Fuel cell system control method, fuel cell vehicle, and fuel cell system

Abstract

The present invention relates to a control method for a fuel cell system, a fuel cell vehicle, and a fuel cell system. An electronic control device (50) of a fuel cell vehicle (10) controls the output of a fuel cell (20), i.e., the power generation output (Pfc), so that the storage voltage (Vbat) of a power storage device (24) is not lower than the power generation voltage (Vfc) of the fuel cell (20).

Description

Technical Field

[0001] The present invention relates to a control method for a fuel cell system, a fuel cell vehicle, and a fuel cell system, each comprising a motor driven by a so-called hybrid power source based on the output of a fuel cell (power generation output, in [W]) and the output of a power storage device (power storage output, in [W]). Background Art

[0002] For example, Patent Document 1 discloses the following technology. This technology maximizes the use of the combined output of power generation and storage for driving a motor. To achieve this, it includes a fuel cell converter that converts the low-voltage power generation output to a high-voltage power generation output, and a power storage device converter that converts the low-voltage storage output to a high-voltage storage output.

[0003] In this case, the boost ratios of the two converters are changed to perform control so that the output voltage (generated voltage) of the fuel cell does not exceed the output voltage (stored voltage) of the power storage device.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese JP2017-051042A Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, cost reduction is an important issue in fuel cell systems and fuel cell vehicles. For example, it is believed that reducing the number of converters used in the power storage device can reduce the cost of the fuel cell system and the fuel cell vehicle.

[0009] However, when the converter for the power storage device is eliminated and the output of the fuel cell converter is directly connected to the power storage device (direct connection), the following problems may occur when attempting to maximize the combined output of the power generation output and the power storage output.

[0010] When the stored power is used at high output, the voltage of the power storage device (storage voltage) drops. If the dropped storage voltage falls below the generated voltage, the fuel cell converter cannot be controlled to boost the voltage. This can lead to a so-called direct connection between the fuel cell and the power storage device.

[0011] In this direct connection state, the output voltage (power generation voltage) of the fuel cell becomes the same as the output voltage (storage voltage) of the power storage device. Therefore, there is a problem that the power generation output cannot be controlled, resulting in degradation of the fuel cell.

[0012] Solutions for solving problems

[0013] The object of the present invention is to solve the above-mentioned problems.

[0014] One aspect of the present invention is a control method for a fuel cell system, wherein the fuel cell system comprises: a fuel cell that generates a power generation voltage; a power storage device that generates a power storage voltage; a load that includes a motor and an inverter, wherein the DC end of the inverter is connected to the power storage device and the AC end is connected to the motor; and a boost converter whose input end is connected to the fuel cell and whose output end is connected to the DC end of the inverter and the power storage device. The control method includes: a process of obtaining the power generation voltage and the power storage voltage; and a process of controlling the output of the fuel cell, i.e., the power generation output, so that the power storage voltage is not lower than the power generation voltage.

[0015] Other aspects of the present invention relate to a fuel cell system (fuel cell vehicle) comprising: a fuel cell that generates a power generation voltage; a power storage device that generates a power storage voltage; a load that includes a motor and an inverter, the DC end of the inverter being connected to the power storage device and the AC end being connected to the motor; a boost converter whose input end is connected to the fuel cell and whose output end is connected to the DC end of the inverter and the power storage device; a memory; and a CPU that executes a program recorded in the memory, and when the CPU executes the program recorded in the memory to thereby control the fuel cell, the power storage device, the motor, the inverter, and the boost converter, the CPU controls the output of the fuel cell, i.e., the power generation output, so that the power storage voltage is not lower than the power generation voltage.

[0016] Effects of the Invention

[0017] According to the present invention, the fuel cell's power output is controlled so that the storage voltage does not fall below the generated voltage—in other words, the generated voltage is kept below the storage voltage. This allows the boost converter to consistently boost the generated voltage to the storage voltage. This prevents a situation where the generated voltage exceeds the storage voltage, rendering the boost converter unable to perform a boost operation and causing the fuel cell and the storage device to be directly connected via the boost converter in its non-boosted state. This prevents fuel cell degradation caused by a failure to control the generated output.

[0018] As a result, the conventional buck-boost converter for the power storage device, placed between the power storage device and the DC side of the inverter, can be eliminated. This reduces costs by an amount equivalent to the eliminated buck-boost converter. Furthermore, the space available for the buck-boost converter can be expanded.

[0019] The above-mentioned objects, features, and advantages will be easily understood from the following description of the embodiments described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic overall configuration diagram of a fuel cell vehicle according to an embodiment of a fuel cell system control method according to an embodiment of the present invention.

[0021] Figure 2 yes Figure 1 The simplified block diagram of the fuel cell vehicle is shown.

[0022] Figure 3 This is the IV characteristic diagram of the fuel cell.

[0023] Figure 4 This is a characteristic diagram of the storage voltage and generated voltage relative to the power supply output.

[0024] Figure 5 This is an output distribution table showing the distribution of power supply output with respect to load output required by loads.

[0025] Figure 6 This is a flowchart showing the procedure for using the output allocation table.

[0026] Figure 7 This is a flowchart for explaining the operation of a fuel cell vehicle according to one embodiment.

[0027] Figure 8 is a timing diagram, where Figure 8 A is a timing chart showing the utilization of the stored power output for the load. Figure 8 B is a timing chart showing the transition of the stored voltage and the generated voltage according to the load utilization status. Figure 8 C is a time chart showing a utilization status of the power generation output for the load. DETAILED DESCRIPTION

[0028] Regarding the fuel cell system and the control method of the fuel cell system according to the present invention, in relation to a fuel cell vehicle implementing the method, preferred embodiments are given with reference to the attached drawings. Figure 1 While explaining.

[0029] [Description of the Configuration Related to the Control Method of a Fuel Cell Vehicle]

[0030] Figure 1 A schematic configuration diagram of a fuel cell vehicle 10 (hereinafter also referred to as “FCV 10 ” or “vehicle 10 ”) serving as a fuel cell system according to the present embodiment is shown.

[0031] Figure 2A simplified block diagram of the FCV 10 is shown.

[0032] When the main load of the fuel cell system is the motor 12 for driving, the fuel cell system is referred to as FCV 10. The control method of the fuel cell system according to this embodiment can also be applied to fuel cell systems whose main load is a motor other than driving, such as industrial equipment such as factory facilities.

[0033] like Figure 1 As shown, the FCV 10 basically comprises a fuel cell (also referred to as FC) 20, a boost converter (also referred to as an FC converter or FCVCU (VCU: voltage control unit)) 22, a battery device (also referred to as a battery-electrical device) 24, an inverter (also referred to as an inverter) 26, a motor 12, a transmission (T / M) 28, wheels 30, and an electronic control unit 50 (hereinafter also referred to as "ECU 50") that controls these components.

[0034] Moreover, in Figure 1 In order to avoid complexity, wiring (signal lines, etc.) between the ECU 50 and various components is partially omitted.

[0035] The fuel cell 20 and the power storage device 24 basically function as a parallel power supply (so-called hybrid power supply) for the FCV 10. This power supply supplies output [W] to a load (also referred to as a main load) 18 including an inverter 26 and the motor 12.

[0036] That is, the electric power (relatively low-voltage power generation output) Pfc [W] of the fuel cell 20 is converted into a relatively high-voltage power generation output Pfc via the boost converter 22 and supplied to the load 18 .

[0037] On the other hand, the relatively high-voltage electric power (electricity storage output) Pbat [W] of the electricity storage device 24 is directly supplied to the load 18 .

[0038] Although not shown, the stored power output Pbat is supplied not only to the load 18 but also to auxiliary loads such as an air pump driving the fuel cell 20 , and lighting and electric power steering of the FCV 10 .

[0039] The fuel cell 20 has, for example, a structure in which fuel cell units are stacked, each of which is formed by sandwiching a solid polymer electrolyte membrane between an anode electrode and a cathode electrode.

[0040] Although not shown in the figure, the vicinity of the fuel cell 20 includes an anode system including a fuel gas supply source having a fuel tank, a cathode system including an oxidant gas supply source having an air pump, and a cooling system including a cooling pump.

[0041] The anode system supplies and discharges fuel gas (hydrogen) to and from the anode of the fuel cell 20. The cathode system supplies and discharges air containing oxygen (oxidant gas) to and from the cathode of the fuel cell 20. The cooling system cools the fuel cell 20 using a coolant to maintain a predetermined temperature.

[0042] The power storage device 24 is an energy storage unit including a plurality of battery cells, and can utilize, for example, a lithium-ion secondary battery, a nickel-metal hydride secondary battery, etc. In this embodiment, a lithium-ion secondary battery is utilized. A capacitor can also be used as the power storage device 24 .

[0043] Boost converter 22 is a chopper-type boost converter (boost voltage converter). As shown in the figure, boost converter 22 is composed of, for example, a choke coil (inductor) L1, a diode D1, a switching element (transistor) T1, and smoothing capacitors C11 and C12.

[0044] The boost converter 22 performs duty cycle control, switching the switching element T1 on and off (repeatedly switching on and off) according to the duty cycle D (the ratio of the "on period" of the switching element T1 to the "on period and off period"). This duty cycle control boosts the output voltage of the fuel cell 20, i.e., the generated voltage Vfc, and applies it to the inverter 26 on the secondary side 2S as the inverter DC terminal voltage Vinvdc (Vinvdc = Vbat). As is well known, the boost ratio (Vbat / Vfc) is calculated as (Vbat / Vfc) = {1 / (1-D)}.

[0045] The inverter 26 is, for example, a three-phase full-bridge type and is a bidirectional DC / AC converter. During power operation of the FCV 10 (motor 12), in which the motor 12 is driven by the output of the fuel cell 20 and / or the power storage device 24, the inverter 26 converts the DC power generated at the DC terminal of the inverter 26 into three-phase AC power based on the generated output Pfc and / or the stored output Pbat, and supplies the power to the motor 12.

[0046] On the other hand, during regeneration when the motor 12 is rotated without being driven by the inverter 26 , the inverter 26 converts the three-phase AC power generated in the motor 12 into DC power (regenerative power) and supplies it to the power storage device 24 .

[0047] A voltage sensor 80 for detecting a generated voltage Vfc of the fuel cell 20 and a current sensor 82 for detecting a generated current Ifc of the fuel cell 20 are arranged between the fuel cell 20 and the primary side 1S of the boost converter 22 .

[0048] A voltage sensor 84 for detecting a stored voltage Vbat of the power storage device 24 and a current sensor 86 for detecting a stored current Ibat of the power storage device 24 are arranged between the secondary side 2S of the boost converter 22 and the power storage device 24 .

[0049] A current sensor 88 for detecting the boosted generated current Ifc2 is provided on the secondary side 2S of the boost converter 22 .

[0050] A current sensor 90 for detecting the inverter DC-end current Iinvdc is disposed at the DC end of the inverter 26 .

[0051] exist Figure 1 、 Figure 2 In this FCV 10, since the power storage device 24 is directly connected to the DC terminal of the inverter 26 (direct connection), it is important to ensure that the inverter DC terminal voltage Vinvdc of the inverter 26 is equal to the power storage voltage Vbat (Vinvdc=Vbat). In other words, the inverter DC terminal voltage Vinvdc can be detected (measured) by the voltage sensor 84.

[0052] The FCV 10 is provided with an accelerator pedal 110 for increasing, decreasing, or maintaining vehicle speed. The accelerator pedal 110 is provided with a depression amount sensor 112 for detecting the depression amount of the accelerator pedal 110 as an accelerator pedal opening θap.

[0053] The motor 12 is provided with a rotation speed sensor 114 for detecting the rotation speed Nmot thereof.

[0054] Furthermore, a power switch (power SW) 116 of the FCV 10 is arranged on the instrument panel.

[0055] Signals from these sensors and power switch 116 are supplied via signal lines (partially not shown) to ECU (Electronic Control Unit) 50, a control device. ECU 50 receives signals such as physical quantities from various sensors and the on / off status of power switch 116 via the signal lines. Signal lines are not limited to wired and can also be wireless.

[0056] The ECU 50 includes input / output devices, a computing device (including a CPU), and a storage device (memory). The ECU 50 detects the aforementioned signals and executes a program (control program) stored in the storage device, thereby functioning as various functional units and controlling the FCV 10. The ECU 50 is not limited to a single unit; it may be divided into separate units for controlling the fuel cell 20, the load 18, and the power storage device 24.

[0057] Figure 3 An output characteristic (IV characteristic) 102 of the fuel cell 20 is shown.

[0058] The output characteristic 102 of the fuel cell 20 is as follows: as the generated voltage Vfc decreases from the open-circuit voltage Vfcocv, the generated current Ifc increases. More specifically, when the generated current Ifc is increased to the threshold generated current Ifca from the fuel cell 20 at the open-circuit voltage Vfcocv, the generated voltage Vfc decreases from the open-circuit voltage Vfcocv at a relatively steep slope.

[0059] Next, when the generated current Ifc is increased from the threshold generated current Ifca to the threshold generated current Ifcb, the generated voltage Vfc decreases at a gentle slope.

[0060] Furthermore, when the generated current Ifc is increased to a value equal to or higher than the threshold generated current Ifcb, the generated voltage Vfc decreases at a steep slope.

[0061] Figure 4 It is a characteristic diagram showing a characteristic 106 of the power generation voltage Vfc with respect to the power supply output Ppower (power generation output Pfc) [W] and a characteristic 104 of the power storage voltage Vbat with respect to the power supply output Ppower (power storage output Pbat) [W].

[0062] As can be seen from the characteristic 106 , the power generation voltage Vfc of the fuel cell 20 decreases in a quadratic function of the decreasing function as the power generation output Pfc increases.

[0063] As can be seen from the characteristic 104 , the storage voltage Vbat of the power storage device 24 decreases in an inversely proportional linear function (linearly) as the storage output Pbat increases.

[0064] Figure 5 The output allocation table 52 recorded in advance in the storage device of the ECU 50 is shown.

[0065] The horizontal axis represents the load output Pload [W], which is the output required by the load 18 (the inverter 26 and the motor 12 ), and the vertical axis represents the power output Ppower [W] supplied as the load output Pload.

[0066] The power supply output Ppower is a combined output of the power generation output Pfc and the power storage output Pbat (Ppower=Pfc+Pbat).

[0067] In a small output range Psd from the load output Pload [W] having an electric power value of 0 to the load output P1, the load output Pload is provided only by the power storage output Pbat indicated by the dotted line.

[0068] In the middle output region Pmd from the load output P1 to the load output P2, the threshold output is provided by the combined output (Pbatconst+Pfc) of the fixed output storage output Pbatconst indicated by the dotted line and the power generation output Pfc indicated by the chain line.

[0069] In the large output region Pld above the load output P2, a combined output (Pfcconst+Pbat) of the power generation output Pfcconst shown by the chain line and maintained at a fixed value and the power storage output Pbat shown by the dotted line is provided.

[0070] The thick solid line shows the combined output, that is, the power output Ppower (Ppower=Pbat+Pfc).

[0071] Figure 6 1 is a flowchart showing a procedure for the ECU 50 to utilize the output allocation table 52 .

[0072] When the power switch 116 of the FCV 10 is turned on, the ECU 50 compares the load output Pload required by the load 18 with the load output P1 and the load output P2 , which are threshold values (reference values), in step S1 .

[0073] When the load output Pload is smaller than the load output P1 (Pload<P1), in step S2, the power output Ppower is set to the power storage output Pbat (Ppower=Pbat).

[0074] When the load output Pload is greater than the load output P1 and less than the load output P2 (P1≤Pload<P2), in step S3, the power output Ppower is set to the combined output of the fixed storage output Pbatconst and the power generation output Pfc (Ppower=Pfc+Pbatconst).

[0075] When the load output Pload is equal to or greater than the load output P2 (Pload≥P2), in step S4, the power output Ppower is set to the combined output of the fixed power generation output Pfcconst and the power storage output Pbat (Ppower=Pfcconst+Pbat).

[0076] Thus, the output allocation table 52 is an output allocation reference that predetermines the load output Pload according to the magnitude of the load output Pload, which is the power required by the load 18. As will be described in detail later, the ECU 50 controls the boost converter 22 and the like in such a manner that the distribution of the power generation output Pfc and the power storage output Pbat is set (determined) according to the output allocation reference determined based on the output allocation table 52, and the load output Pload is provided.

[0077] [FCV 10 basic operation instructions]

[0078] Basically, the basic operation (power running control and regeneration control) of the FCV 10 configured as described above will be described first.

[0079] During travel, the ECU 50 generates a load output request (required load output) corresponding to the depression amount (accelerator pedal opening) θap obtained from the accelerator pedal 110 depression amount sensor 112 (during power operation of the motor 12).

[0080] Based on the demand for the load output Pload, the load 18 is driven by the power generation output Pfc (Pfc=Ifc×Vfc) supplied from the fuel cell 20 in power generation and / or the storage output Pbat (Pbat=Vbat×Ibatd) supplied from the storage device 24 (Ibatd: discharge current).

[0081] In this case, the motor 12 driven via the inverter 26 generates driving force, which is power for traveling. The driving force is used to rotate and drive the wheels 30 via the transmission 28, so that the FC vehicle 10 travels.

[0082] In this way, the ECU 50 performs power running control.

[0083] On the other hand, during regeneration of the motor 12 , that is, during deceleration when the accelerator pedal 110 is released and the depression amount (accelerator pedal opening) θap obtained from the depression amount sensor 112 of the accelerator pedal 110 is zero, the ECU 50 performs regeneration control.

[0084] In this regenerative control, the inverter 26 converts the inverter AC-end power (regenerative power) based on the regenerative output of the AC generated by the motor 12 into the inverter DC-end power {(DC-end voltage Vinvdcx×inverter DC-end current Iinvdc (regenerative current Iinvr))}.

[0085] The regenerative electric power generated by the regeneration of the motor 12 is stored (charged) in the power storage device 24 as a storage current Ibatc.

[0086] [Description of the control method of FCV 10]

[0087] Next, based on Figure 7 Flowchart and Figure 8 A~ Figure 8 The control method of the FCV 10 according to the embodiment will be described with reference to the timing chart shown in FIG.

[0088] Figure 8The value of 0 for the storage output Pbat and the value of 0 for the power generation output Pfc shown in A and 8C mean that the electric power supplied as the load output Pload is 0.

[0089] The routine related to the flowchart is executed by the ECU 50 as a control subject.

[0090] In step S11 , it is monitored whether the power switch 116 is switched from the OFF state to the ON state. If it is confirmed that the power switch 116 has been switched to the ON state (step S11 : YES), the process proceeds to step S12 .

[0091] In step S12 , the fuel cell 20 starts generating power and is kept in an idle state.

[0092] like Figure 8 As shown in A to 8C, during the period from time t0 to time t1 (time ta, etc.), the generated voltage Vfc is maintained at Figure 3 The appropriate voltage between the open circuit voltage Vfcocv and the power generation voltage Vfca is the idle power generation voltage Vfcidle ( Figure 8 B).

[0093] The power generation output Pfcidle related to the idle power generation voltage Vfcidle is supplied to an auxiliary load (not shown) or is charged in the power storage device 24 .

[0094] During the idling power generation period (t0-t1), the power output Pbat of the power storage device 24 is supplied to auxiliary loads such as the air pump. The power storage voltage Vbat of the power storage device 24 is maintained at a value close to the open circuit voltage Vbatocv. Figure 8 A represents the electric power supplied to the load 18 and therefore becomes a value of 0 during the period from the time point t0 to the time point t1.

[0095] On the other hand, after time point t0 (step S12), until the power switch 116 is switched from the on state to the off state, the boost converter 22 is controlled by the ECU 50 with a boost ratio {Vbat(Vinvdc) / Vfc} so that the generated voltage Vfc becomes the set voltage (target voltage).

[0096] Furthermore, during the period from time t0 to time t1, the voltage step-up ratio of the voltage step-up converter 22 is set to Vbatocv / Vfcidle (see Figure 8 B).

[0097] Next, in step S13, the power storage output Pbat is set as the load output Pload, and the FCV 10 travels (time point tb between time point t1 and time point t2, etc.) That is, the load output Pload is provided only by the power storage output Pbat.

[0098] In this case, in step S14 , as shown from time point t1 to time point t2 , it is monitored that the storage voltage Vbat decreases.

[0099] During the period from time point t1 to time point t2 , the boost ratio of boost converter 22 is set to Vbat / Vfcidle.

[0100] Next, in step S15 , it is determined whether the voltage difference (Vbat−Vfc) between the decreasing storage voltage Vbat and the generated voltage Vfc (in this case, the idle generated voltage Vfcidle) has dropped to a predetermined threshold voltage difference ΔVth (≈0 V).

[0101] If the voltage has not dropped to the threshold voltage difference ΔVth (step S15 : NO), in step S16 , it is monitored whether the generated voltage Vfc falls below the stored voltage Vbat (Vfc<Vbat) (time point tb, etc.).

[0102] Next, in step S17, the same process as in step S1 ( Figure 6 ) is the same processing as described in ).

[0103] The ECU 50 compares the load output Pload required by the load 18 with the load output P1 and the load output P2.

[0104] When the load output Pload is smaller than the load output P1 (Pload<P1), the power supply output Ppower is set to the power storage output Pbat (Ppower=Pbat) in steps S12 to S17.

[0105] When the processing of steps S12 to S17 is repeated, and the stored voltage Vbat decreases to the point where the determination in step S15 is "Yes" (Vbat-Vfc=ΔVth), the process proceeds to step S19.

[0106] In step S19 , for example, at time tc between time t2 and time t3 , the load output Pload is provided by the power output Ppower which is the combined output of the constant power storage output Pbatconst and the power generation output Pfc.

[0107] In step S20 , the decrease in the generated voltage Vfc corresponding to the increase in the generated output Pfc is monitored, and the process proceeds to step S16 .

[0108] In step S16 , it is monitored that the generated voltage Vfc is lower than the stored voltage Vbat (Vfc<Vbat).

[0109] Then, in step S17, the same process as step S1 ( Figure 6That is, the ECU 50 compares the load output Pload required by the load 18 with the load output P1 and the load output P2.

[0110] When the load output Pload is greater than or equal to the load output P1 and less than the load output P2 (P1≤Pload<P2), the process returns to step S19, and the load output Pload is provided by the power supply output Ppower, which is the combined output of the fixed storage output Pbatconst and the power generation output Pfc.

[0111] While the process of repeating step S17 → step S19 → step S20 → step S16 continues, if the load output Pload is greater than the load output P2 (Pload ≥ P2) in the determination of step S17, the process proceeds to step S18.

[0112] In step S18, a large load output Pload is provided by the power supply output Ppower (Ppower=Pfcconst+Pbat), which is a combined output of the fixed power storage output Pbatconst and the power storage output Pbat (after time point t3).

[0113] Thereafter, the processes of step S16 → step S17 → step S18 are repeated, and a process is selected based on the determination result of step S17 .

[0114] [Modification]

[0115] The above-mentioned embodiment can also be modified as follows.

[0116] When the process is about to proceed from step S17 to step S18, in other words, when the load output Pload is about to shift from the medium output range Pmd to the large output range Pld, the generated voltage Vfc may be decreased to a predetermined generated voltage (threshold voltage) Vfcb ( Figure 3 ), or when the generated current Ifc exceeds a predetermined threshold generated current Ifcb ( Figure 3 By performing such a transition control, it is possible to switch between the medium output region Pmd and the large output region Pld by simple control.

[0117] [Inventions that can be understood from the embodiments and modifications]

[0118] Here, the invention that can be grasped based on the above-mentioned embodiment is described below. In addition, for easy understanding, some of the components are marked with the reference numerals used in the above-mentioned embodiment, but the components are not limited to the components marked with the reference numerals.

[0119] The present invention is a control method for a fuel cell system, wherein the fuel cell system comprises: a fuel cell 20, which generates a power generation voltage Vfc; a power storage device 24, which generates a power storage voltage Vbat; a load 18, which includes a motor 12 and an inverter 26, the DC end of the inverter 26 is connected to the power storage device 24 and the AC end is connected to the motor 12; and a boost converter 22, the input end of which is connected to the fuel cell 20, and the output end is connected to the DC end of the inverter 26 and the power storage device 24. The control method includes: a process of obtaining the power generation voltage Vfc and the power storage voltage Vbat (step S16); and a process of controlling the output of the fuel cell 20, i.e., the power generation output Pfc, so that the power storage voltage Vbat is not lower than the power generation voltage Vfc (steps S16, S17, S12, S18, S19).

[0120] In this way, the power generation output Pfc of the fuel cell 20 is controlled so that the storage voltage Vbat does not fall below the power generation voltage Vfc. In other words, the power generation voltage Vfc is lower than the storage voltage Vbat. As a result, the boost converter 22 can always boost the power generation voltage Vfc to the storage voltage Vbat. This avoids a situation where the boost converter 22 is unable to perform a boost operation due to the power generation voltage Vfc exceeding the storage voltage Vbat, and the fuel cell 20 and the storage device 24 are directly connected via the boost converter 22 in a non-boosted state. Therefore, it is possible to prevent degradation of the fuel cell 20 due to the inability to control the power generation output Pfc.

[0121] As a result, the conventionally required buck-boost converter for the power storage device, placed between the power storage device 24 and the DC terminal of the inverter 26, can be eliminated. This reduces costs by an amount equivalent to the eliminated buck-boost converter. Furthermore, the space available for the buck-boost converter can be expanded.

[0122] In addition, in the control method of the fuel cell system, the process of controlling the power generation output Pfc is controlled in the following manner: according to the output distribution standard predetermined according to the size of the load output Pload, the power required by the load 18, namely the load output Pload, is provided by the power generation output Pfc and the storage output Pbat of the storage device 24.

[0123] Thereby, the power generation output Pfc can be mechanically controlled (processed) according to a predetermined output distribution standard.

[0124] Furthermore, in the control method of the fuel cell system, in the process of controlling the power generation output, control is performed in the following manner: in the small output area Psd of the power required by the load 18, that is, the load output Pload, the power of the storage device 24 is made variable and the load output Pload is provided only by the storage output Pbat; in the middle output area Pmd of the load output Pload, the load output Pload is provided by the fixed value of the storage output Pbatconst and the power generation output Pfc obtained by making the power of the fuel cell 20, that is, the power generation output Pfc, variable; in the large output area Pld of the load output Pload, the load output Pload is provided by the fixed value of the power generation output Pfcconst and the storage output Pbat obtained by making the power storage output Pbat variable.

[0125] As a result, the power output Ppower of the fuel cell system becomes a mixed power output of the power storage output Pbat and the power generation output Pfc.

[0126] In the low output range Psd of the load output Pload, the low-efficiency power generation output Pfc is not used, and the power storage output Pbat is used instead. In the medium output range Pmd of the load output Pload, both the high-efficiency power generation output Pfc and the power storage output Pbat are used. In the high output range Pld of the load output Pload, the power storage output Pbat and the fixed-value power generation output Pfcconst in the high-efficiency range are used.

[0127] By performing control in this manner, the fuel cell system can be operated with high power efficiency over the entire range from the low output region Psd to the high output region Pld of the power output Ppower (load output Pload).

[0128] In addition, in the control method of the fuel cell system, in the process of controlling the power generation output, when migrating from the small output area Psd of the load output Pload to the medium output area Pmd, the migration is performed when the voltage difference (Vbat-Vfc) obtained by subtracting the power generation voltage Vfc from the storage voltage Vbat becomes a small voltage up to a predetermined threshold voltage difference ΔVth.

[0129] Thus, it is possible to switch between the small output region Psd and the medium output region Pmd through simple control.

[0130] Furthermore, in the control method of the fuel cell system, in the process of controlling the power generation output Pfc, when migrating from the medium output region Pmd of the load output Pload to the large output region Pld, the migration is performed when the power generation voltage Vfc drops to a predetermined threshold voltage Vfcb, or when the power generation current Ifc becomes a current exceeding a predetermined threshold power generation current Ifcb.

[0131] In this case as well, switching between the medium output region Pmd and the large output region Pld can be performed by simple control.

[0132] Furthermore, the motor 12 can be used as a driving motor for the fuel cell vehicle 10 .

[0133] The fuel cell system and fuel cell vehicle 10 involved in the present invention include: a fuel cell 20, which generates a power generation voltage Vfc; a power storage device 24, which generates a power storage voltage Vbat; a load 18, which includes a motor 12 and an inverter 26, the DC end of the inverter 26 is connected to the power storage device 24 and the AC end is connected to the motor 12; a boost converter 22, whose input end is connected to the fuel cell 20 and the output end is connected to the DC end of the inverter 26 and the power storage device 24; a memory; and a CPU, which executes a program recorded in the memory. When the CPU executes the program recorded in the memory to thereby control the fuel cell 20, the power storage device 24, the motor 12, the inverter 26, and the boost converter 22, the CPU controls the output of the fuel cell 20, i.e., the power generation output Pfc, so that the power storage voltage Vbat is not lower than the power generation voltage Vfc.

[0134] In this fuel cell system and fuel cell vehicle 10, the boost converter 22 can consistently boost the generated voltage Vfc to the stored voltage Vbat. This prevents a situation where the boost converter 22 becomes unable to perform a boost operation due to the generated voltage Vfc exceeding the stored voltage Vbat, and the fuel cell 20 and the power storage device 24 become directly connected via the boost converter 22 in its non-boosted state. This prevents degradation of the fuel cell 20 due to an inability to control the generated output Pfc.

[0135] As a result, the conventionally required buck-boost converter for the power storage device, placed between the power storage device 24 and the DC terminal of the inverter 26, can be eliminated. This reduces costs by an amount equivalent to the eliminated buck-boost converter. Furthermore, the space available for the buck-boost converter can be expanded.

[0136] Furthermore, the present invention is not limited to the above-described embodiment, and various configurations can be employed without departing from the gist of the present invention.

Claims

1. A method for controlling a fuel cell system, wherein: The fuel cell system comprises: a fuel cell (20) that generates a power generation voltage; a power storage device (24) that generates a power storage voltage; A load (18) includes a motor (12) and an inverter (26), wherein a DC terminal of the inverter (26) is connected to the power storage device and an AC terminal is connected to the motor; as well as a boost converter (22) having an input end connected to the fuel cell and an output end connected to the DC end of the inverter and the power storage device, The control method includes: a step of obtaining the generated voltage and the stored voltage; as well as The step of controlling the power generation output of the fuel cell so that the stored voltage does not fall below the power generation voltage is performed as follows: In a small output range of the power required by the load, that is, the load output, the power of the power storage device is made variable and the load output is provided only by the power storage output. In the middle output range of the load output, the load output is provided by the fixed value of the stored power output and the power generation output of the fuel cell, which is a variable power generation output. In a large output range of the load output, the load output is provided by the fixed-value power generation output and the variable power storage output.

2. The fuel cell system control method according to claim 1, wherein: In the step of controlling the power generation output, When the load output is to transition from a low output range to a medium output range, the transition is performed when the voltage difference obtained by subtracting the generated voltage from the stored voltage becomes a low voltage equal to a predetermined threshold voltage difference.

3. The control method of the fuel cell system according to claim 1 or 2, characterized in that: In the step of controlling the power generation output, When the load output is to transition from the medium output range to the high output range, the transition is performed when the generated voltage drops to a predetermined threshold voltage or when the generated current exceeds a predetermined threshold generated current.

4. A fuel cell vehicle comprising: a fuel cell that generates a voltage for generating electricity; a power storage device that generates a power storage voltage; a load comprising a motor and an inverter, wherein a DC terminal of the inverter is connected to the power storage device and an AC terminal of the inverter is connected to the motor; a boost converter having an input end connected to the fuel cell and an output end connected to a DC terminal of the inverter and the power storage device; Memory; and a CPU that executes a program recorded in the memory, When the CPU executes the program recorded in the memory to thereby control the fuel cell, the power storage device, the motor, the inverter, and the boost converter, the CPU controls the power output of the fuel cell so that the power storage voltage does not fall below the power generation voltage. In controlling the power output, the CPU performs control in the following manner: In a small output range of the power required by the load, that is, the load output, the power of the power storage device is made variable and the load output is provided only by the power storage output. In the middle output range of the load output, the load output is provided by the fixed value of the stored power output and the power generation output of the fuel cell, which is a variable power generation output. In a large output range of the load output, the load output is provided by the fixed-value power generation output and the variable power storage output.

5. A fuel cell system comprising: a fuel cell that generates a voltage for generating electricity; a power storage device that generates a power storage voltage; a load comprising a motor and an inverter, wherein a DC terminal of the inverter is connected to the power storage device and an AC terminal of the inverter is connected to the motor; a boost converter having an input end connected to the fuel cell and an output end connected to a DC terminal of the inverter and the power storage device; Memory; and a CPU that executes the program recorded in the memory, When the CPU executes the program recorded in the memory to thereby control the fuel cell, the power storage device, the motor, the inverter, and the boost converter, the CPU controls the power output of the fuel cell so that the power storage voltage does not fall below the power generation voltage. In controlling the power output, the CPU performs control in the following manner: In a small output range of the power required by the load, that is, the load output, the power of the power storage device is made variable and the load output is provided only by the power storage output. In the middle output range of the load output, the load output is provided by the fixed value of the stored power output and the power generation output of the fuel cell, which is a variable power generation output. In a large output range of the load output, the load output is provided by the fixed-value power generation output and the variable power storage output.

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