Harmonic closed-loop transfer analysis method and system of grid-connected inverter considering broadband coupling

Abstract

The present application belongs to the technical field of grid-connected inverter harmonic analysis, and specifically discloses a grid-connected inverter harmonic closed-loop transfer analysis method and system considering wideband coupling; the method comprises the following steps: respectively establishing harmonic component transfer functions of each module; based on the harmonic component transfer functions of the sampling module, the harmonic active power and the harmonic reactive power input to the power outer loop control module are calculated; based on the harmonic component transfer functions of the power outer loop control module, the harmonic current component in the reference current signal output by the power outer loop is calculated; based on the harmonic component transfer functions of the current inner loop control module, the three-phase modulation voltage harmonic component and the inverter port voltage harmonic component are obtained through coordinate inverse transformation; based on the inverter port voltage harmonic component, combined with the main circuit harmonic transfer equation, the grid-connected point harmonic current component is calculated; the present application overcomes the defects of the traditional analysis method, such as the inability to consider the full loop of closed-loop control and the insufficient consideration of wideband coupling.

Description

Technical Field

[0001] This invention relates to the field of harmonic analysis technology for grid-connected inverters, and in particular to a method and system for closed-loop harmonic transfer analysis of grid-connected inverters that takes into account wideband coupling. Background Technology

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

[0003] With the rapid development of renewable energy power generation technologies such as photovoltaics and wind power, grid-connected inverters, as the core interface devices connecting distributed generation units and the public power grid, directly affect the efficiency, power quality, and stable and safe operation of renewable energy power generation systems. Unlike traditional power systems dominated by synchronous generators, the extensive integration of inverters based on power electronic converters has drastically altered the dynamic characteristics of the power grid, giving it new features such as "low inertia, weak damping, and multi-scale" characteristics. This presents unprecedented challenges to the analysis and control of grid-connected inverters.

[0004] To conduct in-depth research on the grid-connected characteristics of grid-connected inverters, the first and crucial step is to establish an accurate and applicable mathematical model. Traditional modeling methods typically treat the inverter as a whole, using state-space averaging or small-signal linearization to build a simplified model. While these methods reveal the system's stability boundaries to some extent, they often obscure the interactions between different dynamic components within the system, making it difficult to accurately characterize dynamic processes such as high-frequency oscillations and subsynchronous oscillations between the inverter and the grid under complex operating conditions. Furthermore, traditional modeling methods often model only a single type of harmonic, such as low-frequency characteristic harmonics or high-frequency sideband harmonics, neglecting the broadband coupling relationship between low-frequency and high-frequency harmonics (the coupling relationship between low-order and high-order harmonics). This may lead to broadband oscillations at the grid connection point, affecting the normal operation of power electronic equipment and, in severe cases, causing renewable energy power plants to disconnect from the grid. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a harmonic closed-loop transfer analysis method and system for grid-connected inverters that considers wideband coupling. By taking into account the wideband coupling effect of harmonics, the grid-connected inverter is decoupled into multiple key functional sub-links, and accurate transfer functions or state equations are established for each sub-link. This allows for accurate calculation of the contribution of any sub-link in the control loop to a certain frequency harmonic and its wideband coupled harmonics.

[0006] In some implementations, the following technical solutions are adopted:

[0007] A method for harmonic closed-loop transfer analysis of grid-connected inverters considering wideband coupling includes:

[0008] The grid-connected inverter is decoupled into a sampling module, a pulse width modulation module, a phase-locked loop module, a power outer loop control module, a current inner loop control module, and the grid equivalent impedance, and the harmonic component transfer function of each module is established; based on the coupling characteristics between modules, the coupling frequency of the target harmonic is calculated.

[0009] The three-phase current and voltage at the grid connection point are collected. Based on the harmonic component transfer function of the sampling module, the dq-axis harmonic current and harmonic voltage output from the sampling stage are obtained through coordinate transformation. The harmonic active power input to the power outer loop control module is then calculated. P h Harmonic reactive power Q h ;

[0010] Based on the harmonic component transfer function of the power outer loop control module, and combined with the harmonic current components output by the sampling stage, the harmonic current components in the reference current signal output by the power outer loop are calculated.

[0011] Based on the harmonic component transfer function of the current inner loop control module, the harmonic components in the DC component reference signal of the dq axis voltage are calculated, and the harmonic components of the three-phase modulated voltage and the inverter port voltage are obtained through coordinate inverse transformation.

[0012] Based on the inverter port voltage harmonic components and combined with the main circuit harmonic transmission equation, the grid connection point harmonic current components are calculated.

[0013] Calculate the harmonic contribution of each module to the target harmonics, and determine the module with the greatest impact on the target harmonics.

[0014] As a further solution, it also includes: inputting the q-axis voltage component containing harmonics from the sampling stage output into the phase-locked loop module, wherein the output angle of the phase-locked loop module is used to provide the rotation angle for coordinate transformation; the output angle Specifically:

[0015] ;

[0016] in, The pass function for the PI controller of the phase-locked loop module. Harmonic component angular frequency and sampling time T s The product; It is the fundamental component of the phase-locked loop output angle, which is also the fundamental component of the phase angle of the grid-connected voltage. It is the harmonic component of the phase-locked loop output angle. for f The angular frequencies of the first harmonic, U1, U5, and U0, are respectively the frequencies of... f 1. fThe harmonic voltage and fundamental voltage of 5.

[0017] As a further approach, the harmonic active power input to the power outer loop control module is calculated. P h Harmonic reactive power Q h Specifically:

[0018] ;

[0019] in, , The dq axis outputs of the sampling stage are respectively i Subharmonic voltage; , The dq axis outputs of the sampling stage are respectively i Subharmonic current; for and The phase difference; for and The phase difference; for and phase difference, for and The phase difference.

[0020] As a further approach, the harmonic current components in the reference current signal output by the power outer loop are calculated, specifically:

[0021] ;

[0022] in, , These are the d-axis and q-axis harmonic current components in the reference current signal output from the power outer loop, respectively. The transfer function for the PI controller of the power outer loop control module. The fundamental angular frequency, For the first i The angular frequency of the subharmonic.

[0023] As a further approach, the harmonic components in the DC component reference signal of the dq-axis voltage are calculated, specifically as follows:

[0024] ;

[0025] in, , These are the harmonic components in the DC component reference signal of the dq-axis voltage, respectively. This is the transfer function for the PI controller in the current inner loop control module. , These are the harmonic components of the d-axis and q-axis reference currents, respectively. , These are the d-axis and q-axis components of the harmonic current at the grid connection point, respectively. , These are the d-axis and q-axis components of the capacitor current, respectively. , These are the d-axis and q-axis components of the harmonic voltage at the grid connection point, respectively. It is the capacitor current compensation coefficient. It is the dq-axis current decoupling coefficient. It is the voltage feedforward compensation coefficient.

[0026] As a further approach, the harmonic components of the three-phase modulated voltage are obtained through inverse coordinate transformation, specifically:

[0027] ;

[0028] in, A ij These are the transfer coefficients of the inverse Park transform. For rotation angle, U si The i-th harmonic component of the modulation voltage. , , , , The frequencies are respectively f 1- f 5 harmonic voltage, , , , , The frequencies are respectively f 1- f 5 harmonic current, , , , , The frequencies are respectively f 1- f The three-phase modulated voltage harmonic components of 5.

[0029] As a further solution, the inverter port voltage harmonic components Specifically:

[0030] ;

[0031] in, K pwm The equivalent modulation coefficient of the pulse width modulation module. Indicates frequency as f i The inner loop output voltage.

[0032] As a further approach, based on the inverter port voltage harmonic components and combined with the main circuit harmonic transmission equation, the grid connection point harmonic current components are calculated, specifically:

[0033] ;

[0034] ;

[0035] ;

[0036] ;

[0037] in, The frequency of the port current is f i The amount; U ci The frequency of the voltage in the filter capacitor is f i The amount; I ci The frequency of the filter capacitor current is f i The amount; L 1. R 1 represents the inductance and resistance on the inverter side of the LCL filter; L 2. R 2 represents the mains inductance and resistance of the LCL filter, respectively; C , R C These are the filter capacitor and its additional resistor, respectively. R g , L g These are the equivalent resistance and inductance of the power grid, respectively. This refers to the harmonic components of the inverter port voltage. The frequency at the grid connection point is f i Harmonic voltage, For frequency f i Harmonic angular frequency, The frequency at the port is f i Harmonic voltage, The frequency at the port is f i Harmonic currents, Frequency is f i The capacitor harmonic current.

[0038] As a further step, the harmonic contribution of each module to the target harmonic is calculated, specifically as follows:

[0039] The set parameter values ​​of each module under ideal conditions are used as the baseline values. K i1b The corresponding harmonic current at this time I The content of 1 is used as the benchmark value. X 1b Among them, the set parameter values ​​of the phase-locked loop module, the power outer loop control module, and the current inner loop control module are integral coefficients, and the set parameter values ​​of the sampling module and the pulse width modulation module are the delay time and the modulation coefficient, respectively.

[0040] The set parameter value is continuously increased to the predetermined level, and the corresponding harmonic current is recorded. I The content of 1; establishing harmonic current I The relationship between the content of 1 and the set parameter value is used to select the linear segment data in the relationship and calculate the harmonic contribution of the corresponding module. :

[0041] ;

[0042] in, This indicates the number of parameter values ​​set for the linear segment. This represents the k-th set parameter value in the linear segment data, where k = 1, 2, ..., m. This indicates that the parameter value is set to... The content of harmonic currents corresponding to the time.

[0043] In other embodiments, the following technical solutions are adopted:

[0044] A harmonic closed-loop transfer analysis system for grid-connected inverters considering wideband coupling, comprising:

[0045] The decoupling module is configured to decouple the grid-connected inverter into a sampling module, a pulse width modulation module, a phase-locked loop module, a power outer loop control module, a current inner loop control module, and the grid equivalent impedance, and to establish the harmonic component transfer function of each module; based on the coupling characteristics between the modules, the coupling frequency of the target harmonic is calculated;

[0046] The sampling module is configured to collect three-phase current and voltage at the grid connection point. Based on the harmonic component transfer function of the sampling module, the dq-axis harmonic current and harmonic voltage output from the sampling stage are obtained through coordinate transformation. The harmonic active power input to the power outer loop control module is then calculated. P h Harmonic reactive power Q h ;

[0047] The power outer loop control module is configured to calculate the harmonic current components in the reference current signal output by the power outer loop based on the harmonic component transfer function of the power outer loop control module and the harmonic current components output by the sampling stage.

[0048] The current inner loop control module is configured to calculate the harmonic components in the DC component reference signal of the dq axis voltage based on the harmonic component transfer function of the current inner loop control module, and obtain the harmonic components of the three-phase modulated voltage and the harmonic components of the inverter port voltage through inverse coordinate transformation.

[0049] The grid connection point harmonic current calculation module is configured to calculate the grid connection point harmonic current components based on the inverter port voltage harmonic components and the main circuit harmonic transmission equation.

[0050] The harmonic contribution calculation module is configured to calculate the harmonic contribution of each module to the target harmonic and determine the module with the greatest impact on the target harmonic.

[0051] Compared with the prior art, the beneficial effects of the present invention are:

[0052] (1) Based on the actual physical structure of the grid-connected inverter, this invention establishes the accurate harmonic component transfer function of each sub-link separately and considers the signal connection relationship between them, and finally integrates them into a complete wideband coupling model of the whole system. This overcomes the problems of traditional methods being unable to reflect the internal structure of the inverter and being inconvenient to reveal its complex interaction mechanism with the power grid. It also overcomes the defects of traditional analysis methods being unable to take into account the entire closed-loop control circuit and insufficient consideration of wideband coupling. Furthermore, it can accurately calculate the contribution of any link in the control loop to a certain frequency harmonic and its coupled harmonic.

[0053] (2) This invention fully considers the wideband coupling relationship between sampling harmonics, PWM harmonics and harmonics caused by asymmetry in the control loop. By considering the coupling relationship between different links in the grid-connected inverter control loop, the coupling relationship between different types of harmonics caused by different links is analyzed, thereby establishing the wideband coupling relationship between low-frequency coupled harmonics and high-frequency sampling harmonics. This solves the defect of the traditional method in not fully considering wideband coupling and improves the accuracy of harmonic coupling analysis of grid-connected inverters.

[0054] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0055] Figure 1 This is a flowchart of the harmonic closed-loop transfer analysis method for grid-connected inverters that takes into account wideband coupling in an embodiment of the present invention.

[0056] Figure 2 This is an equivalent circuit diagram of the grid-connected inverter control in an embodiment of the present invention. Detailed Implementation

[0057] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0058] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0059] Example 1

[0060] In one or more embodiments, a harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling is disclosed, combined with... Figure 1 and Figure 2 Specifically, it includes the following processes:

[0061] S101: Decouple the grid-connected inverter into a sampling module, a pulse width modulation module, a phase-locked loop module, a power outer loop control module, a current inner loop control module, and the grid equivalent impedance ( Figure 2 Z in g The harmonic component transfer function of each module is established; based on the coupling characteristics between modules, the coupling frequency of the target harmonic is calculated.

[0062] It should be noted that low-frequency coupled harmonics refer to harmonics caused by asymmetry in the control loop, while high-frequency sampling harmonics refer to harmonics at frequencies near the switching frequency generated by the switching characteristics of the power electronic devices themselves, also known as sideband harmonics; the coupling relationship between low-frequency harmonics and high-frequency harmonics is the broadband coupling relationship between low-frequency harmonics and high-frequency harmonics.

[0063] Figure 2 The topology diagram of the grid-connected inverter is given. In the main circuit section, L1 is the AC-side inductor, C is the filter capacitor, L2 is the grid-side inductor, and Z... g This is the equivalent impedance of the power grid.

[0064] Combination Figure 2 The specific control process for the grid-connected inverter is as follows:

[0065] S&T stands for Sampling Module. The sampling module collects the three-phase current and voltage at the grid connection point. After sampling, the signal undergoes an abc-dq coordinate transformation to obtain the d-axis and q-axis components of the current and voltage at the grid connection point, respectively. i d , i q , u d , u q .

[0066] Phase-locked loop module: q-axis component of grid connection point voltage u q As the input to the phase-locked loop (PLL) module, the output angle of the PLL module is... Used to provide the rotation angle for abc-dq coordinate transformation or dq-abc coordinate transformation.

[0067] The power outer loop control module: This module controls the active power P and reactive power Q output by the grid-connected inverter, and their respective active power reference values ​​P. ref and reactive power reference value Q ref After the difference is calculated, the difference is passed through a PI controller to obtain the reference current i of the outer power loop output on the d-axis and q-axis. dref and i qref It serves as the input to the current inner loop control module.

[0068] Inner current control module: Based on the reference current i on the d-axis and q-axis outputs of the outer power control module. dref and i qref The d-axis and q-axis components of the grid-connected point current output by the sampling module are respectively compared with those of the sampling module. i d , i q The difference is calculated, and the difference values ​​are then processed by a PI controller, combined with the dq-axis current decoupling coefficient K. i Voltage proportional feedforward coefficient K, and d-axis and q-axis components of the grid connection point voltage. u d , u q The reference voltages u along the d-axis and q-axis are obtained. dref and u qref The reference voltage is subtracted from the d-axis and q-axis components of the capacitor current, and after inverse abc / dq coordinate transformation, the PWM three-phase modulation signal is obtained.

[0069] In this embodiment, a certain harmonic is selected as the target harmonic for analysis. Based on the harmonic coupling mechanism of the dq axis asymmetry of the sampling module, pulse width modulation module, and current inner loop control module, the coupling frequency of the target harmonic is calculated.

[0070] As a specific example, select positive sequence harmonics. f 1. To analyze the target harmonics, the coupling frequency harmonics are as follows:

[0071] ;

[0072] in, f c This is the switching frequency of the grid-connected inverter, and this inverter uses symmetrical sampling. f 0 is the fundamental frequency; where, f 2. f 4. f 5 is a negative-order component. f 3 is the zero-order component. f 0 represents the fundamental frequency. Additionally, there are positive sequence voltage harmonics. f 1. In addition to coupling out harmonic currents of other frequencies, it can also generate harmonic currents of the same frequency. f The harmonic current of 1.

[0073] f 1. f 2. f 3. f 4. f 5 represents five sets of harmonics that are coupled to each other after selecting f1 as the analysis target. For example: if f If 1 is the 7th positive sequence harmonic, then its coupling frequency includes the 32nd harmonic. f 2) 33rd harmonic ( f 3) 8th harmonic ( f 4) and the 5th harmonic ( f 5).

[0074] Therefore, for the selected positive sequence harmonics f 1. When analyzing target harmonics, the inverter grid connection point voltage for:

[0075] ;

[0076] in, , , , , , The fundamental voltage and frequency at the grid connection point are respectively... f 1. f 2. f 3. f 4. f The harmonic voltage component of 5.

[0077] S102: Collect the three-phase current and voltage at the grid connection point. Based on the harmonic component transfer function of the sampling module, obtain the sampled current and voltage. After coordinate transformation, obtain the dq-axis harmonic current and harmonic voltage output by the sampling stage, and then calculate the harmonic active power input to the power outer loop control module. P h Harmonic reactive power Q h .

[0078] In this embodiment, after the sampling process, and , and The components are coupled to each other, therefore the voltage output by the sampling module... As shown in the following formula:

[0079] (1)

[0080] in, Let this be the delay function of the sampling process. , , , , , These represent the fundamental frequency and frequency, respectively. f 1- f The harmonic angular frequency of 5.

[0081] Formula (1) is the harmonic component transfer function of the sampling module.

[0082] q-axis component of grid connection point voltage u q As the input to the phase-locked loop module, the q-axis component containing harmonics is input, and the output angle is... An offset will occur, and because the bandwidth of the phase-locked loop is relatively narrow, only the harmonic frequencies caused by the asymmetry of the dq axis need to be considered. f 1 and f 5. Output Angle Specifically:

[0083] (2)

[0084] in, The transfer function of the phase-locked loop. Harmonic component angular frequency and sampling time T s The product; It is the fundamental component of the phase-locked loop output angle, which is also the fundamental component of the phase angle of the grid-connected voltage. It is the harmonic component of the phase-locked loop output angle. forf The angular frequencies of the first harmonic, U1, U5, and U0, are respectively the frequencies of... f 1. f The harmonic voltage and fundamental voltage of 5.

[0085] The transfer function of the PI controller in the phase-locked loop module is as follows:

[0086] ;

[0087] Among them, K pp K is the proportional gain of the phase-locked loop. ip represents the integral coefficient of the phase-locked loop.

[0088] Formula (2) is the harmonic component transfer function of the phase-locked loop module.

[0089] S103: Based on the harmonic component transfer function of the power outer loop control module, and combined with the harmonic current components output by the sampling stage, the harmonic current components in the reference current signal output by the power outer loop are calculated.

[0090] In this embodiment, based on the power outer loop control structure, the harmonic component transfer function of the power outer loop control module is established. Based on the obtained dq axis components of the grid-connected point sampled harmonic voltage and current, the reference current signal can be calculated as the input of the current inner loop control module.

[0091] After Park transformation f 1- f 5. The fifth harmonic current and voltage are converted into voltage and current harmonic components along the dq axis. U dn ( n =1, 2, 3, 4) and I dn ( n =1, 2, 3, 4). It can be seen that compared to the fifth harmonic component of the abc axis, the dq axis only has fourth harmonic components. This is due to the abc axis's... f 1 and f 5. After Park transform, the components are coupled into harmonic components of the same frequency. U d1 and I d1 .

[0092] Therefore, the harmonic active power input to the outer loop power control module P h Harmonic reactive power Q h It can be calculated using the following formula:

[0093] (3)

[0094] in, , These are the i-th harmonic voltages on the dq axis output by the sampling module, respectively. , These are the i-th harmonic currents on the dq axis output by the sampling module, respectively. for and The phase difference; for and The phase difference; for and phase difference, for and The phase difference.

[0095] according to Figure 2 The control structure block diagram of the grid-connected inverter shown is shown, with the power outer loop control module outputting... i ref Harmonic components in i refh for:

[0096] (4)

[0097] in, This is the transfer function of the PI controller in the power outer loop control module; , These are the d-axis and q-axis harmonic current components in the reference current signal output from the power outer loop, respectively. The fundamental angular frequency, For the first i The angular frequency of the subharmonic.

[0098] Formulas (3) and (4) together form the harmonic component transfer function of the power outer loop control module.

[0099] S104: Based on the harmonic component transfer function of the current inner loop control module, calculate the harmonic components in the DC component reference signal of the dq axis voltage, and obtain the harmonic components of the three-phase modulated voltage and the inverter port voltage through inverse coordinate transformation.

[0100] In this embodiment, based on the structure of the inner loop control module, an inner loop harmonic component transfer function is established. By inputting the current signal, capacitor current signal, and grid connection point voltage dq-axis component, the DC component reference signal of the dq-axis voltage is calculated. The three-phase modulation voltage harmonic components and inverter port voltage harmonic components are obtained through inverse Park transformation.

[0101] The output of the current inner loop control module is the reference value of the DC component of the dq-axis voltage.U dref and U qref Its harmonic components U drefh and U qrefh It can be derived from the control block diagram of the current inner loop control module, as shown in the following formula:

[0102] (5)

[0103] In the formula, H in This is the transfer function of the PI controller in the current inner loop control module. , These are the harmonic components in the DC component reference signal of the dq-axis voltage, respectively. , These are the harmonic components of the d-axis and q-axis reference currents, respectively. , These are the d-axis and q-axis components of the harmonic current at the grid connection point, respectively. , These are the d-axis and q-axis components of the capacitor current, respectively. , These are the d-axis and q-axis components of the harmonic voltage at the grid connection point, respectively. It is the capacitor current compensation coefficient. It is the dq-axis current decoupling coefficient. It is the voltage feedforward compensation coefficient.

[0104] After the inverse Park transformation U dref and U qref Obtain the three-phase modulation voltage U s The harmonic components are shown in the following formula:

[0105] (6)

[0106] In the formula, A ij These are the transfer coefficients of the inverse Park transform. U si These are the harmonic components of the modulated voltage;

[0107] Inverter port voltage harmonic components U ri for:

[0108] (7)

[0109] In the formula K pwmThis represents the equivalent modulation coefficient of the PWM stage.

[0110] Formulas (5) and (6) together form the harmonic component transfer function of the current inner loop control module; Formula (7) is the harmonic component transfer function of the pulse width modulation module.

[0111] It should be noted that the transfer functions of the PI controllers in the phase-locked loop module, the power outer loop control module, and the current inner loop control module are all existing technologies and will not be described in detail here.

[0112] S105: Based on the inverter port voltage harmonic components and combined with the main circuit harmonic transmission equation, the grid connection point harmonic current components are calculated. .

[0113] In this embodiment, according to the topology of the grid-connected inverter main circuit, the grid-connected inverter main circuit is a circuit composed of inductor L1, inductor L2 and capacitor C.

[0114] The harmonic transmission equation of the main circuit is established, and the harmonic current component at the grid connection point is calculated using the obtained port voltage harmonic components.

[0115] Specifically, the relationship between the voltage and current harmonic components at various points in the main circuit is as follows:

[0116] (8)

[0117] (9)

[0118] (10)

[0119] (11)

[0120] in, The frequency of the port current is f i The amount; U ci The frequency of the voltage in the filter capacitor is f i The amount; I ci The frequency of the filter capacitor current is f i The amount; L 1. R 1 represents the inductance and resistance on the inverter side of the LCL filter; L 2. R 2 represents the mains inductance and resistance of the LCL filter, respectively; C , R C These are the filter capacitor and its additional resistor, respectively. Rg , L g These are the equivalent resistance and inductance of the power grid, respectively. This refers to the harmonic components of the inverter port voltage. The frequency at the grid connection point is f i Harmonic voltage, For frequency f i Harmonic angular frequency, The frequency at the port is f i Harmonic voltage, The frequency at the port is f i Harmonic currents, Frequency is f i The capacitor harmonic current.

[0121] S106: Calculate the harmonic contribution of each module to the target harmonic and determine the module with the greatest impact on the target harmonic.

[0122] In this embodiment, the first is defined x The harmonic contribution of each module to the h-th harmonic is determined by fixing the parameters of other modules and only changing the parameters of the h-th module. x The key parameters of the module are calculated to obtain the first... x Harmonic contribution of each module C xh .

[0123] The specific calculation method is as follows:

[0124] The set parameter values ​​of each module under ideal conditions are used as the baseline values. K i1b The corresponding harmonic current at this time I The content of 1 is used as the benchmark value. X 1b Among them, the set parameter values ​​of the phase-locked loop module, the power outer loop control module, and the current inner loop control module are all integral coefficients of the corresponding PI controllers, and the set parameter values ​​of the sampling module and the pulse width modulation module are the delay time and the modulation coefficient, respectively.

[0125] The set parameter value is continuously increased to the predetermined level, and the corresponding harmonic current is recorded. I The content of 1; establishing harmonic current I The relationship between the content of 1 and the set parameter value is used to select the linear segment data in the relationship and calculate the harmonic contribution of the corresponding module. :

[0126] (12)

[0127] in, This indicates the number of parameter values ​​set for the linear segment. This represents the k-th set parameter value in the linear segment data. k =1,2,…,m, This indicates that the parameter value is set to... The content of harmonic currents corresponding to the time.

[0128] The following section calculates the contribution of the inner-loop control module for the current calculation. C xh Let's take an example to illustrate:

[0129] The integral coefficient of the current inner loop PI controller under ideal conditions K i As a benchmark value K i1b At this time, harmonic current I The content of 1 is used as the benchmark value. X 1b .

[0130] Change the integral coefficient to K i1p Record the corresponding harmonic current content respectively. X 1p ; p =1,2,…,n, where n is the number of reference gears.

[0131] Based on the changes in harmonic current content, the saturation segment data is removed, retaining only the linear segment data where the harmonic current content changes with the integral coefficient; the integral coefficient in the linear segment data is... K i1k The corresponding harmonic current content is X 1k k = 1, 2, ..., m, where m is the number of changes in the integral coefficients of the linear segment.

[0132] Finally, based on the linear segment data, the contribution of the current inner loop control module is calculated using formula (12). C xh .

[0133] By calculating the contribution of each module to the target harmonics C xh This allows us to identify the component that has the greatest impact on the target harmonics, thus providing data support for subsequent harmonic suppression work.

[0134] Example 2

[0135] In one or more embodiments, a harmonic closed-loop transfer analysis system for grid-connected inverters considering wideband coupling is disclosed, comprising:

[0136] The decoupling module is configured to decouple the grid-connected inverter into a sampling module, a pulse width modulation module, a phase-locked loop module, a power outer loop control module, a current inner loop control module, and the grid equivalent impedance, and to establish the harmonic component transfer function of each module; based on the coupling characteristics between the modules, the coupling frequency of the target harmonic is calculated;

[0137] The sampling module is configured to collect three-phase current and voltage at the grid connection point. Based on the harmonic component transfer function of the sampling module, the dq-axis harmonic current and harmonic voltage output from the sampling stage are obtained through coordinate transformation. The harmonic active power input to the power outer loop control module is then calculated. P h Harmonic reactive power Q h ;

[0138] The power outer loop control module is configured to calculate the harmonic current components in the reference current signal output by the power outer loop based on the harmonic component transfer function of the power outer loop control module and the harmonic current components output by the sampling stage.

[0139] The current inner loop control module is configured to calculate the harmonic components in the DC component reference signal of the dq axis voltage based on the harmonic component transfer function of the current inner loop control module, and obtain the harmonic components of the three-phase modulated voltage and the harmonic components of the inverter port voltage through inverse coordinate transformation.

[0140] The grid connection point harmonic current calculation module is configured to calculate the grid connection point harmonic current components based on the inverter port voltage harmonic components and the main circuit harmonic transmission equation.

[0141] The harmonic contribution calculation module is configured to calculate the harmonic contribution of each module to the target harmonic and determine the module with the greatest impact on the target harmonic.

[0142] It should be noted that the specific implementation methods of the above modules are the same as those in Example 1, and will not be described in detail again.

[0143] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for harmonic closed-loop transfer analysis of grid-connected inverters considering wideband coupling, characterized in that, include: The grid-connected inverter is decoupled into a sampling module, a pulse width modulation module, a phase-locked loop module, a power outer loop control module, a current inner loop control module, and the grid equivalent impedance, and the harmonic component transfer function of each module is established; based on the coupling characteristics between modules, the coupling frequency of the target harmonic is calculated. The three-phase current and voltage at the grid connection point are collected. Based on the harmonic component transfer function of the sampling module, the dq-axis harmonic current and harmonic voltage output from the sampling stage are obtained through coordinate transformation. The harmonic active power input to the power outer loop control module is then calculated. P h Harmonic reactive power Q h ; Based on the harmonic component transfer function of the power outer loop control module, and combined with the harmonic current components output by the sampling stage, the harmonic current components in the reference current signal output by the power outer loop are calculated. Based on the harmonic component transfer function of the current inner loop control module, the harmonic components in the DC component reference signal of the dq axis voltage are calculated, and the harmonic components of the three-phase modulated voltage and the inverter port voltage are obtained through coordinate inverse transformation. Based on the inverter port voltage harmonic components and combined with the main circuit harmonic transmission equation, the grid connection point harmonic current components are calculated. Calculate the harmonic contribution of each module to the target harmonics, and determine the module with the greatest impact on the target harmonics.

2. The harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling as described in claim 1, characterized in that, Also includes: The q-axis voltage component, containing harmonics, output from the sampling stage is input to the phase-locked loop (PLL) module. The output angle of the PLL module is used to provide the rotation angle for coordinate transformation. Specifically: ； in, The pass function for the PI controller of the phase-locked loop module. Harmonic component angular frequency and sampling time T s The product; It is the fundamental component of the phase-locked loop output angle, which is also the fundamental component of the phase angle of the grid-connected voltage. It is the harmonic component of the phase-locked loop output angle. for f The angular frequencies of the first harmonic, U1, U5, and U0, are respectively the frequencies of... f 1. f The harmonic voltage and fundamental voltage of 5.

3. The harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling as described in claim 1, characterized in that, The harmonic active power input to the power outer loop control module is calculated. P h Harmonic reactive power Q h Specifically: ； in, , The dq axis outputs of the sampling stage are respectively i Subharmonic voltage; , The dq axis outputs of the sampling stage are respectively i Subharmonic current; for and The phase difference; for and The phase difference; for and phase difference, for and The phase difference.

4. The harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling as described in claim 3, characterized in that, The harmonic current components in the reference current signal output by the power outer loop are calculated as follows: ； in, , These are the d-axis and q-axis harmonic current components in the reference current signal output from the power outer loop, respectively. The transfer function for the PI controller of the power outer loop control module. The fundamental angular frequency, For the first i The angular frequency of the subharmonic.

5. The harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling as described in claim 1, characterized in that, The harmonic components in the DC component reference signal of the dq-axis voltage are calculated as follows: ； in, , These are the harmonic components in the DC component reference signal of the dq-axis voltage, respectively. This is the transfer function for the PI controller in the current inner loop control module. , These are the harmonic components of the d-axis and q-axis reference currents, respectively. , These are the d-axis and q-axis components of the harmonic current at the grid connection point, respectively. , These are the d-axis and q-axis components of the capacitor current, respectively. , These are the d-axis and q-axis components of the harmonic voltage at the grid connection point, respectively. It is the capacitor current compensation coefficient. It is the dq-axis current decoupling coefficient. It is the voltage feedforward compensation coefficient.

6. The harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling as described in claim 1, characterized in that, The harmonic components of the three-phase modulated voltage are obtained through inverse coordinate transformation, specifically: ； in, A ij These are the transfer coefficients of the inverse Park transform. For rotation angle, U si The first modulation voltage i Second harmonic components , , , , The frequencies are respectively f 1- f 5 harmonic voltage, , , , , The frequencies are respectively f 1- f 5 harmonic current, , , , , The frequencies are respectively f 1- f The three-phase modulated voltage harmonic components of 5.

7. The harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling as described in claim 1, characterized in that, inverter port voltage harmonic components Specifically: ； in, K pwm The equivalent modulation coefficient of the pulse width modulation module. Indicates frequency as f i The inner loop output voltage.

8. The harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling as described in claim 1, characterized in that, Based on the inverter port voltage harmonic components and combined with the main circuit harmonic transmission equation, the grid-connected point harmonic current components are calculated as follows: ； ； ； ； in, The frequency of the port current is f i The amount; U ci The frequency of the voltage in the filter capacitor is f i The amount; I ci The frequency of the filter capacitor current is f i The amount; L 1. R 1 represents the inductance and resistance on the inverter side of the LCL filter; L 2. R 2 represents the mains inductance and resistance of the LCL filter, respectively; C , R C These are the filter capacitor and its additional resistor, respectively. R g , L g These are the equivalent resistance and inductance of the power grid, respectively. This refers to the harmonic components of the inverter port voltage. The frequency of the inverter port current is f i Harmonic components, The frequency at the grid connection point is f i Harmonic voltage, For frequency f i Harmonic angular frequency, The frequency at the port is f i Harmonic voltage, The frequency at the port is f i Harmonic currents.

9. The harmonic closed-loop transfer analysis method for grid-connected inverters considering wideband coupling as described in claim 1, characterized in that, The harmonic contribution of each module to the target harmonic is calculated as follows: The set parameter values ​​of each module under ideal conditions are used as the baseline values. K i1b The corresponding harmonic current at this time I The content of 1 is used as the benchmark value. X 1b Among them, the set parameter values ​​of the phase-locked loop module, the power outer loop control module, and the current inner loop control module are integral coefficients, and the set parameter values ​​of the sampling module and the pulse width modulation module are the delay time and the modulation coefficient, respectively. The set parameter value is continuously increased to the predetermined level, and the corresponding harmonic current is recorded. I The content of 1; establishing harmonic current I The relationship between the content of 1 and the set parameter value is used to select the linear segment data in the relationship and calculate the harmonic contribution of the corresponding module. : ； in, This indicates the number of parameter values ​​set for the linear segment. This represents the k-th set parameter value in the linear segment data, where k = 1, 2, ..., m. This indicates that the parameter value is set to... The content of harmonic currents corresponding to the time.

10. A harmonic closed-loop transfer analysis system for grid-connected inverters considering wideband coupling, characterized in that, include: The decoupling module is configured to decouple the grid-connected inverter into a sampling module, a pulse width modulation module, a phase-locked loop module, a power outer loop control module, a current inner loop control module, and the grid equivalent impedance, and to establish the harmonic component transfer function of each module; based on the coupling characteristics between the modules, the coupling frequency of the target harmonic is calculated; The sampling module is configured to collect three-phase current and voltage at the grid connection point. Based on the harmonic component transfer function of the sampling module, the dq-axis harmonic current and harmonic voltage output from the sampling stage are obtained through coordinate transformation. The harmonic active power input to the power outer loop control module is then calculated. P h Harmonic reactive power Q h ; The power outer loop control module is configured to calculate the harmonic current components in the reference current signal output by the power outer loop based on the harmonic component transfer function of the power outer loop control module and the harmonic current components output by the sampling stage. The current inner loop control module is configured to calculate the harmonic components in the DC component reference signal of the dq axis voltage based on the harmonic component transfer function of the current inner loop control module, and obtain the harmonic components of the three-phase modulated voltage and the harmonic components of the inverter port voltage through inverse coordinate transformation. The grid connection point harmonic current calculation module is configured to calculate the grid connection point harmonic current components based on the inverter port voltage harmonic components and the main circuit harmonic transmission equation. The harmonic contribution calculation module is configured to calculate the harmonic contribution of each module to the target harmonic and determine the module with the greatest impact on the target harmonic.

Images