Fuel cell power generation system

Abstract

To provide a fuel cell power generation system for controlling the output of a fuel cell and provided with a power conditioner, in which a deviation between the current command value and the actual output current value of the fuel cell is suppressed.SOLUTION: The fuel cell power generation system comprises a fuel cell 10, a fuel cell control unit 12, and a power conditioner 20. The fuel cell control unit sets an output power command value P* which is the target generated power of the fuel cell and a current command value Isofc* which is the target generated current of the fuel cell, and exercises fuel cell control so that necessary fuel is supplied to the fuel cell in order for the fuel cell to generate power with the current command value Isofc*. The power conditioner exercises maximum power point tracking control and converts the DC power generated by the fuel cell into AC power. The power conditioner is constituted so as to limit the generated power of the fuel cell on the basis of an input signal from the outside, and the fuel cell control unit transmits an output power command value to the power conditioner.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell power generation system in which DC power generated by a fuel cell is converted into AC power by a power conditioner. [Background technology]

[0002] Patent Document 1 discloses a fuel cell power generation system in which DC power generated by a fuel cell is converted to AC power by a power conditioner (hereinafter also referred to as "PCS (Power Conditioning System)"). In the fuel cell power generation system of Patent Document 1, a current current command value is constantly output from the fuel cell's control unit to the PCS control unit so that the PCS does not request excessive power from the fuel cell, and the PCS control unit controls the converter and inverter based on the current command value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-71998 Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration of Patent Document 1, the PCS operates based on a current command value from the control unit of the fuel cell, so a PCS dedicated to the fuel cell is required.

[0005] On the other hand, it is possible to use a general-purpose solar cell PCS with a fuel cell, but the solar cell PCS performs maximum power point tracking (hereinafter also referred to as "MPPT (Maximum Power Point Tracking)") independently of the fuel cell. As a result, the fuel cell's current command value and actual output current value become dissociated, and if the output current becomes excessive, there is a risk of the fuel cell deteriorating or being damaged. Furthermore, if the amount of gas supplied to the fuel cell is less than the specified amount, there is a risk of the fuel cell deteriorating or being damaged, and if the amount of gas supplied is more than the specified amount, the power generation efficiency will decrease.

[0006] In view of the above, the present invention aims to prevent the current command value of a fuel cell from becoming dissociated from the actual output current value in a fuel cell power generation system equipped with a power conditioner that controls the output of the fuel cell. [Means for solving the problem]

[0007] In order to achieve the above object, claims 1 to The fuel cell power generation system described includes a fuel cell (10), a fuel cell control unit (12), and a power conditioner (20). The fuel cell generates power when fuel is supplied. The fuel cell control unit sets an output power command value (P*) that is the target power generation of the fuel cell, and a current command value (Isofc*) that is the target power generation current of the fuel cell, and performs fuel supply control so that the fuel cell is supplied with the amount of fuel necessary for the fuel cell to generate power at the current command value (Isofc*). The power conditioner To connect to the commercial power grid (31) Maximum power point tracking control is performed to operate the fuel cell at the operating point where the output power of the fuel cell is maximum, and the DC power generated by the fuel cell is converted to AC.

[0008] The power conditioner is configured to limit the power generated by the fuel cell based on an external input signal. The fuel cell control unit transmits an output power command value as an input signal to the power conditioner. The power conditioner If the output power is below the output power command value, maximum power point tracking control is performed, and if the output power is not below the output power command value, the power generated by the fuel cell is limited.

[0009] This allows the fuel cell control unit to externally control the fuel cell output control by the power conditioner. The power conditioner can perform output power suppression control of the fuel cell based on the output power command value, and in a fuel cell power generation system equipped with a power conditioner that performs MPPT control, it is possible to prevent the current command value of the fuel cell from diverging from the actual output current value.

[0010] The reference numerals in parentheses for the above components indicate the corresponding relationship with the specific means described in the embodiments to be described later. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an overall configuration diagram of a fuel cell power generation system according to a first embodiment. [Figure 2] 3 is a flowchart showing the operation of the fuel cell power generation system of the first embodiment. [Figure 3] 4 is a graph showing the relationship between power and voltage of the fuel cell of the first embodiment. [Figure 4] 4 is a graph showing the relationship between current and voltage of the fuel cell of the first embodiment. [Figure 5] 10 is a graph showing a change over time in an output current value Isofc in the first embodiment. [Figure 6] 10 is a graph showing a change over time in an output current value Isofc in a comparative example of the first embodiment. [Figure 7] 6 is a flowchart showing the operation of a fuel cell power generation system according to a second embodiment. [Figure 8] 10 is a graph showing the relationship between power and voltage of a fuel cell according to a second embodiment. [Figure 9] 10 is a graph showing the relationship between current and voltage of a fuel cell according to a second embodiment. [Figure 10] 10 is a graph showing a change over time in the output current value Isofc of the second embodiment. [Figure 11] FIG. 10 is an overall configuration diagram of a fuel cell power generation system according to a third embodiment. [Figure 12]10 is a flowchart showing the operation of a fuel cell power generation system according to a third embodiment. [Figure 13] FIG. 10 is an overall configuration diagram of a fuel cell power generation system according to a fourth embodiment. [Figure 14] 10 is a flowchart showing the operation of a fuel cell power generation system according to a fourth embodiment. [Figure 15] FIG. 10 is an overall configuration diagram of a fuel cell power generation system according to a fifth embodiment. [Figure 16] FIG. 10 is an overall configuration diagram of a fuel cell power generation system according to a sixth embodiment. [Figure 17] FIG. 10 is a control block diagram of a fuel cell power generation system according to a sixth embodiment. [Figure 18] 10 is a flowchart showing the operation of a fuel cell power generation system according to a sixth embodiment. [Figure 19] FIG. 13 is a diagram showing current variations in a fuel cell power generation system according to a sixth embodiment. [Figure 20] FIG. 13 is a control block diagram of a fuel cell power generation system according to a seventh embodiment. [Figure 21] 12 is a flowchart showing the operation of the fuel cell power generation system of the seventh embodiment. [Figure 22] FIG. 10 is an overall configuration diagram showing a modified example of a fuel cell power generation system. [Figure 23] FIG. 10 is an overall configuration diagram showing a modified example of a fuel cell power generation system. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, several embodiments for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, parts corresponding to matters described in the preceding embodiment will be assigned the same reference numerals, and duplicated explanations may be omitted. In each embodiment, when only a part of the configuration is described, other previously described embodiments may be applied to the other parts of the configuration. In addition to combinations of parts that are specifically specified as being combinable in each embodiment, it is also possible to partially combine embodiments even if not specified, as long as there is no particular problem with the combination.

[0013] (First embodiment) A first embodiment of the present invention will now be described. As shown in Fig. 1, a fuel cell power generation system 1 includes a fuel cell 10 and a PCS 20. In the fuel cell power generation system 1 of this embodiment, DC power generated by the fuel cell 10 is converted to AC power by the PCS 20 and consumed by a load 30. The fuel cell power generation system 1 can be used in a factory, for example, and the load 30 can be, for example, electrical equipment in the factory.

[0014] The fuel cell 10 is a power generation device that generates electric power by utilizing an electrochemical reaction between hydrogen as a fuel and oxygen as an oxidant. The fuel cell 10 has a stack structure in which multiple unit cells, each having an electrolyte sandwiched between a pair of electrodes, are stacked. In this embodiment, the fuel cell 10 is a solid oxide fuel cell (SOFC) that uses an electrolyte made of an oxygen ion conductive oxide.

[0015] Hydrogen is supplied to the fuel cell 10 from a fuel supply device 11. For example, a hydrogen tank filled with high-pressure hydrogen can be used as the fuel supply device 11. The amount of hydrogen supplied from the fuel supply device 11 to the fuel cell 10 is controlled by a fuel cell control unit 12.

[0016] Although not shown in Figure 1, air is supplied to the fuel cell 10. In the fuel cell 10, an electrochemical reaction occurs between hydrogen and oxygen in the air, generating electrical energy. Of the hydrogen supplied to the fuel cell 10, unreacted hydrogen that is not used in the electrochemical reaction is discharged from the fuel cell 10 as exhaust gas.

[0017] A current command value Isofc*, which is the target power generation current of the fuel cell 10, is output from the fuel cell control unit 12 to the fuel supply device 11. The current command value Isofc* is a value equivalent to the amount of hydrogen supply required for the fuel cell 10 to generate power at the current command value Isofc*. The fuel supply device 11 adjusts the amount of hydrogen supply to the fuel cell 10 based on the current command value Isofc*. In other words, in this embodiment, fuel supply control for the fuel cell 10 is performed using the current command value Isofc*. In this embodiment, symbols marked with "*" indicate control command values ​​sent to the controlled device.

[0018] A power command value P0* can be input from the power company to the fuel cell control unit 12. The power command value P0* is the amount of power generated by the fuel cell 10 specified by the power company, and is input to the fuel cell control unit 12 by the power company when, for example, the power company limits the amount of power generated by the fuel cell 10.

[0019] When a power command value P0* is input, the fuel cell control unit 12 determines an output power command value P* within a range not exceeding the power command value P0*, and when a power command value P0* is not input, the fuel cell control unit 12 determines the output power command value P* based on the required power of the load 30. The output power command value P* is the target power generation power of the fuel cell 10, and is output from the fuel cell control unit 12 to a PCS control unit 23, which will be described later.

[0020] The wiring for supplying power to the fuel cell 10 is provided with an FC output current sensor 13 that detects the output current value Isofc of the fuel cell 10, and an FC output voltage sensor 14 that detects the output voltage value Vsofc of the fuel cell 10. The output current value Isofc detected by the FC output current sensor 13 and the output voltage value Vsofc detected by the FC output voltage sensor 14 are each input to the fuel cell control unit 12.

[0021] The PCS 20 is a power conditioner that converts DC power output by the fuel cell 10 into AC power in order to connect to the commercial power grid 31. In this embodiment, a solar cell PCS with an MPPT control function is used as the PCS 20.

[0022] The PCS 20 of this embodiment converts the DC power output by the fuel cell 10 into three-phase AC power of 200 V, the same as that of the commercial power system 31. The load 30 is supplied with power from either the PCS 20 or the commercial power system 31, or from both the PCS 20 and the commercial power system 31.

[0023] The PCS 20 has a converter 21, an inverter 22, and a PCS control unit 23. The converter 21 receives DC power generated by the fuel cell 10 and converts and boosts the voltage of the input DC power. The converter 21 can change the output voltage of the fuel cell 10. The inverter 22 converts the DC power boosted by the converter 21 into AC power. The PCS control unit 23 controls the operation of the converter 21 and the inverter 22.

[0024] The PCS 20 performs maximum power point tracking control (MPPT control) to operate the fuel cell 10 at the operating point where the output power of the fuel cell 10 is maximized. In MTTP control, the output voltage of the fuel cell 10 is varied, the output power of the fuel cell before and after the output voltage variation is compared, and the output voltage is controlled so that the output power is maximized.

[0025] The PCS control unit 23 performs output power suppression control to limit the power generated by the fuel cell 10 based on an external input signal. An output power command value P* is input to the PCS control unit 23 from the fuel cell control unit 12 as an input signal. The PCS control unit 23 performs output power suppression control of the fuel cell 10 so that the output power value P of the fuel cell 10 does not exceed the output power command value P*. In other words, the output control of the fuel cell 10 by the PCS control unit 23 can be controlled externally.

[0026] The PCS 20 is provided with a PCS input current sensor 24 that detects the output current value Isofc of the fuel cell input to the converter 21, and a PCS input voltage sensor 25 that detects the output voltage value Vsofc of the fuel cell input to the converter 21. The output current value Isofc detected by the PCS input current sensor 24 and the output voltage value Vsofc detected by the PCS input voltage sensor 25 are each input to the PCS control unit 23.

[0027] The PCS 20 is provided with a PCS output current sensor 26 that detects an AC current value Iac output by the inverter 22, and a PCS output voltage sensor 27 that detects an AC voltage value Vac output by the inverter 22. The AC current value Iac detected by the PCS output current sensor 26 and the AC voltage value Vac detected by the PCS output voltage sensor 27 are each input to the PCS control unit 23.

[0028] Next, the operation of the fuel cell power generation system 1 having the above configuration will be described using the flowchart in Fig. 2. Each process in the flowchart shown in Fig. 2 is repeatedly executed. The flowchart shown in Fig. 2 includes processes performed by the fuel cell control unit 12 and processes performed by the PCS control unit 23. In Fig. 2, S101 and S103 are processes performed by the fuel cell control unit 12, and processes other than S101 and S103 are processes performed by the PCS control unit 23.

[0029] First, in S100, the voltage control value V and the output power value P are set to their previous values ​​Vs and Ps, respectively. The voltage control value V is a control target value for voltage control of the fuel cell 10 by the PCS 20. The output power value P is a measured value of the DC power generated by the fuel cell 10. In this embodiment, the symbols with "s" attached indicate the previous values ​​used in the processing before the flowchart in FIG. 2 was completed.

[0030] Next, in S101, it is determined whether or not to update the current command value Isofc* and the output power command value P*. The current command value Isofc* and the output power command value P* are updated in the following cases, for example. Since the output power of the fuel cell 10 gradually increases at startup, the current command value Isofc* and the output power command value P* are updated in accordance with the rate of increase in the output power, and the amount of hydrogen supplied to the fuel cell 10 is increased. Alternatively, if the power required by the load 30 fluctuates, the current command value Isofc* and the output power command value P* are updated, and the amount of hydrogen supplied to the fuel cell 10 is changed.

[0031] If it is determined in S101 that the current command value Isofc* and the output power command value P* should not be updated, ΔV is added to the voltage control value V in S102. ΔV is a variable that increases or decreases the voltage control value V, and is set to a sign of "+" or "-". If the sign of ΔV is set to "+", the voltage control value V increases by ΔV in S102, and if the sign of ΔV is set to "-", the voltage control value V decreases by ΔV in S102. The PCS 20 controls the voltage of the fuel cell 10 using the converter 21 based on the voltage control value V.

[0032] Next, in S103, the output power value P is measured. The output power value P can be calculated from the product of the output current value Isofc detected by the PCS input current sensor 24 and the output voltage value Vsofc detected by the PCS input voltage sensor 25.

[0033] Next, in S104, it is determined whether the output power value P is below the output power command value P*. If it is determined in S104 that the output power value P is below the output power command value P*, it is determined in S105 whether the output power value P is above the previous power value Ps.

[0034] If it is determined in S105 that the output power value P is greater than the previous power value Ps, it can be determined that the maximum power point has not been reached, and so the sign of ΔV is not changed in S106 and is left as is. On the other hand, if it is determined in S105 that the output power value P is not greater than the previous power value Ps, it can be determined that the maximum power point has been reached, and so the sign of ΔV is inverted in S107. In other words, if the sign of ΔV is "+", it is changed to "-", and if the sign of ΔV is "-", it is changed to "+".

[0035] Then, in S108, the output power value P is set to the previous power value Ps, and the process returns to S101. Through the above processing, the fuel cell power generation system 1 can perform MPPT control.

[0036] Next, if it is determined in S101 that the current command value Isofc* and the output power command value P* should be updated, the voltage control value V and the output power value P after the current command value Isofc* etc. are updated in S109 are set as the previous values ​​Vs and Ps, respectively, and the process returns to S100. This makes it possible to prevent the previous values ​​Vs and Ps from deviating significantly from the current voltage control value V and the output power value P.

[0037] Next, if it is determined in S104 that the output power value P is not below the output power command value P*, output power suppression control is performed in S110 to S112 to suppress the power generated by the fuel cell 10.

[0038] In S110, the output power value P is output electric power directive Value P * In step S110, it is determined whether the output power value P is equal to output electric power directive Value P * If it is determined that the voltage control value V is equal to the previous power value Ps, the output power value P is set to the previous power value Ps in step S111, and the process returns to step S103. As a result, unless the output power value P fluctuates due to some factor, the voltage control value V is not changed, and the output power value P remains constant.

[0039] On the other hand, the output power value P at S110 output electric power directive Value P* If it is determined that the output power value P is not equal to the output power command value P*, that is, if it is determined that the output power value P is greater than the output power command value P*, the sign of ΔV is set to "-" in S112, and the process proceeds to S101. As a result, ΔV is subtracted from the voltage control value V in the next S102.

[0040] Next, the output power value P, voltage control value V, and output current value Isofc of the fuel cell 10 of this embodiment will be described with reference to Figures 3 and 4. In the example shown in Figure 3, P5 is the maximum power point of the fuel cell 10.

[0041] First, a description will be given of the case where output power suppression control is performed in S104 and S110 to S112 in Fig. 2. As shown in Fig. 3, it is assumed that the output power command value P* is set between P4 and P5, and as shown in Fig. 4, the current command value Isofc* is set between I4 and I5.

[0042] When the voltage control value V changes in the order of V0, V1, V2, etc., the output current value Isofc changes in the order of I0, I1, I2, and the output power value P changes in the order of P0, P1, P2, etc. When the output power value P reaches the maximum power point P5, it is determined in S104 that the output power value P is not below the output power command value P*.

[0043] In S110, it is determined that the output power value P is not equal to the previous power value Ps, i.e., the output power value P is greater than the output power command value P*, and in S112 the sign of ΔV is inverted from "+" to "-", and in the next S102, ΔV is subtracted from the voltage control value V. As a result, the voltage control value V changes from V5 to V4, the output current value Isofc changes from I5 to I4, and the output power value P measured in S103 changes from P5 to P4.

[0044] In S104, it is determined that the output power value P is not below the output power command value P*, in S105 it is determined that the output power value P is not above the previous power value Ps, and in S107 the sign of ΔV is reversed from "-" to "+".

[0045] In the next step S102, ΔV is added to the voltage control value V. As a result, the voltage control value V changes from V4 to V5, the output current value Isofc changes from I4 to I5, and the output power value P measured in step S103 changes from P4 to P5.

[0046] That is, in MPPT control that performs output control processing in S104 and S110 to S112, the output power value P fluctuates in the order of P4-P5-P4. Therefore, as shown in Fig. 3, the output power value P pulsates between P4 and P5. As shown in Figs. 3 and 4, the output voltage value Vsofc pulsates between V4 and V5. As shown in Figs. 4 and 5, the output current value Isofc pulsates between I4 and I5.

[0047] Next, MPPT control in the case where the output power suppression control in S104 and S110 to S112 in FIG. 2 is not performed will be described as a comparative example.

[0048] When the voltage control value V changes in the order of V0, V1, V2, etc., the output current value Isofc changes in the order of I0, I1, I2, and the output power value P changes in the order of P0, P1, P2, etc. The output power value P increases until it is determined in the determination process of S105 that the output power value P does not exceed the previous value Ps.

[0049] When the output power value P shifts from P5 to P6, the determination process in S105 determines that the output power value P does not exceed the previous power value Ps, and the sign of ΔV is reversed in S107. As a result, the output power value P shifts from P6 to P5, and then to P4.

[0050] When the output power value P shifts from P5 to P4, the determination process in S105 determines that the output power value P does not exceed the previous power value Ps, and the sign of ΔV is reversed in S107. As a result, the output power value P decreases from P4 to P5, and then shifts to P6.

[0051] That is, in MPPT control without performing the output control processes of S104 and S110 to S112, the output power value P fluctuates in the order of P4-P5-P6-P5-P4, and pulsation occurs between P4 and P6 in the output power value P. Also, as shown in Fig. 6, pulsation occurs in the output current value Isofc between I4 and I6.

[0052] In the embodiment described above, the fuel cell control unit 12 transmits an output power command value P* to the PCS control unit 23, and the PCS control unit 23 performs output power suppression control of the fuel cell 10 based on the output power command value P*. In other words, the fuel cell control unit 12 externally controls the output control of the fuel cell 10 by the PCS 20. In the output power suppression control of the fuel cell 10, the voltage control value V is reduced when the output power value P of the fuel cell 10 exceeds the output power command value P*, and the output power value P is kept constant when the output power value P of the fuel cell 10 matches the output power command value P*.

[0053] This reduces the fluctuation range and suppresses pulsation of the output current value Isofc of the fuel cell 10. As a result, in the fuel cell power generation system 1 equipped with the PCS 20 that performs MPPT control, it is possible to suppress the current command value Isofc* of the fuel cell 10 from deviating from the actual output current value Isofc.

[0054] (Second embodiment) Next, a second embodiment of the present invention will be described, focusing on only the differences from the first embodiment.

[0055] The fuel cell power generation system 1 of the second embodiment has the same configuration as the first embodiment described above with reference to Fig. 1. In the second embodiment, the output power command value P* is adjusted so that the difference between the current command value Isofc* and the output current value Isofc becomes small.

[0056] The operation of the fuel cell power generation system 1 of the second embodiment will be described using the flowchart of Fig. 7. The flowchart of Fig. 7 shows the processing executed by the fuel cell control unit 12. Each processing shown in Fig. 7 is carried out in parallel with each processing explained in the first embodiment using Fig. 2.

[0057] First, in S200, the current command value Isofc* and the output power command value P* are set to their previous values ​​Isofcs* and Ps*, respectively, and the Flag is set to "0." The Flag indicates whether or not the output power value P has exceeded the maximum power point in the output characteristics of the fuel cell 10 at the currently set current command value Isofc*. If the output power value P has not exceeded the maximum power point, the Flag is set to "0," and if the output power value P has exceeded the maximum power point, the Flag is set to "1." The Flag is set in S206 or S207, which will be described later.

[0058] Next, in S201, it is determined whether or not to update the current command value Isofc*. If it is determined in S201 that the current command value Isofc* should not be updated, in S202, ΔP* is added to the output power command value P*. ΔP* is a variable that increases or decreases the output power command value P*, and is set to a sign of "+" or "-". If the sign of "+" is set to ΔP*, the output power command value P* is increased by ΔP* in S202, and if the sign of "-" is set to ΔP*, the output power command value P* is decreased by ΔP* in S202.

[0059] The output power command value P* set in S202 is transmitted from the fuel cell control unit 12 to the PCS control unit 23. The PCS control unit 23 controls the output of the fuel cell 10 based on the output power command value P*.

[0060] Next, in S203, the current value difference ΔIsofc is obtained. In S203, ΔIsofc is calculated as the absolute value of the difference obtained by subtracting the current command value Isofc* from the output current value Isofc.

[0061] Next, in S204, it is determined whether or not Flag = 0. In S204, it is determined that Flag = 0 if the output power value P has not reached the maximum power point after the output power command value P* has been changed in S202 and the process of changing the sign of ΔP* has not been performed in S208, which will be described later.

[0062] If it is determined in S204 that Flag=0, i.e., that the output power value P does not exceed the maximum power point, the current value difference ΔIsofc is compared with the previous value ΔIsofcs in S205. The previous value ΔIsofcs is the previous value of the current value difference ΔIsofc used in the processing before the flowchart in FIG. 7 was completed, and is the value before the output power command value P* was changed in S202.

[0063] When the output current value Isofc is approaching the current command value Isofc*, the current value difference ΔIsofc is smaller than the previous value ΔIsofcs. When the output current value Isofc is moving away from the current command value Isofc*, the current value difference ΔIsofc is larger than the previous value ΔIsofcs.

[0064] When the output power value P does not exceed the maximum power point, the current value difference ΔIsofc decreases from the previous value ΔIsofcs, and when the output power value P exceeds the maximum power point, the current value difference ΔIsofc increases from the previous value ΔIsofcs. By comparing the current value difference ΔIsofc with the previous value ΔIsofcs, it is possible to determine whether the output power value P has exceeded the maximum power point obtained with the current current command value Isofc*.

[0065] If it is determined in S205 that the current value difference ΔIsofc is smaller than the previous value ΔIsofcs, the sign of ΔP* is not changed and Flag is set to "0." On the other hand, if it is determined in S205 that the current value difference ΔIsofc is larger than the previous value ΔIsofcs, the sign of ΔP* is inverted and Flag is set to "1."

[0066] Then, in S208, the previous power command value Ps* is set to the output power command value P*, the previous current command value Isofc* is set to the current command value Isofc*, and the process returns to S201.

[0067] Next, if it is determined in S201 that the current command value Isofc* should be updated, the updated current command value Isofc* is set to the previous value Isofcs*, and the updated output power command value P* is set to the previous value Ps* in S209. This makes it possible to prevent the previous values ​​Isofcs* and Ps* from deviating significantly from the current current command value Isofc* and output power command value P*.

[0068] Next, if it is determined in S204 that Flag is not 0, that is, that the output power value P exceeds the maximum power point, it is determined in S210 whether ΔIsofc is equal to or less than a predetermined value. The predetermined value is an allowable value for the difference between the output current value Isofc and the current command value Isofc*, and can be set arbitrarily.

[0069] If it is determined in S210 that ΔIsofc is equal to or less than the predetermined value, ΔP* is set to "0" in S211 and the process returns to S201. As a result, the output power command value P* is not changed in S202 from the next time onwards, and the output power command value P* remains constant.

[0070] On the other hand, if it is determined in S210 that ΔIsofc is not equal to or less than the predetermined value, ΔP* is multiplied by 1 / 2 in S212, the flag is set to "0", and the process returns to S201. This makes it possible to reduce the fluctuation range of the output power command value P* in S202.

[0071] Next, the output power value P, voltage control value V, and output current value Isofc of the fuel cell power generation system 1 of the second embodiment will be described with reference to Figures 8 and 9. In the example shown in Figure 8, P5 is the maximum power point of the fuel cell 10.

[0072] As shown in Fig. 8, the output power command value P* is set between output power values ​​P4 and P5, and as shown in Fig. 9, the current command value Isofc* is set between output current values ​​I4 and I5. By executing the control processing of S210 to S212 in the second embodiment, the output power command value P* gradually approaches a power control point such as P4 or P5, thereby reducing pulsation. Furthermore, as shown in Figs. 9 and 10, the output current value Isofc approaches I4 or I5, thereby reducing pulsation.

[0073] In the second embodiment described above, the output power command value P* is adjusted so as to reduce the difference between the current command value Isofc* and the output current value Isofc. Specifically, the output power command value P* is varied, and when the difference between the current command value Isofc* and the output current value Isofc increases, it is determined that the output power value P has exceeded the maximum power point, and the fluctuation range of the output power command value P* is reduced. This allows the output power command value P* to approach one of the power control points. As a result, the difference between the current command value Isofc* and the output current value Isofc can be reduced.

[0074] (Third embodiment) Next, a third embodiment of the present invention will be described, focusing only on the differences from the above embodiments.

[0075] 11 , in the fuel cell power generation system 1 of the third embodiment, an output current sensor 32 and an output voltage sensor 33 are provided on the power supply wiring of the PCS 20. The output current sensor 32 detects the AC current value Iac output by the PCS 20. The output voltage sensor 33 detects the AC voltage value Vac output by the PCS 20. The AC current value Iac detected by the output current sensor 32 and the AC voltage value Vac detected by the output voltage sensor 33 are each input to the fuel cell control unit 12.

[0076] Next, the operation of the fuel cell power generation system 1 of the third embodiment will be described using the flowchart of Fig. 12. The flowchart of Fig. 12 shows the processing executed by the fuel cell control unit 12. In Fig. 12, the processing of S200 to S212 is the same as that of the second embodiment, and therefore the description thereof will be omitted.

[0077] In the third embodiment, after ΔIsofc is calculated in S203, the power value difference ΔP is acquired in S213. In S213, ΔP is calculated as the absolute value of the difference obtained by subtracting the output power command value P* from the output power value P of the PCS 20. The output power value P of the PCS 20 is AC power obtained by multiplying the AC current value Iac detected by the output current sensor 32 and the AC voltage value Vac detected by the output voltage sensor 33.

[0078] Next, in S214, it is determined whether ΔP is equal to or less than a predetermined value. The predetermined value is an allowable value for the difference between the output power value P and the output power command value P*, and can be set arbitrarily.

[0079] If it is determined in S214 that ΔP is equal to or less than the predetermined value, the process proceeds to S204. On the other hand, if it is determined in S214 that ΔP is not equal to or less than the predetermined value, it can be determined that the output power command value P* is too high with respect to the output power value P. Therefore, in S215, the output power command value P* and the current command value Isofc* are reduced, and the process proceeds to S201. Since it is determined in S201 that Isofc* has been updated, the process proceeds to S209.

[0080] In the third embodiment described above, the output power command value P* and the current command value Isofc* are adjusted so that ΔP, which is the difference between the output power value P and the output power command value P*, becomes small. This makes it possible to appropriately correct the output power command value P* and the current command value Isofc* depending on the power generation state of the fuel cell 10.

[0081] In the fuel cell 10, it generally takes time for the output power value P and the output current value Isofc to change after the output power command value P* or the current command value Isofc* is changed. In contrast, the PCS 20 controls the voltage of the fuel cell 10 based on the changed output power command value P*, which can result in a large difference between the output power command value P* and the output power value P. For this reason, by correcting the output power command value P* based on ΔP, the PCS 20 can control the voltage of the fuel cell 10 in accordance with the power generation state of the fuel cell 10.

[0082] Furthermore, in the third embodiment, the AC power output by the PCS 20 is used as the output power value P of the fuel cell 10. Therefore, the output power command value P* can be adjusted taking into account the power loss in the PCS 20 and the like.

[0083] (Fourth embodiment) Next, a fourth embodiment of the present invention will be described, focusing only on the differences from the above embodiments.

[0084] As shown in Figure 13, the fuel cell power generation system 1 of the fourth embodiment is provided with a hydrogen sensor 15 that detects the concentration of hydrogen contained in exhaust gas after power generation by the fuel cell 10. The hydrogen sensor 15 detects the concentration of hydrogen that is discharged from the fuel cell 10 without being used for power generation, out of the hydrogen supplied to the fuel cell 10. The hydrogen concentration detected by the hydrogen sensor 15 is input to the fuel cell control unit 12. The hydrogen sensor 15 corresponds to the fuel sensor of the present invention.

[0085] Next, the operation of the fuel cell power generation system 1 of the fourth embodiment will be described using the flowchart of Fig. 14. The flowchart of Fig. 14 shows the processing executed by the fuel cell control unit 12. In Fig. 12, the processing of S200 to S212 is the same as that of the second embodiment, and the processing of S213 to S215 is the same as that of the third embodiment, so description thereof will be omitted.

[0086] 14, in the fourth embodiment, if it is determined in S201 that the current command value Isofc* should not be updated, it is determined in S216 whether the hydrogen concentration detected by the hydrogen sensor 15 is within a predetermined range. The "predetermined range" is the range of hydrogen concentration contained in the exhaust gas when the fuel cell 10 is supplied with the amount of hydrogen necessary to generate the current command value Isofc*.

[0087] If it is determined in S216 that the hydrogen concentration is within the predetermined range, it can be determined that the amount of hydrogen supplied to the fuel cell 10 is normal, and the process proceeds to S202. On the other hand, if it is determined in S216 that the hydrogen concentration is not within the predetermined range, the current command value Isofc* and the output power command value P* are adjusted in S217, and the process proceeds to S202.

[0088] In S217, the current command value Isofc* and the output power command value P* are increased or decreased based on the hydrogen concentration.

[0089] If the hydrogen concentration is higher than the predetermined range, it can be determined that the amount of hydrogen supplied to the fuel cell 10 is excessive and that a large amount of hydrogen is not used in the electrochemical reaction, so the current command value Isofc* or the output power command value P* is reduced to reduce the amount of hydrogen supplied to the fuel cell 10. This reduces the amount of hydrogen supplied to the fuel cell 10, and the power generation efficiency of the fuel cell 10 can be improved.

[0090] If the hydrogen concentration is lower than the predetermined range, it can be determined that the amount of hydrogen supplied to the fuel cell 10 is insufficient and that the fuel cell 10 may be oxidized and deteriorated, so the current command value Isofc* or the output power command value P* is increased to increase the amount of hydrogen gas supplied. This makes it possible to increase the amount of hydrogen supplied to the fuel cell 10.

[0091] In the fourth embodiment described above, the current command value Isofc* is adjusted based on the hydrogen concentration in the exhaust gas of the fuel cell 10. This makes it possible to appropriately adjust the current command value Isofc* and the output power command value P* according to the power generation state of the fuel cell 10.

[0092] (Fifth embodiment) Next, a fifth embodiment of the present invention will be described, focusing only on the differences from the above embodiments.

[0093] 15, the fuel cell power generation system 1 of the fifth embodiment is not provided with an FC output current sensor 13 or an FC output voltage sensor 14. The PCS control unit 23 transmits to the fuel cell control unit 12 the output current value Isofc detected by the PCS input current sensor 24 and the output voltage value Vsofc detected by the PCS input voltage sensor 25. The fuel cell control unit 12 performs various controls using the output current value Isofc and output voltage value Vsofc received from the PCS control unit 23.

[0094] According to the fifth embodiment described above, the PCS 20 transmits the output current value Isofc and the output voltage value Vsofc to the external fuel cell control unit 12, thereby making it possible to omit the FC output current sensor 13 and the FC output voltage sensor 14. This simplifies the configuration of the fuel cell power generation system 1.

[0095] (Sixth embodiment) Next, a sixth embodiment of the present invention will be described, focusing only on the differences from the above embodiments.

[0096] 16, in the fuel cell power generation system 1 of the sixth embodiment, a voltage command value Vsofc* is transmitted from the fuel cell control unit 12 to the PCS control unit 23. The voltage command value Vsofc* is a target power generation voltage of the fuel cell 10. When the PCS control unit 23 receives the voltage command value Vsofc* from the outside, it stops MPPT control and performs constant voltage control to control the output voltage value Vsofc of the fuel cell 10 to be constant based on the voltage command value Vsofc*.

[0097] Next, the procedure by which the fuel cell control unit 12 acquires the voltage command value Vsofc* will be described with reference to the control block diagram of FIG.

[0098] First, the fuel cell control unit 12 acquires the output characteristics that indicate the relationship between the current and voltage of the fuel cell 10. The output characteristics of the fuel cell 10 are obtained as a regression line with the current and voltage of the fuel cell 10 as variables.

[0099] The output characteristics of the fuel cell 10 can be obtained by performing a regression calculation using the output current value Isofc detected by the FC output current sensor 13 and the output voltage value Vsofc detected by the FC output voltage sensor 14. Alternatively, if the output characteristics of the fuel cell 10 are known, preset output characteristics may be used without measuring the current and voltage of the fuel cell 10.

[0100] Because the output characteristics of the fuel cell 10 vary depending on the temperature of the fuel cell 10, the fuel cell control unit 12 acquires the output characteristics at the temperature set value T(i)*. The temperature set value T(i)* is a value set as the operating temperature of the fuel cell 10. Because the operating temperature of the fuel cell 10 varies depending on factors such as the amount of fuel supplied, the temperature set value T(i)* can be set based on the current command value Isofc*. Note that the i in T(i)* is a natural number, and can be set, for example, as T(1)*=600°C, T(2)*=650°C, T(3)*=700°C, and so on.

[0101] The fuel cell control unit 12 calculates a provisional voltage command value Vsofc(T(i)*)* using the current command value Isofc* and the output characteristics of the fuel cell 10. Furthermore, the fuel cell control unit 12 calculates the voltage command value Vsofc* by adding the provisional voltage command value Vsofc(T(i)*)* to a correction term of PI control for correcting the difference between the output current value Isofc and the current command value Isofc*.

[0102] Next, the operation of the fuel cell power generation system 1 of the sixth embodiment will be described with reference to the flowchart of Fig. 18. The flowchart of Fig. 18 shows the processing executed by the fuel cell control unit 12.

[0103] First, in S300, the current command value Isofc* and the temperature set value T(i)* are set, and in S301, it is determined whether or not these set values ​​(Isofc*, T(i)*) have been changed.

[0104] If it is determined in S301 that the set value has not been changed, the process returns to S300. On the other hand, if it is determined in S301 that the set value has been changed, the output current value Isofc is detected using the FC output current sensor 13 in S302.

[0105] Next, in S303, the output characteristics of the fuel cell 10 are obtained using the temperature set value T(i)*. Subsequently, in S304, the current command value Isofc* is used to calculate a provisional voltage command value Vsofc(T(i)*)* from the output characteristics of the fuel cell 10. Vsofc(T(i)*)* is obtained as a regression line that shows the output characteristics of the fuel cell 10 at T(i)*. In S304, the provisional voltage command value Vsofc(T(i)*)* can be calculated using the following formula (1):

[0106] Vsofc(T(i)*)*=a(T(i)*)×Isofc* + b(T(i)*)…(1) In equation (1), a(T(i)*) is the slope of the regression line, and b(T(i)*) is the intercept of the regression line.

[0107] Next, in S305, the voltage command value Vsofc* is calculated. In S305, the voltage command value Vsofc* can be calculated by the following formula (2).

[0108] Vsofc*=Vsofc(T(i)*)* + PI control correction term…(2) The provisional voltage command value Vsofc(T(i)*)* is a feedforward term calculated from the output characteristics of the fuel cell 10 and the current command value Isofc*. The PI control correction term is a correction term for PI control for correcting the difference between the output current value Isofc and the current command value Isofc*.

[0109] The fuel cell control unit 12 transmits the voltage command value Vsofc* obtained by executing each of the above processes to the PCS control unit 23. Upon receiving the voltage command value Vsofc*, the PCS control unit 23 performs constant voltage control of the fuel cell 10 so that the output voltage value Vsofc output by the fuel cell 10 becomes the voltage command value Vsofc*.

[0110] Next, the current variation of the fuel cell 10 when constant voltage control of the sixth embodiment is performed will be described with reference to Figure 19. In Figure 19, the horizontal axis represents the output power value P of the fuel cell 10, and the vertical axis represents the output current value Isofc input to the PCS 20.

[0111] In Fig. 19, the current variation in the sixth embodiment is indicated by an "x". For comparison, in Fig. 19, the current variation when only MPPT control is performed is indicated by a "□", and the current variation when the output power suppression control of the first embodiment is performed is indicated by a "◯".

[0112] As shown in Figure 19, when only MPPT control is performed, the output current value varies greatly. The output power value P of the fuel cell 10 acquired by the PCS control unit 23 may vary due to sensor errors, etc. In MPPT control, the output of the fuel cell 10 is controlled based on the varied output power value P, which tends to result in large fluctuations in the current and voltage of the fuel cell 10.

[0113] In contrast, when the output power suppression control of the first embodiment is performed, the variation in the output current value is smaller than when only MPPT control is performed. Furthermore, when the constant voltage control of the sixth embodiment is performed, the variation in the output current value is smaller than when the output power suppression control of the first embodiment is performed, and the output current value is almost constant.

[0114] In the sixth embodiment described above, the fuel cell control unit 12 transmits the voltage command value Vsofc* to the PCS control unit 23, so that the PCS control unit 23 does not perform MPPT control but performs constant voltage control based on the voltage command value Vsofc*. This makes it possible to suppress current variations in the fuel cell 10 and to suppress deviation of the output current value Isofc from the current command value Isofc*.

[0115] Furthermore, in the sixth embodiment, the voltage command value Vsofc* is calculated using the provisional voltage command value Vsofc(T(i)*)* obtained from the output characteristics of the fuel cell 10 and the current command value Isofc*, and the PI control correction term obtained from the output current value Isofc and the current command value Isofc*. This makes it possible to appropriately calculate the voltage command value Vsofc* in consideration of the output characteristics of the fuel cell 10 and the difference between the output current value Isofc and the current command value Isofc*.

[0116] (Seventh embodiment) Next, a seventh embodiment of the present invention will be described, focusing only on the differences from the above embodiments.

[0117] 20, the fuel cell power generation system 1 of the seventh embodiment is provided with a temperature sensor 16 that detects a measured temperature value T of the fuel cell 10. The measured temperature value T of the fuel cell 10 detected by the temperature sensor 16 is input to the fuel cell control unit 12.

[0118] In the seventh embodiment, the output characteristics of the fuel cell 10 are corrected based on the measured temperature value T of the fuel cell 10. When the measured temperature T is between the temperature set value T(i)* and the temperature set value T(i+1)*, linear interpolation is performed using a regression line that shows the output characteristics of the fuel cell 10 at T(i)* and T(i+1)* to obtain the output characteristics of the fuel cell 10 at the measured temperature T. For example, when T(i)*=600°C, T(i+1)*=650°C, and T=630°C, linear interpolation is performed using the regression line that shows the output characteristics of the fuel cell 10 at 600°C and 650°C to obtain the output characteristics of the fuel cell 10 at 630°C.

[0119] Next, the operation of the fuel cell power generation system 1 of the seventh embodiment will be described with reference to the flowchart of Fig. 21. The flowchart of Fig. 21 shows the processing executed by the fuel cell control unit 12.

[0120] First, in S400, the current command value Isofc* and the temperature set value T(i)* are set, and in S401, it is determined whether or not these set values ​​(Isofc*, T(i)*) have been changed.

[0121] If it is determined in S401 that the set value has not been changed, the process returns to S400. On the other hand, if it is determined in S401 that the set value has been changed, the temperature sensor 16 is used to detect the measured temperature value T of the fuel cell 10 in S402. Next, the FC output current sensor 13 is used to detect the output current value Isofc, and the FC output voltage sensor 14 is used to detect the output voltage value Vsofc in S403.

[0122] Next, in S404, it is determined whether the measured temperature T is between the temperature set values ​​T(i)* and T(i+1)*. For example, if T(i)*=600°C and T(i+1)*=650°C, it is determined whether the measured temperature T is between 600°C and 650°C.

[0123] If it is determined in S404 that the measured temperature T is not between T(i)* and T(i+1)*, the process returns to S402. On the other hand, if it is determined that the measured temperature T is between T(i)* and T(i+1)*, the output characteristics of the fuel cell 10 at T(i)* and T(i+1)* are obtained in S405.

[0124] Next, in S406, the current command value Isofc* is used to calculate provisional voltage command values ​​Vsofc(T(i)*)* and Vsofc(T(i+1)*)* from the output characteristics of the fuel cell 10. Vsofc(T(i)*)* is obtained as a regression line showing the output characteristics of the fuel cell 10 at T(i)*. Vsofc(T(i+1)*)* is obtained as a regression line showing the output characteristics of the fuel cell 10 at T(i+1)*.

[0125] In S406, the provisional voltage command values ​​Vsofc(T(i)*)* and Vsofc(T(i+1)*)* can be calculated by the following formulas (1) and (1a).

[0126] Vsofc(T(i)*)*=a(T(i)*)×Isofc* + b(T(i)*)…(1) Vsofc(T(i+1)*)*=a(T(i+1)*)×Isofc* + b(T(i+1)*)…(1a) In equations (1) and (1a), a(T(i)*) and a(T(i+1)*) are the slopes of the regression lines, and b(T(i)*) and b(T(i+1)*) are the intercepts of the regression lines.

[0127] Next, in S407, a provisional voltage command value Vsofc(T)* is calculated by linear interpolation using the regression lines at T(i)* and T(i+1)*. In S407, the provisional voltage command value Vsofc(T)* can be calculated by the following formula (3).

[0128] Vsofc(T)*=((Vsofc(T(i+1)*)*-Vsofc(T(i)*)*) / (T(i+1)*-T(i)*))×(TT(i)*)+Vsofc(T(i)*)*…(3) Next, in S408, the voltage command value Vsofc* is calculated. In S408, the voltage command value Vsofc* can be calculated by the following formula (2).

[0129] Vsofc*=Vsofc(T)* + PI control correction term…(2) The provisional voltage command value Vsofc(T)* is a feedforward term calculated from the output characteristics and the current command value Isofc* of the fuel cell 10. The PI control correction term is a correction term for PI control for correcting the difference between the output current value Isofc and the current command value Isofc*.

[0130] The fuel cell control unit 12 transmits the voltage command value Vsofc* obtained by executing each of the above processes to the PCS control unit 23. Upon receiving the voltage command value Vsofc*, the PCS control unit 23 controls the voltage of the fuel cell 10 so that the output voltage value Vsofc output by the fuel cell 10 becomes the voltage command value Vsofc*.

[0131] In the seventh embodiment described above, when the measured temperature value T of the fuel cell 10 is between the temperature set values ​​T(i)* and T(i+1)*, the provisional voltage command value Vsofc(T)* at the measured temperature value T is calculated by linear interpolation using the regression line between T(i)* and T(i+1)*. This makes it possible to set the voltage command value Vsofc* to a more appropriate value based on the measured temperature value T of the fuel cell 10.

[0132] (Other embodiments) The present invention is not limited to the above-described embodiments, and various modifications can be made as follows without departing from the spirit of the present invention. Furthermore, the means disclosed in each of the above-described embodiments may be combined as appropriate within the scope of feasibility.

[0133] For example, in each of the above embodiments, a solid oxide fuel cell (SOFC) is used as the fuel cell 10, but this is not limiting, and the fuel cell 10 may also be a molten hydrochloric acid fuel cell (MCFC, Molten Carbonate Fuel Cell), a phosphoric acid fuel cell (PAFC, Phosphoric Acid Fuel Cell), an alkaline aqueous fuel cell (AFC, Alkaline Fuel Cell), or the like.

[0134] Furthermore, in each of the above embodiments, a solar cell PCS is used as the PCS 20, but a different type of PCS may also be used.

[0135] For example, a PCS for a storage battery capable of charging and discharging a battery of a Home Energy Management Service (HEMS) shown in Fig. 22 may be used as the PCS 20. While the converter 21 of the PCS 20 in each of the above embodiments has a boost function, the boost / buck converter 34 of the PCS 20 for a storage battery shown in Fig. 22 has a function of boosting and bucking input DC power.

[0136] Furthermore, a PCS for wind power generation shown in Fig. 23 may be used as PCS 20. As shown in Fig. 23, PCS 20 for wind power generation is provided with an AC-DC converter 35 that converts AC power generated by wind power generator 16 into DC power. The DC power output from AC-DC converter 35 is input to inverter 22 and converted into AC power.

[0137] Furthermore, in each of the above embodiments, the PCS 20 is configured to convert the output power of the fuel cell 10 into three-phase AC power, but this is not limited thereto, and the PCS 20 may also be configured to convert the output power of the fuel cell 10 into single-phase AC power.

[0138] Furthermore, in each of the above embodiments, the fuel supply to the fuel cell 10 is controlled using the current command value Isofc*, but the fuel supply to the fuel cell 10 may be controlled using a power command value Wsofc* instead of the current command value Isofc*. The power command value Wsofc* is a value equivalent to the amount of hydrogen supply required for the fuel cell 10 to generate power in accordance with the power command value Wsofc*. The fuel supply device 11 can adjust the amount of hydrogen supply to the fuel cell 10 based on the power command value Wsofc*.

[0139] In addition, in the above-mentioned fourth embodiment, the current command value Isofc* or the output power command value P* is increased or decreased based on the hydrogen concentration in the exhaust gas of the fuel cell 10 detected by the hydrogen sensor 15, but this configuration may also be applied to the above-mentioned sixth and seventh embodiments in which the voltage command value Vsofc* is transmitted from the fuel cell control unit 12 to the PCS control unit 23.

[0140] Specifically, if the hydrogen concentration detected by the hydrogen sensor 15 is higher than a predetermined range, the amount of hydrogen supplied to the fuel cell 10 can be reduced by reducing the voltage command value Vsofc* or the output power command value P*. If the hydrogen concentration is lower than the predetermined range, the amount of hydrogen supplied to the fuel cell 10 can be increased by increasing the voltage command value Vsofc* or the output power command value P*. [Explanation of symbols]

[0141] 10 fuel cell 12 Fuel cell control unit 15 Hydrogen sensor (fuel sensor) 20 PCS (power conditioner) 21 Converter 22 Inverter 23 PCS control unit

Claims

1. a fuel cell (10) that generates electricity when supplied with fuel; a fuel cell control unit (12) that sets an output power command value (P*) that is a target power generation power of the fuel cell and a current command value (Isofc*) that is a target power generation current of the fuel cell, and performs fuel supply control so that the fuel cell is supplied with fuel necessary for the fuel cell to generate power at the current command value (Isofc*); a power conditioner (20) that performs maximum power point tracking control to operate the fuel cell at an operating point where the output power of the fuel cell is maximized, and converts DC power generated by the fuel cell into AC power in order to connect the fuel cell to a commercial power grid (31); Equipped with the power conditioner is configured to limit the power generated by the fuel cell based on an external input signal; the fuel cell control unit transmits the output power command value as the input signal to the power conditioner; The power conditioner performs the maximum power point tracking control when the output power is below the output power command value, and limits the power generated by the fuel cell when the output power is not below the output power command value. Fuel cell power generation system.

2. 2. The fuel cell power generation system according to claim 1, wherein the fuel cell control unit adjusts the output power command value so that a difference between an output current value (Isofc) of the fuel cell and the current command value becomes small.

3. 2. The fuel cell power generation system according to claim 1, wherein the fuel cell control unit adjusts the output power command value so that a difference between an output power value (P) of the fuel cell and the output power command value becomes small.

4. 4. The fuel cell power generation system according to claim 3, wherein the output power value is AC power converted by the power conditioner.

5. a fuel sensor (15) for detecting the concentration of fuel discharged from the fuel cell without being used for power generation, out of the fuel supplied to the fuel cell; 5. A fuel cell power generation system as described in any one of claims 1 to 4, wherein the fuel cell control unit increases the current command value when the concentration of the fuel discharged from the fuel cell is below a predetermined range, and decreases the current command value when the concentration of the fuel discharged from the fuel cell is above the predetermined range.

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