Comparative Analysis of Carbon Footprints and Material Usage of Solid-State Transformers and Low-Frequency-Transformer-Based MVac-LVdc Interfaces for High-Power EV Charging

Medium-voltage (MV) ac to low-voltage (LV) dc conversion for, e.g., high-power EV charging can be realized either with a low-frequency transformer (LFT) and a downstream LV ac-dc converter, or, alternatively, as a modular solid-state transformer (SST) that employs high-frequency (HF) transformers to provide galvanic isolation. Both solutions achieve similar power conversion efficiencies in the order of 98% but differ significantly regarding complexity and the types and amounts of employed components and materials. Thus, this paper compares the two approaches regarding the embodied carbon footprint and the material usage, on the basis of industrial 400 kW first-generation and 1200 kW second-generation SST demonstrators, highlighting the potential of SST technology to benefit from improvements in power electronics whereas the LFT-based solutions remain constrained by high material usage for the transformer. Specifically, the 1200 kW second-generation SST demonstrator features only about 40% of the mass (2 kg/kW) and about 2/3 of the embodied carbon footprint (13.7 kg CO2eq/kW) of an equally rated LFT-based solution.