Support control method, device and control system under hybrid wind power plant fault

Abstract

The invention discloses a support control method, device and control system under a hybrid wind power plant fault, and belongs to the technical field of wind power generation, and the support control method under the hybrid wind power plant fault comprises the steps: starting an active frequency support when only the frequency variation is greater than a first threshold value, at the moment, the following net type fan adopts the leading fan to actively respond to other fans to actively follow, the limit supporting capacity of the following net type is exerted, and a net type fan active response control scheme is constructed; and when only the grid-connected voltage variation is greater than a second threshold value, the active voltage support is started, and the active support voltage is controlled by adopting a network construction type voltage outer ring to promote the recovery of the voltage. When the frequency variation is greater than a first threshold value and the grid-connected voltage variation is greater than a second threshold value, preferentially starting the active frequency support, and then starting the active voltage support; not only can network construction and network following control capabilities be fully excavated, but also the capability of coping with strong and weak network changes can be improved, and development and utilization of large-scale renewable energy sources are promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of wind power generation, and more specifically, relates to a support control method, device and control system under a hybrid wind farm fault. Background Art

[0002] The collaborative optimization problem of multiple power generation units in large-scale wind and solar power plants can be described using a scenario where wind farms, photovoltaic systems, and energy storage systems exist simultaneously in the system. The control methods can be divided into grid-following control and grid-forming control.

[0003] Power electronics technology is particularly important as a vehicle for connecting renewable energy. This technology enables effective control of renewable energy sources. This control system maximizes the proactive support and stability of renewable energy sources, achieving external and regulatory characteristics comparable to those of traditional synchronous generators, and maximizing the utilization potential of renewable energy. Frequency and voltage issues for wind and solar power units focus on achieving the same external characteristics as traditional synchronous generators. Stability issues for integrating renewable energy units into the grid primarily focus on voltage and frequency. In the event of a system fault, renewable energy sources can proactively ride through the fault. They can also proactively support frequency and voltage in the event of a system shock from operating conditions, maximizing the stability of the renewable energy system.

[0004] However, how to maintain the stable operation of wind and solar power generation systems and further tap their flexibility under the random fluctuations of wind and solar resources, changes in the intensity of grid access, and various disturbance conditions is the core bottleneck that restricts new energy from becoming the main power source. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a support control method, device and control system under hybrid wind farm faults, which aims to solve the technical problem of how to maintain stable operation of wind and solar power generation systems under random fluctuations in wind and solar resources, changes in the strength of the access grid and various disturbance conditions.

[0006] To achieve the above object, according to one aspect of the present invention, a support control method for a hybrid wind farm under fault conditions is provided, comprising:

[0007] Detecting a frequency change of a grid-connected side load and a grid-connected voltage change of a hybrid wind farm, wherein the hybrid wind farm includes a grid-following wind turbine and a grid-forming wind turbine;

[0008] When only the frequency change is greater than the first threshold, active frequency support is initiated; in the active frequency support stage, one of the grid-following wind turbines is selected as a leading wind turbine to actively respond, and the other grid-following wind turbines are selected as follower wind turbines to actively follow the leading wind turbine, and the grid-forming wind turbines each actively respond;

[0009] When only the grid-connected voltage change amount is greater than the second threshold, active voltage support is started; during the active voltage support stage, a voltage preset value is provided for the voltage outer loop in the grid-forming wind turbine for active voltage support, and the grid-following wind turbine is controlled to provide an additional reactive power reference value for the reactive power outer loop for active voltage support;

[0010] When the frequency change amount is greater than the first threshold and the grid-connected voltage change amount is greater than the second threshold, active frequency support is preferentially started. If the frequency change amount is lower than the first threshold after active frequency support, active voltage support is then started.

[0011] Further, the control process of the grid-following wind turbine in the active frequency support stage is expressed as:

[0012] where x i and x j respectively represent the state information amounts of the i-th and j-th grid-following wind turbines, N is the total number of grid-following wind turbines, a ij is the communication weight between the i-th grid-following wind turbine and the j-th grid-following wind turbine, a i(n+1) represents the communication weight between the i-th grid-following wind turbine and the reference wind turbine (n + 1), x ref is the reference value of the state information amount of the grid-following wind turbine, N is the number of grid-following wind turbines, P i and P j respectively represent the active power output values of the i-th and j-th grid-following wind turbines, d P，i is the per-unit coefficient of the i-th grid-following wind turbine, d P，j is the per-unit coefficient of the j-th grid-following wind turbine, P o,i is the output power of the i-th grid-following wind turbine, P ref,i is the output power reference value of the i-th grid-following wind turbine, P MPPT,i is the maximum power tracking power reference value of the i-th grid-following wind turbine, k PP,i and k IP,i respectively represent the proportional coefficient and integral coefficient of the state difference amount between the i-th grid-following wind turbine and the adjacent wind turbines.

[0013] Further, the output power reference value of the grid-following wind turbine is expressed as:

[0014]

[0015] where L represents the number of the leading wind turbine, F represents the number of the following wind turbine, P ref,L and P ref,F respectively represent the output power reference values corresponding to the grid-following wind turbine as the leading wind turbine and the following wind turbine, PMPPT,L and P MPPT,F respectively represent the maximum power tracking power reference values corresponding to the grid - following wind turbine as the leading wind turbine and the following wind turbine. K dr and K in respectively represent the droop coefficient and the integral coefficient of the virtual inertia comprehensive control of the wind turbine. s represents the frequency - domain variable after Laplace transform, f0 and f respectively represent the power frequency and the actual frequency value.

[0016] Furthermore, the control process of the grid - following wind turbine in the active voltage support stage is expressed as: where, I dref is the d - axis current reference value, I dref0 is the initial d - axis current reference value, ΔI dref is the change value of the initial d - axis current reference value, K is the proportional coefficient, U dref is the voltage reference value during the voltage support process of the grid - following wind turbine, U d is the actual value of the grid - connected voltage of the grid - following wind turbine.

[0017] Furthermore, the control process consistency factor of the grid - following wind turbine in the active voltage support stage is expressed as: where, I sdref is the d - axis current reference value, I sdref0 is the initial d - axis current reference value, I sdrefmax is the maximum value constraint of the inner - loop current.

[0018] Furthermore, the control process of the grid - forming wind turbine in the active frequency support stage is expressed as: where, s represents the frequency - domain variable after Laplace transform, P0, P e and J are the active power output to the grid - connected node and its reference value, and the inertia constant, ω0 is the rated operating value of the grid - connected node voltage, D is the damping coefficient, ω represents the actual frequency value of the grid - connected node voltage, x i and x j respectively represent the state information quantities of the i - th and j - th grid - forming wind turbines, k PP,i 、k IP,i respectively represent the proportional coefficient and the integral coefficient of the state difference quantity between the i - th grid - forming wind turbine and the adjacent wind turbines.

[0019] Furthermore, the control process of the grid - forming wind turbine in the active voltage support stage is expressed as: where, U dref is the d - axis voltage reference value, U dref0 is the initial d - axis voltage reference value, ΔU dref is the change value of the initial d - axis voltage reference value, K GFM is the proportional and integral coefficient of the DC voltage synchronous controller.

[0020] Further, the method further includes: in the active frequency support stage and the active voltage support stage, if any of the network-forming wind turbines reaches its own maximum current inner loop constraint, it is switched to a grid-following wind turbine.

[0021] According to another aspect of the present invention, there is provided a support control device for a hybrid wind farm under fault, including:

[0022] A fault detection module for detecting the frequency change amount and grid-connected voltage change amount of the load on the grid-connected side of the hybrid wind farm, where the hybrid wind farm includes grid-following wind turbines and network-forming wind turbines;

[0023] A first support module for starting active frequency support when only the frequency change amount is greater than a first threshold; in the active frequency support stage, selecting one of the grid-following wind turbines as a leading wind turbine to actively respond, and other grid-following wind turbines as following wind turbines to actively follow the leading wind turbine, and the network-forming wind turbines each actively respond;

[0024] A second support module for starting active voltage support when only the grid-connected voltage change amount is greater than a second threshold; in the active voltage support stage, providing a voltage preset value for the voltage outer loop of the network-forming wind turbines for active voltage support, and controlling the grid-following wind turbines to provide an additional reactive power reference value for the reactive power outer loop for active voltage support;

[0025] A third support module for, when the frequency change amount is greater than the first threshold and the grid-connected voltage change amount is greater than the second threshold, preferentially starting active frequency support, and starting active voltage support if the frequency change amount is lower than the first threshold after active frequency support.

[0026] According to another aspect of the present invention, there is provided a control system for a hybrid wind farm, including a memory and a processor, where the memory stores a computer program, and when the processor executes the computer program, the steps of the above method are implemented.

[0027] Generally speaking, compared with the prior art by the above technical solution conceived by the present invention, the following beneficial effects can be achieved:

[0028] (1) The present invention provides a support control method for a hybrid wind farm under faults. Considering the coupling between active frequency support and the active power output of the system, and the coupling between active voltage support and the reactive power of the system, the focus is on analyzing the constraint relationship between active and reactive power to achieve decoupled control of active and reactive power, and starting corresponding supports when the system frequency fluctuates and the grid-connected voltage changes to achieve active power regulation and frequency fluctuation suppression. Specifically, when only the frequency change amount is greater than the first threshold, active frequency support is started. At this time, the grid-following wind turbines actively respond to the leading wind turbine, and other wind turbines actively follow, exerting the maximum support ability of the grid-following type to form an active response control scheme for the grid-forming wind turbines. When only the grid-connected voltage change amount is greater than the second threshold, active voltage support is started, and the grid-forming type voltage outer loop is adopted to actively support the voltage, promoting the voltage recovery, and further realizing hybrid active support based on frequency and voltage. When the frequency change amount is greater than the first threshold and the grid-connected voltage change amount is greater than the second threshold, active frequency support is preferentially started. If the frequency change amount is lower than the first threshold after active frequency support, active voltage support is then started. This can not only fully exploit the capabilities of grid-forming and grid-following control to achieve active support for frequency and voltage, but also improve the ability to cope with the changes between strong and weak grids, and further promote the development and utilization of large-scale renewable energy.

[0029] (2) In this solution, during the active frequency support stage, the consistency factor in the control process of the grid-following wind turbines is: The advantage of such a design is that the grid-following wind turbines can participate in active frequency control in a consistent manner, and reasonably distribute the output active power among the wind turbines according to the status and capabilities of the wind turbines.

[0030] (3) In this solution, the reference value of the output power of the grid-following wind turbines is expressed as: The advantage of such a design is that the grid-following wind turbines can achieve fast frequency support based on the rapid response of the leading wind turbine, avoiding the complexity of the frequency support control design for each grid-following wind turbine. Further, it can also reduce the communication volume while realizing the energy-based output of each wind turbine, and improve the communication reliability.

[0031] (4) In this solution, the control process of the grid-following wind turbines during the active voltage support stage is expressed as: The advantage of such a design is that the grid-following wind turbines can achieve voltage support in a consistent manner according to the control margin of their own inner-loop current.

[0032] (5) In this solution, the consistency factor in the control process of the grid-following wind turbines during the active voltage support stage is expressed as: The advantage of such a design is that, based on considering the controllable support margin of each grid-following wind turbine, it can achieve maximum active voltage support while ensuring.

[0033] (6) In this solution, the control process of the network-forming wind turbines in the active frequency support stage is expressed as: The advantage of such a design is that it ensures that each network-forming wind turbine can exchange status information with neighboring wind turbines, and through consistent coordination of the active power virtual synchronization process, the reasonable distribution of frequency support power is achieved through the consensus algorithm.

[0034] (7) In this solution, the control process of the network-forming wind turbines in the active voltage support stage is expressed as: The advantage of such a design is that it ensures that each network-forming wind turbine can exchange status information with neighboring wind turbines, and through consistent coordination of the active voltage support control, the reasonable distribution of voltage support power is achieved through the consensus algorithm.

[0035] (8) In the active frequency support stage and the active voltage support stage of this solution, if any of the network-forming wind turbines reaches its own maximum current inner loop constraint, it will be switched to a grid-following wind turbine. The advantage of such a design is that in the frequency and active voltage support stages, the network-forming wind turbines with saturated inner loop current are switched to grid-following control, ensuring that the network-forming wind turbines can achieve active frequency and voltage support within the safe operating range, and avoiding damage to the wind turbines caused by the output current exceeding the limit. Description of the Drawings

[0036] Figure 1 is the flowchart of the support control method for a hybrid wind farm under faults provided in Embodiment 1 of the present invention;

[0037] Figure 2 is the block diagram of the control method of active frequency support first and then active voltage support in the support control method for a hybrid wind farm under faults provided in Embodiment 1 of the present invention;

[0038] Figure 3 is the curve diagram of the grid-connected voltage, output power of the grid-following wind turbine, output power of the network-forming wind turbine, and grid-connected frequency after a 500MW sudden increase in single-phase load in the support control method for a hybrid wind farm under faults provided in Embodiment 1 of the present invention;

[0039] Figure 4 is the curve diagram of the output power of the network-forming wind turbine, grid-connected voltage, grid-connected frequency, and output power of the grid-following wind turbine after a 1000MW sudden increase in single-phase load in the support control method for a hybrid wind farm under faults provided in Embodiment 1 of the present invention. Detailed Embodiment

[0040] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Embodiment 1

[0042] This embodiment provides a support control method under the fault of a hybrid wind farm, as Figure 1 shown, including: detecting the frequency change amount and grid-connected voltage change amount of the grid-connected side load of the hybrid wind farm, where the hybrid wind farm includes grid-following wind turbines and grid-forming wind turbines; starting active frequency support when only the frequency change amount is greater than a first threshold; in the active frequency support stage, selecting one grid-following wind turbine as the leading wind turbine to actively respond, and other grid-following wind turbines as the following wind turbines to actively follow the leading wind turbine, and the grid-forming wind turbines actively respond respectively; starting active voltage support when only the grid-connected voltage change amount is greater than a second threshold; in the active voltage support stage, providing a voltage preset value for the voltage outer loop in the grid-forming wind turbines for active voltage support, and controlling the grid-following wind turbines to provide an additional reactive power reference value for the reactive power outer loop for active voltage support; when the frequency change amount is greater than the first threshold and the grid-connected voltage change amount is greater than the second threshold, actively frequency support is preferentially started, and if the frequency change amount is lower than the first threshold after the active frequency support, then the active voltage support is started. Figure 2 It is a block diagram of the control method of active frequency support first and then active voltage support under the severe fault of a grid-following / grid-forming hybrid wind farm.

[0043] Based on the grid-following / grid-forming control, the hybrid wind farm detects the changes in the active power and reactive power of the grid-connected side load, and allocates the targets of active voltage and active frequency support according to the changes in the active power and reactive power, and determines the start control signal. For example, when the frequency change amount is greater than a first threshold (which can be 0.1 Hz), active frequency support is started; when the grid-connected voltage change amount is greater than a second threshold (which can be 0.1 p.u.), active voltage support is started; it should be noted that the above thresholds and their adjacent values can all achieve the start of support, and in addition, the specific thresholds can also be set according to the actual scenario. Among them, the grid-following / grid-forming control process is calculated as:

[0044]

[0045] In the formula, θ GFM is the output phase angle based on DC voltage synchronization, ω b is the frequency reference value, K p , K i are the proportional and integral coefficients of the DC voltage synchronization controller, θGFL and ω GFL are the output phase angle and angular frequency of the phase-locked loop. The subscript GFL represents the variables of the phase-locked loop-based control system, which are distinguished from the actual system variables. K ppll and K ipll are the proportional and integral coefficients of the phase-locked loop controller H GFL (s). u t0 represents the reference value of the modulation voltage, and Q ref represents the reactive power reference value. k Q represents the control gain of the reactive power loop, and S n represents the rated capacity of the system, and u t represents the modulation voltage.

[0046] Furthermore, the control process of the grid-following wind turbine in the active frequency support stage is expressed as: where x i and x j represent the state information quantities of the i-th and j-th grid-following wind turbines respectively. N is the total number of grid-following wind turbines. a ij is the communication weight between the i-th and j-th grid-following wind turbines, and a i(n+1) represents the communication weight between the i-th grid-following wind turbine and the reference wind turbine (n + 1). x ref is the reference value of the state information quantity of the grid-following wind turbine. N is the number of grid-following wind turbines. P i and P j represent the active power output values of the i-th and j-th grid-following wind turbines respectively. d P，i is the per-unit coefficient of the i-th grid-following wind turbine, and d P，j is the per-unit coefficient of the j-th grid-following wind turbine. P o,i is the output power of the i-th grid-following wind turbine, and P ref,i is the output power reference value of the i-th grid-following wind turbine, and P MPPT,i is the maximum power tracking power reference value of the i-th grid-following wind turbine. k PP,i and k IP,i represent the proportional coefficient and integral coefficient of the state difference quantity between the i-th grid-following wind turbine and its adjacent wind turbines respectively.

[0047] Furthermore, the output power reference value of the grid-following wind turbine is expressed as:

[0048]

[0049] where L represents the number of the leading wind turbine, and F represents the number of the following wind turbine. P ref,L and P ref,F represent the output power reference values of the grid-following wind turbine as the leading wind turbine and the following wind turbine respectively. P MPPT,L and PMPPT,F respectively represent the maximum power tracking power reference values corresponding to the grid-following wind turbines as the leading wind turbine and the following wind turbine, K dr and K in respectively represent the droop coefficient and the integral coefficient of the virtual inertia comprehensive control of the wind turbine, s represents the frequency-domain variable after Laplace transform, f0 and f respectively represent the power frequency and the actual frequency value.

[0050] Furthermore, the control process of the grid-following wind turbine in the active voltage support stage is expressed as: where, I dref is the d-axis current reference value, I dref0 is the initial d-axis current reference value, ΔI dref is the change value of the initial d-axis current reference value, K is the proportionality coefficient, U dref is the voltage reference value in the voltage support process of the grid-following wind turbine, U d is the actual value of the grid-connected voltage of the grid-following wind turbine.

[0051] Furthermore, the control process consistency factor of the grid-following wind turbine in the active voltage support stage is expressed as: where, I sdref is the d-axis current reference value, I sdref0 is the initial d-axis current reference value, I sdrefmax is the maximum value constraint of the inner-loop current.

[0052] Furthermore, the control process of the grid-forming wind turbine in the active frequency support stage is expressed as: where, s represents the frequency-domain variable after Laplace transform, P0, P e and J are the active power output to the grid-connected node and its reference value, and the inertia constant, ω0 is the rated operating value of the grid-connected node voltage, D is the damping coefficient, ω represents the actual frequency value of the grid-connected node voltage, x i and x j respectively represent the state information quantities of the i-th and j-th grid-forming wind turbines, k PP,i 、k IP,i respectively represent the proportionality coefficient and the integral coefficient of the state difference quantity between the i-th grid-forming wind turbine and the adjacent wind turbines.

[0053] Furthermore, the control process of the grid-forming wind turbine in the active voltage support stage is expressed as: where, U dref is the d-axis voltage reference value, U dref0 is the initial d-axis voltage reference value, ΔU dref is the change value of the initial d-axis voltage reference value, K GFM is the proportional and integral coefficients of the DC voltage synchronous controller.

[0054] Further, the support control method for a hybrid wind farm under a fault further includes: in the active frequency support stage and the active voltage support stage, if any grid-forming wind turbine reaches its own maximum current inner-loop constraint, it is switched to a grid-following wind turbine.

[0055] Among them, the grid-following / grid-forming switching process is calculated as:

[0056]

[0057] The re-synchronization process after switching is calculated as:

[0058]

[0059] In the formula, i dref_GFM represents the reference value of the current inner loop of the grid-forming type; i dref_GFL is the reference value of the current inner loop of the grid-following type; Δi represents the compensation amount of the current loop, K ii represents the compensation coefficient of the current, Δω syn represents the compensation amount of the DC synchronization loop control, ΔE syn represents the compensation amount of the internal electromotive force.

[0060] Embodiment 2

[0061] A support control device for a hybrid wind farm under a fault in this embodiment includes: a fault detection module, a first support module, a second support module, and a third support module. Among them, the fault detection module is used to detect the frequency change amount and grid connection voltage change amount of the grid connection side load of the hybrid wind farm, and the hybrid wind farm includes grid-following wind turbines and grid-forming wind turbines. The first support module is used to start active frequency support when only the frequency change amount is greater than a first threshold; in the active frequency support stage, select a grid-following wind turbine as the leading wind turbine to actively respond, and other grid-following wind turbines as the following wind turbines to actively follow the leading wind turbine, and the grid-forming wind turbines each actively respond. The second support module is used to start active voltage support when only the grid connection voltage change amount is greater than a second threshold; in the active voltage support stage, provide a voltage preset value for the voltage outer loop in the grid-forming wind turbines for active voltage support, and control the grid-following wind turbines to provide an additional reactive power reference value for the reactive power outer loop for active voltage support. The third support module is used to give priority to starting active frequency support when the frequency change amount is greater than the first threshold and the grid connection voltage change amount is greater than the second threshold, and start active voltage support if the frequency change amount is lower than the first threshold after active frequency support.

[0062] The division of each module in the above frequency-based active voltage support control system based on grid-following, grid-forming, and switching control is only for illustrative purposes. In other embodiments, the frequency-based active voltage support control system based on grid-following, grid-forming, and switching control can be divided into different modules as needed to complete all or part of the functions of the above frequency-based active voltage support control system based on grid-following, grid-forming, and switching control.

[0063] To verify the practicability of the present invention, simulation experiments are carried out in this embodiment under different active and reactive power deficits, and the simulation results are as Figures 3 to 4 . Among them, Figure 3 (a), (b), (c), and (b) in are the grid-connected voltage, the output power of the grid-following wind turbine, the output power of the grid-forming wind turbine, and the grid-connected frequency after a sudden increase of 500 MW in a single-phase load, respectively. Figure 4 (a), (b), (c), and (b) in are the output power curve of the grid-forming wind turbine, the grid-connected voltage, the grid-connected frequency, and the output power curve of the grid-following wind turbine after a sudden increase of 1000 MW in a single-phase load, respectively. It can be seen from Figures 3 to 4 that by adopting the control method of active frequency support first and then active voltage support under severe faults in the grid-following / grid-forming hybrid wind farm proposed by the present invention, not only can the capabilities of grid-forming and grid-following control be fully exploited to achieve active support for frequency and voltage, but also the ability to cope with the changes between strong and weak grids can be improved, further promoting the development and utilization of large-scale renewable energy.

[0064] It is easy for those skilled in the art to understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A support control method under faults of a hybrid wind farm, characterized in that Including: Detecting the frequency change amount and grid-connected voltage change amount of the load on the grid-connected side of the hybrid wind farm, where the hybrid wind farm includes grid-following wind turbines and grid-forming wind turbines; When only the frequency change amount is greater than the first threshold, initiating active frequency support; in the active frequency support stage, selecting one of the grid-following wind turbines as the leading wind turbine to actively respond, and other grid-following wind turbines as follower wind turbines to actively follow the leading wind turbine, and the grid-forming wind turbines each actively respond; When only the grid-connected voltage change amount is greater than the second threshold, initiating active voltage support; In the active voltage support stage, providing a voltage preset value for the voltage outer loop in the grid-forming wind turbines for active voltage support, and controlling the grid-following wind turbines to provide an additional reactive power reference value for the reactive power outer loop for active voltage support; When the frequency change amount is greater than the first threshold and the grid-connected voltage change amount is greater than the second threshold, preferentially initiate active frequency support, and if the frequency change amount is lower than the first threshold after active frequency support, then initiate active voltage support.

2. The support control method under the fault of the hybrid wind farm according to claim 1, wherein, The control process of the grid-following wind turbines in the active frequency support stage is expressed as: Among them, x i and x j represent the state information quantities of the i-th and j-th network-following wind turbines respectively, N is the total number of network-following wind turbines, a ij is the communication weight between the i-th and j-th network-following wind turbines, a i(n+1) represents the communication weight between the i-th network-following wind turbine and the reference wind turbine (n + 1), x ref is the reference value of the state information quantity of the network-following wind turbine, N is the number of network-following wind turbines, P i and P j represent the active power output values of the i-th and j-th network-following wind turbines respectively, d P，i is the per-unit coefficient of the i-th network-following wind turbine, d P，j is the per-unit coefficient of the j-th network-following wind turbine, P o,i is the output power of the i-th network-following wind turbine, P ref,i is the reference value of the output power of the i-th network-following wind turbine, P MPPT,i is the reference value of the maximum power tracking power of the i-th network-following wind turbine, k PP,i and k IP,i represent the proportional coefficient and integral coefficient of the state difference quantity between the i-th network-following wind turbine and the adjacent wind turbines respectively.

3. The support control method under the fault of the hybrid wind farm according to claim 2, wherein, The output power reference value of the grid-following wind turbines is expressed as: Among them, L represents the number of the leading wind turbine, F represents the number of the following wind turbine, P ref,L and P ref,F respectively represent the output power reference values corresponding to the network-following wind turbine as the leading wind turbine and the following wind turbine, P MPPT,L and P MPPT,F respectively represent the maximum power tracking power reference values corresponding to the network-following wind turbine as the leading wind turbine and the following wind turbine, K dr and K in respectively represent the droop coefficient and the integral coefficient of the virtual inertia comprehensive control of the wind turbine, s represents the frequency domain variable after Laplace transform, and f0 and f respectively represent the power frequency and the actual frequency value.

4. The support control method under the fault of the hybrid wind farm according to claim 2, wherein, The control process of the grid-following wind turbines in the active voltage support stage is expressed as: Among them, I dref is the d-axis current reference value, I dref0 is the initial d-axis current reference value, ΔI dref is the change value of the initial d-axis current reference value, K is the proportionality coefficient, U dref is the voltage reference value during the voltage support process of the grid-connected wind turbine, U d is the actual grid-connected voltage value of the grid-connected wind turbine.

5. The support control method under the fault of the hybrid wind farm according to claim 4, characterized in that, The consistency factor of the control process of the grid-following wind turbines in the active voltage support stage is expressed as: where, I sdref is the d-axis current reference value, I sdref0 is the initial d-axis current reference value, I sdrefmax is the maximum value constraint of the inner-loop current.

6. The support control method under faults of the hybrid wind farm according to claim 1, characterized in that The control process of the grid-forming wind turbines in the active frequency support stage is expressed as: Among them, s represents the frequency-domain variable after Laplace transform, P0, P e and J are the active power output to the grid connection node and its reference value, related to the inertia constant, ω0 is the rated operating value of the grid connection node voltage, D is the damping coefficient, ω represents the actual frequency value of the grid connection node voltage, x i and x j respectively represent the state information quantities of the i-th and j-th grid-forming wind turbines, k PP,i 、k IP,i respectively represent the proportional coefficient and integral coefficient of the state difference quantity between the i-th grid-forming wind turbine and the adjacent wind turbines.

7. The support control method under the fault of the hybrid wind farm according to claim 6, characterized in that, The control process of the grid-forming wind turbines in the active voltage support stage is expressed as: Among them, U dref is the d-axis voltage reference value, U dref0 is the initial d-axis voltage reference value, ΔU dref is the change value of the initial d-axis voltage reference value, K GFM is the proportional and integral coefficient of the DC voltage synchronous controller.

8. The support control method under the fault of the hybrid wind farm according to any one of claims 1-7, characterized in that, Also including: In the active frequency support stage and the active voltage support stage, if any of the grid-forming wind turbines reaches its own maximum current inner loop constraint, switch it to a grid-following wind turbine.

9. A support control device under the fault of a hybrid wind farm, characterized in that, Including: A fault detection module for detecting the frequency change amount and grid-connected voltage change amount of the load on the grid-connected side of the hybrid wind farm, where the hybrid wind farm includes grid-following wind turbines and grid-forming wind turbines; A first support module for initiating active frequency support when only the frequency change amount is greater than the first threshold; in the active frequency support stage, selecting one of the grid-following wind turbines as the leading wind turbine to actively respond, and other grid-following wind turbines as follower wind turbines to actively follow the leading wind turbine, and the grid-forming wind turbines each actively respond; A second support module for initiating active voltage support when only the grid-connected voltage change amount is greater than the second threshold; In the active voltage support stage, providing a voltage preset value for the voltage outer loop in the grid-forming wind turbines for active voltage support, and controlling the grid-following wind turbines to provide an additional reactive power reference value for the reactive power outer loop for active voltage support; A third support module for preferentially initiating active frequency support when the frequency change amount is greater than the first threshold and the grid-connected voltage change amount is greater than the second threshold, and initiating active voltage support if the frequency change amount is lower than the first threshold after active frequency support.

10. A control system for a hybrid wind farm, comprising a memory and a processor, the memory storing a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 8.

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