Functions
8.15 Brake functions
Control Units CU240S
Operating Instructions, 11/2006, A5E00766042B AA
8-89
The chopper switch-in threshold V
DC chopper
is calculated as a function of parameter P1254
(Auto detect V
DC
switch-on levels), either directly using the line supply voltage P0210 or
indirectly using the DC link voltage and r1242.
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Figure 8-61 Mode of operation of the dynamic braking
The regenerative (braking) energy is converted into thermal energy using the chopper
resistor. A braking module (chopper control) is integrated in the DC link for this purpose. The
chopper of the braking module switches the resistor with a mark-space ratio corresponding
to the regenerative power to be dissipated. The braking module is only active if, as a result of
the regenerative operation, the DC link voltage lies above the chopper switch-in threshold
V
DC chopper
. This means that the braking module is not active in normal operation when
motoring.
The chopper resistor is only designed for a specific power and a certain load duty cycle and
can only absorb a limited amount of braking energy within a specific time period. The
chopper resistors, specified in SINAMICS G120 Catalog, have the following load duty cycle
as shown in the figure below.
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Figure 8-62 Load duty cycle - chopper resistors
This load duty cycle is saved in the SINAMICS G120 inverter for P1237 = 1 (→ 5 %). If the
values are exceeded due to the load required, then when the maximum acceptable braking
energy is reached, the load duty cycle monitoring controls the chopper so that the value is
reduced to the value entered in parameter P1237. This means that the energy to be
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