A modeling method and system for harmonic characteristics of three-phase uncontrolled rectifier

Abstract

The present application discloses a modeling method and system for harmonic characteristics of a three-phase uncontrolled rectifier, the method comprising: based on the topological structure of the three-phase uncontrolled rectifier, obtaining the parameters of the three-phase uncontrolled rectifier, including the DC side filter inductance, filter capacitor and DC side load resistance; using the parameters of the three-phase uncontrolled rectifier, determining the DC port response of the three-phase uncontrolled rectifier; establishing a small signal model according to the DC port response, determining the coupling relationship between the port impedance of the three-phase uncontrolled rectifier and multiple harmonics; analyzing the large signal relationship on the AC side based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier. Compared with the traditional theoretical model, the present application has higher accuracy, can accurately describe the harmonic current generation mechanism of the three-phase uncontrolled rectifier and the action mechanism between multiple harmonics, and has guiding significance for the characterization and management of the power quality problems commonly existing in the power grid.

Description

Technical Field

[0001] The present application relates to the technical field of rectifier harmonic characteristic analysis, and in particular to a modeling method and system for harmonic characteristics of a three-phase uncontrolled rectifier. Background Art

[0002] Since the three-phase uncontrolled rectifier circuit does not require control, the circuit is reliable, the switch tube operates quickly, and the rectification effect can meet the needs of most working occasions, the three-phase uncontrolled rectifier circuit has been widely used. However, the working current of the three-phase uncontrolled rectifier circuit is discontinuous, which becomes one of the main nonlinear loads in the circuit and has become a research focus in the process of power quality management. Among them, the dynamic characteristics of the nonlinear load are an important part of determining stability. It is necessary to establish a more accurate model to describe the small signal transmission relationship of the nonlinear load and explain the harmonic generation mechanism of the three-phase uncontrolled rectifier from the perspective of large signals.

[0003] At present, the industry has a shallow understanding of the harmonic characteristics of three-phase uncontrolled rectifier equipment. The established model only equates the three-phase uncontrolled rectifier equipment to the source of harmonic current emission. This modeling method has two main disadvantages: first, it cannot accurately calculate the magnitude of the harmonic current, and second, it cannot characterize the interaction between the harmonic currents, and thus cannot fundamentally explain how the grid voltage performs a series of coupling actions to generate harmonic currents. Therefore, there is an urgent need for a method to more accurately model the harmonic characteristics of three-phase uncontrolled rectifiers. Summary of the invention

[0004] The purpose of the present application is to provide a method and system for modeling the harmonic characteristics of a three-phase uncontrolled rectifier, so as to solve the problems of low accuracy and inability to characterize the interaction relationship between harmonic currents in the existing three-phase uncontrolled rectifier harmonic characteristics modeling method.

[0005] To achieve the above objectives, the present application provides a modeling method for harmonic characteristics of a three-phase uncontrolled rectifier, comprising:

[0006] Based on the topological structure of the three-phase uncontrolled rectifier, the parameters of the three-phase uncontrolled rectifier are obtained, including the DC side filter inductor, filter capacitor and DC side load resistance;

[0007] Using the parameters of the three-phase uncontrolled rectifier, determine the DC port response of the three-phase uncontrolled rectifier;

[0008] A small signal model is established based on the DC port response to determine the coupling relationship between the three-phase uncontrolled rectifier port impedance and multiple harmonics;

[0009] The large signal relationship on the AC side is analyzed based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier.

[0010] Further, the determining of the DC port response of the three-phase uncontrolled rectifier by using the parameters of the three-phase uncontrolled rectifier includes:

[0011] Using the parameters of the three-phase uncontrolled rectifier, determine the port characteristics of the DC side load of the three-phase uncontrolled rectifier:

[0012]

[0013] Where, L d , C d are the DC side filter inductor and filter capacitor respectively, R d is the DC side load resistance, S a , S b , S c They are the switching functions of the three phases a, b and c respectively;

[0014] Using Laplace transform, the port characteristics are converted into time domain expressions to obtain the DC port response:

[0015] y d (t) = L -1 {Y d (s)};

[0016] In the formula, y d (t) is the DC port response, which represents the port admittance characteristics of the DC port load.

[0017] Furthermore, the small signal model is established according to the DC port response to determine the coupling relationship between the three-phase uncontrolled rectifier port impedance and multiple harmonics, including:

[0018] Using the switching function of the three-phase uncontrolled rectifier, the functional relationship between the voltage and current of the AC port and the voltage and current of the DC port is established as the first equation:

[0019]

[0020] In the formula, v d is the DC port voltage, v a , v b , v c are the three-phase voltage of the AC port, S αβ =S α +jS β is the switching function vector, For S αβ The conjugate of αβ =v α +jv β is the AC port voltage vector, v αβ The conjugate of d is the DC port voltage, id is the DC port current, y d (t) is the port admittance characteristic of the DC port load, and the operator * indicates convolution; i L is the AC side current;

[0021] Solving the first equation, we get the relationship between the voltage and current at the AC port of the three-phase uncontrolled rectifier as the second equation:

[0022]

[0023] Furthermore, after obtaining the second equation, the second equation is simplified as follows:

[0024]

[0025] In the formula, i Lp and i Ln i L The intrinsic frequency response and coupled frequency response of are considered as two independent state quantities, v gp and v gn They are the intrinsic frequency component and coupling frequency component of the AC port voltage on the grid side, respectively. The superscript * indicates conjugate. L (t) is the AC port admittance, ω 1 is the angular frequency on the AC side, S 1 For S αβ The amplitude and phase of the fundamental component of

[0026] Further, the large signal relationship of the AC side is analyzed based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier, including:

[0027] Determine the harmonic currents of a three-phase uncontrolled rectifier:

[0028]

[0029] Among them, v k represents the kth harmonic voltage at the AC port, which is the intrinsic frequency component. represents the 2-kth harmonic voltage, which is the coupled frequency component, I k is the equivalent kth harmonic current source;

[0030] Based on the harmonic current of the three-phase uncontrolled rectifier, the harmonic generation mechanism of the three-phase uncontrolled rectifier is analyzed.

[0031] The present application also provides a modeling system for harmonic characteristics of a three-phase uncontrolled rectifier, comprising:

[0032] A parameter acquisition unit, used for acquiring parameters of the three-phase uncontrolled rectifier based on the topological structure of the three-phase uncontrolled rectifier, including a DC side filter inductor, a filter capacitor and a DC side load resistor;

[0033] A port response calculation unit, used to determine a DC port response of the three-phase uncontrolled rectifier using parameters of the three-phase uncontrolled rectifier;

[0034] A coupling relationship analysis unit, used to establish a small signal model according to the DC port response and determine the coupling relationship between the three-phase uncontrolled rectifier port impedance and multiple harmonics;

[0035] The harmonic mechanism analysis unit is used to analyze the large signal relationship on the AC side based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier.

[0036] Furthermore, the port response calculation unit is also used for:

[0037] Using the parameters of the three-phase uncontrolled rectifier, determine the port characteristics of the DC side load of the three-phase uncontrolled rectifier:

[0038]

[0039] Where, L d , C d are the DC side filter inductor and filter capacitor respectively, R d is the DC side load resistance, S a , S b , S c They are the switching functions of the three phases a, b and c respectively;

[0040] Using Laplace transform, the port characteristics are converted into time domain expressions to obtain the DC port response:

[0041] y d (t) = L -1 {Y d (s)};

[0042] In the formula, y d (t) is the DC port response, which represents the port admittance characteristics of the DC port load.

[0043] Furthermore, the coupling relationship analysis unit is also used for:

[0044] Using the switching function of the three-phase uncontrolled rectifier, the functional relationship between the voltage and current of the AC port and the voltage and current of the DC port is established as the first equation:

[0045]

[0046] In the formula, v dis the DC port voltage, v a , v b , v c are the three-phase voltage of the AC port, S αβ =S α +jS β is the switching function vector, For S αβ The conjugate of αβ =v α +jv β is the AC port voltage vector, v αβ The conjugate of d is the DC port voltage, i d is the DC port current, y d (t) is the port admittance characteristic of the DC port load, and the operator * indicates convolution; i L is the AC side current;

[0047] Solving the first equation, we get the relationship between the voltage and current at the AC port of the three-phase uncontrolled rectifier as the second equation:

[0048]

[0049] Furthermore, the coupling relationship analysis unit is also used for:

[0050]

[0051] In the formula, i Lp and i Ln i L The intrinsic frequency response and coupled frequency response of are considered as two independent state quantities, v gp and v gn They are the intrinsic frequency component and coupling frequency component of the AC port voltage on the grid side, respectively. The superscript * indicates conjugate. L (t) is the AC port admittance, ω 1 is the angular frequency on the AC side, S 1 For S αβ The amplitude and phase of the fundamental component of

[0052] Furthermore, the harmonic mechanism analysis unit is also used for:

[0053] Determine the harmonic currents of a three-phase uncontrolled rectifier:

[0054]

[0055] Among them, v k represents the kth harmonic voltage at the AC port, which is the intrinsic frequency component. represents the 2-kth harmonic voltage, which is the coupled frequency component, I k is the equivalent kth harmonic current source;

[0056] Based on the harmonic current of the three-phase uncontrolled rectifier, the harmonic generation mechanism of the three-phase uncontrolled rectifier is analyzed.

[0057] Compared with the prior art, the beneficial effects of this application are:

[0058] The present application provides a modeling method for the harmonic characteristics of a three-phase uncontrolled rectifier. By constructing a three-phase switching function, the relationship between the voltage and current of the AC and DC ports is established based on small signal modeling, and then the coupling relationship between the AC port impedance and the multiple harmonics of the rectifier is derived. On this basis, the large signal relationship is analyzed to reveal the harmonic generation mechanism of the three-phase uncontrolled rectifier. Finally, the accuracy and effectiveness of this model are compared by comparing the theoretical calculation value and the result value of software simulation. In the traditional theoretical model, with the compensation effect of APF on the harmonic current of the system, since the harmonic current in the rectifier is equivalent to a harmonic current source, the change relationship of the kth harmonic current of the rectifier AC port will not be predicted. Compared with the traditional theoretical model, this method has higher accuracy, accurately depicts the harmonic current generation mechanism of the three-phase uncontrolled rectifier and the mechanism of action between multiple harmonics. It is a key progress in the research of three-phase uncontrolled rectifier equipment, and has guiding significance for the characterization and management of the power quality problems that are prevalent in the power grid, which is conducive to stability analysis in the power grid system and control design of power quality management equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the implementation manner will be briefly introduced below. Obviously, the drawings described below are only some implementation manners of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0060] Figure 1 It is a flow chart of a method for modeling harmonic characteristics of a three-phase uncontrolled rectifier provided in a certain embodiment of the present application;

[0061] Figure 2 It is a schematic diagram of the topological structure of a three-phase uncontrolled rectifier provided in a certain embodiment of the present application;

[0062] Figure 3 It is a schematic diagram of the principle of a three-phase switching function provided in a certain embodiment of the present application;

[0063] Figure 4 It is a signal flow diagram of the voltage and current at the AC port of a three-phase uncontrolled rectifier provided in a certain embodiment of the present application;

[0064] Figure 5 It is a large signal relationship between the kth harmonic and the 2-kth harmonic of the AC port of a three-phase uncontrolled rectifier provided in a certain embodiment of the present application;

[0065] Figure 6 It is the large signal relationship between the kth harmonic and the 2-kth harmonic of the AC port of the three-phase uncontrolled rectifier after the parallel APF provided in a certain embodiment of the present application;

[0066] Figure 7 It is a structural schematic diagram of a simulation model provided by a certain embodiment of the present application;

[0067] Figure 8 It is a schematic diagram of comparison results of a theoretical calculated value and a simulated value of the growth multiple of the kth harmonic of the AC port of a three-phase uncontrolled rectifier provided in a certain embodiment of the present application;

[0068] Fig. 9 It is a structural schematic diagram of a modeling system for harmonic characteristics of a three-phase uncontrolled rectifier provided in a certain embodiment of the present application. DETAILED DESCRIPTION

[0069] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0070] It should be understood that the step numbers used in this document are only for convenience of description and are not intended to limit the order in which the steps are executed.

[0071] It should be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0072] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0073] The term "and / or" means and includes any and all possible combinations of one or more of the associated listed items.

[0074] See also Figure 1In one embodiment of the present application, a method for modeling harmonic characteristics of a three-phase uncontrolled rectifier is provided. Figure 1 As shown, the modeling method of the harmonic characteristics of the three-phase uncontrolled rectifier includes steps S10 to S40. The specific steps are as follows:

[0075] S10. Based on the topological structure of the three-phase uncontrolled rectifier, parameters of the three-phase uncontrolled rectifier are obtained, including a DC side filter inductor, a filter capacitor, and a DC side load resistor.

[0076] In this step, based on Figure 2 The circuit topology of the three-phase uncontrolled rectifier is shown in Figure 1, and the DC side filter inductance L is recorded. d , filter capacitor C d and DC side load resistance R d .Depend on Figure 2 It can be seen that the three-phase uncontrolled rectifier adopts a three-phase diode uncontrolled rectifier.

[0077] S20. Determine a DC port response of the three-phase uncontrolled rectifier using parameters of the three-phase uncontrolled rectifier.

[0078] Specifically, step S20 includes the following contents:

[0079] Assume S 1 ~S 6 are the switching functions of diodes 1 to 6, respectively. When the diode is turned on, the function value is 1, and when the diode is turned off, the function value is 0. Assume that S a , S b , S c is the switching function of each phase a, b, and c, which is defined as the difference between the switching functions of the upper and lower diodes of each bridge arm. The image of this function is shown in Figure 3 As shown, its expression is as follows:

[0080]

[0081] The three-phase switching function is converted to the αβ coordinate system through 3 / 2 transformation to obtain the switching function vector: S αβ =S α +jS β , if the commutation process and current discontinuity are not considered, S α +jS β These are six vectors of equal action time. These six vectors act respectively Electrical angle.

[0082] The specific conversion process is:

[0083]

[0084] Since the port characteristics of the DC side load of the three-phase uncontrolled rectifier equipment are:

[0085]

[0086] Where, L d , C d are the DC side filter inductor and filter capacitor respectively, R d is the DC side load resistance.

[0087] Using Laplace transform, it is converted into a time domain expression to represent the unit impulse response on the DC side, that is, the DC port response:

[0088] y d (t) = L -1 {Y d (s)} (4)

[0089] S30. Establish a small signal model according to the DC port response to determine the coupling relationship between the three-phase uncontrolled rectifier port impedance and multiple harmonics.

[0090] In a specific embodiment, step S30 further includes the following sub-steps:

[0091] 3.1) Using the switching function of the three-phase uncontrolled rectifier, the functional relationship between the voltage and current of the AC port and the voltage and current of the DC port is established as the first equation:

[0092]

[0093] In the first equation, v d is the DC port voltage, v a , v b , v c are the three-phase voltage of the AC port, S αβ =S α +jS β is the switching function vector, For S αβ The conjugate of αβ =v α +jv β is the AC port voltage vector, v αβ The conjugate of; in the second equation, v d is the DC port voltage, i d is the DC port current, y d (t) is the port admittance characteristic of the DC port load, and the operator * represents convolution; in the third equation, i L is the AC side current.

[0094] It should be noted that the three equations in the equation respectively represent the relationship between the AC port voltage and the DC port voltage, the relationship between the DC port voltage and the DC port current, and the relationship between the DC port current and the AC port current, from which the relationship between the AC voltage and the AC current can be derived.

[0095] 3.2) Solve the first equation to obtain the relationship between the voltage and current at the AC port of the three-phase uncontrolled rectifier as the second equation:

[0096]

[0097] Since the switching function S αβ The main signal content in is the fundamental wave. Using this relationship, the above expression is simplified, and the α and β components in the vector expression are decomposed to obtain the following equation:

[0098]

[0099] Among them, i Lp and i Ln i L The intrinsic frequency response and coupled frequency response of are considered as two independent state quantities, v gp and v gn They are the intrinsic frequency component and coupling frequency component of the AC port voltage on the grid side, respectively. The superscript * indicates conjugate. L (t) is the AC port admittance, ω 1 is the angular frequency on the AC side, S 1 For S αβ The fundamental component amplitude and phase is a complex number, but due to the switching function S a , S b , S c The fundamental components of the three-phase AC voltage are in phase with each other, so S 1 The imaginary part is zero, that is, S 1 is a real number,

[0100] In a specific embodiment, for a more intuitive analysis, equation (7) is represented by a signal flow graph as follows: Figure 4 The relationship shown. Figure 4From the signal transmission relationship of the DC side of the diode uncontrolled rectifier shown in , it can be seen that the nonlinear load admittance shows the same action characteristics on the intrinsic frequency component and the reflected coupling frequency component, which shows that the diode rectifier is a strongly coupled system. The theoretical derivation in this step shows that at the AC port of the diode rectifier, the disturbance of the kth harmonic voltage will cause the response of the kth and 2-kth harmonic currents of equal amplitude, which makes the two frequency harmonic systems connected to each other. In the system composed of the converter, the power grid and the rectifier load, the signals of the two frequencies are coupled with each other, which is of guiding significance for the establishment of the system signal model, the writing of the system characteristic equation and the analysis of the system power quality problems.

[0101] S40: Analyze the large signal relationship on the AC side based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier.

[0102] In this step, in order to reveal the generation mechanism of harmonic current at the AC side port of the three-phase uncontrolled rectifier, it is necessary to first analyze the large signal relationship on the AC side, and further study the filtering effect of APF on harmonic current during the simulation verification process. The harmonic current changes of the system before and after the APF is added to the system are used to achieve accurate verification of the harmonic generation model of the three-phase rectifier.

[0103] First, large signal relationship modeling is performed: by analyzing the large signal relationship on the AC side of the rectifier, the harmonic generation mechanism of the three-phase uncontrolled rectifier is explained.

[0104]

[0105] Among them, v k is the kth harmonic voltage at the AC port, i.e., the intrinsic frequency component, is the 2-kth harmonic voltage, i.e. the coupled frequency component, I k is the equivalent kth harmonic current source.

[0106] In the large signal analysis process, the source of the k-th harmonic generation mechanism is equivalent to the k-th harmonic current source, and then the k-th harmonic current generated by the three-phase rectifier can be described by the above formula (8). The reason for equivalentizing the source of the k-th harmonic generation mechanism to the k-th harmonic current source is characterized by the small signal model in this method, that is, the current source influencing factor of the k-th harmonic of the converter is mainly the fundamental voltage. The fundamental voltage can stimulate the k-th harmonic current through the harmonic action relationship characterized by the small signal model, and the stimulated content is also mainly characterized by the harmonic action relationship. In the equivalent process, since the main content of the grid voltage is the fundamental voltage, which is relatively constant, and the coupling relationship between other harmonics and the k-th harmonic is very weak, the source of the k-th harmonic generation mechanism can be equivalent to the k-th harmonic current source.

[0107] When the three-phase uncontrolled rectifier is connected to the grid, due to the reflection effect of the grid impedance on the harmonic current, the large signal relationship between the kth harmonic and the 2-kth harmonic generated by the three-phase uncontrolled rectifier is as follows: Figure 5 As shown, I k is the harmonic current source, i g and v gp They are the grid side, i.e., AC current and AC voltage, respectively. The subscripts p and n represent the intrinsic frequency component and the coupled frequency component, respectively. The underlined physical quantity represents the conversion of the frequency of the 2-k harmonics (i.e., the coupled frequency component) to the kth order, such as Z g is the AC side port impedance, Y L is the AC side port admittance.

[0108] When the APF is connected in parallel to the system, the APF is used to accurately compensate for the kth harmonic current, which is equivalent to weakening the load-side current i in the kth harmonic coupling loop. Lp Current to the grid side i gp The signal transmission relationship in the system is given by Figure 5 becomes Figure 6 , where m is the harmonic current compensation coefficient of APF.

[0109] In a specific embodiment, in order to verify the accuracy of the modeling method, a simulation model is also built using PLECS, and its structure is as follows: Figure 7 In the signal coupling loop proposed in the present application, the APF absorbs the kth harmonic current, detects the change relationship of the kth harmonic current and the 2-kth coupled harmonic current on the AC side of the diode rectifier, and then verifies the correctness of the modeling method.

[0110] When the parallel APF is compensating for the 13th harmonic and the harmonic current compensation coefficient is set to 0.8, the harmonic model theory of the three-phase uncontrolled rectifier proposed in this application is used to calculate the growth multiple of the kth harmonic of the three-phase uncontrolled rectifier AC port when the system state changes, and the growth multiple of the kth harmonic is detected in the simulation system. The comparison between the theoretical calculation value and the simulation result value is as follows: Figure 8 shown.

[0111] exist Figure 8In the figure, the gray curve is the theoretical change multiple of harmonic currents of different frequencies before and after the APF is added to the rectifier grid-connected system. The black dots in the figure are the change multiples of the specified filtered harmonic current measured by simulation. This result can well reflect the accuracy of the model proposed in this application. This result cannot be predicted by the traditional rectifier equivalent harmonic current source theory. In the traditional theoretical model, with the compensation effect of APF on the system harmonic current, since the harmonic current in the rectifier is equivalent to a harmonic current source, the change relationship of the kth harmonic current at the rectifier AC port cannot be predicted. This is the improvement of the model proposed in this application compared to the traditional model. A more accurate system model is conducive to stability analysis in the power grid system and control design of power quality management equipment.

[0112] In summary, the modeling method of the harmonic characteristics of the three-phase uncontrolled rectifier provided in this application has higher accuracy than the traditional theoretical model, and accurately depicts the harmonic current generation mechanism of the three-phase uncontrolled rectifier and the action mechanism between multiple harmonics. It is a key advancement in the research of three-phase uncontrolled rectifier equipment, and has guiding significance for the characterization and management of the power quality problems that are common in power grids. It is conducive to stability analysis in power grid systems and the control design of power quality management equipment.

[0113] See also Fig. 9 A certain embodiment of the present application further provides a modeling system for harmonic characteristics of a three-phase uncontrolled rectifier, comprising:

[0114] The parameter acquisition unit 01 is used to acquire the parameters of the three-phase uncontrolled rectifier based on the topological structure of the three-phase uncontrolled rectifier, including the DC side filter inductor, filter capacitor and DC side load resistance;

[0115] The port response calculation unit 02 is used to determine the DC port response of the three-phase uncontrolled rectifier by using the parameters of the three-phase uncontrolled rectifier;

[0116] A coupling relationship analysis unit 03 is used to establish a small signal model according to the DC port response and determine the coupling relationship between the three-phase uncontrolled rectifier port impedance and multiple harmonics;

[0117] The harmonic mechanism analysis unit 04 is used to analyze the large signal relationship on the AC side based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier.

[0118] In one embodiment, the port response calculation unit 02 is further used for:

[0119] Using the parameters of the three-phase uncontrolled rectifier, determine the port characteristics of the DC side load of the three-phase uncontrolled rectifier:

[0120]

[0121] Where, L d , C d are the DC side filter inductor and filter capacitor respectively, R d is the DC side load resistance,

[0122] S a , S b , S c They are the switching functions of the three phases a, b and c respectively;

[0123] Using Laplace transform, the port characteristics are converted into time domain expressions to obtain the DC port response:

[0124] y d (t) = L -1 {Y d (s)} (10)

[0125] In the formula, y d (t) is the DC port response, which represents the port admittance characteristics of the DC port load.

[0126] In one embodiment, the coupling relationship analysis unit 03 is further used for:

[0127] Using the switching function of the three-phase uncontrolled rectifier, the functional relationship between the voltage and current of the AC port and the voltage and current of the DC port is established as the first equation:

[0128]

[0129] In the formula, v d is the DC port voltage, v a , v b , v c are the three-phase voltage of the AC port, S αβ =S α +jS β is the switching function vector, For S αβ The conjugate of αβ =v α +jv β is the AC port voltage vector, v αβ The conjugate of d is the DC port voltage, i d is the DC port current, y d (t) is the port admittance characteristic of the DC port load, and the operator * indicates convolution; i L is the AC side current;

[0130] Solving the first equation, we get the relationship between the voltage and current at the AC port of the three-phase uncontrolled rectifier as the second equation:

[0131]

[0132] In one embodiment, the coupling relationship analysis unit 03 is further used for:

[0133]

[0134] In the formula, i Lp and i Ln i L The intrinsic frequency response and coupled frequency response of are considered as two independent state quantities, v gp and v gn They are the intrinsic frequency component and coupling frequency component of the AC port voltage on the grid side, respectively. The superscript * indicates conjugate. L (t) is the AC port admittance, ω 1 is the angular frequency on the AC side, S 1 For S αβ The amplitude and phase of the fundamental component of

[0135] In one embodiment, the harmonic mechanism analysis unit 04 is further used for:

[0136] Determine the harmonic currents of a three-phase uncontrolled rectifier:

[0137]

[0138] Among them, v k represents the kth harmonic voltage at the AC port, which is the intrinsic frequency component. represents the 2-kth harmonic voltage, which is the coupled frequency component, I k is the equivalent kth harmonic current source;

[0139] Based on the harmonic current of the three-phase uncontrolled rectifier, the harmonic generation mechanism of the three-phase uncontrolled rectifier is analyzed.

[0140] It can be understood that the system provided in this embodiment is used to execute the modeling method of harmonic characteristics of a three-phase uncontrolled rectifier as described in any of the above embodiments, and achieve the same effect as the above embodiments, which will not be further described here.

[0141] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is only a logical function division. There may be other division methods when implementing them in actual applications. For example, multiple units or page components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, and the indirect coupling or communication connection of devices or units can be electrical, mechanical or other forms.

[0142] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0143] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0144] The above-mentioned integrated unit implemented in the form of a software functional unit can be stored in a computer-readable storage medium. The above-mentioned software functional unit is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor to perform some steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk and other media that can store program code.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A modeling method for the harmonic characteristics of a three-phase uncontrolled rectifier. It is characterized in that include: Based on the topological structure of the three-phase uncontrolled rectifier, the parameters of the three-phase uncontrolled rectifier are obtained, including the DC side filter inductor, filter capacitor and DC side load resistance; Using the parameters of the three-phase uncontrolled rectifier, determining the DC port response of the three-phase uncontrolled rectifier includes: using the parameters of the three-phase uncontrolled rectifier, determining the port characteristics of the DC side load of the three-phase uncontrolled rectifier: Where, L d , C d are the DC side filter inductor and filter capacitor respectively, R d is the DC side load resistance; Using Laplace transform, the port characteristics are converted into time domain expressions to obtain the DC port response: y d (t)=L -1 {Y d (s)}; In the formula, y d (t) is the port admittance characteristic of the DC port load; A small signal model is established based on the DC port response to determine the coupling relationship between the three-phase uncontrolled rectifier port impedance and multiple harmonics; The large signal relationship on the AC side is analyzed based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier.

2. The modeling method of harmonic characteristics of a three-phase uncontrolled rectifier according to claim 1, It is characterized in that The method of establishing a small signal model according to the DC port response and determining the coupling relationship between the three-phase uncontrolled rectifier port impedance and multiple harmonics includes: Using the switching function of the three-phase uncontrolled rectifier, the functional relationship between the voltage and current of the AC port and the voltage and current of the DC port is established as the first equation: In the formula, v d is the DC port voltage, v a , v b , v c are the three-phase voltage of the AC port, S αβ =S α +jS β is the switching function vector, For S αβ The conjugate of αβ =v α +jv β is the AC port voltage vector, v αβ The conjugate of v d is the DC port voltage, i d is the DC port current, y d (t) is the port admittance characteristic of the DC port load, and the operator * indicates convolution; i L is the AC side current, S a , S b , S c They are the switching functions of the three phases a, b and c respectively; Solving the first equation, we get the relationship between the voltage and current at the AC port of the three-phase uncontrolled rectifier as the second equation:

3. The modeling method of harmonic characteristics of a three-phase uncontrolled rectifier according to claim 2, It is characterized in that After obtaining the second equation, the second equation is simplified as follows: In the formula, i Lp and i Ln i L The intrinsic frequency response and coupled frequency response of are considered as two independent state quantities, v gp and v gn They are the intrinsic frequency component and coupling frequency component of the AC port voltage on the grid side, respectively. The superscript * indicates conjugate. L (t) is the port admittance characteristic of the DC port load, ω 1 is the angular frequency on the AC side, S 1 For S αβ The amplitude and phase of the fundamental component of 4. The modeling method of harmonic characteristics of a three-phase uncontrolled rectifier according to claim 1, It is characterized in that Analyzing the large signal relationship on the AC side based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier includes: Determine the harmonic currents of a three-phase uncontrolled rectifier: Among them, v k represents the kth harmonic voltage at the AC port, which is the intrinsic frequency component. represents the 2-kth harmonic voltage, which is the coupled frequency component, I k is the equivalent kth harmonic current source; Based on the harmonic current of the three-phase uncontrolled rectifier, the harmonic generation mechanism of the three-phase uncontrolled rectifier is analyzed.

5. A modeling system for harmonic characteristics of three-phase uncontrolled rectifiers, It is characterized in that include: A parameter acquisition unit, used for acquiring parameters of the three-phase uncontrolled rectifier based on the topological structure of the three-phase uncontrolled rectifier, including a DC side filter inductor, a filter capacitor and a DC side load resistor; The port response calculation unit is used to determine the DC port response of the three-phase uncontrolled rectifier by using the parameters of the three-phase uncontrolled rectifier, including: determining the port characteristics of the DC side load of the three-phase uncontrolled rectifier by using the parameters of the three-phase uncontrolled rectifier: Where, L d , C d are the DC side filter inductor and filter capacitor respectively, R d is the DC side load resistance, s is the frequency domain independent variable in Laplace transform; Using Laplace transform, the port characteristics are converted into time domain expressions to obtain the DC port response: y d (t)=L -1 {Y d (s)}; In the formula, y d (t) is the port admittance characteristic of the DC port load, L -1 is the transformation symbol of the inverse Laplace transform; A coupling relationship analysis unit, used to establish a small signal model according to the DC port response and determine the coupling relationship between the three-phase uncontrolled rectifier port impedance and multiple harmonics; The harmonic mechanism analysis unit is used to analyze the large signal relationship on the AC side based on the coupling relationship to determine the harmonic generation mechanism of the three-phase uncontrolled rectifier.

6. The modeling system for harmonic characteristics of a three-phase uncontrolled rectifier according to claim 5, It is characterized in that The coupling relationship analysis unit is further used for: Using the switching function of the three-phase uncontrolled rectifier, the functional relationship between the voltage and current of the AC port and the voltage and current of the DC port is established as the first equation: In the formula, v d is the DC port voltage, v a , v b , v c are the three-phase voltage of the AC port, S αβ =S α +jS β is the switching function vector, For S αβ The conjugate of αβ =v α +jv β is the AC port voltage vector, v αβ The conjugate of v d is the DC port voltage, i d is the DC port current, y d (t) is the port admittance characteristic of the DC port load, and the operator * indicates convolution; i L is the AC side current, S a , S b , S c are the switching functions of the three phases a, b, and c, respectively, and v α 、v β are the AC port voltage after Clark transformation, S α , S β are the switching functions after Clarke transformation respectively; Solving the first equation, we get the relationship between the voltage and current at the AC port of the three-phase uncontrolled rectifier as the second equation:

7. The modeling system for harmonic characteristics of a three-phase uncontrolled rectifier according to claim 6, It is characterized in that The coupling relationship analysis unit is further used for: In the formula, i Lp and i Ln i L The intrinsic frequency response and coupled frequency response of are considered as two independent state quantities, v gp and v gn They are the intrinsic frequency component and coupling frequency component of the AC port voltage on the grid side, respectively. The superscript * indicates conjugate. L (t) is the port admittance characteristic of the DC port load, ω 1 is the angular frequency on the AC side, S 1 For S αβ The amplitude and phase of the fundamental component of e is a natural constant, t is the independent time variable, and j is a complex unit.

8. The modeling system for harmonic characteristics of a three-phase uncontrolled rectifier according to claim 5, It is characterized in that The harmonic mechanism analysis unit is also used for: Determine the harmonic currents of a three-phase uncontrolled rectifier: Among them, v k represents the kth harmonic voltage at the AC port, which is the intrinsic frequency component. represents the 2-kth harmonic voltage, which is the coupled frequency component, I k is the equivalent kth harmonic current source, S 1 is the switching function vector S αβ The amplitude and phase of the fundamental wave component, Y d (s) is the port characteristic of the DC side load of the three-phase uncontrolled rectifier; Based on the harmonic current of the three-phase uncontrolled rectifier, the harmonic generation mechanism of the three-phase uncontrolled rectifier is analyzed.

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