Bus Regulation 2-49
Bus voltage regulation is the highest priority of the three components of this
controller because minimal drive current will result when limiting the bus
voltage and therefore, current limit will not occur.
PowerFlex 70/700
The user selects the bus voltage regulator using the Bus Reg Mode
parameters. The available modes include:
• off
• frequency regulation
• dynamic braking
• frequency regulation as the primary regulation means with dynamic
braking as a secondary means
• dynamic braking as the primary regulation means with frequency
regulation as a secondary means
The bus voltage regulation setpoint is determined off of bus memory (a
means to average DC bus over a period of time). The following graph and
tables describe the operation.
!
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.
1. 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 will occur if the speed reaches
[Max Speed] + [Overspeed Limit]. 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).
2. Actual deceleration times can be longer than commanded
deceleration times; however, a “Decel Inhibit” fault 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.
Note: These faults are not instantaneous and have shown test
results that take between 2 and 12 seconds to occur.
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