KR20130049920A - Method for estimating battery soc of vehicle - Google Patents

Abstract

PURPOSE: A method for predicting vehicle battery state is provided to predict the battery state accurately by applying an algorithm capable of obtaining numerical solution of a two-dimensional model using a finite element method. CONSTITUTION: Operation factors and reaction speed factors are inputted to a calculation part respectively as input elements. The operation factors includes physical and chemical factors of a battery, a shape factor of the battery, an operation current and temperature of the battery. Battery SoC(State of Charge) is calculated by performing mathematical modeling using the input elements and at the same time calculating temporal change of the battery SoC on the basis of the mathematical modeling. [Reference numerals] (AA) Start; (BB) Charging/discharging mode select; (CC) SOC calculation; (DD) Electrode charge conservation equation; (EE) Ion mass conservation equations; (FF) Electrolyte charge conservation equation; (GG) Momentum conservation equation; (HH) Electrochemical reaction equation; (II) Porosity change equation; (JJ) Charging state equation

Description

Method for estimating battery status for a vehicle {Method for estimating battery SOC of vehicle}

The present invention relates to a method of predicting a battery charge state of a vehicle, and more particularly, to a method of predicting a battery charge state of a vehicle, which can accurately predict a state of charge (SOC) of a vehicle using various factors of a battery. will be.

In general, a 12-V lead acid battery is used as a battery for a vehicle, and this 12-V lead acid battery is composed of a positive electrode of PbO ₂ , a negative electrode of porous Pb, and a sulfuric acid electrolyte.

As shown in FIG. 5, the lead acid battery converts chemical energy into electrical energy through a discharge reaction in which PbO ₂ of the positive electrode and Pb of the negative electrode react with sulfate ions to form PbSO ₄ and water, and also PbSO ₄ and The water is decomposed and returned to the original dischargeable state through a charging reaction in which PbO ₂ and Pb are reduced, and the chemical reaction occurring in the lead acid battery is as follows.

(Reaction at Lead Acid Battery Anode)

(Reaction at Lead Acid Battery Anode)

(Reaction of the whole lead acid battery)

These lead-acid batteries are inexpensive and reliable compared to other rechargeable batteries, so to this day, the vehicle's electrical load, including the starting, lighting, and ignition functions of the vehicle, It is responsible for supplying extra energy when exceeding, and in next-generation vehicles, mechanical components such as steering, braking, and air-conditioning are the same for safety, economy, and comfort. Considering that it is being replaced by an electrical component that performs a function, the electrical load required for the lead acid battery is increasing rapidly.

In such a more severe charging / discharging environment, a lead acid battery must operate stably to supply sufficient power to a vehicle. For this purpose, it is essential to accurately predict a lead acid battery, that is, a battery condition (SOC).

The power generation control and ISG system applied to the vehicle are technologies applied to reduce electric energy. The most important part of the power generation control and ISG system configuration is the battery charging and discharging efficiency. And an algorithm for controlling this, and eventually it is necessary to accurately predict the battery state (SOC).

In other words, BMS (Battery Management System) technology provides information such as battery voltage (V), battery current (A), battery temperature (℃), battery charge status (SOC), battery aging (SOH), and battery function (SOF). If this information is provided to the ECU from the BMS, the ECU performs power distribution control for various electric loads, generation control such as the operation control of the alternator charging the battery, and ISG system control. Can be said to be an important factor in improving fuel efficiency of the power generation control / ISG system, and further improving fuel efficiency can be obtained by increasing the accuracy of the battery status information.

The conventional battery state prediction method is a prediction method through the development of an electric equivalent battery model, as shown in the accompanying Figure 6 to build a battery charging or discharging model that simulates the electrochemistry in an electric equivalent method, in this model The battery status was estimated by integrating the battery charge and discharge currents, but the accuracy of the battery status (SOC) is ± 10%, which can be used as a control signal for controllers such as BMS and ECU, It is required.

The present invention has been devised in view of the above, and sets a mathematical model in which various phenomena such as electrochemical reaction of a battery, transfer of ions by flow and convection of an electrolyte, and porosity of an electrode are considered in combination. It is an object of the present invention to provide a method for predicting the state of charge of a battery for a vehicle, which can more accurately predict a battery state (hereinafter referred to as a battery SOC) by applying an algorithm that can obtain a numerical solution of a two-dimensional model using the element method.

The present invention for achieving the above object is: as an input element, the physical and chemical properties of the battery, the form factor of the battery, the operating factors including the operating current and temperature of the battery, and the reaction rate factors are respectively calculated in the calculation unit An input step; Calculating a battery SOC by performing a mathematical modeling using an input element at the same time and calculating a change over time of the battery SOC based on the mathematical modeling; Transmitting an SOC calculated to be utilized as various electronic equipment control data to a vehicle controller; The calculated SOC is fed back as an initial SOC and input to an operation unit; It provides a vehicle battery state prediction method comprising a.

The physical properties of the input element include the ion diffusion coefficient in the electrolyte, the conductivity, viscosity, and density of the electrolyte, and the chemical properties include the initial concentration of the electrolyte.

The shape factor of the input element is characterized in that it includes the size of the battery, the thickness and porosity of the positive and negative electrodes, the gap between the pole plates, the thickness and porosity of the separator.

The operation factor of the input element is characterized in that it comprises the operating current and the operating temperature of the battery.

According to the present invention, the rate of change over time of the battery SOC is determined by inputting each input element to a calculation unit.

)과, Equation preservation equation of solid electrode

)and,

)과, Equation for preserving charge of electrolyte

)and,

)에 각각 대입된 후, Electrochemical kinetics (

) Respectively,

)을 통하여 산출되는 것을 특징으로 한다.
State of charge equation (

It is characterized in that it is calculated through.

Through the above-mentioned means for solving the problems, the present invention provides the following effects.

According to the present invention, a number of phenomena such as mathematical modeling for predicting the charging and discharging behavior of a lead acid battery, ie, electrochemical reactions occurring inside the lead acid battery, ion transfer by flow and convection of an electrolyte, and porosity of an electrode are combined. Considering the mathematical modeling, it is possible to more realistically predict the current density, electrolyte concentration, and SOC distribution in the lead acid battery.

In particular, it is possible to establish a mathematical model that considers various phenomena such as the electrochemical reaction of the battery, the transfer of ions by the flow and convection of the electrolyte, and the porosity of the electrode, and to obtain the numerical solution of the two-dimensional model using the finite element method. By applying the same algorithm, the SOC can be predicted more accurately.

Therefore, the control of the power distribution for various electric loads in the various controllers of the vehicle, the generation control such as the operation control of the alternator for charging the battery, and the control of the ISG system, the accurate calculated SOC information is used, so that the fuel economy of the vehicle Improvement can be aimed at.

1 is a control diagram illustrating a vehicle battery state prediction method according to the present invention;
2 is a schematic diagram illustrating input and output factors of a vehicle battery state prediction method according to the present invention;
3 is a graph showing an experimental example result for a vehicle battery state prediction method of the present invention;
4 is a table for explaining terms of respective equations used for mathematical modeling of a vehicle battery state prediction method according to the present invention;
5 is a schematic diagram of a cell unit of a battery (lead storage battery);
Figure 6 is a schematic diagram showing the modeling of the electric equivalent method for the conventional battery state prediction method.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, input elements including the physical and chemical properties of the battery, the form factor of the battery, the operating factors including the operating current and temperature of the battery, the reaction rate factor, and the like are input to the calculation unit and used for constructing a mathematical model. .

Physical property factors of the input element include ion diffusion coefficient (cm / s) in electrolyte, conductivity (S / cm), viscosity (g / cm · s), density (g / cm 2) The property factors include the initial concentration of the electrolyte (mol / cm 2), and the shape factors include the size of the battery (width, length, width), the thickness (cm) and porosity of the positive and negative electrodes, the spacing between the electrode plates (cm), The thickness of the separator (cm) and the porosity, the operating factor includes the operating current (A) and the operating temperature (° C) of the battery, the reaction rate factor means various chemical reaction rate constant of the battery.

When these input elements are input to the calculator, mathematical modeling is performed using the input elements, and the battery SOC is calculated by calculating a change over time of the battery SOC based on the mathematical modeling.

Here, referring to Figures 1 and 2 attached to the mathematical modeling based on the input elements and the calculation process of the battery SOC through the same as follows.

A mathematical model is set up to model the constant-current (constant-voltage) charge / discharge characteristics of a 12-V battery (lead acid battery) to predict the state of the battery.The mathematical model preserves the amount of charge in the solid part of the electrode and in the electrolyte solution , Differential equations representing mass preservation of ions by flow and convection, butler-volmer electrochemical reaction rate, change of state of charge (SOC) indicating charge state, and porosity change of electrode.

For reference, the meanings of the terms of each equation described below are as collectively described in the accompanying table of FIG.

First, the differential equation representing the preservation of the charge amount of the solid part of the electrode and the electrolyte solution impregnated in the electrode, the total current density (i) generated during the discharge and charging reaction is the current density flowing in the solid-state electrode reaction ( i _s ) is expressed as the sum of the current density (i _l ) resulting from the transfer of charge in the electrolyte solution, and the total current density divergence (assuming that the charge from the solid electrode must flow into the liquid phase in the pore). divergence) is zero. This is summarized as Equations 1 and 2 below.

The charge flux flowing from the electrolyte solution of the battery is defined as the area (A) of the interface between the electrode active material and the electrolyte in the electrode pores and the transfer current density defined by Butler-Volmer's electrochemical reaction rate equation as shown in Equation 3 below. Expressed by the product of the transfer current density, j), the transfer current density is expressed by Equation 4 below.

, Pb에 대하여

로 정의되고, PbO₂의 경우 평형전위(ΔU_PbO2 )는 전극과 전해액의 조성과 온도의 함수이다. In equation (4), the overpotential η is equal to PbO ₂

, Against Pb

For a definition and, PbO ₂ in equilibrium potential (ΔU _PbO2) is a function of composition and temperature of the electrode and the electrolyte.

In the mathematical model according to the present invention, for simplicity of the model, this equilibrium potential is assumed as a constant (2.05), and α _a (α _c ) is an apparent transfer coefficient of the anode (cathode). , α _a = 1.5 and α _c = 0.6.

At this time, the solid-state electrode current density (i _s ) of the battery is proportional to the potential gradient inside the solid as shown in Equation 5 below according to Ohm's law.

Here, the conductivity (σ) of the porous solid electrode is corrected by the porosity (ε = 0.6) to use an effective conductivity value expressed by Equation 6 below.

In addition, the current density i ₁ of the electrolyte in the electrode pores is proportional to the potential gradient and the concentration gradient of the electrolyte, and is expressed by Equation 7 below.

는 이온의 확산에 의해 이동하는 하전입자들의 속도로 측정되는 확산전도도 값으로서, 이를 토대로 고체부분과 전극에 함침된 전해질 용액의 전하량 보존을 나타내는 미분방정식을 나타내면 다음의 수학식 8 및 9와 같이 표현된다.here

Is a diffusion conductivity value measured by the velocity of charged particles moving by diffusion of ions, and based on this, a differential equation representing the charge retention of the electrolyte solution impregnated in the solid part and the electrode is expressed as in Equations 8 and 9 do.

The electrically activated area (A) is one of the form factors representing the performance of lead acid batteries. The reason for this is that as the electrochemical reaction proceeds, the material is moved by the chemical reaction between the electrode and the electrolyte. This is because the activated area does not match the area in the charging reaction.

Thus, the electrically activated area is represented by an empirical equation using SOC values as shown in Equations 10 and 11 below.

In Equation 11, A _max is the maximum value of the activated area.

Here, the equation representing the change over time of the battery SOC is expressed as Equation 12 below based on Equations 3 and 4 above.

In Equation 12, Q _max represents the maximum amount of charge available from the electrode in the fully charged state.

On the other hand, the effective properties (superscript eff) used in Equations 5 to 9 are closely related to the porosity, which is another form factor representing the performance of the lead acid battery. Equation 13

는 이온 플럭스(flux)값으로, 패러데이(Faraday)법칙을 따르는 전기화학반응에서 발생된 전류전달(Aㆍj)에 기인하고, 또한 a₁은 전환된 활물질의 몰당 부피변화로, PbO₂에 대하여

, Pb에 대하여

이다.here

Is the ion flux value, which is due to the current transfer (A · j) generated in the electrochemical reaction following Faraday's law, and a ₁ is the volume change per mole of the converted active material, with respect to PbO ₂

, Against Pb

to be.

On the other hand, in the mass transfer phenomenon due to convection, diffusion, migration (migration) the equation for the conservation of ions is expressed by the following equation (14).

, Pb에 대하여

이고, 또한 t₊는 전달수(transference number)이다.In Equation 14, a ₂ is PbO ₂

, Against Pb

And t ₊ is the transmission number.

Finally, the flow of the battery electrolyte can be expressed by the Navier-Stokes equation including Boussinesq approximation and continuous equations as shown in Equations 15 and 16 below.

는 유체의 점도와 침투도에서 기인하는 항력(drag)과 관련되어 있는 항이고, 또한 누출속도 (εv)는 낮은 침투도를 가진 전극에서 아래의 수학식 17과 같이 Darcy의 법칙을 따른다.In Equation (15)

Is a term related to drag due to the viscosity and permeability of the fluid, and the leak rate (εv) follows Darcy's law as shown in Equation 17 below for an electrode with low permeability.

Penetration degree (K) in the above Equation 17 can be obtained through Kozeny-Carman equation as shown in Equation 18 below.

In Equation 18, d is the average diameter of the particles constituting the electrode.

Input factors used in the mathematical modeling of lead acid batteries according to the present invention can be classified into property factors, form factors, operating factors, and reaction rate factors, and the property factors include diffusion coefficient of ions in electrolyte solution, conductivity of electrolyte, viscosity, The concentration of the electrolyte, which is a physical and chemical property such as density, and the form factor includes the size of the battery, the thickness and porosity of the pole plate, the gap between the pole plates, the thickness and porosity of the separator, and the operating factors include There is temperature, and the reaction rate factor is input various reaction rate constants.

)과, 전해질의 전하량 보존방정식(

)과, 전기화학 반응속도식(

)에 각각 대입된 후, 충전상태 방정식(

)를 통하여 시간에 따른 SOC 변화율을 구할 수 있게 된다.In this way, input elements inputted to the calculator are charge conservation equations of the solid electrode.

) And the charge storage equation of the electrolyte (

), And the electrochemical kinetics equation (

), And then the state of charge equation (

) Can be used to find the rate of change of SOC over time.

), 운동량 보존방정식(

), 공극률 변화 방정식(

) 등을 통하여 시간에 따른 공극율 변화율을 구할 수 있으며, 결과적으로 연산부에서 배터리의 전지 전압(cell voltage) 및 전류밀도, SOC, 전해액의 농도가 출력된다.At this time, the mass conservation equation of the ion (

), Momentum conservation equation (

), Porosity change equation (

The porosity change rate with time can be obtained, and as a result, the cell voltage and current density of the battery, the concentration of the SOC, and the electrolyte are output from the calculation unit.

Accordingly, the calculator performs mathematical modeling using each input element and calculates a battery SOC by calculating a change over time of the battery SOC based on the mathematical modeling. The calculated SOC is fed back as an initial SOC to the calculator. At the same time, it is transmitted to various controllers of the vehicle to be utilized as various electronic equipment control data.

Here, as an experimental example of the present invention, a battery discharge test was carried out. When the battery was discharged, the battery voltage value obtained by using the battery state prediction method of the present invention as described above, and the battery was discharged by using a voltage sensor while actually discharging the battery. The actual voltage values were measured and compared, and the results are as shown in the accompanying FIG. 3.

That is, C / 3 (30A discharge), C / 5 (18A discharge), C / 10 (9A discharge) that can represent various discharge states in a real vehicle using a 12-V (90Ah) lead acid battery for vehicles ), C / 20 (4.5A discharge) was performed for 5 hours, 10 hours and 20 hours, and the discharge experiment was performed up to 10.5V set as the termination voltage.

In the attached graph of FIG. 3, the solid line portion is a voltage value measured using an actual voltage sensor, and the line in a continuous shape indicates a simulation result using the battery prediction method of the present invention as described above. The difference in is almost similar.

In other words, as shown in the attached graph of FIG. 3, the voltage value measured using the voltage sensor during actual discharge and the simulated voltage value through mathematical modeling generally match, and each discharge voltage tends to change. It can be seen that the similarity, and since the discharge time is the same, the battery state prediction method based on the mathematical modeling according to the present invention well simulates the nonlinear discharge behavior of the lead acid battery.

As a result, as can be seen from the above experimental example, when the SOC value accurately calculated through the mathematical modeling of the present invention is transmitted to the controller of the vehicle, power distribution control for various electric loads, and an alternator for charging the battery It is possible to more precisely control the generation control and ISG system control such as the operation control of the vehicle, it is possible to improve the fuel economy of the vehicle.

Claims (6)

As an input element, a physical and chemical property factor of the battery, a shape factor of the battery, an operation factor including an operating current and a temperature of the battery, and a reaction rate factor are respectively input to the operation unit;
Calculating a battery SOC by performing a mathematical modeling using the input element and calculating a change over time of the battery SOC based on the mathematical modeling;
Vehicle state estimation method for a vehicle comprising a.
The method according to claim 1,
Transmitting the calculated battery SOC to the vehicle controller so as to be utilized as various electrical appliance control data;
The calculated SOC is fed back as an initial SOC and input to an operation unit;
Vehicle state estimation method for a vehicle further comprising.
The method according to claim 1,
The physical property factor of the input element includes the ion diffusion coefficient in the electrolyte, the conductivity, viscosity, density of the electrolyte, and the chemical property factor comprises the initial concentration of the electrolyte.
The method according to claim 1,
The shape factor of the input element includes a battery size, the thickness and porosity of the positive electrode and the negative electrode, the gap between the electrode plate, the thickness and porosity of the separator, characterized in that the vehicle battery state prediction method.
The method according to claim 1,
The operation factor of the input element is a vehicle battery state prediction method, characterized in that including the operating current and operating temperature of the battery.
The method according to claim 1,
The rate of change over time of the battery SOC is calculated by preserving a charge amount conservation equation of a solid electrode by inputting each input element to a calculation unit.

)and,
Equation for preserving charge of electrolyte

)and,
Electrochemical kinetics (

) Respectively,
State of charge equation (

Vehicle state estimation method for a vehicle, characterized in that is calculated through.

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