AT512853B1 - Differential drive for an energy recovery plant - Google Patents

Abstract

An electric machine having a rotor and a stator has axially aligned ventilation channels (26) in the rotor (32). At least one cooling channel is arranged on a housing. The ventilation channels (26) of the rotor (32) are connected to the at least one cooling channel (30) on the housing. 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%, more preferably at least 30%, most preferably at least 45% and most preferably at least 60%. Thus, the rotor has both good cooling and a small mass moment of inertia.

Description

Austrian Patent Office AT512 853B1 2014-08-15

Description: The invention relates to an electric machine having a rotor, in which axially aligned ventilation channels are arranged, a stator and a housing, on which at least one cooling channel is arranged.

From DE 101 22 425 A1, such an electric machine is known which has an air-cooled rotor and a water-cooled 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 or outputs, with a first drive with the drive shaft, an output to the generator and a second drive with a differential drive is connected and wherein the differential gear is a planetary gear.

Finally, the invention relates to a drive unit with a drive shaft, a main drive and a differential gear with three inputs and outputs, with a first drive to the drive shaft, an output to the main drive and a second drive with a differential drive is connected and wherein the differential gear is a planetary gear.

Variable speed drives, e.g. 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 systems 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 connected to the medium-voltage network externally-excited medium voltage generators in combination with a differential gear and an auxiliary drive, which preferably provides a permanent magnet synchronous machine in combination with an IGBT frequency converter smaller power use. This so-called servomotor is exposed due to the usually high gear ratio very high dynamic loads.

The high dynamic stress in turn leads to a correspondingly large thermal load of the servomotor, which subsequently requires a dimensioned above the standard cooling system. In addition, WO 2010/108209 proposes the smallest possible moment of inertia in order to optimize the control behavior for a plant with differential drive.

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 moment of inertia are sufficiently satisfied simultaneously.

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

This object is further achieved with an energy recovery system having the features of claim 14 and a drive unit having the features of claim 15.

Thus, the requirement for a long life under high dynamic stress, as e.g. for energy recovery plants is typical, and a small moment of inertia are sufficiently satisfied.

Preferred embodiments of the invention are subject of the dependent claims. [0013] Hereinafter, preferred embodiments of the invention will be described in detail with reference to the attached drawings. In the drawings: Fig. 4 Fig. 4 shows the principle of an electromechanical differential system with a servo motor according to the prior art, the typical structure of a Servo motor according to the prior art, an embodiment of a servomotor according to the invention, a cross section of the servo motor according to FIG. 3 and the influence of the size of the ventilation ducts on the moment of inertia of the rotor of the servomotor.

In the following the principle of a differential drive using the example of a wind turbine is described. The power of the rotor of a wind turbine is calculated from the formula

Rotor power = Rotor area * Power coefficient * Air density / 2 * Wind speed3, whereby the power coefficient depends on the speed of rotation (= ratio of 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 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, the on a Drive shaft 2 is seated, drives a main transmission 3 at. The main transmission 3 is usually a 3-stage transmission with two planetary stages and a spur gear, but can 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 gear 3 and the generator 8 is the differential stage 4, which is driven by the main gear 3 via a planet 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 and is 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 provides an adjustment gear stage 5 in the form of a spur gear between the differential stage 4 and the servo motor 6. Since in the range of the differential drive 6 is also a massive clutch 14 as a connecting element between the main transmission and differential gear, under certain circumstances, a correspondingly large axial offset for the servomotor 6 is required. In this case, this can be realized for the adjustment gear stage 5 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, a permanent-magnet synchronous machine is preferably selected as servomotor 6. However, the servomotor can in principle be any conceivable type of electrical machine.

The speed equation for the differential gear is:

Speed generator = x * SpeedRotor + y * Speed servomotor, where the speed generator is constant and the factors x and y are selected from the selected gearbox

Austrian Patent Office AT512 853B1 2014-08-15 Transmission of main gearbox and differential gear can be derived. 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 servo motor is constant, which allows the torque in the drive train to be controlled by the servo motor. The torque equation for the servomotor is:

Torque servomotor = torque Ro, or * 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 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 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 small speed range requires a correspondingly large gear ratio of the differential gear in order to interpret the servomotor with typical rated speeds - preferably between 1 .OOOrpm and 1,500 rpm. However, a large gear ratio of the 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 mass moment of inertia of the servomotor.

In order to make good use of the differential drive, this is operated both motor and generator. As a result, power is fed into the differential stage 4 during engine operation, and power is taken from the differential stage 4 during regenerative operation. 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 embodiment described is only an example and is also feasible in technically similar applications. This concerns v.a. Hydro turbines and pumps and installations for the production of energy from ocean currents. For these applications, the same basic conditions apply as for wind turbines, namely variable flow rate. The drive shaft is in each case driven directly or indirectly by the device driven by the flow medium, for example water.

In addition, the above also applies to any type of systems, which use differential drives for realizing 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 called generator 6 is at, for. 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 for a good control behavior of a wind turbine with electric differential drive a maximum moment of inertia for the differential drive JDA, max, which can be calculated according to the following formula:

where fA is an application factor, which is a measure of the control behavior of the wind turbine to be achieved. The variable sges is the ratio of the speed range of the differential drive to the speed range of the rotor of the wind turbine (sges = speed range differential drive / speed range rotor) and JR is the mass moment of inertia of the rotor of the wind turbine tan. With an application factor of fA = 0.2, according to WO 2010/108209 3/11 Austrian Patent Office AT512 853B1 2014-08-15, good results regarding control behavior can already be achieved. Basically, however, it is found that with decreasing fA even better results can be achieved, for applications with smaller fA additional effort to reduce the mass of the rotor of the differential drive is necessary.

According to WO 2010/108209, a reduction of the application factor to e.g. fA = 0.10 a further improvement necessary for highly dynamic applications. However, this is associated with increasing manufacturing costs for the rotor of the differential drive.

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. An alternative design with low mass moment of inertia would be to attach the permanent magnets directly to the circumference of the rotor shaft 21, which, however, can lead to significant limitations of the performance (field weakenability, dynamics, efficiency, etc.) of the servomotor. Housed in the housing 20 is the wound stator 23. This housing 20 has e.g. an integrated water jacket, which has the task to dissipate due to the power dissipation waste heat 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 the application factor fA <0.15, so you would need for a typical 3MW Windkraf tan lays a servo motor with embedded permanent magnets and a moment of inertia of &lt; 1.6kgm2. This can be with a servo motor like. Although realize, but requires special measures in the design.

In addition, one must not neglect the thermal load of the rotor 22 in the case of highly dynamic loads and operation in the field weakening range. 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 ensure the life of the servo motor in the amount of, for example, in the wind energy required 175,000 operating hours.

3 and 4 show an embodiment of a servo motor according to the invention, which fulfills the above requirements. On the rotor shaft 21, which can be designed to reduce the mass moment of inertia 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 has bearing plates 27, a water-cooled jacket 28 and optionally one or more attachments 29, which receive cooling channels 30 and either mitgegossen with the water-cooled jacket 28 or are cast on these or attached as separate attachments. Through the ventilation channels 26 and the cooling channels 30, an air flow can circulate, which allows the heated air from the rotor heat dissipates the heat when flowing through the cooling channels 30 in the water-cooled jacket 28 of the housing. Alternatively, a separate heat exchanger can be integrated into the cooling air circuit. The rotor 32 is constructed, for example, so that during its rotational movement, the air is automatically circulated in the cooling air passages 26 and 30. However, to improve the circulation, a fan 24 may be attached to the rotor shaft 21. 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 you decide 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 flow rate is the direction of rotation of the servomotor, resulting in the higher rotor losses.

In order to obtain an optimum overall result, the cooling air channels for the guidance of the cooling air or the fan 24 are preferably designed so that the air gap between the laminated core 25 and the stator 23 is vented and thus cooled. Another improvement measure is to provide substantially radial ventilation ducts in the rotor laminations 25, in which the cooling air from the ventilation duct 26 extends substantially radially outward into the air gap between the laminated core 25 and the stator 23 can flow. This will, i.a. also achieved by the centrifugal force-induced acceleration of the cooling air in the radial ventilation ducts, an additional improvement in the cooling of the rotor 32.

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 servo motor according to FIG. 3. In section can be seen by way of example two attachments 29, which receive the 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 cooled in a separate recooling unit. In Fig. 4, cooling fins 31 are arranged in the cooling channels 30, which ensure improved 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 servo motor 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 designed once or several times per pole and can be packed in a single-layered or multi-layered manner. Further configuration options are e.g. V-shaped arrangement (as shown in Fig. 4 single layer), embedded or attached to the circumference of the rotor. Here, all technically feasible variants can be implemented. The size, number and location of the ventilation channels 26 is preferably selected so that the field current lines produced in the rotor by the permanent magnets 34 are not interrupted or only in the economically / technically optimal extent. This is e.g. achieved by the substantially parallel arrangement of the wall portions adjacent to the permanent magnet 34. Another 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 ducts 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. So is in the selected Embodiment, which assumes a rotor design designed for a small mass moment of inertia (such as an elongate rotor 32) to meet the requirement for a moment of inertia of <1.6kgm2 to achieve an application factor fA <0.15.

To achieve an inertia of 1.1 kgm2 in order to achieve an application factor fA <0.1, according to the invention ventilation ducts in the amount of about 60% of the sheet metal cross-section are provided.

The additional requirement for a sufficient cooling of the rotor is normally fulfilled by ventilation ducts in the amount of a total of approximately> 5% of the sheet metal cross section AT 512 853 B1 2014-08-15. 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. If dynamic requirements come more to the fore, 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. 6/11

Claims (15)

Austrian Patent Office AT512 853B1 2014-08-15 Claims 1. An electric machine having a rotor (32) in which axially aligned ventilation channels (26) are arranged, a stator (23) and a housing, arranged on the at least one cooling channel (30) is, characterized in that the ventilation channels (26) of the rotor (32) with the at least one cooling channel (30) are connected to the housing. 2. Electrical machine according to claim 1, characterized in that the surface portion of the ventilation channels (26) on the cross-sectional area of the rotor (32) at least 5%, preferably at least 15%, more preferably at least 30%, most preferably at least 45% and in particular at least 60%. 3. Electrical machine according to claim 1 or 2, characterized in that a rotor shaft (21) of the rotor (32) is a hollow shaft. 4. Electrical machine according to one of claims 1 to 3, characterized in that extending from the axial ventilation ducts (26) further ventilation ducts radially outwards. 5. Electrical machine according to one of claims 1 to 4, characterized in that a fan wheel (24) is provided which generates a different sized volume flow at the same speed in different directions of rotation. 6. 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 the same speed in different directions of rotation a different volume flow, so in both directions an approximately equally good ventilation of the rotor (32) takes place. 7. Electrical machine according to one of claims 1 to 6, characterized in that the housing has a water-cooled jacket (28). 8. Electrical machine according to one of claims 1 to 7, characterized in that the housing has cooling ribs (31) which protrude into the cooling channel (30). 9. Electrical machine according to one of claims 1 to 8, characterized in that on the rotor (32) permanent magnets (34) are arranged, which are at least partially between ventilation ducts (26). 10. Electrical machine according to one of claims 1 to 9, characterized by a separately driven fan. 11. Electrical machine according to claim 10, characterized in that the fan in the cooling channel (30) is arranged. 12. Electrical machine according to one of claims 1 to 11, characterized by a heat exchanger which communicates with the ventilation channels (26) in flow communication. 13. Electrical machine according to one of claims 9 to 12, characterized in that the permanent magnets (34) adjacent wall portions of the ventilation ducts (26) are arranged substantially parallel to the permanent magnet (34). 14. Energy production plant, in particular wind power plant, with a drive shaft, a generator (8) and with a differential gear (4, 11 to 13) with three inputs or outputs, wherein a first drive (12) with the drive shaft, an output (13 ) is connected to 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) An electric machine according to any one of claims 1 to 13. 7/11 Austrian Patent Office AT512 853 B1 2014-08-15 15. Drive unit with a drive shaft, a main drive and a differential gear with three drives or drives, 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 Planetary gear is, characterized in that the differential drive (6) is an electric machine according to one of claims 1 to 13. For this 3 sheets drawings 8/11