# Advanced Progress of Optical Wireless Technologies for Power Industry: An Overview
## 3 Wireless Power Transfer of Power Industry Optical Wireless Communications  
Wired power transmission has some unsafe factors, such as line aging and tip discharge, which cannot be used on some special occasions, such as seabed and mines. In addition, cable transmission requires too many lines, which brings inconvenience to people's lives. Therefore, wireless power transfer (WPT) technology arises at the historic moment. Recent development of WPT provides a new node model for wireless sensor networks technique to extend their lifetime by the redistribution of energy [82]. It does not require a power transfer from the power supply conductors to the energy receiver technology. WPT technology development focused on applications requiring unidirectional power transmission [83].  
WPT technology consists of two types: near field and far field [84]. The former is suitable for applications where the distance between transmitter and receiver is within a few millimeters or centimeters, such as handheld device charging, radio frequency identification technology, induction cooking technology, and wireless charging or continuous WPT of implanted medical devices. In [85], authors validated the use of WPT technology in medical settings and for the elderly and disabled. On the country, the latter approach allows for longer distances. It is applicable to applications where the distance between transmitter and receiver is within kilometers [86].  
The development of WPT technology is mainly concentrated in application areas that require unidirectional power transmission. In recent years, bidirectional WPT (BD-WPT) systems in electric vehicles (EVs) grid integration of vehicle to grid (V2G) to realize the concept has been widely applied [83]. In order to reduce the impact caused by the intermittency of renewable energy systems and promote dynamic demand management, the V2G concept can be used as a cost-effective alternative energy storage unit. There have been many reports on the converter design, compensation topology and control technology of BD-WPT systems. One of the key issues of the Beidou-WPT system is to use external communication links to realize information sharing between main and auxiliary components. In [87], the secondary side controller is used to achieve synchronization between the two parties and control the power transmission. In [88], the author accurately modeled the BD-WPT system and proposed several methods to analyze the power flow.  
In order to realize the concepts of V2G and grid to vehicle, a two-way converter between the power grid and electric vehicles is needed to facilitate the transmission of electric energy between the power grid and electric vehicles. In an electric vehicle charging system, it is necessary to ensure that the working characteristics of the converter do not affect the grid-side current. In [89], a single-phase DQ controller for grid-side bidirectional converters is proposed. In [90], an optical WPT system was proposed, which could finish fast charging over a long distance while satisfying human body safety. A single junction gallium arsenide solar cell is designed to maximize the output power of the solar cell. In the rechargeable battery of portable equipment, a step-up direct current-direct current (DC-DC) converter is used to offer a stable current and convert it to the desired DC voltage.