AT511782A1 - ENERGY EQUIPMENT, IN PARTICULAR WIND POWER PLANT - Google Patents

Abstract

An energy generation plant, in particular wind power plant, has a drive shaft connected to a rotor (1), a generator (13) connected to a network (9), a differential gear (10 to 12) from which a drive with an electric differential drive (18 ), and an electrical energy store (32), wherein the generator (13) has an exciter control (35) and wherein the differential drive (18) is connected to a frequency converter (19). Both the exciter control (35) and the frequency converter (19) of the differential drive (14) are connected to the energy store (32).

Description

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The invention relates to a power transmission plant, in particular a wind power plant, having a drive shaft connected to a rotor, a generator connected to a network

Differential gear, of which a drive is connected to an electric differential drive, and with an electrical energy storage, wherein the generator has an exciter control and wherein the differential drive is connected to a frequency converter.

Wind power plants are becoming increasingly important as energy production plants. As a result, the percentage of electricity generated by wind is continuously increasing. 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 mentioned higher demands on the power quality, here highly dynamic or even in case of network faults controllable plants gain special importance.

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 only be connected to the medium-voltage network by means of transformers and (b) the frequency converters required for the variable speed are very powerful and therefore a source of efficiency losses. Alternatively, therefore, so-called differential drives are used, which directly connected to the medium-voltage network externally-excited medium-voltage synchronous generators in combination with a differential gear and an auxiliary drive, which preferably has a permanent magnet

Synchronous machine in combinatit> * n * ^ i £ * provides a low-power ÖGB'i ^ frequency inverter use.

WO 2010/121783 A shows a differential system with an electric servo drive with a permanent magnet synchronous machine in combination with an IGBT frequency converter.

The excitation of externally excited medium-voltage synchronous generators, for example, by means of a so-called static excitation, which essentially supplies the rotor winding of the synchronous generator via slip ring with regulated excitation current. Alternatively, so-called brushless excitation devices are used, which usually have an exciter machine with a rotating diode rectifier arranged at the end of the synchronous generator facing away from the drive. The exciter machine is also supplied with regulated excitation current, which, however, in comparison to the former solution with much lower currents is the Auslangen. The control of the excitation device has essentially the tasks (a) to regulate the amplitude of the voltage at the generator terminals constant to a predetermined value, (b) to set the predetermined power factor (cos-phi) and (c) to protect the field winding from overloading.

The new standards for grid feeding of

Energy recovery systems, in particular wind turbines, make it necessary that in the case of network faults, the controllability of both the differential drive and the exciter control is maintained throughout the duration of the network fault. In addition, state-of-the-art excitation control systems are only capable if they are equipped with a complex UPS system.

The invention is therefore based on the task of taking appropriate precautions so that the full function of differential drive and exciter control is maintained at the least possible expense.

This object is achieved with an energy recovery system having the features of claim 1.

Preferred embodiments of the invention are the subject of I I.

«· · J * · V f ·

Dependent claims. * ·· *

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

Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 shows the principle of a differential gear with an electric differential drive according to the prior art, shows the principle of a static excitation control according to the prior art, shows a possible emergency power supply of a differential drive shows by way of example the course of the reactive current output of a third-excited synchronous generator during a network fault, with and without emergency power supply for the excitation control, shows the configuration according to the invention of the emergency power supply for the excitation control.

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

Rotor power = Rotor area * Power coefficient * Wind speed3 * Air density / 2 where the power coefficient depends on the speed of rotation (= blade tip speed to wind speed ratio) 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 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. Between main gear 3 and generator 13 is a differential stage 4, which is driven by the main gear 3 via a planet carrier 10 of the differential stage 4. The generator 13 B preferably a third-excited medium voltage synchronous generator - 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 to ensure a variable speed of the rotor 1, a constant speed of the generator 13 and on the other hand to regulate the torque in the 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 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.

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 A') times rotor power. Accordingly, a large speed range basically requires a correspondingly large dimensioning of the differential drive 14. That is, the smaller the necessary speed range on the drive shaft, the smaller the required differential drive and, consequently, the effort for its production and operation. Turbomachines of any kind, such as Wind turbines, water turbines or BPumpen, plants for the production of energy from ocean currents, or any type of industrial plants, which operate at a limited speed range, are therefore the ideal application for differential systems.

Fig. 2 shows the principle of a static exciter device with the essential components: uninterruptible power supply (UPS), exciter transformer for adjusting the voltage level (T), controlled rectifier (GR), de-excitation device (EE), exciter winding (EW) and exciter control (ER ). The components UPS and de-energizing equipment (EE) are optional and only necessary if a uniform control dynamics is required in case of network faults.

Fig. 3 shows a possible basic structure of the electrical part of a differential system according to Fig, 1. With the 5 I t < ··· I »» * I f »» ··· * ·

Three-phase machine 18 is a * so-called * Fr «eznenzumrichter-Endstuf e 22 connected. This consists essentially of controlled IGBT full bridge 19, controller, DC link capacitors 20,

Current measurement and DC fuses 21. The cooling, in particular of the IGBTs, is preferably water cooling, but can also be carried out as air cooling.

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 resistors is preferably also connected here. This brake chopper 24 can be used at e.g. Power failure also convert excess energy into heat.

In addition, it is used for power generation plants

Differential systems also used an emergency power supply 25. This emergency power supply 25 preferably consists essentially of high-performance capacitors connected to the DC voltage intermediate circuit 23. To make the voltage level or the operating voltage of these high-performance capacitors optimal or flexible, they can be connected via DC / DC converter to the DC voltage intermediate circuit 23.

Depending on the operation of the power plant, the emergency power supply 25 may also take over the function of the brake chopper 24 in whole or in part. Between DC voltage intermediate circuit 23 and network 26, the same frequency converter output stages 22 are preferably used.

In the case of a differential system like. Fig. 1 works this both regenerative and motor. That is, in the motor mode, the machine-side frequency converter output stage 22 operates as a speed / torque control inverter and the line-side frequency converter output stage 22 as a rectifier module. In generator mode, the machine-side frequency converter output stage 22 operates as a controlled rectifier module and the network-side frequency converter output stage 22 as a so-called active grid feed module (inverter),

Thus, the network-side frequency converter output stage 22 of the

Network operators required Str, omqwa * l "ität * 3) irite, t» i «n meet, a so-called LCL filter 27 is provided. In addition, there are fuses 28, circuit breaker 29 and a power transformer 30, which adapts the preferably low voltage of the differential drive to the voltage of the network 26.

Fig. 4 shows the course of - Blindstromabgabe a third-excited synchronous generator during a power failure, with (continuous line) and without (dashed line) emergency power supply for the excitation control. In this case, a rapid break in the mains voltage from 100¾ to 10% is assumed. The mains voltage then remains at this level for ls and then goes back to the original output value. Usually, the grid codes require that during a mains voltage dip, the power generation systems feed at least the rated current as reactive current into the grid. Fig. 4 shows that you can not meet the grid codes without emergency power supply for the excitement, because it is no longer possible after about 200ms to give reactive power in the network (dashed line). That is exactly what is important to support the network.

Another advantage is that the generator can be more easily maintained at rated speed when the excitation remains on.

In addition, during this voltage dip, the reactive current output by the generator 13 can not be regulated, or adjusts depending on the mains voltage break-in duration and size in accordance with the design parameters of the synchronous generator. As a result, you can not meet any deviating requirements.

5 shows the inventive design of the uninterruptible emergency power supply 25 for the frequency converter 19 of the differential drive 18, which is preferably a low-voltage frequency converter, and the exciter device 35 of the generator 13. As already described with reference to FIG. 3, so-called IGBTs are also shown here. Full bridges 19 connected to the three-phase machine 18 or via transformer 30 to the medium-voltage network 26. The DC voltage intermediate circuit 23 is the connecting element for the individual IGBT full bridges 19. The capacitors 31 connected in the DC voltage intermediate circuit are preferably foil capacitors and serve, above all, for smoothing the intermediate circuit voltage or the ripple current. To protect the

Frequency converter against overvoltage is here preferably connected to a so-called brake chopper 24 with resistors controlled via an IGBT half-bridge. This brake chopper 24 has the task of sucking any occurring in the DC voltage intermediate circuit 23 voltage peaks' and thereby avoid system shutdown due to overvoltage. To be at e.g. Mains faults to ensure the power supply of the frequency converter 19, an emergency power supply 25 is connected, which is preferably connected to the DC voltage intermediate circuit 23

High performance capacitors 32 exists. The emergency power supply 25 may, however, instead of the high-performance capacitors also have accumulators or other electrical storage media.

The rated voltage of the DC intermediate circuit 23 is in the case of the use of 1700V IGBT modules usually around 1050Vdc and should ideally be controlled in a range of a maximum of 1150Vdc and minimum lQOOVdc, so as not to restrict the control capacity of the differential drive. If the emergency power supply 25 were to be designed for this voltage range, it would become very large and consequently correspondingly expensive due to the (a) necessary high number of parallel capacitors and (b) the small realizable range between the maximum and minimum permitted voltage of the DC intermediate circuit. In order to optimally design the voltage level or the operating voltage of these high-power capacitors, they are therefore preferably connected to the DC voltage intermediate circuit 23 via a DC / DC converter consisting, for example, of an IGBT half-bridge 33 and an inductor 34. The maximum voltage for the high power capacitors 32 may then be set to e.g. 300-400Vdc be limited. Preferably, the DC / DC converter 33 described above is a bidirectional buck converter. Optionally, the DC / DC converter can also be designed with IGBT full bridge.

The excitation device 35 of the synchronous generator 13 operates in contrast to the frequency converter 19 at a much lower voltage level or operating voltage, namely typically in a range of about 80Vdc to 130Vdc. If you were to try here to realize the supply of the excitation device directly from the DC voltage intermediate circuit 23 to use the emergency power supply 25, this would be due to the high

Voltage difference with a »* DC / BC-Wan« 14 * It is extremely difficult to realize. With a further DC / DC converter, consisting for example of an IGBT half-bridge 36 and an inductance, which is at the voltage level of the high-power capacitors 32, a power supply for the excitation winding with a voltage in the range of 80-13OVdc can be realized with simple means. In this case, a unidirectional DC converter (unidirectional buck converter) is preferably designed in the form of an IGBT full bridge, but may also consist of an IGBT half bridge or one or three chopper modules (half bridge consisting of a diode and an IGBT) Advantage that standard power converter hardware can be used and the output current ripple is smaller than with a half-bridge and thus the filtering is facilitated at the output Depending on the design of energy storage, an additional capacitor at the

DC-DC input may be required because the high current ripple reduces the life of the energy storage. The filter of the buck converter 35 can be used with regard to (a) control dynamics, (b)

Current ripple (improved power quality of the generator), (c)

Common mode voltage (avoidance of bearing currents) can be optimized.

If a fast de-energizing is relevant for the application, a bidirectional DC-DC converter can be used. This can be de-energized with the negative DC link voltage. Preferably, the bidirectional DC-DC converter can be implemented by an IGBT full bridge (standard converter), wherein the field winding is switched to two half-bridge outputs and a half-bridge output remains free, but can also be realized by two IGBT half-bridges.

For the purposes of the invention, this means that in the ideal case the voltage level or the operating voltage of the emergency power supply 25 is between the necessary operating voltage levels of the DC intermediate circuit 23 and the exciter control 35. In order for an optimal dimensioning of the energy storage 32 is ensured with simultaneous use by both frequency 16 and excitation control 35.

The energy flow for the supply of the excitation control 35 takes place in normal operation via the network-side IGBT full bridge 19, DC / DC converter 33,

High Performance Capacitors> 2 * and 'Oe / DO Wandd'isr 36.

The main advantages of the configuration described are (a) the DC link voltage of the DC intermediate circuit 23 can also be regulated in case of network errors, (b) the energy content of the energy storage 32 can be better utilized, (c) the excitation of the synchronous generator 13 can also be regulated in the event of a power failure and (d) the excitation control 35 can be realized easily and inexpensively.

The described embodiments are only examples and are preferably used in wind turbines, but are also feasible in technically similar applications. This concerns v.a. Hydro turbines or pumps and systems for the extraction 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 devices driven by the flow medium, for example water.

In addition, what is said also applies to any type of system which, due to the general conditions, uses differential drives to realize variable speed on the drive shaft, that is to say any type of drives for (industrial) systems which are operated with limited speed range.

Claims (1)

Energy generation plant, in particular a wind power plant, having a drive shaft connected to a rotor (1), a generator (13) connected to a network (9), a differential gear (10 to 12), of which a drive is connected to an electric differential drive (18), and to an electrical energy store (32), wherein the generator (13) has an exciter control (35) and wherein the differential drive (18) is connected to a frequency converter (19), characterized in that both the excitation control (35) and the frequency converter (19) of the differential drive (14) to the energy storage (32) are connected. Energy production plant according to claim 1, characterized by an emergency power supply (25) containing the energy store (32). Energy production plant according to claim 1, characterized in that the exciter control (35) contains the energy store (32). Power generation plant according to one of claims 1 to 3, characterized in that the differential drive (18) via the frequency converter (19) with a DC intermediate circuit (23) is connected. Power generation plant according to one of claims 1 to 4, characterized in that the DC intermediate circuit (23) by means of a DC / DC converter (33) to the energy storage device (32) is connected. Energy recovery system according to one of claims 1 to 5, characterized in that the excitation control (35) by means of a DC / DC converter (36) to the energy storage device (32) is connected. Power generation plant according to one of claims 1 to 6, characterized in that the DC / DC converter (33, 36) is a preferably bidirectional DC chopper. Energy recovery plant »* naeh * β · ί · ήβ» ι ** άβΗ claims 1 to 7, characterized in that the DC / DC converter {33, 36) IGBT full bridges and / or thyristors. Energy production plant according to one of claims 1 to 9, characterized by an exciter control (35) for controlling the voltage and / or the reactive current of the generator (13). Energy production plant according to one of claims 1 to 10, characterized in that the operating voltage of the energy store (32) between the operating voltages of the DC intermediate circuit (23) and the exciter control (35)