Second Order Control System
Question:
What are the damping ratio (ζ) and undamped natural frequency (ωₙ) if the output of a control system is:
What are the damping ratio (ζ) and undamped natural frequency (ωₙ) if the output of a control system is:
c(t) = 1 + 0.25e-50t - 1.25e-10t
1. Identify the Exponential Terms
The response contains two exponential terms:
- e-50t
- e-10t
These correspond to the system poles.
s₁ = -50
s₂ = -10
2. Form the Characteristic Equation
For poles s₁ and s₂:
(s - s₁)(s - s₂) = 0
Substitute the values:
(s + 50)(s + 10) = 0
Expanding:
s² + 60s + 500 = 0
3. Compare with Standard Second-Order Form
s² + 2ζωₙ s + ωₙ²
Comparing with:
s² + 60s + 500
We get:
2ζωₙ = 60
ωₙ² = 500
4. Calculate Undamped Natural Frequency
ωₙ = √500
ωₙ = 22.36 rad/s
5. Calculate Damping Ratio
ζ = 60 / (2 × 22.36)
ζ ≈ 1.34
Final Results
- Undamped Natural Frequency (ωₙ) = 22.36 rad/s
- Damping Ratio (ζ) = 1.34
Conclusion: Since ζ > 1, the system is overdamped (non-oscillatory response).