Modular lithium iron phosphate battery with partial charge protection circuit

Abstract

The application discloses a modular lithium iron phosphate battery group provided with a partial charging protection circuit and belongs to the technical field of lithium batteries. The lithium iron phosphate battery group comprises a plurality of battery modules which are mechanically independent and are arranged in series, the battery modules comprise a plurality of standard battery modules and a protection battery module, the protection battery module is located at the total negative electrode position of the lithium iron phosphate battery group, a plurality of batteries which are connected in series are included in the standard battery modules and the protection battery module respectively, a two-terminal voltage stabilizing tube type equalization circuit is connected in parallel at both ends of each battery, and a charging protection circuit is further connected in parallel at both ends of all or part of the batteries in the protection battery module. The protection battery module is always in a leading position of charge compared with the standard battery module, charging protection is provided in the charging process of the battery group, and the safety is high; meanwhile, a discharge protection circuit does not need to be arranged in the battery group, and actual discharge protection depends on an under-voltage protection device provided by an external circuit or an electric appliance.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a modular lithium iron phosphate battery pack with partial charging protection circuitry. Background Technology

[0002] A lithium-ion battery pack is a battery assembly composed of multiple lithium-ion batteries connected in series. The charging process of a lithium-ion battery pack can generally be divided into two stages. The first stage is the direct charging stage, where all batteries in the same series receive the same amount of charge until one battery with a leading voltage reaches its full charge voltage first. Afterwards, the second stage, the equalization charging stage, begins. The equalization circuit across the battery that reached full charge voltage first starts conducting, bypassing a portion of the charging current. This bypass current is the equalization current. Batteries are gradually equalized until the lagging battery also reaches full charge, ending the charging process. During this process, because the charging current is generally greater than the equalization current, the voltage of a fully charged battery continues to rise, triggering charging protection to disconnect the charging circuit. At this point, due to the continued operation of the equalization circuit or the effect of battery self-discharge, the battery voltage gradually decreases until it reaches the value needed to disengage the protection, the charging channel reopens, and the battery voltage begins to rise again. This cycle repeats until all batteries are fully charged. The equalization charging time depends on the maximum charge difference between the individual batteries in the battery pack and the equalization current. This charge difference is generally equal to the product of the difference in self-discharge current between the leading and lagging batteries and the time interval between the two charging cycles. Under normal circumstances, the aforementioned leading voltage battery is not a specific battery; therefore, the voltage of each battery in the battery pack needs to be effectively monitored. Similarly, for discharge protection, the voltage of all batteries needs to be monitored. When the battery voltage exceeds the set charge / discharge protection limits, the battery management system (hereinafter referred to as BMS) will shut down the electrical connection between the battery pack and external circuitry, terminating any potentially unsafe or unreliable conditions. More advanced BMSs also integrate communication functions.

[0003] Because a complete BMS circuit needs to monitor the voltage of each battery in the battery pack, the required test cables are connected to both ends of each battery under test. These cables are then combined into a circuit board with a master control function. Due to the large number of wires and their thin diameter, these test wires cannot be used as external leads to bridge different battery modules. Therefore, lithium-ion battery packs with a complete BMS circuit are generally integrated designs. These integrated lithium-ion battery packs are often large in size and difficult to modify in structure, which greatly limits their application range.

[0004] Typical lithium-ion battery charge / discharge management systems include a switching equalization circuit design. When the battery voltage reaches a specific value (~3.65V), the equalization circuit begins to conduct; when the voltage drops to a specific value, it restarts. These switching devices are generally field-effect transistors (FETs), numerous in number, and highly susceptible to assembly environment variations, resulting in slightly lower reliability. However, even if any one of these equalization circuits fails, the battery pack will not be damaged due to the presence of a complete BMS circuit. Consumers will not easily notice this. The partial loss of functionality in the switching equalization circuit gradually diminishes the consistency of the battery pack, causing a faster decline in usable capacity. This decline stems from the widening difference in charge between leading and lagging batteries, rather than individual battery degradation. Furthermore, the actual installation environment of the equalization circuit in a typical BMS design is often space-constrained, making heat dissipation difficult. Therefore, the power of the equalization circuit is severely limited, especially for lithium iron phosphate (LFP) battery packs. Thus, it is evident that existing LFP batteries face the following technical challenges: Existing BMS circuits are typically complete circuits and generally integrated designs, resulting in large battery packs with difficult structural modifications, limiting their application range, particularly in the replacement of lead-acid batteries. Meanwhile, the switching equalization circuit has low power and poor reliability. Its failure will cause a rapid decline in the usable capacity of the battery pack, thereby reducing the overall lifespan of the battery pack. Furthermore, this switching equalization circuit must rely on a complete charge and discharge protection circuit to provide sufficient protection. Summary of the Invention

[0005] Self-discharge is a key indicator of a battery's charge retention capability, an inherent limitation. The industry generally considers lithium iron phosphate (LFP) batteries to have poor consistency, primarily referring to their higher self-discharge current and poorer charge retention compared to other lithium-ion batteries. The charge differences among cells within a LFP battery pack require a balancing circuit to compensate for these differences, necessitating a more efficient balancing circuit design. Within the same battery pack, the inconsistent self-discharge rates of individual cells, accumulated over time, significantly impact the state of charge (SOC) of each cell, thus affecting the overall consistency of the pack. Cells with lower SOCs become the leading cells, while those with higher SOCs become the lagging cells. This invention patent application introduces a circuit that provides a considerable balancing current at the full-charge voltage of the LFP battery, while allowing for adjustments to the operating current at the LFP battery voltage plateau. This allows for the design of one or more leading charged cells with corresponding charging protection circuitry.

[0006] The purpose of this patent application is to utilize the two-terminal Zener diode-type balancing circuit disclosed in the applicant's prior patent application (201710601910.9, A Composite Voltage Regulator Circuit for Lithium Iron Phosphate Battery Packs) to replace the general switching-type balancing circuit in lithium iron phosphate battery packs. This two-terminal Zener diode-type balancing circuit design uses high-power semiconductor devices and a thermally conductive PCB substrate, resulting in a simple design with high power output. The presence of this high-power continuous balancing circuit avoids the need for a complete charge / discharge protection circuit in certain situations. The lithium iron phosphate battery pack designed in this way can be easily decomposed into multiple module batteries, and the capacity decay of this battery pack is slower, solving several technical problems mentioned in the background art.

[0007] As disclosed in the prior patent application, as the best implementation, this two-terminal Zener diode balancing circuit consists of exactly two power diodes connected in series, at least one of which is a light-emitting diode (LED). Its current at the lithium iron phosphate battery plateau voltage (~3,300V) (hereinafter referred to as the operating current, which is adjustable), while much smaller than its balancing current at full charge voltage, is much larger than the battery's self-discharge current. Therefore, when a battery is connected to a Zener diode with a relatively small operating current, this battery becomes the leading battery in the battery pack. This two-terminal Zener diode balancing circuit has advantages such as low cost, simple design, high power, high voltage withstand capability, and high reliability.

[0008] To achieve the above objectives, this invention discloses a modular lithium iron phosphate battery pack with partial charging protection circuitry, comprising several mechanically independent battery modules connected in series. Each battery module includes multiple standard battery modules and one protection battery module, wherein the protection battery module is located at the overall negative electrode position of the lithium iron phosphate battery pack. Each standard battery module and the protection battery module contains multiple batteries connected in series, and each battery has a two-terminal Zener diode-type balancing circuit connected in parallel across its two ends, which also serves as a self-discharge control circuit. Furthermore, some or all of the batteries in the protection battery module have a charging protection circuit connected in parallel across their two ends; the battery with the parallel charging protection circuit is the protection battery.

[0009] Furthermore, the total number of battery strings in the lithium iron phosphate battery pack is m, and the number of protective battery strings is n, wherein 1 ≤ n ≤ 25%·m.

[0010] Furthermore, the capacity deviation of all batteries is ≤5%.

[0011] Furthermore, the operating current of the two-terminal Zener diode type balancing circuit connected in parallel across the two ends of the protection battery is lower than the operating current of the two-terminal Zener diode type balancing circuit connected in parallel across the two ends of other batteries in the lithium iron phosphate battery pack.

[0012] Furthermore, the operating current of the two-terminal Zener diode type balancing circuit connected in parallel across the two ends of the protection battery is 5%-20% lower than the operating current of the two-terminal Zener diode type balancing circuit connected in parallel across the two ends of other batteries in the lithium iron phosphate battery pack.

[0013] Furthermore, the two-terminal Zener diode type equalization circuit includes a Zener diode.

[0014] Furthermore, the two-terminal Zener diode type equalization circuit includes two forward-connected diodes, at least one of which is a light-emitting diode (LED) device.

[0015] Furthermore, the modular lithium iron phosphate battery pack does not contain any discharge protection circuits.

[0016] Compared to existing integrated battery pack products, this invention adopts a modular design based on lead-acid battery packs, aiming to serve as an alternative in the existing lead-acid power battery aftermarket. The battery pack consists of multiple battery modules, one of which is a charging protection battery. This charging protection battery maintains a higher charge level than other standard batteries in the same pack, providing charging protection during the charging process. Simultaneously, the lithium iron phosphate battery pack is decomposed into several independent battery modules. Using lead-acid battery plastic casings as the outer shell of the battery modules offers significant ease of installation in the lead-acid battery aftermarket. Furthermore, its discharge voltage is set according to the same specifications as lead-acid batteries, so electrical appliances do not require any changes to the internal wiring. Attached Figure Description

[0017] Figure 1 Discharge performance test curve of 12V module battery.

[0018] Figure 2 The circuit diagram of the modular lithium iron phosphate battery pack of the present invention includes partial charging protection circuitry.

[0019] Figure 3 : Circuit diagram of the two-terminal Zener diode type equalization circuit in this invention.

[0020] Figure 4 : A circuit diagram of a preferred modular lithium iron phosphate battery pack of the present invention.

[0021] Figure 5 The charging performance test curves of each battery module in the modular lithium iron phosphate battery pack of the present invention are shown.

[0022] Explanation of reference numerals in the attached diagram: 1-Standard battery module; 2-Protective battery module; 11-First standard battery module; 12-Second standard battery module; 13-Third standard battery module; 21-Charging protection circuit. Detailed Implementation

[0023] The technical solution of the present invention will be described in detail below through specific embodiments.

[0024] Lead-acid batteries, invented over 160 years ago, are widely used in various homes and workplaces today due to their high safety, economy, and durability. They serve as power batteries, starting batteries, UPS systems, and energy storage batteries. A typical lead-acid battery pack consists of multiple battery modules connected one-to-one at their positive and negative terminals. Unlike lithium-ion batteries, lead-acid battery packs do not require a BMS (Battery Management System) for protection; their basic protection comes from charging protection provided by the charger and undervoltage protection provided by the appliance. A significant difference from lithium batteries, which have a fully integrated BMS, is the modular nature of lead-acid batteries, making assembly and installation very convenient. Compared to lead-acid power batteries, lithium-ion battery packs have overwhelming advantages in terms of lifespan and energy density. With the increasing popularity of electric vehicles and the maturation of lithium-ion battery technology, their unit cost has gradually decreased, making economical replacement of lead-acid batteries possible. However, the currently prevalent integrated lithium-ion battery products face significant obstacles in the vast aftermarket for lead-acid power batteries due to their form factor limitations, which is precisely the problem this patent application aims to solve.

[0025] Individual lithium iron phosphate batteries have extremely long cycle life, but due to system integration issues, the power of general-purpose switching equalization circuits is relatively low and their reliability is slightly worse. This makes it difficult to meet consumer expectations for the lifespan of commonly designed lithium iron phosphate battery packs, and the long cycle life expected is hard to achieve, hindering the development of its market.

[0026] The invention patent application (201710601910.9, A Composite Voltage Regulator Circuit for Lithium Iron Phosphate Battery Packs) discloses a method using a two-terminal Zener diode-type balancing circuit as the balancing circuit for lithium iron phosphate battery packs. The method provided in this invention patent application aims to solve this problem by utilizing a high-power Zener diode circuit (with a balancing current requirement of 1-10% of the battery capacity) and permanently connecting it. Simultaneously, it strictly suppresses the operating current and its variation at the lithium iron phosphate battery plateau voltage (3.300V), avoiding excessive leakage when the battery pack is idle for extended periods, and preventing serious adverse effects on its state of charge (or balancing state). The current control requirement at 3.300V is 5%, equivalent to a voltage deviation of less than 3 millivolts for this precision Zener diode during constant temperature and constant current testing.

[0027] In the aforementioned patent application, the precision composite two-terminal Zener diode balancing circuit consists of two diode elements connected in series, at least one of which is an LED. It exhibits precise and consistent current-voltage characteristics at the lithium iron phosphate battery's plateau voltage of 3.3V, and excellent voltage regulation characteristics across the entire operating voltage range of 2.5V to 4.0V. This two-terminal circuit is permanently connected to both ends of each cell within the lithium iron phosphate battery pack. It has a strictly consistent operating current at the lithium iron phosphate battery plateau voltage of 3.300V, and a considerable balancing current (hereinafter referred to as balancing current) at the fully charged voltage of 4.0V. The operating current of this balancing circuit at 3.3V is much greater than the cell's self-discharge current. Since the charge-discharge efficiency of lithium-ion batteries is close to 100%, deep discharge generally does not affect the charge leadership of each cell. The operating current of this two-terminal Zener diode circuit is also part of the battery's total self-discharge. When there are differences in the total self-discharge of cells within the same battery pack, after a certain period of accumulation, it will cause significant changes in the state of charge of each cell within the battery pack. When a Zener diode circuit with a small operating current is connected to several specific batteries, these batteries become the leading charge batteries due to their lower total self-discharge. They reach full charge voltage earlier during charging. Installing charging protection circuits on these leading charge batteries can protect all batteries from overvoltage damage. Simultaneously, a higher-power Zener diode balancing circuit can quickly reduce the charge differences among the batteries, rapidly leveling the voltage of each battery to a uniform full charge voltage.

[0028] Battery packs equipped only with the aforementioned two-terminal voltage regulator balancing circuits without any built-in protection circuits can be acceptable in specific applications, especially where the maximum output voltage of the charger needs to be strictly limited. However, in real-world open-ended applications, such as overvoltage damage due to charger misuse, excessive leakage due to prolonged high-temperature storage, or severe imbalances within the battery pack, the probability of battery pack charging and discharging failure increases dramatically. Therefore, while maintaining the existing battery product form factor, it is necessary to incorporate certain charging protection designs and provide necessary warnings regarding discharge usage under specific conditions.

[0029] It's also important to note that the common industry perception is that lithium batteries are unsafe and require a Battery Management System (BMS) to control safety risks under various abuse conditions while ensuring optimal battery performance. This is because the safety characteristics of different lithium batteries cannot be easily measured and compared. Lithium iron phosphate (LFP) batteries are far safer than ternary lithium batteries or lithium cobalt oxide batteries. Referring to news reports about the probability of spontaneous combustion in electric vehicles equipped with different types of lithium batteries, and as various books have stated, LFP batteries possess extremely high safety. Therefore, the safety protection requirements for LFP batteries do not need to be as stringent as those for polymer lithium batteries. Based on the aforementioned technical solutions, leveraging the high safety of LFP batteries and appropriately strengthening the product structure, the applicant believes that manufacturing a long-life LFP battery pack without a complete BMS circuit is a entirely feasible solution.

[0030] The main circuit of the BMS (Battery Management System) contains two sets of semiconductor switching devices, used to control the charging current and discharging current respectively. These switching devices are typically MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). Since the current-carrying capacity of a single-package MOSFET is limited, multiple MOSFETs are often connected in parallel to achieve greater control capability and a larger current output. In power battery applications, whether lead-acid or lithium-ion, the charging current is generally much smaller than the allowable discharging current; therefore, a larger number of MOSFETs are used for discharge control.

[0031] In practical applications of power battery packs for vehicle propulsion, the battery is charged using a corresponding charger, and the motor is discharged. When protection is triggered, the corresponding MOSFET needs to be turned off. The voltage drop across the charging MOSFET switch is generally no greater than 12V, while the voltage drop across the discharging MOSFET switch is the battery pack voltage, or slightly higher. Furthermore, for a power battery, the lower the total internal resistance, the better its output characteristics and the higher its driving efficiency. The MOSFET used for discharge control contributes to this. The on-resistance of a MOSFET is nearly proportional to its voltage rating. Therefore, compared to MOSFETs used for charging control, MOSFETs used for discharging control require greater current and voltage ratings. These discharge control MOSFETs must also have minimal on-resistance. Resolving this contradiction requires significant investment, and reliability becomes an issue. Conversely, MOSFETs used for charging control have lower current and voltage requirements, resulting in lower costs and higher design reliability.

[0032] Lithium iron phosphate (LFP) batteries exhibit a flat charge-discharge voltage curve, with the majority of energy concentrated near their plateau voltage, slightly higher during charging and slightly lower during discharging. During discharge, approximately 90% of the charge is released at the voltage plateau; however, the discharge voltage drops rapidly in the final 10% as residual capacity is released. When the charge consistency of each battery is good and the capacity difference is less than 5%, the final discharge voltage difference between each battery is minimal. Furthermore, LFP batteries have good tolerance to undervoltage discharge; therefore, monitoring the overall voltage of the battery pack and implementing appropriate undervoltage protection are sufficient to prevent over-discharge of individual cells.

[0033] Such undervoltage protection devices are standard equipment on two- and three-wheeled electric vehicles originally equipped with lead-acid batteries. Therefore, in these specific applications, replacing the corresponding lead-acid batteries with the lithium iron phosphate battery pack disclosed in this invention does not require changing any vehicle wiring, especially the controller. A crucial prerequisite is that the capacity differences between the individual cells within the battery pack are small, and that they remain in a good balanced state. Achieving this good balance requires a high-power, stable, and reliable balancing circuit, which is a characteristic of this high-power voltage regulator balancing circuit.

[0034] A 20AH module battery, consisting of four lithium iron phosphate batteries connected in series with a nominal voltage of 12V (actual 12.8V), was used for discharge testing. The discharge test curve at 0.5C (=10A) is shown below. Figure 1 As shown, the generally set discharge cutoff voltage is 10.5V, consistent with 12V lead-acid batteries. The actual depth of discharge for lithium iron phosphate batteries can be even deeper (~2V per string). The module monitors battery voltage changes. During the final ~10% discharge, the battery voltage drops sharply, triggering discharge protection. When the capacity difference between multiple batteries within the same module is small, this drop is relatively synchronized, and the minimum discharge voltage of each battery module will be concentrated around 10.5V. Therefore, a certain safety design margin is maintained above the absolute lower limit (~8V).

[0035] As we can see, by utilizing the near-linear characteristics at the end of the lithium iron phosphate battery discharge curve, effectively controlling battery capacity differences, using a high-power voltage regulator circuit to ensure the battery pack is always in a good balanced state, and setting an appropriate undervoltage protection device on the external circuit, the above design can avoid the use of BMS discharge management circuit. In addition to cost savings and improved power and reliability, this design ensures the feasibility of this modular battery design.

[0036] When a lithium iron phosphate (LFP) battery pack is charging, once the voltage of a single cell exceeds 3.50V, the capacity increase from continued charging is minimal. However, even up to 4.0V, the LFP battery will not suffer overvoltage damage in a short period. Therefore, the upper limit of the charging voltage for LFP batteries is very flexible. We call 4.0V the ultimate tolerance voltage of the LFP battery. At this voltage, the current of the Zener diode balancing circuit is the maximum balancing current. The minimum fully charged voltage of the LFP module battery constructed based on the precision Zener diode continuous balancing circuit of the aforementioned patent application is 3.50V. Because the Zener diode balancing circuit configured in the battery pack is permanently connected and always in an effective balancing state, the voltage setting required by the charger has great flexibility, ranging from 3.50V to 4.00V. Therefore, the newly designed LFP battery pack can set a lower total charging voltage, minimizing the risk of overcharging.

[0037] The charging protection circuit of a typical lithium iron phosphate battery is set with a start-up voltage between 3.65 and 3.75V. When the voltage of any monitored battery reaches the set protection point, the charging circuit is shut off until the battery voltage drops (through self-discharge or balancing circuitry) to the set voltage value for releasing the protection. Then, the charging channel reopens and charging resumes. This process repeats, and due to the presence of this high-power continuous balancing circuit, the voltage of each battery is gradually leveled out to achieve a consistent equilibrium state.

[0038] Like other lithium batteries, lithium iron phosphate (LFP) batteries have a very high charge-discharge cycle efficiency, approaching 100%. By effectively controlling the battery's leakage current and adjusting the operating current of the connected Zener diode balancing circuit, we can design a few leading batteries. These batteries will be in a leading state during charging, and by detecting their voltages, rather than the voltages of all batteries in the pack, we can effectively protect all batteries. This Zener diode-type continuous balancing circuit, in addition to providing a large balancing current, allows us to significantly reduce the charging voltage, typically set to 3.55V multiplied by the number of battery cells, which is 0.10V lower than the typical charging voltage of an LFP battery pack. It should be noted that incorrectly using a charger with a higher voltage (+12V) will not cause immediate failure of the battery pack. Furthermore, LFP batteries have high safety, therefore this newly designed LFP battery pack has good compatibility with various chargers, or rather, higher resistance to abuse.

[0039] Because the state of charge (SOC) of the protected battery is slightly higher than that of the unprotected battery, in extreme cases, such as deep discharge after long-term idle storage, the standard battery with a lower SOC will reach depletion before the protected battery. With the overall discharge protection voltage limit unchanged, these standard batteries will discharge more deeply. To avoid damage caused by this, the number of protected batteries in series needs to be limited. Based on the proportion of the total number of series in the battery pack, when this proportion is below 25%, the risk of over-discharge damage under this abnormal state can be effectively controlled. Even if such damage eventually occurs, and a few batteries fail, the total battery voltage will drop significantly during the next charging cycle due to the protection circuitry, while the remaining batteries can still be effectively charged. The vehicle can still be ridden, but if the user can promptly detect the problem and report it for repair, further battery damage can be avoided, preventing further impact on user experience.

[0040] Generally, a four-cell lithium iron phosphate (LFP) battery module is used to replace a 12V lead-acid battery, and the subsequent tests were also arranged accordingly. However, since the discharge plateau voltage of a four-cell LFP battery is 12.8V, in higher voltage battery packs, the total number of cells can be appropriately reduced. For example, a nineteen-cell LFP battery pack can be used instead of a twenty-cell pack to replace a 60V lead-acid battery pack. This provides more adequate discharge protection for the battery pack. Based on a 52.5V limit for the 60V lead-acid battery, the cutoff voltage of a single cell can be increased from 2.63V to 2.76V. The resulting problems include slightly reduced power and inconsistent voltage across the battery modules.

[0041] Besides the battery's own self-discharge requiring timely replenishment by the balancing circuit, any circuit connected to a single battery, if its operation depends on the power supply of that single battery rather than the entire battery pack, will have an independent operating current. These operating current values ​​will not be strictly consistent, and their differences will cause the same effect as the battery's self-discharge, leading to a gradual imbalance in the battery pack over time.

[0042] The balancing circuit, typically controlled by the BMS, is usually turned off during non-charging periods or near the battery's plateau voltage. The operating current required by the battery management system comes from the entire battery pack, so the amount of charge lost by each battery over time is exactly the same. The balancing circuit is not needed to replenish this consistently lost charge, and it can be replenished during the direct charging phase.

[0043] like Figure 2The diagram shown is a circuit diagram of a modular lithium iron phosphate battery pack with partial charging protection circuitry provided by the present invention. The lithium iron phosphate battery pack includes an n-string series of lithium iron phosphate batteries B1......Bx......By, Bz......Bn, including multiple standard battery modules 1 and one protection battery module 2. The protection battery module 2 is located at the overall negative terminal of the lithium iron phosphate battery pack. Each standard battery module 1 and protection battery module 2 contains multiple batteries connected in series. In the protection battery module 2, except for the first battery, a charging protection circuit 21 is connected in parallel across both ends of the remaining batteries. The batteries in the protection battery module 2 with the charging protection circuit 21 connected in parallel are protection batteries. Simultaneously, in both the standard battery module 1 and the protection battery module 2, a two-terminal Zener diode type balancing circuit D1......Dx......Dy, Dz......Dn is connected in parallel across both ends of each battery. There are three circuit design methods for the two-terminal Zener diode type balancing circuit, such as... Figure 3 As shown: (1) 3a: a single Zener diode; (2) 3b: two diodes connected in series in forward direction, one of which is a light-emitting diode (LED); (3) 3c: two diodes connected in series in forward direction, both of which are light-emitting diodes (LEDs).

[0044] The two-terminal Zener diode balancing circuit Dz......Dn connected in parallel across the two ends of the protection battery has different parameters compared to the two-terminal Zener diode balancing circuits D1......Dx, Dy connected in parallel across the two ends of other batteries. Specifically, the operating current of the two-terminal Zener diode balancing circuit Dz......Dn is about 5%-20% lower than that of the two-terminal Zener diode balancing circuits D1......Dx, Dy. Therefore, the corresponding battery Bz......Bn (i.e., the protection battery) in the protection battery module 2 is always in a leading charge position.

[0045] A charging protection line 21 is provided on the batteries in the battery protection module 2. Specifically, a charging protection line 21 is provided on all batteries in the battery protection module 2 except for the first battery. In other embodiments, a charging protection line 21 can be provided on all batteries in the battery protection module 2.

[0046] The charging protection circuit 21 can adopt any lithium iron phosphate battery charging protection circuit currently available on the market. For example, the charging protection circuit design in Chinese Invention Patent Application 201910063687.6 (A Safe Charging Protection Method for Lithium Battery Pack and Its Charging Protection Circuit) can be referenced. The charging protection circuit 21 can monitor the voltage of the corresponding battery and shut down the charging channel P- when necessary. B+ and B- are the total positive and negative terminals of the discharge channel, while P- is the negative terminal channel for charging protection. This design is also called a heterogeneous port design, that is, the negative terminals for charging and discharging are set at different ports. When a diode or MOSFET is connected between P- and B- to allow unidirectional current flow during battery discharge, the battery pack is designed as a homogeneous port design, that is, the negative terminals for charging and discharging are both P-, while the B- port is idle.

[0047] When the battery pack is in the above-mentioned port design, there are no semiconductor switching devices on the discharge channel, which provides a ready-made charging channel for electric vehicles with energy recovery, instead of going through the original dedicated charging negative terminal P-.

[0048] In this embodiment, the entire battery pack is divided into several battery modules, namely multiple standard battery modules 1 and one protective battery module 2. Generally, the plastic casing of existing lead-acid batteries can be used as the casing for these battery modules, offering excellent ease of installation in practical applications as a replacement for lead-acid batteries.

[0049] like Figure 3 As shown, this is a preferred embodiment of the present invention. In this embodiment, the battery module includes three standard battery modules and one protection battery module 2. The three standard battery modules are referred to as the first standard battery module 11, the second standard battery module 12, and the third standard battery module 13. Each standard battery module has four batteries connected in series, namely B1-B4, B5-B8, and B9-B12. In the protection battery module 2, four batteries are also connected in series, namely B13-B16; however, charging protection is only provided on the three batteries B14-B16.

[0050] In standard battery module 1, each battery B1-B12 has a two-terminal Zener diode-type balancing circuit D1-D12 connected in parallel across its ends; in protected battery module 2, each battery B13-B16 has a two-terminal Zener diode-type balancing circuit D13-D16 connected in parallel across its ends; in protected battery module 2, charging protection circuit 21 is connected in parallel across the ends of batteries B14-B16 respectively, that is, in protected battery module 2, some batteries have charging protection circuit 21 connected in parallel across their ends. The charging protection circuit 21 includes multiple parallel-connected single-cell protection ICs and a transistor, such as... Figure 4As shown, the charging protection circuit 21 includes three single-cell protection ICs connected in parallel. These three ICs are connected to a transistor, which is simultaneously connected to both the battery pack's total negative terminal and the charging protection negative terminal. At each end of batteries B14-B16, a single-cell protection IC is connected in parallel to detect the real-time voltage of each connected battery. This voltage is then used to control the transistor in the charging protection circuit 21, thereby controlling the opening and closing of the charging negative terminal channel.

[0051] The operating current of the two-terminal Zener diode balancing circuit D14-D16 at room temperature is slightly lower than that of the two-terminal Zener diode balancing circuit D1-D13, specifically 5%-20% lower. Part of this lower current is used to compensate for the operating current required by the connected charging protection circuit. At the same time, the operating current of this two-terminal Zener diode balancing circuit is greatly affected by temperature, while the standby operating current of the charging protection circuit has resistive characteristics and is independent of temperature. Therefore, the operating current setting of this two-terminal Zener diode balancing circuit at room temperature also needs to take into account the influence of ambient temperature.

[0052] In this invention, for example Figure 3 The modular lithium iron phosphate battery pack of the preferred embodiment shown above was subjected to charging performance testing, and the charging process curve is as follows: Figure 5 As shown, the charging channels for the three standard battery modules are CH11, CH12, and CH13, respectively, and the charging channel for the protection battery module is CH21. Each standard battery module and the protection battery module consists of four 3.2V batteries connected in series. The nominal voltage of each module is 12V (the actual voltage is 12.8V), and the nominal voltage of the entire battery pack is 48V. It can be seen that the voltages eventually converge and become completely balanced.

[0053] In this embodiment, the charge differences among the four battery modules in the modular lithium iron phosphate battery pack are as follows: the total charged capacity of the batteries in the first standard battery module 11, the second standard battery module 12, and the third standard battery module 13 is 0.33%, 0.67%, and 1.00% lower than that of the batteries in the protection battery module 2, respectively. Therefore, the batteries in the protection battery module 2 are in a leading position. After being fully charged, their voltage surges rapidly and triggers the charging protection circuit 21, cutting off the charging channel. Subsequently, due to the continuous current flowing through the two-terminal Zener diode balancing circuit, the voltages of the protection battery and the standard battery begin to drop. The voltage value of the protection battery module CH21 shown in the curve includes the voltage dropped across the circuit switching device.

[0054] A few minutes later, the battery voltage drops to the protection release value set by the charging protection circuit 21, and the charging circuit resumes conduction. The battery voltage then begins to rise again until the protection is triggered again, repeating this process multiple times. Due to the near-logarithmic voltage-current relationship of the Zener diode, even a small voltage difference can generate a large current difference. The original difference in charge level is quickly filled. Then, the voltages of each battery module quickly level off, and the battery pack is in a completely uniform balanced state. It is evident that the efficient operation of the charging protection circuit 21 and the two-terminal Zener diode balancing circuit can quickly fill this difference.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the design concept of the present invention should be included within the protection scope of the present invention.

Claims

1. A modular lithium iron phosphate battery pack with partial charging protection circuitry, characterized in that: The system comprises several mechanically independent battery modules connected in series. Each battery module includes multiple standard battery modules and one protection battery module, with the protection battery module located at the negative electrode of the lithium iron phosphate battery pack. Each standard battery module and the protection battery module contains multiple batteries connected in series, with a two-terminal Zener diode-type equalization circuit connected in parallel across both ends of each battery. Some or all of the batteries in the protection battery module also have a charging protection circuit connected in parallel across both ends; the batteries with the parallel charging protection circuit are designated as protection batteries. The capacity deviation of all batteries is ≤5%. The standard battery module and the protection battery module contain the same number of batteries.

2. The modular lithium iron phosphate battery pack with partial charging protection circuitry as described in claim 1, characterized in that: The total number of battery strings in the lithium iron phosphate battery pack is m, and the number of protection battery strings is n, where 1 ≤ n ≤ 25% ˙ m.

3. The modular lithium iron phosphate battery pack with partial charging protection circuitry as described in claim 1, characterized in that: The operating current of the two-terminal Zener diode balancing circuit connected in parallel across the two ends of the protection battery is lower than the operating current of the two-terminal Zener diode balancing circuit connected in parallel across the two ends of other batteries in the lithium iron phosphate battery pack.

4. The modular lithium iron phosphate battery pack with partial charging protection circuitry as described in claim 3, characterized in that: The operating current of the two-terminal Zener diode equalization circuit connected in parallel across the two ends of the protection battery is 5%-20% lower than the operating current of the two-terminal Zener diode equalization circuit connected in parallel across the two ends of other batteries in the lithium iron phosphate battery pack.

5. The modular lithium iron phosphate battery pack with partial charging protection circuitry as described in claim 1, characterized in that: The two-terminal Zener diode type equalization circuit includes a Zener diode.

6. The modular lithium iron phosphate battery pack with partial charging protection circuitry as described in claim 1, characterized in that: The two-terminal Zener diode type equalization circuit includes two forward-connected diodes, at least one of which is a light-emitting diode (LED) device.

7. The modular lithium iron phosphate battery pack with partial charging protection circuitry as described in any one of claims 1-6, characterized in that: The modular lithium iron phosphate battery pack does not have any discharge protection circuits.

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