×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Digital Controller Implementation

Digital Controller Implementation

Digital Controller Implementation

(OP)
I do not know if this is the right place to ask. I am trying my best to implement a PI compensator for an integrator plant using a Micro-controller. Simulation in Matlab gets me a good result. But in real life, the digital controller lags and fails to track the input signal perfectly. Used floating point math to perform the job. Everything has been checked and all the computations are within the sampling interval time ( 2.5KHz). What could be wrong and how can it corrected.

RE: Digital Controller Implementation

There is probably a difference between the simulation and the real plant Gain. An Integrating Plant has an Integral Gain which is the plant gain at one radian per second.

RE: Digital Controller Implementation

(OP)
Hi

I would be thankful, if you could elaborate on your point and suggest me the workaround

RE: Digital Controller Implementation

Mathematically if you input a 1 volt, 1 radian/sec sine wave to the plant input (Vin) and measure the plant output voltage (Vout) (Again a sine wave at 1 radian/sec with an amplitude A) the plant gain is Gain = Vout/Vin = A/1 = A

RE: Digital Controller Implementation

I may not be understanding your question, but lag, or time delay between input and response, is a characteristic of real world processes. PI controllers do not deal with it well. The derivative function in PID control, and feed forward functions are useful to improve response. But even then, time delays can make control difficult or impossible if the time lag is long compared to process perturbations.

RE: Digital Controller Implementation

A PI filter can be a good regulator for a Type 1 (single integration) plant, but it is error driven, so cannot track optimally. That is, it requires an error to create a command. The integrator can eventually reduce that error for a ramp (constant change) setpoint input, but not if the setpoint changes arbitrarily.

For good tracking, you want a feedforward component to the control output as well. The feedforward should be your best "guess" based on your plant model and the desired trajectory as to what is needed to track optimally.

Also, do examine all sources of time delay, as Compositepro suggests. If you are not careful, you can add one or two cycles of "transport delay" in your real system that may not be present in your simulation.

Curt Wilson
Omron Delta Tau

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

eBook - Manufacturing the Cars of Tomorrow
In this ebook, we'll explore how additive manufacturing is going to transform the way cars are made. This includes commentary from thought leaders such as Ford's CTO, Ken Washington, Customer case studies of ways 3D printing is being used today, and a variety of part examples where 3D printing is already impacting how automobiles are made. Download Now
White Paper - Smart Manufacturing for Semiconductor
New technologies and approaches present great opportunities for semiconductor manufacturers to achieve high levels of innovation, yield and improvement. This white paper explores some of these cutting-edge technologies and how they can be applied effectively in the semiconductor industry. Read about how Smart Manufacturing is transforming the semiconductor industry. Download Now
White Paper - Analysis and Simulation in Aircraft Structure Certification
Organizations using simulation and analysis tools effectively see the benefits in their ability to achieve certification faster and with drastically less total cost than those who do not maximize these tools. Read this White Paper to learn about how digital tools such as analysis and simulation help in aircraft structure certification. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close