INVT Goodrive350 Series Operation Manual page 119

Goodrive350 series high-performance multifunction VFD
difference between feedback signal of controlled variables and signal of the target, thus forming a
negative feedback system to keep the controlled variables above the target. It is suitable for flow
control, pressure control, temperature control, etc. Diagram of basic principles for output frequency
regulation is shown in the figure below.
Pre-set PID reference of
keypad
P09.01
Keypad
(PID reference source)
AI1
0
AI2
1
AI3
2
3
HDIA
4
Multi-step
speed
5
6
MODBUS
7
PROFIBUS\CANopen
8
Ethernet
9
HDIB
EtherCat/Profinet 10
11
PLC card
Introduction to the working principles and control methods for PID control
Proportional control (Kp): When the feedback deviates from the reference, the output will be
proportional to the deviation, if such deviation is constant, the regulating variable will also be constant.
Proportional control can respond to feedback changes rapidly, however, it cannot eliminate the error
by itself. The larger the proportional gain, the faster the regulating speed, but too large gain will result
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 (eg,
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
P09.00
PID reference
value
P17.23
+
Reference-
feedback<P09.08？
-
P09.08 (Limit of PID control
P09.02
(PID feedback source)
P17.24
PID feedback
value
Terminal function 25
PID control pause
Y
Valid
Keep current frequency
N Invalid
deviation)
Kp P09.04 (proportional gain)
AI1
Ti P09.05 (integral time)
0
AI2
Td P09.06 (differential time)
1
AI3
2
3
HDIA
4
MODBUS
5
6
PROFIBUS\CANopen
7
Ethernet
8
HDIB
EtherCat/Profinet
9
PLC card
10
-110-
Basic operation instructions
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