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Белое и Черное или Черное и Белое Смотрим с разных сторон

Белое и Черное или Черное и Белое Смотрим с разных сторон

Что позволено маркетингу, не известно потребителю. Интересная статья 20-ти летней давности. Несмотря на возраст, статьи нет в паблике. Для осмысления не достаточно вспомнить ТОЭ. Очень много букв понятных не всем. Черное и Белое или Белое и Черное?


Ничего необычного. Но на самом деле это не перемена местами слов, а переименование Черного в Белое?

Безумный маркетинг производителя оборудования порождает "Безнадежную Легенду" и практически сразу же группа авторов различных производителей отвечает. И кто же судьи? Вот список: AEG SVS, MGE UPS Systems, Piller, Sicon-Socomec, Siemens, Victron, IMV Invertomatic. Полный список авторов под статьей. Оригинал статьи с обзором Delta-Conversion (Дельта-преобразования) против традиционной On-Line технологии в преобразователях и ИБП (UPS). Перевод дополнительно, после текста оригинальной статьи.

Delta - Преобразование как схемотехника в преобразователях идея имеющая право на жизнь. Но ее применение ограничено возможностями.

Кроме ИБП, подобное решение есть в стабилизаторах напряжения. В этом нет ничего удивительного. Убираем Аккумуляторную Батарею (АКБ), возможность заряда и управления режимами работы и получаем стабилизатор.

Как это работает: 

Delta - преобразование в стабилизаторах напряжения
Еще один вариант, Delta - преобразование в стабилизаторах напряжения

Функция стабилизации напряжения реализована на включенном последовательно входной сети трансформаторе. Если сказать другими словами, компенсация повышения или понижения входного напряжения (Дельты, относительно средней точки 220 Вольт) до необходимого уровня.

Недостатки такой схемотехники:

Напряжение в нагрузке не может быть изменено мгновенно. Протекание тока происходит через последовательно включенную обмотку трансформатора и в соответствии с математическими законами, ток в индуктивности не может меняться мгновенно. Ток связан с напряжением как минимум законом Ома. Если ток не может менять значение мгновенно, значит напряжение.... В итоге: задержка в корректировке напряжения в нагрузке при падении напряжения на входе стабилизатора видна например, при подключении лампы накаливания в качестве нагрузки. Кроме того, диапазон регулирования, стабилизации напряжения не не может быть широким. Это обусловлено трансформаторной конструкцией и для реализации большого диапазона стабилизации вес и габариты трансформатора должны быть внушительно большими. Это существенный недостаток для наших сетей электроснабжения. Для расширения диапазона стабилизации напряжения в этом стабилизаторе добавлены две дополнительные корректирующие обмотки-ступени на автотрансформаторе. В результате диапазон стабилизации напряжения расширен.

Эти ступени регулировки видны на Вольт-Амперной характеристике снятой с выхода стабилизатора, выделены желтым цветом.

Вольт-Амперная характеристика стабилизатора

Оригинал статьи с обзором Delta-Conversion (Дельта-преобразования) против традиционной On-Line технологии в преобразователях и ИБП (UPS) 
Перевод дополнительно, после текста оригинальной статьи

On-Line Against Delta Technology

1. Abstract

This document was released by a group of true on-line, double conversion UPS manufacturers as a tool for arguing against Silcon units. It groups various technical issues focused on explaining the differences between the two technologies.

2. UNINTERRUPTIBLE POWER SUPPLY - System Concepts

The purpose of an uninterruptible power supply systems (UPS) is to guarantee a continuous AC supply for critical consumers. In order to achieve the necessary quality of uninterrupted supply the separate components of the power supply must be matched and optimised. Naturally, this requires that the essential characteristics of the different components and their variants are known. Standby power supply systems are required when long bridging times and capacities are needed. This article discusses the qualities of UNINTERRUPTIBLE POWER SUPPLY techniques for continuous operation (double conversion) and mains-inverter (UPS) parallel operation in detail.

2.1 Summary

  • Losses in different types of UPS systems are comparable. There are no major advantages between the different concepts with regard to practical operation.
  • Modern UNINTERRUPTIBLE POWER SUPPLY systems in continuous operation (figure 1) achieve comparable efficiency today, both in the partial load range and for non-linear loads.
  • Small efficiency gains for mains-inverter-parallel operation (figure 2) are revealed only if this UNINTERRUPTIBLE POWER SUPPLY can be operated at its optimum working point, however, this lacks practicality. Efficiency deteriorates clearly in the case of non-linear loads, mains voltage deviations as well as partial loads. De-coupling of the input and output frequencies does not occur in the case of mains-inverter parallel operation. This can make the use of a standby power supply system impossible.
  • With continuous operation, de-coupling of the inverter via the DC link during operation with standby power supply systems therefore yields definite advantages. The double conversion shows its advantages during all kinds of mains failures. The quality of the supply voltage and of the frequency at the output of the UPS system is better in the case of mains failures, and saves on investment capital through low battery loading. Since no additional inverter is necessary for the double conversion technique for compensation of system weaknesses, it has the advantage of a more reliable operation.
  • Modern double conversion techniques in three-phase current design use 12-pulse rectifier connections or PWM techniques so that the system perturbation of the described UPS concepts can be regarded as equal.

The minor advantage in the improvement of the efficiency, only possible under specific conditions, compared to modern double conversion techniques is bought by additional risks.

2.2 Continuous operation (double conversion)

Figure 1 shows the basic circuit, which essentially consists of the following components: Inverter for supply of critical consumers with constant sinusoidal AC voltage, frequency and amplitude in continuous operation Battery as energy storage for bridging of the specified breakdown time, Rectifier for the battery charge and for supply to the inverter. Mode of operation In normal operation the rectifier converts the single- or three phase mains voltage into a DC voltage in order to charge the battery, and for the supply to the inverter.

The battery is in standby parallel operation. The inverter generates a sinusoidal AC voltage from the DC for the supply of connected critical consumers. Mains and load voltages are in phase. Mains voltage and frequency fluctuations are compensated by the rectifier. The load on the inverter is virtually independent of the mains voltage. The load currents can be of any phase angles.

Figure 1: Continuous operation

Losses

Energy is twice converted; therefore, this technique is called double conversion. Every conversion is inflicted with losses, with the individual efficiencies

  • PV1 for the rectifier and
  • PV2 for the inverter

With modern techniques, in continuous operation a total efficiency of up to h Total = 0.95 is achieved. To a large extent the efficiency is independent of the consumer load. Modern UPS systems are optimised specifically for high efficiency in the partial load range. Furthermore, the load voltage remains uninfluenced by disturbing events on the mains side because of the DC intermediate circuit and the battery connected to it.

Behaviour during mains failure

During a mains failure, the inverter (and therefore the consumer) is supplied by the battery without interruption. There are no switching functions with the mains supply.

2.3 Mains-inverter (UPS)

Parallel Operation

The mains-inverter (UPS) parallel operation is carried out in various ways, however, the basic characteristics are similar. Figure 2 shows an often used circuit, which essentially consists of the following components:

Line reactor L required for the de-coupling of consumer- and mains voltage

Bidirectional converter (USR) for charging the battery and supply of the consumers in the event of a mains failure. The converter must supply the reactive (harmonic) power required by the load in normal operation and caused by the line reactor.

Fast electronic switch for disconnection of the mains in case of a mains failure. Battery as energy storage.

Mode of operation

A line reactor L is connected between the mains and the USR. This is needed for sufficient decoupling of the load voltage from the line voltage. For proper operation the voltage drop across the reactor Vline reactor needs to be about 33% of nominal voltage at rated current. During normal operation, supply of the consumers with active power is carried out from the mains, the USR does not supply any active power to the consumers.

Parallel to the mains - de-coupled by the line reactor- the USR is operated. It controls and determines the load voltage. In case of a mains failure, switching operations are required. The mains must be disconnected. In order to carry that out without a supply break, an electronic switch, which generates additional losses, is required.

The consumers are then supplied only by the USR from the battery. For the secured supply to very critical consumers, this technique can be risky because of the switching time of up to 15 ms. In order to justify this or in order to give additional decision aids for an individual case this mains invertor parallel operation should be described more precisely /1,..,6/). At a corresponding dimensioning of the line reactor, mains and load voltages are sufficiently isolated. The reactor voltage Vline reactor is, for nominal operation, about 33% of the rated power voltage.

Figure 2: Mains inverter (UPS) - parallel operation

Figure 2 shows the equivalent circuit and phasor diagram. The load voltage VLoad compared to the mains voltage VMains is made lagging by the angle j. The differential voltage across the line reactor L, VChoke , forces a current IMains through the reactor.

Figure 2: Mains inverter (UPS) - parallel operation Total V1 V2 V3 The "current difference" IInv between AC mains power IMains and load current ILoad must be supplied by the USR. The phasor diagram shows that the required invertor current IInv can become greater than the load current ILoad. Therefore, it cannot be claimed that the USR is only operated in no-load condition. This current loads the power semiconductors and other components in the USR, and losses are the result ! The amount of the "current difference" IInv greatly depends on the kind of the consumer load and considerably on the amplitude of the mains voltage.

There is no operating condition in which the USR is not loaded. Additionally the consumers normally have a non-linear current-voltage characteristic. Therefore in the UPS product standard EN 50 091 part 1 there is indicated a power factor l= 0.7 as "an example of normal load conditions". The distorted currents defined in this standard additionally load the USR because harmonics can only be supplied by the USR.

A de-coupling of the input and output frequencies does not occur. This can make the operation of a standby power supply system impossible.

Losses

The UPS losses in the mains-inverter-parallel operation are strongly dependent on the respective mode of working:

  • Type of the consumer
  • Mains voltage (mains over- or -undervoltage)
  • Power demand.

Efficiency indications under nominal conditions are therefore not meaningful for this kind of UNINTERRUPTIBLE POWER SUPPLY. The dependence of the losses on the mains voltage and the load described here was already represented in detail in the IEEE report /1/ in 1982.

Losses originate in three components

  • PV1 for the electronic switch
  • PV2 for the reversible converter USR
  • PV3 for the line reactor L.

Figures 3a and 3b show the total efficiency at different loads and its change for mains voltage deviation and non-linear loads.

Figure 3a: Efficiency characteristics of a 20 kVA UPS system in mains-invertor-parallel operation at linear load
Figure 3b: Efficiency characteristics of a 20 kVA UPS in mains-inverter-parallel operation at non-linear load

Behaviour during mains failure In this case, the electronic switch (figure 2) plays a very important role. It has to disconnect the mains very fast and permanently ! This switching operation is essential and critical to the function of the UNINTERRUPTIBLE POWER SUPPLY: A mains failure can represent a short circuit for the UPS input (in prEN 50091-3:1994 /4/: niederohmiger Netzausfall / low-resistance mains failure). The USR then has to feed into this short circuit via the line reactor as well as the critical consumers at the output of the UPS.

The USR will feed the mains with a current limited by the reactor up to the point of switching off of the electronic switch (reversal of current). In the event of reactor saturation, the current would become excessively high and is therefore limited by the USR. The connected critical consumers are then no longer supplied with sufficient current and a considerable voltage dip is created for the consumer.

2.4 Mains- inverter- (UPS) Parallel Operation With Additional Inverter

Figure 4 shows the basic circuit, which essentially consists of the following components: Reversible converter for the supply of the consumers during mains failure, supply of the required (harmonic -) reactive power in normal operation, battery charge and guarantee of the internal energy balance. Additional inverter with specific transformer for compensation of the voltage difference between the mains voltage and the voltage demanded by the consumer. Fast electronic switch for disconnection of the mains in case of mains failure or short circuit.

Battery as energy storage During mains-inverter-parallel operation with an additional inverter, the purpose of the line reactor L , namely the de-coupling and the compensation of the voltage difference, is taken over by a special transformer and an additional inverter/rectifier (ZWR). For sufficient de-coupling of the load voltage from transients on the mains (IEC 1000-4 part 5) as well as for the safe switching operation of the IGBTs in the inverter/rectifier (ZWR) a "rest" of line reactor is required. This function can be integrated in the transformer.

Figure 4: Mains-inverter-(UPS) parallel operation with additional invertor

Mode of operation There are various possibilities for control. Preferably the system is controlled in such a way that mains voltage and mains current remain in phase. The phasor diagram shows the relationships in figure 4. Compared to the system with line reactor only, this UPS is seen from the mains as an ohmic consumer. The special transformer with ZWR only has to compensate the voltage difference between the mains and the load voltage, as well as the voltage drop of the remaining reactor function V.

Energy shift, battery charging In this mode of operation, only active power is taken from the mains. The consumer reactive power must be supplied by the USR. The phasor diagram further shows that the inverter/rectifier (ZWR) has to be considered as an energy source, energy consumer, supplier of reactive power and consumer of reactive power according to load and mains conditions.

The USR must supply the differential power in each case, otherwise, the battery would constantly be charged or discharged. The controls must master these complex courses of events. The primary of the special transformer constantly carries the full load current, which is transferred onto the secondary side. Therefore, the inverter/rectifier (ZWR) also carries its maximum current constantly. Losses originate in four components PV1 for the electronic switch PV2 for the reversible converter USR PV3 for the special transformer PV4 for the additional inverter (inverter/rectifier (ZWR))

Compared to the previous device with only the line reactor, a further component, the inverter/rectifier (ZWR), has been added. Attainable efficiency lies in the scale of up to 95%. With the additional inverter the efficiency becomes more independent from the respective working mode of the system, but all in all it becomes worse. The reliability of the system decreases because the number of components is increased considerably.

Behaviour in case of mains failure and variations in mains voltage The required switching operation during a mains failure (electronic switch) could lead to a supply break in the design as shown in figure 2. In the technique described in figure 4, similar problems can occur unless special measures are taken. Battery stress: In order to master the above-mentioned switching operation safely under all mains conditions, it must be switched over to battery operation at each mains failure, even very short ones (e.g. frequency, voltage, spikes ....). The battery is unloaded for some hundred milliseconds, until the electronic switch is ready to transfer back to mains supply. In the event of unreliable mains this may happen often, thereby creating stress for the battery.

This document is due to a contribution of the following:

Companies Authors

AEG SVS Horst Scholz / Wilhelm Sölter

MGE UPS Systems Mr. Böschen / Mr. Odenthal

Piller Mr. Darrelmann / Mr. Sachs

Sicon-Socomec Mr. Neutzner

Siemens Mr. Fischer

Victron Mr. Raap

IMV Invertomatic Mr. Schwerzmann


References:

  • William J. Raddi & Robert W. Johnson: A UTILITY INTERACTIVE PWM SINE-WAVE INVERTOR CONFIGURED AS A HIGH EFFICIENCY UPS, 1982 IEEE
  • Clewing, M.: Emergency power supply as a concept overall: More than the sum of its components. Conference proceedings for the 7th "Power management VZM safety conference", Bonn 16.05.1995, P. 75-119, SIMEDIA Ltd. Bonn (in German)
  • EN 50091, Teil 1:1994 (VDE 0558 part 510): Uninterruptible current supply (UNINTERRUPTIBLE POWER SUPPLY). General orders and safety regulations. VDE Verlag, Berlin
  • prEN 50091-3:1994 (VDE 0558 part 531): Uninterruptible current supply (UNINTERRUPTIBLE POWER SUPPLY). General demands on the operational behavior. VDE Verlag, Berlin
  • Guideline for the connection of UNINTERRUPTIBLE POWER SUPPLY plants in three-phase engineering in the construction unit of 10 kVA to 2 MVA to the public net. Editor: VDEW-e.V and ZVEI, 1994, VDEW Verlag Frankfurt am Main (in German)


Оригинал документа и перевод на русский язык:

Авторские права

© AEG SVS Horst Scholz / Wilhelm Sölter MGE UPS Systems Mr. Böschen / Mr. Odenthal Piller Mr. Darrelmann / Mr. Sachs Sicon-Socomec Mr. Neutzner Siemens Mr. Fischer Victron Mr. Raap IMV Invertomatic Mr. Schwerzmann Сергей Твед. Перевод на русский язык: Александр Киселев

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