Selec VFD Series

47
User Manual
Please refer to the following brief introduction of operating principles and regulation methods:
Integral time (I) determines the speed of integral regulation on the difference between PI feedback
quantity and given quantity. The less integral time is, the higher the intensity of adjustment will be.
Proportional gain (P) determines the intensity of adjustment of PI regulator; the larger P-value is, the
higher the intensity of adjustment will be.
PI is the most common control method for process control; the function of each part is different from the
other.
Proportional gain (P) : There will be a proportional adjustment between output and deviation if there is a
difference between feedback value and set value; if the deviation is constant, regulating variable is also
constant. Proportional control responses to the change of feedback quickly; however, error control can't
be proceeded only by proportional control.
Integral time (I) : when there is difference between feedback value and set value, regulating variable of
output should be accumulated continuously; if the deviation can't be eliminated, the regulating variable
should be increased continuously until there is no deviation. Deviation can be eliminated effectively by
integral controller. However, overshoot may be caused repeatedly if the adjustment of integral controller
is too much, which makes system unstable and even causes vibration. If vibration is caused by excessive
integral action, following characteristics can be observed oscillation of feedback signal on given quantity,
expanding amplitude of oscillation, even vibration. The parameter of integral time should be adjusted
generally from maximum value to minimum value so that the integral time can be changed gradually.
Observation should be made on the effect on the system. Adjustment can't be stopped until the sable
speed of system meets the requirements
The greater the proportional gain is, the smaller the adjusting speed of the system will be. But the
proportional gain is excessive, it may cause vibration. The adjustment method is to extend the integral
time and make the system running only by proportional control; meanwhile, the set value should be
changed to observe its stable deviation (static error) between the feedback signal and given quantity; if
the static error is incompatible with the change of given quantity, proportional gain can be increased
continuously, for example increasing given quantity, or feedback quantity is always less than given
quantity after system is stable; otherwise, please reduce it. The instruction above should be implemented
repeatedly until deviation is optimized/ minimized.
P7-06
Deviation limit
0.0 to 20.0
Default: 2.0
Deviation limit of PI control defines the comparison between PI system output and maximum
deviation value which is limited by closed-loop set value. As is shown in the graph, PI regulator is
shut down while it's within deviation limit. The precision and stability of PI system can be improved by
setting this function code properly.