Suppressed By The Running Of Three-phase Induction Motor Asymmetry And Negative Sequence

Induction motors ,as a major kind of motors, consume sixty percents of the power in our country every year. In power system, because of the unbalance of three-phase load ,single-phase load and the resistance of the transmission line, there is resulting unbalanced voltage, which have great effects on the performance of the induction motors. It may lead to unbalanced currents ,torque variation, speed variation, increasing losses and overheating. Without considering the effects of unbalanced voltage on induction motors before designing, it is very important to study the operation of the induction motors under unbalanced voltage supply conditions.According to the equivalent circuit of the three-phase induction motor, the positive sequence voltage encounters much higher impedance than the negative sequence voltage, so there is significantly high negative sequence current in the windings of the stator, which leads to increasing losses, overheating, deterioration of efficiency. In this paper, the model of the three-phase induction motors is established, based on this model ,the effects of the unbalanced voltage on induction motors is well studied. A device is adopted to decrease the negative sequence current in order to minimize the effects of the unbalanced voltage.This paper is consisted of four parts:Firstly, based on the conception of symmetry components method and Cvuf (complex voltage unbalance factor), the operation of the three-phase induction motors under unbalanced voltage is studied, the curves of torque variation ,speed variation ,and starting time are drawn ,some conclusions related to the performance of the induction motors are obtained.Secondly, based on MATLAB/SIMULINK ,the model of three-phase induction motor with negative sequence current decreasing device is established .without considering the mutual inductance between the windings of motor and the windings of the device.Thirdly, based on the principle of the negative sequence current decreasing device, the mathematic model of the three-phase induction motor with negative...