The Propulsion System of Rail Transit: Efficient Drive

Ⅰ. Core Components of the Propulsion System

1. Traction System
   • Electric Traction: The mainstream solution is the Permanent Magnet Synchronous Motor (PMSM), with an efficiency ratio of over 95%, representing a significant improvement compared to the traditional asynchronous motor (85%), which reduces energy consumption by approximately 20% per kilometer. For example, after Chengdu Metro Line 7 adopted PMSM, it saved over 3 million kWh of electricity annually.
   • Hybrid Power: Combining the advantages of electric motors and internal combustion engines, it is suitable for areas with unstable power grids. Through intelligent power distribution strategies, it optimizes energy utilization under different operating conditions.
   • Hydrogen Fuel Cells: An emerging zero-carbon technology, such as CRRC Changke’s 400kW hydrogen energy system (4×100kW modules), with a speed of 160km/h and a full life cycle carbon emission of less than 5kg CO₂/km (diesel locomotives >120kg).
2. Energy Recovery System
   • Regenerative braking is a key energy-saving technology. Using supercapacitors or regenerative converters, it converts braking thermal energy into electrical energy and feeds it back to the power grid. Shanghai Maglev Line’s application of the regenerative braking system recovers 300 million kWh of electricity annually, equivalent to saving 300,000 tons of standard coal.
3. Auxiliary Power System
   • It supplies power to on-board equipment such as air conditioners and lighting and is gradually introducing clean energy supplements like solar power and fuel cells to reduce dependence on the power grid.

II. Core Components of the Propulsion System

1. Breakthroughs in Permanent Magnet Motor Thermal Management
   • During high-speed operation, permanent magnet motors are prone to overheating. Through liquid cooling systems (such as in Changsha Metro projects) and structural optimization, the stability issue under high-temperature conditions has been resolved.
2. Intelligent Control Systems
   • Multi-Stack Collaborative Algorithm: For hydrogen fuel cells, dynamic load allocation technology (Patent CN202310000000.1) is adopted, with an efficiency fluctuation rate of less than 2% under variable load conditions.
   • 1500V High-Voltage DC Platform: Breaking through the traditional 750V limitation, power transmission losses are reduced by 36%, making it suitable for heavy-haul applications (such as in the Guoneng Xinshuo Railway project).
3. Lightweight and Integrated Design
   • Using carbon fiber composite materials and modular structures, the body weight is reduced by 30%, lowering operating energy consumption. Through integrated design, the volume of high-speed train power units is reduced by 40%.

III. Future Trends: Integration of Green and Intelligent Technologies

1. Scaling Up Hydrogen Energy Applications
   • Focusing on non-electrified railways (China’s existing 70,000 km), the penetration rate is expected to reach 30% by 2030. Foshan hydrogen-powered trams reduce carbon emissions by 11,000 tons annually, saving 37% of electricity compared to grid power supply.
2. Digital Twins and Intelligent Maintenance
   • With 128 sensors implanted to monitor system status in real-time, combined with AI fault warning (accuracy >95%). In the Qingdao hydrogen locomotive project, the application of digital twin technology achieves a lifespan prediction error of less than 3%.
3. Superconducting Maglev Technology
   • Breakthroughs in superconducting materials are driving the commercialization of maglev technology, such as demonstration lines in Shanghai and Changsha, achieving zero mechanical friction, low noise, and high-speed operation of over 600km/h.

IV. Challenges and Responses

1. Technological Bottlenecks
   • The hydrogen storage density of hydrogen fuel cells (currently 5.7wt%) needs to be improved. Research and development of liquid hydrogen storage materials such as ethyl carbazole (theoretical value 6.2wt%) is ongoing.
2. Cost Control
   • Promoting domestic substitution (for example, the domestication rate of Shijia Tobe blowers has reached 85%, reducing costs by 40%).
3. Standard Development
   • Accelerating the formulation of China-led international standards for hydrogen rail transit (ISO/TC197) to support the “Belt and Road” technology export.

V. Conclusion

The technological innovation of rail transit propulsion systems is essentially about balancing efficiency and sustainability. From permanent magnet motors to hydrogen applications, from energy recovery to intelligent control, every breakthrough reshapes the energy paradigm of rail transit. In the future, with the deep integration of green technologies and digitalization, rail transit will not only be the lifeline of cities but also a core carrier for a zero-carbon future.