JP5286663B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  In general, a fuel cell may be used in a situation where an output required from an external load frequently fluctuates, such as being mounted on a vehicle. In such a situation of use, the output demand from the external load may increase rapidly, and in such a case, various problems will occur. For example, there is a problem that the time (response time) until the actual output power value of the fuel cell reaches the required output power value is delayed, and the output power becomes insufficient during that time. A fuel cell system that compensates for such a problem by the output of an auxiliary power source such as a secondary battery has been proposed (Patent Document 1, etc.).

JP 2002-271909 A JP-A-2005-57929 JP2002-8694 JP 2004-327317 A

  In addition, there are the following problems. In general, a catalyst layer on which a catalyst for promoting a fuel cell reaction is supported is formed on the electrode layer constituting the fuel cell. However, it is known that the catalyst in the catalyst layer elutes and decreases when the fuel cell is used for a long period of time, leading to deterioration of the fuel cell such as a decrease in fuel cell performance. The inventor of the present invention indicates that such catalyst elution tends to occur when the potential of the fuel cell rapidly decreases, that is, when the output demand for the fuel cell increases rapidly as described above. I found it.

  Not only the elution of the catalyst, but also when the output demand from the external load increases rapidly, there is a possibility that the fuel cell is deteriorated. However, the fact is that no sufficient ingenuity has been made for these problems.

  An object of this invention is to provide the technique which suppresses deterioration of a fuel cell.

In order to achieve the above object, the present invention provides a fuel cell system, wherein the fuel cell, an auxiliary power source, and outputs of the fuel cell and the auxiliary power source in response to an output request to the fuel cell system from an external load A control unit that controls the output , wherein the control unit detects the output request at a predetermined cycle, and when the output request increases from a first value to a second value , (i) the first When the change amount of the output request, which is the absolute value of the difference between the second value and the second value, is less than or equal to a predetermined threshold value, the output value of the fuel cell is set to the first value. A normal control for immediately changing the first command value for the fuel cell from the first command value to the second command value for outputting the output power corresponding to the second value; and (ii) for the catalyst Assuming that an output request with a heavy load was made The arrival time from when the change in the output request is detected until the output power of the fuel cell reaches the output power corresponding to the second value is reached when the normal control is performed. Output that suppresses the catalyst from eluting from the electrode by gradually increasing the command value of the output of the fuel cell from the first command value to the second command value so as to be longer than the time. There line suppression control, the control section, at the output suppression control, as the change amount of the output request is large, longer the arrival time gradually changing the command value of the output of the fuel cell, the control In the normal control and the output suppression control, the unit performs output compensation control that causes the auxiliary power supply to compensate for insufficient power that the output of the fuel cell is insufficient for the output request.

  According to this configuration, even when a sudden output increase request is made for the fuel cell system, the auxiliary power supply supplies insufficient power to the requested output while suppressing the rapid increase in the output of the fuel cell. Can compensate. Therefore, the load applied to the fuel cell is reduced in response to a sudden increase in output of the external load, and deterioration of the fuel cell can be suppressed.

In order to achieve the above object, the present invention provides a fuel cell system comprising: a fuel cell; an auxiliary power source; and the fuel cell and the auxiliary power source in response to an output request to the fuel cell system from an external load. A control unit that controls the output of the output, wherein the control unit detects the output request at a predetermined cycle, and when the output request increases from a first value to a second value , (i) The output of the fuel cell is predetermined when the change amount of the output request, which is the absolute value of the difference between the first value and the second value, is equal to or less than a predetermined threshold value, or when the change in the output request is detected. The output value of the fuel cell is equivalent to the second value from the first command value for the fuel cell when the output request is the first value. To the second command value to output the output power , Performs the normal control to change soon, (ii) the larger than required output change amount is the predetermined threshold value, and wherein when the output of the fuel cell at the time of detecting the change in the output request is a predetermined output smaller Furthermore, it is assumed that an output request with a large load on the catalyst is made, and from the time when the change in the output request is detected until the output power of the fuel cell reaches the output power corresponding to the second value. The fuel cell output command value gradually increases from the first command value to the second command value so that the arrival time of the fuel cell becomes longer than the arrival time when the normal control is performed. There line output suppression control for suppressing said catalyst is elutes from the electrode, wherein, in the output suppression control, as the change amount of the output request is large, the output of the fuel cell Longer the arrival time gradually changing the instruction value, wherein, in the output suppression control and the normal control, the auxiliary power supply shortage power output of the fuel cell is insufficient for the required output It is characterized in that output compensation control is performed to compensate.

  According to this configuration, in response to an output request in which the output of the fuel cell suddenly changes from a low load state with a high potential / low output below a predetermined threshold to a low potential / high output state below a predetermined threshold, The change in the output of the fuel cell can be moderated. Therefore, deterioration of the fuel cell can be suppressed.

  The predetermined threshold value may be set such that the amount of the catalyst supported on the electrode layer constituting the fuel cell with respect to the output change amount of the fuel cell is less than a prescribed amount.

  According to this configuration, it is possible to set a predetermined threshold value that can prevent the elution amount of the catalyst of the fuel cell from becoming significant even when a sudden increase in output is requested to the fuel cell system. Degradation of the fuel cell due to elution can be suppressed.

  The control unit may be configured such that, in the output suppression control, the control unit makes the change in the command value for the output change of the fuel cell more gradual as the change amount of the output request is larger.

  According to this configuration, the change in the output of the fuel cell becomes gentler as the change amount of the output request to the fuel cell system is larger. Therefore, deterioration of the fuel cell can be further reduced.

  The auxiliary power source is capable of charging power generated by the fuel cell, and the control unit may charge the auxiliary power source with surplus power generated exceeding the output requested in the output request. good.

  According to this configuration, the fuel cell system can be operated while charging the auxiliary power source with surplus power.

  The surplus power includes power obtained by continuing the operation in which the fuel cell increases the output power even after the output of the fuel cell reaches the output requested in the output request by the output suppression control. It is good as a thing.

  According to this configuration, since charging is performed immediately after the auxiliary power supply outputs, a high-power / low-capacity auxiliary power supply (for example, a capacitor) can be employed, and the fuel cell system is more stable. Output can be done.

  The said control part is good also as what changes the output of the said fuel cell by a fixed ratio in the said output suppression process.

  According to this configuration, since the control is performed so that the output voltage value or the output power value of the fuel cell is decreased or increased at a constant ratio, the output suppression control can be easily performed. Note that when the output power value of the fuel cell is controlled to increase at a constant rate, there may be a time period in which the amount of change in the output voltage value of the fuel cell per unit time becomes significantly large. Therefore, it is preferable to increase the output voltage value of the fuel cell at a constant ratio because the amount of the catalyst contained in the electrode layer of the fuel cell can be suppressed from being eluted into the electrolyte membrane.

  The fuel cell system further includes a remaining charge detection unit that detects a remaining charge amount of the auxiliary power source, and the control unit detects a remaining charge amount of the auxiliary power source when executing the output suppression control. In the output compensation control, the output suppression control may be performed so that the amount of power output from the auxiliary power source does not exceed the remaining charge amount.

  According to this configuration, it is possible to prevent the remaining amount of charge of the auxiliary power supply from being insufficient, and it is possible to stably perform output compensation control.

  Note that the present invention can be realized in various forms, for example, in the form of a fuel cell system including a fuel cell, a vehicle equipped with the fuel cell system, and the like.

A. Overall system configuration:
FIG. 1 is a schematic diagram showing the configuration of a fuel cell system as an embodiment of the present invention. The fuel cell system 100 includes a control unit 10, a fuel cell stack FC, and a hydrogen system 20 and an air system 30 connected to the fuel cell stack FC.

  The fuel cell stack FC is a polymer electrolyte fuel cell that receives a supply of a fuel gas (hydrogen) and an oxidizing gas (air) and generates electric power through its electrochemical reaction. The fuel cell stack FC has a stack structure in which single cells as power generation modules are stacked. The fuel cell stack FC is provided with a voltage sensor 40 that can measure the potential of each single cell.

  Each single cell has a membrane electrode assembly in which an electrolyte membrane is sandwiched between electrode layers, and each electrode layer has a catalyst layer on which a catalyst for promoting an electrochemical reaction (fuel cell reaction) is supported. Is formed. For example, platinum (Pt) can be employed as the catalyst.

  The hydrogen system 20 is responsible for supplying and discharging hydrogen to the fuel cell stack FC. In the hydrogen system 20, a hydrogen tank 21 for storing hydrogen and a fuel cell stack FC are connected by a hydrogen supply pipe 22. The hydrogen supply pipe 22 is provided with a pressure adjustment valve 23 for adjusting the pressure of hydrogen, and a gas flow meter 24 for measuring the flow rate of hydrogen is provided downstream thereof.

  Further, the hydrogen system 20 includes a hydrogen discharge pipe 25 for discharging anode exhaust gas containing hydrogen that has not been subjected to an electrochemical reaction to the outside of the fuel cell stack FC. The hydrogen discharge pipe 25 is provided with a pressure gauge 26 for measuring the hydrogen pressure and a hydrogen discharge valve 27 in order from the upstream. The hydrogen discharge valve is an on-off valve for stopping discharge of anode exhaust gas to the outside as necessary. The hydrogen discharge pipe 25 may discharge hydrogen to the outside of the fuel cell system 100, or may connect hydrogen to the hydrogen supply pipe 22 to circulate hydrogen.

  The air system 30 is responsible for supplying and discharging air to the fuel cell stack FC. In the air system 30, an air compressor 31 and a fuel cell stack FC are connected by an air supply pipe 32. The air supply pipe 32 is provided with a pressure adjustment valve 33 for adjusting the pressure of the compressed air supplied from the air compressor 31, and a gas flow meter 34 for measuring the flow rate of air downstream thereof. Is provided.

  The air system 30 also includes an air discharge pipe 35 for discharging cathode exhaust gas containing oxygen that has not been subjected to an electrochemical reaction to the outside of the fuel cell stack FC. The air discharge pipe 35 is provided with a pressure gauge 36 for measuring the pressure of the cathode exhaust gas. The air discharge pipe 35 may discharge the cathode exhaust gas to the outside of the fuel cell system 100, or the downstream side of the air discharge pipe 35 is connected to the air supply pipe 32, thereby discharging the water generated in the fuel cell stack FC. It is good also as what circulates air.

  The control unit 10 receives an output request for the fuel cell system 100 from the outside. For example, when the fuel cell system 100 is mounted on a moving body such as a vehicle, an output request is made from the outside via the accelerator pedal 50 or the like. In that case, the control unit 10 calculates an output request according to the accelerator opening.

  The control unit 10 also receives system status information from the above-described two gas flow meters 24 and 34, two pressure gauges 26 and 36, and various sensors such as the voltage sensor 40. Based on the status information, the control unit 10 operates the pressure adjustment valves 23 and 33 and the hydrogen discharge valve 27 of the fuel cell system 100 so that an output (request output) according to an output request from the outside can be obtained. Control. The control unit 10 also controls the entire system in the electrical configuration of the fuel cell system 100 described later.

  FIG. 2 is a block diagram showing an electrical configuration of the fuel cell system 100. The fuel cell system 100 includes a secondary battery 60, a DC / DC converter 70, and a DC / AC inverter 80. The fuel cell stack FC is connected to a DC / AC inverter 80 via a DC power supply line DCL. The secondary battery 60 is connected to the DC power supply line DCL via the DC / DC converter 70. The DC / AC inverter 80 is connected to a motor MT that is an external load.

  The secondary battery 60 functions as an auxiliary power source of the fuel cell stack FC, and can be constituted by, for example, a chargeable / dischargeable lithium ion battery. The DC / DC converter 70 has a function as a charge / discharge control unit that controls charging / discharging of the secondary battery 60, and variably adjusts the voltage level of the DC power supply line DCL according to an instruction from the control unit 10. When the output of the fuel cell stack FC is insufficient, the DC / DC converter 70 causes the secondary battery 60 to discharge so as to compensate for the shortage. The auxiliary power supply may not be rechargeable like the secondary battery 60 but may be only dischargeable, but is preferably a chargeable / dischargeable one that can continue to be used repeatedly. For example, a capacitor may be used instead of the secondary battery 60.

  The DC / AC inverter 80 converts the DC power obtained from the fuel cell stack FC and the secondary battery 60 into AC power. The motor MT can be composed of a three-phase motor or the like, and generates a rotational driving force in accordance with AC power from the DC / AC inverter 80. When the rotor is rotated by an external force, the motor MT functions as a generator and generates AC power (regenerative power). Such regenerative power is converted to DC power by the DC / AC inverter 80 and charged to the secondary battery 60 via the DC / DC converter 70.

  The control unit 10 obtains output power (requested output power) corresponding to the requested output from the output voltage value of the fuel cell stack FC obtained from the voltage sensor 40 described in FIG. 1 and the charging state of the secondary battery 60. The required output voltage (required output voltage) is determined, and this required output voltage is set as the output voltage of the DC / DC converter 70. A specific control method will be described in an embodiment described later. Further, the control unit 10 generates a torque necessary for the motor MT by controlling the frequency of the AC power by the DC / AC inverter 80.

B. First embodiment:
FIG. 3 is a flowchart showing a control procedure of the fuel cell system 100 performed by the control unit 10 as the first embodiment of the present invention. This control procedure is periodically executed every predetermined minute unit time. In step S10, the control unit 10 detects a request output command from the outside. Then, the control unit 10 calculates the required output power that the fuel cell system 100 should output based on the required output command. Here, the required output command and the required output power are normally controlled to coincide . For example, when the fuel cell system 100 is operated is installed in a vehicle is provided as vehicle speed and (amount of depression of the accelerator pedal) the accelerator opening is required output command, the required output power is determined according to . In this case, it is preferable that a map indicating the value of the requested output power corresponding to the requested output command is stored in advance in a memory (not shown) in the control unit 10.

FIG. 4A is a graph showing an example of the time change of the required output power Wr. This graph shows the detection of an increase in the required output power Wr from time T ₀ Odor Te power W ₀ to the power W _1. Hereinafter, the power W _{0 is referred} to as “pre-request output power W ₀ ”, and the power W ₁ is referred to as “post-request output power W ₁ ”. Further, the difference between the output power W ₀ before request and the output power W ₁ after request, which is an increase amount of the required output power, is referred to as “request increase amount ΔWr”.

In step S20, the control unit 10 determines the magnitude of the load on the catalyst of the fuel cell stack FC from the pre-request output power W ₀ and the post-request output power W ₁ detected in step S10. Here, the “load on the catalyst” refers to a factor that leads to an unstable state in which the catalyst is easily eluted from the catalyst layer. This will be described in more detail below.

  It is known that the catalyst supported on the electrode layer is eluted and decreased from the catalyst layer when the fuel cell is used. When the amount of elution is excessive, the power generation performance of the fuel cell is lowered, which causes deterioration of the fuel cell itself. This elution of the catalyst is considered as one of the causes of the occurrence of the catalyst moving to the electrolyte membrane together with the hydroxyl group (OH group) generated on the surface of the cathode electrode layer. Such elution of the catalyst is observed particularly when the potential of the fuel cell is high, and becomes prominent when the potential is suddenly lowered (in a short time) from the high potential state. Specifically, for example, when platinum is employed as the catalyst, platinum is in an unstable state in which it easily elutes when the voltage value per unit cell is about 1 V to about 1.2 V. When the potential drops to about 0.5 V in a short time (for example, about 1 second), the state becomes more unstable.

Accordingly, in the present specification, the “load on the catalyst” means a change in the potential of the fuel cell or the output of the fuel cell, and the “size of the load on the catalyst” means a large value of the potential of the fuel cell. In addition, it means the amount of change per unit time of the potential of the fuel cell. That is, in the determination of step S20 in FIG. 3, the output voltage V ₀ before request, which is the voltage value of the fuel cell when the output power W ₀ is before request, and the voltage value of the fuel cell, when the output power W ₁ is after request. The output voltage V ₁ after a certain request is obtained, and the magnitude of the load on the catalyst is determined.

FIG. 5 is a graph showing the relationship between the power W, voltage V, and current I of the fuel cell stack FC. In general, in a fuel cell, as the current increases, the voltage decreases (V-I characteristic), but the power increases (WI characteristic). By utilizing such a relationship, the output voltage V ₀ before request and the output voltage V ₁ after request can be obtained.

In step S20 of FIG. 3, when both of the following two determination conditions are satisfied, it is determined that the load on the catalyst is large.
Output voltage before request V ₀ ≧ Vth (1)
Voltage difference ΔVr ≧ ΔVth (2)
Here, Vth is a predetermined voltage threshold. The “voltage difference ΔVr” is an absolute value | V ₁ −V ₀ | of a difference between the pre-request output voltage V ₀ and the post-request output voltage V ₁ , and ΔVth is a predetermined threshold value.

  The predetermined threshold values Vth and ΔVth are values determined in advance as threshold values so that the elution amount of the catalyst is smaller than the target specified amount based on the relationship between the amount of change in the voltage value obtained through experiments and the elution amount of the catalyst. It is preferable that the value is determined by the constituent material of the fuel cell. For example, in a polymer electrolyte fuel cell using a platinum catalyst, Vth = about 1.0V and ΔVth = about 0.5V can be set as values per unit cell.

  In the determination conditions (1) and (2), the voltage value of the fuel cell is used as a determination criterion, but the determination may be made based on the power value of the fuel cell. However, as described above, since the elution amount of the catalyst is affected by the voltage value and its change amount, it is preferable to use the voltage value as a reference. In this specification, the term “output of the fuel cell” is used to mean both or either of the output voltage and output power of the fuel cell. Therefore, for example, “the output of the fuel cell is small” means that the voltage value of the fuel cell is high and / or the output power value of the fuel cell is low.

  When the determination condition (1) or the determination condition (2) is not satisfied, the control unit 10 determines that the load on the catalyst is small. In step S20, the determination on the load on the catalyst may be performed using only the determination condition (2) without using the determination condition (1).

When it is determined in step S20 that the load on the catalyst is large, the control unit 10 starts “FC output suppression processing”. FIG. 4B is a graph showing the time change of the output power of the fuel cell stack FC when the FC output suppression process is performed. In this graph, the change in the actual output power Wf of the fuel cell stack FC is indicated by a solid line. The time T ₀ and the output powers W ₀ and W ₁ are the same as the values shown in the graph of FIG.

For comparison, the change in the output power Wfa of the fuel cell stack FC when the FC output suppression process is not performed and the FC normal output control is performed is indicated by a heavy chain line on the graph of FIG. 4B. As shown in the graph, when the FC output suppression process is not performed, the output power Wfa of the fuel cell stack FC reaches the post-request output power W ₁ at the time when the time Tw has elapsed from the time T _0. the T _1. Thus, the time taken from when the output request is made from the outside (time T ₀ ) to when the fuel cell stack FC actually outputs the requested output power W ₁ is referred to as “response time Tw”. This response time Tw usually occurs when the fuel cell outputs in response to an external request. This response time Tw is a minute time, but becomes prominent when a sudden output increase request is made to determine that the load on the catalyst is large.

First, the control unit 10 as the FC output suppression processing determines the processing time Tf (time T ₀ through T ₂₎ for performing the processing (step S30). The processing time Tf is preferably set so as to become longer according to the required increase amount ΔWr. For example, as the processing time Tf, a time satisfying the following formula (3) can be set.
Tf = α × ΔWr + β (3) (α and β are non-negative constants)
According to Equation (3), the processing time Tf is set to be longer in proportion to the required increase amount ΔWr. It should be noted that the constants α and β in Equation (3) are preferably determined such that the processing time Tf is longer than the response time Tw of the fuel cell. The reason for this will be described later.

Next, the control unit 10 obtains the output increase rate Iw by dividing the required increase amount ΔWr by the processing time Tf. Thereafter, the control unit 10 performs control so that the output power Wf increases at the output increase rate Iw (step S40). Therefore, the output power Wf of the fuel cell stack FC reaches the requested output power W ₁ at time T ₂ . Hereinafter, the control in step S40 is referred to as “FC output suppression control”. The “FC output suppression process” refers to a series of processes including the process in step S30 and the FC output suppression control in step S40.

  6A and 6B are explanatory diagrams for more specifically explaining the FC output suppression control. FIG. 6A is a graph showing the time change of the output power of the fuel cell stack FC in which the FC output suppression process is performed, except that the processing time Tf is divided at equal intervals by a minute time. It is almost the same as 4 (B). FIG. 6B is a graph showing the time change of the output voltage Vf of the fuel cell stack FC, and the time axis thereof corresponds to the time axis of FIG.

After determining the processing time Tf and the output increase rate Iw in the FC output suppression processing, the control unit 10 divides the processing time Tf into minute intervals at times t ₁ to t _{9 as} shown in FIG. . The division unit and the number of divisions are arbitrary. Control unit 10, the output increasing rate Iw, at time t ₁ ~t ₉ can be obtained an output power w ₁ to w ₉ the fuel cell stack FC to be output, the time t ₁ ~ shown in FIG. 6 (B) it can be obtained an output voltage v ₁ to v ₉ of the fuel cell stack FC in t _9. Control unit 10, while the FC output suppressing process is performed, the fuel cell system 100 as the fuel cell stack FC outputs an output power w ₁ to w ₉ each time t ₁ ~t ₉ minute intervals The valves 23, 27 and 33 (FIG. 1) are adjusted. Further, DC / DC converter 70, the output voltage of the fuel cell stack FC adjusts the voltage level of the DC power supply line DCL to a value v ₁ to v ₉ for each time t ₁ ~t _9. By performing such control, FC output suppression processing can be realized.

  As described above, the processing time Tf is set to be longer according to the required increase amount ΔWr. Therefore, in the FC output suppression control, as the request increase amount ΔWr, which is the output request change amount, is larger, the fuel cell output increase amount (output increase rate Iw) per unit time is suppressed, and the fuel cell output change is reduced. Be gentle.

  Here, it returns to FIG. 4 (A) and (B). Comparing FIG. 4A and FIG. 4B, the output power Wf of the fuel cell stack FC is insufficient with respect to the requested output during the processing time Tf during which the FC output suppression process is performed. I understand that. In FIG. 4B, the insufficient output power at time t is indicated as insufficient power Wne. The control unit 10 performs control so that the insufficient power Wne is compensated by the secondary battery 60 (FIG. 2). Specifically, the DC / DC converter 70 maintains the voltage level of the DC power supply line DCL so that the secondary battery 60 outputs the insufficient power Wne.

FIG. 4C is a graph showing the change over time in the output power of the secondary battery 60. In this graph, the output power of the secondary battery at an arbitrary time t is indicated by a solid line as the output power Wb. Also, the times T ₀ , T _1, T ₂ and the output powers W ₀ , W ₁ shown in the graph are the same as the values shown in the graph of FIG. That is, the output power Wb of the secondary battery at an arbitrary time t coincides with the insufficient power Wne shown in FIG. 4B at the same time t. Therefore, even if the output of the fuel cell stack FC is suppressed by the FC output suppression process, the required output power W ₁ can be obtained when viewed in the fuel cell system 100 as a whole.

When it is determined in step S20 of FIG. 3 that the load on the catalyst is small, the control unit 10 performs “FC normal output control” (step S35). That is, the control unit 10 performs control so that the fuel cell stack FC immediately outputs the requested output power W ₁ . Note that the response time Tw described with reference to FIG. 4B also occurs in this case, and the secondary battery 60 compensates for the shortage of output power in the response time Tw. However, in this case, since the increase amount ΔWr is small, the response time Tw is also a minute time, and the load on the secondary battery 60 is smaller than the load during the response time Tw when the FC output suppression control is performed.

The process in which the control unit 10 performs the determination using the above-described determination condition (1) is that the output request is changed when the change amount of the output request is larger than a predetermined threshold when the change of the output request is detected . The larger the amount of change , the longer the time it takes for the fuel cell stack FC to actually output the requested output power W ₁ by gradually changing the command value of the output to the fuel cell stack FC. Is also possible. Here, the "fuel cell command value of the output of the stack FC", the output power w ₁ to w ₉ which is set in the fuel cell stack FC every time t ₁ ~t ₉ minute intervals Fig Equivalent to. Further, the control unit 10 performs the output compensation control that causes the auxiliary power source to compensate for the insufficient power that the output of the fuel cell is insufficient with respect to the output request together with the FC output suppression control, and the fuel cell system 100 is requested as the entire system. To achieve the output.

  Further, the process in which the control unit 10 performs the determination using both the determination conditions (1) and (2) is such that when the change in the output request is detected, the change amount of the output request is greater than a predetermined threshold value, and The output suppression control and the output compensation control can be considered to be performed when the output of the fuel cell when a change in output request is detected is smaller than a predetermined output. In this case, since the output state of the fuel cell stack FC when the output request changes is taken into consideration as a determination condition, it is possible to further specify a change in the output request that leads to deterioration of the fuel cell stack FC.

  In step S30, the processing time Tf is determined to be longer than the response time Tw. The reason is as follows. When the output request to the fuel cell changes stepwise, a predetermined percentage (for example, 90%) of the total change requested by the fuel cell from the moment when the fuel cell receives the output change command. The time required to output the amount of change is called “fuel cell response delay time”. The response delay time of the fuel cell is generated by the travel time required for the amount of protons necessary for the fuel cell reaction to reach the cathode side through the electrolyte membrane. The response time Tw described above is a time caused by the response delay time of the fuel cell.

  Therefore, during the response time Tw, the cathode electrode layer is in a state where protons are insufficient and a large amount of OH groups are generated that cause elution of the catalyst. Further, as described above, the catalyst is in an unstable state particularly when the output increase request is made and the voltage of the fuel cell drops. Therefore, the amount of catalyst elution increases during the response time Tw. Therefore, as described above, if the decrease in the potential of the fuel cell stack FC is moderated by making the processing time Tf of the FC output suppression processing longer than the response time Tw (or the response delay time of the fuel cell), the proton movement time is reduced. Can be secured. Therefore, a sufficient amount of protons is supplied to the OH group that causes the catalyst to be eluted, and the amount of catalyst eluted is also reduced. Therefore, the possibility of fuel cell performance degradation and deterioration is reduced. Further, in the past, an excessive amount of catalyst was supported in consideration of the elution of the catalyst. However, according to the configuration of this embodiment, the amount of the extra amount supported can be reduced, so that the cost of the fuel cell can be reduced. Can also be expected.

In determining the processing time Tf, the value obtained by the following equation (4) may be used as the constant α in the equation (3).
α = (C / 4) × (d ² / 6D) (4)
Here, C is a constant, d is the membrane pressure of the electrolyte membrane of the fuel cell, and D is the diffusion coefficient of protons in the membrane. This equation (4) takes into account the proton migration time obtained by the diffusion equation, and is obtained experimentally. If the constant α obtained by the equation (4) is used, the processing time Tf is longer than the response time Tw and can be obtained as a time considering the proton migration time. The constant β may be set to 0.

By the way, in this embodiment , at time T ₀ , a request is made to increase the output power from the pre-request output power W ₀ to the post-request output power W ₁ , and the voltage values V ₀ and V ₁ for the two powers W ₀ and W ₁ are made. _The case where the load on the catalyst is determined by comparing with ₁ has been described . However, in practice, the output increase request is not performed step by step, but is performed continuously. Therefore, in the fuel cell system 100 of the present embodiment, the control unit 10 performs the output power before request W ₀ and the output power W ₁ after request every minute time (for example, a negligible time of about several microseconds). preparative to repeat determination of the load on the catalyst by detecting.

  Further, in the above embodiment, the control unit 10 determines the load on the catalyst (step S20), and performs the FC output suppression process when the load is large, but does not determine the load on the catalyst and always performs the determination. It is good also as what performs FC output suppression processing. However, since the load of the auxiliary power supply is large while the FC output suppression process is being performed, the load on the auxiliary power supply can be reduced by performing the FC output suppression process as necessary as in the above-described embodiment.

C. Second embodiment:
FIG. 7 is a block diagram showing an electrical configuration of a fuel cell system 100A as a second embodiment of the present invention. FIG. 7 is the same as FIG. 2 except that a capacitor 65 is used as an auxiliary power source instead of the secondary battery 60. As the capacitor 65, an electric double layer capacitor can be adopted, but it may be constituted by another auxiliary power source that can be charged and discharged. The system configuration of the other fuel cell system 100A is the same as that of the fuel cell system 100 of FIG.

  FIG. 8 is a flowchart showing a processing procedure performed by the control unit 10 when an external output increase request is made to the fuel cell system 100A. FIG. 8 is the same as FIG. 3 except that step S32 and step S50 are added. The added process will be described below.

  FIG. 9A shows the time change of the output request from the outside to the fuel cell system 100A detected in step S10, and is the same as FIG. 4A of the first embodiment. Accordingly, in this case as well, it is determined that the load on the catalyst is large (step S20), and the FC output suppression process is performed as in the first embodiment (steps S30 and S40). In the present embodiment, compensation for insufficient power is performed by the capacitor 65.

FIGS. 9B and 9C are graphs showing temporal changes in the output power of the fuel cell stack FC and the capacitor 65 when FC output suppression processing and FC surplus output control in step S32 described later are performed. The change in the output power up to time T ₂ when the output power of the fuel cell stack FC reaches the post-request output power W ₁ shown in these two graphs indicates the processing time Tf of the FC output suppression process shortly. Except for this point, it is almost the same as FIGS. 4B and 4C of the first embodiment.

As shown in the graph of FIG. 9B, the fuel cell stack FC continues the process of increasing the output power after the time T ₂ when the FC output suppression process is performed and the requested output power W ₁ is reached. After the request, extra power exceeding the output power W ₁ is output. Hereinafter, the control performed at times T _{2 to} T ₄ is referred to as “FC surplus output control”, and this excess output power is referred to as “surplus output power”. The hatched area in the graph of FIG. 9B indicates the surplus output power amount Wfs.

After time T _{2 in} the graph of FIG. 9C, the output power Wb of the capacitor 65 shows a negative value, which indicates that the capacitor 65 is charged. That is, the surplus output power output from the fuel cell stack FC in the FC surplus output control is charged to the capacitor 65 by the DC / DC converter 70. The hatched area at times T _{2 to} T ₄ in FIG. 9C indicates the amount of charge power Wbc charged in the capacitor 65. The amount of charge power Wbc and the amount of surplus output power Wfs are the same.

In the graph of FIG. 9C, the hatched region between times T _{0 and} T ₂ indicates the compensation power amount Wbs output by the capacitor 65 in the FC output suppression process. It is preferable that the compensation power amount Wbs is equal to the charging power amount Wbc (surplus output power amount Wfs). In this case, it is understood that the hatching area indicating the compensation power amount Wbs and the hatching area indicating the surplus output power amount Wfs have the same area. From this, the FC surplus output control can be realized by controlling as follows.

In step S32, the control unit 10 obtains the time Tf2 from the following mathematical formula (5).
Tf2 = Tf × 2 ⁻² (5)

Control unit 10 during the time Tf2 at time T ₂ through T ₃ are gradually increasing the output power of the fuel cell stack FC in the same increasing rate Iw and FC output reducing process. Only during the time again Tf2 from time T _3, the control unit 10, will reduce the output power of the negative of the output increase rate Iw as the output rate of descent. DC / DC converter 70, the time T _2, and later, the capacitor 65 is charged, to maintain the voltage level of the DC power supply line DCL. The time T ₄ after the fuel cell stack FC performs output in the request after the output power W _1.

When the output power is increased in the FC surplus output control, an increase rate different from the previous increase rate Iw may be used. It is also possible as being set regardless of the processing time Tf of processing time Tf2 also FC output suppression processing for increasing / decreasing the output power, and time interval between time T ₂ through T _3, time T ₃ may not be the same as the time interval of ~T _4. However, by controlling as in the present embodiment, surplus output power can be obtained with an output increase rate Iw with a small load on the catalyst, and the same charging power amount as the compensation power amount output by the capacitor 65 can be easily obtained. Control can be obtained.

  Thus, by performing FC surplus output control in addition to the FC output suppression processing, the compensation power output from the auxiliary power supply is immediately charged by the fuel cell stack FC, so that the FC surplus output control is performed as in the first embodiment. A low-capacity auxiliary power supply can be employed as compared with the case where the operation is not performed. Therefore, in this embodiment, the capacitor 65 is employed as an auxiliary power source instead of the secondary battery 60 of the first embodiment. In this way, if the capacitor 65 is used as an auxiliary power source, the amount of power that can be instantaneously extracted can be made larger than that of the secondary battery 60, and more stable power can be output as the entire fuel cell system. Further, since the capacitor 65 smaller than the secondary battery 60 is employed, the system is downsized, which is advantageous when the system is mounted in a limited space such as a vehicle. Therefore, when the fuel cell system 100A of this embodiment is mounted on a moving body such as a vehicle, it can be expected to improve the acceleration performance and drivability of the vehicle.

D. Third embodiment:
In the present embodiment, the system configuration and processing procedure are the same as those in the first embodiment except for the control method of the FC output suppression control (step S40 in FIG. 3) of the first embodiment. Therefore, only the difference will be described below.

FIGS. 10A and 10B are graphs for specifically explaining the FC output suppression control in the third embodiment. In the first embodiment, the output increase rate Iw is obtained from the processing time Tf and the requested increase amount ΔWr, and the fuel is produced at every time t _{1 to} t ₉ obtained by dividing the processing time Tf increased according to the output increase rate Iw at a minute interval. The output powers w _{1 to} w ₉ to be output by the battery stack FC were determined and output (FIG. 6).

In the present embodiment, as shown in the graph of FIG. 10A, the control unit 10 determines that the output voltage Vf of the fuel cell stack FC is a constant ratio from the voltage V ₀ to the voltage V ₁ during the processing time Tf. Control to descend with. Then, as the output voltage decreases, the output power Wf of the fuel cell stack FC increases in a curved manner as shown in FIG. Specifically, the control unit 10 performs control as follows.

The control unit 10 determines the output voltage drop rate Fv by dividing the difference between the pre-request output voltage V ₀ and the post-request output voltage V ₁ by the processing time Tf. Control unit 10, an output voltage value v ₁ to v ₉ per time t ₁ ~t ₉ when lowering the output voltage in accordance with the drop rate Fv determined, for each time t ₁ ~t _9, the voltage value v fuel cell stack FC in ₁ to v ₉ controls the fuel cell system 100 to output. Further, DC / DC converter 70, the output voltage of the fuel cell stack FC every time t ₁ ~t ₉ maintains the voltage level of the DC power supply line DCL to a value v ₁ to v _9.

Further, the system configuration and the processing procedure are the same as those in the second embodiment, and the FC output suppression control can be performed as in the present embodiment. The time change of the output voltage Vf in this case is shown in FIG. 11A, and the time change of the output power Wf is shown in FIG. 11B. In this graph, as FC surplus output control after performing FC output suppression control (processing time Tf), during the time Tf2 (time T _{2 to} T ₃ ), the output voltage drop rate Fv is the same as that of FC output suppression processing. in lowering the output voltage, during a subsequent time Tf3 (time T ₃ through T ₄₎ it is controlled such that the output power is increased at a constant rate. Note that it is desirable to set the times Tf2 and Tf3 so that the compensation power amount output from the auxiliary power source can be charged.

  As described in the first embodiment, the catalyst becomes particularly unstable when the potential of the fuel cell drops from a high potential to a low potential, and the possibility of elution increases. In the case of the first embodiment and the second embodiment, as can be understood from the graph of FIG. 6B, there is a time zone in which the potential decreases significantly immediately after the start of the FC output suppression process. Therefore, the possibility of the elution of the catalyst can be reduced in the present embodiment than in the first embodiment and the second embodiment.

E. Fourth embodiment:
FIG. 12 is a flowchart showing a control procedure of the fuel cell system 100 performed by the control unit 10 as the fourth embodiment of the present invention. FIG. 12 is the same as FIG. 3 of the first embodiment except that the process of step S25 is added. The fuel cell system of the present embodiment is the same as the system configuration of the first embodiment described with reference to FIGS. Differences from the first embodiment will be described below.

  In this embodiment, after determining the load on the catalyst in step S20, in step S25, the state of charge (SOC) of the secondary battery 60, that is, the remaining charge power of the secondary battery 60 (hereinafter referred to as “power remaining amount”). (Referred to as “P”). The secondary battery 60 may be provided with a unit for monitoring the remaining power P for detecting the state of charge. Or the control part 10 is good also as what has stored the electric power residual amount P calculated from the output electric energy of the secondary battery 60 until then on the memory which is not shown in figure.

  In this embodiment, when determining the processing time Tf in step S30, the remaining power P obtained in step S25 is also taken into consideration. That is, the control unit 10 stores a map in which the processing time Tf can be determined according to the remaining power P in a memory (not shown) of the control unit 10, thereby determining the processing time Tf. As the processing time Tf in this case, it is desirable that the compensation power amount output from the secondary battery 60 in the FC output suppression processing during the processing time Tf is a value that does not exceed the remaining power P. By adopting such a configuration, it is possible to prevent the power of the secondary battery 60 from being insufficient in the FC output suppression process.

F. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

F1. Modification 1:
In the above embodiment, the polymer electrolyte fuel cell is used as the fuel cell stack FC, but another fuel cell may be used. For example, a hydrogen separation membrane battery including a hydrogen separation membrane may be used. Further, although the fuel cell systems 100 and 100A are provided with the hydrogen tank 21, other hydrogen storage devices may be provided, for example, a reformer may be provided.

F2. Modification 2:
In the above embodiment, in the FC output suppression control, the output power or the output voltage is changed at a constant rate per unit time. However, it is not necessary to change the output power or the output voltage at a constant rate. For example, the output power or the output voltage is prepared in advance. It may be controlled according to the map.

F3. Modification 3:
In the above-described embodiment, the magnitude of the load on the catalyst is determined in step S20. However, it may not be a criterion based on the load on the catalyst. For example, the load may be abrupt that leads to deterioration of the electrolyte membrane of the fuel cell. It may be a criterion for determining whether or not it is a request for a change in output.

F5. Modification 5:
In the above embodiment, as the FC normal output control, after the output request is made to the fuel cell system 100, the control is performed to set the command value so as to output the requested output power W ₁ immediately. It does not have to be such control. That is, there may be a slight delay time (for example, a delay time of 1 second or less) after the output request is made to the fuel cell system 100 until the post-request output power W1 is set as the command value. However, even in that case, it is preferable that the processing time Tf in the FC suppression output processing is set longer than the delay time.

F6. Modification 6:
In the above embodiment, as a method for determining which of the FC output suppression process and the FC normal output control process is executed, a method other than that used in the above embodiment can be employed. For example, when a request to increase the output from the external load is made to the fuel cell system, the output before the request, which is the output of the fuel cell at the time of the requested request, and the output requested by the request When the output change amount, which is an absolute value of the difference from the output, is compared with a predetermined threshold value and the first condition including that the output change amount is smaller than the predetermined threshold value is met, the fuel cell immediately outputs the output after the request. It is also possible to perform normal control for controlling to output. Further, when the second condition including that the output change amount is larger than a predetermined threshold is met, the fuel cell output arrival time required for the fuel cell to output the output after the request is normal control. The output suppression control is performed so as to be longer than the fuel cell output arrival time in the case of being performed, and the output compensation control is performed so that the auxiliary power supply compensates the output that the output of the fuel cell is insufficient with respect to the output after the request. good.

  Note that the first condition may not be determined, and only when the second condition is satisfied, the output suppression control and the output compensation control may be performed. Further, when neither the first condition nor the second condition is met, the output compensation control may not be performed together with the output suppression control, or may be performed. Or it is good also as what controls by another control method.

Schematic which shows the structure of a fuel cell system. The block diagram which shows the electric constitution of a fuel cell system. The flowchart which shows the control procedure of the fuel cell system in 1st Example. The graph for demonstrating the output control of the fuel cell system in 1st Example. The graph which shows the relationship between the output electric power of a fuel cell, an output voltage, and an output current. The graph for demonstrating the FC output suppression process of 1st Example. The block diagram which shows the electric constitution of the fuel cell system in 2nd Example. The flowchart which shows the control procedure of the fuel cell system in 2nd Example. The graph for demonstrating the output control of the fuel cell system in 2nd Example. The graph for demonstrating the FC output suppression process of 3rd Example. The graph for demonstrating the output control of the fuel cell system in 3rd Example. The flowchart which shows the control procedure of the fuel cell system in 4th Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Control part 20 ... Hydrogen system 21 ... Hydrogen tank 22 ... Hydrogen supply piping 23 ... Pressure adjustment valve 24 ... Gas flow meter 25 ... Hydrogen discharge piping 26 ... Pressure gauge 27 ... Hydrogen discharge valve 30 ... Air system 31 ... Air compressor 32 ... Air supply pipe 33 ... Pressure adjustment valve 34 ... Gas flow meter 35 ... Air discharge pipe 36 ... Pressure gauge 40 ... Voltage sensor 50 ... Accelerator pedal 60 ... Secondary battery 65 ... Capacitor 70 ... DC / DC converter 80 ... DC / AC Inverter 100, 100A ... Fuel cell system DCL ... DC power supply line FC ... Fuel cell Fv ... Output voltage drop rate Iw ... Output increase rate MT ... Motor Td ... Delay time Tf, Tf2, Tf3 ... Processing time Ti ... Increase request time Tw ... Fuel cell response time Vf ... Fuel cell output voltage ΔVr ... Voltage difference Wb ... Output power Wbs ... compensation output electric energy Wbc ... charged electrical energy Wf of aid power supply, Wfa ... output power WFS ... surplus output power amount WNE ... insufficient power DerutaWr ... demand increase

Claims (7)

A fuel cell system,
A fuel cell having a catalyst disposed on the electrode;
Auxiliary power,
A control unit for controlling the output of the fuel cell and the auxiliary power supply in response to an output request to the fuel cell system from an external load;
With
The control unit detects the output request at a predetermined cycle, and when the output request increases from a first value to a second value ,
(I) When the change amount of the output request, which is the absolute value of the difference between the first value and the second value, is equal to or less than a predetermined threshold value, the command value of the output of the fuel cell is set as the output request Performing normal control to immediately change from the first command value for the fuel cell at the first value to the second command value for outputting output power corresponding to the second value;
(Ii) When the change amount of the output request is larger than a predetermined threshold, it is assumed that an output request with a large load on the catalyst has been made, and the output power of the fuel cell is detected from when the change in the output request is detected. The command value of the output of the fuel cell is set so that the arrival time until the output power corresponding to the second value is reached is longer than the arrival time when the normal control is performed. wherein from 1 the command value to the second command value progressively increases have line output suppression control for suppressing said catalyst is eluted from the electrode,
In the output suppression control, the control unit gradually changes the command value of the output of the fuel cell to increase the arrival time as the amount of change in the output request increases.
In the normal control and the output suppression control, the control unit performs output compensation control that causes the auxiliary power supply to compensate for an insufficient power that the output of the fuel cell is insufficient for the output request. Battery system. A fuel cell system,
A fuel cell having a catalyst disposed on the electrode;
Auxiliary power,
A control unit for controlling the output of the fuel cell and the auxiliary power supply in response to an output request to the fuel cell system from an external load;
With
The control unit detects the output request at a predetermined cycle, and when the output request increases from a first value to a second value ,
(I) The fuel cell when an output request change amount, which is an absolute value of a difference between the first value and the second value, is equal to or less than a predetermined threshold value, or when a change in the output request is detected. When the output of the fuel cell is equal to or higher than a predetermined output, the command value of the output of the fuel cell is calculated from the first command value for the fuel cell when the output request is the first value. A normal control for immediately changing to the second command value for outputting the output power corresponding to the value of
(Ii) the amount of change in the output request is greater than a predetermined threshold value, and wherein when the fuel cell output is a predetermined output smaller than the output required load is greater for said catalyst at the time of detecting a change in the output request Assuming that the arrival time from when the change in the output request is detected until the output power of the fuel cell reaches the output power corresponding to the second value, the normal control is performed. The catalyst is eluted from the electrode by gradually increasing the command value of the output of the fuel cell from the first command value to the second command value so as to be longer than the arrival time in the case of There line output suppression control for suppressing the,
In the output suppression control, the control unit gradually changes the command value of the output of the fuel cell to increase the arrival time as the amount of change in the output request increases.
In the normal control and the output suppression control, the control unit performs output compensation control that causes the auxiliary power supply to compensate for an insufficient power that the output of the fuel cell is insufficient for the output request. Battery system. The fuel cell system according to claim 1 or 2 , wherein
The auxiliary power source is capable of charging power generated by the fuel cell,
The said control part is a fuel cell system which charges the surplus electric power generated exceeding the output requested | required in the said output request | requirement to the said auxiliary power supply. The fuel cell system according to claim 3 ,
The surplus power includes power obtained by continuing the operation in which the fuel cell increases the output power even after the output of the fuel cell reaches the output requested in the output request by the output suppression control. , Fuel cell system. A fuel cell system according to any one of claims 1 to 4 , wherein
The said control part is a fuel cell system which changes the output of the said fuel cell by a fixed ratio in the said output suppression process. The fuel cell system according to any one of claims 1 to 5 , further comprising:
A remaining charge detection unit for detecting the remaining charge of the auxiliary power supply;
The control unit detects the remaining charge amount of the auxiliary power source when executing the output suppression control, and prevents the amount of power output from the auxiliary power source in the output compensation control from exceeding the remaining charge amount. A fuel cell system that performs the output suppression control. A method for controlling a fuel cell system, comprising: a fuel cell in which a catalyst is disposed on an electrode; an auxiliary power source; and a control unit that controls the output of the fuel cell and the auxiliary power source in response to an output request from an external load. Because
(A) detecting the output request at a predetermined period ;
(B) When the output request increases from the first value to the second value in the step (a) ,
(I) When the change amount of the output request, which is the absolute value of the difference between the first value and the second value, is equal to or less than a predetermined threshold value, the command value of the output of the fuel cell is set as the output request Performing normal control to immediately change from the first command value for the fuel cell at the first value to the second command value for outputting output power corresponding to the second value;
(Ii) When the change amount of the output request is larger than a predetermined threshold, it is assumed that an output request with a large load on the catalyst has been made, and the output power of the fuel cell is detected from when the change in the output request is detected. The command value of the output of the fuel cell is set so that the arrival time until the output power corresponding to the second value is reached is longer than the arrival time when the normal control is performed. Performing an output suppression control for gradually increasing the command value from 1 to the second command value to suppress the catalyst from eluting from the electrode ;
(C) In the output suppression control, the larger the amount of change in the output request, the longer the arrival time by gradually changing the output command value of the fuel cell;
(D) In the normal control and the output suppression control, output compensation control is performed to cause the auxiliary power supply to compensate for insufficient power that the output of the fuel cell is insufficient for the output request.

Images