A switching control method for bypass switches in the charging and discharging process of a series battery pack system

Abstract

The application provides a switching control method for bypass switches in the charging and discharging process of a series battery pack system, comprising: obtaining voltage and current information of each battery unit and judging the charging and discharging state of the battery unit; for the battery unit in the charging or discharging state, if the voltage reaches a preset charging cutoff voltage, a switch A connected in series with the battery unit is gradually turned off, and a switch B connected in parallel with the battery unit is gradually turned on, so that the battery unit is bypassed; in the process of switching the switch A and the switch B, the on-resistance of the switch A and the switch B is adjusted, so that the current flowing through the turned-off switch gradually decreases to zero, the current flowing through the turned-on switch gradually increases, the total current of the switch A and the switch B is kept constant, the total current is the charging current of the system, soft switching of the bypass switch is realized, and the charging and discharging process of the battery pack is kept continuous, so that the stability of the whole system is realized.

Description

Technical Field

[0001] The present invention relates to the field of electronic equipment or battery energy storage equipment, and more particularly to a switching control method for a bypass switch during the charging and discharging process of a series battery pack system. Background Art

[0002] In electronic devices or battery energy storage devices, as the total battery capacity increases, a series battery pack system is often used without changing the rated current of the system. However, due to the inconsistency of the series batteries, the effective total battery capacity will decrease. Therefore, the invention patent No. 202310819802.4 "A Battery Management System and Method" and the invention patent No. 202311225112.2 "A Chip Management System for a Multi-cell Series Battery Structure" propose using a set of switches to implement the bypass battery function. This not only solves the problem of a decrease in the effective capacity of the series battery pack caused by the performance degradation of a single battery cell, but also avoids the failure of the entire battery string caused by the failure of a single battery cell. In addition, the switch can be switched to achieve the effect of fast charging and deep discharge of the entire battery string.

[0003] During the charging process of the entire battery string, if one of the batteries is fully charged first, the switch will bypass this battery and no longer charge it, but the other batteries will continue to charge, achieving a fast charging effect; during the discharging process of the entire battery string, if one of the batteries is discharged first, the switch will bypass this battery and no longer discharge it, but the other batteries can continue to discharge, achieving a full discharge effect.

[0004] During the charging or discharging process, the battery status is usually judged by detecting the battery voltage and current to determine whether the battery needs to be bypassed. Due to the internal resistance of the battery itself, the battery voltage and current will suddenly change before and after being bypassed.

[0005] During charging, the battery voltage increases due to the charging current before the battery is bypassed, and then drops suddenly after the battery is bypassed. Conversely, during discharging, the battery voltage decreases due to the discharge current before the battery is bypassed, and then rises suddenly after the battery is bypassed. On the one hand, sudden changes in battery voltage can easily cause the corresponding voltage monitoring circuit to make incorrect judgments, requiring more complex state control to avoid errors. On the other hand, sudden changes in current can also cause instantaneous high voltage on the switch due to parasitic effects, which can damage the switch.

[0006] In summary, how to effectively solve the problem of system instability caused by abnormal voltage of battery unit during the charging and discharging process of the series battery pack system, especially how to realize smooth switching of the bypass switch, accurately control the current change, avoid voltage fluctuation and current impact, and ensure the safety and reliability of the battery unit and the entire system, is the core technical problem to be solved at present. SUMMARY

[0007] The purpose of the present application is to solve the above-mentioned problems caused by voltage and current mutation when using a switch to switch the battery bypass function. A switching control method for bypass switches in the charging and discharging process of a series battery pack system is proposed. Through a soft switching method, the voltage and current change of the battery during switching is changed from rapid mutation to continuous gradual change, thereby avoiding the potential risk of voltage mutation in the system.

[0008] The technical solution of the present application is:

[0009] The present application provides a switching control method for bypass switches in the charging and discharging process of a series battery pack system. The battery pack system includes a plurality of series-connected battery modules. The battery module includes a switch A, a switch B, a battery unit, and a controller. The switch A and the battery unit are connected in series to form a branch. The switch A is used to control the conduction and shutdown of the battery unit. The switch B is connected in parallel with the series branch formed by the switch A and the battery unit. The switch B is used to control whether the battery unit is bypassed. The controller is connected to the switch A, the switch B, and the battery unit, and is used to acquire voltage signals across the battery unit, the switch A, and the switch B, and to control the on-off of the switch A and the switch B. The switching control method includes the following steps:

[0010] Obtain the voltage and current information of each battery unit and determine the charging and discharging state of the battery unit.

[0011] For a battery unit in charging or discharging state, if its voltage reaches a preset charging cutoff voltage, control the switch A connected in series with the battery unit to gradually turn off, and control the switch B connected in parallel with the battery unit to gradually turn on, thereby realizing the bypass of the battery unit.

[0012] During the switching process of the switch A and the switch B, the on-resistance of the switch A and the switch B is adjusted to gradually reduce the current flowing through the disconnected switch to zero, while gradually increasing the current flowing through the connected switch, and keeping the total current of the switch A and the switch B constant. The total current is the charging current of the system, thereby realizing soft switching of the bypass switch.

[0013] Further, the determination of the charging and discharging state of the battery unit includes:

[0014] comparing the real-time voltage value of each battery cell with a preset charging cutoff voltage threshold value, if the real-time voltage value is less than or equal to the charging cutoff voltage threshold value, and the current flows from the positive terminal of the battery into the battery, it is determined that the battery cell is in the charging state;

[0015] comparing the real-time voltage value of each battery cell with a preset discharging cutoff voltage threshold value, if the real-time voltage value is greater than or equal to the discharging cutoff voltage threshold value, and the current flows from the positive terminal of the battery into the battery, it is determined that the battery cell is in the discharging state.

[0016] Further, the control switch A is gradually turned off and the control switch B is gradually turned on, including:

[0017] For the battery cell in the charging or discharging state, when the on-off switch is switched from switch A to switch B, the control voltage VG_B of switch B is gradually increased to change from the off state to the on state, and the on-resistance gradually decreases, while the control voltage of switch A is gradually reduced, and the on-resistance gradually increases.

[0018] Further, in the process of adjusting the on-resistance of switch A and switch B, the current flowing through switch A is detected in real time, and when the current approaches zero, the control voltage of switch A is pulled down to a preset low level, and the control voltage of switch B is pulled up to a preset high level, switch A is completely turned off, and switch B is completely turned on.

[0019] Further, in the process of adjusting the on-resistance of switch A and switch B, the control voltage VG_B of switch B is adjusted to approach the threshold voltage VTH, and then the control voltage VG_B is gradually increased;

[0020] Synchronously keep the control voltage VG_A of switch A close to constant, and detect the current of switch A in real time, when the current of switch A approaches zero, the control voltage of switch A is pulled to a preset low level, switch A is completely turned off, and then the control voltage of switch B is pulled up to a preset high level, switch B is turned on to a low resistance state.

[0021] Further, the speed of the control voltage VG_B of switch B before reaching the threshold voltage VTH is greater than the speed of the control voltage VG_B after reaching the threshold voltage VTH.

[0022] Further, the total current of switch A and switch B is kept constant, including:

[0023] Obtaining the charging and discharging current target value of the series battery pack; detecting the sum of the current values flowing through switch A and switch B in real time; controlling the on-resistance of switch A and switch B, so that the sum of the current flowing through switch A and the current flowing through switch B is equal to the charging and discharging current target value of the system.

[0024] Further, the switch A and the switch B are field effect tubes, and the conduction resistance of the switch A and the switch B is controlled by adjusting the gate voltage.

[0025] Advantages of the present application:

[0026] The present application realizes the soft switching of the bypass switch, the conduction resistance of the switch A and the switch B is accurately controlled, the current is gradually changed, the total current of the system is kept constant, the voltage fluctuation and the system instability caused by the sudden change of the current are effectively avoided, the safety and reliability of the battery pack system are improved, the battery life is prolonged, and the charging and discharging efficiency is optimized.

[0027] The present application discloses a switching control method of a bypass switch suitable for a series battery pack system in the charging and discharging process, and aims to solve the problem of system instability caused by voltage abnormality of the battery unit in the charging and discharging process. In the switching process, the controller detects the sum of the currents flowing through the switch A and the switch B in real time, and adjusts the conduction resistance of the switch to ensure the constant total current, so that the charging and discharging process of the battery pack is kept continuous, thereby realizing the stability of the whole system.

[0028] Other features and advantages of the present application will be described in detail in the following specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0029] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which:

[0030] Figure 1 A structure schematic diagram of a series battery pack system is shown.

[0031] Figure 2 A single battery module charging structure schematic diagram according to one embodiment of the present application is shown.

[0032] Figure 3 A single battery module discharging structure schematic diagram according to one embodiment of the present application is shown.

[0033] Figure 4 One of the control voltage and switch current corresponding relationship schematic diagrams in the process of gradually turning off the switch A and gradually turning on the switch B according to one embodiment of the present application is shown.

[0034] Figure 5 The second of the control voltage and switch current corresponding relationship schematic diagrams in the process of gradually turning off the switch A and gradually turning on the switch B according to one embodiment of the present application is shown. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present application will be described in more detail with reference to the drawings. Although the preferred embodiments of the present application are shown in the drawings, it is understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein.

[0036] As Figure 1-3 illustrated, the present application provides a switching control method for bypass switch in charging and discharging process of series battery pack system, the battery pack system includes a plurality of series connected battery modules, the battery module includes switch A, switch B, battery cell and controller, the switch A and battery cell are connected in series to form a branch, the switch A is used to control the on and off of the battery cell; switch B is connected in parallel with the series branch formed by switch A and battery cell, the switch B is used to control whether the battery cell is bypassed; the controller is connected with switch A, switch B and battery cell, used to acquire voltage signal of battery cell, switch A and switch B, and control on and off of switch A and switch B; the switching control method includes the following steps:

[0037] acquiring voltage and current information of each battery cell, and judging the charging and discharging state of the battery cell;

[0038] for the battery cell in charging or discharging state, if the voltage reaches the preset charging cutoff voltage, the switch A connected in series with the battery cell is controlled to be gradually turned off, and the switch B connected in parallel with the battery cell is controlled to be gradually turned on, to realize the bypass of the battery cell;

[0039] in the process of controlling the switching of switch A and switch B, by adjusting the on-resistance of switch A and switch B, the current flowing through the turned-off switch is gradually reduced to zero, and the current flowing through the turned-on switch is gradually increased, and the total current of switch A and switch B is kept constant, the total current is the charging current of the system, to realize the soft switching of the bypass switch.

[0040] In this embodiment, as Figure 1 illustrated, the minimum unit is composed of battery, switch A and switch B and controller, wherein the controller controls the state of switch A and B by detecting the voltage signal of battery voltage, voltage signal of switch A / B, in the process of charging ( Figure 2 ) or discharging ( Figure 3 ) of the battery. In particular, the on-resistance of the switch is controlled in the process of closing to opening, or opening to closing, to realize safer switching.

[0041] Figure 2, is the charging process of the battery, the voltage across the battery is V1, V1=RCxI_A+VC, RC is the internal resistance of the battery, VC is the open circuit voltage of the battery, when the battery voltage is full, it is necessary to disconnect switch A through VG_A, and at the same time, switch B is turned on through VG_B; when switch A is disconnected, because the current I_A becomes 0, then V1 will be lower than before RCxI_A, especially when I_A is relatively large, the change of V1 will reach tens or hundreds of millivolts, which often also leads to the error of the controller to estimate the state of the battery (such as capacity); therefore, the method of the application provides a control loop, so that switch A is slowly disconnected, that is, I_A slowly becomes 0, and at the same time, switch B is slowly turned on, that is, I_B slowly changes from 0 to I_C, in the whole switching process, I_A+I_B=I_C, and I_C is the charging current of the system; this will make the charging current of the system not change due to the switching of the switch, that is, it can ensure that the system continuously charges with a relatively constant current;

[0042] Figure 3 , is the discharging process of the battery, the voltage across the battery is V1, V1=VC-RCxI_A, RC is the internal resistance of the battery, VC is the open circuit voltage of the battery, when the battery voltage is full, it is necessary to disconnect switch A through VG_A, and at the same time, switch B is turned on through VG_B; when switch A is disconnected, because the current I_A becomes 0, then V1 will be higher than before RCxI_A, especially when I_A is relatively large, the change of V1 will reach tens or hundreds of millivolts, which often also leads to the error of the controller to estimate the state of the battery (such as capacity); therefore, the method of the application provides a control loop, so that switch A is slowly disconnected, that is, I_A slowly becomes 0, and at the same time, switch B is slowly turned on, that is, I_B slowly changes from 0 to I_C, in the whole switching process, I_A+I_B=I_C, and I_C is the discharging current of the system; this will make the discharging current of the system not change due to the switching of the switch, that is, it can ensure that the system continuously discharges with a relatively stable current.

[0043] In one example, the judging the charging and discharging state of the battery unit comprises:

[0044] Comparing the real-time voltage value of each battery unit with the preset charging cut-off voltage threshold value, which is usually 4.2V for lithium batteries, if the real-time voltage value is less than or equal to the charging cut-off voltage threshold value, and the current flows from the positive terminal of the battery into the battery, it is determined that the battery unit is in the charging state;

[0045] Compare the real-time voltage value of each battery cell with the preset discharge cut-off voltage threshold, which is usually 3.0V for lithium batteries. If the real-time voltage value is greater than or equal to the discharge cut-off voltage threshold and current flows out of the battery from the positive terminal, the battery cell is determined to be in a discharge state.

[0046] In this embodiment, the battery's charge and discharge status are confirmed through dual determination of voltage and current, providing a reliable basis for subsequent battery management. Setting appropriate voltage thresholds for different battery types ensures that each battery can be charged and discharged at optimal conditions, thereby improving the performance and reliability of the entire battery system.

[0047] In one example, the control switch A is gradually disconnected and the control switch B is gradually turned on, including: for a battery cell in a charging or discharging state, when the on-switch is switched from switch A to switch B, the control voltage VG_B of switch B is gradually increased to change it from an off state to an on state, and the on-resistance gradually decreases, and at the same time, the control voltage VG_A of switch A is gradually reduced to gradually increase its on-resistance.

[0048] like Figure 4 As shown in FIG. 1 , it is a schematic diagram of the corresponding relationship between the control voltage and the switch current in the process of gradually disconnecting the control switch A and gradually turning on the control switch B. Figure 4 It is a nonlinear change diagram.

[0049] During the process of adjusting the on-resistance of switches A and B, the current flowing through switch A is detected in real time. When the current approaches zero, the control voltage of switch A is lowered to a preset low level, for example, VG_A=V1, and the control voltage of switch B is raised to a preset high level, for example, VG_B=V1, to completely turn off switch A and completely turn on switch B.

[0050] like Figure 5 The figure shows the second schematic diagram of the corresponding relationship between the control voltage and the switch current during the process of gradually disconnecting the control switch A and gradually turning on the control switch B. Figure 5 It is a linear change diagram.

[0051] In the process of adjusting the on-resistance of switch A and switch B, the control voltage VG_B of switch B is adjusted to be close to the threshold voltage VTH, and then the control voltage VG_B is gradually increased; the increase rate of the control voltage VG_B of switch B before reaching the threshold voltage VTH is greater than the increase rate of the control voltage VG_B after reaching the threshold voltage VTH;

[0052] The control voltage VG_A of switch A is kept nearly constant, and the current of switch A is detected in real time. When the current of switch A approaches zero, that is, when V1=V2, the control voltage of switch A is pulled to a preset low level to completely disconnect switch A. Then, the control voltage of switch B is pulled up to a preset high level to turn on switch B to a low-impedance state.

[0053] In one example, maintaining the total current of switch A and switch B constant includes:

[0054] Obtain a target charge and discharge current value of the series battery pack; detect the sum of the current values ​​flowing through switch A and switch B in real time; and control the on-resistance of switch A and switch B so that the sum of the current flowing through switch A and the current flowing through switch B is equal to the target charge and discharge current value of the system.

[0055] In this embodiment, the target charge and discharge current value I_C for the series battery pack is obtained and stored in the controller memory. Current sensors detect the current I_A flowing through switch A and the current I_B flowing through switch B in real time, obtaining the real-time values ​​of I_A and I_B. Based on the detection results, the sum of I_A and I_B is calculated to obtain the total current I_total.

[0056] If I_total is not equal to I_C, the current adjustment value ΔI is calculated based on the difference I_C - I_total. The on-resistance adjustment direction of switches A and B is determined based on ΔI, resulting in the target on-resistance values ​​R_A and R_B.

[0057] The controller outputs voltage signals VG_A and VG_B, adjusting the on-resistance of switches A and B to R_A and R_B. The battery voltage V1 is detected in real time, and the difference between V1 and the battery open-circuit voltage VC is calculated to obtain the internal resistance voltage drop RCI_A. If the rate of change of RCI_A exceeds a preset threshold, the output rates of VG_A and VG_B are adjusted based on the rate of change to obtain a new regulation rate. The output signals of VG_A and VG_B are updated with the new regulation rate to control the on-resistance of switches A and B, maintaining I_A + I_B = I_C.

[0058] In one example, the switch A and the switch B are field effect transistors, and the on-resistance of the switch A and the switch B is controlled by adjusting the gate voltage thereof.

[0059] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for switching and controlling a bypass switch during the charging and discharging process of a series battery pack system, characterized in that: The battery pack system includes a plurality of battery modules connected in series, each of which includes a switch A, a switch B, a battery cell, and a controller. The switch A is connected in series with the battery cell to form a branch circuit, and the switch A is used to control the conduction and shutdown of the battery cell. The switch B is connected in parallel with the series branch circuit formed by the switch A and the battery cell, and the switch B is used to control whether the battery cell is bypassed. The controller is connected to the switch A, the switch B, and the battery cell, and is used to obtain voltage signals across the battery cell, the switch A, and the switch B, and to control the on and off of the switch A and the switch B. The switching control method includes the following steps: Obtain the voltage and current information of each battery cell to determine the charge and discharge status of the battery cell; For a battery cell in a charging or discharging state, if its voltage reaches a preset charge or discharge cut-off voltage, the switch A connected in series with the battery cell is controlled to be gradually disconnected, and the switch B connected in parallel with the battery cell is controlled to be gradually turned on, thereby bypassing the battery cell. During the switching process of switch A and switch B, the on-resistance of switches A and B is adjusted so that the current flowing through the off switch gradually decreases to zero, while the current flowing through the on switch gradually increases, while keeping the total current of switches A and B constant. The total current is the charging or discharging current of the system, thus achieving soft switching of the bypass switch. In the process of adjusting the on-resistance of switch A and switch B, the control voltage VG_B of switch B is adjusted to be close to the threshold voltage VTH, and then the control voltage VG_B is gradually increased; The control voltage VG_A of switch A is kept nearly constant while monitoring the current of switch A in real time. When the current of switch A approaches zero, the control voltage of switch A is pulled to a preset low level to completely disconnect switch A. Then, the control voltage of switch B is raised to a preset high level to turn on switch B to a low-impedance state. The speed increase of the control voltage VG_B of the switch B before reaching the threshold voltage VTH is greater than the speed increase of the control voltage VG_B after reaching the threshold voltage VTH; The determining of the charge and discharge status of the battery cell includes: Comparing the real-time voltage value of each battery cell with a preset charge cut-off voltage threshold, if the real-time voltage value is less than or equal to the charge cut-off voltage threshold and current flows into the battery from the positive terminal of the battery, then the battery cell is determined to be in a charging state; The real-time voltage value of each battery cell is compared with the preset discharge cut-off voltage threshold. If the real-time voltage value is greater than or equal to the discharge cut-off voltage threshold and current flows out of the battery from the positive terminal of the battery, the battery cell is determined to be in a discharge state.

2. The method for switching and controlling a bypass switch during charging and discharging of a series battery pack system according to claim 1, wherein: The method of maintaining the total current of switch A and switch B constant includes: Obtain a target charge and discharge current value of the series battery pack; detect the sum of the current values ​​flowing through switch A and switch B in real time; and control the on-resistance of switch A and switch B so that the sum of the current flowing through switch A and the current flowing through switch B is equal to the target charge and discharge current value of the system.

3. The switching control method for a bypass switch in a series battery pack system during charging and discharging as claimed in claim 1, characterized in that: The switch A and the switch B are field effect transistors, and the on-resistance of the switch A and the switch B is controlled by adjusting the gate voltage thereof.

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