System and method for improving the reactive power response time in a wind turbine

Abstract

A method for improving the reactive power response time of a renewable energy generation system connected to a power grid, the method comprising: Providing a conditional logic relating to the energy supply network by means of a control device of the renewable energy generation system; Determining, by means of the controller, a reactive power reference command for the renewable energy generation system in response to the condition logic being satisfied and generating a reactive power pulse command for the renewable energy generation system; Determining a total reactive current command by means of the control device by combining the reactive current reference command and the reactive current pulse command; and Operating the renewable energy generation system based on the total reactive power command to improve the power response time of the renewable energy generation system.

Description

BACKGROUND OF THE INVENTION

[0001] The present disclosure relates generally to wind turbines and, more particularly, to a system or method for improving reactive power response time in a wind turbine during an undervoltage event in a power grid. BACKGROUND OF THE INVENTION

[0002] In general, a wind turbine consists of a turbine with a rotor containing a rotatable hub assembly with multiple blades. The blades convert wind energy into mechanical torque, which drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally connected to the rotor via a gearbox. The gearbox increases the rotor's low speed for the generator to convert the mechanical rotational energy into electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct-drive wind turbines also exist. The rotor, generator, gearbox, and other components are typically mounted within a housing or nacelle located on top of a base, which may be a rack or a tubular tower.

[0003] To provide power to the power grid, wind turbines must meet certain requirements. For example, wind turbines may be required to provide fault tolerance capability (e.g., undervoltage tolerance capability), which requires a wind turbine to remain connected to the power grid during one or more grid faults. As used herein, the terms "grid fault," "fault," or the like are intended to encompass a change in the magnitude of the grid voltage for a specific period of time. For example, the voltage in the system may drop by a significant amount for a short period of time (e.g., typically less than 500 milliseconds) when a grid fault occurs.In addition, grid faults can occur for a variety of reasons, including, but not limited to, a phase conductor being connected to ground (i.e., a ground fault), a short circuit between two or more phase conductors, lightning and / or wind storms, and / or an inadvertent connection of a transmission line to ground.

[0004] In the past, it was acceptable for a wind turbine to be immediately disconnected during these unintended faults whenever the voltage reduction occurred. However, as wind turbines continue to grow in size and the penetration of wind turbines on the grid increases, it is desirable for wind turbines to remain connected and operate through faults. Furthermore, it is also important for wind turbines to generate power after the fault has been cleared. While the fault is still present and before it is cleared, it is beneficial for the wind turbine to supply reactive current to the utility grid. Since grid faults are of short duration, it is reasonable for the reactive current response to be such that it reaches a certain amount within a certain time.Therefore, grid regulations for some countries require a minimum reactive power response time during the onset of a low-voltage tolerance event (LVRT). US Pat. No. 8,295,988 B2 discloses a method for a renewable energy generation system, including providing a condition logic related to the power grid by means of a control device and determining a reactive power reference command in response thereto. Furthermore, operating the system based on the reactive power command is shown.

[0005] In many cases, it may not be optimal for the response time of the fastest current controllers of the power converter to be fast enough to meet the requirements of the grid regulation. Therefore, it may be advantageous for the control device responsible for reactive power control to obtain the required response time by requesting a reactive current amount that is greater than the regulation requires for a period of time sufficient to accelerate the response time to achieve the required current amount. Such a reactive current reference command can result in the required current being reached more quickly than would have been possible without the additional command.

[0006] More specifically, the present disclosure provides a transient pulse that can be combined with the reference reactive current required for the LVRT event to obtain a temporarily higher total reactive current command. This temporarily higher current command improves the wind turbine's current response time and also prevents an excessive current command that may exceed the system's capabilities. BRIEF DESCRIPTION OF THE INVENTION

[0007] Aspects and advantages of the invention are set forth in the following description or will be apparent from the description or may be learned by practicing the invention.

[0008] An exemplary aspect of the present disclosure is directed to a method for improving the reactive power response time of a renewable energy generation system connected to a power grid. The method includes providing conditional logic with respect to the power grid by a controller of the renewable energy generation system. In response to the conditional logic being satisfied, the method also includes determining a reactive power reference command by the controller and generating a reactive power pulse command for the renewable energy generation system. The controller may then determine a total reactive power command by combining the reactive power reference command and the reactive power pulse command.The method also includes operating the renewable energy generation system based on the total reactive power command to improve the power response time of the renewable energy generation system.

[0009] In one embodiment, the condition logic may include any one or a combination of the following: an occurrence of a problem grid voltage event, a time condition to delay the reactive power pulse command, a time condition that limits the reactive power pulse command to a certain repetition rate, a magnitude of a grid fault's reverse voltage, or the like. Furthermore, the problem grid voltage event may include any substantial change in the grid voltage of the utility grid, including, but not limited to, an undervoltage tolerance (LVRT) event (e.g., a grid fault), an overvoltage tolerance (HVRT) event, or the like.

[0010] In another embodiment, the step of generating the reactive power pulse command for the renewable energy generation system may further include determining a difference between a grid voltage and an activation voltage threshold. Therefore, another step of the method may include determining a magnitude and duration for the reactive power pulse command based on the difference, wherein the magnitude and duration of the reactive power pulse command are sufficient to increase the reactive power response time of the renewable energy generation system. In a particular implementation, the conditional logic may be considered satisfied when the grid voltage falls below the activation voltage threshold, such that the difference is positive. In certain embodiments, the activation voltage threshold may be less than or equal to 90% of a nominal grid voltage.In still other embodiments, the activation voltage threshold may be any percentage of the nominal grid voltage.

[0011] In another embodiment, the method may also include a step of determining an upper limit for the reactive power pulse command for the renewable energy generation system to keep the current within the system's capabilities. In yet another embodiment, the step of determining the total reactive power command by combining the reactive power reference command and the reactive power pulse command may further include adding or summing the reactive power reference command and the reactive power pulse command.

[0012] In yet another embodiment, the renewable energy generation system as described herein may comprise any suitable power generation system, including, but not limited to, a wind power generation system (e.g., a wind turbine) or a solar power generation system.

[0013] In another aspect, the present disclosure is directed to a method for improving the reactive power response time of a renewable energy generation system connected to a power grid after a problem voltage condition has occurred in the grid. The method includes generating, via a renewable energy generation system controller, a reactive power pulse command for the renewable energy generation system. A further step includes determining a total reactive power command based at least in part on the reactive power pulse command. The method also includes operating the renewable energy generation system based on the total reactive power command to improve the power response time of the renewable energy generation system. It should also be understood that the method may further include any of the additional steps and / or features described herein.

[0014] In any embodiment of the method, it may be advantageous for the method to further comprise providing conditional logic relating to the power grid and, in response to the conditional logic being satisfied, generating the reactive power pulse command for the renewable energy generation system.

[0015] In any embodiment of any method, it may be advantageous for the condition logic to include an occurrence of a problem grid voltage event and / or a time condition to delay the reactive current pulse command and / or a time condition that limits the reactive current pulse command to a certain repetition rate and / or an amount of a back voltage of a grid fault and / or one or more grid properties.

[0016] In any embodiment of any method, it may be advantageous for the problem grid voltage to include an undervoltage tolerance event (LVRT) and / or an overvoltage tolerance event (HVRT) and / or a grid fault.

[0017] In any embodiment of any method, it may be advantageous that generating the reactive power pulse command for the renewable energy generation system further comprises: determining a difference between a grid voltage and an activation voltage threshold; and determining a magnitude and a duration for the reactive power pulse command based on the difference, wherein the magnitude and duration of the reactive power pulse command are sufficient to increase the reactive power response time of the renewable energy generation system.

[0018] In any embodiment of any method, it may be advantageous for the difference to be positive and the conditional logic to be satisfied when the grid voltage falls below the activation voltage threshold.

[0019] In any embodiment of any method, it may be advantageous for the activation voltage threshold to be less than or equal to 90% of a nominal grid voltage.

[0020] In any embodiment of any method, it may be advantageous for the method to further comprise determining an upper current limit for the reactive current pulse command.

[0021] In any embodiment of any method, it may be advantageous that determining the total reactive current command by combining the reactive current reference command and the reactive current pulse command further comprises adding the reactive current pulse command to the reactive current reference command.

[0022] In any embodiment of any method, it may be advantageous for the renewable energy generation system to comprise a wind energy generation system and / or a solar energy generation system.

[0023] In yet another aspect, the present disclosure is directed to a system for improving the reactive power response time of a renewable energy generation system connected to a power grid. The system includes a controller configured to perform one or more operations.For example, in one embodiment, the one or more operations include at least providing conditional logic related to the power grid, determining a reactive power reference command for the renewable energy generation system in response to satisfying the conditional logic, generating a reactive power pulse command for the renewable energy generation system, determining a total reactive power command by combining the reactive power reference command with the reactive power pulse command, and operating the renewable energy generation system based on the total reactive power command to improve the power response time of the power grid.

[0024] These and other features, aspects, and advantages of the present invention will be better understood by reference to the following description and the appended claims. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] A complete and practical disclosure of the present invention, including the preferred embodiment thereof, directed to one of ordinary skill in the art is set forth in the description which refers to the accompanying drawings in which: Fig. 1 illustrates an embodiment of an exemplary renewable energy generation system according to the present disclosure; Fig. 2 illustrates a block diagram of an embodiment of a control device suitable for use in the Fig. 1 shown renewable energy generation system is configured according to the present disclosure; Fig. 3 illustrates a schematic representation of an embodiment of a control scheme implemented by the control device of Fig. 2, particularly illustrating a reactive current pulse command combined with the reactive current reference command according to the present disclosure; Fig. 4 illustrates a plurality of curves, particularly illustrating the desired output of an embodiment of a method for improving reactive power response time in a power grid according to the present disclosure; Fig. 5 illustrates a plurality of curves according to an embodiment of the present disclosure, particularly a problem voltage event, a total reactive current command, a reactive current pulse, and a desired output; and Fig. 6 illustrates an embodiment of a flowchart of an exemplary method for improving the reactive power response time of a power grid according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0026] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided for the purpose of illustrating the invention and not for limiting the invention. Indeed, it will be apparent to those skilled in the art that various modifications and variations of the present invention can be made without departing from the scope and spirit of the invention. For example, features illustrated or described as part of one embodiment may be used with another embodiment to obtain yet another embodiment. Therefore, it is intended that the present invention include such modifications and variations that come within the scope of the appended claims and their equivalents.

[0027] Generally, the present disclosure relates to a system and method for improving reactive power response time in a renewable energy generation system connected to a power grid after a problem voltage event (e.g., an LVRT event or an HVRT event) has occurred in the grid. More specifically, a controller of the renewable energy generation system generates a reactive power pulse command in response to the problem voltage event and combines the reactive power pulse command with a reactive power reference command required for the event to obtain a temporarily higher total reactive current. The controller then operates the renewable energy generation system based on the temporarily higher total reactive current command to achieve the desired response time and avoid excessive currents within the power generation system that could exceed the system capabilities.

[0028] Referring now to the drawings, Fig. 1 illustrates an exemplary wind-driven doubly fed induction generator (DFIG) system 100 according to an embodiment of the present disclosure. Exemplary aspects of the present disclosure are described with reference to the DFIG wind turbine 10 of Fig. 1 for purposes of illustration and explanation. Those of ordinary skill in the art using the disclosure provided herein should understand that exemplary aspects of the present disclosure are also applicable in other power generation systems, such as wind, solar, gas turbine, or other suitable power generation systems.

[0029] In the exemplary system 100, a rotor 106 includes a plurality of rotor blades 108 connected to a rotatable hub 110, collectively forming a propeller. The propeller is optionally connected to a gearbox 118, which in turn is connected to a generator 120. In accordance with aspects of the present disclosure, the generator 120 may be any suitable generator, including, but not limited to, a doubly fed induction generator (DFIG) or a fully fed induction generator. The generator 120 is typically connected to a stator bus 154 and, via a rotor bus 156, to a power converter 162. The stator bus 154 provides multi-phase output power (e.g., three-phase power) from a stator of the generator 120, and the rotor bus 156 provides multi-phase output power (e.g., three-phase power) from a rotor of the generator 120.

[0030] With reference to the power converter 162, the DFIG 120 is connected to a rotor-side converter 166 via the rotor bus 156. The rotor-side converter 166 is connected to a line-side converter 168, which in turn is connected to a line-side bus 188. In exemplary embodiments, the rotor-side converter 166 and the line-side converter 168 are configured for normal operation in a three-phase pulse-width modulated (PWM) arrangement using insulated-gate bipolar transistor (IGBT) switching elements. The rotor-side converter 166 and the line-side converter 168 may be connected via a DC link 136 across which a DC link capacitor 138 is present.

[0031] The power generation system 100 may also include a controller 174 configured to control the operation of the various components of the system 100, as well as to implement any method steps as described herein. Therefore, the controller 174 may include any number of control devices. In an implementation as described in Fig. 2, the controller 174 may include one or more processors 176 and associated memory devices 178 configured to execute a number of computer-implemented functions and / or instructions (e.g., performing the methods, steps, calculations, and the like, and controlling the relevant data as disclosed herein). The instructions, when executed by the processor 176, may cause the processor 176 to perform operations including providing control commands to the various system components. Furthermore, the controller 174 may include a communication module 180 to enable communication between the controller 174 and the various components of the power generation system 100, for example, any of the components of Fig. 1. Additionally, the communication module 180 may include a sensor interface 182 (e.g., one or more analog-to-digital converters) to enable the signals transmitted by one or more sensors to be converted into signals that can be understood and processed by the processors 176. It should be understood that the sensors (e.g., sensors 181, 183, 184) may be communicatively connected to the communication module 180 using any suitable means. For example, as shown, the sensors 181, 183, 185 are connected to the sensor interface 182 via a wired connection. However, in other embodiments, the sensors 181, 183, 185 may be connected to the sensor interface 182 via a wireless connection, such as through the use of any suitable wireless communication protocol as known in the art.As such, the processor 176 may be configured to receive one or more signals from the sensors.

[0032] As used herein, the term "processor" refers not only to integrated circuits, which are referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application-dependent integrated circuit, and other programmable circuits. The processor 176 is also configured to process more sophisticated control algorithms and communicate using a variety of Ethernet or serial-based protocols (Modbus, OPC, CAN, etc.). In addition, the memory device(s) 178 may generally comprise a memory element(s).Memory elements, including, but not limited to, a computer-readable medium (e.g., random access memory (RAM)), a computer-readable non-transitory medium (e.g., flash memory), a floppy disk drive, a compact disk read-only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD), and / or other suitable memory elements. Such memory element(s) 178 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 176, configure the controller 174 to perform the various functions described herein.

[0033] During operation, alternating current (AC) power generated at the DFIG 120 by the rotation of the rotor 106 is provided to an electrical grid 160 via a dual path. The dual paths are formed by the stator bus 154 and the rotor bus 156. On the rotor bus side 156, a sinusoidal multi-phase (e.g., three-phase) AC power is provided to the power converter 162. The rotor-side power converter 166 converts the AC power provided by the rotor bus 156 to direct current (DC) power and provides the DC power to the DC link 136. Switching elements (e.g., IGBTs) used in bridge circuits of the rotor-side power converter 166 may be modulated to convert the AC power provided by the rotor bus 156 into DC power suitable for the DC link 136.

[0034] The line-side converter 168 converts the DC power at the DC link 136 into an AC output suitable for the electrical grid 160. In particular, the switching elements (e.g., IGBTs) used in bridge circuits of the line-side power converter 168 can be modulated to convert the DC power at the DC link 136 into AC power at the line-side bus 188. The AC power of the power converter 168 can be combined with the power from the stator of the DFIG 120 to provide multi-phase power (e.g., three-phase power) having a frequency maintained substantially at the frequency of the electrical grid 160 (e.g., 50 Hz / 60 Hz).

[0035] Various circuit breakers and switches, such as converter switch 186, may be included in the power generation system 100 to connect or disconnect corresponding buses, for example, when the current flow is excessive and may damage components of the system 100 or for other operational considerations. Additional protection components may also be included in the power generation system 100.

[0036] Still referring to Fig. 1, the power generation system 100 may also include a battery energy storage system (BESS) 200 connected to the power converter 162. More specifically, as shown in the illustrated embodiment, the BESS 200 may be connected in parallel with the DC link 136 of the power converter 162. The battery energy storage system 200 may be used to provide power to the DC link 136 under certain conditions. For example, the BESS 200 may be used to provide power to the DC link 136 to increase the power output of the power generation system 100 when wind speed decreases. Power may also be supplied and stored in the BESS 200 during operation of the power generation system 100.

[0037] Referring now to Fig. 3, a schematic representation of a control scheme that may be implemented by controller 174 to improve the reactive power response time of power generation system 100 connected to power grid 160, according to one embodiment of the present disclosure, is illustrated. As shown, total reactive power command 222 is obtained by combining or summing reactive power reference command 214 and reactive power pulse command 218. Reactive power reference command 214 may be determined by conventional means known in the art and may be used during normal operation or during a problem voltage event. Additionally, reactive power pulse command 218 may be determined using a variety of methods.As shown, for example (as indicated by the dashed box), control scheme 220 illustrates one embodiment for generating reactive power pulse command 218 for power generation system 100. In most cases, reactive power pulse command 218 is zero because the grid voltage is operating within predetermined tolerances (i.e., no problem voltage condition is occurring). Therefore, in certain embodiments, controller 174 is configured to activate control scheme 220 to generate reactive power control command 218 only when certain conditional logic 224 is met. For example, in some embodiments, conditional logic 224 may include certain criteria, such as characteristics of certain types of grid events, time conditions for delaying the pulse, time conditions that only activate the pulse at a certain repetition rate, and / or the like.Conditional logic 224 may also be activated based on the magnitude or percentage of a reverse voltage of the grid fault(s). As such, as in the illustrated embodiment of FIG. Fig. 4, the condition logic is activated when the voltage magnitude 201 falls below an activation voltage threshold 202.

[0038] Once the conditional logic 224 is satisfied, the control scheme 220 is configured to generate a pulse command 218 using any suitable means known in the art. For example, in one embodiment, the control scheme 220 includes determining a difference 226, or "trigger error," between the activation voltage threshold 202 and the grid voltage magnitude 201. In various embodiments, the activation voltage threshold 202 may be a percentage of the nominal grid voltage. For example, in certain embodiments, the activation voltage threshold 202 may be from about 20% to about 90% of the nominal grid voltage, more preferably from about 30% to about 80%, and more preferably from about 40% to about 60% of the nominal grid voltage. Therefore, the trip error 226 will become positive when the mains voltage 201 drops below the activation voltage threshold 202.Accordingly, the conditional logic 224 is configured to monitor a positive trip fault 226 and use the positive trip fault 226 with further combinational logic to issue the reactive current pulse command 218 and allow the integrator 228 to drive the current of the power generation system 100 in a positive direction until it reaches a maximum pulse current value. The maximum pulse current value can then be set as the reactive current pulse command 218.

[0039] In additional embodiments, the rate at which the pulse command 218 reaches its maximum value through the integrator 228 is a function of the trigger gain 232 and the magnitude of the trigger error 226. Therefore, the rate may be increased or decreased accordingly. Furthermore, the integrator 228 may be configured to provide upper and lower current limits to prevent an excessive current command from the power generation system 100 that exceeds the system's capabilities.

[0040] In further embodiments, once the line voltage 201 operates within predetermined limits, the resulting pulse 218 may drop to zero, either by removing the conditional logic 224 or by allowing the line voltage 201 to exceed the activation voltage threshold 202. For example, the trigger decay constant 230 of the control scheme 220 may be used to cause the pulse to decay through the output value of the integrator 228 until the integrator 228 reaches zero, when the conditional logic 224 is no longer active. In additional embodiments, the control scheme 220 may also include an indicator (e.g., a trigger limit flag 236) that may be set when the integrator 228 reaches zero.

[0041] Referring to Fig. 4 illustrates a plurality of curves, particularly illustrating a problem voltage event and the desired output value of the control scheme from Fig. 3. As shown, the upper curve illustrates the voltage magnitude 201 around the time of a grid voltage event (e.g., the LVRT event). More specifically, as shown at time T1, the voltage magnitude 201 decreases to a level requiring a reactive power input. For example, as illustrated, the voltage magnitude 201 falls below the activation voltage threshold, as indicated by line 202. The controller 174 is configured to request or command the required target current level 204 of the power generation system 100 at this time, as shown in the bottom curve, after a certain conditional logic has been met.

[0042] To achieve the target current level 204, the controller 174 generates a current pulse 206 in the power generation system 100, as shown in the middle curve, which typically has a constant magnitude for a predetermined time 208. After the predetermined time 208, the control scheme 220 may allow the current pulse 206 to decay at a predetermined rate, as shown at 210. In certain embodiments, the current pulse 206 is designed to be of a fixed but adjustable duration that depends on the voltage event. For example, in one embodiment, a timer may be used to determine the duration of the current pulse 206 for the power generation system 100.Additionally, the control scheme 220 may be configured to terminate the current pulse 206 if the voltage event ends before a predetermined time elapses, to prevent the input of the current pulse 206 when it is not needed or when it may be undesirable. The controller 174 may then determine the composite or total reactive current command 212 by summing the required target current level 204 (e.g., the reactive current reference command) and the pulse command 206, as shown in the bottom trace. Additionally, as shown at time T2, once the voltage magnitude 201 has recovered (e.g., the condition is no longer active or the voltage 201 exceeds the activation voltage threshold 202), the control scheme 220 allows the current pulse 206 to decay to zero, and the total reactive current command returns to the value determined by the required target current level 204.In addition, the reactive current command pulse returns to zero if the grid event ends during the current pulse.

[0043] Referring to Fig. 5 illustrates another plurality of curves, particularly illustrating the line voltage magnitude 201 during a problem voltage event (curve A) that does not end during the time shown, a total reactive current command 222 (curve B), a reactive current pulse command (curve C), and a conditional logic output value 234 (curve D) according to the control scheme 220 of Fig. 3. More specifically, curve (A) illustrates a voltage drop at time T1, representing an undervoltage or zero-voltage event (e.g., grid fault) occurring in the power grid 160. Curve (B) illustrates the total reactive current command 222 of the power system 100, which provides the required reactive current to the power grid 160 to help achieve the required response time and prevents an excessive current command that exceeds the system capabilities by falling back to a continuous rated current after time T2. Curve (C) illustrates the reactive current pulse 218 used by the controller 174 to obtain the total reactive current command 222. Curve (D) illustrates one embodiment of a conditional logic output value 234 (e.g., Boolean data) indicating that the conditional logic is satisfied between T1 and T2.More specifically, as shown between T1 and T2, the pulse formation control scheme 220 of FIG. Fig. 3 may be activated to generate a current pulse through the power generation system 100 that improves the current response time of the system 100 because the condition logic is met (i.e., the voltage is below the activation voltage threshold and the duration is within reactive power injection requirements).

[0044] Now referring to Fig.6, a flowchart of an exemplary method 300 for improving reactive power response time in a renewable energy generation system connected to a power grid is illustrated, according to the present disclosure. As illustrated, the method 300 includes a step 302 of providing conditional logic related to the power grid. In response to the conditional logic being met, the method 300 includes determining a reactive power reference command for the renewable energy generation system and generating a reactive power pulse command for the renewable energy generation system (step 304). The method 300 may also include determining a total reactive power command by combining (e.g., adding) the reactive power reference command and the reactive power pulse command (step 306).Additionally, as shown, method 300 includes operating the renewable energy generation system based on the total reactive power command to improve the power response time of the renewable energy generation system (step 308).

[0045] Although specific features of various embodiments of the invention are shown in some drawings and not in others, this is merely for convenience. In accordance with the principles of the invention, any feature of one drawing may be referenced and / or claimed in combination with any feature of any other drawing.

[0046] The written description uses examples to disclose the invention, including the preferred embodiment, and also to enable one skilled in the art to practice the invention, including making and using any device or system and performing any incorporated method. The patentable scope of the invention is defined by the claims and may include other embodiments disclosed 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 depart from the language of the claims or if they include equivalent structural elements with insubstantial differences from the language of the claims.

[0047] The present disclosure is directed to a system and method for improving reactive power response time in a renewable energy generation system connected to a power grid. The method includes providing conditional logic related to the power grid by a controller of the power generation system. A further step includes determining a reactive power reference command for the renewable energy generation system by a controller of the renewable energy generation system in response to the conditional logic being met. The method also includes generating a reactive power pulse command for the renewable energy generation system by the controller. Therefore, the controller is configured to determine a total reactive power command by combining the reactive power reference command and the reactive power pulse command.The method also includes operating the renewable energy generation system based on the total reactive power command to improve the power response time. LIST OF REFERENCE SYMBOLS 100 Renewable Energy Generation System 106 Rotor 108 rotor blades 110 Rotating hub 118 Optional transmission 120 DFIG 136 DC link 138 DC link capacitor 144 Positive connection 146 Negative connection 154 Stator bus 156 Rotorbus 160 Electrical network 162 power converters 166 Rotor-side converter 168 Line-side converter 174 Control device 176 processor(s) 178 storage device(s) 180 communication module 181 Sensor 182 Sensor interface 183 Sensor 185 Sensor 186 converter switches 188 Line-side bus 200 battery energy storage system 201 Voltage amount / Mains voltage amount 202 Activation voltage threshold 204 Target current level 206 pulse 208 pulse duration 210 Waste rate 212 Total reactive current command 214 Reactive current reference command 216 Reactive current reference command path 218 Reactive current pulse command path 220 tax scheme 222 Total reactive current command 224 Conditional logic 226 Difference 228 Integrator 230 tripping drop constant 232 Trigger gain 234 Condition logic output value 236 Trigger limit flag 300 procedures 302 Process step 304 Process step 306 Process step 308 Process step

Claims

[1] A method for improving the reactive power response time of a renewable energy generation system connected to a power grid, the method comprising: Providing a conditional logic relating to the energy supply network by means of a control device of the renewable energy generation system; Determining, by means of the controller, a reactive power reference command for the renewable energy generation system in response to the condition logic being satisfied and generating a reactive power pulse command for the renewable energy generation system; Determining a total reactive current command by means of the control device by combining the reactive current reference command and the reactive current pulse command; and Operating the renewable energy generation system based on the total reactive power command to improve the power response time of the renewable energy generation system. [2] The method of claim 1, wherein the condition logic comprises an occurrence of a problem voltage event and / or a time condition to delay the reactive current pulse command and / or a time condition that limits the reactive current pulse command to a certain repetition rate and / or an amount of a back voltage of a grid fault and / or one or more grid properties. [3] The method of claim 2, wherein the problem voltage event comprises an undervoltage tolerance event (LVRT) and / or an overvoltage tolerance event (HVRT) and / or a grid fault. [4] A method according to any one of the preceding claims, wherein generating the reactive power pulse command for the renewable energy generation system further comprises: Determining a difference between a mains voltage and an activation voltage threshold; and Determining a magnitude and duration for the reactive power pulse command based on the difference, wherein the magnitude and duration of the reactive power pulse command are sufficient to increase the reactive power response time of the renewable energy generation system. [5] The method of claim 4, wherein the difference is positive and the conditional logic is satisfied when the grid voltage falls below the activation voltage threshold. [6] The method of claim 4 or 5, wherein the activation voltage threshold is less than or equal to about 90% of a nominal grid voltage. [7] The method of any preceding claim, further comprising determining an upper current limit for the reactive current pulse command. [8] The method of any preceding claim, wherein determining the total reactive current command by combining the reactive current reference command and the reactive current pulse command further comprises adding the reactive current pulse command to the reactive current reference command. [9] A method for improving the reactive power response time of a renewable energy generation system connected to a power grid after a problem voltage condition has occurred in the power grid, the method comprising: Generating a reactive current pulse command for the renewable energy generation system by means of a control device of the renewable energy generation system; Determining a total reactive current command by means of the control device based at least in part on the reactive current pulse command; and Operating the renewable energy generation system based on the total reactive power command by means of the controller to improve the power response time of the renewable energy generation system. [10] A system for improving the reactive power response time of a renewable energy generation system coupled to a power grid, the system comprising: a control device which is arranged to carry out one or more operations, wherein the one or more have several operations: Providing conditional logic related to the energy supply network; Determining a reactive power reference command for the renewable energy generation system in response to the condition logic being satisfied and generating a reactive power pulse command for the renewable energy generation system; Determining a total reactive current command by combining the reactive current reference command and the reactive current pulse command; and Operating the renewable energy generation system based on the total reactive power command to improve the power response time of the renewable energy generation system.

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