Gating Unit; Firing Angle Limits - Siemens SINAMICS DCM 6RA80 Faq

settings if non-linear smoothing reactors exist in the armature circuit, e.g. two-value reactor in
12-pulse operation or iron-cored reactors on applications for old motors.
P50153 = 3 Precontrol assumes EMF zero, this is for applications that do not use EMF and
for high inductance loads in field supply or solenoid applications.

Gating unit

The gating unit is the interface to the power section. The firing instant of the thyristors is
defined by the offset of the firing angle from which an alternating variable direct voltage is
formed. Phase control of the AC input voltage with suitable assignment of the thyristors to be
fired is performed in such a way that a variable direct voltage occurs at the output, see
below. The firing angle is calculated as a function of the zero crossing of the line voltage
(voltage measurement of 1U1/1V1/1W1 on the power interface board).
The gate pulses are formed on the CUD, the gate pulse transformers are located on the
power interface module. The gate pulse transformer receives the chopped pulses, see
below. The duration of the firing pulse burst is 0.89 ms for a short pulse setting of p50079 = 0
(factory setting). For a long pulse setting of p50079 = 1 the duration of the pulse burst is 0.1
ms before issue of the subsequent firing pulse.
Note: For normal applications always use short pulses with p50079 = 0. p50079 =1 Long
pulses, intended for supplying large inductance to ensure that thyristors trigger. In the case
of long pulses, the thyristors might not block on some network configurations, detailed
support on this effect is available from Technical Support. When supplying large inductances
with short pulses, a resistance must be implemented parallel to the load with a current of
approx. 500 mA at nominal voltage for the load, to ensure that the thyristor attains the
holding current of approx. 200 mA for the duration of the firing pulse. The thyristor will only
remain conductive when the holding current is reached.
Example of parallel resistance: Nominal direct voltage 310 V / 0.5 A = approx. 680 ohm, load
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capability in watts: (line voltage * 1.35) / resistance in ohms. In the above example, a 400 V
line voltage and 680 ohms results in approx. 450 watts load capability for the resistance. –
End of note-
Operation on weak networks (generator with diesel drive):
On weak-frequency networks, frequency changes of up to 10 Hz per second are permissible.
For this, parameter p50152 Line frequency correction armature (factory setting 20) must be
set to lower values. The correct setting depends on the system conditions and must be
verified with trace recordings. The current measured should exhibit a steady current without
current peaks. Parameter p50252 must be observed for the integrated field supply.
Note: A diesel generator cannot absorb regenerative current. In such a case, it is therefore
important that load resistors on the AC infeed side of the SINAMICS DCM are switched on
during braking mode with a resistance value that is high enough to ensure that the generator
always works generatively. Engineering support on request.

Firing angle limits

Sheet 6860.
Control limit Alpha G: The setting of Alpha G (p50150) determines the maximum possible
output voltage of the SINAMICS DCM. Smaller angle values mean higher voltage possible.
For calculation see below. Factory setting 5 degrees for 2Q devices, and 30 degrees for 4Q
devices and for 2Q with field switchover 30 degrees like for 4Q is required to ensure that the
output voltage in motor operation is not too high and that on transition to braking mode with
Alpha W 150 degrees enough back-EMF can be accumulated. If the output voltage of the
device before transition into braking mode is too high, F60043 is output in order to protect the
drive from conduction-through. See also the description for F60043.
Inverter stability limit Alpha W: Alpha W is set at p50151, factory setting 150 degrees. Limit
Alpha W is required to provide the necessary protection angle to allow the thyristor to block
before commutation to the next thyristor. On weak power supply networks it may be
necessary to reduce Alpha W, for example, set 145 degrees. For discontinuous current, the
angle can be larger because the thyristor no longer carries current during commutation, so
that Alpha W 165 degrees becomes active if zero current is signaled. This offset to 165
degrees can be prevented with p50192 = 1, then p50151 is always active.
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