Rockwell Automation 20B PowerFlex 70, PowerFlex 700 Reference Manual - Manual (Page 56)

Bus Regulation
56 Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
Bus Regulation
[Bus Reg Gain]
[Bus Reg Mode A, B]
Some applications, such as the hide tanning shown here, create an intermittent
regeneration condition. When the hides are being lifted (on the left), motoring
current exists. However, when the hides reach the top and fall onto a paddle, the
motor regenerates power back to the drive, creating the potential for a nuisance
overvoltage trip.
When an AC motor regenerates energy from the load, the drive DC bus voltage
increases unless there is another means (dynamic braking chopper/resistor, etc.)
of dissipating the energy.
Without bus regulation, if the bus voltage exceeds the operating limit established
by the power components of the drive, the drive will fault, shutting off the output
devices to protect itself from excess voltage.
With bus regulation enabled, the drive can respond to the increasing voltage by
advancing the output frequency until the regeneration is counteracted. This
keeps the bus voltage at a regulated level below the trip point.
Since the same integrator is used for bus regulation as for normal frequency ramp
operation, a smooth transition between normal frequency ramp operation and
bus regulation is accomplished.
The regulator senses a rapid rise in the bus voltage and activates prior to actually
reaching the internal bus voltage regulation set point Vreg. This is important
since it minimizes overshoot in the bus voltage when bus regulation begins
thereby attempting to avoid an over-voltage fault.
Motoring Regenerating
0V Fault @V
bus
Max
Drive Output Shut Off
Ch1
Ch3
Single Seq 500 S/s
100mV
500mV
Ch2 100mV M 1.00s Ch3 1.47 V
3
2
1