Siemens MICROMASTER 420 - Manual (Page 131)

Issue 07/04 3 Functions
MICROMASTER 420 Operating Instructions
6SE6400-5AA00-0BP0 131
3.17 Closed-loop Vdc control
3.17.1 Vdc_max controller
Parameter range: P1240, r0056 bit 14
r1242, P1243
P1250 – P1254
Warnings A0502, A0910
Faults F0002
Function chart number:
FP4600
DC link undervoltage
Cause:
Line supply voltage failure or dip (blackout or brownout)
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 3.18) and
is known as kinetic buffering.
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 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. 3-55). If the DC link threshold r1242 is again fallen below, then the Vdc_max
controller withdraws the extension of the braking ramp.
t
t
 f 
1
-controller active V
DC_max
t
V
DC
r1242
0
r0056 Bit 14
f
f
act
set
A0911
Fig. 3-55 Vdc_max controller