CN112072701A - Improved torque limit control method based on double-fed wind turbine generator - Google Patents

Improved torque limit control method based on double-fed wind turbine generator Download PDF

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CN112072701A
CN112072701A CN202010932436.XA CN202010932436A CN112072701A CN 112072701 A CN112072701 A CN 112072701A CN 202010932436 A CN202010932436 A CN 202010932436A CN 112072701 A CN112072701 A CN 112072701A
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doubly
fed
wind turbine
power
output
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CN112072701B (en
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唐飞
刘涤尘
卿梦琪
刘福锁
吴雪莲
王玉
都念纯
胡本溪
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Wuhan University WHU
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

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

Abstract

The invention discloses an improved torque limit control method based on a doubly-fed wind turbine generator, which comprises the following steps of: when an electric power system after wind power integration encounters a frequency disturbance accident, the active output of the double-fed fan is increased instantaneously, and then the active output is reduced by a quadratic function of the rotating speed until the difference between the output electromagnetic power of the double-fed fan and the captured mechanical power approaches zero; and then the active power of the doubly-fed fan slowly declines along with time, then the constant is maintained until the active power is equal to the maximum power tracking output value, and finally the doubly-fed fan returns to the maximum power tracking control state. The double-fed fan has higher rotating speed recovery speed, can avoid the problem of frequency secondary falling to the maximum extent, and can effectively improve the lowest point of frequency falling in different frequency responses.

Description

Improved torque limit control method based on double-fed wind turbine generator
Technical Field
The invention relates to the technical field of electromechanical control, in particular to an improved torque limit control method based on a double-fed wind turbine generator.
Background
In recent years, variable speed wind generators (WTGs), typically represented by Doubly Fed Induction Generators (DFIGs), have become the most widely used wind generators on the market due to their advanced control performance. The generator set realizes variable-speed constant-frequency control on the wind turbine generator set through the converter connected to the side of the rotor, and captures the maximum wind energy. However, the power electronic converter decouples the rotational speed of the wind turbine from the grid frequency, and the rotational kinetic energy accumulated in the rotor cannot be effectively released, which hardly contributes to the inertia of the power system, and this adversely affects the frequency stability. Therefore, how to make the wind turbine generator participate in the system frequency control is the key to maintain the safe and stable operation of the power grid. At present, the mainstream frequency control method for the doubly-fed wind turbine generator mainly comprises two methods: one is that the generator set runs in a load shedding state to provide power support through the overspeed running of the rotor or the change of the pitch angle, but the long-term load shedding operation of the wind turbine set has influence on the economy of the system. The other type is that the kinetic energy of a rotor of the wind turbine generator is released through control, power support is provided for the system in a frequency fluctuation stage, and the method can fully adjust active power output based on the advantage of large rotating speed adjusting range of the wind turbine generator, so that the wind turbine generator has certain inertia response capability. However, since the control process only establishes the active-time relationship and neglects the change of the rotating speed and the change of the mechanical power, the kinetic energy of the rotor is easily released excessively. Meanwhile, the inertia response capability of the fan is weakened along with the reduction of the rotating speed, so that subsequent active power is insufficient in the frequency recovery process, and the phenomenon of secondary frequency drop is caused. When the system frequency falls for the second time, the quality of electric energy is seriously influenced, and the production process of each department is influenced or even destroyed. Meanwhile, the power generator has great harm to a steam turbine of a power plant, and the output of plant machinery of the power plant is obviously reduced, so that the output of the power generator is reduced, the power is more deficient, the frequency is further reduced, and even the frequency collapse phenomenon is caused.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an improved torque limit control method based on a double-fed wind turbine generator set, aiming at the defects in the prior art, so that the double-fed wind turbine generator set can have a faster rotating speed recovery speed, the problem of frequency secondary falling can be avoided to the greatest extent, and the lowest point of frequency falling can be effectively improved in different frequency responses.
The technical scheme adopted by the invention for solving the technical problems is as follows:
an improved torque limit control method based on a doubly-fed wind turbine generator set comprises the following steps:
step 1), a frequency detection module is arranged in the double-fed fan, and when the frequency detection module detects that the frequency deviation and the frequency change rate of the power system reach a set starting threshold, the double-fed fan is determined to have a disturbance accident;
step 2), adjusting a controllable switch of the double-fed fan to enable the double-fed fan to provide electromagnetic power support, wherein the output electromagnetic power value of the double-fed fan is a certain value which is instantly increased on the basis of a steady-state value before a disturbance accident; at the moment of increasing to a fixed value, the output electromagnetic power value of the double-fed fan is adjusted to be reduced by a quadratic function of the rotating speed on the basis of the output fixed value;
step 3), when the difference between the output electromagnetic power of the doubly-fed fan and the mechanical power captured by the fan is gradually reduced to zero through the frequency detection module, adjusting a controllable switch of the doubly-fed fan to enable the output electromagnetic power of the doubly-fed fan to linearly reduce for a certain time at a certain speed along with the time, and then keeping the output electromagnetic power unchanged;
and 4), when the output electromagnetic power of the double-fed fan at a certain moment is equal to the output electromagnetic power of the double-fed fan under the maximum power tracking control at the moment, adjusting a controllable switch of the double-fed fan to switch the double-fed fan to the maximum power tracking control, and completing the rest rotating speed recovery process.
According to the technical scheme, in the step 1), the condition that the double-fed fan generates the disturbance accident is determined as follows: detecting that the frequency deviation and the change rate of the doubly-fed fan reach a set starting threshold:
|Δf|≥T1 or|df/dt|≥T2
where f is the system frequency, Δ f is the system frequency deviation, T1And T2Respectively, the frequency deviation and the rate of change.
According to the technical scheme, in the step 2), the instantaneous output power value provided by the doubly-fed fan is provided when the system frequency is disturbed
PITLC＝PB＝P0+ΔPUP
In the formula, P0For steady value of output power of doubly-fed wind turbine before disturbance, delta PUPIs a constant value, PBAnd the instantaneous output power value is provided for the doubly-fed fan at the moment of system frequency disturbance, namely the output electromagnetic power of the doubly-fed fan when the doubly-fed fan operates at the working point B.
According to the above technical scheme, in the step 2), the adjustment of the output electromagnetic power value of the doubly-fed wind turbine to be reduced by a quadratic function of the rotating speed on the basis of the instant output fixed value means that
Figure BDA0002670688960000021
In the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, PBThe instantaneous output power value is provided for the doubly-fed fan at the moment of system frequency disturbance, namely the output electromagnetic power of the doubly-fed fan when the doubly-fed fan operates at the working point B; omegar0The initial rotor speed of the doubly-fed fan is the initial rotor speed of the doubly-fed fan when the system is not disturbed; omegarminThe minimum rotating speed allowed by the operation of the double-fed fan is set; pr_minAnd the output electromagnetic power is controlled by adopting maximum power tracking for the doubly-fed wind turbine and is operated at the lowest allowable rotating speed.
According to the above technical scheme, in the step 3), the gradual reduction of the difference between the output electromagnetic power of the doubly-fed wind turbine and the captured mechanical power to approach zero means that:
|PITLC-PMACH|＜5×10-4or | d ωr/dt|＜5×10-4
In the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, PMACHMechanical power difference, omega, captured for doubly-fed wind turbinesrThe rotating speed of the rotor of the doubly-fed wind turbine is shown, and t is time.
According to the technical scheme, in the step 3), the certain speed is 0.01-0.015 pu/s, and the certain time is 3-5 seconds.
According to the technical scheme, the double-fed fan is connected with the control system, the control system is further connected with the controllable switches and the frequency detection module, and the control system detects the state of the double-fed fan through the frequency detection module so as to adjust and start the controllable switches.
The invention has the following beneficial effects:
the improved torque limit control of the invention establishes the relation between the output active power and the rotor rotating speed in the rotor deceleration stage, and considers the change based on mechanical power in the rotor acceleration stage, thereby eliminating the hidden danger of the rotor kinetic energy over-release; meanwhile, when the rotating speed of the rotor is high, the active output after sudden increase is slowly reduced, and the variable quantity of the unbalanced power at the initial moment of the rotating speed recovery stage is reduced by adopting a mode of slowly reducing the active output at the rotating speed increasing stage, so that the secondary frequency drop phenomenon can be effectively improved, and the lowest point of the system frequency drop can be effectively improved.
Drawings
Fig. 1 shows the characteristic that the output power of a doubly-fed wind turbine changes with the rotating speed under the improved torque limit control method based on the doubly-fed wind turbine generator set.
Fig. 2 is an active reference value curve of the doubly-fed wind turbine under the improved torque limit control method based on the doubly-fed wind turbine generator set.
Fig. 3 is a control block diagram of the improved torque limit control method based on the doubly-fed wind turbine generator set, which is implemented in a doubly-fed wind turbine.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and examples.
Referring to fig. 1 to fig. 3, in an embodiment of the present invention, an improved torque limit control method based on a doubly-fed wind turbine includes the following steps:
step 1), a frequency detection module is arranged in the double-fed fan, and when the frequency detection module detects that the frequency deviation and the frequency change rate of the power system reach a set starting threshold, the double-fed fan is determined to have a disturbance accident;
step 2), adjusting a controllable switch of the double-fed fan to enable the double-fed fan to provide electromagnetic power support, wherein the output electromagnetic power value of the double-fed fan is a certain value which is instantly increased on the basis of a steady-state value before a disturbance accident; at the moment of increasing to a fixed value, the output electromagnetic power value of the double-fed fan is adjusted to be reduced by a quadratic function of the rotating speed on the basis of the output fixed value;
step 3), when the difference between the output electromagnetic power of the doubly-fed fan and the mechanical power captured by the fan is gradually reduced to zero through the frequency detection module, adjusting a controllable switch of the doubly-fed fan to enable the output electromagnetic power of the doubly-fed fan to linearly reduce for a certain time at a certain speed along with the time, and then keeping the output electromagnetic power unchanged;
and 4), when the output electromagnetic power of the double-fed fan at a certain moment is equal to the output electromagnetic power of the double-fed fan under the maximum power tracking control at the moment, adjusting a controllable switch of the double-fed fan to switch the double-fed fan to the maximum power tracking control, and completing the rest rotating speed recovery process.
Further, in the step 1), the condition that the double-fed fan has a disturbance accident is determined as follows: detecting that the frequency deviation and the change rate of the doubly-fed fan reach a set starting threshold:
|Δf|≥T1 or|df/dt|≥T2
where f is the system frequency, Δ f is the system frequency deviation, T1And T2Respectively, the frequency deviation and the rate of change.
Further, in the step 2), the instantaneous electromagnetic power output value provided by the doubly-fed wind turbine is provided
PITLC＝PB＝P0+ΔPUP
In the formula, P0For steady value of output power of doubly-fed wind turbine before disturbance, delta PUPIs a fixed value; pBAnd the instantaneous output power value is provided for the doubly-fed fan at the moment of system frequency disturbance, namely the output electromagnetic power of the doubly-fed fan when the doubly-fed fan operates at the working point B.
Further, in the step 2), the output electromagnetic power value of the doubly-fed wind turbine is adjusted to an expression of a quadratic function based on the rotating speed on the basis of the instant output fixed value, and the expression is as follows:
Figure BDA0002670688960000041
in the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, PBThe instantaneous output power value provided for the doubly-fed fan at the moment of system frequency disturbance, namely the output electromagnetic power omega of the doubly-fed fan when the doubly-fed fan operates at the working point Br0The initial rotor speed of the doubly-fed fan is the initial rotor speed of the doubly-fed fan when the system is not disturbed; omegarminThe minimum rotating speed allowed by the operation of the double-fed fan is set; pr_minAnd the output electromagnetic power is controlled by adopting maximum power tracking for the doubly-fed wind turbine and is operated at the lowest allowable rotating speed.
Further, in the step 3), the gradual reduction of the difference between the output electromagnetic power of the doubly-fed wind turbine and the captured mechanical power to approach zero means that:
|PITLC-PMACH|＜5×10-4or | d ωr/dt|＜5×10-4
In the formula，PITLCFor doubly-fed wind turbine output of electromagnetic power, PMACHMechanical power difference, omega, captured for doubly-fed wind turbinesrThe rotating speed of the rotor of the doubly-fed wind turbine is shown, and t is time.
Further, in the step 3), the certain speed is 0.01 to 0.015pu/s, and the certain time is 3 to 5 seconds.
Furthermore, the double-fed fan is connected with a control system, the control system is further connected with each controllable switch and the frequency detection module, and the control system detects the state of the double-fed fan through the frequency detection module so as to adjust and start the controllable switches.
Further, the step 1) is a frequency accident detection step, the step 2) is a double-fed fan inertia response deceleration stage, the step 3) is a double-fed fan inertia response acceleration stage, and the step 4) is a maximum power tracking control stage.
In one embodiment of the invention, the improved torque limit control method based on the doubly-fed wind turbine generator set comprises the following steps:
step 1, detecting frequency accidents: the improved torque limit control is connected to the active control loop of the doubly-fed wind turbine through the first controllable switch 1 in fig. 3. A frequency detection module is provided and the first controllable switch 1 in fig. 3 provides a trigger signal. When the monitored frequency deviation and rate of change reach the start-up threshold, i.e. when the system frequency satisfies:
|Δf|≥T1 or|df/dt|≥T2
where f is the system frequency, Δ f is the system frequency deviation, T1And T2Respectively, the frequency deviation and the rate of change.
At this time, it is assumed that a frequency accident occurs in the system, and the improved torque limit control is started.
Step 2, during the inertial response deceleration stage of the doubly-fed wind turbine: after the system is detected to be disturbed, the controllable switch is switched on, so that the double-fed fan releases the kinetic energy of the rotor and provides the electromagnetic power to support the frequency recovery of the power-assisted system. At the moment of disturbance, the output electromagnetic power value of the double-fed fan is increased by a certain value on the basis of a steady-state value before a disturbance accident; at the moment of increasing to a fixed value, the output electromagnetic power value of the double-fed fan is adjusted to be reduced by a quadratic function of the rotating speed on the basis of the output fixed value; the specific control method of the inertia response deceleration stage in the step 2 is as follows:
step 2.1, after the system is detected to be disturbed, the third controllable switch 3 in fig. 3 is switched on a segment a → B in fig. 1 and fig. 2, the doubly-fed wind turbine is in a running state of a point B, and an electromagnetic power value P is outputITLCSteady state value P before disturbance0Adding a certain value delta P on the basis ofUP。
PITLC＝PB＝P0+ΔPUP
And 2.2, at the moment of increasing to a fixed value, adjusting the output electromagnetic power value of the doubly-fed fan to be reduced by a quadratic function of the rotating speed on the basis of the output fixed value (namely, a section B → C in the graph 1 and the graph 2). Output power value P of double-fed fanITLCCan be expressed as:
Figure BDA0002670688960000051
in the formula, PITLCTo output power value, PBRotating speed and active power output of the doubly-fed wind turbine at the point B are achieved under the control of the improved torque limit, namely the instantaneous output power value provided by the doubly-fed wind turbine at the moment of system frequency disturbance in the step 2.2; omegar0The initial rotor speed of the doubly-fed fan is the initial rotor speed of the doubly-fed fan when the system is not disturbed; omegarminThe lowest rotation speed allowed by the operation of the doubly-fed wind turbine (namely the rotation speed of an operation point C' in the figure 1); pr_minAnd (3) adopting maximum power tracking control for the doubly-fed fan and operating the output electromagnetic power at the lowest allowable rotating speed (namely the output electromagnetic power at the operating point C' in the figure 1).
Step 3, the double-fed fan inertia response acceleration stage: when the difference between the output electromagnetic power of the doubly-fed fan and the captured mechanical power is gradually reduced to approach zero, assuming that the doubly-fed fan operates at a working point C at the moment, reading the output electromagnetic power of the working point C and the moment of operating to the working point, enabling the output electromagnetic power of the doubly-fed fan to linearly decrease for a certain time along with the time at a certain speed, and then keeping the output electromagnetic power unchanged. Taking the speed of 0.01pu/s and the time of 3 seconds as an example, the specific control method of the inertia response acceleration stage in the step 2 is as follows:
step 3.1, when the difference between the output electromagnetic power and the captured mechanical power of the doubly-fed wind turbine in the section B → C in fig. 1 and fig. 2 is gradually reduced and approaches to zero:
|PITLC-PMACH|＜5×10-4or | d ωr/dt|＜5×10-4
In the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, PMACHMechanical power difference, omega, captured for doubly-fed wind turbinesrThe rotating speed of the fan rotor is shown, and t is time.
At this time, it can be considered that the fan rotor speed has converged to point C. The second controllable switch 2 switches on the acceleration phase.
And 3.2, after the acceleration stage is started, the fourth controllable switch 4 is firstly switched on the section C → D, and the output power of the fan is linearly reduced along with time at the speed of 0.01 pu/s. Double-fed fan output electromagnetic power PITLCIs shown as
PITLC＝PC-0.01×(t-tC)
In the formula, PITLCFor output power values, t is time, PCAnd tCAnd the active reference value and the moment of the doubly-fed wind turbine operating at the point C are obtained.
And 3.3, after the output electromagnetic power of the doubly-fed fan linearly decreases for 3 seconds along with time at the speed of 0.01pu/s, the fan operates to a point D. At this time:
PITLC＝PD＝PC-0.03pu
in the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, PDActive reference value P for doubly-fed wind turbine operating at point DCAnd the active reference value of the doubly-fed wind turbine running at the point C is obtained.
And 3.3, when the doubly-fed wind turbine runs at the point D, the fourth controllable switch 4 is switched on the segment D → E in the figure 1 and is kept unchanged. Output power P at this timeITLCCan be expressed as
PITLC＝PE＝PD-0.03pu
In the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, PEActive reference value P for operating the doubly-fed wind turbine at point E in FIGS. 1 and 2DAnd the active reference value is the active reference value of the doubly-fed wind turbine running at the point D.
Step 4, a maximum power tracking control stage: when the doubly-fed fan is in maximum power tracking control at a certain moment under the rotating speed, the output electromagnetic power PMPPTAnd D → E section double-fed fan output electromagnetic power PITLCAnd when the residual rotation speed is equal to the residual rotation speed, the double-fed fan is switched to the maximum power tracking control, and the residual rotation speed recovery process is completed.
Figure BDA0002670688960000061
In the formula, PITLCFor double-fed fan output of electromagnetic power, omegarThe rotating speed k of the wind driven generator for entering a rotating speed constant regionoptIs the maximum power tracking coefficient.
In conclusion, the doubly-fed wind turbine generator establishes a relation between an output active power and the rotor rotating speed in the rotor deceleration stage, and considers the change based on mechanical power in the rotor acceleration stage, so that the hidden danger of rotor kinetic energy over-release can be eliminated; meanwhile, when the rotating speed of the rotor is high, the active output after sudden increase is slowly reduced, and the variable quantity of the unbalanced power at the initial moment of the rotating speed recovery stage is reduced by adopting a mode of slowly reducing the active output at the rotating speed increasing stage, so that the frequency secondary falling phenomenon can be effectively improved.
The above is only a preferred embodiment of the present invention, and certainly, the scope of the present invention should not be limited thereby, and therefore, the present invention is not limited by the scope of the claims.

Claims (7)

1. An improved torque limit control method based on a doubly-fed wind turbine generator is characterized by comprising the following steps:
step 1), a frequency detection module is arranged in the double-fed fan, and when the frequency detection module detects that the frequency deviation and the frequency change rate of the power system reach a set starting threshold, the double-fed fan is determined to have a disturbance accident;
step 2), adjusting a controllable switch of the double-fed fan to enable the double-fed fan to provide electromagnetic power support, wherein the output electromagnetic power value of the double-fed fan is a certain value which is instantly increased on the basis of a steady-state value before a disturbance accident; at the moment of increasing to a fixed value, the output electromagnetic power value of the double-fed fan is adjusted to be reduced by a quadratic function of the rotating speed on the basis of the output fixed value;
step 3), when the difference between the output electromagnetic power of the doubly-fed fan and the mechanical power captured by the doubly-fed fan is gradually reduced to approach zero through the frequency detection module, adjusting a controllable switch of the doubly-fed fan to enable the output electromagnetic power of the doubly-fed fan to linearly reduce for a certain time at a certain speed along with the time, and then keeping the output electromagnetic power unchanged;
and 4), when the output electromagnetic power of the double-fed fan at a certain moment is equal to the output electromagnetic power of the double-fed fan under the maximum power tracking control at the moment, adjusting a controllable switch of the double-fed fan to switch the double-fed fan to the maximum power tracking control, and completing the rest rotating speed recovery process.
2. The improved torque limit control method based on the doubly-fed wind turbine generator set according to claim 1, wherein in the step 1), the condition that the doubly-fed wind turbine has a disturbance accident is determined as follows: detecting that the frequency deviation and the change rate of the doubly-fed fan reach a set starting threshold:
|Δf|≥T1 or|df/dt|≥T2
where f is the system frequency, Δ f is the system frequency deviation, T1And T2Respectively, the frequency deviation and the rate of change.
3. The improved torque limit control method based on the doubly-fed wind turbine generator set as claimed in claim 1, wherein in the step 2), the instantaneous output power value provided by the doubly-fed wind turbine generator set is adopted during system frequency disturbance
PITLC＝PB＝P0+ΔPUP
In the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, P0For steady value of output power of doubly-fed wind turbine before disturbance, delta PUPAt a certain value, PBAnd the instantaneous output power value is provided for the doubly-fed fan at the moment of system frequency disturbance, namely the output electromagnetic power of the doubly-fed fan when the doubly-fed fan operates at the working point B.
4. The improved torque limit control method based on the doubly-fed wind turbine generator set according to claim 1, wherein in the step 2), the doubly-fed wind turbine output electromagnetic power value is adjusted to be decreased by a quadratic function of the rotating speed on the basis of the instant output fixed value, and the step is as follows:
Figure FDA0002670688950000011
in the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, PBInstantaneous output power value omega provided for medium system frequency disturbance instantaneous double-fed fanr0The initial rotor speed of the doubly-fed fan is the initial rotor speed of the doubly-fed fan when the system is not disturbed; omegarminThe minimum rotating speed allowed by the operation of the double-fed fan is set; pr_minAnd the output electromagnetic power is controlled by adopting maximum power tracking for the doubly-fed wind turbine and is operated at the lowest allowable rotating speed.
5. The method for controlling the improved torque limit of the doubly-fed wind turbine generator set according to claim 1, wherein in the step 3), the step of gradually reducing the difference between the output electromagnetic power of the doubly-fed wind turbine and the captured mechanical power to approach zero is that:
|PITLC-PMACH|＜5×10-4or | d ωr/dt|＜5×10-4
In the formula, PITLCFor doubly-fed wind turbine output of electromagnetic power, PMACHMechanical power difference, omega, captured for doubly-fed wind turbinesrThe rotating speed of the rotor of the doubly-fed wind turbine is shown, and t is time.
6. The improved torque limit control method based on the doubly-fed wind turbine generator set according to claim 1, wherein in the step 3), the certain speed is 0.01-0.015 pu/s, and the certain time is 3-5 seconds.
7. The improved torque limit control method based on the doubly-fed wind turbine generator set according to claim 1, characterized in that the doubly-fed wind turbine generator set is connected with a control system, the control system is further connected with each controllable switch and a frequency detection module, and the control system detects the state of the doubly-fed wind turbine generator set through the frequency detection module so as to adjust and start the controllable switches.
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