energies Article Gathering Energy of the Stray Currents in Electrified Railways Environment for Power Supply Grzegorz Wieczorek, Krzysztof Bernacki * , Zbigniew Rymarski and Wojciech Oliwa   Citation: Wieczorek, G.; Bernacki, K.; Rymarski, Z.; Oliwa, W. Gathering Energy of the Stray Currents in Electrified Railways Environment for Power Supply. Energies 2021, 14, 6206. https://doi.org/10.3390/en14196206 Academic Editor: Andrea Mariscotti Received: 31 August 2021 Accepted: 25 September 2021 Published: 28 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Electronics, Electrical Engineering and Microelectronics, Faculty of Automatic Control, Electronics and Computer Science, Silesian University of Technology, 44-100 Gliwice, Poland; grzegorz.wieczorek@polsl.pl (G.W.); zbigniew.rymarski@polsl.pl (Z.R.); wojciech.oliwa@polsl.pl (W.O.) * Correspondence: krzysztof.bernacki@polsl.pl Abstract: The paper presents a new, unconventional energy harvesting (EH) method for supplying low-power devices on electrified railway lines that utilises stray currents and the non-zero potential of the rails to the ground. The EH device gathers the energy and stores it in batteries. It could even work in extremely unfavourable weather conditions and could be easily placed in almost any location. The presented real-life data show that the average available power is less than 250 mW and the average useful power is about 100 mW. This is enough to supply ultra-low power microcontrollers, which only occasionally use energy-consuming modules to perform measurements or communicate. The disadvantage of the EH method is the introduction of resistance between the rail and the earth, which increases stray currents and could increase the electrochemical corrosion of the rail. To reduce the impact of this resistance, a method for balancing the flowing charge is proposed. After balancing, the average of the flowing current is zero and electrochemical corrosion should be reduced. The proposed charge balancing algorithms could reduce the unbalanced charge to nearly zero at the expense of energy gathering efficiency, which decreases by 20–40%. Keywords: rails; rail potential; stray currents; energy harvesting; electrochemical corrosion; con- trol algorithm 1. Introduction Modern railway infrastructure requires more and more complex safety, control, and supervision systems (peripheral systems), including remote sensors, telemetry systems, and wireless sensor networks (WSN). All these devices need a continuous, reliable, and maintenance-free power supply and they are usually low power devices. On the other hand, railway lines are often built without access to 110/230 VAC supply and the only available conventional power source is medium-voltage (e.g., 3 kV DC) used to supply electric locomotives. Converting medium-voltage to a low-voltage to supply low power peripheral systems (safety, control, and supervision systems) is expensive mainly because of the necessity to use high-voltage elements and protections. The aforementioned devices are frequently powered by the off-grid installation of renewable energy sources. This solution allows for the generation of enough energy for the ongoing requirements of the supplied system as well as storage of the excess energy in batteries for use at night or in unfavourable weather conditions [1,2]. These installations usually use photovoltaic cells (PV) or wind turbines. Other less frequently used alternatives include fuel cells or a variety of other solutions of unconventional energy harvesting (EH), such as thermoelectric power, microbial fuel cells, enzymatic fuel cells [3], etc. The importance of PV systems and small wind turbines as power sources, is hard to overestimate, but these kinds of power supplies are highly unpredictable, which necessi- tates the use of batteries, often with large capacities. In many cases, the use of large-sized PV panels or wind turbines is impossible for aesthetic or security reasons, the risk of van- dalism, or a lack of required space. Another reason may be problematic location, e.g., under Energies 2021, 14, 6206. https://doi.org/10.3390/en14196206 https://www.mdpi.com/journal/energies