Vf-constrained ηρ-pareto optimisation of medium frequency transformers in ISOP-DAB converters

This study deals with $\eta \rho $ηρ (efficiency-power density) pareto optimisation of medium frequency transformers (MFTs) with considerations of voltage and frequency (Vf) constraints of semiconductors for mega-watt range input-series output-parallel (ISOP) connected dual-active bridges (DABs). A simple design methodology to include the Litz wire configuration in the optimisation process is proposed. Based on the presented design methodology, the effects of the semiconductors blocking voltage and switching frequency on the $\eta \rho $ηρ-pareto optimisation are evaluated. First, an idealised optimisation is carried out to understand the general behaviour of the optimum point. Second, brute-force optimisation is utilised to find the practical optimum solution based on the market availability of MFT components. Designing MFTs for a 1 MW 10 kV/600 V ISOP-DAB converter is the subject of numerical studies. The best trade-off between $\eta \rho \, {\rm and}\, Vf$ηρandVf is selected as the final optimal solution and its design correctness is validated using three-dimensional finite-element analysis. Experimental tests on a 3 kW downscaled MFT prototype show that the proposed method is valid in practice.