Ideal Green UPSs
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The Ideal
Green UPS
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The Ideal Green UPS
Next generation of „green“
UPS technology gives the
DP300E series of 3 phase
UPS products unique performance.
Introduction
Traditional Double-conversion UPS increasingly become a problem for utilities and for power consumers that are not
protected by a UPS.
This is because of the harmonic currents, such traditional UPS send upstream the powerlines. Such harmonic
currents disturb the voltage quality on
the power line which in turn may cause
sensitive equipment to malfunction,
power factor controlling capacitor banks
to explode as well as distributiontransformers to overheat.
Traditional Double-conversion UPS
waste a lot of energy because of the inherently high losses, and as UPS are normally operated 24 hours a day, 365 days
a year, the waste amounts of energy lost
really count on the energy bill, as well
as impacting the global resources of energy in a negative direction.
Traditional Double-conversion UPS do
not efficiently utilize the utility network
and the local installation because of a low
input power factor on the UPS.
This leads to requirements for overdimensioned power installations, locally,
on distribution level and eventually on
the transmission level. Also an optional
diesel generator would have to be significantly oversized.
This has all been changed with the introduction of Silcon’s next generation of
„green“ UPS technology called Deltaconversion, for the first time applied in
the new DP300E 3 phase on-line UPS
systems.
Compared to traditional Double- conversion UPS, the new technology provides:
- Energy waste reduction from presently 10% down to 3%
- Harmonic current reduction from
presently 30% down to less than 3%.
- Utilization of power installation etc.
from presently 80% up to 99%.
In fig 1, 2 and 3 the three principles Double-conversion, Single-conversion and
Delta-conversion are shown in single line
schematics.
The Double-conversion scheme is
readily understood, the rectifier charges
the battery and supplies the inverter with
DC power, the inverter supplies the load
with continuous, regulated AC power and
during mains outages energy is taken
from the battery until the mains is available again. The rectifier then charges the
battery again while still supplying the
inverter with DC power. All transitions
from mains to battery operation and vice
versa take place without any interruption
on the output and the load is thus supplied by a continuous, regulated AC voltage of high quality.
Such qualities are inherent qualities of
on-line UPS systems and such qualities
are therefore also found in the Singleconversion UPS as well as in the new
Delta-conversion UPS shown in fig. 2
and 3. All types are normally equipped
with an electronic bypass switch and this
will not be discussed here.
In fig. 2 showing the well proven Single-conversion scheme, the biggest difference to fig. 1 is the lack of a separate
rectifier. Instead the inverter is of the 4quadrant type meaning that it can pass
power in either direction. Therefore it can
replace the rectifier.
In normal operation, the mains switch
is closed and power is taken from the
mains. The majority of power is passed
on to the load via the choke, thus the
power is not converted twice as in the
Double-conversion system. This means
very low losses compared to the Double-conversion system.
It may not be obvious, but the inverter
is still controlling the output voltage although the majority of the power is not
converted.
Since the output voltage is always sinusoidal, it follows that the current taken
First generation
Single-conversion UPS:
Second generation
Delta-conversion UPS:
Basic principles:
Double-conversion UPS:
Mains
Load
Mains
Load
Mains
Load
1
2
•
•
30% current distortion
low power factor
•
•
no current distortion
power factor varies
with load and mains
•
•
no current distortion
power factor ~ 1
regulated
•
energy losses = 8-12%
•
energy losses = < 5%
•
energy losses = < 3%
Fig. 1
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Fig. 2
Fig. 3
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from the mains via the choke is also sinusoidal, thus there are no mains harmonic currents from this system. This is
in contrast to the Double-conversion type
with its well known thyristor controlled
rectifier, burdening the mains with heavy
harmonic currents.
In case of a mains outage the Singleconversion system performs identical to
the Double-conversion type, energy is
simply taken from the battery, and the
inverter, which is continuously running
and in regulation, now supplies the load
from the battery. In order not to feed back
into the mains during battery operation,
the mains switch is opened.
Upon mains restoration the switch is
closed again and the load is now again
supplied via the choke from the mains,
but the inverter still controls the output
voltage. At the same time the inverter
now also works as a rectifier, charging
the battery in a controlled way simply
by passing power in the reverse direction into the battery.
Thus the Single-conversion UPS seems
pretty ideal with its low losses, sinusoidal mains current and simplicity, but it
has one drawback common with the Double-conversion system and that is a relatively low power factor to the mains. Furthermore the power factor varies with the
mains voltage and partly with the load.
Thus, utilization of the mains installation is not optimum.
Also, at high mains voltage (+10% to
+15% of nom.) losses increase in a Single-conversion system as shown in fig.
2.
This is because of increasingly higher
reactive currents that the inverter has to
support when the difference between
mains voltage and output voltage is high
(large voltage across the choke). Even
with such small drawbacks, the Singleconversion system is by far superior to
the Double-conversion UPS.
The Delta-conversion principle
Continuos search for improvement, and
new technology becoming available have
led to the next generation UPS technology called Delta-conversion.
This technology eliminates the small
drawbacks of the Single-conversion UPS
and comes very close to an ideal solution.
As can be seen from fig 3. the system
has 2 inverters connected to a common
battery. Inverter 1 is rated at typical 20%
of the output power of the UPS, and is
connected via a transformer in series with
the mains supplying the load. Inverter 2
is a fully rated inverter and has basically
the same function as the inverter in the
Single-conversion UPS.
Both inverters have 4 quadrant capabilities.
Double-conversion UPS:
Mains
Inverter 2 keeps the voltage to the load
stable and precisely regulated be it in
mains operation or in battery operation
or during transitions from mains – to battery operation or vice versa.
Inverter 1, called the Delta inverter,
makes up for any difference between the
voltage on the output of the UPS and the
voltage from the mains.
The Delta inverter also controls the
input power factor to unity as it is controlled to take up current from the mains
that is sinusoidal and in-phase with the
mains voltage.
Furthermore the Delta inverter controls
the charging of the battery.
The mains switch has the same function as in the Single-conversion UPS
namely protection against back-feed into
the mains.
Let us recall the performance differences between the 3 different types of
UPS. In fig. 4 the heavily distorted input
current of a Double-conversion UPS is
seen to distort the mains voltage severely.
Especially the notches in the voltage
waveform should be noted, they result
from the unavoidable commutation process in the thyristor controlled rectifier.
Such notches can cause other equipment,
connected to the same mains, to malfunction and can cause extremely high
peak currents to flow in compensation
capacitors, with a high possibility of destroying such capacitors.
First generation
Single-conversion UPS:
Load
Mains
Second generation
Delta-conversion UPS:
Load
Mains
Load
1
1
2
1
1
2
2
2
1: Mains voltage
2: Mains current
Fig. 4
4
1: Mains voltage
2: Mains current
Fig. 5
1: Mains voltage
2: Mains current
Fig.6
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In fig. 5 we have the current from the
Single-conversion UPS and since this
current is nicely sinusoidal in shape there
is no resulting distortion of the mains
voltage. But it can also be seen that there
is a certain phase deviation between voltage and current, hence the power factor
is not unity, which is desirable for the
best utilization of the power grid.
Fig. 6 shows the „ideal“ UPS, the
Delta-conversion type.
As can be seen there is no current distortion or voltage distortion and voltage
and current are nicely in-phase, hence
unity power factor.
So far so good, but haven’t we made a
UPS with the losses of Double-conversion type now that we have two converters?
Not at all, this new system is much
more „clever“ than it seems at a first
glance.
Let us go through some different operating conditions and watch the power
flow, size and direction, during these different conditions.
Fig. 7 shows the nominal condition i.e.
there is no difference between mains and
output voltage, batteries are fully charged
and load is 100%.
The Delta inverter (1) is only supporting the mains current, which in this case
is equal to the load current (linear resistive load assumed). Since the „delta voltage“ across the transformer is zero it follows that the netpower from or to the
Delta inverter is zero.
Voltage 100%
100%
100%
Current 100%
100%
100%
Power 100%
100%
100%
Mains
0%
0%
1
2
Fig. 7
100%
100%
Current 115%
115%
100%
Power 100%
115%
100%
Voltage 85%
15%
Mains
15%
1
15%
2
Also the main inverter (2) is idling
since its regulated output voltage is exactly equal to the mains voltage.
So in the idealized form all power is
going directly to the load, nothing is converted, hence no losses. In practice there
are of course small losses from the idling
power circuitry, magnetic components
and fans.
In case that the load is not resistive but
also has a reactive or a harmonic part,
such reactive or harmonic currents are
supported by the main inverter since they
cannot be taken from the mains (this is
prevented by the way the Delta inverter
takes up the mains current).
Such reactive or harmonic currents will
increase the total losses slightly but efficiency is still exceptionally high.
In fig. 8 it starts to get
really interesting. Here
we have a situation with
under voltage on the
mains, in this case -15%
Since the output voltage must remain stable
and regulated to within
+/- 1%, it follows that
the Delta inverter via its
transformer must „add
Load
15% to the mains voltage“.
But where does this
additional power come
from?
It is simply taken from
the mains via the output
of the main inverter,
passed
backwards
through this inverter, via
the DC link and finally
forwards through the
Delta inverter to the
transformer.
This is a true Doubleconversion process with
related losses, but the
big difference here compared to traditional
Double-conversion is
Load
that it is only the delta
between input and output that is converted, so
if we f.ex. assume the
total losses in a traditional Double-conversion UPS to be 10%, and
Fig. 8
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100%
100%
Current 85%
85%
100%
Power 100%
85%
100%
Voltage 115%
15%
Mains
15%
15%
Load
1
2
Fig. 9
Voltage 100%
100%
100%
Current 110%
110%
100%
Power 110%
110%
100%
Mains
10%
0%
Load
10%
1
2
Fig. 10
assume that our two inverters together
have a similar efficiency, then it follows
that our total losses in the -15% mains
case will only be 0,15 x 10% = 1,5% because only 15% of the total power is converted.
At -10% mains the losses would then
be 0,10 x 10% = 1% and so on.
Fig. 9 shows the case of high mains
voltage.
Now the Deltainverter must „absorb
15% of the mains voltage“ to make the
balance.
In this case 15% of the power is passed
via the Delta inverter, via the DC link
and finally via the main inverter to the
load. Again a Double-conversion process, where the same loss considerations
as in the fig. 8 case apply.
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In fig. 10 we again have a nominal situation except that the battery is being
charged.
Here we see 110% power being taken
from the mains and since the load is not
taking more than 100% the remaining
10% is passed backwards through the
main inverter and absorbed in the battery as charging current.
There is an interesting „job sharing“
between the two inverters.
The main inverter just keeps syncronized to the mains and controls the output voltage in all operation modes. (In
battery operation its frequency is controlled by an internal frequency reference as
in all other on-line UPS).
The Delta inverter controls the input
power factor, the charging of the battery
by „importing“ more or less power from
the mains than necessary for supporting
the load, and finally it makes up for any
difference in voltage and curveform between the mains and the output voltage.
In the battery charging mode the main
inverter is passing the „excess“ mains
power into the battery, but the control of
the charging is done by the Delta inverter.
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Performance of the new system
In the following various performance
curves are shown, to prove the advantages of the new topology.
Fig. 11 shows the overall efficiency as
a function of load and mains within
±15%. It is seen that the efficiency is exceptionally high, the curve is flat and virtually independent of the mains voltage.
This all means low losses, also under non
ideal conditions.
Fig. 12 shows the input power factor
under similar conditions as in fig. 11.
Again we notice an extremely high
power factor of more than 0,99 in a very
wide operating range.
In fig. 13, just to avoid any misunderstanding as to whether this type of UPS
is on-line or not, output voltage is shown
during transitions of mains outage and
mains recovery.
As can be seen the output voltage is
unaffected by such transitions, proving
on-line capabillity.
Efficiency %
Delta-conversion
Double-conversion
Load %
Fig. 11
Input power factor
Comparison and conclusion
In fig. 14 a comparison between the
three UPS types is made. It is seen here
that the Delta-conversion UPS comes
close to and ideal “green” UPS, i.e. minimum energy waste and no mains pollution.
The Double-conversion UPS will certainly have a hard time among energy
conscious engineeers and customers in
the future, now that a true “green” UPS
is available.
It is also interesting to note what it
would take to make a traditional Double
conversion UPS match the Delta conversion UPS, just on the mains side qualities.
This is shown in fig. 15.
Even adding all this hardware which
costs a horrendous amount of money, the
Double conversion UPS will never be
able to match the efficiency of a Delta
conversion UPS.
One should be careful to believe in certain extremely high efficiencies claimed
by some vendors of double conversion
UPS.
These figures only apply in the by-pass
mode where there is no regulation of the
output voltage and hence the system is
an off-line system or may be it is an on-
Load %
Fig. 12
Mains
voltage
Output
voltage
Fig. 13
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line type, but then operated in the offline mode.
Some systems are claimed to be „intelligent“ and normally operated as offline, then if there are too many problems
with the mains they switch to on-line
automatically. But then it is probably too
late and the customer may have lost his
computer. Anyway, when such systems
are working in the on-line mode they are
not more efficient than they used to be,
so the whole manoeuvre seems to be to
mislead the customer with confusing
specs.
With the new 300E performance it is
understandable that competitors, offering Double-conversion UPS are terrified,
but it is still not very nice to mislead
customers!
Comparison chart
Basic properties
Doubleconv. UPS
Single-conv.
UPS
Delta-conv.
UPS
True On-Line function
Yes
Yes
Yes
True two-way filter finction
Yes
Yes
Yes
Input side harmonics
Yes >30%
No
No
Unity input PF
No
No, but can
be compensated
Yes
Energy losses, small systems
< 10 kVA
> 10-15%
< 8%
< 5%
Energy losses, large systems
> 10 kVA < 100 kVA
> 8-12%
< 5%
< 4%
Energy losses, very
large systems > 100 kVA
> 6,5-10%
< 4%
< 4%
Capability of running SMPS
load, without derating
Yes
Yes
Yes
Fig.14
DATAPOWER DP300E with Delta-conversion
UPS
Mains
Load
Mains
Power
factor
compensator
Harmonic
filter
12 pulse rectifier
Traditional UPS with Double-conversion
UPS
Load
Extra equipment necessary to
match input performance of Delta
conversion
Fig.15
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For more information call:
Tel: (800) 800-4APC - US & Canada
Tel: (401) 789-0204 - Worldwide
APC Corporate
132 Fairgrounds Road
West Kingston, RI 02892
USA
Tel:
(401)789-0204
Fax:
(401)789-3710
Internet:
apcinfo@apcc.com
PowerFax™:
(800) 347 - FAXX
APC Web site: www.apcc.com
APC Europe /
Silcon Power Electronics A/S
Silcon Allé
DK-6000 Kolding
Denmark
Tel:
(+45) 75 54 22 55
Fax:
(+45) 75 54 27 89
E-mail:
Info@silcon.dk
Homepage:
www.silcongroup.com
APC Asia / Pacific
Level 27 Northpoint
100 Miller Street
North Sydney, NSW 2060
Australia
Tel:
(+612) 9955-9366
Fax:
(+612) 9955-2840
Toll free technical support
1-877-287-7835 (1-877-2UPS-TEK)
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