Electrical power systems and subsystems

An electrical power system includes a cluster of electrical power subsystems, each of the electrical power subsystems including a power converter electrically coupled to a generator having a generator rotor and a generator stator. Each of the electrical power subsystems defines a stator power path and a converter power path for providing power to the power grid, the converter power path including a partial power transformer. Each of the electrical power subsystems further includes a low voltage distribution panel electrically coupled to the converter power path, a first switch on the stator power path, and a second switch on the converter power path.

FIELD OF THE INVENTION

The present disclosure relates generally to electrical power systems for providing power to a power grid from, for example, wind turbines.

BACKGROUND OF THE INVENTION

Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.

For example,FIGS. 1 and 2illustrate a wind turbine10and associated power system suitable for use with the wind turbine10according to conventional construction. As shown, the wind turbine10includes a nacelle14that typically houses a generator28(FIG. 2). The nacelle14is mounted on a tower12extending from a support surface (not shown). The wind turbine10also includes a rotor16that includes a plurality of rotor blades20attached to a rotating hub18. As wind impacts the rotor blades20, the blades20transform wind energy into a mechanical rotational torque that rotatably drives a low-speed shaft22. The low-speed shaft22is configured to drive a gearbox24(where present) that subsequently steps up the low rotational speed of the low-speed shaft22to drive a high-speed shaft26at an increased rotational speed. The high-speed shaft26is generally rotatably coupled to a generator28(such as a doubly-fed induction generator or DFIG) so as to rotatably drive a generator rotor30. As such, a rotating magnetic field may be induced by the generator rotor30and a voltage may be induced within a generator stator32that is magnetically coupled to the generator rotor30. The associated electrical power can be transmitted from the generator stator32to a main three-winding transformer34that is typically connected to a power grid via a grid breaker36. Thus, the main transformer34steps up the voltage amplitude of the electrical power such that the transformed electrical power may be further transmitted to the power grid.

In addition, as shown, the generator28is typically electrically coupled to a bi-directional power converter38that includes a rotor-side converter40joined to a line-side converter42via a regulated DC link44. The rotor-side converter40converts the AC power provided from the rotor30into DC power and provides the DC power to the DC link44. The line side converter42converts the DC power on the DC link44into AC output power suitable for the power grid. Thus, the AC power from the power converter38can be combined with the power from the stator32to provide multi-phase power (e.g. three-phase power) having a frequency maintained substantially at the frequency of the power grid (e.g. 50 Hz/60 Hz).

As shown inFIG. 2, the illustrated three-winding transformer34typically has (1) a 33 kilovolt (kV) medium voltage (MV) primary winding33connected to the power grid, (2) a 6 to 13.8 kV MV secondary winding35connected to the generator stator32, and (3) a 690 to 900 volt (V) low-voltage (LV) tertiary winding37connected to the line-side power converter42.

Referring now toFIG. 3, individual power systems of a plurality of wind turbines10may be arranged in a predetermined geological location and electrically connected together to form a wind farm46. More specifically, as shown, the wind turbines10may be arranged into a plurality of groups48with each group separately connected to a main line50via switches51,52,53, respectively. In addition, as shown, the main line50may be electrically coupled to another, larger transformer54for further stepping up the voltage amplitude of the electrical power from the groups48of wind turbines10before sending the power to the grid.

One issue with such systems, however, is that the three-winding transformers34associated with each turbine10are expensive. Particularly, the secondary winding35of the transformer34that is connected to the generator stator32can be costly. Thus, it would be advantageous to eliminate such three-winding transformers from wind turbine power systems. Additionally, simplification of the protective components of such systems would be advantageous.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one embodiment, an electrical power system connectable to a power grid is provided. The electrical power system includes a cluster of electrical power subsystems, each of the electrical power subsystems including a power converter electrically coupled to a generator having a generator rotor and a generator stator. Each of the electrical power subsystems defines a stator power path and a converter power path for providing power to the power grid, the converter power path including a partial power transformer. Each of the electrical power subsystems further includes a low voltage distribution panel electrically coupled to the converter power path, a first switch on the stator power path, and a second switch on the converter power path. The electrical power system further includes a cluster transformer electrically coupled to the cluster of electrical power subsystems, and a cluster power path extending between each electrical power subsystem and the cluster transformer to electrically couple the cluster transformer to the cluster of electrical power subsystems. The electrical power system further includes a substation transformer for connecting the cluster transformer to the power grid, and a collection system power path extending between the cluster transformer and the substation transformer.

In accordance with another embodiment, an electrical power subsystem for connection to a power grid is provided. The electrical power subsystem includes a generator including a generator stator and a generator rotor, and a power converter electrically coupled to the generator. The power converter includes a rotor-side converter, a line-side converter, and a regulated DC link electrically coupling rotor-side converter and the line-side converter. The electrical power subsystem further includes a stator power path for providing power from the generator stator to the power grid, and a converter power path for providing power from the generator rotor through the power converter to the power grid. The electrical power subsystem further includes a partial power transformer provided on the converter power path, a low voltage distribution panel electrically coupled to the converter power path, a first switch on the stator power path, and a second switch on the converter power path between the partial power transformer and the cluster power path.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIG. 4, a schematic diagram of one embodiment of an electrical power subsystem102according to the present disclosure is illustrated. It should be understood that the term “subsystem” is used herein to distinguish between the individual power systems (e.g. as shown inFIG. 4orFIG. 2) and the overall electrical power system105ofFIG. 5orFIG. 3that includes a plurality of electrical power subsystems102. Those of ordinary skill in the art, however, will recognize that the electrical power subsystem102ofFIG. 4(orFIG. 2) may also be referred to more generically, such as a simply a system (rather than a subsystem). Therefore, such terms may be used interchangeably and are not meant to be limiting.

Further, as shown, the electrical power subsystem102may correspond to a wind turbine power system100. More specifically, as shown, the wind turbine power system100includes a rotor104that includes a plurality of rotor blades106attached to a rotating hub108. As wind impacts the rotor blades106, the blades106transform wind energy into a mechanical rotational torque that rotatably drives a low-speed shaft110. The low-speed shaft110is configured to drive a gearbox112that subsequently steps up the low rotational speed of the low-speed shaft110to drive a high-speed shaft114at an increased rotational speed. The high-speed shaft114is generally rotatably coupled to a doubly-fed induction generator116(referred to hereinafter as DFIG116) so as to rotatably drive a generator rotor118. As such, a rotating magnetic field may be induced by the generator rotor118and a voltage may be induced within a generator stator120that is magnetically coupled to the generator rotor118. In one embodiment, for example, the generator116is configured to convert the rotational mechanical energy to a sinusoidal, three-phase alternating current (AC) electrical energy signal in the generator stator120. Thus, as shown, the associated electrical power can be transmitted from the generator stator120directly the grid.

In addition, as shown, the generator116is electrically coupled to a bi-directional power converter122that includes a rotor-side converter124joined to a line-side converter126via a regulated DC link128. Thus, the rotor-side converter124converts the AC power provided from the generator rotor118into DC power and provides the DC power to the DC link128. The line side converter126converts the DC power on the DC link128into AC output power suitable for the power grid. More specifically, as shown, the AC power from the power converter122can be combined with the power from the generator stator120via a converter power path127and a stator power path125, respectively. For example, as shown, and in contrast to conventional systems such as those illustrated inFIGS. 1-3, the converter power path127may include a partial power transformer130for stepping up the voltage amplitude of the electrical power from the power converter122such that the transformed electrical power may be further transmitted to the power grid. Thus, as shown, the illustrated system102ofFIG. 4does not include the conventional three-winding main transformer described above. Rather, as shown in the illustrated embodiment, the partial power transformer130may correspond to a two-winding transformer having a primary winding132connected to the power grid and a secondary winding134connected to the line side converter126. Notably, the partial power transformer may in some embodiments include a third auxiliary winding for auxiliary loads, as discussed herein.

In addition, the electrical power subsystem102may include a controller136configured to control any of the components of the wind turbine100and/or implement the method steps as described herein. For example, as shown particularly inFIG. 6, the controller136may include one or more processor(s)138and associated memory device(s)140configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like and storing relevant data as disclosed herein). Additionally, the controller136may also include a communications module142to facilitate communications between the controller136and the various components of the wind turbine100, e.g. any of the components ofFIGS. 4 and 5. Further, the communications module142may include a sensor interface144(e.g., one or more analog-to-digital converters) to permit signals transmitted from one or more sensors139,141,143to be converted into signals that can be understood and processed by the processors138. It should be appreciated that the sensors139,141,143may be communicatively coupled to the communications module142using any suitable means. For example, as shown inFIG. 6, the sensors139,141,143may be coupled to the sensor interface144via a wired connection. However, in other embodiments, the sensors139,141,143may be coupled to the sensor interface144via a wireless connection, such as by using any suitable wireless communications protocol known in the art. As such, the processor138may be configured to receive one or more signals from the sensors139,141,143.

In operation, alternating current (AC) power generated at the generator stator120by rotation of the rotor104is provided via a dual path to the grid, i.e. via the stator power path125and the converter power path127. More specifically, the rotor side converter124converts the AC power provided from the generator rotor118into DC power and provides the DC power to the DC link128. Switching elements (e.g. IGBTs) used in bridge circuits of the rotor side converter124can be modulated to convert the AC power provided from the generator rotor118into DC power suitable for the DC link128. The line side converter126converts the DC power on the DC link128into AC output power suitable for the grid. In particular, switching elements (e.g. IGBTs) used in bridge circuits of the line side converter126can be modulated to convert the DC power on the DC link128into AC power. As such, the AC power from the power converter122can be combined with the power from the generator stator120to provide multi-phase power having a frequency maintained substantially at the frequency of the grid. It should be understood that the rotor side converter124and the line side converter126may have any configuration using any switching devices that facilitate operation of electrical power system as described herein.

Further, the power converter122may be coupled in electronic data communication with the turbine controller136and/or a separate or integral converter controller154to control the operation of the rotor side converter124and the line side converter126. For example, during operation, the controller136may be configured to receive one or more voltage and/or electric current measurement signals from the first set of voltage and electric current sensors139,141,143. Thus, the controller136may be configured to monitor and control at least some of the operational variables associated with the wind turbine100via the sensors139,141,143. In the illustrated embodiment, the sensors139,141,143may be electrically coupled to any portion of electrical power subsystem102that facilitates operation of electrical power subsystem102as described herein.

It should also be understood that any number or type of voltage and/or electric current sensors may be employed within the wind turbine100and at any location. For example, the sensors may be current transformers, shunt sensors, rogowski coils, Hall Effect current sensors, Micro Inertial Measurement Units (MIMUs), or similar, and/or any other suitable voltage or electric current sensors now known or later developed in the art. Thus, the converter controller154is configured to receive one or more voltage and/or electric current feedback signals from the sensors139,141,143. More specifically, in certain embodiments, the current or voltage feedback signals may include at least one of line feedback signals, line-side converter feedback signals, rotor-side converter feedback signals, or stator feedback signals.

Referring particularly toFIG. 5, individual power systems (such as the power subsystem102illustrated inFIG. 4) may be arranged in at least two clusters137to form an electrical power system105. More specifically, as shown, the wind turbine power systems100may be arranged into a plurality of clusters137so as to form a wind farm. Thus, as shown, each cluster137may be connected to a separate cluster transformer145,146,147via switches151,152,153, respectively, for stepping up the voltage amplitude of the electrical power from each cluster137such that the transformed electrical power may be further transmitted to the power grid. In addition, as shown, the transformers145,146,147are connected to a main line148(via a substation transformer as discussed herein) that combines the power from each cluster137before sending the power to the grid. In other words, as shown, the stator power circuit of all the wind turbines100share a common ground reference provided by the neutral of the secondary winding124of the cluster transformer145,146,147or by a separate neutral grounding transformer. Each subsystem102may be connected to the cluster137via a subsystem breaker135, as shown.

Referring still toFIG. 5, and as discussed, the cluster137includes a cluster transformer145,146,147connecting each cluster137of electrical power subsystems102to the power grid. Thus, the cluster137includes a cluster switch151,152,153configured with the cluster transformer145,146,147. A cluster power path170may electrically connect the cluster137to the cluster transformer145,146,147, such as via cluster switches151,152,153. The cluster power path170may, for example, extend from each subsystem102, such as the converter power path127and stator power path125thereof, to the cluster transformer145,146,147, such as to the winding of the cluster transformer to which the subsystem102is connected.

The cluster transformer145,146,147is, in exemplary embodiments, a two-winding transformer145,146,147. Further, in exemplary embodiments, the cluster transformer145,146,147steps the voltage up from a low voltage level at the substation level to a medium voltage at the cluster level.

For example, the voltage on the stator power path125of each subsystem102may be a medium voltage, such as between 6 and 14 kV, or between 12 and 14 kV. The voltage on the converter power path127after the power converter122may be a low voltage, such as between 600 and 900 V. This voltage may be stepped up to the medium voltage level of 6 and 14 kV, or between 12 and 14 kV, by the partial power transformer130. Partial power transformer130may thus include a primary winding132having a voltage between 6 and 14 kV, or between 12 and 14 kV, and a secondary winding134having a voltage between 600 and 900 V.

Each cluster transformer145,146,147may include a primary winding202and a secondary winding204. The secondary winding204may be connected to the cluster power path170, and the primary winding202may be connected to a collection system power path180leading to the power grid. The primary winding202may have a voltage between 30 and 35 Kilovolts, and the secondary winding204may have a voltage between 11 and 15 Kilovolts.

The collection system power path180may extend between each cluster transformer145,146,147and a substation transformer210. In exemplary embodiments, substation transformer210is a two-winding transformer. The substation transformer210may electrically connect the cluster transformers145,146,147to the power grid. The substation transformer210may include a primary winding212and a secondary winding214. The secondary winding214may be connected to the collection system power path180, and the primary winding212may be connected to a main line148leading to the power grid. The primary winding212may have a voltage between 110 and 250 Kilovolts, and the secondary winding214may have a voltage between 30 and 35 Kilovolts.

Referring now toFIGS. 7-9, in exemplary embodiments, each subsystem102of the system105ofFIG. 5may include various features for reducing cost and increasing efficiency. Such features may advantageously simplify the protective scheme and necessary components thereof for the subsystems102and system105generally. For example, as shown, each subsystem102may include a low voltage distribution panel220which is electrically coupled to the converter power path127, such as the line side thereof as shown. The low voltage distribution panel220may provide power to auxiliary loads, such as lighting and other relatively small loads within the wind turbine of the subsystem102.

In some embodiments, as illustrated inFIGS. 7 and 8, the partial power transformer130is a three-winding transformer which includes an auxiliary winding133in addition to primary winding132and secondary winding134. Auxiliary winding133may be a low voltage (300-900 V) winding. Power may be provided through auxiliary winding133to the low voltage distribution panel220. An auxiliary power path222thus extends between and electrically couples the panel220and auxiliary winding133.

In other embodiments, as illustrated inFIG. 9, the partial power transformer130is a two-winding transformer which includes only the primary winding132and secondary winding134. In these embodiments, power may be provided to the low voltage distribution panel220via an electrical coupling of the low voltage distribution panel220to the primary winding132side of the converter power path127, such as to the converter power path127between the transformer130and the cluster power path170, via the auxiliary power path222. In these embodiments an auxiliary power transformer230may be provided on the auxiliary power path222, and may provide such electrical coupling. The auxiliary power transformer230may, in exemplary embodiments, be a two-winding transformer with low voltage (600-900 V) primary winding and medium voltage (6-14 or 12-14 mV) secondary winding.

Subsystem102may further include various switches, which may be relatively low cost switches due to the high efficiency nature of the subsystem102.

For example, a first switch240may be provided on the stator power path125. In some embodiments, as shown inFIG. 7, the first switch240is a contactor, such as a vacuum contactor. In these embodiments, a fuse241may additionally be provided on the stator power path125, such that the switch240is configured as a contactor and fuse. In alternative embodiments, as shown inFIGS. 8 and 9, the first switch240is a circuit breaker. Alternatively, other suitable switches may be utilized.

Additionally or alternatively, a second switch142may be provided on the converter power path127, such as on the line side between the partial power transformer130and the cluster power path170(i.e. on the primary winding132side of the converter power path127). In some embodiments, as shown inFIG. 7, the second switch242is a contactor, such as a vacuum contactor. In these embodiments, a fuse243may additionally be provided on the converter power path127, such that the switch242is configured as a contactor and fuse. In alternative embodiments, as shown inFIGS. 8 and 9, the second switch242is a circuit breaker. Alternatively, other suitable switches may be utilized.

In some embodiments, as illustrated inFIGS. 7 and 8, a third switch144may be provided on the converter power path127, such as on the line side between the power converter122and the partial power transformer130(i.e. on the secondary winding134side of the converter power path127). For example, such third switch144may be provided in embodiments wherein the partial power transformer130is a three-winding transformer. Alternatively, in other embodiments as illustrated inFIG. 9, no third switch144is necessary in this location. For example, the third switch144may be eliminated in embodiments wherein the partial power transformer130is a two-winding transformer. Further, in some embodiments as illustrated inFIG. 9when a two-winding partial power transformer130is utilized, a fourth switch146may be provided. For example, as shown, the fourth switch146may be provided on the auxiliary power path222between the auxiliary transformer230and the converter side power path127.