Page 42 - Energize July 2021

TECHNICAL

The economy (ECO) mode UPS system
The ECO solution is an attempt at combining the higher efficiency
of the line interactive version while maintaining the full functionality
of the double conversion system. ECO mode involves modifying
the DC topology as shown in Figure 5.

Figure 5: ECO mode topology.
Figure 6: Output voltage waveforms standard ECO vs. Advanced ECO
In the ECO system the DC topology is used, but the inverter is (Schneider).
switched off (i.e., in standby mode) and the load is supplied directly
from the incoming supply. Under power failure or supply disturbance reduction in disruption that any connected loads would be exposed
conditions, the inverter is turned on and the load is supplied by the to in the event of a power failure.
UPS. The main benefit of ECO mode is the increased efficiency of Advanced ECO mode can offer other advantages over standard
the bypass line, which typically runs at 98% to 99% compared to ECO mode. DC UPSs operating in online mode have the ability
standard online UPS efficiency of 93% to 97%. 2 to act as filters for harmonic currents generated by the loads
The difference, of anywhere between 2% to 5%, has the which have a great impact where the supply comes from standby
potential to deliver significant savings, particularly in a large-scale generators. In principle, this harmonic filtering function could filter
facility, where even a 1% improvement in efficiency could equate to harmonics to nearly the same level and quality as the filtering
tens or even hundreds or thousands a year in lower energy costs. provided by a double-conversion UPS.
The main problems with ECO mode are firstly the transition While advanced ECO mode offers advantages over standard
time for changeover to the inverter, which includes start-up time ECO mode, it does come with a trade-off. Since the inverter circuit
for the inverter, and secondly the fact that no power conditioning is active, the overall efficiency of the UPS is less than it would be if
of either the supply or the load is possible. If there is a utility power it operated in standard eco-mode. The difference is in the 0,5% to
failure when the inverter is in standby, then both the UPS’s output 1,0% range typically. While advanced ECO mode efficiency is less
voltage and current waveforms will be negatively affected. It takes than standard ECO mode, it is still better than traditional online mode.
time for the UPS to detect the failure, turn on the inverter and
supply clean power to the load from the batteries. This transfer Multi-mode UPS systems
time allows the input disruption to briefly reach the output of the The multimode UPS offers the advantages of the DC topology
UPS. ECO mode is only recommended on sites where the utility in handling disturbances and power conditioning, as well as
supply is relatively stable, and the load generates low harmonics the efficiency advantages of the ECO mode. The operation is
so is not sensitive to any mains interference. illustrated in Figure 7.

ECO Plus system or advanced ECO mode
High-efficiency operational modes that go beyond eco-mode
have been developed. In the advanced eco-mode, the inverter
is operational but carrying no load. This allows faster transfer of
load to the inverter, but more importantly, allows the inverter to
act as a harmonic and disturbance filter on the input to the load.
In advanced eco-mode, the primary power path during normal
operation is through the bypass path, the same as eco-mode.
But with advanced mode, the inverter remains active, operating in
parallel with the input without actually handling the load current.
Since the inverter is already active it can more seamlessly take over
the supply to the output where there is a supply failure.
Figure 6 shows a comparison of the output voltage waveforms
of standard and advanced eco-modes. It clearly shows the Figure 7: Multimode UPS operation.

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