CN117955165A - Net-structured low-frequency wind generating set, control method thereof and wind power transmission system - Google Patents

Net-structured low-frequency wind generating set, control method thereof and wind power transmission system Download PDF

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Publication number
CN117955165A
CN117955165A CN202211336721.0A CN202211336721A CN117955165A CN 117955165 A CN117955165 A CN 117955165A CN 202211336721 A CN202211336721 A CN 202211336721A CN 117955165 A CN117955165 A CN 117955165A
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China
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frequency
grid
low
phase
power
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CN202211336721.0A
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Inventor
毛绍冉
于笑
艾斯卡尔
吕梁年
阮景锋
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Beijing Goldwind Science and Creation Windpower Equipment Co Ltd
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Beijing Goldwind Science and Creation Windpower Equipment Co Ltd
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Priority to CN202211336721.0A priority Critical patent/CN117955165A/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The application discloses a net-structured low-frequency wind generating set, a control method thereof and a wind power transmission system, and belongs to the technical field of wind power generation. The method comprises the following steps: before grid connection of a grid-formed low-frequency wind generating set, a first phase-locked loop is utilized to obtain a first influence parameter according to the three-phase voltage of low-frequency electric energy output by a grid-side converter; after grid connection of the grid-formed low-frequency wind generating set, a first synchronous ring is utilized to obtain a second influence parameter according to a given value of the DC bus voltage of the DC bus and an actual measurement value of the DC bus voltage; and generating a pulse control signal to control the power switch module based on the second influence parameter and a second amplitude value obtained according to the reactive power given value and the reactive power actual measurement value. According to the embodiment of the application, the conveying capacity and the stability of the net-structured wind generating set can be improved.

Description

Net-structured low-frequency wind generating set, control method thereof and wind power transmission system
Technical Field
The application belongs to the technical field of wind power generation, and particularly relates to a grid-structured low-frequency wind power generator set, a control method thereof and a wind power transmission system.
Background
A wind power generator set is a device capable of converting wind energy into electrical energy. The electric energy generated by the wind generating set can be transmitted to the power grid through the power transmission network, and the power grid is used in a distributed mode. The wind generating set can adjust the rotating speed and the active output of the wind generating set along with the change of wind speed so as to output electric energy. However, when the phenomena such as frequency attenuation and the like occur in the power grid, the wind generating set cannot provide inertia and frequency support for the power grid. Moreover, the electrical energy output by the wind power generator set often needs to be transmitted over a distance to reach the power grid, in which case the transport capacity and stability of the wind power generator set are of vital importance.
Disclosure of Invention
The embodiment of the application provides a net-structured low-frequency wind generating set, a control method thereof and a wind power transmission system, which can improve the conveying capacity and stability of the net-structured low-frequency wind generating set.
In a first aspect, an embodiment of the present application provides a control method for a grid-formed low-frequency wind turbine generator system, where the grid-formed low-frequency wind turbine generator system includes a generator, a machine side converter, a dc bus, and a grid side converter that are electrically connected in sequence, the grid side converter includes a power switch module, the grid-formed low-frequency wind turbine generator system outputs low-frequency electric energy, and the frequency of the low-frequency electric energy is lower than power frequency, the method includes: before grid connection of a grid-formed low-frequency wind generating set, a first phase-locked loop is utilized to obtain a first influence parameter according to the three-phase voltage of low-frequency electric energy output by a grid-side converter, wherein the first influence parameter comprises a first phase and/or a first frequency; after grid connection of the grid-formed low-frequency wind generating set, a first synchronous ring is utilized to obtain a second influence parameter according to a direct current bus voltage given value and a direct current bus voltage actual measurement value of the direct current bus, the second influence parameter comprises a second phase and/or a second frequency, and the difference value between the second influence parameter and the first influence parameter is smaller than a preset impact threshold value; and generating a pulse control signal to control the power switch module based on the second influence parameter and a second amplitude value obtained according to the reactive power given value and the reactive power actual measurement value.
In a second aspect, an embodiment of the present application provides a grid-structured low-frequency wind power generator set, where the grid-structured low-frequency wind power generator set outputs low-frequency electric energy, the frequency of the low-frequency electric energy is lower than power frequency, and the grid-structured low-frequency wind power generator set includes a generator, a machine side converter, a dc bus and a grid side converter that are electrically connected in sequence, where the grid side converter includes a control module and a power switch module; the control module is used for: before grid connection of a grid-formed low-frequency wind generating set, a first phase-locked loop is utilized to obtain a first influence parameter according to the three-phase voltage of low-frequency electric energy output by a grid-side converter, wherein the first influence parameter comprises a first phase and/or a first frequency; after grid connection of the grid-formed low-frequency wind generating set, a first synchronous ring is utilized to obtain a second influence parameter according to a direct current bus voltage given value and a direct current bus voltage actual measurement value of the direct current bus, the second influence parameter comprises a second phase and/or a second frequency, and the difference value between the second influence parameter and the first influence parameter is smaller than a preset impact threshold value; and generating a pulse control signal to control the power switch module based on the second influence parameter and a second amplitude value obtained according to the reactive power given value and the reactive power actual measurement value.
In a third aspect, an embodiment of the present application provides a wind power transmission system, including a grid-structured low-frequency wind power generator set, a low-frequency power transmission line and a power exchange station electrically connected in sequence, where the power exchange station is configured to convert low-frequency electric energy transmitted from the low-frequency power transmission line into power frequency electric energy and transmit the power frequency electric energy to a power grid.
The embodiment of the application provides a grid-structured low-frequency wind generating set, a control method thereof and a wind power transmission system, wherein before and after grid connection of the grid-structured low-frequency wind generating set, the grid-structured low-frequency wind generating set is switched from a first phase-locked loop to a first synchronous loop, the first phase-locked loop obtains a first influence parameter based on three-phase voltage of low-frequency electric energy output by a grid-side converter, the first synchronous loop obtains a second influence parameter based on a given value of DC bus voltage and an actual measurement value of the DC bus voltage, and the second influence parameter participates in generation of pulse control signals after grid connection of the grid-structured wind generating set. When the grid-structured low-frequency wind generating set is switched from grid connection to grid connection, the influence parameters are changed from the first influence parameters to the second influence parameters. The first influence parameter is obtained based on the three-phase voltage of the low-frequency electric energy output by the grid-side converter, the first influence parameter corresponds to the frequency of the low-frequency electric energy, the grid-connected grid-formed low-frequency wind power generator set also needs to generate the low-frequency electric energy, the second influence parameter corresponds to the frequency of the low-frequency electric energy, the difference value of the first influence parameter and the second influence parameter is smaller than the impact threshold value, the change is smaller, the change of the frequency, the current and the like generated at the moment of grid connection cannot form impact, the possibility that the grid-formed low-frequency wind power generator set fails due to the impact of the frequency, the current and the like at the moment of grid connection of the grid-formed wind power generator set is reduced, and the low-frequency electric energy with the output frequency lower than the power frequency of the grid-formed low-frequency wind power generator set can reduce the reactance of a transmission line, so that the conveying capacity and the stability of the grid-formed low-frequency wind power generator set are improved.
Drawings
In order to more clearly illustrate the technical solution of the embodiments of the present application, the drawings that are needed to be used in the embodiments of the present application will be briefly described, and it is possible for a person skilled in the art to obtain other drawings according to these drawings without inventive effort.
FIG. 1 is a schematic diagram of a grid-structured low-frequency wind turbine generator system according to an embodiment of the present application;
FIG. 2 is a flowchart of a control method of a grid-structured low-frequency wind turbine generator system according to an embodiment of the present application;
FIG. 3 is a flowchart of a control method of a grid-structured low-frequency wind turbine generator system according to another embodiment of the present application;
FIG. 4 is a schematic diagram of an exemplary method for controlling a grid-formation type low-frequency wind turbine generator system according to an embodiment of the present application;
fig. 5 is a schematic structural diagram of a wind power transmission system according to an embodiment of the present application.
Detailed Description
Features and exemplary embodiments of various aspects of the present application will be described in detail below, and in order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be described in further detail below with reference to the accompanying drawings and the detailed embodiments. It should be understood that the particular embodiments described herein are meant to be illustrative of the application only and not limiting. It will be apparent to one skilled in the art that the present application may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the application by showing examples of the application.
A wind power generator set is a device capable of converting wind energy into electrical energy. The electric energy generated by the wind generating set can be transmitted to the power grid through the power transmission network, and the power grid is used in a distributed mode. The wind generating set can adjust the rotating speed and the active output of the wind generating set along with the change of wind speed so as to output electric energy. However, when the phenomena such as frequency attenuation and the like occur in the power grid, the wind generating set cannot provide inertia and frequency support for the power grid. Moreover, the electrical energy output by the wind power generator set often needs to be transmitted over a distance to reach the power grid, in which case the transport capacity and stability of the wind power generator set are of vital importance.
The embodiment of the application provides a grid-structured low-frequency wind generating set, a control method thereof and a wind power transmission system. The net-structured wind generating set has the characteristic of a self-synchronizing power grid and can externally display the characteristic of voltage source control. Under off-grid scenes, the grid-structured wind generating set can also serve as a voltage source to supply power for some electric equipment. Under the grid-connected scene, the grid-structured wind generating set can provide inertial support and frequency support for a power grid electrically connected with the wind generating set. The net-structured wind generating set in the embodiment of the application is a net-structured low-frequency wind generating set, can output low-frequency electric energy, has the frequency lower than the power frequency, can reduce the reactance of a transmission line in the transmission process, and improves the transmission capacity of the net-structured low-frequency wind generating set. In addition, in the grid-connected operation process of the grid-connected low-frequency wind generating set, the phase-locked loop and the synchronous loop can be switched, so that the frequency, the current and other changes at the moment of grid connection of the grid-connected low-frequency wind generating set are ensured to be small, the impact of the frequency, the current and the like at the moment of grid connection of the grid-connected low-frequency wind generating set is reduced, and the stability of the grid-connected low-frequency wind generating set is improved.
The application provides a net-structured low-frequency wind generating set, a control method thereof and a power transmission system.
For convenience of explanation, the structure of the grid-structured low-frequency wind generating set will be briefly described. Fig. 1 is a schematic structural diagram of a grid-structured low-frequency wind turbine generator system according to an embodiment of the present application, and as shown in fig. 1, the grid-structured low-frequency wind turbine generator system 10 may include a generator 11, a machine-side converter 12, a dc bus 13, and a grid-side converter 14 electrically connected in sequence. The grid-side converter 14 is configured to be electrically connected to the power grid 20, and other devices, apparatuses, components, etc. may be further included between the grid-side converter 14 and the power grid 20, which are not limited herein. AC in fig. 1 refers to alternating current, DC refers to direct current, and the machine side converter 12 may convert alternating current electric energy into direct current electric energy, and the grid side converter 14 may convert direct current electric energy into alternating current electric energy. The grid-side converter 14 may include a power switching module and a control module. The power switching module includes a plurality of power switching devices. The control module can execute a control method, generates a pulse control signal to control the on and off of the power switch device so as to control the power switch module and realize the control of the grid-structured low-frequency wind generating set. The net-structured low-frequency wind generating set in the embodiment of the application outputs low-frequency electric energy, the frequency of the low-frequency electric energy is lower than the power frequency, and the power frequency is 50 hertz (Hz). In some examples, the frequency of the low frequency electrical energy may be less than or equal to 20Hz, e.g., the frequency of the low frequency electrical energy may be 16.67hz±0.5Hz, approximately one third of the power frequency.
The first aspect of the present application provides a control method of a grid-configured low-frequency wind generating set, which may be performed by the grid-side converter in the foregoing embodiment, and further, the method may be performed by the control module in the grid-side converter in the foregoing embodiment. Fig. 2 is a flowchart of a control method of a grid-structured low-frequency wind turbine generator system according to an embodiment of the present application, as shown in fig. 2, the control method of the grid-structured low-frequency wind turbine generator system may include steps S301 to S303.
In step S301, a first phase-locked loop is utilized to obtain a first influencing parameter according to a three-phase voltage of low-frequency electric energy output by a grid-side converter before grid connection of a grid-formed low-frequency wind generating set.
The input signal of the first phase-locked loop may include a three-phase voltage of the low frequency electric energy output by the grid-side converter, and the output signal of the first phase-locked loop may include a first influencing parameter obtained according to the three-phase voltage of the low frequency electric energy output by the grid-side converter. The first influencing parameter is a parameter related to frequency before grid connection generated by the first phase-locked loop, the first influencing parameter can comprise a first phase and/or a first frequency, and the first phase and the second frequency can be mutually converted. The first influence parameter can be used for safety protection of the grid-side converter, obtaining a voltage effective value and a current effective value output by the grid-side converter, coordinate transformation of the voltage and the current and the like.
The first phase-locked loop can carry out low-frequency phase locking before grid connection, and the phase of the grid-side converter is locked into the phase of low-frequency electric energy output by the grid-side current transformer. In some examples, the first phase-locked loop may include a Proportional-Integral (PI) controller, a Proportional-Integral-Derivative (PID) controller, or the like, without limitation.
In step S302, after the grid-connected low-frequency wind turbine generator system is connected, a second influencing parameter is obtained by using the first synchronization ring according to the given value of the dc bus voltage and the measured value of the dc bus voltage of the dc bus.
The input signal of the first synchronizing ring can be obtained based on the given value of the DC bus voltage of the DC bus and the actual measurement value of the DC bus voltage. The output signal of the first synchronizer ring may include a second influencing parameter derived from the dc bus voltage setpoint and the dc bus voltage actual measurement. The second influencing parameter is a parameter related to frequency after grid connection generated by the first synchronous ring, the second influencing parameter comprises a second phase and/or a second frequency, and the second phase and the second frequency can be mutually converted. The second influencing parameter is involved in generating the pulse control signal for controlling the power switching module. The difference value between the second influence parameter and the first influence parameter is smaller than a preset impact threshold, the impact threshold is an influence parameter threshold capable of inducing impact before and after grid connection, and when the influence parameter before grid connection of the grid-built wind turbine generator set and the influence parameter after grid connection of the grid-built wind turbine generator set are larger than or equal to the impact threshold, the impact of frequency, current, voltage and the like can be received when the grid-built wind turbine generator set is switched from grid connection to grid connection. When the influence parameters before grid connection of the grid-built wind turbine generator system and the influence parameters after grid connection of the grid-built wind turbine generator system are smaller than the impact threshold value, the impact of frequency, current, voltage and the like can not be generated when the grid-built wind turbine generator system is switched from grid connection to grid connection.
The first synchronization ring can perform phase synchronization after grid connection, and the phase of the grid-side converter is synchronized into a phase determined based on the given value of the DC bus voltage and the actual measurement value of the DC bus voltage. In some examples, the first synchronization loop may include a Proportional-Integral (PI) controller, a Proportional-Integral-Derivative (PID) controller, or the like, without limitation.
In step S303, a pulse control signal is generated to control the power switching module based on the second influencing parameter and a second amplitude value obtained from the reactive power setpoint value and the reactive power actual measurement value.
In some examples, the second amplitude may be derived from a difference between the reactive power setpoint and the reactive power actual measurement using a reactive loop. Based on the second influence parameter and the second amplitude, generating a pulse control signal through multiple transformation processing. The pulse control signal is used for controlling a power switch module in the grid-side converter after grid connection of the grid-formed low-frequency wind generating set.
Under the condition of frequency attenuation of the power grid, the grid-structured low-frequency wind generating set can convert energy stored by a rotor of a generator into active power to be provided for the power grid, so that the frequency and inertial support of the power grid are realized.
In the embodiment of the application, before and after grid connection of the grid-formed low-frequency wind generating set, the first phase-locked loop is switched into the first synchronous loop, the first phase-locked loop obtains a first influence parameter based on the three-phase voltage of the low-frequency electric energy output by the grid-side converter, the first synchronous loop obtains a second influence parameter based on the given value of the voltage of the direct-current bus and the actual measurement value of the voltage of the direct-current bus, and the second influence parameter participates in generation of pulse control signals after grid connection of the grid-formed wind generating set. When the grid-structured low-frequency wind generating set is switched from grid connection to grid connection, the influence parameters are changed from the first influence parameters to the second influence parameters. The first influence parameter is obtained based on the three-phase voltage of the low-frequency electric energy output by the grid-side converter, the first influence parameter corresponds to the frequency of the low-frequency electric energy, the grid-connected grid-formed low-frequency wind power generator set also needs to generate the low-frequency electric energy, the second influence parameter corresponds to the frequency of the low-frequency electric energy, the difference value of the first influence parameter and the second influence parameter is smaller than the impact threshold value, the change is smaller, the change of the frequency, the current and the like generated at the moment of grid connection cannot form impact, the possibility that the grid-formed low-frequency wind power generator set fails due to the impact of the frequency, the current and the like at the moment of grid connection of the grid-formed wind power generator set is reduced, and the low-frequency electric energy with the output frequency lower than the power frequency of the grid-formed low-frequency wind power generator set can reduce the reactance of a transmission line, so that the conveying capacity and the stability of the grid-formed low-frequency wind power generator set are improved.
In some embodiments, the first synchronization loop includes a first PI controller that may generate a pulse control signal for controlling the power switch module using a reactive loop, a voltage loop, a current loop, and the like. Fig. 3 is a flowchart of a control method of a grid-structured low-frequency wind turbine generator system according to another embodiment of the present application, and fig. 4 is a logic schematic diagram of an example of the control method of the grid-structured low-frequency wind turbine generator system according to the embodiment of the present application. The control method of the grid-formed low-frequency wind turbine generator system is further described below with reference to fig. 3 and 4. Here, fig. 3 is different from fig. 2 in that step S302 shown in fig. 2 may be specifically thinned into step S3021 and step S3022 shown in fig. 3, and step S303 shown in fig. 2 may be specifically thinned into steps S3031 to S3036 shown in fig. 3.
In step S3021, a first difference between a dc bus given value and a dc bus voltage actual measurement value is obtained.
In step S3022, the first difference is taken as an input of the first PI controller, and the second influencing parameter is obtained according to the output of the first PI controller.
As shown in fig. 4, the difference between the given value of the dc bus and the measured value of the dc bus voltage, that is, the first difference is denoted as Δudc, the first difference Δudc is used as an input of the first PI controller, the output of the first PI controller is the output of the first synchronous loop, and the first synchronous loop outputs the second influencing parameter theta_s2. If the first synchronous ring is switched, the first synchronous ring outputs a second influencing parameter theta_s2 to the subsequent other control rings.
In some examples, in order to adapt to the low-frequency power output by the grid-formation type low-frequency wind generating set, the stability of the grid-formation type low-frequency wind generating set is further ensured, and the proportional feedforward coefficient of the first PI controller required for outputting the power frequency power can be increased, that is, in the embodiment of the present application, the proportional feedforward coefficient of the first PI controller can be greater than the proportional feedforward coefficient of the second PI controller matched with the power frequency. The second PI controller is a PI controller in a synchronous ring of a wind generating set which is suitable for outputting power frequency electric energy. The increased proportion feedforward coefficient can reduce the fluctuation of the voltage of the direct current bus, avoid the problems of overvoltage, undervoltage and the like of the direct current bus, improve the stability of the grid-side converter and further improve the stability of the grid-structured low-frequency wind generating set.
In step S3031, the second amplitude is obtained by using the first reactive ring according to the reactive power set value and the reactive power actual measurement value.
In step S3032, a three-phase voltage setpoint is obtained using the first reactive ring according to the second influencing parameter and the second amplitude.
The input signal of the first reactive ring may include a difference Δq between the reactive power given value and the reactive power measured value, and the first reactive ring may obtain a second amplitude according to the difference Δq between the reactive power given value and the reactive power measured value, and convert and output three-phase voltage given values Uat, ubt, and Uct according to the second amplitude and a second phase in the obtained second influencing parameter. The second phase may be obtained directly or according to a second frequency conversion.
In some examples, in order to adapt to the frequency of the low-frequency electric energy output by the grid-formation type low-frequency wind generating set, so that the loop can stably operate when the grid-formation type low-frequency wind generating set operates, the bandwidth of the first reactive ring can be smaller than the bandwidth of a second reactive ring matched with the power frequency, and the second reactive ring is a reactive ring matched with the power frequency. The bandwidth may be reduced on the basis of the reactive bandwidth matching the power frequency to obtain a bandwidth matching the frequency of the low frequency power, i.e. the bandwidth of the first passive loop. The bandwidth of the reactive ring refers to the cut-off frequency of the transfer function of the reactive ring, also referred to as the bandwidth frequency, which is the frequency at which the amplitude-frequency characteristic of the reactive ring drops to-3 decibels (dB).
The first reactive loop includes a fourth PI controller or a second PID controller. The fourth PI controller may be adjusted to have a bandwidth of the first reactive loop that is lower than a bandwidth of the second reactive loop that is matched to the power frequency by adjusting a scaling factor and/or an integration factor. Or the proportional and/or integral coefficients of the second PID controller can be adjusted so that the bandwidth of the first reactive loop is lower than the bandwidth of the second reactive loop that matches the power frequency. Specifically, after determining the target bandwidth lower than the bandwidth of the second reactive ring matched with the power frequency, the scaling factor of the fourth PI controller, the integration factor of the fourth PI controller, the scaling factor of the second PID controller, the integration factor of the second PID controller, etc. that can make the bandwidth of the first reactive ring reach the target bandwidth may be calculated according to the transfer function of the first reactive ring.
In step S3033, a two-phase static coordinate system current setpoint is obtained based on the three-phase voltage setpoint and the second influencing parameter using the voltage loop.
As shown in fig. 4, the three-phase voltage can be converted by the voltage loop into a setpoint value Uat, ubt, uct and into two static coordinate system current setpoint values iα_set and iβ_set according to a second phase and/or a second frequency in the second influencing parameter.
In step S3034, current clipping processing is performed on the current set point of the two-phase static coordinate system to obtain a three-phase current set point.
As shown in fig. 4, the current limiting process is performed on the current given value of the two-phase static coordinate system, and three-phase current given values ia_set and ib_set and ic_set are obtained through conversion.
In step S3035, a voltage standard value of the two-phase static coordinate system is obtained by using the current loop based on the three-phase current set point, the three-phase current actual measurement value and the second influence parameter.
As shown in fig. 4, the input of the current loop includes three-phase current set values ia_set and ib_set and ic_set, three-phase current actual measurement values ia_meas, ib_meas and ic_meas and a second influence parameter, and the output of the current loop includes two static coordinate system voltage standard values uα_ref and uβ_ref.
In some examples, the current loop includes a first proportional resonance (Proportion Resonant, PR) controller. The first PR controller is a PR controller that is frequency matched to the low frequency power. The input to the first PR controller may include a second difference between the three-phase current setpoint and the three-phase current actual measurement, abbreviated ΔI in FIG. 4; the output of the first PR controller may include two static coordinate system voltage standard values uα_ref and uβ_ref. The first PR controller has control parameters including a bandwidth and a center frequency of the first PR controller. In order to meet the requirement of the grid-formed low-frequency wind generating set for outputting low-frequency electric energy, the response speed and control precision of the current loop are improved, the center frequency of the first PR controller can be set to be lower than that of the second PR controller matched with the power frequency, and the center frequency of the first PR controller can be obtained by performing down-regulation on the basis of the center frequency of the second PR controller matched with the power frequency.
In step S3036, the voltage standard value of the two-phase static coordinate system is modulated, and a pulse control signal is generated to control the power switch module.
As shown in fig. 4, the voltage standard value of the two-phase static coordinate system may be modulated to generate a pulse control signal for controlling the power switch module after grid connection.
As shown in fig. 4, the input signal of the first phase-locked loop includes three-phase voltages Ua, ub and Uc of the low-frequency electric energy output by the grid-side converter, and the first phase-locked loop outputs a first influencing parameter theta_s1. Before grid connection of the grid-formed wind generating set, switching to a first phase-locked loop; and after grid connection of the grid-structured generator set, cutting into a first synchronous ring.
In some examples, to adapt to the frequency of the low-frequency electric energy output by the grid-configured low-frequency wind generating set, and improve the low-frequency phase locking capability of the grid-side converter when the grid frequency is attenuated, the bandwidth of the first phase-locked loop may be lower than the bandwidth of a second phase-locked loop matched with the power frequency, where the second phase-locked loop is a phase-locked loop matched with the power frequency. The bandwidth may be reduced based on the bandwidth of the phase-locked loop matching the power frequency to obtain a bandwidth matching the frequency of the low frequency power, i.e., the bandwidth of the first phase-locked loop. The bandwidth of a phase-locked loop refers to the cut-off frequency, also called the bandwidth frequency, of the transfer function of the phase-locked loop, which is the frequency at which the amplitude-frequency characteristic of the phase-locked loop drops to-3 decibels (dB).
The first phase locked loop may include a third PI controller or a first PID controller. The low bandwidth of the first phase locked loop may be achieved by adjusting the configuration coefficients of the third PI controller or the configuration coefficients of the first PID controller. The scaling factor and/or integration factor of the third PI controller may be adjusted such that the bandwidth of the first phase locked loop is lower than the bandwidth of the second phase locked loop that matches the power frequency. Or adjusting the proportional coefficient and/or the integral coefficient of the first PID controller so that the bandwidth of the first phase-locked loop is lower than that of the second phase-locked loop matched with the power frequency. Specifically, after determining a target bandwidth lower than the bandwidth of the second phase-locked loop matching the power frequency, the scaling factor of the third PI controller, the integration factor of the third PI controller, the scaling factor of the first PID controller, the integration factor of the first PID controller, etc. that can make the bandwidth of the first phase-locked loop reach the target bandwidth may be calculated according to the transfer function of the first phase-locked loop.
In some embodiments, to improve the protection capability of the network side converter, the network side converter may be further protected, where the protection may include frequency protection, voltage effective value protection, current effective value protection, and the like, and is not limited herein. The frequency protection may include a frequency high protection and a frequency low protection, and the voltage effective value protection may also include a voltage effective value high protection and a voltage effective value low protection, and the current effective value protection may include a current effective value high protection, which is not limited herein.
In some examples, the first influencing parameters corresponding to the first phase-locked loop may be collected before grid connection of the grid-formed wind generating set; obtaining a first frequency related parameter according to the first influence parameter; before and after grid connection of the grid-formed low-frequency wind generating set, if the first frequency related parameter exceeds a preset safety parameter range, a shutdown instruction is sent to a main controller of the grid-formed low-frequency wind generating set, so that the main controller controls the grid-formed low-frequency wind generating set to shutdown.
The first frequency-dependent parameter comprises a frequency-dependent parameter, which is obtainable from the first influencing parameter. For example, the first frequency-related parameter may include a frequency, a current effective value, a voltage effective value, etc., where the current effective value and the voltage effective value refer to an effective value of a current and an effective value of a voltage output by the grid-side converter. Because the difference value between the first influence parameter and the second influence parameter is smaller than the impact threshold value, the first frequency related parameter obtained according to the first influence parameter can be used for safety protection before and after grid connection of the grid-built wind generating set.
In some examples, the first influencing parameters corresponding to the first phase-locked loop may be collected before grid connection of the grid-formed low-frequency wind generating set; obtaining a first frequency related parameter according to the first influence parameter; before grid connection of the grid-formed low-frequency wind generating set, if the first frequency related parameter exceeds the safety parameter range, sending a shutdown instruction to a main controller of the grid-formed low-frequency wind generating set; after grid connection of the grid-formed low-frequency wind generating set, collecting a second influence parameter corresponding to the first synchronous ring; obtaining a second frequency related parameter according to the second influence parameter; after grid connection of the grid-structured low-frequency wind generating set, if the second frequency related parameter exceeds the safety parameter range, a shutdown instruction is sent to a main controller of the grid-structured low-frequency wind generating set.
The content of the first frequency-related parameter may be referred to the related description above, and will not be described herein. The second frequency-dependent parameter comprises a frequency-dependent parameter, which is obtainable from the second influencing parameter. For example, the second frequency-related parameter may include a frequency, a current effective value, a voltage effective value, and the like. Before grid connection of the grid-formed wind generating set, safety protection can be carried out by utilizing a first frequency related parameter obtained according to a first influence parameter; and after grid connection of the grid-structured wind generating set, performing safety protection by using a second frequency related parameter obtained according to the second influence parameter.
The safety parameter range may be set according to a scene, a requirement, experience, etc., and is not limited herein. For example, the first frequency-related parameter, the second frequency-related parameter comprises a frequency, and the safety parameter comprises a safety frequency range, the safety frequency range comprising the frequency of the low frequency power, i.e. the safety frequency range may comprise a range in which the frequency of the low frequency power fluctuates up and down, e.g. if the frequency of the low frequency power is 16.67Hz, the safety frequency range may be [13Hz,20Hz ]; if the accuracy of the frequency of the low-frequency electric energy is required to be higher, the safe frequency range can be set to be [16.17Hz,17.17Hz ]. Similarly, the first frequency related parameter and the second frequency related parameter include a voltage effective value and a current effective value, and correspondingly, the safety parameter range may include a safety voltage effective value range and a safety current effective value range.
If the first frequency related parameter and the second frequency related parameter are lower than the lower limit value of the safety parameter range, the first frequency related parameter and the second frequency related parameter indicate that the grid-side converter may have faults or risks and needs to be subjected to safety low protection, and the control module of the grid-side converter can send a shutdown instruction to the main controller of the grid-structure low-frequency wind generating set so as to control the grid-structure low-frequency wind generating set to shutdown.
If the first frequency related parameter and the second frequency related parameter are higher than the upper limit value of the safety parameter range, the first frequency related parameter and the second frequency related parameter indicate that the grid-side converter may have faults or risks and needs to be subjected to high safety protection, and the control module of the grid-side converter can send a shutdown instruction to the main controller of the grid-formed low-frequency wind generating set so as to control the grid-formed low-frequency wind generating set to shutdown.
The second aspect of the application provides a net-structured low-frequency wind generating set, which outputs low-frequency electric energy, and the frequency of the low-frequency electric energy is lower than the power frequency. The structure of the grid-structured low-frequency wind turbine generator system can be seen in fig. 1 and the related description in the above embodiments, and will not be described herein.
The grid-side converter 14 in the grid-formed low-frequency wind power generator set 10 comprises a control module and a power switch module.
The control module may be configured to: before grid connection of a grid-formed low-frequency wind generating set, a first phase-locked loop is utilized to obtain a first influence parameter according to the three-phase voltage of low-frequency electric energy output by a grid-side converter, wherein the first influence parameter comprises a first phase and/or a first frequency; after grid connection of the grid-formed low-frequency wind generating set, a first synchronous ring is utilized to obtain a second influence parameter according to a direct current bus voltage given value and a direct current bus voltage actual measurement value of the direct current bus, the second influence parameter comprises a second phase and/or a second frequency, and the difference value between the second influence parameter and the first influence parameter is smaller than an impact threshold value; and generating a pulse control signal to control the power switch module based on the second influence parameter and a second amplitude value obtained according to the reactive power given value and the reactive power actual measurement value. .
In some examples, the low frequency electrical energy has a frequency of less than or equal to 20 hertz.
In the embodiment of the application, before and after grid connection of the grid-formed low-frequency wind generating set, the first phase-locked loop is switched into the first synchronous loop, the first phase-locked loop obtains a first influence parameter based on the three-phase voltage of the low-frequency electric energy output by the grid-side converter, the first synchronous loop obtains a second influence parameter based on the given value of the voltage of the direct-current bus and the actual measurement value of the voltage of the direct-current bus, and the second influence parameter participates in generation of pulse control signals after grid connection of the grid-formed wind generating set. When the grid-structured low-frequency wind generating set is switched from grid connection to grid connection, the influence parameters are changed from the first influence parameters to the second influence parameters. The first influence parameter is obtained based on the three-phase voltage of the low-frequency electric energy output by the grid-side converter, the first influence parameter corresponds to the frequency of the low-frequency electric energy, the grid-connected grid-formed low-frequency wind power generator set also needs to generate the low-frequency electric energy, the second influence parameter corresponds to the frequency of the low-frequency electric energy, the difference value of the first influence parameter and the second influence parameter is smaller than the impact threshold value, the change is smaller, the change of the frequency, the current and the like generated at the moment of grid connection cannot form impact, the possibility that the grid-formed low-frequency wind power generator set fails due to the impact of the frequency, the current and the like at the moment of grid connection of the grid-formed wind power generator set is reduced, and the low-frequency electric energy with the output frequency lower than the power frequency of the grid-formed low-frequency wind power generator set can reduce the reactance of a transmission line, so that the conveying capacity and the stability of the grid-formed low-frequency wind power generator set are improved.
In some embodiments, the first synchronization loop may include a first PI controller.
The control module may be configured to: acquiring a first difference value between a given value of a direct current bus and an actual measurement value of the voltage of the direct current bus; and taking the first difference value as the input of a first PI controller, and obtaining a second phase according to the output of the first PI controller, wherein the proportional feedforward coefficient of the first PI controller is larger than that of a second PI controller matched with the power frequency.
In some embodiments, the bandwidth of the first phase-locked loop is lower than the bandwidth of the second phase-locked loop that matches the power frequency, the first phase-locked loop including a third PI controller or a first PID controller.
The control module may also be configured to: adjusting the proportional coefficient and/or the integral coefficient of the third PI controller to enable the bandwidth of the first phase-locked loop to be lower than that of the second phase-locked loop matched with the power frequency; or adjusting the proportional coefficient and/or the integral coefficient of the first PID controller so that the bandwidth of the first phase-locked loop is lower than that of the second phase-locked loop matched with the power frequency.
In some embodiments, the control module may be further operable to: obtaining a second amplitude value according to the reactive power given value and the reactive power actual measurement value by using the first reactive ring; obtaining a three-phase voltage given value according to the second influence parameter and the second amplitude by using the first reactive ring; obtaining a current given value of the two-phase static coordinate system based on the three-phase voltage given value and the second influence parameter by using the voltage ring; carrying out current limiting treatment on the given value of the current in the two-phase static coordinate system to obtain a given value of the three-phase current; obtaining a voltage standard value of the two-phase static coordinate system based on the three-phase current given value, the three-phase current actual measurement value and the second influence parameter by using the current loop; modulating the voltage standard value of the two-phase static coordinate system to generate a pulse control signal to control the power switch module.
In some examples, the current loop includes a first proportional resonant controller that is matched to a frequency of the low frequency electrical energy, an input of the first proportional resonant controller includes a second difference between the three-phase current setpoint and the three-phase current actual measurement, and an output of the first proportional resonant controller includes a two-phase static coordinate system voltage standard value. The center frequency of the first proportional resonance controller is lower than that of the second proportional resonance controller matched with the power frequency.
In some examples, the bandwidth of the first reactive loop is less than the bandwidth of the second reactive loop that matches the power frequency, the first reactive loop including a fourth PI controller or a second PID controller.
The control module may also be configured to: adjusting the proportional coefficient and/or the integral coefficient of the fourth PI controller to enable the bandwidth of the first reactive ring to be lower than that of the second reactive ring matched with the power frequency; or adjusting the proportional coefficient and/or the integral coefficient of the second PID controller so that the bandwidth of the first reactive ring is lower than the bandwidth of the second reactive ring matched with the power frequency.
In some embodiments, the control module may be further operable to: before grid connection of a grid-formed low-frequency wind generating set, collecting a first influence parameter corresponding to a first phase-locked loop; obtaining a first frequency related parameter according to the first influence parameter; before and after grid connection of the grid-formed low-frequency wind generating set, if the first frequency related parameter exceeds a preset safety parameter range, a shutdown instruction is sent to a main controller of the grid-formed low-frequency wind generating set, so that the main controller controls the grid-formed low-frequency wind generating set to shutdown.
In some embodiments, the control module may be further operable to: before grid connection of a grid-formed low-frequency wind generating set, collecting a first influence parameter corresponding to a first phase-locked loop; obtaining a first frequency related parameter according to the first influence parameter; before grid connection of the grid-formed low-frequency wind generating set, if the first frequency related parameter exceeds the safety parameter range, sending a shutdown instruction to a main controller of the grid-formed low-frequency wind generating set; after grid connection of the grid-formed low-frequency wind generating set, collecting a second influence parameter corresponding to the first synchronous ring; obtaining a second frequency related parameter according to the second influence parameter; after grid connection of the grid-structured low-frequency wind generating set, if the second frequency related parameter exceeds the safety parameter range, a shutdown instruction is sent to a main controller of the grid-structured low-frequency wind generating set.
The third aspect of the application also provides a wind power transmission system. Fig. 5 is a schematic structural diagram of a wind power transmission system according to an embodiment of the present application, and as shown in fig. 5, the wind power transmission coefficient may include a grid-structured low-frequency wind power generator set 10, a low-frequency power transmission line 41 and a power exchange station 42 electrically connected in sequence.
The low-frequency electric energy output by the grid-structured low-frequency wind generating set 10 can be transmitted to the power conversion 42 through the low-frequency power transmission line 41. The power conversion station 42 converts the low-frequency power transmitted from the low-frequency power transmission line 41 into power frequency power and transmits the power frequency power to the power grid 20.
The wind power transmission system can be applied to medium and long transmission distance scenes. For example, the grid-structured low-frequency wind turbine generator system 10 may be installed on the sea, the low-frequency power transmission line 41 may be a submarine cable, and the power exchange station 42 may be installed on the land. The frequency of the low-frequency electric energy is lower than the power frequency, the impedance of the low-frequency electric transmission line 41 can be reduced, so that the transmission quality is improved, the power transmission requirement can be met by arranging a converter station 42 in the wind power transmission system, and the structure of the wind power transmission system is simplified.
The specific structure and control method of the grid-structured low-frequency wind turbine generator system can be referred to the related description in the above embodiments, and will not be described herein. AC in fig. 5 refers to alternating current and DC refers to direct current.
It should be understood that, in the present specification, each embodiment is described in an incremental manner, and the same or similar parts between the embodiments are all referred to each other, and each embodiment is mainly described in a different point from other embodiments. For the embodiment of the grid-structured low-frequency wind generating set and the embodiment of the wind power transmission system, relevant parts can be seen from the description part of the embodiment of the control method. The application is not limited to the specific steps and structures described above and shown in the drawings. Those skilled in the art will appreciate that various alterations, modifications, and additions may be made, or the order of steps may be altered, after appreciating the spirit of the present application. Also, a detailed description of known method techniques is omitted here for the sake of brevity.
Aspects of the present application are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions/acts specified in the flowchart and/or block diagram block or blocks. Such a processor may be, but is not limited to being, a general purpose processor, a special purpose processor, an application specific processor, or a field programmable logic circuit. It will also be understood that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware which performs the specified functions or acts, or combinations of special purpose hardware and computer instructions.
Those skilled in the art will appreciate that the above-described embodiments are exemplary and not limiting. The different technical features presented in the different embodiments may be combined to advantage. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in view of the drawings, the description, and the claims. In the claims, the term "comprising" does not exclude other means or steps; the word "a" does not exclude a plurality; the terms "first," "second," and the like, are used for designating a name and not for indicating any particular order. Any reference signs in the claims shall not be construed as limiting the scope. The functions of the various elements presented in the claims may be implemented by means of a single hardware or software module. The presence of certain features in different dependent claims does not imply that these features cannot be combined to advantage.

Claims (10)

1. The control method of the grid-structured low-frequency wind generating set is characterized in that the grid-structured low-frequency wind generating set comprises a generator, a machine side converter, a direct current bus and a grid side converter which are electrically connected in sequence, the grid side converter comprises a power switch module, the grid-structured low-frequency wind generating set outputs low-frequency electric energy, and the frequency of the low-frequency electric energy is lower than power frequency, and the method comprises the following steps:
Before grid connection of the grid-formed low-frequency wind generating set, a first phase-locked loop is utilized to obtain a first influence parameter according to the three-phase voltage of the low-frequency electric energy output by the grid-side converter, wherein the first influence parameter comprises a first phase and/or a first frequency;
After the grid connection of the grid-formed low-frequency wind generating set, a first synchronous ring is utilized to obtain a second influence parameter according to a direct current bus voltage given value and a direct current bus voltage actual measurement value of the direct current bus, the second influence parameter comprises a second phase and/or a second frequency, and the difference value between the second influence parameter and the first influence parameter is smaller than a preset impact threshold value;
And generating a pulse control signal to control the power switch module based on the second influence parameter and a second amplitude value obtained according to the reactive power given value and the reactive power actual measurement value.
2. The method of claim 1, wherein the first synchronizer ring comprises a first PI controller,
The obtaining of the second influencing parameter by the first synchronizing ring according to the given value of the DC bus voltage and the actual measurement value of the DC bus voltage of the DC bus comprises the following steps:
Acquiring a first difference value between the given value of the direct current bus and the actual measurement value of the voltage of the direct current bus;
And taking the first difference value as the input of the first PI controller, obtaining the second phase according to the output of the first PI controller, wherein the proportional feedforward coefficient of the first PI controller is larger than that of a second PI controller matched with the power frequency.
3. The method of claim 1, wherein the bandwidth of the first phase-locked loop is lower than the bandwidth of a second phase-locked loop matched to the power frequency, the first phase-locked loop comprising a third PI controller or a first PID controller,
The method further comprises the steps of:
adjusting the proportional coefficient and/or the integral coefficient of the third PI controller to enable the bandwidth of the first phase-locked loop to be lower than that of the second phase-locked loop matched with the power frequency;
Or alternatively
And adjusting the proportional coefficient and/or the integral coefficient of the first PID controller so that the bandwidth of the first phase-locked loop is lower than that of the second phase-locked loop matched with the power frequency.
4. The method of claim 1, wherein generating a pulse control signal to control the power switching module based on the second influencing parameter and a second amplitude derived from a reactive power setpoint, a reactive power actual measurement, comprises:
obtaining the second amplitude value according to the reactive power given value and the reactive power actual measurement value by using a first reactive ring;
obtaining a three-phase voltage given value according to the second influence parameter and the second amplitude by using the first reactive ring;
obtaining a current given value of a two-phase static coordinate system based on a three-phase voltage given value and the second influence parameter by using a voltage ring;
Carrying out current limiting treatment on the given value of the current in the two-phase static coordinate system to obtain a given value of the three-phase current;
Obtaining a voltage standard value of the two-phase static coordinate system based on the three-phase current given value, the three-phase current actual measurement value and the second influence parameter by using a current loop;
And modulating the voltage standard value of the two-phase static coordinate system, and generating the pulse control signal to control the power switch module.
5. The method of claim 4, wherein the current loop comprises a first proportional resonant controller matched to the frequency of the low frequency electrical energy, an input of the first proportional resonant controller comprising a second difference between the three-phase current setpoint and the three-phase current actual measurement, an output of the first proportional resonant controller comprising the two-phase static coordinate system voltage standard value;
The center frequency of the first proportional resonance controller is lower than that of the second proportional resonance controller matched with the power frequency.
6. The method of claim 4, wherein the bandwidth of the first reactive loop is less than the bandwidth of a second reactive loop that matches the power frequency, the first reactive loop comprising a fourth PI controller or a second PID controller,
The method further comprises the steps of:
adjusting the proportional coefficient and/or the integral coefficient of the fourth PI controller to enable the bandwidth of the first reactive power loop to be lower than that of a second reactive power loop matched with the power frequency;
Or alternatively
And adjusting the proportional coefficient and/or the integral coefficient of the second PID controller so that the bandwidth of the first reactive power loop is lower than that of a second reactive power loop matched with the power frequency.
7. The method as recited in claim 1, further comprising:
before grid connection of the grid-formed low-frequency wind generating set, collecting a first influence parameter corresponding to the first phase-locked loop; obtaining a first frequency related parameter according to the first influence parameter; before and after grid connection of the grid-formed low-frequency wind generating set, if the first frequency related parameter exceeds a preset safety parameter range, sending a shutdown instruction to a main controller of the grid-formed low-frequency wind generating set so that the main controller controls the grid-formed low-frequency wind generating set to shutdown;
Or alternatively
Before grid connection of the grid-formed low-frequency wind generating set, collecting the first influence parameters corresponding to the first phase-locked loop; obtaining the first frequency-related parameter according to the first influence parameter; before grid connection of the grid-formed low-frequency wind generating set, if the first frequency related parameter exceeds the safety parameter range, sending the shutdown instruction to a main controller of the grid-formed low-frequency wind generating set; collecting the second influence parameters corresponding to the first synchronizing ring after the grid-connected low-frequency wind generating set is connected; obtaining a second frequency related parameter according to the second influence parameter; and after the grid connection of the grid-structured low-frequency wind generating set, if the second frequency related parameter exceeds the safety parameter range, sending the shutdown instruction to a main controller of the grid-structured low-frequency wind generating set.
8. The method according to any one of claims 1 to 7, wherein the frequency of the low frequency electrical energy is less than or equal to 20 hz.
9. The grid-structured low-frequency wind generating set is characterized by outputting low-frequency electric energy, wherein the frequency of the low-frequency electric energy is lower than the power frequency, and the grid-structured low-frequency wind generating set comprises a generator, a machine side converter, a direct current bus and a grid side converter which are electrically connected in sequence, wherein the grid side converter comprises a control module and a power switch module;
The control module is used for: before grid connection of the grid-formed low-frequency wind generating set, a first phase-locked loop is utilized to obtain a first influence parameter according to the three-phase voltage of the low-frequency electric energy output by the grid-side converter, wherein the first influence parameter comprises a first phase and/or a first frequency; after the grid connection of the grid-formed low-frequency wind generating set, a first synchronous ring is utilized to obtain a second influence parameter according to a direct current bus voltage given value and a direct current bus voltage actual measurement value of the direct current bus, the second influence parameter comprises a second phase and/or a second frequency, and the difference value between the second influence parameter and the first influence parameter is smaller than a preset impact threshold value; and generating a pulse control signal to control the power switch module based on the second influence parameter and a second amplitude value obtained according to the reactive power given value and the reactive power actual measurement value.
10. A wind power transmission system is characterized by comprising the grid-structured low-frequency wind power generator set, the low-frequency power transmission line and a power exchange station which are electrically connected in sequence,
The power conversion station is used for converting the low-frequency electric energy transmitted from the low-frequency transmission line into power frequency electric energy and transmitting the power frequency electric energy to a power grid.
CN202211336721.0A 2022-10-28 2022-10-28 Net-structured low-frequency wind generating set, control method thereof and wind power transmission system Pending CN117955165A (en)

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