INVT Goodrive300-01A Series, Руководство по эксплуатации

Страница: 89 / 175

Goodrive300-01A series VFD for air compressor Function code description
-84-
in oscillation. To solve this problem, first, set the integral time to a large value and the derivative time
to 0, and run the system by proportional control, and then change the reference to observe the
deviation between feedback signal and the reference (static difference), if the static difference is (e.g.,
increase the reference, and the feedback variable is always less than the reference after system
stabilizes), continue increasing the proportional gain, otherwise, decrease the proportional gain;
repeat such process until the static error 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.
5.3.1 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.
c. Determining derivative time Td
The derivative time Td is generally set to 0.
If you need to set Td to another value, set in the same way with P and Ti, namely set Td to 30% of the
value when there is no oscillation.