On-off control is the simplest method of feedback control where the motor power is either switched fully on or off depending on whether the actual speed is higher or lower than the desired speed. A PID controller is a more advanced control method that uses proportional, integral and derivative terms to provide smoother control compared to on-off control and help reduce steady-state error. PID control is almost an industry standard approach for feedback-based motor speed regulation.

1. Control

2. On-Off Control
• we require feedback on a motor’s current speed in order to control it.
• Setting a certain PWM level alone will not help, since the motor’s
speed also depends on its load.
• The idea behind feedback control is very simple. In principle the
action always looks similar like this:
• In case desired speed is higher than actual speed:
Increase motor power by a certain degree.
• In case desired speed is lower than actual speed:
Decrease motor power by a certain degree.

3. On-Off Control
• n the simplest case, power to the motor is either switched on (when
the speed is too low) or switched off (when the speed is too high).

4. On-Off Control
• On-Off Control  piecewise constant controller or bang-bang
controller

5. On-Off Control
• The on-off controller is the simplest possible method of control.
• Examples are a refrigerator, heater, thermostat, etc.
• The formula for an on-off controller with hysteresis is: (This prevents
a too high switching frequency near the desired value)
•

6. PID Control
• A more advanced controller and almost industry standard is the PID
controller.
• It comprises a proportional, an integral, and a derivative control part.
• Proportional Controller
• The abrupt change between a fixed motor control value and zero does not
result in a smooth control behavior.
• The formula for the proportional controller (P controller) is:

7. PID Control
• Proportional Controller

8. PID Control
• Integral Controller
• The I controller (integral controller) is rarely used alone, but mostly in
combination with the P or PD controller.
• The idea for the I controller is to reduce the steady-state error of the
P controller.

9. PID Control
• Derivative Controller
• Similar to the I controller, the D controller (derivative controller) is
rarely used by itself, but mostly in combination with the P or PI
controller.
• The idea for adding a derivative term is to speed up the P controller’s
response to a change of input.

10. PID Control

11. Summary