Controller Using Bode Plots

In summary, the conversation discusses designing a controller to ensure a steady state error of less than ±0.5%, settling time of less than 1.5 seconds, and overshoot of less than 5%. The equations and steps for calculating the gain for the controller are provided, but there is uncertainty on how to calculate the rise time, peak overshoot, and settling time. It is suggested to plot the time response to a step input and measure these parameters directly from the graph.
  • #1
topcat123
78
1

Homework Statement


This is the second part my problem. In the first part the Open Loop and Closed loop TF where worked out from design parameters. In later questions a lead or lag commentator is needs to be designed.

Design an appropriate controller to ensure the steady state
error in the liquid level in the tank when it undergoes a step
change is always less than ±0:5%. The settling time and
overshoot of the system response should also be less than
1:5 seconds and 5%, respectively.

I am unsure on how to calculate these parameters.

Homework Equations


The system is a negative unity feedback.

The Attempt at a Solution


Open loop TF
$$G(s)=\frac{0.213}{s(0.66s+3.5)+1}$$
Closed Loop TF
$$G(s)=\frac{0.213}{s(0.66s+3.5)+1.213}$$

Using the Steady Stat Error ##(e_{ss})=0.005##to work out the gain for the controler
$$e(s)=\frac{R(s)}{1+KpG(s)}$$
With A step ##\frac{1}{s}##
$$e(s)=\frac{\frac{1}{s}}{1+KpG(s)}$$
As ##\lim_{ss \rightarrow \infty} e(t)=\lim_{s \rightarrow 0} se(s)=0.005##
##s=0##
Therefor
$$0.005=\frac{s\frac{1}{s}\left[s(0.66s+3.5)+1\right]}{s(0.66s+3.5)+1+0.213Kp}$$
Giving A ##Kp=934.27##
How do I calculate the rise time, peak overshoot and the settling time.

Any tips or help would be appreciated.
Thanks
Tim
 
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  • #2
The only thing I have ever seen is to plot its time response to a step input and determine those numbers from the graph.
 
  • #3
Plot it how? Bode, Root locus.
 
  • #4
topcat123 said:
Plot it how? Bode, Root locus.
No. Plot the response signal versus time. Feed a step function into the transformation and measure how it responds in time. All the requirements you listed in your post #1 can be measured by looking at the plot of response versus time.
 

1. What is a Bode plot?

A Bode plot is a graphical representation of the frequency response of a system. It shows the gain and phase shift of a system as a function of frequency.

2. How is a Bode plot used in controller design?

Bode plots are commonly used in controller design to analyze and adjust the frequency response of a system. They can help determine the stability and performance of a system and guide the selection of appropriate control parameters.

3. What is the significance of the gain and phase margins in a Bode plot?

The gain margin and phase margin are important indicators of system stability. The gain margin is the amount of gain that can be added to the system before it becomes unstable, while the phase margin is the amount of phase shift that can be introduced before the system becomes unstable.

4. Can Bode plots be used to design both analog and digital controllers?

Yes, Bode plots can be used to design both analog and digital controllers. However, for digital controllers, the Bode plot must be transformed into the discrete domain using methods such as the Z-transform.

5. What are the limitations of using Bode plots in controller design?

Bode plots are limited to linear systems and do not take into account non-linearities in the system. They also assume that the system operates in the frequency domain, which may not always be the case. Additionally, Bode plots do not provide information about the transient response of the system.

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