**1. Introduction**

Recently, studies regarding wireless charging technology for supplying electric power to electric vehicles, various IoT (Internet of Things) devices, and unmanned moving objects have been actively conducted. Hitherto, wireless charging technology has been mainly studied based on magnetic induction, magnetic resonance, and electromagnetic wave methods. The magnetic induction method is mainly used when the distance between the transmitting and receiving coils is short (1–2 cm for electronic products or 0.15 m for electric vehicles), and the magnetic resonance method is applied when *Electronics* **2020**, *9*, 1745 induction, magnetic resonance, and electromagnetic wave methods. The magnetic induction method is mainly used when the distance between the transmitting and receiving coils is short (1–2 cm for

the transmission distance is longer than the magnetic induction method. In this case, the main target is a distance of less than 10 m. The electromagnetic wave method enables power to be transmitted up to a transmission distance of several kilometers compared with the other two methods; however, its transmission e fficiency is low, and it is harmful to the human body [1–4]. electronic products or 0.15 m for electric vehicles), and the magnetic resonance method is applied when the transmission distance is longer than the magnetic induction method. In this case, the main target is a distance of less than 10 m. The electromagnetic wave method enables power to be transmitted up to a transmission distance of several kilometers compared with the other two methods; however, its transmission efficiency is low, and it is harmful to the human body [1–4].

On the other hand, the wireless charging method using the laser is also being studied in military and space applications [2,5]. Figure 1 shows a schematic diagram of an unmanned aerial vehicle (UAV) wireless power transmission system using a laser beam proposed in [5]. The light energy of the laser beam irradiated from the ground is transferred to the laser photovoltaic (PV) module installed inside the UAV and converted into electric energy. The converted electrical energy is used to charge the battery through a power converter or as energy for components mounted on the UAV. Research on the laser wireless charging system to date is as follows. On the other hand, the wireless charging method using the laser is also being studied in military and space applications [2,5]. Figure 1 shows a schematic diagram of an unmanned aerial vehicle (UAV) wireless power transmission system using a laser beam proposed in [5]. The light energy of the laser beam irradiated from the ground is transferred to the laser photovoltaic (PV) module installed inside the UAV and converted into electric energy. The converted electrical energy is used to charge the battery through a power converter or as energy for components mounted on the UAV. Research on the laser wireless charging system to date is as follows. 

#### **Figure 1.** Laser wireless charging system configuration of unmanned aerial vehicle (UAV) [5]. **Figure 1.** Laser wireless charging system configuration of unmanned aerial vehicle (UAV) [5].

Results pertaining to the voltage, current, and efficiency based on the material type used and the laser wavelength in a laser PV cell are presented in [5,6]. However, in addition to these results, a method to control a converter that can charge a battery when a laser PV module is applied to a UAV is necessitated. Results pertaining to the wavelength and temperature output characteristics of PV panels applied to charging systems using laser beams as well as the mathematical modeling of PV panels are presented in [7]. In this study, the modeling of the laser PV module proposed in [7] was used to design a PV module applied to a simulation model; however, the output characteristics were analyzed through testing a prototype laser PV module. In addition, a control design method that can generate the maximum power from a laser PV module using a battery charging converter was investigated. In [8], the concept of the maximum power point tracking (MPPT) algorithm applied with a neural network (NN) algorithm considering the characteristics of a PV module, and a laser beam was presented. However, in that paper, the improvement compared with perturb-and-observe and incremental conductance methods, as well as the specific design method and experimental Results pertaining to the voltage, current, and e fficiency based on the material type used and the laser wavelength in a laser PV cell are presented in [5,6]. However, in addition to these results, a method to control a converter that can charge a battery when a laser PV module is applied to a UAV is necessitated. Results pertaining to the wavelength and temperature output characteristics of PV panels applied to charging systems using laser beams as well as the mathematical modeling of PV panels are presented in [7]. In this study, the modeling of the laser PV module proposed in [7] was used to design a PV module applied to a simulation model; however, the output characteristics were analyzed through testing a prototype laser PV module. In addition, a control design method that can generate the maximum power from a laser PV module using a battery charging converter was investigated. In [8], the concept of the maximum power point tracking (MPPT) algorithm applied with a neural network (NN) algorithm considering the characteristics of a PV module, and a laser beam was presented. However, in that paper, the improvement compared with perturb-and-observe and incremental conductance methods, as well as the specific design method and experimental results of NN, were not presented.
