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.
The former Taiki elementary school was built in the Samoto district, Susami town, Wakayama prefecture in 1903 and was extended in 1913. This paper demonstrates the value of the wooden elementary school as property of the region, based on the measuring survey of the school and the village landscape survey. The results show the following indications: Taiki elementary school is the oldest wooden school building in Wakayama prefecture. It shows characteristics of the village landscape. It has kept its authenticity for 117 years. It has been influenced by village conditions and building techniques of that time.