JP2019145288A - Fuel cell system - Google Patents

Abstract

To accurately determine a lower limit value for keeping an on-off valve that controls the supply of a reaction gas to a fuel cell stack in the open state.SOLUTION: A fuel cell system includes an on-off valve, a controller, a current sensor, and a pressure sensor. The on-off valve is provided in a supply path of a reaction gas to a fuel cell stack. The opening/closing of the on-off valve is controlled by a drive current. The controller controls the drive current of the on-off valve according to the duty ratio. The current sensor measures the current flowing through the on-off valve. The pressure sensor is provided on the downstream side of the on-off valve of the supply path. The controller gradually decreases the duty ratio when the on-off valve is open, and determines whether the on-off valve is switched from open to closed on the basis of a change in the measured value of the pressure sensor. The controller determines a lower limit value of the current for holding the on-off valve in the open state on the basis of the measured value of the current sensor when the on-off valve is switched from open to closed.SELECTED DRAWING: Figure 2

Description

  The technology disclosed in this specification relates to a fuel cell system. In particular, the present invention relates to a fuel cell system having an on-off valve provided in a supply path for supplying a reaction gas to a fuel cell stack.

  The fuel cell system includes an on-off valve called an injector in a reaction gas supply path to the fuel cell stack. A normally closed type that opens with an energizing current (driving current) is used for the on-off valve so that gas does not leak when the current is interrupted. The controller controls the drive current of the on-off valve according to the duty ratio of the PWM signal. In order to suppress the power consumption of the fuel cell system itself, it is desirable that the open / close valve can be kept open with the minimum necessary current. In Patent Document 1, the duty ratio supplied to the on-off valve is gradually reduced in a state in which the on-off valve is opened, and the duty ratio when the on-off valve is closed is set to the lower limit value of the duty ratio for maintaining the open state. The technology is disclosed.

JP 2011-086392 A

  The relationship between the duty ratio supplied to the on-off valve and the drive current flowing through the on-off valve may vary depending on the voltage change of the power source of the drive current and the temporal change of the internal resistance of the on-off valve. Therefore, in the technique of Patent Document 1, the held duty ratio may deviate from the true lower limit value. The present specification provides a technique for accurately determining a lower limit value of control for keeping an on-off valve provided in a supply path for supplying a reaction gas to a fuel cell stack in an open state.

  The fuel cell system disclosed in this specification includes an on-off valve, a controller, a current sensor, and a pressure sensor. The on-off valve is provided in the reaction gas supply path to the fuel cell stack. The opening / closing of the on / off valve is controlled by a drive current. The controller controls the drive current to the on-off valve according to the duty ratio. The current sensor measures the current flowing through the on-off valve. The pressure sensor is provided on the downstream side of the on-off valve of the supply path. The controller gradually decreases the duty ratio when the on-off valve is open, and determines whether the on-off valve is switched from open to closed based on a change in the measured value of the pressure sensor. The controller determines a lower limit value of the current for maintaining the open state of the on-off valve based on the measured value of the current sensor when the on-off valve is switched from open to closed. The fuel cell system disclosed in this specification determines the lower limit value based on the current value, not the duty ratio when the on-off valve is switched from open to closed. Therefore, the controller can reliably maintain the open state of the on-off valve regardless of the state of the battery or the fluctuation of the internal resistance of the on-off valve by flowing a current equal to or higher than the determined lower limit value. . The controller may hold, for example, a value obtained by adding a predetermined margin to the measured value of the current sensor when the on-off valve is switched from open to closed as the lower limit value. Further, the controller may determine the lower limit value by a predetermined learning algorithm by combining the current value acquired this time and the current value acquired in the past.

  Details and further improvements of the technology disclosed in this specification will be described in the following “DETAILED DESCRIPTION”.

It is a block diagram of the fuel cell system of an Example. It is a flowchart of the lower limit determination process which a controller performs. It is a time chart of a lower limit determination process.

  A fuel cell system 2 according to an embodiment will be described with reference to the drawings. FIG. 1 shows a block diagram of the fuel cell system 2. The fuel cell system 2 is a device that is mounted on an automobile and supplies electric power to a traveling motor. In FIG. 1, a broken arrow line means a signal line.

  The fuel cell system 2 includes a fuel cell stack 3, a hydrogen tank 4, a supply path 5 that supplies hydrogen gas (reactive gas) from the hydrogen tank 4 to the fuel cell stack 3, an injector 6, and a controller 10. . The fuel cell stack 3 has a large number of power generation units called cells connected in series. The fuel cell stack 3 generates power when hydrogen is supplied to the fuel electrode (anode) and oxygen (air) is supplied to the air electrode (cathode). The fuel cell system 2 has a system for supplying oxygen (air), but the illustration of the oxygen supply system is omitted. Oxygen (air) remaining from the reaction in the fuel cell stack 3 is discharged to the outside through the air discharge path 24 and the muffler 25.

  Hydrogen gas is sent from the hydrogen tank 4 to the fuel electrode of the fuel cell stack 3 through the supply path 5. The supply path 5 is provided with an injector 6 and two pressure sensors 7 and 8. The pressure sensor 7 is attached to the supply path 5 on the downstream side of the injector 6, and the pressure sensor 8 is attached to the supply path 5 on the upstream side of the injector 6. The pressure sensor 7 (8) measures the internal pressure of the supply path 5 on the downstream side (upstream side) of the injector 6. The pressure measured by the pressure sensors 7 and 8 is sent to the controller 10.

  The injector 6 is a device that limits the pressure of the hydrogen gas in the hydrogen tank 4 to a pressure suitable for the fuel cell stack 3, but the structure is a simple on-off valve. Since the injector 6 is opened and closed by a solenoid valve, a DC power source 21 is connected. The injector 6 is a normally closed type so that hydrogen gas does not escape when power is cut off. The injector 6 opens when a current (drive current) larger than a predetermined current value is supplied, and remains closed at a drive current below the predetermined current value.

  A current sensor 9 is provided on the power line between the DC power source 21 and the injector 6. The current sensor 9 measures a drive current supplied from the DC power source 21 to the injector 6. The measured current value is sent to the controller 10.

  The controller 10 controls the entire fuel cell system 2 including the injector 6. In this embodiment, since attention is paid to the control of the injector 6, illustration and description of the control of devices other than the injector 6 are omitted. The controller 10 receives a command from the host controller 30 and controls the injector 6 and other devices. The controller 10 includes a memory 12 that stores programs and the like, and a CPU 13 (Central Processing Unit 13) that executes the programs stored in the memory 12. In addition to the program, the memory 12 also stores data such as a lower limit value of a current necessary for holding the injector 6 in an open state.

  As described above, the injector 6 opens when a driving current larger than a predetermined current value is supplied, and remains closed at a driving current smaller than the predetermined current value. The controller 10 supplies a PWM signal to the injector 6 and controls the drive current of the injector 6. A larger drive current flows as the duty ratio of the PWM signal increases.

  If the injector 6 is used for a long period of time, the electric resistance component of the injector becomes large, the current flowing even at the same duty ratio becomes small, and the injector may be closed. On the other hand, it is a waste of power consumption to keep flowing a current sufficiently larger than the switching current threshold to keep the injector 6 open. Therefore, the controller 10 executes a process of specifying (determining) the lower limit value of the current that keeps the injector 6 open. Such processing is executed at the time of parking purge. The parking purge is a process of discharging the residual gas from the fuel cell stack 3 and discharging moisture remaining in the muffler 25 to the outside while the vehicle is stopped. While the vehicle is traveling, the injector 6 is opened and closed quickly in order to precisely control the power generated by the fuel cell stack 3. On the other hand, at the time of parking purge, since the high-speed operation is not required when closing the injector 6, the controller 10 executes processing for determining the lower limit value of the current at the time of parking purge. Hereinafter, the lower limit value of the current necessary for maintaining the open state of the injector 6 is simply referred to as “lower limit value”.

  FIG. 2 shows a flowchart of processing for determining the lower limit value. The processing of FIG. 2 is executed when the controller 10 receives a command to close the injector 6 from the host controller 30 in the parking purge. Before the process of FIG. 2 is disclosed, a command to open the injector 6 is output from the host controller 30. The controller 10 supplies a PWM signal having a predetermined duty ratio to the injector 6 based on a command from the host controller 30 and keeps the injector 6 open.

  When receiving a command to close the injector 6 from the host controller 30, the controller 10 slightly lowers the duty ratio of the PWM signal supplied to the injector 6 from the duty ratio so far (step S2). For example, the controller 10 reduces the duty ratio by 3%. Since the duty ratio decreases, the drive current slightly decreases in the injector 6 that receives the PWM signal.

  Next, the controller 10 acquires the measurement data of the pressure sensors 7 and 8 and calculates the pressure difference between the upstream and downstream of the injector 6 (step S3). The controller 10 compares the pressure difference calculated in step S3 with a predetermined pressure difference threshold value (step S4). While the injector 6 is open, the pressure difference is small. When the injector 6 is closed, the pressure on the downstream side decreases and the pressure on the upstream side increases, so the pressure difference increases rapidly. The pressure difference threshold value is set to an intermediate value between the estimated value of the pressure difference generated when the injector 6 is closed and the estimated value of the pressure difference when the injector 6 is open. That is, if the determination in step S4 is NO, it means that the injector 6 is still open, and if the determination in step S4 is YES, it means that the injector 6 has been closed. By the process in step S4, the controller 0 determines (detects) whether the injector 6 is switched from open to closed.

  When the determination in step S4 is NO (that is, when the injector 6 is open), the controller 10 returns to the process in step S2 and further slightly decreases the duty ratio of the PWM signal. And the controller 10 repeats the process of step S3, S4. The controller 10 repeats the processes in steps S2 to S4 until the determination in step S4 becomes YES. Each time the processes in steps S2 to S4 are repeated, the duty ratio commanded to the injector 6 slightly decreases. That is, the controller 10 gradually decreases the duty ratio commanded to the injector 6.

  If determination of step S4 becomes YES, the controller 10 will acquire the drive current of the injector 6 at that time from the current sensor 9 (step S5). The current value at this time is a current value when the injector 6 switches from open to closed. That is, the current value at this time corresponds to the switching current threshold described above. A current value slightly higher than the current value (switching current threshold value) at this time corresponds to the lower limit value of the current necessary to hold the injector 6 in the open state.

  If the switching current threshold value can be specified, the controller 10 reduces the duty ratio to zero at once (step S5). Finally, the controller 10 determines a new lower limit value based on the acquired current value (switching current threshold value) and the data acquired in the past lower limit value determination process (step S6). In the process of step S6, the controller 10 specifically performs the following process to determine a new lower limit value. The controller 10 stores the current value acquired in step S5 in the memory 12 for the past 10 times of the lower limit determination process. The controller 10 calculates a moving average of the current value newly acquired this time and the current value for the past 10 times. The past lower limit value in the memory 12 is updated with a value obtained by adding a predetermined margin to the calculated moving average as a new lower limit value.

  With the above processing, the controller 10 updates the lower limit value of the current necessary for holding the injector 6 in the open state. Thereafter, when the controller 10 receives a command to open the injector 6 from the host controller 30, the controller 10 determines the duty ratio so that the drive current of the injector 6 becomes equal to or higher than the lower limit value. Thus, the fuel cell system 2 can reliably hold the injector 6 in an open state without consuming unnecessary power.

  The time chart of the parking purge process when determining the lower limit value will be described with reference to FIG. It is assumed that the parking purge process has already been notified from the host controller 30 to the controller 10. FIG. 3 (1) shows a command that the host controller 30 gives to the controller 10. The host controller 30 outputs a command to open the injector 6 at time t1, and outputs a command to close the injector 6 to end the parking purge process at time t4.

  FIG. 3B shows the duty ratio of the PWM signal that the controller 10 gives to the injector 6. FIG. 3 (3) shows the drive current of the injector 6. FIG. 3 (4) shows the pressure difference between the upstream and downstream of the injector 6. Before time t1, since the injector 6 is closed, the pressure difference is large (location indicated by the arrow P1 in FIG. 3).

  When an open command is received from the host controller 30 at time t1, the controller 10 first sends a PWM signal with a duty ratio of 100% to the injector 6 (the location indicated by the arrow P2 in FIG. 3). Then, the maximum drive current I1 flows through the injector 6 (the position indicated by the arrow P3 in FIG. 3), and the injector 6 is immediately switched from the closed state to the open state. Since the injector 6 is switched to the open state, the pressure difference is rapidly reduced (location indicated by the arrow P4 in FIG. 3). On the other hand, after instructing the duty ratio of 100% for a certain time, the controller 10 adjusts the duty ratio so that the drive current maintains the lower limit value I2 at that time (locations indicated by arrows P5 and P6 in FIG. 3). The lower limit value I2 is the lower limit value determined in the previous process of FIG. Since the injector 6 is open while the drive current of the injector 6 is held at the lower limit value I2, the pressure difference remains small (location indicated by the arrow P7 in FIG. 3).

  When receiving a command to close the injector 6 from the host controller 30 at time t4, the controller 10 gradually decreases the duty ratio (location indicated by an arrow P8 in FIG. 3). As the duty ratio decreases, the drive current of the injector 6 also gradually decreases (indicated by an arrow P9 in FIG. 3).

  The injector 6 switches from open to closed when the magnitude of the drive current falls below the current required to keep the solenoid valve of the injector 6 open. When the injector 6 is switched from open to closed, the pressure difference suddenly increases (location indicated by the arrow P10 in FIG. 3). The controller 10 acquires the value of the drive current (current value I3) when the pressure difference suddenly increases, and determines a new lower limit value by the process of step S6 in FIG. The current value I3 corresponds to the switching current threshold described above.

  Advantages of the lower limit determination process executed by the fuel cell system 2 of the embodiment will be given. The controller 10 monitors the drive current of the injector 6, identifies the time point when the injector 6 is estimated to be closed from the pressure difference, and determines the lower limit value of the current based on the drive current at that time point. In general, there may be a relationship between the duty ratio given to the injector 6 and the drive current flowing depending on the duty ratio. The cause of the shift is the voltage fluctuation of the power source of the drive current (DC power source 21 in FIG. 1), the fluctuation of the internal resistance of the solenoid valve of the injector 6, and the like. That is, the drive current may change even with the same duty ratio. Therefore, if the lower limit value that keeps the injector 6 open is determined by the duty ratio, it may not be accurate. In the fuel cell system 2 of the embodiment, the lower limit value of the control necessary for maintaining the open state of the injector 6 is determined by the magnitude of the drive current. Therefore, the above-described problem of the duty ratio does not occur.

  Points to be noted regarding the technology described in the embodiments will be described. In the lower limit determination processing of the example, the switching current threshold is specified using the moving average of the current value when the pressure difference suddenly changes and the past current value, and a new lower limit value is determined based on that value. The controller 10 may determine a new lower limit value with another algorithm. For example, the controller 10 may determine a new lower limit value using a learning algorithm using the latest current value and the past current value. Alternatively, the controller 10 may simply determine a value obtained by adding a predetermined margin to the current value acquired in step S5 as a new lower limit value. The controller 10 may determine a new lower limit value based on the current value when the pressure difference changes suddenly while gradually decreasing the duty ratio.

  In the flowchart of FIG. 2, the controller 10 detects the switching of the injector 6 from the open state to the closed state based on the difference (pressure difference) between the upstream pressure and the downstream pressure of the injector 6. The controller 10 may detect a change from the open state to the closed state from a change in pressure on the downstream side of the injector 6. This is because when the injector 6 is switched from open to closed, the downstream pressure rapidly decreases.

  The injector 6 according to the embodiment corresponds to an example of an on-off valve. The technology disclosed in this specification can be applied to the determination of the lower limit value of the on-off valve provided in the supply path for supplying the reaction gas to the fuel cell stack. That is, the technique disclosed in this specification may be applied to the determination of the lower limit value of the on-off valve provided in the supply path for supplying oxygen gas (air) to the fuel cell stack.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Fuel cell system 3: Fuel cell stack 4: Hydrogen tank 5: Supply path 6: Injector 7, 8: Pressure sensor 9: Current sensor 10: Controller 12: Memory 13: CPU
21: DC power supply 24: Air discharge path 25: Muffler 30: Host controller

Claims (1)

An on-off valve that is provided in a reaction gas supply path to the fuel cell stack and is current-controlled;
A controller that controls the drive current of the on-off valve according to a duty ratio;
A current sensor for measuring a current flowing through the on-off valve;
A pressure sensor provided downstream of the on-off valve in the supply path;
With
The controller gradually decreases the duty ratio when the on-off valve is open, determines whether the on-off valve is switched from open to closed based on a change in a measured value of the pressure sensor, and A fuel cell system that determines a lower limit value of a current for maintaining an open state of the on-off valve based on a measured value of the current sensor when the valve is switched from open to closed.

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