Method for operating a fuel cell system, fuel cell system and program product

Abstract

The invention presented relates to a method (100) for operating a fuel cell system (200), the procedure (100) comprises: - Determining (101) a mass flow rate, temperature and glycol concentration of coolant flowing through the fuel cell system (200) based on signals obtained by at least one sensor (215) for measuring the coolant, - Determining (103) a state of the fuel cell system (200) based on the determined signals, - Output (105) a warning message in case the state of the fuel cell system (200) deviates from a specified state.

Description

[0001] The presented invention relates to a method for operating a fuel cell system, a fuel cell system and a program product according to the appended claims. State of the art

[0002] Polymer electrolyte membrane (PEM) fuel cell systems convert hydrogen using oxygen to electrical energy, generating waste heat and water.

[0003] Converting hydrogen means that hydrogen molecules are consumed or removed on the anode side.

[0004] A PEM fuel cell consists of an anode supplied with hydrogen, a cathode supplied with air, and a polymer electrolyte membrane placed in between.

[0005] Several individual fuel cells are stacked together to increase the generated electrical voltage. Within a fuel cell stack, or "stack," are supply channels that supply the individual cells with hydrogen and air, and transport the depleted moist air and the depleted anode exhaust gas away.

[0006] In vehicles with PEM fuel cells, the waste heat generated in the fuel cell system is usually dissipated via liquid cooling or heat is added before the optimal operating temperature is reached.

[0007] It is important to precisely maintain temperature levels and temperature differences across the fuel cell stack in order to achieve optimum safety, efficiency and service life.

[0008] If a temperature difference across the fuel cell stack is exceeded, thermal damage to the membrane can occur, which in the worst case can lead to the release of hydrogen.

[0009] If coolant freezes due to an inappropriate glycol content, components in the cooling system can be damaged and, as a result, not only coolant loss but also hydrogen can be released unintentionally.

[0010] Typically, coolant used in fuel cell systems has certain properties, such as antifreeze, corrosion protection, and additives to maintain insulation or electrical conductivity.

[0011] In order to maintain these properties during operation of a fuel cell system, a certain concentration of substances such as water and glycol as the main components must be maintained.

[0012] Among other material properties, glycol and water have very different specific heat capacities at constant pressure. Due to various effects, such as the enthalpy of mixing, the specific heat capacity (at constant pressure) of the water-glycol mixture does not change linearly with the mixing ratio and is temperature-dependent.

[0013] The composition of the coolant may be outside the required limits due to incorrect operation, such as filling with the wrong concentration or incorrect substances, leaks, decomposition or evaporation over the course of operation.

[0014] If temperature sensors are used to determine a medium temperature, depending on the design, there can be reaction times of up to one minute until the sensor measures the medium temperature with sufficient accuracy. Disclosure of the invention

[0015] Within the scope of the invention presented, a method for operating a fuel cell system, a fuel cell system, and a program product are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the fuel cell system according to the invention or the program product presented, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0016] The invention presented serves in particular to provide a durable and safe fuel cell system.

[0017] Thus, according to a first aspect of the invention presented, a method for operating a fuel cell system is presented.

[0018] The presented method comprises determining a mass flow, a temperature and a glycol concentration of coolant flowing through the fuel cell system based on signals determined by at least one sensor for measuring the coolant, determining a state of the fuel cell system based on the determined signals and outputting a warning message in the event that the determined state of the fuel cell system deviates from a predetermined state.

[0019] In the context of the invention presented, issuing a warning message refers to a process in which a warning message is transferred to a memory and / or output on an output unit. A warning message can include information about a detected condition and / or respective measured values. In particular, a warning message can inform a user about an internal condition of the fuel cell system and recommend action to the user, such as a visit to a workshop. Optionally, a warning message can include control commands for controlling the fuel cell system.

[0020] The presented method is based on a signal provided by a single sensor for measuring the coolant flow through a fuel cell system or fuel cell stack. This sensor can be, for example, an ultrasonic sensor.

[0021] Based on signals detected by the sensor, a mass flow, a temperature, and a glycol concentration or coolant composition are determined. For this purpose, an assignment scheme can be specified, for example, that assigns a value for mass flow, temperature, and glycol concentration, and possibly also water concentration, to the respective measured values ​​detected by the sensor.

[0022] Based on the mass flow, the temperature, and the glycol concentration of the coolant, the condition of the fuel cell system can be determined, for example, by calculating a heat balance of the fuel cell system. In particular, by regularly determining a key figure quantifying the condition of the fuel cell system, a history of the condition of the fuel cell system can be determined. Accordingly, if the condition or key figure deviates from a predetermined condition, which is quantified, for example, by a threshold value, a warning message can be issued.

[0023] Alternatively or in addition to issuing the warning message, a coolant flow with which the coolant flows through the fuel cell system and, as a result, a temperature of the fuel cell system can be regulated based on the determined state of the fuel cell system.

[0024] It may be provided that the glycol concentration is determined based on a spectrogram of the signals detected by the sensor.

[0025] Using a spectrogram of each signal measured by the sensor, specific components in the coolant can be identified and their concentrations quickly and reliably determined. The spectrogram can then be used to determine the coolant's composition.

[0026] It may further be provided that the energy efficiency of the fuel cell system is determined based on the signals detected by the sensor.

[0027] The energy efficiency of the fuel cell system can be determined using a quotient of an energy flow of hydrogen converted by the fuel cell system and a waste heat flow of the fuel cell system in the coolant.

[0028] It may further be provided that a key figure quantifying a service life of the fuel cell system is determined based on a ratio of the energy efficiency of the fuel cell system to a waste heat flow of the fuel cell system.

[0029] Since the higher the mileage of a fuel cell system, the higher its heat output at the same net power output (the efficiency decreases with increasing age), the service life of the fuel cell system can be precisely determined based on a ratio of the energy efficiency of the fuel cell system to a waste heat flow of the fuel cell system.

[0030] It can further be provided that the waste heat flow is calculated as the product of the mass flow, the temperature and a heat capacity of the coolant at constant pressure, wherein the heat capacity of the coolant at constant pressure is calculated based on the glycol concentration in the coolant.

[0031] The heat capacity of the coolant can be calculated using formula (1): Qab⋅=m˙KM∗Cp,KM∗ΔTKM

[0032] Q αb for a waste heat stream, ṁ KM for a mass flow of the coolant, C p,KM for a heat capacity of the coolant at constant pressure, and ΔT KM for a temperature difference of the coolant. The temperature difference is calculated from the difference between the measured temperatures of the coolant at the fuel cell stack outlet and the fuel cell stack inlet.

[0033] It can further be provided that the glycol concentration is determined based on a speed of sound of the coolant, wherein the speed of sound of the coolant is determined based on the signals detected by the sensor.

[0034] The speed of sound of a medium can be determined particularly quickly, so that the determination of the glycol concentration based on the speed of sound of the coolant can also be carried out particularly quickly.

[0035] Conversely, it can be assumed that during normal operation, the glycol concentration does not change so rapidly over time. If, assuming a constant glycol concentration, the measured speed of sound changes within a measurement interval of, for example, 0.1 s to 10 s, it can be assumed that the coolant temperature has changed. The spectrogram therefore changes much faster than, for example, a temperature sensor can measure. This information can be incorporated into the temperature control of the fuel cell system to make it faster and more robust.

[0036] Alternatively or additionally, the signal can be used to detect a thermal fault in the fuel cell stack. It is important to attach the sensor to the coolant outlet of the fuel cell stack.

[0037] It can further be provided that a coolant flow with which the coolant flows through the fuel cell system is regulated depending on the signals determined by the sensor.

[0038] Since the signals determined by the sensor according to the invention provide particularly fast and particularly precise information about the heat balance of the fuel cell system, the coolant flow with which the coolant flows through the fuel cell system can be adjusted particularly quickly and precisely based on the signals.

[0039] It can further be provided that the signals detected by the sensor are entered as input signals into a data model in order to determine at least the glycol concentration.

[0040] Using a data model that simulates, for example, the behavior of the fuel cell system, the glycol concentration can be determined dynamically and continuously depending on other parameters, such as the temperature of the fuel cell system.

[0041] According to a second aspect, the presented invention relates to a fuel cell system for converting energy.

[0042] The presented fuel cell system comprises a fuel cell stack through which a coolant flow flows, a single sensor for measuring the coolant flow and a computing unit, wherein the computing unit is configured to carry out a possible embodiment of the presented method.

[0043] The presented method is used in particular for the operation of the presented fuel cell system.

[0044] It can be provided that the sensor is an ultrasonic sensor which is configured to emit an ultrasonic signal orthogonally or at an angle between 0° and 30° in or against a flow direction of the coolant and to receive the ultrasonic signal in a receiving module.

[0045] An ultrasonic sensor has proven to be a fast and robust sensor for implementing the proposed method. In particular, a single ultrasonic sensor can be used to determine a mass flow, temperature, and concentration of components of a coolant. For this purpose, an ultrasonic echo or signal detected by the ultrasonic sensor can be subjected to spectral analysis to evaluate, for example, the signal strength at frequencies characteristic of specific components, particularly glycol.

[0046] The sensor can, for example, be arranged at a coolant outlet from the fuel cell stack of the fuel cell system presented.

[0047] By arranging the sensor at an angle between 0° and 30° in or against a flow direction of the coolant, so that, for example, a receiver is arranged offset between 0° and 30° to a sound source of the sensor, a movement or volume flow of the coolant can be detected particularly well.

[0048] According to a third aspect, the presented invention relates to a program product. The presented program product comprises program code means that configure a computing unit to carry out a possible embodiment of the presented method when executed on the computing unit.

[0049] Advantages that are described in detail for the method for operating a fuel cell system according to the first aspect of the invention apply equally to the fuel cell system for converting energy according to the second aspect of the invention and the program product according to the third aspect of the invention.

[0050] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

[0051] They show: Fig. 1 a possible design of the presented procedure, and Fig. 2 a possible design of the presented fuel cell system.

[0052] In Fig. 1 shows a method 100 for operating a fuel cell system.

[0053] The method 100 comprises a determination step 101 in which a mass flow, a temperature and a composition, in particular a glycol concentration of coolant flowing through the fuel cell system are determined on the basis of signals determined by at least one sensor for measuring the coolant.

[0054] Furthermore, the method 100 comprises a determination step 103 in which a state of the fuel cell system is determined based on the signals determined in the determination step 101, and an output step 105 in which a warning message is output in the event that the state of the fuel cell system deviates from a predetermined state.

[0055] To determine the state in the determination step 103, the determination step 101 can be carried out repeatedly, for example at regular time intervals, so that currently determined values ​​of mass flow, temperature and composition of the coolant can be compared with historical values ​​in order to detect a change in the fuel cell system, ie, a change in a state of the fuel cell system.

[0056] For example, output step 105 can be initialized in the event that a deviation between currently determined values ​​of mass flow, temperature, and coolant composition and historical values ​​is greater than a diagnostic threshold. The diagnostic threshold can be predefined or determined dynamically, e.g., based on a variance of the historical values.

[0057] In Fig.Figure 2 illustrates a fuel cell system 200 for converting energy. The fuel cell system 200 includes a fuel cell stack 201 with an anode inlet 203, an anode outlet 205, a cathode inlet 207, a cathode outlet 209, a coolant inlet 211, and a coolant outlet 213.

[0058] Furthermore, the fuel cell system 200 comprises an ultrasonic sensor 215 with a sound source 217 and a receiver 219, which measure a coolant flow flowing through a coolant line 221.

[0059] The fuel cell system 200 further includes a computing unit 223. The computing unit 223 is configured to determine a mass flow, a temperature, and a glycol concentration of coolant flowing through the fuel cell system based on signals detected by the ultrasonic sensor 215, to determine a state of the fuel cell system 200 based on the detected signals, and to issue a warning message if the state of the fuel cell system deviates from a predetermined state. Optionally, the temperature of the coolant can be measured using a temperature sensor 225. Alternatively, the temperature of the coolant can be calculated using a mathematical model, so that only the ultrasonic sensor 215 is used as a sensor for determining signals describing the coolant.

[0060] For example, the computing unit 223 can execute a mathematical model that mathematically simulates the fuel cell system 200 and receives as input values ​​the respective values ​​determined by the ultrasonic sensor 215.

[0061] Accordingly, the mathematical model can continuously and dynamically determine or monitor the state of the fuel cell system 200.

Claims

[1] A method (100) for operating a fuel cell system (200), the method (100) comprising: - determining (101) a mass flow, a temperature and a glycol concentration of coolant flowing through the fuel cell system (200) based on signals determined by at least one sensor (215) for measuring the coolant, - determining (103) a state of the fuel cell system (200) based on the determined signals, - Outputting (105) a warning message in the event that the state of the fuel cell system (200) deviates from a predetermined state. [2] Method (100) according to claim 1, characterized by that the glycol concentration is determined based on a spectrogram of the signals detected by the at least one sensor (215). [3] Method (100) according to claim 1 or 2, characterized bythat an energy efficiency of the fuel cell system (200) is determined on the basis of the signals determined by the at least one sensor (215). [4] Method (100) according to claim 3, characterized by that the energy efficiency is determined based on a quotient of an energy flow of hydrogen converted by the fuel cell system (200) and a waste heat flow of the fuel cell system (200) in the coolant. [5] Method (100) according to claim 3 or 4, characterized by , that a key figure which quantifies a service life of the fuel cell system (200) is determined based on a ratio of the energy efficiency of the fuel cell system (200) to a waste heat flow of the fuel cell system (200). [6] Method (100) according to claim 4 or 5, characterized by , that the waste heat flow is calculated as the product of the mass flow, the temperature and a heat capacity of the coolant at constant pressure, where the heat capacity of the coolant at constant pressure is calculated based on the glycol concentration in the coolant. [7] Method (100) according to one of the preceding claims, characterized by , that the glycol concentration is determined based on the speed of sound of the coolant, wherein the speed of sound of the coolant is determined based on the signals detected by the at least one sensor (215). [8] Method (100) according to one of the preceding claims, characterized by that a coolant flow with which the coolant flows through the fuel cell system (200) is regulated as a function of the signals determined by the at least one sensor (215). [9] Method (100) according to one of the preceding claims, characterized bythat the signals determined by the at least one sensor (215) are entered as input signals into a data model in order to determine at least the glycol concentration. [10] Method (100) according to one of the preceding claims, characterized by that the warning message includes control commands that switch the fuel cell system (200) into emergency operation. [11] Fuel cell system (200) for converting energy, characterized by that the fuel cell system (200) comprises: - a fuel cell stack (201) through which a coolant flow flows, - at least one sensor (215) for measuring the coolant flow, - a computing unit (223), wherein the computing unit (223) is configured to execute a method (100) according to one of claims 1 to 10. [12] Fuel cell system (200) according to claim 11, characterized byin that the at least one sensor (215) is an ultrasonic sensor which is configured to emit an ultrasonic signal orthogonally or at an angle between 0° and 30° in or against a flow direction of the coolant and to receive the ultrasonic signal in a receiving module. [13] A program product, wherein the program product comprises program code means that configure a computing unit to perform a method (100) according to any one of claims 1 to 10 when executed on the computing unit.

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