JP6816522B2 - Fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

As a fuel cell system, a system that uses the electric power of a secondary battery for scavenging treatment for discharging water in the fuel cell system and exhausting impurities such as nitrogen is known. Patent Document 1 describes a fuel cell system that repeats discharging for performing scavenging processing and pausing for voltage recovery of the secondary battery as a control method for the secondary battery.

Japanese Unexamined Patent Publication No. 2004-171864

In the scavenging control of the fuel cell system below the freezing point, if the discharge of the secondary battery is suspended, the generated water may freeze before the voltage of the secondary battery is restored depending on the pause time. Therefore, a technique capable of suppressing freezing of parts during scavenging suspension has been desired.

The present invention has been made to solve at least a part of the above-mentioned problems, and can be realized as the following forms.
According to one embodiment of the present invention, a fuel cell system is provided. This fuel system controls a fuel cell, a plurality of scavenging components used for scavenging processing to discharge water in the fuel cell, a secondary battery capable of supplying power to the scavenging component, and the scavenging component. For a certain period of time, the strength of the scavenging is weakened at different timings for each scavenging component so that the scavenging is performed in order from the component located on the upstream side of the reaction gas flow path of the fuel cell to the component located on the downstream side. The control unit includes a control unit that executes the scavenging process, and the control unit starts the scavenging process while the power generation of the fuel cell system is stopped, and after the start of the scavenging process, the voltage of the secondary battery is predetermined. When the voltage drops to the required voltage, the scavenging process is temporarily suspended, and after the scavenging process is temporarily suspended, the voltage of the secondary battery is restored to a voltage at which the power required for the scavenging process after resumption can be secured. When the time required for the above elapses, the scavenging process is restarted. The present invention can also be realized in the following forms.

According to one embodiment of the present invention, a fuel cell system is provided. This fuel cell system controls the fuel cell; the scavenging component used for the scavenging process to discharge the water in the fuel cell; the secondary battery capable of supplying power to the scavenging component; A control unit that executes the scavenging process for a certain period of time; the control unit; starts the scavenging process while the power generation of the fuel cell system is stopped, and after the start of the scavenging process, the secondary battery The scavenging process is paused when the voltage drops to a predetermined voltage; after the scavenging process is paused, the voltage of the secondary battery can secure the power required for the scavenging process after restarting. When the time required to recover to the voltage has elapsed, the scavenging process is restarted. According to this form of fuel cell system, the control unit suspends the scavenging process due to the voltage drop of the secondary battery, and then raises the voltage of the secondary battery to a voltage that can secure the power required for the scavenging process after restarting. Since the scavenging process can be resumed when the scavenging is recovered, the period during which the scavenging is stopped can be minimized. Therefore, freezing of parts during scavenging suspension can be suppressed.

The present invention can be realized in various forms, for example, a power generation device equipped with a fuel cell system, a vehicle equipped with a fuel cell system, and the like.

It is explanatory drawing which shows the schematic structure of the fuel cell system. It is a reference figure which showed the relationship between the power consumption by a scavenging process, and the voltage of a secondary battery. It is a flowchart which shows the outline of a scavenging process. It is a figure which showed the relationship between the power consumption by a scavenging control process, and the voltage of a secondary battery. It is a figure which showed the relationship between the power consumption by the scavenging control process in 2nd Embodiment, and the voltage of a secondary battery.

A. First Embodiment:
FIG. 1 is a schematic view showing a schematic configuration of a fuel cell system 100 according to an embodiment of the present invention. The fuel cell system 100 includes a fuel cell 10, a control unit 20, an oxidation gas flow path system 30, and a fuel gas flow path system 50. Further, the fuel cell system 100 includes a DC / DC converter 90, a secondary battery 92, a load 93, and an SOC detection unit 94. The fuel cell system 100 of the present embodiment is mounted on, for example, a fuel cell vehicle.

The fuel cell 10 is a solid polymer fuel cell that generates electricity by receiving the supply of hydrogen (fuel gas) and air (oxidizing gas) as reaction gases. The fuel cell 10 has a stack structure in which a plurality of cells 11 are stacked. Each cell 11 has a membrane electrode assembly (not shown) in which electrodes are arranged on both sides of an electrolyte membrane (not shown), and a set of separators that sandwich the membrane electrode assembly. The electric power generated by the fuel cell 10 is stored in the secondary battery 92 via the DC / DC converter 90.

Various loads 93 are connected to the secondary battery 92. The fuel cell 10 and the secondary battery 92 can supply electric power to the air compressor 32, the circulation pump 64, and various valves, which will be described later. The secondary battery 92 is a lithium ion battery in this embodiment. The secondary battery 92 may be composed of, for example, a nickel hydrogen battery. When the secondary battery 92 is continuously discharged for a long time, lithium, which is a carrier of electric charges, becomes non-uniform, and the overvoltage increases. Further, by suspending the discharge, the overvoltage is reduced and the voltage is recovered by diffusing and homogenizing lithium.

The SOC detection unit 94 is also connected to the secondary battery 92. The SOC detection unit 94 detects the stored amount (SOC) [%] of the secondary battery 92 and transmits it to the control unit 20. In the present embodiment, the “storage amount (SOC)” means the ratio of the remaining charge to the current charge capacity of the secondary battery 92. The SOC detection unit 94 detects the temperature, output voltage value, and output current value of the secondary battery 92, and detects the amount of electricity stored (SOC) based on these detected values. Further, the SOC detection unit 94 of the present embodiment also transmits the temperature of the secondary battery 92 to the control unit 20.

The oxidation gas flow path system 30 includes an oxidation gas pipe 31, an air compressor 32, an on-off valve 33, a cathode off gas pipe 41, and a regulator 42. The oxidation gas flow path system 30 includes a flow path on the cathode side in the fuel cell 10.

The air compressor 32 is connected to the fuel cell 10 via an oxidation gas pipe 31. The air compressor 32 compresses the air taken in from the outside in response to the control signal from the control unit 20, and supplies the air as an oxidation gas to the fuel cell 10.

The on-off valve 33 is provided between the air compressor 32 and the fuel cell 10, and opens and closes according to the flow of the supply air in the oxidation gas pipe 31. Specifically, the on-off valve 33 is normally in a closed state, and opens when air having a predetermined pressure is supplied from the air compressor 32 to the oxidation gas pipe 31.

The cathode off gas pipe 41 discharges the cathode off gas discharged from the cathode of the fuel cell 10 to the outside of the fuel cell system 100. The regulator 42 adjusts the pressure of the cathode-off gas (back pressure on the cathode side of the fuel cell 10) in the cathode-off gas pipe 41 in response to the control signal from the control unit 20.

The fuel gas flow path system 50 includes a fuel gas pipe 51, a hydrogen tank 52, an on-off valve 53, a regulator 54, an injector 55, an exhaust / drain valve 60, an anode off-gas pipe 61, a circulation pipe 63, and circulation. A pump 64 and a gas-liquid separator 70 are provided. The fuel gas flow path system 50 includes a flow path on the anode side in the fuel cell 10. In the following, the fuel gas pipe 51 is composed of a downstream side of the injector 55, a flow path on the anode side in the fuel cell 10, an anode off-gas pipe 61, a circulation pipe 63, and a gas-liquid separator 70. The flow path is also referred to as a circulation flow path 65. The circulation flow path 65 is a flow path for circulating the anode off gas of the fuel cell 10 to the fuel cell 10.

The hydrogen tank 52 is connected to the anode of the fuel cell 10 via the fuel gas pipe 51, and supplies the hydrogen filled therein to the fuel cell 10. The on-off valve 53, the regulator 54, and the injector 55 are provided in the fuel gas pipe 51 in this order from the upstream side, that is, the side close to the hydrogen tank 52.

The on-off valve 53 opens and closes in response to a control signal from the control unit 20 to control the inflow of hydrogen from the hydrogen tank 52 to the upstream side of the injector 55. The on-off valve 53 is closed when the fuel cell system 100 is stopped. The regulator 54 adjusts the hydrogen pressure on the upstream side of the injector 55 in response to the control signal from the control unit 20. The injector 55 is an electromagnetically driven on-off valve in which the valve body is electromagnetically driven according to the drive cycle and valve opening time set by the control unit 20. The control unit 20 controls the amount of hydrogen supplied to the fuel cell 10 by controlling the drive cycle and valve opening time of the injector 55.

The anode off-gas pipe 61 is a pipe that connects the outlet of the anode of the fuel cell 10 and the gas-liquid separator 70. The anode off-gas pipe 61 guides the anode-off gas containing fuel gas, nitrogen gas, etc., which has not been used in the power generation reaction, to the gas-liquid separator 70.

The gas-liquid separator 70 is connected between the anode off-gas pipe 61 of the circulation flow path 65 and the circulation pipe 63. The gas-liquid separator 70 separates the generated water from the anode off gas in the circulation flow path 65 and stores it.

The circulation pipe 63 is connected downstream from the injector 55 of the fuel gas pipe 51. The circulation pipe 63 is provided with a circulation pump 64 that is driven in response to a control signal from the control unit 20. The circulation pump 64 sends out the anode-off gas from which the generated water is separated by the gas-liquid separator 70 to the fuel gas pipe 51. As described above, in the fuel cell system 100, the anode off gas containing hydrogen is circulated and supplied to the fuel cell 10 again to improve the efficiency of hydrogen utilization.

The exhaust drain valve 60 is provided in the lower part of the gas-liquid separator 70. The exhaust / drain valve 60 drains the generated water stored in the gas-liquid separator 70 and exhausts the anode off gas in the gas-liquid separator 70. During the operation of the fuel cell system 100, the exhaust / drain valve 60 is normally closed and opens / closes in response to a control signal from the control unit 20. In the present embodiment, the exhaust drain valve 60 is connected to the cathode off gas pipe 41, and the generated water and the anode off gas discharged by the exhaust drain valve 60 are discharged to the outside through the cathode off gas pipe 41.

In the present embodiment, the control unit 20 controls the air compressor 32, the on-off valve 53, the exhaust / drain valve 60, and the circulation pump 64 to perform scavenging processing while the fuel cell system 100 is suspended from power generation. These parts used for scavenging are collectively called "scavenging parts". The "scavenging treatment" in the present embodiment is to supply electric power to the scavenging components to drive them for a certain period of time, and to discharge the water existing in the scavenging components themselves and the flow path downstream of the scavenging components. .. In the scavenging process of the present embodiment, the control unit 20 drives all the scavenging components at the same time. The control unit 20 also monitors the temperature and voltage of the secondary battery 92 transmitted from the SOC detection unit 94.

The control unit 20 is configured as a computer including a CPU, a memory, and an interface circuit to which the above-mentioned components are connected. The CPU controls the power generation by the fuel cell system 100 by executing the control program stored in the memory, and also controls the scavenging components to execute the scavenging process while the power generation of the fuel cell system 100 is stopped. Hereinafter, the scavenging process performed while the power generation of the fuel cell system 100 is stopped is simply referred to as "scavenging process". Since the scavenging process in the present embodiment is performed while the power generation of the fuel cell system 100 is stopped, power is supplied to the scavenging component from the secondary battery 92.

FIG. 2 is a reference diagram showing the relationship between the power consumption due to the scavenging process and the voltage of the secondary battery 92. The control unit 20 continuously discharges the secondary battery 92 in the scavenging process of the scavenging component. The upper graph shows the change in the voltage of the secondary battery 92, and the vertical axis shows the voltage. The lower graph shows the power consumption required to complete the scavenging process by the scavenging components, and the vertical axis shows the power. In both the upper and lower graphs, the horizontal axis shows time.

As shown in FIG. 2, when the scavenging component is driven to perform the scavenging process, the voltage of the secondary battery 92 gradually decreases and reaches the lower limit voltage. If the voltage of the secondary battery 92 is lower than the lower limit voltage, the performance of the secondary battery 92 may deteriorate. Therefore, power cannot be supplied to the scavenging component after the lower limit voltage is reached. As a result, there is a shortage of power to drive the scavenging components. Therefore, in the present embodiment, as described below, the secondary battery 92 is prevented from running out of power by temporarily suspending the scavenging process. The lower limit voltage can be determined by experimentally obtaining a voltage value at which the performance of the secondary battery 92 deteriorates.

FIG. 3 is a flowchart showing an outline of the scavenging control process in the present embodiment. The scavenging control process in the present embodiment is a process executed by the control unit 20 while the fuel cell system 100 is stopped, for example, immediately after the fuel cell system 100 is stopped, or when a predetermined time has elapsed from the stop of the fuel cell system 100. Is. At the start of the scavenging control process, it is assumed that the amount of electricity stored (SOC) and the voltage of the SOC detection unit 94 are sufficient.

In the scavenging control process of the present embodiment, first, the control unit 20 drives the scavenging component to start the scavenging process (step S100). Then, it is determined whether or not the voltage of the secondary battery 92 detected by the SOC detection unit 94 has dropped to a predetermined voltage (step S110). The predetermined voltage is hereinafter referred to as a "threshold value". The threshold value is preferably equal to or higher than the above-mentioned lower limit voltage. When the voltage of the secondary battery 92 has not dropped to the threshold value (step S110: NO), the control unit 20 continues to drive the scavenging component and continue the scavenging process. On the other hand, when the voltage of the secondary battery 92 drops to the threshold value (step S110: YES), the control unit 20 stops driving the scavenging component and suspends the scavenging process (step S120). In step S110, if the scavenging process continues for a predetermined period without the voltage reaching the threshold value, the scavenging control process may be terminated.

After suspending the scavenging process, the control unit 20 calculates the time required for the voltage of the secondary battery 92 to rise (recover) to the target voltage (hereinafter, referred to as “voltage recoverable time”) (step S130). .. Specifically, the control unit 20 first sets the remaining scavenging time and the voltage capable of supplying power until the completion of the scavenging process of the scavenging component as the target voltage, and is based on a map or function showing the relationship between the voltage and the scavengable time. Ask. Then, based on a map or function that defines the relationship between the storage capacity (SOC) of the secondary battery 92 and the temperature of the secondary battery 92 and the time required for voltage recovery, the voltage for recovering to the target voltage is set. Calculated as recoverable time.

After obtaining the voltage recoverable time, the control unit 20 temporarily suspends the scavenging process in step S120, and then determines whether or not the voltage recoverable time has elapsed (step S140). If the voltage recoverable time has not elapsed (step S140: NO), the control unit 20 waits until the voltage of the secondary battery 92 recovers to the target voltage, and if the voltage recoverable time has elapsed (step S140: NO). S140: YES), the control unit 20 restarts the scavenging process (step S150).

FIG. 4 is a diagram showing the relationship between the power consumption by the above-mentioned scavenging control process and the voltage of the secondary battery 92. As shown in FIG. 4, the control unit 20 stops the driving of the scavenging component at the timing t1 when the voltage of the secondary battery 92 drops to a predetermined threshold value after the start of the scavenging process, and temporarily stops the scavenging process. Take a break. Then, the control unit 20 determines the timing t2 so that the interval (voltage recoverable time) for recovering the voltage of the secondary battery 92 to the target voltage can be secured, and when the elapsed time after the stop has passed the timing t2. , Drive the scavenging component to restart the scavenging process. As a result, the voltage of the secondary battery 92 is restored, and all the electric power required for driving the scavenging component can be supplied.

According to the fuel cell system 100 of the present embodiment described above, the control unit 20 can secure the electric power required for the scavenging process after the scavenging process is temporarily suspended due to the voltage drop of the secondary battery 92. Since the scavenging process can be restarted when the voltage of the secondary battery 92 recovers to the voltage, the period for suspending the scavenging can be minimized. Therefore, freezing of parts during scavenging suspension can be suppressed.

B. Second embodiment:
In the above embodiment, the control unit 20 simultaneously drives all the scavenging components in the scavenging process. On the other hand, in the second embodiment, the scavenging control process is performed at different timings for each scavenging component. For example, in the fuel gas flow path system 50, scavenging of each component in the order of the fuel cell 10, the gas-liquid separator 70, and the exhaust drain valve 60 while reducing the scavenging strength from the component on the upstream side to the component on the downstream side. To carry out.

FIG. 5 is a diagram showing the relationship between the power consumption by the scavenging control process and the voltage of the secondary battery 92 in the second embodiment. The control unit 20 performs scavenging of the fuel cell 10 during the period from timing t0b to timing t1b, scavenging of the gas-liquid separator 70 during the period from timing t2b to timing t3b, and exhausts during the period from timing t4b to timing t5b. Scavenging the drain valve 60 is performed. The control unit 20 determines the timing t2b and the timing t4b so as to secure an interval for the voltage of the secondary battery 92 to rise according to the voltage capable of supplying electric power until the completion of the scavenging process of each scavenging component, and the scavenging component. Controls to restart the scavenging process.

According to the fuel cell system 100 of the second embodiment described above, it is possible to prevent insufficient scavenging of downstream parts due to inflow of liquid water from the upstream. Therefore, freezing of parts during scavenging suspension can be suppressed.

C. Modification example:
<First modification>
In the above embodiment, the scavenging process means that the control unit 20 drives the scavenging components for a predetermined time and discharges the scavenging components themselves and the water existing in the flow path downstream of the scavenging components. .. In other words, the control unit 20 uses "time" as an index of the scavenging process. On the other hand, the control unit 20 may use "the amount of water in the scavenging component" as an index of the scavenging process. The amount of water in the scavenging component can be obtained by using, for example, an estimated value of the amount of residual water or a measured value based on impedance.

<Second modification>
In the first embodiment, the control unit 20 elapses the voltage recoverable time by one discharge pause. On the other hand, the control unit 20 may restore the voltage of the secondary battery to the target voltage by suspending the discharge two or more times.

<Third modification example>
When the power generation of the fuel cell system 100 is stopped, the control unit 20 may perform the scavenging control process not only once but also a plurality of times.

The present invention is not limited to the above-described embodiments and modifications, and can be realized with various configurations without departing from the spirit of the present invention. For example, the embodiment corresponding to the technical feature in each embodiment described in the column of the outline of the invention, the technical feature in the modified example, in order to solve the above-mentioned problem, or a part or all of the above-mentioned effect. It is possible to replace or combine as appropriate to achieve this. Further, if the technical feature is not described as essential in the present specification, it can be appropriately deleted.

10 ... Fuel cell 11 ... Cell 20 ... Control unit 30 ... Oxidation gas flow path system 31 ... Oxidation gas piping 32 ... Air compressor 33, 53 ... On-off valve 41 ... Cathode off gas piping 42, 54 ... Regulator 50 ... Fuel gas flow path system 51 ... Fuel gas piping 52 ... Hydrogen tank 55 ... Injector 60 ... Exhaust / drain valve 61 ... Anodic off gas piping 63 ... Circulation piping 64 ... Circulation pump 65 ... Circulation flow path 70 ... Gas / liquid separator 90 ... DC / DC converter 92 ... Secondary battery 93 ... Load 94 ... SOC detector 100 ... Fuel cell system

Claims (1)

It ’s a fuel cell system,
With a fuel cell
A plurality of scavenging parts used for the scavenging process for discharging water in the fuel cell, and
A secondary battery that can supply power to the scavenging component,
By controlling the scavenging component , scavenging is performed at different timings for each scavenging component so that scavenging is performed in order from the component located on the upstream side of the reaction gas flow path of the fuel cell to the component located on the downstream side for a certain period of time. A control unit that executes the scavenging process while weakening the strength of the
The control unit
The scavenging process is started while the power generation of the fuel cell system is stopped, and when the voltage of the secondary battery drops to a predetermined voltage after the start of the scavenging process, the scavenging process is temporarily suspended.
After the suspension of the scavenging process, the scavenging process is restarted when the time required for the voltage of the secondary battery to recover to a voltage at which the power required for the scavenging process after the restart can be secured has elapsed. Fuel cell system.

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