Energy-optimal torque control and dimensioning of high dynamic induction moor drives under consideration of transient skin effect

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A high torque dynamic is demanded in modern power converter powered AC drives for a high productivity. The rapid change of torque, however, requires a correspondingly rapid change of the winding currents, which leads to stimulation of transient skin effect in the rotor bars of squirrel-cage motors. The skin effect, in turn, results in the additional rotor winding losses especially during fast load cycles, an increase of temperature in rotor, and therefore, overheating problems. In addition, the transient skin effect affects the control quality of the two most widely used control methods (FOC and DTC). The transient skin effect leads to a dynamic change in the rotor parameters. Any deviation from the real machine parameters leads to an incorrect calculation of the decoupling and to an incorrect estimation of the flux angle. Representative examples of such transient skin effect are the cross cutter drives in paper machines, the shears in rolling mills and the test bench drives in the automotive industry. During the project, it was shown that the additional rotor losses caused by the transient skin effect can be effectively reduced by means of an energy-efficient high-dynamic torque control and by an improved rotor geometry. At the same time, the machine dynamics and the other operating characteristics of the induction motor are not negatively affected. It could still be shown that the control quality is improved on the one hand by the exact modeling of the transient skin effect in the rotor bars and on the other hand by the real-time tracking of the rotor parameters by means of on-line parameter identification methods. In the further work, the theoretically gained knowledge should be tested experimentally. In parallel, the last gap in the theory of this topic should be concluded by the online parameter identification of the rotor time constant and the Pareto Optimum for the two important target variables (transient skin effect losses and moment of inertia).