η-ρ Pareto optimization of 3-phase 3-level T-type AC-DC-AC converter comprising Si and SiC hybrid power stage

In this paper, the η-ρ (efficiency - power density) Pareto front of a 20 kVA Uninterruptible Power Supply (UPS), comprising a Si and SiC hybrid 3-level T-type rectifier and inverter stage, and input / output side filters, is determined. A multi-objective optimization procedure is detailed, which employs an electrical converter model and coupled electro-thermal component models. Each component model determines the corresponding losses, volumes, and temperature rises. A detailed description of the inductor model is given which considers high frequency winding losses as well as core losses, and calculates the temperature rises inside the inductor, e.g. the hot-spot winding temperature. Based on the determined η-ρ Pareto front, the most suitable realization of the proposed UPS system is determined, which is based on the resulting sensitivities of the design parameters (switching frequency, current ripples, magnetic materials, etc.) on the performance of power converter system (efficiency and power density). As a result, a switching frequency of 16 kHz, maximum relative input and output side current ripples of 20%, amorphous core materials for DM inductors, and nanocrystalline core materials for CM inductors are selected in order to achieve a converter efficiency of 96.6% at a power density of 2.3 kVA/dm³.