Research Of Mining Asymmetric Coil Structure Magnetically Coupled Resonant Wireless Power Transfer System

Coal is the main primary energy in China,plays an irreplaceable role in economic and social development.Safe and efficient mining can't do without monitoring and communication system.But the traditional way of wire power supply has been restricting the layout of monitoring sensors.And in coal mine both bare wires and sparks have the potential to cause serious accidents.At present,the mining portable equipment mainly relies on battery power supply,but in coal mine it is forbidden to open the flameproof enclosure and replace batteries.And the battery charging must be done on the ground.These problems have great influence on the safe and efficient mining.Magnetically coupled resonant(MCR)wireless power transfer(WPT)technology has the advantages of high efficiency,high transfer power,small electromagnetic radiation and longer transfer distance,and also the physical contact can be avoided.If the MCR-WPT technology can be used in the underground coal mine,the problem of the arrangement of monitoring sensors and the portable equipment cannot be charged in coal mine will be solved.It is of great significance to ensure safe and efficient mining and to improve the current grim situation of mining.At present the MCR-WPT system on the ground mainly adopt the parallel coaxial coil structure and the coils parameters are identical.But there are so many kinds of electrical equipment in the coal mine,and the electrical equipment needs to be equipped with flameproof enclosure.However,the tunnel space of coal mine is very narrow.If every charged equipment is equipped with a dedicated wireless charging transmitter equipment,there will be lots of transmitter equipment,the type of equipment will be multiplied.As a result,the tunnel space will be more crowded,and the cost of equipment maintenance and management are also increased.So the key problem needs to be solved urgently by the MCR-WPT system in coal mine is that the same transmitter can charge different sizes and types equipments separately.In order to solve this key problem,it is necessary to consider that the distributed parameters of the coils of different sizes are different.And this makes the frequency splitting phenomenon of the asymmetric coil structure MCR-WPT system was difficult to suppress due to the different coil parameters.Also it is unrealistic to align the two coils in different flameproof enclosures during the wireless charging,that is there will be misalignments between the coils,and the misalignments will causes a decrease in the transmission efficiency.So in order to apply the WPT technology to the coal mine,it is necessary to research the asymmetric coil structure MCR-WPT system.Based on the circuit theory,the frequency characteristics of the asymmetric coil structure MCR-WPT system and the effects of the misalignments on the transmission efficiency were researched in the paper through modeling,theoretical derivation,simulation and experimental verification.And the main research work are as follows:(1)The effect of radial distance on the transmission efficiency was researched.The model of the MCR-WPT system was built based on the equivalent circuit theory and the transmission efficiency formula with radial distance and axial distance was deduced.And the effect of radial distance on the transmission efficiency with different axial distances and the effect of axial distance on the transmission efficiency with different radial distances were researched through simulation and experimental analysis.And the effect of radial distance on the transmission efficiency and the effect of axial distance on the transmission efficiency was compared.And the conclusions providing an useful theoretical reference for the research of the effects of the misalignments on the transmission efficiency,and also can offer theoretical references for the optimization of the transmission efficiency..(2)The transmission efficiency of the asymmetric and non-parallel coaxial coils structure MCR-WPT system was researched.The concept of the ratio of transfer distance to radius and the concept of the ratio of the radius of the two coils were proposed,and the transmission efficiency formula was deduced.And the change laws of the effect of the ratio of transfer distance to radius,the ratio of the radius and the angular misalignment on the transmission efficiency were obtained through simulation and experimental analysis.The research conclusions lay a theoretical foundation for the design of the transmitting and receiving coil of the WPT system in coal mine,and also has a great significance to determine the effective transfer range of the WPT system.(3)The effects of the misalignments between the coils on the transmission efficiency of the MCR-WPT system were researched.In the paper the misalignments between the coils was divided into angular misalignment and lateral misalignment,and the model of the MCR-WPT system with misalignments was built based on the equivalent circuit theory.The effects of the angular misalignment and lateral misalignment on the transmission efficiency were researched through simulation and experimental analysis.And the changing regularity of the transmission efficiency with the angular misalignment and lateral misalignment were obtained.And the optimization methods were proposed that when there is an angular misalignment between the transmitting coil and receiving coil,the transmission efficiency can be optimized by adjusting the lateral misalignment between the coils,and when there is a lateral misalignment between the coils,the transmission efficiency can be optimized by adjusting the angular misalignment between the coils.And the conclusions provide a theoretical reference for the research of the transmission efficiency optimization method of the MCR-WPT system with misalignments.And also provide beneficial guides for the designing of the MCR-WPT system in coal mine.(4)The frequency characteristic of the asymmetric coil structure MCR-WPT system was researched.The concept of the quality factor ratio of the transmitting coil to the receiving coil was proposed,and the formula between the output power and the quality factor ratio of the coils was deduced.By using normalization method,the regular pattern of the effects of generalized coupling factor,generalized detuning factor,the quality factor ratio and the frequency splitting factor on the output power and the transmission efficiency were obtained through the simulation experiments,and also validate the condition of the output power achieving the local maximum value as the frequency splitting phenomenon occurs.The obtained conclusions are reference to optimize the output power and transmission efficiency of the asymmetric coil structure MCR-WPT system in coal mine.(5)Finally the work and innovations of the paper were summarized,and the next step work suggestions are also put forward.The obtained conclusions about the researches of the asymmetric coil structure MCR-WPT system not only enrich the theory of the MCR-WPT technology,lays a foundation for the study of WPT technology in coal mine,but also has a guiding significance on the design of the MCR-WPT system in coal mine.