Charge and discharge control method and system for parallel battery pack

Abstract

The invention discloses a parallel battery pack charging and discharging control method and system, which are used for controlling the charging and discharging states of a plurality of battery packs connected in parallel, and the method comprises the following steps: when any battery pack is in a charging state or a discharging state, controlling a charging switch and a discharging switch to which the battery pack belongs to to be in a conducting state at the same time; when any battery pack is in a charging protection state, controlling a charging switch to which the battery pack belongs to be in an off state, and controlling the state of the charging switch to which the battery pack belongs according to the difference value between the total battery voltage and the bus voltage of the battery pack or the discharging current of the battery pack; and when any battery pack is in a discharge protection state, controlling the discharge switch to which the battery pack belongs to be in an off state, and controlling the state of the discharge switch to which the battery pack belongs according to a difference value between the bus voltage and the total battery voltage of the battery pack. According to the control method, automatic equalization and simultaneous charging or discharging of the plurality of battery packs connected in parallel in the power supply loop can be ensured without a communication bus.

Description

Technical Field

[0001] The present invention relates to the technical field of rechargeable batteries, and in particular to a parallel battery pack charge and discharge control method and system. Background Art

[0002] Traditional lead-acid batteries are simple in structure, low in cost, and do not require complex protection circuits. Therefore, in most battery application scenarios, especially where large-capacity power is required, lead-acid batteries are usually connected in parallel to increase system capacity. This method is simple and low in cost, but with the development of battery technology, especially the widespread application of lithium-ion batteries, lead-acid batteries are gradually being replaced by lithium-ion batteries.

[0003] Lithium-ion batteries have obvious advantages in terms of power density, cycle life and weight. However, lithium-ion batteries have high requirements for battery management systems (BMS) during use, especially when used in parallel. Lithium-ion batteries must be equipped with a protection circuit board to ensure the safety and stability of their charging and discharging processes. This requirement makes the parallel use of lithium batteries much more complicated than lead-acid batteries. Each lithium-ion battery needs to have independent battery management and protection functions, and when multiple lithium batteries are connected in parallel, the charge and discharge status of the batteries needs to be managed synchronously, otherwise some batteries may be overcharged or over-discharged, affecting the performance and life of the batteries.

[0004] In the prior art, such as the "Dual-lithium Battery Management System and Control Method" disclosed in Chinese patent CN117465293A, the discharge switching, charge switching and charge and discharge management functions of the dual-lithium battery can be realized through the CAN bus and the complex dual-lithium battery system management method. Although this solution can effectively realize the coordination and management between batteries, it relies on communication connections and complex interactive protocols, and the system cost is high and the wiring is complex, which limits the increase in the number of batteries in parallel and reduces the flexibility of the system. At the same time, the increased system cost and complex installation process also make this technology face many challenges in practical applications.

[0005] In order to reduce costs and simplify wiring, some lithium-ion batteries use parallel modules to assist in parallel connection of batteries. These parallel modules simplify battery management to a certain extent, but due to the lack of effective communication and interaction means, they still fail to completely solve the problem of "high-capacity batteries are fully charged first, but discharge later". In a parallel battery system, due to the different charging and discharging processes of each battery, there is a phenomenon that high-capacity batteries are fully charged first but discharge later. This phenomenon may cause low-capacity batteries to discharge before they are fully charged, thus affecting the "same charge and same discharge" efficiency of the system. More importantly, long-term imbalanced power will shorten the cycle life of low-capacity batteries and even cause battery inconsistency within the battery system, thus affecting the overall performance and use value of the parallel battery system.

[0006] In summary, existing battery parallel connection technologies either rely on complex communication and protocol management, resulting in high system cost and poor flexibility, or rely on simple parallel connection modules, but still have serious problems in battery charge and discharge balance.

[0007] Therefore, there is an urgent need for a new battery management solution that can reduce costs, simplify system structure, and ensure the charge and discharge balance of lithium batteries and extend battery life during parallel use. Summary of the invention

[0008] The object of the present invention is to provide a parallel battery pack charge and discharge control method and system which can reduce costs, simplify system structure, and ensure charge and discharge balance of batteries during parallel use.

[0009] In order to achieve the above-mentioned object, the present invention provides a parallel battery pack charge and discharge control method for controlling the charge and discharge state of a plurality of battery packs connected in parallel, wherein the plurality of battery packs are arranged in parallel in a power supply circuit through a power bus; a charging switch and a discharging switch connected in series are further configured for each of the battery packs; the charging switch and the discharging switch are used to control the charge state and the discharging state of the battery pack, respectively; The control method comprises: Collecting the total voltage of each battery pack in real time to obtain the total battery voltage, and collecting the charging current and discharging current of each battery pack in real time; and collecting the voltage of the power bus output port in real time to obtain the bus voltage; When any of the battery packs is in a charging state or a discharging state, the charging switch and the discharging switch belonging to the battery pack are controlled to be in a conducting state at the same time; When any of the battery groups is in a charging protection state, the charging switch of the battery group is controlled to be in an off state, the discharging switch is controlled to be in an on state, and the state of the charging switch of the battery group is controlled according to the difference between the total voltage of the battery and the bus voltage or the discharge current of the battery group; When any of the battery packs is in a discharge protection state, the discharge switch of the battery pack is controlled to be in an off state, the charging switch is in an on state, and the state of the discharge switch of the battery pack is controlled according to the difference between the bus voltage and the total battery voltage of the battery pack.

[0010] Preferably, when any of the battery packs is in a charging protection state, when any one of the following conditions 1 and 2 is met, the charging switch to which the battery pack belongs is controlled to be turned on; The first condition: the difference between the total battery voltage of the battery pack and the bus voltage is greater than or equal to a preset first threshold; The second condition: the discharge current of the battery pack is greater than or equal to a preset second threshold.

[0011] Preferably, when any of the battery packs is in a discharge protection state, when the following condition three is met, the discharge switch of the battery pack is controlled to return to a conducting state; Condition three: the difference between the bus voltage and the total battery voltage of the battery pack is greater than a preset third threshold.

[0012] Preferably, when any of the battery packs is in a discharge protection state, when the following condition 4 or condition 5 is met, the discharge switch of the battery pack is controlled to be restored to a conducting state, and the priority of the condition 4 and the condition 5 is greater than that of the condition 3; Condition 4: the charging current of the battery pack is greater than or equal to a preset fourth threshold; Condition 5: The battery pack exits the discharge protection state.

[0013] Preferably, each of the battery packs further comprises a plurality of battery cells, and the temperature of any of the battery cells in the battery pack is collected in real time to obtain the battery cell temperature, and the corresponding charging switch or discharging switch is controlled according to the battery cell temperature.

[0014] The present invention also provides a parallel battery pack charging and discharging system, which includes a power circuit for electrically connecting to a charging device or a load device, the power circuit includes a power bus and battery cells connected in parallel through the power bus, each of the battery cells includes a battery pack and a battery management system electrically connected to the battery pack; The battery management system includes a controller and a voltage detector, a charging switch, a discharging switch and a current detector electrically connected to the controller; the charging switch and the discharging switch are used to control the charging state and the discharging state of the battery pack respectively; the voltage detector is used to detect the bus voltage on the power bus in the power supply circuit; the current detector is used to detect the charging current or the discharging current of the battery pack; the controller is also electrically connected to the battery pack to detect the total battery voltage of the battery pack; When the controller detects that any of the battery packs is in a charging state or a discharging state, the controller controls the charging switch and the discharging switch of the battery pack to be in a conducting state at the same time; When the controller detects that any of the battery packs is in a charging protection state, the controller controls the charging switch of the battery pack to be in an off state, the discharging switch to be in an on state, and controls the state of the charging switch of the battery pack according to the difference between the total voltage of the battery and the bus voltage or the discharge current of the battery pack; When the controller detects that any of the battery packs is in a discharge protection state, the controller controls the discharge switch of the battery pack to be in an off state, the charging switch to be in an on state, and controls the state of the discharge switch of the battery pack according to the difference between the bus voltage and the total battery voltage of the battery pack.

[0015] Preferably, when any of the battery packs is in a charging protection state, when any one of the following conditions 1 and 2 is met, the controller controls the charging switch of the battery pack to turn on; The first condition: the difference between the total battery voltage of the battery pack and the bus voltage is greater than or equal to a preset first threshold; The second condition: the discharge current of the battery pack is greater than or equal to a preset second threshold.

[0016] Preferably, when any of the battery packs is in a discharge protection state, when the following condition three is met, the controller controls the discharge switch of the battery pack to return to a conducting state; Condition three: the difference between the bus voltage and the total battery voltage of the battery pack is greater than a preset third threshold.

[0017] Preferably, when any of the battery packs is in a discharge protection state, when the following condition 4 or condition 5 is met, the controller controls the discharge switch of the battery pack to return to a conducting state, and the priority of the condition 4 and the condition 5 is greater than that of the condition 3; Condition 4: the charging current of the battery pack is greater than or equal to a preset fourth threshold; Condition 5: The battery pack exits the discharge protection state.

[0018] Preferably, each of the battery packs also includes a plurality of battery cells, and the battery pack is also provided with a plurality of temperature sensors for collecting temperature of each of the battery cells respectively. The controller also collects the temperature of the battery cells in real time through the temperature sensors in the battery pack, and controls the corresponding charging switch or discharging switch according to the battery cell temperature.

[0019] Compared with the prior art, the parallel battery pack charge and discharge control method provided by the above technical solution of the present invention controls the charging switch and the discharging switch to be in the on state at the same time when the battery pack is in the charging or discharging state, thereby controlling the battery packs connected in parallel to be in the same charging and discharging state; in addition, for any battery pack, whether it is in the charging protection state or the discharging protection state, the charging switch or the discharging switch is dynamically adjusted according to the relationship between the total battery voltage and the bus voltage, thereby ensuring that multiple parallel battery packs in the power supply circuit are automatically balanced and charged or discharged at the same time without going through a communication bus, and automatically performing charging or discharging protection on the battery pack, which can effectively solve the problem of high-power batteries being fully charged first and then discharged, avoid excessive discharge of low-power batteries, extend battery life, and save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a circuit schematic diagram of parallel battery packs in an embodiment of the present invention.

[0021] Figure 2 is a circuit schematic diagram of any battery unit in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to explain the technical content, structural features, achieved objectives and effects of the present invention in detail, the following is a detailed description in conjunction with the implementation methods and the accompanying drawings.

[0023] This embodiment discloses a parallel battery pack charge and discharge control method for controlling the charge and discharge states of a plurality of battery packs BT connected in parallel. Figure 1 and Figure 2 In this embodiment, a plurality of battery packs BT are connected in parallel in a power supply circuit through a power supply bus L, and a charging switch K1 and a discharging switch K2 connected in series are also configured for each battery pack BT. The charging switch K1 and the discharging switch K2 are used to control the charging state and the discharging state of the battery pack BT, respectively. Specifically, the charging switch K1 and the discharging switch K2 are both MOS switch tubes.

[0024] Based on the circuit structure of the battery pack BT, the control method in this embodiment includes: S1: Collect the total voltage of each battery pack BT in real time to obtain the total battery voltage, collect the charging current and discharging current of each battery pack BT in real time, and collect the voltage of the output port of the power bus L in real time to obtain the bus voltage.

[0025] S2: When any of the battery packs BT is in a normal charging state or discharging state, the charging switch K1 and the discharging switch K2 belonging to the battery pack BT are controlled to be in an on state at the same time. It should be noted that any of the battery packs BT being in a normal charging state or discharging state means that the battery pack BT has no faults or has not entered a protection state, and the protection state includes an undervoltage protection state and an overcharge protection state. When the charger is connected to the power supply circuit, since the charging switch K1 and the discharging switch K2 of each battery pack BT are in an on state, each battery pack BT can be charged at the same time.

[0026] S3: When any of the battery packs BT is in a charging protection state, for example, a battery pack BT enters an overcharging protection state due to being fully charged, the charging switch K1 belonging to the battery pack BT is controlled to be in an off state, and the discharging switch K2 is controlled to be in an on state, and the state of the charging switch K1 belonging to the battery pack BT is controlled according to the difference between the total battery voltage and the bus voltage or the discharge current of the battery pack BT.

[0027] S4: When any of the battery packs BT is in a discharge protection state, for example, a battery pack BT enters an undervoltage protection state due to insufficient power, the discharge switch K2 belonging to the battery pack BT is controlled to be in an off state, the charging switch K1 is in an on state, and the state of the discharge switch K2 belonging to the battery pack BT is controlled according to the difference between the bus voltage and the total battery voltage of the battery pack BT.

[0028] In this embodiment, when the battery pack BT is in a charging or discharging state, the charging switch K1 and the discharging switch K2 are controlled to be in a conducting state at the same time, so as to control a plurality of battery packs BT connected in parallel to be in a simultaneous charging and discharging state.

[0029] In addition, for any battery pack BT, whether it is in the charging protection or discharging protection state, the charging switch K1 or the discharging switch K2 is dynamically adjusted according to the relationship between the total battery voltage and the bus voltage, so as to ensure that multiple parallel battery packs BT in the power supply circuit are automatically balanced and charged or discharged at the same time, and the battery pack BT is automatically charged or discharged to protect it, which can effectively solve the problem of high-capacity batteries being fully charged before discharging, avoid excessive discharge of low-capacity batteries, extend battery life, and save costs.

[0030] On the other hand, when any of the battery packs BT is in the charging protection state, when any of the following conditions 1 and 2 is met, the charging switch K1 belonging to the battery pack BT is controlled to turn on; The first condition: the difference between the total battery voltage of the battery pack BT and the bus voltage is greater than or equal to a preset first threshold; The second condition: the discharge current of the battery pack BT is greater than or equal to a preset second threshold.

[0031] When any of the battery packs BT is in a discharge protection state, when the following condition three is met, the discharge switch of the battery pack is controlled to return to a conducting state; Condition three: the difference between the bus voltage and the total battery voltage of the battery pack is greater than a preset third threshold.

[0032] That is, determine whether the difference between the bus voltage and the total battery voltage of the battery pack BT is less than or equal to a preset third threshold value. If so, control the discharge switch K2 belonging to the battery pack BT to remain in the disconnected state. If not, control the discharge switch K2 belonging to the battery pack BT to return to the on state.

[0033] In addition, when any of the battery packs is in a discharge protection state, when the following condition 4 or condition 5 is met, the discharge switch of the battery pack is controlled to be restored to a conducting state, and the priority of the condition 4 and the condition 5 is greater than that of the condition 3; Condition 4: the charging current of the battery pack is greater than or equal to a preset fourth threshold; Condition 5: The battery pack exits the discharge protection state.

[0034] Specifically, the working principle of the above-mentioned parallel battery pack charge and discharge control method is described in detail below by taking three lithium iron phosphate battery packs BT as an example.

[0035] 1. When the charging device is online, charge three parallel battery packs BT simultaneously. All battery packs BT have no fault or protection, and the charging switch K1 and the discharging switch K2 are in the on state.

[0036] When one of the battery packs BT (for example, 1# battery pack BT) is fully charged first, the overcharge protection is triggered, and the charging switch K1 of the battery pack BT is turned off, so that the 1# battery pack BT stops charging, but allows discharging. The remaining 2# and 3# battery packs BT continue to charge.

[0037] When the charging equipment (such as the mains power outage or the solar photovoltaic power generation stops) is offline, if the power supply circuit is connected to the load equipment, the battery pack BT enters the discharge state. At this time, since the 1# battery pack BT is in a fully charged state, the total battery voltage V1 is high, while the 2# and 3# battery packs BT are not fully charged, and the total battery voltages V2 and V3 are low. At this time, although V1 is the highest, since the charging switch K1 is turned off, there is a diode voltage drop at the charging switch K1 (from the diode in the MOS tube and the diode for safety protection connected in parallel with the charging switch K1), and the charging switch K1 and the discharge switch K2 of the 2# and 3# battery packs BT are both in the on state, so the bus voltage VP is clamped by the low voltage battery pack BT voltage, and: V2≈V3≈VP.

[0038] During the discharge process, the magnitude relationship between V1 and VP is compared in real time, and the discharge current of battery pack 1 BT is detected. When one of the following conditions is met, the charging switch K1 of battery pack 1 BT is forced to turn on: Condition 1: V1-VP≥VX1 (first threshold, for example, 0.2V).

[0039] Condition 2: the discharge current of battery pack BT #1 is greater than or equal to a second threshold value IX (eg, 0.3 A).

[0040] After the charging switch K1 of the 1# battery pack BT is forced to be turned on, the 1# battery pack BT, the 2# battery pack BT, and the 3# battery pack BT automatically discharge at the same time. In this way, the three battery packs BT are automatically and evenly discharged at the same time, ensuring the effect of the parallel battery system discharging at the same time and evenly, and the power difference between the parallel battery packs BT is minimized.

[0041] When one of the battery packs BT (for example, the 2# battery pack BT) enters the discharge undervoltage protection first (the discharge switch K2 is turned off, and the charging switch K1 is in the on state), the voltage of the 1# and 3# battery packs BT is still high and is still discharging, and the 2# battery pack BT may be ring-charged at the same time. In order to avoid frequent ring-current charging, a third threshold VX2 (for example, 0.2V) is set. When VP-V2 ≤ VX2, the discharge switch K2 of the 2# battery pack BT continues to remain in the off state to reduce or avoid frequent charging ring current phenomena. Only when VP-V2>VX2, or the charging current of the battery pack is greater than or equal to the preset fourth threshold, or the undervoltage protection value is restored, the discharge switch K2 of the 2# battery pack BT is turned on again.

[0042] In this way, the battery packs BT implement discharge protection in turn until all parallel battery packs BT enter the discharge protection state, stop discharging to the load device, and wait for the charging device to be connected to resume charging. The whole process repeats the above steps in a cycle.

[0043] On the other hand, the battery pack BT includes a plurality of battery cells. The battery total voltage is obtained by collecting the single cell voltage of each battery cell in the battery pack BT and accumulating the voltage, or the battery pack BT voltage is obtained by collecting the port voltage of the battery pack BT.

[0044] On the other hand, the temperature of any battery cell in the battery pack BT is collected in real time to obtain the battery cell temperature T, and the corresponding charging switch K1 or discharging switch K2 is controlled according to the battery cell temperature T, thereby improving the safety performance of the battery pack BT.

[0045] In another preferred embodiment of the present invention, a parallel battery pack charging and discharging system is also disclosed, such as Figure 1 and Figure 2 , including a power circuit for electrically connecting to a charging device or a load device, the power circuit including a power bus L and battery cells connected in parallel through the power bus L, each of the battery cells including a battery pack BT and a battery management system electrically connected to the battery pack BT.

[0046] The battery management system includes a controller 10 and a voltage detector 11, a charging switch K1, a discharging switch K2 and a current detector 12 electrically connected to the controller 10; the charging switch K1 and the discharging switch K2 are respectively used to control the charging state and the discharging state of the battery pack BT; the voltage detector 11 is used to detect the bus voltage on the power bus L described in the power supply circuit; the current detector 12 is used to detect the charging current or the discharging current of the battery pack BT; the controller 10 is also electrically connected to the battery pack BT to detect the total battery voltage of the battery pack BT.

[0047] When the controller 10 detects that any of the battery packs BT is in a charging state or a discharging state, the controller 10 controls the charging switch K1 and the discharging switch K2 of the battery pack BT to be in an on state at the same time.

[0048] When the controller 10 detects that any of the battery packs BT is in a charging protection state, the controller 10 controls the charging switch K1 belonging to the battery pack BT to be in an off state, and the discharging switch K2 to be in an on state, and controls the state of the charging switch K1 belonging to the battery pack BT according to the difference between the total battery voltage and the bus voltage or the discharge current of the battery pack BT.

[0049] When the controller 10 detects that any of the battery packs BT is in a discharge protection state, the controller 10 controls the discharge switch K2 belonging to the battery pack BT to be in an off state, the charging switch K1 to be in an on state, and controls the state of the discharge switch K2 belonging to the battery pack BT according to the difference between the bus voltage and the total battery voltage of the battery pack BT.

[0050] When any of the battery packs BT is in the charging protection state, when any one of the following conditions 1 and 2 is met, the controller 10 controls the charging switch K1 of the battery pack BT to turn on.

[0051] The first condition is that the difference between the total battery voltage of the battery pack BT and the bus voltage is greater than or equal to a preset first threshold.

[0052] The second condition: the discharge current of the battery pack BT is greater than or equal to a preset second threshold.

[0053] In addition, when any of the battery packs BT is in the discharge protection state, when the following condition three is met, the controller 10 controls the discharge switch K2 belonging to the battery pack BT to return to the on state; Condition three: the difference between the bus voltage and the total battery voltage of the battery pack BT is greater than a preset third threshold.

[0054] In addition, when any of the battery packs BT is in the discharge protection state, when the following condition 4 or condition 5 is met, the controller 10 controls the discharge switch K2 belonging to the battery pack BT to return to the on state, and the priority of the condition 4 and the condition 5 is greater than the condition 3; Condition 4: the charging current of the battery pack BT is greater than or equal to a preset fourth threshold; Condition 5: The battery pack BT exits the discharge protection state.

[0055] In addition, the battery pack BT includes a plurality of battery cells. The controller 10 acquires the single cell voltage of each battery cell in the battery pack BT and performs cumulative calculation to obtain the total battery voltage, or acquires the port voltage of the battery pack BT to obtain the battery pack BT voltage.

[0056] Furthermore, the battery pack BT is also provided with a plurality of temperature sensors for collecting temperature of each battery cell. The controller 10 also collects the battery cell temperature in real time through the temperature sensors in the battery pack BT, and controls the corresponding charging switch K1 or discharging switch K2 according to the battery cell temperature.

[0057] For the working principle of the parallel battery pack charging and discharging system in this embodiment, please refer to the above-mentioned parallel battery pack charging and discharging control method for details, which will not be repeated here.

[0058] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the scope of the patent application of the present invention are still within the scope covered by the present invention.

Claims

1. A parallel battery pack charge and discharge control method, characterized in that: Used to control the charge and discharge state of a plurality of battery packs connected in parallel, wherein the plurality of battery packs are arranged in parallel in a power supply circuit through a power supply bus; each of the battery packs is also provided with a charging switch and a discharging switch connected in series; the charging switch and the discharging switch are used to control the charge state and the discharging state of the battery pack, respectively; The control method comprises: Collecting the total voltage of each battery pack in real time to obtain the total battery voltage, and collecting the charging current and discharging current of each battery pack in real time; and collecting the voltage of the power bus output port in real time to obtain the bus voltage; When any of the battery packs is in a charging state or a discharging state, the charging switch and the discharging switch belonging to the battery pack are controlled to be in a conducting state at the same time; When any of the battery groups is in a charging protection state, the charging switch of the battery group is controlled to be in an off state, the discharging switch is controlled to be in an on state, and the state of the charging switch of the battery group is controlled according to the difference between the total voltage of the battery and the bus voltage or the discharge current of the battery group; When any of the battery packs is in a discharge protection state, the discharge switch of the battery pack is controlled to be in an off state, the charging switch is in an on state, and the state of the discharge switch of the battery pack is controlled according to the difference between the bus voltage and the total battery voltage of the battery pack.

2. The parallel battery pack charge and discharge control method according to claim 1, characterized in that: When any of the battery packs is in a charging protection state, when any of the following conditions 1 and 2 is met, the charging switch of the battery pack is controlled to be turned on; The first condition: the difference between the total battery voltage of the battery pack and the bus voltage is greater than or equal to a preset first threshold; The second condition: the discharge current of the battery pack is greater than or equal to a preset second threshold.

3. The parallel battery pack charge and discharge control method according to claim 1, characterized in that: When any of the battery packs is in a discharge protection state, when the following condition three is met, the discharge switch of the battery pack is controlled to return to a conducting state; Condition three: the difference between the bus voltage and the total battery voltage of the battery pack is greater than a preset third threshold.

4. The parallel battery pack charge and discharge control method according to claim 3, characterized in that: When any of the battery packs is in a discharge protection state, when the following condition 4 or condition 5 is met, the discharge switch of the battery pack is controlled to be restored to a conducting state, and the priority of the condition 4 and the condition 5 is greater than that of the condition 3; Condition 4: the charging current of the battery pack is greater than or equal to a preset fourth threshold; Condition 5: The battery pack exits the discharge protection state.

5. The parallel battery pack charge and discharge control method according to claim 1, characterized in that: Each of the battery packs further includes a plurality of battery cells, and the temperature of any of the battery cells in the battery pack is collected in real time to obtain the battery cell temperature, and the corresponding charging switch or discharging switch is controlled according to the battery cell temperature.

6. A parallel battery pack charging and discharging system, characterized in that: A power circuit for electrically connecting to a charging device or a load device, the power circuit comprising a power bus and battery units connected in parallel via the power bus, each of the battery units comprising a battery pack and a battery management system electrically connected to the battery pack; The battery management system includes a controller and a voltage detector, a charging switch, a discharging switch and a current detector electrically connected to the controller; the charging switch and the discharging switch are used to control the charging state and the discharging state of the battery pack respectively; the voltage detector is used to detect the bus voltage on the power bus in the power supply circuit; the current detector is used to detect the charging current or the discharging current of the battery pack; the controller is also electrically connected to the battery pack to detect the total battery voltage of the battery pack; When the controller detects that any of the battery packs is in a charging state or a discharging state, the controller controls the charging switch and the discharging switch of the battery pack to be in a conducting state at the same time; When the controller detects that any of the battery packs is in a charging protection state, the controller controls the charging switch of the battery pack to be in an off state, the discharging switch to be in an on state, and controls the state of the charging switch of the battery pack according to the difference between the total voltage of the battery and the bus voltage or the discharge current of the battery pack; When the controller detects that any of the battery packs is in a discharge protection state, the controller controls the discharge switch of the battery pack to be in an off state, the charging switch to be in an on state, and controls the state of the discharge switch of the battery pack according to the difference between the bus voltage and the total battery voltage of the battery pack.

7. The parallel battery pack charging and discharging system according to claim 6, characterized in that: When any of the battery packs is in a charging protection state, when any of the following conditions 1 and 2 is met, the controller controls the charging switch of the battery pack to turn on; The first condition: the difference between the total battery voltage of the battery pack and the bus voltage is greater than or equal to a preset first threshold; The second condition: the discharge current of the battery pack is greater than or equal to a preset second threshold.

8. The parallel battery pack charging and discharging system according to claim 6, characterized in that: When any of the battery packs is in a discharge protection state, when the following condition three is met, the controller controls the discharge switch of the battery pack to return to a conducting state; Condition three: the difference between the bus voltage and the total battery voltage of the battery pack is greater than a preset third threshold.

9. The parallel battery pack charging and discharging system according to claim 8, characterized in that: When any of the battery packs is in a discharge protection state, when the following condition 4 or condition 5 is met, the controller controls the discharge switch of the battery pack to return to a conducting state, and the priority of the condition 4 and the condition 5 is greater than that of the condition 3; Condition 4: the charging current of the battery pack is greater than or equal to a preset fourth threshold; Condition 5: The battery pack exits the discharge protection state.

10. The parallel battery pack charging and discharging system according to claim 6, characterized in that: Each of the battery packs also includes a number of battery cells, and the battery pack is also provided with a number of temperature sensors for collecting temperature of each of the battery cells. The controller also collects the battery cell temperature in real time through the temperature sensors in the battery pack, and controls the corresponding charging switch or discharging switch according to the battery cell temperature.

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