A photovoltaic power station grid-connected harmonic detection and dynamic compensation control system and method

Abstract

The application provides a kind of photovoltaic power station grid-connected harmonic detection and dynamic compensation control system, method, related to compensation control technical field, system includes: harmonic detection module, harmonic analysis and parameter calculation are carried out to grid-connected point current voltage signal;Dynamic compensation module, based on grid-connected harmonic key parameter trend prediction, combined with photovoltaic inverter operating state and harmonic trend parameter dynamic compensation analysis;Compensation control module, compensation current is injected into power grid, and real-time monitoring obtains the power grid operating state parameters and grid-connected system operating state parameters in compensation process;Self-adaptive adjustment module, initial compensation current parameter is regulated and controlled calculation, and feedback closed-loop control is carried out through compensation current correction amount.The application can solve the technical problems of low precision of photovoltaic power station grid-connected harmonic detection and dynamic compensation control in the prior art, and achieve the technical effect of improving the precision of harmonic detection and dynamic compensation control.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of compensation control, in particular to a photovoltaic power station grid-connected harmonic detection and dynamic compensation control system and method. BACKGROUND

[0002] With the continuous expansion of photovoltaic power generation scale and the increasing proportion of renewable energy in the power system, the influence of photovoltaic power station grid-connected operation on power grid power quality is increasingly prominent.

[0003] At present, existing photovoltaic inverters will generate harmonics of different frequencies during grid connection. The superposition of these harmonics in the power grid will cause problems such as voltage waveform distortion, increased current harmonics, and decreased power factor. In severe cases, it may cause overheating of power equipment, insulation damage, and even system tripping. In addition, the output of photovoltaic power stations is greatly affected by environmental factors such as light intensity, temperature changes, and the operating state of the inverter itself, making the harmonic characteristics exhibit strong nonlinearity and dynamic variation characteristics. Traditional harmonic suppression methods mainly rely on passive filters or fixed-parameter active filters, and their compensation effect depends on preset parameters, making it difficult to adapt to the rapid fluctuations of photovoltaic output. Therefore, there are obvious limitations in harmonic suppression accuracy and response speed. For example, when the conventional active filter cannot adjust the compensation current in time when the output power suddenly increases from 200 kilowatts to 400 kilowatts due to sudden increase in light intensity, the 3rd harmonic amplitude increases from 0.8 amperes to 1.2 amperes, and the total harmonic distortion of the power grid increases from 5% to 8%, which seriously affects the power quality.

[0004] In summary, the existing technology lacks real-time monitoring, dynamic analysis, and intelligent closed-loop compensation control of photovoltaic grid-connected harmonics, resulting in unstable harmonic compensation effect and slow response speed, which further affects the power quality of the power grid, the safety of photovoltaic inverter operation, and the stability and reliability of the entire power system. SUMMARY

[0005] The purpose of the present application is to provide a photovoltaic power station grid-connected harmonic detection and dynamic compensation control system and method to solve the technical problem that the lack of real-time monitoring, dynamic analysis, and intelligent closed-loop compensation control of photovoltaic grid-connected harmonics in the existing technology leads to unstable harmonic compensation effect and slow response speed, which further affects the power quality of the power grid, the safety of photovoltaic inverter operation, and the stability and reliability of the entire power system.

[0006] In view of the above problems, the present application provides a photovoltaic power station grid-connected harmonic detection and dynamic compensation control system and method.

[0007] In a first aspect, the application provides a photovoltaic power station grid-connected harmonic detection and dynamic compensation control system, comprising: a harmonic detection module, configured to collect grid-connected point current and voltage signals of a target photovoltaic power station using a voltage and current transformer, perform harmonic analysis and parameter calculation on the grid-connected point current and voltage signals, and obtain grid-connected harmonic key parameters; a dynamic compensation module, configured to perform trend prediction based on the grid-connected harmonic key parameters, determine harmonic trend parameters, perform dynamic compensation analysis in combination with photovoltaic inverter operating states and the harmonic trend parameters, and generate initial compensation current parameters; a compensation control module, configured to control a harmonic compensation device to inject compensation current into a power grid based on the initial compensation current parameters, and monitor grid operating state parameters and grid-connected system operating state parameters obtained in a compensation process in real time; and an adaptive adjustment module, configured to perform regulation calculation on the initial compensation current parameters based on the grid operating state parameters and the grid-connected system operating state parameters, determine a compensation current correction amount, and perform feedback closed-loop control through the compensation current correction amount.

[0008] Preferably, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system further comprises: an initialization unit, configured to perform noise identification on the grid-connected point current and voltage signals, obtain multi-frequency noise distribution characteristics, and initialize a digital filter according to the multi-frequency noise distribution characteristics; a filter preprocessing unit, configured to perform filter preprocessing on the grid-connected point current and voltage signals using the digital filter, and obtain available grid-connected point current and voltage signals; a window processing unit, configured to select a target window function according to harmonic detection accuracy, perform window processing on the available grid-connected point current and voltage signals based on the target window function, and obtain standard grid-connected point current and voltage signals; and a harmonic analysis unit, configured to perform harmonic analysis and parameter calculation based on the standard grid-connected point current and voltage signals, and obtain grid-connected harmonic key parameters.

[0009] Preferably, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system further comprises: a normalization processing subunit, configured to perform normalization processing and Fourier transform on the standard grid-connected point current and voltage signals, and obtain grid-connected point current and voltage frequency domain signals; a three-spectral-line interpolation correction subunit, configured to perform three-spectral-line interpolation correction on the grid-connected point current and voltage frequency domain signals, and obtain grid-connected point current and voltage correction signals; a harmonic component identification subunit, configured to perform frequency spectrum distribution analysis and harmonic component identification based on the grid-connected point current and voltage correction signals, and determine harmonic component identification information; and a key parameter calculation subunit, configured to perform key parameter calculation on the harmonic component identification information according to a harmonic key analysis index set, and obtain the grid-connected harmonic key parameters.

[0010] Preferably, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system further comprises: a sequence division identification unit, configured to collect photovoltaic power station grid-connected historical harmonic data, perform sequence division identification on the photovoltaic power station grid-connected historical harmonic data according to a preset prediction period, and obtain photovoltaic power station grid-connected historical harmonic samples; a verification and tuning unit, configured to perform prediction training and verification tuning on the photovoltaic power station grid-connected historical harmonic samples using an ARIMA network structure, and generate a harmonic trend predictor; and a trend prediction unit, configured to perform trend prediction on the grid-connected harmonic key parameters based on the harmonic trend predictor, and determine the harmonic change trend parameters.

[0011] Preferably, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system further comprises: an association model establishing unit, configured to establish an inverter operating state-harmonic parameter association model; a harmonic influence evaluation unit, configured to perform harmonic influence evaluation on the photovoltaic inverter operating state based on the inverter operating state-harmonic parameter association model, and determine harmonic change influence parameters; a parameter appending unit, configured to append the harmonic change influence parameters to the harmonic change trend parameters to obtain harmonic comprehensive change parameters; and a dynamic compensation analysis unit, configured to set a harmonic compensation target, perform dynamic compensation analysis on the harmonic comprehensive change parameters according to the harmonic compensation target, and generate the initial compensation current parameters.

[0012] Preferably, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system further comprises: a correlation analysis subunit, configured to sequentially perform correlation analysis on each of the photovoltaic inverter operating parameters and the grid-connected harmonic key parameters, and obtain inverter operating parameter correlation coefficients; a preferred subunit, configured to perform preference on the photovoltaic inverter operating parameters according to the inverter operating parameter correlation coefficients, and obtain inverter key operating parameters; and an association model establishing subunit, configured to perform multiple regression fitting and significance test optimization on the inverter key operating parameters as independent variables and the grid-connected harmonic key parameters as dependent variables, and establish the inverter operating state-harmonic parameter association model.

[0013] Preferably, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system further comprises: an association feature extraction unit, configured to perform association feature extraction on the power grid operating state parameters and the grid-connected system operating state parameters, and obtain a power grid harmonic compensation feature set; a compensation effect evaluation unit, configured to perform compensation effect evaluation on the power grid harmonic compensation feature set according to a harmonic compensation evaluation index set, and obtain a harmonic compensation effect parameter; and a regulation and control calculation unit, configured to perform regulation and control calculation on the initial compensation current parameters based on the harmonic compensation effect parameter, and determine a compensation current correction amount.

[0014] Preferably, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system further comprises: a compensation current correction direction determination subunit, configured to determine a compensation current correction direction based on the harmonic compensation effect parameter regulating and analyzing the initial compensation current parameter; a current correction amount selection threshold generation subunit, configured to generate a current correction amount selection threshold based on the harmonic compensation effect parameter regulating and analyzing the initial compensation current parameter according to the compensation current correction direction; and a global optimization subunit, configured to determine a compensation current correction amount based on global optimization of the harmonic compensation evaluation index set within the current correction amount selection threshold.

[0015] Preferably, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system further comprises: an initialization channel configured to initialize a harmonic compensation particle space according to the current correction amount selection threshold; and an iterative simulation optimization channel configured to determine the compensation current correction amount based on iterative simulation optimization of the harmonic compensation evaluation index set within the harmonic compensation particle space.

[0016] In a second aspect, the present application also provides a photovoltaic power station grid-connected harmonic detection and dynamic compensation control method, comprising: using a voltage current transformer to collect grid-connected point current voltage signals of a target photovoltaic power station, performing harmonic analysis and parameter calculation on the grid-connected point current voltage signals to obtain grid-connected harmonic key parameters; performing trend prediction based on the grid-connected harmonic key parameters to determine harmonic trend parameters, combining photovoltaic inverter operating states and the harmonic trend parameters to perform dynamic compensation analysis to generate initial compensation current parameters; controlling a harmonic compensation device to inject compensation current into the power grid based on the initial compensation current parameters, and monitoring to obtain power grid operating state parameters and grid-connected system operating state parameters in a compensation process in real time; performing regulating and calculating the initial compensation current parameters based on the power grid operating state parameters and the grid-connected system operating state parameters to determine a compensation current correction amount, and performing feedback closed-loop control through the compensation current correction amount.

[0017] The technical solutions provided in the present application have at least the following technical effects or advantages: by achieving the technical target of real-time detection, trend prediction and dynamic compensation of photovoltaic grid-connected harmonics, the technical effects of fast response to harmonic fluctuations, accurate control of compensation current, effective reduction of harmonic amplitude and total harmonic distortion, and improvement of power grid power quality and photovoltaic inverter operating reliability are achieved.

[0018] The above description is only a summary of the technical solutions of the present application. In order to enable the technical means of the present application to be more clearly understood, and to be implemented according to the content of the description, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more apparent and easy to understand, the following specific embodiments of the present application are described. It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present application, nor is it intended to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only exemplary, and other drawings can be obtained by the provided drawings without creative labor for those skilled in the art.

[0020] Figure 1 The structure schematic diagram of a photovoltaic power station grid-connected harmonic detection and dynamic compensation control system of the present application.

[0021] Figure 2 The flowchart of a photovoltaic power station grid-connected harmonic detection and dynamic compensation control method of the present application.

[0022] Explanation of reference signs: harmonic detection module 1, dynamic compensation module 2, compensation control module 3, adaptive adjustment module 4. DETAILED DESCRIPTION

[0023] The present application provides a photovoltaic power station grid-connected harmonic detection and dynamic compensation control system and method, which solves the technical problem in the prior art that due to the lack of real-time monitoring, dynamic analysis and intelligent closed-loop compensation control means for photovoltaic grid-connected harmonics, the harmonic compensation effect is unstable and the response speed is slow, which further affects the power quality of the power grid, the operation safety of the photovoltaic inverter and the stability and reliability of the entire power system. The technical target of real-time detection, trend prediction and dynamic compensation of photovoltaic grid-connected harmonics is achieved, and the technical effects of fast response to harmonic fluctuation, accurate control of compensation current, effective reduction of harmonic amplitude and total harmonic distortion, and improvement of power quality of the power grid and operation reliability of the photovoltaic inverter are achieved.

[0024] Below, the technical solutions in the present application will be described clearly and completely with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. It should be understood that the present application is not limited by the example embodiments described herein. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, not all.

[0025] Embodiment one, please refer to the attached Figure 1 The present application provides a kind of photovoltaic power station grid-connected harmonic detection and dynamic compensation control system, specifically includes:

[0026] Harmonic detection module 1, for using voltage current transformer acquisition target photovoltaic power station's grid-connected point current voltage signal, harmonic analysis and parameter calculation are carried out to the grid-connected point current voltage signal, obtain grid-connected harmonic key parameter.

[0027] Further, the present application also includes: initialization unit, for carrying out noise identification to the grid-connected point current voltage signal, obtains the multi-frequency noise distribution characteristics, and initializes digital filter according to the multi-frequency noise distribution characteristics;Filter pre-processing unit, for using the digital filter to carry out filter pre-processing to the grid-connected point current voltage signal, obtains available grid-connected point current voltage signal;Window processing unit, for selecting target window function according to harmonic detection accuracy, obtains standard grid-connected point current voltage signal based on the target window function to the available grid-connected point current voltage signal carries out window processing;Harmonic analysis unit, for carrying out harmonic analysis and parameter calculation based on the standard grid-connected point current voltage signal, obtains grid-connected harmonic key parameter.

[0028] Further, the present application also includes: normalization processing subunit, for carrying out normalization processing and Fourier transform to the standard grid-connected point current voltage signal, obtains grid-connected point current voltage frequency domain signal;Three spectral line interpolation correction subunit, for carrying out three spectral line interpolation correction to the grid-connected point current voltage frequency domain signal, obtains grid-connected point current voltage correction signal;Harmonic component identification subunit, for carrying out frequency spectrum distribution analysis and harmonic component identification based on the grid-connected point current voltage correction signal, determines harmonic component identification information;Key parameter calculation subunit, for carrying out key parameter calculation to the harmonic component identification information according to harmonic key analysis index set, obtains the grid-connected harmonic key parameter.

[0029] Specifically, the voltage and current signals of the grid-connected point of the target photovoltaic power station are collected using a voltage and current transformer, i.e., real-time voltage and current data are obtained at the node where the photovoltaic power station is connected to the public grid using a measuring device. The voltage transformer is a device that converts high voltage into low voltage in proportion for measurement; the current transformer is a device that converts large current into small current in proportion for accurate measurement of the current size of the grid-connected point. The voltage and current signals of the grid-connected point are waveform information of electrical quantities at the connection point of the photovoltaic power station output end and the grid, containing fundamental wave, harmonic and noise components.

[0030] The voltage and current signals of the grid-connected point are subjected to noise identification, i.e., waveform data of the current and voltage at the node where the photovoltaic power station is connected to the grid are obtained, and then the interference components therein are identified, i.e., the strength distribution of noise in different frequency ranges is analyzed to obtain the multi-frequency noise distribution characteristics. For example, there may be small noise near the 50 Hz fundamental wave, and the noise amplitude is large near the harmonic frequencies of 150 Hz or 250 Hz.

[0031] Based on the multi-frequency noise distribution characteristics, a digital filter can be initialized, which is a filtering tool realized by mathematical calculation, and can suppress or pass specific signals according to the designed frequency range, thereby providing clean input for subsequent processing.

[0032] Then, the voltage and current signals of the grid-connected point are subjected to filtering preprocessing using the digital filter, so that the high-frequency noise or low-frequency interference therein is weakened, leaving more clear voltage and current information, and obtaining usable voltage and current signals of the grid-connected point, i.e., data that is free of the main noise influence and can be directly used for subsequent analysis.

[0033] Then, a target window function is selected according to the harmonic detection accuracy, which is used to control the balance between spectral leakage and resolution. The usable voltage and current signals of the grid-connected point are subjected to windowing processing based on the target window function, i.e., the current and voltage signals are multiplied by the target window function, so that the truncated signal is more clear in the frequency domain, and a standard voltage and current signal of the grid-connected point is obtained, which can accurately reflect the amplitude and phase of different frequency components.

[0034] Finally, the standard grid-connected point current and voltage signals are normalized and Fourier transformed. The collected signal values are normalized to adjust them to a uniform numerical range, avoiding unstable calculation due to excessively large or small amplitude. Fourier transform is a mathematical operation method that can decompose time-domain signals into frequency domain, thereby revealing the amplitude and phase of different frequency components in the signal. The grid-connected point current and voltage frequency domain signals obtained are frequency spectrum information with frequency as the horizontal axis and amplitude as the vertical axis. For example, when the time-domain signal voltage fluctuates between 0 and 1000 volts, it can be scaled to the interval of 0 to 1 through normalization, and after Fourier transform, the frequency spectrum may show that there is a significant fundamental component at 50 Hz, and harmonic peaks exist at 150 Hz and 250 Hz.

[0035] The grid-connected point current and voltage frequency domain signals are corrected by three-spectrum line interpolation, that is, the information of the target frequency point and its adjacent two frequency points in the grid-connected point current and voltage frequency domain signals is used to correct the amplitude and phase error of the frequency spectrum by mathematical interpolation. Three-spectrum line interpolation can reduce the deviation caused by spectrum leakage, making the frequency components closer to the true values. The corrected grid-connected point current and voltage signals are more accurate frequency spectrum signals.

[0036] Based on the corrected grid-connected point current and voltage signals, spectrum distribution analysis and harmonic component identification are performed, that is, the overall distribution of the corrected frequency spectrum data is analyzed to find the amplitude and position of the fundamental and each harmonic. Harmonic component identification determines the frequencies that belong to harmonics in the frequency spectrum, as well as the specific amplitude and phase, thereby forming harmonic component identification information.

[0037] According to the harmonic key analysis index set, key parameter calculation is performed on the harmonic component identification information, that is, the identified harmonic data is quantitatively calculated, such as total harmonic distortion, harmonic proportion, harmonic power factor, etc. The obtained grid-connected harmonic key parameters are numerical sets after calculation, which can be used as the basis for subsequent trend prediction and compensation control.

[0038] The dynamic compensation module 2 is used to perform trend prediction based on the grid-connected harmonic key parameters, determine harmonic change trend parameters, combine the photovoltaic inverter operating state and the harmonic change trend parameters to perform dynamic compensation analysis, and generate initial compensation current parameters.

[0039] Further, the application further comprises: a sequence division identification unit, configured to collect grid-connected historical harmonic data of a photovoltaic power station, perform sequence division identification on the grid-connected historical harmonic data of the photovoltaic power station according to a preset prediction period, and obtain grid-connected historical harmonic samples of the photovoltaic power station; a verification and tuning unit, configured to perform prediction training and verification tuning on the grid-connected historical harmonic samples of the photovoltaic power station by using an ARIMA network structure, and generate a harmonic trend predictor; and a trend prediction unit, configured to perform trend prediction on the grid-connected harmonic key parameters based on the harmonic trend predictor, and determine the harmonic change trend parameters.

[0040] Further, the application further comprises: a correlation model establishing unit, configured to establish an inverter operating state-harmonic parameter correlation model; a harmonic influence evaluation unit, configured to perform harmonic influence evaluation on the photovoltaic inverter operating state based on the inverter operating state-harmonic parameter correlation model, and determine harmonic change influence parameters; a parameter appending unit, configured to append the harmonic change influence parameters to the harmonic change trend parameters to obtain harmonic comprehensive change parameters; and a dynamic compensation analysis unit, configured to set a harmonic compensation target, perform dynamic compensation analysis on the harmonic comprehensive change parameters according to the harmonic compensation target, and generate the initial compensation current parameters.

[0041] Further, the application further comprises: a correlation analysis subunit, configured to sequentially perform correlation analysis on each of the grid-connected harmonic key parameters and photovoltaic inverter operating parameters, and obtain inverter operating parameter correlation coefficients; an optimization subunit, configured to perform optimization on the photovoltaic inverter operating parameters according to the inverter operating parameter correlation coefficients, and obtain inverter key operating parameters; and a correlation model establishing subunit, configured to perform multiple regression fitting and significance test optimization by taking the inverter key operating parameters as independent variables and the grid-connected harmonic key parameters as dependent variables, and establish the inverter operating state-harmonic parameter correlation model.

[0042] Specifically, the grid-connected historical harmonic data of the photovoltaic power station is collected, that is, the amplitude, frequency and other information of harmonics in current and voltage are recorded at the node where the photovoltaic power station accesses the power grid, reflecting the contribution of the power station to the power grid harmonics at different time periods. The grid-connected historical harmonic data of the photovoltaic power station is divided and identified according to a preset prediction period, and is divided at a certain time interval, for example, 1 hour as a period, to form a group of data sequences, and then the grid-connected historical harmonic samples of the photovoltaic power station are obtained.

[0043] The ARIMA network structure is used to predict, train and verify the historical harmonic samples of the grid-connected photovoltaic power station, that is, a time series modeling method combining autoregression, difference and moving average is used to analyze the sample data. The prediction training is to let the ARIMA network structure learn the change rule of the harmonic in the historical sample, and the verification and optimization is to adjust the parameters to improve the prediction accuracy of the ARIMA network structure, and then the generated harmonic trend predictor is the final established mathematical model, which can be used to predict the harmonic change in the future period.

[0044] Based on the harmonic trend predictor, the trend of the grid-connected harmonic key parameters is predicted, the possible change trend in the future period is calculated, and the harmonic change trend parameters are determined, that is, the prediction results are converted into quantitative indicators, for example, the 3rd harmonic may increase by 20% in the next 2 hours, the 5th harmonic may remain unchanged, and the total harmonic distortion rate may rise by 5%, which can reflect the dynamic trend of the future harmonic level.

[0045] The harmonic data of the grid-connected harmonic key parameters, such as the amplitude of each harmonic, the phase and the total harmonic distortion rate, are sequentially correlated with the output power, voltage, current, switching frequency and temperature in the photovoltaic inverter operating parameters, and the correlation degree is calculated. The results of the correlation analysis are represented by the inverter operating parameter correlation coefficient, the coefficient range is between-1 and 1, which is used to measure the strength and direction of the linear relationship between two variables, for example, the correlation coefficient between the 5th harmonic amplitude and the inverter switching frequency is 0.85, which means that the 5th harmonic amplitude increases significantly when the switching frequency increases.

[0046] According to the size of the inverter operating parameter correlation coefficient, the photovoltaic inverter operating parameters are optimized, and the most sensitive inverter operating parameters to harmonic change are selected as the inverter key operating parameters. Through optimization, the model input can be simplified, the calculation efficiency can be improved, and the main influencing factors can be retained, for example, among the many operating parameters, the output power, the switching frequency and the DC bus voltage are selected as the key parameters, while the parameters with small influence of temperature change on the harmonic are ignored.

[0047] The inverter key operating parameters are used as independent variables and the grid-connected harmonic key parameters are used as dependent variables for multiple regression fitting and significance test optimization, and the inverter operating state-harmonic parameter correlation model is established, that is, the multiple regression method is used to establish a mathematical function relationship between the key operating parameters and the harmonic parameters, and the insignificant variables are removed through significance test, so as to obtain a reliable model for predicting and analyzing the influence of different operating states on the harmonic, for example, the model shows that when the output power increases from 400 kW to 500 kW, the 5th harmonic amplitude may increase from 0.8 A to 1.0 A, and the change of the switching frequency has little effect on the 3rd harmonic amplitude.

[0048] The harmonic change influence parameter is obtained by evaluating the influence of the current operating state of the photovoltaic inverter on the harmonic based on the inverter operating state-harmonic parameter correlation model. The harmonic change influence parameter is a quantitative result used to represent the contribution or interference intensity of each operating state on different harmonics. For example, when the inverter output power is 500 kW and the temperature is 45°C, the 3rd harmonic may increase by 0.3 A, while the 7th harmonic hardly changes.

[0049] The harmonic change influence parameter is added to the harmonic change trend parameter to obtain a harmonic comprehensive change parameter, that is, the future trend information obtained by prediction is combined with the influence of the current inverter operating state on the harmonic to form a comprehensive index. The harmonic comprehensive change parameter can reflect the influence of the time series trend and the operating state at the same time. For example, the 3rd harmonic trend is predicted to increase by 0.2 A in the next 1 hour, combined with the operating state influence to increase by 0.3 A, and the comprehensive change is 0.5 A.

[0050] A harmonic compensation target is set, and a dynamic compensation analysis is performed on the harmonic comprehensive change parameter according to the harmonic compensation target to generate an initial compensation current parameter, that is, a compensation strategy is formulated according to the allowed harmonic limit or power quality requirement of the power grid, and the compensation current amplitude and phase to be injected are calculated. The initial compensation current parameter is the starting instruction of the compensation control system. For example, in order to control the total harmonic distortion rate within 5%, the compensation current of 0.4 A for the 3rd harmonic and 0.2 A for the 5th harmonic needs to be injected.

[0051] The compensation control module 3 is used to control the harmonic compensation device to inject compensation current into the power grid based on the initial compensation current parameter, and to monitor the power grid operating state parameters and grid-connected system operating state parameters in real time during the compensation process.

[0052] Specifically, the harmonic compensation device is controlled to inject compensation current into the power grid based on the initial compensation current parameter, that is, the initial compensation current amplitude and phase calculated are used as control instructions to let the harmonic compensation device inject current into the power grid to offset or weaken the harmonics in the power grid. The harmonic compensation device includes an active filter or an inverter, which can generate a current opposite to the harmonic component according to the control signal, thereby improving the power quality of the power grid. For example, if the 3rd harmonic current amplitude is measured to be 1 A, the initial compensation current parameter calculates that 0.8 A of reverse current needs to be injected.

[0053] The grid operation state parameters and grid-connected system operation state parameters in the compensation process are monitored in real time, that is, while the compensation current is injected, the data of voltage, current, total harmonic distortion rate and the like at the grid end, and the output power, voltage, current, switching frequency and the like of the photovoltaic inverter are continuously collected. The grid operation state parameters reflect the compensation effect and grid stability, and ensure that the compensation does not cause new problems; the grid-connected system operation state parameters are used to judge the response of the inverter and the compensation device, and ensure the control accuracy. For example, after 0.8 ampere compensation current is injected, it is found through monitoring that the total harmonic distortion rate decreases from 6% to 3%, and at the same time, the inverter current fluctuation is about 500 amperes, indicating that the compensation process is stable and effective.

[0054] The adaptive adjustment module 4 is configured to perform regulation calculation on the initial compensation current parameter based on the grid operation state parameters and grid-connected system operation state parameters, determine a compensation current correction amount, and perform feedback closed-loop control through the compensation current correction amount.

[0055] Further, the application further comprises: an associated feature extraction unit configured to extract associated features of the grid operation state parameters and grid-connected system operation state parameters to obtain a grid harmonic compensation feature set; a compensation effect evaluation unit configured to evaluate the grid harmonic compensation feature set according to a harmonic compensation evaluation index set to obtain a harmonic compensation effect parameter; and a regulation calculation unit configured to perform regulation calculation on the initial compensation current parameter based on the harmonic compensation effect parameter to determine a compensation current correction amount.

[0056] Further, the application further comprises: a compensation current correction direction determination subunit configured to perform regulation analysis on the initial compensation current parameter based on the harmonic compensation effect parameter to determine a compensation current correction direction; a current correction amount selection threshold generation subunit configured to perform regulation analysis on the initial compensation current parameter based on the harmonic compensation effect parameter according to the compensation current correction direction to generate a current correction amount selection threshold; and a global optimization subunit configured to perform global optimization within the current correction amount selection threshold based on the harmonic compensation evaluation index set to determine a compensation current correction amount.

[0057] Further, the application further comprises: an initialization channel configured to initialize a harmonic compensation particle space according to the current correction amount selection threshold; and an iterative simulation optimization channel configured to perform iterative simulation optimization within the harmonic compensation particle space based on the harmonic compensation evaluation index set to determine the compensation current correction amount.

[0058] Specifically, the grid operating state parameters and grid-connected system operating state parameters are associated with feature extraction to obtain a grid harmonic compensation feature set, that is, from real-time collected grid parameters such as voltage, current, total harmonic distortion rate, and inverter operating parameters such as output power, switching frequency, bus voltage, etc., the most representative and sensitive feature information for harmonic compensation effect is extracted through mathematical methods. Further, the grid harmonic compensation feature set is sorted and used for subsequent analysis.

[0059] The grid harmonic compensation feature set is evaluated according to the harmonic compensation evaluation index set to obtain a harmonic compensation effect parameter, that is, the extracted features are analyzed using a pre-defined index system such as harmonic suppression amplitude, total harmonic distortion rate improvement value, and harmonic reduction ratio to quantify the effect of the current compensation scheme. The harmonic compensation effect parameter is a quantitative result, for example, the 3rd harmonic amplitude is reduced from 1 ampere before injection to 0.3 ampere after compensation, and the total harmonic distortion rate is reduced from 6% to 3%, and the evaluation result shows that the compensation effect is good.

[0060] Based on the harmonic compensation effect parameter obtained in the closed-loop feedback evaluation, the initial compensation current parameter is analyzed, for example, the decrease of each harmonic amplitude and the improvement of the total harmonic distortion rate, to analyze whether the initial injected current needs to be increased or decreased, and how to adjust the amplitude or phase, and then determine the compensation current correction direction and the adjustment trend, for example, the 3rd harmonic is injected at 0.3 ampere, which is still higher than the ideal value of 0.2 ampere, so the correction direction is to reduce; the 5th harmonic is injected at 0.2 ampere, which is insufficient, so the correction direction is to increase.

[0061] According to the compensation current correction direction, the initial compensation current parameter is analyzed based on the harmonic compensation effect parameter to generate a current correction amount selection threshold, that is, a reasonable correction amplitude range is calculated. The current correction amount selection threshold defines the upper and lower limits of the compensation current that can be increased or decreased to prevent system oscillation or compensation failure caused by excessive adjustment. For example, the 3rd harmonic correction direction is to reduce, and the correction amount threshold can be set to 0 to 0.1 ampere, and the 5th harmonic correction direction is to increase, and the threshold is 0 to 0.05 ampere.

[0062] According to the current correction amount selection threshold, the harmonic compensation particle space is initialized, that is, the calculated current correction amplitude range is used as the boundary to construct a searchable solution space as the harmonic compensation particle space. Each "particle" represents a possible compensation current correction scheme, including the amplitude and phase combination of each harmonic. For example, if the 3rd harmonic correction amount threshold is 0 to 0.1 ampere and the 5th harmonic is 0 to 0.05 ampere, the particle space can contain all possible schemes combined with 0 to 0.1 ampere and 0 to 0.05 ampere, which can be used for subsequent optimization search.

[0063] Based on the harmonic compensation evaluation index set, such as the amplitude change of each harmonic, the improvement of total harmonic distortion rate, and the stability of power grid, etc., iterative simulation optimization is carried out in the harmonic compensation particle space, and the particle position is updated through multiple iterations to find the correction amount that optimizes the harmonic compensation effect and determine the compensation current correction amount. Iterative simulation optimization can use algorithms such as particle swarm optimization or genetic algorithm. For example, through iteration, the optimal correction amount of the 3rd harmonic is to reduce 0.08 amperes, and the optimal correction amount of the 5th harmonic is to increase 0.04 amperes, so that the total harmonic distortion rate is further reduced from 3% to 2.5%.

[0064] The compensation current correction amount is used for feedback closed-loop control, i.e., the calculated compensation current correction amount is used as a control instruction to adjust the output current of the harmonic compensation device in real time, so that the harmonics in the power grid are continuously optimized. Feedback closed-loop control is an automatic control method in which the output state is continuously measured, the measurement result is compared with the target value, the correction amount is calculated according to the difference, and the control signal is adjusted, so that the ideal state is gradually approached. The compensation current correction amount is an adjustment signal that can change the amplitude or phase of each harmonic, for example, the 3rd harmonic is reduced to 0.22 amperes by injecting a correction current of 0.08 amperes, the 5th harmonic is increased to 0.24 amperes by increasing a correction current of 0.04 amperes, and the total harmonic distortion rate is reduced from the initial 6% to 2.5%.

[0065] In summary, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system provided by the present application has the following technical effects: by achieving the technical target of real-time detection, trend prediction and dynamic compensation of photovoltaic grid-connected harmonics, the technical effects of fast response to harmonic fluctuations, accurate control of compensation current, effective reduction of the amplitude of each harmonic and total harmonic distortion rate, and improvement of power quality and operation reliability of the power grid and photovoltaic inverter are achieved.

[0066] Embodiment two, based on the same inventive concept as the photovoltaic power station grid-connected harmonic detection and dynamic compensation control system in the foregoing embodiments, the present application also provides a photovoltaic power station grid-connected harmonic detection and dynamic compensation control method, please refer to the attached Figure 2comprises: acquiring grid-connected point current and voltage signals of a target photovoltaic power station using a voltage and current transformer, performing harmonic analysis and parameter calculation on the grid-connected point current and voltage signals to obtain grid-connected harmonic key parameters; performing trend prediction based on the grid-connected harmonic key parameters to determine harmonic trend parameters, performing dynamic compensation analysis in combination with photovoltaic inverter operating states and the harmonic trend parameters to generate initial compensation current parameters; controlling a harmonic compensation device to inject compensation current into the power grid based on the initial compensation current parameters, and monitoring to obtain power grid operating state parameters and grid-connected system operating state parameters in a compensation process in real time; performing regulation and calculation on the initial compensation current parameters based on the power grid operating state parameters and the grid-connected system operating state parameters to determine compensation current correction amounts, and performing feedback closed-loop control through the compensation current correction amounts.

[0067] Further, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method further comprises: performing noise identification on the grid-connected point current and voltage signals to obtain multi-frequency noise distribution characteristics, and initializing a digital filter according to the multi-frequency noise distribution characteristics; performing filter preprocessing on the grid-connected point current and voltage signals using the digital filter to obtain available grid-connected point current and voltage signals; selecting a target window function according to harmonic detection accuracy, performing windowing processing on the available grid-connected point current and voltage signals based on the target window function to obtain standard grid-connected point current and voltage signals; and performing harmonic analysis and parameter calculation based on the standard grid-connected point current and voltage signals to obtain grid-connected harmonic key parameters.

[0068] Further, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method further comprises: performing normalization processing and Fourier transform on the standard grid-connected point current and voltage signals to obtain grid-connected point current and voltage frequency domain signals; performing three-spectrum line interpolation correction on the grid-connected point current and voltage frequency domain signals to obtain grid-connected point current and voltage correction signals; performing frequency spectrum distribution analysis and harmonic component identification based on the grid-connected point current and voltage correction signals to determine harmonic component identification information; and performing key parameter calculation on the harmonic component identification information according to a harmonic key analysis index set to obtain the grid-connected harmonic key parameters.

[0069] Further, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method further comprises: acquiring photovoltaic power station grid-connected historical harmonic data, performing sequence division identification on the photovoltaic power station grid-connected historical harmonic data according to a preset prediction period to obtain photovoltaic power station grid-connected historical harmonic samples; performing prediction training and verification optimization on the photovoltaic power station grid-connected historical harmonic samples using an ARIMA network structure to generate a harmonic trend predictor; and performing trend prediction on the grid-connected harmonic key parameters based on the harmonic trend predictor to determine the harmonic trend parameters.

[0070] Further, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method further comprises: establishing an inverter operating state-harmonic parameter correlation model; based on the inverter operating state-harmonic parameter correlation model, performing harmonic influence evaluation on the photovoltaic inverter operating state to determine harmonic change influence parameters; appending the harmonic change influence parameters to the harmonic change trend parameters to obtain harmonic comprehensive change parameters; setting a harmonic compensation target, and performing dynamic compensation analysis on the harmonic comprehensive change parameters according to the harmonic compensation target to generate the initial compensation current parameters.

[0071] Further, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method further comprises: sequentially performing correlation analysis on the grid-connected harmonic key parameters and each parameter in the photovoltaic inverter operating parameters to obtain an inverter operating parameter correlation coefficient; performing optimization on the photovoltaic inverter operating parameters according to the inverter operating parameter correlation coefficient to obtain inverter key operating parameters; performing multiple regression fitting and significance test optimization on the inverter key operating parameters as independent variables and the grid-connected harmonic key parameters as dependent variables to establish the inverter operating state-harmonic parameter correlation model.

[0072] Further, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method further comprises: performing correlation feature extraction on the power grid operating state parameters and the grid-connected system operating state parameters to obtain a power grid harmonic compensation feature set; performing compensation effect evaluation on the power grid harmonic compensation feature set according to a harmonic compensation evaluation index set to obtain a harmonic compensation effect parameter; based on the harmonic compensation effect parameter, performing regulation and control calculation on the initial compensation current parameters to determine a compensation current correction amount.

[0073] Further, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method further comprises: based on the harmonic compensation effect parameter, performing regulation and control analysis on the initial compensation current parameters to determine a compensation current correction direction; based on the compensation current correction direction, performing regulation and control analysis on the initial compensation current parameters based on the harmonic compensation effect parameter to generate a current correction amount selection threshold; based on the harmonic compensation evaluation index set, performing global optimization within the current correction amount selection threshold to determine the compensation current correction amount.

[0074] Further, the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method further comprises: based on the current correction amount selection threshold, initializing a harmonic compensation particle space; based on the harmonic compensation evaluation index set, performing iterative simulation optimization within the harmonic compensation particle space to determine the compensation current correction amount.

[0075] The various embodiments described in the specification are intended to be exemplary only and the present application is not limited to the embodiments described. The above-described embodiments of the present application are intended to be illustrative only and in no way limit the scope of the present application. Numerous modifications and variations are possible in light of the above teachings and no limitations are implied by the description and drawings to a specific embodiment disclosed. More generally, the present application embraces all alternatives, modifications, additions or omissions as is reasonably inferred by the foregoing disclosure. The above description is the only preferred embodiment of the application. Various modifications and changes can be made thereto without departing from the spirit and scope of the application as set forth. The scope of the application is not to be determined by the above description but is to be determined by the claims.

[0076] The above description discloses only typical embodiments of the application and modifications and alterations are obvious to others skilled in the art from this disclosure. It is intended to encompass all alternatives, modifications and alterations falling within the scope of the application. Therefore, the application is not to be limited by the foregoing description but is to be defined by the scope of the claims appended hereto.

[0077] Obviously, numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the application, the application can be practiced otherwise than as specifically set forth herein. With the above claims in mind, therefore, the application is deemed to cover all such modifications and variations as fall within the scope of the present application.

Claims

1. A photovoltaic power station grid-connected harmonic detection and dynamic compensation control system, characterized in that, The system comprises: a harmonic detection module, configured to collect grid-connected point current and voltage signals of a target photovoltaic power station using a voltage current transformer, perform harmonic analysis and parameter calculation on the grid-connected point current and voltage signals, and obtain grid-connected harmonic key parameters; a dynamic compensation module, configured to perform trend prediction based on the grid-connected harmonic key parameters, determine harmonic change trend parameters, perform dynamic compensation analysis in combination with photovoltaic inverter operating states and the harmonic change trend parameters, and generate initial compensation current parameters; a compensation control module, configured to control a harmonic compensation device to inject compensation current into a power grid based on the initial compensation current parameters, and monitor grid operating state parameters and grid-connected system operating state parameters obtained in a compensation process in real time; an adaptive adjustment module, configured to perform regulation calculation on the initial compensation current parameters based on the grid operating state parameters and the grid-connected system operating state parameters, determine a compensation current correction amount, and perform feedback closed-loop control through the compensation current correction amount; the dynamic compensation module comprises: a sequence division identification unit, configured to collect photovoltaic power station grid-connected historical harmonic data, perform sequence division identification on the photovoltaic power station grid-connected historical harmonic data according to a preset prediction period, and obtain photovoltaic power station grid-connected historical harmonic samples; a verification and tuning unit, configured to perform prediction training and verification and tuning on the photovoltaic power station grid-connected historical harmonic samples using an ARIMA network structure, and generate a harmonic trend predictor; a trend prediction unit, configured to perform trend prediction on the grid-connected harmonic key parameters based on the harmonic trend predictor, and determine the harmonic change trend parameters; the dynamic compensation module further comprises: an associated model establishment unit, configured to establish an inverter operating state-harmonic parameter associated model; a harmonic influence evaluation unit, configured to perform harmonic influence evaluation on the photovoltaic inverter operating states based on the inverter operating state-harmonic parameter associated model, and determine harmonic change influence parameters; a parameter appending unit, configured to append the harmonic change influence parameters to the harmonic change trend parameters, and obtain harmonic comprehensive change parameters; a dynamic compensation analysis unit, configured to set a harmonic compensation target, perform dynamic compensation analysis on the harmonic comprehensive change parameters according to the harmonic compensation target, and generate the initial compensation current parameters.

2. The photovoltaic power station grid-connected harmonic detection and dynamic compensation control system according to claim 1, characterized in that, the harmonic detection module comprises: an initialization unit, configured to perform noise identification on the grid-connected point current and voltage signals, obtain multi-frequency noise distribution characteristics, and initialize a digital filter according to the multi-frequency noise distribution characteristics; a filter preprocessing unit, configured to perform filter preprocessing on the grid-connected point current and voltage signals using the digital filter, and obtain available grid-connected point current and voltage signals; a window processing unit, configured to select a target window function according to harmonic detection accuracy, perform window processing on the available grid-connected point current and voltage signals based on the target window function, and obtain standard grid-connected point current and voltage signals; a harmonic analysis unit, configured to perform harmonic analysis and parameter calculation based on the standard grid-connected point current and voltage signals, and obtain grid-connected harmonic key parameters.

3. The photovoltaic power station grid-connected harmonic detection and dynamic compensation control system according to claim 2, characterized in that, the harmonic analysis unit comprises: The normalization processing subunit is configured to perform normalization processing and Fourier transform on the standard grid-connected point current voltage signal to obtain a grid-connected point current voltage frequency domain signal; The three-spectrum line interpolation correction subunit is configured to perform three-spectrum line interpolation correction on the grid-connected point current voltage frequency domain signal to obtain a grid-connected point current voltage correction signal; The harmonic component identification subunit is configured to perform frequency spectrum distribution analysis and harmonic component identification based on the grid-connected point current voltage correction signal to determine harmonic component identification information; The key parameter calculation subunit is configured to perform key parameter calculation on the harmonic component identification information according to a harmonic key analysis index set to obtain the grid-connected harmonic key parameter.

4. The photovoltaic power station grid-connected harmonic detection and dynamic compensation control system of claim 1, wherein, The correlation model establishing unit comprises: The correlation analysis subunit is configured to sequentially perform correlation analysis on each parameter in the photovoltaic inverter operating parameter and the grid-connected harmonic key parameter to obtain an inverter operating parameter correlation coefficient; The optimization subunit is configured to perform optimization on the photovoltaic inverter operating parameter according to the inverter operating parameter correlation coefficient to obtain an inverter key operating parameter; The correlation model establishing subunit is configured to perform multiple regression fitting and significance test optimization on the inverter key operating parameter as an independent variable and the grid-connected harmonic key parameter as a dependent variable to establish the inverter operating state-harmonic parameter correlation model.

5. The photovoltaic power plant grid-connected harmonic detection and dynamic compensation control system of claim 1, wherein, The adaptive adjustment module comprises: The correlation feature extraction unit is configured to perform correlation feature extraction on the power grid operating state parameter and the grid-connected system operating state parameter to obtain a power grid harmonic compensation feature set; The compensation effect evaluation unit is configured to perform compensation effect evaluation on the power grid harmonic compensation feature set according to a harmonic compensation evaluation index set to obtain a harmonic compensation effect parameter; The regulation and control calculation unit is configured to perform regulation and control calculation on the initial compensation current parameter based on the harmonic compensation effect parameter to determine a compensation current correction amount.

6. The photovoltaic power plant grid-connected harmonic detection and dynamic compensation control system of claim 5, wherein, The regulation and control calculation unit comprises: The compensation current correction direction determination subunit is configured to perform regulation and control analysis on the initial compensation current parameter based on the harmonic compensation effect parameter to determine a compensation current correction direction; The current correction amount selection threshold generation subunit is configured to perform regulation and control analysis on the initial compensation current parameter based on the harmonic compensation effect parameter according to the compensation current correction direction to generate a current correction amount selection threshold; The global optimization subunit is configured to perform global optimization within the current correction amount selection threshold based on the harmonic compensation evaluation index set to determine a compensation current correction amount.

7. The photovoltaic power plant grid-connected harmonic detection and dynamic compensation control system of claim 6, wherein, The global optimization subunit comprises: The initialization channel is configured to initialize a harmonic compensation particle space according to the current correction amount selection threshold; The iterative simulation optimization channel is configured to perform iterative simulation optimization within the harmonic compensation particle space based on the harmonic compensation evaluation index set to determine the compensation current correction amount.

8. A method for photovoltaic power station grid-connected harmonic detection and dynamic compensation control, characterized in that, The photovoltaic power station grid-connected harmonic detection and dynamic compensation control system of any one of claims 1 to 7 is executed, and the photovoltaic power station grid-connected harmonic detection and dynamic compensation control method comprises: The voltage current transformer is used to collect the grid-connected point current voltage signal of the target photovoltaic power station, harmonic analysis and parameter calculation are performed on the grid-connected point current voltage signal, and grid-connected harmonic key parameters are obtained; Based on the grid-connected harmonic key parameters, trend prediction is performed to determine harmonic change trend parameters, dynamic compensation analysis is performed in combination with the photovoltaic inverter operation state and the harmonic change trend parameters, and initial compensation current parameters are generated; The harmonic compensation device injects compensation current into the power grid based on the initial compensation current parameters, and real-time monitoring is performed to obtain power grid operation state parameters and grid-connected system operation state parameters in the compensation process; Based on the power grid operation state parameters and the grid-connected system operation state parameters, the initial compensation current parameters are regulated and calculated to determine the compensation current correction amount, and feedback closed-loop control is performed through the compensation current correction amount.

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