Improved Stability of DC Catenary Fed Traction Drivers and Auxiliary Converters using QFT Robust Technique

This paper introduces a novel method of designing voltage controllers to improve the stability problem in the Common-Connection Point of the DC catenary railway system, using the QFT control technique. The considered stability problem is due to the interaction between the resonance of the LC filter connected to the DC catenary with the traction and auxiliary converters (3-phase inverters) it feeds, which behave like CPLs. An stability improvement is achieved by shaping the closed-loop input impedance of a three-phase inverter using impedance-based stability criteria. The obtained simulation results, under unfavourable conditions, verify the theoretical development.