3.2 UPS operating modes
Table 3: UPS operating modes
UPS operating mode
Description
Normal operating modes:
Double conversion mode
Critical load is supplied by the inverter,
which derives its power from rectified utility
AC power. In this mode, the battery charg-
er also provides charging current for the
battery, if needed.
Variable Module Management System
(VMMS) mode
Critical load is supplied by the inverter. The
inverter derives its power from rectified util-
ity AC power, identically to double conver-
sion mode. In the VMMS mode, the UPS
system is able to optimise the load level
per power module: the operating efficiency
is significantly improved when operating
load is below 50% of UPS capacity. The
UPS system will automatically place the re-
dundant power modules to suspended
mode. In case of any anomalies in utility or
a sudden load increase, the suspended
power modules are able to transfer to on-
line mode with less than 2 ms transition
time.
Energy Saver System (ESS mode)
Critical load is supported securely by utility
power through the static bypass switch with
double conversion available on-demand
with typically less than a 2 ms transition
time, should any abnormal condition be de-
tected in the utility. When operating in the
ESS mode, the load is protected with inher-
ent surge suppression. Operating the UPS
in the ESS mode increases system effi-
ciency up to 99%, allowing significant sav-
ings in energy losses without compromis-
ing system reliability.
Other operating modes:
Stored energy mode
Energy is drawn from a DC backup power
source and converted to AC power by the
UPS inverter. Most commonly VRLA bat-
teries are introduced to the system for this
purpose, and the mode of operation is
called the battery mode.
Bypass mode
Critical load is supported directly by utility
power through the UPS static switch.
Eaton 91PS/93PS UPS 8–40 kW
User's and installation guide
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Eaton Corporation plc 2018. All rights reserved.
Revision: 005
Document ID: P-164000493
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