EP2347126A2

EP2347126A2 - Differential for a wind power station

Info

Publication number: EP2347126A2
Application number: EP09744910A
Authority: EP
Inventors: Gerald Hehenberger
Original assignee: Individual
Current assignee: HEHENBERGER, GERALD
Priority date: 2008-10-09
Filing date: 2009-10-09
Publication date: 2011-07-27
Also published as: US20110234179A1; WO2010040165A2; CA2740076A1; WO2010040165A3; AU2009301621A1; CN102177365A; AT507395A3; BRPI0920325A2; KR20110084205A; AT507395A2

Abstract

A differential for a power generation station, in particular a wind power station, comprises three input elements or output elements. A first input element is connected to a drive shaft of the power generation station, an output element is connected to a generator (8), and a second input element is connected to an electric motor (6) as the differential drive. The first input element that is connected to the drive shaft rotates at a basic speed. The speed range of the first input element amounts to a minimum of -/+ 6.0 percent and a maximum of -/+ 20.0 percent of the basic speed while the electric motor (6) is operated at the nominal speed.

Description

Differential gearbox for wind turbine

The invention relates to a differential gear for an energy production plant, in particular for a wind turbine, a method for operating such a Differenzialgetrie- bes and an energy production plant, in particular a wind turbine, with such a differential gear.

Wind power plants are becoming increasingly important as electricity generation plants. As a result, the percentage of electricity generated by wind increases continuously. This, in turn, requires new standards of power quality on the one hand and a trend towards even larger wind turbines on the other. 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 the wind turbines in the offshore area, the efficiency and availability of the turbines are of particular importance here.

All systems have in common is the need for a variable rotor speed, on the one hand to increase the aerodynamic efficiency in the partial load range and on the other hand to control the torque in the drive train of the wind turbine. The latter for the purpose of speed control of the rotor in combination with the rotor blade adjustment. At present, mostly wind turbines are in use, which meet this requirement by using variable-speed generator solutions in the form of so-called double-fed three-phase machines or synchronous generators in combination with frequency converters. However, these solutions have the disadvantage that (a) the electrical behavior of the wind turbines only partially meets the requirements of the electricity supply companies in the event of a power failure, (b) the wind turbines can only be connected to the medium-voltage network by means of a transformer station and (c) the variable speed necessary frequency converters are very powerful and therefore a source of efficiency losses.

These problems can be solved by the use of externally-excited medium-voltage syringe generators. However, this requires alternative solutions to meet the demand for variable rotor speed or torque control in the drive train of the wind turbine. One possibility is the use of differential gears which allow by changing the gear ratio at a constant generator speed, a variable speed of the rotor of the wind turbine.

WO2004 / 109157 A1 shows a complex, hydrostatic "multi-way" concept with several parallel differential stages and several switchable couplings, which can be switched between the individual paths. With the shown technical solution the power and thus the losses of the hydrostatics can be reduced. A major disadvantage, however, is the complicated structure of the entire unit. In addition, the circuit between the stages represents a problem in the control of the wind turbine. Furthermore, this publication shows a mechanical brake which acts directly on the generator shaft. WO 2006/010190 A1 shows a simple electrical concept with a multi-stage differential gear, which preferably provides an asynchronous generator as a differential drive. The rated speed of the differential drive of 1500rpm is extended in the motor operation by 1/3 to 2000rpm, which means a field weakening range of about 33%.

EP 1283359 A1 shows a 1-stage and a multi-stage differential gear with electric differential drive, wherein the 1-stage version has a co-axial to the input shaft mounted special rotary-commutator with high rated speed, which due to the design of an extremely high on the rotor shaft related mass moment of inertia Has. Alternatively, a multi-stage differential gear with high-speed standard three-phase machine is proposed, which is aligned parallel to the input shaft of the differential gear.

The disadvantages of known designs are, on the one hand, high losses in the differential drive or, on the other hand, in concepts which solve this problem, complex mechanics or special electric machine construction and thus high costs. In addition, the life of the pumps used in hydrostatic solutions is a problem or a high effort to adapt to extreme environmental conditions required. In general, it should be noted that the selected rated speed ranges are too large either for the compensation of extreme loads or too large for an optimal energy yield of the wind turbine. In addition, in known electrical solutions for the differential drive to determine that they provide an unfavorable division between rated speed range and field weakening range and control criteria such as the related to the rotor mass moment of inertia of the differential drive (J _red ) were not sufficiently considered.

The object of the invention is largely to avoid the above-mentioned disadvantages and to provide a differential drive which, in addition to the lowest possible costs, ensures both maximum energy yield and optimum regulation of the wind power plant.

This problem is solved with a differential gear having the features of claim 1.

This object is further achieved with an energy recovery system having the features of claim 13.

Finally, this object is achieved with a method having the features of claims 15 and 16.

Preferred embodiments of the invention are the subject of the remaining subclaims.

By limiting the speed to the specified ranges an optimal balance between a higher aerodynamic efficiency and efficiency losses is achieved by the differential drive, while taking into account the Regulatory conditions in energy production plants, in particular wind turbines.

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 the principle of a hydrostatic differential drive with pump / motor combination according to the prior art,

4 shows the principle of a coaxial with the input shaft of the differential stage aligned special three-phase machine according to the prior art,

5 shows the speed ratios on the rotor of the wind turbine and the resulting maximum input torques M _max for the differential drive,

6 shows by way of example the speed and power ratios of an electric differential drive over the wind speed,

FIG. 7 shows the maximum torques and the size factor y / x as a function of the nominal rotational speed range for the 1-stage differential gearing.

8 shows gear ratios and torques for the differential drive with 1-stage and, alternatively, with 2-stage differential gear and the effects on J _red ,

Fig. 9 shows the multiplication factor f (J) for 1-stage and 2-stage differential gears, respectively, with which the value of the mass moment of inertia J of the differential drive is to be multiplied by the rotor shaft J _rec j at the minimum rotor speed (n _mpn ),

10 shows, for 1-stage or 2-stage differential gear, the required torque in order to be able to regulate a speed jump on the rotor with an electric differential drive in terms of rotational speed,

11 shows the speed / torque characteristic of an electric differential drive (PM synchronous motor) incl. Field weakening range compared to the required torque for the differential drive,

Fig. 12 shows the maximum input torques for the differential drive and the size factor y / x as a function of the field weakening range of the electric differential drive. FIG. 13 shows the difference of the gross energy yield as a function of the area of the weakened area,

14 shows the difference of the gross energy yield for different nominal speed ranges at different average annual wind speeds for an electric differential drive with 80% field weakening range,

15 shows the difference of the gross energy yield for different nominal speed ranges at different mean annual wind speeds for a hydraulic differential drive,

16 shows the power production costs for an electric differential drive at various rated speed ranges for 1-stage differential gears;

Fig. 17 shows the current production cost of an electric differential drive at various rated speed ranges for 2-stage differential gears;

18 shows a short-circuited with interposed electrical resistors three-phase machine,

FIG. 19 shows a solution with a 1-stage differential gear integrated in the main transmission, FIG.

FIG. 20 shows a solution with a 1-stage differential gear integrated in the synchronous generator, FIG.

Fig. 21 shows an alternative solution for a 1-stage differential gear with a coaxial connection zw. Ring gear and differential drive.

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

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

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 power coefficient based on a fast running speed to be determined in the course of the development (usually a value between 7 and 9). 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 maximum speed range of the rotor or an optimal speed number of 8.0-8.5. From the graph, it can be seen that as soon as the high-speed number deviates from its optimum value of 8.0-8.5, the power coefficient drops, and then Thus, according to the above formula reduces the rotor power according to the aerodynamic characteristics of the rotor.

Fig. 2 shows a possible principle of a differential system for a wind turbine consisting of differential stage 3 or 11 to 13, a matching gear stage 4 and a differential drive 6. The rotor 1 of the wind turbine, which sits on the drive shaft for the main transmission 2, drives the main gear 2. The main transmission 2 is a 3-stage transmission. with two planetary stages and one spur gear stage. 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 foreign-excited synchronous generator, which may also have a nominal voltage greater than 2OkV if required '- 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 in order to ensure a constant speed of the generator 8 at variable speed of the rotor 1 and on the other hand to control 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 adaptive gearboxes..4 thus form the 2-stage differential gearbox. The differential drive is a three-phase machine, which is connected via frequency converter 7 and transformer 5 to the mains. Alternatively, as shown in Fig. 3, the differential drive may also be used as e.g. Hydrostatic pumps / motor combination 9 are executed. In this case, the second pump is preferably connected via adaptation gear stage 10 to the drive shaft of the generator 8.

Fig. 4 shows another possible embodiment of the differential gear according to the prior art. Here, in the manner already shown, the planet carrier 12 is driven by the main gear 2 and the generator 8 is connected to the ring gear 13 and the pinion with the electric differential drive 6. This embodiment represents a 1-stage solution, in which case for design reasons a special three-phase machine is used, which is much more expensive compared to standard three-phase machines and also has a very high moment of inertia. In terms of control engineering, this has a particularly negative effect with regard to the mass moment of inertia of the differential drive 6, which is related to the rotor 1.

The speed equation for the differential gear are: speed _G enerator = x ^* speed _rotor + y ^* speed _Different i _a i _-Antriebl wherein the generator speed is constant, and the factors can be x and y are derived from the selected gear ratios of the main transmission and differential gears. The torque on the rotor is determined by the upcoming wind supply and the aerodynamic efficiency of the rotor. The ratio between the torque on the rotor shaft and that on the differential drive is constant, which increases the torque in the drive train can be regulated by the differential drive. The torque equation for the differential drive is:

Torque _{Dlfferential-Antπeb} = Torque _Rotor * y / x, where the size factor y / x is a measure of the required design torque of the differential drive.

The performance of the differential drive is essentially proportional to the product of percent deviation of the rotor speed from its base speed times rotor power. Accordingly, a large speed range basically requires a correspondingly large dimensioning of the differential drive.

FIG. 5 shows this by way of example for different speed ranges. The - / + rated speed range of the rotor defines its percentage speed deviation from the basic speed of the rotor, which can be realized with rated speed of the differential drive (- ... motor or + ... regenerative) without field weakening. In the case of a three-phase electric machine, the rated speed (n) of the differential drive defines that maximum speed at which it can permanently produce the rated torque (M _n ) or the nominal power (P _n ).

In the case of a hydrostatic drive, such as a hydraulic axial piston pump, the rated speed of the differential drive is the speed at which it can deliver maximum continuous power (P _{0 ma} χ) with maximum torque (T _ma χ). Nominal pressure (p _N ) and nominal size (NG) or displacement volume (V _{9 max} ) of the pump determine the maximum torque (T _max ).

In the rated power range, the rotor of the wind turbine rotates at the average speed n _rated between the limits n _max and n _mln-maxP , in the partial load range between n _rat ed and n _min , achievable in this example with a field weakening range of 80%. The control speed range between n _max and n _min-m3X p, which can be realized without load reduction, is chosen to be large in order to be able to compensate for wind gusts. The size of this speed range depends on the gustiness of the wind or the inertia of the rotor of the wind turbine and the dynamics of the so-called pitch system (rotor blade adjustment system), and is usually about - / + 5%. In the example shown, a control speed range of - / + 6% has been selected in order to have adequate reserves for the control of extreme conditions by means of differential drives. Wind turbines with very sluggish pitch systems can, however, also be designed for control speed ranges of approximately - / + 7% to - / + 8%. In this control speed range, the wind turbine must produce rated power, which means that the differential drive is loaded with maximum torque. This means that the - / + rated speed range of the rotor must be about the same size, because only in this range, the differential drive can make its rated torque. In electric and hydrostatic differential drives with a differential stage, the rotor speed at which the differential drive has the speed equal to 0, called the basic speed. Now, since at low rotor speed ranges, the basic speed over n _m j _n-maxP is, the differential drive must be able to provide the same nominal torque at 0, the speed of rotation. However, differential drives, whether electric or hydraulic, can only generate a torque at speed equal to 0, which is significantly lower than the rated torque, which can be compensated by a corresponding oversizing in the design. However, since the maximum design torque is the sizing factor for a differential drive, for this reason, a small speed range has a limited positive effect on the size of the differential drive.

In the case of a drive concept with more than one differential stage, or with a hydrodynamic differential drive, the - / + rated speed range can be replaced by the formula

- / + nominal speed range = - / + (n _max - n _min ) / n _max + n _min ) for a basic speed = (n _max + n _min ) ^* 0.5. In this case, the rated speed of the differential drive is set as a substitute with its speeds at n _max and n _m j _n .

FIG. 6 shows by way of example the speed or power ratios for a differential stage. The speed of the generator, preferably a third-excited medium voltage synchronous generator is constant by the connection to the frequency-fixed power grid. In order to be able to make good use of the differential drive, this drive is operated as a motor in the range below the basic speed and as a generator in the range above the basic speed. 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. In the case of a hydraulic differential drive, the power is preferably taken from the generator shaft or supplied thereto. The sum of generator power and power differential drive gives the total power delivered to the grid for an electric differential drive.

The input torque for the differential drive depends in addition to the torque at the differential input also significantly from the transmission ratio of the differential gear. If the analysis is based on the assumption that the optimum gear ratio of a planetary stage is at a so-called stationary ratio of about 6, then with a 1-stage differential gear the torque for the differential drive will not be proportional to the speed range smaller. There are technically larger stand translations feasible, which at best reduces this problem, but not eliminated.

7 shows, for a 1-stage differential gear, the maximum torques and the size factor y / x (multiplied by -5,000 for reasons of representation) as a function of the nominal Speed range of the rotor. At a nominal speed range of about - / + 14% to - / + 17% results for the differential drive, the smallest size factor and consequently also the smallest maximum torque (M _max ).

The graph shows for 1-stage differential gearbox that as the nominal speed range decreases, the design torques for the differential drive increase. To solve this problem, one can e.g. Use 2-speed differential gear. This can be achieved, for example, by implementing a matching gear stage 4 between differential stage 3 and differential drive 6 or 9. However, the input torque for the differential stage, which essentially determines their cost, can not be reduced thereby.

8 shows the comparison of the torques of the differential drive for a 1-stage and a 2-stage differential gear and the factor J (red), which is the ratio of the mass moment of inertia (J _red ) of both variants related to the rotor shaft. It is clear from Fig. 8 that with free choice of the transmission ratio of the differential gear - in the case shown for a rated speed of the differential drive of about 1500rpm - the required torque of the differential drive with decreasing speed range is correspondingly smaller. Above a rated speed range of about - / + 16.5% is sufficient in this Ausführungsbeispjel assumed stationary ratio of the 1 -stages differential gear to reach the rated speed of the differential drive of 1500rpm without additional adjustment gear stage. The disadvantages of a multi-stage differential gear, however, are the slightly higher transmission losses and higher transmission costs. In addition, the higher gear ratio causes a higher moment of inertia of the differential drive relative to the rotor shaft of the wind turbine (J _re d), although the mass moment of inertia of the differential drive with smaller nominal torque is also smaller. However, since the controllability of the wind turbine depends strongly on this J _red - the lower in comparison to the moment of inertia of the rotor of the wind turbine the better the control dynamics of the differential drive - is in the case shown at a small speed range of the rotor of the wind turbine of about 2.6 times the value of J _red for a 2-step versus a 1 -stage differential gear is a disadvantage of the (a) requires a correspondingly larger dimensions of the differential drive or (b) if no corresponding compensation measures are taken, due to the worse control properties leads to higher loads on the wind turbine and poorer power quality. Therefore, and also because of the higher transmission costs and losses, a 1-stage differential gear is compared to multi-stage solutions only conditionally and only at low rated speed ranges is a technically possible alternative.

The same argument for J _re d applies generally also in the choice of the speed range. Fig. 9 shows at minimum rotor speed multiplication factor f (J) with which the value of the mass moment of inertia of the differential drive is to multiply to the rotor shaft related J _{red of} the differential drive at the lowest rotor speed (n _min ) , In order to compensate for speed jumps of the rotor of the wind turbine, the differential drive must be over-dimensioned accordingly, which with increasing J _re d, ie with increasing nominal speed range or multi-stage differential drive even at lower speed ranges, a significant cost factor represents.

Fig. 10 shows the required torque for the differential drive to be able to balance a gust of wind. Assuming a gust of wind which accelerates from 4.5 m / s to 11.5 m / s within 2 seconds, depending on the nominal rotational speed range of the rotor of the wind power plant, this causes a speed jump of 5.6 to 10, 3rpm on the same speed of 11, 7rpm for all rated speed ranges. The differential drive has to follow this speed jump, whereby the required acceleration torque corresponding to J _r ed and magnitude of the speed jump fails. It is clearly recognizable that multistage differential gearboxes require higher torques because of the higher transmission gear ratio.

One possibility with constant transmission ratio of the differential gear to extend the speed range of the rotor of the wind turbine and thus to increase the energy yield is the utilization of the so-called field weakening range of electric differential drives as in the case of e.g. Permanent magnet synchronous three-phase machine with frequency converter.

The field weakening range is that rotational speed range which is above the nominal rotational speed of the rotary electric machine. For this rated speed also the nominal torque or .. the nominal tilting torque is defined. In the tables and other descriptions, the field weakening range is defined as a percentage of the speed above the rated speed - i. the e.g. 1.5 times rated speed corresponds to a field weakening range of 50%.

11 shows by way of example the values for maximum torque or tilting torque of an electric differential drive with a rated speed of 1500 rpm. It is clearly recognizable that the maximum achievable moments become smaller both at a speed equal to zero and above the rated speed. An essential characteristic of wind turbines, however, is that in the partial load range, in the example shown corresponds approximately to the engine operation, the required torques are much lower than the maximum permitted. In generator mode, for speeds greater than about 1730rpm, load reduction is required for the wind turbine to ensure that the permitted maximum torques are not exceeded. Fig. 10 shows a field weakening range of 80% of up to 1, 8 times the rated speed, which represents a technically meaningful upper limit for the selected for the example electric drive.

It is worth noting here that e.g. permanent magnet synchronous three-phase machines in field weakening have very good efficiencies, which is a major advantage in connection with the efficiency of the differential drive.

The operation in the field weakening range for three-phase machines depends on their design up to 50% to 60%, ie about 1, 5 times to 1.6 times the rated speed without Speed feedback possible, in addition, the use of eg encoders is necessary. Since the use of an encoder represents an additional source of error, and the so-called sensorless torque or speed control is dynamically better, when defining the field weakening range an optimum is found between control dynamics and optimum annual energy yield. This means that at high mean wind speeds and the associated extreme gusts, a field weakening range is to be selected, which allows the encoderless control to be able to compensate for these gusts accordingly. At low mean wind speeds with rather small gusts to be compensated, attention is paid to the optimal annual energy yield and therefore a maximum field weakening range with rotational speed feedback is selected. This also fits very well with the speed characteristics of the differential drive of a wind turbine, which exploits the highest possible engine speed range at low wind speeds.

In order to verify the effect of the size of the field weakening range on the size of the differential drive or the energy yield of the wind turbine at different average annual wind speeds, you can vary the field weakening range of the differential drive at a fixed speed range of the rotor of the wind turbine, while adjusting the translation of the differential.

Figure 12 shows the maximum input torques for the differential drive and the size factor y / x (multiplied by -5,000 for purposes of illustration) versus field weakening range. From a field weakening range of approx. 70%, optimum differential factors result for the differential drive, and consequently also the smallest maximum torques (M _m3x ), the absolute minimum being a field weakening range of 100%.

Fig. 13 shows the difference of the gross energy yield as a function of the field weakening range for different average annual wind speeds. The optimum is achieved with a field weakening range between 100% to 120%. Based on these conditions, a field weakening range is selected depending on the conditions of use, but in each case ≥ 50%.

The mean annual wind speed is the annual mean of the wind speed measured at hub height (corresponds to the center of the rotor). The maximum average annual wind speeds of 10.0 m / s, 8.5 m / s, 7.5 m / s and 6.0 m / s correspond to the so-called IEC type classes 1, 2, 3 and 4. As a statistical frequency distribution, a Rayleigh Distribution accepted.

In addition, it is worth noting that permanent magnet synchronous three-phase machines as differential drive still have the advantage of having a small moment of inertia compared to rated torque compared to three-phase machines of other type, which, as already described, as advantageous in terms of control of the wind turbine proves, with which the effort for a particularly mass inertia-poor design of the differential drive will always be worthwhile. Alternatively, so-called reluctance machines also have a very small mass inertia but typically higher rated speeds. It is known that reluctance machines are extremely robust, which is particularly positive for use in the offshore sector.

The same applies in principle to the size of the differential drive, of course, has a significant impact on the overall efficiency of the wind turbine. Considering the embodiments described above, the basic insight arises that a large speed range of the rotor of the wind turbine causes a better aerodynamic efficiency, but on the other hand also requires a larger dimensioning of the differential drive. This in turn leads to higher losses, which counteracts a better system efficiency (determined by the aerodynamics of the rotor and the losses of the differential drive).

Fig. 14 shows the difference of the gross energy yield of the wind turbine with electric differential drive at different mean annual wind speeds depending on the rated speed range of the rotor of the wind turbine. The gross energy yield is based on the output power of the rotor of the wind turbine minus the losses of differential drive (including frequency converter) and differential gear. A rated speed range of - / + 6% is the basis according to the invention, which is required by the minimum required speed control range in the rated power range of wind turbines with differential drives, the nominal speed range means that rotor speed range, which can be rated at the rated speed of Differential drive can realize. In addition, a field weakening range of up to 80% is assumed above the rated speed of the differential drive. From the graph, it is easy to see that the optimum is achieved at a nominal speed range of about - / + 20%, and an extension of the rated speed range, moreover, brings no benefits.

Fig. 15 shows the difference of the gross energy yield of the wind turbine with hydraulic differential drive at different mean annual wind speeds. Here, the significantly higher losses in hydraulic differential drives have a negative effect on the energy yield, whereby a nominal speed range between the minimum required for control purposes - / + 6% and the energy yield optimum of - / + 10% at high mean annual wind speeds ( greater than 8.5 m / s) and - / + 15% at lower average annual wind speeds makes sense. The break in the curve at about - / + 12% rated speed range results from the high nominal torque of the differential drive at speed equal to 0 irri nominal operating range of the wind turbine and the low gear ratio in the matching gear stage 4.

Ultimately, the goal is to develop a powertrain that allows the lowest power production costs. The relevant points in the optimization of differential drives are (a) the gross energy yield, (b) the manufacturing costs for the differential drive and (c) the quality of the torque or speed control of the wind turbine influencing the total manufacturing costs. The gross energy yield is proportional to the electricity Production costs and thus in the economy of a wind farm. The manufacturing costs are related to the total cost of producing a so-called wind farm, but only with the percentage of the proportionate capital cost of the wind turbine to the total cost of the wind farm including maintenance and operating costs. On average, this wind power plant-specific share of the electricity production costs is about 2/3 for onshore projects and about 1/3 for offshore projects. On average, therefore, you can define a percentage of about 50%. This means that a difference in the annual energy yield is on average twice as high as the difference in the manufacturing costs of the wind turbine. That is, if in the example shown for electric differential drives an optimal size factor already sets at a rated speed range of about - / + 14% to - / + 17%, so this cost-determining factor has a percentage of less on the power production costs as the optimum energy output from a nominal speed range of about - / + 20%.

Fig. 16 shows the effects of different speed ranges on the electricity production costs of the wind farm with 1-stage differential gear and electric differential drive. Here is a very good value for all wind speed conditions at a rated speed range between - / + 15.0% and - / + 20.0% and an optimum of about - / + 17.5%.

Fig. 17 shows the effects of different speed ranges on the electricity production costs of the wind farm with 2-stage differential gear (below a nominal speed range of about - / + 16.5%) with electric differential drive. Especially at lower average annual wind speeds, the optimum is also apparent here at a speed range between 15.0% and 20.0%. At average annual wind speeds greater than 8.5 m / s, however, a small speed range of from regulatory reasons at least +/- 6% to about - / + 10% is an attractive option. That means that multi-stage differential gear at very high mean annual wind speeds competitive with 1-stage solutions are.

When designing differential drives, however, there are other important special cases to consider. For example, by the constant ratio of rotor speed to speed at the differential drive, a failure of the differential drive serious damage. An example is the failure of the differential drive in nominal operation of the wind turbine. At the same time, the transmittable torque on the drive train approaches zero. The speed of the rotor of the wind turbine is in this case preferably suddenly reduced by a rapid adjustment of the RotorblattversteHung and the generator disconnected from the grid. Due to the relatively high inertia of the generator, this will only slowly change its speed. As a result, unless the differential drive can not at least partially maintain its torque without delay, an overspeed of the differential drive is unavoidable.

For this reason, for example when using hydrostatic differential drives, a mechanical brake is provided which, in the event of failure of the differential drive for the engine sträng harmful overspeeding prevented. WO2004 / 109157 A1 shows for this purpose a mechanical brake, which acts directly on the generator shaft and thus can decelerate the generator accordingly.

The above-mentioned permanent magnet synchronous three-phase machines, which can be used in combination with a frequency converter as a differential drive, have the advantage that they are very fail-safe, and simply by short-circuiting the primary winding, with or without interposed electrical resistors, a torque can be maintained up to about the height of the nominal torque. This means that - e.g. in the case of a converter failure - the synchronous three-phase machine can be short-circuited automatically (fail-safe) by a simple electrical circuit, and thus a torque is maintained, which may have at rated speed to about nominal size, and decreases with decreasing speed accordingly, at go to 0 at very low speeds. As a result, an overspeed of the differential drive is prevented in a simple manner.

Fig. 18 shows a possibility of short-circuiting a three-phase machine with electrical resistances interposed therebetween.

In the case of failure of the permanent magnet synchronous three-phase machine, the speed of the rotor is to be controlled so that the speed of the differential drive does not exceed a critical speed damaging the drive. Based on the measured speeds of generator and rotor of the wind turbine is according to the speed equation for the differential gear

Speed generator = X * Speed _R otor + y * Speed counter drive, using rotor blade adjustment to control the speed of the rotor so that the speed of the differential drive does not exceed a specified critical limit.

In case of failure of the control of the wind turbine, which may also result in the simultaneous failure of rotor blade control and regulation of the differential drive result in the short-circuiting of the primary winding of the permanent magnet synchronous three-phase machine that a torque is maintained, which prevents their overspeed. From a simultaneous failure of regulation of the wind turbine and permanent magnet synchronous three-phase machine is not expected.

If the wind turbine is e.g. In addition, by short-circuiting the permanent magnet synchronous three-phase machine, undesirable acceleration of the differential drive can be prevented.

For reasons described above, the optimal wind turbine control, the overall efficiency and the simple or cost-optimal mechanical structure of the differential gear is a 1-stage differential gear is the ideal technical solution. There are different approaches for the constructive integration of the differential drive.

19 shows a possible embodiment variant according to the present invention. The rotor 1 drives the main gear 2 and this via planet carrier 12, the differential stage 11 to 13. The generator 8 is connected to the ring gear 13, and the pinion 11 with the differential drive 6. The differential gear is 1-stage, and the Differential drive 6 is in coaxial arrangement both to the output shaft of the main transmission 2, as well as to the drive shaft of the generator 8. Since the connection between pinion 11 and differential drive 6 passes through the spur gear and the output shaft of the main transmission 2, the differential stage is preferred an integral part of the main gear 2 and this is then preferably connected via a brake 15 which acts on the rotor 1, and a clutch 14 to the generator 8.

Fig. 20 shows another possible embodiment according to the present invention. Again, the rotor 1 drives the main gear 2 and this via planet carrier 12, the differential stage 11 to 13. The generator 8 is connected to the ring gear 13 and the pinion 11 with the differential drive 6. The differential gear is 1-stage, and Differential drive 6 is in coaxial arrangement both to the output shaft of the main transmission 2, as well as the drive shaft of the generator 8. Here, however, the generator 8. A hollow shaft is provided which allows the differential drive on the side facing away from the differential gear of the generator 8 is positioned. As a result, the oifferent stage is preferably a separate module which is connected to the generator 8 and which is then preferably connected to the main gearbox 2 via a clutch 14 and a brake 15. The connecting shaft 16 between the pinion 11 and the differential drive 6 may preferably be in a particularly low-inertia variation as e.g. Fiber composite shaft to be made with glass fiber or carbon fiber.

The main advantage of the shown coaxial, 1-stage embodiment of both variants are (a) the constructive simplicity of the differential gear, (b) the resulting high efficiency of the differential gear and (c) the relatively low on the rotor 1 related moment of inertia of the differential drive 6. In addition, in the embodiment of FIG. 19, the differential gear can be manufactured as a separate assembly and implemented and maintained independently of the main transmission. Of course, the differential drive 6 can also be replaced by a hydrostatic drive, for which, however, a second pump element which interacts with the hydrostatic differential drive must be driven by the generator 8, preferably.

For high mean annual wind speeds can be used for the versions acc. FIGS. 19 and 20 illustrate an adjustment gear stage 4 (as generally shown in FIGS. 2 or 3) between differential stage 11 to 13 and differential drive 6.

The variants of embodiment according to FIG. 19 and FIG. 20 differ from the prior art according to FIG. 4 essentially by the substitutability of a standard Three-phase machine and the simple and inexpensive construction of the differential stage which makes no Hohlweiieπ solution for three-phase machine and pinion necessary, and with respect to moment of inertia relative to the rotor shaft (J _red ) have significant advantages in terms of control of the wind turbine.

However, the embodiments according to FIG. 19 and FIG. 20 differ substantially with respect to the effects of a so-called emergency braking of the wind power plant by means of a brake 15. Assuming that when the brake 15 is activated, it is usually a braking torque of up to 2.5 times the nominal torque acts, so this affects divided rotor, generator and differential drive according to their reduced mass moments of inertia. These are of course dependent on the mass ratios of the running wind turbine. As a realistic example, with nominal operation of a 5 MW wind power plant with respect to the brake 15, approximately 1,900 kgm2 for the rotor 1, approximately 200 kgm2 for the synchronous generator 8 and approximately 10 kgm2 for the differential drive 6 can be assumed. That is, a large part (about 90% or 2.2 times the rated rotor torque) of the braking torque acts on the rotor shaft of the wind turbine. Since the differential drive in the torque flow between the brake 15 and the rotor 1 is now in the embodiment of FIG. 19, it must also hold about 2.2 times the rated torque according to the constant torque ratios between the rotor and differential drive.

A significant advantage of the embodiment according to FIG. 20 is that when the brake 15 is engaged, its braking torque does not act on the mass moment of inertia via differential gear. In this case, only about 9.5% of the braking torque acting on the generator 8 and about 0.5% to the differential drive 6. By the arrangement shown in FIG. 19 of brake 15 and differential gear 11 to 13, makes the short-circuiting The permanent-magnet synchronous three-phase machine for maintaining the torque in the differential drive sense only, otherwise would be pending a torque whose nominal torque significantly exceeded torque in an emergency.

Figure 21 shows another possible Ausfühvυngsform the differential gear. Here, in the manner already shown, the planet carrier 12 is driven by the main gear 2, but the generator 8 is connected to the pinion 11 and the ring gear with the electric differential drive consisting of rotor 17 and stator 18. This embodiment also provides a coaxial, 1 -stufige solution, with transmission technical conditions lead to a relatively low speed of the rotor 15. This affects control technology particularly positive in relation to the related to the rotor 1 mass moment of inertia of the differential drive 17 to 18.

The embodiments described above are also feasible in technically similar applications. This applies especially to hydropower plants for the exploitation of river and ocean currents. For this application, the same basic requirements apply as for wind turbines, namely variable flow rate. In these cases, the drive shaft is driven by the devices driven by the flow medium, for example water. driven directly or indirectly. Subsequently, the drive shaft drives directly or indirectly the Differenzia igelriebe.

Claims

claims:

1. differential gear for an energy production plant, in particular for a wind power plant, with three input or output drives, wherein a first drive with a drive shaft of E- nergiegewinnungsanlage, an output with a generator (8) and a second drive with an electric machine (6 ) is connected as a differential drive, and wherein the first drive connected to the drive shaft rotates at a basic speed, characterized in that the speed range of the first drive at least - / + 6.0% and at most - / + 20.0% of the base speed is while the electric machine (6) is operated at rated speed.

2. differential gear for an energy production plant, in particular for a wind turbine, with three input or output drives, wherein a first drive with a drive shaft of e- nergiegewinnungsanlage, an output with a generator (8) and a second drive with a hydraulic differential drive (6), and wherein the first drive connected to the drive shaft rotates at a base speed, characterized in that the speed range of the first drive is at least - / + 6.0% and at most - / + 15.0% of the base speed, while the hydraulic differential drive (6) is operated at rated speed.

3. differential gear according to claim 1 or 2, characterized in that the speed range is at least - / + 7.0% of the base speed.

4. differential gear according to claim 1 or 2, characterized in that the speed range is at least - / + 8.0% of the base speed.

5. Differential gear according to one of claims 1 or 2, characterized in that the speed range is at least - / + 10.0% of the base speed.

6. Differential gear according to claim 1, characterized in that the speed range is at most - / + 17.5% of the base speed.

7. differential gear according to claim 1, characterized in that the speed range is at most - / + 15.0% of the base speed.

8. differential gear according to one of claims 1 to 5, characterized in that the speed range is at most - / + 14.0% of the base speed.

9. differential gear according to one of claims 1 to 5, characterized in that the speed range is at most - / + 10.0% of the base speed.

10. Differential gear according to claim 1, characterized in that the electrical machine (6) is a three-phase machine.

11. Differential gear according to claim 10, characterized in that the electric machine (6) is a permanent magnet synchronous three-phase machine.

12. Differential gear according to one of claims 1 to 11, characterized in that the second drive is directly connected to the differential drive (6).

13. Energy production plant, in particular wind turbine, with a drive shaft, a generator (8) and with a differential gear (11 to 13), characterized in that the differential gear (11 to 13) is designed according to one of claims 1 to 12.

14. Energy production plant according to claim 13, characterized in that it has only one differential stage (11 to 13).

15. Energy production plant according to one of claims 1 to 14, characterized in that it comprises a single-stage differential gear (3).

16. Energy production plant according to one of claims 1 to 14, characterized in that it comprises a multi-stage differential gear (3, 4).

17. A method for operating a differential gear for an energy production plant, in particular for a wind turbine, with three inputs or outputs, wherein a first drive with a drive shaft of the energy production plant, an output with a generator (8) and a second drive with an electric machine (6) is connected as a differential drive, and wherein the first drive connected to the drive shaft rotates at a base speed, characterized in that the first drive in a speed range of at least - / + 6.0% and at most - / + 20, 0% of the base speed is driven while the electric machine (6) is operated at rated speed.

18. A method for operating a differential gear for an energy production plant, in particular for a wind turbine, with three inputs or outputs, wherein a first drive with a drive shaft of the power plant, an output with a generator (8) and a second drive with a hydraulic differential Drive (6) is connected, and wherein the first drive connected to the drive shaft rotates at a basic speed, characterized in that the first drive in a speed range of at least - / + 6.0% and at most - / + 15.0% the base speed is driven while the hydraulic differential drive (6) is operated at rated speed.

19. The method according to claim 17 or 18, characterized in that the speed range is at least - / + 7.0% of the base speed.

20. The method according to claim 17 or 18, characterized in that the speed range is at least - / + 8.0% of the base speed.

21. The method according to claim 17 or 18, characterized in that the speed range is at least - / + 10.0% of the base speed.

22. The method according to claim 17, characterized in that the speed range is at most - / + 17.5% of the base speed.

23. The method according to claim 17, characterized in that the speed range is at most - / + 15.0% of the base speed.

24. The method according to any one of claims 17 to 23, characterized in that the speed range is at most - / + 14.0% of the base speed.

25. The method according to any one of claims 17 to 23, characterized in that the speed range is at most - / + 10.0% of the base speed.

26. The method according to claim 17, characterized in that the electric machine (6) can be operated in the field weakening range, and that the electric machine (6) is at least temporarily operated in a field weakening range of at least 50%.

27. The method according to claim 26, characterized in that the electrical machine (6) is at least temporarily operated in a field weakening range of at least 60%.

28. The method according to claim 26, characterized in that the electrical machine (6) is at least temporarily operated in a field weakening range of at least 70%.

29. The method according to claim 26, characterized in that the electrical machine (6) is at least temporarily operated in a field weakening range of at least 80%.

30. The method according to any one of claims 26 to 29, characterized in that the electrical machine (6) is at least temporarily operated in a field weakening range of up to 100%.

31. The method according to any one of claims 26 to 29, characterized in that the electrical machine (6) is at least temporarily operated in a field weakening range of up to 120%.

32. The method according to any one of claims 26 to 31, characterized in that the electrical machine (6) is operated without a sensor.

33. The method according to any one of claims 26 to 31, characterized in that the electrical machine (6) is operated with a transmitter.

34. The method of claim 32 and 33, characterized in that the electrical machine (6) is partially operated with and partly without encoder.

35. The method according to any one of claims 32 to 34, that the electric machine is operated over a field weakening range of 50% with encoder.

36. The method according to any one of claims 32 to 34, that the electric machine is operated under a field weakening range of 60% without encoder.