Research on a unistor equivalent circuit of linear induction motor and its parameter estimation.

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By analyzing a 3-phase equivalent ciercuit of linear induction motor (LIM) based on an imaginary element unistor, investigators made the following points clear.(1) Input voltage and current on each terminal of 3-phase LIM are unbalanced under the driving condition. The cause of this phenomenon comes from the end effect of LIM.Therefore LIM should be represented by a 3-phase equivalent circuit with 4 terminals, not by a single phase equivalent circuit.(2) By reason of the effect of LIM,magnetic distribution in the air gap changes with velocity of secondary conductor. The iron loss and other parameters on the equivalent circuit are the functions of velocity. Therefore the determination of circuit parameters should be done under the driving condition.(3) The distribution of power was estimated by the complex power matrix. According to the power matrix, the power is usually unbalanced in each phase of LIM and source.(4) The instantaneous secondary power on the secondary resistance in each phase was estimated. This instantaneous secondary power produces the thrust ripple. As the thrust ripple is dangerous if it resonate with mechanical system of the vertical transportation, the decrease of ripple is the most problem to solve today.(5) Ripple coefficients K_C and K_S were induced and estimated from the equations of instantaneous secondary power. They were verified by the measurement of cylindrical LIM in vertical driving system.