Filter-containing rectification load parameter identification method and system based on Z transformation

Abstract

The invention belongs to the technical field of power electronics, and provides a filter-containing rectification load parameter identification method and system based on Z transformation, and the method comprises the steps: obtaining the equivalent topology of a filter; determining a transfer function between the alternating current side current and the alternating current side voltage of the filter according to the obtained equivalent topology of the filter; processing the determined transfer function based on bilinear transformation and Z transformation to obtain a matrix expression between the alternating current side voltage and the alternating current side current; obtaining an unknown element parameter expression in the equivalent topology according to the obtained matrix expression; and solving unknown parameters in an unknown element parameter expression in the obtained equivalent topology based on a gradient identification algorithm, and completing filter topology parameter identification based on Z transformation.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a method and system for identifying parameters of a filter-containing rectifier load based on Z transformation. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the rapid development of power electronics technology and the popularization of new electrical equipment, the proportion of single-phase uncontrolled rectifier bridge devices in residential and commercial electricity consumption continues to rise. Nonlinear loads inject characteristic harmonics into the power grid during operation, particularly odd-order harmonics, primarily the third, fifth, and seventh harmonics. This not only significantly increases the total harmonic distortion (THD) of the power supply system but also causes serious power quality issues. In actual operation, harmonic pollution not only causes additional iron and copper losses in transformers and motors and accelerates insulation aging, but also leads to systemic risks such as abnormally increased neutral current and harmonic resonance in capacitor banks. These negative effects directly manifest themselves in prominent issues such as reduced power conversion efficiency, shortened equipment life, and malfunctioning relay protection.

[0004] To meet increasingly stringent power quality standards, electrical equipment manufacturers are adopting multi-stage filtering architectures, including front-stage EMI filters to suppress high-frequency conducted interference, intermediate-stage passive LC filters to absorb key characteristic harmonics, and post-stage active filters to dynamically compensate for residual harmonics. However, the introduction of filtering devices presents challenges in system modeling, such as increased topological complexity and increased sensitivity to high-frequency parasitic parameters. The nonlinear characteristics of filters require comprehensive consideration of component parasitics during modeling, placing higher demands on the robustness of parameter identification algorithms and the effectiveness of model reduction techniques. Summary of the Invention

[0005] To solve the above problems, the present invention proposes a Z-transform-based method and system for identifying the parameters of a rectifier load containing a filter. Based on the equivalent topological characteristics of a typical single-phase uncontrolled rectifier bridge device containing an LC / LCL filter on the AC side, gradient optimization is used to overcome the nonlinear solution problem caused by the coupling of component parameters, thereby achieving accurate identification of the key parameters of the filter, constructing a digital twin physical model with clear physical meaning, and efficiently and quickly identifying the unknown parameters of the components in the topology without destroying the equipment.

[0006] According to some embodiments, a first solution of the present invention provides a method for identifying load parameters of a filter-containing rectifier based on a Z transform, which adopts the following technical solutions: A Z-transform-based method for identifying parameters of a filter-containing rectifier load comprises: Get the equivalent topology of the filter; Determine the transfer function between the AC side current and the AC side voltage of the filter based on the obtained filter equivalent topology; Based on the transfer function determined by bilinear transformation and Z-transformation, the matrix expression between the AC side voltage and the AC side current is obtained; According to the obtained matrix expression, the unknown component parameter expression in the equivalent topology is obtained; The unknown parameters in the unknown component parameter expressions in the equivalent topology obtained by solving the gradient identification algorithm are used to complete the filter topology parameter identification based on Z transform.

[0007] As a further technical limitation, the process of solving the unknown parameters in the unknown component parameter expression in the equivalent topology obtained by the gradient identification algorithm is: obtaining estimated values calculated by the component expression of the unknown parameters in the equivalent topology; preprocessing the unknown component parameter expression in the equivalent topology, extracting estimated values with poor stability, and merging close numerical values in the obtained estimated values; calculating the degree of difference between the differential equation parameters and the current waveform based on multiple groups of estimated values; according to the trend of decreasing difference between the differential equation parameters and the current waveform difference, repeatedly updating the estimated values until the parameters converge, thereby completing the solution of the unknown parameters in the unknown component parameter expression in the equivalent topology.

[0008] Furthermore, the current waveform difference degree is the difference degree between the current data obtained after simulation of the circuit composed of the solved parameters and the actual measured data, that is, the current waveform difference degree I acerr for ;in, I sim is the measured RMS value of the input current, i sim ( t n )and i cal ( t n ) is the instantaneous value of the circuit current simulation at the same moment when the input current corresponds to the iterative component parameters, N is the total number of current data.

[0009] Furthermore, the difference equation parameter difference is used to evaluate whether the element parameters calculated iteratively are accurate, that is, the difference equation parameter difference for ;in, N is the total number of current data, that is, the total number of differential equation parameters, P cal With P act The number of elements in the matrix composed of the difference equation parameters obtained by different calculation methods is NColumn vector of .

[0010] Furthermore, the smaller the difference between the differential equation parameters and the current waveform, the more accurate the circuit element parameters are; the difference between the current waveform I acerr and the difference equation parameter difference Unify the similarity as the objective function of optimization and define the similarity index as ;in, is the similarity, α and β are weights, α + β =1.

[0011] Furthermore, the magnitude of the impact of the similarity change is evaluated by the relative value of the estimated value change of different components, that is, the degree of change of each component parameter in the process of similarity changing from small to large, and the relative value of the estimated value change for ;in, Represents the parameter value with smaller similarity, Represents the parameter value when the similarity is large, X is a component in the circuit to be estimated.

[0012] Furthermore, when a parameter needs to change in a smaller direction, ; When a parameter needs to change in a large direction, ;in, and Represents the value of a parameter after update. and Represents the value of a parameter before updating. λ and γ is the weight assigned.

[0013] As a further technical limitation, in the process of processing the determined transfer function based on the bilinear transformation and the Z transform, the determined transfer function is transformed by the bilinear transformation. s Domain converted to z domain, and obtain the relationship between the AC side current and the AC side voltage z Domain transfer function, according to the obtained z The coefficients in the domain transfer function determine the parametric equations.

[0014] As a further technical limitation, the equivalent topology of the obtained filter includes at least an equivalent topology of a single-phase uncontrolled rectifier bridge device including an LC filter and an equivalent topology of a single-phase uncontrolled rectifier bridge device including an LCL filter.

[0015] According to some embodiments, a second solution of the present invention provides a filter-containing rectifier load parameter identification system based on Z transform, which adopts the following technical solutions: A Z-transform-based rectifier load parameter identification system including a filter comprises: an acquisition module configured to acquire an equivalent topology of a filter; a determination module configured to determine a transfer function between the AC side current and the AC side voltage of the filter based on the obtained filter equivalent topology; obtain a matrix expression between the AC side voltage and the AC side current based on the transfer function determined by bilinear transformation and Z transformation processing; and obtain an expression for unknown component parameters in the equivalent topology based on the obtained matrix expression; The identification module is configured to complete the Z-transform-based filter topology parameter identification based on unknown parameters in the unknown component parameter expression in the equivalent topology obtained by solving the gradient identification algorithm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention is based on the equivalent topology of single-phase uncontrolled rectifier bridge equipment, and derives expressions of unknown parameter values of components in the equivalent topology through Z transformation; uses measured AC side voltage and current data, and constructs a matrix expression between AC side voltage and current through expressions of unknown parameter values of components, and solves the matrix to obtain parameter values of components; by deriving expressions of unknown parameter values of components in the set topology, no additional calculations are required after obtaining the expressions, and no specific heuristic algorithms or professional knowledge in the field of electrical engineering are relied upon. Only measured voltage and current data need to be input, and the unknown parameters of components in the topology can be identified without damaging the equipment. The identification process has low time complexity and is short in time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the specification of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments and descriptions of this embodiment are used to explain this embodiment and do not constitute an improper limitation on this embodiment.

[0018] Figure 1 Flowchart of the filter topology parameter identification method based on Z transform in the first embodiment of the present invention; Figure 2 This is a schematic diagram of the load principle and the topological structure of the conduction equivalent circuit of a single-phase uncontrolled rectifier bridge with an LC filter in Example 1 of the present invention; Figure 3 This is a schematic diagram of the load principle and the topological structure of the conduction equivalent circuit of a single-phase uncontrolled rectifier bridge with an LCL filter in the first embodiment of the present invention; Figure 4This is a structural block diagram of a filter topology parameter identification system based on Z transform in the second embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0021] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0022] In the present invention, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention, and do not specifically refer to any part or element in the present invention, and should not be understood as limiting the present invention.

[0023] In the present invention, terms such as "fixed connection," "connected," and "connection" should be interpreted broadly to mean a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediary. Relevant researchers or technicians in this field may determine the specific meanings of these terms in the present invention based on specific circumstances, and they should not be construed as limitations of the present invention.

[0024] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0025] Example 1 The first embodiment of the present invention introduces a method for identifying parameters of a filter-containing rectifier load based on Z transform.

[0026] like Figure 1 The equivalent topology of the acquisition filter is shown; Determine the transfer function between the AC side current and the AC side voltage of the filter based on the obtained filter equivalent topology; Based on the transfer function determined by bilinear transformation and Z-transformation, the matrix expression between the AC side voltage and the AC side current is obtained; According to the obtained matrix expression, the unknown component parameter expression in the equivalent topology is obtained; The unknown parameters in the unknown component parameter expressions in the equivalent topology obtained by solving the gradient identification algorithm are used to complete the filter topology parameter identification based on Z transform.

[0027] The forward impedance of the diode is extremely small when it is turned on. The equivalent topology circuit schematic diagram of the single-phase uncontrolled rectifier bridge device with LC filter and the equivalent circuit diagram when it is turned on are as follows: Figure 2 As shown, where D is the diode that constitutes the rectifier bridge, R is the AC side resistance, L 、 C 1. R 1 is the filter inductance, capacitance and parasitic resistance, C 2 and R 2 is the DC side capacitance and resistance, i ac and u ac are voltage and current respectively.

[0028] according to Figure 2 The ratio of the transfer function of the AC side current and the AC side voltage can be obtained as shown in G 3( s ) is: (1) in, G 3( s ) is the transfer function, R is the AC side resistance, L is the filter inductance, C 1 is the filter capacitor, R 1 is the parasitic resistance of the filter capacitor, C 2 is the DC side capacitance, R 2 is the DC side resistance.

[0029] Using bilinear transformation to process equation (1), the transfer function is given by s Domain Transformation z domain, formula (1) is transformed into: (2) In formula (2), the coefficients of the transfer function can be expressed as: (3) In formula (3), the difference equation parameters A to G The expression is: (4) right G 3(z ) and perform the inverse transformation to obtain: (5) According to the relationship in formula (3), we can get a 3= a 1+ a 2- a 4, and bring it into formula (5), it can be rewritten as: (6) in, I ( n )and U ( n ) are the first n values, a 1. a 2. a 3. a 4. b 1. b 2 and b 3 is the coefficient of the difference equation.

[0030] When obtained N After adding one set of AC side voltage and current data, formula (6) can be rewritten into a matrix form. Its matrix expression is: (7) in, ; .

[0031] The compact form of formula (7) is: (8) Among them, A is the matrix composed of current and voltage sampling values within half a power frequency cycle, and B is the matrix composed of the second to the first groups. N The vector matrix composed of the current sampling values of the group, X is the vector matrix of the circuit parameters to be estimated.

[0032] The solution based on the least squares method is: (9) After the above calculations, formula (3) can be used to solve the a 1. a 2. a 3. a 4. b 1. b 2 and b 3 represents A arrive G The coefficients can be solved by the compact form, that is, formula (9)a 1. a 2. a 3. a 4. b 1. b 2 and b 3.

[0033] By transforming and deducing formula (4), we can obtain the expressions of circuit element parameters as follows: (10) Formula (10) can be used to calculate the parameters of the unknown components in the topology model. First, the parameters of the components related to the AC side and the DC side are calculated, and then the parameters of the components included in the filter are calculated using the calculated parameter values. A to G Calculated by formula (3): (11) in, .

[0034] Since the forward impedance of the uncontrolled diode is very small when it is turned on, its influence on the circuit is very small, so the effect of its forward voltage drop is ignored. The circuit schematic diagram of the equivalent topology of the single-phase uncontrolled rectifier bridge device with LCL filter and the equivalent circuit diagram when it is turned on are as follows: Figure 3 As shown, including the AC side resistance R , AC side LCL filter component parameters L 、 L 1. C 1 and capacitor branch damping R 1. DC side capacitor C 2 and equivalent load R 2.

[0035] according to Figure 3 As shown, the ratio of the transfer function of the AC side current and the AC side voltage can be obtained. G 4( s ) is: (12) in, G 4( s ) is the transfer function, R is the AC side resistance, L and L 1 are filter inductors, C 1 is the filter capacitor, R 1 is the parasitic resistance of the filter capacitor, C 2 is the DC side capacitor, R 2 is the DC side resistance.

[0036] Using bilinear transformation, formula (12) is transformed into s Domain converted to z domain, and obtain the AC side current and AC side voltage z Domain Transfer Function for: (13) In formula (13), the coefficients of the transfer function can be expressed as: (14) (15) In formula (14) and formula (15), the difference equation parameters A to H The expression is: (16) right G 4( z ) and perform the inverse transformation to obtain: (17) in, I ( n )and U ( n ) are the first n values, a 1. a 2. a 3. a 4. a 5. b 1. b 2. b 3 and b 4 is the coefficient of the difference equation.

[0037] According to the relationship between formula (14) and formula (15), a 5= a 1+ a 2- a 3- a 4, and put it into formula (17), we get: (18) When obtained N After adding one set of AC side voltage and current data, equation (30) is rewritten into a matrix form, and its matrix expression is: (19) in, ; .

[0038] The compact form of formula (19) is: (20) Among them, A is the matrix composed of current and voltage sampling values within half a power frequency cycle, and B is the matrix composed of the second to the first groups. N The vector matrix composed of the current sampling values of the group, X is the vector matrix of the circuit parameters to be estimated.

[0039] The solution based on the least squares method is: (twenty one) After the above calculations, the formula (14) and formula (15) can be used to solve the use a 1. a 2. a 3. a 4. a 5. b 1. b 2. b 3 and b 4 represents A arrive H The coefficients can be solved by the compact form, that is, formula (21) a 1. a 2. a 3. a 4. a 5. b 1. b 2. b 3 and b 4.

[0040] The expressions of various parameters can be solved from formula (16): (twenty two) In the calculation process, the parameters of the AC side inductance need to be calculated first, and then the optimization algorithm proposed in the next section is used to solve the remaining parameters. A to H Calculated by formula (14) and formula (15): (twenty three) in, .

[0041] Due to the influence of sampling frequency, equipment accuracy and other issues, there is an inherent error between the coefficients of the differential equations solved by formula (7) and formula (19) and the actual values. At the same time, due to the characteristics of the matrix structure, it tends to be singular and pathological during the solution process. Therefore, it is necessary to combine numerical methods to improve the stability of the solution.

[0042] The algorithm designed in this embodiment consists of the following four parts: obtaining the initial interval of circuit component parameter values, parameter interval preprocessing, parameter value update iterative calculation and output. In the calculation process of the circuit containing LC filter and the circuit containing LCL filter, there are differences in the way of obtaining the initial interval of circuit component parameter values. The circuit containing LC filter can calculate the initial interval of all parameters through the derived formula, while the circuit containing LCL filter needs to first complete the AC side resistance in the process of obtaining the initial interval. R , and then use the derived formula to calculate the parameters of the remaining components.

[0043] Due to the morbidity and singularity problems of the parameter solution matrix, the parameters solved by the solution matrix composed of different data fluctuate around the true value. Therefore, it is necessary to obtain multiple sets of possible parameters by changing the input data to form an initial range of estimated values for different components.

[0044] Since the initial values calculated in the initial value interval fluctuate around the true value, there will be a large number of initial values with little difference. To ease the calculation pressure for such parameters, when the relative change rate of adjacent parameters is less than 1 / 3000 of the interval range, the two values are merged into their mean. The calculation expression for the relative change rate of two adjacent parameters is: (twenty four) in, X max The maximum value of the interval of the estimated value of a component, X min The minimum value of the interval of the estimated value of a component, The minimum range allowed for variation is set to 3000 in this embodiment.

[0045] There are a large number of erroneous values in the initially obtained interval that deviate greatly from the true value. In order to make the estimated value closer to the true value, two indicators are set up in the algorithm of this embodiment, one of which is called the differential equation parameter and the other is the degree of current waveform difference.

[0046] The difference equation parameters are given in formula (4) and formula (16): A to H, is a variable that appears in the calculation process and is completely determined by the component parameters and sampling frequency. There are two ways to calculate this parameter. The first way is to solve the differential equation, obtain the value of the differential equation coefficient, and then solve it through formula (11) and formula (23); the second way is to use the circuit component parameters to calculate through formula (4) and formula (16). The two calculation methods of differential equation parameters have different characteristics. The former calculation is not limited by whether the component parameters are clear; the latter is limited by whether the component parameters are clear. When the component parameters are accurate, accurate calculation can be achieved. Therefore, the AC side resistance calculated in each iteration is R The remaining component parameters are converted into corresponding differential equation parameters and compared with the differential equation parameters calculated by input data to evaluate whether the component parameters calculated in each iteration are accurate. The specific evaluation formula is shown in formula (25).

[0047] (25) in, is the degree of difference of the difference equation parameters, N is the total number of difference equation parameters, P cal With P act The matrix consisting of the difference equation parameters calculated by two different calculation methods has the following elements: N Column vector of .

[0048] Current waveform difference I acerr It is defined as the degree of difference between the current data obtained after simulation of the circuit composed of the solved parameters and the actual measured data. Its definition is shown in formula (26).

[0049] (26) in, I acerr is the degree of difference in current waveform, I sim is the measured RMS value of the input current, i sim ( t n )and i cal ( t n ) is the instantaneous value of the circuit current simulation at the same moment when the input current corresponds to the iterative component parameters, N is the total number of current data.

[0050] Obviously, and I acerr The smaller it is, the more accurate the estimated circuit component parameters are. andI acerr Unified as similarity, as the objective function of optimization, the similarity index is defined as: (27) in, is the similarity, α and β is the weight determined according to the actual situation. α + β =1.

[0051] Different parameter estimates will produce different similarities. During the iterative calculation process, each round of calculation determines the iterative update direction of the estimated value according to the trend of decreasing similarity. Generally speaking, multiple parameters often change at the same time. Under the influence of such changes, the similarity differs from the similarity of the previous round. Therefore, it is necessary to evaluate the impact of the iterative direction of the estimated value on the similarity according to the speed of similarity change. To improve the stability of the entire iterative process, the change gradient of the component parameters with a greater impact on the similarity change will be appropriately reduced in the next iteration. Conversely, the change gradient of the component parameters with a smaller impact on the similarity change will be appropriately increased in the next iteration. Since the true value is unknown, the magnitude of the impact on the similarity change is evaluated by the relative value of the estimated value change of different components. This relative value refers to the degree of change of each component parameter in the process of similarity changing from small to large. The relative value of the estimated value change is: (28) in, is the relative value of the estimated value change, Represents the parameter value with smaller similarity, Represents the parameter value when the similarity is large, X is a component in the circuit to be estimated.

[0052] The estimated values are ranked in order of relative value, and weights are assigned in reverse order. In practical applications, the speed and accuracy of the solution process can be controlled by controlling the size of the total weight. For circuits with good stability, the total weight can be increased to speed up the solution, while for circuits with poor stability, the total weight can be reduced to improve the accuracy of the solution. The specific parameter estimate value update equation is shown in formula (29) and formula: When a parameter needs to change in a smaller direction, (29) When a parameter needs to change in a large direction, (30) in, and Represents the value of a parameter after update. and Represents the value of a parameter before updating. λ and γ is the weight assigned.

[0053] The specific process of the gradient-based model unknown parameter identification algorithm can be described as: Step 1: Obtain estimated values calculated from component expressions of unknown parameters in the equivalent topology; Step 2: Preprocess the received data, extract the less stable estimates, merge the closer estimates, reduce the total amount of data to be processed, and recombine the less stable estimates; Step 3: Calculate the difference between the differential equation parameters and the current waveform based on the multiple sets of estimated values obtained; Step 4: Follow and I acerr The estimated value update strategy is determined and steps 3 and 4 are repeated until all parameters converge and the solved parameters are output.

[0054] This embodiment is based on the set equivalent topology of a single-phase uncontrolled rectifier bridge device containing a resistive inductor and an LC filter on the AC side, and a resistive inductor and an LCL filter on the AC side. Expressions for unknown parameter values of components in the equivalent topology are derived through Z transformation. Measured AC side voltage and current data are used to construct a matrix expression between the AC side voltage and current through expressions for the unknown parameter values of the components, and the matrix is solved to obtain the parameter values of the components. By deriving expressions for the unknown parameter values of the components in the set topology, no additional calculations are required after obtaining the expressions, and no specific heuristic algorithms or expertise in the field of electrical engineering are relied upon. Only the measured voltage and current data need to be input, so that the unknown parameters of the components in the topology can be identified without damaging the equipment. The identification process has low time complexity and is short in time.

[0055] Example 2 The second embodiment of the present invention introduces a Z-transform-based rectifier load parameter identification system including a filter.

[0056] like Figure 4 The Z-transform-based rectifier load parameter identification system includes: an acquisition module configured to acquire an equivalent topology of a filter; a determination module configured to determine a transfer function between the AC side current and the AC side voltage of the filter based on the obtained filter equivalent topology; obtain a matrix expression between the AC side voltage and the AC side current based on the transfer function determined by bilinear transformation and Z transformation processing; and obtain an expression for unknown component parameters in the equivalent topology based on the obtained matrix expression; The identification module is configured to complete the Z-transform-based filter topology parameter identification based on unknown parameters in the unknown component parameter expression in the equivalent topology obtained by solving the gradient identification algorithm.

[0057] The detailed steps are the same as those of the filter topology parameter identification method based on Z transform provided in Example 1, and will not be repeated here.

[0058] The above description is merely a preferred embodiment of this embodiment and is not intended to limit this embodiment. Those skilled in the art will readily appreciate that this embodiment may be modified and varied in various ways. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this embodiment shall be within the scope of protection of this embodiment.

Claims

1. A method for identifying parameters of a filter-containing rectifier load based on Z transform, characterized in that: include: Get the equivalent topology of the filter; Determine the transfer function between the AC side current and the AC side voltage of the filter based on the obtained filter equivalent topology; Based on the transfer function determined by bilinear transformation and Z-transformation, the matrix expression between the AC side voltage and the AC side current is obtained; According to the obtained matrix expression, the unknown component parameter expression in the equivalent topology is obtained; The unknown parameters in the unknown component parameter expressions in the equivalent topology obtained by solving the gradient identification algorithm are used to complete the filter topology parameter identification based on Z transform.

2. A method for identifying load parameters of a filter-containing rectifier based on Z transform as claimed in claim 1, characterized in that: The process of solving the unknown parameters in the unknown component parameter expression in the equivalent topology obtained by the gradient identification algorithm is as follows: obtaining an estimated value calculated from the component expression of the unknown parameter in the equivalent topology; The unknown component parameter expressions in the equivalent topology are preprocessed to extract less stable estimated values and merge the close values obtained. Based on multiple sets of estimated values, the degree of difference between the differential equation parameters and the current waveform is calculated. According to the trend of decreasing difference between the differential equation parameters and the current waveform, the estimated values are repeatedly updated until the parameters converge, thus completing the solution of the unknown parameters in the unknown component parameter expressions in the equivalent topology.

3. A method for identifying load parameters of a filter-containing rectifier based on Z transform as claimed in claim 2, characterized in that: The current waveform difference degree is the difference degree between the current data obtained after simulation of the circuit composed of the solved parameters and the actual measured data, that is, the current waveform difference degree I acerr for ;in, I sim is the measured RMS value of the input current, i sim ( t n )and i cal ( t n ) is the instantaneous value of the circuit current simulation at the same moment when the input current corresponds to the iterative component parameters, N is the total number of current data.

4. A method for identifying load parameters of a filter-containing rectifier based on Z transform as claimed in claim 3, characterized in that: The difference equation parameter difference is used to evaluate whether the element parameters calculated iteratively are accurate, that is, the difference equation parameter difference for ;in, N is the total number of current data, that is, the total number of differential equation parameters, P cal With P act The number of elements in the matrix composed of the difference equation parameters obtained by different calculation methods is N Column vector of .

5. A method for identifying load parameters of a filter-containing rectifier based on Z transform as claimed in claim 4, characterized in that: The smaller the difference between the differential equation parameters and the current waveform, the more accurate the circuit element parameters are; the current waveform difference I acerr and the difference equation parameter difference Unify the similarity as the objective function of optimization and define the similarity index as ;in, is the similarity, α and β are weights, α + β =1.

6. A method for identifying load parameters of a filter-containing rectifier based on Z transform as claimed in claim 2, characterized in that: The magnitude of the impact of the similarity change is evaluated by the relative value of the estimated value change of different components, that is, the degree of change of each component parameter in the process of similarity changing from small to large, and the relative value of the estimated value change for ;in, Represents the parameter value with smaller similarity, Represents the parameter value when the similarity is large, X is a component in the circuit to be estimated.

7. A method for identifying load parameters of a filter-containing rectifier based on Z transform as claimed in claim 6, characterized in that: When a parameter needs to change in a smaller direction, ; When a parameter needs to change in a large direction, ;in, and Represents the value of a parameter after update. and Represents the value of a parameter before updating. λ and γ is the weight assigned.

8. A method for identifying load parameters of a filter-containing rectifier based on Z transform as claimed in claim 1, characterized in that: In the process of processing the transfer function determined based on bilinear transformation and Z transformation, the transfer function determined is transformed from s Domain converted to z domain, and obtain the relationship between the AC side current and the AC side voltage z Domain transfer function, according to the obtained z The coefficients in the domain transfer function determine the parametric equations.

9. A method for identifying load parameters of a filter-containing rectifier based on Z transform as claimed in claim 1, characterized in that: The obtained equivalent topology of the filter at least includes an equivalent topology of a single-phase uncontrolled rectifier bridge device including an LC filter and an equivalent topology of a single-phase uncontrolled rectifier bridge device including an LCL filter.

10. A Z-transform-based filter-containing rectifier load parameter identification system, characterized in that: include: an acquisition module configured to acquire an equivalent topology of a filter; a determination module configured to determine a transfer function between the AC side current and the AC side voltage of the filter based on the obtained filter equivalent topology; obtain a matrix expression between the AC side voltage and the AC side current based on the transfer function determined by bilinear transformation and Z transformation processing; and obtain an expression for unknown component parameters in the equivalent topology based on the obtained matrix expression; The identification module is configured to complete the Z-transform-based filter topology parameter identification based on unknown parameters in the unknown component parameter expression in the equivalent topology obtained by solving the gradient identification algorithm.

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