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Engineering Guide CDA3000
3 Selection of inverter module
Figure 3.38 Project planning notes for DC network operation
Subject Project planning notes
Design of the
external braking
resistors
If the energy balance in DC network operation is regenerative in individ-
ual operating situations, the inverter modules must be operated with
external braking resistors to absorb the regenerative energy.
The following conditions must be met when designing the braking
resistors:
1. The ohmic value of the external braking resistor must not be less
than the minimum ohmic connected load permitted by the inverter
module.
2. Adding together the peak braking powers of all braking resistors
operated in the DC network produces the peak braking power
referred to the DC network.
P
SDC
= P
SW1
+ P
SW2
+ ....P
SWn
P
SDC
= total peak braking power in the DC network
P
SW1
= peak braking power of braking resistor 1
3. The continuous braking power of the individual braking resistor is
ascertained by calculation of the effective braking power.
P
SW
= peak braking power of the selected braking resistor
t1, 2xn = braking time 1, 2 m ... n
The permissible continuous braking power of the
selected braking resistor must be > P
eff
. The sampling
time (T) must be <150 s.
P
eff
P
SW
2
t
1
P
SW
2
t
2
…P
SW
t
n
⋅+⋅+⋅
T
-----------------------------------------------------------------------------=
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