Output Voltage Regulation of a Unidirectional Isolated DC-DC Converter Used as an Auxiliary Power Supply for Electric Commuter Trains

This paper provides a theoretical and experimental discussion on a unidirectional isolated dc-dc converter equipped with a high-frequency transformer. It focuses on an application of the dc-dc converter to an auxiliary power supply for electric commuter trains. This specific dc-dc converter is required to tolerate sudden and frequent changes in the catenary voltage with a nominal value of 1.5kVdc, and has to maintain a constant output voltage. This auxiliary power supply is characterized by an input-series, output-parallel circuit configuration of two identical unidirectional isolated dc-dc converters. This configuration allows the dc-dc converter to eliminate a boost converter at the front end and a switchover circuit between series and parallel connections. The 600-Vdc, 6-kW, 16-kHz downscaled experimental system using SiC-MOSFET/SBD modules is designed, constructed and tested to verify the validity of the specially-constructed control system for regulating the dc output voltage to a reference of 150Vdc. Experimental waveforms show that the dc output voltage is well regulated even when a sudden input voltage change from 600 to 350V occurs, and a sudden load change from 3 to 6kW occurs.