New energy grid-connected broadband oscillation suppression method based on inverter damping control

Abstract

The invention relates to the technical field of broadband oscillation suppression, in particular to a new energy grid-connected broadband oscillation suppression method based on inverter damping control, and the method comprises the steps: obtaining the output current and output power of each generator set after new energy grid connection, and the power generation amount of a power supply side and the power consumption of a load side after new energy grid connection in real time; setting a time window with a preset duration; determining the harmonic influence degree of each generator set in each time window; obtaining a state evaluation value of each generator set in each time window; constructing a feature distribution sequence; calculating a relative difference coefficient of each time window; determining the oscillation saliency of each time window; and determining a damping coefficient of each time window, and suppressing the broadband oscillation of the new energy grid connection in combination with a VSG control algorithm. According to the application, the broadband oscillation of the new energy grid connection is suppressed by adjusting the damping characteristic of the inverter in time, the suppression effect on the broadband oscillation is improved, and the stability of the new energy grid connection is improved.

Description

Technical Field

[0001] This application relates to the technical field of broadband oscillation suppression, and particularly to a method for suppressing broadband oscillation in new energy grid connection based on inverter damping control. Background Art

[0002] With the rapid development of new energy power generation technology, especially the large-scale access of photovoltaic power generation and wind power generation to the power grid, the power grid system shows highly power electronic characteristics. Its dynamic interaction with the power grid is complex and prone to broadband oscillation. The phenomenon of broadband oscillation will not only cause fluctuations in voltage and current in the power grid, but even seriously affect the normal power consumption of power grid equipment and users.

[0003] After new energy is grid-connected, the control performance of the inverter is crucial for the stability and power quality of new energy grid connection. Existing damping control methods fail to consider that after new energy is grid-connected, it has complex nonlinear and time-varying characteristics. These characteristics may cause the frequency and amplitude of broadband oscillation to change with time, and are affected by the proportion of electricity consumed in the new energy power generation process, which will increase the difficulty of suppressing broadband oscillation, resulting in poor suppression effect on broadband oscillation and low stability after new energy is grid-connected. Summary of the Invention

[0004] In order to solve the above technical problems, a method for suppressing broadband oscillation in new energy grid connection based on inverter damping control is provided to solve the existing problems.

[0005] The solution of this application to solve the technical problem is to provide a method for suppressing broadband oscillation in new energy grid connection based on inverter damping control, including the following steps:

[0006] Obtain in real time the output current, output power of each generating unit after new energy is grid-connected, the power generation amount on the power supply side after new energy is grid-connected, and the power consumption amount on the load side;

[0007] Set a time window with a preset duration; analyze the proportion degree of harmonic components in the frequency domain of the output current within each time window for each generating unit, as well as the symmetric distribution of interharmonics, and determine the harmonic influence degree of each generating unit within each time window;

[0008] Determine the time-varying characteristic value of each generating unit within each time window through the difference change of interharmonics in the frequency domain of the output current between each time window and the remaining time windows, and combine the harmonic influence degree to obtain the state evaluation value of each generating unit within each time window;

[0009] Perform modal decomposition on the output power of each generating unit within each time window, analyze the average level of energy of different modal components at all frequency components in the frequency domain, as well as the average level of output power within each time window, and construct a characteristic distribution sequence in combination with the state evaluation value; calculate the relative difference coefficient of each time window through the difference situation of the characteristic distribution sequences of different generating units under each time window.

[0010] Analyze the proportion of the power generation on the power supply side to the power consumption on the load side under each time window, and determine the oscillation significance of each time window in combination with the relative difference coefficient; based on the oscillation significance, determine the damping coefficient of each time window, and in combination with the VSG control algorithm, suppress the broadband oscillation of new energy grid connection.

[0011] Preferably, the further measurement process of the proportion degree is as follows:

[0012] Perform frequency domain analysis on all output currents of each generating unit within each time window to obtain a spectrogram.

[0013] Obtain all the wave peaks in the spectrogram; record the frequency component corresponding to the maximum peak in the spectrogram as the fundamental wave component.

[0014] Record the sum value of the energies corresponding to all frequency components except the fundamental wave component in the spectrogram as the total harmonic content.

[0015] Calculate the ratio of the total harmonic content to the sum of the energies corresponding to all frequency components in the spectrogram, and record it as the harmonic ratio.

[0016] Preferably, determining the harmonic influence degree of each generating unit in each time window includes:

[0017] Record the frequency components that are not integer multiples of the fundamental wave component in the spectrogram as interharmonic components; starting from the fundamental wave component, number the interharmonic components on both sides of the fundamental wave component respectively.

[0018] Calculate the metric distance between the frequency corresponding to each interharmonic component and the frequency corresponding to the fundamental wave component; record the difference in the metric distance between the interharmonic components with the same serial number on both sides of the fundamental wave component as the relative difference.

[0019] Record the sum value of all the relative differences on both sides of the fundamental wave component as the asymmetry coefficient.

[0020] The harmonic influence degree is the product of the asymmetry coefficient and the harmonic ratio.

[0021] Preferably, determining the time-varying characteristic value of each generating unit in each time window includes:

[0022] Form a two-dimensional array with the frequencies corresponding to the inter-harmonic components in the spectrogram and their corresponding energies;

[0023] Arrange all the two-dimensional arrays in the spectrogram under each time window in descending order of the frequencies corresponding to the inter-harmonic components to form an inter-harmonic sequence;

[0024] The time-varying eigenvalue is the reciprocal of the mean of the distances between the inter-harmonic sequences between each time window and multiple previous time windows.

[0025] Preferably, obtaining the state evaluation value of each generator set at each time window includes:

[0026] Calculate the average value of the harmonic influence degrees of each time window and multiple previous time windows under each generator set;

[0027] The state evaluation value is the product of the average value and the time-varying eigenvalue.

[0028] Preferably, the construction process of the characteristic distribution sequence is as follows:

[0029] Perform frequency-domain analysis on each modal component to obtain a spectrogram; record the mean of the energies corresponding to all frequency components in the spectrogram corresponding to each modal component as the average energy;

[0030] Calculate the mean of all output powers of each generator set within each time window and record it as the average power;

[0031] Form a characteristic distribution sequence with the state evaluation value, the average power, and the average energies of all modal components.

[0032] Preferably, the relative difference coefficient is the sum of the distances between the characteristic distribution sequences of all any two generator sets under each time window.

[0033] Preferably, the further measurement process of the proportion ratio is: calculate the ratio between the mean of the power generation amounts of the power supply side at all times within each time window and the mean of the power consumption amounts of the load side at all times within each time window as the proportional coefficient of each time window.

[0034] Preferably, determining the oscillation significance of each time window includes:

[0035] Based on a preset first weight and a preset second weight, perform weighted summation on the relative difference coefficient and the proportional coefficient and then perform normalization processing to obtain the oscillation significance of each time window, where the sum of the preset first weight and the preset second weight is 1, and the preset first weight is greater than the preset second weight.

[0036] Preferably, the damping coefficient D of the i-th time window iThe calculation formula of D is as follows: i = α + (β - α) × Z i where α is the preset minimum damping coefficient, β is the preset maximum damping coefficient, and Z i is the normalized oscillation saliency under the i-th time window.

[0037] This application has at least the following beneficial effects:

[0038] This application determines the harmonic influence degree of each generator set in each time window through the content of harmonic components contained in the output current of each generator set in each time window and the symmetric distribution of simple harmonic waves relative to the fundamental wave component in the frequency domain. The beneficial effect is that it considers the harmonic components contained in the output current to evaluate the distortion of the output current of the generator set, and then reflects the influence degree of the nonlinear characteristics of the power grid system; by determining the difference in inter-harmonics contained in the output current between different time windows, the time-varying characteristic value of each generator set in each time window is determined, and combined with the harmonic influence degree, the state evaluation value of each generator set in each time window is obtained. The beneficial effect is that it considers the time-varying characteristics of the harmonic components contained in the output current in different time windows to evaluate the time-varying and nonlinear characteristics of the output current of the generator set, so as to illustrate the operating state of the generator set, and then reflects the oscillation situation of the power grid system; secondly, a characteristic distribution sequence is constructed; the relative difference coefficient of each time window is calculated. The beneficial effect is that it considers the differences in the operating states, power distribution, and randomness of the output power oscillation frequencies between different generator sets under the same time window, and then reflects the situation of broadband oscillation in the power grid system; by the proportion of the power generation on the power supply side to the power consumption on the load side under each time window, combined with the relative difference coefficient, the oscillation saliency of each time window is determined. The beneficial effect is that it considers the consumption of the power generation on the power supply side to reflect the broadband oscillation situation caused by the unstable characteristics of new energy generation; the damping coefficient of each time window is determined, and combined with the VSG control algorithm, the broadband oscillation of new energy grid connection is suppressed. The beneficial effect is that through the significant situation of the broadband oscillation of the power grid system under different time windows, the damping coefficient of the VSG control algorithm is adjusted in real time, and the broadband oscillation of new energy grid connection is suppressed by adjusting the damping characteristics of the inverter in a timely manner, improving the suppression effect of the broadband oscillation and enhancing the stability of new energy grid connection. Description of the Drawings

[0039] The following further details the method for suppressing broadband oscillation of new energy grid connection based on inverter damping control of this application with reference to the drawings.

[0040] Figure 1The flowchart of the steps of the new - energy grid - connected broadband oscillation suppression method based on inverter damping control provided by the embodiment of the present application;

[0041] Figure 2 The flowchart of the steps of the method for obtaining the state evaluation value of each generating unit in each time window provided by the embodiment of the present application;

[0042] Figure 3 The flowchart of the steps of the method for obtaining the relative difference coefficient of each time window provided by the embodiment of the present application. Detailed implementation manners

[0043] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the new - energy grid - connected broadband oscillation suppression method based on inverter damping control proposed in the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs.

[0045] Please refer to Figure 1 , which shows the flowchart of the steps of the new - energy grid - connected broadband oscillation suppression method based on inverter damping control provided by an embodiment of the present application. The method includes the following steps:

[0046] Step 1, obtain in real - time the output current, output power of each generating unit after the new energy is connected to the grid, the power generation amount on the power supply side after the new energy is connected to the grid, and the power consumption amount on the load side.

[0047] With the high - proportion access of new energy to the power grid system, the power grid presents characteristics such as non - linearity, time - variability, heterogeneity, strong coupling, and multi - time scales, which bring new challenges to the safe and stable operation of the power grid. Secondly, the direct current generated by new - energy generating units is converted into alternating current by inverters and then connected to the power grid, and the control technology of inverters directly affects the power quality and grid - connection stability. At present, power - electronic devices use the virtual synchronous generator (VSG) technology to control inverters. Among them, the VSG technology can make the inverter simulate the behavior of traditional synchronous generators, thereby improving the grid - connected power quality and the stability of the system power grid.

[0048] As a new energy power generation technology, the distributed photovoltaic power generation mode has been rapidly popularized and applied. Among them, multiple photovoltaic generating units constitute a distributed photovoltaic power generation system. In each generating unit, the photovoltaic power source is connected to an inverter, and these generating units supply power to the power grid system in parallel. However, when power electronic devices control the inverter, due to the interactive coupling effect between different inverters, multi-time scale oscillation phenomena will be triggered, and due to the coupling phenomenon between the power electronic devices and the power grid in each line, the power grid system will oscillate within a wide frequency domain. To comprehensively consider the wide-frequency oscillation caused by various factors, by analyzing the mutual influence relationship between generating units and the mutual influence relationship between generating units and the power grid system, the characteristics of wide-frequency oscillation are clarified.

[0049] Based on the above analysis, taking the distributed photovoltaic power generation system as an example, the output current and output power of each generating unit are collected in real time;

[0050] In this embodiment, the collection frequency of the output current and output power is 1KHz. As other implementation methods, the implementer can set it according to the actual situation.

[0051] Secondly, in the power grid system, the higher the proportion of the electric energy generated by photovoltaic power generation consumed, the wider the oscillation frequency band triggered, and the greater the impact on the grid connection stability. Therefore, through the distributed photovoltaic power generation system, the power supply quantity on the power supply side during the photovoltaic power generation process is obtained in real time, and the power consumption quantity on the load side is obtained in real time through an intelligent electricity meter.

[0052] In this embodiment, the collection frequency of the power supply quantity on the power generation side and the power consumption quantity on the load side is 10Hz. As other implementation methods, the implementer can set it according to the actual situation.

[0053] It should be noted that the collection frequency of the output current and output power should be higher than that of the power generation quantity and power consumption quantity. That is, for the output current and output power, each generating unit collects 1000 output currents and output powers per second; for the power generation quantity and power consumption quantity, 10 power supply quantities and power consumption quantities are collected per second.

[0054] So far, the output current and output power of each generating unit are obtained in real time, and the power generation quantity on the power supply side and the power consumption quantity on the load side are obtained in real time.

[0055] Step 2: Set a time window with a preset duration; analyze the proportion of harmonic components in the output current of each generator set in the frequency domain within each time window, as well as the symmetric distribution of interharmonics, to determine the harmonic influence degree of each generator set in each time window; determine the time-varying eigenvalue of each generator set in each time window through the difference change of interharmonics in the frequency domain between each time window and the remaining time windows, and combine the harmonic influence degree to obtain the state evaluation value of each generator set in each time window.

[0056] Photovoltaic power generation and photovoltaic grid-connected control circuits both rely on power electronic devices for control. Different power electronic devices have different control links, and the control links include, but are not limited to, phase-locked loops, filters, voltage and current loop controls. The interaction and coupling between these devices will cause complex coupling characteristics and trigger multi-time scale oscillation phenomena. Due to the randomness and volatility of photovoltaic power generation, the control links need to be continuously adjusted, which further exacerbates the coupling complexity. After multiple generator sets are connected in parallel on the power supply side, their output impedances will be coupled with each other to form a complex impedance network. Uneven power distribution may cause some inverters to be overloaded while other inverters operate lightly loaded. This imbalance will trigger circulating current and excite oscillations. Therefore, the power supply instability of a single generator set and the power supply difference characteristics between different generator sets are both important inducements for broadband oscillations. In addition, the interaction between the power supply side and the power grid will also trigger broadband oscillations. Therefore, due to the dynamic characteristics of power electronic devices, the change of the operating conditions of the power grid system, and the complex interaction between multiple devices, the analysis and suppression of broadband oscillations are more complex.

[0057] Secondly, the randomness and volatility of photovoltaic power generation result in a relatively complex and frequency-time-varying spectrum of its output current. The interharmonics generated may induce forced oscillations. At the same time, a large number of power electronic devices are used in the grid-connected process, and their topological structures and control parameters will change with the operating conditions. The adjustment of these parameters will cause the oscillation frequency to drift within a wide range, showing time-variation. There are complex interactions between power electronic devices, synchronous generators, and transmission power grids, which further enhance the nonlinearity of the power grid system. These time-varying and nonlinear characteristics are likely to cause oscillation stability problems in the power grid system.

[0058] First, analyze the interharmonics in the output current of the generator set to obtain the interharmonic components, specifically:

[0059] Set a time window with a preset duration;

[0060] In this embodiment, the duration of the time window is 1 s. As other implementation methods, the implementer can set it according to the actual situation.

[0061] Perform frequency domain analysis on all output currents of each generator set within each time window to obtain a spectrogram;

[0062] In this embodiment, fast Fourier transform is used for frequency domain analysis. Among them, fast Fourier transform is a well-known technology and will not be elaborated here.

[0063] Obtain all the wave peaks in the spectrogram;

[0064] The frequency component corresponding to the maximum peak in the spectrogram is denoted as the fundamental wave component; the frequency components that are non-integer multiples of the fundamental wave component in the spectrogram are denoted as each interharmonic component;

[0065] In this embodiment, the findpeaks function is used to obtain the wave peaks. Among them, the findpeaks function is a well-known technology and will not be elaborated here. As other implementation manners, implementers can adopt other methods of the existing technology, for example, the AMPD peak detection algorithm, etc. This embodiment does not make special restrictions on this.

[0066] Furthermore, the interharmonic component is a non-integer multiple of the fundamental wave component. Usually, the energy corresponding to the interharmonic is relatively small. Under the coupling effect of multiple generator sets in parallel, it will cause an increase in the interharmonic content. And the interharmonic components are distributed on both sides of the fundamental wave component and are symmetrically distributed. However, time-variation will cause the frequency and energy of the interharmonic components to show an asymmetric distribution on both sides of the fundamental wave component. Therefore, analyzing the symmetry characteristics of the interharmonic components specifically includes:

[0067] Taking the fundamental wave component as the starting point, number the interharmonic components on both sides of the fundamental wave component respectively;

[0068] Calculate the metric distance between the frequency corresponding to each interharmonic component and the frequency corresponding to the fundamental wave component; the difference in the metric distance between the interharmonic components with the same serial number on the left and right sides of the fundamental wave component is denoted as the relative difference;

[0069] In this embodiment, the metric distance is calculated by calculating the Euclidean distance between the frequency corresponding to each interharmonic component and the frequency corresponding to the fundamental wave component. Among them, the calculation of the Euclidean distance is a well-known technology; secondly, the absolute value of the difference in the distance between the interharmonic components with the same serial number on the left and right sides of the fundamental wave component is denoted as the relative difference.

[0070] It should be noted that the relative difference is the absolute value of the difference in the distance between the k-th interharmonic component on the left side of the fundamental wave component and the k-th interharmonic component on the right side of the fundamental wave component.

[0071] The sum value of all the relative differences on the left and right sides of the fundamental wave component is used as the asymmetry coefficient of each generator set in each time window;

[0072] It should be noted that the larger the asymmetry coefficient, the worse the symmetry degree of the intermediate harmonics of the output current under this time window.

[0073] Secondly, in the spectrogram of the output current, in addition to interharmonics, there may be harmonic components that are integer multiples of the fundamental wave component. Both interharmonics and harmonic components will cause distortion of the output current. Therefore, analyze the intermediate harmonics and harmonic components of the output current, and combine with the asymmetry coefficient to calculate the harmonic influence degree, specifically as follows:

[0074] Denote the sum of the energies corresponding to all frequency components other than the fundamental wave component in the spectrogram as the total harmonic amount;

[0075] Calculate the ratio of the total harmonic amount to the sum of the energies corresponding to all frequency components in the spectrogram, and denote it as the harmonic proportion;

[0076] Take the product of the asymmetry coefficient and the harmonic proportion as the harmonic influence degree of each generator set in each time window;

[0077] It should be noted that the larger the harmonic proportion, the higher the intermediate harmonics and harmonic components of the output current, and the more likely it is affected by nonlinear loads; the larger the obtained harmonic influence degree, the more harmonic components in the output current, and the more abnormal the distribution of simple harmonics, and the more significant the influence of the nonlinear characteristics of the power grid system.

[0078] Furthermore, analyze the time-varying characteristics of simple harmonics in different time windows, and combine with the harmonic influence degree to calculate the state evaluation value. The step flow chart of the method for obtaining the state evaluation value of each generator set in each time window provided by the embodiments of the present application is as Figure 2 shown, specifically including:

[0079] Form a two-dimensional array with the frequency corresponding to each interharmonic component in the spectrogram and its corresponding energy;

[0080] Arrange all the two-dimensional arrays in the spectrogram in each time window in descending order according to the frequency corresponding to the interharmonic component to form an interharmonic sequence;

[0081] Calculate the DTW distance of the interharmonic sequence between each time window and multiple time windows before it;

[0082] In this embodiment, it is measured by calculating the DTW distance of the interharmonic sequence between each time window and the 5 time windows before it. As other implementation manners, implementers can set it by themselves according to actual situations.

[0083] Take the reciprocal of the mean value of the DTW distances between each time window and multiple time windows before it as the time-varying characteristic value of each time window;

[0084] It should be noted that the larger the time-varying eigenvalue is, the more obvious the change of the intermediate harmonics of the output current with time is, and the more significant the time-varying characteristics are.

[0085] Calculate the average value of the harmonic influence degrees of each time window and multiple time windows before it.

[0086] In this embodiment, calculate the average value of the harmonic influence degrees of each time window and the 5 time windows before it. As other implementation manners, the implementer can set it according to the actual situation.

[0087] Take the product of the average value and the time-varying eigenvalue as the state evaluation value of each generator set in each time window.

[0088] It should be noted that the larger the state evaluation value is, the more significant the time-varying and non-linear characteristics of the output current are in this time window, and the easier it is to cause oscillations in the power grid system, thus reflecting the operating state of this generator set.

[0089] Thus, the state evaluation value of each generator set in each time window is obtained.

[0090] Step 3: Perform modal decomposition on the output power of each generator set in each time window, analyze the average level of energy of all frequency components in the frequency domain of different modal components, and the average level of the output power in each time window. Combine the state evaluation value to construct a characteristic distribution sequence; calculate the relative difference coefficient of each time window according to the difference situation of the characteristic distribution sequences of different generator sets under each time window.

[0091] Furthermore, multiple generator sets are interrelated, and the change of the operating state of one generator set will affect the stability of other generator sets. Secondly, the uneven power distribution among generator sets will cause different inverters to operate overloaded or lightly loaded, and the interaction of multiple inverters may excite high-frequency oscillations.

[0092] Secondly, if the output power difference between different inverters is too large, it will cause a circulating current to form between the inverter devices and excite high-frequency oscillations. Moreover, the output power of the generator set has non-stationarity and randomness of the oscillation frequency, and the frequency range of its output power in the frequency domain will also change greatly, causing oscillations in the power grid system. Therefore, analyze the difference situation of the output power of each generator set in the frequency domain, calculate the relative difference coefficient, and the step flow chart of the method for obtaining the relative difference coefficient of each time window provided in the embodiment of the present application is as Figure 3 shown, and specifically includes:

[0093] Perform modal decomposition on all the output power of each generator set in each time window to obtain multiple modal components.

[0094] In this embodiment, the improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) algorithm is used for mode decomposition. The ICEEMDAN algorithm is a well-known technology and will not be elaborated here.

[0095] Perform frequency-domain analysis on each modal component to obtain a spectrogram, and denote the mean of the energies corresponding to all frequency components in the spectrogram corresponding to each modal component as the average energy.

[0096] In this embodiment, Hilbert transform is used to perform frequency-domain analysis on each modal component to obtain the corresponding Hilbert spectrum, calculate the marginal spectrum corresponding to the Hilbert spectrum, and denote the mean of the energies corresponding to all frequencies in the marginal spectrum as the average energy.

[0097] It should be noted that the Hilbert spectrum reflects the variation characteristics of the spectrum of the corresponding modal component over time. The larger the average energy, the higher the energy of the output power at the frequency where the corresponding modal component is located. Secondly, the calculation of the Hilbert transform and the marginal spectrum is a well-known technology and will not be elaborated here.

[0098] Calculate the mean of all output powers of each generator set within each time window, and denote it as the average power.

[0099] Form a feature distribution sequence with the state evaluation value, the average power, and the average energies of all modal components.

[0100] It should be noted that the average energy of the modal component reflects the non-stationarity of the output power and the randomness of the oscillation frequency. The feature distribution sequence comprehensively combines multiple features such as the operating state of the generator set, the power distribution situation, and the randomness of the output power oscillation frequency.

[0101] Calculate the sum of the distances between the feature distribution sequences of all any two generator sets under each time window as the relative difference coefficient for each time window.

[0102] In this embodiment, the distance is measured by calculating the SBD (Shape Based Distance) distance between the feature distribution sequences of all any two generator sets under each time window. The calculation process of the SBD distance is a well-known technology and will not be elaborated here.

[0103] It should be noted that the relative difference coefficient comprehensively evaluates the differences between the operating states, power distribution situations, and the randomness of the output power oscillation frequencies of different generator sets. The larger the obtained relative difference coefficient, the greater the difference in the operating states between different generator sets under the same time window, and the more likely it is to cause broadband oscillation due to frequent adjustment of the equipment for stable power supply.

[0104] Thus, the relative difference coefficients for each time window are obtained.

[0105] Step 4: Analyze the proportion of the power generation on the power supply side to the power consumption on the load side for each time window, and combine with the relative difference coefficient to determine the oscillation significance for each time window; based on the oscillation significance, determine the damping coefficient for each time window, and combine with the VSG control algorithm to suppress the broadband oscillation of new energy grid connection.

[0106] Furthermore, there will also be an interaction between the power supply side and the power grid, which may trigger broadband oscillation. Among them, the higher the proportion of the electric energy generated by the photovoltaic power supply consumed in the entire power grid system, it indicates that the entire power grid system is more dependent on the electric energy provided by photovoltaic power generation. Due to the instability of photovoltaic power generation, the wider the oscillation frequency band is triggered, and the greater the impact on the stability of photovoltaic grid connection.

[0107] Therefore, during the analysis of the distributed photovoltaic power generation process, analyze the proportion of the power generation on the power supply side to the power consumption on the load side, and combine with the relative difference coefficient to calculate the oscillation significance, so as to evaluate the impact of the mutual influence between different generator sets on the power supply side and between the power supply side and the power grid on the grid connection stability. Specifically:

[0108] Calculate the ratio of the mean value of the power generation at all times within each time window on the power supply side to the mean value of the power consumption at all times within each time window on the load side as the proportional coefficient for each time window;

[0109] Based on a preset first weight and a preset second weight, perform weighted summation on the relative difference coefficient and the proportional coefficient and then perform normalization processing to obtain the oscillation significance for each time window, where the sum of the preset first weight and the preset second weight is 1, and the preset first weight is greater than the preset second weight;

[0110] In this embodiment, since the greater the difference in the operating states between different generator sets, the greater the impact of the broadband oscillation phenomenon caused by frequent adjustment of the equipment on the grid connection stability. Therefore, the preset first weight is greater than the preset second weight. Then, the preset first weight takes a value of 0.6, and the preset second weight takes a value of 0.4. As other implementation manners, the implementer can set them according to the actual situation. Secondly, the sigmoid function is used for normalization processing. The sigmoid function is a well-known technology and will not be elaborated here. As other implementation manners, the implementer can adopt other methods of the existing technology, such as the tanh function, etc. This embodiment does not make special restrictions on this.

[0111] It should be noted that the larger the proportional coefficient, the higher the proportion of the power supply of photovoltaic power generation, and the greater the impact on the grid connection stability. The greater the oscillation significance, the more significant the possible broadband oscillation in the power grid system.

[0112] Furthermore, the greater the oscillation significance in different time windows of the power grid system, the worse the stability of the power grid system, and the greater the impact of broadband oscillation. When suppressing broadband oscillation by adjusting the damping coefficient of the VSG technology, a relatively large damping coefficient needs to be set to reduce the oscillation amplitude of the power grid system; conversely, the smaller the oscillation significance, the better the stability of the power grid system, and the smaller the impact of broadband oscillation, so a relatively small damping coefficient is set to adapt to different operating conditions.

[0113] Therefore, based on the oscillation significance, the damping coefficient is determined, specifically:

[0114] The calculation formula for the damping coefficient of each time window is:

[0115] D i = α + (β - α) × Z i

[0116] where D i is the damping coefficient of the i-th time window, α is the preset minimum damping coefficient, β is the preset maximum damping coefficient, and Z i is the oscillation significance of the i-th time window.

[0117] In this embodiment, to make the value range of the damping coefficient be in [1, 10], therefore, the preset minimum damping coefficient α is set to 1, and the preset maximum damping coefficient β is set to 10. As other implementation manners, the implementer can set them according to the actual situation.

[0118] Thus, based on the damping coefficient, the damping performance of the inverter is adjusted through the VSG technology, and then the broadband oscillation of the power grid system after photovoltaic grid connection is suppressed.

[0119] It should be understood that although Figure 1 the steps in the flowchart of Figure 1 are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear indication in this article, the execution of these steps has no strict order limit, and these steps can be executed in other orders. Moreover,

[0120] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0121] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made. Therefore, all simple modifications, equivalent changes and decorations made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application belong to the protection scope of the technical solution of the present application.

Claims

1. A new energy grid-connected broadband oscillation suppression method based on inverter damping control, characterized in that The method includes the following steps: Obtain in real time the output current, output power of each generator set after new energy is connected to the grid, the power generation amount on the power supply side after new energy is connected to the grid, and the power consumption amount on the load side; Set a time window with a preset duration; analyze the proportion degree of the harmonic components in the frequency domain of the output current within each time window for each generator set, as well as the symmetric distribution of inter-harmonics, and determine the harmonic influence degree of each generator set in each time window; Determine the time-varying eigenvalue of each generator set in each time window through the difference change situation of the inter-harmonics in the frequency domain between each time window and the remaining time windows, and combine the harmonic influence degree to obtain the state evaluation value of each generator set in each time window; Perform modal decomposition on the output power of each generator set within each time window, analyze the average level of the energy of different modal components under all frequency components in the frequency domain, as well as the average level of the output power within each time window, and combine the state evaluation value to construct a characteristic distribution sequence; calculate the relative difference coefficient of each time window through the difference situation of the characteristic distribution sequences of different generator sets under each time window; Analyze the proportion of the power generation amount on the power supply side to the power consumption amount on the load side under each time window, and combine the relative difference coefficient to determine the oscillation significance degree of each time window; based on the oscillation significance degree, determine the damping coefficient of each time window, and combine with the VSG control algorithm to suppress the broadband oscillation of new energy grid connection.

2. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 1, wherein The further measurement process of the proportion degree is as follows: Perform frequency domain analysis on all the output currents of each generator set within each time window to obtain a spectrogram; Obtain all the wave peaks in the spectrogram; record the frequency component corresponding to the maximum peak value in the spectrogram as the fundamental wave component; Record the sum value of the energies corresponding to all the frequency components except the fundamental wave component in the spectrogram as the total harmonic amount; Calculate the ratio of the total harmonic amount to the sum of the energies corresponding to all the frequency components in the spectrogram, and record it as the harmonic proportion.

3. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 2, characterized in that, The determination of the harmonic influence degree of each generator set in each time window includes: Record the frequency components that are not integer multiples of the fundamental wave component in the spectrogram as each inter-harmonic component; starting from the fundamental wave component, number the inter-harmonic components on both sides of the fundamental wave component respectively; Calculate the measurement distance between the frequency corresponding to each inter-harmonic component and the frequency corresponding to the fundamental wave component; record the difference in the measurement distance between the inter-harmonic components with the same serial number on both sides of the fundamental wave component as the relative difference; Record the sum value of all the relative differences on both sides of the fundamental wave component as the asymmetry coefficient; The harmonic influence degree is the product of the asymmetry coefficient and the harmonic proportion.

4. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 3, characterized in that, The determination of the time-varying eigenvalue of each generator set in each time window includes: Form a two-dimensional array with the frequency corresponding to each inter-harmonic component in the spectrogram and its corresponding energy; Arrange all the two-dimensional arrays in the spectrogram under each time window in descending order according to the frequency corresponding to the inter-harmonic component to form an inter-harmonic sequence; The time-varying eigenvalue is the reciprocal of the mean value of the distances between each time window and multiple previous time windows of the inter-harmonic sequence.

5. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 1, characterized in that Obtaining the state evaluation values of each generating set in each time window includes: Calculating the average value of the harmonic influence degrees in each time window and multiple time windows before it for each generating set; The state evaluation value is the product of the average value and the time-varying eigenvalue.

6. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 1, characterized in that The construction process of the characteristic distribution sequence is as follows: Performing frequency-domain analysis on each modal component to obtain a spectrogram; denoting the mean value of the energies corresponding to all frequency components in the spectrogram corresponding to each modal component as the average energy; Calculating the mean value of all output powers of each generating set in each time window, denoted as the average power; The state evaluation value, the average power, and the average energies of all modal components Form a characteristic distribution sequence.

7. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 1, characterized in that The relative difference coefficient is the sum of the distances between the characteristic distribution sequences of all any two generating sets in each time window.

8. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 1, characterized in that, The further measurement process of the proportion ratio is: calculating the ratio between the mean value of the power generation amounts of the power supply side at all times in each time window and the mean value of the power consumption amounts of the load side at all times in each time window as the proportionality coefficient of each time window.

9. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 8, characterized in that Determining the oscillation significance of each time window includes: Based on a preset first weight and a preset second weight, performing weighted summation on the relative difference coefficient and the proportionality coefficient and then performing normalization processing to obtain the oscillation significance of each time window, where the sum of the preset first weight and the preset second weight is 1, and the preset first weight is greater than the preset second weight.

10. The new energy grid-connected broadband oscillation suppression method based on inverter damping control according to claim 1, characterized in that, The damping coefficient D of the i-th time window i The calculation formula is: D i = α + (β - α) × Z i , where α is the preset minimum damping coefficient, β is the preset maximum damping coefficient, and Z i is the normalized oscillation significance under the i-th time window.

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