A method and device for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery, and a storage medium

Abstract

The application discloses a kind of vehicle-mounted lithium iron phosphate battery state of charge calculation method, device and storage medium, comprising: reading historical SOC;Current battery state is obtained, and the SOC of battery is determined based on the battery state according to the historical SOC, wherein the battery state includes power-on and power-off;When the battery state is power-on, the SOC of battery is calculated using ampere-hour integration and constant voltage charging calibration based on the historical SOC;When the battery state is power-off, the open-circuit voltage of battery is obtained, the SOC confidence interval corresponding to the open-circuit voltage is determined according to SOC curve, and the historical SOC is calibrated based on the SOC confidence interval to calculate the SOC of battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric vehicle batteries, in particular to a state of charge calculation method, device and storage medium for a vehicle-mounted lithium iron phosphate battery. BACKGROUND

[0002] The current electric vehicle market is developing rapidly. Although the ternary lithium battery is widely used due to its high energy density, it also brings many problems. In terms of energy, the wide application of ternary lithium batteries increases the dependence of new energy vehicles on rare metals such as nickel and cobalt; in terms of safety, the chemical mechanism of ternary lithium batteries increases the possibility of battery self-ignition, explosion and combustion; in terms of cost, the cost of ternary lithium batteries is high, which leads to high vehicle prices. Based on the above background, lithium iron phosphate batteries, which do not depend on rare metals, have higher safety and lower cost, have once again entered the sight of people.

[0003] For ternary lithium batteries, the SOC calculation module in the battery management system generally uses ampere-hour integral calculation, and uses OCV open circuit voltage calibration after static to make up for the ampere-hour integral error; but for lithium iron phosphate batteries, due to its relatively flat OCV curve, it is difficult to accurately calibrate the SOC by static OCV open circuit voltage, resulting in low accuracy of the SOC calculation of the lithium iron phosphate electric vehicle battery management system.

[0004] Based on the above background, the existing SOC calculation method is not suitable for lithium iron phosphate batteries, and a more suitable SOC fusion calculation method for the lithium iron phosphate electric vehicle battery management system is proposed to solve the problem of inaccurate SOC calculation of lithium iron phosphate batteries. SUMMARY

[0005] To solve at least one aspect of the above problem, the present application provides a state of charge calculation method for a vehicle-mounted lithium iron phosphate battery, comprising: reading a historical SOC; obtaining a current battery state, and determining the SOC of the battery based on the battery state according to the historical SOC, wherein the battery state includes power-on and power-off; when the battery state is power-on, the SOC of the battery is calculated based on the historical SOC using ampere-hour integral and constant voltage charging calibration; when the battery state is power-off, the open circuit voltage of the battery is obtained, the SOC confidence interval corresponding to the open circuit voltage is determined according to the SOC curve, and the historical SOC is calibrated based on the SOC confidence interval to calculate the SOC of the battery.

[0006] Preferably, the step of determining the SOC confidence interval corresponding to the open-circuit voltage according to the SOC curve, and calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery comprises: determining a voltage interval [Umin, Umax] corresponding to the open-circuit voltage according to the measurement accuracy, wherein Umin=U-1, Umax=U+1, and U is the open-circuit voltage; obtaining SOCrefmin and SOCrefmax corresponding to the voltage interval [Umin, Umax] based on the SOC curve, and determining the SOC confidence interval as [SOCrefmin, SOCrefmax]; when the historical SOC is greater than or equal to SOCrefmin and less than or equal to SOCrefmax, storing the historical SOC; when the historical SOC is less than SOCrefmin or greater than SOCrefmax, storing the SOC as the average of the SOCrefmin and the SOCrefmax.

[0007] Preferably, when the battery state is power-off, before the step of obtaining the open-circuit voltage of the battery, the method further comprises: obtaining the duration of the battery state, and calculating the SOC of the battery according to the duration of the battery state; when the duration of the battery state is less than or equal to a set time, storing the historical SOC; when the duration of the battery state is greater than the set time, obtaining the open-circuit voltage of the battery, determining the SOC confidence interval corresponding to the open-circuit voltage according to the SOC curve, and calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery.

[0008] Preferably, when the battery state is power-on, the step of calculating the SOC of the battery based on the historical SOC by adopting ampere-hour integration further comprises: judging whether the power-on state of the battery state is charging or discharging; when the battery state is discharging, calculating the SOC of the battery by adopting ampere-hour integration, and storing the calculated SOC; when the battery state is charging, calculating the SOC of the battery by adopting ampere-hour integration, and storing the SOC after constant-voltage charging calibration when the SOC value is 1.

[0009] Preferably, when the battery state is charging, after the step of calculating the SOC of the battery by adopting ampere-hour integration, and before the step of storing the SOC after constant-voltage charging calibration when the SOC value is 1, the method further comprises: performing constant-voltage charging calibration on the SOC when the SOC is equal to a preset step threshold.

[0010] Preferably, in the step of performing constant-voltage charging calibration on the SOC, the constant-voltage charging calibration is completed when the battery is controlled to perform constant-voltage charging until the charging current is less than a preset current.

[0011] In another aspect, an apparatus is provided, comprising: a storage module configured to store a SOC; a collection module configured to collect a current and a voltage of a battery; a calculation module communicatively connected with the storage module to read a historical SOC and / or store a SOC, the calculation module communicatively connected with the collection module to receive the current and the voltage collected by the collection module, the calculation module communicatively connected with a battery management system to implement the method for calculating a state of charge of a vehicle-mounted lithium iron phosphate battery as any one of the preceding aspects.

[0012] In another aspect, a storage medium is provided, configured to store computer program instructions, which, when executed by a processor, implement the method for calculating a state of charge of a vehicle-mounted lithium iron phosphate battery as any one of the preceding aspects.

[0013] The method for calculating a state of charge of a vehicle-mounted lithium iron phosphate battery has the following beneficial effects:

[0014] (1) By using the SOC confidence interval to calibrate the SOC when the battery state is powered off, the accuracy of the SOC value is increased.

[0015] (2) By using the SOC confidence interval to calibrate the SOC when the battery state is powered off, the accuracy of the SOC value is increased. BRIEF DESCRIPTION OF DRAWINGS

[0016] For better understanding of the above and other objects, features, advantages and functions of the present application, reference should be made to the embodiments illustrated in the drawings. Those skilled in the art should understand that the drawings are intended to schematically illustrate the preferred embodiments of the present application, and have no limiting effect on the scope of the present application.

[0017] Figure 1 A flowchart of the method for calculating a state of charge of a vehicle-mounted lithium iron phosphate battery according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0018] Exemplary embodiments of the present disclosure are described below with reference to the accompanying drawings, which include various details of the embodiments of the present disclosure to assist in the understanding of the present disclosure, and should be considered as merely exemplary. Therefore, those of ordinary skill in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Also, in order to be clear and concise, descriptions of well-known functions and structures are omitted in the following description.

[0019] As used herein, the term "includes" and its variants are intended to be open-ended, meaning that there is no limitation as to what the term covers. The term "comprising" means "including, but not limited to." The term "or" is meant to be inclusive, meaning that it includes any one or more of the listed options. The term "based on" means "based, at least in part, on." The terms "one example embodiment" and "an example embodiment" mean "at least one example embodiment." The term "another embodiment" means "at least one additional embodiment." The terms "a first," "a second," etc. do not require that there be only one of the identified objects. Other explicit or implicit definitions can also be included below.

[0020] To at least partially address one or more of the above-referenced issues and other potential issues, one embodiment of the present disclosure proposes a method for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery, comprising: reading a historical SOC; obtaining a current battery state, determining the SOC of the battery based on the battery state according to the historical SOC, wherein the battery state includes power-up and power-down; when the battery state is power-up, calculating the SOC of the battery based on the historical SOC using ampere-hour integration and constant voltage charging calibration; when the battery state is power-down, obtaining the open-circuit voltage of the battery, determining the SOC confidence interval corresponding to the open-circuit voltage according to the SOC curve, and calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery.

[0021] Specifically, the battery management system is used for battery terminal voltage measurement, battery pack total voltage measurement, battery pack total current measurement, dynamic monitoring of the working state of the power battery pack, data recording and analysis, SOC (State of Charge) calculation, and communication networking functions, etc., to realize the monitoring, management and maintenance of the battery. In this embodiment, the historical SOC stored at the previous time is read by the battery management system to start the calculation of the state of charge of the battery; the voltage and current of the battery and the dynamic monitoring result of the battery are obtained by the battery management system to determine the current state of the battery, and the SOC of the battery is calculated based on the read historical SOC according to the current state of the battery.

[0022] When the current state of the battery is determined to be power-up according to the battery information obtained by the battery management system, the SOC is calculated using the ampere-hour integration algorithm. Wherein,

[0023] The SOC calculation formula for the charging state is:

[0024] The SOC calculation formula for the discharging state is:

[0025] SOC0 is the read historical SOC, Q is the maximum charge capacity of the battery when it is fully charged, and i(t) is the real-time current collected by the battery management system.

[0026] When it is determined according to the battery information acquired by the battery management system that the battery is currently in the power-off state, the step of determining the SOC confidence interval corresponding to the open-circuit voltage according to the SOC curve, and calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery comprises:

[0027] The voltage interval [Umin, Umax] corresponding to the open-circuit voltage is determined according to the measurement accuracy, wherein Umin=U-1 and Umax=U+1, and U is the open-circuit voltage.

[0028] Specifically, the open-circuit voltage U is acquired by the battery management system. Since there is a certain measurement error, the measurement accuracy of the open-circuit voltage is set to 1 mV, and the confidence interval [Umin, Umax] of the open-circuit voltage is [U-1, U+1]. It can be understood by those skilled in the art that in another embodiment, according to the different measurement accuracy of the open-circuit voltage, the confidence interval of the open-circuit voltage can also be [U-0.5, U+0.5], [U-1.5, U+1.5], etc.

[0029] The SOCrefmin and SOCrefmax corresponding to [Umin, Umax] are acquired based on the SOC curve, and the determined SOC confidence interval is [SOCrefmin, SOCrefmax].

[0030] Specifically, the SOC curve of the battery is acquired by the battery management system, and the SOC confidence interval is determined by querying the SOC value corresponding to the confidence interval [Umin, Umax] of the voltage through the SOC curve. The read historical SOC is calibrated through the determined SOC confidence interval.

[0031] When the historical SOC is greater than or equal to SOCrefmin and less than or equal to SOCrefmax, the historical SOC is stored.

[0032] Specifically, when the value of the historical SOC belongs to the SOC confidence interval, it is determined that the acquired historical SOC corresponds to the current acquired open-circuit voltage, that is, the historical SOC reflects the current state of charge of the battery, and the historical SOC is stored.

[0033] When the historical SOC is less than SOCrefmin or greater than SOCrefmax, the stored SOC is the average of SOCrefmin and SOCrefmax.

[0034] Specifically, when it is determined that the historical SOC does not belong to the SOC confidence interval, it is determined that the historical SOC cannot accurately correspond to the current open-circuit voltage of the battery, that is, it cannot accurately reflect the current state of charge of the battery, and the current SOC value of the battery is determined according to the SOC confidence interval determined by the acquired open-circuit voltage, that is, the current SOC value of the battery is the average of the maximum value and the minimum value of the SOC confidence interval.

[0035] In some embodiments, when the battery state is powered off, before the step of obtaining the open circuit voltage of the battery, the method further comprises: obtaining the duration of the battery state, and calculating the SOC of the battery according to the duration of the battery state; when the duration of the battery state is less than or equal to a set time, storing the historical SOC; when the duration of the battery state is greater than the set time, obtaining the open circuit voltage of the battery, determining the SOC confidence interval corresponding to the open circuit voltage according to the SOC curve, and calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery.

[0036] Specifically, the duration of the battery powered-off state is obtained by the battery management system. When the duration of the battery is less than a set time, the electrolyte inside the battery is unevenly distributed, and the open circuit voltage cannot be measured stably. Therefore, the open circuit voltage is measured when the duration of the battery powered-off state is greater than the set time, so that the electrolyte inside the battery is evenly distributed to obtain a stable terminal voltage. In this embodiment, the set time of the battery powered-off state is 30 minutes. In another embodiment, the set time can be 60 minutes or the like according to the characteristics of the battery, so that a stable terminal voltage can be obtained.

[0037] In some embodiments, when the battery state is powered on, the step of calculating the SOC of the battery based on the historical SOC using ampere-hour integration further comprises: determining whether the powered-on state of the battery state is charging or discharging; when the battery state is discharging, calculating the SOC of the battery using ampere-hour integration and storing the calculated SOC; when the battery state is charging, calculating the SOC of the battery using ampere-hour integration and storing the SOC after constant voltage charging calibration when the SOC value is 1.

[0038] Specifically, the process of constant voltage charging is a process in which the open circuit voltage of the battery gradually approaches the voltage of the charger, which belongs to an electrochemical depolarization process. Since the cutoff current of the constant voltage charging step is very small, the difference between the open circuit voltage of the battery and the voltage of the charger is very small when the constant voltage charging ends, i.e., it is ensured that the SOC is equal to 1 when the battery is in a full charge state.

[0039] In some embodiments, when the battery state is charging, the step of calculating the SOC of the battery using ampere-hour integration is followed by the step of storing the SOC after constant voltage charging calibration when the SOC value is 1, and is further followed by the step of performing constant voltage charging calibration on the SOC when the SOC is equal to a preset step threshold.

[0040] Specifically, according to the SOC curve of the battery, the preset step threshold of the SOC corresponds to the point with the largest slope change on the SOC curve. When the SOC calculated based on the historical SOC through the ampere-hour integral calculation reaches the preset step threshold, the battery is controlled to perform constant-voltage charging until the charging current is less than the preset current (for example, 0.2 A), and the constant-voltage charging calibration is completed. It should be noted that the preset step threshold is determined based on the slope of the SOC curve.

[0041] Embodiment 1

[0042] As Figure 1 shown, the embodiment of the method for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery of the application includes the following steps:

[0043] Read the historical SOC through the battery management system, wherein the historical SOC is the last SOC of the battery stored by the battery management system.

[0044] Obtain the current power-on and power-off state of the battery through the battery management system, and select a calculation unit based on the judgment result of the power-on and power-off state of the battery, wherein the calculation unit includes a power-on calculation unit and a power-off calculation unit.

[0045] When the battery is in the power-off state, select the power-off calculation unit to calculate the SOC of the battery. The battery power-off calculation unit includes a standing time judgment unit, which judges the standing time of the battery through the battery management system, and the preset battery standing time is 30 minutes. When the battery standing time is less than or equal to 30 minutes, the battery power-off unit outputs and stores the historical SOC. When the battery standing time is greater than 30 minutes, obtain the open-circuit voltage of the battery through the battery management system, set the open-circuit voltage confidence interval according to the accuracy of the open-circuit voltage, determine the SOC confidence interval based on the open-circuit voltage confidence interval and the SOC curve, and judge whether the historical SOC belongs to the SOC confidence interval. When the historical SOC belongs to the SOC confidence interval, output and store the historical SOC; when the historical SOC does not belong to the SOC confidence interval, output and store the average value of the maximum and minimum values of the SOC confidence interval.

[0046] When the battery is in the power-on state, select the power-on calculation unit to calculate the SOC of the battery. The power-on calculation unit includes a charging judgment unit. When it is judged that the battery is in the discharging state, take the historical SOC as the initial value, and use the ampere-hour integral to calculate and output the SOC and store it.

[0047] When it is judged that the battery is in the charging state, it includes:

[0048] Step S1, take the historical SOC as the initial value, and use the ampere-hour integral to calculate the SOC.

[0049] Step S2, setting an SOC step threshold (SOCspe) according to the SOC curve slope of the battery, and judging whether the SOC is equal to the SOC step threshold.

[0050] Step S3, when the SOC is equal to the SOC step threshold, performing constant voltage charging calibration on the battery.

[0051] When the SOC is not equal to the SOC step threshold, performing step S31, judging whether the SOC is less than the SOC step threshold, when the SOC is less than the SOC step threshold, repeating step S2; when the SOC is greater than the SOC step threshold, performing step S4.

[0052] Step S4, continuing to calculate the SOC by using the ampere-hour integration.

[0053] Step S5, judging whether the SOC value is 100%.

[0054] Step S6, when the SOC value is not equal to 100%, returning to step S4; when the SOC value is equal to 100%, outputting the SOC after performing constant voltage charging calibration on the battery and storing.

[0055] On the other hand, an apparatus is provided, comprising: a storage module, the storage module being configured to store the SOC; an acquisition module, the acquisition module being configured to acquire the current and voltage of the battery; a calculation module, the calculation module being communicatively connected with the storage module to read the historical SOC and / or the stored SOC, and being communicatively connected with the acquisition module to receive the current and voltage acquired by the acquisition module, and being communicatively connected with the battery management system to implement any of the foregoing methods for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery.

[0056] Specifically, the storage module uses a readable storage unit to store the SOC determined by the calculation module. The acquisition module is configured to acquire parameters including but not limited to the current, voltage and standing time of the battery, to determine the state of the battery. The calculation module uses a processor to obtain the historical SOC and the state of the battery through the connection with the storage module and the acquisition module, to calculate the SOC of the battery. Specifically, when the state of the battery is powered on, the calculation module calculates the SOC of the battery based on the historical SOC by using the ampere-hour integration and the constant voltage charging calibration; when the state of the battery is powered off, the calculation module obtains the open circuit voltage of the battery, determines the SOC confidence interval corresponding to the open circuit voltage according to the SOC curve, and calibrates the historical SOC based on the SOC confidence interval to calculate the SOC of the battery.

[0057] On the other hand, a storage medium is provided, the storage medium being configured to store computer program instructions, the computer program instructions implementing any of the foregoing methods for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery when executed by a processor.

[0058] Having described various embodiments of the disclosure above, the descriptions are not exhaustive and are not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art. The selection of terms to be used in the description is intended to best explain the principles of the embodiments, practical application, or technical improvement over the prior art, or to enable other skilled persons in the art to understand the present document.

Claims

1. A method for calculating a state of charge of an on-vehicle lithium iron phosphate battery, characterized by, The method comprises the following steps: reading a historical SOC, reading a historical SOC stored at a previous time by a battery management system to start the calculation of the state of charge of the battery; obtaining a current battery state, and determining the SOC of the battery based on the historical SOC according to the battery state, wherein the battery state comprises power-on and power-off; when the battery state is power-on, calculating the SOC of the battery based on the historical SOC by adopting ampere-hour integration and constant voltage charging calibration; when the battery state is power-off, obtaining the duration of the battery state, and calculating the SOC of the battery according to the duration of the battery state; when the duration of the battery state is less than or equal to a set time, storing the historical SOC; when the duration of the battery state is greater than the set time, obtaining an open circuit voltage of the battery, determining a SOC confidence interval corresponding to the open circuit voltage according to a SOC curve, calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery, determining a voltage interval [Umin, Umax] corresponding to the open circuit voltage according to a measurement accuracy, setting the measurement accuracy of the open circuit voltage to 1 mV, wherein Umin = U-1 and Umax = U+1, and U is the open circuit voltage; obtaining SOCrefmin and SOCrefmax corresponding to the voltage interval [Umin, Umax] based on the SOC curve, and determining the SOC confidence interval as [SOCrefmin, SOCrefmax]; when the historical SOC is greater than or equal to SOCrefmin and less than or equal to SOCrefmax, storing the historical SOC; when the historical SOC is less than SOCrefmin or greater than SOCrefmax, the stored SOC is the average of the SOCrefmin and the SOCrefmax.

2. The method of claim 1, wherein, When the battery state is power-on, the step of calculating the SOC of the battery based on the historical SOC by adopting ampere-hour integration further comprises: judging whether the power-on state of the battery state is charging or discharging; when the battery state is discharging, calculating the SOC of the battery by adopting ampere-hour integration, and storing the calculated SOC; when the battery state is charging, calculating the SOC of the battery by adopting ampere-hour integration, and storing the SOC after constant voltage charging calibration when the SOC value is 1.

3. The method of claim 2, wherein, After the step of calculating the SOC of the battery by adopting ampere-hour integration when the battery state is charging, and before the step of storing the SOC after constant voltage charging calibration when the SOC value is 1, the method further comprises the step of performing constant voltage charging calibration on the SOC when the SOC is equal to a preset step threshold.

4. The method of claim 3, wherein, In the step of performing constant voltage charging calibration on the SOC, the constant voltage charging calibration is completed when the battery is controlled to perform constant voltage charging until the charging current is less than a preset current.

5. An apparatus, comprising: The method comprises the following steps: a storage module for storing the SOC; a collection module for collecting the current and voltage of the battery; A computing module, which is communicatively connected with the storage module to read the historical SOC and / or store the SOC, is communicatively connected with the acquisition module to receive the current and voltage acquired by the acquisition module, and is communicatively connected with the battery management system to implement the method for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery according to any one of claims 1-4.

6. A storage medium, characterized by The storage medium is used to store computer program instructions, which, when executed by a processor, implement the method for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery according to any one of claims 1-4.

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