Reconfigurable battery pack and battery fault diagnosis method

Abstract

The application discloses a reconfigurable battery pack and a battery fault diagnosis method, which comprises a battery reconfiguration circuit, a battery state acquisition circuit and a controller; the battery reconfiguration circuit is used for controlling series entry or bypass of battery monomers in the battery pack, and completing battery module reconfiguration; the battery state acquisition circuit is used for acquiring voltage and current of any battery monomer under any reconfiguration state of the battery pack; and the controller is used for calculating SOC of the battery according to acquisition data of the battery state acquisition circuit, acquiring equivalent DC internal resistance of the battery through DC pulse discharge test according to the SOC of the battery, and judging whether the battery monomer appears fault according to the equivalent DC internal resistance of the battery. The application has the advantages that whether the battery appears fault is judged by detecting equivalent DC internal resistance of each battery monomer in the battery pack, the battery pack is reconfigured after the fault is found, the fault battery is cut off and the normal battery is connected, and thus the performance of the battery pack is optimized.

Description

Technical Field

[0001] This invention relates to a reconfigurable battery pack and a battery fault diagnosis method, belonging to the field of lithium-ion battery technology. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, energy storage stations, and mobile electronic devices due to their advantages such as high power density, high energy density, and no memory effect. However, after batteries are used in a battery pack, the uniformity of individual cells and aging have a significant impact on the energy utilization efficiency of the battery pack. The failure or performance degradation of individual cells can cause safety hazards to the battery pack. The charge uniformity of fixed-connection topology battery packs can only be adjusted by equalization, but it is powerless to address abnormal aging or even failure of individual cells. Currently, in the study of battery health status, the internal resistance of the battery is an important parameter for measuring the battery's health status. As the number of battery cycles increases, its internal resistance also gradually increases.

[0003] To ensure the performance of the battery pack, it is necessary to identify faulty batteries through diagnostics and promptly remove them from the pack through battery pack reconfiguration. Currently, most related research focuses on the construction of reconfigurable systems or only studies battery fault diagnosis strategies, without considering both aspects in combination. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a reconfigurable battery pack and a battery fault diagnosis method, which has the functions of battery pack reconfiguration, fault diagnosis, and passive equalization, and can solve the problems of individual battery cell faults affecting the overall performance of the battery pack and the inconsistency of the charge of each cell in the battery pack. The reconfigurable circuit hardware includes a battery reconfiguration circuit and a battery status acquisition circuit.

[0005] To solve the above-mentioned technical problems, the present invention provides a reconfigurable battery pack, including: a battery reconfiguration circuit, a battery status acquisition circuit, and a controller;

[0006] The battery reconfiguration circuit is used to perform serial or bypass control on individual battery cells in the battery pack to complete the battery module reconfiguration.

[0007] The battery status acquisition circuit is used to acquire the voltage and current of any individual battery cell under any reconfiguration state of the battery pack.

[0008] The controller is used to calculate the SOC of the battery based on the data collected by the battery state acquisition circuit, obtain the equivalent DC internal resistance of the battery based on the SOC and through a DC pulse discharge test, and determine whether a single battery cell has a fault based on the equivalent DC internal resistance of the battery.

[0009] Furthermore, the battery reconfiguration circuit includes: a plurality of battery circuits connected in sequence; the battery circuit includes a battery cell, a bypass unit, and a test unit;

[0010] The bypass unit and the test unit are connected in parallel to the battery unit, all the battery units are connected in series, all the bypass units are connected in series, and all the test units are connected in series.

[0011] Furthermore, the battery unit includes battery cells connected in series and an access switch; the bypass unit includes a bypass switch; and the test unit includes a test switch connected in series and a test resistor.

[0012] Furthermore, one of the battery cells is a backup battery cell.

[0013] Furthermore, the battery status acquisition circuit includes: a voltage sampling circuit and a current sampling circuit;

[0014] The voltage sampling circuit is used to collect the voltage across each battery cell;

[0015] The current sampling circuit is used to collect the charging and discharging current of a single battery cell.

[0016] Furthermore, the voltage sampling circuit includes: a voltage follower, an inverting proportional amplifier, and an inverting follower;

[0017] The collected battery terminal voltage is sequentially converted into a voltage range that the controller can collect through three stages: a voltage follower, an inverting proportional amplifier, and an inverting follower.

[0018] Furthermore, the current sampling circuit includes: a Hall current sensor and a voltage follower;

[0019] The battery current is converted into a voltage signal by a Hall current sensor, and then input to the controller via a voltage follower.

[0020] A battery fault diagnosis method for a reconfigurable battery pack includes:

[0021] The battery voltage is measured, and the initial SOC of each battery cell is calculated based on the OCV-SOC correspondence curve after long-term static storage.

[0022] When the SOC of the highest SOC cell in the battery pack is in the range of 40%-60%, close the access switch and test switch of each cell in the battery pack to perform a pulse discharge test on all cells in the battery pack.

[0023] Measure the terminal voltage and discharge current of all individual cells in the battery pack during pulse discharge;

[0024] Based on the measured terminal voltage and discharge current of all individual cells in the battery pack during the pulse discharge process, the terminal voltage that drops rapidly at the start of discharge due to the presence of internal resistance is calculated, and the equivalent DC internal resistance of the battery is calculated by dividing it by the discharge current.

[0025] Determine if the resistance value is within the normal range. If it is not within the normal range, then the battery is considered faulty.

[0026] Remove the faulty battery detected and connect a normal backup battery.

[0027] Furthermore, the initial SOC is obtained by combining the open-circuit voltage method and the ampere-hour integration method.

[0028] Furthermore, the calculation of the battery's equivalent DC internal resistance includes:

[0029] The voltage drop and discharge current of the battery during the pulse discharge process are used to determine the voltage drop and discharge current at the battery terminals.

[0030] The equivalent DC internal resistance of the battery is obtained by dividing the voltage drop at the battery terminals by the discharge current.

[0031] Furthermore, the step of determining whether the resistance value is within the normal range, and if it is not within the normal range, then determining it as a faulty battery, includes:

[0032] Obtain the battery's internal resistance R1 at the factory and its internal resistance R2 at the end of its life. If the calculated equivalent DC internal resistance exceeds the range of R1-R2, the battery is judged to be faulty.

[0033] Furthermore, the step of disconnecting the detected faulty battery and connecting a normal backup battery includes:

[0034] Disconnect the power switch of the faulty battery, close its bypass switch to disconnect it, and at the same time disconnect the bypass switch of the backup battery and close its power switch to connect it to the battery pack.

[0035] Furthermore, when the battery pack is at rest, by simultaneously closing the battery access switch and the test switch, the cells with higher charge in the battery pack are discharged through the test resistor to achieve passive balancing.

[0036] Furthermore, the condition for the passive equilibrium is:

[0037] The SOC of each cell in the battery pack is estimated by the open-circuit voltage method. If the SOC difference between the cell with the highest capacity and the cell with the lowest capacity in the battery pack is greater than 3%, passive balancing is performed.

[0038] Furthermore, the passive balancing process includes:

[0039] Select the battery cell with the highest SOC in the battery pack and discharge it until its SOC differs from that of the battery cell with the lowest SOC in the battery pack by less than 3%. The discharge time is calculated using the ampere-hour integration method. After one round of equalization, continue to passively equalize other battery cells in the battery pack that meet the passive equalization conditions until the SOC of all batteries in the battery pack no longer meets the passive equalization conditions.

[0040] The beneficial effects achieved by this invention are as follows:

[0041] This invention determines battery malfunctions by detecting the equivalent DC internal resistance of each individual cell in the battery pack. Upon detection of a malfunction, the battery pack is reconfigured, the faulty cell is removed, and a backup, functioning cell is connected, thereby optimizing battery pack performance. Simultaneously, the test resistor in the battery internal resistance detection circuit can be reused as a discharge resistor for passive battery equalization. By controlling the circuit, higher-charge cells are discharged through the test resistor, improving the consistency of the battery pack. Compared to circuits without fault detection and reconfiguration functions, this invention improves the overall performance and safety of the battery pack. Attached Figure Description

[0042] Figure 1 This is a circuit structure diagram of the present invention;

[0043] Figure 2 This is the topology diagram of the battery pack self-diagnosis reconfiguration circuit;

[0044] Figure 3 This is a schematic diagram of the voltage sampling circuit.

[0045] Figure 4 This is a schematic diagram of the working principle of the current sampling circuit;

[0046] Figure 5 It shows the battery current and voltage curves during pulse discharge;

[0047] Figure 6 This is a diagram of passive equilibrium. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0049] like Figure 1 As shown, a reconfigurable battery pack has the functions of battery pack reconfiguration, fault diagnosis, and passive balancing. It can solve the problems of individual battery cell failure affecting the overall performance of the battery pack and the inconsistent charge of individual cells in the battery pack. It includes: a battery reconfiguration circuit, a battery status acquisition circuit, and a controller.

[0050] Battery reconfiguration circuit: Used to realize the serial insertion and bypass control of specific battery cells in the battery pack, thereby realizing the reconfiguration of the battery module. After a faulty battery is detected in the battery pack, the faulty battery is disconnected and a spare battery is connected to the battery pack. In addition, the battery can be discharged to the test resistor by controlling the switch to perform passive equalization.

[0051] Battery reconfiguration circuit, such as Figure 2 As shown, it includes:

[0052] The system consists of batteries C1, C2, C3, C4, C5, C6, and C7; bypass switches S21, S22, S23, S24, S25, S26, and S27; access switches S11, S12, S13, S14, S15, S16, and S17; test switches S31, S32, S33, S34, S35, S36, and S37; and test resistors R31, R32, R33, R34, R35, R36, and R37.

[0053] Each individual battery cell is connected in series to a switch, and both are connected in parallel to a bypass switch. This bypass method connects the faulty battery without affecting the charging and discharging of the other batteries. A battery test switch and a test resistor are connected in series and then in parallel with the bypass switch. During battery discharge testing and passive equalization, the bypass switch for that battery is opened, and its test switch and charging switch are closed, allowing the battery to discharge through the test resistor. The circuit contains seven batteries in total, one of which is a spare.

[0054] Battery Status Acquisition Circuit: This circuit acquires the voltage and current of each individual battery cell under any reconfigurable state of the battery pack, thereby determining the battery's equivalent DC internal resistance as a criterion for diagnosing faults. The battery status acquisition circuit includes a voltage sampling circuit and a current sampling circuit. The voltage sampling circuit includes a voltage follower, an inverting proportional amplifier, and an inverting follower, directly acquiring the terminal voltage of each battery cell. The differential operational amplifier uses the AD620ARZ-REEL chip with dual power supply mode to achieve voltage following; the inverting proportional amplifier and operational amplifier use LM358P dual-channel operational amplifier chips. Figure 3 As shown, the voltage signal is reduced by half, making it conform to the acquisition range of the microcontroller's ADC corresponding to the controller. Figure 4 As shown, the current sampling circuit is used to collect the battery discharge current and transmit it to the microcontroller. The battery current is converted into a voltage signal by the ACS712 Hall current sensor, and then input to the microcontroller through the voltage follower.

[0055] The microcontroller corresponding to the controller is used to calculate the battery's SOC based on the data collected by the battery status acquisition circuit, obtain the battery's equivalent DC internal resistance based on the battery's SOC and through a DC pulse discharge test, and determine whether a single battery cell has a fault based on the battery's equivalent DC internal resistance.

[0056] Battery internal resistance is an important factor in measuring battery health. To improve the overall performance of the battery pack, this reconfiguration circuit determines whether a battery is faulty by detecting the equivalent DC internal resistance of each cell. Once a faulty battery is detected, it is disconnected and connected to a normal backup battery.

[0057] A battery fault diagnosis method based on a reconfigurable battery pack includes:

[0058] (1) The initial SOC of the battery is estimated by combining the open-circuit voltage method and the ampere-hour integration method.

[0059] (2) When the SOC of the highest SOC cell in the battery pack is in the range of 40%-60%, close the access switch and test switch of each battery cell in the battery pack to perform a pulse discharge test on the battery. During the test, turn on its access switch and test switch to discharge the battery to the test resistor for 10s.

[0060] (3) Measure the battery voltage and discharge current during the discharge process. The voltage and current curves are shown in the figure. Figure 5 As shown. After applying a discharge current pulse, the battery voltage rapidly decreases from Va to Vb, then slowly decreases. After 10 seconds of discharge, the test switch is disconnected, and the voltage quickly recovers and gradually stabilizes. The detection circuit samples the voltage and current for 25ms, continuously acquiring the battery voltage and current status during the discharge process.

[0061] (4) The drop in battery terminal voltage during discharge is caused by the battery internal resistance. Therefore, the equivalent DC internal resistance of the battery can be obtained by dividing the voltage difference Va-Vb by the discharge current.

[0062] (5) The internal resistance of a battery can reflect its health status to a certain extent. As the number of battery cycles increases, its internal resistance will continue to increase. Based on this, determine whether the battery resistance value calculated in step (4) is within the normal range. Assume that the battery's internal resistance at the factory is R1 and its internal resistance at the end of its lifespan is R2. If the battery's internal resistance is found to be outside the range of R1-R2, the battery is considered faulty.

[0063] (6) Disconnect the connection switch of the faulty battery and close its bypass switch to disconnect it. At the same time, disconnect the bypass switch of the backup battery and close its connection switch to connect it to the battery pack.

[0064] This method allows for passive equalization of the battery pack while it is stationary, improving the consistency of each individual cell. A schematic diagram of the passive equalization process is shown below. Figure 6 As shown. After estimating the SOC of each battery cell using the open-circuit voltage method, if the SOC difference between the battery with the highest and lowest charge levels in the battery pack is greater than 3%, its charging switch and test switch are closed to discharge it through the test resistor until its SOC differs from that of the battery with the lowest charge level in the battery pack by less than 3%. The discharge time of the passive equalization process is calculated using the ampere-hour integration method. After this process ends, this method is used to passively equalize other batteries with higher charge levels in the battery pack until the SOC of all batteries in the battery pack tends to be consistent.

[0065] This circuit has a passive battery balancing function. When the battery pack is idle, by simultaneously closing the battery charging switch and the test switch, the cells with higher charge in the battery pack are discharged through the test resistor, thereby achieving charge balancing and improving the consistency of charge of each cell in the battery pack.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A reconfigurable battery pack, characterized in that, include: Battery reconfiguration circuit, battery status acquisition circuit, and controller; The battery reconfiguration circuit is used to perform serial or bypass control on individual battery cells in the battery pack to complete the battery module reconfiguration. The battery status acquisition circuit is used to acquire the voltage and current of any individual battery cell under any reconfiguration state of the battery pack. The controller is used to calculate the SOC of the battery based on the data collected by the battery state acquisition circuit, obtain the equivalent DC internal resistance of the battery based on the SOC and through a DC pulse discharge test, and determine whether a single battery cell is faulty based on the equivalent DC internal resistance of the battery. The battery reconfiguration circuit includes: a plurality of battery circuits connected in sequence; the battery circuit includes a battery cell, a bypass unit, and a test unit; The bypass unit and the test unit are connected in parallel to the battery unit, all the battery units are connected in series, all the bypass units are connected in series, and all the test units are connected in series. The battery unit includes individual battery cells connected in series and an access switch; the bypass unit includes a bypass switch; the test unit includes a test switch connected in series and a test resistor. One of the battery cells is a backup battery cell.

2. The reconfigurable battery pack according to claim 1, characterized in that, The battery status acquisition circuit includes: a voltage sampling circuit and a current sampling circuit; The voltage sampling circuit is used to collect the voltage across each battery cell; The current sampling circuit is used to collect the charging and discharging current of a single battery cell.

3. The reconfigurable battery pack according to claim 2, characterized in that, The voltage sampling circuit includes: a voltage follower, an inverting proportional amplifier, and an inverting follower; The collected battery terminal voltage is sequentially converted into a voltage range that the controller can collect through three stages: a voltage follower, an inverting proportional amplifier, and an inverting follower.

4. The reconfigurable battery pack according to claim 2, characterized in that, The current sampling circuit includes: a Hall current sensor and a voltage follower; The battery current is converted into a voltage signal by a Hall current sensor, and then input to the controller via a voltage follower.

5. A battery fault diagnosis method based on the reconfigurable battery pack according to claim 1, characterized in that, include: The battery voltage is measured, and the initial SOC of each battery cell is calculated based on the OCV-SOC correspondence curve after long-term static storage. When the SOC of the highest SOC cell in the battery pack is in the range of 40%-60%, close the access switch and test switch of each cell in the battery pack to perform a pulse discharge test on all cells in the battery pack. Measure the terminal voltage and discharge current of all individual cells in the battery pack during pulse discharge; Based on the measured terminal voltage and discharge current of all individual cells in the battery pack during the pulse discharge process, the terminal voltage that drops rapidly at the start of discharge due to the presence of internal resistance is calculated, and the equivalent DC internal resistance of the battery is calculated by dividing it by the discharge current. Determine whether the equivalent DC internal resistance is within the normal range. If it is not within the normal range, then the battery is considered faulty. Remove the faulty battery detected and connect a normal backup battery; The calculation of the battery's equivalent DC internal resistance includes: determining the voltage drop at the battery terminals and the discharge current using the battery voltage and discharge current collected during the pulse discharge process; and dividing the voltage drop at the battery terminals by the discharge current to obtain the battery's equivalent DC internal resistance. The step of determining whether the equivalent DC internal resistance is within the normal range, and if it is not within the normal range, then it is determined to be a faulty battery, includes: obtaining the battery's internal resistance R1 at the time of manufacture and its internal resistance R2 at the end of its lifespan; if the calculated equivalent DC internal resistance exceeds the range of R1-R2, then it is determined to be a faulty battery. The step of disconnecting the detected faulty battery and connecting a normal backup battery includes: disconnecting the connection switch of the faulty battery, closing its bypass switch to disconnect it, and simultaneously disconnecting the bypass switch of the backup battery and closing its connection switch to connect it to the battery pack.

6. The battery fault diagnosis method according to claim 5, characterized in that, The initial SOC is obtained by combining the open-circuit voltage method and the ampere-hour integration method.

7. The battery fault diagnosis method according to claim 5, characterized in that, When the battery pack is at rest, by simultaneously closing the battery access switch and the test switch, the cells with higher charge in the battery pack are discharged through the test resistor to achieve passive balancing.

8. The battery fault diagnosis method according to claim 7, characterized in that, The conditions for the passive equilibrium are: The SOC of each cell in the battery pack is estimated by the open-circuit voltage method. If the SOC difference between the cell with the highest capacity and the cell with the lowest capacity in the battery pack is greater than 3%, passive balancing is performed.

9. The battery fault diagnosis method according to claim 8, characterized in that, The passive balancing process includes: Select the battery cell with the highest SOC in the battery pack and discharge it until its SOC differs from that of the battery cell with the lowest SOC in the battery pack by less than 3%. The discharge time is calculated using the ampere-hour integration method. After one round of equalization, continue to passively equalize other battery cells in the battery pack that meet the passive equalization conditions until the SOC of all batteries in the battery pack no longer meets the passive equalization conditions.

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