The Finite Element Analysis Of Sinusoidal Time-Varying Field And The Optimum Design For Variable Frequency Motor

Variable frequency and variable speed motor system is of high reliability, fault-tolerant capability and high intelligence. With country economy increasing, electric and electronic technology advancing rapidly, variable frequency motor begins to apply in such industry as machine tool, metallurgy, electric power, pulling, chemical industry, textile industry, water supply, paper making, building material, agriculture, and so on, and it is much evidently energy-saving.In this paper, firstly the mathematic model for variable frequency motor is developed, and harmonic wave is analyzed when variable frequency motor is fed by inversion. Secondly, the solved region, boundary condition and hypothesis condition of the electromagnetic field in electric machine are given. In virtue of variation theory, boundary problem of magnetic field that is to be solved is changed into equivalent variable problem. The procedure of element analysis, discrete format and collective composition equation are given. In the process of numerical calculation of electromagnetic field, stator ending voltage is taken as constraint condition and stator current under load is iterated, then stable-state current of variable frequency motor at normal frequency is obtained. Thirdly, stable-state performance of motor is calculated, by comparing with testing results, we find that the calculation results of stable-state performance for variable frequency motor meet the demand with project practice, and it proves reliable to use FEM to analyze sinusoidal electromagnetic field of motor. At the same time, the effect of different air gap length on motor performances is analyzed, the whole performances of motor get to improve, the conclusion that is accord with project practice is drawn, and slot leakage inductance of seven rotor slots at different air gap length is calculated, simultaneously results calculated show respective slot leakage inductance is different. Finally, rotor slot of variable frequency motor is optimum, stable-state performances and slot leakage inductance of respective rotor slot at different air gap length are calculated after motor is optimum. And the variation tendency of stable-state performances and slot leakage inductance is consistent with that before optimum.