2.8.12 Tuning the Adjustable FrequencyDrive Closed-loop ControllerOnce the adjustable frequency drive's closed-loopcontroller has been set up, the performance of thecontroller should be tested. In many cases, its performancemay be acceptable using the default values of 20-93 PIDProportional Gain and 20-94 PID Integral Time. However, insome cases it may be helpful to optimize these parametervalues to provide faster system response while stillcontrolling speed overshoot.2.8.13 Manual PID Adjustment1. Start the motor.2. Set 20-93 PID Proportional Gain to 0.3 andincrease it until the feedback signal begins tooscillate. If necessary, start and stop theadjustable frequency drive or make step changesin the setpoint reference to attempt to causeoscillation. Next reduce the PID proportional gainuntil the feedback signal stabilizes. Then reducethe proportional gain by 40–60%.3. Set 20-94 PID Integral Time to 20 s and reduce ituntil the feedback signal begins to oscillate. Ifnecessary, start and stop the adjustable frequencydrive or make step changes in the setpointreference to attempt to cause oscillation. Next,increase the PID integral time until the feedbacksignal stabilizes. Then increase of the integraltime by 15–50%.4. 20-95 PID Differentiation Time should only be usedfor very fast-acting systems. The typical value is25% of 20-94 PID Integral Time. The differentialfunction should only be used when the setting ofthe proportional gain and the integral time hasbeen fully optimized. Make sure that oscillationsof the feedback signal are sufficiently dampenedby the low-pass filter for the feedback signal(parameters 6-16, 6-26, 5-54 or 5-59 as required).Introduction to VLT® HVAC D... Design GuideMG11BC22 Danfoss A/S © Rev. 06/2014 All rights reserved. 452 2
