Stochastic optimization of a stationary energy storage system for a catenary-free tramline

To realize economical operation of a catenary-free tramline, we propose installing a stationary energy storage system (SESS) to assist the electric grid for trams charging. As the tram operation may not be fully aligned with a predetermined timetable, an economical coordination of the electric grid and the SESS under uncertain charging demands is investigated. To this end, a chance-constrained program is formulated where demanded charging of the tramline is satisfied in a probabilistic sense. The introduced chance-constrained program is translated into a robust and deterministic mixed-integer second-order cone program (MISOCP) by first saturating charging power to a stochastic upper limit and then prolonging charging periods until entire energy is delivered for all charging scenarios that are being investigated. A case study for the Haizhu line in Guangzhou, China, shows that a cost–benefit of 13.70% can be obtained by installing an SESS when charging power is fully delivered for all scenarios, while a 28.47% cost-saving can be achieved when charging power is delivered 99% of the time.