Inertia compensation control method for wind farm based on frequency security constraint-inertia weakening allocation

Abstract

The wind farm inertia compensation control method based on frequency security constraint-inertia weakening allocation first solves the critical inertia of the power grid to maintain dynamic frequency stability according to the power grid frequency security constraint index. H min , and combined with the actual inertia of the power grid to obtain the target value of the power grid inertia compensation Δ H Then, the virtual inertia of wind farms is coordinated and allocated according to the idea of ​​inertia reduction responsibility sharing, and the virtual inertia target value of each wind farm / wind turbine is obtained. H wf , H equ ; Then dynamically set the control parameters according to the fan virtual inertia target K df , execute the virtual inertia compensation control strategy. The method proposed by the present invention enables the virtual inertia compensation targets of each wind farm to be distributed most fairly, and by executing the virtual inertia compensation control strategy of the wind farm, the safety and stability of the power grid frequency can be effectively guaranteed.

Description

Technical Field

[0001] The invention relates to the research field of frequency security of a power system containing multiple wind farms, and in particular to a wind farm inertia compensation control method based on frequency security constraint-inertia weakening sharing. Background Art

[0002] As new energy sources such as wind power are connected to the power grid on a larger scale and with a higher penetration rate, the proportion of new energy generation capacity in the power grid will increase significantly, which will seriously weaken the inertia of the power grid and reduce the inertia support capacity of the system. Large-scale wind power grid connection has led to the continuous weakening of the inertia of the power grid and the deterioration of the system frequency characteristics. Wind farms should assume the obligation to ensure the safety and stability of the power grid frequency based on the inertia reduction responsibility. At present, in order to address the problem of insufficient inertia support capacity of the power grid caused by large-scale wind power grid connection, virtual inertia control is mainly adopted to make the wind turbine have a virtual inertia similar to that of a synchronous generator. However, how to coordinate the virtual inertia distribution between wind turbines and perform inertia compensation control is an urgent problem to be solved.

[0003] The current research on virtual inertia allocation does not allocate virtual inertia fairly based on reasonable allocation basis, and does not study the impact of virtual inertia allocation on the overall inertia level of the power grid and the impact of this allocation method on the frequency stability of the system after a large disturbance from the perspective of the system. In the research on virtual inertia compensation control, each wind farm has not formulated an effective inertia compensation control strategy based on the allocated virtual inertia compensation target. Therefore, the invention of the wind farm inertia compensation control method based on frequency security constraint-inertia weakening sharing has important research significance. Summary of the invention

[0004] The present invention proposes a wind farm inertia compensation control method based on frequency safety constraint-inertia reduction sharing, wherein the critical inertia and the grid inertia are obtained according to the grid dispatching information and the system frequency safety constraint index, and then the inertia compensation target of each wind farm is allocated according to the ratio of the wind farm inertia reduction amount, and the virtual inertia compensation target of the wind turbines in the station is further obtained; finally, each wind turbine executes the inertia compensation control strategy according to the allocated virtual inertia compensation target, so that the grid inertia is always kept above the critical inertia, eliminating the hidden danger of system frequency safety.

[0005] The technical solution adopted by the present invention is:

[0006] The inertia compensation control method for a wind farm based on frequency security constraint-inertia weakening allocation includes the following steps:

[0007] Step 1: Calculate the grid inertia: Calculate the grid inertia H at each time period of the day based on the power generation plan and wind power forecast information. (1) ;

[0008] Step 2: Solve the critical inertia of the power grid based on the system frequency safety constraint: Solve the critical inertia H according to the maximum frequency deviation constraint and the maximum frequency change rate constraint. min ;

[0009] Step 3: Grid inertia compensation target: According to the inertia H and critical inertia H of each period min , screen the time period in a day that does not meet the critical inertia, and calculate the grid inertia compensation target ΔH within this time period;

[0010] Step 4: Wind farm virtual inertia allocation strategy: The grid inertia reduction caused by the grid connection of each wind farm is used as the basis for allocating the wind farm virtual inertia. min , and obtain the virtual inertia compensation target H of each wind farm wf and the virtual inertia compensation target value H of each fan equ ;

[0011] Step 5: Virtual inertia compensation control strategy: According to the virtual inertia compensation target value H of each fan equ,kj , by adjusting the control parameter K in real time df,kj , execute the virtual inertia compensation control strategy, and then respond to the virtual inertia compensation target H equ,kj , the entire wind farm can also respond to the compensation target H wfk , thereby compensating the grid inertia to the critical inertia.

[0012] In step 1, the grid inertia H of each time period is calculated. (1) :

[0013]

[0014] In formula (1), the wind farm has no virtual inertia control characteristics, H (1) is the equivalent inertia of the power grid; subscript 1 indicates that the wind farm is in the grid-connected state; H Gi , S Gi are the inertia and rated capacity of the i-th synchronous generator set respectively; S wfj is the rated capacity of the jth wind farm; m and n represent the number of synchronous generator sets and wind farms respectively.

[0015] In step 2, the critical inertia H min The solution is as follows:

[0016]

[0017] In formula (9), H Δf represents the critical inertia of the system under the maximum frequency deviation constraint, ΔP max is the power shortage; f B is the reference frequency; tmax-C is the time corresponding to the maximum frequency deviation safety value; Δf max-C It is the maximum frequency deviation safety value.

[0018]

[0019] In formula (12), H RoCoF represents the critical inertia of the system under the maximum frequency change rate constraint, S b is the system capacity, f0 is the system initial frequency, RoCoF max-C It is the maximum frequency change rate safety value.

[0020] In summary, the critical inertia of the power grid takes the larger value of the two, that is:

[0021]

[0022] In step 3, during the period when the system inertia does not meet the critical inertia, the grid inertia compensation target ΔH is:

[0023]

[0024] In formula (16), H wfj represents the equivalent virtual inertia of the j-th wind farm.

[0025] In step 4, the virtual inertia compensation target value H of each wind turbine in the wind farm k is equ for:

[0026]

[0027] In formula (25), ΔH wfk represents the reduction in grid inertia caused by the grid connection of wind farm k; H equ,k1 , H equ,k2 ...H equ,kL is the virtual inertia compensation target of unit 1, unit 2...unit L in wind farm k; H wfk represents the virtual inertia compensation target of wind farm k.

[0028] In step 5, by adjusting the control parameter K in real time df,kj , execute the virtual inertia compensation control strategy, and then respond to the virtual inertia compensation target H equ,kj :

[0029]

[0030] In formula (32), K df,kj is the fan inertia control parameter; ω r0 Expressed as the initial angular velocity of the rotor; ω s0 Expressed as the initial angular velocity of the system; ωnom is the rated angular frequency of the fan; T f is the filtering time constant of the virtual inertial controller; Δ=(K pT / 2H DFIG ) 2 -2K iT / H DFIG For equation s 2 +K pT / (2H DFIG )s+K iT / (2H DFIG )’s discriminant;

[0031] When α1, α2, α3 are Δ≥0 (s+1 / T f )(s 2 +K pT / (2H DFIG )s+K iT / (2H DFIG )) = 0 when the three simple roots;

[0032] K1, K2, K3 are the expansion coefficients of the corresponding partial fractions;

[0033] α1', α2'±jβ are respectively f )(s 2 +K pT / (2H DFIG )s+K iT / (2H DFIG A simple root and a pair of conjugate complex roots when ))=0, θ=∠K2', K1' and K2' are the expansion coefficients of the corresponding partial fractions.

[0034] In summary, when a large disturbance occurs in the system, in the inertial response stage, each wind turbine adjusts the control parameter K in real time according to the relationship between the real-time wind speed of the wind farm and the wind turbine inertia compensation target and the virtual inertial control gain. df,kj , which can respond to the virtual inertia compensation target H equ,kj , so that the virtual inertia of the wind farm is maintained at a constant level.

[0035] The wind farm inertia compensation control method based on frequency safety constraint-inertia weakening and sharing of the present invention has the following technical effects:

[0036] 1) During the period when there are potential frequency safety hazards in the power grid, the method proposed in the present invention is applied to ensure that the virtual inertia compensation targets of each wind farm are distributed most fairly. By executing the virtual inertia compensation control strategy of the wind farm, the safety and stability of the power grid frequency can be effectively guaranteed.

[0037] 2) The virtual inertia coordination compensation control method proposed in the present invention can be extended to the situation where new energy sources such as photovoltaics are connected to the grid. In the process of building a new power system in the future, my country's new energy will be connected to the power grid on a larger scale. The method proposed in the present invention is an effective measure to deal with the safety and stability of the power grid frequency under this situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a flow chart of an embodiment of the present invention.

[0039] Figure 2 4 is a simulation system diagram of an embodiment of the present invention.

[0040] Figure 3 It is a curve diagram of grid inertia and critical inertia in each period of a day of the simulation system according to an embodiment of the present invention.

[0041] FIG4( a ) is a graph showing the actual virtual inertia curves of each wind farm in a certain period of time during a day in wind farm 1;

[0042] FIG4( b ) is a graph showing the actual virtual inertia curves of each wind farm in a certain period of time during one day in wind farm 2;

[0043] FIG4( c ) is a graph showing the actual virtual inertia curves of each wind farm in wind farm 3 during a certain period of time in one day.

[0044] Figure 5 It is a curve chart of the grid inertia compensation situation during a certain period of time in a day.

[0045] Figure 6 This is the grid frequency response curve under different wind power penetration rates.

[0046] Figure 7 This is the RoCoF curve of the power grid under different wind power penetration rates. DETAILED DESCRIPTION

[0047] A coordinated inertia compensation control method for multiple wind farms based on frequency security constraint-inertia weakening and sharing. First, the critical inertia H of the power grid that maintains the dynamic stability of the frequency is solved according to the power grid frequency security constraint index. min , and combined with the actual inertia of the power grid to obtain the target value of the power grid inertia compensation ΔH. Then, according to the idea of ​​inertia reduction responsibility sharing, the virtual inertia of the wind farm is coordinated and allocated to obtain the virtual inertia target value H of each wind farm / wind turbine wf , H equ ; Then dynamically set the control parameter K according to the virtual inertia target of the fan df , and execute the virtual inertia compensation control strategy; finally, the effectiveness and practicality of the proposed method are verified through the IEEE-39 node example system. Figure 1 As shown, the following steps are included:

[0048] Step 1: Calculation of grid inertia:

[0049] If the power grid contains m synchronous units and n wind farms, the equivalent inertia of the power grid is:

[0050]

[0051] In formula (1), the wind farm has no virtual inertia control characteristics, H (1) is the equivalent inertia of the power grid, and the subscript 1 indicates that the wind farm is in the grid-connected state; H Gi , S Gi are the inertia and rated capacity of the i-th synchronous generator set respectively; S wfj is the rated capacity of the jth wind farm.

[0052] Step 2: Solve the critical inertia calculation of the power grid based on the system frequency security constraint:

[0053] The frequency response characteristics of a power system containing multiple synchronous units can be represented by an average system frequency response model, and the first-order inertia link is used to approximately describe the response process of the speed control system model of each synchronous unit.

[0054] The primary frequency regulation mechanical power increment of the synchronous unit can be expressed as:

[0055]

[0056] In formula (2), ΔP mi K is the primary frequency regulation mechanical power increment of the i-th synchronous unit; i is the generator power-frequency characteristic coefficient; T i is the speed regulator response time constant; Δω is the system angular frequency deviation; s is the frequency domain operator.

[0057] In the short time after the system disturbance occurs, the frequency change is small, and the equivalent unit damping D can be ignored; at the same time, considering that the primary frequency modulation response has not occurred when the speed control system mechanical device is in action, ΔP mi =0, the system frequency response expression can be obtained:

[0058]

[0059] In formula (3), H represents the system equivalent inertia; ΔP L is the total load power increment.

[0060] The maximum frequency deviation of the system usually occurs 3 to 5 seconds after the disturbance occurs, at which time the primary frequency modulation response begins to work. Therefore, to simplify the solution, the frequency deviation Δω calculated by formula (3) before the maximum frequency deviation occurs can be used as the calculation ΔP m Input.

[0061] Substituting equation (3) into equation (2) and performing a pull-type inverse transformation, the mechanical power increment of the synchronous unit can be expressed as:

[0062]

[0063] In formula (4), The solution can be simplified by approximating the mechanical power increment of the synchronous unit with a linear function with a constant coefficient.

[0064] From the above analysis, the dynamic frequency equation of the entire system after the disturbance occurs is:

[0065]

[0066] In formula (5), m is the number of synchronous units.

[0067] After integrating and sorting out formula (5), we can get:

[0068]

[0069] Derivative (6) is given by The time corresponding to the maximum frequency deviation of the system can be obtained:

[0070]

[0071] Substituting equation (7) into equation (6) yields the maximum frequency deviation of the system, which is then converted into the nominal value of the system frequency:

[0072]

[0073] In formula (8): f B is the reference frequency.

[0074] In the above derivation process, the power shortage and the maximum frequency deviation are known quantities, and ΔP is taken as L =ΔP max , Δf max =Δf max-C , Δf max-C is the maximum frequency deviation safety value; in addition, the time corresponding to the maximum frequency deviation of the system can be calculated using the MATLAB solver, taking t max =t max-C , t max-C is the time corresponding to the maximum frequency deviation safety value. Combining equations (7) and (8), we can get the critical inertia expression under the maximum frequency deviation constraint:

[0075]

[0076] According to the equivalent rotor motion equation of the power system, the system frequency change rate expression can be obtained as follows:

[0077]

[0078] In formula (10), time 0 is the time when the frequency disturbance occurs.

[0079] SystemRoCoF max It appears at the instant after the disturbance occurs (t0), at which time the equivalent damping coefficient and mechanical power increment can be ignored. RoCoF can be obtained from formula (10): max is equivalent to:

[0080]

[0081] In formula (11), S b is the system capacity, and f0 is the initial frequency of the system.

[0082] To solve the critical inertia, take RoCoF max =RoCoF max-C , ΔP L =ΔP max ,RoCoF max-C is the maximum frequency change rate safety value. According to formula (11), the critical inertia expression under the maximum frequency change rate constraint is obtained:

[0083]

[0084] In summary, the critical inertia of the power grid should be the larger value of equation (9) and equation (12), that is:

[0085]

[0086] Step 3: Calculation of grid inertia compensation target:

[0087] If the power grid contains m synchronous units and n wind farms with virtual inertia control, the equivalent inertia of the power grid is H' (1) for:

[0088]

[0089] In formula (14), H wfj is the equivalent virtual inertia of the j-th wind farm.

[0090] To ensure the stability of system frequency, the actual inertia of the power grid should not be less than the critical inertia:

[0091]

[0092] According to formula (15), considering the situation that the grid inertia is just compensated to the critical inertia, the inertia that needs to be compensated for the grid is:

[0093]

[0094] According to formula (16), in order to compensate the grid inertia to the critical inertia, the total inertia that all wind farms need to compensate for the grid is the target value ΔH.

[0095] Step 4: Wind farm virtual inertia allocation strategy:

[0096] For any wind farm k, in both the grid-connected and off-grid states, the grid inertia can be expressed as:

[0097]

[0098]

[0099] In the formula, H (1)k , H (0)k are the grid inertias when wind farm k is connected to the grid and off the grid, respectively. The subscripts 1 and 0 represent the grid-connected and off-grid states of the wind farm, respectively.

[0100] The reduction in grid inertia caused by the grid connection of wind farm k can be calculated by H (0)k With H (1)k The difference is determined by:

[0101]

[0102] In formula (19), ΔH wfk is the reduction in grid inertia caused by the grid connection of wind farm k.

[0103] Based on the idea of ​​sharing the responsibility for grid inertia reduction, this paper uses the grid inertia reduction caused by the grid connection of each wind farm as the basis for allocating the virtual inertia of the wind farm. According to this allocation idea, the relationship between the virtual inertia compensation target of each wind farm and the corresponding inertia reduction can be obtained as follows:

[0104]

[0105] In formula (20), H wf1 ,H wf2 ,...,H wfn is the virtual inertia compensation target of wind farm 1, wind farm 2, ..., wind farm n, indicating the distribution of virtual inertia of each wind farm.

[0106] Combining equations (16) and (20), we have:

[0107]

[0108] From equation group (21), the virtual inertia compensation target of the k-th wind farm in the system can be obtained as:

[0109]

[0110] For any wind farm k in the system, it is assumed that there are L wind turbines in the farm. From formula (19), it can be seen that the inertia reduction caused by the grid connection of any wind farm in the system is only related to the rated capacity of the wind farm. By analogy to the situation of wind turbines, it can be seen that each wind turbine in wind farm k should be assigned the same virtual inertia compensation target:

[0111] H equ,k1 =H equ,k2 =…=H equ,kL (twenty three)

[0112] In formula (23), H equ,k1 , H equ,k2 ...H equ,kL is the virtual inertia compensation target of unit 1, unit 2, ..., unit L in wind farm k.

[0113] If the wind farm k is equivalent to a unit, the virtual inertia of the wind farm is equal to the ratio of the total kinetic energy stored in the wind farm to the total capacity:

[0114]

[0115] In formula (24), P, S N , J equ ,ω s0 are the pole pair number, rated capacity, virtual moment of inertia, and initial synchronous angular velocity of the system of the fan.

[0116] According to equations (23) and (24), it can be obtained that the virtual inertia compensation target of each wind turbine in wind farm k is equal to the compensation target of the wind farm:

[0117]

[0118] Step 5: Wind farm virtual inertia compensation control strategy:

[0119] From the published patent document “A method for calculating the equivalent virtual inertia time constant of a doubly-fed wind turbine” (application number: 201510201589.6, application date: 2015-04-24), it can be known that the virtual inertia of the wind turbine is:

[0120]

[0121] In formula (26), J DFIG ,ω r0 , Δω r They are respectively represented as the inherent moment of inertia of the doubly fed wind turbine, the initial angular velocity of the rotor and the increment of the angular velocity of the rotor; Δω s Represents the system synchronization angular frequency increment; ω nom is the rated angular frequency of the fan; H DFIG =ω 2 nomJ DFIG / (2P 2 S N ) is the inherent inertia time constant of the fan.

[0122] Combining formula (26) and references, we can get H equ The transfer function is:

[0123]

[0124] In formula (27), K df , T f , K pT , K iT They are the filter time constant of the virtual inertia controller, the inertia control gain, the proportional coefficient and the integral coefficient of the speed controller respectively.

[0125] Performing an inverse Laplace transform on equation (27), we can obtain H equ The time domain expression is:

[0126]

[0127] From formula (28), we can know that the determination of H equ The parameter of (t) is the control gain K df and the initial angular frequency of the fan rotor ω r0 Therefore, in the inertial response stage, each wind turbine can respond according to the real-time wind speed and the corresponding angular frequency ω r0 , by setting K df The size of the fan's virtual inertia is controlled to H equ .

[0128] To simulate the virtual inertia H corresponding to equation (25): equ,kj When executing the virtual inertia control of the fan, the compensation target H assigned to each fan should be equ,kj Conversely determine the corresponding control parameter K df,kj Then, by transforming equation (28), we can obtain the control gain K of the jth wind turbine in any wind farm k: df,kj expression:

[0129]

[0130] From equation (29), we know that equation s 2 +K pT / (2H DFIG )s+K iT / (2H DFIG )'s discriminant Δ=(K pT / 2H DFIG ) 2 -2K iT / HDFIG , the following discussion is divided into two cases according to the positive or negative value of Δ.

[0131] 1) When Δ≥0,

[0132]

[0133] In formula (30), α1, α2, α3 are three simple roots, and K1, K2, K3 are the expansion coefficients of the partial fraction of formula (29).

[0134] 2) When Δ≤0,

[0135]

[0136] In formula (31), α1~, α2′±jβ are a simple root and a pair of conjugate complex roots respectively; θ = ∠K2′; K1′ and K2′ are the expansion coefficients of the partial fraction of formula (29).

[0137] According to equations (30) and (31), the control parameter K can be obtained df，kj The expression is:

[0138]

[0139] In summary, when a large disturbance occurs in the system, in the inertial response stage, each wind turbine adjusts the control parameter K in real time according to the relationship between the real-time wind speed of the wind farm and the wind turbine inertia compensation target and the virtual inertial control gain. df，kj , which can respond to the virtual inertia compensation target H equ，kj , so that the virtual inertia of the wind farm is maintained at a constant level.

[0140] Step 6: The above-established wind farm inertia compensation control method based on frequency security constraint-inertia weakening allocation is verified through simulation examples.

[0141] In the Matlab / simulink environment, we established Figure 2 The simulation system adds renewable energy generation, namely wind farms, to the 10 machines and 39 nodes in New England. The entire simulation system includes 10 synchronous generators and 3 wind farms.

[0142] The simulation parameters are as follows: Doubly fed wind turbine parameters: Rated voltage V n =575V, rated power P n =1.5MW, stator resistance R s =0.023pu, stator inductance L s =0.18pu, rotor resistance R r =0.016pu, rotor inductance L r =0.16pu, excitation inductance L m=2.9pu, inherent inertia time constant H DFIG =5.29s, speed controller integral coefficient K i =0.6. Rated angular velocity ω nom =157.08rad / s, rated wind speed V wN =11.7m / s, converter time constant τ =0.02s. Generator parameters are shown in Table 1.

[0143] Table 1 Generator parameters

[0144] dynamo H / s K T / s G1 6.7 16.67 8 G2 5.2 14.28 6 G3 4.8 16.67 7 G4 5.2 16.67 6 G5 4.5 14.28 6 G6 5.4 16.67 8 G7 5.4 16.67 7 G8 4.2 16.67 7 G9 5.4 16.67 6 G10 4.2 14.28 6

[0145] The simulation projects include:

[0146] 1): According to the power generation plan and wind farm power generation forecast information, the grid inertia value is calculated for each period of the day, and the critical value of the grid inertia is obtained under the maximum power shortage and the maximum RoCoF. Figure 3 verify.

[0147] 2): Compare the grid inertia of each time period with the critical value of grid inertia, select the time period that does not meet the critical grid inertia, and calculate the grid inertia compensation target. According to the compensation target, coordinate the virtual inertia of each wind farm to obtain the actual virtual inertia of each wind farm and the actual inertia of the grid after compensation. Figure 5 verify.

[0148] 3): Compare the effects of compensation control under different wind power penetration rates, and obtain the system frequency response curve and RoCoF curve of wind farm with virtual inertia compensation (wind power penetration rate 20%), with virtual inertia compensation (wind power penetration rate 30%), and without virtual inertia compensation. Figure 6 , Figure 7 verify.

[0149] Depend on Figure 4(a) to Figure 4(c) It can be seen that the grid inertia and critical inertia in different time periods are calculated by applying the predicted power generation value of the wind farm and the changes in the units in each time period. The grid inertia in the time periods of 0:00-3:00, 6:00-8:00, 18:00-23:00 is less than the critical inertia, and the inertia support capacity of the grid is poor.

[0150] Depend on Figure 4(a) to Figure 4(c) , Figure 5It can be seen that the actual virtual inertia of each wind farm is basically consistent with its target value, the maximum deviation is controlled within 2%, and the virtual inertia of the wind farm is stable within the target range. After compensation, the grid inertia quickly increased from 3.89s before the disturbance to 4.81s, and finally stabilized near the critical inertia (4.95s), the maximum deviation was controlled within 1%, and the system had sufficient inertia support capacity under frequency accidents.

[0151] from Figure 6 , Figure 7 It can be seen that by fairly allocating the inertia support capacity of each wind farm and implementing the virtual inertia compensation control strategy, the grid inertia is compensated to the critical inertia, so that the frequency drop to the lowest point (49.06Hz) is limited to within the 49Hz safety threshold, and RoCoF max It is just limited to the safety threshold of -0.5Hz / s. In addition, the frequency response curve and RoCoF curve corresponding to the two wind power penetration levels are close, and both can accurately compensate for the grid inertia and have a good control effect, thus ensuring the safe and stable operation of the grid.

Claims

1. A wind farm inertia compensation control method based on frequency security constraint-inertia weakening allocation is characterized by: The following steps are involved: Step 1: Calculate the grid inertia H at each time period of the day based on the power generation plan and wind power forecast information (1) ; Step 2: Solve the critical inertia H according to the maximum frequency deviation constraint and the maximum frequency change rate constraint min ; Step 3: According to the inertia H and critical inertia H of each period min , screen the time period in a day that does not meet the critical inertia, and calculate the grid inertia compensation target ΔH within this time period; Step 4: The grid inertia reduction caused by the grid connection of each wind farm is used as the basis for allocating the virtual inertia of the wind farm. min , and obtain the virtual inertia compensation target H of each wind farm wf and the virtual inertia compensation target value H of each fan equ ; Step 5: Compensate the virtual inertia target value H of each fan according to the obtained value equ,kj , by adjusting the control parameter K in real time df,kj , execute the wind farm virtual inertia compensation control strategy, and then respond to the virtual inertia compensation target H equ,kj ; The wind farm virtual inertia compensation control strategy is as follows: The virtual inertia of the fan is: In formula (26), J DFIG ,ω r0 , Δω r They are respectively represented as the inherent moment of inertia of the doubly fed wind turbine, the initial angular velocity of the rotor and the increment of the angular velocity of the rotor; Δω s Represents the system synchronization angular frequency increment; ω nom is the rated angular frequency of the fan; H DFIG =ω 2 nom J DFIG / (2P 2 S N ) is the inherent inertia time constant of the fan; Combining formula (26), we can get H equ The transfer function is: In formula (27), K df , T f , K pT , K iT They are the filter time constant, inertia control gain, proportional coefficient and integral coefficient of the virtual inertia controller respectively; Performing an inverse Laplace transform on equation (27), we can obtain H equ The time domain expression is: From formula (28), we can know that the determination of H equ The parameter of (t) is the control gain K df and the initial angular frequency of the fan rotor ω r0 Therefore, in the inertial response stage, each wind turbine can respond according to the real-time wind speed and the corresponding angular frequency ω r0 , by setting K df The size of the fan's virtual inertia is controlled to H equ ; To simulate the virtual inertia H corresponding to equation (25): equ,kj When executing the virtual inertia control of the fan, the compensation target H assigned to each fan should be equ,kj Conversely determine the corresponding control parameter K df,kj Then, by transforming equation (28), we can obtain the control gain K of the jth wind turbine in any wind farm k: df,kj expression: From equation (29), we know that equation s 2 +K pT / (2H DFIG )s+K iT / (2H DFIG )'s discriminant Δ=(K pT / 2H DFIG ) 2 -2K iT / H DFIG , the following two cases are discussed according to the positive and negative value of Δ: 1) When Δ≥0: In formula (30), α1, α2, α3 are three simple roots, K1, K2, K3 are the expansion coefficients of the partial fraction of formula (29); 2) When Δ≤0: In formula (31), α1', α2'±jβ are a simple root and a pair of conjugate complex roots respectively; θ = ∠K2'; K1' and K2' are the expansion coefficients of the partial fractions of formula (29); According to equations (30) and (31), the control parameter K can be obtained df,kj The expression is: In summary, when a large disturbance occurs in the system, in the inertial response stage, each wind turbine adjusts the control parameter K in real time according to the relationship between the real-time wind speed of the wind farm and the wind turbine inertia compensation target and the virtual inertial control gain. df,kj , which can respond to the virtual inertia compensation target H equ,kj , so that the virtual inertia of the wind farm is maintained at a constant level.

2. The wind farm inertia compensation control method based on frequency security constraint-inertia weakening and sharing according to claim 1 is characterized by: In step 1, the grid inertia H of each time period is calculated. (1) : In formula (1), the wind farm has no virtual inertia control characteristics, H (1) is the equivalent inertia of the power grid; subscript 1 indicates that the wind farm is in the grid-connected state; H Gi , S Gi are the inertia and rated capacity of the i-th synchronous generator set respectively; S wfj is the rated capacity of the jth wind farm; m and n represent the number of synchronous generator sets and wind farms respectively.

3. The wind farm inertia compensation control method based on frequency safety constraint-inertia weakening and sharing according to claim 1 is characterized by: In step 2, the critical inertia H min The solution is as follows: In formula (9), H Δf represents the critical inertia of the system under the maximum frequency deviation constraint, ΔP max is the power shortage; f B is the reference frequency; t max-C is the time corresponding to the maximum frequency deviation safety value; Δf max-C is the maximum frequency deviation safety value; In formula (12), H RoCoF represents the critical inertia of the system under the maximum frequency change rate constraint, S b is the system capacity, f0 is the system initial frequency, RoCoF max-C is the maximum frequency change rate safety value; In summary, the critical inertia of the power grid takes the larger value of the two, that is:

4. The wind farm inertia compensation control method based on frequency security constraint-inertia weakening allocation according to claim 1 is characterized by: In step 3, during the period when the system inertia does not meet the critical inertia, the grid inertia compensation target ΔH is: In formula (16), H wfj represents the equivalent virtual inertia of the j-th wind farm.

5. The wind farm inertia compensation control method based on frequency security constraint-inertia weakening and sharing according to claim 1 is characterized by: In step 4, the virtual inertia compensation target value H of each wind turbine in the wind farm k is equ for: In formula (25), ΔH wfk represents the reduction in grid inertia caused by the grid connection of wind farm k; H equ,k1 , H equ,k2 ...H equ,kL is the virtual inertia compensation target of unit 1, unit 2...unit L in wind farm k; H wfk represents the virtual inertia compensation target of wind farm k.

6. The wind farm inertia compensation control method based on frequency security constraint-inertia weakening allocation according to claim 1 is characterized by: In step 5, by adjusting the control parameter K in real time df,kj , execute the virtual inertia compensation control strategy, and then respond to the virtual inertia compensation target H equ,kj : In formula (32), K df,kj is the fan inertia control parameter; ω r0 Expressed as the initial angular velocity of the rotor; ω s0 Expressed as the initial angular velocity of the system; ω nom is the rated angular frequency of the fan; T f is the filtering time constant of the virtual inertia controller; Δ=(K pT / 2H DFIG ) 2 -2K iT / H DFIG For equation s 2 +K pT / (2H DFIG )s+K iT / (2H DFIG )’s discriminant; When α1, α2, α3 are Δ≥0 (s+1 / T f )(s 2 +K pT / (2H DFIG )s+K iT / (2H DFIG )) = 0 when the three simple roots; K1, K2, K3 are the expansion coefficients of the corresponding partial fractions; α1', α2'±jβ are respectively f )(s 2 +K pT / (2H DFIG )s+K iT / (2H DFIG A simple root and a pair of conjugate complex roots when ))=0, θ=∠K2', K1' and K2' are the expansion coefficients of the corresponding partial fractions.

7. The wind farm inertia compensation control method based on frequency security constraint-inertia weakening and sharing according to claim 6 is characterized by: When a large disturbance occurs in the system, in the inertial response stage, each wind turbine adjusts the control parameter K in real time according to the relationship between the real-time wind speed of the wind farm and the wind turbine inertia compensation target and the virtual inertial control gain. df,kj , which can respond to the virtual inertia compensation target H equ,kj , so that the virtual inertia of the wind farm is maintained at a constant level.

Images