Unmanned aerial vehicles (UAVs), also known as drones, are used today for various purposes, including disaster prevention, power line inspection, forest monitoring, and military operations. They typically transport high-energy batteries, such as lithium batteries, which enable flight times of 20 to 40 minutes.
However, due to their limited battery capacity, UAVs face serious problems with range and endurance. UAV batteries cannot be made larger because doing so would make them heavier, which is a serious issue. UAV battery charging has been the subject of numerous research studies, but more in-depth research is still needed.
Researchers have proposed several strategies to extend flying time, including (i) equipping drones with large batteries, though doing so may make them heavier. (ii) battery switching after the drone has landed (however, switching systems can be complicated and expensive) (iii) charging base stations.
This post will explore some of the key battery charging techniques for drones today, including Wireless Power Transfer (WPT).
1. Wireless Power Tranfer (WPT)
Wireless Power Transfer (WPT) is expected to generate 12,000 million dollars in revenue in 2020, according to reports from the WPT market. By 2025, the drone market is anticipated to generate total sales of $43 billion with a Compound Annual Growth Rate (CARG) of 13.8 percent. It is because numerous applications in the electronic sector have several important advantages, including safety, convenience, dependability, and a fully automated charging system. Various WPT methods can be used to achieve these advantages.
A crucial aspect of WPT is that it is necessary for various settings where wired power transfer is risky, challenging, or impractical, such as harsh underwater environments and high voltage power applications. The research community has been investigating trade-offs and analyzing various WPT methods. These methods fall into radiative electromagnetic (EM) and non-EM.
Power is transferred in non-EM using acoustic or optical sources, like a laser. Further divisions of EM include non-radiative, mid-field radiative, and radiative far-field. When transmitting non-radiative power, capacitive, inductive, and magnetic resonance coupling is used instead of RF.
These WPT techniques are currently being developed for various applications and are commercially available for applications like charging smartphones and implantable medical devices, among others. Next, we’ve highlighted a few WPT strategies and some WPT-related research contributions.
Utilizing WPT techniques, wireless power transmission between the base station and the UAV is reliable and effective. When using WPT technology with UAVs, it’s important to consider factors like misalignment, interference, and payload. A lightweight UAV-based WPT system is required to prevent payload reduction.
Additionally, the WPT techniques must guarantee high landing precision, efficient power transfer, and misalignment tolerance between coils. Due to UAVs’ poor landing accuracy, misalignment effects stand out among these difficulties. As a result, it impacts power transfer, transfer efficiency, and coupling factor. These significant problems with recharging UAV batteries using WPT techniques have been documented in numerous research studies.
Inductive coupling WPT can be used to charge UAVs, increasing their range and flight time for monitoring, surveillance, and inspection tasks. Existing inspection methods have several limitations that can be overcome by UAV-powered inspection techniques, including high costs and risky operations involving manned helicopters.
2. Photovoltaic Cell-Based UAV Charging
UAVs frequently use photovoltaic cells to charge batteries and extend flight times. Sunlight is used by PV cells to charge the UAVs’ batteries. PV cells provide the necessary power to the UAV whenever sunlight is present, and batteries are used to provide the necessary power to the UAV when sunlight is not present.
According to studies on solar-powered UAVs, several factors are crucial, including temperature intensity, sunlight angle of incidence, PV cell geometry, orientation, and position. This technique is inappropriate in situations where there is not enough sunlight. When sunlight isn’t available, alternate tactics must be used to continue UAV flights. These techniques include more power sources, more powerful batteries, larger PV cells, and automatic position adjustment in response to the sun’s position.
Fixed-wing UAVs can carry PV cells because they have a larger payload and longer wings. Furthermore, environmental factors like humidity, temperature, fog, and clouds affect the system’s dependability and efficiency. Therefore, it is important to take these atmospheric factors into account.
Several research teams are now interested in developing UAVs that run on solar energy. The right choice of PV cells can provide sufficient flight power, and considering efficiency and weight is the key to ensuring long flight times and high endurance in solar-powered UAVs. Solar cells are made from various materials to achieve cost-effectiveness and high efficiency. Due to their low cost and high efficiency, monocrystalline silicon PV cells have been recommended in some studies. The high flexibility offered by monocrystalline silicon PV cells facilitates simple integration in the UAV wing.
3. Charging with Laser Beaming
Another technique for charging UAVs is laser power transfer (LPT), primarily used in military and space applications. In this charging method, PV cells mounted on a UAV are fed using a laser beam with a specific wavelength and frequency. These PV cells use the power generated by laser transmitters to run UAVs and replenish their battery packs. Both fixed-wing and rotary-wing UAVs employ the laser beaming method. Unlimited endurance is now a workable solution. Narrow beam divergence can deliver high energy to the receiver.
Numerous UAV missions that require a lot of energy over long distances are anticipated to be powered by laser power transfer. Some major LPT concerns are blockage, mobility, and performance during long-range flights. This technique is only permitted in places like military bases, airports, and situations where a laser beam threatens people’s health and residential areas.
