A battery pack balancing system and method

Abstract

This invention proposes a battery pack balancing system and method. Based on an existing balancing circuit, a parallel balancing circuit is added, and a first and a second differential pressure threshold are set. If the first differential pressure threshold is less than the second, the balancing strategy corresponding to the first differential pressure threshold is activated first. Once the second differential pressure threshold is reached, the balancing strategy corresponding to the second differential pressure threshold is activated. Furthermore, the activation or deactivation of the balancing circuit is controlled according to the temperature of the internal resistance in the balancing circuit. By switching between the first and second balancing circuits, the balancing current can be increased or decreased, further reducing balancing time and extending battery life.

Description

Technical Field

[0001] This invention belongs to the field of battery balancing technology, and particularly relates to a battery pack balancing system and method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With continuous technological iteration and innovation, new energy vehicles have gained widespread consumer acceptance. However, due to factors such as cell self-discharge and vehicle operating conditions, significant differences in the voltage of individual cells within the battery system emerge after a period of driving, primarily manifested as an increasing voltage difference between cells. Initially, a fixed threshold is typically designed for the individual cell voltage difference range of the battery system. Under normal operating conditions, the battery system's performance remains unaffected within this threshold, and the Battery Management System (BMS) can ignore the increasing voltage difference trend within this threshold. However, when the cell voltage difference exceeds the initially designed threshold, the BMS intervenes, treating the large voltage difference as a system fault and uploading it to the BMS. The BMS then takes appropriate action, typically derating the battery system's output power; in severe cases, it may force the battery system to shut down, significantly impacting user experience and affecting the battery system's cycle life.

[0004] Currently, the conventional approach to addressing large cell voltage differences involves balancing strategies, including active and passive balancing strategies. Passenger vehicles typically employ passive balancing. A passive balancing strategy involves the Battery Management System (BMS) detecting an increasing trend in the cell voltage difference within the battery pack. It then uses a balancing resistor and a small current discharge method to create a closed-loop discharge circuit for a specific string of cells with higher voltage, continuing until the voltage of that high-voltage cell drops back to near the levels of the other cells.

[0005] However, this passive balancing scheme has drawbacks. Since the resistance value of the balancing resistor is fixed, the balancing current is also fixed. If the balancing current is designed to be too large, it will cause the local temperature of the balancing resistor to become too high and terminate the balancing process. If the balancing current is designed to be too small, although it can ensure that the internal resistance of the balancing resistor will not overheat, it will prolong the voltage balancing time and cause the system to have insufficient balancing capability. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a battery pack balancing system and method, which achieves variable balancing current (i.e., increases or decreases) by switching back and forth between a first balancing circuit and a second balancing circuit, thereby further reducing balancing time and extending battery life.

[0007] The specific technical solution adopted in this application is as follows:

[0008] A first aspect of this application provides a battery pack balancing system, the system comprising:

[0009] A battery pack consists of multiple individual battery cells;

[0010] The first and second equalization circuits, connected in parallel, are disposed at both ends of the single cell.

[0011] The analog front end is used to collect the voltage of the individual battery cells, as well as the temperature of the equalization internal resistance in the first equalization circuit and the second equalization circuit.

[0012] The battery management system, connected to the analog front end, is configured to: activate one of the equalization circuits corresponding to the individual battery cell to be equalized when the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold; and activate both the first equalization circuit and the second equalization circuit corresponding to the individual battery cell to be equalized when the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold; wherein the preset first voltage difference upper limit threshold is less than the preset second voltage difference upper limit threshold.

[0013] Optionally, both the first equalization circuit and the second equalization circuit include a resistor and a MOS switch. One end of the resistor is connected to the negative terminal of the single cell, the other end of the resistor is connected to the input terminal of the MOS switch, the output terminal of the MOS switch is connected to the positive terminal of the single cell, and the gate of the MOS switch is connected to the analog front end.

[0014] Optionally, the battery management system is configured to: after the vehicle is powered on, read whether there is a historical fault where the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold; if so, control the first equalization circuit corresponding to the individual battery to start.

[0015] Optionally, the battery management system is configured to: after the vehicle is powered on, read whether there is a historical fault where the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold; if so, control both the first equalization circuit and the second equalization circuit corresponding to the individual battery cell to start.

[0016] Optionally, the battery management system is configured to: after the vehicle is powered on, read whether there is a historical fault where the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold, or a historical fault where the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold; if neither exists, then no equalization start command is issued.

[0017] Optionally, the battery management system is configured to: when the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold, control the first equalization circuit corresponding to the single cell to be equalized to start; during the voltage equalization process of the first equalization circuit and the second equalization circuit, when the equalization resistance temperature of the first equalization circuit or the equalization resistance temperature of the second equalization circuit is not less than a preset second temperature threshold, control the second equalization circuit to shut down.

[0018] Optionally, the battery management system is configured to: during the voltage balancing process of the first balancing circuit, when the internal resistance temperature of the first balancing circuit is not greater than a preset first temperature threshold, control the second balancing circuit to start.

[0019] Another aspect of this application provides a battery pack balancing method, including the following steps:

[0020] A first equalization circuit and a second equalization circuit are connected in parallel on a single cell.

[0021] Determine whether the voltage difference of the battery pack is greater than the preset first voltage difference upper limit threshold. If so, activate one of the equalization circuits corresponding to the individual battery cell to be equalized.

[0022] Determine whether the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold. If so, then connect the first equalization circuit and the second equalization circuit corresponding to the individual cell to be equalized; wherein, the preset first voltage difference upper limit threshold is less than the preset second voltage difference upper limit threshold.

[0023] Optionally, it also includes: after the vehicle is powered on, detecting whether there is a historical fault where the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold; if so, then activating the first equalization circuit corresponding to the individual battery; detecting whether there is a historical fault where the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold; if so, then activating the first equalization circuit and the second equalization circuit corresponding to the individual battery.

[0024] Optionally, it further includes: when the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold, the first equalization circuit corresponding to the single cell is turned on; during the voltage equalization process of the first equalization circuit and the second equalization circuit, when the equalization resistance temperature of the first equalization circuit or the equalization resistance temperature of the second equalization circuit is not less than a preset second temperature threshold, the second equalization circuit corresponding to the single cell is turned off; when the equalization resistance temperature of the first equalization circuit is not greater than the preset first temperature threshold, the second equalization circuit is turned on.

[0025] The above one or more technical solutions have the following beneficial effects:

[0026] In this invention, a parallel equalization circuit is added to the existing equalization circuit, and a first and a second differential pressure upper limit threshold are set. If the first differential pressure upper limit threshold is less than the second differential pressure upper limit threshold, then when the equalization strategy is triggered, the equalization strategy corresponding to the first differential pressure upper limit threshold is activated first. The equalization strategy corresponding to the second differential pressure upper limit threshold is then activated after the second differential pressure upper limit threshold is reached. By switching back and forth between the first and second equalization circuits, the equalization current can be increased or decreased, further reducing the equalization time and extending battery life.

[0027] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0029] Figure 1 A battery pack balancing system topology diagram provided in this application embodiment;

[0030] Figure 2 A schematic diagram of the balancing system principle of a battery pack provided in an embodiment of this application;

[0031] Figure 3 This is a flowchart of a battery pack balancing method provided in an embodiment of this application. Detailed Implementation

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0034] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0035] This application provides a battery pack balancing system, such as... Figure 1 As shown, the system includes:

[0036] A battery pack consists of multiple individual battery cells;

[0037] The first and second equalization circuits are connected in parallel and set at both ends of the individual battery cell;

[0038] The analog front end is used to collect the voltage of a single cell, as well as the temperature of the equalization internal resistance in the first and second equalization circuits.

[0039] The battery management system, connected to the equalization simulation front end, is configured to: activate one of the equalization circuits corresponding to the individual battery cell to be equalized when the differential pressure of the battery pack is greater than a preset first differential pressure upper limit threshold; and activate both the first and second equalization circuits corresponding to the individual battery cell to be equalized when the differential pressure of the battery pack is greater than a preset second differential pressure upper limit threshold; wherein the preset first differential pressure upper limit threshold is less than the preset second differential pressure upper limit threshold.

[0040] A single battery cell refers to a single battery unit, also commonly called a battery cell or individual cell. In the early stages of development, the voltage difference range of a single battery cell in a battery system is typically designed with a fixed threshold. Under normal operating conditions, the battery system's performance is unaffected by this threshold. However, when the voltage difference exceeds the initially designed threshold, a balancing strategy is needed to derating the battery system's output power.

[0041] Current passive balancing strategies use a balancing resistor and a small current discharge method to discharge a string of high-voltage cells in a closed loop until the voltage of the high-voltage cell drops back to a level close to that of the other cells. However, since the resistance of the balancing resistor is fixed, the balancing current is also fixed. This can lead to problems such as excessively high balancing current causing the balancing resistor to overheat and terminate balancing, while insufficient balancing current will prolong the voltage balancing time and result in inadequate balancing capability.

[0042] This application adds a parallel equalization circuit to the existing equalization circuit and sets a first and a second upper limit threshold for differential pressure. If the first upper limit threshold is less than the second upper limit threshold, the equalization strategy corresponding to the first upper limit threshold will be activated first. Once the second upper limit threshold is reached, the equalization strategy corresponding to the second upper limit threshold will be activated. Furthermore, the activation or deactivation of the equalization circuit is controlled according to the temperature of the equalization internal resistance within the equalization circuit. By switching between the first and second equalization circuits, the equalization current can be increased or decreased, further reducing the equalization time and extending battery life.

[0043] like Figure 2 As shown, the first equalization circuit and the second equalization circuit each include a switching transistor and a resistor. This application takes the use of a MOS switching transistor as an example for illustration. The input terminal of the first MOS switching transistor in the first equalization circuit is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the negative terminal of the single cell. The output terminal of the first MOS switching transistor is connected to the positive terminal of the single cell, and the gate of the first MOS switching transistor is connected to the analog front end.

[0044] Similarly, in the second equalization circuit, the input terminal of the second MOS switch is connected to one end of resistor R2, and the other end of resistor R2 is connected to the negative terminal of the single cell; the output terminal of the second MOS switch is connected to the positive terminal of the single cell, and the gate of the second MOS switch is connected to the analog front end.

[0045] Typically, a battery pack may include one single cell, or two or more single cells. The first equalization circuit and the second equalization circuit correspond to one single cell and are used to equalize the voltage of that single cell.

[0046] For example, the first single cell corresponds to a first equalization circuit and a second equalization circuit connected in parallel within a first group. In the first equalization circuit within the first group, the input terminal of the first switch is connected to one end of a first resistor, and the other end of the first resistor is connected to the negative terminal of the first single cell. The output terminal of the first switch is connected to the positive terminal of the first single cell, and the gate of the first switch is connected to an analog front end. In the second equalization circuit within the first group, the input terminal of the second switch is connected to one end of a second resistor, and the other end of the second resistor is connected to the negative terminal of the first single cell. The output terminal of the second switch is connected to the positive terminal of the first single cell, and the gate of the second switch is connected to an analog front end.

[0047] Similarly, the second single cell corresponds to the first and second equalization circuits connected in parallel within the second group. The input terminal of the third switch in the first equalization circuit of the second group is connected to one end of the third resistor, and the other end of the third resistor is connected to the negative terminal of the second single cell. The output terminal of the third switch is connected to the positive terminal of the second single cell, and the gate of the third switch is connected to the analog front end. The input terminal of the fourth switch in the second equalization circuit of the second group is connected to one end of the fourth resistor, and the other end of the fourth resistor is connected to the negative terminal of the second single cell. The output terminal of the fourth switch is connected to the positive terminal of the second single cell, and the gate of the fourth switch is connected to the analog front end.

[0048] The analog front end is used to collect voltage data for each individual cell, as well as the temperature of the equalization internal resistance in the first and second equalization circuits corresponding to each individual cell.

[0049] This application sets two upper limit thresholds for differential pressure: a first upper limit threshold V1 and a second upper limit threshold V2. These two thresholds describe the current differential pressure in the battery system. The first upper limit threshold V1 < the second upper limit threshold V2. This means that when the equalization strategy is triggered, the equalization strategy at level V1 is activated first, while the equalization strategy at level V2 is not activated. The equalization current at level V2 is greater than the equalization current at level V1, i.e., I... V1 <I V2 .

[0050] The battery management system is configured to: activate the first equalization circuit corresponding to the individual cell to be equalized when the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold; and activate both the first equalization circuit and the second equalization circuit when the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold.

[0051] In this embodiment, the analog front-end is also used to collect the temperature of the equalization internal resistance in the first and second equalization circuits, and sets two temperature thresholds, namely a first temperature threshold T1 and a second temperature threshold T2. The first temperature threshold T1 and the second temperature threshold T2 are calibration values ​​from the initial development stage. The first temperature threshold T1 represents the temperature threshold at normal temperature, and the second temperature threshold T2 represents the temperature threshold at high temperature. Furthermore, the second temperature threshold T2 generally only appears after the V2 level equalization is started, because the equalization current increases, according to I... 2 When R = Q, the resistance will generate more heat.

[0052] When the temperature of the equalization resistance of the first equalization circuit or the temperature of the equalization resistance of the second equalization circuit is not less than the preset second temperature threshold, the battery management system controls the second equalization circuit to shut down. At this time, only the first equalization circuit works. Due to the increase in internal resistance, according to Ohm's law I=U / R, the current will decrease. At this time, the equalization current will decrease. As time increases, the temperature of the equalization internal resistance will return to or below the first temperature threshold T1. At this time, the second equalization circuit restarts until equalization is completed.

[0053] In this embodiment of the application, by setting a first temperature threshold and a second temperature threshold, the start or stop of the equalization circuit is controlled, thereby avoiding the problem of the equalization circuit terminating due to excessively high local temperature.

[0054] like Figure 3 As shown in the embodiments of this application, the equalization method of the battery pack equalization system also includes:

[0055] Step 1: After the vehicle is powered on, the battery management system reads the memory to check for any historical faults with large trigger voltage differences, and then proceeds to the next step.

[0056] Step 2: If there are no historical faults with large voltage differences in the memory, the battery management system (BMS) will not issue a start-up equalization command;

[0057] Step 3: If the memory stores historical faults of large differential pressure triggered by a single cell, the battery management system (BMS) will determine whether the first differential pressure upper limit threshold V1 or the second differential pressure upper limit threshold V2 was triggered.

[0058] It should be noted that historical data refers to the data from the last power-off to the current power-on. If a large differential pressure fault exists and will not disappear before power-on, then steps 1-3 will be performed to read and judge the historical data. If the vehicle has been stationary for a long time and the large differential pressure problem has indeed disappeared, then no action will be taken.

[0059] Step 4: If the first differential pressure upper limit threshold V1 is triggered, the battery management system (BMS) issues a command to the analog front-end (AFE) to start the first equalization circuit, and the equalization is started.

[0060] Step 5: If the second differential pressure upper limit threshold V2 is triggered, the battery management system (BMS) issues an instruction to the analog front-end (AFE) to start the first and second equalization circuits, and the equalization is started.

[0061] Step 6: During the balancing process, the analog front-end AFE monitors the temperature of the balancing resistor R1 in the first balancing circuit and the balancing resistor R2 in the second balancing circuit in real time. If the temperature of either balancing resistor is greater than or equal to the second temperature threshold T2, the analog front-end AFE uploads the over-temperature information of the balancing resistor to the battery management system (BMS). After receiving the feedback from the analog front-end AFE that the balancing resistor temperature is greater than or equal to the second temperature threshold T2, the battery management system (BMS) issues a command to shut down the second balancing circuit to the analog front-end AFE. After receiving the command from the battery management system (BMS), the analog front-end AFE executes the action of shutting down the second balancing circuit, and the first balancing circuit works alone. At this time, because the balancing resistor in the balancing circuit increases, according to Ohm's law I = U / R, the current in the first balancing circuit decreases, so the temperature of the balancing internal resistance R1 in the first balancing circuit will decrease.

[0062] Step 7: Similarly, when the first equalization circuit is working, the analog front-end AFE monitors the temperature of the equalization resistor R1 in the first equalization circuit in real time. When the temperature of the equalization resistor R1 in the first equalization circuit is less than or equal to the first temperature threshold T1, the analog front-end AFE will report the temperature of the equalization resistor R1 in the first equalization circuit to the battery management system BMS. After receiving the feedback from the analog front-end AFE that the temperature of the equalization resistor R1 in the first equalization circuit is less than or equal to the first temperature threshold T1, the battery management system BMS issues an instruction to start the second equalization circuit to the analog front-end AFE. After receiving the instruction from the battery management system BMS, the analog front-end AFE executes the action of starting the second equalization circuit. At this time, the first equalization circuit and the second equalization circuit work simultaneously.

[0063] Step 8: Repeat the above steps until balancing is complete.

[0064] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only.

[0065] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A battery pack balancing system, characterized in that, The system includes: A battery pack consists of multiple individual battery cells; The first and second equalization circuits, connected in parallel, are disposed at both ends of the single cell. The analog front end is used to collect the voltage of the individual battery cells, as well as the temperature of the equalization internal resistance in the first equalization circuit and the second equalization circuit. A battery management system, connected to the analog front end, is configured to: activate one of the equalization circuits corresponding to the individual battery cell to be equalized when the voltage difference of the battery pack exceeds a preset first voltage difference upper limit threshold; activate both the first and second equalization circuits corresponding to the individual battery cell to be equalized when the voltage difference of the battery pack exceeds a preset second voltage difference upper limit threshold; wherein the preset first voltage difference upper limit threshold is less than the preset second voltage difference upper limit threshold; activate the first equalization circuit corresponding to the individual battery cell to be equalized when the voltage difference of the battery pack exceeds the preset first voltage difference upper limit threshold; activate the second equalization circuit when the equalization resistance temperature of the first or second equalization circuit is not less than a preset second temperature threshold during voltage equalization of the first and second equalization circuits; and activate the second equalization circuit when the equalization internal resistance temperature in the first equalization circuit is not greater than a preset first temperature threshold during voltage equalization of the first equalization circuit.

2. The battery pack balancing system as described in claim 1, characterized in that, Both the first equalization circuit and the second equalization circuit include a resistor and a MOS switch. One end of the resistor is connected to the negative terminal of the single cell, and the other end of the resistor is connected to the input terminal of the MOS switch. The output terminal of the MOS switch is connected to the positive terminal of the single cell, and the gate of the MOS switch is connected to the analog front end.

3. The battery pack balancing system as described in claim 1, characterized in that, The battery management system is configured to: after the vehicle is powered on, read whether there is a historical fault where the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold; if so, control the first equalization circuit corresponding to the individual battery cell to start.

4. The battery pack balancing system as described in claim 1, characterized in that, The battery management system is configured to: after the vehicle is powered on, read whether there is a historical fault where the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold; if so, control the first equalization circuit and the second equalization circuit corresponding to the individual battery cell to start.

5. The battery pack balancing system as described in claim 1, characterized in that, The battery management system is configured to: after the vehicle is powered on, read whether there is a historical fault where the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold, or a historical fault where the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold. If neither exists, then no equalization start command is issued.

6. A battery pack balancing method, characterized in that, Includes the following steps: A first equalization circuit and a second equalization circuit are connected in parallel on a single cell. Determine whether the voltage difference of the battery pack is greater than the preset first voltage difference upper limit threshold. If so, activate one of the equalization circuits corresponding to the individual battery cell to be equalized. Determine whether the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold. If so, then connect the first equalization circuit and the second equalization circuit corresponding to the individual cell to be equalized. Wherein, the preset first voltage difference upper limit threshold is less than the preset second voltage difference upper limit threshold. When the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold, the first equalization circuit corresponding to the individual battery is turned on; during the voltage equalization process of the first equalization circuit and the second equalization circuit, when the equalization resistance temperature of the first equalization circuit or the equalization resistance temperature of the second equalization circuit is not less than a preset second temperature threshold, the second equalization circuit corresponding to the individual battery is turned off; when the equalization resistance temperature of the first equalization circuit is not greater than a preset first temperature threshold, the second equalization circuit is turned on.

7. The battery pack balancing method as described in claim 6, characterized in that, Also includes: After the vehicle is powered on, it is detected whether there is a historical fault where the voltage difference of the battery pack is greater than a preset first voltage difference upper limit threshold. If so, the first equalization circuit corresponding to the individual battery is turned on. It is also detected whether there is a historical fault where the voltage difference of the battery pack is greater than a preset second voltage difference upper limit threshold. If so, the first equalization circuit and the second equalization circuit corresponding to the individual battery are turned on.

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