CN103887853A - Balance control method of lithium-ion battery set - Google Patents

Abstract

The invention discloses a balance control method of a lithium-ion battery set. Internal parameters of each single battery of the battery set and an accurately estimated SOC value serve as the reference quantity of a battery set balance control algorithm; the safety problem possibly caused by overcharging and overdischarging of the battery set is resolved through the balance control scheme, the service life of the battery set is prolonged, and the performance of the battery set is improved. Through the balance control method of the lithium-ion battery set, balance control can be carried out on the work state and performance of the lithium-ion battery set, an active balance control method based on the SOC estimation value is built, and the intelligent balance control method of the lithium-ion battery set is designed through the electronic technique and the computer control technology. The implementation of the balance control method of the lithium-ion battery set has great significance for promoting the popularization of lithium-ion batteries, improving the energy storage capacity and the utilization rate of the lithium-ion battery set, and prolonging the cycle life of the lithium-ion battery set, overcomes the defects of a lithium-ion battery set balance control system, and promotes the application and popularization of the new energy electric car technology based on lithium-ion batteries.

Description

A kind of lithium ion battery group balance control method

Technical field

The present invention relates to a kind of control method, more specifically, it relates to a kind of lithium ion battery group balance control method.

Background technology

New Energy Industry is that national economy is strategic, advanced sector, to spurring economic growth, industry restructuring, promotion industrial repositioning upgrading, break through energy bottleneck constraint and have a very important role.Since nineteen nineties, lithium ion battery is as one of developing direction of New Energy Industry, be subject to more and more domestic and international researchers' attention, and obtain great progress, China is in " 15 " and the Eleventh Five-Year Plan period list key research project in, nearly 1,000,000,000 yuan of funds intensity developing power energy storage lithium ion battery.Be devoted to both at home and abroad at present to study lithium ion battery as auxiliary power source, strive for obtaining more quantum jump at large-scale applied environments such as space flight, military project, renewable energy system energy storage.

Lithium ion battery has following good performance characteristics: voltage is high, specific energy is large, have extended cycle life, security performance is good, self discharge is little, but because lithium ion battery group is modularization, so can involve in actual applications the problem that security performance and battery cycle life etc. are new, if these problems can not get timely solution, it will restrict the application of lithium power battery pack in new-energy automobile.

Summary of the invention

The object of the invention is to overcome deficiency of the prior art, provide a kind of rational in infrastructure, control precision is high, discharges and recharges effective lithium ion battery group balance control method.

This lithium ion battery group balance control method:

Step 1, data processing and monomer SOC calculated value; Calculate the method for residual capacity in conjunction with Ah method, definition lithium-ion battery monomer SOC calculation expression is as follows:

$\mathrm{SOC}\left(t\right)=\mathrm{SOC}\left(t_0\right)+\stackrel{`}{O_{t_0}^t}\frac{\mathrm{hI}\left(t\right)}{{\mathrm{<figure-callout\; id="0"\; label="Q"\; filenames="HDA0000478561670000011.png,HDA0000478561670000041.png"\; state="\{\{state\}\}">Q</figure-callout>}}_0}\mathrm{dt}---\left(1\right)$

In formula, SOC (t) is real-time cell SOC value, SOC (t ₀) be initial SOC value, h is for discharging and recharging coefficient, and I (t) is battery charging and discharging electric current;

Step 1-1, in conjunction with lithium ion battery second-order circuit equivalent model, sets up Mathematical Modeling equation and is:

${\stackrel{\&CenterDot;}{V}}_f=-\frac{1}{R_f{C}_f}{V}_f+\frac{1}{C_f}{I}_B---\left(2\right)$

${\stackrel{\&CenterDot;}{V}}_S=-\frac{1}{R_S{C}_S}{V}_S+\frac{1}{C_S}{I}_B---\left(3\right)$

In formula, R _f, C _fand R _s, C _srepresent respectively polarization parameter and concentration difference parameter, V _fand V _srepresent polarizing voltage and concentration difference voltage;

Step 1-2, obtains internal resistance parameter value accurately by lithium-ion battery tester, draws the dynamic electric voltage calculated value in polarization resistance and concentration difference internal resistance by expression formula (2) and (3);

Step 1-3, the cell voltage obtaining by battery parameter test module, electric current and temperature value, obtain cell SOC dynamic calculation expression formula by expression formula (3):

$V_{\mathrm{SOC}}^{\&CenterDot;}=-\frac{1}{R_{\mathrm{sd}}{C}_b}{V}_{\mathrm{SOC}}+\frac{1}{C_b}{I}_B---\left(4\right)$

In formula, V _sOCfor battery equivalent electric circuit total voltage, it represents the functional relation of SOC value of battery;

Step 1-4, by expression formula (4), monomer battery voltage/current parameters value that integrating step 1-2 measures, calculates real-time cell SOC value;

Step 2, the real-time SOC value of cell of utilizing step 1 to obtain is carried out cell charge and discharge balancing;

Step 2-1, the SOC value obtaining according to step 1 is carried out cell sequence, SOC minimum threshold is set is 0.4 and judge;

Step 2-2, detects the cell quantity n that SOC value is greater than 0.4, if the balanced initialize routine of controlling is carried out in n≤6;

Step 2-3, according to after step 2-2 initialization, calculates SOC value difference value between each cell; Cell SOC value is less than 1 (SOC≤1), and difference is greater than 0.2 (Δ SOC >=0.2), the corresponding relay of unlatching balancing control circuit; Take equalization discharge as example, establish cell SOC value and be respectively SOC (Bi), i=1,2 ..., 6;

(1) calculate adjacent monomer battery SOC difference:

ΔSOC(1,2)＝SOC(B1)-SOC(B2)

ΔSOC(2,3)＝SOC(B2)-SOC(B3)

......

(2) utilize robust filter to judge the difference DELTA SOC (k, k+1) calculating, eliminate pseudo error value; If measuring difference is Δ SOC (i), i=1,2 ... the weight coefficient of 5 differences is { P _i, obtain thresholding computing formula according to least square method:

ΣP _iΔSOC ²(i)＝min

(3) introduce the M estimation criterion in robust computational methods, thresholding computing formula is:

Σρ(ΔSOC(i))＝min

Order

weight factor computing formula is:

(4) recalculate cell SOC value difference value weight coefficient, can obtain

when meeting, least-squares estimation thresholding formula is as follows, can error in judgement value be effective error:

$\mathrm{\&Sigma;}\stackrel{\&OverBar;}{P}\mathrm{\&Delta;}{\mathrm{SOC}}^2\left(i\right)=\min$

(5) reject pseudo error value, if the difference number of Δ SOC (i) >=0.2 is greater than 2, need the cell of balanced discharge more than 3, Δ SOC () is carried out to sequence from big to small, first 2 cells that difference is larger carry out balance policy control;

(6) carry out again the judgement of SOC value size to carrying out 2 cells of balance policy control, if SOC (Bi) is larger, open corresponding relay switch;

(7) other cell of Real-Time Monitoring SOC value and corresponding Δ SOC (), loops judgement until SOC≤0.4 is carried out cell electric discharge or charges and supplement, and completes the object of balance charge/discharge;

Step 2-4, judges whether cycle-index i exceedes battery series connection maximum, if wait for, if not, continue to calculate cell SOC value and SOC difference, carry out the control step of next balanced control switch.

The invention has the beneficial effects as follows: by the inner parameter of batteries monomer battery and the accurate estimation of SOC value, as the reference quantity of battery pack balancing control algolithm; Solve by balanced control program the safety problem that battery pack super-charge super-discharge may bring, improve life-span and the performance of battery pack.The present invention can carry out equilibrium to the operating state of lithium power battery pack, performance and control, and sets up the active equalization control method based on SOC estimated value, adopts electronic technology and Computer Control Technology to design intelligent lithium power battery pack balance control method.The enforcement of invention achievement is for promoting the popularization of lithium dynamical battery, energy storage capability, utilance and the cycle life of raising lithium power battery pack to have important realistic meaning, overcome the shortcoming of lithium power battery pack balance control system simultaneously, promote application and the popularization of the new energy electric motor vehicle technology based on lithium dynamical battery.

Accompanying drawing explanation

Fig. 1 is SOC algorithm for estimating flow chart;

Fig. 2 is the balance module circuit theory diagrams based on SOC;

Fig. 3 is master control program flow chart;

Fig. 4 is that OCV-SOC discharges and recharges matched curve;

Fig. 5 is the voltage-contrast figure of 6 time points of cell (10) discharge test;

Fig. 6 is cell (6) equalizing charge control design sketch.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described further.Although the present invention is described in connection with preferred embodiment, should know, do not represent to limit the invention in described embodiment.On the contrary, the present invention is by alternative, modified model and the equivalent contained in the scope of the present invention that can be included in attached claims restriction.

Battery pack balancing control program:

Step 1, data processing and monomer SOC calculated value.The present invention calculates the method for residual capacity in conjunction with Ah method, definition lithium-ion battery monomer SOC calculation expression is as follows:

$\mathrm{SOC}\left(t\right)=\mathrm{SOC}\left(t_0\right)+\stackrel{`}{O_{t_0}^t}\frac{\mathrm{hI}\left(t\right)}{{\mathrm{<figure-callout\; id="0"\; label="Q"\; filenames="HDA0000478561670000011.png,HDA0000478561670000041.png"\; state="\{\{state\}\}">Q</figure-callout>}}_0}\mathrm{dt}---\left(1\right)$

In formula, SOC (t) is real-time cell SOC value, SOC (t ₀) be initial SOC value, h is for discharging and recharging coefficient, and I (t) is battery charging and discharging electric current.

Step 1-1, the present invention is in conjunction with lithium ion battery second-order circuit equivalent model, sets up Mathematical Modeling equation to be:

${\stackrel{\&CenterDot;}{V}}_f=-\frac{1}{R_f{C}_f}{V}_f+\frac{1}{C_f}{I}_B---\left(2\right)$

${\stackrel{\&CenterDot;}{V}}_S=-\frac{1}{R_S{C}_S}{V}_S+\frac{1}{C_S}{I}_B---\left(3\right)$

In formula, R _f, C _fand R _s, C _srepresent respectively polarization parameter and concentration difference parameter, V _fand V _srepresent polarizing voltage and concentration difference voltage.

Step 1-2, utilizes lithium-ion battery tester to obtain internal resistance parameter value accurately, draws the dynamic electric voltage calculated value in polarization resistance and concentration difference internal resistance by expression formula (2) and (3);

Step 1-3, utilizes outside batteries parameter testing module that the present invention designs as Fig. 3, and the cell voltage, electric current and the temperature value that obtain, obtain cell SOC dynamic calculation expression formula by expression formula (3):

$V_{\mathrm{SOC}}^{\&CenterDot;}=-\frac{1}{R_{\mathrm{sd}}{C}_b}{V}_{\mathrm{SOC}}+\frac{1}{C_b}{I}_B---\left(4\right)$

In formula, V _sOCfor battery equivalent electric circuit total voltage, it represents the functional relation of SOC value of battery.

Step 1-4, by expression formula (4), monomer battery voltage/current parameters value that integrating step 1-2 measures, calculates real-time cell SOC value.

Step 2, the real-time SOC value of cell of utilizing step 1 to obtain is carried out cell charge and discharge balancing, realizes general flow chart as shown in Figure 1, and equalizing circuit hardware circuit diagram is as shown in Figure 2.

Step 2-1, Fig. 1 shows, the SOC value obtaining according to step 1 is carried out cell sequence, SOC minimum threshold is set is 0.4 and judge.

Step 2-2, detects the cell quantity n that SOC value is greater than 0.4, if the balanced initialize routine of controlling is carried out in n≤6.

Step 2-3, according to after step 2-2 initialization, calculates SOC value difference value between each cell.Cell SOC value is less than 1 (SOC≤1), and difference is greater than 0.2 (Δ SOC >=0.2), the corresponding relay of unlatching balancing control circuit, switch S 1-S6 as shown in Figure 2.Take equalization discharge as example, suppose that cell SOC value is respectively SOC (Bi), i=1,2 ..., 6.

(1) calculate adjacent monomer battery SOC difference:

ΔSOC(1,2)＝SOC(B1)-SOC(B2)

ΔSOC(2,3)＝SOC(B2)-SOC(B3)

......

(2) utilize robust filter to judge the difference DELTA SOC (k, k+1) calculating, eliminate pseudo error value.Suppose that measuring difference is Δ SOC (i), i=1,2 ... the weight coefficient of 5 differences is { P _i, obtain thresholding computing formula according to least square method:

ΣP _iΔSOC ²(i)＝min

(3) introduce the M estimation criterion in robust computational methods, thresholding computing formula is:

Σρ(ΔSOC(i))＝min

Order

weight factor computing formula is:

(4) recalculate cell SOC value difference value weight coefficient, can obtain when meeting, least-squares estimation thresholding formula is as follows, can error in judgement value be effective error:

$\mathrm{\&Sigma;}\stackrel{\&OverBar;}{P}\mathrm{\&Delta;}{\mathrm{SOC}}^2\left(i\right)=\min$

(5) reject pseudo error value, if the difference number of Δ SOC (i) >=0.2 is greater than 2, need the cell of balanced discharge more than 3, Δ SOC () is carried out to sequence from big to small, first 2 cells that difference is larger carry out balance policy control;

(6) carry out again the judgement of SOC value size to carrying out 2 cells of balance policy control, if SOC (Bi) is larger, open relay switch Si (i=1,2 ..., 6), open K0 simultaneously, and in succession open K1-K3 according to external voltage and capacity requirement;

(7) other cell of Real-Time Monitoring SOC value and corresponding Δ SOC (), loops judgement until SOC≤0.4 is carried out cell electric discharge or charges and supplement, and completes the object of balance charge/discharge.

Step 2-4, according to Fig. 2 and step 2-3, the basis that the monomer SOC value of calculating based on filter is balanced control procedure, three relay switches of strategy major control, cell connecting valve S1-S6, discharge resistance connecting valve K0, output total voltage control switch K1-K4.

Step 2-5, judges whether cycle-index i exceedes battery series connection maximum, if wait for, if not, continue to calculate cell SOC value and SOC difference, carry out the control step of next balanced control switch.

Be illustrated in figure 1 SOC algorithm for estimating flow chart:

(1) balanced control hardware circuit and control program mainly design according to cell SOC value, and control the start and stop of relevant relay, and workflow is as follows:

(2) battery pack is started working, and waits for that cell discharges and recharges Warning Mark, judges whether normal work according to cell size of current;

(3) if without Warning Mark, continue to wait for, if battery normally discharges and recharges work, utilize three parameters of battery to carry out cell SOC value and estimate, and sort according to the SOC value of each battery;

(4) loop initialization number of times i=0, for judging the open and close number of times of balanced control switch;

(5) judge whether cycle-index i exceedes battery series connection maximum, if wait for, if not, continue to calculate the SOC value between cell;

(6) cell SOC value is greater than 1, and difference is greater than 0.2, opens the corresponding relay of balancing control circuit, discharges or charge supplementaryly, completes the object of balance charge/discharge.

Be illustrated in figure 2 balanced control decision module and discharge and recharge and control protection hardware circuit diagram:

This modular circuit comprises relay switch Si, DC/DC voltage inverter, balanced discharge network and power-off protecting circuit.According to the actual characteristic of monomer lithium ion battery, that the present invention has designed is with low cost, be convenient to the composite balancing control hardware circuit that industrialization realizes.

(1) composition: relay network, discharge resistance network, balanced DC/DC power supply voltage converter that equalizing circuit is mainly made up of relay switch form.

(2) operation principle: the control signal obtaining according to the balanced control decision module of higher level, control 10 monomer lithium ion batteries and whether discharge and recharge in hardware circuit.

(3) innovative point: take real-time cell SOC value as basis, to discharge strategy, equalizing resistance control of discharge strategy, three control modules of output voltage control strategy as prerequisite based on battery cell SOC value, reach the object of 10 monomer lithium ion battery balance charge/discharges, improve battery pack gross power, extending battery life.Resistance R is as balanced discharge resistance, and switch ki control inputs, to the total voltage of DC/DC inverter, finally offers load as general supply.

Be illustrated in figure 3 master control program module scheme, main control module scheme practical function is as follows:

(1) initialization collector, equalizing circuit and main control chip, gathers battery current, voltage and temperature data;

(2) according to the battery cell voltage/current state information gathering, judge battery current state, if battery current is not equal to 0, can judge battery operatedly at charging and discharging state, carry out the SOC numerical computations based on Ah method of estimation;

(3) discharge and recharge under operating state, continue to judge electric current, if be greater than 0, battery operated in discharge condition, if be less than 0, battery operated middle charged state;

(4) according to the SOC value of battery of the battery cell information, loop current size and the real-time estimation that gather, under batteries charging or discharge condition, determine whether to open balanced control algolithm, thereby realize charging, electric discharge achieve effective control and the management of battery, guarantee the use safely and efficiently of battery;

(5) utilizing SPI communication module and CAN communication module to carry out host computer communicates by letter.

The test of actual battery group balance control method:

Step 1, sets up lithium ion battery external parameter computation model, discharges and recharges experiment current value I is set _b=1500mA (discharge-rate is 1C).

Step 1-1, according to dynamic end voltage tester data, battery charging and discharging capacity numerical value, the MATLAB curve that utilizes experimental data to carry out based on least square obtains second-order equation matching, and Fig. 4 is charging curve comparison diagram and discharge curve comparison diagram.Simulation parameter is calculated as follows, the wherein parameter a OCV-SOC parameter fitting result that represents to discharge, and the parameter b OCV-SOC parameter fitting result that represents to charge, can try to achieve fit equation suc as formula shown in (5) and (6).

a＝36.1425-198.4752?263.2273

b＝1.0e+003*0.9296-5.5797?8.3471

Electric discharge: V _oC(SOC)=36.1425-198.472SOC+263.2273SOC ²(5)

Charging: V _oC(SOC)=929.6-5579.7SOC+8347.1SOC ²(6)

SOC=[0-1], OCV is mV unit.

Step 1-2, according to repeatedly discharging and recharging experiment, chooses wherein three secondary data and utilizes lithium-ion battery tester, obtains the Ohmic resistance R of equivalent-circuit model ₀, polarization parameter R _f, C _fwith concentration difference parameters R _s, C _sbe worth as follows:

(1) discharge cycle parameter value for the first time:

R ₀＝(3.3779-3.3333)V/0.75A＝0.0446V/0.75A＝0.0595Ω

R _f＝91.23mW，R _s＝84.17mW

(2) discharge cycle parameter value for the second time:

R ₀＝(3.3537-3.3097)/0.75A＝0.044V/0.75A＝0.0587Ω

R _f＝74.81mW，R _s＝78.52mW

(3) discharge cycle parameter value for the third time:

R ₀＝(3.3469-3.3026)/0.75A＝0.0443V/0.75A＝0.0590Ω

R _f＝63.85mW，R _s＝70.23mW

(4) discharge and recharge cycle parameter mean value:

Time constant t _f=[78.50s, 85.23s, 83.16s] t _s=[585.8s, 641.3s, 627.6s]

Concentration polarization internal resistance:

Electric current/concentration polarization resistance product R _fc _f=[68.42536,56.1043,47.8860]

Electric current/electrochemical polarization resistance product R _sc _s=[63.1276,58.8902,52.6750]

Resistance parameter R ₀=59.1m Ω, R _f=76.63mW, R _s=77.64mW

Step 2, cell SOC dynamic estimation value, discharges and recharges experiment current value I is set _b=3000mA (discharge-rate is 1C).Step 2-1, according to equivalent circuit theory and expression formula (2) and (3), release cell terminal voltage expression formula is:

V _B＝V _OC(SOC)-R ₀I _B-V _f-V _S

Step 2-2, the real-time cell voltage, electric current and the temperature value that record according to cell tester, integrating step 1 is calculated Inside Parameter Value, expression formula (5) and (6), obtains SOC estimated value as table 1:

Table 12C discharge test ohmic internal resistance/voltage/SOC relation data

Step 3, the equilibrium control based on SOC value

The real-time SOC value of cell of utilizing step 2-2 to obtain sorts to battery, SOC minimum threshold is set is 0.4 and judge, implements the balanced control program that the present invention proposes.

Fig. 5 represents that battery pack balancing discharges and recharges the magnitude of voltage of 6 time points of cell.Experiment arranges electric discharge 10min, leaves standstill 5min, and charging 10min, as a charge and discharge cycles.Get 10 battery samples, at t ₀, t ₁, t ₂, t ₃, t ₄, t ₅6 time points carry out the measurement of battery terminal voltage, obtain drawing a conclusion:

(1) before electric discharge starts, cell initial voltage V (t ₀) there are differences, battery #2 terminal voltage maximum (3.43V), battery #7 voltage minimum (3.35V), difference maximum is 80mV;

(2) electric discharge starting point voltage V (t ₁+), battery #2 terminal voltage maximum (3.198V), battery #2 terminal voltage minimum (2.988V), difference maximum is 200mV;

(3) electric discharge voltage V (t in mid-term ₂) and electric discharge voltage V (t in latter stage ₃-), cell terminal voltage difference maximum is respectively 100mV and 80mV, and along with the work of balance controller, battery discharge terminal voltage is tending towards identical as seen;

(4) electric discharge voltage V (t in latter stage ₄) and standing period voltage V (t ₅), maximum difference only has 5mV-10mV left and right, represents that the accuracy of equalization of the equalizing circuit cell of the present invention's design can reach 5mV-20mV.

Fig. 6 represents in 6 cell equalizing charge control procedures, voltage curve.Abscissa is time (0-500s), and ordinate is cell terminal voltage value.In figure, curve and data are known, and the charging initial stage, 6 monomer battery voltage values existed notable difference; Along with the prolongation in charging interval, balance control system carries out charge balancing control according to the real-time SOC value of cell, reaches the object that cell terminal voltage difference reduces; About in the time of charging 350s, 6 cell terminal voltage difference minimums; Charging end time section, battery terminal voltage moment rises, and occurs voltage differences, and 3 batteries converge on 4.0V left and right, and 3 batteries converge on 3.8V left and right.Illustrate that equalizing circuit hardware designs and equalization algorithm have good control effect for discharging and recharging under lithium ion battery normal operating conditions.

The technical indicator drawing:

(1) electronic load

Power bracket: 10KW current range: 50A, 100A, 200A, 400A, 1000A voltage range: 100V, 200V, 400V

(2) battery capacity and SOC estimation precision

Range of capacity: 1.5Ah～15Ah SOC estimated accuracy: 5%

(3) monomer battery voltage protection

Cell under-voltage protection value: 2.75V cell overvoltage protection value: 3.9V or 4.25V

(4) cell overcurrent protection value

3A (can recover)

(5) cell parameter measurement precision

Voltage control precision: 0.5%FS Current Control precision: 0.5%FS

(6) battery pack balancing control

Battery balanced precision: 5mV-20mV cell euqalizing current: 1.5A (MAX15A)

(7) battery pack temperature control

Battery pack temperature protection value: 65 ℃ of nominal operation ambient temperatures :-20 ℃～50 ℃

Nominal operation envionmental humidity: <80%.

Claims (1)

1. a lithium ion battery group balance control method, is characterized in that:

Step 1, data processing and monomer SOC calculated value; Calculate the method for residual capacity in conjunction with Ah method, definition lithium-ion battery monomer SOC calculation expression is as follows:

In formula, SOC (t) is real-time cell SOC value, SOC (t ₀) be initial SOC value, h is for discharging and recharging coefficient, and I (t) is battery charging and discharging electric current;

Step 1-1, in conjunction with lithium ion battery second-order circuit equivalent model, sets up Mathematical Modeling equation and is:

In formula, R _f, C _fand R _s, C _srepresent respectively polarization parameter and concentration difference parameter, V _fand V _srepresent polarizing voltage and concentration difference voltage;

Step 1-2, obtains internal resistance parameter value accurately by lithium-ion battery tester, draws the dynamic electric voltage calculated value in polarization resistance and concentration difference internal resistance by expression formula (2) and (3);

Step 1-3, the cell voltage obtaining by battery parameter test module, electric current and temperature value, obtain cell SOC dynamic calculation expression formula by expression formula (3):

In formula, V _sOCfor battery equivalent electric circuit total voltage, it represents the functional relation of SOC value of battery;

Step 1-4, by expression formula (4), monomer battery voltage/current parameters value that integrating step 1-2 measures, calculates real-time cell SOC value;

Step 2, the real-time SOC value of cell of utilizing step 1 to obtain is carried out cell charge and discharge balancing;

Step 2-1, the SOC value obtaining according to step 1 is carried out cell sequence, SOC minimum threshold is set is 0.4 and judge;

Step 2-2, detects the cell quantity n that SOC value is greater than 0.4, if the balanced initialize routine of controlling is carried out in n≤6;

Step 2-3, according to after step 2-2 initialization, calculates SOC value difference value between each cell; Cell SOC value is less than 1 (SOC≤1), and difference is greater than 0.2 (Δ SOC >=0.2), the corresponding relay of unlatching balancing control circuit; Take equalization discharge as example, establish cell SOC value and be respectively SOC (Bi), i=1,2 ..., 6;

(1) calculate adjacent monomer battery SOC difference:

ΔSOC(1,2)＝SOC(B1)-SOC(B2)

ΔSOC(2,3)＝SOC(B2)-SOC(B3)

......

(2) utilize robust filter to judge the difference DELTA SOC (k, k+1) calculating, eliminate pseudo error value; If measuring difference is Δ SOC (i), i=1,2 ... the weight coefficient of 5 differences is { P _i, obtain thresholding computing formula according to least square method: Σ P _iΔ SOC ²(i)=min

(3) introduce the M estimation criterion in robust computational methods, thresholding computing formula is: Σ ρ (Δ SOC (i))=min

Order

weight factor computing formula is:

(4) recalculate cell SOC value difference value weight coefficient, can obtain when meeting, least-squares estimation thresholding formula is as follows, can error in judgement value be effective error:

(5) reject pseudo error value, if the difference number of Δ SOC (i) >=0.2 is greater than 2, need the cell of balanced discharge more than 3, Δ SOC () is carried out to sequence from big to small, first 2 cells that difference is larger carry out balance policy control; (6) carry out again the judgement of SOC value size to carrying out 2 cells of balance policy control, if SOC (Bi) is larger, open corresponding relay switch;

(7) other cell of Real-Time Monitoring SOC value and corresponding Δ SOC (), loops judgement until SOC≤0.4 is carried out cell electric discharge or charges and supplement, and completes the object of balance charge/discharge;

Step 2-4, judges whether cycle-index i exceedes battery series connection maximum, if wait for, if not, continue to calculate cell SOC value and SOC difference, carry out the control step of next balanced control switch.

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