CN102645638A - SOC (Stress Optical Coefficient) estimating method of lithium battery pack - Google Patents

Abstract

The invention relates to an SOC (Stress Optical Coefficient) estimating method of a lithium battery pack. The SOC estimating method of the lithium battery pack comprises the following steps of judging whether the balance of a battery balance management system of a battery to be measured is powered on, if the balance is not powered on, calculating the SOC of the battery according to a charge/discharge current of the battery; if the battery is at the balance state, the current flowing through the battery is calculated according to the balance direction and the balance current of the battery, and calculating the SOC of a single battery according to the current flowing through the battery. The method has the beneficial effects that the current flowing through the battery is calculated by using the balance management system of the battery group and according to the charge/discharge current of the battery, the battery balance direction of the battery and the balance current, and the current value is used as the basis for calculating the SOC value of the battery; and the SOC value of the balance battery can be estimated accurately.

Description

A kind of lithium battery group SOC evaluation method

Technical field

The present invention relates to a kind of lithium battery group SOC evaluation method.

Background technology

In order to reduce environmental pollution and to alleviate serious day by day lack of energy problem, but lithium battery just progressively is applied to a plurality of fields such as electric motor car, energy storage and compact power as a kind of clean energy resource of second use.Country's 12 planning also develop new energy technology as main project.From consideration, need supporting battery management system that the parameters such as voltage, temperature, charging and discharging currents and SOC of lithium battery are monitored in real time in actual use to lithium battery self character and secure context.Yet the complicated characteristic of battery itself makes battery have inconsistency, will show certain " short slab effect " in the battery use.In the battery set charge/discharge process, the charging and discharging capabilities of electric battery will show with the most weak battery, in order to address this problem, improves the overall performance of electric battery, a kind ofly arises at the historic moment with balanced battery management system.Because the influence of euqalizing current, the SOC estimation of cell is particularly important.Existing SOC evaluation method mainly contains open-circuit voltage method, ampere-hour integral method, Kalman filtering method etc., and wherein the most frequently used is the ampere-hour integral method.In the lithium battery management system of this band equalization function, conventional ampere-hour integral method can not meet the demands.

Summary of the invention

The objective of the invention is to solve the current battery group and cause problem owing to euqalizing current influences the error of battery SOC estimation at charge and discharge process.

The present invention provides a kind of lithium battery group SOC evaluation method for solving the problems of the technologies described above, and the step of this lithium battery group SOC evaluation method is following:

1). whether the cell of judging the mesuring battary group is at equilibrium, and if not at equilibrium, rated capacity and its SOC of charging and discharging currents calculating according to battery if this battery is at equilibrium, then get into step 2);

2). the electric current of crossing this battery according to the equilibrium direction and the euqalizing current calculated flow of battery;

3). according to electric current that flows through this battery and rated capacity, calculate the SOC of this cell;

4). repeat above-mentioned steps 1), 2) and 3), the SOC of all cells in calculating this electric battery;

5). the SOC value of each cell in the electric battery relatively, find out the cell of SOC value minimum, with the SOC value of this cell SOC value as this electric battery.

Need to judge earlier the equilibrium direction of battery when said step 2) calculated flow is crossed the electric current of battery; If the equilibrium direction of this cell is inside; The electric current that then flows through this cell is that the charging current or the discharge current of this cell adds its euqalizing current; If the equilibrium direction of cell outwards is, the electric current that then flows through this cell is that the charging current or the discharge current of this cell deducts its euqalizing current.

The used formula of SOC that described step 3) is calculated cell is:

$\mathrm{SOC}\left(t\right)=\left(\frac{Q_0-{\∫}_0^t\mathrm{Idt}}{Q_0}\right)\×100\%$

Q wherein ₀Be the rated capacity of battery, I is for flowing through the electric current of cell in the time at t.

The invention has the beneficial effects as follows: the present invention is through utilizing the balanced management system of electric battery; Calculate the electric current that flows through this battery according to the charging and discharging currents of battery and battery balanced direction and euqalizing current; With the foundation of this current value, improve accuracy to the estimation of balancing battery group SOC value as counting cell SOC value.

Description of drawings

Fig. 1 is the system chart of lithium battery balanced management system;

Fig. 2 is the process flow diagram of lithium battery group SOC evaluation method of the present invention.

Embodiment

Below in conjunction with accompanying drawing technology implementation process of the present invention is done further explanation.

Fig. 1 has provided lithium battery balanced management system system chart, and this system mainly comprises main control unit, current acquisition unit, gathers balanced unit and 4 parts of display unit.Wherein gather balanced unit and realize cell voltage, temperature acquisition and function such as battery balanced, comprise DC/DC Switching Power Supply, gate-controlled switch group, switch drive module, battery management IC, temperature sensor, CAN communication module and MCU.DC/DC Switching Power Supply and gate-controlled switch group are formed balanced control module jointly, select the switch that needs action according to balance policy, realizes between two cells or cell and electric battery between the energy transfer, reach balanced purpose.The gate-controlled switch group is realized by miniature relay; Connect different way relays respectively according to different balanced implementations; According to the size of desired euqalizing current, require the maximum contact current of relay to be greater than certain value, gather the magnitude of voltage that balanced unit collects every batteries; Through calculating the voltage difference of minimum voltage battery and ceiling voltage battery, determining needs balanced battery.Each collection balanced unit links to each other with battery through gathering equilibrium line, and is different based on the different maximum attachable cell number of design.

To the estimation of cell SOC based on following formula:

$\mathrm{SOC}\left(t\right)=\left(\frac{Q_0-{\∫}_0^t\mathrm{Idt}}{Q_0}\right)\×100\%$

Q wherein ₀Be the rated capacity of battery, I is for flowing through the electric current of cell in the time at t, and the calculating of I divides two kinds of situation:

When equilibrium was not opened: this moment, I was battery charge or discharge current.

During balanced the unlatching: battery is divided into by balanced and balanced two states, is that charging current or discharge current add by euqalizing current I by balancing battery I _{By balanced}, balancing battery I is that charging current or discharge current deduct euqalizing current I _Balanced

According to judgement to the cell equilibrium state; From above-mentioned two kinds of I computing method, select corresponding method and calculate monomer SOC; SOC estimates to monomer; The SOC value of battery management system provides with monomer and total SOC dual mode, and monomer SOC provides with the monomer estimated value, and total SOC provides with the minimum SOC of monomer.

Above-mentioned management system powers on preceding and the back SOC estimation that powers on is carried out according to the following step:

1. judge according to the lithium battery balanced management system whether the cell of mesuring battary group is at equilibrium, if not at equilibrium, according to rated capacity and its SOC of charging and discharging currents calculating of this cell, computing formula is: $\mathrm{SOC}\left(t\right)=\left(\frac{Q_0-{\∫}_0^t\mathrm{Idt}}{Q_0}\right)\×100\%$

Q wherein ₀Be the rated capacity of this cell, I is the charging and discharging currents at t this cell in the time, if this cell is at equilibrium, then gets into step 2.

2. the electric current of crossing this battery according to the equilibrium direction and the euqalizing current calculated flow of this cell; If the equilibrium direction of this cell is inwardly (by equilibrium); The electric current that then flows through this battery is that the charging current or the discharge current of battery adds its euqalizing current, promptly flows through the electric current I=I of cell _{Charge/discharge current}+ I _{Euqalizing current}If the equilibrium direction of this cell is outwards (equilibrium), the electric current that then flows through this cell is that the charging current or the discharge current of this cell deducts its euqalizing current, promptly flows through the electric current I=I of this cell _{Charge/discharge current}-I _{Euqalizing current}

3. according to electric current that flows through this battery and rated capacity, calculate the SOC of this cell, the estimation of cell SOC is based on following formula:

$\mathrm{SOC}\left(t\right)=\left(\frac{Q_0-{\∫}_0^t\mathrm{Idt}}{Q_0}\right)\×100\%$

Q wherein ₀Be the rated capacity of cell, I is for flowing through the electric current of cell in the time at t.

4. repeat above-mentioned steps 1,2 and 3, the SOC of all cells in calculating this electric battery.

5. the SOC value of each cell in the electric battery is relatively found out the cell of SOC value minimum, with the SOC value of this cell SOC value as this electric battery.

Claims (3)

1. lithium battery group SOC evaluation method, it is characterized in that: the step of this lithium battery group SOC evaluation method is following:

1). judge whether the cell in the mesuring battary group is at equilibrium, if not at equilibrium, rated capacity and its SOC of charging and discharging currents calculating according to battery if this battery is at equilibrium, then get into step 2);

2). the electric current of crossing this battery according to the equilibrium direction and the euqalizing current calculated flow of battery;

3). according to electric current that flows through this battery and rated capacity, calculate the SOC of this cell;

4). repeat above-mentioned steps 1), 2) and 3), the SOC of all cells in calculating this electric battery;

5). the SOC value of each cell in the electric battery relatively, find out the cell of SOC value minimum, with the SOC value of this cell SOC value as this electric battery.

2. lithium battery group SOC evaluation method according to claim 1; It is characterized in that: needs were judged the equilibrium direction of battery earlier when said step 2) calculated flow was crossed the electric current of cell; If the equilibrium direction of this cell is inside; The electric current that then flows through this cell is that the charging current or the discharge current of this cell adds its euqalizing current; If the equilibrium direction of cell outwards is, the electric current that then flows through this cell is that the charging current or the discharge current of this cell deducts its euqalizing current.

3. lithium battery group SOC evaluation method according to claim 1 is characterized in that: the used formula of SOC that described step 3) is calculated cell is:

$\mathrm{SOC}\left(t\right)=\left(\frac{Q_0-{\∫}_0^t\mathrm{Idt}}{Q_0}\right)\×100\%$

Q wherein ₀Be the rated capacity of cell, I is for flowing through the electric current of this cell in the time at t.

Images