WO2013166533A2

WO2013166533A2 - Differential drive assembly for an energy production plant

Info

Publication number: WO2013166533A2
Application number: PCT/AT2013/000083
Authority: WO
Inventors: Gerald Hehenberger
Original assignee: Gerald Hehenberger
Priority date: 2012-05-10
Filing date: 2013-05-06
Publication date: 2013-11-14
Also published as: AT512853A1; AT512853B1; WO2013166533A3

Abstract

An electric machine comprising a rotor and a stator has axially aligned ventilating channels (26) in the rotor (32). The surface area portion taken up by the ventilating channels (26) on the cross-sectional surface of the rotor (32) is at least 5%, preferably at least 15%, especially preferably at least 30%, more particularly at least 45% and in particular at least 60%. The rotor thus has both an excellent cooling system and a small moment of inertia.

Description

Differential drive for an energy recovery plant

The invention relates to an electrical machine with a rotor and a stator.

The invention further relates to an energy production plant, in particular wind turbine, with a drive shaft, a generator and a differential gear with three inputs and outputs, with a first drive to the drive shaft, an output to the generator and a second drive with a

Differential drive is connected and where the

Differential gear is a planetary gear.

Variable speed drives, such as for power generation plants or industrial applications, in many cases require the use of a variable speed, on the one hand to increase the efficiency in the partial load range and on the other hand to control the torque or the speed in the drive train of the system.

Currently plants are in use, which meet this requirement by using variable speed generator solutions, increasingly in the form of so-called permanent magnet-excited low-voltage synchronous generators in combination with IGBT frequency converters. However, these solutions have the disadvantage that the plants are to be connected by means of transformers to the medium-voltage network and the necessary for the variable speed frequency correspondingly powerful and therefore a source of efficiency losses and unwanted failures.

Alternatively, therefore, so-called differential drives are used, which directly to the medium-voltage network

connected externally excited medium voltage generators in

Combination with a differential gear and a

Auxiliary drive, which preferably provides a permanent magnet synchronous machine in combination with a smaller power IGBT frequency converter, use. This so-called

Servomotor is exposed due to the usually high gear ratio very high dynamic loads.

The high dynamic load in turn leads to a

correspondingly large thermal load of the servomotor, resulting in Another consequence requires a standard sized cooling system. In addition, the O2010 / 108209 proposes the lowest possible moment of inertia in order to optimize the control behavior for a differential drive system.

The object of the invention is therefore to be interpreted as an electric machine for use as a servomotor so that the demands for adequate cooling and a small

Mass moment of inertia are sufficiently satisfied simultaneously.

This object is achieved with a servomotor with the features of claim 1.

Thus, the requirement for a long life under high dynamic stress, as e.g. For

Energy recovery systems is typical, as well as a small

Moment of inertia are sufficiently met.

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. It shows:

Fig. 1, the principle of an electromechanical

Differential system with a servo motor according to the prior art,

Fig. 2 shows the typical structure of a servo motor according to the state of

Technology,

Fig. 3 shows an inventive ührungsform a

Servomotor

Fig. FIG. 4 shows a cross section of the servomotor according to FIG. 3 and FIG

5 shows the influence of the size of the ventilation channels on the

Moment of inertia of the rotor of the servomotor.

The following describes the principle of a differential drive using the example of a wind turbine. 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 ³ , where the power coefficient is dependent on the speed ratio {= blade tip speed to wind speed ratio) of the rotor of the wind turbine. The rotor of a

Wind turbine is for an optimal performance coefficient

based on one to be determined in the course of the development

High-speed number (usually a value between 7 and 9) designed. For this reason, when operating the wind turbine in

Partial load range to set a correspondingly low speed in order to ensure optimum aerodynamic efficiency.

Fig. 1 shows a possible principle of a differential drive for a wind turbine consisting of a differential stage 4 as a differential gear 11 to 13, a matching gear stage 5, an electric servomotor 6 and a

Frequency converter 7, The rotor 1 of the wind turbine, which sits on a drive shaft 2, drives a main gear 3 at. The main transmission 3 is usually a 3-stage transmission with two

Planetary stages and a spur gear, but also, especially when using higher-pole generators, with fewer stages, including in combination with so-called stepped planets or so-called power-split gear stages, executed. Between the main transmission 3 and the generator 8 is the differential stage 4, which is driven by the main transmission 3 via a pianist carrier 12 of the differential stage 4. The generator 8, preferably a third-excited medium voltage synchronous generator, is connected to a ring gear 13 of the

Differential stage 4 is connected and driven by this. A pinion 11 of the differential stage 4 is connected to the servo motor 6. The speed of the servomotor 6 is controlled to ensure a constant speed of the generator 8 at a variable speed of the rotor 1 and to regulate the torque in the drive train of the wind turbine. In order to increase the input speed for the servo motor 6, a multi-stage differential gear is selected in the case shown, which is an adjustment gear stage 5 in the form of a

Spur gear between the differential stage 4 and the servo motor 6 provides. Since in the range of the differential drive 6 and a massive clutch 14 as a connecting element between the main transmission and differential gear is under some circumstances a

correspondingly large axial offset for the servomotor 6

required. In this case, this may be for the

Adjustment gear stage 5 can be realized either by large gear diameter or a multi-stage version of this adaptation gear stage 5. The servo motor 6 is a three-phase machine, which is connected via a frequency converter 7 and a transformer 9 to the network. Due to the high dynamic requirements is as servo motor 6 is preferably a

permanent magnet synchronous machine selected. However, the servomotor can in principle every conceivable type of electrical

Machine.

The speed equation for the differential gear is:

Speed _Ganerator = x * Speed _Rotor + y * Speed _{Se derotor} , where the speed _{generator is} constant and the factors x and y can be derived from the selected gear ratios of the main gearbox and the differential gearbox. 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 servo motor is constant, which increases the torque in the drive train through the

Servomotor regulate. The torque equation for the

Servo motor is:

Torque _Servoraoco = torque _Rotcr y / x, where the size factor y / x is a measure of the necessary design torque of the servomotor. The power of the servomotor is essentially proportional to the product of percentage

Deviation of the rotor speed from its basic speed times rotor power. Accordingly, a large speed range basically requires a correspondingly large dimensions of the

Servomotor. That is, the smaller the necessary speed range on the drive shaft, the smaller can be the required servomotor and consequently also the cost of its production and operation. On the other hand, a smaller one requires Speed range a correspondingly large transmission ratio of the differential gear to the servomotor with typical

Rated revolutions - preferably zw. L.OOOrpm and l.SOOrpm ~ to interpret. A big gear ratio of the

However, differential gear on the other hand leads to a large dynamic load of the servomotor, since a speed change on the rotor causes a correspondingly large change in the servo motor. This is the reason for the above-mentioned demands for improved cooling and low moment of inertia of the

Servo motor.

In order to make good use of the differential drive, it is operated both as a motor and as a generator. As a result, power is fed into differential stage 4 in motor operation and in regenerative mode

Operation power is taken from the differential stage 4. In the case of an electric differential drive, this power is preferably fed into the network or taken from it. That is, the electric machine referred to as a servomotor 6 is operated both as a motor and as a generator.

The described embodiment is only an example and is also feasible in technically similar applications. This concerns v.a. Hydro turbines or pumps and systems for

Extraction of energy from ocean currents. For these applications, the same basic requirements apply as for

Wind turbines, namely variable flow rate. The drive shaft is in each case from that of the flow medium,

For example, water, driven equipment driven directly or indirectly.

In addition, the above also applies to any type of systems that use Differenziaiantriebe to realize variable speed on the drive shaft due to the conditions, that is, any type of drives for (industrial) systems, which are operated with limited speed range.

The example of the wind turbine generator mentioned 6 is in eg industrial or pump drives a motor, in which case the power flow described in FIG. 1 turns over. Likewise, it is obvious that a drive is operated application-specific both motor and generator.

WO2010 / 108209 recommends a maximum moment of inertia for the differential drive J _DA , _majt , which can be calculated according to the following formula for a good control behavior of a wind power plant with an electric differential drive:

where f _{A is} an application factor, which is a measure of the control behavior of the wind turbine to be achieved. The

Variable s _ges is the ratio of the speed range of the

Differential drive to the speed range of the rotor

Wind turbine (s _gas = speed range differential drive / speed range rotor) and J _R is the mass moment of inertia of the rotor of the wind turbine. With an application factor of f _A = 0.2, according to WO2010 / 108209, good results with regard to control behavior can already be achieved. Basically, however, it is found that with decreasing f _A even better

Results can be achieved, where for applications with smaller f _A additional effort to reduce the mass of the rotor of the differential drive is necessary.

According to WO2010 / 108209, a reduction of the application factor to eg f _A = 0.10 is another improvement which is necessary for highly dynamic applications. However, this is increasing

Manufacturing costs for the rotor of the differential drive connected.

Fig. 2 shows a typical configuration of a servomotor according to the prior art. On a rotor shaft 21, the rotor laminated core 22 is seated with preferably so-called embedded permanent magnet. This design is preferably used for servomotors, which also work in the so-called field weakening range. A

alternative, low-inertia construction would be the

Permanent magnets directly on the circumference of the rotor shaft 21 to

attach, but this leads to significant limitations of

Performance (field weakenability, dynamics, efficiency, etc.) of the servo motor can lead. In the housing 20 is the wound stator 23. This housing 20 has, for example, a integrated water jacket, which has the task to dissipate the waste heat due to the power loss of the stator. Since the permanently magnetically excited rotor 22 often has only very low losses, it is not necessary to cool it separately.

Assuming that for a good controllability of

Application factor f _A <0.15, so one needs for one

typical 3MW wind turbine a servomotor with embedded permanent magnets and a mass moment of inertia of <l, 6kgm2. This can be done with a servomotor gem. Fig. 2 though

but requires special measures in the

Construction.

In addition, in the case of highly dynamic loads and when operating in the field weakening range, the thermal load of the rotor 22 can not be neglected. An aggravating factor is the fact that permanent magnets are very sensitive to temperature and rapidly lose their magnetization at temperatures above 160 ° C. This fact requires a powerful rotor cooling to increase the life of the servomotor at the level of, for example, 175,000 operating hours required in wind energy

guarantee .

Figs. 3 and 4 show an embodiment of a servo motor according to the invention, which meets the above requirements. On the rotor shaft 21, which for the reduction of

Mass moment of inertia can also be designed as a hollow shaft, sits a laminated core 25, which has ventilation ducts 26. Thus, the rotor 33 is essentially formed by the rotor shaft 21 and the laminated core 25. A housing includes end shields 27, a water cooled jacket 28, and optionally one or more

Attachment parts 29, which receive cooling channels 30 and either cast with the water-cooled jacket 28 or are cast on this or attached as separate attachments. Through the ventilation ducts 26 and the cooling channels 30 can a

Circulating air flow, which allows the heated air from the rotor, the heat emits when flowing through the cooling channels 30 in the water-cooled jacket 28 of the housing. alternative a separate heat exchanger can be integrated into the cooling air circuit. The rotor 32 is so for example

designed that during its rotary motion, the air is automatically circulated in the cooling air channels 26 and 30. However, the

To improve circulation, a fan 24 at the

Rotor shaft 21 are attached. Alternatively, it is advisable to integrate a separately (mechanically or electrically) driven fan in the cooling air circuit, whereby the cooling of the speed and the direction of rotation of the rotor shaft is independent. If one decides to use a fan 24 with variable air flow at different directions of rotation or speeds, it is important to note that the

Direction of rotation with higher cooling air throughput is the direction of rotation of the servomotor, which causes the higher rotor losses.

In order to obtain an optimum overall result, the cooling air ducts for guiding the cooling air or the fan wheel 24 are preferably designed so that the air gap between the laminated core 25 and the stator 23 is also ventilated and thus cooled.

Another improvement measure is to provide in the rotor laminations 25 substantially radial ventilation ducts in which the cooling air from the ventilation duct 26 can flow substantially radially outward into the air gap between the laminated core 25 and the stator 23. This will, i.a. also by the

centrifugal force-induced acceleration of the cooling air in the radial ventilation ducts, an additional improvement of the cooling of the rotor 32 achieved.

In addition, the use of two or more

Fan wheels 24, e.g. on both sides of the laminated core 25, to. In this case, as a variant embodiment, the direction of rotation for optimal air flow for the two fans interpreted in opposite directions. This approach achieves approximately the same air throughput in both directions of rotation of the servomotor.

FIG. 4 shows the cross section of the servomotor according to FIG. 3. In section, two attachment parts 29 can be seen by way of example, which are the Record cooling channels 30. However, the housing can also be carried out with only one or more than two attachments 29. The number of attachments 29 ultimately depends on the extent of the losses to be cooled and the manufacturing capabilities. Alternatively, the sprues 29 can also be omitted and the air flowing through the ventilation ducts 26 can also be separated

Refrigeration unit to be cooled. In Fig. 4, cooling fins 31 are arranged in the cooling channels 30, which improved

Ensure heat transfer into the water-cooled jacket 28 of the housing. Additionally or alternatively, a heat exchanger can be integrated into the cooling air circuit.

In this sectional view of the servomotor, a possible embodiment of the invention for the ventilation ducts 26 is shown. Number, shape and position of these ventilation channels 26 depend on the number of pole pairs of the servomotor and the formation of the permanent magnets 34 in the rotor of the servomotor 6 from. In Fig. 4, the permanent magnets 34 are shown only for one pole, but in the real version on the entire circumference, according to the number of pole pairs of the rotor 32 of the servomotor, distributed. The ventilation channels 26 should be radially as far outside as possible in order to realize the lowest possible moment of inertia or optimal cooling. The permanent magnets 34 are preferably mounted in the region of the outer contour of the rotor. The ventilation channels are then to be positioned between the permanent magnets 34. The permanent magnets 34 are simply or multiply executed per pole and can be single-layered or even

be packed in several layers. Further configuration options are e.g. V-shaped arrangement (as in Fig. 4, a single layer

represented}, embedded or attached to the circumference of the rotor. Here, all technically feasible variants can be implemented. The size, number and location eisΣ LIi¬tungskanäle 26 is preferably selected so that in the rotor by the permanent magnets 34th

resulting field current lines not ode

economically / technically optimal extent are interrupted. This is achieved, for example, by the substantially parallel arrangement of the wall sections adjacent to the permanent magnets 34. A further framework condition to be fulfilled for the dimensioning of the ventilation ducts 26 is that the mechanical connection to the rotor shaft 21 and the rotor laminated core 25 itself are sufficiently mechanically and electrically dimensioned. The variation of the cross section and the position of the ventilation channels 26 causes a correspondingly variable inertia of the rotor 32 of the servomotor 6. Fig. 5 shows the influence of the size of the ventilation ducts on the moment of inertia of the rotor 32 of the servomotor 6. Thus, in the selected embodiment, which assuming a rotor design designed for a small mass moment of inertia (such as an elongated rotor 32), the requirement for an inertia of <1, 6kgm ² to achieve an application factor f _A <0.15.

For realizing a mass moment of inertia of 1, Ikgm ² , in order to achieve an application factor f _A <0.1, are

According to the invention ventilation ducts in the amount of about 60% of

Sheet metal cross-section provide.

The additional requirement for a sufficient cooling of the rotor is in the normal case by ventilation ducts in the extent of a total of about 5% of the sheet metal cross section met. At high thermal load of the rotor, however, they must be sized larger or increased their number.

A good compromise between mechanical

Strength requirements and optimum magnetic flux in the rotor of the servomotor can be achieved by optimally dimensioned

Ventilation channels 26 in the extent of a total of about 15% to 30% of the sheet metal cross-section can be achieved. Kicking dynamic

If the requirements are more prominent, it is advisable to realize optimally dimensioned ventilation ducts 26 in the total amount of around 45% to 75% of the sheet metal cross-section.

Claims

Claims:

Electric machine with a rotor and a stator, characterized in that in the rotor {32} axially

aligned ventilation ducts (26) are arranged.

Electric machine according to claim 1, characterized

characterized in that the area fraction of the ventilation channels (26) at the cross-sectional area of the rotor (32) is at least 5%, preferably at least 15%, particularly preferably at least 30%, very particularly preferably at least 45% and in particular at least 60%.

Electric machine according to claim 1 or 2, characterized in that a rotor shaft (21) of the rotor (32) is a hollow shaft.

Electrical machine according to one of claims 1 to 3, characterized in that from the axial

Ventilation ducts (26) extend further ventilation ducts radially outward.

Electrical machine according to one of claims 1 to 4, characterized in that a fan wheel (24) is provided, which at the same speed in different

Direction of rotation generates a different volume flow.

Electrical machine according to one of claims 1 to 4, characterized in that at each end of the rotor (32) at least one fan (24) is arranged, which generates at different speeds in different directions of rotation a different volume flow, so in both directions of rotation approximately equally good ventilation of the rotor (32) takes place.

Electrical machine according to one of claims 1 to 6, characterized in that it comprises a housing to the at least one with the ventilation channels (26) connected to the cooling channel (30) is arranged.

Electric machine according to claim 7, characterized

characterized in that the housing is a water-cooled

Sheath (28).

9. Electrical machine according to claim 7 or 8, characterized

in that the housing has cooling ribs (31) which project into the cooling channel (30).

10. Electrical machine according to one of claims 1 to 9,

characterized in that on the rotor (32} permanent magnets (34) are arranged, which are at least partially between ventilation channels (26).

11. Electrical machine according to one of claims 1 to 10,

characterized by a separately driven fan.

12. Electrical machine according to claim 11, characterized

in that the fan is arranged in the cooling channel (30).

13. Electrical machine according to one of claims 1 to 12,

characterized by a heat exchanger associated with the

Ventilation channels (26) is in flow communication.

14. Electrical machine according to one of claims 10 to 13, characterized in that the permanent magnet (34) adjacent wall portions of the ventilation ducts (26) in

Substantially parallel to the permanent magnets (34)

are arranged.

15. Energy production plant, in particular wind turbine, with a drive shaft, a generator (8) and with a

Differential gear (4, 11 to 13) with three on or

Abtrieb, wherein a first drive (12) with the

Drive shaft, an output (13) with the generator (8) and a second drive (11) with a differential drive (6) and wherein the differential gear (4, 11 to 13) is a planetary gear, characterized in that the differential drive (6) is an electric machine according to one of claims 1 to 14.

Drive unit with a drive shaft, a main drive and a differential gear with three on or

Driven, wherein a first drive to the drive shaft, an output to the main drive and a second drive is connected to a differential drive and wherein the differential gear is a planetary gear, characterized in that the differential drive a

electric machine is after 1 to 14