Research On Magnetically Coupled Resonance Wireless Power Transmission In Coal Mine

Coal is an important energy source in China.However,coal mine safety has been restricting the development of China's coal industry.Wireless power transmission(WPT) technology is contactless charging,which makes the underground electrical equipment completely free from the shackles of cable,and greatly facilitates the maintenance and management of the equipment.If the problem of wireless charging of electrical equipment in the underground explosion environment can be solved well,it will significantly improve the technical guarantee level of mine safety production.Magnetically coupled resonance(MCR)WPT technology has the advantages of large transmission distance,high transmission efficiency,low electromagnetic radiation and penetration,especially suitable for coal mine WPT.However,for this technology,the maximum transmission efficiency and output power can be achieved only when the transmitting coil and the receiving coil are fully aligned.The underground space of coal mine is small and there are many kinds of electrical equipment.It is very hard to satisfy this condition.Therefore,the transmission efficiency of MCR-WPT in underground coal mine are not high.To solve this problem,this paper studies the MCR-WPT system in underground coal mine in detail.Aiming at the problem that the position of the four coils of the traditional four-coil MCR-WPT system is relatively fixed and can not be changed at will,and the underground environment of coal mine is complex,so the traditional four-coil MCR-WPT system has its limitations in use,a new four-coil structure is proposed:power supply coil,load coil and lumped power coil,respectively.The power coil can produce magnetic resonance with the transmitting coil,the load coil can produce magnetic resonance with the receiving coil,at the same time,the relative position of the four coils can be changed,and the distance between the four coils can be adjusted properly,which can not only increase the transmission distance of the electric energy,but also improve the frequency splitting,so that the output power of the system and The transmission efficiency is the highest.The WPT system based on double two-way spiral coil is proposed.For the traditional MRR system based on single one-way spiral coil with fixed frequency,frequency splitting phenomenon will occur in the short distance transmission,a design method of double two-way spiral coil is proposed.This paper analyzes the impact of the inner and outer radius,turns and pitch of turns of double two-way spiral coils,and the other factors on the transmission efficiency of WPT system.This method counteracts the increase of coupling coefficient caused by short distance by the structure of spiral coil itself,reduces the over-coupling area of MCR-WPT system,compensates for the influence of frequency splitting on transmission efficiency in short-distance wireless transmission,reduces the frequency splitting area of the system,and improves the energy transmission efficiency in short-distance.The safety of the electromagnetic wave energy transmitted by the wireless power in the coal mine underground to the explosive gas is studied.The underground metal structure in the radiation field of the transmitting coil can be equivalent to the receiving antenna.The electromagnetic wave energy focused on the metal structure will be released in the form of discharge spark under the condition of scraping.At present,there is no test method and experimental equipment for the discharge spark caused by the electromagnetic wave energy Line test.In order to solve this problem,this paper studies the electromagnetic energy security analysis and test platform.Three modular test instruments are designed:radiation field coupling energy test device,electromagnetic wave energy magnetic resonance coupling power test device,electromagnetic wave energy discharge spark test device.The main feature and innovation of radiation field coupling energy test device is to realize the equivalent receiving antenna output power test of metal structure through the design of impedance matching device;electromagnetic wave energy magnetic resonance coupling The main feature and innovation of the power testing device is to test the output power of the metal structure equivalent coil by studying the structure mutual inductance and transmission efficiency of the asymmetrical coil coupled with the near-field magnetic resonance;the main feature and innovation of the electromagnetic wave energy discharge spark experimental device is to realize the electromagnetic wave power discharge at the breakpoint of the metal structure through the design of the directional coupler and the matching load Test of different explosive gases ignited by electric spark.The existing technical conditions and basis to achieve the above three modular detection instruments are feasible,there is no technical bottleneck that is difficult to overcome.The combination of the three modules can achieve the goal of igniting explosive gas with electromagnetic wave energy,and provide experimental and inspection means for measuring the safety of electromagnetic wave energy transmitted by radio energy in the coal mine underground in explosive gas.