A Modern UPS (and a bit of
history…)
Aalto, April 2016
Teemu Paakkunainen
Senior Application Engineer, Critical Power Solutions
Electrical Sector – Eaton Corporation
© 2013 Eaton. All Rights Reserved.
About Eaton
•
The company is founded in 1911
•
Customers in more than 175 countries
•
103,000 employees worldwide
•
Worldwide sales of 21.8 billion USD in 2012
•
Headquarters in Dublin, Ireland
UPS factory in
Finland
Key facts – From Fiskars to
Eaton Electrical
•
A centre of excellence in large UPS systems
•
Design, production and customisation of high
power UPS solutions
•
150 employees
•
UPS manufacturing since 1962:
Fiskars Elektroniikka
1962-1982
Fiskars Tehoelektroniikka
1982-1987
Fiskars Power Systems
1987-1996
Exide Electronics
1996-1999
Powerware
Eaton Power Quality
Eaton Electrical
2012-
1999-2004
2004-2012
4
Why a UPS?
In today’s world...
• Consumers demand 24/7 availability –
internet, on-demand video services, social
media, on-line shopping, e-mails etc.
• Interruption in a process can cause severe
loss of material in process industry – worth
of millions in worst case
• Some applications require continuous power
due to safety - air traffic controls, SOLAS,
hospitals, authority networks, military, etc.
• 1 hour of downtime can cost up to 10’s of
millions in lost revenue for a credit card
company or other financial institutes
© 2013 Eaton. All Rights Reserved.
5
When things go south…
Manhattan, NYC, October 2012
Hurricane Sandy
© 2013 Eaton. All Rights Reserved.
6
1 UPS Topologies
Uniterruptible Power Supply (UPS) is:
Combination of convertors, switches and
energy
storage
devices
(such
as
batteries), constituting a power system
for maintaining continuity of load power
in case of input power failure
NOTE Input power failure occurs when voltage and frequency
are outside rated steady-state and transient tolerance bands
or when distortion or interruptions are outside the limits
specified for the UPS.
Source: IEC 62040-3 Edition 2.0 2011-03
© 2013 Eaton. All Rights Reserved.
7
1.1 Stand-by (off-line)
topology
Input
Stand-by topology comprises a battery
charger, a d.c. to a.c. converter,
generally a unidirectional inverter and
a UPS switch.
In normal mode of operation, the load
is supplied with a.c. input power via
the UPS switch.
Output
When the a.c. input supply is out of
UPS preset tolerances, the UPS unit
enters stored energy mode of operation,
and the load is transferred to the
inverter
directly
or
via
the UPS
switch.
© 2013 Eaton. All Rights Reserved.
8
1.2 Line-interactive topology
Input
Line-interactive topology comprises a
bi-directional a.c. to d.c. converter,
generally a bidirectional inverter and
an a.c. power interface.
Output
In normal mode of operation, the load is
supplied with conditioned power via a
parallel connection of the a.c. input
and the UPS inverter. The inverter or
the power interface is operating to
provide
output
voltage
conditioning
and/or battery charging. The output
frequency is dependent upon the a.c.
input frequency.
In stored energy mode of operation the
9
switch disconnects the a.c. input supply
© 2013 Eaton. All Rights Reserved.
1.3 Double Conversion Topology
Input
Double-conversion
comprises
an
a.c.
converter, generally a
and a d.c.
to a.c
generally an inverter.
topology
to
d.c.
rectifier,
converter,
In normal mode of operation, the
load is continuously supplied by
the rectifier/inverter combination.
Output
When the a.c. input supply is out
of UPS preset tolerances, the UPS
enters
stored
energy
mode
of
operation
where
the
battery/inverter
combination
continues to support the load
© 2013 Eaton. All Rights Reserved.
10
1.4 UPSs in various sizes
(<1kVA – 1200kVA)
© 2013 Eaton. All Rights Reserved.
11
2 Main components (static
double conversion)
Input
1. RECTIFIER - Rectifies
incoming mains into DC
to provide energy for
and
typically
also
charging.
1
3
4
2
Output
AC-voltage of
that is used
the inverter
for
battery
2. INVERTER - Converts the DC voltage
from DC-link into clean sinusoidal AC
voltage and regulates the UPS output
voltage, feeds energy for the load.
3. CHARGER - Typically used to charge,
and discharge, batteries thus other
DC sources can be used as well such
as flywheel (kinetic storage) or
ultra-capacitors. Converters voltage
level of the DC source to suitable
level for the inverter and vice
versa. In older designs the battery
was directly coupled into DC-link.
4. BYPASS – Circuit bypassing the UPS12
© 2013 Eaton. All Rights Reserved.
3 Rectifier
• Rectifies AC-voltage of incoming mains into DC
that is used to provide energy for the inverter
and typically also for battery charging.
• Regulates the DC-link voltage
suitable level for inverter.
to
keep
it
in
• Often rectifier output directly connected to
batteries and then rectifier output voltage is
controlled to provide correct charging voltage /
current for batteries.
• Sometimes galvanic isolation required between AC
and DC, in industrial applications for example (DC
ground fault tolerant design)
• Various designs exist for single and three phase
units
• Technological
© 2013 Eaton. All Rights Reserved.
development
aims
for
13
higher
3.1 Thyristor (SCR) rectifier
(legacy)
(+)
•
Rather simple
circuits
•
Traditional and considered as robust
and is therefore often specified for
industrial UPS’s.
•
Typically regulated ”floating”
link (buck converter)
•
High input current harmonics (2- and
6-pulse)
•
Considerable level of ripple in the
output (DC link), requires more
filter capacitors
•
Low input power factor, especially
when regulating DC link to lower
level
(beginning
of
battery
charging)
(-)
(+)
3~
(-)
3~
30°
driver
and
control
DC-
•
Often tuned passive filters used in
front to correct harmonics and power
© 2013 Eaton. Allfactor
Rights Reserved.
14
•
Harmonics, line-notching and filter
3.2 IGBT rectifier (modern)
(+)
(+)
L
3~
N
(-)
N
(-)
•
Single or three phase AC-to-DC
switching power transistors
•
Regulated double sided or floating high DC-link voltage, allows
transformerless inverter
•
High switching frequency, less ripple, less capacitors needed
and smaller inductors
•
Low input current harmonics
•
Power factor corrected – practically unity from rather low load
levels
•
Bi-directional,
algorithm)
can
booster
feed
to
© 2013 Eaton.energy
All Rights Reserved.
circuit
mains
(up
using
to
fast
control15
3.3 Rectifier features
• New technology rectifiers have unity input power
factor and low level of current harmonics
• This minimises the amount of current needed for
UPS and allows savings in installation (breakers,
cables, transformer, generator)
• IGBT rectifiers often have wide input frequency
range (45...65Hz) and can operate with low mains
voltage (partial load levels especially)
• Rectifiers have various features such as input
current limitation, power sharing with battery,
ramping functions, start delays etc. to better
match the UPS with upstream electrical systems and
limitations
• Same features can be used for additional savings
in installation or to improve reliability by 16
avoiding nuissance tripping, overheating etc.
© 2013 Eaton. All Rights Reserved.
4 Inverter
• Converts DC-voltage into (pure sinusoidal) ACvoltage that is used to provide energy for the
loads powered and protected by a UPS.
• Regulates the UPS output voltage to keep it in
suitable level for loads.
• Various designs exist for single and three phase
units
• Old UPS inverters were using output transformers
for galvanic isolation and voltage conversion
• Modern inverters have high switching frequency
with IGBT’s and LC-filter using transformerless
design throughout UPS power ranges
• Sometimes
galvanic
isolation
required
today
between
DC
and
AC
output,
in
industrial
applications for example, or by conservative data17
© 2013 Eaton. All Rights Reserved.
4.1 Inverter Operation
•
•
•
•
Inverter IGBTs produce Pulse Width Modulated switching pattern
to output of the inverter leg
LC-filter smoothens it into a perfect sinewave (<1% THD)
Produced clean sinusoidal voltage is connected to load
- Inverter control algorithm keeps voltage amplitude (L-N) and
waveform while load level varies
- Possible neutral current due to harmonics or unbalanced
loading is circulating through
the ”neutral leg” or balancer of the UPS
Eaton. All Rights Reserved.
Inverter synchronises to© 2013mains
and regulates output frequency.
When mains frequency goes outsideof limits, inverter frequency
18
4.2 2-level vs 3-level topology
A typical UPS power electronics main circuit with
IGBT’s, 2 level topology
•
High frequency switching
•
No 50Hz transformers
Rectifier
Battery
Inverter
Circuit
© 2013 Eaton. All Rights Reserved.
Static
Switch
19
4.3 2-level vs 3-level topology
High efficiency UPS power electronics main circuit
with IGBT’s, 3 level topology
•
High frequency switching
•
No 50Hz transformers
•
More components and increase cost
•
Lower losses due to lower switching voltage
•
Different peak efficiency point (switching vs
conduction losses)
Rectifier
Battery Circuit
© 2013 Eaton. All Rights Reserved.
Inverter
Static Switch
20
4.4 2-level vs 3-level topology
© 2013 Eaton. All Rights Reserved.
21
5 Charger
• Typically used to charge, and discharge, batteries
thus other DC sources can be used as well such as
flywheel (kinetic storage) or ultra-capacitors.
• Converts voltage level of the DC source to
suitable level for the inverter (DC-link) and vice
versa. Operates as DC-DC buck-boost converter
• In some (older) designs the battery is directly
coupled
into
DC-link
and
rectifier
performs
battery charging.
• Separate charger (battery converter) gives more
freedom in selection of DC-link voltage, suites
better for transformerless UPS designs
• Since battery is not directly coupled to DC-link,
it is not subject to DC voltage ripple created by
unbalanced and non-linear loads
22
© 2013 Eaton. All Rights Reserved.
5.1 Charger Operation
• DC-DC
converter
has
IGBT’s,
inductors and filter capacitors.
• Some models have ”common mode
choke”
removing
switching
BATTERY CONVERTER &
frequency
components
from
COMMON MODE CHOKE
battery connection enabling the
use of same battery for multiple
• units.
When charging the battery, converter operates
typically in buck mode
• When
discharging,
the
typically boost mode
converter
operates
in
• Charger is limiting the charging current for the
batteries, typically 0,1...0,15 x C10 (C10 =
nominal 10 hour Ah rating of the battery)
• During battery
DC-link
• Typically
operation,
rectifier
the
© 2013 Eaton. All Rights Reserved.
and
charger
charger
can
regulates
operate
23
6 Bypass
• A circuit bypassing the UPS converters in case of
a failure, overload, over temperature or other
anomaly.
• Also
used
to
provide
more
fault
capability for downstream short-circuits
clearing
• Some models use bypass to energise the load during
start-up, especially with multi-module systems
• Inverter is synchronised to bypass voltage
enable smooth no-break transfer to bypass mode
to
• Asynchronous transfer to bypass is typically done
with
small
break
(4... 10 msec), if feature in use
• Most designs with continuous duty static swtich,
some older products use momentary static switch
© 2013 Eaton. All Rights Reserved.
24
6.1 Continuous duty static
switch
BACKFEED PROTECTION
STATIC SWITCH
uR FUSES
• Static switch is made with thyristors as 3-phase (1phase) AC-switch
• Thyristors are thermally rated to continuously feed full
load current
• Large UPS have fuses in series
protect
them
from
excessive
downstream short-circuits
with thyristors to
overcurrent
during
• Backfeed protection required by legislation, must be
opened when mains is removed to prevent leaking
hazardous voltages upstream UPS system (safety of
maintenance personnel)
• Thyristor modules used in small, medium and large units,
25
hockey pucks in very biggest static switches
© 2013 Eaton. All Rights Reserved.
6.2 Bypass requirements and
IEC62040-1:2008 Amendment
1:2013
• UPS manufacturers need to declare ICW or
ICC
• Rated short-time withstand current (ICW):
r.m.s. value of short-time current, declared by
the UPS manufacturer, that can be carried without
damage under specified conditions, defined in
terms of a current and time.
• Rated conditional short-circuit current (ICC):
r.m.s. value of prospective short-circuit current,
declared by the UPS manufacturer, that can be
withstood for the total operating time
(clearing time) of the short-circuit protective
device (SCPD)
under specified conditions.
NOTE The short-circuit protective device may form
an integral part of the UPS or may be a separate
unit.
© 2013 Eaton. All Rights Reserved.
26
7. UPS main circuit example –
modular UPS
© 2013 Eaton. All Rights Reserved.
27
8. Large 3-phase UPS (600kVA)
© 2013 Eaton. All Rights Reserved.
28
9. Batteries
• Batteries are crucial part of a UPS system
• Batteries provide the energy for inverter during a
mains failure
• UPS back-up time depends on size, and health, of
the battery
• Typical back-up time is over 5 minutes, 8 - 15
minutes most commonly
• Various battery technologies do exist in the
market, but still lead acid battery is the most
common solution
• Other battery
Lithium etc.
technologies
are
NiCd,
SoNick,
• Other battery technologies are more expensive thus
limiting demand
© 2013 Eaton. All Rights Reserved.
29
• Beside batteries, other forms of energy storage
9.1 Batteries – Lead Acid types
Flooded
battery
AGM battery
© 2013 Eaton. All Rights Reserved.
Gel battery
30
9.2 Batteries – Nickel Cadmium
Advantages:
• Very good high power rating and low internal
resistance
• Wider temperature range
• Insensitive against deep discharge
• Long shelf life
• Insensitive against misuse and optimised for
harsh operating conditions
• Long lifetime (up to 20 years)
Disadvantages:
• 2,5 – 3,5 times higher cost per Ah
• Higher number of cells in series (1,2V vs 2,0V cell
voltage)
• High charging voltage and low cut-off, wider voltage
operation range for electronics
© 2013 Eaton. All Rights Reserved.
31
9.3 Batteries – Lithium-ion
Polymer
Advantages:
• Wider ambinet temperature range
• High number of cycles, >5000 with 70% DoD
• Gives 94% energy with 10 minute discharge
• Lighter and smaller than lead acid
• Fast recharge after full discharge
• Long life, up to 15 years @ 25°C
Disadvantages:
• Safety concerns
• Requires control electronics
• Maximum discharge can be limited
• Expensive, 3 – 6x cost of lead acid battery. Not yet
commonly used with UPS’s
• In future re-use of automotive lithium batteries seen
as possible scenario
© 2013 Eaton. All Rights Reserved.
32
9.4 Super(Ultra)capacitors
Advantages:
• Excellent for cyclic operation, peak shaving etc. due
to >1 000 000 cycles
• Works for high discharge current rates, high power
applications
• Fast recharge after full discharge
• Long life, up to 20 years @ 30°C
• Storage up to 2 years
• Maintenance free
Disadvantages:
• Back-up only for some seconds
• Cyclic use requires (active) balancing
• UPS needs a wide DC voltage window to get most of
energy
• Expensive, considered for applications where lead
© 2013 Eaton. All Rights Reserved.
33
9.4 Flywheel
Advantages:
• Excellent for cyclic operation, peak
shaving etc.
due to “unlimited” cycles
• Wide operation temperature range, 20°C to +40 °C
• High power density, compact size and
light weight
• Constant DC output voltage during
discharge
• Long lifetime, up to 20 years and low
(but expensive) maintenance
Disadvantages:
• Back-up time only for some seconds
• Some data centre customers prefer
flywheels, also used
for medical and industrial
© 2013 Eaton. All Rights Reserved.
34
10 Data center efficiency and
UPS
© 2013 Eaton. All Rights Reserved.
35
10.1 Data center UPS efficiency
– Energy Efficiency Enhancing
Operation Modes
• For Tier II, III and IV data center electrical
infrastructure, UPS systems with N+1, N+N, 2(N+1) level
of redundancy are used
• As redundancy increases, the UPS load levels during
normal operation decreases and reduces overall system
efficiency
• Typical load levels for UPS in a data center are about
25-30%
© 2013 Eaton. All Rights Reserved.
36
10.2 Data center UPS efficiency
– VMMS
• Load is concentrated to required amount of power modules
(compare to multicore processor) and other power modules
are in suspend state with minimal idle losses
• System automatically starts and suspends power modules to
optimise efficiency
• Suspended power modules are rotated motnhly basis to have
equal running hours
37
© 2013 Eaton. All Rights Reserved.
• Stress on components is less in suspend state, resulting
10.3 Data center UPS efficiency
– ESS
• If the mains conditions allow and no active
power conditioning is needed, all power modules
can be suspended and load is supported via
static bypass
• System continuously monitors mains and output voltage and
reacts in less than 2 ms in case of interruption
© 2013 Eaton. All Rights Reserved.
38
10.4 Data center UPS efficiency
Improved energy efficiency
especially at typical load
levels resulting better PUE
and savings in opex
© 2013 Eaton. All Rights Reserved.
39
11 Evolving UPS technology
© 2013 Eaton. All Rights Reserved.
40
11.1 Cost reduction points due
to evolved UPS
© 2013 Eaton. All Rights Reserved.
41
Contact: TeemuPaakkunainen@eaton.com
© 2013 Eaton. All Rights Reserved.
42