Method for measuring internal resistance of high-voltage battery pack based on multi-frequency mixed injection

The invention discloses a method for measuring the internal resistance of a high-voltage battery pack based on multi-frequency mixed injection, and the method comprises the following steps: S1, outputting superposed mixed voltage signals, and outputting square wave signals which have the same frequency and phase with a single sine wave before synthesis one by one; generating a mixed current signal through a voltage-current conversion circuit; s2, carrying out high-voltage coupling processing on the mixed excitation signal source, and injecting the mixed excitation signal source into the high-voltage battery pack; and S3, amplifying a weak signal by using an amplifying circuit, extracting a small signal in a noise floor by using a synchronous detector, and controlling two analog switches by using a square wave signal. And after passing through the low-pass filter, the output voltage and the battery pure internal resistance have a direct proportion function relationship. S4, an ADC is used for collecting and ou