Grid-connected equipment harmonic disturbed emission iteration method and system based on small signal increment

Abstract

The invention discloses a grid-connected equipment harmonic disturbed emission iteration method and system based on small signal increment. The method comprises the following steps: listing a voltage and current relation equation required for calculating harmonic current; representing related data variables of an initial steady-state working point of a typical photovoltaic grid-connected inverter structure by using a steady-state component and a small signal component; substituting the steady-state component and the small signal component for representation to obtain a system small signal linearization equation; substituting the small signal component into a small signal linearization equation of the system to obtain an invariant equation set during small signal linearization; dividing background harmonic voltage in the power grid voltage into small disturbances of multiple stages, and determining the amplitude of Vgn; superposing a result into a steady-state component to update a steady-state working point to obtain a small signal linearization time-invariant equation set required for solving in the next stage; continuously updating the steady-state working point and the equation set until the applied background harmonic voltage is updated to be the same as the set target; and the amplitude and phase of each output current harmonic wave are obtained.

Description

Background Art

[0002] With the large-scale grid connection of new energy through fully controlled power electronic equipment, the harmonic problem in the distribution network has become increasingly prominent. The distribution and propagation of harmonic sources are widespread, and the proportion has increased significantly, which has had a significant impact on the stable operation of the power grid and the quality of power. Various power electronic equipment generates harmonic currents under the excitation of the grid voltage, which leads to grid voltage distortion. Therefore, it is necessary to calculate and study the characteristics of the harmonic currents generated by power electronic equipment under the excitation of the grid voltage.

[0003] For power electronic devices using uncontrolled or semi-controlled devices such as diodes or thyristors, the current characteristics under specific voltage excitation are easy to calculate due to the limited control of their on and off. At present, the research on the characteristics of their harmonic disturbance emission is relatively mature. With the advancement of device level, the application of equipment using fully controlled power electronic devices is becoming more and more extensive. Compared with equipment using uncontrolled or semi-controlled devices, fully controlled power electronic devices can control the device to open and close through digital signals, and digital signals can be generated in many ways. At present, the most commonly used is pulse width modulation technology, which is generated by comparing the modulation wave generated by digital control with the carrier signal. Because its control has more nonlinear links, its switching function has strong nonlinear characteristics, and it is difficult to directly calculate the steady-state harmonic current under voltage disturbance linearly based on the voltage and current equations, and the calculation cost is high and the speed is slow.

[0004] The existing research focuses on summarizing the characteristics of the emission characteristics of specific devices, but there is less exploration of their intrinsic emission mechanisms and their equivalent models. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an iterative method and system for harmonic disturbed emission of grid-connected equipment based on small signal increments in response to the deficiencies in the above-mentioned prior art. The method and system reveal the inherent harmonic emission mechanism of a certain type of fully-controlled power electronic equipment through fast and accurate calculation, and comprehensively analyze and summarize the emission characteristics, so as to solve the technical problem of computational difficulties caused by the nonlinearity and time-varying voltage and current equations of the fully-controlled power electronic equipment.

[0006] The present invention adopts the following technical solutions:

[0007] The iterative method for harmonic disturbance emission of grid-connected equipment based on small signal increment includes the following steps:

[0008] S1. Obtain the initial steady-state operating point related data of the typical photovoltaic grid-connected inverter structure, and write the voltage-current relationship equation required to calculate the harmonic current according to the relationship between the AC and DC circuits and the control;

[0009] S2, expressing the initial steady-state operating point related data variables of the typical photovoltaic grid-connected inverter structure obtained in step S1 by steady-state components and small signal components;

[0010] S3, substituting the steady-state component and small-signal component obtained in step S2 into the voltage-current relationship equation obtained in step S1, retaining the small-signal component relationship, and obtaining the system small-signal linearization equation;

[0011] S4, expressing each small signal component in the small signal linearization equation obtained in step S3 by the sum of harmonics;

[0012] S5, substituting the small signal component obtained in step S4 into the small signal linearization equation obtained in step S3, multiplying the periodic time-varying coefficient and the periodic time-varying variable to convert into the product between each harmonic, expressed as the relationship between the amplitudes of each harmonic, and obtaining a small signal linearization time-invariant equation group;

[0013] S6, substituting other steady-state components under the fundamental component of the grid voltage into the small signal linearization time-invariant equation group obtained in step S5, to determine the DC voltage V dc0 , output current command I ref1 , output fundamental current amplitude I1, modulation wave fundamental amplitude M1, grid voltage fundamental amplitude V g1 , the value of the grid fundamental voltage frequency ω1;

[0014] S7, divide the background harmonic voltage in the grid voltage into multiple stages of small disturbances, substitute the grid harmonic voltage amplitude of the first stage into the small signal linearization time-invariant equation group obtained in step S5, and determine V gn The amplitude of

[0015] S8, solving the small signal linearization time-invariant equation group obtained in step S5, and obtaining the small disturbance response of each state variable under the background harmonic voltage disturbance in this stage; superimposing the small disturbance response of each state variable obtained by solving to the steady-state component, updating the steady-state operating point, and obtaining the small signal linearization time-invariant equation group required for solving in the next stage; continuously updating the steady-state operating point and the equation group until the applied background harmonic voltage is updated to be the same as the set target;

[0016] S9. Solve the small signal linearization time-invariant equation group to obtain the amplitude and phase of each output current harmonic.

[0017] Preferably, the initial steady-state operating point related data of the typical photovoltaic grid-connected inverter structure includes the fundamental amplitude of the grid voltage V g1 , DC voltage V dc0 , output current command I ref1 , output AC current amplitude I1, modulation wave amplitude M1, grid voltage phase θ.

[0018] Preferably, the voltage-current relationship equation required for calculating the harmonic current includes:

[0019] The voltage-current relationship of line inductance is:

[0020]

[0021] Where L is the inductance of the inverter and the grid connection, i is the output AC current, t is the time, v dc is the DC voltage, m is the modulation wave, v g is the AC voltage;

[0022] The relationship between the DC side and AC side current is:

[0023]

[0024] Among them, C dc is the DC side capacitance, * denotes conjugation;

[0025] The current controller controls the output current to track the current command, and the relationship between the modulation wave and the output current is:

[0026] m=G PR (t)*(e jθ i ref -i)

[0027] Among them, G PR (t) is the current controller, θ is the grid voltage phase extracted by the phase-locked loop, i ref is the output current instruction;

[0028] The inverter adopts DC voltage control mode, and the active current command is generated by the DC side voltage. The relationship between the two is:

[0029] i ref =H dvc (t)*(v dc -V dcR )

[0030] Among them, H dvc (t) is the DC voltage controller, V dcR is the DC voltage command;

[0031] The phase-locked loop extracts the grid-connected point voltage phase θ as:

[0032]

[0033] Among them, h pll (t) is the phase-locked loop controller, v gb is the grid voltage after fundamental bandpass filtering;

[0034] The grid voltage is filtered by bandpass filter v gb for:

[0035] vgb =G bd (t)*v g

[0036] Among them, G bd (t) is a fundamental bandpass filter.

[0037] Preferably, in step S2, the steady-state component is expressed as follows using the sum of the fundamental steady-state component and each harmonic subcomponent:

[0038]

[0039] Where ω1 is the fundamental voltage frequency, v dc is the DC voltage, V dcn is the nth DC voltage amplitude, is the small signal component of DC voltage, i ref is the output current command, I refn is the n-times output current command amplitude, is the output current command small signal component, i is the output AC current, I n is the n-times output current amplitude, is the small signal component of the output current, m is the modulation wave, M n is the amplitude of the n-th modulation wave, is the small signal component of the modulation wave, v g is the AC voltage, V gn is the nth alternating voltage amplitude, is the small signal component of AC voltage, v gb is the grid voltage after fundamental bandpass filtering, V g1 is the fundamental amplitude of AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, θ is the grid voltage phase extracted by the phase-locked loop, It is the small signal component of grid voltage phase.

[0040] Preferably, in step S3, the small signal linearization equation of the system is as follows:

[0041]

[0042] Where, L is the inductance of the connection between the inverter and the grid, is the small signal component of the output current, V dcn is the nth order DC voltage amplitude, ω1 is the fundamental voltage frequency, is the small signal component of the modulation wave, M n is the amplitude of the n-th modulation wave, is the small signal component of DC voltage, is the small signal component of AC voltage, C dc is the DC side capacitance, is the small signal component of DC voltage, * represents conjugation, I n is the n-times output current amplitude, G PR (t) is the current controller, is the small signal component of the output current command, I refn is the n-times output current command amplitude, is the small signal component of the grid voltage phase, H dvc (t) is the DC voltage controller.

[0043] Preferably, in step S4, each small signal component in the small signal linearization equation is represented by the sum of a series of harmonics, as follows:

[0044]

[0045] in, is the small signal component of DC voltage, is the small signal component of the output current command, is the small signal component of the output current, is the small signal component of the modulation wave, is the small signal component of the AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, is the small signal component of the grid voltage phase, ω1 is the fundamental voltage frequency, is the amplitude of the nth DC voltage small signal component, is the amplitude of the small signal component of the n-th output current command, is the amplitude of the n-th output current small signal component, is the amplitude of the small signal component of the n-th modulation wave, is the amplitude of the small signal component of the nth AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, It is the small signal component of grid voltage phase.

[0046] Preferably, in step S5, the small signal linearization time-invariant equation group is:

[0047]

[0048] Among them, A1, A2, A3 are coefficient matrices, L is the inductance of the inverter and the grid connection, is the amplitude of the n-th output current small signal component, is the amplitude of the small signal component of the n-th modulation wave, is the amplitude of the nth DC voltage small signal component, is the amplitude of the small signal component of the nth AC voltage.

[0049] Preferably, the coefficient matrices A1, A2, A3 are respectively:

[0050]

[0051]

[0052] Where n is the harmonic order, ω1 is the fundamental voltage frequency, V d,cn is the nth DC voltage amplitude, M n is the amplitude of the n-th modulation wave.

[0053] Preferably, in step S7, the amplitude of the harmonic small disturbance in each stage does not exceed 3% of the fundamental voltage amplitude.

[0054] In a second aspect, an embodiment of the present invention provides a small signal increment-based grid-connected device harmonic disturbed emission iteration system, comprising:

[0055] The data module obtains the initial steady-state operating point related data of the typical photovoltaic grid-connected inverter structure, and writes the voltage-current relationship equation required to calculate the harmonic current based on the relationship between the AC and DC circuits and the relationship between the controls;

[0056] The representation module represents the initial steady-state operating point related data variables of the typical photovoltaic grid-connected inverter structure with steady-state components and small-signal components; the steady-state components and small-signal components are substituted into the voltage-current relationship equation, the small-signal component relationship is retained, and the system small-signal linearization equation is obtained; each small-signal component in the small-signal linearization equation is represented by the sum of harmonics;

[0057] Equation module, substitute the small signal component into the small signal linearization equation, multiply the periodic time-varying coefficient and the periodic time-varying variable to convert it into the product between each harmonic, expressed as the relationship between the amplitudes of each harmonic, and obtain the small signal linearization time-invariant equation group; substitute other steady-state components under the fundamental component of the grid voltage into the small signal linearization time-invariant equation group to determine the DC voltage V dc0 , output current command I ref1 , output fundamental current amplitude I1, modulation wave fundamental amplitude M1, grid voltage fundamental amplitude V g1 , the value of the grid fundamental voltage frequency ω1;

[0058] The background harmonic voltage in the grid voltage is divided into multiple stages of small disturbances. The amplitude of the grid harmonic voltage in the first stage is substituted into the small signal linearization time-invariant equation group to determine V gn The amplitude of

[0059] The iterative module solves the small signal linearized time-invariant equation group to obtain the small perturbation response of each state variable under the background harmonic voltage disturbance in this stage; superimposes the small perturbation response of each state variable solved into the steady-state component, updates the steady-state operating point, and obtains the small signal linearized time-invariant equation group required for solving the next stage; continuously updates the steady-state operating point and the equation group until the applied background harmonic voltage is updated to the same as the set target; solves the small signal linearized time-invariant equation group to obtain the amplitude and phase of each output current harmonic.

[0060] In a third aspect, a computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the above-mentioned iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increments are implemented.

[0061] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, including a computer program, which, when executed by a processor, implements the steps of the above-mentioned small signal increment-based iterative method for harmonic disturbed emission of grid-connected equipment.

[0062] In a fifth aspect, a chip comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the above-mentioned iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increments are implemented.

[0063] In a sixth aspect, an embodiment of the present invention provides an electronic device, including a computer program, which, when executed by the electronic device, implements the steps of the above-mentioned small signal increment-based iterative method for harmonic disturbed emission of grid-connected equipment.

[0064] Compared with the prior art, the present invention has at least the following beneficial effects:

[0065] An iterative method for the harmonic disturbance emission of grid-connected equipment based on small signal increments Figure 1The harmonic calculation of the photovoltaic inverter is to use the grid voltage as input to calculate the harmonic characteristics of the output current under the excitation of the grid voltage; the formula obtained in step S1 has typical nonlinear characteristics such as multiplication between variables and exponential operations. At the same time, the AC voltage and current in the equation are still time-varying variables, so it is very difficult to directly calculate the harmonics; in order to solve the nonlinear problem, step S2 represents the variables appearing in step S1 with steady-state components and small signal components; then step S3 adopts the small signal linearization method to convert the nonlinear equation in step S1 into a linearized equation near the working point , since the steady-state quantity is a known quantity and the small signal quantity is a quantity to be solved, there is no longer a situation of multiplying variables in the equation, and there is no exponential equation at the same time. The equation is linear. Obviously, the linearized equation is easier to calculate than the nonlinearized equation, and the amount of calculation is reduced exponentially; since the steady-state quantity coefficient in step S3 varies with time, and varies periodically with the fundamental period, in order to convert the equation with periodic time-varying coefficients into an equation with periodic time-invariant coefficients, step S4 also splits the small signal variable into a sum of a series of harmonics, and this series of harmonics has the same reference frequency as the periodic time-varying coefficients. Step S5 and step S4 together use the method of harmonic transfer function to convert the multiplication of periodic time-varying coefficients (steady-state quantity coefficients) and periodic time-varying variables (small signal quantities) into the product between each harmonic, and further simplify it as the relationship between the amplitudes of each harmonic. Through the above steps, the nonlinear time-varying equation is converted into a linear time-invariant equation system. At the same time, a series of coefficients can also be represented by a matrix with obvious characteristics, and it is very convenient to use matrix calculation for linear solution. The process of dynamic iterative calculation is given, that is, the background harmonic voltage "large disturbance" is dispersed into multiple stages of "small disturbance", the disturbance response under the excitation of the "small disturbance" in each stage is superimposed on the steady-state component, the steady-state operating point is updated, and the next stage iteration is performed more accurately until the harmonic voltage reaches the predetermined target. In this process, the calculation result of the previous stage is superimposed on the steady-state workload of the previous stage to obtain the steady-state workload of the next stage. Therefore, the coefficients of the variables to be solved in the equations of each stage are known, and the calculation relationship between harmonics and fundamental waves, and between harmonics and harmonics can be considered at the same time, and finally the steady-state results of the harmonic disturbed emission are accurately and quickly calculated.

[0066] Furthermore, according to the main circuit structure and control structure of a typical photovoltaic grid-connected inverter, the grid voltage, output current, DC side current, DC side voltage, modulation wave, and grid voltage phase will interact with each other and are related to control links such as the current controller, DC voltage controller, and phase-locked loop controller. Therefore, a voltage-current relationship equation is set to quantitatively calculate the harmonic current emission of the converter under background harmonic voltage excitation.

[0067] Furthermore, since typical photovoltaic grid-connected inverters use fully controlled power electronic devices, the switching function has strong nonlinearity, which will produce current harmonic responses different from the voltage excitation harmonic orders. By representing the steady-state components with fundamental waves and harmonic components, the situation of harmonic disturbance emission can be more clearly represented. At the same time, considering that the present invention splits the harmonic large disturbance into multiple stages of harmonic small disturbances, the current equation of each stage will be updated, that is, the steady-state operating point is updated, and the use of harmonic subcomponents can describe the impact of different harmonic sub-excitations.

[0068] Furthermore, the original nonlinear equations contain multiplication of variables and exponential operations, which makes the calculations complicated. By using small signal decomposition, the nonlinear equations are transformed into linearized equations near the steady-state operating point. Since the steady-state quantities are known quantities and the small signal quantities are quantities to be solved, there are no multiplication of variables in the equations, and there are no exponential equations. The equations are linear. Obviously, linearized equations are easier to calculate than nonlinear equations, and the amount of calculations is reduced exponentially.

[0069] Furthermore, since the steady-state coefficients in the above-mentioned small-signal linearization equation are periodically time-varying, in order to convert the equation with periodically time-varying coefficients into the equation with periodically time-invariant coefficients, the harmonic transfer function method is adopted, that is, each small signal component in the small-signal linearization equation is represented by the sum of a series of harmonics. After substituting the sum of a series of harmonic small-signal components into the small-signal linearization equation, the multiplication of the periodically time-varying coefficients (steady-state coefficients) and the periodically time-varying variables (small-signal quantities) can be converted into the product of each harmonic, and can be expressed as the relationship between the amplitudes of each harmonic. This conversion solves the problem that the coefficient time-varying equation is difficult to calculate.

[0070] Furthermore, when the harmonic component in the external grid voltage belongs to a "large disturbance", it is very likely that it does not meet the characteristics of a "small disturbance". At this time, the small signal equation cannot describe the nonlinear characteristics of this harmonic "large disturbance". Therefore, a multi-stage small signal incremental iterative calculation is used to approximate the nonlinear process of the "large disturbance". The method of dividing the stages is that the amplitude of the harmonic small disturbance in each stage does not exceed 3% of the fundamental voltage amplitude, ensuring that the small signal equation can effectively calculate the changes in each stage.

[0071] It can be understood that the beneficial effects of the second to sixth aspects mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0072] In summary, the present invention solves the problem of calculating and analyzing harmonic emissions of fully controlled power electronic equipment under the excitation of a "large disturbance" of background voltage. By dispersing the "large disturbance" into multiple stages of "small disturbances", using the small signal equation to solve the "small disturbance" response and superimposing it on the steady-state component, and updating and iteratively calculating the new small signal equation, the steady-state harmonic response under the "large disturbance" can be accurately and quantitatively solved with high calculation accuracy. At the same time, the present invention uses small signal equation linearization and harmonic transfer function transformation to convert the periodic time-varying nonlinear equation group into a linear time-invariant equation group, and can use matrix operations for linear solution, greatly reducing the calculation complexity.

[0073] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a typical photovoltaic grid-connected inverter control structure diagram;

[0075] Figure 2 It is a flow chart of iterative calculation of harmonic disturbed emission based on small signal increment;

[0076] FIG3 is a comparison diagram of the theoretical calculated value and the simulated value of the harmonic current of a typical photovoltaic grid-connected inverter, where (a) is a comparison diagram of the harmonic current amplitude, and (b) is a comparison diagram of the harmonic current phase;

[0077] Figure 4 A schematic diagram of a computer device provided by an embodiment of the present invention;

[0078] Figure 5 The block diagram of a chip provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0079] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0080] In the description of the present invention, it should be understood that the terms “include” and “comprises” indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0081] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0082] It should be further understood that the term "and / or" used in the present specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects are in an "or" relationship.

[0083] It should be understood that, although the terms first, second, third, etc. may be used to describe preset ranges, etc. in the embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish preset ranges from each other. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0084] The word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0085] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0086] The present invention provides an iterative method for the disturbed harmonic emission of grid-connected equipment based on small signal increments, which can not only target harmonics of multiples of the fundamental wave, but also be used to calculate the emission of harmonic currents under the excitation of three-phase unbalanced negative sequence voltage and interharmonic voltage. For the three-phase unbalanced negative sequence voltage, it can be regarded as a harmonic voltage with a frequency of -ω1. For the interharmonic voltage, the reference frequency can be reduced, such as from a 50Hz interval to a 10Hz interval, and the interharmonic components can be calculated.

[0087] See also Figure 2 The present invention provides an iterative method for harmonic disturbance emission of grid-connected equipment based on small signal increment, comprising the following steps:

[0088] S1. For a typical photovoltaic grid-connected inverter structure, obtain the initial steady-state operating point related data, that is, the fundamental amplitude of the grid voltage V g1 , DC voltage V dc0 , output current command I ref1 , output AC current amplitude I1, modulation wave amplitude M1, grid voltage phase θ; based on the relationship between AC and DC circuits and the relationship between controls, write the voltage-current relationship equation required to calculate harmonic current;

[0089] The voltage-current relationship of line inductance is

[0090]

[0091] Where L is the inductance of the inverter and the grid connection, i is the output AC current, t is the time, v dc is the DC voltage, m is the modulation wave, v g is an AC voltage.

[0092] The relationship between the DC side and the AC side current is

[0093]

[0094] Among them, C dc is the DC side capacitance, * Indicates conjugation.

[0095] The current controller controls the output current to track the current command, so the relationship between the modulation wave and the output current is:

[0096] m=G PR (t)*(e jθ i ref -i) (3)

[0097] Among them, G PR (t) is the current controller, θ is the grid voltage phase extracted by the phase-locked loop, i ref is the output current command.

[0098] The inverter adopts a DC voltage control method, and the active current command is generated by the DC side voltage. The relationship between the two is:

[0099] i ref =H dvc (t)*(v dc -V dcR ) (4)

[0100] Among them, H dvc (t) is the DC voltage controller, V dcR is the DC voltage command.

[0101] The phase-locked loop extracts the grid-connected point voltage phase, and its calculation formula is:

[0102]

[0103] Among them, h pll (t) is the phase-locked loop controller, v gb is the grid voltage after fundamental bandpass filtering.

[0104] The calculation formula of the grid voltage after bandpass filtering is:

[0105] v gb =G bd (t)*v g (6)

[0106] Among them, G bd (t) is a fundamental bandpass filter.

[0107] S2, the variables such as voltage, current, modulation wave, phase, etc. appearing in step S1 are represented by steady-state components and small signal components, that is, the representation of the seven variables of DC voltage, output current command, output AC current, modulation wave, AC voltage, grid voltage after fundamental wave bandpass filtering, and grid voltage phase; for the steady-state component, the sum of the fundamental wave steady-state component and each harmonic subcomponent is represented as follows:

[0108]

[0109] Where ω1 is the fundamental voltage frequency, v dc is the DC voltage, V dcn is the nth DC voltage amplitude, is the small signal component of DC voltage, i ref is the output current command, I refn is the n-times output current command amplitude, is the output current command small signal component, i is the output AC current, I n is the n-times output current amplitude, is the small signal component of the output current, m is the modulation wave, Mn is the amplitude of the n-th modulation wave, is the small signal component of the modulation wave, v g is the AC voltage, V gn is the nth alternating voltage amplitude, is the small signal component of AC voltage, v gb is the grid voltage after fundamental bandpass filtering, V g1 is the fundamental amplitude of AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, θ is the grid voltage phase extracted by the phase-locked loop, is the small signal component of the grid voltage phase.

[0110] S3, substitute the steady-state component and small-signal component formula (7) obtained in step S2 into the voltage-current relationship equation formulas (1)-(6) obtained in step S1, retain the small-signal component relationship therein, and obtain the small-signal linearization equation of the system, see formulas (8)-(12);

[0111]

[0112]

[0113] Where, L is the inductance of the connection between the inverter and the grid, is the small signal component of the output current, V dcn is the nth order DC voltage amplitude, ω1 is the fundamental voltage frequency, is the small signal component of the modulation wave, M n is the amplitude of the n-th modulation wave, is the small signal component of DC voltage, is the small signal component of AC voltage, C dc is the DC side capacitance, is the small signal component of DC voltage, * represents conjugation, I n is the n-times output current amplitude, G PR (t) is the current controller, is the small signal component of the output current command, I refn is the n-times output current command amplitude, is the small signal component of the grid voltage phase, H dvc (t) is the DC voltage controller.

[0114] S4. For the small signal linearization equation obtained in step S3, formulas (8)-(12), each small signal component therein is represented by the sum of a series of harmonics, namely, 7 small signal components: DC voltage, output current command, output AC current, modulation wave, AC voltage, grid voltage after fundamental bandpass filtering, and grid voltage phase;

[0115]

[0116] in, is the small signal component of DC voltage, is the small signal component of the output current command, is the small signal component of the output current, is the small signal component of the modulation wave, is the small signal component of the AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, is the small signal component of the grid voltage phase, ω1 is the fundamental voltage frequency, is the amplitude of the nth DC voltage small signal component, is the amplitude of the small signal component of the n-th output current command, is the amplitude of the n-th output current small signal component, is the amplitude of the small signal component of the n-th modulation wave, is the amplitude of the small signal component of the nth AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, It is the small signal component of grid voltage phase.

[0117] S5, substituting the small signal component formula (13) obtained in step S4 into the small signal linearization equation formulas (8)-(12) obtained in step S3, multiplying the periodic time-varying coefficient (steady-state quantity coefficient) and the periodic time-varying variable (small signal quantity) to convert into the product between each harmonic, and can be expressed as the relationship between the amplitudes of each harmonic;

[0118] The following only lists the transformation of formula (8), and the resulting formula is shown in (14). The coefficients of this system of equations are time-invariant and it is a linear system of equations.

[0119]

[0120] Among them, A1, A2, and A3 are all matrices. In order to express the multiplication relationship between harmonics, A2 and A3 are in the form of Toeplitz matrices (the elements on the main diagonal are equal, and the elements on the lines parallel to the main diagonal are also equal), and their specific expressions are as follows:

[0121]

[0122]

[0123] S6, substituting the other steady-state components of the grid voltage fundamental component obtained in step S1 into the small signal linearization time-invariant equation group obtained in step 6, that is, determining V dc0 ,I ref1 、I1、M1、Vg1 , the value of ω1;

[0124] S7, divide the background harmonic voltage in the grid voltage into multiple stages of small disturbances, and the amplitude of the harmonic small disturbance in each stage does not exceed 3% of the fundamental voltage amplitude. Substitute the first stage grid harmonic voltage amplitude into the small signal linearization time-invariant equation group obtained in step S5, and determine V gn The amplitude of , the other undetermined steady-state components in the system of equations are all zero;

[0125] S8, solving the small signal linearization time-invariant equation group obtained in step S5, and obtaining the small disturbance response of each state variable under the background harmonic voltage disturbance in this stage; superimposing the solved small disturbance response of each state variable into the steady-state component, updating the steady-state operating point, thereby obtaining the small signal linearization time-invariant equation group required for solving in the next stage; continuously updating the steady-state operating point and the equation group until the applied background harmonic voltage is updated to be the same as the set target;

[0126] S9. By solving the small signal linearization time-invariant equation group, the amplitude and phase of each output current harmonic can be obtained.

[0127] It will be appreciated by those skilled in the art that various aspects of the present invention may be implemented as systems, methods or program products. Therefore, various aspects of the present invention may be specifically implemented in the following forms, namely: complete hardware implementation, complete software implementation (including firmware, microcode, etc.), or a combination of hardware and software implementations, which may be collectively referred to herein as "circuits", "modules" or "platforms".

[0128] In another embodiment of the present invention, a small signal increment-based iterative system for harmonic disturbed emission of grid-connected equipment is provided. The system can be used to implement the above-mentioned small signal increment-based iterative method for harmonic disturbed emission of grid-connected equipment. Specifically, the small signal increment-based iterative system for harmonic disturbed emission of grid-connected equipment includes a data module, a representation module, an equation module, a division module and an iteration module.

[0129] The data module obtains the initial steady-state operating point related data of the typical photovoltaic grid-connected inverter structure, and writes the voltage-current relationship equation required for calculating the harmonic current according to the relationship between the AC and DC circuits and the control.

[0130] The representation module represents the initial steady-state operating point related data variables of the typical photovoltaic grid-connected inverter structure with steady-state components and small-signal components; the steady-state components and small-signal components are substituted into the voltage-current relationship equation, the small-signal component relationship is retained, and the system small-signal linearization equation is obtained; each small-signal component in the small-signal linearization equation is represented by the sum of harmonics;

[0131] Equation module, substitute the small signal component into the small signal linearization equation, multiply the periodic time-varying coefficient and the periodic time-varying variable to convert it into the product between each harmonic, expressed as the relationship between the amplitudes of each harmonic, and obtain the small signal linearization time-invariant equation group; substitute other steady-state components under the fundamental component of the grid voltage into the small signal linearization time-invariant equation group to determine the DC voltage V dc0 , output current command I ref1 , output fundamental current amplitude I1, modulation wave fundamental amplitude M1, grid voltage fundamental amplitude V g1 , the value of the grid fundamental voltage frequency ω1;

[0132] The background harmonic voltage in the grid voltage is divided into multiple stages of small disturbances. The amplitude of the grid harmonic voltage in the first stage is substituted into the small signal linearization time-invariant equation group to determine V gn The amplitude of

[0133] The iterative module solves the small signal linearized time-invariant equation group to obtain the small perturbation response of each state variable under the background harmonic voltage disturbance in this stage; superimposes the small perturbation response of each state variable solved into the steady-state component, updates the steady-state operating point, and obtains the small signal linearized time-invariant equation group required for solving the next stage; continuously updates the steady-state operating point and the equation group until the applied background harmonic voltage is updated to the same as the set target; solves the small signal linearized time-invariant equation group to obtain the amplitude and phase of each output current harmonic.

[0134] In another embodiment of the present invention, a terminal device is provided, the terminal device including a processor and a memory, the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, graphics processors (GPU), tensor processors (TPU), digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions to implement the corresponding method flow or corresponding functions; the processor described in the embodiment of the present invention can be used for the operation of the iterative method for the harmonic disturbance emission of the grid-connected equipment based on small signal increments, including:

[0135] Obtain the initial steady-state operating point related data of the typical photovoltaic grid-connected inverter structure, and write the voltage-current relationship equation required for calculating the harmonic current according to the relationship between the AC and DC circuits and the relationship between the controls; represent the initial steady-state operating point related data variables of the typical photovoltaic grid-connected inverter structure with steady-state components and small-signal components; substitute the steady-state components and small-signal components into the voltage-current relationship equation, retain the small-signal component relationship, and obtain the system small-signal linearization equation; represent each small-signal component in the small-signal linearization equation with the sum of harmonics; substitute the small-signal component into the small-signal linearization equation, and multiply the periodic time-varying coefficient with the periodic time-varying variable to convert it into the product between each harmonic, expressed as the relationship between the amplitudes of each harmonic, and obtain the small-signal linearization time-invariant equation group; substitute other steady-state components under the fundamental component of the grid voltage into the small-signal linearization time-invariant equation group to determine the DC voltage V dc0 , output current command I ref1 , output fundamental current amplitude I1, modulation wave fundamental amplitude M1, grid voltage fundamental amplitude V g1 , the value of the grid fundamental voltage frequency ω1; the background harmonic voltage in the grid voltage is divided into multiple stages of small disturbances, and the amplitude of the grid harmonic voltage in the first stage is substituted into the small signal linearization time-invariant equation group to determine V gnamplitude; solve the small signal linearization time-invariant equation group to obtain the small disturbance response of each state variable under the background harmonic voltage disturbance in this stage; superimpose the small disturbance response of each state variable solved to the steady-state component, update the steady-state operating point, and obtain the small signal linearization time-invariant equation group required for solving the next stage; continuously update the steady-state operating point and the equation group until the applied background harmonic voltage is updated to the same as the set target; solve the small signal linearization time-invariant equation group to obtain the amplitude and phase of each output current harmonic.

[0136] See also Figure 4 , the terminal device is a computer device, and the computer device 60 of this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When the computer program 63 is executed by the processor 61, the method for iterating the harmonic interference emission of the grid-connected device based on the small signal increment in the embodiment is implemented. To avoid repetition, it is not described one by one here. Alternatively, when the computer program 63 is executed by the processor 61, the functions of each model / unit in the iterative system for the harmonic interference emission of the grid-connected device based on the small signal increment in the embodiment are implemented. To avoid repetition, it is not described one by one here.

[0137] The computer device 60 may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will appreciate that Figure 4 This is only an example of the computer device 60 and does not constitute a limitation of the computer device 60. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the computer device may also include input and output devices, network access devices, buses, etc.

[0138] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, graphics processing units (GPU), tensor processing units (TPU), digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0139] The memory 62 may be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 may also be an external storage device of the computer device 60, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc., equipped on the computer device 60.

[0140] Furthermore, the memory 62 may include both an internal storage unit of the computer device 60 and an external storage device. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is to be output.

[0141] See also Figure 5 , the terminal device is a chip, and the chip 600 of this embodiment includes a processor 622, which may be one or more, and a memory 632 for storing a computer program executable by the processor 622. The computer program stored in the memory 632 may include one or more modules, each corresponding to a set of instructions. In addition, the processor 622 may be configured to execute the computer program to execute the above-mentioned small signal increment-based grid-connected device harmonic disturbed emission iteration method.

[0142] In addition, the chip 600 may further include a power supply component 626 and a communication component 650, wherein the power supply component 626 may be configured to perform power management of the chip 600, and the communication component 650 may be configured to implement communication, for example, wired or wireless communication, of the chip 600. In addition, the chip 600 may further include an input / output interface 658. The chip 600 may operate based on an operating system stored in the memory 632.

[0143] In another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It can be understood that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and the extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs. It should be noted that the computer-readable storage medium here can be a high-speed RAM memory, or a non-volatile memory (Non-VolatileMemory), such as at least one disk memory.

[0144] One or more instructions stored in a computer-readable storage medium may be loaded and executed by a processor to implement the corresponding steps of the iterative method for harmonic disturbed transmission of grid-connected equipment based on small signal increments in the above embodiment; one or more instructions in the computer-readable storage medium are loaded and executed by the processor as follows:

[0145] Obtain the initial steady-state operating point related data of the typical photovoltaic grid-connected inverter structure, and write the voltage-current relationship equation required for calculating the harmonic current according to the relationship between the AC and DC circuits and the relationship between the controls; represent the initial steady-state operating point related data variables of the typical photovoltaic grid-connected inverter structure with steady-state components and small-signal components; substitute the steady-state components and small-signal components into the voltage-current relationship equation, retain the small-signal component relationship, and obtain the system small-signal linearization equation; represent each small-signal component in the small-signal linearization equation with the sum of harmonics; substitute the small-signal component into the small-signal linearization equation, and multiply the periodic time-varying coefficient with the periodic time-varying variable to convert it into the product between each harmonic, expressed as the relationship between the amplitudes of each harmonic, and obtain the small-signal linearization time-invariant equation group; substitute other steady-state components under the fundamental component of the grid voltage into the small-signal linearization time-invariant equation group to determine the DC voltage V dc0 , output current command I ref1 , output fundamental current amplitude I1, modulation wave fundamental amplitude M1, grid voltage fundamental amplitude V g1 , grid fundamental voltage frequency, ω1 value; divide the background harmonic voltage in the grid voltage into multiple stages of small disturbances, substitute the first stage grid harmonic voltage amplitude into the small signal linearization time-invariant equation group, and determine V gn amplitude; solve the small signal linearization time-invariant equation group to obtain the small disturbance response of each state variable under the background harmonic voltage disturbance in this stage; superimpose the small disturbance response of each state variable solved to the steady-state component, update the steady-state operating point, and obtain the small signal linearization time-invariant equation group required for solving the next stage; continuously update the steady-state operating point and the equation group until the applied background harmonic voltage is updated to the same as the set target; solve the small signal linearization time-invariant equation group to obtain the amplitude and phase of each output current harmonic.

[0146] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0147] The simulation results verify the accuracy and reliability of the present invention. Figure 1 The typical photovoltaic inverter grid-connected simulation model shown in the figure uses simulation parameters as shown in the following table:

[0148] The harmonic content of the output current is measured in the simulation. At the same time, the small signal stepping method proposed in the present invention calculates the harmonic current content under the same simulation parameters. For comparison, a large signal equation ignoring the product between harmonics is also used for solution, as shown in FIG3 .

[0149] From the comparison results in Figure 3, it can be seen that, firstly, for fully controlled power electronic equipment, under the excitation of harmonic voltage, not only harmonic currents of the same frequency components will be generated, but also currents of other harmonic frequencies will be coupled. Secondly, the harmonic current content of the generated same-frequency components is much larger than the current of the coupled harmonic frequencies. Finally, the calculation results of the small signal stepping method proposed in the present invention are very close to the simulation, and the calculation accuracy of the amplitude and phase of the harmonic current is better than the method of solving the steady-state equation.

[0150] In summary, the present invention provides an iterative method and system for disturbed harmonic emission of grid-connected equipment based on small signal increments. The present invention solves the problem of harmonic emission calculation and analysis of fully controlled power electronic equipment under the excitation of a "large disturbance" of the background voltage. By dispersing the "large disturbance" into "small disturbances" of multiple stages, using the small signal equation to solve the "small disturbance" response and superimposing it on the steady-state component, updating the iterative calculation of the new small signal equation, the steady-state harmonic response under the "large disturbance" can be accurately and quantitatively solved with high calculation accuracy. At the same time, the present invention uses small signal equation linearization and harmonic transfer function transformation to convert the periodic time-varying nonlinear equation group into a linear time-invariant equation group, and can use matrix operations for linear solution, greatly reducing the computational complexity.

[0151] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0152] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0153] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in the present invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0154] In the embodiments provided by the present invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or 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, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0155] 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.

[0156] In addition, each functional unit in each embodiment of the present invention 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 software functional units.

[0157] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0158] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices, and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0159] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0160] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0161] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. An iterative method for harmonic disturbance emission of grid-connected equipment based on small signal increments, characterized in that: The following steps are involved: S1. Obtain the initial steady-state operating point related data of the typical photovoltaic grid-connected inverter structure, and write the voltage-current relationship equation required to calculate the harmonic current according to the relationship between the AC and DC circuits and the control; S2, expressing the initial steady-state operating point related data variables of the typical photovoltaic grid-connected inverter structure obtained in step S1 by steady-state components and small signal components; S3, substituting the steady-state component and small-signal component obtained in step S2 into the voltage-current relationship equation obtained in step S1, retaining the small-signal component relationship, and obtaining the system small-signal linearization equation; S4, expressing each small signal component in the small signal linearization equation obtained in step S3 by the sum of harmonics; S5, substituting the small signal component obtained in step S4 into the small signal linearization equation obtained in step S3, multiplying the periodic time-varying coefficient and the periodic time-varying variable to convert into the product between each harmonic, expressed as the relationship between the amplitudes of each harmonic, and obtaining a small signal linearization time-invariant equation group; S6, substituting other steady-state components under the fundamental component of the grid voltage into the small signal linearization time-invariant equation group obtained in step S5, to determine the DC voltage V dc0 , output current command I ref1 , output fundamental current amplitude I1, modulation wave fundamental amplitude M1, grid voltage fundamental amplitude V g1 , the value of the grid fundamental voltage frequency ω1; S7, divide the background harmonic voltage in the grid voltage into multiple stages of small disturbances, substitute the grid harmonic voltage amplitude of the first stage into the small signal linearization time-invariant equation group obtained in step S5, and determine V gn The amplitude of S8, solving the small signal linearization time-invariant equation group obtained in step S5, and obtaining the small disturbance response of each state variable under the background harmonic voltage disturbance in this stage; superimposing the small disturbance response of each state variable obtained by solving to the steady-state component, updating the steady-state operating point, and obtaining the small signal linearization time-invariant equation group required for solving in the next stage; continuously updating the steady-state operating point and the equation group until the applied background harmonic voltage is updated to be the same as the set target; S9. Solve the small signal linearization time-invariant equation group to obtain the amplitude and phase of each output current harmonic.

2. The iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increment according to claim 1, characterized in that: The initial steady-state operating point data of a typical photovoltaic grid-connected inverter structure include the fundamental amplitude of the grid voltage V g1 , DC voltage V dc0 , output current command I ref1 , output AC current amplitude I1, modulation wave amplitude M1, grid voltage phase θ.

3. The iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increment according to claim 1, characterized in that: The voltage-current relationship equations required to calculate harmonic currents include: The voltage-current relationship of line inductance is: Where L is the inductance of the inverter and the grid connection, i is the output AC current, t is the time, v dc is the DC voltage, m is the modulation wave, v g is the AC voltage; The relationship between the DC side and the AC side current is Among them, C dc is the DC side capacitance, * denotes conjugation; The current controller controls the output current to track the current command, and the relationship between the modulation wave and the output current is: m=G PR (t)*(e jθ i ref -i) Among them, G PR (t) is the current controller, θ is the grid voltage phase extracted by the phase-locked loop, i ref is the output current instruction; The inverter adopts DC voltage control mode, and the active current command is generated by the DC side voltage. The relationship between the two is: i ref =H dvc (t)*(v dc -V dcR ) Among them, H dvc (t) is the DC voltage controller, V dcR is the DC voltage command; The phase-locked loop extracts the grid-connected point voltage phase θ as: Among them, h pll (t) is the phase-locked loop controller, v gb is the grid voltage after fundamental bandpass filtering; The grid voltage is filtered by bandpass filter v gb for: v gb =G bd (t)*v g Among them, G bd (t) is a fundamental bandpass filter.

4. The iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increment according to claim 1, characterized in that: In step S2, for the steady-state component, the sum of the fundamental steady-state component and each harmonic subcomponent is expressed as follows: Where ω1 is the fundamental voltage frequency, v dc is the DC voltage, V dcn is the nth DC voltage amplitude, is the small signal component of DC voltage, i ref is the output current command, I refn is the n-times output current command amplitude, is the output current command small signal component, i is the output AC current, I n is the n-times output current amplitude, is the small signal component of the output current, m is the modulation wave, M n is the amplitude of the n-th modulation wave, is the small signal component of the modulation wave, v g is the AC voltage, V gn is the nth alternating voltage amplitude, is the small signal component of AC voltage, v gb is the grid voltage after fundamental bandpass filtering, V g1 is the fundamental amplitude of AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, θ is the grid voltage phase extracted by the phase-locked loop, It is the small signal component of grid voltage phase.

5. The iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increment according to claim 1, characterized in that: In step S3, the small signal linearization equation of the system is as follows: Where, L is the inductance of the connection between the inverter and the grid, is the small signal component of the output current, V dcn is the nth order DC voltage amplitude, ω1 is the fundamental voltage frequency, is the small signal component of the modulation wave, M n is the amplitude of the n-th modulation wave, is the small signal component of DC voltage, is the small signal component of AC voltage, C dc is the DC side capacitance, is the small signal component of DC voltage, * represents conjugation, I n is the n-times output current amplitude, G PR (t) is the current controller, is the small signal component of the output current command, I refn is the n-times output current command amplitude, is the small signal component of the grid voltage phase, H dvc (t) is the DC voltage controller.

6. The iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increment according to claim 1, characterized in that: In step S4, each small signal component in the small signal linearization equation is represented by the sum of a series of harmonics, as follows: in, is the small signal component of DC voltage, is the small signal component of the output current command, is the small signal component of the output current, is the small signal component of the modulation wave, is the small signal component of the AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, is the small signal component of the grid voltage phase, ω1 is the fundamental voltage frequency, is the amplitude of the nth DC voltage small signal component, is the amplitude of the small signal component of the n-th output current command, is the amplitude of the n-th output current small signal component, is the amplitude of the small signal component of the n-th modulation wave, is the amplitude of the small signal component of the nth AC voltage, is the small signal component of the grid voltage after fundamental bandpass filtering, It is the small signal component of grid voltage phase.

7. The iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increment according to claim 1, characterized in that: In step S5, the small signal linearization time-invariant equation group is: Among them, A1, A2, A3 are coefficient matrices, L is the inductance of the inverter and the grid connection, is the amplitude of the n-th output current small signal component, is the amplitude of the small signal component of the n-th modulation wave, is the amplitude of the nth DC voltage small signal component, is the amplitude of the small signal component of the nth AC voltage.

8. The iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increment according to claim 7, characterized in that: The coefficient matrices A1, A2, and A3 are: Where n is the harmonic order, ω1 is the fundamental voltage frequency, V d,cn is the nth DC voltage amplitude, M n is the amplitude of the n-th modulation wave.

9. The iterative method for harmonic disturbed emission of grid-connected equipment based on small signal increment according to claim 1, characterized in that: In step S7, the amplitude of the harmonic small disturbance in each stage does not exceed 3% of the fundamental voltage amplitude.

10. A small signal increment based grid-connected equipment harmonic disturbance emission iteration system, characterized in that: include: The data module obtains the initial steady-state operating point related data of the typical photovoltaic grid-connected inverter structure, and writes the voltage-current relationship equation required to calculate the harmonic current based on the relationship between the AC and DC circuits and the relationship between the controls; The representation module represents the initial steady-state operating point related data variables of the typical photovoltaic grid-connected inverter structure with steady-state components and small-signal components; the steady-state components and small-signal components are substituted into the voltage-current relationship equation, the small-signal component relationship is retained, and the system small-signal linearization equation is obtained; each small-signal component in the small-signal linearization equation is represented by the sum of harmonics; Equation module, substitute the small signal component into the small signal linearization equation, multiply the periodic time-varying coefficient and the periodic time-varying variable to convert it into the product between each harmonic, expressed as the relationship between the amplitudes of each harmonic, and obtain the small signal linearization time-invariant equation group; substitute other steady-state components under the fundamental component of the grid voltage into the small signal linearization time-invariant equation group to determine the DC voltage V dc0 , output current command I ref1 , output fundamental current amplitude I1, modulation wave fundamental amplitude M1, grid voltage fundamental amplitude V g1 , the value of the grid fundamental voltage frequency ω1; The background harmonic voltage in the grid voltage is divided into multiple stages of small disturbances. The amplitude of the grid harmonic voltage in the first stage is substituted into the small signal linearization time-invariant equation group to determine V gn The amplitude of The iterative module solves the small signal linearized time-invariant equation group to obtain the small perturbation response of each state variable under the background harmonic voltage disturbance in this stage; superimposes the small perturbation response of each state variable solved into the steady-state component, updates the steady-state operating point, and obtains the small signal linearized time-invariant equation group required for solving the next stage; continuously updates the steady-state operating point and the equation group until the applied background harmonic voltage is updated to the same as the set target; solves the small signal linearized time-invariant equation group to obtain the amplitude and phase of each output current harmonic.

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