CN102540096B - Self-correction method for remaining capacity estimation of lithium iron phosphate power battery - Google Patents

Abstract

The invention discloses a self-correction method for remaining capacity estimation of a lithium iron phosphate power battery. The conventional method cannot meet national standard well. According to the self-correction method disclosed by the invention, compensation and correction are performed on the basis of estimating the remaining capacity of the lithium iron phosphate power battery by using an ampere-hour method; and according to the characteristic that voltage of the lithium iron phosphate power battery abruptly changes at the end stage of charging or discharging, the actual remaining capacity SOC (State Of Charge) is corrected when dV/dSOC' is detected to be greater than or equal to 0.05, so that accumulative estimation error existing during independent use of the ampere-hour method is reduced. The self-correction method is based on the ampere-hour method, is simple and easy and is easier to apply and generalize. Meanwhile, the invention also provides a calculation method of aging rate gamma. By continuously updating the aging rate, the error for estimation by using the ampere-hour method is reduced again.

Description

A kind of method for residual capacity of iron-lithium phosphate power cell estimation self-correction

Technical field

The invention belongs to chemical energy source applied technical field, be specifically related to a kind of method for residual capacity of iron-lithium phosphate power cell estimation self-correction.

Background technology

Outstanding along with the enhancing of global environmental consciousness and energy problem, electric automobile has become the topmost developing direction of Green Vehicle.The electrokinetic cell that is applied at present electric automobile mainly contains lead-acid battery, Ni-MH battery and lithium ion battery, respectively has relative merits.Lithium iron phosphate dynamic battery is long owing to having the life-span, uses safety, and electric current fast charging and discharging, high temperature resistant greatly, large capacity, and the advantages such as memory-less effect can better meet the requirement of electric automobile to on-vehicle battery, and are applied rapidly and promote.

Battery dump energy claims that again the state-of-charge (State of Charge, i.e. SOC) of battery is one of major parameter of battery status, for the control strategy of electric automobile whole provides foundation.Ensure that SOC maintains in rational scope, prevent owing to overcharging or the damage of overdischarge to battery, thereby forecast that at any time electric automobile energy-storage battery also remains the state-of-charge of how many energy or energy-storage battery, for we rationally utilize battery, improve battery, reducing maintenance cost provides technique direction.How accurately to obtain reliably again battery remaining power is in battery intelligent management system, to be substantially the most also most important task.

At present aspect the accurate estimation of battery remaining power, doing many research both at home and abroad, conventional method mainly contains: ampere-hour integral method, open-circuit voltage method, fuzzy neural network method and Kalman filtering method etc.

Ampere-hour integral method is to estimate the SOC of battery by calculating the accumulation electric weight of battery when the charge or discharge.Ampere-hour method is current most widely used general, the most simple method for estimating remaining capacity.But the SOC that the method obtains estimates to exist larger cumulative errors.

Open-circuit voltage method is to utilize the dull corresponding relation of the open-circuit voltage of battery and the SOC of battery, sets up residual capacity (SOC)--the relation curve between open-circuit voltage (OCV), estimate SOC value by the open-circuit voltage of measuring battery.The method is measured stricter to SOC-OCV relation, be only suitable for SOC and change obvious battery with OCV.

Fuzzy neural network method is to rely on a large amount of sample datas to train the fuzzy neural network model of building up, this method is larger to the dependence of training method and training data, domestic and international most achievements rest on the Computer Simulation stage at present, also have certain distance from concrete practical application.

Kalman filtering method is that the state of power system is made to the optimal estimation in minimum variance meaning, but the method needs a large amount of calculating.

Lithium iron phosphate dynamic battery is owing to having very smooth charge and discharge platform, and the SOC of battery management system needs precision high, and be real-time On-line Estimation, the remaining capacity calculation method relevant with open-circuit voltage method is just no longer applicable to lithium iron phosphate dynamic battery so.And the control strategy of electric automobile is to adjust at any time according to the SOC of electric battery, current SOC value all must be provided at any time accurately, this just needs to have cumulative errors, and national standard requires error to be no more than 8% at present, and the method for estimation of prior art is not easy to meet.

Summary of the invention

The object of the invention is for the deficiency existing in prior art, a kind of method that can estimate more accurately residual capacity of iron-lithium phosphate power cell is provided.

The inventive method, detect and obtain at a time temperature T, electric current I and the magnitude of voltage V of t of lithium iron phosphate dynamic battery by external circuit, in conjunction with the reference residual capacity SOC ' being obtained by ampere-hour method, when detect dV/d SOC '>=0.05 time, to real surplus capacity, SOC revises, and completes ageing rate in the makeover process that carries out residual capacity simultaneously renewal.

The concrete implementation step of the inventive method is as follows:

Step (1). whole charge and discharge process adopts ampere-hour method lithium iron phosphate dynamic battery to be carried out to the estimation of residual capacity, and the reference residual capacity being estimated by ampere-hour method is designated as SOC ';

Step (2). carve at a time t according to lithium iron phosphate dynamic battery and detect the temperature T obtaining, the relation curve of controlled temperature and capacity, calculates current temperature factor of influence α, carries out temperature compensation;

Step (3). carve at a time t according to lithium iron phosphate dynamic battery and detect the electric current I obtaining, bring formula (1) into, calculate charge-discharge magnification factor of influence β, carry out the compensation of charge-discharge magnification.

（1）

Wherein, n is the constant relevant to lithium iron phosphate dynamic battery type, I ₀it is lithium iron phosphate dynamic battery rated current;

Step (4). in charge and discharge process, if dV/dSOC '>=0.05 detecting, implementation step (5) (7); If the dV/dSOC ' < detecting 0.05, implementation step (8); Wherein dV/dSOC ' is the rate of change of wire-end voltage with respect to the reference residual capacity of ampere-hour method estimation;

Step (5). when dV/dSOC '>=0.05 detecting in lithium iron phosphate dynamic battery charging process, and while obtaining SOC ' >10% by ampere-hour method, this t ₁under state, real surplus capacity SOC is once revised as follows:

（2）

（3）

Now SOC ₁substitute the reference residual capacity SOC ' being calculated by ampere-hour method, record the now value of SOC ' simultaneously, be designated as SOC ' ₀, wherein SOH is lithium iron phosphate dynamic battery health status, SOC ₁t ₁the residual capacity of corresponding lithium iron phosphate dynamic battery under state, SOH ₁t ₁the health status of lithium iron phosphate dynamic battery under state;

Step (6). when dV/dSOC '>=0.05 detecting in lithium iron phosphate dynamic battery discharge process, and while obtaining SOC ' <10% by ampere-hour method, this t ₂under state, real surplus capacity SOC is once revised as follows:

（4）

Now SOC ₂substitute the reference residual capacity SOC ' being calculated by ampere-hour method, record the now value of SOC ' simultaneously, be designated as SOC ' ₀, wherein, SOC ₂t ₂the residual capacity of corresponding lithium iron phosphate dynamic battery under state, SOH ₂t ₂the health status of lithium iron phosphate dynamic battery under state;

Step (7). in the use procedure of lithium iron phosphate dynamic battery, in the time of step (5) or step (6) generation, carrying out the real surplus capacity of lithium iron phosphate dynamic battery after revising for the n time is SOC _n, in conjunction with last to residual capacity SOC _n-1correction, can upgrade as follows ageing rate:

（5）

(6)

Calculate thus the ageing rate γ after renewal _n+1, and replace previous ageing rate γ _n, skip to step (9); The initial value γ of ageing rate ₀, γ ₁be 100%;

Step (8). the ageing rate of lithium iron phosphate dynamic battery is not upgraded, and continues the ageing rate before continuing to use;

Step (9). determine the value of ageing rate γ, carry out the compensation of ageing rate;

Step (10). export revised real surplus capability value SOC.

Compare existing evaluation method, the inventive method beneficial effect is as follows:

1, the inventive method is based on ampere-hour method, simple, is more easily applied and promotes.

2, the inventive method is in the charge and discharge process of battery, when detect dV/dSOC ' >=0.05 time, to residual capacity, SOC revises, so because using separately the SOC cumulative errors of the continuous increase that ampere-hour method exists, almost negligible in the method.

3, the inventive method has proposed a kind of new ageing rate computing method, and a difficult problem of having avoided cycle index to be difficult to define, by constantly ageing rate being upgraded, has been dwindled the error that the estimation of ampere-hour method exists again.

Brief description of the drawings

Fig. 1 is the discharge curve under the different discharge-rates of certain lithium iron phosphate dynamic battery under room temperature;

Fig. 2 is the charging and discharging curve under certain multiplying power of certain lithium iron phosphate dynamic battery under room temperature;

Fig. 3 is that under room temperature, under the different discharge-rates of certain lithium iron phosphate dynamic battery, voltage is relatively and the image of residual capacity rate of change;

Fig. 4 is that under room temperature, voltage is relatively and the image of residual capacity rate of change when the charging of certain lithium iron phosphate dynamic battery;

The process flow diagram of Fig. 5 the inventive method estimation residual capacity of iron-lithium phosphate power cell.

Embodiment

Below in conjunction with accompanying drawing, the inventive method is described further.

The inventive method comprises the steps: as shown in Figure 5

Step (1). the value initialization to real surplus capacity SOC: taking the rated capacity C of lithium iron phosphate dynamic battery as reference value;

Step (2). whole charge and discharge process adopts ampere-hour method lithium iron phosphate dynamic battery to be carried out to the estimation of residual capacity, and the reference residual capacity being estimated by ampere-hour method is designated as SOC ';

Step (3). under different temperatures, lithium iron phosphate dynamic battery is carried out to charge-discharge test, construct the relation curve of lithium iron phosphate dynamic battery temperature and capacity, carve at a time t according to lithium iron phosphate dynamic battery and detect the temperature T obtaining, the relation curve of controlled temperature and capacity, calculate current temperature factor of influence α, carry out temperature compensation;

Step (4). carve at a time t according to lithium iron phosphate dynamic battery and detect the electric current I obtaining, bring formula (1) into, calculate charge-discharge magnification factor of influence β, carry out the compensation of charge-discharge magnification;

（1）

Wherein, n is the constant relevant to lithium iron phosphate dynamic battery type, can be according to formula calculate, K is the constant relevant with active matter quality, is discharged the needed time according to battery under two kinds of electric currents, calculates the value of n, I ₀be lithium iron phosphate dynamic battery rated current, and then calculate the charge-discharge magnification factor of influence β under certain moment t electric current I, be illustrated in figure 1 the discharge curve of certain lithium iron phosphate dynamic battery under several different discharge-rates under room temperature;

Step (5). in charge and discharge process, if dV/dSOC '>=0.05 detecting, implementation step (6) (8), if the dV/dSOC ' < detecting 0.05, implementation step (9), wherein dV/dSOC ' is the rate of change of wire-end voltage V with respect to the reference residual capacity SOC ' of ampere-hour method estimation;

Fig. 2 is the charging and discharging curve that under room temperature, certain lithium iron phosphate dynamic battery charging or discharging current is 7.5A, dV/dSOC '=0.05 o'clock, t ₁state and t ₂state institute correspondence position as shown in Figure 2.Fig. 3 and Fig. 4 are derived function (the relative rate of change with residual capacity SOC ' of the voltage V) image of certain lithium iron phosphate dynamic battery discharge curve under room temperature and the derived function image of charging curve, in charging latter stage and electric discharge dV/dSOC ' sharp increase in latter stage, the inventive method is carried out the estimation of residual capacity just based on this feature of lithium iron phosphate dynamic battery.

Step (6). when dV/dSOC '>=0.05 detecting in lithium iron phosphate dynamic battery charging process, and while obtaining SOC ' >10% by ampere-hour method, this moment t ₁under state, real surplus capacity SOC is once revised as follows:

（2）

（3）

Now SOC ₁substitute the reference residual capacity SOC ' being estimated by ampere-hour method, record the now value of SOC ' simultaneously, be designated as SOC ' ₀, wherein SOH is lithium iron phosphate dynamic battery health status, SOC ₁state t ₁the residual capacity of lower corresponding lithium iron phosphate dynamic battery, SOH ₁state t ₁the health status of lower lithium iron phosphate dynamic battery;

Step (7). when dV/dSOC '>=0.05 detecting in lithium iron phosphate dynamic battery discharge process, and while obtaining SOC ' <10% by ampere-hour method, this moment t ₂under state, real surplus capacity SOC is once revised as follows:

（4）

Now SOC ₂substitute the reference residual capacity SOC ' being calculated by ampere-hour method, record the now value of SOC ' simultaneously, be designated as SOC ' ₀, wherein, SOC ₂state t ₂the residual capacity of lower corresponding lithium iron phosphate dynamic battery, SOH ₂state t ₂the health status of lower lithium iron phosphate dynamic battery;

Step (8). in the use procedure of lithium iron phosphate dynamic battery, in the time of step (6) or step (7) generation, carrying out the real surplus capacity of lithium iron phosphate dynamic battery after revising for the n time is SOC _n, in conjunction with last to residual capacity SOC _n-1correction, can upgrade as follows ageing rate:

（5）

(6)

Calculate thus current ageing rate γ _n+1, and replace previous ageing rate γ _n, skip to step (10); The initial value γ of ageing rate γ ₀, γ ₁be 100%;

Step (9). the ageing rate of lithium iron phosphate dynamic battery is not upgraded, and continues the ageing rate before continuing to use;

Step (10). determine the value of ageing rate γ, carry out the compensation of ageing rate;

Step (11). export revised real surplus capability value SOC.

Claims (1)

1. for a method for residual capacity of iron-lithium phosphate power cell estimation self-correction, it is characterized in that comprising the steps:

Step (1). whole charge and discharge process adopts ampere-hour method lithium iron phosphate dynamic battery to be carried out to the estimation of residual capacity, and the reference residual capacity being estimated by ampere-hour method is designated as SOC ';

Step (2). carve at a time t according to lithium iron phosphate dynamic battery and detect the temperature T obtaining, the relation curve of controlled temperature and capacity, calculates current temperature factor of influence α, carries out temperature compensation;

Step (3). carve at a time t according to lithium iron phosphate dynamic battery and detect the electric current I obtaining, bring formula (1) into, calculate charge-discharge magnification factor of influence β, carry out the compensation of charge-discharge magnification;

$\mathrm{\&beta;}={\left(I_{0/I}\right)}^n---\left(1\right)$

Wherein, n is the constant relevant to lithium iron phosphate dynamic battery type, I ₀it is lithium iron phosphate dynamic battery rated current;

Step (4). in charge and discharge process, if dV/dSOC ' >=0.05 detecting, implementation step (5)～(7); If the dV/dSOC ' < detecting 0.05, implementation step (8); Wherein dV/dSOC ' is the rate of change of wire-end voltage with respect to the reference residual capacity of ampere-hour method estimation;

Step (5). when dV/dSOC '>=0.05 detecting in lithium iron phosphate dynamic battery charging process, and while obtaining SOC ' >10% by ampere-hour method, this t ₁under state, real surplus capacity SOC is once revised as follows:

SOH＝α×β×γ（2）

SOC＝SOC ₁＝SOH ₁×98%（3）

Now SOC ₁substitute the reference residual capacity SOC ' being calculated by ampere-hour method, record the now value of SOC ' simultaneously, be designated as SOC ' ₀, wherein SOH is lithium iron phosphate dynamic battery health status, SOC ₁t ₁the residual capacity of corresponding lithium iron phosphate dynamic battery under state, SOH ₁t ₁the health status of lithium iron phosphate dynamic battery under state;

Step (6). when dV/dSOC '>=0.05 detecting in lithium iron phosphate dynamic battery discharge process, and while obtaining SOC ' <10% by ampere-hour method, this t ₂under state, real surplus capacity SOC is once revised as follows:

SOC＝SOC ₂＝SOH ₂×5%（4）

Now SOC ₂substitute the reference residual capacity SOC ' being calculated by ampere-hour method, record the now value of SOC ' simultaneously, be designated as SOC ' ₀, wherein, SOC ₂t ₂the residual capacity of corresponding lithium iron phosphate dynamic battery under state, SOH ₂t ₂the health status of lithium iron phosphate dynamic battery under state;

Step (7). in the use procedure of lithium iron phosphate dynamic battery, in the time of step (5) or step (6) generation, carrying out the real surplus capacity of lithium iron phosphate dynamic battery after revising for the n time is SOC _n, in conjunction with last to residual capacity SOC _n-1correction, can upgrade as follows ageing rate:

${\mathrm{SOC}}_n\&times;{\mathrm{\&gamma;}}_{n+1}/{\mathrm{\&gamma;}}_n-{\mathrm{SOC}}_{n-1}\&times;{\mathrm{\&gamma;}}_n/{\mathrm{\&gamma;}}_{n-1}={{\mathrm{SOC}}^{\&prime;}}_0$

$\mathrm{\&gamma;}={\mathrm{\&gamma;}}_{n+1}={\mathrm{SOC}}_{n-1}\&times;{\mathrm{\&gamma;}}_n\&times;{\mathrm{\&gamma;}}_n/{\mathrm{SOC}}_n\&times;{\mathrm{\&gamma;}}_{n-1}+{{\mathrm{SOC}}^{\&prime;}}_0\&times;{\mathrm{\&gamma;}}_n/{\mathrm{SOC}}_n---\left(6\right)$

Calculate thus the ageing rate γ after renewal _n+1, and replace previous ageing rate γ _n, skip to step (9); The initial value γ of ageing rate ₀, γ ₁be 100%;

Step (8). the ageing rate of lithium iron phosphate dynamic battery is not upgraded, and continues the ageing rate before continuing to use;

Step (9). determine the value of ageing rate γ, carry out the compensation of ageing rate;

Step (10). export revised real surplus capability value SOC.