High Efficiency LLC Resonant Converter With Wide Output Range of 200–1000 V for DC-Connected EVs Ultra-Fast Charging Stations

Abstract

DC-connected ultra-fast chargers consist of isolated DC/DC converter modules to provide the required charging profile. This paper proposes a charging module that interfaces with a fixed voltage DC-bus and covers a wide variety of electric vehicles (EVs) with battery voltages ranging from 200 to 1000 V. DC/DC converters for EVs charging has been discussed several times in the literature, however the DC-connected structure with fixed DC-bus voltage is rarely considered. This paper proposes a full-bridge LLC DC/DC converter module with a configurable secondary. This configuration extends the converter’s charging voltage range without adding stress on the resonant components or operating far from the unity gain point. Due to wide output range, the converter parameters are optimized using the time-domain analytical model to cover the required range without adding unnecessary circulating current that compromises the efficiency. First, the LLC resonant converter fundamentals are briefly introduced. Then, the proposed topology operation and advantages are discussed. After which, the converter’s requirements and design method are presented, focusing on circulating current minimization. Finally, the effectiveness of the proposed converter and the optimized design strategy is verified experimentally on a 10 kW prototype with an input of 800 V and an output of 200 - 1000 V.