CN102645638B - 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 estimation method

Technical field

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

Background technology

In order to reduce environmental pollution and alleviate day by day serious lack of energy problem, lithium battery can just progressively be applied to multiple fields such as electric motor car, energy storage and compact power by the clean energy resource that utilizes of secondary as a kind of.Country 12 planning also develops new energy technology as main project.For the consideration to lithium battery self character and secure context, supporting battery management system is needed to monitor in real time the voltage of lithium battery, temperature, the parameter such as charging and discharging currents and SOC in actual use.But the characteristic of battery complexity itself makes battery have inconsistency, will show certain " short-board effect " in battery use procedure.In battery set charge/discharge process, the charging and discharging capabilities of electric battery shows with the most weak battery, in order to address this problem, improves the overall performance of electric battery, and a kind of battery management system with equilibrium arises at the historic moment.Due to the impact of euqalizing current, the SOC estimation of cell is particularly important.Existing SOC estimation method mainly contains open-circuit voltage method, ampere-hour integral method, Kalman filtering method etc., and wherein the most frequently used is 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 object of the invention is to solve current battery group at charge and discharge process because euqalizing current impact causes the problem of the error to battery SOC estimation.

The present invention is for solving the problems of the technologies described above and providing a kind of lithium battery group SOC estimation method, and the step of this lithium battery group SOC estimation method is as follows:

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

2). calculate according to the equilibrium direction of battery and euqalizing current the electric current flowing through this battery;

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

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

5). compare the SOC value of each cell in electric battery, find out the cell that SOC value is minimum, using the SOC value of this cell as the SOC value of this electric battery.

Described step 2) calculate the equilibrium direction needing first to judge battery when flowing through the electric current of battery, if the equilibrium direction of this cell is inside, the electric current then flowing through this cell is that the charging current of this cell or discharge current add its euqalizing current, if the equilibrium direction of cell is outside, then the electric current flowing through this cell is that the charging current of this cell or discharge current deduct its euqalizing current.

Described step 3) formula that calculates the SOC of cell used is:

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

Wherein Q ₀for the rated capacity of battery, I is the electric current flowing through cell within the t time.

The invention has the beneficial effects as follows: the present invention is by utilizing the balanced management system of electric battery, the electric current flowing through this battery is calculated according to the charging and discharging currents of battery and battery balanced direction and euqalizing current, using this current value as the foundation calculating SOC value of battery, improve the accuracy to the estimation of balancing battery group SOC value.

Accompanying drawing explanation

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

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

Embodiment

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

Fig. 1 gives lithium battery balanced management system system chart, and this system mainly comprises main control unit, current acquisition unit, gathers balanced unit and display unit 4 parts.Wherein gather balanced unit and realize cell voltage, temperature acquisition and the 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 form equalization control module jointly, select the switch needing action, realize the energy trasfer between two cells or between cell and electric battery, reach balanced object according to balance policy.Gate-controlled switch group is realized by miniature relay, different way relay is connected respectively according to different balanced realization modes, according to the size of required euqalizing current, require that the maximum contact current of relay is greater than certain value, gather the magnitude of voltage that balanced unit collects every batteries, by calculating the voltage difference of minimum voltage battery and ceiling voltage battery, determining and needing balanced battery.Each gathers balanced unit and is connected with battery by gathering equilibrium line, different according to the maximum attachable cell number of the difference of design.

To the estimation of cell SOC based on following formula:

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

Wherein Q ₀for the rated capacity of battery, I is the electric current flowing through cell within the t time, the calculating of I in two kinds of situation:

When equilibrium is not opened: now I is battery charge or discharge current.

During balanced 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 _balanced, balancing battery I is that charging current or discharge current deduct euqalizing current I _balanced.

According to the judgement to cell equilibrium state, from above-mentioned two kinds of I computing method, select corresponding method calculate monomer SOC, monomer SOC is estimated, the SOC value of battery management system provides with monomer and total SOC two kinds of modes, monomer SOC provides with monomer estimated value, and total SOC provides with the minimum SOC of monomer.

SOC estimation is carried out according to the following step before above-mentioned management system powers on and after powering on:

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

Wherein Q ₀for the rated capacity of this cell, I is the charging and discharging currents of this cell within the t time, if this cell is at equilibrium, then enters step 2.

2. calculate according to the equilibrium direction of this cell and euqalizing current the electric current flowing through this battery, if the equilibrium direction of this cell inwardly (balanced) is, the electric current then flowing through this battery is that the charging current of battery or discharge current add its euqalizing current, namely flows through the electric current I=I of cell _{charge/discharge current}+ I _{euqalizing current}if the equilibrium direction of this cell outwards (equilibrium) is, then the electric current flowing through this cell is that the charging current of this cell or discharge current deduct its euqalizing current, namely flows through the electric current I=I of this cell _{charge/discharge current}-I _{euqalizing current}.

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

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

Wherein Q ₀for the rated capacity of cell, I is the electric current flowing through cell within the t time.

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

5. compare the SOC value of each cell in electric battery, find out the cell that SOC value is minimum, using the SOC value of this cell as the SOC value of this electric battery.

Claims (2)

1. a lithium battery group SOC estimation method, is characterized in that: the step of this lithium battery group SOC estimation method is as follows:

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

2). calculate the electric current flowing through this battery, using this current value as the foundation calculating SOC value of battery according to the equilibrium direction of battery and euqalizing current;

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

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

5). compare the SOC value of each cell in electric battery, find out the cell that SOC value is minimum, using the SOC value of this cell as the SOC value of this electric battery;

Described step 2) calculate the equilibrium direction needing first to judge battery when flowing through the electric current of cell, if the equilibrium direction of this cell is inside, the electric current then flowing through this cell is that the charging current of this cell or discharge current add its euqalizing current, if the equilibrium direction of cell is outside, then the electric current flowing through this cell is that the charging current of this cell or discharge current deduct its euqalizing current.

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

$\mathrm{SOC}\left(t\right)=\left(\frac{Q_0-{\∫}_0^t\mathrm{Idt}}{Q^0}\right)\×100\%$

Wherein Q ₀for the rated capacity of cell, I is the electric current flowing through this cell within the t time.