An electrolyzer power supply system, a method for operating an electrolysis system, a computer program, a computer-readable storage medium, a controller and an electrolysis system

Abstract

The present invention relates to an electrolyzer power supply system (1) which comprises a transformer (2), particularly a medium to low voltage transformer (2), and a converter (3) which is electrically connected to the transformer (2), wherein the transformer (2) is adapted to receive an electrical power output (4) from an electrical power source (5) and to provide the electrical power output (4) to the converter (3), wherein the converter (3) is adapted to convert the electrical power output (4) into an electrical power input (6) for an electrolyzer (7). According to the invention, the transformer (2) is an on-load tap changing transformer (2) and the converter (3) is a self-commutated converter (3), wherein a tap selection of the on-load tap changing transformer (2), particularly between a first tap and a second tap, is only changed at a tap changing voltage (U Tap ) of the electrolyzer (7).

Description

[0001] Description

[0002] An electrolyzer power supply system, a method for operating an electrolysis system, a computer program, a computer- readable storage medium, a controller and an electrolysis system

[0003] Technical Field

[0004] The present invention relates to an electrolyzer power supply system, a method for operating an electrolysis system, a computer program, a computer-readable storage medium having stored thereon said computer program, a controller and an electrolysis system .

[0005] Technological Background

[0006] The present application targets the operation of a power supply of an electrolysis system that overcomes the limitation of previous market existing solutions and which optimi zes the converter operation for electrolysis applications .

[0007] Summary of the invention

[0008] It is an obj ect of the present invention to provide an improved electrolyzer power supply system and an improved method for operating an electrolysis system .

[0009] A solution is provided by the subj ect matter according to the independent claims . Advantageous additional embodiments of the invention are described by the dependent claims , the following description and the figures .

[0010] The invention relates to an electrolyzer power supply system comprising a trans former, particularly a medium to low voltage trans former, and a converter which is electrically connected to the trans former, wherein the trans former is adapted to receive an electrical power output from an electrical power source and to provide the electrical power output to the converter, wherein the converter is adapted to convert the electrical power output into an electrical power input for an electrolyzer .

[0011] According to the invention, the trans former is an on-load tap changing trans former and the converter is a sel f-commutated converter .

[0012] In other words , the electrolyzer power supply system may comprise an on-load tap changing trans former and an insulated gate bipolar transistor ( IGBT ) type converter, which may be operated together with the on-load tap changing trans former and which together may provide the electrical power input to the electrolyzer . The electrolyzer may be adapted to trans form the electrical power input into an energy carrier by means of an electrolysis process . The energy carrier may be hydrogen, for instance . The on-load tap changing trans former may be a trans former which may comprise an onload tap changer .

[0013] The trans former may comprise multiple windings and / or may comprise a plurality of multiple trans formers , particularly a series of multiple trans formers . The tap changer may be adapted to change a turn ratio of the trans former, particularly at a converter winding of the trans former which may be electrically connected to the converter . The converter may be a single converter or may comprise a plurality of converters , which particularly are electrically connected in series and / or in parallel .

[0014] The electrical power source may be at least one generator of an electrical power station, particularly a renewable electrical power station, and / or an electrical grid . The electrical grid may comprise at least one transmission line between the electrical power source and the electrolyzer power supply system in an island operation mode or a plurality thereof in a network operation mode . The converter may be adapted to convert the alternating current electrical power output from the electrical power source , which is received by the converter from the on-load tap changing trans former, into a direct current electrical power input for the electrolyzer . Additionally, the converter may be adapted to drop and / or boost the direct voltage for the electrolyzer . Thus , the converter may be sel f-commutated, such as an IGBT based converter . The electrolyzer power supply system may hence be adapted to provide the direct current electrical power input to the electrolyzer .

[0015] This provides the technical ef fect that the number of converters which is needed for the entire li fetime of the electrolyzer from beginning of li fe to end of li fe of the electrolyzer can be reduced . Further, the combined operation of the on-load tap changing trans former and the sel fcommutated converter can avoid the necessity to add any other additional converters to be used for an extended pre-charge operation, such as thyristor based converters . Further, the operation of the on-load tap changing trans former allows the electrolyzer power supply system to operate at an increased alternating voltage of the electrical power output from the electrical power source and can thus decrease a corresponding alternating current of the electrical power output from the electrical power source , thereby providing an improved ef ficiency . Further, a feedback of current harmonics into the electrical grid from an operation of the converter can be reduced .

[0016] The electrolyzer power supply system and the method for operating an electrolysis system also include embodiments by which additional advantages are obtained .

[0017] In one embodiment , the sel f-commutated converter is adapted to adj ust a voltage of the electrical power input to a polari zation voltage of the electrolyzer at a selected first tap of the on-load tap changing trans former, wherein the polari zation voltage particularly is lower than a minimum operating voltage of the electrolyzer . In other words , the sel f-commutated converter may be adapted to drop and / or boost the direct current voltage of the electrical energy input to the polari zation voltage of the electrolyzer when the first tap of the on-load tap changing trans former is selected . The polari zation voltage may provide an initiating polari zation of the electrolyzer, wherein particularly an electrolysis process in the electrolyzer does not commence . For instance , when the first tap is selected, the on-load tap changing trans former may be adapted to provide a voltage of the electrical power output to the converter such that the converter may recti fy the voltage of the electrical power output from the on-load tap changing trans former to the direct polari zation voltage of the electrolyzer . This provides the advantage that any other pre-charge operation converters such as additional thyristor based converters may not be needed .

[0018] In one embodiment , the sel f-commutated converter is adapted to adj ust the voltage of the electrical power input to a tap changing voltage of the electrolyzer, which particularly is higher than or equal to the minimum operating voltage of the electrolyzer, at the selected first tap and / or at a selected second tap of the on-load tap changing trans former . In other words , the sel f-commutated converter may be adapted to boost the direct current voltage of the electrical power input from the polari zation voltage to the tap changing voltage when the first tap of the on-load tap changing trans former is selected .

[0019] Additionally, the converter may be adapted to drop the voltage from a rated operating voltage to the tap changing voltage when the second tap of the on-load tap changing trans former is selected . When the second tap is selected, the on-load tap changing trans former may be adapted to provide an increased voltage of the electrical power output to the converter than when the first tap is selected, particularly on a converter side of the on-load tap changing trans former . This provides the advantage that the electrolyzer can be operated safely, particularly during a ramp-up and a rampdown procedure , since the on-load tap changing trans former may only be operated when the tap changing voltage or minimum tap changing voltage of the electrolyzer is reached .

[0020] In one embodiment , the on-load tap changing trans former is adapted to change a tap selection, particularly between the first tap and the second tap, when the sel f-commutated converter adj usts the voltage of the electrical power input to the tap changing voltage . In other words , the on-load tap changing trans former may be adapted to switch from the first selected tap to the second tap, wherein the on-load tap changing trans former may be adapted to provide a higher voltage of the electrical power output to the converter when the second tap is selected than when the first tap is selected .

[0021] Additionally, the sel f-commutated converter may be adapted to maintain its operation or to continue to adj ust the voltage of the electrical power input to the tap changing voltage during the change of the tap selection . Here , the on-load tap changing trans former may be adapted such that the change of the tap selection may provide a voltage of the electrical power input which may remain within a ramp-up and / or rampdown limit of the electrolyzer .

[0022] This provides the advantage that the electrolyzer can be operated safely, particularly during a ramp-up and a rampdown procedure , since the on-load tap changing trans former may only be operated when the tap changing voltage of the electrolyzer is reached .

[0023] Further, increasing the voltage by means of changing the tap selection of the on-load tap changing trans former may further reduce a current harmonics feedback . In one embodiment , the on-load tap changing trans former is adapted to alter the change of the tap selection, particularly to select a third tap instead of the second tap, corresponding to an aging parameter of the electrolyzer . In other words , the on-load tap changing trans former may be adapted to replace the selected second tap by a third tap, wherein the on-load tap changing trans former may be adapted to provide a higher voltage of the electrical power output to the converter than when the second tap is selected . This can compensate a shi fted current-voltage characteristic of the electrolyzer due to aging .

[0024] Additionally, the on-load tap changing trans former may be adapted such that the change of the tap selection from the second tap to the third tap may provide a voltage increase of the electrical power input which may be adapted to compensate an aging ef fect of the electrolyzer .

[0025] The aging ef fect may be determined by means of the aging parameter which may comprise a duration of operation of the electrolyzer and / or a time distance to a recent maintenance of the electrolyzer .

[0026] Additionally, the on-load tap changing trans former may be adapted to provide an amount of steps between the second tap and the third tap for compensating the aging of the electrolyzer based on the aging parameter .

[0027] This provides the advantage that aging ef fects can be compensated for a safe operation over the whole li fe of the electrolyzer .

[0028] In one embodiment , the sel f-commutated converter is adapted to adj ust the voltage of the electrical power input to a rated operating voltage of the electrolyzer, which particularly is higher than the tap changing voltage , at the selected second tap of the on-load tap changing trans former . In other words , the sel f-commutated converter may be adapted to drop and / or boost the voltage of the electrical power input to the rated operating voltage when the second tap is selected . The rated operating voltage point may be between the minimum operating voltage and a maximum operating voltage of the electrolyzer . Here , the term "between" may mean "higher than" or " lower than" and / or "equal to" . This provides the advantage that the electrolyzer can be operated more ef ficiently due to increased voltage and less currents . Further, the converter needs to boost or drop less such that a feedback of current harmonics to the electrical grid can be decreased .

[0029] In one embodiment , the sel f-commutated converter is adapted to adj ust the voltage of the electrical power input corresponding to a current-voltage characteristic of the electrolyzer, particularly between the polari zation voltage and the tap changing voltage and / or between the tap changing voltage and the rated operating voltage . In other words , the sel f-commutated converter and / or the on-load tap changing trans former at the selected first tap and / or at the selected second tap and / or at the selected third tap may be adapted to boost or to drop the voltage of the electrical power input corresponding to a ramp-up and / or ramp-down characteristic of the electrolyzer . The current-voltage characteristic may correspond to a current-voltage curve of the electrolyzer operation or to ramp-up and / or ramp-down limit . Further, the term "between" may mean "higher than" or lower than" and / or "equal to" . This provides the technical ef fect that the electrolyzer can be operated safely and may thus not be damaged or have to be shut down during operation .

[0030] Additionally, the on-load tap changing trans former may comprise a voltage di f ference between the taps such that a voltage di f ference of the electrical power output provided to the converter may be correspond to the current-voltage characteristic of the electrolyzer . This provides the advantage that the electrolyzer is operated safely, particularly corresponding to a ramp-up and / or rampdown limit .

[0031] The invention further relates to a method for operating an electrolysis system comprising an electrolyzer and an on-load tap changing trans former, particularly a medium to low voltage on-load tap changing trans former, and a sel fcommutated converter which is electrically connected to the on-load tap changing trans former, wherein the on-load tap changing trans- former receives an electrical power output from an electrical power source and provides the electrical power output to the sel f-commutated converter, wherein the sel f-commutated converter converts the electrical power output into an electrical power input for the electrolyzer, comprising the steps of :

[0032] - Adj usting a voltage of the electrical power input by means of the sel f-commutated converter to a tap changing voltage , which particularly is higher than or equal to a minimum operating voltage of the electrolyzer, at a selected first tap and / or at a selected second tap of the on-load tap changing trans former ;

[0033] - Changing a tap selection of the on-load tap changing trans former, particularly between the first tap and the second tap, at the tap changing voltage .

[0034] In other words , the sel f-commutated converter may boost the voltage of the electrical power input to the tap changing voltage when the first tap of the on-load tap changing converter is selected and / or may drop the voltage of the electrical power input to the tap changing voltage when the second tap and / or a third tap of the on-load tap changing converter is selected . The on-load tap changing trans former may provide a lower voltage of the electrical power output to the sel f-commutated converter when the first tap of the onload tap changing trans former is selected than when the second tap is selected . Further, the on-load tap changing trans former may provide a higher voltage of the electrical power output to the sel f-commutated converter when the third tap is selected than when the second tap is selected . Thus , the tap of the on-load tap changing trans former may only be switched when the sel f-commutated converter may adj ust the voltage of the electrical power input by means of the sel fcommutated converter to the tap changing voltage . This provides the technical ef fect that the electrolyzer may be operated safely and an unwanted shutdown can be avoided .

[0035] In one embodiment , the method further comprises the step or steps of :

[0036] - Adj usting the voltage of the electrical power input by means of the sel f-commutated converter between a polari zation voltage and the tap changing voltage of the electrolyzer at the selected first tap of the on-load tap changing trans former, wherein the polari zation voltage particularly is lower than the minimum operating voltage of the electrolyzer ; and / or

[0037] - Adj usting the voltage of the electrical power input by means of the sel f-commutated converter between the tap changing voltage and a rated operating voltage of the electrolyzer, which particularly is higher than the tap changing voltage , at the selected second tap of the onload tap changing trans former .

[0038] In other words , the sel f-commutated converter may boost the voltage of the electrical power input from the polari zation voltage to the tap changing voltage when the first tap of the on-load tap changing trans former is selected . Here , the term "between" may mean "higher than" or " lower than" and / or "equal to" . In particular, the on-load tap changing trans former may provide an alternating voltage of the electrical power output to the converter that corresponds to a direct polari zation voltage of the electrolyzer when the first tap is selected .

[0039] Additionally or alternatively, the sel f-commutated converter may boost and / or drop the voltage from the tap changing voltage to the rated operating voltage when the second tap of the on-load tap changing trans former is selected . In particular, the trans former may provide a higher voltage of the electrical power output to the converter when the second tap is selected than when the first tap is selected .

[0040] This provides the advantage that the electrolyzer can be operated safely, particularly during a ramp-up and a rampdown procedure , since the on-load tap changing trans former may only be operated when the tap changing voltage of the electrolyzer is reached .

[0041] In one embodiment , the sel f-commutated converter adj usts the voltage of the electrical power input corresponding to a current-voltage characteristic of the electrolyzer, particularly between the polari zation voltage and the tap changing voltage and / or between the tap changing voltage and the rated operating voltage . In other words , the sel fcommutated converter may boost or drop the voltage within a ramp-up and / or ramp-down limit of the electrolyzer between the polari zation voltage and the tap changing voltage when the first tap of the on-load tap changing trans former is selected . The current-voltage characteristic may comprise the ramp-up and / or ramp-down limit of the respective electrolyzer . Here , the term "between" may mean "higher than" or " lower than" and / or "equal to" .

[0042] Additionally or alternatively, the sel f-commutated converter may boost or drop the voltage within a ramp-up and / or rampdown limit of the electrolyzer between the tap changing voltage and the rated operating voltage when the second tap and / or the third tap of the on-load tap changing trans former is selected .

[0043] This provides the advantage that the electrolyzer is operated safely and prevented from an unwanted shutdown . In one embodiment , changing the tap selection of the on-load tap changing trans former is altered, particularly a third tap is selected instead of the second tap, corresponding to an aging parameter of the electrolyzer . In other words , the onload tap changing trans former may adj ust the tap selection or increase the voltage on the converter side of the trans former based on the aging parameter of the electrolyzer . Based on the aging parameter, the on-load tap changing trans former may select the third tap instead of the second tap, wherein the trans former may provide a higher voltage of the electrical power output to the converter when the third tap is selected than when the second tap is selected . The aging parameter may be received from an electrolyzer controller, wherein the aging parameter may particularly comprise a duration of operation of the electrolyzer and / or a time distance to a recent maintenance of the electrolyzer . This provides the advantage that an aging of the electrolyzer can be compensated and further that a number of converters can be reduced for the entire li fetime of the electrolyzer from beginning of li fe to end of li fe of the electrolyzer .

[0044] The invention further relates to a computer-program comprising instructions which, when the program is executed by a controller, particularly an electrolyzer controller and / or a converter controller and / or a tap changer controller, cause the controller to carry out the steps of said method . The controller may comprise means to execute said method, particularly means to convert an alternating current electrical power output from an electrical power source into a direct current electrical power input for an electrolyzer and / or comprise means to drop and / or boost a voltage of the electrical power input to the electrolyzer .

[0045] Additionally or alternatively, the controller may comprise means to switch a tap of the on-load tap changing trans former and / or means to display when a tap selection is to be changed and / or which tap is to be selected for a manual operation of the on-load tap changing trans former . The invention also relates to a computer-readable storage medium having stored thereon said computer program . In other words , the computer-readable storage medium may be a punched card, a ( floppy) disk storage medium, a hard disk, a CD, a DVD, an USB (Universal Serial Bus ) storage device , a RAM (Random Access Memory) , a ROM (Read Only Memory) and / or an EPROM (Erasable Programmable Read Only Memory) . Preferably, the computer-readable storage medium may be a RAM or a ROM, wherein particularly a flash memory is used . The computer readable-storage medium may also be a data communication network which allows downloading a program code , such as the Internet for example , or further systems .

[0046] The invention further relates to a controller or more particularly a control or controller arrangement . The controller or controller arrangement comprise an electrolyzer controller and / or a converter controller and / or a tap changer controller, comprising said computer-readable storage medium . The controller or control arrangement may each be programmable logic controller ( PLC ) . The controller or control arrangement may hence comprise at least one processor and said computer-readable storage medium, wherein the computer-readable storage medium comprises said computer program which, when executed by the at least one processor, cause the controller to perform the method as described above .

[0047] In other words , the at least one processor may be a microprocessor and / or a microcontroller and / or a FPGA ( Field Programmable Gate Array) and / or a DSP ( Digital Signal Processor ) .

[0048] In an embodiment , the control arrangement comprises an electrolyzer controller which is adapted to send a setpoint of the tap changing voltage , like e . g . derived from a status of the electrical power source or grid status , to a converter controller as an additional part of the control arrangement . In other words , said setpoint may as well be indicated or provided as a grid service requirement from a transmission grid operator, for instance . Thus , advantageously, the setpoint can be considered in the controls of the converter .

[0049] According to a more speci fic embodiment of the control arrangement , the setpoint is chosen based on the respective polari zation voltage of the electrolyzer and an aging status of the same . Consequently, polari zation voltage and aging status can beneficially be taken into account for the inventive control functionality .

[0050] In total this allows for providing a smart and robust operating procedure of the electrolyzer system, particularly during startup and shutdown and in dependence of an actual grid requirement , which may be demanded by a transmission system operator, for example .

[0051] The controller may comprise means to execute said method, particularly means to convert an alternating current electrical power output from an electrical power source into a direct current electrical power input for an electrolyzer and / or comprise means to drop and / or boost a voltage of the electrical power input to the electrolyzer .

[0052] Additionally or alternatively, the controller may comprise means to switch a tap of the on-load tap changing trans former and / or means to display when a tap selection is to be changed and / or which tap is to be selected for a manual operation of the on-load tap changing trans former .

[0053] The invention also relates to an electrolysis system comprising said controller and / or said electrolyzer power supply system . The electrolysis system may comprise an electrolyzer and said electrolyzer power supply system . The invention also relates to reali zations comprising a combination of the features of several of the described embodiments .

[0054] Brief description of the drawings

[0055] The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawings in which :

[0056] Figure 1 shows a schematic view of an electrolysis system comprising the electrolyzer power supply system and an electrolyzer ;

[0057] Figure 2 schematically shows a typical current-voltage characteristic according to which an electrolyzer is operated;

[0058] Figure 3 schematically shows a change in the current-voltage characteristic of the electrolyzer between a beginning of li fe and an end of li fe of the electrolyzer ; and

[0059] Figure 4 schematically shows a flow diagram of a method for operating the electrolyzer power supply system and the electrolyzer .

[0060] Figure 5 schematically indicates an electrolyzer system with a modi fied power supply topology as compared to the one shown in Figure 1 .

[0061] Description of the embodiments

[0062] In the following, the invention will be explained in more detail with reference to the accompanying figure . In the Figure , like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies . Figure 1 schematically shows an electrolysis system 11 comprising an electrolyzer 7 and an electrolyzer supply system 1 , wherein the electrolyzer supply system 1 , particularly the trans former 2 , is connected to the electrical power source 5 via an alternating current electrical connection 12 . The electrical power source 5 may be a generator of a power plant , particularly of a renewable power plant , or an electrical grid, which provide their electrical power output to the trans former 2 of the electrolyzer power supply system 1 via the alternating current electrical connection 12 , particularly at medium voltage level . The alternating current electrical connection 12 may thus comprise additional trans formers , particularly from high-voltage to medium- voltage level which are not shown .

[0063] The trans former 2 is an on-load tap changing trans former 2 which is electrically connected to the sel f-commutated converter 3 by means of the alternating current electrical connection 12 , particularly at low voltage level . The on-load tap changing trans former 2 is adapted to increase the voltage of the electrical power output 4 from the electrical power source 5 on a converter side of the on-load tap changing trans former 2 where the on-load tap changing trans former 2 is electrically connected to the converter by changing a tap selection of the on-load tap changer . The tap changer of the on-load tap changing trans former 2 is adapted to change from a selected first tap to a second or third tap, wherein the on-load tap changing trans former 2 is adapted to provide a lower voltage of the electrical power output 4 to the converter 3 when the first tap is selected than when the second or third tap is selected . Here , the first tap may correspond to a minimum voltage level of the electrical power output 4 provided to the converter 3 which may be recti fied and optionally be dropped to a polari zation voltage UPof the electrolyzer 7 by the converter 3 . The converter 3 is a sel f-commutated converter 3 which converts the alternating voltage of the electrical power output provided by the trans former 2 to the converter 3 into a direct voltage of electrical power input 6 for the electrolyzer 7 .

[0064] Additionally, the converter 3 may be adapted to boost and / or drop the voltage of the electrical power input 6 of the electrolyzer 7 , particularly between the polari zation voltage UEand the tap changing voltage UTapof the electrolyzer 7 and / or between the tap changing voltage UTapand a rated operating voltage UOpof the electrolyzer 7 .

[0065] In particular, the converter 3 is adapted to adj ust the voltage of the electrical power input 6 within a ramping-up and / or ramping-down limit of the electrolyzer 7 . To perform these operations , the sel f-commutated converter 3 may be an insulated gate bipolar ( IGBT ) type converter .

[0066] The electrolyzer 7 trans forms the electrical power input 6 the received from the converter 3 into an energy carrier by means of an electrolysis process , wherein the energy carrier may be hydrogen, for instance .

[0067] The on-load tap changing trans former 2 switches the selected tap when the converter 3 adj usts the voltage of the electrical power input 6 to the tap changing voltage UTapof the electrolyzer 7 , which is higher than or equal to a minimum operating voltage Uminof the electrolyzer 7 . Here , the polari zation voltage UP, the tap changing voltage UTapand / or the minimum operating voltage Uminand / or the maximum operating voltage Umaxmay correspond to a respective type of the electrolyzer 7 . The polari zation voltage UPcorresponds to a voltage level of the electrolyzer 7 where the anode and cathode may receive a polari zation where the electrolysis process does not commence . The minimum operating voltage Uminand maximum operating voltage Umaxmay denote an operation interval of the electrolyzer 7 , where the electrolysis process takes place . The operating voltage UOpis thus between the minimum operating voltage Uminand the maximum operating voltage Umax.

[0068] The electrolysis system 11 comprises an electrolyzer controller 8 which may be connected to the converter controller 9 and / or optionally to the tap changer controller 10 by means of the data connection 14 . The electrolyzer power supply system 11 comprises the converter controller 9 and optionally the tap changer controller 10 . Alternatively, the on-load tap changing trans former 2 may be operated manually .

[0069] Altogether, the mentioned controllers may form or form part of an inventive control arrangement (not explicitly indicated) . Particularly, said control arrangement comprises the electrolyzer controller 8 being adapted to send a setpoint of the tap changing voltage UTap, as e . g . derived from a grid status or grid service requirement , to the converter controller 9 of the control arrangement . The setpoint can particularly be chosen based on the polari zation voltage UPof the electrolyzer 7 and an aging status of the electrolyzer 7 as detailed herein .

[0070] The electrolyzer controller 8 may control the converter controller 9 for adj usting the voltage UEof the electrical power input 6 and optionally the tap changer controller 10 for controlling a tap selection of the on-load tap changing trans former 10 .

[0071] Alternatively, the converter controller 9 may control the tap changer controller 10 for controlling the tap selection of the on-load tap changing trans former 10 .

[0072] Alternatively, the electrolyzer controller 8 and / or the converter controller 9 may output a signal indicating when the tap selection is to be changed and / or which tap is to be selected for a manual operation of the on-load tap changing trans former 2 . Figure 2 schematically shows a method for operating the electrolyzer 7 by means of the electrolyzer power supply system 1 according to a current-voltage characteristic of the electrolyzer 7 . The current-voltage characteristic of the electrolyzer 7 may correspond to a ramp-up and / or ramp-down limit or behavior of the electrolyzer 7 and is depicted as a current-voltage curve (I -U curve ) , wherein the voltage UEof the electrical power input is adj usted by the converter 3 corresponding to the current-voltage characteristic . The electrolyzer 7 has got a polari zation voltage UPwhere no electrolysis reaction may occur . The electrolyzer 7 performs the electrolysis process between the minimum operating voltage Uminand the maximum operating voltage Umaxat their respective corresponding minimum operating current lmtnand maximum operating current Imax• The tap changing voltage UTapis higher than or equal to the minimum operating voltage Uminand may indicate an operating point of the electrolyzer 7 , where a change of the tap selection of the on-load tap changing trans former remains within a ramp-up and / or rampdown limit of the electrolyzer 7 .

[0073] The line in the I -U diagram of Figure 2 indicates the voltage UEof the electrical power input 6 provided by the converter 3 to the electrolyzer 7 which is adj usted by means of the converter 3 and / or the on-load tap changing trans former 2 between the polari zation voltage UPand the maximum operating voltage Umaxaccording to the following ramp-up procedure :

[0074] In a first ramp-up step RU1 , the electrolyzer power supply system 1 selects a first tap of the on-load tap changing trans former 2 , wherein the on-load tap changing trans former 2 provides a voltage of the electrical power output 4 to the converter 3 , which may be recti fied into the direct polari zation voltage UEof the electrolyzer 7 by the converter 3 , when the first tap is selected . For instance , the voltage of the electrical power output 4 provided by the on-load tap changing trans former 2 to the converter may be the smallest voltage among the voltages of the electrical power output the on-load tap changing trans former is adapted to provide to the converter 3 .

[0075] The converter 3 adj usts , particularly boosts , the voltage UEof the electrical power input 6 , which is provided to the electrolyzer 7 by the converter 3 , from the polari zation voltage UPuntil it reaches the tap changing voltage UTap. The tap changing voltage UTapis higher than or equal to a minimum operating voltage Uminof the electrolyzer 7 and may indicate a voltage level of the electrolyzer 7 which allows a change of the tap selection of the on-load tap changing trans former 2 . The minimum operating voltage should be determined based on the minimum electrolyzer load, electrolyzer behavior, or other internal considerations . In the first ramp-up step RU1 , the selected first tap of the onload tap changing trans former 2 is not changed, yet .

[0076] Once the voltage UEof the electrical power input 6 provided by the converter 3 to the electrolyzer 7 has reached the tap changing voltage UTap, the tap selection of the on-load tap changing trans former 2 is changed in the second ramp-up step RU2 , wherein a second tap of the on-load tap changing trans former 2 is selected . The on-load tap changing trans former 2 is adapted to provide a higher voltage of the electrical power output 4 to the converter 3 when the second tap is selected than when the first tap is selected . Thus , the on-load tap changing trans former 2 provides an alternating voltage to the converter 3 which is higher than the voltage when the first tap is selected . For this , the electrolyzer controller 8 and / or the converter controller 9 may output a signal via the data connection 14 to change from the first tap to the second tap . The signal may be a command for the tap changer controller 10 and / or a noti fication for performing a manual tap selection operation of the on-load tap changing trans former 2 . Additionally, during the change of the tap selection, the converter 3 may continue its operation of providing the tap changing voltage UTap.

[0077] Additionally, the change of the tap selection is altered based on an aging parameter of the electrolyzer 7 . Particularly, a third step of the on-load tap changing trans former 2 is selected instead of the second tap, wherein the on-load tap changing trans former 2 is adapted to provide a higher voltage of the electrical power output 4 to the converter 3 when the third tap is selected than when the second tap is selected . Thus , the third tap replaces the second tap . The voltage di f ference between the third tap and the second tap may allow a compensation of an aging ef fect of the electrolyzer 7 .

[0078] Once the second tap has been selected, the converter adj usts , particularly boosts or drops , the voltage UEof the electrical power input 6 to a rated operating voltage UOpof the electrolyzer 7 in a third ramp-up step RU3 , wherein the rated operating voltage UOpmay be between the tap changing voltage UTapand the maximum operating voltage Umax.

[0079] Additionally after the third ramp-up step RU3 , the converter 3 adj usts , particularly boosts and / or drops , the voltage UEof the electrical power input 6 upwards and downwards between the minimum operating voltage Uminand the maximum operating voltage Umaxduring an operation of the electrolyzer 7 . Here , the on-load tap changing trans former 2 is kept in the selected second or third tap .

[0080] The voltage UEof the electrical power input 6 provided by the converter 3 to the electrolyzer 7 is adj usted by means of the converter 3 and / or the on-load tap changing trans former 2 between the maximum operating voltage Umaxand the polari zation voltage UPaccording to the following ramp-down procedure : For the first ramp-down step RD1 , the converter adj usts , particularly drops , the voltage UEof the electrical power input 6 from the current rated operating voltage UOpto the tap changing voltage UTap. During the first ramp-down step, the tap of the on-load tap changing trans former 2 remains at the second tap or third tap .

[0081] Once the sel f-commutated converter 3 has adj usted the voltage UEof the electrical power input 6 to the minimum tap changing voltage UTap, the tap selection of the on-load tap changing trans former 2 is changed from the selected second or third tap to the first tap at the second ramp-down step RD2 .

[0082] Additionally, during the change of the tap selection, the converter 3 may maintain its operation of providing the tap changing voltage UTap.

[0083] Once the first tap of the on-load tap changing trans former 2 has been selected, the sel f-commutated converter adj usts the voltage UEof the electrical power input 6 from the tap changing voltage UTapto the polari zation voltage UPof the electrolyzer 7 . Additionally, the electrolyzer 7 may be shut down .

[0084] For said steps of ramping-up and ramping-down, the converter 3 adj usts the voltage UEof the electrical power input 6 corresponding to the current-voltage characteristic of the electrolyzer 7 , particularly within the ramp-up and / or rampdown limit of the electrolyzer 7 .

[0085] Due to an aging of the electrolyzer 7 , the current-voltage characteristic of the electrolyzer 7 may change or shi ft . Figure 3 schematically shows a further step for adapting the method of Figure 2 to an aging of the electrolyzer 7 .

[0086] Figure 3 schematically shows how the current voltage characteristic of the electrolyzer 7 di f fers with respect to the states at a beginning of li fe BOL and an end of li fe EOL of the electrolyzer 7. At the end of life EOL, the electrolyzer 7 may require a higher voltage for the same current as depicted in Figure 3, where the minimum operating voltage UminE0Lof the electrolyzer 7 at the end of life EOL is higher than the minimum operating voltage UminB0Lat the beginning of life BOL . The voltage difference to compensate between the beginning of life BOL and the end of life EOL may be indicated by means of an aging parameter, such as operating hours of the electrolyzer for instance. However, the operation and methodology of ramping up and down remain the same throughout the life of the electrolyzer 7 as schematically depicted in Figure 2 for the beginning of life BOL and the end of life EOL. Thus, the method is the same in both situations of beginning of life BOL and end of life EOL.

[0087] The only difference between the beginning of life BOL and end of life EOL of the electrolyzer 7 is that the change of the tap selection of the on-load tap changing transformer 2 is to be performed differently. As shown in Figure 3, the electrolyzer 7 requires an elevated amount of voltage UEof the electrical power input at the end of life EOL than at the beginning of life BOL. This voltage difference can be compensated by adjusting the change of the tap selection corresponding to the aging parameter. Said change of the tap selection comprises replacing the selected second tap with a third tap, wherein the on-load tap changing transformer 2 is adapted to provide a higher voltage of the electrical power output 4 to the converter 3 when the third tap is selected than when the second tap is selected. A difference between the second tap and the third tap is determined based on the aging parameter. Thus, the third tap provides a higher voltage at the converter side of the on-load tap changing transformer 2 than the second selected tap.

[0088] For instance, the tap selection is changed at the beginning of life BOL to step x as the selected second tap of the onload tap changing transformer 2, where the tap changing voltage at the beginning of life UTapB0Lis reached. At the end of life EOL, the tap changing voltage UTapB0Lmay change to a higher tap changing voltage UTap,E0Lat the same minimum loading current Imin, wherein the difference between UTapE0Land UTapB0Lrequires n additional steps of the on-load tap changing transformer 2 to compensate. Thus, the third selected tap replacing the second selected tap may comprise x+n steps for compensating the minimum operating voltage difference between UTapB0Land UTapB0L. The number n of additional steps may be derived from the aging parameter. Thus, the age of the electrolyzer 7 can be compensated by altering the tap selection of the on-load tap changing transformer 2, particularly for reaching the respective tap changing voltage UTapB0L, UTapB0Lfor the same operating current IOpcorresponding to the aging parameter.

[0089] Additionally, an operation of the converter 3, particularly a boost factor of the converter 3, may be adjusted for reaching the minimum operating voltage UminB0L, UminE0Lcorresponding to the aging parameter.

[0090] The converter 3 is adapted to adjust the respective operating voltage at the beginning of life UOpBOLand the operating voltage at the end of life UOpEOLbetween the respective minimum operating voltage UminB0L, UminE0Land maximum voltage Umax and / or between the polarization voltage UPand the respective minimum operating voltage UminB0L, UminE0Lcorresponding to the aging parameter and / or the respective current-voltage characteristic at the beginning of life BOL and end of live EOL.

[0091] Consequently, the on-load tap changing transformer 2 may be designed with an increased number of steps to meet the current-voltage characteristic of the electrolyzer 7 respectively at the beginning of life BOL and the end of life EOL.

[0092] Figure 4 shows a schematic flow diagram of a method for ramping the electrolyzer 7 up and down. For ramping the electrolyzer 7 up, the following steps RU1 to RU3 are performed :

[0093] In a first ramp-up step RU1 , the electrolyzer power supply system 1 selects a first tap of the on-load tap changing trans former 2 . For instance , the voltage of the electrical power output 4 provided by the on-load tap changing trans former 2 to the converter may be the smallest voltage among the voltages of the electrical power output 4 which the on-load tap changing trans former is adapted to provide to the converter 3 . The converter 3 adj usts , particularly boosts , the voltage UEof the electrical power input 6 , which is provided to the electrolyzer 7 by the converter 3 , from the polari zation voltage UPuntil it reaches the tap changing voltage UTap. In the first ramp-up step RU1 , the selected first tap of the on-load tap changing trans former 2 is not changed .

[0094] Once the voltage UEof the electrical power input 6 provided by the converter 3 to the electrolyzer 7 has reached the tap changing voltage UTap, the tap selection of the on-load tap changing trans former 2 is changed in the second ramp-up step RU2 , wherein a second tap of the on-load tap changing trans former 2 is selected . The on-load tap changing trans former 2 may be adapted to provide a higher voltage of the electrical power output 4 to the converter 3 when the second tap is selected than when the first tap is selected . Particularly, the electrolyzer controller 8 and / or the converter controller 9 may output a signal via the data connection 14 to change from the first tap to the second tap . The signal may be a command for the tap changer controller 10 and / or a noti fication for performing a manual tap selection operation of the on-load tap changing trans former 2 .

[0095] Additionally, during the change of the tap selection, the converter 3 may continue to provide the tap changing voltage UTap, particularly may maintain its operation . Additionally, the change of the tap selection is altered based on an aging parameter of the electrolyzer 7 . Particularly, a third step of the on-load tap changing trans former 2 is selected instead of the second tap, wherein the on-load tap changing trans former 2 may be adapted to provide a higher voltage of the electrical power output 4 to the converter 3 when the third tap is selected than when the second tap is selected . The voltage di f ference between the third tap and the second tap may allow a compensation of an aging of the electrolyzer 7 .

[0096] Once the second tap has been selected, the converter adj usts , particularly boosts or drops , the voltage UEof the electrical power input 6 to a rated operating voltage UOpof the electrolyzer 7 in a third ramp-up step RU3 , wherein the rated operating voltage UOpmay be between the tap changing voltage UTapand the maximum operating voltage Umax.

[0097] Additionally after the third ramp-up step RU3 , the converter 3 adj usts , particularly boosts and / or drops , the voltage UEof the electrical power input 6 upwards and downwards between the minimum operating voltage Uminand the maximum operating voltage Umaxduring an operation of the electrolyzer 7 . Here , the on-load tap changing trans former 2 is kept in the selected second tap .

[0098] For ramping and / or or shutting the electrolyzer 7 down, the following steps RD1 to RD3 are performed :

[0099] For the first ramp-down step RD1 , the converter adj usts , particularly drops , the voltage UEof the electrical power input 6 from the current rated operating voltage UOpto the tap changing voltage UTap. During the first ramp-down step RD1 , the tap of the on-load tap changing trans former 2 remains at the second tap or third tap . Once the sel f-commutated converter 3 has adj usted the voltage UEof the electrical power input 6 to the minimum tap changing voltage UTap, the tap selection of the on-load tap changing trans former 2 is changed from the selected second or third tap to the first tap at the second ramp-down step RD2 .

[0100] Additionally, during the change of the tap selection, the converter 3 may continue to provide the tap changing voltage UTap, particularly may maintain its operation .

[0101] Once the first tap of the on-load tap changing trans former 2 has been selected, the sel f-commutated converter adj usts the voltage UEof the electrical power input 6 from the tap changing voltage UTapto the polari zation voltage UPof the electrolyzer 7 . Additionally, the electrolyzer 7 may be shut down .

[0102] For said steps of ramping-up and ramping-down, the converter 3 adj usts the voltage UEof the electrical power input 6 corresponding to the current-voltage characteristic of the electrolyzer 7 , particularly within the ramp-up and / or rampdown limit of the electrolyzer 7 .

[0103] Figure 5 shows an alternative schematic view of the inventive electrolysis system 11 . Here , instead of a two-winding trans former, a three-winding trans former is applied, wherein on each of the two indicated secondary windings ( cf . right side ) , an AC Bus or electrical connections 16 is shown . To each of the AC bus connections 16 , at least two sel fcommutating or line-commutating converters 3 , preferably IGBT converters , are connected in parallel between the on-load tab changing trans former 2 on AC side and the electrolyzer or electrolyzer stack 7 on the DC side . Each of the four indicated branches (not explicitly indicated here ) through which preferably the same or a similar current flow, may be controlled or secured via an automatic circuit breaker ACB which may interrupt the related electrical circuit when a short circuit or overload occurs as a result of an excessively high current in the system .

[0104] Further, an inductance L and / or a capacitance C or a related (built-in) filtering functionality may be employed . It is also shown in Figure 5 that all DC terminals of the converters lead to a j oint DC bus 13 for the electrolyzer or the electrolyzer system 7 . Furthermore , a DC switch or connector 15 is shown for each of the indicated branches with which electrical connection can be either established or interrupted selectively .

[0105] The present solution overcomes the limitation of the previous solution available on the market and optimi zes the IGBT converter capability required for electrolysis applications , wherein the operation of the electrolysis is guaranteed in all situations based on the electrolysis state (Beginning of Li fe BOL or End of Li fe EOL ) .

[0106] It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities . Hence , the embodiments shown here should not be understood to form a limitation of these features and configurations . Any possible combination and configuration of the described features can be chosen according to the scope of the invention .

Claims

1. Patent claims1. Electrolyzer power supply system (1) comprising a transformer (2) , particularly a medium to low voltage transformer (2) , and a converter (3) which is electrically connected to the transformer (2) , wherein the transformer (2) is adapted to receive an electrical power output (4) from an electrical power source (5) and to provide the electrical power output (4) to the converter (3) , wherein the converter (3) is adapted to convert the electrical power output (4) into an electrical power input (6) for an electrolyzer (7) , wherein the transformer (2) is an on-load tap changing transformer (2) and the converter (3) is a self-commutated converter (3) characterized in that the self-commutated converter (3) is adapted to adjust a voltage (UE) of the electrical power input (6) to a polarization voltage (UP) of the electrolyzer (7) at a selected first tap of the on-load tap changing transformer (2) , wherein the polarization voltage (UP) particularly is lower than a minimum operating voltage (Umin) of the electrolyzer (7) , wherein the selfcommutated converter (3) is adapted to adjust the voltage (UE) of the electrical power input (6) to a tap changing voltage (UTap) of the electrolyzer (7) , which particularly is higher than or equal to the minimum operating voltage (Umin) of the electrolyzer (7) , at the selected first tap and / or at a selected second tap of the on-load tap changing transformer (2) , and wherein the on-load tap changing transformer (2) is adapted to change a tap selection, particularly between the first tap and the second tap, when the self-commutated converter (3) adjusts the voltage (UE) of the electrical power input (6) to the tap changing voltage (UTap) .

2. Electrolyzer power supply system (1) according to claim 1, characterized in that the on-load tap changing transformer (2) is adapted to alter the change of the tap selection, particularly to select a third tap instead of the second tap, corresponding to an aging parameter (BOL, EOL) of the electrolyzer (7) .

3. Electrolyzer power supply system (1) according to one of the preceding claims, characterized in that the selfcommutated converter (3) is adapted to adjust the voltage (UE) of the electrical power input (6) to a rated operating voltage (UOp) of the electrolyzer (7) , which particularly is higher than the tap changing voltage (UTap) , at the selected second tap of the on-load tap changing transformer (2) .

4. Electrolyzer power supply system (1) according to one of the preceding claims, characterized in that the selfcommutated converter (3) is adapted to adjust the voltage (UE) of the electrical power input (6) corresponding to a current-voltage characteristic of the electrolyzer (7) , particularly between the polarization voltage (UP) and the tap changing voltage (UTap) and / or between the tap changing voltage (UTap) and the rated operating voltage (UOp) .

5. Method for operating an electrolysis system comprising an electrolyzer (7) and an on-load tap changing transformer (2) , particularly a medium to low voltage on-load tap changing transformer (2) , and a self-commutated converter (3) which is electrically connected to the on-load tap changing transformer (2) , wherein the on-load tap changing transformer (2) receives an electrical power output (4) from an electrical power source (5) and provides the electrical power output (4) to the self-commutated converter (3) , wherein the self-commutated converter (3) converts the electrical power output (4) into an electrical power input (6) for the electrolyzer (7) , comprising the steps of:- Adjusting a voltage (UE) of the electrical power input (6) by means of the self-commutated converter (3) to a tap changing voltage (UTap) , which particularly is higher than or equal to a minimum operating voltage (Umin) of the electrolyzer (7) , at a selected first tap and / or at a selected second tap of the on-load tap changing transformer- Changing a tap selection of the on-load tap changing transformer (2) , particularly between the first tap and the second tap, at the tap changing voltage (UTap) .

6. Method according to claim 5, further comprising the step or steps of:- Adjusting the voltage (UE) of the electrical power input (6) by means of the self-commutated converter (3) between a polarization voltage (UP) and the tap changing voltage (UTap) of the electrolyzer (7) at the selected first tap of the onload tap changing transformer (2) , wherein the polarization voltage (UP) particularly is lower than the minimum operating voltage (Umin) of the electrolyzer (7) ; and / or- Adjusting the voltage of the electrical power input (6) by means of the self-commutated converter (3) between the tap changing voltage (UTap) and a rated operating voltage (UOp) of the electrolyzer (7) , which particularly is higher than the tap changing voltage (UTap) , at the selected second tap of the on-load tap changing transformer (2) .

7. Method according to claim 5 or 6, wherein the selfcommutated converter (3) adjusts the voltage (t / F) of the electrical power input (6) corresponding to a current-voltage characteristic of the electrolyzer (7) , particularly between the polarization voltage (t / P) and the tap changing voltage (UTap) and / or between the tap changing voltage (UTap) and the rated operating voltage (UOp) .

8. Method according to one of the claims 5 to 7, wherein changing the tap selection of the on-load tap changing transformer (2) is altered, particularly wherein a third tap is selected instead of the second tap, corresponding to an aging parameter (BOL, EOL) of the electrolyzer (7) .

9. Computer program comprising instructions which, when the program is executed by a controller, particularly by an electrolyzer controller (8) and / or a converter controller (9)and / or a tap changer controller (10) , cause the controller to carry out the steps of the method of one of the claims 5 to 8.

10. Computer-readable storage medium having stored thereon the computer program of claim 9.

11. Control arrangement particularly comprising an electrolyzer controller (8) and / or a converter controller (9) and / or a tap changer controller (10) , comprising a computer- readable storage medium having stored thereon the computer program of claim 9 and optionally means to execute the method of one of the claims 5 to 8.

12. Control arrangement according to claim 11, comprising an electrolyzer controller (8) being adapted to send a setpoint of the tap changing voltage (UTap) to a converter controller (9) of the control arrangement.

13. Control arrangement according to claim 12, wherein the setpoint is chosen based on the polarization voltage (UP) of the electrolyzer (7) and an aging status of the electrolyzer (7) .

14. Electrolysis system (11) comprising the control arrangement of claim 11 to 13 and / or the electrolyzer power supply system (1) of one of the claims 1 to 4.

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