Nguyễn Công Phương

CONTROL SYSTEM DESIGN

Frequency Response Methods

Contents

Introduction

I. II. Mathematical Models of Systems III. State Variable Models IV. Feedback Control System Characteristics V. The Performance of Feedback Control Systems VI. The Stability of Linear Feedback Systems VII. The Root Locus Method VIII.Frequency Response Methods IX. Stability in the Frequency Domain X. The Design of Feedback Control Systems XI. The Design of State Variable Feedback Systems XII. Robust Control Systems XIII.Digital Control Systems

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2

Frequency Response Methods

1. Introduction 2. Frequency Response Plots 3. Performance Specifications in the Frequency

Domain

4. Frequency Response Methods Using Control

System Software

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3

Introduction (1)

• The frequency response of a system: the steady – state response of the system to a sinusoidal input signal.

• The sinusoid is a unique input signal, and the resulting output signal for a linear system, as well as signals throughout the system, is sinusoidal in the steady state.

• It differs from the input waveform only in

amplitude and phase angle.

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4

Introduction (2)

m s ( )

=

=

T s ( )

n

m s ( ) q s ( )

+

(

s

p

)

i

= 1

i

=

w

(cid:213)

r t ( )

A

sin

t

= ( ) R s

2

2

w A +

w

s

a

= ( ) Y s

= ( ) ( ) R s T s

2

k 1 +

k +

b + s w + 2

s

+ n p

s

s

+ + ... p 1

n

a

1

+ np t

= ( ) y t

+ + p t ... 1

L

k e 1

k e n

2

b + s w + 2

  

  

s

a

- - - fi

1

=

=

y

t ( )

L

steady state

2

y t lim ( ) t

lim t

b + s w + 2

  

  

s

=

+

= — w

w A T j (

w ) sin(

f t

f ),

T j (

)

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5

- - fi ¥ fi ¥

Frequency Response Methods

1. Introduction 2. Frequency Response Plots 3. Performance Specifications in the Frequency

Domain

4. Frequency Response Methods Using Control

System Software

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6

Frequency Response Plots (1)

=

+

=

w G j (

)

G s ( )

Re[

w ( G j

)]

Im[

w G j (

)]

=

w

j

s

+

=

w (

R

)

w jX

(

)

f w ( j

)

=

=

w G j (

)

e

w ( G j

fw )

[ (

)]

2

w

w 2

=

+

R

(

)

X

(

w 1 ) {tan [ X

(

w ) /

R

(

)]}

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7

- —

Frequency Response Plots (2)

Ex. 1

+

+

=

=

=

V

s ( )

I s ( )

R

.

V s ( ) 2

capacitor

1 Cs

1 Cs

+

R

1( )V s

2( )V s

V s ( ) 1 1 Cs

C

= ( ) G s

+

1 RCs

1

( ) V s = 2 V s ( ) 1

- - fi

0.5

= w G j ( )

G s ( )

=

= w j

s

Positive w Negative w

1 w j RC (

+ ) 1

0.4

0.3

1

=

=

w

,

0.2

1

1 RC

j

(

w w /

+ ) 1

1

0.1

)

(w

0

X

-0.1

w w /

1

=

j

2

2

-0.2

1 w w /

+ 1 (

)

w w + 1 (

/

)

1

1

-0.3

-0.4

-

=

-0.5

1 tan (

w w /

)

1

2

1 w w /

+ 1 (

)

1

0

0.2

0.4

0.6

0.8

1

R(w

)

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8

- — -

Frequency Response Plots (3)

Semilog plots of the magnitude (in decibels) and phase (in degrees) of a transfer function versus frequency

=

20log

T

10

f

T=T

 dBT  f 

=

=

f

f

f

...

...

T T T T 3

1 2

T 1

3

=

f

) +

( (

( 2T )

)1 ...

...

T T T 1 2 3

( )2 3T f+ f + 2

1

3

+

+

+

20log

20log

...

T 1

T 2

10

T 3

10

= +

20log 10 + ...

 20 log 10  f f f + =  1

T f 2

3

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9

Frequency Response Plots (4)

2

j

1

1

+

+

w K j (

)

1

...

zw 2 j w

  

  

 w +  w 

  

w j z 1

k

k

  1  

   

=

w

T (

)

2

j

2

+

+

1

...

z w 2 j w

  

  

w  +  w 

  

w j p 1

n

n

  1  

   

K

: gain

1

1

: quadratic pole

: pole at the origin

: simple pole

2

1 jw

j

j

+

+

1

1

z w 2 2 w

w j p 1

w  +  w 

  

n

n

2

j

j

+

+

1

: simple zero

jw

: zero at the origin

1

: quadratic zero

zw 12 w

w j z 1

w  +  w 

  

k

k

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10

Frequency Response Plots (5)

=

20 log

K

10

w

=

T (

)

K

0

 dBT  = f

f

dBT 20 log K

10

0

0.1

10

100 w

10

100 w

1

0.1

1

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11

Frequency Response Plots (6)

= -

w

20 log

10

w

=

T (

)

o

1 w j

90

 dBT  = - f 

f

dBT 20

0

o0

w

w

10

0.1

1

10

1

0.1

20

-

o90

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12

-

Frequency Response Plots (7)

=

w

20 log

10

w

=

w

T (

j

)

o

90

 dBT  = f

f

o90

dBT 20

0

o0

w

w

10

0.1

1

10

1

0.1

20

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13

-

Frequency Response Plots (8)

= -

T

+ 20log 1

dB

10

1

w j p 1

w

=

T (

)

w

+

1

1

=

tan

w j p 1

 - 

  

     f  

p 1

dBT 5

-

0

-5

-10

-15

w

-20

0.1p 1

1p

10 p 1

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14

-25

Frequency Response Plots (9)

= -

T

+ 20log 1

dB

10

1

w j p 1

w

=

T (

)

w

+

1

1

=

tan

w j p 1

 - 

  

     f  

p 1

f

0.1p 1

1p

10 p 1

-

100 p 1 w

0

-10

-20

-30

-40

-50

-60

-70

-80

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15

-90 -100

Frequency Response Plots (10)

=

+

T

20log 1

dB

10

w j z 1

= +

w

T (

) 1

w

w j z 1

1

tan

  

  

     = f  

z 1

dBT 25

-

20

15

10

5

w

0

0.1z 1

1z

110z

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16

-5

Frequency Response Plots (11)

=

+

T

20log 1

dB

10

w j z 1

= +

w

T (

) 1

w

w j z 1

1

tan

  

  

     = f  

z 1

f

-

100

90

80

70

60

50

40

30

20

w

10

0.1z 1

1z

110z

100z 1

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17

0

Frequency Response Plots (12)

2

j

j

= -

T

+ 20log 1

dB

10

z w 2 2 w

w  +  w 

  

n

n

1

=

w

T (

)

2

j

j

/

j

1

+

+

1

= -

tan

z w 2 2 w

w   w 

  

-

n

n

z w w 2 2 2 w w /

1

   

   

n 2 n

      f   

-

0.05

z = 2

dBT

20

0.2

z = 2

0.4

z = 2

10

0

0.707

z = 2

z = 2 1.5

-10

-20

w

-30

w

w 0.1 n

n

w 10 n

w 100 n

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18

-40

Frequency Response Plots (13)

2

j

j

= -

T

+ 20log 1

dB

10

z w 2 2 w

w  +  w 

  

n

n

1

=

w

T (

)

2

j

j

/

j

1

+

+

1

= -

tan

z w 2 2 w

w   w 

  

-

n

n

z w w 2 2 2 w w /

1

   

   

n 2 n

      f   

w

f

w 0.1 n

n

w 10 n

-

w 100 n w

0

1.5

z = 2

-20

-40

0.707

-60

z = 2

-80

0.4

-100

0.2

-120

-140

0.05

z = 2 z = 2 z = 2

-160

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19

-180

Frequency Response Plots (14)

2

j

j

=

+

T

20log 1

dB

10

2

z w 2 2 w

w  +  w 

  

n

n

j

j

w

= +

+

T (

) 1

z w 2 2 w

w   w 

  

n

n

/

j

1

tan

-

z w w 2 2 2 w w /

1

   

   

n 2 n

      f =  

-

dBT

1.5

z = 2

40

30

0.707

z = 2

20

0.4

z = 2

10

0

0.2

0.05

z = 2

w

z = 2

-10

w

w 0.1 n

n

w 10 n

w 100 n

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20

-20

Frequency Response Plots (15)

2

j

j

=

+

20log 1

T

10

dB

2

z w 2 2 w

w  +  w 

  

n

n

j

j

w

= +

+

T (

) 1

z w 2 2 w

w   w 

  

n

n

/

j

1

tan

-

z w w 2 2 2 w w /

1

   

   

n 2 n

      f =  

-

0.05

f

z = 2

180

0.2

z = 2

160

0.4

z = 2

140

120

100

0.707

80

z =

z = 2 2 1.5

60

40

w

20

w

w 0.1 n

n

w 10 n

w 100 n

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21

0

Frequency Response Plots (16)

N

K

jw

(

) N

1 ) N jw

(

 + 1 

  

w j z

20

N

dB/decade

20 log K

1

20

dB/decade

N

w

10

20

N

dB/decade

1

w

z

w

w

o

o

90N

90N

w

o0

o0

o

w

w

-

z

w

10z

90N

z 10

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22

-

Frequency Response Plots (17)

1

N

N

N

j

j

j

j

+

+

z w 2 2 w

zw 12 w

w  +  w 

2   

w  +  w 

2   

k

k

n

n

1 w j p

  

 + 1 

  1  

   

  1  

   

w

k

p

N

40

dB/decade

w

w

20

N

dB/decade

40

N

dB/decade

w

w

n

o

180N

w

w

k 10

k

w 10 k

p

10 p

p 10

w

o0

w

o0

w

o0 w

o

w

- -

n

w 10 n

180N

o

90N

n 10

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23

- -

Frequency Response Plots (18)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

=

w T (

)

+

+ w

(1

w j

j

/10)

o

=

90

1 w tan (

/ 5)

1 w tan (

/10)

+

w j 10 / 5)(1 w j 10 + w / 5 1

1

w j

j

/10

=

+

+

+

20 log 10 20 log

w j

20 log

20log

10

10

10

10

dBT

+

+ w

1 w j

1

/ 5

1 j

1

/10

- - - -

o

1

+

+

90

tan

tan

w

1 / 5

1 /10

  

  

 1  w 

  

     = f  

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24

- -

Frequency Response Plots (19)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

=

+

+

+

20log 10 20log

w j

20log

20log

+

+ w

1 w j

1

/ 5

1 j

1

/10

dBT 10 10 10 10

dBT

20 log 10

40

10

K

30

20

20log K

10

w

10

w

0

-10

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-20 0.1 1 5 10 20 100 500 200 25

Frequency Response Plots (20)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

=

+

+

+

20log 10 20log

w j

20log

20log

+

+ w

1 w j

1

/ 5

1 j

1

/10

dBT 10 10 10 10

dBT

20 log 10

40

10

30

jw

(

)N

20

20 log

jw

20

N

dB/decade

10

w

10

1

w

0

-10

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-20 0.1 1 5 10 20 100 500 200 26

Frequency Response Plots (21)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

=

+

+

+

20log 10 20log

w j

20log

20log

+

+ w

1 w j

1

/ 5

1 j

1

/10

dBT 10 10 10 10

dBT

20 log 10

40

10

1

30

N

20

w j p

  

 + 1 

20 log

jw

10

w

p

10

w

0

20

N

dB/decade

20 log

10

1 jw+

1

/ 5

- -10

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-20 0.1 1 5 10 20 100 500 200 27

Frequency Response Plots (22)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

=

+

+

+

20log 10 20log

w j

20log

20log

+

+ w

1 w j

1

/ 5

1 j

1

/10

dBT 10 10 10 10

dBT

20 log 10

40

10

1

30

N

20

w j p

  

 + 1 

20 log

jw

10

w

p

10

w

20log

0

10

20

N

dB/decade

20 log

10

1 jw+

1

/10

1 jw+

1

/ 5

- -10

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-20 0.1 1 5 10 20 100 500 200 28

Frequency Response Plots (23)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

=

+

+

+

20log 10 20log

w j

20log

20log

+

+ w

1 w j

1

/ 5

1 j

1

/10

dBT 10 10 10 10

Sl ope = 0 + 20 – 20

dBT

20 log 10

40

10

30

20

20 log

jw

10

w

10

20log

10

0

20 log

1 jw+

1

/10

10

1 jw+

1

/ 5

-10

29

-20 1 10 5 100 200 500 0.1 20 s i tes.google.com/site/ncpdhbkhn

Frequency Response Plots (24)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

o

1

1

=

+

+

90

tan

tan

w

1 / 5

1 /10

  

  

  w 

  

o90

f f 90

jw

(

)N

w

o

90N

- -

w

60 40 20 0 -20 -40 -60

0.1

0.5

1

5

10

20

50

100

200

500

30

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-90

Frequency Response Plots (25)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

o

1

1

=

+

+

90

tan

tan

w

1 / 5

1 /10

  

  

  w 

  

o90

f f 90

N

1 w j p

  

 + 1 

w

p

10 p

tan

w

p 10 o0

-  1  

  

1 /5w

- -

o

60 40 20 0 -20 -40 -60

90N

0.1

0.5

1

5

10

20

50

100

200

500

31

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- -90

Frequency Response Plots (26)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

o

1

1

=

+

+

90

tan

tan

w

1 / 5

1 /10

  

  

  w 

  

o90

f f 90

N

1 w j p

  

 + 1 

w

p

10 p

tan

w

-  1  

  

tan

1 /10

w

p 10 o0

-  1  

  

1 /5w

- -

o

60 40 20 0 -20 -40 -60

90N

0.1

0.5

1

5

10

20

50

100

200

500

32

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- -90

Frequency Response Plots (27)

Ex. 2

=

=

w T (

)

+

+

w +

500 + w 5)(

w j j

w j

(

10)

(1

w j

j

/10)

w j 10 / 5)(1

o

1

1

f

=

+

+

90

tan

tan

w

1 / 5

1 /10

  

  

  w 

  

o90

f 90

w

tan

w

-  1  

  

tan

1 /10

-  1  

  

1 /5w

- -

60 40 20 0 -20 -40 -60

0.1

0.5

1

10

20

5

50

100

200

500

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33

-90

Frequency Response Plots (28)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

40

dBT

20 log 8

20

10

w

0

-20

K

-40

20 log K

10

-60

w

-80

-100

0.1

1

5

10

20

50

100

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34

Frequency Response Plots (29)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

40

+

20 log 1

dBT

10

jw 20

20 log 8

20

10

w

0

-20

N

w j z

 + 1 

  

-40

20 dB/decade

N

-60

z

w

-80

-100

0.1

1

5

10

20

50

100

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35

Frequency Response Plots (30)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

40

+

20 log 1

dBT

10

jw 20

20 log 8

20

10

w

0

20 log

10

1 jw

-20

1 jw )N

(

-40

-60

1

w

20 dB/decade

N

-80

-100

0.1

1

5

10

20

50

100

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36

-

Frequency Response Plots (31)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

40

+

20 log 1

dBT

10

20 log

10

2

jw 20

(1

/ 5)

1 jw+

20 log 8

10

20

w

0

20 log

10

1 jw

-20

N

-40

1 w j p

  

 + 1 

p

-60

w

N- 20 dB/decade

-80

-100

0.1

1

5

10

20

50

100

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37

Frequency Response Plots (32)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

40

+

20 log 1

dBT

10

20 log

10

2

jw 20

(1

/ 5)

1 jw+

20 log 8

10

20

w

0

20 log

10

1

1 jw

-20

N

2

j

j

+

z w 2 2 w

w  +  w 

  

k

k

  1  

   

-40

kw

w

-60

40

N

dB/decade

-80

20 log

10

2

+

1 +

1

w 4 /10 (

/10)

w j

j

-100

0.1

1

5

10

20

50

100

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38

-

Frequency Response Plots (33)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

40

dBT

20

w

0

-20

-40

-60

-80

-100

0.1

1

5

10

20

50

100

39

Frequency Response - s i tes.google.com/site/ncpdhbkhn

Frequency Response Plots (34)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

90

f

50

w

0

-50

N

-90

w j z

 + 1 

  

o

90N

-180

-200

w

z

10z

o0 z 10

-270

-300

-360

0.1

0.2

0.5

1

10

50

100

200

500

2 s i tes.google.com/site/ncpdhbkhn

40

Frequency Response Plots (35)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

90

f

50

w

0

-50

-90

1 )N jw

(

-180

-200

w

o

90N

-270

-300

-360

0.1

0.2

0.5

1

10

50

100

200

500

2 s i tes.google.com/site/ncpdhbkhn

41

-

Frequency Response Plots (36)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

90

f

50

w

0

-50

1

-90

N

w

j p

  

 + 1 

-180

p

10p

-200

w

p 10 o0

o

90N

-270

-300

-360

0.1

0.2

0.5

1

10

50

100

200

500

2 s i tes.google.com/site/ncpdhbkhn

42

-

Frequency Response Plots (37)

Ex. 3

+

+

w j

w j

=

=

T

w (

)

2

2

+ w

20) w +

+

+

w j

(1

j

j

/ 20) + w 4 /10 (

j

/10)

(

j

5)

40

j

)

w w j (

j

100

8(1  + w 2 / 5) 1 

 

1000(  2 w 

 

90

f

50

w

0

-50

1

N

-90

2

j

j

+

z w 2 2 w

w  +  w 

  

k

k

   

w

-180

k

w 10 k

-200

w

  1   kw 10 o0

o

180N

-270

-300

-360

0.1

0.2

0.5

1

10

50

100

200

500

2 s i tes.google.com/site/ncpdhbkhn

43

-

Frequency Response Plots (38)

Ex. 4 Find the transfer function from the Bode plot?

Sl ope = 0

dBH

jw

(

)N

40

30

20 dB/decade

N

20

1

w

jw

10

w

0

-10

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44

-20 0.1 1 5 10 20 100 200 500

Frequency Response Plots (39)

Ex. 4 Find the transfer function from the Bode plot?

Sl ope = 0

dBH

K

20 log 10

40

10

30

20 log K

10

20

w

jw

10

w

0

-10

45

s i tes.google.com/site/ncpdhbkhn

-20 0.1 1 5 10 20 100 200 500

Frequency Response Plots (40)

Ex. 4 Find the transfer function from the Bode plot?

Sl ope = 0

dBH

1

20 log 10

40

10

w j p

N   

 + 1 

30

p

w

20

N- 20 dB/decade

jw

10

w

0

20log

10

1 jw+

1

/ 5

-10

46

s i tes.google.com/site/ncpdhbkhn

-20 0.1 1 5 10 20 100 200 500

Frequency Response Plots (41)

=

Ex. 4 Find the transfer function from the Bode plot?

w T (

)

+

+ w

w j 10 / 5)(1

(1

w j

j

/10)

Sl ope = 0

dBH

1

N

20 log 10

40

10

w j p

  

 + 1 

30

p

w

20

N- 20 dB/decade

20 log

10

jw

1 jw+

1

/10

10

w

0

20log

10

1 jw+

1

/ 5

-10

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47

-20 0.1 1 5 10 20 100 200 500

Frequency Response Methods

1. Introduction 2. Frequency Response Plots 3. Performance Specifications in the

Frequency Domain

4. Frequency Response Methods Using Control

System Software

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48

Performance Specifications in the Frequency Domain (1)

2

w

w =

z

<

z 1 2

,

0.707

resonant

n

-

2

=

=

<

z

-

M

w G j (

)

z 1 2

0.707

z 2

,

-

(

) 1

w p

r

0.05

z = 2

dBT

20

0.2

z = 2

0.4

z = 2

10

1

=

G

w (

)

2

0

z =

j

j

2 0.707

+

1

z w 2 2 w

1.5

z = 2

w  +  w 

  

n

n

-10

-20

w

-30

w

w 0.1 n

n

w 10 n

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w 100 n 49

-40

2

=

=

<

z

-

Performance Specifications in the Frequency Domain (2) z 2 M 0.707

w G j (

z 1 2

)

,

) 1

(

w p

r

5.5

5

4.5

4

3.5

pw

M

3

2.5

2

1.5

1 0.1

0.2

0.3

0.4

0.5

0.6

0.7

-

zw

z

nt

= +

q +

y t ( ) 1

Be

w cos(

)

t 1

Resonant magnitudes should be relatively small: Mpω < 1.5, for example

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50

-

Frequency Response Methods

1. Introduction 2. Frequency Response Plots 3. Performance Specifications in the Frequency

Domain

4. Frequency Response Methods Using

Control System Software

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51

Ex.

=

T s ( )

+

Frequency Response Methods Using Control System Software s 500 + s 5)(

10)

(

s

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52