Highly isolated switching mode power supply for solid-state transformers in railway vehicles

Abstract

This paper discusses an isolated switching mode power supply (SMPS) with an AC 30 kVrms insulation capability for application to the solid-state transformers (SSTs) in railway vehicles. The insulation capability of the SMPS should be higher than AC 25 kVrms for application at the SSTs in railway vehicles. The proposed highly isolated SMPS is superior to commercial isolated power supplies with low insulation capability, which is normally less than 20 kV. The input side of the proposed isolated SMPS is physically separated from its output side by a specially designed miniature high-frequency (HF) transformer to obtain high insulation capability. The core of the miniature HF transformer is separated by insulation material. The primary and secondary coils are wound around each separated core. A CLLC resonant converter that consists of a primary resonant capacitor (C), two inductors (LL), and a secondary resonant capacitor (C) is applied as the proposed isolated SMPS topology to improve the output voltage regulation performance, which varies due to a large leakage inductance derived from the airgap of the proposed miniature HF transformer. Experiments are carried out to verify the CLLC resonant converter of the proposed isolated SMPS. Electrostatic finite element method (FEM) simulations and high potential (HiPot) tests are carried out to verify the AC 30 kVrms insulation capability of the proposed isolated SMPS. The electrostatic FEM simulations demonstrate the DC 42.43 kV insulation capability, and the HiPot tests verify the insulation capability from AC 5 kVrms to AC 30 kVrms.