Explanations For The Function Diagrams - Siemens SINAMICS S120 Function Manual

absolutely essential to use a higher-level controller (e.g. SIMATIC S7) for this system. Control
functions can also be implemented using DCCs in individual CUs.
9.9.4

Explanations for the function diagrams

The function of the "Master/Slave infeed units" function module is shown in function diagrams
8940 and 8948 (see SINAMICS S120/S150 List Manual). Individual function block diagrams
are explained in the following.
● Current setpoint interconnection
Parameter p3570 is used to connect the setpoint for the closed-loop current control (active
current setpoint from the master). Using parameter p3513, which can be changed in the
"ready for operation" state, it is possible to switch between master (V
p3513 = 0) and slave (current control, parameter p3513 = 1) from the higher-level controller.
● Selection of the current setpoint
The current setpoint can be selected by means of a control word (XCS) (p3572) using a
multiplexer with four inputs (X0 ... X3) (p3571.0 ... p3571.3). This means that the current
setpoint of the new master can be selected when the old master has failed.
● Selection of the current distribution factor
To prevent a reduction in control dynamics of the DC-link voltage controller for non-
symmetrical loads, this current distribution factor must be updated immediately when an
infeed unit fails or is activated.
The current distribution factor is calculated from the number of active infeed units and their
rated data. The sum of the current distribution factors of all active infeed units must always
equal 100%.
The current distribution factor can be selected by means of a control word (XCS) (p3577)
using a multiplexer with six inputs (X0 ... X5) (p3576.0...5).
Alternatively, a new current distribution factor can be calculated in the higher-level
controller, sent via cyclic PROFIBUS PZD telegrams and interconnected directly to the
connector input "Infeed: additional current distribution factor" (p3579).
A further alternative is to update the current distribution factor via an acyclic PROFIBUS
parameter write order of p3516. This produces dead times however.
For alternatives without multiplexer, this can be used for a different function.
● V
The V
(e.g. load surges or emergency stop). For this reason, the DC-link voltage is monitored on
the basis of a V
hysteresis - set in parameter p3574.0/1 (upper/lower limit V
(hysteresis upper/lower voltage limit). A signal is generated if the DC-link voltage leaves this
voltage range. By evaluating this signal, the slave is changed over from closed-loop current
to closed-loop voltage control. When the DC-link voltage returns to within the control band,
the slave is switched back to closed-loop current control. The V
permanently in "standby mode" so that it can be re-activated when necessary.
Drive functions
Function Manual, 06/2019, 6SL3097-5AB00-0BP2
control band
dc
limits can be violated in Master/Slave operation if the DC-link load changes abruptly
dc
control band. The V
dc
9.9 Master/slave function for Active Infeed
control band defines a specific voltage range with
dc
dc
Function modules
control, parameter
dc
voltage band) and p3574.2/3
control operates
dc
513