Siemens SINAMICS S150 - Page 376

SINAMICS S120
Engineering Information
SINAMICS Engineering Manual – November 2015
Ó Siemens AG
376/528
Key to formula:
· R
BR-min
: Minimum braking resistance value in the cold state.
· R
BR-max
: Maximum braking resistance value at operating temperature, allowing
for production tolerances of typically about 10 %.
The resistance must not drop below the value R
BR-min
in order to ensure that the maximum braking current
I
max-Brake
= 1.5 • I
L-Brake
is not exceeded with the response threshold V
DC-Brake
selected in each case, and thus that the
risk of tripping on overcurrent is avoided. The minimum braking resistance value is specific to the individual unit and
application, and is calculated by the follow formula:
Brake
BrakeDC
Brake
BrakeDC
Brake
R
BR
I
V
I
V
I
V
statecoldR
BR
-
-
-
-
-
-
×
=
×
==×
maxmaxmax
min
40415.0
3
7.0
)(
.
The minimum resistance values R
BR-min
are stated in the table of unit-specific technical data. They refer in each case
to the upper response thresholds, i.e. to V
'DC-max
= 774 V at line supply voltages of 380 V to 480 V and to
V
DC-max
= 1158 V at line supply voltages of 500 V to 690 V. For other response thresholds, the minimum resistance
values R
BR-min
can be calculated as a function of V
DC-Brake
according to the formula shown above.
The resistance must not exceed the value R
BR-max
in order to ensure that the maximum required braking power
P
max-Brake
can be achieved with the response threshold V
DC-Brake
selected in each case. The maximum braking
resistance value is specific to the individual unit and application, and is calculated by the follow formula:
Brake
BrakeDC
Brake
BrakeDC
Brake
R
BR
P
V
P
V
P
V
etemperaturoperatingR
BR
-
-
-
-
-
-
×
=
÷
ø
ö
ç
è
æ
×
×
=
×
=×
max
2
max
2
max
2
max
49.0
3
7.0
3
3
)(
.
In this formula, the term P
max-Brake
stands for the maximum total braking power of the MoMo working as a Braking
Module, or the maximum total braking power of all three braking resistors, which is required for the specific
application.
In order to guarantee the required braking power and at the same time to maintain a sufficient control margin, the
actual resistance value R
BR
(operating temperature) should be lower than the calculated value
BR-max
(operating
temperature) if possible.
The Braking resistors are not available as standard components in the SINAMICS S120 modular system product
range. They must either be selected from the standard product ranges of suitable manufacturers, or requested from
these manufacturers, e.g. from GINO ESE (www.gino.de), as customized products dimensioned for the required
resistance value and load duty cycle.
Control of the Braking Module
With firmware version 4.3, the Motor Module which functions as a Braking Module must be operated as vector-type
drive object in "V/f control mode with independent voltage setpoint" and at constant frequency (50 Hz). The voltage
setpoint must be generated by means of free function blocks (see Function Manual "Free Function Blocks"), or by
DCCs (see Function Manual "SINAMICS / SIMOTION Description of Standard DCC Blocks"). For this purpose, a
subtractor block is used to compare the current DC link voltage with the freely programmable response threshold. If
the DC link voltage is higher than the response threshold, the inverter enable signal is issued for the Motor Module
functioning as a Braking Module. The difference between the current DC link voltage and the response threshold is
passed through a limiter stage, amplified by a multiplier and finally output as a voltage setpoint to the Motor Module
operating as a Braking Module.
With firmware version 4.4 or higher, the Motor Module which functions as a Braking Module can be operated as
vector-type drive object in V/f control mode "Operation with braking resistor". Parameter p1300 must be set to "15" for
this purpose. The settings of parameters p1360 to p1364 determine the resistance of the braking resistor, the
response threshold and the output voltage. Details are described in function manual "SINAMICS S120 Drive
Functions" and in the List Manual for SINAMICS S120 / S150.