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Figure 19 1+1 system block diagram
BATTERY 1
5.2.4
Operating Principles
Redundancy Paralleling
The redundancy parallel system can noticeably improve system reliability. In normal condition, nei-
ther UPS module works at full load. That means that even if the load is increased, the system will not
transfer to bypass. And when a UPS module shuts down due to any failure, the remaining UPS mod-
ule can still power and protect the load. When redundancy is lost due to module failure or load
increase, the parallel system will trigger an alarm.
5.2.5
Operation Modes Summary
The parallel system also has operation modes such as normal, battery, bypass and maintenance
bypass. All UPS modules in the 1+1 parallel system operate in coordination.
• Normal Mode Operation
The load is powered by the inverters of all the UPS modules in the system. If the frequency of
bypass is within the synchronous range, the inverter will be synchronized with the bypass. Other-
wise, the system will operate at nominal frequency.
• Battery Mode Operation
The batteries of all UPS modules power the load through their inverters. The system operates at
nominal frequency.
• Bypass Mode Operation
The condition to transfer to bypass mode is essentially the same as that of single module system.
The bypass of all the UPS modules powers the load.
• Maintenance Bypass Mode Operation
The sequence to transfer to maintenance bypass mode is the same as for transferring a single-
module system. The maintenance bypass switches should be switched on as synchronously as pos-
sible. Thus the system can be repaired without interrupting the power supply to critical load.
N
SUPPLIED BY OTHERS
INPUT MAINS
SUPPLY A B C
CB1
UPS1
RECTIFER
SW1-C
FUSE
STATIC
SWITCH
CHARGER
INVERTER
SW1-D
SW1-A
A B C
Q1EXT
QUPS
DISTRIBUTION PANEL
TO LOAD
N
INPUT MAINS
SUPPLY A B C
CB1
UPS2
RECTIFER
SW1-C
FUSE
STATIC
SWITCH
CHARGER
BATTERY 2
INVERTER
SW1-A
A B C
Q2EXT
QBYP
35
SW1-D
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