A grid-connected converter adaptive active support method for different grid impedance ratios

Abstract

The application discloses a grid-connected converter adaptive active support method for different resistance-inductance ratios of power grids, and comprises the following steps: firstly, a three-phase disturbance source is injected into a grid-connected point to measure disturbance responses of grid voltage and current, and to calculate resistance and resistance-inductance ratio of the power grid; secondly, based on the resistance of the power grid, a reference coupling coefficient matrix set containing a cross and a disturbance group is constructed, and a reference coupling coefficient matrix with the highest coefficient fitness is obtained; then, a small signal model of active power and reactive power is established, a per-unit coupling coefficient matrix for evaluating the coupling relationship is calculated; finally, a Hadamard product operation is performed on the reference coupling coefficient matrix and the per-unit coupling coefficient matrix to obtain an actual coupling coefficient matrix, and a grid-connected converter frequency and voltage control equation with both active and reactive components is designed. The application is a grid-connected converter active support method suitable for different resistance-inductance ratios of power grids, and can adaptively adjust controller parameters according to dynamic changes of the resistance of the power grid, so that active support of frequency and voltage can be realized under various working conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of new energy grid-connected power generation, and particularly relates to a grid-connected converter adaptive active support method for different resistance and inductance ratios of power grids. BACKGROUND

[0002] With the rapid development of renewable energy, especially the wide application of wind power and photovoltaic power generation, the proportion of distributed power generation in power grids gradually increases. These distributed power sources are usually connected to power grids through grid-connected converters. The grid-connected converters not only need to convert the direct current of the power source into alternating current synchronized with the power grid, but also need to ensure the stability of the power grid and provide voltage and frequency support capability. The grid-connected converters are mainly divided into grid-following converters and grid-forming converters. Among them, the grid-forming converter can actively control the voltage and frequency, provide the required reactive power and short-term dynamic support of the power grid, and improve the stability of the power grid, so it has become a current research hotspot.

[0003] The control method of the grid-forming grid-connected converter mainly includes virtual synchronous machine control and droop control. The virtual synchronous machine control can provide inertia response similar to the physical synchronous machine, and improve the stability of the power grid under frequency disturbance, but the control logic is complex and the dynamic response speed is slow; the principle of the droop control is simple, does not need complex model or algorithm, and is convenient for engineering implementation, and is suitable for different types of distributed power sources, but the control method assumes that the inductance of the power grid impedance is much larger than the resistance, so that the frequency is only related to the active power and the voltage is only related to the reactive power, and the active power-reactive power coupling relationship cannot be accurately modeled.

[0004] The existing active support method of the grid-connected converter has the following problems:

[0005] (1) The current control method of the grid-connected converter assumes that the inductance of the power grid impedance is much larger than the resistance, and assumes that the active power and the reactive power are independently decoupled, and ignores the coupling relationship between the frequency, voltage, active power and reactive power caused by the power grid impedance. This control method is not suitable for the current complex power grid working condition. When the resistance of the power grid increases, using this method may lead to poor dynamic response of the system, intensified voltage fluctuation, and even cause system oscillation or stability problems;

[0006] (2) The existing control method is usually based on idealized assumptions, i.e. the power grid impedance remains constant and unchanged, and the controller coefficient remains unchanged. However, in the actual power grid, the power grid impedance has dynamic change characteristics due to load fluctuation, line switching or other power source grid connection and other factors, which makes the output power of the converter deviate greatly from the expected value, and even leads to instability, especially in weak power grid or long line environment;

[0007] (3) Many active support methods pay more attention to the recovery ability of frequency and voltage and other steady-state performances, but do not consider the balance between dynamic performance and stability margin. SUMMARY

[0008] The present application aims at the problems existing in the prior art, and provides a grid-connected converter adaptive active support method for different grid impedance ratios, which can be applied to current complex grid operating conditions.

[0009] To solve the above technical problems, the present application provides the following technical scheme: a grid-connected converter adaptive active support method for different grid impedance ratios, comprising the following steps:

[0010] S1, a three-phase current disturbance source is constructed, a grid-connected point is injected at a grid voltage zero-crossing point, then grid voltage and current electrical quantities are measured, and the grid voltage and current electrical quantities are input into a two-stage series complex coefficient filter to obtain a disturbance response of the voltage and current electrical quantities;

[0011] S2, the filtered voltage is divided by the current to obtain a grid impedance, and the grid reactance is further divided by the grid resistance to obtain a grid impedance ratio;

[0012] S3, based on the reactance and resistance of the grid in S2, a reference coupling coefficient matrix set containing a cross and a disturbance group is constructed, two groups of reference coupling coefficient matrices with the highest coefficient fitness are obtained, and the two groups of reference coupling coefficient matrices are combined into a reference coupling coefficient matrix corresponding to the current grid impedance

[0013] S4, according to the input grid voltage and current, expressions of input grid active power and reactive power are obtained, the expressions are linearized near a steady-state operating point, and then rewritten into a matrix form to obtain a coupling coefficient matrix H' describing the relationship between frequency, voltage, active power and reactive power PQ ;

[0014] S5, the coupling coefficient matrix H' PQ is subjected to Hadamard product operation with a transpose of an inverse matrix of the coupling coefficient matrix H' PQ -1 T to obtain a unit coupling coefficient matrix Λ'(H PQ ) evaluating the coupling relationship, then the reference coupling coefficient matrix H in S3 is subjected to Hadamard product operation with the unit coupling coefficient matrix Λ'(H PQ ) to obtain an actual coupling coefficient matrix H;

[0015] ​​S6, design grid-connected converter frequency and voltage control equation with active and reactive components: the column matrix composed of frequency and voltage is equal to the column matrix composed of rated frequency and rated voltage, superimposed with the column matrix composed of active deviation and reactive deviation, left multiplied by the actual coupling coefficient matrix H, and finally the equation of the grid-connected converter controller is constructed, the output angular frequency and output voltage of the controller are combined to synthesize the voltage phasor, and the voltage phasor is used as the reference voltage of the voltage loop controller for subsequent grid-connected converter control.

[0016] Further, the aforementioned step S1 comprises the following substeps:

[0017] S101, according to the switching frequency and dead zone setting of the grid-connected inverter, Fourier analysis is performed on the deviation voltage generated by the dead zone time to obtain a set of background harmonic frequencies of the inverter: wherein f1 is the fundamental frequency, i is a constant, n is the number of background harmonic frequencies, f vsci is the i-th background harmonic frequency of the inverter;

[0018] S102, Fourier analysis is performed on the voltage and current components of the grid-connected point to obtain the grid background harmonics generated by the nonlinear load, and a set of background harmonic frequencies of the three-phase grid is obtained: wherein, is the i-th background harmonic frequency of the three-phase grid;

[0019] S103, set the intersection of the set of injectable harmonic frequencies of the grid-connected point and the set of inverter background harmonic frequencies to be an empty set, and the intersection of the set of injectable harmonic frequencies of the grid-connected point and the set of grid background harmonic frequencies to be an empty set: wherein, set Q represents the current frequency that can be injected into the grid-connected point, and Φ represents an empty set;

[0020] S104, select the frequency f disq from set Q, take I disq as the amplitude, and θ disq as the phase angle, construct a three-phase current disturbance source, and inject it into the grid-connected point at the zero-crossing point of the grid voltage by using parallel injection: S105, measure the grid voltage and current electrical quantities after injecting the three-phase current disturbance source, convert the two electrical quantities to the αβ coordinate system, take the α-axis component of the electrical quantity in the αβ coordinate system as the real part and the β-axis component as the imaginary part, construct a complex electrical quantity, and obtain the voltage complex vector U αβ (s), the current complex vector I αβ (s), and the complex vector X αβ (s) is used to represent them.

[0021] X αβ (s) = X α (s) + jX β (s;

[0022] S106, input the complex vector X αβ (s) the multiple complex coefficient filter G of the pre-stage non-disturbance decoupling module MCCF (s),

[0023]

[0024] P i+ and P i- represent the first-order filter corresponding to different background harmonic frequencies: ω i represent the angular frequency of the i-th harmonic, ω ic is the cut-off frequency of the corresponding first-order complex coefficient filter;

[0025] S107, input the initial response X αβ (s) of the voltage or current αβ (s), the transfer function corresponding to the initial response to the filtered response is 1-G MCCF (s), calculate the disturbance response of the voltage and current as follows:

[0026] X' αβq (s) = (1-G MCCF (s))X αβ (s)

[0027] S108, input the disturbance response X' αβq (s) of the voltage and current at the disturbance frequency into the post-stage second-order complex coefficient filter G q+ (s) and G q- (s), separate the positive sequence X' αβq (s) and the negative sequence component X' αβq+ (s) of X' αβq- (s), as follows:

[0028]

[0029] ω q is the angular frequency of the disturbance source ω q = 2πf q , ω qc is the cut-off frequency of the second-order complex coefficient filter;

[0030] S109, the disturbance source injected into the grid point is a three-phase symmetric disturbance source, the negative sequence component response is zero, and the filtered voltage and current positive sequence component responses are reserved, as follows:

[0031]

[0032] Further, the aforementioned step S2, the reactance and resistance of the power grid are calculated in the following steps:

[0033] S201, divide the filtered voltage by the current to obtain the impedance of the power grid Z(jω q ), as follows:

[0034]

[0035] S202, divide the reactance of the power grid by the resistance of the power grid to obtain the reactance-to-resistance ratio X / R of the power grid, as follows:

[0036] X / R = X q (jω q ) / R q = X q / R q ;

[0037] In the formula, X q is the reactance of the power grid, and R q is the resistance of the power grid;

[0038] Further, the aforementioned step S3 includes the following sub-steps:

[0039] S301, based on the reactance X q of the power grid in step S201, randomly generate N sets of initial reference coupling coefficients, each set containing an active-frequency coupling coefficient and a reference reactive-voltage coupling coefficient, with the initial value range set as K PW ∈[a1, b1], K QV ∈[a2, b2], input each set of reference coupling coefficients into the built Simulink simulation model, measure the dynamic performance and stability margin, and input the comprehensive objective function to calculate the fitness value f(K PWi , K QVi ):

[0040] f(K PWi , K QVi ) = α1f dyn (K PWi , K QVi ) + α2f stab (K PWi , K QVi )

[0041] Comprehensive objective function: In the formula, f dyn (K PWi , K QVi ) is the dynamic performance score of the system when the current coupling coefficients are used, the lower the performance, the better, including the regulation time t s and the overshoot σ%, f stab (K PWi , KQVi ) is a stability margin score of the system with the current coupling coefficient, GM is a maximum value of gain margin to maintain stability, PM is a minimum phase angle to maintain stability, GM min , PM min are threshold values of stability margin, α1, α2, ω s , ω σ％ , ω GM , ω PM are weight coefficients, α1+α2=1, ω s +ω σ％ =1, ω GM +ω PM =1

[0042] S302, substitute N groups of reference coupling coefficients into the comprehensive objective function to calculate fitness f(K PWi , K QVi ), and keep the reference coupling coefficients with high fitness in the first N / 2 groups;

[0043] S303, design an adaptive crossover probability P c : wherein and are lower and upper limits of the crossover probability respectively, σ f is a standard deviation of fitness of the N / 2 groups of reference coupling coefficients, σ0 is a constant, and α is a control parameter;

[0044] According to the crossover probability P c , two groups of reference coupling coefficients (K PWa , K QVa ) and (K PWb , K QVb ) in step 3202 are randomly selected, and a new two groups of reference coupling coefficients are generated by using linear combination:

[0045]

[0046] wherein η∈[0, 1] is a random crossover factor, and the step can obtain new N / 2 groups of reference coupling coefficients;

[0047] S304, design an adaptive disturbance probability P m : wherein and are lower and upper limits of the disturbance probability respectively, and β is a control parameter;

[0048] According to the disturbance probability P m , one group of reference coupling coefficients (K PWc , K QVc) applying perturbation, generating a new set of reference coupling coefficients:

[0049]

[0050] wherein δ1∈[a1, b1], δ2∈[a2, b2] are random perturbation factors, and step S304 obtains another new N / 2 sets of reference coupling coefficients;

[0051] S305, combining the reference coupling coefficients in step S303 and step S304 to obtain a new N sets of reference coupling coefficients, repeating steps S302-S304 until the maximum iteration number T is reached, stopping iteration, and outputting the set of reference coupling coefficients with the highest fitness in the current N sets of reference coupling coefficients

[0052] S306, calculating the optimal reference reactive-power-frequency coupling coefficient and the optimal reference active-voltage coupling coefficient corresponding to the resistance of the power grid in step S301 according to steps S301-S305;

[0053] S307, combining the optimal reference active-power-frequency coupling coefficient and the optimal reference reactive-voltage coupling coefficient in step S305 with the optimal reference reactive-power-frequency coupling coefficient and the optimal reference active-voltage coupling coefficient in step S306 to construct a reference coupling coefficient matrix

[0054] Further, the aforementioned step S4 comprises the following sub-steps:

[0055] S401, the current from the grid-connected point to the power grid is: According to the active power and reactive power calculation formula of three-phase circuit P=Re(VI * ), Q=Im(VI * ),

[0056] The active power is calculated as follows:

[0057]

[0058] The reactive power is calculated as follows:

[0059]

[0060] wherein V pcc is the grid-connected point voltage amplitude, V g is the grid voltage amplitude, δ is the power angle related to frequency, θ q is the impedance angle corresponding to the grid impedance, and the relationship with the short-circuit ratio is θ q =arctan(X q / R q );

[0061] S402, small signal linearization of active and reactive power expressions around steady state operating point, Taylor expansion of active power expression and reactive power expression of step S401 around steady state operating point (V pcc , θ q ) and keeping first order terms:

[0062]

[0063] Where partial derivatives are:

[0064]

[0065] Arranging four partial derivatives into matrix form, coupling coefficient matrix H PQ describing the relationship of frequency, voltage, active power and reactive power is obtained:

[0066]

[0067] S403, combining the condition that V pcc ≈V g at steady state and power angle is zero, coupling coefficient matrix H' PQ is simplified as follows:

[0068]

[0069] Further, the aforementioned step S5 includes the following sub-steps:

[0070] S501, inverse matrix of coupling coefficient matrix H' PQ is taken and transpose operation is performed to obtain ((H' PQ ) - ) 1T :

[0071] S502, Hadamard product calculation of coupling coefficient matrix H' PQ and transpose matrix of inverse matrix of coupling coefficient matrix H' PQ ) -1 ) T , unit coupling coefficient matrix Λ'(H PQ ) evaluating coupling relationship is obtained:

[0072]

[0073] In the formula, is Hadamard product, the operation represented by is the product of corresponding elements of matrix, is active-frequency unit coupling coefficient, is reactive-frequency unit coupling coefficient, is reactive-voltage unit coupling coefficient, is the active-voltage coupling coefficient;

[0074] S503, the unit coupling coefficient matrix Λ'(H PQ ) in step S502 and the reference coupling coefficient matrix Λ in step 307 are subjected to Hadamard product operation to obtain an actual coupling coefficient matrix H:

[0075]

[0076] Further, the aforementioned step S6 comprises the following sub-steps:

[0077] S601, according to the actual coupling coefficient matrix H in step S503, a frequency and voltage control equation of the grid-connected converter with both active and reactive components is designed: a column matrix composed of frequency and voltage is equal to a column matrix composed of rated frequency and rated voltage, superimposed with a column matrix composed of active deviation and reactive deviation left multiplied by the actual coupling coefficient matrix H:

[0078]

[0079] In the formula, =ω ref is the rated angular frequency, U ref is the rated voltage, P ref is the rated active power, Q ref is the rated reactive power, P is the actual active power of the power grid, and Q is the actual reactive power of the power grid.

[0080] The specific equation of the grid-connected converter controller is:

[0081]

[0082] S602, the output angular frequency and the output voltage of the controller are combined to synthesize a voltage phasor, which is used as the reference voltage of the voltage loop controller for subsequent grid-connected converter control.

[0083] Compared with the prior art, the beneficial technical effects of the above technical solutions of the present application are as follows:

[0084] (1) For different resistance-inductance ratios of the power grid, the coupling coefficient matrix can be adaptively adjusted, effectively reducing the influence of the resistance-inductance ratio change of the power grid on the control performance, and ensuring that the converter can realize stable operation in weak power grids and different resistance-inductance ratio scenarios;

[0085] (2) The control method can capture the dynamic coupling characteristics of the power grid through an accurate model, further optimize the controller design, enhance the dynamic response capability of the system to disturbances, effectively reduce the control deviation caused by model errors, and improve the steady-state performance;

[0086] ​(3) The control method not only improves the support capability of frequency and voltage, but also optimizes the dynamic performance and stability margin through the optimization algorithm, so that the system reaches the optimal balance between different performance indicators. BRIEF DESCRIPTION OF DRAWINGS

[0087] Figure 1 is the overall flowchart of the present application;

[0088] Figure 2 is the control block diagram of the present application;

[0089] Figure 3 is the relationship between the per unit coupling coefficient and the resistance-inductance ratio in the present application;

[0090] Figure 4 is the waveform diagram of the frequency support under different resistance-inductance ratios in the present application;

[0091] Figure 5 is the waveform diagram of the voltage support under different resistance-inductance ratios in the present application. DETAILED DESCRIPTION

[0092] In order to better understand the technical content of the present application, specific embodiments are described below with reference to the accompanying drawings.

[0093] Aspects of the present application are described in this detailed description and illustrated in the accompanying drawings by various illustrative embodiments. Embodiments of the present application are not limited to the drawings described. It should be understood that the present application is implemented by any one of the above-mentioned concepts and embodiments, and the concepts and embodiments described in detail below, because the concepts and embodiments disclosed in the present application are not limited to any embodiment. In addition, some aspects disclosed in the present application can be used alone, or in any suitable combination with other aspects disclosed in the present application.

[0094] Reference Figure 1 , the present application provides a grid-connected converter adaptive active support method for different resistance-inductance ratios of power grid, comprising the following steps:

[0095] S1, construct a three-phase current disturbance source, inject the grid point at the zero crossing point of the grid voltage, then measure the grid voltage and current electrical quantities, and input the grid voltage and current electrical quantities into a two-stage series complex coefficient filter to obtain the disturbance response of the voltage and current electrical quantities;

[0096] S2, divide the filtered voltage by the current to obtain the grid impedance, and further divide the grid reactance by the grid resistance to obtain the resistance-inductance ratio of the grid;

[0097] S3. Based on the reactance and resistance of the power grid in S2, construct a set of reference coupling coefficient matrices containing crossover and disturbance groups. Calculate the two sets of reference coupling coefficient matrices with the highest coefficient fitness and merge them into a reference coupling coefficient matrix corresponding to the current power grid impedance.

[0098] S4. Based on the voltage and current of the input grid, obtain the expressions for the active and reactive power of the input grid. Perform small-signal linearization on these expressions near the steady-state operating point, and then rewrite them in matrix form to obtain the coupling coefficient matrix H′ describing the relationship between frequency, voltage, active power, and reactive power. PQ ;

[0099] S5. The coupling coefficient matrix H′ PQ Its inverse matrix transpose ((H) ′ PQ ) -1 ) T Performing the Hadamard product operation yields the per-unit coupling coefficient matrix Λ′(H) that evaluates the coupling relationship. PQ Then, the reference coupling coefficient matrix in S3 is... Coupling coefficient matrix Λ′(H) with per unit PQ The actual coupling coefficient matrix H is obtained by performing the Hadamard product operation.

[0100] S6. Design the frequency and voltage control equations for the grid-connected converter that combine active and reactive components: The column matrix composed of frequency and voltage is equal to the column matrix composed of rated frequency and rated voltage. The column matrix composed of active deviation and reactive deviation is superimposed and multiplied by the actual coupling coefficient matrix H on the left. Finally, the equations of the grid-connected converter controller are constructed. The output angular frequency and output voltage of the controller are combined to synthesize the voltage phasor. The voltage phasor is used as the reference voltage of the voltage loop controller for subsequent grid-connected converter control.

[0101] In a preferred embodiment of the present invention, step S1 includes the following sub-steps:

[0102] S101. Based on the switching frequency and dead-time settings of the grid-connected inverter, the background harmonic frequency set of the inverter is obtained by performing Fourier analysis on the deviation voltage caused by the dead time:

[0103] In the formula, f1 is the fundamental frequency, i is a constant, n is the number of background harmonic frequencies, and f vsci Let i be the background harmonic frequency of the i-th inverter;

[0104] S102. Perform Fourier analysis on the voltage and current components at the grid connection point to obtain the background harmonics of the power grid generated by the nonlinear load, and obtain the set of background harmonic frequencies of the three-phase power grid: in, Let i be the frequency of the i-th three-phase power grid background harmonic;

[0105] S103. Set the set of harmonic frequencies that can be injected into the grid connection point to be an empty set when it intersects with the set of background harmonic frequencies of the inverter, and also to be an empty set when it intersects with the set of background harmonic frequencies of the power grid: In the formula, set Q represents the current frequency that can be injected into the grid, and Φ represents the empty set;

[0106] S104. Select frequency f from set Q. disq , take I disq For amplitude, θ disq To determine the phase angle, a three-phase current disturbance source is constructed, and a parallel injection method is used to inject it into the grid connection point when the grid voltage crosses zero. S105. Measure the voltage and current electrical quantities of the power grid after injecting a three-phase current disturbance source. Transform the two electrical quantities to the αβ coordinate system, and construct complex electrical quantities by taking the α-axis component of the electrical quantities in the αβ coordinate system as the real part and the β-axis component as the imaginary part, thus obtaining the complex voltage vector U. αβ (s), complex current vector I αβ (s), uniformly represented by the complex vector X αβ (s) represents X αβ (s)=X α (s)+jX β (s;

[0107] S106, the complex vector X αβ (s) The multi-complex coefficient filter G of the input pre-stage perturbation-free decoupling module MCCF (s),

[0108]

[0109] In the formula, P i+ and P i- This represents a first-order filter corresponding to different background harmonic frequencies: ω i ω represents the angular frequency of the i-th harmonic. ic It is the cutoff frequency of the corresponding first-order complex coefficient filter;

[0110] S107, The initial response X of voltage or current αβ (s) Subtract X' from the output of the pre-stage filter αβ (s), the transfer function corresponding to the initial response to the filtered response is 1-G. MCCF (s), calculate the disturbance response of voltage and current, as follows:

[0111] X' αβq (s)=(1-G MCCF (s))X αβ (s)

[0112] S108. The disturbance response X' of voltage and current at the disturbance frequency. αβq (s) Input post-stage second-order complex coefficient filter G q+ (s) and G q- (s), separating X' αβq (s) in ascending order X' αβq+ (s) and negative order component X' αβq- (s), as shown in the following formula:

[0113]

[0114] In the formula, ω q ω is the angular frequency of the disturbance source. q =2πf q ω qc This is the cutoff frequency of the second-order complex coefficient filter;

[0115] S109. The disturbance source injected into the grid connection point is a three-phase symmetrical disturbance source with zero negative sequence component response. The filtered positive sequence voltage and current component responses are retained, as shown in the following equation:

[0116]

[0117] In a preferred embodiment of the present invention, the specific steps for calculating the reactance and resistance of the power grid in step S2 are shown in the table below:

[0118] S201. Divide the filtered voltage by the current to obtain the grid impedance Z(jω). q ), as shown in the following formula:

[0119]

[0120] S202. Divide the grid reactance by the grid resistance to obtain the grid inductance ratio X / R, as shown in the following formula:

[0121] X / R = X q (jω q ) / R q =X q / R q ;

[0122] In the formula, X q R is the power grid reactance. q The resistance of the power grid;

[0123] In a preferred embodiment of the present invention, step S3 includes the following sub-steps:

[0124] S301, Based on the reactance X of the power grid in step S201 qN sets of initial reference coupling coefficients are randomly generated using a MATLAB program. Each set includes an active-frequency coupling coefficient and a reference reactive-voltage coupling coefficient. The initial value range is set to K. PW ∈[a1, b1], K QV ∈[a2, b2], input each set of baseline coupling coefficients into the constructed Simulink simulation model, measure dynamic performance and stability margin, and input the comprehensive objective function to calculate the appropriate value f(K). PWi K QVi ):

[0125] f(K PWi ,K QVi )=α1f dyn (K PWi ,K QVi )+α2f stab (K PWi ,K QVi )

[0126] Overall objective function: In the formula, f dyn (K PWi K QVi This represents the dynamic performance score of the system using the current coupling coefficient; a lower score indicates better performance, including the settling time t. s and overshoot σ%, f stab (K PWi K QVi ) represents the system's stability margin score with the current coupling coefficients, GM represents the gain margin (maximum value for maintaining stability), and PM represents the phase margin (minimum phase angle for maintaining stability). min PM min The threshold for stability margin, α1, α2, ω s ω σ％ ω GM ω PM For the weighting coefficients, α1 + α2 = 1, ω s +ω σ％ =1, ω GM +ω PM =1;

[0127] S302. Substitute the N sets of benchmark coupling coefficients into the comprehensive objective function to calculate the fitness f(K). PWi K QVi ), retain the benchmark coupling coefficients with high fitness in the first N / 2 groups;

[0128] S303, Design an adaptive crossover probability P c : In the formula and These are the lower and upper bounds of the crossover probability, respectively, and σ.f σ0 is the standard deviation of the fitness of the N / 2 group of benchmark coupling coefficients, σ0 is a constant, and α is a control parameter;

[0129] According to the crossover probability P c Randomly select two sets of reference coupling coefficients (K) in step 3202 PWa K QVa (K) PWb K QVb Two new sets of reference coupling coefficients are generated by cross-referencing using a linear combination method:

[0130]

[0131] In the formula, η∈[0,1] is a random crossover factor, and this step can obtain a new N / 2 sets of benchmark coupling coefficients;

[0132] S304, Design an adaptive perturbation probability P m : In the formula and These are the lower and upper limits of the disturbance probability, respectively, and β is the control parameter;

[0133] According to the disturbance probability P m Randomly select a set of reference coupling coefficients (K) in step S302 PWc K QVc Apply a perturbation to generate a new set of reference coupling coefficients:

[0134]

[0135] In the formula, δ1∈[a1, b1] and δ2∈[a2, b2] are random perturbation factors. Step S304 yields another N / 2 sets of reference coupling coefficients.

[0136] S305. Combine the baseline coupling coefficients from steps S303 and S304 to obtain N new sets of baseline coupling coefficients. Repeat steps S302-S304 until the maximum number of iterations T is reached, then stop iterating and output the set of baseline coupling coefficients with the highest fitness among the current N sets of baseline coupling coefficients.

[0137] S306. Calculate the optimal reference reactive-frequency coupling coefficient and reference active-voltage coupling coefficient corresponding to the grid resistance in step S301, according to steps S301 to S305.

[0138] S307. Combine the optimal reference active-frequency coupling coefficient and reference reactive-voltage coupling coefficient from step S305 with the optimal reference reactive-frequency coupling coefficient and reference active-voltage coupling coefficient from step 306 to construct a reference coupling coefficient matrix.

[0139] As a preferred embodiment of the present application, step S4 comprises the following sub-steps:

[0140] S401, the current from the grid-connected point to the power grid is: According to the active power and reactive power calculation formula of three-phase circuit P=Re(VI * ), Q=Im(VI * ),

[0141] The active power is calculated as follows:

[0142]

[0143] The reactive power is calculated as follows:

[0144]

[0145] In the formula, V pcc is the grid-connected point voltage amplitude, V g is the power grid voltage amplitude, δ is the power angle related to frequency, θ q is the impedance angle corresponding to the power grid impedance, and the relationship with the short-circuit ratio is θ q =arctan(X q / R q );

[0146] S402, small signal linearization of active and reactive power expressions near the steady-state operating point, Taylor expansion of the active power expression and the reactive power expression of step S401 near the steady-state operating point (V pcc , θ q ) is carried out, and the first-order term is retained:

[0147]

[0148] Among them, the partial derivative is:

[0149]

[0150] The four partial derivatives are arranged in matrix form to obtain the coupling coefficient matrix H PQ describing the relationship between frequency, voltage, active power and reactive power:

[0151]

[0152] S403, combining the condition that V pcc ≈V g at steady state and the power angle is zero to simplify the coupling coefficient matrix H' PQ , as follows:

[0153]

[0154] As a preferred embodiment of the present application, step S5 comprises the following sub-steps:

[0155] S501, calculate the coupling coefficient matrix H' of the power grid: PQ Take the inverse matrix and then transpose to get ((H' )-1 PQ ) -1 T

[0156]

[0157] S502, calculate the Hadamard product of the coupling coefficient matrix H' of the power grid and the transposed matrix of the inverse matrix ((H' )-1 PQ ) PQ -1 T to obtain the unit coupling coefficient matrix Λ'(H PQ ) for evaluating the coupling relationship:

[0158]

[0159] In the formula, is the Hadamard product, and the operation represented by is the product of the corresponding elements of the matrix, is the active-frequency unit coupling coefficient, and the greater the value, the greater the coupling degree of frequency and active power, is the reactive-frequency unit coupling coefficient, and the greater the value, the greater the coupling degree of frequency and reactive power, is the reactive-voltage unit coupling coefficient, and the greater the value, the greater the coupling degree of voltage and reactive power, is the active-voltage unit coupling coefficient, and the greater the value, the greater the coupling degree of voltage and active power;

[0160] S503, calculate the Hadamard product of the unit coupling coefficient matrix Λ'(H PQ ) in step S502 and the reference coupling coefficient matrix in step S307 to obtain the actual coupling coefficient matrix H:

[0161]

[0162] As a preferred embodiment of the present application, step S6 comprises the following sub-steps:

[0163] S601, according to the actual coupling coefficient matrix H in step S503, design the frequency and voltage control equation of the grid-connected converter with active and reactive components: the column matrix composed of frequency and voltage is equal to the column matrix composed of rated frequency and rated voltage, and is multiplied by the actual coupling coefficient matrix H of the column matrix composed of active deviation and reactive deviation: ​​​​

[0164]

[0165] In the formula, =ω ref is the rated angular frequency, U ref is the rated voltage, P ref is the rated active power, Q ref is the rated reactive power, P is the actual active power of the power grid, and Q is the actual reactive power of the power grid.

[0166] The specific equation of the grid-connected converter controller is:

[0167]

[0168] S602, combine the output angular frequency of the controller with the output voltage to synthesize a voltage phasor, and use it as the reference voltage of the voltage loop controller for subsequent grid-connected converter control.

[0169] The method will be further described below in combination with specific embodiment results. Table 1 shows the key simulation parameters of the grid-connected converter model facing different resistance-inductance ratios of the power grid:

[0170] Table 1

[0171]

[0172]

[0173] Three-phase disturbance sources are injected into three power grids to measure three sets of grid impedance, Z1=(0.0735+j0.679)Ω, Z2=(0.106+j0.532)Ω, and Z3=(0.142+j0.498)Ω. Table 2 shows the reference coupling coefficient matrix corresponding to the three kinds of impedance, and Table 3 shows the resistance-inductance ratio and the per-unit coupling coefficient matrix under three different grid impedances.

[0174] Table 2

[0175]

[0176] Table 3

[0177]

[0178] Figure 2 is the overall control block diagram, and the shaded part is the controller part designed by the application; Figure 3 is the per-unit coupling coefficient corresponding to different resistance-inductance ratios, and the per-unit coupling coefficient corresponding to each grid impedance angle is determined; Figure 4 is the adaptive support effect of the frequency under three impedance ratios, and it can be seen that the frequency response is fast and has no overshoot; Figure 5The adaptive support effect of the voltage when the three impedance ratios are disturbed can be seen from the fact that the overvoltage amplitude is small, the overall response is rapid, and the final overshoot is small.

[0179] In the description of the present specification, the description referring to the terms "one embodiment", "an example", "a specific example" and the like means that the specific feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. In the present specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific feature, structure, material or characteristic described can be combined in an appropriate manner in any one or more embodiments or examples.

[0180] Although the present application has been described in connection with the preferred embodiment thereof with reference to the drawings, it is not intended to limit the present application to the preferred embodiment and numerous modifications and variations could be devised by those skilled in the art without departing from the spirit and scope of the present application. Therefore, it is intended that the scope of the present application be governed by the scope of the claims and their equivalents.

Claims

1. A grid-connected converter adaptive active support method for different grid impedance ratios, characterized in that, The method comprises the following steps: S1, constructing a three-phase current disturbance source, injecting the grid-connected point at the zero-crossing point of the grid voltage, then measuring the grid voltage and current electrical quantities, and inputting the grid voltage and current electrical quantities into a two-stage series complex coefficient filter to obtain the disturbance response of the voltage and current electrical quantities; S2, dividing the filtered voltage by the current to obtain the grid impedance, and further dividing the grid reactance by the grid resistance to obtain the resistance-reactance ratio of the grid; S3, constructing a set of reference coupling coefficient matrices containing cross and disturbance groups based on the reactance and resistance of the power grid in S2, obtaining two groups of reference coupling coefficient matrices with the highest coefficient fitness, and merging them into a reference coupling coefficient matrix corresponding to the current power grid impedance S4. Based on the voltage and current of the input grid, obtain the expressions for the active and reactive power of the input grid. Perform small-signal linearization on these expressions near the steady-state operating point, and then rewrite them in matrix form to obtain the coupling coefficient matrix H′ describing the relationship between frequency, voltage, active power, and reactive power. PQ ; S5、coupling coefficient matrix H' is obtained by making Hadamard product operation between the coupling coefficient matrix H and the inverse matrix of the coupling coefficient matrix H PQ and its transpose ((H' PQ ) -1 ) T Hadamard product operation is made between the coupling coefficient matrix H and the inverse matrix of the coupling coefficient matrix H PQ to obtain the unit coupling coefficient matrix Λ'(H ) for evaluating the coupling relationship, and then the reference coupling coefficient matrix H PQ in S3 and the unit coupling coefficient matrix Λ'(H PQ ) are made to have Hadamard product operation to obtain the actual coupling coefficient matrix H; S6, designing a grid-connected converter frequency and voltage control equation with both active and reactive components: the column matrix composed of frequency and voltage is equal to the column matrix composed of rated frequency and rated voltage, multiplied by the actual coupling coefficient matrix H of the column matrix composed of active deviation and reactive deviation, and finally constructing the equation of the grid-connected converter controller, combining the output angular frequency and output voltage of the controller to synthesize a voltage vector, and taking the voltage vector as the reference voltage of the voltage loop controller for subsequent grid-connected converter control.

2. The grid adaptive active support method for grid different reactance ratio of grid-connected converter according to claim 1, characterized in that, Step S1 comprises the following sub-steps: S101、According to the switching frequency of the grid-connected inverter and the dead zone setting, the background harmonic frequency set of the inverter is obtained by Fourier analysis of the deviation voltage generated by the dead zone time: V: In the formula, f1 is the fundamental frequency, i is a constant, n is the number of background harmonic frequencies, f vsci is the i-th inverter background harmonic frequency; S102. Perform Fourier analysis on the voltage and current components at the grid connection point to obtain the background harmonics of the power grid generated by the nonlinear load, and obtain the set of background harmonic frequencies of the three-phase power grid: G: wherein, is the i-th three-phase grid background harmonic frequency; S103, set the harmonic frequency set of the injectable grid point intersecting with the inverter background harmonic frequency set as an empty set, and the harmonic frequency set intersecting with the grid background harmonic frequency set as an empty set: In the formula, set Q represents the current frequency of the injectable grid point, and Φ represents an empty set. S104, select the frequency f in the set Q disq , take I disq for amplitude, θ disq for phase angle, construct a three-phase current disturbance source, adopt parallel injection method, inject at the grid voltage zero point: S105, measure the grid voltage and current electrical quantities after injecting the three-phase current disturbance source, convert the two electrical quantities to the αβ coordinate system, and take the α-axis component of the electrical quantity in the αβ coordinate system as the real part and the β-axis component as the imaginary part to construct a complex electrical quantity, to obtain a voltage complex vector U αβ (s), a current complex vector I αβ αβ (s) represents X αβ (s) = X α (s) = X β (s) = X​ S106, the complex vector X αβ (s) inputting a multi-complex coefficient filter G of the pre-stage disturbance-free decoupling module MCCF (s), where P i+ and P i- denotes a first order filter corresponding to different background harmonic frequencies: ω i denotes the angular frequency of the i-th harmonic, ω ic is the cut-off frequency of the corresponding first order complex coefficient filter; S107, subtracting the initial response X αβ (s) of the pre-stage filter output X' αβ (s), the transfer function corresponding to the initial response to the filtered response is 1 - G MCCF (s), calculating the perturbation response of the voltage and the current as follows: X' αβq (s) = (1 - G MCCF (s)) X αβ (s) S108, the disturbance response X' of the voltage and current under the disturbance frequency αβq (s) input post-stage second-order complex coefficient filter G q+ (s) and G q- (s), separate out the positive sequence X' of X' αβq (s) and the negative sequence component X' αβq+ (s) and the negative sequence component X' αβq- (s), as follows: where ω q is the angular frequency of the disturbance source ω q = 2πf q , ω qc is the cutoff frequency of the second-order complex coefficient filter; S109, the disturbance source injected into the grid-connected point is a three-phase symmetric disturbance source, the negative sequence component response is zero, and the filtered voltage and current positive sequence component responses are retained, as follows:

3. The adaptive active support method for grid- connected converters with different grid impedance ratios according to claim 1, characterized in that, In step S2, the specific steps for calculating the reactance and resistance of the grid are as follows: S201, divide the filtered voltage by the filtered current to obtain the grid impedance Z(jω q ), as follows: S202, dividing the grid reactance by the grid resistance to obtain the resistance-reactance ratio X / R of the grid, as follows: X / R = X q (jω q ) / R q = X q / R q ; where X q is the grid reactance, R q is the grid resistance.

4. The grid adaptive active support method for grid different reactance ratio of grid-connected converter according to claim 1, characterized in that, Step S3 comprises the following sub-steps: S301、based on the step S201 of the grid reactance X q , randomly generate N groups of initial reference coupling coefficients, each group containing active-frequency coupling coefficient and reference reactive-voltage coupling coefficient, initial value range setting K PW ∈[a1, b1], K QV ∈[a2, b2], input each group of reference coupling coefficients into the built Simulink simulation model, measure dynamic performance and stability margin, input comprehensive objective function to calculate appropriate value f(K PWi , K QVi ): The comprehensive objective function is: wherein f dyn (K PWi , K QVi ) is the dynamic performance score of the system using the current coupling coefficient, the lower the performance the better, including the adjustment time t s and the overshoot σ%, f stab (K PWi , K QVi ) is the stability margin score of the system using the current coupling coefficient, GM is the gain margin, the maximum value to maintain stability, PM is the phase margin, the minimum phase angle to maintain stability, GM min , PM min is the threshold value of the stability margin, α1, α2, ω s , ω σ％ , ω GM , ω PM is the weight coefficient, α1+α2=1, ω s +ω σ％ =1, ω GM +ω PM =1. S302, substitute the N groups of reference coupling coefficients into the comprehensive objective function to calculate the fitness f(K PWi , K QVi ), and keep the reference coupling coefficients with high fitness in the first N / 2 groups. S303, design adaptive crossover probability P c : wherein and are the lower and upper limits of the crossover probability, respectively, σ f is the standard deviation of the N / 2 groups of reference coupling coefficient fitness, σ0is a constant, and α is a control parameter; According to the cross probability P c The two sets of reference coupling coefficients (K PWa , K QVa ), (K PWb , K QVb ) in the random selection step 3202 are cross-generated in a linear combination manner to generate two new sets of reference coupling coefficients: In the formula, η∈[0, 1] is a random crossover factor, and this step can obtain N / 2 new sets of reference coupling coefficients; S304、design an adaptive disturbance probability P m : wherein and are the lower and upper limits of the disturbance probability, respectively, and β is a control parameter. According to the disturbance probability P m A set of reference coupling coefficients (K PWc , K QVc ) is randomly selected in step S302, and a new set of reference coupling coefficients is generated by applying a disturbance In the formula, δ1∈[a1, b1] and δ2∈[a2, b2] are random disturbance factors, and step S304 obtains another N / 2 new sets of reference coupling coefficients; S305, combine the reference coupling coefficient sets in step S303 and step S304 to obtain a new N sets of reference coupling coefficients, repeat step S302-step S304 until the maximum iteration number T is reached, stop iteration, and output the set of reference coupling coefficients with the highest fitness in the current N sets of reference coupling coefficients S306, calculating the optimal reference reactive-frequency coupling coefficient and reference active-voltage coupling coefficient corresponding to the resistance of the grid in step S301 according to steps S301 to S305; S307, combine the optimal reference active-power-frequency coupling coefficient and the reference reactive-power-voltage coupling coefficient in step S305 with the optimal reference reactive-power-frequency coupling coefficient and the reference active-power-voltage coupling coefficient in step S306 to construct a reference coupling coefficient matrix 5. The adaptive active support method for grid- connected converters with different grid impedance ratios according to claim 1, characterized in that, Step S4 comprises the following sub-steps: S401、the current from the grid-connected point to the power grid is: According to the active power and reactive power calculation formula of the three-phase circuit P = Re(VI * ), Q = Im(VI * ), The active power is calculated as follows: The reactive power is calculated as follows: where V pcc is the grid voltage amplitude, V g is the grid voltage amplitude, δ is the power angle related to frequency, θ q is the impedance angle corresponding to the grid impedance, and the relationship with the short circuit ratio is θ q = arctan(X q / R q ); S402, small signal linearization of active and reactive power expressions around steady state operating point, Taylor expansion of the active power expression and the reactive power expression of step S401 around the steady state operating point (V pcc , θ q ) is performed and the first order terms are retained: Where the partial derivative is: The four partial derivatives are arranged into a matrix form to obtain a coupling coefficient matrix H describing the relationship between frequency, voltage, active power and reactive power PQ : S403、Combine the steady-state V pcc ≈V g , the condition that the power angle is zero simplifies the coupling coefficient matrix H' PQ as follows:

6. The grid-oriented adaptive active support method for different grid reactance ratio of the grid-connected converter according to claim 1, characterized in that, Step S5 comprises the following sub-steps: S501、To the coupling coefficient matrix H' PQ Take inverse matrix and transpose operation to get ((H' PQ ) -1 ) T : S502、coupling coefficient matrix H PQ is calculated, and the transposed matrix of the inverse matrix of H PQ ) -1 ) T is calculated, and the transposed matrix of the inverse matrix of H PQ ) is calculated. wherein is the Hadamard product, the operation denoted by represents the product of the corresponding elements of the matrices, is the active-frequency per unit coupling coefficient, is the reactive-frequency per unit coupling coefficient, is the reactive-voltage per unit coupling coefficient, is the active-voltage per unit coupling coefficient; S503, perform Hadamard product operation on the normalized coupling coefficient matrix Λ'(H PQ ) in step S502 and the reference coupling coefficient matrix Λ(H ) in step S307 to obtain the actual coupling coefficient matrix H:

7. The grid adaptive active support method for grid different reactance ratio oriented grid-connected converter according to claim 1, characterized in that, Step S6 comprises the following sub-steps: S601, according to the actual coupling coefficient matrix H in step S503, designing a grid-connected converter frequency and voltage control equation with both active and reactive components: the column matrix composed of frequency and voltage is equal to the column matrix composed of rated frequency and rated voltage, multiplied by the actual coupling coefficient matrix H of the column matrix composed of active deviation and reactive deviation: where = ω ref is the rated angular frequency, U ref is the rated voltage, P ref is the rated active power, Q ref is the rated reactive power, P is the actual active power of the grid, and Q is the actual reactive power of the grid. The specific equation of the grid-connected converter controller is as follows: S602, combining the output angular frequency and output voltage of the controller to synthesize a voltage vector, and taking the voltage vector as the reference voltage of the voltage loop controller for subsequent grid-connected converter control.

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