Proportional Integral Differential (PID) Motor Control

PID is a control 'filter' , which helps you get to a goal setpoint as fast as possible without overshoot or oscillation. The technique is siple realy:

1. Find the 'error' ie the difference between where the system is, and where it needs to be. Multipl this error by a gain value known as Kp. This is the proportional component of the output.
2. Find the difference between the last error and the current error and multiply by another gain known as Kd. This is the differential component of the output. It is responsible for accelerating the motor if the error is large.
3. Find the running average of errors, and multiply by another gain value known as Ki. This term is responsible for damping the system to prevent overshoot and oscillation.
4. Add the proportional, differential and integral terms together and scale the result down to 255 max, and use this value as a PWM value.

The algorithim gives more power to the motor when it's further from the target, and less power when it's close to the target.

By choosing the Kp, Kd and Ki terms properly you can 'tune' the filter to respond smoothly and rapidly to any position demand without overshooting.

Thanks to: Mark Hull  Engineering/Technical EMS (Africa) (Pty) Ltd For that introduction

NEW! MassMind.org BOB PID Servo Motor Control

Tuning a PID Motor Controller

See also:

• http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/ Starts from the most common implementation of PID and takes it through 8 significant improvements. This is one of the best series on PID.
  
• http://www.hugoordonez.com/pid.html
• http://www.siebe-env-controls.com/news/links/pid.htm
• http://www.expertune.com tutor artCE87
• http://real.uwaterloo.ca/~robot/Mc_sw.html
• http://192.195.23.217/robots/mogotut/PID.htm - has some information about PID and PWM. Be sure to look at the other links on the page.
• http://www.jashaw.com/pid/tutorial/
• http://www.mechatronics.me.vt.edu/labs/lab5.html basics
• http://www.microchip.com/Download/Appnote/Category/16CXX/00701a.pdf PID for a Buck Boost Power supply.
• http://www.mcjournal.com/main/vol1num2/articles/tutser2/tutser2.htm
• http://members.aol.com/pidcontrol/pid_algorithm.html (cached 20010425154541 )
• http://rclsgi.eng.ohio-state.edu/matlab/PID/PID.html
• http://instserv.com/pid.htm
• http://www.jashaw.com/pid/

Interested:

Archive:

• PICList post "Need help with PID for motor control on a F877"
• PICList post "PWM motor control"
• PICList post "PID controllers (was PWM motor control)"

Comments:

An AC spindle motor will not benefit from PID mode in a driving VFD unless the motor is rated for full torque at zero speed. Otherwise, the best you can do is mechanically gear the motor down so it can run at high speed while the spindle is running slowly. Then the PID will have some effect.