Research On Double- System Electric Locomotives Energy Storage System Based On Supercapacitor

The multi-system electric locomotive can run under the AC power supply network and DC power supply network.When the power supply system is changing,there is no need to take intermediate transfer station,which makes the transportation more convenient and bring a new possibility to solve the interconnection problem between different rail transits.For independent power supply systems that have been used on Chinese electric locomotives for a long time,researches on multi-system traction drive systems have lagged.In the long term,China must develop a high-performance multi-system traction driving system with independent intellectual property rights and needs to overcome a series of key technical problems including low energy utilization and DC voltage fluctuations during power supply system switching.Supercapacitor has unique advantages and development prospects in improving the energy utilization rate of regenerative braking of rail trains due to its fast charging and discharging speed,low pollution,high efficiency,long cycle life,etc.Moreover,its peak-filling of DC voltage provides a new idea to solve voltage fluctuations during power supply system switching.Based on this background,the work done in this paper is as follows:(1)This paper introduces the composition of the traditional double-system electric locomotive traction drive system and studied the working principle of the PWM rectifier,the two-level inverter and the traction motor.It established a mathematical model of the rectifier and inverter and proposed the control methods of rectifier,traction inverter and traction motor,and it also verified the correctness of the control method by simulation.Aimed at solving the problem of low energy utilization rate of locomotive regenerative braking,this paper proposes a supercapacitor-based double-system locomotive energy storage system.(2)According to the characteristics of the supercapacitor and the operating characteristics of the double-system locomotive,the paper determined an installation method of the energy storage system and selected the topology of the bidirectional DC/DC converter.It calculated the inductance and capacitance in the energy storage system through analysis and comparison and verified that the first-order RC supercapacitor model has sufficient accuracy to meet control requirements of the double-system locomotive's energy storage system.According to the first-order model,it studied the charging efficiency of supercapacitors in different model.(3)The paper proposed the control method of energy storage system.The energy storage can quickly charge the DC side capacitor and reduce the voltage fluctuation during starting period.It can also effectively recover braking energy during braking period to improve the recovery rate of braking energy.Derived the mathematical expression of the voltage of the conventional double-system locomotive during the switching of the power supply system,it can be seen that there will be voltage fluctuations in the transient process.Due to the peak-filling effect of the supercapacitor,the DC side capacitor voltage can be effectively maintained stable during the system switching,realizing the voltage smooth switching of the power supply system.The effectiveness of the research and verification of energy storage structure is of great significance for improving the range and development direction of double-system electric locomotives.