WO2015024732A1

WO2015024732A1 - Control of the rotational speed of a rotating wave energy system as a function of the flow speed

Info

Publication number: WO2015024732A1
Application number: PCT/EP2014/065993
Authority: WO
Inventors: Alexander Poddey; Daniel Seiler-Thull; Michael Hilsch; Nik Scharmann; Johannes Nitzsche; Matthias Lenssen; Benjamin Hagemann; Carolina Passenberg
Original assignee: Robert Bosch Gmbh
Priority date: 2013-08-19
Filing date: 2014-07-25
Publication date: 2015-02-26
Also published as: DE102013216339A1

Abstract

The invention relates to a method for operating a wave energy system (1) for converting energy from a wave motion of a fluid into another form of energy, wherein the wave energy system (1) has a lever arm (4) which is mounted so as to be rotatable about a rotational axis (x) of a rotor and has a coupling body (3), and an energy converter (2, 7) which is coupled to the rotatably mounted lever arm (4), wherein in a first operating mode the wave energy system (1) is to be operated in such a way that a rotational speed (ω₁) of the lever arm (4) about the rotational axis (x) of the rotor corresponds when averaged over time over a rotation to an orbital speed (Ω) of the wave motion, wherein in a second operating mode the wave energy system (1) is operated in such a way that the rotational speed (ω₁) of the lever arm (4) about the rotational axis (x) of the rotor does not correspond when averaged over time over a rotation to the orbital speed (Ω) of the wave motion, wherein the wave energy system (1) is operated in the second operating mode if a variable (H) which characterises a flow speed (v) undershoots a lower threshold value.

Description

Control of the rotational speed of a rotating wave energy plant in

Dependence on the flow velocity

description

The present invention relates to a method for operating a wave energy plant for converting energy from a wave motion of a fluid into another form of energy, a computing unit for its implementation and a wave energy plant.

State of the art

Wave energy plants (also referred to as wave energy converters or wave power plants) convert the energy of sea waves into another form of energy, for example, for the production of electricity. Newer design approaches use rotating units (rotors), which convert the wave motion into a torque. These may have one or more lever arms with coupling bodies attached thereto. Hydrodynamic buoyancy bodies (ie bodies that generate buoyancy when circulating, such as buoyancy profiles and / or Flettner rotors using the Magnus effect) may be used as coupling bodies by means of which buoyancy forces from the incoming wave and by the arrangement of the coupling bodies on the lever arm, a torque is generated, which is convertible into a rotational movement of the lever arm about a rotor axis of rotation. By a superimposed flow from the orbital flow of the wave motion and the rotation of the rotor itself buoyancy forces on the coupling bodies, whereby a torque is introduced into the rotor. For example, DE 10 201 1 105 177 A1 discloses a system concept in which the buoyancy of a buoyant buoyant body is converted into a rotational movement. The rotor with its coupling bodies should advantageously largely wave-synchronous, ie orbit with a mean rotational speed which is equal to or proportional to the wave orbital motion. If, for example, the rotational frequency of the rotor corresponds to the shaft frequency, substantially stationary flow conditions on the coupling bodies result, which lead to a largely continuous torque on the rotor shaft. This can be fed directly into a generator. Excessive mechanical loads and / or unevenness in the output power of the wave energy system are thereby avoided. However, especially in the open sea, very different wave conditions exist. In addition to so-called old lakes, where the waves occur very regularly, this also includes wave states in which the wave characteristic changes continuously as a result of the superposition of different waves. The first wave state is referred to in this application as "monochromatic", the second wave state as "multichromatic". Completely monochromatic wave states hardly occur in nature, so that the term "monochromatic" also includes waves with a certain, but low, multichromatic effect.

Although the wave states generally do not change abruptly and are also relatively predictable, in practice the rotational speed of a corresponding rotor can often not be adapted with sufficient speed. This applies in particular to multichromatic wave states. In DE 10 2012 012 096.6, therefore, a synchronicity is required only in the time average per revolution. However, even in real waters, especially in the sea, this operating mode does not provide optimal results in all situations.

The invention aims to improve the operation of generic wave energy systems in multichromatic wave states. Disclosure of the invention

According to the invention, a method for operating a wave energy plant for converting energy from a wave motion of a fluid into another form of energy, a computing unit for its implementation and a wave energy plant with the Characteristics of the independent claims proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The invention makes it possible to operate a wave energy plant with the highest possible energy yield. This is achieved by starting from a substantially synchronous first operating mode (ie rotational speed of the rotor corresponds on average over one revolution of the orbital speed of the shaft movement) in an asynchronous second operating mode (ie rotational speed of the rotor does not correspond over one revolution over a period of time Orbitalgeschwindigkeit the wave motion) is changed when a flow rate characterizing size (eg wave height or flow velocity itself) at the location of the wave energy plant falls below a lower threshold.

In multichromatic waves (also called irregular wave) there can be a sudden change of the residence-induced orbital flow, since there are times when the flow almost disappears. For such cases, it is energetically extremely unfavorable to track the rotor these jumps. The flow rate is negligible in such situations, which is why an energy gain due to hydrodynamic losses is usually not given anyway. This invention provides a solution that can be used to effectively generate energy in multichromatic waves with the wave energy plant. The invention makes possible an energetically meaningful operation of a wave energy plant in multichromatic waves. For this purpose, it is decided on the basis of the flow information, which can be obtained directly or indirectly by suitable sensors, whether it is energetically meaningful at the current time with regard to the hydrodynamic losses to actively track the rotor in the flow direction (ie to operate in the first operating mode ) or not (ie operate in the second operating mode). According to an advantageous development, a suitable specification of an adjustment parameter influencing the strength of the coupling (for example a pitch angle in the case of flow bodies or a self-rotation speed in Flettner rotors) of hydrodynamic coupling bodies also takes place in the operating modes. According to linear wave theory, waves that occur in the sea largely consist of several frequency components. These components superimposed result in a more or less regular wave field with certain wave heights (see Figure 3). Due to the underlying wave mechanics, it is known that at low wave height there is also only one flow at a low velocity below it. Depending on this flow velocity, it does not always make sense energetically to insist on a synchronous movement of the rotor with the orbital motion, since there are frequent small reversals in the wave height, which represent as jumps in the course of the flow direction.

An arithmetic unit according to the invention, e.g. a control unit of a wave energy plant, is, in particular programmatically, adapted to perform a method according to the invention.

Also, the implementation of the invention in the form of software is advantageous because this allows very low cost, especially if an executing processing unit is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of exemplary embodiments in the drawing and will be described in detail below with reference to the drawing. figure description

FIG. 1 shows a preferred embodiment of a wave energy plant according to the invention in a perspective view.

FIG. 2 shows the wave energy installation according to FIG. 1 in a side view and illustrates the pitch angle a _P and the phase angle Δ between rotor and orbital flow.

FIG. 3 shows a dependence of a wave height on time for a multichromatic one

Wave of two frequencies.

FIGS. 4-7 show different possibilities for controlling the rotational angle position of the rotor over time for situations where the flow velocity is too low.

Detailed description of the drawing

In the figures, the same or equivalent elements are given identical reference numerals. A repeated explanation is omitted for clarity.

The present invention relates to the operation of rotating equipment for the recovery of energy from moving fluids, for example from the sea. The functional principle of such systems is first explained below with reference to Figures 1 and 2.

1 shows a wave energy plant 1 with a rotor base 2, a housing 7 and four each attached via lever arms 4 to the rotor base 2 coupling body 3. The wave energy plant 1 is provided for operation below the water surface of a wavy body of water - for example, an ocean. The coupling body 3 are profiled in the example shown, but can also be designed as Flettner rotors, ie cylinders with additional self-rotation. Conveniently, for each of the coupling An adjustment device 5 with at least one degree of freedom is available to change the orientation (eg "pitch angle", ie the angle between chord and tangential velocity) of the respective coupling body and thus to influence the interaction between the fluid and the coupling body. The degree of freedom of the displacement devices is described here by adjustment parameters (pitch angle). Alternatively, in the case of Flettner rotors as coupling bodies, the rotational speed of the Flettner rotors can also be adapted. The adjusting devices are preferably hydraulic (or electromotive or pneumatic) adjusting devices. Preferably, a sensor 6 is also available for detecting the current adjustment. The components 2, 3, 4, 5, 6 are components of a rotor 1 1, which rotates about a rotor axis x.

The housing 7 is part of a frame 12. The rotor 1 1 is rotatably mounted relative to the frame 12. In the example shown, the frame 12 is non-rotatably connected to a stator of a directly driven generator for power generation, the rotor 1 1 (here the rotor base 2) is non-rotatably connected to a rotor of this directly driven generator. It may also be provided a gear or a hydrostatic drive train between the rotor base and generator rotor. An arithmetic unit which is set up to carry out a method according to the invention is arranged inside the housing 7 and serves to control the operation of the wave power plant 1. Not shown is an intended attachment of the wave energy plant 1 on the seabed, which can be done for example by a mooring system, in particular a monopile.

Figure 2 shows a side view of the system with rotated by 90 ° to the position shown in Figure 1 lever arms. The adjustment parameters can be seen as the pitch angle a _P between the chord of the coupling body 3 and the tangent (shown by an arrow) on the circular path through the suspension point (pivot point) of the coupling body. Preferably, the coupling bodies 3 are suspended at their pressure point in order to reduce rotational torques occurring during operation to the coupling bodies and thus to reduce the requirements for the holder and / or the adjusting devices.

The representation of the coupling body in Figure 2 and in the other figures is only exemplary for the definition of the different machine parameters. In addition, a curvature of the coupling body to the circular path may be advantageous. The wave energy plant 1 is surrounded by a flow vector field v. In the described embodiments, it is assumed that the

Flow around the orbital flow of sea waves whose direction is continuously changing. In the case shown, the rotation of the orbital flow is oriented in the counterclockwise direction, ie the associated wave propagates from right to left. In the monochromatic case, the flow direction at the rotor axis of rotation (x in FIG. 1) changes with the angular velocity Ω = 2πί = const, where f represents the frequency of the monochromatic wave. In multichromatic waves, on the other hand, Ω undergoes a temporal change, Ω = f (t), since the frequency f is a function of time, f = f (t).

The flow causes forces on the coupling bodies. Characterized the angle </ i ( "rotor angle") of the rotor base 2 relative to the horizontal varies with the rotational speed _ω ι = _ψ ι (ψ ₁ denotes the derivative of the time-dependent quantity </ i after the

Time). Accordingly, Ψ denotes the angle between the flow direction and the horizontal, which is hereinafter referred to as "flow angle".

It is envisaged that the lever arm 4 rotates in the first mode of operation in time synchronous with the orbital flow of the wave motion with u> i. In this case, for example, Ω «u> i. A value or a range of values for an angular velocity u> i of the rotor is thus predefined or adapted on the basis of an angular velocity Ω of the orbital flow. This can be done a constant control or a short-term or short-term adjustment.

On the rotor 1 1, a variable load moment M _L acts between the rotor base 2 and the housing 7 or frame 12. The load torque can act in a positive direction (counter to

Rotational speed ω-ι) but also in the negative direction (ie driving) act. The load torque is caused for example by a power generation in the generator.

An angle between the rotor orientation, indicated by a lower dashed line passing through the rotor axis of rotation and the center of the two adjusters 5, and the direction of the orbital flow, represented by an upper dashed line passing through one of the velocity arrows v runs, is referred to as phase angle Δ = Ψ - Ω, the amount by the adjustment of the drive torque and / or the load torque can be influenced. In this case, a phase angle at the rotor rotational axis of -25 ° to 25 °, preferably from -10 ° to 10 ° and particularly preferably from about 0 ° for generating the drive torque appears to be particularly advantageous, since in this case the orbital flow and the flow due to the intrinsic rotation largely perpendicular oriented to each other, which leads to a maximization of the amount of the resulting flow. For further details on the operation of such a wave energy system, reference is made to the already mentioned in the introduction of DE 10 201 1 105 177 A1 and DE 10 2012 012 096 A1. In FIG. 3, to illustrate the invention, a wave height H resulting at a location, in particular above a wave energy installation 1, which results from the superimposition of two waves with different frequencies, is shown over time t. Overall, a so-called beating wave, the wave height H, as shown clearly varies over time.

In FIG. 3, in particular, three regions marked with a frame in the figure can be identified, in which the wave height H and thus the flow velocity prevailing below the water surface become very small and are no longer suitable for energy-producing operation of the wave energy plant 1.

In the case of stationary multichromatic waves (waves with several, different frequency and amplitude components, these shares are constant) or multichromatic waves (the frequency and amplitude components are time-varying) can be as local orbital flow, an effectively resulting value, such as an average or a Value of the main part, to be used. The local orbital flow can be measured or calculated. For example, the wave height can be measured above the wave energy plant or at a location at which the wave passes in time before the wave energy plant. From this the orbital flow velocity can be calculated. One possibility for prognosis is described in DE 10 2013 002 127.8. Accordingly, the variable characterizing a flow rate is preferably measured at the location of the wave energy plant or calculated at the location of the wave energy plant from a measurement at a location different from the location of the wave energy plant. In the context of the invention, therefore, the wave energy plant is operated in two different operating modes, the decision as to which operating mode is to be used being made dependent on the flow velocity. In particular, a variable characterizing the flow rate is measured, here preferably the wave height H and / or the flow velocity itself, and compared with one or more threshold values. It is advisable to carry out the change between the operating modes as a function of different threshold values (referred to here as lower threshold value and upper threshold value) in order to introduce a hysteresis between the operating mode changes and to reduce the frequency of change to a necessary or appropriate level. In the context of the invention, it is therefore preferable to switch from the first to the second operating mode when the flow rate characterizing variable falls below a lower threshold value and to return from the second operating mode to the first operating mode when the flow rate indicative variable exceeds an upper threshold value. For the sake of completeness, it should be noted that the lower threshold and the upper threshold may also be identical.

In FIGS. 4 to 7, different embodiments for the second operating mode will now be explained. In the figures, a profile of the flow angle Ψ and of the rotor angle ψ ^ is in each case in the upper half. In the lower half, the power P generated in each case is plotted against the time t. In the first operating mode, a substantially synchronous operation takes place, so that the angles Ψ and </ i run synchronously. The rotational speed ωι of the rotor accordingly corresponds in the time average over one revolution of the orbital velocity Ω.

In FIGS. 4 to 7, it is assumed in each case that, at the time t = t _0, the variable characterizing a flow velocity falls below the lower threshold value and thus is changed into the second operating mode. In FIG. 4, the second operating mode does not include a specification or influencing of the rotational speed, whereas in FIGS. 5-7, the rotational speed or the rotor angle profile is still influenced in one way or another.

In FIG. 4 it is shown that, at the time t = t _0, a regulation of the rotor angle </ i is terminated, ie the rotational speed or the rotor angle progression are no longer affected. As a result, no energy can be gained from this point on, but no energy needs to be expended. The rotor will continue to rotate due to inertia, with the rotational speed slightly decreasing. For this purpose, the adjustment parameters of the coupling bodies are expediently selected such that they cause the lowest possible flow resistance, so that the rotor retains its rotational speed as far as possible. Alternatively, it is conceivable to adjust the adjustment parameters so that the coupling bodies cause the greatest possible flow resistance in order to be exposed to kinetic energy as early as possible as a resistance runner.

In Figure 4 is about at a time

is exceeded by the flow velocity characterizing size of the upper threshold, so that is changed back to the first operating mode. Here, energy must first be used to restore the synchronous rotation between (/ -i and Ψ.

FIG. 5 shows that, according to an alternative preferred embodiment, in the second operating mode, the rotor is advanced at a constant rotational speed Ω. This is to avoid large accelerations and thereby caused large energy losses. In accordance with FIG. 4, too, after the renewed change to the first operating mode (after the upper threshold value has been exceeded by the variable characterizing a flow speed), more or less energy is expended in order to restore the synchronous operation.

FIG. 6 shows a further preferred embodiment, in which the rotor is essentially stopped in the second operating mode. This means that the setpoint for the rotor angle is no longer the flow angle Ψ (if applicable ± phase angle Δ), but a fixed angle. This fixed angle may be a previously defined fixed angle or an angle resulting from the previous movement of the rotor. The purpose of this mode of operation is to position the rotor so that energy from the shaft can be used to restart the rotor and not, as in the two previously described embodiments, an active and thus energy-consuming acceleration is necessary. The adjustment parameters of the coupling body are here zweckweiße chosen so that during standstill the lowest possible flow resistance prevails and to restart the largest possible flow resistance is generated in order to enable a quick and energetically favorable restart of the rotor.

Finally, FIG. 7 shows a further preferred embodiment in which a predetermined trajectory is traveled in the second operating mode. As a trajectory, a dependence of the rotor angle </ i of the time is defined here. This can be advantageously combined with a time prediction of the wave motion so that an energetically optimal trajectory can be planned over time to accelerate the rotor as little as possible, yet at the ideal time to the right position at the right speed respectively. The adjustment parameters of the coupling bodies are preferably selected such that the coupling bodies generate the lowest possible flow resistance in order to ensure energy-efficient continuity of the rotor. Alternatively, the adjustment parameters can also be adapted to the respective present flow direction during the further operation in order to be able to convert as much energy as possible during the further operation.

Claims

claims

1 . Method for operating a wave energy plant (1) for converting energy from a wave movement of a fluid into another form of energy,

wherein the wave energy plant (1) has a lever arm (4) rotatably mounted about a rotor axis of rotation (x) and carrying a coupling body (3), and an energy converter (2,7) coupled to the rotatably mounted lever arm (4),

wherein in a first operating mode, the wave energy plant (1) is operated so that a rotational speed (ω-ι) of the lever arm (4) about the rotor rotational axis (x) in the time average over one revolution of an orbital velocity (Ω) corresponds to the wave motion,

wherein in a second operating mode, the wave energy plant (1) is operated such that the rotational speed (ω-ι) of the lever arm (4) around the rotor rotational axis (x) over one revolution does not correspond to the orbital velocity (Ω) of the wave motion over one revolution

wherein the wave energy plant (1) is operated in the second operating mode when a variable (H) characterizing a flow velocity (V) falls below a lower threshold value.

2. The method of claim 1, wherein the wave energy plant (1) is operated in the first operating mode when the flow velocity (v) characteristic size (H) exceeds an upper threshold.

3. The method according to claim 1 or 2, wherein the flow velocity (v) characterizing variable is the flow velocity (v) and / or a wave height (H).

4. The method according to any one of the preceding claims, wherein in the second operating mode, the rotational speed (ω-ι) of the lever arm (4) about the rotor rotational axis (x) is not specified.

5. The method according to any one of claims 1 to 3, wherein in the second operating mode, the rotational speed (ω-ι) of the lever arm (4) about the rotor axis (x) is set so that the lever arm (4) performs a predetermined movement.

6. The method of claim 5, wherein the movement is predetermined in response to a temporal prediction of the wave motion.

7. The method of claim 5 or 6, wherein in the second operating mode, the rotational speed (ω-ι) of the lever arm (4) about the rotor rotational axis (x) is constant.

8. The method of claim 7, wherein in the second operating mode, the rotational speed (ω-ι) of the lever arm (4) about the rotor rotational axis (x) is zero.

9. Method according to one of the preceding claims, wherein in the second operating mode an adjustment parameter (a _{Pi 1} , a _Pi2 ) which influences a strength of a coupling of the coupling body with the fluid is predetermined.

10. The method according to any one of the preceding claims, wherein the flow velocity (v) characterizing size (H) at the location of the wave energy plant (1) is measured or at the location of the wave energy plant (1) from a measurement at one of the location of the wave energy plant ( 1) different location is calculated.

1 1. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims.

12. wave energy plant (1) for converting energy from a wave motion of a fluid in another form of energy, comprising a about a rotor rotational axis (x) rotatably mounted lever arm (4) carrying a coupling body (3), one with the rotatably mounted lever arm ( 4) coupled energy converter (2,7) and a computing unit according to claim 1 1.