Goodrive300-21 integrated machine for air compressor
Function description
-
64
-
Introduction to the working principles and control methods for PID control:
Proportional control (Kp):
When the feedback is different from the reference, the output will be 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 is different from reference, the output regulating variable accumulates continuously, if
the difference persists, the regulating variable will increase continuously until difference disappears.
The 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 occurs. The
integral time parameter is generally regulated gradually from large to small until the stabilized system
speed fulfills the requirement.
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.
5.3.1 General procedures for PID parameter setup
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 the entire
commissioning procedure of proportional gain P.
