Kruger Ecowatt K320 Series Operation Manual page 122

Ecowatt Drive K320 series Basic operation guidelines
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feedback signal and reference. If the static difference occurs in the direction of reference
change (such as reference increase, where the feedback is always less than the reference after
system stabilizes), continue increasing the proportional gain; otherwise, decrease the
proportional gain. Repeat this process until the static difference becomes small.
Integral time (Ti): When feedback deviates from reference, the output regulating variable
accumulates continuously, if the deviation persists, the regulating variable will increase
continuously until deviation disappears. Integral regulator can be used to eliminate static
difference; however, too large regulation may lead to repetitive overshoot, which will cause
system instability and oscillation. The feature of oscillation caused by strong integral effect is
that the feedback signal fluctuates up and down based on the reference variable, and
fluctuation range increases gradually until oscillation occurred. Integral time parameter is
generally regulated gradually from large to small until the stabilized system speed fulfills the
requirement.
Derivative time (Td): When the deviation between feedback and reference changes, output the
regulating variable which is proportional to the deviation variation rate, and this regulating
variable is only related to the direction and magnitude of the deviation variation rather than
the direction and magnitude of the deviation itself. Differential control is used to control the
feedback signal variation based on the variation trend. Differential regulator should be used
with caution as it may easily enlarge the system interferences, especially those with high
variation 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 settings
a. 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 whole commissioning process of proportional gain P.
b. Determine integral time Ti
After proportional gain P is determined, set the initial value of a larger integral time Ti, and
decrease Ti gradually until system oscillation occurred, and then in turn, increase Ti until
system oscillation disappears, record the Ti at this point, and set the integral time constant Ti
of PID to 150%–180% of current value. This is the commissioning process of integral time
constant Ti.
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