Equivalent parameter estimation of a single-sided linear induction motor based on electromagnetic field induced by current FFT-wave

For the ideal no-load condition of a single-sided linear induction motor (SLIM), with no current in the secondary, it is difficult to obtain accurate characteristics due to the larger air gap and eddy currents in the secondary. In addition, traction LIMs are always mounted in the trains, so there is no ideal no-load operation condition for them. Thus, the traditional no-load test for a rotating induction motor is unsuitable for a SLIM. In order to solve this problem, this paper proposes a method of no-load test with an equivalent secondary: a soft-ferrite back plate substitutes for back iron to meet the requirement of no eddy current in the secondary while the magnetizing inductance (Lm) keeps constant, which results in the name `equivalent parameter estimation´. Taking the end effect and the slot effect into account, we assume a travelling wave current layer which is described by FFT decomposition and consequently named as `current FFT-wave´, instead of previous excitation modeling methods considering only the fundamental wave. Then a two-dimensional model of the electromagnetic field induced by the n-order harmonic component is established so as to derive the effect of the relative permeability of the soft-ferrite back plate on the magnetizing inductance. Keeping Lm constant, the equivalent secondary is designed in consideration of each order of harmonic component, and verified via finite element analysis. Moreover, the equation of Lm has been simplified to some extent to a form which fits the control strategy of a SLIM.