Methods for controlling a fuel cell system

Abstract

A method for controlling a fuel cell system (100) with at least two bypass valves (40a; 40b) arranged between a passage within an inlet of a fuel cell stack (50) and a bypass passage branching off from the passage within the inlet and connected to an exhaust port of the fuel cell stack (50); and a control (80) configured to redirect air supplied by an air blower (20) to the exhaust port by adjusting the degree of opening of each of the bypass valves (40a; 40b), the method comprising: determining, by a control (80), after ignition is switched off or after hydrogen is supplied by a wake-up, hydrogen concentrations in an air supply system and an air exhaust system; and adjusting, by the control (80), the degree of opening of each bypass valve (40a;40b), when the vehicle is subsequently started, based on the determined hydrogen concentrations, wherein the air outlet system comprises an air outlet section that discharges air from a fuel cell stack (50), wherein the air supply system comprises a cathode of the fuel cell stack (50), a humidifying device (30) and an air blower (20), and wherein: determining the hydrogen concentrations comprises: determining, by the control (80), by measuring an elapsed time after the ignition is switched off or after hydrogen is supplied by waking up, that the hydrogen concentrations in the air supply system and the air outlet system are increased when the measured time is greater than a first reference time period;and by adjusting the opening degree of the bypass valve (40a) the air supplied by the air blower (20) is diverted to an exhaust port of the fuel cell stack (50) when it is determined that the hydrogen concentrations are increased.

Description

BACKGROUND 1. Field of the invention

[0001] The present invention generally relates to a fuel cell system and a method for controlling the fuel cell system. More particularly, the present invention relates to a fuel cell system and a method for controlling the same that dilute exhausted hydrogen using a bypass valve disposed between a bypass passage and a passage at an inlet of a fuel cell stack. 2. Description of the state of the art

[0002] A fuel cell vehicle includes a fuel cell stack having a plurality of laminated fuel cells used as a power source; a fuel supply system configured to supply hydrogen as a fuel for the fuel cell stack; an air supply system configured to supply oxygen as an oxidant necessary for electrochemical reactions; and a water and heat management system configured to adjust the temperature of the fuel cell stack. The fuel supply system decompresses compressed hydrogen within a hydrogen tank and supplies the decompressed hydrogen to a fuel electrode (anode) of the stack. The air supply system is configured to supply air, drawn from the outside using an air blower, to an air electrode (cathode) of the stack.

[0003] When hydrogen and air are supplied to the fuel electrode and the air electrode of the stack, respectively, hydrogen ions are extracted through a catalytic reaction at the fuel electrode. The separated hydrogen ions are delivered to the anode through an electrolyte membrane, and the hydrogen ions and electrons from the fuel electrode create an electrochemical reaction with oxygen to generate electrical energy at the anode. Specifically, electrochemical oxidation of hydrogen at the fuel electrode and electrochemical reduction of oxygen at the air electrode cause the electrons to move, and moving electrons generate electricity and heat. Additionally, water vapor, or water, is generated by the chemical action of combining / bonding hydrogen with oxygen.

[0004] An exhaust device is configured to exhaust unreacted hydrogen and oxygen and byproducts generated during electric power generation, including water vapor, water, and heat. Further, gases such as water vapor, hydrogen, and oxygen are exhausted into the air through a ventilation hood. Regarding emissions, in order to meet environmental standards, hydrogen should be exhausted after being diluted with air. Accordingly, a method for reducing the amount of hydrogen when an ignition of a fuel cell vehicle is turned off has been disclosed. However, according to this prior art method, the durability of a fuel cell stack may be impaired, and thus, a method for diluting hydrogen with air supplied from an air supply system of the fuel cell system is needed. SUMMARY

[0005] Accordingly, the present invention provides a fuel cell system and a method for controlling the same that can dilute discharged hydrogen using a bypass valve disposed between a bypass passage and a passage at an inlet of a fuel cell stack.

[0006] A fuel cell system according to an embodiment of the present invention may include: at least one bypass valve disposed between a passage in an inlet of a fuel cell stack and a bypass passage branched from the passage in the inlet and connected to a discharge port of the fuel cell stack; and a controller for bypassing air supplied from an air blower to the discharge port of the fuel cell stack by adjusting an opening degree of the bypass valve. The bypass valve may be disposed at a location between the air blower and a humidifier and / or between the humidifier and an inlet of a fuel cell stack.

[0007] A method for controlling the fuel cell system according to an embodiment of the present invention may include: evaluating / estimating, after an ignition is turned off or after hydrogen is supplied through a wake-up state, hydrogen concentrations in an air supply system and an air discharge system including an air discharge portion for discharging / exhausting air from a fuel cell stack, the air supply system including a cathode of the fuel cell stack, a humidifier, and an air blower; and adjusting an opening degree of a bypass valve when the vehicle is subsequently started based on the evaluated / estimated hydrogen concentrations.

[0008] The evaluation / estimation of the hydrogen concentrations may include determining, by measuring an elapsed time after the ignition is turned off or after hydrogen is supplied through a wake-up mode or state, that the hydrogen concentrations in the air supply system and the air exhaust system are / will be increased if the measured time is greater than a first reference time period. Furthermore, in adjusting the opening degree of the bypass valve, air supplied from the air blower may be diverted to an exhaust port of the fuel cell stack by adjusting the opening degree of the bypass valve if it is predicted / predicted that the hydrogen concentrations are / will be increased.

[0009] Further, the evaluation / estimation of the hydrogen concentrations may include determining, by measuring an elapsed time after the ignition is turned off or after hydrogen is supplied by a wake-up, that the hydrogen concentrations in the air supply system and the air exhaust system are / are reduced when the measured time is greater than a second reference time period. Additionally, in the adjustment of the opening degree of the bypass valve, air supplied from the air blower is not diverted to a discharge port of the fuel cell stack by adjusting the opening degree of the bypass valve when it is predicted / predicted that the hydrogen concentrations are / are reduced.

[0010] The evaluation / estimation of the hydrogen concentrations may also include determining, by measuring an elapsed time after the ignition is turned off or after hydrogen is supplied by a wake-up, that the hydrogen concentrations in the air supply system and the air exhaust system have increased when the measured time is between a first reference time period and a second reference time period. Furthermore, in adjusting the opening degree of the bypass valve, air supplied from the air blower may be diverted to an exhaust opening by adjusting the opening degree of the bypass valve when it is predicted / predicted that the hydrogen concentrations have increased.

[0011] Adjusting the opening degree of the bypass valve may include changing an amount of air bypassed to the discharge port by adjusting the opening degree of the bypass valve based on the estimated / assessed hydrogen concentrations. The method may also include increasing the amount of air bypassed to the discharge port by increasing the opening degree of the bypass valve when the estimated / assessed hydrogen concentrations are substantially high (e.g., greater than a predetermined hydrogen concentration) and increasing the amount of air bypassed to the discharge port by increasing a period of time during which the opening degree of the bypass valve is adjusted when the estimated / assessed hydrogen concentrations are substantially high.

[0012] The hydrogen concentrations evaluated / estimated in the evaluation / estimation of the hydrogen concentrations may be proportional to a hydrogen pressure measured at an anode when an external hydrogen supply is stopped. The hydrogen concentrations may also be proportional to an amount of purged hydrogen when hydrogen purging occurs after the ignition is turned off. The first reference time period may be reduced if an amount of hydrogen crossover from an anode to a cathode of a fuel cell stack is increased.

[0013] Furthermore, the amount of hydrogen transfer depends on a pressure at the anode and a temperature or humidified state of a fuel cell stack, and the amount of hydrogen transfer may increase as the pressure at the anode increases, as the temperature of the fuel cell stack increases, and as the humidified state of the fuel cell stack increases. The first reference time period, which is set when hydrogen purging occurs after the ignition is turned off, may be shorter than the time period set when hydrogen purging does not occur. The second reference time period may decrease as an inflow of air from outside to a fuel cell stack increases.

[0014] The increase in the inflow of air from the outside may be determined by a value measured by an air flow sensor, or by whether a temperature of the fuel cell stack increases, or whether an air shutoff valve for preventing inflow of air from the outside is operating. The second reference time period may be increased when a pressure of hydrogen at an anode is increased, and the second reference time period may be decreased when the pressure of hydrogen at the anode decreases, wherein the pressure of hydrogen at the anode is measured when a supply of hydrogen from the outside is stopped. The second reference time period, which is set when hydrogen purging occurs after the ignition is turned off, may be longer than the time period set when hydrogen purging does not occur.

[0015] A fuel cell system and a method for controlling the same according to an embodiment of the present invention can bypass air to a discharge port through a bypass valve and a bypass passage arranged in an outlet of an air blower or arranged in a passage at an inlet of a fuel cell stack. Accordingly, although hydrogen accumulated in an air supply system is rapidly discharged when the air blower is started, the hydrogen diluted with the bypassed air can be discharged. In addition, since a hydrogen concentration in the air supply system can be estimated, the opening degree of the bypass valve can be adjusted based on the estimated hydrogen concentration, and air whose amount corresponds to the amount of hydrogen to be discharged can be supplied to the discharge port. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. In the figures:

[0017] Fig. 1 and Fig. 2 exemplary block diagrams of a fuel cell system according to an embodiment of the present invention;

[0018] Fig. 3 is an exemplary block diagram illustrating relationships among a fuel cell stack, a humidifier, an air blower, and an air discharge port in a fuel cell system according to an embodiment of the present invention; and

[0019] Fig. 4 is an exemplary graph illustrating a change in a hydrogen concentration within an air supply system included in a fuel cell system of the present invention according to elapsed time after an ignition of a fuel cell vehicle is turned off or after a wake-up, according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] Specific structural or functional descriptions in the embodiments of the present invention disclosed in the specification should not be construed as limiting the invention, and are merely for describing the embodiments of the present invention, which may be embodied in various forms. Particular embodiments are illustrated in the drawings and described in detail in the present specification or application because the embodiments of the present invention may have various forms and modifications. It should be understood, however, that there is no intention to limit the embodiments of the present invention to the specific embodiments, but is intended to cover all modifications / changes, equivalents, and alternatives included within the scope of the present invention.

[0021] It is understood that the term "vehicle" or "vehicle," or other equivalent terms as used herein, includes motor vehicles in general, such as passenger cars, including sports utility vehicles (SUVs), buses, trucks, various utility vehicles, watercraft, including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuel derived from sources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more power sources, such as both gasoline-powered and electric-powered vehicles.

[0022] Although the terms "first," "second," etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another element. For example, a first element could be referred to as a second element, and similarly, a second element could be referred to as a first element without departing from the scope of the present invention. It should be understood that when an element is referred to as being "coupled" or "connected" to another element, it may be directly coupled or connected to the other element, or there may be intervening elements. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, no intervening elements are present.Other words / expressions used to describe the relationship between elements should be interpreted in a similar manner (e.g., “between” versus “directly between,” “adjacent / next to” versus “directly adjacent / next to,” etc.).

[0023] The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is further understood that the terms "comprising" and / or "comprising," when used in this specification, describe the presence of the specified features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0024] Unless otherwise specified, all terms / expressions (including technical and scientific terms / expressions) used herein have the same meaning as those commonly understood by one of ordinary skill in the art to which this invention belongs. It is further understood that terms / expressions, such as those defined in commonly used dictionaries, should be interpreted to have a meaning consistent with their meaning in the context of the prior art and should not be interpreted in an idealized or overly formal sense, unless expressly provided herein.

[0025] Although the embodiment is described as using a plurality of units to perform the example process, it is understood that the example processes may also be performed by one or more modules. Furthermore, it is understood that the term controller / controller refers to a hardware device including a memory and a processor. The memory is configured to store the modules, and the processor is specifically configured to execute said modules to perform one or more processes described below.

[0026] Furthermore, the control logic of the present invention may be embodied as non-transitory computer-readable media on a computer-readable medium comprising executable program instructions executed by a processor, controller, or the like. Examples of computer-readable storage media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards, and optical data storage devices. The computer-readable recording medium may also be decentralized in network-coupled computer systems such that the computer-readable medium is stored and executed in a distributed manner, e.g., through a telematics server or a controller area network (CAN).

[0027] Reference is now made to the drawings, in which the same reference numerals are used throughout the various drawings to designate the same or similar components.

[0028] Fig. 1 and Fig. 2 show exemplary block diagrams of a fuel cell system 100 according to an embodiment of the present invention. With reference to Fig. 1 and Fig. 2, a fuel cell system 100 according to an embodiment of the present invention comprise an air shut-off valve 10 within an inlet, an air blower 20 , a humidification device (humidifier) 30 , bypass valves 40a and 40b , a fuel cell stack 50 , an air shut-off valve 60 within an outlet, a hydrogen tank 70 and a control 80 . In addition, the fuel cell system can100 further comprise a filter (not shown) which is located in front of the air shut-off valve 10 located within the inlet, and a silencer (not shown) located between an inlet of the air blower 20 and an outlet of the air shut-off valve 10 within the inlet of the fuel cell system 100 A purge valve (not shown) and a drain valve (not shown) arranged within an outlet of an anode (fuel electrode) may be further included. Since the parts of the fuel cell system 100 generally understood by a person skilled in the art, descriptions for each of the parts are omitted.

[0029] A fuel cell system 100 According to an embodiment of the present invention, bypass valves 40a and 40b The Fig. 1 bypass valve shown 40acan be placed between an outlet of an air blower 20 and an inlet of a humidification device 30 By setting the degree of opening of the bypass valve 40a can a control 80 a part of the air that is fed to the humidification device 30 by the air blower 20 to be fed to an ejection opening. Based on the setting of the opening degree by the control 80 The amount of air to be diverted to the exhaust opening can be adjusted.

[0030] The Fig. 2 bypass valve shown 40b can be connected between an outlet of a humidification device 30 and an inlet of a fuel cell stack 50 By adjusting the opening degree of the bypass valve 40b can a control 80 a part of the air that is fed to the inlet of the fuel cell stack50 through the humidification device 30 to be fed to an ejection opening. In other words, based on the setting of the opening degree, which is determined by the control 80 The amount of air to be diverted to the discharge opening can be adjusted. The bypass valves 40a and 40b can be switched between a bypass passage and a passage at an inlet of the fuel cell stack 50 be arranged.

[0031] Fig. 3 shows an exemplary block diagram illustrating relationships between a fuel cell stack, a humidifier, an air blower, and an air discharge port in a fuel cell system according to an embodiment of the present invention. Hydrogen transferred from an anode to the cathode and purged / purged hydrogen, which are determined by the temperature and humidified state of the fuel cell stack, are shown in FIG. 50 and can be generated by the difference between the anode pressure and the cathode pressure, can be supplied to an ejection opening through the humidifying device 30 Although an air shut-off valve 60 can be arranged within the outlet to prevent air from flowing from the discharge opening to the humidifying device 30 To prevent this, air can flow into the system from the outside.

[0032] Furthermore, one or more bypass valves40a and 40b be arranged within a fuel cell system. A first bypass valve 40a can be switched between an air blower 20 and a humidification device 30 and a second bypass valve 40b can be used between the humidification device 30 and an inlet of a fuel cell stack 50 The bypass valves 40a and 40b can each be a three-way valve located at a branch point between a passage at an inlet of the fuel cell stack 50 and bypass passages 45a and 45b is arranged.

[0033] By adjusting the degree of opening of the bypass valves 40a and 40b the control 80be configured to adjust the amount of air flowing through the stack and the amount of air bypassing the stack. In addition, the control 80 be arranged to estimate a hydrogen concentration within an air supply system, which will be described later, and may be arranged to determine the degree of opening of the bypass valves 40a and 40b based on the estimated hydrogen concentration.

[0034] Fig. 4 shows an exemplary graph illustrating a change in a hydrogen concentration within an air supply system included in a fuel cell system of the present invention according to the elapsed time after an ignition of a fuel cell vehicle is turned off or after a wake-up mode. Specifically, a wake-up mode or state is described as follows. In response to determining that an ignition-off state in which a fuel cell system is not operating / in operation has been active for a predetermined period of time, a controller may 80 of a fuel cell vehicle to be equipped with an air shut-off valve 60 to prevent air from flowing into a fuel cell stack from outside 50However, over time, air flowing from the outside to a cathode is supplied to an anode. In this situation, when the vehicle is started, a substantially high voltage may be partially generated and a carbon support material may be oxidized, causing a deterioration in performance in a fuel cell. Consequently, in order to adjust the supply of hydrogen, it is necessary for a fuel cell controller 80 is periodically awakened (e.g., initiated from a standby mode or activated from a sleep mode). This process is referred to as wake-up. In other words, it can refer to a period when no hydrogen is supplied to a fuel cell stack, both after the ignition is turned off and after wake-up.

[0035] A method for controlling a fuel cell system of the present invention may include: estimating hydrogen concentrations in an air supply system and in an air exhaust system after an ignition is turned off or after wake-up; and adjusting an opening degree of a bypass valve when the vehicle is started based on the estimated hydrogen concentration. Specifically, the air supply system may include a cathode of a fuel cell stack, a humidifier, and an air blower, and the air exhaust system may include an air exhaust section for discharging / exhausting air from the fuel cell stack. The subject of the above-mentioned method may be a fuel cell controller or a specific controller (e.g., the controller may be configured to execute the method).

[0036] To estimate a hydrogen concentration, the elapsed time after an ignition is turned off or the elapsed time after hydrogen is supplied by a wake-up may be measured. If the measured time is greater than a first reference time period, it may be predicted that the hydrogen concentrations in the air supply system and in the air outlet system are increased. Additionally, the elapsed time after the ignition is turned off or the elapsed time after hydrogen is supplied by a wake-up may be measured, and if the measured time is greater than a second reference time period, it may be predicted that the hydrogen concentrations in the air supply system and in the air outlet system are decreased.

[0037] Furthermore, the elapsed time after the ignition is turned off or the elapsed time after hydrogen is supplied by wake-up may be measured, and if the measured time is between the first reference time period and the second reference time period, it may be predicted that the hydrogen concentrations in the air supply system and the air exhaust system have been increased. Specifically, the first reference time period may be set to decrease as the amount of hydrogen crossover from an anode to a cathode in a fuel cell stack increases. The amount of hydrogen crossover depends on the pressure at an anode side and the temperature or a humidified state of the fuel cell stack.As the pressure at the anode side increases, as the temperature of the fuel cell stack increases, and as the humidified state of the fuel cell stack increases, the amount of hydrogen transfer may increase.

[0038] Furthermore, the first reference time period, which is set when hydrogen purging occurs after an ignition is turned off, may be set to be shorter than the time period set when hydrogen purging does not occur. The second reference time period may be set to be decreased when an inflow of air from an outside into the fuel cell stack increases. The increase in the air flow may be measured by an air flow sensor (not shown). If the air flow sensor is malfunctioning, the increase in the air flow may be determined by determining whether the temperature of the fuel cell stack is increasing or whether an air shutoff valve that prevents an inflow of air from the outside is malfunctioning.

[0039] The hydrogen pressure may be measured at the anode side when supply of hydrogen from the outside is stopped, and when the hydrogen pressure measured at the anode side increases, the second reference time period may be set to be increased. On the other hand, when the hydrogen pressure measured at the anode side decreases, the second reference time period may be set to be increased. The second reference time period, which is set when hydrogen purging occurs after the ignition is turned off, may also be set to be longer when hydrogen purging does not occur.

[0040] The above descriptions are shown in a graph in Fig. 4. In other words, when a predetermined period of time elapses, a hydrogen concentration increases. Then, when another predetermined period of time elapses, the hydrogen concentration decreases. Between the two different periods of time, the hydrogen concentration may remain substantially high. When a hydrogen concentration is predicted to be increased, or when it is predicted that the hydrogen concentration has been increased, air supplied from an air blower may be diverted to a discharge port of a fuel cell stack by adjusting an opening degree of a bypass valve. When a hydrogen concentration is predicted to be decreased, air supplied from the air blower is not diverted to the discharge port of the fuel cell stack by adjusting the opening degree of the bypass valve.

[0041] Furthermore, the amount of air bypassed to the discharge port can be changed by adjusting the opening degree of the bypass valve based on the estimated hydrogen concentration. As the estimated hydrogen concentration increases, the amount of air bypassed to the discharge port can be increased by increasing the opening degree of the bypass valve. Furthermore, as the estimated hydrogen concentration increases, the amount of air bypassed to the discharge port can be increased by increasing the time period during which the opening degree of the bypass valve is adjusted. In other words, by adjusting the opening degree of the bypass valve, the amount of air bypassed to the discharge port of the fuel cell stack can be increased.Specifically, after the valve remains open to a predetermined degree, the opening degree of the bypass valve can be readjusted to supply air to the inlet of the fuel cell stack. In other words, to adjust the amount of air to be bypassed to the exhaust port, the opening degree of the bypass valve can be increased and the time period during which the valve is open to a predetermined degree can be increased.

[0042] The estimated hydrogen concentration may be proportional to the hydrogen pressure measured on the anode side when the external hydrogen supply is stopped. If hydrogen purging occurs after the ignition is turned off, the estimated hydrogen concentration may be proportional to the amount of purged / purged hydrogen. The total amount of hydrogen in a fuel cell stack 50may be a sum of the amount of residual hydrogen in an anode and the amount of purged / discharged hydrogen by hydrogen purging that takes place after the ignition of a fuel cell vehicle is turned off, wherein the amount of residual hydrogen is calculated by the hydrogen pressure after the voltage of the fuel cell stack 50 is completely eliminated. The maximum hydrogen concentration in an air supply system of a fuel cell system 100 can be proportional to the total amount of hydrogen.

[0043] Furthermore, the rate of movement of hydrogen moving to the inside of the air supply system may be the rate of hydrogen transfer from an anode to a cathode. Purged hydrogen may move directly to the air supply system. When air flows in from the outside, the voltage of the fuel cell stack may 50Then, when the voltage is increased by a voltage connected to the fuel cell stack 50 connected fuel cell load device (not shown) is removed, the remaining hydrogen within the fuel cell stack 50 be consumed.

[0044] As in Fig. As shown in Figure 4, a hydrogen concentration in the air supply system can vary according to the total amount of hydrogen, the rate of movement of hydrogen, and the inflow rate of air from outside. Based on these data, the control 80 be set up to estimate the hydrogen concentration in the air supply system and can control the degree of opening of the bypass valves 40a and 40b based on the estimated hydrogen concentration. Especially if an air blower 20is started, hydrogen accumulated in the air supply system can be quickly removed. By estimating the concentration of hydrogen that has accumulated in the air supply system, bypass valves 40a and 40b be operated when the air blower is started. Consequently, the air blower can 20 directed air is supplied to the discharge port to dilute the hydrogen.

[0045] A fuel cell system and a method for controlling the same according to an embodiment of the present invention can bypass air to a discharge port through a bypass valve and a bypass passage disposed within an outlet of an air blower or disposed within a passage at an inlet of a fuel cell stack. Accordingly, although hydrogen accumulated in an air supply system may be rapidly discharged, when the air blower is started, the hydrogen diluted with the bypassed air can be discharged. Moreover, since a hydrogen concentration in the air supply system can be estimated, the opening degree of the bypass valve can be adjusted based on the estimated hydrogen concentration, whereby the air whose amount corresponds to the amount of hydrogen to be discharged can be supplied to the discharge port.

[0046] Although the embodiments of the present invention have been described for illustrative purposes, one of ordinary skill in the art will recognize that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the disclosure as disclosed in the appended claims.

Claims

[1] Fuel cell system, comprising: at least one bypass valve arranged between a passage within an inlet of a fuel cell stack and a bypass passage branched from the passage within the inlet and connected to a discharge opening of the fuel cell stack; and a controller configured to divert air supplied from an air blower to the discharge port by adjusting an opening degree of the bypass valve. [2] The fuel cell system according to claim 1, wherein the bypass valve is arranged between the air blower and a humidifying device and / or between the humidifying device and an inlet of a fuel cell stack. [3] A method for controlling the fuel cell system according to claim 1, comprising: Estimating, by a controller, after an ignition is turned off or after hydrogen is supplied by a wake-up, hydrogen concentrations in an air supply system and an air outlet system; and Setting, by the controller, a degree of opening of a bypass valve when the vehicle is subsequently started, based on the estimated hydrogen concentrations, wherein the air outlet system comprises an air outlet section that discharges air from a fuel cell stack, and wherein the air supply system comprises a cathode of the fuel cell stack, a humidifier, and an air blower. [4] A control method according to claim 3, wherein: estimating the hydrogen concentrations comprises: predicting, by the controller, by measuring an elapsed time after the ignition is turned off or after hydrogen is supplied by the wake-up, that the hydrogen concentrations in the air supply system and the air outlet system will be increased if the measured time is greater than a first reference time period; and in adjusting the opening degree of the bypass valve, air supplied from the air blower is diverted to a discharge port of the fuel cell stack by adjusting the opening degree of the bypass valve when it is predicted that the hydrogen concentrations will be increased. [5] A control method according to claim 3, wherein: estimating the hydrogen concentrations comprises predicting, by the controller, by measuring an elapsed time after the ignition is turned off or after hydrogen is supplied by the wake-up, that the hydrogen concentrations in the air supply system and the air outlet system will be reduced if the measured time is greater than a second reference time period; and in adjusting the opening degree of the bypass valve, air supplied from the air blower is not diverted to a discharge port of the fuel cell stack by adjusting the opening degree of the bypass valve when it is predicted that the hydrogen concentrations are reduced. [6] A control method according to claim 3, wherein: estimating the hydrogen concentrations comprises predicting, by the controller, by measuring an elapsed time after the ignition is turned off or after hydrogen is supplied by a wake-up, that the hydrogen concentrations in the air supply system and the air outlet system have been increased if the measured time is between a first reference time period and a second reference time period; and in adjusting the opening degree of the bypass valve, air supplied from the air blower is diverted to a discharge port of the fuel cell stack by adjusting the opening degree of the bypass valve when it is predicted that the hydrogen concentrations have been increased. [7] The control method according to claim 3, wherein adjusting the opening degree of the bypass valve comprises changing, by the controller, an amount of air bypassed to the discharge port by adjusting the opening degree of the bypass valve based on the estimated hydrogen concentrations. [8] The control method according to claim 7, wherein the adjustment of the opening degree of the bypass valve comprises increasing, by the controller, the amount of air bypassed to the discharge port by increasing the opening degree of the bypass valve when the estimated hydrogen concentrations are increased. [9] The control method according to claim 7, wherein the adjustment of the opening degree of the bypass valve comprises increasing, by the controller, the amount of air bypassed to the discharge port by increasing a time period during which the opening degree of the bypass valve is adjusted when the estimated hydrogen concentrations are increased. [10] The control method according to claim 7, wherein the estimated hydrogen concentrations are proportional to a pressure of hydrogen measured at an anode when a supply of hydrogen from the outside is stopped. [11] The control method according to claim 7, wherein the estimated hydrogen concentrations are proportional to an amount of hydrogen spooled when hydrogen spooling occurs after the ignition is turned off. [12] The control method according to claim 4, wherein the first reference time period is decreased as an amount of hydrogen crossover from an anode to a cathode of a fuel cell stack is increased. [13] A control method according to claim 12, wherein: the amount of hydrogen transfer depends on a pressure at the anode and a temperature or humidified state of a fuel cell stack, and the amount of hydrogen transfer is increased as the pressure at the anode is increased, as the temperature of the fuel cell stack is increased, and as the humidified state of the fuel cell stack is increased. [14] The control method according to claim 4, wherein the first reference time period set when hydrogen purging takes place after the ignition is turned off is smaller than the first reference time period set when hydrogen purging does not take place. [15] The control method according to claim 5, wherein the second reference time period is reduced as an inflow of air from outside to a fuel cell stack is increased. [16] The control method according to claim 15, wherein the increase in the inflow of air from the outside is determined by a value measured by an air flow sensor, or is determined by whether a temperature of the fuel cell stack increases or whether an air shutoff valve for preventing an inflow of air from the outside is in operation. [17] The control method according to claim 5, wherein the second reference time period is increased when a pressure of hydrogen at an anode is increased, and the second reference time period is decreased when the pressure of hydrogen at the anode is decreased, wherein the pressure of hydrogen at the anode is measured when a supply of hydrogen from the outside is stopped. [18] The control method according to claim 5, wherein the second reference time period set when hydrogen purging takes place after the ignition is turned off is longer than the second reference time period set when hydrogen purging does not take place. [19] The control method according to claim 6, wherein the first reference time period is decreased as an amount of hydrogen transfer from an anode to a cathode of a fuel cell stack is increased. [20] The control method according to claim 6, wherein the first reference time period set when hydrogen purging takes place after the ignition is turned off is smaller than the first reference time period set when hydrogen purging does not take place. [21] The control method according to claim 6, wherein the second reference time period is reduced as an inflow of air from outside to a fuel cell stack is increased. [22] The control method according to claim 6, wherein the second reference time period is increased when a pressure of hydrogen at an anode is increased, and the second reference time period is decreased when the pressure of hydrogen at the anode is decreased, wherein the pressure of hydrogen at the anode is measured when a supply of hydrogen from the outside is stopped. [23] The control method according to claim 6, wherein the second reference time period set when hydrogen purging takes place after the ignition is turned off is longer than the second reference time period set when hydrogen purging does not take place.

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