ANALYSIS OF GENERATOR-DRIVEN LINEAR INDUCTION LAUNCHERS

This paper deals with the analysis and design of high-speed, multi-sec tion, generator-driven, poly-phase, linear-induction-type electromagne tic 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-dr iven launchers. This model, as well as its related computer code, is a lso applicable to generator-driven launchers. From earlier work, we fo und that simultaneous energizing of the three phases of generator-driv en launchers gives rise to de current components in the barrel-coils t hat can cause strong braking forces, especially at the transitions bet ween sections. In this paper, an alternate energizing mode, in which t he three phases of the barrel coils are switched on in sequence, phase by phase, with the appropriate phase shifts, is investigated. Numeric al results of the transient simulation show that the initial position of the projectile at a section transition at switch-on time, and the s witch-on phase angle, significantly influence the performance. With so me poorly-chosen initial positions or phase angles, dc components of t he currents in the armature can produce very large retarding forces, t hus resulting in actual deceleration of the projectile. On the basis o f the transient model, simulations were done to search for the optimal switch-on phase angles and initial positions of the projectile. The r esults show that smoother transitions between sections and higher muzz le velocities can be achieved with these optimal phase angles and init ial positions.