JP3555438B2 - Compressor control device for vehicle fuel cell system - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compressor control technique in a fuel cell for driving a vehicle.
[0002]
[Prior art]
In a vehicle fuel cell system, air required for the fuel cell is supplied using a compressor. In the conventional fuel cell system, only one compressor is provided, and the compressor is set so as to have a maximum efficiency point (maximum efficiency generation flow rate) at an air supply amount near the rated output (maximum output) of the fuel cell. ing. However, in a fuel cell system for a vehicle, the partial load region is used more frequently, and thus the above-described control reduces the overall efficiency. For example, FIG. 10 is a characteristic diagram showing the relationship between the air flow rate, the fuel cell load, and the efficiency when the conventional compressor control as described above is performed. As shown in FIG. 10, when the efficiency of the compressor is set to be maximum near the rated load, the efficiency of the fuel cell stack increases in the low-load region where the frequency of use is high, but the efficiency of the compressor is significantly increased. As a result, the efficiency of the entire fuel cell system is reduced. The reason for this is that the compressor occupies most of the auxiliary equipment driving force that reduces the fuel cell stack efficiency.
[0003]
Also, in order to improve the efficiency in the low load range, a method of using a fuel cell system intermittently at the maximum efficiency point of the system using a secondary battery as a buffer (the compressor is also operated intermittently in accordance with the fuel cell system) To do). However, this method has the following practical problems. That is, in a practical system, a device that generates hydrogen from a fuel such as methanol by using a reformer (catalyst device) may be used. In this case, even if the fuel pump is stopped, the fuel will remain in the piping. Since hydrogen continues to be generated from the remaining fuel for a while, if the fuel cell is intermittently stopped, hydrogen during that time will be exhausted unnecessarily, and the system efficiency will not increase.
[0004]
[Problems to be solved by the invention]
As described above, the control of the compressor in the conventional fuel cell system has a problem that the efficiency of the entire system is reduced in a partial load region frequently used for vehicles.
[0005]
The present invention has been made in order to solve the problems of the prior art as described above, and is intended to improve the efficiency of a fuel cell system in an entire area including a frequently used low load area. An object of the present invention is to provide a compressor control device for a battery system.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as described in the claims. That is, according to the first aspect of the present invention, a plurality of compressors each having a different maximum efficiency generation flow rate are provided, and the plurality of compressors are switched according to the output required of the fuel cell, and the air is supplied to the fuel cell. Is controlled to be sent. For example, the small compressor sets the maximum efficiency generation flow rate in a partial load range (for example, an urban driving mode range: the range of the fuel cell output is usually 10 kW or less depending on the vehicle), and the large compressor sets the rated point (maximum horsepower). (The generation area) is set near the maximum efficiency generation flow rate, and the large and small compressors are switched according to the output value required by the fuel cell and the maximum efficiency generation flow rate of the large and small compressors. The compressor can always be operated in an efficient state in the entire operation range including the load range. Further, since the operation of the fuel cell is not interrupted, hydrogen is not wasted as in the conventional example.
[0007]
The invention according to claims 2 to 4 shows a specific configuration of the compressor control in claim 1. The above configuration corresponds to, for example, a first embodiment described later.
[0008]
Further, the invention according to claim 5 sets the value obtained by adding the maximum efficiency generation flow rate of the large compressor and the maximum efficiency generation flow rate of the small compressor to the rated output of the fuel cell, In a region where the flow rate is equal to or higher than the maximum efficiency generation flow rate, a mode is provided in which the large compressor and the small compressor are simultaneously operated. With this configuration, the capacity of the large compressor can be set smaller than the rated output, so that the size can be reduced. Note that the above configuration corresponds to, for example, a second embodiment described later.
[0009]
【The invention's effect】
According to the present invention, in the operating region of the total, the drop in efficiency is not, it is possible to realize a high fuel cell system efficiency, the effect is obtained that.
Further, according to the fifth aspect of the invention, an effect is obtained that the large compressor can be reduced in size.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.
First, the configuration will be described. Air is supplied to the fuel cell 4 by switching the discharge air of the large compressor 1 and the small compressor 2 by the switch 3. The large compressor 1 is a compressor having a large air flow rate, and the small compressor 2 is a compressor having a smaller air flow rate. For example, the large compressor 1 is located near a rated point (maximum horsepower generation area). The small compressor 2 has a maximum efficiency generated flow rate in a partial load range (for example, an urban driving mode range: usually, a fuel cell output is 10 kW or less, depending on the vehicle). is there. The motor for driving the compressor is not shown, but is assumed to be included in the compressor. On the other hand, the example in which the fuel such as methanol is reformed by a reformer (catalyst device) 5 is used for supplying hydrogen to the fuel cell 4, but the supply of hydrogen from a hydrogen storage alloy or a hydrogen tank is, of course, performed. I don't care. In this case, the reformer 5 is unnecessary. Further, since air and hydrogen are supplied to the fuel cell 4 in a slightly larger amount than required for power generation, surplus air and hydrogen are exhausted.
[0011]
The output of the fuel cell 4 is adjusted to a predetermined voltage by a voltage converter 6 according to an operation instruction signal S1 from a controller 10 and supplied to a motor 7 for driving a vehicle and a battery 8 for a buffer. The battery 8 is provided with a DOD sensor 9 for detecting the depth of discharge DOD of the battery (100% for full discharge, 0% for full charge), and the charge (discharge) state of the battery 8 is input to the controller 10. .
[0012]
Further, the controller 10 determines the output of the fuel cell 4 by performing a predetermined calculation based on, for example, the accelerator opening signal S6, the accelerator opening change rate signal S7, and the vehicle speed signal S8, and Operation instruction signals S2 to S5 are output to the compressor 3, the large compressor 1, and the small compressor 2 so as to supply a predetermined amount of air and hydrogen to the fuel cell 4. The output signal S9 of the fuel cell 4 is fed back to the controller 10. The above-mentioned signals S6 to S9 are given from respective sensors, but these sensors are not shown.
[0013]
Next, the operation will be described.
As the simplest example of compressor control when two large and small compressors are provided as described above, as shown in the characteristic diagram of FIG. 9, the large compressor 1 is located near the rated point (maximum output generation area). The maximum efficiency point is set, and the small compressor 2 sets the maximum efficiency point in the partial load range, and selects the compressor that can efficiently generate the air amount corresponding to the output of the fuel cell system required from the running state. A method for controlling the operation is considered. However, in this case, the compressor efficiency near the switching point A of the large and small compressors is considerably reduced as compared with the maximum efficiency point. , The efficiency of the fuel cell system is reduced in the output region corresponding to. For this reason, the present embodiment is configured as described below.
[0014]
FIG. 2 is a characteristic diagram showing a relationship between the air flow rate / fuel cell load and efficiency according to the first embodiment. In the present embodiment, two large and small compressors are switched as shown in FIG. 2 to improve the efficiency of the entire system.
[0015]
First, air flow rate G ₀ required for the fuel cell 4 according to the vehicle running state, in a range smaller than the maximum efficiency occurred flow G ₁ of the small compressor 2 and islanding small compressor 2. The method controls for example the discharge flow rate of performing rotational speed control small compressor 2 so as to match the G _0. Although the maximum efficiency generated flow rate of the large compressor 1 is set near the rated value, the small compressor 2 sets the maximum efficiency generated flow rate to a range of 10 kW or less of the fuel cell output required for the city running mode of the vehicle.
[0016]
Also, usually, the maximum efficiency of the large compressor 1 is higher than the maximum efficiency of the small compressor. Therefore, in the range where the efficiency of the large compressor 1 is lower than the maximum efficiency of the small compressor 2 (G ₁ <G ₀ <G ₂ ), the large and small compressors are switched to operate at the maximum efficiency point. This specific switching method will be described later. Compressor efficiency in this range is as shown in E _1, the efficiency of the entire fuel cell system is as shown in E _2. Therefore, the efficiency is improved more than the characteristic shown in FIG. 9 by the range described as “the fuel cell system efficiency improvement margin” in FIG.
[0017]
In the range of G ₀ ≧ G ₂ , the large compressor 1 is operated independently. In this method, as in the case of G ₁ ≧ G ₀ , the number of revolutions is controlled to adjust the discharge flow rate of the large compressor 1 to G ₀ .
[0018]
The maximum because generally the maximum efficiency of a large compressor 1 is higher than the maximum efficiency of the small compressor, said although defines G ₂ as the maximum efficiency of a large compressor 1 temporarily is smaller compressor 2 When the efficiency is equal to or smaller than the efficiency, G ₂ is defined as the maximum efficiency generated flow rate of the large compressor 1.
[0019]
The magnitude of the compressor by operating as described above, the system efficiency, compared to using switching becomes the E ₂ so 2, a compressor with higher simply efficiency shown in FIG. 9 Therefore, there is no drop and high efficiency is achieved in the whole area. In addition, since power is continuously generated by the fuel cell by driving either the large or small compressor, as described above, hydrogen continues to be generated after stopping the power generation of the fuel cell, resulting in reduced system efficiency. Not even.
[0020]
Next, a first embodiment of a method of switching between the large and small compressors in the region of G ₁ <G ₀ <G ₂ will be specifically described with reference to flowcharts shown in FIGS. FIGS. 3 and 4 are connected at points (A) to (G), respectively, forming one flowchart. The normal system control is described in the main routine, and only the switching part of the compressor according to the present invention is described as this subroutine.
[0021]
3 and 4, it is assumed that the compressor switching flags n _S (corresponding to a small compressor) and n _B (corresponding to a large compressor) are initialized to 0 when the vehicle is started (key-on). Further, the output of the fuel cell 4 determined by the controller 10 based on the vehicle running state (for example, the accelerator opening signal S6, the accelerator opening change rate signal S7, the vehicle speed signal S8) is W ₀ , and the fuel cell 4 is required at that time. the air flow rate and _{G 0.} It is assumed that W ₀ and G ₀ are calculated in the main routine. It is also assumed that the DOD signal has been read in the main routine.
[0022]
The compressor operation subroutine, first, the value of G ₀ in block 11 to determine whether the G ₁ or less. In the case of "yes", the small compressor 2 is operated independently as described above, and the routine proceeds to block 12. Here and check the flag n _S is small compressor 2 or not yet started the operation, it is determined whether. If “no” (n _S = 1), it is determined that the small compressor 2 is already operating, and the process returns to the main routine. For "yes", it instructs to operate together small compressor 2 to _{G 0} at block 13. Specifically, for example, the number of rotations is instructed.
[0023]
Next, in block 14, the small compressor 2 is operated, and the stop of the large compressor 1 is reflected in the flag (n _S = 1, n _B = 0). Then, a stop command is issued to the large compressor 1 in block 15, and the switch 3 is switched in block 16 so that the discharge air of the small compressor 2 is guided to the fuel cell 4.
[0024]
On the other hand, if it was "no" at block 11, the process proceeds to block 17, the value of _{G 0} is determined whether greater than _{G 2.} In the case of "yes", the large compressor 1 is operated independently as described above, and the routine proceeds to block 18. Where it checks the flag n _B is a large compressor 1 or not yet started the operation, it is determined whether. If “no” (n _B = 1), the large compressor 1 has already been operated, so the process returns to the main routine. For "yes", it instructs to drive the combined large compressor 1 to _{G 0} at block 19. Specifically, the number of rotations is specified. In the next block 20, driving a large compressor 1, causing reflected flag to stop the small compressor _{2 (n B = 1, n} S = 0). Then, a stop command is issued to the small compressor 2 in block 21 and the switch 3 is switched in block 22 so that the discharge air of the large compressor 1 is guided to the fuel cell 4.
[0025]
For "no" at block 17, it means that _{G 1 <G 0 <G 2} , will be operated while appropriately switching the two major compressor 1 and the small compressor at its maximum efficiency generation point. In this state, when driving a large compressor 1, since the output W _m of the fuel cell 4 generates greater than the output W ₀ being requested, the difference △ W to be stored in the battery 8 (Charging). Conversely, when the small compressor 2 is operating, it is taken out of the battery 8 by ΔW (discharge). In the region of G ₁ <G ₀ <G ₂ , the charging / discharging speed of the battery 8 changes depending on the magnitude of ΔW. Therefore, the battery 8 is completely discharged and the vehicle cannot run, or the vehicle is fully charged and regenerative energy is stored. It is necessary to change the switching point from charging (large compressor 1 operation) to discharging (small compressor 2 operation) or vice versa as shown in FIG. In FIG. 5, the charge start line and the discharge start line are linearly changed so that the DOD is switched at a position farther from 0% to 100% as the value of ΔW increases.
[0026]
Returning to FIG. 3 and FIG. 4, if G ₁ ≦ G ₀ <G ₂ (“no” in block 17), ２３W is calculated in block 23. Next, in block 24, while reading the map of FIG. 5, it is determined whether or not the value of DOD is smaller than the discharge start line (state close to full charge). In the case of "yes", the large compressor 1 is stopped and the small compressor 2 is operated. Note that the functions of the blocks 25 to 29 are the same as those of the blocks 12 to 16 described above, and a description thereof will be omitted.
[0027]
If "no" in the block 24, the process proceeds to a block 30, and it is determined whether or not the value of the DOD is larger than the charge start line (a state close to the completion of the discharge) while reading the map of FIG. In the case of "yes", the small compressor 2 is stopped and the large compressor 1 is operated. Note that the functions of the blocks 31 to 35 are the same as those of the blocks 18 to 22 described above, and a description thereof will be omitted.
[0028]
If "no" in block 30, the value of DOD is in the middle of the charge start line and the discharge start line, and it is unnecessary to switch the compressor, and the process returns to the main routine.
[0029]
Next, FIG. 6 and FIG. 7 are flowcharts showing control contents in a second embodiment of the compressor control according to the present invention. FIGS. 6 and 7 are connected at points (A) to (K), respectively, and form one flowchart. The normal system control is described in the main routine, and only the switching part of the compressor according to the present invention is described as this subroutine.
[0030]
In this embodiment, the maximum efficiency generation flow rate of the large compressor 1 is set to be smaller than the rated value, and at the rated value, both the large and small compressors are operated to secure the air amount necessary for the fuel cell 4. . This has the advantage that the large compressor 1 can be made one size smaller than in the first embodiment.
[0031]
Similarly to the first embodiment, here, basically, the maximum efficiency of the large compressor 1 is assumed to be higher than the maximum efficiency of the small compressor 2, and the efficiency of the large compressor 1 is A range lower than the maximum efficiency is defined as (G ₁ <G ₀ <G ₂ ), and the maximum efficiency generation flow rate of the large compressor 1 is defined as G _3. However, if the maximum efficiency of the large compressor 1 is small compression, When it is equal to or lower than the maximum efficiency of the compressor ₂ , it is defined as G ₂ = G ₃ = the maximum efficiency generation flow rate of the large compressor 1. In this case, the single operation region of the large compressor 1 disappears.
[0032]
The flow charts shown in FIGS. 6 and 7 are basically the same as those in FIGS. 3 and 4, but are used to determine the single operation area of the large compressor 1 and the operation area of the large compressor 1 + small compressor 2. Since blocks 36 to 45 have been added, only this part will be described.
[0033]
For "yes" in block 17, _{G 0,} it is determined whether _{G 3} or proceeds to block 36. In the case of “no”, since G ₂ <G ₀ <G _3, the process proceeds to block 18 to operate the large compressor 1 independently. From here onward, the operation is basically the same as that of the first embodiment. However, in this embodiment, since there is a region where the large compressor 1 and the small compressor 2 are operated at the same time, the blocks 12, 18, in the flag judgment step such as 25,31,39,45, it adapted to determine for both _{n S} and _{n B.}
[0034]
Next, if “yes” in block 36 (G ₀ ≧ G ₃ ), the large compressor 1 is operated and the value of △ W calculated in block 37 and the DOD read in blocks 38 to 44 and △ It is determined on the map of W (FIG. 5) whether the small compressor 2 needs to be operated. In this region _{(G 0} ≧ _{G 3)} of the sole operation of the large compressor 1 (corresponding to _{G 3),} the battery 8 becomes discharged state (corresponding to _{G 3)} large compressor 1 + primary compressor 2 _{(G 1} ), The battery 8 is charged. That is, in the case of "yes" in the block 38, it is necessary to discharge the battery 8, and in the blocks 39 to 43, a command is issued to operate the large compressor 1 alone.
[0035]
If the block 38 is "no" and the block 44 is "yes", the battery 8 needs to be charged, and commands are issued in blocks 45 to 49 to operate the large compressor 1 + small compressor 2. At this time, the switch 3 specified by the block 49 needs to have a mode in which the discharge air of the two large and small compressors flows into the fuel cell 4 at the same time. Therefore, a simple three-way switching valve cannot be used as the switching device 3 in the present embodiment as in the first embodiment.
[0036]
FIG. 8 is a characteristic diagram showing the relationship between the air flow rate / fuel cell load and the efficiency in the second embodiment. As shown in FIG. 8, in this embodiment, the G ₃ or more regions, and a case of operating only large compressor 1 and when the large compressor 1 and the small compressor 2 is both operate. Compressor efficiency is as shown in E _3, in _G 1 _<G 0 _<nominal range (2 large compressor 1+ small compressor), the efficiency of the compressor is substantially flat.
[0037]
Incidentally, the thick line portions of the left half of the E ₃ is the efficiency of space to operate by switching a large compressor 1 and a small compressor 2, the right half the large compressor is always operated, a small compressor intermittently Efficiency in the operating area. Also, the efficiency of the entire fuel cell system at that time is as shown in E _4.
[0038]
In this embodiment, the maximum efficiency generated flow rate of the large compressor 1 + small compressor 2 may be adjusted to the rated output, so that the maximum efficiency generated flow rate of the large compressor 1 can be set smaller than the rated output. , There is an advantage.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing a relationship between air flow rate / fuel cell load and efficiency in the first embodiment.
FIG. 3 is a part of a flowchart showing the content of compressor control according to the first embodiment of the present invention.
FIG. 4 is another part of the flowchart showing the content of the compressor control according to the first embodiment of the present invention.
FIG. 5 is a characteristic diagram showing switching characteristics between charging and discharging.
FIG. 6 is a part of a flowchart showing the content of compressor control according to the second embodiment of the present invention.
FIG. 7 is another part of the flowchart showing the content of the compressor control according to the second embodiment of the present invention.
FIG. 8 is a characteristic diagram showing a relationship between an air flow rate / fuel cell load and efficiency according to the second embodiment.
FIG. 9 is a characteristic diagram showing an example of compressor control when two large and small compressors are provided.
FIG. 10 is a characteristic diagram showing the relationship between the air flow rate / fuel cell load and efficiency when conventional compressor control is performed.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 large compressor 2 small compressor 3 switch 4 fuel cell 5 reformer 6 voltage converter 7 motor 8 battery 9 DOD sensor 10 controller

Claims (5)

A fuel cell, a secondary battery that is charged at least with power from the fuel cell, a motor that drives a vehicle with at least power from the fuel cell, a device that supplies hydrogen to the fuel cell, and an air supply to the fuel cell. in the vehicle fuel cell system and a compression machine you supply,
The compressor is a plurality of large and small compressors, each having a different maximum efficiency generation flow rate , and at least one of the plurality of compressors is controlled in accordance with an output required for the fuel cell , compressor control device for a vehicular fuel cell system characterized by comprising a control means to control to send air to the fuel cell. The control means includes:
In the first region where the air flow rate corresponding to the output required for the fuel cell is equal to or less than the maximum efficiency generation flow rate of the small compressor, only the small compressor is operated,
In the second region where the air flow rate corresponding to the required output is larger than the maximum efficiency generation flow rate of the small compressor and the efficiency of the large compressor is a flow rate range equal to or less than the maximum efficiency of the small compressor. Switch between large and small compressors
In the third region in which the air flow rate corresponding to the required output is a flow rate range in which the efficiency of the large compressor is equal to or more than the maximum efficiency of the small compressor, control is performed such that only the large compressor is operated. The compressor control device for a vehicle fuel cell system according to claim 1, wherein: The switching control between the large compressor and the small compressor in the second region is performed by operating the large compressor in a state where the secondary battery needs to be charged in accordance with the state of charge of the secondary battery. 3. The compressor control device for a vehicle fuel cell system according to claim 2, wherein control is performed to operate the small compressor in a state where discharge of the secondary battery is required. The switching point between the large compressor and the small compressor in the second region is changed according to a difference between an actual output of the fuel cell and an output required from a vehicle running state. Item 4. A compressor control device for a vehicle fuel cell system according to item 3. A value obtained by adding the maximum efficiency generation flow rate of the large compressor and the maximum efficiency generation flow rate of the small compressor to the rated output of the fuel cell is set, and the flow rate is equal to or more than the maximum efficiency generation flow rate of the large compressor. in the region, the compressor control unit of a fuel cell system for a vehicle according to claim 1, characterized in that it comprises a mode for operating the said large compressor and the small compressor at the same time.

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