CN113013896A - Coordination control method for jointly participating in primary frequency modulation of power grid by light storage - Google Patents

Coordination control method for jointly participating in primary frequency modulation of power grid by light storage Download PDF

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CN113013896A
CN113013896A CN202110249651.4A CN202110249651A CN113013896A CN 113013896 A CN113013896 A CN 113013896A CN 202110249651 A CN202110249651 A CN 202110249651A CN 113013896 A CN113013896 A CN 113013896A
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energy storage
frequency modulation
photovoltaic
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CN113013896B (en
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傅质馨
张晶晶
朱俊澎
袁越
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Hohai University HHU
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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
    • H02J3/28—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
    • H02J3/38—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
    • H02J3/38—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
    • 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
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • 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

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Abstract

The invention discloses a coordination control method for jointly participating in primary frequency modulation of a power grid by light storage, which comprises the following steps: modeling a photovoltaic power generation system and an energy storage system respectively to obtain a photovoltaic power generation system model and an energy storage system model; the photovoltaic power generation system is used for participating in power grid frequency modulation through a dynamic variable load shedding method following system output and frequency change; under the basis of coordinated droop control and positive and negative virtual inertia control, energy storage combined frequency modulation is adopted based on an energy storage variable coefficient self-adaptive control strategy; the capacity of the stored energy is set, so that the inertial response matched with the synchronous generator set can be provided, and the coordination control of the primary frequency modulation of the light storage support power grid is realized by adopting photovoltaic variable load shedding and configured energy storage combined frequency modulation. The invention can improve the inertia and frequency response capability of the optical storage system, can also take frequency modulation and energy storage capacity into account, is beneficial to exerting comprehensive benefits, and improves the utilization rate of new energy while improving the stability level of the system.

Description

Coordination control method for jointly participating in primary frequency modulation of power grid by light storage
Technical Field
The invention belongs to the field of new energy grid-connected frequency stability, relates to a primary frequency modulation control method, and particularly relates to a coordination control method for jointly participating in primary frequency modulation of a power grid by light storage.
Background
With the great increase of the photovoltaic power generation permeability, the frequency regulation characteristic under the power system fault disturbance is remarkably deteriorated. In order to improve the photovoltaic utilization rate, photovoltaic power generation generally works at the maximum power point, inertia support is not provided, necessary energy reserves are not considered, and the voltage and frequency support effect on a power grid is extremely limited. Considering the active supporting effect on the system, it is particularly urgent to regulate the frequency and voltage of the system by the photovoltaic power generation. In addition, from the perspective of utilizing a new supporting means, the quick and flexible response characteristic of energy storage is exerted, the coordination control of photovoltaic and energy storage is developed, the comprehensive benefits are favorably exerted, and the utilization rate of new energy is improved while the stability level of the system is improved.
However, the existing photovoltaic frequency modulation strategy still needs to be improved for how to realize dynamic matching of the photovoltaic power frequency characteristic control coefficient and the load shedding reserve capacity, and the problems of frequency modulation parameter setting flexibility, adaptability and the like in the energy storage frequency modulation control strategy. The energy storage can not only smooth the power fluctuation of the photovoltaic, but also make up the defect that the photovoltaic participates in frequency modulation alone. At present, researches related to light storage coordination and primary frequency modulation in a large power grid are few, and an effective technical scheme is urgently needed to solve the existing technical problems.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problem that photovoltaic power generation is not connected to the grid through a power electronic interface, the coordination control method for the light storage to jointly participate in the primary frequency modulation of the power grid is provided, the inertia and the frequency response capability of a light storage system can be improved, the frequency modulation and the energy storage capacity can be kept simultaneously, the comprehensive benefits can be brought into play, the stability level of the system is improved, and meanwhile, the utilization rate of new energy is improved.
The technical scheme is as follows: in order to achieve the purpose, the invention provides a coordination control method for jointly participating in primary frequency modulation of a power grid by light storage, which comprises the following steps:
s1: modeling a photovoltaic power generation system and an energy storage system respectively to obtain a photovoltaic power generation system model and an energy storage system model; the photovoltaic power generation system comprises a photovoltaic array, a Boost converter, a grid-connected inverter, a filter and a control system thereof; the energy storage system comprises an energy storage battery, a Buck-Boost converter, a grid-connected inverter, a filter and a control system thereof;
s2: the photovoltaic power generation system is used for participating in power grid frequency modulation through a dynamic variable load shedding method following system output and frequency change; the dynamic variable load shedding method for the output and frequency change of the photovoltaic following system comprises the following steps: obtaining maximum active output P by photovoltaic in a maximum power point tracking modempptAfter variable load shedding control and amplitude limiting, the output power is used as new photovoltaic active power and given and is output to a control system of a Boost converter;
s3: under the basis of coordinated droop control and positive and negative virtual inertia control, energy storage combined frequency modulation is adopted based on an energy storage variable coefficient self-adaptive control strategy;
s4: the capacity of the stored energy is set, so that the inertial response matched with the synchronous generator set can be provided, and the coordination control of the primary frequency modulation of the light storage support power grid is realized by adopting photovoltaic variable load shedding and configured energy storage combined frequency modulation.
Further, the photovoltaic power generation system in step S1 specifically includes: DC voltage V output by photovoltaic arraypvAnd a direct current IpvAfter passing through the maximum power point tracking controller, a DC voltage reference value V is generatedrefmppt，VrefmpptAnd VPVThe error signal is integrated to obtain the given P of the photovoltaic output active powerref，PrefAnd active power P of high-voltage side of boost converterdcGenerating a duty ratio d after PI control, and driving a Boost converter to work so as to realize MPPT control of the photovoltaic array; grid-connected inverter working in unit power factor state igq *When the voltage of the photovoltaic array is increased by the Boost converter, the direct current voltage U is obtaineddcAnd a voltage reference value UrefAfter difference is made, a current inner ring reference value i is generated through PI controldrefThen the sampled actual current value id、iqAfter deviation is subjected to PI controller and current decoupling control, the voltage given u is obtainedsq、usdFinally, obtaining a trigger pulse S of the grid-connected inverter through pulse width modulation after coordinate transformationgTherefore, active and reactive decoupling control and grid-connected operation of the grid-connected inverter are achieved.
Further, the energy storage system in step S1 specifically is: the energy storage system realizes charge-discharge switching of energy storage through a buck-boost chopper circuit; sampling voltage and current V of Buck-Boost low-voltage sideL、ILMultiplying to obtain the battery power Pbat. When the DC/DC converter works in a discharging mode, the active reference is given by PrefAnd battery power PbatComparing, regulating by PI controller to obtain duty ratio signal D _ Boost, and generating pulse signal G for driving Boost converter by interpolating trigger pulse together with frequency signal generated by variable frequency sawtooth generatorBoost. When the converter is operated in the charging mode, P is setrefTaking the inverse of battery power PbatMultiplying the difference by-1, and performing similar control in a discharging mode to obtain a trigger signal G for driving Buck to actBuck。
Further, the control characteristic curve expression of the dynamic variable load shedding in step S2 is as follows:
σ％＝K0×(Pmppt/PN+Δf/Δfmax) (1)
in the formula: pNRated active power of the photovoltaic system under standard conditions; pmpptThe maximum active power of the photovoltaic system under the current working condition; Δ fmaxMaximum frequency deviation allowed for the system; Δ f is the system frequency deviation; k0The load shedding rate in the initial condition; sigmamax% is the upper limit of the load shedding ratio.
Further, the droop control method in step S3 is
Energy storage is divided into four intervals: smax: the maximum working limit of the energy storage battery; shigh: the upper limit value of the normal work of the energy storage battery; slow: the lower limit value of the energy storage battery in normal operation; smin: a minimum limit for operation of the energy storage battery;
adopting a Logistic function to carry out self-adaptive control on the droop coefficient, wherein the curve function expression is as follows:
Figure BDA0002965458390000021
in the formula: p0Is an initial value; k is the final value; r measures the increasing speed of the curve;
with SOC as an argument, P0And r is used as a parameter variable, the charge-discharge coefficient is used as a dependent variable, and the following equation is constructed:
1) discharging of battery
Figure BDA0002965458390000031
2) Battery charging
Figure BDA0002965458390000032
In the formula: kmaxThe final value of the droop coefficient during charging and discharging; ssocIs the state of charge of the stored energy; kbcAnd KbdThe coefficients corresponding to discharging and charging, respectively.
Further, the positive virtual inertia control method in step S3 is:
the positive virtual inertial response equation is:
ΔPbess＝-Mbpdf/dt (5)
Figure BDA0002965458390000033
Figure BDA0002965458390000034
in the formula: mbpSimulating inertia for positive virtualA coefficient of sex; mbp-c、Mbp-dRespectively positive virtual inertia coefficients during energy storage charging and discharging; mpIs an adjustment coefficient which changes along with the frequency deviation; n is a parameter; c. C1Is the initial value of the positive virtual inertia coefficient. DpIs a positive virtual inertial frequency rate-of-change dead zone.
Further, the negative virtual inertia control method in step S3 is:
the negative virtual inertial response formula is:
ΔPbess＝-Mbn df/dt (8)
Figure BDA0002965458390000035
Figure BDA0002965458390000036
in the formula: mbnIs a negative virtual inertia coefficient; mbn-c、Mbn-dRespectively negative virtual inertia coefficients during charging and discharging; b1Is the initial value of the negative virtual inertia coefficient; mb1Is an adjustment coefficient that varies with respect to the frequency deviation; f. ofbess-dAn energy storage frequency modulation dead zone; f. ofmaxThe maximum frequency deviation amplitude allowed by the power grid.
Further, the method for configuring the energy storage capacity in step S4 includes:
in order to ensure that the configured energy storage can provide an inertial response matched with the synchronous generator set, the capacity of the energy storage is set as follows:
when the rotating speed of the generator is omega, the synchronous generator has the rotating energy of
Figure BDA0002965458390000041
When the motor speed follows the system frequency from omega0Change to omega1Time of flight
Figure BDA0002965458390000042
The speed of the synchronous generator is proportional to the system frequency and typically varies over a small range. Grid operation and maintenance guidelines specify that in special cases the system frequency may rise to 51Hz or fall to 48Hz in a short period of time. With the frequency decline analysis, the rotational speed range of synchronous generator rotor is 0.95 ~ 1pu, and the kinetic energy that can release is:
Figure BDA0002965458390000043
the energy storage device is only limited by SOC, and can generally realize large-range power throughput, so that the frequency modulation effect same as that of a conventional generator set can be realized by smaller energy storage capacity. When the photovoltaic power station configured with the energy storage replaces a conventional generator set and is incorporated into a power grid, the energy storage power meets the requirement when the energy storage power meets the requirement because the energy storage charging and discharging time is generally longer than the inertia response time.
If the energy released by the energy storage system in delta t is the same as the kinetic energy of the same rotor, the following steps are provided:
ΔEbess＝PbessΔt＝0.0784HSN (14)
let Δ t be 2H
Pbess＝0.0392SN (15)
In the formula: delta Ebess、PbessCapacity and power for stored energy, respectively; sNIs the rated capacity of the generator; h is an inertia constant; j is the inertia time constant of the generator.
Further, in step S4, the method for optical storage combined frequency modulation includes:
1) the energy storage system provides an inertial response matched with a conventional generator set for the initial frequency change stage of the power system;
2) the photovoltaic jointly participates in primary frequency modulation by using a variable load shedding frequency modulation strategy and an energy storage self-adaptive control strategy.
The invention respectively provides strategies of photovoltaic and energy storage participating in primary frequency modulation of a power grid: the photovoltaic adopts a dynamic variable load shedding frequency modulation strategy following the system output and frequency change, so that the system frequency fluctuation is responded in real time, and the frequency stability of the photovoltaic power station is improved. The energy storage adopts an adaptive control strategy following the change of the state of charge, the frequency change rate and the frequency deviation, and droop control dynamically adjusts a control coefficient based on a logistic function; positive virtual inertia control is combined with the influence of frequency deviation and frequency change rate; the negative virtual inertia comprehensively considers the SOC of the battery, the frequency change rate and the frequency deviation to adjust the output power; the coordination and the advantage complementation of the three are realized. In order to reduce the power loss caused by fixed load shedding and reduce the cost of an energy storage system as much as possible, a measure of combining photovoltaic variable load shedding and energy storage is adopted: the energy storage provides inertial response for the initial change stage of the frequency of the power system, and the photovoltaic jointly participates in primary frequency modulation by utilizing variable load reduction and energy storage, so that the coordinated operation of the energy storage and the photovoltaic is realized.
The invention provides a coordination control method for participating in primary frequency modulation of a power grid by using a light storage combination. Because the photovoltaic is influenced by environmental factors such as illumination intensity, temperature and the like, the photovoltaic power generation has the characteristics of randomness, volatility, uncertainty and the like. Photovoltaic arrays typically operate at the maximum power point, have no rotating equipment that can store kinetic energy and provide inertia, and cannot provide the necessary voltage, frequency support and damping for the grid. With the increasing photovoltaic proportion, the power electronic interface gradually replaces the mechanical switch interface in a large scale, the integral inertia level of the power system is reduced, the threat to the safe and stable operation of the power system is increasingly shown, and the frequency adjustment of the photovoltaic participation system is more and more necessary. The energy storage can not only smooth the power fluctuation of the photovoltaic, but also make up the defect that the photovoltaic participates in frequency modulation alone. In order to reduce the power loss caused by fixed load shedding and reduce the cost of an energy storage system as much as possible, a measure of combining photovoltaic variable load shedding and energy storage is adopted: therefore, the coordination control method for the light storage joint to participate in the primary frequency modulation of the power grid has very important practical significance.
The invention firstly analyzes the frequency modulation characteristics of the photovoltaic system and the energy storage system. Secondly, strategies that photovoltaic and energy storage participate in primary frequency modulation of the power grid are respectively provided: the photovoltaic adopts a dynamic variable load shedding frequency modulation method following the system output and frequency change; the energy storage adopts an adaptive control method following the change of the state of charge, the frequency change rate and the frequency deviation. In order to reduce the power loss caused by fixed load shedding and reduce the cost of an energy storage system as much as possible, a measure of combining photovoltaic variable load shedding and energy storage is adopted: the energy storage provides inertial response for the initial change stage of the frequency of the power system, and the photovoltaic jointly participates in primary frequency modulation by utilizing variable load reduction and energy storage, so that the coordinated operation of the energy storage and the photovoltaic is realized. And finally, carrying out simulation verification on the proposed strategy by using a typical regional power grid example.
The invention provides a photovoltaic variable load shedding frequency modulation method, which comprises the following steps: obtaining maximum active output P by photovoltaic in a maximum power point tracking modempptAnd the photovoltaic active power is given as the new photovoltaic active power after variable load shedding control and amplitude limiting and is output to a Boost converter control system. On one hand, the variable load shedding control coefficient can dynamically change the output along with the frequency deviation and the maximum active output of the system, and on the other hand, the load shedding rate of the system is reversely adjusted, so that the system has the capacity of primary frequency modulation, the problem of selecting a droop characteristic slope when a load shedding and droop control strategy is used is solved, and the system has flexible self-adaptability.
The invention provides a self-adaptive control method for battery energy storage, which comprises the following steps: droop control is based on the characteristics of a Logistic function, only one function is respectively set in a charging and discharging interval by utilizing symmetry, and the droop coefficient is adaptively adjusted by adopting SOC partitions, so that the complexity of setting a piecewise function is avoided; the positive virtual inertia coefficient and the negative virtual inertia coefficient are set by using a frequency deviation change function as an adjusting factor and combining the frequency change rate and the SOC change characteristic; the coordination of the three components not only ensures the charge state of the stored energy, but also plays the advantage of primary frequency modulation of the stored energy.
The invention provides a coordination control method for jointly participating in primary frequency modulation of a power grid by light storage. The energy storage system provides inertial response similar to that of a conventional generator set for the initial frequency change stage of the power system; the photovoltaic jointly participates in primary frequency modulation by using a variable load shedding frequency modulation strategy and an energy storage self-adaptive control strategy. The load shedding standby capacity of the photovoltaic is effectively utilized, and the capacity allocation ratio of the stored energy is reduced.
The photovoltaic power generation system is innovative in that a variable load shedding frequency modulation method is used in the photovoltaic power generation system, so that on one hand, the output can be dynamically changed along with the frequency deviation of the system and the maximum active output; on the other hand, the load shedding rate of the system is reversely adjusted, so that the system has the primary frequency modulation capability. The method avoids the problem of selecting the droop characteristic slope when a virtual droop control strategy is used, and has flexibility. The innovation of the method is that droop control is based on a Logistic function, and a droop coefficient is adaptively adjusted by utilizing an SOC partition; the positive virtual inertia coefficient and the negative virtual inertia coefficient are set by using a frequency deviation change function as an adjusting factor and combining the frequency change rate and the SOC change characteristic; the coordination and the advantage complementation of the three are realized, and the self-adaption is better. The charge state of the stored energy is ensured and the advantage of primary frequency modulation of the stored energy is exerted. And finally, providing inertial response for the initial change stage of the frequency of the power system by the energy storage, and jointly participating primary frequency modulation by the photovoltaic by utilizing variable load reduction and energy storage, thereby realizing the coordinated operation of the energy storage and the photovoltaic.
Has the advantages that: compared with the prior art, the photovoltaic and energy storage control system adopts a double-loop control strategy of a power outer loop and a current inner loop, and the active increment obtained by superposing respective frequency modulation control strategies is added into an active control loop, so that the primary frequency modulation capability is realized. The positive and negative inertia control and droop control of the variable coefficient in the energy storage control strategy can dynamically adjust the output of the stored energy, thereby not only ensuring the charge state of the stored energy, but also playing the advantage of primary frequency modulation of the stored energy. The photovoltaic adopts a variable load shedding frequency modulation control method, the strategy control mode is simple, the photovoltaic load shedding coefficient can be dynamically changed along with the frequency deviation and the output change, and the inflexibility of control parameter selection in the conventional control strategy is avoided. The energy storage is utilized to provide inertial support for the power grid in the initial frequency drop stage, primary frequency modulation is carried out by combining the inertial support with the photovoltaic, and the frequency stability of the system is greatly improved. Under the photovoltaic occupation ratios of 19.05% and 28.57%, the energy storage capacity is respectively saved by 3% and 2.5%, and the load reduction standby capacity of the photovoltaic is effectively utilized, and the capacity allocation occupation ratio of the energy storage is reduced.
Drawings
FIG. 1 is a block diagram of a primary frequency modulation coordination control process of a light storage combined participation power grid according to the present invention;
FIG. 2 is a schematic view of a photovoltaic power generation system of the present invention;
FIG. 3 is a schematic diagram of a photovoltaic variable load shedding strategy of the present invention;
FIG. 4 is a schematic view of an energy storage system of the present invention;
FIG. 5 is a schematic diagram of energy storage operating region setup according to the present invention;
FIG. 6 shows the energy storage droop control coefficient K of the present inventionbWith P0R, a graph of variation;
FIG. 7 is a diagram illustrating an adjustment factor M in the energy storage positive virtual inertia control according to the present inventionpAnd an energy storage frequency modulation output variation curve chart;
FIG. 8 is a diagram illustrating an adjustment factor M in the energy storage negative virtual inertia control according to the present inventionb1And negative virtual inertia coefficient MbnA variation graph;
FIG. 9 is a schematic diagram of a three-machine nine-node typical regional power grid frequency modulation simulation model for simulation analysis simulation according to an embodiment of the present invention;
FIG. 10 is a graph of frequency and photovoltaic output characteristics under photovoltaic load shedding backup simulated by simulation analysis in accordance with the present invention;
fig. 11 is a frequency and SOC comparison diagram of the K-fixed method and the K-variable method when the initial SOC of the stored energy is 0.6 according to the simulation analysis simulation of the present invention;
fig. 12 is a comparison graph of frequency and SOC of the K-timing method and the K-varying method when the initial SOC of the stored energy is 0.3 according to the simulation;
FIG. 13 is a graph of frequency variation curves and results of different frequency modulation modes of energy storage according to simulation analysis and simulation of the present invention;
FIG. 14 is a graph of frequency, photovoltaic output, and stored energy output characteristics at 19.05% photovoltaic ratio under light-storage combined frequency modulation simulated by simulation analysis according to the present invention;
fig. 15 is a frequency, photovoltaic output, and stored energy output characteristic curve at 28.57% photovoltaic ratio under the optical storage combined frequency modulation simulated by simulation analysis according to the present invention.
Detailed Description
The present invention is further illustrated by the following figures and specific examples, which are to be understood as illustrative only and not as limiting the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which may occur to those skilled in the art upon reading the present specification.
The invention provides a coordination control method for jointly participating in primary frequency modulation of a power grid by light storage, and the overall design principle, the method flow and the simulation analysis of the scheme are respectively explained below.
1. Coordination control method for jointly participating in primary frequency modulation of power grid by light storage
The invention firstly provides the strategies of photovoltaic and energy storage participating in primary frequency modulation of the power grid respectively: photovoltaic adopts a dynamic variable load shedding frequency modulation strategy following the system output and frequency change. The energy storage adopts an adaptive control strategy following the change of the state of charge, the frequency change rate and the frequency deviation, and droop control dynamically adjusts a control coefficient based on a logistic function; positive virtual inertia control is combined with the influence of frequency deviation and frequency change rate; the negative virtual inertia comprehensively considers the SOC of the battery, the frequency change rate and the frequency deviation to adjust the output power; the coordination and the advantage complementation of the three are realized. Further, in order to reduce the power loss caused by fixed load shedding and reduce the cost of the energy storage system as much as possible, measures of photovoltaic variable load shedding and energy storage combined frequency modulation are adopted: the energy storage provides inertial response for the initial change stage of the frequency of the power system, and the photovoltaic jointly participates in primary frequency modulation by utilizing variable load reduction and energy storage, so that the coordinated operation of the energy storage and the photovoltaic is realized. And finally, carrying out simulation verification on the proposed strategy by using a typical regional power grid example.
1.1 model of photovoltaic Power Generation System and energy storage System
And respectively modeling the photovoltaic power generation system and the energy storage system. As shown in fig. 2, the photovoltaic power generation system mainly comprises a photovoltaic array, a Boost converter, a grid-connected inverter, a filter and a control system thereof. As shown in fig. 4, the energy storage system mainly comprises an energy storage battery, a Buck-Boost converter, a grid-connected inverter, a filter and a control system thereof.
1.2 photovoltaic variable deloading standby frequency modulation method
As shown in the attached figure 3, the maximum active output P is obtained by photovoltaic in a maximum power point tracking modempptAnd the photovoltaic active power is given as the new photovoltaic active power after variable load shedding control and amplitude limiting and is output to a Boost converter control system. The variable load shedding control characteristic curve expression is as follows.
σ％＝K0×(Pmppt/PN+Δf/Δfmax) (1)
When the system frequency is reduced, the delta f is negative, the load shedding coefficient is reduced along with the frequency deviation dynamically, and the active power output is increased. When the system frequency rises, the delta f is positive, the load shedding coefficient dynamic becomes larger along with the frequency deviation, and the active power output is reduced. Thereby participating in primary frequency modulation in response to power system frequency changes. In the variable load shedding frequency modulation control strategy proposed herein, on the one hand, the control coefficient σ% can dynamically change the output following the system frequency deviation and the maximum active output. On the other hand, the load shedding rate of the system is reversely adjusted, so that the system has the primary frequency modulation capability. The method avoids the problem of selecting the droop characteristic slope when a load shedding and droop control strategy is used, and has flexible self-adaptability.
1.3 energy storage adaptive frequency modulation strategy
Droop control dynamically adjusts the control coefficients based on a logistic function, see FIG. 6, by varying the curve pair P0And r are selected; the Logistic curve has a natural relief. The self-adaptive strategy of energy storage can give consideration to frequency modulation and SOC keeping effects. When the stored energy is discharged and the stored energy capacity is sufficient, the curve is convex, and the unit regulating power of the stored energy can be ensured to be at a relatively larger value. If the energy storage capacity is insufficient, the curve is downward convex, the discharging speed is reduced along with the reduction of the SOC, and the unit regulating power is at a smaller value at the moment to keep the SOC effect. Positive virtual inertia control is combined with the influence of frequency deviation and frequency change rate; the frequency is changed into a large rate initially and then gradually reduced until the maximum frequencyThe rate of change at the rate deviation point becomes 0. The control coefficient at the initial stage is slightly smaller and is larger near the point of maximum frequency deviation. The energy storage can uniformly output power, and the initial frequency change rate and the maximum frequency deviation are synchronously improved. The negative virtual inertia comprehensively considers the SOC of the battery, the frequency change rate and the frequency deviation to adjust the output power; considering the frequency recovery stage, the maximum frequency deviation is large, but the frequency change rate is low, and a large coefficient can be multiplied at the moment, so that the frequency of the system is recovered quickly. Along with the extension of time, the frequency deviation is reduced, the SOC value of the stored energy is reduced, and the SOC maintaining effect of the stored energy is ensured by multiplying a smaller coefficient at the moment. The coordination and the advantage complementation of the three are realized.
1.4 coordination control method for jointly participating in primary frequency modulation of power grid by light storage
The energy storage system provides an inertial response similar to a conventional generator set for the initial period of a power system frequency change. The photovoltaic jointly participates in primary frequency modulation by using a variable load shedding frequency modulation strategy and an energy storage self-adaptive control strategy. The load shedding standby capacity of the photovoltaic is effectively utilized, and the capacity allocation ratio of the stored energy is reduced.
2. Method flow
As shown in fig. 1, the invention provides a method for controlling a primary frequency modulation of a power grid by a light storage combined system.
Referring to fig. 1, the specific steps are as follows:
s1: models of a photovoltaic power generation system and an energy storage system are given. The photovoltaic power generation system mainly comprises a photovoltaic array, a Boost converter, a grid-connected inverter, a filter and a control system thereof. The energy storage system mainly comprises an energy storage battery, a Buck-Boost converter, a grid-connected inverter, a filter and a control system thereof.
S2: the existing photovoltaic frequency modulation strategy mainly utilizes a virtual synchronous generator technology or controls photovoltaic output voltage not to run at a maximum power point and reserve load reduction frequency modulation for standby expansion. However, the matching of the power frequency characteristic control coefficient and the load shedding reserve capacity is not flexible, so that a dynamic variable load shedding method which follows the system output and frequency change is adopted to participate in the frequency modulation of the power grid, the frequency fluctuation of the system is responded in real time, and the frequency stability of the photovoltaic power station is improved.
S3: in order to enhance the economy of photovoltaic frequency modulation, energy storage combined frequency modulation is adopted. The problems of frequency modulation parameter setting flexibility, adaptability and the like in the conventional energy storage frequency modulation control strategy still need to be improved. Under the characteristics of coordinated droop control and positive and negative virtual inertia control, the energy storage variable coefficient self-adaptive control strategy following the change of the state of charge, frequency deviation and frequency change rate is provided, and the state of charge of energy storage can be well maintained while the frequency modulation effect is improved.
S4: in order to reduce the power loss caused by fixed load shedding during photovoltaic single frequency modulation as much as possible and reduce the cost of an energy storage system. The capacity of the stored energy is set to provide an inertial response similar to a synchronous generator set. And finally, photovoltaic variable load shedding and energy storage configuration combined frequency modulation are adopted, so that the coordination control of the primary frequency modulation of the optical storage supporting power grid is realized.
The photovoltaic power generation system mainly comprises a photovoltaic array, a Boost converter, a grid-connected inverter, a filter and a control system thereof. In this embodiment, the DC voltage V output by the photovoltaic arraypvAnd a direct current IpvAfter passing through the maximum power point tracking controller, a DC voltage reference value V is generatedrefmppt，VrefmpptAnd VPVThe error signal is integrated to obtain the given P of the photovoltaic output active powerref，PrefAnd the active power P of the high-voltage side of the Boost converterdcAnd generating a duty ratio d after PI control, and driving a Boost converter to work, thereby realizing MPPT control of the photovoltaic array. The control of the inverter is essentially a double closed loop control system, which is mainly composed of an inner loop (current control loop) and an outer loop (power control loop). Normally, the inverter operates in a unity power factor state with a current reference of reactive power i qref0. The photovoltaic array is boosted by a Boost converter to obtain a direct current voltage UdcAnd a voltage reference value UrefAfter difference is made, a current inner ring reference value i is generated through PI controldref. Then the sampled actual current value id、iqAfter deviation is subjected to PI controller and current decoupling control, the voltage given u is obtainedsq、usd. Finally, obtaining the trigger pulse S of the inverter through pulse width modulation after coordinate transformationg. Therefore, active and reactive decoupling control and grid-connected operation of the inverter are realized.
The energy storage system mainly comprises an energy storage battery, a Buck-Boost converter, a grid-connected inverter, a filter and a control system thereof. The buck-boost chopper circuit realizes charge-discharge switching of energy storage. Sampling voltage and current V of Buck-Boost low-voltage sideL、ILMultiplying to obtain the battery power Pbat. When the DC/DC converter works in a discharging mode, the active reference is given by PrefAnd battery power PbatComparing, regulating by PI controller to obtain duty ratio signal D _ Boost, and generating pulse signal G for driving Boost converter by interpolating trigger pulse together with frequency signal generated by variable frequency sawtooth generatorBoost. When the converter is operated in the charging mode, P is setrefTaking the inverse of battery power PbatMultiplying the difference by-1, and performing similar control in a discharging mode to obtain a trigger signal G for driving Buck to actBuck. The main control principle of the grid-connected inverter is similar to that of a photovoltaic power generation system, and the description is omitted here.
In step S2 of this embodiment, the method for dynamically varying the load shedding of the photovoltaic system according to the variation of the system output and frequency is as follows:
obtaining maximum active output P by photovoltaic in a maximum power point tracking modempptAnd the photovoltaic active power is given as the new photovoltaic active power after variable load shedding control and amplitude limiting and is output to a control system of a Boost converter.
The variable load shedding control characteristic curve expression is as follows:
σ％＝K0×(Pmppt/PN+Δf/Δfmax) (1)
in the formula: pNRated active power, MW, of the photovoltaic system under standard conditions; pmpptThe maximum active power, MW, of the photovoltaic system under the current working condition; Δ fmaxTaking 0.5Hz as the maximum frequency deviation allowed by the system; Δ f is the system frequency deviation, Hz; k0For the initial load shedding rate, the photovoltaicThe capacity of participating in frequency modulation at any time is realized; sigmamax% is the upper limit value of the load shedding rate; k0And σmaxThe% can be determined according to the output condition of the photovoltaic power station.
As can be seen from equation (1), when the system frequency decreases, Δ f is negative, the load shedding coefficient decreases dynamically following the frequency deviation, and the active power output increases. When the system frequency rises, the delta f is positive, the load shedding coefficient dynamic becomes larger along with the frequency deviation, and the active power output is reduced. Thereby participating in primary frequency modulation in response to power system frequency changes. In the variable load shedding frequency modulation control strategy proposed herein, on the one hand, the control coefficient σ% can dynamically change the output following the system frequency deviation and the maximum active output. On the other hand, the load shedding rate of the system is reversely adjusted, so that the system has the primary frequency modulation capability. The method avoids the problem of selecting the droop characteristic slope when a load shedding and droop control strategy is used, and has flexible self-adaptability.
The droop control method in step S3 of the present embodiment is
Referring to fig. 5, the present embodiment divides the battery energy storage into five intervals: smax: the maximum limit value of the battery work, which is 0.9; shigh: the upper limit value of the normal operation of the battery is 0.55; slow: the lower limit value of the normal operation of the battery is 0.45; smin: the minimum limit for battery operation, here 0.1.
The Logistic function has natural exponential, concave-convex and saturation. The embodiment adopts the adaptive control method to adaptively control the droop coefficient. The self-adaptive strategy of energy storage can give consideration to frequency modulation and SOC keeping effects. The curve function expression is as follows:
Figure BDA0002965458390000101
in the formula: p0Is an initial value, P0The larger the value, the shorter the time to reach saturation; k is the final value; r measures the speed of curve increase, and the larger r, the faster the curve increase.
When the energy storage is discharged and the energy storage capacity is sufficient, the curve is in an upward convex shape, so that the energy storage can be ensuredIs at a relatively larger value. When the energy storage capacity is insufficient, the curve is downward convex, the discharging speed is reduced along with the reduction of the SOC, and the unit regulating power is at a smaller value at the moment to keep the SOC effect. When the stored energy is charged, the process is similar to that described above. With SOC as an argument, P0And r is used as a parameter, and the charge-discharge coefficient is used as a dependent variable. The following equation is constructed.
1) Discharging of battery
Figure BDA0002965458390000111
2) Battery charging
Figure BDA0002965458390000112
In the formula: kmaxThe final value of the droop coefficient during charging and discharging; ssocIs the state of charge of the stored energy; kbcAnd KbdThe coefficients corresponding to discharging and charging, respectively.
r and P0Respectively change of KbThe curves are shown in figure 6. It can be seen that when r, P0When it is too large, KbThe self-adaptive capacity is weak because the SOC is greatly changed only in a small range. When r, P0When it becomes smaller, KbThe more sensitive is the change with SOC.
In order to make full use of the energy storage battery within the upper and lower limit values (0.45, 0.55) of normal operation. To r and P0And (4) carrying out appropriate selection. The large control coefficient is ensured to be within the maximum limit value of energy storage operation and the upper limit value of normal energy storage operation. Taking energy storage discharge as an example, when the SOC is greater than the upper limit value of normal operation of energy storage, the coefficient varies with the SOC and is still at a relatively large value. When the SOC is smaller than the lower limit value of normal work of energy storage, the SOC maintaining effect is considered more, and the control coefficient is reduced. Herein r is 8, P00.02 was taken.
The droop control provided by the embodiment is based on the characteristics of the Logistic function, only one function is respectively set in the charging and discharging interval by utilizing the symmetry, and the droop coefficient is adaptively adjusted by adopting the SOC partition, so that the frequency modulation capability of the energy storage of the battery is fully utilized, the SOC maintaining effect is also considered, and the complexity of the setting of the piecewise function is avoided.
In this embodiment, the method for controlling positive virtual inertia of transform coefficient in step S3 includes:
the virtual inertia control strategy simulates an inertia response process of the synchronous generator. Because the rotating speed of the generator rotor can not change suddenly, the mechanical power can be kept unchanged in a short time, and the rotating speed of the rotor is reduced by increasing the electromagnetic power to release kinetic energy. The inertial response equation is as follows:
ΔPbess＝-Mb df/dt (5)
in the formula: mbIs the coefficient of inertia.
In the initial disturbance stage, df/dt is large, and Δ f is small, and the frequency modulation requirement cannot be met only by droop control. After the positive virtual inertia control is added, the frequency deviation can be reduced to a certain extent while the initial frequency change rate is reduced. The response time of the positive virtual inertia is short and the state of charge of the stored energy can be disregarded. The response formula is as follows:
ΔPbess＝-Mbpdf/dt (6)
Figure BDA0002965458390000113
Figure BDA0002965458390000121
in the formula: mbpIs a positive virtual inertia coefficient; mbp-c、Mbp-dRespectively positive virtual inertia coefficients during energy storage charging and discharging; mpIs an adjustment coefficient which changes along with the frequency deviation; n is a parameter; c. C1The initial value of the positive virtual inertia coefficient is obtained; dpIs a positive virtual inertial frequency rate-of-change dead zone.
In the present embodiment, the coefficient M is adjustedpAnd energy storage frequency modulation output change curve chartAs shown in fig. 7. MpIs related to the value of n, if n is too small, M ispThe value is small, and the positive virtual inertia capability cannot be fully exerted; if n is too large, a slight increase in Δ f will result in MpThe frequency curve may jitter with a sharp increase. N-6 is chosen herein after general consideration.
The positive virtual inertia strategy provided by the embodiment can take into account the characteristics that the initial change rate of the frequency is large, and then gradually becomes small until the change rate at the maximum frequency deviation point becomes 0. The control coefficient at the initial stage is slightly smaller and is larger near the point of maximum frequency deviation. The energy storage can uniformly output power, and the initial frequency change rate and the maximum frequency deviation are synchronously improved.
In step S3, the negative virtual inertia control method for the transform coefficient in this embodiment is:
when the frequency deviation reaches a maximum and frequency recovery is started, the polarity of the frequency change rate changes. The response output of the positive virtual inertia is opposite to the frequency modulation demand direction, and if the response output is not corrected, the response output is a new disturbance to the system, and the recovery of the power grid frequency is not facilitated. Therefore, to switch to the negative virtual inertia control, the negative virtual inertia has a long action time, and the SOC of the stored energy needs to be considered. The response formula is as follows:
ΔPbess＝-Mbn df/dt (9)
Figure BDA0002965458390000122
Figure BDA0002965458390000123
in the formula: mbnIs a negative virtual inertia coefficient; mbn-c、Mbn-dRespectively negative virtual inertia coefficients during charging and discharging; b1Is the initial value of the negative virtual inertia coefficient; mb1Is an adjustment coefficient that varies with respect to the frequency deviation; f. ofbess-dAn energy storage frequency modulation dead zone; f. ofmaxThe maximum frequency deviation amplitude allowed for the grid,here, 0.5Hz was taken. .
In the present embodiment, the coefficient M is adjustedb1And negative virtual inertia coefficient MbnThe graph of the variation is shown in fig. 8. When n is too large, Mb1The frequency deviation is reduced rapidly and then slowly along with the reduction of the frequency deviation, so that the utilization of the negative virtual inertia control capability is not facilitated; when n becomes small, Mb1The decreasing trend gradually tends to be linear and smooth, and n is 2 after comprehensive consideration.
The negative virtual inertia strategy provided by this embodiment considers the frequency recovery phase, and the maximum frequency deviation is large, but the frequency change rate is low, and at this time, a large coefficient can be multiplied, so that the frequency of the system is recovered quickly. Along with the extension of time, the frequency deviation is reduced, the SOC value of the stored energy is reduced, and the SOC maintaining effect of the stored energy is ensured by multiplying a smaller coefficient at the moment.
The method for configuring the energy storage capacity in step S4 in this embodiment is as follows:
to ensure that the configured energy storage can provide an inertial response similar to a synchronous generator set, the capacity of the energy storage is sized as follows:
when the rotating speed of the generator is omega, the synchronous generator has the rotating energy of
Figure BDA0002965458390000131
When the motor speed follows the system frequency from omega0Change to omega1Time of flight
Figure BDA0002965458390000132
The speed of the synchronous generator is proportional to the system frequency and typically varies over a small range. Grid operation and maintenance guidelines specify that in special cases the system frequency may rise to 51Hz or fall to 48Hz in a short period of time. With the frequency decline analysis, the rotational speed range of synchronous generator rotor is 0.95 ~ 1pu, and the kinetic energy that can release is:
Figure BDA0002965458390000133
the energy storage device is only limited by SOC, and can generally realize large-range power throughput, so that the frequency modulation effect same as that of a conventional generator set can be realized by smaller energy storage capacity. When the photovoltaic power station configured with the energy storage replaces a conventional generator set and is incorporated into a power grid, the energy storage power meets the requirement when the energy storage power meets the requirement because the energy storage charging and discharging time is generally longer than the inertia response time.
If the energy released by the energy storage system in delta t is the same as the kinetic energy of the same rotor, the following steps are provided:
ΔEbess＝PbessΔt＝0.0784HSN (15)
here, the inertia time constant H of the generator set is about 5s, and Δ t is 2H.
Pbess＝0.0392SN (16)
In the formula: delta Ebess、PbessCapacity and power for stored energy, respectively; sNIs the rated capacity of the generator; h is an inertia constant; j is the inertia time constant of the generator. From equation (16), when energy storage of 3.92% of rated power of the photovoltaic power plant is configured, inertial response similar to that of a synchronous generator set can be realized. The capacity of the stored energy can be widened to 5% of the rated power in consideration of the condition of up-down regulation of the stored energy.
In step S4, the method for performing optical storage combined frequency modulation in this embodiment includes:
1) the energy storage system provides an inertial response similar to a conventional generator set for the initial period of a power system frequency change.
2) The photovoltaic jointly participates in primary frequency modulation by using a variable load shedding frequency modulation strategy and an energy storage self-adaptive control strategy.
3. Simulation analysis
Based on an IEEE3 machine 9 node typical system, a PSCAD simulation system model is built, as shown in FIG. 9. The hydroelectric generating set G1 and the thermal generating sets G2 and G3 are formed by a speed regulator and a prime motor to participate in frequency modulation, the total rated capacity is 567.5MVA, and the total load capacity is 315+ j115 MVA. Photovoltaic and energy storage are respectively connected to a Bus8 Bus to verify the effectiveness of the strategy provided by the text. And finally, the light storage combination is put into use, and the simulation light storage combination system participates in the superiority of the power grid primary frequency modulation coordination control strategy.
3.1 photovoltaic frequency modulation optimization strategy simulation verification
At Bus8 Bus in fig. 9, a 90MW photovoltaic equivalent power source is connected. The load of 16MW was added at Bus6 Bus 3 s. The simulation photovoltaic does not participate in frequency modulation, and the photovoltaic adopts a variable load shedding control strategy (the initial load shedding rate is 5% and 10% respectively), and the like. As can be seen from fig. 10, when the photovoltaic does not participate in frequency modulation, the lowest point of frequency drop is 49.4 Hz. After considering the variable load shedding frequency modulation strategy provided by the invention, the photovoltaic power generation can effectively utilize the load shedding spare capacity, and the dynamic adjustment is carried out along with the change of the system frequency, so that the frequency recovery response characteristic is improved. The lowest point of frequency dip is 49.5Hz when the initial load shedding ratio is 5%. The lowest point of frequency dip is 49.65Hz when the initial load shedding rate is 10%. It can be seen that the larger the initial load shedding level is, the larger the frequency modulation capacity which can be increased in the transient process is, and the stronger the capability of participating in the frequency modulation of the system is. However, due to the fact that the working efficiency of the photovoltaic array is reduced due to the excessively large deloading level, power loss under the normal operation condition is caused, the adoption of the photovoltaic single frequency modulation is limited by deloading capacity, and the frequency modulation effect is still not ideal.
3.2 verification of adaptive control method for participating in primary frequency modulation by energy storage
The Bus of Bus8 in FIG. 9 is connected to an energy storage equivalent power source with the capacity of 4.5 MW. Simulation contrasts the frequency modulation characteristics of the K method and the K-variable method (used herein) under the condition of step load disturbance by droop control. A load input of 12MW is applied at bus6 bus 3 s. The simulation was performed at both initial SOC of 0.6 and 0.3.
As can be seen from fig. 11, when the initial value of the SOC is high, i.e., the battery energy is sufficient. The K method effect is related to the value of K, the larger the K value is, the smaller the maximum frequency deviation is, the better the frequency modulation effect is, but the faster the battery energy is reduced. By properly selecting K, the frequency modulation effect and the charge state equivalent to that of a K-varying method can be realized. As shown in the figure, the K-method K is equivalent to the K-method K-changing effect when the K-method K is 9. And selecting a constant K method (K is 9) and a variable K method for comparison. It can be seen from fig. 12 that when the initial SOC is 0.3, that is, the charge amount is small. In order to keep the SOC maintaining effect and reduce the output of droop control, the maximum frequency deviation of the fixed K method is 0.18Hz, and the variable K method is 0.2 Hz. The frequency modulation effect of the variable K method is slightly weaker than that of the fixed K method. However, the K-determination method does not take the influence of the energy storage SOC into consideration. The SOC change curve is rapidly reduced, and the energy storage capacity limit value is easily reached to quit frequency modulation in advance, so that the secondary frequency drop is caused.
Aiming at the same calculation example, simulation energy storage does not participate in frequency modulation, and simulation is carried out by utilizing five conditions of droop control (a fixed K method), droop control (a variable K method), droop control + virtual inertia, the method used in the text and the like so as to verify the effectiveness and superiority of the method provided in the text. As can be seen from fig. 13, by using the energy storage adaptive control strategy adopted herein, the initial frequency change rate is at least-0.03 Hz/s, the maximum frequency deviation is 0.27Hz, and the negative virtual inertia provided after the frequency recovery can significantly improve the frequency recovery speed. The superiority of the proposed method is thus evident.
3.3 optical storage Combined frequency modulation control strategy verification
In the simulation system of fig. 9, 4.5MW stored energy and photovoltaic were jointly connected to Bus8 Bus. When the photovoltaic output is 60MW and 90MW respectively, namely, the power system under the photovoltaic proportion of 19.05% and 28.57%, 16MW load disturbance is added, the simulation photovoltaic does not participate in frequency modulation, only the energy storage participates in frequency modulation, only the photovoltaic participates in frequency modulation, and the light storage participates in frequency modulation (the strategy herein) in cooperation with other frequency modulation modes of 4 systems.
As can be seen by 14a (frequency curve) and 14b (photovoltaic output curve) in fig. 14, the lowest point of frequency is 49.45Hz at 19.05% photovoltaic fraction when only the conventional generator is involved in frequency modulation. At 28.57% photovoltaic fraction, the lowest point of frequency is 49.41 Hz. It can be seen from this that: the larger the photovoltaic fraction, the more severe the frequency droop. When the system is added with photovoltaic frequency modulation, the frequency modulation effect is obviously improved, but the frequency modulation effect is limited by the total spare capacity due to the limited photovoltaic load shedding spare; only under the energy storage frequency modulation mode, the energy storage can actively respond to the frequency change: when the photovoltaic proportion is 19.05%, the energy storage peak power accounts for 13% of the photovoltaic power station, and the frequency lowest point ratio is improved by 51% when not controlled; when the photovoltaic proportion is 28.57%, the energy storage peak power accounts for 9.2% of the photovoltaic power station, and the frequency lowest point ratio is improved by 54% when the frequency lowest point ratio is not controlled. When the light-storage combined frequency modulation is adopted, the frequency stability of the power system is greatly improved after the photovoltaic variable load shedding frequency modulation and the energy storage self-adaptive adjustment strategy are comprehensively utilized. As can be seen in conjunction with fig. 14 and 15: the whole primary frequency modulation process not only makes full use of the load shedding spare capacity of the photovoltaic, but also has no obvious peak characteristic of the output of the energy storage frequency modulation, and is beneficial to the charge state maintenance of the energy storage. As can be seen from fig. 14c (energy storage output characteristic curve), when the frequency lowest point is restored to the stable value of 49.8Hz, the energy storage capacity required to be configured accounts for 10% of the photovoltaic power plant. Also from fig. 15, it can be seen from fig. 15 that the required energy storage capacity is 6.7%. After the light storage coordination control is adopted, the energy is saved by 3 percent and 2.5 percent respectively compared with the energy storage independent regulation. In summary, the method reduces the energy storage configuration capacity as much as possible, and simultaneously makes the whole optical storage combined frequency modulation effect better.

Claims (9)

1. A coordination control method for jointly participating in primary frequency modulation of a power grid by light storage is characterized by comprising the following steps: the method comprises the following steps:
s1: modeling a photovoltaic power generation system and an energy storage system respectively to obtain a photovoltaic power generation system model and an energy storage system model; the photovoltaic power generation system comprises a photovoltaic array, a Boost converter, a grid-connected inverter, a filter and a control system thereof; the energy storage system comprises an energy storage battery, a Buck-Boost converter, a grid-connected inverter, a filter and a control system thereof;
s2: the photovoltaic power generation system is used for participating in power grid frequency modulation through a dynamic variable load shedding method following system output and frequency change; the dynamic variable load shedding method for the output and frequency change of the photovoltaic following system comprises the following steps: obtaining maximum active output P by photovoltaic in a maximum power point tracking modempptAfter variable load shedding control and amplitude limiting, the output power is used as new photovoltaic active power and given and is output to a Boost converter control system;
s3: under the basis of coordinated droop control and positive and negative virtual inertia control, energy storage combined frequency modulation is adopted based on an energy storage variable coefficient self-adaptive control strategy;
s4: the capacity of the stored energy is set, so that the inertial response matched with the synchronous generator set can be provided, and the coordination control of the primary frequency modulation of the light storage support power grid is realized by adopting photovoltaic variable load shedding and configured energy storage combined frequency modulation.
2. The coordination control method for the optical storage combination to participate in the primary frequency modulation of the power grid according to claim 1, is characterized in that: the photovoltaic power generation system in step S1 specifically includes:
DC voltage V output by photovoltaic arraypvAnd a direct current IpvAfter passing through the maximum power point tracking controller, a DC voltage reference value V is generatedrefmppt，VrefmpptAnd VPVThe error signal is integrated to obtain the given P of the photovoltaic output active powerref，PrefAnd active power P of high-voltage side of boost converterdcGenerating a duty ratio d after PI control, and driving a Boost converter to work so as to realize MPPT control of the photovoltaic array; grid-connected inverter working in unit power factor state igq *When the voltage of the photovoltaic array is increased by the Boost converter, the direct current voltage U is obtaineddcAnd a voltage reference value UrefAfter difference is made, a current inner ring reference value i is generated through PI controldrefThen the sampled actual current value id、iqAfter deviation is subjected to PI controller and current decoupling control, the voltage given u is obtainedsq、usdFinally, obtaining a trigger pulse S of the grid-connected inverter through pulse width modulation after coordinate transformationgTherefore, active and reactive decoupling control and grid-connected operation of the grid-connected inverter are achieved.
3. The coordination control method for the optical storage combination to participate in the primary frequency modulation of the power grid according to claim 1, is characterized in that: the energy storage system in step S1 specifically includes:
the energy storage system realizes charge-discharge switching of energy storage through a buck-boost chopper circuit; sampling voltage and current V of Buck-Boost low-voltage sideL、ILMultiplying to obtain the battery power Pbat. When the DC/DC converter works in a discharging mode, the active reference is given by PrefAnd battery power PbatComparing, regulating by PI controller to obtain duty ratio signal D _ Boost, and generating pulse signal G for driving Boost converter by interpolating trigger pulse together with frequency signal generated by variable frequency sawtooth generatorBoost. When the converter is operated in the charging mode, P is setrefTaking the inverse of battery power PbatMultiplying the difference by-1, and performing similar control in a discharging mode to obtain a trigger signal G for driving Buck to actBuck。
4. The coordination control method for the optical storage combination to participate in the primary frequency modulation of the power grid according to claim 1, characterized in that: the control characteristic curve expression of the dynamic variable load shedding in step S2 is as follows:
σ％＝K0×(Pmppt/PN+Δf/Δfmax) (1)
in the formula: pNRated active power of the photovoltaic system under standard conditions; pmpptThe maximum active power of the photovoltaic system under the current working condition; Δ fmaxMaximum frequency deviation allowed for the system; Δ f is the system frequency deviation; k0The load shedding rate in the initial condition; sigmamax% is the upper limit of the load shedding ratio.
5. The coordination control method for the optical storage combination to participate in the primary frequency modulation of the power grid according to claim 1, characterized in that: the droop control method in the step S3 comprises
Energy storage is divided into four intervals: smax: the maximum working limit of the energy storage battery; shigh: the upper limit value of the normal work of the energy storage battery; slow: the lower limit value of the energy storage battery in normal operation; smin: a minimum limit for operation of the energy storage battery;
adopting a Logistic function to carry out self-adaptive control on the droop coefficient, wherein the curve function expression is as follows:
Figure FDA0002965458380000021
in the formula: p0Is an initial value; k is the final value; r measures the increasing speed of the curve;
with SOC as an argument, P0And r is used as a parameter variable, the charge-discharge coefficient is used as a dependent variable, and the following equation is constructed:
1) discharging of battery
Figure FDA0002965458380000022
2) Battery charging
Figure FDA0002965458380000023
In the formula: kmaxThe final value of the droop coefficient during charging and discharging; ssocIs the state of charge of the stored energy; kbdAnd KdcThe coefficients corresponding to discharging and charging, respectively.
6. The coordination control method for the optical storage combination to participate in the primary frequency modulation of the power grid according to claim 1, characterized in that: the positive virtual inertia control method in the step S3 includes:
the positive virtual inertial response equation is:
ΔPbess＝-Mbpdf/dt (5)
Figure FDA0002965458380000024
Figure FDA0002965458380000031
in the formula: mbpIs a positive virtual inertia coefficient; mbp-c、Mbp-dRespectively positive virtual inertia coefficients during energy storage charging and discharging; mpIs an adjustment coefficient which changes along with the frequency deviation; n is a parameter; c. C1The initial value of the positive virtual inertia coefficient is obtained; dpIs a positive virtual inertial frequency rate-of-change dead zone.
7. The coordination control method for the optical storage combination to participate in the primary frequency modulation of the power grid according to claim 1, characterized in that: the negative virtual inertia control method in step S3 includes:
the negative virtual inertial response formula is:
ΔPbess＝Mbndf/dt (8)
Figure FDA0002965458380000032
Figure FDA0002965458380000033
in the formula: mbnIs a negative virtual inertia coefficient; mbn-c、Mbn-dRespectively negative virtual inertia coefficients during charging and discharging; b1Is the initial value of the negative virtual inertia coefficient; mb1Is an adjustment coefficient that varies with respect to the frequency deviation; f. ofbess-dAn energy storage frequency modulation dead zone; f. ofmaxThe maximum frequency deviation amplitude allowed by the power grid.
8. The coordination control method for the optical storage combination to participate in the primary frequency modulation of the power grid according to claim 1, is characterized in that: the method for configuring the energy storage capacity in step S4 includes:
in order to ensure that the configured energy storage can provide an inertial response matched with the synchronous generator set, the capacity of the energy storage is set as follows:
when the rotating speed of the generator is omega, the synchronous generator has the rotating energy of
Figure FDA0002965458380000034
When the motor speed follows the system frequency from omega0Change to omega1Time of flight
Figure FDA0002965458380000035
The kinetic energy that can be released is:
Figure FDA0002965458380000036
if the energy released by the energy storage system in delta t is the same as the kinetic energy of the same rotor, the following steps are provided:
ΔEbess＝PbessΔt＝0.0784HSN (14)
let Δ t be 2H
Pbess＝0.0392SN (15)
In the formula: delta Ebess、PbessCapacity and power for stored energy, respectively; sNIs the rated capacity of the generator; h is an inertia constant; j is the inertia time constant of the generator.
9. The coordination control method for the optical storage combination to participate in the primary frequency modulation of the power grid according to claim 1, is characterized in that: the method for optical storage combined frequency modulation in step S4 includes:
1) the energy storage system provides an inertial response matched with a conventional generator set for the initial frequency change stage of the power system;
2) the photovoltaic jointly participates in primary frequency modulation by using a variable load shedding frequency modulation strategy and an energy storage self-adaptive control strategy.
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