Automation Direct DURApulse GS4 User Manual page 518

Appendix F: PID Control
PiD C
ontrol
This appendix covers the topic of Proportional-Integral-Derivative (PID) control by the GS4 series
AC drives.
Pid c o
ontrol
PID control is an output and feedback loop for the purpose of automatically controlling a portion
of a process to a specific condition by means of utilizing a target setpoint and the machine's actual
condition as the control's feedback. You set a goal and let the system reach that goal using the
systems conditional feedback and the PID control system.
PID control allows a process to reach and maintain the desired value (Setpoint) of the quantity
being controlled (Process Variable) more smoothly and consistently than does a simple On-Off
control system. On-Off control systems continually bounce back and forth above and below the
Setpoint value, but cannot maintain the Process Variable at the Setpoint value. PID controllers
constantly assess the rate of change of the Process Variable and its deviation from the Setpoint,
and then variably adjust the Control Output as much or as little as needed to keep the Process
Variable as close to the Setpoint as possible.
• P = Proportional control (gain)
• I = Integral control (time)
• D = Derivative (or Differential) control (The terms Derivative and Differential are used
interchangeably in industry to explain this type of control)
• Process Variable = the quantity being controlled
• Setpoint (or Target Value) = the desired value of the Process Variable
Setpoint
1
1) Setpoint: -100% to +100% (PID Setpoint Gain + PID Setpoint Offset)
2) Feedback: -100% to +100% (Feedback Gain)
3) Error: -100% to +100% (in percent Change)
4) I Limit: 0~150% (Torque Limit (Current Limit) P638)
5) PID Offset: P724 determines how the PID Offset will be controlled; by P704, or by an Analog
6) PID F
cmd
Since a PID controller relies only on the measured Process Variable, instead of knowledge of the
underlying process, it is applicable to a broad variety of system processes. By tuning the three
parameters of the model, a PID controller can deal with specific process requirements. The
response of the controller can be described in terms of its responsiveness to an error, the degree
to which the system overshoots a setpoint, and the degree of any system oscillation. The use of
the PID algorithm does not guarantee optimal control of the system or even its stability.
Some applications may require using only one or two terms to provide the appropriate system
control. This is achieved by setting the other parameters to zero. A PID controller is called a PI,
PD, P, or I controller in the absence of the other respective control actions. PI controllers are fairly
common, since Derivative action is sensitive to measurement noise, whereas the absence of an
Integral term may prevent the system from reaching its target value.
Page F–2
verview
P
3
E
I
+ -
Feedback
D
2
Input (P402, P403, P404)
Limit: See P625/P626
DuRA
pulse
5
PID
Offset
4 +
+
+
+
I Limit
Px
+
GS4 AC Drive User Manual – 1st Ed, Rev A - 10/20/2017
6
PID F cmd
PID F cmd
Limit