WO2021186316A1

WO2021186316A1 - A method for controlling a fuel cell system, an electronic fuel pressure regulator for performing this method, and fuel cell system comprising this regulator

Info

Publication number: WO2021186316A1
Application number: PCT/IB2021/052118
Authority: WO
Inventors: Stefano Bertalmio; Emilio BERTRAND; Andrea Briatore; Pierpaolo DEL GOBBO; Federico MICHELINI; Domenico PENNACCHIO; Andrea PIOVESAN
Original assignee: Metatron S.P.A
Priority date: 2020-03-19
Filing date: 2021-03-15
Publication date: 2021-09-23
Also published as: EP4122035A1; IT202000005917A1

Abstract

A fuel cell system (1) comprises a supply line for a fuel, for example hydrogen, including a fuel tank (11) and a pressure reducer (12) for obtaining a first stage of reducing the pressure of the fuel coming from the tank (11). A second pressure reduction stage is achieved by means of an electronic pressure regulator (R), which comprises a proportional solenoid valve (100) and an electronic control unit (E1), which communicates with an electronic control unit (E) of the fuel cell (2). The electronic control unit (E1) of the electronic pressure regulator (R) is configured and programmed to control the proportional solenoid valve (100) to regulate the flow rate and pressure of the fuel supplied to the fuel cell (2) according to a demand for electrical energy to be delivered by the fuel cell (2), keeping the difference between the air pressure and the fuel pressure within the fuel cell (2) within a predetermined range. The electronic control unit (E1) of the electronic regulator (R) is also configured and programmed to detect an actuation of a fuel purge valve (16) and/or a water drain valve (33), and to control the proportional solenoid valve in such a way as to compensate for the pressure variations deriving from the aforesaid actuation. The electronic unit (E1) of the pressure regulator (R) also closes a shut-off valve (34) located downstream of the tank (11) when it detects a pressure drop indicative of an abnormal operating condition.

Description

“A method for controlling a fuel cell system, an electronic fuel pressure regulator for performing this method, and fuel cell system comprising this regulator”

Field of the invention

The present invention relates to a method for controlling a fuel cell system.

In particular, the invention relates to fuel cell systems of the known type comprising:

- a fuel cell,

- a fuel supply line, for supplying a fuel, for example, hydrogen, to an inlet at an anode side of the fuel cell,

- an excess fuel discharge line for discharging excess fuel from an outlet at an anode side of the fuel cell,

- a pressurized air supply line, for supplying pressurized air to an inlet at a cathode side of the fuel cell,

- an excess air discharge line, for discharging excess air from an outlet at a cathode side of the fuel cell, - an excess fuel recirculation line, including a recirculation pump, for recirculating excess fuel from the anode side outlet of the fuel cell to the anode side inlet of the fuel cell,

- wherein said fuel supply line comprises, arranged in series, in the direction of said anode side inlet of the fuel cell: - a fuel tank,

- a first pressure reducing device, for obtaining a first fuel pressure reduction stage, from the pressure value inside said tank to a first stage reduced pressure value,

- a second pressure reducing device, for obtaining a second fuel pressure reduction stage, from the first stage reduced pressure value to a final reduced pressure value, suitable for correct operation of the fuel cell, said second pressure reducing device comprising a proportional solenoid valve,

- wherein said pressurized air supply line comprises an air compressor, driven by an electric motor, - wherein said excess fuel discharge line comprises a purge valve for removing fuel, said system also comprising:

- at least one first fuel pressure sensor and one second fuel pressure sensor arranged, respectively, upstream and downstream of said second pressure reducing device, along said fuel supply line,

- at least one air pressure sensor, located downstream of said air compressor, along said air supply line, and

- an electronic fuel cell control unit, configured to receive signals at least from said first and second fuel pressure sensors and from said air pressure sensor.

Prior art

A fuel cell system of the type indicated above is known from US 2008/166611 A1. Similar systems are known from the documents WO 2012/127402 A1 , W0200165619 A2, US9806357 B2, US7309537 B2, US20130323619 A1, US10361443 B2, US8486577 B2, US20060073363 A1 , WO2019106010 A1 , US20150037700 A1 , WO2013129241 A1 , US8771886 B2, US20170175899 A1 , KR20090058096, and

US20190267645 A1. An electronic fuel pressure regulator is known, in the field of internal combustion engines fueled by methane, by the document EP 1 936 174 A1.

Fuel cell systems of the type indicated above have been developed in recent years for various applications, but are finding renewed interest, particularly with reference to the generation of electrical energy for driving electric vehicles or hybrid vehicles.

However, the systems developed so far have not proved to be entirely satisfactory due to a series of problems.

A first problem lies in the impossibility of producing a single standard fuel cell system suitable for use in different applications, and - in particular - in different vehicle types or models, since it is generally necessary to adapt both the system components and the control methods, for each specific application.

Another difficulty that is recorded - in particular - in systems with fuel cells of the proton membrane type, lies in the relative difficulty of ensuring correct operation of the system in all conditions, taking into account both variations in the electrical energy that the fuel cell must deliver, and variations in the operating parameters of the system deriving from highly dynamic phenomena (such as the operation of the fuel purge valve or the water drain valve). Furthermore, the prolonged operation of these systems may lead to a deterioration of the metal parts that come into contact with the hydrogen that is used in the fuel cell.

There is, therefore, a need for a fuel cell system that is capable of efficiently overcoming all the aforesaid problems.

Object of the invention

It is therefore an object of the present invention to provide a method for controlling a fuel cell system that simply and efficiently overcomes all the above problems.

One particular object of the invention is to provide a method for controlling a fuel cell system which can be adapted to various applications with extremely simple and economical operations.

Another particular object of the invention is to control all the operating parameters of the system in a precise and efficient way, both as a function of variations in the energy demand by the user, and also taking into account highly dynamic events, such as actuation of the fuel purge valve and/or the water drain valve, or also in order to intervene promptly in the event of operating anomalies.

The main object of the invention is to provide a method for controlling a fuel cell system which is particularly suitable for use in supplying electrical energy on board a vehicle with purely electric drive or a hybrid vehicle. However, another preferred object of the invention is to provide a method for controlling a fuel cell system that can also be used for applications other than motor-vehicles, for example, for stationary plants for generating electrical energy, or also for providing transportable units in order to replace or integrate conventional electric batteries.

Summary of the invention

In order to achieve one or more of the aforesaid purposes, the invention relates to a method for controlling a fuel cell system having the characteristics indicated at the beginning of the present description, and characterized in that an electronic fuel pressure regulator is provided as a second pressure reducing device, including a regulator body incorporating the proportional solenoid valve and an electronic control unit associated with the regulator body, which is configured to communicate at least with the main electronic control unit of the fuel cell, and in that the electronic control unit associated with the regulator body controls the proportional solenoid valve in such a way as to regulate the flow rate and pressure of the fuel supplied to the anode side inlet of the fuel cell according to a request for electric energy to be delivered by means of said fuel cell, keeping the difference between the pressure of air supplied to said fuel cell cathode side inlet, and the pressure of fuel supplied to said fuel cell anode side inlet within a predetermined range, so that the electronic control unit associated with the regulator body can be programmed according to each specific application of the fuel cell system, while the main electronic control unit of the fuel cell can be a standard unit that remains substantially unchanged as the application of the fuel cell system varies.

According to another preferred characteristic, said electronic control unit directly or indirectly associated with the electronic fuel pressure regulator detects, by means of said electronic fuel cell control unit, an actuation of said fuel purge valve and/or of a water drain valve associated with said line for discharging excess fuel, and for controlling the proportional solenoid valve, so as to compensate for changes in fuel pressure deriving from said actuation of the purge valve and/or of the water drain valve.

According to another characteristic, said system also comprises a shut-off valve along said fuel supply line, upstream of the electronic regulator, and said electronic control unit associated with the electronic fuel pressure regulator receives directly or indirectly, through said unit fuel cell electronic control unit, signals from said first and second fuel pressure sensors and/or from said air pressure sensor, and commands a closure of said shut-off valve when said signals indicate a loss of fuel pressure greater than a threshold value, indicative of an abnormal operating condition of the fuel cell system. In the preferred embodiment, the electronic control unit associated with the electronic pressure regulator is programmed to apply a PID control strategy, by continuously calculating the difference between a required set value of the cathode side air pressure of the fuel cell and the measured fuel pressure at the anode side inlet of the fuel cell, and to apply a correction based on proportional, integral and derivative terms.

According to another preferred characteristic, the electronic control unit associated with the electronic pressure regulator performs the following additional functions:

- detects malfunctions of the control valve,

- detect anomalies in the communication with the electronic control unit of the fuel cell.

Thanks to the aforesaid characteristics, the method according to the invention allows a series of relevant advantages to be obtained.

First of all, the provision of an electronic pressure regulator with its own electronic control unit allows it to delegate functions to it that are easily reconfigurable for each specific application, with the advantage of being able to provide a fuel cell system with a fuel cell electronic control unit of the standard type common to all applications, since only the programming of the electronic unit of the electronic pressure regulator can be varied according to each specific application.

Secondly, thanks to the characteristics that have been specified above, and for reasons that will become clearer in the following description, the electronic pressure regulator used in the system according to the invention allows obtaining a more efficient, more precise and safer control of the operation of the fuel cell system.

The present invention also relates to an electronic pressure regulator configured to carry out the control method described above, as well as a fuel cell system comprising this regulator.

Detailed description of preferred embodiments

Further characteristics and advantages of the invention will become apparent from the description that follows with reference to the attached drawings, provided purely by way of non-limiting example, wherein:

- Figures 1A, 1 B and 2 are diagrams, known in the technical literature, which illustrate the general operating principle of a conventional fuel cell system,

- Figures 3, 4 and 5 are diagrams of embodiments of the fuel cell system according to the invention,

- Figures 6, 7 are perspective views illustrating a preferred embodiment of an electronic fuel pressure regulator according to the invention,

- Figure 8 is a cross-sectional view of the lower part of the body of the electronic regulator of Figures 6, 7,

- Figure 9 is a side elevation view of the upper body containing the solenoid of the electronic regulator of Figures 6, 7,

- Figure 10 is a schematic cross-sectional view of the detail of Figure 9,

- Figure 11 is a perspective view of the casing of the upper part of the body of the electronic regulator according to the invention,

- Figure 12 is a perspective view of an embodiment example of an electronic control board associated with the body of the electronic regulator according to the invention,

- Figures 13, 14 are block diagrams illustrating different control strategies of the fuel cell system according to the invention, and

- Figure 15 is a block diagram of the control system of the proportional solenoid valve that is part of the electronic regulator according to the invention.

Principle of operation of a fuel cell

A fuel cell is a device that converts stored chemical energy in a fuel such as hydrogen, through an electrochemical reaction, directly into electrical energy. The reaction does not involve any type of combustion so that it does not involve any harmful by-products. The basic physical structure of a fuel cell is illustrated in Figure 1A of the attached drawings. The structure comprises an electrolyte layer in contact on its opposite sides with a porous anode and a porous cathode. Figure 1A shows the reaction gases (hydrogen as fuel and oxygen as oxidant) and the flow directions of positive and negative ions through the cell.

In a typical fuel cell, gaseous fuel is fed continuously to the anode side, while an oxidant (oxygen from the air) is fed continuously to the cathode side. Electrochemical reactions take place at the electrodes and lead to the production of electric current that flows through the user load.

Various types of fuel cells are known, which differ mainly in the type of electrolyte, the fuel and the operating temperature. Therefore, the operation principle may vary according to the type of fuel cell.

Fuel cells with proton-exchange membranes (PEM cells) have a thin polymer membrane as their electrolyte. The main characteristic of this membrane is that it allows the passage of protons but, conversely, prevents the passage of electrons. The catalyst is typically platinum supported on carbon. The most important characteristic of this type of fuel cell is the low operating temperature (between 60°C and 80°C). This characteristic allows the use of this type of fuel cell in various applications and - in particular - in automotive applications, in stationary power generation plants and in transportable applications. The efficiency of this type of fuel cell is between 30% and 45%, although the most recent PEM fuel cells can achieve 60% efficiency.

The operating principle of the fuel cell is relatively simple, and its initial development was due to the scientist William Grove in 1839. The basic operating principle is the following. Hydrogen flows through the supply channels of the anode (see Figure 1 B), distributes itself through the diffusion layer and reaches the catalytic layer where it is oxidized by releasing electrons:

2H₂ 4H⁺+4e-

The released electrons are conducted through the metal of the catalyst through the carbon granules of the catalytic layer of the anode until reaching the cathode through the outer circuit, where the protons are transported through the membrane to the catalytic layer of the cathode. At the same time, oxygen is injected into the supply channels of the cathode and is distributed through the diffusion layer and through the catalyst layer, where it reacts with protons and electrons, generating water:

0₂+4H⁺+4e- 2H₂0 Therefore, the overall reaction in the fuel cell is:

2H2+O2 2H2O

The reaction at the cathode is exothermic: the release of heat is dependent on the voltage, which is directly related to the efficiency of the system. That described above is schematically illustrated in Figure 1 B of the attached drawings, which shows the circulation of gases and electrons and the passage of ions through the membrane.

Known applications of fuel cells to propulsion of a vehicle

A fuel cell system must be integrated with various auxiliary components to form a complete system, particularly suitable for generating electrical energy on board a purely electrically-driven vehicle or a hybrid vehicle.

Figure 2 of the attached drawings shows a diagram of a fuel cell system applied to the generation of electrical energy for driving a motor- vehicle, according to the prior art.

In this figure, the fuel cell system as a whole is indicated with 1. The fuel cell system 1 includes a fuel cell stack 2, a line 3 for supplying a fuel, in the example illustrated - hydrogen - to an anode side inlet 4 of the stack 2, and a line 5 for supplying pressurized air to a cathode side inlet 6 of the stack 2. The system 1 also comprises a line 7 for discharging excess hydrogen coming from an anode side outlet 8 of the fuel cell stack 2 and a line 9 for discharging excess air from a cathode side outlet 10 of the stack of fuel cells 2.

The line 3 for supplying hydrogen includes a hydrogen tank 11 , where hydrogen is stored at high pressure, and then in succession, arranged in series with each other, in the direction of the inlet 4 of the fuel cell stack, a first pressure reducer device 12, to provide a first stage of hydrogen pressure reduction, from the pressure value inside the tank 11 to a first stage reduced pressure value, a second pressure reducer device 13, to provide a second hydrogen pressure reduction stage, from the first stage reduced pressure value to a final reduced pressure value, configured for the correct operation of the fuel cell stack. In the case of the example illustrated in Figure 2, the line 3 also comprises a humidifier 14 and a heat exchanger 15 for controlling the temperature of the fuel supplied to the fuel cell stack.

The line 7 for discharging excess hydrogen comprises an electrically-operated purge valve 16 for purging excess hydrogen.

The line 5 for supplying pressurized air comprises, in succession, a compressor 17 driven by an electric motor 18, a humidifier 19 and a heat exchanger 20 for controlling the temperature of the air supplied to the stack of fuel cells.

The humidifiers 14, 19 are served by a water supply line 21 , including a tank 22 and a pump 23.

The line 9 for discharging excess air comprises an electrically- operated control valve 24, and a water separator 25 from which water can be discharged into the tank 22.

The system 1 also comprises an excess fuel recirculation line 26, including a recirculation pump 27, for recirculating excess hydrogen from the anode side outlet 8 of the fuel cell stack to the anode side inlet 4 of the fuel cell stack,

A cooling system is also associated with the fuel cell stack 2, which - in the example - consists of an electric fan 28. According to the prior art, the electrically-operated components of the system are controlled by a fuel cell electronic control unit E.

The poles of the fuel cell stack 2 are connected to a power conditioning unit 29, which powers an electric motor 30 for driving the wheels R of a motor-vehicle. The unit 29 is also electrically connected to a battery pack 31.

The storage pressure of the hydrogen in the tank is primarily a function of the volume of the tank itself. Light-duty applications (e.g. cars) use small tanks, therefore, the quantity of hydrogen in the tank is increased, significantly increasing the storage pressure, up to 700 bar, for example. Heavy-Duty applications (e.g. trucks) may, for obvious reasons of space, have a cylinder pack of considerable size; there is therefore no need to increase the storage pressure beyond 250 bar. The hydrogen pressure at the inlet 4 of the fuel cell stack is very low (from 0.8-0.9 bar up to 3 bar). The pressure downstream of the first pressure reducer 13 is generally in the order of 15 bar. The first pressure reducer 12 is a non- adjustable mechanical reducer, while the second pressure reducer 13 is typically a solenoid valve, or a mechanical pressure reducer, or a system with injectors/ejectors.

In known systems, the fuel cell electronic control unit operates the reducer 13 (for example, a proportional solenoid valve) to regulate the flow rate of fuel through the fuel supply line, maintaining the required pressure. The flow rate of hydrogen supplied to the fuel cell is proportional to the production of electricity required, which is communicated to the fuel cell electronic control unit. The quantities of air and the quantity of hydrogen supplied to the fuel cell are regulated according to the demand for electricity, taking into account that the ratio between these quantities must correspond to the stoichiometric ratio.

The problem with fuel cells with a proton-exchange membrane is that the pressure differential across the membrane must be close to zero to avoid damage to the membrane, which requires the ability to regulate the supply pressure of the hydrogen, with an accuracy in the order of a few tens of millibars (for example, 50 millibars).

Another problem is related to water management. Water management is a critical factor for efficient fuel cell operation. In this type of fuel cells it is important to maintain a high water content in the electrolyte to ensure high proton conductivity. The proton conductivity of the electrolyte is high when the membrane is completely saturated with water, and consequently offers a minimum resistance to the passage of ions, increasing the efficiency of the cell especially at high current densities. The water content in the cathode and in the anode is determined by the water balance in the respective volumes, the balance being the result of the inlets and outlets of water. There is normally an inlet of water with the incoming gas, and there is a transport of water across the membrane. The transport of water during operation is a function of the cell current and the characteristics of the membrane and electrodes. The main mechanism of transport of the water through the membrane is linked to the entrainment of water molecules by protons: each proton drags between 1 and 2.5 molecules of water. If more water comes out of the cell than that produced in the cell, it is important to humidify the incoming gas on the anode side and/or on the cathode side. Nevertheless, if there is excessive humidification, the diffusion layers are excessively flooded, which causes problems in the diffusion of the gas.

The fuel cell system according to the invention

Figures 4, 5 show two different operating modes of an embodiment of the fuel cell system according to the invention. The heart of the fuel cell system according to the invention consists of a new electronic pressure regulator that is used to obtain the second fuel pressure reduction stage along the fuel supply line.

In Figures 4, 5, the parts common with those of Figures 2 are indicated by the same reference numbers. The main difference with respect to the known solution illustrated in Figure 2 lies in the fact that, in the case of the invention, the second stage of reducing the fuel pressure (for example, hydrogen) along the fuel supply line 3 is obtained by means of an electronic regulator R constituted, configured and controlled in the manner that will be illustrated in detail below. The solution illustrated in Figures 4, 5 also comprises an electrically-operated shut-off valve 34, arranged between the high pressure reducer 12 and the electronic regulator R. In the case of the embodiment illustrated in Figures 4, 5, the system also comprises pressure and temperature sensors Pi, Ti arranged along the supply line 3 to detect the fuel pressure and temperature upstream of the electronic regulator R, pressure and temperature sensors PH, TH of the pressure and temperature of the fuel at the inlet of the fuel cell 2, and a pressure sensor PA of the air pressure at the inlet of the fuel cell 2.

The water drainage

As indicated above, the particular functioning of the proton membrane of the fuel cell leads to the accumulation of water in the tubes on the anode side. It is imperative that water is supplied to the fuel cell in the correct proportion in order to minimize power losses.

For this reason, a possible solution is to adopt a drainage system such as the one illustrated in Figure 3 of the attached drawings. In this solution, a drainage chamber 32 is arranged along the line 7 for the outlet of excess hydrogen. The water tends to accumulate in the lower part of the chamber 32 and from this it can be drained towards a drain through a drain valve 33. The gaseous component tends to accumulate in the upper part of the chamber 32 and from here, through the purge valve 16, it can be made to flow towards the drain, together with the drained water. The hydrogen that is not discharged, on the other hand, continues through the recirculation line 26 towards the recirculation pump 27. The purge valve 16 is dedicated to restoring the purity of the hydrogen, while the drain valve 33 maintains the correct level of humidity. Depending on the level of water present in the chamber 32, the operation of the drain valve may lead to the purging of only water, water and gas together, or only gas.

The electronic pressure regulator of the fuel

A preferred embodiment of the electronic regulator R is illustrated in Figures 6-12 of the attached drawings.

With reference to Figures 6, 7, the electronic regulator R comprises a regulator body 35, including a lower valve body 36, within which a solenoid valve 100 (Figure 7) is contained, and an upper body 37 for supporting the solenoid of the proportional solenoid valve.

With reference to Figure 8, the lower valve body 36 consists of a metal body, preferably of stainless steel. Even more preferably, the stainless steel is protected with a chemical nickel plating (an electrolytic nickel plating produces hydrogen ions that can be absorbed by the base material), so as not to be exposed to degradation following contact with hydrogen.

The metal body 36 includes an upper surface 36A wherein a cylindrical cavity 38 is formed, which is intended to constitute the seat that receives the lower portion 39 of the casing 37 (see Figure 9).

The metal body 36 has a lower surface 36B in which a cylindrical cavity 40 is formed, coaxial with the cavity 38. The cylindrical cavities 38, 40 are separated from each other by a wall 41 in which a communication hole 42 is formed.

The cavity 40 communicates with a fuel inlet 43 defined, in the example illustrated, by a connecting element 44 having a tubular body with one end that is screw-mounted in a side hole 45 of the body 36 which opens onto the cavity 40, with the interposition of a sealing ring 46.

The cavity 38 communicates with a fuel outlet 47 defined, in the example illustrated, by a connecting element 48 having a tubular body with one end that is screw-mounted, with the interposition of a sealing ring 49 within a side hole 50 of the metal body 36, which communicates with the cavity 38.

A seat is formed in the bottom wall of the cavity 38 for receiving, with the interposition of a sealing ring 51 , a ring 52, for example, of synthetic material or steel, having a central hole with a countersunk upper end, which acts as a valve seat for a disc B (see Figure 8), for example, having a spherical shape or having any other configuration. The disc is associated with a valve member 53 (Figures 9, 10) intended to be controlled by a solenoid of the electronic regulator R.

A cap 54 is screwed in the lower cavity 40, which holds a cylindrical tubular filter 55 of any known type in position within the bottom of the cavity 40.

With reference to Figure 8, the fuel (for example, hydrogen) is intended to pass through the lower body 36 of the electronic regulator R flowing from the inlet 43 through the filter 55 into the cavity 40 and from there, through the hole 42 and the central hole of the ring 52, in the cavity 38, from which the gas can leave through the outlet 47.

The passage through the valve seat consisting of the central hole of the ring 52 is controlled by the proportional solenoid valve 100, the components of which are illustrated in Figures 9, 10. The proportional control solenoid valve comprises a solenoid S mounted inside the upper body 37 of the electronic regulator R. The solenoid S has a cylindrical tubular configuration. Inside the solenoid S there is a stationary cylindrical body 56 within which a cylindrical element 57 is slidably mounted, having a lower rod, protruding from the body 56, which constitutes the valve member cooperating with the valve seat 52, with the interposition of the disc B. A helical spring 57 is operatively interposed between the stationary body 56 and the movable body 57 to push the valve member 53 into an operative position which, in the example illustrated, corresponds to the obstruction of the valve seat, that is, to the closed condition of the valve. Theoretically, it would also be possible to provide a normally open valve, wherein the spring tends to hold the valve member towards an open position. For security reasons, the Normally Closed configuration is preferred.

According to a preferred characteristic of the invention, all the metal parts capable of coming into contact with hydrogen and, therefore, in particular the elements 56, 57 and the spring 58, are made of stainless steel, preferably coated with a chemical nickel plating, so as not to be subject to degradation following contact with hydrogen.

With reference to Figure 11, the upper body 37 is enclosed within a casing of synthetic material 37A incorporating a portion 56 that encloses one or more electronic boards (Figure 12 shows an example of the electronic board in perspective view) constituting an electronic control unit E1 of the electronic regulator R.

The electronic regulator R of the present invention has the object of allowing a precise adjustment of the fuel flow rate and supply pressure throughout the operating range, improving the performance of the fuel cell and its duration over time.

Conventional systems with mechanical reducers do not naturally allow pressure regulation. The injector-ejector solutions give rise to an impulsive behavior of the pressure of the fuel supplied to the fuel cell, with a consequent coarse and unstable pressure control.

As mentioned, solutions of fuel cell systems are also known wherein the second pressure reduction stage is obtained by means of a proportional solenoid valve. In common with these systems, the system of the present invention is characterized in that it provides a proportional type solenoid valve. Flowever, as has been indicated, the electronic regulator of the invention differs from known solutions in that it incorporates a local electronic control unit directly associated with the body of the electronic regulator.

According to the invention, the electronic control unit E1 associated with the body of the electronic regulator is configured to communicate at least with the electronic control unit E of the fuel cell 2, and is programmed to control the solenoid S of the proportional solenoid valve of the electronic regulator in order to perform the following main functions:

- adjust the fuel flow rate and pressure supplied to the anode side inlet of the fuel cell 2, according to a request for electrical energy received by the electronic control unit E of the fuel cell, indicative of a level of electrical energy to be delivered by means of the fuel cell;

- operate the solenoid S of the proportional solenoid valve of the electronic regulator in such a way as to maintain - within a predetermined range - the difference between the pressure of air supplied to the cathode side inlet of the fuel cell and the pressure of fuel supplied to the anode side inlet fuel cell.

Furthermore, the electronic control unit E1 associated with the electronic regulator R is configured to directly or indirectly detect, through the electronic control unit E of the fuel cell 2, an actuation of the purge valve 16 and/or of the water drain valve 33. When an actuation of the purge valve 16 and/or the water drain valve 33 is detected, the electronic control unit E1 associated with the electronic regulator R is configured and programmed to regulate the flow rate of fuel supplied to the anode side inlet of the fuel cell to an extent to compensate for pressure variations of the fuel within the fuel cell deriving from the aforesaid actuation.

The system according to the invention may directly manage the pressure variations. A decrease in pressure may be caused by the consumption of hydrogen inside the fuel cell stack or by fuel purge or water drain events.

Air pressure variations are managed by the compressor 17: an increase/decrease in air pressure results in a request for an increase/decrease in hydrogen pressure.

Still preferably, the electronic control unit E1 associated with the electronic regulator R is configured to receive directly or indirectly, by means of the electronic control unit E of the fuel cell 2, signals from the fuel pressure sensors PH and Pi and from the air pressure sensor PA, and to command closing of the cut-off valve 34 when a loss of fuel pressure greater than a threshold value is detected, indicative of an anomalous operating condition of the system.

According to another preferred characteristic, the electronic control unit E1 associated with the electronic regulator R is also configured to perform additional functions, in particular, for detecting operating anomalies of the proportional solenoid valve, for detecting operating anomalies of the actuating system of the proportional solenoid valve, and also for detecting operating anomalies in the communication between the electronic control unit of the electronic regulator and the electronic control unit of the fuel cell.

Thanks to the characteristics indicated above, the electronic regulator of the invention is able to detect directly and autonomously any leaks and/or leakage from the system and to proceed with the closure of the cut-off valve 34, supplying information on the detection of an anomaly to the electronic control unit E of the fuel cell.

In the operating mode illustrated in Figure 4, the electronic control unit E1 forming part of the electronic regulator R is not only in communication with the electronic control unit E of the fuel cell 2, but is also capable of directly receiving signals from the pressure and temperature sensors PH, TH, PA, PI , Ti and from an actuation sensor of the purge valve 16 and/or from an actuation sensor of the water drain valve 33, as well as to directly send command signals to the solenoid S of the electronic regulator R and to the shut-off valve 34. In the simplified operating mode of Figure 5, the electronic control unit E1 of the electronic regulator R is simply in communication with the electronic control unit E of the fuel cell 2 and is, therefore, able to receive signals through the electronic unit control E and to issue commands via the electronic control unit E.

During normal operation of the fuel cell system, the main function of the electronic control unit E1 associated with the body of the electronic regulator R is to control the operation of the solenoid S of the proportional solenoid valve according to a predetermined control strategy in order to maintain a required target pressure at the inlet of the fuel cell system. At the same time, the electronic control unit E1 directly associated with the body of the electronic regulator R is also configured to communicate with the electronic control unit E of the fuel cell 2 to perform diagnostic functions, according to a master/slave approach.

Returning to the proportional solenoid valve 100 incorporated in the electronic regulator R, when the solenoid is energized, the movable part moves upwards (with reference to Figure 10) against the action of the spring 58, for a length that is proportional to the current. The solenoid S can be controlled in Pulse Width Modulation (PWM) mode.

The object of the proportional solenoid valve incorporated in the regulator R is to control the flow rate of fuel supplied to the fuel cell system and to shut off the flow completely when the system is not operating, ensuring the inner airtightness of the supply system of the fuel.

The valve of the electronic regulator R is built to withstand pressure of the gas for its entire service life.

In a preferred embodiment, the synthetic material casing 37A that encloses the support body of the solenoid S is made by additive manufacturing technology (in the preferred embodiment the material is nylon PA 12).

As already clarified above, the main tasks of the electronic control unit E1 associated with the body of the electronic regulator R are substantially the following:

- to impart commands to the solenoid S of the proportional solenoid valve according to a predetermined control strategy in order to maintain the required target pressure for the fuel supplied to the fuel cell inlet;

- to detect abnormal conditions and proceed with appropriate reactions;

- to communicate with the electronic control unit E of the fuel cell 2 for functional and diagnostic purposes, with a master/slave approach.

The electronic unit E1 associated with the body of the electronic regulator R can be configured in different ways.

In general, the pressure generated in the fuel supply line downstream of the electronic regulator R is the result of the following contributions:

1) regulation of the fuel flow carried out by means of the electronic regulator R;

2) the consumption of hydrogen within the fuel cell system, following the functioning of the proton membrane;

3) the amount of hydrogen that is recirculated by the recirculation pump 27;

4) the amount of hydrogen removed from the system by means of hydrogen purging and water drainage operations.

The contributions 2), 3) and 4), from the point of view of pressure and flow control, are disturbances that act directly on the outlet variable. The flow pressure is controlled by the electronic regulator R, taking into account the feedback signal provided by the pressure sensor PH of the fuel pressure at the inlet of the fuel cell, according to a closed-loop strategy. However, this type of control would not in itself be sufficient to avoid excessive oscillations in the pressure value downstream of the regulator, due to the fact that events such as the activation of the hydrogen purge valve and the drain valve are substantially impulsive events. For this reason, according to the invention, the control logic is further expanded with functions intended to compensate for the aforesaid operations, as described below.

The preferred control technique, which can be implemented by means of an electronic regulator according to the invention, intends to correctly manage two operating modes of the fuel cell system, which are very different from each other from the fluid-dynamic point of view:

- slow dynamic phenomena: normal mode of operation of the fuel cell, with low gradients of the hydrogen flow rate;

- highly dynamic phenomena: they correspond to the operating mode of the fuel cell with high and impulsive gradients in the hydrogen flow rate, following, for example, activation of the hydrogen purge valve and/or activation of the water drain valve.

The command signal for the solenoid S of the proportional solenoid valve and the electronic regulator R is basically the sum of several contributions:

- open-loop contributions: operation based on input;

- closed-loop contributions: operating on the feedback relative to the fuel pressure value at the fuel cell inlet.

The open-loop consists of two different parallel software strategies:

- a first strategy is dedicated to managing the purging event;

- a second strategy is dedicated to managing the water drainage event.

Each of these strategies is activated when an actuation of the corresponding purge valve 16 or of the corresponding water drain valve 33 is detected.

Figure 15 of the attached drawings shows the software control architecture. The “purge manager” and “drain manager” blocks indicate the software strategies for managing the purge event and the water drainage event that impose a behavior on the solenoid S of the proportional solenoid valve in order to compensate for the strong and impulsive variation of the fuel flow resulting from a sudden opening of the purge valve 16 or of the water drain valve 33 towards a non-pressurized environment. In this system, a large increase in the fuel flow rate causes a decrease in the pressure upstream of the purge and water drain valves, on the anode side of the fuel cell system. The sudden collapse of the pressure is compensated by a sudden increase in the opening of the proportional solenoid valve and the electronic regulator R.

Closed-loop control is based on a PID controller, which continuously calculates the value of the difference between a required set point (cathode side pressure) and a measured process variable (anode side pressure), and applies a correction based on proportional, integral and derivative terms (respectively P, I, D). The closed-loop consists of a PID controller, wherein the coefficients are calculated as a function of system parameters Pi, PH, and the functional status (purge, water drainage, normal operation). The equivalent PID control function is:

- Figure 13 is a block diagram illustrating the configuration of the electronic regulator R as a “smart actuator”. In this configuration, the functions of controlling the pressure and the flow rate of the fuel along the fuel supply line are performed by a block 60 inside the electronic control unit E of the fuel cell system. The signals coming from the various sensors arrive at a block 61 for calculating the set point, which sends the signal indicative of the target pressure to block 60. The block 60 sends a command to an actuation block 62 forming part of the electronic control unit E1 associated with the body of the electronic regulator R, which consequently controls the solenoid S of the proportional solenoid valve.

Figure 14 illustrates a preferred embodiment, wherein the pressure and flow rate control function is performed by a block 60A, which is inside the electronic control unit E1 associated with the electronic regulator R, instead of inside the electronic control unit E of the fuel cell system, as it was in the case of Figure 13.

The main advantage of the solution of Figure 14 lies in the fact that, with this solution, it is possible to provide fuel cell systems with an electronic control unit E of the standard type fuel cell, independent of the application to which the cell a fuel is intended. It is, in fact, the electronic regulator R that, being equipped with its own local electronic control unit E1 , can be adapted each time to the needs of each specific application.

As already indicated above, all the metal parts of the proportional solenoid valve forming part of the electronic regulator R which are likely to come into contact with hydrogen are made of stainless steel. Preferably, the parts most exposed to the gas flow may also be subjected to a chemical nickel lacquering in order to further reduce the diffusion of hydrogen in the metallic material.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated purely by way of example, without departing from the scope of the present invention.

Claims

1. A method for controlling a fuel cell system, wherein the fuel cell system comprises: - a fuel cell (2),

- a fuel supply line (3), for supplying a fuel, for example, hydrogen, to an inlet (4) at an anode side of the fuel cell (2),

- an excess fuel discharge line (7) for discharging excess fuel from an outlet (8) at an anode side of the fuel cell (2), - a pressurized air supply line (5), for supplying pressurized air to an inlet (6) at a cathode side of the fuel cell (2),

- an excess air discharge line (9), for discharging excess air from an outlet (10) at a cathode side of the fuel cell (2),

- an excess fuel recirculation line (26), including a recirculation pump (27), to recirculate excess fuel from the anode side outlet (8) of the fuel cell to the anode side inlet (4) of the fuel cell (2),

- wherein said fuel supply line (3) comprises, arranged in series, in the direction of said anode side inlet (4) of the fuel cell:

- a fuel tank (11), - a first pressure reducing device (12), for obtaining a first fuel pressure reduction stage, from the pressure value inside said tank (11 ) to a first stage reduced pressure value,

- a second pressure reducing device (13), for obtaining a second fuel pressure reduction stage, from the first stage reduced pressure value to a final reduced pressure value, suitable for the correct operation of the fuel cell (2), said second pressure reducing device (13) comprising a proportional solenoid valve (100),

- wherein said pressurized air supply line (5) comprises an air compressor (17), driven by an electric motor (18), - wherein said excess fuel discharge line (7) comprises a purge valve (16) for removing fuel, said system also comprising:

- at least one first fuel pressure sensor (Pi) and one second fuel pressure sensor (PH) arranged, respectively, upstream and downstream of said second pressure reducing device (13), along said fuel supply line (3), - at least one air pressure sensor (PA), located downstream of said air compressor (17), along said air supply line (5), and

- a main electronic fuel cell control unit (E), configured to receive signals at least from said first and second fuel pressure sensors (Pi, PH) and from said air pressure sensor (PA), said method being characterized in that the second pressure reducing device is constituted by an electronic fuel pressure regulator (R) including a regulator body (36) incorporating said proportional solenoid valve (100), and an electronic control unit (E1) associated with the regulator body (36), which is configured to communicate at least with said electronic fuel cell control unit (E), and in that the electronic control unit (E1) associated with the regulator body (36) controls said proportional solenoid valve so as to regulate the flow rate and the pressure of the fuel supplied to said anode side inlet (4) of the fuel cell (2) as a function of a request for electrical energy to be supplied by said fuel cell (2), keeping the difference between the air pressure supplied to said cathode side inlet (6) of the fuel cell (2) and the fuel pressure supplied to said anode side inlet (4) of the fuel cell within a predetermined range, in such a way that the electronic control unit (E1) associated with the regulator body (36) can be programmed according to each specific application of the fuel cell system, while the main electronic control unit (E) of the fuel cell can be a standard unit that remains substantially unchanged as the application of the fuel cell system varies.

2. A method according to claim 1 , characterized in that said electronic control unit (E1), associated with the electronic fuel pressure regulator, directly or indirectly detects, by means of said main electronic fuel cell control unit (E), an actuation of said fuel purge valve (16) and/or of a water drain valve (33) associated with said line (7) for discharging excess fuel, and controls said proportional solenoid valve (100), so as to compensate for changes in fuel pressure deriving from said actuation of the purge valve (16) and/or of the water drain valve (33).

3. A method according to claim 1 , characterized in that the fuel cell system further comprises a shut-off valve (34) upstream of said electronic pressure regulator (R) along said fuel supply line (3), and in that said electronic control unit (E1) associated with the electronic fuel pressure regulator (R) directly or indirectly receives, by means of said main electronic fuel cell control unit (E), signals from said first and second fuel pressure sensor (P-i, PH) and/or from said air pressure sensor (PA), and commands a closure of said shut-off valve (34) when a loss of fuel pressure is detected that is greater than a threshold value indicative of an abnormal operating condition.

4. A method according to claim 1 , characterized in that the electronic control unit (E1) associated with the electronic pressure regulator (R) applies a PID control strategy by continuously calculating the difference between a required set value of the cathode side air pressure of the fuel cell, and the measured fuel pressure at the anode side inlet of the fuel cell, and to apply a correction based on proportional, integral and derivative terms.

5. A method according to claim 1 , characterized in that the electronic control unit (E1) associated with the electronic fuel pressure regulator (R) performs the additional following functions:

- detecting malfunctions of the proportional solenoid valve (100),

- detecting anomalies in the communication between the electronic control unit (E1) associated with the electronic fuel pressure regulator (R) and the electronic fuel cell control unit (E).

6. A method according to claim 5, characterized in that the electronic fuel pressure regulator (R) comprises:

- a proportional solenoid valve (100) including:

- a valve body (36) having a fuel inlet (43), a fuel outlet (47) and a passage (40, 42, 38) for communication between the inlet (43) and the outlet (47), defining a valve seat (52),

- a valve member (53) cooperating with said valve seat (52),

- an elastic element (58) for recalling said valve member (53) towards a first operating position,

- a solenoid (S), for recalling said valve member (53) towards a second operating position, against the action of said elastic element (58), and in that said electronic control unit (E1) associated with the electronic fuel pressure regulator (R) controls the solenoid (S) in PWM mode.

7. An electronic fuel pressure regulator for a fuel supply line, for example, hydrogen, to a fuel cell, comprises:

- a proportional solenoid valve (100) including:

- a valve member (53) cooperating with said valve seat (52),

- an elastic element (58) for recalling said valve member (53) towards a first operating position, - a solenoid (S), for recalling said valve member (53) towards a second operating position, against the action of said elastic element (58), said regulator being characterized in that it comprises an electronic control unit (E1) associated with the valve body (36) and configured to implement a control method according to any of the preceding claims.

8. A fuel cell system, characterized in that it is arranged to implement the method of claim 1.

9. A fuel cell system, characterized in that it comprises an electronic fuel pressure regulator according to claim 7.