Fuel cell system

Abstract

The present invention provides a fuel cell system that improves fuel efficiency and maintains output performance under continuous high-load conditions, such as on high-speed uphill roads. [Solution] A fuel cell system 100 including a fuel cell 10, wherein the output command value for the fuel cell 10 is set according to the moving average value of the requested output value over a predetermined period in the past.

Description

Technical Field

[0001] The present invention relates to a fuel cell system.

Background Art

[0002] There is disclosed a control device for controlling the startup and stop of a fuel cell of a fuel cell vehicle including a fuel cell, a secondary battery that charges at least the generated power of the fuel cell, and a drive motor driven by at least the power supplied from the secondary battery (Patent Document 1). It includes a driving environment detection unit that detects a driving environment based on a moving average of driving state information indicating the driving state of the fuel cell vehicle, a fuel cell startup determination unit that determines the startup and stop of the fuel cell based on the driving environment, and a fuel cell control unit that controls the startup and stop of the fuel cell based on the result of the determination.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a fuel cell system using a fuel cell and a secondary battery as power sources, it is necessary to improve fuel consumption performance and maintain the output by satisfying the outputs of the fuel cell and the secondary battery during high loads such as high-speed uphill driving. On the other hand, in order to limit the space when the fuel cell system is mounted on a vehicle and reduce the cost (capital cost), it is desired to use a fuel cell system with the capacities of the fuel cell and the secondary battery reduced as much as possible. That is, it is required to achieve both fuel consumption performance and driving performance, and it is necessary to appropriately control the outputs of the fuel cell and the secondary battery.

[0005] Furthermore, if the required power output of a fuel cell fluctuates rapidly over time, it may lead to a deterioration or damage to the fuel cell's performance. Therefore, technologies are needed to prevent the deterioration and damage of fuel cells. [Means for solving the problem]

[0006] One aspect of the present invention is a fuel cell system including a fuel cell, characterized in that an output command value for the fuel cell is set according to a moving average value of the requested output value over a predetermined period in the past.

[0007] In this case, it is preferable to provide a secondary battery that is provided together with the fuel cell to satisfy the requested output value, and to set the output command value for the fuel cell according to the difference between the SOC control target value of the secondary battery and the actual SOC of the secondary battery.

[0008] Furthermore, it is preferable that the requested output value is set according to at least one of the following: the output of a motor that receives power from the fuel cell; the sum of the motor's output and the power consumption of a device that receives power from the fuel cell and the secondary battery; the accelerator opening by the driver of the vehicle equipped with the fuel cell; and the requested output power to the fuel cell and the secondary battery estimated from data on the vehicle's speed and the road gradient on which the vehicle travels.

[0009] Furthermore, it is preferable to set the output command value for the fuel cell so as not to exceed the upper limit of the fuel cell's output. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a fuel cell system that can improve fuel efficiency and maintain output performance under conditions of continuous high load, such as on a high-speed uphill road. [Brief explanation of the drawing]

[0011] [Figure 1]This figure shows the configuration of a fuel cell system in an embodiment of the present invention. [Figure 2] This diagram shows the relationship between fuel cell output and output efficiency (system efficiency). [Figure 3] This diagram explains the symbols used in formula (1). [Figure 4] This figure shows the time-series data during vehicle operation in an embodiment of the present invention. [Modes for carrying out the invention]

[0012] As shown in Figure 1, the fuel cell system 100 in the embodiment of the present invention can be configured as a vehicle system. However, the scope of application of the fuel cell system of the present invention is not limited to vehicle systems, and any system that can exhibit the configuration and effects of the present invention is acceptable.

[0013] The fuel cell system 100 comprises a fuel cell 10, a secondary battery 12, a DC / DC converter 14, a motor 16, a regenerative braking system 18, and a control unit 20.

[0014] The fuel cell 10 is a device that generates electricity using a chemical reaction between hydrogen and oxygen. The fuel cell 10 functions as the main power source for a vehicle. The fuel cell 10 generates electricity by using hydrogen supplied from a hydrogen tank and reacting it with oxygen (usually oxygen from the air). The fuel cell 10 may also be a fuel cell stack in which multiple fuel cell cells are connected.

[0015] The secondary battery 12 is a rechargeable and dischargeable battery. The secondary battery 12 can be, for example, a lithium-ion battery. The secondary battery 12 generates electricity together with the fuel cell 10 to meet the required output value. The secondary battery 12 also plays a role in temporarily storing the electricity generated by the fuel cell 10. It also outputs electricity during high-load situations such as vehicle acceleration or high-speed uphill driving.

[0016] Here, the required output value is a value related to the power required as output for the fuel cell 10 and the secondary battery 12. The required output value can be, for example, the output of the motor 16, the sum of the output of the motor 16 and the power consumption of devices that receive power supply from the fuel cell 10 and the secondary battery 12 such as auxiliary equipment, the accelerator opening by the driver, and the required output power for the fuel cell 10 and the secondary battery 12 estimated from data on the vehicle speed and road gradient.

[0017] The secondary battery 12 can also store the power from the regenerative brake of the vehicle. By efficiently using the regenerative energy, the consumption of wasted energy can be suppressed. Also, by appropriately controlling the output power from the secondary battery 12, the load on the fuel cell 10 can be reduced, and the effect of extending the life of the fuel cell 10 can also be obtained.

[0018] The DC / DC converter 14 is a circuit for adjusting the voltages of the fuel cell 10 and the secondary battery 12. The DC / DC converter 14 adjusts the voltages of the fuel cell 10 and the secondary battery 12 and supplies power to the motor 16. Also, the DC / DC converter 14 receives power from the regenerative brake system 18 and supplies regenerative energy to the secondary battery 12.

[0019] The motor 16 outputs power for driving the vehicle using the power supplied from the fuel cell 10 or the secondary battery 12. The motor 16 may include an inverter. The inverter converts the DC power supplied from the DC / DC converter 14 into AC power and supplies it to the motor 16, and controls the rotational speed and torque of the motor 16.

[0020] The regenerative brake system 18 uses the motor 16 as a generator when the vehicle decelerates, converts the kinetic energy into electric power, and supplies it to the secondary battery 12 via the DC / DC converter 14. The secondary battery 12 is charged by the regenerative energy. By the regenerative brake system 18, the energy lost during braking can be reused to improve the fuel efficiency.

[0021] The control unit 20 integrally controls the fuel cell system 100. The control unit 20 is configured to include an energy management system (EMS). The control unit 20 generates output command values for the fuel cell 10 and the secondary battery 12 according to the required output value in the motor 16 of the vehicle, and controls the outputs of the fuel cell 10 and the secondary battery 12. For example, at low load, the fuel cell 10 is mainly used, and control is performed to charge the secondary battery 12 as necessary. Also, at high load, power is supplied from the secondary battery 12, and control is performed to supplement the shortage of power supply from the fuel cell 10. The control unit 20 efficiently consumes energy and optimizes the overall fuel consumption and power consumption of the fuel cell system 100.

[0022] In a vehicle equipped with a fuel cell system using the fuel cell 10 and the secondary battery 12, in order to ensure vehicle mounting performance and reduce capital costs, the fuel cell 10 and the secondary battery 12 with limited capacity are used. Therefore, during high-load driving, the fuel cell 10 alone cannot maintain the load for a long time. Therefore, control is performed to satisfy the output during high load by using the output of the secondary battery 12 in combination with the output of the fuel cell 10.

[0023] Here, since the energy capacity of the secondary battery 12 is finite, it is necessary to control the state of charge (SOC) of the secondary battery 12 to a certain value or more in preparation for high-load driving conditions. Also, as shown in FIG. 2, the output efficiency of the fuel cell 10 is high at low output and exhibits peak efficiency. However, if the fuel cell 10 is controlled only under the peak efficiency condition for fuel consumption performance, the output of the fuel cell 10 will often be insufficient, and the state where the output from the secondary battery 12 is required will become long, resulting in a decrease in the SOC of the secondary battery 12. In such control, there is a risk that the secondary battery 12 cannot be fully utilized under high-load driving conditions.

[0024] Therefore, in the fuel cell system 100 of this embodiment, the control unit 20 sets the output command value for the fuel cell 10 according to the moving average value of the requested output value over a predetermined past period (average interval) T for the fuel cell 10. In other words, by using the moving average of the driving load from the past to the present time as the power generation output of the fuel cell 10, it becomes possible to drive the fuel cell 10 in accordance with the requested output value that indicates the required driving load. The predetermined period T is set appropriately according to the capacity of the fuel cell 10, etc.

[0025] On the other hand, under high-load driving conditions, the fuel cell 10 is used with poor output efficiency, resulting in the fuel cell 10 not being used optimally throughout the entire driving time. In addition, the secondary battery 12 is not effectively utilized, requiring a large-capacity fuel cell 10. Therefore, an output limit (FC power limit) is set for the output command value to the fuel cell 10 based on the moving average value of the requested output value, and the output of the fuel cell 10 is limited by this output limit (FC power limit). This makes it possible to suppress the decrease in output efficiency during high-load driving.

[0026] The output limit is set arbitrarily within the maximum output that the fuel cell 10 can output, or within the maximum output that the fuel cell 10 can output. In particular, when setting the output limit arbitrarily within the maximum output of the fuel cell 10, it is preferable to set the output limit considering the output distribution between the fuel cell 10 and the secondary battery 12. Setting the output limit low increases the output distribution of the secondary battery 12, and setting the output limit high increases the output distribution of the fuel cell 10.

[0027] On the other hand, if high-load driving continues, the amount of power generated by the fuel cell 10 becomes insufficient, and the secondary battery 12 is used, causing the State of Charge (SOC) of the secondary battery 12 to decrease. Therefore, in order to compensate for the insufficient charge state of the secondary battery 12 during light-load driving, the system controls the output command value to the fuel cell 10 according to the SOC of the secondary battery 12.

[0028] Specifically, the control is performed to set the output command value for the fuel cell 10 according to the difference (deviation) between the target SOC control value of the secondary battery 12 and the actual SOC of the secondary battery 12. For example, feedback control by PI control is applied according to the difference (deviation) between the target SOC control value of the secondary battery 12 and the actual SOC of the secondary battery 12, and the output command value for the fuel cell 10 is set according to the control value of the feedback control. In this case, it is preferable to set an upper limit (FB upper limit) for the control value of the feedback control and to perform control so that the control value of the feedback control does not exceed the upper limit (FB upper limit).

[0029] The above control can be expressed by equation (1). Figure 3 shows an explanation of the symbols used in equation (1).

number

[0030] In other words, the control unit 20 selects a value smaller than either the control value for PI control corresponding to the difference (deviation) between the target SOC control value of the secondary battery 12 and the actual SOC of the secondary battery 12, or its upper limit (FB upper limit). Then, it adds the selected value to the moving average of the requested output values ​​over a predetermined past period (average interval) T, and selects the smaller of these values ​​to set as the output command value (power generation command value) for the fuel cell 10, so that the added value does not exceed the upper limit of the fuel cell 10's output (FC power upper limit). The output command value (power generation command value) for the secondary battery 12 is the value obtained by subtracting the output command value (power generation command value) for the fuel cell 10 from the current requested output value.

[0031] Figure 4(a) shows the vehicle's required power output (required driving load) for a certain driving pattern. Figure 4(b) shows the moving average value (solid line) of the required power output (required driving load) and the output command value (power generation command value) for the fuel cell 10 (dashed line). Figure 4(c) shows the change in the State of Charge (SOC) of the secondary battery 12 during that time.

[0032] During light-load driving from the start of control (0) to approximately 0.3 hours later, the moving average of the vehicle's requested output value (required driving load) becomes the output command value (power generation command value) of the fuel cell 10, and the State of Charge (SOC) of the secondary battery 12 remains around 60% of the set target value.

[0033] Between 0.3 and 0.7 hours into the test cycle, the moving average of the vehicle's required power output (required driving load) falls below the driving load, causing the State of Charge (SOC) of the secondary battery 12 to decrease from the target value. A correction is then applied through SOC feedback, causing the output command value (power generation command value) for the fuel cell 10 to exceed the moving average of the vehicle's required power output (required driving load). This suppresses the decrease in the SOC of the secondary battery 12 and ensures sufficient energy (SOC) for assistance from the secondary battery 12 during high-load driving.

[0034] Between approximately 0.7 and 1.1 hours, the vehicle enters a high-load driving state, and the moving average value of the vehicle's required power output (driving load) increases. During this time, the upper limit of the fuel cell 10 (FC power limit) acts as a constraint on the moving average value of the vehicle's required power output (driving load), and this upper limit of the fuel cell 10 (FC power limit) is set as the output command value (power generation command value) of the fuel cell 10. The insufficient power generation from the fuel cell 10 relative to the vehicle's required power output (driving load) is compensated for by the output from the secondary battery 12. Consequently, it can be confirmed that the State of Charge (SOC) of the secondary battery 12 decreases. However, because control was implemented to ensure that the SOC of the secondary battery 12 is maintained during light-load driving between 0 and 0.7 hours, the SOC of the secondary battery 12 required during high-load driving does not decrease, and the entire fuel cell system 100 is able to meet the vehicle's required power output (driving load).

[0035] After 1.1 hours, the vehicle returns to light load operation, and the power generation of the fuel cell 10 is controlled so that energy is secured in the secondary battery 12 when the State of Charge (SOC) of the secondary battery 12 falls below the target value.

[0036] As described above, the fuel cell system 100 in this embodiment enables energy management that avoids high-output power generation that degrades the efficiency of the fuel cell 10, and allows the secondary battery 12 to compensate for any shortfall in the required output value during high-load driving. This makes it possible to provide a fuel cell system that improves fuel efficiency and maintains output performance under continuous high-load conditions such as high-speed uphill driving. Furthermore, it is possible to suppress deterioration and damage to the fuel cell even when the required output to the fuel cell fluctuates rapidly over time.

[0037] Furthermore, the scope of application of the fuel cell system 100 in this embodiment is not limited to vehicle-mounted fuel cell systems 100, but is applicable to any system where the load fluctuates.

[0038] [Configuration of the present invention] [Configuration 1] A fuel cell system including a fuel cell, A fuel cell system characterized by setting an output command value for the fuel cell according to the moving average value of the requested output value over a predetermined period in the past. [Configuration 2] The fuel cell system described in Configuration 1, The fuel cell is provided with a secondary battery that satisfies the required output value, A fuel cell system characterized by setting the output command value for the fuel cell according to the difference between the SOC control target value of the secondary battery and the actual SOC of the secondary battery. [Configuration 3] The fuel cell system described in configuration 2, The fuel cell system is characterized in that the requested output value is set according to at least one of the following: the output of a motor that receives power from the fuel cell; the sum of the output of the motor and the power consumption of a device that receives power from the fuel cell and the secondary battery; the accelerator opening by the driver of a vehicle equipped with the fuel cell; and the requested output power to the fuel cell and the secondary battery estimated from data of the vehicle speed and the road gradient on which the vehicle travels. [Structure 4] A fuel cell system as described in any one of items 1 to 3, A fuel cell system characterized in that the output command value for the fuel cell is set so as not to exceed the upper output limit of the fuel cell. [Explanation of Symbols]

[0039] 10 fuel cells, 12 secondary batteries, 14 DC / DC converters, 16 motors, 18 regenerative braking systems, 20 control units, 100 fuel cell systems.

Claims

1. A fuel cell system including a fuel cell, A fuel cell system characterized by setting an output command value for the fuel cell according to the moving average value of the requested output value over a predetermined period in the past.

2. A fuel cell system according to claim 1, The fuel cell is provided with a secondary battery that satisfies the required output value, A fuel cell system characterized by setting the output command value for the fuel cell according to the difference between the SOC control target value of the secondary battery and the actual SOC of the secondary battery.

3. A fuel cell system according to claim 2, A fuel cell system characterized in that the requested output value is set according to at least one of the following: the output of a motor that receives power from the fuel cell; the sum of the output of the motor and the power consumption of a device that receives power from the fuel cell and the secondary battery; the accelerator opening by the driver of a vehicle equipped with the fuel cell; and the requested output power to the fuel cell and the secondary battery estimated from data of the vehicle speed and the road gradient on which the vehicle travels.

4. A fuel cell system according to any one of claims 1 to 3, A fuel cell system characterized in that the output command value for the fuel cell is set so as not to exceed the upper output limit of the fuel cell.

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