Single-phase 50-kW, 16.7-Hz railway-grid representation featuring variable grid parameters

Railway grid interaction is a major concern when developing the power train of a railway traction vehicle and its control. Two main areas have to be taken into account: Line current harmonics are limited - with often extremely low limit values, compared to nominal current - respecting the properties and safety issues of railway track circuits. Grid stability is influenced by the varying grid impedance seen by the moving vehicle, in connection with varying resonances, influenced by other vehicles and the actual grid configuration. The development of an optimized control scheme for the power train of a railway traction vehicle operating at the 15 kV,16.7Hz grid widely used in central Europe requires advanced simulation tools as well as suitable laboratory experiments for verification. This paper describes the simulation concept, the control concept and the realization of an advanced railway-grid representation in the lab, featuring real-time adjustable impedance and voltage harmonics. The power-electronic basis for the grid representation in the lab, feed-back and feed-forward control, including compensation of nonlinear effects of the inverter, are described. Simulation and measurement results for stationary and dynamic behavior are presented, verifying excellent operation.