Download In this paper, an LLC resonant converter design

OPTIMAL DESIGN METHODOLOGY FOR LLC RESONANT CONVERTER IN
BATTERY CHARGING APPLICATIONS BASED ON TIME-WEIGHTED AVERAGE
EFFICIENCY
ABSTRACT:
In this paper, an LLC resonant converter design methodology for battery charging
applications is proposed aiming at achieving high efficiency. Compared with traditional resistive
or constant power load applications, the battery voltage and current are nonlinear and vary with
the charging profiles, making the optimal design of battery charger more difficult and
complicated. Based on the characteristics of the battery charging profiles, a new time-weighted
average efficiency (TWAE) index is proposed, which represents the average weight of
conversion efficiency during battery charging period. Converter’s losses are calculated based on
the standard loss models using the current and voltage information derived from the LLC steadystate model, which is solved utilizing the numerical non-linear programming techniques. In
addition, the TWAE is achieved serving as the objective function to optimize the converter
parameters. To reduce the search space and speed up the search algorithm, a variable-step
exhaustive search algorithm is applied considering the constraints of operation and variable
range. Finally, a 3 kW prototype LLC converter, which converts 220 VAC from the grid to a
wide output voltage range from 60 to 100 V is built and a TWAE of 94.74% and a peak
efficiency of 95.19% are achieved, validating the effectiveness of the presented method
INTRODUCTION:
The problems of storage capacity and weight reduction represent the challenging issues for many
EV applications. Lithium-ion (Li-ion) batteries are becoming mainstream power sources of
vehicles among various batteries due to their superiorities such as high energy density, long
cycle life, high voltage, and absence of memory effects.
However, with the improvement of battery performance, charging algorithms of these batteries
keep gaining complexity so as to maximize battery life and shorten the charging time. Smart
battery chargers with high efficiency and high power density are needed to implement high
capability battery fast charging, which should also meet the widely variable battery voltage
requirements of charging algorithms.
A battery charger usually consists of an ac–dc converter with power factor correction (PFC) and
a followed isolated dc–dc converter. Conventional pulse-width-modulation converter with high
switching frequency leads to degraded efficiency, in spite of high power density. Therefore, soft
switching converters are proposed for high switching frequency applications, such as phase-shift
converter and resonant converter.
Among these converters, LLC resonant converter with high efficiency and power density is
widely used. Zero voltage switching (ZVS) at primary side and zero current switching (ZCS) at
secondary side are implemented to achieve high efficiency. Moreover, this converter can operate
at a wide output voltage range with a comparatively small variation of switching frequency.
EXISTING SYSTEM:
The LLC resonant converter is receiving a lot of attention because of its high efficiency
through zero voltage switching (ZVS) and its narrow operating frequency variation under overall
load conditions, despite the fact that designing these converters is somewhat complicated
PROPOSED SYSTEM:
Although LLC converters have been used in many applications with constant output voltage, the
design requirements of charging applications are significantly different due to the fact that
voltage and conversion efficiency vary with the state-of-charge (SOC) of batteries during
charging process. To evaluate the efficiency adequately, a new TWAE index is defined to assess
the performance of charger, which represents the average weight of conversion efficiency under
different conditions. Compared to normal applications, a wide operation range will be achieved
and TWAE needs to be optimized in order to reduce the total energy losses in battery charging
process. A variable-step exhaustive search algorithm is presented in this paper to optimize the
converter parameters for high TWAE
ADVANTAGES:

High reliabilty
BLOCK DIAGRAM:
TOOLS AND SOFTWARE USED:

MPLAB – microcontroller programming.

ORCAD – circuit layout.

MATLAB/Simulink – Simulation
APPLICATIONS:

Electric vehicle (EV) and plug-in hybrid EV (PHEV).
CONCLUSION:
This paper proposes a design methodology of the LLC resonant converter for battery
charging applications. Since the battery voltage and current are nonlinear, a new TWAE index is
proposed based on the characteristics of the battery charging profiles. This index considers the
total energy losses during whole charging procedure, which can represent the average weight of
conversion efficiency during battery charging period. Power loss analysis has been expressed.
The simple approximation formulas are built to calculate the power losses using data-sheet
parameters. Conversion efficiency is calculated by using the current and voltage information
derived from the LLC steady state model. Then the proposed new TWAE is achieved, serving as
the objective function to optimize the converter parameters
REFERENCES:
[1] M.Yilmaz and P. T.Krein, “Reviewof battery charger topologies, charging power levels, and
infrastructure for plug-in electric and hybrid vehicles,” IEEE Trans. Power Electron., vol. 28, no.
5, pp. 2151–2169, May 2013.
[2] J.-S. Kim, G.-Y. Choe, H.-M. Jung, B.-K. Lee, Y.-J. Cho, and K.-B. Han, “Design and
implementation of a high-efficiency onboard battery charger for electric vehicles with frequency
control strategy,” in Proc. IEEE Vehicle Power Propulsion Conf., 2010, pp. 1–6.
[3] M. Chen and G. A. Rinc´on-Mora, “Accurate, compact and power-efficient Li-ion battery
charger circuit,” IEEE Trans. Circuits Syst. II, Exp. Briefs, vol. 53, no. 11, pp. 1180–1184, Nov.
2006.
[4] S. Dearborn, “Charging Li-ion batteries for maximum run times,” Power Electron. Technol.
Mag., vol. 31, no. 4, pp. 40–49, Apr. 2005.
[5] C. Chen, S. Duan, T. Cai, B. Liu, and G. Hu, “Optimal allocation and economic analysis of
energy storage system in microgrids,” IEEE Trans. Power Electron., vol. 26, no. 10, pp. 2762–
2773, Oct. 2011