EP4630686A1

EP4630686A1 - Improvements relating to hydrogen electrolysis systems

Info

Publication number: EP4630686A1
Application number: EP23825211.8A
Authority: EP
Inventors: Christian Jeppesen; Anders Tuxen; Gert Karmisholt Andersen
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2022-12-08
Filing date: 2023-12-04
Publication date: 2025-10-15
Also published as: WO2024120594A1; CN120187948A

Abstract

A hydrogen generation system comprising a wind turbine installation including a wind energy generator (18) connected to a hydrogen electrolyser (30) by a power converter system (22) The power converter system (22) comprises a generator-side converter (24) and a electrolyser-side converter (26) which are coupled together electrically by a DC-link (28), and a converter controller (50) comprising a generator-side control module (50) coupled to the generator-side converter and a electrolyser-side control module (52) coupled to the electrolyser-side converter. The converter controller is configured to control the load torque on the wind energy generator and the electrical power fed to the electrolyser to implement a mechanical damping function associated with the wind turbine installation whilst maintaining a stable DC-link voltage. Beneficially, therefore, the wind turbine installation can implement active control of electromechanical damping systems whilst operating the electrolyser at an efficient operating point.

Description

IMPROVEMENTS RELATING TO HYDROGEN ELECTROLYSIS SYSTEMS

TECHNICAL FIELD

The invention relates to a system for hydrogen electrolysis and a method for operating an electrolysis system.

BACKGROUND

It is known that hydrogen is a highly effective energy carrier which results in no CO2 emissions when energy is released. It can be readily stored and transported making it a viable alternative to fossil fuels such as petrol and diesel. However, hydrogen production via water electrolysis requires a tremendous amount of electricity thereby potentially reducing the positive environmental impact of moving to hydrogen fuel.

Hydrogen produced by renewable energy sources such as wind or solar power is the environmental ideal since no fossil fuels are used in its production. Hydrogen produced in this way is known as green hydrogen. However, because wind and solar power production is dependent on ever changing environmental conditions, it is difficult in practice to produce hydrogen efficiently from these power sources. Despite these challenges, electrolysis of water using renewable energy sources has great potential. A particularly efficient arrangement is to connect an electrolyser directly to the output of a wind turbine. Such an arrangement can potentially provide many advantages in terms of lower cost due to the omission of a grid transformer and switchgear, and improved electrical efficiency as fewer power electronics need to be used. However, for efficient operation of the electrolyser, it is important for it to be supplied with a stable voltage. This can be challenging in a wind turbine context when there can be varying power demands due to wider control requirements from the wind turbine installation. For example, power train damping and tower damping requirements are typically controlled through a generator torque approach, which will have an effect on the available power of the generator and also, therefore, will impact the stability of the output voltage that can be achieved on DC busbars/DC links.

It is desirable to be able to integrate hydrogen electrolysers in wind turbine installations having full mechanical damping functionality. It is against this background that the present invention has been developed.

SUMMARY OF THE INVENTION In a first aspect, the examples of the invention provide a hydrogen generation system in accordance with Claim 1. In a second aspect, the examples of the invention provide a method in accordance with Claim 13.

Preferred and/or optional features are set out in the dependent claims.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a wind turbine in which a hydrogen generation system in accordance with the invention may be incorporated;

Figure 2 is a schematic view of the of a hydrogen generation system in accordance with an embodiment of the invention;

Figures 3 and 4 are schematic views of first exemplary control structures associated with a converter system of the hydrogen generation system in Figure 2;

Figures 5 and 6 are schematic views of second exemplary control structures associated with the converter system of the hydrogen generation system in Figure 2;

Figure 7 illustrates a series of data plots a-d illustrating various operating parameters associated with the operation of the hydrogen generation system of the invention.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice the invention. Other embodiments may be utilised, and structural changes may be made without departing from the scope of the invention as defined in the appended claims.

Figure 1 shows a schematic view of a wind turbine 1 in which the invention may be incorporated. The wind turbine 1 includes a nacelle 2 that is supported on a generally vertical tower 4. The nacelle 2 supports a main rotor arrangement 6. The main rotor arrangement 6 comprises a hub 8 and a plurality of wind turbine blades 10 connected to the hub 8. In this example, the wind turbine 1 comprises three wind turbine blades 10. The wind turbine 1 in Figure 1 is a well-known horizontal-axis wind turbine which is the most common form of large- scale wind turbine, but other formats would be acceptable for the invention.

The nacelle 2 also houses many functional components of the wind turbine 1. Typically, such a wind turbine 2 would be used to generate electrical energy in AC or DC form for supply to an associated electrical distribution grid. However, in this embodiment of the invention the wind turbine 1 incorporates an integrated hydrogen generation system that uses the electrical power generated by a generator housed inside the nacelle 2 into stored energy in the form of hydrogen gas by an electrolysis system.

Whereas Figure 1 illustrates a typical wind turbine in which the invention can be implemented, Figure 2 shows a systems-level overview of a hydrogen generation system 12 in accordance with an embodiment of the invention.

In overview, the hydrogen generation system 12 comprises a power generation system 14 which is coupled to an electrolysis system 16.

The power generation system 14 comprises the main rotor arrangement 6, hereinafter called simply the ‘rotor’, which drives an electrical generator 18 through a gearbox 20. It is to be noted that although a gearbox is a component that is typical in utility-scale wind turbine generators, systems are also known that are based on a so-called direct drive architecture which do not use a gearbox. The embodiments of the invention are applicable to both types of systems.

The generator 18 is electrically connected to a power converter system 22. Typically, the generator 18 and the primary power converter system 22 would operate on a three-phase electrical architecture, although this is not essential.

The power converter system 22 provides an input power source to the electrolysis system 16 via an electrical coupling or electrolyser busbar 23. The power converter system 22 comprises a machine-side or generator-side converter 24 and an electrolyser-side converter 26. The generator-side converter 24 is electrically coupled to the electrolyser-side converter 26 by a busbar or ‘DC link’ 28.

The generator-side converter 24 is an AC-DC converter and, as such, converts the AC power generated by the generator 18 into DC power onto the DC link 28. Conversely, the electrolyser-side converter is a DC-AC converter and, as such, feeds from the DC and generates AC power for the electrolysis system 16.

The skilled person would appreciate that the power converter system 22 and the DC link 24 in effect comprise what would usually be understood as a full-scale back-to-back power converter system architecture that is common in utility-scale wind turbines for the provision of variable frequency electrical power and associated reactive power support. In such a power scheme, the AC power that is placed onto the electrolyser busbar 23 is decoupled from the AC power that is generated by the generator 18. Therefore the electrolyser-side converter 26 has control over the voltage that is delivered to the electrolysis system 16.

The form of converter system that may be used for the generator-side converter 24 and the electrolyser-side converter 26 is well known in the art and within the capabilities of the skilled person to specify in a particular power generation application.

Turning to the electrolysis system 16 in more detail, in overview that system comprises an electrolysis cell stack or ‘electrolyser’ 30. The electrolyser 30 is fed with an input water stream 32 by an appropriate water source 33. That water source 33 may supply fresh water, for example from storage tanks or from a pipe. Alternatively in the case of a system based offshore, a de-saliniser may be used to remove salts from seawater and supply fresh water to the electrolyser 30. Such a de-saliniser is a known system that would be understood by the skilled person and so a full technical description will not be provided here.

The electrolyser 30 provides a hydrogen output stream 34 to a user 35 of the generated hydrogen. The user 35 may be a direct supply to a distribution network, or it may be a suitable storage capacity such as a set of tanks. The hydrogen user 35 may also include a suitable compressor/dryer system to compress the hydrogen to a suitable pressure level (e.g. 700 bar) before being stored or supplied onward to another user. In this embodiment, the electrolyser 30 may be of the type to provide non-pressurised hydrogen, that is to say hydrogen at substantially atmospheric pressure, such that a compressor is required to pressurise the hydrogen output stream for usage and/or storage purposes. However, in examples where the electrolyser is a high-pressure system, then a compressor may not be required, as would be understood by a skilled person. At this point, it should be noted that in principle any suitable type of electrolyser 30 may be used, the specification of which would be within the understanding of a skilled person. For instance, the electrolyser 30 may be an alkaline electrolyser, a polymer-electrolyte membrane (PEM) electrolyser, or an solid-oxide electrolyser (SOEC), by way of example.

The electrolyser system 16 also includes a secondary power converter 36 that is configured to control the incoming AC power delivered by the busbar 23 to DC power supplied to the electrolyser 30 itself. In the illustrated example, it is envisaged that the secondary power converter 36 of the electrolyser system 16 may be implemented as a passive rectifier unit, which is preferably three-phase in in utility-scale applications. Such a rectifier may be implemented with suitable semi-conductor devices such as diodes and/or thyristors, although it may be implemented in a more sophisticated manner with transistor-based switching devices. The choice of current switching device such as diodes, thyristors and semi-conductor switches is within the capabilities of a skilled person. However, the function of the secondary power converter 36 is to convert the AC power from the busbar 23 to DC power for the electrolyser 30 without any regulation of power delivered.

The hydrogen generation system 12 also comprises a control system 40. The control system 40 is shown here as a single functional block for simplicity, although it should be noted that this is not intended to infer any physical or logical restrictions on the actual implementation of the control system 40. As such, the control system 40 may be implemented as a standalone computing device which is configured to communicate via a wired or wireless connection with the systems, sub-systems, sensing units and so on under its control. The control system 40 may also be implemented as distributed control units, for example to provide redundancy. The precise physical and logical implementation of the control system 40 is not central to the invention and so a detailed discussion is outside the scope of this disclosure.

The control system 40 is coupled to the power converter system 22 via suitable first and second control channels 42,44 in order to control the output power that is delivered to the electrolyser 30 over the busbar 23. The control channels 42,44 are also configured to return sensing information to the control system 40 that it may need to perform its control objectives. The control system 40 is also configured to receive data input 46 from other sources. Such data input may include: pitch angle of one or more blades of the rotor, rotational speed of the generator and wind speed.

The control system 40 comprises a generator-side control module 50 and an electrolyser-side control module 52. The first control channel 42 couples the generator-side control module 50 to the generator-side converter 24, and the second control channel 44 couples the electrolyser-side control module 52 to the electrolyser-side converter 26.

Having described the schematic overview of the hydrogen generation system 12 with reference to Figure 2, the discussion will now turn to specific functionality features of the control system 40 taken in context with the hydrogen generation system 12.

In the hydrogen generation system 12 shown in Figure 2, it will be appreciated that the busbar

23 represents what can be considered to be an electrical power network. Although the coupling is connected to a single electrolyser 30 in the illustrated embodiment, in principle the busbar 23 may provide more than one connection point to respective electrolysers. As shown, however, the busbar 23 connects a single generator 18 to a single electrolyser 30 in a one-to- one connection.

In such a configuration, it is important that the voltage on the busbar remains stable at a predetermined nominal voltage level for proper operation of the electrolyser 30. Typically the busbar voltage should not vary by more than 5%-10%. Such an objective is usually achievable through a wide range of wind conditions since the control system 40 is able to adjust operation of the generator-side converter 24 and the electrolyser-side converter 26 in order to maintain a stable busbar voltage.

However, as green hydrogen generation is scaled up to larger wind turbine capacities, there is a need for the wind turbine installations to implement various mechanical damping functions by means of controlling the mechanical loads on the wind turbine structure. For example, it is known that damping of tower oscillations can be achieved through regulation of the generator torque such that regulation of the electrical load (i.e. torque) on the generator 18 creates a reaction force that opposes the lateral oscillations of the wind turbine nacelle, and similar generator torque control approach are used to damp torsional drivetrain vibrations [1], [2],

The use of such damping functions affects the output power of the generator which, in turn can affect the power that the power converter system 22 is able to put onto the busbar 23 to drive the electrolyser 30. In particular, a variable input power to the generator-side converter

24 can affect the voltage on the DC link 28 if the electrolyser-side converter 26 is driving the electrolyser with a constant input power, and in extreme scenarios this can adversely effect the performance of the electrolyser-side converter 26.

However, to mitigate against this issue, the control system 22 is configured to control the load torque on the wind energy generator 18 and the electrical power fed to the electrolyser 30 to implement a damping function associated with the wind turbine installation whilst maintaining a stable DC-link voltage. In more detail, the generator-side control module 50 and the electrolyser-side control module 52 are configured to control the respective generator-side converter 24 and the electrolyser-side converter 26 in a complementary manner to balance the load torque on the wind energy generator 18 and the power fed to the electrolyser 30. As a result, the control methodology described herein has the advantage of balancing the power flow in both the generator-side converter and the electrolyser-side converter to keep the DC link voltage stable, or at least within predetermined limits. Note that those limits may be configurable to provide a narrower or wider control band, as required.

Figures 3 and 4 illustrate control algorithms, structures or schemes embodied in the control system 40. The electrolyser-side control module 52 implements a first control structure 100 as shown in Figure 3, whilst the generator-side control module 50 implements a second control structure 200, shown in Figure 4.

Referring firstly to Figure 3, the first control structure 100 includes a first controller 102 which is configured to output a power reference P_ref1 to control the electrolyser-side converter 26. In response, the electrolyser-side converter 26 outputs suitable AC output power onto the busbar 23. The first controller 102 maybe any suitable controller type, such as a PI D controller, or a more simple controller such as a PI controller. More complex controllers such as a model predictive controllers may also be used, as would be understood by the skilled person.

The principle control objective of the first controller 102 is to control the electrolyser 30 by outputting power to the busbar 23 via the electrolyser-side converter 26 in order to keep the DC link 28 at a stable voltage level. In principle the first controller 102 would work to maintain the DC link voltage to a constant level. However, in practice the DC link voltage is permitted to fluctuate by a small amount, which may be within 5-10% of a nominal DC link voltage level.

For this reason, therefore, the third controller 302 receives a voltage error value V_error associated with a DC link voltage measurement V_dc_link that is provided by way of a feedback signal that represents the measured output from the DC link 28.

The voltage error value V_error is generated from a summing junction 104 which also receives a DC link voltage reference signal V_dc_link_ref. The reference signal V_dc_link_ref is a predetermined signal generated internally that is set for proper operation of the electrolyser 30 and to fit the voltage levels of the converters. This may be based on various factors, including the required hydrogen generation output of the electrolyser 30. The first controller 102 therefore acts on the voltage error V_error and functions to reduce that error value to zero, as in the known function of closed loop controllers.

As discussed above, the first controller 102 outputs a power reference signal P_ref1 which is fed to the electrolyser-side converter 26. However, the power reference signal P_ref1 is combined with a signal derived from further signal components P_damp and P_aux at summing junction 106 in order to generate a second power reference signal P_ref 2 that is input into the electrolyser-side converter 26.

The purpose of combining the base power reference signal P_ref1 with further signal components is to overlay a variable power demand which is representative of transitory power demands of the wind turbine installation. For example, a side-to-side tower damping function may require a generator torque demand that varies sinusoidally in order to counteract the swaying motion of the tower 4. Similarly, a variable generator torque demand may be imposed in order to counter torque spikes in the drive train due to wind gusts.

In this connection, summing junction 108 combines at least two power component signals. In the illustrated example, the summing junction 108 combines three power component signals. The first power component signal is a steady state power level, labelled P_gen_ss_ref, which is a base power reference that is an indication of the power available from the prevailing wind conditions. As can be seen, the signal P_gen_ss_ref is passed through a high pass filter 110 in order to filter out a constant (DC) level in the signal and pass the variable power level that is governed by the relatively slowly varying power of the wind.

The second power signal component provides an indication of the power required by one or more electromechanical damping systems of the wind turbine 1 and is labelled P_damp. The second power signal component P_damp is shown as a single input here as representing one damping power requirement but the skilled person will appreciate that the signal component P_damp may comprise multiple signals. Examples of such damping systems that may influence such a signal component are a lateral tower oscillation damping function, fore-aft tower damping function in a floating foundation and also a drive train damping function.

A third power signal component, labelled as P_aux, provides an indication of a power requirement for one or more internal systems such as environmental conditioning systems, oil cooling system, hydraulic pressurisation systems, control systems and other auxiliary power consumers. The output of the summing junction 108 provides a time-varying power requirement signal P_ref3 which is input into the summing junction 106 as a feed forward term, after passing through a gain block 112 which may provide a configurable gain value to influence the effects of the feed-forward power signal component terms, as would be understood by a skilled person. Beneficially, feeding forward the dynamically varying signal components allows for a fast response of the converter system to adapt to the changes.

The effect of the first control structure 100 in Figure 3 is to balance the power required by the internal wind turbine systems with a corresponding regulation of the power supplied to the electrolyser 30. The first control structure 100 functions in synchronisation with the second control structure 200 in Figure 4. It will be noted that the second control structure 200 is simplified compared to the first control structure 100 in Figure 3. The second control structure 200 includes a second controller 202 which provides an input signal P_ref4 into the generatorside converter 24 in response to a power reference signal P_ref3 thereby controlling the torque or current applied to the generator 18. It should be noted that the technical principle for controlling generator torque by full-scale power converters is technology that is considered well understood by the skilled person so further detail is not within the scope of this discussion.

The second controller 202 receives an error signal P_gen_error which is a sum of the P_ref3 signal and a feedback signal P_gen which is the output power from the generator. Note that the P_ref3 signal is the same signal that is input to summing junction 106 in the control structure 100 of Figure 3.

The second controller 202 functions to control the generator-side converter 50 to drive the error signal to zero. As a result, the second control structure 200 functions to ensure that the output power generated by the generator matches the variable power reference P_ref3 generated by the compound power reference signal P_gen_ref which combines the steady state power reference P_gen_ss_ref and the internal power demand references (P_damp and P_aux) for the wind turbine.

The effect of this can be appreciated by viewing the plots shown in Figure 7. Figure 7a illustrates the variable signal P_ref3 which combines the steady state power reference with the variable internal power demands of the wind turbine 1. For illustrative purposes, the P_ref3 signal varies approximately sinusoidally in Figure 7a. This may represent the power requirements of an oscillation damping function for the wind turbine since side to side swaying of the tower 4 may be corrected with a sinusoidally-varying generator torque variation, as is known in the art. It should be noted, however, that the varying power reference signal may not be a simple sinusoidal signal and other forms of variation are to be expected.

Whereas Figure 7a shows the time-varying P_ref3 signal, Figure 7b shows the result of the control signal delivered to the generator-side converter 24 by illustrating the varying generator torque which follows the P_ref3 signal. Accordingly, Figure 7c shows the resultant power produced by the generator 18, which is controlled by the second control structure 200 shown in Figure 4.

To balance out the variable power output of the generator 18, Figure 7d shows the variable power that is delivered to the electrolyser. It will be apparent to the reader that the power delivered to the electrolyser 30 is balanced by the power generated by the generator 18. Therefore, in principle the input load on the DC link 28 will be balanced or countered by the output load which will mean that the voltage on the DC link 28 will remain stable, if not precisely constant.

Figure 7e demonstrates the DC link voltage and it will be seen that in an idealised situation the DC link voltage will remain constant. However, from a practical perspective the DC link voltage is allowed to vary by a predetermined amount, which is envisage to be between 5% an 10%. Some variation is therefore accepted, as is seen by the dashed line V_DC’.

It will be appreciated in the above discussion that the time-varying output power of the generator 18 and the power delivered to the electrolyser 30 are in synchronisation, for the purposes of illustration. This is based on the assumption that there are no lag effects based on the electrical system dynamics between the generator and the electrolyser. If there are significant electrical dynamics, then the control structures may be configured to provide a suitable compensation for the system dynamics. For example, the electrical capacitance of the DC link 28 may mean that a delay may need to be introduced between the output power of the generator 18 increasing and the increase of the power delivered to the electrolyser 30.

Therefore, to accommodate the electrical capacitance phenomenon, the first control structure 100 may be implemented with a delay function 120, as illustrated in dashed lines in Figure 3 as an optional feature.

An alternative example implementing the invention is illustrated in Figure 5 and Figure 6, where Figure 5 shows a third control structure 300 and Figure 6 shows a fourth control structure 400. It will be noted that the third control structure 300 in Figure 5 is comparable to the first control structure 100 in Figure 3 although controls the generator-side converter 24, whereas the fourth control structure 400 in Figure 6 is comparable to the second control structure 200 in Figure 4, although controls the electrolyser-side converter 26.

As in previous example of the invention shown in Figure 3 and 4, in the example shown in Figures 5 and 6 the control structures 300, 400 function in a complementary manner to balance the load torque on the wind energy generator 18 and the power fed to the electrolyser 30.

Referring firstly to Figure 5, the third control structure 300 includes a first controller 302 which is configured to output a power reference P_ref1 to control the generator-side converter 24. In response, the generator-side converter 24 outputs suitable power onto the DC-link 28. The third controller 202 maybe any suitable controller type, as discussed above.

The third control structure 300 controls the generator 18 by outputting power to the DC link 28 via the generator-side converter 24 in order to keep the DC link 28 at a stable voltage level whilst also providing for the variable power demands of active damping functions. In principle the third controller 302 would work to maintain the DC link voltage to a constant level, although, in practice the DC link voltage is permitted to fluctuate by a small amount, which may be within 5-10% of a nominal DC link voltage level.

In order to provide this functionality, the third controller 302 receives a voltage error value V_error associated with a DC link voltage measurement V_dc_link that is provided by way of a feedback signal that represents the measured voltage on the DC link by virtue of the operation of the generator-side converter 24.

The voltage error value V_error is generated from a summing junction 304 which also receives a DC link voltage reference signal V_dc_link_ref. The reference signal V_dc_link_ref is a predetermined signal generated internally that is set for proper operation of the electrolyser 30. This may be based on various factors, including the required hydrogen generation output of the electrolyser 30.

The third controller 302 therefore acts on the voltage error V_error and functions to reduce that error value to zero, as in the known function of closed loop controllers.

As discussed above, the third controller 302 outputs a power reference signal P_ref1 which is fed to the generator-side converter 24. However, the power reference signal P_ref1 is combined with a signal derived from further signal components P_damp and P_aux at summing junction 306 in order to generate a second power reference signal P_ref 2 that is input into the generator-side converter 24. It should be noted that the technical principle for controlling generator torque by full-scale power converters is technology that is considered well understood by the skilled person so further detail is not within the scope of this discussion.

The purpose of combining the base power reference signal P_ref1 with further signal components is to overlay a variable power demand which is representative of transitory power demands of the wind turbine installation, for example electromechanical active damping functions such as lateral/side-to-side tower damping.

In this connection, summing junction 308 combines at least two power component signals. In the illustrated example, the summing junction 308 combines three power component signals. The first power component signal is a steady state power level, labelled P_gen_ss_ref, which is a base power reference that is an indication of the power available from the prevailing wind conditions. As can be seen, the signal P_gen_ss_ref is passed through a high pass filter 310 in order to filter out a constant level in the signal and pass the variable power level that is governed by the relatively slowly varying power of the wind.

The second power signal component provides an indication of the power required by one or more electromechanical damping systems of the wind turbine and is labelled P_damp. The second power signal component P_damp is shown as a single input here as representing one damping power requirement but the skilled person will appreciate that the signal component P_damp may comprise multiple signals. As discussed above, examples of such damping systems that may influence such a signal component are a lateral tower oscillation damping function and also a drive train damping function.

A third power signal component, labelled as P_aux, provides an indication of a power requirement for one or more internal systems such as environmental conditioning systems, oil cooling system and hydraulic pressurisation systems.

The output of the summing junction 308 provides a variable power requirement signal P_ref3 which is input into the summing junction 306 as a feed forward term, after passing through a gain block 312 which may provide a configurable gain value to influence the effects of the feed-forward power signal component terms. The effect of the third control structure 300 in Figure 5 is to balance the power required by the internal wind turbine systems with a corresponding regulation of the generator torque control applied to the generator 18. The third control structure 300 functions in synchronisation with the fourth control structure 400 in Figure 6. It will be noted that the fourth control structure 400 is simplified compared to the third control structure 300 in Figure 5 and corresponds closely in structure to the second control structure 200 shown in Figure 4.

The fourth control structure 400 includes a fourth controller 402 which provides an input signal P_ref4 into the electrolyser-side converter 26 in response to power reference signal P_ref3 thereby controlling the power supplied to the electrolyser 30. The output of the electrolyser- side converter 26, labelled P_ely, is measured by way of a feedback signal indicating the power that is provided to the electrolyser 30.

The fourth controller 402 receives an error signal P_ely_error which is a sum of the P_ref3 signal and the feedback signal P_ely. Note that the P_ref3 signal is the same signal that is input to summing junction 306 in the control structure 300 of Figure 5.

The fourth controller 402 functions to control the electrolyser-side converter 26 to drive the error signal P_ely_error to zero. As a result, the fourth control structure 400 functions to ensure that the power delivered to the electrolyser 30 matches the variable power reference P_ref3 generated by the compound power reference signal P_gen_ref which combines the steady state power reference P_gen_ss_ref and the internal power demand references (P_damp and P_aux) for the wind turbine.

As in the previous example of the invention, the control structure 300,400 may be configured to compensate for electrical system dynamics, for example the capacitance of the DC link 28. This is illustrated in Figure 5 by a delay function 320 that acts on the time-varying parameter P_ref3 and which is input into summing junction 306.

The resulting function of the third and fourth control structures 300, 400 is comparable to the function of the first and second control structures 100, 200 and has been described above with reference to Figures 7a-e.

The skilled person would understand that various modification and adaptation may be made to the illustrated and described examples without departing form the inventive concept as defined by the claims. For example, the illustrated examples have been described with reference to a system architecture having a generator-side converter 24, being an AC-DC converter, an electrolyser- side converter 26, being a DC-AC converter, and furthermore a secondary converter system 36 featuring a AC-DC converter. In principle, the invention applies to other system architectures. For example, in the illustrated example, the electrolyser-side converter 26 and the secondary converter system 36 may be substituted for a DC-DC power converter coupled between the DC-link 28 and the electrolyser 30. In such a configuration, the first control structure 100 in Figure 3 and the fourth control structure 400 in Figure 6 would be suitable for controlling such a DC-DC power converter system.

[1] Active Damping of Torsional Vibrations in the Drive Train of a DFIG wind turbine; Chen, Xu, and Wenske.

[2] Dynamic and Control of Lateral Tower Vibrations in Offshore Wind Turbines by Means of Active Generator Torque; Zhang, Nielsen; Blaabjerg, Zhou.

Claims

1. A hydrogen generation system comprising: a wind turbine installation including a wind energy generator (18) connected to a hydrogen electrolyser (30) by a power converter system (22), wherein the power converter system (22) comprises a generator-side converter (24) and a electrolyser-side converter (26) which are coupled together electrically by a DC-link (28); a converter controller (50), comprising a generator-side control module (50) coupled to the generator-side converter and an electrolyser-side control module (52) coupled to the electrolyser-side converter; wherein the converter controller is configured to control the load torque on the wind energy generator and the electrical power fed to the electrolyser to implement a mechanical damping function associated with the wind turbine installation whilst maintaining a stable DC- link voltage.

2. The system of Claim 1 , wherein the generator-side control module (50) and the electrolyser-side control module (52) are configured to control the respective generator-side converter (24) and the electrolyser-side converter (26) in a complementary manner to balance the load torque on the wind energy generator and the power fed to the electrolyser.

3. The system of Claim 1 , wherein the electrolyser-side control module obtains a time-varying power reference (P_ref3) that includes a reference component (P_damp) from at least one mechanical damping function and obtains a voltage reference (V_dc_link_ref) indicative of the required voltage on the DC-link, and wherein, in response, the electrolyser-side control module is configured to control the power delivered to the electrolyser from the electrolyser-side converter to maintain a stable DC-link voltage.

4. The system of Claim 3, wherein the generator-side control module obtains the time-varying power reference (P_ref3) and, in response, is configured to control the load torque applied by the wind energy generator to satisfy the time-varying power reference (P_ref3).

5. The system of Claim 1 , wherein the generator-side control module (50) obtains a time-varying power reference (P_ref3) that includes a reference component (P_damp) from at least one mechanical damping function and obtains a voltage reference (Vdc link ref) indicative of the required voltage on the DC-link, wherein, in response, the generator-side control module (50) is configured to control the load torque applied by the wind energy generator (18) to maintain a stable DC link voltage.

6. The system of Claim 5, wherein the electrolyser-side control module (52) obtains the time-varying power reference (P_ref3) and, in response, is configured to control the power delivered to the electrolyser (30) from the electrolyser-side converter (26) to satisfy the time-varying power reference (P_ref3).

7. The system of Claim 2, wherein the electrolyser-side control module (52) is configured to control the power delivered to the electrolyser (30) from the electrolyser-side converter (26) whilst compensating for system dynamics.

8. The system of Claim 7, wherein compensating for system dynamics includes factoring in a time-delay to account for the capacitance of the DC-link.

9. The system of Claim 8, wherein the electrolyser-side control module is configured to factor in the time delay by implementing a time delay function on the obtained time-varying power reference (P_ref3).

10. The system of Claim 5, wherein the generator-side control module is configured to control the load torque applied by the wind energy generator whilst compensating for system dynamics.

11 . The system of Claim 10, wherein compensating for system dynamics includes factoring in a time-delay to account for the capacitance of the DC-link.

12. The system of Claim 11 , wherein the generator-side control module is configured to factor in the time delay by implementing a time delay function on the obtained time-varying power reference (P_ref3).

13. The system of any one of the preceding claims, wherein the converter controller (50) is configured to maintain the stable DC-link voltage to within +/- 10% around a nominal voltage level, and preferably to within +/- 5%.

14. A method of operating a hydrogen generation system comprising a wind turbine installation including a wind energy generator (18) connected to a hydrogen electrolyser (30) by a power converter system (22), wherein the power converter system (22) comprises a generator-side converter (24) and a electrolyser-side converter (26) which are coupled together electrically by a DC-link (28); and a converter controller (50), comprising a generator-side control module (50) coupled to the generator-side converter and a electrolyser- side control module (52) coupled to the electrolyser-side converter, wherein the method comprises controlling the load torque on the wind energy generator and the electrical power fed to the electrolyser to implement a mechanical damping function associated with the wind turbine installation whilst maintaining a stable DC-link voltage.