A method and system for identifying parameters of a rectifier load with filter based on Z transform

Abstract

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

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a filter-containing rectifier load parameter identification method and system based on Z transformation. BACKGROUND

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

[0003] With the rapid development of power electronics technology and the popularity of new types of electrical equipment, the proportion of single-phase uncontrolled rectifier bridge type equipment in residential and commercial electricity continues to rise. Nonlinear loads inject characteristic harmonics into the power grid during operation, especially odd harmonics of 3rd, 5th and 7th orders, which not only significantly increase the total harmonic distortion rate of the power supply system, but also cause serious power quality problems. In actual operation, harmonic pollution not only causes additional iron and copper losses of transformers and motors, accelerates insulation aging, but also causes abnormal increase of neutral line current, harmonic resonance of capacitor banks and other systemic risks. These negative effects directly manifest as power conversion efficiency reduction, equipment life shortening and relay protection misoperation.

[0004] To cope with increasingly stringent power quality standards, electrical equipment manufacturers generally adopt multi-stage filtering protection architectures, including front-stage EMI filters to suppress high-frequency conducted interference, intermediate-stage passive LC filters to absorb main characteristic harmonics, and rear-stage active filters to dynamically compensate residual harmonics, and other composite governance solutions. However, the introduction of filtering devices makes system modeling face challenges such as complex topology structure and increased sensitivity of high-frequency parasitic parameters. The nonlinear characteristics of filters require that element parasitic parameters be considered during modeling, which puts higher technical requirements on the robustness of parameter identification algorithms and the effectiveness of model reduction techniques. SUMMARY

[0005] To solve the above problems, the application provides a filter-containing rectifier load parameter identification method and system based on Z transformation, which is based on the equivalent topology characteristics of typical single-phase uncontrolled rectifier bridge type equipment with LC / LCL filters on the AC side, uses gradient optimization to overcome the nonlinear solving problem caused by element parameter coupling, realizes accurate identification of key parameters of the filter, and constructs a digital twin physical model with clear physical meaning, thereby efficiently and quickly identifying unknown parameters of elements in the topology without damaging the equipment.

[0006] According to some embodiments, the first aspect of the application provides a filter-containing rectifier load parameter identification method based on Z transformation, which adopts the following technical scheme:

[0007] A filter-containing rectifier load parameter identification method based on Z transformation, comprising:

[0008] obtaining an equivalent topology of the filter;

[0009] 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;

[0010] obtaining a matrix expression between the alternating current side voltage and the alternating current side current based on the determined transfer function and Z transform processing;

[0011] obtaining an unknown element parameter expression in the equivalent topology according to the obtained matrix expression;

[0012] solving the unknown parameters in the obtained unknown element parameter expression in the equivalent topology based on a gradient identification algorithm, to complete the filter topology parameter identification based on Z transform.

[0013] As a further technical limitation, the process of solving the unknown parameters in the obtained unknown element parameter expression in the equivalent topology based on the gradient identification algorithm is: obtaining estimated values calculated by the element expression of the unknown parameters in the equivalent topology; preprocessing the unknown element parameter expression in the equivalent topology, extracting the estimated values with poor stability, and merging the close values in the obtained estimated values; calculating the difference equation parameter and the current waveform difference degree according to the multiple sets of estimated values; according to the trend of reducing the difference degree of the difference equation parameter and the current waveform difference, repeatedly updating the estimated values until each parameter converges, to complete the solving of the unknown parameters in the unknown element parameter expression in the equivalent topology.

[0014] Further, 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 actually measured data, i.e. the current waveform difference degree I acerr For ; wherein, I sim is the measured input current root mean square value, i sim ( t n ) and i cal ( t n ) is the circuit current simulation instantaneous value corresponding to the same time of the input current and the iterated element parameter, N is the total number of current data.

[0015] Further, the difference equation parameter difference degree is used to evaluate whether the iterated element parameter is accurate, i.e. the difference equation parameter difference degree is ; wherein, NP is the total number of current data, i.e. the total number of differential equation parameters cal P is the total number of current data, i.e. the total number of differential equation parameters act P is the total number of current data, i.e. the total number of differential equation parameters N P is the total number of current data, i.e. the total number of differential equation parameters

[0016] Further, the smaller the difference between the differential equation parameters and the current waveform, the more accurate the circuit element parameters are; the degree of difference between the current waveform I acerr and the difference between the differential equation parameters are unified as the similarity as the optimization objective function, and the similarity index is defined as ; wherein, is the similarity, α and β are weights, α + β =1.

[0017] Further, the size of the impact on the similarity change is evaluated by the relative value of the estimated value change of different elements, i.e. the degree of change of each element parameter in the process of the similarity from small to large, and the relative value of the estimated value change is ; wherein, represents the parameter value when the similarity is small, represents the parameter value when the similarity is large, X is one element in the circuit to be estimated.

[0018] Further, when a certain parameter needs to change in the small direction, ; when a certain parameter needs to change in the large direction, ; wherein, and represent the value of a certain parameter after updating, and represent the value of a certain parameter before updating, λ and γ are the assigned weights.

[0019] As a further technical limitation, in the process of determining the transfer function based on the bilinear transformation and the Z transformation, the determined transfer function is converted from the s domain to the z domain by bilinear transformation to obtain the z domain transfer function between the alternating current and the alternating voltage, and the parameter equation is determined according to the coefficients in the obtained z domain transfer function.

[0020] As a further technical limitation, the acquired equivalent topology of the filter at least includes an equivalent topology of a single-phase uncontrolled rectifier bridge type device with an LC filter and an equivalent topology of a single-phase uncontrolled rectifier bridge type device with an LCL filter.

[0021] According to some embodiments, a second aspect of the present application provides a Z-transform-based filter-containing rectifier load parameter identification system, which adopts the following technical solution:

[0022] A Z-transform-based filter-containing rectifier load parameter identification system comprises:

[0023] An acquisition module configured to acquire an equivalent topology of a filter;

[0024] A determination module configured to determine a transfer function between an AC side current and an AC side voltage of the filter according to the acquired equivalent topology of the filter; process the determined transfer function based on a bilinear transformation and a Z transformation to obtain a matrix expression between the AC side voltage and the AC side current; and obtain an unknown element parameter expression in the equivalent topology according to the obtained matrix expression;

[0025] An identification module configured to solve unknown parameters in the obtained unknown element parameter expression in the equivalent topology based on a gradient identification algorithm, and complete Z-transform-based filter topology parameter identification.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] The present application is based on the equivalent topology of a single-phase uncontrolled rectifier bridge type device, and the expression of unknown parameter values of elements in the equivalent topology is derived through Z transformation. The measured AC side voltage data and current data are used to form a matrix expression between the AC side voltage and the current through the expression of unknown parameter values of elements, and the parameter values of the elements are obtained by solving the matrix. The expression of unknown parameter values of elements in the set topology is derived, and no additional calculation is required after obtaining the expression, which does not depend on specific heuristic algorithms or professional knowledge in the field of electrical engineering, and only needs to input the measured voltage data and current data. The unknown parameters of the elements in the topology can be identified without damaging the device, the time complexity of the identification process is low, and the time consumption is short. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings constituting a part of this embodiment are used to provide a further understanding of this embodiment, and the schematic embodiments of this embodiment and the description thereof are used to explain this embodiment, and do not constitute an improper limitation on this embodiment.

[0029] Figure 1 A flowchart of the Z-transform-based filter topology parameter identification method in the first embodiment of the present application;

[0030] Figure 2 The single-phase uncontrolled rectifier bridge load principle diagram and the conduction equivalent circuit topology structure diagram of the LC filter in the embodiment one of the present application are shown in the figure.

[0031] Figure 3 The single-phase uncontrolled rectifier bridge load principle diagram and the conduction equivalent circuit topology structure diagram of the LCL filter in the embodiment one of the present application are shown in the figure.

[0032] Figure 4 The structure block diagram of the filter topology parameter identification system based on Z transform in the embodiment two of the present application is shown in the figure. DETAILED DESCRIPTION

[0033] The present application will be further described below in conjunction with the drawings and embodiments.

[0034] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains.

[0035] It should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and furthermore, it should be understood that when the terms "comprise" and / or "include" are used in the specification, there is a presence of a feature, step, operation, device, component and / or combination thereof.

[0036] In the present application, the terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicate the orientation or positional relationship shown in the drawings, which is only a relationship word determined for the convenience of describing the structural relationship of the components or elements of the present application, and is not intended to specify any component or element in the present application, and cannot be understood as a limitation of the present application.

[0037] In the present application, the terms such as "fixedly connected", "connected", "connected" should be understood broadly, which means that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. For related researchers or technicians in the art, the specific meaning of the above terms in the present application can be determined according to the specific circumstances, and cannot be understood as a limitation of the present application.

[0038] In the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0039] Embodiment one

[0040] The embodiment one of the present application introduces a filter-containing rectifier load parameter identification method based on Z transform.

[0041] As shown in the equivalent topology of the filter; Figure 1

[0042] According to the obtained equivalent topology of the filter, the transfer function between the AC side current and the AC side voltage of the filter is determined;

[0043] Based on the determined transfer function, the matrix expression between the AC side voltage and the AC side current is obtained through bilinear transformation and Z transform processing;

[0044] According to the obtained matrix expression, the unknown element parameter expression in the equivalent topology is obtained;

[0045] Based on the gradient identification algorithm, the unknown parameters in the obtained unknown element parameter expression in the equivalent topology are solved, and the filter topology parameter identification based on Z transform is completed.

[0046] The diode has a minimum forward impedance when conducting, and the equivalent topology circuit principle diagram and the equivalent circuit diagram when conducting of the single-phase uncontrolled rectifier bridge device containing LC filter are as shown in Figure 2 , wherein D is a diode constituting the rectifier bridge, R is an AC side resistance, L , C 1, R 1 is a filter inductance, capacitance and parasitic resistance, C 2 and R 2 is a DC side capacitance and resistance, i ac and u ac are voltage and current respectively.

[0047] According to Figure 2 , the expression of the ratio of the transfer function of the AC side current and the AC side voltage G 3( s ) is obtained.

[0048] (1)

[0049] Among them, G 3( s ) is the transfer function, R is an AC side resistance, L is a filter inductance, C 1 is a filter capacitance, R 1 is a parasitic resistance of the filter capacitance, C 2 is a DC side capacitance, R 2 is a DC side resistance.

[0050] ​Using the bilinear transformation, equation (1) is processed, and the transfer function is transformed from s domain to z domain, and equation (1) is transformed to:

[0051] (2)

[0052] In equation (2), the coefficients of the transfer function can be expressed as:

[0053] (3)

[0054] In equation (3), the expression of the difference equation parameters A to G is:

[0055] (4)

[0056] The inverse transformation of G 3( z ) can be obtained:

[0057] (5)

[0058] According to the relationship of equation (3), we can get a 3= a 1+ a 2- a 4, which is brought into equation (5), and it can be rewritten as:

[0059] (6)

[0060] Wherein, I ( n ) and U ( n ) are the first n values in the measured current data and voltage data, a 1、 a 2、 a 3、 a 4、 b 1、 b 2 and b 3 are the difference equation coefficients.

[0061] When the data of N +1 sets of alternating current voltage and current are obtained, equation (6) can be rewritten in matrix form, and the matrix expression is:

[0062] (7)

[0063] Wherein,

[0064] ;

[0065] .

[0066] The compact form of equation (7) is:

[0067] (8)

[0068] Where A is the matrix composed of current and voltage sampling values in half of the power frequency cycle, B is the vector matrix composed of the 2nd to 4th group of current sampling values, and X is the vector matrix of circuit parameters to be estimated. N

[0069] The solution based on the least square method is:

[0070] (9)

[0071] Through the above calculation, the expression of 1, 2, 3, 4, 1, 2 and 3 can be solved by equation (3). Through the compact form, i.e. equation (9), the coefficients 1, 2, 3, 4, 1, 2 and 3 can be solved. a a a a b b b A G a a a a b b b

[0072] Through transformation and derivation of equation (4), the expression of circuit element parameters can be obtained as:

[0073] (10)

[0074] Through equation (10), the parameters of unknown elements in the topology model can be calculated. First, the element parameters related to the AC side and the DC side are calculated, and then the element parameters contained in the filter are calculated using the calculated parameter values. Among them, A G

[0075] (11)

[0076] Where, .

[0077] ​​​​​​​​​​​​​​​​​​​Since the forward impedance of the uncontrolled diode is very small when it is on, the influence on the circuit is very small, so the effect of the forward voltage drop is ignored. The circuit schematic diagram and the equivalent circuit diagram when it is on of the equivalent topology of the single-phase uncontrolled rectifier bridge type device with LCL filter are shown in FIGS. 1 and 2, which include the AC side resistance R1, the LCL filter inner element parameters L1, L2, C1, the capacitor branch damping R1, the DC side capacitor C2 and the equivalent load R2. Figure 3 R L L C R C R

[0078] According to FIG. 3, the expression of the ratio of the transfer function of the AC side current and the AC side voltage is as follows: Figure 3 G s

[0079] (12)

[0080] wherein, G4(jω) is the transfer function, R1 is the AC side resistance, L1 and L2 are the filter inductances, C1 is the filter capacitance, R1 is the parasitic resistance of the filter capacitance, C2 is the DC side capacitance, and R2 is the DC side resistance. G s R L L C R C R

[0081] By using the bilinear transformation, formula (12) is converted from the s domain to the z domain, and the z domain transfer function of the AC side current and the AC side voltage is as follows: s z z

[0082] (13)

[0083] In formula (13), the coefficients of the transfer function can be expressed as:

[0084] (14)

[0085] (15)

[0086] In formula (14) and formula (15), the expressions of the difference equation parameters from to are as follows: A H

[0087] ​​​​​​​​​​​​​​​​​​​​​​​​​​ (16)

[0088] For G 4( z ) the inverse transform gives:

[0089] (17)

[0090] where I ( n ) and U ( n ) are the first n values of the measured current and voltage data respectively, a 1、 a 2、 a 3、 a 4、 a 5、 b 1、 b 2、 b 3 and b 4 are the difference equation coefficients.

[0091] According to the relationship in equation (14) and equation (15) we have a 5= a 1+ a 2- a 3- a 4, which is substituted into equation (17) to give:

[0092] (18)

[0093] When the data of N +1 sets of AC side voltage and current are obtained, equation (30) is rewritten in matrix form, and its matrix expression is:

[0094] (19)

[0095] where

[0096] ;

[0097] .

[0098] The compact form of equation (19) is:

[0099] (20)

[0100] where A is the matrix composed of current and voltage sampling values in half of the power frequency period, B is the vector matrix composed of the second to N set of current sampling values, and X is the vector matrix of the estimated circuit parameters.

[0101] Based on the least square method, the following is obtained:

[0102] (21)

[0103] Through the above calculation, the expression of the coefficients a 1、 a 2、 a 3、 a 4、 a 5、 b 1、 b 2、 b 3 and b 4 can be solved by formula (14) and formula (15). A H The coefficients a 1、 a 2、 a 3、 a 4、 a 5、 b 1、 b 2、 b 3 and b 4 can be solved by formula (21) in a compact form.

[0104] The expression of each parameter solved by formula (16) is as follows:

[0105] (22)

[0106] In the calculation process, the parameters of the AC side inductance need to be calculated first, and then the remaining parameters are solved by using the optimization algorithm proposed in the next section. Among them, A H The following is calculated by formula (14) and formula (15):

[0107] (23)

[0108] Among them, .

[0109] Due to the influence of sampling frequency, equipment precision and other problems, there is an inherent error between the coefficients of the difference equation solved by formula (7) and formula (19) and the actual value, and due to the characteristics of the matrix structure, it tends to be singular and ill-conditioned in the solving process, so it is necessary to combine numerical methods to improve the stability of the solution.

[0110] ​​The algorithm designed in this embodiment consists of the following four parts: obtaining the initial interval of the parameter value of the circuit element, parameter interval preprocessing, parameter value update iteration calculation and output. In the calculation process of LC filter circuit and LCL filter circuit, the initial interval of the circuit element parameter value is different. The initial interval of all parameters of the LC filter circuit can be calculated by the derived formula, while the LCL filter circuit needs to first complete the calculation of the resistance of the alternating current side in the initial interval acquisition process, and then calculate the parameters of the remaining elements by the derived formula. R

[0111] Due to the ill-conditioned and singular problems of the parameter solving matrix, the parameters solved by the solving matrix composed of different data fluctuate around the true value, so it is necessary to obtain multiple possible parameters by changing the input data to form the initial interval of the estimated value of different elements.

[0112] Since the initial value calculated in the initial value interval fluctuates around the true value, there will be a large number of initial values that are not much different. To alleviate the calculation pressure, when the relative change rate of adjacent parameters is less than 1 / 3000 of the interval range, the two values are combined into their mean value. The calculation expression of the relative change rate of the adjacent two parameters is:

[0113] (24)

[0114] wherein, X max is the maximum value of the interval of the estimated value of a certain element, X min is the minimum value of the interval of the estimated value of a certain element, is the minimum range allowed to change, which is set to 3000 in this embodiment.

[0115] There are a large number of error values with large deviations from the true value in the initially obtained interval. In order to make the estimated value closer to the true value, two indicators are set in the algorithm in this embodiment, one is called difference equation parameter, and the other is current waveform difference degree.

[0116] The difference equation parameter is given in formula (4) and formula (16) A to H ​is a variable in the calculation process, which is determined by the element parameters and the sampling frequency. There are two ways to calculate this parameter. The first way is to solve the difference equation and obtain the value of the difference equation coefficient, and then solve it by formula (11) and formula (23). The second way is to calculate it by formula (4) and formula (16) using circuit element parameters. The two calculation methods of the difference equation parameter have different characteristics. The former is not limited by whether the element parameters are clear or not; the latter is limited by whether the element parameters are clear or not, and can be accurately calculated under the condition that the element parameters are accurate. Therefore, the AC side resistance R and the rest of the element parameters obtained by each iteration are converted into the corresponding difference equation parameters, and compared with the difference equation parameters calculated by the input data, so as to evaluate whether the element parameters calculated by each iteration are accurate. The specific evaluation formula is shown in formula (25).

[0117] (25)

[0118] wherein, is the difference degree of the difference equation parameter, N is the total number of difference equation parameters, P cal and P act is a matrix composed of difference equation parameters calculated by two different calculation methods, and the element number is the column vector of N .

[0119] Current waveform difference degree I acerr is defined as the difference degree of the current data obtained after simulation of the circuit composed of the solved parameters and the actually measured data, and its definition formula is shown in formula (26).

[0120] (26)

[0121] wherein, I acerr is the current waveform difference degree, I sim is the measured input current root mean square value, i sim ( t n ) and i cal ( t n ) are the input current and the same time circuit current simulation instantaneous value corresponding to the element parameters obtained by iteration, N is the total number of current data.

[0122] Obviously, and I acerrThe smaller, the more accurate the estimated circuit element parameters represent. The With I acerr The similarity is unified as the objective function of optimization, and the similarity index is defined as:

[0123] (27)

[0124] Wherein, The similarity is, α And β The weight is determined according to the actual situation, α + β =1.

[0125] Different parameter estimates will produce different similarities. In the iterative calculation process, the iterative update direction of the estimated value is determined according to the trend of smaller similarity in each round of calculation. Generally, multiple parameters change at the same time, and the similarity changes under the influence of this change, thus the influence of the estimated value iteration direction on the similarity needs to be evaluated according to the speed of the similarity change. In order to improve the stability of the whole iteration process, the change gradient of the element parameter which has greater influence on the similarity in the next iteration will be appropriately reduced, and conversely, the change gradient of the element parameter which has less influence on the similarity in the next iteration will be appropriately improved. Since the true value is unknown, the size of the influence on the similarity change is evaluated by the relative value of the estimated value change, which refers to the degree of change of each element parameter in the process of the similarity changing from small to large. The relative value of the estimated value change is:

[0126] (28)

[0127] Wherein, The relative value of the estimated value change is, The parameter value when the similarity is small, The parameter value when the similarity is large, X The element to be estimated in the circuit.

[0128] According to the size order of the relative value of the estimated value change, the weight is assigned in reverse order. In practical application, the speed and accuracy of the solving process can be controlled by controlling the size of the total weight. For a circuit with good stability, the total weight can be increased to speed up the solution, and for a circuit with poor stability, the total weight can be reduced to improve the accuracy of the solution. The specific parameter estimation value update equation is shown in formula (29) and formula (30):

[0129] When a certain parameter needs to change in the small direction,

[0130] (29)

[0131] When a certain parameter needs to change in a large direction,

[0132] (30)

[0133] wherein, and represents the value of a certain parameter after updating, and represents the value of a certain parameter before updating, λ and γ is the assigned weight.

[0134] The specific process of the gradient-based model unknown parameter identification algorithm can be described as follows:

[0135] Step 1: obtaining the estimated value calculated by the element expression of the unknown parameter in the equivalent topology;

[0136] Step 2: preprocessing the received data, extracting the estimated value with poor stability, merging the values close to each other in the estimated value, reducing the total amount of data to be processed, and recombining the estimated value with poor stability;

[0137] Step 3: calculating the difference equation parameter and the current waveform difference degree according to the obtained multiple sets of estimated values;

[0138] Step 4: determining the estimated value updating strategy according to the and I acerr reducing trend, repeating steps 3 and 4 until each parameter converges, and outputting the solved parameters.

[0139] The embodiment is based on the equivalent topology of the single-phase uncontrolled rectifier bridge device with resistance and LC filter on the AC side and the single-phase uncontrolled rectifier bridge device with resistance and LCL filter on the AC side. The expression of the unknown parameter value of the element in the equivalent topology is derived by Z transform. The matrix expression between the AC side voltage and current is formed by the expression of the unknown parameter value of the element by using the measured AC side voltage data and current data. The parameter value of the element is obtained by solving the matrix. By deriving the expression of the unknown parameter value of the element in the set topology, the expression is obtained without additional calculation, and it does not depend on specific heuristic algorithms or professional knowledge in the field of electrical engineering. Only the measured voltage data and current data need to be input. The unknown parameters of the elements in the topology can be identified without damaging the device. The identification process has low time complexity and short time consumption.

[0140] Embodiment two

[0141] Embodiment two of the application introduces a filter-containing rectifier load parameter identification system based on Z transform.

[0142] As shown in Figure 4 a filter-based rectifier load parameter identification system based on Z transform, comprising:

[0143] An acquisition module configured to acquire an equivalent topology of the filter;

[0144] A determination module configured to determine a transfer function between an AC side current and an AC side voltage of the filter according to the acquired equivalent topology of the filter; obtain a matrix expression between the AC side voltage and the AC side current based on a bilinear transformation and a Z transform processing of the determined transfer function; and obtain an unknown element parameter expression in the equivalent topology according to the obtained matrix expression;

[0145] An identification module configured to solve unknown parameters in the obtained unknown element parameter expression in the equivalent topology based on a gradient identification algorithm, and complete the filter topology parameter identification based on the Z transform.

[0146] The detailed steps are the same as the filter topology parameter identification method based on the Z transform provided in Embodiment One, and will not be repeated here.

[0147] The above only provides preferred embodiments of the present embodiment and is not intended to limit the present embodiment. For those skilled in the art, the present embodiment can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present embodiment shall be included in the protection scope of the present embodiment.

Claims

1. A method for identifying parameters of a rectified load with a filter based on Z-transform, characterized in that, include: Obtain the equivalent topology of the filter; Based on the obtained equivalent filter topology, determine the transfer function between the AC side current and AC side voltage of the filter; Based on the transfer function determined by bilinear transformation and Z-transform, a matrix expression for the relationship between AC side voltage and AC side current is obtained. Based on the obtained matrix expression, the parameter expressions of the unknown elements in the equivalent topology are obtained; The unknown parameters in the expression of unknown element parameters in the equivalent topology obtained by the gradient identification algorithm are solved to complete the identification of filter topology parameters based on Z-transform. The process of solving the unknown parameters in the expression of unknown element parameters in the equivalent topology based on the gradient identification algorithm is as follows: obtain the estimated value calculated from the element expression of the unknown parameters in the equivalent topology; The expression for the parameters of the unknown components in the equivalent topology is preprocessed to extract the estimated values ​​with poor stability and merge the close values ​​among the estimated values. Based on multiple sets of estimated values, the degree of difference between the parameters of the difference equation and the current waveform is calculated. According to the decreasing trend of the degree of difference between the parameters of the difference equation and the degree of difference between the current waveform, the estimated values ​​are repeatedly updated until each parameter converges, thus completing the solution of the unknown parameters in the expression for the parameters of the unknown components in the equivalent topology. The smaller the difference between the parameters of the difference equation and the difference between the current waveform, the more accurate the circuit element parameters; the degree of difference between the current waveform and the current waveform... I acerr Difference of parameters in sum difference equations We unify similarity as the objective function for optimization, and define the similarity index as follows: ;in, For similarity, α and β All are weights. α + β =1; The magnitude of the impact of similarity changes is assessed by the relative changes in the estimated values ​​of different components, that is, the degree of change in the parameters of each component as the similarity increases, and the relative changes in the estimated values. for ;in, The parameter value represents the smaller the similarity. This represents the parameter value when the similarity is high. X This is a component in the circuit to be estimated; When a parameter needs to be changed to a smaller value When a parameter needs to change in a larger direction, ;in, and This represents the value of a parameter after the update. and This represents the value of a parameter before the update. λ and γ The weights assigned.

2. The method for identifying parameters of a rectified load with a filter based on Z-transform as described in claim 1, characterized in that, The degree of difference in current waveform refers to the difference between the current data obtained after simulation of the circuit constructed from the solved parameters and the actual measured data, i.e., the degree of difference in current waveform. I acerr for ;in, I sim The measured root mean square value of the input current. i sim ( t n )and i cal ( t n The input current and the iterated component parameters correspond to the instantaneous values ​​of the circuit current at the same moment in the simulation. N This represents the total number of current data.

3. The method for identifying parameters of a rectified load with a filter based on Z-transform as described in claim 2, characterized in that, The difference equation parameter variability is used to evaluate whether the component parameters calculated in the iterative calculation are accurate, i.e., the difference equation parameter variability. for ;in, N P represents the total number of current data, i.e., the total number of parameters in the difference equation. cal With P act The number of elements in the matrix formed by the parameters of the difference equations obtained by different calculation methods is N Column vectors.

4. The method for identifying parameters of a rectified load with a filter based on Z-transform as described in claim 1, characterized in that, In the process of determining the transfer function based on bilinear transformation and Z-transform, the determined transfer function is transformed by bilinear transformation... s Domain transformation z The domain is used to obtain the relationship between the AC side current and the AC side voltage. z The domain transfer function, based on the obtained z The coefficients in the domain transfer function determine the parametric equations.

5. The method for identifying parameters of a rectified load with a filter based on Z-transform as described in claim 1, characterized in that, The obtained equivalent topology of the filter includes at least the equivalent topology of a single-phase uncontrolled rectifier bridge device with LC filter and the equivalent topology of a single-phase uncontrolled rectifier bridge device with LCL filter.

6. A Z-transform-based system for identifying parameters of a rectified load with a filter, comprising the Z-transform-based method for identifying parameters of a rectified load with a filter as described in any one of claims 1-5, characterized in that, include: An acquisition module, configured to acquire the equivalent topology of the filter; The determination module is configured to determine the transfer function between the AC side current and AC side voltage of the filter based on the obtained equivalent filter topology; obtain the matrix expression between the AC side voltage and AC side current based on the determined transfer function processed by bilinear transformation and Z-transform; and obtain the expression of the parameters of unknown components in the equivalent topology based on the obtained matrix expression. The identification module is configured to solve for the unknown parameters in the expression of unknown element parameters in the equivalent topology obtained by the gradient identification algorithm, and to complete the identification of filter topology parameters based on Z-transform.

Images