Energy Management of Superconducting Magnetic Energy Storage Applied to Urban Rail Transit for Regenerative Energy Recovery

Recent urban rail vehicles use regenerative braking that lead to high energy efficiency. However, the intermittency and random nature of regenerative power causes limitation of regenerative energy recycling rate in DC electrification. To overcome the problem, energy storage system (ESS) plays an important role. Many applications of ESS to railway systems have been seen by using batteries, supercapacitors, and flywheels. This paper proposes to apply the superconducting magnetic energy storage (SMES) to railway systems as ESS. SMES holds bright application prospects due to its quick response, high power density and high energy storage efficiency. One of the major differences from other storage devices is that SMES has characteristics of a DC current source. It is inevitable to consider the converter configuration and energy and power management in the combination of SMES and DC electrified feeders. In this paper, energy and power management is proposed taking characteristics of SMES and its converter into account. Besides, the converter topology and specification of SMES will be also investigated. Finally, it will be demonstrated that SMES system for railway ESS will work to smooth the fluctuation of regenerative power.