LQ-optimized multivariable control for a 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 and grid stability. The development of an optimized control scheme for a converter-based single-phase 15-kV, 16.7-Hz railway-grid representation requires advanced simulation tools as well as suitable laboratory experiments for verification. This paper describes the derivation of a multivariable control and the initial operation of a grid-representation test bench. The power-electronic basis for the grid representation in the lab and the multivariable control concept based on LQ-optimization, including modelling, set-point value computation, feed-forward control, observer and compensation of nonlinear effects of the inverter are described. Measurement results for stationary and dynamic behaviour are presented, verifying excellent operation.