BATTERY CONTROL SYSTEM AND METHOD OF FUEL CELL VEHICLE

A battery control system and method of a fuel cell vehicle includes a battery, a fuel cell, and a controller. The battery provides driving energy of a vehicle. The fuel cell provides the driving energy of the vehicle or charging the battery. The controller estimates a degree of deterioration of the fuel cell, derive a change rate in an SOC value of the battery based on the degree of deterioration of the fuel cell, and change a charge control factor or a discharge control factor of the battery according to the derived change rate in the SOC value of the battery.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2022-0071605 filed on Jun. 13, 2022, the entire contents of which is incorporated herein for all purposes by this reference.

Background of the Present Disclosure

FIELD OF THE PRESENT DISCLOSURE

The present disclosure relates, generally, to a battery control system and method of a fuel cell vehicle, and more particularly, to a battery control system and method of a fuel cell vehicle, the system and method being able to derive the change rate in the state of charge (SOC) value of a battery based on the degree of deterioration of a fuel cell and change the charge control factor or the discharge control factor of the battery according to the derived change rate in the SOC value of the battery, preventing the battery from being overcharged or overdischarged.

DESCRIPTION OF RELATED ART

Recently, the distribution of eco-friendly vehicles, such as electric vehicles (EVs), is increasing due to environmental issues of internal combustion engine (ICE) vehicles. In general, an EV refers to a vehicle which is propelled using driving power of a motor actuated using electrical energy.

Such EVs may include a hybrid electric vehicle (HEV) that produces driving power from a motor using electrical energy charged in a vehicle high-voltage battery in addition to a conventional ICE, a fuel cell electric vehicle (FCEV) that produces driving power from a motor using electrical energy generated by a fuel cell, and the like.

A fuel cell disposed in a fuel cell vehicle is a device that generates electrical energy through an electrochemistry reaction inside a fuel cell stack by receiving hydrogen and air from external sources. The fuel cell has an output voltage of about −1 V to about 1.2 V.

Such a fuel cell is advantageously eco-friendly but is disadvantageously unsuitable to rapidly supply power in response to changes in output power of a vehicle.

Thus, to cope with such changes in the output power of a vehicle, even a fuel cell vehicle is generally provided with a high-voltage battery (hereinafter, referred to as a “battery”) to provide driving power of a motor.

That is, a fuel cell in a fuel cell vehicle serves as a main power source that provides driving energy of the fuel cell vehicle by generating electrical energy by an electrochemistry reaction, whereas a battery serves as an auxiliary power source that provides driving energy of the fuel cell vehicle together with the fuel cell provided as the main power source.

Furthermore, electrical energy generated by the fuel cell is configured to be supplied to a load of the vehicle or the battery to drive the load or charge the battery. The electrical energy charged in the battery is discharged from the battery to supplement driving energy of the fuel cell vehicle when the load of the vehicle is increasing rapidly (e.g., when high output power is required).

Meanwhile, the battery disposed in the fuel cell vehicle may store regenerative braking energy occurring during gliding (or coasting drive) or decelerating drive of the vehicle.

Here, the coasting refers to a state in which a vehicle is being moved by inertia according to the current speed when the driver is pressing neither the accelerator pedal nor the brake pedal during the driving of the vehicle, whereas the decelerating drive refers to a state in which the vehicle is moving while being rapidly decelerated by the driver pressing the brake pedal during the driving of the vehicle.

Furthermore, in the regenerative braking, when a vehicle is gliding or the brake pedal is pressed, power that has been supplied to the motor is cut off but counter electromotive force is generated from the motor by wheels rotating due to the inertia of the moving vehicle. When the counter electromotive force is applied to the motor, reverse torque (i.e., regenerative braking torque) occurs in the motor, generating braking force of the vehicle.

Such regenerative braking recovers energy that would otherwise be wasted, achieving an effect of improved fuel efficiency. Regenerative braking is applied to most commercial vehicles. Regenerative braking energy in a fuel cell vehicle is used to charge a battery.

Meanwhile, when overcharged, a battery has a risk of explosion. When overdischarged, internal electrodes (i.e., a cathode and an anode) inside a high-voltage battery may be permanently damaged due to sulfation, making it impossible to reuse the battery.

In this regard, to ensure the durability of a battery in a fuel cell vehicle, the battery is managed by setting the lower limit and the upper limit to the SOC value of the battery so that the SOC thereof remains at a suitable level.

That is, in a predetermined situation such as when the SOC value of the battery reaches the upper limit (hereinafter, when the “battery is overcharged”) or when the SOC value of the battery reaches the lower limit (hereinafter when the “battery is overdischarged”), the charging or discharging of the battery is restricted.

When the battery is overcharged, the battery may not be able to store regenerative braking energy any Furthermore, and thus regenerative braking is stopped. At the instant time, the vehicle is free from load and accelerated, and thus the driving quality of the vehicle is degraded. In response to the regenerative braking being stopped, the fuel efficiency may be lowered, which is problematic.

In the overdischarging of the battery, when the load of the vehicle rapidly increases, for example, instantaneous high power is required, a necessary amount of output power cannot be obtained from the battery. In the instant case, driving energy of the fuel cell vehicle should be provided only using the output power of the fuel cell, and thus the motor of the vehicle may fail to sufficiently provide an instantaneously required voltage, disadvantageously degrading the accelerating performance of the vehicle.

Accordingly, provision of a technology able to prevent special situations in which the charging or discharging of the battery is restricted as described above is urgently required.

BRIEF SUMMARY

Various aspects of the present disclosure are directed to providing a battery control system and method of a fuel cell vehicle, the system and method being able to derive the change rate in the SOC value of a battery based on the degree of deterioration of a fuel cell and change the charge control factor or the discharge control factor of the battery according to the derived change rate in the SOC value of the battery, preventing the battery from being overcharged or overdischarged.

To obtain at least one of the above-described objectives, according to an exemplary embodiment of the present disclosure, provided is a battery control system of a fuel cell vehicle. The battery control system may include: a battery providing driving energy of the vehicle; a fuel cell providing the driving energy of the vehicle or charging the battery; and a controller configured to estimate a degree of deterioration of the fuel cell, derive a change rate in an SOC value of the battery based on the degree of deterioration of the fuel cell, and change a charge control factor or a discharge control factor of the battery according to the derived change rate in the SOC value of the battery.

The controller may estimate the degree of deterioration of the fuel cell based on an operating time of the fuel cell or I-V characteristics curves of the fuel cell.

The controller may be configured to determine the degree of deterioration of the fuel cell based on the I-V characteristics curves of the fuel cell. The degree of deterioration of the fuel cell may be estimated based on a voltage of the fuel cell measured at a predetermined reference current.

The predetermined reference current may be a current measured at an upper limit voltage of the fuel cell having a fresh state.

The controller may divide the degrees of deterioration of the fuel cell, estimated based on the operating time of the fuel cell or the I-V characteristics curves of the fuel cell, into a plurality of deterioration sections and derive the change rate in the SOC value of the battery from each of the deterioration sections.

The controller may derive a first change rate of the SOC value of the battery based on the degree of deterioration of the fuel cell, measure a current SOC value of the battery while driving of the vehicle, and derive a second change rate of the SOC value of the battery according to a difference between the current SOC value of the battery measured during the driving of the vehicle and a predetermined reference value.

The controller may derive a third change rate of the SOC value of the battery based on the derived first change rate of the SOC value of the battery and the derived second change rate of the SOC value of the battery.

The controller may change the charge control factor of the battery according to the first change rate of the SOC value of the battery and change the discharge control factor of the battery according to the third change rate of the SOC value of the battery.

The charge control factor of the battery may be an upper limit voltage of the fuel cell, and the discharge control factor of the battery may be an amount of output of the battery.

The controller may change the amount of output of the battery by adjusting a ratio of an output of the battery and an output of the fuel cell or adjusting the upper limit voltage of the battery.

According to an exemplary embodiment of the present disclosure, provided is a battery control method of a fuel cell vehicle. The battery control method may include: estimating, by the controller, the degree of deterioration of the fuel cell; deriving, by the controller, the change rate in the SOC value of the battery based on the degree of deterioration of the fuel cell; and changing, by the controller, the charge control factor or the discharge control factor of the battery according to the derived change rate in the SOC value of the battery.

In the estimating of the degree of deterioration of the fuel cell, the controller may estimate the degree of deterioration of the fuel cell based on an operating time of the fuel cell and I-V characteristics curves of the fuel cell.

The deriving of the change rate in the SOC value of the battery may include: deriving, by the controller, a first change rate of the SOC value of the battery based on the degree of deterioration of the fuel cell; measuring, by the controller, a current SOC value of the battery while driving of the vehicle and deriving, by the controller, a second change rate of the SOC value of the battery according to a difference between a current SOC value of the battery measured while driving of the vehicle and a predetermined reference value; and deriving, by the controller, a third change rate of the SOC value of the battery based on the first change rate of the SOC value of the battery and the second change rate of the SOC value of the battery.

In the changing of the charge control factor or the discharge control factor of the battery, the controller of change the charge control factor of the battery according to the first change rate of the SOC value of the battery and change the discharge control factor of the battery according to the third change rate of the SOC value of the battery.

In the changing of the charge control factor or the discharge control factor of the battery, the controller may change an upper limit voltage of the fuel cell or changes an amount of output of the battery.

The battery control system and method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure has the following effects.

First, it is possible derive the change rate of the SOC value of the battery based on the degree of deterioration of the fuel cell and change the charge control factor or the discharge control factor of the battery according to the derived change rate of the SOC value of the battery, preventing the battery from being overcharged or overdischarged.

Second, it is possible to divide reasons for the change rate of the SOC value of the battery into the degree of deterioration of the fuel cell or the driving pattern of the vehicle and change the charge control factor or the discharge control factor of the battery in response to respective situations, stably adjusting the SOC value of the battery.

Third, it is possible to prevent the battery from being overcharged or overdischarged by stably adjusting the SOC value of the battery, preventing the problems of reduced fuel efficiency and reduced acceleration performance of the vehicle caused by the stopping of the regenerative braking.

DETAILED DESCRIPTION

Furthermore, it will be understood that, although ordinal terms, such as “first” and “second,” may be used herein to describe various elements, these elements may not be limited by these terms. These terms are only used to distinguish one element from another element.

In the description of the present disclosure, when it is determined that the detailed description of related art would obscure the gist of the present disclosure, the detailed description thereof will be omitted. Furthermore, the attached drawings are merely intended to be able to readily understand the exemplary embodiments disclosed herein, and thus the technical idea disclosed herein is not limited by the attached drawings, and it should be understood to include all changes, equivalents, and substitutions included in the idea and technical scope of the present disclosure.

A controller300according to an exemplary embodiment of the present disclosure may include: a communication device communicating with another controller300or a sensor to control undertaking functions; a memory storing an operating system, logic commands, input/output information, and the like; and one or more processors performing judgment, calculation, determination, and the like required to control the undertaking functions.

Hereinafter, the configuration and operating principles of several embodiments of the included disclosure will be described in detail with reference to the drawings. Throughout the drawings, identical or similar constituent elements are provided the same reference numerals, and repeated description thereof will be omitted.

FIG.1is a block diagram illustrating a battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure,FIG.2is a flowchart illustrating a battery control method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure,FIG.3is a graph illustrating I-V characteristics curves of fuel cells200,FIG.4is a graph illustrating the degree of deterioration of the fuel cell200estimated based on the I-V characteristics curves of the fuel cell200,FIG.5is a table illustrating the degrees of deterioration of the fuel cell200estimated based on the I-V characteristics curves of the fuel cell200and divided into a plurality of deterioration sections,FIG.6is a table illustrating the degrees of deterioration of the fuel cell200estimated based on the operating time of the fuel cell200and divided into a plurality of deterioration sections,FIG.7is a table illustrating the rates of change in the SOC value of a battery100individually derived in the respective deterioration sections divided inFIG.5andFIG.6,FIG.8is a table illustrating a second change rate in the SOC value of the battery100derived according to the current SOC value of the battery measured during the driving of a vehicle,FIG.9is a table illustrating changes in the charge control factor of the battery100, andFIG.10is a table illustrating changes in the discharge control factor of the battery100.

Referring toFIG.1, the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure includes the battery100providing driving energy of a vehicle, the fuel cell200providing driving energy of the vehicle or charging the battery100, and the controller300configured to estimate the degree of deterioration of the fuel cell200, derive the change rate in the state of charge (SOC) value of the battery100based on the degree of deterioration of the fuel cell200, and change the charge control factor or the discharge control factor of the battery100according to the derived change rate in the SOC value of the battery100.

In the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure, the “SOC value of the battery100” means a value expressed as a percentage (%) by dividing the currently available capacity of the battery100with the entire capacity of the battery100, and is generally abbreviated to SOC. When the SOC value of the battery100is 100%, this indicates a state in which the battery100is fully charged. In contrast, when the SOC value of the battery100is 0%, this indicates a state in which the battery100is completely exhausted.

As illustrated inFIG.1, the fuel cell vehicle may include the fuel cell200providing driving energy to a motor500of the vehicle, a high-voltage junction box400controlling power supplied to a load600of the vehicle by receiving power from the fuel cell200, and the like as essential components, and may further include the battery100as an auxiliary power source.

Here, the load600of the vehicle may be interpreted as including high-voltage components, such as a vehicle heater, an air conditioner, and a cooling fan, which need to be supplied with power.

As described above in the Background section, in the fuel cell vehicle, in general, the SOC value of the battery100is managed to remain at a suitable level by setting the upper limit and the lower limit of the SOC value of the battery100to obtain the durability of the battery100.

That is, when the battery100is overcharged (i.e., the SOC value of the battery100has reached the upper limit), the charging of the battery100is restricted. Thus, regenerative braking is stopped, and fuel efficiency of the vehicle is reduced. When the battery100is overdischarged (i.e., the SOC value of the battery100has reached the lower limit), the discharging of the battery100is restricted. Thus, the acceleration performance of the vehicle is reduced, which is problematic.

Thus, the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure is directed to estimate the degree of deterioration of the fuel cell200by the controller300, derive the change rate in the SOC value of the battery100based on the degree of deterioration of the fuel cell200, and change the charge control factor or the discharge control factor of the battery100according to the derived change rate in the SOC value of the battery100to prevent a special situation in which the charging or discharging of the battery100is restricted as described above, preventing the problem of reduced fuel efficiency or reduced acceleration performance of the vehicle.

Here, specific operating principles of estimating the degree of deterioration of the fuel cell200and changing the charge control factor or the discharge control factor of the battery100will be described later, and the “change rate in the SOC value of the battery100” will be described first.

As described above, in the fuel cell vehicle, the upper limit and the lower limit of the SOC value of the battery100are set to manage the SOC value of the battery100at an appropriate level. In the instant case, a middle value of the upper limit and the lower limit of the SOC value of the battery100may be set as a target SOC, and the SOC value of the battery100may be controlled to maintain the target SOC.

In this regard, the situation in which the charging or discharging of the battery100is restricted may be prevented by quantifying the degree by which the SOC value of the battery100deviates from the target value as a specific value and changing the charge control factor or the discharge control factor of the battery100according to the quantified value.

That is, according to an exemplary embodiment of the present disclosure, the “change rate in the SOC value of the battery100” may be interpreted as a specific value obtained by quantifying the degree by which the SOC value of the battery100deviates from the target value.

Furthermore, in the following description of the present specification, for a better understanding of the present disclosure, the change rate in the SOC value of the battery100will be expressed according to levels as illustrated inFIG.7,FIG.8,FIG.9and FIG.

For example, situations in which the SOC value of the battery100is the same as the target value will be represented as “level 0,” situations in which the SOC value of the battery100is greater than the target value will be represented as “level+1,” “level+2,” and “level+3” by sequentially expressing increasing positive integers, and situations in which the SOC value of the battery100is smaller than the target value will be represented as “level −1,” “level −2,” and “level −3” by sequentially expressing decreasing negative integers.

When the change rate in the SOC value of the battery100corresponds to a positive integer, the controller300may change the charge control factor so that the ratio of charge of the battery100is reduced and change the discharge control factor so that the ratio of discharge of the battery100is increased.

In contrast, when the change rate in the SOC value of the battery100corresponds to a negative integer, the controller300may change the charge control factor so that the ratio of charge of the battery100is increased and change the discharge control factor so that the ratio of discharge of the battery100is reduced.

That is, the charge control factor or the discharge control factor of the battery100may be changed according to the change rate in the SOC value of the battery100derived as above based on the degree of deterioration of the fuel cell200, preventing the situation in which the charging or discharging of the battery100is restricted.

Meanwhile, as described above, the “change rate in the SOC value of the battery100” means a specific value obtained by quantifying the degree by which the SOC value of the battery100deviates from the target value. The degree by which the SOC value of the battery100deviates from the target value may vary depending on the degree of deterioration of the fuel cell200.

The degree of deterioration of the fuel cell200is a factor directly related to the performance of the fuel cell200. As the degree of deterioration of the fuel cell200is lower, the performance of the fuel cell200may be determined to be higher. When the fuel cell200has high performance, the fuel cell200may generate an excessive amount of electrical energy to meet the required output of the vehicle. As the battery100is charged with the excessive amount of electrical energy generated in the present manner, the SOC value of the battery100may be increased.

In contrast, when the fuel cell200has low performance due to high degree of deterioration of the fuel cell200, the fuel cell200may fail to generate a sufficient amount of electrical energy to meet the required output of the vehicle. In the instant case, the battery100may be discharged to supplement the insufficient portion of the electrical energy, reducing the SOC value of the battery100.

That is, the SOC value of the battery100may be increased or reduced due to the degree of deterioration of the fuel cell200, increasing the change rate in the SOC value of the battery100.

Thus, the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure is directed to derive the change rate in the SOC value of the battery100based on the degree of deterioration of the fuel cell200and change the charge control factor or the discharge control factor of the battery100according to the derived change rate in the SOC value of the battery100to prevent the battery100from being overcharged or overdischarged, prevent the problem of the reduced fuel efficiency or the reduced acceleration performance of the vehicle caused by the stopped regenerative braking.

Hereinafter, specific operating principles of estimating the degree of deterioration of the fuel cell200will be described.

FIG.3is a graph illustrating I-V characteristics curves of the fuel cell200, andFIG.4is a graph illustrating the degree of deterioration of the fuel cell200estimated based on the I-V characteristics curves of the fuel cell200.

Referring toFIG.3andFIG.4, the controller300of the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure may estimate the degree of deterioration of the fuel cell200based on the operating time of the fuel cell200or the I-V characteristics curves of the fuel cell200.

When the fuel cell200is used for an extended time, internal components of the fuel cell200deteriorate due to a variety of reasons, such as pollutants in the air, insufficient supply of a reaction gas while driving, periodic repetition of operation and stopping, the degeneration of electrolyte films, and imperfect driving conditions.

That is, the degree of deterioration of the fuel cell200may generally be proportional to the operating time of the fuel cell200. Thus, the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure estimates the degree of deterioration of the fuel cell200based on the operating time of the fuel cell200.

For example, when the operating time of the fuel cell200is relatively short, the degree of deterioration of the fuel cell200may be estimated to be low. When the operating time of the fuel cell200is relatively long, the deterioration of the fuel cell200may be estimated to be high. In this regard, inFIG.6, the degrees of deterioration of the fuel cell200estimated based on the operating time of the fuel cell200are expressed as being divided into a plurality of deterioration sections of the fuel cell200. Here, the degrees of deterioration of the fuel cell200divided into a plurality of deterioration sections will be described later.

Furthermore, the degree of deterioration of the fuel cell200may be determined based on the I-V characteristics curves of the fuel cell200. The “I-V characteristics curves of the fuel cell200” indicate the performance curves of the fuel cell200, and will be described with reference toFIG.3.

FIG.3illustrates a current-voltage tendency curve A of a fuel cell that has not deteriorated and a current-voltage tendency curve B of a fuel cell that has deteriorated. That is, in the “I-V characteristics curves of the fuel cell200,” I indicates the current of the fuel cell200, and V indicates the voltage of the fuel cell200.

Furthermore, the fuel cell that has not deteriorated indicates an initial fuel cell having a fresh state or a beginning of lift (BOL) state. The deteriorated fuel cell may be interpreted as a fuel cell that needs to be replaced due to the end portion of life (EOL) thereof resulting from deterioration or a fuel cell in a middle of life (MOL) state gradually converting from the BOL state to the EOL state.

Referring toFIG.3, when currents are the same, it may be understood that the current-voltage tendency curve A of the fuel cell that has not deteriorated is positioned above the current-voltage tendency curve B of the fuel cell that has deteriorated.

That is, a voltage drop occurs in which the output voltage of the deteriorated fuel cell is lowered compared to the same current. Thus, the degree of deterioration of the fuel cell200may be estimated according to the degree by which the output voltage of the fuel cell200is lowered when the output voltage is measured by setting a specific current value as a reference current.

The controller300of the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure estimates the degree of deterioration of the fuel cell200based on the I-V characteristics curves of the fuel cell200. Here, the degree of deterioration of the fuel cell200may be estimated based on the voltage of the fuel cell200measured at a predetermined reference current. At the instant time, the predetermined reference current may be characterized by being a current measured at the upper limit voltage of the fuel cell200having a fresh state.

Before a detailed description of the present feature, the upper limit voltage of the fuel cell200will be described for a better understanding of the present disclosure.

The fuel cell vehicle may not only manage the SOC value of the battery100at a suitable level by setting the upper limit and the lower limit of the SOC value of the battery100but also limit the output voltage of the fuel cell200to obtain the durability of the fuel cell200.

Setting the upper limit to the output voltage of the fuel cell200prevents the output voltage of the fuel cell200from being excessively high. When the output voltage of the fuel cell200is higher than the upper limit voltage, an excessive amount of power generated is used to charge the battery100. Consequently, the output voltage of the fuel cell200may be maintained to not exceed the upper limit voltage.

However, in the overcharging of the battery100, electrical energy generated by the fuel cell200may not be stored in the battery100any further. Thus, the output voltage of the fuel cell200may be excessively high, degrading the durability and the performance of the fuel cell200. For example, the fuel cell200may deteriorate.

To prevent this, the upper limit voltage of the fuel cell200may be controlled differently according to the SOC value of the battery100.

For example, when the SOC value of the battery100is near to the upper limit, the upper limit voltage of the fuel cell200may be increased to reduce the excessive amount of generated power used in the charging of the battery100. In contrast, when the SOC value of the battery100is near to the lower limit, the upper limit voltage of the fuel cell200may be lowered, increasing the excessive amount of generated power used in the charging of the battery100.

As the excessive amount of generated power used in the charging of the battery100is increased or reduced in the present manner, the SOC value of the battery100may be adjusted.

Meanwhile, the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure estimates the degree of deterioration of the fuel cell200based on the output current of the fuel cell200measured at the above-described upper limit voltage. This feature will be described in detail with reference toFIG.3andFIG.4.

InFIG.3andFIG.4, C may indicate the upper limit voltage of the fuel cell200. InFIG.3, D may indicate the output current of the fuel cell200in the case of high-power driving. InFIG.4, E may be understood as indicating the output current of the fuel cell200measured at the upper limit voltage of the fuel cell200having a fresh state. That is, according to an exemplary embodiment of the present disclosure, the predetermined reference current may be understood as corresponding to E inFIG.4.

Meanwhile, describing an area (i.e., an area to the right of D inFIG.3) corresponding to an output current higher than D inFIG.3, it may be understood that the difference between the output voltage of the fuel cell200that has not deteriorated and the output voltage of the fuel cell200that has deteriorated decreases with increases in the output current of the fuel cell200.

In other words, the difference between the current-voltage tendency curve A of the fuel cell that has not deteriorated and the current-voltage tendency curve B of the fuel cell that has deteriorated decreases with increases in output power with which the fuel cell vehicle is propelled. Thus, the degree of deterioration of the fuel cell200may not be easily distinguished based on the I-V characteristics curves of the fuel cell200. Accordingly, it is difficult to estimate the degree of deterioration of the fuel cell200.

In contrast, when E inFIG.4is set as a reference current, it may be understood that not only the difference between the current-voltage tendency curve A of the fuel cell that has not deteriorated and the current-voltage tendency curve B of the fuel cell that has deteriorated is relatively large, but also the difference between the current-voltage tendency curve A of the fuel cell that has not deteriorated and the current-voltage tendency curve B of the fuel cell that has deteriorated increases more or less even in the case that the output current of the fuel cell200is greater than E.

Thus, when E inFIG.4is set as the reference current, the degree of deterioration of the fuel cell200may be distinguished based on the I-V characteristics curves of the fuel cell200more easily than in the foregoing case (i.e., a case in which the determination is conducted based on the area to the right of D inFIG.3).

Furthermore, the output current of the fuel cell200measured at the upper limit voltage of the fuel cell200having a fresh state is a value which may be previously derived through a plurality of experiments. The output current of the fuel cell200may be processed into data to be stored in an internal memory of the controller300, and as an advantage, may be easily used as a reference current.

Next, operating principles of deriving the change rate in the SOC value of the battery100based on the degree of deterioration of the fuel cell200estimated by the controller300will be described in detail.

FIG.5is a table illustrating the degrees of deterioration of the fuel cell200estimated based on the I-V characteristics curves of the fuel cell200and divided into a plurality of deterioration sections,FIG.6is a table illustrating the degrees of deterioration of the fuel cell200estimated based on the operating time of the fuel cell200and divided into a plurality of deterioration sections, andFIG.7is a table illustrating the rates of change in the SOC value of a battery100individually derived in the respective deterioration sections divided inFIG.5andFIG.6.

Referring toFIG.5,FIG.6andFIG.7, the controller300of the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure may divide the degrees of deterioration of the fuel cell200, estimated based on the operating time of the fuel cell200or the I-V characteristics curves of the fuel cell200, into a plurality of deterioration sections, and derive each change rate in the SOC value of the battery100for a corresponding one of the plurality of deterioration sections.

InFIG.5, the output voltages of the fuel cell200include four deterioration sections including “More than a,” “a˜b,” “b˜c,” and “Less than c” based on the I-V characteristics curves of the fuel cell200. The degrees of deterioration of the fuel cell200estimated in the respective deterioration sections are expressed as “F, G, H, and I.”

Here, “a, b, and c” are the same as “a, b, and c” illustrated inFIG.4. It may be understood that the output voltages measured from the output current of the fuel cell200measured at the upper limit voltage of the fuel cell200having a fresh state include four deterioration sections.

Furthermore, inFIG.6, the operating times of the fuel cell200include four deterioration sections including “Less than 500 (h),” “500˜1000 (h),” “1000˜2000 (h),” and “More than 200 (h)”, and the degrees of deterioration of the fuel cell200estimated the in respective deterioration sections are expressed as “F, G, H, and I.”

Furthermore, inFIG.7, the degrees of deterioration of the fuel cell200estimated inFIG.5are set as a vertical axis (Estimated by FC I-V Curve), and the degrees of deterioration of the fuel cell200estimated inFIG.6are set as a horizontal axis (Estimated by FC Operating Time). Furthermore, the change rate in the SOC value of the battery100(Change rate in Battery SOC) is expressed as a level.

Here, the change rate in the SOC value of the battery100is expressed as, for example, “level+1”, “level+2,” and “level+3,” by applying a greater positive weight when the degree of deterioration of the fuel cell200is smaller. When the degree of deterioration of the fuel cell200is greater, the change rate in the SOC value of the battery100is expressed as, for example, “level −1,” “level −2,” and “level −3,” by applying a greater negative weight. Furthermore, when all of the degrees of deterioration of the fuel cell200estimated inFIG.5andFIG.6are “H,” the SOC value of the battery100is a same as a target value (Target SOC) which is a middle value of the upper limit and the lower limit. In the instant case, the change rate in the SOC value of the battery100is expressed as “level 0.”

The change rate in the SOC value of the battery100may be derived by dividing the degrees of deterioration of the fuel cell200estimated based on the operating time of the fuel cell200in the present manner and the degrees of deterioration of the fuel cell200estimated based on the I-V curves of the fuel cell200in the present manner into a plurality of deterioration sections and applying weights according to the degree of deterioration of the fuel cell200estimated in the respective deterioration sections.

For reference, the respective deterioration sections divided into a plurality of deterioration sections inFIG.5,FIG.6andFIG.7and a variety of numerical values are only illustrative for a better understanding of the present disclosure, and it may not be understood that the scope of the present disclosure is not limited thereby.

Meanwhile,FIG.8illustrates a second change rate in the SOC value of the battery100derived according to the current SOC value of the battery measured during the driving of the vehicle.

Referring toFIG.8, the controller300of the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure may derive a first change rate of the SOC value of the battery100based on the degree of deterioration of the fuel cell200, measure the current SOC value of the battery100during the driving of the vehicle, and derive the second change rate of the SOC value of the battery100according to the difference between the current SOC value of the battery100measured during the driving of the vehicle and a predetermined reference value. Furthermore, the controller300of the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure may derive a third change rate of the SOC value of the battery100based on the first rate and the second change rate of the SOC value of the battery100derived above.

Factors having effects on the change rate in the SOC value of the battery100include not only the degree of deterioration of the fuel cell200described above but also a “driving pattern of a vehicle.”

Here, the driving pattern of a vehicle may be interpreted as a driving pattern in a variety of situations, for example, as in a case in which an air conditioning system (e.g., an air conditioner or a heater) of a vehicle is not used frequently, a case in which the vehicle frequently repeats driving and stopping, and a case in which regenerative braking is frequently performed, for example, when the vehicle travels on a downhill for an extended time.

In a situation like the driving pattern, the state of discharge of the battery100is relatively reduced or electrical energy with which the battery100is charged is relatively increased, increasing the SOC value of the battery100. In contrast, in a situation opposite to the driving pattern, the state of discharge of the battery100is relatively increased or electrical energy with which the battery100is charged is relatively reduced, reducing the SOC value of the battery100.

That is, when the vehicle is being driven for an extended time in a situation like the above-described driving pattern, the change rate in the SOC value of the battery100increases.

However, the driving pattern is necessarily different according to the vehicle driver, and thus, it is difficult to quantitatively measure an effect on the change rate in the SOC value of the battery100.

Meanwhile, when the current SOC value of the battery100is measured during the driving of the vehicle, the change rate in the SOC value of the battery100may be derived in real time. Furthermore, the change rate in the SOC value of the battery100derived in real time during the driving of the vehicle includes both the degree of deterioration of the fuel cell200and an effect according to the driving pattern of the vehicle.

Thus, the change rate in the SOC value of the battery100according to the driving pattern of the vehicle may be derived by subtracting the change rate in the SOC value of the battery100derived based on the degree of deterioration of the fuel cell200from the change rate in the SOC value of the battery100derived in real time during the driving of the vehicle.

In this regard, the controller300of the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure is configured to derive the first change rate of the SOC value of the battery100based on the degree of deterioration of the fuel cell200, derive the second change rate of the SOC value of the battery100according to the current SOC value of the battery100measured during the driving of the vehicle, and derive the third change rate of the SOC value of the battery100by subtracting the first change rate of the SOC value of the battery100from the second change rate of the SOC value of the battery100.

That is, according to an exemplary embodiment of the present disclosure, it may be understood that the “first change rate of the SOC value of the battery100” means the change rate in the SOC value of the battery100derived based on the degree of deterioration of the fuel cell200, the “second change rate of the SOC value of the battery100” means the change rate in the SOC value of the battery100derived in real time during the driving of the vehicle, and the “third change rate of the SOC value of the battery100” means the change rate in the SOC value of the battery100according to the driving pattern of the vehicle.

Here, the second change rate of the SOC value of the battery100may be derived by the controller300measuring the current SOC value of the battery100during the driving of the vehicle, and according to the difference between the current SOC value of the battery100measured during the driving of the vehicle and the predetermined reference value.

Furthermore, the “predetermined reference value” may be interpreted as being a target value (Target SOC), i.e., a middle value of the upper limit and the lower limit of the SOC value of the battery100.

As a result, the change rate in the SOC value of the battery100according to the driving pattern of the vehicle (i.e., the third change rate of the SOC value of the battery100) may be derived by subtracting the first change rate of the SOC value of the battery100from the second change rate of the SOC value of the battery100as described above.

Accordingly, it is possible to clearly distinguish factors having effects on the change rate in the SOC value of the battery100and thus differently control the effects according to the factors, more effectively preventing the overcharging or overdischarging of the battery100.

FIG.9is a table illustrating changes in the charge control factor of the battery100, andFIG.10is a table illustrating changes in the discharge control factor of the battery100.

Referring toFIG.9andFIG.10, the controller300of the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure may change the charge control factor of the battery100according to the first change rate of the SOC value of the battery100and change the discharge control factor of the battery100according to the third change rate of the SOC value of the battery100.

Here, the charge control factor of the battery100may be characterized by being the upper limit voltage of the fuel cell200, and the discharge control factor of the battery100may be characterized by being the amount of output of the battery100.

That is, the controller300of the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure may change the upper limit voltage of the fuel cell200according to the first change rate of the SOC value of the battery100, and change the amount of output of the battery100according to the third change rate of the SOC value of the battery100.

Here, the amount of output of the battery100may be changed by adjusting the ratio of the output of the fuel cell200and the output of the fuel cell200or adjusting the upper limit voltage of the battery100.

As described above, the “first change rate of the SOC value of the battery100” means the change rate in the SOC value of the battery100derived based on the degree of deterioration of the fuel cell200, and the “third change rate of the SOC value of the battery100” means the change rate in the SOC value of the battery100according to the driving pattern of the vehicle.

That is, according to an exemplary embodiment of the present disclosure, when the change rate in the SOC value of the battery100is derived based on the degree of deterioration of the fuel cell200, the controller300may change the amount of output of the battery100by changing the upper limit voltage of the fuel cell200. When the change rate in the SOC value of the battery100is based on the driving pattern of the vehicle, the controller300may change the amount of output of the battery100by adjusting the ratio of the output of the battery100and the output of the fuel cell200or adjusting the upper limit voltage of the battery100. Hereinafter, these features will be described in more detail with reference toFIG.9andFIG.10.

When the control is performed in J direction inFIG.9, the degree of deterioration of the fuel cell200is relatively low, and the SOC value of the battery100is relatively high. Thus, it may be understood that the control is performed to reduce electrical energy with which the battery100is charged by increasing the upper limit voltage of the fuel cell200.

In contrast, when the control is performed in K direction inFIG.9, the degree of deterioration of the fuel cell200is relatively high, and the SOC value of the battery100is relatively low. Thus, it may be understood that the control is performed to increase electrical energy with which the battery100is charged by reducing the upper limit voltage of the fuel cell200.

When the control is performed in L direction inFIG.10, the driving pattern of the vehicle corresponds to a driving situation of increasing the SOC value of the battery100, and the state of discharge of the battery100is relatively small. Thus, it may be understood that the control is performed to increase electrical energy discharged from the battery100by increasing the amount of output of the battery100.

In contrast, when the control is performed in M direction inFIG.10, the driving pattern of the vehicle corresponds to a driving situation of reducing the SOC value of the battery100, and the state of discharge from the battery100is relatively large. Thus, it may be understood that the control is performed to reduce electrical energy discharged from the battery100by reducing the amount of output of the battery100.

Meanwhile, the battery100disposed in the fuel cell vehicle is used as an auxiliary power source. InFIG.10, it is illustrated that the amount of output of the battery100is changed by adjusting the ratio of the output of the battery100and the output of the fuel cell200.

However, this is only illustrative for a better understanding of the present disclosure, and it may not be understood that the scope of the present disclosure is limited thereby. That is, alternatively, the amount of output of the battery100may be changed by adjusting the upper limit voltage of the battery100.

As a result, it is possible to prevent the battery100from being overcharged or overdischarged by changing the charge control factor or the discharge control factor of the battery100in the present manner.

FIG.2is a flowchart illustrating a battery control method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure.

Referring toFIG.2, the battery control method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure includes: step S100of estimating, by a controller, the degree of deterioration of a fuel cell; steps S210, S220, and S230of deriving, by the controller, the change rate in the SOC value of a battery based on the degree of deterioration of the fuel cell; and steps S310and S320of changing, by the controller, a charge control factor or a discharge control factor of the battery according to the derived change rate in the SOC value of the battery.

In the battery control method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure, the S100of estimating the degree of deterioration of the fuel cell may determine, by the controller, the degree of deterioration of the fuel cell based on the operating time of the fuel cell and the I-V characteristics curves of the fuel cell.

Furthermore, in the battery control method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure, the steps S210, S220, and S230of deriving the change rate in the SOC value of the battery may include: step S210of deriving, by the controller, the first change rate of the SOC value of the battery based on the degree of deterioration of the fuel cell; step S220of measuring, by the controller, the current SOC value of the battery while driving of a vehicle and deriving, by the controller, the second change rate of the SOC value of the battery according to the difference between the current SOC value of the battery measured during the driving of the vehicle and a predetermined reference value; and step S230of deriving, by the controller, the third change rate of the SOC value of the battery based on a first change rate of the SOC value of the battery and a second change rate of the SOC value of the battery.

Meanwhile, in the battery control method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure, the steps S310and S320of changing the charge control factor or the discharge control factor of the battery may change, by the controller, the charge control factor of the battery according to the first change rate of the SOC value of the battery in S310and change, by the controller, the discharge control factor of the battery according to the third change rate of the SOC value of the battery in S320.

Furthermore, in the battery control method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure, the steps S310and S320of changing the charge control factor or the discharge control factor of the battery may change, by the controller, the upper limit voltage of the fuel cell in S310or change the amount of output of the battery in S320.

In each of the steps of the above-described battery control method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure, a specific control method performed by the controller300and a specific operating principle are the same as those described above in the battery control system of a fuel cell vehicle according to an exemplary embodiment of the present disclosure, and repeated descriptions thereof will be omitted.

As set forth above, the battery control system and method of a fuel cell vehicle according to an exemplary embodiment of the present disclosure can derive the change rate in the SOC value of the battery100based on the degree of deterioration of the fuel cell200, change the charge control factor or the discharge control factor of the battery100according to the derived change rate in the SOC value of the battery100, divide reasons for the change rate of the SOC value of the battery100into the degree of deterioration of the fuel cell200or the driving pattern of the vehicle, and change the charge control factor or the discharge control factor of the battery100in response to respective situation. Thus, as an effect, the SOC value of the battery100may be stably adjusted.

Accordingly, it is possible to prevent the battery100from being overcharged or overdischarged, preventing the problems of reduced fuel efficiency and reduced accelerating performance of the vehicle caused by stopped regenerative braking.

In various exemplary embodiments of the present disclosure, each operation described above may be performed by a control device, and the control device may be configured by multiple control devices, or an integrated single control device.