An adaptive method for charging current and charging start temperature of lithium-ion power battery system

Abstract

This invention discloses an adaptive method for the charging current and charging start temperature of a lithium-ion power battery system, comprising: step S1, obtaining the adaptive charging current Ix of the battery system at multiple preset initial charging temperatures based on a known original charging current table; step S2, when the battery system needs to be charged, obtaining the highest single-cell temperature Tmax of the lithium-ion power battery system in the initial charging state, wherein Tmax in the initial charging state is the initial charging temperature of the lithium-ion power battery system; step S3, comparing Tmax obtained in step S2 with a preset temperature threshold Tx, and executing a preset charging operation based on the comparison result. This invention can automatically adjust the charging current according to different charging start temperatures of the battery system, thereby reducing the battery cycle temperature and improving the battery cycle life without increasing the charging time of the battery system.

Description

Technical Field

[0001] This invention relates to the field of power battery management system technology, and in particular to an adaptive method for the charging current and charging start temperature of a lithium-ion power battery system. Background Technology

[0002] As the warranty mileage requirements for new energy vehicles gradually increase, maintaining good operational status of the power battery, assuming its cycle life meets the requirements, has become a crucial factor in the cycle life of the power battery system. The Battery Management System (BMS) in a lithium-ion power battery system plays a vital role in optimizing power battery performance and preventing vehicle misuse.

[0003] As is well known, the cycle life of a power battery is strongly correlated with temperature. The cycle life at high temperatures is significantly lower than that at room temperature (sometimes even by half). Therefore, reducing the high temperature amplitude of the power battery system can effectively improve the cycle life of the power battery system.

[0004] Currently, the most common cooling measure for power battery systems is to add a liquid cooling device. This measure can effectively adjust the temperature of the power battery system. However, for naturally cooled battery systems (i.e., battery systems that are not cooled by active cooling devices such as liquid cooling devices), heat cannot be dissipated through active heat exchange, and the temperature is prone to accumulate in the battery box, resulting in a high temperature state.

[0005] Since the temperature rise of the naturally cooled battery system mainly occurs during the charging process, current BMS systems typically design a charging current meter based on the cell performance during the initial design phase of the lithium-ion power battery system. This charging current meter pre-sets a one-to-one correspondence between the real-time charging temperature of the battery system (specifically, the real-time charging temperature range) and different charging currents. Then, during the charging process, the battery is charged according to the charging current meter. Different battery temperatures correspond to different charging currents to ensure that the charging time requirements of the entire vehicle are met, and the current is gradually reduced in the high-temperature zone to prevent the battery from stopping charging due to overheating.

[0006] However, due to the complex and varied actual operating environment of naturally cooled battery systems, when the initial charging temperature is low, the designed charging current meter can gradually reduce the current as the charging temperature gradually rises, preventing the battery temperature from becoming too high. However, in some cases, if the initial charging temperature of the battery system is already at a high temperature, if charging continues according to the originally designed charging current meter, the charging current set according to the charging temperature will rise rapidly to the next current reduction stage. After several current reductions, the charging will remain at a high temperature, which is detrimental to the cycle life of the battery system.

[0007] However, if the charging current is simply reduced to ensure a lower charging temperature when designing the charging current meter, it will affect the charging time of the battery system and reduce the user experience.

[0008] Therefore, there is an urgent need to develop a technology that can solve the above-mentioned technical problems. Summary of the Invention

[0009] The purpose of this invention is to address the technical deficiencies of existing technologies by providing an adaptive method for the charging current and charging start-up temperature of a lithium-ion power battery system.

[0010] Therefore, the present invention provides an adaptive method for the charging current and charging start temperature of a lithium-ion power battery system, characterized by comprising the following steps:

[0011] Step S1: Based on the known original charging current meter, obtain the adaptive charging current Ix of the lithium-ion power battery system at multiple preset initial charging temperatures.

[0012] Step S2: When the lithium-ion power battery system needs to be charged, obtain the highest single cell temperature Tmax of the lithium-ion power battery system in the initial charging state. The highest single cell temperature Tmax in the initial charging state is the initial charging temperature of the lithium-ion power battery system.

[0013] Step S3: The highest single-cell temperature Tmax obtained from step S2 is compared with the preset temperature threshold Tx, and then a preset charging operation is performed based on the comparison result.

[0014] Preferably, the feature is that, based on the comparison result, a preset charging operation is performed, specifically as follows:

[0015] If Tmax is greater than Tx, then based on the initial charging temperature of the lithium-ion power battery system obtained in step S2, the corresponding adaptive charging current Ix is read and the lithium-ion power battery system is charged according to the adaptive charging current Ix.

[0016] If Tmax is less than Tx, the charging current corresponding to Tmax is obtained from the original charging current meter, and then the lithium-ion power battery system is charged according to the charging current corresponding to Tmax.

[0017] Preferably, step S1 specifically includes the following steps:

[0018] Step S11: Based on the known original charging ammeter, obtain the charging currents I1, I2, I3...In used by the lithium-ion power battery system in multiple different real-time charging temperature ranges; where n is a natural number greater than 3.

[0019] Step S12: The initial charging temperature of the lithium-ion power battery system is adjusted to a plurality of preset initial charging temperatures T1, T2, T3...Tn.

[0020] For a lithium-ion power battery system adjusted to any initial charging temperature, the lithium-ion power battery system is charged according to the charging current used in the real-time charging temperature range where the initial charging temperature is located.

[0021] During the charging process, the charging current corresponding to the real-time charging temperature range where the highest single cell temperature in the lithium-ion power battery system is located is read in real time, and the lithium-ion power battery system is charged. The charging time in the real-time charging temperature range is also counted. As the highest single cell temperature in the lithium-ion power battery system increases, the charging time t1, t2, t3...tn is recorded when charging with the charging current I1, I2, I3...In corresponding to each real-time charging temperature range where the highest single cell temperature is located. The charging continues until the target SOC is reached.

[0022] Step S13: Calculate the adaptive charging current Ix of the lithium-ion power battery system at each initial charging temperature according to the preset calculation formula.

[0023] Preferably, in step S11, based on the known original charging current table, all the charging currents used in multiple different real-time charging temperature ranges recorded in the original charging current table are obtained.

[0024] Preferably, in step S12, the target SOC is 100% SOC.

[0025] Preferably, in step S13, the formula for calculating the adaptive charging current Ix of the lithium-ion power battery system is as follows:

[0026] Ix=(I1﹡t1+I2﹡t2+I3﹡t3+…+In﹡tn) / (t1+t2+t3+…+tn).

[0027] As can be seen from the technical solution provided by the present invention above, compared with the prior art, the present invention provides an adaptive method for the charging current and charging start temperature of a lithium-ion power battery system. Its design is scientific and can automatically adjust the charging current according to the different charging start temperatures of the lithium-ion power battery system. In this way, the battery cycle temperature can be reduced and the battery cycle life can be improved without increasing the charging time of the battery system, which has great practical significance.

[0028] Given that existing fixed charging current meters (MAPs) are insufficient to meet the charging time requirements of battery systems while keeping lithium-ion power battery systems within their optimal temperature range, this invention demonstrates that the method designed in this paper can meet the charging time requirements of battery systems while keeping lithium-ion power battery systems within their optimal temperature range. Compared with existing technologies, this represents a significant technological advancement. Attached Figure Description

[0029] Figure 1 A flowchart of an adaptive method for charging current and charging start temperature in a lithium-ion power battery system provided by the present invention;

[0030] Figure 2 A schematic diagram illustrating the effect of achieving the target charging temperature change objective involved in this invention;

[0031] Figure 3 This is a schematic diagram of the measured charging temperature rise curve according to an embodiment of the present invention. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0033] See Figures 1 to 3 This invention provides an adaptive method for the charging current and charging start-up temperature of a lithium-ion power battery system, comprising the following steps:

[0034] Step S1: Based on the known original charging current meter, obtain the adaptive charging current Ix of the lithium-ion power battery system under multiple preset initial charging temperatures (T1, T2, T3...Tn).

[0035] It should be noted that multiple different initial charging temperatures can be preset, which can be selected in advance as needed. For example, multiple temperature values ​​or multiple temperature ranges within the temperature range of 0℃ to 60℃ can be selected.

[0036] Step S1 specifically includes the following steps:

[0037] Step S11: Based on the known original charging current table, obtain the charging current (e.g., I1, I2, I3...In) used by the lithium-ion power battery system in multiple different real-time charging temperature ranges (i.e., temperature stages); where n is a natural number greater than 3.

[0038] It should be noted that the known original charging current meter (i.e. the original charging current meter that is already available in new energy vehicles and is matched with the lithium-ion power battery system) has multiple different real-time charging temperature ranges (i.e. temperature stages, which are temperature ranges of the battery system, usually the temperature range where the highest single cell temperature in the battery system is located) and multiple charging current magnitudes used in each temperature range. That is, a one-to-one correspondence between multiple different real-time charging temperature ranges of the battery system and multiple charging currents has been pre-set.

[0039] It should be noted that the initial charging temperature of a lithium-ion power battery system, as the real-time charging temperature in the initial state, is located within a real-time charging temperature range, and the corresponding charging current can be obtained from the original charging current table.

[0040] In step S11, specifically, based on the known original charging current table, the charging current used in all and multiple different real-time charging temperature ranges (i.e., temperature stages) recorded in the original charging current table is obtained.

[0041] Step S12: The initial charging temperature of the lithium-ion power battery system is adjusted to a plurality of preset initial charging temperatures T1, T2, T3...Tn.

[0042] For a lithium-ion power battery system adjusted to any initial charging temperature, the lithium-ion power battery system is charged according to the charging current used by the lithium-ion power battery system in the real-time charging temperature range where the initial charging temperature is located.

[0043] During the charging process, the charging current corresponding to the highest single cell temperature in the lithium-ion power battery system is read in real time according to the real-time charging temperature range (which can be read according to step S11), and the lithium-ion power battery system is charged. The charging time in the real-time charging temperature range is also counted. As the highest single cell temperature in the lithium-ion power battery system increases (i.e., rises to higher and different real-time charging temperature ranges), the charging time (e.g., t1, t2, t3...tn, these times are the charging time of each charging current in its corresponding real-time charging temperature range) when charging with the charging current (e.g., I1, I2, I3...In) corresponding to the highest single cell temperature range is recorded. The charging continues until the target SOC is reached (the target SOC is, for example, 100% SOC, at which point the charging time of the charging current used in a certain real-time charging temperature range is equal to zero).

[0044] It should be noted that, for the present invention, steps S11 and S12 can be used to obtain different charging times corresponding to different charging currents when charging at different initial charging temperatures.

[0045] Step S13: Calculate the adaptive charging current Ix of the lithium-ion power battery system at each initial charging temperature (e.g., T1, T2, T3...Tn) according to the preset calculation formula;

[0046] In step S13, specifically, the calculation formula for the adaptive charging current Ix of the lithium-ion power battery system is as follows:

[0047] Ix=(I1﹡t1+I2﹡t2+I3﹡t3+……+In﹡tn) / (t1+t2+t3+……+tn);

[0048] Step S2: When the lithium-ion power battery system needs to be charged, obtain the highest single cell temperature Tmax of the lithium-ion power battery system in the initial charging state (i.e., when charging just started). The highest single cell temperature Tmax in the initial charging state is the initial charging temperature of the lithium-ion power battery system.

[0049] It should be noted that the highest single-cell temperature Tmax of the lithium-ion power battery system in the initial charging state (i.e., at the beginning of charging) can be obtained through the existing battery management system (BMS).

[0050] Step S3: Compare the highest single-cell temperature Tmax with the preset temperature threshold Tx, and then perform the preset charging operation based on the comparison result.

[0051] Based on the comparison results, a preset charging operation is performed, as follows:

[0052] If Tmax is greater than Tx, then based on the initial charging temperature of the lithium-ion power battery system obtained in step S2, the corresponding adaptive charging current Ix is read (and obtained based on the processing result of step S1) and the lithium-ion power battery system is charged according to the adaptive charging current Ix.

[0053] It should be noted that at this time, the charging process is no longer based on the original charging ammeter, but on constant current charging based on Ix. This ensures consistent charging time and reduces the temperature during the charging process.

[0054] If Tmax is less than Tx, the charging current corresponding to Tmax is obtained from the original charging current meter, and then the lithium-ion power battery system is charged according to the charging current corresponding to Tmax; that is, the charging operation is performed according to the original charging current meter.

[0055] It should be noted that, since the technical solution of this invention is aimed at high-temperature charging, it is not necessary to implement this invention when the battery temperature is comfortable or low. Therefore, Tx is set as the temperature dividing point. Only when the temperature is greater than Tx is the adaptive charging current Ix proposed by the technical solution of this invention required.

[0056] In practice, the preset temperature threshold Tx can be obtained based on the temperature rise of the target battery system when charging with the original charging ammeter at different initial charging temperatures. If the battery temperature rises linearly throughout the charging process using the original ammeter at a certain initial charging temperature, the effect of this invention is limited, and the original ammeter is continued. When the initial charging temperature reaches Tx, a thermal equilibrium stage appears in the later stages of charging (i.e., the temperature rises to a certain level, and due to current reduction, the battery temperature is maintained at a certain level and is difficult to rise further). This critical temperature is the preset temperature threshold required by this invention. If there are no testing conditions in practical applications, the recommended value of Tx of 45℃ can be used (generally, above 45℃ is considered high temperature).

[0057] In this invention, the derivation process of the calculation formula for the adaptive charging current Ix in step S13 is explained as follows:

[0058] Since charging the lithium-ion power battery system based on the original charging ammeter and charging the lithium-ion power battery system based on the adaptive charging current Ix in the technical solution of this invention both result in the same SOC range (i.e., both starting from the same initial SOC and charging to 100% SOC or a preset target SOC), then:

[0059] I1﹡t1+I2﹡t2+I3﹡t3+……+In﹡tn=Ix﹡t1';

[0060] Since charging time cannot be extended, in order to minimize temperature, then:

[0061] t1+t2+t3+……+tn=t1';

[0062] Solving the system of equations, we can obtain the following formula:

[0063] Ix=(I1﹡t1+I2﹡t2+I3﹡t3+……+In﹡tn) / (t1+t2+t3+……+tn);

[0064] Based on the above process, the optimal charging current solution set at different temperatures can be obtained.

[0065] In this invention, it should be noted that t1' is the assumed charging duration for constant current charging, and Ix is the assumed constant current value. For this invention, the constant current charging duration is required to be equal to the total charging duration of the original ammeter, thus yielding the equation: t1 + t2 + t3 + ... + tn = t1'.

[0066] Furthermore, based on the consistency of the total charging SOC (i.e., the total charging SOC of constant current charging should be equal to the total charging SOC of the original ammeter), the charging capacity (current * time = capacity) is equal, thus obtaining another equation for equal charging capacity: I1*t1 + I2*t2 + I3*t3 + ... + In*tn = Ix*t1', thus finally solving for the constant current value Ix (i.e., the adaptive charging current Ix) that satisfies the equality of charging time.

[0067] Based on the above technical solutions, it can be seen that, for the present invention, the charging current is adjusted accordingly based on the highest single cell temperature Tmax of the lithium-ion power battery system in the initial charging state (i.e., the initial charging temperature of the lithium-ion power battery system), which can reduce the temperature of the cell during the cycle without changing the charging time.

[0068] To better understand the technical solution of the present invention, the following specific embodiments will be used to illustrate the technical solution of the present invention.

[0069] Example 1.

[0070] For a lithium-ion power battery system, if the highest single-cell temperature Tmax (i.e. the initial charging temperature of the lithium-ion power battery system) in the initial charging state is greater than the preset temperature threshold Tx, then the charging process is as follows: the batteries in the lithium-ion power battery system are charged with an adaptive charging current Ix at the initial charging temperature of the lithium-ion power battery system until the preset target SOC is reached, and the charging ends.

[0071] Example 2.

[0072] For a lithium-ion power battery system, if the highest single-cell temperature Tmax in the initial charging state is less than the preset temperature threshold Tx, then the charging operation is performed according to the original charging ammeter.

[0073] As an example, the charging process using the original charging ammeter in this embodiment of the invention is as follows:

[0074] The initial battery temperature is T1 (i.e., the highest single cell temperature Tmax). The battery is charged with a charging current I1 (obtained from the original charging current table, corresponding to T1). When the temperature rises to T2, time t1 is used to enter the next temperature stage.

[0075] The battery is charged with a charging current I2 (obtained from the original charging current table, corresponding to T2). When the temperature rises to T3, time t2 is used to enter the next temperature stage.

[0076] The battery is charged with a charging current I3 (obtained from the original charging current table, corresponding to T3). When the temperature rises to T4, the time is t3. At this time, the preset target SOC (e.g., 100% SOC) is reached, and the charging ends.

[0077] Example 3.

[0078] like Figure 2 As shown, this is a comparison chart of the measured temperature rise data of the original charging ammeter and the ideal temperature rise curve (i.e., the target temperature rise curve) after implementing the strategy of this invention. It can be clearly seen that the temperature decreases throughout the process. Taking the measured data of this experiment as a calibration experiment, as an embodiment of this invention, Table 1 shows the original MAP (charging ammeter) of this test. In the original charging ammeter, the charging current corresponding to the temperature of 45-48℃ is 0.8C, the charging current corresponding to the temperature of 48-50℃ is 0.6C, the charging current corresponding to the temperature of 50-52℃ is 0.4C, and the charging current corresponding to the temperature of 52-55℃ is 0.2C.

[0079] Table 1: Charging current table of embodiments of the present invention;

[0080]

[0081] Table 2: Calibration data illustration of the embodiments of the present invention.

[0082] Current (C) 0.8 0.6 0.4 0.2 Charging time (s) 1337 1579 3577 0

[0083] According to the test results and Table 2, during the actual charging process of the battery system (specifically, charging to 100% SOC), the 0.8C charging portion took 1337 seconds, the 0.6C charging portion took 1579 seconds, the 0.4C charging portion took 3577 seconds, and the 0.2C charging portion took 0 seconds.

[0084] Substitute into the formula:

[0085] Ix=(I1﹡t1+I2﹡t2+I3﹡t3+……+In﹡tn) / (t1+t2+t3+……+tn);

[0086] We can obtain:

[0087] Adaptive charging current

[0088] Ultimately, the adaptive charging current Ix = 0.53C.

[0089] like Figure 3 The figure shows the measured charging temperature rise curve of an embodiment of the present invention, proving that the present invention can achieve the expected cooling purpose without prolonging the charging time.

[0090] In summary, compared with the prior art, the adaptive method for charging current and charging start temperature of a lithium-ion power battery system provided by this invention is scientifically designed and can automatically adjust the charging current according to different charging start temperatures of the lithium-ion power battery system. This allows the battery cycle temperature to be reduced and the battery cycle life to be improved without increasing the charging time of the battery system, which has significant practical implications.

[0091] Given that existing fixed charging current meters (MAPs) are insufficient to meet the charging time requirements of battery systems while keeping lithium-ion power battery systems within their optimal temperature range, this invention demonstrates that the method designed in this paper can meet the charging time requirements of battery systems while keeping lithium-ion power battery systems within their optimal temperature range. Compared with existing technologies, this represents a significant technological advancement.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An adaptive method for charging current and charging start-up temperature in a lithium-ion power battery system, characterized in that, Includes the following steps: Step S1: Based on the known original charging ammeter, obtain the adaptive charging current Ix of the lithium-ion power battery system at several preset initial charging temperatures. Specifically, the following steps are included: Step S11: Based on the known original charging ammeter, obtain the charging currents I1, I2, I3, ..., In used by the lithium-ion power battery system in multiple different real-time charging temperature ranges; where n is a natural number greater than 3. Step S12: The initial charging temperature of the lithium-ion power battery system is adjusted to a number of preset initial charging temperatures T1, T2, T3, and Tn respectively. For a lithium-ion power battery system adjusted to any initial charging temperature, the lithium-ion power battery system is charged according to the charging current used in the real-time charging temperature range where the initial charging temperature is located. During the charging process, the charging current corresponding to the real-time charging temperature range where the highest single cell temperature in the lithium-ion power battery system is located is read in real time, and the lithium-ion power battery system is charged. The charging time in the real-time charging temperature range is also counted. As the highest single cell temperature in the lithium-ion power battery system increases, the charging time t1, t2, t3, to tn is recorded when charging with the charging current I1, I2, I3, to In corresponding to each real-time charging temperature range where the highest single cell temperature is located. The charging continues until the target SOC is reached. Step S13: Calculate the adaptive charging current Ix of the lithium-ion power battery system at each initial charging temperature according to the preset calculation formula. The formula for calculating the adaptive charging current Ix of a lithium-ion power battery system is as follows: Ix = (I1*t1 + I2*t2 + I3*t3 + up to ln*tn) / (t1 + t2 + t3 + up to tn); Step S2: When the lithium-ion power battery system needs to be charged, obtain the highest single cell temperature Tmax of the lithium-ion power battery system in the initial charging state. The highest single cell temperature Tmax in the initial charging state is the initial charging temperature of the lithium-ion power battery system. Step S3: The highest single-cell temperature Tmax obtained from step S2 is compared with the preset temperature threshold Tx. Then, based on the comparison result, a preset charging operation is performed. If Tmax is greater than Tx, the corresponding adaptive charging current Ix is read based on the initial charging temperature of the lithium-ion power battery system obtained from step S2, and the lithium-ion power battery system is charged according to the adaptive charging current Ix. If Tmax is less than Tx, the charging current corresponding to Tmax is obtained from the original charging current meter, and then the lithium-ion power battery system is charged according to the charging current corresponding to Tmax.

2. The adaptive method for charging current and charging start temperature of a lithium-ion power battery system as described in claim 1, characterized in that, In step S11, based on the known original charging current table, all the charging currents used in multiple different real-time charging temperature ranges recorded in the original charging current table are obtained.

3. The adaptive method for charging current and charging start temperature of a lithium-ion power battery system as described in claim 1, characterized in that, In step S12, the target SOC is 100% SOC.

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