Middle-Frequency Isolation Transformer Design Issues for the High-Voltage DC/DC Converter

This paper addresses some specific design issues encountered in the development of isolation transformers for the rolling stock auxiliary power supply (APS). The optimal transformer design rule of the copper and core loss equalization will not work for middle-frequency (500...3000 Hz) high-power transformers. Main attention here must be paid to selection of the proper material for the magnetic core and to define an optimal operating flux density to minimize the dimensions and to improve operability and efficiency of the transformer, respectively. In the isolation transformers design for the APS converters with high input voltage and load variations, a threat related to magnetic core saturation caused by transient conditions should be considered. These and some other specific design issues (minimization of leakage inductance and parasitic capacitances, high-voltage isolation, etc.) make the design of such devices very challenging.