An isolated medium frequency zero voltage zero current switching (ZVZCS) DC/DC converter for HVDC transmission system is proposed. Soft switching is achieved over the entire load range, via resonance between transformer leakage inductance and capacitance across primary switches. Since transformer leakage inductance is utilized in the resonant circuit, its design procedure is elaborated as well. Finite element simulation aided iterative design ensures transformer has leakage inductance close enough to desired value. Controller design is completed and the closed-loop system is simulated in PLECS^®. Converters series connected at the output are also simulated to show scalability.