JP2006221986A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the dispersion of a starting voltage in voltage decreasing processing in the starting of a plurality of fuel cells and prevent the deterioration of performance. <P>SOLUTION: The difference between oxygen concentrations in an oxidant electrode 3 of each fuel cell 1 is discriminated based on the oxygen concentration 3 of each fuel cell 1 detected by oxygen concentration sensors 14-17, and when the discriminated difference is a prescribed discrimination value or more, the oxidant electrode 3 of each fuel cell 1 is replaced with air before the starting of a system, and when the difference between oxygen concentrations is not larger than a prescribed value, loads of variable resistors 18, 19 are connected to each fuel cell 1 to decrease a voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system that performs start-up control based on the oxygen concentration of an oxidizer electrode when a plurality of fuel cells are started.

  As a technique for removing combustible gas and condensed water remaining in the fuel cell system, for example, a technique described in the following document is known (Patent Document 1). In the technique described in this document 1, when the purge operation is performed on the fuel reformer, the fuel cell main body, and the fuel supply system, the purge operation with steam is first performed, and then the purge operation with air is performed. The flammable gas and condensed water remaining in the system are surely removed.

On the other hand, as a technique for monitoring phosphoric acid deficiency caused by the amount of phosphoric acid retained in the matrix of each unit cell in a phosphoric acid fuel cell being scattered during power generation and decreasing, for example, the technology described in the following documents Is known (Patent Document 2). In the technique described in this document 1, an oxygen concentration sensor that detects the oxygen concentration in the off-gas discharged from the outlet of the fuel electrode and the oxidant electrode is provided, and the oxygen concentration or the increase in concentration detected by the oxygen concentration sensor is provided. When the rate exceeds a predetermined level, a decrease in the remaining amount of phosphoric acid is notified.
JP2002-231293 Japanese Patent Laid-Open No. 03-101061

  When starting a plurality of fuel cells at the same time, if the fuel cells are started with the oxygen concentrations in the oxidant electrodes of the respective fuel cells being different, a problem has occurred in the voltage drop process at the time of startup. In other words, due to the difference in oxygen concentration at the oxidant electrode of each fuel cell, a fuel cell that is likely to react with hydrogen of the fuel gas and a fuel cell that is difficult to react are produced, and there is a difference in the starting voltage of each fuel cell. As a result, some fuel cells may be in a negative voltage state at startup. By repeating such a state at the time of start-up, there is a problem that the catalyst layer of the fuel cell is deteriorated.

  However, the above problems have not been solved only by purging combustible gas or condensed water and detecting the oxygen concentration in the off-gas, as in the prior art described above.

  Accordingly, the present invention has been made in view of the above, and an object of the present invention is to suppress a variation in start-up voltage in a voltage drop process at the time of start-up of a plurality of fuel cells, and to prevent a decrease in performance. To provide a system.

  In order to achieve the above object, means for solving the problems of the present invention comprises a plurality of fuel cells that generate power by an electrochemical reaction between a fuel gas supplied to the fuel electrode and an oxidant gas supplied to the oxidant electrode. In the fuel cell system, the difference in oxygen concentration of the oxidant electrode of each fuel cell is determined based on the oxygen concentration detected by the detection unit and the detection unit that detects the oxygen concentration of the oxidant electrode of each fuel cell. And determining means for determining, and control means for determining and executing a starting method of the fuel cell system based on a difference in oxygen concentration determined by the determining means.

  According to the present invention, the start-up method of the fuel cell system is determined based on the difference in oxygen concentration of the oxidant electrode of each fuel cell, thereby preventing variations in the start-up voltage of each fuel cell at the time of system start-up. Can do.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best embodiment for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a fuel cell system according to Embodiment 1 of the present invention. The system of Embodiment 1 shown in FIG. 1 includes two fuel cells 1, and fuel gas and oxidant gas are supplied in parallel to the fuel electrode 2 and the oxidant electrode 3 of the two fuel cells 1. . That is, for example, hydrogen gas fuel gas stored in the fuel tank 4 controls the fuel supply pipe 6 provided in parallel to each fuel cell 1 and the fuel supply, and selectively shuts off the fuel cell 1 and the outside air. The fuel is supplied to the fuel electrode 2 of each fuel cell 1 through the fuel supply valve 10 to be controlled. The fuel off-gas discharged from each fuel cell 1 is diluted and exhausted through a fuel exhaust pipe 7 and a fuel exhaust check valve 11 provided in parallel to each fuel cell 1.

  On the other hand, the air serving as the oxidant gas controls the oxidant blower 5 that compresses and supplies the air, the oxidant supply pipe 8 provided in parallel to each fuel cell 1 and the supply of the oxidant and the fuel cell 1. The gas is supplied to the oxidant electrode 3 of each fuel cell 1 via an oxidant supply valve 12 that selectively controls the outside air. The oxidant off-gas discharged from each fuel cell 1 is exhausted through an oxidant exhaust pipe 9 and an oxidant exhaust check valve 13 provided in parallel to each fuel cell 1.

  Oxygen concentration sensors 14 to 17 as means for detecting the oxygen concentration are provided at the junction between the oxidant supply pipe 8 and the oxidant exhaust pipe 9 and the oxidant electrode 3. That is, the oxygen concentration sensor 14 detects the oxygen concentration on the oxidant electrode inlet side of one fuel cell 1, and the oxygen concentration sensor 15 detects the oxygen concentration on the oxidant electrode outlet side of one fuel cell 1, The oxygen concentration sensor 16 detects the oxygen concentration on the oxidant electrode inlet side of the other fuel cell 1, and the oxygen concentration sensor 17 detects the oxygen concentration on the oxidant electrode outlet side of the other fuel cell 1.

  The length and the pipe diameter of the oxidant supply pipe 8 from the inlet of the oxidant electrode 3 of each fuel cell 1 to the junction where the oxidant supply pipe 8 merges are the same, and the oxidant electrode 3 of each fuel cell 1 is formed. The length and the pipe diameter of the oxidant exhaust pipe 9 from the outlet of the oxidant exhaust pipe 9 to the junction part 23 of the oxidant exhaust pipe 9 are formed to be the same, and the oxidant exhaust pipe 9 downstream of the junction part 23 by the oxidant exhaust check valve 13. Thus, outside air is prevented from entering the fuel cell 1.

  A variable resistor 18 connected in series and a relay 20 of a switching element are connected between output terminals for taking out the power obtained by the power generation of one fuel cell 1, and similarly obtained by the power generation of the other fuel cell 1. A variable resistor 19 connected in series and a relay 21 of a switching element are connected between output terminals for extracting power. The output terminals of each fuel cell 1 are selectively short-circuited through the variable resistors 18 and 19, and a voltage drop process is performed in each fuel cell 1 at the time of startup. The resistance values of the variable resistors 18 and 19 are varied under the control of the control unit 22. The relays 20 and 21 are switching-controlled by the control unit 22.

  The control unit 22 functions as a control center for controlling the operation of the system, and includes, for example, a microcomputer including resources such as a CPU, a storage device, and an input / output device necessary for a computer that controls various operation processes based on a program. Etc. The control unit 22 reads signals from sensors (not shown) including the oxygen concentration sensors 14 to 17 and controls the relays 20 and 21 based on the read various signals and control logic (program) stored in advance in the inside. A command is sent to each component of the system including this, and all operations necessary for operation / stop of the system including the operation at the time of starting described below are managed and controlled.

  FIG. 2 is a flowchart showing the procedure of the start-up control process for the fuel cell system according to the first embodiment. When the fuel cell system is started, if fuel gas is introduced into the fuel electrode 2 in a state where the oxygen concentrations in the oxidant electrodes 3 of the plurality of fuel cells 1 are different, the fuel cell system is started at the oxidant electrode 3 having a low oxygen concentration. While the voltage does not stand, the starting voltage stands at the oxidant electrode 3 having a high oxygen concentration. In such a case, if a voltage drop process is performed in which a plurality of fuel cells 1 short-circuit between output terminals via a load, a difference occurs in the starting voltage of each fuel cell 1. In order to prevent this, starting control of the fuel cell system is performed according to the procedure shown in FIG.

  In FIG. 2, when the start of the fuel cell system is instructed first, the oxygen concentration in the oxidant electrode 3 of each fuel cell 1 is detected by the oxygen concentration sensors 14 to 17 before the system is started. If the detected oxygen concentration at the inlet side and the oxygen concentration at the outlet side of the oxidant electrode 3 are different from each other, the oxygen concentration at the higher concentration is set to the oxygen concentration at the oxidant electrode 3 of the fuel cell 1. Set as concentration. Thereafter, a difference in oxygen concentration in the oxidant electrode 3 of the fuel cell 1 is calculated by the control unit 22, and it is determined whether or not the difference is greater than or equal to a predetermined determination value set in advance (step S21).

When two or more fuel cells are provided, the difference in oxygen concentration between the fuel cells is calculated for all combinations.

  As a result of the determination, if the difference is equal to or larger than the determination value, the oxidant blower 5 is operated to supply the oxidant gas air to each fuel cell 1, and the inside of the oxidant electrode 3 of all the fuel cells 1 is supplied. The oxygen concentration in all the oxidant electrodes 3 is set to the same state (step S22). Steps S21 and S22 are repeated until the difference in oxygen concentration between the fuel cells is equal to or less than the determination value. When the difference is equal to or less than the determination value, the control unit 22 turns on the relays 20 and 21 to change the variable resistance. After short-circuiting between the output terminals of each fuel cell 1 via 18 and 19 and performing a voltage drop process, the system is started (step S23).

  As described above, in the first embodiment, in the fuel cell system including a plurality of fuel cells 1 that generate electric power by electrochemical reaction, oxygen concentration sensors installed on the inlet side and the outlet side of the oxidant electrode 3 in each fuel cell 1. Based on the oxygen concentration detected in 14 to 17, the oxygen concentration in the oxidant electrode 3 of each fuel cell 1 is made substantially uniform, so that the start-up voltage of each fuel cell 1 in the voltage drop process at the time of system start-up Can be prevented.

  Oxygen concentration sensors 14 to 17 are provided at the junction between the oxidant supply pipe 8 and the oxidant gas inlet of the fuel cell 1 and at the junction between the oxidant exhaust pipe 9 and the oxidant offgas outlet of the fuel cell 1. The oxygen concentration in the oxidant electrode 3 that cannot be directly measured can be detected with high accuracy.

  The lengths and pipe diameters of the oxidant supply pipes 8 until the oxidant supply pipes 8 of the plurality of fuel cells 1 branch and are distributed to the oxidant electrodes 3 of the respective fuel cells 1 are the same, and the plurality of fuel cells 1 In the oxidant exhaust pipe 9 of the battery 1, the length and the pipe diameter of the oxidant exhaust pipe 9 from the oxidant electrode 3 to the oxidant electrode 3 are made the same, so that outside air can enter each fuel cell 1 through the pipe. Even if it exists, it becomes easy to keep the oxygen concentration in the oxidant electrode 3 of each fuel cell 1 almost in the same state, and when the oxidant supply system is purged with air, the oxidant electrode of each fuel cell 1 It becomes possible to make the oxygen concentration in 3 almost the same state.

  An oxidant supply valve 12 is provided in the oxidant supply pipe 8, an oxidant exhaust check valve 13 is provided in the oxidant exhaust pipe 9, a fuel supply valve 10 is similarly provided in the fuel supply pipe 6, and a fuel exhaust pipe 7 is provided. By installing the fuel exhaust check valve 11, each valve is closed to block outside air entering the oxidant electrode 3 from the outside, and the oxygen concentration in each oxidant electrode 3 is kept low. be able to.

  By detecting the oxygen concentrations in the oxidant supply pipes 8 and the oxidant exhaust pipes 9 of the plurality of fuel cells 1 with the oxygen concentration sensors 14 to 17, the difference in oxygen concentration among the plurality of fuel cells 1 can be accurately grasped. can do.

  By performing air replacement of the oxidant electrodes 3 of the plurality of fuel cells 1 before starting the fuel cell system only when the difference in oxygen concentration of the oxidant electrodes 3 in the plurality of fuel cells 1 is greater than or equal to a predetermined determination value, The oxygen concentration in each oxidant electrode 3 can be made substantially the same.

  FIG. 3 is a flowchart showing the processing procedure of the start control process of the fuel cell system to which the second embodiment is applied, and the configuration is the same as that of the first embodiment shown in FIG. In FIG. 3, when the start of the fuel cell system is first commanded, the oxygen concentration in the oxidant electrode of each fuel cell 1 is detected by the oxygen concentration sensors 14 to 17 before the system is started. If the detected oxygen concentration at the inlet side and the oxygen concentration at the outlet side of the oxidant electrode 3 are different from each other, the oxygen concentration at the higher concentration is set to the oxygen concentration at the oxidant electrode 3 of the fuel cell 1. Concentration. Thereafter, a difference in oxygen concentration of the oxidant electrode of each fuel cell 1 is calculated by the control unit 22, and it is determined whether or not the difference is greater than or equal to a predetermined determination value set in advance (step S31).

  If the difference is equal to or larger than the determination value as a result of determination, the oxygen concentration value of each fuel cell 1 is recognized (step S32), and a voltage drop process is performed according to each oxygen concentration value (step S33). That is, the control unit 22 adjusts and sets the variable resistors 18 and 19 corresponding to each fuel cell 1 to a resistance value corresponding to the oxygen concentration value, and uses the adjusted and set variable resistors 18 and 19 as in the first embodiment. Perform voltage drop processing. The relationship between the oxygen concentration value of the oxidant electrode 3 and the load (resistance values of the variable resistors 18 and 19) is acquired in advance through experiments and desk studies, and stored in the control unit 22 as a table.

  On the other hand, if the difference in oxygen concentration is equal to or less than the determination value in the previous step S31, the voltage drop process is performed in the same manner as in the first embodiment with the variable resistors 18 and 19 having preset resistance values. Thereafter, the system is activated (step S34).

  In the second embodiment, the same effects as those of the first embodiment can be obtained, and the start-up voltages of the plurality of fuel cells 1 at the start of the fuel cell system can be made substantially the same. .

  FIG. 4 is a flowchart showing the processing procedure of the start control process of the fuel cell system to which the third embodiment is applied, and the configuration is the same as that of the first embodiment shown in FIG. In FIG. 4, when the start of the fuel cell system is instructed, the oxygen concentration in the oxidant electrode 3 of each fuel cell 1 is detected by the oxygen concentration sensors 14 to 17 before the system is started. If the detected oxygen concentration at the inlet side and the oxygen concentration at the outlet side of the oxidant electrode 3 are different from each other, the oxygen concentration at the higher concentration is set to the oxygen concentration at the oxidant electrode 3 of the fuel cell 1. Concentration. Thereafter, a difference in oxygen concentration of the oxidant electrode 3 of each fuel cell 1 is calculated by the control unit 22, and it is determined whether or not the difference is greater than or equal to a predetermined determination value set in advance (step S41).

  If the difference is equal to or greater than the determination value as a result of determination, the fuel cell 1 with the lowest oxygen concentration is specified (step S42). Subsequently, the voltage drop processing of all the fuel cells 1 is similarly performed according to the lowest oxygen concentration value (step S43). That is, the control unit 22 adjusts and sets the variable resistors 18 and 19 corresponding to each fuel cell 1 to the resistance value corresponding to the lowest oxygen concentration value, and with the adjusted variable resistors 18 and 19 in the first embodiment, Similarly, a voltage drop process is performed. Here, the resistance values of the variable resistors 18 and 19 are selected so that the output voltage of the fuel cell 1 does not become a negative voltage even when the voltage drop process is performed in the fuel cell 1 having the lowest oxygen concentration. The relationship between the oxygen concentration value of the oxidant electrode 3 and the load (resistance values of the variable resistors 18 and 19) is acquired in advance through experiments and desk studies, and stored in the control unit 22 as a table.

  On the other hand, if the difference in oxygen concentration is equal to or less than the determination value in the previous step S41, the voltage drop process is performed in the same manner as in the first embodiment with the variable resistors 18 and 19 having preset resistance values. Thereafter, the system is activated (step S44).

  In the third embodiment, in addition to obtaining the same effects as those of the first embodiment, it is possible to prevent the starting voltage of each fuel cell 1 from becoming a negative voltage.

  FIG. 5 is a flowchart showing the processing procedure of the startup control process of the fuel cell system to which the fourth embodiment is applied, and the configuration is the same as that of the first embodiment shown in FIG. In FIG. 5, when the start of the fuel cell system is instructed first, the oxygen concentration in the oxidant electrode 3 of each fuel cell 1 is detected by the oxygen concentration sensors 14 to 17 before the system is started. If the detected oxygen concentration at the inlet side and the oxygen concentration at the outlet side of the oxidant electrode 3 are different from each other, the oxygen concentration at the higher concentration is set to the oxygen concentration at the oxidant electrode 3 of the fuel cell 1. Concentration. Subsequently, it is determined whether or not the oxygen concentration of the oxidizer electrode 3 of all the fuel cells 1 is equal to or lower than a predetermined determination value (which is different from the determination values of the first to third embodiments). Step S51).

  As a result of the determination, when the oxygen concentration of the oxidant electrode 3 of all the fuel cells 1 is equal to or less than the determination value, the start-up is started without performing the voltage drop process at the start-up of the fuel cell system (step S52). Thereby, it is possible to prevent the start-up voltage of the fuel cell 1 having a low oxygen concentration from becoming a negative voltage by the voltage drop process at the start-up of the fuel cell system.

  On the other hand, if at least one oxygen concentration is equal to or higher than the determination value in the determination result of the previous step S51, the previous embodiment is provided with the variable resistors 18 and 19 having resistance values set in advance when the fuel cell system is started. After performing the voltage drop process in the same manner as 1, the system is started (step S 53).

  In the fourth embodiment, it is possible to avoid a load on the fuel cell 1 due to the voltage drop process in a state where the oxygen concentration is low and the starting voltage is not established. Further, since the voltage drop process is not selectively performed at the time of starting the system, it is possible to reduce the time required for starting the system.

  In addition, in the said Examples 1-4, although the case where there were two fuel cells was demonstrated, even if there are two or more fuel cells, it can carry out similarly and can acquire the same effect, and the said Examples 1- You may implement combining 4 suitably.

It is a figure which shows the structure of the fuel cell system which concerns on Example 1 of this invention. It is a flowchart which shows the operation | movement procedure of the system which concerns on Example 1 of this invention. It is a flowchart which shows the operation | movement procedure of the system which concerns on Example 2 of this invention. It is a flowchart which shows the operation | movement procedure of the system which concerns on Example 3 of this invention. It is a flowchart which shows the operation | movement procedure of the system which concerns on Example 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell 2 ... Fuel electrode 3 ... Oxidant electrode 4 ... Fuel tank 5 ... Oxidant blower 6 ... Fuel supply piping 7 ... Fuel exhaust piping 8 ... Oxidant supply piping 9 ... Oxidant exhaust piping 10 ... Fuel supply valve 11 ... Fuel exhaust check valve 12 ... Oxidant supply valve 13 ... Oxidant exhaust check valve 14-17 ... Oxygen concentration sensor 18,19 ... Variable resistance 20,21 ... Relay 22 ... Control part 23 ... Joint part

Claims (9)

In a fuel cell system including a plurality of fuel cells that generate electricity by an electrochemical reaction between a fuel gas supplied to a fuel electrode and an oxidant gas supplied to an oxidant electrode,
Detecting means for detecting the oxygen concentration of the oxidant electrode of each fuel cell;
Discriminating means for discriminating the difference in oxygen concentration of the oxidant electrode of each fuel cell based on the oxygen concentration detected by the detecting means;
And a control unit that determines and executes a starting method of the fuel cell system based on a difference in oxygen concentration determined by the determination unit. An oxidant supply pipe for supplying an oxidant gas to the oxidant electrode of each fuel cell;
An oxidant exhaust pipe for discharging oxidant off-gas from the oxidant electrode of each fuel cell,
The detection means includes a first oxygen concentration sensor that detects an oxygen concentration in the oxidant supply pipe and a second oxygen concentration sensor that detects an oxygen concentration in the oxidant exhaust pipe. The fuel cell system according to claim 1. In the oxidant supply pipe, the length and the pipe diameter of the oxidant supply pipe are the same while being distributed from the branch part of the oxidant supply pipe to each oxidant electrode,
3. The fuel cell system according to claim 2, wherein, in the oxidant exhaust pipe, the length and the pipe diameter of the oxidant exhaust pipe until the oxidant exhaust pipes merge from each other are the same. An oxidant supply pipe for supplying an oxidant gas to the oxidant electrode of each fuel cell;
A valve body provided in the oxidant supply pipe for selectively blocking the oxidant electrode and outside air;
An oxidant exhaust pipe for discharging oxidant off-gas from the oxidant electrode of each fuel cell;
A check valve that is provided in the oxidant exhaust pipe and in which the direction in which the oxidant off-gas flows through the oxidant exhaust pipe is normally open;
Fuel supply piping for supplying fuel gas to the fuel electrode of each fuel cell;
A valve body provided in the fuel supply pipe to selectively shut off the fuel electrode and outside air;
A fuel exhaust pipe for discharging fuel off-gas from the fuel electrode of each fuel cell;
4. The fuel cell system according to claim 2, further comprising a check valve that is provided in the fuel exhaust pipe and is normally open in a direction in which fuel off-gas flows to the outside through the fuel exhaust pipe. 5. Based on the oxygen concentration detected by the first oxygen concentration sensor and the oxygen concentration detected by the second oxygen concentration sensor, the oxygen concentration of the oxidant electrode of each fuel cell is set,
5. The fuel according to claim 2, wherein the determination unit determines a difference in oxygen concentration of an oxidant electrode of each fuel cell based on the set oxygen concentration. Battery system. If the determination means determines that the difference in oxygen concentration of the oxidant electrode of each fuel cell is greater than or equal to a preset first determination value, each fuel cell system is started before the fuel cell system is started. The fuel cell system according to any one of claims 1, 2, 3, 4 and 5, further comprising means for supplying air to an oxidant electrode of the battery. When the determination means determines that the difference in oxygen concentration of the oxidant electrode of each fuel cell is greater than or equal to a predetermined first determination value set in advance, the control means 3. The voltage drop process is performed in each fuel cell using a load corresponding to the oxygen concentration of each oxidant electrode of each fuel cell detected by the detection means before starting. , 3, 4 and 5. The fuel cell system according to claim 1. If the determination means determines that the difference in oxygen concentration of the oxidant electrode of each fuel cell is equal to or greater than a predetermined determination value set in advance, the control means may The voltage drop process is performed in each fuel cell using a load corresponding to the lowest oxygen concentration among the oxygen concentrations of the respective oxidant electrodes of each fuel cell detected by the detecting means. The fuel cell system according to any one of claims 1, 2, 3, 4, and 5. The determination means compares the oxygen concentration of the oxidant electrode of each fuel cell detected by the detection means with a predetermined second determination value set in advance,
The control means performs a voltage drop process in each fuel cell when all of the oxygen concentration of the oxidant electrode of each fuel cell is equal to or less than the second judgment value in the comparison result of the discrimination means. The fuel cell system according to any one of claims 1, 2, 3, 4 and 5, wherein the fuel cell system is started without being started.

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