Optimal Design Methodology for LLC Resonant Converter in Battery Charging Applications Based on Time-Weighted Average Efficiency

Transcription

1 LeMeniz Infotech Page number 1 Optimal Design Methodology for LLC Resonant Converter in Battery Charging Applications Based on Time-Weighted Average Efficiency Abstract 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

2 Page number 2 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

3 Page number 3 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 Applications Electric vehicle (EV) and plug-in hybrid EV (PHEV).

4 Page number 4 Block diagram AC INPUT DIODE BRIDGE RECTIFIER BOOST CONVERTER FULL BRIDGE INVERTER WITH RESONANT CIRCUIT 12V DC ISOLATION CIRCUIT CENTER TAPPED TRANSFORMER FILTER 5V DC PIC CONTROLLER WITH BUFFER LOAD

5 LeMeniz Infotech Page number 5 Tools and software MPLAB microcontroller programming. ORCAD circuit layout. MATLAB/Simulink Simulation.