CN108663621B - Charge state calculation method and system for power battery pack - Google Patents

Charge state calculation method and system for power battery pack Download PDF

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CN108663621B
CN108663621B CN201710200054.6A CN201710200054A CN108663621B CN 108663621 B CN108663621 B CN 108663621B CN 201710200054 A CN201710200054 A CN 201710200054A CN 108663621 B CN108663621 B CN 108663621B
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state
charge
current
power battery
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CN108663621A (en
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廉玉波
凌和平
陈昊
陶雷
陈本洁
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BYD Co Ltd
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    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
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Abstract

The invention provides a method and a system for calculating the charge state of a power battery pack, wherein the ampere-hour charge state and the estimated charge state of the power battery pack are respectively calculated by an ampere-hour integration method and an open-circuit voltage method, then the ampere-hour charge state is corrected by judging whether the difference value between the ampere-hour charge state and the estimated charge state meets a preset correction condition, if not, the ampere-hour charge state is considered to be accurate and is directly used as the actual charge state of the power battery pack, and if the difference value is corrected, the corrected ampere-hour charge state is used as the actual charge state of the power battery pack, so that the error generated in the charge state calculation process can be corrected in time, the calculation precision of the charge state is effectively improved, the calculation amount is small, and the method and the system are easy to realize.

Description

Charge state calculation method and system for power battery pack
Technical Field
The embodiment of the invention belongs to the technical field of power battery packs, and particularly relates to a method and a system for calculating the charge state of a power battery pack.
Background
With the continuous development and progress of power battery pack technology, power battery packs are widely applied to electric vehicles, electric trains, electric bicycles, golf carts and other equipment. In the using process of the power battery pack, the power battery pack needs to be effectively managed to ensure that the power battery pack can work in a normal state, so that the service life of the power battery pack is prolonged. The State of Charge (SOC) of the power battery pack is one of important parameters for measuring the working State of the power battery pack, accurately calculates the SOC of the power battery pack, and plays a vital role in effectively preventing the power battery pack from being overcharged or overdischarged, improving the safety performance of the power battery pack and prolonging the service life of the power battery pack.
However, at present, the state of charge of the power battery pack is usually calculated by an open-circuit voltage method, an ampere-hour integration method, an internal resistance method, a neural network method or a kalman filtering method, all of the algorithms have accumulated errors in a long-term use process, and the calculation accuracy of calculating the state of charge by using one method alone is low, so that the state of charge of the power battery pack cannot be calculated effectively and accurately for a long time.
Disclosure of Invention
The embodiment of the invention provides a method and a system for calculating the state of charge of a power battery pack, which can correct errors generated in the state of charge calculation process in time, effectively improve the calculation precision of the state of charge, have small calculation amount and are easy to realize.
An embodiment of the present invention provides a method for calculating a state of charge of a power battery pack, including:
acquiring the current, the current highest cell voltage, the current lowest cell voltage, the initial charge state and the initial nominal capacity of the power battery pack;
calculating the ampere-hour charge state of the power battery pack by an ampere-hour integration method according to the current, the initial charge state and the initial nominal capacity;
calculating the estimated state of charge of the power battery pack by an open-circuit voltage method according to the current, the current highest cell voltage, the current lowest cell voltage, a preset OCV-SOC curve and a preset direct-current internal resistance table;
if the difference value between the ampere-hour charge state and the estimated charge state does not meet the preset correction condition, taking the ampere-hour charge state as the actual charge state of the power battery pack; and otherwise, correcting the ampere-hour charge state according to a preset correction coefficient until the corrected ampere-hour charge state is larger than the estimated charge state, and taking the corrected ampere-hour charge state as the actual charge state of the power battery pack.
In another aspect, an embodiment of the present invention further provides a system for calculating a state of charge of a power battery pack, including:
the parameter acquisition unit is used for acquiring the current, the current highest cell voltage, the current lowest cell voltage, the initial charge state and the initial nominal capacity of the power battery pack;
the ampere-hour charge state calculating unit is used for calculating the ampere-hour charge state of the power battery pack by an ampere-hour integration method according to the current, the initial charge state and the initial nominal capacity;
the estimated state of charge calculation unit is used for calculating the estimated state of charge of the power battery pack through an open-circuit voltage method according to the current, the current highest cell voltage, the current lowest cell voltage, a preset OCV-SOC curve and a preset direct-current internal resistance table;
the actual charge state determining unit is used for taking the ampere-hour charge state as the actual charge state of the power battery pack if the difference value between the ampere-hour charge state and the estimated charge state does not meet the preset correction condition; and otherwise, correcting the ampere-hour charge state according to a preset correction coefficient until the corrected ampere-hour charge state is larger than the estimated charge state, and taking the corrected ampere-hour charge state as the actual charge state of the power battery pack.
According to the embodiment of the invention, the ampere-hour charge state and the estimated charge state of the power battery pack are respectively calculated by an ampere-hour integration method and an open-circuit voltage method, then the ampere-hour charge state is corrected by judging whether the difference value between the ampere-hour charge state and the estimated charge state meets the preset correction condition, if not, the ampere-hour charge state is considered to be accurate and is directly used as the actual charge state of the power battery pack, and if so, the corrected ampere-hour charge state is used as the actual charge state of the power battery pack, so that errors generated in the charge state calculation process can be corrected in time, the calculation accuracy of the charge state is effectively improved, the calculation amount is small, and the method is easy to realize.
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In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a basic flow diagram of a method for calculating the state of charge of a power battery according to an embodiment of the present invention;
fig. 2 is a graph of temperature compensation coefficients of a power battery pack at different temperatures, which are measured experimentally in advance, according to an embodiment of the present invention;
fig. 3 is a graph of different-rate discharge curves of a power battery pack at 25 ℃ and a graph of different-rate charge curves of the power battery pack at 23 ℃ which are measured experimentally in advance according to an embodiment of the invention;
fig. 4 is a preset OCV-SOC curve of a power battery pack, which is measured experimentally in advance, according to an embodiment of the present invention;
fig. 5 is an equivalent circuit model of a power battery pack in an operating state according to an embodiment of the present invention;
fig. 6 is a graph showing the relationship between the current and the terminal voltage of the power battery pack measured in advance according to the experiment during the charging and discharging process, with time, according to an embodiment of the present invention;
fig. 7 is a block diagram illustrating a detailed flow of step S30 according to an embodiment of the present invention;
fig. 8 is a block diagram illustrating a detailed flow of step S40 according to an embodiment of the present invention;
fig. 9 is a block flow diagram of a method for calculating a state of charge of a power battery pack according to an embodiment of the present invention;
fig. 10 is a block flow diagram of a method for calculating a state of charge of a power battery pack according to an embodiment of the present invention;
fig. 11 is a block diagram illustrating a basic configuration of a state of charge calculation system of a power battery pack according to an embodiment of the present invention;
fig. 12 is a block diagram of the estimated state of charge calculation unit 30 according to an embodiment of the present invention;
fig. 13 is a block diagram of an actual state of charge determination unit 40 according to an embodiment of the present invention;
fig. 14 is a block diagram of a state of charge calculation system for a power battery pack according to an embodiment of the present invention;
fig. 15 is a block diagram of a state of charge calculation system of a power battery pack according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood by those skilled in the art, the technical solutions in the embodiments of the present invention will be clearly described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The terms "comprises" and "comprising," and any variations thereof, in the description and claims of this invention and the above-described drawings are intended to cover non-exclusive inclusions. For example, a process, method, or system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus. Furthermore, the terms "first," "second," and "third," etc. are used to distinguish between different objects and are not used to describe a particular order.
As shown in fig. 1, an embodiment of the present invention provides a method for calculating a state of charge of a power battery pack, including:
step S10: and acquiring the current, the current highest cell voltage, the current lowest cell voltage, the initial charge state and the initial nominal capacity of the power battery pack.
In this embodiment, the current refers to the current flowing through the power battery pack acquired at the present moment; the current highest single voltage refers to the voltage of a single battery with the highest current voltage in a plurality of single batteries included in the power battery pack; the current lowest single voltage refers to the voltage of the single battery with the lowest current voltage in a plurality of single batteries included in the power battery pack; the initial state of charge refers to the state of charge of the power battery pack acquired at the current moment; the initial nominal capacity refers to the nominal capacity of the power battery pack acquired at the current moment.
Step S20: and calculating the ampere-hour charge state of the power battery pack by an ampere-hour integration method according to the current, the initial charge state and the initial nominal capacity.
In a specific application, the method can be based on a calculation formula of an ampere-hour integral method:
Figure GDA0002372177370000051
Figure GDA0002372177370000052
calculating the ampere-hour charge state of the power battery pack;
therein, SOC(K)For the state of charge of the power battery at time K, in this embodiment, SOC(K)Namely the ampere-hour charge state SOC of the power battery packAH；SOC(K-1)For the state of charge of the power battery at time K-1, SOC is the present example(K-1)I.e. initial state of charge SOC0(ii) a I is the instantaneous value of the working current of the power battery pack, I takes a positive value when the power battery pack is discharged, I takes a negative value when the power battery pack is charged, and I is the current I in the embodiment; k is a radical ofLThe aging coefficient of the power battery pack is known; k is a radical ofIThe charge-discharge multiplying power corresponding to the i can be obtained by inquiring known discharge curve graphs with different multiplying powers or charge curve graphs with different multiplying powers; k is a radical ofTThe temperature compensation coefficient can be obtained by inquiring a known temperature compensation coefficient map; q0Is the initial nominal capacity of the power battery pack; DHQKThe historical total discharge electric quantity of the power battery pack at the moment of K is obtained; DHQK-1The historical total discharge electric quantity of the power battery pack at the moment of cutting to K-1 is obtained; CHQKFor power battery up to time KHistorical total charge capacity; CHQK-1The historical total charging capacity of the power battery pack at the moment of K-1 is obtained; in this embodiment, K is the current time.
As shown in fig. 2, a temperature compensation coefficient map of the power battery pack at different temperatures is obtained according to the experiment, and the specific experimental process is as follows:
1. selecting a plurality of power battery packs which are high in consistency, produced in the same batch and same in model, fully charging the power battery packs until the state of charge is 100%, and then standing the power battery packs for a period of time; in specific application, the number and the standing time of the power battery packs in the current step can be selected according to actual needs, and in the experimental process, the number of the power battery packs in the current step is preferably 12, and the standing time is preferably 4 hours;
2. respectively placing the power battery packs after standing in different temperature environments, discharging at a constant current at a certain discharging speed until a certain voltage is reached, and respectively measuring the discharged electric quantity of each power battery pack at the moment; in specific application, the temperature environment, the discharge speed and the voltage after discharge in the current step can be set according to actual needs, and in the experimental process, the temperature environment in the current step preferably comprises-20 ℃, -15 ℃, -10 ℃, -5 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 30 ℃, 40 ℃ and 50 ℃, the preferred discharge speed is 1/3 ℃, and the preferred voltage after discharge is 2V;
3. respectively placing the power battery packs discharged to a certain voltage in different temperature environments, charging the power battery packs to a certain voltage at a constant current at a certain charging speed until the power battery packs are charged to the certain voltage, and respectively measuring the charged electric quantity of each power battery pack at the moment; in a specific application, the charging speed in the current step and the voltage after charging can be set according to actual needs, and in the experimental process, the charging speed in the current step is preferably 1/3C, and the voltage after charging is preferably 3.75V.
In specific application, different multiplying power discharge curves and different multiplying power charge curves of the power battery pack in different temperature environments can be measured in advance according to experiments, and the specific experimental process is as follows:
1. selecting a plurality of power battery packs which are high in consistency, produced in the same batch and same in model, fully charging the power battery packs until the state of charge is 100%, and then standing the power battery packs for a period of time; in specific application, the number and the standing time of the power battery packs in the current step can be selected according to actual needs, and in the experimental process, the number of the power battery packs in the current step is preferably 10, and the standing time is preferably 4 hours;
2. respectively placing the power battery packs which are kept stand in different temperature environments, respectively discharging to a certain voltage at constant currents with different multiplying powers, and respectively measuring the discharged electric quantity of each power battery pack when the power battery packs are discharged to the certain voltage under different multiplying powers; in a specific application, the temperature environment, the multiplying power and the voltage after discharging in the current step can be set according to actual needs, in the experimental process, the temperature environment in the current step preferably comprises 23 ℃, 55 ℃, 15 ℃, 10 ℃, 5 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃ and-20 ℃, the preferred multiplying power comprises 0.5C, 1C, 2C, 3C, 4C and 4.8C, and the preferred voltage after discharging is 2V;
3. respectively placing the power battery packs discharged to a certain voltage in different temperature environments, charging the power battery packs to a certain voltage at a constant current with a certain multiplying power until the power battery packs are charged to the certain voltage, and respectively measuring the charged electric quantity of each power battery pack when each power battery pack is charged to the certain voltage under different multiplying powers; in a specific application, the multiplying power in the current step and the voltage after discharging can be set according to actual needs, and in the experimental process, the multiplying power in the current step preferably includes 0.2C, 0.5C, 1C and 2C, and the voltage after charging is preferably 3.8V.
As shown in fig. 3, the different-rate discharge curve of the power battery pack at 25 ℃ and the different-rate charge curve of the power battery pack at 23 ℃ are measured in advance according to experiments.
Step S30: and calculating the estimated state of charge of the power battery pack by an open-circuit voltage method according to the current, the current highest cell voltage, the current lowest cell voltage, a preset OCV-SOC curve and a preset direct-current internal resistance table.
The OCV-SOC curve in the present invention refers to an Open Circuit Voltage (OCV) -State of Charge (SOC) curve.
In a specific application, a preset OCV-SOC curve of the power battery pack can be measured in advance according to an experiment, and the specific experiment process is as follows:
1. selecting a plurality of power battery packs which are high in consistency, produced in the same batch and same in model, discharging the power battery packs to a certain voltage by using a certain discharge current, setting the charge state of each power battery pack to be 0, and standing the power battery packs for a period of time; in specific application, the number, the discharge current and the standing time of the power battery packs can be selected according to actual needs, and in the experimental process, the number of the power battery packs is preferably 2, the discharge current is preferably 2A, and the standing time is preferably 2 hours;
2. charging the power battery packs after standing at a constant current for a certain time at a certain charging speed to enable the voltage of the battery packs to be lower than the upper limit voltage, standing the power battery packs for a period of time, and repeatedly executing the current step for a certain number of times; in specific application, the charging speed, the charging time, the upper limit voltage, the standing time and the number of times for repeatedly executing the current step in the current step can be set according to actual needs, and in the experimental process, the charging speed is preferably 0.2C, the charging time is preferably 3 minutes, the upper limit voltage is preferably 3.8V, the standing time is preferably 2 hours, and the number of times for repeatedly executing the current step is preferably 100;
3. charging the power battery packs at a constant current at a certain charging speed to a certain upper limit voltage respectively, limiting the cut-off current in the charging process, and then standing the power battery packs for a period of time; in specific application, the charging speed, the upper limit voltage and the cut-off current in the current step can be set according to actual needs, and in the experimental process, the charging speed, the upper limit voltage and the cut-off current in the current step are preferably 0.2C, 3.8V and 0.75A respectively;
4. collecting the voltage and the power of each power battery pack at intervals of a certain time in the process of executing the steps 1-3; in specific application, the interval time for collecting the voltage and the power in the current step can be set according to actual needs, and the interval time in the current step is preferably 10 seconds in the experimental process;
5. and (4) carrying out peak power test on the power battery packs after the step (4) is completed.
As shown in fig. 4, a preset OCV-SOC curve chart of the power battery pack is measured in advance according to experiments.
In specific application, a preset direct current internal resistance table of the power battery pack can be prepared in advance according to a dynamic open-circuit voltage formula, a preset OCV-SOC curve and direct current internal resistance obtained through calculation by a direct current internal resistance method.
FIG. 5 shows an equivalent circuit model of the power battery pack in the operating state, R in FIG. 50Is ohmic internal resistance, R1Is a polarization resistance, C1Is a polarization capacitance, R2Is a diffusion resistance, C2Is a diffusion capacitance. When the power battery is applied to equipment such as an electric vehicle and the like, the current of the power battery in the charging and discharging process is large, so that the direct current internal resistance of the power battery pack can be directly used as the total direct current internal resistance. Establishing a relation among the current of the power battery pack, the terminal voltage of the current single battery, the real-time open-circuit voltage of the current single battery and the direct-current internal resistance according to the model shown in fig. 5, namely a dynamic open-circuit voltage formula: u shapeOCV＝V+I*ZDCIR(ii) a Wherein, UOCVIs the real-time open-circuit voltage of the current single battery, V is the terminal voltage of the current single battery, I is the current, ZDCIRIs the direct current internal resistance.
As shown in fig. 6, it is a graph of the relationship between the current and terminal voltage of the power battery pack during charging and discharging, measured in advance according to experiments, with time. As can be seen from FIG. 6, the total internal resistance of DC during the discharging process of the power battery pack
Figure GDA0002372177370000081
Total internal DC resistance in charging process
Figure GDA0002372177370000082
Step S40: if the difference value between the ampere-hour charge state and the estimated charge state does not meet the preset correction condition, taking the ampere-hour charge state as the actual charge state of the power battery pack; and otherwise, correcting the ampere-hour charge state according to a preset correction coefficient until the corrected ampere-hour charge state is larger than the estimated charge state, and taking the corrected ampere-hour charge state as the actual charge state of the power battery pack.
In a specific application, the preset correction condition may include:
1. SOC at an hourAHAnd estimating state of charge SOCyuguAbsolute value of difference of (1 | SOC)AH-SOCyugu|≥F1(SOCyugu)；
2. SOC at an hourAHAnd estimating state of charge SOCyuguAbsolute value of difference of (1 | SOC)AH-SOCyugu|≥F2(SOCyugu)；
3. SOC at an hourAHAnd estimating state of charge SOCyuguAbsolute value of difference of (1 | SOC)AH-SOCyugu|≥F3(SOCyugu)；
Wherein, F1(SOCyugu)、F2(SOCyugu) And F3(SOCyugu) To and estimate the state of charge SOCyuguA related value or function.
In a specific application, the preset correction coefficient corresponds to a preset correction condition.
The ampere-hour charge state and the estimated charge state of the power battery pack are respectively calculated by an ampere-hour integration method and an open-circuit voltage method, then the ampere-hour charge state is corrected by judging whether the difference value between the ampere-hour charge state and the estimated charge state meets a preset correction condition, if not, the ampere-hour charge state is considered to be accurate and is directly used as the actual charge state of the power battery pack, and if so, the corrected ampere-hour charge state is used as the actual charge state of the power battery pack, so that errors generated in the charge state calculation process can be corrected in time, the calculation accuracy of the charge state is effectively improved, the calculation amount is small, and the method is easy to realize.
An embodiment of the present invention provides a method for further improving the state of charge calculation of the power battery pack based on the embodiment corresponding to fig. 1, as shown in fig. 7, the method provided in this embodiment is different from the embodiment corresponding to fig. 1 in that step S30 in fig. 1 specifically includes:
step S31: inquiring the direct current internal resistance corresponding to the current in a preset direct current internal resistance table;
step S32: and calculating the current highest open-circuit voltage corresponding to the current highest cell voltage and the current lowest open-circuit voltage corresponding to the current lowest cell voltage by an open-circuit voltage method according to the current, the current highest cell voltage, the current lowest cell voltage and the direct-current internal resistance.
In specific application, the current I and the current highest monomer voltage U are measuredmaxCurrent lowest cell voltage UminAnd the direct current internal resistance R1 are respectively substituted into a dynamic open-circuit voltage formula: u shapeOCV＝V+I*ZDCIRCalculating to obtain the current highest open-circuit voltage UOCV-max＝Umax+ l R1 and the current lowest open circuit voltage UOCV-min＝Umin+I*R1。
Step S33: and inquiring the current maximum state of charge corresponding to the current highest open-circuit voltage and the current minimum state of charge corresponding to the current lowest open-circuit voltage in the preset OCV-SOC curve.
In specific application, the current maximum state of charge SOC is obtained by inquiring a preset OCV-SOC curvemaxAnd current minimum state of charge SOCmin。
Step S34: and carrying out weighted average calculation on the current maximum charge state and the current minimum charge state to obtain the current average charge state.
In a specific application, the SOC is based on a formulaavg＝mSOCmax+nSOCminAnd calculating to obtain the current average state of charge (SOC)avgWherein m + n is 1 and m and n are both greater than or equal toEqual to 0 and less than or equal to 1.
In a specific application, the specific values of m and n may be set according to actual needs, that is, the weight for performing weighted average calculation on the current maximum state of charge and the current minimum state of charge may be set according to actual needs.
Step S35: and if the power battery pack is in a discharging state and the current minimum state of charge is greater than or equal to a first state of charge threshold, taking the current maximum state of charge as a first target value of the estimated state of charge and correcting the estimated state of charge to the first target value by a first preset step length.
In a specific application, the first state of charge threshold may be set according to actual needs, and in this embodiment, the first state of charge threshold is preferably 80%.
Step S36: and if the power battery pack is in a discharging state, and the current minimum state of charge is greater than a second state of charge threshold and smaller than a first state of charge threshold, taking the current average state of charge as a second target value of the estimated state of charge and correcting the estimated state of charge to the second target value by a second preset step length.
In a specific application, the second state of charge threshold may be set according to actual needs, and in this embodiment, the second state of charge threshold is preferably 40%.
Step S37: and if the power battery pack is in a discharging state and the current minimum state of charge is smaller than a second state of charge threshold value, taking the current minimum state of charge as a third target value of the estimated state of charge and correcting the estimated state of charge to the third target value by a third preset step length.
Step S38: and if the power battery pack is in a charging state and the current maximum state of charge is greater than or equal to a third state of charge threshold, taking the current average state of charge as a fourth target value of the estimated state of charge and correcting the estimated state of charge to the fourth target value by a fourth preset step length.
In a specific application, the third state of charge threshold may be set according to actual needs, and in this embodiment, the third state of charge threshold is preferably 70%.
Step S39: and if the power battery pack is in a charging state and the current maximum state of charge is smaller than a third state of charge threshold, taking the current maximum state of charge as a fifth target value of the estimated state of charge and correcting the estimated state of charge to the fifth target value by a fifth preset step length.
The first step size to the fifth step size in this embodiment may be set according to actual needs.
According to the method, the target values of the estimated state of charge of the power battery pack in different states are calculated by comprehensively evaluating the current charge-discharge state, the current highest cell voltage and the current lowest cell voltage of the power battery pack, the current estimated state of charge is corrected according to the calculated target values, the current estimated state of charge of the power battery pack is transited to the target values, and the accuracy of the estimated state of charge calculated by an open-circuit voltage method can be effectively improved.
An embodiment of the present invention provides a method for further improving the state of charge calculation of the power battery pack based on the embodiment corresponding to fig. 1, as shown in fig. 8, the method provided in this embodiment is different from the embodiment corresponding to fig. 1 in that step S40 in fig. 1 specifically includes:
step S41: and judging whether the absolute value of the difference value between the safety time charge state and the estimated charge state is greater than a first preset difference value, a second preset difference value or a third preset difference value, wherein the first preset difference value is greater than the second preset difference value and the third preset difference value.
In a specific application, the first preset difference, the second preset difference and the third preset difference may be set according to actual needs, and may specifically be values or functions related to the estimated state of charge, and may be respectively represented as the first preset difference F1(SOCyugu) A second predetermined difference F2(SOCyugu) And a third predetermined difference F3(SOCyugu)。
Step S42: and if the absolute value is smaller than or equal to a third preset difference value, taking the ampere-hour charge state as the actual charge state of the power battery pack.
Step S43: and if the absolute value is larger than a first preset difference value, correcting the ampere-hour charge state according to a first preset coefficient.
Step S44: and if the absolute value is larger than a second preset difference value and smaller than or equal to a first preset difference value, correcting the ampere-hour charge state according to a second preset coefficient.
Step S45: and if the absolute value is larger than a third preset difference and smaller than or equal to a second preset difference, correcting the ampere-hour charge state according to a third preset coefficient.
In specific application, the first preset coefficient, the second preset coefficient and the third preset coefficient can be determined according to the current ampere-hour charge state and the estimated charge state, and can also be set according to actual needs by comprehensively considering the current electric quantity state of the power battery pack, and the current electric quantity state of the power battery pack can be respectively expressed as KS1、KS2And KS3。
Step S46: and judging whether the corrected ampere-hour charge state is larger than the estimated charge state.
Step S47: and if the corrected ampere-hour charge state is larger than the estimated charge state, taking the corrected ampere-hour charge state as the actual charge state of the power battery pack.
Step S48: if the corrected ampere-hour state of charge is less than or equal to the estimated state of charge, returning to step S41.
According to the embodiment, the ampere-hour charge state and the estimated charge state are compared, and when the difference value between the ampere-hour charge state and the estimated charge state meets the preset correction condition, the ampere-hour charge state is corrected according to the correction coefficient corresponding to the preset correction condition, so that the actual charge state is obtained, the accuracy of obtaining the charge state of the power battery pack through calculation only by an ampere-hour integration method or only by an open-circuit voltage method can be effectively improved, and the complementation of the ampere-hour integration method and the open-circuit voltage method is realized.
An embodiment of the present invention provides a method for calculating a state of charge of a power battery pack, which is further improved on the basis of the embodiment corresponding to fig. 1, as shown in fig. 9, the method provided by this embodiment is different from the embodiment corresponding to fig. 1 in that before step S20 in fig. 1, the method further includes:
step S50: and correcting the initial state of charge according to the current lowest cell voltage, the initial nominal capacity and the preset OCV-SOC curve.
In an embodiment of the present invention, step S50 specifically includes:
step S51: if the power battery pack is used after being charged fully and electrified for the first time, correcting the initial charge state to be 100%;
step S52: and if the interval between the current power-on time and the last power-off time of the power battery pack is greater than or equal to first preset time and the current lowest cell voltage is less than or equal to first preset cell voltage, correcting the initial state of charge to be the state of charge corresponding to the current lowest cell voltage in the preset OCV-SOC curve.
In a specific application, the first preset time and the first preset cell voltage may be set according to actual needs, and in this embodiment, the first preset time is preferably 2 hours.
Step S53: and if the interval between the current power-on moment and the last power-off moment of the power battery pack is greater than or equal to a first preset time, the current lowest cell voltage is greater than a first preset cell voltage, and the state of charge of the last power-off moment is not within a preset state of charge range, correcting the initial state of charge into the state of charge corresponding to the current lowest cell voltage in the preset OCV-SOC curve.
In a specific application, the preset state of charge range may be set according to actual needs, and in this embodiment, the preset state of charge range is preferably 30% to 80%.
Step S54: if the interval between the current power-on moment and the last power-off moment of the power battery pack is larger than or equal to a first preset time, the current lowest cell voltage is larger than a first preset cell voltage, and the state of charge of the last power-off moment is within a preset state of charge range, judging whether the historical total discharge electric quantity of the power battery pack is larger than the initial nominal capacity or not when the initial state of charge is corrected last time and the current moment is reached, if so, correcting the initial state of charge to be the state of charge corresponding to the current lowest cell voltage in the preset OCV-SOC curve, and otherwise, correcting the initial state of charge to be the state of charge of the last power-off moment.
Step S55: if the interval between the current power-on moment and the last power-off moment of the power battery pack is larger than a second preset time and smaller than a first preset time, judging whether the historical total discharge electric quantity of the power battery pack is larger than the initial nominal capacity or not when the initial charge state is corrected to the current moment, if so, correcting the initial charge state to be the charge state corresponding to the current lowest cell voltage in the preset OCV-SOC curve, and otherwise, correcting the initial charge state to be the charge state at the last power-off moment.
In a specific application, the second preset time may be set according to actual needs, and in this embodiment, the second preset time is preferably 10 minutes.
Step S56: and if the interval between the current power-on time and the last power-off time of the power battery pack is less than or equal to a second preset time, correcting the initial charge state to be the charge state of the last power-off time.
According to the embodiment, the initial charge state of the power battery pack during the current power-on use is corrected by combining the power-on use time of the power battery pack and the initial charge state during the last shutdown of the power battery pack, so that the accuracy of the initial charge state of the power battery pack can be ensured, and the accuracy of the subsequent ampere-hour charge state calculated by an ampere-hour integration method can be effectively improved.
An embodiment of the present invention provides a method for calculating a state of charge of a power battery pack, which is further improved on the basis of the embodiment corresponding to fig. 1, and as shown in fig. 10, the method provided by the present embodiment is different from the embodiment corresponding to fig. 1 in that after step S40 in fig. 1, the method includes:
step S60: correcting the initial nominal capacity according to the current highest cell voltage, the current lowest cell voltage, the initial state of charge and the actual state of charge
In an embodiment of the present invention, step S60 specifically includes:
step S61: and when the power battery pack is detected to be discharged from a full-charge state to a preset charge state or below, recording the discharged capacity and the residual capacity of the power battery pack, and recording the sum of the discharged capacity and the residual capacity as the actual capacity of the power battery pack.
In a specific application, the preset state of charge may be set according to actual needs, and in this embodiment, the preset state of charge is preferably 10%.
Step S62: and if the power battery pack is detected to be discharged from a full charge state to a preset charge state or below by the continuous preset times at the current moment, judging whether the initial nominal capacity is larger than or equal to the maximum value in the actual capacity recorded by the continuous preset times.
In a specific application, the preset number of times may be set according to actual needs, and in this embodiment, the preset number of times is preferably 2 times.
Step S63: and if the initial nominal capacity is greater than or equal to the maximum value in the actual capacities, correcting the initial nominal capacity to be the initial nominal capacity-a first preset capacity correction factor (the maximum value in the initial nominal capacity-the actual capacities).
In a specific application, the first preset capacity correction coefficient may be set according to actual needs, and in this embodiment, the first preset capacity correction coefficient is preferably 1/2.
Step S64: and if the initial nominal capacity is smaller than the maximum value in the actual capacities, correcting the initial nominal capacity to be the initial nominal capacity plus a second preset capacity correction factor (the maximum value in the actual capacities-the initial nominal capacity).
In a specific application, the second preset capacity correction coefficient may be set according to actual needs, and in this embodiment, it is preferable that the second preset capacity correction coefficient is 1/5.
Step S65: in the discharging process of the power battery, if the lowest cell voltage of the power battery pack is detected to be less than or equal to a preset lowest voltage threshold value and the actual state of charge is detected to be greater than or equal to a preset lowest state of charge within a continuous preset time period by the current moment, correcting the actual state of charge to be the preset lowest state of charge and correcting the initial nominal capacity to be the initial nominal capacity-a third preset capacity correction coefficient
Figure GDA0002372177370000151
Figure GDA0002372177370000152
In a specific application, the continuous preset time period, the preset minimum voltage threshold, the preset minimum state of charge, and the third preset capacity correction coefficient may be set according to actual needs, and in this embodiment, the continuous preset time period is preferably 8 seconds, and the preset minimum state of charge is preferably 5%.
Step S66: in the charging process of the power battery, if the actual state of charge of the power battery pack is detected to be greater than or equal to a preset maximum state of charge and the maximum cell voltage is smaller than a preset maximum voltage threshold, recording a first historical total charge at the moment and stopping calculating the actual state of charge of the power battery pack, and if the current maximum cell voltage is greater than or equal to the preset maximum voltage threshold by the current moment, recording a second historical total charge at the current moment and correcting the initial nominal capacity to be the initial nominal capacity + a fourth preset capacity correction coefficient (the second historical total charge-the first historical total charge).
In a specific application, the preset maximum voltage threshold, the preset maximum state of charge, and the fourth preset capacity correction coefficient may be set according to actual needs, and in this embodiment, the preset maximum voltage threshold is preferably 3.8V, and the preset maximum state of charge is preferably 99%.
According to the embodiment, the initial nominal capacity of the power battery pack is corrected by combining the current charge-discharge state, the current highest cell voltage, the current lowest cell voltage, the initial charge state and the actual charge state of the power battery pack, so that the accuracy of the initial nominal capacity of the power battery pack can be ensured, and the accuracy of the ampere-hour charge state obtained by the subsequent ampere-hour integration calculation can be effectively improved.
As shown in fig. 11, an embodiment of the present invention provides a state of charge calculation system 100 for a power battery pack, configured to execute the method steps in the embodiment corresponding to fig. 1, including:
a parameter obtaining unit 10, configured to obtain a current of the power battery pack, a current highest cell voltage, a current lowest cell voltage, an initial state of charge, and an initial nominal capacity;
the ampere-hour charge state calculating unit 20 is used for calculating the ampere-hour charge state of the power battery pack by an ampere-hour integration method according to the current, the initial charge state and the initial nominal capacity;
the estimated state of charge calculation unit 30 is configured to calculate an estimated state of charge of the power battery pack through an open-circuit voltage method according to the current, the current highest cell voltage, the current lowest cell voltage, a preset OCV-SOC curve and a preset direct-current internal resistance table;
the actual state of charge determining unit 40 is configured to, if the difference between the ampere-hour state of charge and the estimated state of charge does not meet a preset correction condition, use the ampere-hour state of charge as the actual state of charge of the power battery pack; and otherwise, correcting the ampere-hour charge state according to a preset correction coefficient until the corrected ampere-hour charge state is larger than the estimated charge state, and taking the corrected ampere-hour charge state as the actual charge state of the power battery pack.
The ampere-hour charge state and the estimated charge state of the power battery pack are respectively calculated by an ampere-hour integration method and an open-circuit voltage method, then the ampere-hour charge state is corrected by judging whether the difference value between the ampere-hour charge state and the estimated charge state meets a preset correction condition, if not, the ampere-hour charge state is considered to be accurate and is directly used as the actual charge state of the power battery pack, and if so, the corrected ampere-hour charge state is used as the actual charge state of the power battery pack, so that errors generated in the charge state calculation process can be corrected in time, the calculation accuracy of the charge state is effectively improved, the calculation amount is small, and the method is easy to realize.
As shown in fig. 12, in one embodiment of the present invention, the estimated state of charge calculation unit 30 in fig. 11 includes the following structure for performing the method steps in the corresponding embodiment of fig. 7:
a dc internal resistance query unit 31, configured to query a dc internal resistance corresponding to the current in a preset dc internal resistance table;
an open-circuit voltage calculating unit 32, configured to calculate, according to the current, the current highest cell voltage, the current lowest cell voltage, and the direct-current internal resistance, a current highest open-circuit voltage corresponding to the current highest cell voltage and a current lowest open-circuit voltage corresponding to the current lowest cell voltage by using an open-circuit voltage method;
a state of charge query unit 33, configured to query a current maximum state of charge corresponding to the current highest open-circuit voltage and a current minimum state of charge corresponding to the current lowest open-circuit voltage in the preset OCV-SOC curve;
the weighted average calculating unit 34 is configured to perform weighted average calculation on the current maximum state of charge and the current minimum state of charge to obtain a current average state of charge;
a first estimated state of charge correction unit 35, configured to, if the power battery pack is in a discharge state and the current minimum state of charge is greater than or equal to a first state of charge threshold, take the current maximum state of charge as a first target value of the estimated state of charge and correct the estimated state of charge to the first target value by a first preset step length;
a second estimated state of charge correction unit 36, configured to, if the power battery pack is in a discharge state and the current minimum state of charge is greater than a second state of charge threshold and smaller than a first state of charge threshold, take the current average state of charge as a second target value of the estimated state of charge and correct the estimated state of charge to the second target value by a second preset step length;
a third estimated state of charge correction unit 37, configured to, if the power battery pack is in a discharge state and the current minimum state of charge is smaller than a second state of charge threshold, take the current minimum state of charge as a third target value of the estimated state of charge and correct the estimated state of charge to the third target value by a third preset step length;
a fourth predicted state of charge correction unit 38, configured to, if the power battery pack is in a charging state and the current maximum state of charge is greater than or equal to a third state of charge threshold, use the current average state of charge as a fourth target value of the predicted state of charge and correct the predicted state of charge to the fourth target value by a fourth preset step length;
a fifth predicted state of charge correction unit 39, configured to, if the power battery pack is in a charging state and the current maximum state of charge is smaller than a third state of charge threshold, take the current maximum state of charge as a fifth target value of the predicted state of charge and correct the predicted state of charge to the fifth target value by a fifth preset step length.
According to the method, the target values of the estimated state of charge of the power battery pack in different states are calculated by comprehensively evaluating the current charge-discharge state, the current highest cell voltage and the current lowest cell voltage of the power battery pack, the current estimated state of charge is corrected according to the calculated target values, the current estimated state of charge of the power battery pack is transited to the target values, and the accuracy of the estimated state of charge calculated by an open-circuit voltage method can be effectively improved.
As shown in fig. 13, in one embodiment of the present invention, the actual state of charge determination unit 40 in fig. 11 includes the following structure for performing the method steps in the corresponding embodiment of fig. 8:
a difference value determining unit 41, configured to determine whether an absolute value of a difference value between the at-rest state of charge and the estimated state of charge is greater than a first preset difference value, a second preset difference value, or a third preset difference value, where the first preset difference value > the second preset difference value > the third preset difference value;
a first state of charge determining unit 42, configured to, if the absolute value is less than or equal to a third preset difference, take the at-rest state of charge as an actual state of charge of the power battery pack;
a first ampere-hour charge state correction unit 43, configured to correct the ampere-hour charge state according to a first preset coefficient if the absolute value is greater than a first preset difference;
a second ampere-hour charge state correction unit 44, configured to correct the ampere-hour charge state according to a second preset coefficient if the absolute value is greater than a second preset difference and is less than or equal to a first preset difference;
a third ampere-hour charge state correction unit 45, configured to correct the ampere-hour charge state according to a third preset coefficient if the absolute value is greater than a third preset difference and is less than or equal to a second preset difference;
the charge state judging unit is used for judging whether the corrected ampere-hour charge state is larger than the estimated charge state or not;
a second state of charge determining unit 46, configured to use the corrected ampere-hour state of charge as the actual state of charge of the power battery pack if the corrected ampere-hour state of charge is greater than the estimated state of charge;
a returning unit 47, configured to return to the difference determining unit if the corrected ampere-hour state of charge is less than or equal to the estimated state of charge.
According to the embodiment, the ampere-hour charge state and the estimated charge state are compared, and when the difference value between the ampere-hour charge state and the estimated charge state meets the preset correction condition, the ampere-hour charge state is corrected according to the correction coefficient corresponding to the preset correction condition, so that the actual charge state is obtained, the accuracy of obtaining the charge state of the power battery pack through calculation only by an ampere-hour integration method or only by an open-circuit voltage method can be effectively improved, and the complementation of the ampere-hour integration method and the open-circuit voltage method is realized.
As shown in fig. 14, in one embodiment of the present invention, the state of charge calculation system 100 of the power battery pack shown in fig. 11 further comprises the following structure for performing the method steps shown in fig. 9:
and the initial state of charge correcting unit 50 is configured to correct the initial state of charge according to the current lowest cell voltage, the initial nominal capacity, and the preset OCV-SOC curve.
In one embodiment, the initial state of charge correction unit 50 includes:
the first initial charge state correction unit is used for correcting the initial charge state to be 100% if the power battery pack is electrified for the first time after being fully charged;
the second initial state-of-charge correction unit is used for correcting the initial state-of-charge to a state-of-charge corresponding to the current lowest cell voltage in the preset OCV-SOC curve if the interval between the current power-on time and the last power-off time of the power battery pack is greater than or equal to first preset time and the current lowest cell voltage is less than or equal to first preset cell voltage;
a third initial state of charge correction unit, configured to correct the initial state of charge to a state of charge corresponding to the current lowest cell voltage in the preset OCV-SOC curve if a current power-on time and a last power-off time interval of the power battery pack are greater than or equal to a first preset time, the current lowest cell voltage is greater than a first preset cell voltage, and the state of charge of the last power-off time is not within a preset state of charge range;
a fourth initial state of charge correction unit, configured to, if a current power-on time interval of the power battery pack and a last power-off time interval of the power battery pack is greater than or equal to a first preset time, the current lowest cell voltage is greater than a first preset cell voltage, and a state of charge of the last power-off time is within a preset state of charge range, determine whether a historical total discharge electric quantity of the power battery pack is greater than the initial nominal capacity when the initial state of charge is corrected last time to the current time, correct the initial state of charge to a state of charge corresponding to the current lowest cell voltage in the preset OCV-SOC curve if the historical total discharge electric quantity is greater than the initial nominal capacity, and correct the initial state of charge to the state of charge of the last power-off time if the initial state of charge is not;
a fifth initial state of charge correction unit, configured to, if an interval between a current power-on time and a last power-off time of the power battery pack is greater than a second preset time and less than a first preset time, determine whether a historical total discharge electric quantity of the power battery pack is greater than an initial nominal capacity by the last time of correction of the initial state of charge until the current time, correct the initial state of charge to a state of charge corresponding to the current lowest cell voltage in the preset OCV-SOC curve if the historical total discharge electric quantity is greater than the initial nominal capacity, and correct the initial state of charge to the state of charge at the last power-off time if the historical total discharge electric quantity is not greater than the initial nominal capacity;
and the sixth initial charge state correction unit is used for correcting the initial charge state to be the charge state of the last power-off time if the interval between the current power-on time and the last power-off time of the power battery pack is less than or equal to a second preset time.
According to the embodiment, the initial charge state of the power battery pack during the current power-on use is corrected by combining the power-on use time of the power battery pack and the initial charge state during the last shutdown of the power battery pack, so that the accuracy of the initial charge state of the power battery pack can be ensured, and the accuracy of the subsequent ampere-hour charge state calculated by an ampere-hour integration method can be effectively improved.
As shown in fig. 15, in one embodiment of the present invention, the state of charge calculation system 100 of the power battery pack shown in fig. 11 further comprises the following structure for performing the method steps shown in fig. 10:
an initial nominal capacity correction unit 60, configured to correct the initial nominal capacity according to the current highest cell voltage, the current lowest cell voltage, the initial state of charge, and the actual state of charge.
The initial nominal capacity correction unit 60 in one embodiment of the present invention comprises:
the actual capacity calculation unit is used for recording the discharged capacity and the residual capacity of the power battery pack when detecting that the power battery pack is discharged from a full-charge state to be lower than a preset charge state, and recording the sum of the discharged capacity and the residual capacity as the actual capacity of the power battery pack;
the maximum capacity judging unit is used for judging whether the initial nominal capacity is larger than or equal to the maximum value in the actual capacity recorded by the continuous preset times or not if the power battery pack is detected to be discharged from the full-charge state to the preset charge state or below by the continuous preset times at the current moment;
a first capacity correction unit for correcting the initial nominal capacity to the initial nominal capacity-a first preset capacity correction factor (the initial nominal capacity-the maximum value of the actual capacity) if the initial nominal capacity is greater than or equal to the maximum value of the actual capacity;
a second capacity correction unit, configured to correct the initial nominal capacity to the initial nominal capacity + a second preset capacity correction factor (maximum value in the actual capacities — the initial nominal capacity) if the initial nominal capacity is smaller than a maximum value in the actual capacities;
a third capacity correction unit, configured to, in a discharging process of the power battery, correct the actual state of charge to a preset minimum state of charge and correct the initial nominal capacity to the initial nominal capacity-a third preset capacity correction coefficient if it has been detected that a lowest cell voltage of the power battery pack is less than or equal to a preset minimum voltage threshold and the actual state of charge is greater than or equal to a preset minimum state of charge within a continuous preset time period by a current time point
Figure GDA0002372177370000211
Figure GDA0002372177370000212
And a fourth capacity correction unit, configured to, during the charging of the power battery, record a first historical total charge amount at the current time and stop calculating the actual state of charge of the power battery pack if it is detected that the actual state of charge of the power battery pack is greater than or equal to a preset maximum state of charge and the maximum cell voltage is less than a preset maximum voltage threshold, and record a second historical total charge amount at the current time and correct the initial nominal capacity to the initial nominal capacity + a fourth preset capacity correction coefficient (the second historical total charge amount-the first historical total charge amount) if the current maximum cell voltage is greater than or equal to the preset maximum voltage threshold by the current time.
According to the embodiment, the initial nominal capacity of the power battery pack is corrected by combining the current charge-discharge state, the current highest cell voltage, the current lowest cell voltage, the initial charge state and the actual charge state of the power battery pack, so that the accuracy of the initial nominal capacity of the power battery pack can be ensured, and the accuracy of the ampere-hour charge state obtained by the subsequent ampere-hour integration calculation can be effectively improved.
The power battery pack provided in all embodiments of the present invention may be specifically a lithium iron phosphate power battery pack formed by connecting at least two single lithium iron phosphate batteries in series.
In an embodiment of the present invention, the method and the system for calculating the state of charge of the power BATTERY pack can be specifically applied to a BATTERY management system (BATTERY MANAGEMENT SYSTEM, BMS) for managing the power BATTERY pack.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A state of charge calculation method for a power battery pack, the state of charge calculation method comprising:
acquiring the current, the current highest cell voltage, the current lowest cell voltage, the initial charge state and the initial nominal capacity of the power battery pack;
calculating the ampere-hour charge state of the power battery pack by an ampere-hour integration method according to the current, the initial charge state and the initial nominal capacity;
calculating the estimated state of charge of the power battery pack by an open-circuit voltage method according to the current, the current highest cell voltage, the current lowest cell voltage, a preset OCV-SOC curve and a preset direct-current internal resistance table, wherein the method comprises the following steps:
inquiring the direct current internal resistance corresponding to the current in a preset direct current internal resistance table;
according to the current, the current highest cell voltage, the current lowest cell voltage and the direct current internal resistance, calculating the current highest open-circuit voltage corresponding to the current highest cell voltage and the current lowest open-circuit voltage corresponding to the current lowest cell voltage through an open-circuit voltage method;
inquiring the current maximum state of charge corresponding to the current highest open-circuit voltage and the current minimum state of charge corresponding to the current lowest open-circuit voltage in the preset OCV-SOC curve;
performing weighted average calculation on the current maximum charge state and the current minimum charge state to obtain a current average charge state;
if the power battery pack is in a discharging state and the current minimum state of charge is greater than or equal to a first state of charge threshold, taking the current maximum state of charge as a first target value of the estimated state of charge and correcting the estimated state of charge to the first target value by a first preset step length;
if the power battery pack is in a discharging state, and the current minimum state of charge is greater than a second state of charge threshold and smaller than a first state of charge threshold, taking the current average state of charge as a second target value of the estimated state of charge and correcting the estimated state of charge to the second target value by a second preset step length;
if the power battery pack is in a discharging state and the current minimum state of charge is smaller than a second state of charge threshold value, taking the current minimum state of charge as a third target value of the estimated state of charge and correcting the estimated state of charge to the third target value by a third preset step length;
if the difference value between the ampere-hour charge state and the estimated charge state does not meet the preset correction condition, taking the ampere-hour charge state as the actual charge state of the power battery pack; and otherwise, correcting the ampere-hour charge state according to a preset correction coefficient until the corrected ampere-hour charge state is larger than the estimated charge state, and taking the corrected ampere-hour charge state as the actual charge state of the power battery pack.
2. The method of calculating the state of charge of a power battery according to claim 1, wherein after said performing a weighted average calculation of said current maximum state of charge and said current minimum state of charge to obtain a current average state of charge, said method further comprises:
if the power battery pack is in a charging state and the current maximum state of charge is greater than or equal to a third state of charge threshold, taking the current average state of charge as a fourth target value of the estimated state of charge and correcting the estimated state of charge to the fourth target value by a fourth preset step length;
and if the power battery pack is in a charging state and the current maximum state of charge is smaller than a third state of charge threshold, taking the current maximum state of charge as a fifth target value of the estimated state of charge and correcting the estimated state of charge to the fifth target value by a fifth preset step length.
3. The method for calculating the state of charge of the power battery pack according to claim 1, wherein if the difference between the ampere-hour state of charge and the estimated state of charge does not satisfy a preset correction condition, the ampere-hour state of charge is used as the actual state of charge of the power battery pack; otherwise, the ampere-hour state of charge is corrected according to a preset correction coefficient until the corrected ampere-hour state of charge is larger than the estimated state of charge, and the corrected ampere-hour state of charge is used as the actual state of charge of the power battery pack, and the method comprises the following steps:
judging whether the absolute value of the difference value between the safety time charge state and the estimated charge state is greater than a first preset difference value, a second preset difference value or a third preset difference value, wherein the first preset difference value is greater than the second preset difference value and the third preset difference value;
if the absolute value is smaller than or equal to a third preset difference value, taking the ampere-hour charge state as the actual charge state of the power battery pack;
if the absolute value is larger than a first preset difference value, correcting the ampere-hour charge state according to a first preset coefficient;
if the absolute value is larger than a second preset difference value and smaller than or equal to a first preset difference value, correcting the ampere-hour charge state according to a second preset coefficient;
if the absolute value is larger than a third preset difference and smaller than or equal to a second preset difference, correcting the ampere-hour charge state according to a third preset coefficient;
judging whether the corrected ampere-hour charge state is larger than the estimated charge state or not;
if the corrected ampere-hour state of charge is larger than the estimated state of charge, taking the corrected ampere-hour state of charge as the actual state of charge of the power battery pack;
and if the corrected safe-time charge state is smaller than or equal to the estimated charge state, returning to the step of judging whether the absolute value of the difference value between the safe-time charge state and the estimated charge state is larger than a first preset difference value, a second preset difference value or a third preset difference value.
4. The method of calculating the state of charge of a power battery according to claim 1, wherein before calculating the ampere-hour state of charge of the power battery by an ampere-hour integration method based on the current, the initial state of charge and the initial nominal capacity, the method further comprises:
and correcting the initial state of charge according to the current lowest cell voltage, the initial nominal capacity and the preset OCV-SOC curve.
5. The power battery pack state of charge calculation method of claim 1, further comprising:
and correcting the initial nominal capacity according to the current highest cell voltage, the current lowest cell voltage, the initial charge state and the actual charge state.
6. A state of charge calculation system for a power battery, the state of charge calculation system comprising:
the parameter acquisition unit is used for acquiring the current, the current highest cell voltage, the current lowest cell voltage, the initial charge state and the initial nominal capacity of the power battery pack;
the ampere-hour charge state calculating unit is used for calculating the ampere-hour charge state of the power battery pack by an ampere-hour integration method according to the current, the initial charge state and the initial nominal capacity;
the estimated state of charge calculation unit is used for calculating the estimated state of charge of the power battery pack through an open-circuit voltage method according to the current, the current highest cell voltage, the current lowest cell voltage, a preset OCV-SOC curve and a preset direct-current internal resistance table, and comprises the following steps:
the direct current internal resistance query unit is used for querying the direct current internal resistance corresponding to the current in a preset direct current internal resistance table;
an open-circuit voltage calculation unit, configured to calculate, according to the current, the current highest cell voltage, the current lowest cell voltage, and the direct-current internal resistance, a current highest open-circuit voltage corresponding to the current highest cell voltage and a current lowest open-circuit voltage corresponding to the current lowest cell voltage by an open-circuit voltage method;
the state of charge query unit is used for querying the current maximum state of charge corresponding to the current highest open-circuit voltage and the current minimum state of charge corresponding to the current lowest open-circuit voltage in the preset OCV-SOC curve;
the weighted average calculation unit is used for carrying out weighted average calculation on the current maximum charge state and the current minimum charge state to obtain a current average charge state;
the first estimated state of charge correction unit is used for taking the current maximum state of charge as a first target value of the estimated state of charge and correcting the estimated state of charge to the first target value by a first preset step length if the power battery pack is in a discharging state and the current minimum state of charge is greater than or equal to a first state of charge threshold;
the second estimated state of charge correction unit is used for taking the current average state of charge as a second target value of the estimated state of charge and correcting the estimated state of charge to the second target value by a second preset step length if the power battery pack is in a discharging state and the current minimum state of charge is greater than a second state of charge threshold and smaller than a first state of charge threshold;
a third estimated state of charge correction unit, configured to, if the power battery pack is in a discharge state and the current minimum state of charge is smaller than a second state of charge threshold, take the current minimum state of charge as a third target value of the estimated state of charge and correct the estimated state of charge to the third target value by a third preset step length;
the actual charge state determining unit is used for taking the ampere-hour charge state as the actual charge state of the power battery pack if the difference value between the ampere-hour charge state and the estimated charge state does not meet the preset correction condition; and otherwise, correcting the ampere-hour charge state according to a preset correction coefficient until the corrected ampere-hour charge state is larger than the estimated charge state, and taking the corrected ampere-hour charge state as the actual charge state of the power battery pack.
7. The power battery pack state of charge calculation system of claim 6, wherein the estimated state of charge calculation unit further comprises:
a fourth estimated state of charge correction unit, configured to, if the power battery pack is in a charging state and the current maximum state of charge is greater than or equal to a third state of charge threshold, use the current average state of charge as a fourth target value of the estimated state of charge and correct the estimated state of charge to the fourth target value by a fourth preset step length;
and the fifth estimated state of charge correction unit is used for taking the current maximum state of charge as a fifth target value of the estimated state of charge and correcting the estimated state of charge to the fifth target value by a fifth preset step length if the power battery pack is in a charging state and the current maximum state of charge is smaller than a third state of charge threshold.
8. The power battery pack state of charge calculation system of claim 6, wherein the actual state of charge determination unit comprises:
a difference value judging unit, configured to judge whether an absolute value of a difference value between the at-rest state of charge and the estimated state of charge is greater than a first preset difference value, a second preset difference value, or a third preset difference value, where the first preset difference value > the second preset difference value > the third preset difference value;
the first charge state determining unit is used for taking the ampere-hour charge state as the actual charge state of the power battery pack if the absolute value is less than or equal to a third preset difference value;
the first ampere-hour charge state correction unit is used for correcting the ampere-hour charge state according to a first preset coefficient if the absolute value is larger than a first preset difference value;
the second ampere-hour charge state correction unit is used for correcting the ampere-hour charge state according to a second preset coefficient if the absolute value is larger than a second preset difference and is smaller than or equal to a first preset difference;
a third ampere-hour charge state correction unit, configured to correct the ampere-hour charge state according to a third preset coefficient if the absolute value is greater than a third preset difference and less than or equal to a second preset difference;
the charge state judging unit is used for judging whether the corrected ampere-hour charge state is larger than the estimated charge state or not;
a second state of charge determining unit, configured to use the corrected ampere-hour state of charge as an actual state of charge of the power battery pack if the corrected ampere-hour state of charge is greater than the estimated state of charge;
and the return unit is used for returning to the difference value judgment unit if the corrected ampere-hour charge state is less than or equal to the estimated charge state.
9. The power cell pack state of charge calculation system of claim 6, further comprising:
and the initial charge state correcting unit is used for correcting the initial charge state according to the current lowest cell voltage, the initial nominal capacity and the preset OCV-SOC curve.
10. The power cell pack state of charge calculation system of claim 6, further comprising:
and the initial nominal capacity correcting unit is used for correcting the initial nominal capacity according to the current highest cell voltage, the current lowest cell voltage, the initial charge state and the actual charge state.
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