Switching control method suitable for bypass switch in charging and discharging process of series battery pack system

Abstract

The invention provides a bypass switch switching control method suitable for the charging and discharging process of a series battery pack system, and the method comprises the steps: obtaining the voltage and current information of each battery unit, and judging the charging and discharging states of the battery units; for a battery unit in a charging or discharging state, if the voltage of the battery unit reaches a preset charging cut-off voltage, a switch A connected in series with the battery unit is controlled to be switched off step by step, and meanwhile, a switch B connected in parallel with the battery unit is controlled to be switched on step by step, so that bypass of the battery unit is realized; in the process of controlling the switching of 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 switch-off switch is gradually reduced to zero, the current flowing through the switch-on switch is gradually increased, the total current of the switch A and the switch B is kept constant, the total current is the charging current of the system, and the soft switching of the bypass switch is realized; the charging and discharging process of the battery pack is kept continuous, so that the working 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. 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.

[0005] In summary, how to effectively solve the system instability problem caused by abnormal battery cell voltage during the charging and discharging process of the series battery pack system, especially how to achieve smooth switching of the bypass switch, accurately control current changes, avoid voltage fluctuations and current shocks, and ensure the safety and reliability of the battery cells and the entire system, is a core technical issue that needs to be solved urgently. Summary of the Invention

[0006] The purpose of the present invention is to solve the above-mentioned problems caused by sudden changes in voltage and current when using switch switching to implement the battery bypass function. A switching control method for a bypass switch suitable for the charging and discharging process of a series battery pack system is proposed. Through a soft switching method, the switch can change the battery voltage and current changes from rapid mutations to continuous and gradual changes during the switching process, thereby avoiding the potential risks caused by sudden voltage changes in the system.

[0007] The technical solution of the present invention is: The present invention provides a switching control method for a bypass switch during the charging and discharging process of a series battery pack system, wherein the battery pack system includes a plurality of battery modules connected in series, and the battery module 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 the preset charge 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. 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 off switch is gradually reduced to zero, while the current flowing through the 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, thereby realizing soft switching of the bypass switch.

[0008] Furthermore, determining 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.

[0009] Furthermore, the step of gradually turning off the switch A and gradually turning on the switch B comprises: For a battery cell in a charging or discharging state, when the conduction 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. At the same time, the control voltage of switch A is gradually reduced to gradually increase its on-resistance.

[0010] Furthermore, 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. When the current is close to 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, thereby completely turning off switch A and completely turning on switch B.

[0011] Furthermore, 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, and the current of switch A is detected 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 pulled up to a preset high level to turn on switch B to a low-impedance state.

[0012] Furthermore, the increase in speed of the control voltage VG_B of the switch B before reaching the threshold voltage VTH is greater than the increase in speed of the control voltage VG_B after reaching the threshold voltage VTH.

[0013] Furthermore, 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.

[0014] Furthermore, 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.

[0015] Beneficial effects of the present invention: The present invention achieves soft switching of the bypass switch. By precisely controlling the on-resistance of switch A and switch B, the current changes gradually, keeping the total system current constant, and effectively avoiding voltage fluctuations and system instability caused by sudden current changes. It also improves the safety and reliability of the battery pack system, extends the battery life, and optimizes the charging and discharging efficiency.

[0016] This invention discloses a method for switching and controlling bypass switches during the charging and discharging process of a series battery pack system. This method aims to address system instability caused by abnormal battery cell voltages during the charging and discharging process. During the switching process, a controller monitors the sum of the currents flowing through switches A and B in real time and adjusts the on-resistance of the switches to ensure a constant total current. This ensures a continuous charging and discharging process for the battery pack, thereby ensuring operational stability for the entire system.

[0017] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0019] Figure 1 A schematic structural diagram of a series battery pack system is shown.

[0020] Figure 2 A schematic diagram of a charging structure of a single battery module according to an embodiment of the present invention is shown.

[0021] Figure 3 A schematic diagram of the discharge structure of a single battery module according to an embodiment of the present invention is shown.

[0022] Figure 4 One of the schematic diagrams showing the corresponding relationship between the control voltage and the switch current in the process of gradually turning off the control switch A and gradually turning on the control switch B according to an embodiment of the present invention is shown.

[0023] Figure 5 The second schematic diagram of the corresponding relationship between the control voltage and the switch current in the process of gradually turning off the control switch A and gradually turning on the control switch B according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0025] like Figure 1-3 As shown, the present invention provides a switching control method for a bypass switch during the charging and discharging process of a series battery pack system, wherein the battery pack system includes multiple battery modules connected in series, and the battery module 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, 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 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 the preset charge 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. 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 off switch is gradually reduced to zero, while the current flowing through the 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, thereby realizing soft switching of the bypass switch.

[0026] In this embodiment, if Figure 1 As shown, the minimum unit consists of a battery, switch A, switch B and a controller, wherein the controller detects the battery voltage and the voltage signals at both ends of switch A / B to charge the battery ( Figure 2 ) or discharge ( Figure 3 ) process to control the state of switches A and B. In particular, the on-state voltage of the switches is controlled during the process from closed to open, or from open to closed, to achieve safer switching.

[0027] Figure 2, represents the battery charging process. The voltage across the battery is V1, where V1 = RC × I_A + VC, where RC is the battery's internal resistance and VC is the battery's open-circuit voltage. When the battery is fully charged, switch A needs to be disconnected via VG_A, while switch B needs to be turned on via VG_B. When switch A is disconnected, since current I_A becomes zero, V1 will be lower by RC × I_A than before disconnection. Especially when I_A is large, the change in V1 can reach tens or hundreds of millivolts, which often causes errors in the controller's estimation of the battery's state (e.g., capacity). Therefore, the method of the present invention provides a control loop that causes switch A to slowly disconnect, i.e., I_A slowly becomes zero, while simultaneously switching switch B slowly on, i.e., I_B slowly changes from 0 to I_C. During the entire switching process, I_A + I_B = I_C, where I_C is the system's charging current. This ensures that the system's charging current is not affected by the switching of the switches, ensuring that the system continues to charge at a relatively constant current. Figure 3 , represents the battery discharge process. The voltage across the battery is V1, where V1 = VC - RC × I_A, where RC is the battery's internal resistance and VC is the battery's open-circuit voltage. When the battery is fully charged, switch A needs to be disconnected via VG_A, while switch B needs to be turned on via VG_B. When switch A is disconnected, since current I_A becomes zero, V1 will be higher than before disconnection by an amount equal to RC × I_A. Especially when I_A is large, the change in V1 can reach tens or hundreds of millivolts, which often causes errors in the controller's estimation of the battery's state (e.g., capacity). Therefore, the method of the present invention provides a control loop that causes switch A to slowly disconnect, i.e., I_A slowly becomes zero, while simultaneously switching switch B slowly on, i.e., I_B slowly changes from 0 to I_C. During the entire switching process, I_A + I_B = I_C, where I_C is the system's discharge current. This ensures that the system's discharge current is not affected by the switching of the switches, thus ensuring that the system continuously discharges at a relatively stable current.

[0028] In one example, determining the charge and discharge status of the battery cell includes: Compare the real-time voltage value of each battery cell with the preset charge cut-off voltage threshold, which is usually 4.2V for lithium batteries. 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, the battery cell is determined to be in the charging state; 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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; 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.

[0035] In one example, 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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 the preset charge 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. 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 off switch is gradually reduced to zero, while the current flowing through the 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, thereby realizing soft switching of the bypass switch.

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 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.

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 step of gradually turning off the control switch A and gradually turning on the control switch B comprises: For a battery cell in a charging or discharging state, when the conduction 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. At the same time, the control voltage of switch A is gradually reduced to gradually increase its on-resistance.

4. The method for switching and controlling a bypass switch during charging and discharging of a series battery pack system according to claim 1 or 3, wherein: During the process of adjusting the on-resistance of switch A and switch 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, and the control voltage of switch B is raised to a preset high level, completely turning off switch A and completely turning on switch B.

5. The switching control method for a bypass switch in a series battery pack system during charging and discharging as claimed in claim 1 or 3, characterized in that: 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, and the current of switch A is detected 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 pulled up to a preset high level to turn on switch B to a low-impedance state.

6. The switching control method for a bypass switch in a series battery pack system during charging and discharging as claimed in claim 5, characterized in that: The increase in speed of the control voltage VG_B of the switch B before it reaches the threshold voltage VTH is greater than the increase in speed of the control voltage VG_B after it reaches the threshold voltage VTH.

7. 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.

8. 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 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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