JP2009277584A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system with fuel consumption improved with power performance maintained. <P>SOLUTION: The fuel cell system is provided with a fuel cell (11) supplying power to a driving motor (16), a secondary battery (13) connected in parallel with the fuel cell capable of gradually changing output voltages to the driving motor, a boosting device (12) raising voltage outputted from the fuel cell and supplying the voltage boosted to the driving motor, and a control means (5) controlling a boosting operation of the boosting device and output voltages of the secondary battery based on each output voltage of the fuel cell and the secondary battery as well as a required voltage of the driving motor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power control technique for a fuel cell system including a fuel cell and a secondary battery.

  A fuel cell is a device that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas. The fuel cell outputs the required power from the drive motor by controlling the supply amounts of the fuel gas and the oxidant gas. In a fuel cell system using this fuel cell as a power source, the responsiveness of the output from the fuel cell may be low, and a secondary battery is mounted to compensate for this. The secondary battery stores regenerative energy generated when the drive motor decelerates and electric power generated by the fuel cell. The secondary battery supplements the output of the fuel cell by discharging the stored electric power.

  In such a fuel cell system, the fuel cell and the secondary battery are connected in parallel via a DC-DC converter. This DC-DC converter enables the combined use of both by converting the output voltage of the fuel cell or secondary battery.

However, in this DC-DC converter, power loss occurs during voltage conversion. Therefore, various methods for improving output efficiency in a fuel cell system including a voltage converter such as a DC-DC converter have been proposed (see Patent Documents 1, 2, and 3 below).
JP 2002-118981 A JP 2006-288129 A JP 2007-335151 A

  In the fuel cell system as described above, it is desired that the fuel cell and the secondary battery are further reduced in cost, reduced in weight, reduced in size, and the like. When each device is miniaturized due to such a requirement, the number of cells is reduced, and the output power from the fuel cell and the secondary battery is reduced.

  On the other hand, the drive motor that is the load of such a fuel cell system is desired to have a high rotation speed in order to improve the power performance. Further, it is desired to reduce the size of the inverter that converts the DC power provided from the fuel cell system into AC power and sends it to the drive motor. As a result, it is desired to increase the inverter input voltage.

  In order to satisfy both of the above requirements, a configuration is adopted in which the output of the fuel cell is boosted by a DC-DC boost converter and the boosted power is applied to the inverter. However, in such a configuration, power loss occurs in the DC-DC boost converter as described above, which results in deterioration of fuel consumption.

  An object of the present invention is to provide a fuel cell system that improves fuel efficiency while maintaining power performance.

The present invention employs the following means in order to solve the above-described problems. That is, the present invention relates to a fuel cell that supplies electric power to a drive motor, a secondary battery that is connected in parallel to the fuel cell with respect to the drive motor and can switch an output voltage stepwise, and the fuel cell. Based on the output voltage of the fuel cell and the secondary battery and the required voltage of the drive motor, the booster device boosts the output voltage and supplies the boosted voltage to the drive motor. The present invention relates to a fuel cell system comprising a boosting operation and a control means for controlling the output voltage of the secondary battery.

  According to the aspect of the present invention, the boosting operation of the boosting device is controlled, and the output voltage of the secondary battery is switched in a stepwise manner, thereby improving the fuel efficiency while maintaining the power performance.

  Therefore, preferably, the control means is configured to stop the boosting operation of the boosting device when the output voltage of the fuel cell is higher than or approximates the required voltage of the drive motor and the output voltage of the secondary battery.

  According to this configuration, the power performance of the drive motor can be maintained because a voltage higher than or approximate to the required voltage of the drive motor is output from the fuel cell, and the boost operation of the boost device is stopped. The power loss caused by this boosting operation can be reduced.

  Preferably, when the output voltage of the fuel cell is equal to or higher than the required voltage of the drive motor, the control means is configured so that the output voltage of the secondary battery is lower or approximate to the output voltage of the fuel cell. The output voltage is switched in stages.

  In this configuration, the output voltage of the secondary battery can be switched stepwise in accordance with the output voltage of the fuel cell, the required voltage of the drive motor, etc., without providing a booster for controlling the output of the secondary battery. Therefore, compared with a system including a booster that controls the output of the secondary battery, pressure loss due to the boosting operation of the booster can be eliminated, and a high fuel efficiency system can be realized. Further, by switching the output voltage of the secondary battery in this way, it is possible to increase the operation region in which the boosting operation of the boosting device is stopped, so that the fuel efficiency can be further improved.

  According to the present invention, it is possible to realize a fuel cell system that improves fuel efficiency while maintaining power performance.

  Hereinafter, specific examples of the fuel cell system according to the embodiment of the present invention will be described. The fuel cell system according to the present embodiment is generally applied to a power source such as a ship or a vehicle, but may be applied to an object that needs to be supplied with electric power other than these. Each Example given below is an illustration, respectively, and this invention is not limited to the structure of each following Example.

  Hereinafter, a first example of a fuel cell system as an embodiment of the present invention will be described.

〔System configuration〕
The system configuration of the fuel cell system in the first embodiment will be described with reference to FIG. FIG. 1 shows a schematic configuration of the fuel cell system in the first embodiment. A fuel cell system 1 according to the first embodiment includes a fuel cell (hereinafter also referred to as FC) 11, an FC boost converter 12, a battery 13, an inverter 15, a drive motor 16, an ECU (Electric Control Unit) 5, and the like. .

The FC 11 is an electrochemical reaction between a fuel gas (for example, hydrogen gas) sent from the fuel gas tank 18 and pressure-adjusted and an oxidant gas (for example, compressed air) taken from the atmosphere via an air filter or the like and compressed by the compressor 19. Power is generated by reaction. The FC 11 is electrically connected to the inverter 15 together with the battery 13 in parallel. The FC boost converter 12 is connected to the power line connecting the FC 11 and the battery 13.

  The FC boost converter 12 operates as a boost type DC-DC converter, and boosts (converts) the voltage output from the FC 11 by an internal power transistor or the like. At this time, the FC boost converter 12 controls its boost ratio, that is, the ratio of the output voltage applied to the inverter 15 with respect to the input output voltage of the FC 11 in accordance with a control signal from the ECU 5. As a result, the output voltage from the FC 11 is boosted to a voltage corresponding to the control signal from the ECU 5 within a range controllable by the FC boost converter 12 and applied to the inverter 15. The FC boost converter 12 may operate not only as a boost converter but also as a buck-boost converter.

  Further, the FC boost converter 12 has an operation mode (bypass mode or through mode) (hereinafter referred to as boost stop mode) for outputting the output power from the FC 11 without conversion. In this operation mode, the FC boost converter 12 bypasses the primary side voltage and applies it to the secondary side as it is, for example, by turning off a predetermined switch element. Thereby, in this operation mode, since the voltage boosting operation is not executed, power loss can be suppressed. The FC boost converter 12 shifts to this boost stop mode in response to a control signal from the ECU 5, and returns from this boost stop mode.

  The battery 13 is a power storage device that can be charged and discharged, and is electrically connected in parallel to the inverter 15 together with the FC 11. Thereby, the output voltage from the battery 13 is applied to the inverter 15. Conversely, when the drive motor 16 generates regenerative power during vehicle braking or the like, the regenerative power is charged to the battery 13 from the inverter 15. On the other hand, the battery 13 is electrically connected to the FC 11 via the FC boost converter 12. As a result, the battery 13 is charged with the output power from the FC 11 that is boosted and controlled by the FC boost converter 12 in accordance with the amount of remaining power. The battery 13 is charged and discharged under the control of the FC boost converter 12 by the ECU 5.

  2A and 2B are diagrams schematically showing an electric circuit configuration of the battery 13 in the first embodiment. The battery 13 in the first embodiment is configured such that the output voltage can be changed stepwise. In the embodiment shown in FIGS. 2A and 2B, the battery 13 includes battery modules 26 and 27 including six cells, and switches 21, 22, and 23 that connect the battery modules 26 and 27.

  The battery 13 controls the opening / closing operations of the switches 21, 22, and 23 in accordance with a control signal sent from the ECU 5, and its output voltage is adjusted in two stages. Specifically, when the switches 21 and 23 are set to the OFF state and the switch 22 is set to the ON state based on the control signal from the ECU 5, the battery modules 26 and 27 are electrically connected to the input / output terminals. Therefore, the total voltage of the battery modules 26 and 27 becomes the output voltage of the battery 13. On the other hand, when the switches 21 and 23 are set to the ON state and the switch 22 is set to the OFF state, the battery modules 26 and 27 are electrically connected to the input / output terminals in parallel. The voltage of one battery becomes the output voltage of the battery 13. That is, the output voltage of the battery 13 in the first embodiment is adjusted in two stages by switching the electrical connection of the internal battery modules 26 and 27 between serial and parallel. Hereinafter, the higher voltage of the output voltage from the battery 13 may be referred to as a first output voltage, and the lower voltage may be referred to as a second output voltage.

The inverter 15 converts the DC power supplied from the FC 11 via the FC boost converter 12 and the DC power supplied from the battery 13 into three-phase AC power, and sends it to the drive motor 16. The drive motor 16 is, for example, a three-phase AC motor, and constitutes a main power source of a vehicle on which the fuel cell system 1 is mounted, such as rotating a wheel shaft by AC power supplied from the inverter 15. Note that the load device to which power is supplied from the fuel cell system 1 need not be limited to the drive motor 16.

  The ECU 5 includes a CPU (Central Processing Unit), a memory, an input / output interface, and the like. The ECU 5 implements various controls by the CPU executing a control program stored in the memory. The ECU 5 is connected to the FC 11, the FC boost converter 12, the battery 13, the inverter 15, the drive motor 16, and the like described above by signal lines, and acquires various information from each signal line, so that at least the operation mode of the FC boost converter 12 and The output voltage and the output voltage of the battery 13 are controlled. In controlling each circuit, the ECU 5 transmits a control signal using the signal line.

  The ECU 5 receives information relating to the output voltage of the battery 13 from a voltage sensor (not shown) installed between the terminals of the battery 13 as a signal necessary for controlling the battery 13, and a power line connected to the output terminal of the battery 13. The information regarding charging / discharging current is acquired from the current sensor (not shown) attached to. The ECU 5 calculates the remaining power storage amount of the battery 13 based on the information on the charge / discharge current.

  The ECU 5 acquires the opening information of the accelerator pedal that receives an acceleration request from the user, the rotation speed information of the drive motor 16 and the like as signals necessary for controlling the boost converter 12, and based on these information, the necessary information is obtained. A voltage to be applied to the inverter 15 so that electric power is supplied to the drive motor 16 (hereinafter referred to as a motor required voltage) is calculated. Furthermore, ECU5 acquires the information regarding the output voltage of FC11 from the voltage sensor (not shown) installed between the terminals of FC11.

  The ECU 5 controls the boosting operation of the FC boost converter 12 based on the boosting ratio calculated based on the required motor voltage and the output voltage of the FC11 among the information acquired as described above, and as a result, the FC boosting is performed. The output voltage of the converter 12 is controlled. On the other hand, the ECU 5 controls the operation mode (the transition to the boost stop mode and the return from the boost stop mode) of the FC boost converter 12 based on the required motor voltage, the output voltage of the FC 11 and the output voltage of the battery 13. . Further, the ECU 5 controls the output voltage of the battery 13 in a stepwise manner based on the remaining storage amount and output voltage of the battery 13 and the output voltage of the FC 11. As described above, the stepwise control of the output voltage of the battery 13 is realized by switching the switches 21, 22 and 23 in the battery 13 between ON and OFF states.

  3A and 3B are graphs showing the relationship between the output power of the FC 11, the output power of the battery 13, and the required motor power in the fuel cell system. In the figure, the vertical axis represents voltage, the horizontal axis represents output power, and the voltage-power characteristics of each value are shown.

  When the electric power to be supplied to the drive motor 16 is increased, the back electromotive voltage of the drive motor 16 is increased, so that the required motor voltage is also increased as shown in FIGS. 3A and 3B. Further, in the voltage-power characteristic of FC11, when the output power of FC11 increases, the output voltage decreases. As shown in FIGS. 3A and 3B, the output voltage of the battery 13 is substantially constant regardless of the output power when it has an allowable remaining power storage amount. FIG. 3A shows the voltage-power characteristics when the maximum voltage is output from the battery 13 (in the serial connection state of FIG. 2A), and FIG. 3B shows the case where the small voltage is output from the battery 13. The voltage-power characteristics (in the parallel connection state of FIG. 2B) are shown.

In order to maintain power performance, the ECU 5 controls the boost ratio of the FC boost converter 12 so that a voltage exceeding the above-described motor required voltage is always applied to the inverter 15. In addition, E
The CU 5 shifts the FC boost converter 12 to the boost stop mode when there is no need to boost the output voltage of the FC 11 in order to suppress power loss in the FC boost converter 12 and improve fuel efficiency. Basically, when the output voltage of the FC 11 exceeds the motor required voltage, it is not necessary to boost the FC boost converter 12. Therefore, basically, the boosting operation of the FC boost converter 12 can be stopped in an operation region where the required motor voltage is lower than the point B shown in FIGS. 3A and 3B, that is, when the load is lighter than the point B.

  However, when the output voltage of FC11 is lower than the output voltage of battery 13 (when the load is higher than point A in FIGS. 3A and 3B), it is necessary to boost the output of FC11 by FC boost converter 12. Further, if a voltage exceeding the allowable range is continuously applied to the terminal of the battery 13, the battery 13 may be broken. Therefore, the difference between the output voltage of the FC 11 and the output voltage of the battery 13 needs to be suppressed within the allowable range. is there.

  The ECU 5 controls the operation mode and output voltage (step-up ratio, etc.) of the FC boost converter 12 and the output voltage of the battery 13 in consideration of the above points. Details of the control by the ECU 5 will be described in the following operation example. In the first embodiment, the control of the battery 13 and the FC boost converter 12 will be mainly described. However, the ECU 5 may also execute the power generation amount control of the FC 11. The present invention does not limit the control other than the control of the battery 13 and the FC boost converter 12.

[Operation example]
Hereinafter, as an operation example of the fuel cell system 1 in the first embodiment, the control of the ECU 5 will be described with reference to FIG. FIG. 4 is a graph showing a control example of the fuel cell system 1 in the first embodiment. Hereinafter, the control of the ECU 5 will be described taking as an example the case of shifting from a light load to a high load.

  The ECU 5 determines the output power of the FC 11 according to the required motor power at light load, and controls the FC 11, the fuel gas tank 18, the compressor 19 and the like so that the determined power is output. As a result, the output voltage of the FC 11 is sufficiently higher than the motor required voltage.

  At this time, the ECU 5 controls the battery 13 so that the first output voltage is output. Specifically, the ECU 5 instructs the battery 13 so that the battery 13 is in the series connection state of FIG. 2A (a state where the switch 21 is set to OFF, the switch 22 is set to ON, and the switch 23 is set to OFF). Thereby, the difference between the output voltage of the FC 11 and the output voltage of the battery 13 is suppressed within an allowable range. The first output voltage of the battery 13 is designed so that the difference from the maximum output voltage of the FC 11 is within an allowable range.

  The ECU 5 instructs the FC boost converter 12 to shift to the boost stop mode in a region where the output voltage of the battery 13 is smaller than the output voltage of the FC 11 (lower load region than the point A). As a result, the output voltage of the FC 11 is applied to the inverter 15 without being converted. Therefore, power loss due to the boosting operation can be prevented while the FC boost converter 12 is shifted to the boost stop mode.

  The ECU 5 instructs the FC boost converter 12 to return from the boost stop mode when the required motor voltage increases and the output voltage of the FC 11 falls below the point A. This is because, as it is, the output voltage of the FC 11 becomes lower than the allowable range of the output voltage of the battery 13. The ECU 5 controls the FC boost converter 12 so that the output voltage of the FC 11 is boosted until it approximates the output voltage of the battery 13 within an allowable range.

  The ECU 5 controls the battery 13 so that the second output voltage is output when the required motor voltage further increases and the output voltage of the FC 11 further decreases. Specifically, the ECU 5 instructs the battery 13 so that the battery 13 is in the parallel connection state of FIG. 2B (a state where the switch 21 is set to ON, the switch 22 is set to OFF, and the switch 23 is set to ON). Thereby, the output voltage of the battery 13 becomes lower than the output voltage of the FC 11. The second output voltage of the battery 13 is designed so that the difference from the output voltage of the FC 11 at the time of switching from the first output voltage is within an allowable range.

  As a result, the output voltage of the FC 11 becomes higher than the required voltage of the motor and the output voltage of the battery 13, so the ECU 5 instructs the FC boost converter 12 to shift to the boost stop mode. As a result, power loss due to the boosting operation can be prevented while the FC boost converter 12 is shifted to the boost stop mode.

  When the motor required voltage becomes higher than the point B, the output voltage of FC11 becomes lower than the motor required voltage. Thereby, the ECU 5 instructs the FC boost converter 12 to return from the boost stop mode. The ECU 5 controls the FC boost converter 12 so that the output voltage of the FC 11 is boosted until it becomes higher than the motor required voltage.

  When the required motor voltage further increases, the ECU 5 controls the battery 13 so that the first output voltage is output. As a result, the ECU 5 suppresses the difference between the output voltage of the FC boost converter 12 and the second output voltage of the battery 13 within an allowable range. Thereafter, the ECU 5 controls the boost operation of the FC boost converter 12 according to the relationship between the first output voltage of the battery 13 and the required motor voltage.

[Operation and effect of the first embodiment]
In the fuel cell system 1 in the first embodiment, the FC 11 is electrically connected in parallel to the inverter 15 (load device) via the FC boost converter 12, and the battery 13 is connected to the inverter 15 without passing through the boost converter. They are electrically connected in parallel.

  Thus, according to the first embodiment, compared to a system in which the battery 13 is connected to the load device via the boost converter, power loss due to the boost operation of the boost converter can be reduced, and a high fuel efficiency system is achieved. Can be realized.

  Further, in the first embodiment, the ECU 5 controls the output voltage and operation mode of the FC boost converter 12 and the output voltage of the battery 13.

  Specifically, the FC boost converter 12 boosts the output voltage of the FC 11 and outputs a voltage higher than the required motor voltage to be applied to the inverter 15. Thereby, the power performance of the motor 16 is maintained. Further, the FC boost converter 12 shifts to the boost stop mode when the output voltage of the FC 11 is higher than the motor required voltage and the output voltage of the battery 13. Thereby, the power loss due to the boosting operation of the FC boost converter 12 is reduced.

  As described above, according to the fuel cell system 1 in the first embodiment, a system with high fuel consumption can be realized while maintaining the power performance.

In the first embodiment, the battery 13 is configured such that its output voltage can be switched in stages. In order to provide many periods during which the FC boost converter 12 is in the boost stop mode, the output voltage of the battery 13 is switched in stages. Specifically, in an operation region where the output voltage of FC11 is higher than the required voltage of the motor, the difference between the output voltage of FC11 and the output voltage of battery 13 is within an allowable range, and the output voltage of FC11 is the output voltage of battery 13. The output voltage of the battery 13 is controlled in a stepwise manner so that the higher operating region becomes larger.

  As a result, since there are many operating regions in which the boost operation of the FC boost converter 12 is stopped, the power loss can be reduced and a high fuel efficiency system can be realized.

[Modification]
In the first embodiment described above, the output voltage of the battery 13 is switched stepwise by switching whether the internal battery modules 26 and 27 are connected in series or in parallel. As shown in FIGS. 5A and 5B, the output voltage of the battery 13 may be switched in stages by switching the number of battery modules.

  5A and 5B are diagrams schematically showing an electric circuit configuration of the battery 13 in a modified example. The battery 13 in the modified example includes battery modules 26 and 27 and switches 51 and 52 as in the first embodiment. The battery 13 is controlled to open and close the switches 51 and 52 in accordance with a control signal sent from the ECU 5.

  Specifically, when the switch 51 is turned off and the switch 52 is turned on (see FIG. 5A), the battery modules 26 and 27 are electrically connected in series with the input / output terminals. Therefore, the total voltage of the battery modules 26 and 27 becomes the output voltage (first output voltage) of the battery 13. On the other hand, when the switch 51 is set to the ON state and the switch 52 is set to the OFF state (see FIG. 5B), only the battery module 26 is electrically connected to the input / output terminals. 26 voltage becomes the output voltage (second output voltage) of the battery 13.

It is a figure which shows schematic structure of the fuel cell system in 1st Example. It is a figure which shows typically the electric circuit structure (series connection state) of the battery in 1st Example. It is a figure which shows typically the electric circuit structure (parallel connection state) of the battery in 1st Example. It is a graph which shows the relationship between the output power of FC in a fuel cell system, the output power (high) of a battery, and motor required power. It is a graph which shows the relationship between the output power of FC in a fuel cell system, the output power (low) of a battery, and motor required power. It is a graph which shows the example of control of the fuel cell system in the 1st example. It is a figure which shows typically the electric circuit structure (2 modules) of the battery in a modification. It is a figure which shows typically the electric circuit structure (1 module) of the battery in a modification.

Explanation of symbols

5 ECU
11 Fuel cell (FC)
12 FC boost converter 13 Battery 15 Inverter 16 Drive motor 21, 22, 23, 51, 52 Switch

Claims (5)

A fuel cell for supplying power to the drive motor;
A secondary battery connected in parallel to the fuel cell with respect to the drive motor and capable of switching output voltage stepwise;
A booster that boosts the voltage output from the fuel cell and supplies the boosted voltage to the drive motor;
Control means for controlling the boosting operation of the boosting device and the output voltage of the secondary battery based on the output voltages of the fuel cell and the secondary battery and the required voltage of the drive motor;
A fuel cell system comprising:   The control means stops the boosting operation of the boosting device when the output voltage of the fuel cell is higher than or approximates the required voltage of the drive motor and the output voltage of the secondary battery. Item 4. The fuel cell system according to Item 1.   When the output voltage of the fuel cell is greater than or equal to the required voltage of the drive motor, the control means is configured to make the output voltage of the secondary battery lower or approximate to the output voltage of the fuel cell. The fuel cell system according to claim 1, wherein the output voltage is switched stepwise. The secondary battery includes a plurality of cells and a switch for switching the electrical connection of the plurality of cells in parallel or in series,
The control means controls the output voltage of the secondary battery by switching an open / close state of the switch of the secondary battery;
The fuel cell system according to any one of claims 1 to 3, wherein The secondary battery includes a plurality of cells and a switch for switching the number of cells electrically connected to an input / output terminal of the plurality of cells,
The control means controls the output voltage of the secondary battery by switching an open / close state of the switch of the secondary battery;
The fuel cell system according to any one of claims 1 to 3, wherein

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