In a significant stride towards greening electric railways, researchers have developed a method to integrate large-scale photovoltaic energy storage systems (PV-ESS) into traction power supply systems (TPSS), addressing stability challenges that have previously hindered progress. The study, led by Peng Peng from the School of Electrical Engineering at Beijing Jiaotong University, was recently published in the *International Journal of Electrical Power & Energy Systems*.
The integration of MW-level PV-ESS into TPSS presents a promising avenue for reducing energy consumption and emissions in electric railways. However, the multi-converter interconnection structure of these systems introduces complex stability issues. “The main challenge lies in the system’s instability caused by the negative impedance characteristic of the charging energy storage system,” Peng explained. To tackle this, the research team developed small-signal impedance models that capture the dynamic characteristics of single-phase grid-connected converters, PV systems, and energy storage systems within the multi-converter framework.
The team introduced the sub-impedance ratio criterion to evaluate system stability and identify the dominant units causing instability. They then quantified the impacts of power flow conditions, circuit parameters, and control parameters on system stability. Their findings revealed that the negative impedance characteristic of charging ESS was the primary culprit behind instability issues.
To address this, the researchers proposed a sliding-mode parallel virtual impedance method. By introducing DC-link voltage feedforward, they successfully shaped the ESS impedance to a positive characteristic, significantly enhancing the system’s stability margin. “Our method not only suppresses system instability but also maintains reasonable dynamic performance,” Peng noted.
The implications of this research are substantial for the energy sector. As the demand for sustainable and efficient transportation solutions grows, the ability to integrate renewable energy sources like photovoltaics into electric railway systems becomes increasingly important. The stability analysis and impedance shaping techniques developed in this study provide a robust framework for future implementations, paving the way for more reliable and environmentally friendly electric railways.
The study’s findings were published in the *International Journal of Electrical Power & Energy Systems*, a prestigious journal dedicated to advancing the understanding and application of electrical power and energy systems. This research not only addresses current challenges but also sets the stage for future developments in the field, offering valuable insights for engineers, researchers, and industry professionals working towards a more sustainable energy future.