1930s Nyquist developed a method for analyzing the stability of controlled systems 1940s Frequency response methods made it possible to design linear closed-loop control systems 1950s Root-locus method due to Evans was fully developed 1960s State space methods, optimal control, adaptive control and 1980s Learning controls are begun to investigated and developed. Present and on-going research fields. Recent application of modern control theory includes such non-engineering systems such as biological, biomedical, economic and socio-economic systems
7
Examples of Modern Control Systems
(a) Automobile steering control system. (b) The driver uses the difference between the actual and the desired direction of travel to generate a controlled adjustment of the steering wheel. (c) Typical direction-of-travel response.
8
Examples of Modern Control Systems
9
Examples of Modern Control Systems
10
Examples of Modern Control Systems
11
Examples of Modern Control Systems
12
Examples of Modern Control Systems
13
The Future of Control Systems
14
The Future of Control Systems
15
Control System Design
17
Design Example
18
Design Example CVN(X) FUTURE AIRCRAFT CARRIER
19
Design Example
20
Design Example
21
Design Example
23
Sequential Design Example
24
Block Diagram fundamentals & reduction techniques
25
Introduction Block diagram is a shorthand, graphical representation of a physical system, illustrating the functional relationships among its components. OR A Block Diagram is a shorthand pictorial representation of the cause-and-effect relationship of a system. A cause-effect relationship is a relationship in which one event (the cause) makes another event happen (the effect). The loud sound of the alarm was the cause. Without the alarm, you probably would have overslept. In this scenario the alarm had the effect of you waking up at a certain time.
26
Introduction The simplest form of the block diagram is the single block, with one input and one output. The interior of the rectangle representing the block usually contains a description of or the name of the element, 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.
27
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. Any number of inputs may enter a summing point. The output is the algebraic sum of the inputs. Some books put a cross in the circle.
28
Components of a Block Diagram for a Linear Time Invariant System
System components are alternatively called elements of the system. Block diagram has four components: Signals System/ block Summing junction Pick-off/ Take-off point
30
In order to have the same signal or variable be an input to more than one block or summing point, a takeoff point is used. Distributes the input signal, undiminished, to several output points. This permits the signal to proceed unaltered along several different paths to several destinations.
31
Example-1 Consider the following equations in which x1, x2, x3, are variables, and a1, a2 are general coefficients or mathematical operators.
32
Block Diagram fundamentals & reduction techniques
33
Introduction Block diagram is a shorthand, graphical representation of a physical system, illustrating the functional relationships among its components. OR A Block Diagram is a shorthand pictorial representation of the cause-and-effect relationship of a system. A cause-effect relationship is a relationship in which one event (the cause) makes another event happen (the effect). The loud sound of the alarm was the cause. Without the alarm, you probably would have overslept. In this scenario the alarm had the effect of you waking up at a certain time.
34
Introduction The simplest form of the block diagram is the single block, with one input and one output. The interior of the rectangle representing the block usually contains a description of or the name of the element, 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.
35
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. Any number of inputs may enter a summing point. The output is the algebraic sum of the inputs. Some books put a cross in the circle.
36
Components of a Block Diagram for a Linear Time Invariant System
System components are alternatively called elements of the system. Block diagram has four components: Signals System/ block Summing junction Pick-off/ Take-off point
38
In order to have the same signal or variable be an input to more than one block or summing point, a takeoff point is used. Distributes the input signal, undiminished, to several output points. This permits the signal to proceed unaltered along several different paths to several destinations.
39
Example-1 Consider the following equations in which x1, x2, x3, are variables, and a1, a2 are general coefficients or mathematical operators.
40
Example-1 Consider the following equations in which x1, x2, x3, are variables, and a1, a2 are general coefficients or mathematical operators.
41
Example-2 Consider the following equations in which x1, x2,. . . , xn, are variables, and a1, a2,. . . , an , are general coefficients or mathematical operators.
42
Example-3 Draw the Block Diagrams of the following equations.
43
Topologies We will now examine some common topologies for interconnecting subsystems and derive the single transfer function representation for each of them. These common topologies will form the basis for reducing more complicated systems to a single block. Topolgy: the way in which constituent parts are interrelated or arranged
44
CASCADE Any finite number of blocks in series may be algebraically combined by multiplication of transfer functions. That is, n components or blocks with transfer functions G1 , G2, , Gn, connected in cascade are equivalent to a single element G with a transfer function given by
45
Example Multiplication of transfer functions is commutative; that is,
GiGj = GjGi for any i or j .
46
Cascade: Figure: a) Cascaded Subsystems.
b) Equivalent Transfer Function. The equivalent transfer function is
47
Parallel Form: Parallel subsystems have a common input and an output formed by the algebraic sum of the outputs from all of the subsystems. Figure: Parallel Subsystems.
48
Parallel Form: Figure: a) Parallel Subsystems.
b) Equivalent Transfer Function. The equivalent transfer function is
49
Feedback Form: The third topology is the feedback form. Let us derive the transfer function that represents the system from its input to its output. The typical feedback system, shown in figure: Figure: Feedback (Closed Loop) Control System. The system is said to have negative feedback if the sign at the summing junction is negative and positive feedback if the sign is positive.
50
Feedback Form: Figure: Feedback Control System.
Simplified Model or Canonical Form. c) Equivalent Transfer Function. The equivalent or closed-loop transfer function is
51
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: Refer to Nise-5th edition
52
Canonical Form of a Feedback Control System
The system is said to have negative feedback if the sign at the summing junction is negative and positive feedback if the sign is positive.
53
Open loop transfer function
Feed Forward Transfer function control ratio feedback ratio error ratio closed loop transfer function characteristic equation closed loop poles and zeros if K=10.
54
Characteristic Equation
55
Unity Feedback System
56
Reduction techniques 1. Combining blocks in cascade
2. Combining blocks in parallel
57
Reduction techniques 3. Moving a summing point behind a block
58
Reduction techniques 3. Moving a summing point ahead of a block
4. Moving a pickoff point behind a block 5. Moving a pickoff point ahead of a block
59
Reduction techniques 6. Eliminating a feedback loop
7. Swap with two neighboring summing points
60
Block Diagram Transformation Theorems
The letter P is used to represent any transfer function, and W, X , Y, Z denote any transformed signals.
61
Transformation Theorems Continue:
62
Transformation Theorems Continue:
63
Reduction of Complicated Block Diagrams:
64
Example-4: Reduce the Block Diagram to Canonical Form.
65
Example-4: Continue. However in this example step-4 does not apply.
66
Example-5: Simplify the Block Diagram.
67
Example-5: Continue.
68
Example-6: Reduce the Block Diagram.
69
Example-6: Continue.
70
Example-7: Reduce the Block Diagram. (from Nise: page-242)
71
Example-7: Continue.
72
Example-8: For the system represented by the following block diagram determine:
Open loop transfer function Feed Forward Transfer function control ratio feedback ratio error ratio closed loop transfer function characteristic equation closed loop poles and zeros if K=10.
73
Example-8: Continue First we will reduce the given block diagram to canonical form
74
Example-8: Continue
75
Example-8: Continue Open loop transfer function
Feed Forward Transfer function control ratio feedback ratio error ratio closed loop transfer function characteristic equation closed loop poles and zeros if K=10.
76
Example-9: For the system represented by the following block diagram determine:
Open loop transfer function Feed Forward Transfer function control ratio feedback ratio error ratio closed loop transfer function characteristic equation closed loop poles and zeros if K=100.
77
Example-10: Reduce the system to a single transfer function
Example-10: Reduce the system to a single transfer function. (from Nise:page-243).
78
Example-10: Continue.
79
Example-10: Continue.
80
Example-11: Simplify the block diagram then obtain the close-loop transfer function C(S)/R(S). (from Ogata: Page-47)
81
Example-11: Continue.
82
Example-12: Reduce the Block Diagram.
_ + _ + +
83
Example-12: _ _ + + +
84
Example-12: _ _ + + +
85
Example-12: _ _ + + + +
86
Example-12: _ _ + +
87
Example-12: _ _ + +
88
Example-12: _ +
89
Example-12:
90
Example 13: Find the transfer function of the following block diagrams.
91
Solution: 1. Eliminate loop I 2. Moving pickoff point A behind block Not a feedback loop
92
3. Eliminate loop II
93
Superposition of Multiple Inputs
94
Example-14: Multiple Input System
Example-14: Multiple Input System. Determine the output C due to inputs R and U using the Superposition Method.
95
Example-14: Continue.
96
Example-14: Continue.
97
Example-15: Multiple-Input System
Example-15: Multiple-Input System. Determine the output C due to inputs R, U1 and U2 using the Superposition Method.
98
Example-15: Continue.
99
Example-15: Continue.
100
Example-16: Multi-Input Multi-Output System
Example-16: Multi-Input Multi-Output System. Determine C1 and C2 due to R1 and R2.
101
Example-16: Continue.
102
Example-16: Continue. When R1 = 0, When R2 = 0,
103
Skill Assessment Exercise:
104
Answer of Skill Assessment Exercise:
Schaum’s series- solved problems- Pg#163 Nise-5th edition- problems- pg# 242
105
SIGNAL FLOW GRAPH
106
Outline Introduction to Signal Flow Graphs Mason’s Gain Formula
Definitions Terminologies Mason’s Gain Formula Examples Signal Flow Graph from Block Diagrams Design Examples
107
Signal Flow Graph (SFG)
Alternative method to block diagram representation, developed by Samuel Jefferson Mason. Advantage: the availability of a flow graph gain formula, also called Mason’s gain formula. A signal-flow graph consists of a network in which nodes are connected by directed branches. It depicts the flow of signals from one point of a system to another and gives the relationships among the signals.
108
Fundamentals of Signal Flow Graphs
Consider a simple equation below and draw its signal flow graph: The signal flow graph of the equation is shown below;
109
Important terminology :
Branches :- line joining two nodes is called branch. Branch Dummy Nodes:- A branch having one can be added at i/p as well as o/p. Dummy Nodes
110
Input & output node Input node:-
It is node that has only outgoing branches. Output node:- It is a node that has incoming branches. b x4 x3 x2 x1 x0 h f g e d c a Input node Out put node
111
Forward path:- Any path from i/p node to o/p node. Forward path
112
Loop :- A closed path from a node to the same node is called loop.
113
Self loop:- A feedback loop that contains of only one node is called self loop. Self loop
114
Loop gain:- The product of all the gains forming a loop
Loop gain = A32 A23
115
Path & path gain Path:- A path is a traversal of connected branches in the direction of branch arrow. Path gain:- The product of all branch gains while going through the forward path it is called as path gain.
116
Feedback path or loop :-
it is a path to o/p node to i/p node.
117
Touching loops:- when the loops are having the common node that the loops are called touching loops.
118
Non touching loops:- when the loops are not having any common node between them that are called as non- touching loops.
119
Non-touching loops for forward paths
120
Chain Node :- it is a node that has incoming as well as outgoing branches. Chain node
121
SFG terms representation
input node (source) Chain node Chain node forward path path loop branch node transmittance input node (source) Output node
122
Mason’s Rule (Mason, 1953) The block diagram reduction technique requires successive application of fundamental relationships in order to arrive at the system transfer function. On the other hand, Mason’s rule for reducing a signal-flow graph to a single transfer function requires the application of one formula. The formula was derived by S. J. Mason when he related the signal-flow graph to the simultaneous equations that can be written from the graph.
123
Mason’s Rule :- The transfer function, C(s)/R(s), of a system represented by a signal-flow graph is; Where n = number of forward paths. Pi = the i th forward-path gain. ∆ = Determinant of the system ∆i = Determinant of the ith forward path
124
∆ is called the signal flow graph determinant or characteristic function. Since ∆=0 is the system characteristic equation. ∆ = 1- (sum of all individual loop gains) + (sum of the products of the gains of all possible two loops that do not touch each other) – (sum of the products of the gains of all possible three loops that do not touch each other) + … and so forth with sums of higher number of non-touching loop gains ∆i = value of Δ for the part of the block diagram that does not touch the i-th forward path (Δi = 1 if there are no non-touching loops to the i-th path.)
125
Example1: Apply Mason’s Rule to calculate the transfer function of the system represented by following Signal Flow Graph Therefore, There are three feedback loops Continue……
126
There are no non-touching loops, therefore
∆ = 1- (sum of all individual loop gains) There are no non-touching loops, therefore Continue……
127
∆1 = 1- (sum of all individual loop gains)+... ∆1 = 1
Eliminate forward path-1 ∆1 = 1 ∆2 = 1- (sum of all individual loop gains)+... Eliminate forward path-2 ∆2 = 1 Continue……
129
From Block Diagram to Signal-Flow Graph Models
- C(s) R(s) G1 G2 H2 H1 G4 G3 H3 E(s) X1 X2 X3 Example2 R(s) -H2 1 G4 G3 G2 G1 C(s) -H1 -H3 X1 X2 X3 E(s) Continue……
130
R(s) -H2 1 G4 G3 G2 G1 C(s) -H1 -H3 X1 X2 X3 E(s)
131
Design example Example 3
132
Example 4 Continue……
133
Continue……
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.