INVT Goodrive350 Series Operation Manual page 120

Goodrive350 IP55 High-ingress Protection Series VFD
Differential time (Td):
When the difference between feedback and reference changes, there is output of the
regulating variable that is proportional to the difference variation rate, and this regulating
variable is only related to the direction and magnitude of the difference change rather than the
direction and magnitude of the difference itself. Differential control is used to control the
feedback signal variation based on the change trend. Exercise caution before using the
differential regulator since it may enlarge the system interferences, especially those with high
change frequency.
When the frequency command selection (P00.06, P00.07) is 7 or the voltage setting channel
selection (P04.27) is 6, the VFD is process PID controlled.
5.5.15.1 General procedures for PID parameter setup
Step 1 Determining proportional gain P
When determining proportional gain P, first, remove the integral term and derivative term
of PID by making Ti=0 and Td=0 (see PID parameter setup for details), thus turning PID
into pure proportional control. Set the input to 60%–70% of the max. allowable value,
and increase proportional gain P gradually from 0 until system oscillation occurred, and
then in turn, decrease proportional gain P gradually from current value until system
oscillation disappears, record the proportional gain P at this point and set the
proportional gain P of PID to 60%–70% of current value. This is the entire commissioning
procedure of proportional gain P.
Step 2 Determine integral time Ti
After proportional gain P is determined, set the initial value of integral time Ti to a large
value, and decrease Ti gradually until system oscillation occurs. Then in reverse,
increase Ti until system oscillation disappears. Record the value of Ti at this point. Set
the integral time constant Ti of PID to 150%–180% of this value. This is the
commissioning procedure of integral time constant Ti.
Step 3 Determining derivative time Td
The differential time Td is generally set to 0.
If you need to set Td to another value, the setting method is similar to that for P and Ti,
namely, set Td to 30% of the value when there is no oscillation.
Step 4 Empty system load, perform load-carrying joint debugging, and then fine-tune PID
parameter until fulfilling the requirement.
5.5.15.2 How to fine-tune PID
After setting the parameters controlled by PID, you can adjust these parameters by the
following means.
Control overshoot: When overshoot occurred, shorten the derivative time (Td) and prolong
integral time (Ti).
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Basic operation guidelines