Danfoss VLT AutomationDrive FC 360 Design Manual

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2.5.3 Process Control Relevant ParametersParameter Description of function7-20 Process CL Feedback 1 Resource Select from which source (i.e. analog or pulse input) the process PID should get itsfeedback7-22 Process CL Feedback 2 Resource Optional: Determine if (and from where) the process PID should get an additionalfeedback signal. If an additional feedback source is selected, the 2 feedback signals areadded together before being used in the process PID control.7-30 Process PID Normal/ Inverse Control Under [0] Normal operation, the process control responds with an increase of the motorspeed if the feedback is lower than the reference. Under [1] Inverse operation, the processcontrol responds with a decreasing motor speed instead.7-31 Process PID Anti Windup The anti-windup function ensures that when either a frequency limit or a torque limit isreached, the integrator is set to a gain that corresponds to the actual frequency. Thisavoids integrating on an error that cannot be compensated for by a speed change. Thisfunction can be disabled by selecting [0] Off.7-32 Process PID Start Speed In some applications, reaching the required speed/set point can take a long time. In suchapplications, it may be an advantage to set a fixed motor speed from the frequencyconverter before the process control is activated. This is done by setting a process PIDstart value (speed) in 7-32 Process PID Start Speed.7-33 Process PID Proportional Gain The higher the value, the quicker the control. However, too large a value may lead tooscillations.7-34 Process PID Integral Time Eliminates steady state speed error. A lower value means a quicker reaction. However, toosmall a value may lead to oscillations.7-35 Process PID Differentiation Time Provides a gain proportional to the rate of change of the feedback. A setting of 0 disablesthe differentiator.7-36 Process PID Diff. Gain Limit If there are quick changes in reference or feedback in a given application (which meansthat the error changes swiftly), the differentiator may soon become too dominant. This isbecause it reacts to changes in the error. The quicker the error changes, the stronger thedifferentiator gain is. The differentiator gain can thus be limited to allow setting of thereasonable differentiation time for slow changes.7-38 Process PID Feed Forward Factor In applications where there is a good (and approximately linear) correlation between theprocess reference and the motor speed necessary for obtaining that reference, the feedforward factor can be used to achieve better dynamic performance of the process PIDcontrol.• 5-54 Pulse Filter Time Constant #29 (Pulseterm. 29)• 5-59 Pulse Filter Time Constant #33 (Pulseterm. 33)• 6-16 Terminal 53 Filter Time Constant(Analog term 53)• 6-26 Terminal 54 Filter Time Constant(Analog term. 54)If there are oscillations of the current/voltage feedback signal, these can be dampened bya low-pass filter. The pulse filter time constant represents the speed limit of the ripplesoccurring on the feedback signal.Example: If the low-pass filter has been set to 0.1 s, the limit speed is 10 RAD/s (thereciprocal of 0.1 s), corresponding to (10/(2 x π))=1.6 Hz. This means that allcurrents/ voltages that vary by more than 1.6 oscillations per second are damped by thefilter. The control is only carried out on a feedback signal that varies by a frequency(speed) of less than 1.6 Hz.The low-pass filter improves steady state performance, but selecting a too long filter timedeteriorates the dynamic performance of the process PID control.Table 2.8 Process Control ParametersProduct Overview Design GuideMG06B402 Danfoss A/S © 09/2014 All rights reserved. 332 2