DE102017214726A1 - Method for evaluating a coolant flow of a coolant circuit of a fuel cell system, fuel cell system and vehicle - Google Patents

Abstract

A method for evaluating a coolant flow of a cooling circuit (41) of a fuel cell system comprising a fuel cell stack (10), a controller (60) adapted to carry out the method, an anode supply (20), a cathode supply (30), and a refrigeration cycle (41), wherein in the cooling circuit (41) has a coolant pump (42), a thermostatic valve (47) and at the entrance of the fuel cell stack (10) a temperature sensor (49) for detecting the temperature (T _a) and at the output of the fuel cell stack (10 ) has a temperature sensor (50) for detecting the temperature (T _off ), which provides a secure component protection with the least possible use of sensors, it is proposed that the method comprises the following steps:
• Detection of whether the coolant circuit has settled,
Determination of the difference of a coolant pump setpoint speed (control signal) to a value stored in the pilot control characteristic,
• evaluation of the difference,
• Initiate action.
In addition, a fuel cell system (100) and a vehicle are disclosed.

Description

The invention relates to a method for evaluating a coolant flow of a cooling circuit of a fuel cell system, a fuel cell system with a control device that is configured to carry out the method, and a vehicle.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as core component the so-called membrane electrode assembly (MEA) for membrane electrode assembly, which is a microstructure of an ion-conducting (usually proton-conducting) membrane and in each case on both sides of the membrane arranged catalytic electrode (anode and cathode). The latter mostly comprise supported noble metals, in particular platinum. In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane-electrode assembly on the sides of the electrodes facing away from the membrane. As a rule, the fuel cell is formed by a multiplicity of stacked MEAs whose electrical powers add up. Between the individual membrane electrode assemblies bipolar plates (also called flow field plates) are usually arranged, which ensure a supply of the individual cells with the operating media, ie the reactants, and usually also serve the cooling. In addition, the bipolar plates provide an electrically conductive contact to the membrane-electrode assemblies.

During operation of the fuel cell, the fuel (anode operating medium), in particular hydrogen H ₂ or a hydrogen-containing gas mixture, is supplied to the anode via an anode-side open flow field of the bipolar plate, where an electrochemical oxidation of H ₂ to H ⁺ takes place with release of electrons (H ₂ → 2 H ⁺ + 2 e ^- ). Via the electrolyte or the membrane, which separates the reaction spaces gas-tight from each other and electrically isolated, takes place (water-bound or anhydrous) transport of protons H ⁺ from the anode compartment in the cathode compartment. The electrons provided at the anode are supplied to the cathode via an electrical line. The cathode is supplied via a cathode-side open flow field of the bipolar plate oxygen or an oxygen-containing gas mixture (for example, air), so that a reduction of O ₂ to O ^2- takes place under absorption of the electrons (½ O ₂ + 2 e ^- → O ^2- ) , At the same time, the oxygen anions in the cathode compartment react with the protons transported via the membrane to form water (O ^2- + 2 H ⁺ → H ₂ O).

In order to supply a fuel cell stack with its operating media, so the reactants, this has on the one hand an anode supply and on the other hand, a cathode supply. The anode supply includes an anode supply path for supplying an anode operating gas into the anode compartments and an anode exhaust path for discharging an anode exhaust gas from the anode compartments. Similarly, the cathode supply includes a cathode supply path for supplying a cathode operating gas into the cathode compartments and a cathode exhaust path for discharging a cathode exhaust gas from the cathode compartments of the fuel cell stack.

The cathode operating gas is transported to the fuel cell stack via a compressor and provided with the required humidity via a humidification module before it enters the fuel cell stack. The temperature of the compressed cathode operating gas is beyond a thermal limit of the humidification module and the fuel cell stack. Therefore, in order to prevent damage to the humidifier module and the fuel cell stack, it is known to temper the air supplied to the humidification module or the fuel cell stack via a coolant from a cooling circuit of the fuel cell stack. For this purpose, a heat exchanger is used, which is connected downstream of the air compressor.

Degradation of the heat exchanger or an inhibited coolant flow may result in a damaging increase in the temperature of the incoming air at the humidifier module or at the fuel cell stack.

In the coolant supply of a fuel cell system, there are two controlled variables, the coolant inlet temperature and the temperature difference across the fuel cell stack. For this purpose, usually a temperature sensor is provided at the stack entrance and exit.

A fuel cell system typically has a high number of sensors used for media supply control and regulation as well as for diagnostics and safety. However, prior art engine control devices often do not have a sufficiently sized I / O interface. Therefore, an attempt is made to keep the number of required sensors as low as possible, even with regard to costs and complexity.

The invention is based on the object of providing a method for evaluating a coolant flow of a cooling circuit of a fuel cell system, which offers reliable component protection with the least possible use of sensors. Furthermore, a suitable fuel cell system is to be provided.

This object is achieved by a method having the features of claim 1 and a Fuel cell system solved with the features of claim 5.

Advantageous embodiments of the invention are characterized in the subclaims.

Advantageously, by means of the inventive method based on the existing sensors in the cooling circuit, namely a temperature sensor at the input and output of the fuel cell stack and the speed feedback of the coolant pump and the position of the thermostatic valve of the coolant flow, an assessment of the state of the cooling circuit or its components.

It can be advantageously detected by the inventive method, a degradation of components in the coolant flow, so that early measures for component protection, such as the humidifier module can be initiated. In addition, references to problems with components such as heat exchangers, coolant pump and the like are given, so that, for example, a maintenance of the fuel cell system or certain components can be requested by a controller. Thus, components of the refrigeration cycle and the fuel cell system can be protected from over-temperature, which do not have their own temperature monitoring.

For this purpose, a method for evaluating a coolant flow of a cooling circuit of a fuel cell system, which is specified below, is provided according to the invention.

The fuel cell system according to the invention has a fuel cell stack with an anode supply, a cathode supply, a cooling circuit and a controller, which is set up to carry out the method, wherein the cooling circuit comprises a compressor, a coolant pump and a thermostatic valve. Optionally, a cooler and a thermostat are also provided. At the entrance of the fuel cell stack is a temperature sensor for detecting the temperature T _a and at the output of the fuel cell stack is a temperature sensor for detecting the temperature T _off arranged. To control the fuel cell system and to carry out the method according to the invention, a control is provided accordingly.

• • Erkennung, ob der Kühlkreislauf eingeschwungen ist,
• • Ermittlung der Differenz einer Kühlmittelpumpen-Soll-Drehzahl (Ansteuersignal) zu einem in einer Vorsteuerkennlinie hinterlegten Wert,
• • Bewertung der Differenz,
• • Einleiten von Maßnahmen, beispielsweise Ausgabe einer Fehlermeldung und/oder Abschaltung des Brennstoffzellensystems, oder Fortfahren im Normalbetrieb.

The method according to the invention for evaluating a coolant flow of a coolant system of a fuel cell system has the following steps in normal operation:

• • Detection of whether the cooling circuit has settled,
• Determination of the difference of a coolant pump setpoint speed (control signal) to a value stored in a pilot control characteristic,
• • evaluation of the difference,
• • Initiate measures, such as issuing an error message and / or switching off the fuel cell system, or proceeding in normal operation.

According to a preferred embodiment of the method according to the invention, a function for detecting a steady-state coolant circuit is implemented in the controller.

Advantageously, a characteristic related to the specific system can be used via such a function, as described below, so that a degradation of components of the cooling circuit can be precisely determined.

The function is obtained during initial commissioning of the fuel cell system by a pilot control of the coolant pump control / characteristic curve: control signal of the coolant pump as a function of the load point.

This determines on the one hand based on the position of the thermostatic valve, the settling of the operating temperature to the desired value, and on the other hand based on the course of the differential temperature of T _a to T _off taking into account the deviation from setpoint to actual value, the achievement of a stable operating point (both assessed via a tolerance window). This is required to perform a reliable evaluation below.

During initial commissioning, it can be assumed that the components at this time have the status BOL (Begin Of Life) and are not yet subject to degradation so that any subsequent degradation of the components can be reliably detected.

If this has taken place, the difference of the coolant pump setpoint speed (control signal) to the value stored in the pilot control characteristic is determined in the further. Based on an evaluation of this difference, a problem in the coolant flow can be signaled depending on the threshold value.

The above statements relate equally to the method according to the invention and the fuel cell system according to the invention.

Another aspect of the invention relates to a vehicle having such a fuel cell system. This is preferably a Vehicle having an electric motor as a traction motor, with the vehicle alone or in combination with an internal combustion engine is driven.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

• 1 ein Blockschaltbild eines Brennstoffzellensystems gemäß einer bevorzugten Ausgestaltung der Erfindung;
• 2 ein Flussdiagramm des erfindungsgemäßen Verfahrens.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

• 1 a block diagram of a fuel cell system according to a preferred embodiment of the invention;
• 2 a flow chart of the method according to the invention.

1 shows a fuel cell system generally designated 100 according to a preferred embodiment of the present invention. The fuel cell system 100 is part of a not further illustrated vehicle, in particular an electric vehicle having an electric traction motor, by the fuel cell system 100 is supplied with electrical energy.

The fuel cell system 100 comprises as a core component a fuel cell stack 10 having a plurality of arranged in stack form, but not shown here individual cells. To the fuel cell stack 10 to supply with the operating gases, the fuel cell system 100 on the one hand, an anode supply 20 and on the other hand, a cathode supply 30 on.

The anode supply 20 serves to supply an anode operating medium (the fuel), for example hydrogen. For this purpose, an anode supply path connects 21 a fuel storage, not shown, with an anode inlet of the fuel cell stack 10 , The anode supply 20 further includes an anode exhaust path 22 containing the anode exhaust via an anode outlet of the fuel cell stack 10 dissipates.

The cathode supply 30 includes a cathode supply path 31 which is the fuel cell stack 10 supplying an oxygen-containing cathode operating medium, in particular air which is drawn in from the environment. The cathode supply 30 further includes a cathode exhaust path 32 which removes the cathode exhaust gas from the fuel cell stack 10 dissipates and optionally this feeds an exhaust system, not shown.

For conveying and compressing the cathode operating medium is in the cathode supply path 31 a compressor 33 arranged. In the illustrated embodiment, the compressor 33 as a mainly electric motor driven compressor 33 designed, the drive via a with a corresponding power electronics 35 equipped electric motor 34 he follows. The compressor 33 may also be through a in the cathode exhaust path 32 arranged turbine 36 (optionally with variable turbine geometry) are supported by a common shaft (not shown) driven.

The cathode supply 30 may also according to the illustrated embodiment, a wastegate line 37 having the cathode supply line 31 with the cathode exhaust gas line 32 connects, so a bypass of the fuel cell stack 10 represents. The wastegate pipe 37 allows excess air mass flow at the fuel cell stack 10 to pass without the compressor 33 shut down. One in the wastegate pipe 37 arranged adjusting means 38 serves to control the amount of the fuel cell stack 10 immediate cathode operating medium.

The fuel cell system 100 also has a humidifier module 39 on. The humidifier module 39 on the one hand is in the cathode supply path 31 arranged to be flowed through by the cathode operating gas. On the other hand, it is so in the cathode exhaust path 32 arranged so that it can be flowed through by the cathode exhaust gas. The humidifier module 39 typically has a plurality of water vapor permeable membranes formed either flat or in the form of hollow fibers. In this case, one side of the membranes is overflowed by the comparatively dry cathode operating gas (air) and the other side by the comparatively moist cathode exhaust gas (exhaust gas). Driven by the higher partial pressure of water vapor in the cathode exhaust gas, there is a transfer of water vapor across the membrane in the cathode operating gas, which is moistened in this way.

Between the humidifier module 39 and the compressor 33 is in the cathode supply line 31 a heat exchanger 40 provided in a cooling circuit 41 for temperature control of the fuel cell stack 10 is involved. The cooling circuit 41 has a compressor 42 , as a mainly electric motor driven compressor 42 is designed, the drive via a with a corresponding power electronics 43 equipped electric motor 44 he follows. In addition, can be found in the cooling circuit 41 a cooler 45 , one parallel to the radiator 45 arranged thermostat 46 with a thermostatic valve 47 , being for the thermostat 46 a bypass line 48 is provided. At the entrance of the fuel cell stack 10 is a temperature sensor 49 for detecting the temperature T _a and at the exit of the fuel cell stack 10 is a temperature sensor 50 for detecting the temperature T _off arranged.

Parallel to the humidifier module 39 is the heat exchanger 40 downstream of a bypass line 51 provided behind the humidifier module 39 back into the cathode supply line 31 discharges, being in the bypass line 51 and in the cathode supply line 31 behind the humidifier module 39 one, mechanically interacting control means 52 . 53 is provided.

Furthermore, the fuel cell system has an electronic control device 60 on that the operation of the fuel cell system 100 , in particular its anode and cathode supply 20 . 30 and the cooling circuit 41 and controls its components.

All adjusting means 38 . 47 . 52 . 53 of the fuel cell system 100 can be designed as controllable or non-controllable valves or flaps.

Various other details of the anode and cathode supply 20 . 30 and the coolant circuit 41 are in the simplified 1 not shown for reasons of clarity.

The sequence of the method according to the invention, for its execution, the control unit 60 is set up in 2 shown.

The method is based on a pre-control of the control of the coolant pump which is applied as exactly as possible during system initial startup 42 (Characteristic: control signal coolant pump depending on the load point). It can be assumed that the components of the coolant circuit 41 at this time have the condition BOL (Begin Of Life), and are not subject to any degradation yet.

As for the evaluation of the coolant circuit 41 it is necessary to determine a suitable evaluation period becomes a function 61 to detect a steady coolant circuit 41 in the control unit 60 implemented. The function 61 determined on the one hand by the position TV of the thermostatic valve 47 the settling of the operating temperature to a setpoint S , and on the other hand, the course of the differential temperature from temperature T _a and temperature T _off Taking into account the deviation from the setpoint to the actual value. This is evaluated via a tolerance window. This is required to perform a reliable evaluation below.

If this detection has taken place, the difference of the coolant pump setpoint speed (activation signal) will be determined in the further VS to the value stored in the pilot control characteristic SW determined. Based on a rating 62 this difference can be dependent on a threshold value 63 , provided 64 that the cooling circuit 41 settled (function 61 ), a problem in the coolant flow is signaled.

LIST OF REFERENCE NUMBERS

100

The fuel cell system

10

fuel cell stack

20

anode supply

21

Anode supply path

22

Anode exhaust gas path

30

cathode supply

31

Cathode supply path

32

Cathode exhaust path

33

compressor

34

electric motor

35

power electronics

36

turbine

37

Waste gate line

38

actuating means

39

humidifier

40

heat exchangers

41

Cooling circuit

42

Coolant pump

43

power electronics

44

electric motor

45

cooler

46

thermostat

47

thermostatic valve

48

Bypass line

49, 50

temperature sensor

51

Bypass line

52, 53

Control means interacting with each other

60

control device

61

function

62

rating

63

threshold

64

Requirement,

S

setpoint

TV

Position TV of the thermostatic valve

VS

Coolant pump target speed

SW

Value stored in the pilot control characteristic

T _a

temperature

T _off

temperature

Claims (6)

A method of evaluating a coolant flow of a refrigeration cycle (41) of a fuel cell system (100), wherein the fuel cell system (100) comprises a fuel cell stack (10), a controller (60) adapted to perform the method, an anode supply (20), a cathode supply (30) and a cooling circuit (41), wherein in the cooling circuit (41) has a coolant pump (42), a thermostatic valve (47) and at the entrance of the fuel cell stack (10) a temperature sensor (49) for detecting the temperature (T _a) and at the output of the fuel cell stack (10) comprises a temperature sensor (50) for detecting the temperature (T _off ), wherein the following steps are performed: • Detection of whether the cooling circuit (41) is settled, • Determining the difference of a desired coolant pump speed (VS) (control signal) to a value stored in a pilot control characteristic, • Evaluation of the difference, • Initiation of measures or continue in normal operation. Method according to Claim 1 , characterized in that a function (61) for detecting a steady cooling circuit (41) is implemented in the control. Method according to Claim 2 , characterized in that the function (61) is obtained at Systemerstinbetriebnahme by a pilot control of the coolant pump / characteristic: control signal of the coolant pump (42) depending on the load point, the position of the thermostatic valve (47) the transient of the operating temperature to a desired value (S ), the course of the temperature difference of T _and T are _out, and a deviation of the setpoint and actual value used. Method according to one Claims 1 to 3 , characterized in that an error message is issued as a measure and / or a shutdown of the fuel cell system (100). A fuel cell system (100) comprising a fuel cell stack (10) and a controller (60) arranged to perform the method of any one of Claims 1 to 4 wherein the fuel cell stack (10) has an anode supply (20) and a cathode supply (30) and a cooling circuit (41), wherein in the cooling circuit (41) a coolant pump (42), a thermostatic valve (47) and at the input of the fuel cell stack 10th a temperature sensor 49 for detecting the temperature T _and the output of the fuel cell stack 10 has a temperature sensor (50) for detecting the temperature T _of having. Vehicle (200) with a fuel cell system (100) according to Claim 5 ,

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