Method and system for suppressing circulating current of multi-branch power battery system based on ampere-hour integral difference

Abstract

The application belongs to the technical field of power batteries, and particularly relates to a multi-branch power battery system circulating current suppression method and system based on ampere-hour integral difference, which comprises the following steps: collecting parallel branch currents in real time and calculating cumulative ampere-hour integrals; calculating the difference between the ampere-hour integral of each branch and the average ampere-hour integral of all branches; when the integral difference of a certain branch exceeds a first threshold value, disconnecting the main relay of the branch and closing the pre-charging relay, so that the current flows through a large-power pre-charging resistor in series to reduce the current of the branch; when the integral difference falls within a second threshold value, closing the main relay and disconnecting the pre-charging relay, and bypassing the resistor. The application can realize active suppression of circulating current by using only pre-charging circuit elements, without adding a DC / DC converter, and has the advantages of low cost, small energy loss, simple and reliable control, and is suitable for the whole charging and discharging process, which can effectively improve the consistency, safety and service life of the multi-branch parallel battery system.

Description

Technical Field

[0001] This invention belongs to the field of power battery technology, specifically relating to a method and system for suppressing circulating current in a multi-branch power battery system based on ampere-hour integral difference. Background Technology

[0002] High-capacity power battery systems are widely used in electric vehicles and energy storage power stations. To meet power and capacity requirements, multiple battery branches are often connected in parallel. However, in actual engineering, the internal resistance, aging level, operating temperature, and state of charge of each battery branch are rarely completely consistent. This inconsistency directly leads to the generation of unbalanced currents between parallel branches. The problems caused by unbalanced currents are quite obvious: on the one hand, they cause additional energy loss; on the other hand, they accelerate the aging of some battery branches, and in severe cases, they may even cause thermal runaway accidents. Therefore, how to effectively suppress circulating currents between parallel branches has always been an important issue in the design of battery management systems.

[0003] Several technical solutions have been proposed and applied to address this issue.

[0004] CN111009949A proposes a current sharing control method for parallel lithium battery packs. The core idea is to adjust the charging and discharging capacity by actively regulating the system connection impedance of each branch, keeping the current in each branch as consistent as possible. CN106953391A employs a strategy of directly comparing the real-time current differences between each branch. Once an instantaneous current deviation is detected, the connected resistor is adjusted. Both schemes share a common characteristic: the control is based on instantaneous current or voltage values, aiming to make the current in each branch as equal as possible at any given moment. This control logic frequently triggers relays in actual operation because the instantaneous current value is significantly affected by load fluctuations, measurement noise, and other factors. Repeated relay switching not only increases system losses but also accelerates device fatigue. More importantly, equal instantaneous current does not mean that the accumulated charge passing through each branch is balanced; the long-term ampere-hour integral deviation between branches is not improved simply by leveling the instantaneous current.

[0005] Another approach is active balancing. CN116707076A proposes an active balancing method based on SOC (State of Charge), which uses a bidirectional DC / DC converter to transfer energy between branches, moving energy from branches with higher SOC to branches with lower SOC. This method effectively suppresses circulating current, but at the cost of requiring additional power converters, significantly increasing the overall system cost and size. The control strategy also becomes more complex, making its engineering implementation and subsequent maintenance costs high in large-scale energy storage systems.

[0006] Furthermore, the pre-charge resistor is actually a standard feature in power battery systems. It is typically used only to limit the surge current at the moment the system is powered on, and is bypassed after pre-charging is complete, with virtually no further regulatory function during subsequent operation. Existing technologies also utilize the pre-charge resistor for voltage balancing during battery cluster connection, but these are mostly limited to the startup or connection phase and lack the ability to continuously monitor and dynamically adjust throughout the entire charging and discharging process. In actual operation, factors such as different aging rates and uneven temperature distribution among the various branches will continuously lead to a gradual increase in the cumulative charge deviation, making balancing during the startup phase far from sufficient.

[0007] In summary, existing technical solutions each have their limitations: methods based on instantaneous current comparison result in frequent relay operation and discrepancies between control objectives and actual needs; solutions based on DC / DC converters are costly and structurally complex; the utilization value of pre-charge resistors has not been fully realized, and there is a lack of a dynamic adjustment mechanism that can be implemented throughout the entire operation process. Summary of the Invention

[0008] The purpose of this invention is to provide a circulating current suppression method and system for multi-branch power battery systems based on ampere-hour integral difference. It aims to solve the problems of frequent relay operation caused by reliance on instantaneous current comparison in existing technologies, or the high cost caused by the use of DC / DC converters. It achieves dynamic circulating current suppression and inter-branch cumulative charge balance in the entire charging and discharging process of multi-branch parallel battery systems in a low-cost, low-complexity and low-loss manner.

[0009] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a circulating current suppression method for a multi-branch power battery system based on ampere-hour integral difference, comprising the following steps: Step S1: Real-time acquisition of instantaneous current values ​​of each parallel battery branch. ,in = 1,2,…,n, where n is the total number of parallel branches; Step S2: Integrate the current of each branch over time to obtain the cumulative ampere-hour integral of each branch. ; Step S3: Calculate the difference between the ampere-hour integral of each branch and the average ampere-hour integral of all branches. ; Step S4: Determine whether the ampere-hour integral difference of each branch exceeds the preset first threshold; Step S5: For a branch whose ampere-hour integral difference exceeds the first threshold, disconnect the main relay of the branch and simultaneously close the pre-charge relay of the branch, so that the current of the branch flows through the high-power pre-charge resistor connected in series with the pre-charge relay to reduce the current of the branch. Step S6: Continuously monitor the ampere-hour integral difference of this branch. When it falls back to within the preset second threshold, close the main relay of this branch and open the pre-charge relay of this branch to bypass the high-power pre-charge resistor. Step S7: Repeat steps S1 to S6.

[0010] Preferably, the first threshold includes a first positive threshold. and the first negative threshold - The second threshold includes a second positive threshold. Second negative threshold ,in < ; Under discharge conditions, when the ampere-hour integral difference of a certain branch is greater than the first positive threshold... When the branch is identified as a high-discharge branch, a resistor is connected in series; when the ampere-hour integral difference of the branch falls back to the second positive threshold... When the following occurs, the resistor is removed; Under charging conditions, the charging current is defined as negative. When the ampere-hour integral difference of a certain branch is less than the first negative threshold, the charging current is considered negative. When the branch is identified as a high-charge branch, a resistor is connected in series; when the ampere-hour integral difference of the branch rises back to the second negative threshold... When the above is reached, remove the resistor.

[0011] Preferably, the calculation of the ampere-hour integral difference in step S3 is alternatively based on the branch with the smallest ampere-hour integral, and the difference between the ampere-hour integral of each branch and the ampere-hour integral of the benchmark branch is calculated.

[0012] Preferably, the resistance value of the high-power pre-charge resistor is determined based on the system's rated voltage, rated current, and maximum allowable branch voltage deviation; a recommended resistance value is... ,in The maximum allowable branch voltage deviation, This is the system's rated current.

[0013] Preferably, the main relay and the precharge relay are replaced with power electronic switching devices.

[0014] Preferably, the high-power pre-charge resistor is configured as a multi-level adjustable resistor, and different resistance values ​​are dynamically switched according to the magnitude of the ampere-hour integral difference to achieve graded current limiting adjustment.

[0015] Preferably, the cumulative ampere-hour integration in step S2 is calculated using a moving window integration method to calculate the recent cumulative deviation.

[0016] The present invention also discloses a circulating current suppression system for a multi-branch power battery system based on ampere-hour integral difference, comprising: at least two parallel battery branches, each branch including a battery pack, a current sensor, a main relay, a pre-charge relay and a high-power pre-charge resistor, wherein the pre-charge relay and the high-power pre-charge resistor are connected in series and then connected in parallel with the main relay; A central controller, electrically connected to the current sensors, main relays, and precharge relays of each branch, is used to perform the following operations: Receive the instantaneous current values ​​of each branch collected by each current sensor, and calculate the cumulative ampere-hour integral of each branch; Calculate the difference between the ampere-hour integral of each branch and the average ampere-hour integral of all branches; When the ampere-hour integral difference of a certain branch exceeds the preset first threshold, the main relay of that branch is controlled to open and the pre-charge relay is controlled to close, so that the current flows through the high-power pre-charge resistor. When the integral difference of the branch falls back to within the preset second threshold, the main relay of the branch is closed and the precharge relay is opened, and the high-power precharge resistor is bypassed.

[0017] Preferably, the central controller is an automotive-grade MCU.

[0018] Preferably, the central controller is also used to perform current validity detection, and to prohibit relay switching operations when an abnormal current sampling is detected.

[0019] The beneficial effects of this invention are as follows: This invention employs a hysteresis comparison control strategy based on the ampere-hour integral difference, using the deviation between the cumulative ampere-hour integral of each branch and the average value as the criterion. It achieves circulating current suppression using only the existing pre-charge relays and pre-charge resistors in the battery system, eliminating the need for additional active balancing equipment such as DC / DC converters. This significantly reduces system hardware costs and size while avoiding the reliability risks that active balancing control may bring. Since the resistor is only briefly connected when the ampere-hour integral difference exceeds the first threshold and has a bidirectional hysteresis threshold (second threshold less than the first threshold) exit mechanism, compared to schemes based on instantaneous current comparison, it avoids frequent relay operation, thus extending their service life, and greatly reduces the reliability risks associated with long-term resistor operation in traditional passive balancing methods. The energy loss caused by the series insertion is far less than that of the continuous equalization scheme. At the same time, the method and system are uniformly applicable to the entire charging and discharging process, and can dynamically adjust the current of each branch in real time to reduce the ampere-hour integral difference between branches, thereby indirectly improving the consistency of the state of charge (SOC) of each branch. It effectively suppresses the circulating current and unbalanced current caused by the inconsistency of branch internal resistance, aging degree, temperature and SOC, thereby reducing the risk of accelerated battery aging and thermal runaway, and helping to extend the overall service life and safety of the battery pack. In addition, the control method is based on the cumulative domain control of ampere-hour integral rather than instantaneous domain control, which does not require complex filtering algorithms or system identification, has low computational load, and is easy to implement in real time on embedded platforms such as automotive-grade MCUs, and has good engineering practicality and promotion value. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the topology of the circulating current suppression system for a multi-branch power battery system provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the branch structure of the multi-branch power battery system circulating current suppression system under the resistor series insertion operation state provided in the embodiment of the present invention; Figure 3 This is a control flowchart of the circulating current suppression method for a multi-branch power battery system based on ampere-hour integral difference provided in an embodiment of the present invention; Figure 4 This is a comparison chart of the current change curves of the two branches before and after the connection resistor, provided in an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. The term "connection" should be interpreted broadly; for example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a signal connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] like Figure 1 As shown, the present invention provides a circulating current suppression system for a multi-branch power battery system based on ampere-hour integral difference, including at least two parallel battery branches (this embodiment uses two branches as an example for illustration, but the present invention is not limited to this and can be extended to n branches, n≥2).

[0024] Each branch includes: battery packs (B1, B2), current sensors (CS1, CS2), main relays (K1_main, K2_main), precharge relays (K1_pre, K2_pre), and high-power precharge resistors (R1, R2). The precharge relays and precharge resistors are connected in series and then in parallel with the main relays. Taking branch 1 as an example, the positive terminal of battery pack B1 is connected to the positive terminal of the DC bus via current sensor CS1 and main relay K1_main; the precharge relay K1_pre and precharge resistor R1 are connected in series and then in parallel across the main relay K1_main. The negative terminals of all branches are connected to the negative terminal of the DC bus. The central controller (MCU / ECU) is electrically connected to the control terminals of each current sensor, main relay, and precharge relay to receive current signals and execute relay on / off control.

[0025] like Figure 3 As shown, the circulating current suppression method for multi-branch power battery systems based on ampere-hour integral difference provided by the present invention includes the following steps: Step S1: Real-time acquisition of current in each branch.

[0026] The instantaneous current value of each branch is obtained by using a current sensor. ,in = 1,2,…,n, where n is the total number of parallel branches. The current sensor can be a Hall effect current sensor or a shunt, and the sampling frequency is preferably 100Hz to 1000Hz to ensure effective capture of dynamic current changes.

[0027] Step S2: Calculate the ampere-hour integral for each branch.

[0028] The central controller integrates the current of each branch over time to obtain the cumulative ampere-hours for each branch: ; In the formula, t0 is the system's start time or the last time the integral was cleared.

[0029] Step S3: Calculate the ampere-hour integral difference between branches.

[0030] Calculate the difference between each branch and the average ampere-hour integral of all branches: ; As an alternative, the branch with the smallest ampere-hour integral can be used as the benchmark, and the difference between each branch and the benchmark can be calculated.

[0031] Step S4: Determine whether a series resistor is needed.

[0032] Under discharge conditions (defining the discharge current as positive), if the ΔAh of a certain branch... i Greater than the preset first positive threshold (This indicates that the cumulative discharge of the branch is significantly higher than the average level), so the branch is determined to be a "high discharge branch" and its discharge current needs to be reduced.

[0033] Under charging conditions (defining the charging current as negative), if the ΔAh of a certain branch... i Less than the preset first negative threshold - If the absolute value of its accumulated charging capacity is significantly higher than the average level, then the branch is determined to be a "high charging capacity branch" and its charging current needs to be reduced.

[0034] First threshold The value is determined based on factors such as battery system capacity and allowable imbalance, with a preferred range of 0.05 Ah to 1 Ah. Second threshold The exit threshold is less than the first threshold, preferably in the range of 0.01Ah to 0.1Ah.

[0035] Step S5: Dynamically insert a high-power resistor.

[0036] For branches identified as having high discharge or high charge, the central controller sends a control signal to disconnect the main relay of that branch and simultaneously close its pre-charge relay, forcing the branch current to flow through the high-power pre-charge resistor in series (e.g., Figure 2 (As shown). After the resistor is connected in series, the equivalent impedance of the branch increases, and the branch current decreases significantly, thereby slowing down the rate at which its ampere-hour integral increases in the direction of increasing deviation.

[0037] The value of the pre-charge resistor is determined based on the system's rated voltage, rated current, and maximum allowable branch voltage deviation. It is recommended to calculate it using the following formula: in, The maximum allowable branch voltage deviation (e.g., 20V). The rated current of the system is 400A (e.g., 400A). In practical applications, a power resistor can be selected in the range of 0.02Ω to 0.1Ω, and a heat sink or forced air cooling can be provided.

[0038] Step S6: Monitor and exit the resistor.

[0039] The central controller continuously monitors the ΔAh of this branch. i : Under discharge conditions, when ΔAh i Falling back to the second positive threshold+ ( < When below; Under charging conditions, when ΔAh i Rebound to the second negative threshold - (i.e., absolute value less than) When above ); The central controller sends a control signal to close the main relay of the branch, then disconnects the pre-charge relay, bypasses the pre-charge resistor, and restores the normal low-impedance path.

[0040] Step S7: Execute repeatedly.

[0041] Repeat steps S1 to S6 to achieve real-time dynamic suppression of the circulation.

[0042] Example 1: Discharge Condition like Figure 1 As shown, taking a power battery system with two parallel branches as an example, branches 1 and 2 are completely symmetrical in circuit structure. Each branch includes: battery packs (B1, B2), current sensors (CS1, CS2), main relays (K1_main, K2_main), precharge relays (K1_pre, K2_pre), and precharge resistors (R1, R2). The precharge resistors are all 0.05Ω with a rated power of 8kW. The central controller uses an automotive-grade MCU to drive the coils of each relay through I / O ports.

[0043] In the initial state of the system, the main relays of both branches are closed, the pre-charge relay is open, the pre-charge resistor is bypassed, and the system discharges normally. The initial state of charge (SOC) of the battery packs in both branches is similar, and the open-circuit voltage is basically the same.

[0044] Operation process: (1) At the initial moment, the voltages of the two branches are similar, the current of branch 1 is about 200A, the current of branch 2 is about 208A, and the initial value of the ampere-hour integral of both branches is 0Ah.

[0045] (2) After the system runs for 100 seconds, the ampere-hour integral of branch 1, Ah1 ≈ 5.556 Ah, and the ampere-hour integral of branch 2, Ah2 ≈ 5.774 Ah. The average ampere-hour integral of the two branches is approximately 5.665 Ah, and the difference between branch 2 and the average is ΔAh2 = 5.774 - 5.665 = 0.109 Ah. A preset first threshold is established. =0.1Ah, second threshold =0.02Ah.

[0046] (3) The ampere-hour integral of branch 2 is higher than the average value and the difference exceeds the first threshold of 0.1Ah. The central controller judges that branch 2 is a high discharge branch.

[0047] (4) The central controller sends a drive signal: closes the pre-charge relay K2_pre of branch 2, and at the same time disconnects the main relay K2_main of branch 2. The current of branch 2 is forced to flow through the pre-charge resistor R2 (0.05Ω). Due to the increase in branch impedance after the series resistor is added, the current of branch 2 drops to about 198A; at the same time, the current of branch 1 rises to about 210A.

[0048] (5) After the resistor is connected in series, the current in branch 2 decreases, and its ampere-hour integral growth rate slows down. After about 54 seconds of continuous monitoring, the difference between the ampere-hour integral of branch 2 and the average value is reduced to ΔAh2≈0.019Ah, which is lower than the second threshold of 0.02Ah.

[0049] (6) The central controller sends a drive signal: first closes the main relay K2_main of branch 2, and then disconnects the pre-charge relay K2_pre of branch 2. Branch 2 restores the low impedance path, and the currents of the two branches tend to return to a balanced state.

[0050] (7) The system continuously monitors the current and ampere-hour integral of each branch and repeats the above adjustment process, such as Figure 4 The comparison of the current variation curves of the two branches is shown.

[0051] Example 2: Charging Condition During charging, the charging current is defined as negative. The central controller collects the instantaneous charging current (negative value) of each branch through the current sensor, and calculates the cumulative ampere-hour integral (negative value) of each branch using the same integration method.

[0052] During system operation, if a branch has a lower internal resistance or lower state of charge (SOC), resulting in a larger charging current, its ampere-hour integral will deviate negatively from the average value. Taking a two-branch system as an example, assuming the charging current of branch 2 is -210A and the charging current of branch 1 is -200A, after 100 seconds of operation, the ampere-hour integral of branch 1, Ah1 ≈ -5.556Ah, and the ampere-hour integral of branch 2, Ah2 ≈ -5.833Ah, with an average value of approximately -5.695Ah. The difference between branch 2 and the average value, ΔAh_2 = -5.833 - (-5.695) = -0.138Ah.

[0053] Preset first negative threshold - =-0.1Ah, and the ΔAh2=-0.138Ah of branch 2 is less than -0.1Ah, so the central controller determines that branch 2 is a high-charge branch. The controller then disconnects the main relay K2_main of branch 2 and simultaneously closes the pre-charge relay K2_pre, connecting the pre-charge resistor R2 in series with branch 2. After the resistor is connected in series, the equivalent impedance of branch 2 increases, the charging current decreases (the absolute value decreases), and the rate of negative growth of its ampere-hour integral slows down.

[0054] The central controller continuously monitors ΔAh2 of branch 2, and when it rises back to the second negative threshold - When the value is above -0.02Ah (i.e., ΔAh2≥-0.02Ah), the controller first closes the main relay K2_main, then opens the precharge relay K2_pre, bypasses the precharge resistor, and restores branch 2 to normal charging state.

[0055] Example 3: Selection and Thermal Management of Pre-charge Resistor The choice of pre-charge resistance value directly affects the circulating current suppression effect and system energy consumption. This invention recommends selecting the appropriate value based on the following principles: in V max For the maximum permissible branch voltage deviation (e.g., 20V), I max For the system's rated current (e.g., 400A), R = 0.05Ω. In practical applications, a power resistor can be selected in the range of 0.02Ω to 0.1Ω, and equipped with a heat sink or forced air cooling.

[0056] In the above embodiments, the main relay and pre-charge relay can be replaced by power electronic switching devices such as MOSFETs and IGBTs. Power electronic switches have advantages such as fast operation, no mechanical contacts, and no electric arc, enabling faster turn-on and turn-off. When using power electronic switches, the control signal is output from the PWM port of the central controller, amplified by the drive circuit, and then controls the gate or base of the switching device.

[0057] The pre-charge resistor can be configured with a multi-level adjustable structure, achieving dynamic switching of different resistance values ​​through multiple resistors connected in series and parallel and switching combinations. The central controller can apply different resistance values ​​in stages according to the magnitude of the ampere-hour integral difference: when ΔAh i When the resistance value is slightly exceeded (slightly exceeding the first threshold), a smaller resistance value is applied. When ΔAh i When the current exceeds the first threshold, a larger resistance value is applied to achieve graded current limiting regulation, thereby further optimizing the balance between energy loss and control effect.

[0058] The calculation of the ampere-hour integral difference is not limited to comparing with the average value of all branches. Alternatively, a fixed reference branch can be selected (for example, always using the branch with the smallest ampere-hour integral as the benchmark), and the difference between each branch and the benchmark branch can be calculated. When the difference between a branch and the benchmark branch exceeds a first threshold, a resistor is connected in series with that branch; when the difference shrinks to within a second threshold, the resistor is removed.

[0059] The calculation of cumulative ampere-hour integrals is not limited to full-cycle integration starting from the system's initial moment; a moving window integration method can be used, calculating only the cumulative deviation within the most recent window. Moving window integration can more sensitively reflect recent imbalance trends and avoid threshold triggering delays caused by historical cumulative effects. The window duration can be dynamically adjusted according to system operating conditions, with an optimal range of 1 to 30 minutes.

[0060] A current validity detection mechanism can be added to the control strategy. After each sampling, the central controller verifies the rationality of the current value. When the current sampling value is detected to be outside the normal range (such as exceeding 1.5 times the maximum system current or being below -1.5 times) or an abnormal jump occurs, it is determined to be an abnormal current sampling, the relay switching operation is prohibited, and a fault alarm signal is issued to avoid malfunctions due to inaccurate ampere-hour integration caused by abnormal sampling.

[0061] Using the circulating current suppression method and system provided by this invention, measured data of a two-branch parallel system under discharge conditions show that: without this invention, the current deviation between the two branches continues to increase, reaching more than 8A after 100 seconds, and the ampere-hour integral deviation continues to accumulate; with this invention, when the ampere-hour integral difference exceeds the first threshold, a resistor is actively connected in series, the branch current deviation is effectively limited, the ampere-hour integral difference is controlled within the second threshold, and the imbalance between branches is significantly reduced during the dynamic operation of the system.

[0062] Calculations show that the pre-charging resistor is only briefly engaged when the ampere-hour integral difference exceeds the threshold, resulting in a significantly lower total energy loss compared to continuous passive balancing. Furthermore, since no additional power conversion equipment such as a DC / DC converter is required, the system cost is significantly lower than that of active balancing schemes, and the control logic is simple and easy to implement in a battery management system (BMS).

[0063] For those skilled in the art, various improvements and modifications can be made without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention.

Claims

1. A method for suppressing circulating current in a multi-branch power battery system based on ampere-hour integral difference, characterized in that, Includes the following steps: Step S1: Real-time acquisition of instantaneous current values ​​of each parallel battery branch. ,in = 1,2,…,n, where n is the total number of parallel branches; Step S2: Integrate the current of each branch over time to obtain the cumulative ampere-hour integral of each branch. ; Step S3: Calculate the difference between the ampere-hour integral of each branch and the average ampere-hour integral of all branches. ; Step S4: Determine whether the ampere-hour integral difference of each branch exceeds the preset first threshold; Step S5: For a branch whose ampere-hour integral difference exceeds the first threshold, disconnect the main relay of the branch and simultaneously close the pre-charge relay of the branch, so that the current of the branch flows through the high-power pre-charge resistor connected in series with the pre-charge relay to reduce the current of the branch. Step S6: Continuously monitor the ampere-hour integral difference of this branch. When it falls back to within the preset second threshold, close the main relay of this branch and open the pre-charge relay of this branch to bypass the high-power pre-charge resistor. Step S7: Repeat steps S1 to S6.

2. The circulating current suppression method for a multi-branch power battery system based on ampere-hour integral difference according to claim 1, characterized in that, The first threshold includes a first positive threshold. and the first negative threshold - The second threshold includes a second positive threshold. Second negative threshold ,in < ; Under discharge conditions, when the ampere-hour integral difference of a certain branch is greater than the first positive threshold... When the branch is identified as a high-discharge branch, a resistor is connected in series; when the ampere-hour integral difference of the branch falls back to the second positive threshold... When the following occurs, the resistor is removed; Under charging conditions, the charging current is defined as negative. When the ampere-hour integral difference of a certain branch is less than the first negative threshold, the charging current is considered negative. When the branch is identified as a high-charge branch, a resistor is connected in series; when the ampere-hour integral difference of the branch rises back to the second negative threshold... When the above is reached, remove the resistor.

3. The circulating current suppression method for a multi-branch power battery system based on ampere-hour integral difference according to claim 1, characterized in that, The calculation of the ampere-hour integral difference in step S3 is alternatively based on the branch with the smallest ampere-hour integral, and the difference between the ampere-hour integral of each branch and the ampere-hour integral of the benchmark branch is calculated.

4. The circulating current suppression method for a multi-branch power battery system based on ampere-hour integral difference according to claim 1, characterized in that, The resistance value of the high-power pre-charge resistor is determined based on the system's rated voltage, rated current, and maximum allowable branch voltage deviation. A recommended resistance value is... ,in The maximum allowable branch voltage deviation, This is the system's rated current.

5. The circulating current suppression method for a multi-branch power battery system based on ampere-hour integral difference according to claim 1, characterized in that, The main relay and the precharge relay are replaced with power electronic switching devices.

6. The circulating current suppression method for a multi-branch power battery system based on ampere-hour integral difference according to claim 1, characterized in that, The high-power pre-charge resistor is configured as a multi-level adjustable resistor, which dynamically switches different resistance values ​​according to the magnitude of the ampere-hour integral difference to achieve graded current limiting adjustment.

7. The circulating current suppression method for a multi-branch power battery system based on ampere-hour integral difference according to claim 1, characterized in that, The cumulative ampere-hour integration in step S2 is calculated using a moving window integration method to calculate the recent cumulative deviation.

8. A circulating current suppression system for a multi-branch power battery system based on ampere-hour integral difference, characterized in that, include: At least two parallel battery branches, each branch including a battery pack, a current sensor, a main relay, a pre-charge relay and a high-power pre-charge resistor, wherein the pre-charge relay and the high-power pre-charge resistor are connected in series and then connected in parallel with the main relay; The central controller is electrically connected to the current sensor, main relay, and precharge relay of each branch, and is used to perform the following operations: receive the instantaneous current value of each branch collected by each current sensor, calculate the cumulative ampere-hour integral of each branch; and calculate the difference between the ampere-hour integral of each branch and the average ampere-hour integral of all branches. When the ampere-hour integral difference of a certain branch exceeds a preset first threshold, the main relay of that branch is controlled to open and the pre-charge relay is controlled to close, so that the current flows through the high-power pre-charge resistor; when the ampere-hour integral difference of that branch falls back to within a preset second threshold, the main relay of that branch is controlled to close and the pre-charge relay is controlled to open, so that the high-power pre-charge resistor is bypassed.

9. The circulating current suppression system for a multi-branch power battery system based on ampere-hour integral difference according to claim 8, characterized in that, The central controller is an automotive-grade MCU.

10. The circulating current suppression system for a multi-branch power battery system based on ampere-hour integral difference according to claim 8, characterized in that, The central controller is also used to perform current validity detection, and to prohibit relay switching operations when an abnormal current sampling is detected.

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