Research on the Commutation-Induced Voltage of Helical Coil Electromagnetic Launchers

Helical coil electromagnetic launchers (HEMLs) using brush-commutation strategy, solving the problem of synchronization control perfectly, have a promising prospect in accelerating big mass to high speed. One of its current technical bottlenecks is the arc erosion caused by the brush commutation, which damages the current-fed rails, besides reduces the energy conversion efficiency of HEMLs. During the commutation process, the leading, trailing edges of the commutating brush act as the closing, opening switches, respectively. When the brush-controlled circuit turns ON and OFF, the commutation-induced voltage (CIV) is a key to research the arc erosion of brushes. It can be concluded that the CIV is proportional to the current, the commutation inductance gradient (CIG), and the projectile velocity by a theoretical analysis and numerical simulation. The CIG is a critical structural parameter of HEMLs, and the formulas of the CIG for single and multiple turn commutation are deduced. Compared with single turn commutation, the current in the commutating turns changes moderately, and the CIV is lower in the case of multiple turn commutation. Two armatures of 35 turns and 135 turns were tested in an HEML of coil-unit barrel; the experimental results are in good agreement with the theoretical calculations.