EP-4736290-A1 - ELECTROLYSIS SYSTEM COMPRISING AN ELECTROLYSIS PLANT AND A RENEWABLE POWER GENERATION PLANT AND METHOD FOR CONTROLLING AN ELECTROLYSIS SYSTEM

Abstract

The present invention relates to an electrolysis system (100) comprising a renewable power generation plant (1) and an electrolysis plant (3) that both are connected to a common AC bus bar (5) such that an islanded grid is formed, wherein the electrolysis plant (3) comprises a rectifier (7) whose AC input (9) is connected to the AC bus bar (5) and whose DC output (11) is arranged to supply DC current to operate an electrolysis process, and wherein an inverter-based energy storage system (13) with a storage unit (15) and a storage controller (17) is provided, the storage unit (15) being implemented in parallel to the electrolysis plant (3) and connected to the AC bus bar (5), and the storage controller (17) being configured to control the active power (PS) of the storage unit (15) in such a way that the operation of a synchronous generator is provided to stabilize the AC input voltage. Bidirectional grid forming inverters (23) are provided that are programmed to behave like a voltage source and thus enable to react to the demand of the islanded grid such that from the storage unit (15) instantaneous reserve can be provided to stabilize the AC input voltage at the AC input (9). The invention further relates to a method for operating an electrolysis system.

Inventors

• SCHUMANN, SVEN
• LOKU, Fisnik

Assignees

• Siemens Energy Global GmbH & Co. KG

Dates

Publication Date

20260506

Application Date

20240806

Claims (1)

1. 2023PF12096 – Subsequent Application 27 Claims 1. Electrolysis system (100) comprising a renewable power generation plant (1) and an electrolysis plant (3) that both are connected to a common AC bus bar (5) such that an island- ed grid is formed, wherein the electrolysis plant (3) com- prises a rectifier (7) whose AC input (9) is connected to the AC bus bar (5) and whose DC output (11) is arranged to supply DC current to operate an electrolysis process, wherein an in- verter-based energy storage system (13) with a storage unit (15) and a storage controller (17) is provided, the storage unit (15) being implemented in parallel to the electrolysis plant (3) and connected to the AC bus bar (5), wherein the inverter-based energy storage system (13) comprises a battery energy storage system (BESS) with a plurality of battery units switched in parallel, whereby each battery unit is con- nected to and supplied from a respective bidirectional grid forming inverter (23) that is connected to the AC bus bar (5), the grid forming inverters (23) are programmed to behave like a voltage source and thus enabled to react to the demand of the islanded grid such that from the storage unit (15) in- stantaneous reserve can be provided to stabilize the AC input voltage at the AC input (9). 2. Electrolysis system (100) according to claim 1, wherein the storage controller (17) is configured to receive as input signal a virtual angular frequency (∆ω) from a free-running oscillator such that during operation a virtual inertia is provided in the AC grid, whereby the operation of a synchro- nous generator can be effectuated from the bidirectional grid forming inverter (23) to stabilize the AC input voltage. 3. Electrolysis system (100) according to claim 1 or 2, wherein the storage controller (17) is configured to provide as output signal an AC control signal (∆I AC ) usable to con- trol operation of the storage unit (15) at a determined ac- tive power (P S ). 2023PF12096 – Subsequent Application 28 4. Electrolysis system (100) according to claim 1, 2 or 3, wherein a droop-control is implemented to stabilize the AC grid, wherein in the droop-control the dependency of the ac- tive power (P) on the alternating current frequency (ω) is stored. 5. Electrolysis system (100) according to one of the preced- ing claims, wherein the rectifier (7) comprises a thyristor- based rectifier. 6. Electrolysis system (100) according to claim 5, comprising a first active power sensor (S1) located at an AC connecting line of the renewable power generation plant (1) and a second active power sensor (S2) located at an AC connection line of the electrolyser plant (3), and comprising a comparator de- vice (19) with an minuend input and a subtrahend input, the first active power sensor (S1) is connected to the minuend input and the second active power sensor (S2) is connected to the subtrahend input. 7. Electrolysis system (100) according to one of the preced- ing claims, wherein the electrolysis plant (3) comprises an electrolysis active power controller (21) enabled such that during operation a control of the active power (P) at the re- spective DC-output of a thyristor-based rectifier (7) to a set point (P set ) of the electrolysis plant (3) is achieved. 8. Electrolysis system (100) according to one of the preced- ing claims, wherein the inverter-based energy storage system (13) comprises a battery energy storage system (BESS) with a plurality of battery units switched in parallel. 9. Electrolysis system (100) according to one of the preced- ing claims, wherein the renewable power generation plant (1) comprises a wind power plant with an AC output that is con- nected to the AC bus bar (5). 2023PF12096 – Subsequent Application 29 10. Electrolysis system (100) according to one of the preced- ing claims, wherein the renewable power generation plant (1) comprises a photovoltaic plant with a voltage-source convert- ers connected with its AC output to the AC bus bar (5). 11. Method for operating an electrolysis system (100) accord- ing to one of the preceding claims, whereby the active power (P S ) of the storage unit (15) is controlled from the storage controller (17), whereby grid forming inverters (23) being provided that are programmed to behave like a voltage source and thus react to the demand of the islanded grid such that from the storage unit (15) instantaneous reserve is provided, whereby the AC input voltage is stabilized at the AC input (9). 12. Method according to claim 11, whereby the storage con- troller (17) receives as input signal a virtual angular fre- quency (∆ω) from a free-running oscillator such that during operation a virtual inertia is supplied into the AC grid by the effect that the operation of a synchronous generator is caused from the bidirectional grid forming inverter (23) such that the AC input voltage is stabilized. 13. Method according to claim 11 or 12, whereby the storage controller (17) provides as output signal an AC control sig- nal (∆I AC ) that is used to control operation of the storage unit (15) at a determined active power setpoint (P S,set ). 14. Method according to one of the claims 11, 12 or 13, whereby a droop-control is being performed based on a prede- termined dependency of the active power (P) on the alternat- ing current frequency (ω) that is applied.

Description

2023PF12096 – Subsequent Application 1 Description Electrolysis system comprising an electrolysis plant and a renewable power generation plant and method for controlling an electrolysis system. The present invention relates to an electrolysis system com- prising an electrolysis plant and a renewable power genera- tion plant. Furthermore, the invention relates to a method for controlling the electrolysis system. Electrolysis is a widely known electro-chemical method, wherein a direct (electrical) current (DC) is used to drive an otherwise non-spontaneous chemical reaction. Electrolysis has recently received high attention as a factor in fighting against climate change, as it may be utilized in so-called “power to X” processes. In said processes, a supply medium (such as water or CO2) is generally converted by means of re- newable electrical energy into chemical energy via electroly- sis. The electrolysis products containing this energy ranging from e.g. hydrogen H2 (with O2 as by-product) over small hy- drocarbons like methane CH4 (also termed “synthetic natural gas” SNG or synthetic LNG in its liquid form), ethylene C2H4 or ethanol C2H5OH to ammonia NH3 or carbon monoxide CO. Said molecules may be used as fuel, e.g. for vehicles or genera- tors, or as feedstock for the chemical industry. An electrolysis system is a device that uses electricity from an electrical power source to convert substances (electroly- sis). Corresponding to the variety of different electrochemi- cal electrolysis processes, also a high number of different electrolysis systems a proposed, such as an electrolysis sys- tem for water electrolysis. Hydrogen is a particularly environmentally friendly and sus- tainable energy source. It has the unique potential of real- izing energy systems, transportation systems and large parts of chemical industry without CO2 emissions. For this to suc- 2023PF12096 – Subsequent Application 2 ceed, however, the hydrogen must not come from fossil sources, but must be produced with the help of renewable en- ergies. At least a growing proportion of the electricity gen- erated from renewable sources is now being fed into the pub- lic grid. Thus, according to the electricity mix, at least a corresponding and increasing proportion of green hydrogen can be generated if an electrolysis system is operated with elec- tricity from the public grid. Hydrogen is nowadays generated from water, for example, by means of a proton exchange membrane (PEM) electrolysis or an alkaline electrolysis. The electrolysis systems use electri- cal energy to produce hydrogen and oxygen from the water sup- plied. This process takes place in an electrolysis stack com- posed of several electrolysis cells. Several electrolysis cells are connected in series to form an electrolysis module, or module for short. Several modules in turn are connected in series to form an electrolysis stack. Water is introduced as a reactant into the electrolysis stack, which is under direct current (DC voltage), and after the water has flowed through the electrolysis cells, two fluid streams emerge as electrol- ysis products, consisting of water and gas bubbles (O2 and H2). In general, said electrolysis process needs to be supplied with a predictable power input. Whereas the generation of re- newable energy is known to provide a fluctuating power due to various reasons. For example, the amount of generated energy is dependent on weather conditions or on the position of the sun. Further, the amount of generated energy depends on the current season as well as on the course of the day. To pro- tect electrolysis cells from damage caused by fluctuations in the input power, they must be operated in such a way that no energy shortage occurs during operation. To this end, gener- ated power cannot be consumed entirely, but has sometimes to be partly wasted. 2023PF12096 – Subsequent Application 3 It is therefore very desirable to combine in an electrolysis system a renewable energy plant directly with an electrolysis plant to produce hydrogen to obtain in the best mode hydrogen that is 100% generated from a renewable energy source or at least based on a high portion of renewable energy generation and exhibits only a minor consumption, in case needed only, of electricity from the public grid with fossil-based power contributions. However, for the operation of large-scale electrolysis plants high DC currents are required to supply the electrolysers that are usually arranged in parallel and connected to an AC bus bar. Large rectifier systems are re- quired to extract on the rectifier input side the AC current from the AC bus bar that is provided from the renewable ener- gy plant and to convert the AC current into DC current avail- able at the rectifier output to supply the electrolysers ac- cordingly. In weak power networks or island mode of a com- bined renewable energy plant with an electrolysis plant main- taining a stable operation is a technical challenge. Disturb-