Design of Online Detection System for Insulation Resistance of Electric Vehicle Based on Unbalanced Bridge

The insulation resistance between the DC bus and the whole vehicle is an important parameter to ensure the safety of the electric vehicle. In view of the low precision, longer measuring time, and poor reliability of the existing insulation detection methods for electric vehicle. The intrinsic mechanism which affects the measurement precision and reliability of insulation resistance is analyzed firstly, and then an insulation resistance detection circuit of unbalanced bridge based which the optical control relay and high-precision instrument amplifier is designed. Furthermore, an improved four-step insulation resistance online calculation approach is proposed. Finally, based on a light electric truck, measurements of multiple sets of insulation resistance values are performance, and the detection error is analyzed under different state of charge and compared with the traditional bridge method. The measurement results show that the measurement error of the proposed electric vehicle insulation detection system has been kept within 5%. What's more, the proposed electric vehicle insulation detection system has advantages of both on-line detection and high reliability.