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

Abstract

This application relates to the field of broadband oscillation suppression technology, specifically to a method for suppressing broadband oscillations in new energy grid connection based on inverter damping control. This method includes: real-time acquisition of the output current and output power of each generator unit after grid connection, as well as the power generation on the power supply side and the power consumption on the load side; setting a preset time window; determining the harmonic influence degree of each generator unit in each time window; obtaining the state evaluation value of each generator unit in each time window; constructing a characteristic distribution sequence; calculating the relative difference coefficient of each time window; determining the oscillation significance of each time window; determining the damping coefficient of each time window; and combining the method with the VSG control algorithm to suppress broadband oscillations in new energy grid connection. This application timely suppresses broadband oscillations in new energy grid connection by adjusting the damping characteristics of the inverter, improving the suppression effect of broadband oscillations and enhancing the stability of new energy grid connection.

Description

Technical Field

[0001] This application relates to the field of broadband oscillation suppression technology, specifically to a method for suppressing broadband oscillations in new energy grid connection based on inverter damping control. Background Technology

[0002] With the rapid development of new energy power generation technologies, especially the large-scale grid connection of photovoltaic and wind power generation, the power grid system has become highly electronic, and its dynamic interaction with the grid is complex, easily triggering broadband oscillations. Broadband oscillations not only cause fluctuations in voltage and current in the power grid, but can also seriously affect the normal power consumption of grid equipment and users.

[0003] After renewable energy is connected to the grid, the control performance of the inverter is crucial to the stability of the grid connection and the power quality. Existing damping control methods fail to consider the complex nonlinear and time-varying characteristics of renewable energy after grid connection. These characteristics may cause the frequency and amplitude of broadband oscillations to vary over time, and are also affected by the proportion of electricity consumed during renewable energy generation, which increases the difficulty of suppressing broadband oscillations, resulting in poor suppression effects and lower stability after renewable energy is connected to the grid. Summary of the Invention

[0004] To address the aforementioned technical issues, a broadband oscillation suppression method for new energy grid connection based on inverter damping control is provided to resolve existing problems.

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

[0006] Real-time acquisition of the output current and output power of each generator set after the new energy is connected to the grid, as well as the power generation on the power supply side and the power consumption on the load side after the new energy is connected to the grid;

[0007] Set a preset time window; 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 symmetrical distribution of interharmonics, and determine the harmonic influence of each generator set in each time window.

[0008] By analyzing the differences in harmonic variations of the output current in the frequency domain between each time window and other time windows, the time-varying characteristic value of each generator set in each time window is determined. Combined with the harmonic influence degree, the state evaluation value of each generator set in each time window is obtained.

[0009] Modal decomposition is performed on the output power of each generator set within each time window. The average energy level of different modal components under all frequency components in the frequency domain, as well as the average output power level within each time window, are analyzed. Combined with the state assessment value, a characteristic distribution sequence is constructed. The relative difference coefficient of each time window is calculated by the differences in the characteristic distribution sequences of different generator sets under each time window.

[0010] The proportion of power generation on the power supply side to power consumption on the load side is analyzed in each time window. Based on the relative difference coefficient, the oscillation significance of each time window is determined. Based on the oscillation significance, the damping coefficient of each time window is determined. Combined with the VSG control algorithm, the broadband oscillation of new energy grid connection is suppressed.

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

[0012] Frequency domain analysis was performed on all output currents of each generator set within each time window to obtain the spectrum.

[0013] Obtain all peaks in the spectrum; denote the frequency component corresponding to the maximum peak in the spectrum as the fundamental component;

[0014] The sum of the energy corresponding to all frequency components in the spectrum other than the fundamental component is denoted as the total harmonics.

[0015] The ratio between the total amount of harmonics and the sum of the energies corresponding to all frequency components in the spectrum is calculated and denoted as the harmonic percentage.

[0016] Preferably, determining the harmonic impact degree of each generator set in each time window includes:

[0017] The frequency components that are non-integer multiples of the fundamental component in the spectrum are denoted as interharmonic components; the interharmonic components on both sides of the fundamental component are numbered starting from the fundamental component.

[0018] Calculate the metric distance between the frequency corresponding to each interharmonic component and the frequency corresponding to the fundamental component; record the difference in the metric distance between the interharmonic components with the same index on the left and right sides of the fundamental component as the relative difference;

[0019] The sum of all the relative differences between the left and right sides of the fundamental component is denoted as the asymmetry coefficient.

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

[0021] Preferably, determining the time-varying characteristic values ​​of each generator set in each time window includes:

[0022] The frequencies corresponding to each interharmonic component in the spectrum and their corresponding energies are combined into a two-dimensional array;

[0023] Arrange all two-dimensional arrays in the spectrum diagram under each time window in descending order according to the frequency corresponding to the interharmonic components to form an interharmonic sequence;

[0024] The time-varying characteristic value is the reciprocal of the mean of the distances between each time window and the interharmonic sequences of the preceding multiple time windows.

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

[0026] Calculate the average value of the harmonic influence for each time window and multiple time windows prior to each generator set;

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

[0028] Preferably, the process of constructing the feature distribution sequence is as follows:

[0029] Frequency domain analysis is performed on each modal component to obtain the spectrum; the average energy is the mean of the energy corresponding to all frequency components in the spectrum of each modal component.

[0030] Calculate the average output power of each generator set within each time window, and denot it as the average power.

[0031] The state assessment value, the average power, and the average energy of all modal components are combined to form a characteristic distribution sequence.

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

[0033] Preferably, the further measurement process of the proportion is as follows: calculate the ratio between the average power generation of the power supply side at all times in each time window and the average power consumption of the load side at all times in each time window, and use it as the proportion coefficient for each time window.

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

[0035] Based on the preset first weight and the preset second weight, the relative difference coefficient and the proportional coefficient are weighted and summed and then normalized to obtain the oscillation significance of each time window. 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 in the i-th time window iThe 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 Let represent the normalized oscillation significance under the i-th time window.

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

[0038] This application determines the harmonic impact of each generator set in each time window by analyzing the harmonic content in the output current of each generator set within each time window and the symmetrical distribution of simple harmonics relative to the fundamental component in the frequency domain. Its advantage lies in considering the harmonic components in the output current to assess the distortion of the generator set's output current, thereby reflecting the degree of influence of nonlinear characteristics in the power grid system. By analyzing the differences in interharmonics contained in the output current between different time windows, the time-varying characteristic values ​​of each generator set in each time window are determined. Combined with the harmonic impact, a state evaluation value for each generator set in each time window is obtained. Its advantage lies in considering the characteristics of the harmonic components in the output current changing over time within different time windows to assess the significance of the time-varying and nonlinear characteristics of the generator set's output current, thereby explaining the generator set's operating state and reflecting the oscillation of the power grid system. Secondly, a characteristic distribution sequence is constructed; and the values ​​of each... The relative difference coefficient of the time window has the advantage of considering the differences in operating status, power distribution, and randomness of output power oscillation frequency among different generator sets within the same time window, thus reflecting the wide-frequency oscillations that cause the power grid system to experience wide-frequency oscillations. By combining the ratio of power generation on the supply side to power consumption on the load side within each time window with the relative difference coefficient, the oscillation significance of each time window is determined. This has the advantage of considering the consumption of power generation on the supply side, reflecting the wide-frequency oscillations caused by the instability of new energy power generation. Determining the damping coefficient for each time window, combined with the VSG control algorithm, suppresses the wide-frequency oscillations of new energy grid connection. This has the advantage of adjusting the damping coefficient of the VSG control algorithm in real time based on the significance of the wide-frequency oscillations of the power grid system within different time windows, thereby improving the suppression effect of wide-frequency oscillations and enhancing the stability of new energy grid connection. Attached Figure Description

[0039] The following section provides a more detailed description of the broadband oscillation suppression method for new energy grid connection based on inverter damping control, in conjunction with the accompanying drawings.

[0040] Figure 1A flowchart illustrating the steps of a new energy grid-connected broadband oscillation suppression method based on inverter damping control provided in this application embodiment;

[0041] Figure 2 A flowchart illustrating the steps of the method for obtaining the state evaluation value of each generator set in each time window, as provided in the embodiments of this application;

[0042] Figure 3 A flowchart illustrating the steps of the method for obtaining the relative difference coefficients of each time window provided in the embodiments of this application. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description, in conjunction with the accompanying drawings and implementation examples, provides a more comprehensive explanation of the proposed method for suppressing broadband oscillations in new energy grid connection based on inverter damping control. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0045] Please see Figure 1 The document illustrates a flowchart of a method for suppressing broadband oscillations in new energy grid connection based on inverter damping control, according to an embodiment of this application. The method includes the following steps:

[0046] Step 1: Real-time acquisition of the output current and output power of each generator set after the new energy is connected to the grid, as well as the power generation on the power supply side and the power consumption on the load side after the new energy is connected to the grid.

[0047] With a high proportion of new energy sources being integrated into the power grid, the grid exhibits characteristics such as nonlinearity, time-varying nature, heterogeneity, strong coupling, and multiple time scales, posing new challenges to the safe and stable operation of the grid. Secondly, the direct current (DC) generated by new energy generators is converted into alternating current (AC) by inverters before being connected to the grid. The control technology of these inverters directly affects power quality and grid connection stability. Currently, power electronic equipment uses Virtual Synchronous Generator (VSG) technology to control inverters. VSG technology enables inverters to simulate the behavior of traditional synchronous generators, thereby improving grid-connected power quality and system grid stability.

[0048] Photovoltaic power generation, as a new energy power generation technology, has seen rapid promotion and application in its distributed photovoltaic (PV) power generation mode. In this system, multiple PV generators constitute a distributed PV power generation system, with each generator's photovoltaic power source connected to an inverter. These generators supply power to the grid system through parallel operation. However, when power electronic equipment controls the inverters, the interaction and coupling between different inverters can induce oscillations across multiple time scales. Furthermore, the coupling between power electronic equipment and the grid in each line can also cause oscillations in the grid system over a wide frequency range. To comprehensively consider the wide-frequency oscillations caused by various factors, this paper analyzes the mutual influence relationships between generators and between generators and the grid system, thereby clarifying the characteristics that cause wide-frequency oscillations.

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

[0050] In this embodiment, the sampling frequency of output current and output power is 1KHz. As for 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 electricity generated by photovoltaic power generation that is consumed, the wider the frequency band causing oscillations, and the greater the impact on grid connection stability. Therefore, distributed photovoltaic power generation systems can obtain the power supply from the power supply side in real time during the photovoltaic power generation process, and smart meters can obtain the electricity consumption from the load side in real time.

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

[0053] It should be noted that the sampling frequency of output current and output power is higher than that of power generation and power consumption. That is, for output current and output power, each generator set samples 1,000 output current and output power per second; for power generation and power consumption, 10 power supply and power consumption samples are collected per second.

[0054] At this point, the output current and output power of each generator set can be obtained in real time, as well as the power generation on the power supply side and the power consumption on the load side.

[0055] Step 2: Set a preset time window; 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 symmetrical distribution of interharmonics, to determine the harmonic influence of each generator set in each time window; determine the time-varying characteristic value of each generator set in each time window by the difference in interharmonics in the frequency domain between each time window and other time windows, and obtain the state evaluation value of each generator set in each time window by combining the harmonic influence.

[0056] Both photovoltaic (PV) power generation and grid-connected PV control circuits rely on power electronic devices for control. Different power electronic devices have different control loops, including but not limited to phase-locked loops (PLLs), filters, and voltage-current loop control. The interaction and coupling between these devices can cause complex coupling characteristics, leading to oscillations across multiple time scales. The randomness and volatility of PV power generation necessitate continuous adjustment of the control loops, further exacerbating the coupling complexity. When multiple generator sets are connected in parallel on the power supply side, their output impedances couple with each other, forming a complex impedance network. Uneven power distribution can cause some inverters to overload while others operate under light load; this imbalance can induce circulating currents and trigger oscillations. Therefore, the power supply instability of individual generator sets and the power supply differences between different units are significant contributing factors to broadband oscillations. Furthermore, the interaction between the power supply side and the grid can also trigger broadband oscillations. Thus, the dynamic characteristics of power electronic devices, changes in grid system operating conditions, and the complex interactions between multiple devices make the analysis and suppression of broadband oscillations even more complex.

[0057] Secondly, the randomness and volatility of photovoltaic power generation result in a complex and time-varying spectrum of its output current. The interharmonics generated can induce forced oscillations. Furthermore, the extensive use of power electronic equipment during grid connection means that its topology and control parameters change with operating conditions. Adjustments to these parameters cause the oscillation frequency to drift over a wide range, exhibiting time-varying characteristics. The complex interactions between power electronic equipment, synchronous generators, and the transmission network further enhance the nonlinearity of the power grid system. These time-varying and nonlinear characteristics easily lead to oscillation stability problems in the power grid system.

[0058] First, analyze the interharmonics present in the output current of the generator set and 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 second. As for other implementation methods, the implementer can set it according to the actual situation.

[0061] Frequency domain analysis was performed on all output currents of each generator set within each time window to obtain the spectrum.

[0062] In this embodiment, the Fast Fourier Transform (FFT) is used for frequency domain analysis. The FFT is a well-known technique and will not be described in detail here.

[0063] Obtain all peaks in the spectrum;

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

[0065] In this embodiment, the findpeaks function is used to obtain the peaks. The findpeaks function is a well-known technology and will not be described in detail here. As other implementation methods, implementers can use other methods of the prior art, such as the AMPD peak detection algorithm, etc. This embodiment does not impose any special restrictions on this.

[0066] Furthermore, interharmonic components are non-integer multiples of the fundamental component. Typically, the energy corresponding to interharmonics is relatively small. However, under the coupling effect of multiple generator units connected in parallel, the interharmonic content increases. Moreover, the interharmonic components are symmetrically distributed on both sides of the fundamental component. Time-varying characteristics, however, cause the frequency and energy of the interharmonic components to exhibit an asymmetrical distribution on both sides of the fundamental component. Therefore, the symmetry characteristics of the interharmonic components are analyzed as follows:

[0067] Starting from the fundamental component, the interharmonic components on both sides of the fundamental component are numbered respectively.

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

[0069] In this embodiment, the distance is measured by calculating the Euclidean distance between the frequency corresponding to each interharmonic component and the frequency corresponding to the fundamental component, wherein the calculation of the Euclidean distance is a known technique; secondly, the absolute value of the difference between the distances between the interharmonic components with the same index on the left and right sides of the fundamental component is denoted as the relative difference.

[0070] It should be noted that the relative difference is the absolute value of the difference between the distances between the kth interharmonic component to the left of the fundamental component and the kth interharmonic component to the right of the fundamental component.

[0071] The sum of all the relative differences on the left and right sides of the fundamental 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 of the intermediate harmonic of the output current under that time window.

[0073] Secondly, in addition to interharmonics, the output current spectrum may contain harmonic components that are integer multiples of the fundamental frequency component. Both interharmonics and harmonic components can cause distortion in the output current. Therefore, by analyzing the intermediate harmonics and harmonic components of the output current and combining them with the aforementioned asymmetry coefficient, the harmonic influence is calculated as follows:

[0074] The sum of the energy corresponding to all frequency components other than the fundamental component in the spectrum is denoted as the total harmonics.

[0075] The ratio between the total amount of harmonics and the sum of the energies corresponding to all frequency components in the spectrum is calculated and denoted as the harmonic percentage.

[0076] The product of the asymmetry coefficient and the harmonic proportion is used as the harmonic influence degree of each generator set in each time window.

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

[0078] Furthermore, the time-varying characteristics of the simple harmonic wave in different time windows are analyzed, and the state assessment value is calculated in combination with the harmonic influence degree. The flowchart of the method for obtaining the state assessment value of each generator set in each time window provided in this application embodiment is as follows: Figure 2 As shown, it specifically includes:

[0079] The frequency corresponding to each interharmonic component in the spectrum and its corresponding energy are combined into a two-dimensional array;

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

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

[0082] In this embodiment, the DTW distance of the interharmonic sequence between each time window and the five time windows preceding it is used for measurement. As for other implementation methods, the implementer can set it according to the actual situation.

[0083] The reciprocal of the mean of the DTW distances between each time window and the previous multiple time windows is used as the time-varying characteristic value of each time window;

[0084] It should be noted that the larger the time-varying characteristic value, the more obvious the change of the intermediate harmonic of the output current with time, and the more significant the time-varying characteristics.

[0085] Calculate the average value of the harmonic influence degree for each time window and multiple time windows preceding it;

[0086] In this embodiment, the average value of the harmonic influence degree of each time window and the five time windows preceding it is calculated. As for other implementation methods, the implementer can set it according to the actual situation.

[0087] The product of the average value and the time-varying characteristic value is used as the state evaluation value of each generator set in each time window;

[0088] It should be noted that the larger the state assessment value, the more significant the time-varying and nonlinear characteristics of the output current under that time window, and the more likely it is to cause oscillations in the power grid system, thus reflecting the operating status of the generator set.

[0089] At this point, the status evaluation values ​​of each generator set in each time window are obtained.

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

[0091] Furthermore, multiple generator sets are interconnected, and changes in the operating status of one generator set can affect the stability of other generator sets. In addition, uneven power distribution among generator sets can lead to overload or light load operation of different inverters, and the interaction of multiple inverters may induce high-frequency oscillations.

[0092] Secondly, if the output power difference between different inverters is too large, circulating currents may form between the inverter devices, triggering high-frequency oscillations. Furthermore, the output power of generator sets is non-stationary and the oscillation frequency is random, resulting in significant variations in the frequency range of their output power in the frequency domain, causing oscillations in the power grid system. Therefore, analyzing the differences in the output power of each generator set in the frequency domain and calculating the relative difference coefficient is crucial. The flowchart of the method for obtaining the relative difference coefficient for each time window provided in this application embodiment is shown below. Figure 3 As shown, it specifically includes:

[0093] Modal decomposition is performed on all output power of each generator set within each time window to obtain multiple modal components;

[0094] In this embodiment, the improved adaptive noise complete set empirical mode decomposition (ICEEMDAN) algorithm is used for mode decomposition. The ICEEMDAN algorithm is a well-known technique and will not be described in detail here.

[0095] Frequency domain analysis is performed on each modal component to obtain a spectrum diagram. The average energy is the mean of the energy corresponding to all frequency components in the spectrum diagram of each modal component.

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

[0097] It should be noted that the Hilbert spectrum reflects the time-varying characteristics of the spectrum of the corresponding modal component. The larger the average energy, the higher the energy of the output power at the frequency of the corresponding modal component. Furthermore, the calculation of the Hilbert transform and the marginal spectrum are well-known techniques and will not be elaborated here.

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

[0099] The state evaluation value, the average power, and the average energy of all modal components are combined to form a characteristic distribution sequence;

[0100] It should be noted that the average energy of the modal components reflects the non-stationarity of the output power and the randomness of the oscillation frequency. The characteristic distribution sequence integrates multiple characteristics such as the generator set operating status, power distribution, and the randomness of the output power oscillation frequency.

[0101] The sum of the distances between the characteristic distribution sequences of any two generator sets under each time window is calculated 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 characteristic distribution sequences of all two generator sets under each time window. The calculation process of the SBD distance is a well-known technique and will not be described in detail here.

[0103] It should be noted that the relative difference coefficient comprehensively evaluates the differences between the operating status, power distribution, and randomness of the output power oscillation frequency of different generator sets. The larger the relative difference coefficient, the greater the difference in the operating status between different generator sets under the same time window. In order to stabilize the power supply, the equipment needs to be adjusted frequently, which makes it easier to cause wide-frequency oscillation.

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

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

[0106] Furthermore, the interaction between the power supply side and the grid can also cause broadband oscillations. The higher the proportion of electricity generated by photovoltaic power sources that is consumed in the entire grid system, the more the entire grid system relies on the electricity provided by photovoltaic power generation. Due to the instability of photovoltaic power generation, the wider the frequency band of oscillations caused, the greater the impact on the stability of photovoltaic grid connection.

[0107] Therefore, in the process of distributed photovoltaic power generation, the proportion of power generation on the supply side to power consumption on the load side is analyzed. Combined with the relative difference coefficient, the oscillation significance is calculated to assess the impact of different generator sets on the supply side and the interaction between the supply side and the grid on grid connection stability. Specifically:

[0108] The ratio of the average power generation of the power supply side at all times within each time window to the average power consumption of the load side at all times within each time window is calculated and used as the proportional coefficient for each time window.

[0109] Based on the preset first weight and the preset second weight, the relative difference coefficient and the proportional coefficient are weighted and summed and then normalized to obtain the oscillation significance of each time window. 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 operating status between different generator sets, the greater the impact of wideband oscillation caused by frequent adjustments to the equipment on grid connection stability, the first preset weight is greater than the second preset weight. Therefore, the first preset weight is set to 0.6 and the second preset weight is set to 0.4. As other implementation methods, implementers can set these values ​​according to actual conditions. Secondly, the sigmoid function is used for normalization. The sigmoid function is a well-known technology and will not be described in detail here. As other implementation methods, implementers can use other methods of the prior art, such as the tanh function. This embodiment does not impose any special restrictions on this.

[0111] It should be noted that the larger the ratio coefficient, the higher the proportion of photovoltaic power generation in the total power supply, and the greater the impact on grid connection stability. The greater the oscillation significance, the more significant the broadband oscillation may exist 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 oscillations. When suppressing broadband oscillations by adjusting the damping coefficient of VSG technology, a larger 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 less impact it is on broadband oscillations. Therefore, a smaller damping coefficient should be set to adapt to different operating conditions.

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

[0114] The formula for calculating the damping coefficient for each time window is as follows:

[0115] D i =α+(β-α)×Z i

[0116] Among them, D i Z is the damping coefficient for the i-th time window, α is the preset minimum damping coefficient, β is the preset maximum damping coefficient, and Z is the damping coefficient for the ith time window. i Let represent the oscillation significance of the i-th time window.

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

[0118] Therefore, based on the damping coefficient, the damping performance of the inverter is adjusted through VSG technology, thereby suppressing the broadband oscillation of the grid system after photovoltaic grid connection.

[0119] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but may be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but may be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0120] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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, they should be considered to be within the scope of this specification.

[0121] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application, without departing from the content of the technical solution of this application, shall fall within the protection scope of the technical solution of this application.

Claims

1. A method for suppressing broadband oscillations in new energy grid connection based on inverter damping control, characterized in that, The method includes the following steps: Real-time acquisition of the output current and output power of each generator set after the new energy is connected to the grid, as well as the power generation on the power supply side and the power consumption on the load side after the new energy is connected to the grid; Set a preset time window; 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 symmetrical distribution of interharmonics, and determine the harmonic influence of each generator set in each time window. By analyzing the differences in harmonic variations of the output current in the frequency domain between each time window and other time windows, the time-varying characteristic value of each generator set in each time window is determined. Combined with the harmonic influence degree, the state evaluation value of each generator set in each time window is obtained. Modal decomposition is performed on the output power of each generator set within each time window. The average energy level of different modal components under all frequency components in the frequency domain, as well as the average output power level within each time window, are analyzed. Combined with the state assessment value, a characteristic distribution sequence is constructed. The relative difference coefficient of each time window is calculated by the differences in the characteristic distribution sequences of different generator sets under each time window. The proportion of power generation on the power supply side to power consumption on the load side is analyzed in each time window. Based on the relative difference coefficient, the oscillation significance of each time window is determined. Based on the oscillation significance, the damping coefficient of each time window is determined. Combined with the VSG control algorithm, the broadband oscillation of new energy grid connection is suppressed.

2. The method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 1, characterized in that, The further measurement process for the aforementioned proportion is as follows: Frequency domain analysis was performed on all output currents of each generator set within each time window to obtain the spectrum. Obtain all peaks in the spectrum; denote the frequency component corresponding to the maximum peak in the spectrum as the fundamental component; The sum of the energy corresponding to all frequency components in the spectrum other than the fundamental component is denoted as the total harmonics. The ratio between the total amount of harmonics and the sum of the energies corresponding to all frequency components in the spectrum is calculated and denoted as the harmonic percentage.

3. The method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 2, characterized in that, The determination of the harmonic impact degree of each generator set in each time window includes: The frequency components that are non-integer multiples of the fundamental component in the spectrum are denoted as interharmonic components; the interharmonic components on both sides of the fundamental component are numbered starting from the fundamental component. Calculate the metric distance between the frequency corresponding to each interharmonic component and the frequency corresponding to the fundamental component; record the difference in the metric distance between the interharmonic components with the same index on the left and right sides of the fundamental component as the relative difference; The sum of all the relative differences between the left and right sides of the fundamental component is denoted as the asymmetry coefficient. The harmonic influence is the product of the asymmetry coefficient and the harmonic proportion.

4. The method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 3, characterized in that, The determination of the time-varying characteristic values ​​of each generator set in each time window includes: The frequencies corresponding to each interharmonic component in the spectrum and their corresponding energies are combined into a two-dimensional array; Arrange all two-dimensional arrays in the spectrum diagram under each time window in descending order according to the frequency corresponding to the interharmonic components to form an interharmonic sequence; The time-varying characteristic value is the reciprocal of the mean of the distances between each time window and the interharmonic sequences of the preceding multiple time windows.

5. The method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 1, characterized in that, The process of obtaining the status evaluation value of each generator set in each time window includes: Calculate the average value of the harmonic influence for each time window and multiple time windows prior to each generator set; The state evaluation value is the product of the average value and the time-varying feature value.

6. The method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 1, characterized in that, The process of constructing the feature distribution sequence is as follows: Frequency domain analysis is performed on each modal component to obtain the spectrum; the average energy is the mean of the energy corresponding to all frequency components in the spectrum of each modal component. Calculate the average output power of each generator set within each time window, and denot it as the average power. The state assessment value, the average power, and the average energy of all modal components are used. Composition of characteristic distribution sequences.

7. The method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 1, characterized in that, The relative difference coefficient is the sum of the distances between the characteristic distribution sequences of all two generator sets under each time window.

8. The method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 1, characterized in that, The further measurement process of the proportion is as follows: calculate the ratio between the average power generation of the power supply side at all times in each time window and the average power consumption of the load side at all times in each time window, and use it as the proportion coefficient for each time window.

9. The method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 8, characterized in that, Determining the oscillation significance of each time window includes: Based on the preset first weight and the preset second weight, the relative difference coefficient and the proportional coefficient are weighted and summed and then normalized to obtain the oscillation significance of each time window. 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 method for suppressing broadband oscillations in new energy grid connection based on inverter damping control as described in claim 1, characterized in that, The damping coefficient D in 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 Let represent the normalized oscillation significance under the i-th time window.

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