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The file contains details of dc-dc power coveerter
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© www.anoopmathew.110mb.com
Choppers- Fixed DC to Variable DC Converters
- Anoop MathewHOD, ECE Dept.Vedavyasa Institute of TechnologyVedavyasa Hills, Malappuaram Dist.Kerala 673632
© www.anoopmathew.110mb.com
Classification of Chopper
§ Based on input/output voltage levelsØ Step-down Chopper (Buck converter)Ø Step-up Chopper (Boost Converter)
n Direction of output voltage and currentØ Class AØ Class BØ Class CØ Class D
Contd ...
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Classification of Chopper
n Based on Circuit operationØ First (Single) Quadrant ChopperØ Two-quadrant ChopperØ Four Quadrant Chopper
n Based on Commutation Method Ø Voltage Commuted ChopperØ Current Commuted ChopperØ Load commuted ChopperØ Impulse Commuted Chopper
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Classes of chopper (A,B,C,D &E
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Buck Converter (Step-down chopper)
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Discontinuous load current
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Continuous load current
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Principle of operation
Ø Duty ratio (k) = (Ton/ Ton+Toff)
Ø At Ton, Switch is closed.
Ø At Ton,load current freewheels through DF – effectively, load terminals are short circuited and load voltage is zero.
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Analysis
Ø Average load voltage, Vo = Vs.kØ Output voltage varies linearly with “k”.Ø Ton+Toff = chopping periodØ Load voltage can be controlled by changing
the duty ratio.Ø As k reduces, current becomes discontinuous.Ø Average load current, Io = Vs.k/RØ Vo(RMS) = kVkV ss =2
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Boost Converter (Step-up chopper)
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Waveforms
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Principle of operation
Ø When S is ON à L charges.Ø When ‘S’ is OFF à inductor current
flows through diode and load during Toff
Ø Vo = Vs+L(di/dt)Ø High value inductor is preferred
for lower ripples.
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Analysis
Energy stored in the inductor W1, during TON :
W1 = Vs. Is. TON
During TOFF, Energy released by the inductor to the load is:
W0 = (Vo-Vs). Is. TOFF
At steady state and consider the system is lossless;
Vs. Is. TON = (Vo-Vs). Is. TOFF
ie, Vo = [(TON +TOFF)/ TOFF] x Vs
Vo = Vs/(1-k)
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References
[1] A. Maamoun, “DEVELOPMENT OF CYCLOCONVERTERS”, IEEE Trans. 2003.
[2] Ned Mohan et al, “Power Electronics”, Weilypublications 2005
[3] M.D. Singh & K.B Khanjandani, “Power Electronics”,TMH 2006
[4] Cyril W. Lander “ Power Electronics”, McGraw Hill International Editions 2007