Patent Publication Number: US-2016230743-A1

Title: Wind turbine converter

Description:
I. FIELD OF THE INVENTION 
     The present invention relates generally to wind turbines. More particularly, the present invention relates to positioning of wind turbine power generators. 
     II. BACKGROUND OF THE INVENTION 
     In recent years, as the supply of our fossil energy resources, such as oil and coal, decreases and the prices and the effort to recover them increase, alternative energy resources, for example, such as wind energy produced by wind turbines, have become popular for supplying the increasing demand for electric power. Wind turbines are one type of renewable energy-based power unit that competes with traditional forms of electric power generation. As a result, wind turbines capture wind energy and convert it to electrical energy in a cost effective, reliable, and safe manner such that it is suitable for delivery miles away. 
     In operation, the wind turbines may include multiple rotating blades that are connected to a rotor shaft and rotated by the wind. The rotation of the blades by the wind spins the rotor shaft to generate a rotational torque or force that drives one or more generators to convert mechanical energy to electrical energy. The rotor shaft and generator are mounted within a housing or nacelle that is positioned on top of a truss or tubular tower. The electrical energy generated in the nacelle is distributed down through the tower to a utility grid via a transformer. 
     Wind energy has several applications, ranging from large fields of wind turbines, interconnected and delivering power to the utility grid, to individual, isolated wind turbines that may or may not be grid-connected. As such, wind turbines can be used to produce electricity for a single home or building, or they can be connected to an electricity grid for more widespread electricity distribution. The interconnection of the wind turbines to the electrical grid can be grouped into classifications based on the size of the installations, the size of the contribution to a total electricity supply (wind penetration), whether the electricity is used for frequency or reactive power, and the degree of integration with other power sources. 
     Some wind turbine configurations include doubly fed induction generators (DFIGs). Such configurations may also include alternating current (AC)-direct current (DC)-AC frequency converters that are used to convert a frequency of generated electric power to a frequency substantially similar to a utility grid frequency. Moreover, such converters, in conjunction with the DFIG, also transmit electric power between the utility grid and the generator as well as transmit generator excitation power to a wound generator rotor from one of the connections to the electric utility grid connection. 
     Alternatively, some wind turbine configurations include, but are not limited to, alternative types of induction generators, permanent magnet (PM) synchronous generators and electrically-excited synchronous generators and switched reluctance generators. These alternative configurations may also include power converters that are used to convert the frequencies as described above and transmit electrical power between the utility grid and the generator. 
     In some known wind turbines, the nacelle of a wind turbine contains the essential machinery and power electronic devices that enable the efficient conversion of wind energy into electrical energy such as the generator and possibly the power converter. As heart of a wind turbine, the nacelle must function reliably and cost efficiently throughout the service life of the wind turbine. Usually, the space inside the nacelle is limited and a high number of power cables or bus-bars are used to connect the individual power electronic components, which add costs. Thus sometimes, the converter is in the lower part of a wind turbine tower. 
       FIG. 1  is a perspective view of a portion of an exemplary DFIG wind turbine system  100 . Wind turbine  100  includes a nacelle  102  housing a generator  118  (shown in  FIG. 2 ). Nacelle  102  is mounted on a tower  104  (a portion of tower  104  being shown in  FIG. 1 ). Tower  104  may have any suitable height that facilitates operation of wind turbine  100 . Wind turbine  100  also includes a rotor  106  that includes three blades  108  attached to a rotating hub  110 . Alternatively, wind turbine  100  includes any number of blades  108  that facilitates operation of wind turbine  100 . In the exemplary embodiment, wind turbine  100  includes a gearbox  114  (shown in  FIG. 2 ) operatively coupled to rotor  106  and a generator  118  (shown in  FIG. 2 ). 
       FIG. 2  is a schematic view of an exemplary electrical and control system  200  that may be used with wind turbine  100 . Rotor  106  includes blades  108  coupled to hub  110 . Rotor  106  also includes a low-speed shaft  112  rotatably coupled to hub  110 . Low-speed shaft  112  is coupled to a step-up gearbox  114  that is configured to step up the rotational speed of low-speed shaft  112  and transfer that speed to a high-speed shaft  116 . In the exemplary embodiment, gearbox  114  has any suitable step-up ratio that facilitates operation of wind turbine  100 . 
     High-speed shaft  116  is rotatably coupled to generator  118 . In the exemplary embodiment, generator  118  can be configured as a wound rotor, three-phase, asynchronous DFIG that includes a generator stator  120  magnetically coupled to a generator rotor  122 . 
     During operation, the wind turns the propellers  108  attached to gearbox  114  inside the nacelle  102 , coupled to generator  118 . The wind turbine system  100  includes an AC-DC-AC converter  124  (shown in  FIG. 2 ) which controls the generator  118  through rotor bus  126 . Converter  124  also connects to an oil-filled pad mounted transformer  128  through line bus  130  and converter circuit breaker (CB)  132 . Generator  118  connects to the transformer  128  through stator bus  134  and stator sync switch  136 . The oil-filled pad mounted transformer  128  steps up the voltage and feeds power to the high voltage (HV) utility grid  138 . 
     In some known wind turbines, the converter  124  is located in the lower part of the wind turbine tower  104  and the oil-filled pad mounted transformer  128  is located outside of the tower  104 , as exemplified in  FIG. 1 . In  FIG. 1 , the converter  124  and the oil-filled pad mounted transformer  128  are separate and independent components. The maximum efficiency for a wind turbine is achieved at the generator frequency and voltage rather than the grid frequency. This makes it necessary to include an AC-DC-AC frequency converter within the system. However, the AC-DC-AC frequency converter can be expensive, unreliable, complicated and have a high power loss. 
     Furthermore, known wind turbines have a plurality of mechanical and electrical components, which may have independent or different operating limitations, such as current, voltage, power, and/or temperature limits, than other components. Many of the electrical and/or mechanical components come together for the first time after being installed in the wind turbine. 
     For this purpose, it will be appreciated that easy testing of the mechanical and power electronic components before installation, to ensure an optimum compatibility between the components and an efficient, harmonious, long-lasting and trouble-free operation of the wind turbine is desired. Further, easy repair and exchange of faulty parts as well as the reduction of material costs inside the wind turbine and an increase in overall efficiency of the wind turbine is desirable. 
     III. SUMMARY OF EMBODIMENTS OF THE INVENTION 
     Given the aforementioned deficiencies, a need exists for improved assembly methods and systems, in particular with respect to transformers and power converters. These improved assembly methods and systems are needed to achieve the aforementioned cost, reliability, spatial, material and maintenance benefits. A need also exists to provide a system and method that easily eliminates water, improves cooling, and improves isolation. It may be desirable to provide a system and method that offers higher power density and higher reliability. 
     In certain embodiments, a wind turbine system is provided. In various embodiments, the system includes a nacelle supported by a tower. At least one rotor blade is rotatably connected with the nacelle to capture wind energy. The at least one rotor blade rotates relative to the nacelle for generating electricity. A generator is coupled to the nacelle for converting the wind energy into electrical energy. A transformer-converter assembly comprises a converter and a transformer such that the converter is integrally connected to the transformer. An electrical and control module is electronically coupled to the generator and the transformer-converter assembly. 
     In other embodiments, a method is provided for generating electricity, which includes supporting a nacelle by a tower; connecting at least one rotor blade with the nacelle to capture wind energy such that the at least one rotor blade rotates relative to the nacelle for generating electricity; coupling a generator to the nacelle and for converting the wind energy into electrical energy; providing a transformer-converter assembly, comprising: a converter; a transformer; and wherein the converter is integrally connected to the transformer; and electronically coupling an electrical and control module to the generator and the transformer-converter assembly. 
     Further features and advantages, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. The invention is not limited to the specific embodiments described herein. The embodiments are presented for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. 
    
    
     
       IV. BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic and block diagram of an example of a DFIG wind power system for use with the wind turbine shown in  FIG. 2 ; 
         FIG. 2  is a perspective view of a portion of an exemplary wind turbine; 
         FIG. 3  is a perspective view of a portion of an exemplary wind turbine in accordance with the present disclosure; 
         FIG. 4A  is a perspective view of a portion of another exemplary wind turbine in accordance with a second embodiment of the present disclosure; 
         FIG. 4B  is a perspective view of a portion of another exemplary wind turbine in accordance with a third embodiment of the present disclosure; 
         FIG. 5  is schematic and block diagram of an example of a DFIG wind power system in accordance with the present disclosure; and 
         FIG. 6  is a flowchart of an exemplary method of practicing the present invention in accordance with the present disclosure. 
     
    
    
     The present disclosure may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The present disclosure is illustrated in the accompanying drawings, throughout which, like reference numerals may indicate corresponding or similar parts in the various figures. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the disclosure. Given the following enabling description of the drawings, the novel aspects of the present disclosure should become evident to a person of ordinary skill in the art. 
     V. DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     The following detailed description is merely exemplary in nature and is not intended to limit the applications and uses disclosed herein. On the contrary, the disclosure is intended to cover alternatives, modifications, and equivalents. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet further embodiments. It is intended that the present disclosure includes such modifications and variations. Further, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. While embodiments of the present technology are described herein primarily in connection with DFIG wind power systems, the concepts are also applicable to other types of wind turbine system having a converter such as full power converter wind power systems or other similar systems with a converter. 
     Throughout the application, description of various embodiments may use “comprising” language, however, it will be understood by one of skill in the art, that in some specific instances, an embodiment can alternatively be described using the language “consisting essentially of” or “consisting of.” 
     For purposes of better understanding the present teachings and in no way limiting the scope of the teachings, it will be clear to one of skill in the art that the use of the singular includes plural unless specifically stated otherwise. Therefore, the terms “a,” “an” and “at least one” are used interchangeably in this application. 
     As used herein, the term “blade” is intended to be representative of any device that provides a reactive force when in motion relative to a surrounding fluid. As used herein, the term “wind turbine” is intended to be representative of any device that generates rotational energy from wind energy, and more specifically, converts kinetic energy of wind into mechanical energy. As used herein, the term “wind generator” is intended to be representative of any wind turbine that generates electrical power from rotational energy generated from wind energy, and more specifically, converts mechanical energy converted from kinetic energy of wind to electrical power. 
     As used herein, the term “converter” is intended to be representative of an AC-DC-AC power converter optionally including a DC link. Further, the term “converter” may also be representative of an AC-DC power converter or a DC-AC power converter both optionally with part of a DC link. As used herein the term “full frequency converter” is intended to be representative of a converter that is able to convert frequencies in the range of 0 to 200 Hz or more. 
     As used herein the term “generator-side converter” is intended to be representative of the portion of a power converter that is linked with the rotor or stator of a power generator, and usually includes an AC-DC converter and optionally part of a DC link. As used herein the term “line-side converter” is intended to be representative of the portion of a power converter that is linked with an electrical supply grid, and usually includes a DC-AC converter and optionally part of a DC link. 
     As used herein, the term “inside the tower” is intended to be representative of any location inside a wind turbine base, tower or nacelle. As used herein, the term “outside the tower” is intended to be representative of any location outside of a wind turbine. 
     The embodiments described herein include a wind turbine system that includes an oil-filled transformer that houses a converter and all electrical components in the power flow path to form a transformer-converter assembly. Thus, the converter can be mechanically attached or integrally connected to the oil-filled transformer. The transformer-converter assembly can be mechanically attached to or positioned nearby a wind turbine. Hence, in one embodiment, the transformer-converter assembly may be mechanically attached to the wind turbine nacelle, base or tower. In another embodiment, the transformer-converter assembly may be located nearby the tower. 
     Attaching the converter in or on the oil-filled pad mounted transformer allows for an integrated packaging of the system and frees up space. Through the compact and integrated design, material savings may be made, because the converter and the transformer may include a number of the same pieces. 
     In further embodiments herein, the transformer-converter assembly may be attached somewhere along and around the nacelle. Hence, easy access to the transformer-converter assembly would be enabled. Not limited to a particular embodiment the transformer-converter assembly may be attached to the nacelle mechanically or physically, for instance, by welding, screwing, bolting or any other friction/form fit that may, for example, include magnetic or adhesive forces. 
     In embodiments herein, the individual DC links of the one or more separate full frequency AC-DC and DC-AC converters may be connected to a DC collector system directly. The DC collector system may connect the individual DC links of AC-DC generator-side converters of more than one wind turbine for instance of an on-or offshore wind park in series or parallel to one or more central full frequency DC-AC line-side converters. In a similar fashion one or more full frequency AC-DC-AC converters of more than one wind turbine for instance of an on- or offshore wind park may be connected in series or parallel before eventually being fed into an electrical supply grid. 
       FIGS. 3-4  illustrate a perspective view of a portion of an exemplary wind turbine  300 . Wind turbine  300  includes a nacelle  302  housing a generator  318  (shown in  FIG. 5 ). Nacelle  302  is mounted on a tower  304  (a portion of tower  304  being shown in  FIGS. 3-4 ). Tower  304  may have any suitable height that facilitates operation of wind turbine  300  as described herein. Wind turbine  300  also includes a rotor  306  that includes three blades  308  attached to a rotating hub  310 . Alternatively, wind turbine  300  includes any number of blades  308  that facilitates operation of wind turbine  300  as described herein. 
     Also included, is a transformer-converter assembly  340 , discussed in greater detail below. In  FIG. 3 , by way of example only and not limitation, the transformer-converter assembly  340  is shown positioned proximate to the nacelle  302 . In a second embodiment illustrated in  FIG. 4A , however, the transformer-converter assembly  340  is shown positioned at the base of the tower  304 .  FIG. 4B  is an illustration of a third embodiment depicting the transformer-converter assembly  340  inside of the base of the tower  304 . 
     In the exemplary embodiment, wind turbine  300  includes a gearbox  314  (shown in  FIG. 5 ) operatively coupled to rotor  306  and a generator  318  (shown in  FIG. 5 ). 
       FIG. 5  is a schematic view of an exemplary electrical and control system  400  that may be used with wind turbine  300 . Rotor  306  includes blades  308  coupled to hub  310 . Rotor  306  also includes a low-speed shaft  312  rotatably coupled to hub  310 . Low-speed shaft  312  is coupled to a step-up gearbox  314  that is configured to step up the rotational speed of low-speed shaft  312  and transfer that speed to a high-speed shaft  316 . In the exemplary embodiment, gearbox  314  has any suitable step-up ratio that facilitates operation of wind turbine  300 . As a further alternative, wind turbine  300  includes a direct-drive generator that is rotatably coupled to rotor  306  without any intervening gearbox. 
     High-speed shaft  316  is rotatably coupled to generator  318 . In the exemplary embodiment, generator  318  can be configured as a wound rotor, three-phase, DFIG that includes a generator stator  320  magnetically coupled to a generator rotor  322 . In an alternative embodiment, generator rotor  322  includes a plurality of permanent magnets in place of rotor windings. Hence, in general, and not limited to a particular embodiment the generator may be any type of synchronous generator with electrical excitation. 
     During operation, the wind turns the propellers  308  attached to gearbox  314  inside the nacelle  302 , coupled to generator  318 . The wind turbine system  300  includes an AC-DC-AC converter  324  (shown in  FIG. 5 ) which controls the generator  318  through rotor bus  326 . Converter  324  also connects to an oil-filled pad mounted transformer  328  through line bus  330  and converter CB  332 . Generator  318  connects to the transformer  328  through stator bus  334  and stator sync switch  336 . The oil-filled pad mounted transformer  328  steps up the voltage and feeds power to the HV utility grid  338 . 
     In  FIG. 5 , wind turbine system  500  is configured such that oil-filled transformer  328  houses converter  324  and all electrical components in the power flow path to form the transformer-converter assembly  340 . Namely, transformer-converter assembly  340  is configured to include a set of components assembled together to make a finished product. Thus, the converter  324  can be mechanically attached or integrally connected to the oil-filled transformer  328 . The transformer-converter assembly  340  can be mechanically attached to or positioned nearby a wind turbine. Hence, in one embodiment, as shown in  FIG. 3 , the transformer-converter assembly  340  may be mechanically attached to the wind turbine nacelle, base or tower. In another embodiment, as shown in  FIG. 4A , the transformer-converter assembly  340  may be located nearby the tower. 
     Attaching the converter  324  in or on the oil-filled pad mounted transformer  328  allows for an integrated packaging of the system and frees up space. Through the compact and integrated design, material savings may be made, because the converter and the transformer may include a number of the same pieces. 
     In further embodiments herein, the transformer-converter assembly  340  may be attached somewhere along and around the nacelle, as shown in  FIG. 3 . Hence, easy access to the transformer-converter assembly  340  would be enabled. Not limited to a particular embodiment the transformer-converter assembly  340  may be attached to the nacelle mechanically or physically, for instance, by welding, screwing, bolting or any other friction/form fit that may, for example, include magnetic or adhesive forces. 
     The electrical and control system  400  may comprise a turbine controller (not shown). In various embodiments, the turbine controller can include at least one processor and a memory, at least one processor input channel, at least one processor output channel, and may include at least one computer. As used herein, the term computer is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a processor, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. 
     In the exemplary embodiment, memory may include, but is not limited to, a computer-readable medium, such as a random access memory (RAM). Alternatively, one or more storage devices, such as a floppy disk, a compact disc read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) may also be used. Also, in the exemplary embodiment, additional input channels may be, but are not limited to, computer peripherals associated with an operator interface such as a mouse and a keyboard. Further, in the exemplary embodiment, additional output channels may include, but are not limited to, an operator interface monitor. 
     Processors are provided for the turbine controller to process information transmitted from a plurality of electrical and electronic devices that may include, but are not limited to, voltage and current transducers. RAM and/or storage devices store and transfer information and instructions to be executed by the processor. RAM and/or storage devices can also be used to store and provide temporary variables, static (i.e., non-changing) information and instructions, or other intermediate information to the processors during execution of instructions by the processors. Instructions that are executed include, but are not limited to, resident conversion and/or comparator algorithms. The execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions. 
     The turbine controller (not shown) may also be configured to receive a plurality of voltage and electric current measurement signals from voltage and electric current sensors. Moreover, turbine controller may be configured to monitor and control at least some of the operational variables associated with wind turbine  500 . 
     During operation, wind impacts blades  308  and blades  308  transform wind energy into a mechanical rotational torque that rotatably drives low-speed shaft  312  via hub  310 . Low-speed shaft  312  drives gearbox  314  that subsequently steps up the low rotational speed of low-speed shaft  312  to drive high-speed shaft  316  at an increased rotational speed. High speed shaft  316  rotatably drives generator rotor  322 . A rotating magnetic field is induced by generator rotor  322  and a voltage is induced within generator stator  320  that is magnetically coupled to generator rotor  322 . In this exemplary embodiment, generator  318  converts the rotational mechanical energy to a sinusoidal, three-phase AC electrical energy signal in generator stator  320 . The associated electrical power is transmitted to transformer  328  via stator bus  334  and stator synchronizing switch  336 . Transformer  328  steps up the voltage amplitude of the electrical power and the transformed electrical power is further transmitted to a grid  338 . 
       FIGS. 3 and 4  illustrate different locations of the transformer-converter assembly  340 , which includes converter  324  and all electrical components in the power flow path housed within transformer  328  according to embodiments described herein. In various embodiments, the transformer  328  may be an oil-filled pad mounted transformer. In some typical wind turbines, as illustrated in  FIGS. 1 and 2 , the converter  124  and the oil-filled pad mounted transformer  128  are separate and independent components, which are positioned at different locations within the wind turbine system. Converter  124  is located in the lower part of the wind turbine tower, and the oil-filled pad mounted transformer  128  is located outside of the tower. 
     In  FIG. 3 , the transformer-converter assembly  340 , which includes the converter housed within the transformer, may be mechanically attached to the wind turbine nacelle, base or tower. In various embodiments, transformer-converter  340  may be attached somewhere along and around the nacelle. Not limited to a particular embodiment the transformer-converter assembly  340  may be attached to portions of the wind turbine mechanically or physically, for instance, by welding, screwing, bolting or any other friction/form fit that may, for example, include magnetic or adhesive forces. 
       FIG. 4A  illustrates positioning transformer-converter assembly  340  nearby the tower of wind turbine  300 . Transformer-converter assembly  340  may be positioned above or below surface  342 . In this case, surface  342  may be representative of onshore ground level. However, in further embodiments, surface  342  may be, for example, water in an offshore environment. 
     In addition, and not limited to a particular embodiment described herein, a single transformer-converter assembly may be connected to a plurality of transformer-converter assemblies of one or more wind turbines. Such layout enables a plurality of wind turbines to be interconnected to form, for example, an on- or offshore wind park with more redundancy, and further reduction in spatial and material requirements. 
       FIG. 6  is a flow chart of an exemplary method  600  for attaching a converter to a transformer of a wind turbine. In block  610 , a converter and a transformer are provided. The converter is mechanically attached to the transformer such that the transformer houses the converter and all electrical components in the power flow path to form a transformer-converter assembly, in block  620 . Typically, now the electrical energy flow between the converter and transformer may be tested. Finally, in block  630 , the transformer-converter assembly is installed such that it is attached to a nacelle, a base or a tower of a wind turbine or, alternatively, positioned nearby the wind turbine. 
     The above-described systems and methods facilitate a more compact assembly of the transformer and converter, and also enable testing and harmonizing the two components with each other before installation. More specifically, installing the converter within the transformer frees space in the wind turbine. Additionally, material costs are reduced through shortened cooling system connections, reduced cable and conventional generator connections. Finally, due to the reduced cabling and connections, in case of malfunctions or normal wear through use, it is easy to exchange the transformer-converter assembly. 
     Exemplary embodiments of systems and methods for a wind turbine system including a transformer housing a converter are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, attaching the transformer-converter assembly on the nacelle of a vertical wind turbine, and hence are not limited to practice with only the wind turbine systems as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other generators or converter applications in for, for instance, other rotor blade applications. 
     Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, 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. While various specific embodiments have been disclosed in the foregoing, those skilled in the art will recognize that the spirit and scope of the claims allows for equally effective modifications. Especially, mutually non-exclusive features of the embodiments described above may be combined with each other. 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 have 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 language of the claims.