CN114859255A - A kind of BMS lithium battery SOH detection method - Google Patents

Abstract

The invention discloses a lithium battery SOH detection method of a BMS, which comprises the steps of utilizing the frequency domain response characteristic of an alternating small signal of a lithium battery, applying specific frequency excitation through scanning, respectively detecting the voltage response and the current response of the alternating small signal of the lithium battery under specific frequency, and then carrying out superposition calculation with the excitation signal to obtain the impedance data of the alternating small signal of the battery under the specific frequency, and even further calculating an impedance angle, a quality factor, a loss factor and the like. By analyzing the impedance data under a plurality of groups of frequencies, the impedance Nyquist diagram of the alternating current small signal of the battery in a section of frequency can be fitted. And comparing the impedance diagram of the battery when the battery leaves the factory with the impedance diagram after multiple charging and discharging, and obtaining the aging condition of the battery, namely the SOH. The beneficial effects of the invention are: the frequency domain response characteristic of the alternating current small signal impedance of the battery is utilized to scan the alternating current small signal impedance of the battery within a certain frequency range to obtain a nyquist diagram of the battery, and the nQuistle diagram is compared with data of the battery when the battery leaves a factory, so that the SOH of the battery can be calculated.

Description

A kind of BMS lithium battery SOH detection method

technical field

The invention relates to a lithium battery detection method, in particular to a BMS lithium battery SOH detection method, and belongs to the technical field of the new energy lithium battery energy storage industry.

Background technique

With the country's policy inclination towards the new energy industry, lithium batteries and BMS systems are widely used in many fields. Among them, lithium battery SOH is an important indicator to reflect the health of the battery. Timely measurement of the battery SOH status can detect aging batteries in time and avoid possible risks.

Usually, the SOH of the lithium battery in the energy storage system is 100% when it leaves the factory, and then gradually decreases as the battery ages. However, in the case of the same city, the BMS system estimates the loss of battery capacity based on the loss of battery capacity, which cannot be judged by direct measurement. The SOH data in the usual BMS system is not accurate. Some BMS devices can estimate the SOH of lithium batteries by calculating the battery capacity based on the collected voltage and current data, but the estimated value may have large errors, and complex calculations accurate to a single battery require higher computing power for BMS devices.

Usually, the measurement method of lithium battery SOH is to charge the battery slowly and then fully discharge it, and estimate the battery SOH by measuring the battery capacity and comparing it with the rated capacity of the battery. However, this total measurement method only indirectly calculates the SOH of the lithium battery through the external performance of the battery, rather than direct measurement, and the estimation accuracy is low to evaluate the aging degree of the battery.

In the factory test of lithium battery, the manufacturer will provide the AC small signal impedance curve of the battery at different frequencies. When the battery ages, its electrochemical characteristics will be clearly reflected in the AC small signal impedance curve, so it can be calculated by the curve. Change, accurate to judge the health of the battery.

The increase in internal resistance is the main manifestation of battery aging. An aging battery is more likely to generate heat, has a smaller capacity, and is often easier to fill or discharge. It is also easier to heat up than other batteries. However, the internal resistance of lithium batteries is divided into ohmic internal resistance and polarization internal resistance, and their AC small signal impedances at different frequencies are different. At the same time, with the aging of the battery, the curvature of each part of the curve will change with the change of the chemical properties of the battery, which can effectively help the judgment of the battery SOH.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a BMS lithium battery SOH detection method in order to solve at least one of the above technical problems.

The present invention achieves the above object through the following technical solutions: a BMS lithium battery SOH detection method, comprising the following steps

Step 1. Using the frequency domain response characteristics of the lithium battery's AC small signal, and applying a specific frequency excitation by scanning, respectively detect the AC small signal voltage response and current response of the lithium battery at a specific frequency;

Step 2: Perform superposition calculation with the excitation signal to obtain the AC small signal impedance data of the lithium battery at this frequency;

Step 3: By analyzing the impedance data at multiple frequencies, the Nyquist diagram of the AC small signal impedance of the battery within a frequency can be fitted;

Step 4. Compare the impedance diagram of the battery when it leaves the factory with the impedance diagram after multiple charging and discharging, and then the aging of the battery can be obtained, that is, SOH;

Among them, the circuit for detecting the SOH of the lithium battery includes:

A battery pack, which is composed of several batteries in series, and the battery pack is electrically connected with an active balancing circuit for storing battery balancing energy, a sinusoidal excitation circuit for sending different sinusoidal AC signals, and a voltage detection for voltage detection. A circuit, a current detection circuit for current detection, the active equalization circuit and the sinusoidal excitation circuit are both controlled by a single chip, and the detection signals of the voltage detection circuit and the current detection circuit are transmitted to the single chip.

As a further solution of the present invention: the entire SOH detection circuit of the lithium battery is integrated in the sampling slave board of the BMS system.

As a further solution of the present invention: in the second step, when the resistance detection of the lithium battery is performed, the internal resistance of the lithium battery is detected after the charging and discharging is completed.

As a further solution of the present invention, an active balanced switch matrix is connected to the connection circuit of the battery pack.

As a further solution of the present invention, both the positive and negative electrodes of the battery pack are connected with DC-blocking coupling capacitors.

As a further solution of the present invention: when the SOH detection circuit of the lithium battery is initially detected, the circuit resistance is first determined.

The beneficial effects of the present invention are:

1. The entire SOH detection system is integrated in the sampling slave board of the BMS system, which can regularly detect the SOH status of the battery. And different from indirect estimation through data, the on-board circuit detects the actual value of the impedance within a certain frequency of the battery, and the error is extremely small;

2. Since the battery impedance will change slightly with the change of the charge and discharge capacity of the battery, the internal resistance of the battery is detected after the charge and discharge is completed, which can assist in the calibration of the battery soc condition. At the same time, batteries with larger impedance deviations from the average value can be found in time, early warning and timely replacement;

3. The method of using AC small signal to detect the battery impedance to determine the battery SOH is small in size, low in cost and easy to implement. At the same time, it is easy to transform with the active equalization circuit;

4. Since the detection circuit borrows the active equalization circuit, it needs to pass through several relays, and the detection circuit is long, so in order to accurately detect the battery impedance, it is necessary to estimate the line resistance at the beginning to eliminate interference.

Description of drawings

1 is a schematic diagram of the SOH detection circuit principle of the present invention;

Fig. 2 is the schematic diagram of the SOH detection function principle of the present invention;

Fig. 3 is the Nyquist diagram of the AC small signal impedance of the battery of the present invention;

FIG. 4 is a Nyquist diagram of the AC small-signal impedance of the battery aging according to the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

As shown in Figure 1, a BMS lithium battery SOH detection method, BAT1 ~ BAT4 are lithium batteries, here means that all batteries in the battery pack are connected in series, in practice, more than a dozen batteries are often connected in series, and K1 ~ K8 are switches The matrix, respectively, is the positive switch (connected to the positive electrode of the battery) and the negative switch (connected to the negative electrode of the battery); K9 and K10 are active equalization switches, which are used to connect the active equalization to the circuit. L1 is the active balancing energy storage inductor. When K9 and K10 are closed, it is used to store battery balancing energy. The principle of active balancing is not explained here; K11 and K12 are impedance detection switches; when the battery impedance needs to be detected, disconnect K9 and K10 Close K11, K12; C1, C2 are DC blocking coupling capacitors, connected to the positive electrode of the battery, the other end of C1 is connected to the sinusoidal AC excitation circuit, and the other end of C2 is connected to the voltage detection circuit. The sinusoidal AC excitation circuit is composed of a U1 voltage follower, R4~R7, C5~C7 to form a band-pass filter, and U2 is a sinusoidal signal generator, which is configured here to generate 48 sets of AC signals from 0.1Hz to 10kHz. U2 communicates with U13 , U13 is a single-chip microcomputer, which controls U2 to generate sinusoidal signals of different frequencies; the voltage detection circuit consists of three integrated operational amplifiers U3, U4, and U5, which are responsible for amplifying the AC small signal voltage response at both ends of the battery and transmitting it to the subsequent phase detector. ; K12 is the battery negative switch, connecting the excitation source virtual ground and the current detection circuit. U6 is an operational amplifier, which constitutes a virtual ground due to the high impedance of its virtual-off characteristic; U7, U8, and U9 three integrated operational amplifiers constitute a current detection circuit, R20 is a current detection resistor, and R20 converts the current signal into the voltage drop on both sides , amplified by U7, U8, U9, and transmitted to the subsequent phase detector. SW1 is an analog switch, which is controlled by the microcontroller U13 and used to select voltage detection and current detection. After the analog switch, connect a band-pass filter to filter out high-order harmonics; then connect a half-wave phase detector, which multiplies the excitation signal with the voltage or current signal, and detects its amplitude and phase signal. , transmitted into the microcontroller, and the battery impedance is calculated by the microcontroller.

Embodiment 2

As shown in Figure 1 to Figure 4, a BMS lithium battery SOH detection method includes the following steps

Step 1. Using the frequency domain response characteristics of the lithium battery's AC small signal, and applying a specific frequency excitation by scanning, respectively detect the AC small signal voltage response and current response of the lithium battery at a specific frequency;

Step 2: Perform superposition calculation with the excitation signal to obtain the AC small signal impedance data of the lithium battery at this frequency;

Step 3: By analyzing the impedance data at multiple frequencies, the Nyquist diagram of the AC small signal impedance of the battery within a frequency can be fitted;

Step 4. Compare the impedance diagram of the battery when it leaves the factory with the impedance diagram after multiple charging and discharging, and then the aging of the battery can be obtained, that is, SOH;

Among them, the circuit for detecting the SOH of the lithium battery includes:

A battery pack, which is composed of several batteries in series, and the battery pack is electrically connected with an active balancing circuit for storing battery balancing energy, a sinusoidal excitation circuit for sending different sinusoidal AC signals, and a voltage detection for voltage detection. A circuit, a current detection circuit for current detection, the active equalization circuit and the sinusoidal excitation circuit are both controlled by a single chip, and the detection signals of the voltage detection circuit and the current detection circuit are transmitted to the single chip.

In the embodiment of the present invention, the entire SOH detection circuit of the lithium battery is integrated in the sampling slave board of the BMS system, which can regularly detect the SOH state of the battery, and is different from indirect estimation through data, the on-board circuit detects the battery within a certain frequency. The actual value of the impedance, the error is very small.

In the embodiment of the present invention, in the second step, when the impedance detection of the lithium battery is performed, the internal resistance of the lithium battery is detected after charging and discharging. At the same time, it can also timely find the battery whose impedance deviates from the average value in time, give early warning and replace it in time.

In the embodiment of the present invention, an active balanced switch matrix is connected to the connection circuit of the battery pack, and any battery can be connected to the internal resistance detection circuit.

In the embodiment of the present invention, the positive and negative electrodes of the battery pack are connected with DC blocking coupling capacitors to ensure that the DC signal of the battery does not affect the circuit.

In the embodiment of the present invention, the SOH detection circuit of the lithium battery first determines the line resistance during the initial detection. Since the detection circuit borrows the active equalization circuit, it needs to pass through several relays, and the detection circuit is long, so in order to accurately detect the battery Impedance, the line resistance needs to be estimated initially to eliminate interference.

Among them, Figure 3 is the Nyquist diagram of the AC small signal impedance of the battery, and the vertical axis is the imaginary part. It can be seen from the figure that the impedance curves of the battery at different frequencies, where the position where the curve intersects the horizontal axis is the battery ohmic internal resistance, The curve to the right of the intersection superimposes the polarization internal resistances generated by the various stages of the electrochemical reaction. After multiple charging and discharging, the internal ohmic resistance and polarization internal resistance of the battery will change with the aging of the battery;

Figure 4 is a Nyquist diagram of the AC small-signal impedance of the battery aging. One of the curves is the batteries with different aging degrees. Obviously, the battery SOH can be calculated according to the different characteristics of the curves.

Working principle: Using the active balanced switch matrix, any battery can be connected to the internal resistance detection circuit; because the positive and negative electrodes of the battery have DC blocking coupling capacitors, the DC signal of the battery does not affect the circuit; The battery applies 48 sinusoidal AC signals from 0.1Hz to 10kHZ; each signal is selected to detect the voltage signal or the current signal by controlling the analog switch, and the signal obtained at this time is the AC voltage response and AC current response of the battery; in order to obtain the AC The amplitude and phase information of the signal requires a phase detector to process the signal; the phase detector first multiplies the reference signal of the corresponding frequency with the voltage and current responses to obtain 4 signals with double angular frequency, 1 angular frequency, and phase information. Equation; use a low-pass filter to filter out the double-frequency component, and then the DC components of the voltage and current can be obtained; at this time, the battery impedance can be obtained by dividing the voltage amplitude by the current amplitude; each battery scans Its impedance Nyquiset diagram can be obtained from the AC small signal response of 0.1Hz to 10kHZ; by comparing the impedance diagram detected in real time with the impedance diagram of the battery when it leaves the factory, the battery SOH can be calculated.

It will be apparent to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, but that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments are to be regarded in all respects as illustrative and not restrictive, and the scope of the invention is to be defined by the appended claims rather than the foregoing description, which are therefore intended to fall within the scope of the claims. All changes within the meaning and scope of the equivalents of , are included in the present invention. Any reference signs in the claims shall not be construed as limiting the involved claim.

In addition, it should be understood that although this specification is described in terms of embodiments, not each embodiment only includes an independent technical solution, and this description in the specification is only for the sake of clarity, and those skilled in the art should take the specification as a whole , the technical solutions in each embodiment can also be appropriately combined to form other implementations that can be understood by those skilled in the art.

Claims (6)

1. a lithium battery SOH detection method of BMS, is characterized in that: comprise the following steps Step 1. Using the frequency domain response characteristics of the lithium battery's AC small signal, and applying a specific frequency excitation by scanning, respectively detect the AC small signal voltage response and current response of the lithium battery at a specific frequency; Step 2: Perform superposition calculation with the excitation signal to obtain the AC small signal impedance data of the lithium battery at this frequency; Step 3: By analyzing the impedance data at multiple frequencies, the Nyquist diagram of the AC small signal impedance of the battery within a frequency can be fitted; Step 4. Compare the impedance diagram of the battery when it leaves the factory with the impedance diagram after multiple charging and discharging, and then the aging of the battery can be obtained, that is, SOH; Among them, the circuit for detecting the SOH of the lithium battery includes: A battery pack, which is composed of several batteries in series, and the battery pack is electrically connected with an active balancing circuit for storing battery balancing energy, a sinusoidal excitation circuit for sending different sinusoidal AC signals, and a voltage detection for voltage detection. A circuit, a current detection circuit for current detection, the active equalization circuit and the sinusoidal excitation circuit are both controlled by a single chip, and the detection signals of the voltage detection circuit and the current detection circuit are transmitted to the single chip. 2 . The lithium battery SOH detection method of a BMS according to claim 1 , wherein the entire SOH detection circuit of the lithium battery is integrated in the BMS system sampling slave board. 3 . 3. The lithium battery SOH detection method of a BMS according to claim 1, characterized in that: in the second step, when the resistance detection is performed on the lithium battery, the internal resistance of the lithium battery is detected after charging and discharging. 4 . The SOH detection method of a BMS lithium battery according to claim 1 , wherein an active equalization switch matrix is connected to the connection circuit of the battery pack. 5 . 5 . The SOH detection method of a BMS lithium battery according to claim 1 , wherein the positive and negative electrodes of the battery pack are connected with DC-blocking coupling capacitors. 6 . 6 . The SOH detection method of a BMS lithium battery according to claim 1 , wherein the SOH detection circuit of the lithium battery firstly determines the line resistance during initial detection. 7 .

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