Page 149 - Power Quality in Electrical Systems

Uninterruptible Power Supplies 131

Utility or E/G set input

Main bus

Input
CB

Solid state Battery
switch charger

Battery
Reactor
Inverter

Output
CB

Emergency AC bus

To load
(b)
Figure 9.1b Delta UPS: solid-state switch; reactor; battery
charger; inverter; battery.

voltage and the required load voltage. The Delta UPS is more efficient
than the double-conversion UPS because the load power is supplied
directly from the line nearly all of the time. The inverter and battery
still have to be sized for the longest utility outage time.

History
The silicon-controlled rectifier (SCR) was introduced in 1957. The devel-
opment of inverters using SCRs for UPS was expedited by the book,
Principles of Inverter Circuits, by Bedford and Hoft, published in 1964 [9.2].
An early publication by Fink, Johnston, and Krings in 1963 described
three-phase static inverters for essential loads up to 800 kVA [9.3].
Kusko and Gilmore described in 1967 a four-module redundant UPS for