In railway systems, the constant power load (CPL) behavior of both traction and auxiliary power system (APS) converters interacts negatively with the variable impedance of the catenary and can lead to voltage fluctuations and compromise the stability of the railway line. This paper proposes the use of a structured H∞ synthesis to design an AC voltage controller for the APS converter that models the converter's DC input admittance. The resulting low-order controller guarantees catenary stability, ensures tracking of the AC output voltage reference, and provides robustness against non-modeled uncertainties. Experimental evaluation demonstrates its compliance with railway standards and modeling of the specified impedance.
