Research On Energy Conversion Technologies Of The Helical Coil Electromagnetic Launcher

The energy conversion efficiency is an important indicator of the helical coil electromagnetic launcher?HEML?,also is an important basis of its application.This dissertation focuses on some key issues related to the energy conversion efficiency of the HEML,mainly including the following aspects:The related energy conversion problems of the HEML are analyzed theoretically.The physical process of the HEML is divided into two parts:acceleration and commutation processes.The energy conversion relationship during the acceleration process is obtained,that is,the power balance equation.The equivalent circuit models of the front and rear commutation processes are established,and the energy conversion efficiency formula of the launcher is obtained.The energy conversion efficiency of the launcher is mainly affected by such factors as mutual inductance gradient,Joule heat loss,commutation loss and muzzle loss.The theoretical efficiency of the launcher and its influencing factors are studied.The results show that the theoretical efficiency can exceed 50%while the HEML operates in a constant current mode.The parameter criterion of its theoretical efficiency greater than 50%under the constant current mode is derived.The calculated theoretical efficiency of the launcher can reach 82.1%for a typical structure with the armature coil of 109 turns and the launcher length of 3m.The electromagnetic accelerating force is studied and optimized.The element method and the equivalent circular loop method are adopted to calculate the accelerating force,in which the element method has better universality and accuracy?<0.1%?,and the equivalent circular loop method has faster calculation speed?single runtime⁴ ms?.The relationship between the accelerating force and the position of the armature coil is obtained,so as to determine the position of the armature coil for maximum accelerating force.The influence of the structure of armature and stator coils on accelerating force is simulated,and the armature with two D-shaped coils is proposed to double the accelerating force.The stress distribution of the stator coil is analyzed.A reinforced stator coil structure consisting of modular units is designed to withstand higher accelerating forces.The influence of the shield material and its structure on the accelerating force is analyzed and verified by experiments.The results show that the shield of ferromagnetic material is helpful to enhance the accelerating magnetic field of the launcher.The smaller the gap between the shield and the stator coil,the better the shield effect.However,the eddy current in the conductive shield may generate a pulling-back force on the armature and generate Joule heat loss,which reduces the energy conversion efficiency.The unit barrel HEML with barrel length of 1m,diameter of 120mm,and projectile mass of 4.5kg is designed.The speed of 47.5m/s and conversion efficiency of 8.72%are achieved in the experiments.After several shots,it can be verified that the unit barrel structure can bear a peak 35kA operating current.The commutation and muzzle losses of the HEML are studied.The influence factors on the commutation induced voltage are studied and the formula of commutation induced voltage is derived.Given the fixed operating current and speed of projectile,the greater the number of turns in the armature and stator coils,the higher the possibilities of commutation arc ablation.By theoretical analysis,the number of turns in the armature coil is determined to satisfy the condition of complete induction commutation,avoiding large current on and off during commutation.The armature coil turns are changed in experiments to compare the ablation of the commutation brushes,and the theoretical results are verified.The current conversion conditions of multi-turn commutation are studied.When multi-turn commutation is carried out,the current in the commutation turns changes slowly and the commutation induced voltage is low.The typical commutation induced voltage is calculated to be 13.2V by the formula.When the two-turn commutation proposal is adopted,the commutation induced voltage is calculated as 5.1V.The transient physical model,control equations and numerical solution of the HEML are established.The influencing factors of the muzzle loss are simulated and a stator coil structure with non-uniform turn density is proposed.The new structure decreases the muzzle current by 45%,effectively inhibiting the formation of the muzzle arc,while improving the energy conversion efficiency.Finally,the overall structural parameters of the launcher are optimized.A mathematical model is proposed and an improved adaptive genetic algorithm is designed.Under the constraints of temperature rise and launcher length,the multi-objective optimization of HEML structural parameters such as velocity,efficiency and power is conducted.The improved genetic algorithm makes the mutation probability change adaptively betweenP_m0/3?25?P_m0with the diversity of the population.In addition,the improved genetic algorithm adopting the elites retention strategy,makes sure that the excellent solutions emerging on the early execution of the program are retained.Thus,the algorithm execution efficiency is greatly improved.The calculation results show that the optimization algorithm can provide reasonable structural parameters for different application requirements.