KR20130127289A - Apparatus and method for monitoring of fuel cell using step signal - Google Patents

Abstract

The present invention relates to a device and a method for monitoring a fuel cell using step signals. The device for monitoring a fuel cell using step signals according to one embodiment comprises a signal generator applying step signals to a fuel cell; a signal processor calculating impedance of the fuel cell using measured step response signals when the step signals are applied; and a determination unit determining the abnormality of the fuel cell by comparing the calculated impedance of the fuel cell to a predetermined reference impedance. As a result, the device quickly monitors the fuel cell by applying the step signals to the fuel cell, analyzing a response thereof, and calculating the impedance of the fuel cell. [Reference numerals] (20) Load;(31) Signal generation unit;(32) Signal processing unit;(33) Determination unit

Description

Apparatus and method for diagnosing the state of fuel cell using step signal {APPARATUS AND METHOD FOR MONITORING OF FUEL CELL USING STEP SIGNAL}

The present invention relates to an apparatus and method for diagnosing a state of a fuel cell using a step signal, and more particularly, a technique of determining a state of a fuel cell membrane by applying a step signal to a fuel cell and measuring a response thereof.

Currently, as the power supply for driving a vehicle, the type of polymer electrolyte membrane fuel cell (PEMFC) having the highest power density among fuel cells (PEMFC) is being studied. Fast start-up time and fast power conversion response time. The polymer electrolyte membrane fuel cell evenly distributes the reaction gas generated through a membrane electrode assembly (MEA) having a catalytic electrode layer having an electrochemical reaction on both sides of the solid polymer electrolyte membrane in which hydrogen ions move, and generated. Gas Diffusion Layer (GDL), which serves to transfer electrical energy, gaskets and fasteners for maintaining the tightness and proper fastening pressure of the reaction gases and cooling water, and separators for moving the reaction gases and cooling water. (Bipolar Plate) is included.

A plurality of unit cells are stacked on the unit cell, a current collector, an insulating plate, and an end plate for supporting the stacked cells are coupled to the outermost unit cell. Thereby forming a fuel cell stack. In order to obtain a potential required in an actual vehicle, unit cells must be stacked as many as required, and stacking unit cells is a stack. The electromotive force of the unit cell depends on fuel and oxygen. For example, in the case of a hydrogen fuel cell using hydrogen, the ideal output voltage is about 1.3V, so that a plurality of cells are stacked in series to produce electric power for driving a vehicle.

On the other hand, in the fuel cell vehicle, the cell voltage is used for grasping the stack performance, operation state, failure, etc., and is used for various control of the system such as flow rate control of the reaction gas. It is measured by connecting to cell voltage measuring device by lead wire.

In the conventional method of determining the performance of a fuel cell, it is determined whether the performance is abnormal depending on the wet state by using the resistance of the electrolyte membrane of the fuel cell. In this case, there is a method of measuring impedance by applying a specific frequency within a frequency range corresponding to the internal resistance of the fuel cell. However, this method takes a long time to measure the impedance of the fuel cell, has a problem of synchronizing signals, and precisely manipulating the frequency of the signals.

The background technology of the present invention is described in Korean Patent Publication No. 10-0985149 (2010. 09. 28).

The technical problem to be achieved by the present invention is to diagnose the state according to the amount of water in the fuel cell electrolyte membrane by calculating the impedance of the fuel cell by applying the step signal to the fuel cell and analyzing the response to diagnose the state of the fuel cell And to provide a technique for determining the appropriate operating conditions.

An apparatus for diagnosing a state of a fuel cell using a step signal according to an embodiment of the present invention includes a signal generator for applying a step signal to a fuel cell, and a step response signal measured when the step signal is applied to the fuel cell. And a signal processor to calculate an impedance of the fuel cell, and a determiner to determine whether the fuel cell is abnormal by comparing the calculated impedance of the fuel cell with a preset reference impedance.

The step signal is a signal of a current component, and the step response signal is a signal of a voltage component.

The signal processor may calculate an impedance of the fuel cell by using a Laplace transform of the step signal and the step response signal as a function of time.

In addition, the signal processor may use the following equation to calculate the impedance of the fuel cell:

Where Z (s) is the impedance of the fuel cell, I ₂ (s) is the Laplace transform of the step signal i ₂ (t), and V (s) is the Laplace transform of the step response signal v (t).

The signal processor may calculate the membrane resistance of the fuel cell using an initial step response signal among the step response signals.

The signal processor may calculate an active resistance of the fuel cell using a steady state step response signal among the step response signals.

In addition, the signal processor may apply an edge detection algorithm or a Fourier transform to the step response signal to calculate a boundary between the characteristics of the membrane resistance of the fuel cell and the characteristics of the active resistance of the fuel cell and the electric double layer capacitance. A fuel cell state diagnosis device using a step signal.

According to still another aspect of the present invention, there is provided a method of diagnosing a state of a fuel cell using a step signal, the method comprising: applying a step signal to a fuel cell, measuring a step response signal corresponding to the step signal from the fuel cell; And calculating an impedance of the fuel cell by using the measured step response signal, and determining whether the fuel cell is abnormal by comparing the calculated impedance of the fuel cell with a preset reference impedance.

Thus, according to the present invention, by applying the step signal to the fuel cell and analyzing the response to calculate the impedance of the fuel cell, it is possible to quickly diagnose the state of the fuel cell. In addition, since the impedance of the fuel cell can be calculated in the time domain, the configuration of the diagnostic device can be simplified and the cost can be reduced.

1 is a block diagram of an apparatus for diagnosing a state of a fuel cell using a step signal according to an embodiment of the present invention;
2 is a flowchart illustrating a method of diagnosing a state of a fuel cell using a step signal using the apparatus for diagnosing state of a fuel cell according to FIG. 1;
3 is a circuit diagram of a fuel cell passive element used in the apparatus for diagnosing a state of a fuel cell according to FIG. 1;
4 shows an exemplary diagram of a step response signal for the fuel cell model according to FIG. 3.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The terms used are terms selected in consideration of the functions in the embodiments, and the meaning of the terms may vary depending on the user, the intention or the precedent of the operator, and the like. Therefore, the meaning of the terms used in the following embodiments is defined according to the definition when specifically defined in this specification, and unless otherwise defined, it should be interpreted in a sense generally recognized by those skilled in the art.

1 is a block diagram of an apparatus for diagnosing a state of a fuel cell using a step signal according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the apparatus 30 for diagnosing the state of the fuel cell 10 using the step signal according to an embodiment of the present invention is connected to the fuel cell 10 to apply a step signal i ₂ (t). Then, the step response signal v (t) is measured therefrom to determine the deterioration of the performance of the fuel cell 10. In this case, the fuel cell 10 refers to a term including a stack including one or more cells. The fuel cell 10 flows current from the fuel cell 10 to the load 20 by the fuel cell signal i ₁ (t) generated by the fuel cell 10 while being connected to the load 20. .

Meanwhile, the state diagnosis device 30 includes a signal generator 31, a signal processor 32, and a determiner 33. The signal generator 31 includes a function generator and applies a step signal i ₂ (t) as an input signal to the fuel cell 10. The step signal is a discontinuous function that is a unit step function, and has a value of 0 in a time t <0, and a value of 1 in a time t≥0. The step signal i ₂ (t) may be applied to the fuel cell 10 as a signal of a current component. Therefore, the signal i (t) obtained by adding the fuel cell signal i ₁ (t) and the step signal i ₂ (t) is supplied to the load 20.

The signal processor 32 calculates an impedance of the fuel cell 10 using the step response signal v (t) measured when the step signal i ₂ (t) is applied to the fuel cell 10. The step response signal v (t) means an output signal of a voltage component of the fuel cell 10 according to the step signal i ₂ (t). The step signal i ₂ (t) and the step response signal v (t) may both be expressed as time functions that change with time.

In addition, the signal processor 32 may calculate the impedance of the fuel cell 10 by using the Laplace transformation of the step signal i ₂ (t) and the step response signal v (t), which are time functions. Can be. In this case, the signal processor 32 may use the following Equation 1 to calculate the impedance Z (s) of the fuel cell 10.

In Equation 1, Z (s) is the impedance of the fuel cell 10, I ₂ (s) is the Laplace transform of the step signal i ₂ (t), and V (s) is the Laplace transform of the step response signal v (t). Indicates. Here, since the step signal i ₂ (t) is a unit step function u (t) (0, t <0; 1, t ≧ 0), the Laplace transform thereof is calculated at 1 / s. Therefore, the impedance Z (s) of the fuel cell 10 is calculated as sV (s).

In addition, the signal processor 32 may calculate the membrane resistance R _mem of the fuel cell 10 using the initial step response signal among the step response signals. The initial step response signal v (0) represents a step response signal at the time t = 0. Since the Laplace transform is a time domain to a frequency domain, the step response signal at time t = 0 is the same as the output signal of the fuel cell 10 at the frequency ω = ∞. Therefore, the membrane resistance generated in the electrolyte membrane of the fuel cell 10 can be calculated using the initial step response signal v (0).

In addition, the signal processor 32 may calculate an activation resistance R _act of the fuel cell 10 using the steady state step response signal among the step response signals. The active resistance is a resistance component that increases as the catalyst activity in the fuel cell 10 decreases. The steady state step response signal v (∞) represents a step response signal at a time t = ∞. Since the Laplace transform is a time domain to a frequency domain, the step response signal at time t = ∞ is the same as the output signal of the fuel cell 10 at the frequency ω = 0. Therefore, the active resistance generated inside the fuel cell 10 can be calculated using the steady state step response signal v (∞).

In addition, the signal processor 32 detects edges with respect to the step response signal in order to calculate a boundary value between the membrane resistance of the fuel cell 10 and the characteristics of the active resistance and the electric double layer capacitance. You can apply algorithms or Fourier transforms. This is because the capacitor component is generated by the connection of the signal lines in the process of measuring the state of the fuel cell 10, so that it is easier to distinguish the boundary value. For example, when the edge value is calculated using an edge detection algorithm, the edge detection algorithm used is not limited to any specific method. The step response signal is analyzed and the step function component and the exponential function are analyzed. By separating the components, a point that is converted to the exponential component after the step signal may be detected using an edge detection algorithm. In addition, the step response signal may be sampled to set the boundary value when the difference between the current value and the previous value or the current value and the subsequent value that are continuous to each other exceeds a preset value.

On the other hand, the Fourier Transformation (Fourier Transformation) for the step response signal can be used to calculate the film resistance generated in the electrolyte membrane of the fuel cell 10 in the frequency domain. That is, the Fourier transform of the step response signal v (t) = R _act [1-e- ^{(t / τ)} ] + R _mem is V (ω) = -R _act [1 / ((1 / τ) + j2πf)] + [R _act + R _mem ] · δ (f), and if f = 0 V (0) =-R _act τ + [R _act + R _mem ] = R _act [ Since 1-τ] + R _mem , if R _act ≠ f (water contents) is a constant, R _mem is calculated, and thus the membrane resistance generated in the electrolyte membrane can be calculated.

The determination unit 33 compares the impedance of the fuel cell 10 calculated by the signal processor 32 with a preset reference impedance to determine whether the fuel cell 10 is abnormal. The membrane resistance of the electrolyte membrane of the fuel cell 10 is measured differently according to the moisture state, and the resistance of the activity of the fuel cell 10 is measured differently according to the degree of catalyst activity. The reference impedance is a threshold impedance value for a wet state in which the membrane of the fuel cell 10 may operate normally or a threshold impedance value due to catalytic activity of the fuel cell 10, and may be differently set according to a user's setting.

In addition, when the value of the calculated impedance becomes higher than the value of the reference impedance, the determination unit 33 generates a warning sound through an alarm device (not shown) connected to the outside or sends a warning message to a display (not shown). Can be generated. In this case, the determination unit 33 may provide information for changing operating conditions to a controller (not shown) that controls the operation of the fuel cell stack 10.

2 is a flowchart illustrating a method of diagnosing a state of a fuel cell using a step signal using the apparatus for diagnosing state of a fuel cell according to FIG. 1.

Hereinafter, the description of FIG. 2 will be described using the configuration of the state diagnosis apparatus 30 of the fuel cell of FIG. 1.

Referring to FIG. 2, in the method for diagnosing the state of the fuel cell 10 using the step signal according to another embodiment of the present invention, the signal generator 31 first applies the step signal to the fuel cell 10 ( S210). In this case, the step signal is applied to the fuel cell 10 once, but is not necessarily limited thereto.

Next, the signal processor 32 measures the step response signal corresponding to the step signal applied from the fuel cell 10 (S220). For example, the measurement of the step response signal may be measured when t = 0, the initial time at which the signal is applied, when t = ∞, the steady state time, and at the transient time. The steady state time may be, for example, 4τ and may be set differently by a user.

Next, the signal processor 32 calculates the impedance of the fuel cell 10 using the step response signal measured at the initial time, the steady state time or the transient state time (S230). In this case, the impedance value can be calculated by performing Laplace transform on the step signal and the step response signal. The Laplace operation may use Equation 1 described above.

Next, the determination unit 33 compares the impedance of the fuel cell 10 calculated by the signal processor 32 with a preset reference impedance to determine whether the fuel cell 10 is abnormal (S240). The abnormality of the fuel cell 10 is determined by comparing the membrane resistance of the electrolyte membrane of the fuel cell 10 or the active resistance indicating the catalytic activity inside the fuel cell 10 with the reference impedance. You can judge.

3 is a circuit diagram of a fuel cell passive element used in the apparatus for diagnosing a state of a fuel cell according to FIG. 1.

Referring to FIG. 3, i ₂ (t) represents a step signal applied to the fuel cell, v (t) represents a step response signal output from the fuel cell, R _mem represents an electrolyte membrane resistance of the fuel cell, R _act represents the active resistance of the fuel cell and C _dl represents the electric double layer capacity of the fuel cell.

The fuel cell model 300 may be implemented as an equivalent impedance model including an electrolyte membrane resistance (R _mem ) of the fuel cell, an active resistance (R _act ) of the fuel cell, and an electric double layer capacity (C _dl ) of the fuel cell. In this case, if the circuit is analyzed using Kirchhoff's circuit laws (KVL) using a closed loop formed in the circuit, the step response signal is v (t) = R _act [1-e- ^{(t / τ)} ] + R _mem (t = 0, R _mem [v]; t → ∞, R _act + R _mem [v]). Here, time constant τ = R _act · C _dl is set.

4 shows an exemplary diagram of a step response signal for the fuel cell model according to FIG. 3.

Referring to Fig. 4, the step response signal v (t) when the step signal is a unit step is shown. As described above, the step response signal of the fuel cell is: v (t) = R _act [1-e- ^{(t / τ)} ] + R _mem (t = 0, R _mem [v]; t → ∞, R _act + R _mem [v]). Here, the step response signal v (t) is the signal V _mem of the step response signal region 410 due to the film resistance, and the step response signal region 420 of the active resistance and the electric double layer capacitance C _dl . It is divided into a signal V _RC .

For example, when R _mem = 200 [mΩ], R _act = 100 [mΩ], C _dl = 1 [F], and time constant τ = R _act · C _dl = 100 [ms], the initial step response signal Is measured as 200 [mV] in the step response signal region 410 due to the membrane resistance, and the steady state step response signal is 300 when the preset steady state time has elapsed among the step response signal region 420 due to the active resistance. It is measured in [mV], and V _RC becomes 100 [mV].

Therefore, the membrane resistance of the fuel cell can be quickly calculated by measuring the initial step response signal, and it is possible to determine the abnormality of the electrolyte membrane of the fuel cell using this.

Thus, according to the embodiment of the present invention, by applying the step signal to the fuel cell and analyzing the response to calculate the impedance of the fuel cell, it is possible to quickly diagnose the state of the fuel cell. In addition, since the impedance of the fuel cell can be calculated in the time domain, the configuration of the diagnostic device can be simplified and the cost can be reduced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, Therefore, the present invention should be construed as a description of the claims which are intended to cover obvious variations that can be derived from the described embodiments.

10: Fuel cell
20: load
30: status diagnosis device
31: signal generator
32: signal processing unit
33: judgment unit
300: fuel cell model
410: step response signal area due to membrane resistance
420: step response signal area by active resistance

Claims (14)

A signal generator for applying a step signal to the fuel cell;
A signal processor configured to calculate an impedance of the fuel cell using the step response signal measured when the step signal is applied to the fuel cell; And
And a determination unit determining whether the fuel cell is abnormal by comparing the calculated impedance of the fuel cell with a preset reference impedance. The method of claim 1,
The step signal is a signal of the current component,
And the step response signal uses a step signal that is a signal of a voltage component. The method of claim 1,
The signal processing unit,
And a step signal for calculating an impedance of the fuel cell by using Laplace transform on the step signal and the step response signal as a function of time. The method of claim 3,
The signal processing unit,
An apparatus for diagnosing a state of a fuel cell using a step signal using the following equation to calculate an impedance of the fuel cell:

Where Z (s) is the impedance of the fuel cell, I ₂ (s) is the Laplace transform of the step signal i ₂ (t), and V (s) is the Laplace transform of the step response signal v (t). The method of claim 1,
The signal processing unit,
And a step signal for calculating a membrane resistance of the fuel cell using an initial step response signal among the step response signals. The method of claim 1,
The signal processing unit,
And a step signal for calculating an active resistance of the fuel cell using a steady state step response signal among the step response signals. The method according to claim 5 or 6,
The signal processing unit,
An edge detection algorithm or a Fourier transform is applied to the step response signal to calculate a boundary value between the characteristics of the fuel cell membrane resistance and the characteristics of the fuel cell active resistance and the electric double layer capacity. Battery diagnostic device. In the fuel cell state diagnosis method using the fuel cell state diagnosis apparatus,
Applying a step signal to the fuel cell;
Measuring a step response signal corresponding to the step signal from the fuel cell;
Calculating an impedance of the fuel cell using the measured step response signal; And
And comparing the calculated impedance of the fuel cell with a preset reference impedance to determine whether there is an abnormality of the fuel cell. 9. The method of claim 8,
The step signal is a signal of the current component,
And the step response signal is a signal of a voltage component. 9. The method of claim 8,
Computing the impedance of the fuel cell,
And a step signal for calculating an impedance of the fuel cell using Laplace transform of the step signal and the step response signal as a function of time. The method of claim 10,
Computing the impedance of the fuel cell,
Method for diagnosing a state of a fuel cell using a step signal using the following equation to calculate the impedance of the fuel cell:

Where Z (s) is the impedance of the fuel cell, I ₂ (s) is the Laplace transform of the step signal i ₂ (t), and V (s) is the Laplace transform of the step response signal v (t). 9. The method of claim 8,
Computing the impedance of the fuel cell,
And a step signal for calculating a membrane resistance of the fuel cell using an initial step response signal among the step response signals. 9. The method of claim 8,
Computing the impedance of the fuel cell,
And a step signal for calculating an active resistance of the fuel cell using a steady state step response signal among the step response signals. The method according to claim 12 or 13,
Computing the impedance of the fuel cell,
An edge detection algorithm or a Fourier transform is applied to the step response signal to calculate a boundary value between the characteristics of the fuel cell membrane resistance and the characteristics of the fuel cell active resistance and the electric double layer capacity. How to diagnose the condition of the battery.

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