A lithium battery internal resistance detection circuit integrated in a BMS system

Abstract

The application relates to a lithium battery internal resistance detection circuit integrated in a BMS system, which comprises an active equalization circuit, the active equalization circuit comprises a positive electrode switch and a negative electrode switch, an internal resistance detection switch K11 is connected with the positive end of a direct-current isolation coupling capacitor C1, the negative end of the direct-current isolation coupling capacitor C1 is connected with a sinusoidal alternating current excitation circuit, the sinusoidal alternating current excitation circuit generates an alternating current signal of 1KHz; the internal resistance detection switch K11 is connected with the positive end of a direct-current isolation coupling capacitor C2, the negative end of the direct-current isolation coupling capacitor C2 is connected with a voltage detection circuit; the voltage detection circuit transmits the amplified alternating current small signal voltage response between the two ends of the battery to a half-wave phase detector; the internal resistance detection switch K12 is connected with a virtual ground and a current detection circuit, and the output of the current detection circuit is transmitted to the half-wave phase detector. The lithium battery internal resistance detection circuit adopts the method of detecting the battery internal resistance through an alternating current small signal, is small in size, low in cost, easy to realize, and is easy to transform in cooperation with the active equalization circuit.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium battery internal resistance detection, and particularly relates to a lithium battery internal resistance detection circuit integrated in a BMS system. BACKGROUND

[0002] Lithium batteries and BMS systems are widely applied in many fields. The lithium battery internal resistance as an important index reflecting the aging condition of the battery, timely measurement of the battery internal resistance state can timely find the aged battery and avoid possible risks.

[0003] Generally, the lithium battery internal resistance in an energy storage system is measured and matched by the manufacturer when the lithium battery is shipped, and cannot be measured subsequently, so the BMS system does not have the ability to measure the lithium battery internal resistance. Some BMS devices can estimate the lithium battery internal resistance through calculation according to the collected voltage and current data, but the estimated value may have a large error, and the complex calculation has a high requirement on the computing power of the BMS device.

[0004] Generally, the measurement method of the lithium battery internal resistance is to instantaneously apply a large current to both ends of the battery, and to measure the current value and the battery voltage value at this time, so as to calculate the battery internal resistance. However, this measurement method needs a large current source, and generally needs to provide a current of more than 5C, which may be thousands of amperes, which is undoubtedly impossible to realize in the BMS system.

[0005] In the factory test of the lithium battery, the battery internal resistance curve provided by the manufacturer is usually in the time domain, and there is also a frequency domain response curve of the battery internal resistance corresponding to the battery internal resistance curve. The small signal alternating current impedance of the battery at a specific frequency is measured by selecting an effective frequency excitation signal, so as to obtain the battery internal resistance.

[0006] The increase of the internal resistance is the main performance of the battery aging, the aged battery is more prone to heat, has smaller capacity, is more prone to be fully charged or discharged, and is more prone to heat than other batteries. A single aged battery often drags the capacity of the entire energy storage system, although the equalization function of the BMS can improve part of the condition, but the aged battery still has a vicious cycle and cannot be fundamentally solved. Therefore, it is necessary to timely detect the battery internal resistance and timely judge the aging condition of the battery. SUMMARY

[0007] The technical problem to be solved by the application is to provide a lithium battery internal resistance detection circuit integrated in a BMS system, which can timely detect the lithium battery internal resistance.

[0008] The technical scheme adopted by the present application to solve its technical problems is: a lithium battery internal resistance detection circuit integrated in a BMS system, comprising an active equalization circuit, the active equalization circuit comprises a positive electrode switch connectable with a positive electrode of a battery, a negative electrode switch connectable with a negative electrode of the battery, an internal resistance detection switch K11 connectable with a positive end of a direct-current isolation coupling capacitor C1, a negative end of the direct-current isolation coupling capacitor C1 connected with a sinusoidal alternating current excitation circuit, the sinusoidal alternating current excitation circuit generates an alternating current signal of 1 KHz;

[0009] The internal resistance detection switch K11 is connected with a positive end of a direct-current isolation coupling capacitor C2, and a negative end of the direct-current isolation coupling capacitor C2 is connected with a voltage detection circuit; the voltage detection circuit transmits an amplified alternating current small signal voltage response between the two ends of the battery to a half-wave phase detector;

[0010] The internal resistance detection switch K12 connectable with the negative electrode switch is connected with a virtual ground and a current detection circuit, and an output of the current detection circuit is transmitted to the half-wave phase detector;

[0011] The sinusoidal excitation circuit comprises a sinusoidal signal generator U2, the sinusoidal signal generator U2 is in communication connection with a single-chip microcomputer U13, and the single-chip microcomputer U13 controls the sinusoidal signal generator U2 to output a sinusoidal signal; an output of the half-wave phase detector is transmitted to the single-chip microcomputer U13.

[0012] Preferably, the negative end of the direct-current isolation coupling capacitor C1 is connected with a voltage follower U1, a first band-pass filter and the sinusoidal signal generator U2 through a resistor R2.

[0013] Preferably, the negative end of the direct-current isolation coupling capacitor C2 is connected with an input side of the voltage detection circuit through a capacitor C9 and a resistor R10; the internal resistance detection switch K12 is connected with another input side of the voltage detection circuit through a capacitor C10 and a resistor R12.

[0014] Preferably, the internal resistance detection switch K12 is connected with an input side of the current detection circuit through a resistor R18 and a capacitor C11; the internal resistance detection switch K12 is connected with another input side of the current detection circuit through a resistor R18, a resistor R20 and a capacitor C12.

[0015] The internal resistance detection switch K12 is connected with a negative input end of an operational amplifier U6 through a resistor R18 and a resistor R19,

[0016] A positive input end of the operational amplifier U6 is grounded, the operational amplifier U6 constitutes a virtual ground, and an output end of the operational amplifier U6 is connected with another input side of the current detection circuit through the capacitor C12.

[0017] Preferably, it also includes an analog switch SW1 controlled by a microcontroller U13. The common terminal of the analog switch SW1 is connected to the input terminal of the second bandpass filter, the output terminal of the second bandpass filter is connected to the input terminal of the half-wave phase detector, all switching ports of the analog switch SW1 are connected to the output terminal of the voltage detection circuit, and the other switching port of the analog switch SW1 is connected to the output terminal of the current detection circuit.

[0018] Preferably, the lithium battery internal resistance detection circuit is integrated into the sampling slave board of the BMS system.

[0019] Preferably, the positive switch is connected to one end of the active balancing energy storage inductor L1 via the active balancing switch K9, and the negative switch is connected to the other end of the active balancing energy storage inductor L1 via the active balancing switch K10.

[0020] The beneficial effects of this invention are: This invention utilizes an active balancing circuit to achieve a single circuit for detecting the internal resistance of all batteries. Taking advantage of the AC small-signal frequency domain response characteristics of lithium batteries, by applying a specific frequency excitation, the AC small-signal voltage and current responses of the lithium battery at that specific frequency are detected. These responses are then superimposed with the excitation signal to obtain the battery internal resistance data. The lithium battery internal resistance detection circuit of this invention, employing an AC small-signal method for detecting battery internal resistance, is small in size, low in cost, and easy to implement. Furthermore, combined with the active balancing circuit, it is easily modified. Attached Figure Description

[0021] Figure 1 This is a circuit diagram of the lithium battery internal resistance detection circuit of the present invention;

[0022] Figure 2 This is a functional schematic diagram of the lithium battery internal resistance detection circuit of the present invention;

[0023] Figure 3 It is the Nyquist plot of the small-signal impedance of the battery. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below:

[0025] This invention can be implemented in many different forms and should not be considered as limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully express the scope of the invention to those skilled in the art.

[0026] like Figure 1 , Figure 2 As shown, a lithium battery internal resistance detection circuit is integrated into a BMS system. The lithium battery internal resistance detection circuit is integrated into the sampling slave board of the BMS system. The lithium battery internal resistance detection circuit includes an active balancing circuit, which includes a positive switch that can be connected to the positive terminal of the battery and a negative switch that can be connected to the negative terminal of the battery.

[0027] The positive end of the DC isolation coupling capacitor C1 is connected to the internal resistance detection switch K11 connected to the positive electrode switch, and the negative end of the DC isolation coupling capacitor C1 is connected to the sinusoidal AC excitation circuit, which generates an AC signal of 1KHz. The positive end of the DC isolation coupling capacitor C2 is connected to the internal resistance detection switch K11, and the negative end of the DC isolation coupling capacitor C2 is connected to the voltage detection circuit; the voltage detection circuit transmits the amplified AC small signal voltage response between the two ends of the battery to the half-wave phase detector. The internal resistance detection switch K12 connected to the negative electrode switch is connected to the virtual ground and the current detection circuit, and the output of the current detection circuit is transmitted to the half-wave phase detector.

[0028] The sinusoidal excitation circuit includes a sinusoidal signal generator U2, which is in communication connection with the single-chip microcomputer U13 and controlled by the single-chip microcomputer U13 to output a sinusoidal signal; the output of the half-wave phase detector is transmitted to the single-chip microcomputer U13.

[0029] The positive electrode switch is connected to one end of the active equalization energy storage inductor L1 through the active equalization switch K9, and the negative electrode switch is connected to the other end of the active equalization energy storage inductor L1 through the active equalization switch K10.

[0030] The negative end of the DC isolation coupling capacitor C1 is connected to the voltage follower U1, the first band-pass filter, and the sinusoidal signal generator U2 through the resistor R2. The negative end of the DC isolation coupling capacitor C2 is connected to one input side of the voltage detection circuit through the capacitor C9 and the resistor R10; the internal resistance detection switch K12 is connected to the other input side of the voltage detection circuit through the capacitor C10 and the resistor R12; the internal resistance detection switch K12 is connected to one input side of the current detection circuit through the resistor R18 and the capacitor C11; the internal resistance detection switch K12 is connected to the other input side of the current detection circuit through the resistor R18, the resistor R20, and the capacitor C12.

[0031] The internal resistance detection switch K12 is connected to the negative input end of the operational amplifier U6 through the resistor R18 and the resistor R19; the positive input end of the operational amplifier U6 is grounded, and the operational amplifier U6 constitutes a virtual ground; the output end of the operational amplifier U6 is connected to the other input side of the current detection circuit through the capacitor C12.

[0032] The lithium battery internal resistance detection circuit further includes an analog switch SW1 controlled by the single-chip microcomputer U13, the common end of the analog switch SW1 is connected to the input end of the second band-pass filter, the output end of the second band-pass filter is connected to the input end of the half-wave phase detector, one switching port of the analog switch SW1 is connected to the output end of the voltage detection circuit, and the other switching port of the analog switch SW1 is connected to the output end of the current detection circuit.

[0033] Figure 1BAT1~BAT4 are lithium batteries, which represent multiple series-connected batteries in the battery pack. In practice, ten or more batteries are often connected in series, but due to the size limitation of the circuit diagram, only four batteries are represented here. Switches K1~K8 are switch matrices, which are positive electrode switches (connected to the positive electrode of the battery) and negative electrode switches (connected to the negative electrode of the battery). Active balancing switches K9 and K10 are used to connect the active balancing circuit. When active balancing switches K9 and K10 are closed, the active balancing energy storage inductor L1 is used to store battery balancing energy. When it is necessary to detect the battery internal resistance, active balancing switches K9 and K10 are opened, and internal resistance detection switches K11 and K12 are closed. The direct current blocking capacitors C1 and C2 are connected to the positive electrode of the battery, one end of the direct current blocking capacitor C1 is connected to the sinusoidal alternating excitation circuit, and the other end of the direct current blocking capacitor C2 is connected to the voltage detection circuit. The sinusoidal alternating excitation circuit includes a voltage follower U1, a first band-pass filter composed of resistors R4~R7 and capacitors C5~C7, and a sinusoidal signal generator U2, which is configured to generate a 1KHz alternating signal. The sinusoidal signal generator U2 communicates with the single-chip microcomputer U13 to control the generation of the sinusoidal signal by the sinusoidal signal generator U2. The voltage detection circuit is composed of integrated operational amplifiers U3, U4, and U5, which are responsible for amplifying the alternating small signal voltage response between the two ends of the battery and transmitting it to the subsequent half-wave phase detector. The internal resistance detection switch K12 connects the excitation source virtual ground and the current detection circuit. Due to the high impedance of the virtual open characteristic of the operational amplifier U6, a virtual ground is formed. Integrated operational amplifiers U7, U8, and U9 constitute the current detection circuit, and the current detection resistor R20 converts the current signal into a voltage drop on both sides, which is amplified by integrated operational amplifiers U7, U8, and U9 and transmitted to the subsequent half-wave phase detector. The analog switch SW1 is controlled by the single-chip microcomputer U13 to select the voltage detection circuit or the current detection circuit. The analog switch SW1 is connected to the second band-pass filter, which is used to filter out high-order harmonics. The second band-pass filter is connected to the half-wave phase detector, which multiplies the excitation signal with the voltage or current signal and detects the amplitude and phase signals. The output of the half-wave phase detector is transmitted to the single-chip microcomputer U13, which calculates the battery internal resistance.

[0034] Figure 3 is the Nyquist plot of the battery alternating small signal impedance. The vertical axis is the imaginary part. Figure 3The imaginary part signal is not present in the part of about 1 KHz, that is, the battery is entirely ohmic internal resistance response and no polarization internal resistance response, so 1 KHz is used as the excitation frequency in the circuit. The conventional internal resistance detection is to use the time domain response characteristics of the battery and use the pulse current detection. This method needs to provide a large current and needs a very fast and accurate sensor, so it cannot be equipped in the BMS device. However, by using the AC small signal impedance frequency domain response characteristics of the battery, a specific frequency is selected, so that the battery only shows ohmic internal resistance characteristics, and the battery internal resistance can also be calculated.

[0035] The positive switch and the negative switch of the active balancing circuit can connect any battery to the internal resistance detection circuit. Because the DC blocking coupling capacitor C1 and the DC blocking coupling capacitor C2 are arranged, the DC signal of the battery does not affect the circuit. First, the sine signal generator U2 applies a 1 KHz sine AC signal to the battery, and then the control analog switch SW1 is selected to connect the voltage detection circuit to detect the voltage signal or connect the current detection circuit to detect the current signal, at this time the obtained signal is the AC voltage response or AC current response of the battery. In order to obtain the amplitude and phase information of the AC signal, a half-wave phase detector is needed to process the signal. The phase detector first multiplies the 1 KHz reference signal with the voltage response and the current response to obtain four equations with 2 times the angular frequency, 1 times the angular frequency and phase information. Using the second band-pass filter to filter out the 2 times frequency component, the DC component of the voltage and current can be obtained. At this time, only the voltage amplitude divided by the current amplitude can obtain the battery impedance, that is, the internal resistance.

[0036] The battery impedance is calculated as follows:

[0037] 1) Calculate the angular frequency ω corresponding to the test frequency f:

[0038] ω = 2πf

[0039] 2) Calculate the reference signal u refI , the reference signal u refQ :

[0040]

[0041] 3) Calculate the measured element voltage u DUT , the measured element current i DUT :

[0042]

[0043] 4) The measured element voltage u DUT , the measured element current i DUT are multiplied by the reference signal u refI , the reference signal u refQ :

[0044]

[0045]

[0046] 5) through the second band-pass filter low-pass filter, filter out 2 times the component, left DC component, calculate the DC voltage component U DUT_I , DC voltage component U DUT_Q , DC current component I DUT_I , DC current component I DUT_Q :

[0047]

[0048] 6) calculate the measured element voltage amplitude U Z , measured element current amplitude I Z , voltage phase φ relative to the reference sinusoidal signal U , current phase φ relative to the reference sinusoidal signal i :

[0049]

[0050] 7) calculate the impedance modulus |Z DUT | and impedance angle θ:

[0051]

[0052] 8) calculate the real part R and the imaginary part X of the impedance (impedance Z DUT =R+jX):

[0053]

[0054] 1) the present application is based on the BMS active balancing circuit to be modified, using active balancing circuit to realize a set of circuit detection of all battery resistance.2) using the lithium battery AC small signal frequency domain response characteristics, by applying a specific frequency excitation, detection of lithium battery at a specific frequency of AC small signal voltage response and current response, and then with the excitation signal superposition solution, get the battery resistance data, even can further calculate the impedance angle, quality factor, loss factor, etc.3) the whole resistance detection circuit is integrated in the BMS system sampling from the board, can detect the battery resistance state at any time, and different from the indirect estimation through data, through the form of on-board circuit detection of battery resistance actual value, the error is minimal.4) since the battery resistance will change with the battery charge and discharge capacity changes slightly, after the end of charge and discharge, the battery resistance can assist in calibrating the battery soc condition. At the same time, it can also find the battery with large deviation from the average value of resistance, early warning, timely replacement.5) the lithium battery resistance detection circuit of the present application adopts the method of AC small signal detection of battery resistance, which is small in size, low in cost and easy to realize, and is easy to modify with the active balancing circuit.

[0055] The above-described embodiments according to the present application are intended to be illustrative only. Changes can be made by those skilled in the art, without departing from the scope of the present application, which is defined by the following claims. The technical scope of the present application is not limited to the above-described embodiments. The technical scope of the present application must be determined based on the scope of the claims.

Claims

1. A lithium battery internal resistance detection circuit integrated in a BMS system, comprising an active equalization circuit, the active equalization circuit comprising a positive electrode switch connected to a positive electrode of a battery, a negative electrode switch connected to a negative electrode of the battery, characterized in that: The inner resistance detection switch K11 connected with the positive electrode switch connects the positive end of the direct-current isolation coupling capacitor C1, and the negative end of the direct-current isolation coupling capacitor C1 is connected with a sinusoidal alternating excitation circuit, which generates an alternating signal of 1KHz. The inner resistance detection switch K11 connects the positive end of the direct-current isolation coupling capacitor C2, and the negative end of the direct-current isolation coupling capacitor C2 is connected with a voltage detection circuit; the voltage detection circuit transmits the amplified alternating small signal voltage between the battery to a half-wave phase detector. The inner resistance detection switch K12 connected with the negative electrode switch connects a virtual ground and a current detection circuit, and the output of the current detection circuit is transmitted to the half-wave phase detector. The sinusoidal alternating excitation circuit comprises a sinusoidal signal generator U2, the sinusoidal signal generator U2 is in communication connection with a single-chip microcomputer U13, and the sinusoidal signal generator U2 outputs a sinusoidal signal controlled by the single-chip microcomputer U13; the output of the half-wave phase detector is transmitted to the single-chip microcomputer U13. The lithium battery inner resistance detection circuit further comprises an analog switch SW1 controlled by the single-chip microcomputer U13, the common end of the analog switch SW1 is connected with the input end of a second band-pass filter, the output end of the second band-pass filter is connected with the input end of the half-wave phase detector, one switching port of the analog switch SW1 is connected with the output end of the voltage detection circuit, and the other switching port of the analog switch SW1 is connected with the output end of the current detection circuit. Through the sinusoidal signal generator U2, a sinusoidal alternating signal of 1KHz is applied to the battery, and then the analog switch SW1 is controlled to select the voltage detection circuit to detect the voltage signal or the current detection circuit to detect the current signal, so that the obtained signal is the alternating voltage response or the alternating current response of the battery. The positive electrode switch is connected with one end of a main active equalization energy storage inductor L1 through a main active equalization switch K9, and the negative electrode switch is connected with the other end of the main active equalization energy storage inductor L1 through a main active equalization switch K10.

2. The lithium battery inner resistance detection circuit integrated in the BMS system according to claim 1, characterized in that: The negative end of the direct-current isolation coupling capacitor C1 is connected with a voltage follower U1, a first band-pass filter and a sinusoidal signal generator U2 through a resistor R2.

3. The lithium battery internal resistance detection circuit integrated in the BMS system according to claim 1, characterized in that: The negative end of the direct-current isolation coupling capacitor C2 is connected with an input side of the voltage detection circuit through a capacitor C9 and a resistor R10; the inner resistance detection switch K12 is connected with the other input side of the voltage detection circuit through a capacitor C10 and a resistor R12.

4. The lithium battery inner resistance detection circuit integrated in the BMS system according to claim 1, characterized in that: The inner resistance detection switch K12 is connected with an input side of the current detection circuit through a resistor R18 and a capacitor C11; the inner resistance detection switch K12 is connected with the other input side of the current detection circuit through a resistor R18, a resistor R20 and a capacitor C12; The inner resistance detection switch K12 is connected with the negative input end of the operational amplifier U6 through a resistor R18 and a resistor R19, The positive input end of the operational amplifier U6 is grounded, the operational amplifier U6 constitutes a virtual ground, and the output end of the operational amplifier U6 is connected with the other input side of the current detection circuit through a capacitor C12.

5. The lithium battery internal resistance detection circuit integrated in the BMS system according to claim 1, characterized in that: The lithium battery inner resistance detection circuit is integrated in a sampling slave board of the BMS system.

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