Series resonant megawatt-level DC transformers with high step-up and low costs are the key equipment for large-scale photovoltaic DC collection. This paper proposes a 1.5 kV/10 MW high power DC transformer topology based on IGCTs (IGCT- HDCT) and lossless series diodes. The 3.34 MW sub-unit adopts a series resonance method to reduce IGCT switching losses. To clarify the applicability differences between LC and LLC topologies

this paper first presents the parameter design fundamentals and key specifications of the IGCT-HDCT. Subsequently

the influence of lossless snubber capacitors

used for series diode voltage balancing

on the resonance process is analyzed in detail. The soft-switching characteristics of both LC and LLC topologies across the full power range considering the additional resonant effect are studied

and an optimization method for the switching frequency is proposed. By establishing the model of currents and loss of IGCT

the optimized switching frequency is derived. It is demonstrated that the LC solution can reduce switching energy consumption by 78.6% in photovoltaic applications. A laboratory prototype of the IGCT-HDCT is developed

and comparative experiments are conducted to validate the proposed analysis. As of 2024

the proposed IGCT-HDCT solution has been applied to the 1.5 kV/±15 kV/50 MW photovoltaic medium-voltage DC collection project in Golmud

Qinghai.