Analysis of the insulation detection principle of DC charging pile

With the rapid development of the new energy vehicle industry, there are more and more electric vehicles on the road, and people’s demand for charging is also growing. In particular, customers with charging needs, represented by operating vehicles, require a faster charging experience. However, city space is limited and DC charging stations cannot be built on a large scale. Therefore, faster high-voltage liquid-cooled charging equipment has become a development direction of the charging pile market. However, along with increasingly higher charging voltages comes increasing concern about the insulation of charging equipment and cables. Cable insulation detection technology has therefore become an essential function of charging equipment.

The following will briefly introduce a cable insulation detection solution for DC piles:

Cable insulation testing for DC piles

In the figure, EV+ is the positive pole of the power module output, EV- is the negative pole of the power module output, R+ is the insulation resistance of the positive pole to the ground, R- is the insulation resistance of the negative pole to the ground, R1 and R2 are the bridge arm resistors, and Rs is the sampling resistor. The R1/R2 resistor’s value determines the insulation resistance’s sampling range, so it is generally in the MΩ level; Rs is within 10kΩ.

The three switches S1, S2, and S3 have their uses. In the non-insulation detection state, all three switches are disconnected. Different switch states will have different circuit topologies:

1. S1 closes, S2 opens, and S3 closes to get the following formula:

S1 closes, S2 opens, and S3 closes to get the following formula

2. S1 opens, S2 opens, and S3 closes, and the following formula is obtained:

S1 opens, S2 opens, and S3 closes, and the following formula is obtained

3. S1 closes, S2 closes, S3 closes:

S1 closes, S2 closes, S3 closes

According to the above formula, the values of insulation resistance R+ and R- can be calculated.

The above is the formula calculation method for the insulation detection principle of the DC charging pile. I hope it will be helpful to everyone.

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