JP4992261B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly, to a fuel cell system that performs an idle stop that temporarily stops power generation at a low load.

  Since fuel cell systems generally have low power generation efficiency at low loads, fuel cell systems for fuel cell vehicles with large load fluctuations generally perform idle stop. For this reason, the fuel cell system is equipped with a secondary battery that stores surplus power, and when the load is low, the power generation of the fuel cell is temporarily stopped and the power is supplied from the secondary battery to the load device. Control is performed to return to the power generation state from the idle stop.

In a fuel cell system having such an idle stop function, even if the load condition satisfies the idle stop condition, depending on the state of the fuel cell system, when the idle stop is performed, the engine may return from the idle stop to the power generation state. In addition, there is a possibility that problems such as a reduction in power generation output and a limitation of vehicle driving force may occur. For this reason, the state of the fuel cell system, for example, the cell voltage is also considered in the idle stop condition, and the idle stop is prohibited when the cell voltage is equal to or lower than a predetermined value (Patent Document 1).
JP 2004-173450 A (page 6, FIG. 3)

  However, in the above-described prior art, when determining to shift to the idle stop in the power generation state before entering the idle stop, a value is set so as to permit the idle stop even in the cell voltage when the power is generated with relatively large power. If it is determined, idle stop is permitted even with an unstable cell voltage when the power is small, and there is a problem that the power performance when returning to the power generation state is lowered.

  Also, if the cell voltage threshold is determined under the condition that the stack voltage at the lowest power is high, idle stop is not permitted when a large amount of power is taken out, and the frequency of idle stop is reduced, improving fuel efficiency. There is a problem that it is limited.

The present invention in order to solve the above problems, a fuel cell that generates electricity through an electrochemical reaction between fuel gas and oxidant gas, the target current of the fuel cell, target power, the actual current is the one of real power operating condition detecting means for detecting the load information as the driving state of the fuel cell, and the voltage parameter detecting means for detecting a voltage parameter of the fuel cell, the current-voltage characteristics learning means for learning a current-voltage characteristic of the fuel cell, the current a voltage parameter threshold calculation means for calculating reduced threshold voltage parameters for values larger the idle stop permission judgment of load information is referring to the operating condition detecting means learning result of the voltage characteristic learning means has detected, the voltage The idle stop permission is determined based on the output of the parameter threshold value calculation means and the output of the voltage parameter detection means. And an idle stop control means for controlling the idle stop based on the output of the idle stop permission means, wherein the idle stop permission means has a detection value of the voltage parameter, The gist is to allow idle stop when the voltage parameter threshold value is larger .

  In the present invention, the operation state of the fuel cell including the load information of the fuel cell is detected, and based on this load information, a voltage parameter threshold value for determining whether to allow idling stop is calculated, and this voltage parameter threshold value is detected. By comparing the voltage parameter with the idling stop permission judgment, the idling stop permission judgment can be performed accurately over a wide range of the fuel cell load.

  According to the present invention, since an appropriate idle stop permission condition can be calculated according to the load information immediately before the idle stop, it becomes possible to enter the idle stop under an appropriate condition without excess or shortage even if the immediately preceding load state is different. The frequency of idle stop is improved, the fuel efficiency of the fuel cell system can be improved, and the fuel cell output can be quickly raised at the time of restart after the idle stop is released.

  The present invention will be described below with reference to the drawings. Although not particularly limited, each embodiment described below is a fuel cell system suitable for a fuel cell vehicle.

  FIG. 1 is a diagram showing a main configuration of a fuel cell system according to the present invention. In FIG. 1, the fuel cell system detects a fuel cell (not shown), an operating state detecting means 101 for detecting an operating state of the fuel cell including at least load information of the fuel cell, and a voltage parameter that is information on the voltage of the fuel cell. Of the voltage parameter detecting means 102 for calculating the voltage parameter threshold value for determining idling stop permission based on the load information value detected by the operating state detecting means 101, and the voltage parameter detecting means 102 An idle stop permission means 104 for permitting an idle stop when the detected voltage parameter satisfies an idle stop permission condition with respect to the voltage parameter threshold value calculated by the voltage parameter threshold value calculation means 103; Idle strike based on output And a idling stop control unit 105 for controlling the up.

  The operating state detection unit 101 is a unit that detects any one of the target current, target power, actual current, and actual power of the fuel cell as load information. In addition to the load information, the operation state detection unit 101 may detect the fuel cell temperature, fuel gas pressure, air pressure, fuel gas excess rate, and oxidant gas excess rate.

  The voltage parameter threshold value calculation means 103 is a means for calculating a voltage parameter threshold value that becomes an idle stop permission condition based on the load information or the load information and the other operating state of the fuel cell. Usually, a map stored in a non-volatile memory is used as a map of voltage parameter threshold values with respect to load information values.

  When the operating state detection means 101 detects operating state parameters such as fuel cell temperature, fuel gas pressure, oxidant gas pressure, fuel gas excess rate, oxidant gas excess rate in addition to load information, a voltage parameter threshold value The calculating means 103 can be a means for calculating a voltage parameter threshold value based on the load information and a multidimensional control map based on these operating state parameters. Thereby, even if the gas pressure including the immediately preceding load state, warm-up state, atmospheric pressure change and the like is different, it is possible to enter the idle stop under appropriate conditions without excess or deficiency.

  FIG. 2 is a configuration provided with IV characteristic learning means 206 for learning the current-voltage characteristics of the fuel cell in addition to the basic configuration of FIG. The voltage parameter threshold value calculating means 203 is a means for calculating a voltage parameter threshold value for permitting idle stop based on the output of the operating state detecting means 101 and the output of the IV characteristic learning means 206. The other configuration is the same as that of FIG.

  The IV characteristic learning method of the IV characteristic learning means 206 is not particularly limited, but according to the following method, the secular change of the fuel cell can be reflected in the IV characteristic. First, the current value and voltage value of the fuel cell in the quasi-steady state where the change in the operating state of the fuel cell is not so large are sampled and stored. When the storage of a certain number of samples is completed, the old sample is removed and the current-voltage characteristic curve of the fuel cell is obtained by the least square method or the like based on the relatively new sample and stored.

  FIG. 3 is a diagram showing an overall configuration of a fuel cell system to which the present invention is applied. In the fuel cell 1, hydrogen gas is supplied to the anode and air is supplied to the cathode, and the electrode reaction shown below proceeds to generate electric power.

Anode (hydrogen electrode): H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode (oxygen electrode): 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
Hydrogen supply to the anode is performed from the hydrogen tank 2 through the hydrogen tank main valve 3, the pressure reducing valve 4, and the hydrogen supply valve 5. The high-pressure hydrogen supplied from the hydrogen tank 2 is mechanically reduced to a predetermined pressure by the pressure reducing valve 4, and the hydrogen pressure is controlled to be reduced to the operating pressure of the fuel cell by the hydrogen supply valve 5. The hydrogen circulation device 7 using a pump or the like is installed to recirculate the hydrogen that has not been consumed at the anode to the anode inlet via the hydrogen circulation path 19. The hydrogen pressure of the anode is controlled by driving the hydrogen supply valve 5 by feeding back the hydrogen pressure detected by the controller 30 with the pressure sensor 6a. By controlling the hydrogen pressure to a desired target pressure, the hydrogen consumed by the fuel cell is automatically compensated.

  The purge valve 8 plays the following role. (A) The nitrogen accumulated in the hydrogen system is discharged to ensure the hydrogen circulation function. (B) In order to recover the cell voltage, the water clogged in the gas flow path is blown away. (C) The gas in the hydrogen system is discharged to replace the hydrogen system with hydrogen at the time of startup. Here, the hydrogen system is the anode of the fuel cell 1, the hydrogen circulation path 19, the hydrogen circulation device 7, and a pipe line connecting them.

  The exhaust hydrogen treatment device 9 dilutes the gas containing hydrogen discharged from the purge valve 7 with air so that the hydrogen concentration is lower than the flammable concentration, and discharges it out of the system, or reacts hydrogen and air to burn. To reduce the exhaust hydrogen concentration.

  Air to the cathode is supplied by the compressor 10. The humidifier 11 humidifies the supplied air. The air pressure of the cathode is controlled by driving the air pressure regulating valve 12 by feeding back the air pressure detected by the controller 30 with the pressure sensor 6b.

  Cooling water to the cooling water flow path is supplied by the cooling water pump 13. The three-way valve 16 switches or shunts the flow path of the cooling water between the direction of the radiator 17 and the direction of the radiator bypass. The radiator fan 18 cools the cooling water by passing air through the radiator. The temperature of the cooling water is adjusted by detecting the temperature of the fuel cell inlet with the temperature sensor 14 and the temperature of the fuel cell outlet with the temperature sensor 15, and the controller 30 drives the three-way valve 16 and the radiator fan 18 based on these. To do.

  The power manager 21 is a device that extracts an output from the fuel cell 1. The power manager 21 extracts an output (current or electric power) from the fuel cell 1 and supplies it to a load device 23 (for example, a vehicle drive motor). In addition, the power manager 21 monitors the storage amount (SOC) of the power storage device 22 using a secondary battery or a capacitor. When the SOC becomes a predetermined amount or less, the power manager 21 charges the power storage device 22 for charging or charging. Request power to controller 30.

  A vehicle speed sensor and an accelerator sensor (not shown) are connected to the controller 30, and a vehicle speed signal and an accelerator operation amount signal are input. The controller 30 calculates the vehicle driving current or the vehicle driving power based on the vehicle speed signal and the accelerator operation amount signal, and adds the charging current or the charging power to each of them to obtain the target current or target power of the fuel cell 1. Calculate Then, the operating state of the fuel cell, for example, hydrogen gas pressure, air pressure, etc. is controlled in accordance with the target current or target power.

  The voltage value of each cell of the fuel cell 1 is detected by the voltage sensor 24, and the controller 30 can read the voltage value of each cell. The fuel cell 1 may be configured by a group of cells in which a plurality of cells are connected in series, and the voltage sensor 24 may detect the voltage value of each cell group.

  The controller 30 reads various sensor values, drives each actuator, and controls the entire fuel cell system and controls related to idle stop.

  The controller 30 is a part of the voltage parameter detection unit 102 in FIGS. 1 and 2, the voltage parameter threshold value calculation units 103 and 203, the idle stop permission unit 104, the idle stop control unit 105, and the IV characteristic learning unit 206. .

  Although not particularly limited, in the present invention, the controller 30 includes a microprocessor including a CPU, a program ROM, a working RAM, and an input / output interface.

  FIG. 4 is a diagram illustrating an example of current-voltage characteristics (IV characteristics) of each cell constituting the fuel cell 1. In the figure, the solid line is the standard cell voltage of a normally operating cell, and the broken line is the lower limit cell voltage at which it can be determined that there is no water clogging or nitrogen accumulation. It is the current voltage characteristic to be used. As shown in FIG. 4, the smaller the current extracted from the fuel cell, the higher the voltage of the fuel cell.

  FIG. 5 shows an idle stop permission determination in a comparative example to which the present invention is not applied. As shown in FIG. 5A, if the current I1 [A] is taken out in the normal idle state, the typical cell voltage at that time is V1 [V], and some variation is taken into consideration. However, if there is a cell voltage equal to or higher than Vs [V] in all the cells, the fuel cell is considered to be in a normal state with no cell water clogging. Now, in the comparative example of FIG. 5A, a case is shown in which the transition to idle stop is determined when the minimum cell voltage is higher than Vs. In this case, if all the cell voltages at the time of idle power generation before entering the idle stop are equal to or higher than Vs, it is determined that the control of shifting to the idle stop can be executed. Here, in FIG. 5 (a), when the generated current shifts to I1, the minimum cell voltage becomes higher than Vs, so that it is possible to normally determine whether to allow idling stop. However, depending on the state of charge of the battery of the vehicle, there may be a case where the current taken out during idle power generation is taken out to I2 [A] which is larger than I1. In such a case, the idling stop permission determination is made Vs. 5 (b), when the extraction current shifts to I2, the minimum cell voltage increases only to V2 and the idle stop permission condition is not satisfied, so that the fuel cell is normal. Even if there is, it will be impossible to shift to idle stop.

  FIG. 6 shows an example of the case where the present invention is applied. Based on the idle stop permission lower limit cell voltage (Vx) curve shown by the broken line in FIG. The threshold value is changed. That is, the cell voltage threshold is changed from moment to moment based on the extraction current from the fuel cell and the broken line characteristic (Vx) in FIG. 4. When the extraction current is I1, Vs, and when the extraction current is I2, Vt becomes the cell voltage threshold value, and the cell voltage threshold value for the idle stop permission determination can be appropriately set according to the power generation state at that time.

  FIG. 6A shows a case where the current taken out during idle power generation according to the present invention is I1, and in this case, the permission determination for idling stop is made based on Vs as in the case of FIG. FIG. 6B shows a case where the current taken out during idle power generation is I2, and the idle stop permission determination is performed with the threshold value Vt determined from the characteristics of Vx. Become.

  FIG. 6 shows the case where the idle stop permission determination is performed from the characteristics of FIG. 4 and the minimum cell voltage. The relationship between the cell voltage variation (dispersion, etc.) and the current density of the fuel cell is shown in FIG. Utilizing the fact that the cell voltage variation increases as the density increases, the cell voltage obtained from the idle stop permission cell voltage variation upper limit (Dx) characteristic indicated by the broken line in FIG. 7 and the measured value of the cell voltage of the fuel cell The same can be done using variation.

  Next, the idling stop permission control in the first embodiment of the fuel cell system according to the present invention will be described with reference to the control flowchart of FIG. The configuration of this embodiment is the configuration shown in FIG. 1 or FIG. In this embodiment, the target current of the fuel cell is used as the load information, the cell voltage is used as the voltage parameter, and the permission determination for idling stop is performed based on whether the minimum cell voltage satisfies the lower limit value corresponding to the target current. This is an example.

  The flowchart of FIG. 8 is executed periodically (for example, every 10 ms) during normal operation of the fuel cell system. Before this flowchart is started, the controller 30 reads the detected values of the sensors such as the pressure sensors 6a and 6b, the temperature sensors 14 and 15, the voltage sensor 24, and a vehicle speed sensor not shown in FIG. It shall be assumed. Further, it is assumed that the controller 30 has already calculated the target current of the fuel cell 1 by reading the charging current from the power manager 21 and adding the vehicle driving current thereto.

  In step 801, it is determined whether an idle stop permission condition other than the cell voltage, for example, whether the vehicle speed or the gas pressure has decreased to a predetermined value, or whether the temperature satisfies the predetermined condition. If the condition of step 801 is not satisfied, the procedure is terminated as it is, but if the condition is satisfied, the process proceeds to step 802. In step 802, the target current of the fuel cell is read. In step 803, the lower limit cell voltage Vx of the idling stop permission corresponding to the target current of the fuel cell is obtained by referring to a control map having current-voltage characteristics as shown in FIG.

  Here, in the characteristics of FIG. 4, the horizontal axis is the current density, but the target current may be converted to the current density by dividing by the effective area of the cell. Further, the control map referred to in step 803 may be a learning result of the IV characteristic learning means 206 (FIG. 2) for learning the current voltage characteristic of the fuel cell 1. In this case, a voltage obtained by subtracting a predetermined voltage from the learned standard cell voltage is set as the idle stop permission lower limit voltage. As a result, an accurate idle stop condition can be determined even when the fuel cell changes with time.

  In step 804, the lowest cell voltage Vc_min is calculated from all the cell voltages of the fuel cell 1. In step 805, it is determined whether or not the minimum cell voltage Vc_min is greater than Vx. If it is not greater than Vx, the procedure is terminated. To do.

  As described above, according to the present invention, since an appropriate idle stop permission condition can be calculated according to the load information immediately before the idle stop, even if the immediately preceding load state is different, the idle stop can be entered under an appropriate condition without excess or deficiency. It becomes possible.

  Next, with reference to the control flowchart of FIG. 9, the idling stop permission control in the second embodiment of the fuel cell system according to the present invention will be described. The configuration of this embodiment is the configuration shown in FIG. 1 or FIG. In this embodiment, the target current of the fuel cell is used as the load information, the cell voltage is used as the voltage parameter, and the idling stop permission determination is made based on whether or not the dispersion value satisfies the upper limit value as the cell voltage variation. It is an example.

  The flowchart of FIG. 9 is executed periodically (for example, every 10 ms) during normal operation of the fuel cell system. In step 901, it is determined whether an idle stop permission condition other than voltage, for example, whether the vehicle speed or gas pressure has dropped to a predetermined value, or whether the temperature satisfies a predetermined condition. If the condition of step 901 is not satisfied, the procedure is terminated as it is, but if the condition is satisfied, the process proceeds to step 902. In step 802, the target current of the fuel cell is read. In step 903, an upper limit variation value Dx of the idle stop permission cell voltage corresponding to the target current of the fuel cell is obtained with reference to a control map having the characteristics of FIG. Here, in the characteristics of FIG. 7, the horizontal axis represents the current density, but the target current may be converted into the current density by dividing by the effective area of the cell. In step 904, all cell voltages Vcell (i) (i = 1 to N) of the fuel cell are read, and in step 905, the cell voltage dispersion value Dcell is calculated.

  The dispersion value Dcell may be obtained by the following equation (1).

Dcell = Σ {Vcell (i) −Vcell_ave} ^ 2 / Ncell (i = 1, 2,..., Ncell) (1)
Here, Vcell_ave is an average cell voltage, and Ncell is the total number of cells.

  In step 906, it is determined whether or not the cell voltage dispersion value Dcell is smaller than Dx. If it is not smaller than Dx, the procedure is terminated, and if Dcell is smaller than Dx, the process proceeds to step 907 to control the transition to idle stop. Execute.

  In the embodiments described so far, the target current of the stack is used as the load information. However, this may use target power, actual current, or actual power. Further, although the cell voltage is used as the voltage parameter, this may be the voltage of a cell group composed of a plurality of cells, or when the fuel cell is composed of a plurality of stacks, the respective stack voltages may be used. In the first embodiment, the total stack voltage may be used.

In the second embodiment, the variance value is used as the variation of the voltage parameter. This is the maximum deviation from the average value of the voltage parameter.
max (| Voltage parameter (i) −Voltage parameter average value |) (2)
Or the ratio of the deviation of the parameter with the maximum deviation from the average value to the average value,
max (| Voltage parameter (i) −Voltage parameter average value |) / Voltage parameter average value (3)
But the same can be achieved.

1 is a basic configuration diagram of a fuel cell system according to the present invention. It is a basic block diagram in the case of learning the current voltage characteristic of a fuel cell. 1 is a configuration diagram showing the overall configuration of a fuel cell system to which the present invention is applied. It is a figure showing the characteristic of the cell voltage with respect to the current density of a fuel cell, and how to determine the threshold value of the minimum cell voltage with respect to the current density. It is a figure which shows the mode of idle stop transfer judgment when not applying this invention. It is a figure which shows the mode of the idle stop transfer judgment to which this invention is applied. It is a figure which shows the variation characteristic of the cell voltage with respect to the current density of a fuel cell, and how to determine the cell voltage variation upper limit with respect to the current density. 5 is a flowchart for explaining idle stop transition determination in the first embodiment. It is a flowchart explaining the idle stop transfer determination in Example 2.

Explanation of symbols

1: Fuel cell 2: Hydrogen tank 3: Hydrogen tank main valve 4: Pressure reducing valve 5: Hydrogen supply valve 6a, 6b: Pressure sensor 7: Hydrogen circulation device 8: Purge valve 9: Waste hydrogen treatment device 10: Compressor 11: Humidification Device 12: Air pressure regulating valve 13: Cooling water pump 14, 15: Temperature sensor 16: Three-way valve 17: Radiator 18: Radiator fan 19: Hydrogen circulation path 20: Key switch 21: Power manager 22: Power storage device 23: Load device 24 : Voltage sensor

Claims (7)

A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas;
Target current of fuel cells, and a target power, the actual current, operating condition detecting means for the load information is either the actual power to detect a driving state of the fuel cell,
One of the cell voltage for each cell of the fuel cell, the cell group voltage for each cell group composed of a plurality of cells connected in series, the voltage for each stack of the plurality of stacks constituting the fuel cell, or the total voltage of the fuel cell stack Voltage parameter detection means for detecting a certain voltage parameter;
Current-voltage characteristics learning means for learning the current-voltage characteristics of the fuel cell;
A voltage parameter threshold calculation means for calculating reduced threshold voltage parameter for learning results referring to the operating condition detecting means value of the load information detected by the larger the idle stop permission judgment of the current-voltage characteristic learning means,
Idle stop permission means for making an idle stop permission determination based on the output of the voltage parameter threshold value calculation means and the output of the voltage parameter detection means,
An idle stop control means for controlling the idle stop based on the output of the idle stop permission means, and a fuel cell system comprising:
The idle stop permission means, the detected value of the voltage parameter, a fuel cell system and permits an idle stop is larger than the voltage parameter threshold. The voltage parameter threshold calculation means comprises a current-voltage characteristic of the fuel cell, based on the operation state, the fuel cell system according to claim 1, characterized in that the means for calculating a threshold voltage parameter. A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas;
An operation state detection means for detecting load information which is one of the target current, target power, actual current, and actual power of the fuel cell as the operation state of the fuel cell;
One of the cell voltage for each cell of the fuel cell, the cell group voltage for each cell group composed of a plurality of cells connected in series, the voltage for each stack of the plurality of stacks constituting the fuel cell, or the total voltage of the fuel cell stack Voltage parameter detection means for detecting a certain voltage parameter;
A voltage parameter threshold value calculating means for calculating the threshold value of the voltage parameter variation for idle stop permission determination as the value of the load information detected by the operating state detecting means increases;
Idle stop permission means for making an idle stop permission determination based on the output of the voltage parameter threshold value calculation means and variations in the output of the voltage parameter detection means,
An idle stop control means for controlling the idle stop based on the output of the idle stop permission means, and a fuel cell system comprising:
The idle stop permission means, the variation of the detected value of the voltage parameters, fuel cell systems that and permits an idle stop is smaller than the voltage parameter variation threshold. The operating state detection means is means for detecting at least one of a fuel cell temperature, a fuel gas pressure, an oxidant gas pressure, a fuel gas excess rate, and an oxidant gas excess rate in addition to the load information,
4. The voltage parameter threshold value calculating means is means for calculating a voltage parameter threshold value based on the detected values of the operating state detecting means. Fuel cell system. The fuel cell system according to claim 3 , wherein the voltage parameter variation is a variance value of a plurality of voltage parameters. 4. The fuel cell system according to claim 3 , wherein the voltage parameter variation is a maximum deviation from an average value of a plurality of voltage parameters. 4. The fuel cell system according to claim 3 , wherein the voltage parameter variation is a ratio of a deviation of a parameter having a maximum deviation from an average value among a plurality of voltage parameters to the average value.

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