Siemens SINAMICS S120 Function Manual page 500

Function modules
7.9 Master/slave function for Active Infeed
Function diagrams
The function of the "Master/slave infeeds" function module is shown in function diagrams
8940 and 8948 (see SINAMICS S120/S150 List Manual).
Explanations for the function diagrams
● Current setpoint interconnection
● Selection of the current setpoint
● Selection of the current distribution factor
● V
498
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
parameter p3513 = 0) and slave (current control, parameter p3513 = 1) from the higher-
level control system.
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.
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 fails or is activated.
The current distribution factor is calculated from the number of active infeeds and their
rated data. The sum of the current distribution factors of all active infeeds 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.
control band
dc
The V limits can be violated in master/slave operation if the DC-link load changes
dc
abruptly (e.g. load surges or emergency stop). For this reason, the DC-link voltage is
monitored on the basis of a V
voltage range with hysteresis - set in parameter p3574.0/1 (upper/lower limit V
band) and p3574.2/3 (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 control operates permanently in "standby mode" so that it can be re-
dc
activated when necessary.
control band. The V
dc dc
Function Manual, (FH1), 01/2013, 6SL3097-4AB00-0BP3
dc
control band defines a specific
control,
voltage
dc
Drive functions