Control and Protection of a Synergetically Controlled Two-Stage Boost-Buck PFC Rectifier System under Irregular Grid Conditions

Abstract

There is an increasing demand for three-phase mains interfaced high power EV chargers that provide a wide output voltage range while featuring low losses and a high power density. In this context, a synergetic control structure for a two-stage three-phase boost PFC rectifier with subsequent DC/DC buck stage was proposed, which allows to only switch one out of the three rectifier bridge legs, leading to switching loss savings of over 66 %. This is achieved by varying the voltage of the intermediate DC-link, which features a small capacitance, with six times mains frequency, always following the maximum three-phase mains line-to-line voltage. Although this concept has been proven to work correctly for ideal three-phase mains conditions, it is unclear whether it can safely operate under irregular three-phase grid conditions such as heavy harmonic distortions, unbalances, phase failures, and grid overvoltages caused by, e.g., lightning. Hence, after a short review of the employed synergetic control structure, this paper focuses on the operation of the proposed boost-buck converter for an application subject to a wide variety of three-phase grid disturbances. Comprehensive analysis with respect to irregular grid conditions is performed, resulting in a slight modification of the converter's front-end and its control structure in order to be able to handle faulty mains conditions. The proposed hardware and control modifications enabling the proper converter functionality under regular and irregular grid conditions are verified by circuit simulations. Finally, design guidelines are given for the hardware implementation of a resilient three-phase grid interfaced EV charger that can fulfill all required grid standards.