A method for identifying control parameters of voltage and current loop in grid-connected new energy sources

Abstract

This invention discloses a method for identifying control parameters of the voltage and current loop in grid-connected renewable energy systems, belonging to the field of power distribution system parameter identification technology. The method includes establishing a high-order closed-loop transfer function for the voltage and current loop, then decoupling the different response times caused by different control bandwidths in different control links, using the Routh approximation to reduce the order of the high-order transfer function to obtain a second-order transfer function of the output voltage, and using a particle swarm optimization algorithm to identify the parameters of the equivalent voltage and current control loop model after the order reduction. This avoids the influence of uniform identification and high-sensitivity parameters on the identification results of low-sensitivity parameters, achieving accurate parameter identification. This invention has certain noise resistance and good stability, and exhibits high identification accuracy.

Description

Technical Field

[0001] This invention relates to the field of power distribution system parameter identification technology, and in particular to a method for identifying control parameters of voltage and current loops in grid-connected new energy sources. Background Technology

[0002] As the penetration rate of new energy sources in the power system continues to increase, grid-connected new energy power sources, represented by photovoltaic and wind power, have become an important part of the distribution network. These power sources are connected to the grid through inverters, and their operating characteristics are fundamentally different from those of traditional synchronous generators, resulting in a significant change in the operating characteristics of the distribution network.

[0003] Grid-connected renewable energy converters exhibit "voltage source" characteristics, possessing the ability to autonomously construct voltage and frequency. They can provide stable AC voltage in weak power grids and have garnered widespread attention in new power systems dominated by renewable energy. The large-scale integration of grid-connected converters alters the fault characteristics of power systems, necessitating the establishment of accurate simulation models of power systems incorporating grid-connected inverters for fault analysis and protection design. However, due to manufacturers' confidentiality measures, key control parameters are unavailable, making it difficult for simulation models to accurately simulate real faults. Therefore, it is crucial to identify the control parameters of grid-connected inverters during fault transients. The uncertainty and volatility of distributed power source integration make traditional fixed-parameter current protection strategies ill-suited to handle dynamic system changes, easily leading to insufficient protection sensitivity or malfunctions. Summary of the Invention

[0004] The purpose of this invention is to provide a method for identifying control parameters of voltage and current loops in grid-connected new energy sources, thereby solving the problem of low accuracy in existing identification methods.

[0005] To achieve the above objectives, this invention provides a method for identifying control parameters of the voltage and current loop in a grid-connected new energy system, comprising the following steps:

[0006] S1. Establish the inverter circuit model and transform the circuit equations to two-phase synchronous rotation. dq In coordinate system;

[0007] S2, using feedforward compensation to... dq The coupling and disturbance components of the shaft are compensated and decoupled to obtain a complete voltage and current dual-loop control block diagram; dq The mathematical equations in the coordinate system are transformed by Laplace to obtain the circuit equations in the frequency domain. The complete voltage and current double-loop control block diagram is combined with the circuit equations in the frequency domain to obtain the equivalent control block diagram.

[0008] S3. Based on the equivalent control block diagram, write down the output capacitor voltage. With input reference voltage Closed-loop transfer function between them;

[0009] S4. Calculate all closed-loop poles of the closed-loop transfer function and analyze the distance of each pole from the imaginary axis;

[0010] S5. Use the improved Routh approximation method to reduce the order of the fourth-order closed-loop transfer function.

[0011] S6. Introduce the performance indicators of integral absolute error and time integral absolute error to verify the effectiveness of the order reduction.

[0012] S7. Perform an inverse Laplace transform on the expression for the output capacitor voltage of the current loop in the complex frequency domain after the order reduction simplification.

[0013] S8. Introduce structural similarity based on graph similarity as the objective function to perform structural similarity discrimination;

[0014] S9. Use the particle swarm optimization algorithm to perform global optimization of the parameters and obtain the final identification result output.

[0015] Preferably, in step S1, Kirchhoff's laws are used to establish an inverter circuit model. The circuit equations in the coordinate system are:

[0016] ;

[0017] ;

[0018] In the formula, R e This is the equivalent resistance from the inverter port to the grid connection point. L e The equivalent inductance from the inverter port to the grid connection point. This refers to the three-phase capacitor voltage value. This represents the three-phase inductor current value. t For time, The three-phase electromotive force output by the inverter. C This is the capacitance value of the capacitor connected in parallel at the inverter output. This refers to the three-phase load current output by the inverter.

[0019] Preferably, in step S3, the closed-loop transfer function is:

[0020] ;

[0021] In the formula, This is the voltage inner loop proportional coefficient. The voltage inner loop integral coefficient, This is the proportionality coefficient for the inner current loop. The integral coefficient of the inner current loop. L The equivalent inductance of the circuit,C For the circuit output capacitor, r The equivalent resistance of the circuit. s For the complex frequency variable of the Laplace transform;

[0022] make, l 0= LC , , , , , , , , l 0、 l 1. l 2. l 3. l 4. c 0、 c 1. c 2 are intermediate algebraic symbols, and the closed-loop transfer function is simplified as follows:

[0023] .

[0024] Preferably, in step S4, the expression for calculating the closed-loop poles of the closed-loop transfer function is:

[0025] ;

[0026] ;

[0027] In the formula, All are closed-loop poles. j For imaginary units, y 1. y 2. y All three are intermediate variables;

[0028] in:

[0029] ;

[0030] In the formula, A , B , D These are all underlying variables. i For angle variables;

[0031] A , B , D The specific solution method is as follows:

[0032] ;

[0033] In the formula, C This is the redundancy coefficient; E ,F All are solutions A , B , D Process variables;

[0034] Based on the distance of the real part of each closed-loop pole from the imaginary axis, determine whether there is a dominant closed-loop pole.

[0035] Preferably, in step S5, the parameter expression in the Routh stability matrix list is:

[0036] ;

[0037] In the formula, For the index of the row in the list of Routh stability matrix, ; For the index of a column in the Routh stability matrix list, ;in e 11 = l 0, e 21 = l 1, e 12 = l 2, e 22 = l 3, e 13 = l 4, e 23 =0;

[0038] The expression for the denominator polynomial of the closed-loop transfer function after order reduction using the Routh approximation method is as follows:

[0039] ;

[0040] The specific expression for the coefficients of the denominator polynomial of the reduced closed-loop transfer function is as follows:

[0041] .

[0042] Preferably, in step S5, the expression for the numerator polynomial of the closed-loop transfer function after order reduction using the Routh approximation method is:

[0043] ;

[0044] in, β 1. β The numerator coefficients of the closed-loop transfer function after order reduction to 0.

[0045] ;

[0046] The expression for the second-order closed-loop transfer function after Routh approximation reduction is:

[0047] .

[0048] Preferably, in step S6, the expressions for the two performance indicators, integral absolute error (IAE) and time integral absolute error (ITAE), are as follows:

[0049] ;

[0050] ;

[0051] in, y ( t i )for t i The unit step response of the original higher-order system at time t, y r ( t i )for t i The unit step response of the time-decrease system.

[0052] Preferably, in step S7, the inverse Laplace transform is:

[0053] ;

[0054] In the formula, The output capacitor voltage in the reduced-order model. For the inverse Laplace transform, This represents the virtual electromotive force inside the inverter.

[0055] ;

[0056] In the formula, The steady-state virtual potential before the fault. b This represents the steady-state virtual potential after the fault. e ( t ) is a unit step function.

[0057] Preferably, in step S8, the structural similarity expression is:

[0058] ;

[0059] In the formula, X and Y The waveform data sequence to be compared is as follows: m x and m y Represent X and Y mean s x and s y Let X and Y represent the variances, respectively. s xy represent X and Y covariance; C 1 and C 2 represents the stability coefficient, taken as... They are 0.01 and 0.03 respectively; L’ This represents the maximum magnitude difference.

[0060] Preferably, in step S9, the global optimization of parameters using the particle swarm optimization algorithm specifically involves:

[0061] Initialize particle swarm parameters, , , As a position parameter of the particle, k ii The parameters are fixed and do not participate in the first round of iterative optimization. , , The parameters and external characteristics of the LC filter are used in iterative optimization. After obtaining the optimal voltage inner loop proportional coefficient, voltage inner loop integral coefficient, and current inner loop proportional coefficient through the optimization algorithm, the... , , The current inner loop integral coefficient is fixed as a known quantity; the current inner loop integral coefficient is set as an unknown quantity to participate in the second round of iterative optimization to obtain the current inner loop integral coefficient.

[0062] The advantages and positive effects of the grid-type new energy voltage and current loop control parameter identification method described in this invention are:

[0063] 1. This invention establishes a high-order closed-loop transfer function for the voltage and current loops, decouples them by utilizing the different response times caused by different control bandwidths in different control loops, reduces the order of the high-order transfer function using the Routh approximation, and then combines it with the particle swarm optimization algorithm for global parameter optimization. This avoids the influence of unified identification and high-sensitivity parameters on the identification results of low-sensitivity parameters, and achieves accurate identification of parameters such as the voltage inner loop proportional coefficient, voltage inner loop integral coefficient, current inner loop proportional coefficient, and current inner loop integral coefficient.

[0064] 2. By using feedforward compensation to compensate and decouple the coupling and disturbance components of the dq axis, a complete voltage and current dual-loop control block diagram is obtained, enabling the system to better cope with complex operating conditions such as grid fluctuations and load changes, and improving the stability and reliability of the inverter participating in the distribution network operation.

[0065] 3. This invention introduces integral absolute error and time integral absolute error performance indicators to verify the effectiveness of the order reduction. By using structural similarity based on the degree of graphic similarity as the objective function for discrimination, the consistency between the reduced model and the original system is ensured, thereby improving the accuracy of the entire parameter identification.

[0066] 4. This invention uses an improved Routh approximation method to reduce the order of a fourth-order closed-loop transfer function, simplifying the high-order system into a second-order system, which greatly reduces computational complexity, improves computational efficiency, and ensures the accuracy of the model, thus providing convenience for engineering applications.

[0067] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0068] Figure 1 This is a flowchart of the method for identifying control parameters of grid-type new energy voltage and current loops according to the present invention.

[0069] Figure 2 This is a block diagram of the equivalent structure of the inverter in the dq coordinate system of the present invention;

[0070] Figure 3 This is an equivalent control block diagram of the present invention;

[0071] Figure 4 The measured voltage data of phase A under three different voltage drop levels are shown, along with the identified fitted waveforms: (a) voltage drop depth of 40%, (b) voltage drop depth of 60%, and (c) voltage drop depth of 80%. Detailed Implementation

[0072] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In case of any inconsistency, the meaning set forth in this specification or derived from the content described herein shall prevail. Furthermore, the terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit the scope of this application.

[0073] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0074] like Figure 1 As shown. A method for identifying control parameters of voltage and current loop in grid-connected new energy sources includes the following steps:

[0075] S1. Establish the inverter circuit model and transform the circuit equations to two-phase synchronous rotation. dq In a coordinate system.

[0076] Using Kirchhoff's laws, establish an inverter circuit model. The circuit equations in the coordinate system are:

[0077] ;

[0078] ;

[0079] In the formula, R e This is the equivalent resistance from the inverter port to the grid connection point. L e The equivalent inductance from the inverter port to the grid connection point. This refers to the three-phase capacitor voltage value. This represents the three-phase inductor current value. t For time, The three-phase electromotive force output by the inverter. C This is the capacitance value of the capacitor connected in parallel at the inverter output. This refers to the three-phase load current output by the inverter.

[0080] S2, using feedforward compensation to... dq The coupling and disturbance components of the shaft are compensated and decoupled to obtain a complete voltage and current dual-loop control block diagram.

[0081] Feedforward compensation is used to compensate and decouple the coupling and disturbance components of the dq axis. To ensure that the system can respond quickly and operate stably and efficiently, both the voltage and current inner loops adopt proportional-integral control. The complete voltage and current dual-loop control block diagram is obtained by combining the circuit equations shown above.

[0082] The complete voltage and current dual-loop control block diagram is as follows: Figure 3 The left side shows the section used to precisely regulate the inverter's output voltage and current, enabling the inverter to stably participate in the distribution network operation. The inner loop voltage control determines the target, while the inner loop current control tracks it quickly. Through dual-loop coordination, it addresses operating conditions such as grid fluctuations and load changes. The left-side inner voltage loop includes a voltage loop reference value. Voltage feedback u C And a voltage PI controller. The voltage PI controller calculates the voltage deviation and, through PI adjustment, outputs a current loop reference value. The function of the voltage PI controller is to quickly respond to voltage deviations, eliminate steady-state errors, and ensure that the voltage stably tracks the reference value. The right-hand inner current loop includes the current loop reference value. Current feedback And a current PI controller. The current PI controller calculates the current deviation and outputs a modulated signal through PI adjustment. The function of the current PI controller is to quickly track the current reference value, suppress current fluctuations, and indirectly regulate the dynamic response of the output voltage through inductor current control.

[0083] To simplify control, the circuit equations in the abc coordinate system are transformed into mathematical equations in the dq coordinate system and then subjected to Laplace transform to the frequency domain, yielding the circuit equations in the frequency domain:

[0084] ;

[0085] In the formula, for d / q Shaft input voltage, The voltage across the capacitor. For inductor current, For input current, L The equivalent inductance of the circuit, C For the circuit output capacitor, r The equivalent resistance of the circuit. s Let be the complex frequency variable of the Laplace transform. This leads to the equivalent block diagram of the inverter in the dq coordinate system, as shown below. Figure 2 As shown.

[0086] Combining the complete voltage and current dual-loop control block diagram with the circuit equations in the frequency domain, we obtain the equivalent control block diagram of the inverter, such as... Figure 3 As shown.

[0087] S3. Based on the equivalent control block diagram, write down the output capacitor voltage. With input reference voltage The closed-loop transfer function between them.

[0088] Output capacitor voltage With input reference voltage The closed-loop transfer function between them is:

[0089] ;

[0090] In the formula, This is the voltage inner loop proportional coefficient. The voltage inner loop integral coefficient, This is the proportionality coefficient for the inner current loop. The integral coefficient of the inner current loop. L The equivalent inductance of the circuit, C For the circuit output capacitor, r The equivalent resistance of the circuit. s For the complex frequency variable of the Laplace transform;

[0091] make, l 0= LC , , , , , , , , l 0、 l 1. l 2. l 3. l 4. c 0、 c 1. c 2 are intermediate algebraic symbols, and the closed-loop transfer function is simplified as follows:

[0092] .

[0093] S4. Calculate all closed-loop poles of the closed-loop transfer function and analyze the distance of each pole from the imaginary axis.

[0094] The closed-loop poles are the solutions to the closed-loop transfer function when the denominator is zero, reflecting the system's stability and dynamic response speed. If the real part of the closed-loop pole is negative, it indicates that the system is stable; the more negative the real part, the faster the response. If the real part of the closed-loop pole is positive, it indicates that the system is unstable; the more positive the real part, the faster the divergence.

[0095] The expression for calculating the closed-loop poles of the closed-loop transfer function is as follows:

[0096] ;

[0097] ;

[0098] In the formula, All are closed-loop poles. j For imaginary units, y 1. y 2. y All three are intermediate variables.

[0099] in:

[0100] ;

[0101] In the formula, A , B , D These are all underlying variables. i For angle variables;

[0102] A , B , D The specific solution method is as follows:

[0103] ;

[0104] In the formula, C This is the redundancy coefficient; E , F All are solutions A , B , D Process variables.

[0105] A , B , C , D、E , F All of these are variables in the calculation process, including the five coefficients in the fourth-order equation of the closed-loop transfer function. l 0、 l 1. l 2. l 3. l 4. The amount required to transform into a cubic equation A , B , C , D、E , F Essentially, it reduces the order of higher-order equations.

[0106] In engineering practice, the concept of dominant poles is often used to approximate the analysis of high-order systems. The dynamic performance of the system is basically determined by the closed-loop poles closest to the imaginary axis. The dominant poles are used to replace all closed-loop poles to estimate the system's performance indicators. In practical applications, one or several closed-loop poles closest to the imaginary axis are selected as dominant poles from all closed-loop poles, while closed-loop poles that are two or three times or more away from the imaginary axis than the dominant poles are neglected. Therefore, the gain of high-order systems is often adjusted to give the system a pair of conjugate dominant closed-loop poles, and the dynamic performance of the high-order system is estimated using the dynamic performance of the second-order system.

[0107] The selection of filter network parameters (L, C, R) for grid-connected inverters must comply with electromagnetic transient characteristics and system stability requirements. Based on practical experience in engineering projects and a comprehensive analysis of the equipment technical parameters from mainstream equipment manufacturers such as Hopewind, XJ Electric, and NARI Group, combined with the standardized design specifications for secondary equipment parameters in power systems, the typical order ranges for filter inductance, filter capacitor, and filter resistor are determined to be 10. -3 10 -5 10 -2 To achieve fast command tracking performance in the inverter, the parameter tuning of the proportional-integral regulator in the voltage and current dual closed-loop control system must meet the overdamped dynamic response characteristics.

[0108] Based on the above analysis of closed-loop pole theory, the analytical expression shows that the system has two pairs of conjugate complex poles. By focusing on the distance of the real part from the imaginary axis, the dominant closed-loop poles can be determined. Numerical calculations and theoretical analysis show that... and The real part magnitudes differ significantly, with a relative distance exceeding 200%, satisfying the closed-loop dominant pole condition.

[0109] S5. Use the improved Routh approximation method to reduce the order of the fourth-order closed-loop transfer function.

[0110] The Routh stability array table is obtained by calculating the coefficients of each term in the denominator of the closed-loop transfer function. The parameter expressions in the Routh stability array table are as follows:

[0111] ;

[0112] In the formula, For the index of the row in the list of Routh stability matrix, ; For the index of a column in the Routh stability matrix list, The first two rows of parameters in the Routh stable array table consist of the coefficients of the terms in the denominator of the closed-loop transfer function, i.e. e 11 = l 0, e 21 = l 1, e 12 = l 2, e 22 = l 3, e 13 = l 4, e 23 =0.

[0113] The expression for the denominator polynomial of the closed-loop transfer function after order reduction using the Routh approximation method is as follows:

[0114] ;

[0115] e 31 = e 12 -( e 11 . e 22 ) / e 21 , e 41 = e 22 -( e 21 . e 32 ) / e 31 , e 32 = e 13 -( e 11 . e 23) / e 21 .

[0116] The specific expression for the coefficients of the denominator polynomial of the reduced closed-loop transfer function is as follows:

[0117] .

[0118] The expression for the numerator polynomial of the closed-loop transfer function after order reduction using the Routh approximation method is as follows:

[0119] ;

[0120] in, β 1. β The numerator coefficients of the closed-loop transfer function after order reduction to 0. The method for solving the numerator coefficients is as follows:

[0121] ;

[0122] The expression for the second-order closed-loop transfer function after Routh approximation reduction is:

[0123] .

[0124] S6. Introduce the performance indicators of integral absolute error and time integral absolute error to verify the effectiveness of the order reduction.

[0125] The expressions for the two performance indicators, Integral Absolute Error (IAE) and Time Integral Absolute Error (ITAE), are as follows:

[0126] ;

[0127] ;

[0128] in, y ( t i )for t i The unit step response of the original higher-order system at time t, y r ( t i )for t i The unit step response of the time-decrease system.

[0129] While reducing the order of a high-order model can improve computational speed, it may reduce the accuracy of the analysis. The effectiveness of the order reduction is verified using the absolute error of integration and the absolute error of time integration to ensure the effectiveness of the identification method. There is no unified absolute range for the absolute error of integration and the absolute error of time integration, as their values ​​are highly dependent on the dynamic characteristics of the specific system; in practical applications, smaller values ​​are better.

[0130] S7. Perform an inverse Laplace transform on the expression for the output capacitor voltage of the current loop in the complex frequency domain after the order reduction simplification.

[0131] The reduced-order complex frequency domain ( s The expression for the capacitor voltage in the time domain, converted back to the time domain. t The complex frequency domain (CFD) facilitates the analysis of transient processes. It includes two main actions: (1) Performing an inverse Laplace transform on the reduced-order complex frequency domain capacitor voltage expression to establish a mapping from the "complex frequency domain mathematical relationship" to the "time domain physical signal". (2) Combining transient characteristics, splitting the steady-state and transient components of the virtual potential, substituting them into the calculation, and then performing another inverse transform to finally obtain the time domain capacitor voltage.

[0132] The inverse Laplace transform is:

[0133] ;

[0134] In the formula, The output capacitor voltage in the reduced-order model. For the inverse Laplace transform, This is the virtual electromotive force inside the inverter.

[0135] During the transient period, the reactive power control loop will quickly reach a steady state, from which the virtual electromotive force inside the inverter can be obtained. E ref After the fault occurs, the stable operating value is maintained. Mutation to b ,

[0136] ;

[0137] In the formula, This represents the steady-state virtual potential before the fault, corresponding to the steady-state response. b For the steady-state virtual potential after the fault, ( b - a ) e ( t This corresponds to the transient response. e(t) A unit step function describes the abrupt change in time when the fault occurs; for example... t The fault occurs at time =0. When ) is 0, ( When ), it is 1.

[0138] S8. Introduce structural similarity based on the degree of graphic similarity as the objective function to perform structural similarity discrimination.

[0139] By introducing structural similarity based on the degree of graphic similarity as the objective function, it can judge the structural similarity of image data from three perspectives: mean, variance, and covariance, and can sensitively reflect subtle changes in voltage waveform.

[0140] The structural similarity expression is:

[0141] ;

[0142] In the formula, X and Y The waveform data sequence to be compared is as follows: m x and m y Represent X and Y mean s x and s y Let X and Y represent the variances, respectively. s xy represent X and Y covariance; C 1 and C 2 represents the stability coefficient, taken as... They are 0.01 and 0.03 respectively; L’ This represents the maximum magnitude difference.

[0143] S9. Use the particle swarm optimization algorithm to perform global optimization of the parameters and obtain the final identification result output.

[0144] The specific steps for global parameter optimization using the particle swarm optimization algorithm are as follows:

[0145] Initialize particle swarm parameters, , , As a position parameter of the particle, The parameters are fixed and do not participate in the first round of iterative optimization. , , The parameters and external characteristics of the LC filter are used in iterative optimization. After obtaining the optimal voltage inner loop proportional coefficient, voltage inner loop integral coefficient, and current inner loop proportional coefficient through the optimization algorithm, the... , , The current inner loop integral coefficient is fixed as a known quantity; the current inner loop integral coefficient is set as an unknown quantity to participate in the second round of iterative optimization to obtain the current inner loop integral coefficient.

[0146] Example

[0147] Based on the circuit equations and control strategies of the grid-type inverter, the fourth-order closed-loop transfer function of the voltage and current inner loop is derived.

[0148] By solving the closed-loop characteristic equation, two pairs of conjugate poles are determined. and ,in This allows the real part to be closer to the pole of the imaginary axis, providing a mechanism for reducing the order of the model.

[0149] Construct a Routh-stabilized array table and extract key coefficients. e 31 , e 32 , e 41 As the denominator coefficients of the reduced second-order transfer function, and using dynamic response performance indicators such as integral absolute error (IAE) and time integral absolute error (ITAE), the dynamic response error between the reduced model and the original system is verified, ensuring that the core characteristics of the actual control loop are preserved during the reduction process.

[0150] In the experimental platform, a three-phase symmetrical fault was simulated on the 35kV busbar on the grid side, and three-phase voltage data at the point of common coupling (PCC) were collected.

[0151] Based on the phase information provided by the active frequency loop, Voltage data in coordinate system converted to dq Coordinate system components.

[0152] Calculate the output data by combining the randomly given control parameters and the external characteristic data of the LC filter. U Ccal The structural similarity (SSIM) function is used as the objective function to describe the computation of the output data. U Ccal The degree of fit between the data and the measured data.

[0153] The particle swarm optimization algorithm is used to globally optimize the parameters, ultimately yielding the optimal result. ， ， ， The value is output as the final identification result.

[0154] The main parameters of the embodiment are shown in Table 1.

[0155] Table 1 Main parameters of the embodiment

[0156] ;

[0157] To verify the effectiveness of the identification method described in this invention, three different voltage drop scenarios were investigated. Figure 4 Measured voltage data of phase A under three different voltage drop levels were used to identify and fit waveforms. Data with voltage drop depths of 40%, 60%, and 80% were collected for parameter identification. Figure 4 The actual value is the measured output voltage waveform of phase A of the inverter, reflecting the dynamic changes in voltage under real operating conditions; the fitted value is the phase A voltage waveform calculated using the identification method described in this invention. Figure 4 As can be seen, the waveforms of the actual and fitted values ​​are consistent, and the amplitude deviation is very small, indicating that the control parameters obtained by the identification method described in this invention are accurate and the model has high accuracy.

[0158] Therefore, the method for identifying voltage and current loop control parameters of grid-type new energy sources described in this invention can correctly identify voltage and current loop control parameters, solving the problem that traditional identification methods are difficult to correctly identify.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for identifying control parameters of voltage and current loops in grid-connected new energy sources, characterized in that, Includes the following steps: S1. Establish the inverter circuit model and transform the circuit equations to two-phase synchronous rotation. dq In coordinate system; S2, using feedforward compensation to... The coupling and disturbance components of the shaft are compensated and decoupled to obtain a complete voltage and current dual-loop control block diagram; The mathematical equations in the coordinate system are transformed by Laplace to obtain the circuit equations in the frequency domain. The complete voltage and current double-loop control block diagram is combined with the circuit equations in the frequency domain to obtain the equivalent control block diagram. S3. Based on the equivalent control block diagram, write down the output capacitor voltage. With input reference voltage Closed-loop transfer function between them; S4. Calculate all closed-loop poles of the closed-loop transfer function and analyze the distance of each pole from the imaginary axis; S5. Use the improved Routh approximation method to reduce the order of the fourth-order closed-loop transfer function. S6. Introduce the performance indicators of integral absolute error and time integral absolute error to verify the effectiveness of the order reduction. S7. Perform an inverse Laplace transform on the expression for the output capacitor voltage of the current loop in the complex frequency domain after the order reduction simplification. S8. Introduce structural similarity based on graph similarity as the objective function to perform structural similarity discrimination; S9. Use the particle swarm optimization algorithm to perform global optimization of the parameters and obtain the final identification result output; In S3, the closed-loop transfer function is: ； In the formula, This is the voltage inner loop proportional coefficient. The voltage inner loop integral coefficient, This is the proportionality coefficient for the inner current loop. The integral coefficient of the inner current loop. The equivalent inductance of the circuit, For the circuit output capacitor, The equivalent resistance of the circuit. For the complex frequency variable of the Laplace transform; make, , , , , , , , , , , , , , , , All are intermediate algebraic symbols. The closed-loop transfer function is simplified as follows: ； In step S5, the coefficients of each term in the denominator of the closed-loop transfer function are calculated to obtain the Routh stability array table. The parameter expressions in the Routh stability array table are as follows: ； In the formula, For the index of the row in the list of Routh stability matrix, =1,2,3,4; For the index of a column in the Routh stability matrix list, =1,2,3; where , , , , , ; The expression for the denominator polynomial of the closed-loop transfer function after order reduction using the Routh approximation method is as follows: ； The specific expression for the coefficients of the denominator polynomial of the reduced closed-loop transfer function is as follows: 。 2. The method for identifying control parameters of grid-type new energy voltage and current loops according to claim 1, characterized in that, In S1, Kirchhoff's laws are used to establish an inverter circuit model. The circuit equations in the coordinate system are: ； ； In the formula, This is the equivalent resistance from the inverter port to the grid connection point. The equivalent inductance from the inverter port to the grid connection point. This refers to the three-phase capacitor voltage value. This represents the three-phase inductor current value. For time, The three-phase electromotive force output by the inverter. This is the capacitance value of the capacitor connected in parallel at the inverter output. This refers to the three-phase load current output by the inverter.

3. The method for identifying control parameters of grid-type new energy voltage and current loops according to claim 2, characterized in that, In S4, the expression for calculating the closed-loop poles of the closed-loop transfer function is: ； ； In the formula, All are closed-loop poles. For imaginary units, All are intermediate variables; in: ； In the formula, A , B , D These are all underlying variables. For angle variables; A , B , D The specific solution method is as follows: ； In the formula, C This is the redundancy coefficient; E , F All are solutions A , B , D Process variables; Based on the distance of the real part of each closed-loop pole from the imaginary axis, determine whether there is a dominant closed-loop pole.

4. The method for identifying control parameters of voltage and current loop in a grid-connected new energy system according to claim 3, characterized in that: In S5, the expression for the numerator polynomial of the closed-loop transfer function after order reduction using the Routh approximation method is as follows: ； in, These are all numerator coefficients of the reduced-order closed-loop transfer function. ； The expression for the second-order closed-loop transfer function after Routh approximation reduction is: 。 5. The method for identifying control parameters of grid-type new energy voltage and current loops according to claim 4, characterized in that, In S6, the expressions for the two performance indicators, integral absolute error (IAE) and time integral absolute error (ITAE), are as follows: ； ； in, for The unit step response of the original higher-order system at time t, for The unit step response of the time-decreasing system.

6. The method for identifying control parameters of grid-type new energy voltage and current loops according to claim 5, characterized in that, In S7, the inverse Laplace transform is: ； In the formula, The output capacitor voltage in the reduced-order model. For the inverse Laplace transform, This represents the virtual electromotive force inside the inverter. ； In the formula, The steady-state virtual potential before the fault. This represents the steady-state virtual potential after the fault. It is a unit step function.

7. The method for identifying control parameters of grid-type new energy voltage and current loops according to claim 6, characterized in that, In S8, the structural similarity expression is: ； In the formula, X and Y The waveform data sequence to be compared is as follows: and Represent X and Y mean and Let X and Y represent the variances, respectively. represent X and Y covariance; C 1 and C 2 represents the stability coefficient, taken as... , , They are 0.01 and 0.03 respectively; This represents the maximum magnitude difference.

8. The method for identifying control parameters of grid-type new energy voltage and current loops according to claim 7, characterized in that, In S9, the global optimization of parameters using the particle swarm optimization algorithm is specifically as follows: Initialize particle swarm parameters, As a position parameter of the particle, The parameters are fixed and do not participate in the first round of iterative optimization. The parameters and external characteristics of the LC filter are used in iterative optimization. After obtaining the optimal voltage inner loop proportional coefficient, voltage inner loop integral coefficient, and current inner loop proportional coefficient through the optimization algorithm, the... , , The current inner loop integral coefficient is fixed as a known quantity; the current inner loop integral coefficient is set as an unknown quantity to participate in the second round of iterative optimization to obtain the current inner loop integral coefficient.

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