978-1-7281-6990-3/20/$31.00 ©2020 IEEE Temperature Dependent Charging Algorithm of Supercapacitor Module Ivan Župan Department of Control and Computer Engineering, Faculty of Electrical Engineering and Computing University of Zagreb Zagreb, Croatia ivan.zupan@fer.hr Željko Ban Department of Control and Computer Engineering, Faculty of Electrical Engineering and Computing University of Zagreb Zagreb, Croatia zeljko.ban@fer.hr Dubravko Krušelj Traction Systems Konþar – Electronics and Informatics, Inc Zagreb, Croatia dkruselj@koncar-inem.hr Viktor Šunde Department of Electric Machines, Drives and Automation, Faculty of Electrical Engineering and Computing University of Zagreb Zagreb, Croatia viktor.sunde@fer.hr Abstract— In order to increase energy efficiency in distributed energy generation systems, energy storage systems are used. Supercapacitors are one type of energy storage elements whose characteristics include high power density, long cycle life and low energy density. Since they are better suited for usage in high power applications, it is important to consider their temperature in order to avoid overheating and cause irreversible damage. This paper presents a supercapacitor charging algorithm that takes into account its temperature in order to increase energy efficiency. The algorithm is part of a regenerative braking system integrated within an electric railway vehicle. The foundation of the temperature dependent charging algorithm is the supercapacitor's electro-thermal model, which includes forced air-cooling, and its development within MATLAB. The electro-thermal model consists of a supercapacitor’s electrical model and thermal model; the electric model’s rheostatic loss is the input for the thermal model, which outputs the supercapacitor’s temperature. The resulting algorithm outputs the maximum allowed charging/discharging current depending on the supercapacitor temperature, and results in an increase in energy savings, as well as lowering the impact of the light electric railway vehicle’s accelerating and braking on the power grid concerning current and voltage peak values. Keywords—supercapacitor modeling, charging algorithm, supercapacitor temperature, electric railway vehicle, energy savings I. INTRODUCTION Reducing greenhouse gas emissions, increasing the efficiency of electricity use and increasing the share of renewable sources necessarily requires the development and application of energy storage systems(ESS). One type of ESS are supercapacitor modules, which are characterized by high charging and discharging power, and a larger number of cycles, but also lower energy density compared to batteries. Supercapacitors are suitable for applications in which a fast cycling of large amounts of power is required, e.g. in electric vehicles, and for covering peak power demands in distributed power generation networks. In electric railway vehicles, supercapacitors allow the storage of braking energy if there is no possibility of returning energy to the power grid. The stored energy is used to accelerate the vehicle, and can act as an additional energy source during peak load periods. The consequences are energy savings in the power supply grid of rail vehicles, and indirectly, savings in the distributed generation grid and stabilization of the power grid's voltage. The operation of supercapacitors at high power makes them susceptible to overheating. Prolonged operation at elevated temperatures accelerates the aging of supercapacitors [1-5]. Increasing their temperature above 65 ° C, the process of accelerated decomposition of electrolytes and complete destruction of supercapacitors begins. It follows that supercapacitor temperature control is one of the essential requirements to increase efficiency and preserve the declared cycle life. For this purpose, it is necessary to measure the temperature and use it as an additional control variable in the charging and discharging algorithm in order to regulate the current flow depending on the highest cell temperature. At lower temperatures, higher charging currents can be used, increasing the system efficiency. At higher temperatures, the charging/discharging current is limited, extending the cycle life of the supercapacitor. During the design phase of the regenerative braking system, and primarily in the optimization phase of the charging and discharging algorithm, it is necessary to know the ESS temperature. For this purpose, it is possible to use different electro-thermal models of supercapacitors. In the electrical part of the supercapacitor model, power dissipation is calculated, and in the thermal system model, the temperature due to dissipation. The electrical model of a supercapacitor is most often represented by a series connection of a resistance (equivalent series resistance - ESR) and a capacitance. More complex electrical models with multiple different RC combinations are used to model the dynamic behavior of supercapacitors [6-9]. The model of the thermal system of supercapacitors is modeled by electrical RC networks of different complexity, in which the electrical resistances and capacities are analogous to the thermal resistances and capacities [10-13]. The current source within these networks is analogous to dissipation, i.e. the heat dissipated at the equivalent series resistance of a supercapacitor. The voltage response of the All the costs of publishing of this paper are co-financed by the "KONTRACT GP170DC_SK" project co-funded under the Competitiveness and Cohesion Operational Program from the European Regional Development Fund. 511 thorized licensed use limited to: University of Zagreb: Faculty of Electrical Engineering and Computing. Downloaded on November 25,2020 at 09:13:04 UTC from IEEE Xplore. Restrictions appl