Math Problem Statement

Kuntakente Sdn. Bhd. plan to use Bode plot approach to determine the stability of asystem given by the transfer function below : G(s)= s(s+10)(s+50)/ 2000(s+0.5) ​

Solution

The transfer function provided is:

G(s)=s(s+10)(s+50)2000(s+0.5)G(s) = \frac{s(s+10)(s+50)}{2000(s+0.5)}

Steps to Analyze Stability Using the Bode Plot Approach:

  1. Rewrite the Transfer Function: Simplify the given transfer function to identify its gain, poles, and zeros.

    • The numerator (s)(s+10)(s+50)(s)(s+10)(s+50) gives zeros at s=0,10,50s = 0, -10, -50.
    • The denominator 2000(s+0.5)2000(s+0.5) gives a pole at s=0.5s = -0.5 and a gain factor of 12000\frac{1}{2000}.

    The transfer function becomes: G(s)=s3+60s2+500s2000(s+0.5).G(s) = \frac{s^3 + 60s^2 + 500s}{2000(s + 0.5)}.

  2. Break Down the Magnitude Response:

    • At low frequencies (s0s \to 0), the magnitude is governed by the (s+0.5)(s+0.5) pole.
    • As frequency increases, the magnitude will be affected by the zeros and poles.
    • Each pole decreases the slope of the magnitude plot by 20 dB/decade20\ \text{dB/decade}, and each zero increases it by 20 dB/decade20\ \text{dB/decade}.
  3. Phase Response:

    • Each pole contributes 90-90^\circ to the phase shift.
    • Each zero contributes +90+90^\circ to the phase shift.
  4. Determine Stability:

    • Use the Gain Margin and Phase Margin criteria from the Bode plot to assess stability.
    • A system is stable if the gain margin and phase margin are both positive.
  5. Draw the Bode Plot:

    • Use the transfer function to calculate the magnitude and phase for a range of frequencies (typically logarithmic scale).
    • Plot the results to analyze the stability.

Would you like a detailed plot or step-by-step analysis of the magnitude and phase responses?


Related Questions:

  1. How can poles and zeros affect the system's stability in the frequency domain?
  2. What is the significance of the gain margin and phase margin in determining stability?
  3. How can the Nyquist criterion complement the Bode plot approach in stability analysis?
  4. What changes in the transfer function G(s)G(s) would make the system unstable?
  5. How does scaling the gain (20002000) affect the Bode plot and system stability?

Tip:

To simplify Bode plots, break the system into first-order and second-order components and analyze each separately.

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Math Problem Analysis

Mathematical Concepts

Control Systems
Bode Plot
Stability Analysis
Transfer Function

Formulas

G(s) = (s(s+10)(s+50)) / 2000(s+0.5)
Magnitude Response: 20 log|G(jω)|
Phase Response: ∠G(jω)
Gain Margin: 1 / |G(jω) at phase -180°|
Phase Margin: phase of G(jω) at gain crossover frequency

Theorems

Nyquist Criterion
Bode Stability Criterion

Suitable Grade Level

Undergraduate (Engineering, Control Systems)