| With the further development of national power industry,high voltage,extra-high voltage(EHV)and ultra-high voltage power transmission lines are of great necessity to maintain social stability and security.High voltage power transmission lines together compose a giant electric network,which is always exposed in the wild.As a result,both the geography and the weather are inevitably terrible and fickle so that the giant network is at the risk of being destroyed.Once some nodes in the network are damaged,chain reaction would be triggered.When the problems are serious,the power grid would run into collapse,leading to inestimable economic loss.Online monitoring equipments for high-voltage power transmission lines can be used to achieve thorough and multi-functional supervision of power lines working conditions.The applications of such monitoring equipments reduce the risks of the power line paralysis.Moreover,system breakdown can be avoided on the basis of the feedback.Nevertheless,the complexity and instability of the traditional power supplies(battery replacement and new energy power supply)are unable to satisfy the demand of more and more online monitoring nodes.In order to overcome the above problems,a new power supply mode combining the energy harvesting by electromagnetic induction with wireless power transfer(WPT)is proposed.Stable output power with constant output voltage is supposed to be generated and used to supply the monitoring devices over the insulation distance.The paper not only introduces the brand new idea of online energy harvesting device on high voltage power transmission lines but also helps to lay the foundation of industrialization.At the meanwhile,the work contributes to the theoretical research on the mechanism,influence factors and performance optimization as well as practical applications of the mid-range wireless power transfer systems.The research and results of the paper are organized as follows:1)Systematic optimization and parameter design of the energy harvesting devices for online monitoring devices over high voltage power transmission lines are discussed.Firstly,the configuration of the wireless charging system is introduced.Afterwards,according to the model of traditional wireless power transfer systems,the power demand of the energy harvesting devices is derived by taking the insulating safety distance between the power transmission line and the tower into consideration.The mathematical expression of the extracting power of the energy harvesting device can then be deduced on the basis of the equivalent circuit model.Apart from the summary of the vector relationship among system parameters,optimal design of the core materials,air gap length and the turns of the secondary coil are carried out within threshold values.Finally,simulation and experiments are conducted to verify the theoretical analyses.2)Several key technologies of the magnetic coupled resonant wireless power transfer systems over middle and long distances are analyzed theoretically.In the first step,considering that the storage battery serves as the power supply for online monitoring devices and the load of magnetic coupled resonant wireless power transfer system simultaneously,its equivalent impedance is discussed so that the best compensation topology can be selected to achieve maximum charging power.In the second step,on the basis of the mutual coupling theory,the mutual inductance between the hollow spiral coils is calculated and the method to increase mutual inductance is proposed.In addition,the influence of the mutual inductance on the optimal working frequency is analyzed so that frequency splitting can be avoided by choosing appropriate mutual inductance.In the last step,the models of the three-coil and four-coil wireless power transfer systems are constructed.The effect of several key parameters such as resonant frequency,coil loss,transmitting distance and resonator sizes on the output power and power transfer efficiency are then investigated,which can provide efficient guidance for practical applications.3)The optimization design of wireless charging system for online monitoring devices on high voltage power transmission lines is proposed.In the first place,110kV transmission line is taken as an example to verify whether the application of relay coil can enhance system performance.In detail,three-dimensional modeling and simulation are employed to simulate the scaled-down tower,insulator and relay coil.The relay coil,which serves as the moving window of impedance matching,can be adjusted to satisfy the optimization goals under different working conditions.Additionally,a method to arrange the distribution of multiple receiving coils is introduced to make sure that each receiver can be charged with identical power.More comprehensive analyses are carried out to deal with the situations when the number of receiving coils changes.Optimal working frequency and charging power can be kept stable according to the proposed optimization strategy by adjusting the distribution radius of the receiving coils.Specific method to determine the optimal distribution radius and corresponding efficient range is derived based on the function fitting.Finally,a rotating receiving coil with mixed magnetoelectric conversion function is presented,which can further increase the output power as well as the power transfer efficiency.The work offers a brand new idea to improve the performance of wireless power transfer systems over middle and long distances.4)An experimental prototype of the wireless charging system for online monitoring devices on high voltage power transmission lines is built and corresponding performance test is implemented.On the basis of the theoretical analyses and optimization design of several crucial components,a principle prototype is constructed to test the working performance including switching-on current,drive capability,ZVS switching characteristic,load characteristic and overall power transfer efficiency.The feasibility of the principle prototype has been validated. |
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