Dc Link Buffering - Siemens SIMODRIVE 611 Planning Manual

05.01
9.12.3

DC link buffering

The energy, available in the DC link of the drive units is calculated as follows at
power failure:
E = 1/2 * C * (V
In this case,
Example:
For
is obtained as follows:
E = 1/2 * 4800mF *((550V)
This energy, under load conditions is available for a time of
t
min
in order to initiate emergency retraction.
In this case,
For the example above, with:
is obtained as follows:
t
min
as minimum achievable buffer duration for emergency retraction.
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SIMODRIVE 611 Planning Guide (PJU) – 05.01 Edition
2 2
– V )
DC link min
E= energy in Watt seconds [Ws]
C= total capacitance of the DC link in Farad [F]
V = DC link voltage (response limit, line supply failure)
DC link
V = lower limit for safe reliable operation
min
(taking into account the motor–specific EMF, in any case,
above the switch–off threshold of e.g.350V)
C= 6000µF (refer to Table 9-3, 1. line) – 20% = 4800 µF
V = 550V
DC link
V = 350V
min
2
– (350V)
* h
= E / P
max
t = buffer time in milliseconds [ms]
min
P = power in Kilowatt [kW]
max
h = efficiency of the drive unit
E = 432Ws
P = 16kW (refer to Table 9-3, 1. line)
max
h = 0.90
= 432Ws / 16kW * 0.9 = 24.3ms
9 Important Circuit Information
9.12 Operation at power failure
2
) = 432Ws
9
9-299