CN-122017634-A - Alternating current signal extraction circuit and impedance on-line detection method

CN122017634ACN 122017634 ACN122017634 ACN 122017634ACN-122017634-A

Abstract

The application belongs to the field of impedance detection of energy storage systems, and particularly discloses an alternating current signal extraction circuit and an impedance online detection method. The application adopts a Wheatstone bridge with at least one bridge arm as an impedance unit and the rest as a resistance unit and asymmetric branches. Under the direct current condition, the impedance unit presents a fixed resistance, so that the bridge meets the balance proportion, thereby counteracting direct current bias and inhibiting noise. Under the alternating current condition, the impedance value is reduced along with the increase of frequency, the balance of the bridge is broken, and differential voltage proportional to alternating current components is generated between output nodes due to the asymmetry of the branch structures, so that an alternating current signal is accurately extracted. Compared with the prior art, the circuit effectively extracts the alternating current signal while inhibiting the direct current noise, remarkably improves the signal to noise ratio and solves the problem that the alternating current signal in the direct current system is difficult to extract accurately.

Inventors

CAI TAO
SU GEN
WANG ZHANQIANG
LIU ZHENGCHEN
JIANG DONG

Assignees

华中科技大学

Dates

Publication Date: 20260512
Application Date: 20260122

Claims (10)

1. The alternating current signal extraction circuit is characterized by comprising a first bridge arm unit, a second bridge arm unit, a third bridge arm unit and a fourth bridge arm unit, wherein the first bridge arm unit and the second bridge arm unit are connected in series to form a first branch, the third bridge arm unit and the fourth bridge arm unit are connected in series to form a second branch, the first branch and the second branch are connected in parallel between a first input node and a second input node, and respective series nodes of the first branch and the second branch are respectively defined as a first output node and a second output node so as to form a first Wheatstone bridge; In the four bridge arm units, at least one bridge arm unit is an impedance unit, the rest bridge arm units are resistance units, and the first branch and the second branch are asymmetric in structure; The impedance value of the resistance unit is a fixed resistance value which does not change with frequency; the impedance unit is configured to present a fixed resistance value under a direct current condition so as to allow a direct current component to pass through, and the impedance value under an alternating current condition is reduced along with the increase of the signal frequency, wherein the fixed resistance value of each bridge arm unit under the direct current condition meets the conditions that the ratio of the fixed resistance value of the first bridge arm unit to the fixed resistance value of the second bridge arm unit is equal to the ratio of the fixed resistance value of the third bridge arm unit to the fixed resistance value of the fourth bridge arm unit; The first Wheatstone bridge is used for equalizing the electric potential of the first output node and the electric potential of the second output node under the action of the direct current component when the received input signal contains the direct current component and the alternating current component so as to realize direct current offset cancellation, and entering an unbalanced state under the action of the alternating current component so as to generate a differential voltage signal proportional to the alternating current component between the first output node and the second output node so as to extract the alternating current signal.
2. The ac signal extraction circuit of claim 1, wherein the first leg unit and the fourth leg unit are impedance units, or wherein the second leg unit and the third leg unit are impedance units.
3. The alternating current signal extraction circuit according to claim 1 or 2, wherein the impedance unit includes a first resistive element and a capacitive element; The first end of the resistive element is respectively connected with the first end of the capacitive element and the input node, and the second end of the resistive element is respectively connected with the second end of the capacitive element and the output node of the branch; The first resistive element is a series, parallel or series-parallel combination of one or more resistors, and the capacitive element is a capacitor, or a series, parallel or series-parallel combination structure of a plurality of capacitors.
4. The AC signal extraction circuit as claimed in claim 1, wherein said resistive element includes a second resistive element; The first end of the second resistive element is connected with an input node, and the second end of the second resistive element is connected with an output node of the branch; The second resistive element is a resistor, or a series, parallel or series-parallel combination of resistors.
5. The AC signal extraction circuit as claimed in claim 1, wherein the AC signal extraction circuit further comprises an amplitude conditioning unit, an input resistor, and a first isolation operational amplification unit; the two input ends of the first Wheatstone bridge are connected in parallel with the energy storage unit to be detected, and the two output ends of the first Wheatstone bridge are respectively connected with the two input ends of the amplitude conditioning unit; The amplitude conditioning unit is configured to directly output to the first isolation operational amplification unit when the amplitude of the alternating current signal is smaller than a preset value, and to limit amplitude of the alternating current signal and then output to the first isolation operational amplification unit when the amplitude of the alternating current signal is larger than or equal to the preset value; The first isolation operational amplification unit is configured to isolate and differentially amplify an input alternating current component in a voltage range and output a first alternating current voltage signal proportional to the alternating current component.
6. The AC signal extraction circuit as claimed in claim 5, further comprising a first sampling unit, a second Wheatstone bridge, and a second isolated operational amplification unit; the second Wheatstone bridge is consistent with the first Wheatstone bridge in structure; The first sampling unit is connected in series with the energy storage unit to be tested, and two input ends of the second isolation operation amplifying unit are connected in parallel with the first sampling unit; The second isolation operation amplifying unit is configured to carry out isolation amplification on the voltage signals at two ends of the first sampling unit and output the amplified voltage signals to the second Wheatstone bridge; the second Wheatstone bridge is configured to extract a second alternating voltage signal proportional to the alternating current component flowing through the energy storage unit to be measured from the voltage signal output by the second isolation operation amplifying unit.
7. The AC signal extraction circuit as claimed in claim 6, wherein the AC signal extraction circuit further comprises a differential amplification unit, and an ADC and filter unit; the first input end to the fourth input end of the differential amplification unit are respectively connected with the two output ends of the first isolation operation amplification unit and the two output ends of the second Wheatstone bridge; the differential amplifying unit is configured to calculate and output an analog voltage signal proportional to the alternating current impedance of the energy storage unit to be measured based on the first alternating current voltage signal and the second alternating current voltage signal; the ADC and filtering unit is configured to perform analog-to-digital conversion and digital filtering on the analog voltage signal output by the differential amplifying unit to obtain a digital signal representing the alternating current impedance.
8. The alternating current signal extraction circuit according to claim 1, wherein the alternating current signal extraction circuit further comprises a second sampling unit and a third isolation operational amplification unit; The second sampling unit is connected in series with the energy storage unit to be tested, and two input ends of the third isolation operation amplifying unit are connected in parallel with the first sampling unit; the second sampling unit is configured to convert a current signal flowing through the energy storage unit to be measured into a voltage signal proportional to the current signal; The third isolation operation amplifying unit is configured to perform isolation amplification on the voltage signals at two ends of the second sampling unit, and output the amplified voltage signals to the first Wheatstone bridge.
9. An impedance on-line detection method, comprising: applying excitation to the energy storage unit to be tested, so that a terminal voltage signal of the energy storage unit to be tested contains a direct current component and an alternating current component of expected frequency; acquiring terminal voltage signals of the energy storage unit to be detected, and obtaining a first differential voltage signal reflecting the alternating current component after DC offset cancellation through a first Wheatstone bridge; collecting a current signal flowing through the energy storage unit to be detected, and converting the current signal into a first voltage signal; Isolating and amplifying the first voltage signal, and passing the amplified signal through a second Wheatstone bridge to extract a second differential voltage signal reflecting the alternating current component, wherein the structure of the second Wheatstone bridge is consistent with that of the first Wheatstone bridge; And calculating based on the first differential voltage signal and the second differential voltage signal to obtain an analog voltage signal proportional to the alternating current impedance of the energy storage unit to be detected under the expected frequency, and performing analog-to-digital conversion and digital filtering processing on the analog voltage signal to obtain a digital signal representing the alternating current impedance of the energy storage unit to be detected.
10. The method for online impedance detection according to claim 9, wherein collecting the terminal voltage signal of the energy storage unit to be detected and obtaining a first differential voltage signal reflecting the ac component after dc offset cancellation by a first wheatstone bridge comprises: collecting terminal voltage signals of the energy storage unit to be detected, and enabling the terminal voltage signals to pass through a first Wheatstone bridge to obtain alternating current signals which reflect the alternating current components after direct current offset is counteracted; When the amplitude of the alternating current signal is smaller than a preset value, the alternating current signal is considered as the first differential voltage signal and is output; when the amplitude of the alternating current signal is larger than or equal to the preset value, limiting the alternating current signal, and recognizing and outputting the alternating current signal as a first differential voltage signal after limiting.

Description

Alternating current signal extraction circuit and impedance on-line detection method Technical Field The application belongs to the field of impedance detection of energy storage systems, and particularly relates to an alternating current signal extraction circuit and an impedance online detection method. Background With the rapid development of electrochemical energy storage technology, battery energy storage systems have been widely used in the fields of grid frequency modulation, renewable energy grid connection, peak clipping and valley filling, standby power supply and the like. Large energy storage systems typically consist of a layered architecture of cells, modules, and high voltage battery clusters, with terminal voltages on the order of magnitude different from 3.2V, tens of volts to kilovolts. During long-term operation, the internal impedance of the battery changes with cycling, aging, temperature changes and abuse conditions, and impedance parameters become important quantitative indicators for judging the state of health (SOH), consistency, life and safety risk of the battery. Therefore, the on-line detection of the impedance is realized in the whole hierarchy of the energy storage system, and the method has important engineering significance for improving the running safety of the battery and maintaining the stability of the energy storage station. Currently, the dominant method for electrochemical impedance online detection is to apply a small amplitude ac current (or voltage) excitation signal to the battery and measure its ac voltage (or current) response at the port. To ensure that the system is in an approximately linear range, the amplitude of the response voltage generated by the ac injection signal generally must not exceed 1% or even less of the dc voltage of the battery. However, in practical engineering applications, the dc bias of the ports between different levels of the energy storage system is very different, i.e., the cell ports are typically about 3.2V, the module can reach 24 to 80V, and the voltage at the battery cluster end can reach 800 to 1500V. In this context, the ac response signal, superimposed with a substantial dc bias, has a very low signal-to-noise ratio, resulting in difficult accurate extraction. In addition, the bandwidth characteristics of the voltage divider chains, long-distance cables, and isolation amplifiers of the high-voltage cluster stage also introduce frequency dependent attenuation, so that the low-frequency alternating current quantity is weakened. Disclosure of Invention Aiming at the defects of the prior art, the application aims to provide an alternating current signal extraction circuit and an impedance on-line detection method, and aims to solve the problems that the extraction of alternating current components in the existing direct current system is limited by extremely low signal to noise ratio and is difficult to extract accurately. In order to achieve the above object, in a first aspect, the present application provides an ac signal extraction circuit, including a first bridge arm unit, a second bridge arm unit, a third bridge arm unit, and a fourth bridge arm unit; the first bridge arm unit and the second bridge arm unit are connected in series to form a first branch, the third bridge arm unit and the fourth bridge arm unit are connected in series to form a second branch, the first branch and the second branch are connected in parallel between a first input node and a second input node, and the respective series nodes of the first branch and the second branch are respectively defined as a first output node and a second output node so as to form a first Wheatstone bridge; among the four bridge arm units, at least one bridge arm unit is an impedance unit, the rest bridge arm units are resistance units, the first branch and the second branch are asymmetric in structure, the impedance value of the resistance unit is a fixed resistance value which does not change with frequency, the impedance unit is configured to present a fixed resistance value under a direct current condition so as to allow a direct current component to pass through and reduce the impedance value under an alternating current condition along with the increase of the frequency of a signal, the fixed resistance value of each bridge arm unit under the direct current condition meets the conditions that the ratio of the fixed resistance value of the first bridge arm unit to the fixed resistance value of the second bridge arm unit is equal to the ratio of the fixed resistance value of the third bridge arm unit to the fixed resistance value of the fourth bridge arm unit, the first Wheatstone bridge is used for enabling the electric potential of the first output node to be equal to the electric potential of the second output node under the effect of the direct current component to realize direct current bias cancellation under the effect of the unbalanced direct current component,