METHOD FOR CONTROLLING A FUEL CELL

Abstract

A method is provided for controlling an ion-exchange-membrane type fuel-cell stack installed in a system that includes a cooling circuit and a cooling pump for circulating coolant liquid in the cooling circuit. The method includes, in a start-up phase of starting up the fuel-cell stack, determining an internal temperature of the fuel-cell stack; measuring a temperature in the cooling circuit; applying a start-up current to the fuel-cell stack; and, in parallel: controlling the cooling pump to operate in a pulsed mode when the internal temperature of the fuel-cell stack is above a first predetermined threshold and the temperature of the cooling circuit is below a second predetermined threshold, and controlling the cooling pump to operate in a continuous mode when the temperature in the cooling circuit rises above the second predetermined threshold.

Claims

1-7. (canceled)

8. A method for controlling an ion-exchange-membrane type fuel-cell stack installed in a system that includes a cooling circuit and a pump for circulating coolant liquid in the cooling circuit, the method comprising a start-up phase of starting up the fuel cell stack, the start-up phase including steps of: determining an internal temperature of the fuel-cell stack; measuring a temperature in the cooling circuit; applying a start-up current to the fuel-cell stack, and, when the internal temperature of the fuel-cell stack is above a first predetermined threshold, in parallel: controlling the cooling pump to operate in a pulsed mode when the temperature of the cooling circuit is at or below a second predetermined threshold, and controlling the cooling pump to operate in a continuous mode when the temperature in the cooling circuit rises above the second predetermined threshold.

9. The method according to claim 1, wherein the first predetermined threshold is 20° C. at atmospheric pressure.

10. The method according to claim 8, wherein the second predetermined threshold is 5° C. at atmospheric pressure.

11. The method according to claim 8, wherein the step of determining the internal temperature of the fuel-cell stack takes into account: a heat capacity and a mass of materials constituting the fuel-cell stack, and thermal energy dissipated by the fuel-cell stack.

12. The method according to claim 8, wherein, in the step of applying the start-up current, the start-up current is ramped at a rate of 0.015 A/cm.sup.2/s up to a limit of 0.5 A/cm.sup.2.

13. The method according to claim 8, further comprising a dry-out phase of the fuel-cell stack, the dry-out phase including a step of drying out the fuel-cell stack after each shut-down of the fuel cell stack.

14. The method according to claim 8, wherein an activation frequency of the cooling pump in the pulsed mode is determined so as to achieve a rise in the internal temperature of the fuel-cell stack by a predetermined value between two pulses.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0041] Other objectives and advantages of the invention will appear clearly in the following description of a preferred, but non-limiting, embodiment, illustrated by the following figures in which:

[0042] FIG. 1 shows the voltages across the terminals of the cells of a fuel cell stack in the case that the cooling pump is activated in continuous mode in a cold start phase.

[0043] FIG. 2 shows the variation in multiple temperatures within the fuel cell stack in the case that the cooling pump is started up after a delay, and activated in pulsed mode in a cold start phase.

[0044] FIG. 3 shows the voltages across the terminals of the cells of a fuel cell stack in the case that the cooling pump is started up after a delay, and activated in pulsed mode in a cold start phase.

DESCRIPTION OF THE BEST EMBODIMENT OF THE INVENTION

[0045] FIG. 1 shows the variation in the voltages across the terminals of the cells of a fuel cell stack during a cold start at −15° C. managed according to the methods of the prior art, namely by operating the cooling pump in continuous mode.

[0046] A gradual decrease in the voltage across the terminals of the set of cells is observed, followed by a collapse, starting at 13 seconds, of the voltage across the terminals of the first cell (lowest curve on the graph), followed shortly after by the voltage across the terminals of the second cell.

[0047] This rapid drop in voltage reveals a blockage linked to the freezing of the water produced in the fuel cell stack. As a result, the operation of the stack is negatively affected.

[0048] FIGS. 2 and 3 show the variation in parameters in a fuel cell stack for which a control method according to the invention is implemented. Thus, these two graphs show the variation for a cold start during which the stack is first operated without circulation of coolant liquid, then the cooling pump is operated in pulsed mode.

[0049] In FIG. 2, the curve C1 shows the estimated temperature of the fuel cell stack, the curve C2 shows the control setpoint of the cooling pump and the curve C3 shows the temperature at the inlet of the stack. After around 65 seconds, the temperature, shown by curve C1, reaches a value of 20° C. This value corresponds to a first predetermined threshold in one embodiment of the invention. The cooling pump, or water pump, is then controlled in pulsed mode, as shown on the curve C2.

[0050] After 135 seconds of operation, the temperature of the coolant liquid at the inlet of the stack, shown on curve C3, becomes higher than 5° C. This value corresponds to a second predetermined threshold in one embodiment of the invention. The cooling pump is then operated in continuous mode. From this moment on, the coolant liquid circulates continuously, resulting in quite a rapid decrease, then disappearance, of the difference in temperature of the coolant liquid between the inlet and the outlet of the fuel cell stack.

[0051] At the same time, FIG. 3 shows the corresponding variation in the individual voltages of the cells of the fuel cell stack when a method according to the invention is implemented. It is observed in this figure that, unlike in FIG. 1, the first cells of the fuel cell stack retain an acceptable voltage level, or have a voltage level that quickly bounces back, when the cooling pump is activated. The cooling pump is activated in pulsed mode. It is observed that each injection of cold water results in a drop in the set of voltages, shown in FIG. 3 by ripples. The frequency of the pulses of the cooling pump, and hence of the injection of coolant liquid, is determined so as to allow time for the voltage across the terminals of the cells to return to an acceptable level before another injection. In the present example, one injection takes place every 0.6 second.

[0052] Such a control method makes it possible to warm up the liquid contained in the cooling circuit while holding an acceptable voltage across the terminals of the cells of the fuel cell stack throughout the start-up phase.