Siemens sinumerik 840D sl Function Manual page 372

Detailed description
2.7 Extended stop and retract (ESR)
Generator operation
Generator operation is possible in the event that the intermediate circuit power is insufficient
for safe retraction (for a period of at least 3 interpolator cycles). The mechanical power of a
spindle/axis is used and the energy is optimally fed back to the DC link. The DC link voltage
is kept within the limits set in the machine data by means of a two-step control.
In this case, the axis/spindle parameterized as a generator measures the intermediate circuit
voltage if it falls below the value set in the ms cycle. Thus the DC link is backed up within 2
ms. (Under normal conditions measurement every 4 ms.)
The energy stored in the drive
E = 1/2 * Θ * ω
with
Θ = total moment of inertia
ω = rotational speed at the time of switch-over to generator operation
is recovered with approx. 90% efficiency.
For generator operation, it is advisable, especially when using large machines with powerful
I/RF units (55, 80, 120kW), to use a separate drive with centrifugal mass which, after
acceleration to maximum speed, only has to generate the friction loss.
Of course, it is also possible to use any other drive as long as it is not directly participating in
the controlled stop/retract.
Axes that are participating in gearbox links that must be specifically maintained are not
suitable for this purpose.
Note
A minimum speed limit for the generator ($AA_ESR_STAT, bit 4) can also be the source for
the retraction process. This is advisable, for example, when generator operation is to be
used to bridge short power interruptions.
In order to prevent the intermediate circuit voltage from becoming too high when braking
starts and to prevent the drive from reacting with pulse suppression (which would cause
uncontrolled coasting down), it is necessary to use suitable pulse resistor modules.
152
2
Special functions: Axis Couplings and ESR (M3)
Function Manual, 11/2006, 6FC5397-2BP10-2BA0