CN117477550A - Subsynchronous oscillation suppression method based on PLL system optimal damping ratio - Google Patents

Subsynchronous oscillation suppression method based on PLL system optimal damping ratio Download PDF

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Publication number
CN117477550A
CN117477550A CN202311463459.0A CN202311463459A CN117477550A CN 117477550 A CN117477550 A CN 117477550A CN 202311463459 A CN202311463459 A CN 202311463459A CN 117477550 A CN117477550 A CN 117477550A
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subsynchronous
damping ratio
pll
optimal
current
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Inventor
王畅
石振江
姜宇
张立斌
郭昊
吕科
赵旷怡
杨林
夏曼曼
白坤
肖林
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Beijing Jingyan Electric Power Engineering Design Co ltd
State Grid Corp of China SGCC
Economic and Technological Research Institute of State Grid Hebei Electric Power Co Ltd
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Beijing Jingyan Electric Power Engineering Design Co ltd
State Grid Corp of China SGCC
Economic and Technological Research Institute of State Grid Hebei Electric Power Co Ltd
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Priority to CN202311463459.0A priority Critical patent/CN117477550A/en
Publication of CN117477550A publication Critical patent/CN117477550A/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
    • H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
    • 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
    • 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
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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)
  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention discloses a subsynchronous oscillation suppression method based on an optimal damping ratio of a PLL (phase locked loop) system, which belongs to the field of stable control of new energy systems and specifically comprises the following steps: according to input system parameters, respectively calculating a subsynchronous torque coefficient and a subsynchronous damping torque coefficient through a subsynchronous torque coefficient and subsynchronous damping torque coefficient formula; calculating the damping ratio of the PLL system according to the complex torque damping ratio formula; judging whether the damping ratio of the PLL system is in a target interval or not, and if not, starting subsynchronous oscillation suppression control; setting an optimal damping ratio according to the self requirement of the system; and obtaining the optimal current corresponding to the optimal damping ratio according to the relation between the damping ratio and the output current, and setting the optimal current as an additional current reference value. The invention can establish a relation between the subsynchronous oscillation damping ratio of the phase-locked loop and the output current of the fan, can ensure the damping requirement of the system, inhibit subsynchronous oscillation and improve the safety of wind power grid connection.

Description

Subsynchronous oscillation suppression method based on PLL system optimal damping ratio
Technical Field
The invention belongs to the field of new energy system stability control, and particularly relates to a subsynchronous oscillation suppression method based on an optimal damping ratio of a PLL (phase locked loop) system.
Background
In recent years, renewable energy is accessed into a power grid in a large scale, and in consideration of the influence of geographic and economic factors, the renewable energy is often accessed into the power grid in a cluster and long feeder line mode, and the short circuit ratio of the system is low, so that subsynchronous oscillation is generated due to the interaction of the renewable energy and a weak power grid. The wind turbine generator is connected with the grid through a power electronic converter, wherein a phase-locked loop (PLL) has obvious influence on system oscillation. The PLL calculates the phase angle and frequency from the voltage at the Point of Common Connection (PCC), thereby implementing the converter control dq coordinate tracking system dq coordinates. However, under the weak grid condition, the PLL and the grid-connected current loop are coupled through the PCC point voltage, and the improper parameter setting can help to increase the electric negative damping of the wind turbine. Regarding the subsynchronous oscillation problem caused by fan phase locking, a clear oscillation suppression mechanism is still needed at present, so that the controller design can be further optimized. The relation between the damping ratio of the PLL system and the active current of the wind turbine can be established by a complex torque method widely applied to researching the damping characteristic of the power system, and a new solution can be provided for restraining subsynchronous oscillation caused by fan phase locking.
Disclosure of Invention
In order to solve the above problems, the present invention provides a method for suppressing subsynchronous oscillation based on an optimal damping ratio of a PLL system, comprising the steps of:
acquiring a subsynchronous torque coefficient and a subsynchronous damping torque coefficient according to input system parameters of the PLL system, and obtaining a damping ratio of the PLL system according to a complex torque method;
obtaining an optimal current corresponding to the optimal damping ratio according to the relation between the damping ratio and the output current by setting the optimal damping ratio of the PLL system, and setting the optimal current as an additional current reference value;
and processing by using a PI controller by utilizing the difference value between the active current and the optimal current at the outlet bus of the wind power plant, limiting the additional current reference value not to be larger than the rated current of the wind turbine generator, and finally injecting the additional current reference value into an inner loop current control link of the controller to inhibit and control subsynchronous oscillation.
Preferably, in the process of acquiring the subsynchronous torque coefficient, the grid-connected voltage U of the wind turbine generator is obtained according to the initial moment s First phase-locked loop parameter K PLL_I Grid frequency omega s Line inductance L l And output current active value i rd0 And acquiring a subsynchronous torque coefficient.
Preferably, in the process of acquiring the subsynchronous damping torque coefficient, the grid-connected voltage U of the wind turbine generator at the initial moment is used s First phase-locked loop parameter K PLL_I Second phase-locked loop parameter K PLL_P Grid frequency omega s Line inductance L l And output current active value i rd0 And obtaining a subsynchronous damping torque coefficient.
Preferably, in the process of acquiring the damping ratio of the PLL system, the damping ratio is acquired by acquiring a subsynchronous torque coefficient and a subsynchronous damping torque coefficient based on a complex torque method.
Preferably, in the process of performing the suppression control on the subsynchronous oscillation, a target interval of a system damping ratio is set according to the stability requirement of the wind turbine system, whether the obtained damping ratio of the PLL system is in the target interval is judged, and if not, the suppression control is performed on the subsynchronous oscillation.
The invention discloses a subsynchronous oscillation suppression system based on an optimal damping ratio of a PLL system, which is used for realizing a subsynchronous oscillation suppression method and comprises the following steps:
the data acquisition module is used for acquiring grid-connected voltage U of the wind turbine generator s First phase-locked loop parameter K PLL_I Second phase-locked loop parameter K PLL_P Grid frequency omega s Line inductance L l And output current active value i rd0 ；
The data processing module is used for acquiring a subsynchronous torque coefficient and a subsynchronous damping torque coefficient according to the data acquired by the data acquisition module and obtaining the damping ratio of the PLL system according to a compound torque method;
the judging module is used for judging whether the damping ratio of the PLL system is in the target section according to the set target section of the system damping ratio, if so, continuously detecting the system damping ratio, and if not, generating a control instruction for executing subsynchronous oscillation suppression;
the reference value setting module is used for obtaining an optimal current corresponding to the optimal damping ratio according to the relation between the damping ratio and the output current by setting the optimal damping ratio of the PLL system, and setting the optimal current as an additional current reference value;
and the suppression module is used for processing the difference value between the active current at the outlet bus of the wind power plant and the optimal current through the PI controller according to the acquired control instruction, limiting the additional current reference value not to be larger than the rated current of the wind power generator, and finally injecting the additional current reference value into an inner loop current control link of the controller to perform suppression control on subsynchronous oscillation.
Preferably, the data processing module is further configured to perform grid-connected voltage U of the wind turbine according to the initial time s First phase-locked loop parameter K PLL_I Grid frequency omega s Line inductance L l And output current active value i rd0 And acquiring a subsynchronous torque coefficient.
Preferably, the data processing module is further configured to perform grid-connected voltage U of the wind turbine according to the initial time s First phase-locked loop parameter K PLL_I Second phase-locked loop parameter K PLL_P Grid frequency omega s Line inductance L l And output current active value i rd0 And obtaining a subsynchronous damping torque coefficient.
Preferably, the data processing module is further configured to obtain the damping ratio by obtaining a subsynchronous torque coefficient and a subsynchronous damping torque coefficient based on a complex torque method.
The invention discloses the following technical effects:
the invention can establish a relation between the subsynchronous oscillation damping ratio of the phase-locked loop and the output current of the fan, can ensure the damping requirement of the system, inhibit subsynchronous oscillation and improve the safety of wind power grid connection.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method according to the present invention;
FIG. 2 is a grid-connected structure diagram of a direct-drive fan according to an embodiment of the invention;
fig. 3 is a block diagram of an inner loop control structure of a current converter according to an embodiment of the present invention;
fig. 4 is a block diagram of a phase-locked loop control structure according to an embodiment of the present invention;
FIG. 5 is a graph showing the dynamic relationship between the oscillation damping ratio and the output active current of a PLL system according to an embodiment of the present invention;
FIG. 6 is an additional current control block diagram based on the optimal damping ratio of the phase locked loop system according to an embodiment of the present invention;
FIG. 7 is a power response of a blower without additional control in accordance with an embodiment of the present invention;
FIG. 8 is a fan power response under additional control in accordance with an embodiment of the present invention.
Detailed Description
For the purposes of making the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, which are generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present application, as provided in the accompanying drawings, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, are intended to be within the scope of the present application.
As shown in fig. 1-8, the present invention provides a method for suppressing subsynchronous oscillation based on an optimal damping ratio of a PLL system, which specifically includes the following steps:
acquiring a subsynchronous torque coefficient and a subsynchronous damping torque coefficient according to input system parameters of the PLL system, and obtaining a damping ratio of the PLL system according to a complex torque method;
obtaining an optimal current corresponding to the optimal damping ratio according to the relation between the damping ratio and the output current by setting the optimal damping ratio of the PLL system, and setting the optimal current as an additional current reference value;
and processing by using a PI controller by utilizing the difference value between the active current and the optimal current at the outlet bus of the wind power plant, limiting the additional current reference value not to be larger than the rated current of the wind turbine generator, and finally injecting the additional current reference value into an inner loop current control link of the controller to inhibit and control subsynchronous oscillation.
Further preferably, in the subsynchronous oscillation suppression method provided by the invention, in the process of obtaining the subsynchronous torque coefficient, the grid-connected voltage U of the wind turbine generator at the initial moment is used for controlling the grid-connected voltage U of the wind turbine generator s First phase-locked loop parameter K PLL_I Grid frequency omega s Line inductance L l And output current active value i rd0 And acquiring a subsynchronous torque coefficient.
Further preferably, in the subsynchronous oscillation suppression method provided by the invention, in the process of obtaining the subsynchronous damping torque coefficient, the grid-connected voltage U of the wind turbine generator set at the initial moment is used for controlling the grid-connected voltage U of the wind turbine generator set s First phase-locked loop parameter K PLL_I Second phase-locked loop parameter K PLL_P Grid frequency omega s Line inductance L l And output current active value i rd0 And acquiring a subsynchronous torque coefficient.
Still preferably, in the subsynchronous oscillation suppression method provided by the present invention, in a process of obtaining a damping ratio of a PLL system, the damping ratio is obtained by obtaining a first state variable Δω and a second state variable Δθ based on a complex torque method, where ω is a rotation angle frequency signal and θ is a phase signal.
Still preferably, in the method for suppressing subsynchronous oscillation provided by the present invention, in the process of suppressing subsynchronous oscillation, a target interval of a system damping ratio is set according to a stability requirement of a wind turbine system, and whether the obtained damping ratio of the PLL system is in the target interval is determined, if not, the subsynchronous oscillation is suppressed.
The invention discloses a subsynchronous oscillation suppression system based on an optimal damping ratio of a PLL system, which is used for realizing the subsynchronous oscillation suppression method provided by the invention, and comprises the following steps:
the data acquisition module is used for acquiring grid-connected voltage U of the wind turbine generator s First phase-locked loop parameter K PLL_I Second phase-locked loop parameter K PLL_P Grid frequency omega s Line inductance L l And output current active value i rd0 ；
The data processing module is used for acquiring a subsynchronous torque coefficient and a subsynchronous damping torque coefficient according to the data acquired by the data acquisition module and obtaining the damping ratio of the PLL system according to a compound torque method;
the judging module is used for judging whether the damping ratio of the PLL system is in the target section according to the set target section of the system damping ratio, if so, continuously detecting the system damping ratio, and if not, generating a control instruction for executing subsynchronous oscillation suppression;
the reference value setting module is used for obtaining an optimal current corresponding to the optimal damping ratio according to the relation between the damping ratio and the output current by setting the optimal damping ratio of the PLL system, and setting the optimal current as an additional current reference value;
and the suppression module is used for processing the difference value between the active current at the outlet bus of the wind power plant and the optimal current through the PI controller according to the acquired control instruction, limiting the additional current reference value not to be larger than the rated current of the wind power generator, and finally injecting the additional current reference value into an inner loop current control link of the controller to perform suppression control on subsynchronous oscillation.
Example 1: the invention provides an additional current subsynchronous oscillation suppression method based on an optimal damping ratio of a PLL system, which specifically comprises the following steps:
step 1: according to input system parameters, respectively calculating a subsynchronous torque coefficient and a subsynchronous damping torque coefficient through a subsynchronous torque coefficient and subsynchronous damping torque coefficient formula;
step 2: calculating the damping ratio of the PLL system according to the complex torque damping ratio formula;
step 3: judging whether the damping ratio of the PLL system is in a target interval or not, and if not, starting subsynchronous oscillation suppression control;
step 4: setting an optimal damping ratio according to the self requirement of the system;
step 5: and obtaining the optimal current corresponding to the optimal damping ratio according to the relation between the damping ratio and the output current, and setting the optimal current as an additional current reference value.
Permanent magnet synchronous generator (permanent magnetic synchronous generator, PMSG) is connected to infinite power grid through transmission line, FIG. 2 is grid-connected structure diagram thereof, R c And L c Resistance and inductance of the converter station, R l And L l The resistance and the inductance of the power transmission line are respectively, u c For the voltage of the converter, u p Is the voltage of the common connection point (point of common coupling, PCC), u s Is the voltage of an infinite grid.
The voltage balance equation of the grid-connected structure can be established under the dq coordinate system as follows
Wherein i is rd 、i rq Dividing the current on the converter into values on the dq axis, u cd 、u cq Divided into values of converter voltage on dq axis, u pd 、u pq Divided into values of the common junction voltage on the dq axis, ω s To fix the angular frequency of the system.
The goal of the inner loop current controller in the VSC control system is to keep the dq component of the converter current consistent with the reference current, as shown in fig. 3, the function of the control can be written as
Wherein K is d_P 、K d_I For the d-axis PI parameter, K q_P 、K q_I For the q-axis PI parameter, i rd_ref 、i rd_ref Respectively dq axis current reference values.
In order to derive the synchronisation and damping coefficients of the investigated system by means of the complex torque method, the PLL is first converted into a second order structure similar to the movement of the synchronous generator rotor. According to the structure of the PLL shown in fig. 4, the linearization model thereof can be written as
Wherein ω is a rotation angle frequency signal, θ is a phase signal, K PLL_P And K PLL_I Is the PI parameter of the PLL.
Combining formulas (1) - (4), and performing Laplace transformation on the linearized equation to obtain a frequency domain equation
The time constant t of the current inner loop control is the ratio of the internal resistance and reactance of the converter to the PI parameter of the inner loop, namely
To ensure fast regulation characteristics of the current inner loop in the converter, t is typically set to a few milliseconds. Thus, R is c Relative to K d_P And K d_I Can be ignored and expressed as
Δu pq ＝-u pd0 Δθ-G(s)Δθ (7)
Wherein,
the transfer function G(s) may reflect the effect of the dynamics of the grid on the PLL performance.
The PLL model taking into account the dynamic effects of the line impedance and current inner loop control can be written as
According to the complex torque method, the system damping torque is proportional to the state variable Δω and the system synchronizing torque is proportional to the state variable Δθ. Consider the relationship of sΔθ=Δω, and let s=jω n The substitution formula (9) includes:
u can be set up as pd0 From i rd0 And i rq0 Expressed as:
the analytical expressions for obtaining the synchronization coefficient and the damping coefficient are as follows:
in general, K PLL_P ＜＜K PLL_I 、ω n τ < 1 and q=0, then the formulas (12) and (13) can be expressed as:
from equation (10), the damping ratio of the PLL system can be calculated as:
generally speaking, the system phase-locked loop parameter K PLL_P ，K PLL_I The dynamic relationship between the damping ratio and the output active current can be plotted according to equation (16) with the above parameters known, without changing the voltage, frequency, and line reactance, as shown in fig. 5. Of the reference parameters of the graph, K PLL_P ＝7，K PLL_I =70, rated voltage and frequency.
In consideration of the system stability requirement, the damping ratio target interval (ζ min ＜ζ＜ζ max ) Calculation is performed using equation (16) to obtain the line desired current range (i min <i rd <i max ). In addition, if ζ=ζ is based on the optimal damping ratio op By performing calculation, the line optimum current i can be obtained by using the equation (16) as well op 。
Therefore, the grid-connected voltage Us of the wind turbine generator at the initial moment is input, and the phase-locked loop parameter K is input PLL_P 、K PLL_I Grid frequency omega s Line inductance L l And an output current active value i rd0 The current PLL system subsynchronous oscillation damping ratio can be obtained, and when the PLL system oscillation damping ratio exceeds the set damping ratio target interval, subsynchronous oscillation risk exists, and subsynchronous oscillation suppression control can be started at this time.
In order to realize the suppression of the sub-synchronous oscillation of the PLL system, the grid-connected voltage U of the wind turbine generator set at the initial moment is input s Phase-locked loop parameter K PLL_P 、K PLL_I Grid frequency omega s Line inductance L l And the optimal damping ratio z of the system settings op According to the relation between the subsynchronous oscillation damping ratio of the phase-locked loop and the output current of the fan, the optimal current i is obtained op . Based on the optimal current i op The invention provides an additional current controller of a wind turbine generator, as shown in fig. 6. The controller feeds back the difference value between the active current and the optimal damping current at the outlet bus of the wind power plant, obtains an additional current signal through an additional current control link, and finally is injected into an inner loop current control link of the controller. The controller can increase the damping of the system when the system lacks damping, thereby inhibiting subsynchronous oscillationActing as a medicine.
In order to verify the suppression effect of the additional current control method based on the optimal damping ratio on subsynchronous oscillation caused by a fan phase-locked loop, a direct-drive fan grid-connected simulation system is built by using DIgSILENT/PowerFactoy software. The simulation system adopts an IEEE3 machine 9 node system, comprises a wind power plant, consists of 50X 2MW double-fed units, and is provided with a 10MW/39kAh (10 kV) storage battery. Three synchronous generator sets (G) 1 ,G 2 ,G 3 ) The capacities were 190MW, 150MW and 120MW, respectively. The wind power storage system performs power transmission through a double-loop circuit. In the simulation, the initial wind speed was set to 8m/s.
When the simulation is set to 0s, the outgoing line is cut off once. FIG. 7 is an active power dynamic response of a wind turbine without additional control. When the wind power plant outgoing line is cut off for one time, the reactance of the outgoing transmission line is increased, SCR at the grid-connected bus is reduced, damping of a PLL oscillation loop in the system is weakened, the active power output by the wind power plant is caused to generate subsynchronous oscillation, and even the system is caused to generate continuous oscillation. FIG. 8 shows that the active power dynamic response of the wind turbine generator set controlled by the method is additionally arranged, so that the system obtains a remarkable oscillation suppression effect, and the safety of wind power grid connection in a weak electric network is greatly improved.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or 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, embedded processor, 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, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
In the description of the present invention, it should be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims (9)

1. The subsynchronous oscillation suppression method based on the optimal damping ratio of the PLL system is characterized by comprising the following steps of:
acquiring a subsynchronous torque coefficient and a subsynchronous damping torque coefficient according to input system parameters of a PLL system, and obtaining a damping ratio of the PLL system according to a complex torque method;
obtaining an optimal current corresponding to the optimal damping ratio according to the relation between the damping ratio and the output current by setting the optimal damping ratio of the PLL system, and setting the optimal current as an additional current reference value;
and processing by using a PI controller according to the difference value between the active current at the outlet bus of the wind power plant and the optimal current, limiting the additional current reference value not to be larger than the rated current of the wind power generator, and finally injecting the additional current reference value into an inner loop current control link of the controller to inhibit and control subsynchronous oscillation.
2. The method for suppressing subsynchronous oscillation based on the optimal damping ratio of the PLL system according to claim 1, wherein:
in the process of acquiring the subsynchronous torque coefficient, grid-connected voltage U of the wind turbine generator at the initial moment s First phase-locked loop parameter K PLL_I Grid frequency omega s Line inductance L l And output ofCurrent active value i rd0 And acquiring the subsynchronous torque coefficient.
3. The method for suppressing subsynchronous oscillation based on the optimal damping ratio of the PLL system according to claim 2, wherein:
in the process of acquiring the subsynchronous damping torque coefficient, the grid-connected voltage U of the wind turbine generator set at the initial moment is obtained s First phase-locked loop parameter K PLL_I Second phase-locked loop parameter K PLL_P Grid frequency omega s Line inductance L l And output current active value i rd0 And acquiring the subsynchronous damping torque coefficient.
4. A method of subsynchronous oscillation suppression based on the optimal damping ratio of a PLL system as claimed in claim 3, wherein:
in the process of acquiring the damping ratio of the PLL system, the damping ratio is acquired by acquiring a subsynchronous torque coefficient and a subsynchronous damping torque coefficient based on the complex torque method.
5. The method for subsynchronous oscillation suppression based on the optimal damping ratio of the PLL system according to claim 4, wherein:
in the process of suppressing and controlling the subsynchronous oscillation, a target interval of a system damping ratio is set according to the stability requirement of the wind turbine system, whether the obtained damping ratio of the PLL system is in the target interval or not is judged, and if not, the subsynchronous oscillation is suppressed and controlled.
6. A method for subsynchronous oscillation suppression based on an optimal damping ratio of a PLL system according to any one of claims 1-5, wherein,
a subsynchronous oscillation suppression system for implementing a subsynchronous oscillation suppression method includes:
the data acquisition module is used for acquiring grid-connected voltage U of the wind turbine generator s First phase-locked loop parameter K PLL_I Second phase-locked loop parameter K PLL_P Grid frequency omega s Line inductance L l And output current active value i rd0 ；
The data processing module is used for acquiring a subsynchronous torque coefficient and a subsynchronous damping torque coefficient according to the data acquired by the data acquisition module and obtaining the damping ratio of the PLL system according to a compound torque method;
the judging module is used for judging whether the damping ratio of the PLL system is in the target section according to the set target section of the system damping ratio, if so, continuing to detect the system damping ratio, and if not, generating a control instruction for executing subsynchronous oscillation suppression;
the reference value setting module is used for obtaining an optimal current corresponding to the optimal damping ratio according to the relation between the damping ratio and the output current by setting the optimal damping ratio of the PLL system, and setting the optimal current as an additional current reference value;
and the suppression module is used for processing the difference value between the active current at the outlet bus of the wind power plant and the optimal current through the PI controller according to the acquired control instruction, limiting the additional current reference value not to be larger than the rated current of the wind power generator, and finally injecting the additional current reference value into an inner loop current control link of the controller to perform suppression control on subsynchronous oscillation.
7. The method for subsynchronous oscillation suppression based on the optimal damping ratio of the PLL system according to claim 6, wherein:
the data processing module is further used for generating grid-connected voltage U of the wind turbine generator according to the initial moment s First phase-locked loop parameter K PLL_I Grid frequency omega s Line inductance L l And output current active value i rd0 And acquiring the subsynchronous torque coefficient.
8. The method for subsynchronous oscillation suppression based on the optimal damping ratio of the PLL system according to claim 7, wherein:
the data processing module is also used for generating grid-connected voltage of the wind turbine generator set according to the initial momentU s First phase-locked loop parameter K PLL_I Second phase-locked loop parameter K PLL_P Grid frequency omega s Line inductance L l And output current active value i rd0 And acquiring the subsynchronous damping torque coefficient.
9. The method for suppressing subsynchronous oscillation based on the optimal damping ratio of the PLL system according to claim 8, wherein:
the data processing module is further used for obtaining the damping ratio by obtaining a subsynchronous torque coefficient and a subsynchronous damping torque coefficient based on the complex torque method.
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