Rules for Construction of Bode Plots
Follow these rules while constructing a Bode plot.
· Represent the open loop transfer function in the standard time constant form.
· Substitute, s=jω in the above equation.
· Find the corner frequencies and arrange them in ascending order.
· Consider the starting frequency of the Bode plot as 1/10th of the minimum corner frequency or 0.1 rad/sec whichever is smaller value and draw the Bode plot upto 10 times maximum corner frequency.
· Draw the magnitude plots for each term and combine these plots properly.
· Draw the phase plots for each term and combine these plots properly.
Note − The corner frequency is the frequency at which there is a change in the slope of the magnitude plot.
Example
Consider the open loop transfer function of a closed loop control system
Stability Analysis using Bode Plots
From the Bode plots, we can say whether the control system is stable, marginally stable or unstable based on the values of these parameters.
- Gain cross over frequency and phase cross over frequency
- Gain margin and phase margin
