Contact-wire/battery hybrid trains are the energy-saving ones that store energy regenerated during braking into onboard batteries by applying power recycling technology. The RTRI has developed and manufactured prototype trains that can run even between non-electrified sections through the application of the technology of power recycling vehicle driven by the onboard batteries and the power from contact wires (Fig. 1). For continuous running between non-electrified sections, the batteries on the trains can quickly be charged with a large current during the short dwell time at midway stations.

The RTRI therefore developed a technology to quickly charge batteries from rigid contact wires through pantographs. For this purpose, the vehicles use lightweight lithium ion batteries that allow charging with a large current. The RTRI also developed a cooling structure to maintain the battery temperature below a certain level, as well as a contact-wire/battery hybrid power conversion circuit with a charging capacity of 1,000 A at 600 V. To check whether melting would occur at the charging contact point, the RTRI implemented current-carrying tests with different combinations of rigid contact wires and pantograph contact strips, both made of different materials. The results confirmed that no melting occurred with any combination of these two components.

In a test to charge the batteries of a test train at 1,000 A during a dwell time of about 60 seconds (Fig. 2), the temperature rise of the batteries was suppressed at 3°C or less without the occurrence of melting at the contact point. After quick-charge operation of about 60 seconds, the test train was run with power supplied from the batteries alone. The test indicated that such a period of power charging enabled the train to run about 7 km or over, or 4 km or over with air conditioning at the maximum load (Table 1). The RTRI plans to promote further research to check the durability of the batteries.