System and method for estimating electrical characteristics of an electrolyzer

Abstract

A device for estimating electrical properties of an electrolyzer (103) includes a data processing system (102) for estimating electrical values ​​of the electrolyzer, such as membrane resistance, based on the initial value and decay time constant of the electrolyzer's differential voltage, current (I), and double-layer capacitance voltage during shutdown of the electrolyzer. The differential voltage is the difference between the electrolyzer's voltage (U) and the electrolyzer's total reversible voltage. The initial value and decay time constant of the double-layer capacitance voltage are estimated based on the value of the differential voltage when the current is zero and the differential voltage is equal to the double-layer capacitance voltage. The electrical values ​​can be estimated even if a gradual interruption of the electrolyzer's current is not possible.

Description

Technical Field

[0001] The present disclosure relates to an apparatus and method for estimating electrical characteristics of an electrolyzer. Furthermore, the present disclosure relates to a computer program for estimating electrical characteristics of an electrolyzer. Furthermore, the present disclosure relates to an electrolysis system. Background Art

[0002] The electrochemical process in which the material interacts with the electrodes can be, for example, an electrolytic process, such as, for example, water electrolysis, in which electrical energy is converted into chemical energy carried by hydrogen, and oxygen is produced as a byproduct. A direct current is passed between the two electrodes, producing hydrogen at the cathode (i.e., the negative electrode) and oxygen at the anode (i.e., the positive electrode). Faraday's law of electrolysis shows that the production of hydrogen is directly proportional to the charge transferred on the electrodes. Therefore, the average value of the direct current determines the rate of hydrogen production.

[0003] In many cases, it is necessary to estimate the electrical properties of the electrolyzer. The electrical properties may include, for example, ohmic resistance, i.e., the membrane resistance of the electrolysis cell of the electrolyzer, the charge transfer resistance, and the double layer capacitance. For example, reversible degradation in the electrolysis cell is associated with an increase in the above-mentioned membrane resistance, which makes online estimation of the membrane resistance particularly attractive. More information can be found in publications such as I. Dedigama, P. Angeli, K. Ayers, J. Robinson, P. Shearing, D. Tsaoulidis and D. Brett: In situ diagnostic techniques for characterization of polymer electrolyte membranewater electrolysers flow visualisation and electrochemical impedance spectroscopy, Int. J. Hydrogen Energy 39, 9, 2014, pp. 4468-4482. The estimated electrical properties of the electrolyzer can be used to control the operation of the electrolyzer to improve efficiency and / or extend the service life of the electrolyzer.

[0004] There are many known methods for estimating the electrical characteristics of electrolyzers, such as polarization curve identification, electrochemical impedance spectroscopy (EIS), current mapping (CM), and current interruption (CI). Polarization curve identification provides the current-voltage behavior of an electrolysis cell or stack, and can be used to assess the overall performance of the electrolyzer. The collection of polarization curve data requires testing steady-state operation over a range of operating conditions (i.e., at different current densities), and therefore can be time-consuming and cumbersome to perform in conjunction with an industrial electrolyzer.

[0005] In electrochemical impedance spectroscopy (EIS), a DC current with an AC component superimposed on it is supplied to an electrolysis cell. This method can provide detailed, small-signal-level information about the cell's performance, but it requires the ability to add a suitable AC component to the DC current and to measure both current and voltage with high accuracy at a high sampling frequency. Consequently, its application to industrial, megawatt-scale electrolyzers faces significant challenges compared to single-cell identification using EIS.

[0006] In the current mapping "CM" method, the local current density distribution is analyzed. Some current mapping methods require physical modifications to the electrolysis cell structure in order to be able to measure the current distribution within the electrolysis cell area. A known non-invasive current mapping method has been proposed by K.-H. Hauer, R. Potthast, T. Wüster: Magnetotomography-a new method for analysis formance and quality, J. Power Sources 143, 1, 2005, pp. 67-74. This non-invasive current mapping method is based on the three-dimensional measurement of the magnetic flux caused by the current in the electrolysis cell. This non-invasive current mapping method requires additional equipment and its accuracy may not be sufficient for industrial electrolyzers.

[0007] The current interruption "CI" method includes two parts: 1) natural voltage response, in which the steady-state operation of the electrolyzer is suddenly stopped and the voltage response is recorded, and 2) current switching technology. In the first part, the membrane resistance is estimated, and then in the second part, the charge transfer resistance and double layer capacitance are identified. In some cases, the Warburg impedance (Warburg impedance) that works at high current density is also identified. More information can be found in publications such as J. van der Merwe, K. Uren, G. van Schoor, D. Bessarabov: Characterization tools development for PE Melectrolysers, Int. J. Hydrogen Energy 39, 26, 2014 pp. 14212-14221. In industrial, megawatt-class electrolyzers in particular, the current drop rate is limited by the rectifier safety conversion rate and by the di / dt limit caused by the inductance of the rectifier output filter. Since stepwise current interruption is not possible to integrate with industrial electrolysers, the electrical properties cannot be estimated using the conventional current interruption “Cl” method. Summary of the Invention

[0008] The following is a simplified summary to provide a basic understanding of some aspects of various embodiments. This summary is not an extensive overview of the present invention. It is neither intended to identify the main or key elements of the present invention nor to delineate the scope of the present invention. The following summary merely presents some concepts in a simplified form as a prelude to a more detailed description of exemplary and non-limiting embodiments.

[0009] According to the present invention, a novel apparatus for estimating the electrical characteristics of an electrolyzer is provided. The apparatus according to the present invention comprises current and voltage sensors for measuring the voltage applied to the electrolyzer and the current flowing through the electrolyzer. Furthermore, the apparatus comprises a data processing system for:

[0010] - storing data indicating the value u0 of the differential voltage prevailing at the beginning of the shutdown of the electrolyzer, the differential voltage being the difference between the voltage applied to the electrolyzer and the total reversible voltage of the electrolyzer, and the value I0 of the electrolyzer current prevailing at the beginning of the shutdown,

[0011] - in response to the current having reached zero, calculating, based on two or more values ​​of the differential voltage when the current is zero and the differential voltage is therefore equal to the double layer capacitance voltage of the electrolyzer, an estimate τ of the time constant of the exponential decay of the double layer capacitance voltage and an estimate u of the double layer capacitance voltage that prevails at the start of shutdown 0C ,as well as

[0012] - Calculate at least one of the following: i) the membrane resistance R of the electrolyzer m Estimate of R m =(u0–u 0C ) / I0, ii) Charge transfer resistance R of electrolyzer ct Estimate of R ct =u 0C / I0, and iii) the double layer capacitance C of the electrolyzer dl The estimated C dl =τI0 / u 0C .

[0013] Even if a gradual interruption of the electrolyzer current is not possible, it is possible to estimate the membrane resistance R m and / or charge transfer resistance R ct and / or double layer capacitance C dl Gradual current interruption is difficult or even impossible, especially in conjunction with industrial electrolysers, where the rate of current reduction is limited by the safe conversion ratio of the rectifier and by the di / dt limitation of the rectifier output filter inductance.

[0014] According to the present invention, there is also provided a novel electrolysis system, the electrolysis system comprising:

[0015] - electrolyzer,

[0016] a rectifier circuit for receiving one or more alternating voltages and for supplying a direct current to the electrodes of the electrolyser,

[0017] - a controller for controlling the DC current supplied to the electrodes of the electrolyser, and

[0018] - A device according to the invention for estimating the electrical characteristics of an electrolyser.

[0019] The electrolyzer can, for example, but need not be, an alkaline water electrolyzer, wherein the electrodes operate in an alkaline liquid electrolyte, which may include, for example, an aqueous solution of potassium hydroxide "KOH" or an aqueous solution of sodium hydroxide "NaOH."

[0020] According to the present invention, a new method for estimating the electrical characteristics of an electrolyzer is also provided. The method according to the present invention comprises:

[0021] - storing data indicating the value u0 of the differential voltage prevailing at the beginning of the shutdown of the electrolyzer, the differential voltage being the difference between the voltage applied to the electrolyzer and the total reversible voltage of the electrolyzer, and the value I0 of the electrolyzer current prevailing at the beginning of the shutdown,

[0022] - in response to the current having reached zero, calculating, based on two or more values ​​of the differential voltage when the current is zero and the differential voltage is therefore equal to the double layer capacitance voltage of the electrolyzer, an estimate τ of the time constant of the exponential decay of the double layer capacitance voltage and an estimate u of the double layer capacitance voltage that prevails at the start of shutdown 0C ,as well as

[0023] - Calculate at least one of the following: i) the membrane resistance R of the electrolyzer m Estimate of R m =(u0–u 0C ) / I0, ii) Charge transfer resistance R of electrolyzer ct Estimate of R ct =u 0C / I0, and iii) the double layer capacitance C of the electrolyzer dl The estimated C dl =τI0 / u 0C .

[0024] In case the electrolysis system comprises means for eg electrochemical impedance spectroscopy "EIS" and / or another evaluation method, the method according to the invention can be used in combination with electrochemical impedance spectroscopy and / or other evaluation methods.

[0025] According to the present invention, there is also provided a novel computer program for estimating the electrical characteristics of an electrolyzer. The computer program according to the present invention comprises computer executable instructions for controlling a programmable processor to:

[0026] - receiving data indicative of the voltage applied to the electrolyser and the current of the electrolyser from voltage and current sensors,

[0027] - storing data indicating the value u0 of the differential voltage prevailing at the beginning of the shutdown of the electrolyzer, the differential voltage being the difference between the voltage applied to the electrolyzer and the total reversible voltage of the electrolyzer, and the value I0 of the electrolyzer current prevailing at the beginning of the shutdown,

[0028] - in response to the current having reached zero, calculating, based on two or more values ​​of the differential voltage when the current is zero and the differential voltage is therefore equal to the double layer capacitance voltage of the electrolyzer, an estimate τ of the time constant of the exponential decay of the double layer capacitance voltage and an estimate u of the double layer capacitance voltage that prevails at the start of shutdown 0C ,as well as

[0029] - Calculate at least one of the following: i) the membrane resistance R of the electrolyzer m Estimate of R m =(u0–u 0C ) / I0, ii) Charge transfer resistance R of electrolyzer ct The estimated R ct =u 0C / I0, and iii) the double layer capacitance C of the electrolyzer dl The estimated C dl =τI0 / u 0C .

[0030] According to the present invention, there is also provided a novel computer program product comprising a non-volatile computer readable medium (eg a compact disc "CD") encoded with a computer program according to the present invention.

[0031] Exemplary and non-limiting embodiments are described in the appended dependent claims.

[0032] Various exemplary and non-limiting embodiments, both as to construction and method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplary and non-limiting embodiments when read in connection with the accompanying drawings.

[0033] The verbs "to comprise" and "to include" are used in this document as open limitations, neither excluding nor requiring the presence of unrecited features. The features recited in the dependent claims are freely combinable with each other unless expressly stated otherwise. Furthermore, it will be understood that the use of "a" or "an" throughout this document refers to the singular and does not exclude the plural. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Exemplary and non-limiting embodiments and their advantages are described in more detail below by way of example and with reference to the accompanying drawings, in which:

[0035] Figure 1a An electrolysis system is shown comprising a device for estimating electrical characteristics of an electrolyzer of the electrolysis system according to an exemplary and non-limiting embodiment,

[0036] Figure 1b shows the equivalent circuit of an electrolytic cell,

[0037] Figure 1c shows exemplary time trends of the voltage and current of the electrolyzer during shutdown of the electrolyzer, and

[0038] Figure 2 A flow chart illustrating a method for estimating electrical characteristics of an electrolyzer according to an exemplary and non-limiting embodiment is shown. DETAILED DESCRIPTION

[0039] The specific examples provided in the description given below should not be construed as limiting the scope and / or applicability of the appended claims.The lists and groups of examples provided in the description given below are not exhaustive unless expressly stated otherwise.

[0040] Figure 1aAn electrolysis system according to an exemplary and non-limiting embodiment is shown. The electrolysis system includes an electrolyzer 103, which includes one or more electrolysis cells, each of which includes an anode, a cathode, and an electrolyte. In this exemplary case, the electrolyzer 103 is a water electrolyzer, in which electrical energy is converted into chemical energy carried by hydrogen H2. Oxygen O2 is produced as a by-product. The electrolyzer 103 can, for example, but not necessarily, be an alkaline water electrolyzer, in which each electrolysis cell includes an alkaline liquid electrolyte and a porous diaphragm that separates the electrolysis cell into a cathode chamber containing a cathode and an anode chamber containing an anode. The alkaline liquid electrolyte can include, for example, a potassium hydroxide "KOH" aqueous solution or a sodium hydroxide "NaOH" aqueous solution. The electrolyzer 103 can include, for example, dozens or even hundreds of electrolysis cells. However, the electrolyzer 103 may also include one to ten electrolysis cells. The electrolysis cells can be electrically connected in series or in parallel. However, it is also possible to arrange the electrolysis cells in series groups forming parallel electrolysis cells, or in parallel groups of series electrolysis cells, or to electrically connect the electrolysis cells to one another in some other way.

[0041] The electrolysis system includes a rectifier circuit 104 for receiving an AC voltage and for supplying a DC current I to the electrodes of an electrolyzer 103. In this exemplary embodiment, the rectifier circuit 104 includes forced-commutated converter bridges 106, 108, and 109, and a supply inductor 107 on the AC voltage side of the forced-commutated converter bridges. Furthermore, the rectifier circuit 104 includes a DC current filter 113 for smoothing the current I of the electrolyzer 103. The forced-commutated converter bridges 106, 108, and 109 are connected to one another so that the current supplied to the DC current filter 113 is the sum of the DC currents generated by the forced-commutated converter bridges. Each of the forced-commutated converter bridges 106, 108, and 109 includes a converter branch, each including an AC voltage terminal and each connected between the DC voltage terminals of the converter bridge in question. Each converter branch comprises a bidirectional upper branch controllable switch and a bidirectional lower branch controllable switch, the bidirectional upper branch controllable switch being between the AC voltage terminal and a positive one of the DC voltage terminals of the converter branch under consideration, and the bidirectional lower branch controllable switch being between the AC voltage terminal and a negative one of the DC voltage terminals of the converter branch under consideration. Figure 1a In the exemplary embodiment shown, each bidirectional controllable switch includes an insulated gate bipolar transistor (IGBT) and an antiparallel diode. However, each bidirectional controllable switch may also include, for example, a gate turn-off thyristor (GTO), a metal oxide semiconductor field effect transistor (MOSFET), or some other suitable semiconductor switch instead of an IGBT.

[0042] The electrolysis system includes a controller 105 for controlling the operation of controllable switches so that a desired current is supplied to the electrolyzer 103 and a desired AC voltage is generated at the AC voltage terminals of the forced-commutated converter bridges 106, 108, and 109. Forced commutation of the bidirectional switches of the converter bridges 106, 108, and 109 can reduce current ripple in the current I supplied to the electrolyzer 103. Furthermore, forced commutation of the bidirectional switches can control the power factor of the electrolysis system's AC voltage supply and current harmonics injected into the AC voltage supply.

[0043] Figure 1b The equivalent circuit of the electrolytic cell of the electrolyzer 103 is shown. The impedance of the electrolytic cell is determined by the membrane resistance R m , charge transfer resistance R ct and double layer capacitance C dl Taking into account the mass transfer loss, the Warburg impedance Z wbg will be included in the equivalent circuit. However, Z wbg It is only relevant at high current densities and low frequencies. Consider further, assuming that the Warburg impedance Z wbg is zero. rev is the reversible voltage of the electrolytic cell. rev It is the minimum battery voltage at which electrochemical reaction occurs. rev Can be estimated based on the operating temperature and pressure of the electrolyzer.

[0044] For example, an estimate of the reversible voltage for alkaline water electrolysis is given by:

[0045] U rev =ΔG0 / (2F)–ln(P / P0)RT / (2F),

[0046] Where ΔG0 is the increase in Gibbs free energy, F is the Faraday constant, R is the gas constant, T is the absolute temperature, and P0 and P are the vapor pressures of pure water and electrolyte, respectively. ΔG0 / (2F) is 1.226 volts at 298 K and 1 atm.

[0047] Figure 1b The equivalent circuit shown can be used for the series connection of electrolytic cells, so that the membrane resistance R m Considered to correspond to the membrane resistance of the series electrolytic cell, the charge transfer resistance R ct It is considered to correspond to the charge transfer resistance of the series electrolytic cell, the double layer capacitance C dl is considered to correspond to the double layer capacitance of the series electrolytic cells, U rev is considered to correspond to the total reversible voltage of the series-connected electrolytic cells, and U is the voltage of the series-connected electrolytic cells. Accordingly, Figure 1bThe equivalent circuit shown can be used for the parallel connection of electrolytic cells.

[0048] Figure 1c 1 shows an exemplary time trend of the differential voltage u and the current I of the electrolyzer 103 during shutdown of the electrolyzer. The differential voltage u is the difference between the voltage U applied to the electrolyzer and the total reversible voltage of the electrolyzer, i.e. u=U−U rev .

[0049] Figure 1a The electrolysis system shown in comprises an apparatus for estimating electrical characteristics of an electrolyzer 103 according to an exemplary and non-limiting embodiment. The apparatus comprises a current and voltage sensor 101 for measuring a voltage U applied to the electrolyzer 103 and a current I of the electrolyzer 103. Furthermore, the apparatus comprises a data processing system 102 configured to store data in a memory circuit indicating the value u0 of the differential voltage prevailing before and at the start of the shutdown of the electrolyzer 103 and the value I0 of the current I prevailing before and at the start of the shutdown. Figure 1c In the exemplary case shown, the shutdown begins at time t0. The data processing system 102 is configured based on the fact that the current I is zero and the difference voltage u is equal to the double layer capacitance voltage u of the electrolyzer. C When the difference voltage u is two or more values, calculate the double layer capacitance voltage u C An estimate of the time constant of the exponential decay τ and an estimate of the double layer capacitance voltage that dominates at the beginning of shutdown u 0C .

[0050] When the current I is zero, the above-mentioned difference voltage u can be estimated using the following formula:

[0051] u=u 0C e -(t-t0) / τ ,

[0052] where u 0C is an estimate of the double-layer capacitance voltage of the electrolyzer that dominates at the start of shutdown, and e is the Napier constant ≈ 2.71828. The double-layer capacitance voltage u C It can be estimated as u at the beginning of the shutdown of the electrolyzer and after the shutdown begins (i.e., time ≥ t0) 0C e -(t-t0) / τ .

[0053] Figure 1c Exemplary values ​​u1 and u2 of the differential voltage u corresponding to the instants t1 and t2 when the current I is zero are shown. In the arrangement according to the exemplary and non-limiting embodiment, the data processing system 102 is configured to calculate the estimated τ and u by means of the following formulas 0C :

[0054] τ = (t2 – t1) / ln(u1 / u2), and

[0055] u 0C =u1 e (t1-t0) / τ =u2 e (t2-t0) / τ .

[0056] Since u1 and u2 are the values ​​of the differential voltage u corresponding to the instants t1 and t2 when the current I is zero, we have u1 = u 0C e -(t1-t0) / τ and u2=u 0C e -(t2-t0) / τ This gives u1 / u2=e (t2-t1) / τ , and thus τ=(t2−t1) / ln(u1 / u2). The value u2 is advantageously u1 / e, in which case ln(u1 / u2)=ln(e)=1 and it is clear that τ is t2−t1.

[0057] In an apparatus according to another exemplary and non-limiting embodiment, Figure 1a The data processing system 102 is shown configured to calculate estimates of τ and u using a curve fit (e.g., a least mean square "LMS" fit). 0C , use u 0C and τ as fitting parameters so that the curve u 0C e -(t-t0) / τ A curve is fitted to the differential voltage u over the time interval where the current I is zero (eg, the time interval from t1 to t2).

[0058] Figure 1a The data processing system 102 is shown configured to calculate at least one of the following: i) the membrane resistance R of the electrolyzer 103 m Estimate of R m =(u0–u 0C ) / I0, ii) the charge transfer resistance R of the electrolyzer 103 ct Estimate of R ct =u 0C / I0, and iii) the double layer capacitance C of the electrolyzer 103 dl The estimated C dl =τI0 / u 0C .

[0059] The reversible degradation in the electrolytic cell of the electrolyzer 103 is related to the membrane resistance R m Therefore, the membrane resistance R m Indicates the status of the electrolyzer 103.

[0060] In the apparatus according to the exemplary and non-limiting embodiment, the data processing system 102 is configured to calculate the membrane resistance R of the electrolyzer 103 when the electrolyzer 103 is continuously shut down. mEstimation and detection of the calculated membrane resistance R m estimated increase.

[0061] In an arrangement according to an exemplary and non-limiting embodiment, the data processing system 102 is configured to respond to the detected calculated membrane resistance R m The estimated increase in the energy consumption of the electrolyzer 103 may be used to activate a process for recovering from the reversible degradation to improve the life of the electrolyzer 103. The process may include, for example, continuous shutdown and startup of the electrolyzer 103 to facilitate recovery from the reversible degradation.

[0062] Data processing system 102 can be implemented using one or more processor circuits, each of which can be a programmable processor circuit provided with appropriate software, a dedicated hardware processor such as, for example, an application specific integrated circuit "ASIC," or a configurable hardware processor such as, for example, a field programmable gate array "FPGA." In addition, data processing system 102 can include one or more memory devices, each of which can be, for example, a random access memory "RAM" circuit.

[0063] Figure 2 A flow chart of a method for estimating electrical characteristics of an electrolyzer according to an exemplary and non-limiting embodiment is shown. The method comprises the following actions:

[0064] Action 201: Storing data indicating the value u0 of the differential voltage prevailing at the start of the shutdown of the electrolyzer and the value I0 of the electrolyzer current prevailing at the start of the shutdown, the differential voltage being the sum of the voltage U applied to the electrolyzer and the total reversible voltage U of the electrolyzer rev The difference between

[0065] Action 202: In response to the current having reached zero, calculating an estimate τ of the time constant of the exponential decay of the double layer capacitance voltage and an estimate u of the double layer capacitance voltage that prevails at the start of shutdown based on two or more values ​​of the differential voltage when the current is zero and the differential voltage is therefore equal to the double layer capacitance voltage of the electrolyzer 0C ,as well as

[0066] - Action 203: Calculate at least one of the following: i) the membrane resistance R of the electrolyzer m Estimate of R m =(u0–u 0C ) / I0, ii) Charge transfer resistance R of electrolyzer ct Estimate of R ct =u 0C / I0, and iii) the double layer capacitance C of the electrolyzer dl The estimated C dl =τI0 / u 0C .

[0067] In combination with the above method, the above current value I0 is required and only a zero current condition needs to be detected after shutdown begins. This gives an advantage in industrial scale electrolysis systems where it may be difficult to measure high current trends accurately enough.

[0068] The method according to an exemplary and non-limiting embodiment comprises calculating the membrane resistance R of the electrolyzer during successive shutdowns of the electrolyzer. m , and detecting increases in the calculated estimate.

[0069] The method according to the exemplary and non-limiting embodiment comprises calculating the membrane resistance R in response to the detected m The method according to the exemplary and non-limiting embodiment includes a process for continuously shutting down and starting up the electrolyzer to recover from the reversible degradation.

[0070] The computer program according to the exemplary and non-limiting embodiments comprises computer-executable instructions for controlling a programmable processor to perform actions associated with the method according to any one of the exemplary and non-limiting embodiments described above.

[0071] The computer program according to an exemplary and non-limiting embodiment comprises a software module for estimating electrical characteristics of an electrolyzer. The software module comprises computer executable instructions for controlling a programmable processor to:

[0072] - storing data indicating the value u0 of the differential voltage prevailing at the beginning of the shutdown of the electrolyzer, the differential voltage being the difference between the voltage applied to the electrolyzer and the total reversible voltage of the electrolyzer, and the value I0 of the electrolyzer current prevailing at the beginning of the shutdown,

[0073] - in response to the current having reached zero, calculating an estimate τ of the time constant of the exponential decay of the double layer capacitance voltage and an estimate u of the double layer capacitance voltage that prevails at the start of shutdown based on two or more of the differential voltages when the current is zero and the differential voltage is therefore equal to the double layer capacitance voltage of the electrolyzer 0C ,as well as

[0074] - Calculate at least one of the following: i) the membrane resistance R of the electrolyzer m Estimate of R m =(u0–u 0C ) / I0, ii) Charge transfer resistance R of electrolyzer ct Estimate of R ct =u 0C / I0, and iii) the double layer capacitance C of the electrolyzer dl The estimated C dl =τI0 / u 0C .

[0075] The above-mentioned software modules can be, for example, subroutines or functions implemented in a suitable programming language.

[0076] A computer program product according to an exemplary and non-limiting embodiment comprises a computer readable medium, such as a compact disc "CD", encoded with a computer program according to an embodiment of the invention.

[0077] A signal according to an exemplary and non-limiting embodiment is encoded to carry information defining a computer program according to an embodiment of the invention. In this exemplary case, the computer program can be downloaded from a server, which may form part of a cloud service, for example.

[0078] The specific examples provided in the description given above should not be construed as limiting the applicability and / or interpretation of the appended claims.Unless expressly stated otherwise, the lists and groups of examples provided in the description given above are not exhaustive.

Claims

1. A device for estimating electrical characteristics of an electrolyzer, said device comprising a current and voltage sensor (101) for measuring a voltage (U) applied to the electrolyzer and a current (I) of the electrolyzer, said device being characterized in that it comprises a data processing system (102) for: - storing data indicating the value u0 of the differential voltage prevailing at the beginning of shutdown of the electrolyzer, and the value I0 of the current of the electrolyzer prevailing at the beginning of shutdown, the differential voltage being the difference between the voltage applied to the electrolyzer and the total reversible voltage of the electrolyzer, - in response to the current having reached zero, calculating, based on two or more values ​​of the differential voltage when the current is zero and the differential voltage is equal to the double-layer capacitance voltage of the electrolyzer, an estimate τ of the time constant of the exponential decay of the double-layer capacitance voltage and an estimate u of the double-layer capacitance voltage that prevails at the start of the shutdown 0C ,as well as - Calculate at least one of the following: i) the membrane resistance R of the electrolyzer m The estimate of R m =(u0–u 0C ) / I0, ii) the charge transfer resistance R of the electrolyzer ct The estimate of R ct =u 0C / I0, and iii) Double layer capacitance C of the electrolyzer dl As an estimate of C dl =τI0 / u 0C .

2. The device according to claim 1, wherein The data processing system is configured to: Calculate the membrane resistance R of the electrolyzer during the continuous shutdown of the electrolyzer m , and detecting an increase in the calculated estimate.

3. The device according to claim 2, wherein The data processing system is configured to: A process of recovering from reversible degradation of an electrolysis cell of the electrolyzer is activated in response to a detected increase in the calculated estimate of the membrane resistance.

4. The device according to claim 3, wherein The process involves successive shutdowns and startups of the electrolyzer.

5. An electrolysis system comprising: - an electrolyzer (103), a rectifier circuit (104) for receiving one or more alternating voltages and for supplying a direct current to the electrodes of the electrolyser, - a controller (105) for controlling the direct current supplied to the electrodes of the electrolyser, and - Device for estimating electrical characteristics of the electrolyser according to any one of claims 1 to 4.

6. The electrolysis system according to claim 5, wherein: The rectifier circuit comprises a force-commutated converter bridge (106) and a supply inductor (107) on the AC voltage side of the force-commutated converter bridge.

7. The electrolysis system according to claim 6, wherein: The rectifier circuit comprises at least one further forced-commutated converter bridge (108, 109) such that the direct current supplied to the electrodes of the electrolyser is the sum of the direct currents of the forced-commutated converter bridges (106, 108, 109) of the rectifier circuit.

8. The electrolysis system according to claim 5, wherein: The electrolyzer (103) is configured to decompose water into hydrogen and oxygen.

9. A method for estimating the electrical characteristics of an electrolyzer, characterized in that The method comprises: - storing (201) data indicating the value u0 of the differential voltage prevailing at the beginning of the shutdown of the electrolyzer, and the value I0 of the current of the electrolyzer prevailing at the beginning of the shutdown, the differential voltage being the difference between the voltage applied to the electrolyzer and the total reversible voltage of the electrolyzer, - in response to the current having reached zero, calculating (202) an estimate τ of the time constant of the exponential decay of the double layer capacitance voltage and an estimate u of the double layer capacitance voltage that prevails at the start of the shutdown based on two or more values ​​of the differential voltage when the current is zero and the differential voltage is equal to the double layer capacitance voltage of the electrolyzer 0C ,as well as - Calculate (203) at least one of the following: i) the membrane resistance R of the electrolyzer m The estimate of R m =(u0–u 0C ) / I0, ii) the charge transfer resistance R of the electrolyzer ct The estimate of R ct =u 0C / I0, and iii) Double layer capacitance C of the electrolyzer dl As an estimate of C dl =τI0 / u 0C .

10. The method according to claim 9, wherein: The method comprises: Calculate the membrane resistance R of the electrolyzer during the continuous shutdown of the electrolyzer m , and detecting an increase in the calculated estimate.

11. The method according to claim 10, wherein: The method comprises: A process of recovering from reversible degradation of an electrolysis cell of the electrolyzer is activated in response to a detected increase in the calculated estimate of the membrane resistance.

12. The method according to claim 11, wherein The process involves successive shutdowns and startups of the electrolyzer.

13. A non-transitory computer-readable medium encoded with a computer program for estimating electrical characteristics of an electrolyzer, characterized in that The computer program comprises computer-executable instructions for controlling a programmable processor to: - receiving data indicating the voltage applied to the electrolyser and the current of the electrolyser from voltage and current sensors, - storing data indicating the value u0 of the differential voltage prevailing at the beginning of shutdown of the electrolyzer, the differential voltage being the difference between the voltage applied to the electrolyzer and the total reversible voltage of the electrolyzer, and the value I0 of the current of the electrolyzer prevailing at the beginning of shutdown, - in response to the current having reached zero, calculating, based on two or more values ​​of the differential voltage when the current is zero and the differential voltage is equal to the double-layer capacitance voltage of the electrolyzer, an estimate τ of the time constant of the exponential decay of the double-layer capacitance voltage and an estimate u of the double-layer capacitance voltage that prevails at the start of the shutdown 0C ,as well as - Calculate at least one of the following: i) the membrane resistance R of the electrolyzer m The estimate of R m =(u0–u 0C ) / I0, ii) the charge transfer resistance R of the electrolyzer ct The estimate of R ct =u 0C / I0, and iii) Double layer capacitance C of the electrolyzer dl As an estimate of C dl =τI0 / u 0C .

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