Rockwell Automation 20B PowerFlex 700 AC Drives Vector Control (v4.001 and up) - Manual (Page 12)

12 Rockwell Automation Publication 20B-UM002G-EN-P - July 2014
Preface
ATTENTION: The “adjust freq” portion of the bus regulator function is
extremely useful for preventing nuisance overvoltage faults resulting from
aggressive decelerations, overhauling loads, and eccentric loads. It forces the
output frequency to be greater than commanded frequency while the drive's
bus voltage is increasing towards levels that would otherwise cause a fault.
However, it can also cause either of the following two conditions to occur.
• Fast positive changes in input voltage (more than a 10% increase within 6
minutes) can cause uncommanded positive speed changes. However an
“OverSpeed Limit” fault (F25) will occur if the speed reaches [Maximum Speed]
+ [Overspeed Limit], (parameters 82 and 83). If this condition is unacceptable,
action should be taken to 1) limit supply voltages within the specification of
the drive and, 2) limit fast positive input voltage changes to less than 10%.
Without taking such actions, if this operation is unacceptable, the “adjust freq”
portion of the bus regulator function must be disabled (see parameters 161
and 162).
• Actual deceleration times can be longer than commanded deceleration times.
However, a “Decel Inhibit” fault (F24) is generated if the drive stops
decelerating altogether. If this condition is unacceptable, the “adjust freq”
portion of the bus regulator must be disabled (see parameters 161 and 162). In
addition, installing a properly sized dynamic brake resistor will provide equal or
better performance in most cases.
These faults are not instantaneous. Test results have shown that they can take
between 2…12 seconds to occur.