JP5410729B2 - Fuel cell system and control method thereof - Google Patents

Description

  The present invention relates to a fuel cell system that operates a fuel cell, for example, a fuel cell system that can be used for cogeneration, a fuel cell vehicle, and the like, and a control method therefor.

Conventionally, for example, techniques disclosed in Patent Documents 1 and 2 are disclosed as techniques for suitably operating a fuel cell by controlling the operation of the fuel cell.
The technique of Patent Document 1 is intended to improve the followability to the power consumption of the load connected to the fuel cell, and is a separately calculated correction based on the standard flow rate of the fuel flow based on the initial IV characteristics. The flow rate is added. Here, the correction of the decrease in the power generation capacity of the fuel cell (for example, a cell stack in which a plurality of power generation cells is stacked) is performed using the deviation between the specified value and the actual measurement value of the cell stack voltage obtained from the initial IV characteristics as a parameter This is realized by adding the corrected flow rate.

The technique of Patent Document 2 takes into account load fluctuations and deterioration of the fuel cell. The IV characteristics themselves are stored while being corrected by actual measurement, and the stored data is always updated with reference to the stored data. The optimal air flow rate is calculated on the basis of the IV characteristics.
JP-A-9-147893 JP 2004-296374 A

However, the above-described conventional technique has a problem that the control method is complicated, and particularly when the power consumption of the load changes, the change cannot be promptly handled.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel cell system capable of quickly responding to a change in power consumption of a load by a simpler technique than before and a control method thereof. There is to do.

(1) The invention of claim 1 is a fuel cell, a fuel supply unit that supplies fuel gas to the fuel cell, an oxidant supply unit that supplies oxidant gas to the fuel cell, and an output voltage of the fuel cell. In the fuel cell system, the control unit is detected by the voltage detection unit. The fuel cell system includes: a voltage detection unit that detects an output current; a current detection unit that detects an output current of the fuel cell; and a control unit that controls the system. The first control means for calculating the fuel flow rate so that the output voltage thus obtained becomes the target voltage and supplying the fuel flow rate to the fuel cell, and the load power consumption increases when the load power consumption changes so that the output voltage after it becomes a reference target voltage which is a target voltage during the stable of the load power is added to the reference target voltage based on the change amount of the detected output current by the current detecting section Calculating a calculated voltage, characterized in that a value obtained by adding the sum voltage to the reference target voltage and a second control means for setting as the target voltage.

In the present invention, the first control means calculates the fuel flow rate so that the output voltage (for example, cell stack voltage) of the fuel cell becomes the target voltage (for example, target cell stack voltage), and supplies the fuel flow rate to the fuel cell. The current detection unit is controlled by the second control unit so that the output voltage after the increase in the load power consumption becomes the reference target voltage that is the target voltage when the load power consumption is stable, when the load power consumption changes. Since the addition voltage to be added to the reference target voltage is calculated based on the change amount of the output current (for example, cell stack current) detected by, and the value obtained by adding the addition voltage to the reference target voltage is set as the target voltage, It is possible to respond quickly to changes in load power consumption by a simpler technique than before.

That is, since the future load power consumption is predicted based on the amount of change in the output current and the target voltage is set, stable power generation that quickly follows the increase in load power consumption becomes possible.
Further, in the present invention, the fuel increase in preparation for the increase in the load power consumption can be realized by increasing the set value of the target voltage. Therefore, the flow rate calculation can be performed by the same process, and the control is simple.

Furthermore, in the present invention, by controlling the output voltage of the fuel cell to the target voltage, the optimum fuel flow rate can be calculated without being aware of the current-voltage characteristics (IV characteristics) of the fuel cell.
In addition, in the present invention, by performing the above-described control, it is possible to generate power with the optimum fuel flow rate after correcting the decrease in power generation capacity due to various conditions. Note that the decrease in the power generation capacity of the fuel cell can be automatically corrected by feedback control to the target voltage.

(2) In the invention of claim 2, the addition voltage is obtained by a map or a conversion formula showing a relationship between the amount of increase in current of the fuel cell and the addition voltage obtained in advance based on characteristics of the fuel cell. It is characterized by.
The present invention exemplifies a configuration for obtaining the addition voltage.
( 3 ) In the invention of claim 3, the current detection unit directly obtains the output current using an ammeter, or detects the power consumption of a load connected to the fuel cell, and the load consumption The output current is obtained indirectly from electric power.

The present invention exemplifies a configuration of a current detection unit for obtaining an output current.
When the output current is obtained indirectly from the load power consumption, for example, the output current can be calculated by calculating (load power consumption / output voltage) using the load power consumption and the output voltage.

( 4 ) The invention of claim 4 is a fuel cell, a fuel supply unit for supplying fuel gas to the fuel cell, an oxidant supply unit for supplying oxidant gas to the fuel cell, and an output voltage of the fuel cell. In a control method for a fuel cell system, comprising: a voltage detection unit that detects the output of the fuel cell; and a current detection unit that detects an output current of the fuel cell, so that the output voltage detected by the voltage detection unit becomes a target voltage. A first control step for calculating a fuel flow rate and controlling the fuel flow rate to be supplied to the fuel cell; and when the load power consumption changes, the output voltage after the increase in the load power consumption is equal to the load power consumption. to be a reference target voltage which is a target voltage at the stable state, it calculates the sum voltage to be added to the reference target voltage based on the change amount of the detected output current by the current detection unit, the reference target electrostatic A second control step of setting a value obtained by adding the sum voltage as the target voltage, and having a.

In the present invention, the target voltage is set based on the amount of change in the output current and the fuel flow rate is controlled so as to be the target voltage, as in the first aspect of the invention. The same effects as those of the first aspect of the invention can be achieved, such as being able to respond quickly to changes in load power consumption by a simpler method.

(5) In the invention of claim 5, the addition voltage is obtained by a map or a conversion formula showing a relationship between the increase amount of the current of the fuel cell and the addition voltage obtained in advance based on characteristics of the fuel cell. It is characterized by.
The present invention exemplifies a method for obtaining the added voltage.
( 6 ) In the invention of claim 6, the current detection unit obtains the output current directly using an ammeter, or detects the power consumption of a load connected to the fuel cell, and the load consumption The output current is obtained indirectly from electric power.

The present invention exemplifies the configuration of the current detection unit for obtaining the output current, as in the third aspect of the invention.
Here, each structure of each said invention is demonstrated.

  As the fuel cell, a fuel cell stack (for example, a solid oxide fuel cell) in which a plurality of power generation cells as power generation units are stacked can be used. Examples of the power generation cell include a solid electrolyte substrate (solid electrolyte layer) provided with an air electrode and a fuel electrode.

  Among these, as the solid electrolyte layer, known materials such as YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), SDC (samaria-added ceria), GDC (gadolinium-added ceria), and perovskite oxide can be used. As the air electrode, perovskite oxide, various precious metals, cermets of precious metals and ceramics can be used, and as the fuel electrode, various precious metals, base metals such as Ni, cermets of these metals and ceramics can be used. .

  The solid electrolyte layer is moved by using a part of one of the fuel gas (combustible gas) introduced into the fuel electrode or the oxidant gas (combustion gas) introduced into the air electrode during operation of the fuel cell. It has ionic conductivity that can be achieved. Examples of the ions include oxygen ions and hydrogen ions. Further, the fuel electrode comes into contact with the fuel gas that becomes the reducing agent and functions as a negative electrode in the cell. The air electrode is in contact with an oxidant gas serving as an oxidant and functions as a positive electrode in the cell.

Next, an example of the best mode of the present invention will be described.
[Embodiment]
a) First, the configuration of the fuel cell system according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, the fuel cell system of this embodiment includes a fuel cell (cell stack) 3 in which a plurality of power generation cells are stacked in a heat insulating container 1, and reforming of fuel gas supplied to the cell stack 3. And a catalytic combustor 7 for burning the exhaust gas discharged from the cell stack 5 is housed.

  Among these, the cell stack 3 is a device that generates power by receiving supply of fuel gas (specifically, hydrogen in the fuel gas) and oxidant gas (specifically, oxygen in the air). Although not shown, the cell stack 3 is, for example, a plate-shaped power generation unit (solid oxide fuel cell) that is a power generation unit, and a plate-shaped interface that secures conduction between the cells and blocks the gas flow path. It is possible to adopt one in which connectors are alternately stacked. As the power generation cell, for example, an air electrode is formed on one side of a solid electrolyte body made of, for example, Sc-stabilized zirconia solid solution having plate-like oxygen ion conductivity, and a fuel electrode is formed on the other side. Can be used.

The reformer 5 is a device that reforms a fuel gas such as city gas using a catalyst such as nickel or platinum to generate hydrogen gas that reacts with oxygen.
The catalytic combustor 7 is a device that burns the remaining combustible gas contained in the exhaust gas discharged from the cell stack 3 using a catalyst such as platinum, rhodium, palladium, or the like. By the combustion in the catalytic combustor 7, the temperature in the heat insulating container 1 can be kept at a temperature (for example, about 700 ° C.) at which the power generation in the cell stack 3 is suitably performed.

  On the other hand, an oxidant supply unit (air supply unit) 9 connected to the cell stack 3 and a fuel supply unit 11 connected to the reformer 5 are arranged outside the heat insulating container 1. The air supply unit 9 supplies air as an oxidant gas to the cell stack 3, and the fuel supply unit 11 includes hydrogen as a fuel gas to the reformer 5, for example, before reforming. City gas is supplied.

A first voltmeter 17 and a first ammeter 19 are connected to the power supply path 15 from the cell stack 3 to the constant voltage converter 13 (device that converts the output voltage of the cell stack 3 into a predetermined constant voltage) 13. A second voltmeter 25 and a second ammeter 27 are disposed in the power supply path 23 that is disposed and reaches the load 21 from the constant voltage converter 13.

In addition, although the electric power is normally supplied to the load 21 also from a system | strain power line via the distribution board which is not shown in figure, the description is abbreviate | omitted here.
b) Next, the basic operation of the fuel cell system will be described.

  When power generation is performed by the fuel cell system, air is supplied from the air supply unit 9 to the cell stack 3 (specifically, to the air electrode side of each power generation cell). At the same time, city gas is supplied from the fuel supply unit 11 to the reformer 5, and the reformer 5 reforms the city gas to take out hydrogen gas. The hydrogen gas is supplied to the cell stack 3 ( For details, supply to the fuel electrode side of each power generation cell).

  Thereby, in each power generation cell, power generation is performed by a reaction between oxygen and hydrogen, and the power generated by this power generation is sent from the cell stack 3 to the constant voltage converter 13. Note that the exhaust gas discharged from the cell stack 3 contains the city gas that has not been reformed, the reformed gas that includes hydrogen that has not been used for power generation, and the oxygen-containing air. Hydrogen etc.) and combustion-supporting gas (oxygen) are combusted in the catalytic combustor 7, whereby the inside of the heat insulating container 1 can be heated to an appropriate temperature.

The output voltage and current of the cell stack 3 are measured by a first voltmeter 17 and a first ammeter 19, and the output voltage and current of the constant voltage converter 13 are measured by a second voltmeter 25 and a second ammeter. 27.

A signal (a signal indicating voltage and a signal indicating current) from the first voltmeter 17 and the first ammeter 19 and the second voltmeter 25 and the second ammeter 27 is sent to a control unit (electronic control device) 29. Is input. In the control unit 29, calculation described later is performed based on those signals and the like, and the flow rate of air sent to the cell stack 3 and the fuel gas sent to the reformer 5 to the air supply unit 9 and the fuel supply unit 11. A control signal for adjusting the flow rate (fuel flow rate Q of city gas or the like) is output.

For example, the fuel flow rate can be calculated by the following formula (1) or (2).

<When cell stack current is used directly>
Q = (Is · α) / (Uf · Vh 2/100) (1)

<Indirect calculation of cell stack current from load power consumption>
Q = [(P · Es) · α] / (η · Uf · Vh 2/100) (2)

Q: Fuel flow rate [L / min]
Es: Cell stack voltage [V]
Is: Cell stack current [A]
P: Load power consumption [W]
α: Hydrogen flow rate [L / min · A] required for taking out the cell stack current 1 [A]
η: Conversion efficiency of constant voltage converter [%]
Uf: Fuel utilization rate [%]
Vh2: Hydrogen ratio in fuel [%]

In this formula (1) or (2), the fuel utilization rate Uf is the ratio of the flow rate that contributes to power generation with respect to the total flow rate of fuel such as city gas, and the hydrogen ratio Vh2 in the fuel is the city It is the ratio of hydrogen contained in fuel gas such as gas.

As for the air flow rate, for example, it is assumed that the fuel flow rate is multiplied by a coefficient that becomes the set air-fuel ratio.
c) Next, the principle for controlling the fuel cell system will be described with reference to FIGS.

(1) Power generation characteristics of fuel cell FIG. 2 shows current-voltage characteristics (IV characteristics) of the cell stack 3.
As is clear from FIG. 2, the power generation capacity increases as the fuel utilization rate decreases (ie, the fuel flow rate increases), and conversely, the power generation capacity increases as the fuel utilization rate increases (ie, the fuel flow rate decreases). Becomes lower.

  Note that reducing the fuel utilization rate means increasing the proportion of fuel that is discharged without contributing to power generation, but instead increasing the proportion of fuel for maintaining temperature by catalytic combustion and compensating for deterioration of the cell stack 3. In other words, there is an inversely proportional relationship between the fuel utilization rate and the fuel flow rate.

  Further, if the cell stack 3 has a temperature drop or deterioration, the power generation capacity is reduced. Therefore, a state where the fuel utilization rate is increased (that is, a state where the fuel flow rate is reduced) is equivalent to a temperature drop or deterioration of the cell stack 3. Can think.

  Furthermore, when the load power consumption is constant (see, for example, the equal power line 600 [W]), the cell stack voltage increases as the power generation capacity increases (thus, the fuel utilization rate is low and the fuel flow rate is high).

(2) Gas flow control of the fuel cell As shown in FIG. 3, based on the initial IV characteristics (for example, the lower curve including the point A), the target voltage (reference target voltage) serving as a reference for the cell stack voltage is set. The fuel usage rate in the fuel flow rate calculation formula (1) or (2) is controlled to be variable (actually, the fuel flow rate is controlled) so as to be set and kept constant. As a result, the IV characteristics change according to the load power consumption (see, for example, an intermediate curve including point B or an upper curve including point C in FIG. 3).

  That is, for example, when the target voltage (reference target voltage) is 12 [V], when the load is different (for example, when the load is increased from 360 [W] to 600 [W]), the reference target voltage of 12 [V] V] can be secured by reducing the fuel utilization rate (and thus increasing the fuel flow rate).

  Here, the target voltage is on the left side of the inflection point from the inflection point where the voltage on the IV characteristic decreases in order to prevent fuel depletion even if the load power consumption suddenly increases. It is desirable to set.

  Further, when the control is not performed at the maximum power point, surplus fuel (unburned fuel) is generated as compared with the case where it is not, but the unburned fuel is used by the catalytic fuel unit 7 to maintain the temperature of the cell stack 3. Therefore, it is not wasted as a system.

  Further, by setting the target voltage as described above, even when the power generation capacity of the cell stack 3 is reduced, the fuel utilization rate that is changed by the control becomes lower than before the deterioration (that is, it is changed by the control). When the fuel flow rate is higher than before deterioration, the power generation capacity is automatically corrected to a desired value.

(3) Fuel cell load following control As shown in FIG. 4, when the load power consumption is constant and stable, that is, when the change amount of the cell stack current is 0 [A], the reference target voltage (for example, 12 [ V]), and a voltage obtained by adding a voltage (added voltage) corresponding to the amount of increase in the cell stack current to the target voltage, and the fuel utilization rate (ie, fuel flow rate) is controlled.

  For example, in the process of increasing the current load power consumption from 360 [W] to 600 [W], the target voltage is set to be larger than the reference target voltage in accordance with the degree of increase in the cell stack current. For example, about 1 [V] is set as the voltage increase (voltage deviation) from point A to point A ′ in FIG. In order to eliminate the voltage deviation, the fuel utilization rate is lowered (that is, the fuel flow rate is increased), and when it reaches 600 [W] and stabilizes, the reference target voltage corresponding to point B is reached. To control. At this time, since the current is 50 [A], the load power consumption is 600 [W].

  In other words, the IV characteristic is equivalent to that corresponding to the load power consumption after a certain time, and this control enables stable power generation that quickly follows a sudden increase in load power consumption.

c) Next, a control method of the fuel cell system performed by the control unit 29 based on the above-described principle will be described with reference to FIGS.
(1) Main Routine As shown in FIG. 5, this main routine is started when the power source for operating the control unit 29 of the fuel cell system is turned on.

  First, when the process is started, in step (S) 100, it is determined whether or not it is a cycle for calculating the fuel flow rate (for example, 100 [ms]). If an affirmative determination is made here, the process proceeds to step 110. If a negative determination is made, similar determination is repeated, for example, every 1 [ms].

In step 110, the cell stack voltage is measured by the first voltmeter 17.
In the following step 120, it is determined whether or not to directly measure the cell stack current, that is, whether to directly measure the cell stack current or to indirectly calculate the cell stack current by measuring the load power consumption. If an affirmative determination is made here, the process proceeds to step 130, while if a negative determination is made, the process proceeds to step 140. This determination can be made using, for example, a flag indicating which process is to be performed.

In step 130, the cell stack current is measured by the first ammeter 19, and the process proceeds to step 160.
On the other hand, in step 140, load power consumption is calculated from the voltage measured by the second voltmeter 25 and the current measured by the second ammeter 27.

  In the following step 150, a cell stack current is calculated based on the load power consumption calculated in step 140 and the cell stack voltage measured in step 110, and the process proceeds to step 160. Specifically, the cell stack current can be obtained by calculating (load power consumption / cell stack voltage).

In the following step 160, the fuel flow rate is calculated by a fuel flow rate calculation routine described later, and the process returns to step 100.
(2) Fuel flow rate calculation routine As shown in FIG. 6, in step 200, the amount of change in the cell stack current is obtained. Specifically, the difference between the cell stack current measured this time and the cell stack current measured 3 seconds ago, for example, and the difference divided by the unit time (for example, 3 seconds described above) is the cell stack current change. Calculated as an amount (increase) [A / sec].

Therefore, in the following, based on this increase amount, the target voltage is varied according to the increment.
In subsequent step 210, it is determined whether or not the cell stack current change amount is positive, that is, whether or not the cell stack current is increasing. If an affirmative determination is made here, the process proceeds to step 220, while if a negative determination is made, the process proceeds to step 230.

  In step 220, an addition voltage is set according to the cell stack current change amount. For example, as shown in FIG. 4, as the amount of increase in the cell stack current increases, the added voltage (for example, the voltage increasing from the point A to the point A ′ at the same current value) is increased, for example, by experimentation in advance. 3 is examined, the relationship between the cell stack current and the addition voltage is obtained to obtain a map and a conversion formula, and the addition voltage is obtained using the map and the conversion formula.

On the other hand, in step 230, since the cell stack current has not increased, the added voltage is set to 0 and the process proceeds to step 240.
In step 240, an addition target cell stack voltage (for example, a voltage difference from point A to point A ′) is added to a reference target cell stack voltage (for example, voltage at point A in FIG. 4), and target cell stack that is a target control voltage. Find the voltage.

  In the subsequent step 250, the cell deviation voltage (voltage Es actually measured by the first voltmeter 17) is subtracted from the target cell stack voltage to obtain a voltage deviation. Therefore, in the following control (feedback control: PID control), control is performed so that the voltage deviation becomes 0 [V].

  In the subsequent step 260, the fuel utilization rate is obtained according to the voltage deviation. For example, the fuel utilization rate is set so that the lower curve including the point A in FIG. 4 becomes an intermediate curve including the point B (lowering the fuel utilization rate).

  For example, the characteristics of the cell stack 3 are examined in advance by experiments or the like, the relationship between the voltage deviation and the fuel utilization rate is obtained to obtain a map or conversion formula, and the fuel utilization rate is obtained using this map or conversion formula.

In the following step 270, the fuel flow rate is obtained according to the cell stack current and the fuel utilization rate. For example, the fuel flow rate is calculated by substituting a necessary value into the above-described formula (1) or (2).
In step 280, the current cell stack current is set to the previous cell stack current, and the process is temporarily terminated.

  d) Thus, in this embodiment, the future cell stack current is predicted from the change amount (increase amount) of the cell stack current, the target cell stack voltage is varied according to the increment, and the target cell stack voltage is changed. Thus, the fuel flow rate is controlled so that the change in the power consumption of the load can be promptly dealt with by a simpler method than in the prior art. That is, stable power generation that quickly follows the increase in load power consumption is possible.

  Further, in the present embodiment, in order to realize an increase in fuel in preparation for an increase in load power consumption by increasing the set value of the target cell stack voltage, the flow rate calculation can be performed by the same process, and simple control It becomes.

Furthermore, in this embodiment, by controlling the cell stack voltage to the target cell stack voltage, it is possible to calculate the optimum fuel flow rate without being aware of the IV characteristics of the cell stack 3.
In addition, in the present embodiment, by performing the above-described control, it is possible to generate power with the optimum fuel flow rate after correcting the decrease in power generation capacity due to various conditions.

  In addition, this invention is not limited to the said embodiment at all, and it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from this invention.

It is explanatory drawing which shows the fuel cell system of embodiment. It is a graph which shows the electric power generation characteristic of a fuel cell. It is a graph for demonstrating the principle of gas flow rate control of a fuel cell. It is a graph for demonstrating the principle of load follow-up control of a fuel cell. It is a flowchart which shows the main routine of the control method of a fuel cell system. It is a flowchart which shows the fuel flow rate calculation routine of the control method of a fuel cell system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Thermal insulation container 3 ... Cell stack 5 ... Reformer 7 ... Catalytic combustor 9 ... Air supply part 11 ... Fuel supply part 13 ... Constant voltage converter 21 ... Load 29 ... Control part

Claims (6)

A fuel cell;
A fuel supply section for supplying fuel gas to the fuel cell;
An oxidant supply unit for supplying an oxidant gas to the fuel cell;
A voltage detector for detecting an output voltage of the fuel cell;
A current detector for detecting an output current of the fuel cell;
A control unit for controlling the system;
In a fuel cell system comprising:
The controller is
First control means for calculating the fuel flow rate so that the output voltage detected by the voltage detection unit becomes a target voltage, and controlling the fuel flow rate to be supplied to the fuel cell;
When the load power consumption changes, the output current detected by the current detection unit is adjusted so that the output voltage after the load power consumption increases becomes a reference target voltage that is a target voltage when the load power consumption is stable . A second control means for calculating an addition voltage to be added to the reference target voltage based on a change amount, and setting a value obtained by adding the addition voltage to the reference target voltage as the target voltage;
A fuel cell system comprising: 2. The added voltage is obtained according to a map or a conversion formula showing a relationship between the amount of increase in the current of the fuel cell, which is obtained in advance based on characteristics of the fuel cell, and the added voltage, or a conversion formula. Fuel cell system. The current detection unit directly obtains the output current using an ammeter, or detects power consumption of a load connected to the fuel cell, and indirectly obtains the output current from the load power consumption. The fuel cell system according to claim 1 or 2 , wherein A fuel cell;
A fuel supply section for supplying fuel gas to the fuel cell;
An oxidant supply unit for supplying an oxidant gas to the fuel cell;
A voltage detector for detecting an output voltage of the fuel cell;
A current detector for detecting an output current of the fuel cell;
In a control method of a fuel cell system comprising:
A first control step of calculating a fuel flow rate so that an output voltage detected by the voltage detection unit becomes a target voltage, and controlling the fuel flow rate to be supplied to the fuel cell;
When the load power consumption changes, the output current detected by the current detection unit is adjusted so that the output voltage after the load power consumption increases becomes a reference target voltage that is a target voltage when the load power consumption is stable . A second control step of calculating an addition voltage to be added to the reference target voltage based on a change amount, and setting a value obtained by adding the addition voltage to the reference target voltage as the target voltage;
Control method for a fuel cell system characterized by having a. 5. The added voltage is obtained by a map or a conversion formula showing a relationship between an amount of increase in the current of the fuel cell, which is obtained in advance based on characteristics of the fuel cell, and the added voltage. Control method of fuel cell system. The current detection unit directly obtains the output current using an ammeter, or detects power consumption of a load connected to the fuel cell, and indirectly obtains the output current from the load power consumption. 6. The control method for a fuel cell system according to claim 4, wherein the control method is a fuel cell system.

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