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Concept for the Use of the Existing Trolleybus Power Supply Networks as Infrastructure for the Electric Vehicle Charging Stations

Valentin Gyurov
Department of Electric Power Supply and Equipment, Technical University of Varna

Vladimir Chikov
Department of Electric Power Supply and Equipment, Technical University of Varna

Nikola Makedonski
Department of Electric Power Supply and Equipment, Technical University of Varna

Yuliyan Yordanov
Department of Electric Power Supply and Equipment, Technical University of Varna

Abstract
Technical solutions to electric power supply systems for trolleybus transport are commonly known and extremely widespread among the cities with urban electric transport. Distinctive features of their topology include medium voltage (MV) power lines, MV/LV (DC) rectifiers and catenary. The requirements for ensuring optimal voltage levels of the catenary, low voltage and power losses and attainment of optimal power load, determine the presence of a uniform distribution of rectifier stations as graphically represented in the cities’ cadastral maps. In view of the fact that the trolleybus transport runs through major transport arteries, the catenary lines cover principal city roads, which belong to the highest category of roads according to the classification of national roads (main streets, boulevards, etc.). The traction infrastructure inclusive of its power lines, rectifier stations, poles and catenary, is a technical system with a high investment value of millions of euros and has a relatively high transmission capacity of 1.5-5MW [3]. Trolleybus transport is defined by a specific load profile and characteristic load schedules determined by the different intensity of the traffic load during different hours of the day. Thus, peak values are normally observed in the hours between 8:00-11:00 a.m. and 15:00-18:00 p.m., as against the 23:00-7:00 a.m. period when the power consumption is near zero and the system is in idle. The development of EV- charging infrastructure is a topical issue arising from the vital necessity for the provision of vast sources of power. [1], [2]. This, in turn, corresponds closely with the need for maximized nighttime power generation that would be used for a more cost-effective EV charging. Even more, the proposed concept has two further extremely beneficial effects. The first addresses the provision of another efficient way to use the regenerative braking energy that is fed back to the catenary systems for the operation of the new generations of trolleybuses during daytime braking and power the electric vehicles directly if there is no other trolleybus getting catenary supply at that time, and only if the rectifier station is that of uncontrolled rectifier type that blocks energy transfer to medium voltage level. The second effect is related to the integration of photovoltaic systems into the trolleybus transportation sector. It is generally acknowledged that the most effective place for their connection is the low voltage side of the power transformers in rectifier stations. Subsequently, the generated renewable energy can thereby be used by the trolleybuses, and in the absence of sufficient load, it can be directly consumed by the EV- charging stations. The presented concept is an innovative solution with three interrelated aspects of successful application in the electric power supply systems for urban electric transport.