Switch Mode Rectifier
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Transcript of Switch Mode Rectifier
SINGLE PHASESWITCH MODE RECTIFIER
WITH AN IMPROVED DESIGN
Prepared by Treasa Sebastian S7 EEE Roll no:54
OVERVIEW Introduction Standard switch mode rectifier (SMR-S) Operating principle of SMR-S Need for boost converter Advantages Disadvantages Improved SMR-S Performance of proposed SMR-S Conclusion references
INTRODUCTION SMR is an essential
component in UPS and SMPS
SMR-S is the standard single phase boost type switch mode rectifier
STANDARD SWITCH MODE RECTIFIER (SMR-S)
SMR-S Consists of diode bridge rectifier and a boost converter
Diode bridge rectifier performs AC to DC conversion
Boost converter is a DC-DC step up chopper
Inductor Lm is source impedence
OPERATION OF SMR-S Operates in 2 modes
ON mode –period during which switch is on
OFF mode- period during which switch is off
ON MODE
Switch S is closed Input voltage after rectification
appears across the inductor Boost inductor Lb stores
energy No transfer of energy from
source to load
OFF MODE Switch S is open Stored energy in the
inductor along with supply is released to the load
Thus voltage is stepped up
need for boost converter Voltage across the
capacitor is always close to the peak value of AC input voltage
So, diodes remain reverse biased during major part of each half cycle
need for boost converter Diodes are forward biased only when AC input voltage
exceeds the capacitor voltage Bridge circuit has supply current only when instantaneous
magnitudes of rectified sine wave are closer to peak magnitude
Thus waveform of AC line current will be in the form of short narrow pulses
AC line current
need for boost converter All the harmonic components of pulsed AC line current
increases rms value of total line current ,thus
power factor decreases Supply voltage gets distorted Power supply environment gets polluted /power quality
decreases
need for boost converter In a boost converter ,
Chopper is operated at a high switching frequency (100kHz)
Duty cycle of chopper is continuously varied during each half cycle
need for boost converter
Chopper maintains the output at the high fixed value by automatic variation of the duty cycle
chopper input voltage is just below the rectified value of AC input voltage
Diode bridge is enabled to feed current into the chopper during entire duration of each half cycle
ADVANTAGES Operates at unity power factor Exhibits negligible harmonics in input current Acceptable ripples in DC bus voltage
DISADVANTAGES High switching losses ,because of high switching
frequency , and results in reduction in efficiency Requirement of input filter Exhibits poor performance and distorted input current
under light load conditions SMR-S with satisfactory operation is not available above
2kW
DISADVANTAGES To get a sinusoidal reference current waveform
inductor Lm having a large value is used Switching frequency is increased
As the value of Lm increases , its size also increases So , high switching frequency is employed
DISADVANTAGES high switching frequency implies high turn on and off rate
of a high current
Therefore switching losses increases
Efficiency of SMR decreases
PROPOSED TOPOLOGY OF SMR
PROPOSED TOPOLOGY OF SMR
Two boost converters are used Main boost converter Auxiliary boost converter
Switch of main boost converter is operated at a high frequency
Auxiliary switch is operated at a low frequency Current in main switch Sm is diverted through low
frequency auxiliary switch Sa
Functions of auxiliary switch it works as a current absorber for switch in main boost
converter It works as a current source for the DC bus capacitor Cdc
PERFORMANCE OF PROPOSED SMR
Very low frequency auxiliary boost converter controls almost all power delivered from source to load
High frequency main switch operates at a low current
Modified topology of SMR has minimum power dissipation , as chopping of high current at high frequency does not take place
PERFORMANCE OF PROPOSED SMR
Very high operating frequency of main boost converter does not pose operational challenges, because, once the auxiliary converter comes into action the current through main switch is very small and does not cause a noticeable power loss.
PERFORMANCE OF PROPOSED SMR
Switching action of main boost converter provides sinusoidal shape to the input supply current
Sinusoidal shaped supply current is locked in phase with the source voltage
Thus power factor is maintained at a high value
APPLICATIONS SMPS UPS For battery charging Traction drives
CONCLUSION
Switch mode rectifier operates at unity power factor at input and manageabe ripples in the DC load voltage
High switching frequency of boost converter shapes the input current close to sinusoidal
But it has high switching losses An auxiliary boost converter in tandem with main boost
converter is capable of eliminating high switching losses
REFERENCES
Brij.N.Singh ,Ambrish Chandra ,Parviz Rastogoufard ,”Single phase switch mode boost rectifier: an improved design/control applied to AC-DC system to power up telecommunication system”, Telecom. energy conference , pg.no:611-618,Dec 2002.
Dawande.M.S , G.K.Dubey.”Single phase switch mode rectifiers”, IEEE power electronics pg :637-643 vol.2 ,1996.
Joseph Vithayathil ,”Power electronics-principles and applications” , 1995 by McGraw-Hill , Inc.
www.fairchildsemi.com