Patent Application
20180187652
The present subject matter relates generally to renewable energy sources, and more particularly to power converter topologies for full power conversion wind turbine systems.
Wind turbines have received increased attention as a renewable energy source. Wind turbines use the wind to generate electricity. The wind turns multiple blades connected to a rotor. The spin of the blades caused by the wind spins a shaft of the rotor, which connects to a generator that generates electricity. Certain wind turbine systems include a full power generator to convert wind energy into electrical power suitable for output to an electrical grid. Full power generators are typically connected to a converter that regulates the flow of electrical power between the generator and the grid. More particularly, the converter allows the wind turbine to output electrical power at the grid frequency regardless of the rotational speed of the wind turbine blades.
A typical full power conversion system includes a full power generator having a rotor and a stator. The generator can be coupled to a power converter having a generator side converter and a line side converter. The generator side converter can receive alternating current (AC) power from the generator via a stator bus and can convert the AC power to a direct current (DC) power. The line side converter can then convert the DC power to AC power having a suitable output frequency, such as the grid frequency. The AC power is provided to the electrical grid via a line bus. An auxiliary power feed can be coupled to the line bus to provide power for components used in the wind turbine system, such as fans, pumps, motors, and other components of the wind turbine system.
A typical full power conversion system includes a two-winding transformer having a medium voltage primary (e.g. 6 KVAC, 12 KVAC, etc.) and a low voltage secondary (e.g. 575 VAC, 690 VAC, etc.) to couple the system to the electrical grid. As used herein, the term “low voltage” can refer to voltages less than or equal to 1.5 kV, and the term “medium voltage” can refer to voltages greater than 1.5 kV and less than 100 kV. For instance,
Such transformers can be used to increase the low voltage provided by the power converter via the line bus to a medium voltage suitable for output to the electrical grid. However, the transformers can be costly and can have a considerable effect on the overall size of the wind turbine system.
Aspects and advantages of embodiments of the present disclosure will be set forth in part in the following description, or may be learned from the description, or may be learned through practice of the embodiments.
One example embodiment of the present disclosure is directed to a wind turbine system. The wind turbine system includes a full power generator having a rotor and a stator. The generator is configured to provide a low voltage alternating current power on a stator bus of the wind turbine system. The wind turbine system further includes a power converter configured to convert the low voltage alternating current power provided on the stator bus to a medium voltage multiphase alternating current output power suitable for provision to the electrical grid. The power converter includes a plurality of conversion modules. Each conversion module includes a plurality of bridge circuits. Each bridge circuit includes a plurality of silicon carbide switching devices coupled in series. Each conversion module is configured to provide a single phase of the medium voltage multiphase alternating current output power on a line bus of the wind turbine system.
Another example aspect of the present disclosure is directed to a power converter for use in a full conversion wind turbine system having a full power generator, a rotor and a stator. The full power generator is configured to provide a low voltage alternating current power on a stator bus of the wind turbine system. The power converter includes a plurality of conversion modules. Each conversion module includes a plurality of bridge circuits. Each bridge circuit includes a plurality of silicon carbide switching devices coupled in series. The power converter is configured to convert the low voltage alternating current power provided by the full power generator to a medium voltage multiphase alternating current output power suitable for provision to the electrical grid. Each conversion module is configured to provide a single phase of the medium voltage multiphase alternating current output power on a line bus of the wind turbine system.
Yet another example aspect of the present disclosure is directed to a power conversion system including a plurality of conversion modules. Each conversion module includes a plurality of bridge circuits and an isolation transformer coupled to at least two of the bridge circuits. Each bridge circuit includes a plurality of switching devices coupled in series. The power conversion system is configured to convert a low voltage alternating current power provided by a full power generator to a medium voltage multiphase alternating current output power suitable for provision to an alternating current power system. Each conversion module is configured to provide a single phase of the medium voltage multiphase alternating current output power on a line bus associated with the power conversion system
Variations and modifications can be made to these example aspects of the present disclosure.
These and other features, aspects and advantages of various embodiments will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the related principles.
Detailed discussion of embodiments directed to one of ordinary skill in the art are set forth in the specification, which makes reference to the appended figures, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Example aspects of the present disclosure are directed to power converters for use in a full power conversion wind turbine system. In particular, example aspects of the present disclosure are directed to power converters capable of converting a low voltage (LV) power to a medium voltage (MV) power. The wind turbine system can include a full power generator having a rotor and a stator. A power converter can be used to couple the generator to an electrical grid. In some implementations, the power converter can be a two stage power converter that includes a generator side converter and a line side converter coupled together by a DC link. In some implementations, the power converter can be a single stage converter. The power converter (e.g. the generator side converter and/or the line side converter) can include a plurality of bridge circuits coupled in parallel. Each of the bridge circuits can include a pair of switching devices coupled in series with one another. At least a subset of the switching devices can be silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs). In some implementations, at least a subset of the switching devices can be insulated gate bipolar transistors (IGBTs). The bridge circuits can be controlled, for instance using gate timing commands provided to the switching devices, to provide a desired output to the electrical grid.
According to example aspects of the present disclosure the power converter can include a plurality of power conversion modules. Each power conversion module can be associated with a single phase of a multiphase (e.g. three-phase) AC power. In this manner, the number of power conversion modules can correspond to the number of phases in the multiphase AC power. Each power conversion module can include one or more module branches. The module branches can include a plurality of bridge circuits coupled in parallel. The module branches can further include an isolation transformer coupled to at least a portion of the bridge circuits. The module branches can be coupled to each other in parallel on a LV side of the conversion module, and in series on a MV side of the conversion module.
In particular, the module branches can be configured to convert a LV DC input power to a MV AC output power, and to provide the MV AC output power on a line bus of the wind turbine system. For instance, the SiC MOSFETs can be switched at a sufficient frequency to allow for small scale isolation transformers to be implemented within each of the module branches. The isolation transformers can be configured as step-up or step-down transformers depending on the direction of the flow of power through the power converter. More particularly, the transformer winding facing the MV side of the module branch can have a greater number of turns than the transformer winding facing the LV side of the module branch. The particular configurations of the transformers can be selected based at least in part on the grid voltage and/or the voltage provided by the generator.
Each module branch contributes to at least a portion of the MV AC output. In this manner, the number of module branches in each conversion module can be determined based at least in part on a desired AC output. In some implementations, the conversion modules can be replaceable units, such that the power converter can be implemented in a modular manner by adding or removing the conversion module units to produce a desired output. For instance, the conversion modules can be configured as individual units capable of being selectively coupled to the power converter through one or more interface components. In this manner, a technician or user of the wind turbine system can add or remove the modules by coupling the modules to the system via the interface components.
Implementing power converters in accordance with example aspects of the present disclosure within the wind turbine system can allow the line bus to be coupled to the electrical grid without the need for a transformer (e.g. a 50 Hz transformer of 60 Hz transformer) to convert the line bus voltage to a MV suitable for the electric grid. In this manner, the 50/60 Hz transformer can be replaced by smaller, lower frequency transformers in each module branch. Such smaller module branch transformers can allow for an overall reduction in size of the wind turbine system. In addition, the use of SiC MOSFETs as switching devices in the power converter can increase an efficiency of the power converter via increased switching frequencies and reduced switching losses relative, for instance, to IGBT switching devices. It will be appreciated that any suitable high frequency switching device can be used to provide the increased switching frequencies.
With reference now to the figures, example aspects of the present disclosure will be discussed in greater detail. For instance,
In the example system 100, a rotor 106 includes a plurality of rotor blades 108 coupled to a rotating hub 110, and together define a propeller. The propeller is coupled to an optional gear box 118, which is, in turn, coupled to a generator 120. In accordance with aspects of the present disclosure, the generator 120 is a full power generator 120.
Generator 120 is typically coupled to a stator bus 154 and a power converter 162 via the stator bus 154. The stator bus provides an output multiphase power (e.g. three-phase power) from a stator of generator 120. The power converter 162 can be a bidirectional power converter configured to provide output power to the electrical grid 184 and/or to receive power from the electrical grid 184. As shown, generator 120 is coupled via the stator bus 154 to a generator side converter 166. The generator side converter 166 is coupled to a line side converter 168 which in turn is coupled to a line side bus 188.
In example configurations, the generator side converter 166 and the line side converter 168 are configured for normal operating mode in a three-phase, pulse width modulation (PWM) arrangement using SiC MOSFETs and/or IGBTs as switching devices. In some implementations, the generator side converter 166 and/or the line side converter 168 can include a plurality of conversion modules, each associated with a an output phase of the multiphase power, as will be discussed in more detail with respect to
The power converter 162 can be coupled to a controller 174 to control the operation of the generator side converter 166 and the line side converter 168. It should be noted that the controller 174, in typical embodiments, is configured as an interface between the power converter 162 and a control system 176.
In operation, power generated at generator 120 to electrical grid 184 via the power converter 162. In particular, the sinusoidal multiphase (e.g. three-phase) power is provided to the power converter 162 via the stator bus 154. The AC power provided via the stator bus 154 can be a LV AC power. The generator side converter 166 converts the LV AC power provided from the generator 120 into DC power and provides the DC power to the DC link 136. Switching devices (e.g. SiC MOSFETs and/or IGBTs) used in bridge circuits of the generator side converter 166 can be modulated to convert the AC power provided on the stator bus 154 into DC power suitable for the DC link 136. Such DC power can be a LV DC power.
The line side converter 168 converts the LV DC power on the DC link 136 into a MV AC power suitable for the electrical grid 184. In particular, switching devices (e.g. SiC MOSFETs) used in bridge circuits of the line side power converter 168 can be modulated to convert the DC power on the DC link 136 into AC power on the line bus 188. In addition, one or more isolation transformers coupled to one or more of the bridge circuits can be configured to step the voltage up to the MV voltage. The MV AC power from the power converter 162 can be a multiphase power (e.g. three-phase power) having a frequency maintained substantially at the frequency of the electrical grid 184 (e.g. 50 Hz/60 Hz), and can be provided to the electrical grid 184 via the line bus 188.
Various circuit breakers and switches, such as grid breaker 182, stator sync switch 158 can be included in the system 100 for isolating the various components as necessary for normal operation of generator 120 during connection to and disconnection from the electrical grid 184. In this manner, such components can be configured to connect or disconnect corresponding buses, for example, when current flow is excessive and can damage components of the wind turbine system 100 or for other operational considerations. Additional protection components can also be included in the wind turbine system 100, such as one or more additional breakers, one or more fuses, one or more lockout tagout devices, etc.
The power converter 162 can receive control signals from, for instance, the control system 176 via the controller 174. The control signals can be based, among other things, on sensed conditions or operating characteristics of the wind turbine system 100. Typically, the control signals provide for control of the operation of the power converter 162. For example, feedback in the form of sensed speed of the generator 120 can be used to control the conversion of the output power from the stator bus 154 to maintain a proper and balanced multiphase (e.g. three-phase) power supply. Other feedback from other sensors can also be used by the controller 174 to control the power converter 162, including, for example, stator bus voltages and current feedbacks. Using the various forms of feedback information, switching control signals (e.g. gate timing commands for switching devices), stator synchronizing control signals, and circuit breaker signals can be generated.
Each conversion module 200-204 includes a plurality of module branches. For instance, as shown, conversion module 200 includes module branch 206, module branch 208, and module branch 210. Each module branch 206-210 comprises a plurality of conversion entities. For instance, module branch 206 includes conversion entity 212, conversion entity 214, and conversion entity 216. Each conversion entity 212-216 can include a plurality of bridge circuits coupled in parallel. For instance, conversion entity 216 includes bridge circuit 218 and bridge circuit 220. As indicated, each bridge circuit can include a plurality of switching devices coupled in series. For instance, bridge circuit 220 includes an upper switching device 222 and a lower switching device 224. The switching devices can be SiC MOSFET switching devices. As shown, each module branch 206-210 further includes an isolation transformer 226. The isolation transformer is coupled to conversion entity 212 and conversion entity 214. As shown, the conversion branches further include capacitors 228 and 230.
The line side converter 168 can be a bidirectional power converter. The line side converter 168 can be configured to convert a LV DC power to a MV AC power and vice versa. For instance, when providing power to the electrical grid 184, the line side converter 168 can be configured to receive a LV DC power from the DC link 136 on a LV side of the line side converter 168, and to output a MV AC power on a MV side of the line side converter 168. The module branches 206-210 can be coupled together in parallel on the LV side and can be coupled together in series on the MV side.
In one particular example implementation, when providing power to the electrical grid 184, the conversion entity 212 can be configured to convert the LV DC on the DC link 136 to a LV AC power. The isolation transformer 226 can be configured to step the LV AC power up to a MV AC power. The conversion entity 214 can be configured to convert the MV AC power to a MV DC power. The conversion entity 216 can be configured to convert the MV DC power to a MV AC power suitable for provision to the electric grid 184.
The module branches 206-210 can be configured to contribute to the overall MV AC power provided by the conversion module 200. In this manner, any suitable number of module branches can be included within the module branches 206-210. As indicated, each conversion module 200-204 is associated with a single phase of output power. In this manner, the switching devices of the conversion modules 200-204 can be controlled using suitable gate timing commands (e.g. provided by one or more suitable driver circuits) to generate the appropriate phase of output power to be provided to the electrical grid. For example, the controller 174 can provide suitable gate timing commands to the gates of the switching devices of the bridge circuits. The gate timing commands can control the pulse width modulation of the IGBTs to provide a desired output.
It will be appreciated, that although
The conversion module 310 can receive a LV AC power from the stator bus 304 on a LV side of the power converter 302. The conversion entity 312 can convert the LV AC power to a LV DC power. As shown, the conversion entity can include a plurality of bridge circuits including a plurality IGBT switching devices (e.g. IGBT 326) coupled in series. Each IGBT switching device includes a diode coupled in parallel to the IGBT switching device. It will be appreciated that the conversion entity 312 can be implemented using various other suitable switching devices, such as SiC MOSFET switching devices. The conversion entity 314 can be configured to convert the LV DC power to a LV AC power, which can be stepped up to a MV AC power by the isolation transformer 320. The conversion entity 316 can be configured to convert the MV AC power to a MV DC power, and the conversion entity 318 can be configured to convert the MV DC power to a MV AC power suitable for provision to the electrical grid 184.
As shown, a single conversion entity 404 can be implemented on the LV side of the converter 400. The conversion entity 404 can be coupled to the single winding on the LV side of the transformer 400. The conversion entity 404 can be configured to convert a LV DC power to a LV AC power. The transformer 402 can be configured to step the LV AC power up to a MV AC power and to provide the MV AC power on each winding of the multiple winding side of the transformer 402. In particular, each winding on the multiple winding side of the transformer 402 can be coupled to a conversion entity (e.g. conversion entities 406-410). The conversion entities 406-410 can be configured to convert the MV AC power to a MV DC power, and to provide the MV DC power to respective other conversion entities for a conversion of the MV DC to a MV AC suitable for provision to a grid.
As shown, a DC-DC portion 422 of the power converter 420 can correspond to converter 400 depicted in
The topologies of the converters 400 and 420 depicted in
Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the present disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
