Wind-solar-storage cooperative frequency control method and system based on frequency index constraint

Abstract

The invention discloses a wind-light storage cooperative frequency control method and system based on frequency index constraints, and belongs to the field of active support of power grid frequency of a wind-light storage hybrid station, and the method comprises the steps: firstly, obtaining disturbance boundary values of light and wind storage which sequentially participate in frequency modulation based on frequency safety index constraints; and according to the frequency change rate at the initial moment of disturbance occurrence, obtaining a disturbance value suffered by the system, comparing the disturbance value with a disturbance boundary value to judge the interval to which the disturbance value belongs, generating a corresponding frequency modulation instruction, and controlling active power output of wind, light and energy storage. According to the invention, adaptive frequency support control of the wind-solar-storage hybrid station grid-connected system under different working conditions can be realized, active power required to be output by the wind-solar-storage hybrid station grid-connected system can be accurately distributed according to frequency modulation requirements, the frequency modulation requirements are reliably met, and the frequency safety of a power grid is guaranteed; the kinetic energy of the rotor is fully utilized and the secondary drop of the frequency is avoided for the wind turbine generator in the collection station; for an energy storage unit in a collection station, the state of charge of energy storage is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of active support for grid frequency in a wind-solar-storage hybrid integrated station grid-connected system, and more specifically, relates to a wind-solar-storage coordinated frequency control method and system based on frequency index constraints. Background Art

[0002] In recent years, the penetration of fluctuating renewable energy sources such as wind power and photovoltaics in the power system has rapidly increased. The declining share of traditional synchronous generators has significantly reduced system inertia and frequency regulation capabilities. Their decentralized, weak support, low inertia, and low interference immunity pose significant challenges to new power systems and pose a serious threat to their stability. Consequently, power grid regulations have been introduced both domestically and internationally, clearly defining frequency regulation technology requirements for renewable energy grid integration. New energy stations must be able to proactively respond to changes in grid frequency and reserve backup frequency regulation power to handle emergencies such as sudden load increases.

[0003] In existing engineering applications, traditional renewable energy frequency support control often uses fixed droop or virtual inertia control parameters to improve frequency deviation and rate of change. This method effectively suppresses frequency fluctuations, but lacks a basis for controller parameter tuning, making it inaccurately meeting system frequency regulation requirements. Furthermore, evaluation relies on online monitoring, making early warning difficult. Summary of the Invention

[0004] In response to the defects of related technologies, the purpose of the present invention is to generate wind, solar and storage hybrid station frequency regulation instructions based on the constraints of frequency safety indicators and the size of the disturbance when a frequency event occurs in the system, and control the active power output of wind, solar and storage. It aims to solve the problems of existing wind, solar and storage coordinated control, such as lack of basis for controller parameter adjustment, failure to fully develop the frequency regulation advantages of various new energy sources, and over-reliance on energy storage response.

[0005] To achieve the above objectives, the present invention provides a wind-solar-storage coordinated frequency control method based on frequency index constraints, which is applied to a wind-solar-storage hybrid integrated station grid-connected system, wherein the wind-solar-storage hybrid integrated station grid-connected system includes a wind turbine, a battery energy storage unit, an AC power grid, and multiple parallel photovoltaic power generation units; the photovoltaic power generation units, wind turbines, and battery energy storage units are respectively connected to the same AC bus by connecting their respective converters and transformers, and then integrated into the AC power grid. The wind-solar-storage coordinated frequency control method based on frequency index constraints includes:

[0006] The photovoltaic power generation unit is subjected to load shedding control to reserve standby power, and the maximum comprehensive inertia control coefficient of the wind turbine is adjusted according to the wind speed of the wind turbine;

[0007] The preset system frequency security index is used as the first constraint to calculate the disturbance boundary ΔP for starting the photovoltaic power generation unit frequency modulation. LG and the disturbance boundary ΔP for starting wind turbine frequency regulationLPV ; Taking the maximum comprehensive inertia control coefficient of the wind turbine as the second constraint, based on the first constraint and the second constraint, calculate the disturbance boundary ΔP for starting the frequency modulation of the battery energy storage unit LW ;

[0008] Monitor the rate of change of frequency of the grid-connected system of the wind-solar-storage hybrid substation, and obtain the disturbance value ΔP of the system L , and based on the comparison result of the disturbance value ΔP L with each disturbance boundary, execute the corresponding frequency regulation strategy:

[0009] If the disturbance value ΔP L belongs to ΔP LG < ΔP L ≤ ΔP LPV interval, then calculate the additional power of the photovoltaic power generation unit to meet the frequency modulation demand based on the preset system frequency safety index;

[0010] If the disturbance value ΔP L belongs to ΔP LPV < ΔP L ≤ ΔP LW interval, the photovoltaic power generation unit outputs at its limit, calculate the active power of the wind turbine based on the preset system frequency safety index, and change its comprehensive inertia control coefficient based on the calculated active power to meet the frequency modulation demand;

[0011] If the disturbance value ΔP L belongs to ΔP L > ΔP LW interval, both the photovoltaic power generation unit and the wind turbine unit output at their limits, and control the active power output of the battery energy storage unit for frequency modulation according to the state of charge to meet the frequency modulation demand.

[0012] Optionally, the step of performing load shedding control on the photovoltaic power generation unit to reserve standby power and setting the maximum comprehensive inertia control coefficient of the wind turbine according to the wind speed where the wind turbine is located includes:

[0013] Set the initial load shedding rate σ0 of the photovoltaic power generation unit, and use the standby power corresponding to the initial load shedding rate σ0 for disturbance frequency modulation control; the standby power ΔP PV = (1 - σ0)P MPPT ;

[0014] Wherein, P MPPT represents the power value of the photovoltaic power generation unit operating at the maximum power point, and the value range of σ0 is 5% - 22%;

[0015] Obtain the extreme value of the rotational speed of the wind turbine and the power increase limit of the fan, respectively obtain the rotational speed change amount according to the extreme value of the rotational speed and the power increase limit of the fan, and determine the maximum rotational speed change amount Δω of the wind turbine from the rotational speed change amount; the calculation formula of the maximum rotational speed change amount Δω is:

[0016]

[0017] Where, ω r0 is the initial rotational speed of the wind turbine, ω rmax and ω rmin are the maximum and minimum rotational speeds for safe operation specified, P n represents the rated power of the fan, k opt represents the maximum power tracking control coefficient, H w represents the fan inertia coefficient, t h is the duration of fan frequency modulation;

[0018] Adjust the maximum comprehensive inertia control coefficient of the wind turbine according to the maximum rotational speed change amount Δω;

[0019]

[0020] Where

[0021] Where, k D is the droop coefficient, k H is the virtual inertia coefficient; ROCOF and Δf max are the maximum frequency change rate and the maximum frequency drop amplitude corresponding to the system disturbance value of ΔP LPV ; k opt represents the fan maximum power tracking coefficient; P ref 、P m (v, ω rmin ) represents the active power command value of the wind turbine at the initial rotational speed ω r0 and the lowest rotational speed ω rmin ; P MPPT (v, ω r0 )、P MPPT (v, ω rmin ) represent the power values of the maximum power operating points of the wind turbine at the initial rotational speed moment and the lowest rotational speed moment; t n represents the time when the frequency reaches the extreme value point; ΔE k represents the change amount of the fan rotor kinetic energy; P m (v, ω r ) represents the mechanical power of the fan.

[0022] Optionally, using the preset system frequency safety index as a constraint, calculate the disturbance boundary ΔP for starting the frequency modulation of the photovoltaic power generation unit respectively LGand the disturbance boundary ΔP for starting the frequency regulation of the wind turbine LPV ; taking the constraints of the preset system frequency safety index and the maximum comprehensive inertia control coefficient of the wind turbine as constraints, calculate the disturbance boundary ΔP for starting the frequency regulation of the battery energy storage unit LW , including:

[0023] Obtain the equivalent inertia coefficient and damping coefficient of the integrated wind-solar-storage power station grid-connected system, and determine the preset system frequency safety index; based on the preset system frequency safety index, use the theoretical formula of the SFR model to calculate the disturbance value corresponding to each safety index, and take the minimum value as the disturbance boundary ΔP for starting the photovoltaic frequency regulation LG ; among them, the preset system frequency safety index includes: the rate of change of frequency does not exceed -0.5Hz / s, the maximum frequency deviation does not exceed -0.5Hz, and the steady-state frequency deviation does not exceed -0.2Hz;

[0024]

[0025] where R represents the governor setting droop coefficient, H eq represents the system equivalent inertia coefficient, D eq represents the system equivalent damping coefficient, Take the limit value of -0.5Hz / s, Δf max Take the limit value of -0.5Hz, Δf ss Take the limit value of -0.2Hz, ΔP L1 , ΔP L2 , ΔP L3 respectively represent the disturbance boundaries when the initial rate of change of frequency, the maximum frequency deviation, and the steady-state frequency deviation take limit values, t n represents the time when the frequency reaches the extreme point, ξ represents the damping ratio, ω n represents the natural oscillation angular velocity, ω d represents the damping angular velocity, F H represents the high-pressure cylinder work ratio of the prime mover, T R represents the reheat time constant;

[0026] Use the theoretical formula of the SFR model to calculate the disturbance boundary value ΔP when the photovoltaic power generation unit outputs at its limit LPV ;

[0027]

[0028] According to the set maximum comprehensive inertia control coefficient of the wind turbine, use the theoretical formula of the SFR model to calculate the disturbance boundary value ΔP when the fan fully utilizes the rotor kinetic energy LW ;

[0029] where

[0030]

[0031] Among them, H' eq represents the equivalent inertia coefficient of the system after adding the comprehensive inertia control of the fan; D' eq represents the equivalent damping coefficient of the system after adding the comprehensive inertia control of the fan; t' n represents the time of the extreme frequency after adding the fan; H G represents the inertia constant of the synchronous machine; S sys represents the total system capacity; S w represents the capacity of the wind turbine generator set; S G represents the capacity of the synchronous machine.

[0032] Optionally, the calculation formula of the disturbance value ΔP L is as follows:

[0033]

[0034] Among them, H eq is the inertia constant of the integrated grid-connected system of the wind-solar-storage hybrid station, and f represents the grid frequency.

[0035] Optionally, if the disturbance value ΔP L belongs to ΔP LG <ΔP L ≤ΔP LPV interval, then the additional power of the photovoltaic power generation unit is calculated based on the preset system frequency safety index to meet the frequency modulation demand, including:

[0036] Calculating the additional power P PV of the standby power of the photovoltaic power generation unit based on the preset system frequency safety index:

[0037]

[0038] Among them, The limit value is -0.5Hz / s, Δf max The limit value is -0.5Hz, Δf ss The limit value is -0.2Hz;

[0039] According to the calculated additional power P PV of the standby power, adjust the DC capacitor side voltage U PV of the photovoltaic power generation unit to meet the frequency modulation demand.

[0040] Optionally, if the disturbance value ΔP L belongs to ΔP LPV <ΔP L ≤ΔP LWDuring the interval, the photovoltaic power generation unit outputs at its maximum limit. The active power of the wind turbine is calculated based on a preset system frequency safety index, and its comprehensive inertia control coefficient is changed based on the calculated active power to meet the frequency regulation requirements, including:

[0041] Based on the frequency safety index constraint, adjust the active power of the wind turbine according to the disturbance to calculate the active power P of the wind turbine W :

[0042]

[0043] where, Δf max takes the maximum frequency deviation limit of -0.5Hz; f0 represents the grid standard frequency, and its value is 50Hz;

[0044] Design the coefficient K according to the index H c1 , so that the virtual inertia coefficient k' H = K c1 k H decreases as the absolute value of the frequency change rate decreases, and the virtual inertia coefficient equals 0 and exits frequency regulation until the frequency change rate is 0;

[0045]

[0046] where, H represents the ratio of the initial frequency change rate before the fan participates in frequency regulation to the real-time frequency change rate after participating in frequency regulation. The minimum value of H min takes 1 - 2, the smaller value of H0 takes 5 - 8, and the smaller value of H low takes 10 - 20; n represents the function curve adaptive factor, and its value range is 10 - 20;

[0047] When the rotational speed of the wind turbine reaches the lowest point, resume the normal operation state of tracking the maximum power.

[0048]

[0049] where, ω r represents the rotational speed of the wind turbine, t off represents the moment when the wind turbine exits frequency regulation; P ref (t off ) represents the active power command value at the moment when the fan starts to exit frequency regulation; Δt represents the duration of the wind turbine exiting frequency regulation; P MPPT represents the power value of the fan operating at the maximum power point tracking; P ref represents the active power reference value of the wind turbine.

[0050] Optionally, if the disturbance value ΔP L belongs to ΔP L > ΔP LWDuring the interval, both the photovoltaic power generation unit and the fan unit output at full capacity. On the premise of ensuring that the state of charge is within the normal range of 0.1 to 0.9, the active power output of the battery energy storage unit for frequency modulation is controlled to meet the frequency modulation requirements, including:

[0051] According to the disturbance value ΔP L And the disturbance boundary ΔP LW For starting energy storage frequency modulation, adjust the output of the battery energy storage unit to participate in frequency modulation;

[0052]

[0053] Among them, P En Represents the rated power of the energy storage battery, set to 10% - 20% of the rated power of the fan; K c 、K d Represents the charging and discharging frequency modulation demand coefficients for the energy storage to participate in frequency modulation; P Esd 、P Esc Represents the charging and discharging power of the energy storage to participate in frequency modulation;

[0054] When the battery energy storage unit is performing frequency modulation output, adjust the charging and discharging frequency modulation demand coefficients K c 、K d According to the state of charge, and control the active power output of the battery energy storage unit for frequency modulation to meet the frequency modulation requirements;

[0055]

[0056] Among them, the minimum value S min Of the state of charge is taken as 0.1, the smaller value S0 is taken as 0.15, the relatively small value S low Is taken as 0.25, the relatively high value S high Is taken as 0.75, the higher value S1 is taken as 0.85, the highest value S max Is taken as 0.9; K max Represents the maximum unit regulation power for frequency modulation, with a value of 1.

[0057] Optionally, it also includes:

[0058] After the system frequency returns to stability, restore the battery energy storage units with the state of charge in the overcharge or over-discharge area to the normal operating range according to the restoration demand coefficient and the restoration constraint coefficient;

[0059] When the frequency deviation exceeds ±0.002Hz, stop the restoration of the state of charge of the battery energy storage unit;

[0060]

[0061] Among them, K c1 And K d1 Are the restoration demand charging coefficient and the restoration demand discharging coefficient corresponding to the state of charge of the battery energy storage unit itself;

[0062]

[0063] Among them, K c2 and K d2 are the recovery constraint coefficients during the charging and discharging processes on the premise of ensuring the stability of the grid frequency; the minimum value of the frequency deviation Δf min is taken as -0.002 Hz, the smaller value Δf0 is taken as -0.0015 Hz, the smaller value Δf low is taken as -0.001 Hz, the higher value Δf high is taken as 0.001 Hz, the higher value Δf1 is taken as 0.0015 Hz, and the highest value Δf max is taken as 0.002 Hz.

[0064] Optionally, obtain the smaller value of the recovery demand coefficient and the recovery constraint coefficient as the state of charge recovery coefficient K of the battery energy storage unit re :

[0065]

[0066] Among them, ΔP ES represents the active power output during the state of charge recovery of the battery energy storage unit.

[0067] In a second aspect, the present invention also provides a wind-solar-storage collaborative frequency control system based on frequency index constraints, including: a memory and a processor, the memory stores a computer program, and when the processor executes the computer program, it executes the method provided in any one of the first aspects.

[0068] Through the above technical solutions conceived by the present invention, compared with the prior art, the following beneficial effects can be achieved:

[0069] 1. The wind-solar-storage collaborative frequency control method based on frequency index constraints provided by the present invention. Due to the characteristics that the active power response speed of photovoltaic is faster than that of wind turbines and the cost of battery energy storage is high, it is decided that the photovoltaic unit, wind turbine unit, and energy storage unit participate in frequency modulation in sequence, which fully exerts the advantages of the photovoltaic system and protects the service life of the battery energy storage unit, and reduces the economic cost. Based on the frequency safety index constraints of the system, combined with the reserve power capacity of photovoltaic and the maximum control coefficient of wind turbine frequency modulation, the disturbance boundaries when the wind-solar-storage participate in frequency modulation in sequence are divided. For different working conditions, it can not only accurately control the active power output of the wind-solar-storage and raise the frequency to the safe range; at the same time, it reasonably utilizes the frequency modulation resources of the hybrid substation.

[0070] 2. The wind-solar-storage coordinated frequency control method based on frequency index constraints provided by the present invention addresses issues such as insufficient utilization of the kinetic energy of the fan rotor, over-response of the comprehensive inertia control coefficient of the fan, and large power deficits caused when the fan exits frequency modulation in a wind-solar-storage hybrid substation grid-connected system. By determining the rotor operating range and integrating the power of the fan operating curve, the maximum comprehensive inertia control coefficient of the fan rotor is adjusted as the wind speed changes below the safe operating range, achieving the effect of fully utilizing the kinetic energy of the fan rotor and avoiding secondary frequency dips in the power grid. At the same time, due to the higher cost and more serious life loss of energy storage, for economic considerations, the state of charge is considered during frequency modulation to avoid exceeding its state of charge limit. At the same time, a charge recovery control strategy is designed to ensure the healthy state of the energy storage battery in the system and pursue economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 It is a schematic flowchart of the wind-solar-storage coordinated frequency control method based on frequency index constraints in an embodiment of the present invention;

[0072] Figure 2 It is a schematic diagram of the structure of a wind-solar-storage hybrid substation grid-connected system and an AC power grid fault in an embodiment of the present invention;

[0073] Figure 3 It is a schematic diagram of the generation of frequency support commands for a wind-solar-storage hybrid substation in an embodiment of the present invention;

[0074] Figure 4(a) is a schematic diagram of photovoltaic frequency support control in an embodiment of the present invention;

[0075] Figure 4(b) is a schematic diagram of wind turbine frequency support control in an embodiment of the present invention;

[0076] Figure 4(c) is a schematic diagram of energy storage frequency support control in an embodiment of the present invention;

[0077] Figure 5 It is a schematic diagram of the simulation results of the control strategy of the present invention, the wind-solar-storage using a fixed comprehensive inertia control coefficient, and the frequency characteristics of MPPT operation control and the output of new energy power stations when the system disturbance is small, where (a) represents the frequency change diagram, (b) represents the active power output diagram of the photovoltaic unit, (c) represents the active power output diagram of the wind turbine, and (d) represents the active power output diagram of the energy storage unit;

[0078] Figure 6In an embodiment of the present invention, the system has large disturbances. When photovoltaic and wind turbines participate in frequency regulation, the following is a schematic diagram of the simulation results of the frequency characteristics of the proposed strategy control and the fixed comprehensive inertia control coefficient and MPPT operation control of the wind-solar-storage system, as well as the output of the new energy power station. Among them, (a) represents the frequency change diagram, (b) represents the active power output diagram of the photovoltaic unit, (c) represents the active power output diagram of the wind turbine, (d) represents the active power output diagram of the energy storage unit, and (e) represents the change diagram of the rotor speed of the wind turbine;

[0079] Figure 7 In an embodiment of the present invention, the system fault is severe. When the wind-solar-storage system participates in frequency regulation together, the following is a schematic diagram of the simulation results of the frequency characteristics of the proposed strategy control and the fixed comprehensive inertia control coefficient and MPPT operation control of the wind-solar-storage system, as well as the output of the new energy power station. Among them, (a) represents the frequency change diagram, (b) represents the active power output diagram of the photovoltaic unit, (c) represents the active power output diagram of the wind turbine, (d) represents the active power output diagram of the energy storage unit, (e) represents the change diagram of the rotor speed of the wind turbine, and (f) represents the change diagram of the state of charge of the energy storage unit.

[0080] In the above figures, the same characters represent the same meaning. The reference numerals are explained as follows:

[0081] G represents four synchronous generators, L1 represents load 1, L2 represents load 2, 1 to 13 represent system network nodes 1 to 13, and the wind-solar-storage hybrid substation is aggregated to node 8 and connected to the power grid; Δf B represents the frequency deviation boundary value for starting the self-recovery stage of the state of charge of the energy storage. Detailed implementation manners

[0082] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0083] The following describes the content involved in the above embodiments in conjunction with a preferred embodiment.

[0084] Embodiment 1

[0085] As Figure 1As shown, the present invention provides a wind-solar-storage coordinated frequency control method based on frequency index constraints, which is applied to a wind-solar-storage hybrid integrated station grid-connected system, wherein the wind-solar-storage hybrid integrated station grid-connected system includes a wind turbine, a battery energy storage unit, an AC power grid, and multiple parallel photovoltaic power generation units; the photovoltaic power generation units, wind turbines, and battery energy storage units are respectively connected to the same AC bus by connecting their respective converters and transformers, and then integrated into the AC power grid. The wind-solar-storage coordinated frequency control method based on frequency index constraints includes:

[0086] S1. Perform load shedding control on the photovoltaic power generation unit to reserve standby power, and adjust the maximum comprehensive inertia control coefficient of the wind turbine according to the wind speed of the wind turbine;

[0087] S2. Take the preset system frequency security index as the first constraint and calculate the disturbance boundary ΔP for starting the frequency modulation of the photovoltaic power generation unit. LG and the disturbance boundary ΔP for starting wind turbine frequency regulation LPV Taking the maximum comprehensive inertia control coefficient of the wind turbine as the second constraint, based on the first and second constraints, calculate the disturbance boundary ΔP for starting the frequency modulation of the battery energy storage unit LW ;

[0088] S3. Monitor the frequency change rate of the wind-solar-storage hybrid station grid-connected system to obtain the disturbance value ΔP suffered by the system. L , and according to the disturbance value ΔP L Compare the results with the disturbance boundaries and execute the corresponding frequency control strategy:

[0089] S4, if the disturbance value ΔP L Belongs to ΔP LG <ΔP L ≤ΔP LPV interval, the additional power of the photovoltaic power generation unit is calculated based on the preset system frequency security index to meet the frequency regulation requirements;

[0090] S5. If the disturbance value ΔP L Belongs to ΔP LPV <ΔP L ≤ΔP LW During the interval, the photovoltaic power generation unit outputs as much as possible, the active power of the wind turbine is calculated based on the preset system frequency safety index, and its comprehensive inertia control coefficient is changed based on the calculated active power to meet the frequency regulation requirements;

[0091] S6, if the disturbance value ΔP L Belongs to ΔP L >ΔP LW During this period, the photovoltaic power generation units and wind turbines are limited in their output, and the active power output of the battery energy storage unit is controlled according to the state of charge to meet the frequency regulation requirements.

[0092] As shown Figure 2 in the figure, in the photovoltaic power generation unit, a photovoltaic power generation array, a DC / DC boost circuit and an inverter are connected in sequence; the wind turbine group is composed of multiple doubly-fed wind turbines, and in the wind turbine group, a doubly-fed induction motor, a rotor-side converter and a stator-side converter are connected in sequence; in the battery energy storage unit, a battery equivalent circuit and an inverter are connected in sequence; the load disturbance appears at node 7; the hybrid wind-solar-storage substation is connected to the power grid through node 8. The generation of the frequency support command for the hybrid wind-solar-storage substation is as Figure 3 shown. According to the constraints of the preset system frequency safety index, the disturbance boundary values for the photovoltaic power generation unit and the wind turbine group to participate in frequency regulation are calculated respectively, and the disturbance boundary value for the battery energy storage unit to participate in frequency regulation is calculated according to the constraints of the preset system frequency safety index and the maximum comprehensive inertia control coefficient of the wind turbine group; the disturbance value obtained by monitoring the frequency change rate of the grid-connected system of the hybrid wind-solar-storage substation is compared with the calculated disturbance boundary value to generate a frequency regulation command, and the active power output of each of the wind, solar and storage is controlled. The schematic diagrams of the frequency support control for the wind, solar and storage are shown in Figs. 4(a), 4(b) and 4(c). Fig. 4(a) shows that when the disturbance value ΔP L belongs to the range of ΔP LG <ΔP L ≤ΔP LPV , the additional power generation of the photovoltaic power generation unit is calculated based on the preset system frequency safety index, and the DC capacitor side voltage U PV of the photovoltaic power generation unit is adjusted; Fig. 4(b) shows that when the disturbance value ΔP L belongs to the range of ΔP LPV <ΔP L ≤ΔP LW , the fan adopts comprehensive inertia control to participate in frequency regulation, and starts the speed recovery process when the speed reaches the lowest point or exceeds 0.7 p.u.; Fig. 4(c) shows that if the disturbance value ΔP L belongs to the range of ΔP L >ΔP LW , on the premise of ensuring that the state of charge is within the normal range of 0.1 to 0.9, the charging and discharging active power output for the frequency regulation of the battery energy storage unit is controlled to meet the frequency regulation requirements; and after the frequency is stable, the state of charge recovery process of the battery energy storage unit is considered in terms of both the state of charge of the battery energy storage unit and the frequency deviation.

[0093] Based on the constraints of the frequency safety index and the reserve power capacity of the photovoltaic and the maximum frequency regulation control coefficient of the wind turbine, the disturbance boundary values for the wind, solar and storage to participate in frequency regulation in sequence are obtained. When a frequency event occurs in the system, according to the frequency change rate measured at the initial moment of the disturbance, the disturbance value received by the system is obtained, and it is compared with the disturbance boundary value to judge the interval it belongs to and generate the corresponding frequency regulation command. If the disturbance is small, only the synchronous machine frequency regulation can meet the frequency regulation requirements, otherwise, according to the size of the disturbance, the active power output of each of the wind, solar and storage is controlled.

[0094] Optionally, the S1 includes:

[0095] S101, setting the initial load reduction rate σ0 of the photovoltaic power generation unit, and using the standby power corresponding to the initial load reduction rate σ0 for disturbance frequency control; the standby power ΔP PV =(1-σ0)P MPPT ;

[0096] Among them, P MPPT It represents the power value of the photovoltaic power generation unit operating at the maximum power point. The initial load reduction rate ranges from 5% to 22%. In this embodiment, the preferred value of σ0 is 20%.

[0097] S102: Obtaining the rotation speed limit of the wind turbine and the wind turbine additional power limit ΔP wmax , the speed variation is obtained according to the speed extreme value and the wind turbine additional power limit respectively, and the maximum speed variation Δω of the wind turbine set is determined from the two speed variations; the calculation formula of the maximum speed variation Δω is:

[0098]

[0099] Among them, ω r0 is the initial speed of the wind turbine, ω rmax and ω rmin is the maximum and minimum speed for safe operation, ω0 is the cut-in speed for the fan to enter the maximum power tracking area, P n Indicates the rated power of the fan, k opt represents the maximum power tracking control coefficient, H w Indicates the fan inertia coefficient, t h is the duration of fan frequency modulation. In this embodiment, ω rmax and ω rmin Take 1.2 times and 0.7 times of the rated speed respectively, t h The value is 3s.

[0100] When a disturbance occurs, the wind turbine uses rotor kinetic energy to participate in frequency modulation by changing the speed, and the maximum speed change needs to be calculated. When no disturbance occurs, the wind turbine maintains normal speed operation. When the frequency drops, the wind turbine releases rotor kinetic energy to provide inertia to suppress frequency changes. In another embodiment, when the disturbance is a negative frequency increase, the wind turbine suppresses frequency fluctuations by absorbing rotor kinetic energy. The amount of rotor kinetic energy is reflected by the range of change of the rotor speed. The range of change of the rotor speed is constrained by the speed extreme value and the wind turbine's additional power limit.

[0101] S103, adjusting the maximum comprehensive inertia control coefficient of the wind turbine generator set according to the maximum speed change Δω;

[0102]

[0103]

[0104] Among them, k D is the droop coefficient, and k H is the virtual inertia coefficient; ROCOF and Δf max are the maximum frequency change rate and the maximum frequency drop amplitude corresponding to the system disturbance value of ΔP LPV ; k opt represents the maximum power tracking coefficient of the wind turbine; P ref , P m (v, ω rmin ) represents the active power command value of the wind turbine at the initial rotational speed ω r0 and the lowest rotational speed ω rmin ; P MPPT (v, ω r0 ), P MPPT (v, ω rmin ) represent the power values of the maximum power operating points of the wind turbine at the initial moment of rotational speed and the moment of the lowest rotational speed; t n represents the time when the frequency reaches the extreme point; ΔE k represents the change in the kinetic energy of the wind turbine rotor; P m (v, ω r ) represents the mechanical power of the wind turbine.

[0105] Among them, the wind turbine participates in frequency regulation through comprehensive inertia control, where the comprehensive inertia control represents the combination of virtual inertia control and droop control.

[0106] Optionally, the S2 specifically includes:

[0107] S201. Obtain the equivalent inertia coefficient and damping coefficient of the integrated wind-solar-storage hybrid substation grid-connected system, and determine the preset system frequency safety index; based on the preset system frequency safety index, use the SFR model theoretical formula to calculate the disturbance values corresponding to each safety index, and take the minimum value as the disturbance boundary ΔP LG for starting photovoltaic frequency regulation; among them, the preset system frequency safety index includes: the frequency change rate does not exceed -0.5 Hz / s, the maximum frequency deviation does not exceed -0.5 Hz, and the steady-state frequency deviation does not exceed -0.2 Hz;

[0108]

[0109] Among them, R represents the governor setting speed regulation coefficient, H eq represents the system equivalent inertia coefficient, D eq represents the system equivalent damping coefficient, take the limit value of -0.5 Hz / s, Δf maxTake the limit value of -0.5Hz, Δf ss Take the limit value of -0.2Hz, ΔP L1 , ΔP L2 , ΔP L3 respectively represent the disturbance boundaries when the initial frequency change rate, the maximum frequency deviation, and the limit value of the steady-state frequency deviation are taken, t n represents the time when the frequency reaches the extreme point, ξ represents the damping ratio, ω n represents the natural oscillation angular velocity, ω d represents the damped angular velocity, F H represents the work ratio of the high-pressure cylinder of the prime mover, T R represents the reheating time constant;

[0110] S202. Calculate the disturbance boundary value ΔP when the photovoltaic power generation unit reaches its maximum output using the theoretical formula of the SFR model LPV ;

[0111]

[0112] S203. According to the set maximum comprehensive inertia control coefficient of the wind turbine, calculate the disturbance boundary value ΔP when the wind turbine maximally utilizes the rotor kinetic energy using the theoretical formula of the SFR model LW ;

[0113] Among them

[0114]

[0115] Among them, H′ eq represents the equivalent inertia coefficient of the system after adding the comprehensive inertia control of the wind turbine; D′ eq represents the equivalent damping coefficient of the system after adding the comprehensive inertia control of the wind turbine; t' n represents the time of the frequency extreme value after adding the wind turbine; H G represents the synchronous machine inertia constant; S sys represents the total system capacity; S w represents the wind turbine capacity; S G represents the synchronous machine capacity.

[0116] Optionally, the calculation formula for the disturbance value ΔP L is:

[0117]

[0118] Among them, H eq is the inertia constant of the hybrid power generation and energy storage station grid-connected system, and f represents the grid frequency.

[0119] Optionally, S4 specifically includes:

[0120] S401. Calculate the additional power P of the reserve power of the photovoltaic power generation unit based on the preset system frequency safety index PV :

[0121]

[0122] Among them, Take the limit value of -0.5Hz / s, Δf max Take the limit value of -0.5Hz, Δf ss Take the limit value of -0.2Hz.

[0123] S402. Adjust the DC capacitor side voltage U of the photovoltaic power generation unit according to the calculated additional power P of the reserve power PV to meet the frequency modulation requirements: the frequency change rate does not exceed -0.5Hz / s, the maximum frequency deviation does not exceed -0.5Hz, and the steady-state frequency deviation does not exceed -0.2Hz. PV Optionally, the S5 specifically includes:

[0124] S501. Calculate the active power P of the wind turbine based on the frequency safety index constraint and adjust the active power of the wind turbine according to the disturbance

[0125] : W :

[0126]

[0127] Among them, Δf max Take the maximum frequency deviation limit value of -0.5Hz; f0 represents the grid standard frequency, and its value is 50Hz.

[0128] Based on the frequency safety index constraint, adjust the power of the fan according to the disturbance; since the frequency deviation is more sensitive to k D Keep the droop coefficient unchanged and change the virtual inertia control coefficient k of the fan with the disturbance size H , generate the active power P of the fan W .

[0129] S502. Design the coefficient K according to the index H c1 , so that the virtual inertia coefficient k' H = K c1 k H gradually exits frequency modulation as the frequency change rate decreases;

[0130]

[0131] Among them, H represents the ratio of the frequency change rate at the initial moment before the fan participates in frequency modulation to the real-time frequency change rate after participating in frequency modulation, and the minimum value of H minTake the smaller value of 1 to 2, H0 takes the value of 5 to 8, and the smaller value H low Take 10 to 20; n represents the function curve adaptive factor, and its value range is 10 to 20.

[0132] Since the frequency starts to recover when it reaches the lowest point and the sign of the frequency change rate changes, the virtual inertia control is equivalent to absorbing power from the system. Therefore, design the coefficient K c1 , so that the virtual inertia coefficient k' H =K c1 k H Gradually exits the frequency regulation as the frequency change rate decreases. In this embodiment, the minimum value H min takes 2, the smaller value H0 takes 6, and the smaller value H low takes 10. When n takes the value of 15, the coefficient K c1 changes with the index H at an appropriate speed, and can take into account the effect of frequency improvement before the virtual inertia control exits the frequency regulation.

[0133] Optionally, after S5, it further includes:

[0134] When the wind turbine speed reaches the lowest point, resume tracking the normal operating state of the maximum power;

[0135]

[0136] Among them, ω r represents the wind turbine speed; t off represents the moment when the wind turbine exits the frequency regulation; P ref (t off ) represents the active power command value at the moment when the fan starts to exit the frequency regulation; Δt represents the duration of the wind turbine exiting the frequency regulation; P MPPT represents the power value of the fan operating at the maximum power point tracking; P ref represents the active power reference value of the wind turbine.

[0137] After the speed reaches the lowest point, the speed starts to recover; in order not to generate a large power deficit, the active power increment smoothly decays to zero. Specifically, if the speed drops to 0.7 p.u., immediately resume the MPPT operating state.

[0138] Optionally, the S6 specifically includes:

[0139] S601. Adjust the output of the battery energy storage unit to participate in the frequency regulation according to the difference between the disturbance value ΔP L and the disturbance boundary ΔP LW for starting the energy storage frequency regulation;

[0140]

[0141] Among them, P EnRepresents the rated power of the energy storage battery, which is set to 10% - 20% of the rated power of the fan; K c 、K d Represents the charging and discharging frequency modulation demand coefficients for the energy storage to participate in frequency modulation; P Esd 、P Esc Represents the charging and discharging power of the energy storage participating in frequency modulation. In this embodiment, P En takes a value of 10%.

[0142] Furthermore, in another embodiment where the disturbance is a negative frequency rise condition, the energy storage suppresses frequency fluctuations by absorbing power from the system for charging.

[0143] S602. When the battery energy storage unit outputs for frequency modulation, it adjusts the charging and discharging frequency modulation demand coefficients K c 、K d , and controls the active power output of the battery energy storage unit for frequency modulation to meet the frequency modulation demand;

[0144]

[0145] Among them, the minimum value S of the state of charge min takes 0.1, the smaller value S0 takes 0.15, the relatively small value S low takes 0.25, the relatively high value S high takes 0.75, the higher value S1 takes 0.85, the maximum value S max takes 0.9; K max represents the maximum unit regulation power for frequency modulation, and takes a value of 1.

[0146] The energy storage output also considers the state of charge of the battery. Specifically, it adjusts the frequency modulation demand coefficient according to the SOC. If the state of charge is too small, it cannot participate in frequency modulation. If the state of charge of the energy storage is too large, charging frequency modulation is not allowed. In this embodiment, the disturbance is a frequency rise condition. Furthermore, in another embodiment, the disturbance is a negative frequency rise condition.

[0147] Optionally, after S6, it further includes:

[0148] When the system frequency returns to stability, the battery energy storage units with the state of charge in the overcharge or over-discharge area are restored to the normal working range according to the restoration demand coefficient and the restoration constraint coefficient;

[0149] When the frequency deviation exceeds ±0.002Hz, the restoration of the state of charge of the battery energy storage unit is stopped;

[0150]

[0151] Among them, K c1 and K d1 are the restoration demand charging coefficient and the restoration demand discharging coefficient corresponding to the state of charge of the battery energy storage unit itself;

[0152] When the frequency deviation exceeds ±0.002 Hz, stop the restoration of the state of charge of the battery energy storage unit;

[0153]

[0154] Among them, K c2 and K d2 are restoration constraint coefficients during the charging and discharging processes on the premise of ensuring the stability of the grid frequency; the minimum frequency deviation Δf min is taken as -0.002 Hz, the smaller value Δf0 is taken as -0.0015 Hz, the smaller value Δf low is taken as -0.001 Hz, the higher value Δf high is taken as 0.001 Hz, the higher value Δf1 is taken as 0.0015 Hz, and the highest value Δf max is taken as 0.002 Hz.

[0155] In this embodiment, the disturbance is a working condition of positive frequency drop. When the frequency returns to stability, it is necessary to restore the energy storage battery with the SOC state in the over-discharge area to the normal working range. Further, in another embodiment, the disturbance is a working condition of negative frequency rise, and the SOC state after the over-response of energy storage charging is restored to the normal state.

[0156] Optionally, in S6, obtain the smaller value of the restoration demand coefficient and the restoration constraint coefficient as the state of charge restoration coefficient K of the battery energy storage unit re :

[0157]

[0158] Among them, ΔP ES represents the active power output during the restoration of the state of charge of the battery energy storage unit.

[0159] To verify the effectiveness of the method provided by the present invention, a four-region two-machine system of a wind-solar-storage hybrid substation as shown in Figure 2 is built on the Matlab / Simulink platform, and the main parameters are shown in Table 1.

[0160] Table 1 Main parameters of the four-region two-machine system of the wind-solar-storage hybrid substation

[0161] System parameters Value Total capacity of PV power station (MVA) 100 Total capacity of wind turbines (MVA) 100 Rated power of energy storage (MW) 10 Capacity of each thermal generator (MVA) 100 System rated frequency (Hz) 50 Loads L1, L2 (MW) 967、1767 Inertia constant of synchronous machine G (s) 117、117、111.15、111.15 System damping constant D 0 Synchronous machine droop rate R 1 / 225 Initial PV load shedding rate 20％ SOC of energy storage 0.6 Wind speed (m / s) 11.358 <![CDATA[Wind turbine speed limit ω rmax and ω rmin (p.u.)]]> 1.2、0.7 <![CDATA[The frequency regulation duration t of the wind turbine h (s)]]> 3 <![CDATA[Minimum value H min 、Smaller value H0, relatively small value H low > 2、6、10

[0162] Simulation setting 1: The grid-connected system of the wind-solar-storage hybrid substation operating at rated power has a grid fault at the 5th second, and the grid disturbance is 4 p.u. At this time, according to the SFR theoretical formula, the disturbance boundary values calculated are ΔP LG = 3.7 pu; ΔP LPV = 4.3 pu; ΔP LW= 4.6 pu; It can be judged that the PV participates in frequency regulation. The simulation results of the frequency characteristics under different controls and the output of the new energy power station are as Figure 5 shown.

[0163] According to Figure 5 the simulation results, when the wind-solar-storage system operates under the maximum power point tracking control, as Figure 5 shown in (a) below, the maximum amplitude of the frequency drop is -0.52 Hz, which does not meet the frequency index condition and there is a risk of instability. Therefore, new energy frequency regulation is required. This method generates a frequency regulation command immediately after the frequency drop occurs, allowing the PV to provide frequency support. According to the frequency index constraint, the PV changes the output of the standby power by changing the voltage on the capacitor side. As Figure 5 shown in (b) below, the active power of the PV changes stepwise to respond to the frequency after 0.2 s, with a fast response speed. Moreover, compared with the method of using a fixed comprehensive inertia control coefficient for the wind-solar-storage system, this method has more PV output, makes full use of the light energy resources for frequency regulation, and ensures the frequency regulation effect. According to Figure 5 shown in (b) below, for the traditional comprehensive inertia control method, there is still a large margin of the PV standby power that can be used for frequency regulation. However, as Figure 5 shown in (c) below and Figure 5 shown in (d) below, the wind turbine and energy storage are started to participate in frequency regulation without fully utilizing the PV resources; although the traditional comprehensive inertia control has a slightly better frequency improvement effect and the lowest frequency point is slightly higher by 0.1 Hz, it causes waste of resources and reduces the economy. Especially for the energy storage resources with high costs, the energy storage does not need to participate in frequency regulation when the disturbance is small, reducing the charge and discharge times of the energy storage.

[0164] Simulation setting 2: A grid fault occurs at the 5 s moment in the PV grid-connected system operating at rated conditions, and the grid disturbance is 4.45 p.u.. It can be judged that only the PV participating in frequency regulation cannot meet the requirements, and the wind turbine also needs to participate in frequency regulation. The simulation results of the frequency characteristics under different controls and the output of the new energy power station are as Figure 6 shown;

[0165] According to Figure 6 the simulation results, if the wind-solar-storage system operates under the maximum power point tracking control, the maximum amplitude of the frequency drop is -0.59 Hz, with large frequency fluctuations, which does not meet the frequency index condition and there is a risk of instability. At this time, as Figure 6 shown in (b) below, this method allows the PV to output all the standby power and return to the MPPT operating state to output power as much as possible, making full use of the light energy resources; while the wind turbine adaptively adjusts the virtual inertia coefficient according to the disturbance to release the rotor kinetic energy. As Figure 6As shown in (a), the maximum frequency change rates under traditional comprehensive inertia control and this strategy are -0.3287 Hz / s and -0.3097 Hz / s respectively; the lowest frequencies are 49.48 Hz and 49.51 Hz respectively; the steady-state frequency deviations are -0.21 Hz and -0.19 Hz respectively. It can be seen that this strategy meets the frequency regulation requirements, while under traditional comprehensive inertia control, the fixed frequency regulation tasks are assigned to the wind-solar-storage system, and the lowest frequency point and the steady-state deviation do not meet the constraint index conditions. According to Figure 6 as shown in (b) of Figure 6 and (c) of Figure 6 as shown in (d) of Figure 6 and (e) of

[0166] Under this method, all the spare power is increased by the photovoltaic system, and the wind turbine also outputs power according to the disturbance size to meet the frequency regulation requirements. For the fixed comprehensive inertia control coefficient frequency regulation method of the wind-solar-storage system, since the control coefficient is fixed and cannot be adjusted according to the disturbance size, the active power outputs of the photovoltaic and wind turbine are not sufficient to meet the frequency regulation requirements. Moreover Figure 7 as shown in

[0167] Under the method with a fixed control coefficient, not only the energy storage output is controlled at 0.5 p.u., but also the wind turbine speed drops more, indicating that the wind turbine releases more rotor kinetic energy than this strategy, resulting in waste of resources. This strategy takes into account both the frequency regulation effect and the reasonable utilization of resources. Figure 7 Figure 7 as shown in (c) of Figure 7 and (d) of Figure 7 In this method, the photovoltaic and wind power output to the limit to participate in frequency regulation, and at the same time the energy storage adjusts its output according to the disturbance size and the state of charge to expand the stability region. As shown in (a) of Figure 7In (b) and Figure 7 The active power output of the photovoltaic and wind turbines shown in (c) is not sufficient to meet the frequency regulation requirements. Under this strategy, as Figure 7 shown in (e), the rotor speed of the wind turbine drops to the minimum speed limit of 0.7 p.u., fully releasing the rotor kinetic energy to achieve maximum utilization. As Figure 7 in (d) and Figure 7 in (f), the energy storage output under fixed integrated inertia control is 0.05 p.u. more than that of this strategy, and the SOC drops faster; moreover, the output does not consider the influence of the state of charge, which is not conducive to the service life of the energy storage.

[0168] In the embodiment of the present invention, by dividing the disturbance boundaries when the photovoltaic, wind power, and energy storage participate in frequency regulation in sequence based on the frequency safety index constraints of the system, corresponding control strategies are designed for different disturbance intervals, and the active power of the wind power, photovoltaic, and energy storage in the hybrid substation is accurately controlled according to the requirements of the frequency safety index, more reliably meeting the frequency regulation requirements; the photovoltaic power generation unit has fast regulation characteristics, and when the disturbance is too small, it controls the photovoltaic to participate in frequency regulation first, and can quickly perform frequency response, ensuring the frequency regulation effect; as the disturbance increases, the wind turbine and the battery energy storage unit are called in sequence to participate in frequency regulation. It solves the technical problems that there is still a lack of basis for tuning the controller parameters in the coordinated control of new energy, the frequency regulation advantages of various new energy sources have not been fully developed, and it is too dependent on the response of energy storage, and realizes the beneficial effect of demonstrating the economy of the reasonable utilization of wind power, photovoltaic, and energy storage on the premise of meeting the frequency regulation requirements.

[0169] Embodiment 2

[0170] The present invention also provides a coordinated frequency control system for wind power, photovoltaic, and energy storage based on frequency index constraints, including: a memory and a processor, the memory stores a computer program, and when the processor executes the computer program, it executes the method provided in any one of the first embodiments.

[0171] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A coordinated frequency control method for wind-solar-storage based on frequency index constraints, which is applied to a grid-connected system of a wind-solar-storage hybrid substation. The grid-connected system of the wind-solar-storage hybrid substation includes wind turbines, battery energy storage units, an AC power grid, and multiple parallel photovoltaic power generation units; the photovoltaic power generation units, wind turbines, and battery energy storage units are respectively aggregated to the same AC bus through their respective converters and transformers and connected to the AC power grid. It is characterized in that, The coordinated frequency control method of wind-solar-storage based on frequency index constraints includes: Performing load shedding control on the photovoltaic power generation unit to reserve standby power, and setting the maximum comprehensive inertia control coefficient of the wind turbine according to the wind speed at which the wind turbine is located; Taking the preset system frequency safety index as the first constraint, calculate the disturbance boundary ΔP for starting the frequency modulation of the photovoltaic power generation unit respectively LG and the disturbance boundary ΔP for starting the frequency modulation of the wind turbine LPV ; Taking the maximum comprehensive inertia control coefficient of the wind turbine as the second constraint, based on the first constraint and the second constraint, calculate the disturbance boundary ΔP for starting the frequency modulation of the battery energy storage unit LW ; Monitor the rate of change of frequency of the grid-connected system of the wind-solar-storage hybrid substation to obtain the disturbance value ΔP suffered by the system L , and according to the comparison result of the disturbance value ΔP L with each disturbance boundary, execute the corresponding frequency regulation strategy: If the disturbance value ΔP L belongs to ΔP LG <ΔP L ≤ΔP LPV interval, then calculate the additional power generation power of the photovoltaic power generation unit based on the preset system frequency safety index to meet the frequency modulation demand; If the disturbance value ΔP L belongs to ΔP LPV <ΔP L ≤ΔP LW interval, the photovoltaic power generation unit outputs power to the limit, calculates the active power of the wind turbine based on the preset system frequency safety index, and changes its comprehensive inertia control coefficient based on the calculated active power to meet the frequency regulation demand; If the disturbance value ΔP L belongs to ΔP L >ΔP LW interval, both the photovoltaic power generation unit and the wind turbine unit output power to the maximum limit, and the active power output of the battery energy storage unit for frequency modulation is controlled according to the state of charge to meet the frequency modulation requirements.

2. The method according to claim 1, wherein The step of performing load shedding control on the photovoltaic power generation unit to reserve standby power and setting the maximum comprehensive inertia control coefficient of the wind turbine according to the wind speed at which the wind turbine is located includes: Set the initial load shedding rate σ0 of the photovoltaic power generation unit, and use the reserve power corresponding to the initial load shedding rate σ0 for disturbance frequency modulation control; the reserve power ΔP PV =(1 - σ0)P MPPT ; Among them, P MPPT represents the power value when the photovoltaic power generation unit operates at the maximum power point, and the value range of σ0 is 5% to 22%; Obtaining the extreme value of the rotational speed of the wind turbine and the power increase limit of the wind turbine, respectively obtaining the change in rotational speed from the extreme value of the rotational speed and the power increase limit of the wind turbine, and determining the maximum change in rotational speed Δω of the wind turbine from the change in rotational speed; the calculation formula for the maximum change in rotational speed Δω is: Among them, ω r0 is the initial rotational speed of the wind turbine, ω rmax and ω rmin are the maximum and minimum rotational speeds specified for safe operation, P n represents the rated power of the wind turbine, k opt represents the maximum power tracking control coefficient, H w represents the inertia coefficient of the wind turbine, t h is the duration of the wind turbine frequency regulation; Setting the maximum comprehensive inertia control coefficient of the wind turbine according to the maximum change in rotational speed Δω; Among them Among them, k D is the sag coefficient, and k H is the virtual inertia coefficient; ROCOF and Δf max are the maximum frequency change rate and the maximum frequency drop amplitude corresponding to the system disturbance value of ΔP LPV ; k opt represents the maximum power tracking coefficient of the wind turbine; P ref (v, ω r0 ), P m (v, ω rmin ) represent the active power command values of the wind turbine at the initial speed ω r0 and the lowest speed ω rmin ; P MPPT (v, ω r0 ), P MPPT (v, ω rmin ) represent the power values of the maximum power operating point of the wind turbine at the initial speed moment and the lowest speed moment; t n represents the time when the frequency reaches the extreme point; ΔE k represents the change in the kinetic energy of the wind turbine rotor; P m (v, ω r ) represents the mechanical power of the wind turbine.

3. The method according to claim 2, wherein Taking the preset system frequency security index as the first constraint, respectively calculate the disturbance boundary ΔP for starting the frequency modulation of the photovoltaic power generation unit LG and the disturbance boundary ΔP for starting the frequency modulation of the wind turbine generator set LPV ; Taking the maximum comprehensive inertia control coefficient of the wind turbine generator set as the second constraint, based on the first constraint and the second constraint, calculate the disturbance boundary ΔP for starting the frequency modulation of the battery energy storage unit LW , including: Obtain the equivalent inertia coefficient and damping coefficient of the grid-connected system of the wind-solar-storage hybrid substation, and determine the preset system frequency safety index; based on the preset system frequency safety index, use the theoretical formula of the SFR model to calculate the disturbance values corresponding to each safety index, and take the minimum value as the disturbance boundary ΔP for starting photovoltaic frequency modulation LG ; where the preset system frequency safety index includes: the rate of change of frequency does not exceed -0.5 Hz / s, the maximum frequency deviation does not exceed -0.5 Hz, and the steady-state frequency deviation does not exceed -0.2 Hz; Among them, R represents the governor setting droop coefficient, H eq represents the system equivalent inertia coefficient, D eq represents the system equivalent damping coefficient, takes the limit value of -0.5Hz / s, Δf max takes the limit value of -0.5Hz, Δf ss takes the limit value of -0.2Hz, ΔP L1 、ΔP L2 、ΔP L3 respectively represent the initial change rate of frequency, the maximum deviation of frequency, and the disturbance boundary when the steady-state deviation of frequency takes the limit value, ξ represents the damping ratio, ω n represents the natural oscillation angular velocity, ω d represents the damped angular velocity, F H represents the work ratio of the high-pressure cylinder of the prime mover, T R represents the reheat time constant; The disturbance boundary value ΔP at the limit output of the photovoltaic power generation unit is calculated using the theoretical formula of the SFR model LPV ; According to the set maximum comprehensive inertia control coefficient of the wind turbine, the theoretical formula of the SFR model is used to calculate the disturbance boundary value ΔP when the wind turbine maximally utilizes the rotor kinetic energy LW ; Among them, H′ eq represents the system equivalent inertia coefficient after adding the fan comprehensive inertia control; D′ eq represents the system equivalent damping coefficient after adding the fan comprehensive inertia control; t' n represents the frequency extreme value time after adding the fan; H G represents the synchronous machine inertia constant; S sys represents the total system capacity; S w represents the wind turbine capacity; S G represents the synchronous machine capacity.

4. The method according to claim 1, wherein The disturbance value ΔP L is calculated by the following formula: Among them, H eq is the inertia constant of the grid-connected system of the hybrid wind-solar-storage substation, and f represents the grid frequency.

5. The method according to claim 2, wherein The disturbance value ΔP L belonging to ΔP LG <ΔP L ≤ΔP LPV interval, the additional power of the photovoltaic power generation unit is calculated based on the preset system frequency safety index to meet the frequency regulation demand, including: Calculate the additional power P of the reserve power of the photovoltaic power generation unit based on the preset system frequency security index PV : Among them, Take the limit value of -0.5 Hz / s, Δf max Take the limit value of -0.5 Hz, Δf ss Take the limit value of -0.2 Hz; According to the additional power P of the reserve power obtained by calculation PV adjust the DC capacitor side voltage U of the photovoltaic power generation unit PV to meet the frequency regulation requirements.

6. The method according to claim 3, wherein The disturbance value ΔP L belongs to ΔP LPV <ΔP L ≤ΔP LW interval, the photovoltaic power generation unit outputs power to the limit, calculates the active power of the wind turbine based on the preset system frequency safety index, and changes its comprehensive inertia control coefficient based on the calculated active power to meet the frequency regulation requirements, including: Based on the frequency security index constraint, adjust the active power of the wind turbine according to the disturbance to calculate the active power P of the wind turbine W : Among them, Δf max takes the maximum frequency deviation limit value of -0.5 Hz; f0 represents the grid standard frequency, and its value is 50 Hz; Design coefficient K according to index H c1 , so that the virtual inertia coefficient k' H = K c1 k H decreases as the absolute value of the frequency change rate decreases, and the virtual inertia coefficient is equal to 0 to exit frequency modulation until the frequency change rate is 0; Among them, H represents the ratio of the initial moment frequency change rate before the fan participates in frequency modulation to the real-time frequency change rate after participating in frequency modulation, and the minimum value of H min ranges from 1 to 2, the smaller value H0 ranges from 5 to 8, and the relatively small value H low ranges from 10 to 20; n represents the function curve adaptive factor, and its value range is from 10 to 20; When the rotational speed of the wind turbine reaches the lowest point, resume the normal operation state of tracking the maximum power; Among them, ω r represents the rotational speed of the wind turbine, and t off represents the moment when the wind turbine exits frequency regulation; P ref (t off ) represents the active power command value at the moment when the fan starts to exit frequency regulation; Δt represents the duration of the wind turbine exiting frequency regulation; P MPPT represents the power value of the fan operating at the maximum power point tracking; P ref represents the active power reference value of the wind turbine.

7. The method according to claim 5, wherein The said disturbance value ΔP L belongs to ΔP L >ΔP LW interval. Both the photovoltaic power generation unit and the fan unit output power to the maximum limit. On the premise of ensuring that the state of charge is within the normal range of 0.1 to 0.9, control the active power output of the battery energy storage unit for frequency modulation to meet the frequency modulation requirements, including: According to the disturbance value ΔP L and the disturbance boundary ΔP LW for starting the energy storage frequency regulation, adjust the output of the battery energy storage unit to participate in frequency regulation; Among them, P En represents the rated power of the energy storage battery, which is set to 10% - 20% of the rated power of the fan; K c and K d represent the charging and discharging frequency modulation demand coefficients for the energy storage to participate in frequency modulation; P Esd and P Esc represent the charging and discharging power of the energy storage to participate in frequency modulation; When the battery energy storage unit performs frequency regulation output, the charge-discharge frequency regulation demand coefficient K is adjusted according to the state of charge. c and K d to control the active power output of the battery energy storage unit for frequency regulation to meet the frequency regulation demand. Among them, the minimum state of charge S min is taken as 0.1, the smaller value S0 is taken as 0.15, and the smaller value S low is taken as 0.25, the higher value S high is taken as 0.75, the higher value S1 is taken as 0.85, and the maximum value S max is taken as 0.9; K max represents the maximum unit regulation power of frequency modulation and takes a value of 1.

8. The method according to claim 7, wherein It further includes: After the system frequency resumes stability, restoring the battery energy storage unit with a state of charge in the overcharge or over-discharge area to the normal working range according to the restoration demand coefficient and the restoration constraint coefficient; When the frequency deviation exceeds ±0.002 Hz, stop the restoration of the state of charge of the battery energy storage unit; Among them, K c1 and K d1 are the charging coefficient and discharging coefficient of the recovery demand corresponding to the state of charge of the battery energy storage unit itself; Among them, K c2 and K d2 are the recovery constraint coefficients during the charging and discharging processes on the premise of ensuring the stability of the power grid frequency; the minimum value of the frequency deviation Δf min is taken as -0.002 Hz, the smaller value Δf0 is taken as -0.0015 Hz, the smaller value Δf low is taken as -0.001 Hz, the higher value Δf high is taken as 0.001 Hz, the higher value Δf1 is taken as 0.0015 Hz, and the maximum value Δf max is taken as 0.002 Hz.

9. The method according to claim 8, wherein Obtain the smaller value of the recovery demand coefficient and the recovery constraint coefficient as the battery energy storage unit state of charge recovery coefficient K re : Among them, ΔP ES represents the active power output when the state of charge of the battery energy storage unit is restored.

10. A wind-solar-storage coordinated frequency control system based on frequency index constraints, characterized in that, It includes: A memory and a processor, the memory stores a computer program, and when the processor executes the computer program, it executes the method provided in any one of claims 1-9.

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