# Application of MMC-RPC in High-Speed Railway Traction Power Supply System Based on Energy Storage
## 6 Conclusions  
This paper proposes an ES type MMC-RPC, aiming at managing the power quality and regenerating braking energy for the \(V/v\) traction power supply system of the high-speed railway. This paper analyzes the mathematical model and control strategy of MMC-RPC, and proposes an improved VSG control strategy with two-stage circulating current suppression measures. Small signal analysis and simulation on Matlab/Simulink platform are carried out. The simulation results show that MMC-RPC can achieve good power quality management and energy utilization. Compared with DCL control, the VSG control proposed in this paper improves the stability of system frequency; compared with the  
Figure 26: The output power of the SC system.  
Figure 25: Capacitor voltage of sub module in one bridge arm based on the SC system.  
traditional circulation suppression strategy, two-stage circulation suppression can better suppress the circulation of single-phase MMC. The research significance of this study also lies in the ES control of VDCM, keeping modular capacitor voltage stable while maintaining the capacitor voltage balance. Under the dynamic change of traction load, the stability and dynamics of ES type MMC-RPC can still be maintained.  
However, this paper does not consider all application scenarios such as installing the equipment of MMC-RPC into the section posts of the traction power supply system other than the traction substations. We look forward to performing further research in the future, and the following conclusions are obtained:  
1. [label=(0)]
2. Quasi proportional complex integral (QPCI) control in the two-stage circulation suppression measures is used to suppress the circulation of the MMC bridge leg. The composite PI-QPR control is an improvement of the VSG strategy and suppresses the circulation inside VSG. The two-stage circulation suppression ensures the stable and effective operation of MMC-RPC based on VSG control.
3. An energy storage-based MMC-RPC controlled by virtual motor is established. Compared with the traditional DCL power control, MMC-RPC under the improved VSG control, can improve the system stability and response speed of frequency and power in the case of a sudden change of traction load. When MMC is put into operation, it can achieve frequency stability faster. Through small signal analysis, the influence of damping parameters on the system is studied, and the stability of VSG control is verified. Under the improved VSG control, MMC-RPC system can better realize the comprehensive management of the power quality of the traction power supply system.
4. A distributed SC type ES scheme is proposed. And a VDCM control is adopted to realize the recovery and utilization of regenerative braking energy, to improve the economy of the railway system.  
In the subsequent research, the application of hybrid energy storage in the MMC-RPC system will be further verified, and the corresponding experimental verification will be carried out.  
All of the authors contributed to the research in the paper. Conceptualization, Y.S.; Methodology, Y.S.; Simulation, Y.S.; Validation, Y.S. and T.L.; Formal analysis, Y.S.; Writing--original draft preparation, Y.S.; Writing--review and editing, T.L.; Supervision, T.L. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.