Smart Infeed - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information

Smart Infeed

The Smart Infeed is a simple, unregulated rectifier / regenerative unit for four-quadrant operation (i.e. the energy
flows from the supply system to the DC link and vice versa).
The Smart Infeed consists of an IGBT inverter, which operates at the line supply as a line commutated 6-pulse bridge
rectifier / regenerative unit. In contrast to the Active Infeed, the IGBTs are not active pulsed using the pulse width
modulation method. In rectifier operation (motor operation) the current flows via the diodes integrated into the IGBT
modules from the line supply to the DC link, so that a line-commutated, 6-pulse diode bridge circuit is present in
motor operation. In regenerative operation the current flows via the IGBTs, which are synchronised at the line
frequency. Thus, a line-commutated, 6-pulse IGBT bridge circuit is present at regenerative operation.
As IGBTs, in contrast to thyristors, can be switched off at any time, inverter shoot-through during regenerative
operation caused by supply system failures cannot occur in contrast to rectifier / regenerative units equipped with
thyristors.
On the line side, the Smart Infeed is normally equipped with a line reactor having a relative short circuit voltage of
u = 4 %.
k
The Smart Infeed is available as a stand-alone infeed of the SINAMICS S120 modular system in Chassis and
Cabinet Modules format.
SINAMICS S120 Smart Infeed comprising a Smart Line Module and a line reactor with u
The IGBTs for regenerative operation of the Smart Infeed are always switched on at the natural firing point and
switched off after 120º (electr.) independently from the direction of the energy flow. As a result of this, a current resp.
energy flow from the supply to the DC link or vice-versa is possible at any time. This control principle offers the
advantage that the Smart Infeed can react relatively fast to load variations and can also change the direction of the
current resp. energy flow at any time.
However, the control principle described creates a capacitive reactive current at no-load operation, which flows on
the line side and cannot be neglected. This leads to a capacitive reactive current on the line side, which decreases
with increasing load of the Smart Infeed and it is no longer present when the rated load is reached.
The magnitude of the capacitive reactive current at no-load condition is depending on the DC link capacitance
connected to the Smart Infeed. At the maximum permissible DC link capacitance of the connected Motor Modules,
the no-load reactive current reaches a magnitude of approx. 15 % to 20 % of the rated current of the Smart Infeed.
The no-load reactive current can, in principle, be prevented by blocking the regenerative operation via corresponding
parametrization of the firmware.
The Smart Infeed is a line-commutated rectifier / regenerative unit and produces an unregulated, load-dependent DC
link voltage V from the three-phase line voltage V
DCLink
peak line voltage value, i.e. V
Basic Infeed, as the voltage drop at the 4 % reactor of the Smart Infeed is bigger than at the 2 % reactor of the Basic
Infeed. At partial-load the DC link voltage will be V
SINAMICS Engineering Manual – May 2008
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© Siemens AG
Line
= 1.41 • V When the DC link is loaded, its voltage drops more than with the
DCLink Line.
≈ 1.32 • V
DCLink
≈ 1.30 • V
V
DCLink
= 4%
k
. Under no-load conditions, the DC link is charged to the
and at full load,
Line
Line