Impact of the surge current on the IGBTmodule properties in servo drives
11.6.2Uninterruptiblepower supply (UPS)
Uninterruptible power supplies are now available in power ratings from just a few 100W
to the MW-range. They are grouped into single-phase and three-phase UPS systems.
While the small power ratings for single-phase UPS systemsmostly use discrete power
electronic devices, only IGBTmodules can be found in the higher power classes and in
the three-phase systems. A distinction is made between so-called "online" and "offline"
UPS systems. In principle, both systems are to provide the consumer or load circuit
continually with energy during a power failure. The energy required in the example of
is drawn from batteries. However, there are also systems in which the
electrical energy is obtained from a flywheel, i.e. the kinetic energy ofmotion.
Online UPS, also known as double conversion UPS, always operate directly between
supply and load network and are bypassed only in the case of service. The efficiency is
<1, because there are losses of the power semiconductors and passive components in
the system. Advantage of these systems is that mains-based dips and voltage
fluctuations are invisible to the consumer (load) side. The offline UPS, however, is
normally equipped with a bypass operation, i.e. it is in standby mode. The efficiency
here is close to 1. Only in case of a power failure are they switched to the inverter
Furthermore, a distinction is made between "transformer-based" and "transformer-less"
UPS. While the transformer-less UPS has no isolated output and the N-potential is
referenced to the DC-bus, the transformer-based UPS has an output transformer as
The secondary star point of the transformer in a three-phase