Operation Theory - Liebert UPS System User Manual

1.3 Operation Theory

The UPS circuit diagram is shown in Figure 1-2.
Q1
A1
B1
C1
A2
B1
C1
N2
BP
BN
Q3BP
U
V
W
N
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.
Chapter 1 Introduction
KM1
FU1
FU2
KA1
FU3
Q2
KM2
Q5
Figure 1-2 Main circuit of UPS
AC2
TR1
Res1
Res2
FU4
FU5
FU6
AC4 AC3
2
L1
DC1
Res3
TR2
DZN6