Wind power network access impact damping suppression method based on branch and bound and knapsack optimization control

Abstract

The invention discloses a wind power network access impact damping suppression method based on branch and bound and knapsack optimization control. Efficient and rapid suppression of wind power fluctuation can be realized. The device is characterized in that the advantages of a thyristor switch filter (TSF) and an active power filter (APF) are combined, and an active damping generator technology capable of carrying out wind power network access impact suppression is developed on the basis of knapsack optimization control. The developed ADG technology has the following advantages: (1) the TSF has the characteristics of harmonic impact suppression, voltage jump suppression and high cost performance; (2) the characteristics that the APF output damping is continuously adjustable and the precision is relatively high are achieved; 3, wind power impact is subjected to finite classification based on branch definition to serve as reference of ADG output maximum damping, and the rapidity and stability of ADG response are effectively improved; and (4) the optimal switching control of the ADG is realized by adopting a Knapback Problem (UKP) thought, and the wind power disturbance impact suppression with the lowest cost and high efficiency is met.

Description

Technical Field

[0001] The present invention belongs to the field of application technology combining power electronics technology development with artificial intelligence algorithms, and relates to a method for suppressing wind power grid-connected impact damping based on branch and bound and backpack optimization control. Background Art

[0002] As the proportion of uncertain wind energy entering the grid increases, the following negative effects will be produced on the "double-high" new power system: ① sensor sampling distortion; ② affecting 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 cost of suppressing wind power surges, it is urgent to solve the above problems from the optimization control level. The difficulty lies in developing a cost-effective damping control technology that takes into account both voltage surge and current surge suppression, highlighting the combination of classic power electronic devices and emerging artificial intelligence methods.

[0003] The feature of the present invention is that, drawing on the idea of ​​the classic knapsack problem, an active damping generation technology with the best cost-effectiveness is developed, and the ideas are as follows: ① The damping required to suppress the fluctuation of wind power input power is the maximum knapsack capacity, which is defined by category by the 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 the active damping generator (ADG) can provide. Summary of the invention

[0004] The purpose of the present invention is to provide a method for damping and suppressing the impact of wind power grid access based on branch delimitation and backpack optimization control, so as to achieve the purpose of quickly suppressing the impact of uncertain wind power grid access power. The feature of the invention is to combine the classic APF with 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 control and high cost performance of TSF; ② It increases the good dynamic adjustment characteristics of APF and improves the flexibility of damping suppression; ③ Based on branch delimitation, the load state is limitedly classified to minimize the possibility of parallel resonance between ADG and the power grid, while improving the rapidity of response; ④ The backpack problem (Knapsack Problem, UKP) control idea is adopted to obtain the optimal ADG switching strategy, so that ADG can suppress wind power impact at the lowest cost.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for suppressing wind power grid-connected impact damping based on branch and bound and backpack optimization control, the method comprising the following steps:

[0007] Step 1: Collect the amplitude and frequency of the bus voltage, bus current, wind power surge current, transformer capacity, short-circuit ratio and equivalent impedance of the wind power grid system, and define the optimal suppression damping that the ADG needs to provide based on this;

[0008] Step 2: Establish a characteristic equation group that satisfies the dynamic characteristics of ADG damping, and calculate the equivalent reactance and equivalent inductive reactance;

[0009] Step 3: Establish the mathematical relationship between the relevant modules in ADG, where the active filter APF is defined as the inrush current i caused by wind power grid access. L and the compensation current i flowing into the node from the APF node c_apf The controlled voltage source u apf ; Classify the different current and voltage conditions of APF output, which are manifested in the system as different damping outputs, and determine the damping combination to lay the foundation for classification optimization;

[0010] Step 4: Use Wu elimination method to derive the system control model under harmonic conditions;

[0011] Step 5: Determine the active damping gain K and the impulse current i L The corresponding relationship with different wind power input power states is used to complete the classification definition; based on the classification definition of this offline method, the impact current i L To quickly calculate APF online, a compensation current i is needed to generate a reverse harmonic component. apf , to achieve rapid damping suppression;

[0012] Step 6: Determine the objective function of backpack optimization, i.e., the maximum damping output, and give the constraint equation according to the actual situation;

[0013] Step 7: Perform knapsack optimization calculation based on the branch and bound method of wind power impact, and pre-calculate the voltage constraint relationship in combination with the classification method to provide an algorithm basis for optimal damping suppression;

[0014] Step 8: Substitute the voltage constraint as an integer bounding condition into the backpack combination calculation to solve the optimal ADG switch control scheme.

[0015] Furthermore, by analyzing and processing the data sampled in step 1, the required parameters of the ADG equivalent circuit obtained by using the processed data in step 2 are specifically calculated as follows:

[0016] Formula 1:

[0017] Formula 2:

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

[0019] Formula 3: u apf =Ki c_apf

[0020] For passively damped TSF there are 3 filter channels (n 51 、n 52 , n7), where n 51 、n 52 and n7 represent the 5th, 5th, and 7th order filtering channels respectively; there are 7 damping combinations, and the combination f is defined j =(L j ,C j )(j=51,52,7), where L j , C j are the inductance and capacitance of a filter channel respectively, f j Indicates a combination of filter channels; the combination form f in the specific case c It is expressed as follows:

[0021] Formula 4:

[0022] Considering the impact of APF on each combination, f apf It is represented as a combination of ADG channel outputs, with a total of 8 damping combinations; corresponding to the working states of different proportions of wind power access, the following control classifications are obtained, as described below:

[0023] Formula 5:

[0024] In order to suppress power or voltage surge, the above damping combination is used to suppress voltage surge and load current surge in real time.

[0025] Furthermore, in step 4, in order to classify the power impact of wind power access with different proportions, to avoid the harmonics emitted by APF in ADG and TSF resonance order being the same and thus offsetting the filtering effect, and causing TSF to generate overcurrent problems, the ADG system control model is derived by Wu elimination method, and the harmonic order is set to n, and the frequency is expressed as f. Then, the harmonic circuit model is calculated when the equivalent reactance is Z.s =R s +jn2πfL s , the equivalent impedance Z emitted by TSF k It is expressed as follows:

[0026] Formula 6: Z tsf =1.0 / (n 51 / Z 51 +n 52 / Z 52 +n 53 / Z 53 )

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

[0028] Formula 8:

[0029] Formula 9: Z k =R+jn2πfL

[0030] Formula 10: i tsf =u k1 / Z tsf

[0031] Among them, j represents the sequence number of the channel, Z tsf is the equivalent impedance of all channels, Z j is the reactance of each filter channel of TSF for the nth harmonic, n j is the switch state of TSF, Z k is the reactance of the TSF equivalent branch, u k1 is the voltage magnitude of the harmonic, i tsf is the equivalent current flowing into TSF, R and L are the equivalent resistance and equivalent inductance of the equivalent reactance.

[0032] Furthermore, in step 5, for the distortion and harmonic disturbance of sampled voltage and sampled current caused by high proportion of wind power grid access, high proportion of power electronics and intelligent grid control strategy, the active filter APF in ADG is used to generate a current that reversely offsets the harmonic component, and the following expression is derived according to Kirchhoff's current law:

[0033] Formula 11: [u k1 -K(i L -i tsf +i apf )] / Z k =-i apf

[0034] Formula 12: -iapf =u k1 / Z s -i tsf +i L

[0035] Combining formulas 6 to 12, we get:

[0036] Formula 13: 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] Formula 13: 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] Formula 14: 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] In order to avoid current oscillation, that is, to avoid i apf For the infinite case, the following damping control analysis is performed:

[0040] Formula 15: KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf ≠0

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

[0042] Formula 16: 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] Formula 17: 0<K≤0.5(Z k Z tsf -Z k Z s -2Z s Z tsf ) / Z tsf

[0044] As shown in Formula 17, the constraint condition of gain K can be obtained, which effectively determines the value range of K; here is the active damping of ADG, Z in Formula 9 k It is called passive damping, which can be mapped one-to-one with the parameters of the relevant circuit; According to Formula 4 to Formula 17, it can be known that K can be determined by offline calculation, and i apf Therefore, due to different wind power impact current i L Rapid determination, i.e., by off-line classification of K, greatly speeds up the output damping of the ADG and lays the foundation for applying backpack optimization ADG to suppress power and voltage shocks.

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

[0046] Since formula 12 can be corrected to:

[0047] When performing reactive power compensation, the TSF part performs graded compensation and plays the main role in compensation. Considering the use of the backpack optimization method, the corresponding relationship is determined:

[0048] Formula 18: -i apf =(u2-u s ) / Z s -i tsf +i L

[0049] u2 represents the fundamental voltage;

[0050] Formula 18 highlights the fundamental wave analysis. APF is based on the wind power impulse current i LThe reactive power compensation current that realizes active damping is defined by the TSF current. The previous equation can be combined to solve the size of u2. Given that TSF performs passive damping suppression through reactive compensation, the reactive power capacity of TSF for each channel is expressed as follows:

[0051] Formula 19:

[0052] Where Q c , Q L is the reactive power provided by capacitors and inductors, and U2 is the fundamental phase voltage, where i n is the nth harmonic current; considering the ±10% perturbation of the grid voltage, the reactive power compensation target borne by the passive damping part of the 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 Indicates the reactive power that each channel can provide, Q Cj , Q Lj are the reactive power emitted by the capacitor and absorbed by the inductor of the channel respectively. Formula 21 satisfies the calculation idea of ​​the backpack problem. Define Q 51 , Q 52 With Q7 being the items to be packed, J being the capacity of the package, and Formula 5 being 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 u is the maximum reactive power compensated by the system. Since the passive damping part in the ADG device is a step-by-step compensation and cannot be compensated continuously, Formula 23 ensures that over-compensation will not occur and cause voltage increase; u 1set It is the limit voltage that the active filter APF can withstand, and u1 is composed of two parts, namely the fundamental wave voltage division of the resonant branch and the voltage division of each harmonic voltage in the power grid on the resonant branch.

[0059] Furthermore, in step 7, the branch and bound method is used to optimize the selection of the backpack capacity; u1 is estimated, that is, u1 is u k1 The sum of the fundamental voltage u2 and the fundamental current i apf2 By calculation, we can get:

[0060] Formula 24:

[0061] Formula 25:

[0062] Formula 26: u1=u k1 +u2

[0063] Based on these three formulas, the branch and bound method for this situation is improved.

[0064] Furthermore, in the step eight, formula 26 is combined with constraint formula 23 to form a real-time judgment condition, and an additional voltage judgment is performed on the determination of the lower bounds of formulas 20 and 21 in the branch and bound algorithm. If the voltage judgment condition is met, the lower bound is updated, otherwise the original lower bound is retained, thereby avoiding the situation where the optimal solution that meets the two constraints is excluded. According to this method, the optimal switch control strategy for wind power shock suppression can be effectively obtained.

[0065] The beneficial effects of the present invention compared to the prior art are:

[0066] (1) The uncertain wind power grid-connected power is classified and analyzed according to the branch definition to form a one-to-one mapping combination with the active damping generator ADG output damping combination, thereby improving the stability, accuracy and response speed of wind power impact suppression; the step of classifying the wind power grid-connected power is used as a reference basis for the combined capacity of items in the backpack.

[0067] (2) The stepped damping of each channel output of TSF is combined with the continuous damping of APF output as the execution means of active damping generator ADG to suppress the fluctuation of high-share wind power, 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 control the ADG by frequency division, thereby avoiding the APF in the ADG emitting harmonics of the same resonance order as the TSF, thereby offsetting the filtering effect and causing the TSF to produce overcurrent problems.

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

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

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

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

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

[0074] Figure 4 Block diagram of algorithm implementation optimized for classification;

[0075] Figure 5 Block diagram of algorithm implementation for backpack optimization;

[0076] Figure 6 A branching tree diagram for the branch and bound method;

[0077] Figure 7 This is the current diagram of the simulated K=0.5, 270kW DC motor;

[0078] Figure 8 It is the spectrum diagram of load current under simulation conditions;

[0079] Fig. 9 The current compensation effect diagram of active damping under load current generation when K = 0.5;

[0080] Fig.10 The waveform diagram of voltage and current before compensation;

[0081] Fig.11 This is the compensated voltage diagram when the active damping generator is in effect;

[0082] Fig.12 This is the speed diagram for ideal compensation. DETAILED DESCRIPTION

[0083] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the design concept scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0084] The present invention provides a method for damping and suppressing the impact of wind power grid access based on branch delimitation and backpack optimization control, which can realize efficient and rapid suppression of wind power fluctuations. The feature of the device is that it combines the advantages of thyristor switched filter (TSF) and active power filter (APF), and develops an active damping generator technology that can suppress the impact of wind power grid access based on backpack optimization control. The developed ADG technology has the following advantages: ① It has the characteristics of TSF suppressing harmonic impact, voltage mutation and high cost performance; ② It has the characteristics of APF output damping that is continuously adjustable and has high precision; ③ Based on branch delimitation, the wind power impact is limitedly classified as a reference for the maximum damping of ADG output, which effectively improves the rapidity and stability of ADG response; ④ The backpack problem (UKP) idea is adopted to realize the optimal switching control of ADG, which meets the lowest cost and high efficiency of wind power disturbance impact suppression.

[0085] Embodiment 1:

[0086] The present invention provides a method for suppressing wind power grid-connected impact damping based on branch and bound and backpack optimization control, so as to quickly suppress the power fluctuation problem caused by uncertain wind power access. The implementation steps are as follows:

[0087] Step 1: Collect the amplitude and frequency of the bus voltage, bus current, wind power surge current, transformer capacity, short-circuit ratio and equivalent impedance of the wind power grid system, and define the optimal suppression damping that the ADG needs to provide based on this;

[0088] Step 2: Establish a characteristic equation group (Formulas 1 and 2) that satisfies the dynamic characteristics of ADG damping, and calculate the equivalent reactance and equivalent inductive reactance;

[0089] Step 3: Establish the mathematical relationship between the relevant modules in ADG, where the active filter APF is defined as the inrush current i caused by wind power grid access. L and the compensation current i flowing into the node from the APF node c_apf The controlled voltage source u apf ; Classify the different current and voltage conditions of APF output, which are manifested in the system as different damping outputs, and determine the damping combination to lay the foundation for classification optimization;

[0090] Step 4: Use Wu elimination method to derive the system control model under harmonic conditions;

[0091] Step 5: Determine the active damping gain K and the impulse current i LThe corresponding relationship with different wind power input power states is used to complete the classification definition; based on the classification definition of this offline method, the impact current i L To quickly calculate APF online, a compensation current i is needed to generate a reverse harmonic component. apf , to achieve rapid damping suppression;

[0092] Step 6: Determine the objective function of backpack optimization, i.e., the maximum damping output, and give the constraint equation according to the actual situation;

[0093] Step 7: Perform knapsack optimization calculation based on the branch and bound method of wind power impact, and pre-calculate the voltage constraint relationship in combination with the classification method to provide an algorithm basis for optimal damping suppression;

[0094] Step 8: Substitute the voltage constraint as an integer bounding condition into the backpack combination calculation to solve the optimal ADG switch control scheme.

[0095] Figure 1 The topology of the power system to be compensated is as follows: Figure 2 The equivalent circuit of the active damping generator is shown.

[0096] By analyzing and processing the data sampled in step 1, the required parameters of the ADG equivalent circuit are obtained using the processed data in step 2. The specific calculation is as follows:

[0097] Formula 1:

[0098] Formula 2:

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

[0100] Formula 3: u apf =Ki c_apf

[0101] For passively damped TSF there are 3 filter channels (n 51 、n 52 , n7), where n 51 、n 52and n7 represent the 5th, 5th, and 7th order filtering channels respectively; there are 7 damping combinations, and the combination f is defined j =(L j ,C j )(j=51,52,7), where L j , C j are the inductance and capacitance of a filter channel respectively, f j Indicates a combination of filter channels; the combination form f in the specific case c It is expressed as follows:

[0102] Formula 4:

[0103] Considering the impact of APF on each combination, f apf It is represented as a combination of ADG channel outputs, with a total of 8 damping combinations; corresponding to the working states of different proportions of wind power access, the following control classifications are obtained, as described below:

[0104] Formula 5:

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

[0106] In step 4, in order to classify the power impact of wind power access with different proportions, to avoid the harmonics emitted by APF in ADG and TSF resonance times being the same, thus offsetting the filtering effect and causing TSF to generate overcurrent problems, the ADG system control model is derived by Wu elimination method, and the harmonic times are set to n and the frequency is expressed as f. Then, the harmonic circuit model is set to Z when the equivalent reactance is s =R s +jn2πfL s , the equivalent impedance Z emitted by TSF k It is expressed as follows:

[0107] Formula 6: Z tsf =1.0 / (n 51 / Z 51 +n 52 / Z 52 +n 53 / Z 53 )

[0108] Formula 7: Z j =j[n2πfL j -1 / (n2πfC j )](j=51,52,7)

[0109] Formula 8:

[0110] Formula 9: Z k =R+jn2πfL

[0111] Formula 10: i tsf =u k1 / Z tsf

[0112] Among them, j represents the sequence number of the channel, Z tsf is the equivalent impedance of all channels, Z j is the reactance of each filter channel of TSF for the nth harmonic, n j is the switch state of TSF, Z k is the reactance of the TSF equivalent branch, u k1 is the voltage magnitude of the harmonic, i tsf is the equivalent current flowing into TSF, R and L are the equivalent resistance and equivalent inductance of the equivalent reactance.

[0113] In step 5, for the distortion of sampling voltage and sampling current and harmonic disturbance caused by high proportion of wind power grid access, high proportion of power electronics and intelligent grid control strategy, the active filter APF in ADG is used to generate a current that reversely offsets the harmonic component. The following expression is derived according to Kirchhoff's current law:

[0114] Formula 11: [u k1 -K(i L -i tsf +i apf )] / Z k =-i apf

[0115] Formula 12: -i apf =u k1 / Z s -i tsf +i L

[0116] Combining formulas 6 to 12, we get:

[0117] Formula 13: 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 13: u k1 =[Z k Zs Z tsf / (KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf )]i L

[0119] Formula 14: 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] In order to avoid current oscillation, that is, to avoid i apf For the infinite case, the following damping control analysis is performed:

[0121] Formula 15: KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf ≠0

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

[0123] Formula 16: 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] Formula 17: 0<K≤0.5(Z k Z tsf -Z k Z s -2Z s Z tsf ) / Z tsf

[0125] As shown in Formula 17, the constraint condition of gain K can be obtained, which effectively determines the value range of K; here is the active damping of ADG, Z in Formula 9 k It is called passive damping, which can be mapped one-to-one with the parameters of the relevant circuit; According to Formula 4 to Formula 17, it can be known that K can be determined by offline calculation, and i apf Therefore, due to different wind power impact current i L Rapid determination, i.e., by off-line classification of K, greatly speeds up the output damping of the ADG and lays the foundation for applying backpack optimization ADG to suppress power and voltage shocks.

[0126] After establishing K, i apf Based on this, we can classify the damping state and adjust K, i apf Thereby speeding up the active damping compensation speed of ADG and optimizing the compensation effect. Figure 4 , first determine K offline according to different load conditions, determine the corresponding K according to different load conditions, and then L Real-time computing apf .

[0127] In step six, the optimization objective function and constraint relationship are determined:

[0128] Since formula 12 can be corrected to:

[0129] When performing reactive power compensation, the TSF part performs graded compensation and plays the main role in compensation. Considering the use of the backpack optimization method, the corresponding relationship is determined:

[0130] Formula 18: -i apf =(u2-u s ) / Z s -i tsf +i L

[0131] u2 represents the fundamental voltage;

[0132] Formula 18 highlights the fundamental wave analysis. APF is based on the wind power impulse current i L The reactive power compensation current that realizes active damping is defined by the TSF current. The previous equation can be combined to solve the size of u2. The purpose of the proposed technology is to use the lower-cost TSF to provide the main step-by-step passive damping suppression, and the remaining part of the system is fine-tuned by the higher-cost APF for active damping, so that the combination of small-capacity APF and TSF can continuously compensate for the access power of wind power. In view of the fact that TSF performs passive damping suppression through reactive compensation, the reactive power capacity of TSF for each channel is expressed as follows:

[0133] Formula 19:

[0134] Where Q c , Q L is the reactive power provided by capacitors and inductors, and U2 is the fundamental phase voltage, where i n is the nth harmonic current; considering the ±10% perturbation of the grid voltage, the reactive power compensation target borne by the passive damping part of the ADG is:

[0135] Formula 20: J = max(n 51 Q 51 +n 52 Q 52 +n7Q7)

[0136] Formula 21: Q j =Q Cj -Q Lj

[0137] In the above formula, Q j Indicates the reactive power that each channel can provide, Q Cj , Q Lj are the reactive power emitted by the capacitor and absorbed by the inductor of the channel respectively. Formula 21 satisfies the calculation idea of ​​the backpack problem. Define Q 51 , Q 52 With Q7 being the items to be packed, J being the capacity of the package, and Formula 5 being the combination of items to be packed, the constraints for this knapsack problem are summarized as follows:

[0138] Formula 22: n 51 Q 51 +n 52 Q 52 +n7Q7≤Q 1set

[0139] Formula 23: u1-u 1set ≤0

[0140] Among them, Q 1set u is the maximum reactive power compensated by the system. Since the passive damping part in the ADG device is a step-by-step compensation and cannot be compensated continuously, Formula 23 ensures that over-compensation will not occur and cause voltage increase; u 1set It is the limit voltage that the active filter APF can withstand, and u1 is composed of two parts, namely the fundamental wave voltage division of the resonant branch and the voltage division of each harmonic voltage in the power grid on the resonant branch.

[0141] Here, Formula 20 is the optimization target, and Formula 22 and Formula 23 are optimization constraints. Since Formula 23 is a nonlinear constraint, it is proposed to perform backpack optimization on the branch and bound method, and combine the previous classification algorithm to estimate the value of u1 as an additional bounding condition for branch optimization, so as to obtain the best switch combination within the constraint limit.

[0142] In step 7, the branch and bound method is used to optimize the backpack capacity; however, since the solution of u1 in formula 22 is a complex nonlinear equation. However, since the previous classification algorithm can estimate u1, that is, u1 is u k1 The sum of the fundamental voltage u2 and the fundamental current i apf2 By calculation, we can get:

[0143] Formula 24:

[0144] Formula 25:

[0145] Formula 26: u1=u k1 +u2

[0146] Based on these three formulas, the branch and bound method for this situation is improved.

[0147] In the step eight, formula 26 is combined with constraint formula 23 to form a real-time judgment condition. An additional voltage judgment is performed on the determination of the lower bounds of formulas 20 and 21 in the branch and bound algorithm. If the voltage judgment condition is met, the lower bound is updated, otherwise the original lower bound is retained, thereby avoiding the situation where the optimal solution that meets the 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 Implementation block diagram for backpack optimization, Figure 6This is a diagram of the branch tree of the improved branch and bound method. The process of solving the basic knapsack problem by formula 20 and formula 22 by the branch and bound method is as follows: ① Relax the original problem from only being able to take 0 and 1 to being able to take any number between 0 and 1. The method of constantly updating the upper and lower bounds during the solution 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 subproblem 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 downward. Whether to branch downward depends on whether the objective function value of the node is better than the lower bound. The important feature of the branch tree is that the objective function of the child node will not be greater than that of the parent node, that is, each objective function is strictly ordered. The update time point of the lower bound is when the integer solution obtained is the current best integer solution, then its lower bound will be recorded to form a new lower bound.

[0149] The change is to add a layer of judgment when determining the lower bound, that is, the Z formed by the integer solution tsf Combined with the corresponding gain K and i L The calculated u1 satisfies the constraint condition formula 22. If it does, the lower bound is updated, otherwise the original lower bound is retained. This modification solves the problem that the knapsack optimization cannot directly solve the nonlinear equation, and effectively reduces the amount of calculation.

[0150] Figure 7 and Figure 8 In order to analyze the active compensation effect of ADG based on simulated wind power impact, Fig. 9 The effect diagram of ADG current compensation shows that the harmonics are greatly reduced and the compensation effect meets expectations. Fig.10 and Fig.11 The voltage comparison before and after compensation shows that ADG has a good harmonic suppression effect. Fig.12 It can be seen that under ideal conditions, the response speed of impact suppression is 5.6ms, which is much smaller than that of general compensation devices, and the compensated power factor also reaches above 0.9, proving the effectiveness of classification optimization and backpack optimization.

Claims

1. A method for suppressing wind power grid-connected impact damping based on branch and bound and backpack optimization control, characterized in that: The method comprises the following steps: Step 1: Collect the amplitude and frequency of the bus voltage, bus current, wind power surge current, transformer capacity, short-circuit ratio and equivalent impedance of the wind power grid system, and define the optimal suppression damping that the ADG needs to provide based on this; Step 2: Establish a set of characteristic equations that satisfy the dynamic characteristics of ADG damping, and calculate the equivalent reactance and equivalent inductive reactance; Step 3: Establish the mathematical relationship between the relevant modules in ADG, where the active filter APF is defined as the inrush current i caused by wind power grid access. L and the compensation current i flowing into the node from the APF node c_apf The controlled voltage source u apf ; Classify the different current and voltage conditions of APF output, which are manifested in the system as different damping outputs, and determine the damping combination to provide a basis for classification optimization; Step 4: Use Wu elimination method to derive the system control model under harmonic conditions; Step 5: Determine the active damping gain K and the impulse current i L The corresponding relationship with different wind power input power states completes the classification definition; Based on the classification of this offline method, the real-time measured impulse current i L To quickly calculate APF online, a compensation current i is needed to generate a reverse harmonic component. apf , to achieve rapid damping suppression; Step 6: Determine the objective function of backpack optimization, i.e., the maximum damping output, and give the constraint equation according to the actual situation; Step 7: Perform knapsack optimization calculation based on the branch and bound method of wind power impact, and pre-calculate the voltage constraint relationship in combination with the classification method to provide an algorithm basis for optimal damping suppression; Step 8: Substitute the voltage constraint as an integer bounding condition into the backpack combination calculation to solve the optimal ADG switch control scheme.

2. According to claim 1, a method for suppressing wind power grid-connected impact damping based on branch and bound and backpack optimization control is characterized in that: By analyzing and processing the data sampled in step 1, the required parameters of the ADG equivalent circuit are obtained using the processed data in step 2. The specific calculation is as follows: Formula 1: Formula 2: Among them, Z s is the equivalent reactance of the power grid in the model; U k is the transformer short-circuit ratio; u s is the amplitude of bus voltage; S N is the capacity of the transformer; L s is the equivalent inductive reactance of the power grid; R s is the transformer equivalent impedance, ω is the bus voltage angular frequency; Formula 3: u apf =Ki c_apf For passively damped TSF there are 3 filter channels (n 51 、n 52 , n7), where n 51 、n 52 and n7 represent the 5th, 5th, and 7th order filtering channels respectively; there are 7 damping combinations, and the combination f is defined j =(L j ,C j )(j=51,52,7), where L j , C j are the inductance and capacitance values ​​of a filter channel respectively, f j Indicates a combination of filter channels; the combination form f in the specific case c It is expressed as follows: Formula 4: Considering the impact of APF on each combination, f apf It is represented as a combination of ADG channel outputs, with a total of 8 damping combinations; corresponding to the working states of different proportions of wind power access, the following control classifications are obtained, as described below: Formula 5: In order to suppress power or voltage surge, the above damping combination is used to suppress voltage surge and load current surge in real time.

3. The method for suppressing wind power grid-connected impact damping based on branch and bound and backpack optimization control according to claim 1 is characterized in that: In step 4, in order to classify the power impact of wind power access with different proportions, to avoid the harmonics emitted by APF in ADG and TSF resonance times being the same, thus offsetting the filtering effect and causing TSF to generate overcurrent problems, the ADG system control model is derived by Wu elimination method, and the harmonic times are set to n and the frequency is expressed as f. Then, the harmonic circuit model is set to Z when the equivalent reactance is s =R s +jn2πfL s , the equivalent impedance Z emitted by TSF k It is expressed as follows: Formula Six: Z tsf = 1.0 / (n 51 / Z 51 + n 52 / Z 52 + n 53 / Z 53 ) Formula 7: Z j =j[n2πfL j -1 / (n2πfC j )](j=51,52,7) Formula 8: Formula 9: Z k =R+jn2πfL Formula 10: i tsf =u k1 / Z tsf Among them, j represents the sequence number of the channel, Z tsf is the equivalent impedance of all channels, Z j is the reactance of each filter channel of TSF for the nth harmonic, n j is the switch state of TSF, Z k is the reactance of the TSF equivalent branch, u k1 is the voltage magnitude of the harmonic, i tsf is the equivalent current flowing into TSF, R and L are the equivalent resistance and equivalent inductance of the equivalent reactance.

4. The method for suppressing wind power grid-connection impact damping based on branch and bound and backpack optimization control according to claim 1 is characterized in that: In step 5, for the distortion of sampling voltage and sampling current and harmonic disturbance caused by high proportion of wind power grid access, high proportion of power electronics and intelligent grid control strategy, the active filter APF in ADG is used to generate a current that reversely offsets the harmonic component. The following expression is derived according to Kirchhoff's current law: Official Eleven: [u k1 -K(i L -i tsf +i apf )] / Z k = -i apf Official Twelve:-i apf =u k1 / Z s -i tsf +i L Combining formulas 6 to 12, we get: 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 Formula XIII: u k1 = [Z k Z s Z tsf / (KZ tsf + Z k Z s - Z k Z tsf + Z s Z tsf )]i L Formula XIV: i apf = [(-KZ tsf -Z s Z tsf ) / (KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf )]i L In order to avoid current oscillation, that is, to avoid i apf For the infinite case, the following damping control analysis is performed: Formula XV: KZ tsf +Z k Z s -Z k Z tsf +Z s Z tsf ≠0 In addition, there are the following boundary conditions for the gain K: Formula XVI: 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 Formula XVII: 0 < K ≤ 0.5(Z k Z tsf -Z k Z s -2Z s Z tsf ) / Z tsf As shown in Formula 17, the constraint condition of gain K can be obtained, which effectively determines the value range of K; here is the active damping of ADG, Z in Formula 9 k It is called passive damping, which can be mapped one-to-one with the parameters of the relevant circuit. According to Formula 4 to Formula 17, it can be known that K can be determined by offline calculation, and i apf Therefore, due to different wind power impact current i L Rapid determination, i.e., by off-line classification of K, greatly speeds up the output damping of the ADG and lays the foundation for applying backpack optimization ADG to suppress power and voltage shocks.

5. The method for suppressing wind power grid-connection impact damping based on branch and bound and backpack optimization control according to claim 1 is characterized in that: In step six, the optimization objective function and constraint relationship are determined: Since formula 12 can be corrected to: When performing reactive power compensation, the TSF part performs graded compensation and plays the main role in compensation. Considering the use of the backpack optimization method, the corresponding relationship is determined: Official 18:-i apf =(u2-u s ) / Z s -i tsf +i L u2 represents the fundamental voltage; Formula 18 highlights the fundamental wave analysis. APF is based on the wind power impulse current i L The reactive power compensation current that realizes active damping is defined by the TSF current. The previous equation can be combined to solve the size of u2. Given that TSF performs passive damping suppression through reactive compensation, the reactive power capacity of TSF for each channel is expressed as follows: Formula 19: Where Q c , Q L is the reactive power provided by capacitors and inductors, and U2 is the fundamental phase voltage, where i n is the nth harmonic current; considering the ±10% perturbation of the grid voltage, the reactive power compensation target borne by the passive damping part of the ADG is: Formula 20: J = max(n 51 Q 51 +n 52 Q 52 +n7Q7) Formula 21: Q j =Q Cj -Q Lj In the above formula, Q j Indicates the reactive power that each channel can provide, Q Cj , Q Lj are the reactive power emitted by the capacitor and absorbed by the inductor of the channel respectively. Formula 21 satisfies the calculation idea of ​​the backpack problem. Define Q 51 , Q 52 With Q7 being the items to be packed, J being the capacity of the package, and Formula 5 being the combination of items to be packed, the constraints for this knapsack problem are summarized as follows: Formula 22: n 51 Q 51 +n 52 Q 52 +n7Q7≤Q 1set Formula 23: u1-u 1set ≤0 Among them, Q 1set is the reactive power of the system with maximum compensation. Since the passive damping part in the ADG device is step-by-step compensation and cannot be compensated continuously, Formula 23 ensures that over-compensation will not occur and cause voltage increase; u 1set It is the limit voltage that the active filter APF can withstand, and u1 is composed of two parts, namely the fundamental voltage division of the resonant branch and the voltage division of each harmonic voltage in the power grid on the resonant branch.

6. The method for suppressing wind power grid-connected impact damping based on branch and bound and backpack optimization control according to claim 1 is characterized in that: In step 7, the branch and bound method is used to optimize the selection of the backpack capacity; u1 is estimated, that is, u1 is u k1 The sum of the fundamental voltage u2 and the fundamental current i apf2 By calculation, we can get: Formula 24: Formula 25: Formula 26: u1=u k1 +u2 Based on these three formulas, the branch and bound method for this situation is improved.

7. The method for suppressing wind power grid-connection impact damping based on branch and bound and backpack optimization control according to claim 1 is characterized in that: In the step eight, formula 26 is combined with constraint formula 23 to form a real-time judgment condition. An additional voltage judgment is performed on the determination of the lower bounds of formulas 20 and 21 in the branch and bound algorithm. If the voltage judgment condition is met, the lower bound is updated, otherwise the original lower bound is retained, thereby avoiding the situation where the optimal solution that meets the two constraints is excluded. According to this method, the optimal switch control strategy for wind power impact suppression can be effectively obtained.

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