JP4228201B2 - Fuel cell output characteristics estimation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an output characteristic estimation device for estimating an output characteristic of a fuel cell and a fuel cell system using the same.
[0002]
[Prior art]
Fuel cells are being used as power sources for building facilities, plants, vehicles, and the like. In addition, a power supply system using both a fuel cell and a commercial power source or a secondary battery is also provided. Since the fuel cell has an internal resistance equivalently, when the output current of the fuel cell increases, the output terminal voltage tends to decrease due to an increase in voltage drop in the internal resistance. Therefore, it is necessary to control the fuel cell operating parameters so as to predict the drop in the output voltage of the fuel cell due to the increase in the load of the connected electrical equipment or the increase in the number of connected equipment, and to compensate for this voltage drop. In addition, it is necessary to grasp the expected supply voltage drop for device operation compensation. Also, the output characteristics of the fuel cell tend to change over time.
[0003]
For this reason, the applicant has proposed an output characteristic estimation device for estimating the output characteristic of a fuel cell according to Japanese Patent Laid-Open No. 14-231295. The output control of the system can be performed using the current output characteristics of the fuel cell estimated by this apparatus. This output characteristic estimation device stores a fuel cell output current versus output voltage characteristic (IV characteristic) stored in advance as a map, and corrects the IV characteristic map with reference to the actual measured current value, thereby correcting the IV characteristic of the fuel cell. It is possible to cope with changes over time.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 14-231295
[Problems to be solved by the invention]
However, in order to identify (correct) the current IV characteristic model, the output characteristic estimation apparatus described above acquires information on various parameters such as the temperature of the fuel cell, the flow rate of the fuel gas, the open circuit voltage, and the internal resistance of the fuel cell. However, it takes a certain amount of time to process the data. Fuel cells with variable load, especially fuel cells used in vehicles, etc., estimate the output characteristics of the fuel cell in a short time because the load on the motor and various electric devices fluctuates rapidly in a short time. It is desirable to make use of it for output control.
[0006]
Therefore, an object of the present invention is to provide an output characteristic estimation device that can estimate the output characteristic of a fuel cell in a relatively short time.
[0007]
Another object of the present invention is to provide an output characteristic estimation apparatus that can realize the output characteristic estimation apparatus with a relatively simple configuration.
[0008]
[Means for solving the problems]
In order to achieve the above object, an output characteristic estimation device for a fuel cell according to the present invention includes a current / voltage detecting means for detecting an output current of a fuel cell and a voltage between its terminals, a detected output current, a voltage between terminals, and a fuel cell. Means for calculating an estimated voltage value from the detected output current and the basic output characteristic of the fuel cell in the fuel cell output characteristic estimation device comprising means for estimating the output characteristic of the fuel cell based on the basic output characteristic of the fuel cell (S36) ), Means for calculating a voltage deviation between the estimated voltage value and the detected voltage value between terminals (S38), and the voltage deviation is converted into an internal resistance deviation and an open circuit voltage deviation of the fuel cell at a predetermined ratio. Means for distributing (S40), and means for correcting basic output characteristics based on the distributed voltage deviation (S42).
[0009]
With this configuration, the basic output of the current fuel cell that takes into account changes in the open circuit voltage (cell internal electromotive force) and changes in internal resistance based on the fuel cell output current, terminal open voltage, and basic output characteristics model The characteristics can be estimated. The basic output characteristics are, for example, output current versus output voltage (terminal voltage) characteristics (IV characteristics).
[0010]
As the basic output characteristic model, for example, battery output terminal voltage (V) = internal electromotive force (V ₀ ) −internal resistance (R) × battery output current (I) can be used. Here, the internal electromotive force (V ₀ ) is equal to the open circuit voltage when the connection of the external circuit to the fuel cell terminal is opened (battery output current (I) = 0).
[0011]
Preferably, the predetermined ratio for distributing the voltage deviation to the internal resistance deviation and the open circuit voltage deviation is variably set corresponding to the detected output current value. Thereby, the voltage deviation of the electromotive force of the basic output characteristic model of the fuel cell (the vertical translation of the IV characteristic curve) is corrected. Further, the influence of the internal resistance of the basic output characteristic model on the voltage between the output terminals (slope of the IV characteristic curve) is corrected so as to depend on the output current. The basic output characteristic model of the fuel cell is modified to the current output characteristic model.
[0012]
Further, the fuel cell system of the present invention includes the above-described fuel cell output estimation device, means for setting the target output of the fuel cell using the estimated output characteristic of the fuel cell (S304), and the set target output Output adjusting means (S306) for adjusting the output of the fuel cell so that is output from the fuel cell. Thereby, the output characteristics are estimated in a short time, and the result is used, so that the control accuracy of the fuel cell is improved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an outline of a configuration of an on-vehicle fuel cell system 20 according to an embodiment of the present invention.
[0014]
As shown in the figure, the fuel cell system 20 includes a fuel cell 26 configured as, for example, a polymer electrolyte fuel cell that generates power using hydrogen from the hydrogen tank 22 and oxygen in the air from the blower 24, A DC / DC converter 32 that charges and discharges the battery 30 that adjusts the voltage of the power line 28 connected to the output terminal and supplies power to the auxiliary machine 33, an inverter 34 connected to the power line 28, and an inverter 34 A motor 36 that is driven and controlled by switching of the switching element and exchanges power with the drive shaft 38, and an electronic control unit 40 that controls the entire system. The drive shaft 38 is connected to the drive wheel 14 via the reduction gear 12, and the power output from the motor 36 to the drive shaft 38 is finally output to the drive wheel 14. Yes.
[0015]
The electronic control unit 40 is configured as a microprocessor centered on a CPU 42. The electronic control unit 40 is a writable flash ROM 44 that stores a processing program in a nonvolatile manner, a RAM 46 that temporarily stores data, and an input / output port (not shown). ). The electronic control unit 40 includes a hydrogen supply pressure Ph from a pressure sensor 50 attached to a supply pipe from the hydrogen tank 22 to the fuel cell 26 and a fuel cell temperature Tfc from a temperature sensor 52 attached to the fuel cell 26. The output voltage Vfc of the fuel cell 26 from the voltage sensor 54 attached between the output terminals of the fuel cell 26, the output current Ifc of the fuel cell 26 from the current sensor 56 attached to the output terminal of the fuel cell 26, and in the inverter 34 Current of each phase applied to the motor 36 from a current sensor (not shown) attached to the motor, the rotation angle of the rotor of the motor 36 from an angle sensor (not shown) attached to the motor 36, and the vehicle speed V from the vehicle speed sensor 58. , Shift position SP from the shift position sensor 61 for detecting the position of the shift lever 60, accelerator pedal The accelerator pedal position AP from the accelerator pedal position sensor 63 that detects the depression amount of the brake pedal 62, the brake pedal position BP from the brake pedal position sensor 65 that detects the depression amount of the brake pedal 64, and the like are input via the input port. Yes.
[0016]
The electronic control unit 40 outputs a drive signal to the blower 24, a control signal to the DC / DC converter 32, a control signal to the inverter 34, a control signal to the reduction gear 12, and the like via an output port. Yes.
[0017]
Next, the operation of the fuel cell system 20 of the embodiment, particularly the operation for estimating the output characteristics of the fuel cell 26 and the operation during output control will be described. In the embodiment, the basic output characteristic model of the fuel cell, specifically, the IV characteristic of the fuel cell is stored as a basic map or function, and the basic output characteristic model is corrected each time by the actually measured output current and terminal voltage in actual operation. Thus, a modified output characteristic model is obtained and used for estimating the output characteristic.
[0018]
FIG. 2 is a flowchart showing an example of a basic model formation routine for obtaining the output characteristics of the fuel cell 26. A pseudo load is connected to the fuel cell 26 to operate the fuel cell 26. The CPU 42 of the electronic control unit 40 gradually increases the output current of the fuel cell 26 from 0 amperes to 400 amperes by a test program incorporated in the computer system, and sequentially outputs the output values of the voltmeter 54 and the ammeter 55 to the internal memory 45. Store (S22). This IV characteristic becomes a basic output characteristic model. The measurement of the IV characteristics may be performed a plurality of times, and the average characteristics may be used as the basic output characteristics model.
[0019]
The IV characteristic as a basic output characteristic model is stored in the ROM 44 in a nonvolatile manner as a basic map composed of sampling current value (grid current) groups at regular intervals and output voltage value (grid voltage) groups corresponding thereto. The IV characteristic may be stored as an approximate expression, for example, V = V ₀ −RI. Here, V is a terminal voltage, V ₀ is a terminal voltage when the load circuit is opened, and R is obtained as the slope of the characteristic curve. I is the output current. In this way, the basic characteristic model is determined and stored in advance. An example of the basic characteristic model is shown by a solid curve A in FIG. 4 (S24).
[0020]
Further, as shown in FIG. 5, a distribution characteristic of output current versus voltage deviation of the fuel cell is obtained in advance by experiments. The voltage deviation distribution characteristic indicates the ratio between the deviation of the open output voltage of the fuel cell and the deviation of the internal resistance voltage corresponding to the output current value.
[0021]
Next, correction of the basic characteristic model will be described. In the actual operating state of the fuel cell, fluctuations in characteristics from the basic characteristic model may occur due to changes in the fuel cell over time, changes in the moisture content of the polymer electrolyte membrane, and the like. Therefore, the basic characteristic model stored in advance is corrected to estimate the output characteristic of the fuel cell.
[0022]
As shown in FIG. 3, the CPU 42 of the electronic control unit 40 commands the occurrence of a certain event, for example, a flag of a timer that generates a time-out output at a certain period during operation of the fuel cell, a change in operating conditions, or the like. When the flag is set, this output characteristic correction processing routine is executed (S32).
[0023]
First, the output V ₁ of the voltage sensor 54 that monitors the output terminal voltage of the fuel cell 26 and the output I ₁ of the current sensor 56 that monitors the output current of the fuel cell are read (S34). The basic characteristic model A described above is read, and an estimated output voltage V _S corresponding to the actually measured output current I ₁ is obtained as shown in FIG. 4 (S36). A voltage deviation ΔV between the actually measured output voltage V ₁ and the estimated output voltage V _S is obtained (S38).
[0024]
Here, the relationship ΔV = V _S −V ₁ = V ₀ −R × I ₁ − ((V ₀ −ΔV ₀ ) − (R + ΔR) × I ₁ )) = ΔV ₀ + ΔR × I ₁ is established. Therefore, the voltage deviation ΔV is divided into a deviation ΔV ₀ of the electromotive force (open circuit voltage) V ₀ and a voltage deviation ΔVR (= ΔR × I ₁ ) due to the resistance deviation ΔR of the internal resistance R of the fuel cell 26.
[0025]
Next, the distribution ratio α of the voltage deviation ΔV in the output current I ₁ is read from the graph shown in FIG. The deviation ΔV ₀ of the electromotive force V ₀ is obtained as (1−α) × ΔV. Voltage deviation [Delta] V _R by the resistance deviation ΔR is determined as alpha × [Delta] V.
[0026]
The basic output characteristic A is corrected by these voltage deviations. First, the basic output characteristic curve A translated vertically by deviations [Delta] V ₀ of the electromotive force, to obtain a curve B that fixes deviations [Delta] V ₀ of the electromotive force. Next, by correcting the characteristic curve B with the voltage drop ΔV _{R corresponding} to the resistance deviation ΔR, the slope of the curve B changes, and the curve C passes through the actual measurement point P ₁ (I ₁ , V ₁ ) on the coordinates. (With a slope of the curve B with the correction of the voltage drop ΔV _{R corresponding to} the resistance value deviation ΔR and a curve set so as to pass through the current measured point P ₁ (I ₁ , V ₁ ). C is obtained.) (S42).
[0027]
The corrected output characteristic curve C indicating the current output characteristic obtained in this way is stored in the ROM 44 or RAM 46 as a map (S44). Further, the approximate expression V _C = (V ₀ −ΔV ₀ ) −α (I _C ) · ΔV may be stored in the memory. Here, V _C represents the measured output voltage, I _C represents the measured output current, and ΔV represents the difference voltage between the measured output voltage and the output value of the basic output characteristic. α (I _C ) indicates a distribution ratio at the output current value I _C. α (I _C ) is obtained from a graph (FIG. 5) determined and stored in advance.
[0028]
According to the procedure described above, the information extracted from the fuel cell and other systems used to obtain the modified output characteristic curve C from the basic output characteristic curve A is only the output voltage and output current of the fuel cell. The operation parameters such as the fuel gas flow rate and the like need not be referred to, and the correction of the output characteristic curve is not troublesome and can be performed in a short time.
[0029]
According to the fuel cell system 20 of the embodiment described above, the output characteristic estimation process and the output characteristic correction process executed by the CPU 42 of the electronic control unit 40 are performed, so that more appropriate output characteristics of the fuel cell 26 used over time can be obtained. Can be obtained. In addition, it is possible to quickly cope with changes in internal resistance due to changes in moisture in the polymer electrolyte membrane of the fuel cell. In the fuel cell system 20 of the embodiment, the output control of the system is performed using the output characteristics of the fuel cell 26 obtained in this way.
[0030]
FIG. 6 is a flowchart illustrating an example of an output control routine executed by the electronic control unit 40 of the fuel cell system 20 according to the embodiment. This routine is repeatedly executed every predetermined time (for example, every 8 msec).
[0031]
When the output control routine is executed, the CPU 42 of the electronic control unit 40 first detects the vehicle speed V detected by the vehicle speed sensor 58, the accelerator pedal position AP detected by the accelerator pedal position sensor 63, and the brake pedal position sensor 65. A process for reading various data such as the brake pedal position BP is executed (step S300). Subsequently, an output to be output to the drive shaft 38 based on the accelerator pedal position AP, the brake pedal position BP, and the vehicle speed V, that is, a required output P0 to the system is calculated (step S302). In the embodiment, the required output P0 is calculated by storing in the ROM 44 a map in which the relationship among the accelerator pedal position AP, the brake pedal position BP, the vehicle speed V, and the required output P0 is determined in advance, and the accelerator pedal position AP and the brake pedal. When the position BP and the vehicle speed V are given, the corresponding required output P0 is derived from the map.
[0032]
When the required output P0 is calculated, the required output P0 is distributed to the fuel cell output Pfc output from the fuel cell 26 and the battery output Pb output from the battery 30 (step S304). Specifically, the distribution of the required output P0 is an output that allows the fuel cell 26 to be operated efficiently from a range that can be output using the output characteristic of the fuel cell 26 estimated or corrected by the output characteristic correction processing routine of FIG. The fuel cell output Pfc is set, and the fuel cell output Pfc set with respect to the required output P0 is assigned to the battery output Pb.
[0033]
When the required output P0 is thus distributed, the operating points Vfc * and Ifc * of the fuel cell 26 are set based on the fuel cell output Pfc (step S306), and the operating point voltage Vfc * set by the voltage of the power line 28 is set. Then, the DC / DC converter 32 is controlled (step S308), and the inverter 34 is controlled so that the required output P0 is output from the motor 36 to the drive shaft 38 (step S310), and this routine is finished.
[0034]
Among the procedures described above, the operation of “setting the fuel cell output Pfc as an output that allows the fuel cell 26 to be efficiently operated from a range that can be output using the estimated or corrected output characteristics of the fuel cell 26” (step S304). , “Means for setting the target output of the fuel cell using the estimated output characteristic of the fuel cell”. The operation of “setting the operating points Vfc * and Ifc * of the fuel cell 26 based on the fuel cell output Pfc” (step S306) is performed so that the set target output is output from the fuel cell. This corresponds to output adjusting means for adjusting the output.
[0035]
According to the fuel cell system 20 of the embodiment described above, since the fuel cell output Pfc is distributed using more appropriate output characteristics of the fuel cell 26, the fuel cell 26 can be operated efficiently. As a result, the energy efficiency of the entire system can be improved. In addition, since the fuel cell output Pfc is covered by the output Pb from the battery 30 for the excess or deficiency with respect to the required output P0, the required output P0 can be output to the drive shaft 38.
[0036]
In addition, the estimated output characteristics can be set and modified using a relatively simple method and device without using the fuel cell temperature, supply gas flow rate, etc., so the current estimated output characteristics can be modified (updated) in a short time. )can do. It is suitable for use in an in-vehicle fuel cell whose operating conditions change drastically like a vehicle.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating an example of an on-vehicle fuel cell system according to the present invention.
FIG. 2 is a flowchart illustrating a procedure for obtaining a basic output characteristic of a fuel cell.
FIG. 3 is a flowchart illustrating a procedure for correcting a basic output characteristic of a fuel cell.
FIG. 4 is an explanatory diagram for explaining a procedure for correcting a basic output characteristic of a fuel cell.
FIG. 5 is a graph illustrating the distribution of voltage deviations.
FIG. 6 is a flowchart illustrating an example of controlling a fuel cell system by estimating output characteristics.
[Explanation of symbols]
26 Fuel cell, 40 Electronic control unit, 54 Voltage sensor, 56 Current sensor

Claims (3)

Current voltage detection means for detecting the output current of the fuel cell and the voltage between its terminals;
Is detected, the voltage between the output current and the terminal, the output characteristic estimating apparatus for a fuel cell comprising means for estimating an output characteristic of the fuel cell based on the basic output characteristic curve representative of the output current versus output voltage of the fuel cell There,
Means for preliminarily storing a ratio of an open circuit voltage deviation and an internal resistance voltage deviation in the fuel cell to the output current of the fuel cell;
Means for calculating an estimated voltage value from the detected output current and a basic output characteristic curve of the fuel cell stored in advance ;
Means for calculating a voltage deviation between the estimated voltage value and the detected inter-terminal voltage value;
Means for distributing the voltage deviation to an internal resistance voltage deviation and an open circuit voltage deviation at the ratio of the detected output current ;
Based on the distributed open circuit voltage deviation and internal resistance voltage deviation, the level and slope of the entire basic output characteristic curve are corrected, respectively, and the output current and the voltage between terminals detected by the basic output characteristic curve are corrected. Means to modify to include ,
An output characteristic estimation device for a fuel cell comprising: The fuel cell output characteristic estimation device according to claim 1, wherein the basic output characteristic curve is stored as a basic map or a function . The fuel cell output estimation device according to claim 1 or 2,
Means for setting a target output of the fuel cell using the estimated output characteristic of the fuel cell;
A fuel cell system comprising: output adjusting means for adjusting the output of the fuel cell so that the set target output is output from the fuel cell.

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