DE102021207940A1 - Monitoring system and monitoring method for monitoring coolant flow in a fuel cell system - Google Patents

Abstract

The presented invention relates to a monitoring system (100) for monitoring a coolant flow in a fuel cell system (105), the monitoring system (100) comprising at least one control device (101),
wherein the control device (101) is configured to determine a primary energy balance based on primary parameters of a coolant flowing at a first location (103) of the fuel cell system (105), wherein the control device (101) is further configured to determine a secondary energy balance based on secondary parameters to determine a second location (109) of the fuel cell system (105),
wherein the first location (103) and the second location (109) are thermally coupled by at least one heat exchanger (111), and wherein the control device (101) is further configured to compare the primary energy balance with the secondary energy balance, and in the event that if the primary energy balance differs from the secondary energy balance by at least a predetermined threshold value, issue a warning message.

Description

State of the art

In vehicles with fuel cell systems, waste heat produced during the operation of a fuel cell system, or thermal energy released, is generally dissipated in the fuel cell system via a liquid cooling system.

Thermal energy is supplied to a fuel cell system before an optimal operating temperature is reached.

In particular when supplying thermal energy to a fuel cell system, for example in a starting phase, it is necessary to precisely maintain temperature levels and temperature differences within the fuel cell system in order to ensure optimum safety, efficiency and service life of the fuel cell system.

If a temperature difference between two measuring points on a fuel cell stack is exceeded, thermal damage to a membrane can occur, which can lead to hydrogen escaping from the fuel cell stack.

If coolant freezes in a fuel cell system due to an unsuitable glycol content, the fuel cell system can be damaged and, in addition to a loss of coolant, hydrogen can also be released unintentionally.

Coolant used in fuel cell systems has predetermined components, such as antifreeze, corrosion protection and additives to maintain an insulating effect or electrical conductivity. In order for these components to show the specified and technically required properties, a certain concentration of the components, such as water and glycol as the main components, must be maintained. In addition to other material properties, glycol and water have very different specific heat capacities at constant pressure. The specific heat capacity at constant pressure of a water-glycol mixture does not change linearly with the mixing ratio due to various effects, e.g. in a mixing enthalpy, and is temperature-dependent.

Furthermore, in a fuel cell system, additional components such as a charge air cooler or a heat exchanger for the hydrogen supplied are temperature-controlled by a coolant circuit or thermally coupled to other components.

Sensors in the coolant circuit, which, for example, measure a flow rate or a concentration of glycol in the coolant, are usually not installed in vehicles for reasons of space, service life and/or cost, or are disadvantageous, or the fuel cell system has no access to this information.

The composition of a coolant circulating in the coolant circuit can change over time due to incorrect operation, such as filling in the wrong concentration, leaks, decomposition or evaporation, or it can lie outside of the respective specifically specified limits, so that an optimum in terms of safety, efficiency and service life of a corresponding one Fuel cell system can not be guaranteed.

Disclosure of Invention

As part of the presented invention, a monitoring system, a fuel cell system and a monitoring method for monitoring a coolant flow in a fuel cell system are presented with the features of the respective independent patent claims. Further features and details of the invention result from the respective dependent claims, the description and the drawings. Features and details that are described in connection with the monitoring system according to the invention also apply, of course, in connection with the monitoring method according to the invention or the fuel cell system according to the invention and vice versa, so that with regard to the disclosure of the individual aspects of the invention, mutual reference is or can always be made .

The invention presented serves to provide a possibility for monitoring a coolant flow in a fuel cell system. In particular, the invention presented serves to ensure optimum safety, efficiency and service life of a fuel cell system.

Thus, in a first aspect of the presented invention, a monitoring system for monitoring a coolant flow in a fuel cell system is presented. The monitoring system includes at least one control device. The control device is configured to determine a primary energy balance based on primary parameters of a coolant flowing at a first location in the fuel cell system. The control device is also configured to determine a secondary energy balance based on secondary parameters at a second location of the fuel cell system, the first location and the second location are thermally coupled by at least one heat exchanger. The monitoring device is also configured to compare the primary energy balance with the secondary energy balance and to issue a warning if the primary energy balance differs from the secondary energy balance by at least a predetermined threshold value.

In the context of the invention presented, an energy balance is to be understood as a sum of thermal energy inputs at a particular location. For example, an energy balance mathematically maps heat input through a fuel cell stack and heat removal through a coolant circuit at an inlet of the fuel cell stack.

The monitoring system presented is based on a control device that is configured to determine two energy balances independently of one another, namely a primary energy balance, which includes at least one input or output of thermal energy by a coolant circulating in a coolant circuit of a respective fuel cell system, and a secondary energy balance , which is determined independently of an input or output of thermal energy by the coolant.

Since the secondary energy balance is independent of a particular coolant, the secondary energy balance can be used to validate the primary energy balance. In other words, the secondary energy balance depicts in particular a heat input through a fuel cell stack, whereas the primary energy balance depicts a heat discharge through a coolant. Due to the thermal transmission element provided according to the invention, it can be concluded from the secondary energy balance how much thermal energy is or should have been received by the coolant. If the secondary energy balance does not match the primary energy balance or a correspondingly determined transmission coefficient, it can be concluded that there is a fault in the coolant circuit and a corresponding error message can be output.

It can be provided that the control device is further configured to select a fuel cell stack current and an efficiency of the fuel cell stack as secondary parameters in the event that the second location is located on a fuel cell stack of the fuel cell system and in the event that the second location is located on a charge air cooler or a hydrogen heat exchanger of the fuel cell system, to select a medium flow, a specific heat capacity at constant pressure and a temperature difference between a medium flowing at the first location and a temperature of the coolant flowing at the second location as secondary parameters.

A large number of secondary parameters can be used to determine the secondary energy balance, in particular values from a temperature sensor can be used at the second location. Alternatively, for a sensor-free and correspondingly robust design, secondary parameters can be read from a control device of a respective fuel cell system, such as a fuel cell stack flow, a coolant flow and/or a media flow, such as a hydrogen flow.

A secondary energy balance, such as a heat flow Q, can be determined for a second location that is tempered by a media flow based on media flows of, for example, air and water at a respective location, such as an intercooler. The secondary energy balance according to formula (1) corresponds to a primary energy balance at a first location tempered by a coolant flow if the coolant flow is faultless and the first location is thermally coupled to the second location by a heat exchanger. $$\dot{Q}={\dot{m}}_{me\mathrm{i.e}}\times c_{p,me\mathrm{i.e}}\times \mathrm{\Delta }{T}_{me\mathrm{i.e}}={\dot{m}}_{KM}\times c_{p,KM}\times \mathrm{\Delta }{T}_{KM}$$

The heat flow Q transferred by the heat exchanger from a coolant (KM) of the coolant flow or the first location to a media side or the second location or vice versa is dependent on media mass flows ṁ, for specific heat capacity at constant pressure c _p and a Temperature difference ΔT between the first location and the second location.

If the respective outlet temperatures rise or fall while the parameters otherwise remain the same at the heat exchanger provided according to the invention or at the second location, a fault in the mass flow of the coolant or an undesired coolant composition can be inferred.

A stationary heat flow Q̇ _S in a fuel cell stack (S) or at a second location, which is transferred from the fuel cell stack to the coolant (KM) or a first location or vice versa, is dependent on media mass flows ṁ, to the specific heat capacity at constant pressure c _p and a temperature difference ΔT between the first location and the second location. The heat flow Q̇ _S is proportional to a fuel cell stack current I and an efficiency ε _S at the second location and a thermal cal mass of the fuel cell stack and an average temperature difference between the fuel cell stack or the second location and coolant or the first location. $${\dot{Q}}_S=e_S\times l_S={\dot{m}}_{KM}\times c_{p,KM}\times \mathrm{\Delta }{T}_{KM}$$

Provision can furthermore be made for the control device to be configured to take into account a predefined thermal mass of the fuel cell stack when determining the secondary energy balance in the event of a thermally transient situation in the fuel cell system.

In order to achieve reliable monitoring of a coolant even in a thermally transient situation of a respective fuel cell system, such as during a start or a warm-up phase, a respective thermal mass of a fuel cell stack of the fuel cell system can be taken into account mathematically when determining the secondary energy balance. For this purpose, a predetermined value of the thermal mass can be included as a storage term in a formula for determining the secondary balance, as exemplified in formula (3). $${\dot{Q}}_S=e_S+I_S+m_S\times c_{p,S}\times \left({\tilde{T}}_S-{\tilde{T}}_{KM}\right)={\dot{m}}_{KM}\times c_{p,KM}\times \mathrm{\Delta }{T}_{KM}$$

Provision can also be made for the control device to be configured to conclude that the composition of the coolant is incorrect in the event that a temperature difference between a temperature at the first location and a temperature at the second location changes while the secondary energy balance remains the same and the coolant mass flow remains the same and issue a warning message.

To determine whether a temperature difference between a temperature at the first location and a temperature at the second location changes while the secondary energy balance and coolant mass flow remain the same, a change threshold value can be specified, for example, so that if the temperature difference falls below or exceeds the change threshold value, a warning message appears, for example a display and/or speaker and/or communication channel to warn a user and/or ancillary system of improper coolant composition.

Provision can furthermore be made for the control device to be configured to determine the coolant mass flow based on a speed and/or an output of a pump of the fuel cell system for pumping the coolant.

An adjustment of a pump, such as a water pump for pumping coolant, has proven to be a reliable indicator for determining a coolant mass flow independently of the coolant mass flow itself.

Provision can also be made for the control unit to be configured to indicate an incorrect coolant mass flow in the event that a temperature difference between a temperature at the first location and a temperature at the second location changes with the secondary energy balance remaining the same and the specific heat capacity remaining the same at constant pressure close and issue a warning message.

Since if there is a change in a temperature difference between a temperature at the first location and a temperature at the second location with the same secondary energy balance and constant specific heat capacity at constant pressure, only an incorrect coolant mass flow can be the cause of the change in the temperature difference, in such a case the monitoring device can do this be configured to conclude that the coolant mass flow is incorrect and to output a corresponding error message.

Provision can also be made for the control device to be configured to selectively change the coolant flow and, in the event that a difference in the primary energy balance to the secondary energy balance behaves disproportionately to a change in the coolant flow, to conclude that the composition of the coolant is incorrect and a to issue a warning message.

A reaction of a system to be monitored to the change can be detected by a predetermined change in a coolant flow.

Similarly, coolant flow, as an independent variable of a test, can be manipulated to test the response of a dependent variable. In the event that the independent variable, such as a temperature of a component of a fuel cell system, changes differently than expected and, for example, assumes a temperature outside of a specified target range, it can be assumed that heat transfer from the component to the coolant flow will not take place runs optimally and there is an error.

Provision can furthermore be made for the control device to be configured to determine a tertiary energy balance using tertiary parameters at a third location of the fuel cell system, the second location and the third location being thermally coupled in series by the coolant flow, and the recording equipment is further configured to issue a warning if the tertiary parameters deviate from corresponding secondary parameters.

By comparing energy balances from several locations, which are tempered by a coolant flow, with the secondary energy balance, which is independent of the coolant flow, a deviation that only acts locally can be identified. Alternatively, an influence of locally acting variances, such as a particularly high heat input, can be minimized by averaging energy balances from several locations that are tempered by the coolant flow.

In a second aspect, the presented invention relates to a monitoring method for monitoring a coolant flow in a fuel cell system. The monitoring method comprises a first determination step, in which a primary energy balance is determined using primary parameters of a coolant flowing at a first location of the fuel cell system, a second determination step, in which a secondary energy balance is determined using secondary parameters at a second location of the fuel cell system, the first location and the second location are thermally coupled by at least one heat exchanger, a reconciliation step in which the primary energy balance is compared with the secondary energy balance, and an output step in which, if the primary energy balance differs from the secondary energy balance by at least a predetermined threshold value, a warning message is issued.

The monitoring method presented serves in particular to operate the monitoring method presented.

In a third aspect, the presented invention relates to a fuel cell system with a possible embodiment of the presented monitoring system.

Further advantages, features and details of the invention result from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

• 1 eine schematische Darstellung einer möglichen Ausgestaltung des vorgestellten Überwachungssystems,
• 2 eine schematische Darstellung einer möglichen Ausgestaltung des vorgestellten Überwachungsverfahrens,
• 3 eine schematische Darstellung einer möglichen Ausgestaltung des vorgestellten Brennstoffzellensystems.

Show it:

• 1 a schematic representation of a possible embodiment of the presented monitoring system,
• 2 a schematic representation of a possible embodiment of the presented monitoring method,
• 3 a schematic representation of a possible embodiment of the presented fuel cell system.

In 1 a monitoring system 100 is shown. The monitoring system 100 includes a control device 101.

The control device 101 is configured to determine a primary energy balance based on primary parameters of a coolant flowing at a first location 103, here by way of example a charge air cooler of a fuel cell system 105.

The control device 101 is also configured to determine a secondary energy balance based on secondary parameters at a second location 109 of the fuel cell system 105, the first location 103 and the second location 109 being thermally coupled by at least one heat exchanger 111, and
wherein the control device 101 is further configured to compare the primary energy balance with the secondary energy balance, and to issue a warning message in the event that the primary energy balance differs from the secondary energy balance by at least a predetermined threshold value.

Here, for example, the heat exchanger 111 is connected to a coolant circuit operated by a pump 113 .

The second location 109 is, for example, a location that is tempered by media flowing in the fuel cell system 105, in particular a water-air mixture. Correspondingly, a heat input into the fuel cell system 105 can be determined by the secondary energy balance, which normally forms a steady state with the primary energy balance according to formula (1) or formula (2), so that the following applies: $$\dot{Q}={\dot{m}}_{me\mathrm{i.e}}\times c_{p,me\mathrm{i.e}}\times \mathrm{\Delta }{T}_{me\mathrm{i.e}}={\dot{m}}_{KM}\times c_{p,KM}\times \mathrm{\Delta }{T}_{KM}$$

The heat flow Q transferred by the heat exchanger 111 from the coolant (KM) or the first location 103 to a media side or the second location 109 or vice versa is dependent on media mass flows ṁ, for the specific heat capacity at constant pressure cp and a Temperature difference ΔT between the first location 103 and the second location 109.

Alternatively, the secondary energy balance can be determined by a fuel cell stack current I flowing in a fuel cell stack according to formula (2), so that: $${\dot{Q}}_S=e_S\times l_S={\dot{m}}_{KM}\times c_{p,KM}\times \mathrm{\Delta }{T}_{KM}$$

A stationary heat flow Q̇ _Ṡ in a fuel cell stack (S) or the second location 109, which is transferred from the fuel cell stack 107 to the coolant (KM) or the first location 103 or vice versa, is dependent on media mass flows ṁ according to formula (2). , to the specific heat capacity at constant pressure cp and a temperature difference ΔT between the first location 103 and the second location 109. The heat flow Q̇ _Ṡ̇ is proportional to a fuel cell stack current I and an efficiency εS at the second location 109 and a thermal mass of the fuel cell stack 107 and an average temperature difference between the fuel cell stack 107 or the second location 109 and coolant or the first location 103.

In 2 a monitoring method 200 is shown. The monitoring method 200 includes a first determination step 201, in which a primary energy balance is determined using primary parameters of a coolant flowing at a first location of the fuel cell system.

Furthermore, the monitoring method 200 includes a second determination step 203, in which a secondary energy balance is determined using secondary parameters at a second location of the fuel cell system, the first location and the second location being thermally coupled by at least one heat exchanger.

Furthermore, the monitoring method 200 includes a comparison step 205, in which the primary energy balance is compared with the secondary energy balance, and
an output step 207 in which a warning message is output if the primary energy balance differs from the secondary energy balance by at least a predetermined threshold value.

In 3 a fuel cell system 300 is shown. The fuel cell system 300 includes a monitoring system 100 for executing the monitoring method 200.

Claims (10)

Monitoring system (100) for monitoring a coolant flow in a fuel cell system (105), wherein the monitoring system (100) comprises at least one control device (101), wherein the control device (101) is configured to determine a primary energy balance based on primary parameters of a coolant flowing at a first location (103) of the fuel cell system (105), wherein the control device (101) is further configured to determine a secondary energy balance based on secondary parameters at a second location (109) of the fuel cell system (105), wherein the first location (103) and the second location (109) are thermally coupled by at least one heat exchanger (111), and wherein the control device (101) is further configured to compare the primary energy balance with the secondary energy balance, and to issue a warning message in the event that the primary energy balance differs from the secondary energy balance by at least a predetermined threshold value. surveillance system (100) after claim 1 , characterized in that the control device (101) is further configured, in the event that the second location (109) is located on a fuel cell stack (107) of the fuel cell system (100), as secondary parameters, a fuel cell stack current and an efficiency of the fuel cell stack ( 107) and, in the event that the second location (109) is located on a charge air cooler or a hydrogen heat exchanger of the fuel cell system (105), a media flow, a specific heat capacity at constant pressure and a temperature difference at the second location ( 109) flowing medium to a temperature of the coolant flowing at the first location (103). surveillance system claim 1 or 2 , characterized in that the control device (101) is configured to take into account a predetermined thermal mass of the fuel cell stack (107) when determining the secondary energy balance in the case of a thermally transient situation of the fuel cell system (100). Monitoring system (100) according to one of the preceding claims, characterized in that the control device (101) is configured in the event that a temperature difference between a temperature at the first location (103) and a temperature at the second location (109) changes with the same secondary energy balance and constant coolant mass flow, to a fal cal composition of the coolant and issue a warning message. surveillance system (100) after claim 4 , characterized in that the control device (101) is configured to determine the coolant mass flow based on a speed and / or a power of a pump of the fuel cell system (105) for pumping the coolant. Monitoring system (100) according to one of the preceding claims, characterized in that the control device (101) is configured in the event that a temperature difference between a temperature at the first location (103) and a temperature at the second location (109) with the same secondary energy balance and constant specific heat capacity at constant pressure, to conclude that the coolant mass flow is incorrect and to issue a warning message. Monitoring system (100) according to one of the preceding claims, characterized in that the control device (101) is configured to change the coolant flow selectively and in the event that a difference in the primary energy balance to the secondary energy balance behaves disproportionately to a change in the coolant flow, to conclude that the composition of the coolant is incorrect and to issue a warning message. Monitoring system (100) according to one of the preceding claims, characterized in that the control device (101) is configured to determine a tertiary energy balance based on tertiary parameters at a third location of the fuel cell system, the second location (109) and the third location being serially transmitted the coolant flow are thermally coupled, and the control device (101) is further configured to conclude a deviation of the tertiary parameters from corresponding secondary parameters and to issue a warning message. Monitoring method (200) for monitoring a coolant flow in a fuel cell system (105), the monitoring method (200) comprising: a first determination step (201), in which a primary energy balance is determined using primary parameters of a coolant flowing at a first location (103) of the fuel cell system (105), a second determination step (203), in which a secondary energy balance is determined using secondary parameters at a second location (109) of the fuel cell system (105), wherein the first location (103) and the second location (109) are thermally coupled by at least one heat exchanger (111), a reconciliation step (205) in which the primary energy balance is reconciled with the secondary energy balance, and an output step (207) in which a warning message is output if the primary energy balance differs from the secondary energy balance by at least a predetermined threshold value. Fuel cell system (300) with a monitoring system (200) according to one of Claims 1 until 8th .

Images