Gamatronic Electronic Industries Ltd.
6
Power+ Technical Guide
The PFC power section block diagram is shown in Figure
2-3. Input currents of the PFC
(without filters) is shown in Figure
2-4; the control scheme is illustrated in Figure
-+
T
Control
-+
+
Ir
+
Control
Is
Control
N
-+
R
S
It
Figure
2-3: Power section of the PFC in a single UPS module
Ir
Is
It
(CCM)
t
-Ipeak
Ipeak
Figure
2-4: Input currents of the PFC (without filters)
2-3, the PFC section operates in Continuous Current Mode (CCM)
conduction, which has many advantages. Input currents are shaped in such a way that they
follow the input voltages with precision.
This makes the system appear to be nothing more than a resistive load with respect to the line
voltage. In other words, the system corrects the input current waveform of the connected load,
and acts as an active power filter.
The PFC section also draws symmetrical currents from each phase, and maintains good
current sharing among identical UPS modules in parallel.
Each phase input is sensed for voltage and current, required to force the input current drawn
from the phase input to follow its voltage and emulate a resistor. Two feedback loops are
