Design Optimization of Isolation Transformer for Synchronous Switching Common High Frequency AC Bus in MMC-PET

This paper conducts a study on the DC/DC conversion channel, specifically emphasizing the high-frequency transformer in a Power Electronics Transformer (PET). The PET is based on a Modular Multilevel Converter (MMC) and features a common high-frequency AC bus configuration for the isolation stage, which plays a crucial role in its overall functionality and performance. By incorporating the parasitic parameters model of the high-frequency transformer, the current response, active power transfer, pulsating current transfer characteristics, voltage clamping characteristics, and the influence of common mode noise in the MMC-PET are analyzed. And then, the constraint of distributed parasitic parameters of the transformer is formed. The modeling of the distributed parameters is conducted while considering the parameters of magnetic core and windings. With the constraints aforementioned, the non-dominated sorting genetic algorithm is used to optimize the transformer with multiple optimization objectives, including temperature rise, insulation voltage, transformer power density, efficiency, and parasitic capacitance. Finally, based on the optimization results, a transformer prototype with a rated power of 50 kW and an operating frequency of 10 kHz is designed. Experimental validation confirms the rationality of the optimized design.