Claims:We claim:

1. A wind turbine (1) comprising
- a generator (12, 12a, 12b, 12c, 12d),
- a main converter (13, 13a, 13b, 13c, 13d) connected to the generator (12, 12a, 12b, 12c, 12d) and
- a yaw system (20, 20a, 20b, 20c, 20d)
characterized by
- a power electronic system (15, 15a, 15b, 15c, 15d) for supplying electrical power to the yaw system (20, 20a, 20b, 20c, 20d) connected with the generator (12, 12a, 12b, 12c, 12d) and the yaw system (20, 20a, 20b, 20c, 20d),
- wherein the power electronic system (15, 15a, 15b, 15c, 15d) comprises a rectifier (16, 16a, 16c, 35, 35d), an inverter (17, 17a, 17b, 17c, 17d) and a DC link (18, 18a, 18b, 18c, 18d) between the rectifier (16, 16a, 16c, 35, 35d) and the inverter (17, 17a, 17b, 17c, 17d) and
- wherein the power electronic system (15, 15a, 15b, 15c, 15d) comprises an energy storage unit (19, 19a, 19b, 19c, 19d), which is connected to the DC link (18, 18a, 18b, 18c, 18d).

2. The wind turbine (1) according to claim 1 characterized by a power back-up system (36, 36d) for supplying electrical power to the power electronic system (15, 15a, 15b, 15c, 15d) and/or to the generator (12, 12a, 12b, 12c, 12d) connected to the power electronic system (15, 15a, 15b, 15c, 15d).

3. The wind turbine (1) according to claim 2 characterized in that the power back-up system (36, 36d) is a photovoltaic system.

4. The wind turbine (1) according to claim 3 characterized in that the photovoltaic system (36, 36d) comprises at least one photovoltaic panel.

5. The wind turbine (1) according to any of the preceding claims characterized in that energy storage unit (19, 19a, 19b, 19c, 19d) is a battery pack.

6. The wind turbine (1) according to any of the preceding claims characterized in that the power electronic system (15, 15a, 15b, 15c, 15d) having a power electronic system controller (22, 22a, 22b, 22c, 22d) for controlling the power electronic system (15, 15a, 15b, 15c, 15d).

7. A method for operating a wind turbine (1) according to one of the claims 1 to 6 in situation of high winds and disconnected from the grid, wherein the method comprises the step of supplying electrical power generated by the generator (12, 12a, 12b, 12c, 12d) over the power electronic system (15, 15a, 15b, 15c, 15d) to the yaw system (20, 20a, 20b, 20c, 20d) for yawing the wind turbine (1).

8. The method according to claim 7 characterized by supplying electrical power to the energy storage unit (19, 19a, 19b, 19c, 19d) for charging the energy storage unit (19, 19a, 19b, 19c, 19d).

9. The method according to claim 7 characterized by discharging the energy storage unit (19, 19a, 19b, 19c, 19d) and supplying the electrical power to the yaw system (20, 20a, 20b, 20c, 20d).

10. The method according to one of the claims 7 to 9 characterized by pitching the blades (6) in a non-feathering position for example an angle in a range between 80° to 89°, preferred 85°.

11. The method according to any of the preceding claims characterized by continuously yawing the wind turbine (1) aligning to the wind direction.

12. The method according to any of the preceding claims characterized by driving the rotor (5) by wind with low rpm for generating electrical power.

13. The method according to claim 12 characterized in that the low rpm is in a range between 1 rpm and 10 rpm, preferred between 1 rpm and 5 rpm and more preferred between 1 rpm and 2 rpm.

14. The method according to any of the preceding claims characterized by providing a power electronic system controller (22, 22a, 22b, 22c, 22d) for controlling the power electronic system (15, 15a, 15b, 15c, 15d) in different operation modes, especially for charging or discharging the energy storage unit (19, 19a, 19b, 19c, 19d) and/or for supplying electrical power to the yaw system (20, 20a, 20, 20c, 20d).

15. A method for operating a wind turbine (1) according to one of the claims 1 to 6 in situation of non-high winds and disconnected from the grid, wherein the method comprises the step of supplying electrical power generated by a power back-up system (36, 36d) over the power electronic system (15, 15a, 15b, 15c, 15d) to the yaw system (20, 20a, 20b, 20c, 20d) and/or to the energy storage unit (19, 19a, 19b, 19c, 19d).

16. The method according to claim 14 characterized in that the power back-up system (36, 36d) is a photovoltaic system.

17. The method according to claim 15 or 16 characterized in that once the rotor (5) rotates in a range between 1 rpm to 10 rpm the method comprises the steps of the method according to one of the claims 7 to 14.
, Description:FIELD OF INVENTION

The invention relates to a wind turbine having a power electronic system for supplying electrical power to a yaw system and a method for operating such a wind turbine.

BACKGROUND

The wind industry trends point out that the entire industry moves towards large wind turbine rotor diameters in both onshore and offshore installation scenarios. The economic benefits of such large rotor diameters come with a certain cost in terms of subcomponent design. To overcome this, designers have to ensure the safety and stability of their subcomponents in every given situation which might occur in the field.

One alternative would be to design the components with increased safety margins in terms of materials but that can have a negative effect during operation or can prove to be extremely costly and in the end, the costs of the entire turbine to point out towards a very costly wind turbine.

A second alternative approach which is also the preferred one is to find solutions which can result in optimized components and at the same time, provide the entire system, the safety and stability, it requires and deserves.

In this situation, by optimally running subcomponents in conditions that avoid scenarios with high stresses on themselves is the key action to be performed by the modern wind turbine technologies in terms of subcomponent protection. Consequently to such actions, the subcomponents costs can be kept under control and the designers can provide optimal techno-commercial solution to the markets worldwide.

The most important component in the wind turbine is by far the blade. The design requirements for blades become more challenging once the wind turbine operates with increased diameters and are stressed by rough environmental conditions.

One extremely stressful situation for the wind turbine blades are the high wind conditions present during typhoon or cyclonic conditions. During a typhoon, winds can reach even 50 m/s, but even so, the turbine must survive and ride through the typhoon without any damage to any of its subcomponents. Obviously, the blades are the most exposed subcomponent and they have to be designed, operated and prepared for typhoon ride-through.

Usually, the wind turbine control system takes into consideration this situation and the first action to protect the blade in such high wind scenario is to stop the wind turbine, bring the blade into feathering position (90 degree position) and actively yaw the wind turbine so the wind turbine is aligned with the wind. In this operation point, the stress to the blades is reduced and the turbine can successfully pass the high winds. Yawing in high wind conditions is ensured by the controller because the wind turbine is stopped and the wind turbine is powered by the normal supply via the wind turbine’s auxiliary supply. The power for yawing is taken from the normal utility grid and the yaw drives are yawing the turbine in accordance with the references given by the turbine controller.

The situation becomes complicated and problematic, in case the normal utility grid experiences difficulties and the supply is interrupted. In this situation, the turbine controller is powered off and has no grip and control over the entire wind turbine. Consequently, the yaw system is not supplied anymore and is not adjusting the azimuth of the wind turbine towards the changing wind conditions, leaving the turbine standing in the last position the power supply was on and controlled by the controller.

In case the wind condition changes, the direction and the angle difference between the turbine azimuth and the wind direction increases. This causes the forces and momentums actively present on the blades to increase as well and have the potential to drive the component into instability points. Such scenario creates harmful conditions that might even permanently damage the blade.

Turbine designers have already started to take into consideration this scenario and analyze solutions to overcome this issue, by offering a secondary power supply to the wind turbine. The secondary power supply can supply the auxiliaries and can safely control the turbine in this situation of high winds and no grid.

Different solutions by means of external diesel generators or uninterruptable power supplies are already present in the market and have the potential to give sustainable power to the auxiliaries.

EP 2 753 825 describes a system and method for generating auxiliary power for a wind turbine. The wind turbine comprises an auxiliary converter having a transformer and an inverter. The auxiliary converter is connected to an auxiliary power distribution system comprising a diesel generator or batteries. The disadvantage of this concept is that the diesel generator will be run out of fuel or the batteries will be run out of energy so a pitching of the blades will not be possible. In result, in an event that the blades can no longer be aligned with the wind, there will be high loads to the blades.

EP 2 169 219 describes a system and method for controlling a wind turbine during loss of grid power and changing wind conditions. The method comprises the steps of continuously adjusting a blade pitch angle of each blade while keeping the orientation of the wind turbine substantially constant. The disadvantage of this concept is that during the pitching of the blades there could occur high loads to the blades. So the risks of damages are very high.

OBJECT OF THE INVENTION

An object of the present invention is to provide a wind turbine and an operation mode for a wind turbine which overcomes the disadvantages of the prior art and reduces the risks of damages.

SUMMARY OF THE INVENTION

The present invention discloses a wind turbine comprising besides others a generator, a main converter connected to the generator, a yaw system and an energy storage unit, wherein the wind turbine further comprises a power electronic system for supplying electrical power to the yaw system, which is connected with the generator and the yaw system, wherein the power electronic system comprises a rectifier, an inverter and a DC link between the rectifier and the inverter and wherein the energy storage unit is connected to the DC link.

In a further embodiment, the wind turbine comprises a power back-up system for supplying electrical power to the power electronic system and/or to the generator connected to the power electronic system. Preferably the power back-up system is a photovoltaic system. Advantageously the photovoltaic system comprises at least one photovoltaic panel.

In a further preferred embodiment of the wind turbine, the energy storage unit is a battery pack.

In a further preferred embodiment of the wind turbine, the power electronic system has a power electronic system controller for controlling the power electronic system. Especially the power electronic system controller is configured to control the power electronic system in different operation modes, namely supplying electrical power from the generator to the yaw system and/or to the energy storage system or discharging the energy storage unit for supplying electrical power to the yaw system and keeping a stable DC link.

Another aspect of the present invention regards to a method for operating said wind turbine.

The method for operating said wind turbine in the situation of high winds and disconnected from the grid, comprises the step of supplying electrical power generated by the generator over the power electronic system to the yaw system for yawing the wind turbine. This manages the yaw system, especially the yaw drives, for yawing the wind turbine into the wind direction. To ensure that the generator can generate sufficient power, the wind turbine has to rotate within a range between 1 rpm to 10 rpm, preferred 1 rpm to 5 rpm and more preferred 1 rpm to 2 rpm. This method makes sure that the wind turbine is always aligned in a correct direction to the wind direction. So the load to the blades is reduced. Consequently the risk of damages is lowered.

In a further preferred embodiment, the method comprises the step of supplying electrical power to the energy storage unit for charging the energy storage unit. Charging the energy storage unit could take place at the same time while supplying electrical power to the yaw system, if the generator generates sufficient electrical power. It should be pointed out that supply of the electrical power to the yaw system has higher priority and will occur first. In the event when the yaw system does not need electrical power, the energy storage unit will be charged. This is controlled by the power electronic system, especially by the power electronic system controller. A full charged energy storage unit makes sure that in any event the yaw system can receive sufficient electrical power and permanently controls the DC link of the entire system. By doing so, the security for the wind turbine is increased and the risk of damages is lowered.

In a further preferred embodiment, the method comprises the step of discharging the energy storage unit and supplying the electrical power from the energy storage unit to the yaw system. This takes place if the generator does not generate sufficient electrical power up to no electrical power. In result, it is possible that the yaw system receives electrical power from the generator as well as from the energy storage unit or by the energy storage unit alone. In any case this is controlled by the power electronic system, especially by the power electronic system controller. The electrical power from the generator and the energy storage unit will be brought together at the DC link of the power electronic system and through the inverter of the power electronic system, especially through the yaw system-sided inverter, directs the electrical power to the yaw system. This allows sufficiently providing electrical power for the yaw system.

In a further preferred embodiment, the method comprises the step of pitching the blades in a non-feathering position. Especially this position includes an angle between 80° to 89°, preferred 85°. It should be understood that the blades in 90° position, also called feathering position, are aligned parallel to the airflow and in 0° position the blades are aligned vertical to the airflow. Advantageously, in this position the rotor can rotate in range between 1 rpm and 10 rpm, preferred 1 rpm and 5 rpm, and more preferred 1 rpm and 2 rpm. This allows generating sufficient electrical power for at least driving the yaw system.

In a further preferred embodiment, the method comprises the step of driving the yaw system continuously yawing the wind turbine aligning to the wind direction. This makes sure that the wind turbine is always correctly aligned to the wind direction. So the load to the blades reduces. Consequently the risk of damages is lowered. At the same time it is possible to generate sufficient electrical power for the yaw system.

In a further preferred embodiment, the method comprises the step of driving the rotor by wind with low rpm for generating electrical power. Hereby, the rotor rotates in range between 1 rpm and 10 rpm, preferred 1 rpm and 5 rpm, and more preferred 1 rpm and 2 rpm.

In a further preferred embodiment, the method comprises the step of providing a power electronic system controller for controlling the power electronic system in different operation modes, especially for charging or discharging the energy storage unit and/or for supplying electrical power to the yaw system. In any case the power electronic system controller is configured to operate in that way that supplying the yaw system with electrical power has high priority and takes place before all other operations.

Additionally, the present invention considered the wind turbine and the method for operating said wind turbine in situation of non-high winds and disconnected from the grid. In other words, the high winds have passed, but the wind turbine is disconnected from the grid. In this case it could happen that the rotor does not rotate with enough speed and the generator could not produce enough electrical power. Therefore the wind turbine comprises a power back-up system, which generates electrical power. The method comprises the step of supplying electrical power generated by a power back-up system over the power electronic system to the yaw system and/or to the energy storage unit. The power back-up system can generate electrical power additional to the generator or alone. This makes sure that in any event the yaw system receives sufficient electrical power to align the wind turbine to the wind direction.

In a preferred embodiment the power back-up system is a photovoltaic system.

In a preferred embodiment of this method, is provided that once the rotor rotates in a range between 1 rpm to 10 rpm this method comprises the steps of the method for operating the wind turbine in situation of high winds and disconnected from the grid. This means that under the conditions of non-high winds and disconnected from the grid the wind turbine can operate same as under conditions of high winds and disconnected from the grid. Therefore the wind turbine has to pitch and or yaw according to the present wind direction.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be explained in more detail with respect to exemplary embodiments with reference to the enclosed drawings, wherein:

Figure 1 shows a schematic view of a wind turbine;

Figure 2 shows a schematic view of the yaw drive concept in general for a wind turbine according to Fig. 1;

Figure 3 shows a schematic view of a yaw drive concept of a wind turbine for offshore applications;

Figure 4 shows a schematic view of a yaw drive concept of a wind turbine for onshore applications;

Figure 5 shows a schematic view of a yaw drive concept with a back-up system of a wind turbine for offshore applications and

Figure 6 shows a schematic view of a yaw drive concept with a back-up system of a wind turbine for onshore applications.

The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 depicts a schematic view of a wind turbine (1) with a tower (2) and a nacelle (3). Depending on given requirements, the wind turbine (1) can be used for offshore or onshore applications. The nacelle (3) is rotatable mounted on the tower (2). The nacelle (3) incorporates a number of components of a drive train chain (4) comprising a rotor shaft (not shown) for example. The nacelle (3) also incorporates a generator (see Figs. 2 to 6) connected with a plurality of electrical components (see Figs. 2 to 6), which are described in detail later. Further the nacelle (3) comprises a yaw system (see Figs. 2 to 6) for rotating the nacelle (3). Said rotor shaft is connected to a rotor (5). The rotor (5) comprises three rotor blades (6) which are mounted to a hub (7). The hub (7) is connected to the rotor shaft of the drive train chain (4). The rotor blades (6) are adjustably mounted on the hub (7). This is realized by means of pitch drives (8), said pitch drives (8) being part of a pitch system (see Figs. 2 to 6). The pitch system controls the rotor speed to given set points. By means of pitch-drives (8), the rotor blades (6) may be moved about a rotor blade (6) axes into different pitch positions, said rotor blade (6) axis extending in an axial direction of the rotor blades (6). Each rotor blade (6) is connected to the hub (7) via its pitch-drive (8). The nacelle (3) is covered by a nacelle cover (9), which has a nacelle cover interface (10). The hub (7) is covered by a spinner (11).

In the following, based on Figure 2 is explained an embodiment of a yaw drive concept for a wind turbine (1) in a condition of high winds and disconnected utility grid and a method for operating the wind turbine (1) under such conditions in general. It should be pointed out that the method for operating the wind turbine (1) is the same for all described embodiments. The different embodiments differ in the used components, which differs from one wind turbine type to another. And for all embodiments applies, that the blades in 90° position, also called feathering position, are aligned parallel to the airflow and in 0° position the blades aligned vertical to the airflow.

Figure 2 depicts a generator (12), which is connected with a main converter (13). The main converter (13) is disconnected from a transformer (14) at a point of common coupling to a utility grid. So the wind turbine (1) cannot supply or receive electrical power from or to the utility grid. Parallel to the main converter (13) the generator (12) is connected to a power electronic system (15). The power electronic system (15) comprises a rectifier (16) and an inverter (17), which are coupled over a DC-link (18). Especially the rectifier (16) is a generator-sided rectifier (16) and the inverter (17) is a yaw system-sided inverter (17). The DC link (18) is connected with an energy storage unit (19). The power electronic system (15) supplies electrical power to the yaw system (20) for yawing the wind turbine (1). The pitch system (21) pitches the blades (6) in a non-feathering position. This pitching of the blades (6) takes place when the wind turbine controller set the wind turbine (1) in a high wind configuration. After this the blades (6) stay in the non-feathering position. The aligning of the wind turbine (1) is only conducted by a continuously yawing over the yaw system (20). Consequently the loads to the blades (6) are regulated because of the alignment of the wind turbine (1). It should be pointed out that under the described situation the yaw system (20) and the pitch system (21) are also disconnected from the utility grid, so they cannot receive any power from there. The yaw system (20) receives the electrical power from the power electronic system (15).

The situation of high winds and the utility grid is disconnected from the wind turbine (1) means that a wind turbine controller (not shown) is completely bypassed since it has no supply. It could happen that the disconnection from the utility grid takes a couple of days or especially for onshore applications for some weeks. The wind turbine (1) is yawed by a power electronic system (15) based on a wind direction provided by the additional wind vane (not shown) installed on the wind turbine (1). This reduces loads to the wind turbine (1), especially the loads to the blades (6), and reduces the risk of damages. It is worth mentioning that the wind turbine controller during a shutdown procedure commands the pitch system (21) to leave the blades (6) in a non-feathering position. Especially the non-feathering position includes an angle between 80° to 89°, preferred 85°. This high wind condition set by the wind turbine controller affects the aerodynamic properties of the rotor (5) of the wind turbine (1). Consequently, during high wind conditions, the rotor will turn (5) with low rpm (round per minute). This low rpm will be sufficient for the power electronic system (15) to extract sufficient power. So the DC link (18) can be fed, the energy storage unit (19) kept charged and the yaw system (20) operating in accordance with the current wind direction situation. Especially the rotor (5) will rotate in low rpm in a range between 1 rpm to 10 rpm, preferred 1 rpm to 5 rpm, and more preferred 1 rpm to 2 rpm. Depends on the transmission of the generator (12) the generator will be driven in a range between 100 rpm to 1000 rpm, preferred 100 rpm to 500 rpm, and more preferred 100 rpm to 200 rpm. It should be pointed out that this is outside the normal operating conditions of the generator (12). Nevertheless, under these operating conditions the generator (12) produces electrical power in a range between 1 kW to 100 kW, preferred 5 kW to 50 kW and more preferred 10 kW to 20 kW. This electrical power is sufficient for charging the energy storage unit (19) and/or driving the yaw system (20). This allows a self-sufficient operation of the wind turbine (1), especially a continuously yawing aligning to the wind direction. Because of the continuously yawing once the loads to the blades (6) are much low as possible and twice the rotor (5) can rotate with equally constant low rotation without an active pitching of the blades (6). In other words, the blades (6) are left in a present pitch angle. Therefore, the losses generated by the pitch system (21) can be avoided as well as the losses of the main converter (13) and all the losses introduced by all sensors and the wind turbine controller. Active pitching is meaningless if the wind turbine (1) is not yawed into the right position anyway.

The electrical power is buffered to the DC link (18). The power electronic system (15) is configured to operate in two modes, namely charging the energy storage unit (19) or supply the electrical power to the inverter (17), which is responsible of driving the yaw system (20). For charging the energy storage unit (19) the rectifier (16) supplies electrical power to the DC link (18), which directs the electrical power to the energy storage unit (19). Normally, the charging of the energy storage unit (19) takes place when enough electrical power generated by the generator (12) is available. This could be when the rotor (5) rotates with enough speed so there will be produced sufficient power for driving the yaw system (20) and/or charging the energy storage unit (19). Another configuration could be charging the energy storage unit (19) and the yaw system (20) is inactive. In case the rectifier (16) cannot extract enough electrical power from the generator (2), maybe because the rotor (5) rotates with a too low speed, the energy storage unit (19) supports the inverter (17) with electrical power over the DC link (18) for driving the yaw system (20). In result the energy storage unit (19) will be discharged. The changing and discharging procedures are handled by a power electronic system controller (22). The inverter (17) is responsible for supplying the yaw system (20) with electrical power and in this way it will yaw the wind turbine (1) in the right wind conditions.

In case the supply power of the utility grid is restored, the wind turbine (1) can reinitiate its own wind turbine controller and the wind turbine controller can take over the commands. In this situation the proposed solution ensures a safe disconnection and a full charged energy storage unit (19). Threshold wind measurement preferably above the rated wind conditions, the wind turbine (1) shall start yawing with proposed concept.

In the following, based on Figure 3 is explained an embodiment of a yaw drive concept for a wind turbine (1) for offshore applications in a condition of high winds and disconnected utility grid and a method for operating the wind turbine (1) under such conditions. Components described before which have the same functions, but differs under constructions, are numbered with an “a”.

Figure 3 shows a schematic view of the yaw drive concept of a wind turbine (1) for offshore applications. For offshore applications wind turbines (1) often have a squirrel cage induction generator (12a), hereinafter called SCIG (12a). The SCIG (12a) is connected to a full power converter (13a), which serves as a main converter. The full power converter (13a) comprises two generator-sided rectifiers (23), hereinafter called FPC-rectifiers (23), and two grid-sided inverters (24), hereinafter called FPC-inverters (24), wherein each FPC-rectifiers (23) and FPC-inverters (24) is connected over a DC link (25), hereinafter called FPC-DC link (25). The full power converter (13a) is disconnected from a transformer (14a) at a point of common coupling to a utility grid. So the wind turbine (1) could not supply or receive electrical power from or to the utility grid. Parallel to the full power converter (13a) the SCIG (12a) is connected with a power electronic system (15a). The power electronic system (15a) comprises a generator-sided rectifier 16a, hereinafter called PES-rectifier (16a), a yaw system-sided inverter (17a), hereinafter called PES-inverter (17a), a power electronic system controller (22a) and a DC link (18a), hereinafter called PES-DC link (18a), which couples the PES-rectifier (16a) with the PES-inverter (17a). Further the power electronic system (15a) comprises a battery pack (26) as an energy storage unit (19a), which is connected to the PES-DC link (18a). The power electronic system (15a) is connected to the yaw system (20a), in particular over the PES-inverter (17a), for supplying electrical power to the yaw system (20a). The yaw system (20a) can comprise min three yaw drives 27. In the shown embodiment the yaw system (20a) comprises six yaw drives (27). The pitch system (21a) pitches the blades (6) in a non-feathering position. The pitching of the blades (6) takes place when the wind turbine controller set the wind turbine (1) in a high wind configuration. After this the blades (6) staying in the non-feathering position. The aligning of the wind turbine (1) is only conducted by a continuously yawing over the yaw drives (27). For pitching the blades 6 the pitch system (21a) comprises three pitch drives (28), wherein each pitch drive (28) is connected to a grid-sided AC/AC converter (29).

The method for operating the wind turbine (1) for this embodiment is the same as described in the above embodiment, and should not be described further in detail in following.

In the following, based on Figure 4 is explained an embodiment of a yaw drive concept for a wind turbine (1) for onshore applications in a condition of high winds and disconnected utility grid and a method for operating the wind turbine (1) under such conditions. Components described before which have the same functions, but differs under constructions, are numbered with a “b”.

Figure 4 depicts a schematic view of a yaw drive concept of a wind turbine (1) for onshore applications. Most of these wind turbines (1) has a doubly fed induction generator (12b), hereinafter called DFI generator (12b). The DFI generator (12b) is connected to the utility grid, in particular over a transformer (14b), over a stator conductor (29) and a rotor conductor (30). At the rotor conductor (30) is arranged a full sized converter (13b), which serves as a main converter. The full sized converter (13b) comprises a generator-sided rectifier (31), hereinafter called FSC-rectifier (31), and a grid-side inverter (32), hereinafter called FSC-inverter (32), which are coupled with a DC link (33), hereinafter FSC-DC link (33). The full sized converter (13b) is disconnected from the transformer (14b) at a point of common coupling to a utility grid. So the wind turbine (1) could not supply or receive electrical power from respectively to the utility grid. Further the DFI generator (12b) is connected to the power electronic system (15b), wherein the power electronic system (15b) is coupled with the stator conductor (29) as well as with the rotor conductor (30). The power electronic system (15b) is connected to the yaw system (20b) having six yaw drives (27b). Because of the DFI generator (12b) the power electronic system (15b) differs from the described ones above. According to this embodiment the power electronic system (15b) comprises a rotor-sided inverter (34), a stator-sided rectifier (35), a PES-inverter (17b), a PES-DC link (18b), a power electronic system controller (22b) and a battery pack (26b) as an energy storage unit (19b). Over the PES-DC link (18b) the rotor-side inverter (34) and the stator-sided rectifier (35) as well as the PES-inverter (17b) are connected to each other. The battery pack (26b) is connected to the PES-DC link (18b) for charging and discharging operations as described above. The rotor-sided inverter (34) is responsible for energizing the rotor part of the DFI generator (12b) during rotation. So the electrical power produced by the DFI generator (12b) can be buffered into the PES-DC link (18b) through the stator-sided rectifier (35). This also allows charging the battery pack (26b) and/or driving the yaw system (20b), especially the yaw drives (27b) are provided by the stator-sided rectifier (34). The power electronic system controller (22b) manages these operations.

The method for operating the wind turbine (1) for this embodiment is the same as described in the above embodiments, and should not be described further in detail in following.

In the following, based on Figure 5 is explained an embodiment of a yaw drive concept for a wind turbine (1) for offshore applications in a condition of non-high winds and disconnected utility grid and a method for operating the wind turbine (1) under such conditions. Components described before which have the same functions, but differs under constructions, are numbered with a “c”.

This embodiment is quite similar to the described embodiment according to Fig. 3. The difference is that the wind turbine comprises additionally a power back-up system (36). In case the high winds situation passed and the pitch system (21c) haven’t enough power to set the blades (6) in a right angle for rotating the rotor (5) there is provided a power back-up system (36) for supplying the necessary electrical power to the power electronic system (15c). The power back-up system (36) is offered by a PV system (photovoltaic system). The PV system (36) comprises one or more PV panels. The at least one PV panel could be mounted at the nacelle (3) and/or at the tower (2).

The PV system (36) is connected with the power electronic system (15c). Most of the commercial PV system (36) comprises an integrated converter, so the PV system (36) is coupled to the PES-rectifier (16c). In case that the PV system (36) does not comprise an integrated converter the PV system (36) could couple to the PES-DC link (18c). Independent therefrom the electrical power of the PV system (36) is directed to the PES-inverter (17c), which supplies the electrical power to the yaw system (20c). It is also possible, if the PV system (36) produces sufficient electrical power, charging the battery pack (26c). However because of the electrical power from the PV system (36) the yaw system (20c) has enough power for yawing the wind turbine (1) in a right angle to the wind, so the rotor (5) can begin to spin. Once the rotor (5) rotates with sufficient rpm, namely between 1 rpm and 10 rpm, the operation mode as described above can conduct. It is clear that all described operation modes are controlled by the power electronic system controller (22c).

In the following, based on Figure 6 is explained an embodiment of a yaw drive concept for a wind turbine (1) for onshore applications in a condition of non-high winds and disconnected utility grid and a method for operating the wind turbine (1) under such conditions. Components described before which have the same functions, but differs under constructions, are numbered with a “d”.

This embodiment is quite similar to the described embodiment according to Fig. 4. The difference is that the wind turbine comprises additionally a power back-up system (36d). In case the high winds situation passed and the pitch system (21d) haven’t enough power to set the blades (6) in a right angle for rotating the rotor (5) there is provided a power back-up system (36d) for supplying the necessary electrical power to the power electronic system (15d). The power back-up system (36d) is offered by a PV system (photovoltaic system). The PV system (36d) can comprise one or more PV panels. The at least one PV panel could be mounted at the nacelle (3) and/or at the tower (2).

The PV system (36d) is connected with the power electronic system (15d). Most of the commercial PV system (36d) comprises an integrated converter, so the PV system (36d) is coupled to the rotor-sided inverter (34d), which serves as a rotor-sided rectifier (34d) in this configuration. Alternatively, it is also possible that PV system (36d) is also coupled to the stator-sided rectifier (35d). In case that the PV system (36d) do not comprises an integrated converter the PV system (36d) could couple to the PES-DC link (18d). Independent therefrom the electrical power of the PV system (36d) is directed to the PES-inverter (17d), which supplies the electrical power to the yaw system (20d). It is also possible, if the PV system (36d) produces sufficient electrical power, charging the battery pack (26d). However because of the electrical power from the PV system (36d) the yaw system (20d) has enough power for yawing the wind turbine (1) in a correct angle to the wind, so the rotor (5) can begin to spin. Once the rotor (5) rotates with sufficient rpm, namely between 1 rpm and 10 rpm, the operation mode as described above can conduct. It is clear that all described operation modes are controlled by the power electronic system controller (22d).

Reference List

1 wind turbine
2 tower
3 nacelle
4 drive train chain
5 rotor
6 rotor blades
7 hub
8 pitch drives
9 nacelle cover
10 nacelle cover interface
11 spinner
12 generator
12a SCIG
12b DFI generator
12c SCIG
12d DFI generator
13 main converter
13a full power converter
13b full sized converter
13c full power converter
13d full sized converter
14 transformer
14a transformer
14b transformer
14c transformer
14d transformer
15 power electronic system
15a power electronic system
15b power electronic system
15c power electronic system
15d power electronic system
16 rectifier
16a PES-rectifier
16c PES-rectifier
17 inverter
17a PES-inverter
17b PES-inverter
17c PES-inverter
17d PES-inverter
18 DC link
18a PES-DC link
18b PES-DC link
18c PES-DC link
18d PES-DC link
19 energy storage unit
19a energy storage unit
19b energy storage unit
19c energy storage unit
19d energy storage unit
20 yaw system
20a yaw system
20b yaw system
20c yaw system
20d yaw system
21 pitch system
21a pitch system
21b pitch system
21c pitch system
21d pitch system
22 power electronic system controller
22a power electronic system controller
22b power electronic system controller
22c power electronic system controller
22d power electronic system controller
23 generator sided rectifiers (FPC-rectifier)
23c generator sided rectifiers (FPC-rectifier)
24 grid sided inverters (FPC- inverter)
24c grid sided inverters (FPC- inverter)
25 DC link (FPC-DC link)
25c DC link (FPC-DC link)
26 battery pack
26b battery pack
26c battery pack
26d battery pack
27 yaw drives
27b yaw drives
27c yaw drives
27d yaw drives
28 AC/AC converter
28b AC/AC converter
28c AC/AC converter
28d AC/AC converter
29 stator conductor
29d stator conductor
30 rotor conductor
30d rotor conductor
31 generator-sided rectifier
(FSC-rectifier)
31d generator-sided rectifier
(FSC-rectifier)
32 grid sides inverter (FSC- inverter)
32d grid sides inverter (FSC- inverter)
33 DC link (FSC DC-link)
33d DC link (FSC DC-link)
34 rotor-sided inverter
34d rotor-sided inverter
35 stator-sided rectifier
35d stator-sided rectifier
36 power back-up system
36d power back-up system