Asymmetrical constants and effect of joints in the secondary conductors of a linear induction motor

In this paper, one method of identification of the linear induction motor (LIM) constants is presented. Beside the asymmetrical nature of the LIM's constants (because of finite winding lengths) it was noticed that when a joint in the secondary conductor moves inside the active area of the LIM it creates variation and fluctuation of the secondary resistance of the LIM. The variation and fluctuation of the secondary resistance affects the thrust of the LIM which also fluctuates. These fluctuations of the thrust are not acceptable in some applications such as linear motor elevators in which the riding comfort is very demanding. A hardware solution to diminish the fluctuations of the thrust is proposed. It consists of adding a secondary joint at half pole pitch distance from the primary joint. This second joint creates another fluctuation that opposes the fluctuation caused by the primary joint. Thus, the secondary joint cancels the fluctuation effect caused by the primary joint. Several experiments were performed to confirm this solution.