OPTI-UPS SS30K33 - Manual (Page 6)

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4- Introduction
Input power is applied across the motor driven variable transformer which has a “center tap”
that divides the variable transformer into bucking and boosting voltage areas.The buck-boost
transformer is a fixed ratio isolation transformer capable of high amperes at low voltage. The
ratio of the buck-boost transformer is determined by the amount of voltage needed to buck or
boost the input line voltage to maintain the specified output level. The buck-boost transformer
secondary is wired in series with the load and the primary is connected across the variable
transformer’s “center tap” and brush terminals.Depending on which side of the “center tap” the
variable transformer brush is positioned, the variable/buck-boost transformer system will add to
(boost) or subtract from (buck) the input line voltage. The further the variable transformer brush
is from the “center tap” the more bucking or boosting of voltage will occur.The key to the proven
reliability and long trouble free service life of a Voltage Regulator is in the combination of a
motor driven variable transformer with buck-boost transformer technology.
Input Output
Figure 1. Single phase regulator block diagram
As shown in figure 1, the only active component in the main power path of the voltage
regulator is the secondary of the buck-boost transformer. This gives the regulator the
advantage of being able to withstand substantial current overloads.The variable transformer
brushes, which are the most vulnerable component in any variable transformer system, are
completely isolated from overload conditions by the buck-boost transformer. Due to transformer
inefficiency above rated design, the amount of current that the buck-boost transformer can
induce across to its primary winding and into the variable transformer circuit is dramatically
decreased as regulator overload
current increases.
The controller monitors the regulator’s output voltage and then uses these feedback signals
to determine drive commands for the variable transformer motor interface circuit. The controller
is designed to adjust the motorized variable transformer to provide a +/-1~2% or better output
voltage regulation over the entire input voltage range.
M Controller
Buck-Boost transformer Variable transformer