Power electronics in German railway propulsion

The state of the art of power electronics is reviewed. Because of the different requirements, such as suburban or long distance traffic and DC or AC supply, various systems are in use and some peculiar configurations, as resistor braking, have become important. With AC supply special line-commutated rectifiers causing low displacement factor and small harmonic content are used for DC motor propulsion. With DC supply choppers allow nondissipative motor control, often combined with special circuits for field weakening and for change of driving/breaking. Particularly important is three-phase propulsion with robust squirrel-cage motors, made possible by the development of suitable variable-frequency inverters. Both current source and voltage source inverters are used in suburban cars as well as for locomotive drives. The most universal but also most complicated system served by the voltage source inverter is described in more detail