Siemens SINAMICS G130 Engineering Manual page 212

Fundamental Principles and System Description
Engineering Information
When the control deviation x exceeds the upper switching hysteresis x
operates in the forward direction; when the control deviation falls below the lower switching hysteresis x
actuating motor is switched off again. If the control deviation falls below the switching hysteresis -x
direction, the actuating motor operates in the reverse direction until the control deviation has been eliminated and the
actuating motor is switched off again when switching hysteresis -x
From the control point of view, the actuating motor on the 3-way valve behaves as an I-controller. It is advisable to
utilize the feedback shown by the dashed line in order to obtain a stable behavior as a P-controller.
The 3-way valve is controlled such that the bypass (path B-AB) is opened when the coolant is cold. The coolant
bypasses the heat exchanger and the temperature of the heat sink and the coolant rises as a result of heat losses
from the power semiconductors in the SINAMICS units. When the temperature T
SINAMICS units reaches the specified setpoint T
through the heat exchanger (path A-AB).
Emulation of
the actuating
motor
Inspection
glass
Dirt trap
Close bypass
M
Open bypass
Actuating motor
for 3-way valve
Heat
exchanger
Example of coolant temperature control by means of a 3-way valve in order to prevent condensation
Coolant temperature control as a function of ambient temperature and air humidity
The table in section "Protection against condensation" is the basis for calculating the required temperature difference
ΔT that must be added to the ambient temperature T
L
temperature always remains higher than the dew point of the ambient air. This table states the dew point T
function of ambient temperature T
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Ó Siemens AG
, the 3-step controller closes the bypass and opens the path
set
3-step controller
y
-x -x
u l
x x
l
-y1
P-feedback
Pressure-relief Pressure
valve < 6 bar indicator
Inflow
AB
3-way valve
(bypass valve)
B
for temperature
A
control
Closed
pressurizer
Pump
and relative air humidity Φ.
a
, the actuating motor is switched on and
u
is reached.
l
+y1
x
x
u
Liquid-cooled SINAMICS
S120 units in Chassis format
Basic
Line Module
Module
Return flow
so as to ensure that the setpoint T
a
in the negative
u
at the coolant inlet of the
act
T T
set max
_
T
min
T
act
(Parameter
r0037[19])
Motor Motor
Module
1 n
Hose
connection
for the coolant
set
, the
l
T
a
+
ΔT
L
as a
dp