Abstract
Disclosed is a method for controlling a pressure regulating valve (6) for regulating the internal pressure (P.sub.int) of a fluid circuit (3) in an electrochemical device (2), said fluid circuit (3) being fed by a compressor (4) drawing air at an external pressure (P.sub.ext) and compressing same at the internal pressure (P.sub.int) according to a compression ratio (A); said method comprises a step of measuring the external pressure (P.sub.ext), determining an internal pressure set point (P.sub.int*) on the basis of the external pressure (P.sub.ext) measured and the compression range (B), so as to promote overall efficiency (R1) of the electrochemical device (2) and the compressor (4) according to the internal pressure (P.sub.int) and the compression ratio (A), and a step of controlling the pressure regulating valve (6) so as to reach the internal pressure set point (P.sub.int*).
Claims
1. Method for controlling a valve for regulating the internal pressure (P.sub.int) of a fluid circuit in an electrochemical device, said fluid circuit being supplied by a compressor configured to take the fluid at an external pressure and compress it to the internal pressure according to a compression ratio belonging to a predetermined compression range, said regulating valve being mounted downstream of the fluid circuit, said method comprising a step of controlling the regulating valve to reach a set internal pressure (P.sub.int*) and wherein: is implemented from predetermined data: the efficiency of the electrochemical device as a function of the internal pressure (P.sub.int), the efficiency of the compressor as a function of the compression ratio, the overall efficiency as a function of the efficiency of the electrochemical device and the efficiency of the compressor, and comprises: a step of measuring the external pressure, and a step of determining the set internal pressure (P.sub.int*) from the measured external pressure and the compression range, so as to favor the overall efficiency.
2. Method according to claim 1, wherein the step of determining the set internal pressure (P.sub.int*) comprises: a phase of calculating a test efficiency of the electrochemical device from a test internal pressure, said test internal pressure being calculated from the measured external pressure and a predetermined compression ratio belonging to the compression range so as to favor the efficiency of the compressor, and as long as the test efficiency of the electrochemical device is less than a predetermined minimum efficiency threshold, a new phase of calculating the test efficiency from a new incremented test compression ratio belonging to the compression range of the compressor, the set internal pressure (P.sub.int*) corresponding to the test internal pressure for which the test efficiency respects the minimum efficiency threshold.
3. Method according to claim 1, wherein the step of determining the set internal pressure (P.sub.int*) comprises: a phase of calculating a range of permissible internal pressures from the measured external pressure and the compression range, and the overall efficiency being redefined thanks to the external pressure measured as a function of the internal pressure (P.sub.int), a phase of maximization of the overall efficiency over the range of permissible internal pressures, the set internal pressure (P.sub.int*) corresponding to the permissible internal pressure for which the overall efficiency is maximum.
4. Method according to claim 1, wherein the efficiency of the electrochemical device is proportional to the internal pressure (P.sub.int) and the efficiency of the compressor is, at fixed external pressure, inversely proportional to the internal pressure (P.sub.int).
5. Method according to claim 1, wherein the electrochemical device is cooled by a cooling circuit having an efficiency predetermined as a function of the internal pressure (P.sub.int), the overall efficiency being a function of the efficiency of the cooling circuit.
6. Method according to claim 1, wherein the efficiency of the electrochemical device is a function of the level of oxygen in the fluid circuit, the control method comprising a step of measuring the level of oxygen in the fluid circuit, the determination step being implemented from the measured level of oxygen.
7. Method according to claim 1, wherein the electrochemical device is in the form of a fuel cell.
8. Method according to claim 1, wherein the electrochemical device comprises a second fluid circuit of second internal pressure controlled by a second regulating valve, the control method comprising a step of controlling the second regulating valve to reach a second set internal pressure (P10*) verifying: |P10*?P.sub.int*|<S2, where (S2) designates a predetermined maximum pressure variation threshold.
9. Method according to claim 1, wherein the electrochemical device is mounted on board an aircraft to ensure at least in part its supply of electrical energy, said method being implemented during the flight of the aircraft.
10. Module for controlling a valve for regulating the internal pressure (P.sub.int) of a fluid circuit in an electrochemical device for the implementation of a method according to claim 1, said fluid circuit being supplied by a compressor configured to take the fluid at an external pressure and compress it to the internal pressure (P.sub.int) according to a compression ratio belonging to a predetermined compression range, said control module comprising: a member for measuring the external pressure, a member for storing predetermined data: the efficiency of the electrochemical device as a function of the internal pressure (P.sub.int), the efficiency of the compressor as a function of the compression ratio, the overall efficiency as a function of the efficiency of the electrochemical device and the efficiency of the compressor, a calculation member configured to determine a set internal pressure (P.sub.int*) from the measured external pressure and the compression range, so as to favor the overall efficiency, and a valve actuator of the regulating valve to reach the set internal pressure.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The invention will be better understood upon reading the following description, given as an example, and in reference to the following figures, given as non-limiting examples, wherein identical references are given to similar objects.
[0047] FIG. 1 is a schematic representation of a fuel cell mounted on board an aircraft according to the prior art.
[0048] FIG. 2 is a schematic representation of a fuel cell mounted on board an aircraft according to one embodiment of the invention.
[0049] FIG. 3 is a schematic representation of a method for controlling a regulating valve of the fuel cell of FIG. 2 according to one embodiment of the invention.
[0050] FIG. 4A is a schematic representation of a step of determining a set internal pressure of the method of FIG. 3 according to one embodiment of the invention.
[0051] FIG. 4B and FIG. 4C are schematic representations of a calculation phase during the implementation of the determination step of FIG. 4A.
[0052] FIG. 5A is a schematic representation of the step of determining a set internal pressure of the method of FIG. 3 according to an alternative embodiment of the invention.
[0053] FIG. 5B and FIG. 5C are schematic representations of the calculation phase during the implementation of the determination step of FIG. 5A.
[0054] FIG. 6A is a schematic representation of a fuel cell mounted on board an aircraft according to another embodiment of the invention.
[0055] FIG. 6B is a schematic representation of the method for controlling the regulating valve of the fuel cell of FIG. 6A according to another embodiment of the invention.
[0056] FIG. 7A is a schematic representation of a fuel cell mounted on board an aircraft according to another embodiment of the invention.
[0057] FIG. 7B is a schematic representation of the method for controlling the regulating valve of the fuel cell of FIG. 7A according to another embodiment of the invention.
[0058] FIG. 8A is a schematic representation of a fuel cell mounted on board an aircraft according to another embodiment of the invention.
[0059] FIG. 8B is a schematic representation of the method for controlling the regulating valve of the fuel cell of FIG. 8A according to another embodiment of the invention.
[0060] It should be noted that the figures set out the invention in detail in order to implement the invention, said figures may of course be used to better define the invention where applicable.
DETAILED DESCRIPTION
[0061] The invention relates to a method for controlling a valve for regulating the internal pressure of a fluid circuit in an electrochemical device. The invention aims, in an environment of varying physical-chemical properties, to favor the efficiency of the electrochemical device on a global scale. The invention is subsequently described in the context of a fuel cell mounted on board an aircraft in order to regulate the internal air pressure in a fluid circuit in the form of a cathode circuit. However, it goes without saying that the electrochemical device could be in a form other than a fuel cell, such as an electrolyzer or a catalytic reactor, and/or be mounted in an environment different from that of an aircraft. The fluid circuit could also be in another form, such as an anode circuit, and/or allow the circulation of any fluid.
[0062] As described in the preamble, a fuel cell makes it possible to produce electrical energy from a redox reaction between a fuel, hydrogen, and an oxidizer, the oxygen present in the air. With reference to FIG. 2, a fuel cell 2 comprises a stack of a plurality of cells 21, in which the redox reaction takes place, which are held between two end plates 22 making it possible to collect the electrical energy produced. The fuel cell 2 also comprises a cathode circuit 3 and an anode circuit 10 making it possible to supply the cells 21 with air and hydrogen respectively and to evacuate the products of the redox reaction, namely water and traces of hydrogen and air.
[0063] As described in the preamble, in the context of a fuel cell 2 mounted on board an aircraft, the air of the cathode circuit 3 is conventionally taken inside or outside the aircraft, namely in an external environment of which the physical-chemical properties are variable as a function of the altitude. In particular, the air pressure, called external pressure P.sub.ext, decreases with altitude and reaches, for example, around 9000 Pa at a high aircraft altitude of 17000 m. The same applies for the temperature and the oxygen concentration of the air notably.
[0064] As described in the preamble and illustrated in FIG. 2, a compressor 4 and a regulating valve 6 are mounted respectively upstream and downstream of the cathode circuit 3. The compressor 4 and the regulating valve 6 together make it possible to control the internal pressure P.sub.int and the mass flow rate Q of the air in the cathode circuit 3, so as to control the operating conditions of the fuel cell 2. More precisely, the compressor 4 makes it possible to compress according to a compression ratio A the air taken from the outside environment at the external pressure P.sub.ext. The compression ratio A belongs to a compression range B that is specific to the compressor 4. The compression ratio A of the compressor 4 is controlled by a control device 5 according to the desired mass flow Q of air in the cathode circuit 3.
[0065] As described in the preamble and illustrated in FIG. 2, the regulating valve 6 comprises for its part a variable passage section controlled by a valve actuator 7 according to the desired internal pressure P.sub.int in the cathode circuit 3. The regulating valve 6 is thus pressure enslaved while the compressor 4 is flow rate enslaved, to control the operating conditions of the fuel cell 2 and consequently its efficiency.
[0066] According to the invention and as illustrated in FIGS. 2 and 3, the internal pressure P.sub.int in the cathode circuit 3 is regulated by the implementation of a method for controlling the regulating valve 6 from predetermined data: [0067] the efficiency R2 of the fuel cell 2 as a function of the internal pressure P.sub.int of the cathode circuit 3, [0068] the efficiency R4 of the compressor 4 as a function of the compression ratio A, and [0069] the overall efficiency R1 as a function of the efficiency R2 of the fuel cell 2 and the efficiency R4 of the compressor 4.
[0070] Still according to the invention and as illustrated in FIGS. 2 and 3, the control method comprises: [0071] a step of measuring EI the external pressure P.sub.ext of the external air. [0072] a step of determining E2 a set internal pressure P.sub.int* from the measured external pressure P.sub.ext and the compression range B of the compressor 4, so as to favor the overall efficiency R1, and [0073] a step of controlling E3 the regulating valve 6 to reach the set internal pressure P.sub.int*.
[0074] As will be described hereafter, the determination step E2 is implemented, according to a first embodiment, by comparing the efficiency R2 of the fuel cell 2 for several internal pressure test values P.sub.int associated with an acceptable efficiency R4 of the compressor 4. According to a second embodiment, the determination step E2 is implemented by maximization of the overall efficiency R1 over a range of internal pressures P.sub.int acceptable for the compressor 4.
[0075] The control method according to the invention thus makes it possible to regulate the internal pressure P.sub.int in the cathode circuit 3 so as to favor the overall performances of an electrical production system 1. As illustrated in FIG. 2, such an electrical production system 1 encompasses the fuel cell 2 as well as the associated elements that enable its operation, such as the compressor 4 which supplies the fuel cell 2 with oxidizer The determined set internal pressure P.sub.int* thus makes it possible to favor the energy produced available for the aircraft, corresponding to the energy produced at the outlet of the fuel cell 2 from which is subtracted the energy consumed by its associated elements, such as the energy used to compress the external air.
[0076] The steps of the control method according to the first embodiment then according to the second embodiment of the invention are described below. Other preferred aspects of the invention are presented at the end.
[0077] As illustrated in FIG. 2, prior to the implementation of the control method, the data of the overall efficiency R1, the efficiency R2 of the fuel cell 2 and the efficiency R4 of the compressor 4 are stored in the valve actuator 7 of the regulating valve 6, or alternatively in any storage member, such as a database of a calculator. In practice, the efficiency data R1. R2, R4 are in the form of variables quantifying the energy performance of the considered system, namely its energy production and/or its energy cost, as a function of one or more parameters. According to a preferred aspect of the invention, one (or more) efficiency data R1, R2, R4 is in the form of: [0078] the quotient of the power produced over the power consumed by the considered system; and/or [0079] the deviation from a predetermined maximum efficiency of the considered system; and/or [0080] the electrical power produced/consumed by the considered system.
[0081] It goes without saying that one or more of the efficiency data R1, R2, R4 could be in the form of another quantification variable of the energy performance than those mentioned.
[0082] According to a preferred aspect of the invention, the efficiency data R1, R2, R4 are in addition in the form of theoretical and/or experimentally obtained models that depend on one or more parameters. As illustrated in FIG. 3, the efficiency R4 of the compressor 4 varies as a function of the compression ratio A of the compressor 4, more precisely in an inversely proportional manner. It should be noted that, by definition, the compression ratio A of the compressor 4 verifies the relationship: A=P.sub.int/P.sub.ext. The efficiency R4 of the compressor 4 thus varies in an inversely proportional manner with the internal pressure P.sub.int, the external pressure P.sub.ext being fixed. Still with reference to FIG. 3, the efficiency R2 of the fuel cell 2 varies for its part as a function of the internal pressure P.sub.int, more precisely in a proportional manner. It goes without saying that additional parameters could be taken into account in the model of the efficiency R2 of the fuel cell 2 and/or the compressor 4, such as the oxygen content in the cathode circuit 3 for the efficiency R2 of the fuel cell 2, as will be described below.
[0083] As illustrated in FIG. 3, the overall efficiency R1 designates the efficiency of the electrical production system 1 previously defined as the assembly of the fuel cell 2 and associated elements enabling its operation. It is considered in this example that the electrical production system 1 is uniquely formed of the fuel cell 2 and the compressor 4. The overall efficiency R1 thus varies as a function of the efficiency R2 of the fuel cell 2 and the efficiency R4 of the compressor 4, in practice in a proportional manner. Preferably, the overall efficiency R1 corresponds to the quotient of the electrical power produced by the fuel cell 2 over the electrical power consumed by the compressor 4.
[0084] It goes without saying that other elements could be added to the electrical production system 1, such as the cooling circuit 9 of the fuel cell 2 as will be described hereafter. Preferably, the associated elements selected are those for which the energy consumption is a function of the operating conditions of the fuel cell 2, and in particular, the internal pressure P.sub.int of the cathode circuit 3. Preferably also, the associated elements selected are those for which the energy consumption is remarkable in comparison with the energy production of the fuel cell 2.
[0085] As shown in FIGS. 2 and 3, the control method starts with a step of measuring E1 the external pressure P.sub.ext of the external air. In this example, the measuring step E1 is implemented by a measuring member 8 connected to the valve actuator 7 of the regulating valve 6, preferably in the form of a pressure sensor. Alternatively, the external pressure P ext could be measured indirectly, for example from an altimetry sensor of the aircraft. At the end of the measurement step E1, the measurement of the external pressure P.sub.ext is transmitted to the valve actuator 7.
[0086] With reference to FIGS. 2 and 3, a step of determining E2 a set internal pressure P.sub.int* for the regulating valve 6 is next implemented. According to a first embodiment illustrated in FIG. 4A, the determination step E2 comprises: [0087] a phase of calculating E2-1 a test efficiency R.sub.T of the fuel cell 2 from a test internal pressure P.sub.T, said test internal pressure P.sub.T being calculated from the measured external pressure P.sub.ext and a predetermined test compression ratio A.sub.T belonging to the compression range B so as to favor the efficiency R4 of the compressor 4, and [0088] as long as the test efficiency R.sub.T of the electrochemical device 2 is less than a predetermined minimum efficiency threshold S1, a new phase of calculating E2-2 the test efficiency R.sub.T from a new incremented test compression ratio A.sub.T belonging to the compression range B.
[0089] Thus, the set internal pressure P.sub.int* determined during the determination step E2 corresponds to the test internal pressure P.sub.T for which the test efficiency R.sub.T respects the minimum efficiency threshold S1.
[0090] In practice, as shown in FIGS. 4A and 4B, the calculation phase E2-1 is implemented from a predetermined test compression ratio A.sub.T that belongs to the compression range B of the compressor 4. Preferably, the test compression ratio A.sub.T is chosen low so as to correspond to a low energy consumption of the compressor 4 and consequently a high efficiency R4 of the compressor 4, verifying R4=f(A.sub.T)>S4. S4 designates a minimum efficiency threshold of the compressor 4, preferably less than the maximum efficiency of the compressor 4 by no more than 50%. Preferably, the test compression ratio A.sub.T is also chosen lower than the median of the compression range B.
[0091] As shown in FIGS. 4A and 4B, during the calculation phase E2-1, the test internal pressure P.sub.T associated with the test efficiency R.sub.T is calculated from the measured external pressure P.sub.ext, in practice by the relationship: P.sub.T=R.sub.T?P.sub.ext. The test efficiency R.sub.T of the fuel cell 2 is determined for its part from the predetermined efficiency R2 of the fuel cell 2 and the test internal pressure P.sub.T, in practice by the relationship: R.sub.T=R2=g(P.sub.T). In the example of FIG. 4B, the test efficiency R.sub.T obtained is lower than the minimum efficiency S1 of the fuel cell 2 such that a new calculation phase E2-2 is implemented with a new test compression ratio A.sub.T incremented by an increment ? (see FIG. 4A).
[0092] FIG. 4C illustrates the calculation phase E2-2 with the new compression ratio A.sub.T, in practice implemented in an identical manner to the previous one. In the example of FIG. 4C, the test efficiency R.sub.T obtained during the calculation phase E2-2 is greater than the minimum efficiency threshold S1. No new calculation phase E2-1, E2-2 is then implemented and the set internal pressure P.sub.int* corresponds to the last test internal pressure P.sub.T calculated, in this example during the calculation phase E2-2. It goes without saying that the number of calculation phases E2-1, E2-2 is arbitrary and notably depends on the test compression ratio A.sub.T selected, the increment e and the minimum efficiency threshold S1. Preferably, the minimum efficiency threshold S1 of the fuel cell 2 is chosen below the maximum efficiency of the fuel cell 2 by no more than 50%.
[0093] Referring to FIGS. 2 and 3, at the end of the determination step E2, the set internal pressure P.sub.int* is transmitted to the valve actuator 7 so as to implement the step of controlling E3 the regulating valve 6. In the example of FIG. 2, the determination step E2 is implemented by the valve actuator 7, but it goes without saying that it could be implemented in any calculation member, connected to the member for storing predetermined data and to the valve actuator 7. The control step E3 is implemented for its part by regulating the passage section of the regulating valve 6 so as to obtain the set internal pressure P.sub.int* in the cathode circuit 3. Such a set internal pressure P.sub.int* makes it possible to both favor the electrical production of the fuel cell 2 and to limit the electrical consumption of the compressor 4. Preferably, such a control method is implemented several times during the flight of the aircraft, preferably at each change in altitude having an impact on the measured external pressure P.sub.ext.
[0094] Advantageously, the set internal pressure P.sub.int* is determined incrementally which meets the minimum efficiency objectives S1 while reducing the consumption of the compressor 4.
[0095] FIG. 5A illustrates a second embodiment of the invention that differs from the previous one in that the determination step E2 comprises: [0096] a phase of calculating E2-A a range of permissible internal pressures PP.sub.A from the measured external pressure P.sub.ext and the compression range B, and [0097] the measured external pressure P.sub.ext making it possible to define the overall efficiency R1 as a function of the internal pressure P.sub.int, a phase of maximization E2-B of the overall efficiency R1 over the range of admissible internal pressures PP.sub.A.
[0098] Thus, the set internal pressure P.sub.int* corresponds to the permissible internal pressure for which the overall efficiency R1 is maximum.
[0099] More precisely, with reference to FIGS. 5B and 5C, the range of permissible internal pressures PP.sub.A determined during the calculation phase E2-A verifies the relationship: PP.sub.A=P.sub.ext?B. The measured external pressure P.sub.ext also makes it possible to rewrite the efficiency R4 of the compressor 4 as a function of the internal pressure P.sub.int only. Thus, at the end of the calculation phase E2-A, as shown in FIGS. 5B and 5C, the efficiency R4 of the compressor 4 and the efficiency R2 of the fuel cell 2 are both as a function of the internal pressure P.sub.int. Consequently, the overall efficiency R1 may also be expressed as a function of the internal pressure P.sub.int only. In addition, the determined range of permissible internal pressures PP.sub.A makes it possible to define the interval over which the overall efficiency R1 may be maximized.
[0100] As shown in FIGS. 5B and 5C, the maximization phase E2-B is implemented from the overall efficiency R1 and makes it possible to determine the set internal pressure P.sub.int* among the range of permissible internal pressures PP.sub.A for which the overall efficiency R1 is maximum.
[0101] With reference to FIGS. 6A and 6B, according to a preferred aspect of the invention, the anode circuit 10 of the fuel cell 2 is also pressure enslaved. More precisely, as illustrated in FIG. 6A, a valve for regulating 11 the internal pressure P10 of the anode circuit 10 is mounted downstream of the anode circuit 10, hereinafter designated second regulating valve 11. For the sake of clarity, the regulating valve 6 of the cathode circuit 3 is for its part here designated first regulating valve 6. As illustrated in FIG. 6A, the second regulating valve 11 comprises a variable passage section controlled by the valve actuator 7, in this example identical to that of the first regulating valve 6, so as to obtain a second set internal pressure P10* in the anode circuit 10. For the sake of clarity, the set internal pressure P.sub.int* of the first regulating valve 6 is here designated first set internal pressure P.sub.int*.
[0102] As illustrated in FIG. 6B, the control method further comprises a step of controlling E4 the second regulating valve 11 to reach the second set internal pressure P10*, which verifies: |P10*?P.sub.int*|<S2, where S2 designates a predetermined maximum pressure variation threshold. This makes it possible to limit the pressure difference between the cathode circuit and the anode circuit, in order to increase the service life of the fuel cell 2.
[0103] With reference to FIGS. 7A and 7B, according to another preferred aspect of the invention, the energy cost of the cooling circuit 9 of the fuel cell 2 is taken into account to determine the set internal pressure P.sub.int* of the regulating valve 6. More precisely, the control method is implemented from a predetermined datum of the efficiency R9 of the cooling circuit 9 as a function of the internal pressure P.sub.int of the cathode circuit 3. The overall efficiency R1 is for its part a function of the efficiency R2 of the fuel cell 2, the efficiency R4 of the compressor 4 and the efficiency R9 of the cooling circuit 9. In other words, the electrical production system 1 is formed of the fuel cell 2, the compressor 4 and the cooling circuit 9.
[0104] With reference to FIGS. 8A and 8B, according to another preferred aspect of the invention, the predetermined efficiency R2 of the fuel cell 2 also depends on the level of oxygen O in the air of the cathode circuit 3. The control method in addition comprises a step of measuring E0 the level of oxygen O in the cathode circuit 3, in this example by means of a dedicated measuring member 12 in the form of a gas sensor. The measurement step E0 is implemented in parallel with the step of measuring E1 the external pressure P.sub.ex and makes it possible to rewrite the efficiency datum R2 of the fuel cell 2 as a function of the internal pressure P.sub.int only. The taking into account of the level of oxygen parameter advantageously makes it possible to determine the set internal pressure P.sub.int* more reliably and precisely.
[0105] To conclude, the regulation of the internal pressure P.sub.int proposed in the invention corresponds to an unprecedented overall approach that takes into account the electrical production of the fuel cell 2, or more generally of an electrochemical device, but also the electrical consumption of its associated elements, in particular the compressor 4 but also the cooling circuit 9 by way of example. The determined set internal pressure P.sub.int* advantageously favors the overall efficiency of the electrical production system, based on the electrical production at the output of the fuel cell 2 minus the electrical consumption of its associated elements, such as the compressor 4. Such an overall approach differs from the prior art where the regulation of the internal pressure P.sub.int only took into account the performances of the fuel cell 2. Such a global approach also makes it possible, in particular, to reduce the dimensioning of the compressor 4 and consequently its mass and bulk on board the aircraft.
