JP2004349114A - Fuel cell output characteristic estimation device - Google Patents

Abstract

An output characteristic estimating device capable of estimating an output characteristic of a fuel cell in a relatively short time is provided.
A current-voltage detecting means (54, 56) for detecting an output current of a fuel cell and a voltage between terminals thereof, and a fuel based on a detected output current, a voltage between terminals, and a basic output characteristic of the fuel cell. A fuel cell output characteristic estimating device including means for estimating the output characteristic of the fuel cell; a means for calculating an estimated voltage value from the detected output current and the basic output characteristic of the fuel cell; Means (S38) for calculating a voltage deviation between the value and the detected inter-terminal voltage value, and means (S40) for distributing the voltage deviation to the internal resistance deviation and the open circuit voltage deviation of the fuel cell at a predetermined ratio. And means (S42) for correcting the basic output characteristics based on the distributed voltage deviation.
[Selection] Figure 3

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an output characteristic estimating 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 equipment, plants, vehicles, and the like. Also, a power supply system using a fuel cell and a commercial power supply or a secondary battery together has been provided. Since the fuel cell equivalently has an internal resistance, when the output current of the fuel cell increases, the output terminal voltage tends to decrease due to an increase in the voltage drop in the internal resistance. Therefore, it is necessary to predict a drop in the output voltage of the fuel cell due to an increase in the load on the connected electric devices or an increase in the number of connected devices, and to control the operating parameters of the fuel cell so as to compensate for this voltage drop. Also, it is necessary to grasp the supply voltage drop expected for compensating the operation of the device. Further, the output characteristics of the fuel cell tend to change over time.
[0003]
For this reason, the applicant has proposed an output characteristic estimating apparatus for estimating the output characteristic of a fuel cell according to Japanese Patent Application Laid-Open No. 14-231295. The output of the system can be controlled using the current output characteristics of the fuel cell estimated by this device. This output characteristic estimating device stores the output current versus output voltage characteristic (IV characteristic) of the fuel cell stored in advance as a map, and corrects the IV characteristic map by referring to the actually measured current value to thereby improve the IV characteristic of the fuel cell. Can change over time.
[0004]
[Patent Document 1]
JP-A-14-231295
[Problems to be solved by the invention]
However, in order to identify (correct) the current IV characteristic model, the output characteristic estimation device 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. It takes a certain amount of time to process the data. Fuel cells with variable loads, especially fuel cells used in vehicles, estimate the output characteristics of the fuel cell in a short period of time because the load on the motor and various electric devices fluctuates rapidly in a short period of time. It is desired to make use of this in output control.
[0006]
Therefore, an object of the present invention is to provide an output characteristic estimating device capable of estimating the output characteristic of a fuel cell in a relatively short time.
[0007]
It is another object of the present invention to provide an output characteristic estimating device that can realize an output characteristic estimating device with a relatively simple configuration.
[0008]
[Means to solve the problem]
In order to achieve the above object, a fuel cell output characteristic estimating apparatus according to the present invention comprises a current voltage detecting means for detecting an output current of a fuel cell and a voltage between terminals thereof, a detected output current, a voltage between terminals, and a fuel cell. In the fuel cell output characteristic estimating apparatus including means for estimating the output characteristic of the fuel cell based on the basic output characteristic of the fuel cell, means for calculating an estimated voltage value from the detected output current and the basic output characteristic of the fuel cell (S36) ), Means for calculating a voltage deviation between the estimated voltage value and the detected inter-terminal voltage value (S38), and converting the voltage deviation into a predetermined ratio between the internal resistance deviation and the open circuit voltage deviation of the fuel cell. A means (S40) for distributing and a means (S42) for correcting basic output characteristics based on the distributed voltage deviation are provided.
[0009]
With this configuration, the current basic output of the fuel cell in which the change in the open circuit voltage (the internal electromotive force of the battery) and the change in the internal resistance are considered based on the output current, the terminal open voltage, and the basic output characteristic model of the fuel cell Characteristics can be estimated. The basic output characteristics are, for example, output current-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 to the fuel cell terminal of the external circuit is opened (battery output current (I) = 0).
[0011]
Preferably, the predetermined ratio for distributing the voltage deviation between the internal resistance deviation and the open circuit voltage deviation is set variably in accordance with the detected output current value. Thereby, the voltage deviation of the electromotive force of the basic output characteristic model of the fuel cell (vertical translation of the IV characteristic curve) is corrected. In addition, the effect of the internal resistance of the basic output characteristic model on the voltage between output terminals (the 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 estimating device, means for setting a target output of the fuel cell using the estimated output characteristics of the fuel cell (S304), and the set target output. Output adjusting means (S306) for adjusting the output of the fuel cell so that the output of the fuel cell is output from the fuel cell. As a result, 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 schematically showing the configuration of a fuel cell system 20 mounted on a vehicle, which is one 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 adjusts the voltage of a power line 28 connected to the output terminal and charges and discharges a battery 30 that supplies power to an auxiliary device 33; an inverter 34 connected to the power line 28; A motor 36, which is driven and controlled by switching of the switching elements to exchange power with a drive shaft 38, and an electronic control unit 40 for controlling 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. I have.
[0015]
The electronic control unit 40 is configured as a microprocessor mainly including a CPU 42, and has a writable flash ROM 44 for storing a processing program in a nonvolatile manner, a RAM 46 for temporarily storing 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, The current of each phase applied to the motor 36 from a current sensor (not shown) attached to the motor 36, the rotation angle of the rotor of the motor 36 from the angle sensor (not shown) attached to the motor 36, and the vehicle speed V from the vehicle speed sensor 58 , A shift position SP from a shift position sensor 61 for detecting the position of the shift lever 60, The accelerator pedal position AP from the accelerator pedal position sensor 63 for detecting the amount of depression of the lever 62, the brake pedal position BP from the brake pedal position sensor 65 for detecting the amount of depression of the brake pedal 64, and the like are input via input ports. I have.
[0016]
From the electronic control unit 40, 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 are output through output ports. I have.
[0017]
Next, the operation of the fuel cell system 20 of the embodiment, particularly, the operation of estimating the output characteristics of the fuel cell 26 and the operation of the 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 a function, and the basic output characteristic model is corrected each time according to the measured output current and terminal voltage in actual operation. Then, a corrected output characteristic model is obtained and used for estimating the output characteristic.
[0018]
FIG. 2 is a flowchart showing an example of a routine for forming a basic model for obtaining output characteristics of the fuel cell 26. The 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 amps to 400 amps according to 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. It is stored (S22). This IV characteristic becomes a basic output characteristic model. The measurement of the IV characteristic may be performed a plurality of times, and the average characteristic thereof may be used as the basic output characteristic model.
[0019]
The IV characteristic, which is a basic output characteristic model, is stored in the ROM 44 in a non-volatile manner as a basic map including a group of sampling current values (grid currents) at regular intervals and a group of output voltage values (grid voltages) corresponding thereto. The IV characteristic may be stored as an approximate expression, for example, V = V ₀ −RI. Here, V is a terminal voltage, E is a terminal voltage V ₀ when the load circuit is opened, and R is obtained as a slope of a characteristic curve. I is the output current. Thus, the basic characteristic model is determined and stored in advance. An example of the basic characteristic model is indicated by a solid curve A in FIG. 4 (S24).
[0020]
In addition, as shown in FIG. 5, the distribution characteristics of the output current versus the voltage deviation of the fuel cell are obtained in advance by experiments. The distribution characteristic of the voltage deviation indicates the ratio of the deviation of the open output terminal voltage of the fuel cell to 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 an actual operation state of the fuel cell, a characteristic change from the basic characteristic model may occur due to a change with time of the fuel cell, a change in the water content of the polymer electrolyte membrane, and the like. Therefore, the output characteristic of the fuel cell is estimated by modifying the basic characteristic model stored in advance.
[0022]
As shown in FIG. 3, the CPU 42 of the electronic control unit 40 instructs the occurrence of a certain event, for example, a flag of a timer that generates a timeout output at a certain cycle during the operation of the fuel cell, a change of an operating condition, and the like. When the flag is set, the output characteristic correction processing routine is executed (S32).
[0023]
First, read the output I ₁ of the current sensor 56 which monitors the output current of the output V ₁ and the fuel cell voltage sensor 54 for monitoring the output terminal voltage of the fuel cell 26 (S34). It reads the basic characteristic model A described above, obtaining the estimated output voltage V _S corresponding to the output current I ₁ that is measured as shown in FIG. 4 (S36). Obtaining a voltage deviation ΔV of the actually measured output voltages _{V 1} and the estimated output voltage _{V S} (S38).
[0024]
_{Here, ΔV = V S -V 1 =} V 0 -R × I 1 - ((V 0 -ΔV 0) - (R-ΔR) × I 1)) = ΔV 0 -ΔR × I 1 becomes relation established I do. 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 ΔV _R (= ΔR × I ₁ ) due to the resistance deviation ΔR of the internal resistance R of the fuel cell 26. .
[0025]
Next, read the ratio α of the distribution of the voltage deviation ΔV in the output current I ₁ from the graph shown in FIG. 5 described above. 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 characteristics A are 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, the slope of the curve B is changed by applying a correction of the voltage drop [Delta] V _R of the resistance deviation ΔR min to the characteristic curve B, curve passes through the measured point P ₁ of the current on the coordinates _(I 1, _{V 1)} C Is obtained (S42).
[0027]
The corrected output characteristic curve C indicating the current output characteristic thus obtained is stored in the ROM 44 or the RAM 46 as a map (S44). Further, the approximation formula _{V C = (V 0 -ΔV 0} ) to -α _{(I C)} · ΔV ₀ or may be stored in memory. Here, the V _C output voltage actually measured, I _C is the output current measured, [Delta] V ₀ represents the voltage difference between the output value of the output voltage and the basic output characteristic was measured. α (I _C ) indicates the distribution ratio at the output current value I _C. α (I _C ) is obtained from a previously determined and stored graph (FIG. 5).
[0028]
According to the procedure described above, the information extracted from the fuel cell and other systems used to obtain the corrected output characteristic curve C from the basic output characteristic curve A is only the output voltage and output current of the fuel cell. It is not necessary to refer to operating parameters such as the fuel gas flow rate and the like, and the output characteristic curve can be corrected in a short time without any trouble.
[0029]
According to the fuel cell system 20 of the embodiment described above, the output characteristic estimation processing and the output characteristic correction processing executed by the CPU 42 of the electronic control unit 40 perform the more appropriate output characteristic of the fuel cell 26 used over time. Can be obtained. In addition, it can quickly respond to changes in internal resistance due to changes in the water content of the polymer electrolyte membrane of the fuel cell. In the fuel cell system 20 of the embodiment, the output of the system is controlled using the output characteristics of the fuel cell 26 thus obtained.
[0030]
FIG. 8 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 of reading various data such as the brake pedal position BP to be performed is executed (step S300). Subsequently, an output to be output to the drive shaft 38, that is, a required output P0 to the system is calculated based on the read accelerator pedal position AP, brake pedal position BP, and vehicle speed V (step S302). In the embodiment, the required output P0 is calculated by storing in the ROM 44 a map in which the relationship between the accelerator pedal position AP, the brake pedal position BP, the vehicle speed V, and the required output P0 is stored in the ROM 44, and the accelerator pedal position AP and the brake pedal are stored. Given the position BP and the vehicle speed V, 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). The distribution of the required output P0 is, specifically, an output that can operate the fuel cell 26 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. This is performed by setting the fuel cell output Pfc and allocating an excess or deficiency in the fuel cell output Pfc set for the required output P0 to the battery output Pb.
[0033]
When the required output P0 is distributed in this manner, 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. The DC / DC converter 32 is controlled so as to satisfy (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 ends.
[0034]
Among the above-described procedures, the operation of setting the fuel cell output Pfc as an output that can efficiently operate the fuel cell 26 from an output range using the estimated or corrected output characteristic of the fuel cell 26 (step S304) , “Means for setting a target output of the fuel cell using the estimated output characteristics 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 such that the set target output is output from the fuel cell. This corresponds to output adjustment means for adjusting the output.
[0035]
According to the fuel cell system 20 of the embodiment described above, the fuel cell output Pfc is distributed using the more appropriate output characteristics of the fuel cell 26, so that the fuel cell 26 can be operated efficiently. As a result, the energy efficiency of the entire system can be improved. Moreover, in the fuel cell output Pfc, the excess or deficiency of the required output P0 is covered by the output Pb from the battery 30, so that the required output P0 can be output to the drive shaft 38.
[0036]
In addition, since the estimated output characteristics are set and corrected by a relatively simple method and apparatus without using the temperature of the fuel cell, the flow rate of the supplied gas, etc., the current estimated output characteristics can be corrected (updated) in a short time. )can do. It is suitable for use in an on-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 a fuel cell system mounted on a vehicle according to the present invention.
FIG. 2 is a flowchart illustrating a procedure for obtaining basic output characteristics 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 illustrating a procedure for correcting a basic output characteristic of a fuel cell.
FIG. 5 is a graph illustrating distribution of a voltage deviation.
FIG. 6 is a flowchart illustrating an example in which the output characteristics are estimated to control the fuel cell system.
[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,
An output characteristic estimating device for a fuel cell, comprising: means for estimating an output characteristic of a fuel cell based on a detected output current, a terminal voltage, and a basic output characteristic of the fuel cell,
Means for calculating an estimated voltage value from the detected output current and basic output characteristics of the fuel cell,
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 deviation and an open circuit voltage deviation at a predetermined rate;
Means for correcting the basic output characteristics based on the distributed voltage deviation,
An output characteristic estimating device for a fuel cell comprising: The fuel cell output characteristic estimating device according to claim 1,
An output characteristic estimating device for a fuel cell, wherein the predetermined ratio is set in accordance with a detected output current value. An output estimating device for a fuel cell according to claim 1 or 2,
Means for setting a target output of the fuel cell using the estimated output characteristics of the fuel cell,
A fuel cell system comprising: an output adjusting unit that adjusts an output of the fuel cell so that the set target output is output from the fuel cell.

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