Optimal Design Method of the LLC resonant converter
using the hybrid current balancing circuit for LED lighting Author Jin-Gu Kim
Department of Electrical & Medical Convergent Engineering
Graduate School, Kangwon National University South Korea.
Abstract
In this thesis, a novel hybrid current balancing circuit and an optimum
design of LLC resonant converter for driving a current balancing circuit are
proposed.
First of all, the hybrid current balancing circuit was proposed for compensating
current deviation among LED strings. LEDs have been widely used in lighting,
automobiles, and airplanes owing to their excellent light output characteristics
and long lifespan. Though LEDs are manufactured under the same process,
variations in impurity concentrations cause electrical deviation among LEDs.
This electrical deviation results in current unbalance of LED strings. The
resulting current unbalance does not only reduce the life time of the LED
but also cause non-uniform luminance of LEDs connected in parallel. The
LED driving circuit is researched to solve the above problems. In this
thesis, a novel hybrid current balancing circuit with a Y-type current
balancing transformer and a voltage doubler rectifier circuit was proposed
for the compensation of 6 LED strings with a simple structure.
Secondly, the Optimal design method of LLC resonant converter for driving
hybrid current balancing circuit was proposed. The difference between the
proposed optimal design method of LLC resonant converter and conventional
design method can be divided into three categories.
First of all, when designing transformer with leakage inductance(Lr ) and
magnetizing inductance(Lm), unwanted leakage inductance of secondary side
(Lr2) which cause error in the process of measuring the leakage inductance
(Lr ) with instrument occurs. This design error could be reduced by taking
into account the leakage inductance of secondary side(Lr2).
Secondly, in general, the voltage gain characteristic curve is applied to
design LLC resonant converter. in this thesis, the current gain characteristic
curve was applied to the design process which is suitable for LED that is
non-linear load and necessary to be controlled to a constant current.
Lastly, the equivalent circuit of LED was applied to the design process.
Normally, a resistive load which has linear load characteristic is used for
designing the LLC resonant converter. However, in this thesis, the
equivalent circuit of LED which includes a voltage source, a resistor and a
diode could be obtained by using the linear approximation method. This
circuit was then applied to the design process for reducing design error.
Experimental results are presented to verify the performance of the
proposed hybrid current balancing circuit and the optimal design method of
the LLC resonant converter. The LED maximum current error rate which
was 19.57% was reduced to 4.5% by Y-type current balancing transformer.
Also, the validity of the proposed optimal design method of the LLC resonant
converter was verified by comparing it with the conventional design method.
An 150W prototype was implemented and used for the performance verification
of the hybrid current balancing circuit and the LLC resonant converter.
LINK: http://www.mediafire.com/file/sfzdhsuo3y91zod/file
