Goodrive350A series high-performance multifunction VFD
Basic operation guidelines
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proportional to the difference. If such a difference is constant, the regulating variable will also be
constant. Proportional control can respond to feedback changes rapidly, however, it cannot eliminate
the difference by itself. A larger proportional gain indicates a faster regulating speed, but a too large
gain will result in oscillation. To solve this problem, set the integral time to a large value and the
differential time to 0, run the system only with proportional control, and then change the reference to
observe the difference (that is, static difference) between the 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
