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16 Operation principle and hardware description
Operation principle
The regenerative rectifier unit (RRU) consists of one rectifier module or
parallel-connected rectifier modules (n×R8i) and an L-filter. Each module consists of
six IGBT components and six diodes connected in anti-parallel. In motoring mode,
current flows from an AC supply through the diodes to a DC bus. In regenerating mode,
current flows from the DC bus through the IGBTs to the supply network.
The IGBTs of the regenerative rectifier unit are switched, conducting only once during
each network voltage half-cycle, which is comparable to a 6-pulse diode supply unit.
This reduces switching losses and allows higher power ratings for the power module.
Because the IGBTs can be switched off at any time, RRU – unlike a thyristor bridge –
is reliable also during supply network failures when in regenerating mode.
Main circuit diagram
Simplified main circuit diagram
￭
The following figure shows the simplified main circuit diagram of the rectifier.
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1
1
AC input
Description
2
AC fuses
1.
AC input
3
L-filter
2.
AC fuses
4
Regenerative rectifier module
3.
L-filter
5
DC fuses
4.
Regenerative rectifier module
6
DC output
5.
DC fuses
Charging
￭
6.
DC output
A charging circuit powers up the DC link capacitors of the drive system smoothly.
Discharged capacitors cannot be directly connected to the full supply voltage. The
Charging
charging current must be limited until the capacitors are charged and ready for normal
use.
Cabinet-installed units have a resisting charging circuit. It consists of fuses, a contactor
and charging resistors. The resistive charging circuit is in use after power-up for as
long as DC voltage has risen to a predefined level.
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