In recent years, new products emerge one after another at short intervals in IT-related technologies to imply that a superior position cannot be maintained in the market without differentiation of product in the highly intensified competition of the present time. Before users become accustomed to a product to some extent, another product makes its debut to embarrass most users.
In contrast, it takes a little longer time to develop technologies to control rolling stock, which are indebted to a large extent to the development of related technologies of the times, as seen in the history of EMU driving system. Most of the newly manufactured EMUs are now equipped with an inverter driving system. However, those manufactured in the recent past are of the DC series-wound motor type, because they feature easy control of speed and torque and have ideal characteristics for EMU powering control. As a matter of fact, a number of EMUs mounted with DC series-wound motors are still in service. Introduction of induction motors into rolling stock, which required a significant technological turnabout, was to cope with the strong demands to improve the maintainability of powering system and enhance the performance of rolling stock. In parallel with the development of power semiconductors and CPU-related parts, the technology to control the speed of induction motor progressed in different industries, which triggered discussions on their applicability to EMUs. The advent of GTO thyristor, together with the development of microcomputer technology, accelerated the development of inverter driving system for EMUs to the zenith of prosperity seen in the current railway industry.
As the performance of permanent magnet has improved, synchronous motors have also made their debut to use a magnet as the rotor, which are now used not only for small-capacity components but also for large-scale machines and systems. They are also being used as the traction motor of rolling stock on a trial basis. They feature high efficiency, since they realize a direct drive system without using reduction gears. It is also important to develop a new system that will save more energy in controlling rolling stock. Inverter control EMUs normally use regenerative brake. A system is now under test to store regenerated power in on-board batteries and use for powering, thereby aiming at the improvement of regenerating efficiency. In this system, a point is the power converter to control the batteries and the current of rolling stock, for which it is essential to develop a core technology.
In any event, it is inevitable to promote research and development on required technologies, in order to execute functions and fulfil performance blended with the rolling stock system. For this purpose as well, it is important to set up an antenna high to positively assess the movement of new technologies not only in railways but also in other industries, isn't it?