Lithium battery equalization system and equalization method thereof

Abstract

The invention discloses a lithium battery equalization system and an equalization method thereof, and mainly relates to the field of lithium battery charging. Comprising a plurality of battery cells and a power supply management system, the power supply management system is connected with each battery cell, and the lithium battery equalization system further comprises a direct charging circuit and a conversion circuit; the direct charging circuit comprises a first switch connected with the power management system; and the first switch is connected in series with the plurality of battery cells. The method has the advantages that the method is used for controlling the cell voltage balancing method in the lithium battery charging process, a traditional lithium battery balancing method is changed, the balancing time in the lithium battery charging process is greatly shortened through conversion between the two circuits, and the temperature generated by a BMS is reduced. In addition, the lithium battery can be quickly charged without causing overcharge of the lithium battery, heat generated during charging of the lithium battery can be reduced, and the heat is concentrated on the charger instead of the lithium battery. The whole circuit is simple in structure, practical and capable of efficiently realizing lithium battery equalization.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery charging, and in particular to a lithium battery equalization system and an equalization method thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Lithium battery balancing technology is an important part of the battery management system BMS. Its main function is to ensure that multiple lithium battery cells connected in series maintain the same voltage level during the charging and discharging process, thereby extending the overall service life of the battery pack, improving the energy utilization efficiency of the battery pack, and ensuring safe use. In a lithium battery pack, due to differences in the internal resistance, capacity, self-discharge rate and other characteristics of the battery cells, after multiple charges and discharges, the voltages of the cells will be inconsistent. Cells with low voltage may not be fully discharged, while cells with high voltage may not be fully charged. This phenomenon is called battery imbalance. If balancing is not performed, the overall performance of the battery pack will be limited by the worst cell, and may cause some battery cells to be overcharged or over-discharged, thereby reducing the battery capacity, damaging the battery, and even causing safety issues.

[0004] At present, lithium battery equalization technology mainly includes the following two types: active equalization and passive equalization. Active equalization: through an active control circuit, the excess energy of the high-voltage unit is directly transferred to the low-voltage battery cell (not fully charged), and the partially charged battery cell is charged through the active control circuit. In this method, the charging time is long, the charging efficiency is low, the equipment is complex, and the converter will generate heat. Passive equalization: discharge the fully charged battery cell, and then discharge the fully charged battery cell to the partially charged battery cell, so as to charge the partially charged battery cell. However, this method takes a long time to charge, especially generates a lot of heat, has low charging efficiency, and low current. It is also subject to the capacity of the fully charged battery cell, especially after the battery cell has been used for a period of time, the battery cell capacity will decrease, so the whole process is affected by the battery cell capacity. For the above two lithium battery charging equalization methods, the first is the large heat generation (especially passive equalization). For lithium batteries, heat is the most important factor affecting the safety and life of lithium batteries. The second is the low equalization efficiency and long time. Passive equalization limits the current size due to the heat generation of the load, and can only consume a small current. The charger will charge as much as it consumes, which takes too long. Active balancing takes time to recover the current of a fully charged cell. After the current is recovered, it is tested again and the battery with the lowest voltage is charged. This repetition increases the time. The flow of current in and out will also increase the heat of the cell. Moreover, the equipment is relatively complex and the failure rate is relatively high. Summary of the invention

[0005] The purpose of the present invention is to provide a lithium battery equalization system and its equalization method, which is used to control the cell voltage equalization method during the lithium battery charging process, and changes the traditional lithium battery equalization method. Through the conversion between the two circuits, the equalization time of the lithium battery charging process is greatly reduced, and the temperature generated by the BMS is reduced. It can also charge the lithium battery quickly without causing the lithium battery to be overcharged, and can reduce the heat generated by the lithium battery during charging, and the heat is concentrated on the charger rather than the lithium battery itself. The overall circuit structure is simple and practical, and can also achieve efficient lithium battery equalization.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A lithium battery equalization system includes a plurality of battery cells and a power management system, wherein the power management system is connected to each battery cell, and the lithium battery equalization system further includes a direct charging circuit and a conversion circuit; the direct charging circuit includes a first switch connected to the power management system; the first switch is connected in series with the plurality of battery cells;

[0008] The conversion circuit includes a second switch connected to a power management system and multiple voltage converters; the number of the voltage converters is adapted to the number of battery cells, the voltage converters are connected in parallel with the battery cells, and the second switch is connected in series with the battery cells and the voltage converters; the power management system controls the opening and closing of the first switch and the second switch according to the battery cell voltage.

[0009] A charging equalization method for a lithium battery equalization system, S1, after the lithium battery equalization system is charged by an external charger, a power management system detects and determines the cell voltage;

[0010] S2, when the voltage of any battery cell is lower than the saturation voltage, the power management system controls the first switch to close and the second switch to open, and the charger charges the multiple battery cells after connecting to the power supply. During the charging process, the power management system monitors the voltage of each battery cell;

[0011] S3, when the voltage of any battery cell is equal to the saturation voltage, the power management system controls the first switch to open and the second switch to close, and the power supply connected to the charger converts the voltage to a voltage suitable for direct charging of the battery cell through a voltage converter. The battery cell that has reached the saturation voltage is controlled by the power management system to no longer be charged, and the battery cells that have not reached the saturation voltage are charged until all the battery cells reach the saturation voltage.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: the present application is used to control the cell voltage equalization method during the lithium battery charging process, which changes the traditional lithium battery equalization method. Through the conversion between the two circuits, the equalization time of the lithium battery charging process is greatly reduced, and the temperature generated by the BMS is reduced. It can also charge the lithium battery quickly without causing the lithium battery to be overcharged, and can reduce the heat generated by the lithium battery during charging, and the heat is concentrated on the charger rather than the lithium battery itself. The overall circuit structure is simple and practical, and can also achieve efficient lithium battery equalization. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Attached Figure 1 It is a circuit diagram of the present invention.

[0014] Numbers shown in the accompanying drawings:

[0015] 1. Battery cell; 2. Power management system; 3. Charger; 4. First switch; 5. Second switch; 6. Voltage converter. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the application equally.

[0017] The present invention describes a lithium battery balancing system, including multiple battery cells 1 and a power management system 2 connected to each battery cell 1. In the existing lithium battery balancing systems, most of them monitor the voltage of one battery cell 1, rather than all of them. This results in that the existing lithium battery balancing systems, whether active or passive balancing, are charged based on one battery cell 1, so the present application improves it. The battery management system (BMS) is a key component in electric vehicles and lithium batteries, and is mainly responsible for monitoring and regulating the operating status of the battery. Its core functions include status monitoring, balancing control, fault diagnosis and protection, communication interface management, thermal management, charging and discharging control, data recording and storage, and user interface interaction to ensure the safety, stability and life of the battery. The BMS in this article is mainly used to monitor the voltage of the battery cell 1 to avoid overcharging of the battery cell 1, and can more reasonably distribute the charging process of the lithium battery cell 1. The conversion of the two circuits of the charging device is controlled by the battery management system. The following is described according to the control process, as shown in the accompanying drawings of the specification. Figure 1 As shown:

[0018] S1, after the lithium battery equalization system is charged by the external charger 3, the power management system 2 detects and judges the voltage of the battery cell 1, and after judgment, selects from the direct charging circuit and the conversion circuit. The direct charging circuit and the conversion circuit and the conversion circuit specifically include: the direct charging circuit includes a first switch 4 connected to the power management system 2, and the first switch 4 is connected in series with multiple battery cells 1; the conversion circuit includes a second switch 5 and multiple voltage converters 6 connected to the power management system 2; the number of the voltage converters 6 is adapted to the number of power battery cells 1, each of the voltage converters 6 is connected in parallel with the battery cell 1, and the second switch 5 is connected in series with the battery cell 1 and the voltage converter 6. The voltage converter 6 is a DC-DC module, which is a device that converts electrical energy of one voltage value into electrical energy of another voltage value in a DC circuit. It adopts microelectronic technology and assembles small surface-mounted integrated circuits and microelectronic components into one body.

[0019] S2, after the battery management system determines that when the voltage of any battery cell 1 is lower than the saturation voltage, the power management system 2 controls the first switch 4 to close and the second switch 5 to open, and the power source connected to the charger 3 is charged through the direct charging circuit, and the charger 3 steps down the power source to a voltage suitable for the lithium battery cell 1 group, and then charges the multiple battery cells 1. During the charging process, the power management system 2 monitors the voltage of each battery cell 1. When any battery cell 1 is fully charged, the voltage will reach the saturation voltage, and the conversion circuit needs to be performed after reaching the saturation voltage;

[0020] S3, when the voltage of any battery cell 1 is equal to the saturation voltage, the power management system 2 controls the first switch 4 to be disconnected and the second switch 5 to be closed. At this time, the direct charging circuit is disconnected and replaced by the conversion circuit. After the circuit is converted, the power supply connected to the circuit converts the voltage to a voltage suitable for direct charging of the battery cell 1 through the voltage converter 6 connected in parallel with the battery cell 1, so that the charger 3 can directly charge the battery cell 1. For the battery cell 1 that has reached the saturation voltage, the battery management system controls the battery cell 1 so that the charger 3 cannot charge the fully charged battery cell 1, and charges the battery cell 1 that has not reached the saturation voltage until all the battery cells 1 reach the saturation voltage.

[0021] For the process of the battery management system controlling the opening and closing of the first switch 4 and the second switch 5, the order of the two cannot be reversed, and the direct charging circuit and the conversion circuit cannot work at the same time. When charging directly with the conversion circuit, the battery is in a low power state. At this time, the charging current through the conversion circuit is large, and the voltage converter 6 will generate heat. Compared with charging with the direct charging circuit, the heat generating component is mainly in the charger 3, not in the lithium battery itself, so the lithium battery is charged through the direct charging circuit first, and when one of the battery cells 1 is fully charged, it is charged through the conversion circuit. At this time, the charging power is reduced, and the heat generated is reduced.

[0022] In summary, the present application is used to control the cell voltage equalization method during the lithium battery charging process, which changes the traditional lithium battery equalization method. Through the conversion between the two circuits, the equalization time of the lithium battery charging process is greatly reduced, and the temperature generated by the BMS is reduced. It can also charge the lithium battery quickly without causing the lithium battery to be overcharged, and can reduce the heat generated by the lithium battery during charging, and the heat is concentrated on the charger 3 rather than the lithium battery itself. The overall circuit structure is simple and practical, and can also achieve efficient lithium battery equalization.

Claims

1. A lithium battery balancing system, comprising a plurality of battery cells (1) and a power management system (2), characterized in that: The power management system (2) is connected to each battery cell, and the lithium battery equalization system further comprises a direct charging circuit and a conversion circuit; The direct charging circuit comprises a first switch (4) connected to a power management system (2); the first switch (4) is connected in series with a plurality of battery cells (1); The conversion circuit comprises a second switch (5) connected to the power management system (2) and a plurality of voltage converters (6); the number of the voltage converters (6) matches the number of the battery cells (1), the voltage converters (6) are connected in parallel with the battery cells (1), and the second switch (5) is connected in series with the battery cells (1) and the voltage converters (6); The power management system (2) controls the opening and closing of the first switch (4) and the second switch (5) according to the voltage of the battery cell (1).

2. A charging equalization method for a lithium battery equalization system, characterized in that: A lithium battery equalization system comprising claim 1; S1, after the lithium battery equalization system is charged by the external charger (3), the power management system (2) detects and determines the voltage of the battery cell (1); S2, when the voltage of any battery cell (1) is lower than the saturation voltage, the power management system (2) controls the first switch (4) to close and the second switch (5) to open, and the charger (3) charges the multiple battery cells (1) after connecting to the power supply, and the power management system (2) monitors the voltage of each battery cell (1) during the charging process; S3, when the voltage of any battery cell (1) is equal to the saturation voltage, the power management system (2) controls the first switch (4) to be disconnected and the second switch (5) to be closed, and the power source connected to the charger (3) converts the voltage to a voltage suitable for direct charging of the battery cell (1) through the voltage converter (6), and the battery cell (1) that has reached the saturation voltage is controlled by the power management system (2) to no longer be charged, and the battery cells (1) that have not reached the saturation voltage are charged until all the battery cells (1) reach the saturation voltage.

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