for the gain k computed in (a), nd the frequency ! > 0 that maxi- mizes the gain of the frequency response of the closed-loop system. compute the corresponding gain.

Respuesta :

The corresponding gain is 7.81×10-³

With compensation G(s) = k / (s+3) (s+1)

a) closed loop characteristic equation is

1 + G(s) = 0

(s+3) (s+1) + k = 0

s² + 4s + k + 3 = 0 ------ (1)

standard form of characteristic equation is

s² + 2ξ ωn + ωn² = 0 ------ (2)

Given ξ = 1/√2

comparing equation (1) and (2)

ωn² = k+3 , ωn = √(k+3)

2 ξ ωn = 4

2 × 1/√2 × √ (k+3) = 4

√(k+3) = 2√2

k + 3 = 8, k = 5

b) closed loop tranfer function

T(s) = G(s) / 1+G(s)

= 5/ s²+4s+8

magnitude |G(s)| = 5/√ [ (64-ω²)² + (4ω)²]

For maximum gain, denominator --> maximum

d/dω [ (64-ω²)² + 16ω²] = 0

2(64-ω²)² (-2ω) + 32ω = 0

4ω ( -4096 - ω⁴+128ω²+8 ) = 0

ω⁴ + 128ω² - 4088 = 0

ω = 26.6 rad/s

Gn = 5/√ [ (64-ω²)² + (4ω)²]

Gain = 7.81×10-³

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