Operation At Power Failure - Siemens SIMODRIVE 611 Planning Manual

05.01
9.12

Operation at power failure

9.12.1 Application and mode of operation
The "operation at power failure" function (power failure buffering) is used, e.g.
for machines where personnel can be in danger or significant material damage
could occur at power failure or for internal control fault messages as a result of
collision hazard during machining. Furthermore, the function is used for machi-
nes performing complex machining operations, e.g. when machining gear
wheels (hobbing, roller grinding) with expensive tools and workpieces which
should, as far as possible, be protected against damage when line supply faults
occur.
For operation at power failure, shutdown and/or retracting drive movements, the
energy, saved in the power DC link capacitors and kinetic energy of the moved
masses when the drives regenerate can be used. In this case, a connection
must be established from the P600/M600 power DC link to the auxiliary power
supply via the P500/M500 terminals in the NE module or monitoring module,
refer to Fig. 9-31.
Beyond this, additional circuit measures are required, for example, buffering the
+24V control voltage and a power failure and/or DC link monitoring to initiate the
appropriate control functions.
The machinery manufacturer must evaluate these risks and requirements using
a hazard analysis and apply appropriate measures to prevent such hazards or
damage from occurring.
The requirements placed on power failure concepts differ widely depending on
the particular user and machines and must therefore be individually configured.
9.12.2 Functions
The ability to quickly detect a line supply fault is an essential criterion when im-
plementing power failure concepts (power failure, line supply undervoltage or
phase failure).
When a line supply fault occurs, the DC link voltage quickly collapses due to the
energy drawn by the drives and the connected power supplies for the drive and
control components. The discharge characteristic depends on the ratio between
the stored DC link capacitance in the power circuit and the power drawn (load
duty cycle) of the drive at the instant that the line supply fault occurs.
For operation at power failure, regenerative feedback of one or several drives
into the DC link must become effective before the DC link voltage drops from
the rated voltage, e.g. 600 V DC to 350 V DC. At approx. 350 V, the impulses
are inhibited in the drive group and the drives coast down.
The 600 V DC link voltage is proportionally simulated at the control level and
can be evaluated in the 611 digital and 611 universal control modules via the
equipment bus. The DC link voltage can be monitored, with a fast response,
using parameterizable limit value stages so that indirectly the system can imme-
diately respond to a line supply voltage.
 Siemens AG 2001 All rights reserved
SIMODRIVE 611 Planning Guide (PJU) – 05.01 Edition
9 Important Circuit Information
9.12 Operation at power failure
9
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