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Bode plots for 2nd Order systems

2nd Order Systems

• Everything applies, except the break point

• Magnitude and Phase with s=jω

22

2

02

)(nn

n

ssCsG

“Double” Breakpoint at ωn

2nd Order Systems

• Everything applies, except the break point

• Magnitude and Phase with s=jω

22

2

02

)(nn

n

ssCsG

“Double” Breakpoint at ωn

Bode Plots Approximations

• Because Double break point at ωn

• If in s2+2ξωns+ωn2 in denominator

• -40 db/decade in denominator at ωn

• -180 deg shift (starting a decade below, to decade above at ωn )

• -90 deg at break point at ωn

G(s)=9/(s2+2s+9)

-80

-60

-40

-20

0

20M

agnitu

de (

dB

)

10-1

100

101

102

-180

-135

-90

-45

0

Phase (

deg)

Bode Diagram

Frequency (rad/sec)

G(s)= 9/(s3+2s2+9s)

-150

-100

-50

0

50

Magnitu

de (

dB

)

10-1

100

101

102

-270

-225

-180

-135

-90

Phase (

deg)

Bode Diagram

Frequency (rad/sec)

G(s)= (s+1)/ (s2+2s+100)

-40

-30

-20

-10

0M

agnitu

de (

dB

)

10-2

10-1

100

101

102

-90

-45

0

45

90

Phase (

deg)

Bode Diagram

Frequency (rad/sec)