WO2019102053A2 - System for monitoring and controlling fuel cells - Google Patents

System for monitoring and controlling fuel cells Download PDF

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Publication number
WO2019102053A2
WO2019102053A2 PCT/ES2018/070748 ES2018070748W WO2019102053A2 WO 2019102053 A2 WO2019102053 A2 WO 2019102053A2 ES 2018070748 W ES2018070748 W ES 2018070748W WO 2019102053 A2 WO2019102053 A2 WO 2019102053A2
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WIPO (PCT)
Prior art keywords
stack
module
cells
cell
current
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PCT/ES2018/070748
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Spanish (es)
French (fr)
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WO2019102053A3 (en
Inventor
Francisca SEGURA MANZANO
José Manuel ANDUJAR MARQUEZ
Ainhoa DE LAS HERAS JIMENEZ
Francisco José VIVAS FERNANDEZ
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Universidad De Huelva
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Publication of WO2019102053A2 publication Critical patent/WO2019102053A2/en
Publication of WO2019102053A3 publication Critical patent/WO2019102053A3/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the invention relates to embedded systems for the monitoring of cell voltage, current and temperature of a PEM-type fuel cell stack, including the detection of deterioration of the cells.
  • the degradation of a fuel cell can be due to different physical-chemical phenomena that result in loss of performance at its point of work. This decrease in performance is reflected in voltage drops along its polarization curve, due to the increase in the so-called activation, ohmic and concentration losses.
  • multiplexed systems are often vulnerable to any electrical failure, which often leads to damage to the electronics of several components.
  • known solutions do not turn out to be fast enough, so it is necessary to use several modules for applications that require a higher operating voltage.
  • stack refers to the set of stacked cells that make up the fuel cell.
  • the terms stack and fuel cell are used to refer to the set of cells in the first case and, in the second case, to the complete system integrated by the stack together with the BoP (Balance of Plant ).
  • the plant balance or BoP includes auxiliary elements, such as valves, sensors, ventilator, etc., which the stack needs in order for the fuel cell system to function correctly.
  • the present invention is conceived to respond to the limitations observed in the state of the art.
  • One of the purposes is to give a complete solution of low cost and easy use that can be used in any sector that involves the use of fuel cells.
  • a preferably embedded system that allows the monitoring of voltage of each cell, as well as the current and temperature of the stack, for a stack of "n" cells, where "n” is an integer number, capable of generating a maximum current of "x" amps. Therefore, it is applicable for a stack of any number of cells and current, that is, for a stack of any power.
  • the stack is the most important and expensive part of a fuel cell.
  • the power that is able to supply a fuel cell is the product of the voltage and current that is capable of supplying its stack.
  • the stack voltage is the sum of the individual voltages of the cells that compose it. It is important to know their values, as this can determine if the operation of the fuel cell is appropriate.
  • the present proposal allows the real-time intercomparison of the polarization point of the fuel cell with respect to the theoretical one, as well as the representation of auxiliary variables such as current, power or temperature, essential for a degradation and life time analysis.
  • the object of the present invention is a characterized fuel cell monitoring and control system that includes an acquisition module comprising a multiplexer whose sample rate depends on the number of cells in the stack; a temperature sensor; a current sensor; a wiring connection module for individually connecting each of the fuel cells to the multiplexer module that multiplexes the individual signals received from each cell; a processing module that includes an analog-digital converter and a microcontroller. This processing module can analyze the polarization point.
  • the processing module stores the theoretical curve and to make a comparison with the actual (measured) curve of the fuel cell.
  • system further includes a display module for representing an interface when a management software is executed in the processing module.
  • the interface represents in real time at least the values of cell voltage at the same time as the current, temperature and power of the stack.
  • connection and processing modules are embedded and implemented in a PCB.
  • the system comprises a digital output port for connection with another electronic device.
  • the system comprises a galvanic isolation module.
  • the system comprises a mechanical clamping module comprising a plurality of retractable probes.
  • the acquisition electronics the pin clamping mechanism, the measuring unit with sensors capable of identifying the real state of the system, and the real-time monitoring capacity of the cell voltage , of the polarization curve and of the power. All this allows to make a complete analysis of the current performance of the system, together with an estimate of its degradation.
  • the most common cell monitoring systems are high cost solutions that are limited to the measurement of fuel cell voltage, ignoring other parameters as important as the current or temperature, fundamental to describe the polarization curve of the stack. In some cases, these systems act only as a generator of alarms at the moment when certain levels of minimum operating voltage are exceeded, so they do not allow the study of degradation, its purpose being exclusively control and safety in the operation of the fuel cell
  • a PCB has been developed which also includes its own signal acquisition module, a fastening module to the fuel cell stack together with the electrical contact, no additional wiring being necessary to each cell of the stack. This guarantees maximum convenience when connecting and reliability during the signal acquisition process. Low cost monitoring hardware that has a multiplexed configuration with isolation is implemented.
  • FIG. 1 Diagram of the assembly on stack of fuel cells.
  • FIG. 2 Porta PCB detail anchored to the stack.
  • FIG. 3 Probe array and acquisition electronics.
  • FIG. 4 Cell-feeler connection detail.
  • FIG. 5 Electronic diagram of the acquisition, processing and control hardware.
  • FIG. 6 Leakage current attenuation effect.
  • FIG. 7 Failure effect in switching with subsequent gain stage.
  • FIG. 8 Failure effect in switching with pre-gain stage.
  • FIG. 9 Graphic interface image representing a bar diagram.
  • FIG. 10 Image of the graphic interface with the temporal history of variables.
  • FIG. 11 Graphic interface image to represent the polarization curve and stack power
  • FIG. 12 Schematic of normal operation of a fuel cell.
  • FIG. 13 Effect of corrosion current and fuel starvation.
  • FIG. 14 Air / Air Region at startup.
  • FIG. 15 Air / Air region with leaking fuel in the membrane.
  • FIG. 16 Air / Air Region with leaks in the hydrogen exhaust line not consumed.
  • FIG. 17 Air / Air Region with leaks in the hydrogen supply line.
  • the hardware component has been designed with the aim of guaranteeing a low cost solution with sufficient precision and security features for the objective pursued.
  • the present system reduces the necessary hardware, mechanically coupling directly on the stack of the fuel cell and feeding directly from a USB port.
  • the software component allows real-time measurements of the voltage of each cell, simultaneously with the current and temperature of the stack, allowing at all times to associate the causes of possible stack degradation (observable mainly by the value of the voltage of each cell) and the point of operation, according to the polarization curve of the monitored fuel cell.
  • the software shows in real time the difference of the polarization point of the complete stack with respect to the initial state, by which it allows to determine the total degradation of the same in all the areas of the polarization curve of the fuel cell, and therefore discover phenomena associated with the different losses.
  • the measurement of the cell voltage will only allow the analysis of voltage differences between cells, but it will not be possible to determine which type of losses may be occurring, since it is necessary to relate the current polarization point (V, I) with respect to the original, being able to determine if the degradation is caused by activation, ohmic or concentration losses.
  • the operating temperature of the stack will allow to determine losses associated with high or low operating temperatures of the stack, as well as to determine possible cooling problems due to different causes, high intensities, stack contamination, humidification problems and product extraction. , etc.
  • FIG. 1 shows an example of the final assembly of the acquisition system 1 on the stack of fuel cell 2 thanks to the PCB 3 holder designed for such use.
  • the auxiliary current sensors 4 and temperature of the stack 5 are represented and located, necessary for the characterization of the operating point thereof. Additionally, electrical auxiliary connections 6 and hydrogen inlet and outlet 7 are shown.
  • FIG. 2 the coupling system or PCB holder 3 is shown in detail on the acquisition module 1, as well as the connection on the stack of fuel cell 2.
  • the securing system to the acquisition module is carried out through two through holes 8 in which the PCB holder is anchored thanks to the use of screw, washer and tightening thread.
  • the system has an oblong hole 9 which allows a longitudinal movement of the threaded rod 10 of stack 2 of fuel cells, in such a way that it allows adjusting the correct distance between the acquisition and control unit and the stack of fuel cells, ensuring a correct electrical contact thanks to the retractable probes 11 (see Figure 3).
  • the correct clamping is guaranteed thanks to the washer and the tightening thread.
  • FIG. 3 shows in more detail the acquisition module, in which the distribution of the retractable stylus comb 11 can be seen with respect to the rest of the acquisition and control circuit 12.
  • FIG. 4 shows an example of embodiment where a set of cells 14 are seen that are wired to resistive dividers 15 that decrease the voltage between their ends so that they can be coupled to a multiplexing module 16.
  • the multiplexing is performed periodically and allows increase the number of acquisition channels without increasing the number of analog-digital converters 21.
  • a discharging stage 17 is used which eliminates the effect of parasitic capacitances in the system, providing fast and safe switching .
  • the output of said stage is connected to a low pass filter 18 which has been designed to eliminate high frequency components and thereby reduce the electromagnetic noise by external interferences.
  • the instrumentation amplifier 19 takes the filtered signal and allows on the one hand to obtain the differential signal corresponding to the voltage of a specific cell, and on the other to eliminate the common mode noise of the input signal, thus increasing the accuracy of the measurement .
  • an insulation amplifier 20 is used, which allows galvanically isolating the input and output of the circuit, obtaining an electrical isolation that allows to preserve the control electronics and successive stages, of possible failures in the high voltage zone.
  • the isolated output is acquired through a 24-bit analog-digital converter 21 with sigma-delta technology of high precision and low cost.
  • the digitized output is processed at all times by the microcontroller 22 which represents the control unit and has the additional functions of external communication with the PC and management software via a USB connection 23, as well as the control of the multiplexer sequence 16 through an optocoupling stage 24, which allows to maintain the electrical isolation between the high voltage zone and the control and processing zone. Additionally, the microcontroller is responsible for reading the auxiliary current and voltage sensors 25, which are treated by a preconditioning stage 26.
  • FIG. 6 shows a configuration different from the one proposed and in this, the resistive divider 15 is located behind the multiplexer 16. In it, the negative effect of the leakage current of the multiplexers on the resistive dividers can be seen.
  • the leakage current of all the inactive multiplexers will generate a parasitic voltage in the resistive divider, which, being of high ohmic values, will cause a deviation in the measurement, resulting in erroneous measurements, which can not be detected by the low pass filter 18 or the instrumentation amplifier 19, since it is of differential origin.
  • FIG. 7 shows the behavior against the security of the previous system against possible failures in the multiplexing sequence 16.
  • the processing module can execute management software so that a display unit can represent in real time all the electrical variables of interest, cell voltage and current of the stack, as well as its temperature.
  • the management software generates an interface with three different windows (FIG 9, FIG 10 and FIG 11) and a general control panel 27 in which the communication port is configured and there are the options of saved from the system. Additionally, there is a warning panel 28 in which the status of three LEDs are displayed, which are programmed by the user and activated when some of the cells in the stack go beyond the marked safety limits, indicating the cell number and the event that originated it.
  • FIG. 9 shows an example of the monitoring window 29 in which the cell voltages of the entire stack are represented in a bar diagram, and therefore allows to see in a very fast way significant differences between two or more fuel cells.
  • the stack temperature is represented in an indicator created for that purpose 30.
  • FIG. 10 shows the second window in which the representation of the time evolution of all the monitored cells 31 is allowed and therefore allows a dynamic study before the different load profiles used.
  • the polarization point of the fuel cell 32 is represented in real time, formed by voltage and current; as well as stack power 33 referred to the theoretical curves provided by the manufacturer, in such a way that it allows us to identify which polarization zone has suffered the most degradation, and therefore to identify the nature of the degradation (activation, ohmic or concentration losses).
  • FIG. 12 shows the diagram of the normal operation of a fuel cell: the hydrogen molecules 34 that enter the anode 35 decompose in H + 36 ions and electrons 37 in the presence of a catalyst 38.
  • the H + ions cross the membrane 39 and the electrons pass through the outer circuit.
  • the oxygen molecules 41 coming from the outside air itself
  • the cathode 40 the oxygen molecules 41 (coming from the outside air itself) recombine with the H + ions and the electrons to form water 42, which constitutes the "residue" of the cell.
  • the cells are assembled next to each other in series, until the required stack is formed.
  • the stack thus constructed can function as a fuel cell (a system powered by hydrogen generates electrical power)
  • the BoP Bose of Plant
  • the BoP Bose of Plant
  • the oxygenation / cooling subsystem integrated by at least one fan / extractor for cooling and stoichiometry adjustment
  • the electrical circuitry which allows to feed to an electrical load
  • the performance of the fuel cell can be affected by various causes, directly influencing its electrical performance (generates less power than expected). It is then decisive to have a system capable of monitoring the status of each cell, in order to analyze its possible degradation and, ultimately, its deterioration. This will make it possible, selectively, to carry out the removal of the damaged cells and, if possible, their replacement by cells in good condition, which will allow recovering the initial performance (power) of the stack. That said, the two main causes of cell deterioration that can also be detected by voltage loss are the corrosion of the coal that is used to deposit the catalyst and the starvation of fuel.
  • the first is due to the fact that in a PEM fuel cell, in the Electrolyte-Membrane-Electrolyte structure, the catalyst that favors the dissociation of the Hydrogen is suspended in a thin layer of carbon that covers the membrane on both sides.
  • this layer of carbon disappears (as a consequence of the reaction of it with water to form C02, H + ions and electrons)
  • the hydrogen-oxygen interface hereinafter hydrogen-air, since the oxygen needed by the fuel cell to reacting, proceeds directly from the surrounding air
  • oxygen-oxygen hereinafter air-air
  • FIGs. 14-17 show some situations in which this adverse situation can occur that causes the deterioration of the stack of a fuel cell and, therefore, its deterioration.
  • FIG. 14 illustrates the case of a battery that has not been running for a certain time (more than 30 minutes), where the anode is filled with air 46. Then, at the moment of starting (activation), when the supplies hydrogen, initially an Air / Air region is generated, with the consequent adverse consequences.
  • FIG. 15 shows another situation in which regions can be generated Air / Air is in the shutdown. After switching off, the consumption of hydrogen at the anode reduces the pressure of the latter below atmospheric pressure, and if there is fuel leakage in the membrane 47, the air enters the anode to occupy the gap released by the hydrogen leak . In this case, the voltage of the damaged cell does not return to its normal value in open circuit, but decreases ostensibly.
  • FIG. 16 illustrates a leak in the unconsumed hydrogen 48 outlet line which again has an effect on the corrosion current.
  • An indicator that there are leaks in the purge valve, is that the voltage of any of the cells in open circuit is decreased until almost annulled.
  • FIG. 17 shows that, if there are leaks in the hydrogen supply line, the Air / Air interface that should have been in a normal shutdown state, is replaced by the H2 / Air 49 interface.
  • the cell voltage will never reach be 0 V (cell voltage if the interface is Air / Air, which means that there are no leaks in the supply valve) having elapsed more than 30 minutes after the battery was turned off.
  • FIG. 13 represents another effect of deterioration (in addition to that of the corrosion current already mentioned), relative to starvation or lack of fuel.
  • This lack of fuel causes an effect similar to the corrosion current on a fuel cell.
  • the carbon in the catalytic layer When there is not enough hydrogen to react with, it is replaced by the carbon in the catalytic layer, so that the carbon reacts with the water to generate protons and electrons, in order to supply the demand of the load. In this situation, the cell voltage can fall below 0 V, reaching an irreversible reverse situation that will mean the definitive disqualification of the same.
  • the cell voltage monitoring systems must comply with minimum restrictions to guarantee an accurate reading. As a general rule, it is estimated that the systems should be able to measure with a minimum sampling frequency of 1-4 Hz, and with an accuracy of ⁇ 100 mV to detect important faults and ⁇ 10 mV for analysis of cell degradation.
  • the first of the options is associated with a decrease in the total accuracy of the system by increasing the sampling frequency, while the second exponentially increases the costs of the acquisition system.

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Abstract

The invention relates to a system for monitoring and controlling fuel cells, which comprises an acquisition module (1) that comprises a multiplexer (16) having a sampling frequency that depends on the number of cells (14) in a stack (2); a temperature sensor (5); a current sensor (4); a module for connecting by means of wires, for connecting individually each fuel cell to the multiplexer module that multiplexes the individual signals received from each cell; and a processing module comprising at least one digital-analogue converter (21) and a microcontroller (22). The processing module allows the polarisation point to be analysed.

Description

SISTEMA DE SUPERVISIÓN Y CONTROL DE CELDAS DE COMBUSTIBLE  SYSTEM OF SUPERVISION AND CONTROL OF CELLS OF FUEL
DESCRIPCIÓN DESCRIPTION
Campo técnico de la invención TECHNICAL FIELD OF THE INVENTION
La invención se relaciona con los sistemas embebidos para la monitorización de tensión de celdas, corriente y temperatura de un stack de pila de combustible tipo PEM, incluyendo la detección de deterioro de las celdas. The invention relates to embedded systems for the monitoring of cell voltage, current and temperature of a PEM-type fuel cell stack, including the detection of deterioration of the cells.
Antecedentes de la invención o Estado de la Técnica Background of the invention or state of the art
Debido a la imperiosa necesidad de encontrar nuevos modelos energéticos sostenibles desde el punto de económico y medioambiental, el uso del hidrógeno y asociado a él, el uso de pilas de combustible, se presenta como una solución de futuro inmediato.  Due to the urgent need to find new sustainable energy models from the point of economic and environmental, the use of hydrogen and associated with it, the use of fuel cells, is presented as a solution for the immediate future.
Entre las bondades de las pilas de combustible y en concreto del tipo PEM (“Proton Exchange Membrame” o membrana de intercambio de protones), se pueden destacar el gran rendimiento de operación, la rápida respuesta del sistema y la nula emisión de gases contaminantes. Sin embargo, sus dos debilidades quizás más importantes son el elevado coste tecnológico y la gran dependencia de su durabilidad respecto a las condiciones de operación. Existe, por tanto, un interés creciente para aumentar la vida útil de las pilas de combustible. Among the benefits of fuel cells and specifically of the PEM type ("Proton Exchange Membrame" or proton exchange membrane), we can highlight the great performance of operation, the rapid response of the system and the zero emission of polluting gases. However, its two most important weaknesses are the high technological cost and the great dependence on its durability with respect to operating conditions. There is, therefore, a growing interest to increase the useful life of fuel cells.
La degradación de una pila de combustible puede ser debida a diferentes fenómenos físico-químicos que se traducen en pérdidas de rendimiento en su punto de trabajo. Esta disminución de rendimiento se ve reflejada en caídas de tensión a lo largo de toda su curva de polarización, debido al aumento de las pérdidas denominadas de activación, óhmicas y concentración. The degradation of a fuel cell can be due to different physical-chemical phenomena that result in loss of performance at its point of work. This decrease in performance is reflected in voltage drops along its polarization curve, due to the increase in the so-called activation, ohmic and concentration losses.
Hasta la fecha, ninguna de las soluciones conocidas posee una estructura "todo en uno", por lo que requieren de conexión externa punto a punto mediante cableado, y la necesidad de electrónicas externas para alimentación general o para posibles sensores externos. Por otro lado, la precisión de los sistemas convencionales para el control del estado de operación de la pila de combustible es muy baja. To date, none of the known solutions has an "all in one" structure, so they require an external point-to-point connection through wiring, and the need for external electronics for general power or for possible external sensors. On the other hand, the accuracy of conventional systems for controlling the operating status of the fuel cell is very low.
En particular, los sistemas multiplexados suelen ser vulnerables a cualquier fallo eléctrico, algo que suele conllevar daños en la electrónica de varios componentes. Por otra parte, para aplicaciones de bajo número de celdas (<50), las soluciones conocidas no resultan ser lo suficientemente rápidas por lo que es necesario la utilización de varios módulos para aplicaciones que requieran un mayor voltaje de operación. In particular, multiplexed systems are often vulnerable to any electrical failure, which often leads to damage to the electronics of several components. On the other hand, for applications with a low number of cells (<50), known solutions do not turn out to be fast enough, so it is necessary to use several modules for applications that require a higher operating voltage.
En otro orden de cosas, muchas soluciones requieren de conector y cableado externo, por lo que presentan problemas de acoplamiento y ruido electromagnético sobre las señales. Finalmente, el coste de la mayoría de soluciones comerciales hace que el uso de este tipo de equipos sea la mayoría de las veces prohibitivo para el usuario final, lo que impide la necesaria monitorización de los stacks de las pilas de combustible en funcionamiento. In another order of things, many solutions require external connector and wiring, so they have coupling problems and electromagnetic noise on the signals. Finally, the cost of most commercial solutions means that the use of this type of equipment is, for the most part, prohibitive for the end user, which prevents the necessary monitoring of the stacks of the fuel cells in operation.
Otras propuestas se limitan a representar la tensión de celda del stack completo, por lo que para conocer el estado de operación del sistema es necesario hacer un post tratamiento de datos. Además, aunque la relación entre las variables principales (tensión, corriente, potencia, temperatura) sea aparentemente conocida, el estado de operación real del sistema puede diferir del teórico, en el sentido de que, para un valor de corriente suministrado, haya un valor de tensión del stack muy diferente del valor teórico. Esto ocasiona que la potencia real obtenida se aleje de la teórica. Other proposals are limited to representing the cell voltage of the complete stack, so to know the operating state of the system it is necessary to do a post-treatment of data. Furthermore, although the relationship between the main variables (voltage, current, power, temperature) is apparently known, the actual operating state of the system may differ from the theoretical one, in the sense that, for a supplied current value, there is a value of stack voltage very different from the theoretical value. This causes the real power obtained to move away from the theoretical power.
Si sólo se tiene información de la tensión de celda, a lo sumo, se puede llegar a conocer la tensión total del stack. En cambio, si no se tiene información sobre ni de la corriente ni de la temperatura reales del stack, el usuario no puede conocer la potencia suministrada por cada celda. En consecuencia, tampoco un posible mal funcionamiento de alguna de las celdas, ni tampoco identificar la causa del mal funcionamiento: exceso o defecto de temperatura. Un exceso de temperatura en la operación del stack puede provocar una disminución de la resistividad de la membrana de las celdas que conforman el stack, mientras que un defecto de temperatura puede provocar inundación de la membrana (exceso de H20 generada durante la operación de la misma). En los dos casos, la consecuencia es la disminución del tiempo de vida del stack por degradación de las membranas de las celdas. En el presente documento, el término stack se refiere al conjunto de celdas apiladas que conforman la pila de combustible. En la comunidad científica y en la industria, se emplean los términos stack y pila de combustible para referirnos al conjunto de celdas en el primer caso y, en el segundo caso, al sistema completo integrado por el stack junto con el BoP (Balance of Plant). El balance de planta o BoP incluye elementos auxiliares, tipo válvulas, sensores, ventilador, etc., que necesita el stack para que el sistema de pila de combustible funcione correctamente. If you only have information about the cell voltage, at most, you can get to know the total voltage of the stack. On the other hand, if you do not have information about the current or the actual temperature of the stack, the user can not know the power supplied by each cell. Consequently, neither a possible malfunction of any of the cells, nor identify the cause of malfunction: excess or defect in temperature. An excess of temperature in the operation of the stack can cause a decrease in the resistivity of the membrane of the cells that make up the stack, while a temperature defect can cause flooding of the membrane (excess of H20 generated during the operation of the same ). In both cases, the consequence is the decrease in the life time of the stack due to degradation of the cells' membranes. In this document, the term stack refers to the set of stacked cells that make up the fuel cell. In the scientific community and in industry, the terms stack and fuel cell are used to refer to the set of cells in the first case and, in the second case, to the complete system integrated by the stack together with the BoP (Balance of Plant ). The plant balance or BoP includes auxiliary elements, such as valves, sensors, ventilator, etc., which the stack needs in order for the fuel cell system to function correctly.
Breve descripción de la invención BRIEF DESCRIPTION OF THE INVENTION
La presente invención se concibe para dar respuesta a las limitaciones observadas en el estado de la técnica. Una de las finalidades es la de dar una solución completa de bajo coste y fácil uso que puede ser utilizada en cualquier sector que implique el uso de pilas de combustible. The present invention is conceived to respond to the limitations observed in the state of the art. One of the purposes is to give a complete solution of low cost and easy use that can be used in any sector that involves the use of fuel cells.
A tal efecto, se propone un sistema preferiblemente embebido que permite la monitorización de tensión de cada celda, así como la corriente y temperatura del stack, para un stack de“n” celdas, siendo“n” un número entero, capaz de generar una corriente máxima de “x” amperios. Por tanto, es de aplicación para un stack de cualquier número de celdas y corriente, esto es, para un stack de cualquier potencia. For this purpose, a preferably embedded system is proposed that allows the monitoring of voltage of each cell, as well as the current and temperature of the stack, for a stack of "n" cells, where "n" is an integer number, capable of generating a maximum current of "x" amps. Therefore, it is applicable for a stack of any number of cells and current, that is, for a stack of any power.
El stack es la parte más importante y costosa de una pila de combustible. La potencia que es capaz de suministrar una pila de combustible es el producto de la tensión y corriente que es capaz de suministrar su stack. La tensión del stack es la suma de las tensiones individuales de las celdas que lo componen. Es importante conocer sus valores, ya que así se puede determinar si el funcionamiento de la pila de combustible es el apropiado. The stack is the most important and expensive part of a fuel cell. The power that is able to supply a fuel cell is the product of the voltage and current that is capable of supplying its stack. The stack voltage is the sum of the individual voltages of the cells that compose it. It is important to know their values, as this can determine if the operation of the fuel cell is appropriate.
La presente propuesta permite la intercomparación en tiempo real del punto de polarización de la pila de combustible respecto al teórico, así como la representación de variables auxiliares como corriente, potencia o temperatura, esenciales para un análisis de degradación y tiempo de vida. The present proposal allows the real-time intercomparison of the polarization point of the fuel cell with respect to the theoretical one, as well as the representation of auxiliary variables such as current, power or temperature, essential for a degradation and life time analysis.
Es objeto de la presente invención, un sistema de supervisión y control de celdas de combustible caracterizado que incluye un módulo de adquisición que comprende un multiplexor cuya frecuencia de muestreo depende del número de celdas del stack; un sensor de temperatura; un sensor de corriente; un módulo de conexión mediante cableado para conectar de forma individual cada una de las celdas de combustible al módulo multiplexor que multiplexa las señales individuales recibidas de cada celda; un módulo de procesamiento que incluye un conversor analógico-digital y un microcontrolador. Este módulo de procesamiento puede analizar el punto de polarización. The object of the present invention is a characterized fuel cell monitoring and control system that includes an acquisition module comprising a multiplexer whose sample rate depends on the number of cells in the stack; a temperature sensor; a current sensor; a wiring connection module for individually connecting each of the fuel cells to the multiplexer module that multiplexes the individual signals received from each cell; a processing module that includes an analog-digital converter and a microcontroller. This processing module can analyze the polarization point.
Opcionalmente, el módulo de procesamiento almacena la curva teórica y para hacer una comparación con la curva real (medida) de la pila de combustible. Optionally, the processing module stores the theoretical curve and to make a comparison with the actual (measured) curve of the fuel cell.
Opcionalmente, el sistema incluye además un módulo de visualización para representar una interfaz cuando se ejecuta un software de gestión en el módulo de procesamiento. Optionally, the system further includes a display module for representing an interface when a management software is executed in the processing module.
Opcionalmente, la interfaz representa en tiempo real al menos los valores de tensión de celda a la vez que la corriente, temperatura y potencia del stack.  Optionally, the interface represents in real time at least the values of cell voltage at the same time as the current, temperature and power of the stack.
Opcionalmente, los módulos multiplexor, de conexión y de procesamiento anteriores se embeben e implementan en una PCB. Optionally, the previous multiplexer, connection and processing modules are embedded and implemented in a PCB.
Opcionalmente, el sistema comprende un puerto de salida digital para conexión con otro dispositivo electrónico. Optionally, the system comprises a digital output port for connection with another electronic device.
Opcionalmente, el sistema comprende un módulo de aislamiento galvánico. Optionally, the system comprises a galvanic isolation module.
Opcionalmente, el sistema comprende un módulo mecánico de sujeción que comprende una pluralidad de sondas retráctiles. Optionally, the system comprises a mechanical clamping module comprising a plurality of retractable probes.
Pueden destacarse varias diferencias respecto a los sistemas existentes: la electrónica de adquisición, el mecanismo de sujeción mediante pines, la unidad de medición con sensores capaces de identificar el estado real del sistema, y la capacidad de monotorización en tiempo real de la tensión de celda, de la curva de polarización y de la potencia. Todo esto permite hacer un completo análisis de rendimiento actual del sistema, junto con una estimación de la degradación del mismo. Actualmente, los sistemas de monitorización de celdas más comunes son soluciones de elevado coste que se limitan a la medida de tensión de celdas de combustible, obviando otros parámetros tan importantes como la corriente o temperatura, fundamentales para describir la curva de polarización del stack. En algunos casos, estos sistemas actúan únicamente como generador de alarmas en el momento en que se sobrepase ciertos niveles de tensión mínima de operación, por lo que no permiten el estudio de degradación, siendo su finalidad exclusivamente el control y la seguridad en la operación de la pila de combustible. Several differences can be highlighted with respect to the existing systems: the acquisition electronics, the pin clamping mechanism, the measuring unit with sensors capable of identifying the real state of the system, and the real-time monitoring capacity of the cell voltage , of the polarization curve and of the power. All this allows to make a complete analysis of the current performance of the system, together with an estimate of its degradation. Currently, the most common cell monitoring systems are high cost solutions that are limited to the measurement of fuel cell voltage, ignoring other parameters as important as the current or temperature, fundamental to describe the polarization curve of the stack. In some cases, these systems act only as a generator of alarms at the moment when certain levels of minimum operating voltage are exceeded, so they do not allow the study of degradation, its purpose being exclusively control and safety in the operation of the fuel cell
Desde el punto de vista del acoplamiento eléctrico del hardware de adquisición a las celdas del stack, lo más utilizado es la unión directa punto a punto a través de cableado, lo que hace que para un gran número de celdas, se tenga una gran cantidad de cableado, más vulnerable al ruido electromagnético circundante. Este hecho unido a la difícil tarea de asegurar un correcto acoplamiento eléctrico puede provocar falsos contactos, los cuales pueden derivar en cortorcircuitos, mediciones incorrectas o simplemente no tener medición alguna, poniendo en riesgo la veracidad de los resultados obtenidos. From the point of view of the electrical coupling of the acquisition hardware to the cells of the stack, the most used is the direct connection point to point through wiring, which means that for a large number of cells, there is a large number of cells. wiring, more vulnerable to surrounding electromagnetic noise. This fact together with the difficult task of ensuring a correct electrical coupling can cause false contacts, which can lead to short circuits, incorrect measurements or simply having no measurement, putting at risk the veracity of the results obtained.
En realizaciones preferentes, se ha desarrollado una PCB que incluye además un módulo propio de adquisición de señal, un módulo de sujeción al stack de pila de combustible junto con el contacto eléctrico, no siendo necesario ningún cableado adicional a cada celda del stack. Esto garantiza máxima comodidad a la hora de conectarlo y fiabilidad durante el proceso de adquisición de señal. Se implementa hardware de monitorización de bajo coste que posean una configuración multiplexada con aislamiento. Opcionalmente, implementa la técnica“plug and play”, enchufar y usar, a través de una conexión USB a cualquier PC. In preferred embodiments, a PCB has been developed which also includes its own signal acquisition module, a fastening module to the fuel cell stack together with the electrical contact, no additional wiring being necessary to each cell of the stack. This guarantees maximum convenience when connecting and reliability during the signal acquisition process. Low cost monitoring hardware that has a multiplexed configuration with isolation is implemented. Optionally, implement the "plug and play" technique, plug and play, through a USB connection to any PC.
Breve descripción de las figuras Brief description of the figures
La FIG. 1 : Esquema del montaje sobre stack de pilas de combustible.  FIG. 1: Diagram of the assembly on stack of fuel cells.
La FIG. 2: Detalle Porta PCB anclado al stack.  FIG. 2: Porta PCB detail anchored to the stack.
La FIG. 3: Array de palpadores y electrónica de adquisición.  FIG. 3: Probe array and acquisition electronics.
La FIG. 4: Detalle de conexión celda-palpador.  FIG. 4: Cell-feeler connection detail.
La FIG. 5: Esquema electrónico del hardware de adquisición, procesado y control. FIG. 5: Electronic diagram of the acquisition, processing and control hardware.
La FIG. 6: Efecto atenuación corriente de fuga. FIG. 6: Leakage current attenuation effect.
La FIG. 7: Efecto fallo en conmutación con etapa de ganancia posterior.  FIG. 7: Failure effect in switching with subsequent gain stage.
La FIG. 8: Efecto fallo en conmutación con etapa de ganancia previa. La FIG. 9: Imagen de la interfaz gráfica representando un diagrama de barras. FIG. 8: Failure effect in switching with pre-gain stage. FIG. 9: Graphic interface image representing a bar diagram.
La FIG. 10: Imagen de la interfaz gráfica con el histórico temporal de variables.  FIG. 10: Image of the graphic interface with the temporal history of variables.
La FIG. 11 : Imagen de la interfaz gráfica para representación de la curva de polarización y potencia del stack  FIG. 11: Graphic interface image to represent the polarization curve and stack power
La FIG. 12: Esquema de funcionamiento normal de una celda de combustible.  FIG. 12: Schematic of normal operation of a fuel cell.
La FIG. 13: Efecto de la corriente de corrosión e inanición de combustible.  FIG. 13: Effect of corrosion current and fuel starvation.
La FIG. 14: Región Aire/Aire en el arranque.  FIG. 14: Air / Air Region at startup.
La FIG. 15: Región Aire/Aire con fugas de combustible en la membrana.  FIG. 15: Air / Air region with leaking fuel in the membrane.
La FIG. 16: Región Aire/Aire con fugas en la línea de salida de hidrógeno no consumido.  FIG. 16: Air / Air Region with leaks in the hydrogen exhaust line not consumed.
La FIG. 17: Región Aire/Aire con fugas en la línea de suministro de hidrógeno.  FIG. 17: Air / Air Region with leaks in the hydrogen supply line.
Descripción detallada de la invención Detailed description of the invention
Sin carácter limitante de su alcance, se ilustra adicionalmente el funcionamiento de la invención mediante unos ejemplos particulares de realización y la referencia a las figuras anteriores. Without limiting its scope, the operation of the invention is further illustrated by means of particular examples of embodiment and reference to the previous figures.
La componente hardware ha sido diseñada con el objetivo de garantizar una solución de bajo coste con prestaciones de precisión y seguridad suficientes para el objetivo perseguido. El presente sistema reduce el hardware necesario, acoplándose mecánicamente de forma directa sobre el stack de la pila de combustible y alimentándose directamente desde un puerto USB. The hardware component has been designed with the aim of guaranteeing a low cost solution with sufficient precision and security features for the objective pursued. The present system reduces the necessary hardware, mechanically coupling directly on the stack of the fuel cell and feeding directly from a USB port.
La componente software permite obtener medidas en tiempo real de la tensión de cada celda, simultáneamente junto con la corriente y temperatura del stack, lo que permite en todo momento asociar las causas de la posible degradación del stack (observable principalmente por el valor de la tensión de cada celda) y el punto de operación, según la curva de polarización de la pila de combustible monitorizada. The software component allows real-time measurements of the voltage of each cell, simultaneously with the current and temperature of the stack, allowing at all times to associate the causes of possible stack degradation (observable mainly by the value of the voltage of each cell) and the point of operation, according to the polarization curve of the monitored fuel cell.
Del mismo modo, el software muestra en tiempo real la diferencia del punto de polarización del stack completo respecto al estado inicial, por lo que permite determinar la degradación total del mismo en todas las zonas de la curva de polarización de la pila de combustible, y por tanto descubrir fenómenos asociados a las distintas pérdidas. La medida de la tensión de celda únicamente permitirá analizar diferencias de voltaje entre celdas, pero no así determinar qué tipología de pérdidas pueden estarse produciendo, debido a que es necesario relacionar el punto de polarización (V, I) actual con respecto al original, pudiendo determinar si la degradación es causada por pérdidas por activación, óhmicas o por concentración. Del mismo modo, la temperatura de operación del stack permitirá determinar pérdidas asociadas a altas o bajas temperaturas de operación del stack, así como determinar posibles problemas de refrigeración debidos a diferentes causas, elevadas intensidades, contaminación del stack, problemas de humidificación y extración de productos, etc. In the same way, the software shows in real time the difference of the polarization point of the complete stack with respect to the initial state, by which it allows to determine the total degradation of the same in all the areas of the polarization curve of the fuel cell, and therefore discover phenomena associated with the different losses. The measurement of the cell voltage will only allow the analysis of voltage differences between cells, but it will not be possible to determine which type of losses may be occurring, since it is necessary to relate the current polarization point (V, I) with respect to the original, being able to determine if the degradation is caused by activation, ohmic or concentration losses. In the same way, the operating temperature of the stack will allow to determine losses associated with high or low operating temperatures of the stack, as well as to determine possible cooling problems due to different causes, high intensities, stack contamination, humidification problems and product extraction. , etc.
En la FIG. 1 se muestra un ejemplo del montaje final del sistema de adquisición 1 sobre el stack de pila de combustible 2 gracias al porta PCB 3 diseñado para tal uso. De forma análoga, se representan y se ubican los sensores auxiliares de corriente 4 y temperatura del stack 5, necesarios para la caracterización del punto de operación del mismo. Adicionalmente, se muestran representadas las conexiones auxiliares eléctricas 6 y de entrada y salida de hidrógeno 7. In FIG. 1 shows an example of the final assembly of the acquisition system 1 on the stack of fuel cell 2 thanks to the PCB 3 holder designed for such use. Analogously, the auxiliary current sensors 4 and temperature of the stack 5 are represented and located, necessary for the characterization of the operating point thereof. Additionally, electrical auxiliary connections 6 and hydrogen inlet and outlet 7 are shown.
En la FIG. 2 se muestra en detalle el sistema de acoplamiento o porta PCB 3 sobre el módulo de adquisición 1 , así como la unión sobre el stack de pila de combustible 2. El sistema de sujeción al módulo de adquisición se realiza a través de dos agujeros pasantes 8 en los que se ancla el porta PCB gracias al uso de tornillo, arandela y rosca de apriete. Por su parte, el sistema dispone de un orificio oblongo 9 el cual permite un movimiento longitudinal de la varilla roscada de apriete 10 del stack 2 de pilas de combustible, de tal forma que permite ajustar la distancia correcta entre la unidad de adquisición y control y el stack de pilas de combustible, asegurando un correcto contacto eléctrico gracias a las sondas retráctiles 11 (ver Figura 3). La correcta sujeción se garantiza gracias a arandela y rosca de apriete. In FIG. 2 the coupling system or PCB holder 3 is shown in detail on the acquisition module 1, as well as the connection on the stack of fuel cell 2. The securing system to the acquisition module is carried out through two through holes 8 in which the PCB holder is anchored thanks to the use of screw, washer and tightening thread. For its part, the system has an oblong hole 9 which allows a longitudinal movement of the threaded rod 10 of stack 2 of fuel cells, in such a way that it allows adjusting the correct distance between the acquisition and control unit and the stack of fuel cells, ensuring a correct electrical contact thanks to the retractable probes 11 (see Figure 3). The correct clamping is guaranteed thanks to the washer and the tightening thread.
La FIG. 3 muestra representada más en detalle el módulo de adquisición, en la que se puede apreciar la distribución del peine de palpadores retráctiles 11 respecto al resto del circuito de adquisición y control 12. FIG. 3 shows in more detail the acquisition module, in which the distribution of the retractable stylus comb 11 can be seen with respect to the rest of the acquisition and control circuit 12.
En la FIG.4 se detalla la conexión entre la sonda palpadora retráctil 11 y la placa bipolar de las celda de combustible 13. Gracias a la capacidad de compresión de la sonda, se garantiza un correcto contacto eléctrico ante irregularidades en la superficie de la placa bipolar, o por imprecisiones en el montaje o ajuste de las sondas. La FIG. 5 muestra un ejemplo de realización donde se aprecia un conjunto de celdas 14 que están cableadas a unos divisores resistivos 15 que disminuyen la tensión entre sus extremos de forma que puedan acoplarse a un módulo de multiplexado 16. La multiplexión se realiza de forma periódica y permite aumentar el número de canales de adquisición sin aumentar el número de convertidores analógico-digitales 21. A continuación del multiplexor 16 se hace uso de una etapa descargadora 17 la cual permite eliminar el efecto de capacidades parásitas en el sistema, proporcionando unas conmutaciones rápidas y seguras. La salida de dicha etapa se encuentra conectada a un filtro paso bajo 18 el cual ha sido diseñado para eliminar componentes de alta frecuencia y reducir de ese modo el ruido electromagnético por interferencias externas. El amplificador de instrumentación 19 toma la señal filtrada y permite por un lado obtener la señal diferencial correspondiente a la tensión de una celda concreta, y por otro eliminar el ruido en modo común de la señal de entrada, aumentando por tanto la precisión de la medida. Con el objetivo de aumentar la seguridad del sistema, se hace uso de un amplificador de aislamiento 20 el cual permite aislar galvánicamente la entrada y salida del circuito, obteniendo un aislamiento eléctrico que permite preservar la electrónica de control y sucesivas etapas, de posibles fallos en la zona de alta tensión. La salida aislada es adquirida a través de un convertidor analógico-digital 21 de 24 bits con tecnología sigma-delta de alta precisión y bajo coste. La salida digitalizada es procesada en todo momento por el microcontrolador 22 quien representa la unidad de control y posee las funciones adicionales de comunicación externa con el PC y software de gestión a través de una conexión USB 23, así como del control de la secuencia del multiplexor 16 a través de una etapa de optoacoplamiento 24, la cual permite mantener el aislamiento eléctrico entre la zona de alta tensión y la zona de control y procesamiento. Adicionalmente, el microcontrolador se encarga de la lectura de los sensores auxiliares de corriente y tensión 25, los cuales son tratados mediante una etapa previa de acondicionamiento 26. In FIG. 4, the connection between the retractable tracer probe 11 and the bipolar plate of the fuel cell 13 is detailed. Thanks to the compression capacity of the probe, a correct electrical contact is guaranteed in the event of irregularities in the surface of the plate. bipolar, or due to inaccuracies in the assembly or adjustment of the probes. FIG. 5 shows an example of embodiment where a set of cells 14 are seen that are wired to resistive dividers 15 that decrease the voltage between their ends so that they can be coupled to a multiplexing module 16. The multiplexing is performed periodically and allows increase the number of acquisition channels without increasing the number of analog-digital converters 21. Next to multiplexer 16, a discharging stage 17 is used which eliminates the effect of parasitic capacitances in the system, providing fast and safe switching . The output of said stage is connected to a low pass filter 18 which has been designed to eliminate high frequency components and thereby reduce the electromagnetic noise by external interferences. The instrumentation amplifier 19 takes the filtered signal and allows on the one hand to obtain the differential signal corresponding to the voltage of a specific cell, and on the other to eliminate the common mode noise of the input signal, thus increasing the accuracy of the measurement . With the aim of increasing the safety of the system, an insulation amplifier 20 is used, which allows galvanically isolating the input and output of the circuit, obtaining an electrical isolation that allows to preserve the control electronics and successive stages, of possible failures in the high voltage zone. The isolated output is acquired through a 24-bit analog-digital converter 21 with sigma-delta technology of high precision and low cost. The digitized output is processed at all times by the microcontroller 22 which represents the control unit and has the additional functions of external communication with the PC and management software via a USB connection 23, as well as the control of the multiplexer sequence 16 through an optocoupling stage 24, which allows to maintain the electrical isolation between the high voltage zone and the control and processing zone. Additionally, the microcontroller is responsible for reading the auxiliary current and voltage sensors 25, which are treated by a preconditioning stage 26.
En la FIG. 6 se muestra una configuración distinta a la que se propone y en ésta, el divisor resistivo 15 se encuentra tras el multiplexador 16. En ella se puede apreciar el efecto negativo de la corriente de fuga de los multiplexores sobre los divisores resistivos. La corriente de fuga de todos los multiplexores inactivos generará una tensión parásita en el divisor resistivo, que al ser de valores óhmicos elevados, provocará una desviación en la medida traduciéndose en mediciones erróneas, las cuales no podrán ser detectadas por el filtro paso bajo 18 ni el amplificador de instrumentación 19, al ser de origen diferencial. In FIG. 6 shows a configuration different from the one proposed and in this, the resistive divider 15 is located behind the multiplexer 16. In it, the negative effect of the leakage current of the multiplexers on the resistive dividers can be seen. The leakage current of all the inactive multiplexers will generate a parasitic voltage in the resistive divider, which, being of high ohmic values, will cause a deviation in the measurement, resulting in erroneous measurements, which can not be detected by the low pass filter 18 or the instrumentation amplifier 19, since it is of differential origin.
De igual manera, en la FIG. 7 se muestra el comportamiento frente a la seguridad del sistema anterior ante posibles fallos en la secuencia de multiplexado 16. Al no disponer de una etapa resistiva previa 15, existe la posibilidad de cortocircuitar celdas anexas 14, con el consiguiente daño para el stack y para el equipo de adquisición. Similarly, in FIG. 7 shows the behavior against the security of the previous system against possible failures in the multiplexing sequence 16. In the absence of a previous resistive stage 15, there is the possibility of short circuiting adjacent cells 14, with consequent damage to the stack and to the acquisition team.
En el caso de disponer de divisor resistivo previo 15 tal y como se representa en la FIG. 8, la elevada resistencia entre celdas ante un fallo del multiplexor 16 provoca que la corriente de fallo sea muy pequeña y no dañe ninguna de las celdas de combustibleIn the case of having a previous resistive divider 15 as shown in FIG. 8, the high resistance between cells in the event of a failure of the multiplexer 16 causes the fault current to be very small and does not damage any of the fuel cells
14. 14.
El módulo de procesamiento puede ejecutar software de gestión para que una unidad de visualización pueda representar en tiempo real todas las variables eléctricas de interés, tensión de celda y corriente del stack, así como la temperatura del mismo. Para ello, el software de gestión genera al ser ejecutado una interfaz de tres ventanas distintas (FIG. 9, FIG 10 y FIG. 11) y un panel de control general 27 en el cual se configura el puerto de comunicación y están las opciones de guardado del sistema. Adicionalmente, se dispone de un panel de aviso 28 en el cual se visualizan el estado de tres leds, los cuales son programados por el usuario y se activan cuando algunas de las celdas del stack traspasan los límites de seguridad marcados, indicando el número de celda y el evento que lo ha originado. The processing module can execute management software so that a display unit can represent in real time all the electrical variables of interest, cell voltage and current of the stack, as well as its temperature. For this, the management software generates an interface with three different windows (FIG 9, FIG 10 and FIG 11) and a general control panel 27 in which the communication port is configured and there are the options of saved from the system. Additionally, there is a warning panel 28 in which the status of three LEDs are displayed, which are programmed by the user and activated when some of the cells in the stack go beyond the marked safety limits, indicating the cell number and the event that originated it.
En la FIG. 9 se presenta un ejemplo de la ventana de monitorización 29 en la cual se representa en un diagrama de barras las tensiones de celda de todo el stack, y por tanto permite ver de una forma muy rápida diferencias significativas entre dos o más celdas de combustible. De forma análoga, la temperatura del stack es representada en un indicador creado para tal fin 30. In FIG. 9 shows an example of the monitoring window 29 in which the cell voltages of the entire stack are represented in a bar diagram, and therefore allows to see in a very fast way significant differences between two or more fuel cells. Analogously, the stack temperature is represented in an indicator created for that purpose 30.
En la FIG. 10 se muestra la segunda ventana en la cual se permite la representación de la evolución temporal de todas las celdas monitorizadas 31 y por tanto permite un estudio dinámico ante los distintos perfiles de carga utilizados. In FIG. 10 shows the second window in which the representation of the time evolution of all the monitored cells 31 is allowed and therefore allows a dynamic study before the different load profiles used.
En la FIG. 11 se representa en tiempo real el punto de polarización de la pila de combustible 32, formado por tensión y corriente; así como potencia del stack 33 referidos a las curvas teóricas proporcionadas por el fabricante, de tal forma que nos permite identificar qué zona de polarización ha sufrido una mayor degradación, y por tanto identificar la naturaleza de la degradación (pérdidas por activación, óhmicas o por concentración). In FIG. 11 the polarization point of the fuel cell 32 is represented in real time, formed by voltage and current; as well as stack power 33 referred to the theoretical curves provided by the manufacturer, in such a way that it allows us to identify which polarization zone has suffered the most degradation, and therefore to identify the nature of the degradation (activation, ohmic or concentration losses).
En la FIG. 12 se muestra el esquema del funcionamiento normal de una celda de combustible: las moléculas de hidrógeno 34 que entran en el ánodo 35 se descomponen en iones H+ 36 y electrones 37 en presencia de un catalizador 38. Los iones H+ atraviesan la membrana 39 y los electrones pasan por el circuito exterior. En el cátodo 40, las moléculas de oxígeno 41 (procedente del propio aire exterior) se recombinan con los iones H+ y los electrones para formar agua 42, la cual constituye el "residuo" de la celda. In FIG. 12 shows the diagram of the normal operation of a fuel cell: the hydrogen molecules 34 that enter the anode 35 decompose in H + 36 ions and electrons 37 in the presence of a catalyst 38. The H + ions cross the membrane 39 and the electrons pass through the outer circuit. In the cathode 40, the oxygen molecules 41 (coming from the outside air itself) recombine with the H + ions and the electrons to form water 42, which constitutes the "residue" of the cell.
Para alcanzar los niveles de potencia deseados, las celdas se ensamblan unas junto a otras en serie, hasta formar el stack requerido. Para que el stack así construido pueda funcionar como pila de combustible (sistema que alimentado por hidrógeno genera potencia eléctrica), necesita de lo que se denomina el BoP ("Balance of Plant" o balance de planta), esto es, un conjunto de subsistemas que proporcionan el suministro de hidrógeno (integrado por válvulas de entrada y salida para alimentación y purga), el subsistema de oxigenación/refrigeración (integrado por al menos un ventilador/extractor para refrigeración y ajuste de estequiometría), la circuitería eléctrica (que permite alimentar a una carga eléctrica) y el control sobre el BoP competo para que el stack pueda funcionar en las condiciones apropiadas. To reach the desired power levels, the cells are assembled next to each other in series, until the required stack is formed. So that the stack thus constructed can function as a fuel cell (a system powered by hydrogen generates electrical power), it needs what is called the BoP ("Balance of Plant"), that is, a set of subsystems that provide the supply of hydrogen (integrated by inlet and outlet valves for supply and purge), the oxygenation / cooling subsystem (integrated by at least one fan / extractor for cooling and stoichiometry adjustment), the electrical circuitry (which allows to feed to an electrical load) and control over the full BoP so that the stack can function in the proper conditions.
Una vez en funcionamiento, el rendimiento de la pila de combustible puede verse afectado por causas diversas, influyendo directamente en sus prestaciones eléctricas (genera menos potencia de la nominal prevista). Es entonces decisivo disponer de un sistema capaz de monitorizar el estado de cada celda, con objeto de analizar su posible degradación y, en última instancia, su deterioro. Esto posibilitará que, de forma selectiva, se pueda llevar a cabo la retirada de las celdas deterioradas y, si es posible, su reemplazo por celdas en buen estado, lo cual permitirá recuperar el rendimiento (potencia) inicial del stack. Dicho lo anterior, las dos principales causas de deterioro de las celdas que además pueden ser detectadas por pérdida de tensión, son la corrosión del carbón que se emplea para depositar el catalizador y la inanición de combustible. La primera se debe a que en una celda de combustible tipo PEM, en la estructura Electrolito-Membrana-Electrolito, el catalizador que favorece la disociación del hidrógeno está suspendido en una fina capa de carbono que cubre a la membrana por ambos lados. Cuando esta capa de carbono desaparece (como consecuencia de la reacción del mismo con agua para formar C02, iones H+ y electrones), la interfaz hidrógeno-oxígeno (en lo sucesivo hidrógeno-aire, ya que el oxígeno que necesita la celda de combustible para reaccionar, procede directamente del aire circundante) que existe en la membrana se convierte en oxígeno-oxígeno (en lo sucesivo aire-aire), generando dos zonas de diferente tensión y por tanto una corriente denominada "corriente de corrosión". Esta corriente aparece durante el arranque de la pila (es la degradación por activación ya mencionada), y también aparece si hay pérdidas de combustible, o si la válvula de suministro o la válvula de purga tienen fugas. Es decir, que si debido a un mal funcionamiento, la región H2/Aire que existe en la interfaz ánodo-membrana-cátodo se transforma en una región Aire/Aire, la celda de combustible deja de funcionar correctamente y la reacción que existe en el ánodo no es la disociación de las moléculas de hidrógeno sino la combinación del carbono (existente en la estructura necesaria para depositar el catalizador), con agua para formar dióxido de carbono como muestra la FIG. 13. Como consecuencia, en una misma celda aparecen dos regiones: una donde existe una mezcla de H2/Aire 43 en la que se mantiene una diferencia de tensión de aproximadamente 1 V, y otra de mezcla Aire/Aire 44 en la que no existe diferencia de tensión. Debido a que los platos bipolares de la celda (responsables de separar las celdas individuales en el stack) son conductores, la diferencia de tensión creada en la región H2/Aire se aplica a la región Aire/Aire. Esta diferencia de tensión aplicada a la región Aire/Aire provoca una corriente denominada "corriente de corrosión" 45 cuyo efecto es el consumo del carbono de la capa catalizadora. Once in operation, the performance of the fuel cell can be affected by various causes, directly influencing its electrical performance (generates less power than expected). It is then decisive to have a system capable of monitoring the status of each cell, in order to analyze its possible degradation and, ultimately, its deterioration. This will make it possible, selectively, to carry out the removal of the damaged cells and, if possible, their replacement by cells in good condition, which will allow recovering the initial performance (power) of the stack. That said, the two main causes of cell deterioration that can also be detected by voltage loss are the corrosion of the coal that is used to deposit the catalyst and the starvation of fuel. The first is due to the fact that in a PEM fuel cell, in the Electrolyte-Membrane-Electrolyte structure, the catalyst that favors the dissociation of the Hydrogen is suspended in a thin layer of carbon that covers the membrane on both sides. When this layer of carbon disappears (as a consequence of the reaction of it with water to form C02, H + ions and electrons), the hydrogen-oxygen interface (hereinafter hydrogen-air, since the oxygen needed by the fuel cell to reacting, proceeds directly from the surrounding air) that exists in the membrane becomes oxygen-oxygen (hereinafter air-air), generating two zones of different voltage and therefore a current called "corrosion current". This current appears during the start of the battery (it is the degradation by activation already mentioned), and also appears if there are fuel losses, or if the supply valve or purge valve leaks. That is, if due to a malfunction, the H2 / Air region that exists at the anode-membrane-cathode interface becomes an Air / Air region, the fuel cell stops working properly and the reaction that exists in the Anode is not the dissociation of the hydrogen molecules but the combination of carbon (existing in the structure necessary to deposit the catalyst), with water to form carbon dioxide as shown in FIG. 13. As a result, two regions appear in the same cell: one where there is a mixture of H2 / Air 43 in which a voltage difference of approximately 1 V is maintained, and another of air / air mixture 44 in which there is no voltage difference. Because the bipolar dishes of the cell (responsible for separating the individual cells in the stack) are conductive, the voltage difference created in the H2 / Air region is applied to the Air / Air region. This voltage difference applied to the Air / Air region causes a current called "corrosion current" 45 whose effect is the carbon consumption of the catalyst layer.
Según lo anterior, se deduce que es muy importante evitar que se generen regiones tipo Aire/Aire. Las FIGs. 14-17 muestran algunas situaciones en las que se puede dar esta situación adversa que provoca el deterioro del stack de una pila de combustible y, por tanto, el deterioro de ésta. According to the above, it follows that it is very important to avoid generating Air / Air type regions. FIGs. 14-17 show some situations in which this adverse situation can occur that causes the deterioration of the stack of a fuel cell and, therefore, its deterioration.
La FIG. 14, a modo de ejemplo, ilustra el caso de una pila que no ha estado funcionando durante cierto tiempo (más de 30 minutos), donde el ánodo se rellena de aire 46. Entonces, en el momento del arranque (activación), cuando se suministra hidrógeno, inicialmente se genera una región Aire/Aire, con las consiguientes consecuencias adversas. La FIG. 15 muestra otra situación en la que se pueden generar regiones Aire/Aire es en el apagado. Después del apagado, el consumo de hidrógeno en el ánodo reduce la presión de éste por debajo de la presión atmosférica, y si hay fuga de combustible en la membrana 47, el aire entra en el ánodo a ocupar el hueco liberado por la fuga de hidrógeno. En este caso, la tensión de la celda dañada no vuelve a su valor normal en circuito abierto, sino que baja ostensiblemente. FIG. 14, by way of example, illustrates the case of a battery that has not been running for a certain time (more than 30 minutes), where the anode is filled with air 46. Then, at the moment of starting (activation), when the supplies hydrogen, initially an Air / Air region is generated, with the consequent adverse consequences. FIG. 15 shows another situation in which regions can be generated Air / Air is in the shutdown. After switching off, the consumption of hydrogen at the anode reduces the pressure of the latter below atmospheric pressure, and if there is fuel leakage in the membrane 47, the air enters the anode to occupy the gap released by the hydrogen leak . In this case, the voltage of the damaged cell does not return to its normal value in open circuit, but decreases ostensibly.
La FIG. 16, ilustra una fuga en la línea de salida de hidrógeno 48 no consumido que vuelve a tener efecto sobre la corriente de corrosión. Un indicador de que existen fugas en la válvula de purga, es que la tensión de alguna de las celdas en circuito abierto se decrementa hasta casi anularse. FIG. 16, illustrates a leak in the unconsumed hydrogen 48 outlet line which again has an effect on the corrosion current. An indicator that there are leaks in the purge valve, is that the voltage of any of the cells in open circuit is decreased until almost annulled.
La FIG. 17 muestra que, si existen fugas en la línea de suministro de hidrógeno, la interfaz Aire/Aire que debería haber en un estado normal de apagado, se sustituye por la interfaz H2/Aire 49. Como consecuencia, la tensión de celda nunca llegará a ser 0 V (tensión de celda si la interfaz es Aire/Aire, lo que equivale a que no existan fugas en la válvula de suministro) habiendo transcurrido más de 30 minutos después del apagado de la pila. FIG. 17 shows that, if there are leaks in the hydrogen supply line, the Air / Air interface that should have been in a normal shutdown state, is replaced by the H2 / Air 49 interface. As a consequence, the cell voltage will never reach be 0 V (cell voltage if the interface is Air / Air, which means that there are no leaks in the supply valve) having elapsed more than 30 minutes after the battery was turned off.
La FIG. 13 representa otro efecto de deterioro (además del de la corriente de corrosión ya comentado), relativo a la inanición o falta de combustible. Esta falta de combustible provoca un efecto similar a la corriente de corrosión sobre una celda de combustible. Cuando no existe suficiente hidrógeno con el que reaccionar, éste es sustituido por el carbono de la capa catalizadora, de forma que el carbono reacciona con el agua para generar protones y electrones, con el fin de abastecer la demanda de la carga. En esta situación, la tensión de celda puede bajar por debajo de 0 V, llegando a una situación inversa irreversible que supondrá la inhabilitación definitiva de la misma. FIG. 13 represents another effect of deterioration (in addition to that of the corrosion current already mentioned), relative to starvation or lack of fuel. This lack of fuel causes an effect similar to the corrosion current on a fuel cell. When there is not enough hydrogen to react with, it is replaced by the carbon in the catalytic layer, so that the carbon reacts with the water to generate protons and electrons, in order to supply the demand of the load. In this situation, the cell voltage can fall below 0 V, reaching an irreversible reverse situation that will mean the definitive disqualification of the same.
Tanto en el caso de corriente de corrosión o inanición de combustible, ambos fenómenos adversos pueden ser detectados mediante la monitorización la tensión de celda, y por tanto mediante el sistema objeto de esta invención. Both in the case of corrosion current or fuel starvation, both adverse phenomena can be detected by monitoring the cell voltage, and therefore by the system object of this invention.
Existen varios métodos para el estudio de diagnóstico de pilas de combustible, entre los cuales se pueden destacar el estudio de la curva de polarización, el estudio de la impedancia por espectroscopia electroquímica, el método de interrupción de corriente y la medición de humedad y presión. De todos los anteriores métodos el primero y el último son los únicos que pueden ser llevados a cabo "on-line" durante la operación normal con carga, siendo el primero el más adecuado para determinar el tipo de pérdidas asociadas, debido a que se estudian los puntos sobre la curva de polarización. Por todo ello, los sistemas de monitorización de tensión de celda junto con otros sensores de tipo físico-químico (humedad, presión, temperatura, corriente, concentración de reactivos, etc) son los más extendidos para los estudios de degradación sobre pilas de combustible. There are several methods for the diagnostic study of fuel cells, among which we can highlight the study of the polarization curve, the study of the impedance by electrochemical spectroscopy, the current interruption method and the measurement of humidity and pressure. Of all the previous methods the first and the The last ones are the only ones that can be carried out "on-line" during the normal operation with load, the first being the most appropriate to determine the type of associated losses, because the points on the polarization curve are studied. For all these reasons, cell voltage monitoring systems together with other physical-chemical sensors (humidity, pressure, temperature, current, concentration of reagents, etc.) are the most widely used for degradation studies on fuel cells.
Dependiendo del estudio a realizar, los sistemas de monitorización de tensión de celda deben cumplir unas restricciones mínimas para garantizar una lectura precisa. Como norma general, se estima que los sistemas deben ser capaces de medir con una frecuencia de muestreo mínima de 1-4 Hz, y con una precisión de ±100 mV para detectar fallos importantes y ±10 mV para análisis de degradación de celdas. Depending on the study to be carried out, the cell voltage monitoring systems must comply with minimum restrictions to guarantee an accurate reading. As a general rule, it is estimated that the systems should be able to measure with a minimum sampling frequency of 1-4 Hz, and with an accuracy of ± 100 mV to detect important faults and ± 10 mV for analysis of cell degradation.
Atendiendo a lo anterior, es necesario el uso de equipos con una velocidad de muestreo alta si el número de canales es elevado, o bien la utilización de tantos canales de instrumentación como canales de monitorización existan. Normalmente, la primera de las opciones lleva asociado una disminución en la precisión total del sistema al aumentar la frecuencia de muestreo, mientras que la segunda aumenta exponencialmente los costes del sistema de adquisición. In view of the above, it is necessary to use equipment with a high sampling rate if the number of channels is high, or the use of as many instrumentation channels as monitoring channels exist. Normally, the first of the options is associated with a decrease in the total accuracy of the system by increasing the sampling frequency, while the second exponentially increases the costs of the acquisition system.
Desde el punto de vista de la seguridad del sistema, es necesario el uso de aislamientos eléctricos para prevenir daños en la electrónica y en las distintas celdas. Esto requiere de un diseño más exhaustivo y el empleo de componentes que encarecen el mismo. From the point of view of the safety of the system, it is necessary to use electrical insulation to prevent damage to the electronics and the different cells. This requires a more exhaustive design and the use of components that make it more expensive.
Teniendo en cuenta la maniobrabilidad del sistema, es necesario el desarrollo de sistemas de adquisición que faciliten su interfaz con la pila de combustible, debido a que las soluciones actuales requieren de grandes mazos de cables crimpados, lo que significa una mayor complejidad de montaje, la posibilidad de malas conexiones poniendo el riesgo la integridad del stack, y la mayor vulnerabilidad a ruido electromagnético debido a las grandes distancias de cable. Taking into account the maneuverability of the system, it is necessary to develop acquisition systems that facilitate its interface with the fuel cell, because current solutions require large harnesses of crimped cables, which means a greater complexity of assembly, possibility of bad connections putting the integrity of the stack risk, and the greater vulnerability to electromagnetic noise due to the large distances of cable.
Finalmente, sería deseable sistemas de bajo coste y filosofía "plug and play", enchufar y usar, con la finalidad de promover el uso de este tipo de tecnologías y facilitar el diseño, estudio y operación de las pilas de combustible en el sector industrial, docente universitario e investigador. Finally, low cost systems and "plug and play" philosophy, plug and play, would be desirable in order to promote the use of this type of technology and facilitate the design, study and operation of fuel cells in the industrial sector, university professor and researcher.

Claims

REIVINDICACIONES
1. Sistema de supervisión y control de celdas de combustible caracterizado por que comprende: 1. Fuel cell monitoring and control system characterized by comprising:
- un módulo de adquisición (1) que comprende un multiplexor (16) cuya frecuencia de muestreo depende del número de celdas (14) del stack (2); - an acquisition module (1) comprising a multiplexer (16) whose sampling frequency depends on the number of cells (14) of the stack (2);
- un sensor de temperatura (5) configurado para medir la temperatura; - a temperature sensor (5) configured to measure the temperature;
- un sensor de corriente (4) configurado para medir la corriente;  - a current sensor (4) configured to measure the current;
- un módulo de conexión mediante cableado para conectar de forma individual cada una de las celdas de combustible al módulo multiplexor que multiplexa las señales individuales recibidas de cada celda;  - a wired connection module for individually connecting each of the fuel cells to the multiplexer module that multiplexes the individual signals received from each cell;
- un módulo de procesamiento que comprende al menos un conversor analógico-digital (21) y un microcontrolador (22), el módulo de procesamiento configurado para analizar el punto de polarización.  - a processing module comprising at least one analog-digital converter (21) and a microcontroller (22), the processing module configured to analyze the polarization point.
2. Sistema según la reivindicación 1 , donde el módulo de procesamiento está configurado para almacenar la curva teórica y para hacer una comparación entre la curva real de la pila de combustible y teórica. System according to claim 1, wherein the processing module is configured to store the theoretical curve and to make a comparison between the actual curve of the fuel cell and theoretical.
3. Sistema según la reivindicación 2, que comprende además un módulo de visualización configurado para representar una interfaz cuando se ejecuta en el módulo de procesamiento un software de gestión. System according to claim 2, further comprising a display module configured to represent an interface when a management software is executed in the processing module.
4. Sistema según la reivindicación 3, donde la interfaz representa en tiempo real al menos los valores de tensión de celda a la vez que la corriente, temperatura y potencia del stack. System according to claim 3, wherein the interface represents in real time at least the values of cell voltage at the same time as the current, temperature and power of the stack.
5. Sistema según una cualquiera de las reivindicaciones anteriores, donde los módulos multiplexor, de conexión y de procesamiento anteriores se implementan en una PCB. System according to any one of the preceding claims, wherein the above multiplexer, connection and processing modules are implemented in a PCB.
6. Sistema según una cualquiera de las reivindicaciones anteriores, , que comprende un puerto de salida para conexión USB (23) plug and play. System according to any one of the preceding claims, comprising an output port for USB (23) plug and play connection.
7. Sistema según una cualquiera de las reivindicaciones anteriores, que comprende un módulo de aislamiento galvánico (20). System according to any one of the preceding claims, comprising a galvanic isolation module (20).
8. Sistema según una cualquiera de las reivindicaciones anteriores, que comprende un módulo mecánico de sujeción que comprende una pluralidad de sondas retráctiles (1 1). System according to any one of the preceding claims, comprising a mechanical fastening module comprising a plurality of retractable probes (11).
PCT/ES2018/070748 2017-11-22 2018-11-20 System for monitoring and controlling fuel cells WO2019102053A2 (en)

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