Analytical Optimization of the Bearing Voltage of Motor Considering the Thickness of Insulating Coating: An Improved Equivalent Circuit Model

Power semiconductors are widely used in ac motors, and this technique improves the performance of the motor but simultaneously leads to the increment of bearing voltage. When the bearing voltage is over the threshold, bearing currents will appear and produce a high temperature in an instant, causing bearings to melt. This article establishes an improved equivalent circuit model of motor for calculating the bearing voltage considering the influence of the insulating coating. First, based on the former work, the calculation formulas of capacitances in the equivalent circuit are modified by reconsidering the internal structure of the motor more carefully. In addition, compared with traditional equivalent circuits, the insulating coating is regarded as a new capacitance and added to the proposed circuit model. The experimental results are basically consistent with simulated values obtained by our model, and simulated values obtained in this article are closer to true values than the results obtained by previous research. Finally, this article concludes the relationship between the thickness of the insulating coating and the bearing voltage, and the multiobjective optimization method is proposed by considering the adhesive property and insulating property of the insulating coating concurrently. The improved nondominated sorting genetic algorithm II (NSGA-II) algorithm is used to determine the optimal thickness of the insulating coating, and the optimized result decreases the bearing voltage to some extent.