Method for controlling an electric compressor, and program and architecture for a fuel cell based on such a method

Abstract

The invention relates to a control method for controlling an electric compressor (eC) in a fuel cell architecture, comprising: - the electric compressor (eC); - an air tank (AT); - a plurality of fuel cell systems, each comprising a humidifier (H), a cooler (R) and a fuel cell stack (FS); the control method comprising the following steps: - determining an air flow and pressure requirement (RI) for the fuel cells; - determining a minimum pressure setpoint and a speed setpoint for the electric compressor (eC); - controlling the electric compressor (eC) on the basis of these setpoint points; - measuring the pressure in the air tank (AT). The invention also relates to a program and an architecture based on such a method.

Description

METHOD FOR CONTROLLING AN ELECTRIFIED COMPRESSOR, PROGRAM AND FUEL CELL ARCHITECTURE BASED ON SUCH A METHOD

[0001] The invention relates to the field of fuel cell systems, in particular for electric motors. The invention relates more particularly to the air supply of these systems.

[0002] This type of fuel cell system is illustrated in Figure 1. The electric motor system EM is of the type powered by a stacked fuel cell system FS coupled to a battery B.

[0003] The control of the fuel cell system is performed by an AMS air management module, while the control of battery B is performed by an EMS energy management module communicating with the AMS air management module.

[0004] Fuel cell electric vehicles (FCEVs) have not yet reached their highest level of market development in the automotive industry due to certain obstacles such as unavailability of hydrogen refueling infrastructure and limited lifespan.

[0005] Combining a battery with a multi-stacked fuel cell system, namely a low-power fuel cell arrangement (designed for passenger cars) rather than a high-power stack, may be a solution to some of the above-mentioned obstacles to fuel cell development.

[0006] The FS stack fuel cell can be connected to a single set of auxiliary equipment, the auxiliary equipment can include a compressor eC, humidifier H, intercooler R, recirculation device, backpressure valve. In other words, all the FS stacks constituting the fuel cell are connected to the single set of equipment. In this case, the air and hydrogen pressure and the air mass flow rate of the various FS stacks (and therefore stack power) cannot be controlled individually.

[0007] Another solution is to duplicate the set of auxiliary equipment for each FS stack as shown in Figure 2.

[0008] In this alternative solution, with an FS stack architecture, each FS stack is therefore connected to its own electrified eC compressor to supply it with oxygen. Each electrified eC compressor is managed independently. Thus, weight and energy consumption can be optimized compared to the solution using a single set of auxiliary equipment.

[0009] An objective of the present invention is to remedy the defects of the prior art, and in particular to propose a solution making it possible to limit the weight of stacked fuel cell systems, and to limit their energy consumption.

[0010] To achieve this objective, the invention proposes a method for controlling an electrified compressor in a fuel cell architecture comprising: - the electrified compressor receiving ambient air, coupled to a first controller; - an air tank in fluid communication downstream of the electrified compressor; - several fuel cell systems coupled to a second controller, being in fluid communication downstream of the air tank, each comprising a humidifier, a cooler and a fuel cell stack; - an air outlet equipped with a pressure valve, in fluid communication downstream of each fuel cell system, the control method comprising the following steps: - a first step of determining a demand for air flow and pressure of the fuel cells; - a second step of determining a minimum pressure set point and an electrified compressor speed set point as a function of the air flow and pressure demand; - a step of measuring the pressure of the air tank; and - a step of controlling the electrified compressor based on the compressor set point so that the air tank pressure reaches the pressure set point.

[0011] Advantageously, the invention allows for space and energy savings by using an electrified compressor connected to several fuel cells.

[0012] Furthermore, the invention allows for managing the loading / unloading of the system's air tank so that appropriate air flows and pressures can be supplied to the batteries and keep the electrified compressor in a good efficiency zone.

[0013] Alternatively, the airflow and pressure demand of the cells is determined based on the power demands of the fuel cells.

[0014] This makes it possible to determine an air flow and pressure that allow the fuel cells to operate optimally.

[0015] Alternatively, the minimum pressure set point and the electrified compressor speed set point are determined by compressor parameters as a function of flow and pressure with same speed curves.

[0016] According to one variant, the step of controlling the electrified compressor comprises the following sub-steps: - activate the electrified compressor with air flow limitation to maximize compressor efficiency; - activate the electrified compressor at the same speed and increasing pressure to reach an optimal target pressure corresponding to the best efficiency; - deactivate the electrified compressor after the target optimum pressure has been reached.

[0017] This keeps operation in the best efficiency zone of the electrified compressor.

[0018] The invention further relates to a computer program comprising program code instructions for executing the steps of the control method according to the invention, when said program operates on a computer.

[0019] Another subject of the invention relates to a fuel cell architecture for implementing a control method according to the invention, the fuel cell architecture comprising: - an electrified compressor receiving ambient air, coupled to a first controller; - an air tank in fluid communication downstream of the electrified compressor; - several fuel cell systems coupled to a second controller, being in fluid communication downstream of the air tank, each comprising a humidifier, a cooler and a fuel cell stack; - an air outlet equipped with a pressure valve, in fluid communication downstream of each fuel cell system, characterized in that it further comprises: - a pressure reducing valve in fluid communication downstream of the air tank and upstream of each fuel cell system, coupled to a third controller.

[0020] This allows the pressure reduction available to the fuel cells to be controlled.

[0021] The invention will be further detailed by the non-limiting description of variants, and on the basis of the appended figures, in which: - [FIG. 1] schematically illustrates a stacked fuel cell system suitable for the invention; - [FIG. 2] schematically illustrates a stacked fuel cell system in an architecture according to the prior art; - [FIG. 3] schematically illustrates a system of fuel cells stacked in an architecture according to the invention; - [FIG. 4] schematically illustrates the control method according to the invention; - [FIG. 5] schematically illustrates a calibration of the efficiency of an electrified compressor suitable for the invention; and - [FIG. 6] schematically illustrates a control method according to a preferred variant of the invention.

[0022] The invention relates to a method for controlling, in other words for monitoring, a fuel cell system with FS stacks, said method being presented with reference to Figures 4, 5 and 6. The invention is applicable to a fuel cell system with FS stacks as illustrated in Figure 1 and Figure 3. The fuel cell system illustrated according to Figure 3 comprises three FS stacks, but this fuel cell system can comprise any number of FS stacks greater than or equal to 2.

[0023] The purpose of the control and the control method is to manage the loading / unloading of an air tank AT of the system so that appropriate air flows and pressures can be supplied to the FS stacks and keep the electrified compressor eC in a good efficiency zone. For this purpose, air flow and pressure demands RI of the stacks are determined as a function of the power demands of the FS fuel cells, in a first determination step E1 illustrated in Figure 6.

[0024] A minimum pressure setpoint for the air tank AT is then calculated based on the stack pressure demands in a second determination step E2 (e.g., this could be the maximum of all individual stack pressures plus a margin).

[0025] On the other hand, the optimal operating points (pressure versus air flow rates) of the eC electrified compressor are assumed to be known or calibrated.

[0026] A working pressure can be defined for the AT air tank as the maximum of: - the minimum pressure setpoint; and - the optimal pressure in relation to the air flow.

[0027] For this purpose, the tank pressure is measured in a measuring step E3.

[0028] In case of low battery charge (low air flow demand), the air tank pressure setpoint AT is the pressure of the best efficiency point of the electrified compressor eC; and the speed setpoint of the electrified compressor eC is the speed at the best efficiency point.

[0029] The electrified compressor eC is then activated in a control step E4, (with an air flow greater than what the FS batteries will consume) until the air tank AT reaches the target pressure.

[0030] More specifically, with reference to the calibration in Figure 5, in a step 1, the eC electrified compressor is activated with an airflow limitation to maximize the compressor efficiency. Then, in a step 2, the eC electrified compressor is activated at the same speed (also called "isoregime") and increasing pressure to reach a target optimal pressure corresponding to the best efficiency of the eC electrified compressor. Then, in a step 3, the eC electrified compressor is deactivated after the target optimal pressure has been reached, and the cycle starts again at step 1.

[0031] The air tank pressure AT then decreases due to the air flow supplied to the fuel cells FS. The electrified compressor eC is reactivated when the tank pressure AT reaches a low value. (The trajectory can be seen in Figure 5).

[0032] In Figure 5, the bottom cycle with steps 1, 2, 3 represents the optimization of the OE efficiency of the electrified compressor eC; the top cycle with steps 1, 2, 3, the RI demand of the stacks (corresponding to a low BFS efficiency); the middle curve, the best efficiency line BE; the slightly right curve, a maximum airflow demand DA to achieve a better efficiency.

[0033] In the case where the airflow demanded RI by the FS stacks is higher than the airflow at the best efficiency of the eC compressor, the pressure setpoint for the AT air tank is taken from the best efficiency line of the eC electrified compressor at the desired airflow. The speed of the eC electrified compressor is then the speed on the best efficiency line at the demanded airflow. As explained above, the eC electrified compressor then operates intermittently to maintain the AT air tank between a low pressure level and the AT air tank pressure setpoint.

[0034] The electrified eC compressor is controlled by the open loop speed target.

Claims

CLAIMS 1. Method for controlling an electrified compressor (eC) in a fuel cell architecture comprising: - the electrified compressor (eC) receiving ambient air (AA), coupled to a first controller (C1); - an air tank (AT) in fluid communication downstream of the electrified compressor (eC); - several fuel cell systems coupled to a second controller (C2), being in fluid communication downstream of the air tank (AT), each fuel cell system comprising a humidifier (H), a cooler (R) and a fuel cell stack (FS); - an air outlet equipped with a pressure valve (PV), in fluid communication downstream of each fuel cell system, the control method comprising the following steps: - a first step of determining (E1) a request for air flow and pressure of the fuel cells (FS); - a second step of determining (E2) a minimum pressure set point and an electrified compressor speed set point (eC) as a function of the air flow and pressure demand; - a measurement step (E3) of the pressure of the air tank (AT); and - a control step (E4) of the electrified compressor (eC) on the basis of the compressor set point so that the pressure of the air tank (AT) reaches the pressure set point.

2. Control method according to claim 1, characterized in that the air flow and pressure demand of the fuel cells (FS) is determined as a function of the power demands of the fuel cells (FS).

3. Control method according to any one of claims 1 to 2, characterized in that the minimum pressure set point and the electrified compressor speed set point (eC) are determined by compressor parameters as a function of flow and pressure with same speed curves.

4. Control method according to any one of claims 1 to 3, characterized in that the control step (E4) of the electrified compressor (eC) comprises the following sub-steps: - activate the electrified compressor (eC) with air flow limitation to maximize compressor efficiency; - activate the electrified compressor (eC) at the same speed and increasing pressure to achieve an optimal target pressure corresponding to the best efficiency; - deactivate the electrified compressor (eC) after the target optimum pressure has been reached.

5. A computer program comprising program code instructions for executing the steps of the control method according to any one of claims 1 to 4, when said program is running on a computer.

6. Fuel cell architecture comprising: - an electrified compressor (eC) receiving ambient air (AA), coupled to a first controller (C1); - an air tank (AT) in fluid communication downstream of the electrified compressor (eC); - several fuel cell systems coupled to a second controller (C2), being in fluid communication downstream of the air tank (AT), each comprising a humidifier (H), a cooler (R) and a fuel cell stack (FS); - an air outlet equipped with a pressure valve (PV), in fluid communication downstream of each fuel cell system, characterized in that it further comprises: - a pressure reducing valve (RV) in fluid communication downstream of the air tank (AT) and upstream of each fuel cell system, coupled to a third controller (C3), the fuel cell architecture being characterized in that it is configured to implement the control method according to one of claims 1 to 4.

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