JP3840908B2 - Fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a fuel cell system suitable for mounting on a moving body such as a fuel cell vehicle.
[0002]
[Prior art and problems to be solved]
In order to suppress fuel consumption in a fuel cell system and improve the efficiency of the system, various types of systems that recirculate unreacted gas discharged from the fuel cell have been proposed. For example, in the one disclosed in JP-A-6-231786, the circulation flow rate of the unreacted gas is not simply changed according to only the load of the fuel cell, but is corrected by the density of the circulation gas, The blower is prevented from over-rotation and always operates stably. Further, in Japanese Patent Application Laid-Open No. 7-240220, the pressure at the compressor inlet is adjusted by a pressure regulating valve installed at the inlet of the circulation compressor so that the circulation flow rate does not fluctuate due to the pressure fluctuation of the circulation part due to the load fluctuation of the fuel cell. Adjustment is performed and control is performed to obtain a stable circulating flow rate. Moreover, in the thing of Unexamined-Japanese-Patent No. 9-213353, it has the structure which used the ejector as a pump for unreacted gas circulation, and in order to operate an ejector efficiently, the flow control valve was installed in the circulation part, and the fuel The circulation flow rate is corrected according to the battery load, and the system is controlled to operate efficiently. Thus, in the conventional fuel cell system, the anode electrode exhaust gas is circulated according to the load to increase the efficiency of the system, and the control method is optimized to achieve a stable operation.
[0003]
By the way, in the case of a polymer electrolyte fuel cell, for example, in order to avoid clogging of the gas flow path due to water intrusion (hereinafter referred to as “flooding”) at low load, It is necessary to supply gas at a ratio of the amount of gas supplied to the amount of gas consumed by In the prior art, the circulation amount and discharge amount at low load can be set as initial values, but correction for the circulation part when flooding occurs during operation is not considered. If flooding occurs by reducing only the load without changing the supply gas flow rate or increasing only the gas supply flow rate without changing the load, the unreacted gas that increases relatively is discharged to the outside. The problem is that excess fuel gas is consumed because it has to be made and the fuel consumption of the system is deteriorated.
[0004]
In addition, in the polymer electrolyte fuel cell, the supply gas needs to be appropriately humidified, and further, the fuel supply device reforms the fuel such as hydrocarbon to provide a hydrogen-rich fuel gas. In the case of a quality device, pure water is also required for the reforming reaction. Recovering the pure water used for these from the cathode exhaust gas of the fuel cell can improve the efficiency of water use as a system, but the supply gas is often operated at a low pressure at low loads, which is necessary for operation. In order to reliably recover a large amount of pure water, it is necessary to perform a water recovery operation in which the pressure of the supply gas is raised for a predetermined time, and flooding is likely to occur unless the circulation amount is changed accordingly, or A problem arises in that efficiency is lowered due to a pressure difference between the anode and the cathode.
[0005]
The present invention has been made paying attention to such conventional problems, and prevents the occurrence of flooding in the fuel cell system, and suppresses deterioration in fuel consumption caused by increasing fuel stoichiometry at low load as a flooding prevention measure. The purpose is that.
[0006]
[Means for Solving the Problems]
The first invention constitutes a fuel cell system including a circulation device that circulates part of the anode exhaust gas again to the anode electrode of the fuel cell, and a control device that controls the anode circulation flow rate by the circulation device. Further, the control device determines a load detection means for detecting a load of the fuel cell, a basic value setting means for setting a basic value of the anode circulation flow rate based on the load, and an implementation state of water recovery from the cathode electrode. Water recovery determination means, correction means for correcting the basic value of the anode circulation flow rate, and flooding detection means for detecting the flooding of the gas flow path, and the control device has a fuel cell with a low load. The basic value is corrected in the high flow rate direction when the water recovery operation is performed, and the basic value of the anode circulation flow rate is corrected in the decreasing direction when the flooding is not detected for the reference time or more during the correction. .
[0007]
In a second aspect of the invention, the control device of the first aspect of the invention is provided with a temperature detection device for detecting the operating temperature of the fuel cell, and the anode circulating flow rate is corrected in the higher flow rate direction as the operating temperature is lower. To do.
[0008]
In a third aspect of the invention, the control device according to any one of the aspects of the invention is configured to perform flooding detection after the anode circulation flow rate correction, and to correct the basic value in a high flow rate direction when the occurrence of flooding is detected .
[0012]
According to a fourth invention, in any one of the inventions described above, the booster circuit is provided in parallel with the circulation device, and the control device is configured to increase the anode circulation flow rate by the booster circuit when flooding is detected.
[0013]
According to a fifth aspect of the present invention, the control device according to any one of the above aspects is configured such that the correction amount of the anode circulation flow rate is initially set to a low value, and the anode circulation flow rate is increased by a predetermined value every time flooding is detected. The circulator is controlled to minimize the flow rate.
[0014]
[Action / Effect]
According to each of the first and subsequent inventions, when the water recovery operation state is detected during low load operation of the fuel cell, the anode circulation flow rate is corrected in the high flow direction, and the stoichiometry of the fuel gas supplied to the fuel cell is corrected. Rises. For this reason, even if the pressure of the supply gas increases due to the water recovery operation, it is possible to suppress the occurrence of flooding , thereby stabilizing the operation of the fuel cell system and always maintaining the pressure balance between the anode and the cathode. Can be kept even. In addition, when the anode circulation flow rate is corrected in the high flow direction in this way and no flooding has occurred for a certain period of time, the anode circulation flow rate is reduced by reducing the basic value, so the burden on the circulation device is reduced accordingly, and the system Increases efficiency.
[0015]
According to the second invention, when the operating temperature of the fuel cell is low, the anode circulation flow rate is increased and corrected, so that flooding due to condensation of humidified steam that is likely to occur at low temperatures inside the fuel cell can be suppressed before it occurs. .
[0016]
According to the third invention, even if flooding occurs, the flooding is eliminated only by correcting the increase of the anode circulation flow rate, so that the operation can be continued without wastefully consuming fuel.
[0019]
According to the fourth aspect of the invention, the circulation flow rate can be increased rapidly by the booster, so that even if flooding occurs, this can be eliminated in a shorter time.
[0020]
According to the fifth aspect of the invention, the anode circulation flow rate is always controlled to be the minimum necessary for the lower limit value, so that the power consumption of the system can be suppressed and the efficiency can be further increased.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a main part of a fuel cell system according to the present invention. 100 is a fuel cell (fuel cell stack), 101 is a fuel supply device that supplies a hydrogen-rich fuel gas to the anode electrode side of the fuel cell 100 via the fuel channel 102, and 103 is an anode exhaust gas channel 104 of the fuel cell 100. A circulation flow path for circulating a part of the anode exhaust gas from the fuel flow path 102, 105 a control valve for controlling the discharge flow rate of the anode exhaust gas, and 106 pressure-feeding the anode exhaust gas of the circulation flow path 103 to the fuel flow path 102. This is a compressor. Although not shown, the fuel cell system is supplied to the fuel cell 100, an air supply device for supplying air to the fuel cell 100, a cooling device for cooling the fuel cell 100, the load of the fuel cell 100, and the fuel cell 100. A detection device that detects the temperature, pressure, and flow rate of each fluid, a control device that controls the control valve 105 and the compressor 106 based on the detection result, and the like are provided.
[0022]
Further, the symbol α in the figure means the stoichiometry of hydrogen gas supplied from the fuel supply device 101, and β means the hydrogen stoichiometry that actually enters the fuel cell 100 including the circulation flow rate. Therefore, the circulation flow rate is β-α, and the amount discharged outside the circulation is α-1.
[0023]
In this fuel cell system control device, the circulating gas pressure value (basic value) is obtained from a table set in advance as shown in FIG. 3 so that the stoichiometric characteristics with respect to the load are satisfied as shown in FIG. The compressor 106 is driven so that this pressure value is achieved. FIG. 4 or FIG. 5 shows an example of the relationship between the flow rates (α, β, β-α) when the anode exhaust gas is circulated. However, FIG. 6 shows the relationship between the flow rates of the respective parts when the flow rate at 100% load is 1.
[0024]
However, if water recovery is started at a low load, the pressure of the supply gas is increased at the time of water recovery, so that when the same mass flow rate is supplied, the flow rate in the fuel cell will decrease and flooding will occur. It becomes easy. Therefore, for example, the start of water recovery is determined based on information from a control system related to water recovery, and the circulation flow rate is corrected in the increasing direction during water recovery. This corresponds to correction for increasing the hydrogen stoichiometry with the characteristics illustrated in FIG. 6, for example. At this time, it is only necessary to first increase the circulation flow rate β 1 α by the compressor 106 of the circulation unit. Since the upper limit of β-α is determined by the capacity of the circulation flow path 103 and the capacity of the compressor 106, the supply amount α is increased in order to increase the stoichiometry. Even when the temperature of the cooling medium coming out of the fuel cell 100 is low, the circulation flow rate β-α is increased in the same manner as when the pressure is increased. As a result, the generation of flooding due to the condensation of the water vapor contained in the supply gas α in the flow path of the fuel cell lower than the water vapor temperature is suppressed.
[0025]
On the other hand, when the flooding is detected by a flooding detection unit (not shown), the control device causes the compressor 106 to increase the circulation flow rate β 1α so that the actual stoichiometric β increases by 10%, for example. When operating in a low load range where it is necessary to increase the stoichiometry in the initial setting, if no flooding is detected, that is, if the engine is operating stably, the circulation flow rate β is increased every time a predetermined time elapses. Reduce α by a predetermined amount to the lower limit (minimum zero).
[0026]
As the flooding detection means, for example, each cell voltage of the fuel cell 100 is detected, and when there is a cell voltage that is 80% or less of the average cell voltage in the operation state at that time, it is determined that flooding has occurred, Increase the flow rate β 1 α. Alternatively, as the flooding detection means, for example, the pressure of the exhaust gas of the fuel cell 100 is detected, and as shown in FIG. 7, the pressure fluctuation of the exhaust gas is not less than a predetermined amplitude or a predetermined frequency, for example, 0.1 to several Hz. Sometimes it is determined that flooding has occurred.
[0027]
FIG. 8 is a flowchart showing an example of processing contents by the control device in time series. This process is executed constantly or periodically by an interrupt process by a control device including a microcomputer and its peripheral devices. In the following, description will be given in order.
S201:
The load of the fuel cell is detected.
S202:
The basic value (initial value) of the circulation flow rate is obtained according to the load. This can be obtained, for example, by searching for a reference pressure with reference to a table set in advance as shown in FIG. 2 or FIG. 3 as described above.
S203:
Determine the presence or absence of water recovery. When water recovery control is not performed, the process proceeds to S216.
S204:
At the time of water recovery, the reference pressure is corrected by a predetermined amount in the increasing direction. In this correction process, the value set in S202 is corrected by operating, and a table set in advance so as to give a control value at the time of water recovery according to the load as shown in FIG. 6 is searched. You may make it implement.
S205:
Detect the occurrence of flooding. As described above, this is detected from the fluctuation of the cell voltage of the fuel cell stack or the pressure fluctuation state of the exhaust gas.
S206:
The presence / absence of flooding is determined based on the detection result. If flooding occurs, the process proceeds to S207, and if not, the process proceeds to S208 and subsequent steps.
S207:
When flooding occurs, the circulating flow rate set in S202 or S204 is corrected by 10%, for example, in the increasing direction.
S208:
After the flow rate correction, if the reference time has elapsed, the process proceeds to S209, and if not, the process proceeds to S213 and subsequent processes.
S209 to S211:
When the reference time has elapsed, the circulating flow rate set in S204 is corrected in the decreasing direction with the basic value as the lower limit.
S212:
A control command is issued to the compressor 106 so as to achieve the circulating flow rate set in the processing after S207 or S209.
S213:
The load of the fuel cell is detected.
S214:
A basic value of the circulation flow rate is obtained according to the load.
S215:
It is determined whether the water recovery operation is continued. If the water recovery control is performed, the process returns to the process of S205. If the water recovery control is completed, the process proceeds to S216. S216:
A control command is issued to the compressor 106 so that the circulating flow rate is achieved by the basic value obtained in S202 or S214.
[0028]
By repeating the above processing, the fuel cell system is operated at the last possible stoichiometric operation without causing flooding, and the driving power of the compressor 106 and the like is suppressed to a necessary minimum. Even when the fuel supply device is a reformer, unreacted exhaust gas to be supplied to the reformer combustor can be minimized, so that fuel consumption can be minimized.
[0029]
FIG. 9 shows a second embodiment of the present invention. This forms a booster circuit 109 interposing a second compressor 107 and a normally closed shut-off valve 108 in parallel with the circulation flow path 103. When the occurrence of flooding is detected, the shut-off valve 108 is opened and the compressor 107 Is driven to rapidly increase the circulation flow rate of the anode exhaust gas. By providing the booster circuit 109, the occurrence of flooding can be eliminated more quickly.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a main part of a first embodiment of a fuel cell system according to the present invention.
FIG. 2 is a characteristic diagram showing a relationship between a load and a stoichiometric basic value of supply gas.
FIG. 3 is a characteristic diagram showing a relationship between a load and a basic value of gas pressure.
FIG. 4 is a first flow rate characteristic diagram showing a relationship between flow rates of respective parts according to a load.
FIG. 5 is a second flow rate characteristic diagram showing the relationship between the flow rates of the respective parts according to the load.
FIG. 6 is a characteristic diagram showing a relationship between a load and a target stoichiometric value during water recovery operation.
FIG. 7 is an explanatory diagram showing an example of a variation state of exhaust gas pressure when flooding occurs.
FIG. 8 is a flowchart showing an operation example of the control device in the embodiment.
FIG. 9 is a schematic configuration diagram of a main part of a second embodiment of a fuel cell system according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Fuel cell 101 Fuel supply apparatus 102 Fuel flow path 103 Circulation flow path 104 Exhaust gas flow path 105 Control valve 106 Compressor 107 Compressor 108 Shut-off valve 109 Booster circuit

Claims (5)

A fuel cell system comprising a circulation device for recirculating a part of the anode exhaust gas to the anode electrode of the fuel cell, and a control device for controlling the anode circulation flow rate by the circulation device,
The control device includes a load detection unit that detects a load of the fuel cell, a basic value setting unit that sets a basic value of an anode circulation flow rate based on the load, and a water that determines an implementation state of water recovery from the cathode electrode. A recovery determination unit, a correction unit that corrects the basic value of the anode circulation flow rate, and a flooding detection unit that detects flooding of the gas flow path ,
The control device corrects the basic value in the high flow rate direction when performing water recovery when the fuel cell is operated at a low load , and when the flooding is not detected for a reference time or more during the correction, the basic flow rate of the anode circulation flow is determined. A fuel cell system, wherein the value is corrected in a decreasing direction . The fuel cell system according to claim 1, wherein
The said control apparatus is provided with the temperature detection apparatus which detects the operating temperature of a fuel cell, and is a fuel cell system which correct | amends an anode circulation flow rate to a high flow direction, so that the said operating temperature is low. The fuel cell system according to claim 1 or 2,
The control device performs a flooding detection after correcting the anode circulation flow rate, and corrects the basic value in a high flow rate direction when the occurrence of flooding is detected . The fuel cell system according to any one of claims 1 to 3 ,
A fuel cell system comprising a booster circuit in parallel with the circulation device, and a control device configured to increase the anode circulation flow rate by the booster circuit when flooding is detected. The fuel cell system according to any one of claims 1 to 4 ,
The control device initially sets the correction amount of the anode circulation flow rate low, increases the anode circulation flow rate by a predetermined value every time flooding is detected, and sets the circulation device to always minimize the circulation flow rate. Fuel cell system to control.

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