Uninterruptible Power Supply

Electronic equipment used in communication devices and systems is currently mainly powered by AC 220 V. Therefore, it is very important to understand the characteristics of the voltage in this network. In accordance with the requirements for sources of electricity ~ 220 V in accordance with GOST R 54149 - 2010:

1. voltage deviation from the nominal should not exceed ± 10%
2. the deviation of the mains frequency from the nominal value of 50 Hz should not exceed ± 0.4 Hz
3. the network power should not be lost for more than 30 seconds

In addition, the network allows the appearance of a pulse increase or decrease in voltage up to 10 ms and fast voltage changes with a frequency of up to 8 Hz and a voltage of up to 1.38 from the nominal value. The voltage form can also be non-harmonic and asymmetric [2]. All these phenomena can lead to instability in the operation of electronic equipment powered by 220 V.

The widespread classical scheme of power supply of electronic equipment ensures uninterrupted power supply. The same functions are performed by other devices that are successfully developed, are separated into a separate class and received the name of an uninterruptible power supply (UPS) device, sometimes they are called uninterruptible power supplies (UPS).

Uninterruptible power supplies make it possible to improve the quality of electric power for electronic equipment and its individual components. A generalized classification of uninterruptible power supplies is shown in Figure 1.

Figure 1. Classification of uninterruptible power supplies

Uninterruptible Power Supply DC

The simplest uninterruptible power supply circuit is a buffer circuit. It uses a battery or a battery of chemical elements as the primary source of power for direct current. A schematic diagram of the buffer connection of the battery to the load is shown in Figure 2.

Figure 2. Buffer circuit of uninterruptible power supply DC

As the main advantage of the buffer circuit connecting the battery should be noted its simplicity. In most schemes of modern portable electronic equipment this scheme is used. In the buffer connection scheme, the battery is involved in the suppression of interference from the power source. This is another advantage of the DC uninterruptible power supply buffer circuit.

As a disadvantage of the buffer circuit, it should be noted the difficulty of the charge-discharge mode of the battery. As a result, batteries often fail. To the design of the battery, too, there are increased requirements - during its work should not be allocated gases that can destroy electronic equipment. For example, during the operation of acid batteries, vapors of acid may be emitted, therefore this type of battery, capable of providing significant currents with small dimensions of the battery, is not used in uninterruptible power supplies. When working with alkaline batteries, it is very important to ensure that the battery is completely discharged, otherwise the battery will quickly fail. Nowadays, either metal hydride or lithium-ion batteries are commonly used, which are less susceptible to the problem described. Nevertheless, from time to time it is required to perform a battery run - several full charge-discharge cycles of batteries.

Figure 3. Diagram of uninterruptible power supply DC with separated AB

Uninterruptible Power Supply (UPS) Uninterruptible Power Supply (UPS ) is a source of secondary power supply, an automatic device whose purpose is to provide electrical equipment connected to it with uninterrupted power supply within normal limits.

GOST 13109-97 (instead of GOST 13109-87) defines the following standards in the power supply network: voltage 220 V ± 5% (limit values ​​± 10%); frequency 50 Hz ± 0.2 Hz (limit values ​​± 0.4 Hz); coefficient of non-linear distortion of the voltage form is less than 8% (long-term) and less than 12% (short-term).

The network faults are:

• network voltage failure (the mains voltage is completely gone);
• high-voltage impulse noise (a sharp increase in voltage up to 6 kV with a duration of 10 to 100 ms);
• long-term and short-term spikes and voltage spikes;
• high-frequency noise (high-frequency noise transmitted over the power grid);
• frequency escape (frequency deviation of more than 3 Hz).

The mass use of the UPS is related to ensuring the uninterrupted operation of computers, allowing equipment connected to the UPS when there is a loss of electric current or when its parameters go beyond acceptable limits, some short time (usually up to 10-15 minutes) to continue working. In addition to computers, the UPS provides power and other electrical loads that are critical to the availability of power with normal parameters of the power supply network, such as control circuits for heating boilers. The UPS is able to adjust the parameters (voltage, frequency) of the output network. Extremely rare instances can be combined with various types of electric power generators (for example, a diesel generator).

Important indicators that determine the choice of the UPS design scheme are load transfer time to battery power and battery run time.

Laptops and other devices that have a built-in rechargeable battery, do not need a UPS - a battery with built-in switching schemes is itself.

Content

• 1 Schemes of construction of the UPS
  • 1.1 Reserve
  • 1.2 Interactive
  • 1.3 Double conversion
• 2 UPS specifications
• 3 Through "zero"
• 4 Choosing a UPS for heating boilers
• 5 Components of the UPS
• 6 International Classification of UPS
• 7 Vendors
• 8 Notes
• 9 References

UPS construction schemes

There are three schemes for building a UPS:

Reserve

Backup circuit (English Off-Line, Standby ) - in normal mode, the connected load is supplied directly from the primary electrical network, which the UPS filters (high-voltage pulses and electromagnetic interference) with passive filters. When the power supply exceeds the normalized voltage values ​​(or its loss), the load is automatically reconnected to the power supply from a circuit that receives electrical energy from its own batteries using a simple inverter. When a voltage within normal limits, again switches the load on the power from the primary network.

Virtues

• Due to the efficiency of about 99% (in the presence of mains voltage), they are virtually silent and have minimal heat dissipation;
• low cost of the UPS in general.

disadvantages

• a relatively long time (about 4..12 ms) switching to battery power;
• inability to adjust either voltage or frequency (VFD according to IEC classification).
• non-sinusoidal output voltage during battery operation (approximated sinusoid, quasi-sinusoid);

Bottom line: Most often, UPSs built according to this scheme are used to power personal computers or workstations of entry-level LANs, for which a timely shutdown in the event of a network failure is not critical. Almost all low-cost low-power UPSs offered on the domestic market are built according to this scheme.

Interactive

Interactive scheme (eng. Line-Interactive ) - the device is similar to the previous scheme; Additionally, a step voltage regulator is present at the input on the basis of an autotransformer, allowing you to get an adjustable output voltage. (VI according to IEC classification). When operating in normal mode, these UPSs do not adjust the frequency, passive filters filter the incoming AC voltage. When the power fails, the UPS transfers to power from the inverter, similar to the previous one.

Inverters of some models of linear-interactive UPS provide voltage as a rectangular or trapezoidal shape, as in the previous version, and sinusoidal form. The switching time is shorter than in the previous version since the inverter is synchronized with the input voltage. KPDnezhny, than at reserve.

Disadvantages: in the “from the network” mode, it does not perform the function of peak filtering, and provides only extremely primitive voltage stabilization (usually 2-3 steps of the autotransformer, switched relay, the function is called “AVR”).

In the “on battery” mode, some, especially cheap, circuits supply a frequency much higher than 50 Hz to the load, and an oscillogram of alternating current that has little in common with a sinusoid. This is due to the use of a classic large-size transformer in the circuit (instead of an inverter on semiconductor switches). Due to the fact that a transformer of this size has (due to hysteresis in the core) a limit on the transmitted power, which rises linearly with the frequency of this transformer (it takes 1/3 of the volume of the whole UPS) is enough to power the battery charging circuit at 50 Hz in the mode "from the network." But, in the “on battery” mode, hundreds of watts of power have to be passed through this transformer, which is possible only by increasing the frequency.

This leads to the inability to power devices using, for example, asynchronous motors (almost all the so-called “white appliances”, including heating systems).

In fact, from such a UPS it is possible to supply only devices that are not demanding to the quality of power, that is, for example, all devices with pulsed power supplies, where the supply voltage is immediately rectified and filtered. That is, computers and much of modern consumer electronics. You can also power the lighting and heating devices.

Double conversion

Double conversion mode [1] ( online , online) - is used to power loaded servers (for example, file servers), high-performance workstations of local computer networks, as well as any other equipment that places high demands on the quality of the power supply (CHECK: server load has no relation to the choice of the UPS circuit, in addition, all the impulse power supplies, and especially high quality ones used in servers of serious manufacturers, have, on the contrary, REDUCED quality requirements wu supply voltage). The principle of operation consists in double conversion of the current type. First, the input AC voltage is converted to DC, then back to AC voltage using an inverter (inverter). When the input voltage disappears, switching the load to the battery power is not required, since the batteries are permanently connected to the circuit (the so-called battery backup mode) and the “switching time” parameter doesn't make sense for these UPSs. For marketing purposes, the phrase “switching time is 0” can be used, correctly reflecting the main advantage of this type of UPS: no time gap between the loss of external voltage and the start of battery power. Double conversion UPSs have low efficiency (from 80 to 96.5%) in on-line mode, due to which they are characterized by increased heat generation and noise level. However, modern medium-size and high-capacity UPSs from leading manufacturers have a variety of intelligent modes that allow you to automatically adjust the mode of operation to increase efficiency up to 99%. In contrast to the two previous schemes, they are able to correct not only voltage, but also frequency (VFI according to IEC classification).

Virtues

• no battery switching time;
• sinusoidal output voltage, that is, the ability to supply any load, including heating systems (in which there are asynchronous motors).
• the ability to adjust both voltage and frequency (moreover, such a device is also the best possible voltage regulator).

disadvantages

• Low efficiency (80–94%), increased noise and heat dissipation. Almost always, the device contains a computer-type fan, and therefore is not silent (as opposed to line-interactive UPS).
• High price. Approximately twice or three times higher than line-interactive.

• 

  “Backup” UPS construction scheme

• 

  "Interactive" UPS construction scheme

• 

  Double Conversion UPS System

UPS characteristics

• output power measured in volt-amperes (VA) or watts (W). It is worth paying attention that the equipment containing powerful electric motors (refrigerator, submersible pumps of autonomous water supply systems and irrigation systems) has “starting currents”. This means that when the engine is started, the device briefly consumes *** the power, 5-7 times higher than the nameplate. UPS should be selected based on this fact. The same applies to laser printers, which are generally generally forbidden to connect to the UPS;
• output voltage , measured in volts, V;
• switching time , that is, the time of the UPS switching to battery power (measured in milliseconds, ms);
• battery life is determined by the capacity of the batteries and the power of equipment connected to the UPS (measured in minutes, min.), for most office UPSs, it is 4-15 minutes; (usually 40-45 minutes with fresh batteries and an unloaded computer).
• the width of the input (mains) voltage range at which the UPS is able to stabilize the power without switching to batteries (measured in volts, V);
• battery life (measured in years, usually lead batteries lose their capacity significantly after 3 years. It strongly depends on the quality, and therefore the price of the UPS, specifically on the degree of primitivity of its battery charging circuit).
• through zero . See below.

Through "zero"

Some types of loads use protective earth conductor (PE) for their working needs.

For example, such is the equipment with gas burners, where the flame control ionization electrode circuit is closed through the burner ground and then through the PE wire. Existing regulations on electrical installations allow such tiny (microamps) operating currents through PE.

This is not a problem with the mains supply, both the TN-CS network and the TT network, since in both of them PE sooner or later communicates with N through the dividing point in the TN-CS or through the physical earth from the consumer to the transformer station with a grounded neutral in the case of a TT, in addition, in the TT network it is also possible to re-ground N on the way from the TP to the consumer. In this case, the above described circuits in the device, connected between L and PE, are operational.

However, in the case when the device is powered from an absolutely isolated and not grounded source (in this case, from a UPS operating on batteries), where there are often no concepts of “phase” and “zero”, but there are 2 sine 110 V out of phase (this the so-called “IT system”), the above-described circuits have a problem due to the lack of any PE message and power supply on the source side (PE can still be used on the source for protective grounding of the housing, screens, etc.).

In practice, this means the absence of the “there is a flame” signal on the automation of the heating boiler and its inoperability.

It is for the support of such consumers that the UPS uses a “through zero” scheme, that is, a direct connection of the N terminals of the input and output power circuits. In this case, even when running on batteries, there is a PE and N message on the load (through the UPS and then through the network where the UPS is connected), and the above described problem does not occur.

However, this situation occurs only in the event of a loss of input voltage to the UPS, for example, due to the actuation of the “automaton” or disconnection from the energy supplier.

In some other situations - tripping of the RCD, complete disconnection of the UPS input from the mains with a plug, “zero firing” on the village overhead line - even the “pass-through zero” in the UPS is not enough to power the above circuits. In this case, it is recommended (for example, by Buderus for heating boilers, the recommendation generally applies to IT supply networks) to install a resistor of about 1..10 MΩ (Buderus recommends purchasing their original resistor, its resistance 10 MΩ) between N and PE at the input of the powered device (or at the output of the UPS).

Choosing a UPS for heating boilers

• Required online UPS (see above).
• mandatory through zero (see above).
• to protect against situations like the operation of an RCD is required extra. resistor (see above in the text about the through zero). Testing such a mode is trivial to pull the input plug of the UPS out of the socket and at the same time monitor the flame indicator on the boiler (should not go out, the boiler should not stop).
• Some boilers use only one (for example, left) of the wires of the power plug to power the flame control circuit. They work only if the plug is plugged in so that it is on this wire that L (and not N) turns out. This is perhaps the only household appliance that requires a specific orientation of the plug in the outlet (the so-called “phase-dependent boiler”). You should pay attention to the fact that the boiler, not phase-dependent when powered from the network, may suddenly become phase-dependent when powered from a UPS with add. resistor, so you should always pay attention to the orientation of the plug of the boiler, stuck in the output of the UPS.

Components of the UPS

Реализация основной функции достигается работой устройства от аккумуляторов, установленных в корпусе ИБП, под управлением электрической схемы, поэтому в состав любого ИБП, кроме схемы управления , входит зарядное устройство , которое обеспечивает зарядку аккумуляторных батарей при наличии напряжения в сети, обеспечивая тем самым постоянную готовность к работе ИБП в автономном режиме. Для увеличения автономного режима работы, можно оснастить ИБП дополнительной (внешней) батареей.

Режим байпас (англ. Bypass , «обход») — питание нагрузки отфильтрованным напряжением электросети в обход основной схемы ИБП. Переключение в режим Bypass выполняется автоматически или вручную (ручное включения предусматривается на случай проведения профилактического обслуживания ИБП или замены его узлов без отключения нагрузки). Байпасом называется один из составляющих ИБП блоков. Может делать т. н. фазануль(«сквозной нуль»). Применяется в online схемах, более того, выключенный кнопкой OFF online UPS остаётся в режиме байпаса, то же самое происходит при разрушении силовых компонентов схемы, определённом управляющими цепями, а также при аварийном отключении схемы по перегрузке выхода. В line-interactive UPS режим работы «от сети» и есть байпас.

" Booster " (English booster ) - the step automatic voltage regulator (English Automatic Voltage Regulation, AVR ), имеющий автотрансформатор в своей основе. Используется в ИБП, которые работают по интерактивной схеме. Часто ИБП оснащается только повышающим «бустером», который имеет всего лишь одну либо несколько ступенек повышения, но есть модели, которые оснащены универсальным регулятором, работающим и на повышение (boost), и на понижение (buck) напряжения. Использование бустеров позволяет создать схему ИБП, способную выдержать долгие глубокие «подсадки» и «проседания» входного сетевого напряжения (одной из наиболее распространённых проблем отечественных электросетей) без перехода на аккумуляторные батареи, что позволяет значительно увеличить срок «жизни» аккумуляторной батареи.

Схема инвертора 12 Вольт постоянного в 230 Вольт переменного напряжения

Инвертор — устройство, которое преобразует род напряжения из постоянного в переменное (аналогично переменное в постоянное). Основные типы инверторов:

• инверторы, которые генерируют напряжение прямоугольной формы;
• инверторы с пошаговой аппроксимацией;
• инвертор с широтно-импульсной модуляцией (ШИМ).
• преобразователь с импульсно-плотностной модуляцией (ИПМ, англ. Pulse-density modulation )

Показатель, который характеризует степень отличия формы напряжения или тока от идеальной синусоидальной формы — коэффициент нелинейных искажений (англ. Total Harmonic Distortion, THD ). Типовые значения:

• 0 % — форма сигнала полностью соответствует синусоиде;
• порядка 3 % — форма близкая к синусоидальной;
• порядка 5 % — форма сигнала приближенная к синусоидальной;
• до 21 % — сигнал имеет трапецеидальную или ступенчатую форму (модифицированный синус или меандр);
• 43 % и свыше — сигнал прямоугольной формы (меандр).

Для уменьшения влияния на форму напряжения в питающей электросети, (если входным узлом ИБП, построенного по схеме с двойным преобразованием, являетсятиристорный выпрямитель, элемент нелинейный и потреб***яющий большой импульсный ток, такой ИБП становится причиной появления гармоник высшего порядка) во входной цепи ИБП устанавливается специальный THD-фильтр . При использовании транзисторных выпрямителей коэффициент нелинейных искажений (англ. Total Harmonic Distortion, THD ) составляет порядка 3 % и фильтры не используют.

Гальваническую развязку между входом и выходом (как правило, в ИБП таковая не делается вообще из принципиальных соображений пропуска «сквозного нуля» на нагрузку, то есть отсутствия любой коммутации провода нейтрали от входа UPS то его выхода), осуществляет установленный во входной цепи ИБП (между электросетью и выпрямителем) входной изолирующий трансформатор . Соответственно, в выходной цепи ИБП между преобразователем и нагрузкой размещён выходной изолирующий трансформатор , который обеспечивает гальваническую развязку между входом со схемы ИБП и выходом на подключенную нагрузку.

Для расширенного мониторинга состояния самого ИБП (например, уровень заряда батарей, параметры электрического тока на выходе) применяются различные интерфейсы: для подключения к компьютеру — USB и последовательный (COM) порт, при этом производителем ИБП поставляется фирменное программное обеспечение, которое позволяет проанализировав ситуацию, определить время работы и дать оператору возможность безопасно выключить компьютер, завершив работу всех программ. Для наблюдения за состоянием источников бесперебойного питания) и другого оборудования через локальную вычислительную сетьиспользуется протокол SNMP и специализированное программное обеспечение.

Для того, чтобы повысить надёжность всей системы в целом, применяется резервирование — схема, которая состоит из двух или более ИБП.

Международная классификация ИБП

Промышленное решение: ИБП, вместе с защищаемым оборудованием, смонтирован в 19-дюймовую стойку

Стандартом IEC 62040-3 введена следующая классификация ИБП:

Пример обозначения типа ИБП: VFI SS 111

1-я группа символов — зависимость выходного сигнала ИБП от входного (сети).

• Класс VFI (Voltage and Frequency Independent) — напряжение и частота на выходе ИБП не зависят от входной сети.
• Класс VI (Voltage Independent) — выход ИБП зависит от частоты входа, но напряжение поддерживается в заданных пределах пассивным или активным регулированием.
• Класс VFD (Voltage and Frequency Dependent) — напряжение и частота на выходе ИБП зависят от входной сети.

2-я группа символов — форма выходного сигнала ИБП.

• SS — синусоидальная форма выходного сигнала (коэффициент гармонических искажений K ги <8 %) при линейной и нелинейной нагрузке.
• XX — несинусоидальная форма выходного сигнала при нелинейной нагрузке (синусоидальная при линейной).
• YY — несинусоидальная форма сигнала при любой нагрузке.

3-я группа символов — динамические характеристики ИБП. Обеспечение стабильности выходного напряжения ИБП при трёх типах переходных процессов (1 — класс 1, отлично; 2 — класс 2, хорошо; и т. д.):

• 1-я цифра: нормальный режим -> автономный режим -> режим bypass,
• 2-я цифра: 100 % изменение линейной нагрузки в нормальном или автономном режиме (худший параметр),
• 3-я цифра: 100 % изменение нелинейной нагрузки в нормальном или автономном режиме (худший параметр).

Vendors

14 февраля 2007 года на мировом рынке источников бесперебойного питания произошло важное событие: компания Schneider Electric завершила приобретение APC и объединение её с подразделением MGE (занимающимся трёхфазными ИБП большой мощности).

В конце июня 2007 однофазный бизнес (MGE OPS) концерн Schneider Electric продаёт компании Eaton Corporation (оборудование под маркой Powerware).

В 2010 году группой Legrand было принято решение и воплощено в жизнь приобретение концерна Inform Electronic. Теперь ИБП Inform, маркируются «by Legrand».

ИБП производства General Electric также известны по предыдущему производителю как Victron или IMV (Invertomatic Victron).

На 2013 год АРС by Schneider Electric является основным вендором и уже долгое время с явным отрывом сохраняет лидерство на рынке ИБП. [2]

Распределение продаж ИБП по производителям (2006 г., «IT Research»):

Notes

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Часть 1 Uninterruptible Power Supply