Modular reactive power compensator system

Abstract

A reactive power compensator system for wind farms includes a multi-winding transformer and multiple modular reactive power compensators (MVBs). The multi-winding transformer includes a primary winding and multiple secondary windings. The primary winding is configured to be coupled to a point of common coupling (POCC) for the wind farm. Each of the multiple MVBs is coupled to a corresponding winding of a plurality of secondary windings.

Description

Technical Field

[0001] The field of this disclosure generally relates to modular reactive power compensators, and more particularly to systems for modular reactive power compensators for wind farms. Background Technology

[0002] As renewable energy has become more prevalent, the requirements for connecting renewable power sources to the power grid (i.e., grid guidelines) have evolved and become more complex, thus placing higher demands on operators of renewable power sources such as wind farms. Typically, grid guidelines specify operational standards, including, for example, active and reactive power control, power factor control, voltage and current waveform quality, response to grid-side frequency and voltage variations, and ride-through capability in the event of grid-side faults.

[0003] Within a wind farm, wind turbines rotate generators (e.g., doubly-fed induction generators (DFIGs)) that generate electrical power, which is supplied to the grid via a point of common coupling (POCC). In a given wind farm with multiple generators, each generator produces power at a generated voltage (which is boosted to be supplied to the POCC). The voltage at the POCC is typically further boosted to the transmission line voltage before being supplied to the grid itself. Wind farms may incorporate one or more reactive power compensators (each referred to as VAR compensators) to help comply with local grid guidelines. One such device is a static synchronous compensator (STATCOM), which can be connected at the POCC or at the turbine to stabilize the voltage. For example, when integrated at the POCC, a single VAR compensator can be designed to comply with local grid guidelines. Alternatively, one or more modular VAR compensators, or “modular VAR boxes” (MVBs), can be connected to the POCC in any amount required for compliance with local grid guidelines. Summary of the Invention

[0004] In one aspect, a system for a reactive power compensator for a wind farm is provided. The system includes a multi-winding transformer and multiple modular reactive power compensators (MVBs). The multi-winding transformer includes a primary winding and multiple secondary windings. The primary winding is configured to be coupled to a point of common coupling (POCC) for the wind farm. Each of the multiple MVBs is coupled to a corresponding winding of the multiple secondary windings.

[0005] In another embodiment, a wind farm is provided. The wind farm includes a point-of-charge (POCC), multiple doubly-fed induction generators (DFIGs), a multi-winding transformer, and multiple multi-mode transformers (MVBs). The POCC is configured to be coupled to a power grid. The multiple DFIGs are configured to generate alternating current (AC) power to be supplied to the POCC. The multi-winding transformer includes a primary winding and multiple secondary windings. The primary winding is configured to be coupled to the POCC used in the wind farm. Each of the multiple MVBs is coupled to a corresponding winding of the multiple secondary windings.

[0006] In another aspect, a method for operating a wind farm is provided. The method includes supplying AC power from a plurality of DFIGs (the plurality of DFIGs being coupled to corresponding wind turbines) to a POCC (the POCC being configured to be coupled to a power grid). The method includes coupling the primary winding of a multi-winding transformer to the POCC. The method also includes coupling a plurality of MVBs to the POCC via corresponding windings of the secondary windings of the multi-winding transformer.

[0007] The present invention provides a set of technical solutions, as follows.

[0008] Technical Solution 1. A system for a reactive power compensator in a wind farm, the system comprising:

[0009] Multi-winding transformers include:

[0010] A primary winding, the primary winding being configured to be coupled to a point of common coupling (POCC) for the wind farm; and

[0011] Multiple secondary windings; and

[0012] Multiple modular reactive power compensators (MVBs) are provided, each of which is coupled to a corresponding winding of the multiple secondary windings.

[0013] Technical Solution 2. The system as described in Technical Solution 1, wherein the primary winding comprises more turns than each of the plurality of secondary windings.

[0014] Technical Solution 3. The system as described in Technical Solution 1 further includes:

[0015] Wind turbines; and

[0016] A doubly-fed induction generator (DFIG) coupled to the wind turbine and configured to generate alternating current (AC) power to be supplied to the POCC.

[0017] Technical Solution 4. The system as described in Technical Solution 1, wherein each of the plurality of MVBs includes: a voltage source; and a bridge converter coupled between the voltage source and the corresponding winding of the plurality of secondary windings.

[0018] Technical Solution 5. The system as described in Technical Solution 4, wherein each of the plurality of MVBs includes a microcontroller configured to execute a control loop to control the switching of semiconductor devices within the bridge converter.

[0019] Technical Solution 6. The system as described in Technical Solution 5, wherein the control loops of the plurality of MVBs are executed independently of each other.

[0020] Technical Solution 7. The system as described in Technical Solution 5, wherein the control loop for each of the plurality of MVBs is a reactive power control loop.

[0021] Technical Solution 8. The system as described in Technical Solution 5, wherein the control loop for each of the plurality of MVBs is a voltage control loop.

[0022] Technical Solution 9. The system as described in Technical Solution 5, wherein the control loop for each of the plurality of MVBs is a current control loop.

[0023] Technical Solution 10. A wind farm, comprising:

[0024] A point of common coupling (POCC), which is configured to be coupled to the power grid;

[0025] Multiple doubly-fed induction generators (DFIGs) configured to generate alternating current (AC) power for supply to the POCC;

[0026] Multi-winding transformers include:

[0027] A primary winding, the primary winding being configured to be coupled to the POCC; and

[0028] Multiple secondary windings; and

[0029] Multiple modular reactive power compensators (MVBs), each of the multiple MVBs being coupled to a corresponding winding of the multiple secondary windings.

[0030] Technical Solution 11. The wind farm as described in Technical Solution 10, wherein the POCC is further configured to be coupled to the power grid via a step-up transformer.

[0031] Technical Solution 12. The wind farm as described in Technical Solution 10, wherein the multi-winding transformer comprises a step-down transformer from the primary winding to each of the plurality of secondary windings.

[0032] Technical Solution 13. The wind farm as described in Technical Solution 10, wherein each of the plurality of DFIGs includes a bidirectional power converter configured to regulate the voltage and current at the rotor of each DFIG in order to synchronize the AC power generated by the plurality of DFIGs to the frequency of the power grid.

[0033] Technical Solution 14. The wind farm as described in Technical Solution 10, wherein each of the plurality of MVBs includes: a voltage source; and a bridge converter coupled between the voltage source and the corresponding winding of the plurality of secondary windings.

[0034] Technical Solution 15. The wind farm as described in Technical Solution 14, wherein each of the plurality of MVBs includes a microcontroller configured to execute a control loop to control the switching of semiconductor devices within the bridge converter.

[0035] Technical Solution 16. The wind farm as described in Technical Solution 15, wherein the control loops of the plurality of MVBs are executed independently of each other.

[0036] Technical Solution 17. A method for operating a wind farm, the method comprising:

[0037] The doubly fed induction generator (DFIG) coupled to the corresponding wind turbine provides alternating current (AC) power to the point of common coupling (POCC) configured to be coupled to the power grid;

[0038] The primary winding of the multi-winding transformer is coupled to the POCC;

[0039] Multiple modular reactive power compensators (MVBs) are coupled to the POCC through corresponding windings of the multiple secondary windings of the multi-winding transformer.

[0040] Technical Solution 18. The method of Technical Solution 17 further includes executing a control loop on a microcontroller for each of the plurality of MVBs to control the switching of semiconductor devices within each MVB.

[0041] Technical Solution 19. The method as described in Technical Solution 18 further includes:

[0042] The total reactive power requirement for the wind farm is estimated by the wind farm controller; and

[0043] The wind farm controller allocates at least a portion of the total reactive power requirement among the plurality of MVBs based on the conditions of the power grid and the conditions of the corresponding wind turbine.

[0044] Technical solution 20. The method as described in technical solution 19 further includes:

[0045] Receive individual reactive power commands based on allocations made by the wind farm controller at the microcontroller for each of the plurality of MVBs; and

[0046] The microcontroller for each MVB executes a reactive power control cycle based on the individual reactive power command. Attached Figure Description

[0047] These and other features, aspects, and advantages of this disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, in which similar characters throughout the drawings denote similar parts, wherein:

[0048] Figure 1 This is a simplified diagram of a demonstration wind farm with a single VAR compensator;

[0049] Figure 2 yes Figure 1 A simplified diagram of a wind farm with multiple modular VAR compensators;

[0050] Figure 3 It is offered in Figure 2 A schematic diagram of a demonstration modular VAR compensator used in a wind farm;

[0051] Figure 4 It is used for Figure 2 and Figure 3 A block diagram of the demonstration control loop of a modular VAR compensator;

[0052] Figure 5 yes Figure 1 and Figure 2 A simplified diagram of a wind farm with multiple modular VAR compensators coupled through a multi-winding transformer;

[0053] Figure 6 It is used for Figure 2 A graph showing the reactive power curves of two modular VAR compensators out of a set of multiple modular VAR compensators.

[0054] Figure 7 It is used for Figure 5 A graph showing the reactive power curves of two modular VAR compensators out of a set of multiple modular VAR compensators; and

[0055] Figure 8 It is an operation Figure 5 A flowchart of a demonstration method for a wind farm.

[0056] Unless otherwise indicated, the accompanying drawings provided herein are intended to illustrate features of embodiments of this disclosure. These features are believed to be applicable to various systems that include one or more embodiments of this disclosure. Therefore, the drawings are not intended to include all conventional features known to those skilled in the art that are required for implementing the embodiments disclosed herein. Detailed Implementation

[0057] In the following description and claims, reference is made to several terms having the following meanings.

[0058] The singular forms “a,” “one,” and “the” include plural references unless the context clearly indicates otherwise.

[0059] "Optional" or "optionally" means that the event or situation described below may or may not occur, and this description includes instances in which the event occurs as well as instances in which the event does not occur.

[0060] As used herein, approximate language can be applied throughout the specification and claims to modify any quantity representation that allows for variation without causing a change in its essential function. Therefore, values ​​modified by one or more terms such as “approximately,” “about,” and “substantially” are not intended to be limited to the specified precise value. In at least some instances, approximate language may correspond to the precision of the instrument used to measure the value. Here and throughout the specification and claims, scope limitations may be combined and / or interchanged; such scopes are identified and include all subscopes contained therein, unless otherwise indicated by context or language.

[0061] Some embodiments relate to the use of one or more electronic processing or computing devices. As used herein, the terms “processor” and “computer,” as well as related terms (e.g., “processing device,” “computing device,” and “controller”), are not limited to those integrated circuits referred to in the art as computers, but are broadly used to mean processors, processing devices, controllers, general-purpose central processing units (CPUs), graphics processing units (GPUs), microcontrollers, microcomputers, programmable logic controllers (PLCs), simplified instruction set computer (RISC) processors, field-programmable gate arrays (FPGAs), digital signal processing (DSP) devices, application-specific integrated circuits (ASICs), and other programmable circuits or processing devices capable of performing the functions described herein, and these terms are used interchangeably herein. The above embodiments are merely examples and are not intended to limit the definition or meaning of the terms processor, processing device, and related terms in any way.

[0062] In the embodiments described herein, memory may include, but is not limited to, non-transitory computer-readable media, such as flash memory, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and non-volatile RAM (NVRAM). As used herein, the term "non-transitory computer-readable media" is intended to mean any tangible computer-readable medium and any other digital source (e.g., a network or the Internet) and digital components still under development, with the sole exception of temporarily propagating signals. Any tangible computer-readable medium includes, but is not limited to, non-transitory computer storage devices, including, but not limited to, volatile and non-volatile media, as well as removable and non-removable media, such as firmware, physical and virtual storage devices, CD-ROMs, and DVDs. Alternatively, floppy disks, compact disc read-only memory (CD-ROM), magneto-optical disks (MOD), digital versatile disks (DVDs), or any other computer-based device implemented according to any method or technology for short-term and long-term storage of information (e.g., computer-readable instructions, data structures, program modules and submodules, or other data) may also be used. Therefore, the methods described herein can be encoded as executable instructions embodied in a non-transitory computer-readable medium, such as "software" and "firmware". Furthermore, as used herein, the terms "software" and "firmware" are interchangeable and include any computer program stored in memory for execution by a personal computer, workstation, client, and server. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. Additionally, as used herein, the term "real-time" refers to at least one of the time of occurrence of a related event, the time of measurement and collection of predetermined data, the time used to process the data, and the time of system response to events and the environment. In the embodiments described herein, these activities and events occur substantially instantaneously.

[0063] Conventionally, modular reactive power compensators (each referred to as a modular VAR box or MVB) systems can operate in a master-slave mode, where the top-level controller commands each MVB to operate in, for example, a voltage control mode or a reactive power control mode, or to switch to standby mode or be powered off when its support is not needed. If this master-slave control approach is not adopted and multiple VAR boxes are integrated without significant impedance in the system, it can lead to various interactions within the MVBs. Interactions within their internal control loops can cause, for example, circulating currents and oscillating reactive power. Additional communication and coordination within the MVBs (e.g., a master-slave architecture) can be employed, but these problems are overcome with greater cost and complexity for wind farm operators.

[0064] Embodiments of the systems and methods described herein provide an architecture for connecting MVBs without additional communication within the MVBs. The systems and methods described herein provide integration of multiple MVBs with a multi-winding transformer coupled between each MVB and a POCC. More specifically, each MVB is coupled to the POCC via a corresponding secondary winding of its own multi-winding transformer. In some embodiments, the voltage on the POCC is reduced by the multi-winding transformer to the operating voltage for the multiple MVBs. The leakage inductance of the multi-winding transformer acts as a high-impedance path for high-frequency circulating currents and isolates circulating currents within the MVB converter. This avoids reactive power oscillations in the connection path and also at the PCC.

[0065] Figure 1 This is a simplified diagram of an example wind farm 100 including a single VAR compensator 102. The wind farm 100 includes a POCC 104, to which the VAR compensator 102 is coupled via a transformer 106. Figure 2 It includes a wind farm 100 comprising multiple MVB 300 units replacing a single VAR compensator 102. Figure 1 A simplified diagram (as shown in the image). Refer to... Figure 1 and Figure 2 The two figures show a wind farm 100 comprising multiple DFIGs 108 (referred to as DFIG 1 to n). Each DFIG 108 includes a rotor 110 and a stator 112. Each DFIG 108 is rotated by a turbine via a gearbox due to wind impacting rotor blades (not shown). As the rotor 110 rotates relative to the stator 112, the DFIG 108 generates power, which is supplied to a POCC 104 via a transformer 114. The transformer 114 converts, for example, the power generated by the DFIGs 108 at a relatively low voltage, upwards to the voltage of the POCC 104. The POCC 104 is a bus or other conductor used to collect current from the DFIGs 108 and transmit it to the power grid 116. The voltage on the POCC 104 is boosted to the transmission line level on the power grid 116 via a transformer 118. In one embodiment, DFIG 108 can generate power at 6 kV, which is boosted to 34.5 kV to supply POCC 104. The transmission lines within the power grid 116 can operate at, for example, 110 kV. In such an embodiment, the 34.5 kV voltage on POCC 104 is boosted to 110 kV by transformer 118.

[0066] Each DFIG 108 includes a bidirectional power converter 120 that enables the DFIG 108 to be synchronized to the power grid 116, regardless of the rotational speed of the rotor 110, i.e., regardless of wind speed. For example, the power generated by each DFIG 108 should be synchronized to the frequency of operation of the power grid 116, such as 50 Hz or 60 Hz. The bidirectional power converter 120 includes a rotor-side converter (RSC) 122, which is coupled to a line-side converter (LSC) 124 via a DC link 126. Both RSC 122 and LSC 124 include one or more switching devices (not shown) controlled by pulse-width modulated switching signals for converting AC to DC or DC to AC according to the operating regime of the DFIG 108. Furthermore, the control of RSC 122 enables further control of the reactive power (and actual power) fed from the DFIG 108 to the power grid 116. When DFIG 108 operates in subsynchronous mode, bidirectional power converter 120 draws power from the line via transformer 114. Typically, voltage and current control at rotor 110 enables DFIG 108 to synchronize with the frequency of power grid 116. More specifically, LSC 124 converts AC power to DC, which is regulated via DC link 126. RSC 122 converts the DC power from DC link 126 to AC power, which is supplied to rotor 110, by an amount sufficient to synchronize the rotation of rotor 110 and, correspondingly, the AC power generated at stator 112 with the frequency of power grid 116. Conversely, when DFIG 108 operates in supersynchronous mode, AC power is generated at rotor 110, supplied to RSC 122, converted to DC via DC link 126, and converted back to AC power by LSC 124 for supply to POCC 104 via transformer 114.

[0067] In some embodiments, the power generated at stator 112 is at the same voltage as the power supplied to the rotor via bidirectional power converter 120, or generated by rotor 110 and then supplied to POCC 104 via bidirectional power converter 120. In such embodiments, transformer 114 may include a two-winding transformer having a winding ratio for boosting the generated voltage to the voltage on POCC 104. For example, in one such embodiment, the voltage at stator 112 and on the line side of LSC 124 is 6 kV, which is boosted to, for example, 34.5 kV on POCC 104. In alternative embodiments, bidirectional power converter 120 operates at a voltage different from the generated voltage at stator 112, for example, a lower voltage. For example, in one such embodiment, as Figure 1 As shown, the bidirectional power converter 120 operates at 690 V on the line side of LSC 124, while the stator 112 generates a voltage of 6 kV. In this type of embodiment, the transformer 114 includes at least three windings, including a first winding 128 coupled to POCC 104, a second winding 130 coupled to stator 112, and a third winding 132 coupled to bidirectional power converter 120.

[0068] Figure 3 It is an MVB 300 ( Figure 2 A schematic diagram of an example (shown in the diagram). The MVB 300 includes a bridge converter 301 having three phase branches (legs) 302, 304, 306, each of which includes a plurality of semiconductor devices 308 configured to switch the three phases 310 to which the MVB 300 is coupled, such as POCC 104. Figure 1 and Figure 2 The three phases are shown in the diagram. Semiconductor device 308 may include, for example, an insulated-gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). Semiconductor device 308 is controlled by a processor (e.g., a microcontroller (not shown)) using PWM signals. MVB 300 also includes voltage source 312 (…). Figure 3 (The image shows a capacitor) and filter 314.

[0069] Typically, the functionality of the MVB 300 also includes, but is not limited to, power factor correction, voltage correction, and harmonic compensation at connection points. When the voltage level on the three phases 310 exceeds the level on the voltage source 312, the semiconductor device 308 is controlled to sink reactive power from the line side (i.e., the three phases 310). Conversely, when the voltage on the voltage source 312 exceeds the voltage level on the three phases 310, the semiconductor device 308 is controlled to source or supply reactive power to the three phases 310. Typically, the VAR compensation capacity of the MVB 300 is a function of the power capacity of the semiconductor device 308 and the voltage source 312. In some embodiments, the MVB 300 may also supply active power to the three phases 310 if sufficient power supply is available for the voltage source 312.

[0070] Figure 4 It is a semiconductor device 308 used to control the MVB 300. Figure 2 and Figure 3 A block diagram of an example control loop 400 (shown in the diagram). Control loop 400 may be embodied in, for example, a microcontroller (not shown) or one or more other suitable processing devices. Control loop 400 includes external (in...) Figure 4(Seen on the left) Reactive power control loop 402, which calculates voltage command 404 (Vcmd) based on reactive power command 406 (Qcmd) and reactive power feedback 408 (Qfbk). A wind farm controller (not shown) estimates the total reactive power requirement of the farm and assigns individual reactive power commands (Qcmd) to the turbines and MVB 300s based on grid and turbine operating conditions. Typically, the wind farm controller is a computing system having one or more processors and memory for storing and executing computer-executable instructions or program code for controlling the wind farm. The wind farm controller can be local or remote to one or all of the wind turbines in the wind farm. For example, the wind farm controller can be integrated within a single wind turbine of the wind farm. In an alternative embodiment, the wind farm controller is incorporated into a separate unit of equipment. In another alternative embodiment, the wind farm controller is local to multiple MVB 300s in the wind farm.

[0071] The control loop 400 for a given MVB 300 includes an internal voltage control loop 410, followed by an internal current control loop 412. The voltage control loop 410 calculates a current command 414 (Icmd) based on a voltage command 404 and voltage feedback 416 (Vfbk). The current control loop 412 calculates a voltage command 418 based on the current command 414 and current feedback 420 (Ifbk). Each of the reactive power control loop 402, voltage control loop 410, and current control loop 412 is governed by a control module (i.e., the Q controller 422, V controller 424, and I controller 426). The control module may include, for example, a proportional-integral (PI) controller, a DSP, or a microcontroller. The control module may be implemented as a software module on a microcontroller (where control loop 400 is implemented) or on a separate processing device.

[0072] The output from the current control loop 412 (i.e., voltage command 418) is supplied to the modulation index 428, which converts the voltage command 418 into a selected set of PWM signals 430 for controlling the semiconductor device 308 of the MVB 300.

[0073] Figure 5 It is a wind farm 100 ( Figure 1 and Figure 2 A simplified diagram (shown in the image) shows that the wind farm 100 includes multiple MVB 300 ( Figure 2As shown in the diagram, the plurality of MVBs 300 are coupled to the POCC 104 via a multi-winding transformer 500 to form a reactive power compensator system 501. The multi-winding transformer 500 includes: a primary winding 502 coupled to the POCC 104; and two or more secondary windings 504, 506 coupled to the respective MVB 300. Each secondary winding of the multi-winding transformer 500 (e.g., secondary windings 504 and 506) is dedicated to a single MVB 300 operating individually with its own control cycle 400.

[0074] The leakage inductance of the multi-winding transformer 500 provides a high-impedance path for high-frequency circulating currents and reduces the occurrence of reactive power oscillations.

[0075] Figure 6 It is a graph 600 including reactive power curve 602 for the first MVB and reactive power curve 604 for the second MVB, wherein the first and second MVBs are coupled to, for example, POCC 104 via transformer 106 (both in Figure 2 (as shown in the image). Figure 7 It is a graph 700 including example reactive power curve 702 for the first MVB and example reactive power curve 704 for the second MVB, wherein the first and second MVBs are connected by a multi-winding transformer 500. Figure 5 The corresponding windings (shown in the diagram) are coupled to POCC104. Reactive power curves 602, 604, 702, and 704 are plotted as reactive megavolt-amperes (MVAR) on the vertical axis and time (seconds) on the horizontal axis.

[0076] Figure 600 illustrates the interaction between the control cycles of the first and second MVBs, as each MVB attempts to control the voltage on the secondary side of transformer 106. Therefore, reactive power curves 602 and 604 oscillate near the setpoints or reactive power commands for the first and second MVBs. For example, in Figure 600, the first MVB operates at a kVAR setpoint of 500 kVAR, and the second MVB operates at a kVAR setpoint of 800 kVAR. Conventionally, additional communication and coordination within the MVBs, and more particularly within their respective control cycles, are employed to overcome the oscillating reactive power responses of the first and second MVBs. For example, the first MVB may be configured as the master, and the second MVB as the slave.

[0077] Figure 700 illustrates the isolation of the control loops of the first and second MVBs, as each MVB is coupled to POCC 104 via dedicated windings (e.g., secondary windings 504, 506) of the multi-winding transformer 500. As in Figure 600, the first MVB operates at a kVAR setpoint of 500 kVAR, and the second MVB operates at a kVAR setpoint of 800 kVAR. Accordingly, reactive power curves 702 and 704 converge rapidly at their respective kVAR settings.

[0078] Figure 8 It is to operate a wind farm 100 ( Figure 5 The flowchart of the exemplary method 800 (shown in the diagram) shows that multiple DFIGs 108 supply 802 AC power to POCC 104 when rotated by their corresponding wind turbines. POCC 104 supplies power to the power grid 116 via transformer 118.

[0079] The multi-winding transformer 500, and more particularly the primary winding 502, is coupled 804 to the POCC 104. The MVB 300 is coupled 806 to the POCC 104 via corresponding secondary windings (e.g., secondary windings 504 and 506).

[0080] In some embodiments, method 800 further includes executing control loop 400 on a microcontroller for each of the MVB 300s to control the switching of semiconductor devices within each MVB 300. For example, the wind farm controller estimates the total reactive power requirement for the wind farm and allocates at least a portion of the total reactive power requirement among the MVBs 300. This allocation is based on conditions on the power grid 116 and is performed for each wind turbine. The microcontroller for each MVB 300 receives an individual reactive power command and executes control loop 400 according to the individual reactive power command. The individual reactive power command is based on or generated from the allocation performed by the wind farm controller.

[0081] The embodiments of the systems and methods described herein provide an architecture for connecting MVBs without additional communication within the MVBs. The systems and methods described herein provide integration of multiple MVBs with a multi-winding transformer coupled between each MVB and a POCC. More specifically, each MVB is coupled to the POCC via the windings of its own multi-winding transformer. In some embodiments, the voltage on the POCC is regulated by the multi-winding transformer to the operating voltage for the multiple MVBs. The leakage inductance of the multi-winding transformer prevents circulating current and isolates and stabilizes the internal control loops of each MVB, as well as preventing reactive power oscillations.

[0082] The demonstrative technical effects of the methods, systems, and devices described herein include at least one of the following: (a) coupling of MVB to POCC via a dedicated winding of a multi-winding transformer; (b) reduced communication within MVBs in a VAR compensator system; (c) reduced circulating current in a VAR compensator system; (d) reduced reactive power oscillations in a VAR compensator system; and (e) reduced system complexity of MVBs.

[0083] Exemplary embodiments of the methods, systems, and apparatuses for VAR compensators are not limited to the specific embodiments described herein, but can be utilized separately and independently from other components and / or steps described herein. For example, the methods can also be used in conjunction with other VAR compensators, and are not limited to implementation using only the systems and methods described herein. Instead, the exemplary embodiments can be implemented and utilized in conjunction with many other applications, apparatuses, and systems that can benefit from reduced costs, reduced complexity, commercial availability, improved manufacturability, and reduced time to market.

[0084] While certain features of the various embodiments of this disclosure may be shown in some figures and not in others, this is merely for convenience. Any feature of any figure may be referenced and / or claimed in accordance with the principles of this disclosure.

[0085] This written description uses examples including best practices to disclose embodiments and also enables any person skilled in the art to implement the embodiments, including making and using any apparatus or system, and performing any combination methods. The patentable scope of this disclosure is defined by the claims and may include other examples that would occur to a person skilled in the art. Such other examples are expected to be within the scope of the claims if they have structural units that are exactly the same as the wording of the claims, or if they contain equivalent structural units that have a non-substantially different wording from the claims.

Claims

1. A system for a reactive power compensator in a wind farm, the system comprising: Wind turbine; A doubly-fed induction generator (DFIG) coupled to the wind turbine and configured to generate alternating current (AC) power for supply to a point of common coupling (POCC) for the wind farm. Multi-winding transformers include: A primary winding, the primary winding being configured to be coupled to the point of common coupling (POCC) upstream of the grid-side step-up transformer; and Multiple secondary windings; and Multiple modular reactive power compensators (MVBs), each of which is coupled to a dedicated secondary winding of multiple secondary windings, wherein the multiple MVBs are integrated with the POCC via a single primary winding upstream of the grid-side step-up transformer. Each of the plurality of MVBs is configured to operate independently of the other MVBs using its own control loop.

2. The system as claimed in claim 1, wherein, The primary winding has more turns than each of the plurality of secondary windings.

3. The system as described in claim 1, wherein, Each of the plurality of MVBs includes: a voltage source; and a bridge converter coupled between the voltage source and the corresponding winding of the plurality of secondary windings.

4. The system as described in claim 3, wherein, Each of the plurality of MVBs includes a microcontroller configured to execute a control loop to control the switching of semiconductor devices within the bridge converter.

5. The system as described in claim 4, wherein, The control loops of the multiple MVBs are executed independently of each other.

6. The system of claim 4, wherein, The control loop used for each of the plurality of MVBs is a reactive power control loop.

7. The system of claim 4, wherein, The control loop used for each of the plurality of MVBs is a voltage control loop.

8. The system of claim 4, wherein, The control loop used for each of the plurality of MVBs is a current control loop.

9. A wind farm, comprising: A point of common coupling (POCC), the POCC being configured to be coupled to a power grid having a grid-side step-up transformer downstream of the POCC; Multiple doubly-fed induction generators (DFIGs) configured to generate alternating current (AC) power for supply to the POCC; Multi-winding transformers include: A primary winding, the primary winding being configured to be coupled to the POCC; and Multiple secondary windings; and Multiple modular reactive power compensators (MVBs), each of which is coupled to a dedicated secondary winding of the multiple secondary windings, wherein the multiple MVBs are integrated with the POCC. Each of the plurality of MVBs is configured to operate independently of the other MVBs using its own control loop.

10. The wind farm as described in claim 9, wherein, The multi-winding transformer includes a step-down transformer from the primary winding to each of the plurality of secondary windings.

11. The wind farm as described in claim 9, wherein, Each of the plurality of DFIGs includes a bidirectional power converter configured to regulate the voltage and current at the rotor of each DFIG in order to synchronize the AC power generated by the plurality of DFIGs to the frequency of the power grid.

12. The wind farm as described in claim 9, wherein, Each of the plurality of MVBs includes: a voltage source; and a bridge converter coupled between the voltage source and the corresponding winding of the plurality of secondary windings.

13. The wind farm as described in claim 12, wherein, Each of the plurality of MVBs includes a microcontroller configured to execute a control loop to control the switching of semiconductor devices within the bridge converter.

14. The wind farm as described in claim 13, wherein, The control loops of the multiple MVBs are executed independently of each other.

15. A method for operating a wind farm, the method comprising: The doubly fed induction generator (DFIG) coupled to the corresponding wind turbine provides alternating current (AC) power to the point of common coupling (POCC) configured to be coupled to the power grid and located upstream of the step-up transformer on the grid side. The primary winding of the multi-winding transformer is coupled to the POCC; Multiple modular reactive power compensators (MVBs) are coupled to the POCC via dedicated secondary windings of multiple secondary windings of the multi-winding transformer, wherein the multiple MVBs are integrated with the POCC via a single primary winding upstream of the grid-side step-up transformer, and each of the multiple MVBs is configured to operate independently of the other MVBs using its own control loop.

16. The method of claim 15, further comprising performing a control loop on a microcontroller for each of the plurality of MVBs to control the switching of semiconductor devices within each MVB.

17. The method of claim 16, further comprising: The total reactive power requirement for the wind farm is estimated by the wind farm controller; as well as The wind farm controller allocates at least a portion of the total reactive power requirement among the plurality of MVBs based on the conditions of the power grid and the conditions of the corresponding wind turbine.

18. The method of claim 17, further comprising: The microcontroller for each of the plurality of MVBs receives individual reactive power commands based on the allocation made by the wind farm controller. as well as The microcontroller for each MVB executes a reactive power control cycle based on the individual reactive power command.

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