Catenary overvoltage stabilization of DC railway electrical system by integrating EV charging stations

The DC railway electrification systems are widely used to supply the national, regional, and urban (metro and tramway) railway systems. However, the catenary line voltage is subject to high voltage variations due to the moving train loads. The catenary line voltage drops when the train accelerates, while the overvoltage occurs when the train brakes. The frequent overvoltages can increase system maintenance costs and reduce life cycles of the onboard devices. In a practical design, if the catenary voltage reaches its upper limit, the rheostat brake is performed to maintain the voltage stability. The braking energy is dissipated as heat by the onboard rheostat, such operation can reduce the global energy efficiency. Therefore, this work proposes to install Electrical Vehicle (EV) charging stations along the DC electric railway line in order to stabilize the catenary voltage. The braking energy is used by charging EV to achieve higher energy efficiency. A regional 850 V DC railway microgrid located in mountain area is considered in this work. Two cases without and with EV chargers are modeled, simulated, and compared by using Matlab/Simulink. The results highlight the performance of the EV charging solution in terms of voltage stabilization and braking energy savings, also economic aspects.