Toshiba T90S3S08KS6XSN Manual page 148

TOSHIBA G9000 UPS White Paper
Due to the dramatic
reduction of switching
losses, a three-level
UPS exhibits over
15% of reduction in
power semiconductor
losses.
FIGURE 10
Typical
semiconductor
losses distribution
in an UPS system.
Numbers for
3-level are
referred to
2-level topology.
© 2008 TOSHIBA INTERNATIONAL CORPORATION – INDUSTRIAL DIVISION
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an interesting improvement toward high efficiency. Basically, switching
losses are a function of the voltage across the semiconductor, switching
frequency, switch current, and the junction temperature. For a given
switching frequency, current level and temperature, three-level converters
show a dramatic reduction of switching losses due to the reduced voltage
stress on each power switch and better characteristics of using an IGBT
with lower voltage ratings.
Considering both types of losses in an UPS, the three-level concept
realizes an overall improvement of power conversion efficiency. Figure 10
shows a typical scenario of power loss distribution in an UPS system for
both circuit topologies. Despite of the fact that conduction losses almost
doubles, switching losses are dramatically reduced in a three-level
double-conversion topology. This loss reduction is translated into a higher
efficiency UPS with lower thermal stresses on power semiconductors.
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