| The development of space industry has promoted the research of microgravity science.However,it is unrealistic to carry out numbers of microgravity experiments by relying on space flight.Microgravity drop tower provides the possibility to realize the microgravity environment on the earth.To obtain a longer microgravity time and higher experimental frequency in the microgravity drop tower system,a novel microgravity drop tower system using electromagnetic launch technology has been proposed by scientists,which will help to better promote the development and progress of microgravity science.Therefore,it is of great engineering value and significance to carry out theoretical research on linear motor for vertical drive.In this dissertation,the air gap magnetic field distribution,electromagnetic thrust,braking force and their ripple,equivalent circuit of the coupling region and secondary structure to reduce thrust and braking force ripple of long primary double-sided linear induction motor(DLIM)in launch system are theoretically studied and calculated,which combined with the motion trajectory of the experimental cabin in the new generation automatic microgravity drop tower system using electromagnetic launch technology.The main research contents include:The analytical formula of electromagnetic field is solved,and its distribution characteristics are analyzed.The analytical calculation model of one-dimensional electromagnetic field of long primary DLIM with the secondary as the motion reference coordinate system is established,the expression of air gap flux density considering the longitudinal end effect is deduced,furthermore,the space-time distribution characteristics of air gap magnetic field and each component are analyzed,and the influence of backward travelling wave magnetic field on normal travelling wave magnetic field is emphatically analyzed,considering the arbitrariness of the secondary length of long primary DLIM.The expression of air gap flux density and secondary current density is verified by finite element method,and the longitudinal characteristics of electromagnetic field of long primary DLIM are revealedThe thrust and thrust ripple characteristics considering the longitudinal end effect is studied.The analytical formula of thrust and thrust ripple considering longitudinal end effect are deduced by using the product integral method of primary surface current density,secondary current density and air gap magnetic field respectively,the similarities and differences of thrust and thrust ripple calculated by these two methods are compared and analyzed.The characteristics of longitudinal end effect thrust are studied,the influence of each end effect force component on the output thrust is analyzed,and the mechanism of thrust ripple of integral pole pitch secondary motor is revealed.Furthermore,the secondary current density is used to calculate the thrust characteristics of the DLIM with non-integer pole pitch secondary,and the source of thrust ripple is analyzed,considering the arbitrariness of the secondary length.The correctness of the thrust analytical formula is verified by the test results of the prototype.It provides a basis for rapid calculation and analysis of thrust characteristics of DLIM with secondary of arbitrary length.The electromagnetic and thrust characteristics of DLIM under braking condition are investigated.Taking the secondary as the motion reference,the expressions of air gap magnetic field and secondary current density under regenerative braking condition are solved,and the analytical formulae of braking force and its ripple are deduced by using secondary current density,the braking force is verified on the test prototype.The longitudinal distribution characteristics of air gap magnetic field and secondary current density in the new drop tower are revealed and compared with that of motoring condition.The characteristics of end effect force,braking force and force ripple of the DLIM with varied secondary length are calculated,the mechanism of each end effect force component on braking force under braking condition is analyzed,the main sources of braking force ripple when the secondary length is an integer pole pitch and a non-integer pole pitch are revealed,and the expressions of braking force and force ripple are simplified,which help lay a foundation for the analysis of electromagnetic field and braking force characteristics,and the suppression of force ripple under the regenerative braking condition of long primary DLIM.An improved equivalent circuit model considering longitudinal end effect,transverse edge effect and skin effect is proposed.The long primary DLIM is decomposed into three independent solving models: longitudinal,transverse and vertical.According to the principle that the complex power calculated by the electromagnetic field is equal to the complex power calculated by the equivalent circuit,the longitudinal end effect correction coefficients of the excitation reactance and secondary resistance are solved by the longitudinal analysis model with the secondary as the motion reference coordinate system.Then,the secondary leakage reactance,and the skin effect correction coefficients of excitation reactance and secondary resistance are deduced,according to vertical model.And then,the improved equivalent circuit model is established,and the mechanical characteristics calculated by improved and traditional equivalent circuit are compared and analyzed.The electromagnetic force is verified by finite element and experiment.The equivalent circuit model proposed in this dissertation can fully consider the end effect and skin effect,and further improve the equivalent circuit model of long primary DLIM.Two secondary structure to suppress the ripple of electromagnetic force is proposed.On the basis of studying of the air gap magnetic field and secondary current density distribution of long primary DLIM under motoring and braking conditions,and combined with the motion trajectory of the secondary in the new drop tower,a wedge-shaped secondary structure is proposed to weaken the thrust and braking force ripple of motor with twice the slip frequency.According to the different phases of thrust ripple generated by DLIMs with different secondary lengths,a shuttle secondary structure which can reduce electromagnetic force ripple under motoring and regenerative braking conditions is proposed.The thrust and thrust ripple characteristics between the two new secondary motors and the traditional plate secondary motor are calculated and compared,which provides a new solution for suppressing the acceleration/deceleration ripple in the launching and braking process of the new drop tower system. |
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