In June, the domestic first green equipment demonstration project for urban rail, the “Energy Router-based Flexible DC Traction Power Supply System” for the first section of the Tianjin city center to Jinghai suburban railway, successfully passed the operational safety evaluation. This marks the final key “pass” for the project before its commercial operation. Tsinghua University is the core research and development team for this project.

Tianjin Jinghai Line (left), Flexible DC Traction Substation (right)

Under the leadership of Professor Lu Chao, the Department of Electrical Engineering and Applied Electronics (EEA) and the Tsinghua Sichuan Energy Internet Research Institute formed the R&D team, with Associate Researcher Wei Yingdong and Associate Researcher Li Xiaoqian responsible for core equipment development and key technology R&D, providing solid technical support for the demonstration project. The Tsinghua team proposed a new generation of flexible DC power supply system technology for urban rail based on fully controlled converters (referred to as flexible DC supply system), achieving domestic breakthroughs in planning design, core equipment, operational control, and testing in multiple key areas for the first time.

Planning Design Breakthrough

The team developed the country's first panoramic operation simulation software for the urban rail flexible DC system, covering locomotives, traction networks, and cooperative control over a large range and long time span. This software provides strong theoretical support and design analysis tools for the core equipment design, operational mode formulation, and system integration of the flexible DC supply system.

R&D urban rail flexible DC system operation simulation software

Core Equipment Innovation

The first domestic 1500V-level multi-port energy router and cooperative control protection system for rail transit, developed by Tsinghua University and manufactured by Tianjin Huakai Electric, was introduced. This equipment enables efficient and flexible integration of photovoltaic direct feeding into the contact network, traction power supply, and regenerative energy recovery from braking, with high short-circuit current feed-in capability and rapid absorption of DC overvoltage.

Energy router (left), control protection system (right)

Intelligent Operation Control

For the first time domestically and internationally, a wide-area cooperative control system platform for urban rail transit was constructed under real-time electric power flow monitoring. This system introduced an innovative mode of photovoltaic DC access along the rail line and direct power supply to the train, maximizing the use of regenerative braking and photovoltaic energy while reducing contact network voltage and rail potential fluctuations, achieving the overall goal of energy saving, carbon reduction, and stable operation for urban rail transit.

Intelligent cooperative control system (left), LCD interface during operation (right)

Comprehensive Testing and Verification

With the support of Tianjin Metro Group, the demonstration project completed the first domestic factory tests, type tests, and on-site joint debugging plans for the flexible DC supply system. It tested the maximum power supply capacity, economic cooperative operation, cross-area power supply, backup self-recovery, contact network short circuits, and other extreme operating conditions, filling the gap in standards and experiences for flexible DC supply systems in construction, debugging, and operation, providing solid protection for the safe and reliable operation of subsequent projects in this field.

Maximum power supply capacity with vehicle test (left), first domestic track-side contact network short circuit test (arc flash on cabinet top) (right)

As a model of industry-university-research collaboration, the project received strong support and assistance from the China Urban Rail Transit Association, Tianjin Metro Group, Tianjin Huakai Electric, China Railway Electrification Research Institute, and China Railway Design Institute. The official operation of the project marks a significant breakthrough in China’s urban rail flexible DC power supply system design, core equipment, and testing technology fields. The Jinghai Line demonstration project is an important practice in China's green and intelligent transformation of urban rail transit and provides a model reference for energy-saving and carbon-reduction paths, new line construction, and expansion and renovation planning decisions for cities such as Beijing and Guangzhou.