Proportional Gain (P) - Automation Direct DURApulse GS4 User Manual

Appendix F: PID Control
C PiD C
onCePt of
When PID is enabled by P7.00, P7.02 "reflects" the PID Setpoint Source determined by what is set
in P4.00 (Remote) or P4.01 (Local), and what Mode the Drive is in, i.e. Remote or Local Mode. PID
control operates with the feedback signal as reflected by P7.02 either 0~10V voltage or 4~20mA
current.
P g
roPortional
The output is proportional to (or a percentage of the) input. With only Proportional Gain control,
there will always be a steady-state error in the control's effort to reach the setpoint.
The first parameter of PID control is Proportional Gain (P). For a given process, if the Proportional
value is set too low, the control action will be too sluggish. If the Proportional value is set too
high, the control action will be unstable (erratic). To find the correct setting for Proportional,
set the Integral Time (I) and Derivative Value (D) to zero (0). Begin tuning the process with a low
Proportional Value, and increase the Proportional value until the system goes unstable (erratic).
When instability is reached, reduce the Proportional value slightly until the system becomes stable
(smaller values reduce system gain). Stability can be tested by moving between two wide-spread
setpoint values. With 10% deviation and P=1, then Px10% = Control Output. For example, if the
speed of a motor is dragged down 10% due to a load increase, a corrective speed signal increase
of 10% is generated. In a perfect world, this increase in speed command should bring the motor
speed back to normal.
i t (i)
ntegral iMe
The controller output is proportional to the integral of the controller input. To eliminate the
steady-state error, an "integral part" needs to be added to the controller. The Integral Time (I)
decides the relation between integral part and error. The integral part will be increased by time
even if the error is small. It gradually increases the controller output to eliminate the error until
it is 0. In this way a system can be stable without the steady-state error caused by using only
proportional gain control.
Begin tuning with a higher number for Integral Time (100.0 is max; 1.0 is default), and slowly move
to a smaller number until you reach the setpoint with minimized overshoot/undershoot. Tuning
is normally done utilizing an oscilloscope, and a step change in set point say 20% steps up and
then down, monitoring the needed set point, and changing the Integral value carefully until you
maintain your set point.
• Overshoot: The Process Variable moves further past the Setpoint than desired
• Undershoot: The Process Variable does not reach the desired Setpoint
Page F–6
ontrol
Setpoint
+
-
feedback signal
K : Proportional gain (P) T : Integral time (l) T
p i
(P)
ain
DuRA
pulse
Drive execute PID control
1
K (1 + + T × S)
p d
T × S
i
sensor
: Derivative control (D) S: Operator
d
GS4 AC Drive User Manual – 1st Ed, Rev A - 10/20/2017
output value
IM