Investigation of shunt active power filters in railway systems, substation installation

25 kV Ac electrified railway power systems have the following shortcomings as far as the quality of their power supply is concerned: higher harmonic supply current pollution, feeder supply voltage perturbations and the demand for reactive power. These power quality issues have a detrimental impact on the railway power supply system itself as well as on the other electric power systems integrated with it. This paper investigates the performance of single phase active power filters (SAPFs) which are introduced in order to address these quality issues. These filters can be installed at either the substation end (S/S) or at the sectioning post (SP) of the railway power system. In this investigation novel control algorithms, based on the synchronously rotating frame of reference, are proposed for the case when the SAPF is installed at the substation end and its performance is assessed. The effectiveness of the proposed control algorithms are illustrated via Matlab/ PowerSim computer simulations and validated via comparisons with other publications. This investigation demonstrated that when the SAPF is installed at the substation side, it can effectively compensate for the higher harmonic supply current. In addition, the reactive power demand is fully compensated for, leading to a unity power factor. However, the voltage drop/sag at the locomotive power entry point is not fully compensated for.