The Need For Ups System Engineering Essay

In a paper written by John D. Harnden in 1978, the description of the improved efficiency of solid province power conditioning was that of excitement

Power quality became a rather serious issue in the 1980, when failure of assorted tonss was attributed to these tonss pulling non-sinusoidal burden from the supply, chiefly due to their non- additive belongingss. These tonss caused changing harmonic deformations in the AC supply line, which intending that power was wasted, and the overall efficiency is reduced. Power conditioning equipments was brought in to rectify this state of affairs, where this equipment was placed at the point of the incoming power supply where the harmonic deformation is most important. These equipment have had a great impact in the heavy setup, and industrial countries for two decennaries earlier, so

Presents, market force per unit area force per unit areas on betterment public presentation have driven the development of better solution for the

The demand for UPS system for proviso of uninterrupted power, and power conditioning of critical tons has seen a wider audience, since the oncoming of power electronics-based tonss, which contain inactive energy-storage-circuit elements such as inductances and capacitance, harmonizing to [ 1 ] and [ 2 ] .

Uninterruptible Power Supply systems are described as systems that produce a steady and uninterrupted jumping current to any applied burden.

A Smart Uninterruptible Power Supply ( UPS ) system is been designed. The smart system uses the progresss in power electronics to carry through such as the vaulting horse and encouragement convertors, which promises a better consequence as opposed to early engineerings, to efficaciously provide a changeless electromotive force to a critical burden.

The online dual transition design scheme has been adopted for this undertaking. This determination was based on the advantages of the online design scheme over others ; these positions are presented backed by clear literature included in this work.

The smart system contains a span rectifier, which takes the nominal AC supply for transition into DC, which is feed to a Buck convertor, whose intent to step-down the coach electromotive force to one acceptable to the back-up battery. The back-up battery is feed energy from the end product of the vaulting horse convertor during normal manner of operation, i.e. the AC supply electromotive force is within the preset scope. The burden sees end product from the back-up battery energy during back-up manner of operation, i.e. the AC supply electromotive force is n’t within the preset scope. This study showcases the design of the vaulting horse convertor and stairss taken to accomplish its stepped down electromotive force.

A Boost convertor follows the vaulting horse convertor, which on having the stepped down electromotive force of the DC coach line, stairss it up to a electromotive force imaginably greater than that demand by the burden. This excess electromotive force is a safety border set to account for the inverter efficiency ; hence the end product electromotive force of the inverter is lower but right for the burden.

The back terminal of the smart system sees the usage of a full-bridge inverter, which achieves 90 % efficiency, due to the employment of the sinusoidal pulse-width transition ( SPWM ) exchanging control technique, programmed into the Amicus 18 development board that incorporates the Microchip PICĀ® microcontroller. The accomplishment of SPWM exchanging form from simulations into a plan for the amicus 18 compiler is presented.

The inverter produces a sinusoidal end product of harmonics content pushed to higher frequences following the acceptance of the SPWM shift form. These harmonic contents are presented and the design of appropriate little sized inactive filter to rarefy the harmonics is discussed. The integrating of the inverter with the inactive filter, allows for the bringing a low total-harmonic deformation ( THD ) sinusoidal end product to the burden.

The ORCAD PSPICE simulation package is adopted to run assorted simulations of each of the power block, every bit good as the complete UPS system. The simulation consequences are explained and referenced to in the practical execution.

The paradigm UPS system was designed to power a 200 VA single-phase rated power burden. The steady province public presentation of the UPS system under such a burden is presented, the consequence explained and a tie in into the simulations and theoretical account design shown. A suited decision to the undertaking and study was reached, which ends this paper.

Scope

The range of this encompasses theoretical analysis focused around the basicss of the UPS system, every bit good as the simulation and paradigm edifice of the smart UPS system.

The basicss of the UPS system includes a definition of UPS systems, power quality and its issues, reappraisal of the bing UPS topologies, and so a expression into the conventional UPS system and its chief constituents, the developed smart UPS system and its chief constituents, exchanging devices and electric energy storage.

This work presents the smart UPS system, which incorporates the single-phase online dual transition design scheme.

Purposes

Aims

The UPS System

Introduction

UPS System

Load

Mains AC supply

Figure 2.1: UPS System Installation [ 2 ]

An uninterruptible power supply ( UPS ) system can be looked at protection of an electrical burden against assorted power quality issues that are seen in electrical systems. As seen in Figure 2.1, the UPS system is ever connected between the point of incoming brinies AC supply and the electrical burden necessitating protection against the supply fluctuations, every bit good as a entire failure of the AC supply, as described in [ 3 ] .

What is a UPS?

A UPS is said to be a system which can supply a uninterrupted, high-quality, and efficient power to electrical tonss, harmonizing to [ 4 ] . An ideal UPS system, harmonizing to [ 4 ] , would be expected to include the undermentioned functionalities:

Ability to stamp down line transients and harmonic perturbations.

Regulated sinusoidal end product electromotive force and current with a low sum harmonics deformation ( THD ) , irrespectively of burden type.

No break even in exchanging clip between assorted manners of operation.

Unity power factor.

Low cost, weight, size, and care, but high efficiency.

Low electromagnetic intervention and noise.

Why is a UPS necessary?

Ideally UPS systems are used to protect chiefly power sensitive burden known as ‘critical tonss ‘ , which are defined as tonss that are rather susceptible to any type of fluctuation seen during its normal operation to the incoming AC-input supply, as mentioned in [ 3 ] .

As the scope of microprocessor-based equipment varies and additions in the industrial and commercial sectors, so besides the discrepancies in the types of burden that are termed to be critical. A figure of electrical tonss fall under the class of critical tonss as mentioned in [ 3 ] , some of which are:

computing machine systems, including those used in control system, informations storage and processing

medical systems, such as life-support and monitoring systems

industrial processing

telecommunication equipment, like PABX

online dealing procedures and direction systems, such as cyberspace banking and shopping.

Protection of these critical tonss against the fluctuation of power or the failure can non be over-exaggerated. Statistics show that the hazard of non protecting the critical tonss can run from loss to production ( downtime ) for few proceedingss to equipment harm conveying approximately inability to merchandise, and in few state of affairss total short down in assorted concern operations, as expressed by [ 3 ] .

Power Problems

Break or in some instances, a entire failure in the normal AC-input supply can happen for a figure of grounds. All this grounds are summarized under power job subject, which goes in deepness to looking at assorted power jobs.

In order to avoid drawn-out treatment and confusion over power quality perturbations, the Institute of Electrical and Electrical Engineer ‘s standardisation organic structure produced the IEEE Std 1159 – 2009 ( latest version ) [ 5 ] , which clarifies the nomenclatures that describes the alleged electromagnetic perturbations.

Power Problem

Subcategories

Definition

Causes

Transients

Figure 2.3: Nine power quality jobs [ 5 ]

How is a UPS used?

UPS Topologies

Introduction

In the 1970s, the market saw a monolithic roar for Uninterruptible Power Supplies ( UPS ) , which was brought on by the demand for power quality in big computing machine systems, every bit good as continuity of electrical power flow. The dramatic rush in digital engineering saw the rise in the sum of applications that were sensitive to brinies supply, which brought upon the demand for more advanced and technologically advanced UPS systems.

In order to maintain up with the progresss in the UPS market, a diverse scope of UPS systems, evaluation from a 100 VA to & A ; gt ; 1000 KVA, was conceived. The diverseness in the UPS systems, lead to some confusion about the description used to place the systems, where at the clip, the normally known are, ‘on-line ‘ UPS and ‘off-line ‘ UPS.

The 1970s saw the online UPS widely used, which was known to picture the burden on AC-input brinies power. This was to be rivalled in the 1980s by the development of the off-line UPS, which was known to stand for the burden non on the AC-input brinies power. The standardization organic structure stepped in, after the development of a 3rd topology in the 1990s, the ‘line interactive ‘ , which was known for implementing reversible inverters.

The standard organic structure formed by the International Electrotechnical Commission ( IEC ) , subsequently published the criterion, IEC 62040-3. This standard splits the topologies into three types: passive standby, line synergistic and dual transition, as illustrated in [ 6 ] .

However, advanced surveies in power electronics have driven these topologies even further and given more assortment when it comes to pick of topology for any application. These surveies have been concentrated on breaking the efficiency and dependability of the system, harmonizing to [ 7 ] .

Whatever manner a UPS topology is been constructed, a common characteristic to all is the inclusion of an energy storage component, such as a battery, which acts as the supply to lade when the regular brinies is interrupted or unavailable. UPS topologies are fundamentally depicting the design of the UPS itself, each with its ain distinguishing public presentation features.

There are a figure of ways to sort the bing UPS systems but presents, these ways have been generalized into three classs, viz. inactive, rotary and intercrossed inactive or rotary, harmonizing to [ 7 ] .

The inactive UPS system are used to depict the UPS as a solid-state equipment, as opposed to the rotary UPS systems that incorporate the usage of traveling portion based around the motor or generator, harmonizing to [ 3 ] . The intercrossed inactive or rotary UPS system on the other manus, brings together the common characteristics of both inactive and rotary, as described by [ 7 ] .

In this chapter, since this the inactive UPS sees its use in bulk of applications in recent old ages and the system developed by this work is based around this, the focal point will merely be on the description and makeup of the inactive UPS system.

Inactive UPS

These systems are the most by and large used wherever a UPS system is seen. This is so because of the easiness of their usage for a wide figure of applications runing from low-power telecommunication systems and personal computing machine ( Personal computer ) , to medium-power medical system to high-power public-service corporation system. Main advantages of the inactive UPS includes its high dependability, efficiency accompanied by low entire harmonic deformation ( THD ) , harmonizing to [ 7 ] .

Inactive UPS modules all autumn under two design types, known as off-line and online. These two types can be farther sub-divided into five others ; Standby and Ferro for the off-line UPS while the online divides into line-interactive, dual transition and delta transition, see Figure 3.2: Inactive UPS System Topology [ 8 ] , where each refer to the UPS in footings of the power public-service corporation, the bringing system of the UPS upstream.

Figure 3.2: Inactive UPS System Topology [ 8 ]

A brief expression into each one of the inactive UPS topology shown in Figure 3.2: Inactive UPS System Topology [ 8 ] will be carried out following, concentrating chiefly on the five changing sub-divided topologies. This will be concluded with a brief treatment on the pick topology used for this work.

Off-Line ( Passive Standby ) UPS System

An Off-line UPS system in general footings, is one that is characterised by the power to the burden straight being supplied by the AC-input supply, in normal manner of operation, intending that the burden is subjected to fluctuations in input frequence and electromotive force within a predetermined bound.

The Passive Standby topology, as shown in Figure 3.3: Off-line UPS with inactive standby topology, has as its chief blocks as, a AC/DC convertor, which can function as the battery courser, a battery bank, a DC/AC inverter, a inactive switch, which changes the power supply to burden from the beltway way to the battery way and frailty versa, so an end product AC to lade.

Inactive Switch

Beltway

AC Supply

AC/DC Rectifier ( Charger )

DC/AC Inverter

Battery Bank

AC Output

Normal Mode

Stored-Energy Mode

Inactive Switch

Figure 3.3: Off-line UPS with inactive standby topology

The switching clip of the inactive switch is entirely dependent on the DC/AC inverter start clip, so it introduces a brief interruption in power supply, which is usually approximately 2 to 10ms ; hence a fast inverter start is ever called for, although most tonss utilizing this constellation would easy be all right with this short interruption. Since the inverter is usually off in this constellation, the UPS is n’t rectifying the power factor. The inverter is usually rated to 100 % of the load demand and is connected in analogue to the burden, stays off in the manner of operation, giving this constellation an improved overall efficiency.

There are two manners of operation for this type of constellation: normal and stored energy.

Normal Mode

During normal manner, the burden is power straight from the brinies AC supply through the beltway line, switched in by the inactive switch, the burden will be susceptible to any perturbations in the brinies supply, which fall within the preset tolerance degree of the beltway electromotive force but most frequently this is reduced by the add-on of a filter/condition ( spike/ rush suppresser or wireless frequence ) .

The AC/DC convertor charges keeps the battery bank to the full charged, so as to be able to supply power to the burden during the stored energy manner of operation. The DC/AC inverter is cautiously off during the manner of operation and will merely be turned on during the stored energy manner of operation.

Stored-Energy Mode

This manner will be called for merely and merely if the power falls outside the predetermined tolerance of the beltway line, where, the burden will be supplied power through the battery bank via the inverter by the inactive switch, until the battery electromotive force reaches its discharge bound or the beltway line electromotive force back within the preset tolerances.

This topology comes with its advantages every bit good as disadvantages for its application in a UPS system.

Advantages

A simple design.

Small size.

Low capital and running cost.

Great overall efficiency.

These advantages owed chiefly to the usage of a low-grade inverter while the rectifier is really low evaluation, since its chief intent is a courser to the battery bank.

Disadvantages

The deficiency of ordinance of the end product electromotive force under normal manner of operation.

Longer switching clip.

A hapless public presentation with non-linear tonss.

Due to these disadvantages, the application of the constellation is besides limited to low-power 1s such as personal computing machines typically & A ; lt ; 2kVA.

Off-Line ( Ferroresonant Standby ) UPS System

This topology work in a similar manner to that of the inactive standby UPS system but in an betterment to that, it offers inactive electromotive force ordinance through its ferroresonant transformer, which is a non-linear transformer, see Figure 3.4: A Ferroresonant Transformer [ 9 ] [ 9 ] . This transformer is been engineered to ever supply about changeless electromotive force at the secondary twist ( end product ) despite any fluctuation in the primary twists ( input ) , by operating at a point of magnetic impregnation, where the Fe nucleus is so strongly magnetized that no addition in magnetic flux is seen, though the weaving current is increased, as described by [ 9 ] .

To contend the consequence of deformation to the sine moving ridge due to the impregnation, a ‘tank circuit ‘ , shown as the resonating LC circuit in Figure 3.4: A Ferroresonant Transformer [ 9 ] , which is adjusted to fit the power supply frequence, acts as a filter that discards any harmonics produced. This non-linear transformer varies from a normal additive transformer in footings of the end product electromotive force, where in the instance of the non-linear ; the end product electromotive force ne’er strays outside a pre-set ordinance set, typically 1 % – 4 % , irrespective of the fluctuation to the input electromotive force while the additive transformer as a direct proportionality to its input, harmonizing to [ 8 ] and [ 9 ] .

Figure 3.4: A Ferroresonant Transformer [ 9 ]

The inclusion of the ferroresonant transformer in the off-line UPS, offers a capableness of siting through short losingss in power due to its armored combat vehicle circuit, which is characterised by its ability to hive away energy for up to half rhythm ; hence when combined with the inverter and inactive transportation switch gives an uninterrupted transportation to an surrogate beginning, harmonizing to [ 9 ] . The topology has in its constellation, as seen in Figure 3.4: On-line UPS with ferroresonant standby topology, an AC supply, a battery courser, the battery bank, a DC/ AC inverter, the ferroresonant transformer and an end product AC to lade.

Ferroresonant Transformer

AC Supply

Battery Charger

DC/AC Inverter

Battery Bank

AC Output

Normal Mode

Stored-Energy Mode

Inactive Switch

Figure 3.4: On-line UPS with ferroresonant standby topology

There are two manners of operation of the ferroresonant standby topology: normal and stored-energy.

Normal Mode

During normal runing conditions, the burden is supplied a changeless electromotive force from the ferroresonant transformer through the inactive switch, irrespective of fluctuation in the input supply and provides good power conditioning for perturbation like that of electrical line noise. The input supply besides charges the battery through the battery courser ; hence the battery is susceptible to the input electromotive force fluctuations.

Stored-Energy Mode

When there is a power outage of the input supply, this manner will be called upon via the inactive switch which sets the power to that from the inverter. During this short switch, the burden wo n’t see this break chiefly due to the stored energy in the armored combat vehicle circuit of the ferroresonant transformer. Power is so supplied to the transformer from the battery through the inverter until the input power is restored but the UPS will close down power to the burden if either the battery electromotive force degree reaches a preset lower bound ( liberty ) or the inverter mistakes, if the input power is non restored.

The ferroresonant standby topology comes with its advantages every bit good as disadvantages for its application in a UPS system.

Advantages

Simplicity.

Preservation of energy in the resonating armored combat vehicle circuit, gives an ability to let short break in power without any break to burden.

Output electromotive force is ever maintained changeless despite significant input electromotive force fluctuation.

The non-linear transformer can digest inordinate burden and even a fleeting electromotive force rush.

Harmonic filtering between the input power and the burden.

Disadvantages

Energy is squandered in the concentrated Fe nucleus due to hysteresis, bring forthing great heat in the procedure.

Frequency differences are non tolerated.

Voltages generated by the armored combat vehicle resonant circuit are rather high, so expensive capacitances are needed and any applied scientist working on this will be exposed to unsafe working electromotive forces.

On-line ( Line-Interactive ) UPS System

Line-interactive UPS, similar to the off-line UPS system, differing by the continuity of power to the burden at all times via the inverter, which besides operates as an AC/DC convertor to bear down the battery, leting for brinies AC supply to be conditioned at the input frequence. This constellation, as shown in Figure 3.5: On-line UPS with line-interactive topology, consists of the AC-input supply, a inactive switch, a bidirectional convertor, the battery bank and the end product AC to lade.

Inactive Switch

AC Supply

Bidirectional Converter

Battery Bank

AC Output

Battery Charger

DC/AC Inverter

Normal Mode

Stored-Energy Mode

Figure 3.5: On-line UPS with line-interactive topology

There are three manners of operation for this topology: normal, energy-stored and beltway.

Normal Mode

During this manner of operation, every bit long as the AC-input supply is within a pre-set scope, the burden is supplied power through inactive switch and the parallel affiliated bidirectional convertor ; therefore the power to burden is conditioned since the reactive power is ever near to integrity. The bidirectional convertor besides does the work of bear downing the battery when needed, while maintaining the end product electromotive force stable and sinusoidal. The current for the burden is chiefly taken from the AC line while the end product frequence is dependent on the input AC-input supply.

Stored-Energy Mode

In this operating manner, the bidirectional convertor Acts of the Apostless as an inverter and supplies power to the burden from the battery bank, when the AC-input supply electromotive force falls outside the preset tolerance. The AC-input supply is prevented from a back flow of electromotive force from the inverter, since the inactive switch is disconnected from it. The UPS system will return to normal manner of operation, when the AC-input supply is within the preset tolerances once more or the battery liberty ( end-of-discharge ) is reached.

Bypass Mode

The line-interactive topology may include this manner for a care beltway. This manner allows for burden to be supplied power via an external beltway line in the juncture of internal malfunction of the UPS, by this work come be done with satisfaction of continual uninterruptible power to burden.

The line-interactive topology offers some advantages and throws back some disadvantages to its usage for a UPS system.

Advantages

Lower costs in comparing to the dual transition of equal power evaluation.

Good harmonic suppression for the input current.

Due to a individual transition in this topology, its efficiency is higher than that of the dual transition.

Disadvantages

Absence of isolation of the burden from the AC line.

With non-linear tonss, it has hapless efficiency, hapless guard against spikes and over electromotive forces.

Due to the inverter in analogue and non in series with the burden, end product electromotive force conditioning is limited.

In add-on to its disadvantages, the fact that frequence ordinance is non likely, the line-interactive topology can non be used for delicate burden of medium to high power evaluation ; it is hence advised to be used in application necessitating low power.

On-line ( Double Conversion ) UPS System

In this constellation ( Figure 3.6: On-line UPS with a dual transition topology ) , the DC/AC inverter is in series between the AC supply and the burden, where power will flux through it continuously, irrespectively of the manner of operation. The topology consists of the rectifier/charger, the battery bank, the inverter, the inactive switch, with an optional beltway AC-input supply and a manual care beltway option as shown by Figure 3.6: On-line UPS with a dual transition topology, harmonizing to [ 6 ] .

Manual Maintenance Bypass

AC Supply

AC/DC Rectifier /Charger

DC/AC Inverter

Battery Bank

AC Output

Normal Mode

Stored-Energy Mode

Inactive Switch

Bypass AC Supply

Bypass Mode

Merely connected if normal AC supply exists

Figure 3.6: On-line UPS with a dual transition topology

There are three manners of operation for this topology: normal, energy-stored and beltway.

Normal Mode

Power is continuously supplied to the burden, through the rectifier/ courser and inverter combination, during this manner of operation ; hence a dual transition happens, that is, AC-DC-AC, where this topology derives its name from, harmonizing to [ 6 ] .

Stored-Energy Mode

The stored-energy manner of operation comes into drama when the AC-input supply electromotive force is seen to hold fallen outside the preset tolerances, at which point the battery bank will continuously supply powers the burden through the inverter.

The UPS system will merely go out this manner, when the AC-input supply is restored or returns back to within the preset tolerances or when the preset battery liberty ( end-of-discharge ) is reached. [ 6 ]

The burden electromotive force will travel in stage with the input electromotive force through a phase-locked cringle ( PLL ) system, when the AC-input supply is returned. The dual transition allows for first-class line conditioning, where the battery bank is charged by the AC/ DC convertor and supplies power to the burden through the inverter. This puts the AC/ DC convertor as the highest cost of the dual transition topology with the highest power evaluation excessively [ 7 ] .

Bypass Mode

The beltway manner is called upon by the inactive switch or inactive beltway, if there is any internal malfunction, overcurrent ( in-rush or mistake glade ) , or when the battery is at its end-of-discharge, where the inverter shuts down. Bypass nevertheless, implies the end product and input frequence must be indistinguishable, this is in order to guarantee successful power transportation. [ 7 ] , [ 6 ]

Synchronism between the beltway AC supply and the AC-input supply is needed, which will guarantee the power transportation is done outright [ 6 ] . As an excess option, the care beltway is added to this topology, constructed to let for care to the UPS system be carried out without break to the flow of power to burden. The care beltway is manually operated by a switch.

As with other topologies, the dual transition topology offers its ain advantages and disadvantages, these are listed following.

Advantages

Double transition topology, offers greatest grade of critical supply unity, since the burden, in most instances, ever receives processed power through the inverter.

Isolation of the burden from the upstream fluctuations such as over electromotive forces, rush or spikes.

Precise end product electromotive force ordinance and a really broad tolerance of the AC-input electromotive force fluctuations.

In the event of AC-input failure, power transportation to battery bank is instantaneous.

A high degree public presentation under transient or steady province conditions.

Output frequence can be exactly regulated or can be changed by merely disenabling the inactive switch.

An added option for system care manually.

Disadvantages

The rectifier in the dual transition topology makes it achieves a lower power factor and high sum harmonic deformation ( THD ) at the input.

A lower efficiency than its other opposite numbers, which is chiefly due to the presence of its dual transition.

There is a high monetary value to pay for this topology.

In retrospective of the drawbacks of the dual transition, it is the most preferable topology, when it comes to power conditioning and ordinance, burden protection or overall public presentation, chiefly due to its legion advantages.

On-line ( Delta-Conversion ) UPS System

This topology was developed in order to counterbalance for the lacks of the typical line interactive and dual transition UPS systems. The delta transition UPS system ( Figure 3.7 ) consists of two bidirectional convertors ; both connected the battery bank, the inactive switch and a series delta transformer. [ 7 ] , [ 10 ]

Inactive Switch

AC Supply

Series Bidirectional Converter ( Charger )

Parallel Bidirectional Converter

Battery Bank

AC Output to Load

Normal Mode

Stored-Energy Mode

Seriess Transformer

Figure 3.7: On-line UPS with a delta-conversion topology

The series bidirectional convertor is rated at 20 % of the end product power and connected to the AC-input supply through the series transformer. It serves as a current regulator, guaranting the input power factor is at integrity and counterbalancing for any differences between the input and end product electromotive forces.

The parallel bidirectional convertor, serves as the normal inverter is connected in analogue to the burden, and to the full rated at 100 % of the end product power. Using pulse-width transition ( PWM ) control, the parallel convertor stabilizes the burden electromotive force and regulates the battery charging, when the AC-input supply is within the preset tolerances. [ 7 ] , [ 8 ] and [ 10 ]

A description of the two manners of operation of the delta-conversion topology: normal and stored-energy, would follow.

Normal Mode

During this manner of operation, if the burden is at 100 % , battery to the full charged and no difference between the burden and AC-input supply, the burden is supplied all power straight from this AC-input through the series transformer with no power through the convertors.

When a electromotive force droop of the AC-input supply is seen the convertors are called into action, where they compensate for the droop by taking from the AC-input supply, foremost through the parallel convertor, so the series convertor and eventually through the series transformer, in that contrary order, adding to the reduced electromotive force to guarantee 100 % rated power is feed to lade, see Figure 3.7.

Inactive Switch

AC Supply

Series Bidirectional Converter ( Charger )

Parallel Bidirectional Converter

Battery Bank

AC Output to Load

Normal Mode

Extra power taken from AC supply

Seriess Transformer

Figure 3.7: Delta-conversion UPS power flow during electromotive force droop

For a electromotive force crestless wave, the series convertor takes in the excess electromotive force from the AC-input supply through the series transformer and feeds it frontward to the burden, adding to the lower electromotive force from the AC-input supply through the parallel inverter, see Figure 3.7.

Inactive Switch

AC Supply

Series Bidirectional Converter ( Charger )

Parallel Bidirectional Converter

Battery Bank

AC Output to Load

Normal Mode

Extra power taken to AC supply

Seriess Transformer

Figure 3.7: Delta-conversion UPS power flow during electromotive force crestless wave

To bear down the batteries, excess power is taken from the brinies and passed backwards through the parallel convertor ; hence the battery charging is done entirely by the parallel convertor. [ 10 ]

Stored-Energy Mode

When AC-input supply falls outside the preset tolerances, power is delivered to the burden the from battery bank through the parallel inverter, in this manner of operation. The parallel inverter is synchronised with the AC-input supply, therefore it controls the end product electromotive force and frequence through an internal frequence mention set by the pulse-width transition control strategy. [ 10 ]

Advantages

High efficiency due to absence of transition of the major per centum of power, around 85 % , fluxing from the AC-input supply to the burden.

Can be used in high power rated applications, which specific efficiency as a cardinal precedence.

Disadvantages

It comes with a complicated control strategy, presenting a hinderance to its use in certain applications.

An obviously deficiency of electrical isolation between the burden and the incoming upstream AC-input supply.

Choice of Topology

In order to reason on any type of topology to utilize for a UPS system, the undermentioned factors are finally the make up one’s minding factors.

Rated power of the burden to be supported by the UPS system.

The available cost

Main Components of a UPS System

Introduction

The chief constituents of any UPS systems are doubtless the inverter, rectifier/ courser and a storage bank such as the battery, see figure xx. These three constituents are non needfully used in all systems but typically when an uninterruptible system is described, they are the dominant constituents, harmonizing to [ 3 ] . In this chapter, the composing of these blocks will be looked into, but foremost the interaction along the UPS system in footings of electromotive force degrees will be introduced.

Voltage Interaction

As this study focuses on the transformerless UPS system, an illustration of electromotive force transition through this will be used. Sing a system, fed with a 240Vac single-phase brinies supply with an intended end product of 240Vac, the electromotive force degrees will be

Inverter

Harmonizing to the IEEE-SA criterions lexicon, an inverter, besides known as a power inverter, is described as a machine, system or device that produces an jumping current ( AC ) by altering from a direct current ( DC ) [ 11 ] . However, an inverter is sometimes used to depict a variable-frequency thrust ; a device used in an AC electric motor, such as an initiation motor, to command its runing velocity that converts incoming fixed AC from one frequence into another [ 12 ] .

An inverter can be a single-phase or three-phase based topology ; since this paper brings to life the single-phase UPS, merely the single-phase inverter will be discussed. This treatment will get down with the categorization of inverters, a brief description of each,

Categorization of Inverters

In UPS systems, the chief intent of the inverter is to change over the DC nexus electromotive force, i.e. energy from the battery bank, into an AC end product suitable for the affiliated burden ; hence the focal point in this paper will be on the DC – AC Inverter topology, which takes the typical block diagram as seen in figure twenty. There are two types related to this topology: current beginning inverter ( VSI ) and electromotive force beginning inverter ( CSI )

Current Source Inverter

VDC

IAC

Output Current

IDC

Liter

Figure 4.3: Block Diagram of a Current Source Inverter ( CSI )

Voltage Source Inverter

The most widely used category of inverter is the electromotive force beginning inverter, as this has seen a great trade of attending

IDC

VDC

IAC

Output Voltage

C

Figure 4.3: Block Diagram of a Voltage Source Inverter

Principle of Operation

There are two chief types used to configure a typical single-phase inverter: half-bridge inverter and full-bridge ( H-bridge ) inverter [ 7 ] . The chief difference between is the usage of four switches in the full-bridge inverter to the two switches used in the half-bridge inverter.

Commonalty between these constellations is the usage of transistor switches. The switches are driven by signals, which turn them on and off every bit desired. The thrust exchanging signal to the switches must ever be in anti-phase, i.e. 180 & A ; deg ; off of stage, in order to accomplish the coveted end product, otherwise, a short circuit is created and harm to equipment is at hand. Besides, an excess step is needed to guarantee that there is ever a dead set between the clip one switch goes away and the other bends on, otherwise a shoot-through mistake will be experienced.

This subdivision of the paper will lucubrate on these two types, peculiarly on the full-bridge inverter, as its application is more normally favoured, besides a note that from here onwards, when an inverter is referred to merely the VSI inverter topology is shown.

Half-Bridge Inverter

The half-bridge inverter has its two switches connected in series across the DC supply, as in Figure 4.3: Half-Bridge Inverter Configuration, the top S1 switch connected to the positive terminus while the bottom switch S2 is connected to the negative terminus. The point of connexion between the two switches provides the end product, either negative or positive.

Figure 4.3: Half-Bridge Inverter Configuration

A simple truth table summarizes the shift form and manner of operation of the half-bridge inverter topology ( Table xx ) , matching to calculate xx.

Table 4.3. : Half-Bridge Inverter Truth Table

S1

S2

Output Condition

Off

Off

No end product

Off

On

Negative

On

Off

Positive

On

On

Short Circuit ( Shoot-Through )

Advantages

Simplicity of utilizing a lower figure of switches

Cheaper cost and simple control

Disadvantages

Lower efficiency

Merely bipolar ( single-pulse ) PWM can be used to drive its switches

Output is a square moving ridge rich in uneven harmonics

Requires a big filter to convey it to the desired sinusoid wave form

These reverses guarantee that this topology is merely used for low-power applications ; medium- and high-octane application will necessitate to be supplied utilizing the full-bridge topology.

Full-Bridge Inverter

The full-bridge inverter, see Figure 4.3: Full-Bridge Inverter Configuration, has its four switches S1, S2, S3 and S4, connected in series two-by-two in two legs. The connexion points in the center of the switches provide the end product, which can be either negative, positive or zero.

Figure 4.3: Full-Bridge Inverter Configuration

A simple truth table summarizes the shift form and the operation of the full-bridge inverter topology ( Table 4.3. : Full-Bridge Inverter Truth Table ) , matching to Figure 4.3: Full-Bridge Inverter Configuration.

Table 4.3. : Full-Bridge Inverter Truth Table

S1

S2

S3

S4

Output Condition

Off

Off

Off

Off

No end product

Off

Off

On

On

Nothing

Off

On

Off

On

Negative

On

Off

On

Off

Positive

On

On

Off

Off

Nothing

On

On

On

On

Short Circuit ( Shoot-Through )

Advantages

Better efficiency

Disadvantages

Complex control technique

Output AC Voltage

As seen from the two inverter constellation, half-bridge and full-bridge, the end product electromotive force though alternating, is a square wave form, whose amplitude is determined by the DC electromotive force input and frequence by the control thrust signals frequence.

For use on critical tonss, which this study deals with, a square wave form end product is merely non sufficient but instead a 50Hz sine wave form is required. The widely used method of obtaining an end product that is of a sinusoidal signifier is the Pulse-Width Modulation ( PWM ) , this method and its control techniques are discussed following.

Pulse-Width Modulation ( PWM )

PWM is a technique of changing the pulse breadth of a control signal in order to command the end product wave form. The pulse breadth is described as the continuance between the 50 % amplitude points on the taking border and the draging border of the pulsation, as shown by [ 13 ] Figure 4.3: Square wave form depicting pulse breadth [ 13 ] , unless otherwise specified [ 14 ] .

Figure 4.3: Square wave form depicting pulse breadth [ 13 ]

The end product electromotive force is straight relative to the responsibility rhythm and the amplitude of the DC input electromotive force, where the responsibility rhythm is calculated utilizing equation 1.

where, vitamin D is the responsibility rhythm, pw is the pulse breadth in seconds and T is the period in seconds ( s ) .

Since the amplitude of the DC input electromotive force is normally fixed, the responsibility rhythm of the control signal into the switches, is varied to determine the end product electromotive force. The consequence of the fluctuation shown in Figure 4.3: The consequence of changing the responsibility rhythm [ 13 ] , is what is known as PWM, the responsibility rhythm calculated by equation 1.

Figure 4.3: The consequence of changing the responsibility rhythm [ 13 ]

A Smart UPS System

Traditional UPS

Power Electronicss Solution

For this study, the

Choice of Topology – Online UPS System

The determination to implement an online UPS system was ruling down to the effectivity of this topology. Other consideration was down to factors such as the size of UPS, burden demand, and burden procedure demands of which there are

Sizing the UPS

Main Components

The execution of the transformerless UPS architecture began by taking a brief reappraisal of the system ‘s chief constituents, described in phases shown as blocks in figure twenty. Each of the blocks will be broken into and the internal composing will be presented.

Inverter

As the chief and most ambitious constituent block is the inverter. It plays the most of import function of bring forthing the accurate power end product at the rated frequence to the critical burden, so a elaborate attending to the inverter is a must. As already elaborated in old chapter, the pick of an H-bridge topology is most advantageous for the online dual conversation ; hence this is used for the execution. The following determination so lied in the type is switch to be used to for the H-bridge, the procedure of which will be presented.

Choice of Switch – Power MOSFET

Deciding on the most equal switch to utilize lied chiefly between the transistor types ; IGBT and power MOSFET, this is because for the intent of the usage in the UPS system, fast shift is needed, that is the switch must be capable of operating at high exchanging frequence. The comparing between these two shown in table twenty, gives a clear indicant that the MOSFET is most equal for the demand.

Speed

The velocity of the MOSFET can be by and large represented as the entire clip it takes to alter province from on to off or frailty versa, cognizing that a considerable sum of power is dissipated when a MOSFET non in either of its operating provinces. The velocity is hence calculated by adding the turn-on hold clip, rise clip, turn-off hold clip, and autumn clip, ensuing in a velocity of 115ns for the IRF740, extracted from the datasheet ( figure twenty ) ; hence a maximal frequence of about 8.7MHz.

Figure 5.3: Switch overing Speeds of IRF740 from the Datasheet

Heat Effectss

Free-wheel rectifying tube

MOSFET Driver

In order to expeditiously power on the MOSFET switch, the electromotive force supplied to the gate terminus, gate-source electromotive force must be greater than the MOSFET ‘s threshold electromotive force ( VGS & A ; gt ; VTH ) and the supply electromotive force to the drain VDS must be greater than VGS – VTH ; hence the demand for an appropriate driver circuit to guarantee this..

The ICL7667 double power MOSFET driver used is one that is designed to change over TTL degree signals to high current end products

Figure 5.3: Conventional Diagram for the MOSFET Driver Circuit

Circuit

Uniting the Power MOSFET and the driver circuit, the finished inverter circuit diagram can be seen in figure twenty, where

The power MOSFET used is the IRF740, with evaluation of 400V, RDS ( ON ) of less than 55m? and ID of 10A.

Opto-isolator

Besides known as optocoupler, this device is a really

Microcontroller – Myamicus