KR20090020174A - Method for calculating battery soc of electronic vehicle - Google Patents

Abstract

A method for calculating a battery SOC(State Of Charge) of an electronic vehicle is provided to enhance utility in a vehicle having a high-capacity battery such as a commercial mild hybrid vehicle by eliminating a reset condition such as a full charge. A constant voltage charging process is performed to charge a constant voltage when a present SOC is lower than a critical SOC after a starting operation. A monitoring process is performed to monitor the amount of charging current during a predetermined reference time t from a charging start time. An SOC estimation process is performed to estimate an initial SOC as a starting point of the constant voltage charging process by comparing a changed slope in the amount of charging current during the reference time t with predetermined measurement data. An updating process is performed to estimate and update the present SOC by integrating the amount of charging current from the start point on the basis of the estimated initial SOC.

Description

Method for estimating battery charge state of an electric vehicle {Method for calculating battery SOC of electronic vehicle}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of estimating battery charge state of an electric vehicle, and more particularly, to a method of resetting and estimating battery state of charge which can be usefully applied in a commercial mild hybrid vehicle. The present invention relates to a method of estimating a state of charge of an electric vehicle for estimating initial state of charge (SOC) using a slope and then resetting and integrating a current amount thereafter to estimate and update a current state of charge.

In general, a hybrid vehicle in a broad sense means to drive a vehicle by efficiently combining two or more different power sources, but in most cases, a vehicle powered by a fuel powered engine and an electric motor driven by battery power. This is called a hybrid electric vehicle, that is, a hybrid electric vehicle (HEV).

Such a hybrid electric vehicle is essentially equipped with a high-voltage battery that provides the driving power of the electric motor, which supplies the necessary power while repeating the charging / discharging while driving the vehicle.

Hybrid electric vehicles improve fuel economy and power performance based on algorithms that drive motors and engines according to the state of charge (hereinafter, referred to as SOC) of high voltage batteries.

On the other hand, as is known, in a pure electric vehicle using the battery as an energy source, an engine hybrid electric vehicle using a battery as an energy buffer, and a fuel cell hybrid electric vehicle, the battery is one of the main components for determining the quality of the vehicle.

Accordingly, the Battery Management System (BMS), which manages the overall state of the battery, prevents premature reduction of battery life and informs the SOC information of the battery to the vehicle controller performing total control. It supports control and driving control.

The main functions of the battery management system (BMS) are to estimate the SOC of the battery and to detect the full charge, to balance the voltage between each cell module, to control the maximum charge and discharge voltage according to the SOC of the battery, safety management and cooling control do.

As described above, it is very important to understand the SOC of the battery in a hybrid electric vehicle or an electric vehicle using a high voltage battery, and also a technology for identifying the remaining capacity of the battery while driving and informing the driver.

As a method of calculating the SOC of the battery while driving, it is commonly used to calculate the current SOC by measuring the charge and discharge current amounts. The current SOC is calculated by integrating the charge / discharge currents measured in the specific SOC as a reference. It is estimated and updated.

In the process of calculating the SOC, the SOC, which is a reference for integrating the charge / discharge currents, is appropriately set, that is, the initial value of the SOC (remaining capacity) of the battery (hereinafter referred to as 'initial SOC') prior to driving is appropriately set. A technique for setting this is required, and the initial SOC is usually set using an open circuit voltage (hereinafter, referred to as 'OCV').

In other words, immediately after turning on the vehicle's ignition key, the OCV is measured and the SOC is estimated therefrom, the estimated SOC is set to the initial SOC as the integration reference, and the subsequent charge / discharge currents are accumulated. It will update the current SOC.

As described above, a method of updating the current SOC by measuring and integrating the amount of current charged / discharged in the initial SOC is called a current integration method, and FIG. 1 is a flowchart illustrating the conventional SOC estimation method.

As shown, after the vehicle's ignition key is on, the current SOC is updated by a current integration method that estimates the initial SOC from the measured OCV and then accumulates the amount of current charged / discharged.

This is the most basic method used in all battery SOC estimation processes, and the equation for calculating the SOC by the current integration method is shown in Equation (1) below.

(1)

(One)

However, according to several experiments and papers, since OCV changes with temperature and time, it is not reliable to estimate SOC simply by measuring OCV value.

In addition, OCV is not known when the battery is being charged or discharged, and since the chemistry inside the battery is not stabilized after a certain time (usually 2-3 hours or more) after charging / discharging is completed, SOC It cannot be estimated based on OCV.

Therefore, under the assumption that charging / discharging has been stopped for a sufficient time (assuming that the internal chemistry of the battery is stabilized), the OCV is measured immediately after the start-up key on, the initial SOC is estimated therefrom, and then the charge / discharge current is integrated to Updating SOC.

However, in the case of passenger cars, the stabilization time of the chemical reaction can be easily obtained, but in the case of commercial vehicles, it is difficult to secure the stabilization time due to frequent operation, so estimation of SOC based on OCV has some error. .

In addition, the current integration method is very useful for SOC estimation, but since the initial SOC obtained from the OCV is used immediately after starting, it continuously accumulates the amount of current during charging / discharging of the vehicle. Errors gradually diverge or converge to zero due to (such as battery deterioration).

In particular, when the charging / discharging is repeated, the actual charging / discharging efficiency changes in the battery, and when the charging / discharging frequently occurs during driving, the SOC that is accumulated and updated from the initial SOC immediately after startup is charged / discharged. As it progresses, it gradually becomes different from the actual value.

Therefore, in order to solve this problem, various SOC reset algorithms for resetting the cumulative reference SOC in the middle, as shown in FIG. 2, are applied. For example, after the 100% full charge is performed with the constant voltage, the reference SOC is reset. For example, there is a method of recharging at a constant voltage and resetting to a predetermined SOC value at a constant charging current.

However, in a hybrid vehicle for passenger use, the time required to fully charge it with a constant voltage is short because the battery capacity is small, whereas in commercial mild hybrid vehicles, a lead storage battery is used and its capacity (about, 400AH) is higher than that for riding (about, 6-7AH). Because of this very large size, it takes several hours to apply the full charge reset method used in passenger vehicles.

3 shows a current curve during constant voltage charging. When charging a constant voltage, the amount of charge current gradually converges to 0 with time, and there is a difference in the amount of charge current curve according to the SOC state of the battery. Full charge of the constant voltage before reaching the reset current takes considerable time due to the large battery capacity.

Moreover, in addition to the time limit described above, there are many difficulties in applying to commercial mild hybrid vehicles because the idle stop, which is one of the main functions of the mild hybrid vehicle, cannot be performed during constant voltage charging.

Hereinafter, the present invention has been invented to solve the above problems, it is unnecessary to reset conditions such as full charge battery charging of an electric vehicle that can be usefully applied to an electric vehicle equipped with a large capacity battery, such as a commercial mild hybrid vehicle The purpose is to provide a state estimation method.

In order to achieve the above object, the present invention provides a method for estimating a state of charge of a battery (hereinafter referred to as SOC) in an electric vehicle,

(a) after the start-up, when the current SOC is below the SOC threshold for charging, charging the constant voltage, and monitoring the amount of charging current for a predetermined reference time t from the time of starting the constant voltage charging;

(g) estimating initial charging SOC which is the SOC at the start of constant voltage charging by comparing the gradient of change in the charging current amount during the reference time t and previously inputted measurement data;

(c) estimating and updating a current SOC by integrating a charging current amount from a charging start time on the basis of the estimated initial charging SOC;

It provides a method for estimating the state of charge of a battery of an electric vehicle comprising a.

Herein, the present invention estimates the initial SOC based on the open circuit voltage (OCV) measured immediately after the start-up when the current SOC is equal to or greater than the SOC threshold that requires charging, and calculates the amount of charge / discharge current based on the initial SOC. Integrating and estimating and updating the current SOC.

After the step (c), when the current SOC becomes equal to or greater than the preset SOC threshold, the step of estimating and updating the current SOC by integrating the charge / discharge current amount based on the SOC at the time of stopping, It further comprises.

In addition, the measurement data are data measured and input in advance through experiments under the condition of charging the same constant voltage, and are defined according to the slope of the charge current amount change measured during the same t time from the start of the same constant voltage charge and the slope of the charge current amount change slope. It is characterized by SOC data at the start of charging.

According to the method of estimating the state of charge of a battery of the present invention having the above characteristics, the initial charge state is reversely estimated by resetting the initial charge state by using the initial slope of the current curve obtained therefrom while charging a constant voltage, and then the amount of current therefrom is integrated. It is configured to estimate and update the current state of charge, so that it is not necessary to reset conditions such as full charge, so that it can be usefully applied to an electric vehicle equipped with a large capacity battery such as a commercial mild hybrid vehicle, and the SOC can be reset at every constant voltage charge. There is an advantage.

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

The present invention can be usefully applied to a commercial mild hybrid vehicle equipped with a large-capacity battery. The initial charging state (SOC) is estimated by initial slope of the charge current curve obtained therefrom during constant voltage charging and then reset. The main characteristic is to estimate and update the current state of charge by integrating the amount of current thereafter.

4 is a current curve for each SOC representing the amount of charge current according to time, and the slope of the current amount change during the initial reference time t hours when the constant voltage is charged in the present invention is shown, and FIG. 5 is a view illustrating an SOC estimation method according to the present invention. Flowchart.

Basically, when charging a constant voltage, the amount of current charged gradually decreases with time by the internal resistance of the battery and converges to zero.In particular, the current curve during constant voltage charging according to the initial SOC (curve indicating the amount of charging current according to time) ), As well as the slope of convergence to zero.

Figure 4 shows a current curve that differs depending on the initial SOC charging during constant voltage charging for each SOC, in the present invention, the current curve measured in real time, not a method of resetting to a specific SOC by charging for a long time using this The initial slope of is used to estimate the initial charging SOC to be used as the reset SOC.

However, immediately after start-up, the current SOC is calculated by integrating the charge / discharge current amount to the initial SOC estimated from the initial OCV according to the existing algorithm.Then, after using the extra capacity with different electric load and reaching the required SOC, the constant voltage is applied. While charging, the initial slope of the current curve representing the amount of charging current over time is monitored to estimate and reset the initial charge SOC (SOC) at the start of charging.

After resetting to the estimated initial charge SOC, the current SOC is calculated in real time by integrating the current amount after the initial charge SOC.

Here, the initial slope of the current curve is calculated from the change amount of the charging current between the start time of the constant voltage charge and the time after a preset reference time t hours as shown in FIG. 4, and the calculated slope is measured data obtained through experiments for each SOC. Compare to and find the corresponding SOC and reset it to the initial charging SOC.

Here, the reference time t is about 2 to 3 minutes depending on the experimental value. Preferably, filtering is necessary to prepare for noise during constant voltage charging.

The SOC estimation process will be described in detail with reference to FIG. 5 as follows.

First, a step (STEP1) of estimating initial SOC immediately after startup is performed, and the SOC is obtained by using a battery OCV (Open Circuit Voltage) immediately after a start-up key as in the prior art.

At this time, the SOC is measured data obtained through the experiment, that is, OCV Vs. Calculated from the SOC map.

As a next step, a step (STEP2) of updating the SOC using the current integration method is performed based on the estimated initial SOC, and the input / output current is measured by DC / DC during the charging / discharging of the battery. According to 1), the SOC is estimated and updated.

Thereafter, whether to charge the constant voltage from the current SOC (STEP3), if the current SOC is lowered to the SOC threshold, for example, less than 60% to be charged, the constant voltage charging is performed (STEP4).

After the constant voltage charging is started, the initial slope of the current curve is calculated using the change amount of the charging current for the reference time t hours, and the slope is compared with the measured data obtained through the experiment for each SOC, SOC at the start of the constant voltage charging, That is, the initial charging SOC is obtained (STEP5).

Here, the measured data is data measured and input through experiments under the condition of charging the same constant voltage, and is defined according to the slope of the charge current amount change measured during the same t time from the start of the same constant voltage charge and the slope of the charge current amount change slope. SOC data at the start of charging.

Subsequently, based on the initial charging SOC obtained as described above, the current amount charged according to Equation (2) is accumulated to obtain the SOC at the present time in real time and updated. Set to '0' and accumulate to 'current time' to update the SOC (STEP 6).

(2)

(2)

Thereafter, the SOC obtained in the above step is used to determine a predetermined SOC threshold value, for example, 60% or more (STEP7), where the constant voltage charging is stopped when the current SOC reaches 60% or more (STEP8), and the SOC, That is, the current integration method is performed based on SOC 60%.

That is, the current SOC is estimated and updated by integrating the amount of current charged / discharged according to the charge / discharge state of the battery thereafter at 60% SOC.

In this way, in the present invention, the initial charge state is estimated and reset by using the initial slope of the charge amount current curve (slope for the reference time t time) determined therefrom during the charging of the constant voltage, and then the current amount is accumulated from thereafter. The current state of charge is estimated and updated.

Since the SOC estimation method does not require a reset condition such as a full charge, the SOC estimation method may be usefully applied to an electric vehicle equipped with a large capacity battery, and the SOC may be reset every time the constant voltage is charged.

1 is a flow chart showing a conventional SOC estimation method,

2 is a flowchart of an SOC estimation method to which a reset algorithm is applied;

3 is a current curve at constant voltage charging,

4 is a charge amount current curve for each SOC indicative of the initial charge current amount change slope defined in the present invention;

5 is a flowchart illustrating a method for estimating SOC according to the present invention.

6 shows an example of a map for estimating SOC from OCV.

Claims (4)

In a method for estimating a state of charge of a battery (hereinafter referred to as SOC) in an electric vehicle, (a) after the start-up, when the current SOC is below the SOC threshold for charging, charging the constant voltage, and monitoring the amount of charging current for a predetermined reference time t from the time of starting the constant voltage charging; (g) estimating initial charging SOC which is the SOC at the start of constant voltage charging by comparing the gradient of change in the charging current amount during the reference time t and previously inputted measurement data; (c) estimating and updating a current SOC by integrating a charging current amount from a charging start time on the basis of the estimated initial charging SOC; Battery charging state estimation method of an electric vehicle comprising a. The method according to claim 1, If the current SOC is above the SOC threshold that needs to be charged immediately after startup, the initial SOC is estimated based on the open circuit voltage (OCV) measured immediately after startup, and the current SOC is accumulated by integrating the charge / discharge currents based on the initial SOC. And estimating and updating the battery charge state of the electric vehicle. The method according to claim 1, After the step (c), if the current SOC reaches a predetermined SOC threshold or more, the step of estimating the constant voltage charging and integrating the charge / discharge current amount based on the SOC at the stop point further estimates and updates the current SOC. Method for estimating the state of charge of the battery of an electric vehicle comprising a. The method according to claim 1, The measured data are data measured and input in advance through experiments under the condition of charging the same constant voltage, and are defined according to the slope of the charge current amount change measured during the same t time from the start of the same constant voltage charge and the charge defined by the charge current amount change slope. Method for estimating the state of charge of a battery of an electric vehicle, characterized in that the SOC data of the start time.

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