CN113162035A - Method and system for suppressing low-frequency oscillation of power grid by additional damping of virtual synchronous wind power plant - Google Patents

Method and system for suppressing low-frequency oscillation of power grid by additional damping of virtual synchronous wind power plant Download PDF

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CN113162035A
CN113162035A CN202110437792.9A CN202110437792A CN113162035A CN 113162035 A CN113162035 A CN 113162035A CN 202110437792 A CN202110437792 A CN 202110437792A CN 113162035 A CN113162035 A CN 113162035A
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power
wind
control
virtual synchronous
additional damping
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CN113162035B (en
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杨蕾
向川
邢超
蔡光
郭成
马遵
许守东
奚鑫泽
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Electric Power Research Institute of Yunnan Power Grid Co Ltd
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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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F03D7/022—Adjusting aerodynamic properties of the blades
    • F03D7/0224—Adjusting blade pitch
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F03D7/0272—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor by measures acting on the electrical generator
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F03D7/04—Automatic control; Regulation
    • F03D7/042—Automatic control; Regulation by means of an electrical or electronic controller
    • F03D7/043—Automatic control; Regulation by means of an electrical or electronic controller characterised by the type of control logic
    • F03D7/046—Automatic control; Regulation by means of an electrical or electronic controller characterised by the type of control logic with learning or adaptive control, e.g. self-tuning, fuzzy logic or neural network
    • 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
    • H02J3/381—Dispersed generators
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/007—Control circuits for doubly fed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/04—Control effected upon non-electric prime mover and dependent upon electric output value of the 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
    • 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
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P2101/00—Special adaptation of control arrangements for generators
    • H02P2101/15—Special adaptation of control arrangements for generators for wind-driven turbines
    • 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
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    • 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
    • Y02E10/72—Wind turbines with rotation axis in wind direction
    • 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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Abstract

The application provides a method and a system for inhibiting low-frequency oscillation of a power grid by additional damping of a virtual synchronous wind power plant. Secondly, when an additional damping controller is designed, in order to enable the double-fed fan to provide output in both a positive half period and a negative half period of oscillation, the double-fed fan is subjected to load shedding operation in a Maximum Power Point Tracking (MPPT) region through overspeed control, and the double-fed fan is subjected to load shedding operation in a rotating speed constant region through pitch angle control; meanwhile, a wind speed self-adaptive device is designed, and the capability of the controller for adapting to wind speed changes is improved; the method has the advantages that the weakening effect of the double-fed wind generating set on system damping is reduced, the rotor of the double-fed wind generating set is subjected to overspeed control, the rotor deviates from a maximum power tracking curve, and a certain active standby is reserved.

Description

Method and system for suppressing low-frequency oscillation of power grid by additional damping of virtual synchronous wind power plant
Technical Field
The application relates to the field of wind power generation and power system control, in particular to a method and a system for suppressing low-frequency oscillation of a power grid by adding damping to a virtual synchronous wind power plant.
Background
With the proportion of new energy power generation in each region power grid becoming higher and higher, the system stability problem brought by new energy grid connection also becomes more and more important, including the low-frequency oscillation phenomenon.
For the low-frequency oscillation phenomenon, the suppression is performed by utilizing a negative damping mechanism, a forced oscillation mechanism, a bifurcation theory and the like. According to a negative damping mechanism, a characteristic root real part corresponding to the rotating speed of a rotor is changed from negative to positive by high amplification factor and quick excitation commonly adopted by a synchronous generator, when oscillation occurs, oscillation current can flow through a rotor and a stator loop of the generator to be directly connected with a power grid, the oscillation current can cause the current of a damping loop and an excitation loop to oscillate, and because the two loops have resistors, the damping system of the synchronous generator can oscillate and generate a damping torque with the same phase as the rotating speed deviation. At present, the main wind generating set is a double-fed wind generating set, and the low-frequency oscillation of the system is restrained, and the traditional vector control is mainly focused on.
However, the grid connection is realized through the power electronic device, the rotating speed of the rotor of the double-fed wind turbine generator is completely decoupled from the system frequency due to the characteristics of the converter, the double-fed wind turbine generator has certain inertia and damping, and the inertia and the damping of the wind turbine are 'hidden' through decoupling control. When power oscillation occurs in a power grid, active power and reactive power output by the double-fed wind turbine generator cannot change along with the change of system power, and the double-fed wind turbine generator lacks the damping capacity for the system power oscillation.
Disclosure of Invention
The application provides a method and a system for restraining low-frequency oscillation of a power grid by adding damping to a virtual synchronous wind power plant, and aims to solve the technical problems that in the prior art, the output power of a double-fed wind generating set cannot respond to the power change of a system, and the suppression of the low-frequency oscillation phenomenon is not contributed.
In order to achieve the above purpose, the embodiments of the present application adopt the following technical solutions:
in a first aspect, a method for suppressing low-frequency oscillation of a power grid by additional damping of a virtual synchronous wind farm is provided, and the method comprises the following steps:
acquiring hidden inertia and damping of a rotor of the doubly-fed wind generating set through virtual synchronous control;
providing additional damping;
measuring the current wind speed in real time;
when the current wind speed is higher than the cut-in wind speed and lower than the rated wind speed, carrying out load shedding control on the double-fed wind generating set, and carrying out wind speed self-adaptive control on the fan;
according to the active power output by the double-fed wind generating set through load shedding control, judging whether the active power oscillates or not;
and when the active power oscillates, performing additional damping control on the virtual synchronous wind power plant.
Further, when the current wind speed is larger than the rated wind speed, the reserved standby power is controlled through the pitch angle.
Further, the load shedding control of the double-fed wind generating set comprises overspeed load shedding control and pitch angle control;
fitting the maximum power tracking curve in the MPPT area to obtain the rotor optimal rotating speed reference value omegaref1Mechanical power P output by the fanmThe relationship between them is:
Figure BDA0003033828980000021
speed reference value omega under overspeed load shedding controlrefMechanical power P output by the fanmThe relationship between them is:
Figure BDA0003033828980000022
in a rotating speed constant region, load shedding is controlled through a pitch angle, and the initial pitch angle is determined by adopting the following method:
Figure BDA0003033828980000023
Figure BDA0003033828980000024
Figure BDA0003033828980000025
in the formula, CpAnd CPLThe coefficient of wind energy utilization before and after load shedding, d is the load shedding coefficient, lambda2As tip speed ratio, omegamaxThe maximum rotating speed is set as the rotating speed,r is the radius of the fan blade, and v is the wind speed.
Further, the adaptive control of wind speed in the MPPT area comprises the following steps:
input parasitic power variation Δ Pw1Determined by external oscillation power, and the reference value omega of the rotor rotating speed after adding additional powerref2Comprises the following steps:
Figure BDA0003033828980000027
in the formula, item 1 is the normal output of the fan; term 2 includes only the power Δ P of the external oscillationw1The determined additional power, independent of the wind speed; item 3 is PmAnd Δ Pw1In which P ismThe size is related to the wind speed and is the item to be compensated.
Further, obtain double-fed wind generating set through virtual synchronous control, include:
Figure BDA0003033828980000026
in the formula, deltaVSGIs the power angle, omega, of the inverterVSGAngular velocity of VSG, virtual moment of inertia of VSG, DpVirtual damping coefficient, omega, for VSG active ring0For rating angular frequency, U, of the networkmFor effective value of grid-connected point voltage, KqAnd KvRespectively a reactive scaling factor and a voltage scaling factor.
Further, according to the load shedding control of the doubly-fed wind turbine generator system to output active power, the method comprises the following steps:
obtaining active power variation;
obtaining a control signal by carrying out proportion, filtering, phase compensation and amplitude limiting on the active power variable quantity;
power oscillation is obtained by the control signal.
In a second aspect, a system for additional damping and suppressing low-frequency oscillation of a power grid of a virtual synchronous wind farm is provided, and the system comprises:
the virtual synchronous machine is used for excavating hidden inertia and damping of the rotor of the doubly-fed wind generating set;
an additional damping controller for providing additional damping;
and the wind speed self-adaption device is used for adding the additional damping controller to adapt to wind speed change.
Further, the system further comprises a load shedding controller;
the load controller includes overspeed load shedding control and pitch angle control.
The application provides a method and a system for inhibiting low-frequency oscillation of a power grid by additional damping of a virtual synchronous wind power plant. Secondly, when an additional damping controller is designed, in order to enable the double-fed fan to provide output in the positive half period and the negative half period of oscillation, the double-fed fan is subjected to load shedding operation in a maximum power tracking area through overspeed control, and the double-fed fan is subjected to load shedding operation in a rotating speed constant area through pitch angle control; meanwhile, a wind speed self-adaptive device is designed, and the capability of the controller for adapting to wind speed changes is improved.
The virtual synchronous machine control technology is adopted, inertia and damping of the double-fed wind generating set are increased, and weakening effect of the double-fed wind generating set on system damping is reduced. After the additional damping controller is designed on the double-fed wind generating set, the double-fed wind generating set can generate more or less power according to the change of the power in the system. In order to enable the double-fed wind generating set to provide output in both the positive half cycle and the negative half cycle of oscillation generation, overspeed load shedding control and pitch angle control are carried out on the double-fed wind generating set. And in a maximum power tracking area, overspeed control is performed on a rotor of the doubly-fed wind generating set, so that the rotor deviates from a maximum power tracking curve and a certain active standby is reserved. Meanwhile, partial capacity is stored in the form of kinetic energy in the rotor of the fan, and the change of system power is responded quickly. When the rotating speed of the rotor reaches the maximum rotating speed, certain active power is reserved for standby through the pitch angle control. According to mathematical analysis, the output additional power of the doubly-fed wind generating set is greatly influenced by the wind speed. In order to reduce the influence of the wind speed on the output additional power, the additional power output by the fan is only determined by the external oscillation power, the output power of the double-fed wind generating set is compensated, and the self-adaptive control of the wind speed is realized. And acquiring the quantity related to low-frequency oscillation in the system on a power transmission line, and controlling the active power output by the double-fed wind generating set under the action of an additional damping controller on an active control loop of the virtual synchronous fan.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a DFIG grid-connected structure according to an embodiment of the application;
FIG. 2 is a main circuit diagram of a virtual synchronous machine according to an embodiment of the present application;
FIG. 3 is a block diagram of a virtual synchronizer control of an embodiment of the present application;
FIG. 4 is a schematic diagram of a virtual synchronous wind farm additional damping control method according to an embodiment of the application;
FIG. 5 is a flow chart of additional damping control of a virtual synchronous wind farm according to an embodiment of the present application;
FIG. 6 is a simplified system simulation architecture diagram of an embodiment of the present application;
FIG. 7 is a natural wind simulation diagram of an embodiment of the present application;
fig. 8 is a diagram of active power change on a transmission line when a conventional control method and a virtual synchronous machine are used for control after a three-phase short circuit fault according to an embodiment of the present application;
FIG. 9 is a graph of active power changes on transmission lines before and after additional damping of a virtual synchronous wind farm after a three-phase short circuit fault according to the embodiment of the application;
fig. 10 is a graph of active power change on a transmission line after damping is added to a virtual synchronous wind farm at different wind speeds after a three-phase short-circuit fault according to the embodiment of the application.
Detailed Description
In order to make the technical solutions better understood by those skilled in the art, 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 obvious that the described embodiments are only partial embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
It should be noted that the terms "first," "second," and the like in the description and claims of this application and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The double-fed wind generating set has the function of Maximum Power Point Tracking (MPPT).
The present application is described in further detail below with reference to the attached drawing figures:
the embodiment of the application provides a method for inhibiting low-frequency oscillation of a power grid by additional damping of a virtual synchronous wind power plant, which comprises the following steps:
acquiring hidden inertia and damping of a rotor of the doubly-fed wind generating set through virtual synchronous control;
providing additional damping;
measuring the current wind speed in real time;
when the current wind speed is higher than the cut-in wind speed and lower than the rated wind speed, carrying out load shedding control on the double-fed wind generating set, and carrying out wind speed self-adaptive control on the fan;
according to the active power output by the double-fed wind generating set through load shedding control, judging whether the active power oscillates or not;
and when the active power oscillates, performing additional damping control on the virtual synchronous wind power plant.
Fig. 1 is a schematic diagram of a doubly-fed wind turbine grid-connected structure. The DFIG of the doubly-fed wind generating set in the figure comprises a wind turbine, a frequency converter, a doubly-fed generator and the like, and virtual synchronous machine control and additional damping control are mainly embodied in the improvement of the structure of the frequency converter.
Wind turbine for capturing wind energy P through bladesbAnd mechanical energy P converted therefrommRespectively as follows:
Figure BDA0003033828980000051
in the formula, rho is the air density of the location of the wind turbine, R is the radius of a wind wheel blade, v is the wind speed, lambda is the tip speed ratio, beta is the pitch angle, CpThe conversion efficiency of wind energy to mechanical energy is expressed by the expression:
Figure BDA0003033828980000052
the main circuit diagram of the virtual synchronous machine is shown in fig. 2, and a three-phase inverter bridge is composed of 6 field effect transistors (MOSFETs) and 6 anti-parallel diodes. u. ofga,ugb,ugcThe inductors L1, L2 and the capacitor C form an LCL type filter with excellent high-frequency harmonic suppression capability for a three-phase power grid.
The virtual synchronous machine simulates a conventional synchronous generator and can equivalently consider the middle point voltage e of a bridge arma、ebAnd ecFor the virtual synchronous generator internal potential, the corresponding value of the virtual synchronous generator internal potential in the dq coordinate system is edAnd eq；ia、ibAnd icCorresponding value in dq coordinate system is idAnd iq(ii) a L1 is the synchronous reactance of the synchronous machine, ua0、ub0And uc0Is the terminal voltage of the virtual synchronous machine.
In fig. 3, the control part of the virtual synchronous machine is divided into an active loop and a reactive loop, and the output of the control part acts on Q1-Q6 of fig. 2 as a modulation wave of PWM inversion. The active loop simulates a rotor motion equation of a synchronous machine, and the output of the active loop determines the frequency and phase angle of the potential in the VSG); the reactive control simulates the primary voltage regulation characteristic of the synchronous machine, and the output of the synchronous machine determines the amplitude of the potential in the VSG. The control block diagram of the virtual synchronous machine is shown in fig. 3, and the mathematical equation of the VSG is as follows:
Figure BDA0003033828980000061
in the formula, deltaVSGIs the power angle, omega, of the inverterVSGAngular velocity of VSG, virtual moment of inertia of VSG, DpVirtual damping coefficient, omega, for VSG active ring0For rating angular frequency, U, of the networkmFor effective value of grid-connected point voltage, KqAnd KvRespectively a reactive scaling factor and a voltage scaling factor. The control of the additional damping of the double-fed fan is mainly embodied in the control of an active loop of the virtual synchronous machine, and a droop control method which is relatively common and easy to control and is shown in figure 2 is adopted for a reactive loop of the double-fed fan.
In the MPPT maximum power tracking area, when the pitch angle of the fan is 0, the fan can realize maximum power tracking at a fixed wind speed. Fitting the maximum power tracking curve in the MPPT area to obtain the rotor optimal rotating speed reference value omegaref1Mechanical power P output by the fanmThe relationship between them is:
Figure BDA0003033828980000062
in order to enable the fan to have sufficient standby power, the doubly-fed fan is subjected to load shedding control. When the wind speed is in the middle or low wind speed, the doubly-fed fan exceeds the speed of the rotorAnd (4) speed control, so that the fan operation curve deviates from the maximum power tracking curve for load shedding. Speed reference value omega under overspeed load shedding controlrefMechanical power P output by the fanmThe relationship between them is:
Figure BDA0003033828980000063
in a rotating speed constant region, load shedding is controlled through a pitch angle, and the initial pitch angle is determined by adopting the following method:
Figure BDA0003033828980000064
Figure BDA0003033828980000065
Figure BDA0003033828980000066
in the formula, CpAnd CPLThe coefficient of wind energy utilization before and after load shedding, d is the load shedding coefficient, lambda2As tip speed ratio, omegamaxThe maximum rotating speed is R is the radius of the fan blade, and v is the wind speed.
From the above analysis, it can be known that the output mechanical power of the wind turbine varies with the wind speed. However, we hope that the input additional power variation Δ P is not influenced by the external wind speedw1Determined by external oscillation power, and the reference value omega of the rotor rotating speed after adding additional powerref2Comprises the following steps:
Figure BDA0003033828980000071
in the formula, item 1 is the normal output of the fan; term 2 includes only the power Δ P of the external oscillationw1The determined additional power, independent of the wind speed; item 3 is PmAnd Δ Pw1In which P ismThe size is related to the wind speed and is the item to be compensated.
The double-fed fan is connected to the grid through the power electronic device, and the output power of the unit cannot respond to the external power change. The introduction of the virtual synchronous control method can increase the contribution of the machine set to the system damping, and has a certain inhibiting effect on the low-frequency oscillation of the system. Meanwhile, the control structure of the new energy unit is adjusted, so that the new energy unit has better capability of inhibiting low-frequency oscillation.
An additional damping device is designed on an active ring of the virtual synchronous wind power plant. The double-fed fan additional damping control is mainly divided into three parts of control input signal selection, a controller and control output signals. The control input signal is divided into a local signal and a wide-area signal, the detection cost of the local signal is low, but the observability of the local signal on oscillation is not necessarily good. The active power variable quantity on the transmission line is selected as the input signal of the controller.
The additional damping controller is generally composed of a proportion link, a filtering link, a phase shifting link and an amplitude limiting link. Additional damping power is generated by inputting variables to the controller related to low frequency oscillations. Because the active control loop and the reactive control loop of the virtual synchronous machine are approximately decoupled, the active loop is only analyzed.
The virtual synchronous wind power plant additional damping control method is shown in fig. 4, and as can be seen from fig. 4, a damping controller takes an active power variable quantity delta P on a transmission line as input, and outputs a quantity delta P related to low-frequency oscillation through filtering, phase shifting, proportion and amplitude limiting linksv. Comparing fig. 3 and fig. 4, it can be seen that the control replaces the virtual damping coefficient of the active control loop of the virtual synchronous machine with the PI controller. For example, when the system frequency exceeds a frequency stability value, when ωVSG-ω0Greater than 0, the negative feedback branch output increases due to the accumulation characteristic of the integrator, resulting in a decrease in the inverter output frequency. The additional damping control strategy of the virtual synchronous wind power plant at different wind speeds is shown in FIG. 5. And when the current wind speed is detected to be between the cut-in wind speed and the rated wind speed, carrying out overspeed load reduction control on the double-fed fan, and simultaneously carrying out self-adaptive control on the wind speed of the fan. This application sets up VBIs 6m/s, VNIs 12 m/s. When wind speed is detectedWhen the wind speed is higher than the rated wind speed, the reserve power is reserved through the pitch angle control, and at the moment, the wind speed self-adaptive control on the fan is not carried out any more.
In order to demonstrate the effects of the embodiments of the present application, the following embodiments are further described.
Fig. 6 is a schematic diagram of a power grid system according to an embodiment of the present application. Specifically, in the system, G1 is a synchronous machine, G2 is an infinite power grid, DFIG is a doubly-fed wind turbine generator, and L1 and L2 are loads. The voltages on the left and right sides of the transformer are respectively 13.8kV and 230 kV.
Natural wind can be decomposed into random wind, basic wind, gradual wind and gust. The present application uses wind speed as shown in fig. 7 to mimic natural wind. As shown in fig. 6, when t is 10s, a three-phase short-circuit fault occurs at a point where the system is merged into an infinite power grid, and the fault is eliminated after 0.1 s. The amount of active power change at bus B1 is monitored as an input to the additional damping control system. The suppression effect of the virtual synchronization control and the additional damping control on the low-frequency oscillation phenomenon is described by the 4 operation conditions shown in table 1.
TABLE 1
Figure BDA0003033828980000081
The working condition 0 in table 1 is a control group, which is a condition when no new energy is connected to the grid. The double-fed fan in the working condition 1 adopts a traditional control method and has no load shedding control. And the working condition 2 adopts VSG control, the topological structure of the circuit is not changed, and the double-fed fan has load shedding control. To illustrate the effect of virtual synchronous control, the active power variation on bus B1 for the three operating conditions described above is selected as shown in FIG. 8.
As can be seen from fig. 8, the active power measured at bus B1 in condition 0 stops oscillating after about 4 cycles of the fault. The period of active power oscillation in the working condition 2 is about 4 periods. This shows that under the control of virtual synchronous machine technology, the wind farm is already substantially close to the traditional synchronous machine in terms of suppressing low frequency oscillations. In the working condition 1, the system frequency gradually subsides after oscillating for about 10 cycles, the oscillation cycle is 2.5 times of that of the working condition 0 and the working condition 2, and the damping of the system is greatly reduced by the traditional control method of the wind power plant. Comparing working condition 1 with working condition 2, the introduction of the virtual synchronous machine technology obviously reduces the period of system power oscillation, and the damping characteristic of the new energy machine set controlled by the technology is better than that of the conventional control method.
The working condition 3 in table 1 is that the doubly-fed wind turbine is controlled by VSG, the load shedding control and the wind speed adaptive control are provided, and an additional damping controller is designed on the wind turbine. To illustrate the effect of the additional damping control, the active power change on bus B1 for both operating conditions 2 and 3 is shown in FIG. 9.
As can be seen from fig. 9, the additional damping control has a relatively large variation in the bus power oscillation. The oscillation frequency is changed from 2.9Hz before the additional damping to 1.7Hz after the additional damping, and the oscillation frequency is reduced. The oscillation period is reduced from 5 periods to 2 periods, and the oscillation is obviously weakened. The damping of the system can be effectively increased by the aid of additional damping control of the virtual synchronous wind power plant, and the recovery capability of the system after the system fails is enhanced.
To verify the effectiveness of the adaptive control of wind speed in this context, the change in active power on bus B1 at 4 different constant wind speeds was tested as shown in fig. 10.
The curves in FIG. 10 represent the power oscillation of the system under the additional damping control of the virtual synchronous wind farm from bottom to top when the wind speeds are 6m/s, 8m/s, 10m/s and 12m/s, respectively. As can be seen from fig. 10, under the adaptive control strategy of the wind speed of the doubly-fed wind turbine, the additional damping control effect is not very different at different wind speeds, only the power flowing through the transmission line is different at different wind speeds,
the application provides a method and a system for inhibiting low-frequency oscillation of a power grid by additional damping of a virtual synchronous wind power plant. Secondly, when an additional damping controller is designed, in order to enable the double-fed fan to provide output in the positive half period and the negative half period of oscillation, the double-fed fan is subjected to load shedding operation in a maximum power tracking area through overspeed control, and the double-fed fan is subjected to load shedding operation in a rotating speed constant area through pitch angle control; meanwhile, a wind speed self-adaptive device is designed, and the capability of the controller for adapting to wind speed changes is improved.
The virtual synchronous machine control technology is adopted, inertia and damping of the double-fed wind generating set are increased, and weakening effect of the double-fed wind generating set on system damping is reduced. After the additional damping controller is designed on the double-fed wind generating set, the double-fed wind generating set can generate more or less power according to the change of the power in the system. In order to enable the double-fed wind generating set to provide output in both the positive half cycle and the negative half cycle of oscillation generation, overspeed load shedding control and pitch angle control are carried out on the double-fed wind generating set. And in a maximum power tracking area, overspeed control is performed on a rotor of the doubly-fed wind generating set, so that the rotor deviates from a maximum power tracking curve and a certain active standby is reserved. Meanwhile, partial capacity is stored in the form of kinetic energy in the rotor of the fan, and the change of system power is responded quickly. When the rotating speed of the rotor reaches the maximum rotating speed, certain active power is reserved for standby through the pitch angle control. According to mathematical analysis, the output additional power of the doubly-fed wind generating set is greatly influenced by the wind speed. In order to reduce the influence of the wind speed on the output additional power, the additional power output by the fan is only determined by the external oscillation power, the output power of the double-fed wind generating set is compensated, and the self-adaptive control of the wind speed is realized. And acquiring the quantity related to low-frequency oscillation in the system on a power transmission line, and controlling the active power output by the double-fed wind generating set under the action of an additional damping controller on an active control loop of the virtual synchronous fan.
The above-mentioned contents are only for explaining the technical idea of the present application, and the protection scope of the present application is not limited thereby, and any modification made on the basis of the technical idea presented in the present application falls within the protection scope of the claims of the present application.
Additionally, the order in which elements and sequences of the processes described herein are processed, the use of alphanumeric characters, or the use of other designations, is not intended to limit the order of the processes and methods described herein, unless explicitly claimed. While various presently contemplated embodiments have been discussed in the foregoing disclosure by way of example, it should be understood that such detail is solely for that purpose and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover all modifications and equivalent arrangements that are within the spirit and scope of the embodiments herein. For example, although the system components described above may be implemented by hardware devices, they may also be implemented by software-only solutions, such as installing the described system on an existing server or mobile device.
Similarly, it should be noted that in the preceding description of embodiments of the application, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the embodiments. This method of disclosure, however, is not intended to require more features than are expressly recited in the claims. Indeed, the embodiments may be characterized as having less than all of the features of a single embodiment disclosed above.
The entire contents of each patent, patent application publication, and other material cited in this application, such as articles, books, specifications, publications, documents, and the like, are hereby incorporated by reference into this application. Except where the application is filed in a manner inconsistent or contrary to the present disclosure, and except where the claim is filed in its broadest scope (whether present or later appended to the application) as well. It is noted that the descriptions, definitions and/or use of terms in this application shall control if they are inconsistent or contrary to the statements and/or uses of the present application in the material attached to this application.

Claims (8)

1. A method for suppressing low-frequency oscillation of a power grid by additional damping of a virtual synchronous wind power plant is characterized by comprising the following steps:
acquiring hidden inertia and damping of a rotor of the doubly-fed wind generating set through virtual synchronous control;
providing additional damping;
measuring the current wind speed in real time;
when the current wind speed is higher than the cut-in wind speed and lower than the rated wind speed, carrying out load shedding control on the double-fed wind generating set, and carrying out wind speed self-adaptive control on the fan;
according to the active power output by the double-fed wind generating set through load shedding control, judging whether the active power oscillates or not;
and when the active power oscillates, performing additional damping control on the virtual synchronous wind power plant.
2. The method for additional damping of the grid low-frequency oscillation suppression of the virtual synchronous wind farm according to claim 1, characterized in that when the current wind speed is greater than the rated wind speed, the reserved standby power is controlled through a pitch angle.
3. The method for additional damping suppression of low-frequency oscillation of a power grid of a virtual synchronous wind farm according to claim 1, characterized in that the load shedding control of the doubly-fed wind generating set comprises overspeed load shedding control and pitch angle control;
fitting the maximum power tracking curve in the MPPT area to obtain the rotor optimal rotating speed reference value omegaref1Mechanical power P output by the fanmThe relationship between them is:
Figure FDA0003033828970000011
speed reference value omega under overspeed load shedding controlrefMechanical power P output by the fanmThe relationship between them is:
Figure FDA0003033828970000012
in a rotating speed constant region, load shedding is controlled through a pitch angle, and the initial pitch angle is determined by adopting the following method:
Figure FDA0003033828970000013
Figure FDA0003033828970000014
Figure FDA0003033828970000015
in the formula, CpAnd CPLThe coefficient of wind energy utilization before and after load shedding, d is the load shedding coefficient, lambda2As tip speed ratio, omegamaxThe maximum rotating speed is R is the radius of the fan blade, and v is the wind speed.
4. The method for suppressing the low-frequency oscillation of the power grid by the additional damping of the virtual synchronous wind power plant according to claim 1, wherein the adaptive control of the wind speed in the MPPT region is adopted and comprises the following steps:
input parasitic power variation Δ Pw1Determined by external oscillation power, and the reference value omega of the rotor rotating speed after adding additional powerref2Comprises the following steps:
Figure FDA0003033828970000021
in the formula, item 1 is the normal output of the fan; term 2 includes only the power Δ P of the external oscillationw1The determined additional power, independent of the wind speed; item 3 is PmAnd Δ Pw1In which P ismThe size is related to the wind speed and is the item to be compensated.
5. The method for suppressing the low-frequency oscillation of the power grid by the additional damping of the virtual synchronous wind power plant according to claim 1, wherein the double-fed wind generating set is obtained by virtual synchronous control, and the method comprises the following steps:
Figure FDA0003033828970000022
in the formula, deltaVSGIs the power angle, omega, of the inverterVSGAngular velocity of VSG, virtual moment of inertia of VSG, DpVirtual damping coefficient, omega, for VSG active ring0For rating angular frequency, U, of the networkmFor effective value of grid-connected point voltage, KqAnd KvRespectively a reactive scaling factor and a voltage scaling factor.
6. The method for suppressing the low-frequency oscillation of the power grid by the additional damping of the virtual synchronous wind power plant according to claim 1, wherein the step of outputting the active power according to the load shedding control of the doubly-fed wind generating set comprises the following steps:
obtaining active power variation;
obtaining a control signal by carrying out proportion, filtering, phase compensation and amplitude limiting on the active power variable quantity;
power oscillation is obtained by the control signal.
7. A system for suppressing low-frequency oscillation of a power grid by additional damping of a virtual synchronous wind power plant is characterized by comprising:
the virtual synchronous machine is used for excavating hidden inertia and damping of the rotor of the doubly-fed wind generating set;
an additional damping controller for providing additional damping;
and the wind speed self-adaption device is used for adding the additional damping controller to adapt to wind speed change.
8. The system for additional damping of the grid low-frequency oscillation suppression of the virtual synchronous wind farm according to claim 7, further comprising a load shedding controller;
the load controller includes overspeed load shedding control and pitch angle control.
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