6-92
Suppressing Short Cycle Vibration
If short cycle vibration occurs reduce the proportional gain (P), or increase the PI delay time constant.
îš„ Setting Precautions
• Parameter b5-04 is used to prevent the calculated integral value from exceeding a specified amount and so
from saturated control. Otherwise, when the load varies rapidly the Inverter response is delayed and the
machine might be damaged or the motor may stall. In this case, reduce the set value to speed up Inverter
response.
• Parameter b5-06 is used to prevent the output value of the PI control calculation from exceeding a speci-
fied amount.
• Parameter b5-07 is used to adjust the PI control offset. It is added to the PI output value. When differential
PI feedback is selected (H3-09=16) parameter b5-07 becomes the PI Setpoint it is added to the difference
between both feedback values.
• Set the filter time constant for the PI control output in b5-08 to prevent machinery resonance when
machinery friction is great or rigidity is poor. In this case, set the constant to a higher value than the reso-
nance frequency oscillation period. Increase this time constant to reduce Inverter responsiveness.
• Parameter b5-09, the PI output polarity can be inverted. If now the PI target value increases the output fre-
quency will be lowered. This function is usable e.g. for vacuum pumps.
• Parameter b5-10 a gain can be applied to the PI control output. Enable this parameter to adjust the amount
of compensation if the PI control output is added to the set frequency reference (b5-01 = 3).
• Parameter b5-11 can be used to determine what happens to the inverter output when the PI control output
is negative: Setting 0 will limit the PI control output to 0 while setting 1 will allow negative output values.
When b1-04 (Prohibition of Reverse Operation) is set to 1 or 3 (revers is disabled), however, the PI output
is limited to 0.
• Parameter b5-17 sets an accel./decel. ramp that raises/lowers the PI setpoint gradually (PI soft starter).
The normally used accel./decel. function (C1- parameters) is allocated after PI control so that, depend-
ing on the settings, resonance with the PI control and hunting in the machinery may occur. Using b5-17
this behaviour can be prevented.
The PI soft starter function can also be disabled or enabled using a digital input (H1- = 34).
Response
Before adjustment
After adjustment
Time
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