Improvement of traction power feeding/regeneration system by means of energy storage devices

Since ac motor traction was widely introduced in early 1990s, distributed traction systems have received much more popularity through better braking characteristics and much less disadvantage due to many traction motors with less individual power thanks to almost no requirement for maintenance works. But if compared with rheostatic brakes, maximum braking power has to be much less because of substantial dependency upon catenary voltage. At the other hand, in road vehicle application, the so-called hybrid car, which uses both battery driven electric motor together with internal combustion engine, has been very popular recently due to its superior petrol consumption rate. For this application, various types of electric energy storage devices (ESD) such as lithium ion battery and electric double-layer capacitor (EDLC) have also been improved. The author will first present state of the art technology of these two topics, especially in Japan, and then proposes the combination of these two important elements, regenerative braking and ESD together with various advantages. The most important feature of this combination is easy realisation of high power regeneration without much burden to catenary system and installed traction power, which can be realised by using overvoltage characteristics of the motor and by charging/discharging of excess power to/from either or both of on-board or wayside ESD.