EP2422421A1

EP2422421A1 - Energy generating installation, especially wind power installation

Info

Publication number: EP2422421A1
Application number: EP10720533A
Authority: EP
Inventors: Gerald Hehenberger
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-04-20
Filing date: 2010-04-20
Publication date: 2012-02-29
Also published as: CA2759250A1; CN102405574A; BRPI1009908A2; AT508182A1; KR20110137803A; WO2010121782A1; AT508182B1; AU2010238786A1; US20120032443A1

Abstract

The invention relates to an energy generating installation, especially a wind power station, comprising a drive shaft connected to a rotor (1), a generator (8) and a differential transmission (11 to 13) provided with three drives or outputs. A first drive is connected to the drive shaft, an output is connected to a generator (8), and a second drive is connected to an electrical differential drive (6, 14). The differential drive (6, 14) is connected to a network (10) by means of a frequency converter (7, 15), the blind current of the frequency converter (7, 15) being regulatable.

Description

Energy production plant, in particular wind turbine

The invention relates to an energy production plant, in particular wind turbine, with a drive shaft connected to a rotor, a generator and a differential gear with three inputs or outputs, wherein a first drive with the drive shaft, an output with a generator and a second drive with a connected to the electric differential drive, and wherein the differential drive is connected via a frequency converter to a network.

The invention further relates to a method for operating such a power generation plant.

Wind power plants are becoming increasingly important as electricity generation plants. As a result, the percentage of electricity generated by wind is continuously increasing. This, in turn, requires new standards in terms of power quality (in particular with regard to reactive current regulation and behavior of the wind power plants in the event of voltage dips in the grid) and, on the other hand, a trend towards even larger wind turbines. At the same time, there is a trend towards offshore wind turbines, which require system sizes of at least 5 MW of installed capacity. Due to the high costs for infrastructure and maintenance of wind turbines in the offshore sector, both the efficiency and manufacturing costs of the plants, with the associated use of medium-voltage synchronous generators, gain in importance here.

WO2004 / 109157 A1 shows a complex, hydrostatic "multi-way" concept with several parallel differential stages and several switchable couplings, which makes it possible to switch between the individual paths With the technical solution shown, the power and thus the losses of the hydrostatics can be reduced. A major disadvantage, however, is the complicated structure of the entire unit.The electrical energy fed into the network comes exclusively from the synchronous generator driven by the differential system.

EP 1283359 A1 shows a 1-stage and a multi-stage differential gear with electric differential drive, which drives via frequency converter mechanically connected to the grid-connected synchronous generator, electric machine. The electrical energy fed into the network also comes in this example exclusively from the synchronous generator driven by the differential system. WO 2006/010190 A1 shows the drive train of a wind power plant with electric differential drive with frequency converter, which is connected in parallel with the synchronous generator to the grid.

Although these technical solutions allow the direct connection of medium-voltage synchronous generators to the network, the disadvantages of known designs, however, are that the reactive current control of the synchronous generators used, and with this the voltage regulation of the network, the demands of modern power plants, due to the relatively long time constants for the regulation of the exciter of the synchronous generator, do not do justice.

The object of the invention is to obviate the abovementioned disadvantages as far as possible and to provide an energy production plant which has the best possible power quality both for the individual energy production plant, in particular wind power plant, and for e.g. guaranteed a wind farm.

This object is achieved in an energy recovery system of the type mentioned according to the invention in that the reactive current of the frequency converter is adjustable.

This object is achieved in a method of the aforementioned type according to the invention in that the reactive current of the frequency converter is controlled.

Thus, the extremely important aspects of the power quality for the power generation plant, in particular wind turbine, solved as well as possible, because by the frequency converter supplied reactive current can be controlled very quickly and effectively.

Preferred embodiments of the invention are subject of the dependent claims.

Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.

1 shows, for a 5MW wind turbine according to the prior art, the power curve, the rotor speed and the resulting characteristic values such as high-speed number and the power coefficient,

2 shows the principle of a differential gear with an electric differential drive according to the prior art, 3 shows by way of example according to the prior art the speed and power ratios of an electric differential drive over the wind speed,

4 shows the network of a conventional wind farm,

5 shows the network of a wind farm with wind turbines with a differential system according to FIG. 2, FIG.

6 shows the time characteristic of the reactive current occurring during a reactive current setpoint step,

7 shows the self-adjusting reactive current during a power jump of the wind turbine,

8 shows a possible control scheme for a combined reactive current control according to the present invention,

9 shows the resulting reactive current during a power jump of the wind power plant with reactive current compensation by a frequency converter,

10 shows an example of the power requirement of the differential drive in LVRT,

11 shows an electric differential drive with intermediate circuit storage,

12 shows the typical electrical harmonics of a medium voltage synchronous generator,

13 shows a possible principle of active harmonic filtering with frequency converters,

Fig. 14 shows the electrical harmonics of a medium voltage synchronous generator with active harmonic filtering with a frequency converter.

The power of the rotor of a wind turbine is calculated from the formula

Rotor power = Rotor area ^* Power coefficient ^* Wind speed3 ^* Air density / 2

where the power coefficient depends on the speed of rotation (= ratio blade tip speed to wind speed) of the rotor of the wind turbine. The rotor of a wind turbine is designed for an optimal performance coefficient based on a As a result of the development, the fast-running number (usually a value between 7 and 9) is designed. For this reason, when operating the wind turbine in the partial load range, a correspondingly low speed must be set in order to ensure optimum aerodynamic efficiency.

Fig. 1 shows the ratios for rotor power, rotor speed, high-speed number and power coefficient for a given speed range of the rotor or an optimal speed number of 8.0-8.5. It can be seen from the graph that as soon as the high-speed number deviates from its optimum value of 8.0-8.5, the coefficient of performance decreases and, according to the above-mentioned formula, the rotor power is reduced according to the aerodynamic characteristic of the rotor.

Fig. 2 shows a possible principle of a differential system for a wind turbine consisting of a differential stage 3 or 11 to 13, an adjustment gear stage 4 and an electric differential drive 6. The rotor 1 of the wind turbine, on the drive shaft 9 for the main transmission 2 sits, drives the main transmission 2. The main transmission 2 is a 3-stage transmission with two planetary stages and a spur gear. Between main gear 2 and generator 8 is the differential stage 3, which is driven by the main gear 2 via planet carrier 12 of the differential stage 3. The generator 8 - preferably a third-excited medium voltage synchronous generator - is connected to the ring gear 13 of the differential stage 3 and is driven by this. The pinion 11 of the differential stage 3 is connected to the differential drive 6. The speed of the differential drive 6 is controlled to one hand, to ensure a constant speed of the generator 8 at variable speed of the rotor 1 and on the other hand to regulate the torque in the complete drive train of the wind turbine. In order to increase the input speed for the differential drive 6, a 2-stage differential gear is selected in the case shown, which provides an adjustment gear stage 4 in the form of a spur gear between differential stage 3 and differential drive 6. Differential stage 3 and adaptation gear stage 4 thus form the 2-stage differential gear. The differential drive is a three-phase machine, which is connected via frequency converter 7 and transformer 5 parallel to the generator 8 to the network 10.

The speed equation for the differential gear is:

Speed generator = x ^* speed rotor + y ^* speed differential drive,

wherein the generator speed is constant, and the factors x and y can be derived from the selected transmission ratios of the main transmission and differential gear. The torque on the rotor is determined by the upcoming wind supply and the aerodynamic efficiency of the rotor. The ratio between the torque at the rotor shaft and that at the differential drive is constant, whereby the torque in the drive train can be controlled by the differential drive. The torque equation for the differential drive is:

Torque differential drive = torque rotor ^* y / x,

wherein the size factor y / x is a measure of the necessary design torque of the differential drive.

The power of the differential drive is substantially proportional to the product of percent deviation of the rotor speed from its base speed times rotor power, the base speed being that speed of the rotor of the wind turbine where the differential drive is at rest, i. the speed is zero. Accordingly, a large speed range basically requires a correspondingly large dimensioning of the differential drive.

In Fig. 3 can be seen by way of example the speed or power ratios for a differential stage according to the prior art. The speed of the generator is determined by the

Connection to the frequency-stable power supply constant. In order to make good use of the differential drive, this drive is in the range of smaller

Basic speed motor-driven and in the range greater than the basic speed operated as a generator. As a result, power is fed into the differential stage in the motor area and power is taken from the differential stage in the generator area. In the case of an electric differential drive, this power is preferably taken from the network or fed into it. The sum of

Generator power and power of the differential drive gives the for a

Wind turbine with electric differential drive into the net delivered total power.

Fig. 4 shows how wind farm nets connecting a large number of wind turbines are usually constructed. For simplicity, only three wind turbines are shown here, and depending on the size of the wind farm, for example, up to 100 or even more wind turbines can be connected in a wind farm network. Several low-voltage wind turbines with a rated voltage of eg 690VAC (usually equipped with so-called double-fed three-phase machines or three-phase machines with full inverters) feed via the plant transformer into a busbar with a voltage level of, for example, 2OkV. Before the grid entry point, which usually the transfer point into the network of Power supply company is switched, a wind park transformer, which increases the wind farm medium voltage to a mains voltage of, for example, 11OkV. For this grid feed-in point, there are guidelines to be met in terms of reactive current factor and voltage constancy, which are usually defined by the electricity supply companies. In order to meet the ever stricter standards of power quality, dynamic reactive current compensation systems are increasingly being implemented on the medium voltage side, which keep the voltage at the grid entry point within prescribed limits by feeding reactive current into the grid or withdrawing reactive current from the grid ,

Fig. 5 shows an alternative wind farm network connecting a large number of wind turbines with differential systems. For the sake of simplicity, only three wind turbines per group are shown here. Several wind turbines in medium voltage version with a rated voltage of e.g. 1OkV (equipped with so-called externally excited synchronous generators and parallel-connected electric differential drives - such as in Fig. 2), feeding into one busbar, and (in the case of very large wind farms) from this via group transformer into another busbar with a voltage level of e.g. 3OkV. Before the grid feed-in point, here too a wind park transformer is connected, which switches the wind farm medium voltage to a mains voltage of e.g. 11OkV increased. Also in this example, a dynamic reactive current compensation system is implemented, which has the task of keeping the voltage delivered to the grid within predetermined limits.

Especially with performance leaps in wind turbines due to wind gusts or power failures, this is a highly dynamic process, which can not be compensated independently of the wind turbines according to the prior art. It is not just about a constant voltage regulation of each wind turbine. The downstream wind farm network, consisting of lines and transformers, moreover, needs to be supplied by the wind turbines reactive current component to compensate for the power fluctuations of the wind turbines resulting voltage fluctuations in the feed point, unless it is supplied by an already mentioned dynamic reactive current compensation system , This reactive current component to be supplied by the wind turbines is largely dependent on the impedance of the wind farm network and on the electrical power to be transmitted to the grid, and can be mathematically calculated from these parameters. This means that in a preferred embodiment of the invention, the control of each individual wind turbine calculates the reactive current component required for, for example, the power fluctuation for power fluctuation-related compensation of the wind farm network, and can pass this to the reactive power control of the wind turbine as an additional reactive power requirement. Alternatively, a central control unit this calculate the reactive power required for the wind farm grid, and pass it on to the individual wind turbines as demand (reactive current setpoint) according to a defined distribution key. This central control unit is then preferably located near the grid feed-in point, and calculates from measured wind farm power and / or measured mains voltage required for a constant voltage reactive power demand.

It should be added that most of the regenerative energy production facilities, such as Wind turbines compared to e.g. caloric power plants have the disadvantage that, due to the stochastic accumulating drive energy (gusty wind), large power jumps occur within a short time constant. As a result, the topic of dynamic reactive current compensation for regenerative power generation systems is of particular importance.

Another possibility to improve the dynamics of a wind farm mains voltage control, the measurement of the wind speed on a preferably separately erected wind measuring mast, which can alternatively be used for wind measurement on one or more wind turbines. Since the output power of a wind turbine changes with more or less great delay according to the stochastically adjusting wind speed, it can be concluded from the measured change in the wind speed on the expected output of the wind turbines. As a result, the reactive current requirement for a constant voltage at the grid feed-in point can be calculated in advance, and thus delays can be compensated in the best possible way by the given measuring and control time constants.

Fig. 6 shows the typical behavior of a third-excited synchronous generator at a setpoint jump for the reactive current to be supplied. At time 1, 0, the idle power requirement is changed from OA to 4OA, resulting in an immediate increase in the excitation voltage in the synchronous generator. It takes about 6 seconds for the reactive current to settle to the required level of 4OA. The generator voltage changes according to the self-adjusting reactive current.

Fig. 7 shows a similar picture for a power jump of the wind turbine from 60% to 100% of the rated power at time 1, 0. The exciter machine takes approx. 5 seconds until the reactive current levels off again approximately to the original setpoint value of OA. The generator voltage also oscillates here according to the self-adjusting reactive current. In this case, improvements can still be achieved with an optimally coordinated regulation of the exciter voltage, but the behavior shown in FIGS. 6 and 7 is not sufficient to meet the ever-increasing demands on the current quality. For this reason, it is necessary to achieve improvements in dynamic reactive current compensation.

An essential feature of electric differential drives according to FIG. 2 in comparison to hydrostatic or hydrodynamic differential drives is the direct power flow from the differential drive 6 via frequency converter 7 into the network. These frequency converters are preferably so-called IGBT converters in which the reactive power delivered into the network or the reactive power received by the network is freely adjustable. For this one can e.g. implement various control methods by means of freely programmable control, or if necessary adapt these also during operation to changing environmental and / or operating conditions of the wind turbine. According to the invention, highly dynamic frequency converters are used, which feed large amounts of reactive current (even up to, for example, rated current of the frequency converter, or even at a reduced frequency of the frequency converter) into the network or remove it from the grid within extremely short times. As a result, a significant disadvantage of externally excited synchronous generators can be compensated.

Fig. 8 shows a control method according to the invention, which meets this requirement. Basically, a reactive current setpoint is specified for the wind farm, which is specified as a constant, or as a variable eg by an external control. This reactive current setpoint can be specified as a fixed parameter or as a variable by a higher-level wind farm control unit corresponding to a fixed or variable distribution key to the individual wind turbines, whereby a value which is preferably not necessarily defined for all wind turbines The reactive current component "Reactive current for wind farm network compensation" required for the necessary compensation of the downstream wind farm grid can be added to this "reactive current wind turbine." The sum of the two values results in the "reactive current setpoint". This "reactive current setpoint" is forwarded to the "Pl-controller reactive current setpoint generator". Fig. 8 shows a PI controller, although other controller types can be used here. The Pl-Governor Reactor Setpoint Generator typically operates with comparatively long time constants, ie the cycle time within which a change in the reactive current value is possible in this case, but can permanently supply large amounts of reactive current due to the large power capacity of the generator In addition, the comparatively low-power frequency converter 7 (FIG. 2) supplies, within a short time, the reactive power missing in accordance with the "reactive current setpoint", or incorporates it into the reactive power setpoint Reactive current excess from the grid. The reactive current to be supplied by the frequency converter 7 is calculated by the "PI controller reactive current setpoint converter." Both control circuits preferably have a so-called "limiter" which limits the possible reactive current for the generator and the frequency converter.

Fig. 9 shows the effect of this control method according to the invention. The known from Fig. 7 time history of "reactive current generator", the "reactive current inverter" is superimposed. It is assumed that the frequency converter can regulate the current from 0 to rated current within 50 ms. By this short time constant, i. the cycle time within which a change in the reactive current value in this case is possible, the frequency inverter can compensate for the unwanted deviation of the "reactive current generator" relatively quickly, whereby the maximum deviation from the "reactive current setpoint" instead of previously 17A is only 3 A. Accordingly, only an insignificant fluctuation of the "WKA stress" can be seen here.

A more accurate or at least even faster compensation of the "reactive current generator" by the frequency converter can be achieved by shortening the time for the reactive current compensation by the frequency converter so far that you due to a power / torque jump command the wind turbine control on closes the changed reactive power demand, and this in the reactive power control with the aid of a mathematical model, based on a network impedance and the power to be transmitted, pretending accordingly.

In addition to the measures described above with respect to reactive current control by means of an electric differential drive, however, there is a further essential point which can be taken into account in the sense of a generally required, high power quality in connection with the invention. This is that wind turbines should remain on the grid even with mains voltage errors. This feature is commonly referred to as Low Voltage Ride-Through (LVRT) or High Voltage Ride-Through (HVRT), which is precisely defined in various policies (eg, E.ON Netz). During an LVRT event with a worst case voltage drop OV in the grid feed-in point or HVRT event with overvoltage, as already mentioned, the wind turbine should remain connected to the grid, which means that the speed of the generator 8 (FIG. must be kept constant so that the generator 8 is synchronous with the mains when the voltage returns (ie return of the voltage to nominal value). In addition, during a HVRT event, the frequency converter may need to be disconnected from the grid to protect it from undue overvoltage, for example, if so-called surge arresters do not provide adequate protection. Fig. 10 shows for a 5MW wind turbine, the performance of the differential drive during a possible LVRT event in which the mains voltage at time O for 500ms falls to zero. With reference to the embodiment of FIG. 2, the differential drive 6 at the beginning of the LVRT event, a power of approx. 30OkW delivers, it falls within a very short time on OkW. Subsequently, the differential drive 6 receives a power of up to approx. 30OkW. Since there is no or at least insufficient power supply at this time, the differential drive 6 can not maintain the necessary speed / torque control, and the rotor 1 of the wind turbine would cause the generator 8 to tilt, causing the generator 8 to demand the required Can no longer keep the speed to synchronize with the mains when the power returns. The example shown represents only one possibility of the time course of the performance of the differential drive 6. According to the stochastic wind conditions and the start of the LVRT event pending speed / power for the rotor 1 of the wind turbine and the differential drive. 6 , it may of course happen equally that the differential drive 6 at the first moment must draw power.

In order to prevent tilting of the generator 8, Fig. 11 shows a differential electric drive having the following configuration. The differential drive 14 is connected to a frequency converter 15, consisting of the motor-side IGBT bridge 16 and the network-side IGBT bridge 17 and the capacitor-supported DC intermediate circuit 18. The voltage of the frequency converter 15 is adjusted by means of transformer 19 to the generator voltage. To the DC intermediate circuit 18, an intermediate circuit memory 20 is connected, which, among other things, preferably comprises capacitors 21. Alternatively, e.g. also accumulators are used. The capacitors 21 are preferably so-called supercaps, which are already widely used in wind turbines as energy storage for Rotorblattverstellsysteme. The necessary capacity of the capacitors 21 to be used is calculated from the sum of the energy required for the drive of the differential drive during a power failure. It should be noted that the intermediate circuit memory 20 must both supply energy and store energy, it is not known which request will arrive first. That Preferably, the intermediate circuit memory 20 is partially charged, then in this state, sufficient capacity bezügl. maximum necessary delivery volume and maximum storage volume must be available.

From the example according to FIG. 10, one can derive an energy production of the differential drive of initially approximately 10 kJ, followed by an energy requirement of approximately 50 kJ. As a result, the production / demand level levels off, or the LVRT event ends anyway after a total of 500ms. This means that an intermediate circuit memory 20 designed for 10OKJ should be preloaded with approx. 5OKJ.

For reasons of optimization, the precharging of the intermediate circuit memory 20 can be made dependent on the operating state of the wind turbine. Since the differential drive is operated by a motor at wind turbine speeds below the base speed, energy is first drawn from the intermediate circuit memory 20 in this operating range. This means that the intermediate circuit memory 20 must be charged according to the maximum energy requirement to be supplied. In contrast, the differential drive at wind turbine speeds above the base speed is operated as a generator, which means that first the differential drive charges the DC link to then gem. Fig. 10 to change reference. In this case, therefore, the precharge may be lower, so that the maximum required storage volume of the intermediate circuit memory 20 is reduced. That in the example acc. 10 from the intermediate circuit memory to be able to provide sufficient energy, this must be preloaded with about 4OkJ. The 1OkJ missing for the total requirement are loaded by the differential drive at the beginning of the LVRT event.

Since the minimum required storage energy is basically related to the rated output of the wind turbine, can thus for the optimized variant that for the

DC link memory 20 minimum required storage energy with approx. 8kJ /

MW (nominal wind power capacity), or including sufficient reserve with approx. 12kJ /

MW (wind turbine rated power) can be defined. On the other hand, at least 2OkJ / MW (rated wind turbine capacity) are required for the first design variant described.

If one takes into account the fact that in many cases the LVRT event lasts a maximum of 150 ms, the required storage energy is reduced to approx. 1/3 of the above-mentioned minimum required storage energy of approx. 8kJ / MW (rated wind turbine capacity), ie approx. 2.5kJ / MW (rated wind turbine capacity).

If the DC link memory is equipped with capacitors, it can be designed according to the following formula:

Energy [J] = Capacity [F] ^* Voltage [V] 2/2

The voltage in the DC intermediate circuit of the frequency converter can typically oscillate between a voltage upper limit SpO = 1150V and a voltage lower limit SpU = 900V. Ie the max. usable storage energy is calculated in this case usable storage energy = capacity ^* (SpO2-SPU2) / 2.

In normal operation of the system, that is, if neither LVRT events nor HVRT events take place, the intermediate circuit memory 20 will be charged depending on the operating condition of the system between 20% and 80% of its usable storage energy, while such a state of charge sufficient capacity for all conceivable operating conditions is available.

In addition, it should be noted that, with a professional design, the overall much smaller capacitor package of the capacitor-based

DC intermediate circuit 18 can replace the intermediate circuit memory 20.

It could also be an energy storage used as a DC link memory 20 which is designed so large that it can not only take over the above-mentioned function of the intermediate circuit memory 20 but at the same time also the function of an energy storage for the supply of other technical facilities of the wind turbine, such as Rotorblattverstellsystem.

The frequency converter 15 has the necessary for the appropriate charge of the intermediate circuit memory 20 control. For this purpose, preferably the voltage of the intermediate circuit memory 20 is measured. Alternatively, the intermediate circuit memory 20 can also be charged by means of a separate charging device.

In the interests of optimal power quality, the topic of harmonic harmonics can also be handled by separately excited synchronous generators. Fig. 12 shows a typical harmonic spectrum of a separately excited synchronous machine. In particular the harmonics of the 3rd, 5th, 7th and 13th order (order) are noticeable here. Compared to wind turbines with e.g. Full inverters are comparatively high and can be reduced by suitable measures. One way to reduce the amount of these harmonics is the corresponding mechanical design of the synchronous generator by means of so-called skewing of the rotor and / or Sehnung of the rotor and stator. However, such measures are associated with increased manufacturing costs, or limit the availability of possible suppliers due to lack of technical requirements.

Therefore, the existing frequency converter 7 is used for active filtering of the harmonics of the synchronous generator. Fig. 13 shows a known method, the so-called frequency domain method, with the stages transformation of the coordinate system, filters, regulators, limiters, decoupling / pre-rotation and Back transformation of the coordinate system. This makes it possible to generate harmonic currents through the frequency converter, which are out of phase with the measured currents, and thus to selectively compensate harmonics in the mains current.

In addition to the harmonics of the generator, other harmonics may also be present in the network, which may be e.g. come from the frequency converter itself or otherwise arise and which also reduce the power quality. By measuring the mains voltage, all harmonics are detected and can be taken into account during active filtering.

Fig. 14 shows the substantial improvement of the harmonic spectrum with the 3rd, 5th, 7th and 13th order active-filtered harmonics. The quality of the improvement depends on the so-called clock frequency of the frequency converter, with better results at higher clock frequencies.

The embodiments described above are also feasible in technically similar applications. This concerns v.a. Hydroelectric power plants to exploit river and ocean currents. For this application, the same basic requirements apply as for wind turbines, namely variable flow rate. The drive shaft is driven directly or indirectly by the devices driven by the flow medium, for example water, in these cases. Subsequently, the drive shaft directly or indirectly drives the differential gear.

Claims

Claims:

1. power generation plant, in particular wind turbine, with a drive shaft connected to a rotor (1), a generator (8) and with a differential gear (11 to 13) with three inputs or outputs, wherein a first

Drive with the drive shaft, an output to a generator (8) and a second drive with a differential electric drive (6, 14) is connected, and wherein the differential drive (6, 14) via a frequency converter (7, 15) is connected to a network (10), characterized in that the reactive current of the frequency converter (7, 15) is adjustable.

2. Energy production plant according to claim 1, characterized in that the reactive current of the generator (8) is controllable.

3. Power generation plant according to claim 1 or 2, characterized in that the reactive current of the frequency converter (7, 15) is adjustable with a first time constant.

4. Power generation plant according to one of claims 1 to 3, characterized in that the reactive current of the generator (8) is controllable with a second time constant.

5. Power generation plant according to claim 3 and 4, characterized in that the first time constant is shorter than the second time constant.

6. Energy production plant according to one of claims 1 to 5, characterized in that the electric machine (6) is a three-phase machine.

7. Energy production plant according to claim 6, characterized in that the electric machine (6) is a permanent magnet synchronous three-phase machine.

8. Energy production plant according to one of claims 1 to 7, characterized in that the drive shaft is the rotor shaft of a wind turbine.

9. Energy production plant according to one of claims 1 to 8, characterized in that the frequency converter (7, 15) in the DC intermediate circuit (18) has an electrical energy store (20).

10. Energy production plant according to one of claims 1 to 9, characterized in that the frequency converter (7, 15) for actively filtering Harmonics of the power generation plant, in particular of the generator (8), is controllable.

11. A method for operating an energy production plant, in particular wind turbine, with a drive shaft connected to a rotor (1)

Generator (8) and with a differential gear (11 to 13) with three input or output drives, wherein a first drive with the drive shaft, an output with a generator (8) and a second drive with an electric differential drive (6, 14), and wherein the differential drive (6, 14) via a frequency converter (7, 15) to a network (10) is connected, characterized in that the reactive current of the frequency converter (7, 15) is controlled.

12. The method according to claim 11, characterized in that the reactive current of the generator (8) is regulated.

13. The method according to claim 11 or 12, characterized in that the reactive current of the frequency converter (7, 15) is regulated with a first time constant.

14. The method according to any one of claims 11 to 13, characterized in that the reactive current of the generator (8) is regulated with a second time constant.

15. The method according to claim 13 and 14, characterized in that the first time constant is shorter than the second time constant.

16. The method according to any one of claims 11 to 15, characterized in that a reactive current setpoint for the power generation plant, the sum of a reactive current of the power generation plant and a reactive current for the compensation of a network network with at least two

Energy recovery systems is.

17. The method according to claim 16, characterized in that the reactive current of the power plant is specified as a constant value.

18. The method according to claim 16, characterized in that the reactive current of the power generation plant is specified as a variable value.

19. The method according to any one of claims 16 to 18, characterized in that at a given change in the power and / or torque of a Power generation plant is given a change in the reactive current for the compensation of the network.

20. The method according to claim 19, characterized in that the change of the reactive current for the compensation of the network system is specified simultaneously with the predetermined change in the power and / or the torque of the power generation plant.

21. The method according to claim 19 or 20, characterized in that the change of the reactive current for the compensation of the network under

With the help of a mathematical model, based on a network impedance and the power to be transmitted, is given accordingly.

22. The method according to any one of claims 16 to 21, characterized in that the reactive currents of the energy recovery plants or groups of

Energy recovery plants are regulated so that the sum of the reactive currents of all energy production plants corresponds to a predetermined value at a grid feed point.

23. The method of claim 11 to 22, characterized in that the predetermined value of the reactive current is controlled so that the voltage delivered to the network at the grid feed point is within predetermined limits.

24. The method according to any one of claims 11 to 23, characterized in that the wind speed is measured, that is calculated from the measured wind speed from a expected power jump of an energy production plant and that is calculated from expected reactive current target value.

25. The method according to claim 24, characterized in that the reactive current setpoint is composed of a reactive current of the wind turbine and a reactive current for the compensation of the network network.

26. The method according to claim 24 and 25, characterized in that the predetermined value of the reactive current is controlled so that the voltage delivered to the network at the grid feed point is within predetermined limits.