Battery pack micro internal resistance detection system with low ground noise

Abstract

The invention discloses a low-background-noise battery pack micro internal resistance detection system, which comprises a signal acquisition module, an excitation source module and a double-channel isolation power supply, and is characterized in that the double-channel isolation 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 driving coupling circuit and is used for injecting an alternating current signal into a battery pack and providing a reference square wave signal required by the detection module, and the signal acquisition module is composed of an input coupling circuit, a front composite amplification circuit, the detection module, a fully differential circuit, an A / D module and an MCU module. According to the technical scheme, the front-end circuit design in the system is simplified, the system performance is optimized, the defect that equivalent input noise is increased due to the fact that the measuring range is increased in a traditional scheme is overcome, and the overall performance and the measuring precision of the system are improved.

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, accurate detection of micro-internal resistance is a key link in ensuring battery performance and vehicle safety. Since the internal resistance of the battery is usually in the milliohm level, especially for large-capacity power batteries, its internal resistance is as low as micro-ohm level, which places extremely high demands on the accuracy of signal processing. At present, the mainstream detection method is to use the AC impedance method to obtain the internal resistance value through four-wire measurement method and detection technology. This technology can greatly 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 at the same time collect the battery pack's response voltage signal to the AC current signal and the phase difference between the two to obtain the impedance information of the battery pack. High stability of signal phase and amplitude is one of the key factors to achieve accurate measurement.

[0003] In the internal resistance measurement of the detection technology, there will be a system-inherent phase error between the reference signal and the input signal, which is an important factor affecting the measurement accuracy. This error usually comes from the non-ideal characteristics of the devices in the measurement system and parasitic parameters. The inherent phase difference will have a significant impact on the demodulation result. There is a nonlinear relationship between its impact on the system measurement accuracy and the phase angle of the battery pack. Especially when the battery pack phase angle is large, the four-wire measurement cable used in the measurement process will affect the measurement accuracy due to the inductive coupling and capacitive coupling. This cable coupling effect interacts with the inherent phase error of the system to form a strong coupling relationship, which further degrades the measurement accuracy. This complex mutual coupling significantly increases the difficulty of system calibration and brings challenges to high-precision measurement. In order to achieve a larger measurement range, traditional measurement schemes usually use front-end amplifier circuits with different gains to expand the range. However, as the range changes, the bandwidth of the front-end amplifier system gradually changes. When the bandwidth margin is insufficient, the zero-pole fluctuation of the loop will significantly affect the measurement accuracy. In addition, under small signal conditions, the change in gain will cause a change in the equivalent input noise, which will further affect the 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 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 an 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 inherent phase error of 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-composite amplifier circuit is composed of a differential amplifier stage composed of two highly matched JFET pairs combined with a low-noise BJT operational amplifier, and is used to amplify the response voltage signal. The circuit has stable amplitude-frequency characteristics and phase-frequency characteristics, and has the advantages of high input impedance and low background noise, which can effectively improve signal quality.

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

[0012] Preferably, the fully differential circuit is composed of a chopper operational amplifier and a low 1 / f noise resistor, and has low offset voltage and low 1 / f noise characteristics, thereby further improving signal quality and reducing low-frequency noise interference. In addition, the input impedance of the circuit reaches 0.1GΩ, which effectively reduces static errors.

[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 beneficial effects achieved by the present invention are:

[0015] (1) The present invention realizes range switching at the excitation source end to ensure that input signals under 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 influence 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 is composed of a differential amplifier stage composed of two highly matched JFET pairs and a low-noise BJT operational amplifier, which not only has stable amplitude-frequency characteristics and phase-frequency characteristics, but also has the advantages of high input impedance and low noise floor. Among them, 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 detection module design of the present invention can convert the noise generated by the analog switch into common-mode noise, thereby effectively suppressing the noise impact and reducing the gain mismatch error. At the same time, its subsequent signal chain design has a low 1 / f noise characteristic, which keeps the noise level of the entire signal chain at a low level, thereby improving the overall performance and measurement accuracy of the system. 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 picture:

[0021] Figure 1 A block diagram of the principle of battery pack micro-internal resistance detection provided by 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 A schematic diagram of a detection module circuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0025] Embodiments of the present invention are combined Figures 1 to 3 , specifically providing 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 supplies 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 full 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 the measurement accuracy and effectively eliminate the influence of the 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 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, 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), orthogonal 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 inherent phase error of the system is calculated and corrected in a closed loop. Through this closed loop operation, the system parameters can be dynamically adjusted to reduce the impact of the inherent phase error of the system 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 parts for calibration, U2 is solved to complete the compensation of the system phase error.

[0031] In this embodiment, combined Figure 2 , Figure 2 Schematic diagram of the preamplifier circuit of the present invention. The preamplifier circuit 102 includes an NMOS Q1, a JFET U1B, a JFET U1C, an operational amplifier U6, an operational amplifier 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] Exemplarily, the operational amplifier U11, the resistor R19, the resistor R21, the resistor R24 ​​and the NMOS Q1 form a constant current source, which determines the steady-state transconductance g of the JFET U1B and the JFET U1C. m , this constant current source and resistor R4, resistor R5, JFET U1B and JFET U1C form a differential amplifier stage, and this differential amplifier stage and operational amplifier U6, resistor R12 and resistor R14 form a closed-loop system. Under this design, by adopting a composite design of JFET and BJT, using JFET as the input stage, it is possible to have an input impedance of the order of TΩ, reducing the source impedance matching effect with the input coupling circuit 101, and also having a lower total noise power. The total noise is mainly 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: 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 composed of the noise e of the JFET. n,1 Therefore, this composite amplifier design can effectively reduce the input impedance and noise selection requirements of the operational amplifier. Under this design, the bandwidth of the pre-composite amplifier circuit 102 is 38M bandwidth, which can ensure that this example has stable amplitude-frequency characteristics and phase-frequency characteristics within a 100M bandwidth. This design significantly reduces the phase noise caused by the zero-pole fluctuation of the loop, and provides a stable phase-frequency characteristic for the system, thereby effectively supporting the feasibility and stability of the above calibration algorithm.

[0033] In this embodiment, combined Figure 3 , Figure 3The 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 pre-composite amplifier circuit 102 is connected to the pin 5 of the analog switch U5 and the pin 7 of the analog switch U7. The reference signal is input to the pin 8 of the analog switch U5 and U7 to control the on and off of the switch 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 to suppress the noise power.

[0034] For example, the positive half-cycle and negative half-cycle outputs of the 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 into the fully differential circuit 104. The final output is This design reduces the mismatch of analog switch noise through reasonable circuit layout and component selection, thereby effectively converting the noise generated by the analog switch into common-mode noise. Common-mode noise is easier to suppress than differential-mode noise because common-mode noise can be effectively eliminated or reduced by the fully differential circuit 104, thereby optimizing the noise performance of the system. Then, the Σ-Δ type high-precision 32-bit-A / D module 105 samples the signal to achieve high-precision and high-resolution signal conversion.

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

[0036] Finally, it should be noted that the above are only 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 can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-noise battery pack micro-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 is composed of an input coupling circuit, a pre-composite amplifier circuit, a detection module, a full 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 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 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.

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 the standard resistance of the battery 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 an input signal to the detection module.

4. A low-noise battery pack micro-internal resistance detection system according to claim 1, characterized in that: 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 of the detection module 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, 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), orthogonal reference signal u r，Q (t) is: The output of the detection module is ideally low-pass filtered 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 inherent phase error of the system is calculated and corrected in a closed loop. The system parameters are dynamically adjusted through closed loop operation. After adjustment, the real part of the output V Re =V Re =U1cos(φ), imaginary part V Im =V Im =-U1sin(φ)+U2. By introducing standard parts for calibration, U2 is calculated to compensate for the system phase error.

5. A low-noise battery pack micro-internal resistance detection system according to claim 4, characterized in that: The pre-composite 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 form a differential amplifier stage, and the differential amplifier stage and the operational amplifier U6, the resistor R12 and the resistor R14 form a closed-loop system.

6. A low-noise battery pack micro-internal resistance detection system according to claim 5, characterized in that: The composite preamplifier circuit also adopts a composite design of JFET and BJT, uses JFET as the input stage, has an input impedance of TΩ, is used to reduce the source impedance matching effect with the input coupling circuit, and has a total noise power. 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 n,1 leading.

7. A low-noise battery pack micro-internal resistance detection system according to claim 1, 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 a 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.

8. A low-noise battery pack micro-internal resistance detection system according to claim 7, characterized in that: The dual analog switch including the analog switch U5 and the analog switch U7 specifically includes: corresponding to the positive half-cycle output and the 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 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 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 .

9. 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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