JP2006286479A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system deciding the need for intermittent operation reflecting output efficiency of the fuel cell, as well as the utilization situation of the output region of the fuel cell. <P>SOLUTION: The fuel cell comprises a fuel cell, a power storage device, a control means which stops power generation of the fuel cell and supplies power to a load from the power storage device, when the output of the fuel cell is within a specified value by a prescribed threshold, a power generation efficiency recording means for recording the relations between output value of the fuel cell and the generation efficiency, a utilization frequency recording means for recording the relations between the output value of the fuel cell and the utilization frequency of that output, and a calculation means for calculating the threshold from the generation efficiency and the utilization frequency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

  In general, the efficiency of a fuel cell is reduced in a light load region with a small current. For this reason, a system configured by combining a fuel cell and a power storage device such as a secondary battery and a capacitor has been proposed as a system for supplying power by the fuel cell. For example, a vehicle including a fuel cell described in Patent Document 1 stops power generation of the fuel cell and supplies power from the secondary battery when the required power is a value in a range where the power generation efficiency of the fuel cell is low. .

In other words, this vehicle stops the fuel cell and auxiliary equipment operating in the vicinity thereof in the region of such required power (or output), and supplies the necessary energy to the ECU, lighting, etc. from the secondary battery during that time. Even when traveling, the motor is driven by the secondary battery. Such operation is called intermittent operation.
JP 2001-307758 A

  However, conventionally, whether to perform intermittent operation or normal operation is simply determined based on the efficiency with respect to the output of the fuel cell, and does not take into account the vehicle usage status of the user. For example, even when driving a vehicle equipped with a fuel cell having the same output efficiency, depending on whether the user has a high output / high acceleration or a user with a high output / high acceleration, the output to be intermittently operated should be It is estimated that the determination of whether or not the region is different. However, conventionally, such consideration has not been made.

  An object of the present invention is to determine whether or not intermittent operation is necessary, reflecting not only the output efficiency of the fuel cell but also the utilization status of the output region of the fuel cell. The object of the present invention is to further increase the output efficiency of the fuel cell based on such determination.

  The present invention employs the following means in order to solve the above problems. That is, the present invention stops the power generation of the fuel cell when the output required for the fuel cell, the power storage device, and the fuel cell is within a range specified by a predetermined threshold value, and loads the power from the power storage device to the load. Control means for supplying electric power, power generation efficiency recording means for recording the relationship between the output value of the fuel cell and power generation efficiency, and a use frequency for recording the relationship between the output value of the fuel cell and the use frequency of the output value A fuel cell system comprising recording means and calculation means for calculating the threshold value from the power generation efficiency and usage frequency.

  The fuel cell system controls whether or not to stop the power generation of the fuel cell based on a threshold value obtained from the relationship between the output value of the fuel cell, the power generation efficiency, and the usage frequency. Therefore, it is possible to perform control that reflects the usage frequency and that matches the actual usage.

  Further, the calculating means is an average of the output value of the fuel cell for the predetermined period in the past and an average output value of the value obtained by dividing the output value of the fuel cell by the power generation efficiency for the predetermined period. Efficiency calculating means for calculating the overall efficiency of the fuel cell system from the value, and means for selecting a threshold value for obtaining the maximum overall efficiency among the plurality of overall efficiencies obtained by changing the threshold value do it.

  With such a configuration, the overall efficiency of the fuel cell system can be obtained quantitatively based on the average output value and power generation efficiency of the fuel cell, and the threshold value can be obtained.

  Further, the fuel cell system may include a correcting unit that corrects the use frequency of the past output value of the fuel cell based on the ratio of the intermittent time to the operation time of the fuel cell system in the past predetermined period. With such a configuration, the threshold value can be set with higher accuracy.

  The correction means increases the frequency of use of the output value when the output value of the fuel cell is in a value range specified by the threshold value, and the output value of the fuel cell is in a value range specified by the threshold value It may be corrected so as to reduce the frequency of use of the output value when it is not. By such correction, it is possible to increase the distribution of the usage frequency of the output value in the intermittent operation region where the usage frequency is reduced due to the intermittent operation, and to approximate the distribution of the usage frequency without the original intermittent operation. Moreover, the distribution of the usage frequency of the output value on the higher output side than the intermittent operation region where the usage frequency has increased due to the intermittent operation can be lowered to approximate the distribution of the usage frequency without the original intermittent operation.

  The fuel cell system further includes means for obtaining a ratio of input power to the load with respect to the output power of the fuel cell in a predetermined period in the past, and the power generation efficiency recording means applies the load to the output power of the fuel cell. The relationship between the output value of the fuel cell and the power generation efficiency may be recorded from the ratio of the input power. With such a configuration, the actual power efficiency can be recorded quantitatively, so that the threshold value can be set with higher accuracy.

  Further, the curve indicating the relationship between the output value of the fuel cell and the power generation efficiency has a monomodal peak, and a monotonically increasing curve portion rising toward the power generation efficiency peak in the low output region of the fuel cell and the power generation efficiency peak The calculation means includes a monotone decreasing curve portion that falls at a rate of change smaller than the monotonically increasing curve portion from a position output value toward a higher output range, and the curve indicating the output frequency has a single peak. May be calculated by shifting the threshold value toward the low output side as the single peak of the output frequency moves away from the output value at the power generation efficiency peak position toward the high output range.

  According to the present invention, it is determined whether to stop power generation of the fuel cell and supply power from the power storage device to the load from the power generation efficiency and usage frequency of the fuel cell. Efficiency can be increased.

  Hereinafter, a fuel cell system according to the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings. The configuration of the following embodiment is an exemplification, and the present invention is not limited to the configuration of the embodiment.

<< First Embodiment >>
Hereinafter, a fuel cell system according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 8.

<System configuration>
FIG. 1 is a system configuration diagram of the fuel cell system. This fuel cell system includes a fuel cell main body 1 (corresponding to the fuel cell of the present invention), a power supply switching device 4 that controls supply and interruption of power output from the fuel cell main body 1, and power supply through the power supply switching device 4. Auxiliary machine 11 and load 21 to be supplied, power storage device 2, power supply switching device 4 for controlling input / output and interruption of power to / from power storage device 2, and ECU (electronic control unit, Equivalent to the control means of the present invention.

  The power switching devices 3 and 4 are, for example, relays, semiconductor switches, and the like. The power switching device 4 supplies or cuts off the electric power generated by the fuel cell main body 1. On the other hand, the power switching device 3 supplies the power of the fuel ionization body 1 supplied from the power switching device 4 to the power storage device 2 and charges the power storage device 2. Further, the power supply switching device 3 supplies the electric power stored in the power storage device 2 to the auxiliary machine 11 and the load 21 when the power supply switching device 4 is in the cut-off state.

  The power storage device 2 is, for example, a secondary battery or a capacitor. During operation of the fuel cell main body 1, the power storage device 2 charges the generated power through the power supply switching devices 3 and 4. The power storage device 2 may store regenerative power from a regenerative braking device (not shown). Furthermore, the power storage device 2 supplies power to the auxiliary machine 11 and the load 21 while the fuel cell main body 1 is stopped.

  The auxiliary machine 11 is, for example, a compressor that supplies air as an oxidant gas to the fuel cell body 1, a pump that supplies water as a refrigerant to the fuel cell body 1, a hydrogen pump that circulates the hydrogen gas in the fuel cell body 1, etc. It is. The load 21 is, for example, a motor inverter that supplies electric power to the motor and the motor at a predetermined frequency.

  The ECU 10 starts and stops the operation of the fuel cell main body 1, monitors the output voltage and output current of the fuel cell main body 1, the temperature, etc., monitors the output voltage and output current of the power storage device 2, and turns on and off the auxiliary machine 11. Control, control of energization and interruption of the load 21, control of the energization state and interruption state of the power supply switching devices 3 and 4, and the like are executed.

  In this way, the present fuel cell system stops the fuel cell main body 1 as necessary, and supplies power from the power storage device 2 to the auxiliary machine 11 and the load 21 to continue the operation of the fuel cell system. It has the function of. The feature of this fuel cell system is that power generation is stopped in a region where the power generation efficiency (hereinafter referred to as system efficiency) of the fuel cell system including the fuel cell main body 1 and the auxiliary machine 11 is reduced, and power is supplied from the power storage device 2. There is in point to do. In this case, the fuel cell system determines whether or not to stop power generation from the relationship between the output frequency distribution of the fuel cell main body 1 when the user operates the fuel cell system and the power generation efficiency of the fuel cell system. .

<Concept of system efficiency>
FIG. 2 is an example of a graph showing the system efficiency of the fuel cell system. In FIG. 2, the system efficiency is shown as a function f (x) with respect to the output power of the fuel cell main body 1 (hereinafter referred to as fuel cell output x). The fuel cell output x is the amount of power generated by the fuel cell main body 1.

The system efficiency of the fuel cell system can be defined as the efficiency including the power generation efficiency of the fuel cell main body 1 and the loss due to the operation of the auxiliary machine 11. That is, the system efficiency f (x) can be defined by a value obtained by subtracting the power consumption of the auxiliary machine 11 from the fuel cell output x and dividing by the hydrogen consumption energy at that time.
(Formula 1)
f (x) = (fuel cell output x-loss by auxiliary machine) / hydrogen consumption energy This is also calculated by dividing the load input power by the output power of the fuel cell body 1 (a value obtained by multiplying by a predetermined constant). You can also Here, the predetermined constant is a correction coefficient that is experimentally determined depending on the configuration of the fuel cell system.
(Formula 2)
f (x) = load input power / (output power of fuel cell body 1 × constant)
For example, in a region where the fuel cell output x is small, even if the power generated by the fuel cell main body 1 is small, it is necessary to supply power of a predetermined value or more to a compressor, a refrigerant pump, a hydrogen pump, or the like. Therefore, in this region, the system efficiency decreases as the fuel cell output x decreases. Conversely, the system efficiency increases as the fuel cell output x increases.

  On the other hand, when the fuel cell output x increases, the power consumption of the compressor, the refrigerant pump, the hydrogen pump, etc. increases accordingly. As a result, the amount of reaction gas charged into the fuel cell body 1 increases. However, in the single cell constituting the fuel cell main body 1, when the flow rate of the reaction gas passing exceeds a predetermined value, the amount of the reaction gas passing through the cell increases without being involved in the reaction as the flow rate increases. That is, the power generation efficiency of the single cell decreases as the current increases.

  For this reason, an increase in the amount of power generation commensurate with the increasing power consumption of the auxiliary machine 11 cannot be obtained, and in a region where the fuel cell output x is greater than or equal to a predetermined value, the system efficiency decreases as the fuel cell output x increases. Therefore, the function f (x) indicating the system efficiency is a graph having a peak f (xp) as shown in FIG. Here, xp is a value of the fuel cell output at which the system efficiency reaches a peak. As shown in FIG. 2, the function f (x) has a low efficiency region (x << xp and xp << x) in which the system efficiency decreases from the peak position xp on the low output side and the high output side. .

  FIG. 2 further shows a function g (x) indicating the output frequency of the fuel cell. The output frequency refers to the distribution of the frequency at which the fuel cell output X is actually generated. The output frequency can also be referred to as a distribution of the number of times the user has used the fuel cell output X. For example, when the fuel cell system is a vehicle driven by a fuel cell, the output frequency is a frequency distribution of electric power generated by the fuel cell main body 1 according to the opening degree of the accelerator pedal.

In the fuel cell system, the efficiency y (corresponding to the overall efficiency of the present invention) is defined by the following equation based on the system efficiency f (x) and the output frequency g (x).
(Formula 3)
y = ∫xg (x) dx / ∫ {xg (x) / f (x)} dx
The numerator of Equation 1 represents the average of the fuel cell output x over a predetermined period. Further, the denominator of Equation 1 is an amount corresponding to the hydrogen energy consumed by the fuel cell system in order to obtain the fuel cell output x and the auxiliary machine loss. Therefore, the efficiency y indicates the ratio of the energy output from the fuel cell main body 1 to the energy input to the fuel cell system in a predetermined integration period.

Here, assuming the case of intermittent operation, it is assumed that power generation of the fuel cell main body 1 is stopped when the fuel cell output x is less than the predetermined value α. In this case, the output frequency can be expressed by the following function h (x). Here, when the fuel cell output x is less than the predetermined value α, the value α is referred to as an intermittent operation threshold in the sense that the power generation of the fuel cell body 1 is stopped and intermittent operation is performed.
(Formula 4)
h (x) = 0 (0 <x <α)
h (x) = g (x) (α ≦ x)
FIG. 3 shows an example of a change in system efficiency when the intermittent operation threshold value α is changed. When the intermittent operation threshold value α is much smaller than the fuel cell output xp at which the system efficiency peak f (xp) is reached, the fuel cell main body 1 generates power in the low efficiency region. Therefore, when such an intermittent operation threshold value α is increased, α approaches xp and the efficiency y increases.

On the other hand, when the intermittent operation threshold value α is much larger than the fuel cell output xp at which the system efficiency peak f (xp) is reached, the fuel cell main body 1 generates power in the low efficiency region. When the intermittent operation threshold value α is increased from such a value, α is separated from xp to the high output side, and the efficiency y is decreased. Therefore, the intermittent operation threshold value α has an optimum value αmax that maximizes the system efficiency y. The system efficiency y shown in FIG. 3 is obtained by changing the intermittent operation threshold value α with respect to the output frequency g (x) and the system efficiency f (x) shown in FIG. It is a result.

In the case of the output frequency distribution g (x) as shown in FIG. 2, the optimum value αmax is a fuel cell output xq to f (x) at which g (x) peaks and is in a region near the value output xp. To position. This is because if the value of α is set to a value much larger than xq, the power in the region of the output having a high frequency with the output frequency g (x) is supplied by the power storage device 2, and the system efficiency f (x This is because the operation of the fuel cell for charging the power storage device 2 with low efficiency is required in the region where the) decreases (xp << x).

  In the present fuel cell system, the ECU 10 accumulates the history of the user's operation state, obtains the output frequency g (x), and obtains the efficiency y with respect to α according to Equations 3 and 4. Then, an optimum value αmax that maximizes the efficiency y is obtained, and intermittent operation is performed using this αmax. With such a procedure, the fuel cell system continues the intermittent operation in a state where the efficiency y reflecting the output frequency that is the usage state of the user is maximized.

<Processing flow>
FIG. 4 shows a flowchart of processing in which the ECU 10 of the fuel cell system determines the optimum value αmax. This process is realized by a control program executed by the ECU 10.

  In this process, first, the ECU 10 refers to a map of system efficiency (S1). The system efficiency map is obtained by holding the relationship between the system efficiency function f (x) shown in FIG. 2 and the fuel cell output x in a memory (corresponding to the power generation efficiency recording means of the present invention), for example, in a table format. is there.

  Next, the ECU 10 refers to an output frequency result map (S2). The output frequency actual result map holds the relationship between the fuel cell output frequency distribution g (x) and the fuel cell output x shown in FIG. 2 in, for example, a table type memory (corresponding to the use frequency recording means of the present invention). It is a thing.

  Next, the ECU 10 calculates the efficiency y (α) according to the equations 3 and 4 (S3). In that case, the ECU 10 changes the value of α at a predetermined interval Δα step, and the efficiency yi (i = 1 to N) for a plurality (here, N) αi (i = 1 to N). Is calculated. However, the implementation of the present invention is not limited to this calculation procedure itself. For example, the value of αmax is obtained by a bisection method for a predetermined section (for example, a section from the minimum value α0 to the maximum value α1). You may make it narrow down.

  Next, an optimum value αmax that is the maximum value ymax is selected from the calculated efficiencies yi (i = 1 to N) (S4). The ECU 10 sets this αmax as the intermittent operation threshold value α. ECU10 which performs the process of S4 is equivalent to a calculation means.

  The determination of the optimum value αmax as described above may be performed periodically by the user while using the fuel cell system (for example, a vehicle). Alternatively, it may be executed when the user gives a predetermined execution instruction (such as pressing an execution button (not shown)). In addition, as a function of the output frequency, a specific pattern, for example, a typical change pattern of the accelerator opening degree during vehicle travel may be prepared, and the optimum value αmax may be determined at the time of factory shipment.

FIG. 5 shows a flowchart of intermittent operation during fuel cell system operation. In this process, the ECU 10 detects the user's requested output x from the accelerator opening (S10). And
The ECU 10 calculates a fuel cell output necessary for the required output (S11). For example, the required fuel cell output is a value obtained by adding the power consumption in the auxiliary machine 11 to the required output.

  Next, the ECU 10 determines whether or not the fuel cell output required at this time is less than the intermittent operation threshold value α (S12). When the required fuel cell output x is less than the intermittent operation threshold value α, the ECU 10 stops the operation of the fuel cell main body 1 and switches to the intermittent operation (S13).

  On the other hand, when the required fuel cell output x exceeds the intermittent operation threshold value α, the ECU 10 starts power generation by the fuel cell main body 1 and switches to normal operation. In the actual fuel cell system, even when the required fuel cell output is less than the intermittent operation threshold α, there are cases where intermittent operation cannot be performed due to other conditions. For example, this is a case where the power storage device 2 is not charged with sufficient power.

<Example of calculating efficiency y>
FIG. 6 to FIG. 8 show examples of the efficiency y1, y2, and y3 calculated from the system efficiency f (x) and the output frequencies g1 (x), g2 (x), and g3 (x). As shown in FIGS. 6 to 8, the system efficiency f (x) increases rapidly as the value of the fuel cell output x increases from around zero. Then, when the system efficiency f (x) passes the peak, the value decreases monotonically at a slower rate of change from the rise as the fuel cell output x increases.

  Thus, in this example, the system efficiency is determined from the monotonic increase curve that rises toward the peak and the monotone decrease curve that falls from the output value at the peak position at a rate of change smaller than the monotone increase curve toward the higher output range. It is a left-right asymmetric single-peak curve.

  On the other hand, the output frequencies g1 (x), g2 (x), and g3 (x) are all unimodal curves that are substantially symmetrical. However, g2 (x) has a peak on the higher output side than g1 (x). Further, g3 (x) has a peak on the higher output side than g2 (x). Therefore, the peak position is shifted to the higher output side than the peak position of the system efficiency g (x) in the order of g1 (x), g2 (x), and g3 (x).

  FIG. 6 shows a change in the efficiency y1 obtained by changing the intermittent operation threshold value α from the system efficiency f (x) and the output frequency g1 (x). Similarly, FIG. 7 shows a change in the efficiency y2 obtained from the system efficiency f (x) and the output frequency g2 (x). Similarly, FIG. 8 shows a change in the efficiency y3 obtained from the system efficiency f (x) and the output frequency g3 (x). As described above, the output frequency g1 (x) => g2 (x) => g3 (x) and the efficiency y1 as the peak shifts to the higher output side than the peak position of the system efficiency g (x). , Y2, and y3, the value of the intermittent operation threshold α at which the efficiency becomes the maximum value decreases as α1 => α2 => α3.

  This is because when the output frequency g (x) shifts to the high output side, the system efficiency in that region decreases, so the fuel cell body from the output xmax at which the system efficiency reaches the peak f (xmax) toward the low output direction. This is because α is shifted in the direction of expanding the power generation range of 1.

  As described above, according to the fuel cell system of the present embodiment, the optimum value αmax of the intermittent operation threshold value α that maximizes the efficiency calculated from the output frequency of the fuel cell main body 1 and the system efficiency is obtained, and the intermittent operation threshold value is obtained. The intermittent operation is executed with α set to the optimum value αmax. In this case, since the output frequency is the output frequency when the user actually uses the fuel cell system, the intermittent operation threshold value α that is optimal with respect to the output frequency can be selected and intermittent operation can be executed.

<< Second Embodiment >>
Hereinafter, the fuel cell system according to the first embodiment of the present invention will be described with reference to FIGS. 9 to 13. In the first embodiment, the optimum value αmax of the intermittent operation threshold α that maximizes the efficiency y calculated from the system efficiency and the output frequency is obtained, and this is set as the intermittent operation threshold, and the intermittent operation is performed. Explained the example.

  In the present embodiment, an example in which the output frequency is calculated from the output history of the fuel cell main body 1 in such a fuel cell system will be described. Other configurations and operations are the same as those in the first embodiment. Therefore, the system configuration, the processing flow, and the like will be described with reference to FIGS.

  FIG. 9 is a diagram showing an example of an output frequency pattern of an actual fuel cell when intermittent operation is performed. In this fuel cell system, the optimum value αmax is set as the intermittent operation threshold value. As shown in FIG. 9, in the actual output frequency pattern, the output frequency does not become zero even when the fuel cell output x is less than the intermittent operation threshold (optimum value αmax). However, compared with the fuel cell output calculated from the request output requested by the user (for example, see g1 (x) in FIG. 6), in the region where the fuel cell output x is less than the intermittent operation threshold (optimum value αmax), Extremely less (graph portion 100B).

  That is, the graph shape of the output frequency during intermittent operation (also referred to as an output frequency pattern in the present embodiment) rises rapidly from the vicinity of the intermittent operation threshold (αmax) as the fuel cell output x increases, and thereafter the peak 100c is displayed. After that, it gradually decreases. Further, there is an output frequency even at 0 output (see bar graph 100A). Even when the fuel cell output x is less than the intermittent operation threshold, the output frequency does not become zero because even in such a case, the power generation of the fuel cell body 1 may not be stopped due to other conditions. It is. For example, when the power storage device 2 is not sufficiently charged, it is necessary to continue power generation of the fuel cell even in a region where the fuel cell output x is less than the intermittent operation threshold.

  Thus, since the output frequency pattern during intermittent operation has a different shape from that during normal operation, recording the output frequency pattern during intermittent operation and setting it as the user's output frequency as it is causes a large error. Become. This embodiment demonstrates the procedure correct | amended from the output frequency pattern at the time of intermittent operation to the original output frequency.

For example, for output frequency g (x) during intermittent operation, i (x) obtained by the following correction formula may be used as the corrected output frequency. The ECU 10 executing the calculation of i (x) corresponds to a means for correcting the usage frequency.
(Formula 5)
k (x) = g (x) / β; (0 <x <α)
k (x) = g (x) × (1−β); (α ≦ x)
Here, β = intermittent operation time / total operation time. That is, β is a value obtained by dividing the time during which the fuel cell main body 1 is stopped by the total operation time.

  Equation 5 scales and reduces the output frequency by 1-β times in the region where the fuel cell output is greater than or equal to the intermittent operation threshold. This is because intermittent output causes the output frequency to increase from the normal operation state in the region above the intermittent operation threshold, so by reducing the frequency by the ratio of the intermittent operation time to the total time, the original output frequency pattern It is for making it approach.

  Further, Expression 5 scales and expands the output frequency to 1 / β times in the region where the fuel cell output is less than the intermittent operation threshold. This is because the output frequency is lower than the normal operation state in the region below the intermittent operation threshold due to the intermittent operation. Therefore, by increasing the frequency by the ratio of the intermittent operation time to the total time, the original output frequency pattern It is for making it approach.

As such correction, the output frequency may be multiplied by (1 + β) instead of dividing by β in the region where the fuel cell output is less than the intermittent operation threshold.

  FIG. 10 shows an example of the output frequency k (x) calculated in this way. In FIG. 10, dotted lines 100 </ b> B and 100 </ b> C are output frequencies during intermittent operation, as in FIG. 9. On the other hand, the thick lines 101B and 101C are corrected output frequencies obtained from the output frequencies (dotted lines 100B and 100C) during intermittent operation by the above calculation.

  As shown in FIG. 10, the output frequency after correction has a gap in which the differential coefficient is discontinuous before and after the intermittent operation threshold αmax, but forms a continuous curve, and the general curve shape is generally It approaches a shape of an appropriate output frequency (for example, an output frequency pattern during traveling when a fuel cell is applied to a vehicle).

  Note that the output frequency may be set to a fixed value k0 in a region where the fuel cell output is less than the intermittent operation threshold with respect to the corrected output frequency obtained in FIG. FIG. 11 shows an example of such output frequency. In this case, the fixed value k0 may be a value corresponding to a decrease in output frequency in a region equal to or higher than the intermittent operation threshold. For example, in FIG. 11, k0 = area S / αmax may be calculated for the area S of the region surrounded by the curves 100C and 101C. That is, k0 may be set so that the straight line 104 indicating the output frequency fixed value k0, x = αmax, and the area of the rectangle formed by the two coordinate axes coincide with the area S.

  Further, the output frequency is virtually set so that the fuel cell output increases linearly from the origin (0, 0) in the region where the fuel cell output is less than the intermittent operation threshold with respect to the corrected output frequency obtained in FIG. May be. FIG. 12 shows an example in which a straight line 105 is set from the origin (0, 0) to the position x = αmax. In this example, the straight line 105 connects the end point of the corrected curve 101C in the region equal to or higher than the intermittent operation threshold from the origin (0, 0). As a result, in the intermittent operation threshold, the output frequency is configured as a graph in which a straight line and a curve are continuous.

  With the correction as described above, the distribution of the usage frequency of the output value in the intermittent operation region where the usage frequency has decreased due to the intermittent operation can be increased, and can be brought close to the distribution of the usage frequency without the original intermittent operation. Moreover, the distribution of the usage frequency of the output value on the higher output side than the intermittent operation region where the usage frequency has increased due to the intermittent operation can be lowered to approximate the distribution of the usage frequency without the original intermittent operation.

Further, for example, j (x) obtained by the following correction equation may be used as the corrected output frequency with respect to the user's requested output frequency g1 (x) during intermittent operation. Here, the user's requested output frequency g1 (x) can be determined from the accelerator opening of the vehicle, for example.
(Formula 6)
j (x) = g1 (x) × (SB / SA)
Here, SA is an area of a region formed by a curve indicating the user request request frequency g1 (x) and the x axis. As is well known, this area is obtained by integrating g1 (x). In addition, SB is an area of the region formed by the curve of the actual output frequency and the x axis during intermittent operation (the hatched region formed by the curves 100B and 100C of FIG. 9 and the x axis).

  That is, the above equation 6 is obtained by proportionally converting the required output frequency by the area ratio between the required output frequency requested by the user during intermittent operation and the output frequency of the fuel cell body 1.

<< Third Embodiment >>
The fuel cell system according to the first embodiment of the present invention will be described below with reference to the drawing of FIG. In the first embodiment, the optimum value αmax of the intermittent operation threshold value α that maximizes the efficiency y calculated from the system efficiency and the output frequency of the fuel cell main body 1 is obtained, and this is set as the intermittent operation threshold value α. An example of a fuel cell system that performs the above has been described. In the second embodiment, the output frequency of the fuel cell main body 1 is calculated from the procedure for correcting the output frequency at the intermittent operation to the output frequency at the normal operation without the intermittent operation, or the requested output frequency requested by the user. An example of the procedure was explained.

  In the present embodiment, a configuration and processing procedure for accumulating system efficiency in such a fuel cell system will be described. Other configurations and operations are the same as those in the first embodiment. Therefore, the same components are denoted by the same reference numerals and the description thereof is omitted. Further, the drawings of FIGS. 1 to 12 of the first embodiment are referred to as necessary.

  FIG. 13 shows an example of a configuration diagram of the fuel cell system according to the present embodiment. In this example, the memory 9 is clearly shown in the ECU 10 as compared with the configuration of FIG. In addition, a motor inverter 21A is shown instead of the load 21. Furthermore, a current sensor 31 that measures the output current of the fuel cell body 1, a voltage sensor 32 that measures the output voltage of the fuel cell body 1, a current sensor 33 that measures an input current to the motor inverter 21A, and a motor inverter 21A. A voltage sensor 34 for measuring the input voltage is provided. In order to simplify the drawing, the auxiliary machine 11 and the power storage device 2 are shown as an auxiliary machine / power storage device 11A.

  With such a configuration, the current sensor 31 measures the output current I1 from the fuel cell body 1 during operation of the fuel cell system. The voltage sensor 32 measures the output voltage V1 from the fuel cell body 1. The current sensor 33 measures an input current I2 to the motor inverter 21A. The voltage sensor 34 measures an input voltage V2 to the motor inverter 21A.

The ECU 10 monitors the measured values I1, I2, V1, and V2 of the current sensors 31 and 33 and the voltage sensors 32 and 34, and stores them in the memory 9. As a result, the system efficiency f with respect to the fuel cell output X = I1 × V1
(Formula 7)
f = (I2 × V2) / (I1 × V1 × constant)
Can be obtained as a map.

1 is a system configuration diagram of a fuel cell system according to a first embodiment of the present invention. It is an example of the graph which shows the system efficiency of a fuel cell system. It is a figure which shows an example of the change of the system efficiency at the time of intermittent operation. It is a flowchart of the process which determines the optimal value (alpha) max of an intermittent driving | operation threshold value. It is a flowchart of the intermittent operation at the time of fuel cell system operation. It is a figure (1) which shows the example of the efficiency computed from system efficiency and output frequency. It is a figure (2) which shows an example of efficiency computed from system efficiency and output frequency. It is a figure (3) which shows an example of efficiency computed from system efficiency and output frequency. It is a figure which shows the example output frequency pattern of the actual fuel cell at the time of intermittent operation execution. It is a figure which shows the example of the corrected output frequency. It is a figure which shows the other example of the curve which shows an output frequency. It is a figure which shows the other example of the curve which shows an output frequency. It is an example of the block diagram of the fuel cell system which concerns on 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Power storage device 3, 4 Power supply switching device 9 Memory 10 ECU
11 Auxiliary machine 21 Load 31, 33 Current sensor 32, 34 Voltage sensor

Claims (6)

A fuel cell;
A power storage device;
Control means for stopping power generation of the fuel cell and supplying power from the power storage device to the load when the output required for the fuel cell is within a range of values specified by a predetermined threshold;
Power generation efficiency recording means for recording the relationship between the output value of the fuel cell and the power generation efficiency;
Usage frequency recording means for recording the relationship between the output value of the fuel cell and the usage frequency of the output value;
A fuel cell system comprising: calculation means for calculating the threshold value from the power generation efficiency and the usage frequency. The calculating means includes an average output value obtained by averaging the output value of the fuel cell according to the usage frequency for a predetermined period in the past, and an average value for the predetermined period obtained by dividing the output value of the fuel cell by the power generation efficiency. Efficiency calculating means for calculating the overall efficiency of the fuel cell system from
2. The fuel cell system according to claim 1, further comprising means for selecting a threshold value for obtaining a maximum overall efficiency among the plurality of overall efficiencies obtained by changing the threshold value.   3. The fuel cell system according to claim 1, further comprising a correcting unit that corrects the use frequency of the past output value of the fuel cell based on a ratio of the intermittent time to the operation time of the fuel cell system in the past predetermined period.   The correction means increases the frequency of use of the output value when the output value of the fuel cell is in a value range specified by the threshold value, and the output value of the fuel cell is in a value range specified by the threshold value The fuel cell system according to claim 3, wherein correction is made so as to reduce the frequency of use of the output value when it is not. Means for obtaining a ratio of input power to the load with respect to output power of the fuel cell in a past predetermined period;
5. The fuel cell according to claim 1, wherein the power generation efficiency recording unit records a relationship between an output value of the fuel cell and power generation efficiency from a ratio of input power to a load with respect to output power of the fuel cell. system. The curve showing the relationship between the output value of the fuel cell and the power generation efficiency has a monomodal peak, a monotonically increasing curve portion rising toward the power generation efficiency peak in the low output region of the fuel cell, and the power generation efficiency peak position When the curve showing the output frequency has a monomodal peak, comprising a monotone decreasing curve portion falling at a smaller rate of change from the output value toward a higher output range than the monotone increasing curve portion.
The calculation means shifts the threshold value toward a low output side as the single peak of the output frequency moves away from the output value at the power generation efficiency peak position toward the high output range, and calculates the output frequency. The fuel cell system according to any one of the above.

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