FR2712099A1 - Process for regulating the pressure of a gas in an enclosure - Google Patents

Abstract

The invention relates to a process and a device for maintaining the pressure of gas in an enclosure at a predetermined desired pressure, in which a valve (8) which fixes the flow rate of the gas in proportion to a set value supplied at the inlet to the said valve (8) is placed between the enclosure (1, 2) and an outside medium (6), an empirically determined initial set value is supplied at the inlet to the said valve (8) so as to obtain the desired pressure in the enclosure (1, 2) at the start of regulation and, periodically, the set value is adjusted as a function of the discrepancy between the measured pressure in the enclosure and the desired pressure, and the set value is increased or decreased depending on whether the pressure measured in the enclosure is below or above the desired pressure.

Description

 The present invention relates to a method for regulating the pressure of a gas in an enclosure, which can be used in particular for regulating the pressure of hydrogen in a supply circuit of a fuel cell.

 It is known that fuel cells must operate under special conditions of temperature and pressure. In particular, it is necessary that the pressure of the hydrogen which is used to supply the cell be maintained at a constant value so as to ensure a homogeneous concentration of hydrogen in the vicinity of the electrodes of the cell.

 If such a condition is not verified, this results in a degradation of the efficiency of the battery, or even an irreversible deterioration of its electrodes.

 The present invention aims to propose a method for regulating the pressure of a gas in an enclosure, which is in particular adapted to maintaining a constant value of the hydrogen pressure in a supply circuit of a fuel cell, and which has the advantage of being particularly simple and economical to use.

 The method according to the invention generally makes it possible to effectively maintain the pressure of a gas in an enclosure at a predetermined desired pressure.

 According to the invention, the term “enclosure” is understood to mean any container, sealed or porous, capable of containing the gas whose pressure is to be regulated.

In the case of regulating the pressure of the hydrogen consumed by a fuel cell, the enclosure is constituted by the fuel cell and the hydrogen supply circuit to which said fuel cell is connected.

This process is characterized by the fact that a valve is placed between the enclosure and an external environment which fixes the gas flow rate in proportion to a set value supplied as input to said valve, which is supplied as input at said valve an initial set value determined empirically to obtain the desired pressure in the enclosure at the start of regulation, and only periodically
- the pressure prevailing in the enclosure is measured, and a correction quantity is added algebraically to the set value, the absolute value of which is an increasing function of the difference between the pressure measured and the desired pressure, and the sign corresponds to an increase in the pressure in the enclosure, in the case where the pressure measured is lower than the desired pressure, and to an increase in the pressure in the enclosure in the contrary case, and
- the pressure prevailing in the enclosure is measured and a predetermined constant is added algebraically to the set value, the sign of which corresponds to an increase in the pressure in the enclosure in the event that the pressure measured is less than the pressure desired, and to decrease the pressure in the enclosure otherwise.

 The method according to the invention comprises two steps for adjusting the set value. These two steps can be carried out simultaneously following a single pressure measurement or separately, at different time intervals.

 The first adjustment step consists in rapidly varying the setpoint taking into account the difference between the actual pressure and the desired pressure in the enclosure, while the second adjustment step consists in varying the finer setpoint by ensuring that this setpoint corresponds to the opening of the proportional valve most favorable for obtaining the desired pressure.

 In other words, the first adjustment step makes it possible to converge the real pressure of the gas towards a target pressure which is not necessarily the desired pressure, and the second adjustment step makes it possible to adjust the reference value of so that said target pressure tends towards the predetermined desired pressure.

 According to the invention, the predetermined constant is advantageously the value +1.

 According to the invention, the term “external medium” is understood to mean a medium from which or to which the gas whose pressure is to be regulated is liable to move.

 If the gas in the enclosure is subjected to untimely pressure increases, the external environment is a reservoir in which a pressure prevails substantially lower than that which prevails in the enclosure to be regulated, and the proportional valve operates as a valve d 'exhaust and regulates the exhaust flow of gas from the enclosure towards the tank so that the pressure remains substantially constant in said enclosure.

 In this case, the sign of the correction quantity to be added algebraically to the set value is positive if the measured pressure is greater than the desired pressure, negative if the measured pressure is less than the desired pressure.

 If, on the contrary, the gas in the enclosure is subjected to untimely pressure drops, the external environment is a reservoir in which there prevails a pressure substantially greater than that which prevails in the enclosure. The proportional valve then functions as an intake valve and regulates the gas intake flow from the tank towards the enclosure. In this case, the sign of the correction quantity is positive if the pressure measured is lower than the desired pressure and vice versa.

 The invention also applies to an enclosure in which a gas is subjected to both untimely increases and pressure drops.

 In this case, two proportional valves are provided, one being in communication with a tank in which there is a higher pressure than that prevailing in the enclosure, the other being in communication with a tank in which there is a lower pressure. to that which reigns in the enclosure.

 Each valve is then individually controlled by implementing the method according to the invention adapted respectively to an inlet valve and to a gas exhaust valve.

 The method according to the invention is particularly suitable for regulating the pressure in the hydrogen supply circuit of a fuel cell.

 In this case, the external medium within the meaning of the invention consists of a pressurized hydrogen tank, that is to say in which a pressure prevails which is higher than that which prevails in the supply circuit in hydrogen, the proportional valve used to regulate the quantity of hydrogen to be introduced into the supply circuit to compensate for the pressure drops.

 In the case of a fuel cell, on the one hand the pressure of hydrogen is likely to drop taking into account the regular purges which are carried out in the circuit and which lead to sudden drops in pressure, and on the other hand , the operation of the fuel cell leads to a consumption of hydrogen, therefore also to a drop in pressure which it is impossible to predict given the very large number of parameters conditioning this consumption.

 Thanks to the method according to the invention, the pressure drops resulting from the purges are compensated by the rapid action of the first step of adjusting the set value, while the pressure drops resulting from the consumption of hydrogen, more are compensated by the second adjustment step.

 Advantageously, the pressure measured is translated into a measurement value expressed on the same scale as the reference value.

 For example, if the set value can vary between 0 and 255, the measurement value is expressed over this interval from 0 to 255, the limits 0 and 255 of this interval corresponding to the minimum and maximum pressures between which the pressure of gas in the enclosure.

 Likewise, the desired pressure on this scale can be expressed as a reference value.

 In this case, and according to a first embodiment of the method according to the invention, the absolute value of the correction quantity can be chosen as being equal to the difference between the measurement value and the reference value.

 Thus, for regulating the hydrogen supply circuit of a fuel cell, the setpoint, during the first adjustment step, is algebraically increased by the difference between the reference value and the measurement value.

 According to a variant of this embodiment, to calculate the new setpoint, the reference value is replaced by the old setpoint which has been previously adjusted, which amounts to determining the correction quantity as being equal the difference between the setpoint and the measured value.

 This variant accounts for the fact that the setpoint is the expression of the value which had been set as a target during the previous adjustment.

 However, taking into account the second adjustment step which makes the target pressure tend towards the desired pressure, the difference between the set value and the measured value is indeed an increasing function of the difference between the measured pressure and the desired pressure.

 The two embodiments described above have the advantage of requiring very simple and inexpensive electronic devices, without thereby increasing the time required for calculation.

 The present invention also relates to a device for implementing the method described above, characterized in that it comprises a proportional valve capable of regulating the passage of gas in response to a set value supplied at the input, a pressure sensor supplying a measured value expressed on the same scale as the reference value supplied as input to the proportional valve, an analog interface connected on the one hand to the proportional valve, on the other hand to the pressure sensor and a microcontroller connected to the analog interface allowing the method described above to be implemented.

 In a preferred embodiment of the invention suitable for regulating the hydrogen pressure of an Alkalyne type fuel cell, the microcontroller is of the MPU 68HCll type, the clock speed of which is 8 MHz, said microcontroller including a sequencer which marks intervals of 8.19 ms, the analog interface being constituted by a digital / analog converter with 8 bits which makes it possible to express the set value, the measured value and the reference value on a scale from 0 to 255.

In order to better understand the invention, we will now describe an embodiment given by way of non-limiting example with reference to the accompanying drawing in which
FIG. 1 schematically represents a circuit for supplying hydrogen to a fuel cell, and
- Figure 2 is a diagram showing the change over time of the pressure and the setpoint during pressure regulation in the circuit of Figure 1 by implementing the method according to the invention.

 In FIG. 1, a fuel cell 1 is supplied with hydrogen by means of a closed circuit 2 in which hydrogen circulates in the direction indicated by the arrows 3.

 Because the operation of the fuel cell 1 pollutes the hydrogen flowing in the circuit 2, it is necessary to regularly evacuate a certain amount of hydrogen, which is possible thanks to a purge system 4, as indicated by arrow 5.

 The hydrogen removed from the volume formed by the closed circuit 2 is replaced by pure hydrogen coming from a pressurized hydrogen tank 6. As indicated by arrow 7, the hydrogen coming from the tank 6 passes through a regulation 8 and enters the circuit 2 through an injector 9.

 According to the invention, the valve 8 is a proportional valve, that is to say that it regulates the passage of the hydrogen coming from the tank 6 in the direction of the injector 9 by fixing the flow rate of this gas in proportion to a set value supplied as input.

 This set value is provided by an electronic device 10 constituted by a microcontroller 11 and an analog interface 12.

 The proportional valve 8 is electrically connected to the analog interface 12 by a wire 13 which conveys the set value, as indicated by the arrow 14.

 A pressure sensor 15 makes it possible to measure the pressure prevailing in the closed circuit 2 and to send, via a wire 16, a measurement value to the analog interface 12, as indicated by the arrow 17.

 In the drawing, the connections between the analog interface 12 and the microcontroller 11 have not been shown, but it is clear that the role of the analog interface is to transform the measurement value obtained from the pressure sensor 15 into a value digital exploitable by the microcontroller 11 and transforming a digital reference value determined by the microcontroller 11 into an analog value which can be supplied as input to the proportional valve 8.

In the following description, the different parameters of the system are designated as follows
P is the instantaneous pressure measured in the closed circuit
feed mes 2,
P is the desired pressure, i.e. the pressure that we
v wishes to establish in the closed supply circuit 2,
V is the value supplied by the pressure sensor measuring
my Pmes pressure,
my
Vref is the value supplied by the pressure sensor for a pressure equal to the desired pressure,
V is the set value supplied as input to the valve
proportional cons,
VV and V are expressed on the same scale, my values varying from 0 to 255.

 FIG. 2 represents the simultaneous evolution of the pressure prevailing inside the closed supply circuit 2 and of the set value supplied at the input to the proportional valve 8.

 At the start of regulation, the fuel cell 1 does not work. There is no consumption of hydrogen in the closed circuit 2.

According to the invention, before the fuel cell 1 is put into operation, the setpoint V to be supplied as input to the proportional valve 8 is empirically determined so that
cons the pressure P prevailing in the closed circuit 2 corresponds to the pressure
my wanted P
v
Thus, at the instant preceding the putting into operation of the fuel cell 1, we have P = P
my v
Because the reference value Vref is expressed on the same scale as the setpoint V, we also have V = V, f3ure V
cons cons ref
This instant corresponds on the diagrams of figure 2 to the instant t = 0.

 The fuel cell 1 is then put into operation, that is to say that its terminals are connected to an electrical load.

As seen in Figure 2, the pressure P begins to
my fall in the closed circuit 2.

 After a time interval of 8.19 ms, the electronic device 10 implements the method according to the invention.

The pressure sensor 15 measures the pressure P and translates it
mes into a value V which is sent to the microcontroller 11 via the interface
mes analog 12.

In response to this measurement, the microcontroller 11 determines a setpoint value V to be sent as an input to the proportional valve 8,
cons via analog interface 12.

In the illustrated embodiment, the new setpoint is determined by the following formula
V = Old V + (V - V
cons cons ref mes
In other words, the setpoint is increased by the difference between the measured value and the reference value, assigned a positive sign if the pressure measured is lower than the desired pressure, negative otherwise.

 This first adjustment of the setpoint makes it possible to quickly reduce the pressure prevailing in the closed circuit 2 to a target pressure close to the desired pressure.

 In the absence of hydrogen consumption by the fuel cell, a given target value supplied as input to the proportional valve 8, systematically corresponds to a determined target pressure.

 The first step of adjusting the setpoint described above should in this case be sufficient to regulate the hydrogen pressure in the closed circuit 2.

 However, the consumption of hydrogen by the fuel cell induces a shift between the scale on which the reference value is expressed and the scale on which the measurement value and the reference value are expressed, so that at a given setpoint does not always correspond to a constant target pressure.

 The second step of adjusting the method according to the invention makes it possible to compensate for this offset by adding to the reference value the constant 1 with the positive sign if the pressure measured is lower than the desired pressure, negative otherwise.

In this case, the new setpoint is obtained by the following formula
V = Old V + (V - V mes) 1.
cons cons ref mes
This two-step adjustment of the setpoint makes it possible to obtain a convergence of the pressure prevailing in the closed supply circuit 2 towards the desired pressure P
v
Due to this convergence, it is possible, according to a variant of the method according to the invention, to calculate the new reference value by replacing, in the calculation of the reference value, the reference value by the old reference value .

The new setpoint is then obtained by the following formula V = Old V + (Old V - v) Vmes) 1.
cons cons cons mes
Is,
V ons = 2. Old V - V 1.
cons cons mes
In FIG. 2, it can be seen that the set value is determined at regular time intervals Ti by adding or removing a quantity proportional to the difference between the measured pressure and the desired pressure, corrected by the constant +1.

During the intervals T1 to T3, the pressure varies as it approaches the desired pressure P
v
A purge occurs during the interval T4, which causes the setpoint to increase during the interval following Tg.

Again, during the intervals T6 to T9, the pressure is brought back to a value close to the desired pressure P
v
It is understood that the mode of implementation which has just been described does not have any limiting character and that it can receive any desirable modifications without departing from the scope of the invention.

 In particular, the invention has been described with first and second adjustment steps carried out successively at identical time intervals, but it is clear that the invention could be implemented by providing for two distinct cycles of setting day of the set value, the first cycle corresponding to the first adjustment step, and the second cycle corresponding to the second adjustment step.

 This variant would make it possible to provide different time intervals for each adjustment step.

Claims (8)

 1. Method for maintaining the gas pressure in an enclosure at a predetermined desired pressure, characterized in that a valve (8) is fixed between the enclosure (1,2) and an external medium (6) the gas flow rate proportional to a set value (V) supplied as input to said valve (8), which is supplied as input  cons said valve (8) an initial set value (cons) empirically determined to obtain the desired pressure (P) in the enclosure (1,2) at the start of regulation and that, periodically  - the pressure (Pmes) prevailing in the enclosure (1,2) is measured and an correction quantity is added algebraically to the reference value (V) whose absolute value is an increasing function of the difference between the measured pressure (Pmes) and the desired pressure (Pv) and the sign of which corresponds to an increase in the pressure in the enclosure (1,2) in the case where the measured pressure (Pmes) is less than the desired pressure (P ) and to an increase in the pressure in the enclosure (1,2)  v otherwise, and  - We measure the pressure (Pmes) prevailing in the enclosure (1,2) and we add algebraically to the set value (cons) a predetermined constant (~ 1) whose sign corresponds to an increase in pressure in the enclosure (1,2) in the case where the measured pressure (Pmes) is lower than the desired pressure (Pv) and a decrease in the pressure in the enclosure (1,2) otherwise.  2. Method according to claim 1, characterized in that the predetermined constant is the value +1.  3. Method according to any one of claims 1 and 2, characterized in that the proportional valve (8) regulates the exhaust flow of the gas from the enclosure (1,2) towards the external environment.  4. Method according to any one of claims 1 and 2, characterized in that the proportional valve (8) regulates the gas intake flow from the external medium (6) towards the enclosure (1,2 ).  5. Method according to any one of claims 1, 2 and 4, applied to the pressure regulation in the hydrogen intake circuit of a fuel cell, characterized in that the external medium consists of a tank pressurized hydrogen (6).  6. Method according to claim 5, characterized in that the correction quantity is equal to the difference between the reference value (Vref) and the measurement value (vmes) the reference value (Vref) translating the desired pressure expressed on the same scale as the setpoint, and the measurement value (Vmes) translating the measured pressure expressed on the same scale as the setpoint.  7. Method according to claim 5, characterized in that the correction quantity is equal to the difference between the set value (cons) which has been previously adjusted, and the measurement value (V), the measurement value ( Vmes) reflecting the pressure measured  mes mes expressed on the same scale as the set value.  8. Device for implementing the method according to any one of the preceding claims, characterized in that it comprises a proportional valve (8) capable of regulating the passage of gas in response to a set value (Vcons) supplied as input, a pressure sensor (15) providing a measurement value (v) expressed on the same scale as the set value (Vcons) supplied as input to the proportional valve (8), an analog interface (12) connected on the one hand to the proportional valve (8) on the other hand to the pressure sensor (15) and a microcontroller (11) connected to the analog interface (12).