Control device and control method for a fuel cell system

Abstract

This invention provides a control method for a fuel cell system that allows the actual output to be increased to the load-required output even when current limiting is implemented when the actual output of the fuel cell reaches its limit. [Solution] In a control device for a fuel cell system that determines a current command value (Ircom) to the fuel cell according to a load request output (output request value) (Pro), and increases the actual output (Pact) of the fuel cell to the load request output (Pro) at a predetermined rate based on the current command value (Ircom), when it is detected that the actual output (Pact) has plateaued before rising to the load request output (Pro) during control of the actual output (Pact) with the current command value (Ircom), the current command value (Ircom) is changed to a lower limit current command value (Ilcom) to control the actual output (Pact).

Description

[Technical Field]

[0001] The present disclosure relates to a control device for a fuel cell system and a control method therefor. [Background Art]

[0002] In recent years, research and development on fuel cells, which contribute to improving energy efficiency, have been conducted to enable more people to secure access to affordable, reliable, sustainable and advanced energy.

[0003] For example, FIGS. 2(a) and 2(b) of International Publication No. 2010 / 053027 disclose a control that sharply increases the generated current to the maximum limit value when the target generated power changes in a stepwise manner.

[0004] At this time, paragraph

[0027] of the publication describes that the generated voltage drops sharply, and the actual generated power greatly deviates from the target generated power.

[0005] In order to prevent this deviation, as shown in FIGS. 3(a) and 3(b) of the publication, control is disclosed that reduces the deviation of the actual generated power from the target generated power by limiting the rising change rate of the generated current when the target generated power changes in a stepwise manner. [Prior Art Documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2010 / 053027 [Summary of the Invention] [Problem to be Solved by the Invention]

[0007] However, even when power generation control is performed by setting the generated current to a value corresponding to the actual generated power (target generated current), there is a problem in that the actual generated power may plateau and decline due to a decrease in the generated voltage, etc., and the actual generated power may not reach the target generated power. This disclosure aims to solve the problems described above. [Means for solving the problem]

[0008] One aspect of the present disclosure is a control device for a fuel cell system that determines a current command value to a fuel cell in accordance with a load request output and increases the actual output of the fuel cell to the load request output at a predetermined rate of increase based on the current command value, wherein when it is detected that the actual output has plateaued before rising to the load request output during control of the actual output with the current command value, the current command value is changed to a lower limit current command value to control the actual output, and after control of the actual output with the limit current command value, the limit current command value is changed to a rate relaxation current command value with a rate of increase smaller than the predetermined rate of increase to control the actual output.

[0009] Another aspect of the present disclosure is a control method for a fuel cell system that determines a current command value to a fuel cell in accordance with a load request output and increases the actual output of the fuel cell to the load request output at a predetermined rate of increase based on the current command value, comprising: a limit current command value control step in which, when it is detected that the actual output has plateaued before rising to the load request output during control of the actual output with the current command value, the current command value is changed to a limit current command value which is lowered and the actual output is controlled; and a rate relaxation current command value control step in which, after control of the actual output with the limit current command value, the limit current command value is changed to a rate relaxation current command value which is lowered to a rate of increase than the predetermined rate of increase and the actual output is controlled. [Effects of the Invention]

[0010] According to this disclosure, when it is detected that the actual output (the output power of the fuel cell, also known as gross power or gross output) has plateaued before rising to the load-requested output, the actual output is controlled by switching to a limiting current command value, which is a reduced current command value. After controlling the actual output with the limiting current command value, the actual output is controlled by switching the limiting current command value to a rate-relaxing current command value.

[0011] In this way, current limiting is implemented when the actual output (gross output) of the fuel cell reaches its limit. Subsequently, the actual output can be increased to the load-required output by increasing the rate relaxation current command value. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram of a fuel cell vehicle incorporating a fuel cell system. [Figure 2] Figure 2 shows example characteristics of the IV and IP characteristics of a fuel cell. [Figure 3] Figure 3 is a flowchart illustrating the control operation of the control device on the fuel cell system during acceleration of a fuel cell vehicle. [Figure 4] Figure 4 shows a map of output request values ​​for the accelerator pedal input detected by the accelerator pedal input sensor, with vehicle speed as the parameter. [Figure 5] Figure 5 is a timing chart used to illustrate an example of the operation described in the flowchart. [Figure 6] Figure 6 is a timing chart used to illustrate another example of the operation described in the flowchart. [Figure 7] Figure 7 is a magnified view of a portion of the timing charts in Figures 5 and 6. [Modes for carrying out the invention]

[0013] [Embodiment] [composition] FIG. 1 is a schematic configuration diagram of a fuel cell vehicle 12 incorporating a fuel cell system 10.

[0014] The fuel cell system 10 can also be incorporated into other moving bodies such as ships, aircraft, and robots other than the fuel cell vehicle 12, or into buildings such as factory equipment.

[0015] The fuel cell vehicle 12 includes the fuel cell system 10, an output unit 80 electrically connected to the fuel cell system 10, and a control device 200 according to an embodiment that controls the entire fuel cell vehicle 12.

[0016] The control device 200 is not limited to one unit, and may be divided into two or more control devices, for example, one for the fuel cell system 10 and one for the output unit 80.

[0017] The fuel cell system 10 includes a fuel cell stack (simply referred to as a fuel cell) 14, a hydrogen tank 42 serving as a fuel tank, an oxidant gas supply device 20, a fuel gas supply device 40, and a coolant supply device 70. The oxidant gas supply device 20 includes a compressor (CP) 22 and a humidifier (HUM) 24.

[0018] The fuel gas supply device 40 includes an injector (INJ) 44, an ejector 46, and a gas-liquid separator 48. The injector 44 may be replaced with a pressure reducing valve. The coolant supply device 70 includes a coolant pump (WP) 76 and a radiator 75.

[0019] The output unit 80 includes a voltage control unit (VCU) 82, a power storage unit 84, an inverter (INV) 85, and a motor (electric motor) 86.

[0020] The output unit 80 includes the voltage control unit 82, the inverter 85, the power storage unit 84, a power storage device (HV BAT) 88, and a power storage device (LV BAT) 90.

[0021] The voltage control unit 82 includes a boost converter (SUC) and the like, which converts the DC generated voltage Vfc into a higher DC stored voltage Vbh.

[0022] The inverter 85 converts the stored voltage Vbh applied to its DC terminal into a three-phase voltage that drives the motor 86 and outputs it to the AC terminal. The stored voltage Vbh applied to the inverter 85 is either the voltage obtained by boosting the generated voltage Vfc by the voltage control unit 82 or the voltage of the energy storage device 88. The fuel cell vehicle 12 moves using the driving force generated by the motor 86 based on the stored voltage Vbh applied to the inverter 85.

[0023] The energy storage device 88 is charged by the power Pfc (Pfc = Vfc × Ifc) generated by the fuel cell stack 14. The energy storage device 88 is also charged by the regenerative power of the motor 86.

[0024] The energy storage unit 84 includes, in addition to the energy storage device 88, a low-voltage energy storage device 90 and a step-down converter (SDC) 89 that converts the high-voltage energy storage voltage Vbh to a low-voltage energy storage voltage Vbl to charge the energy storage device 90. The energy storage device 88 is equipped with an SOC sensor 94 that measures the remaining capacity (SOC) of the energy storage device 88. The energy storage unit 84 applies the energy storage voltage Vbh of the energy storage device 88 to the compressor 22 of the high-voltage auxiliary equipment.

[0025] The energy storage unit 84 applies the energy storage voltage Vbl of the energy storage device 90 to the injector 44, the refrigerant pump 76, and low-voltage auxiliary equipment such as an air conditioner (not shown) and a solenoid valve (described later).

[0026] The loads of the voltage control unit 82 and the energy storage unit 84 connected to the fuel cell 14 include the main motor 86 (main load) and the high-voltage auxiliary equipment and the low-voltage auxiliary equipment (auxiliary load).

[0027] The fuel cell 14 is composed of multiple power generation cells 50 stacked together. Each power generation cell 50 includes an electrolyte membrane / electrode structure (MEA) 52 and separators 53 and 54 that sandwich the electrolyte membrane / electrode structure 52.

[0028] The electrolyte membrane / electrode structure 52 comprises, for example, a solid polymer electrolyte membrane (also simply called an electrolyte membrane) 55 which is a thin film of perfluorosulfonic acid containing water, and a cathode electrode 56 and an anode electrode 57 that sandwich the electrolyte membrane 55.

[0029] The cathode electrode 56 and the anode electrode 57 have a gas diffusion layer (not shown) made of carbon paper or the like. An electrode catalyst layer (not shown) is formed by uniformly coating the surface of the gas diffusion layer with porous carbon particles on which a platinum alloy is supported. The electrode catalyst layer is formed on both sides of the electrolyte membrane 55.

[0030] On one side of the separator 53, a cathode channel (oxidant gas channel) 58 is formed on the surface facing the electrolyte membrane / electrode structure 52, connecting an oxidant gas inlet port 101 and an oxidant gas outlet port 102.

[0031] On the other side of the separator 54 facing the electrolyte membrane / electrode structure 52, an anode channel (fuel gas channel) 59 is formed that connects the fuel gas inlet port 103 and the fuel gas outlet port 104.

[0032] At the anode electrode 57, when fuel gas (hydrogen) is supplied, hydrogen ions are generated from hydrogen molecules through an electrode reaction mediated by a catalyst. These hydrogen ions then permeate the electrolyte membrane 55 and move to the cathode electrode 56, while electrons are released from the hydrogen molecules.

[0033] The electrons released from the hydrogen molecules move from the negative electrode terminal 106 through the voltage control unit 82 and the load such as the motor 86, and then to the cathode electrode 56 via the positive electrode terminal 108.

[0034] At the cathode electrode 56, the hydrogen ions and electrons react with the oxygen contained in the supplied oxidizing gas through the action of the catalyst to produce water.

[0035] A voltage sensor 110 for detecting the generated voltage Vfc of the fuel cell 14 is provided between the electrical wiring connecting the positive terminal 108 and the negative terminal 106 to the voltage control unit 82. A current sensor 112 for detecting the generated current Ifc of the fuel cell 14 is provided in the same electrical wiring.

[0036] A power generation state acquisition unit is formed by the voltage sensor 110 and the current sensor 112 to detect the power generation power Pfc as the power generation state. The power generation status acquisition unit may be formed using only the current sensor 112.

[0037] The compressor 22 consists of a compressor inverter (not shown) to which the stored voltage Vbh of a high-voltage energy storage device 88 is applied, and a mechanical supercharger driven by a compressor motor (not shown) controlled by the three-phase AC output of the compressor inverter.

[0038] The compressor 22 draws in outside air from the outside air intake 26, pressurizes the oxidizer gas, and supplies it to the fuel cell 14 through the humidifier 24 and the oxidizer gas supply channel 62.

[0039] The humidifier 24 has two passages, a passage 31A and a passage 31B. Compressed and heated to a high temperature by the compressor 22, dried air (oxidizer gas) flows into and circulates through passage 31A. Oxidizer off-gas (exhaust gas) discharged from the oxidizer gas outlet communication port 102 of the fuel cell 14 via the oxidizer off-gas outlet 92 flows through passage 31B.

[0040] The humidifier 24 has the function of humidifying the oxidizer gas supplied from the compressor 22. Specifically, the humidifier 24 humidifies the supply gas (oxidizer gas) flowing from the flow path 31B through the internal porous membrane to the flow path 31A by transferring the moisture contained in the oxidizer off-gas, and supplies the humidified oxidizer gas to the fuel cell 14 through the oxidizer gas supply flow path 62 and the oxidizer gas inlet 91.

[0041] Along the oxidizer gas supply channel 62 from the outside air intake 26 to the oxidizer gas inlet 91, the following components are installed in that order from the outside air intake 26: a temperature sensor 115, an airflow sensor (AFS: flow sensor) 116, a compressor 22, an inlet sealing valve 118, and a humidifier 24. Note that the flow channels such as the oxidizer gas supply channel 62, which are drawn with double lines, are formed by piping (the same applies hereafter). The inlet sealing valve 118 opens and closes the oxidizer gas supply channel 62.

[0042] The oxidizer off-gas discharge channel 63, which communicates with the oxidizer off-gas outlet 92, is equipped with a humidifier 24 and an outlet sealing valve 120, which is a back pressure valve, in that order from the oxidizer off-gas outlet 92.

[0043] Between the intake port of the inlet sealing valve 118 and the discharge port of the outlet sealing valve 120, in other words, between the oxidizer gas supply channel 62 and the oxidizer off-gas discharge channel 63, a bypass channel 66 is provided that connects the oxidizer gas supply channel 62 and the oxidizer off-gas discharge channel 63 and bypasses the fuel cell 14. The bypass channel 66 is equipped with a bypass valve 122, which is a flow control valve that opens and closes the bypass channel 66.

[0044] The bypass valve 122 adjusts the flow rate of the oxidizer gas that bypasses the fuel cell 14 and flows into the bypass channel 66.

[0045] When the bypass valve 122 is open, a portion of the oxidizing gas discharged from the compressor 22 flows through the bypass passage 66 to the discharge passage 64. The combined channel of the bypass channel 66 and the oxidizer off-gas discharge channel 63 is connected to the discharge channel 64. The temperature sensor 115 detects the ambient temperature.

[0046] The hydrogen tank 42, which constitutes the fuel gas supply device 40, is equipped with a hydrogen shut-off valve 43 and is a container that stores high-purity hydrogen compressed at high pressure.

[0047] The fuel gas (hydrogen) discharged from the hydrogen tank 42 is supplied to the inlet of the anode passage (fuel gas passage) 59 via the fuel gas inlet 93 and fuel gas inlet communication port 103 of the fuel cell 14, through the injector 44 and ejector 46 provided in the fuel gas supply passage 72.

[0048] In this case, the fuel gas supply passage 72 is provided with a pressure sensor 73 that detects (measures) the gas pressure (anode pressure) Pa of the fuel gas in the fuel gas supply passage 72.

[0049] In the anode channel 59, some of the water generated by the power generation of the fuel cell 14 moves from the cathode channel 58 through the electrolyte membrane / electrode structure 52 via reverse diffusion (permeation) and flows out into the fuel off-gas exhaust channel 74.

[0050] The outlet of the anode passage 59 is connected to the inlet 151 of the gas-liquid separator 48 through the fuel gas outlet communication port 104, the fuel off-gas outlet 95, and the fuel off-gas discharge passage 74.

[0051] The gas-liquid separator 48 is supplied with fuel off-gas, which is a hydrogen-containing gas containing reverse-diffused water, from the anode flow path 59 through the fuel off-gas discharge flow path 74.

[0052] The gas-liquid separator 48, which temporarily stores the reverse-diffusion water, separates the fuel off-gas into a gaseous component and a liquid component (liquid water).

[0053] The gaseous component of the fuel off-gas (fuel off-gas) is discharged from the gas outlet 152 of the gas-liquid separator 48 and supplied to the suction port of the ejector 46 via the circulation channel 77.

[0054] The fuel off-gas flows from the gas outlet 152 of the gas-liquid separator 48 through the purge passage 67, which is equipped with a purge valve 168, to the discharge passage 65.

[0055] The purge valve 168 is temporarily opened during startup or when returning from idle stop operation to normal operation in order to discharge nitrogen that has permeated the electrolyte membrane / electrode structure 52 from the cathode flow path 58 during soaking of the fuel cell vehicle 12 (when the power switch 202 is off) or during idle stop operation.

[0056] The liquid component (liquid water) of the fuel off-gas flows from the liquid outlet 160 of the gas-liquid separator 48 through the drain passage 162, which is equipped with a drain valve 164, to the discharge passage 65.

[0057] The fuel off-gas and liquid water flowing through the discharge channel 65 are mixed with at least a portion of the oxidizer gas and oxidizer off-gas flowing through the discharge channel 64 in order to dilute the hydrogen gas in the fuel off-gas and discharge it to the outside, and are then discharged to the outside air through the exhaust gas outlet 78 via the discharge channel 69.

[0058] The refrigerant supply device 70 of the fuel cell system 10 has a refrigerant flow path 138 for circulating refrigerant (coolant: CLA). The refrigerant flow path 138 has a refrigerant supply flow path 140 and a refrigerant discharge flow path 142. The refrigerant supply flow path 140 supplies refrigerant to the fuel cell 14, and the refrigerant discharge flow path 142 discharges refrigerant from the fuel cell 14. A radiator 75 is connected to the refrigerant supply flow path 140 and the refrigerant discharge flow path 142. A bypass flow path 143 equipped with a thermovalve 139 at one end is provided in parallel with the radiator 75.

[0059] The radiator 75 cools the refrigerant. A refrigerant pump 76 is provided in the refrigerant supply passage 140. The refrigerant pump 76 circulates the refrigerant within the refrigerant circulation circuit. The refrigerant circulation circuit includes the refrigerant supply passage 140, the refrigerant passage 60 inside the fuel cell 14, the refrigerant discharge passage 142, and the radiator 75. A temperature sensor 79 is provided in the refrigerant discharge passage 142. The refrigerant temperature (refrigerant outlet temperature) TRF detected by the temperature sensor 79 may be estimated to be the (internal) temperature of the fuel cell 14.

[0060] Each component of the fuel cell vehicle 12, which is equipped with the fuel cell system 10 configured as described above, is centrally controlled by the control device 200. In addition, the values ​​detected by various sensors are acquired by the control device 200.

[0061] The inlet sealing valve 118, outlet sealing valve 120, drain valve 164, purge valve 168, and bypass valve 122 are solenoid valves whose opening or closing or degree of opening is controlled by the control device 200. The control device 200 is a computer installed in the fuel cell system 10. The control device 200 includes an arithmetic unit (processing unit) 210, a storage unit 224, a display unit (not shown), and an operation unit (not shown).

[0062] The arithmetic unit 210 may be composed of a processor such as a CPU or GPU. In other words, the arithmetic unit may be composed of processing circuits.

[0063] The arithmetic unit 210 includes a determination unit 212 and a control unit 214. The determination unit 212 and the control unit 214 can be realized by the arithmetic unit 210 executing a program stored in the storage unit 224 (memory).

[0064] Furthermore, at least a portion of the control device 200 may be implemented using an integrated circuit such as an ASIC or FPGA. Alternatively, at least a portion of the control device 200 may be composed of an electronic circuit including discrete devices.

[0065] The storage unit 224 may consist of volatile memory and non-volatile memory. Examples of volatile memory include RAM. This volatile memory is used as the working memory of the processor and temporarily stores data necessary for processing or calculation. Examples of non-volatile memory include ROM and flash memory. This non-volatile memory is used as storage memory and stores programs, tables, maps, etc. At least a part of the storage unit 224 may be provided in the processor, integrated circuit, etc. as described above.

[0066] The control device 200 is connected to a power switch (power SW) 202 of the fuel cell vehicle 12, an accelerator pedal operation amount sensor 204 that outputs a signal (operation amount signal) corresponding to the amount of operation of the accelerator pedal (not shown), and a vehicle speed sensor 206.

[0067] Figure 2 shows example characteristic diagrams of the IV characteristic 300 (300a, 300b) and IP characteristic 302 (302a, 302b) of the fuel cell 14. IP characteristic 302a is the current-power characteristic when the fuel cell 14 is in a steady state (normal state).

[0068] Under normal conditions, IP characteristic 302a, the generated power Pfc [kW] increases approximately proportionally to the increase in the generated current Ifc [A]. IP characteristic 302b represents the current-power characteristics of the fuel cell 14 when its performance is degraded.

[0069] IP characteristic 302b during performance degradation refers to situations such as when IV performance is reduced, including during sub-zero startup, where the power generated by the fuel cell 14 (Pfc) is low and the refrigerant temperature does not rise easily.

[0070] Furthermore, IP characteristic 302b during performance degradation includes conditions such as misalignment of the oxidizer gas supply channel 62 piping, open malfunction of the thermovalve 139, and other situations that make it difficult for the refrigerant temperature to rise.

[0071] IV characteristic 300a is the current-voltage characteristic when the fuel cell 14 is in a steady state (normal state). The generated voltage Vfc [V] when the generated current Ifc is approximately 0 is called the open-circuit voltage OCV.

[0072] In IV characteristic 300a, as the generated current Ifc increases from zero, the generated voltage Vfc decreases sharply from the open-circuit voltage OCV, and thereafter, the generated voltage Vfc decreases gradually in accordance with the increase in the generated current Ifc.

[0073] IV characteristic 300b represents the current-voltage characteristics under performance degradation. As mentioned above, IV characteristic 300b under performance degradation corresponds to, for example, sub-zero startup, and can also change due to a malfunction such as the opening of the thermovalve 139.

[0074] The IP characteristics 302a and IV characteristics 300a in the steady state (normal state) are recorded in the storage unit 224 in advance. A detailed explanation of IP characteristic 302b during performance degradation will be provided later.

[0075] The control device 200 can control the generated current Ifc by controlling the generated voltage Vfc via the VCU 82, referring to the IV characteristics 300.

[0076] [Operation] [Explanation using a flowchart] The fuel cell system 10 according to this embodiment is basically configured as described above. The control operation of the control device 200 over the fuel cell system 10 during acceleration of the fuel cell vehicle 12 will now be explained with reference to the flowchart in Figure 3.

[0077] Figure 4 shows a map (characteristic) 310 of the output request value (load request output) Pro [kW] for the accelerator operation amount θ [deg] detected by the accelerator operation amount sensor 204, with vehicle speed Vs [km / h] as a parameter. The map 310 is pre-recorded in the storage unit 224.

[0078] In step S1, the control device 200 calculates the required output value Pro[kW] for the fuel cell 14 of the fuel cell system 10 by referring to the map 310 based on the user's accelerator input θ and vehicle speed Vs during acceleration, and proceeds to step S2.

[0079] The output requirement Pro is the required power Pfc, or gross power, of the fuel cell 14, which is generated from the main load (motor 86) and auxiliary loads (compressor 22, etc.).

[0080] In step S2, the control device 200 refers to the IP characteristics 302a of the fuel cell 14 to calculate the generated current Ifc corresponding to the output request value Pro, and uses the calculated generated current Ifc as the requested current command value (also called the current command value) Ircom (see Figure 2), and proceeds to step S3.

[0081] In step S3, the control device 200 determines the fuel gas pressure and oxidizer gas pressure to the fuel cell 14 based on the requested current command value Ircom, performs power generation control (also called FC control), and proceeds to step S4.

[0082] In this case, the control device 200 increases the actual output Pact of the fuel cell 14 to the output request value Pro at a predetermined rate of increase (referred to as the first rate of increase) based on the requested current command value Ircom.

[0083] In step S4, the control device 200 obtains the generated current Ifc and generated voltage Vfc through the current sensor 112 and voltage sensor 110, and calculates the actual output Pact of the fuel cell 14 (Pact = Ifc × Vfc = Iact × Vact).

[0084] At the same time, the control device 200 calculates the actual output rate Par (Par = ΔPact / Δt), which is the amount of change in the actual output Pact over a predetermined minute time Δt (minute actual output ΔPact), and proceeds to step S5. In step S5, the control device 200 determines whether the actual output Pact has plateaued.

[0085] In this case, even though the generated current Ifc (also called the actual current Iact) measured by the current sensor 112 is increasing, the control device 200 makes a positive determination that the output has plateaued (step S5: YES) when the actual output rate Par, which is the derivative (slope) of the actual output Pact, changes from an upward rate (positive value) to a downward rate (negative value), and the actual output Pact falls below the peak output value Ppk (see IP characteristic 302b in Figure 2), and proceeds to step S6.

[0086] In step S6, the control device 200 converts (sets) the peak value (peak current value) Ipk (see IP characteristic 302b in Figure 2) of the generated current Ifc corresponding to the peak output value Ppk of the actual output Pact to a limiting current command value (first limiting current command value) Ilcom (Ilcom=Ipk) which limits the requested current command value Ircom, and proceeds to step S7. In step S6, the control device 200 also sets the execution time of the limiting current command value Ilcom as a predetermined set time Ts in the timer (timekeeping unit).

[0087] The limiting current command value Ilcom=Ipk corresponds to the peak output value Ppk at which the actual output Pact no longer increases even when the generated current Ifc is increased, as described above. In other words, on IP characteristic 302b, the limiting current command value Ilcom=Ipk is the operating point (Ilcom, Ppk) at which the gross power of the fuel cell 14 reaches its maximum value with respect to the generated current Ifc.

[0088] By generating power with the current limiting command value Ilcom, it is highly likely that power generation at the peak output value Ppk will continue, thus preventing a decrease in the generated voltage Vfc.

[0089] In step S7, the control device 200 performs power generation control (FC control) based on the limiting current command value Ilcom, and proceeds to step S8.

[0090] In step S8, the control device 200 calculates the actual output Pact of the fuel cell 14 (Pact = Ifc × Vfc = Iact × Vact) and the actual output rate Par (Par = ΔPact / Δt), similar to the process in step S4, and proceeds to step S9 (monitoring process of the actual output Pact during control with the limiting current command value Ilcom).

[0091] In step S9, the control device 200 determines whether the execution time at the limit current command value Ilcom has elapsed to the set time Ts.

[0092] If the control device 200 determines that the set time Ts has not elapsed (step S9: NO), it returns to step S7. If it determines that the set time Ts has elapsed (step S9: YES), it proceeds to step S10.

[0093] The current limit in step S6 is performed by feedforward control of VCU82. Therefore, in order to reliably prevent a decrease in the generated voltage Vfc, the negative determination in step S9 may be weighted by the requirement that the actual output rate Par has not fallen below the peak output value Ppk for a predetermined time, in other words, that the actual output rate Par has maintained a positive value for a predetermined time (when it is determined that the actual output Pact is increasing).

[0094] In step S10, the control device 200 releases the limiting current command value Ilcom from the peak current value Ipk, sets a rate relaxation current command value Iucom that gradually increases the limiting current command value Ilcom to the requested current command value Ircom, switches to the rate relaxation current command value Iucom, and proceeds to step S11.

[0095] The rate of increase of the rate relaxation current command value Iucom (referred to as the second rate of increase) is set to a rate smaller than the predetermined rate of increase (the rate at which the actual output Pact of the fuel cell 14 is increased to the output request value Pro based on the requested current command value Ircom).

[0096] In step S11, the control device 200 controls the actual output Pact according to the rate relaxation current command value Iucom (FC control), and proceeds to step S12.

[0097] In step S12, when the actual output Pact matches the output request value Pro, the control device 200 switches (returns) the rate relaxation current command value Iucom to the request current command value Ircom and continues the FC control in step S11. When the actual output Pact matches the output request value Pro, it makes an affirmative decision (step S12: YES, limit removed) and terminates the process.

[0098] In step S5, if the control device 200 determines that the actual output Pact has not reached its limit and is approaching the output request value Pro, and makes a negative determination (step S5: NO), it controls the fuel cell 14 according to the requested current command value Ircom (step S11). In step S12, if the actual output Pact matches the output request value Pro, it makes a positive determination (step S12: YES) and terminates the process.

[0099] In the embodiment described above, when it is detected that the actual output Pact has plateaued as it rises towards the output request value Pro (step S5: YES), the actual output Pact is controlled by switching the request current command value Ircom to a limiting current command value Ilcom (limiting current command value control step).

[0100] During control of the actual output Pact with the limiting current command value Ilcom, when the set time Ts has elapsed (step S9: YES), the limiting current command value Ilcom is switched to a rate relaxation current command value Iucom, which gradually increases the actual output Pact to the requested current command value Ircom, and the control is performed (rate relaxation current command value control step). When the increasing actual output Pact matches the requested output value Pro (step S12: YES), the rate relaxation current command value Iucom is returned to the requested current command value Ircom and control is performed (return control step).

[0101] Therefore, even if the actual output (actual power generated) Pact plateaus and declines due to a decrease in the power generation voltage Vfc or other reasons, the actual output Pact, which is the gross output of the fuel cell 14, can be increased to the output request value (target power generated) Pro, thereby resolving the plateau.

[0102] [Explanation using a timing chart: Operation example 1] An example of the operation described in the flowchart of Figure 3 will be explained with reference to the timing chart in Figure 5. For ease of understanding, step numbers (Sn) from the flowchart will be inserted in some parts of the explanation.

[0103] For example, at the transition time t0 from idle stop operation to normal operation, when the control device 200 detects the accelerator pedal operation amount θ by the driver (user), it calculates an output request value Pro (Figure 4) based on the detected accelerator pedal operation amount θ and the vehicle speed Vs (S1). The control unit 214 calculates a requested current command value Ircom (Figure 2) corresponding to the output request value Pro (S2) and controls the fuel cell 14 (S3).

[0104] Between time points t0 and t1, the actual current Iact increases in line with the requested current command value Ircom, and the actual output Pact increases in line with the requested output value Pro.

[0105] At time t1, the actual output rate Par changes from an increasing rate (positive value) to a decreasing rate (negative value), and the actual current Iact increases. However, as shown between time t1 and time t2, at time t2, when the actual output Pact (=Pfc) is decreasing from the peak output value Ppk, the control device 200 makes a positive determination that the output has plateaued (S5: YES).

[0106] At time t2, the control device 200 converts the requested current command value Ircom into a limiting current command value Ilcom (Ilcom = Ipk, Figure 2) that generates the peak output value Ppk, and controls the actual output Pact for the set time Ts (S6~S9:NO).

[0107] At time t3 (S9:YES), after the set time Ts has elapsed, the control device 200 releases the limiting current command value Ilcom from the peak current value Ipk. In this case, from time t3, the control device 200 switches to a rate relaxation current command value Iucom, which gradually increases the limiting current command value Ilcom to the requested current command value Ircom, and controls the system (S10).

[0108] This control causes the actual output Pact to gradually increase in accordance with the increase in the rate relaxation current command value Iucom. In this example, the power generation is controlled by applying a limiting rate so that the rate of increase (rate of increase) of the rate relaxation current command value Iucom per unit time remains constant, thus suppressing any discomfort for the user.

[0109] At time t5, when the rate relaxation current command value Iucom matches the requested current command value Ircom, in other words, when the actual output Pact matches the requested output value Pro (S12:YES), the control device 200 changes the rate relaxation current command value Iucom to the requested current command value Ircom and continues normal processing.

[0110] In the above-described example of operation 1, when current limiting is applied, if the actual output Pact shows an upward trend (recovery trend), the limiting amount can be gradually reduced toward the required current command value Ircom for the accelerator operation amount θ, thereby increasing the gross output of the fuel cell 14.

[0111] [Explanation using a timing chart: Operation example 2] Operation Example 2 will be explained with reference to the timing chart in Figure 6.

[0112] The control device 200, while controlling the generated current Ifc with the rate relaxation current command value Iucom from time t3 onward, makes a positive determination of plateauing at time t4' if, at time t4, the actual output rate Par changes from an increasing rate to a decreasing rate and the actual current Iact increases, but the actual output Pact decreases again as shown from time t4 to time t4'.

[0113] In fact, the peak output value Ppk at time t4' has shifted to coordinate Q2(Ipk+ΔIfc,Ppk+ΔPfc) in the coordinate system of Figure 2, relative to coordinate Q1(Ipk,Ppk), in the upper right direction.

[0114] At time t4', the control device 200 changes the rate relaxation current command value Iucom to the limiting current command value (second limiting current command value) Ilcom' (Figure 2) and controls the actual output Pact.

[0115] For example, at time t4'' under control with the limiting current command value Ilcom'', the control device 200 determines that no further decrease in the actual output Pact has been detected. At this time t4'', the control device 200 switches from the limiting current command value Ilcom'' to the rate relaxation current command value Iucom, which gradually increases the limiting current command value to the required current command value Ircom, and controls accordingly. At time t5'', the rate relaxation current command value Iucom is switched back to the required current command value Ircom, and control is restored.

[0116] [Explanation using a timing chart: Operation example 3] Operation Example 3 will be explained with reference to Figure 7, which is an enlarged view of Figures 5 and 6 from near time t1 to near time t3.

[0117] In Operation Example 3, when the actual output Pact decreases (times t1 to t2), the steeper the rate of decrease of the actual output Pact (ΔPact / Δt, ΔPact' / Δt) or the larger the amount of decrease of the actual output Pact (ΔPact, ΔPact'), the more gradually the rate of increase of the command value of the rate relaxation current command value Iucom, which is switched at time t3, may be changed to the rate relaxation current command value Iucom' (Iucom → Iucom'), and the system may wait for the actual output Pact to change from decreasing to increasing.

[0118] In Figure 7, for example, since (|ΔPact / Δt|<|ΔPact´ / Δt|), the rate relaxation current command value Iucom is adopted for |ΔPact / Δt|, and a rate relaxation current command value Iucom´, which is less severe than the rate relaxation current command value Iucom, is adopted for |ΔPact´ / Δt|.

[0119] By gradually easing the current limit, it is possible to mitigate the discomfort that users feel when the generated current Ifc increases rapidly (such as a sudden acceleration sensation in response to the accelerator pedal input θ).

[0120] Furthermore, when the rate of decrease (ΔPact / Δt → ΔPact' / Δt) is steep, the control may be adjusted earlier than when the rate of decrease is gradual. For example, in Figure 7, the change from the requested current command value Ircom to the limiting current command value Ircom may be made before time point t2. Controlling the system in this way can further alleviate the discomfort experienced by the user described above.

[0121] [Note] In addition to the disclosures mentioned above, the following further notes are made:

[0122] (Note 1) In a fuel cell system control device (200) of a fuel cell system (10), the control device (200) determines a current command value (Ircom) to the fuel cell (14) in accordance with the load request output (Pro), and increases the actual output (Pact) of the fuel cell to the load request output at a predetermined rate of increase based on the current command value. When the control device detects that the actual output has plateaued before rising to the load request output while controlling the actual output with the current command value, it switches the current command value to a lower limit current command value (Ilcom) and controls the actual output. After controlling the actual output with the limit current command value, it switches the limit current command value to a rate relaxation current command value (Iucom) with a rate of increase smaller than the predetermined rate of increase and controls the actual output.

[0123] With this configuration, when it is detected that the actual output (the output power of the fuel cell, also called gross power or gross output) has plateaued before rising to the load-required output, the current command value is reduced to a limiting current command value to control the actual output. After controlling the actual output with the limiting current command value, the limiting current command value is changed to a rate-relaxing current command value to control the actual output.

[0124] In this way, current limiting is implemented when the actual output (gross output) of the fuel cell reaches its limit. Subsequently, the actual output can be increased to the load-required output by increasing the rate relaxation current command value.

[0125] (Note 2) In the control device for the fuel cell system described in Appendix 1, when the actual output is being controlled with the rate relaxation current command value, the rate relaxation current command value may be returned to the current command value corresponding to the load request output when the actual output matches the load request output. With this configuration, the actual output can be more reliably increased to the load-required output.

[0126] (Note 3) In the control device for the fuel cell system described in Appendix 1 or 2, the plateau in the actual output may be detected by capturing the change in the actual output, which is rising at the predetermined rate of increase, when it changes from rising to falling. With this configuration, the peak (limit) of the actual output can be reliably detected.

[0127] (Note 4) In the control device for the fuel cell system described in Appendix 1 or 2, the limiting current command value may be set to a current value (Ipk) corresponding to the peak value of the actual output that has reached its limit. With this configuration, the fuel cell can be controlled at high-efficiency control points (Ipk, Ppk).

[0128] (Note 5) In the control device for the fuel cell system described in Appendix 1 or 2, the rate of increase of the rate relaxation current command value may be set to a constant value when the actual output increases. With this configuration, the actual output can be increased to the load-required output while maintaining a stable control state.

[0129] (Note 6) In the control device for the fuel cell system described in Appendix 1 or 2, if the actual output changes again from an increasing rate to a decreasing rate while the actual output is being controlled with the rate relaxation current command value, the rate relaxation current command value may be changed to a limiting current command value to control the actual output. With this configuration, the likelihood of increasing the actual output to the load-required output increases.

[0130] (Note 7) In the control device for the fuel cell system described in Appendix 1 or 2, the rate relaxation current command value may be adjusted to increase more gradually the steeper the rate of decrease in the actual output or the larger the amount of decrease in the actual output when the actual output decreases. With this configuration, the likelihood of increasing the actual output to the load-required output increases.

[0131] (Note 8) A fuel cell system control method is a fuel cell system control method which determines a current command value to the fuel cell in accordance with the load request output and increases the actual output of the fuel cell to the load request output at a predetermined rate of increase based on the current command value, and comprises a limit current command value control step in which, when it is detected that the actual output has plateaued before rising to the load request output during the control of the actual output with the current command value, the current command value is changed to a limit current command value which is lowered and the actual output is controlled; and a rate relaxation current command value control step in which, after the actual output has been controlled with the limit current command value, the limit current command value is changed to a rate relaxation current command value which is lowered to a rate of increase smaller than the predetermined rate of increase and the actual output is controlled.

[0132] With this configuration, even if the actual output (gross output) of the fuel cell reaches its limit, the actual output can be increased to the load-required output.

[0133] This disclosure is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the gist of this disclosure or from the spirit of this disclosure derived from the claims and their equivalents. These embodiments can also be implemented in combination. For example, the order of operations and processes in the embodiments described above are given as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above. [Explanation of Symbols]

[0134] 10…Fuel cell system 12…Fuel cell vehicle 14…Fuel cell (fuel cell stack) 20…Oxidizer gas supply device 22... Compressor 40... Fuel gas supply system 50...Power generation cell 70...Refrigerant supply device 82...Voltage control unit 110...Voltage sensor 112...Current sensor 200...Control device 204...Accelerator pedal input sensor 206...Vehicle speed sensor 210...Calculation section 212...Judgment section 214...Control unit 224...Memory unit

Claims

1. In a control device for a fuel cell system, which determines a current command value to the fuel cell in accordance with the load request output and increases the actual output of the fuel cell to the load request output at a predetermined rate based on the current command value, When controlling the actual output with the current command value, if it is detected that the actual output has plateaued before rising to the load request output, the current command value is changed to a lower limit current command value to control the actual output. After controlling the actual output with the limiting current command value, the limiting current command value is changed to a rate relaxation current command value with a rate of increase smaller than the predetermined rate of increase, and the actual output is controlled. Control device for a fuel cell system.

2. In the control device for the fuel cell system according to claim 1, During control of the actual output at the rate relaxation current command value, when the actual output matches the load request output, the rate relaxation current command value is returned to the current command value corresponding to the load request output and control is performed accordingly. Control device for a fuel cell system.

3. In the control device for a fuel cell system according to claim 1 or 2, The plateau in the actual output is detected by capturing the change in the actual output, which is rising at the predetermined rate of increase, when it shifts from rising to falling. Control device for a fuel cell system.

4. In the control device for a fuel cell system according to claim 1 or 2, The limiting current command value is set to a current value corresponding to the peak value of the actual output that has reached its limit. Control device for a fuel cell system.

5. In the control device for a fuel cell system according to claim 1 or 2, When the actual output increases, the rate of increase of the rate relaxation current command value is set to a constant value. Control device for a fuel cell system.

6. In the control device for a fuel cell system according to claim 1 or 2, During the control of the actual output with the rate relaxation current command value, when the actual output changes again from an increasing rate to a decreasing rate, the rate relaxation current command value is changed to the limiting current command value to control the actual output. Control device for a fuel cell system.

7. In the control device for a fuel cell system according to claim 1 or 2, The rate relaxation current command value is set such that when the actual output decreases, the rate of increase becomes more gradual the steeper the rate of decrease in the actual output or the larger the amount of decrease in the actual output. Control device for a fuel cell system.

8. A control method for a fuel cell system that determines a current command value to the fuel cell in accordance with the load request output, and increases the actual output of the fuel cell to the load request output at a predetermined rate based on the current command value, During the control of the actual output with the current command value, if it is detected that the actual output has plateaued before rising to the load request output, a limit current command value control step is performed in which the current command value is lowered to a limit current command value and the actual output is controlled. After controlling the actual output with the limiting current command value, a rate relaxation current command value control step is performed in which the limiting current command value is changed to a rate relaxation current command value with an increase rate smaller than the predetermined increase rate, and the actual output is controlled by the following steps: A control method for a fuel cell system equipped with the following features.

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