Hybrid control approach of CLL resonant converter for EV battery chargers

In this study, a CLL resonant converter with different control strategies; frequency, dc-link, and phase shift control are compared and a hybrid control is proposed to increase the efficiency of the system for Electric Vehicle (EV) battery charger applications. The comparison analysis is examined considering the battery charging control algorithms constant current (CC) and constant voltage (CV) with modeling the battery as a variable load. In order to improve charging efficiency, the system should operate in a close to resonant frequency, achieving ZVS and reducing circulating current. The presented control is achieved by staying around the resonant frequency in all charging conditions. The designed dc/dc resonant converter, fed by a power-factor-corrector (PFC) with 80-120 V output, provides 120 V / 10 A at 1.2 kW maximum power. The application results show that the proposed hybrid control improves overall efficiency 2 %.