Analysis of Active Front End Rectifier with LLC Resonant Converter for EV Charging Application

Abstract

In this work, the active front end (AFE) rectifier with the half bridge resonant inductor-inductor-capacitor (HBLLC) converter for electric vehicle (EV) battery charging application is presented. The EV battery charging system must have efficient power transfer capability and it must be safe to operate. The front-end rectifier is controlled in synchronous reference frame (SRF) to have a unity power factor (UPF). The AFE is synchronised to the grid using a phase locked loop (PLL). DC link voltage of the front-end rectifier is controlled to have a stable DC voltage irrespective of the load, using cascaded loop pulse width modulation (PWM) control. Pre-charging relays are used to protect the system from initial transients to make a safe charging situation. The EV battery charging is demonstrated using two different charging modes: constant current (CC) and constant voltage (CV). The HB resonant LLC converter is used to transfer the maximum power from the grid to the vehicle by allowing the system to operate into the resonance condition. An isolated DCDC conversion stage is controlled using the battery current and voltage cascade PWM control for the chosen frequency range to have soft switching due to zero voltage switching (ZVS). The simulations are performed in MATLAB Simulink and the results and performances during both transient and steady state phases are presented. This work is to be applied to the pre-built charging system of a converted EV at the Instituto de Telecomunicações, IT.