A fan grid-connected system transient control method using energy consumption branch reverse energy absorption

Abstract

This invention discloses a transient control method for a wind turbine grid-connected system that utilizes a reverse energy absorption branch, relating to the field of new energy technology. The energy-consuming branch is connected in parallel to the DC bus capacitor. The grid connection point voltage and DC bus voltage of the wind turbine grid-connected system are acquired. When the grid connection point voltage reaches a preset condition, a reference value for the d-axis current of the grid-side converter is calculated based on the grid connection point voltage and the voltage of the DC bus capacitor. Based on the reference value, the active power state of the grid-side converter is switched to an active power absorption state, allowing the DC bus capacitor to store electrical energy and raise the voltage. When the voltage of the DC bus capacitor is greater than the threshold voltage of the transistor, the transistor is controlled to be in the conducting state. Through this technical solution, the direction of energy flow on the DC bus between the turbine-side converter and the grid-side converter can be changed. Furthermore, by consuming excess energy through resistance, wind turbine output oscillations and DC-side overvoltage can be suppressed, and the synchronous stability of the wind turbine grid-connected system can be improved.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, specifically to a transient control method for a wind turbine grid-connected system that utilizes reverse energy absorption by an energy-consuming branch. Background Technology

[0002] As the grid-connected capacity of new energy sources continues to increase, the synchronization stability of wind turbines under grid fault conditions is becoming increasingly prominent. Especially during grid voltage dips, the grid-side converter of the wind turbine is affected by the voltage drop at the grid connection point, and its active power exchange capacity decreases significantly. Power imbalance is likely to occur between the turbine side and the grid side, leading to DC bus voltage fluctuations. In severe cases, this can trigger overvoltage protection actions, converter lockout, or even turbine disconnection from the grid.

[0003] During low-voltage ride-through, existing wind turbines typically employ measures such as reactive current priority support, current limiting, DC-side overvoltage protection, and energy-dissipating branch protection. Most existing energy-dissipating branches function as passive protection, only activating when the DC bus voltage exceeds a set threshold. They dissipate excess energy through energy-dissipating resistors to prevent overvoltage of the DC bus capacitor and power devices. However, these methods generally only provide protection and are unlikely to actively participate in power redistribution and system damping shaping during faults, potentially leading to instability in the grid-side converter. Summary of the Invention

[0004] The purpose of this invention is to provide a transient control method for a wind turbine grid-connected system that utilizes reverse energy absorption by an energy-consuming branch, in order to solve the technical problems existing in related technologies.

[0005] To achieve the above objectives, the present invention provides a transient control method for a wind turbine grid-connected system that utilizes a reverse energy absorption branch. The wind turbine grid-connected system includes an energy-consuming branch connected to a DC bus and in parallel with the DC bus capacitor. The control method includes:

[0006] The grid connection point voltage and DC bus voltage of the wind turbine grid-connected system are obtained. When the grid connection point voltage reaches the preset condition, the reference value of the d-axis current of the grid-side converter is calculated based on the grid connection point voltage and DC bus voltage. The preset condition is used to characterize the conditions under which the wind turbine grid-connected system will fail.

[0007] The active power state of the grid-side converter is switched to the active power absorption state according to the reference value of the d-axis current of the grid-side converter, so that the DC bus capacitor can store electrical energy and raise the voltage.

[0008] When the voltage of the DC bus capacitor is greater than the threshold voltage of the energy consumption branch, or when the voltage rise rate of the DC bus capacitor is greater than the preset rate, the energy consumption branch is controlled to turn on.

[0009] Optionally, the step of controlling the active power state of the grid-side converter to switch to an active power absorption state based on the reference value of the d-axis current of the grid-side converter includes:

[0010] When the reference value of the d-axis current of the grid-side converter is less than 0, the active power state of the grid-side converter switches to the active power absorption state.

[0011] Optionally, after the energy consumption branch is turned on, the control method further includes:

[0012] When the voltage of the DC bus capacitor is greater than the maximum threshold voltage in the preset threshold voltage range, the absolute value of the reference value of the d-axis current of the control grid-side converter shows a decreasing trend.

[0013] When the voltage of the DC bus capacitor is within the preset threshold voltage range and the energy consumption branch still has energy consumption margin, the absolute value of the reference value of the d-axis current of the control grid-side converter shows an increasing trend.

[0014] Optionally, the energy consumption branch includes an insulated gate bipolar transistor (IGBT) and a capacitor, wherein the collector of the IGBT is connected to the input terminal and DC bus of the grid-side converter, and the emitter of the IGBT is connected to the input terminal and DC bus of the grid-side converter through a resistor.

[0015] The step of controlling the energy consumption branch to conduct when the voltage of the DC bus capacitor is greater than the threshold voltage of the energy consumption branch, or when the voltage rise rate of the DC bus capacitor is greater than a preset rate, includes:

[0016] When the voltage of the DC bus capacitor is greater than the threshold voltage of the insulated gate bipolar transistor (IGBT), or when the voltage rise rate of the DC bus capacitor is greater than a preset rate, the IGBT is turned on.

[0017] Optionally, the step of calculating the reference value of the d-axis current of the grid-side converter based on the grid connection point voltage and the DC bus capacitor voltage includes:

[0018] The reference value of the d-axis current of the grid-side converter is calculated using the following formula;

[0019] ;

[0020] in, This is a reference value for the d-axis current of the grid-side converter. and All are control coefficients. This is the DC bus voltage. The rated grid connection voltage, The voltage at the grid connection point. This is the DC bus reference voltage. To the maximum allowable absorption current, This is the amplitude limiting function.

[0021] Optionally, the electrical energy stored in the DC bus capacitor is expressed by the following formula:

[0022] ;

[0023] in, Electrical energy stored in the DC bus capacitor For DC bus capacitors, This is the DC bus voltage.

[0024] The above technical solution involves connecting an energy dissipation branch in parallel with the DC bus capacitor connecting the turbine-side converter and the grid-side converter. When a fault occurs in the wind turbine grid-connected system, the reference value of the d-axis current of the grid-side converter is calculated based on the grid connection point voltage and the DC bus voltage. Based on this reference value, the active power state of the grid-side converter is switched to an active power absorption state, thereby changing the energy flow direction of the DC bus between the turbine-side and grid-side converters. This allows the DC bus capacitor to store energy and raise the voltage. Simultaneously, when the voltage of the DC bus capacitor exceeds the threshold voltage of the energy dissipation branch, the energy dissipation branch is activated to dissipate power and consume excess energy. This proactive energy regulation during wind turbine grid-connected system faults can suppress wind turbine output oscillations and DC-side overvoltage, thus improving the synchronous stability of the wind turbine grid-connected system.

[0025] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a wind turbine grid-connected system that utilizes energy-consuming branches to absorb energy in reverse, according to an exemplary embodiment of the present invention.

[0027] Figure 2 This is a flowchart illustrating a control method for a wind turbine grid-connected system that utilizes reverse energy absorption via an energy-consuming branch, according to an exemplary embodiment of the present invention.

[0028] Figure 3 This is a structural diagram of a three-machine, nine-node system containing wind power, according to an exemplary embodiment of the present invention.

[0029] Figure 4 This is a diagram illustrating the input signal curve of the power-consuming branch according to an exemplary embodiment of the present invention.

[0030] Figure 5 This is an exemplary embodiment of the present invention illustrating the output active power curve of the fan 2 in this embodiment.

[0031] Figure 6This is an exemplary embodiment of the present invention illustrating the output active power curve of the synchronizer 2 in this embodiment.

[0032] Figure 7 This is an example of an embodiment of the present invention illustrating the introduction of DC bus voltage ( ) in the embodiments of the present invention. (Line graph)

[0033] Figure 8 This is a voltage curve diagram of node 5 and node 7 introduced in an embodiment of the present invention, according to an exemplary embodiment of the present invention.

[0034] Figure 9 This is an exemplary embodiment of the present invention showing the output active power curve of fan 2 under the original system (fan grid-connected system).

[0035] Figure 10 This is an exemplary embodiment of the present invention showing the active power output curve of the synchronous machine 2 under the original system (wind turbine grid-connected system).

[0036] Figure 11 This is an exemplary embodiment of the present invention illustrating the DC bus voltage under the original system (wind turbine grid-connected system). (Line graph)

[0037] Figure 12 This is an exemplary embodiment of the present invention showing the voltage curves of nodes 5 and 7 in the original system (wind turbine grid-connected system). Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, so as to provide a better understanding of the concept of the present invention, the technical problem solved, the technical features constituting the technical solution, and the technical effects brought about.

[0039] like Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram illustrating a wind turbine grid-connected system that utilizes reverse energy absorption via an energy-consuming branch, according to an exemplary embodiment of the present invention. Figure 2 This is a flowchart illustrating a control method for a wind turbine grid-connected system that utilizes reverse energy absorption by an energy-consuming branch, according to an exemplary embodiment of the present invention. (Refer to...) Figure 1 and Figure 2 The wind turbine grid-connected system includes an energy consumption branch, which is connected to the DC bus and in parallel with the DC bus capacitor. The control method includes:

[0040] S101: Obtain the grid connection point voltage and DC bus voltage in the wind turbine grid-connected system, and when the grid connection point voltage reaches the preset condition, calculate the reference value of the d-axis current of the grid-side converter based on the grid connection point voltage and DC bus voltage. The preset condition is used to characterize the conditions under which the wind turbine grid-connected system will experience a fault.

[0041] S102: Based on the reference value of the d-axis current of the grid-side converter, control the active power state of the grid-side converter to switch to the active power absorption state so that the DC bus capacitor stores electrical energy and raises the voltage.

[0042] S103: When the voltage of the DC bus capacitor is greater than the threshold voltage of the energy consumption branch, or when the voltage rise rate of the DC bus capacitor is greater than the preset rate, control the energy consumption branch to be turned on.

[0043] The above technical solution involves connecting an energy dissipation branch in parallel with the DC bus capacitor connecting the turbine-side converter and the grid-side converter. When a fault occurs in the wind turbine grid-connected system, the reference value of the d-axis current of the grid-side converter is calculated based on the grid connection point voltage and the DC bus voltage. Based on this reference value, the active power state of the grid-side converter is switched to an active power absorption state, thereby changing the energy flow direction of the DC bus between the turbine-side and grid-side converters. This allows the DC bus capacitor to store energy and raise the voltage. Simultaneously, when the voltage of the DC bus capacitor exceeds the threshold voltage of the energy dissipation branch, the energy dissipation branch is activated to dissipate power and consume excess energy. This proactive energy regulation during wind turbine grid-connected system faults can suppress wind turbine output oscillations and DC-side overvoltage, thus improving the synchronous stability of the wind turbine grid-connected system.

[0044] To enable those skilled in the art to better understand the transient control method for a wind turbine grid-connected system that utilizes reverse energy absorption via an energy-consuming branch, the following detailed examples illustrate the steps described above.

[0045] For example, a wind turbine grid-connected system can be a system that safely transmits the electricity generated by the wind turbine to the main power grid after conversion, voltage stabilization, filtering, and voltage boosting. This system can be a scenario where a direct-drive wind turbine is connected to the grid. The grid-side converter can be an inverter power electronic device with one end connected to the DC bus and the other end directly connected to the grid; the turbine-side converter can be a power electronic rectifier device directly connected to the AC output of the wind turbine; and the DC bus capacitor can be a high-voltage, high-capacity energy storage capacitor connected in parallel between the turbine-side and grid-side converters.

[0046] In this embodiment of the invention, when a fault occurs in the wind turbine grid-connected system, adjustments can be made using the following method. An energy-consuming branch is connected in parallel with the DC bus capacitor. This energy-consuming branch is used to consume excess electrical energy to maintain the stability of the wind turbine grid-connected system. In the specific control method, the grid connection point voltage and the DC bus capacitor voltage are first acquired. Based on the grid connection point voltage, a fault in the wind turbine grid-connected system can be determined according to preset conditions. These preset conditions can be that the difference between the maximum and minimum values ​​of the grid connection point voltage within a preset time period is greater than a preset voltage difference, or that the grid connection point voltage exhibits abnormal changes. When the grid connection point voltage reaches the preset conditions, it indicates a fault in the wind turbine grid-connected system. Then, a reference value for the d-axis current of the grid-side converter can be calculated based on the grid connection point voltage and the DC bus capacitor voltage. This allows the wind turbine grid-connected system to be identified as being in fault-stabilized enhanced mode. The reference value for the d-axis current of the grid-side converter can be a control command specifying the amount of active current the converter should output, determining whether to supply power to the grid.

[0047] After calculating the reference value of the d-axis current of the grid-side converter, the active power state of the grid-side converter can be controlled based on the reference value of the d-axis current. After the grid-side converter switches to the active power absorption state, the DC bus capacitor between the machine-side converter and the grid-side converter stores the excess energy for a short time, causing the DC bus voltage to rise, as a buffer in the early stage of a fault.

[0048] Specifically, the step of controlling the active power state of the grid-side converter to switch to the active power absorption state based on the reference value of the d-axis current of the grid-side converter includes:

[0049] When the reference value of the d-axis current of the grid-side converter is less than 0, the active power state of the grid-side converter switches to the active power absorption state.

[0050] It should be understood that when the wind turbine grid-connected system is in normal operation, the reference value of the d-axis current of the grid-side converter is positive, and the grid-side converter is in a state of outputting active power to the grid. When a fault occurs in the wind turbine grid-connected system, the reference value of the d-axis current of the grid-side converter can be set to less than 0, thereby controlling the active power state of the grid-side converter to switch to an active power absorption state. When a fault occurs in the wind turbine grid-connected system, the reference value of the d-axis current of the grid-side converter can be set to a negative value, causing the grid-side converter to switch from a normal active power output state to an active power absorption state, thus changing the energy flow direction of the system during the fault period.

[0051] Specifically, the reference value of the d-axis current of the grid-side converter can be calculated using the following formula;

[0052] ;

[0053] in, This is the reference value for the d-axis current of the grid-side converter. and All are control coefficients. This is the DC bus voltage. The rated grid connection voltage, The voltage at the grid connection point. This is the DC bus reference voltage. To the maximum allowable absorption current, This is the amplitude limiting function.

[0054] The above calculations show that the more severe the fault in the wind turbine grid-connected system and the deeper the voltage drop at the grid connection point, the stronger the active power absorption capacity; the higher the DC bus voltage, the stronger the suppression effect on continued active power absorption. This avoids excessive active power absorption even when the DC side voltage has already increased significantly.

[0055] After switching the active power state of the grid-side converter to the active power absorption state, the DC bus capacitor can store electrical energy and simultaneously boost the voltage. At this time, the measured value of the d-axis current component of the grid-side converter can be obtained. It can be based on the measured values Calculate the active power of the grid-side converter at this time. Specifically, this can be expressed by the following formula:

[0056] ;

[0057] in, The voltage component at the grid connection point on the d-axis. This refers to the power output from the grid-side converter to the power grid.

[0058] Furthermore, in the measured values At this time, the grid-side converter automatically switches from the original active power output state to the active power absorption state.

[0059] For example, after the active power state of the grid-side converter switches to the active power absorption state, the voltage of the DC bus capacitor gradually increases. When the voltage of the DC bus capacitor is greater than the threshold voltage of the energy consumption branch, the energy consumption branch can be turned on to dissipate excess energy.

[0060] In one possible configuration, the energy-consuming branch includes an insulated-gate bipolar transistor (IGBT) and a capacitor, with the collector of the IGBT connected to the input terminal and DC bus of the grid-side converter, and the emitter of the IGBT connected to the input terminal and DC bus of the grid-side converter via a resistor.

[0061] The step of controlling the energy consumption branch to conduct when the voltage of the DC bus capacitor is greater than the threshold voltage of the energy consumption branch, or when the voltage rise rate of the DC bus capacitor is greater than a preset rate, includes:

[0062] When the voltage of the DC bus capacitor is greater than the threshold voltage of the insulated gate bipolar transistor (IGBT), or when the voltage rise rate of the DC bus capacitor is greater than a preset rate, the IGBT is turned on.

[0063] It should be understood that in the energy consumption branch, an insulated gate bipolar transistor (IGBT) and a resistor can be connected in series, and then the IGBT can be turned on or off based on the voltage of the DC bus capacitor and / or the threshold voltage of the IGBT.

[0064] Specifically, such as Figure 1 As shown, the wind turbine grid connection system in this embodiment mainly includes a wind turbine, a permanent magnet synchronous generator (PMSG), a turbine-side converter, a DC bus capacitor, an energy-consuming branch, a grid-side converter, a filter device, and a grid-connected transformer. Figure 1 The first device from left to right is a wind turbine, which drives a permanent magnet synchronous generator. The wind turbine drives the permanent magnet synchronous generator to generate electricity. The turbine-side converter completes the electromagnetic power regulation on the generator side, and the grid-side converter completes the power exchange between the DC side and the AC grid. The energy-dissipating branch is connected in parallel to both ends of the DC bus to dissipate excess energy during faults. Figure 1 This corresponds to the overall structure described above. Figure 1 middle, The three-phase current of the machine-side converter, The three-phase voltage of the machine-side converter. This is the reference voltage for the machine-side converter. For grid-side filter inductance, The three-phase current of the grid-side converter, The three-phase voltage of the grid-side converter. The primary and secondary sides of the transformer are connected in a delta configuration and a star configuration, respectively. This is the equivalent line inductance on the grid side.

[0065] Under normal operating conditions, the generator-side converter operates according to wind energy capture or torque control targets, while the grid-side converter maintains a stable DC bus voltage and delivers active power to the grid connection point. The energy-consuming branches are disconnected. Assume the power input to the DC side of the generator-side converter is... The power output of the grid-side converter to the grid is The power dissipation of the energy-consuming branch is Then the DC bus satisfies the energy balance relationship:

[0066] ;

[0067] in, For DC bus capacitors, This is the DC bus voltage. This is the derivative of the change in DC bus voltage with respect to time.

[0068] During normal operation, ,and Therefore, the DC bus voltage remains near the reference value. After a fault occurs, if no effective adjustment measures are taken, the power output capacity of the grid-side converter will rapidly decrease due to the voltage drop at the grid connection point, the power balance will be disrupted, and this will lead to an increase in the DC bus voltage and induce oscillations.

[0069] When the voltage of the DC bus capacitor exceeds the threshold voltage of the transistor in the energy-consuming branch, or when the rate of rise of the DC bus voltage exceeds a set threshold, the energy-consuming branch is controlled to conduct, connecting the energy-consuming resistor to the DC bus circuit. The energy-consuming resistor is used to dissipate excess energy caused by the active power absorption of the grid-side converter and the power imbalance of the wind turbine grid-connected system, preventing overvoltage of the DC bus capacitor and power devices. When energy-consuming branches are put into operation, The energy-consuming branch is disconnected in a timely manner to prevent frequent switching of the energy-consuming branch. This is the threshold voltage of the transistor.

[0070] Specifically, the electrical energy stored in the DC bus capacitor is expressed by the following formula:

[0071] ;

[0072] in, Electrical energy stored in the DC bus capacitor For DC bus capacitors, This is the DC bus voltage.

[0073] The power dissipation of the resistor is expressed by the following formula:

[0074] ;

[0075] in, For power dissipation, This is the resistance value. This is the DC bus voltage.

[0076] After the energy-consuming branch is put into operation, the reference value of the d-axis current of the grid-side converter is dynamically corrected based on the real-time DC bus voltage, DC bus voltage change rate, energy-consuming branch current, and converter current limit, so that the power absorbed by the grid-side converter is coordinated with the energy dissipation. When the DC bus voltage continues to rise, the absolute value of the negative reference value of the d-axis current of the grid-side converter is reduced. When the DC bus voltage is within a safe range and the energy-consuming branch has an energy consumption margin, the absolute value of the negative reference value of the d-axis current of the grid-side converter is increased to improve damping and stability during faults.

[0077] In some possible embodiments, after the energy-consuming branch is turned on, the control method further includes:

[0078] When the voltage of the DC bus capacitor is greater than the maximum threshold voltage in the preset threshold voltage range, the absolute value of the reference value of the d-axis current of the control grid-side converter shows a decreasing trend.

[0079] When the voltage of the DC bus capacitor is within the preset threshold voltage range and the energy consumption branch still has energy consumption margin, the absolute value of the reference value of the d-axis current of the control grid-side converter shows an increasing trend.

[0080] It should be understood that when the energy consumption branch is turned on, the reference value of the d-axis current of the grid-side converter can be adjusted according to the voltage of the DC bus capacitor, thereby improving the damping and stability of the wind turbine grid-connected system during faults.

[0081] When the grid connection point voltage recovers to above the set recovery threshold and the DC bus voltage falls back to a safe range, the energy dissipation branch is controlled to shut down; after the energy dissipation branch shuts down, the reference value of the d-axis current of the grid-side converter is restored from a negative value to the reference value before the fault.

[0082] In summary, when the wind turbine grid-connected system is in a fault state, a coordinated control link can be formed, consisting of "active power absorption by the grid-side converter, transient energy storage by the DC bus capacitor, and energy dissipation by the energy-consuming resistor." Unlike the original system, which relies solely on conventional control, the strategy of this invention can actively intervene in the energy flow during the fault period, thereby reducing the oscillation amplitude of wind turbine output and system voltage.

[0083] In actual operation, such as Figure 3 As shown, when the above technical solution is applied to a three-machine nine-node system containing wind power, the output of new energy accounts for 70% of the total output of the system, and the output of synchronous machines accounts for 30% of the total output of the system. The three-machine nine-node system of wind power consists of three synchronous generators (synchronous machine 1-synchronous machine 3), three wind turbines (wind turbine 1-wind turbine 3) and nine busbars (node ​​1-node 9) connected by transmission lines (line 1-line 9), forming a simple mesh network that includes power generation, transmission and consumption. During the operation of the three-machine nine-node system, a three-phase short-circuit fault occurred on the line between node 5 and node 7 at 4 seconds. The controller immediately detected the voltage drop information at the grid connection point and switched the grid-side converter to the active power absorption state mode. Subsequently, the DC bus capacitor began to store energy for a short time and raise the voltage. When the voltage of the DC bus capacitor reached the operating condition, the transistor was turned on, the energy-consuming branch was connected, and the excess energy was dissipated through the resistor. Throughout the entire adjustment process after the fault, the controller continuously corrected the reference value of the d-axis current of the grid-side converter according to the DC bus voltage and the grid connection point voltage, thereby realizing the energy coordination between the wind turbine-side converter, the synchronous machine side, and the network side. Figure 3The corresponding system is the one containing three wind turbines and nine nodes.

[0084] When the strategy of the present invention is adopted, Figure 4 The input signal curves of the energy-consuming branch under this strategy are given. Figure 5 The output response results of the wind turbine are given. Figure 6 The output response results of the synchronous machine are given. Figure 7 The DC bus voltage response results are given. Figure 8 The voltage response results for node 5 and node 7 are presented. Figures 4 to 8 It can be seen that after the strategy of this invention is applied at the moment of the fault, the energy-consuming branch is put into energy consumption, the output of the wind turbine can remain stable, the output oscillation of the synchronous machine is suppressed, the DC bus voltage can be maintained within a safe range, and the voltages of node 5 and node 7 can also recover to stability relatively quickly.

[0085] In contrast. Figures 9 to 12 The response results of the original system under the same fault conditions are given. Figure 9 It can be seen that the output of fan 2 in the original system became significantly unstable after the fault; by Figure 10 It can be seen that the output of synchronizer 2 also oscillates and becomes unstable; from Figure 11 It can be seen that the DC bus voltage in the original system continues to oscillate; from Figure 12 It can be seen that the voltages at nodes 5 and 7 also exhibited continuous oscillation after the fault, and it was difficult to maintain system stability by relying solely on the original control method.

[0086] comprehensive Figures 5 to 12 As can be seen, this invention does not rely solely on energy-consuming branches for overvoltage protection, but rather integrates with the active power control and energy dissipation of the grid converter at the moment of a fault to construct an active stability control mechanism. This mechanism can simultaneously improve the dynamic characteristics of wind turbine output, synchronous machine output, DC bus voltage, and critical node voltage, making it particularly suitable for power systems with a high proportion of renewable energy.

[0087] The above technical solution enables control to be activated immediately upon the occurrence of a fault in the wind turbine grid-connected system. Instead of relying solely on passive protection of energy-consuming branches, it combines active power control of the grid-connected converter with energy dissipation to form an active energy regulation channel. The transient energy storage function of the DC bus capacitor provides a buffer time for the activation of energy-consuming branches, effectively suppressing the rapid rise in DC voltage at the initial stage of a fault. This simultaneously improves the dynamic response of wind turbine output, synchronous machine output, DC bus voltage, and fault node voltage, enhancing the synchronization stability of high-proportion renewable energy systems.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for transient control of a wind turbine grid-connected system using energy dissipation branch reverse energy absorption, characterized in that, The wind turbine grid-connected system is equipped with an energy consumption branch, which is connected to the DC bus and in parallel with the DC bus capacitor. The control method includes: acquiring the grid connection point voltage and DC bus voltage in the wind turbine grid-connected system, and when the grid connection point voltage reaches a preset condition, calculating the reference value of the d-axis current of the grid-side converter based on the grid connection point voltage and DC bus voltage. The preset condition is used to characterize the conditions under which the wind turbine grid-connected system malfunctions. The active power state of the grid-side converter is switched to the active power absorption state according to the reference value of the d-axis current of the grid-side converter, so that the DC bus capacitor stores electrical energy and raises the voltage. When the voltage of the DC bus capacitor is greater than the threshold voltage of the energy consumption branch, or when the voltage rise rate of the DC bus capacitor is greater than the preset rate, the energy consumption branch is controlled to turn on.

2. The transient control method for a wind turbine grid-connected system utilizing reverse energy absorption by an energy-consuming branch as described in claim 1, characterized in that, The step of controlling the active power state of the grid-side converter to switch to the active power absorption state based on the reference value of the d-axis current of the grid-side converter includes: When the reference value of the d-axis current of the grid-side converter is less than 0, the active power state of the grid-side converter switches to the active power absorption state.

3. The transient control method for a wind turbine grid-connected system utilizing reverse energy absorption by an energy-consuming branch as described in claim 2, characterized in that, After the energy-consuming branch is turned on, the control method further includes: When the voltage of the DC bus capacitor is greater than the maximum threshold voltage in the preset threshold voltage range, the absolute value of the reference value of the d-axis current of the control grid-side converter shows a decreasing trend. When the voltage of the DC bus capacitor is within the preset threshold voltage range and the energy consumption branch still has energy consumption margin, the absolute value of the reference value of the d-axis current of the control grid-side converter shows an increasing trend.

4. A transient control method for a wind turbine grid-connected system utilizing reverse energy absorption by an energy-consuming branch, as described in any one of claims 1-3, characterized in that, The energy consumption branch includes an insulated gate bipolar transistor (IGBT) and a capacitor. The collector of the IGBT is connected to the input terminal and DC bus of the grid-side converter, and the emitter of the IGBT is connected to the input terminal and DC bus of the grid-side converter through a resistor. The step of controlling the energy consumption branch to conduct when the voltage of the DC bus capacitor is greater than the threshold voltage of the energy consumption branch, or when the voltage rise rate of the DC bus capacitor is greater than a preset rate, includes: When the voltage of the DC bus capacitor is greater than the threshold voltage of the insulated gate bipolar transistor (IGBT), or when the voltage rise rate of the DC bus capacitor is greater than a preset rate, the IGBT is turned on.

5. A transient control method for a wind turbine grid-connected system utilizing reverse energy absorption by an energy-consuming branch, as described in claim 4, is characterized in that... The reference value for calculating the d-axis current of the grid-side converter based on the grid connection point voltage and the DC bus capacitor voltage includes: The reference value of the d-axis current of the grid-side converter is calculated using the following formula; ； in, This is a reference value for the d-axis current of the grid-side converter. and All are control coefficients. This is the DC bus voltage. The rated grid connection voltage, The voltage at the grid connection point. This is the DC bus reference voltage. To the maximum allowable absorption current, This is the amplitude limiting function.

6. The transient control method for a wind turbine grid-connected system utilizing reverse energy absorption by an energy-consuming branch as described in claim 1, characterized in that, The electrical energy stored in the DC bus capacitor is expressed by the following formula: ； in, Electrical energy stored in the DC bus capacitor For DC bus capacitors, This is the DC bus voltage.

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