DESIGN AND MODELLING OF HALF BRIDGE LLC RESONANT CONVERTER AND SEPIC CONVERTER FOR ON BOARD FORWARD AND BIDIRECTIONAL CHARGING OF EV BATTERY

Abstract

The combustion of fossil fuels, a non-renewable and limited resources, has caused global warming, ozone damage, air pollution and acid rain. Electric vehicles are eco-friendly with attractive features such as, less emission of greenhouse gases, lower fuel usage and reduced air pollution. The battery charger is one of the most important components of the electric vehicle. This research work focusses on the on-board battery charger. Firstly, a Half-Bridge LLC resonant converter topology is designed which owns soft-switching features, high efficiency, and regulated output voltage. The output voltage is well regulated with the help of conventional PI-controller. It has been also simulated for the all the three modes, at resonance frequency, below resonance frequency and above resonance frequency in order to identify the optimal operating point of the converter. Secondly, the half-bridge LLC resonant converter is integrated with the boost converter to improve the power quality. The boost converter has been employed for the power factor correction. The output voltage is controlled with the PI-controller. The steady state and dynamic performance are analysed in MATLAB software under load and input supply variations. Further improvement has been done to supress the large inrush current observed in boost PFC by replacing boost converter with SEPIC converter. The presence of intermediate capacitor helps to supress the inrush current. There are some other unique features also introduce such as, it always operates near the resonance frequency for different output voltage, it also has the capability to give excellent performance under various input supply voltage, different loads at output. Nevertheless, a bidirectional half-bridge LLC resonant converter is designed which can perform in both forward mode and backward mode. In forward mode, the battery charging has been done and in backward mode, battery supply the power load connected at the supply side of the converter. The bidirectional LLC resonant converter has capability of soft-switching in both the forward and backward mode of operations. In forward mode, control of battery charging has been done with the help of PI controller and in backward mode the voltage across the load is regulated with the PI controller.