Analysis of generator-driven linear induction launchers

Abstract

This paper deals with the analysis and design of high-speed, multi-section, generator-driven, polyphase, linear-induction-type electromagnetic launchers. During a launch, steady state is never reached. Hence, a transient simulation model, based on lumped-circuit parameters, was developed, for purposes of analysis, in earlier work with capacitor-driven launchers. This model, as well as its related computer code, is also applicable to generator-driven launchers. From earlier work, we found that simultaneous energizing of the three phases of generator-driven launchers gives rise to DC current components in the barrel-coils that can cause strong braking forces, especially at the transitions between sections. In this paper, an alternate energizing mode, in which the three phases of the barrel coils are switched on in sequence, phase by phase, with the appropriate phase shifts, is investigated. Numerical results of the transient simulation show that the initial position of the projectile at a section transition at switch-on time, and the switch-on phase angle, significantly influence the performance. With some poorly-chosen initial positions or phase angles, DC components of the currents in the armature can produce very large retarding forces, thus resulting in actual deceleration of the projectile. On the basis of the transient model, simulations were done to search for the optimal switch-on phase angles and initial positions of the projectile. The results show that smoother transitions between sections and higher muzzle velocities can be achieved with these optimal phase angles and initial positions.