JP5800279B2 - Fuel cell system and control method thereof - Google Patents

Description

  The present invention relates to a fuel cell system and a control method thereof. More specifically, the present invention relates to an improvement in control technology in a fuel cell system.

  When starting the fuel cell, by causing at least one of the fuel gas supplied to the anode and the oxidizing gas supplied to the cathode to be in a deficient state, increasing the overvoltage of a part of the electrode to generate further heat, A rapid warm-up technique for increasing the temperature of a fuel cell is disclosed. When performing such rapid warm-up, it is necessary to lower the cell voltage of the fuel cell to a preset threshold value (allowable value).

  However, conventionally, there is a case where current limitation is not performed until the cell voltage falls below an allowable value. If you try to limit the current after the cell voltage falls below the allowable value in this way, the cell voltage will fall significantly below the allowable value because the current voltage cannot catch up due to the rapid decrease in the cell voltage during rapid warm-up. There was a problem.

  Therefore, as a technique for solving such a problem, when the lowest cell voltage detected by the cell monitor has converged continuously in the vicinity of the target value for a certain period of time, the lowest cell voltage target value is reduced to a predetermined width. A technique of updating is disclosed (for example, see Patent Document 1). According to such a technique, when the relationship between the detected cell voltage and the minimum target voltage satisfies a predetermined condition (for example, when the cell voltage converges continuously in the vicinity of the minimum target voltage for a certain period of time, The minimum target voltage is updated step by step when the value is continuously high for a certain time away from the vicinity of the minimum target voltage. When the current is limited, the minimum cell voltage target value updated in this way is used. Therefore, the cell voltage and the minimum target voltage are largely separated from each other, and the cell voltage is not controlled completely and the minimum cell voltage is reached. It is possible to prevent the problem that the voltage is greatly reduced.

JP 2009-158399 A

  However, in the control technique as described above, since cell voltage monitoring is always performed (for example, always during operation of the fuel cell vehicle), the power consumption of the cell monitor is large and wasteful power consumption occurs.

  Therefore, an object of the present invention is to provide a fuel cell system and a control method therefor that can suppress power consumption in a cell monitor while avoiding a significant decrease in cell voltage.

  In order to solve this problem, the present inventor has made various studies. For example, in a fuel cell vehicle, during low load operation such as idling, low speed driving, regenerative braking, etc., fuel cell power generation is temporarily stopped to improve fuel consumption, and power storage means such as batteries and capacitors Some carry out “intermittent operation” for supplying power to the auxiliary machinery (vehicle motor, etc.). When the cell monitor is suspended during the intermittent operation, it is a conventional method to restart the power generation (operation) of the fuel cell and restart the cell monitor after the intermittent operation ends. However, in general, it takes a predetermined time to restart the cell monitor. In the unlikely event that the cell voltage of the fuel cell drops during this cell monitor restart, it is not possible to detect this, so it is not possible to deal with output restrictions, etc., and in some cases damage to the membrane member (such as hole opening) May lead to In order not to fall into such a situation, conventionally, the cell monitor could not be stopped during intermittent operation.

  The present inventor who has repeatedly studied paying attention to the above points and further focusing on the fact that the cell monitor is activated after the end of the intermittent operation is mentioned in the prior art even though the cell monitor is being activated. I came up with an idea that led to the solution of this problem. The present invention is based on such an idea, and during the intermittent operation in which the fuel cell is temporarily suspended at the time of low load of the fuel cell, the cell monitor for measuring the cell voltage of the fuel cell is stopped, and after the intermittent operation is completed. When starting the cell monitor, the output of the fuel cell is limited.

  In the fuel cell system according to the present invention, since the cell monitor is stopped during the intermittent operation, the power consumption of the cell monitor can be suppressed as compared with the case where the cell voltage is constantly monitored. Moreover, since the output (power generation) of the fuel cell is restricted when the cell monitor is restarted after the end of the intermittent operation, it is possible to avoid a significant drop in the cell voltage.

  In the fuel cell system described above, when a predetermined threshold is set as the intermittent termination threshold, and the system required power indicating the output required for the fuel cell from the fuel cell system exceeds the intermittent termination threshold. It is preferable to end the intermittent operation.

Further, in the fuel cell system according to the present invention, the cell monitor activation threshold value is a threshold value for commanding the start of the cell monitor, it is preferable to change to a value smaller than the intermittent end threshold. In this case, the timing for instructing activation of the cell monitor is advanced, and when the intermittent operation ends, the activation of the cell monitor can be completed, so that the output restriction can be reduced or eliminated.

  In the fuel cell system according to the present invention, it is preferable that the output restriction of the fuel cell is relaxed within a range in which the cell voltage does not decrease according to the temperature of the fuel cell. Alternatively, it is also preferable to relax the output limit of the fuel cell in a range where the cell voltage does not decrease according to the impedance of the fuel cell.

  In the fuel cell control method according to the present invention, the cell monitor that measures the cell voltage of the fuel cell is stopped during the intermittent operation in which the fuel cell is temporarily stopped at a low load of the fuel cell. When starting the cell monitor, the output of the fuel cell is limited.

  ADVANTAGE OF THE INVENTION According to this invention, the power consumption in a cell monitor can be suppressed, avoiding the significant fall of a cell voltage.

It is a figure which shows the structural example of the fuel cell system concerning this invention. It is a flowchart which shows one Embodiment of this invention. It is a figure which shows the time-sequential process and operation example, such as operation | movement of each part of the system at the time of controlling according to the flowchart shown in FIG. 2, a control signal, and an output. It is a graph explaining the method of changing the degree of output restriction | limiting with the temperature of a fuel cell. It is a graph explaining the method of changing the degree of output restriction by the impedance of a fuel cell. It is a figure which shows the time-sequential process and operation example when the timing which issues the starting command to a cell monitor is made earlier.

  Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings. Hereinafter, as an example, a case where the present invention is applied to a fuel cell scheduled to be mounted on a fuel cell vehicle or a fuel cell system including the fuel cell will be described as an example. There is no limit.

  1 to 5 show an embodiment of a fuel cell system according to the present invention. The fuel cell system 100 includes a cell (not shown) that generates electricity by electrochemically reacting a fuel gas and an oxidizing gas, a cell stack (not shown) formed by stacking the cells, and a supply flow rate of the fuel gas and the oxidizing gas. And a control device 700 as control means for controlling. In the following, the overall configuration of the fuel cell system 100 will be described first, and then the operation of the cell monitor and the like during and after intermittent operation will be described.

  FIG. 1 shows a schematic configuration of a fuel cell system 100 in the present embodiment. As shown in the figure, a fuel cell system 100 includes a fuel cell 1, an oxidizing gas supply / discharge system (hereinafter also referred to as an oxidizing gas piping system) 300 for supplying air (oxygen) as an oxidizing gas to the fuel cell 1, a fuel A fuel gas supply / discharge system (hereinafter also referred to as a fuel gas piping system) 400 that supplies hydrogen as a gas to the fuel cell 1, a refrigerant piping system 500 that supplies the refrigerant to the fuel cell 1 and cools the fuel cell 1, A power system 600 that charges and discharges system power and a control device 700 that performs overall control of the entire system are provided.

  The fuel cell 1 is composed of, for example, a solid polymer electrolyte type and has a stack structure in which a large number of cells (single cells) are stacked. Each cell has an air electrode on one surface of an electrolyte made of an ion exchange membrane, a fuel electrode on the other surface, and a pair of separators 20 so as to sandwich the air electrode and the fuel electrode from both sides. ing. Fuel gas is supplied to the fuel gas flow path of one separator 20, and oxidizing gas is supplied to the oxidizing gas flow path of the other separator 20, and the fuel cell 1 generates electric power by this gas supply.

  The oxidizing gas piping system 300 has a supply path 111 through which the oxidizing gas supplied to the fuel cell 1 flows, and a discharge path 112 through which the oxidizing off gas discharged from the fuel cell 1 flows. The supply path 111 is provided with a compressor 114 that takes in the oxidizing gas via the filter 113, and a humidifier 115 that humidifies the oxidizing gas fed by the compressor 114. The oxidizing off-gas flowing through the discharge path 112 is subjected to moisture exchange by the humidifier 115 through the back pressure regulating valve 116, and is finally exhausted into the atmosphere outside the system as exhaust gas. The compressor 114 takes in the oxidizing gas in the atmosphere by driving the motor 114a.

  The fuel gas piping system 400 includes a hydrogen supply source 121, a supply path 122 through which hydrogen gas supplied from the hydrogen supply source 121 to the fuel cell 1 flows, and a supply path for supplying hydrogen offgas (fuel offgas) discharged from the fuel cell 1. A circulation path 123 for returning to the confluence point A of 122, a pump 124 that pumps the hydrogen off gas in the circulation path 123 to the supply path 122, and a discharge path 125 that is branched and connected to the circulation path 123. .

  The hydrogen supply source 121 is composed of, for example, a high-pressure tank or a hydrogen storage alloy, and is configured to be able to store, for example, 35 MPa or 70 MPa of hydrogen gas. When the main valve 126 of the hydrogen supply source 121 is opened, hydrogen gas flows out to the supply path 122. The hydrogen gas is finally depressurized to, for example, about 200 kPa by the pressure regulating valve 127 and other pressure reducing valves and supplied to the fuel cell 1.

  A shutoff valve 128 and a pressure sensor 129 for detecting the pressure of hydrogen gas in the supply path 122 are provided on the upstream side of the confluence point A of the supply path 122. The hydrogen gas circulation system is configured by sequentially communicating a flow path downstream of the confluence point A of the supply path 122, a fuel gas flow path formed in the separator of the fuel cell 1, and the circulation path 123. Yes. The hydrogen pump 124 circulates and supplies the hydrogen gas in the circulation system to the fuel cell 1 by driving the motor 124a. Reference numeral 130 denotes a temperature sensor that detects the temperature of the fuel cell 1 or hydrogen gas.

  The circulation path 123 is provided with a pressure sensor 132 that detects the pressure of hydrogen offgas (fuel offgas). The discharge path 125 is provided with a purge valve 133 that is a shutoff valve. By appropriately opening the purge valve 133 when the fuel cell system 100 is in operation, impurities in the hydrogen off gas are discharged together with the hydrogen off gas to a hydrogen diluter (not shown). By opening the purge valve 133, the concentration of impurities in the hydrogen off-gas in the circulation path 123 decreases, and the concentration of hydrogen in the hydrogen off-gas circulated increases.

  The refrigerant piping system 500 includes a refrigerant circulation channel 141 communicating with a cooling channel in the fuel cell 1, a cooling pump 142 provided in the refrigerant circulation channel 141, and a radiator that cools the refrigerant discharged from the fuel cell 1. 143, a bypass flow path 144 that bypasses the radiator 143, and a three-way valve (switching valve) 145 that sets the flow of cooling water to the radiator 143 and the bypass flow path 144. The cooling pump 142 circulates and supplies the refrigerant in the refrigerant circulation channel 141 to the fuel cell 1 by driving the motor 142a.

  The power system 600 includes a high-voltage DC / DC converter 161, a battery (power storage means) 162, a traction inverter 163, a traction motor 164, and various auxiliary inverters 165, 166, and 167. The high-voltage DC / DC converter 161 is a direct-current voltage converter that adjusts the direct-current voltage input from the battery 162 and outputs it to the traction inverter 163 side, and the direct-current input from the fuel cell 1 or the traction motor 164. And a function of adjusting the voltage and outputting it to the battery 162. The charge / discharge of the battery 162 is realized by these functions of the high-voltage DC / DC converter 161. Further, the output voltage of the fuel cell 1 is controlled by the high voltage DC / DC converter 161.

  The battery 162 is configured such that battery cells are stacked so that a constant high voltage is used as a terminal voltage, and surplus power can be charged or supplementary power can be supplied under the control of a battery computer (not shown). The traction inverter 163 converts a direct current into a three-phase alternating current and supplies it to the traction motor 164. The traction motor 164 is, for example, a three-phase AC motor, and constitutes a main power source of, for example, a vehicle on which the fuel cell system 100 is mounted.

  Auxiliary machine inverters 165, 166, and 167 are motor control devices that control driving of corresponding motors 114a, 124a, and 142a, respectively. Auxiliary machine inverters 165, 166, and 167 convert a direct current into a three-phase alternating current and supply it to motors 114a, 124a, and 142a, respectively. Auxiliary machine inverters 165, 166, and 167 are, for example, pulse width modulation type PWM inverters that convert a DC voltage output from fuel cell 1 or battery 162 into a three-phase AC voltage in accordance with a control command from control device 700. The rotational torque generated by each motor 114a, 124a, 142a is controlled.

  The control device 700 is configured as a microcomputer having a CPU, a ROM, and a RAM inside. The CPU executes a desired calculation according to the control program, and performs various processes and controls such as a thawing control of the pump 124. The ROM stores control programs and control data processed by the CPU. The RAM is mainly used as various work areas for control processing. The control device 700 inputs detection signals such as various pressure sensors, temperature sensors, and outside air temperature sensors used in the gas system (300, 400) and the refrigerant piping system 500, and outputs control signals to each component.

  The cell monitor 800 is a voltage sensor that is used for measuring a voltage (cell voltage) in a cell and measuring a power generation state (for example, fluctuation of the cell voltage during power generation) (see FIG. 1). Based on the measurement result by the cell monitor 800, the cell voltage of the fuel cell 1 can be monitored.

  Next, control and operation of the cell monitor and the like during and before intermittent operation will be described (see FIG. 2 and the like).

  In the fuel cell system 100 of the present embodiment, the cell voltage monitoring by the cell monitor 800 is suspended during the intermittent operation of the fuel cell 1, thereby reducing the power consumption of the cell monitor 800. In addition, when the intermittent operation of the fuel cell 1 is terminated and a transition is made to normal power generation, the power generation of the fuel cell 1 is restricted until the cell monitor 800 is completely restarted, thereby suppressing a decrease in cell voltage. To do. Hereinafter, a specific control example will be described using a flowchart (see FIG. 2).

  First, it is determined whether or not the power required by the fuel cell system 100 is below the intermittent termination threshold T1 (step SP1). The intermittent end threshold value T1 is set to end the intermittent operation when the gradually increasing system required power (output) exceeds the threshold value (see FIG. 3). Here, if the required power is below the intermittent end threshold value T1 (YES in step SP1), the intermittent operation is continued and the cell monitor 800 is kept in a resting state (step SP5). On the other hand, if the required power is not lower than the intermittent end threshold value T1 (NO in step SP1), processing for terminating the intermittent operation is performed, and a command to start the cell monitor 800 is issued from the control device 700 (step SP2).

  After the start command of the cell monitor 800, it is determined whether or not the cell monitor 800 is completed (step SP3). If completed (YES in step SP3), the output restriction of the fuel cell 1 is released (step SP6). On the other hand, if not completed (NO in step SP3), the output of the fuel cell 1 is limited (step SP4), and the process returns to step SP1.

  Subsequently, an example (time-series processing / operation example of operation of each part, control signal, output, etc.) in the case of controlling according to the above flowchart will be shown (see FIG. 3). In addition, the arrow in FIG. 3 has shown the flow or relationship of control. As shown in the figure, in the present embodiment, when the system required power becomes equal to or higher than the intermittent termination threshold T1, the intermittent operation of the fuel cell 1 is terminated and a start command for the cell monitor 80 is issued (FIG. 3 (A) to ( C)). Further, when the intermittent operation of the fuel cell 1 is completed, the compressor 114 is operated (see FIG. 3E). Further, as the air flow rate to the fuel cell 1 increases, the upper limit of the FC (fuel cell) output increases (see FIGS. 3F and 3H). Here, in this embodiment, as long as the start of the cell monitor 800 is not completed, the output from the fuel cell 1 is not permitted even if the FC output (P) is greater than 0, and the output is limited to reduce the voltage. (See FIGS. 3F to 3H).

  Further, in this embodiment, the battery power (see FIG. 3I) representing the charge / discharge state of the battery 162 is discharged at Wout or less. If the system required power is too large even with Wout, the required power may not be satisfied.

  Here, in the present embodiment, as illustrated in FIG. 3, the FC output restriction degree is changed depending on the state of the fuel cell 1 in performing the FC output restriction in the cell monitor state. That is, even if the start of the cell monitor 800 is incomplete, depending on the state of the fuel cell 1, the FC output is permitted within a range in which it is possible to ensure that the cell voltage does not decrease. As a result, the opportunity to limit the FC output can be reduced, and finally the drivability (drivability) can be improved.

  Thus, for example, there are the following methods for changing the degree of restriction of the FC output depending on the state of the fuel cell 1. That is, first, there is a method of changing the FC output limiting rate according to the FC temperature (see FIG. 4). Here, the output restriction is relaxed within a range where the fuel cell 1 is sufficiently warmed up and the cell voltage does not decrease. There is also a method of changing the FC output limiting rate according to the impedance (see FIG. 5). Here, the output restriction is eased within a range where the water balance (water balance) in the fuel cell 1 is good. The FC output restriction rate determined by each of these methods is used as a final restriction value by multiplying “FC output restriction from air flow rate” (see FIG. 3F).

  As described so far, in the fuel cell system 100 according to the present invention, since the cell monitor 800 is stopped during the intermittent operation, the power consumption of the cell monitor can be suppressed as compared with the case where the cell voltage is constantly monitored. In addition, after the intermittent operation is completed, when the cell monitor 800 is started (for example, until the restart of the cell monitor 800 is completed), the power generation of the fuel cell 1 is limited, and the power from the battery 162 is used. Thus, it is possible to avoid the cell voltage from greatly decreasing.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in the present embodiment, a method of changing the degree of FC output restriction depending on the state of the fuel cell 1 is exemplified. However, in addition to this, for example, when performing FC output restriction according to the cell monitor state (see FIG. 3), the cell monitor 800 The timing for issuing the start command may be made earlier (see FIG. 6). In such a case, when the intermittent operation of the fuel cell 1 is completed, the start of the cell monitor 800 is completed (see Δt in FIGS. 6B and 6C), thereby reducing the FC output limit. Or it can be made unnecessary. As a result, the opportunity to limit the FC output can be reduced and linked to improved drivability.

  As a specific method, for example, the threshold of the system required power (cell monitor activation threshold T2) for issuing the activation command of the cell monitor 800 can be set to a value smaller than the intermittent termination threshold T1. In such a case, a start command for the cell monitor 800 may be issued when the system required power exceeds this threshold.

  The present invention is suitably applied to a fuel cell system such as a fuel cell vehicle.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 100 ... Fuel cell system, 800 ... Cell monitor, T1 ... Intermittent end threshold value, T2 ... Cell monitor starting threshold value

Claims (6)

During intermittent operation of the fuel cell, the cell monitor that measures the cell voltage of the fuel cell is stopped,
A fuel cell system that limits the output of the fuel cell when the cell monitor is activated after the intermittent operation ends.   A predetermined threshold is set as an intermittent end threshold, and the intermittent operation is terminated when a system required power indicating an output required for the fuel cell from the fuel cell system exceeds the intermittent end threshold; The fuel cell system according to claim 1. The cell monitor activation threshold value is a threshold value for commanding the start of the cell monitor is changed to a value smaller than the previous SL intermittent end threshold, the fuel cell system according to claim 2.   4. The fuel cell system according to claim 1, wherein the output restriction of the fuel cell is relaxed within a range in which the cell voltage does not decrease according to the temperature of the fuel cell. 5.   4. The fuel cell system according to claim 1, wherein the output restriction of the fuel cell is relaxed within a range in which the cell voltage does not decrease according to the impedance of the fuel cell. 5. During intermittent operation of the fuel cell, the cell monitor that measures the cell voltage of the fuel cell is stopped,
A control method for a fuel cell system, wherein the output of the fuel cell is limited when the cell monitor is activated after the intermittent operation ends.

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