INVT Goodrive350 Series Operation Manual page 119

Goodrive350 IP55 High-ingress Protection Series VFD
forming a negative feedback system to keep the controlled variables above the target. It is
applicable to flow control, pressure control, temperature control, and so on. The following is
the basic schematic block diagram for output frequency regulation.
PID digital setting
(PID reference source)
Keypad 0
P09.01
AI1 1
AI2
2
AI3 3
HDIA 4
Multi-step speed
5
6
Modbus/Modbus TCP
PROFIBUS/CANopen/DeviceNet
7
Ethernet 8
HDIB
9
EtherCAT/PROFINET/EtherNet IP 10
Programmable card 11
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.
P09.00
PID reference value
P17.23
+
Reference-
feedback<P09.08？
-
P09.08 (Limit of PID control deviation)
P09.02
(PID feedback source)
P17.24
PID feedback
value
Terminal function 25
PID control pause
Y
Valid
Keep current frequency
N Invalid
Kp P09.04 (proportional gain)
AI1
0
Ti P09.05 (integral time)
Td P09.06 (differential time)
AI2
1
2 AI3
HDIA
3
4 Modbus/Modbus TCP
PROFIBUS/CANopen/DeviceNet
5
Ethernet
6
7 HDIB
EtherCAT/PROFINET/EtherNet IP
8
9 Programmable card
-101-
Basic operation guidelines
PID stops
adjustment
P09.09
（upper limit value of PID
output）
0
1
P09.03
(PID output characteristics)
P09.10
(lower limit value of PID
output)
Set frequency
P17.00
PID output