Fuel cell system incorporating an active starting voltage limiting circuit

Abstract

Fuel cell system (SYS) comprising a fuel cell (FC), a DC-DC converter (DCConv), and a control circuit (ContCirc) connecting the cell to the converter, the control circuit comprising: a main contactor (MCon) connecting the fuel cell to the DC-DC converter; a reverse-current protection circuit (RCProCirc) connecting the fuel cell to the converter in parallel with the main contactor, the reverse-current protection circuit comprising a reverse-current protection diode (D) connected in series with a diode contactor (DCon); during a cell start-up, the control circuit establishes a first connection path (P1) between the cell and the converter through the reverse-current protection circuit, then when a quantity representative of a power generated by the cell reaches a first threshold, establishes a second connection path (P2) between the cell and the DC-DC converter through the main contactor.Figure to be published with the abbreviation: Fig. 1.

Description

Title of the invention: Fuel cell system incorporating an active starting voltage limiting circuit. TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to fuel cell systems incorporating a DC-DC converter for the purpose of distributing an electrical voltage to equipment. TECHNOLOGICAL BACKGROUND

[0002] The start-up of a fuel cell can be defined as the moment when the injection into the cell of gas carrying a reducing fuel and an oxidant begins. From this moment, an electrochemical reaction occurs in each individual cell of the cell, producing an electrical voltage through the oxidation of a reducing fuel (for example, dihydrogen) at a first electrode coupled to the reduction of an oxidant (such as oxygen from the air) at a second electrode.

[0003] When a fuel cell starts up, the output voltage it delivers gradually increases. The loads powered by the cell have requirements that may not be met by the cell's output voltage. Therefore, considerable research has already focused on managing the cell's output voltage during startup and, more generally, during operation, as the examples below demonstrate.

[0004] Document WO 2009 / 126692 discloses a method in which a system comprising a fuel cell is designed to operate using the cell's nominal output voltage, but is also capable of operating with a reduced output voltage, particularly during cell start-up. This document focuses on the effects of temperature on the system's operation.

[0005] Document EP 3 336 943 Al discloses a fuel cell system capable of adjusting the output voltage of a cell at its start-up, based on the use of a battery connected in parallel to the cell with respect to a load receiving the output voltage of the cell via a DC-DC converter.

[0006] US document 2012 / 0015267 Al discloses a fuel cell system controlling the voltage delivered by the cell so as to, at startup, first deliver a voltage lower than its open-circuit voltage and then increase the voltage it delivers.

[0007] Document EP 2 241 473 Al discloses a fuel cell vehicle comprising a DC-DC converter performing a boosting operation when the vehicle is operating in a non-stationary state, and does not perform the boosting operation when the vehicle is operating in a stationary state.

[0008] However, not all needs are yet met, and the proposed technical solutions must address the specific problems of each fuel cell system architecture.

[0009] When a fuel cell starts up, it is not connected to any load. The voltage delivered by the cell gradually increases from a voltage close to 0 V to its maximum open-circuit voltage, which accelerates the aging of the entire system, particularly that of the cell itself, if no countermeasures are taken. Furthermore, in order to ensure the lifespan of the fuel cell cells, it is necessary to limit their voltages to around a voltage that will be called V_idle (V / cell) in the remainder of this document, and which can be 0.8 V / cell in the case of a fuel cell operating on hydrogen and oxygen. This voltage is lower than the open-circuit voltage of an individual cell.This type of need is all the more pressing when the fuel cell used is reactive (i.e., its voltage rises quickly) and when the no-load output voltage it can deliver is high, sometimes higher than the maximum operating voltages for which the downstream components of the fuel cell in the transmission chain of the electrical power generated by the fuel cell are designed. Description of the invention

[0010] A first object of the invention is to provide a fuel cell system capable of managing the operation of the fuel cell, in particular at the time of its start-up.

[0011] In a power architecture, a fuel cell can supply electrical power to an external load via a DC-DC converter. The open-circuit voltage (OCV) of the fuel cell may be higher than the DC-DC converter's permissible voltage. In such a system, the DC-DC converter can be used to regulate the fuel cell's output voltage by converting a greater or lesser portion of the electrical power supplied to it. Indeed, the voltage across a fuel cell decreases as the current supplied by the cell increases. The converter can thus limit the voltage across the fuel cell by converting a sufficient current to maintain this voltage.

[0012] However, the battery may also exhibit a reactivity incompatible with that of the DC-DC converter, which may prove insufficiently reactive to prevent the battery output voltage from reaching a voltage too high for the converter itself.

[0013] One can, for example, consider a DC-DC boost converter, which is a voltage boost converter, very common and economically competitive for applications involving DC-DC conversion of a voltage supplied by a fuel cell. If the fuel cell output voltage reaches or exceeds the DC-DC converter output voltage, the converter will not be able to regulate the current and voltage delivered by the fuel cell (the converter then behaves like a diode) and the system will not be able to start.

[0014] A solution proposed in this document consists of taking advantage of the gradual but rapid rise (of a few seconds) of the battery so that the DC-DC ensures the limitation and regulation of voltage and current at the output of the battery.

[0015] To this end, a first aspect of the invention relates to a fuel cell system intended to provide electrical power to an external electrical device and which comprises: a fuel cell; a DC-DC converter; and a control circuit connecting the fuel cell to the DC-DC converter, the control circuit comprising: a main contactor connecting a first output of the fuel cell to a first input of the DC-DC converter; a reverse-current protection circuit connecting the first output of the fuel cell to the first input of the DC-DC converter in parallel with the main contactor, the reverse-current protection circuit comprising a reverse-current protection diode, connected in series with a diode contactor;and a current-voltage measurement circuit configured to measure a voltage and current output of the fuel cell, the control circuit being configured so that, upon start-up of the fuel cell: establish a first connection path, between the first output of the fuel cell and the first input of the DC-DC converter through the reverse-flash protection circuit, then, when a quantity representative of or related to a current or power generated by the fuel cell reaches a first threshold, establish a second connection path, between the first output of the fuel cell and the first input of the DC-DC converter through the main contactor, and then possibly block the first connection path.

[0016] This system enables operation between the fuel cell and the converter that allows optimal use of the operating ranges and efficiency of the various components, in particular the fuel cell itself, the electrochemical cells that compose it, and the DC-DC converter. The current flow through the diode, a source of electrical losses due to voltage drop across its terminals when it is conducting, is actively managed by forcing the current through the diode when it is low or by directly powering the DC-DC converter when it exceeds a certain value.

[0017] This system thus allows the use of an efficient, compact, economically competitive DC-DC converter employing a more standard conversion mode on the market, despite the fact that it is not necessarily intended to receive as high an input voltage as that which the low current battery is capable of supplying.

[0018] Another advantage is that it allows control of the output voltage of the fuel cell and therefore the voltages applied to each of the cells composing the cell.

[0019] According to additional, non-limiting features of the first aspect of the invention, considered individually or in any technically feasible combination:

[0020] - the control circuit may further include a connected discharge circuit between the first output and the second output of the fuel cell and including a discharge resistor in series with a discharge contactor;

[0021] - the system can be configured such that, when the magnitude representative of or related to the voltage supplied by the fuel cell reaches a second threshold, the control circuit is configured to establish a third connection path, between the first output of the fuel cell and the second output of the fuel cell through the discharge resistor;

[0022] - the control circuit can further be configured to establish the third path connection when the battery is switched off;

[0023] - the DC-DC converter can be configured to regulate an output voltage of the fuel cell which is supplied to it via the control circuit by means of a voltage regulator or limiter function;

[0024] - an open-circuit voltage of the fuel cell may exceed a maximum voltage considered acceptable for the DC-DC converter;

[0025] - the fuel cell system can be configured to provide a voltage at the output of the DC-DC converter which is lower than the open-circuit voltage of the fuel cell;

[0026] - the DC-DC converter can be a boost converter;

[0027] - the control circuit may further include an isolation contactor connecting the second output of the fuel cell to a second input of the DC-DC converter, the control circuit can be configured to: when the first output of the fuel cell is connected to the first input of the converter by at least one of the first connection path and the second connection path, connect the second output of the fuel cell to the second input of the DC-DC converter through the isolation contactor, and when the fuel cell system is not in operation, isolate the DC-DC converter from the fuel cell by opening the main contactor, the diode contactor and the isolation contactor;

[0028] - the system may further include a computer functionally connected to the current-voltage measuring circuit and configured to control the main contactor, the diode contactor, and, where applicable, the discharge contactor and the isolation contactor, in response to measurements taken by the current-voltage measuring circuit.

[0029] A second aspect of the invention relates to an electrical device equipped with the system according to the first aspect of the invention, comprising an electrical distribution bus connected at the output of the DC-DC converter and a battery or other electrical energy storage device connected to the distribution bus.

[0030] According to additional non-limiting features of the second aspect of the invention, the electrical device is a mobile device or a stationary device, comprising an electrical power supply chain integrating the electrical distribution bus. BRIEF DESCRIPTION OF THE FIGURES

[0031] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0032] [Fig.1] Fig.1 represents an electrical diagram of a fuel cell system;

[0033] [Fig.2] Fig.2 represents a block diagram illustrating the operation of the system illustrated by [Fig.1];

[0034] [Fig. 3] [Fig. 3] illustrates devices incorporating the system illustrated by [Fig. 1]; and

[0035] [Fig.4] [Fig.4] illustrates the integration of the system illustrated by [Fig.1] within a electrical power supply chain. DETAILED DESCRIPTION OF THE INVENTION

[0036] A fuel cell system proposed in this document includes a fuel cell whose output voltage is converted by a DC-DC converter for the purpose of supplying electrical power to an external load.

[0037] In such a configuration, it may be necessary to have a power conversion system that is both reactive, that is, capable of rapidly converting electrical power generated by the fuel cell, and capable of limiting the fuel cell voltage so that it does not rise above a predetermined limit, such as a limit equal to the fuel cell's idle voltage (V_ralid) or beyond the input voltage that the DC-DC converter can accept to convert the power. These requirements are particularly stringent in the case of a highly reactive fuel cell system with an output voltage higher than the converter's output voltage and potentially even higher than an input voltage acceptable to the converter. Also, the operating point The idle speed of the battery must correspond to a current-voltage point compatible with the operating range of the DC-DC converter.

[0038] Such a configuration typically corresponds to a system in which the DC-DC converter is a boost converter, and the input voltage (battery side) of the boost converter must be at least a few tens of volts lower than the output voltage of the converter (load side), at least in configurations with standard specifications. Thus, a battery exhibiting high responsiveness and an open-circuit voltage exceeding the converter's permissible input voltage or output voltage requires careful management of its startup.

[0039] The system must also ensure that no reverse current is injected by the converter into the battery in order to avoid the occurrence of an electrolysis reaction in the battery cells.

[0040] A partial solution to the criteria explained above, which would overcome the problems of incompatible voltage levels, would be to use a buck-boost converter. However, these converters are relatively expensive, generally more so than boost converters, usually have lower efficiency, and are bulkier. Finally, buck-boost converters are not very common. Furthermore, such a converter does not protect against reverse currents.

[0041] Also, in the majority of current fuel cell systems, the voltage levels of the cells are lower, and the boost converters available on the market are capable of converting the power supplied by the cells over all the ranges of the voltages they deliver.

[0042] Architectures exist that allow the fuel cell voltage to be limited at startup. For example, document WO 2010 / 112999 proposes connecting the fuel cell to a DC traction bus via a contactor and a diode. The bus is powered at startup by a converter, which is itself powered by a battery. At startup, the converter applies a voltage to the bus. The fuel cell delivers power to the bus via the diode as soon as its voltage reaches the bus voltage. Subsequently, to use the fuel cell across its entire current-voltage characteristic curve, the DC bus voltage must vary according to the fuel cell's operating point for the desired current. This architecture requires a battery and a bus that accepts a variable voltage.Furthermore, given the typical current levels, which reach several hundred amperes, the constant use of a diode generates non-negligible continuous losses (from several hundred watts to a few kilowatts) that must be dissipated thermally, which implies the demanding and costly integration of a diode cooling device.

[0043] It is proposed here to use the DC-DC converter as a voltage limiter on the fuel cell side. At startup, the converter output is powered by the DC bus (itself powered by an external source such as a battery or reversible load). The converter input is connected to the fuel cell via a contactor and a blocking diode. The diode ensures that no reverse current flows from the converter to the fuel cell during this startup phase. It remains connected as long as the power or current supplied is low. When the power supplied increases, another contactor allows the diode to be short-circuited and the fuel cell to be directly connected to the DC-DC converter, thus avoiding additional losses in the diode. If the current drops below a few tens of amperes, this contactor is reopened to pass through the blocking diode again and protect the fuel cell from reverse currents.

[0044] In addition, an emergency discharge resistor of the battery can be used as a pull-up resistor (using a dedicated contactor) in order to lower the battery voltage by current draw if it exceeds the voltage allowing the converter to operate (voltage greater than, or close to, the DC bus voltage at the output of the converter).

[0045] The control of the components (contactors, DC-DC converter, current-voltage sensors) and the measurement are ensured by the fuel cell system computer.

[0046] System hardware configuration

[0047] Fig. 1 illustrates a SYS system configured to implement the approach described above.

[0048] The SYS system is a fuel cell system designed to supply electrical power to an external electrical device such as a DC power distribution bus, for example, a vehicle traction bus or an inverter power supply bus for electricity generation on an electrical grid (isolated or not). The SYS system comprises: a fuel cell (FC); a DC-DC converter designated by "DCConv"; and a control circuit (ContCirc) connecting two outputs, OutlFC and Out2FC, of ​​the fuel cell to two inputs, InlDC and In2DC, of ​​the DC-DC converter, respectively. Two outputs, OutlDC and Out2DC, of ​​the DC-DC converter are connected to two inputs, InlB and In2B, of the DC-DC bus.

[0049] The converter may be a boost converter. It is equipped with internal input and output current and voltage measurement systems, symbolized by "A" and "V" for ammeter and voltmeter, respectively. It has a conventional input voltage regulator or limiter function, which allows, within certain limits discussed elsewhere, the regulation of the fuel cell output voltage. The converter's regulator or limiter function allows... in particular to maintain the voltage supplied to it at the input below a certain predefined limit or one indicated by the user, which allows the output voltage of the fuel cell to be controlled by adapting the current drawn from the fuel cell.

[0050] The ContCirc control circuit includes a main contactor MCon; a backflow protection circuit RCProCirc; a current-voltage measurement circuit MesCirc; a discharge circuit DisCirc; an isolation contactor IsolCon; and a Cale calculator.

[0051] The main contactor MCon is configured to connect or disconnect the first OutlFC output of the fuel cell to the first InlDC input of the DC-DC converter, upon receiving a control signal commanding connection or disconnection. [Fig. 1] illustrates the contactor in a closed state, thus ensuring electrical continuity between the first OutlFC output of the fuel cell and the first InlDC input of the DC-DC converter.

[0052] The RCProCirc reverse-current protection circuit is configured to connect the first OutlFC output of the fuel cell to the first InlDC input of the DC-DC converter in parallel with the main contactor MCon. The reverse-current protection circuit includes a reverse-current blocking diode D connected in series with a diode contactor DCon. The diode contactor DCon is configured to connect or disconnect the first OutlFC output of the fuel cell to the first InlDC input of the DC-DC converter upon receiving a control signal commanding connection or disconnection. Figure 1 illustrates the contactor in an open state, thus breaking electrical continuity between the first OutlFC output of the fuel cell and the first InlDC input of the DC-DC converter. The diode is configured so that, when the diode contactor DCon is closed, it prevents the transmission of an electric current, known as reverse current, from the DC-DC converter to the fuel cell.Such a current could originate from a residual voltage at the DC-DC input that is higher than the battery voltage.

[0053] The DisCirc discharge circuit is connected between the first OutlFC output and the second Out2FC output of the fuel cell FC, and includes a DisRes discharge resistor in series with a contactor, preferably normally closed (to ensure discharge of the cell in the resting state), or a semiconductor (such as a JFET) providing the DisCon discharge connection / disconnection. The DisCon discharge contactor is configured to connect or disconnect the first OutlFC output of the fuel cell to the second Out2FC output of the fuel cell FC, upon receiving a control signal commanding connection or disconnection. [Fig. 1] illustrates the contactor in an open state, thus breaking continuity Electrical current between the first output OutlFC of the fuel cell and the second output Out2FC of the fuel cell FC. This is the normal state of the DisCon contactor when the system is in normal operation, producing energy.

[0054] The IsolCon isolation contactor is configured to connect or not the second output Out2FC of the fuel cell to a second input In2DC of the DC-DC converter, upon receipt of a control signal ordering a connection or a disconnection.

[0055] The MesCirc current-voltage measurement circuit is configured to measure the output voltage and current of the fuel cell FC. For this purpose, it can be connected in series between the output Out2FC and the input In2DC and in parallel between the outputs OutlFC and Out2FC (preferably in such a way as to be able to measure the voltage at the output of the cell even when the contactor IsolCon is open).

[0056] The Cale calculator is functionally connected to the MesCirc current-voltage measurement circuit and configured to control the open or closed states of the main contactor MCon, the diode contactor DCon, the discharge contactor DisCon, and the isolation contactor IsolCon in response to measurements taken by the MesCirc current-voltage measurement circuit or in response to instructions from the system user. The Cale calculator can also be functionally connected to the DC-DC converter so as to control its operations, for example, by defining a threshold used by the converter's voltage regulator or limiter function.

[0057] In this example, the outputs OutlDC and Out2DC constitute the outputs of the SYS system. Here, the SYS system provides a first electrical power to the electrical distribution bus BUS_DC, which is itself supplied with a second electrical power by a power supply battery Alim_BUS_DC, or any other electrical energy storage device, such as a supercapacitor.

[0058] Operation of the SYS system

[0059] The ConCirc control circuit is configured to ensure that the output voltage of the fuel cell remains within acceptable ranges for the operation and longevity of the elements forming the system.

[0060] Fig. 2 illustrates a sequence of operations that the control circuit is configured to perform.

[0061] When the fuel cell is off, ideally no gas circulates within it, therefore no electrochemical reaction takes place within the cells forming the cell, and the cell delivers only zero voltage between the OutlFC and Out2FC outputs. The contactors can be open, with the exception of the DisCon contactor, which is normally closed when the cell is off. In practice, reactive gas bubbles may remain in the cell. Even when stopped, it can still generate voltage. In this context, DisCon is preferably kept closed to prevent the reappearance of voltage at the battery output terminals.

[0062] In a first step S10, a system startup operation begins. With the introduction of gases (air and hydrogen, for example) into the fuel cell, the electrical voltage delivered by the fuel cell gradually increases. At this stage, the MCon contactor is still open, the DisCon contactor has been opened, and the IsolCon and DCon contactors have been closed by the Cale control unit.

[0063] The delivered current passes through a first PI connection path between the first OutlFC output of the fuel cell and the first InlDC input of the DC-DC converter, via the RCProCirc reverse current protection circuit. The delivered voltage is still low, and a zero or very low current (charging the input capacitors of the DC-DC converter) flows through diode D of the reverse current protection circuit, which could potentially expose the fuel cell to a risk of reverse current from the DC-DC converter.

[0064] In a second step S20 following the first step, if a first quantity VI, representative of or related to a current or power generated by the fuel cell, reaches or exceeds a first threshold Thl, as determined by a test Tl performed by the computer, and in response to a positive result Y, the computer establishes a second connection path P2 between the first output OutlFC of the fuel cell and the first input InlDC of the DC-DC converter through the main contactor MCon by closing the contactor MCon. Following the establishment of the second connection path, the computer can block the first connection path by opening the contactor DCon. The closing of contactor MCon and the opening of contactor DCon are staggered in time to ensure continuous current flow in the system and to prevent damage to the contactors.If the user chooses to leave both contactors Dcon and Mcon closed, path P2 will be the preferred path for the current generated by the battery because it has the lowest impedance, due to the presence of the diode in path PI which introduces an additional voltage drop. If the test Tl is negative, as indicated by N in [Fig. 2], no action is taken by the computer, and the contactor configuration remains that of the outcome of step S10.

[0065] The quantity V1 can be the current measured by the MesCirc current-voltage measuring circuit or the power deduced from the voltage and current measurement. The threshold Thl is determined with respect to the current and / or power capacities of the PI branch, and must of course have the same unit as the quantity VL

[0066] At this stage, the current begins to generate substantial losses as it passes through diode D, and the risk of a current reversal occurring in the DC-DC converter to the fuel cell is very low. It is therefore more advantageous to route the current through the second path rather than the first: the diode is no longer needed, and routing the current through the main contactor avoids electrical losses in the diode.

[0067] In a third step S30 following step S20, if the first quantity V1 falls below a third threshold Th3 lower than the first threshold Thl, as determined by a positive result Y in a test T3 performed by the computer, then the computer restores the first connection path PI by ordering the closure of the DCon connector, and then blocks the second connection path P2 by ordering the opening of the MCon connector. The opening of the MCon connector and the closing of the DCon contactor are staggered in time, so as to ensure continuity of current flow in the system operation and to prevent degradation of the contactors.

[0068] This step S30 corresponds to a response of the system to a reduction in the power generated by the fuel cell, for example when the fuel cell is shut down and oxygen and hydrogen are no longer supplied to it.

[0069] The third threshold Th3 is preferably chosen lower than the first threshold Thl, in order to improve the stability of the control of the system by hysteresis.

[0070] The first threshold Thl and the third threshold Th3 can be current thresholds, the third threshold Th3 preferably being lower than the first threshold Thl by a few tens of amperes, depending on the equipment used, and in particular depending on the characteristics of the DC-DC converter.

[0071] Following the shutdown of the battery, it may be preferable to completely isolate the battery from the converter and the circuits downstream of it. In this situation, the computer can command the opening of the DCon, MCon, and IsolCon connectors, and the closing of the DisCon connector to discharge the battery and maintain a voltage-free state across its terminals (consumption of reactive gases present in the battery).

[0072] A fourth stage S40 located between the first stage S10 and the second stage S20 has a system protection function: if a second quantity V2, representative of or related to the voltage generated by the fuel cell, reaches or exceeds a second threshold Th2, as determined by a positive result Y in a test T2 performed by the ECU, the ECU establishes a third connection path P3 between the first output OutlFC of the fuel cell and the second output Out2FC of the fuel cell through the discharge resistor DisRes by ordering the closure of the DisCon connector. Thus, at least part of the current is diverted to the discharge resistor DisRes. The test can be repeated, so that if the quantity V2, such as a voltage, falls below the second threshold Th2, the ECU re-enters the system in the configuration of the end of step S10 by ordering the opening of the DisCon connector after the first PI path of the current has been restored and can act again as the only connection path (the DC-DC converter is effectively able to ensure power conversion).

[0073] This is a step reflecting a protection function for the system components, implemented in parallel with the normal operation of the system, in a low-current, low-power regime. The objective is to dissipate a portion of the power produced by the battery in the discharge resistor for a short period when the battery's operating voltage becomes too high relative to what the converter is designed to accept. Thus, if the voltage supplied by the battery rises above a threshold that could lead to converter failure, the discharge resistor is used to draw current from the battery and lower its voltage in order to return to the operating range of the DC-DC converter and resume the normal PI path.

[0074] If the converter has limited voltage capacity, then the second threshold Th2 is preferably a voltage value representing the maximum voltage permissible for the converter. This value can be the maximum input voltage of the converter as specified by its manufacturer. Furthermore, this value must be greater than 0.8 V per electrochemical cell of the fuel cell or greater than the fuel cell's idle voltage. If electrochemical cells are combined, the fuel cell's output voltage corresponds to the sum of the cell output voltages. It is therefore easy to obtain a fuel cell FC with an open-circuit voltage close to or greater than the maximum input voltage permissible for converter operation.The necessity and advantage of using the ContCirc control circuit to control the operation of the SYS system and protect the DC-DC converter, which would otherwise be subjected to a voltage exceeding its capacity, is therefore clear. If the voltage exceeds the converter's maximum input voltage, the converter will be unable to regulate the voltage generated by the battery, and the system will fail to start. The control circuit becomes even more crucial when the number of cells connected in series is high and the converter's maximum input voltage is low.

[0075] [Fig.3] illustrates in (A) a mobile device Mob, here taking the form of a vehicle and in (B) a stationary device Station for supplying energy in the form of electricity, each equipped with the SYS system of [Fig.1].

[0076] Figure 4 illustrates the integration of the SYS system within a power supply chain in either the mobile device Mob or the stationary device Station. A Gas_Supp unit supplies the SYS system's fuel cell FC with reactive gases. As illustrated in Figure 1, the power distribution bus BUS_DC is connected to the output of the SYS system, which can correspond to the outputs of the DC-DC converter DCConv-. The power distribution bus is here powered by the battery Alim_BUS_DC. In this example, the distribution bus BUS_DC powers a DC-AC converter ConvDC ac configured to generate an alternating voltage from the direct voltage supplied to it by the distribution bus.

[0077] In the case of the vehicle in [Fig. 3](A), the DC-AC converter powers a motor configured to convert the electrical energy transmitted by the distribution bus into mechanical energy to propel the vehicle. In the case of [Fig. 3](B), the electrical voltage supplied by the DC-AC converter is adapted in frequency and / or voltage to its intended use, typically to power an electrical network.

[0078] Of course the invention is not limited to the examples described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Demands

1. Fuel cell system (SYS) intended to provide electrical power to an external electrical device (BUS_DC), the fuel cell system comprising: - a fuel cell (FC); - a DC-DC converter (DCConv); and - a control circuit (ContCirc) connecting the fuel cell (FC) to the DC-DC converter (DC), the control circuit comprising: - a main contactor (MCon) connecting a first output (OutlFC) of the fuel cell to a first input (InlDC) of the DC-DC converter; - a reverse-current protection circuit (RCProCirc) connecting the first output of the fuel cell to the first input of the DC-DC converter in parallel with the main contactor (MCon), the reverse-current protection circuit comprising a reverse-current protection diode (D), connected in series with a diode contactor (DCon);and - a current-voltage measurement circuit (MesCirc) configured to measure a voltage and current output of the fuel cell, the control circuit (ContCirc) being configured so that, when the fuel cell starts up: - establish a first connection path (PI) between the first output (OutlFC) of the fuel cell and the first input (InlDC) of the DC-DC converter through the reverse-flash protection circuit (RCProCirc), then - when a quantity representative of or related to a current or power generated by the fuel cell reaches a first threshold, establish a second connection path (P2) between the first output (OutlFC) of the fuel cell and the first input (InlDC) of the DC-DC converter through the main contactor (MCon), then possibly block the first connection path.;

2. System according to claim 1, wherein the control circuit further comprises a discharge circuit (DisCirc) connected between the first output (OutlFC) and the second output (Out2FC) of the fuel cell (FC), and comprising a discharge resistor (DisRes) in series with a discharge contactor (DisCon).

3. System according to claim 2, configured such that, when the quantity representative of or related to the voltage supplied by the fuel cell reaches a second threshold (Th2), the control circuit is configured to establish a third connection path (P3), between the first output of the fuel cell (OutlFC) and the second output (Out2FC) of the fuel cell through the discharge resistor (DisRes).

4. System according to claim 3, wherein the control circuit is further configured to establish the third connection path (P3) when the stack is shut down.

5. System according to any one of claims 1 to 4, wherein the DC-DC converter (DCc„) is configured to regulate a voltage at the output of the fuel cell supplied to it through the control circuit (ContCirc) by means of a voltage regulator or limiter function.

6. System according to any one of claims 1 to 5, wherein an open-circuit voltage of the fuel cell exceeds a maximum voltage considered acceptable for the DC-DC converter.

7. System according to any one of claims 1 to 6, wherein the fuel cell system (SYS) is configured to provide a DC-DC converter output voltage that is lower than a fuel cell open-circuit voltage.

8. System according to any one of claims 1 to 7, wherein the DC-DC converter is a boost converter.

9. A system according to any one of claims 1 to 8, the control circuit further comprising an isolation contactor (IsolCon) connecting the second output of the fuel cell to a second input of the DC-DC converter, the control circuit being configured to: - when the first output of the fuel cell is connected to the first input of the converter by at least one of the first and second connection paths, connect the second output of the fuel cell to the second input of the DC-DC converter through the isolation contactor, and - when the fuel cell system is not operating, isolate the DC-DC converter from the fuel cell by opening the main contactor, the diode contactor and the isolation contactor.

10. System according to any one of claims 1 to 9, further comprising a calculator (Cale) functionally connected to the current-voltage measuring circuit (MesCirc) and configured to control the main contactor (MCon), the diode contactor (DCon), and, where applicable, the discharge contactor (DisCon) and the isolation contactor (IsolCon), in response to measurements made by the current-voltage measuring circuit (MesCirc).

11. Electrical device equipped with the system according to any one of claims 1 to 10, comprising an electrical distribution bus (BUS_DC) connected at the output of the DC-DC converter and a battery (Alim_BUS_DC) or other electrical energy storage device connected to the electrical distribution bus (BUS_DC).

12. Electrical device according to claim 11, wherein the electrical device is a mobile device (Mob) or a stationary device (Station), comprising an electrical power supply chain integrating the electrical distribution bus (BUS_DC).

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