JP5381427B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system that outputs electric energy from a fuel cell.

  Fuel cells are attracting attention as energy sources, and various fuel cell vehicles equipped with fuel cells have been proposed. In this fuel cell, fuel gas (usually hydrogen gas) and oxidizing gas (usually air) are supplied to the fuel cell and reacted inside the fuel cell to obtain electric power. Here, in each cell, there is a member called a membrane / electrode assembly (MEA) in which a fuel electrode (negative electrode), a solid polymer membrane (electrolyte), and an air electrode (positive electrode) are bonded and integrated. Is provided. And in this MEA, it is necessary to maintain moderate humidity.

  On the other hand, the output of the fuel cell varies depending on the driving torque of the vehicle. Therefore, the operating state of the fuel cell varies greatly depending on the traveling state of the vehicle. As described above, air is usually used as the oxidizing gas, and is supplied to each fuel cell by an air compressor, for example.

JP 2007-157586 A JP 2004-192826 A JP 2007-123169 A JP 2002-203583 A JP 2008-103173 A

  Here, if the supply amount to the fuel cell by the air compressor is too large, the MEA dries and deteriorates, and there is a demand to prevent this.

The present invention is the fuel cell system for driving a motor using electrical energy from the fuel cell, a blower pump for supplying an oxygen-containing gas to the fuel cell, a motor for the blower pump for driving the blower pump, the blower A blower pump inverter for controlling power supply to the pump motor; a motor inverter for controlling power supply to the motor; an impedance measuring means for measuring impedance of the fuel cell; the blower pump inverter; A control unit that controls a motor inverter, and the control unit generates a negative torque command as a drive command for the blower pump motor and reduces the impedance when the flow rate of the blower pump is decreased. If the impedance measured by the means is below the specified value, The air compressor regenerative power is calculated in consideration of brake cooperative regenerative power that can be generated by regenerative braking of the motor, and when the impedance measured by the impedance measuring means exceeds a predetermined value, the regenerative power of the motor at that time is calculated. The air compressor regenerative power is calculated without considering the brake cooperative regenerative power that can be generated by braking, and the generated negative torque command is limited within the calculated regenerative power range. An inverter is controlled to regeneratively brake the blower pump motor.

  Furthermore, it is preferable that the battery has a battery that can be charged based on the output of the fuel cell, and the control unit charges the battery with electric power obtained by regenerative braking of the blower pump motor.

  Further, it is preferable that the control unit controls the electric power obtained by the regenerative braking so as not to exceed the chargeable electric power of the battery.

  Furthermore, it has a converter for supplying electric power obtained by regenerative braking to the battery, and when the passing power of the converter is limited, the control unit regenerative braking so that the passing power is within the limit. Is preferably controlled.

  As described above, according to the present invention, when the air flow rate of the blower pump to the fuel cell is reduced, the blower pump inverter is controlled to regeneratively brake the blower pump motor. As a result, the amount of air blown from the blower pump can be reduced at an early stage, and adverse effects on the fuel cell due to unnecessary air blowing can be prevented.

It is a figure which shows the whole structure of a fuel cell system. It is a figure which shows the condition of the conventional ventilation control. It is a figure which shows the condition of the ventilation control by regeneration of an air compressor. It is a figure which shows the state of the restriction | limiting by the battery chargeable power. It is a figure which shows the state of the restriction | limiting by the converter passing power. It is a figure which shows the state of the restriction | limiting by the air compressor regeneration possible power. It is a figure which shows the example of air compressor regeneration possible power calculation. It is a figure which shows the other example of air compressor regeneration possible power calculation. It is a figure which shows an example of the flowchart of a process of air compressor regeneration possible power calculation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a fuel cell system 100 according to the present embodiment. The fuel cell system 100 shown in the present embodiment is applied to a fuel cell vehicle or the like.

  This fuel cell system has a fuel cell (FC) 10. The fuel cell 10 has a stack structure in which a plurality of fuel cells are stacked in series. In this example, each cell is a solid polymer electrolyte fuel cell and includes an MEA.

  The air (air) supply system to the fuel cell 10 is provided with an air compressor 12 as a blower pump, and the air from the air compressor 12 passes through the intercooler 14 and the humidifier 16 to the cathode (oxygen electrode) of the fuel cell 10. Supplied to the side. Here, the intercooler 14 cools the air with cooling water, and the humidifier 16 dehumidifies the exhaust gas of the air system of the fuel cell 10 to humidify the supply air. Further, hydrogen gas from the hydrogen gas supply source 18 is supplied to the anode (fuel electrode) side of the fuel cell 10. Note that most of the exhaust gas from the fuel cell 10 on the hydrogen gas side is circulated again to the fuel cell 10 and part of it is discharged as exhaust gas.

  An air compressor inverter 20 is connected to the output (DC power output) of the fuel cell 10, and the output of the inverter 20 is supplied to the air compressor motor 22. Therefore, in this example, the air compressor 12 is driven by the output of the fuel cell 10.

  A battery 26 is connected to the output of the fuel cell 10 via a converter 24. The battery 26 is a rechargeable secondary battery such as nickel metal hydride or lithium ion, and supplies power to various on-vehicle devices. Further, the converter 24 functions as a voltage converter (DC / DC converter) that converts the output of the fuel cell 10 into the voltage of the battery 26, and thus the DC voltage of the output of the fuel cell 10 is controlled by the converter 24. . That is, the output current of the fuel cell 10 is controlled by the amount of air supplied from the air compressor 12 (the amount of blown air), and the output voltage is controlled by the converter 24 to control the operating state of the fuel cell 10. Note that the output of the battery 26 may be supplied to the inverter 20 to drive the air compressor motor 22.

  A drive motor 30 is connected to the output of the fuel cell 10 via an inverter 28. The drive motor 30 is for driving a vehicle, and the wheels are rotated by the output of the drive motor 30 to drive the vehicle.

  The control unit 32 determines the output torque of the drive motor 30, the output torque of the air compressor motor 22, the target value of the charge / discharge amount of the battery 26, and the like from various information such as the accelerator depression amount, the brake depression amount, and the vehicle speed. The drive of inverters 28 and 20 and converter 24 is controlled. For such control, the control unit 32 is also supplied with information such as the rotation information of the drive motor 30 and the air compressor motor 22 and the state of charge (SOC) of the battery 26.

  The control unit 32 determines the output current and output voltage of the fuel cell 10 from the output torque of the drive motor 30 and the output torque of the air compressor motor 22 and controls the inverters 28 and 20 and the converter 24. Here, the negative torque corresponding to the engine brake in the drive motor 30 is performed by regenerative braking under the control of the inverter 28, and the generated power is charged to the battery 26 via the converter 24. Further, when the brake is depressed, the drive motor 30 is regeneratively braked to perform a predetermined brake assist. Further, as described above, the output voltage of the fuel cell 10 is controlled by controlling the converter 24.

  In this embodiment, when the rotation speed (air flow rate) of the air compressor 12 is decreased, the control unit 32 controls the drive of the inverter 20 using the output torque command of the air compressor motor 22 as a negative torque command. To do. As a result, the air compressor motor 22 is regeneratively braked and can reduce the rotational speed at an early stage. The electric power obtained by this regenerative braking is charged to the battery 26 via the converter 24. In the normal case, the output torque of the air compressor motor 22 is controlled to 0 when the air flow rate of the air compressor 12 is reduced. However, in such control, there is a problem that it takes time until the amount of blown air actually decreases, and the MEA in the cell of the fuel cell 10 is dried due to this.

  In the present embodiment, since the control unit 32 brakes the air compressor motor 22 by regenerative braking, it is possible to effectively prevent the MEA from drying. In particular, since the control unit 32 uses a method of controlling the inverter 20 with the target output torque of the air compressor motor 22 as a negative torque, this control can be achieved without requiring a new device. . And since the obtained electric power can be collect | recovered by the battery 26, it becomes possible to reduce power consumption. The regenerative braking of the air compressor motor 22 is also simply referred to as regenerative braking of the air compressor.

  Here, the battery 26 cannot be charged any more when its SOC is high. For example, when the SOC exceeds 90%, it is better not to charge the battery 26 any more. The chargeable capacity of the battery 26 varies depending on the temperature. Therefore, the control unit 32 monitors the SOC and temperature of the battery 26, and when the chargeable capacity determined by the SOC and temperature (having a normal map) is equal to or less than a predetermined value, the control unit 32 Regenerative braking control of the motor 22 is prohibited.

  Furthermore, in consideration of vehicle running performance (drivability), regenerative braking equivalent to engine braking is a necessary control. Therefore, it is also preferable to set the upper limit SOC of the battery 26 to a value that takes this into account (for example, about 80%) and give priority to the regenerative braking of the drive motor 30. Furthermore, when regenerative braking of the drive motor 30 is being performed, it is also preferable to prohibit regenerative braking of the air compressor motor 22.

  Furthermore, converter 24 has an upper limit on the passing power. That is, when the temperature of the converter 24 becomes higher than a predetermined value, in order to prevent the power transistor from being damaged, it is necessary to limit the passing power and suppress the temperature rise. Therefore, when there is a possibility that the passing power of the converter 24 exceeds the limit value, it is preferable that the control unit 32 prohibits the regenerative braking of the air compressor motor 22.

  FIG. 2 shows the rotational speed of the conventional air compressor motor 22, the command torque, the amount of air blown from the air compressor 12, and the output power of the battery 26. In other words, it is assumed that air blow to the fuel cell 10 is stopped at a certain time. In this case, the command torque to the air compressor motor 22 becomes zero at that time. Accordingly, the output of the battery 26 is also zero. On the other hand, the number of rotations of the air compressor motor 22 only decreases gradually, and the amount of air also decreases gradually.

  FIG. 3 shows a case where regenerative braking is performed on the air compressor motor 22 according to the present embodiment. In this case, when the air compressor 12 is stopped, the command torque to the air compressor motor 22 becomes negative. As a result, the electric power generated by the air compressor motor 22 is supplied to the battery 26 via the inverter 20, and the battery 26 is charged. Therefore, the output power of the battery 26 becomes negative. Then, the rotational speed of the air compressor motor 22 and the amount of air blown by the air compressor 12 are quickly reduced to zero.

  FIG. 4 shows a case where the battery chargeable power is limited. In this case, the battery power is suppressed to a value close to 0 compared to the case of FIG. That is, the amount of charge is reduced. For this reason, the command torque is suppressed to the lower limit torque calculated from the battery chargeable power, and the time when the air flow rate becomes 0 is slightly delayed compared to the case of FIG.

  FIG. 5 shows a case where the power passing through the converter 24 is limited. In this case, the amount of charge of the battery 26 is limited to a relatively small value corresponding to the limit power by the limit power of the converter 24. Therefore, the command torque to the air compressor motor 22 is also limited to a negative magnitude, and the decrease in the air flow rate is delayed as compared with FIG.

  Furthermore, it is preferable to control the regenerative braking of the air compressor 12 by adopting the lower one of the battery chargeable power shown in FIG. 4 and the limit power of the converter 24 of FIG.

  Here, in the above-described example, the case where the operation of the air compressor 12 is stopped has been described, but regenerative braking may be performed not only when the operation is stopped, but also when the amount of blown air is reduced.

  When the operation of the air compressor 12 is stopped, the generated power is basically used for charging the battery 26. Further, in a situation where the operation of the air compressor 12 is stopped, the output torque of the drive motor 30 is also negative and regenerative braking is often performed. Further, the amount of charge in the battery 26 should also take into account the loss in the inverters 20 and 28.

  Therefore, as shown in FIG. 6, it is preferable to calculate the regenerative power (air compressor regenerative power) in the air compressor motor 22 and adopt this as the upper limit value of the charging power instead of the battery rechargeable power. It is. Then, the negative magnitude of the torque command to the air compressor motor 22 is limited based on the obtained calculation result.

  As shown in FIG. 7, based on the capacity of the battery 26, the SOC at that time, the temperature, etc., the battery chargeable power (electric power) at that time is calculated (S11). Further, in a state where the amount of depression of the accelerator is reduced during traveling, deceleration corresponding to the engine brake is necessary according to the traveling state at that time. Therefore, the drive motor regenerative power corresponding to the engine brake is calculated (S12). Further, in a state where the brake is depressed, deceleration by the mechanical brake is performed. At this time, regenerative braking of the drive motor is also performed in cooperation. Therefore, this brake cooperative regenerative power is calculated (S13). In the case of regenerative braking (S12, S13) of the drive motor 30, there is a loss in the inverter 28. Further, there is a loss in the inverter 20 in regenerating the air compressor regenerative power. That is, the inverters 20 and 28 control the motor current by switching a plurality of power transistors, and there is energy loss here. Therefore, the energy loss in these inverters 20 and 28 is calculated (S14).

  Then, the regenerative power calculated in S12 and S13 is subtracted from the battery chargeable power calculated in S11, and the inverter loss calculated in S14 is added to calculate the air compressor regenerative power (S15).

  Thus, with respect to the air compressor regenerative power, both regenerative braking equivalent to engine braking of the drive motor 30 and brake cooperative regenerative braking can be performed with priority. Therefore, by performing regenerative braking of the air compressor 12 (more precisely, the air compressor motor 22), the influence on the regenerative braking of the drive motor 30 is eliminated. Therefore, it is possible to perform regenerative braking of the air compressor motor 22 by eliminating the influence on the running performance of the vehicle, and to ensure the drivability of the vehicle.

  When the air compressor regenerative power is calculated in this way, the regeneration of the air compressor is controlled with this as the upper limit. That is, the obtained air compressor regenerative power is adopted instead of the battery chargeable power in FIG. As in the case described above, the power that can pass through the converter in FIG. 5 is also taken into consideration, and a lower power may be adopted as the limit value.

  On the other hand, when the drying of the MEA in the fuel cell 10 is progressing, there is also a demand for reducing the air flow rate at an early stage even if the drivability is slightly sacrificed.

  FIG. 8 shows the processing in this case. In this example, the battery chargeable power (electric power) at that time is calculated according to the state of the battery 26 (S11). Further, a drive motor regenerative power corresponding to the engine brake is calculated (S12). Further, the energy loss in the inverters 20 and 28 is calculated (S14).

  Then, the regenerative power calculated in S12 is subtracted from the battery chargeable power calculated in S11, and the inverter loss calculated in S14 is added to calculate the air compressor regenerative power (S15). That is, the deceleration when the brake is depressed is mainly due to the mechanical brake, and the influence on drivability is small even if the brake cooperative regenerative braking is not performed. Therefore, the air compressor regenerative power is calculated without considering the brake cooperative regenerative power.

  Accordingly, with respect to the power that can be regenerated by the air compressor, priority is given to regenerative braking corresponding to the engine brake of the drive motor 30, but priority is given to air compressor regeneration with respect to brake cooperative regenerative braking. Therefore, when the brake is depressed, the air supply can be reduced relatively early, and the drying of the MEA can be more effectively prevented. Note that regeneration of the air compressor is prioritized over brake cooperative regeneration, and when there is a margin in the calculated air compressor regenerative power, it is preferable to perform brake cooperative regeneration accordingly.

  FIG. 9 shows an example of a processing flowchart for calculating the air compressor regenerative power.

  First, it is determined whether air compressor regeneration is required. That is, it is determined whether or not there is a significant decrease in the amount of air blown by the air compressor 12 due to the output of the fuel cell 10 being greatly reduced or stopped (S31). If the determination is NO, air compressor regeneration is not performed, and the process is terminated.

  If the determination in S31 is YES, the battery chargeable power is calculated (S32). In calculating the battery chargeable power, not only the above-described battery state but also the power that can be passed through the converter 24 is taken into consideration, and the lower power may be employed. Next, the impedance of the fuel cell 10 is measured (S33). For this impedance measurement, a method similar to that of a known fuel cell impedance measuring apparatus can be used. The impedance of the fuel cell 10 is measured from the attenuation by applying an alternating current. The degree of drying of the MEA can be estimated from the impedance of the fuel cell 10. In this embodiment, whether the degree of drying of the MEA is equal to or less than a predetermined value is determined based on whether the impedance measured in S33 is equal to or less than a predetermined value.

  If it is determined in S34 that the impedance is equal to or lower than a predetermined value (the degree of drying is equal to or lower than the predetermined value), the brake cooperative regenerative power is prioritized and subtracted to calculate the air compressor regenerative power (S35). . On the other hand, if it is determined in S34 that the impedance exceeds a predetermined value (the degree of drying is equal to or greater than the predetermined value), the brake cooperative regenerative power is ignored, and the air compressor regenerative power without subtraction. Is calculated (S36). When the air compressor regenerative power is calculated, regeneration of the air compressor is controlled with this as the upper limit. Thereby, the air compressor regenerative power can be calculated in consideration of the dry state of the MEA.

  DESCRIPTION OF SYMBOLS 10 Fuel cell, 12 Air compressor, 14 Intercooler, 16 Humidifier, 18 Hydrogen gas supply source, 20, 28 Inverter, 22 Air compressor motor, 24 Converter, 26 Battery, 30 Drive motor, 32 Control part, 100 Fuel cell system.

Claims (4)

In a fuel cell system that drives a motor using electric energy from a fuel cell,
A blower pump for supplying an oxygen-containing gas to the fuel cell,
A blower pump motor for driving the blower pump;
A blower pump inverter that controls power supply to the blower pump motor;
A motor inverter that controls power supply to the motor;
Impedance measuring means for measuring the impedance of the fuel cell;
A controller that controls the inverter for the blower pump and the inverter for the motor;
Including
The controller is
When reducing the amount of air blown by the blower pump, a negative torque command is generated as a drive command for the blower pump motor,
When the impedance measured by the impedance measuring means is less than or equal to a predetermined value, the air compressor regenerative power is calculated in consideration of brake cooperative regenerative power that can be generated by regenerative braking of the motor at that time,
When the impedance measured by the impedance measuring means exceeds a predetermined value, the air compressor regenerative power is calculated without considering the brake cooperative regenerative power that can be generated by regenerative braking of the motor at that time,
The generated negative torque command is limited within a range of calculated regenerative power, and the blower pump inverter is controlled to regeneratively brake the blower pump motor. . The fuel cell system according to claim 1, wherein
further,
A battery that can be charged based on the output of the fuel cell;
The said control part charges the said battery with the electric power obtained by the regenerative braking of the said motor for blower pumps, The fuel cell system characterized by the above-mentioned. The fuel cell system according to claim 2 , wherein
The said control part controls the electric power obtained by the said regenerative braking so that it may not exceed the electric power which can be charged of a battery. The fuel cell system according to claim 2 or 3 ,
further,
Having a converter for supplying electric power obtained by regenerative braking to the battery;
When the passing power of the converter is limited, the control unit controls the regenerative braking so that the passing power is within the limit.

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