Study On The Key Techniques Of High-efficiency Microwave Power Transmission For Long-distance Applications

Microwave power transmission(MPT)technology involves wirelessly transferring power via microwave beam.It is one of the key technologies of solar power satellites,and can also be used to supply power to the distributed reconfigurable satellites,near space airships,wireless sensor networks,remote regions,and so on.In this dissertation,the excitation level distribution across the transmitting aperture and its optimization method are studied to obtain a high DC-DC(direct current to direct current)efficiency of MPT systems.Additionaly,the optimization method of rectenna is discussed.The following four main subjects are included.The optimal continuous excitation level distribution(ELD),namely Fourier-Bessel ELD(FBELD),is proposed for the circular transmitting aperture(CTA)to obtain the maximum beam capture efficiency(BCE),and the synthesis methods of achieving the FBELD across CTA are presented for far-field and near-radiation-field MPT systems.The proposed methods have a wide universality and can be applied to any continuous ELD optimization problems of CTA.In order to improve optimization efficiency,Random-Group Coevolving Differential Evolution(RGCDE)is suggested by combing random-group strategy,coevolving algorithm and differential evolution algorithm.It can be found from the numerical results that(1)FBELD could obtain BCE close to 100%,and(2)the size of transmitting aperture or the receiving angle should be increased to keep the same BCE in near radiation region due to the pattern distortion.Sparsification of a large-scale transmitting array has a practical significance.Moreover,the design,fabrication,and maintenance of feed network would be greatly simplified if all elements of the transmitting array are excited uniformly.Compared with square array,concentric ring array(CRA)has a higher BCE with the same elements.By combining the BCE synthesis methods of far-field and near-radiation-field MPT systems and RGCDE optimization algorithm,uniform exciting strategy and sparsification of array are achieved simultaneously while keeping the high BCE.Compared to the full-filled array,numerical results show that above 30% elements are saved and the reduction of BCE is only 0.4% for achieving uniform exciting strategy and the sparsification.The array pattern distortion caused by excitation errors would decrease the BCE.To solve this problem,excitation amplitude and phase errors of the transmitting array being considered simultaneously for the first time is analyzed and optimized.The effect of random excitation errors on BCE is evaluated by a statistical analysis(SA)method,and the array is optimized to reduce the effect on BCE by combining SA method and RGCDE algorithm.Compared with the unoptimized transmitting array,numerical results show that the decrement of BCE is improved from 8.86% to 5.06%,and the increasement of element number is beneficial to reduce the effect of excitation errors on BCE.Rectenna is composed of receiving antenna and rectifying circuit,and it is time-consuming to analyze the rectifying circuit by fullwave analysis method Finite-Difference Time-Domain(FDTD).Aiming at solving this problem,a fast combined optimization method,which combining FDTD,Harmonic Balance(HB)method and RGCDE algorithm,is presented.By using the HB method results as the initial the electric field in FDTD,the time cost of nolinear circuit fullwave analyzing is significantly declined by 87%,and the effectiveness of the combined optimization method is improved.Two rectennas are designed by the proposed method and the measurements validate its effectiveness.