A/D T
Controller
-
D/A hold
plant c(t) G(s)
b(t)
sensor 1
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The Principle of Automatic Control 2008
Signal types in digital system
• Continuous signals: change continuously in time • Discrete signals: vary only at discrete times. • Sample period T: fixed time period at which all analog-
D/A hold
plant c(t) G(s)
Clock
A/D T
sensor 1
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The Principle of Automatic Control 2008
Discrete/digital control system
digital controller
e(kT)
u(kT)
u(t)
r(t)
Digital
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The Principle of Automatic Control 2008
Analog VS Digital Control (cont.)
Analog control
Digital control
Disadvantages
•Component drift and aging/unstable •Hardwired/not flexible •Limited to classical control theory only •Large parts count for complex systems
•Bandwidth limitations (sampling loop) •Numerical problems (quantization, rounding…) •AD/DA boundary (resolution, speed, cost) •CPU performance limitations •System cost
•Insensitive to environment (temp, drift…) •High reliability •Software programmable/flexible solution •Precise/predictable behavior •Advanced control possible (non-linear, multi-variable) •Can perform multiple loops and “other” functions
to-digital (A/D) converted signals are supplied to the digital computer. • Sampled-data system: having both continuous and discrete signals. • Quantized signals: output of A/D converter stored in a digital word with finite number of digits. • Digital signals: those both discrete and quantized.
+
D(s)
G(s)
-
sensor 1
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The Principle of Automatic Control 2008
Discrete/digital control system
digital controller
r(t) T
e(kT)
u(kT)
u(t)
Digital Controller
b- (kT)
Chapter 7 Analysis and design of discrete-time
system 离散控制系统的分析与设计
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The Principle of Automatic Control 2008
Organization
7-1 Introductory Digital control 7-2 Sampling and hold 7-3 Z-transform 7-4 Mathematical model of discrete
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The Principle of Automatic Control 2008
Analog VS Digital Control
Analog control
Digital control
Advantages
•High bandwidth •High resolution •Easy to understand/use •“Relatively” low cost
control system 7-5 Stability and steady-state error 7-6 Dynamic response 7-7 Discrete design
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The Principle of Automatic Control 2008
7-1 Introductory Digital control
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The Principle of Automatic Control 2008
e*(t) e(kT)
u(kT)
u(t)
The Principle of Automatic Control
自动控制原理
Lecturers：Prof. Jiang Bin Dr. Lu Ningyun
College of Automation Engineering
NUAA，2008. Autumn
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NUAA-The Principle of Automainciple of Automatic Control 2008
Continuous/Analog control system
continuous controller
For example, PID controller
r(t)
e(t) Controller u(t) plant y(t)