CN114035084B - SOC estimation method for hybrid power LFP battery - Google Patents
SOC estimation method for hybrid power LFP battery Download PDFInfo
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 3
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- G—PHYSICS
- 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]
- G01R31/382—Arrangements for monitoring battery or accumulator variables, e.g. SoC
- G01R31/3842—Arrangements for monitoring battery or accumulator variables, e.g. SoC combining voltage and current measurements
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- G—PHYSICS
- 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 relates to the field of battery state estimation, and discloses an SOC estimation method for a hybrid power LFP battery. According to the invention, the compensation voltages of SOH, temperature and current multiplying power are considered, and monomer voltage compensation values between the current temperature, the current charge-discharge multiplying power and the current health state relative to the reference temperature, the reference charge-discharge multiplying power and the reference health state are calculated under the SOC value of 0% -100%; according to the data and the measured voltage value table lookup (SOC-single voltage comparison data), the SOC closest to the true value is estimated, and the relative accuracy is improved; different SOC correction strategies are adopted aiming at the platform region of the LFP and the working conditions of small current and large current, so that SOC estimation errors are reduced as much as possible; and considering the inconsistency of the states of the battery cells, respectively obtaining the maximum SOC and the minimum SOC, and outputting the stably-changed SOC of the battery pack level.
Description
Technical Field
The invention relates to the technical field of battery state estimation, in particular to an SOC estimation method for a hybrid power LFP battery.
Background
The control quantity required by the whole vehicle power system comprises a battery SOC, a State of Health (SOH), a maximum chargeable and dischargeable power (SOP) and the like; the physical quantity which can be directly measured in the running process of the vehicle is only battery terminal voltage (U), battery working current (I), battery temperature (T) and running time (T). The SOC is an important intermediate quantity, and can be converted from the measured physical quantity (U, I, T, t) to the control quantity (SOH, SOP) required for the whole vehicle. Accurate estimation of SOC will directly affect the dynamic behavior of the vehicle and prevent battery life degradation and safety problems due to overcharging and overdischarging. On the other hand, lithium iron phosphate (LFP) batteries are widely used in electric vehicles due to their advantages of good safety, long cycle life, low cost, and the like. However, the SOC estimation accuracy of the voltage platform region of LFP has been a subject of attention in the industry. Meanwhile, the hybrid electric vehicle may not have full charge/full discharge working conditions for a long time in actual running, which brings challenges to eliminating SOC accumulated errors, SOC correction and the like.
In view of the important roles and challenges of the SOC, the current estimation algorithm of the SOC mainly includes a discharge experiment method, an ampere-hour integration method, an open-circuit voltage method, a load voltage method, an internal resistance method, a neural network method, a kalman filtering method, and the like, and has advantages and disadvantages. The discharge experiment method is most accurate, but takes a long time, is not suitable for the driving conditions of the automobile, and is generally only used for SOC off-line calibration. The ampere-hour integration method is most commonly used, but when the current sampling precision or capacity calibration is inaccurate, SOC calculation errors are caused, and the errors are accumulated along with time. The open circuit voltage method maps the SOC by using the corresponding relationship between the OCV and the SOC, and has a good effect in the initial and final stages of charging. The disadvantage of this method is that it requires a long time for the battery to stand so that its open circuit voltage reaches a stable state and is not suitable for lithium iron phosphate voltage plateau. In the charge and discharge process of the battery, if the current is kept unchanged, the change rule of the load voltage along with the SOC is similar to the change rule of the open circuit voltage along with the SOC. Therefore, the SOC can be estimated with the load voltage. The method can estimate the SOC of the battery pack in real time. The constant-current discharge lamp has better effect in constant-current discharge. In practice, however, severely fluctuating battery currents present difficulties for the application of the load voltage method. This method is rarely used alone in electric vehicles. The neural network method is suitable for various batteries, and if the neural network method is trained well, the estimation error is less than 10%, but the estimation accuracy is greatly affected by the training sample and the training method and is easy to interfere. The Kalman filtering algorithm has strong adaptability, but the calculated amount of the method is relatively large, and the requirement on system hardware is high. The state obtained by the deterministic observer is difficult to fully reflect the situation of a real system due to system noise caused by simplification of the model in the system modeling process, measurement noise caused by sensor errors, and the like.
There are some patents that propose SOC dynamic correction methods. The patent (CN 113253114A) ("a dynamic correction and estimation method for power battery SOC") proposes a dynamic correction and estimation method for electric automobile SOC, which mainly comprises the steps of obtaining battery test data, evaluating battery discharge grades during running and calculating running dynamic SOC, and selecting SOC-single voltage data corresponding to corresponding grades according to different battery discharge grades to carry out dynamic correction. The estimation method is only suitable for SOC dynamic correction under the working conditions of low-speed driving and low-current discharging in the driving process, and the influence of temperature on the SOC dynamic correction is not fully considered.
Patent CN109387784a ("method for estimating the SOC in a multi-dimensional state and method for dynamically correcting the SOC") proposes a SOC calibration method taking into account the temperature and current multiplying power. Firstly, taking N standard electric quantity points from 0 to 1 of electric quantity state, and storing a temperature-terminal voltmeter of each standard electric quantity point corresponding to standard charge-discharge multiplying power and a charge-discharge multiplying power-terminal voltmeter of each standard electric quantity point corresponding to standard temperature; then calculating voltage compensation deltaV of the current temperature and the charge-discharge multiplying power relative to the standard temperature and the standard charge-discharge multiplying power, and calculating estimated terminal voltages Vt respectively corresponding to N standard electric quantity points of the current temperature and the current charge-discharge multiplying power according to the voltage compensation quantity deltaV and terminal voltages corresponding to the standard temperature and the standard charge-discharge multiplying power; and finally, corresponding standard electric quantity-terminal voltage comparison data are manufactured according to the estimated terminal voltage Vt corresponding to the N standard electric quantity points respectively, and the effective standard SOC Ca corresponding to the current terminal voltage value V is obtained according to the standard electric quantity-terminal voltage comparison data. If the difference between the effective standard SOC Ca and the ampere-hour integral SOC Ah exceeds a preset threshold, the SOC dynamic correction is carried out, the correction coefficient k= (1-SOC Ah)/(1-SOCCa), and the calculation formula of the final SOC is as followsThe estimation method considers the voltage compensation of temperature and current multiplying power, but only determines whether to dynamically correct the SOC by comparing the deviation between the calibration SOC and the ampere-hour integral SOC, and the applicability of the dynamic correction in the voltage platform area of the LFP battery core and the small current working condition is not estimated, so that errors can be accidentally introduced.
Disclosure of Invention
The invention aims to provide an SOC estimation method for a hybrid power LFP battery, which takes SOH, temperature and current multiplying power compensation voltage into consideration, and calculates monomer voltage compensation values between the current temperature, the current charge and discharge multiplying power, the current health state and the reference temperature, the reference charge and discharge multiplying power and the reference health state under the SOC value of 0-100 percent respectively. According to the data and the measured voltage value table lookup (SOC-single voltage comparison data), the correction SOC closest to the true value is estimated, and the relative accuracy is improved; different SOC correction strategies are adopted aiming at the platform region of the LFP and the working conditions of small current and large current, so that SOC estimation errors are reduced as much as possible; and considering the inconsistency of the states of the battery cells, respectively obtaining the maximum SOC and the minimum SOC, and outputting the stably-changed SOC of the battery pack level.
The technical aim of the invention is realized by the following technical scheme:
S1: acquiring electrical core data: the method comprises the steps of (1) testing a battery cell, and acquiring standard capacity at different temperatures, OCV-SOC data at different temperatures, and SOC-monomer voltage data at different temperatures, different current multiplying powers and different SOHs;
S2: determining a current class classification: dividing the current into a plurality of grades according to the current magnitude, and determining HIGH CRATE SOC-single voltage data, low Crate SOC-single voltage data and an interpolation coefficient K rate of the current actual current relative to High/Low Crate under each grade according to the current grades;
S3: determining whether to perform SOC dynamic correction: preliminarily judging whether the SOC dynamic correction is allowed or not according to the absolute value of the current, executing step S4 if the SOC dynamic correction is allowed, and not performing the SOC dynamic correction if the SOC dynamic correction is not allowed;
S4: calculating a compensation voltage value: the compensation voltage DeltaV SOH of the SOH can be calculated through interpolation so as to obtain SOC-monomer voltage data under the current SOH; calculating the voltage compensation quantity DeltaV T of the current temperature T according to the SOC-monomer voltage data of the compensated SOH; calculating the monomer voltages corresponding to HIGH CRATE and Low Crate of SOC=0-100% at the current temperature T, and then obtaining a calibration SOC according to the actually measured voltage;
S5: selection of a dynamic correction method of the SOC: if the battery is in a non-voltage platform area, using a dynamic correction method 1; if the battery is in the "false" non-voltage plateau region, dynamic correction method 2 is used, and if the battery is in the voltage plateau region, dynamic correction of SOC is not performed.
The invention is further provided with: in the step S2: the SOC-cell voltage data at two standard current rates are defined as:
HighTabRaw = SOC-cell voltage data corresponding to larger current rates within the current class;
LowTabRaw = SOC-cell voltage data corresponding to a smaller current multiplying power within the current class.
The invention is further provided with: in the step S4, according to the current SOH value, the adjacent SOH k,SOHk+1 is selected as two reference SOH values respectively, and the SOC-monomer voltage data obtained under the SOH k＜SOH＜SOHk+1,SOHk health state isThe SOC-monomer voltage data obtained under SOH k+1 health state isCalculating a compensation voltage delta V SOH by using a formula, and then obtaining SOC-monomer voltage data corresponding to the current SOH:
HighTabSOH＝ΔVSOH+HighTabRaw
LowTobSOH＝ΔVSOH+LowTabRaw
The invention is further provided with: in the step S4, according to the current temperature T, adjacent standard temperatures T k and T k+1 are selected as reference temperatures, wherein T k＜T＜Tk+1 is used for obtaining a voltage V k,Vk+1 corresponding to the temperature T k,Tk+1 according to current classification and SOC-monomer voltage data of the compensated SOH; when the temperature is T k+1 and the current multiplying power is HIGH CRATE, the corresponding monomer voltage is V k+1,Hi when soc=0%; at a temperature T k, when the current multiplying power is HIGH CRATE, the corresponding monomer voltage is V k,Hi when soc=0%; when the current multiplying power is HIGH CRATE, the current temperature T is corresponding to the voltage compensation quantity DeltaV T,Hi of the two reference temperatures T k,Tk+1; when the current multiplying power is Low Crate, the current temperature T is voltage compensation delta V T,Lo relative to two reference temperatures T k,Tk+1; when the temperature is T, the corresponding cell voltages at soc=0% when the current ratio is HIGH CRATE and Low rate are:
VT,Hi＝Vk,Hi+ΔVT,Hi
VT,Lo＝Vk,Lo+ΔVT,Lo
Correspondingly, the monomer voltages corresponding to HIGH CRATE and Low Crate of SOC=0 to 100% at the current temperature T can be obtained.
The invention is further provided with: in the step S4, after the voltage compensation amounts of the temperature and the SOH are considered, an SOC-monomer voltage curve HighTab SOH,T,LowTabSOH,T is obtained, in which charging and discharging are performed at the current temperature T at the rates of HIGH CRATE and Low crank, and the SOC values corresponding to Vmax in the two curves are SOC (HighTab SOH,T, vmax) and SOC (LowTab SOH,T, vmax) respectively; the SOC values corresponding to Vmin are SOC (HightTab SOH,T, vmin) and SOC (LowTab SOH,T, vmin), respectively.
The invention is further provided with: in the dynamic correction method 1 in the step 5: and calculating the maximum correction SOC cal,max (t+1) and the minimum correction SOC cal,min (t+1) of the dynamic correction calculated at the time of t+1 according to the SOC max,cal corresponding to the current maximum monomer voltage calculated by the voltage compensation quantity, the correction coefficient K1 and the SOC cal,max (t) obtained by ampere-hour integration.
The invention is further provided with: in the dynamic correction method 1 in step S5: calculating the maximum correction SOC cal,max (t+1) at the time of t+1 according to the SOC max,cal (t) corresponding to the maximum monomer voltage at the current time of t, the correction coefficient k1 and the SOC obtained by ampere-hour integration, which are obtained by calculating the voltage compensation quantity; and calculating the minimum correction SOC cal,min (t+1) at the time of t+1 according to the SOC min,cal corresponding to the current minimum monomer voltage calculated by the voltage compensation quantity, the correction coefficient k1 and the SOC obtained by ampere-hour integration.
The invention is further provided with: the dynamic correction method 2 differs from the dynamic correction method 1 in that: the maximum correction SOC cal,max and the minimum correction SOC cal,min are calculated in different manners.
The invention is further provided with: the SOC of the hybrid LFP battery is calculated from the highest cell SOC max and the lowest cell SOC min:
The beneficial effects of the invention are as follows:
1. The invention considers the compensation voltage of SOH, temperature and current multiplying power. And respectively calculating monomer voltage compensation values between the current temperature, the current charge-discharge multiplying power, the current health state relative to the reference temperature, the reference charge-discharge multiplying power and the reference health state under the SOC value of 0% -100%. According to the data and the measured voltage value table lookup (SOC-single voltage comparison data), the correction SOC closest to the true value is estimated, and the relative accuracy is improved.
2. Different SOC correction strategies are adopted aiming at the platform region of the LFP and the working conditions of small current and large current, so that SOC estimation errors are reduced as much as possible.
3. The invention considers the inconsistency of the battery monomer states, respectively obtains the maximum SOC and the minimum SOC, and outputs the SOC of the stable change of the battery pack level.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a system block diagram of an SOC estimation method for a hybrid LFP battery according to the present invention.
Fig. 2 is a flowchart of an SOC estimation for a hybrid LFP battery according to the present invention.
Fig. 3 is a voltage compensation calculation process for a hybrid LFP battery according to the present invention.
Fig. 4 is a dynamic SOC correction procedure for a hybrid LFP battery according to the present invention.
Detailed Description
The technical scheme of the present invention will be clearly and completely described in connection with specific embodiments. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention.
The present invention is directed to a SOC estimation method suitable for a hybrid LFP battery cell, so as to solve the above-mentioned problems in the related art. The method provided by the invention comprises the following six steps.
Step one, acquiring the electrical core data
The die data required for SOC estimation includes, but is not limited to, the following three categories.
1.1 Standard Capacity at different temperatures
A) Fully charging the battery to 100% SOC by using a standard charging flow at 25 ℃, standing for 30min, fully discharging to 0% SOC by using a standard discharging flow, and recording the discharge capacity;
b) Repeating a) 3 times, and calculating the average value of the average discharge capacity of three times as the standard capacity at 25 ℃;
c) Repeating the steps a) to b) at intervals of 5 ℃ between-30 ℃ and 60 ℃ to obtain standard capacity at different temperatures.
1.2 OCV-SOC data at different temperatures
A) Fully charging the battery to 100% SOC by using a standard charging flow at 25 ℃, and standing for 3h;
b) Discharging at a constant current of 1/3C, discharging 5% of SOC electric quantity, standing for 3h, and recording an OCV value;
c) Repeating a) to b) at intervals of 5% SOC until 0% SOC.
D) Standing for 3h, charging at 1/3C constant current, charging 5% of SOC electric quantity, standing for 3h, and recording OCV value;
e) Repeating c) to d) every 5% SOC until 100% SOC;
f) Repeating the steps a) to e) at intervals of 5 ℃ between-30 ℃ and 60 ℃ to obtain standard capacity at different temperatures.
1.3 SOC-monomer Voltage data at different temperatures, different Current multiplying powers, different SOH
A) Fully charging the battery to 100% of SOC by using a standard charging flow at 25 ℃, discharging at a constant current of 1/3C until reaching 0% of SOC, and recording the voltage value of the monomer every 5% of SOC;
b) At 25 ℃, charging at a constant current of 1/3C until reaching 100% SOC, and recording the voltage value of the monomer at intervals of 5% SOC;
c) And similarly, repeating the steps a) to b) with 1/30C,1/20C,1/10C and 1/5C to obtain charge-discharge SOC-monomer voltage data with different multiplying powers at normal temperature;
d) Repeating the steps a) to c) at intervals of 5 ℃ between 30 ℃ below zero and 60 ℃ to obtain SOC-monomer voltage data with different temperatures and different multiplying powers; and d) repeating the steps a) to d) by selecting the battery cells in different health states to obtain SOC-monomer voltage data with different SOHs, different temperatures and different multiplying powers.
Step two current class classification
It is agreed herein that the charging direction is negative and the discharging direction is positive.
2.1 The current is classified into a plurality of grades according to the current magnitude, and is respectively recorded as Num 1,Num 2,Num 3,Num 4,Num 5.
2.2 A plurality of standard charge-discharge current multiplying powers, respectively Crate 1,Crate 2,Crate 3,Crate4,Crate 5, …, have been obtained in step 1.3; in this example, crag1=1/30C, crag2=1/20C, crag3=1/10C, crag4=1/5C, crag5=1/3C;
2.3 determining Num0 when the absolute value of the average current is equal to or less than Crate 1; when the average current absolute value is between Crate 1 and Crate 2, num1 is determined; when the average current absolute value is between the Crate 2 and Crate 3, it is determined as Num2; when the average current absolute value is between the Crate 3 and Crate 4, it is determined as Num3; when the average current absolute value is between the Crate 4 and Crate 5, it is determined as Num4; when the absolute value of the average current is greater than Crate 5, num 5 is determined;
2.4 determining HighCrateSOC-single voltage data, lowCrateSOC-single voltage data and an interpolation coefficient k rate of the current actual current relative to High/Low Crate under each grade according to the current grade;
Within this class, there are two SOC-cell voltage data at standard current rates, defined as:
HighTabRaw = SOC-cell voltage data corresponding to larger current rates within the current class
LowTabRaw = SOC-cell voltage data corresponding to smaller current rates within the current class
The interpolation coefficient k rate is defined as:
krate＝(Current-Low Crate)/(High Crate-Low Crate)
Description of examples:
The current classification Num 1 is described as an example:
Standard SOC-cell voltage data at HighTabRaw = Crate 2
Standard SOC-cell voltage data at LowTabRaw = Crate 1
krate＝(Current-Crate 1)/(Crate 2-Crate 1)
Step three, judging conditions of dynamic correction of the SOC
And preliminarily judging whether the dynamic correction of the SOC is allowed or not according to the absolute value of the current.
3.1 If the average current is greater than the preset current threshold 1, SOC dynamic correction is not allowed. In this example, the preset current threshold 1 is Crate 5;
3.2 if the average current is less than the threshold current threshold 2, SOC dynamic correction is not allowed. In this example, the preset threshold current 2 is a larger value of both the current sensor zero drift current value and the current sampling accuracy, that is, a preset threshold=max (current sensor zero drift current value, current sampling accuracy).
Step four, calculating the compensation voltage
The SOC-cell voltage data is affected by the battery state of health SOH, temperature, and current draw. The influence of these three factors and their voltage compensation amounts are mainly considered herein.
4.1 Voltage compensation for SOH
Step 1.3 has acquired SOC-cell voltage data for different health states of SOH 1,SOH2,...,SOHn from soh=100% to soh=0%, respectively (decreasing SOH values from SOH 1 to SOH n). The offset voltage DeltaV SOH of the SOH can be calculated by interpolation to obtain SOC-cell voltage data at the current SOH.
4.1.1 According to the current SOH value, selecting adjacent SOH sections, namely SOH k,SOHk+1 as two reference SOH values, and SOH k＜SOH＜SOHk+1
4.1.2 In this example, the compensation voltage is calculated by sampling the linear interpolation
Wherein DeltaV SOH is the voltage compensation amount of the current SOH relative to the reference SOH; The SOC-monomer voltage data is obtained under the condition that the health state is SOH k; in the same way, the processing method comprises the steps of, Is SOC-monomer voltage data obtained under the condition of SOH k+1.
4.1.3 Updating the SOC-monomer voltage data corresponding to the current SOH according to the compensation voltage
HighTabSOH＝ΔVSOH+HighTabRaw
LowTabSOH＝ΔVSOH+LowTabRaw
4.2 Voltage Compensation at temperature
SOC-monomer voltage data at a plurality of standard temperature points of-30 to 60 ℃ are obtained in the step 1.3. The temperature compensation voltage DeltaV T can be calculated by interpolation to obtain SOC-cell voltage data of the current temperature point.
For ease of understanding, the following description will be given by taking soc=0% as an example.
4.2.1 Obtaining the current temperature T, the current multiplying power Crate, the current maximum and minimum monomer voltages Vmax and Vmin
4.2.2 Based on the current temperature T, the adjacent standard temperatures T k and T k+1 are selected as reference temperatures. Wherein T is k＜T＜Tk+1
4.2.3 According to the SOH-compensated SOC-cell voltage data obtained in step 4.1.3, checking the voltage V k,Vk+1 corresponding to the temperature T k,Tk+1. The method comprises the following steps:
a) According to the second step, determining the current classification of the current multiplying power Crate
B) Determination of High Tab SOH and LowTab based on current classification SOH
C) Respectively determining the voltage V corresponding to T k,Tk+1 k,Hi,Vk+1,Hi,Vk,Lo,Vk+1,Lo
4.2.4 Calculating the Voltage Compensation quantity DeltaV of the present temperature T with respect to the reference temperature points T k and T k+1 T
The subscript 'Hi' here indicates a larger current magnification HIGH CRATE in the current gradation where the actual current is located, and the subscript 'Lo' indicates a smaller current magnification Low crawte in the current gradation where the actual current is located.
V k+1,Hi is the temperature T k+1, and when the current multiplying power is HIGH CRATE, the corresponding cell voltage is soc=0%; v k,Hi is the cell voltage corresponding to the soc=0% when the temperature T k and the current ratio are HIGH CRATE. Δv T,Hi represents the voltage compensation amount of the current temperature T with respect to the two reference temperatures T k,Tk+1 when the current magnification is HIGH CRATE. Similarly, Δv T,Lo represents the voltage compensation amount of the current temperature T with respect to the two reference temperatures T k,Tk+1 when the current magnification is Low.
4.2.5 When soc=0% can be calculated according to steps 4.2.1 to 4.2.4, the monomer voltage corresponding to the current temperature T after temperature compensation is considered
VT,Hi＝Vk,Hi+ΔVT,Hi
VT,Lo＝Vk,Lo+ΔVT,Lo
Wherein V T,Hi represents the corresponding monomer voltage when soc=0% when the current multiplying power is HIGH CRATE at the current temperature T;
V T,Lo represents the cell voltage corresponding to soc=0% when the current magnification is Low crank at the current temperature T.
4.2.6 In the same manner, according to steps 4.2.1 to 4.2.5, the monomer voltages corresponding to HIGH CRATE and Low Crate with soc=0 to 100% at the current temperature T can be calculated sequentially and recorded as HighTab SOH,T,LowTabSOH,T.
4.2.7 Finds a corresponding SOC at HighTab SOH,T,LowTabSoH,T according to the current voltage measured voltages Vmax, vmin, namely the calibration SOC:
a) Vmax corresponds to the maximum monomer SOC, i.e
B) Vmin corresponds to the small monomer SOC, i.e
SOCmin,cal＝SOC(HighTabsoH,T,Vmin)*krate+SOC(LowTabsOH,T,Vmin)*(1-krate)
Wherein k rate is the interpolation coefficient determined in step 2.4;
High Tab SOH,T is an SOC-cell voltage curve in which charge and discharge are performed at HIGH CRATE at the current temperature, taking into consideration the temperature and the voltage compensation amount of SOH. The SOC (High Tab SOH,T, vmax) is the SOC corresponding to Vmax in the curve;
LowTab SOH,T is a SOC-cell voltage curve in which charge and discharge are performed at the current temperature at the rate of Low crank in consideration of the temperature and the voltage compensation amount of SOH. SOC (LowTab SOH,T, vmin) is the SOC corresponding to Vmin in the curve;
The SOC max,cal is an SOC corresponding to the maximum cell voltage Vmax at the current temperature T, the current SOH, and the current multiplying power after the voltage compensation is considered. Similarly, the SOC min,cal is an SOC corresponding to the minimum cell voltage Vmin under the current temperature T, the current SOH, and the current multiplying power after the voltage compensation is considered.
By the fourth step, corrected SOC values have been obtained taking into account three influencing factors of temperature, SOH, and current magnification.
Step five SOC dynamic correction
And 5.1, selecting different SOC dynamic correction methods according to whether the system is in an LFP voltage platform region or not.
5.1.1 If the battery is in the non-voltage plateau region, then dynamic correction method 1 is used. The non-voltage plateau region is defined as:
a) The battery is in a discharging working condition, and the SOC value calculated in the step 4.2.7 is smaller than the lower boundary value SOC_ PlatLow of the voltage platform area;
b) Or the battery is in a charging working condition, and the SOC value calculated in the step 4.2.7 is larger than the boundary value SOC_ PlatHigh on the voltage platform area;
5.1.2 if the battery is in the voltage plateau region, the SOC dynamic correction is not performed, and the voltage plateau region is defined as:
a) The battery is in a discharging working condition, the SOC value calculated in the step 4.2.7 is larger than the lower boundary value SOC_ PlatLow of the voltage platform area, and the SOC output by the BMS at the last moment is larger than SOC_ PlatLow;
b) Or the battery is in a charging working condition, the SOC value calculated in the step 4.2.7 is smaller than the upper boundary value SOC_ PlatHigh of the voltage platform area, and the SOC output by the BMS at the last moment is smaller than SOC_ PlatHigh;
5.1.3 if the battery is in a "false" non-voltage plateau region, then dynamic correction method 2 is used. The "false" non-voltage plateau region is defined as:
a) The battery is in a discharging condition, the SOC value calculated in step 4.2.7 is greater than the lower boundary value soc_ PlatLow of the voltage platform region, but the SOC output by the BMS at the previous time is less than soc_ PlatLow. Indicating that the SOC at the previous time may have a larger accumulated error;
b) The battery is in a charging condition, and the SOC value calculated in step 4.2.7 is smaller than the boundary value soc_ PlatHigh on the voltage platform area, but the SOC output by the BMS at the last moment is larger than soc_ PlatHigh. Indicating that the SOC at the previous time may have a larger accumulated error;
For both "false" non-plateau regions, there may be errors in correcting the SOC and the SOC at the previous time. The weight of the correction SOC calculated from the voltage compensation in the dynamic correction method 2 will be reduced compared to the correction method 1.
5.2 Dynamic correction method 1-SOC dynamic correction for non-platform region
A) Before starting correction: firstly, calculating the SOC by using an ampere-hour integration method,
In this example, t0 is 10s, so as to ensure that the sampling value is correct and stable, and then dynamic correction is started.
B) Starting correction:
SOCcal,max(t+1)＝k1·SOCcal,max(t)+(1-k1)·SOCmax,cal
SOC cal,max (t+1) is the maximum correction SOC at time t+1; SOC cal,max (t) is the maximum corrected SOC at time t; the SOC max,ca is the SOC corresponding to the current maximum cell voltage calculated according to the voltage compensation amount in step 4.2.7. k 1 is a correction coefficient of 0 to 1, and the smaller k 1 is, the more trust the dynamic correction method is.
C) The corrected maximum SOC is
K 2 is an SOC update coefficient, and the ampere-hour integral SOC is gradually corrected in accordance with the correction amount SOC cal,max. Jump such as 'steep drop', 'steep rise' and the like of the SOC during correction is avoided.
Similarly, the corrected minimum SOC is
SOCcal,min(t+1)＝k1·SOCcal,min(t)+(1-k1)·SOCmin,cal
5.3 Dynamic correction method 2-SOC correction for "false" non-platform regions
The main difference of method 2 compared to correction method 1 is the calculation of the correction SOC of step b), as follows.
SOCcal,max(t+1)＝SOCcal,max(t)+k3·(SOCmax,cal-SOCcal,max(t))
SOCcal,min(t+1)＝SOCcal,min(t)+k3·(SOCmin,cal-SOCcal,min(t))
Wherein: the definition of SOC cal,max(t+1),SOCcal,max(t),SOCcal,min(t+1),SOCcal,min(t),k1 is the same as described in 5.2.
K 3 is a calibration amount of 0 to 1 for reducing the SOC integration error. If the SOC output from the BMS at the previous time is less than the corrected SOC calculated in step 4.2.7, the SOC is dynamically adjusted in a direction to increase the SOC. And vice versa.
To avoid introducing additional errors, it is recommended that k 3 take a small value to gently adjust the SOC.
Step six, calculating and displaying SOC
For one battery pack, the highest and lowest cell SOCs are well representative.
Taking the primary battery pack full charge test as an example, the battery pack SOC should satisfy the following characteristics:
When the lowest monomer socmin=0%, the battery pack soc=0%;
when the highest cell socmax=100%, the battery pack soc=100%;
The battery pack SOC should be smoothly changed between 0 and 100%.
The calculation expression of the battery pack SOC from the highest monomer SOC and the lowest monomer SOC can be obtained according to the principle
According to the invention, the compensation voltages of SOH, temperature and current multiplying power are considered, and the single voltage compensation values between the current temperature, the current charge-discharge multiplying power and the current health state relative to the reference temperature, the reference charge-discharge multiplying power and the reference health state under the SOC value of 0-100% are calculated respectively. According to the data and the measured voltage value table lookup (SOC-single voltage comparison data), the correction SOC closest to the true value is estimated, and the relative accuracy is improved; different SOC correction strategies are adopted aiming at the platform region of the LFP and the working conditions of small current and large current, so that SOC estimation errors are reduced as much as possible; and considering the inconsistency of the states of the battery cells, respectively obtaining the maximum SOC and the minimum SOC, and outputting the stably-changed SOC of the battery pack level.
Claims (7)
1. An SOC estimation method for a hybrid LFP battery, characterized by: the method comprises the following steps:
S1: acquiring electrical core data: the method comprises the steps of (1) testing a battery cell, and acquiring standard capacity at different temperatures, OCV-SOC data at different temperatures, and SOC-monomer voltage data at different temperatures, different current multiplying powers and different SOHs;
S2: determining a current class classification: dividing the Current into a plurality of grades according to the Current, and determining HIGH CRATE SOC-single voltage data, low Crate SOC-single voltage data and an interpolation coefficient K rate of the Current actual Current relative to High/Low Crate under each grade according to the Current grade;
interpolation coefficient k rate = (Current-Low crawte)/(HIGH CRATE-Low crawte);
S3: determining whether to perform SOC dynamic correction: preliminarily judging whether the SOC dynamic correction is allowed or not according to the absolute value of the current, executing step S4 if the SOC dynamic correction is allowed, and not performing the SOC dynamic correction if the SOC dynamic correction is not allowed;
S4: calculating a compensation voltage value: the compensation voltage DeltaV SOH of the SOH can be calculated through interpolation so as to obtain SOC-monomer voltage data under the current SOH; calculating the voltage compensation quantity DeltaV T of the current temperature T according to the SOC-monomer voltage data of the compensated SOH; calculating the monomer voltages corresponding to HIGH CRATE and Low Crate of SOC=0-100% at the current temperature T, and then calculating according to the measured voltage to obtain a calibration SOC;
s5: selection of a dynamic correction method of the SOC: if the battery is in a non-voltage platform area, using a dynamic correction method 1; if the battery is in a false non-voltage platform area, using a dynamic correction method 2, and if the battery is in the voltage platform area, not carrying out SOC dynamic correction;
The non-voltage plateau region is defined as: the battery is in a discharging working condition, and the calibration SOC value calculated in the step S4 is smaller than the lower boundary value SOC_ PlatLow of the voltage platform region; or the battery is in a charging working condition, and the calibration SOC value calculated in the step S4 is larger than the boundary value SOC_ PlatHigh on the voltage platform area;
The voltage plateau region is defined as: the battery is in a discharging working condition, the calibration SOC value obtained by calculation in the step S4 is larger than the lower boundary value SOC_ PlatLow of the voltage platform region, and the SOC output by the BMS at the last moment is larger than SOC_ PlatLow; or the battery is in a charging working condition, the calibration SOC value calculated in the step S4 is smaller than the upper boundary value SOC_ PlatHigh of the voltage platform area, and the SOC output by the BMS at the last moment is smaller than SOC_ PlatHigh;
The "false" non-voltage plateau region is defined as: the battery is in a discharging working condition, the calibration SOC value calculated in the step S4 is larger than the lower boundary value SOC_ PlatLow of the voltage platform area, but the SOC output by the BMS at the last moment is smaller than the SOC_ PlatLow; the battery is in a charging working condition, the calibration SOC value calculated in the step S4 is smaller than the upper boundary value SOC_ PlatHigh of the voltage platform area, but the SOC output by the BMS at the last moment is larger than SOC_ PlatHigh;
dynamic correction method 1-SOC dynamic correction for non-voltage plateau region
A) Before starting correction: firstly, calculating the SOC by using an ampere-hour integration method,
B) Starting correction:
SOCcal,max(t+1)＝k1·SOCcal,max(t)+(1-k1)·SOCmax,cal
SOC cal,max (t+1) is the maximum correction SOC at time t+1; SOC cal,max (t) is the maximum corrected SOC at time t; SOC max,cal is the SOC corresponding to the current maximum monomer voltage calculated according to the voltage compensation quantity in the step S4, k 1 is a correction coefficient of 0-1, and the smaller k 1 is, the more trust the dynamic correction method is expressed;
c) The corrected maximum SOC is
K 2 is an SOC update coefficient, and the ampere-hour integral SOC is gradually corrected according to the correction quantity SOC cal,max, so that abrupt drop and abrupt rise jump of the SOC during correction are avoided;
Similarly, the corrected minimum SOC is
SOCcal,min(t+1)＝k1·SOCcal,min(t)+(1-k1)·SOCmin,cal
Dynamic correction method 2-SOC correction for "false" non-voltage plateau
The main difference of the correction method 2 compared to the correction method 1 is the calculation of the correction SOC of step b), as follows:
SOCcal,max(t+1)＝SOCcal,max(t)+k3·(SOCmax,cal-SOCcal,max(t))
SOCcal,min(t+1)＝SOCcal,min(t)+k3·(SOCmin,cal-SOCcal,min(t))
Wherein: k 3 is a calibration amount of 0 to 1, and is used for reducing the SOC accumulated error; if the SOC output from the BMS at the previous time is less than the corrected SOC calculated in step S4, dynamically adjusting the SOC in a direction to increase the SOC; and vice versa.
2. The SOC estimation method for a hybrid LFP battery according to claim 1, wherein: in the step S2: HIGH CRATE SOC-monomer voltage data and Low Crate SOC-monomer voltage data are defined as:
HIGH CRATE SOC-cell voltage data: highTabRaw = SOC-cell voltage data corresponding to larger current rates within the current class;
low crank SOC-cell voltage data: lowTabRaw = SOC-cell voltage data corresponding to a smaller current multiplying power within the current class.
3. The SOC estimation method for the hybrid LFP battery according to claim 2, wherein: in the step S4, according to the current SOH value, the adjacent SOH k,SOHk+1 is selected as two reference SOH values respectively, and the SOC-monomer voltage data obtained under the SOH k＜SOH＜SOHk+1,SOH k health state isThe SOC-monomer voltage data obtained under SOH k+1 health state isCalculating a compensation voltage delta V SOH by using a formula, and then obtaining SOC-monomer voltage data corresponding to the current SOH:
HighTabSOH＝ΔVSOH+HighTabRaw
LowTabSOH＝ΔVSOH+LowTabRaw。
4. A SOC estimation method for a hybrid LFP battery according to claim 3, wherein: in the step S4, according to the current temperature T, adjacent standard temperatures T k and T k+1 are selected as reference temperatures, wherein T k<T<Tk+1 is used for obtaining a voltage V k,Vk+1 corresponding to the temperature T k,Tk+1 according to current classification and SOC-monomer voltage data of the compensated SOH; when the temperature is T k+1 and the current multiplying power is HIGH CRATE, the corresponding monomer voltage is V k+1,Hi when soc=0%; at a temperature T k, when the current multiplying power is HIGH CRATE, the corresponding monomer voltage is V k,Hi when soc=0%; when the current multiplying power is HIGH CRATE, the current temperature T is corresponding to the voltage compensation quantity DeltaV T,Hi of the two reference temperatures T k,Tk+1; when the current multiplying power is Low Crate, the current temperature T is voltage compensation delta V T,Lo relative to two reference temperatures T k,Tk+1; when the temperature is T, the corresponding cell voltages at soc=0% when the current ratio is HIGH CRATE and Low rate are:
VT,Hi＝Vk,Hi+ΔVT,Hi
VT,Lo＝Vk,Lo+ΔVT,Lo
Correspondingly, the monomer voltages corresponding to HIGH CRATE and Low Crate of SOC=0-100% at the current temperature T can be obtained.
5. The SOC estimation method for a hybrid LFP battery according to claim 4, wherein: in the step S4, after the voltage compensation amounts of the temperature and the SOH are considered, an SOC-cell voltage curve HighTab SOH,T,LowTabSOH,T is obtained, in which the SOC values corresponding to the maximum cell voltage Vmax in the two curves are SOC (HighTab SOH,T, vmax) and SOC (LowTab SOH,T, vmax) respectively, and the SOC-cell voltage curve HighTab SOH,T,LowTabSOH,T is obtained, in which the charging and discharging are performed at the current temperature T at the rates of HIGH CRATE and Low crank; the SOC values corresponding to the minimum cell voltage Vmin are SOC (HighTab SOH,T, vmin) and SOC (LowTab SOH,T, vmin), respectively;
Finding out corresponding SOCs at HighTab SOH,T,LowTabSOH,T according to the current voltage measured voltages Vmax and Vmin, namely, correcting quantity SOCs max,cal and min,cal for calibrating the SOCs:
a) Vmax corresponds to the maximum monomer SOC max,cal, i.e
SOCmax,cal＝SOC(HighTabSOH,T,Vmax)*krate+SOC(LowTabSOH,T,Vmax)*(1-krate)
B) Vmin corresponds to the small monomer SOC min,cal, i.e
SOCmin,cal＝SOC(HighTabSOH,T,Vmin)*krate+SOC(LowTabSOH,T,Vmin)*(1-krate)。
6. The SOC estimation method for a hybrid LFP battery according to claim 5, wherein: the dynamic correction method 1 in step S5 is calculated by: the ampere-hour integrated SOC is gradually corrected according to the correction amounts SOC max,cal and SOC min,cal, resulting in corrected SOC max and corrected SOC min.
7. The SOC estimation method for a hybrid LFP battery according to claim 6, wherein: the SOC of the hybrid LFP battery is calculated from the corrected SOC max and the corrected SOC min:
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