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switch mode rectifier
(SMR)
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TALK FLOW INTRODUCTION
OPERATING PRINCIPLE OF STANDARD SMR
PWM TECHNIQUES
FEATURES OF THE SMR USED IN THE POWER PLANT
CHARACTERISTICS OF AN IDEAL SMR
ADVANCED VERSION OF SMR
APPLICATIONS
ADVANTAGES
CONCLUSION
REFERENCES
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Switch mode rectifier is a rectifier usedwith an objective to eliminate certainproblems in conventional rectifier. It hasfollowing merits against conventional
rectifier-:Power factor is maintained close to unity.
Source current becomes approximately
sinusoidal.Constant dc output voltage in presence of
variation of input voltage
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Switch mode rectifier is popularlyknown as SMR .
Also referred as Unity powerrectifier(UPR)
Essential component in SMPS and UPS
Widely implemented in the field of
telecommunication. 5
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Basically consists of bridge rectifier and boostconverter
Bridge rectifier performs AC to DC convertion &boost converter is a DC to DC step up chopper
Operates in two modes- ON mode
OFF mode
ON mode-
i)switch S is closed
ii) input voltage after rectification appears acrossthe inductor, boost inductor stores energy
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ContdOFF mode-
i) The switch is open
ii) Stored energy in the inductoralong with supply is released tothe load.
iii) Voltage is stepped up
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CONTD..
Following conditions are to
be maintained during circuitoperation-
The DC output voltage must be greaterthan the peak of source voltage (V dc > Vs).
The power balance is maintained bykeeping Vdc constant irrespective ofsource voltage.
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The PWM techniques used in this caseare in the case of two categories-
A) Sinusoidal PWM (indirect currentcontrol technique)
B) Hysteresis current controltechnique (Direct current controlledPWM)
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In this case the reference modulatingvoltage, which is derived from sourceis in phase with the source voltage.
This voltage is compared with carriersignal and where ever one signal
exceeds/falls below the other one, theswitching instants of the device arederived.
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Most common method used for SMRand easier to implement.
Meant for low power application.
In this method the reference currentsignal (derived from source voltage) is in
phase with source voltage
Reference current is allowed to passthrough a hysteresis band , so that
actual current must follow within the
band. 13
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SMR used commonly in power plants andindustrial sector must have the followingfeatures like-:
light weight
Hot swappable module which allow lowmean time to repair , without requiringpower plant shut down for repair work orpreventive maintenance
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installation must be tool free i.e. modulecan be inserted and removed by hand.
There must be front panel indicator LEDsfor Rectifier failure alarm(RFA).
Separate potentiometer s must present forvoltage adjustment
ON/OFF power switch must disable DCoutput only without interrupting AC
power. 15
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The key components of the
monitoring feature are- Rectifier
Failure alarm (RFA) and LEDindicator
If the rectifier detects a problem,the red front panel LED
illuminates.
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Contd.. The RFA alarm generally signifies a
rectifier output shutdown in followingcondition:
i)When ambient and internal heat sinktemperatures are monitored, RFA isgenerated if ambient temperatureexceeds the normal level (>800) or
internal heat sink occurs(>1100
)
ii)When cooling fan of SMR fails to operatenormally
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iii)When rectifier senses bus voltage more
than the specified value
iv)Some crucial internal function of therectifier not operating correctly
In power plants the rectifier RFA
alarm provides even moreinformation. The plant provide minor
to major alarm upgrades with one or
more failures. controller candetermine the no. of SMRs on line,
detect the AC power failure
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Key components of control feature of theSMR are Remote restart (RS) & high
voltage shut down (HVSD).
The SMR must built in a high voltage shut
down set point. That means no rectifiercomponent failure should result in anoutput voltage greater than that of the setvoltage.
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To restart a rectifier that didnt HVSD
due to any fault of its own
To test a rectifier to determine if it
caused on HVSD occurrence andneeds to be replaced.
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must have an excellent power factor
high efficiencylow cost operation
Hot insertion capability must be available .
because it allows rectifier placementwithout system shutdown
control & monitoring unit must be easy to
install with minimal labour, minimuminstallation expenses and must deliver ahigh performance
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CONTDequipped with over voltage or over
current protection To avoid load or
damage of rectifier
A variable fan must be placed there to
maintain ambient temperature .
user facilities should be placed on the
front panel preferably
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MBR 1060 , MBR 1080 , MBR 1090 :They comprise a series of switchmode rectifier
This series have got guard rings forstress protection
Pb-free packages are available
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low voltage drop
low power loss
High efficiency
High operating junctiontemperature
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widely used in AC-DC converter foractive current shaping.
single phase configuration can beextended to three phase SMR
one of its vital applications is inSwitch mode power supply(smps)
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SMPS is having wide applications in the
following areas chiefly:
Consumer electronics like TVs, PCs,CD players
Tools in industries
Security systems (close circuitcameras)
Support system of PLC etc26
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Input current is approximately sinusoidalPower factor is close to unity
Fast dynamic response
High efficiencyEconomical
Light weight & reduced size .hence portable
Insensitive to variation of input voltage.
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Switch mode rectifier has a wide range of
application in the field of telecommunication
To get sinusoidal reference current inductor
having large value used , so switching frequencyincreases . Hence switching losses increases &efficiency decreases .
An auxiliary boost converter along with mainboost converter is capable of eliminating high
switching losses 28
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Moreover SMR has reached a
matured level for improving
power quality in terms of powerfactor correction(PFC), and
reducing total harmonic distortion
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Baliga, B. jayant, Advanced Power Rectifier Concepts Vol 4, no.6, 1992
Alok Jain, power electronics and its application Vol 8, no. 5, 1996
Mohan, T. undeland, W. Robbins Power Electronics Applications
Keng Wu Power Rectifiers and Converter
William Shepherd, Li zhang ,Li Zhang Crowther Power convertercircuits
http://en.wikibooks.org/wiki/Electronics/rectifier
www.edu-doc.com/pdf/switch-mode-rectifier
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