Floating charge control method, lithium battery equalization circuit and UPS system

Abstract

The invention discloses a floating charge control method, a lithium battery equalization circuit and a UPS system, and relates to the technical field of power supply control. The floating charge control method comprises the step of controlling a floating charge circuit to work when it is detected that the maximum monomer voltage is greater than a first preset voltage during charging. And when it is detected that the maximum monomer voltage is greater than the second preset voltage, the floating charge circuit is controlled to stop working. When it is detected that the maximum monomer voltage is smaller than a third preset voltage, the floating charge circuit is controlled to work, and when it is detected that the maximum monomer voltage is larger than a second preset voltage, the floating charge circuit is controlled to stop working. Wherein the work of the N passive equalization circuits is correspondingly controlled according to the detected single voltage of the N lithium batteries, so that the single voltage of the N lithium batteries is within the preset fluctuation range of the third preset voltage. Therefore, the passive equalization time of the lithium batteries is prolonged, the equalization effect is improved, the consistency of the single voltages of the N lithium batteries is ensured, and the full charge voltage of the lithium battery pack is relatively stable.

Description

Technical Field

[0001] The present application relates to the field of power supply control technology, and in particular to a floating charge control method, a lithium battery balancing circuit and a UPS system. Background Art

[0002] The backup power source used in UPS (Uninterruptible Power Supply) backup power systems on the market is generally lead-acid batteries, and now lithium battery systems are gradually replacing them in the market.

[0003] However, lithium battery systems usually do not have a floating charge mode, only lead-acid batteries have it. This results in the lithium battery directly turning off the charging contactor after being fully charged and no longer charging. At this time, the lithium battery is no longer passively balanced, resulting in a short passive balancing time for the lithium battery and an unobvious balancing effect. At the same time, it also causes the voltage of each lithium battery group in the UPS system to be unstable when fully charged, affecting the backup time of the UPS system.

[0004] The above contents are only used to assist in understanding the technical solution of the present application and do not constitute an admission that the above contents are prior art. Summary of the invention

[0005] The main purpose of the present application is to provide a floating charge control method, which aims to solve the problems of poor passive equalization effect of existing lithium batteries and unstable voltage of lithium battery packs in a fully charged state.

[0006] To achieve the above purpose, the floating charge control method proposed in the present application is applied to a lithium battery balancing circuit, and the lithium battery balancing circuit includes:

[0007] a first power supply terminal;

[0008] A lithium battery pack, comprising N lithium batteries;

[0009] N passive balancing circuits, the N passive balancing circuits being connected to the N lithium batteries in a one-to-one correspondence; the passive balancing circuits being used to reduce the single cell voltage of the correspondingly connected lithium battery;

[0010] A floating charge circuit, the floating charge circuit is connected to the lithium battery pack and the first power supply terminal respectively, and the floating charge circuit is used to limit the charging current of the lithium battery pack;

[0011] The floating charge control method comprises:

[0012] Step S10, when the lithium battery pack is in a charging state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than a first preset voltage, controlling the floating charge circuit to operate so as to limit the charging current of the lithium battery pack;

[0013] Step S20, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, controlling the floating charge circuit to stop working, so that the charging of the lithium battery pack ends;

[0014] Step S30, when it is detected that the maximum single cell voltage of the N lithium batteries is less than the third preset voltage, the floating charge circuit is controlled to work, until it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge circuit is controlled to stop working, so that the charging of the lithium battery pack is terminated;

[0015] Wherein, when executing the steps S10 to S30, the operations of the N passive balancing circuits are controlled accordingly according to the detected single cell voltages of the N lithium batteries, so that the single cell voltages of the N lithium batteries are within the preset fluctuation range of the third preset voltage; wherein the third preset voltage, the first preset voltage and the second preset voltage increase sequentially.

[0016] In one embodiment, the step of controlling the operation of the N passive balancing circuits according to the detected single cell voltages of the N lithium batteries so that the single cell voltages of the N lithium batteries are within the preset fluctuation range of the third preset voltage specifically includes:

[0017] If it is detected that the single cell voltage of any of the lithium batteries is greater than the third preset voltage, the corresponding passive balancing circuit is controlled to start working;

[0018] If it is detected that the single cell voltage of any of the lithium batteries is greater than the fourth preset voltage and less than or equal to the third preset voltage, and at the same time the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is greater than the first preset voltage difference, then the corresponding passive balancing circuit is controlled to start working;

[0019] If it is detected that the single cell voltage of the corresponding lithium battery is greater than or equal to the fifth preset voltage and less than or equal to the third preset voltage, and at the same time, the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is less than the second preset voltage difference, then the corresponding passive balancing circuit is controlled to stop working;

[0020] If it is detected that the single cell voltage of the lithium battery corresponding to the working passive balancing circuit is less than the fifth preset voltage, the corresponding passive balancing circuit is controlled to stop working; wherein, the first preset voltage difference is greater than the second preset voltage difference, and the fifth preset voltage, the fourth preset voltage, and the third preset voltage increase in sequence.

[0021] In one embodiment, the first power supply terminal includes a first positive power supply terminal and a first negative power supply terminal; the floating charge circuit includes a floating charge switch and a floating charge resistor;

[0022] Wherein, the first end of the floating charge switch is connected to the positive electrode of the lithium battery pack, the second end of the floating charge switch is connected to one end of the floating charge resistor, the other end of the floating charge resistor is connected to the first positive power supply terminal, and the negative electrode of the lithium battery pack is connected to the first negative power supply terminal;

[0023] The steps S10 to S30 specifically include:

[0024] Step S11, when the lithium battery pack is in a charging state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the first preset voltage, controlling the floating charge switch to close;

[0025] Step S21, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge switch is controlled to be disconnected, so that the charging of the lithium battery pack ends;

[0026] Step S31, when it is detected that the maximum single cell voltage of the N lithium batteries is less than the third preset voltage, the floating charge switch is controlled to be closed, until it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge switch is controlled to be disconnected, so that the lithium battery pack ends charging.

[0027] In one embodiment, each of the passive balancing circuits includes a balancing switch and a passive balancing resistor; a first end of the balancing switch is connected to one end of the corresponding lithium battery, a second end of the balancing switch is connected to one end of the passive balancing resistor, and the other end of the passive balancing resistor is connected to the other end of the corresponding lithium battery; the step of correspondingly controlling the operation of the N passive balancing circuits according to the detected single cell voltages of the N lithium batteries so that the single cell voltages of the N lithium batteries are within the preset fluctuation range of the third preset voltage specifically includes:

[0028] If it is detected that the single cell voltage of any of the lithium batteries is greater than the third preset voltage, the corresponding balancing switch is controlled to be closed;

[0029] If it is detected that the single cell voltage of any of the lithium batteries is greater than the fourth preset voltage and less than or equal to the third preset voltage, and at the same time, the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is greater than the first preset voltage difference, then the corresponding balancing switch is controlled to be closed;

[0030] If it is detected that the single cell voltage of the corresponding lithium battery is greater than or equal to the fifth preset voltage and less than or equal to the third preset voltage, and at the same time, the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is less than the second preset voltage difference, then the corresponding balancing switch is controlled to be disconnected;

[0031] If it is detected that the single cell voltage of the lithium battery corresponding to the working passive balancing circuit is less than the fifth preset voltage, the corresponding balancing switch is controlled to be disconnected; wherein, the first preset voltage difference is greater than the second preset voltage difference, and the fifth preset voltage, the fourth preset voltage, and the third preset voltage increase in sequence.

[0032] In one embodiment, the lithium battery equalization circuit further includes a charging switch; wherein a first end of the charging switch is connected to a first end of the floating charge switch, and a second end of the charging switch is connected to the other end of the floating charge resistor;

[0033] Before step S11, the floating charge control method further includes:

[0034] Step S01, in response to a charging start instruction, controlling the charging switch to close, and confirming that the lithium battery pack is in a charging state;

[0035] The step S11 specifically includes:

[0036] When the charging switch is in a closed state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the first preset voltage, the floating charge switch is controlled to be closed, and the charging switch is controlled to be opened.

[0037] The present application also proposes a lithium battery balancing circuit, the lithium battery balancing circuit comprising:

[0038] a first power supply terminal;

[0039] A lithium battery pack, comprising N lithium batteries;

[0040] N passive balancing circuits, the N passive balancing circuits being connected to the N lithium batteries in a one-to-one correspondence; the passive balancing circuits being used to reduce the single cell voltage of the correspondingly connected lithium battery;

[0041] A floating charge circuit, the floating charge circuit is connected to the lithium battery pack and the first power supply terminal respectively, and the floating charge circuit is used to limit the charging current of the lithium battery pack;

[0042] A detection control module, the detection control module is respectively connected to the detection ends of the N lithium batteries, the controlled ends of the N passive balancing circuits and the controlled end of the floating charge circuit, and the detection control module is used to apply the floating charge control method as described above.

[0043] In one embodiment, the first power supply terminal includes a first positive power supply terminal and a first negative power supply terminal; the floating charge circuit includes a floating charge switch and a floating charge resistor; the passive balancing circuit includes a balancing switch and a passive balancing resistor; the lithium battery balancing circuit also includes a first diode, a second diode, a charging switch and a discharging switch;

[0044] The first end of the floating charge switch, the first end of the charging switch, and the positive electrode of the first diode are connected to the positive electrode of the battery pack, the second end of the floating charge switch is connected to one end of the floating charge resistor, the negative electrode of the first diode, the negative electrode of the second diode, and the second end of the charging switch are connected to the first end of the discharge switch, the second end of the discharge switch, the positive electrode of the second diode, and the other end of the floating charge resistor are connected to the first positive power supply end; the negative electrode of the lithium battery pack is connected to the first negative power supply end; wherein the detection control module is respectively connected to the controlled end of the floating charge switch, the controlled end of the balancing switch, the controlled end of the charging switch, and the controlled end of the discharge switch.

[0045] In one implementation, the charging switch, the discharging switch and the floating charge switch are all contactors, and the N balancing switches are MOS tubes.

[0046] In one embodiment, the lithium battery balancing circuit further includes a bipolar circuit breaker, a fuse and a shunt; one end of the fuse, the first end of the floating charge switch, and the first end of the charging switch are connected to the positive electrode of the first diode, the other end of the fuse is connected to the first end of the bipolar circuit breaker, the second end of the bipolar circuit breaker is connected to the positive electrode of the lithium battery pack, the negative electrode of the lithium battery pack is connected to the third end of the bipolar circuit breaker, the fourth end of the bipolar circuit breaker is connected to the first end of the shunt, and the second end of the shunt is connected to the first negative power supply end; wherein the detection control module is respectively connected to the controlled end of the bipolar circuit breaker and the signal output end of the shunt;

[0047] The detection control module is further used to control the bipolar circuit breaker to disconnect the lithium battery when it is determined that the current flowing through the shunt is greater than a preset current threshold based on the current detection signal output by the shunt.

[0048] The present application also proposes a UPS system, characterized in that the UPS system includes multiple lithium battery balancing circuits as described above; wherein the first power supply terminal of each of the lithium battery balancing circuits has a first positive power supply terminal and a first negative power supply terminal, the first positive power supply terminals of the multiple lithium battery balancing circuits are connected together, and the first negative power supply terminals of the multiple lithium battery balancing circuits are connected together.

[0049] The technical solution of the present application adopts a floating charge control method, which is applied to a lithium battery equalization circuit. The floating charge control method includes: step S10, when the lithium battery pack is in a charging state, when it is detected that the maximum single cell voltage of N lithium batteries is greater than the first preset voltage, the floating charge circuit is controlled to work to limit the charging current of the lithium battery pack. Step S20, when it is detected that the maximum single cell voltage of N lithium batteries is greater than the second preset voltage, the floating charge circuit is controlled to stop working, so that the lithium battery pack ends charging. Step S30, when it is detected that the maximum single cell voltage of N lithium batteries is less than the third preset voltage, the floating charge circuit is controlled to work until it is detected that the maximum single cell voltage of N lithium batteries is greater than the second preset voltage, and the floating charge circuit is controlled to stop working, so that the lithium battery pack ends charging. Wherein, when executing steps S10 to S30, according to the detected single cell voltages of N lithium batteries, the operation of N passive equalization circuits is controlled accordingly, so that the single cell voltages of the N lithium batteries are within the preset fluctuation range of the third preset voltage. In this way, the present application extends the passive balancing time of the lithium battery, and can ensure that the single cell voltages of the N lithium batteries in the lithium battery pack in the fully charged state are within the preset fluctuation range of the third preset voltage, thereby ensuring the consistency of the single cell voltages of the N lithium batteries. At this time, the voltage of the lithium battery pack is maintained near the product of the third preset voltage and N, and the actual full charge voltage of the lithium battery pack is also relatively stable, thereby ensuring the consistency between the lithium battery packs of the UPS system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0051] Figure 1 A schematic diagram of a flow chart of an embodiment of a floating charge control method provided by the present application;

[0052] Figure 2 An electronic circuit diagram of an embodiment of a lithium battery equalization circuit provided in the present application;

[0053] Figure 3 An electronic circuit diagram of an embodiment of a UPS system provided by the present application;

[0054] Figure 4 A flow chart of another embodiment of the floating charge control method provided by the present application;

[0055] Figure 5 A flow chart of another embodiment of the floating charge control method provided in the present application.

[0056] Description of Figure Numbers:

[0057]

[0058] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0060] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0061] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0062] In UPS (uninterruptible power supply) backup power systems, traditional backup energy sources mainly use lead-acid batteries. However, with the advancement of technology and the increasing demand for higher efficiency, longer life and lighter solutions, lithium-ion battery systems are gradually becoming the mainstream choice in the market. Nevertheless, during the charging and discharging process of lithium-ion batteries, the consistency of single-cell voltage is particularly critical, which is directly related to the backup time of the UPS system. Lithium-ion battery packs are composed of multiple single cells, and the voltage consistency between these single cells is crucial to the performance of the entire system. Due to the existence of the "bucket effect" - that is, the weakest part of a system determines the maximum capacity or performance of the entire system - if the voltage between single cells is inconsistent, those with lower voltages will limit the output capacity of the entire battery pack. In other words, even if some single cells still have remaining power, because other batteries have reached their minimum operating voltage and stop discharging, the entire battery pack ends power supply early, thereby shortening the backup time of the UPS system. The shortcomings of most lithium battery charging strategies currently used on the market include:

[0063] At present, the logic of passive balancing in lithium batteries (i.e., the balancing method that discharges high-voltage single cells through resistors to keep them consistent with low-voltage batteries) is that most passive balancing works during the charging process, and the single cell voltage must be higher than a certain value (for example, lithium iron phosphate is above 3.4V) because of the terminal voltage difference and the energy consumption problem caused by balancing during discharge. However, there is no floating charging method in the lithium battery system, only lead-acid batteries have it. This causes the lithium battery to directly turn off the charging contactor after being fully charged and no longer charge. At this time, passive balancing is no longer turned on, resulting in a short passive balancing time, unclear balancing effect, and difficulty in improving consistency.

[0064] Moreover, in the long-term operation of the UPS system, in addition to the inconsistency of the single cells, it is also very likely that the imbalance between the lithium battery groups will lead to low charging and discharging capacity and short backup time of the UPS system. Most of the current solutions can only ensure the consistency between single cells, but cannot eliminate the inconsistency between lithium battery groups through passive balancing methods. That is, the actual full charge voltage between each lithium battery group is unstable, which affects the backup time of the UPS system.

[0065] The present application proposes a floating charge control method.

[0066] See also Figure 1 In one embodiment of the present application, the floating charge control method is applied to a lithium battery equalization circuit, and the floating charge control method includes:

[0067] a first power supply terminal;

[0068] A lithium battery pack, comprising N lithium batteries;

[0069] N passive balancing circuits, the N passive balancing circuits are connected to the N lithium batteries in a one-to-one correspondence; the passive balancing circuits are used to reduce the single cell voltage of the correspondingly connected lithium battery;

[0070] A floating charging circuit, the floating charging circuit is connected to the lithium battery pack and the first power supply terminal respectively, and the floating charging circuit is used to limit the charging current of the lithium battery pack;

[0071] Float charge control methods include:

[0072] Step S10, when the lithium battery pack is in a charging state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than a first preset voltage, controlling the floating charge circuit to operate so as to limit the charging current of the lithium battery pack;

[0073] Step S20, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge circuit is controlled to stop working, so that the charging of the lithium battery pack ends;

[0074] Step S30, when it is detected that the maximum single cell voltage of the N lithium batteries is less than the third preset voltage, the floating charge circuit is controlled to work, until it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge circuit is controlled to stop working, so that the lithium battery pack ends charging;

[0075] Among them, when executing steps S10 to S30, the operation of N passive balancing circuits is controlled accordingly according to the detected single cell voltages of the N lithium batteries, so that the single cell voltages of the N lithium batteries are within a preset fluctuation range of a third preset voltage; wherein the third preset voltage, the first preset voltage and the second preset voltage increase in sequence.

[0076] It should be noted that floating charge means continuing to charge the battery at a lower constant voltage after it is fully charged to maintain the battery's full charge state and compensate for self-discharge losses. This method is common in lead-acid batteries because they can remain fully charged for a long time in this mode without suffering significant damage. However, lithium-ion batteries are more sensitive to overcharging, so existing lithium battery systems usually do not have a floating charge method. This causes the lithium battery to directly turn off the charging contactor after it is fully charged and no longer charge. Since passive balancing requires power consumption, the lithium battery is no longer passively balanced after the charging is disconnected, resulting in a short passive balancing time for the lithium battery and an unobvious balancing effect.

[0077] It should be noted that, compared with the active balancing circuit, the passive balancing circuit can achieve energy dissipation through a simple passive balancing resistor, and its hardware cost is lower than that of the active balancing circuit containing complex electronic components and control logic. Since the passive balancing circuit has fewer components and a simple structure, it may be more reliable and have a lower failure rate. In this embodiment, by introducing a floating charge circuit, the lithium battery pack of the UPS system can be in a fast recovery floating charge state for a long time like the lead-acid battery pack, and the passive balancing effect can be significantly improved by cooperating with the work of the passive balancing circuit.

[0078] It should be noted that N is a positive integer greater than 2.

[0079] In this embodiment, by introducing a floating charge circuit and dynamically adjusting the working state according to the maximum single cell voltage of N lithium batteries, a certain degree of balancing operation can be continued when the lithium battery pack is close to being fully charged. In conjunction with the passive balancing circuit, the single cell voltages of the N lithium batteries can be within the preset fluctuation range of the third preset voltage, effectively improving the balancing effect. Specifically, the floating charge circuit can be used to charge lithium batteries with a voltage lower than the third preset voltage at a low current to increase their single cell voltages; the passive balancing circuit can be used to consume power for lithium batteries with a voltage higher than the third preset voltage to reduce their single cell voltages. In this way, the balancing effect of the single cell voltages of the N lithium batteries being within the preset fluctuation range of the third preset voltage can be achieved. Compared with the prior art, this embodiment can ensure the consistency of the single cell voltages of the lithium battery pack, that is, it ensures that the single cell voltages of the N lithium batteries in the fully charged state are within the preset fluctuation range of the third preset voltage, and ensures the consistency of the single cell voltages of the N lithium batteries. Similarly, if the lithium battery balancing circuit is applied to a UPS system, the voltage of each lithium battery pack of the UPS system is maintained near the product of the third preset voltage and N, and the actual full charge voltage of the lithium battery pack is relatively stable, thereby ensuring the consistency between the lithium battery packs of the UPS system and preventing the backup time of the UPS system from being affected by the bucket effect.

[0080] The present application provides a floating charge control method, which includes: step S10, when the lithium battery pack is in a charging state, when it is detected that the maximum single cell voltage of N lithium batteries is greater than a first preset voltage, the floating charge circuit is controlled to work to limit the charging current of the lithium battery pack. Step S20, when it is detected that the maximum single cell voltage of N lithium batteries is greater than a second preset voltage, the floating charge circuit is controlled to stop working, so that the lithium battery pack ends charging. Step S30, when it is detected that the maximum single cell voltage of N lithium batteries is less than a third preset voltage, the floating charge circuit is controlled to work until it is detected that the maximum single cell voltage of N lithium batteries is greater than the second preset voltage, and the floating charge circuit is controlled to stop working, so that the lithium battery pack ends charging. Wherein, when executing steps S10 to S30, according to the detected single cell voltages of the N lithium batteries, the operation of the N passive balancing circuits is controlled accordingly, so that the single cell voltages of the N lithium batteries are within the preset fluctuation range of the third preset voltage. In this way, the present application extends the passive balancing time of the lithium battery, and can ensure that the single cell voltages of the N lithium batteries in the lithium battery pack in the fully charged state are within the preset fluctuation range of the third preset voltage, thereby ensuring the consistency of the single cell voltages of the N lithium batteries. At this time, the voltage of the lithium battery pack is maintained near the product of the third preset voltage and N, and the actual full charge voltage of the lithium battery pack is also relatively stable, thereby ensuring the consistency between the lithium battery packs of the UPS system.

[0081] In an embodiment of the present application, the step of controlling the operation of N passive balancing circuits according to the detected single cell voltages of N lithium batteries so that the single cell voltages of the N lithium batteries are within a preset fluctuation range of a third preset voltage specifically includes:

[0082] If it is detected that the cell voltage of any lithium battery is greater than the third preset voltage, the corresponding passive balancing circuit is controlled to start working. In this way, the passive balancing circuit can consume the excess energy of the lithium battery to prevent it from being overcharged, and finally reduce its cell voltage to near the third preset voltage.

[0083] If it is detected that the cell voltage of any lithium battery is greater than the fourth preset voltage and less than or equal to the third preset voltage, and the voltage difference between the cell voltage of the corresponding lithium battery and the minimum cell voltage of the N lithium batteries is greater than the first preset voltage difference, the corresponding passive balancing circuit is controlled to start working. In this way, the voltage of the lithium battery can be reduced, which helps to reduce the voltage difference between lithium battery cells, and can help correct the problem of inconsistent voltage between lithium battery cells, especially when the cell voltage of some lithium battery voltages rises faster during charging.

[0084] If it is detected that the single cell voltage of the corresponding lithium battery is greater than or equal to the fifth preset voltage and less than or equal to the third preset voltage, and the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is less than the second preset voltage difference, the corresponding passive balancing circuit is controlled to stop working. In this way, when the single cell voltages of the lithium batteries are relatively consistent, unnecessary energy consumption can be avoided and power can be saved.

[0085] If it is detected that the single cell voltage of the lithium battery corresponding to the working passive balancing circuit is less than the fifth preset voltage, the corresponding passive balancing circuit is controlled to stop working; wherein the first preset voltage difference is greater than the second preset voltage difference, and the fifth preset voltage, the fourth preset voltage, and the third preset voltage increase in sequence. In this way, over-discharge can be prevented, the lithium battery can be protected from low voltage damage, and power can be saved.

[0086] It should be noted that the preset values ​​of the fifth preset voltage, the fourth preset voltage, the first preset pressure difference and the second preset pressure difference can be specifically set according to the requirements of the preset fluctuation range. When the preset fluctuation range is small, that is, the required accuracy is high, the values ​​of the fifth preset voltage and the fourth preset voltage can be set closer to the third preset range, and the values ​​of the first preset pressure difference and the second preset pressure difference can be set smaller. The settings of the preset voltage and the preset pressure difference can be set according to actual experience and the characteristics of the lithium battery, and this embodiment does not impose specific restrictions.

[0087] In this embodiment, through the multi-level preset voltage and voltage difference judgment mechanism, the single cell voltage of N lithium batteries is finely controlled, and the consistency of the single cell voltage of the lithium battery can be achieved in a short time period. In this embodiment, the work of the floating charge circuit and the work of the passive balancing circuit can be combined to extend the passive balancing time and improve the passive balancing effect, solving the problem of short passive balancing time in traditional lithium battery systems.

[0088] See also Figure 2 In one embodiment of the present application, the first power supply terminal includes a first positive power supply terminal and a first negative power supply terminal; the floating charge circuit includes a floating charge switch KM1 and a floating charge resistor RA;

[0089] The first end of the floating charge switch KM1 is connected to the positive electrode of the lithium battery pack, the second end of the floating charge switch KM1 is connected to one end of the floating charge resistor RA, the other end of the floating charge resistor RA is connected to the first positive power supply terminal, and the negative electrode of the lithium battery pack is connected to the first negative power supply terminal;

[0090] Steps S10 to 30 specifically include:

[0091] Step S11, when the lithium battery pack is in a charging state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the first preset voltage, the floating charge switch KM1 is controlled to close. At this time, a small current flows through to float charge the lithium battery pack.

[0092] Step S21, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge switch KM1 is controlled to be disconnected, so that the charging of the lithium battery pack ends. At this time, the lithium battery is no longer charged to prevent overcharging.

[0093] Step S31, when it is detected that the maximum single cell voltage of the N lithium batteries is less than the third preset voltage, the floating charge switch KM1 is controlled to close, until it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge switch KM1 is controlled to open, so that the lithium battery pack ends charging. In this way, the overcharging problem of the lithium battery can be effectively prevented, and the optimal charging state of the battery can be maintained, the voltage balance inside the lithium battery pack is promoted, and the safety of the circuit is improved.

[0094] In this embodiment, the floating charge resistor RA can be a large resistance, high power gold aluminum shell resistor. The high power resistor can withstand higher energy consumption and ensure long-term stable operation; the higher resistance value helps to limit the charging current to a lower level. The floating charge switch KM1 can be a high voltage, low current contactor. The voltage of the lithium battery system is usually high, especially in the scenario of series use. The high voltage contactor can ensure the safety of the circuit connection; the low current contactor can reduce energy loss and improve efficiency without affecting the function.

[0095] See also Figure 2 In one embodiment of the present application, each passive balancing circuit includes a balancing switch and a passive balancing resistor; a first end of the balancing switch is connected to one end of the corresponding lithium battery, a second end of the balancing switch is connected to one end of the passive balancing resistor, and the other end of the passive balancing resistor is connected to the other end of the corresponding lithium battery; the step of correspondingly controlling the operation of the N passive balancing circuits according to the detected single cell voltages of the N lithium batteries so that the single cell voltages of the N lithium batteries are within a preset fluctuation range of the third preset voltage specifically includes:

[0096] If it is detected that the single cell voltage of any lithium battery is greater than the third preset voltage, the corresponding balancing switch is controlled to be closed;

[0097] If it is detected that the single cell voltage of any lithium battery is greater than the fourth preset voltage and less than or equal to the third preset voltage, and at the same time, the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is greater than the first preset voltage difference, the corresponding balancing switch is controlled to be closed;

[0098] If it is detected that the single cell voltage of the corresponding lithium battery is greater than or equal to the fifth preset voltage and less than or equal to the third preset voltage, and at the same time, the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is less than the second preset voltage difference, the corresponding balancing switch is controlled to be disconnected;

[0099] If it is detected that the single cell voltage of the lithium battery corresponding to the working passive balancing circuit is less than the fifth preset voltage, the corresponding balancing switch is controlled to be disconnected; wherein the first preset voltage difference is greater than the second preset voltage difference, and the fifth preset voltage, the fourth preset voltage, and the third preset voltage increase in sequence.

[0100] In this embodiment, the equalization effect of the lithium battery pack can be achieved by setting a simple passive equalization circuit and a floating charge circuit. Each passive equalization circuit only needs to set an equalization switch and a passive equalization resistor, which is low-cost, simple in structure, and can effectively maintain the voltage consistency in the lithium battery pack.

[0101] See also Figure 2 In one embodiment of the present application, the lithium battery balancing circuit further includes a charging switch KM2; wherein a first end of the charging switch KM2 is connected to a first end of the floating charge switch KM1, and a second end of the charging switch KM2 is connected to the other end of the floating charge resistor RA;

[0102] Before step S11, the floating charge control method further includes:

[0103] Step S01, in response to a charging start instruction, control the charging switch KM2 to close, and confirm that the lithium battery pack is in a charging state. In this way, when the power of the lithium battery pack is low, the lithium battery pack can be charged by inputting a charging start instruction.

[0104] Step S11 specifically includes:

[0105] When the charging switch KM2 is in the closed state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the first preset voltage, the floating charge switch KM1 is controlled to be closed, and the charging switch KM2 is controlled to be opened.

[0106] In this way, this embodiment can achieve a fast switch from a normal charging state to a floating charging state, and can smoothly transition from a high current charging mode to a low current floating charging mode.

[0107] It should be noted that, since the third preset voltage is less than the first preset voltage, before the lithium battery pack switches to the floating charge state, some of the lithium batteries with higher voltages in the lithium battery pack have reached the working conditions for passive balancing, that is, at this time, the corresponding part of the passive balancing circuit is already in working condition, and the lithium battery pack can be voltage balanced. In the prior art, since lithium battery packs usually do not have a floating charge mode, this causes the lithium battery to directly turn off the charging contactor after being fully charged and no longer charge, then the lithium battery is no longer passively balanced at this time, resulting in a short passive balancing time for the lithium battery. In this embodiment, when the maximum single cell voltage is greater than the first preset voltage, it can quickly switch to the floating charge state, which prolongs the passive balancing time and ensures the balancing effect of the single cells of the battery pack.

[0108] In order to explain the implementation principle of the floating charge control method provided in this application, please refer to Figure 2 , Figure 4 and Figure 5 In one embodiment of the present application, the first preset voltage, the second preset voltage, the third preset voltage, the fourth preset voltage and the fifth preset voltage are set to 3.55V, 3.65V, 3.45V, 3.4V and 3.38V respectively, and the first preset voltage difference and the second preset voltage difference are set to 20mV and 10mV respectively.

[0109] In this embodiment, the floating charge control method includes:

[0110] In response to the charging start instruction, the charging switch KM2 is controlled to close and confirm that the lithium battery pack is in the charging state. During the charging process, when the single cell voltage of any lithium battery reaches 3.45V, the balancing switch is closed to balance the voltage. This stage is the passive balancing of the lithium battery pack before entering the floating charge stage.

[0111] When the lithium battery pack is in the charging state, when it is detected that the maximum single cell voltage of N lithium batteries is greater than 3.55V, the floating charge switch KM1 is controlled to close and the charging switch KM2 is controlled to open. At this time, it enters the floating charge stage, continues to charge, and continues to passively balance the lithium battery pack.

[0112] When it is detected that the maximum single cell voltage of the N lithium batteries is greater than 3.65V, the floating charge switch KM1 is controlled to be disconnected, and the charging of the lithium battery pack is terminated at this time to prevent the lithium battery from being overcharged.

[0113] When the maximum single cell voltage of N lithium batteries is detected to be less than 3.45V, the floating charge switch KM1 is controlled to close, until the maximum single cell voltage of N lithium batteries is detected to be greater than 3.65V, the floating charge switch KM1 is controlled to open. In this way, the lithium battery pack can be float charged, the balancing time of the lithium battery pack is extended, and the actual full charge voltage of the lithium battery pack can be close to 3.45V*N. At the same time, the self-discharge loss of the lithium battery can be compensated during the floating charge stage. In this way, the single cell voltage between lithium batteries can be maintained in a consistent state.

[0114] In the above charging control process, if it is detected that the cell voltage of any lithium battery is greater than 3.45V, the corresponding balancing switch is controlled to be closed; if it is detected that the cell voltage of any lithium battery is greater than 3.4V and less than or equal to 3.45V, and the voltage difference between the cell voltage of the corresponding lithium battery and the minimum cell voltage of N lithium batteries is greater than 20mV, the corresponding balancing switch is controlled to be closed; if it is detected that the cell voltage of the corresponding lithium battery is greater than or equal to 3.38V and less than or equal to 3.45V, and the voltage difference between the cell voltage of the corresponding lithium battery and the minimum cell voltage of N lithium batteries is less than 10mV, the corresponding balancing switch is controlled to be disconnected; if it is detected that the cell voltage of the lithium battery corresponding to the working passive balancing circuit is less than 3.38V, the corresponding balancing switch is controlled to be disconnected. In this way, when any cell voltage is greater than 3.45V, the balancing operation is immediately started to adjust the voltage to prevent the voltage from being too high. When the battery voltage is less than 3.38V, the balancing operation is stopped to avoid excessive discharge. Moreover, by monitoring the voltage difference between N lithium battery cells, the balancing circuit can be flexibly started or stopped under different conditions, and the voltage difference between the batteries can be gradually reduced, and finally the voltage consistency can be achieved. It should be noted that the fourth preset voltage, the fifth preset voltage, the first preset voltage difference and the second preset voltage difference can be flexibly set according to the requirements of the preset fluctuation range, and are not limited here.

[0115] In this way, this embodiment prolongs the passive balancing time of the lithium battery, and can ensure that the single cell voltage of N lithium batteries is maintained at around 3.45V, thereby ensuring the consistency of the single cell voltage of the N lithium batteries. At this time, the voltage of the lithium battery pack is maintained near the product of 3.45V and N, and the actual full charge voltage of the lithium battery pack is also relatively stable, thereby improving the passive balancing effect of the lithium battery pack.

[0116] This application also proposes a lithium battery equalization circuit, see Figure 2 , the lithium battery balancing circuit includes:

[0117] a first power supply terminal;

[0118] A lithium battery pack, comprising N lithium batteries;

[0119] N passive balancing circuits, the N passive balancing circuits are connected to the N lithium batteries in a one-to-one correspondence; the passive balancing circuits are used to reduce the single cell voltage of the correspondingly connected lithium battery;

[0120] A floating charging circuit, the floating charging circuit is connected to the lithium battery pack and the first power supply terminal respectively, and the floating charging circuit is used to limit the charging current of the lithium battery pack;

[0121] A detection control module (not shown) is respectively connected to the detection ends of the N lithium batteries, the controlled ends of the N passive balancing circuits, and the controlled end of the floating charge circuit. The detection control module is used to apply the floating charge control method described in the above embodiment.

[0122] Compared with the prior art, the beneficial effects of the lithium battery balancing circuit provided in the present application are the same as the beneficial effects of the floating charge control method provided in the above embodiment, and other technical features in the lithium battery balancing circuit are the same as the features disclosed in the above embodiment method, which will not be repeated here.

[0123] See also Figure 2 In one embodiment of the present application, the first power supply terminal includes a first positive power supply terminal and a first negative power supply terminal; the floating charge circuit includes a floating charge switch KM1 and a floating charge resistor RA; the passive balancing circuit includes a balancing switch and a passive balancing resistor; the lithium battery balancing circuit also includes a first diode D1, a second diode D2, a charging switch KM2 and a discharging switch KM3;

[0124] The first end of the floating charge switch KM1, the first end of the charging switch KM2, and the positive electrode of the first diode D1 are connected to the positive electrode of the battery pack, the second end of the floating charge switch KM1 is connected to one end of the floating charge resistor RA, the negative electrode of the first diode D1, the negative electrode of the second diode D2, and the second end of the charging switch KM2 are connected to the first end of the discharge switch KM3, the second end of the discharge switch KM3, the positive electrode of the second diode D2, and the other end of the floating charge resistor RA are connected to the first positive power supply end; the negative electrode of the lithium battery pack is connected to the first negative power supply end; wherein, the detection control module is respectively connected to the controlled end of the floating charge switch KM1, the controlled end of the balancing switch, the controlled end of the charging switch KM2, and the controlled end of the discharge switch KM3.

[0125] In a feasible implementation, the charging switch KM2, the discharging switch KM3 and the floating charge switch KM1 are all contactors, and the N balancing switches are MOS tubes. Among them, the contactor has the advantage of being able to withstand a higher working voltage, and the MOS tube has an extremely low on-resistance and can achieve a switching speed of microseconds.

[0126] In this embodiment, in response to the discharge start instruction, the discharge switch KM3 is controlled to be closed, the charge switch KM2 is disconnected, and the float charge switch KM1 is disconnected, and the lithium battery pack is discharged. In response to the charge start instruction, the charge switch KM2 is controlled to be closed, the discharge switch KM3 is disconnected, and the float charge switch KM1 is disconnected, and the lithium battery pack is charged, until it is detected that the maximum single cell voltage of the N lithium batteries is greater than the first preset voltage, the float charge switch KM1 is controlled to be closed, and the charge switch KM2 is controlled to be disconnected.

[0127] It should be noted that, in order to achieve the best balancing effect of the lithium battery in a state close to the full charge voltage, in this embodiment, in the charging state, the discharging state or the static state, the detection control module is used to: if it is detected that the single cell voltage of any lithium battery is greater than the third preset voltage, then control the corresponding passive balancing circuit to start working; if it is detected that the single cell voltage of any lithium battery is greater than the fourth preset voltage and less than or equal to the third preset voltage, and the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of N lithium batteries is greater than the first preset voltage difference, then control the corresponding passive balancing circuit to start working; if it is detected that the single cell voltage of the corresponding lithium battery is greater than or equal to the fifth preset voltage and less than or equal to the third preset voltage, and the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of N lithium batteries is less than the second preset voltage difference, then control the corresponding passive balancing circuit to stop working; if it is detected that the single cell voltage of the lithium battery corresponding to the working passive balancing circuit is less than the fifth preset voltage, then control the corresponding passive balancing circuit to stop working. In this way, by adopting a unified detection and passive balancing control logic in the charging state, the discharging state and the static state, combined with the multi-level voltage threshold and the voltage difference judgment mechanism, the best balancing effect of the lithium battery can be achieved.

[0128] See also Figure 2 In one embodiment of the present application, the lithium battery balancing circuit further includes a bipolar circuit breaker MCB, a fuse FU and a shunt FL; one end of the fuse FU, the first end of the floating charge switch KM1, and the first end of the charging switch KM2 are connected to the positive electrode of the first diode D1, the other end of the fuse FU is connected to the first end of the bipolar circuit breaker MCB, the second end of the bipolar circuit breaker is connected to the positive electrode of the lithium battery pack, the negative electrode of the lithium battery pack is connected to the third end of the bipolar circuit breaker, the fourth end of the bipolar circuit breaker is connected to the first end of the shunt FL, and the second end of the shunt FL is connected to the first negative power supply end; wherein the detection control module is respectively connected to the controlled end of the bipolar circuit breaker MCB and the signal output end of the shunt FL;

[0129] The detection control module is also used to control the bipolar circuit breaker MCB to disconnect the lithium battery when it is determined that the current flowing through the shunt FL is greater than a preset current threshold according to the current detection signal output by the shunt FL.

[0130] In this embodiment, the fuse FU automatically blows when the charging current / discharging current of the battery pack exceeds the rated value, cutting off the circuit to prevent overcurrent damage. The bipolar circuit breaker MCB can quickly disconnect or close the circuit according to the instructions of the detection control module to provide additional safety protection. The shunt FL is used to measure the current passing through the lithium battery pack and convert the current information into a voltage signal and output it to the detection control module. The detection control module monitors the current detection signal output by the shunt FL in real time. When the charging current / discharging current flowing through the shunt FL is greater than the preset current threshold, it indicates that there is an overcurrent risk. The detection control module sends a disconnection instruction to the bipolar circuit breaker MCB to quickly cut off the access to the lithium battery. In this way, the safety of this embodiment is relatively strong.

[0131] In the long-term operation of the lithium battery system, in addition to the inconsistency of single cells, it is very likely that the imbalance between different lithium battery modules will lead to low charging and discharging capacity and short backup time of the UPS system.

[0132] In order to solve the above problems, this application also proposes a UPS system, see Figure 3 The UPS system includes a plurality of lithium battery balancing circuits as described above; wherein the first power supply terminal of each lithium battery balancing circuit has a first positive power supply terminal and a first negative power supply terminal, the first positive power supply terminals of the plurality of lithium battery balancing circuits are connected in common, and the first negative power supply terminals of the plurality of lithium battery balancing circuits are connected in common.

[0133] The specific structure of the lithium battery equalization circuit refers to the above embodiments. Since the UPS system adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0134] It should be noted that the UPS system can uniformly implement the functions of the detection and control modules of multiple lithium battery balancing circuits through a battery management system (BMS system), that is, the battery management system can simultaneously control the charging and discharging of multiple lithium battery packs and the start and stop of each passive balancing circuit. In this embodiment, the floating charge circuit can be combined with the passive balancing circuit so that the voltages of multiple lithium battery packs can be maintained near the product of the third preset voltage and N in the fully charged state, thereby ensuring the consistency between the lithium battery packs of the UPS system and significantly improving the charging and discharging capacity and backup time of the system.

[0135] The above description is only an exemplary embodiment of the present application and does not limit the patent scope of the present application. All equivalent structural changes made by using the contents of the present application specification and drawings under the technical concept of the present application, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A floating charge control method, applied to a lithium battery equalization circuit, characterized in that: The lithium battery equalization circuit comprises: a first power supply terminal; A lithium battery pack, comprising N lithium batteries; N passive balancing circuits, the N passive balancing circuits being connected to the N lithium batteries in a one-to-one correspondence; the passive balancing circuits being used to reduce the single cell voltage of the correspondingly connected lithium battery; A floating charge circuit, the floating charge circuit is connected to the lithium battery pack and the first power supply terminal respectively, and the floating charge circuit is used to limit the charging current of the lithium battery pack; The floating charge control method comprises: Step S10, when the lithium battery pack is in a charging state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than a first preset voltage, controlling the floating charge circuit to operate so as to limit the charging current of the lithium battery pack; Step S20, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, controlling the floating charge circuit to stop working, so that the charging of the lithium battery pack ends; Step S30, when it is detected that the maximum single cell voltage of the N lithium batteries is less than the third preset voltage, the floating charge circuit is controlled to work, until it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge circuit is controlled to stop working, so that the charging of the lithium battery pack is terminated; Wherein, when executing the steps S10 to S30, the operations of the N passive balancing circuits are controlled accordingly according to the detected single cell voltages of the N lithium batteries, so that the single cell voltages of the N lithium batteries are within the preset fluctuation range of the third preset voltage; wherein the third preset voltage, the first preset voltage and the second preset voltage increase sequentially.

2. The floating charge control method according to claim 1, characterized in that: The step of controlling the operation of the N passive balancing circuits according to the detected single cell voltages of the N lithium batteries so that the single cell voltages of the N lithium batteries are within the preset fluctuation range of the third preset voltage specifically includes: If it is detected that the single cell voltage of any of the lithium batteries is greater than the third preset voltage, the corresponding passive balancing circuit is controlled to start working; If it is detected that the single cell voltage of any of the lithium batteries is greater than the fourth preset voltage and less than or equal to the third preset voltage, and at the same time the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is greater than the first preset voltage difference, then the corresponding passive balancing circuit is controlled to start working; If it is detected that the single cell voltage of the corresponding lithium battery is greater than or equal to the fifth preset voltage and less than or equal to the third preset voltage, and at the same time, the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is less than the second preset voltage difference, then the corresponding passive balancing circuit is controlled to stop working; If it is detected that the single cell voltage of the lithium battery corresponding to the working passive balancing circuit is less than the fifth preset voltage, the corresponding passive balancing circuit is controlled to stop working; wherein, the first preset voltage difference is greater than the second preset voltage difference, and the fifth preset voltage, the fourth preset voltage, and the third preset voltage increase in sequence.

3. The floating charge control method according to claim 1, characterized in that: The first power supply terminal includes a first positive power supply terminal and a first negative power supply terminal; the floating charge circuit includes a floating charge switch and a floating charge resistor; Wherein, the first end of the floating charge switch is connected to the positive electrode of the lithium battery pack, the second end of the floating charge switch is connected to one end of the floating charge resistor, the other end of the floating charge resistor is connected to the first positive power supply terminal, and the negative electrode of the lithium battery pack is connected to the first negative power supply terminal; The steps S10 to S30 specifically include: Step S11, when the lithium battery pack is in a charging state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the first preset voltage, controlling the floating charge switch to close; Step S21, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge switch is controlled to be disconnected, so that the charging of the lithium battery pack ends; Step S31: when it is detected that the maximum single cell voltage of the N lithium batteries is less than the third preset voltage, the floating charge switch is controlled to be closed, until it is detected that the maximum single cell voltage of the N lithium batteries is greater than the second preset voltage, the floating charge switch is controlled to be disconnected, so that the charging of the lithium battery pack is terminated.

4. The floating charge control method according to claim 3, characterized in that: Each of the passive balancing circuits comprises a balancing switch and a passive balancing resistor; a first end of the balancing switch is connected to one end of the corresponding lithium battery, a second end of the balancing switch is connected to one end of the passive balancing resistor, and the other end of the passive balancing resistor is connected to the other end of the corresponding lithium battery; the step of correspondingly controlling the operation of the N passive balancing circuits according to the detected single cell voltages of the N lithium batteries so that the single cell voltages of the N lithium batteries are within the preset fluctuation range of the third preset voltage specifically comprises: If it is detected that the single cell voltage of any of the lithium batteries is greater than the third preset voltage, the corresponding balancing switch is controlled to be closed; If it is detected that the single cell voltage of any of the lithium batteries is greater than the fourth preset voltage and less than or equal to the third preset voltage, and at the same time, the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is greater than the first preset voltage difference, then the corresponding balancing switch is controlled to be closed; If it is detected that the single cell voltage of the corresponding lithium battery is greater than or equal to the fifth preset voltage and less than or equal to the third preset voltage, and at the same time, the voltage difference between the single cell voltage of the corresponding lithium battery and the minimum single cell voltage of the N lithium batteries is less than the second preset voltage difference, then the corresponding balancing switch is controlled to be disconnected; If it is detected that the single cell voltage of the lithium battery corresponding to the working passive balancing circuit is less than the fifth preset voltage, the corresponding balancing switch is controlled to be disconnected; wherein, the first preset voltage difference is greater than the second preset voltage difference, and the fifth preset voltage, the fourth preset voltage, and the third preset voltage increase in sequence.

5. The floating charge control method according to claim 3, characterized in that: The lithium battery equalization circuit further comprises a charging switch; wherein a first end of the charging switch is connected to a first end of the floating charge switch, and a second end of the charging switch is connected to the other end of the floating charge resistor; Before step S11, the floating charge control method further includes: Step S01, in response to a charging start instruction, controlling the charging switch to close, and confirming that the lithium battery pack is in a charging state; The step S11 specifically includes: When the charging switch is in a closed state, when it is detected that the maximum single cell voltage of the N lithium batteries is greater than the first preset voltage, the floating charge switch is controlled to be closed, and the charging switch is controlled to be opened.

6. A lithium battery equalization circuit, characterized in that: The lithium battery equalization circuit comprises: a first power supply terminal; A lithium battery pack, comprising N lithium batteries; N passive balancing circuits, the N passive balancing circuits being connected to the N lithium batteries in a one-to-one correspondence; the passive balancing circuits being used to reduce the single cell voltage of the correspondingly connected lithium battery; A floating charge circuit, the floating charge circuit is connected to the lithium battery pack and the first power supply terminal respectively, and the floating charge circuit is used to limit the charging current of the lithium battery pack; A detection control module, wherein the detection control module is respectively connected to the detection ends of the N lithium batteries, the controlled ends of the N passive balancing circuits, and the controlled end of the floating charge circuit, and the detection control module is used to apply the floating charge control method as described in any one of claims 1 to 5.

7. The lithium battery equalization circuit according to claim 6, characterized in that: The first power supply terminal includes a first positive power supply terminal and a first negative power supply terminal; the floating charge circuit includes a floating charge switch and a floating charge resistor; the passive balancing circuit includes a balancing switch and a passive balancing resistor; the lithium battery balancing circuit also includes a first diode, a second diode, a charging switch and a discharging switch; The first end of the floating charge switch, the first end of the charging switch, and the positive electrode of the first diode are connected to the positive electrode of the battery pack, the second end of the floating charge switch is connected to one end of the floating charge resistor, the negative electrode of the first diode, the negative electrode of the second diode, and the second end of the charging switch are connected to the first end of the discharge switch, the second end of the discharge switch, the positive electrode of the second diode, and the other end of the floating charge resistor are connected to the first positive power supply end; the negative electrode of the lithium battery pack is connected to the first negative power supply end; wherein the detection control module is respectively connected to the controlled end of the floating charge switch, the controlled end of the balancing switch, the controlled end of the charging switch, and the controlled end of the discharge switch.

8. The lithium battery equalization circuit as claimed in claim 7, characterized in that: The charging switch, the discharging switch and the floating charge switch are all contactors, and the N balancing switches are MOS tubes.

9. The lithium battery equalization circuit according to claim 7, characterized in that: It also includes a bipolar circuit breaker, a fuse and a shunt; one end of the fuse, the first end of the floating charge switch, and the first end of the charging switch are connected to the positive electrode of the first diode, the other end of the fuse is connected to the first end of the bipolar circuit breaker, the second end of the bipolar circuit breaker is connected to the positive electrode of the lithium battery pack, the negative electrode of the lithium battery pack is connected to the third end of the bipolar circuit breaker, the fourth end of the bipolar circuit breaker is connected to the first end of the shunt, and the second end of the shunt is connected to the first negative power supply end; wherein the detection control module is respectively connected to the controlled end of the bipolar circuit breaker and the signal output end of the shunt; The detection control module is further used to control the bipolar circuit breaker to disconnect the lithium battery when it is determined that the current flowing through the shunt is greater than a preset current threshold based on the current detection signal output by the shunt.

10. A UPS system, characterized in that: The UPS system comprises a plurality of lithium battery balancing circuits as described in any one of claims 6 to 9; wherein the first power supply terminal of each of the lithium battery balancing circuits has a first positive power supply terminal and a first negative power supply terminal, the first positive power supply terminals of the plurality of lithium battery balancing circuits are connected in common, and the first negative power supply terminals of the plurality of lithium battery balancing circuits are connected in common.

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