CN111211582B - Power grid comprehensive frequency modulation method based on double-fed fan frequency modulation capability in wind power plant - Google Patents

Power grid comprehensive frequency modulation method based on double-fed fan frequency modulation capability in wind power plant Download PDF

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CN111211582B
CN111211582B CN202010115116.5A CN202010115116A CN111211582B CN 111211582 B CN111211582 B CN 111211582B CN 202010115116 A CN202010115116 A CN 202010115116A CN 111211582 B CN111211582 B CN 111211582B
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frequency
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wind
doubly
frequency modulation
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CN111211582A (en
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王德林
杨仁杰
陈要光
李智
喻心
康积涛
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Southwest Jiaotong University
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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
    • H02J3/48—Controlling the sharing of the in-phase component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

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Abstract

The invention discloses a comprehensive frequency modulation method for a power grid based on the frequency modulation capability of a double-fed fan in a wind power plant, which provides a concept of wind volume from the physical characteristics of a DFIG double-fed wind driven generator and measures the frequency modulation capability of each DFIG device in the wind power plant through the concept of wind volume. Under the condition that the frequency deviation of a power grid is less than 0.2Hz, only the DFIG fan with the largest volume wind product is adopted for independent frequency modulation, so that the frequency deviation is eliminated quickly; under the condition that the frequency deviation of a power grid is greater than 0.2Hz, power task division is carried out according to the volume wind volume of each DFIG device; in the specific details of the single frequency modulation and the multi-machine cooperative frequency modulation, the wind speed factor is also considered, and particularly when the current wind speed is lower than the rated wind speed, the virtual inertia method model parameters are adjusted according to the difference adjustment coefficient calculated according to the wind speed section where the DFIG is located, so that the frequency modulation is quicker and more stable, and the aim of stabilizing the wind power generation frequency under the conditions of a complex wind power plant and differentiated units is finally fulfilled.

Description

Power grid comprehensive frequency modulation method based on double-fed fan frequency modulation capability in wind power plant
Technical Field
The invention relates to the field of wind power generation, in particular to a comprehensive frequency modulation method for a power grid based on the frequency modulation capability of a double-fed fan in a wind power plant.
Background
A Doubly-fed Induction Generator (DFIG) is the most widely applied wind Generator at present and comprises a wound asynchronous Generator with a stator winding directly connected with a fixed-frequency three-phase power grid and a bidirectional back-to-back IGBT voltage source converter arranged on a rotor winding.
According to the national regulation, the frequency of the power grid system is controlled within the range of plus or minus 0.2Hz of the rated frequency error within 98 percent of the time, and when the frequency deviation is greater than 0.2Hz, the power grid needs to take emergency regulation measures. However, due to the complexity of the wind farm and the difference of the wind turbines, if a constant and ideal control means is adopted to drive the DFIG equipment, the frequency of the power grid is difficult to be stabilized within the frequency deviation of 0.2 Hz. Therefore, an economical and practical comprehensive frequency modulation control means based on the macroscopic level of the wind power plant is urgently needed in the engineering field.
Disclosure of Invention
Aiming at the defects in the prior art, the comprehensive frequency modulation method for the power grid based on the frequency modulation capability of the double-fed fan in the wind power plant provided by the invention solves the problem that the existing ideal DFIG control method cannot provide stable power grid frequency under the conditions of a complex wind power plant and differentiated units.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that: a power grid comprehensive frequency modulation method based on the frequency modulation capability of a double-fed fan in a wind power plant comprises the following steps:
s1, judging whether the current wind speed V is in the interval [ V1,V3]In which V is1For cutting into wind speed, V3If the wind speed is cut, jumping to step S2, otherwise, jumping to step S9;
s2, judging whether the deviation between the current frequency of the power grid and the 50Hz standard frequency is less than 0.2Hz, if so, jumping to the step S3, and if not, jumping to the step S8;
s3, judging whether the current wind speed V is less than the rated wind speed V2If yes, go to step S4, otherwise, go to step S5;
s4, performing primary frequency modulation on the power grid by adopting an overspeed and comprehensive virtual inertia method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s5, performing primary frequency modulation on the power grid by adopting a single virtual inertia method, selecting a DFIG doubly-fed wind generator with the largest volume wind volume in the power grid to perform secondary frequency modulation, and jumping to the step S6;
s6, judging whether the current frequency of the power grid deviates from the 50Hz standard frequency again, if so, jumping to the step S7, and if not, ending the process;
s7, performing secondary frequency modulation through the spare fan until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s8, adopting a multi-machine cooperative frequency modulation method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
and S9, taking fan abnormal working measures and ending the process.
Further, the single virtual inertia method of step S5 is: the rotor kinetic energy of the DFIG doubly-fed wind generator is released by the converter, and the active power delta P of the DFIG doubly-fed wind generator is adjusted according to the deviation delta f of the current frequency of a power grid and the standard frequency of 50Hz and the differential relation between the delta f and the active power delta P, so that frequency modulation is realized, and the effect of stabilizing the frequency is achieved; the differential relation between the deviation delta f and the active power delta P is as follows:
Figure BDA0002391251080000021
wherein, KdfIs the coefficient of inertia.
Further, step S8 includes the steps of:
s81, judging whether the current wind speed V is less than the rated wind speed V2If yes, go to step S82, otherwise, go to step S84;
s82, calculating difference adjustment coefficients delta of each DFIG doubly-fed wind generator in the power gridiWherein i is the serial number of the DFIG doubly-fed wind generator, and the value of the serial number is in the interval [1, N ]]And N is the total number of the DFIG doubly-fed wind generators in the power grid, and the step S83 is skipped;
s83, performing primary frequency modulation on the power grid by adopting an overspeed and comprehensive virtual inertia method and combining an optimal delta method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s84, calculating the capacity wind product K of each DFIG doubly-fed wind generator in the power gridSWiAnd go to step S85;
s85, passing wind volume K of each DFIG doubly-fed wind generator in the power gridSWiDistributing the tasks of each DFIG doubly-fed wind driven generator, performing multi-machine cooperative secondary frequency modulation, and jumping to the step S86;
s86, judging whether the current frequency of the power grid deviates from the 50Hz standard frequency again, if so, jumping to the step S87, and if not, ending the process;
and S87, performing secondary frequency modulation through the spare fan until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process.
Further, the adjustment coefficient δ of step S82iThe calculation formula of (2) is as follows:
Figure BDA0002391251080000031
wherein, Δ fWTaking 0.2Hz, f as the frequency variation of the power gridrefIs 50Hz grid standard frequency, delta PWiReserve power for de-rating of DFIG doubly-fed wind generator i, PWNiThe rated active power of the DFIG doubly-fed wind generator i is obtained.
Further, the overspeed and integrated virtual inertia method in step S4 and step S83 includes the steps of:
a1, tracking a secondary optimal rotating speed power curve by adopting the DFIG double-fed wind driven generator, so that the DFIG double-fed wind driven generator is in a load shedding operation state and remains active power for standby;
a2, releasing rotor kinetic energy of the DFIG doubly-fed wind generator by using a converter, and adjusting the active power delta P of the DFIG doubly-fed wind generator according to the deviation delta f of the current frequency of a power grid and the standard frequency of 50Hz and the proportional differential relation between the delta f and the active power delta P, so that frequency modulation is realized, and the effect of stabilizing the frequency is achieved; the proportional differential relation between the deviation delta f and the active power delta P is as follows:
Figure BDA0002391251080000041
wherein, KpfIs the sag factor, KdfIs the coefficient of inertia.
The beneficial effects of the above further scheme are: when overspeed control is adopted, the DFIG double-fed wind generating set is in a load-shedding operation state and is provided with partial active standby by tracking a suboptimal rotating speed power curve on the right side of a maximum power tracking control curve. When the active power of the system is unbalanced, the fan can quickly respond to the frequency change of the power grid and control the rotating speed of the rotor to be reduced, so that the rotating kinetic energy of the rotor is released. In order to take the advantages of virtual inertia control and droop control into consideration, a proportional differential expression of the frequency deviation delta f and the active power delta P is fitted by a comprehensive virtual inertia method, and the relation between active power regulation and frequency support can be reflected more accurately.
Further, the step S83 of using the overspeed and comprehensive virtual inertia method and combining the optimal δ method includes:
b1, adjusting difference coefficient delta according to DFIG doubly-fed wind generator iiCalculating the droop coefficient KpfSag factor KpfDifference coefficient deltaiThe relational expression of (1) is:
Figure BDA0002391251080000042
wherein, PWNiIs the rated active power f of a DFIG doubly-fed wind generator irefThe standard frequency of a 50Hz power grid;
b2, adjusting difference coefficient delta according to DFIG doubly-fed wind generator iiCalculating inertia coefficient KdfSaid coefficient of inertia KdfDifference coefficient deltaiThe relational expression of (1) is:
Figure BDA0002391251080000043
wherein HiIs the inertia time constant, S, of the DFIG doubly-fed wind generator iiFor the rated capacity of the DFIG doubly-fed wind generator i,
Figure BDA0002391251080000044
the rotation speed per unit value of the DFIG doubly-fed wind generator i is obtained;
b3, calculating the droop coefficient K calculated in the step B1 and the step B2pfValue and inertia coefficient KdfAnd (3) substituting the formula (2), releasing the rotor kinetic energy of the DFIG doubly-fed wind driven generator i by using the converter according to the formula (2), and adjusting the active power delta P of the DFIG doubly-fed wind driven generator, so that frequency modulation is realized, and the effect of stabilizing the frequency is achieved.
The beneficial effects of the above further scheme are: the adjustment difference coefficient directly influences the droop control effect of the rotor side of the DFIG double-fed wind driven generator, so that the current theoretical adjustment difference coefficient of the DFIG double-fed wind driven generator is calculated firstly, and then the optimal droop coefficient K is deduced according to the adjustment difference coefficientpfValue and inertia coefficient KdfAnd then the frequency deviation delta f is substituted into a proportional differential expression of the frequency deviation delta f and the active power delta P, and a proper active power regulating value can be calculated more closely, so that the stability of primary frequency modulation of a power grid can be improved more reasonably, and the system frequency is further improved.
Further, the wind capacity K of the DFIG doubly-fed wind generator involved in the steps S5 and S84SWiThe calculation formula of (2) is as follows:
KSWi＝πv3Ri 2/k (6)
wherein R isiAnd k is the wind wheel radius of the DFIG doubly-fed wind generator i, and k is the volume wind volume coefficient.
Further, step S85 includes the steps of:
s851, calculating the active power delta P to be adjusted of the DFIG doubly-fed wind generator according to a proportional differential relation between the formula deviation delta f and the active power delta P;
s852, passing through air volume KSWiActive power proportion type distribution active power delta P which is respectively adjusted by each DFIG doubly-fed wind generator ii(ii) a The volume wind volume KSWiThe active power proportion formula is as follows:
Figure BDA0002391251080000051
and S853, releasing the rotor kinetic energy of each DFIG doubly-fed wind driven generator by using the converter, so as to adjust the active power of each DFIG doubly-fed wind driven generator to meet the calculated value in the step S852, thereby realizing frequency modulation and achieving the effect of stabilizing the frequency.
The beneficial effects of the above further scheme are: the capacity wind volume expression is a variable for measuring the secondary frequency modulation capability of each DFIG double-fed wind driven generator in the wind power plant through theoretical research and derivation according to the physical characteristics of the DFIG double-fed wind driven generator. The capacity wind product is used as the weight to carry out power distribution on the frequency modulation task, so that a machine set with strong frequency modulation capability can share more frequency modulation tasks and ensure that each DFIG doubly-fed wind driven generator can carry out pitch variation within a limited range, and the regulation capability and the frequency stability of a power grid are greatly enhanced; the frequency modulation of each DFIG doubly-fed wind generator within the respective margin range can be ensured, the mechanical loss caused by large-amplitude pitch variation is avoided, and the service life of the unit is prolonged.
Further, step S9 includes the steps of:
s91, judging whether the current wind speed V is less than the cut-in wind speed V1If yes, go to step S92, otherwise, go to step S93;
s92, the DFIG double-fed wind driven generator works in an under-wind energy state, and the grid frequency modulation operation is stopped;
and S93, shutting down all DFIG doubly-fed wind generators in the power grid.
The beneficial effects of the above further scheme are: and the DFIG double-fed wind driven generator is prevented from being damaged by excessive energy.
The invention has the beneficial effects that: based on the physical characteristics of the DFIG doubly-fed wind generator, a concept of wind volume is provided through theoretical research and derivation, and the frequency modulation capability of each DFIG device in a wind power plant is measured through the concept of wind volume. Under the condition that the frequency deviation of a power grid is less than 0.2Hz, only the DFIG fan with the largest volume wind product is adopted for independent frequency modulation, so that the frequency deviation is eliminated quickly, and the real-time frequency error of a power system is ensured to be within 0.2 Hz; under the condition that the frequency deviation of the power grid is greater than 0.2Hz, power tasks are divided according to the volume wind volume of each DFIG device, so that the economy and the scientificity of wind power frequency modulation and the stability of the power grid frequency are greatly improved; in the specific details of the single frequency modulation and the multi-machine cooperative frequency modulation, the wind speed factor is also considered, and particularly when the current wind speed is lower than the rated wind speed, the virtual inertia method model parameters are adjusted according to the difference adjustment coefficient calculated according to the wind speed section where the DFIG is located, so that the frequency modulation is quicker and more stable, and the aim of stabilizing the wind power generation frequency under the conditions of a complex wind power plant and differentiated units is finally fulfilled.
Drawings
FIG. 1 is a schematic flow diagram of a comprehensive frequency modulation method of a power grid based on the frequency modulation capability of a double-fed fan in a wind power plant;
FIG. 2 is a pitch angle and output comparison graph of a DFIG doubly-fed wind generator 1 (referred to as a fan 1 for short) in an MATLAB simulation process;
FIG. 3 is a pitch angle and output contrast diagram of a DFIG doubly-fed wind generator 2 (referred to as a wind turbine 2 for short) in an MATLAB simulation process;
FIG. 4 is a pitch angle and output contrast diagram of a DFIG doubly-fed wind generator 3 (referred to as a fan 3 for short) in an MATLAB simulation process;
FIG. 5 is a comparison graph of system frequency during MATLAB simulation.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
As shown in fig. 1, in an embodiment of the present invention, a method for comprehensive frequency modulation of a power grid based on frequency modulation capability of a doubly-fed wind turbine in a wind farm includes the following steps:
s1, judging whether the current wind speed V is in the interval [ V1,V3]In which V is1For cutting into wind speed, V3If the wind speed is cut, jumping to step S2, otherwise, jumping to step S9;
s2, judging whether the deviation between the current frequency of the power grid and the 50Hz standard frequency is less than 0.2Hz, if so, jumping to the step S3, and if not, jumping to the step S8;
s3, judging whether the current wind speed V is less than the rated wind speed V2If yes, go to step S4, otherwise, go to step S5;
s4, performing primary frequency modulation on the power grid by adopting an overspeed and comprehensive virtual inertia method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s5, performing primary frequency modulation on the power grid by adopting a single virtual inertia method, selecting a DFIG doubly-fed wind generator with the largest volume wind volume in the power grid to perform secondary frequency modulation, and jumping to the step S6;
the single virtual inertia method of step S5 is: the rotor kinetic energy of the DFIG doubly-fed wind generator is released by the converter, and the active power delta P of the DFIG doubly-fed wind generator is adjusted according to the deviation delta f of the current frequency of a power grid and the standard frequency of 50Hz and the differential relation between the delta f and the active power delta P, so that frequency modulation is realized, and the effect of stabilizing the frequency is achieved; the differential relation between the deviation delta f and the active power delta P is as follows:
Figure BDA0002391251080000081
wherein, KdfIs the coefficient of inertia.
S6, judging whether the current frequency of the power grid deviates from the 50Hz standard frequency again, if so, jumping to the step S7, and if not, ending the process;
s7, performing secondary frequency modulation through the spare fan until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s8, adopting a multi-machine cooperative frequency modulation method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
step S8 includes the following steps:
s81, judging the current wind speed vWhether it is less than rated wind speed V2If yes, go to step S82, otherwise, go to step S84;
s82, calculating difference adjustment coefficients delta of each DFIG doubly-fed wind generator in the power gridiWherein i is the serial number of the DFIG doubly-fed wind generator, and the value of the serial number is in the interval [1, N ]]And N is the total number of the DFIG doubly-fed wind generators in the power grid, and the step S83 is skipped;
difference adjustment coefficient delta of step S82iThe calculation formula of (2) is as follows:
Figure BDA0002391251080000082
wherein, Δ fWTaking 0.2Hz, f as the frequency variation of the power gridrefIs 50Hz grid standard frequency, delta PWiReserve power for de-rating of DFIG doubly-fed wind generator i, PWNiThe rated active power of the DFIG doubly-fed wind generator i is obtained.
S83, performing primary frequency modulation on the power grid by adopting an overspeed and comprehensive virtual inertia method and combining an optimal delta method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
the overspeed and integrated virtual inertia method in steps S4 and S83 includes the steps of:
a1, tracking a secondary optimal rotating speed power curve by adopting the DFIG double-fed wind driven generator, so that the DFIG double-fed wind driven generator is in a load shedding operation state and remains active power for standby;
a2, releasing rotor kinetic energy of the DFIG doubly-fed wind generator by using a converter, and adjusting the active power delta P of the DFIG doubly-fed wind generator according to the deviation delta f of the current frequency of a power grid and the standard frequency of 50Hz and the proportional differential relation between the delta f and the active power delta P, so that frequency modulation is realized, and the effect of stabilizing the frequency is achieved; the proportional differential relation between the deviation delta f and the active power delta P is as follows:
Figure BDA0002391251080000091
wherein, KpfIs the sag factor, KdfIs the coefficient of inertia.
When overspeed control is adopted, the DFIG double-fed wind generating set is in a load-shedding operation state and is provided with partial active standby by tracking a suboptimal rotating speed power curve on the right side of a maximum power tracking control curve. When the active power of the system is unbalanced, the fan can quickly respond to the frequency change of the power grid and control the rotating speed of the rotor to be reduced, so that the rotating kinetic energy of the rotor is released. In order to take the advantages of virtual inertia control and droop control into consideration, a proportional differential expression of the frequency deviation delta f and the active power delta P is fitted by a comprehensive virtual inertia method, and the relation between active power regulation and frequency support can be reflected more accurately.
In step S83, the overspeed and integrated virtual inertia methods are used, and the step of combining the optimal δ method is:
b1, adjusting difference coefficient delta according to DFIG doubly-fed wind generator iiCalculating the droop coefficient KpfSag factor KpfDifference coefficient deltaiThe relational expression of (1) is:
Figure BDA0002391251080000092
wherein, PWNiIs the rated active power f of a DFIG doubly-fed wind generator irefThe standard frequency of a 50Hz power grid;
b2, adjusting difference coefficient delta according to DFIG doubly-fed wind generator iiCalculating inertia coefficient KdfSaid coefficient of inertia KdfDifference coefficient deltaiThe relational expression of (1) is:
Figure BDA0002391251080000101
wherein HiIs the inertia time constant, S, of the DFIG doubly-fed wind generator iiFor the rated capacity of the DFIG doubly-fed wind generator i,
Figure BDA0002391251080000102
the rotation speed per unit value of the DFIG doubly-fed wind generator i is obtained;
b3, calculating the droop coefficient K calculated in the step B1 and the step B2pfValue and inertia coefficient KdfAnd (3) substituting the formula (2), releasing the rotor kinetic energy of the DFIG doubly-fed wind driven generator i by using the converter according to the formula (2), and adjusting the active power delta P of the DFIG doubly-fed wind driven generator, so that frequency modulation is realized, and the effect of stabilizing the frequency is achieved.
The adjustment difference coefficient directly influences the droop control effect of the rotor side of the DFIG double-fed wind driven generator, so that the current theoretical adjustment difference coefficient of the DFIG double-fed wind driven generator is calculated firstly, and then the optimal droop coefficient K is deduced according to the adjustment difference coefficientpfValue and inertia coefficient KdfAnd then the frequency deviation delta f is substituted into a proportional differential expression of the frequency deviation delta f and the active power delta P, and a proper active power regulating value can be calculated more closely, so that the stability of primary frequency modulation of a power grid can be improved more reasonably, and the system frequency is further improved.
S84, calculating the capacity wind product K of each DFIG doubly-fed wind generator in the power gridSWiAnd go to step S85;
wind volume K of DFIG doubly-fed wind generator involved in steps S5 and S84SWiThe calculation formula of (2) is as follows:
KSWi＝πv3Ri 2/k (6)
wherein R isiAnd k is the wind wheel radius of the DFIG doubly-fed wind generator i, and k is the volume wind volume coefficient.
S85, passing wind volume K of each DFIG doubly-fed wind generator in the power gridSWiDistributing the tasks of each DFIG doubly-fed wind driven generator, performing multi-machine cooperative secondary frequency modulation, and jumping to the step S86;
step S85 includes the following steps:
s851, calculating the active power delta P to be adjusted of the DFIG doubly-fed wind generator according to a proportional differential relation between the formula deviation delta f and the active power delta P;
s852, passing through air volume KSWiActive power proportion type distribution active power delta P which is respectively adjusted by each DFIG doubly-fed wind generator ii(ii) a The volume wind volume KSWiThe active power proportion formula is as follows:
Figure BDA0002391251080000111
and S853, releasing the rotor kinetic energy of each DFIG doubly-fed wind driven generator by using the converter, so as to adjust the active power of each DFIG doubly-fed wind driven generator to meet the calculated value in the step S852, thereby realizing frequency modulation and achieving the effect of stabilizing the frequency.
The capacity wind volume expression is a variable for measuring the secondary frequency modulation capability of each DFIG double-fed wind driven generator in the wind power plant through theoretical research and derivation according to the physical characteristics of the DFIG double-fed wind driven generator. The capacity wind product is used as the weight to carry out power distribution on the frequency modulation task, so that a machine set with strong frequency modulation capability can share more frequency modulation tasks and ensure that each DFIG doubly-fed wind driven generator can carry out pitch variation within a limited range, and the regulation capability and the frequency stability of a power grid are greatly enhanced; the frequency modulation of each DFIG doubly-fed wind generator within the respective margin range can be ensured, the mechanical loss caused by large-amplitude pitch variation is avoided, and the service life of the unit is prolonged.
S86, judging whether the current frequency of the power grid deviates from the 50Hz standard frequency again, if so, jumping to the step S87, and if not, ending the process;
and S87, performing secondary frequency modulation through the spare fan until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process.
And S9, taking fan abnormal working measures and ending the process.
Step S9 includes the following steps:
s91, judging whether the current wind speed V is less than the cut-in wind speed V1If yes, go to step S92, otherwise, go to step S93;
s92, the DFIG double-fed wind driven generator works in an under-wind energy state, and the grid frequency modulation operation is stopped;
and S93, shutting down all DFIG double-fed wind driven generators in the power grid, and preventing the DFIG double-fed wind driven generators from being damaged by excessive energy.
In order to verify the significance of the concept of the wind volume capacity and the superiority of the frequency modulation task allocation scheme based on the wind volume capacity, simulation is carried out through an MATLAB software Simulink platform, and three DFIG double-fed wind driven generators shown in the table 1 are arranged in the simulation process, and are hereinafter referred to as 'fans'.
TABLE 1 Main operating parameters of the fans
Figure BDA0002391251080000121
The 3 frequency modulation methods of 'distributing according to volume wind volume', 'distributing frequency modulation tasks averagely' and 'modulating frequency only by using a fan 3' are compared and analyzed, and 3 groups of curves in fig. 2, 3 and 4 are pitch angle and active power output comparison graphs of the fan 1, the fan 2 and the fan 3 under the 3 frequency modulation methods respectively.
According to fig. 2, since the wind volume of the fan 1 is the smallest, when the wind volume allocation method is used, the allocated task is smaller than the average allocated frequency modulation task. Therefore, the variable pitch amplitude and the active output value are within a reasonable range by utilizing the capacity wind volume distribution frequency modulation task, and the variable pitch or the output exceeding the frequency modulation margin is avoided.
According to fig. 3, because the wind volume of the fan 2 is moderate, when the wind volume is adopted or the frequency modulation task is averagely distributed, the pitch variation amplitude and the output amplitude are relatively close to each other and are within a reasonable range.
According to fig. 4, the wind volume of the fan 3 is large and the secondary frequency modulation capability is strongest, and when only the fan 3 participates in the secondary frequency modulation in the wind power plant, the pitch variation amplitude and the output force of the wind power plant are obviously larger than those of the wind volume distribution, which is not favorable for the stable operation of the unit and can cause large mechanical loss and influence the service life in the pitch variation process. When the capacity wind volume distribution frequency modulation task is adopted, the variable pitch amplitude and the output value are higher than average distribution, relatively more frequency modulation tasks are born, so that the frequency modulation advantage of the system is fully exerted, and the improvement on the system frequency is facilitated.
By combining the graphs 2, 3 and 4, when frequency modulation tasks are distributed according to the volume wind volume, the pitch variation trend of each fan is basically consistent and is within a reasonable pitch variation margin, the mechanical loss caused by large-amplitude pitch variation is reduced, and the service life of the unit is correspondingly prolonged.
The system frequency is compared with the graph shown in fig. 5, when the secondary frequency modulation is not adopted, the lowest point of the system frequency is already suddenly dropped to 49.7Hz, and the allowable deviation of the power grid frequency, which is regulated by the state, is +/-0.2 Hz. If the secondary frequency modulation is performed only by using the fan 3 with the strongest frequency modulation capability, although the system frequency can be controlled without difference, the stability of the frequency is still a part below 49.8 Hz.
The problem of overlarge frequency deviation can be effectively solved by means of coordinating frequency modulation of the wind turbine generator, when an average distribution method is adopted, the wind turbine generator shares the frequency modulation task to perform cooperative frequency modulation in an equal amount, the stability of frequency is improved, but when the frequency modulation task is distributed according to volume wind volume, the frequency stability is further enhanced, and the frequency can be stably recovered to be higher than 49.8 Hz. Therefore, the frequency modulation technical scheme of 'distributing secondary frequency modulation tasks by using volumetric wind flow' designed by the invention not only can control the variable pitch and the output of each wind turbine generator within a certain range, but also can reasonably distribute the frequency modulation tasks, so that the wind turbine generators with strong frequency modulation capability can play a larger frequency modulation role, and the frequency stability of the system is further promoted.
In conclusion, the invention provides a concept of wind volume through theoretical research and derivation based on the physical characteristics of the DFIG double-fed wind driven generator, and the frequency modulation capability of each DFIG device in the wind power plant is measured through the concept of wind volume. Under the condition that the frequency deviation of a power grid is less than 0.2Hz, only the DFIG fan with the largest volume wind product is adopted for independent frequency modulation, so that the frequency deviation is eliminated quickly, and the real-time frequency error of a power system is ensured to be within 0.2 Hz; under the condition that the frequency deviation of the power grid is greater than 0.2Hz, power tasks are divided according to the volume wind volume of each DFIG device, so that the economy and the scientificity of wind power frequency modulation and the stability of the power grid frequency are greatly improved; in the specific details of the single frequency modulation and the multi-machine cooperative frequency modulation, the wind speed factor is also considered, and particularly when the current wind speed is lower than the rated wind speed, the virtual inertia method model parameters are adjusted according to the difference adjustment coefficient calculated according to the wind speed section where the DFIG is located, so that the frequency modulation is quicker and more stable, and the aim of stabilizing the wind power generation frequency under the conditions of a complex wind power plant and differentiated units is finally fulfilled.

Claims (7)

1. A power grid comprehensive frequency modulation method based on the frequency modulation capability of a double-fed fan in a wind power plant is characterized by comprising the following steps:
s1, judging whether the current wind speed V is in the interval [ V1,V3]In which V is1For cutting into wind speed, V3If the wind speed is cut, jumping to step S2, otherwise, jumping to step S9;
s2, judging whether the deviation between the current frequency of the power grid and the 50Hz standard frequency is less than 0.2Hz, if so, jumping to the step S3, and if not, jumping to the step S8;
s3, judging whether the current wind speed V is less than the rated wind speed V2If yes, go to step S4, otherwise, go to step S5;
s4, performing primary frequency modulation on the power grid by adopting an overspeed and comprehensive virtual inertia method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s5, performing primary frequency modulation on the power grid by adopting a single virtual inertia method, selecting a DFIG doubly-fed wind generator with the largest volume wind volume in the power grid to perform secondary frequency modulation, and jumping to the step S6;
s6, judging whether the current frequency of the power grid deviates from the 50Hz standard frequency again, if so, jumping to the step S7, and if not, ending the process;
s7, performing secondary frequency modulation through the spare fan until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s8, adopting a multi-machine cooperative frequency modulation method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s9, taking fan abnormal working measures and ending the process;
step S8 includes the following steps:
s81, judging whether the current wind speed V is less than the rated wind speed V2If so, go to step S82, otherwise, go to stepA step S84;
s82, calculating difference adjustment coefficients delta of each DFIG doubly-fed wind generator in the power gridiWherein i is the serial number of the DFIG doubly-fed wind generator, and the value of the serial number is in the interval [1, N ]]And N is the total number of the DFIG doubly-fed wind generators in the power grid, and the step S83 is skipped;
s83, performing primary frequency modulation on the power grid by adopting an overspeed and comprehensive virtual inertia method and combining an optimal delta method until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
s84, calculating the capacity wind product K of each DFIG doubly-fed wind generator in the power gridSWiAnd go to step S85;
s85, passing wind volume K of each DFIG doubly-fed wind generator in the power gridSWiDistributing the tasks of each DFIG doubly-fed wind driven generator, performing multi-machine cooperative secondary frequency modulation, and jumping to the step S86;
s86, judging whether the current frequency of the power grid deviates from the 50Hz standard frequency again, if so, jumping to the step S87, and if not, ending the process;
s87, performing secondary frequency modulation through the spare fan until the power grid frequency is not deviated from the 50Hz standard frequency, and ending the process;
wind volume K of DFIG doubly-fed wind generator involved in steps S5 and S84SWiThe calculation formula of (2) is as follows:
KSWi＝πv3Ri 2/k(6)
wherein R isiAnd k is the wind wheel radius of the DFIG doubly-fed wind generator i, and k is the volume wind volume coefficient.
2. The method for comprehensively modulating the frequency of the power grid based on the frequency modulation capability of the doubly-fed wind turbine in the wind farm according to claim 1, wherein the single virtual inertia method in the step S5 is as follows: the rotor kinetic energy of the DFIG doubly-fed wind generator is released by the converter, and the active power delta P of the DFIG doubly-fed wind generator is adjusted according to the deviation delta f of the current frequency of a power grid and the standard frequency of 50Hz and the differential relation between the delta f and the active power delta P, so that frequency modulation is realized, and the effect of stabilizing the frequency is achieved; the differential relation between the deviation delta f and the active power delta P is as follows:
Figure FDA0003498679970000031
wherein, KdfIs the coefficient of inertia.
3. The method for comprehensively modulating the frequency of the power grid based on the frequency modulation capability of the doubly-fed wind turbines in the wind farm according to claim 1, wherein the difference modulation coefficient delta of the step S82iThe calculation formula of (2) is as follows:
Figure FDA0003498679970000032
wherein, Δ fWTaking 0.2Hz, f as the frequency variation of the power gridrefIs 50Hz grid standard frequency, delta PWiReserve power for de-rating of DFIG doubly-fed wind generator i, PWNiThe rated active power of the DFIG doubly-fed wind generator i is obtained.
4. The method for comprehensively modulating the frequency of the power grid based on the frequency modulation capability of the doubly-fed wind turbine in the wind farm according to claim 1, wherein the overspeed and comprehensive virtual inertia method in the steps S4 and S83 comprises the following steps:
a1, tracking a secondary optimal rotating speed power curve by adopting the DFIG double-fed wind driven generator, so that the DFIG double-fed wind driven generator is in a load shedding operation state and remains active power for standby;
a2, releasing rotor kinetic energy of the DFIG doubly-fed wind generator by using a converter, and adjusting the active power delta P of the DFIG doubly-fed wind generator according to the deviation delta f of the current frequency of a power grid and the standard frequency of 50Hz and the proportional differential relation between the delta f and the active power delta P, so that frequency modulation is realized, and the effect of stabilizing the frequency is achieved; the proportional differential relation between the deviation delta f and the active power delta P is as follows:
Figure FDA0003498679970000033
wherein, KpfIs the sag factor, KdfIs the coefficient of inertia.
5. The method for comprehensively modulating the frequency of the power grid based on the frequency modulation capability of the doubly-fed wind turbine in the wind farm according to claim 1, wherein the step S83 adopts an overspeed and comprehensive virtual inertia method, and the step of combining an optimal delta method comprises the following steps:
b1, adjusting difference coefficient delta according to DFIG doubly-fed wind generator iiCalculating the droop coefficient KpfSag factor KpfDifference coefficient deltaiThe relational expression of (1) is:
Figure FDA0003498679970000041
wherein, PWNiIs the rated active power f of a DFIG doubly-fed wind generator irefThe standard frequency of a 50Hz power grid;
b2, adjusting difference coefficient delta according to DFIG doubly-fed wind generator iiCalculating inertia coefficient KdfSaid coefficient of inertia KdfDifference coefficient deltaiThe relational expression of (1) is:
Figure FDA0003498679970000042
wherein HiIs the inertia time constant, S, of the DFIG doubly-fed wind generator iiFor the rated capacity of the DFIG doubly-fed wind generator i,
Figure FDA0003498679970000043
the rotation speed per unit value of the DFIG doubly-fed wind generator i is obtained;
b3, calculating the droop coefficient K calculated in the step B1 and the step B2pfValue and inertia coefficient KdfSubstituting the formula (2), and releasing the DFIG double-fed wind power generator by using the converter according to the formula (2)The rotor kinetic energy of the motor i adjusts the active power delta P of the DFIG doubly-fed wind driven generator, so that frequency modulation is achieved, and the effect of stabilizing the frequency is achieved.
6. The method for comprehensively modulating the frequency of the power grid based on the frequency modulation capability of the doubly-fed wind turbines in the wind farm according to claim 1, wherein the step S85 comprises the following steps:
s851, calculating the active power delta P to be adjusted of the DFIG doubly-fed wind generator according to a proportional differential relation between the deviation delta f and the active power delta P;
s852, passing through air volume KSWiActive power proportion type distribution active power delta P which is respectively adjusted by each DFIG doubly-fed wind generator ii(ii) a The volume wind volume KSWiThe active power proportion formula is as follows:
Figure FDA0003498679970000044
and S853, releasing the rotor kinetic energy of each DFIG doubly-fed wind driven generator by using the converter, so as to adjust the active power of each DFIG doubly-fed wind driven generator to meet the calculated value in the step S852, thereby realizing frequency modulation and achieving the effect of stabilizing the frequency.
7. The method for comprehensively modulating the frequency of the power grid based on the frequency modulation capability of the doubly-fed wind turbines in the wind farm according to claim 1, wherein the step S9 comprises the following steps:
s91, judging whether the current wind speed V is less than the cut-in wind speed V1If yes, go to step S92, otherwise, go to step S93;
s92, the DFIG double-fed wind driven generator works in an under-wind energy state, and the grid frequency modulation operation is stopped;
and S93, shutting down all DFIG doubly-fed wind generators in the power grid.
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