Three phase LLC resonant converter with D-DLL control technique for EV battery chargers

In this paper, Digital Delayed Locked Loop (DDLL) control technique is applied to the three phase LLC resonant converter for Electric Vehicle (EV) battery charger applications. In order to improve charging efficiency, switching losses must be reduced to have a maximum energy transfer among the variable converter components. Also, fast and secure battery charging requires controlling the voltage and current values at the battery terminals. The presented control technique is implemented under soft switching conditions with variable load and variable input voltages. The three phase dc/dc resonant converter, fed by a power-factor-corrector (PFC) with 380-400 V output, provides 360 V / 22.5 A at 8 kW maximum power. At the same time, the output regulation is realized from PFC with a variable dc link. The application results show that soft switching are maintained under different input voltage and output load conditions.