Page 143 - Uninterruptible Power Supplies

Source: Uninterruptible Power Supplies and Standby Power Systems

Chapter
5

Static Uninterruptible

Power Supplies

Definition
A static UPS system is a circuit which ensures a continuous power sup-
ply to the load irrespective of outages , spikes, brownouts, or other dis-
turbances from the normal incoming mains supply. It is achieved by
using solid-state circuitry which employs a battery or possibly kinetic
energy as the alternative energy source.

Background
The development of static UPS clearly was dependent on the availabil-
ity of solid-state switching devices. The earliest conversion systems
available in 1960 for dc to ac were no more than mechanical vibrators
with ratings no higher than 500 VA used for radio/communications
applications. The advent of power transistors enabled the first true sta-
tic inverters to be built, applications in the early years being commu-
nication and instrumenation. Thyristors then became available and,
gradually, ratings of modules increased. It should be remembered in
these early days that switching devices suffered from wandering char-
acteristics due to operating temperature and aging. In time these prob-
lems were solved. By approximately 1960 computers began to require
UPS systems
From inception to todays designs we have seen dramatic impro-
vements, efficiency originally at 80 to 81 percent compares with
claimed efficiencies of up to 98 percent for present designs. The size
of systems also has reduced considerably, modern designs are now
some 60 percent less in proportion. Maintenance costs are much

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