Development and Testing of a 200 MJ / 350 kW Kinetic Energy Storage System for Railways Applications

In 2003, the Spanish Manager for Railways Infrastructure (ADIF) in collaboration with CIEMAT (formerly CEDEX, an Institute belonging to the Public Works Ministry of Spain), launched a project for developing a flywheel energy storage system for power management in railways substations with the aims braking energy recovery in conventional lines supplied with 3000 V DC. At the time of presenting this paper, the first prototype of KESS (Kinetic Energy Storage System) is finished and has been tested at the CIEMAT facilities. Prior to these tests, two previous and smaller prototypes have been developed and tested in the same facilities. The system is based on the use of a metallic flywheel, a switched reluctance motor/generator (SRM) and the corresponding power electronics, including a machine side converter and a grid side converter. 200 MJ (55.6kWh) of energy can be stored in a high strength steel flywheel, rotating over 6.000 rpm, which is magnetically levitated and guided with conventional high speed bearings. A power of 350kW can be exchanged in the electrical machine which is a switched reluctance, 6/4 poles, motor-generator, working in either single pulse or hysteresis band, depending on its speed. The machine is driven with a full H converter per phase, bidirectional in voltage and current thus reducing magnetic losses in the rotor of the SRM. Finally there is a grid side converter connecting the grid of the substation to a dc-link previous to the machine converter in order to supply single phase loads, controlled using a double hysteresis-band current strategy. A specific and very robust digital control platform has also been developed for this application to manage the complete system. The paper will present also the tests of the KESS unit in a real electric substation specially conditioned by ADIF to perform these tests. This substation is very close to Madrid-Atocha station which is a really important railway junction of Madrid commuter lines. Tests in this substation will show the real functioning of the developed KESS as well as the level of reliability achieved in this pioneer project.