AC injection insulation resistance detection circuit and method

Abstract

The invention provides an AC injection insulation resistance detection circuit and method in the technical field of electric vehicles. The detection circuit comprises a single-chip microcomputer U3, an AD conversion chip U4, a voltage holding circuit, a voltage discharge circuit and a voltage turning point extraction circuit. The input end of the voltage holding circuit is connected with the voltage turning point extraction circuit, and the output end of the voltage holding circuit is connected with the AD conversion chip U4; the input end of the single-chip microcomputer U3 is connected with the AD conversion chip U4, and the output end of the single-chip microcomputer U3 is connected with the voltage turning point extraction circuit and the voltage discharge circuit; and the voltage discharge circuit is connected with the voltage holding circuit. The circuit has the advantage that the precision and the speed of insulation resistance detection are greatly improved.

Description

technical field [0001] The invention relates to the technical field of electric vehicles, in particular to an AC injection insulation resistance detection circuit and method. Background technique [0002] With the popularization of electric vehicles, the number of reports on spontaneous combustion incidents of electric vehicles is also increasing, and people begin to pay attention to the safety of electric vehicles, and the insulation of electric vehicle batteries is the most important indicator. For the insulation detection of batteries, there are traditionally two methods: the bridge method and the low-frequency injection method. [0003] Method 1: The test circuit of the bridge method is as follows: Figure 8 As shown, close K1 and K2 respectively to get two sets of equations: [0004] [0005] [0006] By combining the above two sets of equations, the insulation resistance R can be obtained P and insulation resistance R n The resistance value; where U 1 Indicat...

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Problems solved by technology

[0007] However, the traditional bridge method has the following disadvantages: 1. It cannot test the insulation resistance R P and insulation resistance R n Short circuit at the same time; 2. The detection circuit of the bridge method is directly connected to both ends of the battery, and the high voltage of the battery itself will affect the accuracy of the detection circuit; 3. The bridge method is equivalent to directly connecting a resistor to the positive and negative poles of the battery to the body ground , artificially reduces the resistance value of the insulation resistance, which affects the detection accuracy

[0009] However, the traditional low-frequency injection method has the following disadvantages: 1. It is difficult to grasp the sampling time of the circuit; 2. Because the charge stored in the capacitor cannot be discharged in a short time, it takes a long time to detect the insulation resistance for a single time; 3. To measure a wide range of insulation resistance, AD chips with a large number of digits are required, and the requirements for layout and circuit anti-interference design are strict, resulting in high costs; 4. There is a deviation in the calculation of the turning point. When the insulation resistance is low, The turning point is not obvious. When the resistance value is high, the voltage difference between the resistance values ​​is very small, resulting in low accuracy of the insulation resistance reading, such as Figure 11 shown

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