WIND FARM WITH A STABILIZATION UNIT AND SUCH A STABILIZATION UNIT

Description

[0001] The present invention relates to a wind farm comprising a stabilization unit and to such a stabilization unit.

[0002] Wind farms typically consist of a large number of wind turbines connected to each other via a common wind farm network.

[0003] In order to feed the electrical power generated by the wind turbines into an electrical supply network, the wind farm network is usually also connected to the electrical supply network at a grid connection point by means of a connecting line and a transformer.

[0004] Furthermore, wind turbines typically have converters to generate the electrical power themselves, which are mostly designed to shape the current.

[0005] This means that special synchronization units are needed for network detection, in particular to be able to operate the converters properly, especially synchronized, with or on the electrical supply network.

[0006] However, such synchronization units can endanger the stability of the converter and thus the stability of the electrical supply network, especially if the synchronization units of different converters influence each other or oscillate against each other.

[0007] Particularly at weak grid connection points, i.e., grid connection points with low short-circuit power, such oscillations of the synchronization units can lead to the wind farm not being able to operate stably on the electrical supply grid or to the electrical supply grid being destabilized and therefore having to be taken off the grid.

[0008] The German Patent and Trademark Office has searched the following prior art in the priority application for the present application: DE 10 2016 124 602 A1, DE 10 2006 047 792 A1 and DE 10 2014 016 664 A1.

[0009] Article by Chi Li et al.: "Analysis and design of virtual synchronous machine based STATCOM Controller", 2014 IEEE 15TH WORKSHOP ON CONTROL AND MODELING FOR POWER ELECTRONICS (COMPEL), IEEE, June 22, 2014 (2014-06-22), pages 1-6, XP032628822, concerns a control unit of a STATCOM for emulating a virtual synchronous machine.

[0010] US 2010 / 0256970 A1 describes a device for regulating energy supply networks.

[0011] The object of the present invention is therefore to address one of the aforementioned problems, to improve the general state of the art, or to provide an alternative to what is known. In particular, it aims to improve the stability of a wind farm connected to a weak grid connection point, i.e., one with a low short-circuit power (SCR), e.g., less than 10.

[0012] According to the invention, a wind farm for feeding electrical power into an electrical supply network according to claim 1 is thus proposed.

[0013] A wind farm is therefore proposed that has a wind farm nominal output and is designed to feed electrical power into an electrical supply network.

[0014] The wind farm comprises a plurality of wind turbines, an electrical wind farm network connecting the plurality of wind turbines, which is connected to the electrical supply network at a grid connection point by means of a wind farm transformer, and a stabilization unit according to the invention, which is connected to the wind farm network and arranged between the plurality of wind turbines and the electrical supply network, in particular to increase the stability of the wind farm.

[0015] The stabilization unit can be connected, for example, to the wind farm grid or the connecting line between the wind farm transformer and the grid connection point. If the stabilization unit is located between the wind farm transformer and the grid connection point, it can emulate a synchronous machine particularly well, especially at the wind farm level. If the stabilization unit is located within the wind farm grid, stability at the wind turbine level can be further improved.

[0016] The stabilization unit itself comprises at least one electrical energy storage device configured to provide electrical power, a DC link connected to the electrical energy storage device configured to carry at least the electrical power provided by the electrical energy storage device, an inverter connected to the DC link configured to shape at least the electrical power provided by the electrical storage device via the DC link, and a control unit configured to control at least the inverter in such a way that the stabilization unit appears at the wind farm both statically and dynamically like an electromechanical synchronous machine.

[0017] The electrical storage device can, for example, be designed as an electric battery or comprise a multitude of capacitor banks. Preferably, the size of the electrical storage device is selected according to the rated power of the wind farm, and in particular such that the stabilization unit is configured to perform the functions described above or below in order to stabilize the wind farm.

[0018] In a preferred embodiment, the electrical storage device is also configured to extract electrical power from the electrical supply network or the wind farm network by means of the further components of the stabilization unit in order to charge the electrical storage device and / or to feed electrical power into the electrical supply network or the wind farm network, preferably in a voltage-forming manner, in order to stabilize the wind farm.

[0019] In a preferred embodiment, the DC link is also configured to draw electrical power from the electrical supply network or the wind farm network, in particular to charge the electrical storage device.

[0020] In a further preferred embodiment, the DC link also includes a filter, e.g. an LCL filter, which is designed to smooth voltage harmonics in the DC link.

[0021] Preferably, the inverter is also designed as a full inverter. This means that the inverter is configured both to draw electrical power from the DC circuit and feed it into the electrical supply network or the wind farm grid, and to draw electrical power from the electrical supply network or the wind farm grid and feed it into the DC link, in particular to charge the electrical storage system.

[0022] Furthermore, the control unit is preferably also designed to detect at least one state of charge of the electrical storage device in order to take this into account when controlling the inverter.

[0023] In a further preferred embodiment, the control unit stores several operating modes, the activation of which depends on the state of charge of the electrical storage device. For example, operating modes are not executed if the state of charge of the electrical storage device is less than 20 percent. This has the advantage that predetermined capacities of the electrical storage device can be reserved for specific operating modes. For example, 20 percent is reserved for the "grid fault" operating mode. In this case, the stabilization unit is configured to supply power at any time in the event of a grid fault in order to identify the fault location in the electrical supply network.

[0024] In a further preferred embodiment, the control unit is also configured to control a DC-DC converter arranged in the DC link.

[0025] Furthermore, it is specifically proposed that the stabilization unit be operated like a virtual synchronous machine.

[0026] According to the invention, it is particularly proposed to operate a battery-powered virtual synchronous machine in parallel with the wind farm to generate voltage in order to increase the stability of the wind farm.

[0027] The stabilization unit essentially works by generating tension.

[0028] It is therefore proposed that the inverter of the stabilization unit be operated with a voltage-specifying control method, in particular such that the stabilization unit provides a stable voltage for the wind farm at its output.

[0029] In a preferred embodiment, the inverter is further configured to operate in a voltage-generating manner.

[0030] The inverter can therefore also be described as a voltage-sharing inverter.

[0031] A voltage-forming inverter can provide a voltage even under no-load conditions, i.e., feed in without current / power. This allows a grid angle to be provided, particularly for current-forming wind turbines, thus ensuring a correct phase angle. In a preferred embodiment, the voltage-forming inverter or the stabilization unit does not include a synchronization unit.

[0032] Preferably, the stabilization unit further comprises a DC voltage converter arranged between the electrical storage device and the DC intermediate circuit.

[0033] A particular advantage here is that the electrical storage system is decoupled from the electrical supply network or the wind farm network, especially galvanically.

[0034] This makes it possible, for example, to charge or discharge the electrical storage regardless of the operating status of the electrical supply network or the wind farm network.

[0035] The stabilization unit is located at the grid connection point, preferably between the wind farm transformer and the electrical supply network.

[0036] The stabilization unit is therefore located near the grid connection point and not within the wind farm grid. The wind farm and the stabilization unit thus form a functional unit.

[0037] Preferably, the stabilization unit also includes a transformer that is arranged at an output of the inverter to transform the voltage of the supplied power.

[0038] The stabilization unit therefore also includes a transformer designed to connect the stabilization unit to the wind farm network and / or the electrical supply network.

[0039] The stabilization unit and the transformer preferably form a functional unit. This means, in particular, that the stabilization unit and this transformer can be located separately from each other.

[0040] In a particularly preferred embodiment, the stabilization unit and the transformer are installed in a container.

[0041] A particular advantage here is that the stabilization unit according to the invention can be retrofitted to existing wind farms in a simple and practical manner.

[0042] In a further preferred embodiment, the stabilization unit is also designed as described above or below.

[0043] The stabilization unit is designed to operate the wind farm on an electrical supply network with a low short-circuit power, e.g. a short-circuit power of less than 10, preferably less than 8, particularly preferably less than 6, particularly more preferably less than 4, particularly less than 2.

[0044] It is therefore specifically proposed that the components, such as the electrical storage system, be designed so that the stabilization unit enables a wind farm of a specific rated power to be operated at a grid connection point with a specific short-circuit power. For example, the electrical storage system could have a capacity of 10 percent of the wind farm's rated power at a short-circuit power of less than 8.

[0045] The electrical storage capacity of the stabilization unit has been designed taking into account the wind farm's nominal power output and the distance between the stabilization unit and the wind farm or the wind farm transformer.

[0046] Preferably, the electrical storage system has at least 1 percent, preferably at least 5 percent, and most preferably at least 10 percent of the wind farm's rated power.

[0047] Preferably, the stabilization unit is configured to feed active and reactive electrical power into the electrical supply network and / or into the wind farm network and / or to draw power from the electrical supply network and / or from the wind farm network.

[0048] In a particularly preferred embodiment, the stabilization unit is further configured to feed electrical power into the electrical supply network and / or into the wind farm network and / or to draw power from the electrical supply network and / or to draw power from the wind farm network.

[0049] It is therefore specifically proposed that the stabilization unit can be operated in a four-quadrant mode. This means that the stabilization unit can function as both a consumer and a producer with respect to active and reactive power. For example, the stabilization unit can feed reactive power into the electrical grid and simultaneously draw active power from it.

[0050] Preferably, the stabilization unit is designed to support the electrical supply network by means of an active power frequency characteristic and / or a reactive power voltage characteristic.

[0051] It is therefore particularly proposed that both the inverter and the control unit be configured to be operated using an active power frequency characteristic and / or a reactive power voltage characteristic, in particular in such a way that the electrical supply network is supported, preferably by means of a characteristic-corresponding injection of active and / or reactive power.

[0052] For example, the control unit has a register in which the characteristic curves are stored. These characteristic curves can then be activated as needed, for example by a grid operator or a wind farm control unit.

[0053] In a particularly preferred embodiment, the electrical storage unit has at least 20 percent of the rated power of the wind farm. This is because, according to the invention, it was recognized that the electrical storage unit must have a minimum size to perform additional functions besides stabilizing the wind farm.

[0054] The wind turbines operate, particularly by means of a full converter, essentially shaping the electricity supply.

[0055] It was further discovered according to the invention that the stabilization unit according to the invention means that no further voltage-generating sources are needed in or near the wind farm.

[0056] One particular advantage is that the stabilization unit according to the invention can be easily retrofitted to wind farms that are already operating in a current-shaping manner, and that voltage-shaping control methods can be dispensed with in wind farms yet to be built.

[0057] According to the invention, a stabilization unit, in particular for a wind farm, is further proposed, which is designed as described above or below.

[0058] The present invention will now be explained in more detail below by way of example embodiments with reference to the accompanying figures. Fig. 1 shows a schematic view of a wind turbine of a wind farm according to the invention and Fig. 2 shows a schematic structure of a wind farm according to the invention in one embodiment.

[0059] Fig. 1 Figure 1 shows a wind turbine 100 of a wind farm according to the invention, such as in Fig. 2 shown.

[0060] The wind turbine 100 comprises a tower 102 and a nacelle 104. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is mounted on the nacelle 104. During operation, the wind sets the rotor 106 into rotation, thereby driving a generator in the nacelle 104. This generator produces electricity, which is fed via a current-shaping converter to a wind turbine transformer connected to a wind farm grid.

[0061] Fig. 2 shows a schematic structure of a wind farm 1000 according to the invention in one embodiment.

[0062] The wind farm 1000, which has a wind farm nominal output, is connected to an electrical supply network 2000 at the grid connection point PCC via a connecting line 1300 having a wind farm transformer 1310 for feeding in electrical power.

[0063] The wind farm 1000 comprises a large number of wind turbines 1100, e.g. four wind turbines 100, as is preferred in Fig. 1 shown.

[0064] The wind turbines 100 are each designed to generate electricity and are connected via transformers 150 to a wind farm network 1200 that connects the multitude of wind turbines 1100.

[0065] To stabilize the wind farm 1000, a stabilization unit 1400 according to the invention is also provided, which is connected to the connecting line 1300 near the grid connection point PCC by means of a transformer 1450.

[0066] The stabilization unit 1400 comprises an electrical storage device 1410, a DC intermediate circuit 1420 with DC voltage converter 1425, an inverter 1430 and a control unit 1440.

[0067] The electrical storage unit 1410 is designed to provide electrical power, e.g. 10 percent of the wind farm's nominal power.

[0068] The DC link 1420 is connected to the electrical storage device 1410 and to the inverter 1430 via a DC-DC converter 1425. Furthermore, the DC link 1420 is configured to carry at least the electrical power supplied by the electrical energy storage device 1410. Preferably, the DC link 1420 also includes a filter with LCL characteristics.

[0069] The inverter 1430 is connected to the DC link 1420 and also to the transformer 1450. Furthermore, the inverter 1430 is configured to convert at least the electrical power supplied by the electrical storage device 1410 via the DC link 1420.

[0070] The control unit 1440 is preferably connected to the electrical storage device 1410, the DC-DC converter 1425, and the inverter 1430. Furthermore, the control unit 1440 is configured at least to control the inverter 1430 in such a way that the stabilization unit 1400 at the wind farm behaves statically and dynamically like an electromechanical synchronous machine.

[0071] The stabilization unit 1400 is therefore preferably designed to generate voltage and is operated like a virtual synchronous machine.

[0072] The stabilization unit 1400, in particular the control unit 1440 and the electrical storage unit 1410, are further preferably designed in such a way that the wind farm 1000 can be operated on an electrical supply network with a low short-circuit power.

[0073] For this purpose, the electrical storage unit 1410 is preferably designed taking into account the wind farm's nominal power and the distance between the stabilization unit 1400 and the wind farm 1000, in particular taking into account the grid impedance between the wind farm transformer 1310 and the stabilization unit 1400.

[0074] Furthermore, the stabilization unit 1400 is designed to feed electrical power into the electrical supply network 2000 and / or into the wind farm network 1200 and / or to draw power from the electrical supply network 2000 and / or to draw power from the wind farm network 1200.

[0075] Furthermore, the stabilization unit 1400 is designed to support the electrical supply network 2000 by means of an active power frequency characteristic and / or a reactive power voltage characteristic.

[0076] The present invention offers a number of advantages, which are listed below, and not exhaustively: 1. Increasing the stability of a wind farm connected to a weak grid connection point can be achieved by using the stabilization unit according to the invention, whose rated power is less than 10% of the park's power. This provides a particularly cost-effective alternative to previously known solutions. 2. Because the stabilization unit is operated like a virtual synchronous machine, the power required for stabilizing the wind farm can be reduced many times over compared to, for example, known STATCOMs. This also makes the solution according to the invention more cost-effective than previously known alternatives. 3. The stabilization unit is fundamentally designed to provide ancillary services and can be easily configured for this purpose through the dimensioning and control described above. 4.The stabilization unit can also be designed to be installed in so-called containers. This means it can be easily transported and implemented in existing wind farms.

Claims

1. A wind farm (1000), having a wind farm nominal power, for feeding electrical power into an electrical supply network (2000), comprising: - a plurality of wind power installations (1100), - an electrical wind farm network (1200) which connects the plurality of wind power installations (1100), which - is connected to the electrical supply network (2000) at a network connection point (PCC) by means of a wind farm transformer (1310), and - a stabilization unit (1400) which is connected to the wind farm network (1200) and is arranged between the plurality of wind power installations (1100) and the electrical supply network (2000), in order to increase the stability of the wind farm (1000), at least comprising: - an electrical energy storage device (1410) which is set up to provide an electrical power, - a direct voltage intermediate circuit (1420) which is connected to the electrical energy storage device (1410) and which is set up to conduct at least the electrical power provided by the electrical energy storage device (1410), - an inverter (1430) which is connected to the direct voltage intermediate circuit (1420) and which is set up to form at least the electrical power provided by the electrical storage device (1410) via the direct voltage intermediate circuit (1420), and - a control unit (1440) which is set up to control at least the inverter (1430) in such a way that the stabilization unit (1400) at the wind farm (1000) appears, statically as well as dynamically, like an electromechanical synchronous machine; and - the stabilization unit (1400) is set up to operate the wind farm (1000) on an electrical supply network (2000) with a low short circuit power, wherein - the stabilization unit (1400) is arranged at the network connection point (PCC), preferably between the wind farm transformer (1310) and the electrical supply network (2000); and - the stabilization unit (1400) operates in a substantially voltage impressing manner and the wind power installation (100) or the plurality of wind power installations operates in a substantially current impressing manner, wherein - the electrical storage device (1410) of the stabilization unit (1400) has been designed taking into account the wind farm nominal power and a distance between the stabilization unit (1400) and the wind farm (1000).

2. The wind farm (1000) as claimed in claim 1, wherein - the stabilization unit (1400) further comprises a DC-DC converter (1425) which is arranged between the electrical storage device (1410) and the direct voltage intermediate circuit (1420).

3. The wind farm (1000) as claimed in one of the preceding claims, wherein - the stabilization unit (1400) further has a transformer (1450) which is arranged at an output of the inverter (1430), in order to transform the voltage of the power provided.

4. The wind farm (1000) as claimed in one of the preceding claims, wherein - the electrical storage device (1410) has at least 1 percent, preferably at least 5 percent, particularly preferably at least 10 percent, of the wind farm nominal power.

5. The wind farm (1000) as claimed in one of the preceding claims, wherein - the stabilization unit (1400) is set up to feed electrical power into the electrical supply network (2000) and / or into the wind farm network (1200) and / or to extract it from the electrical supply network (2000) and / or from the wind farm network (1200).

6. The wind farm (1000) as claimed in one of the preceding claims, wherein - the stabilization unit (1400) is set up to support the electrical supply network (2000) by means of an active power frequency characteristic and / or a reactive power voltage characteristic.

7. The wind farm (1000) as claimed in one of the preceding claims, wherein - the wind power installations (100) or the plurality of wind power installations (1100) operate in a substantially current impressing manner by means of a full converter.

8. A stabilization unit (1400) for a wind farm (1000) having a plurality of wind power installations (1100), for connecting to a wind farm network (1200), at least comprising: - an electrical energy storage device (1410) which is set up to provide an electrical power, - a direct voltage intermediate circuit (1420) which is connected to the electrical energy storage device (1410) and which is set up to conduct at least the electrical power provided by the electrical energy storage device (1410), - an inverter (1430) which is connected to the direct voltage intermediate circuit (1420) and which is set up to form at least the electrical power provided by the electrical storage device (1410) via the direct voltage intermediate circuit (1420), and - a control unit (1440) which is set up to control at least the inverter (1430) in such a way that the stabilization unit (1400) at the wind farm (1000) appears, statically as well as dynamically, like an electromechanical synchronous machine, and - the stabilization unit (1400) is set up to operate the wind farm (1000) on an electrical supply network (2000) with a low short circuit power, wherein - the stabilization unit (1400) is arranged at the network connection point (PCC), preferably between the wind farm transformer (1310) and the electrical supply network (2000); and - the stabilization unit (1400) operates in a substantially voltage impressing manner and - the wind power installation (100) or the plurality of wind power installations operates in a substantially current impressing manner, wherein - the electrical storage device (1410) of the stabilization unit (1400) has been designed taking into account the wind farm nominal power and a distance between the stabilization unit (1400) and the wind farm (1000).

9. The stabilization unit (1400) as claimed in claim 8 , further comprising: - a DC-DC converter (1425) which is arranged between the electrical storage device (1410) and the direct voltage intermediate circuit (1420).

10. The stabilization unit (1400) as claimed in one of claims 8 to 9, further comprising: - a transformer (1450) which is arranged at an output of the inverter (1430), in order to transform the voltage of the power provided.