Linear induction machine fed on a non-traditional manner to generate force pulses at low speeds

This article introduces a new methodology to generate periodic pulses of force in the linear induction motor, working at low speeds. The proposed method comes of the hypothesis that from the manipulation of a three-phase periodic voltages set, with sinusoidal wave forms, and 120° of electrical phase angle shift to each other, it is possible to generate in the linear motor, determined pulses of force with distinct forms and frequencies. A mathematical modeling is developed, based on the conventional three-phase induction motor with blocked rotor, assuming that for low speeds, the linear induction motor has its behavior similar to the conventional rotary induction motor. The mathematical modeling is used to obtain a set of harmonic voltages, necessary to generate the required pulse of force, and an voltage inverter is utilized to supply the linear motor with these harmonic voltages content. Asymmetry effects, inherent to the linear motor, are compensated with an unbalancing at the voltages amplitudes, which were obtained by the method. The entirely mathematical formulation and the practical experiments, accomplished in a real linear induction motor, are presented in the article.