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Uninterruptible Power Supply Systems


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Recently, there has been a sharp increase in a number of so-called critical equipment of electrical power. Both separated units and complex objects, whose normal operation is strongly influenced by the parameters of electrical power, are included in this equipment.
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Recently, there has been a sharp increase in a number of so-called critical equipment of
electrical power. Both separated units and complex objects, whose normal operation is
strongly influenced by the parameters of electrical power, are included in this equipment.
The critical equipment includes the following objects:
Personal computers (PC) and computer systems;
Electrical equipment for continuous technological processes;
Hospitals and other medical objects with modern furnishing;
Communicational system and equipment;
Security services and alarm systems;
Land aircraft equipment;
Military objects;
At contemporary practice, the normal operation of critical equipment is secured by separated
parts of equipment or whole systems. This equipment is fed by electrical energy delivered
from public distribution electrical systems with a common level of power quality and with
special methods and means for improving the electrical supply quality to a level required for a
the normal operation of the critical equipment. These special methods and means applied in
devices are received popularity as “UPS” (Uninterruptible Power Supplies).
Това наименование първоначално се свързва със строго определена структура на
устройствата, но с развитието им то се променя, като се разширява и до системи -
Uninterruptible Power Supply Systems (Griffith, 1989: Emadi, 2005: Gurrero, 2007).
Users more often associate the installation of UPS to a necessity to secure an operation of a
responsible consumer at a drop off of the source voltage. Different changes in the quality of
the source voltage are possible in practice. More often these changes are:
1. A drop off for a long time Fig.10.1.
Fig.10.1. A drop off of the source voltage for a long period of time
2. A drop off for a half-period or period of the source voltage Fig.10.2.
Fig.10.2. A drop off of the source voltage for a half- period or a period
3. A decrease of the source voltage value below a permissible one Fig.10.3.
Fig.10.3. A decrease of the source voltage value below a permissible one
4. An increase of the source voltage value above a permissible one Fig.10.4.
Fig.10.4. An increase of the source voltage value above a permissible one
5. A change of the source frequency Fig.10.5.
Fig.10.5. A change of the source frequency
6. Transient overvoltages Fig.10.6.
Fig.10.6. Transient overvoltages
7. Transient decrease of the voltage value Fig.10.7
Fig.10.7. Transient decrease of the voltage value
8. Non-periodical disturbances put over the source voltage waveform Fig.10.8.
Fig.10.8. Non-periodical disturbances put over the source voltage waveform
9. An increase of non-sinusoidal coefficient of the voltage waveform above the
permissible one Fig.10.9.
Fig.10.9. An increase of non-sinusoidal coefficient of the waveform above the permissible one
Of course, no all of the abovementioned disturbances in the quality of the source voltage
affects in the same way different consumers (Rasmussen, 2003). The affects depends on the
consumer type - whether it uses directly AC electrical power or power is preliminarily
transferred into DC one in a separated source block (as it is in PCs), also, whether this
transmission is connected also with a stabilizing of output voltages of this block, etc. Besides,
it is worthy to be known that there are also other ways to protect the consumer from a part of
these changes. For example, stabilizers of AC voltages exist to eliminate number 3 and 4;
some companies produce filters protecting the consumer to avoid distributions with number 6,
7, 8 and 9. It has not to look at UPS as a universal means to protects a consumer from all
possible changes because it will be clarified further down that the protection possibilities
depends on the stricture and the way of implementing the UPS itself. Some of the systems
secure supply at a drop off of the electrical source but they do not resist other changes.
Uninterruptible power supplies, whose output voltage has a square waveform (more often of a
low power to supply PC), are yet offered at the Market.
And yet, structures to implement systems capable of eliminating all changes in the quality of
the source voltage, which would be unpleasantly affects a responsible consumer, exist.
When it is necessary to secure uninterruptible power supply for a separated responsible
consumer, UPS intended only for this consumer and with technical data compatible with the
specialty of the consumer is used. Such cases are, for example, these of electrical supply of a
PC or separated telecommunication station.
Uninterruptible power supply for several different consumers may be secured in three ways
centralized, distributed or combined ways. Fig.10.10 shows the centralized topology for an
uninterruptible power supply. A special feature for this version is that all servers are supplied
from a single UPS, as well as all computers, for example, at marketing room are secured also
from a single UPS. Here, reliability is lower than in the other topologies but the system price
is also lower.
Fig.10.10 Centralized topology
Source: : Powerware. Easy UPS solutions for IT systems.pp.4 5.
Fig.10.11 illustrates the distributed topology of uninterruptible power supply. In it, each
server and each computer in the marketing and selling rooms are supplied from a separated
UPS-system. This topology is characterized by a higher reliability but also very often by a
higher price.
Fig.10.11. Distributed topology
Source: : Powerware. Easy UPS solutions for IT systems.pp.4 5.
The third topology of mixed solution for uninterruptible power supply is shown in Fig.10.12.
Regarding the servers this topology is centralized one and regarding the computers
distributed one. Of course, the opposite variant is also possible the servers distributed, and
the computers centralized. From the point of view of reliability and price this topology is at
the middle of the previous two.
Fig.10.12. Mixed topology
Source: : Powerware. Easy UPS solutions for IT systems.pp.4 5.
По статистически данни (Powerware, 2008) при вече инсталираните UPS при IT
systems се наблюдава следното приблизително разпределение: 45% - централизирана
топология; 35% - разпределена и 25% - смесена.
The question about uninterruptible power supply of individual homes is very often put in
practice. Proprietors, designers and design performers are usually considered the aspect of
UPS after all the work upon the electrical installations of the building has been finished. In the
author’s opinion based also in his experience, settling of this issue has to be a part of an initial
design for the electrical installation to be designed in an appropriate way and also to be
located rooms or spaces for the elements of the supply. An idea about UPS for an individual
home is shown in Fig.10.13.
First circuit Second circuit Third circuit
Fig.10.13. An idea about uninterruptible power supply for an individual home
As it is seen, all the electrical power consumers at the home are separated in three circuits,
and also, their tentative powers are shown.
In the first and the most responsible circuits, for example, the following equipment is
connected: lightening, security system, audio and video systems, computer, and other
informational and communicational systems. Thus, the requirements for the parameters of
UPS1 are considered to this equipment. For example, the longest duration of operation may
be required after a drop off of the source voltage, also zero switching time and thoroughly
separation of the disturbances in the source voltage may be required. The first system of UPS
may be of double conversion type, which will be examined further down.
In the second circuit all household appliances may be connected, such as fridge, cooker,
laundry, etc. Obviously, the requirements for UPS2 may be lowered. UPS may be of another
type. After a voltage drop off, the household appliances continue to operate till completion of
their functions for example, food preparation, etc.
Heating and air-conditioning are included in the third circuit. It is initially supplied from the
source voltage and after the drop off of the voltage the circuit may stop to operate for a short
time. After this time, a reserve electrical supply has to be switched on diesel aggregate, and
then sing the source transfer switch 3, the heating and air-conditioning to be supplied again.
Using the source transfer switches 1 and 2, the supply of the other two circuits can also be
passed to the diesel aggregate at the condition that the source voltage is yet missing and the
capabilities of the two UPS are exhausted.
Control of all elements of the supply of the home is using a common microcomputer system
and with parameters, which are set and may change by the proprietor.
Topics about different energy sources, others than the network, are examined in Chapter 9.
Basic Schemas and Their Indicators
According to the accumulator and the means of energy conversions, the systems of
uninterruptible power supplies are in general classified as (Karve, 2005; Cottuli, 2008):
Static ones;
Dynamical ones.
In static UPS, accumulation of energy is made in electrochemical accumulators (secondary
sources) and also the required conversions of electrical power are performed by semi-
conduction converters, which do not contain moving parts and are classified as static ones.
Dynamic UPS are realized using converters with moving parts. Energy in them is stored for a
short time as kinetic energy into moving flywheels. The required energy conversions are
performed in electrical machine. Long-term operation of the dynamic UPS at the drop off of
the electrical supply is secured by motors with inner combustion.
Technical solutions of implementation of UPS have been developing together with the
development of the consumers requiring such a supply. From the beginning of 1970, so-called
on-line UPS shown in Fig.10.14 have found implementation in securing big calculation
Fig.10.14. Structure of on-line UPS
Here, the inverter is fed by the rectifier with DC energy and operates continuously feeding the
load. The rectifier secures also energy to charge the battery. Static bypass may transfer the
supply of the consumer directly to the AC input (to the supply network) without an interrupt
in the case of failure in the main channel or in the processes of initial switching on of the
consumer, when it consumes a high current. It is seen that the structure does not exactly
correspond to its name. Therefore, some authors make more precise the terminology of on-
line as inverter, which feeds continuously the load and connected in series with the network.
At the beginning of 1980, so-called off-line UPS shown in Fig.10.15 have been developed in
opposition to on-line ones.
АС input
inverterbattery charge
Fig.10.15. Off-line UPS topology
The term off-line is used rather as an opposite one to on-line name of the previous topology
because here the term off-line should be understood it as parallel connection of the inverter to
the network. The inverter does not operate continuously, yet it is in a standby mode. The
consumer feeds from the inverter only in the case when the voltage of the AC input leaves the
permission range in particular when it misses. Functions of the block marked as filter include
not only filtering but also, in some systems, stabilizing the value of the voltage passed to the
load. Here, the term off-line also does not reflect the nature of the UPS system.
Development of mini and micro computers, as well as telecommunication systems, has leaded
to invention of new schematic solutions in the systems securing their uninterruptible supply.
The new standard of International Electrotechnical Commission IEC 62040-3 and its
European equivalent ENV 50091-3 currently define three topologies of UPS systems
(Karve, 2000; Solter, 2002; Beaudet, 2005):
passive standby;
line interactive;
double conversion.
The passive standby version shown in Fig.10.16 reminds a lot of off-line topology. Its features
are as follows:
Mode when the source voltage presences load is continuously fed by the AC network
through a filter, which may have also stabilizing functions. The standard does not completely
clarify the stabilizing functions of the block but it mentions that a ferro-resonant stabilizer
may be included in it. The inverter is in passive-standby mode. The battery is in charging
Mode when the source voltage misses when the source voltage leaves the permissible limits,
the consumer is switched to the supply of the inverter output. The switching has to be
performed in less than 10ms using a switch. This mode continues either to the moment of
battery discharge to a permissible level or to the moment of the appearance of the source
voltage within the defined limits.
АС input
battery charge
Mode at a presence of
the source voltage
Mode at an absence of
the source voltage
Fig.10.16. Passive stand-by topology
Advantages of this topology are: simplified structure, low price, small volume and weight.
Disadvantages are: dependence of the voltage supplying the load in normal mode on the
disturbances of the source network; sometimes the switching time appears to be long for the
consumer; frequency of the source voltage supplying the consumer can not be regulated. The
topology is applied in low powers below 2kVA. It can not be used as a frequency converter
for transition between networks with different voltage standards.
Presence of bidirectional converter is typical for line interactive configuration shown in
The standard defines three possible modes of operation for this topology, as follows:
Mode at a presence of the source voltage the consumer feeds from the source voltage, while
the battery is charged through the bidirectional converter operating as AC/DC converter;
Mode at an absence of the source voltage when the source voltage leaves its permissible
limits, the consumer feeds from the battery using the converter operating as DC/AC converter.
The static switch breaks off the connection to the network to isolate the converter output from
Bypass mode some systems of this type can be provided with a possibility for a manual
transferring of the supply of the consumer directly only to the source network in case of a
system failure.
АС input
static switch
converter ~=
Mode at a presence of
the source voltage
Mode at an absence of
the source voltage
Fig.10.17. Line interactive topology
Advantages of the line interactive configurations are: approximately the same price as this of
the second topology and lower than the first topology price. Disadvantages are: there is no
thorough isolation of the consumer from the source network and the consumer is affected by
the disturbances of the source voltage; there is no possibility to regulate the frequency of the
voltage supplying the consumer. This topology implementations are in average power
consumers to 10 kVA, which do not require source voltage with frequency different from the
source one.
A special feature of double conversion topology shown in Fig.10.18 is the supplying of the
consumer always from the inverter output.
For double conversion topology, the standard defines three modes of operation:
Mode at a presence of the source voltage the consumer is continuously fed from the inverter
output using a conversion of AC source voltage first time into DC by the rectifier and second
time into AC. The battery is in charging mode.
Mode at an absence of the source voltage when the source voltage leaves its permissible
limits, the consumer feeds again from the output of the inverter receiving energy from the
Bypass mode this mode is secured automatically by the static switch in several cases. The
first is in the case of failure in the main channel, the second case is in transient increase of the
consumer current (initial turning on or overloading during operation), the third case is in
depletion of battery capacity.
AC input
static switch
(static bypass)
battery charge
АС input
Connection if
separated bypass
input is not available
manual bypass
Mode at a presence of
the source votlage
Mode at an absence of
the source voltage
bypass mode
Fig.10.18. Double conversion topology
Almost each system of this type is provided with a possibility for a manual bypass in the case
of a failure in the rest part of the system.
Advantages of the double conversion are: complete isolation of the load from the disturbances
in the source voltage in normal mode; wide range of a change of the source voltage by a
precise stabilizing of the supply voltage to the consumer; precise regulation of the frequency
of the output voltage and a possibility to use the topology as a frequency converter; there are
no transient processes at switching from the network supply to the inverter supply or in
contrary. Disadvantages are: high price, in some cases reduced efficiency coefficient due to
the double conversion of energy. The UPS, implemented using this topology, are almost every
time used in high powers above 10kVA up to several MVA and at the need of frequency
After the examination of the standard three topologies has been made, it appears that in some
of them elements and functions of the sooner used terms on-line and off-line may be found.
Nevertheless, these terms are not recommended to be used because they are considered not to
reflect the nature of the performed functions and capabilities of the corresponding system.
Besides these basic blocks determining the name of the topology, UPS systems also contain:
systems for control, regulation and diagnostic of the converters, systems for an appropriate
temperature mode, interface and software, system to communicate with the staff performing
prevention measurements or repairing, systems and software for telecommunicational
connections with the producer. So, as a whole, the UPS system is a complex device that is
usually distinguished with a very high reliability. In spite of all, failures are possible in the
system, which implies the necessity to take additional measurements in extremely responsible
consumers, such as hospitals and hospital rooms, control of vehicles, etc.
Fig.10.19 displays a dynamic UPS where DC motor 6 motions electrical generator 5. DC
voltage to supply the motor is generated from the source network by rectifier 8. When the
source voltage drops off, the DC voltage is maintained by the battery 7, which is charged
from the source network 1 using rectifier 8.
When the source voltage drops off, consumers 9 will continue to receive supply from the
generator without an interrupt. In this mode switch 2 is also provided. The switch turns off
when the drop off of the source voltage appears not to pass energy to other consumers.
Manual bypass is also shown in the figure with non-marked circuit-breaker. It is used when
service procedures or prevention measurement of the UPS are taken.
Fig.10.19. Dynamic UPS system
Choosing an appropriate uninterruptible power supply for a consumer, technical data and
parameters given at the producers manuals and datasheets have to be known very well. This
knowledge is necessary for one to be able to choose the most appropriate system for ones
purpose without unnecessary given more money and also to avoid some misunderstandings
and conflicts. The technical data are usually divided into groups.
Technical data concerning the output:
Output power
It is desirable that the producer shows two values of this parameter active power in
Watts and total power in VA. For example, active power 24kW, total power 30kVA.
Load power factor is also usually shown and the type of load more often load power
factor from 1 to 0.8 and inductive type of load.
Output voltage
If the system is a three-phase system, both phase-to-phase and phase voltage values are
indicated. For example, 380/220V, 400/230V, 415/240V. Sometimes, only the value of
phase-to-phase value may be shown for example, 380/400/415V. Some producers
make their configurations according to the client’s choice. Whether a neutral wire is
taken out or not has to be also indicated.
Accuracy of maintaining the output voltage
It is usually shown in static mode for example, 1.5%, and the mode is indicated.
Sometimes a dynamic parameter may be shown transient voltage stability for
example, < 10 % under a 100% change of load. The best producers indicate also
transient time for example, transient time 2 mS.
Accuracy of maintaining the phase angle among the three voltages
It is given only by several companies for example, phase angle accuracy 3.
Total harmonic distortion THD of the output voltage
It is desirable to be indicated also in what type of load the THD is listed. For example,
THD < 2 % in linear load case and THD <5% in non-linear load.
Frequency of the output voltage
It is usually 50/60 Hz with probability to choose. Some producers also indicates whether
a synchronization to the mains exists.
Accuracy of maintaining the output frequency
A value under a full loading of the output is obligatory to be indicated for example,
0.5 Hz or in percentages for example, 1%. Also, the value in free running may be
shown for example, 0.05 %.
Output overloading possibility
This datum is not given by all producers but it is good for the consumer to take it in
mind when choosing the system regarding its load. For example, possible overload of
150% for 30 seconds, 125% for 10 minutes and 110% for 1 hour.
Possibility for parallel operation of the output with other systems
It is given very rarely by single producers and it is mentioned the kind of other systems
with which parallel operation is possible.
Technical data concerning the input:
Value of the input voltage
In three-phase system, both phase-to-phase and phase voltages are shown 380/220V,
400/230V, 415/240V. Only the phase-to-phase voltage may be indicated
380/400/415 V. The type of the source network is obligatory to be shown three
wired (three-phase) system or four wired (three phase and a neutral one) system.
Range of change of the input voltage
It may be shown for the phase-to-phase voltage in values for example, 340 440 V.
It may be indicated in percentage for example, 20 % from the value of the input
Frequency of the source voltage
It may be given in two ways as a value of the frequency and as a percentage of its
change (for example, 50 Hz 10 % or 60 Hz 5%) or as a range of it change (for
example 48-62 Hz).
Power factor
It is extremely important parameter, which determines the behavior of the whole
uninterruptible power system in respect to the source network (Blooming, 2008). This
parameter however is not shown by all producers. Its minimum value is usually
indicated for example, > 0.96. Some companies show lower value, for example, 0.7,
and they offer additional purchase of an active power filter to correct this value up to
Total harmonic distortion of input current THDI
It is shown by very few producers, for example, THDI < 3 %.
Technical data for batteries:
Battery type
It is shown by almost all producers.
Expiring period of the batteries
It is usually 5 or 10 years with a possibility to be chosen.
Recovery battery time after a discharge
It is usually given in dependence on the discharge time for example, 10 times of the
discharged time.
Number of cycles charge/discharge
For example, 500 cycles. Not all producers indicate this parameter.
Common technical data for the whole system:
Type of the system of uninterruptible power supply (technical decision)
Above examined topologies, as double conversion, etc., are had in mind. This
parameter also is not indicated by all companies.
Transient time at a drop off or at an appearance of the source voltage
It is usually less than 10ms for example, 2ms. In some technical decisions, the
experts know that this time is 0 for example, in double conversion topology,
therefore, if the producer is shown the type of the system at the manual he is not
obliged to specify also and this time.
Backup time
This is an extremely important parameter for the user. It is given in dependence on the
battery type 5 or 10 year expiring period. Almost all producers indicate a value
under a 100% loading of the output, for example, 10-12 minutes and 10 year battery.
Only few producers specify the load type linear or non-linear and its power factor.
Common efficiency coefficient
It is usually shown in full loading of the output for example, 93%. Several values
dependent on the output loading may be given in very few occasions.
Level of acoustical noise of the system
The distance may also be shown for example, 60 dB at 1 m. It is usually given for a
full loading of the output, but it also may be shown as a range dependant on the
loading for example, 50 65 dB.
Ambient temperature
Almost all producers give it as a range for example, 0 45 С.
Air humidity of the environment
For example, 15 - 80 % usually without condensation.
Size and weight
The three sizes and the common weight are usually indicated. They may also be given
as separate data for the battery cabinet if it is separated.
Correspondence to international standards
The standard numbers, in accordance with which the experiments have been
performed and to which the correspondence is found, are obligatory to be shown.
Usually, these are two types of standards regarding the technical safeness and the
electromagnetic compatibility.
Technical data concerning communication and software:
Types of communicational interfaces are given for example, RS 232, also data and
possibilities of the software are shown. Usually this is specialized production software.
It advantages for the user are listed, also its possibility to operates with different
operational systems, etc.
As it is seen, summary analysis of all technical data, comparison among different producers
and the decision of the choice are a complex topic, which is very often impossible to be
resolved without a consultation to a specialist in the field of Power Electronics. Besides, not
all data presented in the advertising production materials and additional queries and
specifying are necessary. In all cases, the possibilities service measurements are also analyzed
presence of an official distributor, time of removing the failure, warranty, etc. The
producers almost never show data concerning reliability parameters such as average time to
failure, etc. It is possible to make an additional analysis and comparison of data for already
installed and operating systems at other users for a particular company. Here, the subjects of
price and other economical indicators are not discussed, but additionally to the technical data
they are also important at taking a final decision.
Each of the above described technical parameters is connected to a particular technical device
(basic block) from the UPS system and additional data for some of the parameters are given
further down at the description of the specialties of the separated blocks.
Съвременните изследвания в областта на UPS systems се провеждат в следните
1. по отношение структурата и силовата схема , като например (Kamran, 1998;
Vazquez , 2002; Ming, 2003).
2. по отношение управлението и регулирането, като например (Mattaveli, 2005;
Pai, 2006).
3. по отношение източника на енергия (Tao, 2008).
Methods to Increase the Reliability
Source transfer switch (STS) is a device, which switches critical AC consumer between two
independent sources on one another in dependence on their transient state or on a command
passed by the user. The two sources are very often two undependable UPS systems see
Fig.10.20 (MGE UPS Systems, 2008).
Fig.10.20. Increase of the reliability using two UPS and STS
Source: MGE UPS Systems. Pulsar STS. Source transfer switch.
The two systems and the consumer have a connection by STS both regarding the source
voltage and the data exchange. At failure in one of the systems, the supply is automatically
passed to the other system and the necessary information for the failure state is passed.
Besides the nominal current, which the STS may switch, a basic parameter is transient time.
For example, STS produced by MGE France, so-called Pulsar STS, guarantee currents of 10,
15 and 16 A at transient time of 6ms.
Important function of the control system is to monitor the transient values of the voltages of
both sources, which are usually non-synchronized and to choose the most appropriate moment
for switching, which has to happen at minimum time and minimum disturbance in the
waveform of the supply voltage for the consumer. The best moment to perform the switching
is at the moments when the load current decreases to 0, thus the turning off of the finally
conducting triac is guaranteed, see Fig.10.21.
Triac 1
Triac 2
Source 1
Source 2
Fig.10.21. Contact-free switching between two sources using triacs.
Since sometimes STS are offered undependably from UPS system, it is necessary to know
switch parameters and characteristics.
Technical data concerning the input:
Input voltage
More often this is an output voltage of two undependable one from other UPS systems.
They usually guarantee high stability of the voltage value, besides, for this switch
parameter higher range is permissible for example, 220/230/240 V ±10%.
Frequency of the input voltage
It is usually 50/60 Hz
Number of the inputs and wire standards
For example, 2 corresponding to IEC 320 C13.
Nominal input current
For example 16A.
Technical data concerning the output:
Number of the outputs and wire standards
For example, 6 corresponding to IEC 320 C13
Nominal output current
For example 10A.
Transient switching time
It is obligatory to be lower than the value of the half-period of the input voltage. The
period of 60Hz is 8.33ms. The producer may be shown 10ms, for example. Thus, an
analysis has to be made whether the consumer supplying by this switch may carry a
drop off of the source voltage for this time.
Common technical data:
Sizes and weight
The three sizes and weight are indicated - for example, 400x60x100 mm and 10 kg.
Correspondence to international standards
The standards numbers are obligatory to be given. They are usually regarding the
technical safeness and the electromagnetic compatibility for example, regarding the
electromagnetic compatibility IEC 1000-4, and regarding the technical safeness EN
Different schematic versions are often provided to increase the reliability. The first version is
depicted in Fig.10.22. The main requirement to both separated UPS systems is their capability
of parallel operation and also each of them has to be capable of delivering the total power
required by the load.
normal АС input normal АС input
bypass AC input
Fig.10.22. First schematic version to increase the reliability
In a normal state the power is divided between the two systems, and when a failure occurs in
one of them, the power is delivered only by the other. The possibility of so-called centralized
bypass is also provided.
In high power some producers design the UPS system itself according to a module principle
with possibility for parallel operation of the separate modules and centralized bypass.
Fig.10.23 depicts this version. A possibility for automatic turning on and off of particular
modules dependent on the power loading and the module states is often existed in this
normal АС input
bypass AC input
module 1 module 2 module N
centralized bypass
Fig.10.23. Module principle of UPS applied to increase the reliability
Another version to increase the reliability is shown in Fig.10.24. It is for two UPS systems.
The system contains STS.
At each moment only one of the systems operates, the other is in standby mode. In failure in
one of the systems the supply of the load is passed to the other one, and the passing is made
through the STS. Advantage of the version is the fact that the two systems are not loaded
simultaneously. It has to be mentioned that this version may be extended for a boosted
number of systems and loads using different combinations among them and using several
In all versions examined till now, the time during which the load will be supplied at a drop off
of the source voltage depends on two factors. On one hand, it is the state of the battery
charge degree and capacity; on the other hand, it is power which the load consumed at that
moment. It is clear that this time is limited by these two factors. For example, if the load
consumes power equal to the nominal one of the UPS system and the battery is fully charged,
the time during which supply for the load can be maintained after the drop off of the source
voltage varies in different producers and it is often in the range of 5-20 minutes. If this does
not meet the requirements of the consumer, he may use another UPS system with higher
power than his load will consumed consulting the producer what will be the increase of the
time in this case, of course, on the account of a higher price. Another option is the consumer
to ask for an installation of another battery with an appropriate capacity for the case, of
course, if the producer gives this opportunity, which is cheaper than the previous version.
bypass AC input
normal АС input normal АС input
source transfer
Fig.10.24. Version to increase the reliability for two UPS systems
At very responsible loads a group motor- generator supplied by a liquid fuel (so-called reserve
supply) is added to the blocks of UPS systems described up to here. In this case the supply for
the load relies on from the battery using DC/AC converter for a comparatively short time
during which the motor-generator group begins to operate after the source voltage drops off
and if there is no yet source voltage after the depletion of the capability of the battery then
automatically the supply of the load is transferred to the generator. Thus a reserve electrical
supply is realized. An example of its structure is shown in Fig.10.25.
normal АС input bypass AC input
manual bypass
automatic bypass
liquid fuel
Fig.10.25. A structural schema for a reserve electrical supply
Communication between UPS Systems and Different Systems
It has been clarified at the above made study that the UPS systems are complex devices which
are assigned responsible functions connected to the supply of critical equipment. This imposes
the need of providing special means to monitor the operation of the devices and at failure the
reaction time and the time to eliminate the failure to be as short as possible. The possibilities,
which are provided in this aspect by the producers, very often play a significant role in the
choice which the consumer may be made among the UPS systems offered at the Market.
These possibilities determine in a high degree the speed to eliminate the failures obligation
that the producers take at the contract of warranty.
Recently, a basic share in control systems of power electronic converters used in UPS systems
is taken from digital signal processors. The processors themselves have series peripheral
interfaces or/and series communicational interfaces with possibilities of synchronous or
asynchronous data exchange and thus there embedment in hardware and software systems
meant for communication is simplified. During the design of the control systems, possibilities
for self-diagnostic of the separated blocks are provided, so, the data to be accessible to the
staff. The communication means can be generally divided into two groups:
Means for monitoring, indication, imitation and control at the point of
installation of the UPS system;
Means for monitoring and control from a distance.
Liquid-crystal displays for indication and control used by all producers and most frequently
controlled by a common microprocessors are from the first group of the communication
means. A structure of the system with indication, which blocks operate at that moment is
usually shown at the displays, as also different functional buttons to draw in or out data at the
display are provided.
This permits:
Indication of the currently operating blocks by lightening their symbols at the
block schema at the display;
Indication of voltage, current and frequency of input/output/battery;
Indication of all alarms for operational disturbance and their history;
Indication of remaining operational time at an absence of the source voltage
dependent on the state of the battery, transient load and temperature;
Indication of remaining time of use of the battery dependent on its usage
Enable or disable of sound indication;
Configuration of the above mentioned function dependent on the requirements
of the consumer language, indicated parameters, date, time during which the
battery is tested, etc.
The consumer also has access to the display. So-called remote mimic and control panel is
additionally installed. This panel is a coupling for connection to a special service PC used by
the service engineers and signals of “dry contact” type are brought on the panel, as follows:
Inverter load;
Test for damaged battery;
Network load;
Failure turned off inverter;
Coming stop;
Turned off rectifier;
Turned off battery charge;
Damage in the bypass system, etc.
These are only part of the most important signals, which allow to service engineer to make a
quick diagnostic of the failure and to take a decision how to continue its elimination.
The second group of communication means for a distance monitoring and control is realized
by specially made centers for this purpose by the producers. In these centers, a continuous
flow of information for the state of the most responsible objects arrives using the embedded
modems into UPS system through telephone cable or through Internet. This allows
monitoring the parameters required for a proper operation, passing the state of a particular
system using so-called “reports” at a set period of time. According to the data, eventual
malfunctions of the system can be foreseen and both the consumer and the serves group to be
informed preliminarily. Of course, the producers have necessary software, shaped in separate
parts with different producer names, for means of the two groups. Information about software
can be found in advertising materials of the companies.
If the UPS system is used for computer systems and nets, it has to be known that means for
connection to the computers themselves are provided. Corresponding software, which may be
integrated in different operational system such as
, etc., is offered.
1. WINDOWS is a registered frademark of Microsoft Corporation in the United States
and other countries.
2. UNIX is a registered frademark of The Open Group.
1. Beaudet, J.P., Fiorina, G.N., & Pinon, O. (2005).UPS Topologies and Standards.
France: MGE UPS Systems.
2. Blooming, T.M. (2008). Power factor as it relates to UPS products. USA, Cleveland:
Eaton Corporation. Retrieved from
3. Cottuli, C., Christin, J-F. (2008). Comparison of Static and Rotary UPS. USA:
American Power Conversion.
4. Emadi, A., Nasiri, A., & Bekiarov, S.B. (2005). Uninterruptible Power Supplies and
active filters. USA, Florida: CRC Press.
5. Griffith, D.C. (1989). Uninterruptible Power Supplies. USA/New York: Marcel
Dekker Inc.
6. Gurrero, J.M., De Vicuna, L.G., & Uceda, G. (2007).Uninterruptible power supply
systems provide protection. IEEE Industrial Electronics Magazine, 1(1), pp.28-38.
7. Kamran, F. (1998). A novel on-line UPS with universal filtering capabilities. IEEE
Transaction on Power Electronics, 13(3), pp.410-418.
8. Karve, S. (2000).Three of a kind [UPS topologies, IEC standard]. IEE Review, 46(2),
pp. 27-31.
9. Karve, S. (2005). Static or rotary? - that is the question. France: MGE UPS Systems.
10. Mattaveli, P. (2005). An improved deadbeat control for UPS using disturbance
observer. IEEE Ttransaction on Industrial Electronics, 52(1), pp. 206-211.
11. MGE UPS Systems. Pulsar STS. Source transfer switch. France/Cedex. Retrieved
12. Ming, T.T., & Chia H.L. (2003). Design and implementation of a cost-effective quasi
line-interactive UPS with novel topology. IEEE Transaction on Power Electronics,
18(4), pp.958-965.
13. Pai, F.S., & Huang, S.J. (2006). A novel design of line interactive uninterruptible
power supplies without load current sensors. IEEE Transaction on Power Electronics.
21(1), pp.202-210.
14. Powerware. Easy UP solutions for IT systems.pp.4 5.
15. Rasmussen, N. (2003). The Diferent Types of UPS Systems. USA: American Power
16. Solter, W. (2002). A new international UPS classification by IEC 62040-3. Paper
presented at Telecommunications Energy Conference, 2002.INTELEC.24th Annual
International, pp.541-545.
17. Tao, H., Duarte, J.L., & Hendrix, M.A.M. (2008). Line-interactive UPS using a fuel
cell as the primary source. IEEE Transaction on Industrial Electronics. 55(8),
18. Vazquez, N., Aguilar, C., Arau, G., Caceres, R.O., Barbi, I., & Gallegos, G.A. (2002).
A novel uninterruptible power supply system with active power factor correction.
IEEE Transaction on Power Electronics, 17(3), pp.405-412.
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