Method for measuring impedance of a fuel cell stack in a vehicle

Abstract

The present disclosure relates to a method for accurately measuring the impedance of a fuel cell stack in a vehicle during vehicle operation, the method comprising: determining whether measurement of the impedance of the fuel cell stack is requested during operation of the vehicle driven by utilizing the electric power of the fuel cell stack; when impedance measurement is requested, switching a DC-DC converter connecting the fuel cell stack and a battery to a step-down mode, thereby cutting off the output current of the fuel cell stack from flowing to the battery through the DC-DC converter; determining a first current value of the fuel cell stack for measuring the impedance; controlling the resistance value of a COD variable resistor that consumes the output current of the fuel cell stack based on the first current value; and measuring the impedance of the fuel cell stack while maintaining the output current of the fuel cell stack at the first current value.

Description

Technical Field

[0001] The present disclosure relates to a method for measuring the impedance of a fuel cell stack in a vehicle, and more particularly, to a method for accurately measuring the impedance of a fuel cell stack during vehicle operation. Background Art

[0002] Measuring impedance is a common method for understanding the state of a fuel cell stack. By measuring the impedance of a fuel cell stack at various frequency bands, the physical phenomena of the internal state of the fuel cell stack can be understood.

[0003] In the high-frequency region, ohmic losses can be determined by estimating the charge within the fuel cell stack, while in the low-frequency region, material transfer loss characteristics in the cathode catalyst layer and gas diffusion layer of the fuel cell can be estimated. Furthermore, in the frequency region between the high-frequency and low-frequency regions, activation losses, including hydrogen ion migration and electrochemical reaction characteristics, in the porous catalyst layer of the fuel cell can be determined.

[0004] Typically, at a steady-state operating point of the fuel cell stack (e.g., constant current or constant voltage), after a small AC signal is applied to the voltage terminal (output terminal) of the fuel cell stack for each frequency band, the impedance is measured using the amplitude and phase difference of the response signal to the applied signal.

[0005] However, during vehicle operation, it is difficult for the output of the fuel cell stack to reach a stable state at a predetermined operating point for measuring impedance, and even when it reaches a stable state, it is difficult to maintain the stable state.

[0006] Furthermore, even when the fuel cell stack's output reaches a steady state at a predetermined operating point, it is difficult to accurately measure the stack's impedance due to the impedance of various peripheral components connected to the stack. Consequently, the accuracy of measuring the stack's impedance is reduced.

[0007] The foregoing is only intended to help understand the background of the present disclosure, and is not intended to indicate that the present disclosure falls within the scope of the prior art known to those skilled in the art. Summary of the Invention

[0008] Therefore, the present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a method for measuring the impedance of a fuel cell stack in a vehicle to accurately measure the impedance of the fuel cell stack during operation of the vehicle.

[0009] In order to achieve the above-mentioned purpose according to one aspect of the present disclosure, a method for measuring the impedance of a fuel cell stack in a vehicle is provided, the method comprising: a first step of determining whether measurement of the impedance of the fuel cell stack is requested during operation of a vehicle driven by utilizing the electric power of the fuel cell stack; a second step of switching a DC-DC converter connecting the fuel cell stack and the battery to a step-down mode when impedance measurement is requested, thereby cutting off the output current of the fuel cell stack from flowing to the battery through the DC-DC converter; a third step of determining a first current value of the fuel cell stack for measuring impedance; a fourth step of controlling the resistance value of a COD variable resistor that consumes the output current of the fuel cell stack based on the first current value; and a fifth step of measuring the impedance of the fuel cell stack while maintaining the output current of the fuel cell stack at the first current value.

[0010] According to the present disclosure, when it is determined in the first step that a request is made to measure the impedance of the fuel cell stack, the battery state of charge (SOC) can be increased to a value greater than or equal to a preset first reference value by charging the fuel cell stack before switching the DC-DC converter to the step-down mode.

[0011] In addition, according to the present disclosure, when the DC-DC converter operates in the step-down mode, the fuel cell stack can operate to output current according to the required current of the COD variable resistor and stack peripheral devices.

[0012] Therefore, when the required current for driving the stack peripheral devices changes when measuring the impedance of the fuel cell stack in the fifth step, the resistance value of the variable resistor may be changed for each preset frequency band to maintain the output of the fuel cell stack at the first current value.

[0013] In addition, in the fifth step, the SOC of the battery is monitored while the impedance of the fuel cell stack is measured for each preset frequency band. When the SOC of the battery is less than or equal to a second reference value that is a predetermined value smaller than the first reference value, the impedance measurement of the fuel cell stack may be stopped and the DC-DC converter may be switched to a boost mode so that the output of the fuel cell stack is supplied to the motor for driving the vehicle through the DC-DC converter.

[0014] In addition, according to the present disclosure, when the impedance measurement of the fuel cell stack is completed in the fifth step, it can be determined whether to request the impedance measurement of the fuel cell stack again. When the impedance measurement of the fuel cell stack is re-requested, a second current value for measuring the impedance can be determined, the resistance value of the COD variable resistor can be controlled according to the second current value, and the impedance of the fuel cell stack can be re-measured when the output current of the fuel cell stack maintains the second current value. In this case, the second current value can be different from the first current value.

[0015] As described above, by solving the above-mentioned problem, the present disclosure can control the output current of the fuel cell stack to a desired constant current value when the impedance of the fuel cell stack is requested to be measured. Therefore, the impedance of the fuel cell stack can be measured at a desired operating point (current value), and the impedance of the fuel cell stack can also be measured at various operating points. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 is a diagram showing a fuel cell system of a vehicle according to the present disclosure;

[0018] Figure 2 is a graph showing an example of a current region in which the impedance of a fuel cell stack can be measured;

[0019] Figure 3 is a diagram illustrating a control process for measuring impedance of a fuel cell stack according to the present disclosure; and

[0020] Figure 4 is a graph showing an example of impedance in each frequency band measured at various current values at which the fuel cell stack operates. DETAILED DESCRIPTION

[0021] Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement it. In all drawings, the same reference numerals refer to the same or similar parts.

[0022] Typically, to measure the impedance of a fuel cell stack in a vehicle, the output of the fuel cell stack must reach a steady state of constant current or constant voltage.

[0023] In other words, in order to measure the impedance of a fuel cell stack installed in a vehicle, the output of the fuel cell stack must reach a constant current state, in which the output of the fuel cell stack is maintained at a constant current value, or the output of the fuel cell stack must reach a constant voltage state, in which the output of the fuel cell stack is maintained at a constant voltage value.

[0024] That is, in order to accurately measure the impedance of the fuel cell stack when the vehicle is driven using the power of the fuel cell stack, the fuel cell stack must maintain a state of outputting a constant current or a constant voltage for a predetermined time.

[0025] When the conditions for measuring the impedance of the fuel cell stack are satisfied, impedance measurement may be performed for each frequency band of the fuel cell stack.

[0026] Figure 1is a diagram illustrating a fuel cell system of a vehicle according to the present disclosure.

[0027] like Figure 1 As shown, when a fuel cell stack 1 is installed in a vehicle, the fuel cell stack 1 is configured to be connected to: a battery 2 that can be charged by the output current of the fuel cell stack 1; a DC-DC converter 5 that can perform power switching when the battery 2 is charged; a motor 3 for driving the vehicle and driven by the battery 2 as a power source (power source); and stack peripheral devices 7 used when the fuel cell stack 1 is operating. The stack peripheral devices 7 include an air compressor 7a configured to supply air to the fuel cell stack 1; a coolant pump 7b configured to circulate and supply coolant to the fuel cell stack 1; and other components. For reference, the stack peripheral devices 7 are also referred to as battery-operated parts (BOPs).

[0028] As described above, since the fuel cell stack 1 is connected to various components in the vehicle, it is difficult to accurately measure the impedance of the fuel cell stack 1 during vehicle operation. In addition, even if the impedance of the fuel cell stack 1 is measured when the output of the fuel cell stack 1 reaches a stable state of constant current or constant voltage, the measured impedance value includes the impedance of the components connected to the fuel cell stack 1, thereby reducing the measurement accuracy of the impedance.

[0029] Therefore, in order to accurately measure the impedance of the fuel cell stack 1 , it is necessary to measure only the impedance of the fuel cell stack 1 in a stable state where the fuel cell stack 1 outputs a constant current.

[0030] In addition, since measuring the impedance of the fuel cell stack 1 at a low frequency band requires a relatively long time, in order to measure the impedance of the fuel cell stack 1 at each frequency band, a stable state in which a constant current is output from the fuel cell stack 1 must be maintained for a predetermined time.

[0031] In addition, in order to grasp the physical phenomenon of the internal state of the fuel cell in each current range, it is necessary not only to accurately measure the impedance of the fuel cell stack 1 but also to measure the impedance of the fuel cell stack 1 in each current range.

[0032] Therefore, in the present disclosure, the output current of the fuel cell stack 1 can be accurately measured by maintaining the output current of the fuel cell stack 1 in a stable state for a predetermined time. At the same time, the output current of the fuel cell stack 1 is controlled to a desired current value, thereby measuring the impedance of the fuel cell stack 1 in various current regions.

[0033] Reference Figure 1 The fuel cell system of the present disclosure is configured to include: a DC-DC converter 5 capable of switching the output power of the fuel cell stack 1 and supplying the output power to the battery 2; and a resistor that can deplete the power of the fuel cell stack 1 when the fuel cell system stops.

[0034] Here, the DC-DC converter 5 is electrically connected to the fuel cell stack 1 through the first junction box 9 and is electrically connected to the battery 2 through the second junction box 10. That is, the fuel cell stack 1 is connected to the battery 2 through the DC-DC converter 5.

[0035] In addition, the first junction box 9 electrically connects the fuel cell stack 1 and the DC-DC converter 5 . At the same time, the first junction box 9 electrically connects the fuel cell stack 1 and the stack peripheral device 7 , and electrically connects the fuel cell stack 1 and the COD variable resistor 6 .

[0036] In addition, the second junction box 10 connects the battery 2 and the DC-DC converter 5. At the same time, the second junction box 10 connects the battery 2 and the motor 3, and also connects the battery 2 and the automotive electronic component 4. In addition, in some embodiments, the automotive electronic component 4 is an onboard automotive electronic component driven by consuming the power of the battery 2, and the motor 3 is a device for generating driving force for the vehicle.

[0037] The resistor is a variable resistor whose resistance value changes according to a command of the fuel cell controller 11 , and specifically, the resistor is the COD variable resistor 6 .

[0038] The COD variable resistor 6 may perform the function of rapidly heating the coolant supplied to the fuel cell stack 1 to increase the temperature of the coolant at cold start of the vehicle and the function of removing residual oxygen inside the fuel cell stack 1 at start or shut down of the vehicle.

[0039] The fuel cell controller 11 may change and control the resistance value of the COD variable resistor 6 so that the fuel cell stack 1 operates at at least two current values selected within the current range of the fuel cell stack 1 .

[0040] The current range of the fuel cell stack 1 is a current range that the fuel cell stack 1 can output during operation of the fuel cell stack 1 . Figure 2 is a graph showing the operating point of a fuel cell stack as an example. Figure 2 As shown, the fuel cell stack 1 can operate at predetermined operating points and can output voltage and current corresponding to each operating point. For example, the fuel cell stack 1 can output a current in the range of 0 to 100A with 300V as the reference, and can output a current in the range of 0 to 120A with 250V as the reference.

[0041] More specifically, the fuel cell controller 11 controls the resistance value of the COD variable resistor 6 so that the operation of the fuel cell stack 1 can be performed at a current value at which impedance measurement is desired in the current region of the fuel cell stack 1 .

[0042] The COD variable resistor 6 is a variable resistance device configured such that a resistance value is changed by a command sent from the fuel cell controller 11. Therefore, the output current of the fuel cell stack 1 can be controlled by controlling the resistance value of the COD variable resistor 6.

[0043] When measuring the impedance of the fuel cell stack 1, in order to eliminate the influence of components (motor, automotive electronic components, etc.) connected to the DC-DC converter 5 through the second junction box 10 and ensure the measurement accuracy of the impedance of the fuel cell stack 1, the fuel cell controller 11 switches the DC-DC converter 5 to the step-down mode.

[0044] When the DC-DC converter 5 operates in step-down mode, the current generated in the fuel cell stack 1 is cut off from flowing to the battery 2. That is, when the DC-DC converter 5 operates in step-down mode, the internal circuit that supplies the output current of the fuel cell stack 1 to the second junction box 10 is cut off. In other words, the DC-DC converter 5 may include an internal circuit that is configured to prevent the output current of the fuel cell stack 1 from being applied to the second junction box 10 when operating in step-down mode.

[0045] Therefore, when the DC-DC converter 5 switches to the step-down mode, the output current of the fuel cell stack 1 is cut off from flowing to the battery 2 through the DC-DC converter 5 .

[0046] When the DC-DC converter 5 is not switched to step-down mode, the impedance of the fuel cell stack 1 may be measured with reduced accuracy due to the connection of the battery 2, motor 3, etc. to the second junction box 10. Therefore, when it is required to measure the impedance of the fuel cell stack 1, the DC-DC converter 5 needs to be switched to step-down mode.

[0047] The fuel cell controller 11 may receive a request signal from the impedance meter 8 for measuring the impedance of the fuel cell stack 1. Before measuring the impedance of the fuel cell stack 1, the impedance meter 8 may request the fuel cell controller 11 to establish system conditions for measuring the impedance. If the fuel cell controller 11 receives the request signal from the impedance meter 8, the fuel cell controller 11 may determine that the impedance of the fuel cell stack 1 is being measured.

[0048] Therefore, when the fuel cell controller 11 receives a request signal for measuring the impedance of the fuel cell stack 1 , the fuel cell controller 11 switches the DC-DC converter 5 to the step-down mode.

[0049] In order to ensure normal operation of the motor 3 and the vehicle electronic components 4 driven by the power of the battery 2, the fuel cell controller 11 switches the DC-DC converter 5 to the step-down mode when the state of charge (SOC) of the battery 2 is greater than or equal to a predetermined first reference value α.

[0050] Therefore, when the fuel cell controller 11 receives a request signal for measuring the impedance of the fuel cell stack 1, if the SOC of the battery 2 is less than the first reference value α, the fuel cell controller 11 increases the SOC of the battery 2 to greater than or equal to the first reference value α before switching the DC-DC converter 5 to the step-down mode.

[0051] The fuel cell controller 11 may increase the SOC of the battery 2 by charging the battery 2 using the fuel cell stack 1. In this case, the fuel cell controller 11 may switch the output power of the fuel cell stack 1 supplied to the battery 2 using the DC-DC converter 5.

[0052] Furthermore, after switching the DC-DC converter 5 to the step-down mode, when the SOC of the battery 2 is less than or equal to a second reference value β, the fuel cell control unit 11 switches the DC-DC converter 5 to the step-up mode. The second reference value β is set to an SOC that is a predetermined value lower than the first reference value α.

[0053] When the SOC of battery 2 is less than or equal to a second reference value β, fuel cell controller 11 determines that the driving stability of motor 3 using the power of battery 2 has deteriorated, and switches DC-DC converter 5 to a boost mode to ensure driving safety of the vehicle. The SOC of battery 2 may decrease below the second reference value β due to over-discharge of battery 2.

[0054] When the DC-DC converter 5 operates in the boost mode, the DC-DC converter 5 can convert the power of the fuel cell stack 1 into a power level that can be used by the motor 3, thereby directly applying the converted power of the fuel cell stack 1 to the motor 3. To this end, the DC-DC converter 5 is configured to include an internal circuit to boost the output of the fuel cell stack 1 to a driving voltage level for the motor 3 when operating in the boost mode.

[0055] That is, when the SOC of the battery 2 decreases below the second reference value β, the fuel cell controller 11 switches the DC-DC converter 5 to the boost mode so that the output of the fuel cell stack 1 is used to drive the vehicle.

[0056] After the DC-DC converter 5 switches to the step-down mode, when the SOC of the battery 2 is greater than the second reference value β, the fuel cell controller 11 determines a current value (first current value) for measuring the impedance of the fuel cell stack 1 .

[0057] In this case, the first current value is a current value selected from current values included in the current region of the fuel cell stack 1 , and may be determined as a current value suitable for a physical phenomenon that grasps the internal state of the fuel cell stack 1 .

[0058] After the first current value is determined, the resistance value (first resistance value) of the COD variable resistor 6 may be determined and controlled based on the first current value.

[0059] When the DC-DC converter 5 operates in the step-down mode, the output current of the fuel cell stack 1 is determined according to the required current (current consumption) of the stack peripheral device 7 and the COD variable resistor 6. In other words, when the DC-DC converter 5 operates in the step-down mode, the fuel cell stack 1 works to output current according to the required current of the COD variable resistor 6 and the stack peripheral device 7.

[0060] Therefore, the current consumption of the COD variable resistor 6 can be calculated by subtracting the required current value of the stack peripheral device 7 from the first current value, and the first resistance value of the COD variable resistor 6 can be determined according to the current consumption of the COD variable resistor 6 .

[0061] The resistance value of the COD variable resistor 6 can be controlled to a first resistance value according to a command of the fuel cell controller 11. When the COD variable resistor 6 is controlled to the first resistance value, the fuel cell stack 1 can operate at a first current value. In other words, when the resistance value of the COD variable resistor 6 is controlled to the first resistance value, the fuel cell stack 1 operates in a state of outputting a current corresponding to the first current value.

[0062] Since the COD variable resistor 6 is a component whose power consumption is determined, when the resistance value is controlled to be the first resistance value, a predetermined current is consumed according to the first resistance value.

[0063] Therefore, the operating point of the fuel cell stack 1 can be controlled to the first current value by controlling the resistance value of the COD variable resistor 6 to the first resistance value according to the command of the fuel cell controller 11 .

[0064] After driving the COD variable resistor 6 according to the first resistance value and driving the stack peripheral device 7 to drive the fuel cell stack 1 , the impedance meter 8 measures the impedance of the fuel cell stack 1 for each frequency band when the output current of the fuel cell stack 1 stabilizes to a steady state.

[0065] When the output current of the fuel cell stack 1 maintains the first current value, the impedance meter 8 measures the impedance of the fuel cell stack 1. When the impedance meter 8 measures the impedance of the fuel cell stack 1, the output voltage of the fuel cell stack 1 is constantly controlled.

[0066] In order to ensure that the output current of the fuel cell stack 1 has an amplitude within a predetermined range when measuring impedance, the air compressor 7a can supply a predetermined flow rate of air to the fuel cell stack 1. If the output current of the fuel cell stack 1 deviates from the amplitude within the predetermined range, the amplitude of the output current of the fuel cell stack 1 can be controlled within the predetermined range by adjusting the flow rate of air supplied to the fuel cell stack 1.

[0067] While the impedance meter 8 measures the impedance of the fuel cell stack 1 for each predetermined frequency band, the fuel cell controller 11 monitors the SOC of the cell 2 .

[0068] When the SOC of the battery 2 is less than or equal to the second reference value β during the impedance measurement of the fuel cell stack 1 , the fuel cell controller 11 immediately stops measuring the impedance to ensure driving safety of the vehicle and switches the DC-DC converter 5 to the boost mode.

[0069] When the DC-DC converter 5 operates in the boost mode, the output of the fuel cell stack 1 is used for driving the vehicle.

[0070] On the other hand, since the stack peripheral device 7 includes an air compressor 7a, a coolant pump 7b, etc. related to the operation and power generation of the fuel cell stack 1, the required current for driving the stack peripheral device 7 may vary according to the state of the fuel cell stack 1.

[0071] Therefore, when the required current of the stack peripheral device 7 changes during the measurement of the impedance of the fuel cell stack 1 , the output of the fuel cell stack 1 can be kept at the first current value by changing the resistance value of the COD variable resistor 6 .

[0072] More specifically, the output current of the fuel cell stack 1 may vary when the required current of the stack peripheral device 7 changes, and in this case, it is impossible to measure the impedance of the fuel cell stack 1 for each frequency band.

[0073] Therefore, when the required current of the stack peripheral device 7 changes, the required current of the COD variable resistor 6 is recalculated by subtracting the changed required current of the stack peripheral device 7 from the first current value. Then, the resistance value of the COD variable resistor 6 is re-determined based on the recalculated required current of the COD variable resistor 6. At this time, the re-determined resistance value of the COD variable resistor 6 is the first basic resistance value.

[0074] The fuel cell controller 11 controls the resistance value of the COD variable resistor 6 to the first basic resistance value so that the output current of the fuel cell stack 1 becomes maintained at the first current value.

[0075] When the impedance measurement of the fuel cell stack 1 is completed, the fuel cell controller 11 re-determines whether impedance measurement is required. That is, when the impedance measurement is completed at the first current value, the fuel cell controller 11 determines whether further impedance measurement of the fuel cell stack 1 is required.

[0076] To this end, the fuel cell controller 11 monitors whether a request signal for measuring impedance is re-transmitted from the impedance meter 8. When the impedance meter 8 re-transmits the request signal, the fuel cell controller 11 re-determines another current value (second current value) for measuring the impedance of the fuel cell stack 1.

[0077] In other words, the fuel cell controller 11 determines a second current value for measuring the impedance of the fuel cell stack 1 according to the re-request of the impedance meter 8. Here, the second current value is a current value included in the operating region of the fuel cell stack 1 and is determined to be a current value different from the first current value.

[0078] The fuel cell controller 11 controls the resistance value of the COD variable resistor 6 based on the second current value, and the impedance meter 8 measures the impedance of the fuel cell stack 1 operated to output the second current value.

[0079] At the same time, the fuel cell controller 11 may re-execute the same control process as the control process in which the fuel cell stack 1 operates to output the first current value.

[0080] After measuring the impedance of the fuel cell stack 1 operating at the second current value, another current value can be selected and the impedance of the fuel cell stack 1 can be measured at the selected current value. Therefore, by repeating such a process, the impedance of the fuel cell stack 1 can be measured at various operating points (current values).

[0081] In the following, reference will be made to Figure 3 A control process for measuring the impedance of the fuel cell stack 1 is described.

[0082] like Figure 3 As shown, in step S10, first, the fuel cell controller 11 determines whether to request the measurement of the impedance of the fuel cell stack 1 during vehicle operation. If the fuel cell controller 11 receives a request signal for measuring the impedance of the fuel cell stack 1 from the impedance meter 8, the fuel cell controller 11 determines that the impedance measurement is requested.

[0083] When the fuel cell controller 11 receives the request signal, the fuel cell controller 11 determines whether the SOC of the battery 2 is greater than or equal to a predetermined first reference value α in step S11. When the SOC of the battery 2 is less than the first reference value α, the fuel cell stack 1 is used to charge the battery 2 in step S12. When the SOC of the battery 2 is greater than or equal to the predetermined first reference value α, the DC-DC converter 5 is switched to a step-down mode in step S13.

[0084] Next, in step S14, it is determined whether the SOC of battery 2 exceeds a second reference value β. If the SOC of battery 2 exceeds the second reference value β, in step S15, a first current value is selected for measuring the impedance of fuel cell stack 1, and the resistance value of COD variable resistor 6 is controlled to a first resistance value based on the first current value.

[0085] Next, in order to make the fuel cell stack 1 operable, at step S16 , the stack peripheral device 7 is driven and the COD variable resistor 6 is operated.

[0086] Subsequently, in step S17 , the impedance of the fuel cell stack 1 is measured using the impedance meter 8 .

[0087] At the first current value (operating point) of the fuel cell stack 1, after a very small AC signal is applied to the voltage terminal (output terminal) of the fuel cell stack 1 for each frequency band, the impedance meter 8 measures the impedance of the fuel cell stack 1 using the amplitude and phase difference of the response signal to the applied AC signal.

[0088] The SOC of battery 2 is monitored while measuring the impedance of fuel cell stack 1. Specifically, in step S18, a determination is made as to whether the SOC of battery 2 exceeds a preset second reference value β. If, as a result of this determination, the SOC of battery 2 exceeds the second reference value β, the impedance of fuel cell stack 1 continues to be measured. Furthermore, if the SOC of battery 2 is less than or equal to the second reference value β, in step S19, DC-DC converter 5 is switched to a boost mode.

[0089] In addition, the required current of the stack peripheral device 7 is monitored while measuring the impedance of the fuel cell stack 1 , and in step S20 , it is determined whether the required current of the stack peripheral device 7 has changed.

[0090] When it is determined that the required current of the stack peripheral device 7 has changed, the resistance value of the COD variable resistor 6 is re-determined in step S21 so that the output of the fuel cell stack 1 maintains the first current value.

[0091] When it is determined that the required current of the stack peripheral device 7 does not change, the impedance of the fuel cell stack 1 is continuously measured.

[0092] When measuring the impedance of the fuel cell stack 1 , the fuel cell controller 11 determines in step S22 whether the impedance meter 8 has completed measuring the impedance of the fuel cell stack 1 operating at the first current value.

[0093] On the other hand, when it is determined in step S14 that the SOC of the battery 2 is less than or equal to the second reference value β, in step S19, the fuel cell controller 11 switches the DC-DC converter 5 to the boost mode. When the DC-DC converter 5 operates in the boost mode, the output of the fuel cell stack 1 is supplied through the DC-DC converter 5 to the motor 3 for driving the vehicle.

[0094] When it is determined in step S22 that the measurement of the impedance of the fuel cell stack 1 is completed, the fuel cell controller 11 determines in step S10 whether the impedance meter 8 requests measurement of the impedance of the fuel cell stack 1 again.

[0095] The fuel cell controller 11 determines whether to further request measurement of the impedance of the fuel cell stack 1 to ensure an impedance value required to grasp the physical phenomenon of the internal state of the fuel cell stack 1 .

[0096] When it is determined that the measurement of the impedance of the fuel cell stack 1 is requested again, the fuel cell controller 11 executes steps S11 to S22 again.

[0097] At this time, in the above-mentioned step S15, the current value used to measure the impedance of the fuel cell stack 1 is reselected to a current value (second current value) different from the first current value, the resistance value of the COD variable resistor 6 is controlled according to the second current value, and in step S17, when the output current of the fuel cell stack 1 maintains the second current value, the impedance of the fuel cell stack 1 is remeasured.

[0098] When the measurement of the impedance of the fuel cell stack 1 is requested, the fuel cell controller 11 may repeatedly perform steps S11 to S22 , and thus, the impedance of the fuel cell stack 1 at various current values (operating points) may be measured and obtained.

[0099] As described above, when the physical phenomenon of the internal state of the fuel cell stack 1 is analyzed using the impedance of the fuel cell stack 1 measured at various current values, the analysis can be performed more accurately than when the impedance of the fuel cell stack 1 is measured and obtained at one current value.

[0100] Figure 4 : is a graph showing an example of impedance in each frequency band measured at various current values when the fuel cell stack is operated. Figure 4 , the impedance curves measured at each current value of the fuel cell stack operation show various aspects.

[0101] Therefore, when the impedance of the fuel cell stack is measured and obtained at various current values (operating points), the internal physical phenomena of the fuel cell stack can be grasped more accurately.

[0102] Although preferred embodiments of the present disclosure have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.

Claims

1. A method for measuring the impedance of a fuel cell stack in a vehicle, comprising: In a first step, a fuel cell controller receives an instruction to determine whether measurement of the impedance of the fuel cell stack is requested during operation of the vehicle driven by utilizing electric power of the fuel cell stack; A second step, when a request is made to measure the impedance, switching a DC-DC converter connecting the fuel cell stack and a battery to a step-down mode, thereby cutting off the output current of the fuel cell stack from flowing to the battery through the DC-DC converter, thereby eliminating the influence of components connected to the DC-DC converter through a junction box when measuring the impedance of the fuel cell stack; The third step is to determine a first current value of the fuel cell stack for measuring the impedance; A fourth step is to control the resistance value of a COD variable resistor that consumes the output current of the fuel cell stack based on the first current value, and when the required current of a stack peripheral device changes, recalculate the required current of the COD variable resistor by subtracting the changed required current of the stack peripheral device from the first current value, and then re-determine the resistance value of the COD variable resistor based on the recalculated required current of the COD variable resistor; as well as A fifth step is to measure the impedance of the fuel cell stack while maintaining the output current of the fuel cell stack at the first current value.

2. The method according to claim 1, wherein When it is determined in the first step that the impedance measurement of the fuel cell stack is requested, before the DC-DC converter is switched to the step-down mode, the battery state of charge, i.e., SOC, is increased to a value greater than or equal to a preset first reference value by charging the fuel cell stack.

3. The method according to claim 2, wherein: In the fifth step, the SOC of the battery is monitored during measurement of the impedance of the fuel cell stack for each preset frequency band, and when the SOC of the battery is less than or equal to a second reference value that is a predetermined value smaller than the first reference value, measuring the impedance of the fuel cell stack is stopped and the DC-DC converter is switched to a boost mode so that the output of the fuel cell stack is supplied to a motor for driving a vehicle through the DC-DC converter.

4. The method according to claim 1, wherein When the DC-DC converter operates in the step-down mode, the fuel cell stack operates to output current according to the required current of the COD variable resistor and the stack peripheral devices.

5. The method according to claim 4, wherein When the required current for driving the stack peripheral devices changes when measuring the impedance of the fuel cell stack in the fifth step, the resistance value of the variable resistor is changed for each preset frequency band to maintain the output of the fuel cell stack at the first current value.

6. The method according to claim 2, wherein: After the DC-DC converter switches to the step-down mode, when the SOC of the battery is less than or equal to a second reference value that is a predetermined value smaller than the first reference value, the DC-DC converter is switched to the step-up mode so that the output of the fuel cell stack is supplied to the motor for driving the vehicle through the DC-DC converter.

7. The method according to claim 1, wherein When the measurement of the impedance of the fuel cell stack is completed in the fifth step, it is determined whether to request a new measurement of the impedance of the fuel cell stack.

8. The method according to claim 7, wherein: When the impedance of the fuel cell stack is re-requested to be measured, a second current value for measuring the impedance is determined, the resistance value of the COD variable resistor is controlled according to the second current value, and the impedance of the fuel cell stack is re-measured when the output current of the fuel cell stack maintains the second current value.

9. The method according to claim 8, wherein The second current value is different from the first current value.

10. The method according to claim 4, wherein: The COD variable resistor is electrically connected to the fuel cell stack through a first junction box connecting the fuel cell stack to the DC-DC converter, and the stack peripheral device is electrically connected to the fuel cell stack through the first junction box.

11. The method according to claim 6, wherein: The motor is electrically connected to the battery through a second junction box that connects the battery to the DC-DC converter.

Images