Liebert UPS System - Manual (Page 8)

Chapter 1 Introduction
2
1.3 Operation Theory
The UPS circuit diagram is shown in Figure 1-2.
V
N
U
TR2
BN
N2
A2
W
BP
C1
B1
C1
B1
A1
DZN6
Q5
AC3
FU4
KM1
FU6
Res2
TR1
L1
AC2
Q2
+ DC1
KA1
FU2
Res1
Q1
FU5
Q3BP
FU1
AC4
FU3
Res3
KM2
Figure 1-2 Main circuit of UPS
The utility source is input at Q1 and flows through the fuse, the transformer,
inductor and into the high frequency rectifier which will convert the AC power into
DC power. The rectifier has PFC and charger function and make use of soft start
and DSP digital technology to improve the system immunity against surge, improve
the stability of the DC bus voltage, reduce the charging current ripple and prolongs
the battery life.
The battery is connected to the UPS through contactor. If the DC bus voltage drop
through certain threshold, then the contactor will activate to connect the battery to
the DC bus. The battery will supply the DC power to the inverter through a filtering
circuit.
The inverter uses digital vector control technology based on DSP to modulate six
IGBTs through SVPWM and invert DC power to AC three phase power.
The output is isolated from the load by Delta/Zig-Zag transformer, static switch,
fuse and circuit breakers.
The bypass source is input at Q2 and output through the bypass static switch.