Design and Analysis of Adaptive Impedance Structure for Cophase Railway Traction Supply Power Quality Conditioner

The electrical locomotives are treated as single-phase nonlinear loads, which can cause the low power factor, high contents of harmonic currents, and negative-sequence current. The power quality conditioners are widely used for solving the power quality issues in the railway power system. In power quality conditioners, the coupled impedance can affect the operation voltage, compensation range, and performance. Therefore, this article discusses the effect of different coupled impedances in conditioners, including fixed inductive impedance, fixed capacitive impedance, and adaptive impedance. Moreover, an adaptive impedance-coupled hybrid power quality conditioner (AI-HPQC) is proposed in comparison with inductive-coupled railway power quality compensator (RPC) and capacitive-coupled hybrid power quality conditioner (HPQC). Furthermore, a control method for the AI-HPQC is proposed for the coordination control of the adaptive impedance part and the active inverter part. The validities of the RPC, HPQC, and the proposed AI-HPQC are verified by both simulation and experimental results.