A Robust Voltage Control Method for Universal EV Battery Charger LLC Resonant Converters

In this study, a novel control method for LLC resonant converter with wide output voltage range and constant switching frequency is proposed targeting wide range of Electric Vehicle (EV) battery charger standards. In conventional LLC converter control topologies, in order to reach lower output voltage levels, switching frequency happens to move away from the resonance frequency, increasing in most of the cases. However, the switching losses due to switching devices start to become the main bottleneck at high switching frequency operation. Furthermore, high switching frequency operation may cause irreversible inrush current damage at the input terminals during the start-up with corresponding overshoot at the output voltage as well, risking the clients on this particular supply. The work presented in this paper proposes a robust and reliable control solution for these particular resonant converter drawbacks. Theoretical analysis for both conventional and proposed control methods are presented in detail. In order to show the effectiveness of the proposed technique, performance metrics of the both are compared experimentally on an LLC resonant converter specification having an output voltage range of 150-500 V with a maximum output power of 7.5 kW.