AT510118A1 - SPEED VARIABLE GENERATOR FOR A WIND POWER PLANT AND METHOD FOR OPERATING THIS GENERATOR - Google Patents

Description

L

The invention relates to a variable-speed generator having at least one electrical winding which is connected to at least one generator-side frequency converter output stage and 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 the power plant, an output with a connectable to a grid generator and a second drive is connected to an electric machine as a differential drive.

The invention further relates to a method for operating a variable-speed generator.

Wind power plants are becoming increasingly important as electricity generation plants. As a result, the percentage of electricity generated by wind is continuously increasing. This, in turn, requires new standards of power quality and, on the other hand, a trend towards even larger wind turbines. At the same time, there is a trend towards offshore wind turbines, which require system sizes of at least 5 MW of installed capacity. Due to the high costs for infrastructure and maintenance of the wind turbines in the offshore sector, the availability of the turbines is of particular importance here. 20

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. Currently, therefore, wind turbines are in use, which increasingly meet this requirement by using variable-speed generator solutions in the form of so-called permanent magnet-excited low-voltage synchronous generators in combination with IGBT frequency converters. However, this solution has the disadvantage that (a) the wind turbines can be connected to the medium-voltage network only by means of transformers and (b) the frequency inverters required for the variable speed are very powerful and therefore a source of efficiency losses. Alternatively, therefore, so-called differential drives are used recently, which directly to the medium-voltage network connected externally-excited medium-voltage synchronous 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 low power use ,

The AT 507 395 A shows a differential system with an electric servo drive with a permanent magnet synchronous machine in combination with an IGBT-40 frequency converter. : ι: * * * 2

The service lives of up to 180,000 hours required for energy production plants, in particular wind turbines, are usually not achieved by the IGBT semiconductor modules used. As a result, provided that no scheduled replacement 5 of these modules is provided, failures of the entire system can be expected, which reduces the availability of the facilities accordingly. This becomes all the more critical, the worse the system can be reached for maintenance operations, what v. A. relevant in so-called offshore installations. 10 The described problem of these generator-operated energy production plants can be solved by the use of redundant frequency inverter output stages, whereby in case of short circuit of an IGBT output stage or a winding an undesired braking torque develops. The invention is therefore based on the task of taking appropriate precautions so that the defective drive train provides no or only a negligible braking torque.

This object is achieved with a generator having the features of claim 1 20 and with a differential gear having the features of claim 16.

This object is further achieved by a method having the features of claim 17. WO 2007/104550 A2 shows the electromotive part of an elevator drive consisting of a rotor and a stator, wherein windings of the stator can be designed as single-tooth windings. The individual coils of the stator winding can be connected in parallel or in series with a winding strand and connected to a converter. The use of an electric machine of this type as a generator is not described in WO 2007/104550 A2, nor is the effect used by the present invention that, by using a single-tooth winding, in comparison with a conventional, so-called distributed winding, a substantially higher effect Stray inductance is achieved, resulting in the case of a winding short circuit or IGBT short circuit results in a much smaller 35 braking torque.

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 attached drawings.

3

Fig. 1 shows a wind turbine according to the prior art with an electric drive consisting of permanent-magnet synchronous generator and IGBT frequency converter, 5th

2 shows the principle of a differential gear with an electric differential drive according to the prior art,

3 shows the redundant structure of an electric drive, 10

4 shows the basic structure of a two-layer single-wound,

Fig. 5 shows various stator slot shapes of three-phase machines, Fig. 6 shows various constructional arrangements of the permanent magnets of permanent magnet three-phase machines,

Fig. 7 shows an example of the course of the braking torque at winding short circuit of the stator of a permanent magnet synchronous machine with Einzahnwicklung and 20 embedded permanent magnet.

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

Rotor power = Rotor area * Power factor * Air density / 2 * Wind speed3 25 where the power coefficient depends on the speed of rotation (= blade tip speed to wind speed ratio) of the rotor of the wind turbine. The rotor of a wind power plant is designed for an optimum power coefficient based on a fast-running number (usually a value between 7 and 9) 30 to be determined in the course of the development. For this reason, when operating the wind turbine in Teiilastbereich set a correspondingly low speed to ensure optimum aerodynamic efficiency.

Fig. 1 shows the principle of a variable speed wind turbine according to the prior art 35 with an electric drive with a permanent-magnet synchronous generator and an IGBT frequency converter, which are usually referred to as high-speed full converter systems. A rotor 1 of the wind turbine, which sits on a drive shaft 2 for a main gear 3, drives the main gear 3 at. The main transmission 3 is a 3-stage transmission with two planetary stages and a spur gear stage. Between the main gearbox 3 and the generator 6 there are an emergency brake 4 and a clutch 4 "> The generator 6 - preferably a permanent magnet synchronous generator - is connected via a frequency converter 7 and a transformer 8 to a medium voltage network 9. Fig. 2 shows a possible principle of a differential system for a variable-speed wind turbine. The rotor 1 of the wind turbine, which sits on the drive shaft 2 for the main transmission 3, drives the main gear 3 at. The main transmission 3 is a 3-stage transmission with two planetary stages and a spur gear. Between main gear 3 and generator 13 is a differential stage 4, which is driven by the main gear 3 via 10 a planet carrier 10 of the differential stage 4. The generator 13 - preferably a separately excited synchronous generator, which may also have a rated voltage greater than 20 kV if necessary - is connected to a ring gear 11 of the differential stage 4 and is driven by this. A pinion 12 of the differential stage 4 is connected to a differential drive 14. The speed of the differential drive 14 is controlled 15, on the one hand to ensure a constant speed of the generator 13 at variable speed of the rotor 1 and on the other hand to regulate the torque in the complete drive train of the wind turbine. In order to increase the input speed for the differential drive 14, a 2-stage differential gear is selected in the case shown, which provides an adjustment gear stage 15 in the form of a spur gear between 20 differential stage 4 and differential drive 14. The differential stage 4 and the adjustment gear 15 thus form the 2-stage differential gear. The differential drive 14 is a three-phase machine, which is connected via a frequency converter 16 and a transformer 17 to the medium-voltage network 9. Both the generator 6 according to FIG. 1 and the differential drive 14 according to FIG. 2 are preferably permanent-magnet synchronous machines, but the differential drive 14 can be dimensioned substantially smaller than the generator 6. The same applies mutatis mutandis to the frequency converter of both systems. The power of the differential drive 14 is substantially proportional to the product of percent deviation of the rotor speed from its base speed (usually referred to as "slip") times rotor power. Accordingly, a large speed range basically requires a correspondingly large dimensioning of the differential drive 14. One possibility for expanding the speed range of the rotor of the wind turbine while the slip rate of the differential system remains constant, and thus increasing the energy yield, is the utilization of the so-called field weakening range of e.g. a permanent magnet synchronous three-phase machine as electric differential drive 14. 40 Fig. 3 shows the above-mentioned redundant structure of a variable speed • I < ..... 5 electric machine. By way of example, here is the permanent-magnet synchronous machine 18, which may be either the generator 6 of Fig. 1 or the differential drive 14 of Fig. 2, with two electrically separate windings, usually three-phase windings executed. Permanent magnets are used in the rotor. It may be advantageous to carry out the electric machine not as an internal rotor but as an external rotor, in which case the stator has the permanent magnets and the rotor has the parallel windings.

With this synchronous machine 18, two parallel IGBT full bridges 19 are connected, which are independently controllable with a controller and each provided with 10 capacitors 20 and are connected via DC fuses 21 to a DC intermediate circuit 23. The DC fuses 21 are recommended so that in case of a short circuit in a frequency converter output stage 22 of the DC link is not also shorted and thus further operation of the system is impossible. 15

These frequency converter output stages 22, essentially consisting essentially of controlled IGBT full bridges 19, controllers, capacitors 20, current measurement and DC fuses 21, can be connected to the required busbar A / C on a common carrier plate, which at the same time a part of the heat sink or with this is connected to be mounted. The cooling in particular of the IGBTs is preferably a water cooling, but can also be designed as air cooling. Said carrier plate is preferably guided and fixed in slides. If, in addition, the external power and coolant connections are generally or only partially pluggable, then defective frequency converter output stages 22 can be changed quickly and easily in the event of a fault.

The DC intermediate circuit 23 is the connecting element for the individual frequency converter output stages 22. To protect the frequency converter against overvoltage, a so-called brake chopper 24 with 30 resistors is preferably also connected here. This brake chopper 24 can be used at e.g. Power failure also destroy excess energy.

In addition, for energy recovery systems with differential systems and an energy storage 25 is recommended. This energy store 25 preferably consists essentially of supercaps connected to the DC intermediate circuit 23. To make the voltage level for the operating range of these supercaps optimal or flexible, they can be connected via DC / DC converter to the DC link 23. 40

Depending on the operation of the power plant, the 6

Energy storage 25 may also take over the function of the brake chopper 24. If the aforementioned capacitors 20 are oversized in the frequency converter output stages 22, then one can replace the energy store 25 in the ideal case as well.

Between DC intermediate circuit 23 and network 26, the same frequency converter output stages 22 are preferably used. However, these frequency converter output stages 22 have different functions to be fulfilled on the network side than the machine-side frequency converter output stages described above.

In the case of a high-speed full-speed converter system. Fig. 1 works this mainly regenerative. Thus, the machine-side frequency converter output stages 22 operate as controlled rectifier modules and the network-side

Frequency converter output stages 22 as so-called active grid feed modules (inverters). Physically, the frequency converter output stages 22 are preferably able to perform both functions, only the controller software must be able to support the required functions accordingly.

In the case of a differential system like. Fig. 2 works this both regenerative and motor. That is, in motor operation, the machine-side frequency converter output stages 22 operate as inverter for speed / torque control and the network-side frequency converter output stages 22 as rectifier modules. Accordingly, suitable controller software is required. In regenerative mode, the frequency converter operates as described above for the high-speed full-frequency converter systems.

In summary, this means for the controller software of the frequency converter output stages 22 that preferably all the functions described are stored on the controller hardware and can be called up automatically according to the required function. This can be specified or coordinated by a higher-level controller.

In order for the line-side frequency converter output stages 22 to meet the power quality criteria required by the grid operator, a so-called LCL filter 27 is to be provided. For redundancy reasons, this can be carried out separately for each line-side frequency converter output stage 22. The same applies to fuses 28 and power switch 29. Alternatively, LCL filters 27, fuses 28 and power switch 29 can be easily implemented. However, there is no redundancy for these components. In addition, the grid-side IGBT full bridges would have to be controlled in parallel,

······························································································································? which often leads to unpleasant balancing currents between the frequency converter output stages 22 in practice and thus makes not insignificant performance deductions necessary. The embodiment in Fig. 3 shows two parallel power strings each having a winding of the electric machine 18 and a machine-side, i. generator side, and a network-side frequency converter output stage 22, an LCL filter 27, a fuse 28 and a power switch 29. But it can also be realized a higher number of parallel power lines. In addition, although it is useful not necessary to keep the number of winding types of the synchronous machine 18 the same as the number of the machine-side frequency converter output stages 22. Preferably, however, the number of winding types is not smaller than the number of the machine-side frequency converter output stages 22 be avoided in order to avoid the above-described problem 15 of the then IGBT full bridges to be triggered in parallel.

In order to meet increased requirements for reactive power to be supplied to the grid, e.g. the number of frequency converter output stages 22 is higher on the line side than on the machine side. However, it may also be useful for various reasons to choose the number of frequency converter output stages 22 higher on the machine side than the network side.

The problem of total failure of the power generation plant at e.g. IGBT failure is not completely solved by the redundant design of the frequency converter. If there is a short circuit in the winding or a short circuit in the winding due to a short circuit in one of the machine-side IGBT full bridges, the synchronous machines generate a large braking torque whose size depends on the design of the machines. This would drive a power train in the example of FIG. 3, but the other power train would slow down and further operation of the system would only be poorly possible.

In the event of a short circuit in one of the frequency converter output stages 22, the short-circuited frequency converter output stage 22 could also be disconnected from the connected winding of the generator via a fuse or a circuit breaker. 35

In permanent magnet synchronous machines, a large field weakening range can be realized if a) the magnetic flux linkage between rotor and stator has a high asymmetry between the longitudinal and transverse axes and / or b) the leakage inductance in the stator is large (large series inductance). 40

* · • " 8th

Both of the above properties can be characterized by constructive measures and thereby an increased field weakening range (up to 3 times the rated speed) with operationally sufficient torque (up to 0.4 times the rated torque) can be achieved. 5

High stray inductors are preferably achieved by the use of single - tooth windings with unbalanced groove / pole pair ratio.

The single-tooth winding, which makes it possible to produce motors with a small footprint and high efficiency, is characterized in that each winding coil encloses exactly one stator tooth. By comparison, in a distributed winding, each winding coil always encloses several stator teeth. The single-tooth winding can be designed as a single-layer or two-layer winding. FIG. 4 shows by way of example a stator 31 developed into the plane of the drawing with a single layer winding 33 with nine slots 32 and a rotor 36 with four permanent magnet pole pairs 35. Stand 31 and rotor 36 are separated by the air gap 34.

In the case of two electrically separate winding systems (the first winding has the index 20 a, for example, and the second winding has the index b), the spatial sequence of the three-phase winding (U, V, W) would be exemplary in accordance with FIG. 4: Ua, Ub, Va, Vb,

Wa, Wb. For the number q of slots per pole (2 * p) and phase (m), the relationship 25 q = Q / (2 * p * m) where Q is the total number of stator slots generally holds. q is also called the number of holes. Depending on the ratio Q / (2 * p * m), an asymmetrical flux linkage between rotor and stator is created. Thus, for the two-layer single-tooth winding exemplified in FIG. 4, Q = 9 and 2 * p = 8. In a 3-phase system, m = 3, and thus q = 3/8. 30

The stray inductance can be increased by narrowed slot slots. In Fig. 5a) a typical stator slot shape 37 is shown as used in distributed windings.

The wide slot slot 40 is closed with a slot wedge 39. In Fig. 5b) a possible stator groove shape 38 is shown as it can be used in single-tooth windings 35. The slot slot 41 is narrowed and does not necessarily have to be closed by a slot key b3 40, as shown in FIG. Narrowly narrowed slot slots are relatively problematic in single-tooth windings, since the windings can be introduced in the groove longitudinal direction. An asymmetric flux linkage between rotor 36 and stator 31 is achieved

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9 also by embedded in the rotor 36 and even more embedded in the rotor 36 permanent magnets 35. In Fig. 6 is a section of a developed in the plane of the rotor 36 with various structural arrangements of the permanent magnets 35 is shown schematically. Fig. 6a) shows the magnets 35 constructed on the rotor 31 5, Fig. 6b) shows in the rotor 31 embedded magnets 35 and Figs. 6c) and 6d) show in the rotor 31 embedded magnets 35th

A further reinforcement of the asymmetric flux linkage can be achieved by constructively set, so-called magnetic flux barriers. In FIG. 6d), the arrangement of the magnetic flux barrier 42 is shown by way of example. The magnetic flux barriers 42 can be realized by inserting a magnetically non-conductive material or in the simplest case by a space produced by punching.

A permanent magnet synchronous machine equipped with electrically separated 15 three-phase windings can continue to operate at partial load in the event of a fault (phase short circuit). It should be noted that the short-circuited winding generates a braking torque. This braking torque is much lower at high stray inductance (as described above). FIG. 7 shows, by way of example, the course of the braking torque resulting from a winding short circuit in% of the nominal torque as a function of the rotational speed of the synchronous machine. It can be seen at about 20% of the rated speed a peak, which, however, skipped control technology at a speed increase or -reduction. can be passed quickly. In the remaining speed ranges 25, the torque settles at about 10% of the nominal torque. The course of the braking torque shown here may deviate more or less from the values shown with changed synchronous machine parameters.

If, in the example shown, one assumes a system configuration with two parallel 30 frequency converter output stages, the power generation system can largely continue to be operated with approximately 45% of the rated system torque.

As e.g. Wind turbines are operated over long periods of time in the partial load range, there is an energy yield loss only in the operating range with more than 45% of the nominal 35 torque. Here you can make adjustments in order to temporarily achieve a higher output with higher operating speed, in this case limited to 45% torque. At a mean annual wind speed at hub height of 7.5 m / s with Rayleigh distribution (this covers a large part of the world's commercially exploitable wind areas) is statistically 40 of the energy yield loss only about 1/3 of the achievable with fully functional plant 10

Energy yield.

In principle, it is conceivable in the invention to over-dimension the system insofar as one or more additional power strings are provided, whereby more than 100% of the power required in normal operation is provided by the sum of all power strings. In the event that a power train fails, its power can be taken from a previously unused power train or distributed to the other power strands not fully utilized in normal operation. This is particularly advantageous when the generator 10 is the differential drive of the power generation plant, since the power strands can be dimensioned relatively small in this case and are therefore favorable.

When designing differential drives, however, there are other important 15 special cases to consider. For example, a failure of the differential drive can cause serious damage. An example is a forced emergency stop of the power generation plant at nominal operation. As a result, the generator is disconnected from the mains at the same time and the transmittable torque in the drive train is suddenly at zero. The speed of the rotor of the wind turbine is also controlled in this case 20 preferably by a quick adjustment of the rotor blade adjustment very quickly against a speed equal to zero. Due to the relatively high inertia of the generator but this will only slowly reduce 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 inevitable.

For this reason, e.g. when using hydrostatic differential drives a mechanical brake provided which prevents damaging overspeed in case of failure of the differential drive for the driveline. W02004 / 109157 A1 shows for this purpose a mechanical brake which acts directly on the generator shaft and thus can decelerate the generator accordingly.

Due to the redundant embodiment of the winding of the synchronous machine 18 and the frequency converter output stages 22 shown in FIG. 3, at least 50% of the rated torque is still present as brake torque in the event of failure of an output stage, which may also be temporarily exceeded in accordance with the thermal design. In addition, a possible reduction of the IGBT clock frequency helps here. Preferably, the brake chopper 24 and / or the energy storage 25 are then designed so that the excess energy can be stored. The mentioned 50% of the nominal 40 torque is usually sufficient to overspeed the differential drive to * ι «Μ «« «I I I I I I I I I I I I I I I • • • • • • • • • • • • • · · · · · · · · · · · · · · · · · · · ·. ·. , * · Μ * · 11 prevent the use of a mechanical brake.

A further advantage of the single-tooth winding described above is that the error case (phase short circuit) is very unlikely, since the contact of different phases in a slot is very much reduced compared to the distributed winding (FIG. 4). In the single-layer single-layer winding, there is no contact at all between different phases in a groove because only one winding (one phase) is ever laid in a groove.

The described embodiments are only an example and are preferably used in 10 wind turbines, but are also feasible in technically similar applications. This concerns v.a. Hydroelectric power plants to exploit river and ocean currents. For this application, the same basic requirements apply as for wind turbines, namely variable flow rate. The drive shaft is driven in these cases by the driven by the flow medium, such as water, 15 devices directly or indirectly.

Claims (20)

L / 12 claims: 1. Variable-speed generator (6, 14, 18) with at least one electrical winding which is connected to at least one generator-side frequency converter output stage 5 (22), characterized in that the winding is designed as a single-tooth winding. 2. Generator according to claim 1, characterized in that it has an asymmetrical groove / pole pair - ratio. 10 3. Generator according to claim 1 or 2, characterized in that there are two electrically separate windings, each of which is connected to at least one generator-side frequency converter output stage (22). 4. Generator (6, 14, 18) according to any one of claims 1 to 3, characterized by at least two network-side frequency converter output stages (22). 5. Generator (6, 14, 18) according to one of claims 1 to 4, characterized in that the generator (6, 14, 18) is a permanent magnet synchronous machine 20. 6. generator (6, 14, 18) according to one of claims 1 to 5, characterized in that the Einzahnwicklung on the rotor of the generator (6, 14,18) is arranged. 7. generator (6, 14,18) according to one of claims 1 to 5, characterized in that the Einzahnwicklung on the stator of the generator (6,14, 18) is arranged. 8. generator (6, 14, 18) according to one of claims 1 to 7, characterized in that the frequency converter output stages (22) have IGBT full bridges (19). 30 9. generator (6, 14, 18) according to claim 8, characterized in that between the IGBT full bridges (19) and a DC intermediate circuit (23) fuses (21) are arranged. 10. generator (6, 14, 18) according to one of claims 1 to 9, characterized in that the frequency converter output stages (22) IGBT full bridges (19), capacitors (20), controllers, and fuses (21), which are mounted together on a support plate with a heat sink. A generator (6, 14, 18) according to claim 9 or 10, characterized in that the • · f · * · 4 * · »» · · · < * »* A * * * * * * * a« ·· «· · · ·« «« ..... 13 ...... electrical connection between the frequency converter output stages (22) and the DC link ( 23) is pluggable. 12. generator (6, 14, 18) according to one of claims 5 to 11, characterized 5 characterized in that the permanent magnet synchronous machine has embedded permanent magnets. 13. Generator (6, 14, 18) according to any one of claims 1 to 12, characterized in that between a winding and a connected 10 frequency converter output stage (22) a fuse or a circuit breaker is arranged. 14, generator (6, 14, 18) according to one of claims 1 to 13, characterized in that one or more additional power strands 15 are provided, whereby more than 100% of the power required in normal operation by the sum of all power strands are provided can. 15. Generator (6, 14, 18) according to one of claims 1 to 14, characterized 20 characterized in that the number of the generator side provided frequency converter output stages (22) and the network side provided frequency converter output stages (22) is different. Differential drive for an energy production plant, in particular for a wind turbine, with three inputs or outputs, wherein a first drive with a drive shaft (2) of the power generation plant, an output with a with a network (9) connectable generator (13) and a second drive is connected to an electric machine as a differential drive (14), characterized in that the electric machine is a variable-speed generator 30 (14,18) according to one of claims 1 to 15. 17. Energy production plant, in particular wind power plant, with a drive shaft (2), one with a network (9) connectable generator (13) and with a differential gear with three inputs or outputs, wherein a first drive with the drive shaft 35 (2), an output with the generator (13) and a second drive with an electric machine as a differential drive (14) is connected, characterized in that the electric machine is a variable-speed generator (14,18) according to one of claims 1 to 15. 18. Method for operating a variable-speed generator (6, 14, 18) according to 14 one of claims 1 to 15, characterized in that the operation is maintained when a short circuit occurs in a winding or connected thereto generator side frequency converter output stage (22). 19. The method according to claim 18, characterized in that at a short circuit in a winding or a generator-side frequency converter output stage (22) of the region in which by the short circuit a brake torque peak in the generator (14, 18) occurs, the speed range around the brake torque peak avoided or passed through as quickly as possible. 20, Method according to claim 18 or 19, characterized in that the generator (14, 18) is used as a brake. 10