UPS Technologies explained
Online Double Conversion Technology
An
uninterruptible power supply using
true online double conversion technology provides the highest level of power
protection available. The UPS converts the 230V input AC mains supply to DC power, which is then used to charge the
battery. The DC current flow is then fed through an inverter stage that reconstructs
the 230V AC mains output. Because the AC output is completely regenerated,
it will be completely free from any mains-borne interference such as spikes
and voltage variations. The output voltage and frequency is controlled precisely,
thus ensuring a clean and stable sine wave power output. Online UPS are able
to withstand large fluctuations on the input voltage before transferring to
battery power (typically 276V-184V) thus eliminating unnecessary battery discharges.
Upon mains failure, transfer to battery power is seamless - no break.
Online UPS also have various failsafe and self-diagnostic features that will
instantly transfer the load onto mains power if there is a failure within the
UPS hardware, or if the UPS is overloaded.
Advantages
Continuous & total power conditioning
Failsafe/overload protection with static bypass facility
No break on mains failure
Wide input voltage tolerance
Recommended with Generator sets
Disadvantages:
Because of the technology used online usually cost's more than other
types of UPS technology
Offline-Standby Technology
During
normal operation, the power flows straight through the unit and hence only
RFI filtering is usually provided. When the input voltage fails or fluctuates
outside of a pre-set tolerance window, the UPS detects this and a relay will
close, allowing the UPS to start feeding battery power via the inverter. The
inverter is then switched on and either a square, step or sine wave form output
is supplied. Upon the return of mains power, the output is switched back onto
mains and the inverter is turned off. Typically there will be a break of between
4-10 ms during the transfer to and from the battery mode.
Advantages
Low cost
Silent operation when in standby
Efficient
Disadvantages
Minimal power protection - only protects against a small percentage
of problems
Poor output voltage regulation - fluctuations such as sags and surges
will be passed straight to the load
Break transfer to battery mode
No failsafe - UPS will drop the load if there is a high start-up
current, overload or inverter failure
Not recommended with Generator sets
Line-Interactive
Technology
A line-interactive UPS operates in a very similar fashion
to an offline UPS, except with the advantage of better filtering and output
voltage boost/reduce features. Whilst not eliminating mains-borne interference,
line-interactive technologies reduce the impact of spikes, surges and sags
by 'clipping' the peaks and valleys, boosting power or switching
to battery back up. As with offline UPS, when the input voltage fails or fluctuates
outside of a pre-set tolerance window, the UPS detects this and a relay will
close allowing the UPS to start feeding battery power via the inverter. The
inverter, in a good line-interactive UPS, will supply a sine wave output. Upon
the return of mains power, the output is switched back onto mains and the inverter
is turned off. As with offline UPS, typically there will be a break on the
transfer to and from battery mode, though usually this will be shorter than
with an offline UPS.
Some manufacturers will try to pass their line-interactive
UPS off as online models by calling them 'digital online', 'inline' or 'online
interactive' - make sure you know what technology the UPS you are
buying actually uses.
Advantages
Lower cost than online
Gives better protection than offline
Silent operation when in standby
Efficient
Disadvantages
Fluctuations, such as spikes, can still be passed straight to the load
Break on transfer to battery mode.
No failsafe - UPS will drop the load if there is a high start-up
current, overload or inverter failure
Not recommended with Generator sets
UPS & Generators
Due to the nature of the supply from a Generator we
recommend utilizing Online Double Conversion Technology UPS. Online UPS have
improved input frequency and voltage tolerance over non-online technology,
therefore preventing frequent switching to battery power which maximizes
battery life and UPS reliability. Because Online Double Conversion Technology
completely regenerates the AC output it will be completely free from interference
such as spikes and voltage variations which may adversely affect IT or other
types of sensitive equipment. Non-online UPS will often work, although intermittently,
with a Generator supply but will ultimately fail. Usually the UPS failure
happens under load or when the Generator is providing the main supply. A
Generator backed supply is often a critical one and necessitates the highest
form of protection, Online Double Conversion Technology provides this protection.
About the Author
Mike has been working in the uninterruptible power supply industry for many years, succefully advising and installing UPS and Generator systems for Energy Systems
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