Cell balancing method and cell balancing system

Abstract

A cell balancing method includes acquiring voltage information of a plurality of batteries in a battery pack when charging, acquiring a voltage-time curve of each battery based on the voltage information of the batteries, determining a start time for the battery pack to perform cell balancing, estimating a length of charging time of each battery from the start time to a fully charged time based on the voltage-time curve of each battery, and adjusting a charging power of each battery to balance the power of the batteries in the battery pack based on the length of charging time of each battery.

Description

Technical Field

[0001] This invention discloses a battery power balancing method and a battery power balancing system, particularly a battery power balancing method and system with low complexity and high accuracy. Prior Technology

[0002] With the development of battery technology, the Battery Management System (BMS) plays a crucial role in battery performance, lifespan, and safety. The functions of a BMS encompass communication, monitoring, control, protection, and recording. As BMS technology has advanced, its functionality has evolved from the early safety protection level to the battery performance level. This means that the BMS must perform calculations and evaluations based on the monitored data to make optimal decisions and maximize system efficiency.

[0003] Cell balancing (CB) technology is a crucial component of a Battery Management System (BMS). Due to variations in battery quality during manufacturing and aging during use, battery capacity imbalances can occur. Inconsistent capacity among individual cells in a battery pack affects overall performance, necessitating CB technology to address this imbalance and improve overall battery pack efficiency. CB architectures are primarily divided into active and passive balancing. Active balancing works by adjusting the charge levels between cells to achieve uniformity, but it is more costly. Passive balancing discharges the imbalanced charge, but requires additional heat dissipation management. CB methods are mainly categorized into capacity-based and voltage-based methods. Capacity-based methods require significant space to store open-circuit voltage curves and have higher computational complexity. Voltage-based methods are more common in practical applications because they only require voltage information and have lower computational complexity.

[0004] However, voltage-based battery balancing methods also have some drawbacks. Since only voltage information is available, the IR drop (discharge) or IR increase (charge) under load will vary due to the different resistance within each cell. This makes it impossible to correctly select the cells that need to be balanced or to accurately calculate the amount of charge that needs to be balanced. Summary of the Invention

[0005] One embodiment of the present invention provides a battery charge balancing method. The battery charge balancing method includes collecting voltage information of a plurality of batteries in a battery pack during charging; obtaining a voltage-time curve for each battery based on the voltage information; determining the time point for performing charge balancing on the battery pack; estimating the charging time of each battery from the time point to the full charge time based on the voltage-time curve of each battery; and adjusting the charging power of each battery based on the charging time of each battery, so as to achieve charge balancing among the batteries in the battery pack.

[0006] Another embodiment of the present invention provides a battery charge balancing system. The battery charge balancing system includes a battery pack, a voltage detection circuit, a battery charge balancing control circuit, and a processor. The battery pack includes a plurality of batteries. The voltage detection circuit is coupled to the battery pack to detect the voltage of the batteries. The battery charge balancing control circuit is coupled to the battery pack to control the charging mode of the batteries. The processor is coupled to the voltage detection circuit and the battery charge balancing control circuit to control the voltage detection circuit and the battery charge balancing control circuit. The processor collects voltage information of the batteries in the battery pack during charging through the voltage detection circuit. Based on the voltage information of the batteries, the processor obtains a voltage-time curve for each battery. The processor determines the time point for the battery pack to perform charge balancing. Based on the voltage-time curve of each battery, the processor estimates the charging time length of each battery from the time point to the full charge time point. Based on the charging time length of each battery, the processor uses the battery charge balancing control circuit to adjust the charging power of each battery to achieve charge balancing among the batteries in the battery pack. Simple Explanation of the Diagram

[0007] Figure 1 is a block diagram of an embodiment of the battery power balancing system of the present invention. Figure 2 is a schematic diagram of the battery power balance system in Figure 1, which estimates the charging time of each battery from a given time point to a fully charged time point based on the voltage-time curve of each battery. Figure 3 is a flowchart of the battery power balancing system in Figure 1, illustrating the battery power balancing method. Implementation

[0008] Figure 1 is a block diagram of an embodiment of the battery power balancing system 100 of the present invention. The battery power balancing system 100 is designed to solve the problem of inconsistent battery power among batteries in a battery pack, thereby improving the overall performance of the battery pack. By collecting voltage information during battery charging and discharging, calculating the rate of rise / fall of battery voltage, and then estimating the charging / discharging time required for each battery to reach full charge / depletion, the performance of the battery power balancing technology is improved. For ease of understanding, the battery power balancing system 100 will be described below using the power balancing mechanism of a battery during "charging".

[0009] The battery balancing system 100 includes a battery pack 10, a voltage detection circuit 11, a battery balancing control circuit 12, and a processor 13. The battery pack 10 includes a plurality of batteries 101 to 10N, where N is a positive integer greater than 2. The battery pack 10 is composed of multiple batteries 101 to 10N connected in series for storing electrical energy and providing power. Batteries 101 to 10N can be lithium-ion rechargeable batteries or any reasonable rechargeable battery. The voltage detection circuit 11 is coupled to the battery pack 10 to detect the voltage of the batteries 101 to 10N. For example, the voltage detection circuit 11 can detect the voltage of each battery in the battery pack 10 and transmit the voltage information to the processor 13 for analysis and processing. By monitoring the voltage changes of each battery, the processor 13 can collect voltage information during battery charging and discharging, and thereby calculate the rate of voltage rise or fall, and estimate the time required for each battery to reach full charge or depletion. This information is used to determine the difference in battery capacity and serves as the basis for battery capacity balancing control. The battery capacity balancing control circuit 12 is coupled to the battery pack 10 and controls the charging modes of the batteries 101 to 10N. For example, the battery capacity balancing control circuit 12 can be composed of multiple transistor switches. Under the control of the processor 13, based on the capacity balancing strategy of the battery pack 10, the processor 13 controls the charging current of the multiple transistor switches using the duty cycle, thereby controlling the charging modes of the batteries 101 to 10N. The processor 13 is coupled to the voltage detection circuit 11 and the battery capacity balancing control circuit 12 and controls both circuits.

[0010] In the battery power balancing system 100, the processor 13 collects voltage information of the batteries 101 to 10N in the battery pack 10 during charging via the voltage detection circuit 11. Based on the voltage information of the batteries 101 to 10N, the processor 13 obtains the voltage-time curve for each battery. The processor 13 determines the timing for performing power balancing in the battery pack 10. Based on the voltage-time curve of each battery, the processor 13 estimates the charging time for each battery from the specified time point to the point of full charge. Based on the charging time of each battery, the processor 13 adjusts the charging power of each battery using the battery power balancing control circuit 12 to achieve power balance among the batteries 101 to 101N in the battery pack 10.

[0011] Furthermore, any reasonable hardware modifications to the battery balancing system 100 fall within the scope of this embodiment. For example, the battery balancing system 100 may also include a temperature detection module 14. The temperature detection module 14 is coupled to the battery pack 10 and the processor 13. The processor 13 controls the temperature detection module 14 to detect the temperature of each battery in the battery pack 10. The processor 13 can adjust the discharge rate of each battery based on its temperature using the battery balancing control circuit 12. It should be understood that battery temperature affects its performance and lifespan. Operating a battery outside its temperature specifications, whether too high or too low, will accelerate battery aging and reduce battery capacity. By detecting battery temperature, the processor 13 can adjust the battery discharge rate based on temperature information to protect the battery and extend its lifespan. For example, when the battery temperature is too high, the processor 13 can reduce the discharge rate to avoid overheating. The battery balancing system 100 may also include memory 15. Memory 15 is coupled to processor 13 and stores the code and data required by processor 13 to execute the battery balancing method. Memory 15 can be any suitable memory, such as non-volatile memory (e.g., flash memory, hard disk) or volatile memory (e.g., DRAM, SRAM). It should be understood that the code and data stored in memory 15 can vary depending on the specific application and requirements of battery balancing system 100. For example, memory 15 can store battery voltage-time curves, battery balancing parameter settings, battery temperature information, etc. In other embodiments, battery balancing system 100 may also include a current detection circuit (not shown). The current detection circuit may be coupled to processor 13 and battery pack 10. The current detection circuit detects the current of battery pack 10 and transmits the current information to processor 13. Therefore, processor 13 determines whether battery pack 10 is under load, whether it is charging or discharging, and monitors the magnitude of the charging or discharging current of battery pack 10 based on the current information. In this embodiment, the battery power balancing system 100 can achieve battery power balancing in a voltage-based manner, the details of which will be described later.

[0012] Figure 2 is a schematic diagram illustrating how, in the battery balancing system 100, the charging time of each battery from time point T0 to the full charge time point (TA and TB) is estimated based on the voltage-time curve of each battery. The X-axis is the time axis, and the Y-axis is the voltage axis. In the battery balancing system 100, when battery balancing is not activated in the battery pack 10, the processor 13 can use the voltage detection circuit 11 to measure the corresponding multiple voltages of each battery 101 to 10N in the battery pack 10 at multiple time points. For example, the initial voltage of battery 102 in the battery pack 10 is Vini, and when battery balancing is not activated, the voltage of battery 102 at different times during charging can be multiple voltage nodes on the voltage-time curve CB. In another battery 101 in the battery pack 10, when battery balancing is not activated, the voltage of battery 101 at different times during charging can be multiple voltage nodes on the voltage-time curve CA. It should be understood that all batteries 101 to 10N within battery pack 10 undergo rigorous quality inspection at the factory to ensure their performance and consistency. Therefore, the voltage-time curves of all batteries 101 to 10N should be identical at the time of manufacture. However, with battery use and aging, the internal resistance of each battery will vary, leading to differences in their voltage-time curves. For example, if battery balancing is not enabled, according to the voltage-time curve CB, battery 102 will reach the target voltage Vtar first, i.e., the fully charged state. However, if battery balancing is not enabled, according to the voltage-time curve CA, battery 101 may reach the target voltage Vtar later due to its lower internal resistance.

[0013] In this embodiment, the generation and configuration of multiple voltage nodes can be based on any reasonable strategy. For example, multiple voltage nodes are voltage values ​​recorded at different time points during battery charging. These voltage nodes are used to depict the curve of battery voltage change over time. The configuration of multiple voltage nodes can be in modes such as placing nodes across the entire area, placing nodes only in high and low voltage areas, equidistant nodes, unequally spaced nodes, multi-point averaging of voltage information, and weighted averaging of voltage information. In the mode of placing nodes across the entire area, multiple voltage nodes are recorded evenly distributed across the entire range of battery voltage variation. In the mode of placing nodes only in high and low voltage areas, voltage nodes are recorded only in the highest and lowest ranges of battery voltage, ignoring the intermediate areas of gradual voltage change. In the mode of equidistant nodes, the time interval between each voltage node is the same. In the mode of unequally spaced nodes, the time interval between each voltage node can be different; for example, more densely packed nodes can be set in areas where voltage changes rapidly. In the mode of multi-point averaging of voltage information, the average voltage at multiple time points is taken as the representative voltage for that time period. In the voltage information weighted averaging model, different weights are assigned to the voltage at different time points to calculate the weighted average voltage. Furthermore, the voltage-time curve can be generated linearly or as a multi-point regression curve.

[0014] In this embodiment, the rate of increase of the charging voltage within a time interval can be represented by the slope between two voltage nodes on the voltage-time curve. For example, in the voltage-time curve CA, the slope between voltage node A2 and voltage node A3 can be expressed as:

[0015] in This represents the voltage value at voltage node A3 on the Y-axis. This represents the voltage value at voltage node A2 on the Y-axis. This indicates the moment when voltage node A3 is on the X-axis. This indicates the moment when voltage node A2 is perpendicular to the X-axis. Slope Indicates a point in time up to the time point The processor 13 can interpolate or extrapolate the measured voltages of each battery to generate a voltage-time curve for each battery. The processor 13 can also dynamically adjust the voltage-time curve of each battery as the battery's usage time increases. For example, at any point T0 during battery balancing in the battery pack 10, the current voltage node B1 of battery 102 can be measured, and voltage nodes B2 to B4 on the voltage-time curve CB, along with their corresponding times, are pre-stored in memory 15. Since voltage node B4 can be considered as the voltage node where battery 102 has reached the target voltage Vtar and is fully charged, its corresponding time point is TB. Therefore, the processor 13 can predict that, for battery 102, if battery balancing is not performed, the time required from time point T0 to a fully charged state is TB-T0.

[0016] In another embodiment, at time T0 when the battery pack 10 performs charge balancing, the current voltage node A1 of the battery 101 can be measured, and the voltage nodes A2 to A3 on the voltage-time curve CA and their corresponding times have been pre-stored in memory 15. However, although voltage node A4 and voltage node A5 of the target voltage Vtar are not measured (corresponding to time TA), and their true slopes are unknown (therefore represented by dashed lines), the processor 13 can still estimate, through interpolation calculations, that for the battery 101, if charge balancing is not performed, the time required from time T0 to a fully charged state is TA-T0, as shown below:

[0017] in This indicates the moment when voltage node A2 is on the X-axis. This represents the target voltage Vtar. This represents the voltage value at voltage node A2 on the Y-axis. The slope between voltage nodes A2 and A3 has been described previously. In other words, processor 13 uses voltage detection circuit 11 to measure the voltage corresponding to the time point T0 when each battery in the battery pack 10 performs charge balancing. Based on the voltage corresponding to the time point T0 when each battery performs charge balancing and the voltage-time curve of each battery, processor 13 calculates the charging voltage rise rate of each battery in different time intervals. Then, processor 13 can estimate the charging time length of each battery from time point T0 to the full charge time point based on the charging voltage rise rate of each battery in different time intervals, and the full charge time point corresponds to the time point when each battery is charged to the full charge voltage (which may be equal to the target voltage Vtar).

[0018] One of the design objectives of the battery balancing system 100 is to ensure that, after balancing the charge of batteries 101 to 10N within the battery pack 10, the time required for these batteries 101 to 10N to reach a fully charged state is substantially the same. In other words, after initiating battery balancing of the battery pack 10 at time T0, the goal is to fully charge all batteries 101 to 10N simultaneously (or nearly simultaneously). To achieve this, the battery balancing system 100 implements a mechanism to align full charge. Specifically, if the charging time of one battery within the battery pack 10 is shorter than the charging time of the other batteries within the battery pack 10, it indicates that this battery is expected to reach the target voltage first. Therefore, the battery balancing control circuit 12 can charge this battery within the battery pack 10 in a slow-charging mode and charge the other batteries within the battery pack 10 in a normal mode. In another embodiment, if the charging time of one battery within the battery pack 10 is longer than the charging time of the other batteries within the battery pack 10, it indicates that this battery is expected to reach the target voltage last. Therefore, the battery power balance control circuit 12 can charge this battery in the battery pack 10 in normal mode and charge the other batteries in the battery pack 10 in slow charging mode.

[0019] As mentioned earlier, the battery power balancing control circuit 12 can perform slow charging mode or normal charging mode for certain batteries. The processor 13 can set the duty cycle for each battery during charging based on its charging power. It should be understood that the duty cycle refers to the ratio of charging time to total charging time within a charging cycle. A higher duty cycle results in faster charging, while a lower duty cycle results in slower charging. The battery power balancing control circuit 12 can control the charging speed of batteries through the duty cycle to achieve battery power balancing. For example, if a battery needs to perform slow charging mode, its duty cycle can be reduced to slow down its charging speed, allowing other batteries with lower power levels to catch up. Conversely, if a battery needs to perform normal charging mode, its duty cycle can be increased to speed up its charging speed, allowing it to catch up with other batteries with higher power levels. In other words, an increase in the duty cycle increases the charging power, while a decrease in the duty cycle decreases the charging power.

[0020] Figure 3 is a flowchart illustrating the battery power balancing system 100 and the execution of a battery power balancing method. The battery power balancing method includes steps S301 to S305. Any reasonable changes to the steps fall within the scope of the embodiments disclosed. Steps S301 to S305 are described below. Step S301: Collect voltage information of multiple cells 101 to 10N within the battery pack 10 during charging; Step S302: Based on the voltage information of these batteries from 101 to 10N, the voltage-time curve of each battery was obtained; Step S303: Determine the time point T0 for battery pack 10 to perform charge balancing; Step S304: Based on the voltage-time curve of each battery, estimate the charging time of each battery from time point T0 to the full charge time. Step S305: Based on the charging time of each battery, the charging power of each battery is adjusted to balance the charge of the batteries 101 to 10N in the battery pack 10.

[0021] The details of steps S301 to S305 have been described in detail above, and will not be repeated here. Unlike traditional battery balancing systems that only observe the "current" voltage value to perform balancing, battery balancing system 100 utilizes the voltage-time curve of each battery to accurately estimate the charging time of each battery. Since the voltage-time curve is not linear, traditional battery balancing systems that only observe the "current" voltage value to perform balancing may experience charge deviations in high-voltage areas. Incorrect battery balancing can lead to low charging efficiency or even danger. Therefore, the battery balancing system 100 of this embodiment can accurately perform battery balancing, thus improving charging efficiency and charging safety.

[0022] In summary, the embodiments provide a battery balancing system and a battery balancing method. The battery balancing system and method utilize the voltage-time curve of each battery to accurately estimate the charging time of each battery, thereby improving the efficiency and safety of battery balancing. Furthermore, the voltage-time curve of each battery can be dynamically adjusted to adapt to battery aging and usage conditions. In other embodiments, the battery balancing system and method can adjust the charging and discharging rate of the battery according to its temperature to protect the battery and extend its lifespan. Compared to traditional battery balancing systems, the battery balancing system provided in these embodiments can accurately perform battery balancing, thus improving charging efficiency and safety. Therefore, it is very suitable for various battery packs, such as electric vehicles, energy storage systems, and various electronic products. The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made in accordance with the claims of the present invention shall be covered by the present invention.

[0023] 100: Battery power balancing system 10: Battery Pack 101 to 10N: Battery 11: Voltage Detection Circuit 12: Battery power balance control circuit 13: Processor 14: Temperature Detection Module 15: Memory Vini: Initial Voltage Vtar: Target voltage CA and CB: Voltage-Time Curves A1, A2, A3, A4, A5: Voltage nodes B1, B2, B3, B4: Voltage nodes T0, TA, TB: Time points S301 to S305: Steps

Claims

1. A battery charge balancing method, comprising: collecting voltage information of a plurality of batteries in a battery pack during charging; obtaining a voltage-time curve for each battery based on the voltage information; determining a time point for the battery pack to perform charge balancing; estimating a charging time length for each battery from the time point to a fully charged time point based on the voltage-time curve of each battery; and adjusting a charging power of each battery based on the charging time length of each battery to achieve charge balancing of the batteries in the battery pack.

2. The method as described in claim 1, wherein collecting the voltage information of the batteries in the battery pack during charging includes: measuring the corresponding plurality of voltages of each of the batteries in the battery pack at a plurality of time points when battery power balancing is not enabled.

3. The method as described in claim 2, wherein obtaining the voltage-time curve of each battery based on the voltage information of the batteries comprises: performing numerical interpolation or numerical extrapolation on the corresponding voltages measured for each battery to generate the voltage-time curve of each battery; wherein the voltage-time curve of each battery is dynamically adjusted as the usage time of each battery increases.

4. The method as described in claim 1, further comprising: measuring a voltage corresponding to one of the time points at which each battery in the battery pack performs charge balancing; and calculating the rate of increase of the charging voltage of each battery in different time intervals based on the corresponding voltage at the time point at which each battery performs charge balancing and the voltage-time curve of each battery, using a plurality of slopes.

5. The method as described in claim 4, wherein estimating the charging time length of each battery from the point in time to the point of full charge comprises: estimating the charging time length of each battery from the point in time to the point of full charge based on the rate of increase of the charging voltage of each battery in different time intervals; wherein the point of full charge corresponds to a point in time when each battery is charged to a full charge voltage.

6. The method as described in claim 1, wherein adjusting the charging power of each battery according to the charging time of each battery to balance the charge of the batteries in the battery pack comprises: if the charging time of one battery in the battery pack is greater than the charging time of the other batteries in the battery pack, charging the battery in the battery pack in a normal mode, and charging the other batteries in the battery pack in a slow charging mode.

7. The method as described in claim 1, wherein adjusting the charging power of each battery according to the charging time of each battery to balance the charge of the batteries in the battery pack comprises: if the charging time of one battery in the battery pack is less than the charging time of the other batteries in the battery pack, charging the battery in the battery pack in a slow charging mode, and charging the other batteries in the battery pack in a normal charging mode.

8. The method as described in claim 1, further comprising: setting a duty cycle for each battery during charging based on the charging power of each battery; wherein if the duty cycle increases, the charging power increases, and if the duty cycle decreases, the charging power decreases.

9. The method as described in claim 1, further comprising: detecting a temperature of each of the batteries in the battery pack; and adjusting a discharge rate of each battery based on the temperature of each battery.

10. The method as described in claim 1, wherein the batteries in the battery pack are connected in series, and after the batteries in the battery pack are balanced, the time required for the batteries to be charged to a fully charged state is substantially the same.

11. A battery power balancing system, comprising: a battery pack including a plurality of batteries; a voltage detection circuit coupled to the battery pack for detecting the voltage of the batteries; a battery power balancing control circuit coupled to the battery pack for controlling the charging mode of the batteries; and a processor coupled to the voltage detection circuit and the battery power balancing control circuit for controlling the voltage detection circuit and the battery power balancing control circuit; wherein the processor collects voltage information of the batteries in the battery pack during charging through the voltage detection circuit, the processor obtains a voltage-time curve for each battery based on the voltage information of the batteries, the processor determines a time point for the battery pack to perform power balancing, the processor estimates a charging time length for each battery from the time point to a fully charged time point based on the voltage-time curve of each battery, and the processor adjusts a charging power of each battery using the battery power balancing control circuit based on the charging time length of each battery to achieve power balancing of the batteries in the battery pack.

12. The system as described in claim 11, wherein when battery balancing is not enabled, the processor uses the voltage detection circuit to measure the corresponding plurality of voltages of each of the batteries in the battery pack at a plurality of time points.

13. The system as described in claim 12, wherein the processor performs numerical interpolation or numerical extrapolation on the corresponding voltages measured for each battery to generate the voltage-time curve for each battery, and the processor dynamically adjusts the voltage-time curve for each battery as the usage time of each battery increases.

14. The system as claimed in claim 11, wherein the processor uses the voltage detection circuit to measure a voltage corresponding to one of the time points at which each battery in the battery pack performs charge balancing, and the processor calculates the rate of increase of the charging voltage of each battery in different time intervals based on the corresponding voltage at the time point at which each battery performs charge balancing and the voltage-time curve of each battery with a plurality of slopes.

15. The system of claim 14, wherein the processor estimates the charging time length of each battery from the point in time to the point of full charge based on the rate of increase of the charging voltage of each battery in different time intervals, and the point of full charge corresponds to a point in time when each battery is charged to a full charge voltage.

16. The system as claimed in claim 11, wherein if a charging time of one battery in the battery pack is longer than the charging time of the other batteries in the battery pack, the battery in the battery pack is charged in a normal mode, and the other batteries in the battery pack are charged in a slow charging mode.

17. The system as claimed in claim 11, wherein if the charging time of one battery in the battery pack is less than the charging time of the other batteries in the battery pack, the battery in the battery pack is charged in a slow charging mode, and the other batteries in the battery pack are charged in a normal mode.

18. The system as claimed in claim 11, wherein the processor sets a duty cycle for each battery during charging based on the charging power of each battery, and if the duty cycle increases, the charging power increases, and if the duty cycle decreases, the charging power decreases.

19. The system as claimed in claim 11, further comprising: a temperature detection module coupled to the battery pack and the processor; wherein the processor controls the temperature detection module to detect a temperature of each battery in the battery pack, and the processor adjusts a discharge rate of each battery using a battery charge balance control circuit based on the temperature of each battery.

20. The system as described in claim 11, wherein the batteries in the battery pack are connected in series, and after the batteries in the battery pack are balanced, the time required for the batteries to be charged to a fully charged state is substantially the same.

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