Fuel Cell Systems

Abstract

To improve efficiency of a fuel cell system.SOLUTION: A fuel cell system comprises a fuel cell, a battery, and a control unit that controls the fuel cell and the battery. The control unit cumulatively calculates a first storage power amount that is amount of power generated by the fuel cell, of a power amount stored in the battery. The control unit cumulatively calculates a power generation efficiency average value of the fuel cell which is the value when the first storage power amount is stored. The control unit calculates a request power generation efficiency which is the efficiency in a case where a power satisfying a power request of a load device is generated by the fuel cell. The control unit, under such a first condition that the power generation efficiency average value becomes lower than the request power generation efficiency, causes the fuel cell to generate power satisfying the power request. The control unit, under such a second condition that the power generation efficiency average value becomes higher than the request power generation efficiency, causes the fuel cell to generate power at a specific operation point where the power generation efficiency becomes the maximum, and causes the battery to discharge power deficient with respect to the power request.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This specification discloses a fuel cell system. [Background technology]

[0002] Patent Document 1 discloses a fuel cell system that stops the fuel cell in a low load region (a region where the power demand is relatively low) where the power generation efficiency is low, and supplies power from a charged battery. The aim of this technology is to increase the power generation efficiency in the low load region by implementing intermittent operation of the fuel cell. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-71797 A Summary of the Invention [Problem to be solved by the invention]

[0004] Among the operating points determined by the current and voltage output from the fuel cell, there is a specific operating point at which the power generation efficiency is maximized. The further the operating point deviates from the specific operating point (i.e., the lower the load region or the higher the load region), the lower the power generation efficiency of the fuel cell becomes. The technology of Patent Document 1 does not take into account the high load region where the power demand is large, so the power generation efficiency in the high load region decreases. [Means for solving the problem]

[0005] The fuel cell system disclosed in this specification is a fuel cell system that supplies power to a load device. The fuel cell system includes a fuel cell, a battery, and a control unit that controls the fuel cell and the battery. The fuel cell is configured to be able to supply the generated power to the load device and the battery. The battery is configured to store the power generated by the fuel cell and to discharge the stored power to the load device. The control unit is capable of executing a process to cumulatively calculate a first accumulated power amount, which is the amount of power generated by the fuel cell, among the amount of power stored in the battery. The control unit is capable of executing a process to cumulatively calculate an average power generation efficiency of the fuel cell at the time of storing the first accumulated power amount. The control unit is capable of executing a process to calculate a required power generation efficiency when the fuel cell generates power that satisfies the power request of the load device. Under a first condition in which the average power generation efficiency is lower than the required power generation efficiency, the control unit is capable of executing a process to make the fuel cell generate power that satisfies the power request. Under a second condition in which the average power generation efficiency is higher than the required power generation efficiency, the control unit is capable of executing a process to make the fuel cell generate power at a specific operating point where the power generation efficiency is maximized, and to discharge power that is insufficient for the power request from the battery.

[0006] The more the operating point of the fuel cell moves toward the high load side relative to the specific operating point, the lower the required power generation efficiency becomes. Therefore, when the power demand of the load device becomes large to a certain extent, the second condition may be met in which the average power generation efficiency becomes higher than the required power generation efficiency. Under this second condition, the power generation efficiency of the fuel cell can be maximized by operating the fuel cell at the specific operating point. Furthermore, power that is insufficient relative to the power demand can be made up for by power charged by generating power with a power generation efficiency higher than the average power generation efficiency of the fuel cell. Since the power charged with a high power generation efficiency can be used as auxiliary power, a high power generation efficiency can be achieved for the entire fuel cell system, including the charging power. It is possible to increase the efficiency of the fuel cell system even in the high load range.

[0007] The control unit may, under the second condition, when the power shortage for the power request exceeds the discharge allowable power of the battery, cause the fuel cell to generate the excess power over the discharge allowable power, regardless of the specific operating point. With this configuration, when the battery cannot supply the power shortage for the power request, the state of causing the fuel cell to generate power at the specific operating point can be canceled. Since the shortage can be supplied by the power generation of the fuel cell, it is possible to reliably supply the requested power.

[0008] The control unit may further be capable of executing a process of cumulatively calculating a second accumulated amount of power supplied from sources other than the fuel cell out of the amount of power accumulated in the battery. When the second accumulated amount of power is not zero, the control unit may further be capable of executing a process of causing the fuel cell to generate power at a specific operating point regardless of the magnitude relationship between the average power generation efficiency and the required power generation efficiency, and discharging the power that is insufficient for the power request from the battery. The second accumulated amount of power is the amount of power accumulated without using the fuel cell. In this configuration, when the second accumulated amount of power remains, the second accumulated amount of power can be actively used. Since the usage rate of the second accumulated amount of power can be increased, it is possible to increase the efficiency of the fuel cell system per hour average.

[0009] The load device may include a motor. The battery may be configured to be capable of storing regenerative power generated by the motor. The control unit may calculate a first stored amount of power based on accumulating a charging current from the fuel cell. The control unit may calculate a second stored amount of power based on accumulating a charging current from the motor. With this configuration, the amount of power stored in the battery can be virtually classified into a first stored amount of power stored by the fuel cell and a second stored amount of power stored by the motor. The second stored amount of power is an amount of power that contributes more to increasing the efficiency of the fuel cell system than the first stored amount of power. Since the second stored amount of power can be recognized, it becomes possible to actively use the second stored amount of power.

[0010] The power generation efficiency average value at the current time may be PA(t), the power generation efficiency average value at the time dt ago may be PA(t-1), the first stored energy amount at the current time may be SP1(t), the first stored energy amount at the time dt ago may be SP1(t-1), the change in the first stored energy amount during the elapsed time dt may be SP1(dt), and the power generation efficiency of the fuel cell during the elapsed time dt may be GE(dt). The power generation efficiency average value at the current time may be calculated by the formula "PA(t)=(PA(t-1)×SP1(t-1)+GE(dt)×SP1(dt)) / SP1(t). With this configuration, the power generation efficiency average value can be updated successively. It is possible to keep the power generation efficiency average value up to date.

[0011] Details and further improvements of the technology disclosed in this specification are described in the following "Description of Embodiments of the Invention." [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a portion of an electric vehicle 1. FIG. [Diagram 2] 4 is a graph illustrating the characteristics of the fuel cell 14. [Diagram 3] 3 is a flowchart illustrating the operation of the fuel cell system 10. [Figure 4] 3 is a flowchart illustrating the operation of the fuel cell system 10. [Diagram 5] 1 is a graph illustrating how to determine a required power generation efficiency RP. [Figure 6] 4 is a time chart illustrating a specific example of the operation of the fuel cell system 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Configuration of electric vehicle 1) 1 shows a schematic configuration diagram of a portion of an electric vehicle 1. The electric vehicle 1 includes a fuel cell system 10, a vehicle motor 20, a power conversion device 30, and an accelerator position sensor 40. The fuel cell system 10 is a system that supplies power to the vehicle motor 20 and various accessories (not shown). The fuel cell system 10 includes an ECU 11, a fuel cell 14, a battery 15, and a current sensor 16.

[0014] The fuel cell 14 is connected to the vehicle motor 20 via the power conversion device 30. The fuel cell 14 is also connected to the battery 15. The fuel cell 14 is a power generation device that extracts electric power by electrochemically reacting hydrogen with air. The fuel cell 14 is equipped with various auxiliary devices (e.g., a hydrogen pump, a compressor, valves, etc.) which are not shown. The fuel cell 14 is configured to be able to supply the generated electric power to the vehicle motor 20 and the battery 15.

[0015] The battery 15 is a lithium ion battery. The battery 15 is configured to be able to store the power generated by the fuel cell 14 and to store regenerative power generated by the vehicle motor 20. The battery 15 is also configured to be able to discharge the stored power to the vehicle motor 20. The current sensor 16 detects the charge / discharge current value CDI of the battery 15 and transmits it to the ECU 11. The accelerator position sensor 40 detects the accelerator position AO of an accelerator (not shown) and transmits the detection result to the ECU 11.

[0016] The vehicle motor 20 is an electric motor for moving the vehicle. The power conversion device 30 converts the DC voltage supplied from the fuel cell 14 or the battery 15 into a three-phase AC voltage and supplies it to the vehicle motor 20. The power conversion device 30 also converts the three-phase AC voltage supplied from the vehicle motor 20 by regenerative power generation into a DC voltage and supplies it to the battery 15.

[0017] The ECU 11 is a computer that controls various elements constituting the electric vehicle 1. The ECU 11 includes a CPU 11c and a memory 11m. The memory 11m stores various control programs, a V-characteristic map IM and an efficiency map EM, which will be described later, and the like. The CPU 11c controls the operations shown in Figs. 3 and 4, which will be described later, in accordance with the control programs.

[0018] (Characteristics of fuel cell 14) The characteristics of the fuel cell 14 will be explained using FIG. 2. The IV characteristics map IM is a map showing the relationship between the current and voltage output from the fuel cell 14. The horizontal axis is current, and the vertical axis is voltage. The current value on the horizontal axis corresponds to the vehicle power demand (i.e., the power demand from the vehicle motor 20). The efficiency map EM is a map showing the efficiency of the fuel cell 14. The efficiency is the ratio between the electrical output and the enthalpy of the input fuel. Note that the efficiency of the fuel cell 14 is the efficiency of the system including various auxiliary devices (e.g., hydrogen pump, compressor).

[0019] As can be seen from the efficiency map EM, the fuel cell 14 has a specific operating point OPs where the power generation efficiency is at its maximum. The reason why the efficiency decreases in the region LL on the lower load side of the specific operating point OPs will be explained. The auxiliary devices of the fuel cell 14 (e.g., air compressor, hydrogen pump) consume a certain amount of power regardless of the amount of power generated. Therefore, in the region LL, the proportion of power consumption by the auxiliary devices becomes large, so the efficiency decreases. In addition, the reason why the efficiency decreases in the region HL on the higher load side of the specific operating point OPs will be explained. As can be seen from the IV characteristic map IM, the voltage value decreases as the current value increases. This is because the internal resistance increases and the voltage drops as the current value increases. It is generally known that the power generation efficiency of a fuel cell is proportional to the output voltage. Therefore, the efficiency of the fuel cell 14 decreases as the current value increases (i.e., the load increases).

[0020] (Operation of fuel cell system 10) The operation of the fuel cell system 10 will be described using the flowcharts of Figures 3 and 4. In the following, "step 10" will be abbreviated as "S10". The flows of Figures 3 and 4 are started when the ignition of the electric vehicle 1 is turned on, and are executed until the ignition is turned off. The flows of Figures 3 and 4 may be looped at a predetermined cycle (e.g., 100 ms). The flows of Figures 3 and 4 are roughly divided into three steps, S10, S20, and S30. These are explained below.

[0021] The contents of S10 will be described with reference to Fig. 3. S10 is a step for cumulatively calculating a first accumulated power amount SP1 and a second accumulated power amount SP2. The first accumulated power amount SP1 is the amount of power accumulated by power generation by the fuel cell 14 out of the amount of power accumulated in the battery 15. The second accumulated power amount SP2 is the amount of power accumulated by power supplied from sources other than the fuel cell 14 out of the amount of power accumulated in the battery 15. In this embodiment, the second accumulated power amount SP2 is accumulated by regenerative power generation by the vehicle motor 20.

[0022] S10 includes S11 to S16. In S11, the ECU 11 judges whether the battery 15 is being charged. If the judgement is affirmative (S11: Yes), the process proceeds to S12. In S12, the ECU 11 calculates the FC generation current I1 and the motor regeneration current I2. The FC generation current I1 and the motor regeneration current I2 are virtual classifications of the charging current and discharging current of the battery 15. The motor regeneration current I2 is a current generated by regenerative power generation of the vehicle motor 20. The motor regeneration current I2 may be obtained by subtracting the current consumed by various auxiliary devices from the regenerative power generation current. The FC generation current I1 is a current generated by power generation of the fuel cell 14. The FC generation current I1 may be obtained by subtracting the motor regeneration current I2 from the charging / discharging current value CDI measured by the current sensor 16.

[0023] On the other hand, if it is determined in S11 that the battery 15 is not being charged (S11: No), the process proceeds to S13. In S13, the ECU 11 determines whether or not there is any remaining capacity in the first stored electric energy SP1. The remaining capacity of the first stored electric energy SP1 can be calculated in S16, which will be described later. If the determination is affirmative (S13: Yes), the process proceeds to S14, where the current output from the battery 15 is classified as the FC generation current I1. Specifically, the charge / discharge current value CDI detected by the current sensor 16 is treated as the FC generation current I1.

[0024] On the other hand, if it is determined that there is no remaining capacity in the first stored power amount SP1 (S13: No), the process proceeds to S15. Then, the current output from the battery 15 is classified as the motor regenerative current I2. Specifically, the charge / discharge current value CDI detected by the current sensor 16 is regarded as the motor regenerative current I2.

[0025] In S16, ECU 11 calculates the first stored energy SP1 and the second stored energy SP2. To be more specific, the first stored energy at the current time is SP1(t). The first stored energy at the time preceding the elapsed time dt is SP1(t-1). The FC generation current during the elapsed time dt is I1. Note that the sign of the FC generation current I1 is negative to indicate charging and positive to indicate discharging. The elapsed time dt is, for example, the time required to execute the loop process shown in FIG. 3 and FIG. 4 once. Then, the first stored energy SP1(t) at the current time can be calculated by the following formula (1). SP1(t)=SP1(t-1)+(-I1×dt)...Equation (1) That is, the first accumulated power amount SP1 can be calculated based on accumulating the charging current from the fuel cell 14 for each elapsed time dt. The unit of the first accumulated power amount SP1 is [C(=A·s)].

[0026] Similarly, the second accumulated energy SP2(t) at the current time can be calculated by the following formula (2). SP2(t)=SP2(t-1)+(-I2×dt)...Equation (2) That is, the second accumulated electric energy SP2 can be calculated based on accumulating the charging current from the vehicle motor 20 for each elapsed time dt.

[0027] The contents of S20 will be described with reference to Fig. 3. S20 is a step for cumulatively calculating the power generation efficiency average value PA. The power generation efficiency average value PA is an average value of the power generation efficiencies of the fuel cell 14 when the first accumulated power amount SP1 is accumulated.

[0028] S20 includes S21 to S23. In S21, the ECU 11 judges whether the first accumulated power amount SP1 is greater than zero. If it is judged that the first accumulated power amount SP1 is equal to or less than zero (S21: No), the process proceeds to S23, where the ECU 11 sets the power generation efficiency average value PA to zero.

[0029] On the other hand, if it is determined that the first stored energy SP1 remains (S21: Yes), the process proceeds to S22. In S22, the ECU 11 calculates the average power generation efficiency PA. A more specific explanation will be given. The average power generation efficiency at the current time is PA(t). The average power generation efficiency at the time the elapsed time dt ago is PA(t-1). The first stored energy at the current time is SP1(t). The first stored energy at the time the elapsed time dt ago is SP1(t-1). The amount of change in the first stored energy during the elapsed time dt is SP1(dt). The power generation efficiency of the fuel cell 14 during the elapsed time dt is GE(dt). The charging efficiency of the battery 15 during the elapsed time dt is CE(dt). Then, the average power generation efficiency PA(t) at the current time can be calculated by the following formula (3). PA(t)=(PA(t-1)×SP1(t-1)+GE(dt)×CE(dt)×SP1(dt)) / SP1(t)...Equation (3)

[0030] This calculation method allows the power generation efficiency average value PA to be updated successively. It is possible to keep the power generation efficiency average value PA up to date. The charging efficiency CE(dt) may be omitted. The power generation efficiency GE(dt) and the charging efficiency CE(dt) may be calculated values ​​or may be actual measured values.

[0031] The contents of S30 will be described with reference to Fig. 4. S30 is a step for generating an FC power command, which is information for instructing the fuel cell 14 on the amount of power generation.

[0032] S30 includes S31 to S43. In S31, the ECU 11 judges whether the second accumulated power amount SP2 is greater than zero. If it is judged that the second accumulated power amount SP2 remains (S31: Yes), the process proceeds to S32. In S32, the ECU 11 sets the FC power command to the first mode M1. Then, the process proceeds to S40. The first mode M1 is a mode in which the fuel cell 14 generates power at a fixed power generation amount OPa. In addition, in the first mode M1, when the fixed power generation amount OPa is insufficient for the power request amount from the vehicle motor 20, the insufficient power is discharged from the battery 15, and when the fixed power generation amount OPa is greater than the power request amount, the excess power is charged to the battery 15. That is, in the first mode M1, a power generation command smaller than the fixed power generation amount OPa is not performed. The fixed power generation amount OPa is a power generation amount that is greater than the power generation amount at the specific operating point OPs by an additional power amount that takes into account the average load of the system. Since the operating point for generating the fixed power generation amount OPa is close to the specific operating point OPs, it is possible to prevent a power shortage in the entire system while bringing the power generation efficiency close to the maximum. The added power may be appropriately determined according to the characteristics of the system. In addition, in the setting of the first mode M1, the magnitude relationship between the average power generation efficiency PA and the required power generation efficiency RP is not compared.

[0033] On the other hand, if it is determined in S31 that the second accumulated electric energy SP2 does not remain (S31: No), the process proceeds to S33. In S33, the ECU 11 determines whether the first accumulated electric energy SP1 is greater than the threshold electric energy SPt. The threshold electric energy SPt may be determined in advance based on the minimum value of the SOC of the battery 15, etc. If the determination is affirmative (S33: Yes), it is determined that the first accumulated electric energy SP1 remains sufficiently, and the process proceeds to S34.

[0034] In S34, the ECU 11 calculates a required power generation efficiency RP. The required power generation efficiency RP is the power generation efficiency of the fuel cell 14 when the fuel cell 14 generates power that satisfies the power request from the vehicle motor 20. In other words, this is the power generation efficiency when there is no power supply from the battery 15 and the power request is satisfied only by the fuel cell 14.

[0035] A method for calculating the required power generation efficiency RP will be specifically described with reference to FIG. 5. The efficiency map EM in FIG. 5 is the same as the efficiency map EM described above with reference to FIG. 2. The accelerator pedal depression amount (accelerator depression) of the driver is detected by the accelerator pedal depression sensor 40. The ECU 11 calculates the power demand from the vehicle motor 20 based on the detected accelerator depression. The ECU 11 also calculates the output current OC corresponding to the power demand. The ECU 11 then refers to the efficiency map EM to calculate the required power generation efficiency RP corresponding to the output current OC. For example, when the output current OCa is calculated, the required power generation efficiency RPa is calculated using the efficiency map EM (see arrow A1). When the output current OCb is calculated, the required power generation efficiency RPb is calculated using the efficiency map EM (see arrow A2).

[0036] In S35, the ECU 11 judges whether the first condition or the second condition is satisfied. The first condition is that the power generation efficiency average PA (S22) is lower than the required power generation efficiency RP (S34). On the other hand, the second condition is that the power generation efficiency average PA (S22) is higher than the required power generation efficiency RP (S34).

[0037] This determination can be made using the efficiency map EM shown in Fig. 5. A more specific explanation will be given. The power generating efficiency average value PA is plotted on the efficiency map EM. Then, the power generating efficiency average value PA is compared with the required power generating efficiency RP. For example, when the required power generating efficiency is RPa, the power generating efficiency average value PA is lower than the required power generating efficiency RPa, so it is determined that the first condition holds. On the other hand, when the required power generating efficiency is RPb, the power generating efficiency average value PA is higher than the required power generating efficiency RPb, so it is determined that the second condition holds.

[0038] 5 shows a current range C1 where the first condition is satisfied, and a current range C2 where the second condition is satisfied. In the current range C1 where the first condition is satisfied, the load is relatively small, and the decrease in the efficiency of the fuel cell 14 is small. Therefore, under the first condition, the efficiency of the fuel cell system 10 as a whole is higher when the entire required power is provided only by the fuel cell 14 than when the power stored in the battery 15 is supplied. On the other hand, in the current range C2 where the second condition is satisfied, the load is relatively large, and the decrease in the efficiency of the fuel cell 14 is large. Therefore, under the second condition, the efficiency of the fuel cell system 10 as a whole is higher when the fuel cell 14 generates a fixed power generation amount OPa and the power shortage is provided by the power stored in the battery 15 than when the entire required power is provided only by the fuel cell 14.

[0039] If it is determined in S35 that the second condition is met (S35: second condition), the process proceeds to S36. In S36, the ECU 11 sets the FC power command to the second mode M2. Then, the process proceeds to S40. The second mode M2 ​​is a mode in which the fuel cell 14 generates power at a fixed power generation amount OPa. In addition, in the second mode M2, if the fixed power generation amount OPa is insufficient for the power request amount from the vehicle motor 20, the insufficient power is discharged from the battery 15, and if the fixed power generation amount OPa is greater than the power request amount, the excess power is charged to the battery 15. That is, in the second mode M2, a power generation command smaller than the fixed power generation amount OPa is not issued.

[0040] On the other hand, if it is determined that the first condition is satisfied (S35: first condition), the process proceeds to S37. In S37, the ECU 11 sets the FC power command to the third mode M3. Then, the process proceeds to S40. The third mode M3 is a mode in which the fuel cell 14 generates electric power that satisfies the electric power request from the vehicle motor 20.

[0041] Also, in S33, if it is determined that the first stored electric energy SP1 is smaller than the threshold electric energy SPt (S33: No), the process proceeds to S38. In S38, the ECU 11 sets the FC power command to the fourth mode M4. Then, the process proceeds to S40. The fourth mode M4 is a mode in which the fuel cell 14 generates electric power at a constant load with an output according to the remaining SOC of the battery 15. This makes it possible to increase the first stored electric energy SP1 in the fourth mode M4.

[0042] In S40, the ECU 11 calculates the power deficit by subtracting the discharge allowable power of the battery 15 from the power request from the vehicle motor 20. In S41, the ECU 11 determines which is larger: the FC power command set in any one of the first mode M1 to fourth mode M4, or the power deficit calculated in S40. If the FC power command is larger (S40: FC power command), it is determined that the power deficit can be covered by the power generation amount of the fuel cell 14, and the process proceeds to S42. In S42, the ECU 11 controls the fuel cell 14 based on the FC power command in any one of the first mode M1 to fourth mode M4.

[0043] On the other hand, if the power shortage is greater (S40: power shortage), the process proceeds to S43. In S43, the ECU 11 changes the FC power command to the high power mode MH. The high power mode MH is a mode in which the fuel cell 14 is controlled based on the power request from the vehicle motor 20. As a result, even under the second condition, when the power shortage relative to the power request exceeds the discharge allowable power of the battery 15, the state in which the fixed power generation amount OPa is generated by the fuel cell 14 can be canceled. Therefore, the fuel cell 14 can be made to generate the amount of power in excess of the discharge allowable power, making it possible to reliably supply the requested power. Then, the process returns to S10 to continue the loop process.

[0044] (Specific operation example) A specific operation example of the fuel cell system 10 will be described using the time chart of Fig. 6. The horizontal axis represents time. A case where the second stored power amount SP2 is greater than zero (S31: Yes) at time t1 will be described. In this case, since the system operates in the first mode M1, the FC power command is a command to the fuel cell 14 to generate the fixed power generation amount OPa (see region R1).

[0045] When the second stored energy SP2 becomes 0 at time t2 (S31: No), the first stored energy SP1 is greater than the threshold energy SPt (S33: Yes) and the average power generation efficiency PA is lower than the required power generation efficiency RP (S35: first condition), so the mode switches to the third mode M3 (arrow A11). Therefore, the electric power generated by the fuel cell 14 is supplied to the vehicle motor 20 (see region R2).

[0046] At time t3, when the second condition that the power generation efficiency average PA is higher than the required power generation efficiency RP is met (S35: second condition), the mode is switched to the second mode M2 ​​(arrow A12). Therefore, the FC power command becomes a command to make the fuel cell 14 generate the fixed power generation amount OPa (see region R3).

[0047] At time t4, when the first condition is met that the power generation efficiency average PA is lower than the required power generation efficiency RP (S35: first condition), the mode is switched back to the third mode M3 (arrow A13). Thus, the electric power generated by the fuel cell 14 is supplied to the vehicle motor 20 (see region R4).

[0048] Furthermore, at time t6, when the power shortage becomes greater than the power generated in the second mode M2 ​​(S41: power shortage), the mode is changed from the second mode M2 ​​to the high power mode MH (S43, see region R5). Thus, the power shortage is covered by the power generated by the fuel cell 14 (see region R6). At time t7, when the power shortage becomes smaller than the power generated in the second mode M2, the mode is returned to the second mode M2 ​​(see region R7).

[0049] At time t9, when the second stored power amount SP2 becomes smaller than the threshold power amount SPt (S33: No), the mode is switched to the fourth mode M4 (arrow A14). The FC power command becomes a constant power according to the SOC of the battery 15 (see region R8). Therefore, the first stored power amount SP1 increases (see region R9).

[0050] (effect) In conventional fuel cell systems, the amount of power generated by the fuel cell is determined based on the power required by the vehicle (e.g., the power required by the vehicle motor 20, the power required by the auxiliary devices). Since the operating point of the fuel cell is determined by chance, it is not possible to control the period during which the fuel cell operates at a specific operating point with high efficiency, making it difficult to improve efficiency. In this specification, the average power generation efficiency PA is compared with the required power generation efficiency RP to compare the efficiency when the stored power of the battery 15 is used with the efficiency when the power generated by the fuel cell 14 is directly used (S35). If it is determined that the stored power of the battery 15 is used more efficiently (S35: second condition), the fuel cell 14 is made to generate a fixed amount of power generation OPa, thereby maximizing the period during which the fuel cell 14 operates at an operating point near the specific operating point OPs. In addition, since the power charged in the battery 15 with high power generation efficiency can be used as auxiliary power, it is possible to achieve high power generation efficiency as a whole of the fuel cell system 10, including the charging power.

[0051] The technology of this specification can cumulatively calculate the power generation efficiency average value PA to be compared with the required power generation efficiency RP (S22). Therefore, it is possible to determine whether or not using the stored power of the battery 15 is more efficient by following the changes in the state of the fuel cell system 10. This allows feedback control with a long response time to be performed, further improving the efficiency of the entire fuel cell system 10.

[0052] In the technology of this specification, the amount of electric power stored in the battery 15 can be virtually classified into a first stored electric power amount SP1 and a second stored electric power amount SP2 (S10). The second stored electric power amount SP2 stored by the vehicle motor 20 is an amount of electric power that contributes more to increasing the efficiency of the fuel cell system 10 than the first stored electric power amount SP1 stored by the fuel cell 14. By recognizing this second stored electric power amount SP2, if the second stored electric power amount SP2 remains (S31: Yes), the second stored electric power amount SP2 can be actively used. Since the usage rate of the second stored electric power amount SP2 can be increased, it is possible to increase the time-averaged efficiency of the fuel cell system 10.

[0053] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful.

[0054] (Modification) The application of the fuel cell system 10 of the present technology is not limited to the electric vehicle 1, but can be expanded to various fields. For example, the fuel cell system 10 can be applied to a stationary power source. In this case, the second stored energy SP2 may be electricity stored by photovoltaic power generation or a power grid. Also, for example, the fuel cell system 10 can be applied to various mobile objects such as trains and ships.

[0055] The IV characteristic map IM and the efficiency map EM stored in the memory 11m may be updated as appropriate. This makes it possible to learn the deterioration of the fuel cell 14. It becomes possible to accurately calculate the required power generation efficiency RP. [Explanation of symbols]

[0056] 1: Electric vehicle 10: Fuel cell system 11: ECU 14: Fuel cell 15: Battery 20: Vehicle motor 30: Power conversion device SP1: 1st accumulated energy amount SP2: 2nd accumulated energy amount PA: Average power generation efficiency RP: Required power generation efficiency

Claims

1. A fuel cell system for supplying power to a load device, comprising: A fuel cell; A battery; A control unit that controls the fuel cell and the battery; Equipped with the fuel cell is configured to be able to supply generated electric power to the load device and the battery, the battery is configured to store the electric power generated by the fuel cell and to be able to discharge the stored electric power to the load device; The control unit is a process of cumulatively calculating a first accumulated amount of power, which is an amount of power generated by the fuel cell, out of the amount of power accumulated in the battery; a process of cumulatively calculating an average value of the power generation efficiency of the fuel cell during accumulation of the first accumulated power amount; A process of calculating a required power generation efficiency when the fuel cell generates power that satisfies the power request of the load device; a process of causing the fuel cell to generate electric power that satisfies the electric power request under a first condition in which the average electric power generating efficiency is lower than the required electric power generating efficiency; a process of causing the fuel cell to generate power at a specific operating point where the power generation efficiency is maximized under a second condition where the average power generation efficiency is higher than the required power generation efficiency, and discharging the power that is insufficient for the required power from the battery; A fuel cell system capable of performing the above steps.

2. 2. The fuel cell system of claim 1, wherein when the power shortage for the power request exceeds the discharge allowable power of the battery under the second condition, the control unit causes the fuel cell to generate the excess power over the discharge allowable power regardless of the specific operating point.

3. The control unit is a process of cumulatively calculating a second accumulated amount of electric power supplied from a source other than the fuel cell out of the amount of electric power accumulated in the battery; a process of causing the fuel cell to generate power at the specific operating point and discharging the power that is insufficient for the power request from the battery when the second accumulated power amount is not zero, regardless of the magnitude relationship between the average power generation efficiency and the requested power generation efficiency; The fuel cell system according to claim 1 or 2, further comprising:

4. The load device includes a motor, The battery is configured to be capable of storing regenerative power generated by the motor, The control unit is calculating the first accumulated power amount based on accumulating a charging current from the fuel cell; 4. The fuel cell system according to claim 3, wherein the second accumulated power amount is calculated based on accumulating a charging current from the motor.

5. The power generation efficiency average value at the current time is PA(t), The power generation efficiency average value at the time dt before is defined as PA(t-1), The first accumulated energy amount at the current time is defined as SP1(t), The first stored energy amount at the time dt before is defined as SP1(t-1), The change amount of the first stored power amount during an elapsed time dt is defined as SP1(dt), When the power generation efficiency of the fuel cell during an elapsed time dt is GE(dt), 4. The fuel cell system according to claim 3, wherein the average power generation efficiency at the current time is calculated by the formula "PA(t) = (PA(t-1) x SP1(t-1) + GE(dt) x SP1(dt)) / SP1(t).

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