Method for estimating residual charging duration of electric forklift in low-temperature environment

Abstract

The invention discloses a method for estimating the residual charging duration of an electric forklift in a low-temperature environment, which can smoothly correct the charging duration estimation error and ensure the accurate estimation of the charging duration required by the charging of the electric forklift. The method specifically comprises the steps that in a pure heating stage, a battery is only heated but not charged, and the temperature rise rate of the battery in the stage is obtained through experimental test data so as to estimate the charging duration; in the stage of heating while charging, the battery is heated and charged at the same time, the temperature rise rate of the battery at the moment is obtained through experimental test data, the consumed time of the stage is calculated, and the SOC at the end of the stage is calculated; in the pure charging stage, the time required for charging the SOC to 90% in the pure charging stage is calculated in combination with the SOC value calculated in the stage of charging while heating; when the SOC of the battery reaches 90%, the battery enters a constant-voltage charging stage, the charging rate is 0.1 C, and the time required at the moment is calculated; and the total charging time can be estimated by accumulating the time required by each stage.

Description

Technical Field

[0001] The present invention belongs to the field of forklift battery applications, and in particular relates to a method for estimating the remaining charging time of an electric forklift in a low-temperature environment. Background Art

[0002] Electric industrial vehicles are becoming increasingly popular in industrial production. Compared to fuel-powered forklifts, electric forklifts offer greater energy efficiency, significantly reducing energy costs. They also offer advantages such as energy conservation and environmental protection, quiet operation, and powerful power. However, electric forklifts require a certain amount of time to charge after use, a time significantly longer than the time it takes to fill a tank of fuel forklifts. Furthermore, due to the characteristics of the battery, in low temperatures, the battery must be heated before charging can begin. Therefore, users are very concerned about the charging time of electric vehicles.

[0003] The maximum charging current of a forklift battery is generally 0.5C. Under normal temperature conditions, it can be roughly estimated that it takes more than two hours to fully charge a low-power forklift. However, in low-temperature environments, the battery needs to be heated before charging, so the battery temperature varies greatly during the entire charging process. The battery's charging current is related to the battery temperature, making it more complicated to estimate the charging time of the battery in low-temperature environments.

[0004] The existing technical method is to calculate an initial total charging time based on the battery power and the charging pile power, and then continuously correct the remaining charging time during the charging process based on the charging parameters obtained from experimental tests. This method has two problems: 1) The estimated initial total charging time has a large error; since the charging pile cannot always operate at the maximum output power during the entire charging process, and in low temperature conditions, part of the power must be used to heat the battery, the initial charging time calculated based only on the battery power and the maximum output power of the charging pile has a large error. 2) The charging time cannot be corrected in real time; based on experimental test data and charging parameters, a charging time calculation model can be established, but there will be deviations between the actual charging parameters and the theoretical model, resulting in inaccurate charging time estimates by the model. Summary of the Invention

[0005] In order to make up for the deficiencies of the prior art, the present invention aims to provide a method for estimating the remaining charging time of an electric forklift in a low-temperature environment, so as to solve the problem that the charging time required for charging an electric forklift cannot be accurately estimated.

[0006] The method for estimating the remaining charging time of an electric forklift in a low-temperature environment includes the following:

[0007] Pure heating stage: When the battery temperature is below 0°C, only the heating function is activated to increase the temperature. That is, in this stage, the battery is heated only by the heat generated by the heating film;

[0008] Charging and heating stage: When the battery temperature is between (0°C and 15°C), the battery generates heat through the heating film and the battery's own charging heat to increase the temperature;

[0009] Pure charging stage: When the battery temperature exceeds 15°C, the heat generated by the battery's own charging can make up for the heat dissipated in the low temperature environment. The battery enters the pure charging stage and the heating function is turned off.

[0010] The average temperature rise rate in the above three stages is:

[0011]

[0012] Where, is the average temperature rise rate, They are the temperature rise rates in the pure heating stage, the heating while charging stage, and the pure charging stage;

[0013] Assuming that the initial temperature of the battery is T0 (T0 < 0 ° C) and the initial SOC is SOC0, the total charging time t can be preliminarily estimated based on the initial temperature and initial SOC of the battery. 总 ',t 总 '=t1'+t2'+t3'+t 恒压 ', where t1', t2', t3', t 恒压 'Respectively represent the charging time of pure heating stage, heating while charging stage, pure charging stage and constant voltage stage.

[0014] Furthermore, in the pure heating stage, the required time is:

[0015]

[0016] Furthermore, in the charging and heating stage, the initial battery temperature is 0°C, the initial SOC is SOC0, and the end temperature is 15°C. The time spent in this stage is preliminarily estimated to be:

[0017]

[0018] According to the charging rate table, the SOC at the end of the charging and heating phase can be calculated. The specific calculation process is as follows:

[0019] The initial temperature of the battery is T0∈[T i ,T i+1 ), in this stage the initial temperature of the battery is 0℃, and the starting SOC is SOC0∈[SOC j ,SOC j+1 ), according to the charging rate table, the initial charging rate is C i,j, where i and j represent the temperature row number and SOC column number in the table respectively; the battery starts from SOC0 and passes through C i,j Charge to the next SOC range [SOC j+1 ,SOC j+2 ) The time required is:

[0020]

[0021] Similarly, the battery starts from T0 and is heated at a temperature rise rate v to the interval [T i+1 ,T i+2 ) The time required is:

[0022]

[0023] The temperature rise rate v in this stage is like The battery will cross to the next temperature range first, and vice versa, the SOC will cross to the next range first; therefore, in the current range, the increment of SOC is:

[0024]

[0025] When the temperature or SOC crosses the range, you need to re-query the charge rate table to get the latest charge rate:

[0026]

[0027] The above process is continued to be calculated until the temperature reaches 15°C, and the SOC at the end of the charging and heating stage can be calculated, which is recorded as SOC1.

[0028] Furthermore, in the pure charging stage, the initial battery temperature is 15°C and the initial SOC is SOC1. Similarly, using the same calculation method as the charging and heating stage, the time required to charge the battery from SOC1 to 90% can be calculated, which is recorded as t3';

[0029] When the SOC reaches 90%, the battery needs to enter the constant voltage charging mode, and the charging rate is:

[0030] C 恒压 =0.1C,

[0031] The charging time required in the constant voltage charging stage is:

[0032]

[0033] Furthermore, during the charging process, the three charging stages are divided into x, y, and z temperature intervals with a temperature interval of 3°C. The calibration method for the temperature rise rate is as follows:

[0034] Pure heating stage: divided into pure heating interval 1 (T0 ~ -3 (x-1) ° C), pure heating interval 2 (-3 (x-1) ° C ~ -3 (x-2) ° C) ... pure heating interval x-1 (-6 ° C ~ -3 ° C) and pure heating interval x (-3 ° C ~ -0 ° C) according to the temperature interval of 3 ° C;

[0035] Charging and heating stage: divided into charging and heating zone 1 (0℃~3℃), charging and heating zone 2 (3℃~6℃), charging and heating zone 3 (6℃~9℃), charging and heating zone 4 (9℃~12℃) and pure heating zone 5 (12℃~15℃) according to the temperature interval of 3℃;

[0036] Pure charging stage: divided into pure charging range 1 (15℃~18℃), pure charging range 2 (18℃~21℃)…pure charging range z-1 ((9+3z)℃~(12+3z)℃) and pure charging range z ((12+3z)℃~(15+3z)℃) according to the temperature interval of 3℃;

[0037] Take charging and heating interval 1 and charging and heating interval 2 as examples:

[0038] The average temperature rise rate measured in the test of charging and heating interval 1 and charging and heating interval 2 The preliminary estimates of the time required for the two intervals to heat up are:

[0039]

[0040] The estimated total duration of warming in the two intervals is:

[0041]

[0042] Let t1 be the actual temperature rise time in charging and heating interval 1, and the actual temperature rise rate be:

[0043]

[0044] Using the actual temperature rise rate in this interval to calibrate the time spent in charging and heating interval 2, we can obtain:

[0045]

[0046] It can be concluded that when the actual temperature crosses the charging and heating interval 1, the time spent in the two temperature intervals before and after the temperature dividing point can be calibrated as:

[0047] t"=2×t1,

[0048] The error between the calibration value and the initial estimated duration is:

[0049] Δt=t"-t',

[0050] Add the estimated time error to the initial estimated total charging time t 总 ', and then use the same method to calculate the temperature rise rate in real time during the actual charging process for the remaining temperature ranges and calibrate the charging time.

[0051] Compared with the prior art, the present invention has the following advantages:

[0052] (1) This application divides the battery charging process into three stages according to the actual charging capacity of the battery at different temperatures: a pure heating stage, a charging and heating stage, and a pure charging stage. As shown in Table 1, these three stages represent the battery's zero charging capacity, a small charging capacity, and a normal charging capacity, respectively. Compared with the existing technology, this division method is closer to the actual charging performance of the battery, providing a guarantee for accurately calculating the charging time.

[0053] (2) This application obtains the average temperature rise rate of the above three stages through experimental testing. Combined with the initial temperature and SOC of the battery, it can quickly and accurately calculate the total charging time at the beginning of charging. Compared with the existing method of calculating the total charging time based only on battery capacity and charging pile power, the error is smaller and the calibration amplitude of the charging time can be reduced accordingly, avoiding the situation where the charging time fluctuates greatly during use and brings a bad user experience to customers.

[0054] (3) This application further subdivides the above three charging stages into multiple temperature intervals at a temperature interval of 3°C. For each temperature interval, the battery temperature is monitored in real time and the actual temperature rise rate is calculated. The calculated real-time temperature rise rate is used to calibrate the estimated duration of adjacent temperature intervals, making the charging duration calculation more accurate.

[0055] (4) The calibration method used in this application calibrates adjacent temperature intervals each time, and the temperature range affected by the calibration is small, so the calibration amplitude can be controlled each time, and the charging time will not experience a large jump, making the charging time calibration smoother and bringing a better experience to users. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0058] like Figure 1As shown in the figure, a method for estimating the remaining charging time of an electric forklift in a low-temperature environment is used. According to the temperature, the charging process of a lithium battery can be divided into three stages:

[0059] (1) Pure heating stage

[0060] When the battery temperature is below 0°C, to ensure the battery's service life and safety, charging is prohibited during this stage. Only the heating function is activated to increase the temperature. That is, during this stage, the battery is heated only by the heat generated by the heating film. Therefore, the required charging time t1' in this stage is:

[0061] (2) Charging and heating stage

[0062] As shown in Table 1 (Charging Rate Table), when the battery temperature is between (0°C, 15°C), the battery can be charged at a smaller rate, but further heating is required to increase the temperature to obtain a greater charging capacity. At this stage, the temperature rise of the battery comes from two parts: heat generated by the heating film and heat generated by the battery itself during charging.

[0063] Table 1 Charging rate table

[0064]

[0065] In this stage, the initial battery temperature is 0°C, the initial SOC is SOC0, and the end temperature is 15°C. The preliminary estimate of the charging time t2' spent in the charging and heating stage is: According to the charging rate table, the SOC at the end of the charging and heating phase can be calculated. The specific calculation process is as follows:

[0066] The initial temperature of the battery is T0∈[T i ,T i+1 ), in this stage the initial temperature of the battery is 0℃, and the starting SOC is SOC0∈[SOC j ,SOC j+1 ), according to the charging rate table, the initial charging rate is C i,j , where i and j represent the temperature row number and SOC column number in the table respectively; the battery starts from SOC0 and passes through C i,j Charge to the next SOC range [SOC j+1 ,SOC j+2 ) The time required is:

[0067]

[0068] Similarly, the battery starts from T0 and is heated at a temperature rise rate v to the interval [T i+1 ,T i+2 ) The time required is:

[0069]

[0070] The temperature rise rate v in this stage is like The battery will cross to the next temperature range first, and vice versa, the SOC will cross to the next range first; therefore, in the current range, the increment of SOC is:

[0071]

[0072] When the temperature or SOC crosses the range, you need to re-query the charge rate table to get the latest charge rate:

[0073]

[0074] The above process is continued to be calculated until the temperature reaches 15°C, and the SOC at the end of the charging and heating stage can be calculated, which is recorded as SOC1.

[0075] (3) Pure charging stage

[0076] When the battery temperature rises further and exceeds 15°C, the battery has gained a greater charging capacity. At this time, the heat generated by the battery's own charging can make up for the heat dissipated in the low temperature environment. The battery enters the pure charging stage and the heating function is turned off.

[0077] In this stage, the initial battery temperature is 15°C and the initial SOC is SOC1. Similarly, using the same calculation method as in the charging and heating stage, the time required to charge the battery from SOC1 to 90% can be calculated, recorded as t3'. When the SOC reaches 90%, the battery needs to enter the constant voltage charging mode, and the charging rate is:

[0078] C 恒压 =0.1C,

[0079] The charging time required in the constant voltage charging stage is:

[0080]

[0081] According to experimental tests, the average temperature rise rate of the above three stages is:

[0082]

[0083] Where, is the average temperature rise rate, The temperature rise rates are in the pure heating stage, the charging and heating stage, and the pure charging stage respectively; assuming that the initial temperature of the battery is T0 (T0<0℃) and the initial SOC is SOC0, the total charging time t can be preliminarily estimated based on the initial temperature and initial SOC of the battery.总 ',t 总 '=t1'+t2'+t3'+t 恒压 ', where t1', t2', t3', t 恒压 'Respectively represent the charging time of pure heating stage, heating while charging stage, pure charging stage and constant voltage stage.

[0084] However, during the actual charging process, the battery's temperature rise rate will be affected by the ambient temperature. The calculated deviation of the battery's temperature rise rate will directly affect the estimated charging time. Therefore, the temperature rise rate must be calibrated. The specific calibration method is as follows:

[0085] The three charging stages are divided into x, y, and z temperature intervals at 3°C:

[0086] Pure heating stage: divided into pure heating interval 1 (T0 ~ -3 (x-1) ° C), pure heating interval 2 (-3 (x-1) ° C ~ -3 (x-2) ° C) ... pure heating interval x-1 (-6 ° C ~ -3 ° C) and pure heating interval x (-3 ° C ~ -0 ° C) according to the temperature interval of 3 ° C;

[0087] Charging and heating stage: divided into charging and heating zone 1 (0℃~3℃), charging and heating zone 2 (3℃~6℃), charging and heating zone 3 (6℃~9℃), charging and heating zone 4 (9℃~12℃) and pure heating zone 5 (12℃~15℃) according to the temperature interval of 3℃;

[0088] Pure charging stage: divided into pure charging range 1 (15℃~18℃), pure charging range 2 (18℃~21℃) according to the temperature interval of 3℃...pure charging range z-1 ((9+3z)℃~(12+3z)℃) and pure charging range z ((12+3z)℃~(15+3z)℃).

[0089] Take charging and heating interval 1 and charging and heating interval 2 as examples:

[0090] The average temperature rise rate measured in the test of charging and heating interval 1 and charging and heating interval 2 The time required for the temperature rise in these two intervals can be preliminarily estimated as follows:

[0091]

[0092] The estimated total duration of warming in the two intervals is:

[0093]

[0094] Let t1 be the actual temperature rise time in charging and heating interval 1, and the actual temperature rise rate be:

[0095]

[0096] Using the actual temperature rise rate in this interval to calibrate the time spent in charging and heating interval 2, we can obtain:

[0097]

[0098] It can be concluded that when the actual temperature crosses the charging and heating interval 1, the time spent in the two temperature intervals before and after the temperature dividing point can be calibrated as:

[0099] t"=2×t1,

[0100] The error between the calibration value and the initial estimated duration is:

[0101] Δt=t"-t',

[0102] Add the estimated time error to the initial estimated total charging time t 总 ', then using the same method, calculate the temperature rise rate in real time during the actual charging process for the remaining temperature ranges and calibrate the charging time. According to the above calibration method, the duration of the entire charging process can be calibrated. By calibrating the total charging time in real time during the charging process, this application can more smoothly correct the charging time estimation error.

[0103] The battery charging rate is related to the battery temperature and SOC. Through iterative calculation, the change of the battery charging rate is gradually calculated, and then the time required for each charging stage is calculated; in the actual charging process, the pure heating stage, the heating while charging stage, and the pure charging stage are divided into multiple temperature intervals according to a certain temperature interval. In each charging stage, the average temperature rise rate measured experimentally is used as the initial temperature rise rate value of the first temperature interval of the stage, and then the actual temperature rise rate of each temperature interval is calculated according to the actual time spent in each temperature interval, and the temperature rise rate is used to calibrate the estimated time of the subsequent temperature interval, and the calibration is repeated in sequence.

[0104] From the perspective of temperature, the present application divides the charging process of a battery in a low-temperature environment into three stages: a pure heating stage, a charging and heating stage, and a pure charging stage. In the pure heating stage, the battery is only heated and not charged. The temperature rise rate of the battery in the pure heating stage is obtained through experimental test data, thereby estimating the charging time required for the pure heating stage; in the charging and heating stage, the battery is heated and charged at the same time. The temperature rise rate of the battery at this time is obtained through experimental test data to calculate the time consumed in this stage and the battery SOC at the end of the stage; in the pure charging stage, the battery relies on its own charging to generate heat, and the temperature change is relatively slow and stable. Combined with the SOC value calculated in the charging and heating stage, the charging time required to charge the SOC to 90% in the pure charging stage can be calculated; when the battery SOC reaches 90%, the battery enters the constant voltage charging stage with a charging rate of 0.1C, and the charging time required for the constant voltage charging stage can be calculated; by adding up the charging times required for the above stages, a relatively accurate preliminary estimate of the total charging time of the battery in a low-temperature environment can be obtained.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for estimating the remaining charging time of an electric forklift in a low temperature environment, characterized in that: Includes the following: Pure heating stage: When the battery temperature is below 0°C, only the heating function is activated to increase the temperature. That is, in this stage, the battery is heated only by the heat generated by the heating film; Charging and heating stage: When the battery temperature is between (0°C and 15°C), the battery generates heat through the heating film and the battery's own charging heat to increase the temperature; Pure charging stage: When the battery temperature exceeds 15°C, the heat generated by the battery's own charging can make up for the heat dissipated in the low temperature environment. The battery enters the pure charging stage and the heating function is turned off. The average temperature rise rate in the above three stages is: Where, is the average temperature rise rate, They are the temperature rise rates in the pure heating stage, the heating while charging stage, and the pure charging stage; Assuming that the initial temperature of the battery is T0 (T0 < 0 ° C) and the initial SOC is SOC0, the total charging time t can be preliminarily estimated based on the initial temperature and initial SOC of the battery. 总 ',t 总 '=t1'+t2'+t3'+t 恒压 ', where t1', t2', t3', t 恒压 ' are the charging times for the pure heating stage, the charging and heating stage, the pure charging stage, and the constant voltage stage respectively; during the charging process, the actual temperature rise rate of the interval is calculated based on the actual time spent in the temperature interval, and the temperature rise rate is used to calibrate the estimated time of the subsequent temperature intervals, and the calibration is repeated in sequence.

2. The method for estimating the remaining charging time of an electric forklift in a low temperature environment according to claim 1 is characterized in that: In the pure heating stage, the required time is:

3. The method for estimating the remaining charging time of an electric forklift in a low temperature environment according to claim 1, characterized in that: During the charging and heating phase, the initial battery temperature is 0°C, the initial SOC is SOC0, and the end temperature is 15°C. The time spent in this phase is preliminarily estimated to be: According to the charging rate table, the SOC at the end of the charging and heating phase can be calculated. The specific calculation process is as follows: The initial temperature of the battery is T0∈[T i ,T i+1 ), in this stage the initial temperature of the battery is 0℃, and the starting SOC is SOC0∈[SOC j ,SOC j+1 ), according to the charging rate table, the initial charging rate is C i,j , where i and j represent the temperature row number and SOC column number in the table respectively; the battery starts from SOC0 and passes through C i,j Charge to the next SOC range [SOC j+1 ,SOC j+2 ) The time required is: Similarly, the battery starts from T0 and is heated at a temperature rise rate v to the interval [T i+1 ,T i+2 ) The time required is: The temperature rise rate v in this stage is like The battery will cross to the next temperature range first, and vice versa, the SOC will cross to the next range first; therefore, in the current range, the increment of SOC is: When the temperature or SOC crosses the range, you need to re-query the charge rate table to get the latest charge rate: The above process is continued to be calculated until the temperature reaches 15°C, and the SOC at the end of the charging and heating stage can be calculated, which is recorded as SOC1.

4. The method for estimating the remaining charging time of an electric forklift in a low temperature environment according to claim 1, characterized in that: In the pure charging stage, the initial battery temperature is 15°C and the initial SOC is SOC1. Similarly, the same calculation method as in the charging and heating stage can be used to calculate the time required for the battery to charge from SOC1 to 90%, which is recorded as t3'; When the SOC reaches 90%, the battery needs to enter the constant voltage charging mode, and the charging rate is: C 恒压 =0.1C, The charging time required in the constant voltage charging stage is:

5. The method for estimating the remaining charging time of an electric forklift in a low temperature environment according to claim 1, characterized in that: During the charging process, the three charging stages are divided into x, y, and z temperature intervals at 3°C. The temperature rise rate calibration method is as follows: Pure heating stage: divided into pure heating interval 1 (T0 ~ -3 (x-1) ° C), pure heating interval 2 (-3 (x-1) ° C ~ -3 (x-2) ° C) ... pure heating interval x-1 (-6 ° C ~ -3 ° C) and pure heating interval x (-3 ° C ~ -0 ° C) according to the temperature interval of 3 ° C; Charging and heating stage: divided into charging and heating zone 1 (0℃~3℃), charging and heating zone 2 (3℃~6℃), charging and heating zone 3 (6℃~9℃), charging and heating zone 4 (9℃~12℃) and pure heating zone 5 (12℃~15℃) according to the temperature interval of 3℃; Pure charging stage: divided into pure charging range 1 (15℃~18℃), pure charging range 2 (18℃~21℃)…pure charging range z-1 ((9+3z)℃~(12+3z)℃) and pure charging range z ((12+3z)℃~(15+3z)℃) according to the temperature interval of 3℃; Take charging and heating interval 1 and charging and heating interval 2 as examples: The average temperature rise rate measured in the test of charging and heating interval 1 and charging and heating interval 2 The preliminary estimates of the time required for the two intervals to heat up are: The estimated total duration of warming in the two intervals is: Let t1 be the actual temperature rise time in charging and heating interval 1, and the actual temperature rise rate be: Using the actual temperature rise rate in this interval to calibrate the time spent in charging and heating interval 2, we can obtain: It can be concluded that when the actual temperature crosses the charging and heating interval 1, the time spent in the two temperature intervals before and after the temperature dividing point can be calibrated as: t"=2×t1, The error between the calibration value and the initial estimated duration is: Δt=t"-t', Add the estimated time error to the initial estimated total charging time t 总 ', and then use the same method to calculate the temperature rise rate in real time during the actual charging process for the remaining temperature ranges and calibrate the charging time.

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