Black start recovery

Abstract

Embodiments described herein provide systems and techniques for performing black start operations. For example, one embodiment provides a method for performing a black start operation. The method generally includes operating a wind turbine in a wind farm in a first mode using a control system to provide power to an alternating current (AC) power grid. The control system may include a reactive power control branch and an active power control branch. The method also includes switching the operation of the wind turbine from the first mode to a second mode based on an indication to perform a black start on the electrical grid and by activating a controller with an integral action to increase the output power of the wind turbine, the controller being coupled between the reactive power control branch and the active power control branch, and providing power to the electrical grid when operating in the second mode.

Description

Technical Field

[0001] Embodiments presented in this disclosure relate generally to power restoration, and more particularly to performing a black start of an electrical grid. Background Art

[0002] In many cases, offshore wind turbines are needed rather than onshore wind turbines because offshore locations generally receive stronger wind speeds than on land. In addition, offshore wind turbines are not obstructed by trees, hills, buildings, etc. In order to couple the offshore wind turbines to the onshore grid (which may be located tens or hundreds of kilometers away), the wind turbine operator may use a high-voltage direct current (HVDC) link. The onshore grid may be connected to an onshore wind farm, which may experience a power outage due to one of several factors. In some cases, the national grid operator allocates backup power to perform a black start on a wind farm that experiences a power outage. Summary of the invention

[0003] One embodiment of the present disclosure provides a method for performing a black start operation. The method generally includes: operating a wind turbine in a wind farm in a first mode using a control system to provide power to an alternating current (AC) power grid. The control system may include a reactive power control branch and an active power control branch. The method also includes: switching the operation of the wind turbine from the first mode to a second mode based on an indication to perform a black start on the electrical grid and by activating a controller with an integral action to increase the output power of the wind turbine, the controller being coupled between the reactive power control branch and the active power control branch, and providing power to the electrical grid when operating in the second mode.

[0004] One embodiment of the present disclosure provides a wind turbine. The wind turbine generally includes a control system having a reactive power control branch, an active power control branch, and a controller having an integral action, the controller being selectively coupled between the reactive power control branch and the active power control branch. In certain embodiments, the control system is configured to: operate the wind turbine in a first mode to provide power to a local AC power grid, switch the operation of the wind turbine from the first mode to a second mode based on an indication of performing a black start on the electrical power grid and by activating the controller, thereby increasing the power output of the wind turbine, and provide power to the electrical power grid when operating in the second mode.

[0005] One embodiment of the present disclosure provides a control system for a wind turbine. The control system generally includes a processor and a memory configured to store a program, the program performing an operation when executed by the processor. The operation includes: using the control system to operate the wind turbine in a first mode to provide power to an AC power grid, wherein the control system includes a reactive power control branch and an active power control branch. The operation also includes: based on an indication to perform a black start on the electrical grid and by activating a controller with an integral action to increase the power output of the wind turbine, switching the operation of the wind turbine from the first mode to a second mode, the controller is coupled between the reactive power control branch and the active power control branch, and wherein, when in the second mode, power is provided to the electrical grid when operating in the second mode after the switching operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In order to facilitate the manner in which the above-mentioned features of the present disclosure can be understood in detail, the present disclosure briefly summarized above may be described in more detail by reference to embodiments, some of which are shown in the accompanying drawings. However, it should be noted that the drawings only illustrate typical embodiments of the present disclosure and are therefore not to be considered as limiting the scope thereof, as the present disclosure may allow other equally effective embodiments.

[0007] Figure 1 A schematic diagram of a wind turbine according to embodiments described in the present disclosure is shown.

[0008] Figure 2 A schematic diagram showing components inside a nacelle and tower of a wind turbine according to embodiments described in the present disclosure.

[0009] Figure 3 is a block diagram of a power system according to an embodiment described in the present disclosure.

[0010] Figure 4 A control system for a wind turbine according to embodiments described in the present disclosure is shown.

[0011] Figure 5 is a vector diagram according to an embodiment described in the present disclosure.

[0012] Figure 6 is a flow chart of a method for operating a wind turbine in different modes according to an embodiment described in the present disclosure.

[0013] Figure 7 is a flow chart of an example black start operation according to an embodiment described in the present disclosure.

[0014] Figure 8is a flow chart describing a method for initiating a grid forming mode after a blackout condition is detected according to an embodiment of the present disclosure.

[0015] Fig. 9 is a flow chart describing a method for shutting down one or more wind turbines due to detecting a blackout scenario of a main power grid according to one embodiment of the present disclosure.

[0016] Fig.10 is a block diagram of a wind farm including at least one wind turbine operating in different modes depending on the functionality of an HVDC link according to embodiments described in the present disclosure.

[0017] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. DETAILED DESCRIPTION

[0018] Certain embodiments of the present disclosure are generally directed to techniques for energizing an array of offshore wind turbine farms, offshore substations, and power export cables to be used as a black start block load source for an onshore grid that has lost power. In one embodiment, the offshore wind turbine farm can be used to energize a blacked out physical island, other offshore wind farm units in a larger meshed grid, and / or other offshore wind farms connected to a high voltage direct current (HVDC) interconnector between different synchronization areas.

[0019] As the reliance on electricity usage increases for almost all aspects of urban infrastructure, it is important to restore power losses (blackouts) that may be caused by cascading failures as quickly as possible. Therefore, national grid operators in many countries dispatch backup power sources (typically capable of supplying large loads of 30 to 40 megawatts (MW) and with reactive power capabilities) to perform a black start of the electrical grid (e.g., by using coal or gas-fired power plants) within two hours to restore power to the blacked-out area before resynchronizing it with the rest of the grid.

[0020] Due to the planned closure of fossil fuel power plants, the amount of backup power will decrease in the near future. Certain embodiments of the present disclosure are generally directed to techniques for filling this gap by supplying black start power from offshore wind farms with onshore common coupling points (PCCs) that are widely distributed across the coastline. Many offshore wind farms can provide large load black start power of greater than 60MW, although this may vary with the time of year.

[0021] Certain embodiments of the present disclosure provide a control system for an offshore wind turbine configured to provide power to an HVDC link to be used for a black start operation. In some cases, instead of using a central control system, each wind turbine may have its own control system. During normal operation, the control system of the wind turbine may operate in a grid following mode, in which the wind turbine injects current into a rigid main grid (stiff main grid) with a fixed voltage and frequency. However, in some cases, the main grid may experience a blackout condition, after which the control system may operate in two different modes. For example, the control system may operate in a first mode, which may be referred to as a grid forming mode, in which the wind turbine switches to generate its own voltage at a given frequency at the output of the wind turbine. In the grid forming mode, the wind turbine (and subsequently the entire wind farm) forms its own local grid. Using the grid forming mode, the wind turbine may also be considered to be in a mode referred to herein as an island mode because the wind turbine is isolated from a conventional electrical grid (e.g., the main grid). In island mode, the wind turbines in the wind farm can provide auxiliary power for themselves, or provide auxiliary power for the wind farm platform hardware. Island mode can be used when the wind turbine is not transmitting power on the HVDC link or HVAC link. Instead, the island mode allows the wind turbines in the farm to generate power for auxiliary controls (such as yaw the turbine, cooling pumps, ventilators, air conditioning loads, UPS, and electronic loads). In another example, the wind turbine can be coupled to a local AC grid and can output power to the local grid using island mode. The control system can also operate in a second mode, which can be referred to as a high power mode. In high power mode, the wind turbine increases its output power to perform a black start operation by providing power to the HVDC link.

[0022] In one embodiment, to switch between island mode and high power mode, the wind turbine activates a proportional integral (PI) controller coupled between a reactive power control branch and an active power control branch in its control system. The PI controller receives as input the difference between a desired active power value and an actual active power value generated by the wind turbine and outputs a corresponding voltage regulation. This voltage regulation is then used in the reactive power control branch to change the magnitude of the voltage value. In one embodiment, when switching from island mode to high power mode, the wind turbine activates a PI controller that increases the output power of the wind turbine.

[0023] Example Embodiments

[0024] Figure 1A schematic diagram of a horizontal axis wind turbine generator 100 is shown. The wind turbine generator 100 generally includes a tower 102 and a wind turbine nacelle 104 located on top of the tower 102. A wind turbine rotor 106 may be connected to the nacelle 104 by a low speed shaft extending out of the nacelle 104. The wind turbine rotor 106 includes three rotor blades 108 mounted on a common hub 110 and rotating in a rotor plane, but the wind turbine rotor 106 may include any suitable number of blades (such as one, two, four, five or more blades). The blades 108 (or airfoils) generally each have an aerodynamic shape having a leading edge 112 for facing the wind, a trailing edge 114 located at the opposite end of the chord line of the blade 108, a tip 116, and a root 118 for attaching to the hub 110 in any suitable manner.

[0025] For some embodiments, blades 108 may be connected to hub 110 using pitch bearings 120 so that each blade 108 may be rotated about its longitudinal axis to adjust the pitch of the blade. The pitch angle of blade 108 relative to the rotor plane may be controlled by, for example, a linear actuator, a hydraulic actuator, or a stepper motor connected between hub 110 and blade 108.

[0026] Figure 2 A schematic diagram of typical components inside the nacelle 104 and tower 102 of a wind turbine generator 100 is shown. When wind 200 blows on blades 108, rotor 106 rotates and rotates low-speed shaft 202. Gears in gearbox 204 mechanically convert the low rotational speed of low-speed shaft 202 to a relatively higher rotational speed of high-speed shaft 208 suitable for generating electricity using generator 206.

[0027] The controller 210 may sense the rotational speed of one or both of the shafts 202, 208. If the controller 210 determines that the shaft is rotating too fast, the controller may send a signal to the braking system 212 to slow the rotation of the shaft, which will slow the rotation of the rotor 106 - i.e., reduce the revolutions per minute (RPM). The braking system 212 may prevent damage to components of the wind turbine generator 100. The controller 210 may also receive input from an anemometer 214 (providing wind speed) and / or a wind vane 216 (providing wind direction). Based on the information received, the controller 210 may send a control signal to one or more of the blades 108 to adjust the pitch 218 of the blades. By adjusting the pitch 218 of the blades relative to the wind direction, the rotational speed of the rotor (and therefore the shafts 202, 208) may be increased or decreased. For example, based on wind direction, controller 210 may send control signals to components including yaw motor 220 and yaw drive 222 to rotate nacelle 104 relative to tower 102 such that rotor 106 may be positioned to face more (or in some cases less) upwind.

[0028] Figure 3 3 is a block diagram of an electric power system 300 according to an embodiment described in the present disclosure. The electric power system 300 includes wind turbines 100A-100C, which are coupled to an output cable 335 at a common coupling point (PCC) 330 via an alternating current (AC) grid 331. The output cable 335 is in turn coupled to a grid 345. In one embodiment, the wind turbines 100 are located in an offshore wind farm, and the grid 345 is an onshore electrical grid. However, in other embodiments, the wind farm and the grid 345 may both be onshore. That is, the embodiments described herein are not limited to offshore wind farms, but may be used by onshore wind farms to perform black starts.

[0029] The wind turbine 100A includes: a generator 206 for generating alternating current; a power converter 305 for converting the alternating current signal provided by the generator 206 into a desired frequency; and a filter 320 for removing noise and harmonics from the output of the converter 305. As shown, the power converter 305 includes a generator side converter 310 and a grid side converter 315 coupled together via a direct current (DC) bus 312. In one embodiment, the generator side converter 310 includes a plurality of switches (e.g., power transistors) that convert the alternating current signal provided by the generator 206 into direct current transmitted on the DC bus 312. The grid side converter 315 receives the direct current and converts the direct current back into alternating current (e.g., three-phase alternating current) having a desired frequency (e.g., 50 Hz or 60 Hz) using switches. Although not shown, the wind turbines 100B and 100C may have a similar arrangement to the wind turbine 100A. The wind turbines 110A, 100B, and 100C may be connected using a cable array.

[0030] The wind turbine 100A includes a turbine transformer 325 that couples the wind turbine 100A to the PCC 330 via an alternating current (AC) grid 331. In one embodiment, the grid transformer 325 is within the wind turbine 100A, for example, within the tower. In addition, although not shown, the wind turbines 100B and 100C may also be coupled to the alternating current (AC) grid 331 and the PCC 330 using respective turbine transformers.

[0031] The output of the turbine transformer forms a local AC grid. As described in more detail below, in a first operating mode (e.g., island mode), one or more of the wind turbines 100 provide power to a load 350 coupled to the local AC grid. For example, although the wind turbine 100 may be located in an offshore location, the turbine 100 may be coupled to a local load 350 (such as a nearby densely populated land). Therefore, even when the wind turbine 100 is not transmitting power on the grid 345, the wind turbine 100 can supply power to the local load 350. In addition, when in the island mode, one or more of the wind turbines 100 can supply auxiliary power to the remaining turbines 100 in the farm. For example, some wind turbines 100 can still generate power using the island operating mode to provide auxiliary power to yaw the remaining turbines 100 or to operate the pumps in the turbines 100. This avoids having to have an alternative power source (e.g., a diesel generator) in the offshore wind farm to provide auxiliary power when the wind turbines are not providing power to the grid 345. In certain embodiments, in order to provide power to the grid 345 for black start operation, the wind turbines 100 switch to a second operating mode (e.g., a high power mode) to increase their combined power output at the PCC 330 to exceed a threshold voltage required to provide power to the grid for black start operation. If a grid fault occurs while switching from the first mode to the second mode, it may be advantageous to switch to a third mode when the fault is detected, wherein the third mode includes current limiting so that the turbine follows the grid, whereby it does not provide a maximum current, but only a requested current. Thus, the turbine itself is protected.

[0032] Figure 4 A control system 400 for a wind turbine according to an embodiment described in the present disclosure is shown. In one embodiment, each wind turbine in a wind farm includes a control system 400 for a wind turbine according to an embodiment described in the present disclosure. Figure 4 The control system 400 described herein can be controlled by a wind turbine controller and can be implemented using only software, only hardware, or some mixture of software and hardware elements. In one embodiment, the control system 400 is implemented using a computing system including one or more processors and memory.

[0033] One advantage of the control system 400 is that it may not use high-speed data communications between the control systems 400 in the various wind turbines of the wind farm. That is, although the various control systems 400 may receive reference set points from the central wind farm controller, the control systems 400 in the various wind turbines do not need to be synchronized during operation. By not requiring communications between different control systems 400, the reliability of the control system 400 is improved. In addition, unlike systems that require communication between control systems in wind turbines, the control system 400 does not require a phase-locked loop (PLL) to operate.

[0034] The control system 400 has a reactive power control branch 485 and an active power control branch 480. The reactive power control branch 485 receives a desired reactive power value Q from the wind farm controller. D and receiving an actual reactive power value Q representing the current reactive power generated at the output of the grid side converter 315 A The actual reactive power value Q A Through the optional filter 405, and compared with the desired reactive power value Q D The first adder 410 determines the expected reactive power value Q D (i.e., the reactive power that the wind farm controller wants the wind turbine to output) and the actual reactive power Q currently output by the wind turbine A The difference is input to the voltage lookup module 415, which outputs a voltage adjustment value V for adjusting the output voltage of the wind turbine. ADJ In one embodiment, the voltage lookup module includes a plurality of incremental voltage values ​​that are mapped to corresponding differences between the desired reactive power value and the actual reactive power value. The plurality of voltage values ​​for each control system 400 in the various wind turbines may be different or the same voltage values. That is, the voltage value of the voltage lookup module 415 in one wind turbine may be different from the voltage value in a second wind turbine.

[0035] The second adder 420 adjusts the voltage value V ADJ With nominal voltage V N (which can be provided by the wind farm controller) is added to the output amplitude voltage V MAG The second adder 420 is also coupled to a controller with an integral action (eg, a PI controller 465, which will be described later). MAG Through the optional filter 425 and reach the three-phase conversion module 430. Generally, the three-phase conversion module 430 converts the amplitude voltage V MAG and the voltage factor angle θ output by the active power control branch 480 WConverted into a control signal for the grid side converter 315. In other words, the conversion module 430 uses the outputs of the reactive power control branch 485 and the active power control branch 480 to generate a control signal that operates a switch (e.g., a power transistor) in the grid side converter 315 to output a corresponding three-phase AC voltage signal.

[0036] In the active power control branch 480, the control system 400 receives a desired active power value P from the wind farm controller. D and receiving an actual active power value P representing the current active power output by the grid-side converter 315 A The actual active power value P A The third adder 440 converts the expected active power value P D The actual active power value P A The difference is provided to the angle search module 445, which outputs the corresponding angle adjustment ω. V The angle search module 445 may include a plurality of incremental angle adjustment values ​​corresponding to the actual active power value P A And the expected active power value P D The angle adjustment values ​​stored in the angle lookup module 445 may be the same or different for different wind turbines in the farm.

[0037] The angle adjustment ω output by the angle search module 445 V is transmitted to the fourth adder 450, and the fourth adder 450 adjusts the angle ω V and the desired angle ω received from the wind farm controller D The amplitude voltage V output by the reactive power control branch 485 is MAG controls the amplitude of the AC signal generated by the grid-side converter 315, and the angle ω V and ω D Control the frequency of the AC signal. For example, the desired angle ω D The control system 400 uses the angle adjustment ω V To increase or decrease the active power generated by the grid-side converter to match the desired active power value P D .

[0038] The fourth adder 450 combines the angle ω V * Output to integrator 455, integrator 455 outputs voltage factor angle θ W The three-phase conversion module 430 uses the voltage factor angle θ W And the amplitude voltage V MAGTo generate a control signal that sets the amplitude and frequency of the three-phase AC signal output by the grid-side converter 315.

[0039] The control system 400 also includes a switch 460 that selectively couples the output of the third adder 440 to a PI controller 465, and a switch 470 that selectively couples the output of the first adder 410 to a reactive power regulator 475. When operating in the island mode, the switches 460 and 470 are disconnected, thereby disabling the PI controller 465 and the reactive power regulator 475 so that these components do not affect the voltage factor angle θ generated by the reactive power control branch 485 and the active power control branch 480. W And the amplitude voltage V MAG . However, even when the PI controller 465 and the reactive power regulator 475 are disabled, the control system 400 can still generate an AC signal to power a local load coupled to the local AC grid. As described above, in island mode, the grid-side converter 315 can output AC power for a nearby densely populated land connected to the local AC grid. Additionally or alternatively, one or more of the wind turbines in the electric field can generate auxiliary power for the remaining wind turbines in the electric field. That is, some of the wind turbines can be shut down (i.e., not generating electricity) while other wind turbines are operated in island mode to provide auxiliary power for the shut-down turbines.

[0040] In one embodiment, when operating in island mode, the control system 400 may not be able to output the actual power (ie, the actual reactive power value Q A And the active power value P A ) is set to the expected power value (i.e., the expected reactive power value Q D And the active power value P D ). Instead, the actual power output by a wind turbine is determined by the local load on the turbine.

[0041] To switch from the island mode to the high power mode, the control system 400 closes switches 460 and 470, thereby connecting the inputs of the PI controller 465 and the reactive power regulator 475 to the active power control branch 480 and the reactive power control branch 485, respectively. Although the control system 400 shows the switches connecting the inputs of the controller with integral action (e.g., the PI controller 465) and the reactive power regulator 475 to the corresponding branches 480 and 485, other activation methods (such as turning the power delivered to the PI controller 465 and the reactive power regulator 475 on and off) can be used.

[0042] When the switch 460 is closed, the PI controller 465 receives the desired active power value P from the third adder 440. DThe actual active power value P A Although a PI controller is shown, any controller with an integral action (such as a PI controller 465 or a proportional integral derivative (PID) controller) may be used. In other words, the controller 465 shown is a controller with an integral action. The output of the PI controller 465 is added to the amplitude voltage V MAG The regulated voltage is adjusted until the actual active power value P A and the expected active power value P D In one embodiment, the PI controller 465 causes the reactive power control branch 485 to increase the amplitude of the AC signal generated by the grid-side converter 315 until the amplitude reaches the voltage set for the black start operation. The control system 400 can continue to use the PI controller 465 to control the output power of the wind turbine set by the wind farm controller. That is, unlike when in the island mode, in the high power mode, the control system 400 can control the output power to match the desired power for the black start operation. For example, if the wind farm controller sends a new desired active power value P D , the PI controller 465 can adjust the amplitude of the AC signal to output the desired active power.

[0043] When operating in the high power mode, in addition to activating the PI controller 465, the control system 400 also activates the reactive power regulator 475 by closing the switch 470. In general, the reactive power regulator 475 prevents the formation of circulating reactive power between the wind turbines coupled to the PPC. This may cause circulating reactive power because there are countless scenarios depending on how much reactive power each turbine is generating. When the switch 470 is closed, the desired reactive power value Q output by the adder 410 is D The actual reactive power value Q A The difference (or error) between is provided to the reactive power regulator 475. Then, the reactive power regulator 475 outputs an angle value which is sent to the adder 450. That is, the angle value is added to the angle regulator ω V and the desired angle ω D The voltage factor angle ω is generated by V *. Expected reactive power value Q D The actual reactive power value Q A A larger difference between means that the wind turbine is generating too much reactive power. Therefore, the angle value generated by the reactive power regulator 475 causes the control system 400 to reduce the reactive power output by the grid-side converter 315. In contrast, the desired reactive power value Q D The actual reactive power value Q AA smaller difference between means that the reactive power generated by the wind turbine is too small. In response, the reactive power regulator 475 increases the reactive power generated by the turbine. If each control system 400 of the wind turbines includes a reactive power regulator 475, this results in the wind turbines sharing the generation of reactive current between them and mitigating the possibility of circulating reactive current.

[0044] Figure 5 is a vector diagram 500 according to an embodiment described in the present disclosure. F shows the common voltage at PCC, while the vector V W1 、V W2 ,I W1 and I W2 The two current vectors I represent the corresponding voltages and currents of the two wind turbines in the electric field, namely wind turbine 1 (W1) and wind turbine 2 (W2). W1 and I W2 It is shown that the two wind turbines generate different reactive powers. Specifically, wind turbine 2 delivers more reactive power than wind turbine 1, which means that the voltage vector V W2 In other words, the vector V F and V W2 The angle between is not optimal. Figure 4 As described in the above, the control system 400 includes a reactive power regulator 475, which can regulate the output of the wind turbine 2 so that V F and V W2 The angle between them is closer to V F and V W1 As a result, the wind turbines share the reactive power output more equally, which prevents circulating reactive currents between the wind turbines.

[0045] Figure 6600 is a flow chart of a method for operating a wind turbine in different modes according to an embodiment described in the present disclosure. At box 605, a wind farm controller instructs a control system in each of one or more wind turbines to operate in a first mode (e.g., an island mode or otherwise referred to as a grid formation mode) to provide power to a local AC grid. In some cases, a wind turbine may operate in a first mode in response to determining that a main grid has encountered a power outage, and thus form a local AC grid to provide auxiliary power to one or more wind turbines. In one embodiment, the wind farm controller instructs a subset of wind turbines to operate in a first mode. For example, only a few turbines in the electric field may operate in a first mode to generate auxiliary power for the remaining turbines that do not generate any power. Alternatively, all turbines in the electric field may operate in a first mode to provide power to a local AC grid. In one embodiment, the local AC grid may also provide power to nearby densely populated land (such as an island).

[0046] If at block 610, the wind farm controller determines whether to prepare for black start operation by charging the output cable, and if so, the method 600 proceeds to block 615 to provide power to the grid for black start operation. In one embodiment, the determination to activate black start operation can be based on a command from a transmission system operator (TSO) of the grid. Otherwise, the method 600 returns to block 605, where the one or more wind turbines continue to operate in the first mode.

[0047] At block 615, the wind farm controller initiates the wind turbine shutdown by activating wind turbine controllers (e.g., Figure 4 The control system 400 in FIG. 4 may further include a PI controller between an active control branch and a reactive control branch of the wind turbine controller to instruct at least one of the wind turbines to operate in the second mode. In one embodiment, the PI controller uses a difference (or error) between an actual reactive power value and a desired reactive power value determined in the reactive control branch of the wind turbine controller to generate a voltage regulation used in the active control branch of the turbine controller. The voltage regulation increases the amplitude of the AC voltage generated by the wind turbine to provide sufficient power for the black start operation. At block 620, the one or more wind turbines may perform a black start operation, as described with respect to FIG. Figure 8 In one embodiment, after the desired number of wind turbines have been powered up at a voltage and frequency based on the available wind power and the TSO specified bulk load power setting, the following may be performed: Figure 8 Describes the black start operation.

[0048] As used herein, a first operating mode of a wind turbine generally refers to a grid forming mode, wherein the wind turbine (and subsequently the entire wind farm) forms its own local grid after the main grid experiences a blackout condition. Using the grid forming mode, since the wind turbine is isolated from a conventional electrical grid (e.g., the main grid), the wind turbine may also be considered to be in what is referred to herein as an island mode. Additionally, a second operating mode of a wind turbine generally refers to a high power mode, wherein the wind turbine increases its output power in order to perform a black start operation by providing power to the main grid.

[0049] Figure 7 is a method according to the embodiment described in the present disclosure corresponding to Figure 6 Flowchart of an example black start operation of block 620 of FIG. At block 710, the wind farm controller instructs a control system (e.g., control system 400) to energize an output cable for connecting the offshore wind farm to a grid substation. In one embodiment, by using Figure 4 The control system 400 described gradually increases the output voltage of the wind turbine to perform the energization of the output cable. Once the output cable is energized, the offshore wind farm is in black start mode and waits for a TSO command (e.g., via a farm controller) to connect to the onshore power grid by closing the onshore PCC disconnector (e.g., a circuit breaker). For example, at box 720, an indication may be received from the TSO indicating that the PCC disconnector (e.g., a circuit breaker) has been closed. At box 730, an indication may be received from the TSO indicating the amount of active power (P) and reactive power (Q) to be provided for the black start operation, and at box 740, active power (P) and reactive power (Q) may be provided at line frequency according to the received TSO indication to gradually energize and restore the main power grid.

[0050] In one embodiment, when providing power for a black start operation, wind turbines that are not currently providing power for the black start operation are synchronized with wind turbines that are currently providing power for the black start operation before coupling the wind turbines to the PCC. For example, when electrically coupling a new wind turbine to the PCC, coupling the new wind turbine to wind turbines that are already generating power could cause a short circuit if the angle ω in the control system of the new turbine is not synchronized. Therefore, before adding a new turbine, its control system can synchronize the value of its angle ω with the same angle value used in the control system of the wind turbine that is already providing power for the black start operation. Figure 4In one embodiment, the initial value of the integrator 455 for the new turbine is derived by measuring the phase of the voltage on the low voltage side of the local AC grid. By initializing the integrator 455 to this initial value, the new turbine has the same angle as the currently connected wind turbine, so when the new turbine is coupled to the PCC, the power at the PCC is increased and short circuits are avoided. This synchronization process can be repeated to couple other wind turbines to the PCC as needed.

[0051] return Figure 6 At block 625, the wind farm controller determines whether the wind turbine should remain in the second operating mode. For example, at block 630, the wind farm controller may maintain the various control systems in the high power mode as long as the main grid is in a blackout scenario. However, if the main grid has been restored (e.g., no longer in a blackout condition), at block 635, the wind farm controller instructs the various control systems to deactivate the PI controllers.

[0052] Although the embodiments herein describe a central wind farm controller that sends commands (e.g., a command to switch between a first mode and a second mode, a command containing desired active power values ​​and reactive power values, a power reduction command, etc.) to individual control systems of wind turbines, the individual control systems may operate even if the communication link between the control system and the wind farm controller is lost.

[0053] In some cases, the main grid experiences a partial blackout condition, and thus a low electrical signal may remain at the main grid, requiring additional active / reactive power support from the offshore wind farm. In this case, the wind farm operating in the second mode (e.g., high power mode) can acquire (e.g., determine) the main grid frequency and phase angle (e.g., using a phase-locked loop (PLL)), and synchronize the frequency and phase of the offshore wind farm output electrical signal with the main grid frequency and phase before providing power to the large load requested by the wind farm operator.

[0054] In one embodiment, the wind farm controller may not energize all wind turbines in the offshore wind farm to perform a black start operation. For example, the wind farm controller may energize the minimum number of wind turbines required to provide enough power to black start the main grid. In some cases, the wind farm controller may energize two or more wind turbines that are distributed farthest from each other in the wind farm to reduce wake effects and increase wind capture with minimal wind speed changes for the requested black start bulk load specified by the TSO. This technology, combined with accurate prediction of wind speed time slots, can improve the availability of offshore wind power to provide black start bulk loads.

[0055] Figure 88 is a flow chart describing a method 800 for starting a grid formation mode according to an embodiment of the present disclosure. At box 802, a signal may be received from a TSO indicating that an offshore wind turbine will be used for a black start operation of the main grid. At box 804, the internal power consumption of the wind turbine in the offshore wind farm is switched to a UPS. For example, the power received from the UPS may be used to charge electronic devices, pre-charge a DC link of the wind turbine, and start the wind turbine rotor in the offshore wind farm. At box 806, the power of the wind turbine is reduced, and both the low voltage (LV) circuit breaker and the high voltage switchgear are disconnected. The LV circuit breaker is used to selectively couple a grid-side converter (e.g., a grid-side converter 315) to a transformer (e.g., a transformer 325), and the high voltage (HV) switchgear is used to selectively couple the transformer to a PCC (e.g., PCC 330) via an alternating current (AC) grid 331.

[0056] At box 808, the generator side converter is switched to a DC link control mode. In this mode, the generator side converter pitch controls the rotor speed to generate sufficient power to control the DC link. At box 810, the grid forming mode is activated by controlling (e.g., via the control system 400) the grid side converter. Once the grid side converter is activated, power for internal consumption of the wind turbine is received from the grid side converter. At box 812, the LV circuit breaker is closed, and at box 814, the transformer is gradually energized. At box 816, the wind farm controller determines whether the transformer is energized, and if so, the method 800 continues to box 818, where the HV switchgear is closed.

[0057] At box 820, array cables connecting wind turbines in the wind farm are gradually energized by the wind turbines in the wind farm. At box 822, other wind turbines in the wind farm also energize the array cables in a time-delayed manner to control voltage surges that may otherwise be caused by inrush current if all wind turbines in the wind farm energize the array cables at the same time. At box 824, the wind farm controller determines whether the array cable is energized, and if so, the method 800 continues to box 826, where other array cables that may be coupled to other wind turbines in the wind farm are also energized. For example, depending on the power set point used to perform the black start operation (e.g., as may be specified by the TSO), a certain number of other array cables may be energized to meet the power demand.

[0058] Although the embodiments described herein have provided example techniques for performing black start operations, the techniques described herein may also be used to provide power to adjacent portions of an offshore wind farm in an offshore meshed power grid (where auxiliary backup power may not be available or auxiliary backup power is an expensive option to maintain offshore, and / or where the output cable may be damaged). In addition, power may be provided to an offshore wind farm (where auxiliary backup power may not be available or auxiliary backup power is an expensive option to maintain offshore, and / or the interconnection link power is not available) connected to an HVDC interconnector between different synchronization areas (e.g., an interconnection link between two different countries). In one embodiment, grid-forming power may be provided to a hybrid power plant that may be located further offshore. A hybrid power plant may be a hybrid power plant that uses a renewable power source (e.g., photovoltaic, wave and / or tidal power) and other power sources (e.g., diesel or gas). The hybrid power plant may be located at an offshore power hub, where the point-to-point connections of the wind farm are collected and transmitted onshore via an output cable.

[0059] The embodiments described herein can be used to provide black start support even during low wind periods. These low wind periods can be compensated by increasing the storage capacity of individual wind turbines or of the wind farm as a whole. For example, additional UPS battery storage capacity can be added to each wind turbine. In one embodiment, additional energy storage units can be added to the shore connection point of the offshore wind farm. The capacity of these energy storage units may be as high as 5-10% of the total energy of the wind farm and can be incorporated into existing flexible AC transmission system units that can be used for grid compliance. These energy storage units can also be used to energize the output cables and / or offshore transformers for the black start support described herein.

[0060] Fig. 9 9 is a flow chart describing a method 900 for shutting down one or more wind turbines due to detecting a blackout scenario of a main power grid according to one embodiment of the present disclosure. At block 910, the wind farm controller determines that the main power grid (e.g., Fig.10The method 900 may be used to determine whether a high voltage direct current (HVDC) link (described in more detail) is functioning. For example, the HVDC link may be cut off or the onshore power station may be disconnected, thereby disconnecting the wind farm from the main grid (e.g., the onshore grid). In some cases, the grid operator may voluntarily decide to disconnect the HVDC link. Therefore, whether due to an accident (e.g., a line is cut off or a grid failure) or intentionally (e.g., the onshore grid is not ready to be connected to the wind farm), as long as the HVDC link is not powered, the link is inoperative. If the HVDC link remains functional, the method 900 returns to box 905. However, if the HVDC link is inoperative, the method 900 proceeds to box 915, where the wind farm controller shuts down a portion of the wind turbines in the wind farm. In this example, shutting down the wind turbines means that these wind turbines will not generate output power on the local AC grid. However, other auxiliary systems in the shut down wind turbines (such as yaw motors, pumps, or heating elements for preventing ice accumulation on the nacelle or blades) may still be operated.

[0061] At block 920, at least one of the remaining operating wind turbines in the wind farm (i.e., wind turbines that are not shut down) uses the auxiliary control system to power auxiliary systems in the shut down wind turbine. That is, at least one of the wind turbines in the farm continues to output power on the local AC grid (although no power is transmitted on the HVDC link). The shut down turbine receives this power and uses it to operate its auxiliary systems. Doing so avoids the need to have an alternative energy source (such as a diesel or gas generator) in the wind farm to power auxiliary systems in the wind turbines when the HVDC link is not functional.

[0062] In one embodiment, when the wind turbine is operating in an island mode (grid forming mode) when disconnected from the HVDC link, the auxiliary control system for operating the wind turbine during block 920 is similar to Figure 4 The control system 400 is shown. That is, the auxiliary control system generates power primarily dictated by the load (eg, the power drawn by auxiliary systems on a shut-down wind turbine), rather than the desired power provided by the turbine controller or wind farm controller.

[0063] At box 925, the wind farm controller determines whether the HVDC link is functional. If not, the method 900 returns to box 920. However, if the HVDC link is functional, the method 900 returns to box 905, where all wind turbines in the wind farm are operated using the primary control system and power is transmitted over the HVDC link. In other words, when the HVDC link becomes functional again, the shut down turbines will restart, and the wind turbines operating using the secondary control system will instead operate using the primary control system.

[0064] Fig.10 1 is a block diagram of a wind farm 1000 including a plurality of wind turbines operating in different modes described herein according to embodiments described in the present disclosure. In this example, the wind farm 1000 is an offshore wind farm coupled to an onshore grid 1045 via an HVDC link 1040. However, the following embodiments may also be applied to onshore wind farms that transmit power to a distant grid using an HVDC link 1040 (or a high voltage alternating current (HVAC) link).

[0065] Wind farm 1000 includes three wind turbines 1005A, 1005B, and 1005C, each of which includes a turbine controller 1010 and auxiliary systems 1025 (e.g., yaw controller / motor, pumps, de-icing system, etc.). Turbine controller 1010 has two separate control systems that control the operation of the corresponding wind turbine 1005 depending on the function of HVDC link 1040. When HVDC link 1040 is functional, turbine controller 1010 uses primary control system 1015, which results in power being transmitted from farm 1000 to onshore grid 1045. However, when HVDC link 1040 is not functional, wind farm controller 1050 may instruct one or more of turbine controllers 1010 to operate using auxiliary control system 1020 instead. For example, the three wind turbines 1005 shown here can be designated as backup wind turbines in the farm 1000, which provide power to the auxiliary systems 1020 of all wind turbines in the farm 1000 when the HVDC link 1040 is disconnected. In other words, when the HVDC link is disabled, all wind turbines in the wind farm 1000 except the auxiliary systems 1020 are powered. Fig.10 All but the three turbines 1005 shown in FIG. 1 may be shut down. Instead of being shut down, the wind turbines 1005A, 1005B, and 1005C switch from operating using the primary control system 1015 to operating using the auxiliary control system 1020, which outputs a sufficient amount of power on the local AC grid 1030 to operate the auxiliary systems in the shut down turbines and the auxiliary systems 1025A, 1025B, 1025C on the turbines 1005A, 1005B, and 1005C.

[0066] As shown, the wind turbine 1005 is coupled to the HVDC link 1040 via an offshore grid substation 1033 including an AC-DC converter 1035. In one embodiment, the offshore grid substation 1033 is disposed on a platform in the offshore wind farm 1000 and includes a structure surrounding the AC-DC converter 1035. However, in another embodiment, the offshore grid substation 1033 and the AC-DC converter 1035 may be disposed on the same platform but may be contained in different surrounding structures. In either case, the AC-DC converter 1035 is used to convert power on the local AC grid 1030 into DC power for transmission on the HVDC link 1040.

[0067] The AC-DC converter 1035 can be an uncontrolled converter or a controlled converter (e.g., a self-rectified or even-line rectified converter). For example, many current offshore wind farms use controlled converters to connect turbines to the onshore grid. Regardless of the type of AC-DC converter 1035 used to couple the local AC grid 1030 to the HVDC link 1040, the control techniques described herein can be used. For example, the master control system 1015 can be a control technique in which the AC-DC converter 1035 is actively controlled by the wind farm controller 1050. In one embodiment, the power output by the wind turbine 1005 when using the master control system 1015 is determined by the AC-DC converter 1035. That is, the power output by each wind turbine 1005 can be specified by the converter 1035 rather than by a desired set point transmitted by, for example, the wind farm controller 1050.

[0068] In addition to providing auxiliary power to the shut-down wind turbines in the farm 1000, the wind turbines 1005A-C may also provide power to the offshore grid substation 1033 and the AC-DC converter 1035 when the HVDC link is inoperative. For example, the substation 1033 and the converter 1035 may include a control system and circuitry that can operate using the auxiliary power provided by the turbines 1005A-C when there is no active connection to the onshore grid 1045. Thus, the wind farm 1000 may not require a generator or battery system to provide power to the grid substation 1033 and the converter 1035 when the HVDC link 1040 is inoperative. In one embodiment, additional power may be provided by a generator (e.g., a diesel generator) in the substation.

[0069] In one embodiment, the auxiliary control system 1020 and the main control system 1015 are corresponding software applications or modules executed according to the state of the HVDC link. Therefore, the wind farm controller can instruct each turbine controller to execute the auxiliary control system 1020 or the main control system 1015 according to the state of the HVDC link. For example, the turbine controller 1010 may include at least one processor and sufficient memory to store software applications. However, in other embodiments, the auxiliary control system 1020 and the main control system 1015 include hardware or firmware components.

[0070] In addition, despite Fig.10 Wind farm 1000 is shown coupled to an HVDC link, but in another embodiment, wind farm 1000 is coupled to an HVAC link via an AC-AC converter that converts AC power signals on local AC grid 1030 into high voltage AC power signals suitable for the HVAC link.

[0071] In the foregoing, reference is made to the embodiments presented in this disclosure. However, the scope of the present disclosure is not limited to the specifically described embodiments. Instead, any combination of the features and elements provided above (whether or not they relate to different embodiments) can be envisioned to implement and practice the envisioned embodiments. In addition, although the embodiments disclosed herein can achieve advantages over other possible solutions or over the prior art, whether a specific advantage can be achieved by a given embodiment does not limit the scope of the present disclosure. Therefore, the various aspects, features, embodiments and advantages described herein are merely exemplary and should not be regarded as elements or limitations of the appended claims (unless explicitly stated in the claims).

[0072] As will be appreciated by those skilled in the art, the embodiments disclosed herein may be embodied as systems, methods, or computer program products. Thus, various aspects may take the form of a complete hardware embodiment, a complete software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, which may be collectively referred to herein as a "circuit," "module," or "system." In addition, various aspects may take the form of a computer program product embodied in one or more computer-readable media having computer-readable program code embodied thereon.

[0073] The present invention may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium (e.g., a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof) having thereon computer-readable program instructions for causing a processor to perform various aspects of the present invention.

[0074] Various aspects of the present disclosure are described below with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to the embodiments proposed in the present disclosure. It will be understood that each frame of the flowchart and / or block diagram and the combination of frames in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device create a means for implementing the functions / actions specified in the frames of the flowchart and / or block diagram.

[0075] The flow charts and block diagrams in the accompanying drawings illustrate the architecture, functions and operations of possible implementations of the system, method and computer program product according to various embodiments. In this regard, each frame in the flow chart or block diagram may represent a module, section or part of one or more executable instructions for implementing a specified logical function of the code. It should also be noted that in some alternative implementations, the functions indicated in the frame may not occur in the order indicated in the figure. For example, depending on the functions involved, the two frames shown in succession can actually be executed substantially simultaneously, or sometimes these frames can be executed in reverse order. It should also be noted that each frame of the block diagram and / or flow chart and the combination of the frames in the block diagram and / or flow chart can be implemented by a system based on dedicated hardware that performs a specified function or action, or a combination of dedicated hardware and computer instructions.

[0076] In view of the foregoing, the scope of the present disclosure is determined by the following claims.

Claims

1. A method for performing a black start operation, comprising: operating a wind turbine in a wind farm in a first mode to provide power to an AC grid using a control system, wherein the control system includes a reactive power control branch and an active power control branch, and wherein during the first mode, a controller with an integral action is deactivated or disconnected from the active power control branch; Switching the operation of the wind turbine from the first mode to a second mode based on an indication of performing a black start on the main power grid, wherein the switching from the first mode to the second mode comprises: (i) activating the controller that supplies power to the active power control branch, or (ii) connecting the controller to the active power control branch, wherein in the second mode, an input of the controller is connected to the active power control branch, and an output of the controller is connected to the reactive power control branch, so that the controller outputs a regulated voltage to the reactive power control branch based on the active power produced by the wind turbine, thereby increasing the output power of the wind turbine; and Power is provided to the main grid when operating in the second mode.

2. The method according to claim 1, further comprising: When operating in the first mode, an array of cables connecting the wind turbine to one or more other wind turbines in a wind farm and a transformer of the wind turbine are energized.

3. The method according to claim 2, further comprising: One or more values ​​indicative of a bulk load power to be used for the black start operation are received, wherein the wind turbine is energized according to the one or more values ​​prior to energizing the cable array and the transformer.

4. The method according to any one of the preceding claims, further comprising: Prior to providing power to the main grid, an export cable for connecting the wind farm to the main grid is energized.

5. The method according to claim 4, wherein: The energizing is performed by gradually increasing a voltage of an electrical signal output by the wind turbine.

6. The method according to any one of claims 1 to 3, further comprising: A second indication that the AC grid is coupled to the main grid via closing of a circuit breaker is received, wherein power is provided to the main grid in response to the second indication.

7. The method according to any one of claims 1 to 3, further comprising: A blackout scenario of the main grid is detected, wherein in response to detecting the blackout scenario the wind turbine is operated in the first mode.

8. The method according to claim 7, wherein: Operating in the first mode includes: receiving power from an uninterruptible power supply to start a rotor of the wind turbine; and A voltage of an electrical signal output by the wind turbine is increased to charge a transformer of the wind turbine.

9. The method according to any one of claims 1 to 3, wherein: The power is provided via the main grid to an adjacent offshore wind farm experiencing a power outage condition.

10. The method according to any one of claims 1 to 3, wherein: The power is provided to interconnect nodes between synchronization zones.

11. The method according to any one of claims 1 to 3, wherein: If the amount of power generated by the wind turbine is insufficient to black start the main grid, power is provided to the main grid from both the wind turbine and at least one uninterruptible power supply.

12. The method according to any one of claims 1 to 3, wherein: Providing power to the main grid includes providing power to a hybrid power plant for grid formation, the hybrid power plant being located at an offshore location.

13. The method according to any one of claims 1 to 3, further comprising: A frequency and a phase of an electrical signal at the main grid are determined, wherein providing power while operating in the second mode includes providing power at the determined frequency and phase.

14. The method according to any one of claims 1 to 3, wherein: The wind turbine is one of a plurality of wind turbines in a wind farm, and the method further includes: energizing two or more wind turbines in the wind farm that are farthest from each other to perform a black start on the main grid.

15. A wind turbine comprising: A control system, the control system comprising: Reactive power control branch, Active power control branch, and Controller with integral action, Wherein, the control system is configured as follows: operating the wind turbine in a first mode to provide power to a local AC grid, wherein during the first mode the controller is disabled or disconnected from the active power control branch; switching the operation of the wind turbine from the first mode to a second mode based on an indication of a black start to the main grid and by (i) activating the controller to supply power to the active power control branch, or (ii) connecting the controller to the active power control branch to increase the output power of the wind turbine, wherein in the second mode, an input of the controller is connected to the active power control branch and an output of the controller is connected to the reactive power control branch, so that the controller outputs a regulated voltage to the reactive power control branch based on the active power produced by the wind turbine; and Power is provided to the main grid when operating in the second mode.

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