JP5304037B2 - FUEL CELL SYSTEM AND CONTROL METHOD FOR FUEL CELL SYSTEM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fuel use efficiency in a fuel cell system. <P>SOLUTION: The fuel cell system for supplying loaded power corresponding to electric power load comprises a fuel cell, a power output section for outputting a cell output of the fuel cell by converting it into a loaded output capable of supplying the power load, and a control section for controlling so as to output the cell output corresponding to requested loaded power corresponding to the power load by the fuel cell. The control section can control the fuel use efficiency by alternatively repeating states of a comparatively large change rate and states of a comparatively small change rate as states of a change rate of the fuel use efficiency in the fuel cell in case when the power load is changed. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a technique for controlling a fuel utilization rate in a fuel cell of a fuel cell system.

  2. Description of the Related Art Conventionally, in a fuel cell system, for the purpose of improving power generation efficiency, the fuel utilization rate is controlled so as to operate at the highest possible fuel utilization rate as long as the fuel is not exhausted (for example, , See Patent Document 1). Specifically, a voltage that is a control limit (fuel depletion limit) of the fuel cell set based on data obtained by actually measuring a relationship between the current and voltage of the fuel cell (referred to as “IV characteristic”) as a function of temperature in advance. The fuel utilization rate is controlled so that it does not fall below the lower limit. The control of the fuel utilization rate is controlled by the flow rate of fuel supplied to the fuel cell or the amount of current output from the fuel cell.

JP 2007-59359 A JP 2003-197232 A JP 2005-93111 A Japanese Patent Laid-Open No. 2005-93218 JP 2003-282115 A JP-A-8-7911

  Here, in the case of fuel flow control, it is preferable to use a fuel flow control actuator having excellent flow control resolution such as a mass flow valve (MFC). However, since such an excellent flow channel control resolution is extremely expensive, there is a demand to use an inexpensive one. However, since such an inexpensive flow control actuator has a low flow control resolution, there is a problem that there is a high possibility that it will temporarily fall below the voltage lower limit during the fuel utilization rate control operation.

  In addition, current control is excellent in terms of control resolution, but considering the system responsiveness, as with fuel flow control, it is not suitable for responsive steady load or control when the load decreases. During the control operation, there is a problem that there is a high possibility that the voltage will temporarily fall below the lower limit voltage.

  Therefore, in either case, the control has to be performed in consideration of a certain margin with respect to the voltage lower limit value, and there is room for improvement in terms of the fuel utilization rate.

  Accordingly, an object of the present invention is to provide a technique capable of improving the fuel utilization rate.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
As one form of this invention, it is a fuel cell system for supplying load electric power according to electric power load,
A fuel cell;
A power output unit that converts a battery output of the fuel cell into a load output that can be supplied to the power load and outputs the load output; and
A control unit that controls the fuel cell to output a battery output corresponding to a required load power corresponding to the power load;
With
The controller is
When the power load changes, the change rate of the fuel utilization rate in the fuel cell is relatively large until the output voltage of the fuel cell reaches a limit output voltage determined according to the required load power. By alternately repeating the state of change rate and the state of relatively small change rate, control to gradually increase the fuel utilization rate,
The controller is
i) Fuel amount control for changing the amount of fuel supplied to the fuel cell;
ii) current amount control for changing a control current amount for controlling the operation of the power output unit corresponding to the amount of current output from the fuel cell;
The fuel utilization rate is changed using at least one of
This is a fuel cell system.
According to this aspect, when the power load changes, the fuel utilization rate is gradually increased until the output voltage of the fuel cell reaches a limit output voltage determined according to the required load power. Therefore, it is possible to improve the fuel utilization rate, and it is possible to operate at a high fuel utilization rate corresponding to the limit output voltage. Further, according to the fuel amount control or the current amount control, the fuel utilization rate can be easily changed according to the change rate of the electric power load, and the fuel utilization rate can be improved.

[Application Example 1]
A fuel cell system for supplying load power corresponding to a power load,
A fuel cell;
A power output unit that converts a battery output of the fuel cell into a load output that can be supplied to the power load and outputs the load output; and
A control unit that controls the fuel cell to output a battery output corresponding to a required load power corresponding to the power load;
With
The controller is
When the power load changes, the fuel utilization rate in the fuel cell is alternately changed between a relatively large change rate state and a relatively small change rate state as the fuel utilization rate change state. The fuel cell system characterized by controlling.
In this way, since the fuel utilization rate can be gradually changed, it is possible to improve the fuel utilization rate. Note that the change rate of the fuel utilization rate indicates the amount of change in the fuel utilization rate per unit time, and there are a positive change rate and a negative change rate.

[Application Example 2]
A fuel cell system according to Application Example 1,
Depending on the rate of change of the power load,
The controller is
i) Fuel amount control for changing the amount of fuel supplied to the fuel cell;
ii) current amount control for changing a control current amount for controlling the operation of the power output unit corresponding to the amount of current output from the fuel cell;
A fuel cell system, wherein the fuel utilization rate is changed using at least one of the above.
According to this fuel amount control or current amount control, the fuel utilization rate can be easily changed in accordance with the rate of change of the electric power load, and the fuel utilization rate can be improved.

[Application Example 3]
A fuel cell system according to Application Example 2,
The controller is
The fuel is characterized by alternately repeating the relatively large change rate state and the relatively small change rate state until the output voltage of the fuel cell reaches a limit output voltage determined according to the required load power. Battery system.
In this way, it is possible to operate at a high fuel utilization rate corresponding to the limit output voltage.

[Application Example 4]
A fuel cell system according to Application Example 3,
The relatively large change rate state is a state of increasing the fuel utilization rate,
The fuel cell system according to claim 1, wherein the state of the relatively small change rate is a state of decreasing the fuel utilization rate.
In this way, it is possible to suppress the possibility that the fuel utilization rate exceeds the state corresponding to the limit output voltage.

[Application Example 5]
A fuel cell system according to Application Example 3,
The relatively large change rate state is a state of increasing the fuel utilization rate,
The fuel cell system according to claim 1, wherein the state of the relatively small change rate is a state of increasing the fuel utilization rate smaller than the state of the relatively large change rate.
Even in this case, the possibility that the fuel utilization rate exceeds the state corresponding to the limit output voltage can be suppressed.

[Application Example 6]
A fuel cell system according to Application Example 4,
The fuel cell system, wherein the amount of decrease in the fuel utilization rate in the state of the relatively small change rate is reduced as the change rate of the power load is increased.
In this way, when the rate of change of the power load is large, it is possible to shorten the time until the fuel utilization rate becomes a state corresponding to the limit output voltage. The change rate of the power load indicates the magnitude of the change amount per unit time of the fuel utilization rate.

[Application Example 7]
The fuel cell system according to any one of Application Example 3 to Application Example 6,
The fuel cell system, wherein the larger the rate of change of the power load, the smaller the magnitude of the relatively large rate of change.
In this way, it is possible to suppress the possibility that the fuel utilization rate exceeds the state corresponding to the limit output voltage.

[Application Example 8]
The fuel cell system according to any one of Application Example 3 to Application Example 7,
When the fuel amount control is used, a value smaller by a predetermined amount than the fuel utilization rate at the time when the repetition of the relatively large change rate state and the relatively small change rate state is stopped alternately. The fuel cell system is characterized by learning and storing the fuel utilization rate corresponding to the operating condition including the required load power.
In this way, it is possible to suppress the possibility that the fuel utilization rate exceeds the state corresponding to the limit output voltage.

[Application Example 9]
The fuel cell system according to any one of Application Example 3 to Application Example 7,
When using the current amount control, a value smaller by a predetermined amount than the control current amount at the time when it is stopped to alternately repeat the relatively large change rate state and the relatively small change rate state. A fuel cell system characterized by learning and storing the amount of control current corresponding to an operating condition including the required load power.
In this way, it is possible to suppress the possibility that the fuel utilization rate exceeds the state corresponding to the limit output voltage.

[Application Example 10]
The fuel cell system according to any one of Application Example 2 to Application Example 5,
A fuel cell system, wherein the fuel amount control and the current amount control are switched in accordance with a rate of change of the power load.
If it does in this way, suitable control can be selected according to the rate of change of electric power load.

[Application Example 11]
A fuel cell system according to Application Example 10,
The fuel cell system is characterized in that the fuel amount control is performed when the rate of change of the power load is equal to or greater than a predetermined value, and the current amount control is performed when the rate of change of the power load is equal to or less than a predetermined value.
In this way, when the change rate of the power load that does not require relatively high control accuracy is large, high-speed control is realized as the fuel amount control, and when the change rate of the power load that requires relatively high control accuracy is small. Can realize highly accurate control as current amount control.

[Application Example 12]
A fuel cell system according to Application Example 10,
In the state of current amount control, when the rate of change of the power load is equal to or greater than a first value, switching to the fuel control,
In the fuel amount control state, when the rate of change of the electric power load is a second value smaller than the first value, the fuel cell system is switched to the current control state.
In this way, when the change rate of the power load that does not require relatively high control accuracy is large, high-speed control is realized as the fuel amount control, and when the change rate of the power load that requires relatively high control accuracy is small. Can realize highly accurate control as current amount control. Further, since the first value is a threshold value in the current amount control state and the second value smaller than the first value is a threshold value in the fuel amount control state, the current amount control and the fuel amount control are performed. It is possible to prevent hunting from occurring when switching between and.

  Note that the present invention can be realized in various forms, for example, in various forms such as a fuel cell system and a control method of the fuel cell system.

Embodiments of the present invention will be described in the following order based on examples.
A. General configuration of the fuel cell system:
B. Control operation of the first embodiment:
C. Control operation of the second embodiment:
D. Control operation of the third embodiment:
E. Control operation of the fourth embodiment:
F. Variations:

A. General configuration of the fuel cell system:
FIG. 1 is a block diagram showing a schematic configuration of the fuel cell system 1000. The fuel cell system 1000 includes a fuel cell 100, a power output unit 200, a grid interconnection interface 300, a fuel pump 400, a desulfurizer 500, an evaporator 600, a reformer 700, an air pump 800, And a control device 900.

  The fuel cell 100 generates electric power by an electrochemical reaction between a fuel gas (hydrogen) supplied to the anode and an oxidizing gas (oxygen contained in air) supplied to the cathode. As this fuel cell 100, various fuel cells such as a polymer electrolyte fuel cell can be used. In general, the fuel cell 100 has a stack structure in which a plurality of cells are stacked.

  The fuel gas supplied to the anode is generated by steam reforming the raw fuel sent from the fuel pump 400 in the reformer 700. The raw fuel supplied to the reformer 700 is desulfurized by the desulfurizer 500 and mixed with the steam generated by the evaporator 600. Further, the oxidizing gas supplied to the cathode is included in the air sent from the air pump 800 to the cathode.

  The reformer 700 includes a reforming unit 710 for performing reforming and a heating unit 720 for setting the temperature of the reforming unit to a temperature suitable for reforming. Heating of the reforming unit 710 by the heating unit 720 is performed by combustion of the fuel gas discharged from the anode of the fuel cell 100 and the oxidizing gas discharged from the cathode.

  The power output unit 200 converts the DC voltage V_fc output from the fuel cell 100 into the same AC voltage V_ac (= V_inv) as that of the commercial power and outputs the same. The power output unit 200 includes an inverter (INV) 210 that converts direct current into alternating current, and a DC / DC that converts a direct current voltage V_fc output from the fuel cell 100 into a direct current input voltage V_inv_fin that can be input to the inverter 210. Converter 220.

  The grid interconnection interface 300 adjusts the ratio of the power output from the power output unit 200 and the power supplied from the commercial power grid to the power load. In the case where adjustment is made so that power is not sent from the fuel cell system 1000 to the power system, adjustment may be made so that at least part of the power required by the power load is sent from the commercial power system. preferable.

  The control device 900 controls the fuel flow rate of the fuel pump 400 by giving the fuel amount Qf_fin to the fuel pump 400. The fuel amount Qf_fin is a request for the fuel cell system 1000 among the average cell voltage v_dc_fc of the fuel cell 100, the temperature T_fc of the fuel cell 100, and the power required by the power load, as will be described in an embodiment described later. It is determined based on the power P_ac_rq.

B. Control operation of the first embodiment:
FIG. 2 is a control flowchart showing the control operation of the first embodiment executed by the control device 900. In the control operation of the first embodiment, as described below, when the control device 900 changes in the power load and changes in the required power of the power load in response to this, the control device 900 changes every control cycle time tr. , Step S10 to Step S110 shown in FIG. 2 are executed. Thus, the control device 900 determines the reference fuel amount Qf_bse and the fuel based on the required power P_ac_rq requested by the power load to the fuel cell 100, the temperature T_fc of the fuel cell 100, and the average cell voltage v_dc_fc of the fuel cell 100. The utilization rate Uf_fb_fin is obtained, and the control fuel amount Qf_fin is determined. Then, the control device 900 controls the operation of the fuel pump 400 so that the fuel flow rate becomes the determined control fuel amount Qf_fin.

  First, in step S10, a required current density i_rq corresponding to the required power P_ac_rq is obtained. Here, FIG. 3 is an explanatory diagram showing the relationship between the power P output from the fuel cell 100 and the current density i. The current density i of the current output from the fuel cell 100 varies according to the output power P as shown in FIG. 3, for example. The relationship between the current density i and the power P can be obtained by actually measuring in advance. The relationship between the actually measured current density i and the power P is stored in advance in a map or table. Here, it is assumed that it is stored in the map. Therefore, the required current density i_rq (i_rq = map (P_ac_rq)) corresponding to the required power P_ac_rq can be easily obtained by referring to this map.

  In step S20, a reference voltage v_bse serving as a reference for fuel rate control is obtained based on the required current density i_rq and the temperature T_fc of the fuel cell 100. FIG. 4 is an explanatory diagram showing the characteristics of the output voltage v with respect to the current density i of the fuel cell 100. The voltage v when the output current of the fuel cell 100 becomes the current density i changes according to the current density i and the temperature T_fc, for example, as shown in FIG. The relationship between the current density i, the temperature T_fc, and the voltage v is measured in advance and stored in a map or table. Here, it is assumed that it is stored in the map. Therefore, the reference voltage v_bse (v_bse = map (i_rq, T_fc)) corresponding to the required current density i_rq and the temperature T_fc can be easily obtained by referring to this map.

  In step S30, a reference fuel amount Qf_bse is obtained as a fuel that is sufficiently necessary to output the required current density i_rq. FIG. 5 is an explanatory diagram showing the relationship between the current density i of the fuel cell 100 and the sufficiently required fuel amount Qf. The fuel amount Qf required for the fuel cell 100 to obtain an output current having a current density i varies according to the current density i as shown in FIG. 5, for example. The relationship between the current density i and the fuel amount Qf can be obtained in advance by actual measurement. The relationship between the actually measured current density i and the fuel amount Qf is stored in advance in a map or table. Here, it is assumed that it is stored in the map. Therefore, the reference fuel amount Qf_bse (Qf_bse = map (i_rq)) corresponding to the required current density i_rq can be easily obtained by referring to this map.

  Furthermore, in step S40, based on the required current density i_rq and the temperature T_fc of the fuel cell 100, a reference fuel utilization rate Uf_bse serving as a reference for fuel rate control is obtained. The reference fuel utilization rate Uf_bse is finally operated at a high fuel utilization rate so that the reference fuel utilization rate Uf_bse does not fall below a voltage lower limit value indicating an output voltage indicating a set control limit (fuel depletion limit) of the fuel cell. Therefore, the fuel utilization rate is set lower than the final target fuel utilization rate. The reference fuel utilization rate Uf_bse varies according to the required current density i_rq and the temperature T_fc of the fuel cell 100, and is stored in advance in a map or table. A standard value actually measured in advance is stored in the initial stage, and is learned and stored as a control result in a control operation described later.

  Next, in step S50, a corrected fuel usage rate Uf_fb (Uf_fb = Uf_fb_old + dUf_fb) is obtained by adding the difference change rate dUf_fb to the corrected fuel usage rate Uf_fb_old obtained in the previous control cycle time tr. Note that the difference change rate dU_fb is the first difference change rate dUf_fb (U) used for each control cycle time tr during the period ts, and the period ts (ts = Tc * tr, Tc is the control cycle time in the period ts. second differential change rate dUf_fb (D) used in the control cycle time tr after elapse of (representing the number of cycles of tr). For example, when the first difference change rate dUf_fb (U) is set to Uf_fb_r, the second difference change rate dUf_fb (D) can be set to (−kd * Uf_fb_t (U)). Uf_fb_t (U) represents the first change width (Uf_fb_r * Tc) that has changed at the first difference change rate dUf_fb (U) = Uf_fb_r during the period ts, and the coefficient kd is the second Is set to a value smaller than 1 so that the second difference change rate dUf_fb (D) corresponding to the change width Uf_fb_t (D) is smaller than the first change width Uf_fb_t (U). Is done. In this example, Kd = 0.9.

  In step S60, the candidate fuel utilization rate Uf_fb_fin_trn is obtained by adding the corrected fuel utilization rate Uf_fb to the reference fuel utilization rate Uf_bse. In step S70, the learning memory correction fuel utilization rate β is subtracted from the candidate fuel utilization rate Uf_fb_fin_trn obtained in step S60 to obtain a learning memory candidate fuel utilization rate Uf_fb_fin_end that is a candidate for learning memory. Note that β can be set to (kc * Uf_fb_t (U)), for example. The coefficient kc is (kc * 100)% of the change width Uf_fb_t (U) in order to obtain the learning memory candidate fuel utilization rate Uf_fb_fin_end for learning and storing the fuel utilization rate slightly reduced from the obtained candidate fuel utilization rate Uf_fb_fin_trn. This is a coefficient for setting a value that is decreased by the corrected fuel utilization rate β for learning memory. In this example, kc = 0.05.

  In step S80, the average cell voltage v_dc_fc is subtracted from the reference voltage v_bse to obtain a decrease width dV_fc (= v_bse−v_dc_fc) of the average cell voltage v_dc_fc from the reference voltage v_bse. The reference voltage v_bse is set so as to maintain the relationship of reference voltage v_bse ≧ v_dc_fc. Furthermore, in step S90, the reference voltage v_bse is multiplied by a coefficient α to obtain a limit width Vd_bnd (= α * v_bse) of the decrease in the average cell voltage v_dc_fc. Α is appropriately determined by actually measuring the voltage drop limit value in the fuel cell 100. In this example, for example, α = 0.05.

  In step S100, if the decrease width dV_fc of the average cell voltage v_dc_fc is smaller than the decrease limit width Vd_bnd and the average cell voltage v_dc_fc has not yet decreased to the voltage decrease limit value, the candidate fuel utilization is used as the fuel utilization rate Uf_fb_fin. Select the rate Uf_fb_fin_trn. On the other hand, when the decrease width dV_fc of the average cell voltage v_dc_fc reaches the decrease limit width Vd_bnd and the average cell voltage v_dc_fc decreases to the voltage decrease limit value, the learning memory candidate fuel utilization rate Uf_fb_fin_end is selected. In step S110, the control fuel amount Qf_fin is obtained by dividing the reference fuel amount Qf_fbse by the fuel utilization rate Uf_fb_fin.

  When the decrease width dV_fc of the average cell voltage v_dc_fc reaches the decrease limit width Vd_bnd, the average cell voltage v_dc_fc decreases to the voltage decrease limit value, and the learning memory candidate fuel utilization rate Uf_fb_fin_end is selected and stored. Then, the control operation in steps S10 to S110 ends. Then, the control operation based on the control fuel amount Qf_fin obtained by using the learning memory candidate fuel utilization rate Uf_fb_fin_end stored as the learning memory Uf_fb_fin is maintained.

  FIG. 6 is an explanatory diagram showing a specific example of the control operation executed in accordance with the control flow shown in FIG. FIG. 6 shows an example in which the required power P_ac_rq changes stepwise for ease of explanation.

  The control flow shown in FIG. 2 is started in response to the change in the required power P_ac_rq, and as described above, the required current density i_rq corresponding to the required fuel P_ac_rq is obtained, and for each control cycle time tr, the reference voltage v_bse and The reference fuel amount Qf_bse and the reference fuel utilization rate Uf_bse are obtained. Since it is assumed that the change in the required power P_ac_rq is stepped, any changes in the required current density i_rq, the reference voltage v_bse, and the reference fuel amount Qf_bse are stepped as required.

  At this time, the fuel utilization rate Uf_fb_fin is equal to an increase in the first change width Uf_fb_t (U) obtained by multiplying the first difference change rate dUf_fb (U) (= Uf_fb_r) by the cycle number Tc, and the second difference change rate. The decrease in the second change width Uf_fb_t (D) obtained by multiplying dUf_fb (D) by the cycle number 1 is repeated. Here, Uf_fb_t (U) is smaller than 1 so that the second variation width Uf_fb_t (D) equal to the second differential change rate dUf_fb (D) is smaller than the first variation width Uf_fb_t (U). It is set to a value multiplied by the coefficient Kd. Therefore, the fuel utilization rate Uf_fb_fin is gradually increased from the reference fuel utilization rate Uf_bse by repeating the increase in the first variation width Uf_fb_t (U) and the decrease in the second variation width Uf_fb_t (D). become.

  Then, the control fuel amount Qf_fin gradually decreases from the reference fuel amount Qf_bse while repeatedly decreasing and increasing according to the change in the fuel utilization rate Uf_fb_fin.

  Further, the average cell voltage v_dc_fc gradually decreases from the reference voltage v_bse while repeatedly decreasing and increasing according to the change in the fuel utilization rate Uf_fb_fin. Then, the decrease width dV_fc (= v_bse−v_dc_fc) of the average voltage v_dc_fc from the reference voltage v_bse reaches the decrease limit width Vd_bnd (= α * v_bse) of the average cell voltage v_dc_fc, and the average cell voltage v_dc_fc reaches the decrease limit value. In the case of a decrease, the control flow shown in FIG. 2 is stopped, and a process of repeatedly increasing the first change width Uf_fb_t (U) and decreasing the second change width Uf_fb_t (D) in the fuel utilization rate Uf_fb_fin. Stopped. Then, the value obtained by subtracting the learning storage correction fuel usage rate β from the value of the fuel usage rate Uf_fb_fin at the time of stopping is used as the final fuel usage rate Uf_fb_fin, and this value is learned and stored. Then, the final control fuel amount Qf_fin is determined from the final fuel utilization rate Uf_fb_fin and the reference fuel amount Qf_bse that have been learned and stored, and the operation of the fuel pump 400 is controlled so that the fuel flow rate according to this is determined. Then, the power generation operation of the fuel cell 100 is performed.

  As described above, in the control operation of this embodiment, the fuel utilization rate Uf_fb_fin is set to increase the first change width Uf_fb_t (U) by the first difference change rate dUf_fb (U) and the second difference change rate dUf_fb. By repeating the decrease in the second change width Uf_fb_t (D) due to (D) and gradually increasing from the reference fuel utilization rate Uf_bse, the average cell voltage v_dc_fc falls below the voltage drop limit value, and the fuel It is possible to suppress the possibility that the utilization rate will exceed the limit value and reduce the power generation performance, and to improve the fuel utilization rate.

  The difference change rate dUf_fb of the fuel use rate Uf_fb_fin corresponds to the change rate of the fuel use rate of the present invention, the first difference change rate dUf_fb (U) is a positive change rate, and the second difference change rate dUf_fb. (D) is a negative rate of change. The state of the first differential change rate dUf_fb (U) corresponds to a state of a relatively large change rate of the fuel utilization rate in the present invention, and the state of the second differential change rate dUf_fb (D) is the fuel utilization rate of the present invention. This corresponds to a relatively small change rate state.

C. Control operation of the second embodiment:
FIG. 7 is a control flowchart showing the control operation of the second embodiment executed by the control device 900. In the control operation of the second embodiment, as will be described below, when the control device 900 changes in the power load and changes in the required power of the power load in response to this, the control device 900 changes every control cycle time tr. , Step S210 to Step S300 shown in FIG. 7 are executed. Thus, the control device 900 determines the fixed control fuel amount Qf_fin based on the required power P_ac_rq requested by the power load to the fuel cell 100, the temperature T_fc of the fuel cell 100, and the average cell voltage v_dc_fc of the fuel cell 100. Then, the control current I_inv_fin is obtained. Then, the control device 900 controls the output current from the fuel cell 100 by operating the inverter 210 of the power output unit 200 with the obtained control current I_inv_fin, and as a result, controls the fuel utilization rate in the fuel cell 100.

  First, in step S210, a standard required current I_rq necessary for obtaining the required power P_ac_rq is obtained. Here, the current I output from the fuel cell 100 changes according to the output power P, as in the relationship between the current density i and the power P shown in FIG. The relationship between the current I and the power P can be obtained by actually measuring in advance. The relationship between the actually measured current I and power P is stored in advance in a map or table. Here, it is assumed that it is stored in the map. Therefore, the required current I_rq (= map (P_ac_rq)) corresponding to the required power P_ac_rq can be easily obtained by referring to this map.

  In step S220, as in step S20 of the first embodiment, a reference voltage v_bse serving as a reference for fuel rate control is obtained based on the required current I_rq and the temperature T_fc of the fuel cell 100.

  Further, in step S230, the control fuel amount Qf_fin is obtained as the fuel necessary for outputting the required current I_rq. Here, the fuel amount Qf necessary for the fuel cell 100 to obtain the output current of the current I is in accordance with the output power P, as in the relationship between the current density i and the fuel amount Qf shown in FIG. Change. The relationship between the current I and the fuel amount Qf can be obtained by actually measuring in advance. The relationship between the actually measured current I and the fuel amount Qf is stored in advance in a map or table. Here, it is assumed that it is stored in the map. Therefore, the control fuel amount Qf_fin (Qf_fin = map (i_rq)) corresponding to the required current I_rq can be easily obtained by referring to this map.

  Next, in step S250, the correction current I_inv_fb (I_inv_fb = I_inv_fb_old + dI_fb) is obtained by adding the differential current dI_fb to the correction current I_inv_fb_old obtained in the previous control cycle time tr. Note that the differential current dI_fb is equal to the first differential current dI_fb (U) used for each control cycle time tr during the period ts, and the period ts (ts = Tc * tr, Tc is the control cycle time tr in the period ts. There is a second differential current dI_fb (D) used in the control cycle time tr after elapse of the cycle number). For example, when the first differential current dIf_fb (U) is I_fb_r, the second differential current dI_fb (D) can be set to (−kd * I_fb_t (U)). Note that I_fb_t (U) indicates the first change width (I_fb_r * Tc) changed by the first differential current dI_fb (U) = I_fb_r during the period ts, and the coefficient kd The second differential current dI_fb (D) corresponding to the change width I_fb_t (D) is set to a value smaller than 1 so that the second difference current dI_fb (D) is smaller than the first change width I_fb_t (U). . In this example, Kd = 0.9.

  Then, in step S260, the candidate control current I_inv_fb is obtained by adding the correction current I_inv_fb obtained in step S250 to the required current I_rq obtained in step S210. In step S270, a learning memory candidate control current I_inv_end that is a candidate for learning memory is obtained by subtracting the correction current Ic for learning memory from the required current I_rq. Note that Ic can be set to (kc * I_fb_t (U)), for example. The coefficient kc is decreased by (kc * 100)% of the change width I_fb_t (U) to obtain the learning memory candidate control current I_inv_end for learning and storing the control current slightly decreased from the obtained candidate control current I_inv_trn. It is a coefficient for setting the value to the correction current Ic for learning storage. In this example, kc = 0.05.

  In step S280, as in step S80 of the first embodiment, the average cell voltage v_dc_fc is subtracted from the reference voltage v_bse to obtain a decrease width dV_fc (= v_bse−v_dc_fc) of the average cell voltage v_dc_fc from the reference voltage v_bse. Ask. The reference voltage v_bse is set so as to maintain the relationship of reference voltage v_bse ≧ v_dc_fc. Further, in step S290, as in step S90 of the first embodiment, the reference voltage v_bse is multiplied by a coefficient α to obtain a limit width Vd_bnd (= α * v_bse) of the decrease in the average cell voltage v_dc_fc. Α is appropriately determined by actually measuring the voltage drop limit value in the fuel cell 100. In this example, for example, α = 0.05.

  In step S300, when the decrease width dV_fc of the average cell voltage v_dc_fc is smaller than the decrease limit width Vd_bnd and the average cell voltage v_dc_fc has not yet decreased to the voltage decrease limit value, the control current I_inv_fin is set as the candidate control current I_inv_trn. Select. On the other hand, when the decrease width dV_fc of the average cell voltage v_dc_fc reaches the decrease limit width Vd_bnd and the average cell voltage v_dc_fc decreases to the voltage decrease limit value, the learning memory candidate control current I_inv_end is selected.

  When the decrease width dV_fc of the average cell voltage v_dc_fc reaches the decrease limit width Vd_bnd, the average cell voltage v_dc_fc decreases to the voltage decrease limit value, and the learning memory candidate control current I_inv_end is selected and stored. The control operation in steps S210 to S300 ends. Then, the control operation of the fuel cell 100 is maintained with the learning memory candidate control current I_inv_end stored as the learning current as the control current I_inv_fin.

  FIG. 8 is an explanatory diagram showing a specific example of the control operation executed according to the control flow shown in FIG. FIG. 8 shows, as an example, a case where the required power P_ac_rq changes in a stepped manner for ease of explanation, as in FIG.

  The control flow shown in FIG. 2 is started in response to the change in the required power P_ac_rq, and as described above, the required current I_rq as the reference current corresponding to the required fuel P_ac_rq is obtained, and the reference current I_rq is determined for each control cycle time tr. The voltage v_bse and the control fuel amount Qf_fin are obtained. Since it is assumed that the change in the required power P_ac_rq is stepped, any changes in the required current I_rq, the reference voltage v_bse, and the control fuel amount Qf_fin that are obtained are stepped.

  At this time, the control current I_inv_fin is obtained by increasing the first change width I_fb_t (U) obtained by multiplying the first differential current dI_fb (U) (= I_fb_r) by the cycle number Tc and the second differential current dI_fb (D ) Is repeatedly multiplied by the number of cycles 1 to decrease the second variation width I_fb_t (D). Here, I_fb_t (U) is a coefficient smaller than 1 so that the second variation width I_fb_t (D) equal to the second differential current dI_fb (D) is smaller than the first variation width I_fb_t (U). Set to a value multiplied by Kd. Therefore, the control current I_inv_fin gradually increases from the required current I_bse as the reference current by repeating the increase in the first change width I_fb_t (U) and the decrease in the second change width I_fb_t (D). It will be.

  Here, when the control current I_inv_fin gradually increases, the output current from the fuel cell 100 increases following the change in the control current I_inv_fin, and the amount of fuel consumed by the fuel cell 100 gradually increases. It will be. On the other hand, the amount of fuel supplied to the fuel cell 100 is constant as represented by the control fuel amount Qf_fin. As a result, the fuel utilization rate Uf_fb in the fuel cell 100 increases following the change in the control current I_inv_fin.

  In addition, the average cell voltage v_dc_fc gradually decreases from the reference voltage v_bse while repeatedly decreasing and increasing according to the change in the control current I_inv_fin, that is, the change in the fuel utilization rate Uf_fb. Then, the decrease width dV_fc (= v_bse−v_dc_fc) of the average voltage v_dc_fc from the reference voltage v_bse reaches the decrease limit width Vd_bnd (= α * v_bse) of the average cell voltage v_dc_fc, and the average cell voltage v_dc_fc reaches the decrease limit value. When the voltage decreases, the control flow shown in FIG. 7 is stopped, and the process of repeating the increase in the first change width I_fb_t (U) and the decrease in the second change width I_fb_t (D) in the control current I_inv_fin is stopped. Is done. Then, a value obtained by subtracting the learning storage correction current Ic from the value of the control current I_inv_fin at the stop point is set as a final control current I_inv_fin, and this value is learned and stored. Then, the output current from the fuel cell 100 is controlled based on the final control current I_inv_fin that has been learned and stored, whereby the fuel consumption in the fuel cell 100 is controlled and the power generation operation of the fuel cell 100 is executed. The

  As described above, in the control operation of the present embodiment, the control current I_inv_fin of the inverter 210 corresponding to the output current from the fuel cell 100 is converted into the first change width I_fb_t (by the first difference change rate dI_fb (U). U) and a decrease in the second change width I_fb_t (D) due to the second differential change rate dI_fb (D) are repeated, and the reference current is gradually increased from the required current I_rq. The average cell voltage can be controlled so that the fuel utilization rate is gradually increased by gradually increasing and decreasing the fuel utilization rate indirectly by gradually increasing the required current I_rq as It is possible to suppress the possibility that v_dc_fc falls below the voltage drop limit value, the fuel utilization rate exceeds the limit value, and the power generation performance falls. It is possible to improve the use rate.

  The difference change rate in the control current I_inv_fin substantially corresponds to the change rate of the fuel utilization rate in the present embodiment, the first difference change rate dI_fb (U) is a positive change rate, and the second change rate The difference change rate dI_fb (D) is a negative change rate. The state of the first differential change rate dIf_fb (U) corresponds to the state of a relatively large change rate of the fuel utilization rate in the present invention, and the state of the second differential change rate dI_fb (D) is the fuel utilization rate of the present invention. This corresponds to a relatively small change rate state.

D. Control operation of the third embodiment:
FIG. 9 is an explanatory diagram showing a specific example of the control operation of the third embodiment executed by the control device 900. Note that the control flow of the third embodiment basically controls the fuel utilization rate by controlling the amount of fuel, similarly to the control flow of the first embodiment. In the first embodiment, as shown in FIG. 6, by repeatedly increasing and decreasing the fuel amount, the fuel utilization rate increases and the negative rate of change due to the first differential rate of change, which is a positive rate of change. Although the case where the fuel utilization rate is changed by repeating the state of decrease in the fuel utilization rate due to a certain second difference change rate has been described as an example, as in the present embodiment shown in FIG. The state of increase in the fuel utilization rate due to a certain first difference change rate and the state of increase in the fuel utilization rate due to the second difference change rate that is a positive change rate smaller than the first difference change rate are repeated. It may be changed. Even in this case, since the fuel utilization rate can be controlled to gradually increase, the average cell voltage v_dc_fc falls below the voltage drop limit value, the fuel utilization rate exceeds the limit value, and the power generation performance is reduced. It is possible to suppress the possibility of a decrease and improve the fuel utilization rate.

  In the present embodiment, the first difference change rate is a positive change rate, and the second difference change rate is a positive change rate that is smaller than the first difference change rate. The state of the first differential change rate corresponds to a state of a relatively large change rate of the fuel utilization rate in the present invention, and the state of the second differential change rate is a state of a relatively small change rate of the fuel utilization rate of the present invention. It corresponds to.

  In this embodiment, the fuel amount control corresponding to the first embodiment has been described as an example. However, the present embodiment can be similarly applied to the current amount control corresponding to the second embodiment.

E. Control operation of the fourth embodiment:
FIG. 10 is a flowchart showing the control operation of the fourth embodiment executed by the control device 900. In the control operation of the third embodiment, the control device 900 controls the fuel usage rate by controlling the fuel amount described in the first embodiment (fuel amount control), as will be described below. , Referred to as “fuel amount control system”) and a control operation for controlling the fuel utilization rate by controlling the control current amount of the inverter described in the second embodiment (current amount control) (hereinafter referred to as “current amount control system”). ")." Each control operation is the same as the operation described in the first and second embodiments.

  The control operation shown in FIG. 9 is executed in each control cycle tr before the fuel amount control control flow shown in FIG. 2 or the current amount control control flow shown in FIG. 7 is started. Is selected and the selected control operation is executed.

  First, a power difference Pd (= P_ac_rq−P_inv) between the current output load power P_inv and the required power P_ac_rq is obtained (step S310). The output load power P_inv can be obtained by monitoring the output voltage V_inv and the output current I_inv output from the power output unit 200 and input to the grid interconnection interface 300.

  When the control operation currently selected and set is the current amount control system (step S320: Y), it is determined whether or not the power difference Pd is equal to or greater than the threshold value th1 (step S330). Here, when the power difference Pd is not equal to or greater than the threshold value th1, that is, when the power difference Pd is smaller than the threshold value th1 (step S330: N), the control operation is executed with the current control system maintained. To do. On the other hand, when the power difference Pd is greater than or equal to the threshold th1 (step S330: Y), the control operation is executed by switching to the fuel amount control system (step S340).

  On the other hand, when the control operation currently selected and set is the fuel amount control system (step S320: N), it is determined whether or not the power difference Pd is equal to or less than the threshold value th2 (step S350). The second threshold th2 is set to a value smaller than the first threshold th1. For example, the first threshold th1 is 10% of the rated output of the fuel cell 100, and the second threshold th2 is 5% of the rated output. Here, when the power difference Pd is not less than or equal to the threshold value th2, that is, when the power difference Pd is larger than the threshold value th2 (step S350: N), the control operation is executed with the fuel amount control system kept. And On the other hand, when the power difference Pd is less than or equal to the threshold th2 (step S350: Y), the control is performed by switching from the fuel amount control system to the current amount control system (step S360).

  As described above, in the control operation of the present embodiment, when the power difference Pd between the current output load power P_inv and the required load power P_ac_rq is large, the fuel usage rate is controlled using the fuel amount control system, When the power difference Pd is small, the fuel usage rate is controlled using the current amount control system. Here, while the current amount control can be performed with higher accuracy than the fuel amount control, there is a problem of response delay, and it is not suitable for high-speed tracking when the load fluctuation is large. . On the other hand, the fuel amount control is not suitable for highly accurate control when the resolution of the fuel pump to be used is low. Therefore, in the case of this embodiment, it is possible to control at a higher speed than in the case of only the current control system as in the second embodiment, and in comparison with the case of using only the fuel amount control system as in the first embodiment. High-precision control is possible.

  Further, by setting the second threshold th2 to a value smaller than the first threshold th1 and providing hysteresis, switching from the current amount control system to the fuel amount control system, and the fuel amount control system Hunting can be prevented by switching from the current amount control system to the current amount control system.

F. Variations:
In addition, elements other than the elements claimed in the independent claims among the constituent elements in each of the above embodiments are additional elements and can be omitted as appropriate. The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

(1) In the first embodiment, the first difference change rate dUf_fb (U) is fixed. In the second embodiment, the first difference change rate dI_fb (U) is fixed. However, the present invention is not limited to this. For example, the magnitude of the first difference change rate may be changed according to the magnitude of the change in the power load. In particular, it is preferable to reduce the magnitude of the first difference change rate as the magnitude of the change in the power load increases. In this way, since the degree of change in the fuel utilization rate can be further reduced, the average cell voltage v_dc_fc falls below the voltage drop limit value, the fuel utilization rate rises above the limit value, and the power generation performance decreases. It is possible to further suppress the possibility of doing so.

(2) In the first embodiment, the second change width Uf_fb_t (D) based on the second differential change rate dUf_fb (D) is fixed, and in the second embodiment, the second differential change rate dI_fb (D) is used. The change width I_fb_t (D) of 2 has been described as being fixed. However, the present invention is not limited to this. For example, the magnitude of the second difference change rate is changed according to the magnitude of the change in the power load. It may be. In particular, as the magnitude of the change in the power load is larger, it is preferable to reduce the magnitude of the second difference change rate to reduce the second change width. In this way, since the degree of change in the fuel utilization rate can be increased, the time required to reach the limit fuel utilization rate can be shortened.

1 is a block diagram showing a schematic configuration of a fuel cell system 1000. FIG. FIG. 6 is a control flow diagram showing a control operation of the first embodiment executed by the control device 900. It is explanatory drawing which shows the relationship between the electric power P output from the fuel cell 100, and the current density i. FIG. 5 is an explanatory diagram showing characteristics of output voltage v with respect to current density i of fuel cell 100. It is explanatory drawing which shows the relationship between the current density i of the fuel cell 100, and sufficient fuel quantity Qf. FIG. 3 is an explanatory diagram showing a specific example of a control operation executed according to the control flow shown in FIG. 2. It is a control flowchart which shows the control action of 2nd Example performed by the control apparatus 900. It is explanatory drawing which shows the specific example of the control action performed according to the control flow shown in FIG. It is explanatory drawing which shows the specific example of the control action of 3rd Example performed by the control apparatus. 10 is a flowchart showing a control operation of a fourth embodiment executed by the control device 900.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Fuel cell 200 ... Electric power output part 210 ... Inverter 210 operation | movement ... Inverter 300 ... Grid connection interface 400 ... Fuel pump 500 ... Desulfurizer 600 ... Evaporator 700 ... Reformer 710 ... Reformer 720 ... Heating part 800 ... Air pump 900 ... Control device 1000 ... Fuel cell system

Claims (11)

A fuel cell system for supplying load power corresponding to a power load,
A fuel cell;
A power output unit that converts a battery output of the fuel cell into a load output that can be supplied to the power load and outputs the load output; and
A control unit that controls the fuel cell to output a battery output corresponding to a required load power corresponding to the power load;
With
The controller is
When the power load changes, the change rate of the fuel utilization rate in the fuel cell is relatively large until the output voltage of the fuel cell reaches a limit output voltage determined according to the required load power. By alternately repeating the state of change rate and the state of relatively small change rate , control to gradually increase the fuel utilization rate ,
The controller is
i) Fuel amount control for changing the amount of fuel supplied to the fuel cell;
ii) current amount control for changing a control current amount for controlling the operation of the power output unit corresponding to the amount of current output from the fuel cell;
The fuel cell system , wherein the fuel utilization rate is changed using at least one of the above . The fuel cell system according to claim 1 , wherein
The relatively large change rate state is a state of increasing the fuel utilization rate,
The fuel cell system according to claim 1, wherein the state of the relatively small change rate is a state of decreasing the fuel utilization rate. The fuel cell system according to claim 1 , wherein
The relatively large change rate state is a state of increasing the fuel utilization rate,
The fuel cell system according to claim 1, wherein the relatively small change rate state is a state in which the fuel utilization rate is increased smaller than the relatively large change rate state. The fuel cell system according to claim 2 , wherein
The fuel cell system, wherein the amount of decrease in the fuel utilization rate in the state of the relatively small change rate is reduced as the change rate of the power load is increased. The fuel cell system according to any one of claims 1 to 4,
The fuel cell system characterized in that, as the rate of change of the power load is larger, the amount of increase in the fuel utilization rate in the state of the relatively large rate of change is reduced. The fuel cell system according to any one of claims 1 to 5,
When the fuel amount control is used, a value smaller by a predetermined amount than the fuel utilization rate at the time when the repetition of the relatively large change rate state and the relatively small change rate state is stopped alternately. The fuel cell system is characterized by learning and storing the fuel utilization rate corresponding to the operating condition including the required load power. The fuel cell system according to any one of claims 1 to 5,
When using the current amount control, a value smaller by a predetermined amount than the control current amount at the time when it is stopped to alternately repeat the relatively large change rate state and the relatively small change rate state. A fuel cell system characterized by learning and storing the amount of control current corresponding to an operating condition including the required load power. The fuel cell system according to any one of claims 1 to 3,
A fuel cell system, wherein the fuel amount control and the current amount control are switched in accordance with a rate of change of the power load. The fuel cell system according to claim 8 , wherein
The fuel cell system is characterized in that the fuel amount control is performed when the rate of change of the power load is equal to or greater than a predetermined value, and the current amount control is performed when the rate of change of the power load is equal to or less than a predetermined value. The fuel cell system according to claim 8 , wherein
In the state of current amount control, when the rate of change of the power load is equal to or greater than a first value, switching to the fuel control,
In the fuel amount control state, when the rate of change of the electric power load is a second value smaller than the first value, the fuel cell system is switched to the current control state. A control method of a fuel cell system for using a fuel cell to supply load power corresponding to an electric load,
When the power load changes , the fuel cell change rate state in the fuel cell is relatively large until the output voltage of the fuel cell reaches a limit output voltage determined according to the required load power. By alternately repeating a change rate state and a relatively small change rate state, the fuel utilization rate is controlled to gradually increase ,
i) Fuel amount control for changing the amount of fuel supplied to the fuel cell;
ii) current amount control for changing a control current amount for controlling the operation of the power output unit corresponding to the amount of current output from the fuel cell;
A fuel cell system control method , wherein the fuel utilization rate is changed using at least one of the above .

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