I. Introduction
The use of electromagnetic energy to launch various loads to high speed has inspired the interest of many researchers. There are two kinds of launchers, which are the asynchronous induction coil launcher (AICL) and the synchronous induction coil launcher (SICL). The obvious difficulties between these two launchers are the following: The switching of the SICL must be operated accurately to get synchronism, and power control is very complex for the long stroke. However, the AICL does not suffer from these disadvantages, and it may have the advantages of high efficiency, high thrust density, compact structure, and reliable operation, so it has a brighter prospect for aircraft takeoff or space material conveyance [1]–[3]. This kind of launcher consists of a sectionalized array of drive coil energized by multiphase currents, as shown in Fig. 1. The core set of AICL is the asynchronous induction linear motor (AILM). As the length of the AILM sections is finite and the phase windings are asymmetric, therefore, the phase currents are unbalanced in spite of the balanced terminal voltage input due to the longitudinal end effect. Nowadays, most researches focus on the short primary AILM without multisegment, and the phase unbalance could be ignored when the poles are six or more [4]. However, this phenomenon is serious to the sectionalized AILM even if its poles are in excess of 20, for there is a different movement mode and magnetic field band between the conventional AILM and the sectionalized AILM, which would lead to different static longitudinal end effect.
Basic structure of the AICL.