WO2025252289A1

WO2025252289A1 - A power supply system

Info

Publication number: WO2025252289A1
Application number: PCT/DK2025/050082
Authority: WO
Inventors: Catalin Gabriel DINCAN
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2024-06-03
Filing date: 2025-06-02
Publication date: 2025-12-11
Anticipated expiration: 2026-12-03

Abstract

According to the invention it is provided a power supply system, the system comprising: a DC load; a first power converter, the first power converter being connected to a grid and being configured to power the DC load through a DC link; a grid connected auxiliary transformer configured to power auxiliary loads; a multiport dual active bridge having a primary side and a secondary side, wherein: a first primary side port of the multiport dual active bridge is connected to a downstream side of the auxiliary transformer through a second power converter; a second primary side port of the multiport dual active bridge being connected to the DC link; a first secondary side port of the multiport dual active bridge being connected to an electric energy storage. The invention also relates to a renewable energy power system comprising a power supply system.

Description

A POWER SUPPLY SYSTEM

FIELD OF THE INVENTION

The invention relates to control of grid connected DC loads, and in particular to a power supply system that may provide power to grid connected DC loads.

BACKGROUND OF THE INVENTION

Renewable energy sources, such as, e.g., wind turbines may be connected to an electrical AC grid in order to power the grid. Power converters may be utilized in this regard, e.g., in order to convert AC power generated by a wind turbine to a DC voltage to again be converted to an AC voltage that is adapted to the prevailing grid voltage. Similarly, power converters may be utilized to connect other types of renewable power sources, such as solar power systems, hydroelectric power systems, etc. to a grid for powering the grid, and power converters may also be used to connect DC loads to a grid.

Use of renewable energy may also be further facilitated using power-to-X conversion and reconversion, where DC loads, such as, e.g., electrolyzer stacks, such as hydrogen electrolyzer stacks, may be utilized to store energy being produced by renewable energy sources for later use. This may be used as a means to alleviate impacts of fluctuating power levels being provided by a renewable energy power source. For example, hydrogen electrolyzer stacks may be connected to a grid through a power converter that converts the grid voltage to a DC voltage powering the hydrogen electrolyzer stack, where the power consumption, and thereby the load that the electrolyzer stack imposes on the grid, is controlled by controlling the DC voltage. The hydrogen electrolyzer stack may be configured to generate hydrogen, where the hydrogen may be used in a fuel cell to generate electricity when further electrical power is needed. SUMMARY OF THE INVENTION

It is an object of the invention to provide a power supply system that may be used to provide power to a grid connected DC load in case grid connection is lost, or the grid for other reasons no longer is capable of providing power to the DC load. Another object of the invention is to provide a power supply system that may provide other kinds of control possibilities in a system comprising a grid connected DC load.

According to a first aspect of the invention, it is provided a power supply system comprising: a DC load; a first power converter, the first power converter being connected to a grid and being configured to power the DC load through a DC link; a grid connected auxiliary transformer configured to power auxiliary loads; a multiport dual active bridge having a primary side and a secondary side, wherein: a first primary side port of the multiport dual active bridge is connected to a downstream side of the auxiliary transformer through a second power converter; a second primary side port of the multiport dual active bridge being connected to the DC link; a first secondary side port of the multiport dual active bridge being connected to an electric energy storage.

There exist different types of renewable energy power systems where, for example, a renewable power source such as a wind turbine generator, or other type of renewable energy source, may be configured to be set up, e.g., as a local electrical grid, i.e., operate in an island, off-grid, mode, where the generated power may be utilized to power loads connected to the system. Such loads may, e.g., comprise DC loads, and a particular kind of DC load that may be utilized in this regard are hydrogen electrolyzer stacks that may be utilized to generate hydrogen gas from electrical power being provided by the renewable energy source. With regard to DC loads, e.g. of the exemplified kind, such loads may also be connected to any kind of AC grid from which power may be drawn to produce hydrogen gas. It is also to be noted that other types of DC loads may be used in similar manners.

Further, with regard in particular to off-grid operation, the one or more renewable energy sources will provide energy, although not at a constant rate but, in general, at a varying power rate due to, inter alia, fluctuations in wind, sun etc. This will provide a varying power supply, where DC loads such as hydrogen electrolyzer stacks can be utilized to alleviate such differences by increasing or decreasing power being consumed from the grid. DC loads may also be used in grids in general for such balancing.

A problem with systems of the illustrated kind is that undesired events may occur. For example, the renewable energy source may reduce or stop operation in the off-grid mode, or in case of a grid connected system, the system may undesirably go into an off-grid mode. The latter may occur, for example, in case a fault occurs in the system. In such situations a grid operator may disconnect the renewable energy system from the grid. Although this may solve the problem from a grid side point of view, this may, instead, cause problems in the control of the renewable energy system, where such problems may depend on the particular type of renewable energy system.

In case the renewal energy system is a wind power plant, there are in general means for ensuring a controlled shutdown of the wind turbines in case this is needed, e.g., using UPS (Uninterruptible Power Supply) systems that may oftentimes be present. However, in case the renewable energy system comprises, e.g. electrolyzer stacks, where oftentimes the system may also comprise a plurality of electrolyzer stacks, a sudden disconnection may have negative impacts. DC loads, as is obvious from the name, are power supplied by a DC voltage, where the DC voltage is in general generated from the AC grid voltage through the use of a power converter that converts the AC voltage to a suitable DC voltage.

The power being consumed by, e.g., DC loads in the form of a hydrogen electrolyzer stack is dependent on the DC voltage level powering it, which, in turn, in general is provided by an AC grid through a power converter. There may, however, be restrictions regarding sudden changes in the voltage, and thereby power consumption changes, because this may cause undesired states in the electrolyzer stack, where, e.g., undesired mixing of gases may occur. For example, undesired mixing of hydrogen and oxygen may occur in the anode, which is highly undesirable.

The raising and/or lowering of the DC link voltage may therefore normally be controlled in order to ensure that the operation of the electrolyzer stack is maintained within predetermined limits. However, in case the system is disconnected from the grid, or power supply otherwise is interrupted, the required operating conditions may no longer be upheld due to the lack of power, with the risk that damaging operating states may arise in the DC load.

According to the invention, it is provided a power supply system that may alleviate such problems from arising, and that also may provide other advantages.

According to the invention, the power supply system comprises a DC load and a first power converter, e.g. a full-bridge power converter, that powers the DC load through a DC link from a grid, i.e. , in a manner that DC loads are conventionally being powered for as long as there is power in the grid. Furthermore, the power system comprises a grid connected auxiliary transformer configured to power auxiliary loads. Such auxiliary loads may comprise loads that are utilized in the operation of the electrolyzer stack, and may, e.g., comprise pumps, compressors, etc. for pressurizing and circulating hydrogen and oxygen etc. In order to alleviate problems of prior art solutions, the power supply system further comprises a multiport dual active bridge having a primary side and a secondary side, where a first primary side port of the multiport dual active bridge is connected to a downstream side of the auxiliary transformer through a second power converter, being different from the first power converter, where the second power converter may be a full-bridge AC/DC power converter. The multiport dual active bridge further comprises a second primary side port being connected to the DC link through which the first power converter powers the DC load. The multiport dual active bridge also comprises a first secondary side port that is connected to an electrical energy storage.

This provides for a power supply system that may at least reduce problems of the kind described above. According to the invention, the power source, such as, e.g., an AC grid, that powers the DC load through the first power converter may be cutoff, but the power supply system according to the invention may still provide a sufficient amount of power to controllably shut down various systems, such as electrolyzer stacks.

As was mentioned, in case the system involves electrolyzer stacks, e.g., being used for conversion of electricity to hydrogen, such electrolyzer stacks may not be designed to handle abrupt cut-off of the power that supplies it. In fact, it may be the case that it is in general required that if operation is to be stopped, system operation can continue for a period of time before system can be safely shutdown. For example, there may exist a need that operation of electrolyzer stacks can be maintained for 30-60 min for safety reasons during a controlled shutdown.

This may depend on the type of electrolyzer being used, where various types exist, but where alkaline electrolyzer stacks at present are commonly used in power-to-X plants. Such electrolyzer stacks may be relatively primitive in design, using technology that is known since many years. The electrolyzer stacks may also be designed according to other operating principles, and may, e.g., comprise proton exchange membrane (PEM) electrolyzer technology. Similarly, the electrolyzer stacks may comprise solid oxide electrolyzer stacks.

However, regardless of the type of electrolyzer stack being used, all of these systems in general comprise fluids, and/or gases, such as hydrogen and oxygen mentioned above, where a pressure of the fluid and/or gas may need to be maintained during a period of time also during shutdown of the system in order to safely shut down the system. For example, it may be required to pressurize and circulate generated hydrogen and/or oxygen in order to prevent unfavorable mixture of gasses. There may also be a need for controlling the temperature of the DC load. Also, there may exist a requirement to avoid excessive changes in DC supply voltage to thereby prevent undesired chemical reactions from occurring.

The multiport dual active bridge is a DC-DC converter having a primary side and secondary side providing bidirectional power flow and galvanic isolation between any of the two or more primary side ports and the one or more secondary side ports.

The two or more primary side ports may each comprise full bridge DC/AC power converters, and the at least one secondary side port may comprise a full bridge AC/DC power converter.

According to the invention, it is provided a solution that provide a system for power supply that may be utilized to continue the power supply of auxiliary loads, such as auxiliary loads being used in the operation of DC loads, e.g., electrolyzer stacks. In this way, proper operation may be maintained at least for a period of time. As will be explained, the proposed power supply system also provides a solution that may be used for various other purposes.

According to the invention, when the main power source such as a grid is cut off, the auxiliary loads may be power supplied through the multiport dual active bridge, where the electric energy storage may be utilized to power the auxiliary loads that are used in the operation of the DC load through the first secondary port of the multiport dual active bridge, the first primary port of the multiport dual active bridge, the second power converter and the auxiliary transformer. In this way it can be ensured that critical components that are powered by the auxiliary transformer can be properly powered using power stored in the electric energy storage.

In addition, the connection of the multiport dual active bridge to the DC link being used to power the DC load using the first power converter allows for various other possibilities of the power supply system. For example, this connection may be used to charge the electric energy storage through the first power converter.

In particular, according to aspects of the invention, it is provided a power supply system that that may comprise a certain amount of electrical storage, such as a certain level of battery storage and/or a certain level of super capacitance. In this way the power-to-X plant will be capable of operating for a sufficient period of time also when being disconnected from the grid.

According to aspects of the invention, the grid side of the auxiliary transformer and the grid side of the first power converter are interconnected. That is, both the auxiliary transformer and the first power converter may be connected to the same grid where the auxiliary loads being powered by the auxiliary transformer may be power supplied through the main grid in normal operation. This also allows the electric energy storage to be charged through the auxiliary transformer.

According to aspects of the invention, the electric energy storage that is connected to the first secondary side port of the multiport dual active bridge is a battery energy storage system and/or a supercapacitor. The electric energy storage may hence, e.g., comprise a battery electric storage system that may be designed to store a sufficient amount of energy to ensure desired operation of the system in case, e.g., grid power is lost. The electric energy storage may also, alternatively or in addition, comprise one or more super capacitors which may similarly be designed to comprise a desired amount of energy.

According to aspects of the invention, the electric energy storage is a battery energy storage system, and the power supply system comprises means for charging the battery energy storage system, wherein, when charging the battery energy storage system, charging power is provided to the electric energy storage from any one or more from: the grid through the first power converter, the second primary side port of the multiport dual active bridge and the first secondary side port of the multiport dual active bridge; the grid through the auxiliary transformer, the second power converter, the first primary side port of the multiport dual active bridge, and the first secondary side port.

Consequently, the invention provides for different ways of charging the electric energy system as was also indicated above.

According to aspects of the invention, the multiport dual active bridge comprises a second secondary side port, the second secondary side port being connected to the DC link, wherein the DC link further comprises circuit breaking means between the connection of the second primary side port to the DC link and the second secondary side port to the DC link.

This provides for a solution where there may simultaneously be two different power flows, one power flow between the first power converter and the multiport dual active bridge and a second power flow between the DC load and the multiport dual active bridge, provided that the circuit breaking means interrupt the direct path between the first power converter and the DC load. With regard to the circuit breaking means, such means may comprise, e.g., a DC circuit breaker. DC circuit breakers, however, may not be readily available for the oftentimes high powers, and thereby high currents, that systems of the disclosed kind may operate with. The circuit breaking means may therefore, e.g., comprise a solid-state circuit breaker since such circuit breakers may exhibit advantages over regular DC circuit breakers.

According to aspects of the invention, the power supply system comprises means for pre-charging the DC load, wherein, when pre-charging the DC load, precharging power is provided to the DC load from any one or more of a plurality of alternatives.

According to one alternative, the DC load may be pre-charged from the grid through the auxiliary transformer, the second power converter, the first primary side port of the multiport dual active bridge, and the second secondary side port. The invention may hence provide for a solution that in addition to powering auxiliary loads may provide means for pre-charging the DC load.

DC loads may have an inherent capacitance, and with regard to, e.g., such inherent capacitances may be large and thereby need to be pre-charged upon startup to prevent excess inrush currents that may be damaging to components.

Pre-charging in itself is therefore a problem that needs to properly be accounted for when it comes to DC loads having an inherent capacitance. For example, there exists various different manufacturers of DC loads, such as hydrogen electrolyzer stacks, where each design may have its own inherent capacitance and thereby also particular need for proper pre-charging. The invention provides for a solution where pre-charging may be adapted to suit the particular DC load being utilized irrespective of the type of super capacitance and other particular features of the DC load, where this pre-charging can be effectuated through the use of the multiport dual active bridge, where the control of the multiport dual active bridge can be adapted to the particular DC load that currently is to be pre-charged.

As an alternative, or in addition, the DC load may be pre-charged from the grid through the first power converter, the second primary side port of the multiport dual active bridge and the second secondary side port of the multiport dual active bridge. Hence, DC load may be pre-charged also through the use of the first power converter, but where the power flow is not directly going from the power converter to the DC load that through the multiport dual active bridge and hence with the circuit breaking means open.

As a further alternative, the DC load may be pre-charged through the electric energy storage through the first secondary side port of the multiport dual active bridge and the second a secondary side port of the multiport dual active bridge. The electric energy storage may hence be used to pre-charge the DC load. The DC load may also be powered by the electric energy storage in this manner.

According to aspects of the invention, as was exemplified above, the electric energy storage may be a battery energy storage system, and the power supply system comprises means for providing power through discharging of the battery energy storage system, wherein power from the battery energy storage system may be provided to any one or more from: the grid through the first secondary side port of the multiport dual active bridge, the second primary side port of the multiport dual active bridge and primary converter; the auxiliary transformer through the first secondary side port of the multiport dual active bridge, the first primary side port of the multiport dual active bridge and secondary converter; the DC load through the first and second secondary side port of the multiport dual active bridge.

The power supply system according to the invention may hence be used to power any of the grid, the DC load, and loads powered by the auxiliary transformer using energy stored in the electric energy storage.

According to aspects of the invention, the multiport dual active bridge, in addition to the first secondary side port and the second secondary side port, comprises at least one third secondary side port, wherein the second secondary side port of the multiport dual active bridge connects a battery energy storage system to the multiport dual active bridge, and the at least one third secondary side port connects a super capacitor to the multiport dual active bridge.

The power supply system may hence comprise both a battery energy storage system and one or more super capacitors for use in the assisting of the operation of, e.g., a power-to-X system. This provides for even further control possibilities.

In particular, according to aspects of the invention, the power supply system comprises means for charging the super capacitor wherein, when charging the super capacitor, charging power is provided to the super capacitor from any one or more from: the grid through the first power converter, the second primary side port of the multiport dual active bridge and the third secondary side port of the multiport dual active bridge; the grid through the auxiliary transformer, the second power converter, the first primary side port of the multiport dual active bridge, and the third secondary side port of the multiport dual active bridge the battery energy storage system through the first and third secondary side port of the multiport dual active bridge.

The power supply system may hence provide for various ways of charging a super capacitor.

According to aspects of the invention, the power supply system may also comprise means for providing power through discharging of the super capacitor, wherein power from the super capacitor may be provided to any one or more from: the grid through the third secondary side port of the multiport dual active bridge, the second primary side port of the multiport dual active bridge and the primary converter; the grid through the third secondary side port of the multiport dual active bridge, the first primary side port of the multiport dual active bridge, the secondary converter and the auxiliary transformer; the DC load through the third and second secondary side port of the multiport dual active bridge.

The super capacitor may, as also has been indicated above, be used much in the same manner as, e.g., the battery electric energy system, and also be used in situations where rapid power changes need to be provided.

According to aspects of the invention, the power supply system comprises a plurality of DC loads, each DC load being configured to be powered by a power converter, respectively, the power converters being connected to a grid and being configured to power the DC loads through a DC link, respectively, wherein: the second primary side port, and/or the second secondary side port, of the multiport dual active bridge is configured to be connected to each of the DC links powering a DC load.

The power supply system may hence be configured to provide power to a number of parallel installations, where a power converter each is used to power a DC load, where operation of each of these DC loads may be facilitated using the power supply system according to the invention.

According to aspects of the invention the multiport dual active bridge may comprise individual primary side ports and/or secondary side ports for these DC links and hence DC loads.

Furthermore, there exist situations when the grid is determined to be weak, or when the power supply system is operating in an off-grid mode, or when the power supply system is operating in an island mode, and according to aspects of the invention the power supply system is configured to, in such situations, power the auxiliary loads being connected to the auxiliary transformer through the auxiliary transformer, wherein the auxiliary loads are powered utilizing power of the electric energy storage, wherein power is provided to the auxiliary transformer from the electric energy storage from first secondary side port to the first primary side port of the multiport dual active bridge.

According to aspects of the invention, the power supply system comprises control means configured to provide a black start capability for setting up the grid utilizing the first power converter or the second power converter operating as a grid forming converter, wherein the power system is configured to provide power to the grid through the first power converter or the second power converter, and wherein the power is configured to be supplied by the electric energy storage.

For example, one or more super capacitors may be used in such grid forming, as well as a battery electric storage system. A power converter operating according to a grid forming operating principle allows the power source to create a power grid by powering otherwise depowered power lines. The power supply system according to the invention may thereby provide a black start capability utilizing the energy in the energy storage system.

Hence, by providing the power supply system with, e.g., battery capacity it is possible to support the grid, and even to maintain the grid for at least as long as stored energy is available.

According to aspects of the invention, as was mentioned, the DC load may be an electrolyzer stack, and the power supply to the electrolyzer stack is controlled to thereby control hydrogen production.

According to a further aspect of the invention it is provided a renewable energy power system comprising a renewable energy power source, such as a wind turbine generator, configured to supply power to a grid and a power supply system according to any of the aspects described above, where the renewable energy power system exhibits the same advantages as has been described above. Further advantageous aspects of the power supply system according to the present invention and further advantages with the aspects of the invention emerge from the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Fig. 1 illustrates an example of a power supply system according to prior art;

Fig. 2 illustrates an example of a power supply system according to aspects of the invention;

Fig. 3 illustrates another example of a power supply system according to aspects of the invention;

Fig. 4 illustrates a further example of a power supply system according to aspects of the invention;

Fig. 5 illustrates yet another example of a power supply system according to aspects of the invention.

DETAILED DESCRIPTION

The invention will be exemplified in the following for a power supply system comprising DC loads being constituted by one or more hydrogen electrolyzer stacks, such as, for example, alkaline hydrogen electrolyzer stacks, and in particular DC loads comprising an inherent capacitance. It is to be noted, however, that the invention is equally applicable for any kind of DC loads.

Fig. 1 illustrates a prior art power supply system exemplifying a connection of an electrolyzer stack 101 , such as an alkaline electrolyzer, being connected to a medium voltage AC grid 110 through a line side converter LSC 102. The line side converter 102 is basically an AC to DC converter, e.g., a full bridge converter, for converting the low voltage AC voltage to DC voltage for powering the electrolyzer stack 101 .

Furthermore, according to the illustrated example, a circuit breaker 103 is illustrated as provided for allowing interruption of power provided to the electrolyzer stack 101 . The circuit breaker may be a DC circuit breaker, but it is to be noted in this regard, as was also briefly mentioned above, that DC circuit breakers may not even be commercially available at the high current ratings that may prevail in systems of the kind illustrated in Fig. 1 , where the required current breaking capability may be in the order of 5 kA or even higher currents to be interrupted.

Fig.1 also illustrates connection to the grid 110 through switch gear 109, a medium voltage to low voltage transformer 108, and hence a transformation to a voltage being adapted to the operating voltage of the line side converter 102 and/or the electrolyzer stack 101 . The figure also illustrates an AC circuit breaker 107 that may be used in place of a DC circuit breaker to interrupt power supply to the electrolyzer stack 101 , or trip, in situations where an overcurrent on the DC side reflected by an overcurrent also on the AC side of the line side converter 102.

The figure also illustrates a fuse 104 provided for circuit protection, but, similar to DC circuit breakers, such fuses may be costly, and therefore use of such fuses may desirably be avoided. Fuses being capable of handling very high currents may also be difficult to even obtain. The use of such fuses may therefore be limited or avoided.

In addition, Fig. 1 illustrates pre-charging means to provide for pre-charging of the electrolyzer stack. As was mentioned above, DC loads may comprise an inherent capacitance that require pre-charging to protect the DC load from high inrush currents, where this pre-charging may be accomplished, e.g. This is illustrated by a resistor 105 to provide for resistive pre-charging of the electrolyzer stack, where the resistor 105 can be connected by means of a switch 106. Once pre-charging of the electrolyzer is completed, the resistor 105 is disconnected by opening the switch 106, and the DC circuit breaker 103 that this utilized during normal operation is instead closed. However, again, the solution according to Fig. 1 may currently not be available for high-current operation due to lack of suitable DC circuit breakers, and DC circuit breaker 103 may therefore instead consist of another type switch being capable of handling the required currents. However, resistive pre-charging requires a DC circuit breaker. Also, resistive pre-charging gives rise to power dissipation in the resistor and hence losses and undesired heat. According to the invention, therefore, a solid-state circuit breaker may be used.

Fig. 2 illustrates a first exemplary power supply system 200 according to aspects of the invention. Similar to Fig. 1 , Fig. 2 illustrates a first power converter 201 that is used to convert an AC voltage supplied, e.g., by a grid to DC voltage in order to power a DC load 202 in the form of an electrolyzer stack over a DC link 203. The figure further illustrates an auxiliary transformer 205, and a multiport dual active bridge 206. The multiport dual active bridge 206 comprises a common magnetic core 207 providing galvanic isolation between a primary side 208 and a secondary side 209. The primary side further comprises a second power converter 210 being configured to convert an AC voltage to a DC voltage, where the power converter 210 is connected to the downstream side of the auxiliary transformer 205. The second power converter 210 is connected to a first primary side port 211 of the multiport dual active bridge, where the first primary side port consists of a DC/AC converter, where the output AC voltage may be controlled by the DC/AC converter 211 . The multiport dual active bridge 206 further comprises a first secondary side port 212, consisting of an AC/DC converter. The DC/AC converter 211 and AC/DC converter 212 hence together form a DC/DC converter with galvanic isolation.

In essence, the multiport dual active bridge is a DC-DC converter having a primary side and secondary side providing bidirectional power flow and galvanic isolation between any of the two or more primary side ports and the one, or more as the case may be and as is illustrated below, secondary side ports. Furthermore, the two or more the primary side ports may comprise full bridge DC/AC power converters, and the secondary side port may also comprise a full bridge AC/DC power converter.

The figure further illustrates an electric energy storage in the form of a battery electric storage system 213 connected to the first secondary side port 212. The figure also illustrates a second primary side port 214 of the multiport dual active bridge 206, where the second primary side port 214 is connected to the DC link 203. The second primary side port 214, similarly to the first primary side port consists of a DC/AC converter. The DC/AC converter 214 and AC/DC converter 212 hence together form a further DC/DC converter with galvanic isolation.

The figure also illustrates auxiliary loads being power supplied by the auxiliary transformer 205, where the one or more auxiliary loads are commonly denoted by 220. It is further to be noted that the power supply system of Fig. 2, e.g., may be connected to medium voltage AC system in a manner similar to what has been illustrated in fig. 1. This connection is schematically illustrated by 230.

During normal operation, the electrolyzer stack 202 may be power supplied by the power converter 201 , and the remaining power supply system may, in such a situation, operate in an idle mode. It is also contemplated, that, for example, the battery electric energy storage 213 may be charged, e.g. in case the battery electric storage system is not fully charged. This charging may be carried out, e.g., through the grid, where the power flow may go through the first power converter 201 to the second primary side port 214 of the multiport dual active bridge and further onto the first secondary side port 212 of the multiport dual active bridge, where the DC voltage prevailing on the DC link 203 is first converted to an AC voltage to then be converted to a suitable DC voltage for charging the battery electric storage system 213. It is also possible to, as an alternative or in addition, charge the battery electric storage system 213 from the grid through the auxiliary transformer 205, the second power converter 210, the first primary side port 211 of the multiport dual active bridge, and the first secondary side port 212 of the multiport dual active bridge. Again, the DC/AC conversion in port 211 and AC/DC conversion in port 212 may be adapted so that a suitable voltage for charging the battery electric storage system 213 is provided. In case charging is provided through both the power converter 201 and the auxiliary transformer 205, the first primary port 211 and the second primary port 214 may be controlled to output the same voltage.

However, in case the grid stops supplying power, e.g. due to a malfunction of a renewable energy source or the grid operator for some reason disconnecting the power supply system from the grid this may, as was discussed above, give rise to potential problems in particular with regard to operation of DC loads such as hydrogen electrolyzer stacks.

In particular, such systems in general comprise fluids, and/or gases, such as hydrogen and oxygen, where the fluid and/or gas needs to be suitably pressurized and/or circulated for a period of time also when the system is to be shut down to avoid unfavorable and potentially dangerous mixture of gasses. The power supply system illustrated in Fig. 2 may alleviate problems of this kind by providing means for powering, e.g., pumps and/or circulators and/or other means that are required to safely shut down the DC load.

This is accomplished by power supplying such auxiliary loads through the auxiliary transformer 205 using energy stored in the battery energy storage system 213, in which case power from the battery energy storage system 213 is provided to the first secondary port 212, and further to first primary port 211 to then be converted to a suitable AC voltage by power converter 210 so that the auxiliary loads can be power supplied from the auxiliary transformer 205. The figure also illustrates an AC switch 221 , which may be opened, e.g., when supplying power in this way to account for, e.g., short circuits or other consumers consuming the energy intended for the auxiliary loads. Hence, in this way, devices that are necessary to safely shut down the system may still be power supplied even though grid power is lost. The solution according to Fig. 2 may also be used, in case this would be necessary, to provide power to the grid from the battery electric storage system 213, where such a power could be delivered in a manner reverse to what has been described above with regard to charging the battery electric storage system. This may be the case, e.g., in case the grid is weak. According to aspects of the invention, the battery electric storage system 213 may also consists of one or more super capacitors. As will be discussed further below, combinations are also possible.

Fig. 3 illustrates a further example of a power supply system 300 according to the invention. The solution according to Fig. 3 comprises components similar to Fig. 2, operating in a same manner as has been described above. However, the power supply system differs from the solution according to Fig. 2 by the addition of a second secondary side port 315 which is arranged to be connected to the DC link 303 downstream of a DC link circuit breaker 304. The power supply system according to Fig. 3 hence also comprises a circuit breaker 304 configured to interrupt the power flowing over the DC link 303. Furthermore, the second primary side port 314 is connected to the DC link 303 upstream the circuit breaker 304.

According to aspects of the invention, the second secondary side port 315 may be utilized to pre-charge the DC load, which, as was mentioned, may be required, e.g., upon startup of the system in case the DC load comprises a large inherent capacitance, which as explained is oftentimes the case with regard to electrolyzer stacks, to thereby prevent potentially damaging excess inrush currents. The example illustrated in Fig. 3 provides for different possibilities in this regard.

For example, the DC load 302 may be pre-charged using power supplied by the grid. This may be carried out through a power path going through the auxiliary transformer 305, the second power converter 310, the first primary side port 211 of the multiport dual active bridge, and the second secondary side port 315, while simultaneously keeping the circuit breaker 304 open. The second secondary side port 315 may then control the output DC voltage to successively increase until, e.g., a voltage threshold has been reached that allows closing of the circuit breaker 304 and power being supplied to the DC load by the first power converter 301.

As was discussed above, pre-charging in itself is oftentimes a problem that needs to properly be accounted for, and the power supply system illustrated in Fig. 3 provides a solution that provides for pre-charging while simultaneously providing a solution for powering, e.g. auxiliary loads when power is cut off.

The example according to Fig. 3 also provides for further alternatives regarding possible ways of accomplishing the pre-charging. The DC load may also be precharged using the grid but through the first power converter 301 instead of the path through the auxiliary transformer 305. The circuit breaker is then, similar to the above, open, and the power flow goes through the second primary side port of the multiport dual active bridge and the second secondary side port of the multiport dual active bridge. In this way the DC load may be pre-charged also through the use of the first power converter, but as can be seen from the figure the power flow is not directly going from the first power converter to the DC load but instead through the multiport dual active bridge 306.

As a third alternative, the DC load may be pre-charged through the electric energy storage system 313 through the first secondary side port of the multiport dual active bridge and the second secondary side port of the multiport dual active bridge. Hence, the electric energy storage system may also be used to pre-charge the DC load. It is also possible to use the electric energy storage system to power the DC load in this manner, e.g., in case power needs to be supplied to the DC load while the battery electric storage system simultaneously provides power to auxiliary loads through the auxiliary transformer 305. Fig. 4 illustrates a further example of a power supply system 400 according to aspects of the invention. The solution according to Fig. 4 comprises components similar to Fig. 3, however with the addition of a further, third, secondary side port 416 to the multiport dual active bridge. The third secondary side port is connected to one or more super capacitors, 417.

According to the example illustrated in Fig. 4, the power supply system 400 hence comprises both a battery energy storage system 413 as well as one or more super capacitors 417 that may be used in the operation of, the power supply system 400. The one or more super capacitors 417 may be charged in the same manner as has been described above for the battery electric energy system 413.

Consequently, the one or more super capacitors can be charged by the grid through the first power converter 401 , the second primary side port 414 of the multiport dual active bridge 406 and the third secondary side port 416 of the multiport dual active bridge. Alternatively, the one or more super capacitors 417 can be charged by the grid through the auxiliary transformer 405, the second power converter 410, the first primary side port 411 of the multiport dual active bridge, and the third secondary side port 416 of the multiport dual active bridge. The one or more super capacitors 416 can also be charged by the battery energy storage system 413 through the first 412 and third 416 secondary side ports of the multiport dual active bridge.

The power supply system may hence provide for various ways of charging a super capacitor, and two or more ways may also simultaneously be used to charge the one or more super capacitors 417.

As was mentioned above, the power supply system may provide power using energy stored in the battery energy storage system. This is also the case with regard to the one or more super capacitors 417, where energy stored in the one or more super capacitors 417 may be provided through discharging of the one or more super capacitors 417. Power may be discharged, e.g., to the grid through the third secondary side port 416 of the multiport dual active bridge, the second primary side port 414 of the multiport dual active bridge and the primary converter 401 . Alternatively, power may be supplied to the grid through the third secondary side port 416 of the multiport dual active bridge, the first primary side port 411 of the multiport dual active bridge, the secondary converter 410 and the auxiliary transformer 405. Power may also be discharged to the DC load 413 through the third 416 and second 415 secondary side port of the multiport dual active bridge, e.g. to provide for pre-charging.

The super capacitor may, in addition to be used in the same manner as, e.g., battery electric energy system described above, also be used in situations where rapid power changes need to be provided. For example, the one or more super capacitors may be used in grid forming. This also applies to the battery electric storage system. As is known per se, and was mentioned above, grid forming allows a power source to create a power grid by powering otherwise depowered power lines. The power supply system according to the invention may thereby provide a black start capability. That is, the first power converter or the second power converter may be configured to operate as a grid forming converter, where the power is configured to be supplied by the super capacitor and/or battery electric energy storage, where the one or more super capacitors may be used in particular when rapid changes in supplied power are needed in the grid forming control.

Fig. 5 illustrates yet a further example of a power supply system 500 according to the invention. The power supply system of Fig. 5 may be similar in functionality to any of the systems illustrated in Figs. 2-4. However, in difference to the examples of Figs. 2-4, the power supply system comprises a plurality of parallel DC loads in the form of electrolyzer stacks ELY I, ELY II, ... , ELY N, where each DC load is configured to be powered by a power converter 501 , respectively. The power converters 501 are connected to a common AC grid in a manner similar to the power converters 201 , 301 , 401 illustrated in Figs. 2-4, and are each configured to power the DC loads ELY I, ELY II, ... , ELY N through a DC link 503, respectively. The figure further illustrates a multiport dual active bridge 506. The multiport dual active bridge 506 may provide the same functionality as any of the multiport dual active bridges in Figs. 2-4, but with the difference that the multiport dual active bridge 506 may comprise individual primary and/or secondary side ports connected to the DC links, respectively. This is schematically illustrated by secondary side ports for each of the electrolyzer stacks ELY I, ELY II, ... , ELY N. For simplicity, only individual secondary side ports are illustrated, but the multiport dual active bridge 506 may also comprise individual primary side ports for each of the DC links in a similar manner. Also, the power supply system comprises, although not shown, at least one electric energy storage connected to the secondary side.

In this way, all the features described above may be provided for each of the DC loads, and hence the power supply system may be used to, e.g., provide power to auxiliary loads being used for each of the electrolyzer stacks, and also for precharging of the electrolyzer stacks. Similarly, an electric energy storage in the form of a battery electric storage system and/or one or more super capacitors may be used for any of the uses exemplified above, where such energy storages also may be charged through any of the power converters.

The power supply system may hence be configured to provide power to a number of parallel installations, where a power converter is used to power DC load, where operation of each of these DC loads may be facilitated using the power supply system according to the invention.

Finally, the present invention is not limited to the above-described embodiments.

Instead, the present invention relates to, and encompasses all different embodiments being included within the scope of the independent claim.

Claims

1 . A power supply system, the system comprising: a DC load; a first power converter, the first power converter being connected to an AC grid and being configured to power the DC load through a DC link; a grid connected auxiliary transformer configured to power auxiliary loads; a multiport dual active bridge having a primary side and a secondary side, wherein: a first primary side port of the multiport dual active bridge is connected to a downstream side of the auxiliary transformer through a second power converter; a second primary side port of the multiport dual active bridge being connected to the DC link; a first secondary side port of the multiport dual active bridge being connected to an electric energy storage.

2. A power supply system according to claim 1 , wherein: the grid side of the auxiliary transformer and the grid side of the first power converter are interconnected.

3. A power supply system according to claim 1 or 2, wherein: the electric energy storage connected to the first secondary side port of the multiport dual active bridge is a battery energy storage system and/or a supercapacitor.

4. A power supply system according to any one of the claims 1 -3, wherein the electric energy storage is a battery energy storage system and the power supply system comprises means for charging the battery energy storage system wherein, when charging the battery energy storage system, charging power is provided to the electric energy storage from any one or more from: the grid through the first power converter, the second primary side port of the multiport dual active bridge and the first secondary side port of the multiport dual active bridge; the grid through the auxiliary transformer, the second power converter, the first primary side port of the multiport dual active bridge, and the first secondary side port.

5. A power supply system according to any one of the claims 1 -4, wherein: the multiport dual active bridge comprises a second secondary side port, the second secondary side port being connected to the DC link, wherein: the DC link further comprises circuit breaking means between the connection of the second primary side port to the DC link and the second secondary side port to the DC link.

6. A power supply system according to claim 5, wherein: the power supply system comprises means for pre-charging the DC load, wherein, when pre-charging the DC load, pre-charging power is provided to the DC load from any one or more from: the grid through the auxiliary transformer, the second power converter, the first primary side port of the multiport dual active bridge, and the second secondary side port; the grid through the first power converter, the second primary side port of the multiport dual active bridge and the second secondary side port of the multiport dual active bridge; the electric energy storage through the first secondary side port of the multiport dual active bridge and the second a secondary side port of the multiport dual active bridge.

7. A power supply system according to claim 5 or 6, wherein the electric energy storage is a battery energy storage system and the power supply system comprises means for providing power through discharging of the battery energy storage system, wherein power from the battery energy storage system may be provided to any one or more from: the grid through the first secondary side port of the multiport dual active bridge, the second primary side port of the multiport dual active bridge and primary converter; the auxiliary transformer through the first secondary side port of the multiport dual active bridge, the first primary side port of the multiport dual active bridge and secondary converter; the DC load through the first and second secondary side port of the multiport dual active bridge.

8. A power supply system according to any one of the claims 1 -7, wherein: the multiport dual active bridge comprises at least one third secondary side port, wherein the second secondary side port of the multiport dual active bridge connects a battery energy storage system to the multiport dual active bridge, and the at least one third secondary side port connects a super capacitor to the multiport dual active bridge.

9. A power supply system according to claim 8, wherein the power supply system comprises means for charging the super capacitor wherein, when charging the super capacitor, charging power is provided to the super capacitor from any one or more from: the grid through the first power converter, the second primary side port of the multiport dual active bridge and the third secondary side port of the multiport dual active bridge; the grid through the auxiliary transformer, the second power converter, the first primary side port of the multiport dual active bridge, and the third secondary side port of the multiport dual active bridge the battery energy storage system through the first and third secondary side port of the multiport dual active bridge.

10. A power supply system according to claim 8 or 9, wherein the power supply system comprises means for providing power through discharging of the super capacitor, wherein power from the super capacitor may be provided to any one or more from: the grid through the third secondary side port of the multiport dual active bridge, the second primary side port of the multiport dual active bridge and the primary converter; the grid through the third secondary side port of the multiport dual active bridge, the first primary side port of the multiport dual active bridge, the secondary converter and the auxiliary transformer; the DC load through the third and second secondary side port of the multiport dual active bridge.

11 . A power supply system according to any one of the claims 1 -10, wherein the power supply system comprises a plurality of DC loads, each DC load being configured to be powered by a power converter, respectively, the power converters being connected to a grid and being configured to power the DC loads through a DC link, respectively, wherein: the second primary side port, and/or the second secondary side port, of the multiport dual active bridge is configured to be connected to each of the DC links powering a DC load.

12. A power system according to any one the claims 1 -11 , wherein when the grid is determined to be weak, or when the power supply system is operating in an off-grid mode, or when the power supply system is operating in an island mode: the power supply system is configured to power the auxiliary loads being connected to the auxiliary transformer through the auxiliary transformer, wherein the auxiliary loads are powered utilizing power of the electric energy storage, wherein power is provided to the auxiliary transformer from the electric energy storage from first secondary side port to the first primary side port of the multiport dual active bridge.

13. A power system according to any one of the claims 1-12, further comprising: control means configured to provide a black start capability for setting up the grid utilizing the first power converter or the second power converter operating as a grid forming converter, wherein the power system is configured to provide power to the grid through the first power converter or the second power converter, and wherein the power is configured to be supplied by the electric energy storage.

14. A power system according to any one of the claims 1 -13, wherein the multiport dual active bridge is a DC-DC converter having a primary side and secondary side providing bidirectional power flow and galvanic isolation between any of the two or more primary side ports and the one or more secondary side ports.

15. A power system according to claim 14, wherein the two or more the primary side ports each comprise full bridge DC/AC power converters, and the at least one secondary side port comprises a full bridge AC/DC power converter.

16. A power supply system according to any one of the claims 1 -15, wherein the DC load comprises an inherent capacitance.

17. A power supply system according to any one of the claims 1 -16, wherein the DC load is an electrolyzer stack, and wherein the power supply to the electrolyzer stack is controlled to thereby control hydrogen production.

18. A renewable energy power system, the renewable energy power system comprising a renewable energy power source, such as a wind turbine generator, configured to supply power to a grid, and a power supply system according to any of the claims 1 -17.