To ensure electrical safety and reliability in electric vehicles equipped with a high-voltage battery pack, an insulation monitoring circuit is indispensable to continuously monitor the insulation resistance during charging or driving. Existing methods such as injecting specific signals into the monitoring circuit and earth help to extract the resistance value from the voltage waveform. However, parasitic or stray capacitances in the monitoring circuit, which might introduce higher order dynamics into the waveform, are ignored. To avoid estimation error, the insulation resistance must be known in advance to carry out parameter calibration. In this chapter, one parasitic capacitance is applied in the circuit model and a new adaptive algorithm based on Lyapunov stability is employed to estimate the insulation resistance. This new online monitoring method and circuit are verified through simulation and experimentation, respectively. The results demonstrate that the proposed method can quickly react and track variations of insulation resistance on both positive and negative direct current (DC) lines.
Part of the book: New Trends in Electrical Vehicle Powertrains