Voltage-fed operation of linear induction motors under conditions of supply unbalance

The inherent unbalance in a 3-phase linear induction motor (l.i.m.) operating under a voltage-fed mode is accentuated by end effects at high speeds. The voltage-fed operation is analysed by identifying the slip-dependent inductance coefficients corresponding to the positive- and negative-sequence components, and taking into account the stator resistance and leakage reactances. The approach takes care of the longitudinal end effects and the skin effect in the secondary plate. The model is capable of treating the single-phase and plugging operations as special cases of interest. The theoretical and experimental characteristics of a 4-pole l.i.m. driving a rotating-disc facility under general conditions of supply unbalance are presented. Comparison of the thrust characteristics reveals that while the current-fed operation is superior for normal motor operation, the voltage-fed mode offers higher reliability as a brake.