ABSTRACT
To comprehensively manage power quality problems in traction power supply system, railway static power conditioner based on modular multilevel converter (MMC-RPC) is applied. Although the new MMC-RPC is of various advantages, the problem of a large voltage fluctuation still exists in MMC, especially during low-frequency running of ac locomotives. To solve this problem and to absorb regenerative braking energy during regenerative braking, a novel railway static power conditioner based on modular multilevel converter with integrated super capacitor energy storage system is proposed in this paper. Through analyzing energy flow relationship and the generation principle of voltage fluctuation components in the system, a combined control strategy capable of controlling charging and discharging of SC and simultaneously suppressing the voltage fluctuation is presented. Then simulation results show that the SC-MMC-RPC, under the control of ESS, can not only save energy, but also suppress voltage fluctuation. This reduces the use of large-capacity capacitors and then improves economy comprehensively.
