WO2014186867A1

WO2014186867A1 - Independently controlled three-unit drivetrain assembly for a wind turbine and method for controlling same

Info

Publication number: WO2014186867A1
Application number: PCT/CA2014/000440
Authority: WO
Inventors: Georges EL-HAGE; Pierre GUILLEMETTE
Original assignee: Zec Wind Power Corporation
Priority date: 2013-05-20
Filing date: 2014-05-20
Publication date: 2014-11-27

Abstract

An independently controlled three-unit drivetrain assembly for a wind turbine and method for controlling same is disclosed. The disclosed drivetrain assembly seeks to overcome disadvantages of the prior art such as not being operable in either high or low wind speeds. The disclosed drivetrain assembly includes brakes and clutches. Preferably, the clutches care permanent magnetic clutches. One embodiment discloses a dual-rotor wind turbine drivetrain.

Description

Independently Controlled Three-Unit Drivetrain Assembly for a Wind Turbine and

Method for Controlling Same

Technical field

The invention relates to an independently controlled three-unit drivetrain assembly for a wind turbine and method for controlling same.

Background

Single-rotor turbines are well known in the art as a means of generating electricity from wind. A typical turbine comprises a single, slow turning rotor attached to a speed increasing gearbox, attached to a high speed generator, standing on a tower high enough to access a wind stream.

Canadian Patent Application Number 2343876 discloses a power generation system comprising a magnetic clutch and a magnetic brake in a one rotor system in the form of brake-generator-clutch-impeller. However, the power generation system of Canadian Patent Application Number 2343878 contains a number of disadvantages, namely:

• a slip clutch having a physical connection (whether through the clutch's shaft, frame, or bearing) to other parts of the drivetrain assembly which thus shortens the life of the mechanical components;

• the use of synchronous generators which requires compliance to reduce the magnitude of the transfer function between the aerodynamic input torque and the drive-train torque;

• the system disclosed is a constant torque and constant speed system with the purpose of running a synchronous generator;

l • the configuration proposed is not operational because a magnetic clutch alone would not be able to hold down the system (a mechanical brake is always required between the clutch and the rotor).

Wind turbines typically further comprise a safety system. The safety system may comprise a friction brake for stopping the rotor, and/or a pitch- or stall-control system for power control. Where it is desirable to control rotor speed, at least one of the following is required: a variable speed generator, a multiple speed generator, or a gearbox with variable or multiple speeds. Low wind speed operation is the most important factor in a wind turbine's design because a wind turbine spends over 70% of its time operating in this regime. Low wind speed is generally considered anything below 8 m/s. In order to effectively obtain power from wind at these low velocities, a one-rotor system has to have a significantly oversized rotor. However, an oversized rotor creates an unsafe situation at higher wind speeds unless an expensive and/or complex pitch control system is utilized.

More recently, dual-rotor systems have been developed to obtain as much power as possible from the wind. These systems focus on power optimization rather than control rotor/shaft speed.

Summary of the Invention

The invention seeks to provide a dual-rotor wind turbine that overcomes the above disadvantages. Specifically, the invention comprises a dual-rotor wind turbine having stall- controlled blades. Additionally, the invention comprises magnetic clutches that decouple the rotors from the generator. Preferably, the magnetic clutches comprise permanent magnet clutches.

A dual-rotor system can minimize its maximum rotor size while capturing more energy either through the second rotor or through optimizing one rotor for low wind speeds. Advantageously, the dual-rotors of the invention operate synergistically to control the power of the turbine to provide a flat power curve. The dual-rotors capture maximum energy at low wind speeds while avoiding the large expense of a pitch controlled system. Single-rotor/stall controlled turbines are usually limited to their blades' coefficient of power ("Cp") curve. The dual-rotors of the present invention provide a final power curve which is a function of the individual Cp curves of each rotor. In one embodiment of the invention, for example, one rotor may be designed for high speed winds (i.e. average wind speeds of greater than 8 m/s) while the second rotor is designed for low speed winds. In this scenario, one rotor stops producing power in high speed winds (without any pitch control) while the second rotor continues to produce power. Stall-controlled turbines have a Cp of approximately 0.5 at low wind speeds with a significant drop in Cp (to approximately 0.01 and possibly lower) at high wind speeds. The dual-rotor turbine of the present invention is able to have stall control while maintaining rated power in a much larger window of operation.

Betz's Law is the theoretical maximum energy that can be extracted from a given cross section of wind flow by a one rotor system. According to Betz's law, a turbine cannot capture more than 59.3% of the kinetic energy from the wind. However, the present invention is capable of exceeding Betz's limit due to: (i) the use of a second rotor, (ii) the remaining energy from the wind that passes through the blades of the first rotor to the second rotor, and (iii) the larger rotor's ability to efficiently extract power from the part of the wind stream that was untouched by the first rotor. Since dual-rotor turbines have the ability to designate Cp independently, each rotor can be advantageously designed to have low tip speed ratios while maintaining power production. While some research has shown that aerodynamic noise may be the cause of wind turbine syndrome, a lower tip speed ratio advantageously reduces the aerodynamic noise produced by the turbine. Furthermore, the dual-rotors balance the system in terms of dynamic loading as well as reduce gyroscopic loads. This reduces vibrations in the dual-rotor turbine's tower and thus reduces vibrations transferred to the ground, which some research has shown is the cause of wind turbine syndrome.

Advantageously, connecting the rotor to a generator through a magnetic clutch (as opposed to a direct linkage) eliminates the hammering effect on the gearbox and the generator caused by wind gusts. Sudden jolts are absorbed by slipping of the magnetic clutch. Additionally, the generator's windings are protected from flexing which would occur when there is a sudden load. Wind turbine frames are known to flex and cause unexpected and non-linear loads on the wind turbine. Thus a further advantage of the present invention is that the magnetic clutch permits an approximately quarter inch of misalignment in the coupling without any loss of performance and without the magnetic clutch experiencing any non-torque loads. Many known turbines use their generator in motor mode (called motoring) during the start-up process at low wind speeds. Thus a further advantage of the present invention is that disconnecting the magnetic clutch significantly reduces the amount of startup torque required, therefore rendering a motor unnecessary. Turbines using alternating current generators are usually brought to full speed by the blades, after which the generator is turned on. This creates a large inrush of current. A further advantage of the present invention is that the magnetic clutch can be disengaged during startup. The generator can then be brought to its full speed at the cost of very little energy after which the magnetic clutch can be re-engaged. Thus, the blade's inertia is not felt by the generator during the transient period of its start-up meaning less current is required to get the blades to synchronous speed. By slowly engaging the turbine blades to the generator through gap control of the clutch, the inrush of current into the generator can be reduced, thus prolonging the life of the generator. In a first broad embodiment, the invention seeks to provide a three-unit drivetrain assembly for a wind turbine, the three-unit drivetrain assembly comprising: a first unit;

a second unit, operatively connected to the first unit through at least a first clutch and a first brake;

a third unit, operatively connected to the second unit by a at least a second clutch and a second brake.

Preferably, the first clutch and the second clutch comprise permanent magnetic clutches.

Preferably, each of the first unit, the second unit, and the third unit comprises a driver unit or a driven unit.

Preferably, the driver unit is a wind turbine impeller, a hydro turbine impeller, an electric motor, a gas motor, or a hydrogen motor.

Preferably, the driven unit is an electric generator, a pump, a vehicle axle, a vehicle tire, or a bearing. Preferably, the first unit is a first wind turbine impeller, the second unit is an electric generator, and the third unit is a second wind turbine impeller.

Preferably, the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is a bearing.

Preferably, the first unit is a wind turbine impeller, the second unit is a first electric generator, and the third unit is a second electric generator.

Preferably, the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is a combustion engine. Preferably, the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is an exciter.

Preferably, the three-unit drivetrain assembly further comprising at least one RPM sensor for measuring rotation of a shaft.

Preferably, the three-unit drivetrain assembly further comprising a programmable logic controller operatively connected to the at least one RPM sensor for controlling the operation of the clutch.

Preferably, the three-unit drivetrain assembly further comprising an exciter operatively connected to the electric generator.

In a second broad embodiment, the invention seeks to provide a start-up method for a dual-rotor wind turbine system wherein the blades of the first rotor are larger than the blades of the second rotor, the method comprising:

(a) opening a first adjustable speed drive (ASD) and opening a second ASD while a second brake is engaged;

(b) once the RPM of a second gearbox reaches synchronous speed, closing the second ASD;

(c) connecting a generator to a power grid; and

(d) after the dual-rotor wind turbine system reaches steady state, opening a first brake and slowly closing the first ASD.

In a third broad embodiment, the invention seeks to provide a start-up method for a dual-rotor wind turbine system wherein the blades of the first rotor are larger than the blades of the second rotor, the method comprising:

(a) opening a first adjustable speed drive (ASD) and a second ASD while each of a first brake and a second brake are closed; (b) connecting a generator to a power grid;

(c) once synchronous speed is close to being reached, disengaging the second brake and closing the second ASD;

(d) after the generator goes above synchronous speed, disengaging the first brake and slowly closing the first ASD.

Brief Description of the Drawings

Figure 1 is a partial perspective view of a dual-rotor wind turbine known in the prior art;

Figure 2 is a schematic of a first embodiment of the invention;

Figure 3 is a schematic of a method of soft braking a second rotor with one stopped rotor;

Figure 4 is a schematic of a first method of starting the dual-rotor wind turbine;

Figure 5 is a schematic of a second method of starting the dual-rotor wind turbine;

Figure 6 is a schematic of a modified embodiment of the invention shown in Figure 2, wherein the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is a second wind turbine impeller;

Figure 7 is a schematic of an alternative embodiment of the invention, wherein the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is a bearing;

Figure 8 is a schematic of a further alternative embodiment of the invention, wherein the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is an electric motor;

Figure 9 is a schematic of a further alternative embodiment of the invention, wherein the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is a combustion engine;

Figure 10 is a schematic of a further alternative embodiment of the invention, wherein the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is an excite; and Figure 1 1 is a schematic of a modified embodiment of the invention shown in Figure

6.

Detailed Description

Referring to Figure 1, a single rotor, horizontal axis wind turbine ("HAWT") (1) as known in the prior art is shown. The HAWT (1) comprises a nacelle (2) located at the top of a tower (3). The nacelle (2) contains a low speed shaft (4a) connected at a first end to a gearbox (5). The gearbox (5) is connected to a generator (6) by a high speed shaft (4b). A second end of the low speed shaft (4a) is connected to a rotor (7) from which extends blades (8). The HAWT may further comprise a fail-safe disk braking system (9).

Referring to Figure 2, a first embodiment of a dual-rotor wind turbine (10) of the present invention is shown. While the dual-rotor wind turbine (10) is shown having a horizontal drivetrain, the dual-rotor wind turbine (10) could also be implemented in a vertical wind turbine. The dual-rotor wind turbine (10) comprises a first rotor (70a) and a second rotor (70b). The first rotor (70a) is positioned at a first end of the nacelle (20) and is connected to a first gearbox (50a) through a low speed shaft (90a). The nacelle (20) is positioned at the top of tower (22). Since the dual-rotor turbine (10) is more effective at generating energy at low wind speeds, tower (22) can be shorter in height than wind turbines of the prior art. The gearbox (50a) is connected to a double-shafted generator (100) by a high speed shaft (95a). The generator (100) is connected to a power grid (not shown) to which it supplies power. While a single double-shafted generator (100) is shown, alternatively, two single-shafted generators could be used. Between the gearbox (50a) and the generator (100) are a brake (120a) and an adjustable-speed drive ("ASD") (130a). Bearings (92a) may be provided to support the low speed shaft (90a) on which the rotor (70a) is placed. Additionally, a flex coupling (94a) may be provided to permit some angular misalignment between the low speed shaft (90a) and the gearbox (50a) which is caused by the frame flexing. The second rotor (70b) is positioned at a second end, opposite the first end, of the nacelle (20) and is connected to a second gearbox (50b) through a low speed shaft (90b). The second gearbox (50b) is connected to the generator (100) by a high speed shaft (95b). Between the second gearbox (50b) and the generator (100) are a second brake (120b) and a second ASD (130b). Bearings (92b) may be provided to support the low speed shaft (90b) on which the rotor (70b) is placed. Additionally, a flex coupling (94b) may be provided to permit some angular misalignment between the low speed shaft (90b) and the gearbox (50b) which is caused by the frame flexing.

A sensor (not shown) is operably connected to low speed shafts (90a and 90b) to measure the amount of torque on the low speed shafts (90a and 90b) and the RPM of the rotors (70a, 70b). The sensor is operatively connected to a controller (not shown) which is connected to, and operates, the first and second brake (120a, 120b) and the first and second ASD (130a, 130b).

Extending from the first rotor (70a) and the second rotor (70b) are blades (75a) and blades (75b), respectively. Preferably, the blades (75a) extending from first rotor (70a) are larger in dimension than the blades (75b) extending from second rotor (70b). Alternatively, the blades (75b) extending from second rotor (70b) may be smaller in dimension than the blades (75a) extending from rotor (75a). In a further embodiment, the blades (75a) extending from the first rotor (70a) and the blades (75b) extending from the second rotor (70b) may have the same dimensions. In such an embodiment, blades (75a) and (75b) would be operated at different RPM's.

Preferably, brakes (1 10a, 1 10b) use one of friction, magnetic, or electrical means to stop the rotation of the shafts. In a preferred embodiment, brakes (110a, 1 10b) comprise magnetic brakes. Preferably, the first ASD (130a) and second ASD (130b) each comprise a metallic clutch. Preferably, the first ASD (130a) and second ASD (130b) each comprise a metallic clutch (not shown).

During operation (i.e. in power generation mode), brakes (120a, 120b) are first disengaged. The movement of wind against the first blades (75 a) causes the low speed shaft (90a) to rotate at a particular speed depending on the current wind speed. The gearbox (50a) increases the rate of rotation which is imparted on the high speed shaft (95a). The first ASD (130a) transmits rotation from the high speed shaft (95a) to the motor shaft (97a) which is connected to the generator (100) and which produces electric power. The blades (75b) of the second rotor (70b) operate in a similar manner as the blades (75a) of first rotor (70a). However, the second blades (75b) receive two wind streams: the first being the wind that has passed through the first blades (75a) of the first rotor (70a) to the second rotor, and the second being wind that was untouched by the first rotor (70a) and blades (75a). During operation, the first rotor (70a) is preferably operated concurrently with second rotor (70b). Alternatively, each of the first rotor (70a) and the second rotor (70b) may be used independently. For example, if wind speeds are high and too much energy is being produced, one of the rotors (70a, 70b) may be shut down while the other rotor continues to make power. If one of the rotors is being overstressed or is going into overspeed, the turbine can shut it down and continue operating with the other rotor.

In certain circumstances, it may be desirable to slow the rotation of the first rotor (70a) and/or second rotor (70b) due to changes in wind speed in order to maintain the low speed shafts (90a) and (90b) at a (near) constant rate of rotations per minute. According to the present invention, there are a number of ways in which this may be achieved.

An alternative embodiment of the present invention (not shown) comprises a single- rotor wind turbine. The single-rotor wind turbine comprises substantially the same components in its drivetrain as the dual-rotor wind turbine (10). This includes an ASD, which is preferably a magnetic clutch.

Soft Braking By Stopping the Generator Soft braking by stopping the generator (100) may be used during normal operation when there is a need to stop the first rotor (70a) and the second rotor (70b). This may be necessary, for example, when repairs to the turbine are needed. This is the most commonly used method of braking. During operation, electrical current may be applied to the generator (100) in a certain way such that it acts like a brake. For example, application of direct current ("DC") to an alternating current ("AC") generator would cause the generator to slow. By disconnecting the magnetic clutch (132a, 132b) and using this generator braking method, the magnetic clutch (132a, 132b) can be re-engaged after the generator (100) has been significantly slowed, stopping the blades (75a, 75b) very smoothly without wearing any mechanical components, such as brake pads.

In an emergency situation, when the first rotor (70a) and the second rotor (70b) must be stopped immediately (for example, in overspeed conditions), soft braking is the first resort to stop the rotors. If soft braking does not succeed in fully stopping the first rotor (70a) and the second rotor (70b), the friction brakes (120a and 120b) are immediately engaged. Soft Braking Of Second Rotor with One Stopped Rotor

Soft braking of a second rotor when a first rotor is already stopped may be used if one rotor is unavailable for operation, during startup conditions, or if one rotor needs to be stopped suddenly during high winds. One of the rotors (70a, 70b) may be initially stopped through friction brakes or the "soft braking by stopping the generator" method, described above, while the other rotor is disengaged by the magnetic clutch (132a, 132b). The stopped rotor can then be held stopped by friction brakes (which would remain unused if soft braking is used) and then the second rotor can be stopped by simply re-engaging the metallic clutch (132a, 132b). Referring to Figure 3, a method of soft braking a second rotor with one stopped rotor is shown. During operation, the generator (100) may be running at 1800 rpm. First, the generator (100) is disconnected from the power grid and then connected to a DC power source to begin the braking process. If the generator (100) begins to overheat at this stage, then both sets of brakes are closed immediately. The ASD on the rotor side containing the smaller dimensioned blades is then closed. When the rotations per minute ("RPM") of the small blades drops below a predetermined value (depending on the diameter of the blades), the brake on the rotor side containing the smaller dimensioned blades is closed. After the smaller dimensioned blades are fully stopped, the ASD on the rotor side containing the larger dimensioned blades is closed. Once the RPM of the big blades is less than a predetermined value (depending on the diameter of the blades), the brake on the rotor side containing the larger dimensioned blades is closed. When the big blades are fully stopped, the generator is disconnected (100) from the DC power source, thus completing the shutdown process. During DC braking, if the generator is overheating, both brakes are closed right away. Magnetic Clutch to Vary Blade Speed and Do So Independently

The gap in the magnetic clutch (132a, 132b) can be varied to change the amount of torque transmitted through it. Doing this while the dual-rotor turbine (10) is online permits the blades (75a, 75b) to speed up or slow down. This speed control, which can be performed on either rotor (70a) and (70b) independently if two magnetic clutches are used, or both rotors dependently if one magnetic clutch is used, can be used to maintain the tip speed ratio of the blades (75a, 75b) thus optimizing or controlling power production and torque in the dual-rotor turbine (10). Magnetic Clutch to Ride Through Gusts

A wind gust is a transient increase in wind speed. The magnetic clutch (132a, 132b) can absorb the high torque generated during a wind gust. Furthermore, the magnetic clutch (132a, 132b) can be opened to allow the energy of the wind gust to be absorbed partially as inertia in the rotors (70a, 70b) and smoothly transferred to the generator (100) or dumped magnetically through the clutch (132a, 132b) as losses.

Start-Up: One Set of Blades Can Be Used To Start the Other Set of Blades One set of blades (75a, 75b) may have lower inertia (for example, smaller blades with less mass) or a stronger angle of attack which gives said set of blades the ability to reach operational speed at lower wind speeds. This allows said set of blades to speed up to the necessary RPM with the clutch disengaged. Closing the magnetic clutch then transfers the rotational energy to the other rotor. The other rotor is then accelerated and brought to a tip speed where it can produce energy efficiently. This avoids having the generator (100) act as a motor during the dual-rotor turbine's startup.

Referring to Figure 4, a first start-up method is shown. First each of the first ASD (130a) and the second ASD (130b) are opened and the second brake (95b) is engaged. Once the RPM of the second gearbox (50b) reaches synchronous speed, the second ASD (130b) is closed. Subsequently, the generator (100) is connected to the power grid. After the system reaches steady state (i.e. the desired number of RPM), the first brake (120a) is opened and the first ASD (130a) is slowly closed.

Referring to Figure 5, a second start-up method is shown. First, each of the first ASD (130a) and the second ASD (130b) are opened and each of the first brake (120a) and the second brake (120b) are closed. The generator is then connected to the power grid and the generator (100) is permitted to run close to synchronous speed as a motor. Once this speed is reached, the second brake (120b) is opened and the second ASD (130b) is closed. After the generator (100) goes above synchronous speed, the first brake (120a) is opened and the first ASD (130a) is slowly closed.

Additional Embodiments Referring to Figure 6, a modified embodiment of the three-unit drivetrain assembly wind turbine of the present invention is shown. The three-unit drivetrain assembly comprises a first rotor (670a) having blades (675a) and a second rotor (670b) having blades (675b). The first rotor (670a) is positioned at a first end of the nacelle (not shown) and is connected to a first gearbox (650a) through a low speed shaft (690a). The gearbox (650a) is connected to a double-shafted generator (6100) by a high speed shaft (695a). The generator (6100) is preferably connected to a power grid (not shown) to which it supplies power. While a single double-shafted generator (6100) is shown, alternatively, two single-shafted generators could be used. Between the gearbox (650a) and the generator (6100) are a brake (6120a) and a clutch (6160a). Bearing (692a) may be provided to support the low speed shaft (690a) on which the rotor (670a) is placed. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (690a) and the gearbox (650a) which is caused by the frame flexing.

The second rotor (670b) is positioned at a second end, opposite the first end, of the nacelle and is connected to a second gearbox (650b) through a low speed shaft (690b). The second gearbox (650b) is connected to the generator (6100) by a high speed shaft (695b). Between the second gearbox (650b) and the generator (6100) are a second brake (6120b) and a second clutch (6160b). Bearing (692b) may be provided to support the low speed shaft (690b) on which the rotor (670b) is placed. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (690b) and the gearbox (650b) which is caused by the frame flexing.

Gear boxes (650a) and (650b) are used to obtain the proper speed rotation of the generator shaft.

Three RPM sensors (6140) are shown for measuring the rotation of the shafts. While three RPM sensors (6140) are shown, a person of skill in the art would recognize that any number of RPM sensors could be used. The RPM sensors (6140) are operatively connected to a programmable logic controller (6150) which receives input from the RPM sensors (6140). The RPM sensors (6140) are also operatively connected to clutches (6160a and 6160b) to provide adjustment to the clutches (6160a and 6160b) based on the speed of rotation of the shafts.

Referring to Figure 7, an alternative embodiment of the three-unit drivetrain assembly wind turbine of the present invention is shown. The three-unit drivetrain assembly comprises a first rotor (770a) having blades (775a). The first rotor (770a) is positioned at a first end of the nacelle (not shown) and is connected to a first gearbox (750a) through a low speed shaft (790a). The gearbox (750a) is connected to a double-shafted generator (7100) by a high speed shaft (795a). The generator (7100) is preferably connected to a power grid (not shown) to which it supplies power. While a single double-shafted generator (7100) is shown, alternatively, two single-shafted generators could be used. Between the gearbox (750a) and the generator (7100) are a brake (7120a) and a clutch (7160a). Bearing (792a) may be provided to support the low speed shaft (790a) on which the rotor (770a) is placed. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (790a) and the gearbox (750a) which is caused by the frame flexing.

Instead of a second rotor, this embodiment contains bearing (792b) positioned at a second end, opposite the first end, of the nacelle and connected to a second clutch (7120b) through a low speed shaft (790b). The second clutch (7120b) is connected to the generator (7100) by a high speed shaft (795b). The purpose of the bearing (792b) in this embodiment is for load dumping and to assist synchronizing the generator (7100) to a power grid. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (790b) and the gearbox (750b) which is caused by the frame flexing.

Gear box (750a) is used to obtain the proper speed rotation to the high speed shaft of the generator.

Three RPM sensors (7140) are shown for measuring the rotation of the shafts. While three RPM sensors (7140) are shown, a person of skill in the art would recognize that any number of RPM sensors could be used. The RPM sensors (7140) are operatively connected to a programmable logic controller (7150) which receives input from the RPM sensors (7140). The RPM sensors (7140) are also operatively connected to clutches (7160a and 7160b) to provide adjustment to the clutches (7160a and 7160b) based on the speed of rotation of the shafts. Referring to Figure 8, an alternative embodiment of the three-unit drivetrain assembly wind turbine of the present invention is shown. The three-unit drivetrain assembly comprises a first rotor (870a) having blades (875a). The first rotor (870a) is positioned at a first end of the nacelle (not shown) and is connected to a first gearbox (850a) through a low speed shaft (890a). The gearbox (850a) is connected to a double-shafted generator (8100) by a high speed shaft (895a). The generator (8100) is preferably connected to a power grid (not shown) to which it supplies power. While a single double-shafted generator (8100) is shown, alternatively, two single-shafted generators could be used. Between the gearbox (850a) and the generator (8100) are a brake (8120a) and a clutch (8160a). Bearing (892a) may be provided to support the low speed shaft (890a) on which the rotor (870a) is placed. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (890a) and the gearbox (850a) which is caused by the frame flexing. Instead of a second rotor, this embodiment contains an additional motor or generator

(888) positioned at a second end, opposite the first end, of the nacelle. Preferably, the additional motor or generator (888) is powered by an independent power source (e.g., a battery) which increase the total output of generator (8100) to the power grid. The additional motor or generator (888) is connected to the generator (8100) by a speed shaft (895b). Between the additional motor or generator (888) and the generator (8100) are a second brake (8120b) and a second clutch (8160b). The purpose of the additional motor or generator (888) in this embodiment is for load dumping and to assist synchronizing the generator (8100) to a power grid. Three RPM sensors (8140) are shown for measuring the rotation of the shafts. While three RPM sensors (8140) are shown, a person of skill in the art would recognize that any number of RPM sensors could be used. The RPM sensors (8140) are operatively connected to a programmable logic controller (8150) which receives input from the RPM sensors (8140). The RPM sensors (8140) are also operatively connected to clutches (8160a and 8160b) to provide adjustment to the clutches (8160a and 8160b) based on the speed of rotation of the shafts. Referring to Figure 9, an alternative embodiment of the three-unit drivetrain assembly wind turbine of the present invention is shown. The three-unit drivetrain assembly comprises a first rotor (970a) having blades (975a). The first rotor (970a) is positioned at a first end of the nacelle (not shown) and is connected to a first gearbox (950a) through a low speed shaft (990a). The gearbox (950a) is connected to a double-shafted generator (9100) by a high speed shaft (995a). The generator (9100) is preferably connected to a power grid (not shown) to which it supplies power. While a single double-shafted generator (9100) is shown, alternatively, two single-shafted generators could be used. Between the gearbox (950a) and the generator (9100) are a brake (9120a) and a clutch (9160a). Bearing (992a) may be provided to support the low speed shaft (990a) on which the rotor (970a) is placed. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (990a) and the gearbox (950a) which is caused by the frame flexing. Instead of a second rotor, this embodiment contains a combustion engine (999) positioned at a second end, opposite the first end, of the nacelle. Preferably, the combustion engine (999) is powered by an independent power source (e.g., hydrogen, diesel, hydrocarbon, etc.) which increases the total output of generator (9100) to the power grid. The combustion engine (999) is connected to the generator (9100) by a high speed shaft (995b). Between the combustion engine (999) and the generator (9100) are a second brake (9120b) and a second clutch (9160b). The purpose of the combustion engine (999) in this embodiment is for load dumping and to assist synchronizing the generator (9100) to a power grid. The combustion engine (999) can also assist the rotor (970a) and blade (975a) get out of stall mode during a starting sequence.

Three RPM sensors (9140) are shown for measuring the rotation of the shafts. While three RPM sensors (9140) are shown, a person of skill in the art would recognize that any number of RPM sensors could be used. The RPM sensors (9140) are operatively connected to a programmable logic controller (9150) which receives input from the RPM sensors (9140). The RPM sensors (9140) are also operatively connected to clutches (9160a and 9160b) to provide adjustment to the clutches (9160a and 9160b) based on the speed of rotation of the shafts.

Referring to Figure 10, an alternative embodiment of the three-unit drivetrain assembly wind turbine of the present invention is shown. The three-unit drivetrain assembly comprises a first rotor (1070a) having blades (1075a). The first rotor (1070a) is positioned at a first end of the nacelle (not shown) and is connected to a first gearbox (1050a) through a low speed shaft (1090a). The gearbox (1050a) is connected to a double-shafted generator (10100) by a high speed shaft (1095a). The generator (10100) is preferably connected to a power grid (not shown) to which it supplies power. While a single double-shafted generator (10100) is shown, alternatively, two single-shafted generators could be used. Between the gearbox (1050a) and the generator (10100) are a brake (10120a) and a clutch (10160a). Bearing (1092a) may be provided to support the low speed shaft (1090a) on which the rotor (1070a) is placed. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (1090a) and the gearbox (1050a) which is caused by the frame flexing.

Instead of a second rotor, this embodiment contains an exciter (1010) positioned at a second end, opposite the first end, of the nacelle. The exciter (1010) is operatively connected to the generator (10100) by a high speed shaft (1095b). The exciter (1010) is also connected to the generator (10100) by an electrical connection (10101). Between the exciter (1010) and the generator (10100) are a second brake (10120b) and a second clutch (10160b). The exciter (1010) provides excitation current (VARS). The purpose of the exciter (1010) in this embodiment is for load dumping and to assist synchronizing the generator (10100) to a power grid. The electrical connection (10101) allows the exciter (1010) to provide VARS to the generator (10100).

Three RPM sensors (10140) are shown for measuring the rotation of the shafts. While three RPM sensors (10140) are shown, a person of skill in the art would recognize that any number of RPM sensors could be used. The RPM sensors (10140) are operatively connected to a programmable logic controller (10150) which receives input from the RPM sensors (10140). The RPM sensors (10140) are also operatively connected to clutches (10160a and 10160b) to provide adjustment to the clutches (10160a and 10160b) based on the speed of rotation of the shafts.

Referring to Figure 1 1, an alternative embodiment of the three-unit drivetrain assembly wind turbine of the present invention is shown. The three-unit drivetrain assembly comprises a first rotor (1170a) having blades (1 175a) and a second rotor (1170b) having blades (1 175b). The first rotor (1 170a) is positioned at a first end of the nacelle (not shown) and is connected to a gearbox (1150a) through a low speed shaft (1190a). The gearbox (1150a) is connected to a double-shafted generator (1 1100) by a high speed shaft (1195a). The generator (1 1100) is preferably connected to a power grid (not shown) to which it supplies power. While a single double-shafted generator (11100) is shown, alternatively, two single-shafted generators could be used. Between the gearbox (1 150a) and the generator (11100) are a brake (11 120a) and a clutch (11160a). Bearing (1192a) may be provided to support the low speed shaft (1190a) on which the rotor (1 170a) is placed. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (1 190a) and the gearbox (1150a) which is caused by the frame flexing.

The second rotor (1 170b) is positioned at a second end, opposite the first end, of the nacelle and is connected to an exciter (1 1 11) through a low speed shaft (1190b). The exciter (111 1) is connected to the generator (11 100) by electrical connection (1 1 101). Between the bearing (1 192b) and the exciter (11 1 1) are a second brake (11120b) and a second clutch (11160b). Bearing (1192b) may be provided to support the low speed shaft (1 190b) on which the rotor (1 170b) is placed. Additionally, a flex coupling (not shown) may be provided to permit some angular misalignment between the low speed shaft (1190b) and the gearbox (1 150b) which is caused by the frame flexing.

Three RPM sensors (1 1 140) are shown for measuring the rotation of the shafts. While three RPM sensors (1 1 140) are shown, a person of skill in the art would recognize that any number of RPM sensors could be used. The RPM sensors (11 140) are operatively connected to a programmable logic controller (11 150) which receives input from the RPM sensors (11140). The RPM sensors (1 1140) are also operatively connected to clutches (1 1160a and 1 1 160b) to provide adjustment to the clutches (1 1 160a and 1 1 160b) based on the speed of rotation of the shafts. Operation and Configurations of the Invention

The invention as described above (and shown in the accompanying figures) can be operated in a number of configurations. Various configurations are described below in Table 1.

Third Unit brake.

Impeller or Generator Brake on Ability to decouple Third Unit other while still operating with First driver; Unit and Second Unit. Example: brake off One rotor of the turbine can still run if the other is broken.

Impeller or Generator Impeller or Ability to drive a Second Unit other other with two independent drivers: driver; driver, First Unit and Third Unit.

brake off Brake off Example: a dual rotor wind turbine.

Wheels, Motor Wheels, Ability for Second Unit to drive pump, or pump, or two driven objects, First Unit other other and Third Unit, while controlling driven driven each independently, thus acting object; object. as a motor and differential brake off Brake off simultaneously. Example: Motor driving two front wheels in an electric car or differential between front and rear axle.

Wheels, Motor Brake On Ability to have one motor pump, or (Second Unit) to continue other driving First Unit even though driven Third Unit is down.

object;

brake off

Impeller or Mode 1 : Mode 1 : Ability to have units change other Generator brake on their operating type depending driver; Mode 2: Mode 2: on running conditions, in this brake off Generator Motor case Third Unit. Example: Wind Mode 3: Mode 3: turbine impeller (First Unit) Generator Generator drives the generator during the off, brake day. At night, the generator is off off and a hydrogen generator (Third

Unit) is driven. Then during a day with no wind, The hydrogen generator runs in reverse as a motor, driving the generator and still creating power.

Impeller or Generator Generator The driver (First Unit) can other (exciter) simultaneously drive a main driver; generator (Second Unit) and an brake off exciter (Third Unit). Example:

The exciter will give the excitation to the generator and the clutch control can chpose what speed the generator is excited at by controlling the speed of the exciter.

Impeller or Generator Brake on The power generated by the other driver can be partially dumped driven into Third Unit to help the object; generator brake. Example: one brake off rotor of the turbine can be

braked and the other will continue (First Unit) to generate power while some power is dumped into the stopped rotor (Third Unit) through the clutch between the stopped rotor (Third Unit) and the generator (Second

Unit).

12 Impeller or Motor Impeller or Second Unit can be used to bring other other the two drivers (First Unit and driven driven Third Unit) up to speed with object; object, minimal stress through smooth brake off brake off clutch engagement. Example: A turbine can use the generator in motor mode to bring the impellers up to speed and out of stall mode.

13 Impeller; Brake off Impeller Each component can be

Brake off Brake off decoupled and allowed to run freely. Example: Each rotor of the turbine can be decoupled so it can come to speed with only the friction on its shaft.

14 Impeller or Brake off Impeller or Able to use one running driver other (generator other (First Unit) to accelerate the driven not on) driven other driver (Third C). Example: object; object, One rotor on the turbine is brake off brake off running and its torque will bring the other rotor to speed.

Configurations of the invention may be used to start the wind turbine without power electronics (i.e., solid state electronics with the purpose of controlling and converting electric power) or a soft-start. The most common example of power electronics used in wind turbines are inverters which control permanent magnet generators and transform generated power from AC to DC to AC and then feed it to the power grid. For example, a generator may be run as a motor (motoring), slowly engaging the clutches and bringing the blades up to speed smoothly with minimal current inrush. If desired, this can be performed one rotor at a time. Such an operation would comprise Configuration 3, then Configuration 12, and then Configuration 6. In another example, the rotors are permitted to run in a disengaged manner, driven up to speed by the wind with minimal friction, and then engaging the generator. Such an operation would comprise Configuration 13, then Configuration 6.

In another example, one running rotor's torque could be used to accelerate the other rotor to speed. Such an operation would comprise Configuration 14, then Configuration 6.

In yet another example, one would be able to engage a second rotor if it was not running while the other rotor was running. Such an operation would comprise Configuration 5, then Configuration 6.

The exemplified configurations are advantageous for optimizing operation. For example, while running the wind turbine system, the clutch can be allowed to slip to allow a rotor to change its speed which adjusts the blade's tip speed ratio and allows it to capture more or less energy. Such an operation can be tuned to the wind speed.

In another example, by adjusting both clutches and controlling the speed of each rotor independently, the front rotor can be adjusted to affect the rear rotor's power capture.

In another example, the turbine can be in operation even though it has experienced a mechanical fault on one side (e.g., a blade problem) by simply shutting down that side and generating power from the other rotor. Such operation would comprise Configuration 5.

In yet another example, one of the rotors can be shut down to limit power capture in high winds. Such operation would comprise Configuration 5. The exemplified operations are also advantageous for creating a safe operating environment. For example, the drivetrain is able to act through the clutch as a shock absorber and reduce the magnitude of torque peaks and hammering. These extend mechanical component life by reducing torque spikes and the generator life by reducing flexing of the windings by reducing current inrush. This also reduces blade whipping.

By using a permanent magnet clutch, misalignment in the clutch is greatly tolerated. This means less stress on the gearbox when the frame flexes (which is a significant problem in wind turbines) in which 250 thousandths of an inch is tolerated but a ½ thousandth of an inch is not.

In addition, gust ride through is possible by allowing the drivetrain to absorb sudden gust as inertia by partially decoupling the rotor. Lastly, mechanical anti-islanding is achieved by disengaging the rotors from the generator when a grid loss occurs forcing the generator into motor mode and drawing rather than providing power.

The exemplified operations are also useful when using multi-speed (e.g. two-speed) generators is improved by the drivetrain's ability to disengage loads (rotors) by allowing the generator to change speed with minimal inrush and minimal mechanical shock by disengaging the load (rotors) before changing speed then reengaging smoothly.

The exemplified operations are also useful when for load dumping and storage. For example, if one of the turbine's rotors is producing too much power, the other can be stopped and load can be dumped though the slip of its clutch. Such an operation would comprise Configuration 1 1. The quantity dumped is controlled by the clutch.

The exemplified operations are also useful for braking. For example, one of the three units can be held stopped by a brake and the others can then be slowed down smoothly by engaging the clutches. One of the rotors can be held down or the generator shaft can be held stopped. The advantage of holding the generator shaft is that it takes less power to brake in the first place when disengaged. Alternatively to a mechanical brake, an electrical current can be applied to the generator (if an induction generator is used) to create braking torque then the same procedure, as described in the previous sentence, can be described.

By disengaging the generator, the inertia of the generator (which is very significant in a permanent magnet generator) does not need to be stopped by the generator which allows the rotor to stop faster. The exemplified operations are also useful for braking in single rotor configurations.

For example, instead of a second rotor, a secondary generator (such as a hydrogen generator) can be used. During certain times, the main generator will operate, during others (such as when the main generator's output is not needed at night), the secondary generator will operate to store energy in some fashion (such as to produce hydrogen), which can then be used to drive the secondary generator as a motor (thus driving the main generator) when there is no wind. This secondary generator can be any form of energy storage such as a water pump or hydrogen motor or electric motor storing into batteries.

Alternatively, instead of a second generator, an exciter-generator (AC or DC) may be used to generate excitation to control the main generator. The drivetrain can then control the exciter-generator's output hence also controlling the main generator. Such a configuration can only be used with a one-rotor system.

The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

Claims

1. A three-unit drivetrain assembly for a wind turbine, the three-unit drivetrain assembly comprising:

a first unit;

2. The three-unit drivetrain assembly of Claim 1 wherein the first clutch and the second clutch comprise permanent magnetic clutches.

3. The three-unit drivetrain assembly of Claim 1 or Claim 2, wherein each of the first unit, the second unit, and the third unit comprises a driver unit or a driven unit.

4. The three-unit drivetrain assembly of Claim 3, wherein the driver unit is a wind turbine impeller, a hydro turbine impeller, an electric motor, a gas motor, or a hydrogen motor.

5. The three-unit drivetrain assembly of Claim 3 or Claim 4, wherein the driven unit is an electric generator, a pump, a vehicle axle, a vehicle tire, or a bearing.

6. The three-unit drivetrain assembly of Claim 1, wherein the first unit is a first wind turbine impeller, the second unit is an electric generator, and the third unit is a second wind turbine impeller.

7. The three-unit drivetrain assembly of Claim 1, further comprising an exciter operatively connected to the electric generator.

8. The three-unit drivetrain assembly of Claim 1, wherein the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is a bearing.

9. The three-unit drivetrain assembly of Claim 1, wherein the first unit is a wind turbine impeller, the second unit is a first electric generator, and the third unit is a second electric generator.

10. The three-unit drivetrain assembly of Claim 1, wherein the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is a combustion engine.

1 1. The three-unit drivetrain assembly of Claim 1 , wherein the first unit is a wind turbine impeller, the second unit is an electric generator, and the third unit is an exciter.

12. The three-unit drivetrain assembly of any one of Claims 1 to 11, further comprising at least one RPM sensor for measuring rotation of a shaft.

13. The three-unit drivetrain assembly of Claim 12, further comprising a programmable logic controller operatively connected to the at least one RPM sensor for controlling the operation of the clutch.

14. A start-up method for a dual-rotor wind turbine system wherein the blades of the first rotor are larger than the blades of the second rotor, the method comprising:

(c) connecting a generator to a power grid; and

15. A start-up method for a dual-rotor wind turbine system wherein the blades of the first rotor are larger than the blades of the second rotor, the method comprising:

(a) opening a first adjustable speed drive (ASD) and a second ASD while each of a first brake and a second brake are closed;

(b) connecting a generator to a power grid;