CN115808630A - Charge state calculation method and device for vehicle-mounted lithium iron phosphate battery and storage medium - Google Patents

Abstract

The invention discloses a method and a device for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery and a storage medium, wherein the method comprises the following steps: reading a historical SOC; acquiring a current battery state, and determining the SOC of the battery according to the historical SOC based on 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 by adopting ampere-hour integration and constant-voltage charging calibration based on the historical SOC; when the battery is in a power-off state, acquiring the open-circuit voltage of the battery, determining an SOC confidence interval corresponding to the open-circuit voltage according to an SOC curve, and calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery.

Description

State of charge calculation method, device and storage of a vehicle-mounted lithium iron phosphate battery medium

technical field

The invention relates to the technical field of electric vehicle batteries, in particular to a method, device and storage medium for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery.

Background technique

The current electric vehicle market is developing rapidly. The ternary lithium battery is widely used due to its high energy density, but it also brings many problems. In terms of energy, the wide application of ternary lithium batteries has increased 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 has increased the possibility of spontaneous combustion, explosion, and combustion of batteries ; In terms of cost, the cost of ternary lithium batteries is relatively high, which in turn leads to high vehicle prices. Based on the above background, lithium iron phosphate batteries that do not rely on rare metals, have higher safety, and lower cost have once again come into people's sight.

For ternary lithium batteries, the SOC calculation module in the battery management system generally uses the ampere-hour integral calculation, and uses OCV open circuit voltage calibration after standing to compensate for the ampere-hour integral error; but for lithium iron phosphate batteries, due to its OCV The curve is relatively gentle, and it is difficult to perform accurate SOC calibration through the static OCV open circuit voltage, resulting in low SOC calculation accuracy of the lithium iron phosphate electric vehicle battery management system.

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

Contents of the invention

In order to solve at least one aspect of the above problems, the present invention provides a method for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery, including: reading the historical SOC; obtaining the current battery state, and determining the state of the battery based on the historical SOC The SOC of the battery, 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 integration and constant voltage charging calibration; when the battery When the state is powered off, obtain the open circuit voltage of the battery, determine the SOC confidence interval corresponding to the open circuit voltage according to the SOC curve, and calibrate the historical SOC based on the SOC confidence interval to calculate the SOC of the battery.

Preferably, the SOC confidence interval corresponding to the open circuit voltage is determined according to the SOC curve, and the step of calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery includes: determining the voltage corresponding to the open circuit voltage according to the measurement accuracy Interval [Umin, Umax], wherein, Umin=U-1, Umax=U+1, U is the open circuit voltage; obtain the SOCrefmin and SOCrefmax corresponding to the voltage interval [Umin, Umax] based on the SOC curve, and determine the SOC The confidence interval is [SOCrefmin, SOCrefmax]; when the historical SOC is greater than or equal to SOCrefmin and less than or equal to SOCrefmax, store the historical SOC; when the historical SOC is less than SOCrefmin or greater than SOCrefmax, the stored SOC is the SOCrefmin and the SOCrefmax The average value of the above SOCrefmax.

Preferably, when the battery state is powered off, before the step of obtaining the open-circuit voltage of the battery, the method further includes: 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 the set time, store the historical SOC; when the duration of the battery state is greater than the set time, obtain the open circuit voltage of the battery, and determine the open circuit according to the SOC curve An SOC confidence interval corresponding to the voltage, and the historical SOC is calibrated based on the SOC confidence interval to calculate the SOC of the battery.

Preferably, when the state of the battery is powered on, the step of calculating the SOC of the battery by using the ampere-hour integral based on the historical SOC further includes: judging that the power-on state of the battery state is charging or discharging; when the state of the battery is When discharging, use the ampere-hour integral to calculate the SOC of the battery, and store the calculated SOC; when the battery state is charging, use the ampere-hour integral to calculate the SOC of the battery, and when the SOC value is 1, perform constant voltage charging calibration and store it SOC.

Preferably, when the battery state is charging, after the step of calculating the SOC of the battery by using the ampere-hour integration, and before the step of storing the SOC after performing constant voltage charging calibration when the SOC value is 1, it also includes: when the SOC is equal to the preset step threshold , carry out constant voltage charge calibration on SOC.

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.

In another aspect, a device is provided, including: a storage module, the storage module is used to store the SOC; a collection module, the collection module is used to collect the current and voltage of the battery; The module is connected in communication to read historical SOC and/or store SOC, the calculation module is connected in communication with the collection module to receive the current and voltage collected by the collection module, and the calculation module is connected in communication with the battery management system to realize The method for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery as described in any one of the foregoing.

In another aspect, a storage medium is provided, the storage medium is used for storing computer program instructions, and when the computer program instructions are executed by a processor, the method for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery as described above is implemented.

The method for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery in the embodiment of the present invention has the following beneficial effects:

(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.

(2) When the battery state is charging, perform constant-voltage charging calibration on the SOC at the preset step threshold and equal to 1, so as to increase the accuracy of the determined SOC value.

Description of drawings

For a better understanding of the above and other objects, features, advantages and functions of the present invention, reference may be made to the embodiments shown in the accompanying drawings. It should be understood by those skilled in the art that the accompanying drawings are intended to schematically illustrate preferred embodiments of the present invention, and are not intended to limit the scope of the present invention.

FIG. 1 shows a schematic flowchart of a method for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery according to an embodiment of the present invention.

Detailed ways

Exemplary embodiments of the present disclosure are described below in conjunction with the accompanying drawings, which include various details of the embodiments of the present disclosure to facilitate understanding, and they should be regarded as exemplary only. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the disclosure. Also, descriptions of well-known functions and constructions are omitted in the following description for clarity and conciseness.

As used herein, the term "comprise" and its variants mean open inclusion, ie "including but not limited to". The term "or" means "and/or" unless otherwise stated. The term "based on" means "based at least in part on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment." The term "another embodiment" means "at least one further embodiment". The terms "first", "second", etc. may refer to different or the same object. Other definitions, both express and implied, may also be included below.

In order to at least partially solve one or more of the above problems and other potential problems, an embodiment of the present disclosure proposes a method for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery, including: reading historical SOC; obtaining the current Battery status, based on the battery status to determine the battery SOC according to the historical SOC, where the battery status includes power-on and power-off; when the battery status is power-on, based on the historical SOC, the SOC of the battery is calculated using ampere-hour integration and constant voltage charging calibration; When the battery state is powered 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.

Specifically, the battery management system is used for battery terminal voltage measurement, battery total voltage measurement, battery total current measurement, dynamic monitoring of the working status of the power battery pack, data recording and analysis, SOC (State of Charge, that is, battery charge Status) computing 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 moment 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 results of the battery are obtained by the battery management system to Determine the current state of the battery, and calculate the SOC of the battery based on the current state of the battery based on the read historical SOC.

When it is determined that the battery is currently powered on according to the battery information obtained by the battery management system, the SOC is calculated using the ampere-hour integration algorithm. in,

The SOC calculation formula of the state of charge is:

The calculation formula of SOC in discharge state is:

SOC ₀ is the historical SOC read, Q is the maximum charge capacity when the battery is fully charged, and i(t) is the real-time current collected by the battery management system.

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

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

Specifically, the open circuit voltage U is obtained from the battery management system. Due to certain measurement errors, the measurement accuracy of the open circuit voltage is set to 1mV, and the confidence interval [Umin, Umax] of the open circuit voltage is [U-1, U+1] . Those skilled in the art can understand that, in other embodiments, according to the difference in the 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.

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

Specifically, the SOC curve of the battery is obtained from 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 historical SOC readings are calibrated by the determined SOC confidence interval.

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

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

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

Specifically, when it is judged that the historical SOC does not belong to the SOC confidence interval, it is judged that the historical SOC cannot accurately correspond to the current open-circuit voltage of the battery, that is, it cannot accurately reflect the current nuclear power state of the battery, and the battery is determined according to the SOC confidence interval determined by the obtained open-circuit voltage. The current SOC value, that is, the current SOC value of the battery is the average value of the maximum and minimum values of the SOC confidence interval.

In some embodiments, when the battery state is powered off, before the step of obtaining the open circuit voltage of the battery, it also includes: obtaining the duration of the battery state, and calculating the SOC of the battery according to the duration of the battery state; When the time is less than or equal to the set time, the historical SOC is stored; when the duration of the battery state is greater than the set time, the open circuit voltage of the battery is obtained, and the SOC confidence interval corresponding to the open circuit voltage is determined according to the SOC curve, and the historical SOC is calculated based on the SOC confidence interval. Calibration to calculate the SOC of the battery.

Specifically, the duration of the battery power-off state is obtained through the battery management system. When the battery duration is less than the set time, the electrolyte distribution inside the battery is uneven, and it is impossible to obtain a stable open-circuit voltage for measurement. Therefore, it is necessary to maintain the power-off state of the battery. The duration is greater than the set time to measure the open circuit voltage, 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 power-off state is 30 minutes. In another embodiment, the set time may be 60 minutes or the like according to the characteristics of the battery, so as to obtain a stable terminal voltage.

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 the ampere-hour integral further includes: judging that the power-on state of the battery state is charging or discharging; Calculate the SOC of the battery by time integration and store the calculated SOC; when the battery state is charging, use the ampere-hour integration to calculate the SOC of the battery, and store the SOC after constant voltage charging calibration when the SOC value is 1.

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 the process of electrochemical depolarization. Since the cut-off current of the constant voltage charging step is extremely small, at the end of the constant voltage, the difference between the open circuit voltage of the battery and the voltage of the charger is very small, that is, to ensure that when the SOC is equal to 1, it accurately corresponds to the fully charged state of the battery.

In some embodiments, when the state of the battery is charging, after the step of calculating the SOC of the battery by using ampere-hour integration, and before the step of storing the SOC after performing constant voltage charging calibration when the SOC value is 1, it also includes: when the SOC is equal to the preset step When the threshold is reached, the SOC is calibrated by constant voltage charging.

Specifically, according to the SOC curve of the battery, it can be seen that the preset step threshold of SOC corresponds to the point on the SOC curve with the largest slope change. When the battery is charged at a constant voltage until the charging current is less than a preset current (for example, 0.2A), the constant voltage charging calibration is completed. It should be noted that the preset step threshold value is determined based on the slope of the SOC curve.

Example 1

As shown in Figure 1, the embodiment of the method for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery of the present invention comprises the following steps:

The historical SOC is read through the battery management system, and the historical SOC is the latest SOC of the battery stored in the battery management system.

Obtain the current power-on and power-off status of the battery through the battery management system, and select a computing unit based on the judging result of the power-on and power-on status of the battery, wherein the computing unit includes a power-on computing unit and a power-off computing unit.

When the battery is in the power-off state, select the power-off calculation unit to calculate the battery SOC. The battery power-off calculation unit includes a resting time judging unit, which judges the battery resting time through the battery management system, and the preset battery resting time is 30 minutes. When the battery rest time is less than or equal to 30 minutes, the battery power-off unit outputs and stores the historical SOC. When the battery resting time is more than 30 minutes, the battery open circuit voltage is obtained through the battery management system, and the open circuit voltage confidence interval is set according to the accuracy of the battery open circuit voltage, and the SOC confidence interval is determined by the open circuit voltage confidence interval combined with the SOC curve to determine whether the historical SOC belongs to SOC Confidence interval, when the historical SOC belongs to the SOC confidence interval, the historical SOC is output and stored; when the historical SOC does not belong to the SOC confidence interval, the average value of the maximum and minimum values of the SOC confidence interval is output and stored.

When the battery is in the power-on state, select the power-on calculation unit to calculate the battery SOC. The power-on calculation unit includes a charging judging unit. When it is judged that the battery is in a discharging state, the historical SOC is used as an initial value, and the SOC output is calculated and stored using the ampere-hour integral.

When judging that the battery is in a charging state, including:

Step S1, the power-on calculation takes the historical SOC as the initial value, and calculates the SOC by using the ampere-hour integral.

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

Step S3, when the SOC is equal to the SOC step threshold, the constant voltage charging of the battery is calibrated.

When the SOC is not equal to the SOC step threshold, proceed to step S31 to determine whether the SOC is less than the SOC step threshold, and when the SOC is less than the SOC step threshold, repeat step S2; when the SOC is greater than the SOC step threshold, proceed to step S4.

Step S4, continue to use the ampere-hour integral to calculate the SOC.

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

Step S6, when the value of the SOC is not equal to 100%, return to step S4; when the value of the SOC is 100%, perform constant voltage charging calibration on the battery and output the SOC and store it.

On the other hand, a device is provided, including: a storage module, the storage module is used to store the SOC; a collection module, the collection module is used to collect the current and voltage of the battery; a calculation module, the calculation module is connected to the storage module in communication to read the historical SOC And/or store the SOC, the calculation module is connected to the acquisition module in communication to receive the current and voltage collected by the acquisition module, and the calculation module is connected to the battery management system in communication to realize the calculation of the state of charge of any vehicle-mounted lithium iron phosphate battery as described above method.

Specifically, the storage module uses a readable storage unit to store the SOC determined by the calculation module. The collection module is used to collect parameters including but not limited to battery current, voltage and resting time, so as to determine the state of the battery. The calculation module uses a processor to obtain the historical SOC and battery status through the connection with the storage module and the acquisition module, so as to calculate the battery SOC. Specifically, when the battery state is powered on, the calculation module uses ampere-hour integration and constant voltage charging calibration to calculate the SOC of the battery based on the historical SOC; when the battery state is powered off, the calculation module obtains the open circuit voltage of the battery and determines it according to the SOC curve. The SOC confidence interval corresponding to the open circuit voltage, based on the SOC confidence interval, the historical SOC is calibrated to calculate the SOC of the battery.

In another aspect, a storage medium is provided, and the storage medium is used for storing computer program instructions, and the computer program instructions implement any method for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery when executed by a processor.

Having described various embodiments of the present disclosure above, the foregoing description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and alterations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principle of each embodiment, practical application or technical improvement in the market, or to enable other ordinary skilled in the art to understand this article.

Claims (8)

1. A method for calculating the state of charge of a vehicle-mounted lithium iron phosphate battery, characterized in that, comprising: Read historical SOC; Acquiring the 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 state of the battery is powered on, calculate the SOC of the battery based on the historical SOC using ampere-hour integration and constant voltage charging calibration; When the battery state is powered 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. 2. The method according to claim 1, wherein the SOC confidence interval corresponding to the open circuit voltage is determined according to the SOC curve, and the step of calibrating the historical SOC based on the SOC confidence interval to calculate the SOC of the battery includes : Determine the voltage interval [Umin, Umax] corresponding to the open-circuit voltage according to the measurement accuracy, where 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 the determined SOC confidence interval is [SOCrefmin, SOCrefmax]; When the historical SOC is greater than or equal to SOCrefmin and less than or equal to SOCrefmax, store the historical SOC; When the historical SOC is less than SOCrefmin or greater than SOCrefmax, the stored SOC is the average value of the SOCrefmin and the SOCrefmax. 3. The method according to claim 2, wherein when the battery state is powered off, before the step of obtaining the open circuit voltage of the battery, further comprising: 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 longer than the set time, 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. 4. The method according to claim 1, wherein when the state of the battery is powered on, the step of calculating the SOC of the battery by using the ampere-hour integral based on the historical SOC further comprises: judging that the power-on state of the battery state is charging or discharging; When the state of the battery is discharging, the SOC of the battery is calculated using the ampere-hour integral, and the calculated SOC is stored; When the state of the battery is charging, the SOC of the battery is calculated by using the ampere-hour integration, and the SOC is stored after the constant voltage charging calibration is performed when the SOC value is 1. 5. The method according to claim 4, characterized in that, when the state of the battery is charging, after the step of calculating the SOC of the battery by ampere-hour integration, the step of storing the SOC after the constant voltage charging calibration is performed when the SOC value is 1 Also previously included: performing constant-voltage charge calibration on the SOC when the SOC is equal to a preset step threshold. 6 . The method according to claim 5 , 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. 7. A device, characterized in that it comprises: a storage module, the storage module is used to store the SOC; A collection module, the collection module is used to collect the current and voltage of the battery; A calculation module, the calculation module is connected in communication with the storage module to read the historical SOC and/or store the SOC, the calculation module is connected in communication with the acquisition module to receive the current and voltage collected by the acquisition module, the The calculation module is connected in communication with the battery management system, so as to realize the method for calculating the state of charge of the vehicle-mounted lithium iron phosphate battery according to any one of claims 1-6. 8. A storage medium, characterized in that the storage medium is used to store computer program instructions, and when the computer program instructions are executed by a processor, the vehicle-mounted lithium iron phosphate battery according to any one of claims 1-6 can be realized. State of charge calculation method.

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