High power LLC battery charger: Wide regulation using phase-shift for recovery mode

In order to recover and fully charge Electric Vehicles, battery chargers should work under different loading conditions and output voltage regulations. In this paper, a new hybrid control strategy that includes Variable Frequency and Phase Shifting is introduced and employed in an LLC resonant converter. The LLC resonant converter is implemented with a full-bridge topology to handle high power and deliver wide output voltage regulation without using burst mode, effectively increasing the battery life cycle and reducing Electro Magnetic Interference. In order to investigate the soft switching condition of the full bridge resonant converter, which is vital for a high efficiency and low-noise charger, a new set of analytical equations is obtained for the LLC resonant converter with consideration of separated primary and secondary leakage inductances. Based on the proposed control strategy and analytical equations, a 120VDC, 1kW battery charger with a peak efficiency of 96% has been designed and implemented. The experimental results exhibit the excellent performance of the converter compared to that of the frequency control LLC resonant converter.