A wind power grid-connection impact damping suppression method based on branch and bound and knapsack optimization control

Abstract

A wind power grid impact damping suppression method based on branch and bound and knapsack optimization control can realize efficient and rapid suppression of wind power fluctuation. The device is characterized by combining the advantages of thyristor switched filter (TSF) and active power filter (APF), and developing active damping generator technology based on knapsack optimization control for wind power grid impact suppression. The developed ADG technology has the following advantages: ① It has the characteristics of TSF harmonic impact suppression, voltage mutation and high cost performance; ② It has the characteristics of APF output damping continuous adjustable and high precision; ③ Based on branch and bound, the wind power impact is classified as the reference of the maximum damping of ADG output, which effectively improves the rapidity and stability of ADG response; ④ The knapsack problem (UKP) is used to realize the optimal switching control of ADG, which meets the minimum cost and efficient wind power disturbance impact suppression.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of application of the combination of power electronics technology development and artificial intelligence algorithm, and relates to a wind power grid-connection impact damping suppression method based on branch and bound and knapsack optimization control. BACKGROUND

[0002] With the increase of the proportion of uncertain wind power into the grid, the following negative effects will be caused to the "double high" new power system: ① sensor sampling distortion; ② influence on the active and reactive power flow distribution of the power grid; ③ voltage and power instability. In order to effectively solve the above problems and reduce the suppression cost of wind power impact, it is urgent to solve the above problems from the optimization control level, and the difficulty lies in developing a high cost-effective damping control technology that takes into account voltage impact and current surge suppression, and highlights the combination of classical power electronic devices and emerging artificial intelligence methods.

[0003] The feature of the application is to develop an active damping generation technology with the best cost performance by referring to the classical knapsack problem idea, and the idea is as follows: ① the damping required to suppress wind power input power fluctuation is the maximum knapsack capacity, which is defined by branch and bound method; ② the combination of the output damping of each channel of the thyristor switched filter (TSF) and the output capacity of the active power filter (APF) is the item to be loaded into the knapsack; ③ the combination of TSF and APF is defined as the maximum damping that can be provided by the active damping generator (ADG). SUMMARY

[0004] The purpose of the application is to provide a wind power grid-connection impact damping suppression method based on branch and bound and knapsack optimization control, so as to achieve the purpose of quickly suppressing uncertain wind power grid-connection power impact. The feature of the application is to combine the classical APF and TSF to form an active damping generator. The developed ADG technology has the following advantages: ① it has the characteristics of harmonic suppression, voltage fluctuation regulation and high cost performance of TSF; ② it increases the good dynamic regulation characteristics of APF and improves the flexibility of damping suppression; ③ it classifies the load state based on branch and bound, reduces the possibility of parallel resonance between ADG and power grid to the lowest, and improves the rapidity of response; ④ it adopts the knapsack problem (UKP) control idea to obtain the optimal switching strategy of ADG, so that ADG can suppress wind power impact at the lowest cost.

[0005] To achieve the above purpose, the technical scheme adopted by the application is as follows:

[0006] A wind power grid impact damping suppression method based on branch and bound and knapsack optimization control, the method comprises the following steps:

[0007] Step one: collect the amplitude and frequency of the bus voltage of the wind power grid system, bus current, wind power surge current, capacity of transformer, short circuit ratio and equivalent impedance, and define the optimal suppression damping required by ADG;

[0008] Step two: establish a characteristic equation group that meets the dynamic characteristics of ADG damping, and calculate the equivalent reactance and equivalent inductance;

[0009] Step three: establish the mathematical relationship of the related modules in ADG, wherein the active power filter APF is defined as a controlled voltage source u apf dependent on the impact current i L caused by the wind power grid and the compensation current i c_apf flowing into the node from the APF node; classify the different current and voltage conditions of the APF output, which is represented as different damping outputs in the system, and determine the combination of damping to provide the basis for classification optimization;

[0010] Step four: eliminate the method to derive the system control model under the harmonic condition;

[0011] Step five: determine the corresponding relationship between the active damping gain K and the impact current i L and different wind power input power states, complete the classification definition; on the basis of the classification definition of this offline method, the compensation current i apf required by the APF to generate the reverse harmonic component is calculated online and quickly through the real-time measured impact current i L , and fast damping suppression is realized;

[0012] Step six: determine the target function of knapsack optimization, that is, the maximum damping output, and give the constraint equation according to the actual situation;

[0013] Step seven: perform knapsack optimization calculation based on the branch and bound method of wind power impact, and pre-calculate the voltage constraint relationship combined with the classification method to provide algorithm basis for optimal damping suppression;

[0014] Step eight: bring the voltage constraint as an integer bounding condition into the knapsack combination calculation, so as to solve the optimal ADG switch control scheme.

[0015] Further, by analyzing and processing the data sampled in step one, and using the processed data to obtain the required parameters of the ADG equivalent circuit in step two, the specific calculation is as follows:

[0016] Formula one:

[0017] Equation two:

[0018] Wherein, Z s is the equivalent reactance of the power grid in the model; U k is the short-circuit ratio of the transformer; u s is the amplitude of the bus voltage; S N is the capacity of the transformer; L s is the equivalent inductance of the power grid; R s is the equivalent impedance of the transformer, and ω is the angular frequency of the bus voltage;

[0019] Equation three: u apf = K c_apf

[0020] There are three filter channels (n 51 , n 52 , n7) for passive damping TSF, where n 51 , n 52 and n7 represent 5th, 5th, and 7th filter channels, respectively; there are 7 damping combinations, defined as combination f j = (L j , C j )(j = 51, 52, 7), where L j and C j are the inductance value and capacitance value of one filter channel, respectively, and f j represents one combination of one filter channel; the combination form f c in the specific case is represented as follows:

[0021] Equation four:

[0022] Considering the influence of APF on each combination, f apf is represented as one combination of the ADG path output, and there are a total of 8 damping combinations; corresponding to different working states of wind power access with different proportions, the following control classification is obtained, which is described as follows:

[0023] Equation five:

[0024] In order to suppress power or voltage surges, the above damping combinations are used to suppress voltage surges and load current surges in real time.

[0025] Further, in step four, in order to classify power surges with different proportions of wind power access, avoid the cancellation of the filtering effect caused by the same resonance frequency of the harmonics emitted by the APF in the ADG and the TSF, and cause overcurrent problems in the TSF, the Wu elimination method is used to derive the ADG system control model, set the harmonic frequency as n, and the frequency as f, then the harmonic circuit model iss = R s + jn2πfL s , the equivalent impedance Z k is expressed as follows:

[0026] Equation Six: Z tsf = 1.0 / (n 51 / Z 51 + n 52 / Z 52 + n 53 / Z 53 )

[0027] Equation Seven: Z j = j[n2πfL j - 1 / (n2πfC j )] (j = 51, 52, 7)

[0028] Equation Eight:

[0029] Equation Nine: Z k = R + jn2πfL

[0030] Equation Ten: i tsf = u k1 / Z tsf

[0031] wherein j represents the serial number of the channel, Z tsf is the equivalent impedance of all channels, Z j is the reactance of each filter channel of the TSF to the n-th harmonic, n j is the switching state of the TSF, Z k is the reactance of the equivalent branch of the TSF, u k1 is the voltage of the harmonic, i tsf is the equivalent current flowing into the TSF, and R and L are the equivalent resistance and equivalent inductance of the equivalent reactance.

[0032] Further, in step five, in view of the distortion and harmonic disturbance of the sampling voltage and sampling current caused by the high proportion of wind power into the grid, high proportion of power electronics and intelligent grid control strategy, an active filter APF in the ADG is used to generate a current that reverses and cancels the harmonic component, and the following expression is derived according to Kirchhoff's current law:

[0033] Equation Eleven: [u k1 - K(i L - i tsf + i apf )] / Z k = -i apf

[0034] Equation Twelve: -iapf = u k1 / Z s - i tsf + i L

[0035] Solving equations six through twelve, we get:

[0036] Equation thirteen: u k1 = [Z k Z s Z tsf / (KZ tsf + Z k Z s - Z k Z tsf + Z s Z tsf )]i L

[0037] Equation thirteen: u k1 = [Z k Z s Z tsf / (KZ tsf + Z k Z s - Z k Z tsf + Z s Z tsf )]i L

[0038] Equation fourteen: i apf = [(-KZ tsf - Z s Z tsf ) / (KZ tsf + Z k Z s - Z k Z tsf + Z s Z tsf )]i L

[0039] To avoid the generation of current oscillation, i.e., to avoid the case where i apf goes to infinity, the following damping control analysis is performed:

[0040] Equation fifteen: KZ tsf + Z k Z s - Z k Z tsf + Z s Z tsf ≠ 0

[0041] In addition, for the gain K, there are the following boundary conditions:

[0042] Equation sixteen: 0 < (Z k Z s -Z k Z tsf ) / (KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf )-1≤1

[0043] Equation seventeen: 0 < K ≤ 0.5 (Z k Z tsf -Z k Z s -2Z s Z tsf ) / Z tsf

[0044] As shown in equation seventeen, the constraint condition of gain K can be obtained, which effectively determines the value range of K; here, the active damping of ADG, Z k is called passive damping, which can be one-to-one mapped with the parameters of the related circuit; according to equations four to seventeen, it can be known that K can be determined through offline calculation, and i apf Thus, different wind power impact currents i L can also be quickly determined, that is, through offline classification of K, the speed of output damping of ADG is greatly accelerated, and the foundation for using knapsack optimization ADG to suppress power and voltage impact is laid.

[0045] Further, in step six, the optimization objective function and the constraint relationship are determined:

[0046] Since equation twelve can be modified under the fundamental condition:

[0047] When reactive power compensation is performed, the TSF part performs hierarchical compensation and undertakes the main compensation role, and the method of knapsack optimization is considered to determine the corresponding relationship:

[0048] Equation eighteen: -i apf =(u2-u s ) / Z s -i tsf +i L

[0049] u2 represents the fundamental voltage;

[0050] Equation eighteen highlights the fundamental analysis, and APF according to the wind power impact current i LThe magnitude of the reactive power compensation current for active damping is defined by the TSF current. By combining the previous equations, the magnitude of u2 can be solved. Since the TSF performs passive damping suppression through reactive power compensation, the reactive power capacity of the TSF for each channel is expressed as follows:

[0051] Formula 19:

[0052] Q c Q L The reactive power supplied to the capacitor and inductor, while U2 is the fundamental phase voltage, where i n Let be the nth harmonic current; considering the ±10% perturbation of the grid voltage, the reactive power compensation target undertaken by the passive damping part of ADG is:

[0053] Formula 20: J = max(n 51 Q 51 +n 52 Q 52 +n7Q7)

[0054] Formula 21: Q j =Q Cj -Q Lj

[0055] In the above formula, Q j Q represents the reactive power that each channel can provide. Cj Q Lj Let Q be the reactive power generated by the capacitor and the reactive power absorbed by the inductor in this channel, respectively. Equation 21 satisfies the calculation approach of the knapsack problem; define Q. 51 Q 52 Let Q7 be the items to be packed, J be the capacity of the pack, and Formula 5 be the combination of items to be packed. The constraints for this knapsack problem are summarized as follows:

[0056] Formula 22: n 51 Q 51 +n 52 Q 52 +n7Q7≤Q 1set

[0057] Formula 23: u1-u 1set ≤0

[0058] Among them, Q 1set For the maximum reactive power compensation of the system, since the passive damping part in the ADG device is a stepped compensation and cannot be continuously compensated, Formula 23 ensures that overcompensation will not occur, thus preventing voltage rise; u 1set U1 is the maximum voltage that the active power filter (APF) can withstand. U1 consists of two parts: the fundamental voltage division of the resonant branch and the voltage division of each harmonic voltage in the power grid on the resonant branch.

[0059] Further, in the step seven, the branch and bound method is applied to optimize the selection of the knapsack capacity; u1 is estimated, that is, u1 is u k1 and the sum of the fundamental voltage u2, wherein u2 and the fundamental current i apf2 According to the calculation, the following is obtained:

[0060] Formula twenty-four:

[0061] Formula twenty-five:

[0062] Formula twenty-six: u1 = u k1 + u2

[0063] According to the three formulas, the branch and bound method for this case is improved.

[0064] Further, in the step eight, formula twenty-six is combined with constraint formula twenty-three to form a real-time judgment condition, and the lower bound determination of formula twenty and formula twenty-one in the branch and bound algorithm process is additionally subjected to voltage judgment, if the voltage judgment condition is met, the lower bound is updated, otherwise the original lower bound is retained, so that the optimal solution meeting the two constraints is not excluded, and according to this method, the optimal switch control strategy for wind power impact suppression can be effectively obtained.

[0065] The beneficial effects of the present application relative to the prior art are:

[0066] (1) The uncertain wind power entering the grid is classified and analyzed according to the branch and bound method, forming a one-to-one mapping combination with the output damping combination of the active damper generator ADG, so as to improve the stability, precision and response speed of wind power impact suppression; the step of classifying the wind power entering the grid is taken as the reference basis for the capacity of the knapsack.

[0067] (2) The stepwise damping output by each channel of the TSF is combined with the continuous damping output by the APF, as the execution means of the active damper generator ADG for suppressing high-occupancy wind power fluctuation, and the compensation characteristics are not affected by the grid impedance perturbation.

[0068] (3) The Wu elimination method is used to establish a harmonic model, and the ADG is controlled by frequency, so as to avoid the problem that the APF in the ADG emits a harmonic with the same resonance frequency as the TSF, which cancels the filtering effect and causes the TSF to produce overcurrent.

[0069] (4) The corresponding relationship between the active damping gain K and the wind power impact current I L is derived, and the wind power impact current I LBranch and bound classification optimization is carried out, each load corresponds to an active damping gain K, which effectively increases the damping suppression effect of the active damping generator ADG on wind power fluctuation.

[0070] (5) The voltage estimation formula obtained by classification optimization is combined with the knapsack optimization of the branch and bound method, so that the active damping generator can perform optimal reactive power compensation without exceeding the compensation threshold and voltage limit, balancing the effect and safety of the device. BRIEF DESCRIPTION OF DRAWINGS

[0071] Figure 1 The topological structure diagram of the power system that needs to be compensated;

[0072] Figure 2 The equivalent circuit diagram of the active damping generator;

[0073] Figure 3 The system control model diagram under the action of harmonic current;

[0074] Figure 4 The algorithm implementation block diagram of classification optimization;

[0075] Figure 5 The algorithm implementation block diagram of knapsack optimization;

[0076] Figure 6 The branch tree diagram of the branch and bound method;

[0077] Figure 7 The current diagram of the 270kW DC motor under the condition of K=0.5 simulation;

[0078] Figure 8 The frequency spectrum diagram of the load current under the simulation condition;

[0079] Figure 9 The current compensation effect diagram of the active damping under the condition of K=0.5 and load current generation;

[0080] Figure 10 The voltage and current waveform diagram before compensation;

[0081] Figure 11 The compensated voltage diagram when the active damping generator is in action;

[0082] Figure 12 The speed diagram of ideal compensation. DETAILED DESCRIPTION

[0083] The technical solutions of the present application will be further described below in conjunction with the drawings, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present application without departing from the design idea of the present application shall be covered in the protection scope of the present application.

[0084] The application provides a wind power grid-connection impact damping suppression method based on branch and bound and knapsack optimization control, and can realize efficient and rapid suppression of wind power fluctuation. The device is characterized in that the advantages of a thyristor switched filter (TSF) and an active power filter (APF) are combined, and an active damping generator technology capable of suppressing wind power grid-connection impact is developed based on knapsack optimization control. The developed ADG technology has the following advantages: ① It has the characteristics of TSF in suppressing harmonic impact, voltage mutation and high cost performance; ② It has the characteristics of APF in continuously adjustable output damping and high precision; ③ Based on branch and bound, wind power impact is classified as a reference for the maximum damping of ADG output, which effectively improves the rapidity and stability of ADG response; ④ The knapsack problem (UKP) is used to realize optimal switching control of ADG, and the wind power disturbance impact suppression with the lowest cost and the highest efficiency is realized.

[0085] Embodiment 1

[0086] The application provides a wind power grid-connection impact damping suppression method based on branch and bound and knapsack optimization control, and can realize efficient and rapid suppression of wind power fluctuation. The device is characterized in that the advantages of a thyristor switched filter (TSF) and an active power filter (APF) are combined, and an active damping generator technology capable of suppressing wind power grid-connection impact is developed based on knapsack optimization control. The developed ADG technology has the following advantages: ① It has the characteristics of TSF in suppressing harmonic impact, voltage mutation and high cost performance; ② It has the characteristics of APF in continuously adjustable output damping and high precision; ③ Based on branch and bound, wind power impact is classified as a reference for the maximum damping of ADG output, which effectively improves the rapidity and stability of ADG response; ④ The knapsack problem (UKP) is used to realize optimal switching control of ADG, and the wind power disturbance impact suppression with the lowest cost and the highest efficiency is realized.

[0087] Step one: Collect the amplitude and frequency of the bus voltage of the wind power grid-connection system, the bus current, the wind power surge current, the capacity of the transformer, the short-circuit ratio and the equivalent impedance, and determine the optimal suppression damping required by the ADG according to the above parameters;

[0088] Step two: Establish a characteristic equation group (formula one and two) that meets the dynamic characteristics of the ADG damping, and calculate the equivalent reactance and the equivalent inductance;

[0089] Step three: Establish the mathematical relationship of the related modules in the ADG, wherein the active filter APF is defined as a controlled voltage source u L that depends on the impact current i c_apf of the wind power grid-connection caused and the compensation current i apf flowing into the node from the APF node; classify the different current and voltage of the APF output, which is expressed as outputting different dampings in the system, and determine the combination of the dampings, which is the basis for classification optimization;

[0090] Step four: The Wushan elimination method is used to derive the system control model under the harmonic condition;

[0091] Step five: Determine the active damping gain K and the impact current i LThe corresponding relationship with different wind power input power states is defined; on the basis of the classification defined by the offline method, the impact current i L is measured in real time, and the compensation current i apf of the reverse resistance harmonic component is generated to realize fast damping suppression.

[0092] Step six: determine the objective function of the knapsack optimization, that is, the maximum damping output, and give the constraint equation according to the actual situation;

[0093] Step seven: perform knapsack optimization calculation based on the branch and bound method of wind power impact, and pre-calculate the constraint relationship of the voltage based on the classification method, to provide an algorithm basis for the best damping suppression;

[0094] Step eight: bring the voltage constraint as an integer bounding condition into the knapsack combination calculation, so as to solve the optimal ADG switch control scheme.

[0095] Figure 1 For the topology of the power system that needs to be compensated, the related parameters of the transformer and the related parameters of the load current of the system need to be measured, and the equivalent circuit of the active damping generator is obtained as shown in Figure 2 .

[0096] Through analysis and processing of the data sampled in step one, the required parameters of the ADG equivalent circuit obtained by using the processed data in step two are calculated as follows:

[0097] Formula one:

[0098] Formula two:

[0099] Where, Z s is the equivalent reactance of the grid in the model; U k is the short-circuit ratio of the transformer; u s is the amplitude of the bus voltage; S N is the capacity of the transformer; L s is the equivalent inductance of the grid; R s is the equivalent impedance of the transformer, and ω is the angular frequency of the bus voltage.

[0100] Formula three: u apf = Ki c_apf

[0101] There are three filter channels (n 51 , n 52 , n7) for the passive damping TSF, where n 51 , n 52n7 represents 5, 5, 7 filter channels respectively; there are 7 damping combinations, define combination f j = (L j , C j )(j = 5, 6, 7), wherein L j , C j are the inductance and capacitance values of a filter channel respectively, f j represents a combination of a filter channel; the combination form f c in the specific case is represented as follows:

[0102] Equation four:

[0103] Considering the influence of APF on each combination, f apf is represented as a combination of ADG path output, a total of 8 damping combinations; corresponding to different proportion of wind power access working state, the following control classification is obtained, described as follows:

[0104] Equation five:

[0105] In order to suppress power or voltage impact, the above damping combination is used to suppress voltage impact and load current surge in real time.

[0106] In step four, in order to classify the power impact of different proportion of wind power access, avoid the harmonics emitted by APF in ADG and TSF resonance times to offset the filtering effect, and cause TSF to produce overcurrent problem, Wu elimination method is adopted to derive ADG system control model, set the harmonic number as n, and the frequency as f, then the harmonic circuit model in equivalent reactance Z s = R s +jn2πfL s , the equivalent impedance Z k emitted by TSF is represented as follows:

[0107] Equation six: Z tsf = 1.0 / (n 51 / Z 51 +n 52 / Z 52 +n 53 / Z 53 )

[0108] Equation seven: Z j = j[n2πfL j -1 / (n2πfC j )](j = 5, 6, 7)

[0109] Equation eight:

[0110] Formula nine: Z k = R + jn2pL

[0111] Formula ten: i tsf = u k1 / Z tsf

[0112] wherein j represents the serial number of the channel, Z tsf is the equivalent impedance of all channels, Z j is the reactance of each filter channel of the TSF to the n-th harmonic, n j is the switching state of the TSF, Z k is the reactance of the equivalent branch of the TSF, u k1 is the voltage of the harmonic, i tsf is the equivalent current flowing into the TSF, R and L are the equivalent resistance and the equivalent inductance of the equivalent reactance.

[0113] In step five, in view of the distortion of the sampling voltage and the sampling current and the harmonic disturbance caused by the high proportion of wind power into the grid, the high proportion of power electronics and the intelligentization of the grid-connected control strategy, an active filter APF in the ADG is used to generate a current that reverses and cancels the harmonic component. According to Kirchhoff's current law, the following expression is derived:

[0114] Formula eleven: [u k1 - K(i L - i tsf + i apf )] / Z k = -i apf

[0115] Formula twelve: -i apf = u k1 / Z s - i tsf + i L

[0116] By combining formulas six to twelve, we get:

[0117] Formula thirteen: u k1 = [Z k Z s Z tsf / (KZ tsf + Z k Z s - Z k Z tsf + Z s Z tsf ]i L

[0118] Formula thirteen: u k1 = [Z k Zs Z tsf / (KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf )]i L

[0119] Equation Fourteen: i apf = [(-KZ tsf -Z s Z tsf ) / (KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf )]i L

[0120] To avoid the generation of current oscillations, i apf becomes infinite, the following damping control analysis is performed:

[0121] Equation Fifteen: KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf ≠ 0

[0122] In addition, for the gain K there are the following boundary conditions:

[0123] Equation Sixteen: 0 < (Z k Z s -Z k Z tsf ) / (KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf )-1 < 1

[0124] Equation Seventeen: 0 < K < 0.5(Z k Z tsf -Z k Z s -2Z s Z tsf ) / Z tsf

[0125] As shown in Equation Seventeen, the constraint condition of gain K can be obtained, effectively determining the value range of K; here, the active damping of ADG, Z in Equation Nine k is called passive damping, which can be one-to-one mapped with the parameters of the related circuit; according to Equations Four to Seventeen, it can be known that K can be determined through offline calculation, while i apf Thus, different wind power impact currents i L can also be quickly determined, that is, by classifying K offline, the speed of the output damping of ADG is greatly accelerated, and the foundation for applying knapsack optimization ADG to power and voltage impact suppression is laid.

[0126] On the basis of K, i apf , the damping state can be classified to adjust K, i apf , so as to accelerate the active damping compensation speed of ADG and optimize the compensation effect. The specific implementation method is as follows Figure 4 : K is determined offline according to different load conditions, K corresponding to different load states is determined, and i L is calculated in real time according to i apf .

[0127] In Step Six, the optimization objective function and constraint relationship are determined:

[0128] Since Equation Twelve can be modified under the fundamental condition as follows:

[0129] When reactive power compensation is performed, the TSF part performs hierarchical compensation and bears the main compensation effect, and the knapsack optimization method is considered to determine the corresponding relationship:

[0130] Equation Eighteen: -i apf = (u2-u s ) / Z s -i tsf +i L

[0131] u2 represents the fundamental voltage;

[0132] Equation Eighteen highlights the fundamental analysis, and APF determines the size of the reactive power compensation current of the active damping according to the wind power impact current i L and the TSF current, and the size of u2 can be solved by simultaneously solving the previous equations; the purpose of the technology is to provide the main stepwise passive damping suppression by the TSF with lower cost, and the remaining part of the system is fine-tuned by the APF with higher cost, so that a small-capacity APF and TSF combination can continuously compensate the wind power access power. Since the TSF performs passive damping suppression through reactive power compensation, the reactive power capacity of the TSF of each channel is represented as follows:

[0133] Equation nineteen:

[0134] where Q c , Q L is the reactive power provided by the capacitance and inductance, and U2 is the fundamental phase voltage, where i n is the n-th harmonic current; considering that the grid voltage has a perturbation of ±10%, the target of the reactive power compensation borne by the passive damping part of the ADG is:

[0135] Equation twenty: J = max(n 51 Q 51 +n 52 Q 52 +n7Q7)

[0136] Equation twenty-one: Q j = Q Cj -Q Lj

[0137] In the above equations, Q j represents the reactive power that each channel can provide, Q Cj and Q Lj are the reactive power emitted by the capacitance and the reactive power absorbed by the inductance of the channel, respectively, and equation twenty-one meets the calculation idea of the knapsack problem; define Q 51 , Q 52 and Q7 as the items to be packed, and J as the capacity of the bag, and equation five is the combination of the items to be packed. The constraint conditions of the knapsack problem are summarized as follows:

[0138] Equation twenty-two: n 51 Q 51 +n 52 Q 52 +n7Q7≤Q 1set

[0139] Equation twenty-three: u1-u 1set ≤0

[0140] where Q 1set is the maximum reactive power compensation of the system, and since the passive damping part of the ADG device is a step compensation and cannot be continuously compensated, equation twenty-three ensures that overcompensation does not occur, which would cause the voltage to rise; u 1set is the limit voltage that the active filter APF can withstand, and u1 is composed of two parts, i.e., the fundamental voltage division of the resonance branch and the voltage division of each harmonic voltage in the grid on the resonance branch.

[0141] Here formula twenty is the optimization target, formula twenty-two and formula twenty-three are the optimization constraints. Since formula twenty-three is a nonlinear constraint, a knapsack optimization is proposed for the branch and bound method, and the value of u1 is estimated by the previous classification algorithm as an additional bounding condition for branch optimization, so as to obtain the optimal switch combination within the constraint limit.

[0142] In step seven, the branch and bound method is applied to optimize the selection of knapsack capacity; however, since the solution of u1 in formula twenty-two is a complex nonlinear equation. But the previous classification algorithm can estimate u1, that is, u1 is u k1 And the sum of the fundamental voltage u2, where u2 and the fundamental current i apf2 By calculation, we have:

[0143] Formula twenty-four:

[0144] Formula twenty-five:

[0145] Formula twenty-six: u1 = u k1 +u2

[0146] According to the three formulas, the branch and bound method for this case is improved.

[0147] In step eight, formula twenty-six is combined with constraint formula twenty-three to form a real-time judgment condition. The lower bound determination of formula twenty and formula twenty-one in the branch and bound algorithm process is added with voltage judgment. If the voltage judgment condition is met, the lower bound is updated, otherwise the original lower bound is retained, so as to avoid the case that the optimal solution satisfying two constraints is excluded. According to this method, the optimal switch control strategy for wind power impact suppression can be effectively obtained.

[0148] Figure 5 The implementation block diagram of knapsack optimization, Figure 6The branch and bound method is used to solve the basic knapsack problem of formula twenty and formula twenty-two. The process is as follows: ① Relax the original problem, and relax it to any number between 0 and 1. The method of updating the upper and lower bounds in the solving process is called bounding. The upper bound is determined by the objective function of each open node, and the lower bound is determined by the best integer solution found. ② When the sub-problem has no solution and the node has an integer solution, the node is closed, that is, pruned. ③ When there is a non-integer solution, continue to branch down. Whether to branch down depends on whether the objective function value of the node is better than the lower bound. An important feature of the branch tree is that the objective function of the child node will not be greater than the parent node, that is, each objective function is strictly ordered. The update time of the lower bound is when the integer solution obtained is the best integer solution, and the lower bound will be recorded as the new lower bound.

[0149] The change is to determine the lower bound, add a layer of judgment, that is, the Z tsf Combine the corresponding gain K and i L Calculate whether u1 satisfies the constraint condition formula twenty-two. If it satisfies, update the lower bound, if it does not satisfy, keep the original lower bound. Through this change, the problem of not being able to directly solve nonlinear equations for knapsack optimization is solved, and the amount of calculation is effectively reduced.

[0150] Figure 7 And Figure 8 For the effect analysis of ADG active compensation according to the simulation of wind power impact, Figure 9 The effect diagram of ADG current compensation shows that the harmonics are greatly reduced, and the compensation effect meets the expectation. For voltage, through Figure 10 And Figure 11 The voltage comparison before and after compensation shows that the harmonic suppression effect of ADG is good. And from the simulation Figure 12 It can be seen that the response speed of impact suppression under ideal conditions is 5.6ms, which is much smaller than that of general compensation devices, and the power factor after compensation is also above 0.9, proving the effectiveness of classification optimization and knapsack optimization.

Claims

1. A method for suppressing the impact damping of wind power grid connection based on branch-bound and knapsack optimization control, characterized in that: The method comprises the following steps: Step one: Collecting the amplitude and frequency of the bus voltage of the wind power grid-connected system, bus current, wind power surge current, capacity of the transformer, short-circuit ratio and equivalent impedance, and determining the optimal suppression damping required to be provided by the ADG according to the above; Step two: Establishing a characteristic equation group satisfying the damping dynamic characteristics of the ADG, and calculating the equivalent reactance and equivalent inductance; Step three: Establish the mathematical relationship of the relevant modules in ADG, where the active filter APF is defined as dependent on the impact current caused by the wind power into the grid And the compensation current flowing into the node from the APF node The controlled voltage source ; Classify the different current and voltage of APF output, which is expressed as different damping in the system, and determine the combination of damping, which is the basis for classification optimization Step four: Eliminating method is adopted to derive the system control model under harmonic conditions; Step five: determining active damping gain and the impact current corresponding relationship with different wind power input power state, complete classification definition; On the basis of the classification defined by the off-line method, the impact current The online fast calculation of APF needs to generate compensation current to resist the harmonic component , and achieve fast damping suppression; Step six: Determining the objective function of the knapsack optimization, that is, the maximum damping output, and giving the constraint equation according to the actual situation; Step seven: Based on the branch and bound method of wind power power impact, the knapsack optimization calculation is carried out, and the precalculation of the constraint relationship of voltage is carried out combined with the classification method, thereby providing an algorithm basis for the optimal damping suppression; Step eight: The voltage constraint is brought into the knapsack combination calculation as an integer bounding condition, so as to solve the optimal ADG switch control scheme.

2. The wind power grid impact damping suppression method based on branch and bound and knapsack optimization control according to claim 1, characterized in that: Through the analysis and processing of the data sampled in step one, the required parameters of the ADG equivalent circuit obtained by using the processed data in step two are calculated as follows: Equation One: Equation Two: wherein, X is the equivalent reactance of the grid in the model; X is the short circuit ratio of the transformer; X is the amplitude of the bus voltage; X is the capacity of the transformer; X is the equivalent inductance of the grid; X is the equivalent impedance of the transformer, X is the angular frequency of the bus voltage; Equation Three: There are three filter channels for passive damping TSF , , , wherein , and represent 5th, 5th, 7th filter channels respectively; there are 7 damping combinations, defining combinations , =51, 52, 7, wherein , are inductance value and capacitance value of a filter channel respectively, represents a combination of a filter channel; the combination form in specific case is represented as follows: ​ Equation Four: Considering the influence of APF on each combination, There are 8 combinations of damping in total, which are expressed as the output of ADG channel. According to different working conditions of wind power access, the following control classification is obtained, which is described as follows: Equation Five: In order to suppress power or voltage impact, the above damping combination is used to suppress voltage impact and load current surge in real time.

3. The wind power grid impact damping suppression method based on branch and bound and knapsack optimization control according to claim 2, characterized in that: In step four, in order to classify the power impact of different proportion of wind power access, avoid the same harmonic and TSF resonance frequency of APF in ADG to offset the filtering effect, and lead to over-current problem of TSF, the elimination method is adopted to derive the ADG system control model, the harmonic frequency is set as , the frequency is represented as , the equivalent reactance of the harmonic circuit model is , and the equivalent impedance of TSF is represented as follows: Equation Six: Equation Seven: Equation Eight: Equation Nine: Equation Ten: wherein, with the sequence number of the channel, the overall equivalent impedance of all channels, the reactance of each filter channel of the TSF to the second harmonic, the switching state of the TSF, the reactance of the equivalent branch of the TSF, the voltage magnitude of the harmonic, the equivalent current flowing into the TSF, and the equivalent resistance and the equivalent inductance of the equivalent reactance.

4. The wind power grid impact damping suppression method based on branch and bound and knapsack optimization control according to claim 3, characterized in that: In step five, for the distortion of sampled voltage and current and harmonic disturbance caused by high proportion of wind power grid-connected high proportion of power electronics and intelligent grid-connected control strategy, an active filter APF in the ADG generates a current to cancel the harmonic component in the opposite direction, and the following expression is derived according to Kirchhoff's current law: Equation Eleven: Equation Twelve: By combining formulas six to twelve, the following is obtained: Equation Thirteen: Equation Fourteen: In order to avoid the generation of current oscillations, i.e. to avoid the occurrence of infinite cases, the following damping control analysis is performed: Equation Fifteen: In addition, for the gain There are also the following boundary conditions: Equation Sixteen: Equation Seventeen: As shown in Equation Seventeen, the constraint condition of gain is obtained, which effectively determines the value range of ; here, the active damping of ADG, and in Equation Nine is called passive damping, which can be one-to-one mapped with the parameters of the related circuit; According to equations four to seventeen, Can be determined by offline calculation, while Thus also due to different wind power impact current Quick determination, that is, by for Offline classification, greatly speed up the output damping of ADG, and lay the foundation for the application of knapsack optimization ADG power and voltage impact suppression.

5. The wind power grid impact damping suppression method based on branch and bound and knapsack optimization control according to claim 4, characterized in that: In step six, the optimization objective function and the constraint relationship are determined: Since formula twelve is modified under the fundamental condition: When reactive power compensation is carried out, the TSF part carries out hierarchical compensation and bears the main compensation effect, and the knapsack optimization method is considered to determine the corresponding relationship: Equation eighteen: V0represents the fundamental voltage; Formula 18 emphasizes fundamental frequency analysis; APF is based on wind power impact current. The magnitude of the reactive power compensation current for active damping is defined by the TSF current, and the previous equations are solved simultaneously to obtain... The size; given that the TSF uses passive damping suppression through reactive power compensation, the reactive power capacity of the TSF for each channel is expressed as follows: Equation Nineteen: where , is the reactive power provided by the capacitance and inductance, while is the fundamental phase voltage, where is the sub-harmonic current; considering the existence of ±10% perturbation of the grid voltage, the target of the reactive power compensation undertaken by the passive damping part of the ADG is: Equation Twenty: Equation Twenty-one: In the above formula, represents the reactive power that each channel can provide, , respectively, the reactive power generated by the channel capacitor and the reactive power absorbed by the inductor, formula twenty-one meets the calculation idea of the knapsack problem; define , and are the items to be packed, is the capacity of the bag, and formula five is the combination of the items to be packed. The constraint conditions of the knapsack problem are summarized as follows: Equation Twenty-two: Equation Twenty-three: wherein, is the maximum compensation of the system reactive power, since the passive damping part in the ADG device is a stepped compensation, it cannot be continuously compensated, formula twenty-three ensures that there will be no over-compensation to cause voltage rise; is the limit voltage that the active filter APF can withstand, is composed of two parts, that is, the fundamental voltage division of the resonance branch and the voltage division of each harmonic voltage in the power grid on the resonance branch.

6. The wind power grid impact damping suppression method based on branch and bound and knapsack optimization control according to claim 5, characterized in that: In step seven, the branch and bound method is applied to optimize the selection of knapsack capacity; the is estimated, i.e. is and the fundamental voltage is the sum of the fundamental current and the fundamental current to be compensated is calculated as Formula Twenty-Four: Formula Twenty-Five: Equation twenty-six: = 1 - exp(-2π2σ2N) According to the three formulas, the branch and bound method for this case is improved.

7. The wind power grid impact damping suppression method based on branch and bound and knapsack optimization control according to claim 6, characterized in that: In step eight, formula twenty-six is combined with constraint formula twenty-three to form a real-time judgment condition, and the lower bound of formula twenty and formula twenty-one in the branch and bound algorithm process is additionally judged. If the voltage judgment condition is met, the lower bound is updated, otherwise the original lower bound is retained, so as to avoid excluding the optimal solution that meets the two constraints. According to this method, the optimal switch control strategy for wind power power impact suppression can be effectively obtained.

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