Exploration of the Design and Performance Space of a High Frequency 166 kW/10 kV SiC Solid-State Air-Core Transformer

With the availability of 10 kV SiC MOSFETs with low Zero Voltage Switching (ZVS) losses, Medium-Voltage (MV) converters, e.g., Solid-State Transformers (SST), capable of operation at very high switching frequencies become feasible. However, the optimization of MV and Medium-Frequency (MF) transformer of the dc-dc converter stage of a high power SST reveals that only limited improvements in efficiency and weight result for switching frequencies exceeding 50 kHz. Therefore, air-core transformers are expected to enable a realization with lower weight and, at the same time, simplified insulation coordination. This paper presents a comprehensive exploration of the design and performance spaces (efficiency, mass, volume) of a conventional, i.e., a magnetic-core based, and an air-core transformer employed in a resonant dc-dc converter with input and output voltages of 7 kV and a rated power of 166 kW. As a result, comparable efficiencies are achievable for both transformers (99.3% and 99.0%), but the SST with air-core transformer at a switching frequency of 103.6 kHz features 41% of the mass (10.3 kg) of a conventional transformer (24.9 kg at a switching frequency of 48.5 kHz). Accordingly, air-core transformers are of special interest for future weight-critical SST applications, e.g., in More Electric Aircraft and More Electric Ships.