Insulation Monitoring Method for DC Systems with Ground Capacitance in Electric Vehicles

Owing to the influence of ground capacitance in electric vehicles, in the traditional unbalanced electric bridge DC insulation monitoring (DC-IM) method, the voltage of positive and negative electric bridges changes slowly. To calculate the insulation resistances, sampling should be conducted once the voltage of the bridge becomes stable, that will inevitably extend the monitoring cycle. To reduce the monitoring cycle, this study proposes a three-point climbing algorithm, namely, three-bridge voltage sampling with equal sampling intervals, to predict the evolution of the bridge voltage curve. However, due to the existence of sampling errors, the insulation resistances calculated by sampling values will deviate from the actual values. Then, this article also proposes the filter and correction methods of three sampled voltages to improve monitoring accuracy. Through experimental data, the influences of different parameters on the results are verified, and comparisons with the traditional method are shown in the back. The conclusion is that compared with the traditional method, the proposed method can monitor insulation resistance more quickly and ensure fixed monitoring cycles under different ground capacitance values and keep the similar monitoring accuracy.