JP2007234333A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of concurrently controlling an outlet pressure in the downstream of an ejector and reserving a fuel supply flow volume for a fuel cell merging an offgas from a fuel cell to a main supply fuel within the ejector for circulation. <P>SOLUTION: This system calculates a basic opening degree in opening an injection tip to supply main fuel to an ejector depending on a demanded output for a fuel cell. In addition, this system calculates a correction opening degree for an injection tip in the ejector by correcting the basic degree depending on the condition of pressure in the downstream of the ejector. On the other hand, this method determines an allowable minimum opening degree in the injection tip depending on the demanded output. When the correction opening degree is smaller than the minimum opening degree, this system selects the minimum opening degree. In contrast, when it is larger than the minimum opening degree, this system selects the correction opening degree. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system. More specifically, the present invention relates to a fuel cell system that has a circulation path for joining fuel off-gas discharged from the fuel cell in a fuel supply path for power generation of the fuel cell, and circulates and uses the fuel off-gas. is there.

  Conventionally, Japanese Patent Application No. 2004-95528 discloses a fuel cell system in which off-gas discharged from a fuel cell is recirculated. This system is arranged at the junction of the hydrogen supply path for supplying hydrogen as fuel to the fuel cell, the circulation path for joining off-gas discharged from the fuel cell to the hydrogen supply path, and the circulation path and the hydrogen supply path Equipped with an ejector. The ejector ejects the hydrogen (main hydrogen) supplied from the hydrogen supply path on the upstream side of the ejector from the jet outlet to the downstream side, and the circulation path by the negative pressure near the injection port generated when the main hydrogen is injected. The off-gas from is sucked and mixed with the injected main hydrogen. As a result, the off-gas is recycled to the hydrogen supply path together with the main hydrogen.

  In this prior art system, the hydrogen supply flow rate (necessary hydrogen supply flow rate) required for power generation of the fuel cell and the pressure required during supply (necessary hydrogen supply pressure) are calculated according to the required output required. The More specifically, the required hydrogen supply flow rate and the required hydrogen supply pressure are determined according to the required output based on a map in which the relationship between the required output, the required hydrogen supply flow rate, and the required hydrogen supply pressure is determined in advance. . Thereafter, the ejector opening degree of the ejector pump and the valve opening degree of the regulator are calculated according to these obtained values.

  In this system, the actual hydrogen supply pressure to the fuel cell is further detected, and if the actual hydrogen supply pressure exceeds the allowable range compared to the required hydrogen supply pressure, the calculated ejector is used. Add a correction to reduce the opening. As a result, the opening area of the main hydrogen injection port of the ejector is reduced, and the hydrogen supply flow rate is reduced. As a result, the actual hydrogen supply pressure is reduced and brought close to the necessary hydrogen supply pressure. On the other hand, when the actual hydrogen supply pressure is smaller than the permissible range compared to the required hydrogen supply pressure, a correction for increasing the ejector opening is added. As a result, the opening area of the ejector outlet increases, and the hydrogen supply flow rate increases. As a result, the actual hydrogen supply pressure is increased and brought close to the required hydrogen supply pressure.

JP 2004-95528 A JP-A-2005-129912

  As described above, the prior art system corrects the ejector opening when the difference between the actual hydrogen supply pressure and the required hydrogen supply pressure is large. Here, for example, when the required output sharply decreases, the required required hydrogen supply pressure decreases rapidly accordingly. On the other hand, the actual hydrogen supply pressure does not immediately decrease to the required hydrogen supply pressure, and the difference between the required hydrogen supply pressure and the actual hydrogen supply pressure may temporarily increase. When the pressure difference between the two becomes large in this way, the throttle amount, which is a correction value for the ejector opening, is set large in order to quickly reduce the actual hydrogen supply pressure to the required hydrogen supply pressure.

  When the throttle amount with respect to the ejector opening becomes excessively large, the obtained corrected opening becomes an opening close to the valve closing. In this case, when the ejector opening is set to the corrected opening, the supply of main hydrogen is stopped. Further, since the venturi effect in the ejector is not generated by stopping the supply of main hydrogen, the circulation due to the off-gas suction may be stopped. As a result, hydrogen necessary for power generation of the fuel cell is not supplied, and a situation in which power generation with the required output cannot be performed may occur.

  The present invention has been made to solve the above-described problems, and it is possible to secure the fuel supply flow rate necessary for power generation while controlling the ejector opening in consideration of the fuel supply pressure to the fuel cell. An object of the present invention is to provide a fuel cell system improved so as to be able to do so.

In order to achieve the above object, a first invention is a fuel cell system,
A fuel supply path for supplying main fuel supplied from the fuel supply means to the fuel cell;
A circulation path for joining the fuel off-gas discharged from the fuel cell to the fuel supply path;
A main supply fuel that is provided at a junction between the fuel supply path and the circulation path and that flows in from the fuel supply path via an injection port and a fuel off-gas that flows in from the circulation path are mixed to form a downstream side. An ejector capable of flowing out into the fuel supply path and adjusting an opening of the injection port;
A required main fuel flow rate estimating means for estimating a required main fuel flow rate used for power generation in the fuel cell according to a required output required;
Basic opening degree calculating means for calculating a basic opening degree of the injection port according to the required main fuel flow rate;
In accordance with the state of pressure downstream of the ejector, corrected opening degree calculating means for correcting the basic opening degree and calculating a corrected opening degree;
In accordance with the required output, minimum opening setting means for setting a minimum opening of the injection port allowed,
Minimum opening determination means for determining whether or not the corrected opening is smaller than the minimum opening;
When it is determined that the corrected opening is smaller than the minimum opening, the opening of the injection port is set to the minimum opening, and the correction opening is determined to be greater than or equal to the minimum opening Opening degree setting means for setting the opening degree of the injection port to the corrected opening degree;
It is characterized by providing.

In a second aspect based on the first aspect, the minimum opening setting means is
Fuel cell required fuel for estimating a fuel cell required fuel flow rate as a fuel flow rate that needs to be supplied to the fuel cell in order to obtain the required output by distributing the fuel to each cell stacked in the fuel cell Flow rate estimation means;
A circulating fuel flow rate estimating means for estimating a circulating fuel flow rate contained in the fuel off gas mixed with the main supply fuel;
A minimum main fuel flow rate calculating means for calculating the minimum main fuel flow rate by dividing the circulating fuel flow rate from the fuel cell required fuel flow rate;
Minimum opening calculating means for calculating the minimum opening according to the minimum main fuel flow rate;
It is characterized by providing.

According to a third invention, in the first or second invention, the fuel cell system comprises:
Target outlet pressure calculating means for calculating a target outlet pressure that is a target value of pressure in the fuel supply path downstream of the ejector;
Outlet pressure detecting means for detecting an outlet pressure that is a pressure in the fuel supply path downstream of the ejector,
The corrected opening calculating means corrects the basic opening according to a difference between the outlet pressure and the target outlet pressure.

In a fourth aspect based on any one of the first to third aspects, the fuel cell system comprises:
Maximum opening determination means for determining whether or not the minimum opening is larger than an allowable maximum opening that is an upper limit of the allowable opening of the injection port;
When it is determined that the minimum opening is larger than the allowable maximum opening, an allowable output estimating means for estimating an allowable output that is generated when the opening of the injection port is in the state of the allowable maximum opening;
Output control means for controlling the output of the fuel cell to the allowable output;
It is characterized by providing.

In a fifth aspect based on any one of the first to third aspects, the fuel cell system comprises:
Maximum opening determination means for determining whether or not the minimum opening is larger than an allowable maximum opening that is an upper limit of the allowable opening of the injection port;
When it is determined that the minimum opening is larger than the allowable maximum opening, the fuel of the necessary main fuel flow rate can be supplied in a state where the opening of the injection port is the allowable maximum opening. Target inlet pressure estimating means for estimating the target inlet pressure of the injection port;
An inlet pressure control means for controlling the inlet pressure upstream of the injection port to the target inlet pressure;
It is characterized by providing.

  According to the first invention, when the basic opening degree of the ejection opening of the ejector is corrected according to the pressure state downstream of the ejector, and when the corrected opening degree is smaller than the minimum allowable opening degree of the ejection opening, The opening of the injection port is set to the minimum opening. Therefore, it is possible to avoid a state where the fuel flow rate necessary for power generation is not supplied.

  According to the second aspect of the invention, the minimum required main fuel flow rate is obtained according to the fuel cell required fuel flow rate required to obtain the required output by distributing the fuel to all the stacked cells, and the minimum opening Is set to an opening that can supply the minimum main fuel flow rate. Therefore, even when the corrected opening of the ejection port of the ejector is smaller than the minimum opening, it is possible to supply at least the minimum fuel necessary for power generation to all the cells stacked in the fuel cell. it can.

  According to the third invention, the correction value of the opening of the injection port can be set according to the difference between the target outlet pressure and the actually detected outlet pressure. Therefore, the opening degree of the injection port can be set in consideration of the actual outlet pressure, and supply of the required fuel flow rate can be ensured more reliably.

  According to the fourth invention, when the minimum opening is larger than the allowable maximum opening that is the upper limit of the allowable opening of the injection opening, power is generated in a state where the opening of the injection opening is the allowable maximum opening. The requested output is controlled to the allowable output. Thus, it is possible to avoid a state where an output higher than the power that can be generated within the range in which the opening degree of the injection port is controllable, and to perform control according to the required output within the power generation possible range.

  According to the fifth invention, when the minimum opening is larger than the allowable maximum opening, the target of the injection port that can supply the fuel of the necessary main fuel flow rate when the opening of the injection port is the allowable maximum opening. Set to inlet pressure. As a result, the main supply fuel flow rate that can be supplied at the maximum allowable opening can be increased, and the required output power can be generated.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment 1 FIG.
[Configuration of Fuel Cell System of Embodiment 1]
FIG. 1 is a schematic diagram for illustrating a fuel cell system according to Embodiment 1 of the present invention. As shown in FIG. 1, this system includes a fuel cell 2. In FIG. 1, the fuel cell 2 includes two stacks 4. A plurality of cells 6 (single cells) are stacked in each stack 4. Each cell 6 has a configuration in which an electrolyte membrane is sandwiched between a pair of electrodes.

  This system includes a hydrogen supply source (not shown) for supplying hydrogen as fuel to the hydrogen electrode (negative electrode) of each cell 6 of the fuel cell 2. The end of the main hydrogen supply path 8 is connected to the hydrogen supply source. The main hydrogen supply path 8 is provided with a hydrogen pressure regulating valve 10 that maintains the pressure in the main hydrogen supply path 8 at a predetermined pressure. The main hydrogen supply path 8 is attached with a pressure sensor 12 that generates an output corresponding to the pressure in the main hydrogen supply path 8.

  The downstream end of the main hydrogen supply path 8 is connected to the upstream side of an ejector 14 having a configuration to be described later. One end of the hydrogen path 16 is connected to the downstream side of the ejector 14. The other end of the hydrogen path 16 is connected to the hydrogen supply port of the fuel cell 2. A pressure sensor 18 (outlet pressure detection means) that generates an output corresponding to the hydrogen supply pressure to the fuel cell 2 is attached to the hydrogen path 16.

  On the other hand, a circulation path 20 is connected to the hydrogen discharge port of the fuel cell 2. The circulation path 20 is a path for circulating or discharging hydrogen off-gas (hereinafter “off-gas”) containing unreacted gas discharged from the fuel cell 2. The circulation path 20 is connected to the ejector 14. The off gas discharged from the fuel cell 2 to the circulation path 20 is pulled up by the ejector 14, mixed with main hydrogen supplied from the main hydrogen path 8 in the ejector 14, and supplied again into the fuel cell 2 from the hydrogen path 16. . Hereinafter, in this embodiment, hydrogen supplied from the main hydrogen supply source is referred to as “main hydrogen”, and a mixed gas of main hydrogen and off-gas mixed in the ejector 14 and supplied from the hydrogen path 16 is “ It will be referred to as “feed hydrogen”.

  A pressure sensor 22 that generates an output corresponding to the pressure in the circulation path 20 and a flow rate sensor 24 that outputs an output corresponding to the flow rate of the off-gas in the circulation path 20 are attached to the circulation path 20. A gas-liquid separator 26 is installed in the middle of the circulation path 20. The gas-liquid separator 26 separates and removes moisture in the offgas. A discharge path 28 is connected to the gas-liquid separator 26, and a discharge valve 30 is provided in the discharge path 28. The off-gas in the circulation path 20 is discharged to the outside through the discharge path 28 when the discharge valve 30 is opened.

  In FIG. 1, the illustration regarding the path for supplying and discharging the oxidant is omitted, but in reality, the air supply pipe is connected to the oxidant supply port of the fuel cell 2, and the atmosphere is supplied from the outside by a compressor or the like. It has come to be. The air supplied through the air supply pipe is supplied to the oxygen electrode (positive electrode) side in the fuel cell 2. A discharge path is connected to the oxidant outlet of the fuel cell 8 so that atmospheric off-gas containing unreacted oxidant discharged from the fuel cell is discharged.

  FIG. 2 is a schematic diagram for explaining the ejector according to Embodiment 1 of the present invention. As shown in FIG. 2, the ejector 14 includes a nozzle 32, a main hydrogen port 34, an injection port 36, an offgas port 38, and a discharge port 40. The main hydrogen port 34 is connected to the main hydrogen supply pipe 8, and main hydrogen flows from the main hydrogen port 34. The injection port 36 is an opening provided in the nozzle 32, and the main hydrogen flowing in from the main hydrogen port 34 is injected downstream from the injection port 36. The off gas port 38 is connected to the circulation path 20. The off-gas in the circulation path 20 is sucked into the ejector 14 from the off-gas port 38 by the negative pressure generated in the vicinity of the injection port 36 when main hydrogen is injected, and is mixed with main hydrogen. The discharge port 40 is connected to the hydrogen path 16. The supplied hydrogen mixed in the ejector 14 is discharged from the discharge port 40 to the hydrogen path 16.

  The ejector 14 is provided with a movable needle 42 for adjusting the opening of the nozzle 32, that is, the opening of the injection port 36 (hereinafter referred to as “ejector opening”). The movable needle 42 has a tapered shape that gradually decreases toward the tip. Therefore, the ejector opening degree can be adjusted by moving the movable needle 42 in the axial direction. Specifically, it is possible to control the movable needle 42 so that the ejector opening is reduced by moving the movable needle 42 to the left in FIG. 2 and the ejector opening is increased by moving to the right. Thus, the ejector opening can be controlled arbitrarily.

  As the ejector opening increases, the main hydrogen flow rate increases and the outlet pressure increases. At this time, since the opening area of the injection port 34 is large, the flow rate of the main hydrogen injected from the injection port 34 becomes slow. Therefore, the negative pressure generated near the injection port 34 when main hydrogen is injected is reduced. As a result, the amount of off-gas lifted from the circulation path 20 decreases, and the off-gas circulation flow rate decreases. On the other hand, when the ejector opening becomes small, the main hydrogen flow rate decreases and the outlet pressure decreases. At this time, the flow rate of main hydrogen injected from the injection port is increased. Accordingly, the negative pressure generated in the vicinity of the injection port 34 is increased. As a result, the amount of off-gas raised is increased, and the off-gas circulation flow rate is increased. By adjusting the ejector opening in this way, the flow rate of hydrogen supplied to the fuel cell 2, the circulation flow rate of off-gas supplied from the circulation path 20, and the outlet pressure can be adjusted.

[Basic control of the system of the first embodiment]
During power generation of the fuel cell 2, supply hydrogen is supplied from the hydrogen path 16 to the hydrogen electrode of each cell 6, while air is supplied to the oxygen electrode as an oxidant. As a result, an electrochemical reaction (power generation reaction) between hydrogen and oxygen occurs in each cell 6 to generate power. At this time, the ejector opening is determined according to the required generated current command value Ifc. Specifically, the main hydrogen flow rate required for the power generation reaction of the generated current command value Ifc is obtained, and the ejector opening is determined according to the main hydrogen flow rate.

Here, first, the necessary main hydrogen flow rate Qe used for the power generation reaction for generating the generated current command value Ifc can be obtained according to the following equation (1).
Necessary main hydrogen flow rate Qe = k ・ Generation current command value Ifc (1)
In equation (1), k is a coefficient representing the unit hydrogen flow rate necessary to generate a current of 1 (A).

  FIG. 3 is a graph showing the relationship between the main hydrogen flow rate ejected from the ejection port 36 of the ejector 14 and the basic opening of the ejector. In FIG. 3, the horizontal axis represents the main hydrogen flow rate, and the vertical axis represents the basic opening. The main hydrogen flow rate ejected from the ejection port 36 and the basic opening have a correlation as shown in FIG. That is, when the main hydrogen flow rate is small, the basic opening degree becomes small, and as the main hydrogen flow rate becomes large, the basic opening degree becomes large. Also, the relationship between the main hydrogen flow rate and the basic opening varies depending on the ejector inlet side, that is, the pressure in the main hydrogen supply path 8 (hereinafter referred to as “inlet pressure”). The system according to the first embodiment stores in advance a map that defines the relationship among the inlet pressure of the ejector 14, the main hydrogen flow rate, and the basic opening. The basic opening degree θe is calculated according to this map as an opening degree at which main hydrogen of the required main hydrogen flow rate Qe obtained in the above equation (1) is injected.

  Incidentally, the target value of the outlet pressure downstream of the discharge port 40 of the ejector 14 (hereinafter referred to as “target outlet pressure”) is determined according to the generated current command value Ifc. Here, the basic opening degree θe is a basic value of the opening degree at which the main hydrogen at the required main hydrogen flow rate Qe is ejected and the outlet pressure is set as the target outlet pressure Ptg. Therefore, when the actual outlet pressure Pout is different from the target outlet pressure Ptg, the main hydrogen flow rate is increased or decreased by adjusting the ejector opening so that the actual outlet pressure Pout matches the target outlet pressure Ptg. That is, when the actual outlet pressure Pout is smaller than the target outlet pressure Ptg, the ejector opening is corrected to an opening at which main hydrogen having a flow rate larger than the required main hydrogen flow rate Qe is supplied. As a result, the actual outlet pressure Pout increases and approaches the target outlet pressure Ptg. On the other hand, when the actual outlet pressure Pout is larger than the target outlet pressure Ptg, the ejector opening is corrected to an opening at which main hydrogen having a flow rate smaller than the required main hydrogen flow rate Qe is supplied. As a result, the actual outlet pressure Pout decreases and approaches the target outlet pressure Ptg.

  Specifically, in the first embodiment, the basic opening θe is corrected with the correction value θs, and the corrected opening is calculated. As the correction value θs for the basic opening θe, the correction value θs is obtained according to the difference between the target outlet pressure Ptg and the outlet pressure Pout. Hereinafter, a method for calculating the corrected opening will be specifically described.

  FIG. 4 is a graph showing the relationship between the generated current command value and the target outlet pressure. In FIG. 4, the horizontal axis represents the generated current command value, and the vertical axis represents the target outlet pressure. As shown in FIG. 4, the supply hydrogen to be supplied to the fuel cell 2 increases as the required generation current command value increases, so the target that is the target value of the hydrogen supply pressure supplied to the fuel cell 2 The outlet pressure increases. The system of the first embodiment stores in advance a map that defines the relationship between the generated current command value and the target outlet pressure according to the relationship as shown in FIG. The target outlet pressure Ptg is obtained according to this map according to the generated current command value Ifc. On the other hand, the actual outlet pressure Pout can be detected from the output result of the pressure sensor 18 attached to the hydrogen path 16 downstream of the ejector 14.

From the target outlet pressure Ptg calculated as described above and the detected actual outlet pressure Pout, the outlet pressure deviation ΔP is obtained according to the following equation (2).
Outlet pressure deviation ΔP = Outlet pressure Pout−Target outlet pressure Ptg (2)
The correction value θs for the basic opening θe is obtained, for example, by adding a value obtained by multiplying the proportional term of the outlet pressure deviation ΔP by a predetermined gain and a value obtained by multiplying the integral term of the outlet pressure deviation ΔP by a predetermined gain. Desired.

The corrected opening degree * θe is obtained according to the following equation (3).
Corrected opening * θe = Basic opening θe + Correction value θs (3)
As a result, the basic opening degree θe is corrected in consideration of the actual outlet pressure Pout, and the corrected opening degree * θe is obtained. By setting the ejector opening to the corrected opening * θe, the main hydrogen at the required main hydrogen flow rate Qe required for power generation according to the generated current command value Ifc is more reliably injected, and the outlet pressure is set to the target outlet pressure. Ptg.

[Characteristic Control of the System of Embodiment 1]
Incidentally, the corrected opening degree * θe is an opening degree corrected according to the outlet pressure deviation ΔP which is the difference between the actual outlet pressure Pout and the target outlet pressure Ptg. Here, when the required generated current command value Ifc fluctuates rapidly, the target outlet pressure Ptg fluctuates greatly in conjunction with this. On the other hand, the actual outlet pressure Pout does not change immediately in response to a sudden change in the generated current command value Ifc, and there may be a delay in the response. In this case, a large difference occurs between the target outlet pressure Ptg and the actual outlet pressure Pout. As a result, the correction value θs has a large absolute value so that the actual outlet pressure Pout approaches the target outlet pressure Ptg. That is, when the target outlet pressure Ptg changes rapidly, the value of the outlet pressure deviation ΔP greatly changes. For this reason, the correction value θs calculated based on the outlet pressure deviation ΔP also has a large absolute value.

  As described above, when the generated current command value Ifc decreases rapidly and the target outlet pressure Ptg decreases rapidly, a large difference temporarily occurs between the actual outlet pressure Pout and the target outlet pressure Ptg. The deviation ΔP may become large. In this case, the correction value θs is calculated as a large negative value so that the basic opening θe is excessively reduced so that the actual outlet pressure Pout approaches the target outlet pressure Ptg. Accordingly, the corrected opening * θe is an excessively small opening. As a result, the supply of the necessary main hydrogen flow rate Qe actually required for power generation cannot be ensured, and the necessary power generation may not be performed.

  Therefore, in the first embodiment, the minimum opening θemin is set as the lower limit guard value for the ejector opening. When the corrected opening * θe is equal to or greater than the minimum opening θemin, the ejector opening θ is set to the corrected opening * θe, and when the corrected opening * θe is smaller than the minimum opening θemin, The ejector opening degree θ is forcibly set to the minimum opening degree θemin. Hereinafter, a method for setting the minimum opening θemin will be described.

Since each stack 4 of the fuel cell 2 has a structure in which the cells 6 are stacked, a difference in hydrogen supply flow rate due to pressure loss occurs between the upstream cell and the downstream cell. In consideration of such pressure loss, FC required hydrogen which is the hydrogen supply flow rate to the fuel cell 2 required to supply the minimum hydrogen required for power generation to the cell where the hydrogen supply flow rate is the smallest. The flow rate Qfc is calculated based on the following equation (4).
FC required hydrogen flow rate Qfc = Sth · Required main hydrogen flow rate Qe ··· (4)
In equation (4), Sth is a coefficient that secures a margin in the main hydrogen flow rate so that hydrogen of a flow rate necessary for power generation is supplied to all the cells 6 in consideration of pressure loss and the like. Is a value of about 1.4, for example.

The total hydrogen flow rate supplied to the fuel cell 2 is the sum of the main hydrogen flow rate supplied from the main hydrogen supply path 8 side and the hydrogen flow rate in the mixed off-gas. Therefore, in order to ensure that the FC required hydrogen flow rate Qfc is supplied to the fuel cell 2, the minimum main hydrogen flow rate Qemin, which is the main hydrogen flow rate that needs to be supplied from the main hydrogen supply path 8, is expressed by the following equation (5). Calculated based on
Minimum main hydrogen flow rate Qemin = FC required main hydrogen flow rate Qfc-circulating hydrogen flow rate Qc (5)

In equation (5), the circulating hydrogen flow rate Qc represents the flow rate of hydrogen contained in the off-gas mixed with the supplied hydrogen. The circulating hydrogen flow rate Qc is calculated according to the following equation (6).
Circulating hydrogen flow rate Qc = Off-gas flow rate / Estimated hydrogen concentration (6)
In equation (6), the off-gas flow rate is a flow rate of off-gas that is pulled up from the circulation path 20 to the ejector 14 and reused, and is a detected value that is detected according to the output of the flow sensor 24 arranged in the circulation path 20. is there. The estimated hydrogen concentration is an estimated value of the off-gas hydrogen concentration, and is calculated according to a map stored in advance as parameters such as an elapsed time from the start of power generation and an output.

  The minimum opening θemin set as the lower limit guard value of the ejector opening is the ejector opening necessary for supplying the minimum main hydrogen flow rate Qemin. As described above, the system according to the first embodiment stores a map that defines the relationship among the inlet pressure, the main hydrogen flow rate, and the basic opening. The minimum opening degree θemin is obtained as a value corresponding to the inlet pressure Pin and the minimum main hydrogen flow rate Qemin according to this map.

  As described above, the ejector opening is forcibly set to the minimum opening θemin when the corrected opening * θe is smaller than the minimum opening θemin. Accordingly, when the corrected opening * θe is excessively small, it is possible to avoid the ejector opening being set to the corrected opening * θe. As a result, it is possible to avoid a state in which the necessary supply of hydrogen cannot be ensured, and to ensure a minimum necessary hydrogen flow rate.

  FIG. 5 is a flowchart for illustrating a control routine executed by the system in the first embodiment of the present invention. The routine of FIG. 5 is a routine that is repeatedly executed when the ejector opening degree θ is set. In FIG. 5, first, the generated current command value Ifc is calculated (step S102). The generated current command value Ifc is calculated based on information such as required load, for example. Next, the inlet pressure Pin is detected (step S104). The inlet pressure Pin is obtained according to the output of the pressure sensor 12. Next, the outlet pressure Pout of hydrogen discharged from the ejector 14 into the hydrogen path 16 is detected (step S106). The outlet pressure Pout is obtained based on the output of the pressure sensor 18. Next, the target outlet pressure Ptg is obtained (step S108). The target outlet pressure Ptg is obtained as a value corresponding to the generated current command value Ifc according to a map set in advance based on the relationship shown in the graph of FIG.

  Next, the required main hydrogen flow rate Qe is obtained (step S110). The required main hydrogen flow rate Qe is obtained by multiplying the generated current command value Ifc by a coefficient k according to the equation (1). The required main hydrogen flow rate Qe is the hydrogen flow rate used for the power generation reaction of the generated current command value Ifc. Next, the FC required hydrogen flow rate Qfc is calculated (step S112). The FC required hydrogen flow rate Qfc is obtained by multiplying the required main hydrogen flow rate Qe by a coefficient Sth as in the above equation (4). The obtained FC required hydrogen flow rate Qfc is a hydrogen flow rate that needs to be supplied to the fuel cell 2 because hydrogen at a flow rate required for power generation is supplied to all cells in the generation of the generation current command value Ifc. is there.

  Next, the off-gas flow rate circulating in the circulation path 20 is detected (step S114). The off gas flow rate is obtained based on the output of the flow rate sensor 24 disposed in the circulation path 20. Next, an estimated value of the hydrogen concentration in the off gas is obtained (step S116). The estimated value of the hydrogen concentration in the off gas is calculated according to a map stored in advance. Next, the circulating hydrogen flow rate Qc is obtained (step S118). The circulating hydrogen flow rate Qc is a hydrogen flow rate included in the off gas that is pulled up from the circulation path 20 to the ejector 14, and as expressed by equation (6), the off gas flow rate detected in step S114 and the hydrogen concentration obtained in step S116 Calculated by multiplying the estimated value.

  Next, the minimum main hydrogen flow rate Qemin is obtained (step S120). The minimum main hydrogen flow rate Qemin is calculated as a value obtained by subtracting the circulating hydrogen flow rate Qc from the FC required hydrogen flow rate Qfc as in the above equation (5). The minimum main hydrogen flow rate Qemin is a main hydrogen flow rate that needs to be supplied from the main hydrogen supply path 8 in order to supply the FC required hydrogen flow rate Qfc to the fuel cell 2.

  Next, the basic opening degree θe is obtained according to the required main hydrogen flow rate Qe (step S122). The basic opening degree θe is obtained according to the inlet pressure Pin and the required main hydrogen flow rate Qe according to a map using the inlet pressure and the main hydrogen flow rate as parameters. Next, the minimum opening degree θemin corresponding to the minimum main hydrogen flow rate Qemin is obtained (step S124). Similar to the basic opening degree θe, the minimum opening degree θemin is determined according to the inlet pressure Pin and the minimum main hydrogen flow rate Qemin according to a map using the inlet pressure and the main hydrogen flow rate as parameters.

  Next, the outlet pressure deviation ΔP is obtained (step S126). The outlet pressure deviation ΔP is calculated as a value obtained by subtracting the target outlet pressure Ptg from the outlet pressure Pout as in the above equation (2). Next, a correction value θs for the basic opening θe is obtained according to the outlet pressure deviation ΔP (step S128). Specifically, the correction value θs for the basic opening θe is obtained by adding a value obtained by multiplying the proportional term of the outlet pressure deviation ΔP by a predetermined gain and a value obtained by multiplying the integral term by a predetermined gain. Next, a corrected opening degree * θe is obtained (step S130). The corrected opening degree * θe is a value obtained by adding the correction value θs to the basic opening degree θe obtained in step S122 as expressed by the equation (3), and is a value obtained by correcting the basic opening degree θe according to the outlet pressure deviation ΔP. It becomes.

  Next, it is determined whether or not the corrected opening * θe is equal to or greater than the minimum opening θemin (step S132). If it is determined in step S132 that * θe ≧ θemin is satisfied, the ejector opening θ is set to the corrected opening * θe (step S134). On the other hand, if establishment of * θe ≧ θemin is not recognized in step S132, the ejector opening degree θ is set to θemin (step S136). Thereafter, the ejector opening degree is controlled in accordance with the set ejector opening degree θ (step S138). The ejector opening degree θ is controlled by moving the movable needle 42 according to the set ejector opening degree θ.

  As a result, when the corrected opening * θe is equal to or greater than the minimum opening θemin, the basic opening θe corresponding to the required main hydrogen flow rate Qe is set to the opening corrected by the outlet pressure deviation ΔP. Therefore, the opening degree of the ejector is an opening degree in consideration of the actual outlet pressure Pout, and the hydrogen flow rate necessary for power generation can be supplied to the fuel cell 2 more reliably. When the corrected opening * θe is smaller than the minimum opening θemin, the ejector opening is set to the minimum opening θemin. As a result, when the fluctuation of the generated current command value Ifc is large and the corrected opening * θe is excessively small, the ejector opening is prevented from being set to the corrected opening * θe, and the minimum hydrogen required for power generation is avoided. Can be ensured.

  In the first embodiment, the configuration of the ejector 14 is schematically described. However, the ejector 14 pulls off gas from the circulation path 20 by a so-called Venturi effect and the like, and main hydrogen supplied from the main hydrogen supply path 8. Any other configuration may be used as long as it can be mixed with off-gas and supplied to the fuel cell 2 side.

  In the first embodiment, the case where the minimum opening is set based on the minimum main hydrogen flow rate Qemin has been described. However, the minimum opening, which is the lower guard value, is not limited to this, but can be calculated by other calculation methods, or can be a fixed value set to ensure a minimum hydrogen supply. There may be.

  In the first embodiment, the case where the basic opening is set based on the required main hydrogen flow rate Qe has been described. However, in the present invention, the calculation method of the basic opening is not limited to this, and may be calculated and set by another method as long as it is obtained according to the generation of the required generation current command value Ifc. It may be.

  In the first embodiment, the correction value θs is calculated by adding the proportional term and the integral term of the outlet pressure deviation ΔP obtained from the outlet pressure Pout and the target outlet pressure Ptg. However, in the present invention, the calculation method of the correction value θs is not limited to this, and may be, for example, a value calculated as a value proportional to the outlet pressure deviation ΔP.

  As described above, the ejector opening is a value set on the assumption of target values such as the inlet pressure, the outlet pressure, and the return pressure. However, the actual pressure does not necessarily match the target value. Therefore, if there is a difference between the target value and the actual detected pressure value, it is preferable to correct the basic opening according to the difference. This correction value is not limited to the value corresponding to the difference between the target outlet pressure Ptg and the outlet pressure Pout, and may be obtained, for example, in the relationship between the target outlet pressure Ptg and the detected inlet pressure Pin. . Further, for example, a return pressure that is a pressure in the circulation path 20 circulated to the ejector 14 may be detected, and a correction value may be calculated based on the relationship between the target outlet pressure Ptg and the detected return pressure. Moreover, it is not restricted to the thing according to target outlet pressure Ptg. For example, when a target value of the return pressure is set, a correction value may be calculated in relation to a detected value such as a return pressure, an outlet pressure, or an inlet pressure with respect to the target return pressure. .

  As described above, when the ejector opening is corrected based on the difference between the target outlet pressure or the target return pressure and the actual detection value, the minimum opening value is set as the lower limit guard value as in the first embodiment. A method of setting the degree is effective. That is, when the generated current command value Ifc decreases rapidly and significantly, the difference between the target value and the actual detection value may increase, and the correction opening may be excessively decreased. Therefore, in order to avoid a situation where the corrected opening is set too small, a means for providing a lower limit guard based on the minimum opening is effective as in the first embodiment.

  For example, in the first embodiment, the “outlet pressure detecting means” of the present invention is realized by executing step S106, and the “target outlet pressure calculating means” is realized by executing step S108. Realize. Further, for example, the “required main fuel flow rate estimating means” of the present invention is realized by executing step S110, and the “fuel cell required fuel flow rate estimating means” is realized by executing step S112. By executing S118, “circulated fuel flow rate estimating means” is realized, and by executing step S120, “minimum main fuel flow rate calculating means” is realized. Further, for example, the “basic opening degree calculation means” of the present invention is realized by executing step S122, and the “minimum opening degree calculation means” is realized by executing step S124. Further, for example, by executing steps S112 to S120 and step S124, the “minimum opening degree setting means” of the present invention is realized, and by executing steps S126 to S130, the “corrected opening degree calculating means” is realized. Realize. Further, for example, the “minimum opening degree determination unit” of the present invention is realized by executing step S132, and the “opening degree setting unit” is realized by executing step S134 or step S136.

Embodiment 2. FIG.
The system of the second embodiment has the same configuration as the system shown in FIGS. The system of the second embodiment performs the same control as the system of the first embodiment except that the generated current value is controlled when the calculated minimum opening θemin becomes close to the maximum controllable opening. Do. Specifically, in the second embodiment, when θemin calculated by the same method as in the first embodiment is larger than the maximum opening θmax, the power generation current Imax that can be generated at the maximum opening θmax is The current value is controlled. Here, the maximum opening θmax is a predetermined value close to the maximum controllable opening of the ejector 14 and is, for example, about 95%.

In the second embodiment, the allowable generated current Imax corresponding to the maximum opening degree θmax is obtained as follows. First, the maximum main hydrogen flow rate Qemax, which is the main hydrogen flow rate supplied at the inlet pressure Pin and the maximum opening degree θmax, is estimated according to a map that defines the relationship among the inlet pressure, the basic opening amount, and the main hydrogen flow rate. When the maximum main hydrogen flow rate Qemax is determined, the maximum FC hydrogen flow rate Qfcmax discharged from the ejector 14 to the fuel cell 2 when the maximum main hydrogen flow rate Qe is supplied from the main hydrogen supply path 8 is expressed by the following equation (7 ).
Maximum FC hydrogen flow rate Qfcmax = Maximum main hydrogen flow rate Qemax + Circulating hydrogen flow rate Qc (7)
In the equation (7), the circulating hydrogen flow rate Qc can be obtained according to the equation (6) as described in the first embodiment.

When the maximum FC hydrogen flow rate Qfcmax is obtained, the allowable power generation current Imax that is generated when hydrogen of the maximum FC hydrogen flow rate Qfcmax is supplied is obtained by the following equation (8).
Allowable power generation current Imax = Maximum FC hydrogen flow rate Qfcmax / k · Sth (8)
The equation (8) is obtained from the above equations (1) and (4), the coefficient k is the unit hydrogen flow rate necessary for the power generation of the current of 1 (A), and the coefficient Sth is the pressure loss. Is a coefficient that secures a margin necessary for supplying necessary hydrogen to all the cells 6 in the fuel cell 2.

  From the above, the allowable power generation current Imax that can be generated when the ejector opening is the maximum opening θmax is obtained. In the second embodiment, when the minimum opening θemin is larger than the maximum opening θmax, the generated current is controlled from the generated current command value Ifc to the allowable generated current Imax. Thus, when the calculated minimum opening θemin exceeds the controllable maximum opening θmax, the ejector opening θ is set based on the generation current command value Ifc that cannot generate power, or It is possible to avoid performing other controls.

  FIG. 6 is a flowchart for illustrating a control routine executed by the system in the second embodiment of the present invention. The routine in FIG. 6 is the same as the routine in FIG. 5 except that steps S202 to S210 are included in addition to the routine in FIG. Specifically, after the minimum opening θemin is obtained in step S124 of FIG. 5, it is determined whether or not the minimum opening θemin is equal to or less than the maximum opening θmax (step S202). If it is determined that the minimum opening θemin is equal to or less than the maximum opening θmax, it is considered that the generated current command value Ifc can be generated by controlling the ejector opening in the current state. Accordingly, steps S126 to S138 are executed, and the ejector opening degree θ is controlled to the correction opening degree * θe or the minimum opening degree θemin.

  On the other hand, if the establishment of θemin ≦ θmax is not recognized in step S202, even if the maximum main hydrogen flow rate is secured by controlling the ejector opening θ, there is a case where the required power generation current command value Ifc cannot be generated. it is conceivable that. Therefore, when the establishment of θemin ≦ θmax is not recognized, the maximum main hydrogen flow rate Qemax that can be supplied at the maximum opening degree θmax is first obtained (step S204). The system according to the second embodiment stores in advance a map that defines the relationship among the inlet pressure, the ejector opening, and the main hydrogen flow rate. The maximum main hydrogen flow rate Qemax is obtained according to the inlet pressure Pin and the maximum opening degree θmax according to this map.

  Next, when the maximum main hydrogen flow rate Qemax is supplied, the maximum FC hydrogen flow rate Qfcmax supplied to the fuel cell 2 is obtained (step S206). The maximum FC hydrogen flow rate Qfcmax is obtained as the sum of the maximum main hydrogen flow rate Qemax and the circulating hydrogen flow rate Qc as shown in Equation (7). The obtained maximum FC hydrogen flow rate Qfcmax is a hydrogen flow rate supplied to the fuel cell 2 when the ejector opening degree is the maximum opening degree θmax.

  Next, when the maximum FC hydrogen flow rate Qfcmax is supplied, an allowable power generation current Imax that can be generated in the fuel cell 2 is obtained (step S208). The FC allowable power generation current amount Imax is a power generation current amount that is considered to be capable of generating power when Qfcmax of hydrogen is supplied from the supply port of the fuel cell 2, and is obtained according to the equation (8).

  Next, the generated current command value Ifc is reset to the allowable generated current Imax (step S210). Thereafter, the process returns to step S104, and steps S104 to S124 are executed in the same manner as in the first embodiment. However, since the generated current command value Ifc is reset to the allowable generated current Imax, each value such as the required main hydrogen flow rate Qe obtained in step S110 and subsequent steps corresponds to the allowable generated current Imax. Thereafter, when it is recognized in step S202 that θemin ≦ θmax is established, steps S126 to S138 are executed, and the ejector opening degree θ is controlled to the corrected opening degree * θe or the minimum opening degree θemin.

  As described above, in the second embodiment, when the minimum opening θemin obtained according to the generated current command value Ifc is larger than the maximum opening θmax, the generated current command value is the fuel at the maximum opening θmax. The allowable generation current Imax that can be generated is controlled by the flow rate of hydrogen supplied to the battery 2. Therefore, it is possible to avoid a state in which an output that cannot generate power is required even if the limit value of the ejector opening is exceeded, and to execute control based on a generated current that can be generated.

  For example, in the second embodiment, the “maximum opening degree determining means” of the present invention is realized by executing step S202, and the “allowable output estimating means” is realized by executing step 208. By executing this, an “output control means” is realized.

Embodiment 3 FIG.
The third embodiment has the same configuration as the system shown in FIGS. Further, the system of the third embodiment is the same as the system of the first embodiment except that the inlet pressure Pin of the ejector opening is controlled when it is determined that the minimum opening θemin is larger than the maximum opening θmax. Control. Specifically, the inlet pressure Pin is controlled to be a predetermined control pressure by a hydrogen pressure regulating valve 10 attached to the main hydrogen supply path 8 in a normal state. On the other hand, when the minimum opening θemin is equal to or greater than the maximum opening θmax, control is performed so that the ejector inlet pressure increases. As a result, even at the same ejector opening, more main hydrogen flows into the ejector 14 and the main hydrogen flow rate is increased. Therefore, it is possible to ensure a state in which power generation according to the generated current command value Ifc can be performed.

  The system according to the third embodiment stores in advance a map that defines the relationship among the generated current, the ejector opening, and the inlet pressure. According to this map, when the ejector opening degree is set to θmax, the inlet pressure Pinmax necessary for power generation of the generated current command value Ifc can be obtained. When the minimum opening θemin is larger than the maximum opening θmax, the ejector opening θ is set to the maximum opening θmax, and the inlet pressure is set to the inlet pressure Pinmax. As a result, the main hydrogen flow rate at the maximum opening θmax can be increased to ensure the supply of the necessary main hydrogen flow rate Qe necessary for power generation. Thereby, it is possible to secure the power generation of the generated current command value Ifc.

  FIG. 7 is a flowchart for illustrating a control routine executed by the system in the third embodiment. The routine of FIG. 7 is the same as the routine of FIG. 5 except that steps S302 to S308 are included. Specifically, in the routine of FIG. 7, after the minimum opening θemin is obtained (step S124), it is determined whether the minimum opening θemin is equal to or less than the maximum opening θmax (step S302). Here, when it is recognized that θemin ≦ θmax is established, steps S126 to S138 are executed, and the ejector opening degree θ is controlled to the corrected opening degree * θe or the minimum opening degree θemin.

  On the other hand, in step S302, if the establishment of θemin ≦ θmax is not recognized, then, when the ejector opening is set to the maximum opening θmax, the inlet pressure Pinmax necessary for power generation of the generated current command value Ifc is calculated. (Step S304). The inlet pressure Pinmax is obtained according to a map that defines the relationship among the generated current, the ejector opening, and the inlet pressure according to the generated current command value Ifc and the maximum opening θmax. Next, the inlet pressure is controlled to the inlet pressure Pinmax (step S306). Here, the hydrogen pressure regulating valve 10 is controlled, and the inside of the main hydrogen supply path 8 is controlled to the inlet pressure Pinmax. Next, the ejector opening degree θ is set to the maximum opening degree θmax (step S308). As a result, the main hydrogen flow rate supplied to the ejector 14 at the maximum opening θmax increases, and the supply of the necessary main hydrogen flow rate Qe necessary for power generation at the generated current command value Ifc can be secured. Thereafter, the ejector opening degree θ is controlled to the set maximum opening degree θmax, and this process ends.

  As described above, in the third embodiment, when the minimum opening θemin exceeds the maximum opening θmax, the ejector opening θ is controlled to θmax and the inlet pressure is controlled to be the inlet pressure Pinmax. Therefore, the main hydrogen flow rate that can be supplied at the maximum opening θmax can be increased. Thus, even when the request for the generated current command value Ifc is large, it is possible to perform power generation according to the required output.

  For example, in the third embodiment, the “maximum opening degree determining means” of the present invention is realized by executing step S302, and the “target inlet pressure estimating means” is realized by executing step S304. The “inlet pressure control means” is realized by executing step S306.

  Also, in the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., unless specifically stated or in principle clearly specified by the number, It is not limited to the number mentioned. Further, the structures described in the embodiments, steps in the method, and the like are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

It is a schematic diagram for demonstrating the fuel cell system in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the structure of the ejector in Embodiment 1 of this invention. It is a graph for demonstrating the relationship between required main hydrogen flow volume and ejector opening degree. It is a graph for demonstrating the relationship between a generated current and the target value of ejector outlet pressure. It is a flowchart for demonstrating the routine of control which a system performs in Embodiment 1 of this invention. It is a flowchart for demonstrating the routine of control which a system performs in Embodiment 2 of this invention. It is a flowchart for demonstrating the routine of control which a system performs in Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Fuel cell 4 Stack 6 Cell 8 Main hydrogen supply path 10 Hydrogen pressure regulation valve 12 Pressure sensor 14 Ejector 16 Hydrogen path 18 Pressure sensor 20 Circulation path 22 Pressure sensor 24 Flow rate sensor 26 Gas-liquid separator 28 Exhaust path 30 Exhaust valve 32 Nozzle 34 Main hydrogen port 36 Outlet 38 Off-gas port 40 Discharge port 42 Movable needle

Claims (5)

A fuel supply path for supplying main fuel supplied from the fuel supply means to the fuel cell;
A circulation path for joining the fuel off-gas discharged from the fuel cell to the fuel supply path;
A main supply fuel that is provided at a junction between the fuel supply path and the circulation path and that flows in from the fuel supply path via an injection port and a fuel off-gas that flows in from the circulation path are mixed to form a downstream side. An ejector capable of flowing out into the fuel supply path and adjusting an opening of the injection port;
A required main fuel flow rate estimating means for estimating a required main fuel flow rate used for power generation in the fuel cell according to a required output required;
Basic opening degree calculating means for calculating a basic opening degree of the injection port according to the required main fuel flow rate;
In accordance with the state of pressure downstream of the ejector, corrected opening degree calculating means for correcting the basic opening degree and calculating a corrected opening degree;
In accordance with the required output, minimum opening setting means for setting a minimum opening of the injection port allowed,
Minimum opening determination means for determining whether or not the corrected opening is smaller than the minimum opening;
When it is determined that the corrected opening is smaller than the minimum opening, the opening of the injection port is set to the minimum opening, and the correction opening is determined to be greater than or equal to the minimum opening Opening degree setting means for setting the opening degree of the injection port to the corrected opening degree;
A fuel cell system comprising: The minimum opening setting means includes
Fuel cell required fuel for estimating a fuel cell required fuel flow rate as a fuel flow rate that needs to be supplied to the fuel cell in order to obtain the required output by distributing the fuel to each cell stacked in the fuel cell Flow rate estimation means;
A circulating fuel flow rate estimating means for estimating a circulating fuel flow rate contained in the fuel off gas mixed with the main supply fuel;
A minimum main fuel flow rate calculating means for calculating the minimum main fuel flow rate by dividing the circulating fuel flow rate from the fuel cell required fuel flow rate;
Minimum opening calculating means for calculating the minimum opening according to the minimum main fuel flow rate;
The fuel cell system according to claim 1, comprising: Target outlet pressure calculating means for calculating a target outlet pressure that is a target value of pressure in the fuel supply path downstream of the ejector;
Outlet pressure detecting means for detecting an outlet pressure that is a pressure in the fuel supply path downstream of the ejector,
3. The fuel cell system according to claim 1, wherein the correction opening degree calculation unit corrects the basic opening degree according to a difference between the outlet pressure and the target outlet pressure. Maximum opening determination means for determining whether or not the minimum opening is larger than an allowable maximum opening that is an upper limit of the allowable opening of the injection port;
When it is determined that the minimum opening is larger than the allowable maximum opening, an allowable output estimating means for estimating an allowable output that is generated when the opening of the injection port is in the state of the allowable maximum opening;
Output control means for controlling the output of the fuel cell to the allowable output;
The fuel cell system according to any one of claims 1 to 3, further comprising: Maximum opening determination means for determining whether or not the minimum opening is larger than an allowable maximum opening that is an upper limit of the allowable opening of the injection port;
When it is determined that the minimum opening is larger than the allowable maximum opening, the fuel of the necessary main fuel flow rate can be supplied in a state where the opening of the injection port is the allowable maximum opening. Target inlet pressure estimating means for estimating the target inlet pressure of the injection port;
An inlet pressure control means for controlling the inlet pressure upstream of the injection port to the target inlet pressure;
The fuel cell system according to any one of claims 1 to 3, further comprising:

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