Page 161 - Uninterruptible Power Supplies

Static Uninterruptible Power Supplies
Static Uninterruptible Power Supplies 159

being provided by the inverter, but there is no isolation from mains.
Frequency is dependent on mains supply and voltage conditioning is
clearly limited. The module is competitively priced but restricted to
lower rating systems.
There are many circuits similar in respect to the above basic modules
described, and it is difficult to establish all the properties of UPS mod-
ules particularly at low ratings.
There is a trend dictated by the market to reduce size and weight,
retaining efficiency, and above all reducing unit cost. This is particu-
larly critical at lower ratings as one colleague said we are entering the
“drip dry zone” (no-iron!). Transformers, so long part of the circuit, are
considered heavy and expensive compared to alternative solutions
involving simple solid-state components. Thus, circuits are appearing
at ratings up to 10 kVA as shown in Fig. 5.17. This circuit allows wide

UPS switch
filter / conditioner

AC input load

~
Inverter
==
~
==
normal mode
stored-energy mode
charger battery
Figure 5.15

static switch

AC input load

~
Inverter
==
normal mode
battery stored-energy mode

Figure 5.16

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