Voltage control method and system for fuel cell

Abstract

Method for controlling the voltage of a fuel cell (10), the method comprising steps of: Determine (S100) whether a mode is a high-voltage avoidance mode of the fuel cell (10), Controlling a fuel cell stack voltage so that it is a predetermined reference value or less (S200) when the mode is the high-voltage avoidance mode of the fuel cell (10), Monitoring individual cell voltages of the fuel cell (10) and determining (S300) whether a maximum value of the monitored individual cell voltages exceeds a predetermined individual value, Reducing a reference value of the fuel cell stack voltage (S500) when the maximum value of the monitored individual cell voltages exceeds the predetermined individual value, and Controlling the fuel cell stack voltage to the reduced reference value or less (S600), the method further comprising a step of monitoring (S400) a state of charge (SOC) of a battery (50) before reducing a reference value of the fuel cell stack voltage (S500), wherein in the step of reducing the reference value of the fuel cell stack voltage (S500) a reduction amount of the reference value is set differently according to the monitored state of charge of the battery (50).

Description

Technical field

[0001] The present invention relates to a method and a system for controlling the voltage of a fuel cell, wherein the method and the system are able to improve the durability of a fuel cell stack by varying the maximum command voltage value of the fuel cell stack based on the individual cell voltage. background

[0002] A fuel cell, which is a type of device that converts chemical energy from a fuel into electrical energy through an electrochemical reaction in a fuel cell stack, without converting the chemical energy into heat by burning the fuel, can be used not only to supply energy to industry, households and vehicles, but also to supply energy to small electrical / electronic products, especially mobile devices.

[0003] Recently, research has focused particularly on fuel cells, which utilize energy generated by combining hydrogen and oxygen. If a fuel cell stack is exposed to an OCV (open circuit voltage), it can be damaged and the stack's performance degraded, so technologies to prevent this problem have been investigated.

[0004] A technology for limiting the upper voltage limit of a fuel cell stack to a predetermined level to improve the stack's durability has been disclosed. However, when the upper voltage limit of the entire stack is limited to a predetermined level, voltage differences among the individual cells subject the individual cells of the stack to high stress, even if the overall stack stress does not exceed the upper voltage limit. Therefore, deterioration (e.g., damage, wear, etc.) of individual cells cannot be prevented.

[0005] The description provided above as a related technique of the present disclosure serves only to promote understanding of the background of the present disclosure and should not be regarded as belonging to the prior art as known to the person skilled in the art.

[0006] Furthermore, DE 11 2008 000 096 T5 discloses a fuel cell system comprising: a fuel cell which receives a supplied reaction gas for power generation, and a control device which is designed such that, when a power demand for the fuel cell is less than a predetermined value, it controllably stops the supply of the reaction gas to the fuel cell, and maintains an output voltage of the fuel cell equal to a voltage to avoid a high potential which is lower than an open-circuit voltage, and, when the power demand for the fuel cell is equal to or greater than a predetermined value, controls the output voltage of the fuel cell, wherein the voltage to avoid a high potential is set as an upper limit. Explanation of the invention

[0007] The present invention was made in an effort to solve the problems described above, and one objective of the present invention is to provide a method and a system for controlling a voltage of a fuel cell, wherein the method and the system varies a voltage of a fuel cell stack according to the state of charge of a battery based on the voltage of individual cells (hereinafter also referred to as "individual cell voltage") of a fuel cell stack.

[0008] To achieve the above objective, according to one aspect of the present invention, a method for controlling a fuel cell voltage according to claim 1 is provided, the method comprising steps of: determining whether a mode is a high-voltage avoidance mode (e.g., a control mode is a high-voltage avoidance control) of the fuel cell; controlling a fuel cell stack voltage to a predetermined reference value or less if the mode is the high-voltage avoidance mode of the fuel cell; monitoring individual cell voltages of the fuel cell (e.g., monitoring voltages of individual cells or elementary cells of the fuel cell stack); and determining whether a maximum value of the monitored individual cell voltages exceeds a predetermined individual value (e.g.,The method comprises a step of monitoring the state of charge (SOC) of a battery prior to reducing the reference value of the fuel cell stack voltage. This step involves, according to the invention, the process of reducing the reference value of the fuel cell stack voltage by a variable amount (e.g., the value by which the reference value is reduced) is set according to the monitored state of charge of the battery. The method further includes a step of monitoring the state of charge (SOC) of a battery prior to reducing the reference value of the fuel cell stack voltage. In the step of reducing the reference value of the fuel cell stack voltage, a reduction amount (e.g., the value by which the reference value is reduced) of the reference value is set differently according to the monitored state of charge of the battery.

[0009] In the step of reducing the reference value of the fuel cell stack voltage, the amount by which the reference value of the fuel cell can be reduced the higher the monitored state of charge of the battery is.

[0010] In the step of reducing the reference value of the fuel cell stack voltage, the amount of the reduction in the fuel cell reference value can be greater the lower the monitored state of charge of the battery is.

[0011] If the battery state of charge (SOC) monitored in the battery state of charge monitoring step is a predetermined initial state of charge or higher, when decreasing a reference value of the fuel cell stack voltage, the reference value of the fuel cell stack voltage can be maintained (e.g., instead of decreasing the reference value of the fuel cell stack voltage, the reference value is maintained), even if a maximum (or maximum value) of the individual cell voltages exceeds the predetermined individual value.

[0012] The procedure may, after reducing the reference value of the fuel cell stack voltage, further include steps of: monitoring a charging current for the battery, and reducing an output (e.g., a power output) of the fuel cell stack if the monitored charging current for the battery is a predetermined charging current or more.

[0013] In the step of reducing the output of the fuel cell stack, the amount of air supplied to the fuel cell stack can be reduced.

[0014] In the step of determining whether a mode is a high-voltage avoidance mode, it can be determined that the mode is the high-voltage avoidance mode of the fuel cell if a required (electrical) current for the fuel cell stack is a predetermined required value or less.

[0015] To achieve the above objective, according to a further aspect of the present invention, a system for controlling the voltage of a fuel cell according to claim 8 is provided, wherein the system comprises: a high-voltage avoidance mode detector (e.g., high-voltage avoidance mode detecting device) for determining whether a mode is a high-voltage avoidance mode of the fuel cell, and an individual cell voltage monitor (e.g., individual cell voltage monitoring device) for calculating and monitoring voltages of individual cells (also called single cells or individual cells).Element cells) of the fuel cell, a fuel cell stack voltage control unit for controlling a fuel cell stack voltage so that it is at a predetermined reference value or less when the high-voltage avoidance mode detector determines that the mode is high-voltage avoidance mode, and for reducing the predetermined reference value and controlling the fuel cell stack voltage to the reduced reference value or less when a maximum value of the voltages of the individual cells monitored by the individual cell voltage monitor exceeds a predetermined individual value, and a state-of-charge (SOC) sensor for monitoring a state of charge of a battery, wherein when reducing the reference value of the fuel cell stack voltage, a reduction amount of the reference value is set differently according to the monitored state of charge of the battery.

[0016] The fuel cell stack voltage control unit can decrease the reduction amount of the fuel cell reference value when the battery state of charge monitored by the SOC sensor is high (e.g., less than a first state of charge threshold and greater than or equal to a second state of charge threshold (different from the first state of charge threshold)), and can increase the reduction amount of the fuel cell reference value when the monitored battery state of charge is low (e.g., less than the second state of charge threshold).

[0017] If the battery charge level monitored by the SOC sensor is a predetermined charge level or higher (e.g., greater than or equal to the first charge level threshold), the fuel cell stack voltage control unit can maintain the reference value of the fuel cell stack voltage, even if the maximum value of the individual cell voltages exceeds the predetermined individual value.

[0018] The system may further include: a charging current sensor for monitoring the charging current for the battery, and an output control unit for controlling an output (e.g., a power output) of the fuel cell stack, wherein, if the charging current for the battery monitored by the charging current sensor is a predetermined charging current or greater, the output control unit may reduce the output of the fuel cell stack.

[0019] According to the method and system for controlling the fuel cell voltage, it is possible to further secure the durability and performance of individual fuel cells (e.g., single cells or unit cells of a fuel cell stack) compared to a structure that uses an upper limit voltage of a stack. Brief description of the drawings

[0020] The above and other objectives, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, wherein: Fig. 1 is a flowchart which represents a method of controlling a voltage of a fuel cell according to an embodiment of the present invention, and Fig. 2 is a diagram which represents the structure of a system for controlling a voltage of a fuel cell according to an embodiment of the present invention. Detailed description

[0021] Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. Fig. 1 is a flowchart which represents a method of controlling a voltage of a fuel cell according to an embodiment of the present invention, and Fig. Figure 2 is a diagram illustrating the structure of a system for controlling the voltage of a fuel cell according to an embodiment of the present invention.

[0022] Referring to Fig. 1 comprises a method for controlling a fuel cell voltage according to an embodiment of the present invention, for example: determining whether a mode is a high-voltage avoidance mode of the fuel cell (e.g., a mode for avoiding a high voltage (e.g., high voltage) in the fuel cell) (S100), controlling (e.g., regulating) a fuel cell stack voltage (e.g., a voltage of the entire fuel cell stack) to a predetermined reference value or less when the mode is the high-voltage avoidance mode of the fuel cell (S200), monitoring individual cell voltages of the fuel cell (e.g., monitoring the voltages of the individual cells orUnit cells of the fuel cell stack) and determine whether the maximum value of the monitored individual cell voltages exceeds a predetermined individual value (S300), reduce a reference value of the fuel cell stack voltage if the monitored individual cell voltages exceed the predetermined individual value (e.g., surpass) (S500), and control (e.g., regulate) the fuel cell stack voltage to the reduced reference value or less (S600).

[0023] According to the method of controlling the voltage of a fuel cell, it is possible to ensure the durability (e.g. lifespan) of the individual cells by reducing the reference value of the fuel cell stack by monitoring whether the individual cell voltages of the fuel cell exceed the individual value.

[0024] Referring to Fig. 2 comprises a system for controlling the voltage of a fuel cell according to an embodiment of the present invention, for example: a high-voltage avoidance mode detector 20, which determines whether a mode is the high-voltage avoidance mode of a fuel cell 10; an individual cell voltage monitor 30, which calculates and monitors voltages of individual cells of the fuel cell 10; and a fuel cell stack voltage control unit 40, which controls a fuel cell stack voltage to a predetermined reference value or less when the high-voltage avoidance mode detector determines that the mode is the high-voltage avoidance mode; and which reduces the predetermined reference value and controls the fuel cell stack voltage to the reduced reference value or less when the maximum value of the individual cell voltages monitored by the individual cell voltage monitor 30 is exceeded.exceeds a predetermined individual value.

[0025] The high-voltage avoidance mode detector 20, the individual cell voltage monitor 30 and the fuel cell stack voltage control unit 40 are implemented, for example, by means of software instructions which are executed on a processor.

[0026] The method of controlling the voltage of a fuel cell according to an embodiment of the present invention, which is described in Fig. As shown in Figure 1, the system for controlling the voltage of a fuel cell stack, which is located in Fig. 2 is shown, can be achieved.

[0027] Referring to Fig. 1 and Fig.Step 2 is therefore determining whether a mode is a high-voltage avoidance mode of a fuel cell (S100). This step involves the high-voltage avoidance mode detector 20 determining whether a mode is the high-voltage avoidance mode by determining whether the fuel cell 10 is subjected to a high voltage. Specifically, it is possible to determine that the mode is the high-voltage avoidance mode of the fuel cell if a current required for the fuel cell stack is a predetermined required value or less. The required value A can, for example, be set to 50 A.

[0028] If the fuel cell does not meet the high-voltage avoidance mode condition (S210), it will not enter high-voltage avoidance mode or it will be switched off or deactivated.

[0029] If the fuel cell is in high-voltage avoidance mode, then controlling the fuel cell stack voltage to a predetermined reference value or less (S200) is a step in which the fuel cell stack voltage control unit 40 prevents the fuel cell stack 10 from being exposed to a voltage exceeding a reference value stored in a memory 41 connected to the fuel cell stack voltage control unit 40. The reference value may initially be set to 374 V in the memory 41 (e.g., an initial (unreduced) reference value of 374 volts in the memory 41).

[0030] To control the fuel cell stack voltage to the reference value or less, it may be possible in detail to set a maximum value as a reference value in a command value of a bidirectional (high) voltage converter (BHDC) 51, which is connected to the fuel cell 10 to charge a battery 50, or it may be possible (e.g. by means of current control) to cause a current to be consumed by a low voltage converter (LDC) 42 or a high voltage load 43, which is connected to electrical components.

[0031] Monitoring individual cell voltages of the fuel cell and determining whether the maximum value of the monitored individual cell voltages exceeds a predetermined individual value (S300) is a step in which the individual cell voltage monitor 30 monitors the voltages of the individual cells and determines whether the maximum value exceeds the individual value (e.g., each individual cell of the fuel cell stack is monitored to see if its maximum voltage exceeds a cell-specific (voltage) threshold). The individual value can, for example, be set to 0.85 V (374 V / 440 cells = 0.85 V / cell).

[0032] If the maximum value of the individual cell voltages does not exceed the individual value, it may be possible to maintain the reference value instead of decreasing it (S530).

[0033] If the maximum value of the monitored individual cell voltages exceeds the individual value, it is possible to check the chargeable quantity (e.g. chargeable energy quantity) of the battery 50 by monitoring the state of charge of the battery 50 by means of an SOC sensor 52 connected to the battery 50 when monitoring the state of charge (S400) before reducing the reference value of the fuel cell stack voltage (S500).

[0034] Reducing the reference value of the fuel cell stack voltage (S500) allows the reduction amount to be set differently depending on the battery's state of charge, which is monitored by the fuel cell stack voltage control unit 40. The reduction amount for the battery's state of charge reference value can be pre-stored in memory 41, which is connected to the stack voltage control unit 40.

[0035] In detail, since the battery's chargeable capacity decreases as the monitored state of charge increases, the amount by which the fuel cell's reference value is reduced can be controlled. Conversely, since the battery's chargeable capacity increases as the monitored state of charge decreases, the amount by which the fuel cell's reference value is reduced can be controlled.

[0036] However, if the monitored state of charge of the battery is a predetermined state of charge or higher, it is possible to maintain the reference value of the fuel cell stack voltage (S500) when reducing the reference value of the fuel cell stack voltage, even if the maximum of the individual cell voltages exceeds the predetermined individual value.

[0037] For example, reference values ​​for the battery's state of charge are set as α and β, and it is determined whether the state of charge is less than α (S410), equal to or greater than α and less than β (S420), or β or greater. If the state of charge is less than α, the reduction amount of the reference value is set to V1 (S510); if the state of charge is equal to or greater than α and less than β, the reduction amount of the reference value is set to V2 (S520); and if the state of charge is β or greater, the reference value is retained (S530). For example, β is the predetermined state of charge, and V1 is greater than V2. For example, α can be set to 40% of the maximum state of charge of the battery, β can be set to 60% of the maximum state of charge of the battery, V1 can be set to 20 [V] and V2 can be set to 10 [V].

[0038] Since, when the battery's state of charge is low, the upper voltage reference value of the fuel cell stack is significantly reduced by the control described above during battery charging, the stack's lifespan can be improved. Furthermore, when the battery's state of charge is high, it is difficult to charge the battery further, which is why the upper voltage reference value of the fuel cell stack is slightly reduced or maintained, thus making it possible to improve the system's efficiency.

[0039] Controlling the fuel cell stack voltage to the reduced reference value or less (S600) is a step in which the fuel cell stack voltage control unit 40 controls the voltage of the fuel cell 10 (or the fuel cell stack voltage) to the reduced or maintained reference value or less.

[0040] To control the fuel cell stack voltage to the reference value or less, it may be possible in detail to set a maximum value as a reference value in a command value of a bidirectional (high) voltage converter (BHDC) 51, which is connected to the fuel cell 10 to charge a battery 50, or it may be possible (e.g. by means of current control) to cause a current to be consumed by a low voltage converter (LDC) 42 or a high voltage load 43, which is connected to electrical components.

[0041] After reducing (or maintaining) the reference value of the fuel cell stack voltage, a charging current for the battery is monitored (S700). A charging current sensor 53, connected to the bidirectional (high-)voltage converter 51, determines whether the charging current flowing to the battery 50 is a predetermined charging current or higher. The predetermined charging current can, for example, be set to 2 A. If the charging current flowing to the battery 50 is 2 A or higher, then it can be determined that the charging current for the battery is excessive (e.g., too high).

[0042] If the monitored charging current for the battery is the predetermined charging current or higher, the output (e.g., power output) of the stack is reduced (S800), with an output control unit 60 reducing the stack's output. If the monitored charging current of the battery is not equal to or higher than the predetermined charging current, the stack's output is not reduced.

[0043] In reducing the output of the stack (S800), it is possible in detail to reduce the output of the stack by reducing the amount of air (e.g., oxygen) supplied to the fuel cell stack.

[0044] Although the present invention has been described with reference to specific embodiments shown in the drawings, the person skilled in the art understands that the present invention can be modified and changed in numerous ways without deviating from the scope of the present invention as described in the following claims.

Claims

[1] Method of controlling the voltage of a fuel cell (10), the method comprising steps of: Determine (S100) whether a mode is a high-voltage avoidance mode of the fuel cell (10), Controlling a fuel cell stack voltage so that it is a predetermined reference value or less (S200) when the mode is the high-voltage avoidance mode of the fuel cell (10), Monitoring individual cell voltages of the fuel cell (10) and determining (S300) whether a maximum value of the monitored individual cell voltages exceeds a predetermined individual value, Reducing a reference value of the fuel cell stack voltage (S500) when the maximum value of the monitored individual cell voltages exceeds the predetermined individual value, and Controlling the fuel cell stack voltage to the reduced reference value or less (S600), the method further comprising a step of monitoring (S400) a state of charge (SOC) of a battery (50) before reducing a reference value of the fuel cell stack voltage (S500), wherein in the step of reducing the reference value of the fuel cell stack voltage (S500) a reduction amount of the reference value is set differently according to the monitored state of charge of the battery (50). [2] Method according to claim 1, wherein in the step of reducing the reference value of the fuel cell stack voltage (S500), the higher the monitored state of charge of the battery (50) is, the smaller the reduction amount of the reference value of the fuel cell (10). [3] Method according to claim 1 or 2, wherein in the step of reducing the reference value of the fuel cell stack voltage (S500), the lower the monitored state of charge of the battery (50) is, the greater the reduction amount of the reference value of the fuel cell (10). [4] Method according to any one of claims 1 to 3, wherein, if the state of charge of the battery (50), which is monitored in step (S400) of monitoring the SOC of the battery (50), is a predetermined state of charge (β) or more, the reference value of the fuel cell stack voltage is maintained when a reference value of the fuel cell stack voltage is reduced, even if a maximum of the individual cell voltages exceeds the predetermined individual value. [5] Method according to any one of claims 1 to 4, further comprising steps of: after the step of reducing the reference value of the fuel cell stack voltage (S500), Monitoring a charging current (S700) for the battery (50), and Reducing an output (S800) of the fuel cell stack when the monitored charging current for the battery (50) is a predetermined charging current or more. [6] Method according to claim 5, wherein in the step of reducing the output (S800) of the fuel cell stack, the amount of air supplied to the fuel cell stack is reduced. [7] Method according to any one of claims 1 to 4, wherein in the step of determining (S100) whether a mode is a high-voltage avoidance mode, it is determined that the mode is the high-voltage avoidance mode of the fuel cell (10) if a required current for the fuel cell stack is a predetermined required value (A) or less. [8] System for controlling the voltage of a fuel cell (10), comprising: a high-voltage avoidance mode detector (20) to determine whether a mode is a high-voltage avoidance mode of the fuel cell (10), an individual cell voltage monitor (30) for calculating and monitoring voltages of individual cells of the fuel cell (10), a fuel cell stack voltage control unit (40) for controlling a fuel cell stack voltage so that it is at a predetermined reference value or less when the high-voltage avoidance mode detector (20) determines that the mode is the high-voltage avoidance mode, and for reducing the predetermined reference value and controlling the fuel cell stack voltage to the reduced reference value or less when a maximum value of the voltages of the individual cells monitored by the individual cell voltage monitor (30) exceeds a predetermined individual value, and a state of charge sensor (SOC sensor 52) for monitoring the state of charge of a battery (50), where, when reducing the reference value of the fuel cell stack voltage, the reduction amount of the reference value is set differently according to the monitored state of charge of the battery (50). [9] System according to claim 8, wherein the fuel cell stack voltage control unit (40) decreases the reduction amount of the fuel cell reference value (10) when the state of charge of the battery (50) monitored by the SOC sensor is high, and increases the reduction amount of the fuel cell reference value when the monitored state of charge of the battery (50) is low. [10] System according to claim 8 or 9, wherein, when the state of charge of the battery (50) monitored by the SOC sensor is a predetermined state of charge or greater, the fuel cell stack voltage control unit (40) maintains the reference value of the fuel cell stack voltage, even if the maximum value of the individual cell voltages exceeds the predetermined individual value. [11] System according to any one of claims 8 to 10, further comprising: a charging current sensor (53) for monitoring the charging current for the battery (50), and an output control unit (60) for controlling an output of the fuel cell stack, wherein, if the charging current for the battery (50) monitored by the charging current sensor (53) is a predetermined charging current or greater, the output control unit (60) reduces the output of the fuel cell stack.

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