Experimental Studies of Nonlinear Dynamics of Asynchronous Electric Drives with Variable Load

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This article presents the results of the analysis of experimental data that were obtained during industrial tests of an adjustable asynchronous traction electric drive of a shuttle car for the mining industry. During these tests, by changing the parameters of the stator voltage, the stator currents of the induction motor were optimized when the load changes over a wide range (from −1.5 Tn to + 1.5 Tn). The authors managed to significantly reduce the effective values of the stator currents of the motor, but at the same time it was found that, with the load and even the rate of its change, oscillations of the effective values of currents with variable amplitude and frequency occur. It turned out to be very difficult to explain these oscillations and the variability of their parameters using traditional mathematical methods for describing processes in asynchronous electric motors. Vector equations and diagrams are valid only at constant frequencies of the stator voltage and, in the modes of their significant changes, which exist during self-oscillations of the effective values of the motor stator current, their error is very large. To analyze the conditions of the self-oscillations, it was proposed to use nonlinear continuous transfer functions that describe the formation of torque in induction motors. The article shows how such transfer functions make it possible to take into account the influence of the load torque and the speed of its change on the parameters of the self-oscillations of the effective values of the stator current of asynchronous electric drives experiencing such loads. The article proposes a qualitative analysis of the results of experiments carried out on real tracks of the movement of the shuttle car. The analysis of experimental data confirmed the effectiveness of using nonlinear transfer functions to evaluate the dynamics of asynchronous electric drives and the sufficient accuracy of the proposed method. In the course of research, it is shown how the conditions of the boundary stability of the drive depend on external loads that change the nonlinear transfer function of the induction motor. As a result, it was found that the condition of boundary stability and the parameters of the self-oscillations are affected not only by the magnitude, but also by the rate of load change. The article made assumptions about possible options for the effective correction of asynchronous electric drives experiencing variable loads.