Implementing digital PID control

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Discussion Overview

The discussion centers around the implementation of digital PID control for regulating the RPM of a brushless motor using an electronic speed controller (ESC). Participants explore the application of PID parameters (Kp, Ki, Kd) in adjusting PWM signals to achieve a desired motor speed, as well as considerations regarding the necessity and effectiveness of PID control in different scenarios.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks guidance on how to apply PID control parameters to adjust PWM signals for achieving a target RPM of 5000 from a measured 2000 RPM.
  • Another participant questions the necessity of PID control for motor speed regulation, suggesting that a direct input-output relationship may suffice for basic control.
  • Some participants propose that PID control might be more relevant in scenarios with variable loads, such as in robotics, where conditions change frequently.
  • A participant shares a reference to a review of control theory, indicating a resource for further reading on the topic.
  • Another participant provides a link to a tutorial on PID control, suggesting it may be useful for understanding the characteristics of PID in mechanical systems.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of PID control for motor speed regulation, with some advocating for its use in certain contexts while others argue it may be excessive for straightforward applications. The discussion remains unresolved regarding the best approach to implement the control strategy.

Contextual Notes

Some participants note that the effectiveness of PID control may depend on specific application details that were not provided, highlighting the importance of context in determining control strategies.

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I want to control the rpm of a brushless motor with ESC(Electronic speed controller) using PID control.
Suppose my motor is rotating at 2000 rpm detecting using hall sensor setup.Now I want it to run at 5000 rpm.The speed will be controlled by PWM signals generated by PWM module( 16-bit i.e. 65536 divisions in 0%-100% duty cycle, which we specify) in hardware which is fed to ESC.
How am I going use the PID parameters Kp, Ki and Kd to drive the motor to desired rpm?
desired rpm = 5000
measured rpm = 2000
error = desired - measured = + 3000
C(t) = Kp*e + Ki*∫e.dt + Kd*de/dt in digital form

Suppose somehow I find out PID constants, then how do I modify new PWM based on C(t) and error signal ?

Is New PWM = Old PWM*C(t)*error or New PWM = Old PWM+C(t)*error ?
 
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A decent review of control is Reviews of Modern Physics vol 77, p783.
 
Thanks for replying. i have a simpler query now : Suppose I use a proportional control to drive a motor. Measured rpm = 2000, Required rpm = 5000, Error = +3000. Control signal = K * Error. Now how should I apply this control signal to increase in voltage so as to attain the required rpm ?
 
For a motor I think PID is little over kill. A giving input should correspond to a giving rpm for the motor. Look up the value of the input that corresponds to the output that you want. That will give you a rough agreement. You might need some type of PID for ultra fine control or if the load isn't constant.
 
http://www.engin.umich.edu/group/ctm/PID/PID.html#characteristics
 
For a motor I think PID is little over kill. A giving input should correspond to a giving rpm for the motor. Look up the value of the input that corresponds to the output that you want. That will give you a rough agreement. You might need some type of PID for ultra fine control or if the load isn't constant.
Actually, it really depends on the situation which he unfortunately did not tell us what he is doing. In robotics PID loops generally are not overkill or at least a partial PID loop is because the load is always changing.
 
Ivan Seeking said:
http://www.engin.umich.edu/group/ctm/PID/PID.html#characteristics
Great find Ivan! A fitting tutorial on PID control of a mechanical system..
 

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