DE102014104380B3 - A method of operating a blower to deliver hydrogen in a fuel cell system - Google Patents

Abstract

There are methods for operating a fan (12) for the promotion of hydrogen in a fuel cell system, wherein during operation of the fuel cell system, a delivery wheel of the blower (12) by an electric motor (17) is driven and after switching off the fuel cell system, the electric motor (17) in a shutdown procedure is continued at least temporarily, known. These usually use either purge gas or a heater to ensure a start-up. In order to avoid this additional expense, it is proposed according to the invention that, after switching off the fuel cell system, in a first step, the energization of the electric motor (17) is interrupted for a fixed period of time and in a second step the electric motor (17) for generating a movement of the fan ( 12) is energized, wherein the first and second steps are repeated several times in succession.

Description

The invention relates to a method for operating a blower for the promotion of hydrogen in a fuel cell system, wherein during operation of the fuel cell system, a delivery wheel of the blower is driven by an electric motor and after switching off the fuel cell system, the electric motor is operated at least temporarily in a shutdown procedure.

Hydrogen blowers are used for the circulation of hydrogen with a mostly high water content in the anode gas circuits of fuel cell systems. These fuel cell systems serve to convert chemical reaction energy of a continuously supplied fuel, in particular hydrogen and an oxidant, usually oxygen, into electrical energy, which can be used, for example, as drive energy for vehicles. The drive of these blowers usually takes place via electric motors which are supplied with voltage via the vehicle battery during operation in vehicles.

When the fuel cell systems are switched off, the water content at the system piping but also at the rotating parts of the fan such as the bearing, shaft or impeller settles at low ambient temperatures. At a restart of the fuel cell system, this can lead to a blockage of the engine at too much ice bridge formation, whereby a startup of the system is prevented.

To solve this problem, it was first proposed to expel the water from the system by means of a dry purge gas. Such a method is used, for example, in DE 103 14 820 A1 described.

In order to prevent additional purge gases must be transported, which leads to an undesirable additional expense especially in mobile applications, various methods have become known with which such ice bridge formation without the use of additional purge gases to be prevented or broken. A distinction must be made between methods in which ice formation is to be abolished before the system is started and those methods which carry out corresponding procedures when switching off the system.

The DE 101 37 847 A1 discloses a method of operating a fuel cell system where temperatures in the freezing area of the water may occur. In order to avoid freezing of the fuel cell, an additional substance not influencing the catalytic reaction, such as methanol, which is liquid and otherwise gaseous at the expected freezing temperature, is additionally injected into the fuel cell stack.

Furthermore, from the DE 10 2005 004 388 A1 a wake-up strategy for vehicles is known, with the fuel cell freezing is to be prevented. For this purpose, the fuel cell stack is purged to remove the water with a purge gas falls below a defined temperature threshold.

In addition, in the DE 10 2007 029 420 A1 discloses a water management strategy for fuel cell systems in which a purge gas is passed into the Reaktandenströmungskanäle depending on defined conditions when switching off. Periodically, these conditions are checked below and, if necessary, the rinsing is carried out.

From the DE 10 2010 035 039 A1 It is known to energize before the restart of the fuel cell system, the stator windings of the drive motor of the fan, in order to use the windings as a heater in this way, through which the ice is melted. However, the problem here is that the heating energy is applied outside the hydrogen-carrying lines, so that a lot of energy is needed for heating. Furthermore, there is a delay of the restart.

In the DE 10 2008 031 280 A1 a method is proposed in which immediately before and behind the blower, a flap is arranged, which is closed when switching off the system, so that no water can flow in the direction of the blower. However, this requires an increased expenditure on equipment.

Furthermore, it is from the DE 10 2008 058 959 A1 it is known to run after the shutdown of the fuel cell system with the discharge valve open, the fan, wherein in the region of the blower, a heat source is provided through which takes place a heating of the fuel cell system. This is to remove the moisture present in the system, allowing a quick reboot. However, this system again requires a large amount of energy due to the usually electrical heating energy to be introduced.

It is therefore an object of the invention to provide a method for operating a blower for the promotion of hydrogen in a fuel cell system, with the freezing of the rotating components of the fan and the associated electric motor can be avoided without further components are needed or a increased mounting effort arises. Furthermore, in comparison with known designs, the energy consumption is to be reduced and a delivery of the hydrogen without warm-up time immediately after the start of the system is made possible.

This object is achieved by a method for operating a blower for conveying hydrogen in a fuel cell system with the features of the main claim 1.

Characterized in that after switching off the fuel cell system in a first step, the energization of the electric motor is stopped until the impeller of the fan is stationary and in a second step, the electric motor is energized to drive the fan, the first and second steps are repeated several times in succession, is achieved that the electric motor and thus the pump feed wheel are always moved at a time at which a first ice film can develop in the rotating parts. However, this ice film is still thin enough at this time to be broken by energizing simply by starting the electric motor. Accordingly, the forming bridges are broken up until no further ice formation on the rotating parts is expected. This ensures that all freezing water settles in areas that have no effect on the rotation of the fan parts. Thus, a direct start is possible when restarting the fuel cell system, without having to spend heating energy or using purge gas.

Preferably, only one or two phases of the electric motor are energized in the second step, so that it only completes a rotation of approximately 30 ° to 180 °. A start of the electric motor is not required because a promotion of the gas is not desirable, but only the rotating parts to be broken free. This keeps the energy required low.

Advantageously, the fixed period in the first step is 3 to 30 seconds. In this period, a releasable ice bridge is expected, so that the energy input is achieved in securing a rotation of the fan when restarting the system.

Preferably, the shutdown procedure is started at a fan temperature of less than 2 ° C, since from this temperature is to be expected with an ice formation. At higher temperatures, the energy for the subsequent starts of the electric motor can thus be saved.

Furthermore, the shut-off procedure is stopped at a fan temperature of below -5 ° C, since on reaching this temperature after switching off the fuel cell system it can be assumed that all the water present in the system is frozen.

In an alternative embodiment of the method, the switch-off procedure is ended after a defined time. For this purpose, a meaningful period is set, after the expiration of a complete transition of the water in the solid state of matter is assumed. For example, such a period may be about 5 minutes.

Alternatively, the switch-off procedure can also be terminated and the electric motor can no longer be energized if the water present in the fuel cell system has completely changed to the solid state of matter. To determine this, a moisture sensor can be arranged in the anode gas cycle, which measures the water content in the gas in the anode circuit, is assumed when falling below a defined water content in the gas that the water has completely gone into the solid state.

Furthermore, advantageously, a characteristic field can be stored in a control unit of the electric motor, in which a time for terminating the switch-off procedure is determined as a function of a measured outside temperature and a water content in the gas at the time of switching off the fuel cell system.

Also, it is alternatively possible to measure the current required for starting the electric motor according to step 2 current or time for generating a rotation of the rotor of the electric motor after the first shutdown according to step 1 and falls below a current threshold or a fixed energization period to generate a movement of the rotor of the electric motor to end the shutdown procedure. It is assumed that with each energization a small layer of ice forms on the rotating parts, which must be broken when energized, so that increases the Bestromungsdauer or strength to generate the rotation compared to the freewheel. If the duration or intensity of the current supply is within the same range as during idling, it is possible to conclude that ice bridging has been completed. Thus, for each state, only a minimum number of energization passes are performed according to steps 1 and 2, and at the same time, a fast start-up is ensured upon restart.

There is thus a method for operating a blower to promote hydrogen in a fuel cell system, with which with minimal energy consumption, without the use of additional components or heating elements, an immediate start-up of the fan is ensured when restarting the system.

An embodiment of the method according to the invention will be described below with reference to the figure.

1 shows a schematic diagram of an anode gas cycle of a fuel cell system, the shutdown of the inventive method can be applied.

In the 1 is a fuel cell stack 1 with a cathode 2 and an anode 3 shown. This fuel cell stack 1 is to an anode gas cycle 4 , a cathode gas cycle 5 and a cooling circuit 6 connected.

The not essential to the invention parts of the three circuits 4 . 5 . 6 are not shown in the figure but are briefly described by way of example with reference to a conventional structure of a PEM fuel cell system. The cathode gas cycle 5 may for example consist of a compressor, which has an electric motor 17 is driven and air via a pipe 7 to the cathode side 8th of the fuel cell stack 1 promotes. At the same time in the anode gas cycle 4 compressed hydrogen from a cryogenic storage tank via a pressure reducing valve and a control valve via a pipe 9 the anode side 10 of the fuel cell stack 1 fed.

On the anode side 10 The hydrogen is catalytically oxidized and thereby converted into protons with release of electrons. The electrons are derived from the fuel cell and flow through an electrical load, such as an electric motor 17 for driving a motor vehicle, to the cathode 2 , At the cathode 2 For example, the oxidant, in the present example, oxygen from the air, is reduced to anions by incorporation of the electrons. At the same time, the protons diffuse through the proton exchange membrane between the fuel cells to the cathode 2 and react with the reduced oxygen to form water vapor. In these reactions, an electrical power is generated across the cathode 2 and the anode 3 can be removed.

In these reactions, the hydrogen provided is not completely consumed, so that via a return line 11 the anode-side exhaust gases again the anode side 10 can be supplied. This is in the return line 11 a fan 12 arranged, for example, as via an electronically commutated electric motor 17 driven side channel blower is executed.

The non-recirculated exhaust gases of the anode side 10 , which consist of unused hydrogen, nitrogen and water vapor, are via an outlet 13 and a discharge valve is fed to a catalytic burner in which, with the addition of oxygen, the remaining hydrogen is converted into water, which can then be discharged with the nitrogen into the environment.

The exhaust gases of the cathode side 8th be via an outlet pipe 14 and a valve for operating pressure control is first supplied to a separation device for separating water from the exhaust gas and then discharged the unused atmospheric oxygen and nitrogen into the environment. The cooling circuit 6 can be carried out in very different ways, with both an air cooling and a liquid cooling can be realized. Accordingly, a detailed description of the refrigeration cycle is dispensed with.

After switching off the fuel cell system usually condenses in the anode gas cycle 4 existing water vapor on the pipes and possibly in the fan 12 , At outdoor temperatures below the freezing point of the water, this corresponding to the narrow gap between rotating and stationary components of the fan 12 freeze and thus the blower 12 fix.

For this reason, after the shutdown of the fuel cell system, a shutdown procedure for the blower 12 started. It first checks which temperature on the blower 12 is present. For this purpose, temperature sensors can be arranged for example in the region of the fan head. This check should be carried out after switching off the fuel cell system at regular intervals of, for example, 30 minutes in order to carry out this procedure even at a later cold break after switching off the fuel cell system. Once it is determined that the temperature on the blower 12 falls to a corresponding threshold to be determined, for example, below 2 ° C, the shutdown procedure is started.

First, in a first step, the electric motor 17 of the blower 12 switched off, so not energized. A counter is turned on and waits, for example, for about 10 seconds, in which the electric motor 17 is not energized and thus the impeller of the fan 12 stands still. Of course, this time must be adapted to the existing system. During this time, this is done in the ducts and in the area of the slots between the rotatable and fixed parts of the blower 12 existing water begins to freeze. Accordingly, thin ice sheets are formed. After 10 seconds, the stator of the electric motor 17 briefly energized in a second step. This can be done, for example, in the form that only the first for the start of the electric motor 17 required phase is energized. This leads depending on the number of phases of the electric motor 17 to a rotation of its rotor and thus the delivery wheel of the fan 12 from Z. B. 60 ° and against the holding force by the ice formed. However, the existing ice sheets are still relatively easy to break up.

The broken up by the movement in the area of the column ice is thrown by the movement of the feed wheel in further from the feed wheel remote areas.

Subsequently, it checks if the temperature is in the range of the blower 12 has fallen below -5 ° C. If this is the case, it is assumed that the water present in the anode gas cycle has already completely converted to ice. In this case, the rotating parts of the fan would be 12 when the system is restarted freely rotatable and the shutdown procedure is completed.

Is the temperature in the range of the blower 12 even above -5 ° C, first step 1 is performed and waited 10 seconds until the next second step, the next phase of the electric motor 17 is energized, so that this is again rotated briefly and broken up during the waiting thin ice layers between the rotating and the fixed parts are broken again.

These processes are repeated below until either the temperature falls below -5 ° C or a maximum run time of the shutdown procedure of, for example, 5 minutes is reached. At the end of this time or reaching this temperature, it can be assumed that the water in the system is completely frozen, but without this water being between the rotating and stationary parts of the blower 12 sets. This means that at a restart of the fuel cell system, regardless of the temperature of the blower 12 can be switched on immediately, without blocking is to be feared. Compared to known designs, this shutdown procedure results in a significantly reduced power requirement of, for example, about 20 watts compared to the usual 600 watts that would be required when using a heater.

Ending the shutdown procedure can also be done in other ways. So it is possible in the area of the blower 12 to arrange a moisture sensor over which the system still existing and thus not frozen water content is measured, so that when falling below a corresponding threshold on a complete transition of the water in the solid state can be assumed, so that falls below this threshold, the shutdown procedure is terminated , This switch-off procedure can be improved even further by plotting the threshold value as a function of the outside temperature or the temperature present in the system in a characteristic diagram, and thus falling short of the threshold value corresponding to the measured temperature for terminating the switch-off procedure.

Furthermore, it is possible for the rotation of the electric motor 17 during the second step of the shutdown procedure, to measure the energy or current to be expended or the time required to generate the rotation. This is slightly higher with ice formation, since first the holding torque must be broken by the thin ice bridges. If this applied current falls below a threshold to be determined, which is to be determined by tests, the shutdown procedure is also ended in this embodiment.

In all cases, there is almost no design effort and only a very low energy consumption to ensure an immediate subsequent start-up of the fan when switching on the fuel cell system.

Of course, other conditions for starting or terminating this shutdown procedure according to the invention are conceivable without departing from the scope of the main claim. The waiting times and temperature thresholds described in the exemplary embodiment are optionally adaptable and dependent on the external conditions. Thus, it would be conceivable to extend or shorten the waiting time between the individual energizations depending on the outside temperatures or to choose longer energizing times for the stator of the electric motor, so that it performs more than just a partial rotation.

Claims (10)

Method for operating a blower ( 12 ) for conveying hydrogen in a fuel cell system, wherein during operation of the fuel cell system, a delivery wheel of the blower ( 12 ) by an electric motor ( 17 ) is driven and after switching off the fuel cell system of the electric motor ( 17 ) in a shutdown procedure is at least temporarily continued, characterized in that after switching off the fuel cell system in a first step, the energization of the electric motor ( 17 ) is interrupted for a fixed period of time and in a second step the electric motor ( 17 ) for generating a movement of the blower ( 12 ) is energized, wherein the first and second steps are repeated several times in succession. Method for operating a blower ( 12 ) for conveying hydrogen in a fuel cell system according to claim 1, characterized in that in the second step in each case only one or two phases of the electric motor ( 17 ) are energized. Method for operating a blower ( 12 ) for the promotion of hydrogen in a fuel cell system according to claim 1 or 2, characterized in that the fixed period in the first step is 3 to 30 seconds. Method for operating a blower ( 12 ) for conveying hydrogen in a fuel cell system according to any one of the preceding claims, characterized in that the switch-off procedure at a temperature at the fan ( 12 ) is started from below 2 ° C. Method for operating a blower ( 12 ) for conveying hydrogen in a fuel cell system according to any one of the preceding claims, characterized in that the switch-off procedure at a temperature at the fan ( 12 ) is stopped from below -5 ° C. Method for operating a blower ( 12 ) for the promotion of hydrogen in a fuel cell system according to one of the preceding claims, characterized in that the switch-off procedure is terminated after a defined time. Method for operating a blower ( 12 ) for conveying hydrogen in a fuel cell system according to one of the preceding claims, characterized in that the shut-off procedure is ended and the electric motor ( 17 ) is no longer energized when the water in the fuel cell system has completely gone into the solid state, Method for operating a blower ( 12 ) for conveying hydrogen in a fuel cell system according to claim 7, characterized in that in the anode gas cycle ( 4 ) a moisture sensor is arranged, which determines the proportion of water in the gas in the anode gas cycle ( 4 ), whereby, when falling below a defined water content in the gas, it is assumed that the water has completely changed to the solid state of matter. Method for operating a blower ( 12 ) for conveying hydrogen in a fuel cell system according to one of claims 1 to 4, characterized in that in a control unit of the electric motor ( 17 ) a map is set in which a time for terminating the shutdown procedure in dependence on a measured outside temperature and a water content in the gas is set at the time of switching off the fuel cell system. Method for operating a blower ( 12 ) for conveying hydrogen in a fuel cell system according to one of claims 1 to 4, characterized in that for starting the electric motor ( 17 ) according to the second step necessary current or time for generating a rotation of the rotor of the electric motor ( 17 ) is measured after the first shutdown according to the first step and falls below a current threshold or a fixed Bestromungszeitraums for generating a movement of the rotor of the electric motor ( 17 ) the shutdown procedure is terminated.

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