System and method for transferring power oscillations to energy buffer after grid event

Abstract

A method for controlling a power generation asset connected to a power grid includes receiving, via a controller, a grid power target associated with an operating power level prior to occurrence of one or more grid events in the power grid. The method also includes implementing, via the controller, the power transfer function during recovery from the one or more grid events. The power transfer function includes calculating an expected grid power based on at least one of a grid power target and a grid power limit, calculating a power deviation between a power associated with the driveline and the expected grid power, and diverting at least a portion of the power bias to an energy buffer to prevent the portion of the power bias from reaching the power grid.

Description

Technical Field

[0001] The present disclosure relates generally to power generation and, more particularly, to systems and methods for diverting power oscillations to dynamic brakes of power generation assets following a grid event. Background Art

[0002] Power generation assets can take various forms and rely on renewable and / or non-renewable energy. Those power generation assets that rely on renewable energy can generally be considered one of the cleanest and most environmentally friendly energy sources currently available. For example, wind turbines have received increasing attention in this regard. Modern wind turbines typically include a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The nacelle includes a rotor coupled to a gearbox and coupled to a generator. The rotor and gearbox are mounted on a base support frame located in the nacelle. The rotor blades use the known airfoil principle to capture the kinetic energy of the wind. The rotor blades transmit kinetic energy in the form of rotational energy so as to rotate the shaft that couples the rotor blades to the gearbox (or directly to the generator if a gearbox is not used). The generator then converts the mechanical energy into electrical energy, and the electrical energy can be transmitted to a converter and / or transformer housed in the tower, and then deployed to the utility grid. Modern wind power generation systems typically take the form of a wind farm with multiple wind turbine generators, which are operable to supply power to a transmission system that provides power to the power grid.

[0003] Wind turbines can be divided into two types: fixed speed turbines and variable speed turbines. Traditionally, variable speed wind turbines are controlled as current sources connected to the power grid. In other words, variable speed wind turbines rely on the grid frequency detected by a phase locked loop (PLL) as a reference and inject a specified amount of current into the grid. Conventional current source control of wind turbines is based on the assumption that the grid voltage waveform is a fundamental voltage waveform with a fixed frequency and amplitude, and that the penetration of wind power into the grid is low enough so as not to cause disturbances to the grid voltage amplitude and frequency. Therefore, the wind turbine simply injects a specified current into the grid based on the fundamental voltage waveform.

[0004] Grid faults such as low voltage ride through (LVRT) and / or zero voltage ride through (ZVRT) events generate large transient torques in the mechanical drive train of a wind turbine power system. These torque events may reach large amplitudes, which can damage the gearbox. Therefore, existing drive train designs rely on drive train dampers (DTDs) for mechanical stability. DTDs generate oscillations in the grid power after the fault is cleared, which may cause non-compliance in terms of power overshoot or damping and cause voltage stability problems in very weak grids. In addition, more aggressive DTD gains to reduce mechanical loading can increase the likelihood of non-compliance for power oscillations.

[0005] In view of the foregoing, the art is continually seeking new and improved systems and methods for transferring power oscillations to energy buffers of generation assets following a grid event. Summary of the invention

[0006] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0007] In aspect, the present disclosure is directed to a method for controlling a power generation asset connected to a power grid. The power generation asset has a power converter and a drive train having at least a generator. The method includes receiving, via a controller, a grid power target associated with an operating power level before one or more grid events occurred in the power grid. During recovery from the one or more grid events, the method also includes implementing, via the controller, a power diverter function. The power diverter function includes calculating an expected grid power based on at least one of the grid power target and a grid power limit, calculating a power deviation between a power associated with the drive train and the expected grid power, and diverting at least a portion of the power deviation to an energy buffer to prevent a portion of the power deviation from reaching the power grid.

[0008] In another aspect, the present disclosure is directed to a power generation asset connected to a power grid. The power generation asset includes a generator, a power converter coupled to the generator, and a controller having at least one processor configured to perform a plurality of operations. The plurality of operations include receiving an indication of one or more grid events occurring in the power grid, and during recovery from the one or more grid events, implementing a power shifter function. The power shifter function includes calculating an expected grid power based on at least one of a grid power target and a grid power limit, calculating a power deviation between a power associated with a drive system and the expected grid power, and transferring at least a portion of the power deviation to an energy buffer to prevent a portion of the power deviation from reaching the power grid.

[0009] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A complete and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0011] Figure 1 illustrates a perspective view of an embodiment of a power generation asset configured as a wind turbine power system according to the present disclosure;

[0012] Figure 2 illustrates a schematic diagram of an embodiment of an electrical system for use with a power generation asset configured as a wind turbine power system in accordance with the present disclosure;

[0013] Figure 3 illustrates a block diagram of an embodiment of a controller for use with a power generation asset according to the present disclosure;

[0014] Figure 4 Picture shows Figure 2 A simplified schematic diagram of an electrical system of , particularly illustrating power flow during normal operation and during one or more grid events according to the present disclosure;

[0015] Figure 5 illustrates a flow chart of one embodiment of a method for controlling a power generation asset connected to a power grid according to the present disclosure;

[0016] Figure 6 A schematic diagram illustrating an embodiment of a power softening function according to the present disclosure is illustrated;

[0017] Figure 7 illustrates a schematic diagram of integrating energy buffer power commands from a power softening function into an existing control of a power generation asset in accordance with the present disclosure; and

[0018] Figure 8 A schematic diagram of integrating power commands from a power softening function into existing controls of a power generation asset in accordance with the present disclosure is illustrated.

[0019] Fig. 9 illustrates a flow chart of one embodiment of a method for controlling a power generation asset connected to a power grid according to the present disclosure;

[0020] Fig.10 a schematic diagram illustrating an embodiment of a power shifter function according to the present disclosure; and

[0021] Fig.11 A schematic diagram of integrating a dynamic brake power command from a power shifter function into an existing control of a power generation asset from the present disclosure is illustrated.

[0022] Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. DETAILED DESCRIPTION

[0023] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the present invention rather than by way of limitation of the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature illustrated or described as part of an embodiment may be used together with another embodiment to produce yet another embodiment. Therefore, it is intended that the present invention encompasses such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0024] As used herein, the terms “first,” “second,” and “third” may be used interchangeably to distinguish one component from another, and are not intended to indicate the position or importance of individual components.

[0025] The terms “coupled,” “fixed,” “attached,” and the like refer to both direct coupling, fixing, or attachment as well as indirect coupling, fixing, or attachment through one or more intermediate components or features, unless otherwise specified herein.

[0026] Approximate language, as used herein throughout the specification and claims, is applied to modify any quantitative representation that may be permissibly varied without resulting in a change in the basic function to which it is related. Thus, a value modified by one or more terms, such as "approximately," "approximately," and "substantially," is not limited to the precise value specified. In at least some instances, approximate language may correspond to the precision of an instrument used to measure a value, or the precision of a method or machine used to construct or manufacture a component and / or system. For example, approximate language may refer to within a 10% margin.

[0027] Here and throughout the specification and claims, range limitations are combined and interchanged, such that ranges are identified and include all sub-ranges contained therein unless context or language indicates otherwise. For example, all ranges disclosed herein include the endpoints, and the endpoints are independently combinable with each other.

[0028] Grid events such as low voltage ride-through (LVRT) and / or zero voltage ride-through (ZVRT) events generate large transient torques in the mechanical transmission system of the wind turbine power system, which can damage the gearbox. Therefore, existing transmission system designs for wind turbine power systems generally rely on sliding couplings to meet LVRT / ZVRT requirements. In particular, sliding couplings can be installed to protect the gearbox. However, sliding couplings can wear out quickly and can be expensive to replace. In addition, existing grid specifications require power generation assets to restore active power to pre-fault power levels after a grid fault and avoid excessive deviations from pre-fault power levels. Certain control functions for managing mechanical loading on wind turbines may cause power deviations (deviations from before the grid disturbance) during recovery from grid events. If the power deviation is too large and the grid is weak, such deviations may result in non-compliance with different grid specifications or increase voltage stability risks.

[0029] Thus, the present disclosure is directed to systems and methods for controlling a power generation asset (such as a wind turbine) connected to a power grid that simultaneously commands a non-zero power command (causing active power to flow into the generator stator) and an energy buffer (such as a dynamic brake) to operate. Thus, the converter control has the ability to reduce power variations on the drive system due to a grid event by dissipating or storing power in an energy buffer during a grid fault, thereby providing increased margin for loads on the drive system components. When grid power is limited during a fault, power commands can be used to increase generator torque, and coordinated power commands can be sent to the energy buffer to provide power buffering for the additional power generated during the grid event. Such buffering can include storing and / or dissipating the generated power. Thus, the systems and methods of the present disclosure effectively circulate active power from the generator stator through the line-side converter of the power converter to provide active power within grid constraints to the grid during a grid event.

[0030] In another embodiment, the present disclosure is directed to a system and method for controlling a power generation asset (such as a wind turbine) connected to a power grid, which utilizes a power shifter function in a converter controller to shift power deviations after a grid event by dissipating or storing power in an energy buffer. In such an embodiment, the shifted power does not reach the grid, thereby effectively reducing the deviation of the grid power without affecting the torque / power of the drive system. In addition, in an embodiment, the power shifter function is designed to reduce the deviation of the grid active power after the grid event within a short period of time after the grid fault.

[0031] Now referring to the accompanying drawings, Figure 1A perspective view of one embodiment of a power generation asset 100 according to the present disclosure is illustrated. As shown, the power generation asset 100 may be configured as a wind turbine 102. In additional embodiments, the power generation asset 100 may be configured as a hydroelectric power plant, a fossil fuel generator, and / or a hybrid power generation asset, for example.

[0032] When configured as a wind turbine 102, the power generation asset 100 may generally include a tower 104 extending from a support surface 103, a nacelle 106 mounted on the tower 104, and a rotor 108 coupled to the nacelle 106. The rotor 108 includes a rotatable hub 110 and at least one rotor blade 112 coupled to the hub 110 and extending outwardly from the hub 110. For example, in the illustrated embodiment, the rotor 108 includes three rotor blades 112. However, in alternative embodiments, the rotor 108 may include more or less than three rotor blades 112. Each rotor blade 112 may be spaced about the hub 110 to facilitate rotating the rotor 108, thereby enabling kinetic energy from the wind to be converted into usable mechanical energy and subsequently converted into electrical energy. For example, the hub 110 may be rotatably coupled to an electrical system 200 ( Figure 2 ) of the generator 118( Figure 2 ), to allow the generation of electrical energy.

[0033] The wind turbine 102 may also include a controller 120 centrally located within the nacelle 106. However, in other embodiments, the controller 120 may be located within any other component of the wind turbine 102, or at a location external to the wind turbine 102. In addition, the controller 120 may be communicatively coupled to any number of components of the wind turbine 102 in order to control the components. Thus, the controller 120 may include a computer or other suitable processing unit. Thus, in several embodiments, the controller 120 may include suitable computer-readable instructions that, when implemented, configure the controller 120 to perform a variety of different functions, such as receiving, transmitting, and / or executing wind turbine control signals.

[0034] In addition, if Figure 1 , in an embodiment, the power generation asset 100 may include at least one operation sensor 122. For example, in response to environmental conditions, the operation sensor(s) 122 may be configured to detect the performance of the power generation asset 100. In an embodiment, the operation sensor(s) 122 may be configured to monitor a plurality of electrical conditions, such as slip, stator voltage and current, rotor voltage and current, line-side voltage and current, DC link charge, and / or any other electrical condition of the power generation asset 100.

[0035] It should also be appreciated that, as used herein, the term "monitor" and variations thereof indicate that the various sensors of the power generation asset 100 may be configured to provide direct measurements of monitored parameters or indirect measurements of such parameters. Thus, the sensor(s) 122 described herein may, for example, be used to generate signals related to the monitored parameters, which may then be used by the controller 120 to determine a condition or response of the power generation asset 100.

[0036] Reference now Figure 2 , which illustrates an exemplary electrical system 200 of a power generation asset 100. As shown, a generator 118 may be coupled to a rotor 108 for generating electrical energy from the rotational energy generated by the rotor 108. Thus, in an embodiment, the electrical system 200 may include various components for converting the kinetic energy of the rotor 108 into an acceptable form of electrical output to a power grid 202 via a grid bus 204. For example, in an embodiment, the generator 118 may be a doubly fed induction generator (DFIG) having a stator 206 and a generator rotor 208. The generator 118 may be coupled to a stator bus 210 and a power converter 220 via a rotor bus 212. In such a configuration, the stator bus 210 may provide output multi-phase power (e.g., three-phase power) from the stator of the generator 118, and the rotor bus 212 may provide output multi-phase power (e.g., three-phase power) of the generator rotor 208 of the generator 118. In addition, the generator 118 may be coupled to a rotor-side converter 222 via the rotor bus 212. Rotor-side converter 222 may be coupled to line-side converter 224 , which in turn may be coupled to line-side bus 214 .

[0037] In an embodiment, the rotor side converter 222 and the line side converter 224 can be configured for a normal operating mode in a three-phase pulse width modulation (PWM) arrangement using insulated gate bipolar transistors (IGBTs). Other suitable switching devices may be used, such as insulated gate rectifier thyristors, MOSFETs, bipolar transistors, silicon controlled rectifiers, and / or other suitable switching devices. In addition, as shown, the rotor side converter 222 and the line side converter 224 can be coupled across a DC link capacitor 228 via a DC link 226. In addition, as shown, the power converter 220 can include an energy buffer, such as a dynamic brake 238.

[0038] In an embodiment, the power converter 220 may be coupled to the controller 120 configured as a converter controller 230 to control the operation of the power converter 220. For example, the converter controller 202 may send control commands to the rotor side converter 222 and the line side converter 224 to control the modulation of the switching elements used in the power converter 220 to establish a desired generator torque set point and / or power output.

[0039] like Figure 2 As further depicted in FIG. 2 , in an embodiment, the electrical system 200 may include a transformer 216 that couples the power generation asset 100 to the power grid 202. In an embodiment, the transformer 216 may be a three-winding transformer that includes a high voltage (e.g., greater than 12KVAC) primary winding 217. The high voltage primary winding 217 may be coupled to the power grid 179. The transformer 216 may also include a medium voltage (e.g., 6KVAC) secondary winding 218 coupled to the stator bus 210 and a low voltage (e.g., 575VAC, 690VAC, etc.) auxiliary winding 219 coupled to the line bus 214. It should be appreciated that the transformer 216 may be a three-winding transformer as depicted, or alternatively may be a two-winding transformer having only a primary winding 217 and a secondary winding 218; may be a four-winding transformer having a primary winding 217, a secondary winding 218, an auxiliary winding 219, and an additional auxiliary winding; or may have any other suitable number of windings.

[0040] In an embodiment, the electrical system 200 may include various protection features (e.g., circuit breakers, fuses, contactors, and other devices) to control and / or protect various components of the electrical system 200. For example, in an embodiment, the electrical system 200 may include a grid circuit breaker 232, a stator bus circuit breaker 234, and / or a line bus circuit breaker 236. When a condition of the electrical system 200 approaches a threshold value (e.g., a current threshold value and / or an operating threshold value) of the electrical system 200, the circuit breaker(s) 232, 234, 236 of the electrical system 200 may connect or disconnect corresponding components of the electrical system 200.

[0041] Reference now Figure 3, illustrates a block diagram of an embodiment of suitable components that may be included within a controller 300 of a power generation asset 100, such as a wind turbine 102. For example, as shown, the controller 300 may be a turbine controller 120 or a converter controller 230. Further, as shown, the controller 120 includes one or more processors 302 and associated memory devices 304 configured to perform various computer-implemented functions (e.g., perform methods, steps, calculations, etc., and store related data as disclosed herein). Further, the controller 300 may also include a communication module 306 to facilitate communication between the controller 300 and various components of the power generation asset 100. Further, the communication module 306 may include a sensor interface 308 (e.g., one or more analog-to-digital converters) to allow signals transmitted from the sensor(s) 122 to be converted into signals that can be understood and processed by the processor 302. It should be appreciated that the sensor(s) 122 may be communicatively coupled to the communication module 306 using any suitable means. For example, the sensor(s) 122 may be coupled to the sensor interface 308 via a wired connection. However, in other embodiments, sensor(s) 122 may be coupled to sensor interface 308 via a wireless connection, such as by using any suitable wireless communication protocol known in the art.

[0042] As used herein, the term "processor" refers not only to what is known in the art as an integrated circuit included in a computer, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. In addition, the memory device(s) 304 may generally include memory elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disk-read only memory (CD-ROM), magneto-optical disks (MOD), digital versatile disks (DVD), and / or other suitable memory elements. Such memory devices (one or more) 304 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 302, configure the controller 300 to perform various functions as described herein, as well as various other suitable computer-implemented functions.

[0043] Reference now Figure 4 , which illustrates Figure 22 is a simplified schematic diagram of an electrical system 200, particularly illustrating power flow during normal operation and during one or more grid events in accordance with the present disclosure. More specifically, as shown, power flow during normal operation is represented by solid arrows throughout system 200, while power flow during (one or more) grid events is represented by dashed arrows within dashed boxes throughout system 200. Figure 4 An embodiment of an energy buffer is further shown, which is a dynamic brake 238 between the rotor side converter 222 and the line side converter 224. Also, as shown, the dynamic brake 238 is represented as a resistor. Also, as shown, the power flow at the output of the system 200 (i.e., Figure 4 PT and Pt in ) reflect the grid power / net power output of the system 200. In addition, in an embodiment, the generator power is equal to the electrical torque on the generator 118 multiplied by the operating speed, which is reflected as the power flow through the stator and rotor windings of the generator 118. During normal and grid fault conditions, most of the generator power flows through the stator (i.e., Figure 4 Ps in ).

[0044] Reference now Figure 5 , presents a flow chart of one embodiment of a method 400 for controlling a power generation asset 100, particularly during a grid event. For example, in certain embodiments, a grid event may be a low voltage ride through (LVRT) event or a zero voltage ride through (ZVRT) event. In further embodiments, a grid event may be any event occurring in the grid that results in a large change in generator torque / power that results in stress on drive train components. The method 400 may be implemented using, for example, the method described above with reference to Figure 2-4 For purposes of illustration and discussion, Figure 5 The steps are depicted as being performed in a particular order. Using the disclosure provided herein, one of ordinary skill in the art will appreciate that the various steps of method 400 or any of the methods disclosed herein may be adapted, modified, rearranged, performed simultaneously, or modified in various ways without departing from the scope of the present disclosure.

[0045] As shown at (402), the method 400 may include receiving, via the controller, a grid power limit 502 (e.g., PwrLimGDPLPu) associated with one or more grid events occurring in the power grid. For example, in an embodiment, the method 400 may include calculating the grid power limit based on voltage feedback, a phase-locked loop (PLL) error signal, or the like. By dynamically reducing the grid active power limit during a grid event, along with prioritization of voltage support, the electrical stability of the grid may be improved. However, due to the large changes in power / torque associated with grid power limit activation, such prioritization of grid stability may have a significant impact on drive train components. As shown at (404), to help reduce such adverse effects of large power / torque changes on drive train components, the method 400 may include implementing a power softening function 406 via the controller 300 during the grid event(s). For example, as shown at (408), the power softening function 406 includes increasing the power command of the generator above the grid power limit to avoid large changes in the power of the generator, thereby reducing the possibility of coupling slip of the drive system.

[0046] Additionally, as shown at (410), the power softening function 406 includes transferring additional power generated during the (one or more) grid events to the energy buffer based on the energy buffer power command. In certain embodiments, the power softening function 406 may include simultaneously increasing the power command of the generator and transferring additional power generated during the (one or more) grid events to the energy buffer based on the energy buffer power command. For example, in certain embodiments, the energy buffer may include the dynamic brake 238 of the power converter 200, one or more ultracapacitors, or an energy storage device.

[0047] Furthermore, as shown at (412), the power softening function 406 includes coordinating the energy buffer power command and the power command of the generator to maintain the net power generated by the power generation asset within the grid power limit. Thus, the power softening function 406 is configured to prevent the generator power output of the generator from dropping to zero during the (one or more) grid events, thereby reducing the variation of the power of the drive system caused by the (one or more) grid events.

[0048] refer to Figure 6-8 , for a better understanding Figure 5 The method 400. In particular, Figure 6A schematic diagram 500 of an embodiment of a power softening function 406 according to the present disclosure is illustrated. As shown, the power softening function 406 receives a plurality of inputs. In certain embodiments, as shown, the plurality of inputs may include, for example, a grid power limit 502 (e.g., PwrLimGDPLPu), a speed feedback signal 504 (e.g., SpdFbk), a rotor torque reference 506 (R_TrqRef) of a wind turbine 102 (e.g., from a turbine controller 120), a power reference of a wind turbine 102, or any other suitable input.

[0049] Thus, as shown, the power softening function 406 is configured to determine a grid power reference signal 508 based on the speed feedback signal 504 and the rotor torque reference 506. In addition, as shown, the power softening function 406 is configured to use multiple inputs to determine an error signal 512. More specifically, as shown at 510, the grid power reference signal 508 can be compared with the grid power limit 502 to determine an error signal 512, which is the difference between the grid power reference signal 508 and the grid power limit 502. During normal operation, the error signal 512 is negative because the grid power limit is higher than the operating power. However, during a grid fault, the error signal 512 increases to generate multiple outputs. In a particular embodiment, for example, the error signal is used to generate an energy buffer power command 526 (e.g., PdBCmd) and a generator power output 528 (e.g., PgenCmd) described herein.

[0050] Still refer to Figure 6 , the power softening function 406 is further configured to process the error signal 512. For example, as shown, processing the error signal 512 may include comparing the error signal 512 with an offset 515 (e.g., PmisLoOff) via a comparator 514, limiting the error signal 512 by applying a lower limit 516 (e.g., PmisLoPMin) to the error signal 512, and / or filtering the error signal 512 via a filter 518 (e.g., a low-pass filter). In such an embodiment, for example, the offset 515 and the lower limit 516 together may help to activate the power softening function 406 for more or less severe grid faults, and to maintain the power softening function 406 inactive during normal operating conditions. For example, the offset 515 may be set to 0.3 PU (per unit) of power, and the lower limit 516 may be set to zero, indicating that the error signal 512 must be greater than 0.3 PU before the power softening function 406 becomes active. Similarly, since the error signal 512 is negative during normal operating conditions, the lower limit 516 of zero will keep the power softening function 406 disabled during these conditions.Alternative settings may also be selected to activate the power softening function 406 at smaller or larger power error settings.

[0051] In certain embodiments, as shown, the power softening function 406 is further configured to apply a gain 520 (e.g., PmisLoGn) to the error signal 512. In addition, as shown, the power softening function 406 is configured to apply one or more dynamic power limits 522 to the error signal 512. In such embodiments, for example, the (one or more) dynamic power limits 522 of the power softening function 406 can be calculated to avoid excessive power / energy consumption, avoid overheating of certain components, and / or avoid collapse of the DC voltage. For example, in an embodiment, the dynamic power limit can be calculated based on the magnitude of the voltage feedback (e.g., VFbk) multiplied by the maximum current limit of the line side converter 224, so that as the voltage drops lower, the power softening function 406 is more constrained to constrain the current within the limits of the converter rating. In other embodiments, the power limit can be a fixed value. In other embodiments, if certain feedback exceeds at least one of a temperature limit, a power demand limit, a power consumption limit, a trip limit, a reverse power limit, a load limit, a voltage limit, or any other suitable limit, then the dynamic power limit(s) 522 can be designed to constrain the power softening function 406. Thus, as shown, the dynamic limit(s) 522 can be applied to the error signal 512 via a limiter 524 having maximum and minimum limits (e.g., PmisCmdMax and PmisCmdMin). Further, as shown, the output of the limit is a power command 525 (e.g., PmisLoPCmd). Thus, the power command 525 can be used to generate the outputs of the power softening function 406, which are an energy buffer power command 526 (e.g., PdBCmd) and a generator power output 528 (e.g., PgenCmd).

[0052] In addition, as shown at 530, the power softening function 406 is configured to add the generator power command 528 to the grid power reference 532 (e.g., PtCmd) to generate a power command 534 (e.g., PwrCmd), which can be sent to the downstream rotor regulator 536 to increase the generator torque when the grid power is constrained (e.g., during a grid fault). In addition, as shown at 538, the energy buffer power command 526 can be sent to the energy buffer control. In such an embodiment, the energy buffer power command 526 is configured to provide power absorption for the additional power generated during the grid event. In additional embodiments, the power softening function 406 is configured to coordinate the energy buffer power command 526 and the power command of the generator to maintain the net power generated by the generation asset within the grid power limit.

[0053] Reference now Figure 7 and Figure 8, illustrates a schematic diagram of integrating the outputs from the power softening function 406 (e.g., the energy buffer power command 526 and the power command 534) into the existing control of the power generation asset 100 according to the present disclosure. In particular, Figure 7 illustrates a schematic diagram of integrating the energy buffer power command 526 from the power softening function 406 into the existing control of the dynamic brake of the power generation asset 100 according to the present disclosure; and Figure 8 A schematic diagram of integrating a power command 534 (eg, PwrCmd) from a power softening function 406 into an existing torque control of a power generation asset 100 in accordance with the present disclosure is illustrated.

[0054] Special References Figure 7 , the power softening function 406 is configured to request an energy buffer power command 526. In such an embodiment, the energy buffer power command 526 may be used to calculate the dynamic brake 238 ( Figure 2 and Figure 4 ) is used to determine a duty cycle command 540 (e.g., DcPCmdDuty) from the dynamic brake 238. Thus, as shown at 542, the duty cycle command 540 may be summed with an existing duty cycle command 544 from the DB control to obtain a dynamic brake duty cycle signal 546 for the dynamic brake 238. In certain embodiments, the energy buffer power command 526 may be processed prior to being combined with the existing duty cycle command 544. For example, as shown at 550, the power dissipation capability signal 548 may be applied to the energy buffer power command 526 for determining a power command that is normalized based on the power dissipation capability of the dynamic brake 238. Additionally, as shown at 552, a gain may be applied to the energy buffer power command 526 prior to calculating the duty cycle command 540.

[0055] Special References Figure 8 , the generator power output 528 (e.g., PgenCmd) may be used in conjunction with an alternative implementation of torque control. For example, the generator power output 528 may be divided by the speed feedback signal (e.g., SpdFbk) to obtain the generator torque command. Thus, as shown at 554, during a grid event, the generator torque command may be added to the torque command path 556 of the existing control. Thus, the output 558 of the adder 554 may be used in a downstream rotor regulator to regulate the generator torque.

[0056] Reference now Fig. 9 , presents a flow chart of one embodiment of a method 600 for controlling a power generation asset 100, for example, during recovery from one or more grid events. The method 600 may be used, for example, as described above with reference to Figure 1-4 and Figure 6-8 For purposes of illustration and discussion, Fig. 9The steps are depicted as being performed in a particular order. Using the disclosure provided herein, one of ordinary skill in the art will appreciate that the various steps of method 600 or any of the methods disclosed herein may be deployed, modified, rearranged, performed simultaneously, or modified in various ways without departing from the scope of the present disclosure.

[0057] As shown at (602), method 600 includes receiving, via a controller, a grid power target associated with an operating power level prior to occurrence of one or more grid events in the power grid. During recovery from (one or more) grid events, as shown at (604), method 600 includes implementing, via the controller, a power shifter function 606. In particular, as shown at (608), power shifter function 606 includes at least calculating an expected grid power based on at least one of a grid power target and a grid power limit. As shown at (610), power shifter function 606 includes calculating a power deviation between a power associated with a drive system and the expected grid power. In addition, as shown at (612), power shifter function 606 includes transferring at least a portion of the power deviation to an energy buffer to prevent the portion of the power deviation from reaching the power grid.

[0058] refer to Fig.10 , for a better understanding Fig. 9 The method 600. In particular, Fig.10A schematic diagram of an embodiment of a power transfer function 606 according to the present disclosure is illustrated. Thus, as shown, the power transfer function 606 is configured to receive a grid power target associated with an operating power level before one or more grid events occur in the power grid. The grid power target can be received from a sample and hold function on a grid power reference. As used herein, a sample and hold function generally refers to an analog device that samples the voltage of a continuously changing analog signal and maintains its value at a constant level within a specified minimum time period. For example, if a signal indicating a grid fault indicates the presence of a grid fault (e.g., PmisLoPCmd becomes non-zero), the grid power reference can be sampled (or frozen) and stored for a certain period of time until after the fault ends. During this period of time, this stored version of the grid power reference can be used as a grid power target for the power transfer function 406. More specifically, as shown, the power transfer function 606 is configured to receive a grid power limit 502 (e.g., PwrLimGDPLPu) of a controller of a power generation asset. Additionally, in an embodiment, further inputs to the power shifter function 606 may include a rotor torque reference, a speed feedback signal, a grid power reference signal 508 (e.g., PwrRefPu), a power command 525 (e.g., PmisLoPCmd), a power offset signal 612 from the power softening function 406 (e.g., PdbContPCmd), and / or a torque feedback signal 610 (e.g., TrqFbk).

[0059] Thus, in an embodiment, as shown at 614, the power transfer function 606 may include pre-fault power freeze logic that receives an input and freezes a pre-fault power 616 (e.g., PwrTarg). Thus, as shown at 618, the power transfer function 606 is configured to determine a minimum value 620 between the pre-fault power reference 616 and the grid power limit 502 (e.g., PwrLimGDPLPu). The minimum of the grid power limit and the pre-fault power reference reflects the expected grid power to be injected by the generator 118 during recovery from the grid event (e.g., from the end of the grid event to approximately 1-10 seconds after the end of the grid event).

[0060] Thus, the power shifter function 606 is also configured to calculate a power deviation 624 between the power associated with the drive system and the expected grid power, and to shift at least a portion of the power deviation 624 to an energy buffer (such as the dynamic brake 238) to prevent a portion of the power deviation 624 from reaching the power grid. In particular, as shown, the power shifter function 606 is configured to determine the power deviation 624 using a plurality of inputs. For example, Fig.10As shown in , as shown at 622, the power transfer function 606 is configured to determine a power deviation 624 between the pre-fault grid power and the post-fault driveline power and the power offset signal 612 to allow positive and negative changes in dynamic brake power around the power offset signal 612. The power deviation 624 can then be used by the power transfer function 606 to generate an output 626. Specifically, as shown, the output 626 can include a power transfer command 626 (e.g., PdivPCmd) for the energy buffer. In some embodiments, rather than measuring the driveline power directly, the generator power (or air gap torque) (e.g., Fig.10 The driveline power is calculated by multiplying the TrqFbk 610 in the motor with the measured speed feedback. In addition, in embodiments, the generator electrical torque may not be measured directly, but may be estimated based on electrical feedback of the voltage and current on the stator and rotor and electrical parameters of the generator 118. These feedbacks and parameters may be combined using known electrical relationships of the electric machine to obtain an estimate of the generator electrical torque.

[0061] Still reference Fig.10 , the power shifter command 626 for the energy buffer may include a power offset signal 626 (e.g., PdbContPCmd) and a power command signal associated with a power deviation 628 (e.g., PdivPerrPCmd). In particular, as shown, the power command signal associated with the power deviation 628 generally refers to the power deviation 624 in which one or more limits 629 are applied. In such an embodiment, the limits of the power command signal associated with the power deviation 628 may be proportional to the power offset signal 612, and the power offset signal 612 may be triggered by the presence of (one or more) grid events (e.g., as determined by the power softening function 406). Therefore, in an embodiment, the power offset signal 612 (e.g., PdbContPCmd) allows the power command associated with the power deviation signal 628 to increase and decrease the energy buffer power around the power offset signal 612.

[0062] Additionally, the magnitude of power offset signal 612 determines the limit on the power command signal associated with power deviation 628, which eventually decays to zero after a grid fault. Fig.10As shown in , this can be achieved by a post-fault power offset generator 531, which includes functionality designed to generate a temporary power offset during the recovery period of a grid event. For example, the post-fault power offset generator 531 can cause the power offset to increase at the end of the grid event and slowly decrease the offset until a certain duration after the grid event has ended (e.g., from about 1-10 seconds after the grid event ends). In an embodiment, this type of functionality can be achieved by a first-order fast up, slow down filter.

[0063] In addition, as shown, a power command signal associated with a power deviation 628 can be determined based on a power deviation 624, which represents a difference between a post-fault transmission system power 625 and a pre-fault grid power 616 (e.g., PwrTarg). In other embodiments, a flushing filter can be applied to the power deviation signal to remove the steady-state difference between the transmission system power and the expected grid power. In addition, as shown, the post-fault transmission system power 625 can be filtered via a filter 627 to obtain a filtered power signal 630 (e.g., PdrvFbkFil).

[0064] Reference now Fig.11 , as shown at 632, the power shifter function 606 is configured to add a power shifter command 626 for an energy buffer (such as the dynamic brake 238) to the power command 525 (e.g., PmisLoPCmd) for the dynamic brake 238 from the power softening function 406. Thus, in an embodiment, the power shifter function 606 is configured to match the energy buffer power command to the opposite sign of the power deviation, thereby significantly reducing or eliminating the amount of power deviation that appears in the grid power (or net power).

[0065] In addition, the skilled person will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described and other known equivalents of each such method and feature can be mixed and matched by one of ordinary skill in the art to construct additional systems and techniques according to the principles of the present disclosure. Of course, it is to be understood that according to any particular embodiment, not all such purposes or advantages described above may be achieved. Thus, for example, one skilled in the art will recognize that the systems and techniques described herein may be embodied or performed in a manner that achieves or optimizes one advantage or a group of advantages as taught herein, without necessarily achieving other purposes or advantages as may be taught or suggested herein.

[0066] Further aspects of the invention are provided by the subject matter of the following clauses:

[0067] A method for controlling a power generation asset connected to an electric power grid, the power generation asset having a power converter and a transmission system having at least a generator, the method comprising: receiving, via a controller, a grid power target associated with an operating power level before one or more grid events occurred in the power grid; during recovery from the one or more grid events, implementing, via the controller, a power transferor function, the power transferor function comprising: calculating an expected grid power based on at least one of the grid power target and a grid power limit; calculating a power deviation between a power associated with the transmission system and the expected grid power; and transferring at least a portion of the power deviation to an energy buffer to prevent the portion of the power deviation from reaching the power grid.

[0068] A method as claimed in any preceding claim, further comprising receiving from a sample and hold function the grid power target associated with the operating power level prior to the one or more grid events.

[0069] A method according to any preceding claim, wherein transferring the portion of the power deviation to at least the energy buffer further comprises: receiving a plurality of inputs via the power transferor function; determining the power deviation using the plurality of inputs via the power transferor function; and generating an output based on the power deviation via the power transferor function, the output comprising a power transferor command for the energy buffer.

[0070] A method according to any preceding claim, wherein the plurality of inputs comprises at least one of a torque reference, a speed feedback signal, a power reference, a power reference signal from the power softening function, the grid power limit, a power offset signal, a torque feedback signal, a voltage amplitude signal or a combination thereof.

[0071] A method as claimed in any preceding claim, further comprising determining a power command signal associated only with the power deviation.

[0072] A method according to any preceding claim, wherein generating the output based on the power deviation further comprises: combining the power command signal associated only with the power deviation with a power offset signal to allow positive and negative changes in energy buffer power around the power offset signal.

[0073] A method according to any preceding claim, wherein the power transferor command for the energy buffer comprises the power offset signal and the power deviation, the power offset signal being triggered by the one or more grid events.

[0074] A method according to any preceding claim, wherein the amplitude of the power excursion signal determines the limitation of the power command signal associated only with the power deviation.

[0075] A method according to any preceding claim, wherein the power shifter function further comprises adding the power shifter command for the energy buffer to an energy buffer power command for the energy buffer from the power softening function.

[0076] A method according to any preceding claim, wherein the power shifter function further comprises determining the energy buffer power command for the energy buffer based on a torque command of the generator and a torque reference.

[0077] A method according to any preceding claim, wherein the power shifter function further comprises matching the energy buffer power command to the opposite sign of the power deviation.

[0078] A method according to any preceding claim, wherein the power generating asset is a wind turbine.

[0079] A method according to any preceding claim, wherein the one or more grid events comprises one of a low voltage ride through (LVRT) event or a zero voltage ride through (ZVRT) event.

[0080] A power generation asset connected to an electric power grid, the power generation asset comprising: a power converter coupled to the generator; and a controller, the controller comprising at least one processor configured to perform multiple operations, the multiple operations comprising: receiving an indication of one or more grid events occurring in the power grid; during recovery from the one or more grid events, implementing a power transferor function, the power transferor function comprising: calculating an expected grid power based on at least one of the grid power target and the grid power limit; calculating a power deviation between the power associated with the transmission system and the expected grid power; and transferring at least a portion of the power deviation to an energy buffer to prevent the portion of the power deviation from reaching the power grid.

[0081] A power generation asset as claimed in any preceding claim, further comprising receiving from a sample and hold function the grid power target associated with the operating power level prior to the one or more grid events.

[0082] A power generation asset as claimed in any preceding claim, wherein transferring the portion of the power deviation to at least the energy buffer further comprises: receiving a plurality of inputs via the power transferor function; determining a power deviation using the plurality of inputs via the power transferor function; and generating an output based on the power deviation via the power transferor function, the output comprising a power transferor command for the energy buffer.

[0083] A power generation asset as claimed in any preceding claim, wherein the plurality of inputs comprises at least one of a torque reference, a speed feedback signal, a power reference, a power reference signal from the power softening function, the grid power limit, a power offset signal, a torque feedback signal, a voltage amplitude signal or a combination thereof.

[0084] A power generation asset as claimed in any preceding claim, wherein generating the output based on the power deviation further comprises determining a power command signal associated only with the power deviation, and combining the power command signal associated only with the power deviation with a power offset signal to allow positive and negative changes in energy buffer power around the power offset signal.

[0085] A power generation asset as claimed in any preceding claim, wherein the power shifter command for the energy buffer comprises the power excursion signal and the power deviation, the power excursion signal being triggered by the one or more grid events.

[0086] A power generation asset as claimed in any preceding claim, wherein the power shifter functionality further comprises adding the power shifter command for the energy buffer to an energy buffer power command for the energy buffer from the power softening functionality.

[0087] This written description uses examples, including the best mode, to disclose the invention, and also to enable those skilled in the art to practice the invention, including making and using any device or system, and performing any combined method. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

1. A method for controlling a power generation asset connected to a power grid, the power generation asset having a power converter and a drive train having at least a generator, the method comprising: receiving, via a controller, a grid power target associated with an operating power level prior to occurrence of one or more grid events in the power grid; During recovery from the one or more grid events, a power shifter function is implemented via the controller, the power shifter function comprising: calculating an expected grid power based on at least one of the grid power target and the grid power limit; calculating a power deviation between power associated with the drive system and expected grid power; and At least a portion of the power deviation is transferred to an energy buffer to prevent the portion of the power deviation from reaching the power grid. 2 . The method of claim 1 , further comprising receiving, from a sample and hold function, the grid power target associated with the operating power level prior to the one or more grid events.

3. The method according to claim 1, wherein: Transferring at least the portion of the power deviation to the energy buffer further comprises: receiving a plurality of inputs via the power shifter function; determining, via the power shifter function, the power deviation using the plurality of inputs; and An output is generated via the power shifter function based on the power deviation, the output comprising a power shifter command for the energy buffer.

4. The method according to claim 3, wherein: The plurality of inputs include at least one of a torque reference, a speed feedback signal, a power reference, a power reference signal from the power softening function, the grid power limit, a power offset signal, a torque feedback signal, a voltage amplitude signal, or a combination thereof.

5. The method of claim 6, further comprising determining a power command signal associated only with the power deviation.

6. The method according to claim 5, wherein: Generating the output based on the power deviation further comprises: The power command associated only with the power deviation is combined with a power offset signal to allow for positive and negative changes in energy buffer power around the power offset signal.

7. The method according to claim 6, wherein: The power shifter command for the energy buffer includes the power offset signal and the power deviation, the power offset signal being triggered by the one or more grid events.

8. The method according to claim 7, wherein: The magnitude of the power offset signal determines the limitation of the power command signal associated only with the power deviation.

9. The method according to claim 3, wherein: The power shifter function further comprises adding the power shifter command for the energy buffer to an energy buffer power command for the energy buffer from the power softening function.

10. The method according to claim 9, wherein: The power shifter function further includes determining the energy buffer power command for the energy buffer based on a torque command of the generator and a torque reference.

11. The method according to claim 9, wherein: The power shifter functionality also includes matching the energy buffer power command to an opposite sign of the power deviation to reduce or eliminate the appearance of the power deviation in the grid power output.

12. The method according to claim 1, wherein: The power generating asset is a wind turbine.

13. The method according to claim 1, wherein: The one or more grid events include one of a low voltage ride through (LVRT) event or a zero voltage ride through (ZVRT) event.

14. A power generation asset connected to a power grid, the power generation asset comprising: dynamo; a power converter coupled to the generator; as well as A controller comprising at least one processor configured to perform a plurality of operations comprising: receiving an indication of one or more grid events occurring in the power grid; Implementing a power shifter function during recovery from the one or more grid events, the power shifter function comprising: calculating an expected grid power based on at least one of the grid power target and the grid power limit; calculating a power deviation between power associated with the drive system and expected grid power; and At least a portion of the power deviation is transferred to an energy buffer to prevent the portion of the power deviation from reaching the power grid.

15. The power generation asset of claim 14, further comprising receiving the grid power target associated with the operating power level prior to the one or more grid events from a sample and hold function.

16. The power generation asset of claim 14, wherein: Transferring at least the portion of the power deviation to the energy buffer further comprises: receiving a plurality of inputs via the power shifter function; determining, via the power shifter function, a power deviation using the plurality of inputs; and An output is generated via the power shifter function based on the power deviation, the output comprising a power shifter command for the energy buffer.

17. The power generation asset of claim 16, wherein: The plurality of inputs include at least one of a torque reference, a speed feedback signal, a power reference, a power reference signal from the power softening function, the grid power limit, a power offset signal, a torque feedback signal, a voltage amplitude signal, or a combination thereof.

18. The power generation asset of claim 16, wherein: Generating the output based on the power deviation further comprises: determining a power command signal associated only with the power deviation; and The power command signal associated only with the power deviation is combined with a power offset signal to allow for positive and negative changes in energy buffer power around the power offset signal.

19. The power generating asset of claim 16, wherein: The power shifter command for the energy buffer includes the power offset signal and the power deviation, the power offset signal being triggered by the one or more grid events.

20. The power generation asset of claim 16, wherein: The power shifter function further comprises adding the power shifter command for the energy buffer to an energy buffer power command for the energy buffer from the power softening function.

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