Abstract: Insulation detection modules in the photovoltaic storage charging inspection system need to meet the requirements of small volume, high precision, large range, wide range of operating temperature and working voltage, so the paper proposes an improved imbalance electric bridge circuit and derives its formula, and then designs the insulation resistance detection circuit on this basis. This circuit, taking the GD32 single chip microcomputer as the controlling core, uses a 24-bit ADC chip, a precision reference source and a low-temperature drift resistor as the front-end sampling circuit. Then, it uses the SPI isolator with power supply to realize the signal isolation between high and low voltage, and the MOS optical coupler and high voltage relays to switch imbalance electric bridge. The experimental results show that this scheme can accurately measure the insulation resistance of charging pile DC bus in the photovoltaic storage charging inspection system. The error of insulation resistance measurement is less than or equal to ±1% in the range of -40~+70 ℃, 200~1 000 V and 1 kΩ~30 MΩ. Moreover,the insulation detection module has high integration and small volume, meeting the space requirement of installing split piles in the photovoltaic storage charging inspection system.

    Key words: insulation resistance; charging pile; imbalance electric bridge; photovoltaic storage charging inspection system