Theory and circuit model of brush commutation in helical coil electromagnetic launchers

A model is developed to investigate the commutation process of a helical coil electromagnetic launcher (HCEML) structure. When armature moves, the motion of the projectile coils´ magnetic energy would supply reactive power to move the leakage into and out of the coil windings of the launcher to accomplish the commutation. The energy conversion of the coil electromagnetic launcher can be considered as the process of energy transfer from the back commutation coils to the excited coils and then from the excited turns to the drive coils in front. In this study, governing equations of the commutation was deduced theoretically and Finite Element Model of HCEML was established in ANSOFT. Then a deeper circuit investigation on the overall performance of commutation was carried out by means of PSPICE software. The validity of the theoretical analysis and circuit network model were finally verified by experiments. The results show that during the commutation process, the current of back commutation coil drops to zero with no energy remaining in the internal; the current of front commutation coils and drive - projectile coils system changes to a stable value, which is related to the geometric parameters of the launcher; drive- projectile coils system releases energy overall that is mainly used to increase the kinetic energy of the projectile; the power supply system does little effect on the energy conversion and transformation in the commutation instant and just keeps the voltage and current not decaying from impedance and inductance of launching system.