Optimal Sizing of Energy Storage for Regenerative Braking in Electric Railway Systems

Abstract

The problem of optimally sizing hybrid energy storage systems (HESS) installed in electric railway systems, considering the effect of regenerative braking is studied in this paper. HESSs combine traditional batteries and newly developed ultracapacitors, taking advantage of the high energy capacity of batteries and of the flexibility and ability to capture high power density of ultracapacitors. A novel mixed integer linear programming formulation that includes the counting of battery cycles is presented. Some particularities of battery operation are included in the model, like the dependence of its performance on the number of cycles and the depth of discharge (DOD). Results are reported first for a illustrative case study, allowing us to perform sensitivity studies for several parameters; results are also reported and for a larger case, closely resembling the problem faced by railway energy systems planners and operators.Index Terms-Electric railway systems, hybrid energy storage sizing, mixed integer linear programming. NOMENCLATUREThis section describes the sets, parameters, and variables used in the paper. A. Sets Set of batteries.Time period set. AC/DC inverter set. DC/DC inverter set. B. ParametersMinimum battery unit (MBU) cost .Daily MBU cost for each battery .Minimum ultracapacitor unit (MUU) cost .

Optimized Sizing and Scheduling of Hybrid Energy Storage Systems for High-Speed Railway Traction Substations

“…HESS is proposed with the intention of combining the batteries and UC to obtain both high energy and power density, and thus has an obvious advantage over the single type of energy storage system, especially for the application of peak load shaving and regenerative braking power absorbing in the high-speed railway system. In general, the UC's advantage of long cycle life and fast response make it suitable to capture the railway power peaks and valleys in high frequency, while batteries are more suited for low frequency operation [31,32]. Accordingly, HESS is adopted in this study for the better energy saving performance.…”

“…With regard to HESS, lead-acid (LA) batteries and UCs are considered in this study. All parameters associated with HESS are presented in Table 2 [31,32,47,57]. It is assumed that the service period of this project is 20 years and all the HESS-related devices can serve for the entire project period except for batteries.…”

“…The sampling time interval in [29] is determined as 1 min considering the short braking time. A time period reduction method is applied in [31,32] via combining short 30 s time periods to form longer time periods, yet with the defect of unequal duration between different time periods. The sampling time of power profile and the scheduling time interval of HESS are determined as 1 min in this study, based on the fact that power profiles of traction load and HESS do not change much during this short period.…”

Integration of Photovoltaic Plants and Supercapacitors in Tramway Power Systems

“…Parameter of cost function related to SC energy c 2 Parameter of cost function related to losses c 3 Parameter of cost function related to the energy exchanged with the distribution system E loss Total loss energy E pv,p…”

“…In the recent past, the scientific community has been paying growing attention to the different uses of these technologies in urban and suburban railway traction systems (streetcar, light rail transit, and mass rapid transit) [1,2]. In fact, it has been widely demonstrated that their use enables both the under sizing of the power supply plant in the project stage or a more intensive use of existing subsystems without major modifications (e.g., the repowering of electrical substations and the increase of the cross-sectional area of contact wires), and besides it definitely allows to improve the overall energy efficiency thanks to the recovery of the braking energy and its subsequent release in the starting phase of the traction motors.…”