Stability Enhancement Method Based on Adaptive Virtual Impedance Control for a PV-Integrated Electrified Railway System

Abstract

The integration of photovoltaic (PV) system into electrified railways holds promising prospects. However, with the integration of PVs, traction power supply system (TPSS) has transformed into complex hybrid system with multiple sources and loads, including both AC and DC converters. Traditional small-signal stability enhancement methods designed for vehicle-network system are challenging to apply in multiple converter configurations. To address this challenge, virtual impedance control with adaptive damping gain is proposed. The damping gain adaptively adjusts with the fluctuation of the vehicle DC voltage. The damping gain decreases as the fluctuation decreases, which reduces the impact on the dynamic characteristics of the control system. This adaptive control approach extends the applicability of virtual impedance control. In addition, a comprehensive modeling method for the hybrid system is provided, including components such as the DC impedance of the PV, the AC and DC impedances of the railway power conditioner (RPC), and the AC impedance of the vehicle. AC–DC impedance coupling is considered in the modeling process. This approach solves the difficulties in analyzing the coupling between the DC impedances of the PV and RPC, as well as the AC impedances of the vehicle and RPC. On this basis, the impacts of the circuit and control parameters on system stability, as well as the effectiveness of the proposed control strategy, are quantitatively analyzed. The proposed modeling and control methods are validated through the construction of a hardware-in-the-loop test platform.