A low-noise battery pack micro-internal resistance detection system

Abstract

The present invention discloses a low-noise battery pack micro-internal resistance detection system, including a signal acquisition module, an excitation source module and a dual-channel isolated power supply. The dual-channel isolated power supply module provides low-noise power supplies for the signal acquisition module and the excitation source module respectively. The excitation source module is composed of a waveform generation module, a current source circuit and a drive coupling circuit, and is used to inject an AC current signal into the battery pack and provide a reference square wave signal required by the detection module. The signal acquisition module is composed of an input coupling circuit, a pre-composite amplifier circuit, a detection module, a fully differential circuit, an A / D module and an MCU module, and is used to collect and condition the response voltage signal of the battery pack and calculate the micro-internal resistance value of the battery pack. The technical solution of the present invention simplifies the front-end circuit design in the system and optimizes the system performance. It solves the defect of the traditional solution that the equivalent input noise increases due to the increase in the measuring range, and improves the overall performance and measurement accuracy of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of battery pack internal resistance detection, and in particular to a battery pack micro internal resistance detection system with low background noise. Background Art

[0002] In high-voltage battery packs, accurately detecting micro-internal resistance is a key step in ensuring battery performance and vehicle safety. Since battery internal resistance is usually in the milliohm range, especially for large-capacity power batteries, its internal resistance is as low as micro-ohm, which places extremely high demands on the accuracy of signal processing. Currently, the mainstream detection method uses the AC impedance method, which obtains the internal resistance value through four-wire measurement and detection technology. This technology can significantly suppress noise and improve the system signal-to-noise ratio. Its main principle is to inject an AC current signal of a specific frequency and amplitude into the battery pack, and simultaneously collect the battery pack's response voltage signal to the AC current signal and the phase difference between the two to obtain the battery pack's impedance information. High stability of the signal phase and amplitude is one of the key factors in achieving accurate measurement.

[0003] In internal resistance measurements using detection techniques, inherent phase error exists between the reference signal and the input signal, a significant factor affecting measurement accuracy. This error typically originates from non-ideal characteristics and parasitic parameters of the measurement system's components. This inherent phase error significantly impacts the demodulation results, and its impact on system measurement accuracy is nonlinearly related to the battery pack's phase angle. This is particularly true when the battery pack's phase angle is large. The inductive and capacitive coupling in the four-wire measurement cable used during measurement can affect measurement accuracy. This cable coupling interacts strongly with the inherent phase error, further degrading measurement accuracy. This complex mutual coupling significantly increases the difficulty of system calibration and poses challenges for high-precision measurements. To achieve a wider measurement range, traditional measurement solutions typically employ front-end amplifier circuits with varying gains. However, as the range changes, the bandwidth of the front-end amplifier system gradually changes. When the bandwidth margin is insufficient, loop zero-pole fluctuations can significantly affect measurement accuracy. Furthermore, under small signal conditions, gain changes can cause changes in the equivalent input noise, further impacting measurement results. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-noise battery pack micro-internal resistance detection system to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a low-noise battery pack micro-internal resistance detection system, comprising a signal acquisition module, an excitation source module and a dual-channel isolated power supply; the dual-channel isolated power supply module provides low-noise power supplies for the signal acquisition module and the excitation source module respectively, and realizes electrical isolation between the modules, thereby simplifying the front-end circuit design and optimizing the system performance; the excitation source module is composed of a waveform generation module, a current source circuit and a drive coupling circuit, which is responsible for injecting AC current signals into the battery pack and providing the reference square wave signal required by the detection module; the signal acquisition module is composed of an input coupling circuit, a pre-composite amplifier circuit, a detection module, a fully differential circuit, an A / D module and an MCU module, which is used to collect and condition the response voltage signal of the battery pack, and calculate the micro-internal resistance value of the battery pack.

[0006] Preferably, the signal acquisition module and the excitation source module use a four-wire method to connect the battery pack and a standard resistor for simulating the internal resistance of the battery, so as to improve the measurement accuracy and effectively eliminate the influence of the wire resistance.

[0007] Preferably, the waveform generation module provides a reference square wave signal to the detection module through the isolation module, the excitation source module injects an AC current signal into the object to be measured, and the signal acquisition module conditions the response voltage signal through the input coupling circuit and the pre-composite amplifier circuit, and transmits the conditioned signal as the input signal to the detection module.

[0008] Preferably, the MCU module controls the range switching of the current source module and the phase calibration of the waveform generation module through the isolation module.

[0009] Preferably, the calibration algorithm of the MCU module first compensates for the phase error inherent in the system to complete the decoupling process, and then accurately calibrates the error caused by the cable coupling effect to ensure the accuracy and reliability of the measurement results.

[0010] Preferably, the pre-amplifier circuit is composed of a differential amplifier stage consisting of two highly matched JFET pairs combined with a low-noise BJT operational amplifier, which is used to amplify the response voltage signal. The circuit has stable amplitude-frequency and phase-frequency characteristics, and has the advantages of high input impedance and low background noise, which can effectively improve the signal quality.

[0011] Preferably, the detection module consists of two analog switches and two low-pass filter circuits, using a dual-ended output design to input the signal into a fully differential circuit, thereby converting the noise generated by the analog switches into common-mode noise. Simultaneously, the detection module and the fully differential circuit implement primary and secondary anti-aliasing processing, respectively, to further improve signal quality and suppress high-frequency interference.

[0012] The fully differential circuit, preferably composed of a chopper op amp and low 1 / f noise resistors, exhibits low offset voltage and low 1 / f noise, further improving signal quality and reducing low-frequency noise interference. Furthermore, the circuit's input impedance reaches 0.1 GΩ, effectively reducing static error.

[0013] Preferably, the A / D module uses a Σ-Δ type high-precision 32-bit-ADC to sample the output signal of the fully differential circuit, thereby achieving high-precision and high-resolution signal conversion.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The present invention implements range switching at the excitation source end, ensuring that input signals at different ranges share the same signal path, thereby simplifying the phase calibration process, significantly improving the phase-frequency performance of the preamplifier circuit, reducing the impact of loop zero-pole fluctuations on measurement accuracy, and to a certain extent overcoming the defect of the traditional solution that the equivalent input noise increases due to the increase in range.

[0016] (2) The preamplifier circuit of the present invention combines a differential amplifier stage consisting of two highly matched JFET pairs with a low-noise BJT operational amplifier. It not only exhibits stable amplitude-frequency and phase-frequency characteristics, but also has the advantages of high input impedance and low noise floor. The stable phase-frequency characteristics provide underlying support for the phase compensation algorithm.

[0017] (3) The impedance calibration algorithm of the present invention first compensates for the stable system inherent static phase error, completes the decoupling process from the cable coupling effect, and then compensates for the error caused by the cable coupling effect, thereby effectively eliminating the influence of the measurement cable on the result and improving the measurement accuracy and reliability.

[0018] (4) The detector module design of the present invention converts the noise generated by the analog switch into common-mode noise, effectively suppressing the noise impact and reducing gain mismatch errors. Furthermore, the subsequent signal chain design features low 1 / f noise characteristics, keeping the noise level of the entire signal chain low, thereby improving the overall system performance and measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0020] In the attached figure:

[0021] Figure 1 A block diagram illustrating the principle of detecting micro-internal resistance of a battery pack according to an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of a preamplifier circuit provided by an embodiment of the present invention;

[0023] Figure 3 This is a circuit diagram of a detection module provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] The embodiment of the present invention is combined with Figures 1 to 3 , specifically provide the following technical solutions: a low-noise battery pack micro-internal resistance detection system; exemplary, combined with Figure 1 As shown, the system includes a signal acquisition module 107, an excitation source module 114 and a dual-channel isolated power supply 108. The dual-channel isolated power supply module 108 provides low-noise power for the signal acquisition module 107 and the excitation source module 114 respectively, and realizes electrical isolation between the modules, thereby simplifying the front-end circuit design and optimizing the system performance; the excitation source module 114 is composed of a waveform generation module 113, a current source circuit 112 and a drive coupling circuit 111, and is responsible for injecting an AC current signal into the battery pack 109 and providing a reference square wave signal required by the detection module 103; the signal acquisition module 107 is composed of an input coupling circuit 101, a pre-composite amplifier circuit 102, a detection module 103, a fully differential circuit 104, an A / D module 105 and an MCU module 106, and is used to collect and condition the response voltage signal of the battery pack and calculate the micro internal resistance value of the battery pack.

[0026] Exemplarily, the signal acquisition module 107 and the excitation source module 114 use a four-wire method to connect the battery pack 109 and a standard resistor for simulating the internal resistance of the battery to improve measurement accuracy and effectively eliminate the influence of wire resistance.

[0027] Exemplarily, the waveform generation module 113 provides a reference square wave signal to the detection module 103 through the isolation module 110, the excitation source module 114 injects an AC current signal into the object to be measured, and the signal acquisition module 107 conditions the response voltage signal through the input coupling circuit 101 and the pre-composite amplifier circuit 102, and transmits the conditioned signal as an input signal to the detection module 103.

[0028] In this embodiment, the MCU module 106 controls the range switching of the current source module 112 and the phase calibration of the waveform generation module through the isolation module 110. Due to the cable coupling effect and the inherent phase error of the system, the input signal u of the detection module 103 is s (t) is: Among them, U1 is the amplitude of the response voltage signal, U2 is the noise factor of inductive coupling, U3 is the noise factor of capacitive coupling, ω is the angular frequency of the measurement signal, Δφ is the inherent phase error of the system, φ is the phase shift between the input signal and the reference signal, Δφ is the inherent phase error of the system. When the Kelvin four-wire measurement cable is in contact with the battery, U3 can be approximated to 0. Therefore, the input signal u s (t) may be: The reference signal u of the detection module 103 r,I (t) is: u r,I (t) = cos(ωt), quadrature reference signal u r,Q (t) is:

[0029] That is, the output of the detection module 103 is actually V after ideal low-pass filtering. Re V Re =U1cos(φ+Δφ), its imaginary part V Im =V Im =-U1 sin(φ+Δφ)+U2cosΔφ.

[0030] Exemplarily, the impedance calibration algorithm first uses the real value V Re As the feedback value, the system inherent phase error is closed-loop calculated and corrected. Through this closed-loop operation, the system parameters can be dynamically adjusted to reduce the impact of the system inherent phase error on the cable coupling effect calibration algorithm. After adjustment, the real part of the output V Re =V Re =U1cos(φ), imaginary part V Im =V Im =-U1 sin(φ)+U2. Then, by introducing standard components for calibration, U2 is calculated to complete the compensation of the system phase error.

[0031] In this embodiment, combined Figure 2 , Figure 2 Schematic diagram of a preamplifier circuit according to the present invention. The preamplifier circuit 102 includes an NMOS Q1, a JFET U1B, a JFET U1C, an op amp U6, an op amp U11, a resistor R4, a resistor R5, a resistor R12, a resistor R14, a resistor R19, a resistor R21, a resistor R24, and a capacitor C20.

[0032] For example, op amp U11, resistor R19, resistor R21, resistor R24 ​​and NMOS Q1 form a constant current source to determine the steady-state transconductance g of JFET U1B and JFET U1C. m This constant current source, together with resistors R4, R5, JFET U1B, and JFET U1C, forms a differential amplifier stage. This differential amplifier stage, together with op amp U6, resistors R12, and R14, forms a closed-loop system. In this design, by adopting a composite design of JFET and BJT, using JFET as the input stage, an input impedance of the order of TΩ can be achieved, reducing the source impedance matching effect with the input coupling circuit 101. It also allows for lower total noise power. The total noise is primarily contributed by two components: one is the noise of the JFET differential pair, which is determined by the JFET's equivalent noise voltage e. n,JFET and the equivalent noise current i n,JFET Determines the noise power it provides for: i n,JFET ·R s ) 2 , where e n,JFET is the equivalent noise voltage, R s is the signal source impedance, and the other part is the noise of the op amp e n,op , after the two are superimposed, the total noise power for: Wherein, A1 is the DC gain of the pre-composite amplifier circuit 102. In this application scenario, A1 is usually large, so the total noise power is mainly contributed by the noise e of the JFET. n,1 Therefore, this composite amplifier design can effectively reduce the requirements for op amp input impedance and noise selection. Under this design, the bandwidth of the pre-composite amplifier circuit 102 is 38 MHz, which can ensure that this example has stable amplitude-frequency and phase-frequency characteristics within a 100 MHz bandwidth. This design significantly reduces the phase noise caused by loop zero-pole fluctuations, providing a stable phase-frequency characteristic for the system, thereby effectively supporting the feasibility and stability of the above-mentioned calibration algorithm.

[0033] In this embodiment, combined Figure 3 , Figure 3This is a schematic diagram of the detection module circuit. Detection module 103 includes an analog switch U5, an analog switch U7, a resistor R3, a resistor R8, a capacitor C16, a capacitor C17, a capacitor C21, and a capacitor C22. The output of the preamplifier circuit 102 is connected to pin 5 of analog switch U5 and pin 7 of analog switch U7. A reference signal is input to pins 8 of analog switches U5 and U7 to control the on / off switching of the switches to complete the detection. Resistors R3, capacitors C16, and C17, along with resistors R8, capacitors C21, and C22, form two low-pass filter networks to suppress noise power.

[0034] For example, the positive half-cycle and negative half-cycle outputs of this dual analog switch design correspond to Figure 3 U_PSD_Out_P and U_PSD_Out_N in the figure; assuming that the two low-pass filter networks are ideal low-pass filter networks, U_PSD_Out_P can be U_PSD_Out_N can be Among them, U in is the input signal amplitude, assuming the operating frequency is D is the duty cycle of the square wave, n(x) is the charge injection noise generated by the analog switch switching process, and the frequency of this noise is φ is the phase shift between the input signal and the reference signal. U_PSD_Out_P and U_PSD_Out_N are input to the fully differential circuit 104. The final output is This design reduces analog switch noise mismatch through rational circuit layout and component selection, effectively converting the noise generated by the analog switches into common-mode noise. Common-mode noise is more easily suppressed than differential-mode noise because it can be effectively eliminated or reduced by the fully differential circuit 104, thereby optimizing the system's noise performance. The Σ-Δ high-precision 32-bit A / D module 105 then samples the signal, achieving high-precision, high-resolution signal conversion.

[0035] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0036] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A low-noise battery pack internal resistance detection system, characterized by: It includes the following functional modules: signal acquisition module, excitation source module and dual-channel isolated power supply; The signal acquisition module consists of an input coupling circuit, a pre-composite amplifier circuit, a detection module, a fully differential circuit, an A / D module, and an MCU module, and is used to collect and condition the response voltage signal of the battery pack and calculate the micro internal resistance value of the battery pack; The MCU module controls the range switching of the current source module and the phase calibration of the waveform generation module through the isolation module. The input signal u s (t) is: Among them, U1 is the amplitude of the response voltage signal, U2 is the noise coefficient of inductive coupling, U3 is the noise coefficient of capacitive coupling, ω is the angular frequency of the measurement signal, Δφ is the inherent phase error of the system, and φ is the phase shift between the input signal and the reference signal. When the Kelvin four-wire measurement cable is in contact with the battery, U3 is approximately 0, so the input signal u of the detection module is s (t) can also be: Furthermore, the reference signal u of the detection module r，I (t) is: u r，I (t) = cos(ωt), quadrature reference signal u r，Q (t) is: The output of the detection module is filtered by ideal low-pass filtering and the real part V Re =V Re =U1cos(φ+Δφ), imaginary part V Im =V Im =-U1sin(φ+Δφ)+U2cosΔφ; The phase calibration is performed by first using the real value V Re As the feedback value, the system inherent phase error is closed-loop calculated and corrected, and the system parameters are dynamically adjusted through closed-loop operation. After adjustment, the real part V is output Re =V Re =U1cos(φ), imaginary part V Im =V Im =-U1sin(φ)+U2, by introducing standard parts for calibration, U2 is calculated to complete the compensation of the system phase error; The excitation source module consists of a waveform generation module, a current source circuit and a drive coupling circuit, which is used to inject an AC current signal into the battery pack and provide the reference square wave signal required by the detection module; The dual-channel isolated power supply provides low-noise power to the signal acquisition module and the excitation source module respectively, and realizes electrical isolation between the modules.

2. A low-noise battery pack micro-internal resistance detection system according to claim 1, characterized in that: The signal acquisition module and the excitation source module are connected to the battery pack using a four-wire method to simulate a standard resistor of the battery's internal resistance.

3. A low-noise battery pack micro-internal resistance detection system according to claim 1, characterized in that: The waveform generation module provides a reference square wave signal to the detection module through the isolation module, the excitation source module injects an AC current signal into the object to be measured, and the signal acquisition module conditions the response voltage signal through the input coupling circuit and the pre-composite amplifier circuit, and transmits the conditioned signal as the input signal to the detection module.

4. A low-noise battery pack micro-internal resistance detection system according to claim 3, characterized in that: The pre-amplifier circuit includes NMOS Q1, JFET U1B, JFET U1C, operational amplifier U6, operational amplifier U11, resistor R4, resistor R5, resistor R12, resistor R14, resistor R19, resistor R21, resistor R24, and capacitor C20. The operational amplifier U11, resistor R19, resistor R21, resistor R24 ​​and NMOS Q1 constitute a constant current source for determining the steady-state transconductance g of JFETU1B and JFETU1C. m The constant current source and the resistor R4, the resistor R5, the JFET U1B and the JFETU1C constitute a differential amplifier stage, and the differential amplifier stage and the operational amplifier U6, the resistor R12 and the resistor R14 constitute a closed-loop system.

5. A low-noise battery pack micro-internal resistance detection system according to claim 4, characterized in that: The preamplifier circuit also adopts a composite design of JFET and BJT, uses JFET as the input stage, has an input impedance of the order of TΩ, and is used to reduce the source impedance matching effect with the input coupling circuit. At the same time, it has a total noise power, and the total noise is contributed by two parts: one part is the noise of the JFET differential pair, which is composed of the equivalent noise voltage e of the JFET. n，JFET and the equivalent noise current i n，JFET Determines the noise power it provides for: Among them, e n，JFET is the equivalent noise voltage, R s is the signal source impedance, and the other part is the noise of the op amp e n，op ; After the two are superimposed, the total noise power is Wherein, A1 is the DC gain of the preamplifier circuit, e n，op is the noise of the op amp. The total noise power is mainly composed of the noise of the JFET e n，1 leading.

6. A low-noise battery pack micro-internal resistance detection system according to claim 5, characterized in that: The detection module includes an analog switch U5, an analog switch U7, a resistor R3, a resistor R8, a capacitor C16, a capacitor C17, a capacitor C21 and a capacitor C22; the output of the pre-composite amplifier circuit is connected to pin 5 of the analog switch U5 and pin 7 of the analog switch U7, and the reference signal is input to pin 8 of the analog switches U5 and U7 to control the on and off of the switches to complete the detection. The resistor R3, the capacitor C16, the capacitor C17 and the resistor R8, the capacitor C21, the capacitor C22 form two low-pass filter networks for suppressing noise power.

7. A low-noise battery pack micro-internal resistance detection system according to claim 6, characterized in that: The dual analog switch including analog switch U5 and analog switch U7 specifically includes: corresponding to the positive half-cycle output and negative half-cycle output of U_PSD_Out_P and U_PSD_Out_N respectively, defining two low-pass filter networks as ideal low-pass filter networks, and the U_PSD_Out_P and the U_PSD_Out_N are respectively represented by U r，p and U r，n : in, is the defined operating frequency, U in is the input signal amplitude, D is the square wave duty cycle, n(x) is the charge injection noise generated by the analog switch switching process, and the frequency of the noise is φ is the phase shift between the input signal and the reference signal. U_PSD_Out_P and U_PSD_Out_N are input into the fully differential circuit to obtain the final output U r for: That is, the final output U r Output U for the positive half cycle r，p Subtract the negative half cycle output U r，n .

8. A low-noise battery pack micro-internal resistance detection system according to claim 1, characterized in that: The fully differential circuit is composed of a chopper operational amplifier and a low 1 / f noise resistor. The A / D module uses a Σ-Δ type high-precision 32-bit ADC to sample the output signal of the fully differential circuit to achieve signal conversion.

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