1. Introduction - National Cheng Kung University
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Transcript 1. Introduction - National Cheng Kung University
CH 1 Introduction
Prof. Ming-Shaung Ju
Dept. of Mechanical Engineering
NCKU
1. Introduction
What
is adaptive control?
An adaptive controller is a controller with
adjustable parameters and a mechanism
for adjusting the parameters.
Adaptive control systems have two loops
A
normal feedback with process and
controller
A parameter adjustment loop (slower
dynamics)
Structure of Adaptive Systems
History of adaptive control theory
1950s design of autopilots for high performance
aircraft (gain scheduling) speeds & altitude
1960s control theories : state space & stability,
dynamic programming, system identification
1970s different estimation schemes combined
with various design methods
Late 1970s-1980s proofs for stability of
adaptive systems, merge of robust control and
system identification
USA X-15 experimental aircraft
History of adaptive control theory
(cont’d)
1990s robustness of adaptive controllers,
nonlinear system theory help understanding
adaptive control
2000s related to learning in computer science,
artificial intelligence
Why adaptive control system?
Linear feedback has limited capability to cope
with parameter changes of the process and
variations in disturbance characteristics
Process variations may due to
Nonlinear
actuators
Large deviation of operating point
Examples of variations in disturbance
frequency contents of disturbance
Adaptive Schemes
Gain
scheduling
Model-reference adaptive control
Self-tuning regulator
Dual control
Gain Scheduling
Speed (Mach no.)
Altitude
Note: command & control signal are not utilized
Model-Reference Adaptive Control
Performance specification
e = ym-y
Self-Tuning Regulator
Indirect adaptive
Desired
System identification
Certainty equivalent principle: estimates are used as if they are true parameters
Dual Control
Limitation of above schemes: parameter uncertainties not
considered
When Certainty Equivalence Principle is not valid
Augment process state and parameters into a new state and
formulate a nonlinear stochastic control problem
(stochastic optimal control )
Nonlinear estimator: conditional probability distribution
of state p(z|y, u) (hyper-state)
Feedback controller maps hyperstate to control
Maintain good control and small estimation errors (dual)
Dual Control
Adaptive Control Problem
Process Model
State space model
Transfer function (matrix)
Continuous-time or discrete-time
Controller structure
A controller with adjustable parameters
Direct adaptive control
Parameters tuned without characteristics of the process and its
disturbance
Indirect adaptive control
Process model and disturbance characteristics are estimated then use
these information to design the controller
Design Procedures
1.
2.
3.
4.
Characterize desired behavior of closed-loop
system (stability, performance)
Determine a control law with adjustable
parameters
Find a mechanism for adjusting the parameters
Implement the control law