Parallel battery pack charge and discharge control method and system

Abstract

The present invention discloses a method and system for controlling the charging and discharging states of a parallel battery pack, which are used to control the charging and discharging states of a plurality of battery packs connected in parallel. The method includes: when any battery pack is in a charging state or a discharging state, controlling the charging switch and the discharging switch belonging to the battery pack to be in a conducting state simultaneously; when any battery pack is in a charging protection state, controlling the charging switch belonging to the battery pack to be in an off state, and controlling the state of the charging switch belonging to the battery pack according to the difference between the total voltage of the battery pack and the bus voltage or the discharging current of the battery pack; when any battery pack is in a discharging protection state, controlling the discharging switch belonging to the battery pack to be in an off state, and controlling the state of the discharging switch belonging to the battery pack according to the difference between the bus voltage and the total voltage of the battery pack. The above control method of the present invention can ensure that multiple parallel battery packs in the power supply circuit automatically balance and charge or discharge simultaneously without a communication bus.

Description

Technical Field

[0001] The present invention relates to the technical field of rechargeable batteries, and particularly to a method and system for controlling charging and discharging of a parallel battery pack. Background Art

[0002] Due to its simple structure, low cost, and the absence of a complex protection circuit, traditional lead-acid batteries are commonly used in most battery applications, especially in scenarios where a large-capacity power source is required. In such cases, lead-acid batteries are usually connected in parallel to increase the system capacity. This method is simple and cost-effective. However, 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 relatively high requirements for the battery management system (BMS) during use, especially when connected 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-ion batteries much more complex than that of lead-acid batteries. Each lithium-ion battery needs to have an independent battery management and protection function. When multiple lithium-ion batteries are connected in parallel, the charging and discharging states between the batteries need to be synchronized for management. Otherwise, it may cause some batteries to be overcharged or over-discharged, affecting the performance and lifespan of the batteries.

[0004] In the prior art, such as the "Dual Lithium Battery Management System and Control Method" disclosed in Chinese Patent CN117465293A, through the CAN bus and a complex dual lithium battery system management method, functions such as discharge switching, charging switching, and charge-discharge management of dual lithium batteries can be achieved. Although this solution can effectively coordinate and manage the batteries, due to its reliance on communication connections and complex interaction protocols, the system cost is high and the wiring is complex. This limits the increase in the number of parallel-connected batteries and reduces the flexibility of the system. At the same time, the increased system cost and complex installation process also pose many challenges to the practical application of this technology.

[0005] To reduce costs and simplify wiring, some lithium-ion batteries use parallel modules to assist in battery parallel connection. These parallel modules simplify battery management to a certain extent. However, due to the lack of effective communication and interaction means, the problem of "high-capacity batteries are fully charged first but discharge later" has not been completely solved. 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 start discharging before being fully charged, thus affecting the "simultaneous charging and discharging" efficiency of the system. More importantly, long-term charge imbalance will lead to a shortened cycle life of low-capacity batteries and even cause battery inconsistency within the battery system, thereby affecting the overall performance and usability of the parallel battery system.

[0006] In summary, the existing battery parallel connection technology either relies on complex communication and protocol management, resulting in high system costs and poor flexibility, or relies on simple parallel modules, but there are still 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 the system structure, and ensure charge and discharge balance and extended battery life during the parallel use of lithium batteries. Summary of the Invention

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

[0009] To achieve the above object, the present invention provides a method for controlling the charge and discharge of a parallel battery pack, which is used to control the charge and discharge states of a plurality of battery packs connected in parallel. 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 battery pack; the charging switch and the discharging switch are respectively used to control the charging state and the discharging state of the battery pack;

[0010] The control method includes:

[0011] Real-time collect the total voltage of each battery pack to obtain the total battery voltage, and real-time collect the charging current and discharging current of each battery pack; and real-time collect the voltage at the output port of the power bus to obtain the bus voltage;

[0012] When any one of the battery packs is in the charging state or the discharging state, control the charging switch and the discharging switch belonging to the battery pack to be in the conducting state at the same time;

[0013] When any one of the battery packs is in the charging protection state, control the charging switch belonging to the battery pack to be in the off state, the discharging switch to be in the on state, and control the state of the charging switch belonging to the battery pack according to the difference between the total battery voltage and the bus voltage or the discharging current of the battery pack;

[0014] When any one of the battery packs is in the discharging protection state, control the discharging switch belonging to the battery pack to be in the off state, the charging switch to be in the on state, and control the state of the discharging switch belonging to the battery pack according to the difference between the bus voltage and the total battery voltage of the battery pack.

[0015] Preferably, when any one of the battery packs is in the charging protection state, if any one of the following Condition 1 and Condition 2 is satisfied, control the charging switch belonging to the battery pack to turn on;

[0016] Condition 1: The difference between the total voltage of the batteries in the battery pack and the bus voltage is greater than or equal to a preset first threshold;

[0017] Condition 2: The discharge current of the battery pack is greater than or equal to a preset second threshold.

[0018] Preferably, when any one of the battery packs is in the discharge protection state, if Condition 3 is satisfied, control the discharge switch belonging to the battery pack to resume the on state;

[0019] Condition 3: The difference between the bus voltage and the total voltage of the batteries in the battery pack is greater than a preset third threshold.

[0020] Preferably, when any one of the battery packs is in the discharge protection state, if any one of the following Condition 4 or Condition 5 is satisfied, control the discharge switch belonging to the battery pack to resume the on state, and the priorities of Condition 4 and Condition 5 are higher than that of Condition 3;

[0021] Condition 4: The charging current of the battery pack is greater than or equal to a preset fourth threshold;

[0022] Condition 5: The battery pack exits the discharge protection state.

[0023] Preferably, each battery pack further includes a plurality of battery cells, and also real-time collects the temperature of any one of the battery cells in the battery pack to obtain the cell temperature, and controls the corresponding charging switch or discharge switch according to the cell temperature.

[0024] The present invention further provides a parallel battery pack charge and discharge system, which includes a power supply circuit for electrically connecting to a charging device or a load device. The power supply circuit includes a power supply bus and battery units connected in parallel through the power supply bus. Each battery unit includes a battery pack and a battery management system electrically connected to the battery pack;

[0025] The battery management system includes a controller and a voltage detector, a charging switch, a discharge switch, and a current detector electrically connected to the controller; the charging switch and the discharge switch are respectively used to control the charging state and the discharge state of the battery pack; the voltage detector is used to detect the bus voltage on the power supply bus in the power supply circuit; the current detector is used to detect the charging current or the discharge current of the battery pack; the controller is also electrically connected to the battery pack to detect the total voltage of the battery pack;

[0026] When the controller detects that any one of the battery packs is in a charging state or a discharging state, the controller controls the charging switch and the discharging switch belonging to that battery pack to be in a conducting state simultaneously;

[0027] When the controller detects that any one of the battery packs is in a charging protection state, the controller controls the charging switch belonging to that battery pack to be in an off state, the discharging switch to be in a conducting state, and controls the state of the charging switch belonging to that battery pack according to the difference between the total battery voltage and the bus voltage or the discharging current of the battery pack;

[0028] When the controller detects that any one of the battery packs is in a discharging protection state, the controller controls the discharging switch belonging to that battery pack to be in an off state, the charging switch to be in a conducting state, and controls the state of the discharging switch belonging to that battery pack according to the difference between the bus voltage and the total battery voltage of that battery pack.

[0029] Preferably, when any one of the battery packs is in a charging protection state, when any one of the following Condition 1 and Condition 2 is satisfied, the controller controls the charging switch belonging to that battery pack to switch to a conducting state;

[0030] Condition 1: 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;

[0031] Condition 2: The discharging current of the battery pack is greater than or equal to a preset second threshold.

[0032] Preferably, when any one of the battery packs is in a discharging protection state, when the following Condition 3 is satisfied, the controller controls the discharging switch belonging to that battery pack to resume to a conducting state;

[0033] Condition 3: The difference between the bus voltage and the total battery voltage of that battery pack is greater than a preset third threshold.

[0034] Preferably, when any one of the battery packs is in a discharging protection state, when the following Condition 4 or Condition 5 is satisfied, the controller controls the discharging switch belonging to that battery pack to resume to a conducting state, and the priority of Condition 4 and Condition 5 is greater than that of Condition 3;

[0035] Condition 4: The charging current of that battery pack is greater than or equal to a preset fourth threshold;

[0036] Condition 5: That battery pack exits the discharging protection state.

[0037] Preferably, each of the battery packs further includes a plurality of battery cells, and a plurality of temperature sensors for collecting the temperature of each battery cell are further disposed in the battery pack. 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.

[0038] 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, so as to control a plurality of parallel-connected battery packs to be in the same charging and discharging state; in addition, for any battery pack, whether in the charging protection or 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. Therefore, without using a communication bus, it can ensure that multiple parallel-connected battery packs in the power supply circuit are automatically balanced and charged or discharged simultaneously, and automatically protect the battery pack during charging or discharging. It can effectively solve the problem that the high-capacity battery is fully charged first and then discharged, avoid over-discharging of the low-capacity battery, extend the battery life, and save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a circuit schematic diagram formed by a parallel battery pack in an embodiment of the present invention.

[0040] Figure 2 It is a circuit schematic diagram of any battery unit in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] In order to describe in detail the technical content, structural features, achieved objectives and effects of the present invention, the following is described in detail in conjunction with the embodiments and with reference to the accompanying drawings.

[0042] This embodiment discloses a parallel battery pack charge and discharge control method for controlling the charge and discharge states of a plurality of parallel-connected battery packs BT. As Figure 1 and Figure 2 shown, in this embodiment, a plurality of the battery packs BT are arranged in parallel through a power bus L in a power supply circuit. In this power supply circuit, a charging switch K1 and a discharging switch K2 connected in series are further configured for each of the battery packs BT. 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. Specifically, the charging switch K1 and the discharging switch K2 are both MOS switch tubes.

[0043] Based on the circuit structure of the above battery pack BT, the control method in this embodiment includes:

[0044] 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 at the output port of the power bus L in real time to obtain the bus voltage.

[0045] S2: When any one of the battery packs BT is in a normal charging state or discharging state, control the charging switch K1 and the discharging switch K2 belonging to this battery pack BT to be in the conducting state simultaneously. It should be noted that any one of the battery packs BT being in a normal charging state or discharging state means that this battery pack BT has no faults or has not entered the protection state, and this protection state includes the under-voltage protection state and the over-charging protection state. When the charger is connected to this power circuit, since the charging switches K1 and discharging switches K2 of each battery pack BT are in the conducting state, therefore, each battery pack BT can be charged simultaneously.

[0046] S3: When any one of the battery packs BT is in the charging protection state, for example, a certain battery pack BT enters the over-charging protection state due to being fully charged, control the charging switch K1 belonging to this battery pack BT to be in the off state, and simultaneously control the discharging switch K2 to be in the conducting state, and control the state of the charging switch K1 belonging to this battery pack BT according to the difference between the total battery voltage and the bus voltage or the discharging current of the battery pack BT.

[0047] S4: When any one of the battery packs BT is in the discharging protection state, for example, a certain battery pack BT enters the under-voltage protection state due to insufficient power, control the discharging switch K2 belonging to this battery pack BT to be in the off state, the charging switch K1 to be in the conducting state, and control the state of the discharging switch K2 belonging to this battery pack BT according to the difference between the bus voltage and the total battery voltage of this battery pack BT.

[0048] In this embodiment, when the battery pack BT is in the charging or discharging state, control the charging switch K1 and the discharging switch K2 to be in the conducting state simultaneously, so as to control several parallel-connected battery packs BT to be in the same charging and discharging state.

[0049] In addition, for any battery pack BT, whether it is in the charging protection or discharging protection state, also dynamically adjust the charging switch K1 or the discharging switch K2 according to the relationship between the total battery voltage and the bus voltage, so as to ensure that multiple parallel-connected battery packs BT in the power circuit are automatically balanced for simultaneous charging or discharging, and automatically perform charging or discharging protection on the battery pack BT, which can effectively solve the problem that high-capacity batteries are fully charged first and then discharged, avoid over-discharging of low-capacity batteries, extend the service life of the batteries, and save costs.

[0050] On the other hand, when any one of the battery packs BT is in the charging protection state, if any one of the following Condition 1 and Condition 2 is satisfied, control the charging switch K1 to which the battery pack BT belongs to turn on;

[0051] Condition 1: The difference between the total voltage of the battery pack BT and the bus voltage is greater than or equal to a preset first threshold;

[0052] Condition 2: The discharge current of the battery pack BT is greater than or equal to a preset second threshold.

[0053] When any one of the battery packs BT is in the discharge protection state, if Condition 3 is satisfied, control the discharge switch to which the battery pack belongs to resume the on state;

[0054] Condition 3: The difference between the bus voltage and the total voltage of the battery pack is greater than a preset third threshold.

[0055] That is, determine whether the difference between the bus voltage and the total voltage of the battery pack BT is less than or equal to the preset third threshold. If so, control the discharge switch K2 to which the battery pack BT belongs to remain off. If not, control the discharge switch K2 to which the battery pack BT belongs to resume the on state.

[0056] In addition, when any one of the battery packs is in the discharge protection state, if Condition 4 or Condition 5 is satisfied, control the discharge switch to which the battery pack belongs to resume the on state, and the priority of Condition 4 and Condition 5 is higher than that of Condition 3;

[0057] Condition 4: The charging current of the battery pack is greater than or equal to a preset fourth threshold;

[0058] Condition 5: The battery pack exits the discharge protection state.

[0059] Specifically, the working principle of the above parallel battery pack charge and discharge control method will be described in detail below by taking three lithium iron phosphate battery packs BT as an example.

[0060] 1. When the charging device is online, charge the three parallel battery packs BT simultaneously. All battery packs BT have no faults or protections, and the charging switch K1 and the discharge switch K2 are in the on state.

[0061] When one of the battery packs BT (for example, the 1# battery pack BT) is fully charged first, trigger overcharge protection and turn off the charging switch K1 to which the battery pack BT belongs. Then the 1# battery pack BT stops charging but is allowed to discharge. The remaining 2# and 3# battery packs BT continue to charge.

[0062] When the charging device (such as power failure of the mains or stop of solar PV power generation) drops out of the line, if the power supply circuit is connected to a load device, then the battery pack BT enters the discharge state. At this time, since the 1# battery pack BT is fully charged and 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 voltage drop across the charging switch K1 (the diode from the diode inside the MOS tube and the diode for safety protection connected in parallel with the charging switch K1), and the charging switches K1 and the discharge switches K2 of the 2# and 3# battery packs BT are both in the conducting state, so the bus voltage VP is clamped by the voltage of the low-voltage battery pack BT, and there is: V2≈V3≈VP.

[0063] During the discharge process, the magnitude relationship between V1 and VP is compared in real time, and the discharge current of the 1st battery pack BT is detected. When one of the following conditions is met, the charging switch K1 of the 1# battery pack BT is forced to conduct:

[0064] Condition 1: V1 - VP≥VX1 (the first threshold, for example, 0.2V).

[0065] Condition 2: The discharge current of the 1# battery pack BT is greater than or equal to the second threshold IX (for example, 0.3A).

[0066] After the charging switch K1 of the 1# battery pack BT is forced to conduct, the 1# battery pack BT, the 2# battery pack BT, and the 3# battery pack BT automatically discharge simultaneously. In this way, the three battery packs BT are automatically and evenly discharged simultaneously, ensuring the effect of simultaneous and balanced discharge of the parallel battery system, and minimizing the power difference between the parallel battery packs BT.

[0067] When one of the battery packs BT (such as the 2# battery pack BT) first enters the discharge undervoltage protection (the discharge switch K2 is turned off and the charging switch K1 is in the conducting state), the voltages of the 1# and 3# battery packs BT are still high and are still discharging, and at the same time, the 2# battery pack BT may be charged by circulating current. To avoid frequent circulating current charging phenomena, 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 off, reducing or avoiding frequent charging circulating 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 re-conducted.

[0068] In this way, the battery packs BT achieve discharge protection in sequence until all parallel battery packs BT enter the discharge protection state, stop discharging the load device, and wait for the charging device to be connected and then resume charging. The above process is cyclically repeated.

[0069] On the other hand, the battery pack BT includes a plurality of battery cells. By collecting the individual voltages of each battery cell in the battery pack BT and performing cumulative calculation, the total battery voltage is obtained, or the port voltage of the battery pack BT is collected to obtain the voltage of the battery pack BT.

[0070] On yet another aspect, the temperature of any one of the battery cells in the battery pack BT is also 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.

[0071] 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 , which includes a power supply circuit for electrically connecting to a charging device or a load device. The power supply circuit includes a power supply bus L and battery units connected in parallel through the power supply bus L. Each battery unit includes a battery pack BT and a battery management system electrically connected to the battery pack BT.

[0072] 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 that are 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 supply bus L 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.

[0073] When the controller 10 detects that any one 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 belonging to the battery pack BT to be in a conducting state at the same time.

[0074] When the controller 10 detects that any one 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, the discharging switch K2 to be in a conducting 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 discharging current of the battery pack BT.

[0075] When the controller 10 detects that any one of the battery packs BT is in the discharge protection state, the controller 10 controls the discharge switch K2 belonging to the battery pack BT to be in the off state, the charging switch K1 to be in the 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.

[0076] When any one of the battery packs BT is in the charging protection state, when any one of the following condition 1 and condition 2 is satisfied, the controller 10 controls the charging switch K1 belonging to the battery pack BT to turn to the on state.

[0077] Condition 1: 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.

[0078] Condition 2: The discharge current of the battery pack BT is greater than or equal to a preset second threshold.

[0079] In addition, when any one of the battery packs BT is in the discharge protection state, when the following condition 3 is satisfied, the controller 10 controls the discharge switch K2 belonging to the battery pack BT to resume the on state;

[0080] Condition 3: The difference between the bus voltage and the total battery voltage of the battery pack BT is greater than a preset third threshold.

[0081] In addition, when any one of the battery packs BT is in the discharge protection state, when the following condition 4 or condition 5 is satisfied, the controller 10 controls the discharge switch K2 belonging to the battery pack BT to resume the on state, and the priority of condition 4 and condition 5 is greater than that of condition 3;

[0082] Condition 4: The charging current of the battery pack BT is greater than or equal to a preset fourth threshold;

[0083] Condition 5: The battery pack BT exits the discharge protection state.

[0084] In addition, the battery pack BT includes a plurality of battery cells, and the controller 10 obtains the total battery voltage by collecting the individual voltages of each battery cell in the battery pack BT and performing cumulative calculation, or obtains the battery pack voltage by collecting the port voltage of the battery pack BT.

[0085] Furthermore, a plurality of temperature sensors for collecting the temperature of each battery cell are further provided in the battery pack BT, and 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 discharge switch K2 according to the battery cell temperature.

[0086] For the working principle of the parallel battery pack charging and discharging system in this embodiment, please refer to the above parallel battery pack charging and discharging control method, which will not be elaborated here.

[0087] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the scope of the patent application of the present invention still fall 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 charge 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; 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 any of the battery groups and the bus voltage is greater than or equal to a preset first threshold; The second condition: the discharge current of any of the battery packs is greater than or equal to a preset second threshold; When any of the battery packs is in a discharge protection state, when the following condition three is met, controlling the discharge switch of any of the battery packs to return to a conducting state; Condition three: the difference between the bus voltage and the total battery voltage of any of the battery groups is greater than a preset third threshold.

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 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 any of the battery packs is greater than or equal to a preset fourth threshold; Condition 5: Any of the battery packs exits the discharge protection state.

3. 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.

4. 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 discharging protection state, the controller controls the discharging 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 discharging switch of the battery pack according to the difference between the bus voltage and the total battery voltage of the battery pack; 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 be in an on state; The first condition: the difference between the total battery voltage of any of the battery groups and the bus voltage is greater than or equal to a preset first threshold; The second condition: the discharge current of any of the battery packs is greater than or equal to a preset second threshold; 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 any of the battery groups is greater than a preset third threshold.

5. The parallel battery pack charging and discharging system according to claim 4, 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 any of the battery packs is greater than or equal to a preset fourth threshold; Condition 5: Any of the battery packs exits the discharge protection state.

6. The parallel battery pack charging and discharging system according to claim 4, 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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