Model Free Control design of DC-DC LLC converter with phase shift modulation in V2X mode for EV charger application

Bidirectional charger technology for Electric Vehicle (EV) is becoming increasingly important. It denotes the act of returning the energy stored in an EV battery to Grid (V2G), to Home (V2H), to Load (V2L), or, in a nutshell, V2X mode. The EV onboard charger is of two parts: AC-DC converters and DC-DC converters. Inspired by an industrial collaboration, this paper deals with the bidirectional DC-DC LLC resonant converter in order to improve the control performance in V2X mode considering a wide range of battery voltage and converter power. The new challenge is to improve the DC bus voltage control using the Phase Shift Modulation (PSM) strategy in V2X mode, with constant switching frequency and duty cycle. The main contribution of this paper is to provide a control strategy based on the Model Free Control (MFC) to guarantee the robustness against different disturbances and uncertainties in the LLC converter system. The obtained results show the advantage of the PSM strategy based on MFC in improving the converter efficiency and control performance in the presence of the disturbances. A comparative study between the MFC and the classic control laws is conducted with respect to the DC bus current disturbance and DC bus voltage request variation.