FIELD OF THE INVENTION

The invention relates to renewable power plants, particularly to renewable power plants comprising wind turbines and electrolyzers.

BACKGROUND OF THE INVENTION

Renewable power plants such as wind power plants may be combined with electrolyzers for production of hydrogen. This combination may be advantageous since electrical power from the power plant may be used to produce hydrogen. Furthermore, a location of electrolyzers at the location of the renewable power plant may be an advantage compared to a remote location in view of installation costs such as installation costs for electrical grid installations to a remote location and to minimize transmission losses.

Since electrolyzers may be vulnerable to high voltages the inventors have realized that improvements of present renewable power plants are needed in order to protect the electrolyzers against high voltages in the power supply and have therefore devised the present invention.

SUMMARY

It is an object of the invention to improve renewable power plants which include electrolyzers so that the risk of damaging the electrolyzers due to high voltages in the power supply is reduced.

In a first aspect of the invention a method for operating a renewable power plant comprising at least one wind turbine and an electrolyzer system connected with a grid via an internal grid is presented, wherein the method comprises

- detecting an overvoltage condition relating to a voltage level at a power input of the electrolyzer system,

- sending a warning signal to the at least one wind turbine in response to detecting the overvoltage condition,

- controlling the at least one wind turbine to perform a compensation action for lowering the voltage level at the power input of the electrolyzer system in response to receiving the warning signal. Advantageous, a wind turbine is used to reduce the voltage at the electrolyzer system since wind turbines already have over voltage means installed to handle over voltages in the grid or the internal grid. In this way, the electrolyzer system does not need to be configured with such over voltage means.

The compensation action may comprise controlling the at least one wind turbine to reduce an amount of power supplied to the internal grid. By reducing the amount of power, mainly active power and thereby the current amplitude, injected to the internal grid the currents from the at least one wind turbine and electrolyzer transformer (the transformer connecting the electrolyzer system to the internal grid) can be coordinated to give an appropriate voltage drop on the internal grid.

Particularly, the reduction of the power supplied to the internal grid may be performed for a period long enough for completing the mechanical operation of a switchgear, i.e. a circuit breaker, to disconnect the electrolyzer system from the internal grid.

The electrolyzer system is arranged to be powered via the internal grid. Therefore, the electrolyzer system may be powered via power from the wind turbines or power from the grid.

According to an embodiment, the controlling of a wind turbine to reduce an amount of power supplied to the internal grid comprises reducing power generation. Advantageously, the wind turbine can be controlled by reducing a power setpoint for the desired power production, e.g. during a short period of time.

According to an embodiment, the controlling of a wind turbine to reduce an amount of power supplied to the internal grid comprises dissipating power produced by the at least one wind turbine in at least one dump load comprised by the at least one wind turbine.

It is an advantage to use already installed dump loads in wind turbines instead of configuring the electrolyzer system with a dump load which would also require a more expensive converter of the electrolyzer system due to a need for other types of power semiconductors such as IGBTs in the power converter. Thus, a more material efficient and sustainable solution is achieved by utilizing the already installed dump loads. Furthermore, converter dump load can operate faster than the circuit breaker in front of the electrolyzer, implying that a better over voltage protection is achieved by using the wind turbine dump loads.

It is also possible, that the controlling of a wind turbine to reduce an amount of power supplied to the grid comprises a combination of reducing power generation and power dissipation wherein the power reducing actions may be performed simultaneously or within different overlapping or non-overlapping time periods.

According to an embodiment, the method comprises monitoring a duration of the overvoltage condition and electrically disconnecting the electrolyzer system from the internal grid dependent on the duration of the over voltage condition.

Advantageously, the timer based disconnection of the electrolyzer system provides a secondary protection of the electrolyzers, e.g. in case the other actions for reducing the voltage has not been effective or in case the other actions have not been invoked.

For example, the disconnection may be generated if the duration exceeds a period within a range from 10-100 ms.

According to an embodiment, the electrolyzer system comprises an auxiliary over voltage protection system arranged on a low voltage side of a transformer connected to the internal grid on its high voltage side, wherein the auxiliary over voltage protection system is arranged to clamp the voltage at the low voltage side, wherein the duration of the overvoltage condition is monitored while clamping the voltage at the low voltage side.

Advantageously, the voltage clamping assists in bringing the voltage on the internal grid down. Accordingly, if the over voltage situation persists even with the claiming circuit activated, this indicates a severe over voltage situation requiring a disconnection of the electrolyzer system. According to an embodiment, the overvoltage condition is determined based on measuring a voltage at the low voltage side of the transformer.

It may an advantage to use a voltage measured directly at the input of the electrolyzer system or near the electrolyzer system for the detection of the over voltage situation, since voltages measured at other locations in the power plant may be inaccurate in relation to the actual voltage at the input of the electrolyzer system.

A second aspect of the invention relates to a method for operating a renewable power plant comprising at least one wind turbine and an electrolyzer system connected with an electrical grid via an internal grid so that the electrolyzer system is electrically powered via the internal grid, wherein the electrolyzer system comprises an auxiliary over voltage protection system arranged on a low voltage side of a transformer connected to the internal grid on its high voltage side, wherein the auxiliary over voltage protection system comprises a clamping circuit arranged to clamp the voltage at the low voltage side, wherein method comprises,

- detecting an overvoltage condition relating to a voltage level at a power input of the electrolyzer system,

- clamping the voltage at the low voltage side,

- monitoring a duration of the overvoltage condition, and

- electrically disconnecting the electrolyzer system from the internal grid dependent on the duration of the over voltage condition.

A simple but effective over voltage protection may be achieved by simply disconnecting the electrolyzer system if the over voltage persists for a long enough time.

A third aspect of the invention relates to a renewable power plant comprising at least one wind turbine and an electrolyzer system, wherein the at least one wind turbine and the electrolyzer system are connectable with an electrical grid via an internal grid, and wherein the electrolyzer system is arranged to be electrically powered via the internal grid, wherein the renewable power plant comprises - a voltage detector arranged to detect an overvoltage condition relating to a voltage level at a power input of the electrolyzer system,

- communication means arranged to send a warning signal to the at least one wind turbine in response to detecting the overvoltage condition,

- at least one controller arranged to control the at least one wind turbine to perform a compensation action for lowering the voltage level at the power input of the electrolyzer system in response to receiving the warning signal.

The at least one controller may comprise the power plant controller or other central relay controller arranged to receive the warning signal and control or inform the at least one wind turbine to perform the compensation action. Alternatively, the warning signal may be sent directly via the communication means, e.g. communication means arranged with the voltage detector to a controller of the at least one wind turbine arranged for performing the compensation action.

According to an embodiment, the electrolyzer system comprises an electrolyzer, a converter arranged to convert an AC voltage at the power input of the electrolyzer system into a DC voltage for powering the electrolyzer, a circuit breaker arranged to electrical disconnect the converter from the internal grid, wherein the circuit breaker is controllable to disconnect the electrolyzer system from the internal grid dependent on a duration of the over voltage condition.

According to an embodiment, the electrolyzer system comprises an auxiliary over voltage protection system electrically connected to a low voltage side of a transformer which is electrically connected to the internal grid on its high voltage side, wherein the auxiliary over voltage protection system comprises

- a clamping circuit arranged to clamp the voltage at the low voltage side,

- a voltage detector arranged to monitor a voltage at the low voltage side for determining the overvoltage condition,

- a timer arranged to determine the duration of the over voltage condition.

The timer or equivalent means for determining a time duration such as a counter is arranged to determine the duration of the over voltage condition while the voltage is clamped. A fourth aspect of the invention relates to a computer program comprising instructions which, when the program is executed by a computer, causes the computer to carry out the method of the first and/or the second aspects.

In general, the various aspects and embodiments of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and/or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Fig. 1 shows a renewable power plant including an electrolyzer system.

DETAILED DESCRIPTION

Fig. 1 shows a renewable power plant 100, or power plant 100 in short, such as a wind power plant which comprises one or more wind turbines 101. The power plant 100 may additionally comprise other renewable power generating units such as solar power units 103 (e.g. photovoltaic solar panels). Thus, in one example the power plant comprises only one wind turbine 101. In another example, the power plant comprises a plurality of wind turbines 101.

The power plant 100 further comprises one or more electrolyzer systems 110. For convenience Fig. 1 shows only one electrolyzer system 110.

The electrolyzer system 110 comprises an electrolyzer 113 configured to produce hydrogen through electrolysis. Each electrolyzer system may comprise one or more electrolyzers.

For example, in an off shore wind power plant a single wind turbine 101 is installed on foundation comprising a platform arranged above the sea level. One or more electrolyzers 110 may be arranged on the platform. Thus, the single wind turbine 101 comprising the electrolyzer system 110 may constitute a power plant 100 or a plurality of wind turbines 101, wherein one or more wind turbines comprises an electrolyzer system 110 arranged on e.g. platforms, may be comprised by the power plant 100.

The one or more wind turbines 101 and electrolyzer systems 110 are connected to the grid 190 via an internal grid 191.

Thus, the power plant 100 is connectable with the grid 190 for supplying power from the wind turbines 101 and possibly other power generating units to the grid.

Herein the grid 104 can be any of a distribution grid, a transmission grid, a medium voltage network, a high voltage grid or other electrical grid.

The internal grid 191 may be an intermediate power network comprising a power line such as a medium voltage network. The internal grid may be connected to the wind turbines 101 and electrolyzer systems 110 via transformers 192.

The electrolyzer system 110 further comprises an converter 111, e.g. an IGBT controlled converter, arranged to convert an AC voltage supplied via the internal grid 191 to a power input 114 of the electrolyzer system into a DC voltage. The electrolyzer system 110 may also comprise a DC link 112 arranged to reduce ripple voltage. The converter 111 such as a 4-quadrant converter may function as a controlled rectifier. The electrolyzer system 110 may in an alternative example comprise a thyrister based converter/rectifier 111.

Accordingly, the electrolyzer system 110 is electrically powered via power from the internal grid 191 which may originate from the grid 190, the wind turbines 101 or both.

The electrolyzer system 110 is connected to the internal grid 191 via a controllable a circuit breaker 121 arranged to electrically disconnect the converter 111 and thereby the electrolyzer 113 from the internal grid. The wind turbines 101 may be connected to the internal grid 191 via similar controllable circuit breakers 122. Fig. 1 shows that the electrolyzer circuit breaker 121 and the wind turbine circuit breakers 122 are located on the low voltage sides of the transformers 192. Alternatively, one or more of the circuit breakers 121, 122, particularly when they are configured as switch gears, may be located on the high voltage side of the transformers 192.

The internal grid and thereby the wind turbines 101 and the electrolyzer system 110 is connectable with the grid 190 via a grid circuit breaker 123 such as a common circuit breaker located at or in the vicinity a point of common coupling PCC. The common coupling PCC constitute a point within the internal grid 191 to which the circuit breaker and the wind turbines 101 and the electrolyzer system 110 are connected.

The power plant 100 may comprise a central controller 170, or the power plant controller 170 may be located externally to the power plant 100. The central controller 170 is arranged to control power generation from the wind turbines 101 according to a power plant reference which defines the desired power to be supplied to the grid.

Each wind turbine 101 may comprise a tower and a rotor with at least one rotor blade, such as three blades. The rotor is connected to a nacelle which is mounted on top of the tower and being adapted to drive a generator situated inside the nacelle. The rotor is rotatable by action of the wind. The wind induced rotational energy of the rotor blades is transferred via a shaft to the generator. Thus, the wind turbine is capable of converting kinetic energy of the wind into mechanical energy by means of the rotor blades and, subsequently, into electric power by means of the generator. The generator may include a power converter for converting the generator AC power into a DC power and a power converter for converting the DC power into an AC power to be injected into the electrical power grid. The generator of the wind turbine 102 is controllable to produce power corresponding to power set-points provided by the central controller. For wind turbines, the output power may be adjusted according to the power set-point by adjusting the pitch of the rotor blades or by controlling the power converter to adjust the power production. Electrolyzers 113 need to be protected against high voltages of their power supply. Since situations may occur where the grid voltage at the grid 190 or the voltage at the internal grid 191 increase above nominal levels, the power plant 100 should be configured to protect the electrolyzers against high voltages in such over voltage situations.

Some embodiments are based on utilizing existing functionalities of the wind turbines 101 to alleviate the over voltage situation by performing an action that may result in a reduction of the voltage level at the power input 114 of the electrolyzer system 110.

These embodiments are based on the detection of an overvoltage condition which relates to the voltage level at a power input 114 of the electrolyzer system 110.

For example, the electrolyzer system 110 may be configured with a voltage detector arranged to measure the voltage level at the power input 114 to detect an over voltage situation.

Alternatively, an auxiliary over voltage protection system 140 comprised by the power plant 100 or the electrolyzer system 110 may be configured with a voltage detector arranged to measure a voltage level corresponding to the voltage level at the input 114 of the electrolyzer system 110. The over voltage protection system 140 is connected to the internal grid 191 via a transformer 131 with the low voltage side of the transformer 131 being connected to the over voltage projection system 140 and the high voltage side being connected to the internal grid 191. The voltage detector of the over voltage protection system 140 is arranged on the low voltage side of the transformer.

In another example, a voltage detector comprised by a wind turbine 101, a voltage detector arranged to measure the voltage at the point of common coupling PCC, or other voltage detector comprised by the power plant 100 may be used to detect the over voltage situation relating to a voltage level at a power input 114 of the electrolyzer system. That is, although such voltage detectors may provide a voltage which differs from the actual voltage at the input 114 of the electrolyzer system 110, the provided voltage may at least correlate with the input voltage at the electrolyzer system and thereby provide valid information about a possible over voltage situation at the power input of the electrolyzer system.

In case an overvoltage is detected, a communication means such as a wired or wireless data transmitter sends a warning signal to one or more of the wind turbines 101. The electrolyzer system 110 or the over voltage protection system 140 may comprise the communication means, and/or the communication means may be a communication circuit arranged in connection with the voltage detector arranged to detect the overvoltage condition.

In response to receiving the warning signal, each of the wind turbines that received the signal are configured to perform a compensation action for lowering the voltage level on the internal grid 191 and thereby at the power input 114 of the electrolyzer system 110.

A controller comprised by a wind turbine or a central controller 170 may be configured to control the wind turbine to perform the compensation action. In another example, the warning signal is sent directly to one or more wind turbines and a controller of each wind turbine is configured to perform the compensation action.

In an embodiment the wind turbines are configured to reduce the amount of electrical power injected into the grid 190 by reducing the power generation. The reduction of the power generation may be achieved by modifying the power setpoint and thereby controlling the wind turbine to lower its power production. The reduced power production results in a reduction of the current injected into the grid 190 and thereby a reduction of the voltage on the internal grid 191 and the input 114 at the electrolyzer system 110.

Alternatively, or additionally, each of one or more of the wind turbines can be controlled to reduce the amount of electrical power injected into the grid 190 by dissipating produced power produced in a dump load comprised by a wind turbine. The dump load may be configured as a series connection of a resistor and switch which are arranged in parallel with the DC link of the power converter. Accordingly, the dump load can be activated by closing the switch in response to the warning signal.

Accordingly, existing components such as the dump load and/or existing control methods such as the power production control can be utilized for reducing the input voltage to the electrolyzer system 110, thereby rendering modifications of the electrolyzer system to lower the input voltage unnecessary.

Alternatively or in addition to the steps of:

- sending a warning signal to the at least one wind turbine in response to detecting the overvoltage condition, and

- controlling the at least one wind turbine to perform a compensation action for lowering the voltage level at the power input of the electrolyzer system in response to receiving the warning signal, the power plant 100 may be configured to electrically disconnect the electrolyzer system 110 from the internal grid based on a determination of a duration of the overvoltage condition.

The electrolyzer system 110 or the over voltage protection system 140 may comprise a means for determining the duration of the over voltage condition such as a timer or counter.

Thus, initially the compensation action for lowering the voltage level at the power input 114 of the electrolyzer system may be performed and if the voltage has not decreased to a sufficiently low level such as a predefined level, the electrolyzer system 110 may be disconnected if the over voltage situation has persisted long enough.

Alternatively, e.g. if the power plant is not configured to perform the compensation action, the electrolyzer system 110 may be disconnected if the over voltage situation has persisted long enough without initially performing the compensation action for lowering the input voltage to the electrolyzer system.

The disconnection of electrolyzer system 110 is achieved by controlling the circuit breaker 121 to disconnect the input 114 from the internal grid. The auxiliary over voltage protection system may comprise a clamping circuit 141 arranged to clamp the voltage at the low voltage side of the transformer 131, e.g. dependent on a request. The claiming circuit may be arranged to clamp the voltage to a predetermined voltage. The purpose of the clamping circuit 141 is to protect auxiliary loads against over voltages. The clamping circuit may be activated dependent on a request, such as a determined electrical characteristic of the over voltage protection system 140 so that the circuit will clamp the input voltage of the over voltage protection system 140 if the electrical characteristic becomes too high.

The clamping circuit may comprise a metal-oxide-varistor arranged to clamp the voltage which will cause a reduction of the voltage on the low voltage side of the transformer 131 and therefore also on the high voltage side. Accordingly, activating the clamping circuit also brings down the voltage of the high voltage side of the transformer 131.

The overvoltage voltage projection system 140, such as the timer thereof, may be configured to determine the duration of the over voltage condition while the voltage is clamped. In this way, if the determined duration exceeds a maximum duration this would indicate a more severe over voltage situation with a lot of energy in grid 190, and therefore a need for disconnecting the electrolyzer system