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I (Integral) action
An operation in which the change rate of the MV (manipulated value: output frequency) is proportional to the integral value
of deviation is called I action, which outputs the MV that integrates the deviation. Therefore, I action is effective in bringing
the feedback amount close to the commanded value. For the system whose deviation rapidly changes, however, this action
cannot make it react quickly.
The effectiveness of I action is expressed by integral time as parameter, that is J04 data. The longer the integral time, the
slower the response. The reaction to the external disturbance also becomes slow. The shorter the integral time, the faster the
response. Setting too short integral time, however, makes the inverter output tend to oscillate against the external
disturbance.
D differential time (J05)
Data setting range: 0.00 to 600.00 (s), 0.00 means that the differential component is ineffective.
J05 specifies the differential time for the PID processor.
D (Differential) action
An operation in which the MV (manipulated value: output frequency) is proportional to the differential value of the
deviation is called D action, which outputs the MV that differentiates the deviation. D action makes the inverter quickly
react to a rapid change of deviation.
The effectiveness of D action is expressed by differential time as parameter, that is J05 data. Setting a long differential time
will quickly suppress oscillation caused by P action when a deviation occurs. Too long differential time makes the inverter
output oscillation more. Setting short differential time will weakens the suppression effect when the deviation occurs.
The combined uses of P, I, and D actions are described below.
(1) PI control
PI control, which is a combination of P and I actions, is generally used to minimize the remaining deviation caused by P
action. PI control always acts to minimize the deviation even if a commanded value changes or external disturbance steadily
occurs. However, the longer the integral time, the slower the system response to quick-changed control.
P action can be used alone for loads with very large part of integral components.
(2) PD control
In PD control, the moment that a deviation occurs, the control rapidly generates greater MV (manipulated value) than that
generated by D action alone, to suppress the deviation increase. When the deviation becomes small, the behavior of P action
becomes small.
A load including the integral component in the controlled system may oscillate due to the action of the integral component if
P action alone is applied. In such a case, use PD control to reduce the oscillation caused by P action, for keeping the system
stable. That is, PD control is applied to a system that does not contain any damping actions in its process.
Summary of Contents for FRENIC-MEGA
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