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The growing attention to environmental sustainability of transport systems made necessary to investigate the possibility of energy optimization even in sectors typically characterized by an already high level of sustainability, as in particular the railway system. One of the most promising opportunity is the optimization of the braking energy recovery, which has been already considered in tramway systems, while it is traditionally overlooked for high-speed railway systems. In this research work, the authors have developed two simulation models able to reproduce the behavior of high-speed trains when entering in a railway node, and to analyze the impact of regenerative braking in DC railway systems, including usage of energy storage systems. These models, developed respectively in the Matlab-Simscape environment and in the open source Modelica language, have been experimentally validated considering an Italian high-speed train. After validation, the authors have performed a feasibility analysis considering the use of stationary and on-board storage systems, also by taking into account capital costs of the investment and annual energy saving, to evaluate costeffectiveness of the different solutions. The analysis has shown the possibility to improve the efficiency of high-speed railway systems, by improving braking energy recovery through the installation of such storage systems.

h i g h l i g h t sAn innovative on board hydraulic system fed by a KERS is presented. A complete model of the proposed system is presented. The model is validated on experimental data. a r t i c l e i n f o a b s t r a c tMany conventional truck and working machines are equipped with additional hydraulic tooling or manipulation systems which are usually fed through a mechanical connection with the internal combustion engine, involving a poor efficiency. In particular, this is a common situation for industrial vehicles whose mission profiles involves a relevant consumption of energy by the on board hydraulic systems, respect to the one really needed for only traction purpose. In this work it is proposed an innovative solution based on the adoption of a system aimed to recover braking energy in order to feed an efficient on board hydraulic actuation system. The proposed system is then adopted to a real application, an Isuzu truck equipped with a hydraulic tooling for garbage collection. A prototype of the system has been designed, assembled and tested showing a relevant improvement of system efficiency and the feasibility of the proposed approach. In the paper the proposed solution is presented, showing the simulation models and preliminary validation results including experimental devices assembled to perform the tests.

In the last years, energy storage systems are increasingly involved in applications in which they are required to deliver or adsorb significant charging or discharging currents in short intervals of time, typically a few seconds. Thanks to their high specific power, supercapacitors may represent one of the most promising technologies for this kind of applications. However, one of the main concerns regarding their operation is the accurate estimation of their state of charge; the most common technique, based on ampere-hour counting, typically requires some correction mechanisms, since it implies a significant loss of accuracy over time, due to the accumulation of measuring errors. In the present paper, a novel algorithm to assess the state of charge of supercapacitors is described and implemented. The algorithm is based on the evaluation of the parameters of an equivalent electric circuit of the supercapacitor, and on the consequent use of a Luenberger-style technique for the runtime evaluation of its state of charge, based on the measure of current and voltage at supercapacitor's terminals. The algorithm estimates the cell open circuit voltage while the current is highly variable, as typical in power-oriented applications, hence the corresponding state of charge