4.2 Power failure bridging
4.2.1 Detection of a voltage failure
The mains failure support feature detects a failure of at least two phases of the mains
supply. If no countermeasures are taken, this failure will cause a drop in the DC link
voltage and thus lead to the device being switched off.
In the event of a power failure, the DC link voltage can be supported by using the
motor’s rotational energy. To this end, the motor will be operated as a generator and
decelerated in a controlled manner in the event of a power failure so that a
configurable DC link voltage setpoint will be maintained. This function is especially
useful when it comes to powering the electronics in drives with magnetic bearings,
as this will prevent the assembly from crashing into the safety bearing in the event of
a power failure all the way to the lowest possible speeds.
NOTE
l
Please note that the components which need bridging must be
powered via the DC link (DC power supply). In particular, the
power supply of the servo drive itself (24 V control voltage) must
be ensured.
Image 4.2: Power failure bridging settings screen
MOOG
ID No.: CB40859-001 Date: 11/2020
MSD Servo Drive - Device Help
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4 Power stage
4.2.1.1 Functional description
The P 2940 - CON_PowerFail_Sel selection parameter can be used to select the
following operating modes:
0= (OFF) switched off
1= (Ret) Power failure bridging with power return detection. The system will start up
again if the power returns within a configurable period of time.
2= (NoRet) Power failure bridging with power return detection. The system will not
start up again.
3= (NoLim) Fastest possible speed reduction without power return detection.
5= (RetAbs) Same as 1=Ret, but with absolute voltage levels and without validation
check.
6= (NotRetAbs) Same as 2=NoRet, but with absolute voltage levels and without
validation check.
7= (NoRetAbsPulse) Same as 6=NoRetAbs, but with pulse operation.
4.2.1.2 Parametrisation
P 2941 - CON_POWF_VCtrl is used to configure the voltage controller by adjusting
the corresponding gain and reset time. Within this context, the specified gain refers
to the motor’s rated speed. At lower speeds, the gain will be automatically increased
in order to maintain a constant dynamic performance in the voltage control circuit.
P 2942 - CON_POWF_VLim is used to configure the threshold voltage for detecting
power failures / power returns, as well as the voltage setpoint for the controller. The
configured voltage values will not be absolute values, but will instead be added to
specific DC link threshold values (based on the operating mode). The corresponding
