Optimal control of reversible substations and wayside storage devices for voltage stabilization and energy savings in metro railway networks

Growing concerns about environmental issues dictate the necessity for improving the energy efficiency and total performance of metro railway systems. Proper management of the regenerative energy is a key element in this direction, and several strategies, such as timetable optimization, use of reversible substations, and installation of storage devices, have been proposed. This paper focuses on the optimal control of reversible substations and wayside storage devices for energy savings and voltage stabilization. The methods proposed for maximizing the recovered energy are presented together with their theoretical analysis. A novel optimization strategy, based on the linearization of the dc power flow equations, is analytically explained, while a successive approximation method is used. The proposed control strategy is evaluated through simulations on a modified version of the Thessaloniki metro railway network (Greece). Simulation results show that the system performance is significantly improved when reversible substations or energy storage are in operation.