JP2011258466A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out an anode scavenging properly at the time of fuel cell shutdown.SOLUTION: When a fuel cell battery 1 is shut down, cell voltage is measured by a cell voltage sensor 14 to obtain a first cell voltage value after a lapse of a prescribed period of time from the shutdown; subsequently, after air is introduced into an air supply passage 8 by a compressor 7, the cell voltage sensor is measured again by the cell voltage sensor 14 to obtain a second cell voltage value; an anode voltage after a lapse of a prescribed period of time from the shutdown is estimated on the basis of the first cell voltage value, the second cell voltage value and a cathode voltage measured in advance at the time air is introduced in a cathode of the fuel battery cell 1, the concentration of residual hydrogen in an anode is estimated on the basis of the estimated anode voltage, and it is determined whether the anode scavenging by air is required or not.

Description

  The present invention relates to a fuel cell system including a solid polymer electrolyte membrane fuel cell.

In a fuel cell that has a solid polymer electrolyte membrane, hydrogen (fuel) is supplied to the anode, and air containing oxygen (oxidant) is supplied to the cathode, the hydrogen concentration of the anode (stoichiometric value of the anode) It is important to grasp the above in order to prevent deterioration of the solid polymer electrolyte membrane and stability of power generation.
For example, in Patent Document 1, an anode potential (anode potential) is estimated based on a cell voltage measured during power generation of a fuel cell, and an anode hydrogen shortage is detected from an increase in anode potential. Performing power generation control is disclosed.

JP 2008-171777 A

  However, in the conventional technology described above, the anode potential is estimated during the power generation operation of the fuel cell, and the subsequent power generation of the fuel cell is controlled based on the estimated anode potential. As a result, the situation may change and the response may be delayed.

  Accordingly, the present invention provides a fuel cell system capable of estimating the anode potential before power generation by the fuel cell.

The fuel cell system according to the present invention employs the following means in order to solve the above problems.
The invention according to claim 1 includes a fuel cell (for example, a fuel cell 1 in an embodiment to be described later) having a solid polymer electrolyte membrane and generating fuel by supplying fuel to the anode and oxidant to the cathode, and the fuel cell. A fuel flow path for introducing fuel into the anode (for example, a fuel supply flow path 17 and an anode off-gas flow path 18 in the embodiments described later), and an oxidant flow path for introducing an oxidant into the cathode of the fuel cell ( For example, an air supply flow path 8) in an embodiment to be described later, cell voltage measurement means for measuring a cell voltage of the fuel cell (for example, a voltage sensor 14 in an embodiment to be described later), the oxidizer flow path, and the fuel An oxidant introduction means (for example, a compressor 7, an anode scavenging flow path 27, a scavenging valve 28 in an embodiment described later) that can introduce an oxidant into the flow path, the fuel cell, and the fuel cell And a control unit (for example, a control device 30 in an embodiment to be described later) that controls the agent introduction unit and receives a signal from the cell voltage measurement unit, and the control unit stops the fuel cell. When a predetermined time elapses after the stop, the cell voltage is measured by the cell voltage measuring means to obtain the first cell voltage value, and then the oxidant is introduced into the oxidant flow path by the oxidant introduction means. After that, the cell voltage is measured again by the cell voltage measuring means to obtain the second cell voltage value, and the first cell voltage value, the second cell voltage value, and the oxidant channel measured in advance are oxidant. The fuel cell system is characterized in that the anode potential after the predetermined time has elapsed from the stop is estimated based on the cathode potential at the time of introduction.

  According to a second aspect of the present invention, in the first aspect of the invention, the control unit responds to the estimated anode potential by using a relationship between the anode potential and the anode residual hydrogen concentration which are obtained in advance. The anode residual hydrogen concentration is obtained.

  According to a third aspect of the present invention, in the second aspect of the present invention, when the estimated anode residual hydrogen concentration is equal to or less than a threshold value, the control unit causes the oxidant to be introduced into the fuel flow path by the oxidant introduction unit. Is introduced to discharge the fluid in the fuel flow path.

  According to a fourth aspect of the present invention, in the second aspect of the present invention, the control unit is configured to obtain an average anode residual hydrogen concentration that is an average value of an anode residual hydrogen concentration of a cell of the fuel cell, which is obtained in advance, and the fuel. Using the relationship with the minimum anode residual hydrogen concentration, which is the lowest value of the anode residual hydrogen concentration of the cells in the battery, based on the average value and the minimum value of the estimated anode residual hydrogen concentration, Determining whether or not the fluid needs to be discharged, and if it is determined that the fluid needs to be discharged, the oxidant introduction means introduces an oxidant into the fuel flow path and discharges the fluid in the fuel flow path. Features.

  According to a fifth aspect of the present invention, there is provided a fuel cell (for example, a fuel cell 1 in an embodiment to be described later) having a solid polymer electrolyte membrane and generating fuel by supplying fuel to the anode and oxidant to the cathode, and the fuel cell. A fuel flow path for introducing fuel into the anode (for example, a fuel supply flow path 17 and an anode off-gas flow path 18 in the embodiments described later), and an oxidant flow path for introducing an oxidant into the cathode of the fuel cell ( For example, an air supply flow path 8) in an embodiment to be described later, cell voltage measuring means for measuring a cell voltage of the fuel cell (for example, a voltage sensor 14 in an embodiment to be described later), the fuel cell and the control A control unit (for example, a control device 30 in an embodiment to be described later) that receives a signal from the cell voltage measurement unit, and the control unit starts up the fuel cell. Before power generation, the cell voltage is measured by the cell voltage measuring means to obtain a first cell voltage value, and then the oxidant is introduced into the oxidant flow path by the oxidant introducing means, and then the cell voltage measuring means To measure the cell voltage again to obtain the second cell voltage value, and the first cell voltage value, the second cell voltage value, and the cathode potential when the oxidant is introduced into the oxidant flow path measured in advance. Based on the above, the anode potential at the start-up is estimated.

  The invention according to claim 6 is the invention according to claim 5, wherein the control unit responds to the estimated anode potential by using a relationship between the anode potential and the anode residual hydrogen concentration obtained in advance. The anode residual hydrogen concentration is obtained.

  The invention according to claim 7 is the invention according to claim 6, wherein the control unit uses the relationship between the anode residual hydrogen concentration obtained in advance and the fuel gas replacement amount at the start of the fuel cell to perform the estimation. A fuel gas replacement amount corresponding to the anode residual hydrogen concentration is set, and fuel gas replacement before power generation at the time of starting the fuel cell is performed.

  The invention according to claim 8 is the invention according to claim 6, wherein the control unit uses the relationship between the anode residual hydrogen concentration obtained in advance and the fuel gas replacement pressure at the time of starting the fuel cell, to perform the estimation. The fuel gas replacement pressure is set according to the anode residual hydrogen concentration, and the fuel gas replacement before power generation at the time of starting the fuel cell is performed.

According to the first aspect of the present invention, it is possible to estimate the anode potential after a predetermined time from stopping the fuel cell without directly measuring the anode potential. Therefore, an expensive anode potential measuring device is unnecessary, and the configuration of the fuel cell system can be simplified.
According to the second aspect of the present invention, based on the estimated anode potential, it is possible to easily estimate the residual hydrogen concentration of the anode after a predetermined time after stopping the fuel cell.
According to the third and fourth aspects of the invention, the scavenging of the anode with the oxidant can be performed at an appropriate timing during the stop period of the fuel cell. As a result, it is possible to prevent the catalyst and the oxidant from directly reacting with each other on the catalyst of the solid polymer electrolyte membrane during the anode scavenging. Thereby, the lifetime of the solid polymer electrolyte membrane is extended, and the power generation performance can be maintained over a long period of time.

According to the fifth aspect of the present invention, the anode potential before power generation can be estimated when the fuel cell is started without directly measuring the anode potential. Therefore, an expensive anode potential measuring device is unnecessary, and the configuration of the fuel cell system can be simplified.
According to the sixth aspect of the present invention, the residual hydrogen concentration of the anode before power generation can be easily estimated based on the estimated anode potential when the fuel cell is started.
According to the invention of claim 7, at the time of starting the fuel cell, before the power generation, the fuel gas replacement can be performed with an appropriate fuel gas replacement amount corresponding to the gas state inside the fuel cell at that time. As a result, shortage of gas replacement can be prevented, the deterioration of the solid polymer electrolyte membrane of the fuel cell can be prevented, stable power generation can be performed when shifting to the power generation operation, and the startability is improved.
According to the invention of claim 8, at the time of starting the fuel cell, before the power generation, the fuel gas replacement can be performed at an appropriate fuel gas replacement pressure corresponding to the gas state inside the fuel cell at that time. As a result, shortage of gas replacement can be prevented, the deterioration of the solid polymer electrolyte membrane of the fuel cell can be prevented, stable power generation can be performed when shifting to the power generation operation, and the startability is improved.

It is a schematic block diagram in the Example of the fuel cell system concerning this invention. It is a figure explaining the estimation principle of an anode potential. It is a flowchart which shows the anode scavenging control in the fuel cell system of an Example. It is an anode residual hydrogen concentration map used in anode scavenging control of an Example. It is an anode scavenging judgment map used in the anode scavenging control of an Example. It is another anode scavenging judgment map used in the anode scavenging control of an Example. It is a flowchart which shows OCV purge control in the fuel cell system of an Example. It is an OCV purge amount map used in OCV purge control of an Example. It is an OCV purge pressure map used in OCV purge control of an Example. It is a conceptual diagram which shows an example of the gas state of the anode and cathode after progress for a predetermined time since a fuel cell stop.

  Embodiments of a fuel cell system according to the present invention will be described below with reference to the drawings of FIGS. In addition, the fuel cell system in the Example demonstrated below is the aspect mounted in the fuel cell vehicle.

FIG. 1 is a schematic configuration diagram of a fuel cell system in an embodiment.
The fuel cell 1 is formed by stacking a plurality of cells formed by sandwiching a solid polymer electrolyte membrane made of, for example, a solid polymer ion exchange membrane between an anode and a cathode from both sides, and a fuel flow passage 5 on the anode side. When hydrogen is supplied as fuel to the cathode and oxygen-containing air is supplied to the oxidant flow passage 6 on the cathode side, hydrogen ions generated by a catalytic reaction at the anode pass through the solid polymer electrolyte membrane to the cathode. It moves and generates electricity through an electrochemical reaction with oxygen at the cathode, producing water. Part of the generated water generated on the cathode side permeates the solid polymer electrolyte membrane and back diffuses to the anode side, so that the generated water also exists on the anode side.
The air is pressurized to a predetermined pressure by a compressor 7 such as a supercharger, and supplied to the oxidant flow passage 6 of the fuel cell 1 through an air supply passage (oxidant passage) 8. After the air supplied to the fuel cell 1 is used for power generation, it is discharged from the fuel cell 1 to the air discharge passage 9 together with the produced water on the cathode side, and is discharged to the diluter 11 via the pressure control valve 10.

On the other hand, hydrogen supplied from the hydrogen tank 15 is supplied to the fuel flow passage 5 of the fuel cell 1 through the fuel supply passage 17. The fuel supply channel 17 is provided with a shutoff valve 20, a regulator 16, an ejector 19, and a sealing valve 25 in order from the upstream side, and the hydrogen supplied from the hydrogen tank 15 is reduced to a predetermined pressure by the regulator 16. To the fuel flow passage 5 of the fuel cell 1. Unreacted hydrogen that has not been consumed is discharged from the fuel cell 1 as anode off-gas, sucked into the ejector 19 through the anode off-gas flow path 18, and joined with fresh hydrogen supplied from the hydrogen tank 15. It is supplied to the fuel flow path 5 of the fuel cell 1. That is, the anode offgas discharged from the fuel cell 1 circulates through the fuel cell 1 through the anode offgas passage 18 and the fuel supply passage 17 downstream of the ejector 19.
The fuel supply passage 17 and the air supply passage 8 downstream of the sealing valve 25 are connected by an anode scavenging passage 27 having a scavenging valve 28, and the fuel supply passage is connected via the anode scavenging passage 27. It is possible to introduce air to 17.

The anode off gas flow path 18 is provided with a catch tank 12 that collects condensed water contained in the anode off gas, and the ejector 19 is supplied with hydrogen from which condensed water has been removed. The catch tank 12 has a drain valve 13, and when a predetermined amount of water accumulates in the catch tank 12, the drain valve 13 opens to drain water.
A sealing valve 26 is provided in the anode off gas passage 18 upstream of the catch tank 12.

A purge flow path 22 including a purge valve 21 is branched from the anode off-gas flow path 18 downstream of the catch tank 12, and the purge flow path 22 is connected to the diluter 11. The purge valve 21 is normally closed when the fuel cell 1 generates power, and opens to discharge the anode off gas to the diluter 11 when a predetermined condition is satisfied. Further, the purge valve 21 performs a so-called OCV purge in which the fluid in the fuel supply passage 17, the anode offgas passage 18, and the fuel flow passage 5 of the fuel cell 1 is replaced with new hydrogen when the fuel cell system is started. Sometimes open to perform gas replacement. Further, the purge valve 21 is opened when performing so-called anodic scavenging to scavenge the fuel flow passage 5 of the fuel cell 1 with air when the fuel cell system is stopped, and discharges scavenging gas.
The water drained from the drain valve 13 of the catch tank 12 is also discharged to the diluter 11 through the purge flow path 22.

In the diluter 11, the anode off-gas is diluted by the air discharged from the pressure control valve 10, and the diluted gas is discharged from the diluter 11 to the atmosphere via the exhaust pipe 23. The exhaust pipe 23 is provided with a hydrogen sensor 24 that measures the hydrogen concentration of the exhausted gas.
The fuel cell 1 is provided with a cell voltage sensor (cell voltage measuring means) 14 for measuring a cell voltage. The cell voltage sensor 14 may be installed in each cell, or may be installed in a representative cell set for each block by dividing into blocks for each predetermined number of stacked cells. The cell voltage sensor 14 outputs a signal corresponding to the measured cell voltage to the control device (control unit) 30.

The control device 30 controls the start / stop of the fuel cell system based on the ON / OFF signal input from the ignition switch 31, and the compressor 7 and the pressure control valve 10 according to the control contents such as output control of the fuel cell 1. The shut-off valve 20, the purge valve 21, the sealing valves 25 and 26, the scavenging valve 28, and the like are controlled.
In the first embodiment, the fuel supply channel 17 and the anode off-gas channel 18 constitute a fuel channel for introducing fuel (hydrogen) into the fuel cell 1, and the compressor 7, the anode scavenging channel 27, and the scavenging valve 28 are The oxidant introduction means that allows the oxidant to be introduced into the oxidant flow path and the fuel flow path is configured. Further, the shutoff valve 20 and the purge valve 21 constitute fuel gas replacement means for replacing the fluid in the fuel flow path with new fuel.

In the fuel cell system configured as described above, when the fuel cell system is stopped, air is introduced into the anode of the fuel cell 1 to perform scavenging of the anode, and hydrogen remaining in the anode (residual hydrogen) is discharged.
However, immediately after the fuel cell 1 is stopped, a large amount of hydrogen remains in the anode of the fuel cell 1, and when the anode scavenging is performed with a large amount of hydrogen remaining in the anode, the hydrogen in the anode and the scavenging gas (air) The oxygen inside reacts directly and deteriorates the catalyst of the solid polymer electrolyte membrane. Therefore, in order to prevent deterioration of the solid polymer electrolyte membrane, it is preferable to perform anode scavenging when the anode is low in hydrogen. Therefore, in the fuel cell system of this embodiment, the anode scavenging is performed at an appropriate timing. Therefore, when the fuel cell system is stopped, the anode potential is estimated from the cell voltage after a certain period of time after the power generation of the fuel cell 1 is stopped. Further, the residual hydrogen concentration of the anode is estimated based on the estimated anode potential, and it is determined whether or not to perform the anode scavenging based on the estimated residual hydrogen concentration. To implement.

Further, in this fuel cell system, OCV purge is performed before power generation in the fuel supply flow path 17 and the anode off-gas flow path 18 so that stable power generation can be performed at an early stage when the fuel cell system is started. The remaining fluid is extruded and replaced with new hydrogen.
However, since the gas state of the anode of the fuel cell 1 is not always the same at the start of the fuel cell system, if the OCV purge is performed uniformly, gas replacement is insufficient and the hydrogen concentration of the anode is increased to a desired concentration. It may not be possible.

  For example, while the fuel cell 1 is stopped, gas permeates (crosses over) from the anode to the cathode and from the cathode to the anode through the solid polymer electrolyte membrane mold. The gas state of the anode immediately before the OCV purge is performed (impurity gas crossover amount), depending on conditions such as the wet state of the fuel cell, the stop period of the fuel cell 1, the outside air temperature during the stop period, and the presence or absence of anode scavenging during the stop period. Is not uniform. Therefore, when there is a large amount of impure gas in the anode, the amount of gas replacement by the OCV purge may be insufficient. If the anode hydrogen concentration is insufficient due to insufficient gas replacement in the OCV purge, the solid polymer electrolyte membrane will be deteriorated due to the presence of oxygen in the anode when the power generation operation (including warm-up operation) is performed. It tends to occur or power generation becomes unstable.

  Therefore, in the fuel cell system of this embodiment, in order to optimize gas replacement by OCV purge, the anode potential is estimated from the cell voltage before power generation by the fuel cell 1, and further based on the estimated anode potential. The anode residual hydrogen concentration is estimated, and the purge amount and purge pressure of the OCV purge are determined based on the estimated residual hydrogen concentration, and the OCV purge is performed with the determined purge amount and purge pressure.

Before describing specific examples of the anode scavenging control and the OCV purge control, a method for estimating the anode potential will be described with reference to FIG.
As is well known, the cell voltage V of the fuel cell 1 is a potential difference between the cathode potential Vca and the anode potential Van of a single cell (V = Vca−Van).
Consider a case where the cathode potential Ca and the anode potential Van of a predetermined cell are estimated before the fuel cell 1 is started.

First, the cell voltage (first cell voltage value) V1 of the predetermined cell is measured while the sealing valves 25 and 26 are closed in the stop state before starting (see FIG. 2A).
Next, the cell voltage (second cell voltage value) V2 of the predetermined cell is measured again while supplying air only to the cathode of the fuel cell 1 with the sealing valves 25 and 26 closed (FIG. 2 ( B)). At the time of measuring the cell voltage V2, since the cathode is supplied with sufficient air, the cathode potential Vca is approximately 1.0V. Hereinafter, the cathode potential Vca in a state where air is supplied to the cathode is referred to as a reference cathode potential Vcaba. Here, the reference cathode potential Vcaba is described as 1.0 V. However, when the anode potential Van is actually estimated in the anode scavenging control and OCV purge control, air is supplied to the cathode in advance by a test in order to increase the estimation accuracy. Then, the cathode potential Vca is measured, and this measured value is set to the reference cathode potential Vcaba.

Next, as shown in FIG. 2C, the anode voltage Van is calculated by subtracting the cell voltage V2 from the reference cathode voltage Vcaba (Van = Vcaba−V2). It can be estimated that this anode potential Van is the anode potential before activation.
Further, as shown in FIG. 2D, it can be estimated that the value obtained by adding the cell voltage V1 to the estimated anode potential Van is the cathode potential Ca before activation (Vca = Van + V1).
In this way, it is possible to estimate the anode potential and the cathode potential only by measuring the cell voltage without directly measuring the anode potential or the cathode potential with the potential sensor, and grasp the gas state of the anode and the cathode. be able to. Therefore, an expensive anode potential sensor is unnecessary, and the configuration of the fuel cell system can be simplified.

Next, anode scavenging control will be described with reference to the flowchart of FIG. This anode scavenging control is executed by the control device 30.
First, when the fuel cell system is stopped (ignition switch OFF) in step S101, it is determined in step S102 whether or not a predetermined time has elapsed since the fuel cell system was stopped. The predetermined time is preferably a time from when the power generation of the fuel cell 1 is stopped until the gas state of the anode and the cathode is stabilized (in other words, a time until the gas crossover settles). Determined by the mechanical configuration of the system.
During the stop period of the fuel cell system, the shutoff valve 20, the purge valve 21, the sealing valves 25 and 26, and the scavenging valve 28 are closed and the pressure control valve 10 is opened.

If the determination result in step S102 is “NO” (predetermined time), the process returns to step S102.
If the determination result in step S102 is “YES” (elapsed time), the process proceeds to step S103, the cell voltage of each cell of the fuel cell 1 at that time is measured by the cell voltage sensor 14, and the measured cell The voltage is stored in the storage unit (not shown) of the control device 30 as the first cell voltage value V1 of each cell.

  Next, it progresses to step S104, cathode scavenging is implemented, the fluid in the cathode of the fuel cell 1 is discharged | emitted with air, and new air is distribute | circulated in a cathode. Cathode scavenging is performed by operating the compressor 7 and opening the pressure control valve 10. At this time, the scavenging valve 28 is maintained in a closed state, and the anode of the fuel cell 1 is maintained in a sealed state.

  Next, the process proceeds to step S105, while the cathode scavenging is continued, the cell voltage of each cell of the fuel cell 1 is measured again by the cell voltage sensor 14, and the measured cell voltage is measured as the second cell voltage value V2 of each cell. Is stored in the storage unit of the control device 30.

  Next, proceeding to step S106, based on the first cell voltage value V1 measured in step S103, the second cell voltage value V2 measured in step S105, and the reference cathode potential Vcaba obtained in advance by a test. Then, the anode potential Van and the cathode potential Vca of each cell are calculated (estimated) (Van = Vcab−V2, Vca = Van + V1). The anode potential Van calculated in this way does not deviate from the anode potential after the predetermined time has elapsed since the fuel cell system was stopped.

  Next, the process proceeds to step S107, and referring to the anode residual hydrogen concentration map shown in FIG. 4, based on the anode potential Van of each cell calculated in step S106, the hydrogen concentration remaining in the anode of each cell (hereinafter, referred to as “the anode residual hydrogen concentration map”). (Referred to as anode residual hydrogen concentration). Note that the anode residual hydrogen concentration map is a map obtained by performing a test in advance to obtain the relationship between the anode potential Van and the anode residual hydrogen concentration. As can be seen from this map, the anode residual hydrogen concentration is higher as the anode potential Van is lower, and the anode residual hydrogen concentration is lower as the anode potential Van is higher. The anode residual hydrogen concentration obtained in this manner does not deviate from the anode residual hydrogen concentration after the predetermined time has elapsed since the fuel cell system was stopped.

Next, it progresses to step S108 and it is judged whether anode scavenging is permitted. Here, there are two methods for determining the anode scavenging, and either method may be adopted.
The first method of determining the anode scavenging is a method of calculating an average value of the anode residual hydrogen concentration of all the cells of the fuel cell 1 and determining based on this average value. FIG. 5 is an example of an anode scavenging determination map used in the first method. A region in which the average value of the anode residual hydrogen concentration is lower than a preset threshold value is a region where scavenging of the anode is permitted (scavenging permission region). ), And a region where the average value of the anode residual hydrogen concentration is equal to or greater than the threshold is defined as a region where the scavenging of the anode is disabled (a scavenging impossible region).

  The second method of determining the anode scavenging is a method of determining based on the average value of the anode residual hydrogen concentration and the lowest value of the anode residual hydrogen concentration of all the cells of the fuel cell 1. FIG. 6 is an example of an anode scavenging determination map used in the second method. The average value of the anode residual hydrogen concentration exceeds the preset threshold value, and the minimum value of the anode residual hydrogen concentration is different from the preset value. An area exceeding the threshold is defined as an area where the anode scavenging cannot be performed (an area where scavenging is impossible), and the other area is an area where the execution of the anode scavenging is permitted (a scavenging permission area). In the map of FIG. 6, a region that does not belong to either the scavenging permission region or the scavenging disabled region indicates a region that is not actually possible.

If it is determined in step S108 that anode scavenging cannot be performed, the process returns to step S102, and it is determined whether or not a fixed time has elapsed since it was determined in step S108 that it was impossible.
On the other hand, if execution of anode scavenging is permitted in step S108, the process proceeds to step S109, and anode scavenging is performed. The anode scavenging is performed in parallel with the cathode scavenging, and the scavenging valve 28, the sealing valve 26, and the purge valve 21 are opened to supply air pressurized by the compressor 7 through the anode scavenging flow path 27. It introduces into the flow path 17 and performs. The air introduced into the fuel supply channel 17 does not flow into the fuel supply channel 17 upstream of the seal valve 25 because the seal valve 25 is closed, and flows downstream from the seal valve 25. Then, it flows into the diluter 11 through the fuel flow passage 5 of the fuel cell 1, the anode off-gas flow path 18, the purge valve 21, and the purge flow path 22, is merged with the cathode scavenging air, and is diluted. Discharged from.

After the anode scavenging is performed for a predetermined time (predetermined flow rate), the compressor 7 is stopped, and the purge valve 21, the sealing valve 26, and the scavenging valve 28 are closed to finish the anode scavenging and the cathode scavenging. finish.
By performing anode scavenging control in this way, it is possible to prevent the anode scavenging from being performed when a large amount of hydrogen remains in the anode, and to perform the anode scavenging when the amount of hydrogen remaining in the anode has decreased. Can do. As a result, the anode scavenging can be carried out at an appropriate timing, and at the time of anode scavenging, it is possible to prevent hydrogen and oxygen from directly reacting on the catalyst of the solid polymer electrolyte membrane and deteriorating the catalyst. . Thereby, the lifetime of the solid polymer electrolyte membrane is extended, and the power generation performance can be maintained over a long period of time.

Next, OCV purge control will be described with reference to the flowchart of FIG. This OCV purge control is executed by the control device 30.
In step S201, the fuel cell system is in a stopped state (ignition switch OFF). As described in the anode scavenging control, the shutoff valve 20, the purge valve 21, the sealing valves 25 and 26, and the scavenging valve 28 are closed and the pressure control valve 10 is opened during the stop period of the fuel cell system.
In step S202, it is determined whether or not the ignition switch 31 is turned on.

If the determination result in step S202 is “NO” (OFF), the process returns to step S202.
If the determination result in step S202 is “YES” (ON), the process proceeds to step S203, the cell voltage of each cell of the fuel cell 1 at that time is measured by the cell voltage sensor 14, and the measured cell voltage is calculated. The first cell voltage value V1 of each cell is stored in a storage unit (not shown) of the control device 30.

  Next, in step S204, the compressor 7 is operated, and air is supplied to the cathode of the fuel cell 1. At this time, the scavenging valve 28 is maintained in a closed state, and the anode of the fuel cell 1 is maintained in a sealed state.

  Next, the process proceeds to step S205, while the air supply to the cathode is continued, the cell voltage of each cell of the fuel cell 1 is measured again by the cell voltage sensor 14, and the measured cell voltage is measured as the second cell voltage of each cell. The value V2 is stored in the storage unit of the control device 30.

  Next, proceeding to step S206, based on the first cell voltage value V1 measured in step S203, the second cell voltage value V2 measured in step S205, and the reference cathode potential Vcaba obtained in advance by a test. Then, the anode potential Van and the cathode potential Vca of each cell are calculated (estimated) (Van = Vcab−V2, Vca = Van + V1). The anode potential Van calculated in this way does not deviate from the anode potential when the ignition switch 31 is turned on.

Next, the process proceeds to step S207, and with reference to the anode residual hydrogen concentration map shown in FIG. 4, based on the anode potential Van of each cell calculated in step S206, the hydrogen concentration (anode residual) remaining in the anode of each cell. Determine the hydrogen concentration. The anode residual hydrogen concentration map is the same as that used in the anode scavenging control. The anode residual hydrogen concentration obtained in this way does not deviate from the anode residual hydrogen concentration when the ignition switch 31 is turned on.
Next, the process proceeds to step S208, and based on the anode residual hydrogen concentration obtained in step S207, the purge conditions for performing the OCV purge, that is, the OCV purge amount and the OCV purge pressure are obtained.

The OCV purge amount is obtained using, for example, an OCV purge amount map shown in FIG. In this OCV purge amount map, the higher the anode residual hydrogen concentration, the smaller the OCV purge amount, and the lower the anode residual hydrogen concentration, the greater the OCV purge amount.
This is because when the anode residual hydrogen concentration when the ignition switch 31 is turned on is high, the fluid in the fuel flow path including the anode can be replaced with hydrogen even if the OCV purge amount is small. This is because when the concentration is low, the fluid in the fuel flow path including the anode cannot be replaced with hydrogen unless the OCV purge amount is increased.

Further, when the anode residual hydrogen concentration is high, it is estimated that the generated water in the fuel flow path is small, so that the generated water can be discharged even if the OCV purge amount is small, but when the anode residual hydrogen concentration is low This is because the amount of produced water in the fuel flow path is estimated to be large, and thus the produced water cannot be discharged unless the OCV purge amount is increased.
As the anode residual hydrogen concentration when the OCV purge amount is obtained using the OCV purge amount map, the average value of the anode residual hydrogen concentration of all the cells of the fuel cell 1 may be used, or all of the fuel cells 1 may be used. It may be the lowest value of the cell's anode residual hydrogen concentration.

The OCV purge pressure is obtained using, for example, an OCV purge pressure map shown in FIG. In this OCV purge pressure map, the higher the anode residual hydrogen concentration, the smaller the OCV purge pressure, and the lower the anode residual hydrogen concentration, the greater the OCV purge pressure.
This is because when the anode residual hydrogen concentration when the ignition switch 31 is turned on is high, the fluid in the fuel flow path including the anode can be replaced with hydrogen even if the OCV purge pressure is low. This is because when the concentration is low, the fluid in the fuel flow path including the anode cannot be replaced with hydrogen unless the OCV purge amount is increased.

Further, when the anode residual hydrogen concentration is high, it is estimated that the generated water in the fuel flow path is small. Therefore, the generated water can be discharged even if the OCV purge pressure is low, but when the anode residual hydrogen concentration is low This is because the amount of produced water in the fuel flow path is estimated to be large, and thus the produced water cannot be discharged unless the OCV purge pressure is increased.
As the anode residual hydrogen concentration when the OCV purge pressure is calculated using the OCV purge pressure map, the average value of the anode residual hydrogen concentration of all the cells of the fuel cell 1 may be used, or all of the fuel cells 1 may be used. It may be the lowest value of the cell's anode residual hydrogen concentration.

After the OCV purge condition is determined in step S208, the process proceeds to step S209, and the OCV purge is performed according to the determined OCV purge condition. This OCV purge is performed while continuing to supply air to the cathode without drawing current from the fuel cell 1. In the OCV purge, the shutoff valve 20, the sealing valves 25 and 26, and the purge valve 21 are opened, and fresh hydrogen is supplied from the hydrogen tank 15 to the fuel supply passage 17, the fuel flow passage 5 of the fuel cell 1, and the anode offgas passage 18. The fluid remaining in the flow paths is pushed out and discharged to the diluter 11 through the purge flow path 22. The gas introduced into the diluter 11 merges with the air supplied to the cathode, is diluted, and is discharged from the exhaust pipe 23.
When the OCV purge is finished, the process proceeds to step S210, where preparation for power generation is completed, and execution of this routine is finished.

  By performing the OCV purge control in this way, the OCV purge can be appropriately performed without shortage according to the gas state of the anode of the fuel cell 1 when the ignition switch 31 is turned on. As a result, the fuel cell Since the fuel supply flow path 17 and the anode off-gas flow path 18 including one anode are sufficiently replaced with new hydrogen, the solid polymer electrolyte membrane of the fuel cell 1 can be prevented from being deteriorated, and the operation shifts to power generation operation. When this happens, stable power generation can be performed, and startability is improved. In addition, even when the gas state inside the fuel cell 1 is unknown, such as when starting after the fuel cell 1 is stopped for a short period of time or when starting at a low temperature, an appropriate OCV purge can be performed, so that the startability is improved.

  In the above-described embodiment, the cell voltage measurement targets are all the cells of the fuel cell 1 and the anode potentials of all the cells are estimated. However, the fuel cell 1 is divided into blocks every predetermined number of cell stacks, Measure the cell voltage with the representative cell set for each block as the target of cell voltage measurement, estimate the anode potential of the representative cell of each block, estimate the anode residual hydrogen concentration of the representative cell of each block, and An average value or a minimum value of the hydrogen concentration may be obtained to determine anode scavenging judgment or OCV purge conditions.

Alternatively, because of the structure of the fuel cell 1, it is possible to specify a portion where hydrogen tends to decrease at the anode while the fuel cell 1 is stopped. Therefore, only the cells at the specified portion are subject to cell voltage measurement. The anode potential and the anode residual hydrogen concentration may be estimated based on the cell voltage, and the anode scavenging judgment and the OCV purge condition may be determined.
With reference to FIG. 10, a portion where hydrogen tends to decrease in the anode while the fuel cell 1 is stopped will be described in detail.

  FIG. 10 schematically shows the gas state in the fuel cell 1 being stopped. The left-right direction in FIG. 10 is the cell stacking direction, and it is assumed that a large number of cells are stacked in this stacking direction. In FIG. 10, the upper half shows the cathode portion and the lower half shows the anode portion. For convenience of the following description, the cell of the fuel cell 1 is described by being divided into three blocks ST1, ST2, ST3 in the stacking direction.

  In the fuel cell 1 configured by stacking a large number of cells as described above, generally, an air supply through-passage, an air discharge through-passage, a hydrogen supply through-passage, a hydrogen discharge through-passage (any (Not shown) is provided, and air is supplied from an air manifold (not shown) provided outside the block ST1 side of the fuel cell 1 to the air supply through passage on the block ST1 side, and the cathode of each cell. Is passed through the air discharge through passage, and is discharged to an exhaust manifold (not shown) installed outside the fuel cell 1. On the other hand, hydrogen is supplied from a hydrogen supply manifold (not shown) installed outside the fuel cell 1 to the hydrogen supply through passage of the fuel cell 1, passes through the anode of each cell, and is then discharged to the hydrogen discharge through passage. Then, the fuel is discharged to a hydrogen discharge manifold installed outside the fuel cell 1.

  By the way, as described above, when the fuel cell system is stopped, that is, when the fuel cell 1 is stopped, the hydrogen system includes the sealing valve 25 of the fuel supply passage 17 and the sealing valve 26 of the anode offgas passage 18. Since it is closed, the anode side of the fuel cell 1 is in a sealed state with the inlet / outlet closed, whereas in the air system, the compressor 7 is stopped but the pressure control valve 10 is open. The atmosphere is open.

FIG. 10 shows this state. Since the anode of the fuel cell 1 is in a sealed state, no new hydrogen is supplied, but since the cathode is open to the atmosphere, fresh air can be supplied to the cathode from the air manifold. It becomes a state.
Therefore, on the side close to the air manifold (block ST1), there is a large amount of gas permeation from the cathode to the anode, and oxygen permeated to the anode reacts with the hydrogen of the anode and is consumed, so the hydrogen concentration of the anode is It tends to be low.
On the other hand, on the side far from the air manifold (block ST3), there is sufficient hydrogen at the anode, while the cathode is far from the air manifold and new air is difficult to reach, so the gas permeation from the anode to the cathode increases.

That is, when the fuel cell 1 is stopped, as the time passes, the decrease in the hydrogen concentration of the anode proceeds on the side closer to the air manifold (block ST1 side), and on the side far from the air manifold (block ST3). The hydrogen concentration increases.
When the cell voltage (first cell voltage value V1) is measured at this time, both the blocks ST1 and ST3 show low values.
However, after that, when the sealed state of the anode is maintained, and the cathodes of all the blocks ST1 to ST3 are replaced with fresh air by starting the compressor 7, the cell voltage (second cell voltage value V2) is measured. Then, since there is no change in the gas state, the cell voltage remains low, but in block ST3, the hydrogen present at the cathode is discharged and replaced with air, so the cell voltage increases.

  As described above, in the fuel cell 1 configured such that air is introduced into the cells in the order of the cell stacking direction, the side close to the air manifold is specified as a portion where hydrogen tends to decrease at the anode while the fuel cell 1 is stopped. The second cell voltage value V2 is lowered at this portion. Therefore, one of the cells close to the air manifold is specified, and only this cell is targeted for cell voltage measurement. Based on the cell voltage of this cell, the anode potential and anode residual hydrogen concentration are estimated, and anode scavenging judgment and It is possible to determine OCV purge conditions.

1 Fuel cell 7 Compressor (oxidizer introduction means)
8 Air supply flow path 14 Cell voltage sensor (cell voltage measuring means)
17 Fuel supply channel (fuel channel)
18 Anode off-gas flow path (fuel flow path)
27 Anode scavenging flow path (oxidizer introduction means)
28 Scavenging valve (oxidizer introduction means)
30 Control device (control unit)

Claims (8)

A fuel cell having a solid polymer electrolyte membrane and generating power by supplying fuel to the anode and oxidant to the cathode; and
A fuel flow path for introducing fuel into the anode of the fuel cell;
An oxidant flow path for introducing an oxidant into the cathode of the fuel cell;
Cell voltage measuring means for measuring the cell voltage of the fuel cell;
An oxidant introduction means capable of introducing an oxidant into the oxidant flow path and the fuel flow path;
A control unit for controlling the fuel cell and the oxidant introduction unit and receiving a signal from the cell voltage measurement unit;
With
The control unit obtains a first cell voltage value by measuring a cell voltage by the cell voltage measurement unit after a predetermined time has elapsed from the stop when the fuel cell is stopped, and then the oxidant introduction unit Then, after introducing the oxidant into the oxidant flow path, the cell voltage is measured again by the cell voltage measuring means to obtain the second cell voltage value, and the first cell voltage value, the second cell voltage value, A fuel cell system, wherein an anode potential after the predetermined time has elapsed from the stop is estimated based on a measured cathode potential when an oxidant is introduced into the oxidant flow path.   The said control part calculates | requires the anode residual hydrogen concentration according to the said estimated anode potential using the relationship between the anode potential and anode residual hydrogen concentration which were calculated | required previously. Fuel cell system.   The control unit introduces an oxidant into the fuel flow path by the oxidant introduction unit and discharges the fluid in the fuel flow path when the estimated anode residual hydrogen concentration is less than a threshold value. The fuel cell system according to claim 2.   The control unit is a minimum of the average anode residual hydrogen concentration, which is an average value of the anode residual hydrogen concentration of the cell of the fuel cell, and the minimum value of the anode residual hydrogen concentration of the cell in the fuel cell, which is obtained in advance. Using the relationship with the anode residual hydrogen concentration, based on the estimated average and minimum values of the anode residual hydrogen concentration, it is determined whether or not the fluid needs to be discharged from the fuel flow path, and it is determined that the fluid needs to be discharged. 3. The fuel cell system according to claim 2, wherein the oxidant is introduced into the fuel flow path by the oxidant introduction means and the fluid in the fuel flow path is discharged. A fuel cell having a solid polymer electrolyte membrane and generating power by supplying fuel to the anode and oxidant to the cathode; and
A fuel flow path for introducing fuel into the anode of the fuel cell;
An oxidant flow path for introducing an oxidant into the cathode of the fuel cell;
Cell voltage measuring means for measuring the cell voltage of the fuel cell;
A control unit for controlling the fuel cell and receiving a signal from the cell voltage measuring means;
With
The control unit obtains a first cell voltage value by measuring a cell voltage by the cell voltage measuring unit before power generation when starting up the fuel cell, and then acquires the oxidant flow by the oxidant introduction unit. After introducing an oxidant into the path, the cell voltage is measured again by the cell voltage measuring means to obtain a second cell voltage value, and the first cell voltage value, the second cell voltage value, and the previously measured oxidation A fuel cell system, wherein the anode potential at the time of startup is estimated based on a cathode potential when an oxidant is introduced into the agent flow path.   The said control part calculates | requires the anode residual hydrogen concentration according to the said estimated anode potential using the relationship between the anode potential and anode residual hydrogen concentration which were calculated | required beforehand. Fuel cell system.   The control unit sets the fuel gas replacement amount according to the estimated anode residual hydrogen concentration using the relationship between the anode residual hydrogen concentration obtained in advance and the fuel gas replacement amount at the time of starting the fuel cell, The fuel cell system according to claim 6, wherein fuel gas replacement is performed before power generation when the fuel cell is started.   The control unit sets the fuel gas replacement pressure according to the estimated anode residual hydrogen concentration using the relationship between the anode residual hydrogen concentration determined in advance and the fuel gas replacement pressure at the time of starting the fuel cell, The fuel cell system according to claim 6, wherein fuel gas replacement is performed before power generation when the fuel cell is started.

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