WO2023147840A1

WO2023147840A1 - System and method for supplying power

Info

Publication number: WO2023147840A1
Application number: PCT/EP2022/052323
Authority: WO
Inventors: Xiaobo Yang; Jiakun FANG; Bjorn Jacobson; Philippe Maibach; Jurgen Hafner; YuHeng YING; DanJi HUANG; Zhiyao ZHONG; Kewei HU; Lei Wang
Original assignee: Hitachi Energy Switzerland Ag
Priority date: 2022-02-01
Filing date: 2022-02-01
Publication date: 2023-08-10

Abstract

A system for supplying power including two or more power converting units (11~1n) coupled between a power source (P) and a plurality of electrolysis units (E_1~E_n) for gas production; and a control unit (20) coupled with the two or more power converting units, the control unit being configured to operate at least one power converting unit of the two or more power converting units to supply DC power including an adjustable AC component.

Description

SYSTEM AND METHOD FOR SUPPLYING POWER

TECHNICAL FIELD

The disclosure relates to power-to-gas in general, and more specifically to a system and method for supplying power.

BACKGROUND

Power-to-gas (often abbreviated P2G) is a technology that uses electrical power to produce a gaseous fuel. Most P2G systems use electrolysis to produce hydrogen. The hydrogen ca n be used directly, or further steps (known as two-stage P2G systems) may convert the hydrogen into syngas, methane, or LPG. Single-stage P2G systems to produce metha ne also exist, such as reversible solid oxide cell (ReSOC) technology. Power-to-gas allows energy from electricity to be stored and transported in the form of compressed gas, often using existing infrastructure for long-term transport and storage of natural gas.

P2G, especially water electrolysis, is considered the most promising technology for seasonal renewable energy storage. However, in the prior a rt, the low-temperature electrolyzer used for power-to-gas applications is not completely satisfactory. For example, the diphasic flow of gas a nd electrolyte in a n electrolyzer may cause bubbles to accumulate on the electrode surface, which is called the bubble effect. When the generation of bubbles is fast, covering the electrode and hindering the electrochemical reaction, the performance of the electrolyzer will decline. Specifically, the bubble coverage on the electrode leads to the reduction of the effective area of the electrode. Moreover, the bubbles permeated in the liquid will drag down the conductivity of the electrolyte. SUMMARY

I n view of the above problems in the prior art, the disclosure provides in one aspect a system for supplying power. The system includes two or more power converting units coupled between a power source and a plurality of electrolysis units for gas production; and a control unit coupled with the two or more power converting units, the control unit being configured to operate at least one power converting unit of the two or more power converting units to supply DC power including an adjustable AC component.

The disclosure provides in another aspect a method of controlling supply of power. The method includes operating at least one power converting unit of two or more power converting units, which are coupled between a power source and a plurality of electrolysis units for gas production, to supply DC power including an adjustable AC component.

The present disclosure provides in yet another aspect a system for supplying power. The system includes one or more power converting units coupled between a power source and a plurality of electrolysis units for gas production; a filter unit coupled with the power source, the filter unit being configured to carry out a filtering of at least part of disturbing harmonics in electrical power output from the power source; and a control unit coupled with the one or more power converting units, the control unit being configured to operate at least one power converting unit of the one or more power converting units to convert the electric power which has been filtered to DC power including an adjustable AC component.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features, aspects and details of the disclosure will be explained in more detail in the following text with reference to exemplary embodiments which a re illustrated in the attached drawings, in which, schematically:

Figure 1 is a schematic block diagram of a system for supplying power according to an embodiment of the disclosure;

Figure 2 shows an example of the AC component;

Figure 3 shows an example of the system illustrated in Figure 1;

Figure 4 shows another example of the system illustrated in Figure 1;

Figure 5 is a flowchart of a method for controlling supply of power according to an embodiment of the disclosure;

Figures 6 and 7 each show an example of a system for supplying power according to another embodiment of the disclosure;

Figure 8 is a flowchart of a method for controlling supply of power according to another embodiment of the disclosure;

Figures 9(a)-9(d) show simulation results of the step response of the electrolyzer to different DC step voltages;

Figures 10(a) and 10(b) show simulation results of the response of the electrolyzer to a sinusoidal input.

DETAILED DESCRIPTION

The disclosure relates to a system and method for controlling the supply of power to electrolysis units. The exemplary system and method of the disclosure are applicable for a power-to-gas system. According to an example of the disclosure, the control of converting units is optimized for the best performance of electrolysis units. Moreover, disturbing harmonics as well as voltage fluctuations in the electric power are reduced or eliminated a nd thereby the power quality of the power-to-gas system is improved.

Figure 1 illustrates a n exemplary system for supplying power according to a n embodiment of the disclosure. With reference to Figure 1, the system 100 includes two or more power converting units ll~ln and a control unit 20, n being an integer equal to or greater than two. The two or more power converting units ll~ln are coupled between a power source P and a plurality of electrolysis units E_l~E_n. The control unit 20 is coupled with the two or more power converting units ll~ln. Under the control of the control unit 20, at least one power converting unit of the two or more power converting units supplies DC power including an adjusta ble AC component. That is to say, the control unit 20 operates at least one power converting unit to convert electric power from the power source P to DC power including an adjustable AC component and provide the DC power including the adjustable AC component to at least one of the plurality of electrolysis units E_l~E_n. The DC power including the adjustable AC component is used for powering the at least one electrolysis unit.

Through the employment of such DC power including an adjustable AC component, the performance of the supplied electrolysis unit is significantly increased. For example, the gas production rate and the gas purity of the supplied electrolysis unit are improved. This will be verified by both simulation results and experiment results described later. I n an example, each of the two or more power converting units ll~ln is coupled with a respective one of the plurality of electrolysis units E_l~E_n. The control unit 20 operates each power converting unit to generate DC power including an adjustable AC component and provide the generated DC power including an adjustable AC com ponent to a respective electrolysis unit. For example, with reference to Figure 1, a first converting unit 11 is coupled with a first electrolysis unit E_1 and is operated to provide DC power including an adjustable AC component to the first electrolysis unit E_l; a second converting unit 12 is coupled with a second electrolysis unit E_2 and is operated to provide DC power including an adjustable AC component to the second electrolysis unit E_2 ... an n-th converting unit In is coupled with an n-th electrolysis unit E_n and is operated to provide DC power including an adjustable AC component to the n-th electrolysis unit E_n.

The control unit 20 may perform a voltage modulation or a current modulation as the modulation control of a power converting unit. For example, the control unit 20 sends a voltage modulation signal to a converting unit to perform the voltage modulation of the converting unit; or the control unit 20 sends a current modulation signal to a converting unit to perform the current modulation of the converting unit.

Continuing with reference to Figure 1, the control unit 20 sends a modulation control signal CS_1 to the first converting unit 11, sends a modulation control signal CS_2 to the second converting unit 12 ... sends a modulation control signal CS_n to the n-th converting unit In. Those converting units may be controlled by the current modulation or the voltage modulation or a combination of the current modulation and the voltage modulation. I n other words, each of the modulation control signa ls is a current modulation signal; or each of the modulation control signals is a voltage modulation signal; or the modulation control signa ls include both current modulation signals and voltage modulation signals.

The power source P may be a DC power source (e.g., a DC gird) or an AC power source (e.g., an AC grid). Examples for each of the DC power source and the AC power source will be described later.

I n the disclosure, the term "coupled", along with its derivatives, may mean that two or more elements are in direct physical or electrical contact. However, "coupled" may also mea n that two or more elements are not in direct contact with each other, but yet still cooperate or interact with each other. Thus, a power converting unit may be directly coupled with the power source or coupled with the power source via one or more elements. For example, a converting unit is coupled with the power source via a transformer (not shown).

The electrolysis unit is used for gas production. For example, the electrolysis unit uses electricity to decompose water into hydrogen and oxygen in a process called electrolysis. Through electrolysis, the electrolysis unit creates hydrogen and oxygen. Hydrogen gas released in this way can be used as hydrogen fuel, or remixed with the oxygen to create oxyhydrogen gas, which is used in various applications. The oxygen may be released into the atmosphere or can be captured or stored to supply other industrial processes or even medical gases.

I n the disclosure, the electrolysis units E_l~E_n may be disposed in a hydrogen generation plant. Each of the electrolysis units may include a single electrolyzer or multiple electrolyzers connected in parallel or serial.

An example of the adjustable AC component is shown in Figure 2. As shown in Figure 2, the AC component is superimposed on a DC voltage ( U DC) or DC current (I DC) and has a sinusoidal waveform. It is noted that other waveforms may be also applicable by mea ns of using Fourier decomposition. The adjustable AC component has at least one of an adjustable frequency, amplitude and phase. That is to say, at least one of the frequency, am plitude and phase of the AC component can be adjusted. Examples of the adjustable AC component are described below.

Phase difference

The inventors have observed that not the absolute value of the phase, but the phase difference between AC components in DC power supplied to adjacent electrolysis units is the key factor to be considered. Through the employment of such a phase difference, disturbing harmonics as well as voltage fluctuations in the electric power ca n be reduced or eliminated. For exa mple, the sum total of low-frequency currents from each phase would be zero, i.e. no flicker to the power source (e.g., AC or DC grid). Examples for determining the phase difference are described below.

I n a n example, the control unit 20 determines a phase difference based on a number of the power converting units such that an AC component in DC power supplied to an electrolysis unit has a phase difference with respect to that in DC power supplied to a neighboring electrolysis unit. It is noted that the electrolysis unit and the neighboring electrolysis unit are adjacent electrolysis units that are next to each other. For example, with reference to Figure 1, the first electrolysis unit E_1 and the second electrolysis unit E_2 are next to each other, and the AC component in DC power supplied to the first electrolysis unit E_1 has the determined phase difference with respect to that in DC power supplied to the second electrolysis unit E_2. The phase difference may be equal to 360°/N, where N is the number of the power converting units. For example, if the number of the power converting units is three, the phase difference will be 120°. I n this case, each of the controllable power converting unit generates an AC component in addition to a DC voltage or DC current with an electrical phase angle difference of 120° between them. If the number of the power converting units is two, the phase difference will be 180°. I n this case, each of the controllable power converting unit generates an AC component in addition to a DC voltage or DC current with an electrical phase angle difference of 180° between them.

The phase difference may a lso be equal to 360°/f(N), where N is the number of the power converting units, a nd f(N) is a function of the num ber N . I n this case, the phase difference is 360°divided by the value of the function f(N). For example, if f(N)=2N and the num ber N is three, the phase difference will be 60°. I n this example, each of the controllable power converting units generates a n AC component in addition to a DC voltage or DC current with an electrical phase angle difference of 60° between them.

It is noted that the absolute va lue of the phase may be ca lculated based on a reference, such as a timestamp reference from GPS signals.

There may be a situation where one or more power converting units a re out of service. I n this situation, the control unit 20 calculates a new phase difference based on a num ber of power converting units that are not out of service, i.e., the power converting units that continue to function properly. It is noted that a power converting unit being out of service may include a satiation where the power converting unit exits for maintenance and a situation where the power converting unit fails. Examples of the out-of-service situation are described below. I n an example, the control unit 20 monitors a state of each power converting unit and determines whether an out-of-service occurs in any of the power converting units. If the control unit 20 determines the out-of-service occurs in at least one of the power converting units, the control unit 20 calculates a new phase difference based on a number of power converting units that continue to function properly. Then, the control unit 20 operates the power converting units that continue to function properly such that an AC component in DC power supplied to a power converting unit has the new phase difference with respect to that in DC power supplied to a neighboring electrolysis unit.

Similarly, the new phase difference is equal to 360°/(N-M) or 360°/f(N-M), where N is the number of the total power converting units, M is a num ber of the power converting units that are out of service, and f(N-M) is a function of N-M.

I n this example, the control unit 20 may determine whether a power converting unit is out of service by means of the communication between the power converting unit and itself. For example, when a power converting detects a fault occurs during its self-check, the power converting unit sends an out-of-service signal to the control unit 20, and the control unit determines that the power converting unit is out of service in response to receiving the out-of-service signal. When the control unit 20 detects an error signal included in communication signa ls transmitted between the power converting unit a nd the control unit, the control unit 20 determines that the power converting unit is out of service in response to detecting the error signal. The error signal may be an abnormal heartbeat signal, a wrong verification signal or a signa l indicating the power converting unit has lost its power or control or is about to be maintained. Frequency

The frequency of the AC component is associated with the supplied electrolysis unit. For example, the frequency of the AC component in DC power supplied to the first electrolysis unit E_1 is associated with the first electrolysis unit E_l. Similarly, the frequency of the AC component in DC power supplied to the n-th electrolysis unit E_n is associated with the n-th electrolysis unit E_n. Thus, the frequencies of AC components supplied to different electrolysis units may be the same or different. For example, if the first and the second electrolysis units are of two different types, the frequency of the AC component supplied to the first electrolysis unit a nd that of the AC component supplied to the second electrolysis unit are different. The control unit 20 determines a frequency of an AC component for each of the supplied electrolysis units. For clarity, an example of the frequency determination for a supplied electrolysis unit (e.g., the first electrolysis unit E_l) is described below.

I n an example, the control unit 20 receives a setpoint frequency of a n AC component, which will be supplied to the first electrolysis unit E_l, from a calculating unit 30 (the calculating unit 30 will be described below). The control unit 20 operates the first converting unit 11 such that the frequency of the AC component is adjusted to a frequency that is within a predetermined frequency range associated with the setpoint frequency. The predetermined frequency range may be pre-stored in the control unit 20. The predetermined frequency range may be calculated based on a physical model and/or experimental data. I n this example, the frequency of the AC component may be adjusted to be equal to the setpoint frequency.

Amplitude

The amplitude of the AC component is associated with the supplied electrolysis unit. For example, the amplitude of the AC component in DC power supplied to the first electrolysis unit E_1 is associated with the first electrolysis unit E_l. Similarly, the amplitude of the AC component in DC power supplied to the n-th electrolysis unit E_n is associated with the n-th electrolysis unit E_n. Thus, the amplitudes of AC components supplied to different electrolysis units may be the same or different. The control unit 20 determines an amplitude of an AC component for each of the supplied electrolysis units. For clarity, a n example of the a mplitude determination for a supplied electrolysis unit (e.g., the first electrolysis unit E_l) is described below.

I n an example, the control unit 20 receives a setpoint amplitude of the AC component, which will be supplied to the first electrolysis unit E_l, from the calculating unit 30 which will be described below. The control unit 20 operates the first converting unit 11 such that the amplitude of the AC component is adjusted to an amplitude that is within a predetermined amplitude range associated with the setpoint amplitude. The predetermined amplitude range may be pre-stored in the control unit 20. The predetermined amplitude range may be calculated based on a physical model and/or experimental data. I n this example, the amplitude of the AC component may be adjusted to be equal to the setpoint amplitude.

The system 100 may also include the calculating unit 30 for performing calculations and simulations of pa rameters associated with electrolysis units. The calculating unit 30 may be disposed in the control unit 20. For exam ple, the ca lculating unit 30 is integrated with the control unit 20. I n this case, the calculations and simulations happen inside the control unit 20. The calculating unit 30 may also be disposed in a processing system capable of using physical model and performing calculations and simulations. The process system may be associated with the electrolysis units or gas production plant. The processing system may also be associated with the electric power generation/distribution network, such as a SCADA (Supervisory Control and Data Acquisition) system. I n this case, the calculations and simulations happen outside the control unit 20. I n the case of the ca lculating unit 30 being in the processing system, the control unit 20 may be seen as a high level controller, and the processing system may be seen as a second level controller to the control unit 20. Examples of the calculations and simulations of parameters associated with electrolysis units are described below.

Setpoint frequency

A setpoint frequency of an AC component is selected for the purpose of improving the performance of the supplied electrolysis unit. For exam ple, with an optimal setpoint frequency, the gas production rate of the supplied electrolysis unit will be improved. A setpoint frequency of an AC component is associated with the supplied electrolysis unit. The setpoint frequencies of AC components supplied to different electrolysis units may be the same or different. The calculating unit 30 calculates a setpoint frequency for each of the electrolysis units. For clarity, examples of the calculation of a setpoint frequency for a n electrolysis unit (e.g., the first electrolysis unit) are described below.

I n an example, the calculating unit 30 ca lculates the setpoint frequency for the first electrolysis unit E_1 based on a Reynolds num ber of fluid flowing in the first electrolysis unit, a flow velocity of the fluid flowing in the first electrolysis unit, and a size of the first electrolysis unit. I n this example, the calculating unit 30 may calculate the setpoint frequency for the first electrolysis unit using the following formula (1): f_Set=Re*k*v/y (1) where f_set is the setpoint frequency;

Re is the Reynolds number of the fluid flowing in the first electrolysis unit; v is the flow velocity of the fluid flowing in the first electrolysis unit; and y is the effective area of the cathode plate and/or the anode plate of the first electrolysis unit.

The effective area of a n electrode plate represents the total a rea of regions, in which the electrolytic reaction occurs, of the electrode plate. For example, the effective area of the cathode plate or the anode plate represents the total area of groove regions, which are filled with electrolytic solution, of the cathode plate or the anode plate. It is noted that, in the case that the structure of the anode plate and the structure of the cathode plate are the same, either the effective area of the anode plate or the effective area of the cathode plate can be used to calculate the setpoint frequency. I n the case that the structure of the anode plate and the structure cathode plate are different, a sum of the effective area of the anode plate and that of the cathode plate can be used to calculate the setpoint frequency.

I n another example, the calculating unit 30 calculates the inherent frequency of the diphasic flow in the first electrolysis unit and sets the setpoint frequency for the first electrolysis unit to be equal to the calculated inherent frequency.

Setpoint amplitude

A setpoint amplitude of an AC component is selected for the purpose of improving the performance of the supplied electrolysis unit. The higher the required gas production rate is, the higher the setpoint amplitude will be. On the other hand, the gas purity will become lower as the setpoint amplitude increases. With an optimal setpoint amplitude, the required gas production rate of the supplied electrolysis unit will be satisfied and the gas purity of the supplied electrolysis unit will be improved. A setpoint amplitude of an AC component is associated with the supplied electrolysis unit. The setpoint amplitudes of AC com ponents supplied to different electrolysis units may be the same or different. The calculating unit 30 ca lculates a setpoint amplitude for each of the electrolysis units. For clarity, examples of the calculation of a setpoint amplitude for an electrolysis unit (e.g., the first electrolysis unit) is described below.

I n an example, the calculating unit 30 calculates the setpoint amplitude for the first electrolysis unit based on the required gas production rate and gas purity for the first electrolysis unit. I n this example, the calculating unit 30 may calculate the setpoint amplitude for the first electrolysis unit using the following formula (2):

Aset=k*R/P (2) where A_set is the setpoint amplitude;

R is the required gas production rate of the first electrolysis unit;

P is the required gas purity of the first electrolysis unit; and k is the coefficient of "R/P".

I n this example, the coefficient k is related to both the structure of the electrode plate and the equivalent resistance of the first electrolysis unit. For example, the more complex the structure of the electrode plate of the first electrolysis unit is, the larger the coefficient k is; and the larger the equivalent resistance of the first electrolysis unit is, the larger the coefficient k is. Gas production rate

The calculating unit 30 may calculate a gas production rate for each of the electrolysis units. The gas production rate represents the amount of gas produced per unit time which is proportional to the current according to Faraday's law. I n an example, the calculating unit 30 calculates the gas production rate for a n electrolysis unit using the following formula (3) :

where i represents the current of the electrolysis unit in a period of time, and T represents the period of time (the length of the time period).

Energy conversion efficiency

The calculating unit 30 may calculate the energy conversion efficiency for each of the electrolysis units. The energy conversion efficiency is defined as the ratio of the chemical energy in produced gas to the input electricity. I n an example, the calculating unit 30 calculates the energy conversion efficiency for a n electrolysis unit using the following formula (4) :

where E_rev represents the minimum energy required for water electrolysis, i represents the current of the electrolysis unit and u represents the voltage of the electrolysis unit.

I n an example, the calculating unit 30 may perform the above described calculations using a model based control, such as MPC (Model Predictive Control), which uses a mathematical model of the process involved in the electrolysis units (gas production plant), in order to predict the future dynamic behavior of the electrolysis units and accordingly provide optimal ma nipulated va ria bles for the process a nd operation of the electrolysis units thereof.

Figure 3 shows a n exemplary system 200 of the system 100 in Figure 1. I n the example of Figure 3, the power source is implemented as an AC power source (e.g., an AC grid). Each of the power converting units is implemented as an AC-DC converter having an input end coupled with the AC grid to receive electric power from the AC grid, a control end coupled with the control unit 20 to receive a modulation signal from the control unit 20 and an output end coupled with a n electrolysis unit to provide DC power including an AC component to the electrolysis unit.

With reference to Figure 3, the input end of the first AC-DC converter 11 receives electric power from the AC grid, the control end of the first AC-DC converter 11 receives a modulation control signal CS_1 from the control unit 20, and the output end of the first AC-DC converter 11 provides DC power including an AC component to the first electrolysis unit E_l. Similarly, the input end of the second AC-DC converter 12 receives electric power from the AC grid, the control end of the second AC-DC converter 12 receives a modulation control signal CS_2 from the control unit 20, and the output end of the second AC-DC converter 12 provides DC power including an AC component to the second electrolysis unit E_2 ... the input end of the n-th AC-DC converter In receives electric power from the AC grid, the control end of the n-th AC-DC converter In receives a modulation control signal CS_n from the control unit 20, and the output end of the n-th AC-DC converter In provides DC power including an AC component to the n-th electrolysis unit E_n. Various features of the AC component described above with reference to the system 100 are also applicable to the system 200. Figure 4 shows another exem plary system 300 of the system 100 in Figure 1. I n the example of Figure 4, the power source is implemented as a DC power source (e.g., a DC grid). Each of the power converting units is implemented as an DC-DC converter having an input end coupled with the DC grid to receive electric power from the DC grid, a control end coupled with the control unit 20 to receive a modulation signal from the control unit 20 and an output end coupled with a n electrolysis unit to provide DC power including an AC component to the electrolysis unit.

With reference to Figure 4, the input end of the first DC-DC converter 11 receives electric power from the DC grid, the control end of the first DC-DC converter 11 receives a modulation control signal CS_1 from the control unit 20, and the output end of the first DC-DC converter 11 provides DC power including an AC component to the first electrolysis unit E_l. Similarly, the input end of the second DC-DC converter 12 receives electric power from the DC grid, the control end of the second DC-DC converter 12 receives a modulation control signal CS_2 from the control unit 20, and the output end of the second DC-DC converter 12 provides DC power including an AC component to the second electrolysis unit E_1 ... the input end of the n-th DC-DC converter In receives electric power from the DC grid, the control end of the n-th DC-DC converter In receives a modulation control signal CS_n from the control unit 20, and the output end of the n-th DC-DC converter In provides DC power including an AC component to the n-th electrolysis unit E_n. Various features of the AC component described above with reference to the system 100 are also applicable to system 300.

Figure 5 illustrates a flowchart of a method 500 for controlling supply of power according to an embodiment of the disclosure. The method 500 may be implemented by means of any one of the systems 100-300 or the control unit 20 thereof, and thus various features described above with reference to the systems and the control unit are also applicable to the method 500. The method 500 includes the controlling and calculating performed by the control unit 20.

With reference to Figure 5, in step S510, at least one power converting unit is operated to supply DC power including an adjusta ble AC component. I n a n example, the adjustable AC component in the DC power is supplied to at least one electrolysis unit of the plurality of electrolysis units and has a phase difference with respect to that in DC power supplied to a neighboring electrolysis unit.

According to another embodiment of the disclosure, a system including one or more power converting units, a filter unit and a control unit is provided. The one or more power converting units are coupled between a power source and a plurality of electrolysis units. The filter unit is coupled with the power source. The filter unit is configured to ca rry out a filtering of at least part of disturbing harmonics in electric power output from the power source. The control unit is coupled with the one or more power converting units and is configured to operate at least one power converting unit of the one or more power converting units to convert the electric power which has been filtered to DC power including an adjustable AC component. This system differs from the systems 100-300 in that this system uses the filter unit to reduce or cancel disturbing harmonics in electric power. The above described phase difference configuration is not required in this system. Examples of this system are described below.

Figure 6 shows an exemplary system 400 in the case of one converting unit.

As shown in Figure 6, the system 400 includes a power converting unit 11, a control unit 20, a calculating unit 30 and a filter unit 40. The filter unit 40 carries out a filtering of at least part of disturbing harmonics in electric power output from the power source. The power converting unit 11 is coupled between the power source and an electrolysis unit E_l. The control unit 20 operates the power converting unit 11 to convert the electric power which has been filtered to DC power including an adjustable AC component and provide the DC power including the adjustable AC component to the electrolysis unit E_l. Various features described above with reference to the power converting unit, the control unit and the calculating unit as well as the adjustable AC component is also applicable here.

Figure 7 shows an exemplary system 500 in the case of multiple converting units. For clarity, two converting units are illustrated as an example. As shown in Figure 7, the system 500 includes multiple converting units 11-12, a control unit 20, a calculating unit 30 and a filter unit 40. The filter unit 40 carry out a filtering of at least pa rt of disturbing harmonics in electric power output from the power source. The first power converting unit 11 is coupled between the power source and the first electrolysis unit E_l. The second power converting unit 12 is coupled between the power source and the second electrolysis unit E_2. The control unit 20 operates each the first and second power converting units to convert the electric power which has been filtered to DC power including an adjustable AC component and provide the DC power including the adjusta ble AC component to a respective electrolysis unit. Various features described above with reference to the power converting unit, the control unit and the calculating unit as well as the adjustable AC component is also applicable here.

It is noted that the power source in the examples of Figures 6 and 7 may be a

DC power source, and may also be an AC power source. The filter unit 40 includes at least one of a passive power filter, an active power filter, a static synchronous compensator and a static va r generator. A suitable type of filter may be selected based on whether a DC power source or an AC power source is coupled and further based on system requirements.

Figure 8 illustrates a flowchart of a method 800 for controlling supply of power according to another embodiment of the disclosure. The method 800 may be implemented by means of any one of the systems 400-500 or the control unit 20 thereof, and thus various features described above with reference to the systems and control unit are also applicable to the method 800. The method 800 includes the controlling and calculating performed by the control unit 20.

With reference to Figure 8, in step S810, at least one power converting unit of the one or more power converting units is operated to convert the electrica l power which has been filtered to DC power including an adjusta ble AC component.

Simulation results

Simulations will be described below. The simulations may be performed in the calculating unit 30 using mathematical and physical models. The proposed systems and methods for controlling the supply of power to electrolysis units can be verified by the simulations.

The dynamic response of an electrolyzer containing only one cell is simulated and the main parameters are summarized in Table 1.

Table 1 The main parameters of the simulation

The radius of the cell 2.5 cm

Width of the flow channel 2.4 mm Inlet velocity of the water 1.0 m/s

Temperature 60 °C

Exchange current density of cathode 1.7 A/m²

Exchange current density of anode 1.0 A/m²

The conductivity of the membrane 100 S-m

The conductivity of the electrolyte 140 S-m

In the simulation, we only consider the dynamic response of the electrolyzer under step voltage and sinusoidal voltage. The step response is set as follows: the voltage amplitude is 1.8V, 2.0V, 2.2V DC, the step time is the initial time of the simulation, that is, t=0, and the simulation lasts for 20s. The current density and bubble volume fraction of the electrolyzer at different DC step voltages are shown in Figure 9. The voltage rises from zero to the set value at t=0, since there is no bubble covering the electrode surface, the current density reaches the maximum value. Then, bubbles are formed and accumulate on the electrode surface, the volume fraction increases, and the current density decreases to a steady value. Correspondingly, the bubble volume fraction reaches the final value determined by the diphasic flow. The steady current density and bubble volume fraction under different DC step voltages is shown in Table 2.

Table 2 The current density and bubble volume fraction under different voltage amplitudes

Voltage amplitude (V) 1.8 2.0 2.2

Steady current density

272 953 2091

(A/m²)

Steady bubble volume

2.3% 5.7% 10.2% fraction The sinusoidal response is set as follows: the voltage supplied to the electrolyzer consists of 2V DC and a sinusoidal AC with a frequency of 10Hz and an amplitude of 0.2V and the simulation lasts for 12s. In this case, the voltage, current density, and bubble volume fraction of the electrolyzer are shown in Figure 10. Considering the dynamic process that appears in the step response, Figure 10 only shows five cycles from 10s to 10.5s. Besides, the steady current density and bubble volume fraction are plotted in Figure 10 for comparisons.

The following conclusions can be seen from Figure 10.

First, comparing the current density in the sinusoidal response with that under DC step voltage, the maximum current density is greater than that under 2.2V, while the minimum current density is less than that under 1.8V. When the voltage reaches the maximum (2.2V), the bubble volume fraction is less than that under 2.2V DC (Figure 9(b)), which means that there are fewer bubbles on the electrode surface, increasing the current density. When the voltage reaches the minimum (1.8V), the situation is the opposite.

Second, the average current density is calculated and marked in Figure 9 (a). Comparing with that under 2.0V DC, the average current density is greater. According to the formulas (3) and (4), the comparison of the electrolyzer performance indicators under DC and sinusoidal response is shown in Table 3.

Table 3 The comparison of the electrolyzer performance indicators in simulation

Hydrogen Production Rate Energy Conversion

Voltage (A/m²) Efficiency

2.0V DC 953 61.5%

2.0V

1047 57.3%

DC+0.2V@10Hz

+9.86% -4.2% From Table 3, by superimposing sinusoidal components on DC voltage, the hydrogen production rate is increased with the energy conversion efficiency slightly decreasing.

Experiment results

Experiment results will be described below. The proposed systems and methods for controlling the supply of power to electrolysis units can also be verified by the experiment results.

A sinusoidal response experiment on an alkaline electrolyzer is conducted to verify the effectiveness of the proposed systems and methods. The electrolyzer contains six cells in series and is powered by a power supply, IT-7625, which can provide AC+DC superimposed voltage output.

The experiment is set as follows: the output voltage of the power supply is set as 12V DC superimposed on 1.2V AC with an adjustable frequency including 10Hz, 50Hz, 100Hz, which means the average voltage per cell is 2V+0.2V@10Hz (50Hz, 100Hz). The electrolyzer current is converted into a voltage signal by the current probe at a ratio of 1V/A, and measured by an oscilloscope with the electrolyzer voltage. Besides, as a benchmark of the experiment, the current of the electrolyzer are measured under 12V DC and the performance indicators are calculated from formulas (3) and (4). The benchmark result of the experiment is shown in Table 4.

Table 4 The benchmark result of the experiment

Voltage/V Current/A

12.0 3.04

Hydrogen Production Rate/A Energy Conversion Efficiency

3.04 61.5% According to the performance indicators, the comparison at different frequencies is summarized in Table 5.

Table 5 The comparison of the electrolyzer performance indicators in experiment

Hydrogen Production Rate Energy Conversion

Voltage (A) Efficiency

12.0V DC 3.04 61.5%

12.0V DC+1.2V@10Hz 3.6002 +18.43% 59.49% -2.01%

12.0V DC+1.2V@50Hz 3.5191 +15.76% 59.49% -2.01%

12.0V

3.4886 +14.76% 59.42% -2.08%

DC+1.2V@100Hz

It is seen that, no matter what the frequency is, superimposing a sinusoidal AC component on a DC voltage can increase the hydrogen production rate, accompanied by a slight decrease in the energy conversion efficiency.

Embodiments of the disclosure may be implemented in a non-transitory computer readable medium. The non-transitory computer readable medium may include instructions that, when executed, cause one or more processors to perform any operation of the methods for controlling the supply of power according to an embodiment of the disclosure as described above.

It should be appreciated that all the operations described above are merely exemplary, and the disclosure is not limited to any operations or sequence orders of these operations, and should cover all other equivalents under the same or similar concepts.

Processors are described in connection with various systems and methods. These processors can be implemented using electronic hardware, computer software, or any combination thereof. Whether these processors are implemented as hardware or software will depend on the specific application and the overall design constraints imposed on the system. By way of example, a processor, any portion of a processor, or any combination of processors presented in this disclosure may be implemented as a microprocessor, a micro-controller, a digital signal processor (DSP), a field programmable gate array (FPGA), a programmable logic device (PLD), state machine, gate logic, discrete hardware circuitry, and other suitable processing components configured to perform the various functions described in this disclosure. The functions of a processor, any portion of a processor, or any combination of processors presented in this disclosure may be implemented as software executed by a microprocessor, a micro-controller, a DSP, or other suitable platforms.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein. All structural and functional equivalent transformations to the elements of the various aspects of the disclosure, which are known or to be apparent to those skilled in the art, are intended to be covered by the claims.

Claims

WHAT IS CLAIMED IS:

1. A system for supplying power, comprising: two or more power converting units coupled between a power source and a plurality of electrolysis units for gas production; and a control unit coupled with the two or more power converting units, the control unit being configured to operate at least one power converting unit of the two or more power converting units to supply DC power including an adjustable AC component.

2. The system according to claim 1, wherein the adjustable AC component in the DC power has at least one of an adjustable frequency, amplitude and phase, and the adjustable AC component in the DC power supplied to at least one electrolysis unit of the plurality of electrolysis units has a phase difference with respect to that in DC power supplied to a neighboring electrolysis unit.

3. The system according to claim 2, wherein the control unit is further configured to determine the phase difference based on a number of the power converting units; and optionally, the control unit is configured to determine the phase difference is equal to 360°/N or 360°/f(N), where N is the number of the power converting units, and f(N) is a function of N.

4. The system according to any one of claims 1-3, wherein the control unit is further configured to: receive a setpoint frequency of the adjustable AC component; and operate the at least one converting unit such that the frequency of the adjustable AC component is adjusted to a frequency that is within a predetermined frequency range associated with the setpoint frequency, and optionally, the frequency is equal to the setpoint frequency.

5. The system according to claim 4, wherein the control unit is further configured to: receive a setpoint amplitude of the adjustable AC component; and operate the at least one power converting unit such that the amplitude of the adjustable AC component is adjusted to an amplitude that is within a predetermined amplitude range associated with the setpoint amplitude, and optionally, the amplitude is equal to the setpoint amplitude.

6. The system according to claim 2, wherein the control unit is further configured to: determine whether an out of service occurs in any of the two or more power converting units; in accordance with a determination that the out of service occurs in at least one of the two or more power converting units, calculate a new phase difference based on a number of power converting units that continue to function properly; and update the phase difference between AC components in DC power supplied to the power converting units that continue to function properly with the new phase difference.

7. The system according to claim 6, wherein the control unit is configured to determine the out of service occurs in a power converting unit if the control unit receives an out-of-service signal from the power converting unit, and/or detects an error signal included in communication signals transmitted between the power converting unit and the control unit.

8. The system according to claim 5, further comprising a calculating unit, wherein the calculating unit is configured to calculate parameters including the setpoint frequency, the setpoint amplitude, the gas production rate and the energy conversion efficiency for the supplied electrolysis unit, and optimally, the calculating unit is integrated in the control unit and calculates the parameters using mathematical and physical models pre-stored in the control unit; or the calculating unit is integrated in an MPC controller which is a second level controller to the control unit and calculates the parameters using a model pre-stored in the MPC controller.

9. The system according to claim 8, wherein the calculating unit is further configured to calculate the setpoint frequency based on the following parameters:

- the Reynolds number of fluid flowing in the supplied electrolysis unit;

- the flow velocity of the fluid flowing in the supplied electrolysis unit; and

- the effective area of the electrode plate of the supplied electrolysis unit.

10. The system according to claim 8 or 9, wherein the calculating unit is further configured to calculate the setpoint amplitude based on a required gas production rate and required gas purity of the supplied electrolysis unit.

11. The system according to any one of claims 1-10, wherein the control unit is configured to send a modulation control signal to the at least one power converting unit to operate the at least one power converting unit; and wherein the modulation control signal is a voltage modulation signal for the voltage modulation of the at least one power converting unit, or the modulation control signal is a current modulation signal for the current modulation of the at least one power converting unit.

12. The system according to any one of claims 1-11, wherein the at least one power converting unit comprises an AC/DC converter having an input end coupled with the power source, an output end coupled with the at least one power converting unit and a control end coupled with the control unit; or the at least one power converting unit comprises a DC/DC converter having an input end coupled with the power source, an output end coupled with the at least one power converting unit and a control end coupled with the control unit.

13. A method of controlling supply of power, comprising operating at least one power converting unit of two or more power converting units, which are coupled between a power source and a plurality of electrolysis units for gas production, to supply DC power including an adjustable AC component.

14. A system for supplying power, comprising: one or more power converting units coupled between a power source and a plurality of electrolysis units for gas production; a filter unit coupled with the power source, the filter unit being configured to carry out a filtering of at least part of disturbing harmonics in electrical power output from the power source; and a control unit coupled with the one or more power converting units, the control unit being configured to operate at least one power converting unit of the one or more power converting units to convert the electric power which has been filtered to DC power including an adjustable AC component.

15. The system according to claim 14, wherein the filter unit comprises at least one of a passive power filter, an active power filter, a static synchronous compensator and a static var generator.