Watson-Marlow MM440 - Manual (Page 215)

Issue 10/06 3 Functions
MICROMASTER 440 Operating Instructions
6SE6400-5AW00-0BP0 215
3.18 Closed-loop Vdc control
In addition to DC, compound and dynamic braking, for MICROMASTER it is
possible to prevent a DC link overvoltage condition using the closed-loop Vdc
controller. With this technique, the output frequency is automatically modified
during operation using the closed-loop Vdc controller so that the motor doesn't go
too far into the regenerative mode.
DC link overvoltage
¾ Cause:
The drive regenerates and feeds too much energy back into the DC link.
¾ Remedy:
The DC link voltage is further reduced using the Vdc_max controller (refer to
Section 3.18.1) by reducing the regenerative torque down to zero.
Using the Vdc controller, it is also possible to prevent the drive converter being
shut down (tripped) during brief line supply dips – which cause a DC link
undervoltage condition. Also in this case, the output frequency is automatically
modified by the Vdc controller during operation. Contrary to an overvoltage
condition, in this case the motor is operated with increased regenerative operation
in order to support and buffer the DC link voltage.
DC link undervoltage
¾ Cause:
Line supply voltage failure or dip (blackout or brownout)
¾ Remedy:
A regenerative torque is entered for the operational drive which compensates
the existing losses and therefore stabilizes the voltage in the DC link. This
technique is carried-out using the Vdc_min controller (refer to Section ) and is
known as kinetic buffering.
3.18.1 Vdc_max controller
Parameter range: P1240, r0056 bit 14
r1242, P1243
P1250 – P1254
Warnings A0502, A0910
Faults F0002
Function chart number:
FP4600
A brief regenerative load can be handled using this function (enabled using P1240)
without the drive inverter being shut down (tripped) with fault message F0002 ("DC
link overvoltage"). In this case, the frequency is controlled (closed-loop) so that the
motor doesn't go too far into regenerative operation.
If the drive inverter regenerates too much when braking the machine due to a fast
ramp-down time P1121, then the braking ramp / ramp time are automatically
extended and the drive inverter is operated at the DC link voltage limit r1242 (refer
to Fig. 3-83). If the DC link threshold r1242 is again fallen below, then the Vdc_max
controller withdraws the extension of the braking ramp.