WO2015106691A1

WO2015106691A1 - Soc estimation method for power battery for hybrid electric vehicle

Info

Publication number: WO2015106691A1
Application number: PCT/CN2015/070734
Authority: WO
Inventors: 朱建新; 孙志文; 储爱华; 于海生; 马智涛; 张彤; 王瑞平
Original assignee: 宁波吉利罗佑发动机零部件有限公司; 浙江吉利罗佑发动机有限公司; 济南吉利汽车零部件有限公司; 湖南罗佑发动机部件有限公司; 宁波上中下自动变速器有限公司; 浙江吉利控股集团有限公司
Priority date: 2014-01-17
Filing date: 2015-01-15
Publication date: 2015-07-23
Also published as: CN103969587B; CN103969587A

Abstract

An SOC estimation method for a power battery for a hybrid electric vehicle. The method comprises: first, obtaining charging and discharging capability data of a battery under different temperatures, currents and SOC values through an experimental method, and fitting data through analysis to obtain charging and discharging capability coefficients of the battery; then, in the actual operating process of the battery, calculating Ah integrals through BMS sampled data, and at the same time, judging whether an SOC correction condition is satisfied, if so, conducting SOC correction to correct an SOC value obtained by the current Ah integral to an SOC value calculated via the correction condition according to the step length; otherwise, not conducting SOC correction. The method reduces the accumulated errors of Ah integrals so that a more accurate SOC value can be obtained while avoiding frequent correction, and is suitable for all hybrid electric vehicle battery control systems.

Description

Method for estimating SOC of power battery for hybrid vehicle

Technical field

The invention relates to a charging battery control method, in particular to a CCV correction based power battery SOC estimating method for a hybrid vehicle.

Background technique

In the development of new energy vehicles, as a transition from traditional fuel vehicles to pure electric vehicles, the development of hybrid vehicles has a pivotal strategic significance. As a key energy storage component of hybrid vehicles, power batteries are highly nonlinear in their use, making accurate estimation of SOC more difficult. As the most important parameter of battery characteristics, SOC (state of charge) is the focus and difficulty of research on power battery management system. Only by accurately estimating the SOC of the battery can the battery SOC be maintained within a reasonable target range. The damage to the battery caused by overcharging or overdischarging of the battery is avoided, and the service life of the battery is improved, thereby reducing the running cost of the hybrid vehicle.

The current SOC estimation algorithm is usually Ah (Ah, current and time product) integration combined with CCV (closed voltage) or OCV (open circuit voltage) correction, the charging current is small and maintained for a certain time or the discharge current is small and After maintaining a certain period of time, the theoretical SOC value of the battery in the current state is obtained by calculation or look-up table, and then the current SOC value and the theoretical SOC value are compared to determine whether the battery SOC value needs to be corrected. If the difference between the current SOC value and the theoretical SOC value exceeds a certain range, the correction is performed to correct the current battery SOC value to the theoretical battery SOC value, thereby completing the SOC determination and correction process. This solution has the following problems:

1. The SOC correction will be too frequent, and the correction result will have a large error.

In the operation process of a hybrid vehicle, including various electric operating conditions such as pure electric power and hybrid power, the current magnitude and duration calculated by the current time period are simply used as the conditions for SOC correction, and are often triggered during actual operation. Correct the condition. The polarization effect of the battery is a difficult point affecting the SOC correction. When the battery is operated under transient current conditions, it is affected by the polarization effect of the battery to a certain extent, and the degree of influence of the polarization effect cannot be calculated, which becomes a difficult point of SOC correction. After the battery is affected by the polarization effect, the voltage characteristics of the battery will change, and the voltage value will be higher or lower than the normal value. At this time, if the correction condition is satisfied, it is easy to cause the SOC to be corrected. The SOC correction deviates from the actual SOC value due to the high or low voltage, causing erroneous correction.

2. The cumulative error of Ah integral is large

The battery has different charge and discharge efficiencies at different currents, temperatures, and SOCs. Especially in the battery overcharge phase, a large amount of energy is converted into heat of the battery. If the charging and discharging efficiency is not considered, there will be a large error in the Ah integration process, and as time goes on, the cumulative error will become larger and larger.

3, capacity attenuation causes large SOC calculation error

As the battery continues to be used, the capacity of the battery will decrease. The attenuation of the capacity will bring a large calculation error to the SOC.

Summary of the invention

The invention mainly solves the technical problems that the correction of the prior art is too frequent, the charging and discharging efficiency, the capacity attenuation brings a large error, and the like, and provides a correction only when necessary, considering charging and discharging efficiency and capacity attenuation. Error, high precision hybrid Vehicle SOC estimation method for power battery.

The technical problem of the present invention is mainly solved by the following technical solutions: 1. A method for estimating a SOC of a power battery for a hybrid vehicle, comprising the following steps:

Step 1. During the operation of the battery management system, calculate the current SOC value by the ampere-time integration method, and record it as SOC _now ; collect the current current of the battery through the current sensor, collect the current voltage of the battery through the voltage sensor, collect the battery temperature through the temperature sensor, and then check The table obtains the discharge efficiency η corresponding to the current current, voltage and temperature; obtains the attenuation factor λ of the current accumulated battery capacity under Ah by looking up the table;

Step 2: Calculate the corrected SOC value of the current time of the battery, and calculate the formula as follows:

SOC _i = SOC _i-1 -△SOC (1)

Where SOC _i is the corrected SOC value of the battery at the current time; SOC _i-1 is the corrected SOC value of the battery at the previous time; ΔSOC is the amount of change in the SOC correction value of the battery per unit time, and Δt is the unit sampling time interval; I is the current current, defining the positive direction of the current as the discharge direction, and the negative direction as the charging direction, that is, I is positive for battery discharge, I is negative for battery charging; SOC _std is for battery rated capacity; SOC _std is for amperage;

Step 3: update the maximum or minimum value of the current: if the battery is in a discharged state, update the maximum value of current I _max ; if the battery is in a charged state, update the minimum value of current I _min ;

Step 4: If the current of the sampling current and the direction of the previous sampling current are opposite, let n=1, that is, re-count, and assign the new sampling current value to the average current value, and set flag to 1; if the current is sampled When the value and the last sampled current value are in the same direction, the average current is updated, and the average current is updated as follows: I _avg = (I _avg '×n+I)/(n+1), and then the value of n is increased by 1, I _avg is updated average current, I _avg 'original average current, n is the sample number average current affected, flag is a flag;

Step 5: If the difference between the current sampling current value and the average current is less than ΔI, set flag to 0; if the difference between the current sampling current value and the average current is greater than or equal to ΔI, set flag to 1;

Step 6. If flag=1, and the battery is in a discharge condition, and the difference between the maximum value I _{max of the} discharge current and the average current I _avg is less than ΔI ₁ , and the minimum value I _{min of the} charging current is greater than I _chg , and n is greater than C _Nst , and the difference between SOC _now and SOC _i is greater than SOC _d , then SOC _now is corrected to SOC _i in steps; if flag=1, and the battery is in charge, and the minimum value of charging current I _min and average current I _avg difference is less than ΔI ₁ , and the discharge current maximum I _{max is} less than I _dchg , and n is greater than C _nst , and the difference between SOC _now and SOC _i is greater than SOC _d , then SOC _now is corrected to SOC _i in steps; If any of the above two conditions is not satisfied, then jump to step one; ΔI ₁ , I _chg , C _nst , SOC _{d ,} and I _{dchg are} all preset values.

Preferably, in step 3, the specific operation of updating the maximum value or the minimum value of the current is: if the battery is in a discharging state, comparing the current current with the stored current maximum value, and selecting a larger value as the new current maximum value I _max If the battery is in the charging state, compare the current current with the stored current minimum value, and select the smaller value as the new current minimum value I _min ; when the system is initialized, the current maximum value and the current minimum value are both 0.

Preferably, in step 5, if the first sampling is performed after the system is initialized, the average current is equal to the first sampling current value, and flag is 0.

Preferably, ΔI is 2A to 3A; ΔI ₁ is 0A to 3A; I _chg is _-12A to -6A; I _dchg is 6A to 12A; and C _nst is 1min to 5min. Between SOC _d is 5% to 10%.

Advantageously, the step size will be corrected by the SOC _now to SOC _i specifically, 5% to 10% of the difference correction and second SOC _now the SOC _i.

In this scheme, the corresponding SOC value under different battery temperature, current and voltage, the attenuation factor of battery capacity under different accumulated Ah, and the charging and discharging efficiency of the battery under different battery temperatures and SOC are all obtained through a large number of experiments.

The process of establishing the database is to perform charging and discharging experiments on two sets of new batteries with the same specifications and parameters through the dual-channel battery charging and discharging equipment on the power battery test bench. Record battery SOC value, current, temperature and accumulated Ah data. Through the collation and analysis of experimental data, the corresponding SOC value under different battery temperature, current and voltage, different battery temperature, charge and discharge efficiency η of battery under SOC and attenuation factor λ of battery capacity under different accumulated Ah, λ=( SOC _red ·Ah _use /Ah _pre )/SOC _std , SOC _red is the attenuation of battery capacity when the accumulated Ah number of the battery reaches the expected service life; Ah _use is the current cumulative use of Ah number; Ah _pre is the expected service life of the battery; SOC _std For battery rated capacity. Then, the SOC value corresponding to different battery temperatures, currents, and voltages, and the different battery temperatures, the charge and discharge efficiency η of the battery under SOC, and the attenuation factor λ data of the battery capacity under different accumulated Ah are stored in the battery management system BMS.

When the battery is charged and discharged at a high current, the voltage of the battery will be high or low, and this effect will continue for a while. The degree of influence due to the polarization effect cannot be calculated. Therefore, in the correction, not only the fluctuation range of the current is considered to be small, but also the occurrence of a large current in the previous charge and discharge cycle is avoided, otherwise the correction is not performed. This judgment condition can be It can avoid miscorrected situations and frequent corrections.

The charging and discharging efficiency is considered in the Ah integral process, which reduces the cumulative error of the Ah integral to some extent. In the SOC calculation process, the aging problem of the battery is considered, and the compensation factor is corrected by the attenuation factor, so that the SOC correction can still ensure high accuracy in the battery aging process.

When judging the correction condition, it is necessary to ensure that the current fluctuation is always maintained near the average current and maintained for a certain period of time. In this way, the voltage value fluctuation caused by the current fluctuation in the same direction can be minimized, and the characteristic relationship between the CCV value of the battery and the temperature, current, and SOC value can be ensured as much as possible.

When judging the correction conditions, the influence of the polarization effect caused by the large charge and discharge current on the battery voltage and the erroneous correction caused by it are considered. If the average current is the charging current, the difference between the charging current and I _min should be within a certain range, and considering the influence of the polarization effect caused by the large current discharge, the voltage will be low, so I _max cannot be too large; On the other hand, if the average current is the discharge current, the difference between the discharge current and I _max should be within a certain range. Considering the influence of the polarization effect caused by the large current charge, the voltage will be high, so I _min cannot pass. small.

The substantial effect brought by the invention is that the method is based on the Ah integral and combined with the dynamic CCV for correction, and the charge and discharge efficiency problems under different temperatures and SOCs are considered in the Ah integral process, and the cumulative error of the Ah integral is reduced. According to the aging degree of the battery under the accumulated Ah, the attenuation factor is used to correct the SOC. During the operation of the battery, the dynamic CCV correction is used. The correction affects the influence of the polarization effect on the battery CCV, and avoids frequent SOC. At the same time of correction, the accuracy of the correction is improved; this method improves the SOC The accuracy of the estimation avoids the problem of overcharging or overdischarging of the battery during use, which improves the reliability and safety of the system operation.

DRAWINGS

Figure 1 is a flow chart of the present invention.

detailed description

The technical solutions of the present invention will be further specifically described below by way of embodiments and with reference to the accompanying drawings.

Embodiment: A SOC estimation method for a hybrid vehicle power battery according to the present embodiment, as shown in FIG. 1 , includes the following steps: Step 1: During the operation of the battery management system, the current SOC value is calculated by the ampere-time integration method. For the SOC _now ; collect the current current of the battery through the current sensor, collect the current voltage of the battery through the voltage sensor, collect the battery temperature through the temperature sensor, and then check the table to obtain the current discharge voltage η corresponding to the current, voltage and temperature; obtain the current by looking up the table Cumulative use of the attenuation factor λ of the battery capacity under Ah;

SOC _i = SOC _i-1 -△SOC (1)

Step 3: Updating the maximum value or the minimum value of the current: if the battery is in a discharging state, updating the maximum value of current I _max ; if the battery is in a charging state, updating the minimum value of current I _min ;

In step 3, the specific operation of updating the maximum or minimum value of the current is: if the battery is in a discharged state, compare the current current with the stored current maximum value, and select a larger value as the new current maximum value I _max ; For the state of charge, the current current is compared with the stored current minimum, and the smaller value is selected as the new current minimum value I _min ; when the system is initialized, both the current maximum value and the current minimum value are zero.

In step 5, if the first sampling is performed after the system is initialized, the average current is equal to the first sampling current value, and flag is 0.

ΔI is 2A to 3A; ΔI ₁ is 0A to 3A; I _chg is _-12A to -6A; I _dchg is 6A to 12A; C _nst is between 1min and 5min; The value of SOC _d is 5% to 10%.

The SOC _now corrected in steps to SOC _i Specifically, the correction per 5% to 10% of the difference in SOC _now and SOC _i.

Before the system is running, it is necessary to establish a database first. The specific process is: on the power battery test bench, the two sets of new batteries with the same specifications and parameters are simultaneously charged and discharged through the dual-channel battery charge and discharge equipment. Record battery SOC value, current, temperature and accumulated Ah data. Through the collation and analysis of experimental data, the corresponding SOC value under different battery temperature, current and voltage, different battery temperature, charge and discharge efficiency η of battery under SOC and attenuation factor λ of battery capacity under different accumulated Ah, λ=( SOC _red ·Ah _use /Ah _pre )/SOC _std , SOC _red is the attenuation of battery capacity when the accumulated Ah number of the battery reaches the expected service life; Ah _use is the current cumulative use of Ah number; Ah _pre is the expected service life of the battery; SOC _std For battery rated capacity. Then, the SOC value corresponding to different battery temperatures, currents, and voltages, and the different battery temperatures, the charge and discharge efficiency η of the battery under SOC, and the attenuation factor λ data of the battery capacity under different accumulated Ah are stored in the battery management system BMS.

The advantages of this program are as follows:

1. Combine the Ah integral algorithm and the battery CCV correction to perform the power battery SOC Estimate. The calculated SOC can accurately reflect the state of charge of the power battery, and avoid the overcharge and over discharge behavior of the power battery under the hybrid mode.

2. In the Ah integral algorithm, the charge and discharge capacities under different SOC, temperature and current are considered, which improves the calculation accuracy of Ah integral and reduces the cumulative error of Ah integral.

3. According to the problem that the battery voltage platform rises and the battery capacity is attenuated due to the aging of the battery, the attenuation factor is proposed and used to correct and compensate the SOC, thereby avoiding the problem that the SOC correction is affected by the battery aging after the battery is used.

4. Develop a 4-dimensional form based on a large amount of experimental data. The table considers the relationship between battery temperature, current, voltage, and SOC. The dynamic CCV correction of the power battery is carried out by looking up the table and interpolating, which further improves the accuracy of the SOC correction.

The specific embodiments described herein are merely illustrative of the spirit of the invention. A person skilled in the art can make various modifications or additions to the specific embodiments described or in a similar manner, without departing from the spirit of the invention or as defined by the appended claims. The scope.

Although terms such as Ah, discharge efficiency, attenuation factor, etc. are used more frequently in this paper, the possibility of using other terms is not excluded. These terms are only used to describe and explain the nature of the invention more conveniently; it is to be construed that any additional limitation is inconsistent with the spirit of the invention.

Claims

A method for estimating a SOC of a power battery for a hybrid vehicle, comprising the steps of:

Step 1. During the operation of the battery management system, calculate the current SOC value by the ampere-time integration method, and record it as SOC now ; collect the current current of the battery through the current sensor, collect the current voltage of the battery through the voltage sensor, collect the battery temperature through the temperature sensor, and then check The table obtains the discharge efficiency η corresponding to the current current, voltage and temperature; obtains the attenuation factor λ of the current accumulated battery capacity under Ah by looking up the table;

Step 2: Calculate the corrected SOC value of the current time of the battery, and calculate the formula as follows:

SOC i = SOC i-1 -△SOC (1)

Where SOC i is the corrected SOC value of the current time battery; SOC i-1 is the corrected SOC value of the battery at the previous time; ΔSOC is the amount of change in the SOC correction value of the battery per unit time, and Δt is the unit sampling time interval. η is the charging and discharging efficiency; I is the current current, defining the positive direction of the current as the discharging direction, and the negative direction is the charging direction, that is, I is positive for battery discharge, I is negative for battery charging; SOC std is for battery rated capacity;

Step 3: update the maximum or minimum value of the current: if the battery is in a discharged state, update the maximum value of current I max ; if the battery is in a charged state, update the minimum value of current I min ;

Step 4: If the current of the sampling current and the direction of the previous sampling current are opposite, let n=1, that is, re-count, and assign the new sampling current value to the average current value, and set flag to 1; if the current is sampled When the value and the last sampled current value are in the same direction, the average current is updated, and the average current is updated as follows: I avg = (I avg '×n+I)/(n+1), and then the value of n is increased by 1, I avg is updated average current, I avg 'original average current, n is the sample number average current affected, flag is a flag;

Step 5: If the difference between the current sampling current value and the average current is less than ΔI, set flag to 0; if the difference between the current sampling current value and the average current is greater than or equal to ΔI, set flag to 1;

Step 6. If flag=1, and the battery is in a discharge condition, and the difference between the maximum value I max of the discharge current and the average current I avg is less than ΔI 1 , and the minimum value I min of the charging current is greater than I chg , and n is greater than C Nst , and the difference between SOC now and SOC i is greater than SOC d , then SOC now is corrected to SOC i in steps; if flag=1, and the battery is in charge, and the minimum value of charging current I min and average current I avg difference is less than ΔI 1 , and the discharge current maximum I max is less than I dchg , and n is greater than C nst , and the difference between SOC now and SOC i is greater than SOC d , then SOC now is corrected to SOC i in steps; If any of the above two conditions is not satisfied, then jump to step one; ΔI 1 , I chg , C nst , SOC d , and I dchg are all preset values.
The SOC estimation method for a hybrid vehicle power battery according to claim 1, wherein in step three, the specific operation of updating the maximum value or the minimum value of the current is: if the battery is in a discharged state, the current current is The stored current maximum value is compared, and the larger value is selected as the new current maximum value I max ; if the battery is in the charging state, the current current is compared with the stored current minimum value, and the smaller value is selected as the new current minimum value I Min ; The maximum current and current minimum are 0 when the system is initialized.
The SOC estimation of a hybrid vehicle power battery according to claim 1 or 2 The calculation method is characterized in that, in the fifth step, if the first sampling is performed after the system is initialized, the average current is equal to the first sampling current value, and the flag is 0.
The SOC estimation method for a hybrid vehicle power battery according to claim 3, wherein ΔI takes a value of 2A to 3A; ΔI 1 takes a value of 0A to 3A; and I chg takes a value of -12A to -6A. The value of I dchg is 6A~12A; the value of C nst is between 1min and 5min; the value of SOC d is 5%~10%.
According to a hybrid vehicle battery SOC estimation method according to claim 1, characterized in that, the SOC will now be corrected to the SOC in steps as the difference I specifically now corrected SOC per SOC I and 5 %~10%.