09-11-2012, 04:04 PM
Coupled Inductor and Voltage-Doubler Circuit for
High Step-Up DC-DC Converter
Coupled Inductor and Voltage-Doubler.pdf (Size: 929.53 KB / Downloads: 66)
INTRODUCTION
A DC-DC converter converts directly from dc to
dc and is simply known as a DC converter. A dc converter
can be considered as dc equivalent to an ac transformer with
a continuously variable turn’s ratio. Like a transformer, it
can be used to step down or step up a dc voltage source.
Dc converters are widely used for traction motor
control in electric automobiles, trolley cars, marine hoists
and mine haulers. They provide smooth acceleration control,
high efficiency and fast dynamic response. Dc converters
can be used in regenerative braking of dc motors to return
energy back into the supply and this feature results in
energy savings for transportation systems with frequent
stops. Dc converters are used in dc voltage regulators; and
also used in conjunction with an inductor to generate a dc
current source, especially for the current source inverter.
A boost converter is generally used and it has
several advantages such as simple structure, continuous
input current, and clamped switch voltage stress to the
output voltage. However, it is very difficult to satisfy both
high voltage conversion ratio and high efficiency at once.
This is primarily due to the parasitic resistances, which
cause serious degradation in the step-up ratio and efficiency
as the operating duty increases.
During this time interval, S1 is still turned off and
S2 is still turned on. The current-flow path is shown in Fig.
(d). The DC source, Lm, and Lk1 are series connected to
transfer their energies to Lk2, C1, and the load. Thus, iLm
and iLk1 are decreased and iLk2 is increased. Meanwhile,
the energy stored in Lk1 is recycled to C1 and the load. The
energy stored in C2 is still discharged to the load.
APPLICATIONS
The dc–dc converter with high step-up voltage gain
is widely used for many applications, such as fuel-cell
energy- conversion systems, solar-cell energy-conversion
systems, and high-intensity-discharge lamp ballasts for
automobile headlamps.
In the recent years, more and more industrial
applications have required DC-DC converters able to
provide a large conversion ratio with a good efficiency and
less electromagnetic interference noise. Just a few examples
show the need of a step-up or step-down of the input voltage
of at least ten times: the 48V nominal telecom DC bus has
to be boosted at the intermediate 380V DC bus needed for
the supply system of the servers for data processing when
the telecom industry is used to provide computer services .
The 12V of a car’s battery voltage has to be boosted up to
100Vduring the steady-state operation and even up to 400V
at the start-up of the high-intensity discharge (HID) lamp
ballasts used in the automotive headlamp .
ADVANTAGES
1) The leakage-inductor energy of the coupled
inductor can be recycled.
2) The voltage stresses on the switches are half the
level of the output voltage. Thus, the switches with low
voltage rating and low ON-state resistance RDS (ON) can
be selected.
3) The voltage gain achieved by the proposed
converter is double that of the conventional high step-up
converter. Under the same voltage gain and duty ratio, the
turns ratio of the coupled inductor for the proposed
converter can be designed to be less than the conventional
high step-up converter.
CONCLUSION
The novel high boost converter using the coupled
inductor and voltage doubler was presented and the
operation and features have been described. Experimental
results were discussed with a 200W prototype using voltage
doublers. The proposed method eliminates the problems of
extreme duty ratio or complexity of circuits in the
conventional topology.
Also, the proposed circuit has the following
various advantages compared to the conventional booster
converters: low voltage stress, higher boost rate, higher
efficiency, and several modified circuits for other
applications. Therefore, the proposed converter can be
applied to various high boost applications, such as a battery
back-up system, fuel cells, military applications, etc.