CN114123244A - Power grid frequency characteristic calculation method considering wind-storage-direct combined frequency modulation - Google Patents

Power grid frequency characteristic calculation method considering wind-storage-direct combined frequency modulation Download PDF

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CN114123244A
CN114123244A CN202111420638.7A CN202111420638A CN114123244A CN 114123244 A CN114123244 A CN 114123244A CN 202111420638 A CN202111420638 A CN 202111420638A CN 114123244 A CN114123244 A CN 114123244A
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frequency
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wind
power system
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CN114123244B (en
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刘懿诗
周霞
戴剑丰
张腾飞
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Nanjing University of Posts and Telecommunications
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—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
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • 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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
    • 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
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

Abstract

The invention discloses a power grid frequency characteristic calculation method considering wind-storage-direct combined frequency modulation, which is based on a traditional thermal power, wind power, energy storage and flexible direct-current power transmission combined frequency modulation strategy and comprises the steps of firstly establishing a wind-storage-direct combined frequency modulation frequency response model and analyzing and deducing frequency characteristics; secondly, calculating to obtain a frequency change time domain model, and quantitatively calculating a power system frequency characteristic set A under wind-storage-direct joint frequency regulation according to the frequency change time domain model, wherein the power system frequency characteristic set A comprises a frequency change rate, a maximum frequency deviation and a frequency peak time; and finally, calculating a frequency characteristic set B according to the frequency change frequency domain model, wherein the frequency characteristic set B comprises a steady-state frequency error and an initial frequency change rate. The invention can provide a frequency characteristic calculation method under the background that the 'double-high' characteristic of the current novel power system is increasingly remarkable, and has a promotion effect on the frequency stability analysis of the power system.

Description

Power grid frequency characteristic calculation method considering wind-storage-direct combined frequency modulation
Technical Field
The invention belongs to the field of power system automation, and relates to a power grid frequency characteristic quantitative calculation method based on wind-storage-direct combined frequency modulation.
Background
In recent years, with the low-carbon transformation of energy structures, the access of high-proportion new energy and high-proportion power electronic equipment becomes a remarkable characteristic of modern power systems. On the power supply side, most renewable energy sources represented by wind power are connected to the grid through a power electronic interface, so that power electronic equipment is widely applied; on the power transmission side, the power transmission technologies such as flexible direct current power transmission and the like which are started at the end of the 20 th century promote the continuous improvement of the occupation ratio of power electronic equipment in a power transmission network; on the load side, a power electronic interface is also often used for a new load represented by a new energy vehicle. The power electronics in various aspects of source network load becomes the development trend of modern power systems, and is a great revolution of the power systems on equipment.
However, the frequency modulation resource structures of different regional power grids are differentiated, so that the heterogeneity of the frequency modulation characteristics of each node is more obvious in the frequency dynamic process. In a double-high power system, the two sides of a cross-region connecting line present the characteristics of 'sending end' and 'receiving end', and the equivalent inertia of the power grids on the two sides and the differentiation of frequency modulation resources cause the dynamic process of the regional power grid frequency to generate obvious difference. On the other hand, although the device adopting the power electronic converter interface can provide faster primary frequency support, the device lacks the inertia of the traditional generator, and after a fault occurs, the frequency fluctuation amplitude and the frequency change rate are large, so that a series of frequency stability problems are easily caused.
At present, a frequency modulation strategy controlled by power electronic equipment provides a flexible control means for frequency modulation of a novel power system, but the current power system frequency situation research does not provide basis for frequency characteristic quantitative calculation and combined simulation verification, so that how to quantitatively analyze the power system frequency characteristics becomes a research hotspot. With the gradual improvement of the double-high power system, the frequency characteristic calculation process method of the system has a promoting significance for the frequency stability analysis, frequency modulation unit control, resource configuration optimization and the like of the novel power system.
Disclosure of Invention
In order to solve the technical problems, the invention provides a power grid frequency characteristic calculation method considering wind-storage-direct combined frequency modulation, and solves the technical problem of lack of a power system frequency characteristic calculation method under the traditional thermal power, wind power, energy storage and flexible direct current transmission combined frequency modulation.
The invention relates to a power grid frequency characteristic calculation method considering wind-storage-direct combined frequency modulation, which comprises the following steps of:
step 1, establishing a wind-storage-direct combined frequency modulation power system frequency response model and calculating frequency characteristics according to a traditional thermal power, wind power, energy storage and flexible direct current transmission frequency response model;
step 2, calculating to obtain a power system frequency change time domain expression, and calculating a power system frequency characteristic set A under wind-storage-direct joint frequency regulation based on a power system frequency change time domain model, wherein the power system frequency characteristic set A comprises a frequency change rate, a maximum frequency deviation and a frequency peak time;
and 3, obtaining a frequency change frequency domain expression according to the frequency characteristic function of the power system, and calculating a power system frequency characteristic set B under wind-storage-direct joint frequency regulation based on a power system frequency change S domain model, wherein the power system frequency characteristic set B comprises a steady-state frequency error and an initial frequency change rate.
Further, in step 1, based on the frequency response transfer function of each frequency modulation unit, providing a frequency modulation service according to each generated power, and obtaining a power system frequency response model;
the wind-storage-direct joint frequency modulation power system frequency response transfer function is as follows:
Gsystem(s)＝GR(s)+GWEDC(s)
＝GR(s)+GW(s)+GE(s)+GDC(s)
wherein G issystem(s) is the power system frequency response transfer function of the wind-storage-direct-coupled frequency regulation without disturbance, GR(s) is the frequency response transfer function of conventional fossil power, GW(s) is the wind power frequency response transfer function, GDC(s) is the flexible DC transmission frequency response transfer function, GWEDC(s) is a frequency response transfer function under wind power, energy storage and flexible direct current power transmission combined frequency modulation;
wherein G isWEDC(s) satisfies:
GWEDC(s)＝GW(s)+GE(s)+GDC(s)
the frequency response model of each frequency modulation unit is as follows:
a. the traditional thermal power frequency response model adopts a low-order linear transfer function:
Figure BDA0003376544750000021
r is the primary frequency modulation droop coefficient, delta PRFor power increment of thermal power generating unit, FHIs the coefficient of work of the high-pressure cylinder of the prime mover, TRIs the reheat time constant, kmIs the mechanical power factor; Δ f is the power system frequency variation;
b. wind power frequency additional control adopts inertia control and pitch angle control in a typical frequency control method to establish a wind power frequency response model;
the wind power inertia response transfer function is:
Figure BDA0003376544750000031
in the formula, TωIs the rotor inertial response time constant; k is a radical ofdfIs the inertial response coefficient; delta PωThe power variation provided for rotor inertia control;
the pitch angle control frequency response transfer function is:
Figure BDA0003376544750000032
in the formula, TβIs a variable pitch response time constant; k is a radical ofpfIs a primary frequency modulation coefficient; delta PβProviding a power variation for pitch control;
the wind power frequency response model combines inertial response control and pitch angle control, and the wind turbine generator frequency response transfer function is as follows:
Figure BDA0003376544750000033
ΔPWthe variable quantity of the power output of the wind power frequency modulation unit is obtained;
c. the frequency additional controller is added to the energy storage unit at the outer ring control side of the DC/DC converter, and the energy storage frequency response transfer function is as follows:
Figure BDA0003376544750000034
in the formula kEFor additional control of the proportional coefficient, T, of the energy storage frequencyEFor inner loop control of the response time constant, Δ PESending the power variation to the energy storage system;
d. the flexible direct current transmission provides frequency support through the VSC converter station, and a flexible direct current transmission frequency response model is as follows:
Figure BDA0003376544750000035
in the formula, alpha is the droop coefficient of the flexible direct current transmission frequency control, TDCIs the time constant of the inertial element, Δ PDCAnd increasing the flexible direct current transmission power.
Further, calculating a frequency characteristic, wherein a transfer function of the frequency characteristic of the wind-storage-direct combined frequency modulation power system is as follows:
Figure BDA0003376544750000041
wherein, M is 2H, and H is a system inertia constant; delta PLThe disturbance size of the system; K. etaW、ηE、ηDCRespectively the non-negative frequency modulation coefficients of the conventional generator set, wind power, energy storage and flexible direct current transmission,and satisfies K + etaW+ηE+η DC1 is ═ 1; g(s) is a frequency transfer function of the power system under disturbance.
Further, in the step 2, a frequency change rate, a maximum frequency deviation and a peak time thereof are calculated by using a wind-storage-direct combined frequency modulation power system frequency change time domain model;
1) power system frequency change time domain model:
Δf(t)＝L-1[Δf(s)]＝L-1[Gs_WEDC(s)·ΔPL(s)]
2) deriving the frequency change Δ f (t) to obtain a frequency change expression:
Figure BDA0003376544750000042
3) let the frequency variation expression be zero, i.e. μ (T) be 0, and obtain the maximum frequency deviation TmaxAnd its peak time tp：
Figure BDA0003376544750000043
Further, in the step 3, a steady-state frequency error and an initial frequency change rate are calculated by using an S-domain model of power system frequency change under wind-storage-direct combined frequency regulation;
1) obtaining a frequency change frequency domain expression according to a frequency characteristic transfer function of the power system:
Figure BDA0003376544750000044
2) and deriving a frequency error frequency domain model of the power system under the wind-storage-direct combined frequency modulation by using a final value theorem, wherein the expression formula of the steady-state frequency error containing all frequency modulation coefficients is as follows:
Figure BDA0003376544750000045
the expression formula of the steady-state frequency error without the frequency modulation coefficient of the traditional thermal power generating unit is as follows:
Figure BDA0003376544750000051
3) calculating the disturbed delta P of the power system under the wind-storage-direct combination frequency modulation by using the initial value theoremLThe time-frequency initial change rate per unit value is in the form of
Figure BDA0003376544750000052
Figure BDA0003376544750000053
Actual value form:
Figure BDA0003376544750000054
the invention has the beneficial effects that: 1) the method takes a 'double-high' power system as a background, and a power system frequency response model and a characteristic model under combined frequency modulation are established, so that not only is the traditional thermal power generating unit considered, but also new energy wind power, energy storage and flexible direct-current transmission are considered, and the problem of lack of a power system frequency characteristic calculation method when load disturbance occurs under the 'double-high' background is solved; 2) the invention discloses a calculation method of a power system based on a frequency change time domain model and a frequency change frequency domain model under wind-storage-direct joint frequency modulation, which provides reference for calculation and analysis of the frequency characteristics of the current novel power system.
Drawings
In order that the present invention may be more readily and clearly understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings.
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a flow chart of calculating power system frequency characteristics under joint frequency modulation based on a power system frequency variation time domain model;
FIG. 3 is a flow chart of power system frequency characteristics under joint frequency modulation calculated based on a power system frequency variation S-domain model;
fig. 4 is a frequency response model of the power system under the wind-storage-direct-combination frequency modulation.
Fig. 5 is a frequency variation curve diagram of the power system based on the frequency variation expression (10) and when the frequency modulation coefficient of thermal power, wind power, energy storage and flexible direct-current transmission is 25%;
FIG. 6 is a frequency rate change curve of the power system based on the frequency change expression (12) and with a thermal power, wind power, energy storage and flexible direct-current transmission frequency modulation coefficient of 25%;
fig. 7 is a three-dimensional graph of the relationship between the steady-state frequency error and the additional control proportionality coefficient of the auxiliary frequency modulation unit when the steady-state frequency error formula (14) or (15) is based and the thermal power, wind power, energy storage and flexible direct-current transmission frequency modulation coefficient is 25%.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
In the embodiment, a power system frequency control model containing thermal power, wind power, energy storage and flexible direct-current transmission is established based on Matlab/Simulink; the energy storage is connected in parallel near a wind power outlet in a centralized mode and is connected into a system through a power electronic converter; the energy storage type is power type energy storage, such as a super capacitor, and is characterized by short response time and large power ratio, and meets the requirement of wind power frequency modulation; in consideration of the droop characteristic, the flexible direct current power transmission model adds frequency additional control. The frequency characteristic change of the power system under different working conditions is analyzed below, the load is 1000MW, the wind power rated power is 200MW, and the load disturbance is 60MW (0.06 p.u).
As shown in fig. 1 to 4, the method for calculating the frequency characteristics of the power grid in consideration of wind-storage-direct combined frequency modulation according to the present invention includes the steps of:
step 1, according to a traditional thermal power, wind power, energy storage and flexible direct current transmission frequency response model, a wind-energy storage-direct current combined frequency modulation power system frequency response model is established, and frequency characteristics are calculated.
Step 2, calculating to obtain a power system frequency change time domain expression, and calculating a power system frequency characteristic set A under wind-storage-direct joint frequency regulation based on a power system frequency change time domain model, wherein the power system frequency characteristic set A comprises a frequency change rate, a maximum frequency deviation and a frequency peak time;
and 3, obtaining a frequency change frequency domain expression according to the frequency characteristic function of the power system, and calculating a power system frequency characteristic set B under wind-storage-direct joint frequency regulation based on a power system frequency change S domain model, wherein the power system frequency characteristic set B comprises a steady-state frequency error and an initial frequency change rate.
Further, in step 1, based on the frequency response transfer function of each frequency modulation unit, providing a frequency modulation service according to each generated power, obtaining a frequency response model of the power system, and calculating a frequency characteristic;
1) the frequency response transfer function of the wind-storage-direct joint frequency modulation power system is as follows:
Figure BDA0003376544750000061
wherein G issystem(s) is the power system frequency response transfer function of the wind-storage-direct-coupled frequency regulation without disturbance, GR(s) is the frequency response transfer function of conventional fossil power, GW(s) is the wind power frequency response transfer function, GDC(s) is the flexible DC transmission frequency response transfer function, GWEDCAnd(s) is a frequency response transfer function under the wind power, energy storage and flexible direct current transmission combined frequency modulation.
Wherein G isWEDC(s) satisfies:
GWEDC(s)＝GW(s)+GE(s)+GDC(s) (2)
the frequency response model of each frequency modulation unit is as follows:
a. the traditional thermal power frequency response model adopts a low-order linear transfer function:
Figure BDA0003376544750000071
r is the primary frequency modulation droop coefficient, delta PRFor power increment of thermal power generating unit, FHIs the coefficient of work of the high-pressure cylinder of the prime mover, TRIs the reheat time constant, kmIs the mechanical power factor; Δ f is the power system frequency variation.
b. Wind power frequency additional control adopts inertia control and pitch angle control in a typical frequency control method to establish a wind power frequency response model;
the wind power inertia response transfer function is:
Figure BDA0003376544750000072
in the formula, TωIs the rotor inertial response time constant; k is a radical ofdfIs the inertial response coefficient; delta PωThe power variation provided for rotor inertia control;
the pitch angle control frequency response transfer function is:
Figure BDA0003376544750000073
in the formula, TβIs a variable pitch response time constant; k is a radical ofpfIs a primary frequency modulation coefficient; delta PβProviding a power variation for pitch control;
the wind power frequency response model combines inertial response control and pitch angle control, and the wind turbine generator frequency response transfer function is as follows:
Figure BDA0003376544750000074
ΔPWthe variable quantity of the power output of the wind power frequency modulation unit is obtained.
c. The frequency additional controller is added to the energy storage unit at the outer ring control side of the DC/DC converter, and the energy storage frequency response transfer function is as follows:
Figure BDA0003376544750000075
in the formula kEFor additional control of the proportional coefficient, T, of the energy storage frequencyEFor inner loop control of the response time constant, Δ PESending the power variation to the energy storage system;
d. the flexible direct current transmission provides frequency support through the VSC converter station, and a flexible direct current transmission frequency response model is as follows:
Figure BDA0003376544750000081
in the formula, alpha is the droop coefficient of the flexible direct current transmission frequency control, TDCIs the time constant of the inertial element, Δ PDCIncreasing the flexible direct current transmission power;
2) the wind-storage-direct joint frequency modulation power system frequency characteristic transfer function is as follows:
Figure BDA0003376544750000082
wherein, M is 2H, and H is a system inertia constant; delta PLThe disturbance size of the system; K. etaW、ηE、ηDCThe frequency modulation coefficients (non-negative) of the conventional unit, wind power, energy storage and flexible direct current transmission are respectively realized, and K + eta is satisfiedW+ηE+η DC1 is ═ 1; g(s) is a frequency transfer function of the power system under disturbance.
Further, in the step 2, a frequency change rate, a maximum frequency deviation and a peak time thereof are calculated by using a wind-storage-direct combined frequency modulation power system frequency change time domain model;
1) power system frequency change time domain model:
Δf(t)＝L-1[Δf(s)]＝L-1[Gs_WEDC(s)·ΔPL(s)] (10)
in the example, the frequency modulation coefficients of the traditional thermal power, wind power, energy storage and flexible direct-current transmission are set to be 25%, the rest parameters are shown in an attached table A, and a frequency curve diagram is obtained through simulation, as shown in fig. 5.
2) Deriving the frequency change Δ f (t) to obtain a frequency change expression:
Figure BDA0003376544750000083
3) let the frequency variation expression be zero, i.e. μ (T) be 0, and obtain the maximum frequency deviation TmaxAnd its peak time tp：
Figure BDA0003376544750000084
In the example, the frequency modulation coefficients of traditional thermal power, wind power, energy storage and flexible direct-current transmission are set to be 25%, the rest parameters are shown in an attached table A, a frequency change rate simulation graph is obtained through simulation, and the maximum frequency deviation and the peak time can be known from the graph, as shown in FIG. 6.
TABLE A System parameter settings
Figure BDA0003376544750000091
Further, in the step 3, a steady-state frequency error and an initial frequency change rate are calculated by using an S-domain model of power system frequency change under wind-storage-direct combined frequency regulation;
1) obtaining a frequency change frequency domain expression according to a frequency characteristic transfer function of the power system:
Figure BDA0003376544750000092
2) and (3) deriving a frequency error frequency domain model of the power system under the wind-storage-direct combined frequency modulation by using a final value theorem, wherein the representation modes are two types:
Figure BDA0003376544750000093
Figure BDA0003376544750000094
wherein the formula (14) is a steady-state frequency error containing all frequency modulation coefficients, and the formula (15) is a steady-state frequency error not containing the frequency modulation coefficients of the traditional thermal power generating unit; if only the relation between the frequency modulation coefficient of the unconventional unit and the steady-state frequency error is considered, the formula (15) is selected, and otherwise, the formula (14) is adopted.
In the example, the frequency modulation coefficients of traditional thermal power, wind power, energy storage and flexible direct-current transmission are set to be 25%, the rest parameters are shown in an attached table A, the quantitative relation between the steady-state frequency error and the control proportional coefficient of the auxiliary frequency modulation unit is simulated based on a formula (14), and the result is shown in a figure 7.
3) Calculating the disturbed delta P of the power system under the wind-storage-direct combination frequency modulation by using the initial value theoremLThe time-frequency initial change rate per unit value is in the form of
Figure BDA0003376544750000095
Figure BDA0003376544750000101
Actual value form:
Figure BDA0003376544750000102
in the example, the frequency modulation coefficients of the traditional thermal power, wind power, energy storage and flexible direct-current transmission are set to be 25%, the rest parameters are shown in an attached table A, the power disturbance is-0.06 (p.u), and the initial frequency change rate is-3 Hz s according to a formula (17)-1In fig. 6, the frequency change rate at the time when t is 0 is the same as the derived value.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all equivalent variations made by using the contents of the present specification and the drawings are within the protection scope of the present invention.

Claims (5)

1. A power grid frequency characteristic calculation method considering wind-storage-direct combined frequency modulation is characterized by comprising the following steps:
step 1, establishing a wind-storage-direct combined frequency modulation power system frequency response model and calculating frequency characteristics according to a traditional thermal power, wind power, energy storage and flexible direct current transmission frequency response model;
step 2, calculating to obtain a power system frequency change time domain expression, and calculating a power system frequency characteristic set A under wind-storage-direct joint frequency regulation based on a power system frequency change time domain model, wherein the power system frequency characteristic set A comprises a frequency change rate, a maximum frequency deviation and a frequency peak time;
and 3, obtaining a frequency change frequency domain expression according to the frequency characteristic function of the power system, and calculating a power system frequency characteristic set B under wind-storage-direct joint frequency regulation based on a power system frequency change S domain model, wherein the power system frequency characteristic set B comprises a steady-state frequency error and an initial frequency change rate.
2. The method for calculating the grid frequency characteristic considering wind-storage-direct combined frequency modulation according to claim 1, wherein in the step 1, a frequency modulation service is provided according to respective generated power based on a frequency response transfer function of each frequency modulation unit, so as to obtain a power system frequency response model;
the wind-storage-direct joint frequency modulation power system frequency response transfer function is as follows:
Figure FDA0003376544740000011
wherein G issystem(s) is the power system frequency response transfer function of the wind-storage-direct-coupled frequency regulation without disturbance, GR(s) is the frequency response transfer function of conventional fossil power, GW(s) is the wind power frequency response transfer function, GDC(s) is the flexible DC transmission frequency response transfer function, GWEDC(s) is wind power, energy storage, flexible direct current transmissionCombining frequency response transfer functions under frequency modulation;
wherein G isWEDC(s) satisfies:
GWEDC(s)＝GW(s)+GE(s)+GDC(s)
the frequency response model of each frequency modulation unit is as follows:
a. the traditional thermal power frequency response model adopts a low-order linear transfer function:
Figure FDA0003376544740000012
r is the primary frequency modulation droop coefficient, delta PRFor power increment of thermal power generating unit, FHIs the coefficient of work of the high-pressure cylinder of the prime mover, TRIs the reheat time constant, kmIs the mechanical power factor; Δ f is the power system frequency variation;
b. wind power frequency additional control adopts inertia control and pitch angle control in a typical frequency control method to establish a wind power frequency response model;
the wind power inertia response transfer function is:
Figure FDA0003376544740000025
in the formula, TωIs the rotor inertial response time constant; k is a radical ofdfIs the inertial response coefficient; delta PωThe power variation provided for rotor inertia control;
the pitch angle control frequency response transfer function is:
Figure FDA0003376544740000021
in the formula, TβIs a variable pitch response time constant; k is a radical ofpfIs a primary frequency modulation coefficient; delta PβProviding a power variation for pitch control;
the wind power frequency response model combines inertial response control and pitch angle control, and the wind turbine generator frequency response transfer function is as follows:
Figure FDA0003376544740000022
ΔPWthe variable quantity of the power output of the wind power frequency modulation unit is obtained;
c. the frequency additional controller is added to the energy storage unit at the outer ring control side of the DC/DC converter, and the energy storage frequency response transfer function is as follows:
Figure FDA0003376544740000023
in the formula kEFor additional control of the proportional coefficient, T, of the energy storage frequencyEFor inner loop control of the response time constant, Δ PESending the power variation to the energy storage system;
d. the flexible direct current transmission provides frequency support through the VSC converter station, and a flexible direct current transmission frequency response model is as follows:
Figure FDA0003376544740000024
in the formula, alpha is the droop coefficient of the flexible direct current transmission frequency control, TDCIs the time constant of the inertial element, Δ PDCAnd increasing the flexible direct current transmission power.
3. The method for calculating the grid frequency characteristic considering the wind-storage-direct combined frequency modulation according to claim 2, wherein the frequency characteristic is calculated, and the transfer function of the frequency characteristic of the power system of the wind-storage-direct combined frequency modulation is as follows:
Figure FDA0003376544740000031
wherein, M is 2H, and H is a system inertia constant; delta PLThe disturbance size of the system; K. etaW、ηE、ηDCRespectively the non-negative frequency modulation coefficients of the conventional unit, wind power, energy storage and flexible direct current transmission, and meets the K + etaW+ηE+ηDC1 is ═ 1; g(s) is a frequency transfer function of the power system under disturbance.
4. The method for calculating the grid frequency characteristic considering the wind-storage-direct combined frequency modulation according to claim 1, wherein the method comprises the following steps: in the step 2, calculating the frequency change rate, the maximum frequency deviation and the peak time thereof by using a power system frequency change time domain model under wind-storage-direct joint frequency regulation;
1) power system frequency change time domain model:
Δf(t)＝L-1[Δf(s)]＝L-1[Gs_WEDC(s)·ΔPL(s)]
2) deriving the frequency change Δ f (t) to obtain a frequency change expression:
Figure FDA0003376544740000032
3) let the frequency variation expression be zero, i.e. μ (T) be 0, and obtain the maximum frequency deviation TmaxAnd its peak time tp：
Figure FDA0003376544740000033
5. The method for calculating the grid frequency characteristic considering the wind-storage-direct combined frequency modulation according to claim 1, wherein the method comprises the following steps: in the step 3, a steady-state frequency error and an initial frequency change rate are calculated by using an S domain model of the power system frequency change under wind-storage-direct combination frequency regulation;
1) obtaining a frequency change frequency domain expression according to a frequency characteristic transfer function of the power system:
Figure FDA0003376544740000034
2) and deriving a frequency error frequency domain model of the power system under the wind-storage-direct combined frequency modulation by using a final value theorem, wherein the expression formula of the steady-state frequency error containing all frequency modulation coefficients is as follows:
Figure FDA0003376544740000041
the expression formula of the steady-state frequency error without the frequency modulation coefficient of the traditional thermal power generating unit is as follows:
Figure FDA0003376544740000042
3) calculating the disturbed delta P of the power system under the wind-storage-direct combination frequency modulation by using the initial value theoremLThe time-frequency initial change rate per unit value is in the form of
Figure FDA0003376544740000043
Figure FDA0003376544740000044
Actual value form:
Figure FDA0003376544740000045
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