6
05.01
6.7 DC link options
6-184
© Siemens AG 2008 All Rights Reserved
SIMODRIVE 611 Configuration Manual (PJU) – 05/2008 Edition
The following applies for the storage capacity of the capacitor battery
when the power fails:
Formula: w = ½ S C S (V
2
DC
link
n
– V
2
DC
link
min
)
Assumptions for the example:
Capacitance of the capacitor battery C = 20 mF
Rated DC link voltage V
DClinkn
= 600 V
Minimum DC link voltage V
DClinkmin
= 350 V
––> w = ½ S 20 S 10
–3
F S ((600 V)
2
– (350 V)
2
) = 2375 Ws
For this voltage range, a 20 mF capacitor module can supply energy for
2375 Ws.
Notice
V
DClinkmin
must be 350 V.
For voltages below 350 V, the switched–mode power supply for the electronics
shuts down.
The possible buffer time t
Ü
is calculated as follows with the output DC link
power P
DC
link
:
t
Ü
= w / P
DC
link
Dynamic energy
The DC link capacitors should be considered as being a battery. The capaci-
tance and, thus, the storage capacity are increased as a result of the capacitor
module.
In order to evaluate the required capacitance for a specific requirement in a cer-
tain application, the energy flow must be determined.
The energy flow depends on the following:
S All moved masses and moments of inertia
S Velocity, speed (and their change, acceleration, deceleration)
S Efficiencies: Mechanical system, gear units, motors, inverters (driving/braking)
S Back–up duration, buffering
S DC link voltage and the permissible change, output value, upper/lower limit
value.
In practice, often there is no precise data about the mechanical system. If the
mechanical system data is determined using rough calculations or estimated
values, then the capacitance of the DC link capacitors required can only be de-
termined during tests performed during the commissioning phase.
6 Infeed Modules 11.0502.07
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