# A Novel Charging Station on Overhead Power Lines for Autonomous Unmanned Drones
## 1 Introduction  
The European Union is pushing to reduce greenhouse gas emissions, with a long-term strategy to achieve carbon neutrality by 2050. This goal will require widespread electrification of processes, products and transportation, as well as an expansion of renewable energy sources. Electricity generated from renewable energy is both efficient and environmentally friendly, but it necessitates the expansion of power lines. Every year, significant human and economic resources are necessary to inspect and maintain the electrical transmission and distribution network. Innovative techniques are also imperative to ensure resiliency and reliability, which guarantee the continuity of supply and service quality. Currently, aerial inspections are primarily conducted via helicopters, with maintenance requiring live line working to prevent electrical disruption. However, this method is hazardous to personnel working on electrical equipment. Drones can be fitted with cameras for visual and thermographic inspections to detect anomalous temperatures or with LiDAR sensors to create 3D maps [1] and can operate in remote areas and harsh environments [2]. These techniques for inspection enable both corrective and predictive maintenance [3] and are suitable for use in high-, medium- and low-voltage overhead lines [4; 5; 6; 7]; substations; and protection and remote-control systems, among others. Tasks related to grid maintenance include felling, pruning, clearing and removing elements ofthe forest area from the electrical overhead line. Additionally, drones can inspect areas that are difficult to reach and provide a swift response in emergency situations. In this context, aerial robotic manipulators offer cutting-edge technology to minimize hazardous work and reduce maintenance costs. However, current electric multirotor drones have limited flight times due to battery capacity and weight restrictions. Inspection and maintenance tasks on the electrical grid require large batteries to support the payload and autonomy of the cameras or manipulator, and commercial multirotor drones are typically limited to minutes of flight before the battery runs out, limiting autonomous operations in rural areas. As such, there is growing concern about energy consumption [8; 9; 10; 11; 12] and the availability of charging stations [13; 14; 15; 16; 17; 18; 19; 20; 21; 22] for extended maintenance and inspection tasks. Multirotor drones typically necessitate manual battery replacement by the pilot for connection to the charger. However, the literature has introduced various techniques for automation of the charging process, which can be categorized based on whether they rely on an electromagnetic field (EMF) or not [1; 23; 24; 25]:  
Non-EMF-based techniques for in-flight charging:  
* Gust soaring [26];
* PV-integrated [9];
* Laser beaming [27];
* Battery swapping or dumping [28]. * EMF-based techniques for stationary charging up to several centimeters:
* Capacitive charging [29];
* Inductive charging [4; 30; 31; 32; 33];
* Magnetic resonant charging [34]. Overhead power lines are predominantly located in rural areas, which lack access to energy sources that could facilitate the deployment of charging points. Harnessing renewable energy such as photovoltaics to power drone charging stations is both costly and weather-dependent. In contrast, transmission and distribution lines transport a significant amount of energy. However, accommodating the necessary voltage levels is currently economically challenging. Some papers suggest using energy harvesters placed on overhead power lines to enable drone charging by taking advantage of the power grid itself [12; 35; 36; 37; 38; 39; 40; 41; 42]. However, the reported harvesting technology has significant power limitations and requires further investigation. This paper presents a novel design that addresses certain challenges, specifically the charging power density and mechanical design.