Research On Key Technologies Of Wireless Power Transfer Based On Time Reversal

Radiative wireless power transfer eliminates the power cables between the power source and the electrical devices,significantly enhancing the convenience and flexibility of power supply.In recent years,wireless power transfer has been considered a new emerging wireless research field following wireless communication,holding great promise to drive comprehensive innovation in numerous industrial technologies such as the Internet of Things,industrial internet,smart manufacturing,and unmanned factories,thus bearing significant scientific research value and significance.This dissertation addresses the key technical bottlenecks faced by unmanned scenarios at medium distances of meters.It systematically conducts research on auto-tracking,wide-range and multi-posture,high system efficiency and low system complexity wireless power transfer from three aspects: theoretical analysis,method proposal,and simulation and experimental verification.The main research contents of this dissertation are as follows:1.The discrete time reversal theory is derived and a performance analysis method of wireless power transfer system based on the transmit-receive channel matrix is proposed.This lays the theoretical and numerical calculation foundation for the quantitative research of time reversal wireless power transfer based on discrete time reversal mirrors,guiding the design of wireless power transfer systems.The analysis of the focusing field characteristics of the discrete time reversal mirror at the receiver theoretically reveals the superiority of time reversal technology in terms of spatial focusing and over-the-air efficiency.Moreover,the theoretical expressions for spatial focusing and over-the-air efficiency provide research ideas for subsequent studies on wireless power transfer.2.To achieve efficient,low-consumption and low profile auto-tracking wireless power transfer for a moving receiver,this dissertation proposes a shared aperture scheme that allows all transmitting antennas to emit wireless power transfer signals,achieving higher over-the-air efficiency.An auto-tracking method that judges channel relevance through the output rectification power threshold is proposed.It triggers the retransmission of the ploit signal only after the threshold is reached,reducing the transmission time of the ploit signal and thereby lowering the power loss at the receiver.A radio frequency(RF)channel cascaded topology and an idea of modular design based on the cascaded topology were proposed,laying the groundwork for designing a transmitter with lowprofile,short RF cable lengths,and easily expandable.Utilizing the aforementioned methods,an auto-tracking time reversal wireless power transfer system was designed.The system features a transmitter with the advantages of being low-profile,having short RF cable lengths,and being easily expandable.Simulation and experimental results demonstrated high over-the-air efficiency,spatial focusing,and auto-tracking characteristics.3.To achieve wide-range and multi-posture wireless power transfer for wirelessly powering multi-posture receivers within a large area,guided by the concept of enhancing physical channels,this dissertation proposes a 360° wide-range,low-side-lobe wireless power transfer method based on the superposition of multiple high-order radiation modes.By employing high-order radiation modes with 360° radiation characteristics,an enhancement of the single-transmitter single-receiver physical channel within a wide range was achieved.Furthermore,the optimal weighting coefficients for achieving the lowest side-lobe level were derived.Through the superposition of multiple weighted high-order radiation modes and the time reversal method,360° wide-range wireless power transfer was realized.Subsequently,this dissertation proposes a multi-posture wireless power transfer method based on bidirectional time reversal.By configuring the phase shifters at the receiver using the backward time reversal method,the beam of the posture-changing receiver is aligned with the transmitter,enhancing the physical channel between a single transmitting antenna and the receiver.Then,by configuring the phase shifters at transmitter using the forward time reversal method,the beam of transmitter is aligned with the posture-changing receiver.Ultimately,through the bidirectional time reversal method,a dual alignment of the transmitting and receiving beams is achieved.Simulation and experimental results prove the effectiveness and superiority of the method proposed for achieving wide-range and multi-posture wireless power transfer.4.To achieve multi-target wireless power transfer with high system efficiency,aiming to efficiently wirelessly power multiple receivers,this dissertation introduces a double in-phase superposition time reversal method.By phase weighting the excitation signal vectors that generate the focused signal and sidelobe signals,in-phase superposition of focused signal and sidelobe signals is achieved to optimize the over-theair efficiency of the multi-user time reversal wireless power transfer system.Simulation results demonstrate the effectiveness and superiority of the proposed method.Then,building on the foundation of achieving optimal over-the-air efficiency,this dissertation proposes a high-efficiency multi-user wireless power transfer by sequentially tracking the optimal rectified power of multiple groups with a power-limited transmitter.By optimizing the excitation signals based on the received RF signals with power equal to the optimal rectified power,the minimal power excitation signal and grouping matrix are obtained.This allows multiple groups of receivers to sequentially perform wireless power transfer to achieve optimal system efficiency and maximize average output DC power.Simulation and measurement results have proven the effectiveness and superiority of the proposed method in enhancing system efficiency.Additionally,the method indicates that it can meet the diverse power requirements of multiple receivers,thereby ensuring the same lifetime and demonstrating the potential to enable perpetual operation for multiple receivers.5.To achieve low-complexity wireless power transfer and promote the rapid practical application of time-reversal wireless power transfer systems,this dissertation proposes an asynchronous quadrature demodulation method to reduce the hardware complexity.By forming in-phase component signals and quadrature component signals that carry channel information through the wireless power transfer signal transmission path at different time slots,accurate channel information is obtained through the arctangent function and partition criteria.The asynchronous quadrature demodulation method detects channel information and emits wireless power transfer signals through the wireless power transfer signal transmission path,eliminating the ploit signal transmission path of traditional schemes.This approach reduces the hardware complexity of the timereversal wireless power transfer system.Simulation and experimental results have proven the effectiveness of the asynchronous quadrature demodulation method.The asynchronous quadrature demodulation method reduces the hardware complexity but sacrifices the time complexity.Therefore,based on the asynchronous quadrature demodulation method,this dissertation proposes an asynchronous quadrature demodulation method with the reconstructable sub-array pattern method.By obtaining the required phase of the sub-array pattern and the phase difference between sub-arrays,and applying the principle of pattern multiplication,wireless power transfer with excellent performance is achieved using partial channel information.Ultimately,on the basis of reducing the hardware complexity through the asynchronous quadrature demodulation method,the reconstructable sub-array pattern method further reduces the time complexity of the asynchronous quadrature demodulation method.This lays a technical foundation for low-complexity wireless power transfer.