Externally Requested And Current-Dependent U D Reduction - Siemens Simovert 6SE70 Series Operating Instructions Manual

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09.02
4.3.10.2

Externally requested and current-dependent U d reduction

Up to and including Unit Software Release 3.1, U d reduction was implemented only upon external request by
means of the control word 1 command "U d reduction demanded" (STW1, Bit 11= 1):
When an edge is detected on this command (source selection by P571), the U d setpoint is lowered to the value
(1.35 * U * P318/100.00%) according to P318 (with or without deceleration ramp according to P330,
mains,infeed
depending on whether P330 has an odd or even value) and regenerative feedback is disabled (the message
"Recovery not ready" is displayed, status word ZSW1, Bit 10= 0). The DC link should now discharge (free
discharge or current withdrawal from the DC link). When the DC link voltage has been reduced, the message
"U d is reduced" is issued via ZSW1, Bit 13= 1. Energy recovery is re-released again, the message ZSW1, Bit
10= 1 is issued. When the message "U d is reduced" has been issued, an inverter connected to the DC link may
start returning energy into the DC link.
An external logical linking is required for the energy recovery!
As from Unit Software Release 3.2, the U d can also be reduced automatically, as an alternative, depending on
the DC link current I d :
When the current-dependent U d reduction is released by P323 = 1, the command for the reduction is generated
internally by U d . The U d setpoint is automatically reduced to the value in accordance with P318 when I d
(averaged over 3 current crests) falls below the threshold P321 . If I d exceeds the sum of threshold P321 and
hysteresis P322 , the "full" U d setpoint value (1.35 * U
means of STW1, bit 11, precharge time P329 or discharge time P330 are always active (setpoint input with
ramp) when the U d setpoint is specified internally.
Attention: Undisturbed recovery mode is only possible if, after falling below P321, the load current withdrawn
(by the inverters connected to the DC link) still remains positive for a sufficient length of time before
changing direction to permit a reduction of the DC link voltage to the specified value before recovery
is started. The current-dependent U d reduction functions therefore only if an appropriate load cycle
exists !
Siemens AG 6SE7087-6AK85-1AA0
Rectifier/Regenerating Unit Operating Instructions
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) is selected again. In contrast to U d lowering by
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