Online impedance spectroscopy monitoring system and method for balancing resistor shared by double battery cells

Abstract

The invention belongs to the technical field of battery management systems, and discloses an online impedance spectroscopy monitoring system and method for a balancing resistor shared by double battery cells. Comprising an equalization circuit module, a driving circuit module, a control module, a voltage sampling module, a current sampling module and an impedance calculation module. And the equalization circuit module realizes the switching of the equalization and impedance spectrum monitoring functions of the double battery cells by sharing an equalization resistor and a series excitation resistor. The drive circuit module adopts the combination design of NMOS and PMOS, and ensures that the switch tubes are independently conducted without interference. The control module realizes the conversion between an equalization mode and an electrochemical impedance spectroscopy (EIS) monitoring mode by switching the states of the switches: in the equalization mode, the single switch is switched on to realize passive equalization; in an EIS monitoring mode, the double switches are switched on at the same time to generate large excitation current, and the high-precision requirement of a low-internal-resistance battery is met. The method has the advantages of low hardware cost, large excitation current, high measurement precision and the like.

Description

Technical Field

[0001] This invention belongs to the field of battery management system technology, and particularly relates to an online impedance spectrum monitoring system and method for dual-cell shared equalization resistor. Background Technology

[0002] With traditional energy facing supply crises and emerging energy sources becoming increasingly integrated, energy storage has become a crucial carrier and medium for the storage and utilization of various energy sources. Batteries, due to their high energy density, fast response, and long lifespan, hold a dominant position. The core functions of a Battery Management System (BMS) include State of Charge (SOC) analysis / State of Health (SOH) estimation and battery equalization control. However, existing management systems rely on voltage and current time-domain data, making accurate analysis of the battery's internal state difficult. Electrochemical Impedance Spectroscopy (EIS) applies small-amplitude excitation signals of different frequencies to the battery and measures the corresponding response voltage, obtaining the battery's frequency domain data. Frequency domain analysis can effectively determine the battery's state. However, traditional EIS monitoring requires offline operation and cannot monitor battery state in real time. Existing online EIS monitoring systems suffer from the following problems:

[0003] The literature [Xueyuan Wang et al.“A Novel System for Measuring Alternating Current Impedance Spectra of Series-Connected Lithium-Ion Batteries With a High-Power Dual Active Bridge Converter and Distributed Sampling Units.”IEEE Transactions on Industrial Electronics 68(2021):7380-7390.] generates external excitation signals based on DC / DC converters, resulting in a complex circuit structure and issues such as asynchronous voltage and current measurements. An existing front-end sampling chip that supports battery impedance measurement measures impedance by applying current perturbation across the cell terminals. However, this chip only supports impedance measurement for single cells, making it difficult to adapt to current energy storage battery applications based on series configurations. Furthermore, the generated excitation current is relatively small, at 0.6A, which is insufficient to meet the EIS excitation requirements (≥0.4C) of existing 280Ah and above energy storage cells. International patent WO2023 / 024034 A1 (Detection device and battery management system for electrochemical impedance spectroscopy) uses an independent equalization circuit to generate the excitation current. However, due to the constraint of the equalization resistor value, the excitation current is difficult to increase (in the mA range), which cannot meet the high-precision requirements of low internal resistance batteries (such as 280Ah energy storage cells). Chinese patent CN 115693865 A (Non-isolated bidirectional soft-switching equalization circuit and its method for battery EIS detection) uses an active equalization circuit, which can provide a relatively large current excitation and measure multiple cells in series. However, due to the complexity of the circuit and its large size, there are certain application costs. Summary of the Invention

[0004] The purpose of this invention is to provide an online impedance spectrum monitoring system and method for dual-cell shared equalization resistors, in order to solve the technical problems that the EIS monitoring circuit of energy storage battery requires additional hardware costs, and that the existing equalization circuit-based excitation current is too small, resulting in low measurement accuracy of large-capacity, low-resistance energy storage cells.

[0005] To solve the above-mentioned technical problems, the specific technical solution of the online impedance spectrum monitoring system and method for dual-cell shared equalization resistor of the present invention is as follows:

[0006] An online impedance spectrum monitoring system for dual-cell batteries sharing a balancing resistor adopts a modular design, including a balancing circuit module, a drive circuit module, a control module, a voltage sampling module, a current sampling module, and an impedance calculation module. The balancing circuit module includes a dual-cell V... B1and V B2 Excitation resistor R eis1 and R eis2 Common equalization resistor R bal The system includes switching transistors S1 and S2; the driving circuit module includes NMOS and PMOS transistors for controlling the switching transistors to turn on and off; the control module generates control signals to switch between equalization mode and EIS monitoring mode; the voltage sampling module collects the voltage response signal of the battery cell; the current sampling module obtains the excitation current signal by measuring the voltage drop across the excitation resistor; and the impedance calculation module filters and performs frequency domain analysis on the sampled data to calculate the impedance spectrum of the battery cell.

[0007] Furthermore, the overall circuit uses a dual-cell V... B1 and V B2 As the core unit, each is connected to its respective excitation resistor R. eis1 and R eis2 Excitation resistor R eis1 and R eis2 Located between the positive and negative terminals of the power supply, it is used to control the magnitude of the excitation current and the acquisition of the current signal. The common equalization resistor R... bal With V B1 negative electrode and V B2 The positive terminal is connected to the positive terminal, and the other end is connected to the control switch transistors S1 and S2. Switch transistors Sa1, Sb1 and Sa2, Sb2 respectively form the drive circuits for control switches S1 and S2.

[0008] Furthermore, the drive circuit module uses a drive circuit composed of NMOS and PMOS transistors. S1, S2, Sa1, and Sa2 are selected as PMOS transistors, while Sb1 and Sb2 are selected as NMOS transistors. Switches Sa1 and Sb1 are connected to control signal Vin1, and switches Sa2 and Sb2 are connected to control signal Vin2. The source of switch Sb1 is connected to the negative terminal of battery VB1, and the source of switch Sa1 is connected to battery V. B1 The positive terminal of the circuit is connected to the drain of switching transistor Sb1 and the drain of switching transistor Sa1, which are connected to Vout1. The drain of switching transistor Sb2 and the drain of switching transistor Sa2 are connected to Vout2. Vout1 and Vout2 are connected to the gate of switch S1 in the equalization circuit. The source of switching transistor Sa2 is connected to the gate of switch S2, and the source of switching transistor Sb2 is connected to the cell V. B2 The negative electrode.

[0009] This invention also discloses a control method for an online impedance spectroscopy monitoring system with a shared equalization resistor for two battery cells. The switching between equalization mode and electrochemical impedance spectroscopy monitoring mode is achieved by controlling the on / off states of S1 and S2. When S1 is on and S2 is off, the battery cell V... B1 Entering equalization mode, passive equalization is performed according to the equalization current. The magnitude of the equalization current at this time is... When S1 is closed and S2 is open, cell V B2 Entering equalization mode, the equalization current is at this time. Excitation resistor R eis1 and R eis2 Choose the same resistance value; when S1 and S2 are both turned on, due to the excitation resistor R eis1 and R eis2 Much smaller than the equalization resistance R bal Therefore, it will be in V B1 -R eis1 -S1-S2-R eis2 -V B2 A large excitation current is generated in this circuit, and the magnitude of the excitation current is When R eis1 R eis2 Choose 0.2Ω, R bal With a 30Ω electrode and a cell voltage of 3.2V, the excitation current reaches 16A. By controlling the switching frequency, a corresponding frequency with an amplitude of I is generated in this circuit. eis The impedance spectrum of the battery cell can be plotted by using a pulsed square wave with a measurement range from 0.01Hz to 1KHz and sweeping the frequency at a fixed interval to obtain data from 20-30 frequency points.

[0010] Furthermore, the voltage and current waveforms sampled by the voltage sampling module and the current sampling module are digitally filtered using the FFT algorithm. The calculation formula is as follows:

[0011]

[0012] Where x(n) represents the sampled voltage / current signal, X(k) is the corresponding frequency domain output, N is the total number of sampling points, and j is the imaginary unit. After obtaining the frequency domain data of the voltage and current signals, the impedance is calculated using the following formula. The cell impedance amplitude |Z(f)| and phase angle θ at the corresponding frequency point are obtained.

[0013] Furthermore, the voltage sampling module synchronously samples the cell V. B1 and battery cell V B2 The voltage response on the battery cell is used to obtain the impedance data of the two cells, or the voltage response on only one cell is sampled and the impedance data of that cell is calculated.

[0014] Furthermore, two control modes can be used to control and generate the EIS excitation square wave:

[0015] In high-frequency testing scenarios, the system employs a sequential conduction control mode: the control module first applies a fixed high level to the gate of S1, keeping it continuously conducting and forming a stable current path; then, by sending a high-frequency PWM signal to the gate of S2, it controls the high-frequency switching action of S2, and the excitation current flows through V... B1 -R eis1 -S1-S2-R eis2 -V B2 The flow is in this loop, V B2 The amplitude on the cell is the excitation current I eis V B1 The signal amplitude on the battery cell is I eis -I bal1 ;

[0016] In low-frequency testing scenarios, the system adopts a synchronous conduction control mode: the control unit simultaneously sends fully synchronized PWM signals to the gates of S1 and S2 to ensure that the on / off edges of the two switches are aligned.

[0017] This invention also discloses an online impedance spectrum monitoring system for multiple battery cells sharing a balancing resistor, comprising multiple sets of dual-cell units. Each set of dual-cell units includes a balancing circuit module and a drive circuit module. Each dual-cell unit is a control unit, and adjacent control units are connected by a shared excitation resistor R. eis The connection ensures that the balance between the cells does not affect each other, and a larger impedance detection current is generated by the continuous conduction of multiple control units.

[0018] The online impedance spectrum monitoring system and method for dual-cell shared equalization resistor of the present invention has the following advantages:

[0019] (1) Shared equalizing resistor structure: By sharing a single equalizing resistor (R) in the equalizing circuits of the two series of cells. bal A small-value excitation resistor (R) is connected in series in each cell circuit. eis The equalization / impedance spectrum monitoring mode is switched by controlling the conduction state of the equalization switch of the two cells. When the switches are turned on separately, it is the equalization mode, and when the switches are turned on at the same time, it is the EIS detection mode. By using the principle of small resistance current shunting, the excitation current amplitude in the EIS detection mode is significantly improved (mA level → A level), which meets the high-precision EIS requirements of low internal resistance batteries.

[0020] (2) A dual-switch independent conduction control drive circuit is proposed: Existing equalization circuits typically achieve control through a single independent switch. However, in scenarios where two cells share a common equalization resistor, the source and drain of the two switches (S1, S2) are interconnected. If the upper switch is turned on, the source voltage of the lower switch will fluctuate, making it impossible to maintain a stable switching / closing state. A common approach is to use a bootstrap circuit to form a clamping voltage. However, this invention proposes a switch drive circuit composed of NMOS and PMOS, which can ensure that the two transistors do not affect each other when they are turned on separately, thus ensuring that the cells can be properly balanced. Since no new circuit components are required, this is a low-cost, high-reliability drive solution.

[0021] (3) A method for generating EIS excitation current is proposed, which can be implemented in any of the following ways:

[0022] a. Sequential conduction control: First turn on the first switch (S1), then switch the second switch (S2) at high frequency. Use the conduction path of S1 to generate a stable current. Alternatively, S2 can be turned on first, and then S1 can be switched at high frequency. This is suitable for high-frequency testing and avoids signal disturbance problems caused by asynchronous switching.

[0023] b. Synchronous conduction control: By strictly synchronizing the conduction of the two switching transistors (S1, S2) in sequence, an excitation current is generated in the common circuit, which is suitable for low-frequency testing and can reduce test energy loss.

[0024] This invention is particularly suitable for online monitoring of large-capacity, low-internal-resistance energy storage batteries (such as lithium-ion batteries and supercapacitors), and can be widely used in fields such as electric vehicle battery management systems (BMS), energy storage power stations, and uninterruptible power supplies (UPS). By assessing the battery's state of health (SOH) and changes in internal resistance in real time, it can significantly extend battery life and improve system safety. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall circuit structure proposed in this invention;

[0026] Figure 2 This is a schematic diagram of the dual-switch independent conduction drive control circuit structure of the present invention;

[0027] Figure 3 This is a schematic diagram of the equalization function of the present invention;

[0028] Figure 4 This is a schematic diagram of the EIS function of the present invention;

[0029] Figure 5 This is a schematic diagram of the multi-cell EIS monitoring circuit of the present invention. Detailed Implementation

[0030] To better understand the purpose, structure, and function of this invention, the following detailed description, in conjunction with the accompanying drawings, provides an online impedance spectrum monitoring system and method for dual-cell shared equalization resistors.

[0031] like Figure 1 As shown, the online impedance spectrum monitoring system for dual-cell batteries sharing a balancing resistor according to the present invention adopts a modular design, including a balancing circuit module, a drive circuit module, a control module, a voltage sampling module, a current sampling module, and an impedance calculation module. The balancing circuit module includes a dual-cell V... B1 and V B2 Excitation resistor R eis1 and R eis2 Common equalization resistor R bal And switching transistors S1 and S2. Driver circuit module: includes NMOS and PMOS transistors, used to control the on and off states of the switching transistors. Control module: used to generate control signals to switch between equalization mode and EIS monitoring mode. Voltage sampling module: used to acquire the cell's voltage response signal. Current sampling module: used to obtain the excitation current signal by measuring the voltage drop across the excitation resistor. Impedance calculation module: used to filter and perform frequency domain analysis on the sampled data to calculate the cell's impedance spectrum.

[0032] The overall circuit uses a dual-cell V B1 and V B2 As the core unit, each is connected to its respective excitation resistor R. eis1 and R eis2 These two components are located between the positive and negative terminals of the power supply and are used to control the magnitude of the excitation current and the acquisition of the current signal. The common equalization resistor R... bal With V B1 negative electrode and V B2 The positive terminal is connected to the positive terminal, and the other end is connected to the control switch transistors S1 and S2. Switch transistors Sa1, Sb1 and Sa2, Sb2 respectively form the drive circuits for control switches S1 and S2.

[0033] The switching transistor is a metal-oxide-semiconductor field-effect transistor (MOSFET), as shown in... Figure 2In this example, S1, S2, Sa1, and Sa2 are selected as P-channel MOSFETs (PMOS), while Sb1 and Sb2 are selected as N-channel MOSFETs (NMOS). A MOSFET has a source (S), a gate (G), and a drain (D). Typically, the gate is used to control the conduction of the switch. For NMOS, a voltage higher than the source voltage is applied to the gate to conduct, while for PMOS, a voltage lower than the source voltage is applied to the gate. In this invention, the drive circuit module uses a drive circuit composed of NMOS and PMOS. Generally, the gates (G) of both are connected to the same control signal Vin (such as the control signal provided by the control unit ControlUnit), that is, switches Sa1 and Sb1 are connected to control signal Vin1, and switches Sa2 and Sb2 are connected to control signal Vin2. The source (S) of the NMOS (switch Sb1) is connected to the battery V. B1 negative electrode (V) B1 -), the source of the PMOS (switching transistor Sa1) is connected to the cell V. B1 The positive electrode (V) B1 The drains (D) of the NMOS and PMOS transistors are connected to the same output terminal Vout, and are also connected to the gate of switch S1 in the equalization circuit. Specifically, the drains (D) of switches Sb1 and Sa1 are connected to Vout1, and the drains (D) of switches Sb2 and Sa2 are connected to Vout2. Vout1 and Vout2 are then connected to the gate of switch S1 in the equalization circuit. In the independent equalization circuit, when Vin is high, the PMOS is off, the NMOS is on, Vout is pulled to VB-, and the PMOS switch S1 is on. When Vin is low, the NMOS is off, the PMOS is on, Vout is pulled to VB+, and the PMOS switch S1 is off. However, in the scenario where two cells share a common balancing resistor, the sources and drains of the two switching transistors (S1, S2) are interconnected. If the upper switching transistor is turned on, the source voltage of the lower switching transistor will increase. If the source of the PMOS (switching transistor Sa2) of the lower drive circuit is also connected to its corresponding cell V... B2 The positive electrode (V) B2 If the voltage is increased (+), the gate voltage of the next-stage switch will always be lower than the source voltage, causing the lower switch to turn on as well. Therefore, this invention proposes a new drive circuit connection, such as... Figure 2 As shown, the source of the PMOS (switching transistor Sa2) in the drive switch is connected to the gate of the S2 switch, while the source of the NMOS (switching transistor Sb2) remains connected to the cell V. B2 The negative terminal is connected so that when the control signal of S2 is low, even if S1 is turned on, causing the source voltage of S2 to rise, S2 can still remain in the off state because the gate voltage of the S2 switch changes synchronously with the source voltage.

[0034] The switching between equalization mode and electrochemical impedance spectroscopy (EIS) monitoring mode can be achieved by controlling the on / off states of S1 and S2. For example... Figure 3 As shown, when S1 is on and S2 is off, the cell V B1 Entering equalization mode, passive equalization is performed according to the equalization current. The magnitude of the equalization current at this time is... When S1 is closed and S2 is open, cell V B2 Entering equalization mode, the equalization current is at this time. To ensure circuit consistency, the excitation resistor R is typically used. eis1 and R eis2 You can choose the same resistance value. For example Figure 3 As shown, when S1 and S2 are both turned on, due to the excitation resistor R eis1 and R eis2 Much smaller than the equalization resistance R bal Therefore, it will be in V B1 -R eis1 -S1-S2-R eis2 -V B2 A large excitation current is generated in this circuit, and the magnitude of the excitation current is When R eis1 R eis2 Choose 0.2Ω, R bal With a 30Ω resistor and a cell voltage of 3.2V, the excitation current can reach 16A, far exceeding the 0.6A of traditional solutions. By controlling the switching frequency, an amplitude of I at a corresponding frequency can be generated in this circuit. eis The impedance spectrum is measured using a pulsed square wave. The measurement range is typically from 0.01Hz to 1kHz, with frequency sweeping at fixed intervals to obtain data from 20-30 frequency points, which allows the cell impedance spectrum to be plotted.

[0035] The voltage sampling module is used to collect the voltage response on the battery cell, and the current sampling module collects the voltage response through the excitation resistor R. eis1 and R eis2 The voltage drop across the voltage source yields the excitation current. According to the Nyquist sampling theorem, the sampling frequency needs to be at least twice the frequency of the signal under test. In practical engineering, considering sampling accuracy, a frequency at least five times the measured frequency is typically chosen, and the sampling time is twice the frequency period. Since the excitation signal is a square wave, the data obtained from the voltage and current sampling modules enters the impedance calculation module and needs to be filtered first. Here, the FFT algorithm is used to digitally filter the sampled voltage and current waveforms. The calculation formula is as follows:

[0036]

[0037] Where x(n) represents the sampled voltage / current signal, X(k) is the corresponding frequency domain output, N is the total number of sampling points, and j is the imaginary unit. After obtaining the frequency domain data of the voltage and current signals, the impedance is calculated using the following formula. The cell impedance amplitude |Z(f)| and phase angle θ at the corresponding frequency point can be obtained.

[0038] Because the excitation current acts simultaneously on cell V B1 and battery cell V B2 Therefore, sampling can be performed according to calculation requirements; that is, the voltage sampling module can synchronously sample the cell V. B1 and battery cell V B2 The impedance data of the two cells can be obtained by sampling the voltage response on one cell, or the impedance data of that cell can be calculated by sampling the voltage response on only one cell.

[0039] Two control modes can be used to control and generate EIS-excited square waves.

[0040] In high-frequency testing scenarios (e.g., 100Hz to 1kHz), the system can employ a sequential conduction control mode: the control unit first applies a fixed high level to the gate of S1, keeping it continuously conducting and forming a stable current path; then, by sending a high-frequency PWM signal (e.g., 500Hz, 50% duty cycle) to the gate of S2, the high-frequency switching action of S2 is controlled. The excitation current flows through V... B1 -R eis1 -S1-S2-R eis2 -V B2 This circuit flows, and the continuous conduction of S1 ensures a stable current path, avoiding path switching interference caused by the high-frequency switching of S2. At this time, the amplitude of the current on the VB2 cell is the excitation current I. eis V B1 The signal amplitude on the battery cell is I eis -I bal1 .

[0041] In low-frequency testing scenarios (e.g., 0.1Hz to 100Hz), the system employs a synchronous conduction control mode: the control unit simultaneously sends fully synchronized PWM signals (e.g., 50Hz, 50% duty cycle) to the gates of S1 and S2, ensuring the alignment of the turn-on / turn-off edges of the two switches. Compared to sequential mode, synchronous conduction prevents the generation of single-cell equalization current during cell measurement when one cell is on and the other is off, thus reducing overall energy loss during the measurement process.

[0042] like Figure 5As shown, the proposed dual-cell impedance monitoring circuit can be extended to a multi-cell impedance monitoring circuit. An online impedance spectrum monitoring system with multiple cells sharing a balancing resistor includes multiple sets of dual-cell units. Each set of dual-cell units includes a balancing circuit module and a drive circuit module. Each dual-cell unit is a control unit, still using two cells as one control unit. Adjacent control units are connected through a shared excitation resistor R. eis The connection ensures that the balance between the cells does not affect each other, and at the same time, the continuous conduction of multiple control units can generate a larger impedance detection current, further improving the measurement accuracy.

[0043] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. An online impedance spectrum monitoring system for dual-cell batteries sharing a common equalization resistor, characterized by a modular design, wherein... It includes an equalization circuit module, a drive circuit module, a control module, a voltage sampling module, a current sampling module, and an impedance calculation module. The equalization circuit module includes a dual-cell V... B1 and V B2 Excitation resistor R eis1 and R eis2 Common equalization resistor R bal The system includes switching transistors S1 and S2; the driving circuit module includes NMOS and PMOS transistors for controlling the switching transistors to turn on and off; the control module generates control signals to switch between equalization mode and EIS monitoring mode; the voltage sampling module collects the voltage response signal of the battery cell; and the current sampling module obtains the excitation current signal by measuring the voltage drop across the excitation resistor. The impedance calculation module is used to filter and perform frequency domain analysis on the sampled data to calculate the cell impedance spectrum.

2. The online impedance spectrum monitoring system for dual-cell shared equalization resistors according to claim 1, characterized in that, The overall circuit uses a dual-cell V B1 and V B2 As the core unit, each is connected to its respective excitation resistor R. eis1 and R eis2 Excitation resistor R eis1 and R eis2 Located between the positive and negative terminals of the power supply, it is used to control the magnitude of the excitation current and the acquisition of the current signal. The common equalization resistor R... bal With V B1 negative electrode and V B2 The positive terminal is connected to the positive terminal, and the other end is connected to the control switch transistors S1 and S2. Switch transistors Sa1, Sb1 and Sa2, Sb2 respectively form the drive circuits for control switches S1 and S2.

3. The online impedance spectrum monitoring system for dual-cell shared equalization resistors according to claim 2, characterized in that, The drive circuit module uses a drive circuit composed of NMOS and PMOS transistors. S1, S2, Sa1, and Sa2 are PMOS transistors, while Sb1 and Sb2 are NMOS transistors. Switches Sa1 and Sb1 are connected to the control signal Vin1, and switches Sa2 and Sb2 are connected to the control signal Vin2. The source of switch Sb1 is connected to the battery V. B1 The negative terminal of the switching transistor Sa1 is connected to the source terminal of the cell V. B1 The positive terminal of the circuit is connected to the drain of switching transistor Sb1 and the drain of switching transistor Sa1, which are connected to Vout1. The drain of switching transistor Sb2 and the drain of switching transistor Sa2 are connected to Vout2. Vout1 and Vout2 are connected to the gate of switch S1 in the equalization circuit. The source of switching transistor Sa2 is connected to the gate of switch S2, and the source of switching transistor Sb2 is connected to the cell V. B2 The negative electrode.

4. A control method for an online impedance spectrum monitoring system for dual-cell shared equalization resistors as described in any one of claims 1-3, characterized in that, The circuit switches between equalization mode and electrochemical impedance spectroscopy monitoring mode by controlling the on / off states of S1 and S2. When S1 is on and S2 is off, the cell V... B1 Entering equalization mode, passive equalization is performed according to the equalization current. The magnitude of the equalization current at this time is... When S1 is closed and S2 is open, cell V B2 Entering equalization mode, the equalization current is at this time. Excitation resistor R eis1 and R eis2 Choose the same resistance value; when S1 and S2 are both turned on, due to the excitation resistor R eis1 and R eis2 Much smaller than the equalization resistance R bal Therefore, it will be in V B1 -R eis1 -S1-S2-R eis2 -V B2 A large excitation current is generated in this circuit, and the magnitude of the excitation current is When R eis1 R eis2 Choose 0.2Ω, R bal With a 30Ω electrode and a cell voltage of 3.2V, the excitation current reaches 16A. By controlling the switching frequency, a corresponding frequency with an amplitude of I is generated in this circuit. eis The impedance spectrum of the battery cell can be plotted by using a pulsed square wave with a measurement range from 0.01Hz to 1KHz and sweeping the frequency at a fixed interval to obtain data from 20-30 frequency points.

5. The control method according to claim 4, characterized in that, The voltage and current waveforms sampled by the voltage and current sampling modules are digitally filtered using the FFT algorithm. The calculation formula is as follows: Where x(n) represents the sampled voltage / current signal, X(k) is the corresponding frequency domain output, N is the total number of sampling points, and j is the imaginary unit. After obtaining the frequency domain data of the voltage and current signals, the impedance is calculated using the following formula. The cell impedance amplitude |Z(f)| and phase angle θ at the corresponding frequency point are obtained.

6. The control method according to claim 4, characterized in that, The voltage sampling module synchronously samples the cell V. B1 and battery cell V B2 The voltage response on the battery cell is used to obtain the impedance data of the two cells, or the voltage response on only one cell is sampled and the impedance data of that cell is calculated.

7. The control method according to claim 4, characterized in that, Two control modes are used to control and generate the EIS excitation square wave: In high-frequency testing scenarios, the system employs a sequential conduction control mode: the control module first applies a fixed high level to the gate of S1, keeping it continuously conducting and forming a stable current path; then, by sending a high-frequency PWM signal to the gate of S2, it controls the high-frequency switching action of S2, and the excitation current flows through V... B1 -R eis1 -S1-S2-R eis2 -V B2 The flow is in this loop, V B2 The amplitude on the cell is the excitation current I eis V B1 The signal amplitude on the battery cell is I eis -I bal1 ; In low-frequency testing scenarios, the system adopts a synchronous conduction control mode: the control unit simultaneously sends fully synchronized PWM signals to the gates of S1 and S2 to ensure that the on / off edges of the two switches are aligned.

8. An online impedance spectrum monitoring system for multiple battery cells sharing a common equalization resistor, characterized in that, It includes multiple sets of dual-cell units, each set of dual-cell units including an equalization circuit module and a drive circuit module as described in any one of claims 1-3, each dual-cell unit being a control unit, and adjacent control units being connected by a common excitation resistor R. eis The connection ensures that the balance between the cells does not affect each other, and a larger impedance detection current is generated by the continuous conduction of multiple control units.

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