Employing high frequency (HF) transformer in DC-DC converter is a popular strategy in power electronic industry. Equivalent circuit model of transformer in HF Dual Active Bridge (DAB) converters is investigated along with its impact on power transfer characteristic for Single Phase Shift (SPS) and Extended Phase Shift (EPS) modulation. Equivalent branches of magnetizing inductance allocated in primary and secondary side can inject the inductive current at switching instants to extend Zero Voltage Switching (ZVS) range. ZVS maps are proposed. Based on the power transfer characteristics and ZVS maps, an Advanced Extended Phase Shift (AEPS) modulation method with modified coupling relationship for phase shift is proposed to reduce the current stress and improve the voltage utilization. Finally, AEPS modulation is implemented in PLECS simulations to verify the analyzation presented.