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.

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