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input output equations - 39.16

39.12ROOT LOCUS

-A design point on the root locus curve can be selected for a specific damping coefficient.

θ

cos θ = ζ

 

 

 

 

 

39.13LYAPUNOV’S LINEARIZATION METHOD

This method addresses the local stability of a non-linear system when linearized.

In essense it validated the use of linear control systems on non-linear systems.

input output equations - 39.17

The proof begins with a taylor series expansion of a function that has a continuous differential. The second term in the expression is the higher order terms. There is an assumption that the system starts at equillibrium, so there is no initial value. The result is a linear approximation.

d

=

f( 0)

+

f

 

 

x + f

 

( t) =

f

 

x =

Ax

A =

f

 

----x

x x = 0

 

 

 

 

x x = 0

dt

 

 

 

 

 

 

h.o.t.

x x = 0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

d

 

f

 

 

 

 

 

f

 

 

 

 

 

 

( t)

 

 

 

 

----x =

 

 

 

 

x +

 

 

 

 

 

u + f

h.o.t.

= Ax + Bu

 

 

 

 

 

 

 

 

 

 

 

 

 

dt

 

x x = 0, u = 0

 

u x = 0, u = 0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A =

f

 

 

 

 

 

 

B =

 

f

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

x x = 0, u = 0

 

 

 

 

u

x = 0, u = 0

 

 

 

A linearized model of the control law can be written and the linearized model rewritten.

 

u

x = Gx

u

 

 

x

x = 0

d

( A + BG) x

----x = Ax + BGx =

dt

 

• Lyapunov’s stability theorem focuses on the stablilty (Eigenvalues) of matrix A at a given point.

-The system is asymptotically stable at the equillibrium point if all of the Eigenvalues of A are in the left hand complex plane.

-The system is unstable as the equillibrium point if the matrix A is unstable, with points in the right hand side of the complex plane.

-If all of the Eigenvalues are in the left hand plane, except for one or more on the complex axis, then the system is marginally stable, and the linearization may be stable or unstable.

39.14 XXXXX

- ea.

input output equations - 39.18

39.15XXXXX

-ea.

39.16XXXXX

-ea.

39.17XXXXX

-ea.

39.18XXXXX

-ea.

39.19XXXXX

-ea.

39.20XXXXX

-ea.

39.21SUMMARY

39.22 PRACTICE PROBLEMS

1.

input output equations - 39.19

39.23 PRACTICE PROBLEM SOLUTIONS

1.

39.24 ASSGINMENT PROBLEMS

1.

39.25REFERENCES

39.26BIBLIOGRAPHY

How, J, "16.31 Feedback Control Course Notes", MIT Opencourseware website.