CN116231734A - Micro-grid wind-storage-load layered cooperative frequency modulation control method - Google Patents

Micro-grid wind-storage-load layered cooperative frequency modulation control method Download PDF

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CN116231734A
CN116231734A CN202310070006.5A CN202310070006A CN116231734A CN 116231734 A CN116231734 A CN 116231734A CN 202310070006 A CN202310070006 A CN 202310070006A CN 116231734 A CN116231734 A CN 116231734A
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frequency
frequency modulation
load
wind
energy storage
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王怡聪
柯方超
刘志伟
王廷涛
张东寅
杨东俊
王法靖
苗世洪
胡婷
王雅文
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Huazhong University of Science and Technology
Economic and Technological Research Institute of State Grid Hubei Electric Power Co Ltd
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Huazhong University of Science and Technology
Economic and Technological Research Institute of State Grid Hubei Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0047—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with monitoring or indicating devices or circuits
    • H02J7/0048—Detection of remaining charge capacity or state of charge [SOC]
    • 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
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • 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
    • 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
    • H02J2300/40—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation wherein a plurality of decentralised, dispersed or local energy generation technologies are operated simultaneously

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Abstract

A micro-grid wind-storage-load layered cooperative frequency modulation control method comprises the following steps: s1, establishing a wind-storage-load layered cooperative frequency modulation control framework based on the operation characteristics of each resource in a micro-grid system; s2, respectively establishing a frequency modulation control model of the gas turbine, the doubly-fed wind turbine, the energy storage system and the controllable load, and establishing an integral frequency response model of the micro-grid system; s3, establishing a prediction model of the frequency response characteristic index of the micro-grid system, using the maximum frequency deviation as a frequency layering index, providing a wind-storage-load layering cooperative frequency modulation control strategy based on the prediction model, and compensating the power absorbed by the fan through the energy storage system in a fan rotating speed recovery stage. The invention can control the fan, the energy storage system and the controllable load in advance to participate in frequency modulation, thereby improving the frequency stability of the system.

Description

Micro-grid wind-storage-load layered cooperative frequency modulation control method
Technical Field
The invention belongs to the field of micro-grid frequency control, and particularly relates to a micro-grid wind-storage-load layering cooperative frequency modulation control method.
Background
Micro-grids are rapidly developed as a small-sized power system integrating distributed new energy power generation. The proportion of new energy power generation such as wind power in the micro-grid is continuously improved, so that the micro-grid is cleaner and environment-friendly. However, wind power is connected with the grid through power electronic equipment, the rotor rotating speed is decoupled from the frequency of the grid, and frequency support cannot be directly provided, so that the inertia of the micro grid is reduced, the frequency response capacity is reduced, the capability of resisting frequency fluctuation is weakened, and a serious challenge is brought to the frequency stability of the micro grid.
In order to improve the frequency stability of the micro-grid, students at home and abroad propose to apply additional frequency control to the fan so that the fan has certain frequency modulation capability. In the prior art, virtual inertia control is adopted for the doubly-fed fan, larger inertia can be virtually obtained at the rotor side of the fan, inertia support is provided for the system by releasing rotor kinetic energy, the response speed is high, and the secondary drop of the system frequency can be caused by excessive rotor rotation speed drop. In order to improve primary frequency modulation capability of the fan, virtual inertia control, overspeed load shedding control and pitch angle control are usually combined, and the control enables the fan to leave a certain frequency modulation standby capacity, but wind energy cannot be utilized to the maximum extent at the expense of wind energy.
In recent years, the rapid development of energy storage technology brings a new approach to the frequency adjustment of micro-grids. The energy storage has the advantages of high response speed, flexible adjustment and the like, and can assist wind power to provide frequency support. Meanwhile, loads with energy storage characteristics such as air conditioners, electric water heaters and electric automobiles exist in the micro-grid, and power support can be provided for the micro-grid through a demand response technology. In the prior art, the energy storage assists the fan rotor to recover, so that the occurrence of frequency secondary falling accidents is avoided. The prior art provides a coordinated control strategy of a wind storage system considering wind speed, and reasonable distribution of frequency modulation power is realized based on fuzzy logic control. In the prior art, an air conditioner load cluster control model considering electrical characteristics is established, and based on frequency droop control, the stabilization of micro-grid power fluctuation is realized, and the frequency stability of the system is improved. Aiming at the problem of power grid inertia reduction caused by electric vehicle grid connection, the prior art provides an electric vehicle virtual synchronous machine control strategy considering the charging requirement of a user, realizes primary and secondary frequency modulation of the electric vehicle, and reduces the frequency fluctuation of a power grid on the premise of meeting the use requirement of the user. The research focuses on the coordination control of the wind power storage system and the frequency modulation control of controllable loads, and the research on how to coordinate wind power, store energy and control loads is less. Meanwhile, the researches are all controlled in real time, the severity of the frequency drop of the system cannot be early warned in advance, and when the load mutation is large, frequency modulation resources in the system cannot respond timely, so that the serious frequency drop is caused.
Disclosure of Invention
The invention aims to overcome the defect and problem of poor frequency modulation effect in the prior art and provides a micro-grid wind-storage-load layering cooperative frequency modulation control method with good frequency modulation effect.
In order to achieve the above object, the technical solution of the present invention is: a micro-grid wind-storage-load layered cooperative frequency modulation control method comprises the following steps:
s1, establishing a wind-storage-load layered cooperative frequency modulation control framework based on the operation characteristics of each resource in a micro-grid system;
s2, respectively establishing a frequency modulation control model of the gas turbine, the doubly-fed wind turbine, the energy storage system and the controllable load, and establishing an integral frequency response model of the micro-grid system;
s3, establishing a prediction model of the frequency response characteristic index of the micro-grid system, using the maximum frequency deviation as a frequency layering index, providing a wind-storage-load layering cooperative frequency modulation control strategy based on the prediction model, and compensating the power absorbed by the fan through the energy storage system in a fan rotating speed recovery stage.
In step S1, analyzing the operation characteristics of a gas turbine, a wind turbine generator, an energy storage system and a controllable load in a micro-grid system, establishing a wind-storage-load layered cooperative frequency modulation control architecture, and dividing frequency modulation into four layers: the first layer is gas turbine frequency modulation; the second layer is used for frequency modulation of the wind turbine generator; the third layer is used for frequency modulation of the energy storage system; and the fourth layer is controllable load frequency modulation.
In step S2, the gas turbine frequency modulation control model comprises an inertial response model and a primary frequency modulation model;
the inertial response model is:
Figure SMS_1
wherein DeltaP Gm For gas turbine machineryAmount of change in torque, Δp Ge H is the variation of electromagnetic torque m Is the inertia time constant of the gas turbine, delta f is the system frequency variation, t is time, D m Is the damping coefficient of the gas turbine;
the primary frequency modulation model is as follows:
Figure SMS_2
wherein K is m Is the power frequency characteristic coefficient, T of the gas turbine m The response time constant of the gas turbine is s is complex variable, and Δf(s) is frequency variation in complex frequency domain.
In step S2, the fan frequency modulation control model comprises a virtual inertia control model and an overspeed load shedding control model;
the virtual inertia control model is as follows:
Figure SMS_3
wherein DeltaP W K is the power adjustment quantity of the doubly-fed fan w Is a virtual inertia coefficient, T w The response time constant of the doubly-fed fan is represented by s, s is a complex variable, and Δf(s) is a frequency variation in a complex frequency domain;
the overspeed load shedding control model is as follows:
Figure SMS_4
wherein P is Wm For mechanical power output by the wind turbine, C p For wind energy conversion coefficient ρ a Is air density, S w Is the area of the fan blade of the wind turbine, V ω Is the wind speed;
by adopting overspeed load shedding control, the power-rotating speed curve of the fan under different wind speeds meets the following conditions:
P opt ＝P max ·η
wherein P is max At maximum power, P opt For overspeed load shedding power, η is the load shedding power ratioA rate;
in overspeed load shedding mode, the doubly-fed fan is left with ΔP opt Is involved in frequency modulation:
ΔP opt ＝P max (1-η)
wherein DeltaP opt And the frequency modulation power reserved for the doubly-fed fan.
In step S2, the energy storage system frequency modulation control model is:
Figure SMS_5
/>
wherein lambda is soc Lambda is the state of charge of the energy storage system soc0 P is the initial state of charge of the energy storage system E For the output power of the energy-storage system E N Is the rated capacity of the energy storage system;
providing power support for a microgrid using droop control:
Figure SMS_6
wherein DeltaP E K is the power adjustment quantity of the energy storage system E For the sag coefficient of the energy storage system, T E And s is a complex variable, and Δf(s) is a frequency variation in a complex frequency domain.
In step S2, the controllable load frequency modulation control model is:
Figure SMS_7
wherein DeltaP L K is the power regulation of the controllable load L T is the controllable load sag factor L The response time constant of the controllable load is s is complex variable, and Δf(s) is frequency variation in complex frequency domain.
In step S2, the overall frequency response model of the micro-grid system is:
Figure SMS_8
wherein Δf is the system frequency variation, ΔP 0 To the system load disturbance quantity H s G is the inertial response transfer function of the system L 、G w 、G E 、G L The transfer functions of the frequency response of the gas turbine, the doubly-fed fan, the energy storage system and the controllable load are respectively, u w 、u E 、u L The variable of the frequency modulation state of the controllable load is respectively a doubly-fed fan, an energy storage system and H m Is the inertia time constant of the gas turbine, D m K is the damping coefficient of the gas turbine m Is the power frequency characteristic coefficient, T of the gas turbine m K is the response time constant of the gas turbine w Is a virtual inertia coefficient, T w Is the response time constant of the doubly-fed fan, K E For the sag coefficient of the energy storage system, T E K is the response time constant of the energy storage system L T is the controllable load sag factor L And s is a complex variable, which is a response time constant of the controllable load.
In step S3, the characteristic indexes of the system frequency response include a maximum frequency change rate, a maximum frequency deviation and a steady-state frequency deviation;
when the load is disturbed, the maximum frequency change rate of the system is obtained by the initial value theorem
Figure SMS_9
The method comprises the following steps:
Figure SMS_10
obtaining the steady-state frequency deviation delta f of the system according to the final value theorem ∞ The method comprises the following steps:
Figure SMS_11
equivalent frequency modulation control model of each resource in the system is equivalent to an equivalent frequency modulation control model with the same characteristic, and the transfer function G of the equivalent frequency modulation control model eq The method comprises the following steps:
Figure SMS_12
wherein A is eq 、B eq 、C eq Characteristic parameters of the equivalent model; t is t mid Half of the weighted average value of the frequency modulation steady-state time of each resource;
Figure SMS_13
the variable-frequency steady-state time of the gas turbine, the doubly-fed fan, the energy storage system and the controllable load are respectively;
the time sequence expression deltaf (t) of the frequency deviation of the system equivalent frequency response model is as follows:
Figure SMS_14
Figure SMS_15
Figure SMS_16
c＝6H s C eq (a 2 -b 2 )+2a(2H s +A eq +C eq D eq )+B eq +D eq
d＝12abH s C eq +2b(2H s +A eq +C eq D eq )
g＝(aC eq +1)c+bdC eq ；h＝bcC eq -(aC eq +1)d
wherein M, N, a, b, c, d, h, g is a frequency timing expression parameter; d (D) eq Is the equivalent damping coefficient of the system;
time t of maximum frequency deviation of system tir Maximum frequency deviation Δf max The method comprises the following steps:
Figure SMS_17
Figure SMS_18
in step S3, when the system frequency changes, the gas turbine responds in real time;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max1 When the wind turbine generator is in use, virtual inertia control is adopted to reduce system frequency variation;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max2 When the energy storage system adopts droop control, the system frequency deviation is reduced;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max3 When the controllable load adopts droop control, the load power is increased or decreased to reduce the system frequency deviation.
In step S3, the energy absorbed by the fan is compensated by regulating and controlling the power of the energy storage system until the fan is restored to the initial running state, then the energy storage system starts to smoothly exit the frequency modulation, and finally the frequency modulation power is provided by the gas turbine; after detecting that the system frequency change rate is 0, correcting a frequency modulation control equation of the energy storage system to be:
Figure SMS_19
wherein DeltaP' E For the corrected power adjustment of the energy storage system, Δf(s) is the frequency variation in the complex frequency domain.
Compared with the prior art, the invention has the beneficial effects that:
according to the micro-grid wind-storage-load layered cooperative frequency modulation control method, frequency modulation capacity of each resource in a micro-grid system is fully considered, and the frequency stability of the system is improved through cooperative frequency modulation control of a gas turbine, wind power, an energy storage system and controllable loads; meanwhile, in order to improve the frequency modulation capacity of the fan, overspeed load shedding control is adopted for the fan, a micro-grid system overall frequency response model is established, a calculation method of characteristic indexes of system frequency response is provided, the characteristic indexes comprise maximum frequency change rate, maximum frequency deviation and steady-state frequency deviation, the maximum frequency deviation is used as a wind, storage and load frequency modulation layering index, the maximum frequency deviation of the system is predicted by detecting the initial frequency change rate of the system, and compared with each layering index, whether each resource participates in frequency modulation is judged, so that model prediction control of wind-storage-load frequency modulation is realized, corresponding resources participate in frequency modulation is controlled in advance, the system frequency deviation is effectively reduced, and the stable time of system frequency arrival is shortened; in addition, in the fan rotational speed recovery process, the power absorbed by the fan is compensated by regulating and controlling the power of the energy storage system, so that the system frequency fluctuation can be reduced, the frequency recovery is accelerated, and the secondary frequency drop is avoided.
Drawings
Fig. 1 is a flowchart of a micro-grid wind-storage-load layered cooperative frequency modulation control method of the invention.
Fig. 2 is a structural diagram of a micro grid system in the present invention.
Fig. 3 is a stroke-reservoir-charge hierarchical cooperative fm control architecture of the present invention.
FIG. 4 is a graph of doubly-fed fan power versus speed in accordance with the present invention.
FIG. 5 is a schematic diagram of the frequency modulation process of the doubly-fed wind turbine under overspeed control in the present invention.
Fig. 6 is a model of the overall frequency response of the system of the present invention.
Fig. 7 shows the system frequency change process during the sudden load increase in the present invention.
FIG. 8 is a flow chart of model-based predictive wind-reservoir-load cooperative control in the present invention.
FIG. 9 is a graph showing the frequency response of the system at a load surge of 0.5MW in accordance with the present invention.
FIG. 10 is a graph showing the frequency response of the system at a 1.5MW sudden load increase in accordance with the present invention.
FIG. 11 is a graph showing the frequency response of the system at a load bump of 2.5MW in accordance with the present invention.
FIG. 12 is a graph comparing the effects of the hierarchical control strategy at 0.5MW load spike in the present invention.
FIG. 13 is a graph comparing the effects of the hierarchical control strategy at 1.5MW of load spike in the present invention.
FIG. 14 is a graph comparing the effects of the hierarchical control strategy at a load surge of 2.5MW in the present invention.
Fig. 15 is a graph of the frequency response results of the system before and after energy storage compensation in the present invention.
FIG. 16 is a graph of doubly-fed fan power variation in accordance with the present invention.
Fig. 17 is a graph showing the change of stored power in the present invention.
FIG. 18 is a graph of doubly-fed wind turbine rotational speed variation in accordance with the present invention.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings and detailed description.
The basic idea of the invention is as follows: (1) The operation characteristics of resources such as a gas turbine, wind power, an energy storage system and controllable loads in a micro-grid are analyzed, a wind-storage-load layered cooperative frequency modulation control architecture is constructed, and frequency modulation is divided into 4 layers: the layer 1 is the frequency modulation of the gas turbine, and when the system frequency changes, the gas turbine responds in real time; layer 2 is the frequency modulation of the wind turbine generator, when the maximum frequency deviation of the system is predicted to exceed delta f max1 When the wind turbine generator is in use, virtual inertia control is adopted to reduce system frequency variation; layer 3 modulates the frequency of the energy storage system when the maximum frequency deviation of the system is predicted to exceed delta f max2 When the energy storage system adopts droop control, the system frequency deviation is reduced; layer 4 is a controllable load frequency modulation when it is predicted that the maximum frequency deviation of the system exceeds Δf max3 When the controllable load adopts droop control, the system frequency deviation is reduced by increasing or decreasing the load power. (2) Based on the built wind-storage-load layered cooperative frequency modulation control architecture, frequency modulation control models of a gas turbine, a fan, energy storage and controllable loads are built respectively, and then an integral frequency response model of the micro-grid system is built. (3) Based on the established integral frequency response model of the micro-grid system, a calculation method of the maximum frequency change rate, the maximum frequency deviation and the steady-state frequency deviation of the system is provided; and the maximum frequency deviation is used as a wind, storage and charge frequency modulation layering index to predict the maximum frequency deviation of the system and store the maximum frequency deviationAnd comparing the model predictive control with each layering index to judge whether each resource participates in frequency modulation, thereby realizing the model predictive control of wind-storage-load frequency modulation.
The micro-grid system structure containing wind power, energy storage and controllable load is shown in fig. 2. The wind turbine generator is represented by a doubly fed wind generator (DFIG), and is connected to a micro-grid through a voltage type PWM converter; the energy storage system is represented by electrochemical energy storage, and is connected to a micro-grid through a DC/AC converter; the system load is divided into two types, namely controllable load and uncontrollable load, and is integrated into a micro-grid through a step-up transformer.
In the micro-grid system, the gas turbine is used as a main frequency modulation resource and is required to participate in frequency modulation all the time. The installed capacity of the fan is larger, the permeability is higher, and according to the specification of technical regulation of wind farm access to electric power system, the grid-connected fan needs to have inertia support and primary frequency modulation capability, so that the fan participates in frequency modulation preferentially. The energy storage system has high running cost, and the frequency modulation priority is relatively back. The regulation and control of the controllable load can influence the electricity consumption requirement of a user, and the controllable load can participate in frequency modulation only when the frequency modulation capacity of the gas turbine, the fan and the energy storage is difficult to guarantee the safety requirement of the system frequency in order to guarantee the electricity consumption reliability. Therefore, in order to fully utilize the frequency modulation capability of the resources such as wind power, energy storage and controllable load in the system, and consider the economical efficiency of each resource regulation, the invention adopts a layered cooperative control architecture, namely, different frequency limit values are set for the control mode of each frequency modulation resource, and the working state of each resource is cooperatively controlled by detecting or predicting the maximum deviation of the system frequency, as shown in fig. 3.
Referring to fig. 1, a micro-grid wind-storage-load layered cooperative frequency modulation control method comprises the following steps:
s1, establishing a wind-storage-load layered cooperative frequency modulation control framework based on the operation characteristics of each resource in a micro-grid system;
analyzing the operation characteristics of a gas turbine, a wind turbine generator set, an energy storage system and controllable loads in a micro-grid system, establishing a wind-storage-load layered cooperative frequency modulation control architecture, and dividing frequency modulation into four layers: the first layer is gas turbine frequency modulation; the second layer is used for frequency modulation of the wind turbine generator; the third layer is used for frequency modulation of the energy storage system; and the fourth layer is controllable load frequency modulation.
S2, respectively establishing a frequency modulation control model of the gas turbine, the doubly-fed wind turbine, the energy storage system and the controllable load, and establishing an integral frequency response model of the micro-grid system;
the gas turbine frequency modulation control model comprises an inertial response model and a primary frequency modulation model;
(1) Inertial response model
The inertia of the power system reflects the ability of the system to resist frequency changes, which is primarily provided by the gas turbine; during normal operation, the mechanical torque, electromagnetic torque, friction damping and the like of the gas turbine are balanced, and when a system fails or is disturbed, the electromagnetic torque of the gas turbine is suddenly changed, the rotor kinetic energy is utilized to balance the load change, and the rotor motion state meets the rotor motion equation:
Figure SMS_20
wherein DeltaP Gm Delta P is the variation of the mechanical torque of the gas turbine Ge H is the variation of electromagnetic torque m Is the inertia time constant of the gas turbine, delta f is the system frequency variation, t is time, D m Is the damping coefficient of the gas turbine;
(2) Primary frequency modulation model
The gas turbine has primary frequency modulation capability and is realized through a speed regulation system thereof; the speed regulating system detects the difference between the rotating speed of the rotor and the rated rotating speed in real time, and drives the valve of the steam turbine to act through the comprehensive amplifier and the PID control link, so that the control of the input mechanical power is realized;
the complex frequency domain expression of the primary frequency modulation of the gas turbine is as follows:
Figure SMS_21
wherein K is m Is the power frequency characteristic coefficient, T of the gas turbine m Is the response time constant of the gas turbine, s is a complex variable, and Δf(s) is a complex frequency domainLower frequency variation.
The fan frequency modulation control model comprises a virtual inertia control model and an overspeed load shedding control model;
(1) Virtual inertia control
The doubly-fed wind turbine rotor contains a large amount of rotational kinetic energy and has the capacity of providing inertia for a power grid; however, the doubly-fed wind turbine is connected with the power grid through the power electronic converter, and the rotor of the doubly-fed wind turbine is decoupled from the power grid and cannot respond to the change of the system frequency; therefore, the kinetic energy of the rotor needs to be released through a corresponding auxiliary control strategy to provide inertia support for the power grid;
with reference to the traditional thermal power generating unit inertia control principle, virtual inertia control is adopted on the doubly-fed fan, namely, the output power of the doubly-fed fan is controlled to be in direct proportion to the frequency change rate of a power grid within the rotor rotating speed safety range (0.67-1.33 pu), so that the frequency change speed is slowed down, and the control equation is as follows:
Figure SMS_22
wherein DeltaP W K is the power adjustment quantity of the doubly-fed fan w Is a virtual inertia coefficient, T w The response time constant of the doubly-fed fan is represented by s, s is a complex variable, and Δf(s) is a frequency variation in a complex frequency domain;
(2) Overspeed load shedding control
Based on aerodynamic knowledge, the mechanical kinetic energy output by the wind turbine is shown as follows:
Figure SMS_23
wherein P is Wm Mechanical power output by the wind turbine; c (C) p Wind energy conversion coefficient, which is related to the pitch angle of the fan, wind speed and rotating speed of the fan; ρ a Is air density, S W Is the area of the fan blade of the wind turbine, V ω Is the wind speed;
in order to fully utilize wind energy, a doubly-fed wind turbine is generally controlled by adopting Maximum Power Point Tracking (MPPT), namely, under a certain wind speed and a fixed pitch angle, the output power of the wind turbine is maximized by regulating and controlling the rotating speed of the wind turbine; however, when the doubly-fed wind turbine participates in frequency modulation, the kinetic energy of the rotor of the doubly-fed wind turbine is required to be consumed to provide power support for the power grid, if the doubly-fed wind turbine still operates at a maximum power point, a large amount of kinetic energy of the rotor is consumed, the doubly-fed wind turbine is limited by the safe rotating speed of the rotor, the frequency modulation capacity provided by the doubly-fed wind turbine is smaller, and meanwhile, larger energy is absorbed from the power grid in the process of recovering the rotating speed of the rotor, so that serious frequency secondary drop is caused; therefore, the doubly-fed fan needs to leave certain frequency modulation standby power, and can normally run at two sides of the maximum power point, namely overspeed control or deceleration control; however, the research finds that the deceleration control will cause the problem of static instability, so the invention adopts overspeed load shedding control, see fig. 4, and the fan power-rotating speed curves under different wind speeds satisfy:
P opt ＝P max ·η
wherein P is max At maximum power, P opt For overspeed off-load power, η is off-load power ratio;
in overspeed load shedding mode, the doubly-fed fan is left with ΔP opt The power of (2) participates in frequency modulation, and the frequency modulation capability is improved:
ΔP opt ＝P max (1-η)
wherein DeltaP opt The reserved frequency modulation power is reserved for the doubly-fed fan;
in the overspeed load shedding control mode, the change curve of electromagnetic power and mechanical power in the frequency modulation process of the doubly-fed wind turbine is shown in figure 5; when the system normally operates, the doubly-fed fan stably operates at the point a, when a power grid breaks down and causes load surge, the system frequency is reduced, under the control of virtual inertia, the electromagnetic power output by the doubly-fed fan is increased to the point b, and at the moment, the mechanical power is still at the point a and smaller than the electromagnetic power, the fan starts to release rotor kinetic energy, and the rotating speed is gradually reduced; in the process of reducing the system frequency, under the regulation action of each frequency modulation resource, the change rate of the system frequency is gradually reduced, the electromagnetic power of the doubly-fed fan gradually reduces along a curve bc, the rotating speed of a rotor also reduces along the curve bc, the mechanical power firstly rises and then falls along the curve ac, and the system frequency reaches the lowest point at the point c; after that, the frequency starts to rise, under the control action of virtual inertia, the electromagnetic power of the doubly-fed fan is reduced to a point d, which is smaller than the mechanical power, and the rotor rotation speed starts to recover; in the rotating speed recovery process, the electromagnetic power of the doubly-fed fan gradually rises along a da curve, the mechanical power returns along a ca curve, and finally the doubly-fed fan is stabilized at an initial operating point a;
in summary, the overspeed control utilizes the reserved mechanical power of the doubly-fed fan in the frequency modulation process, and under the condition of providing the same frequency modulation capacity, compared with the MPPT control, the doubly-fed fan rotor speed conversion range adopting the overspeed control is smaller; meanwhile, in the rotational speed recovery process, the reserved mechanical power also accelerates the recovery speed of the rotational speed of the fan.
The electrochemical energy storage has the advantages of high response speed, high energy density, flexible power adjustment and the like, can be rapidly charged and discharged to provide effective frequency support for the system when the power grid fails, is mature in research on the electrochemical energy storage at present, and is widely applied; the energy storage system is connected to a power grid through a bidirectional converter, and power is decoupled from the power grid; when the energy storage system participates in frequency modulation, the grid-connected converter can be controlled to control the charge and discharge power of the energy storage system, so that the frequency modulation requirement of a power grid is met; the state of charge is typically used to represent the energy stored by an energy storage system and is characterized by the following operating characteristics:
Figure SMS_24
wherein lambda is soc Lambda is the state of charge of the energy storage system soc0 P is the initial state of charge of the energy storage system E For the output power of the energy-storage system E N Is the rated capacity of the energy storage system;
in order to exert the frequency modulation capability of the energy storage system, droop control is adopted to provide power support for the micro-grid:
Figure SMS_25
wherein DeltaP E K is the power adjustment quantity of the energy storage system E For the sag coefficient of the energy storage system, T E And s is a complex variable, and Δf(s) is a frequency variation in a complex frequency domain.
The number of the user side loads is huge, and the user side loads can be divided into important loads, transferable loads and interruptible loads according to the importance degree of the user side loads; the important load has higher requirements on electricity reliability, power failure is not allowed in a specific time, the transferable load and the interruptible load can participate in regulation and control of a power grid in a certain range, typical loads are represented by an air conditioner, an electric water heater, an electric automobile and the like, and the loads regulate and control own power through direct load control under the support of a demand response technology, so that power support can be provided for the power grid after faults, and recovery of system frequency is promoted.
The controllable loads in the micro-grid are numerous and distributed, if the distributed control is adopted, the control cost is greatly increased, so that the controllable loads can be aggregated into a whole through a load aggregator to uniformly participate in the frequency control of the grid, and meanwhile, a user is given a certain compensation; droop control is typically employed to provide power support for the grid, namely:
Figure SMS_26
wherein DeltaP L K is the power regulation of the controllable load L T is the controllable load sag factor L The response time constant of the controllable load is that s is a complex variable, and Δf(s) is the frequency variation in the complex frequency domain;
referring to fig. 6, the overall frequency response model of the micro-grid system is:
Figure SMS_27
wherein Δf is the system frequency variation, ΔP 0 To the system load disturbance quantity H s G is the inertial response transfer function of the system T 、G w 、G E 、G L The system comprises a gas turbine, a double-fed fan, an energy storage system and a controllable load frequency response transfer function; u (u) w 、u E 、u L The variable frequency-modulation system is respectively a doubly-fed fan, an energy storage system and a controllable load frequency-modulation state variable, wherein the variable frequency-modulation state variable is 1 when participating in frequency modulation and is 0 when not participating in frequency modulation; h m Is the inertia time constant of the gas turbine, D m K is the damping coefficient of the gas turbine m Is the power frequency characteristic coefficient, T of the gas turbine m K is the response time constant of the gas turbine w Is a virtual inertia coefficient, T w Is the response time constant of the doubly-fed fan, K E For the sag coefficient of the energy storage system, T E K is the response time constant of the energy storage system L T is the controllable load sag factor L And s is a complex variable, which is a response time constant of the controllable load.
Through the synergistic frequency modulation effect of wind power, energy storage and controllable load, the transient frequency stability of the micro-grid can be effectively improved, the frequency deviation of the system is reduced, but on a long time scale, the gas turbine is still required to maintain the power balance of the system.
S3, establishing a prediction model of the frequency response characteristic index of the micro-grid system, using the maximum frequency deviation as a frequency layering index, providing a wind-storage-load layering cooperative frequency modulation control strategy based on the prediction model, and compensating the power absorbed by the fan through an energy storage system in a fan rotating speed recovery stage;
when the micro-grid fails and causes load surge, the change process of the system frequency under the action of each frequency modulation resource is shown in figure 7; according to fig. 7, the characteristic indexes of the system frequency response include a maximum frequency change rate, a maximum frequency deviation, and a steady-state frequency deviation; the steady-state frequency deviation reflects the stability of the system frequency under the primary frequency modulation effect and the maximum frequency change rate and the maximum frequency deviation reflect the short-time stability of the system frequency;
when the load is disturbed, the maximum frequency change rate of the system is obtained by the initial value theorem
Figure SMS_28
The method comprises the following steps:
Figure SMS_29
obtaining the steady-state frequency deviation delta f of the system according to the final value theorem ∞ The method comprises the following steps:
Figure SMS_30
in order to solve the analytic expression of the maximum frequency deviation, a time domain expression of the frequency deviation is required to be solved, the time domain expression is derived from time to time, and then the time of the maximum frequency deviation and the maximum frequency deviation are solved; however, the system is a higher-order system, and after the system is converted into a time domain expression, the maximum frequency deviation moment is difficult to analyze and calculate, so that the system needs to be subjected to order reduction treatment; the transfer functions of the gas turbine, the doubly-fed fan, the energy storage system and the controllable load primary frequency modulation have the same form and can be expressed as the following unified form:
Figure SMS_31
wherein A, B, C is a characteristic parameter;
equivalent frequency modulation control model of each resource in the system is equivalent to an equivalent frequency modulation control model with the same characteristic, and the transfer function G of the equivalent frequency modulation control model eq The method comprises the following steps:
Figure SMS_32
wherein A is eq 、B eq 、C eq Characteristic parameters of the equivalent model; t is t mid Half of the weighted average value of the frequency modulation steady-state time of each resource;
Figure SMS_33
the variable-frequency steady-state time of the gas turbine, the doubly-fed fan, the energy storage system and the controllable load are respectively;
the time sequence expression deltaf (t) of the frequency deviation of the system equivalent frequency response model is as follows:
Figure SMS_34
Figure SMS_35
Figure SMS_36
c＝6H s C eq (a 2 -b 2 )+2a(2H s +A eq +C eq D eq )+B eq +D eq
d＝12abH s C eq +2b(2H s +A eq +C eq D eq )
g＝(aC eq +1)c+bdC eq ；h＝bcC eq -(aC eq +1)d
wherein M, N, a, b, c, d, h, g is a frequency timing expression parameter; d (D) eq Is the equivalent damping coefficient of the system;
time t of maximum frequency deviation of system tir Maximum frequency deviation Δf max The method comprises the following steps:
Figure SMS_37
Figure SMS_38
when the load disturbance is fixed, the maximum frequency change rate of the system is only related to the inertia of the gas turbines, so that as many gas turbines as possible can be integrated into the power grid to increase the inertia of the system; the system steady-state frequency deviation is related to the damping coefficient of the gas turbine and the droop coefficient of a speed regulator of the gas turbine, the droop coefficient of the energy storage system and the droop coefficient of the controllable load, so that the energy storage system and the controllable load are put into frequency modulation, the droop coefficient of the energy storage system and the controllable load is increased, and the system steady-state frequency deviation can be effectively reduced; the maximum frequency deviation of the system is related to the running parameters and the control parameters of each frequency modulation resource, the inertia of the gas turbine is improved, each resource is put into frequency modulation, the frequency modulation coefficient of each resource is increased, and the maximum frequency deviation of the system can be reduced.
In summary, the maximum frequency change rate, the maximum frequency deviation and the steady-state frequency deviation are the system frequency safety and stability indexes; after the fault occurs, the maximum frequency change rate, the maximum frequency deviation and the steady-state frequency deviation can be limited within a safe range through the frequency modulation effect of each resource in the micro-grid system, so that the requirements of the micro-grid frequency safety and stability are met.
When faults or load disturbance occur in the micro-grid, the original power balance of the system is broken, the frequency starts to change, the system power reaches new balance under the action of each frequency modulation resource in the micro-grid, and the frequency reaches a new stable value; wherein, each frequency modulation resource realizes frequency regulation and control mainly through inertia control and sagging control; inertia control is related to the system frequency change rate, so that the system frequency change can be damped, and frequency fluctuation is restrained; the sagging control is related to the frequency deviation amount of the system, so that the frequency deviation can be reduced, and the system frequency recovery can be quickened; the frequency stability of the micro-grid can be effectively improved through the coordination and the coordination of inertia control and sagging control; when the micro-grid fails or loads are switched, if all the resources such as wind, storage, load and the like participate in frequency modulation, the economy of the system is not facilitated; if the frequency modulation capacity of the system is insufficient, the requirement of frequency stability is difficult to meet; therefore, the wind-storage-load layering cooperative frequency modulation control strategy is set based on the frequency safety and stability index.
The analysis shows that the maximum frequency change rate of the system is only related to the inertia of the gas turbine, the inertia of the gas turbine in the system is usually fixed, the requirement of frequency stability can be met, meanwhile, the steady-state frequency deviation of the system reflects the frequency stability under a long time scale, and the invention mainly aims at the problem of frequency stability under transient conditions, so that the invention only considers the maximum frequency deviation of the system and takes the maximum frequency deviation as the index of wind, storage and load frequency modulation layering; in the frequency modulation process, if the system frequency deviation is detected to exceed the layering index, corresponding resources are controlled to participate in frequency modulation, the frequency modulation capability of each resource cannot be fully exerted, and frequency dynamic out-of-limit can be possibly caused; therefore, the maximum frequency deviation of the system needs to be predicted in advance, so that each resource is controlled in advance to participate in frequency modulation; in the actual running process of the micro-grid, the power shortage of the system after the fault is difficult to measure in time, and the initial frequency change rate of the system can be measured in real time by a wide area measurement system, so that the maximum frequency deviation of the system can be predicted by detecting the initial frequency change rate of the system, and comparing the maximum frequency deviation with each layering index to judge whether each resource participates in frequency modulation, thereby realizing model prediction control of wind-storage-load frequency modulation; the model-based predictive wind-reservoir-load cooperative control flow is shown in fig. 8.
When the system frequency changes, the gas turbine responds in real time;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max1 When the wind turbine generator is in use, virtual inertia control is adopted to reduce system frequency variation;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max2 When the energy storage system adopts droop control, the system frequency deviation is reduced;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max3 When the controllable load adopts droop control, the load power is increased or reduced to reduce the frequency deviation of the system;
as can be seen from fig. 5, when the doubly-fed fan participates in frequency modulation, the fan rotational speed gradually recovers during the frequency rebound process, and energy is absorbed from the power grid, which may cause secondary frequency drop, and is unfavorable for the system frequency recovery, so that the system needs to provide additional power support during the fan rotational speed recovery process; in the wind-storage-load system, because the energy storage system has high regulation speed, a large amount of power support can be provided in a short time, the power of the energy storage system is regulated and controlled to compensate the energy absorbed by the fan until the fan is restored to an initial running state, then the energy storage system starts to smoothly exit frequency modulation, and finally the frequency modulation power is provided by the gas turbine; after detecting that the system frequency change rate is 0, correcting a frequency modulation control equation of the energy storage system to be:
Figure SMS_39
/>
wherein DeltaP' E For the corrected power adjustment of the energy storage system, Δf(s) is the frequency variation in the complex frequency domain.
In order to verify the effectiveness of the micro-grid wind-storage-load layering cooperative frequency modulation control method, a micro-grid simulation model shown in figure 2 is built on Matlab/Simulink; wherein the gas turbine capacity is 9MW; the capacity of the doubly-fed fan is 6MW, and the load shedding power ratio of the fan is 0.9; the capacity of the energy storage system is set to be 20% of the wind power capacity and is 1.2 MW.h; the load is 10MW, and the controllable load ratio is 20%; the frequency modulation model parameters of each resource are shown in table 1; setting a layering index delta f max1 、Δf max2 、Δf max3 0.25Hz, 0.5Hz, and 0.75Hz, respectively.
Table 1 frequency modulation model parameters for each resource
Model parameters Numerical value/s Model parameters Numerical value
H m 4 D m 1
T m 3.8 K m 20
T w 0.1 K w 40
T E 0.3 K E 50
T L 1 K L 45
1. System frequency response results under different load disturbances
For different maximum frequency drop values, the frequency modulation resources input by the system are also different. In order to analyze the frequency modulation effect of each resource, the invention respectively sets three scenes of 0.5MW, 1.5MW and 2.5MW of the sudden load increase of the system at 5 s. The maximum frequency deviation of the system is predicted based on the measured initial frequency change rate of the system, and the prediction results are shown in table 2. In three scenarios, the frequency response curves of the system are shown in fig. 9-11.
TABLE 2 thermal power generating unit output
Figure SMS_40
As can be seen from Table 2, when the load suddenly increases by 0.5MW, if only the gas turbine participates in frequency modulation, the maximum frequency deviation of the system is predicted to be 0.394Hz, which is greater than the layering index Δf max1 Wind power is therefore required to participate in the frequency modulation. As can be seen from FIG. 9, the system frequency drops before wind power participates in frequency modulationThe drop is larger, the maximum deviation reaches 0.395Hz, and the maximum deviation is basically consistent with the predicted value; after wind power participates in frequency modulation, under the control of virtual inertia of a fan, the maximum frequency deviation of the system is reduced to 0.221Hz, and meanwhile, the frequency dropping speed is slowed down to some extent, so that the frequency stability of the system is improved; when the load suddenly increases by 1.5MW, if only the gas turbine and the wind power participate in frequency modulation, the maximum frequency deviation is predicted to be 0.666Hz, and energy storage is needed to participate in frequency modulation; as can be seen from fig. 10, after the energy storage participates in frequency modulation, the maximum frequency deviation of the system is reduced to 0.485Hz, and meanwhile, the steady-state frequency deviation of the system is reduced, and the frequency reaching steady time is reduced to 20s; when the load suddenly increases by 2.5MW, if the gas turbine, wind power and energy storage participate in frequency modulation, predicting that the maximum frequency deviation is 0.814Hz, and needing controllable load to participate in frequency modulation; as can be seen from fig. 11, after the controllable load participates in frequency modulation, the maximum frequency deviation of the system is reduced to 0.682Hz, and the steady-state frequency deviation is also reduced.
In summary, the maximum frequency deviation prediction model of the system established by the invention has higher precision, and can predict the maximum frequency deviation of the system, thereby controlling corresponding resources to participate in frequency modulation in advance, reducing frequency drop and improving the frequency stability of the system.
2. In contrast to conventional hierarchical control strategies
In order to further verify the effectiveness of the hierarchical control strategy based on model prediction, the invention compares the strategy with the traditional hierarchical control strategy, and simulation results are shown in fig. 12-14. The traditional hierarchical control strategy is that each frequency modulation resource in the system automatically participates in frequency modulation after detecting that the frequency deviation exceeds a threshold value in real time.
As can be seen from fig. 12 to 14, under the hierarchical control strategy based on model prediction, the system frequency deviation is significantly reduced, the frequency change rate is reduced, and the frequency stabilization time is advanced compared with the conventional hierarchical control strategy. Taking the sudden load increase of 0.5MW as an example for concrete analysis, when the sudden load increase of 0.5MW, under the traditional layered control strategy, the fan participates in frequency modulation after detecting that the frequency deviation exceeds 0.25Hz, and the control strategy provided by the invention can control the fan to participate in frequency modulation in advance, so that the frequency deviation of a system is reduced.
Therefore, the hierarchical control strategy based on model prediction can control corresponding resources to participate in frequency modulation in advance, avoid overlarge system frequency drop and improve the frequency stability of the system.
3. Fan rotational speed recovery control strategy validity verification
To verify the effect of energy storage power compensation in the fan speed recovery stage, the invention compares the frequency response results of the system before and after energy storage compensation when the load suddenly increases by 2.5MW, as shown in FIG. 15. Fig. 16 to 18 show the power change of the blower and the stored energy and the rotation speed change of the blower after the stored energy is compensated.
As can be seen from fig. 15 to 17, after the system frequency reaches the lowest point, the fan will absorb energy from the system, which is not beneficial to frequency recovery, and the system frequency is stable at 20 s. After the energy storage is compensated for power, the system frequency stabilizing time is advanced to 15s, the frequency fluctuation is reduced, and the recovery speed is improved.
As can be seen from fig. 16 and 18, when the fan is operated in the overspeed load shedding mode, the fan speed is reduced, the mechanical power of the wind turbine is improved, a certain frequency modulation power is provided, and the excessive reduction of the fan speed is avoided. Meanwhile, in the rotational speed recovery process, the larger mechanical power also increases the accelerating torque of the rotor, improves the recovery speed of the rotor, provides energy for the recovery of the rotational speed of the rotor, and reduces the energy absorbed by the fan from the system.
In summary, the wind-storage-load layering cooperative frequency modulation control method for the micro-grid can control the fan, energy storage and controllable load to participate in frequency modulation in advance, and improves the frequency stability of the micro-grid.

Claims (10)

1. The utility model provides a micro-grid wind-storage-load layering cooperative frequency modulation control method which is characterized by comprising the following steps:
s1, establishing a wind-storage-load layered cooperative frequency modulation control framework based on the operation characteristics of each resource in a micro-grid system;
s2, respectively establishing a frequency modulation control model of the gas turbine, the doubly-fed wind turbine, the energy storage system and the controllable load, and establishing an integral frequency response model of the micro-grid system;
s3, establishing a prediction model of the frequency response characteristic index of the micro-grid system, using the maximum frequency deviation as a frequency layering index, providing a wind-storage-load layering cooperative frequency modulation control strategy based on the prediction model, and compensating the power absorbed by the fan through the energy storage system in a fan rotating speed recovery stage.
2. The micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 1, wherein the method comprises the following steps of: in step S1, analyzing the operation characteristics of a gas turbine, a wind turbine generator, an energy storage system and a controllable load in a micro-grid system, establishing a wind-storage-load layered cooperative frequency modulation control architecture, and dividing frequency modulation into four layers: the first layer is gas turbine frequency modulation; the second layer is used for frequency modulation of the wind turbine generator; the third layer is used for frequency modulation of the energy storage system; and the fourth layer is controllable load frequency modulation.
3. The micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 1, wherein the method comprises the following steps of: in step S2, the gas turbine frequency modulation control model comprises an inertial response model and a primary frequency modulation model;
the inertial response model is:
Figure FDA0004064415070000011
wherein DeltaP Gm Delta P is the variation of the mechanical torque of the gas turbine Ge H is the variation of electromagnetic torque m Is the inertia time constant of the gas turbine, delta f is the system frequency variation, t is time, D m Is the damping coefficient of the gas turbine;
the primary frequency modulation model is as follows:
Figure FDA0004064415070000012
wherein K is m Power frequency characteristics for gas turbineCoefficient of sex, T m The response time constant of the gas turbine is S, S is a complex variable, and Δf (S) is a frequency variation in the complex frequency domain.
4. The micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 1, wherein the method comprises the following steps of: in step S2, the fan frequency modulation control model comprises a virtual inertia control model and an overspeed load shedding control model;
the virtual inertia control model is as follows:
Figure FDA0004064415070000021
wherein DeltaP W K is the power adjustment quantity of the doubly-fed fan w Is a virtual inertia coefficient, T w The response time constant of the doubly-fed fan is represented by S, S is a complex variable, and Δf (S) is a frequency variation in a complex frequency domain;
the overspeed load shedding control model is as follows:
Figure FDA0004064415070000022
wherein P is Wm For mechanical power output by the wind turbine, C p For wind energy conversion coefficient ρ a Is air density, S w Is the area of the fan blade of the wind turbine, V ω Is the wind speed;
by adopting overspeed load shedding control, the power-rotating speed curve of the fan under different wind speeds meets the following conditions:
P opt ＝P max ·η
wherein P is max At maximum power, P opt For overspeed off-load power, η is off-load power ratio;
in overspeed load shedding mode, the doubly-fed fan is left with ΔP opt Is involved in frequency modulation:
ΔP opt ＝P max (1-η)
wherein DeltaP opt And the frequency modulation power reserved for the doubly-fed fan.
5. The micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 1, wherein the method comprises the following steps of: in step S2, the energy storage system frequency modulation control model is:
Figure FDA0004064415070000023
wherein lambda is soc Lambda is the state of charge of the energy storage system soc0 P is the initial state of charge of the energy storage system E For the output power of the energy-storage system E N Is the rated capacity of the energy storage system;
providing power support for a microgrid using droop control:
Figure FDA0004064415070000031
wherein DeltaP E K is the power adjustment quantity of the energy storage system E For the sag coefficient of the energy storage system, T E And s is a complex variable, and Δf(s) is a frequency variation in a complex frequency domain.
6. The micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 1, wherein the method comprises the following steps of: in step S2, the controllable load frequency modulation control model is:
Figure FDA0004064415070000032
wherein DeltaP L K is the power regulation of the controllable load L T is the controllable load sag factor L The response time constant of the controllable load is s is complex variable, and Δf(s) is frequency variation in complex frequency domain.
7. The micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 2, wherein the method comprises the following steps: in step S2, the overall frequency response model of the micro-grid system is:
Figure FDA0004064415070000033
wherein Δf is the system frequency variation, ΔP 0 To the system load disturbance quantity H s G is the inertial response transfer function of the system T 、G w 、G E 、G L The transfer functions of the frequency response of the gas turbine, the doubly-fed fan, the energy storage system and the controllable load are respectively, u w 、u E 、u L The variable of the frequency modulation state of the controllable load is respectively a doubly-fed fan, an energy storage system and H m Is the inertia time constant of the gas turbine, D m K is the damping coefficient of the gas turbine m Is the power frequency characteristic coefficient, T of the gas turbine m K is the response time constant of the gas turbine w Is a virtual inertia coefficient, T w Is the response time constant of the doubly-fed fan, K E For the sag coefficient of the energy storage system, T E K is the response time constant of the energy storage system L T is the controllable load sag factor L The response time constant of the controllable load is shown, and S is a complex variable.
8. The micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 7, wherein the method comprises the following steps: in step S3, the characteristic indexes of the system frequency response include a maximum frequency change rate, a maximum frequency deviation and a steady-state frequency deviation;
when the load is disturbed, the maximum frequency change rate of the system is obtained by the initial value theorem
Figure FDA0004064415070000041
The method comprises the following steps:
Figure FDA0004064415070000042
obtaining the steady-state frequency deviation delta f of the system according to the final value theorem ∞ The method comprises the following steps:
Figure FDA0004064415070000043
equivalent frequency modulation control model of each resource in the system is equivalent to an equivalent frequency modulation control model with the same characteristic, and the transfer function G of the equivalent frequency modulation control model eq The method comprises the following steps:
Figure FDA0004064415070000044
wherein A is eq 、B eq 、C eq Characteristic parameters of the equivalent model; t is t mid Half of the weighted average value of the frequency modulation steady-state time of each resource;
Figure FDA0004064415070000051
the variable-frequency steady-state time of the gas turbine, the doubly-fed fan, the energy storage system and the controllable load are respectively;
the time sequence expression deltaf (t) of the frequency deviation of the system equivalent frequency response model is as follows:
Figure FDA0004064415070000052
Figure FDA0004064415070000053
/>
Figure FDA0004064415070000054
Figure FDA0004064415070000055
Figure FDA0004064415070000056
c＝6H s C eq (a 2 -b 2 )+2a(2H s +A eq +C eq D eq )+B eq +D eq
d＝12abH s C eq +2b(2H s +A eq +C eq D eq )
g＝(aC eq +1)c+bdC eq
h＝bcC eq -(aC eq +1)d
wherein M, N, a, b, c, d, h, g is a frequency timing expression parameter; d (D) eq Is the equivalent damping coefficient of the system;
time t of maximum frequency deviation of system tir Maximum frequency deviation Δf max The method comprises the following steps:
Figure FDA0004064415070000057
Figure FDA0004064415070000061
9. the micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 8, wherein the method comprises the following steps:
in step S3, when the system frequency changes, the gas turbine responds in real time;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max1 When the wind turbine generator is in use, virtual inertia control is adopted to reduce system frequency variation;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max2 When the energy storage system adopts droop control, the system frequency deviation is reduced;
when the maximum frequency deviation of the system is predicted to exceed the layering index delta f max3 When the controllable load adopts droop control, the load power is increased or decreased to reduce the system frequency deviation.
10. The micro-grid wind-storage-load layered cooperative frequency modulation control method according to claim 9, wherein the method comprises the following steps:
in step S3, the energy absorbed by the fan is compensated by regulating and controlling the power of the energy storage system until the fan is restored to the initial running state, then the energy storage system starts to smoothly exit the frequency modulation, and finally the frequency modulation power is provided by the gas turbine; after detecting that the system frequency change rate is 0, correcting a frequency modulation control equation of the energy storage system to be:
Figure FDA0004064415070000062
wherein DeltaP' E For the corrected power adjustment of the energy storage system, Δf(s) is the frequency variation in the complex frequency domain.
CN202310070006.5A 2023-02-07 2023-02-07 Micro-grid wind-storage-load layered cooperative frequency modulation control method Pending CN116231734A (en)

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CN116565882A (en) * 2023-06-29 2023-08-08 北京大学 Distributed demand response method, device, system and medium
CN116826789A (en) * 2023-08-31 2023-09-29 国网山西省电力公司经济技术研究院 Power distribution system emergency frequency control method based on multi-resource cooperative regulation and control
CN117154756A (en) * 2023-08-30 2023-12-01 南京工程学院 Wind-energy-storage combined frequency modulation control method considering energy storage charge state
CN117713143A (en) * 2024-02-06 2024-03-15 西安热工研究院有限公司 Novel thermal power coupling energy storage multi-time scale coordination control method and system
CN117748544A (en) * 2024-02-20 2024-03-22 华北电力大学 Compressed air energy storage system control system and power system frequency adjusting method

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116565882A (en) * 2023-06-29 2023-08-08 北京大学 Distributed demand response method, device, system and medium
CN116565882B (en) * 2023-06-29 2023-09-19 北京大学 Distributed demand response method, device, system and medium
CN117154756A (en) * 2023-08-30 2023-12-01 南京工程学院 Wind-energy-storage combined frequency modulation control method considering energy storage charge state
CN117154756B (en) * 2023-08-30 2024-05-28 南京工程学院 Wind-energy-storage combined frequency modulation control method considering energy storage charge state
CN116826789A (en) * 2023-08-31 2023-09-29 国网山西省电力公司经济技术研究院 Power distribution system emergency frequency control method based on multi-resource cooperative regulation and control
CN116826789B (en) * 2023-08-31 2023-11-17 国网山西省电力公司经济技术研究院 Power distribution system emergency frequency control method based on multi-resource cooperative regulation and control
CN117713143A (en) * 2024-02-06 2024-03-15 西安热工研究院有限公司 Novel thermal power coupling energy storage multi-time scale coordination control method and system
CN117713143B (en) * 2024-02-06 2024-04-30 西安热工研究院有限公司 Thermal power coupling energy storage multi-time scale coordination control method and system
CN117748544A (en) * 2024-02-20 2024-03-22 华北电力大学 Compressed air energy storage system control system and power system frequency adjusting method
CN117748544B (en) * 2024-02-20 2024-05-24 华北电力大学 Compressed air energy storage system control system and power system frequency adjusting method

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