JP2009277502A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system suitable for conducting a warming-up operation, capable of adjusting promptly an oxygen amount contributing to a power generation reaction by a cathode by compensating a low flow-volume controllability of a turbo compressor. <P>SOLUTION: The fuel cell system includes a fuel cell stack 10, a turbo air compressor 22, a purge piping 54, and an exhaust/drainage valve 52. When warming-up of the fuel cell stack is necessary, the exhaust/drainage valve 52 is opened and hydrogen is supplied to a side of an inhaling port of the air compressor 22. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

  Conventionally, for example, as disclosed in the following patent documents, various fuel cell systems that generate power by supplying hydrogen to an anode and oxygen to a cathode are known.

  During power generation of a fuel cell, oxygen at the cathode is consumed by an electrochemical power generation reaction. If the amount of oxygen contributing to the power generation reaction is sufficient, the fuel cell exhibits good current-voltage characteristics. During normal power generation of the fuel cell, it is preferable to supply a sufficient amount of oxygen-containing gas such as air to the cathode to achieve good current-voltage characteristics.

JP 2002-313388 A JP 09-035735 A JP 2006-040604 A JP 2002-056871 A

  By the way, if power generation is performed in a state where the current-voltage characteristics are deteriorated from the normal characteristics, the power generation efficiency is lowered and the amount of heat generated by the fuel cell accompanying the power generation is increased. Therefore, the fuel cell can be warmed up by generating power by intentionally degrading the current-voltage characteristics as necessary. As a result of intensive studies, the inventor of the present application has found a fuel cell system suitable for performing such warm-up operation.

  As a method for deteriorating current-voltage characteristics, there is a method of reducing the amount of oxygen that contributes to the power generation reaction at the cathode. In a fuel cell system that supplies oxygen to the cathode, an oxygen-containing gas such as air is generally supplied to the cathode at a certain level of pressure using a compressor. The amount of oxygen flowing into the cathode is adjusted by changing the rotation speed of the compressor. However, among the compressors, the turbo type compressor has a characteristic that the flow rate varies greatly according to the discharge pressure. Due to this, the turbo compressor has a disadvantage that it takes a relatively long time until the flow rate converges to a constant value when the flow rate changes.

  The present invention has been made based on the above-described circumstances, and an object thereof is to provide a fuel cell system suitable for performing warm-up operation.

  Another object of the present invention is to provide a fuel cell system capable of quickly adjusting the amount of oxygen contributing to the power generation reaction at the cathode, compensating for the low flow controllability of the turbo compressor. is there.

In order to achieve the above object, a first invention is a fuel cell system,
A fuel cell that generates hydrogen by supplying hydrogen to the anode and oxygen to the cathode;
A cathode gas supply mechanism for supplying an oxygen-containing gas to the cathode during power generation of the fuel cell;
A hydrogen supply mechanism capable of supplying hydrogen to the cathode;
Determination means for determining whether the fuel cell needs to be warmed up;
When the determination unit determines that the fuel cell needs to be warmed up, the fuel cell power generation is performed while supplying the oxygen-containing gas by the cathode gas supply mechanism and supplying the hydrogen by the hydrogen supply mechanism. Control means for performing
It is characterized by providing.

A second invention is a fuel cell system for achieving the above-mentioned other object,
A fuel cell that generates hydrogen by supplying hydrogen to the anode and oxygen to the cathode;
A turbo compressor for flowing an oxygen-containing gas into the cathode;
A hydrogen supply mechanism capable of supplying hydrogen to the cathode, wherein a hydrogen supply amount to the cathode is variable;
It is characterized by providing.

The third invention is the second invention, wherein
The hydrogen supply mechanism supplies hydrogen to the cathode by adding hydrogen to a gas sucked by the turbo compressor.

Moreover, 4th invention is 2nd or 3rd invention,
Determination means for determining whether the fuel cell needs to be warmed up;
Control for generating power of the fuel cell while fixing the number of revolutions of the turbo compressor and supplying hydrogen by the hydrogen supply mechanism when the determination means determines that the fuel cell needs to be warmed up Means,
Is further provided.

The fifth invention is the fourth invention, wherein
Voltage detecting means for detecting the voltage of the fuel cell;
Storage means for storing a target voltage value, which is a voltage value to be displayed by the fuel cell when generating the fuel cell at a predetermined low efficiency;
Further comprising
The control means includes feedback control means for feeding back the voltage value detected by the voltage detection means to the hydrogen supply amount of the hydrogen supply mechanism so that the fuel cell exhibits the target voltage value. And

A sixth invention is a fuel cell system for achieving the other object described above,
A fuel cell that generates hydrogen by supplying hydrogen to the anode and oxygen to the cathode;
A turbo compressor that discharges oxygen-containing gas to the cathode;
Of the gas discharged to the cathode side by the turbo compressor, a part of the gas can flow around the cathode, and the amount of the part gas flowing around the cathode is adjusted. Possible bypass mechanism,
It is characterized by providing.

A seventh invention is the sixth invention, wherein
Determination means for determining whether the fuel cell needs to be warmed up;
When the determination means determines that the fuel cell needs to be warmed up, the rotational speed of the turbo-type compressor is fixed and the part of the gas is caused to flow around the cathode by the bypass mechanism. Control means for generating electricity in the fuel cell;
Is further provided.

The eighth invention is the fourth, fifth or seventh invention,
The control means fixes the rotational speed of the turbo compressor to a predetermined low rotational speed that is set lower than the rotational speed of the turbo compressor during normal power generation.

  According to the first invention, the hydrogen supply mechanism supplies hydrogen to the cathode, whereby a part of oxygen in the oxygen-containing gas can be reacted with hydrogen at the cathode. As a result, the current-voltage characteristics are deteriorated and the amount of generated heat is increased, so that the fuel cell can generate power. At the same time, the fuel cell can be heated by the reaction heat of hydrogen and oxygen at the cathode. Thus, according to the first aspect of the invention, it is possible to simultaneously enjoy the temperature increase effect due to the reaction heat of hydrogen and oxygen while generating power with a high calorific value. Therefore, a fuel cell system suitable for warm-up operation can be obtained.

  According to the second invention, hydrogen and oxygen are reacted in the cathode by using the hydrogen supply mechanism, and the amount of oxygen contributing to the power generation reaction can be reduced separately from the control of the turbo compressor. This compensates for the low flow rate controllability of the turbo compressor, and the amount of oxygen contributing to the power generation reaction at the cathode can be quickly adjusted to a desired amount.

  According to the third invention, it is possible to reduce the amount of oxygen that contributes to the power generation reaction while suppressing a change in the discharge pressure of the turbo compressor.

According to the fourth invention, when the fuel cell needs to be warmed up, the amount of oxygen contributing to the power generation reaction is reduced by reacting hydrogen and oxygen at the cathode to reduce the amount of oxygen contributing to the power generation reaction. The fuel cell can generate electric power in a state that is less than that sometimes (hereinafter also referred to as “low oxygen amount state”). According to the low oxygen amount state, the current-voltage characteristic of the fuel cell is deteriorated, the amount of heat generated by the fuel cell is increased, and the fuel cell can be warmed up. Moreover, according to the fourth aspect of the invention, the fuel cell can generate heat by the reaction between hydrogen and oxygen. Therefore, when realizing a low oxygen amount state for warm-up operation, it is possible to simultaneously enjoy the temperature rise effect due to the reaction heat of hydrogen and oxygen.
Furthermore, according to the fourth invention, the rotational speed of the turbo compressor is fixed, and the amount of oxygen consumed in the power generation reaction at the cathode is reduced by the hydrogen supply mechanism. This reduces the amount of oxygen consumed in the power generation reaction at the cathode while reducing control problems compared to the case where a low oxygen amount state is to be achieved by relying on the rotational speed control of the turbo compressor. be able to.

  According to the fifth aspect of the invention, the amount of hydrogen added by the hydrogen supply mechanism can be adjusted by feedback control while the rotational speed of the turbo compressor is fixed. Accordingly, it is possible to execute feedback control for making the operating point of the fuel cell coincide with the target operating point while avoiding the adverse effect due to the low flow controllability of the turbo compressor.

  According to the sixth aspect of the invention, by flowing a part of the gas downstream of the discharge port of the turbo compressor while bypassing the cathode, the amount of oxygen contributing to the power generation reaction separately from the control of the turbo compressor Can be reduced. Thus, the low flow rate controllability of the turbo compressor can be compensated, and the amount of oxygen contributing to the power generation reaction at the cathode can be quickly adjusted to a desired amount.

According to the seventh invention, when the fuel cell needs to be warmed up, a part of the gas downstream of the discharge port of the turbo compressor is caused to flow around the cathode, thereby reducing the amount of oxygen in the fuel cell. Power can be generated in the state. According to the low oxygen amount state, the current-voltage characteristic of the fuel cell is deteriorated, the amount of heat generated by the fuel cell is increased, and the fuel cell can be warmed up.
Furthermore, according to the seventh invention, the rotational speed of the turbo compressor is fixed, and the amount of oxygen consumed in the power generation reaction at the cathode is reduced by the bypass mechanism. As a result, it is possible to reduce the control problems as compared with the case where the low oxygen amount state is to be realized by relying on the rotational speed control of the turbo compressor.

  According to the eighth aspect, when the warm-up operation is necessary, the turbo compressor can be fixed at a low rotational speed. As a result, the amount of oxygen flowing into the cathode can be reduced first, and then the oxygen amount can be reduced using another mechanism (hydrogen supply mechanism or bypass mechanism).

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a configuration diagram of a fuel cell system according to a first embodiment of the present invention. The fuel cell system according to Embodiment 1 includes a fuel cell stack 10. The fuel cell stack 10 is configured by stacking a plurality of unit cells. Each unit cell has a membrane electrode assembly therein. The membrane / electrode assembly is one in which electrode catalyst layers are provided on both sides of a proton conductive solid polymer electrolyte membrane.

  On each surface of the membrane electrode assembly, a gas diffusion layer made of a carbon sheet or the like and a porous body layer made of a foam metal, an expanded metal or the like are further integrated. These gas diffusion layer and porous body layer function as gas flow paths for the anode and cathode in each unit cell. Note that the fuel cell stack 10 may be configured by a unit cell in which a groove is provided in a separator that partitions individual membrane electrode assemblies and the groove is used as a gas flow path. The electrode catalyst layer on one surface of the membrane electrode assembly functions as a cathode, and the electrode catalyst layer on the other surface functions as an anode. Each unit cell receives the supply of hydrogen as a fuel gas at the anode and the supply of oxygen at the cathode, and generates electricity through an electrochemical reaction.

  A cathode gas supply pipe 20, a cathode gas exhaust pipe 30, and a hydrogen supply pipe 40 are connected to the fuel cell stack 10. The cathode gas supply pipe 20 and the cathode gas exhaust pipe 30 communicate with the cathode of each unit cell in the fuel cell stack 10 (specifically, the cathode gas flow path). One end of the cathode gas supply pipe 20 is open to the atmosphere. The hydrogen supply pipe 40 communicates with the anode of each unit cell in the fuel cell stack 10 (specifically, the anode gas flow path).

  The cathode gas supply pipe 20 includes a turbo type air compressor 22. A pressure sensor 24 is connected to the cathode gas supply pipe 20 downstream of the air compressor 22. The cathode gas exhaust pipe 30 is provided with a pressure sensor 32, a pressure regulating valve 34, and a muffler 36. By adjusting the opening of the pressure regulating valve 34 while driving the air compressor 22, air can be supplied to the cathode of the fuel cell stack 10 at a desired pressure.

  The hydrogen supply pipe 40 connects a hydrogen tank (not shown) and the anode of the fuel cell stack 10. The hydrogen supply pipe 40 includes an injector 42 and a pressure sensor 44. The injector 42 can supply hydrogen to the anode of the fuel cell stack 10 at a desired flow rate.

  The fuel cell system of Embodiment 1 includes a hydrogen circulation conduit 46. One end of the hydrogen circulation pipe 46 is connected to the downstream side of the anode of the fuel cell stack 10, and the other end of the hydrogen circulation pipe 46 is connected to the hydrogen supply pipe 40. The hydrogen circulation line 46 includes a gas-liquid separator 48 and a hydrogen circulation pump 50. By driving the hydrogen circulation pump 50, hydrogen can be circulated through the anode of the fuel cell stack 10.

  The fuel cell system according to Embodiment 1 includes a purge conduit 54. The purge line 54 is a line that connects the gas-liquid separator 48 and the inlet side portion of the air compressor 22 in the cathode gas supply pipe 20. An exhaust / drain valve 52 is provided in the vicinity of the gas-liquid separator 48 of the purge line 54. The exhaust drain valve 52 is a mechanism that can variably set the flow rate. By controlling the exhaust / drain valve 52, a desired amount of hydrogen flowing through the hydrogen circulation pipe 46 can be appropriately supplied to the suction port side of the air compressor 22. In addition, opening the exhaust / drain valve 52 also purges the hydrogen circulation line 46 side. Hereinafter, the amount of hydrogen supplied to the air compressor 22 inlet position via the hydrogen circulation conduit 46 is also referred to as “hydrogen addition amount”.

  The fuel cell system of Embodiment 1 includes a thermometer 14, a voltmeter 16, and an ECU (Electronic Control Unit) 60. The ECU 60 receives the outputs of the thermometer 14, the voltmeter 16, and the pressure sensors 24, 32, and 44, and can detect the temperature, voltage, and pressure in each pipeline of the fuel cell stack 10. Further, the ECU 60 can provide a control signal for controlling the rotational speed to the air compressor 22 and a control signal for controlling switching of opening and closing and an opening degree to the exhaust / drain valve 52, respectively. .

[Operation of Embodiment 1]
Hereinafter, the operation of the fuel cell system of Embodiment 1 will be described.

(Low efficiency power generation)
When the current-voltage characteristics deteriorate, the power generation efficiency decreases, and the amount of heat generated by the fuel cell during power generation increases. As described above, the fuel cell system of Embodiment 1 can realize an operation state in which the amount of heat generation is increased and power is generated with low efficiency. Hereinafter, power generation in an environment in which current-voltage characteristics are deteriorated is also referred to as “low efficiency power generation”.

  FIG. 2 schematically shows the current-voltage characteristics of the fuel cell stack 10. FIG. 2 shows current-voltage characteristics during normal power generation (hereinafter also referred to as “normal IV characteristics”) and current-voltage characteristics during low-efficiency power generation (hereinafter also referred to as “low-efficiency IV characteristics”). Are schematically illustrated.

In the first embodiment, the target operating point of the fuel cell stack 10 during low-efficiency power generation (the operating point at the black circle position in FIG. 2) is determined in advance as follows. From the viewpoint of increasing the calorific value of the fuel cell stack 10 as much as possible, the voltage of the fuel cell stack 10 during low-efficiency power generation is desired to be as low as possible. However, on the other hand, it is desirable to ensure the voltage of the fuel cell stack 10 to the extent that the auxiliary equipment of the fuel cell system can operate. From the balance of these requirements, the voltage _VA at the target operating point can be determined. When the voltage _VA is determined, the current value IA necessary for operating the fuel cell system is derived from the voltage _VA . These voltages V _A and the current I _A, a target operating point in the low-efficiency power generation in the first embodiment.

  As a method for deteriorating the current-voltage characteristics in order to realize low-efficiency power generation, there is a method of reducing the amount of oxygen that contributes to the power generation reaction at the cathode. Hereinafter, a state in which the amount of oxygen contributing to the power generation reaction at the cathode is reduced to such an extent that low-efficiency power generation is realized is also referred to as a “low oxygen amount state”.

(Hydrogenation)
In the first embodiment, as described above, a part of the hydrogen circulated through the hydrogen circulation pipe 46 is added to the gas at the suction port of the air compressor 22 by opening the exhaust / drain valve 52. Can do. In such a case, the air compressor 22 discharges the hydrogen-added air to the fuel cell stack 10 side.

  When the mixed gas of hydrogen and air reaches the anode catalyst layer in the fuel cell stack 10, hydrogen and a part of oxygen in the air react with each other in the anode catalyst layer. The hydrogen introduced into the cathode directly reacts with oxygen on the cathode catalyst, so that the actual stoichiometric ratio is lowered. That is, the amount of oxygen that can actually contribute to the power generation reaction in the cathode is reduced. As a result of this action, the current-voltage characteristics of the fuel cell are deteriorated.

  As the amount of hydrogen added is increased, the current-voltage characteristics can be further deteriorated by the above-described action. By appropriately adjusting the amount of hydrogen addition, the current-voltage characteristics can be intentionally deteriorated to a desired degree. As described above, according to the first embodiment, the low-efficiency IV characteristic described above can be realized by adjusting the amount of hydrogen addition, and the fuel cell stack 10 can be generated with the heat generation amount increased.

  The reaction between hydrogen and oxygen is an exothermic reaction. Therefore, according to the first embodiment, the fuel cell stack 10 can be further warmed up by the reaction heat of hydrogen and oxygen on the cathode catalyst. As described above, according to the first embodiment, it is possible to simultaneously enjoy the temperature increase effect due to the reaction heat of hydrogen and oxygen while generating power with a high calorific value. As a result, the fuel cell stack 10 can be quickly warmed up.

  In the first embodiment, air is supplied to the fuel cell stack 10 using a turbo-type air compressor 22. The turbo compressor has a drawback that the amount of leakage is larger than that of a positive displacement compressor (for example, a scroll compressor). Since the amount of leakage is large, the turbo compressor has a characteristic that the flow rate changes relatively greatly according to the discharge pressure. Due to this, the turbo compressor has a drawback that when the flow rate changes, it takes time until the flow rate thereafter converges to a constant value.

  In this regard, in the first embodiment, the current-voltage characteristics can be deteriorated by adjusting the hydrogen addition amount. That is, according to the first embodiment, by increasing or decreasing the hydrogen addition amount, the low flow rate controllability of the turbo type air compressor 22 is compensated, and the oxygen amount contributing to the power generation reaction at the cathode is reduced by low-efficiency power generation. It can be quickly adjusted to achieve a low oxygen amount for realization.

(Contents of control in Embodiment 1)
Subsequently, the contents of the control executed by the ECU 60 in the first embodiment will be described with reference to FIGS. 2 and 3. In the first embodiment, when the fuel cell stack 10 needs to be warmed up, the fuel cell stack 10 is caused to generate power at the low efficiency IV characteristic of FIG. Specifically, this control realizes the above-described low oxygen amount state by fixing the rotation speed of the air compressor 22 and reducing the amount of oxygen contributing to the power generation reaction at the cathode by hydrogen addition. That's it.

  FIG. 3 is a flowchart of a routine executed by the ECU 60 in the fuel cell system according to the first embodiment. In the first embodiment, the control in FIG. 3 is executed when the system is started. In the routine of FIG. 3, first, it is determined whether or not the current start is a low temperature start (step S100). Specifically, it is determined whether the temperature of the fuel cell stack 10 and the outside air temperature are below a predetermined temperature (for example, below freezing point). Thereby, it can be determined whether the warm-up operation of the fuel cell stack 10 is necessary. If it is determined that the current start is not a low temperature start, it is determined that the warm-up operation is unnecessary. As a result, the current routine ends and the system shifts to normal operation.

  If it is determined in step S100 that the current start is a low temperature start, a process of starting driving the air compressor 22 with the rotation speed set to a predetermined low rotation speed is set in order to set the system to the low efficiency power generation mode. It is executed (step S102). This low rotation speed is set to be lower than the rotation speed of the air compressor 22 during normal power generation so that air flows at a lower flow rate than the flow rate corresponding to the air stoichiometric ratio required during normal power generation. It is.

  In the first embodiment, when the process of the ECU 60 proceeds to a series of processes after step S102, the operation state of the fuel cell system is changed to a mode before full-scale power generation (so-called standby mode). Placed. For example, when the fuel cell system according to the first embodiment is mounted on a vehicle, at this time, the system is started to operate, but the vehicle is not in the drive mode and is placed in a standby state. .

Subsequent to step S102, the start of hydrogen addition to the cathode and the control of the amount of hydrogen added to the cathode are performed (step S104). Here, feedback control of the hydrogen addition amount is performed based on the output of the voltmeter 16 so that the voltage of the fuel cell stack 10 becomes the target voltage (that is, the voltage V _A at the target operating point described above). At this time, the rotation speed of the air compressor 22 remains fixed at the predetermined low rotation speed described above.

  Here, the processing content of step S102 and S104 is demonstrated using FIG. In the first embodiment, when the warm-up operation is necessary, first, the rotational speed of the air compressor 22 is fixed to the predetermined low rotational speed. By doing so, the current-voltage characteristic of the fuel cell stack 10 can be made worse than the normal IV characteristic, as schematically shown by the arrow 80 in FIG. In addition, in the first embodiment, by supplying hydrogen to the cathode, the current-voltage characteristic of the fuel cell stack 10 is finally lowered to the low-efficiency IV characteristic as indicated by an arrow 82. As a result, the fuel cell stack 10 can be generated at a target operating point for realizing low-efficiency power generation.

  Following step S104, it is determined whether or not the warm-up of the fuel cell stack 10 has been completed (step S106). Here, for example, the completion of warm-up is appropriately determined by processing such as comparing the temperature of the fuel cell stack 10 with a predetermined value. If the warm-up has not been completed, the processing from step S102 is repeatedly executed. When the warm-up is completed, the current routine ends, the rotation speed of the air compressor 22 is released, and the system shifts to the normal power generation mode.

  According to the processing described above, when the fuel cell system is started, low-efficiency power generation can be realized stably and quickly, and the fuel cell stack 10 can be warmed up early.

(Comparative example)
Here, the effect of the control of the first embodiment will be described using a comparative example.

  FIG. 6A is a first comparative example with respect to the first embodiment. FIG. 6A shows an image of operating point control in a case where low-efficiency power generation is achieved by relying on the rotational speed control of a positive displacement compressor such as a scroll compressor. The positive displacement compressor has a relatively stable relationship between the rotational speed and the flow rate, and exhibits good flow controllability even in a transient state of the flow rate change (in other words, a state where the flow rate is not constantly stable). To do. For this reason, when the positive displacement compressor is driven at a lower rotational speed for low-efficiency power generation, the current value of the fuel cell is expected to take a stable value as shown in FIG.

On the other hand, FIG. 6B shows an image of operating point control in the case where low-efficiency power generation is achieved by relying on the rotational speed control of the turbo compressor. Hereinafter, this is referred to as a second comparative example. In the second comparative example, control is performed in which the measured value of the fuel cell voltage is fed back to the rotational speed of the turbo compressor so that the voltage value of the fuel cell matches the target voltage _VA . Shall.

  As described above, the turbo compressor has a characteristic that the amount of leakage is large and the flow rate greatly changes in accordance with the change of the discharge pressure. Due to this, in the turbo compressor, when there is a change in flow rate, it takes a relatively long time to converge to a constant flow rate thereafter. Due to this, the following problems may occur.

  Assuming that the pressure in the cathode gas supply pipe is low at the start of the fuel cell system, the pressure on the discharge port side of the turbo compressor increases from the initial state as time passes after the turbo compressor starts to drive. . Even if it is attempted to control the rotational speed of the turbo compressor so as to appropriately adjust the flow rate under such circumstances, the rotational speed is excessively increased or the rotational speed is decreased excessively, and the air to the fuel cell is This will cause a situation where the flow rate is not stable to the target flow rate.

  When the air flow rate becomes unstable, the current-voltage characteristics fluctuate as shown by the arrow 300 in FIG. 6B, and as a result, the current value of the fuel cell fluctuates greatly as shown by the arrow 302. The output of the fuel cell stack 10 during low-efficiency power generation is determined so as to balance mainly with the auxiliary machine loss of the air compressor 22 and the amount of power that can be absorbed by the battery in a battery-mounted system. As described above, when the fluctuation range of the current value is large, the balance between the output of the fuel cell stack 10, the auxiliary machine loss, and the amount of power that can be absorbed by the battery is lost, and the stability of the control is lowered. In addition, since the operating point is unstable, it may take a long time to stabilize the target flow rate, or the control may diverge.

  Therefore, in the first embodiment, low-efficiency power generation is realized by using a method of adjusting the hydrogen addition amount while fixing the rotation speed of the air compressor 22. By doing in this way, oxygen supply at a low flow rate that realizes low-efficiency power generation can be realized promptly while avoiding the control problems described using the second comparative example.

  In particular, in the first embodiment, a purge conduit 54 is connected to the suction port side of the air compressor 22. According to such a configuration, a situation in which the discharge pressure of the air compressor 22 changes due to the addition of hydrogen can be avoided.

  In the first embodiment described above, the fuel cell stack 10 is the “fuel cell” in the first invention, and the air compressor 22 and the cathode gas supply pipe 20 are the “cathode gas supply mechanism” in the first invention. The purge pipe 54, the exhaust / drain valve 52, the air compressor 22 and the cathode gas supply pipe 20 correspond to the “hydrogen supply mechanism” in the first aspect of the invention. In the first embodiment, the “determination means” in the first invention is executed by executing step S100 of the flowchart of FIG. 3, and the steps S102 and S104 of the flowchart of FIG. The “control means” in the first invention is realized.

  In the first embodiment described above, the fuel cell stack 10 is the “fuel cell” in the second invention, the air compressor 22 is the “turbo compressor” in the second invention, the purge line 54, The exhaust / drain valve 52, the air compressor 22, and the cathode gas supply pipe 20 correspond to the “hydrogen supply mechanism” in the second aspect of the present invention.

[Modification of Embodiment 1]
(First modification)
In the first embodiment, as described with reference to the flowchart of FIG. 3, the rotation speed of the air compressor 22 is fixed when the fuel cell stack 10 is warmed up. In the first embodiment, the fixing rotational speed is set to a predetermined low rotational speed that is set lower than the rotational speed during normal power generation. However, the present invention is not limited to this. For example, the rotation speed of the air compressor 22 may be fixed at a rotation speed equivalent to that during normal power generation. Also in this case, the current-voltage characteristics can be deteriorated to the same extent as in the first embodiment by adding more hydrogen.

(Second modification)
In the first embodiment, hydrogen is added to the suction port side of the air compressor 22. However, the present invention is not limited to this. For example, one end of the purge conduit 54 may be connected to the position downstream of the pressure sensor 24 of the cathode gas supply pipe 20 in FIG. 1 and hydrogen may be added to the discharge port side of the air compressor 22.

(Third Modification)
In the first embodiment, the adjustment of the hydrogen addition amount by feedback control is continued until the warm-up of the fuel cell stack 10 is completed. However, the present invention is not limited to this. The hydrogen addition amount may be determined by feedforward control at a certain point during the warm-up operation.

(Fourth modification)
In the first embodiment, a part of the hydrogen circulated through the hydrogen circulation pipe 46 is supplied to the cathode of the fuel cell stack 10. However, the present invention is not limited to this, and hydrogen may be supplied to the cathode by other methods. For example, a pipe line can be appropriately extended from an arbitrary position of the hydrogen supply pipe 40, and this pipe line can be connected to the cathode gas supply pipe 20 via a valve.

  The first embodiment is a type of fuel cell system (so-called circulation type system) in which a circulation system including the anode of the fuel cell stack 10 is constructed and hydrogen is circulated in the circulation system. However, the present invention can also be applied to a so-called circulation-less system that does not circulate hydrogen.

  A typical circulation-less system is a fuel cell system that generates power while closing an exhaust mechanism provided downstream of the gas flow path of the anode of the fuel cell (or narrowing its opening). According to such a fuel cell system, operation is performed with the downstream of the fuel gas passage closed (so-called dead-end operation), or the amount of gas discharged from the downstream of the fuel gas passage is made minute. Operation (so-called small amount exhaust operation).

  Also in the case of a circulation-less system, the gas (anode off gas) discharged from the gas flow path of the anode of the fuel cell may be appropriately supplied to the cathode of the fuel cell as in the first embodiment. Also, in the case of a fuel cell system of the type in which the downstream of the gas flow path of the anode of the fuel cell is completely closed, a pipe line is appropriately extended from the hydrogen tank side so that hydrogen can be supplied to the cathode. Just keep it.

  The first embodiment includes a first idea that “hydrogen is supplied into the cathode in order to deteriorate current-voltage characteristics for realizing low-efficiency power generation during warm-up operation”, and “turbo In order to compensate for the poor flow rate controllability in the low rotation range of the compressor, at least two ideas of the second idea of “using a mechanism for adding hydrogen to the cathode in a system having a turbo compressor” are included. ing. The first of these two ideas may be applied to a fuel cell system using a positive displacement compressor as an air compressor.

Embodiment 2. FIG.
FIG. 4 is a configuration diagram of the fuel cell system according to the second embodiment of the present invention. The fuel cell system according to the second embodiment does not include a hydrogen addition configuration such as the purge conduit 54, but includes a three-way valve 152 and a bypass conduit 154 instead. Except for this point, the fuel cell system of Embodiment 2 has the same configuration as the fuel cell system of Embodiment 1. Hereinafter, the same configurations in Embodiments 1 and 2 are denoted by the same reference numerals, and description thereof is omitted.

  According to the three-way valve 152, the flow rate to the cathode side of the fuel cell stack 10 and the flow rate to the bypass conduit 154 side can be appropriately adjusted. By controlling the three-way valve 152, a part of the air discharged by the air compressor 22 can be released to the bypass line 154 side by a desired amount.

  If the amount of oxygen consumed in the power generation reaction at the cathode is reduced during power generation, the current-voltage characteristics will be deteriorated accordingly. As described above, the amount of heat generated by the fuel cell can be increased by intentionally degrading the current-voltage characteristics and performing power generation.

  The deterioration of the current-voltage characteristics as described above can also be realized by reducing the amount of air itself flowing into the cathode. However, due to the low flow rate controllability of the turbo compressor, various problems as described in the first embodiment may occur. Therefore, in Embodiment 2, the amount of air flowing into the cathode is reduced to an amount that can realize low-efficiency power generation by letting some air escape to the bypass conduit 154 side. As described above, according to the second embodiment, the amount of air flowing into the cathode can be accurately adjusted separately from the control of the air compressor 22 which is a turbo compressor.

  FIG. 5 is a flowchart of a routine executed by the fuel cell system of the second embodiment. In the flowchart of FIG. 5, first, similarly to the flowchart of FIG. 3 of the first embodiment, the processes of steps S100 and S102 are executed.

  Thereafter, the opening degree of the three-way valve 152 is adjusted (that is, the amount of air released from the bypass conduit 154) (step S204). In this step, feedback control is executed with respect to the opening of the three-way valve 152 so that the voltage of the fuel cell stack 10 matches the target voltage value. Thereafter, as in the first embodiment, the feedback control is continued until the determination condition in step S106 is satisfied (that is, until the warm-up operation is completed).

  As described above, according to the second embodiment, the amount of oxygen flowing into the cathode is compensated for instability of the flow control of the turbo compressor, and the amount of oxygen for realizing low-efficiency power generation is reduced. It can be adjusted quickly.

1 is a configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. FIG. FIG. 4 is a current-voltage characteristic diagram for explaining the operation of the fuel cell system according to the first embodiment. 3 is a flowchart of a routine that is executed by an ECU in the first embodiment. It is a block diagram of the fuel cell system of Embodiment 2 of this invention. 4 is a flowchart of a routine that is executed by an ECU in a second embodiment. 6 is a diagram schematically showing a comparative example with respect to Embodiment 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell stack 14 Thermometer 16 Voltmeter 20 Cathode gas supply pipe 22 Air compressor 24 Pressure sensor 30 Cathode gas exhaust pipe 32 Pressure sensor 34 Pressure regulating valve 36 Muffler 40 Hydrogen supply pipe 42 Injector 44 Pressure sensor 46 Hydrogen circulation line 48 Air Liquid separator 50 Hydrogen circulation pump 52 Exhaust drain valve 54 Purge line

Claims (8)

A fuel cell that generates hydrogen by supplying hydrogen to the anode and oxygen to the cathode;
A cathode gas supply mechanism for supplying an oxygen-containing gas to the cathode during power generation of the fuel cell;
A hydrogen supply mechanism capable of supplying hydrogen to the cathode;
Determination means for determining whether the fuel cell needs to be warmed up;
When the determination unit determines that the fuel cell needs to be warmed up, the fuel cell power generation is performed while supplying the oxygen-containing gas by the cathode gas supply mechanism and supplying the hydrogen by the hydrogen supply mechanism. Control means for performing
A fuel cell system comprising: A fuel cell that generates hydrogen by supplying hydrogen to the anode and oxygen to the cathode;
A turbo compressor for flowing an oxygen-containing gas into the cathode;
A hydrogen supply mechanism capable of supplying hydrogen to the cathode, wherein a hydrogen supply amount to the cathode is variable;
A fuel cell system comprising:   The fuel cell system according to claim 2, wherein the hydrogen supply mechanism supplies hydrogen to the cathode by adding hydrogen to the gas sucked by the turbo compressor. The fuel cell system according to claim 2 or 3,
Determination means for determining whether the fuel cell needs to be warmed up;
Control for generating power of the fuel cell while fixing the number of revolutions of the turbo compressor and supplying hydrogen by the hydrogen supply mechanism when the determination means determines that the fuel cell needs to be warmed up Means,
A fuel cell system, further comprising: Voltage detecting means for detecting the voltage of the fuel cell;
Storage means for storing a target voltage value, which is a voltage value to be displayed by the fuel cell when generating the fuel cell at a predetermined low efficiency;
Further comprising
The control means includes feedback control means for feeding back the voltage value detected by the voltage detection means to the hydrogen supply amount of the hydrogen supply mechanism so that the fuel cell exhibits the target voltage value. The fuel cell system according to claim 4. A fuel cell that generates hydrogen by supplying hydrogen to the anode and oxygen to the cathode;
A turbo compressor that discharges oxygen-containing gas to the cathode;
Of the gas discharged to the cathode side by the turbo compressor, a part of the gas can flow around the cathode, and the amount of the part gas flowing around the cathode is adjusted. Possible bypass mechanism,
A fuel cell system comprising: The fuel cell system according to claim 6, wherein
Determination means for determining whether the fuel cell needs to be warmed up;
When the determination means determines that the fuel cell needs to be warmed up, the rotational speed of the turbo-type compressor is fixed and the part of the gas is caused to flow around the cathode by the bypass mechanism. Control means for generating electricity in the fuel cell;
A fuel cell system, further comprising: The fuel cell system according to claim 4, 5 or 7,
The fuel cell system, wherein the control means fixes the rotational speed of the turbo compressor to a predetermined low rotational speed that is set lower than the rotational speed of the turbo compressor during normal power generation.

Images