CN114069729B - Permanent magnet direct-driven wind farm reactive voltage control strategy based on self-adaptive droop control - Google Patents
Permanent magnet direct-driven wind farm reactive voltage control strategy based on self-adaptive droop control Download PDFInfo
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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
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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
- H02J3/12—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
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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
- H02J3/381—Dispersed generators
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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
- 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]
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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
- 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
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- 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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- 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
Abstract
The invention discloses a permanent magnet direct-driven wind farm reactive voltage control strategy based on self-adaptive droop control, which comprises the following steps: firstly, establishing a wind power plant grid-connected model, and determining output power curves of the wind turbine generator set at different wind speeds and reactive capacities of the wind turbine generator set 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 the grid-connected point is stable, and the tip speed ratio is controlled to keep an optimal value so as to achieve a maximum wind energy capturing 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 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 support is provided for the system, and the problem of grid-connected point voltage out-of-limit is solved.
Description
Technical Field
The invention belongs to the field of power system automation, and relates to a permanent magnet direct-driven wind farm reactive voltage control strategy based on self-adaptive droop control.
Background
Wind power generation is widely used in power systems as a renewable energy power generation technology, however, large-scale grid connection of wind power often affects stable operation of the system. The domestic wind farm 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 farm changes greatly, the voltage stability of grid-connected points is obviously reduced, so that the safety and stability of a power system are affected. At present, research on improving reactive power level and grid-connected point voltage quality of a wind farm at home and abroad is mainly carried out from two aspects: reactive compensation equipment is configured in the system to ensure the voltage stability of the wind power plant, or reactive control scheme measures of the wind power plant are formulated from the wind power plant.
Because of the added configuration of reactive compensation equipment, a certain investment is required to be added, and the wind power plant is made to participate in reactive adjustment, so that an economical adjustment means is realized. The permanent magnet direct-driven wind turbine generator and the double-fed wind turbine generator have certain reactive power regulation capability, and when the power grid falls less, the requirement can be met by means of reactive power compensation of the wind turbine generator. Compared with a double-fed wind turbine, the permanent magnet direct-driven wind turbine has better reactive voltage characteristic, and reactive power support is provided for a system by utilizing the reactive power regulation capability of the permanent magnet direct-driven wind turbine. When the system voltage is reduced, the grid-side converter of the permanent magnet direct-driven wind turbine generator controls active and reactive decoupling, and a certain reactive support can be provided for a power grid rapidly through adjustment. At present, a voltage control strategy of wind turbines generally adopts fixed droop gain, and cannot be reasonably distributed according to reactive capacity of each wind turbine, so that an optimal control strategy capable of adaptively adjusting reactive power of the wind turbines according to wind speed conditions is needed.
Disclosure of Invention
In order to solve the technical problems, the invention provides a permanent magnet direct-drive wind farm reactive voltage control strategy based on self-adaptive droop control, which solves the problem of uneven reactive power distribution caused by adopting fixed droop gain in the prior art.
The invention discloses a permanent magnet direct-driven wind farm reactive voltage control strategy based on self-adaptive droop control, which comprises the following steps:
step 1, establishing a wind farm grid-connected system model consisting of a permanent magnet direct drive wind turbine, static loads and synchronous generators, determining output power curves of the wind turbine at different wind speeds, and determining reactive capacity of the wind turbine at different running states according to coupling relations between active power and reactive power;
step 2, detecting 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 carry out step 3; if the voltage of the grid-connected point is out of limit, judging reactive capacity, and when the reactive capacity is sufficient, performing step 4 by adopting self-adaptive droop control on the grid-side converter; 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 is operated 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 an optimal value so as to achieve a maximum wind energy capturing state, and the wind turbine outputs maximum active power;
step 4, the wind turbine generator adopts self-adaptive droop control, a reactive power control link of the grid-side converter is provided with a self-adaptive droop coefficient, the reactive power output of each wind turbine generator can be automatically adjusted along with the change of wind speed, the reactive power output of each wind turbine generator is reasonably distributed to support grid-connected point voltage, and the stable operation of the system is ensured;
and 5, adopting a load shedding operation mode for the wind turbine, adopting a corresponding load shedding method according to wind speed change, adjusting the rotating speed of the rotor, realizing load shedding by combining pitch angle control, increasing reactive power output, and keeping self-adaptive droop control for the grid-side converter.
In the step 1, a grid-connected system model of the permanent magnet direct-drive wind turbine is built according to the operation characteristics of the permanent magnet direct-drive wind turbine, and a relation curve of wind speed and a tip speed ratio curve is determined; wind turbine captured power, rotating speed and pitch angle thereof are related, and per unit value P wt The method comprises the following steps:
wherein P is N For rated power of the wind turbine generator, ρ is air density, R is wind wheel radius, v W For wind speed value, C p For wind energy capture coefficients, this can be expressed as
Wherein lambda is tip speed ratio omega N Rated mechanical speed of rotor, c 1 ～c 6 To fit coefficients, ω t The rotor speed is the rotor speed, and beta is the pitch angle; c when the fitting coefficient takes different values p The functions having different optimum tip speed ratios lambda opt And maximum wind energy capture coefficient C pmax ；
The reactive capacity of the wind turbine generator is determined by active power and apparent power
Wherein: s is S W The apparent power of the wind turbine generator system converter is obtained.
Further, 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 the wind speed change:
the first stage is the optimal rotation speed operation stage, when the wind energy capturing coefficient C p The function takes the maximum value and corresponds to the fixed optimal tip speed ratio lambda opt Regulating the rotational speed omega of a wind turbine t Maintaining the tip speed ratio at lambda opt In this case, the wind turbine is operated at an optimal rotational speed and captures the maximum wind energy;
the second stage is a constant rotation speed operation stage, and when the wind speed continues to increase and the captured power does not exceed the rated power of the wind turbine, the rotation speed of the rotor of the wind turbine is maintained at omega tmax Operating in a constant rotation speed mode;
the third stage 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 generator set wn When the wind turbine is required to operate in a constant power state to prevent overload, as the rotating speed of the wind turbine reaches the upper limit, the pitch angle needs to be increased to limit the capture power of the wind motor.
In 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 adaptive droop control loop is defined as:
wherein: k (k) p Is the proportionality coefficient, k of the PI regulator i Is the integral coefficient of the PI regulator, 1/s is the integral link, Q 0 Is a reactive power reference value, usually set to 0, V sys Is the effective value of voltage, V nom At the value of the rated voltage, the voltage is calculated,for the adaptive droop coefficient, the adaptive droop coefficient is proportional to the reactive power of the wind turbine generator, Q W,i Reactive power of the i-number wind turbine generator; 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 required to be supplied to grid-connected points under the condition of guaranteeing grid-connected voltage stability L Because the output power of the wind turbine generator meetsThe closer the wind turbine generator is to the rated state, the larger the reactive capacity released by the same power is released, so that the load shedding priority of each wind turbine generator needs to be judged, and the wind turbine generator is selected for load shedding control;
wherein: s is the rated power of the wind turbine generator;the active output of the i-number wind turbine generator system; Δp is the load reduction; ΔQ w,i For reactive power increment after load shedding of No. i wind turbine generator, k is the number of the wind turbine generator for load shedding, j is the number of the wind turbine generator for load shedding, n is the number of the wind turbine generator in the wind power plant, and delta Q is calculated by the number of the wind turbine generator k For reactive increment after load shedding of k-number wind turbine generator system, Q W,i Output reactive power for wind turbine generator system, Q L Providing reactive support for the grid-connected points for the wind farm; when the wind turbine generator performs load shedding control, the load shedding level d% of the wind turbine generator can be expressed as d% = Δp W,i /P W,i 。
Further, the step of determining the load shedding mode by considering different wind speed intervals during the load shedding operation mode control is as follows: according to the wind speed, the wind turbine generator is divided into a low wind speed section, a medium wind speed section and a high wind speed section, different load shedding control methods are adopted in each section, and in the low wind speed section, the wind turbine generator is in a maximum power tracking running state, and at the moment, the wind energy capturing coefficient reaches the maximum C pmax The pitch angle beta is 0 DEG, and when the load reduction d% is required, C is calculated according to a blade tip speed ratio-wind energy capture coefficient curve pmax The corresponding tip speed ratio lambda when d% is reduced d1 Further, the reference rotation speed omega of the rotor after load shedding is obtained d1 ；
In the middle wind speed interval, the wind turbine generator is also in a maximum power tracking running state, and the rotor is in an optimal rotating speed omega opt Corresponding active power is P opt When the load reduction is required, if the rotor speed reaches the maximum allowable speed omega during overspeed load reduction max Load shedding is needed to be realized by matching with pitch angle control, and the reference power of the pitch control is set as follows:
in the high wind speed interval, when v W2 <v W <v Wn When the wind turbine generator is in a constant-rotation-speed running mode and d% load shedding is needed, calculating a wind energy capture coefficient C after load shedding pd And solving the pitch angle beta by Newton method d Make adjustments when v Wn <v W <v W_out When the wind turbine generator is in a constant power operation mode, the output power of the wind turbine generator is rated power P n When d% load shedding is needed, only the reference power is set to be (1-d%) P n And (3) obtaining the product.
The beneficial effects of the invention are as follows: the reactive voltage control strategy of the permanent magnet direct-drive electric field provided by the invention can track the voltage change of the grid-connected point, quickly implement reactive voltage regulation, realize accurate control on the grid-connected point voltage of the wind power plant, avoid the problem of voltage out-of-limit caused by disturbance or fault condition of the system, and ensure 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 an additional reactive compensation device and improving the running economy of the system.
Drawings
In order that the invention may be more readily understood, a more particular description of the invention 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 wind energy utilization coefficient versus tip speed ratio;
FIG. 3 is an adaptive droop control element;
FIG. 4 is a graph of wind turbine power versus speed characteristics;
FIG. 5 is a graph of low, medium, and high wind speed divisions.
Detailed Description
As shown in fig. 1, the reactive voltage control strategy of the permanent magnet direct-driven wind farm based on the self-adaptive droop control comprises the following steps:
step 1, establishing a wind farm grid-connected system model consisting of a permanent magnet direct drive wind turbine, static loads and synchronous generators, determining output power curves of the wind turbine at different wind speeds, and determining reactive capacity of the wind turbine at different running states according to coupling relations between active power and reactive power;
step 2, detecting 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 carry out step 3; if the voltage of the grid-connected point is out of limit, judging reactive capacity, and when the reactive capacity is sufficient, performing step 4 by adopting self-adaptive droop control on the grid-side converter; 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 is operated 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 an optimal value so as to achieve a maximum wind energy capturing state, and the wind turbine outputs maximum active power;
step 4, the wind turbine generator adopts self-adaptive droop control, a reactive power control link of the grid-side converter is provided with a self-adaptive droop coefficient, the reactive power output of each wind turbine generator can be automatically adjusted along with the change of wind speed, the reactive power output of each wind turbine generator is reasonably distributed to support grid-connected point voltage, and the stable operation of the system is ensured;
and 5, adopting a load shedding operation mode for the wind turbine, adopting a corresponding load shedding method according to wind speed change, adjusting the rotating speed of the rotor, realizing load shedding by combining pitch angle control, increasing reactive power output, and keeping self-adaptive droop control for the grid-side converter.
In step 1, determining output power curves of the wind turbine generator set at different wind speeds, and determining reactive capacity of the wind turbine generator set at different running states according to coupling relations between active power and reactive power, wherein the specific method comprises the following steps:
wind turbine captured power, rotating speed and pitch angle thereof are related, and per unit value P wt The method comprises the following steps:
wherein P is N For rated power of the wind turbine generator, ρ is air density, R is wind wheel radius, v W For wind speed value, C p For wind energy capture coefficients, this can be expressed as
Wherein lambda is tip speed ratio omega N Rated mechanical speed of rotor, c 1 ～c 6 To fit coefficients, ω t The rotor speed is the rotor speed, and beta is the pitch angle; c when the fitting coefficient takes different values p The functions having different optimum tip speed ratios lambda opt And maximum wind energy capture coefficient C pmax 。
The wind turbine generator is provided with a pitch angle control system, which can adjust the capture power and limit the rotation speed of the wind wheel; when the system is in operation, the rotating speed of the wind turbine is required to be limited not to exceed the upper limit omega tmax When the rotating speed omega of the wind turbine t Less than omega tmax When pitch angle control is not active, 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 figure 2; in the running process of the motor set, the wind energy capturing 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:
wherein: s is S W The apparent power of the wind turbine generator system converter is obtained.
When the output power of the wind turbine reaches rated power and the reactive power shortage is large, the reactive power margin of the wind turbine can be increased through load shedding operation according to the relation between the active power and the reactive power.
In the step 2, a control mode of the wind turbine generator is selected by measuring whether the voltage of the grid-connected point is out of limit; when the voltage of the grid-connected point is within the range of 0.95-1.05pu, a maximum power tracking control mode is adopted; when the voltage of the grid-connected point is lower than 0.95pu, judging the reactive capacity: if it is reactiveCapacity higher than reactive power demand Q L Adopting self-adaptive droop control, entering a step four, and if the reactive capacity is lower than the reactive demand Q L And adopting load shedding control to enter a step five.
In step 3, the wind turbine generator runs in a maximum power tracking mode, and in order to maximize the wind energy utilization coefficient, the maximum power tracking control can be realized by controlling the rotating speed of the fan to track the optimal rotating speed.
The tracking process is divided into three phases according to the wind speed change: first, the optimum rotation speed operation stage is that the wind energy capturing coefficient C p The function takes the maximum value and corresponds to the fixed optimal tip speed ratio lambda opt Regulating the rotational speed omega of a wind turbine t Maintaining the tip speed ratio at lambda opt In this case, the wind turbine is operated at an optimal rotational speed and captures the maximum wind energy; the second is a constant rotation speed operation stage, when the wind speed continues to increase and the captured power does not exceed the rated power of the wind turbine, the rotation speed of the rotor of the wind turbine is maintained at omega tmax Operating in a constant rotation speed mode; thirdly, in a constant power operation stage, when the wind speed exceeds the rated wind speed v corresponding to the rated power of the wind turbine generator set wn When the wind turbine is required to operate in a constant power state to prevent overload, as the rotating speed of the wind turbine reaches the upper limit, the pitch angle needs to be increased to limit the capture power of the wind motor.
In step 4, the wind turbine operates in a self-adaptive droop control mode, the network side converter adopts self-adaptive droop control on reactive power, and the droop coefficient is self-adaptively adjusted according to the current reactive capacity of the wind turbine; when the releasable reactive power of the wind turbine is larger, the sagging coefficient of the wind turbine can be set larger; and when the releasable reactive power is smaller, a smaller droop factor 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:
wherein: k (k) p Is the proportionality coefficient, k of the PI regulator i Is the integral coefficient of the PI regulator, 1/s is the integral link, Q 0 Is a reactive power reference value, usually set to 0, V sys Is the effective value of voltage, V nom At the value of the rated voltage, the voltage is calculated,for the adaptive droop coefficient, the adaptive droop coefficient is proportional to the reactive power of the wind turbine generator, Q W,i Reactive power of the i-number wind turbine generator; 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 the system is facilitated. In addition, the sagging coefficient can be adaptively increased along with the increased reactive power capacity, so that the wind turbine generator is prevented from frequently reaching the maximum reactive power limit, and the abrasion of the converter is reduced.
In step 5, the method for load shedding operation mode control comprises the following steps: determining minimum value Q of reactive power required to be supplied to grid-connected points under condition of guaranteeing grid-connected voltage stability of wind farm L Because the output power of the wind turbine generator meetsThe closer the wind turbine generator is to the rated state, the larger the reactive capacity released by the same power is released, so that the load shedding priority of each wind turbine generator needs to be judged, and the wind turbine generator is selected for load shedding control;
wherein: s is the rated power of the wind turbine generator;the active output of the i-number wind turbine generator system; Δp is the load reduction; ΔQ w,i For reactive power increment after load shedding of No. i wind turbine generator, k is the number of the wind turbine generator for load shedding, j is the number of the wind turbine generator for load shedding, n is the number of the wind turbine generator in the wind power plant, and delta Q is calculated by the number of the wind turbine generator k For reactive increment after load shedding of k-number wind turbine generator system, Q W,i Output reactive power for wind turbine generator system, Q L Providing reactive support for the grid-connected points for the wind farm; when the wind turbine generator performs load shedding control, the load shedding level d% of the wind turbine generator can be expressed as d% = Δp W,i /P W,i 。
The power-rotating speed characteristic curve of the wind turbine generator is shown in fig. 4, and represents the relationship between the output power and the rotating speed of the wind turbine generator at different pitch angles at a certain wind speed. When the wind speed is v W0 When the pitch angle is changed from beta, 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 point 0 Increased to beta 1 The characteristic curve is wholly lowered, and the capture power of the wind turbine generator is reduced, so that load shedding is realized.
The wind turbine generator runs in a load shedding control mode, wind speed is divided into a low section, a medium section and a high section according to the wind speed, as shown in fig. 5, the 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 region is a region surrounded by BCB ', the load reduction is needed through the coordination control of the rotation speed and the pitch angle due to the limitation of the highest rotation speed, the high wind speed region is a line segment C ' D, the C ' point is obtained through the pitch control of the C point, and the wind speed corresponding to the D point is the cut-out wind speed v of the wind turbine W_out In the high wind speed section, the rotating speed reaches the maximum, overspeed control cannot be performed, and load shedding can be realized only through variable pitch control. The low wind speed interval is cut-in wind speed v W_in ～v W1 The stroke speed interval is v W1 ～v W2 The high wind speed interval is v W2 ～v W_out 。
Wherein: omega max Is the maximum allowable rotation speed lambda of the wind turbine d To speed ratio of tip after load shedding, lambda is related to load shedding level opt For optimal tip speed ratio, the load shedding level d% may be expressed as d% = Δp W,i /P W,i 。
In a low wind speed interval, the wind turbine generator is in a maximum power tracking running state, and the wind energy capture coefficient reaches the maximum C pmax The pitch angle beta is 0 DEG, and when the load reduction d% is required, C is calculated according to a blade tip speed ratio-wind energy capture coefficient curve pmax The corresponding tip speed ratio lambda when d% is reduced d1 Further, the reference rotation speed omega of the rotor after load shedding is obtained d1 。
In the middle wind speed interval, the wind turbine generator is also in a maximum power tracking running state, and the rotor is in an optimal rotating speed omega opt Corresponding active power is P opt When the load reduction is required, if the rotor speed reaches the maximum allowable speed omega during overspeed load reduction max Load shedding is needed to be realized by matching with pitch angle control, and the reference power of the pitch control is set as follows:
in the high wind speed interval, when v W2 <v W <v Wn When the wind turbine generator is in a constant-rotation-speed running mode and d% load shedding is needed, calculating a wind energy capture coefficient C after load shedding pd And solving the pitch angle beta by Newton method d Make adjustments when v Wn <v W <v W_out When the wind turbine generator is in a constant power operation mode, the output power of the wind turbine generator is rated power P n When d% load shedding is needed, only the reference power is set to be (1-d%) P n And (3) obtaining the product.
And after the voltage of the grid-connected point is recovered, the wind turbine is recovered to the running state before load shedding control, so that the output power of the wind turbine is increased while the reactive power requirement of the system is met.
The foregoing is merely a preferred embodiment of the present invention, and is not intended to limit the present invention, and all equivalent variations using the description and drawings of the present invention are within the scope of the present invention.
Claims (5)
1. The permanent magnet direct-driven wind farm reactive voltage control strategy based on the self-adaptive droop control is characterized by comprising the following steps:
step 1, establishing a wind farm grid-connected system model consisting of a permanent magnet direct drive wind turbine, static loads and synchronous generators, determining output power curves of the wind turbine at different wind speeds, and determining reactive capacity of the wind turbine at different running states according to coupling relations between active power and reactive power;
step 2, detecting 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 carry out step 3; if the voltage of the grid-connected point is out of limit, judging reactive capacity, and when the reactive capacity is sufficient, performing step 4 by adopting self-adaptive droop control on a grid-side converter of the wind turbine generator; when the reactive capacity is insufficient, the grid-side converter of the wind turbine generator performs load shedding control while adopting adaptive droop control, and step 5 is performed;
step 3, the wind turbine is operated 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 an optimal value so as to achieve a maximum wind energy capturing state, and the wind turbine outputs maximum active power;
step 4, the wind turbine generator adopts self-adaptive droop control, a reactive power control link of the grid-side converter is provided with a self-adaptive droop coefficient, the reactive power output of each wind turbine generator can be automatically adjusted along with the change of wind speed, the reactive power output of each wind turbine generator is reasonably distributed to support grid-connected point voltage, and the stable operation of the system is ensured;
step 5, the wind turbine adopts a load shedding operation mode, a corresponding load shedding method is adopted according to wind speed change, the rotation speed of a rotor is regulated, load shedding is realized by combining pitch angle control, reactive power output is increased, and the grid-side converter keeps self-adaptive droop control;
the step of determining the load shedding mode by considering different wind speed intervals during load shedding operation mode control is as follows: according to the wind speed, the wind turbine generator is divided into a low wind speed section, a medium wind speed section and a high wind speed section, different load shedding control methods are adopted in each section, and in the low wind speed section, the wind turbine generator is in a maximum power tracking running state, and at the moment, the wind energy capturing coefficient reaches the maximum C pmax The pitch angle beta is 0 DEG, and when the load reduction d% is required, C is calculated according to a blade tip speed ratio-wind energy capture coefficient curve pmax The corresponding tip speed ratio lambda when d% is reduced d1 Further, the reference rotation speed omega of the rotor after load shedding is obtained d1 ；
In the middle wind speed interval, the wind turbine generator is also in a maximum power tracking running state, and the rotor is in an optimal rotating speed omega opt Corresponding active power is P opt When the load reduction is required, if the rotor speed reaches the maximum allowable speed omega during overspeed load reduction max Load shedding is needed to be realized by matching with pitch angle control, and the reference power of the pitch control is set as follows:
in the high wind speed interval, when v W2 <v W <v Wn When the wind turbine generator is in a constant-rotation-speed running mode and d% load shedding is needed, calculating a wind energy capture coefficient C after load shedding pd And solving the pitch angle beta by Newton method d Make adjustments when v Wn <v W <v W_out When the wind turbine generator is in a constant power operation mode, the output power of the wind turbine generator is rated power P n When d% load shedding is needed, only the reference power is set to be (1-d%) P n And (3) obtaining the product.
2. The permanent magnet direct drive wind farm reactive voltage control strategy based on adaptive droop control according to claim 1, wherein the strategy is characterized in thatIn the step 1, a grid-connected system model of the permanent magnet direct-driven wind turbine is established according to the operation characteristics of the permanent magnet direct-driven wind turbine, and a relation curve of wind speed and a tip speed ratio curve is determined; wind turbine captured power, rotating speed and pitch angle thereof are related, and per unit value P wt The method comprises the following steps:
wherein P is N For rated power of the wind turbine generator, ρ is air density, R is wind wheel radius, v W For wind speed value, C p For wind energy capture coefficients, this can be expressed as
Wherein lambda is tip speed ratio omega N Rated mechanical speed of rotor, c 1 ～c 6 To fit coefficients, ω t The rotor speed is the rotor speed, and beta is the pitch angle; c when the fitting coefficient takes different values p The functions having different optimum tip speed ratios lambda opt And maximum wind energy capture coefficient C pmax ；
The reactive capacity of the wind turbine generator is determined by active power and apparent power;
wherein: s is S W The apparent power of the wind turbine generator system converter is obtained.
3. The permanent magnet direct-drive wind farm reactive voltage control strategy based on adaptive droop control according to claim 1, wherein in step 3, the wind turbine is normally operated in a maximum power tracking mode, and the tracking process is divided into three stages according to wind speed variation:
the first stage is the optimal rotation speed operation stage, when the wind energy capturing coefficient C p The function being fixed correspondingly when taking maximum valueOptimal tip speed ratio lambda opt Regulating the rotational speed omega of a wind turbine t Maintaining the tip speed ratio at lambda opt In this case, the wind turbine is operated at an optimal rotational speed and captures the maximum wind energy;
the second stage is a constant rotation speed operation stage, and when the wind speed continues to increase and the captured power does not exceed the rated power of the wind turbine, the rotation speed of the rotor of the wind turbine is maintained at omega tmax Operating in a constant rotation speed mode;
the third stage 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 generator set wn When the wind turbine is required to operate in a constant power state to prevent overload, as the rotating speed of the wind turbine reaches the upper limit, the pitch angle needs to be increased to limit the capture power of the wind motor.
4. The reactive voltage control strategy of the permanent magnet direct-drive wind farm based on the adaptive droop control according to claim 1, wherein in the step 4, the grid-side converter in the converter adopts the adaptive droop control, and the setting principle of the droop coefficient is based on the current reactive capacity of the wind turbine; the reactive current output of the adaptive droop control loop is defined as:
wherein: k (k) p Is the proportionality coefficient, k of the PI regulator i Is the integral coefficient of the PI regulator, 1/s is the integral link, Q 0 Is a reactive power reference value, usually set to 0, V sys Is the effective value of voltage, V nom At the value of the rated voltage, the voltage is calculated,for the adaptive droop coefficient, the adaptive droop coefficient is proportional to the reactive power of the wind turbine generator, Q W,i No. i wind turbine generator systemA power; c is a constant coefficient.
5. The permanent magnet direct drive wind farm reactive voltage control strategy based on adaptive droop control according to claim 1, wherein in step 5, the method for load shedding operation mode control is as follows:
determining the minimum value delta Q of reactive power required to be supplied to grid-connected points under the condition of guaranteeing grid-connected voltage stability L Because the output power of the wind turbine generator meetsThe closer the wind turbine generator is to the rated state, the larger the reactive capacity released by the same power is released, so that the load shedding priority of each wind turbine generator needs to be judged, and the wind turbine generator is selected for load shedding control;
wherein: s is the rated power of the wind turbine generator;the active output of the i-number wind turbine generator system; Δp is the load reduction; ΔQ w,i For reactive power increment after load shedding of No. i wind turbine generator, k is the number of the wind turbine generator for load shedding, j is the number of the wind turbine generator for load shedding, n is the number of the wind turbine generator in the wind power plant, and delta Q is calculated by the number of the wind turbine generator k For reactive increment after load shedding of k-number wind turbine generator system, Q W,i Output reactive power for wind turbine generator system, deltaQ L Providing reactive support for the grid-connected points for the wind farm; when the wind turbine generator system performs load shedding control, the load shedding level d% of the wind turbine generator system can be expressedShown as d% = Δp W,i /P W,i 。
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