Development of Improved Performance Switchmode Converters for Critical Load Applications

By: Pattnaik, SwapnajitContributor(s): Panda, Anup Kumar [Supervisor] | Mahapatra, Kamalakanta [Supervisor] | Department of Electrical EngineeringMaterial type: TextTextLanguage: English Publisher: 2011Description: 190 pSubject(s): Engineering and Technology | Electrical Engineering | Power Systems | Power ElectronicsOnline resources: Click here to access online Dissertation note: Thesis (Ph.D)- National Institute of Technology, Rourkela Summary: Emerging portable applications and the r apid advancement of technology have posed rigorous challenges to power engineers for an efficient power delivery at high power density . The foremost objectives are to develop high efficiency , high power density topologies such as: buck, synchronous buck and multiphase buck converters, with the implementation of soft switching technology to reduce switching losses maintaining voltage and c urrent stresses within the permissible range. Demand of low voltage power supply for telecom system leads to narrow duty cycle which compels to increase operating switching frequency. Design of conventional buck converter under narrow duty cycle is quite o bjectionable since it leads to poor utilization of components as well as it degrades the system efficiency . A high switching frequency operation reduces the switch conduction time that leads to large increase in switching losses and increases the control c omplexity. Therefore, duty cycle has to be extended and at the same time switching losses have to be minimized. Transformer based topology can be used to extend the duty cycle. But to reduce switching losses soft switching techniques should be implemented. An isolated buck converter with simple clamp capacitor scheme is proposed to reduce switching losses and to extend duty cycle by optimizing the turn ratio. Extended duty cycle impose limit on dead time. Dead time has to be controlled with respect to duty cycle to reduce body diode conduction loss and to avoid the shoot through conditions in our proposed topology . The proposed clamp capacitor scheme control the dead time as well as provide better efficiency with reduction in switching losses maintaining ri pples within the allowable range. Current trends in consumer electronics demand progressively lower - voltage supplies. Because of significantly lower conduction losses, synchronous rectifiers i.e. MOSFETs, are xi now used essentially in all low - voltage dc powe r supplies. Passive snubbers or an active auxiliary circuit is generally used to reduce the other important loss i.e. switching loss. Also it reduces the voltage and current stresses of the switches. In this work two zero - voltage - transition (ZVT) pulse width modulated (PWM) synchronous buck converter s are proposed , one with passive auxiliary circuit and the other with active auxiliary circuit. These are designed to operate at low voltage and high efficiency typically required for portable systems. The op eration principles and a detailed steady - state analysis of the ZVT - PWM synchronous converter s are presented. All the semiconductor devices besides the main switch operate under soft switching conditions. Thus, the auxiliary circuit provides a larger overal l efficiency. In addition, the circuits are cheaper and more reliable, and had a higher performance/cost ratio. Future microprocessor poses many challenges to its dedicated power supplies, suc h as low voltage, high current, high power density, and high ef ficiency etc. To decrease the power consumption, supply voltage for the next generations of microprocessors must be as low as possible. The supplied voltage is going to drop to a level of 0.7 V, the total power consumption keeps flying up because of the tr emendously increased current. In order to meet the power supply requirements of the new generation microprocessors, a soft - switch multi - phase PWM dc - dc converter with an auxiliary circuit has been proposed. Losses present in multiphase buck converter due t o increase components and switches are reduced with the proposed soft switching technique. The proposed converters presented in this research work are well defined by its mathematical modeling and its mode of operations. The feasibility of all the proposed converters for different applications is confirmed by simulation and experimental results.
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Thesis (Ph.D)- National Institute of Technology, Rourkela

Emerging portable applications and the r
apid advancement of technology have
posed
rigorous challenges to power engineers for an efficient power delivery at high power density
.
The foremost objectives are to develop high
efficiency
, high power density topologies
such
as:
buck, synchronous buck and multiphase buck converters, with the implementation of soft
switching technology to reduce switching losses
maintaining voltage and c
urrent stresses
within the permissible range.
Demand of low voltage power supply for telecom system leads to narrow duty cycle
which compels to increase operating switching frequency. Design of
conventional buck
converter
under narrow duty cycle is quite
o
bjectionable since it leads to poor utilization of
components as well as it degrades the system efficiency
.
A high switching frequency
operation reduces the switch conduction time
that leads to
large
increase in switching losses
and increases the control c
omplexity.
Therefore, duty cycle has to be extended and at the
same time switching losses have to be minimized. Transformer based topology can be used to
extend the duty cycle. But to reduce switching losses soft switching techniques should be
implemented.
An isolated buck converter with simple clamp capacitor scheme is proposed to reduce
switching losses and
to extend duty cycle
by optimizing the turn ratio. Extended duty cycle
impose limit on dead time. Dead time
has
to be
controlled with respect to duty
cycle to
reduce body diode conduction loss and to
avoid the shoot through conditions in our proposed
topology
. The proposed clamp capacitor scheme control the dead time as well as provide
better efficiency with reduction in switching losses maintaining ri
pples within the allowable
range.
Current trends in consumer electronics demand progressively lower
-
voltage supplies.
Because of significantly lower conduction losses, synchronous rectifiers i.e. MOSFETs, are
xi
now used essentially in all low
-
voltage dc powe
r supplies. Passive snubbers
or an active
auxiliary circuit is
generally used to reduce
the
other important loss i.e. switching loss. Also it
reduces the voltage and current stresses
of the switches.
In this
work two
zero
-
voltage
-
transition (ZVT) pulse
width modulated (PWM)
synchronous buck converter
s are proposed
,
one with passive auxiliary circuit and the other
with active auxiliary circuit. These are
designed to operate at low voltage and high efficiency
typically required for portable systems. The op
eration principles and a detailed steady
-
state
analysis of the
ZVT
-
PWM synchronous converter
s
are presented. All the semiconductor
devices besides the main switch operate under soft switching conditions. Thus, the auxiliary
circuit provides a larger overal
l efficiency.
In addition, the circuits are cheaper and more
reliable, and had a higher performance/cost ratio.
Future microprocessor poses many challenges to its dedicated power supplies, suc
h as
low voltage, high current,
high power density, and high ef
ficiency
etc. To decrease the power
consumption, supply voltage for the next generations of microprocessors must be as low as
possible. The supplied voltage is going to drop to a level of 0.7 V, the total power
consumption keeps flying up because of the tr
emendously increased current. In order to meet
the power supply requirements of the new generation microprocessors, a soft
-
switch multi
-
phase PWM dc
-
dc converter with an auxiliary circuit has been proposed.
Losses present in
multiphase buck converter due t
o increase components and switches are reduced with the
proposed soft switching technique.
The proposed converters presented in this
research work
are well defined by its
mathematical modeling and its mode of operations. The feasibility of all the proposed
converters for different applications is confirmed by simulation and experimental results.

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