Danfoss VLT FC 102 Series Design Manual page 47

Introduction to VLT® HVAC D...
2.8.12 Tuning the Adjustable Frequency
Drive Closed-loop Controller
Once the adjustable frequency drive's closed-loop
controller has been set up, the performance of the
controller should be tested. In many cases, its performance
may be acceptable using the default values of 20-93 PID
Proportional Gain and 20-94 PID Integral Time. However, in
some cases it may be helpful to optimize these parameter
values to provide faster system response while still
controlling speed overshoot.
2.8.13 Manual PID Adjustment
1. Start the motor.
2. Set 20-93 PID Proportional Gain to 0.3 and
increase it until the feedback signal begins to
oscillate. If necessary, start and stop the
adjustable frequency drive or make step changes
in the setpoint reference to attempt to cause
oscillation. Next reduce the PID proportional gain
until the feedback signal stabilizes. Then reduce
the proportional gain by 40–60%.
3. Set 20-94 PID Integral Time to 20 s and reduce it
until the feedback signal begins to oscillate. If
necessary, start and stop the adjustable frequency
drive or make step changes in the setpoint
reference to attempt to cause oscillation. Next,
increase the PID integral time until the feedback
signal stabilizes. Then increase of the integral
time by 15–50%.
4. 20-95 PID Differentiation Time should only be used
for very fast-acting systems. The typical value is
25% of 20-94 PID Integral Time. The differential
function should only be used when the setting of
the proportional gain and the integral time has
been fully optimized. Make sure that oscillations
of the feedback signal are sufficiently dampened
by the low-pass filter for the feedback signal
(parameters 6-16, 6-26, 5-54 or 5-59 as required).
MG11BC22
Design Guide
Danfoss A/S © Rev. 06/2014 All rights reserved.
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