The research and application of LLC resonant converter in two-stage charger

Abstract

Aiming at the low power density, low charging efficiency and input current harmonic content of traditional electric vehicle charging machine, a new topology structure is adopted in this paper. The former stage adopts two-stage staggered parallel Boost PFC circuit, which can effectively improve the power density of the former converter and reduce the THD value of the input current. The rear stage adopts the semi-bridge LLC resonant circuit to improve the power density and charging efficiency of the rear converter. The working principles of the two-level staggered parallel Boost PFC and the half-bridge LLC resonant converter are analyzed. The fundamental wave analysis method(First Harmonic Approximation，FHA) is used to do LLC resonant network modeling, and on this basis it determines the scope of switching frequency and the optimum working range. The simulation and experiment validate the correctness of the mathematical model and parameter design. Finally, a charger is designed whose input voltage is 175 V～265 V, and maximum output power is 1.5 kW. The experimental results show that the front-end converter power factor is 0.996, the input current THD is 4%, and the machine efficiency can reach 94%.

Keywords

• charger
• FHA
• Boost PFC
• LLC resonant converter