CN114069729A - Permanent magnet direct-drive wind power plant reactive voltage control strategy based on adaptive droop control - Google Patents

Permanent magnet direct-drive wind power plant reactive voltage control strategy based on adaptive droop control Download PDF

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CN114069729A
CN114069729A CN202111330245.7A CN202111330245A CN114069729A CN 114069729 A CN114069729 A CN 114069729A CN 202111330245 A CN202111330245 A CN 202111330245A CN 114069729 A CN114069729 A CN 114069729A
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wind
wind turbine
power
turbine generator
reactive
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CN114069729B (en
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沈希澄
周霞
解相朋
戴剑丰
马道广
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Nanjing University of Posts and Telecommunications
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Nanjing University of Posts and Telecommunications
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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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/50—Controlling the sharing of the out-of-phase component
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • 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
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)
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Abstract

The invention discloses a permanent magnet direct-drive wind power plant reactive voltage control strategy based on adaptive droop control, which comprises the following steps: firstly, establishing a wind power plant grid-connected model, and determining an output power curve of a wind turbine generator at different wind speeds and reactive capacity of the wind turbine generator at different running states; secondly, two control modes of the wind turbine generator are provided, a maximum power tracking control mode is adopted when the voltage of a grid connection point is stable, and the tip speed ratio is controlled to keep the optimal value so as to achieve the maximum wind energy capture state; when the voltage drop of the grid-connected point is serious, if the reactive capacity of the wind turbine generator is sufficient, the grid-side converter adopts self-adaptive droop control, the droop coefficient is self-adaptively adjusted according to the reactive capacity of the wind turbine generator, and the reactive power output is increased; if the reactive capacity of the wind turbine generator is insufficient, load shedding control is adopted, and corresponding load shedding control methods are adopted in different wind speed intervals, so that more reactive supports are provided for the system, and the problem that the voltage of a grid connection point is out of limit is solved.

Description

Permanent magnet direct-drive wind power plant reactive voltage control strategy based on adaptive droop control
Technical Field
The invention belongs to the field of power system automation, and relates to a permanent magnet direct-drive wind power plant reactive voltage control strategy based on self-adaptive droop control.
Background
Wind power generation is widely applied to an electric power system as a renewable energy power generation technology, but large-scale wind power integration often affects stable operation of the system. The domestic wind power plant is generally located in a remote area, the stability of a connected power grid is relatively weak, and when the output power of the wind power plant is greatly changed, the voltage stability of a grid-connected point can be obviously reduced, so that the safety and stability of a power system are influenced. In recent years, many large-scale wind turbine generator interlocking and grid-off accidents occur in China, and the accidents are closely related to the reactive power and voltage control of a wind power plant. At present, researches for improving the reactive power level of a wind power plant and the voltage quality of a grid connection point at home and abroad are mainly carried out from two aspects: and configuring reactive compensation equipment in the system to ensure the voltage stability of the wind power plant, or making a reactive control scheme measure of the wind power plant from the wind power plant.
Because a certain investment is required to be added when the reactive compensation equipment is additionally configured, the method becomes a relatively economic adjusting means by enabling the wind power plant to participate in reactive adjustment. The permanent magnet direct-drive wind turbine generator and the double-fed wind turbine generator both have certain reactive power regulation capacity, and when the power grid falls down to a small extent, the requirements can be met by means of reactive power compensation of the wind turbine generator. Compared with a double-fed type wind turbine generator, the permanent magnet direct-drive wind turbine generator has better reactive voltage characteristics, and the important means of reactive voltage control is provided by using the reactive power regulation capacity of the permanent magnet direct-drive wind turbine generator to provide reactive support for a system. When the system voltage is reduced, the grid-side converter of the permanent magnet direct-drive wind turbine generator system can quickly provide certain reactive support for the power grid by adjusting active and reactive decoupling control. At present, a voltage control strategy of the wind turbine generator generally adopts fixed droop gain, reasonable distribution can not be carried out according to the reactive capacity of each wind turbine generator, and an optimal control strategy which can adapt to each wind speed condition and carry out self-adaptive adjustment on the reactive power of the wind turbine generator is needed.
Disclosure of Invention
In order to solve the technical problems, the invention provides a reactive voltage control strategy of a permanent magnet direct-drive wind power plant based on self-adaptive droop control, and solves the problem of uneven reactive power distribution caused by the adoption of fixed droop gain in the prior art.
The invention relates to a permanent magnet direct-drive wind power plant reactive voltage control strategy based on self-adaptive droop control, which comprises the following steps:
step 1, establishing a wind power plant grid-connected system model consisting of a permanent magnet direct-drive wind turbine generator, a static load and a synchronous generator, determining output power curves of the wind turbine generator at different wind speeds, and determining reactive capacity of the wind turbine generator in different running states according to a coupling relation between active power and reactive power;
step 2, detecting the grid-connected point voltage of the wind power plant, and if the grid-connected point voltage is normal, adopting a maximum power tracking control mode to perform step 3; if the voltage of the grid-connected point is out of limit, firstly judging the reactive capacity, and when the reactive capacity is sufficient, performing self-adaptive droop control on the grid-side converter to perform step 4; when the reactive capacity is insufficient, carrying out load shedding control while adopting self-adaptive droop control, and carrying out step 5;
step 3, the wind turbine generator operates in a maximum power tracking control mode, the rotating speed of the wind turbine is adjusted according to the current wind speed, the tip speed ratio is kept at the optimal value, the maximum wind energy capture state is achieved, and the wind turbine generator outputs the maximum active power;
step 4, the wind turbine generator sets adopt adaptive droop control, a reactive power control link of a grid-side converter is provided with an adaptive droop coefficient, the adaptive droop coefficient can be automatically adjusted along with the change of wind speed, the reactive power output of each set is reasonably distributed to support the voltage of a grid-connected point, and the stable operation of a system is guaranteed;
and 5, adopting a load shedding operation mode by the wind turbine generator, adopting a corresponding load shedding method according to wind speed change, adjusting the rotating speed of the rotor, combining pitch angle control to realize load shedding, increasing reactive power output, and keeping self-adaptive droop control of the grid-side converter.
Further, step (ii)In the step 1, according to the operating characteristics of a permanent magnet direct-drive wind turbine generator, a permanent magnet direct-drive wind turbine generator grid-connected system model is established, and a relation curve of a wind speed and a tip speed ratio curve is determined; the wind turbine captures power, the rotating speed of the wind turbine is related to the pitch angle, and the per unit value PwtComprises the following steps:
Figure BDA0003348520970000021
in the formula, PNFor rated power of the wind turbine generator, rho is air density, R is radius of the wind wheel, vWIs the value of wind speed, CpIs the wind energy capture coefficient and can be expressed as
Figure BDA0003348520970000022
Where λ is the tip speed ratio, ΩNFor rating the rotor at mechanical speed, c1～c6As fitting coefficient, ωtIs the rotor speed, beta is the pitch angle; when the fitting coefficient takes different values, CpThe functions having different optimum tip speed ratios λoptAnd maximum wind energy capture coefficient Cpmax；
The reactive capacity of the wind turbine generator is determined by active power and apparent power
Figure BDA0003348520970000031
In the formula: sWThe apparent power of the converter of the wind turbine generator is shown.
Further, in step 3, the wind turbine normally operates in the maximum power tracking mode, and the tracking process is divided into three stages according to the change of the wind speed:
the first stage is the optimum rotating speed operation stage when the wind energy capture coefficient CpOptimal tip speed ratio lambda which is correspondingly fixed when the function obtains the maximum valueoptRegulating the rotational speed omega of the wind turbinetSo as to maintain the tip speed ratio of lambdaoptIn this case, the wind turbine is operated at the optimum rotational speedAnd capturing the maximum wind energy;
the second stage is a constant rotating speed operation stage, when the wind speed is continuously increased and the capture power does not exceed the rated power of the wind turbine, the rotating speed of the rotor of the wind turbine is maintained at omegatmaxOperating at a constant rotational speed;
the third stage is a constant power operation stage, and when the wind speed exceeds the rated wind speed v corresponding to the rated power of the wind turbine generatorwnIn time, the wind turbine needs to operate in a constant power state to prevent overload, and as the rotating speed of the wind turbine reaches the upper limit, the pitch angle needs to be increased to limit the power captured by the wind turbine.
Further, in the step 4, the grid-side converter in the converter adopts self-adaptive droop control, and the setting principle of the droop coefficient is based on the current reactive capacity of the wind turbine generator; the reactive current output of the self-adaptive droop control link is defined as:
Figure BDA0003348520970000032
Figure BDA0003348520970000033
in the formula: k is a radical ofpIs the proportionality coefficient, k, of a PI regulatoriIs the integral coefficient of PI regulator, 1/s is the integral link, Q0Is a reactive power reference value, and is usually set to 0, VsysIs an effective value of voltage, VnomThe voltage is a rated voltage value, and the voltage is a rated voltage value,
Figure BDA0003348520970000034
is a self-adaptive droop coefficient which is in direct proportion to the reactive power of the wind turbine generator, QW,iThe reactive power of the No. i wind turbine generator is obtained; c is a constant coefficient.
Further, in step 5, the method for controlling the load shedding operation mode includes:
determining the minimum value Q of reactive power to be supplied to a grid-connected point under the condition of ensuring the grid-connected voltage to be stableLBecause the output power of the wind turbine generator meets the requirement
Figure BDA0003348520970000041
The closer the wind turbine generator is to the rated state, the greater the reactive capacity released by the same load shedding power is, so that the load shedding priority of each generator needs to be judged, and the wind turbine generator is selected for load shedding control;
Figure BDA0003348520970000042
Figure BDA0003348520970000043
Figure BDA0003348520970000044
in the formula: s is the rated power of the wind turbine;
Figure BDA0003348520970000045
the active power output of the No. i wind turbine generator is obtained; Δ P is the decrement amount; delta Qw,iIs the reactive increment of No. i wind turbine generator after load shedding, k is the number of the wind turbine generators for load shedding, j is the number of the wind turbine generators for load shedding, n is the number of the wind turbine generators in the wind power plant, and delta QkIs the reactive increment after the load shedding of the No. k wind turbine generator, QW,iFor wind turbine generator system to output reactive power, QLProviding reactive support for a wind power plant to a grid-connected point; when the wind turbine generator carries out load shedding control, the load shedding level d% can be expressed as d% ═ Δ PW,i/PW,i。
Further, the step of determining the load shedding mode by considering different wind speed intervals during the control of the load shedding operation mode comprises the following steps: the wind power generation system is divided into three wind speed intervals of low, medium and high according to the wind speed, different load shedding control methods are adopted in the intervals, the wind power generation set is in a maximum power tracking running state in the low wind speed interval, and the wind energy capture coefficient reaches the maximum C at the momentpmaxThe pitch angle beta is 0 deg., when d% load reduction is required, according to the blade tip speed ratio-windCan capture the coefficient curve to obtain CpmaxTip speed ratio λ corresponding to d% reductiond1Further, the reference speed omega of the rotor after load shedding is obtainedd1；
In the middle wind speed interval, the wind turbine generator is also in the maximum power tracking running state, and the rotor is in the optimal rotating speed omegaoptCorresponding to active power of PoptWhen d% load shedding is needed, if the rotor speed reaches the maximum allowable speed omega in the process of overspeed load sheddingmaxAnd then, the load shedding is realized by matching with the pitch angle control, and the reference power of the pitch angle control is set as follows:
Figure BDA0003348520970000051
in the high wind speed interval, when vW2<vW<vWnIn the time, the wind turbine generator is in a constant rotating speed operation mode, and when d% of load reduction is needed, the wind energy capture coefficient C after load reduction is calculatedpdAnd solving the pitch angle beta by using the Newton methoddIs adjusted when v isWn<vW<vW_outIn the time, the wind turbine generator is in a constant power operation mode, and the output power of the wind turbine generator is the rated power PnWhen d% of load shedding is needed, the reference power is only set to be (1-d%) PnAnd (4) finishing.
The invention has the beneficial effects that: the reactive voltage control strategy of the permanent-magnet direct-drive electric field can track the voltage change of the grid-connected point, quickly implement reactive voltage regulation, accurately control the voltage of the grid-connected point of the wind power plant, avoid the problem of voltage out-of-limit caused by the disturbance or fault of the system and ensure the safe and stable operation of the system; in addition, the control strategy adopted by the invention fully utilizes the reactive capacity of the wind turbine generator, thereby reducing the configuration of extra reactive power compensation devices and improving the economical efficiency of system operation.
Drawings
In order that the present invention may be more readily and clearly understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings.
FIG. 1 is a reactive voltage control flow diagram;
FIG. 2 is a graph of the relationship between the wind energy utilization coefficient and the tip speed ratio;
FIG. 3 illustrates an adaptive droop control link;
FIG. 4 is a power-rotational speed characteristic curve of a wind turbine;
FIG. 5 is a low, medium and high wind speed plot.
Detailed Description
As shown in fig. 1, the adaptive droop control-based reactive voltage control strategy for the permanent magnet direct-drive wind farm according to the present invention includes the following steps:
step 1, establishing a wind power plant grid-connected system model consisting of a permanent magnet direct-drive wind turbine generator, a static load and a synchronous generator, determining output power curves of the wind turbine generator at different wind speeds, and determining reactive capacity of the wind turbine generator in different running states according to a coupling relation between active power and reactive power;
step 2, detecting the grid-connected point voltage of the wind power plant, and if the grid-connected point voltage is normal, adopting a maximum power tracking control mode to perform step 3; if the voltage of the grid-connected point is out of limit, firstly judging the reactive capacity, and when the reactive capacity is sufficient, performing self-adaptive droop control on the grid-side converter to perform step 4; when the reactive capacity is insufficient, carrying out load shedding control while adopting self-adaptive droop control, and carrying out step 5;
step 3, the wind turbine generator operates in a maximum power tracking control mode, the rotating speed of the wind turbine is adjusted according to the current wind speed, the tip speed ratio is kept at the optimal value, the maximum wind energy capture state is achieved, and the wind turbine generator outputs the maximum active power;
step 4, the wind turbine generator sets adopt adaptive droop control, a reactive power control link of a grid-side converter is provided with an adaptive droop coefficient, the adaptive droop coefficient can be automatically adjusted along with the change of wind speed, the reactive power output of each set is reasonably distributed to support the voltage of a grid-connected point, and the stable operation of a system is guaranteed;
and 5, adopting a load shedding operation mode by the wind turbine generator, adopting a corresponding load shedding method according to wind speed change, adjusting the rotating speed of the rotor, combining pitch angle control to realize load shedding, increasing reactive power output, and keeping self-adaptive droop control of the grid-side converter.
In step 1, determining output power curves of the wind turbine generator at different wind speeds, and then determining reactive capacity of the wind turbine generator in different operating states according to the coupling relation between active power and reactive power comprises the following specific steps:
the wind turbine captures power, the rotating speed of the wind turbine is related to the pitch angle, and the per unit value PwtComprises the following steps:
Figure BDA0003348520970000061
in the formula, PNFor rated power of the wind turbine generator, rho is air density, R is radius of the wind wheel, vWIs the value of wind speed, CpIs the wind energy capture coefficient and can be expressed as
Figure BDA0003348520970000062
Where λ is the tip speed ratio, ΩNFor rating the rotor at mechanical speed, c1～c6As fitting coefficient, ωtIs the rotor speed, beta is the pitch angle; when the fitting coefficient takes different values, CpThe functions having different optimum tip speed ratios λoptAnd maximum wind energy capture coefficient Cpmax。
The wind turbine generator is provided with a pitch angle control system, and can adjust the capture power and limit the rotating speed of a wind wheel; when the system operates, the rotating speed of the wind turbine is required to be limited not to exceed the upper limit omegatmaxWhen the wind turbine rotates at a speed ωtLess than omegatmaxWhen, pitch angle control is inactive, β is set to 0 °;
when the pitch angle is fixed, the wind energy utilization coefficient can reach the maximum value by adjusting the tip speed ratio, as shown in FIG. 2; in the running process of the motor set, the wind energy capture coefficient can be obtained by controlling the rotating speed of the wind turbine to keep the optimal rotating speed corresponding to the current wind speed.
The reactive capacity of the wind turbine generator is determined by active power and apparent power:
Figure BDA0003348520970000071
in the formula: sWThe apparent power of the converter of the wind turbine generator is shown.
When the output power of the wind turbine generator reaches the rated power and the reactive power shortage is large, the reactive power margin of the wind turbine generator can be increased through load shedding operation according to the relation between the active power and the reactive power.
In step 2, selecting a wind turbine generator control mode by measuring whether the grid-connected point voltage is out of limit; when the voltage of the grid connection point is in the range of 0.95-1.05pu, a maximum power tracking control mode is adopted; and when the voltage of the grid-connected point is lower than 0.95pu, judging the reactive capacity: if the reactive capacity is higher than the reactive demand QLAdopting self-adaptive droop control, entering the step four, and if the reactive capacity is lower than the reactive demand QLAnd if so, adopting load shedding control and entering the step five.
In step 3, the wind turbine generator operates in a maximum power tracking mode, and maximum power tracking control can be realized by controlling the rotating speed of the fan to track the optimal rotating speed in order to maximize the wind energy utilization coefficient.
The tracking process is divided into three stages according to the change of the wind speed: the first is the optimal rotating speed operation stage, when the wind energy capture coefficient CpOptimal tip speed ratio lambda which is correspondingly fixed when the function obtains the maximum valueoptRegulating the rotational speed omega of the wind turbinetSo as to maintain the tip speed ratio of lambdaoptIn this case, the wind turbine operates at an optimal rotational speed and captures the maximum wind energy; the second stage is a constant rotating speed operation stage, when the wind speed continues to increase and the capture power does not exceed the rated power of the wind turbine, the rotating speed of the rotor of the wind turbine is maintained at omegatmaxOperating at a constant rotational speed; the third is a constant power operation stage, when the wind speed exceeds the rated wind speed v corresponding to the rated power of the wind turbine generatorwnIn time, the wind turbine needs to operate in a constant power state to prevent overload, and as the rotating speed of the wind turbine reaches the upper limit, the pitch angle needs to be increased to limit the power captured by the wind turbine.
In the step 4, the wind turbine generator operates in a self-adaptive droop control mode, a grid-side converter adopts self-adaptive droop control on reactive power, and a droop coefficient is self-adaptively adjusted according to the current reactive capacity of the wind turbine generator; when the releasable reactive power of the wind turbine generator is large, the droop coefficient of the wind turbine generator can be set to be larger; and when the releasable reactive power is smaller, a smaller droop coefficient is set. The principle of the adaptive droop control is shown in fig. 3, and in the load shedding control mode, the reactive current output of the adaptive droop control link is defined as:
Figure BDA0003348520970000081
Figure BDA0003348520970000082
in the formula: k is a radical ofpIs the proportionality coefficient, k, of a PI regulatoriIs the integral coefficient of PI regulator, 1/s is the integral link, Q0Is a reactive power reference value, and is usually set to 0, VsysIs an effective value of voltage, VnomThe voltage is a rated voltage value, and the voltage is a rated voltage value,
Figure BDA0003348520970000083
is a self-adaptive droop coefficient which is in direct proportion to the reactive power of the wind turbine generator, QW,iThe reactive power of the No. i wind turbine generator is obtained; c is a constant coefficient.
The self-adaptive droop coefficient is a variable related to space and time, the input wind speed of the wind turbine generator changes along with time, and the droop coefficient can be self-adaptively adjusted along with the change of the wind speed, so that the stable operation of a system is facilitated. In addition, the droop coefficient can be adaptively increased along with the increased reactive capacity, so that the wind turbine generator is prevented from frequently reaching the maximum reactive power limit, and the reduction of the abrasion of the converter is facilitated.
In step 5, the method for controlling the load shedding operation mode comprises the following steps: determining the minimum value Q of reactive power required to be provided to a grid-connected point under the condition that the wind power plant ensures the grid-connected voltage to be stableLDue to the wind motorGroup output power satisfies
Figure BDA0003348520970000084
The closer the wind turbine generator is to the rated state, the greater the reactive capacity released by the same load shedding power is, so that the load shedding priority of each generator needs to be judged, and the wind turbine generator is selected for load shedding control;
Figure BDA0003348520970000085
Figure BDA0003348520970000086
Figure BDA0003348520970000087
in the formula: s is the rated power of the wind turbine;
Figure BDA0003348520970000088
the active power output of the No. i wind turbine generator is obtained; Δ P is the decrement amount; delta Qw,iIs the reactive increment of No. i wind turbine generator after load shedding, k is the number of the wind turbine generators for load shedding, j is the number of the wind turbine generators for load shedding, n is the number of the wind turbine generators in the wind power plant, and delta QkIs the reactive increment after the load shedding of the No. k wind turbine generator, QW,iFor wind turbine generator system to output reactive power, QLProviding reactive support for a wind power plant to a grid-connected point; when the wind turbine generator carries out load shedding control, the load shedding level d% can be expressed as d% ═ Δ PW,i/PW,i。
The power-rotation speed characteristic curve of the wind turbine generator is shown in fig. 4, and represents the relationship between the output power and the rotation speed of the wind turbine generator at different pitch angles at a certain wind speed. When the wind speed is vW0In the process, the operating point a is the maximum power operating point, the operating point b is the overspeed load shedding operating point, the operating point c is the pitch changing point, and the pitch angle is changed from beta0Increase to beta1The characteristic curve is wholly reduced, and the wind turbine generator is capturedThe power is reduced to achieve load shedding.
The wind turbine generator operates in a load shedding control mode, wind speed is divided into three sections, namely a low section, a middle section and a high section according to the wind speed, as shown in fig. 5, a low wind speed area is an area surrounded by ABB 'A', and the load shedding requirement is met through overspeed control; the medium wind speed area is an area surrounded by BCB ', the load reduction needs to be carried out through the coordination control of the rotating speed and the pitch angle due to the limitation of the highest rotating speed, the high wind speed area is a line segment C ' D, the point C ' is obtained through the pitch control of the point C, and the wind speed corresponding to the point D is the cut-out wind speed v of the wind turbineW_outIn the high wind speed interval, the rotating speed reaches the maximum, so that overspeed control cannot be performed, and load shedding can be realized only through variable pitch control. Low wind speed interval is cut-in wind speed vW_in～vW1The interval of wind speed is vW1～vW2The high wind speed interval is vW2～vW_out。
Figure BDA0003348520970000091
In the formula: omegamaxFor maximum allowable speed, lambda, of the wind turbinedFor tip speed ratio after load shedding, associated with the level of load shedding, λoptFor optimal tip speed ratio, the level d% of the relief can be expressed as d% ═ Δ PW,i/PW,i。
In a low wind speed interval, the wind turbine generator is in a maximum power tracking running state, and at the moment, the wind energy capture coefficient reaches the maximum CpmaxThe pitch angle beta is 0 degrees, and when d% of load reduction is needed, C is calculated according to a curve of the tip speed ratio-wind energy capture coefficientpmaxTip speed ratio λ corresponding to d% reductiond1Further, the reference speed omega of the rotor after load shedding is obtainedd1。
In the middle wind speed interval, the wind turbine generator is also in the maximum power tracking running state, and the rotor is in the optimal rotating speed omegaoptCorresponding to active power of PoptWhen d% load shedding is needed, if the rotor speed reaches the maximum allowable speed omega in the process of overspeed load sheddingmaxThe reference work of load shedding and pitch control needs to be realized by matching with the pitch angle controlThe ratio was set as:
Figure BDA0003348520970000101
in the high wind speed interval, when vW2<vW<vWnIn the time, the wind turbine generator is in a constant rotating speed operation mode, and when d% of load reduction is needed, the wind energy capture coefficient C after load reduction is calculatedpdAnd solving the pitch angle beta by using the Newton methoddIs adjusted when v isWn<vW<vW_outIn the time, the wind turbine generator is in a constant power operation mode, and the output power of the wind turbine generator is the rated power PnWhen d% of load shedding is needed, the reference power is only set to be (1-d%) PnAnd (4) finishing.
And after the voltage of the grid-connected point is recovered, the wind turbine generator is recovered to the operation state before load shedding control, so that the output power of the wind turbine generator is increased while the reactive power requirement of the system is met.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all equivalent variations made by using the contents of the present specification and the drawings are within the protection scope of the present invention.

Claims (6)

1. The permanent magnet direct-drive wind power plant reactive voltage control strategy based on the self-adaptive droop control is characterized by comprising the following steps:
step 1, establishing a wind power plant grid-connected system model consisting of a permanent magnet direct-drive wind turbine generator, a static load and a synchronous generator, determining output power curves of the wind turbine generator at different wind speeds, and determining reactive capacity of the wind turbine generator in different running states according to a coupling relation between active power and reactive power;
step 2, detecting the grid-connected point voltage of the wind power plant, and if the grid-connected point voltage is normal, adopting a maximum power tracking control mode to perform step 3; if the voltage of the grid-connected point is out of limit, firstly judging the reactive capacity, and when the reactive capacity is sufficient, carrying out self-adaptive droop control on a grid-side converter of the wind turbine generator set to carry out step 4; when the reactive capacity is insufficient, the grid-side converter of the wind turbine generator performs load shedding control while adopting self-adaptive droop control, and the step 5 is performed;
step 3, the wind turbine generator operates in a maximum power tracking control mode, the rotating speed of the wind turbine is adjusted according to the current wind speed, the tip speed ratio is kept at the optimal value, the maximum wind energy capture state is achieved, and the wind turbine generator outputs the maximum active power;
step 4, the wind turbine generator sets adopt adaptive droop control, a reactive power control link of a grid-side converter is provided with an adaptive droop coefficient, the adaptive droop coefficient can be automatically adjusted along with the change of wind speed, the reactive power output of each set is reasonably distributed to support the voltage of a grid-connected point, and the stable operation of a system is guaranteed;
and 5, adopting a load shedding operation mode by the wind turbine generator, adopting a corresponding load shedding method according to wind speed change, adjusting the rotating speed of the rotor, combining pitch angle control to realize load shedding, increasing reactive power output, and keeping self-adaptive droop control of the grid-side converter.
2. The reactive voltage control strategy of the permanent magnet direct-drive wind power plant based on the adaptive droop control as claimed in claim 1, wherein in the step 1, a permanent magnet direct-drive wind power plant grid-connected system model is established according to the running characteristics of the permanent magnet direct-drive wind power plant, and a relation curve of a wind speed and a tip speed ratio curve is determined; the wind turbine captures power, the rotating speed of the wind turbine is related to the pitch angle, and the per unit value PwtComprises the following steps:
Figure FDA0003348520960000011
in the formula, PNFor rated power of the wind turbine generator, rho is air density, R is radius of the wind wheel, vWIs the value of wind speed, CpIs the wind energy capture coefficient and can be expressed as
Figure FDA0003348520960000021
Where λ is the tip speedRatio, omegaNFor rating the rotor at mechanical speed, c1～c6As fitting coefficient, ωtIs the rotor speed, beta is the pitch angle; when the fitting coefficient takes different values, CpThe functions having different optimum tip speed ratios λoptAnd maximum wind energy capture coefficient Cpmax；
The reactive capacity of the wind turbine generator is determined by active power and apparent power.
Figure FDA0003348520960000022
In the formula: sWThe apparent power of the converter of the wind turbine generator is shown.
3. The adaptive droop control-based permanent magnet direct drive wind farm reactive voltage control strategy according to claim 1, wherein in step 3, the wind turbine generator normally operates in a maximum power tracking mode, and the tracking process is divided into three stages according to wind speed changes:
the first stage is the optimum rotating speed operation stage when the wind energy capture coefficient CpOptimal tip speed ratio lambda which is correspondingly fixed when the function obtains the maximum valueoptRegulating the rotational speed omega of the wind turbinetSo as to maintain the tip speed ratio of lambdaoptIn this case, the wind turbine operates at an optimal rotational speed and captures the maximum wind energy;
the second stage is a constant rotating speed operation stage, when the wind speed is continuously increased and the capture power does not exceed the rated power of the wind turbine, the rotating speed of the rotor of the wind turbine is maintained at omegatmaxOperating at a constant rotational speed;
the third stage is a constant power operation stage, and when the wind speed exceeds the rated wind speed v corresponding to the rated power of the wind turbine generatorwnIn time, the wind turbine needs to operate in a constant power state to prevent overload, and as the rotating speed of the wind turbine reaches the upper limit, the pitch angle needs to be increased to limit the power captured by the wind turbine.
4. The adaptive droop control-based reactive voltage control strategy for the permanent magnet direct-drive wind power plant according to claim 1, wherein in the step 4, a grid-side converter in the converter adopts adaptive droop control, and a droop coefficient setting principle is based on the current reactive capacity of a wind turbine generator; the reactive current output of the self-adaptive droop control link is defined as:
Figure FDA0003348520960000023
Figure FDA0003348520960000031
in the formula: k is a radical ofpIs the proportionality coefficient, k, of a PI regulatoriIs the integral coefficient of PI regulator, 1/s is the integral link, Q0Is a reactive power reference value, and is usually set to 0, VsysIs an effective value of voltage, VnomThe voltage is a rated voltage value, and the voltage is a rated voltage value,
Figure FDA0003348520960000032
is a self-adaptive droop coefficient which is in direct proportion to the reactive power of the wind turbine generator, QW,iThe reactive power of the No. i wind turbine generator is obtained; c is a constant coefficient.
5. The adaptive droop control-based permanent magnet direct drive wind farm reactive voltage control strategy according to claim 1, wherein in step 5, the method for controlling the load shedding operation mode comprises the following steps:
determining the minimum value Delta Q of the reactive power required to be provided to a grid-connected point under the condition of ensuring the grid-connected voltage to be stableLBecause the output power of the wind turbine generator meets the requirement
Figure FDA0003348520960000033
The closer the wind turbine generator is to the rated state, the greater the reactive capacity released by the same load shedding power is, so that the load shedding priority of each generator needs to be judged, and the wind turbine generator is selected for load shedding control;
Figure FDA0003348520960000034
Figure FDA0003348520960000035
Figure FDA0003348520960000036
in the formula: s is the rated power of the wind turbine;
Figure FDA0003348520960000037
the active power output of the No. i wind turbine generator is obtained; Δ P is the decrement amount; delta Qw,iIs the reactive increment of No. i wind turbine generator after load shedding, k is the number of the wind turbine generators for load shedding, j is the number of the wind turbine generators for load shedding, n is the number of the wind turbine generators in the wind power plant, and delta QkIs the reactive increment after the load shedding of the No. k wind turbine generator, QW,iFor wind turbine generator system to output reactive power, delta QLProviding reactive support for a wind power plant to a grid-connected point; when the wind turbine generator carries out load shedding control, the load shedding level d% can be expressed as d% ═ Δ PW,i/PW,i。
6. The adaptive droop control-based permanent magnet direct drive wind farm reactive voltage control strategy according to claim 1, wherein the step of determining the load shedding mode in consideration of different wind speed intervals during the control of the load shedding operation mode comprises: the wind power generation system is divided into three wind speed intervals of low, medium and high according to the wind speed, different load shedding control methods are adopted in the intervals, the wind power generation set is in a maximum power tracking running state in the low wind speed interval, and the wind energy capture coefficient reaches the maximum C at the momentpmaxThe pitch angle beta is 0 degrees, and when d% of load reduction is needed, C is calculated according to a curve of the tip speed ratio-wind energy capture coefficientpmaxTip speed ratio λ corresponding to d% reductiond1And then obtainReference rotor speed omega after load sheddingd1；
In the middle wind speed interval, the wind turbine generator is also in the maximum power tracking running state, and the rotor is in the optimal rotating speed omegaoptCorresponding to active power of PoptWhen d% load shedding is needed, if the rotor speed reaches the maximum allowable speed omega in the process of overspeed load sheddingmaxAnd then, the load shedding is realized by matching with the pitch angle control, and the reference power of the pitch angle control is set as follows:
Figure FDA0003348520960000041
in the high wind speed interval, when vW2<vW<vWnIn the time, the wind turbine generator is in a constant rotating speed operation mode, and when d% of load reduction is needed, the wind energy capture coefficient C after load reduction is calculatedpdAnd solving the pitch angle beta by using the Newton methoddIs adjusted when v isWn<vW<vW_outIn the time, the wind turbine generator is in a constant power operation mode, and the output power of the wind turbine generator is the rated power PnWhen d% of load shedding is needed, the reference power is only set to be (1-d%) PnAnd (4) finishing.
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