A grid-connected control system and control method in a solar photovoltaic power generation system

Abstract

The application discloses a grid-connected control system and method in a solar photovoltaic power generation system, and relates to the technical field of photovoltaic power generation control. The grid-connected control method in the solar photovoltaic power generation system comprises the following steps: obtaining power generation operation data when the solar photovoltaic power generation system is connected with a target grid, respectively performing characteristic analysis, obtaining a set of grid-connected evaluation indexes when the solar photovoltaic power generation system is connected with the target grid, and performing comprehensive analysis to obtain a source-grid collaborative safety index when the solar photovoltaic power generation system is connected with the target grid. The application adopts preset grid-connected control measures based on the source-grid collaborative safety index when the solar photovoltaic power generation system is connected with the target grid, thereby realizing dynamic safety evaluation and control in the process of grid connection of the photovoltaic system, ensuring that the photovoltaic system can flexibly adapt to grid connection under different grid conditions, and improving the compatibility and stability of photovoltaic power generation to the grid operation environment as a whole.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic power generation control, in particular to a grid-connected control system and control method in a solar photovoltaic power generation system. BACKGROUND

[0002] Solar photovoltaic power generation has become one of the clean energy forms in China and globally, especially in resource-rich areas, the rapid deployment and grid-connected scale of large-scale centralized photovoltaic power stations continue to expand, which brings higher dynamic adaptability and stability requirements to the operation of traditional power grids. Centralized photovoltaic power stations often have characteristics such as high installed capacity, large current injection, and long-distance power transmission, which are easy to form an impact or disturbance on the target power grid. If there is a lack of fine and dynamic grid-connected control means, it is easy to cause local voltage fluctuation, frequency disturbance, harmonic pollution and other power quality problems, and in severe cases, it may even lead to power station off-grid or system oscillation. Moreover, the existing large-scale photovoltaic grid-connected control method often ignores the overall coupling state between the photovoltaic power station and the target power grid, and only relies on local electrical parameters, which is difficult to reflect the comprehensiveness and dynamic change trend of the current grid-connected conditions.

[0003] The prior art such as the patent application with the publication number CN105790308B discloses a control method for grid-connected operation of a solar photovoltaic power generation system, which includes the following steps: first, a solar photovoltaic power generation experimental system is built, wherein the solar photovoltaic power generation experimental system includes four groups of solar photovoltaic power generation devices with DC / DC converters and one common load, the four groups of solar photovoltaic power generation devices collectively provide electrical energy for the load; second, according to the principles of physics, a mathematical model of the solar photovoltaic power generation experimental system is established, which belongs to an interconnected system with four nonlinear subsystems; finally, based on the mathematical model, a decentralized sampling event-triggered controller is designed, and a simulation test platform of the system is given. The grid-connected operation control scheme provided by the present application can not only ensure the safe and stable operation of the microgrid, but also significantly reduce the communication data between each power generation unit.

[0004] Based on the above scheme, it is found that the limitations of the prior art at least include the following problems: the prior art lacks a deep analysis of the dynamic adaptability of the power grid and the photovoltaic system in the actual grid-connected process, and does not consider the interaction of various complex factors in actual operation, such as the unbalance of power grid load caused by external load fluctuation or sudden events. Such a situation cannot be timely responded and optimized controlled in the prior art, thereby easily leading to poor coordination between the photovoltaic system and the power grid, and further affecting the stability and power quality of the power grid. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a grid-connected control system and a control method for a solar photovoltaic power generation system, and solves the problem that the prior art lacks dynamic adaptability analysis and does not consider various complex factors in actual operation, thereby leading to poor photovoltaic and grid coordination and further affecting stability and power quality.

[0006] To achieve the above object, the application is implemented by the following technical scheme: a grid-connected control method for a solar photovoltaic power generation system, comprising the following steps: obtaining power generation operation data when the solar photovoltaic power generation system is connected to a target grid, including grid equipment operation data, photovoltaic power operation data, and source-grid interaction data; performing feature analysis on the power generation operation data when the solar photovoltaic power generation system is connected to the target grid, respectively, to obtain a set of grid-connected evaluation indexes when the solar photovoltaic power generation system is connected to the target grid, including a grid equipment stability maintenance index, a photovoltaic operation stability index, and a grid-connected adaptability index, and performing comprehensive analysis to obtain a source-grid coordination safety index when the solar photovoltaic power generation system is connected to the target grid; and taking a preset grid-connected control measure based on the source-grid coordination safety index when the solar photovoltaic power generation system is connected to the target grid.

[0007] Further, the specific formula for calculating the source-grid coordination safety index when the solar photovoltaic power generation system is connected to the target grid is as follows: Wherein, BwR is the source-grid coordination safety index when the solar photovoltaic power generation system is connected to the target grid, DwH is the grid equipment stability maintenance index when the solar photovoltaic power generation system is connected to the target grid, α1 is an equipment stability maintenance adjustment coefficient stored in a database, GyW is the photovoltaic operation stability index when the solar photovoltaic power generation system is connected to the target grid, ζ is a photovoltaic operation smoothing coefficient stored in the database, α2 is a photovoltaic operation adjustment coefficient stored in the database, BsY is the grid-connected adaptability index when the solar photovoltaic power generation system is connected to the target grid, and α3 is a grid-connected adaptability adjustment coefficient stored in the database.

[0008] Further, the grid equipment operation data includes an inverter feedforward steady-state index, a circuit breaker feedforward steady-state index, and a transformer feedforward steady-state index, and the specific steps for obtaining the grid equipment stability maintenance index when the solar photovoltaic power generation system is connected to the target grid are as follows: performing comprehensive analysis on the inverter feedforward steady-state index, the circuit breaker feedforward steady-state index, and the transformer feedforward steady-state index when the solar photovoltaic power generation system is connected to the target grid, respectively, to obtain an initial grid equipment stability maintenance index and a device interaction correction index when the solar photovoltaic power generation system is connected to the target grid; and performing comprehensive analysis on the initial grid equipment stability maintenance index and the device interaction correction index when the solar photovoltaic power generation system is connected to the target grid to obtain the grid equipment stability maintenance index when the solar photovoltaic power generation system is connected to the target grid.

[0009] Further, the specific steps for obtaining the inverter feedforward steady-state index when the solar photovoltaic power generation system is connected to the target power grid are as follows: obtaining the inverter steady-flow adaptation index, the inverter current harmonic distortion index, the inverter voltage harmonic distortion index, the inverter resonance impedance index, and the inverter temperature value when the solar photovoltaic power generation system is connected to the target power grid, and performing standardization processing; comprehensively analyzing the inverter steady-flow adaptation index, the inverter current harmonic distortion index, the inverter voltage harmonic distortion index, the inverter resonance impedance index, and the inverter temperature value after standardization processing, to obtain the inverter feedforward steady-state index when the solar photovoltaic power generation system is connected to the target power grid.

[0010] Further, the photovoltaic power operation data includes a string current dispersion index, a backboard temperature gradient index, and a photovoltaic power quality index. The specific steps for obtaining the photovoltaic operation stability index when the solar photovoltaic power generation system is connected to the target power grid are as follows: obtaining the illumination intensity value, the environmental temperature value, and the radiation reflectivity value when the solar photovoltaic power generation system is connected to the target power grid, combining the backboard temperature gradient index, and comprehensively analyzing to obtain a photovoltaic operation correction factor when the solar photovoltaic power generation system is connected to the target power grid; comprehensively analyzing the photovoltaic operation correction factor, the string current dispersion index, and the photovoltaic power quality index when the solar photovoltaic power generation system is connected to the target power grid, to obtain the photovoltaic operation stability index when the solar photovoltaic power generation system is connected to the target power grid.

[0011] Further, the specific steps for obtaining the photovoltaic power quality index when the solar photovoltaic power generation system is connected to the target power grid are as follows: obtaining the voltage deviation value, the current deviation value, the power deviation value, and the three-phase balance index when the solar photovoltaic power generation system is connected to the target power grid, and performing standardization processing; comprehensively analyzing the voltage deviation value, the current deviation value, the power deviation value, and the three-phase balance index after standardization processing, to obtain the photovoltaic power quality index when the solar photovoltaic power generation system is connected to the target power grid.

[0012] Further, the source-grid interaction data includes a coupling driving index, a source-grid symmetric coordination index, a supply-demand current adaptation index, and a grid-side bearing capacity index. The specific steps for obtaining the grid-connection adaptability index when the solar photovoltaic power generation system is connected to the target power grid are as follows: performing normalization processing on the coupling driving index, the source-grid symmetric coordination index, the supply-demand current adaptation index, and the grid-side bearing capacity index of the grid-connection adaptability index when the solar photovoltaic power generation system is connected to the target power grid; and comprehensively analyzing the coupling driving index, the source-grid symmetric coordination index, the supply-demand current adaptation index, and the grid-side bearing capacity index of the grid-connection adaptability index after normalization processing, to obtain the grid-connection adaptability index when the solar photovoltaic power generation system is connected to the target power grid.

[0013] Further, the specific formula of the grid-connected adaptability index of the solar photovoltaic power generation system when connected with the target power grid is as follows: Wherein, BsY is the grid-connected adaptability index of the solar photovoltaic power generation system when connected with the target power grid, YwX' is the normalized source-grid symmetry coordination index of the solar photovoltaic power generation system when connected with the target power grid, μ1 is the symmetry adjustment coefficient stored in the database, GxP' is the normalized supply-demand current adaptation index of the solar photovoltaic power generation system when connected with the target power grid, μ2 is the adaptation adjustment coefficient stored in the database, WsG' is the normalized grid-side bearing capacity index of the solar photovoltaic power generation system when connected with the target power grid, μ3 is the bearing adjustment coefficient stored in the database, DqS' is the normalized coupling driving index of the solar photovoltaic power generation system when connected with the target power grid, μ4 is the driving adjustment coefficient stored in the database, μ5 is the driving adaptation adjustment coefficient stored in the database, and μ6 is the smoothing adjustment coefficient stored in the database.

[0014] Further, the specific steps of the preset grid-connected control measure based on the source-grid collaborative safety index of the solar photovoltaic power generation system when connected with the target power grid are as follows: the source-grid collaborative safety index of the solar photovoltaic power generation system when connected with the target power grid is judged and analyzed with the preset source-grid collaborative safety index threshold value; if the source-grid collaborative safety index of the solar photovoltaic power generation system when connected with the target power grid is lower than or equal to the preset source-grid collaborative safety index threshold value, the first grid-connected control measure is taken; if the source-grid collaborative safety index of the solar photovoltaic power generation system when connected with the target power grid is higher than the preset source-grid collaborative safety index threshold value, the second grid-connected control measure is taken.

[0015] A grid-connected control system in a solar photovoltaic power generation system, comprising: a data acquisition module, configured to acquire power generation operation data of the solar photovoltaic power generation system when connected with a target power grid, including power grid equipment operation data, photovoltaic power operation data, and source-grid interaction data; a feature extraction module, configured to perform feature analysis on the power generation operation data of the solar photovoltaic power generation system when connected with the target power grid, to obtain a grid-connected evaluation index set of the solar photovoltaic power generation system when connected with the target power grid, including a power grid equipment stability index, a photovoltaic operation stability index, and a grid-connected adaptability index; a comprehensive analysis module, configured to perform comprehensive analysis on the grid-connected evaluation index set of the solar photovoltaic power generation system when connected with the target power grid, to obtain a source-grid collaborative safety index of the solar photovoltaic power generation system when connected with the target power grid; and a grid-connected control module, configured to take a preset grid-connected control measure based on the source-grid collaborative safety index of the solar photovoltaic power generation system when connected with the target power grid.

[0016] The present application has the following beneficial effects:

[0017] (1) The grid-connected control method of the solar photovoltaic power generation system, by obtaining the power generation operation data and performing multi-dimensional analysis, the source network coordination safety index is obtained, so as to realize the dynamic safety evaluation and control in the process of photovoltaic system grid connection, and then ensure that the photovoltaic system can adapt to grid connection flexibly under different grid conditions, avoid the instability of the grid or the occurrence of power quality problems, for example, if the grid load suddenly increases, the output power of the photovoltaic system is adjusted to avoid the voltage fluctuation of the grid and ensure that the photovoltaic power generation will not bring additional burden to the grid, thereby improving the stability of photovoltaic grid connection and the safety of grid operation.

[0018] (2) The grid-connected control method of the solar photovoltaic power generation system, by refining the analysis process of the grid equipment stability index, the operation state of the key equipment of the grid such as inverter, circuit breaker and transformer is accurately evaluated, specifically, the pre-inversion feedforward steady-state index, the pre-circuit breaker feedforward steady-state index and the pre-transformer feedforward steady-state index are adopted, which comprehensively reflects the key physical factors such as current, voltage harmonic distortion, temperature change and resonance impedance in the equipment operation, so as to quickly respond to the real-time stability of the equipment, for example, when the temperature of the inverter is too high or the harmonic distortion is serious, the photovoltaic power generation system can timely reduce the output power, thereby effectively preventing the negative impact of equipment overload and resonance on the grid, and significantly reducing the maintenance cost and power failure risk caused by equipment failure.

[0019] (3) The grid-connected control method of the solar photovoltaic power generation system, by constructing the grid-connected adaptability index for the source network interaction characteristics, multi-dimensional parameters are used for comprehensive analysis, which effectively solves the coordination problem in the interaction process of photovoltaic power generation system and grid, especially solves the adaptability problem in the complex operation scene such as grid voltage disturbance, current imbalance and load fluctuation, for example, when the grid load fluctuation is obvious, by timely monitoring the source network symmetry coordination index and supply-demand current adaptation index, the photovoltaic power generation system can actively adjust the photovoltaic output power and power factor, thereby avoiding the additional disturbance to the grid caused by current mismatch or phase asymmetry, so as to significantly improve the robustness and flexible adaptation ability of the photovoltaic system when connected to the grid, thereby improving the compatibility and stability of photovoltaic power generation to the grid operation environment.

[0020] (4), the grid-connected control system in the solar photovoltaic power generation system, through the combination of the system architecture of the data acquisition module, the feature extraction module, the comprehensive analysis module and the grid-connected control module, the automation and intelligent management of the grid-connected control of the solar photovoltaic power generation system are realized, specifically, the data acquisition module collects the multi-dimensional operation data in the grid-connected process in real time, the feature extraction module analyzes the operation characteristics of the grid, the photovoltaic system and the source network interaction in detail, the comprehensive analysis module accurately outputs the source network collaborative safety index, so as to realize the automatic risk assessment and early warning, and the grid-connected control module independently judges and executes the corresponding control measures according to the safety index, for example, automatically enables the reactive power compensation or dynamically adjusts the output power, significantly reduces the demand for human intervention and decision delay, thereby improving the response speed and processing efficiency of the system, and then making the solar photovoltaic power generation system more intelligent to adapt to the grid fluctuation, thereby reducing the operation and maintenance cost and enhancing the system safety and reliability.

[0021] Of course, it is not necessary to achieve all the advantages described above at the same time to implement any product of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A flow chart of a grid-connected control method of a solar photovoltaic power generation system according to the present application.

[0023] Figure 2 A flow chart of specific steps of obtaining the grid-connected adaptability index of the solar photovoltaic power generation system when connected to the target grid in the grid-connected control method of the solar photovoltaic power generation system according to the present application.

[0024] Figure 3 An example diagram of the normalized source network interaction data in the grid-connected control method of the solar photovoltaic power generation system according to the present application.

[0025] Figure 4 A block diagram of a grid-connected control system of a solar photovoltaic power generation system according to the present application. DETAILED DESCRIPTION

[0026] Please refer to Figure 1The embodiment of the present application provides a technical scheme: a grid-connected control method in a solar photovoltaic power generation system, comprising the following steps: obtaining power generation operation data when the solar photovoltaic power generation system is connected with a target grid (i.e. grid-connected), including grid equipment operation data, photovoltaic power operation data, and source-grid interaction data; performing feature analysis on the power generation operation data when the solar photovoltaic power generation system is connected with the target grid, respectively, to obtain a set of grid-connected evaluation indexes when the solar photovoltaic power generation system is connected with the target grid, including a grid equipment stability index, a photovoltaic operation stability index, and a grid-connected adaptability index, and performing comprehensive analysis to obtain a source-grid collaborative safety index (used for measuring the safety when the solar photovoltaic power generation system is connected with the target grid) when the solar photovoltaic power generation system is connected with the target grid; and taking a preset grid-connected control measure based on the source-grid collaborative safety index when the solar photovoltaic power generation system is connected with the target grid.

[0027] The specific formula for calculating the source-grid collaborative safety index when the solar photovoltaic power generation system is connected with the target grid is as follows: Wherein, BwR is the source-grid collaborative safety index when the solar photovoltaic power generation system is connected with the target grid, DwH is the grid equipment stability index when the solar photovoltaic power generation system is connected with the target grid, alpha1 is the equipment stability adjustment coefficient stored in the database, GyW is the photovoltaic operation stability index when the solar photovoltaic power generation system is connected with the target grid, zeta is the photovoltaic operation smoothing coefficient stored in the database, alpha2 is the photovoltaic operation adjustment coefficient stored in the database, BsY is the grid-connected adaptability index when the solar photovoltaic power generation system is connected with the target grid, and alpha3 is the grid-connected adaptability adjustment coefficient stored in the database.

[0028] It should be explained that alpha1, alpha2, and alpha3 can be obtained by the following steps: using historical data, combining the grid equipment stability index, the photovoltaic operation stability index, and the grid-connected adaptability index, performing statistical regression analysis, quantifying the specific influence of each factor on the source-grid collaborative safety index, fitting the initial weight value, then using the sensitivity analysis method to adjust the value range of each coefficient, observing the influence on the source-grid collaborative safety evaluation result, ensuring the stability and rationality of the model, based on the characteristics and actual situation of the solar photovoltaic power generation, correcting and optimizing the initially fitted coefficients, and finally determining the coefficient values suitable for the solar photovoltaic power generation.

[0029] Zeta can be obtained by the following steps: obtaining historical photovoltaic operation stability indexes at historical time points, and performing mean value processing to obtain the photovoltaic operation smoothing coefficient.

[0030] Specifically, the grid equipment operation data includes an inverter feedforward steady-state index (used to measure the stability of an inverter in a solar photovoltaic power generation system), a circuit breaker feedforward steady-state index, a transformer feedforward steady-state index (used to measure the stability of a transformer in a solar photovoltaic power generation system), and the specific steps for obtaining the grid equipment stability maintenance index when the solar photovoltaic power generation system is connected to the target grid are as follows: comprehensive analysis is performed on the inverter feedforward steady-state index, the circuit breaker feedforward steady-state index, and the transformer feedforward steady-state index when the solar photovoltaic power generation system is connected to the target grid to obtain an initial grid equipment stability maintenance index (i.e., weighted processing is performed on the inverter feedforward steady-state index, the circuit breaker feedforward steady-state index, and the transformer feedforward steady-state index) and an equipment interaction correction index (i.e., interaction processing is performed on the inverter feedforward steady-state index, the circuit breaker feedforward steady-state index, and the transformer feedforward steady-state index) when the solar photovoltaic power generation system is connected to the target grid; and comprehensive analysis is performed on the initial grid equipment stability maintenance index and the equipment interaction correction index when the solar photovoltaic power generation system is connected to the target grid to obtain the grid equipment stability maintenance index when the solar photovoltaic power generation system is connected to the target grid.

[0031] The circuit breaker feedforward steady-state index is used to measure the stability of a circuit breaker in a solar photovoltaic power generation system, which can be obtained by acquiring a circuit breaker contact temperature value (which can be acquired by a thermocouple temperature sensor), a circuit breaker contact resistance (the voltage value and the current value of the circuit breaker contact are acquired by a voltage sensor and a current sensor, respectively, and the circuit breaker contact resistance is obtained based on Ohm's law analysis), an electromagnetic field distribution index (distribution of the external electromagnetic field of the circuit breaker), and a contact vibration amplitude value (which can be acquired by a vibration sensor), and performing standardization processing, and weighted processing based on the standardization processing result, and the obtained result is the circuit breaker feedforward steady-state index.

[0032] The electromagnetic field distribution index can be obtained by a Hall effect sensor to acquire the electromagnetic field in multiple directions outside the circuit breaker and perform standard deviation processing.

[0033] The transformer feedforward steady-state index is used to measure the stability of a transformer in a solar photovoltaic power generation system, which can be obtained by acquiring a transformer load rate value, a transformer insulation resistance value (reflecting the health status of the internal insulation layer of the transformer, which is acquired by an insulation resistance measuring instrument), a transformer core temperature value (reflecting the temperature of the transformer core, which is acquired by a core temperature sensor), and a transformer excitation current (which has a direct impact on the efficiency of the transformer and can be acquired by a current sensor), and performing standardization processing, and weighted processing based on the standardization processing result, and the obtained result is the transformer feedforward steady-state index.

[0034] And the transformer load ratio value is the ratio of the load current (output current, obtained by the current sensor) and the rated current (obtained by the technical specification of the transformer stored in the database).

[0035] The transformer current balance index is the balance degree between three-phase currents, which is used to reflect the symmetry of three-phase currents in amplitude and phase, which is easy to cause additional burden and unstable operation of the transformer. It can be obtained by three-phase current sensors to obtain the current value of each phase, and the average value is obtained by averaging. At the same time, the maximum and minimum values of the current are counted, and then the analysis is calculated, that is, (current maximum-current minimum) / current average.

[0036] The specific formula for calculating the grid equipment stability index when the solar photovoltaic power generation system is connected to the target grid is as follows: DwH=Csw β1 *[β2*ln(1+JhY)]; wherein, DwH is the grid equipment stability index when the solar photovoltaic power generation system is connected to the target grid, Csw is the initial grid equipment stability index when the solar photovoltaic power generation system is connected to the target grid, β1 is the initial adjustment coefficient stored in the database, JhY is the equipment interaction correction index when the solar photovoltaic power generation system is connected to the target grid, and β2 is the interaction adjustment coefficient stored in the database.

[0037] It needs to be explained that β1 and β2 can be obtained by the following steps: based on historical data, the initial influence weight of each variable (initial grid equipment stability index, equipment interaction correction index) on the grid equipment stability index is determined by statistical regression analysis, then the value range of the adjustment coefficient is adjusted by using the sensitivity analysis method to evaluate the stability and applicability of these parameters on the formula output, next, the weight is further fitted by model optimization (such as machine learning algorithm) to ensure that the formula can accurately reflect the stability of the actual grid equipment.

[0038] In the embodiment, by fine construction of key indicators such as inverter pre-feedback steady-state index, circuit breaker pre-feedback steady-state index and transformer pre-feedback steady-state index, the precise and real-time evaluation and monitoring of the stability of the three core power grid equipment, i.e., inverter, circuit breaker and transformer, in the solar photovoltaic power generation system is realized. Secondly, the multi-dimensional characteristics such as circuit breaker contact temperature, resistance, electromagnetic field and vibration amplitude, as well as transformer load rate, insulation resistance, core temperature and excitation current are measured comprehensively, and a comprehensive and high-sensitivity equipment stability evaluation system is formed by using standardization and weighting processing. In addition, the initial adjustment coefficient and the interaction adjustment coefficient are dynamically calibrated by historical data statistics, sensitivity analysis and machine learning optimization, so that the evaluation formula can continuously adapt to the actual situation. Finally, through the comprehensive, fine and dynamic equipment stability index construction method, the photovoltaic system has higher anti-disturbance ability and operation reliability under complex working conditions, thereby effectively reducing the equipment failure risk and operation and maintenance cost.

[0039] Specifically, the specific steps of obtaining the inverter pre-feedback steady-state index when the solar photovoltaic power generation system is connected to the target power grid are as follows: obtaining the inverter steady flow adaptation index, inverter current harmonic distortion index, inverter voltage harmonic distortion index, inverter resonance impedance index and inverter temperature value when the solar photovoltaic power generation system is connected to the target power grid, and performing standardization processing; comprehensively analyzing the inverter steady flow adaptation index, inverter current harmonic distortion index, inverter voltage harmonic distortion index, inverter resonance impedance index and inverter temperature value after standardization processing (based on information entropy theory, the uncertainty weight of inverter steady flow adaptation index, inverter current harmonic distortion index, inverter voltage harmonic distortion index, inverter resonance impedance index and inverter temperature value is calculated in real time, multiplied by the corresponding weight, and then added), to obtain the inverter pre-feedback steady-state index when the solar photovoltaic power generation system is connected to the target power grid.

[0040] Among them, the inverter steady flow adaptation index is to measure the stability and adaptation ability of output current, output voltage and DC bus voltage, and can be obtained by obtaining the inverter AC output current value (which can be obtained by inverter AC port current sensor), inverter AC output voltage value (which can be obtained by inverter AC port voltage sensor in real time), inverter DC bus voltage value (which can be obtained by inverter DC port voltage sensor in real time), inverter AC output reference current value (obtained by inverter technical specification stored in the database), inverter AC reference output voltage value (obtained by standard voltage value of power grid stored in the database), inverter DC bus reference voltage value (i.e. output voltage of photovoltaic cell panel), respectively, difference analysis (such as the absolute value of the difference between inverter AC output current value and inverter AC output reference current value), and standardization processing, based on the standardization processing, weighted processing, the result is the inverter steady flow adaptation index.

[0041] The inverter harmonic distortion index is the harmonic content of the inverter output current, which can be obtained by the inverter built-in harmonic analysis module, that is, the inverter measures the current waveform through its internal sensor, and then calculates the total harmonic distortion based on fast Fourier transform and outputs the data.

[0042] The inverter voltage harmonic distortion index is the harmonic content of the inverter output voltage, and its acquisition steps are consistent with the logic of the inverter harmonic distortion index.

[0043] The inverter resonance impedance index is the matching between the inverter and the power grid, which can be obtained by obtaining the output impedance amplitude (the proportional relationship between the output voltage and current), the output impedance phase angle, and the interaction processing, that is, the output impedance amplitude x cos output impedance phase angle, the result is the inverter resonance impedance index, and the output impedance phase angle can be obtained by Fourier transform (FFT) on the voltage and current waveform at the output end of the inverter. The time domain signal of voltage and current can be converted to frequency domain, and in the frequency domain, the output voltage and current of the inverter will have a corresponding phase value (obtained by FFT calculation) respectively, and the output impedance phase angle can be obtained by calculating the difference between the voltage and current phase.

[0044] The inverter temperature value is the temperature of the inverter, which can be obtained by a thermocouple temperature sensor.

[0045] In the embodiment, by constructing a refined pre-inversion feedforward steady-state index evaluation system, the operation state and grid-connected quality of the photovoltaic inverter are realized precise real-time evaluation and control, wherein the steady-flow adaptation index quantifies the deviation between the actual operation state and the ideal state of the output current, voltage and DC bus voltage, the harmonic distortion index comprehensively reflects the potential impact of the inverter output voltage and current on the power quality of the grid, the resonance impedance index accurately reveals the impedance matching and coupling degree between the inverter and the grid, and the inverter temperature value monitors the thermal stability of the inverter in real time. In addition, after standardization processing, the uncertainty weight of each parameter is calculated in real time by using the information entropy theory, so as to dynamically give different parameters more reasonable and more actual weight distribution, so that the evaluation index can quickly and sensitively capture the slight change of the inverter operation state, thereby enhancing the operation safety and service life of the inverter. Finally, the deviation and hysteresis of subjective weight assignment are avoided, so that the inverter state monitoring is more objective and reliable, and the stability, robustness and intelligent management ability of the overall photovoltaic grid-connected system are improved.

[0046] Specifically, the photovoltaic power operation data includes string current dispersion index, backboard temperature gradient index and photovoltaic power quality index, and the specific steps of obtaining the photovoltaic operation stability index when the solar photovoltaic power generation system is connected with the target grid are as follows: obtaining the illumination intensity value (which can be obtained by an illumination intensity sensor), the environmental temperature value (which can be obtained by an RTD sensor) and the radiation reflectivity value (which is the proportion of ground reflected solar radiation and can be obtained by a reflectivity sensor) when the solar photovoltaic power generation system is connected with the target grid, and combining the backboard temperature gradient index to perform comprehensive analysis (standardization processing is performed first, and weighting processing is performed based on the standardization processing result), thereby obtaining a photovoltaic operation correction factor when the solar photovoltaic power generation system is connected with the target grid; and performing comprehensive analysis (standardization processing is performed first, and weighting processing is performed based on the standardization processing result) on the photovoltaic operation correction factor, the string current dispersion index and the photovoltaic power quality index when the solar photovoltaic power generation system is connected with the target grid, thereby obtaining a photovoltaic operation stability index when the solar photovoltaic power generation system is connected with the target grid.

[0047] The string current dispersion index is the standard deviation value of the DC side component string current of each group in the solar photovoltaic power generation system, and each DC side component string current can be obtained by a Hall sensor.

[0048] The backboard temperature gradient index is the temperature distribution degree of the backboard of the solar photovoltaic component. The temperature values of multiple positions of the backboard of the solar photovoltaic component are obtained (by an infrared temperature detector), and standard deviation processing is performed, and the obtained result is the backboard temperature gradient index.

[0049] The specific steps of obtaining the photovoltaic power quality index when the solar photovoltaic power generation system is connected with the target power grid are as follows: obtaining the voltage deviation value (the difference between the output voltage and the rated voltage), the current deviation value (the difference between the output current and the rated current), the power deviation value (the difference between the output power and the rated power), and the three-phase balance index when the solar photovoltaic power generation system is connected with the target power grid, and performing standardization processing; based on the voltage deviation value, the current deviation value, the power deviation value, and the three-phase balance index after standardization processing, comprehensive analysis (i.e. weighted processing) is performed to obtain the photovoltaic power quality index when the solar photovoltaic power generation system is connected with the target power grid.

[0050] Among them, the output voltage, the output current and the output power are obtained through the voltage sensor, the current sensor and the digital power meter in sequence, and the rated voltage, the rated current and the rated power can be obtained through the power grid parameter table stored in the database.

[0051] The three-phase balance index is the balance degree between three-phase currents, which is used to reflect the symmetry of three-phase currents in amplitude and phase. The current value of each phase can be obtained through a three-phase current sensor, and the mean value of the current can be obtained by mean processing. At the same time, the maximum and minimum values of the current are counted, and then the three-phase balance index is calculated and analyzed, i.e. (current maximum value-current minimum value) / current mean value.

[0052] In the embodiment, by establishing a detailed photovoltaic operation stability index evaluation system, the operation state and power generation performance of the photovoltaic module are accurately monitored. Secondly, based on the string current dispersion index, the backboard temperature gradient index and the photovoltaic power quality index and other multi-dimensional characteristic indexes, the current balance situation inside the photovoltaic system, the component backboard temperature distribution characteristics and the output power quality fluctuation can be comprehensively reflected. In addition, combined with the environmental parameters (light intensity, environmental temperature and radiation reflectivity), the photovoltaic operation correction factor is obtained through standardization and weighted processing, so as to significantly improve the sensitivity and adaptability of the stability index to environmental changes. When the environmental temperature suddenly changes or local hot spots appear on the backboard of the component, the photovoltaic system can quickly capture these subtle changes and make real-time adjustments, thereby effectively avoiding the long-term impact of local overheating or uneven operation of the component on the power generation performance, thereby effectively improving the photovoltaic power generation efficiency, prolonging the service life of the photovoltaic module, and reducing the long-term operation and maintenance cost.

[0053] Specifically, as Figure 2As shown, the source grid interaction data includes a coupling driving index, a source grid symmetry coordination index, a supply-demand current adaptation index, and a grid side bearing capacity index. The specific steps for obtaining the grid connection adaptability index of the solar photovoltaic power generation system connected to the target grid are as follows: normalizing the coupling driving index, the source grid symmetry coordination index, the supply-demand current adaptation index, and the grid side bearing capacity index of the grid connection adaptability index of the solar photovoltaic power generation system connected to the target grid; and comprehensively analyzing the coupling driving index, the source grid symmetry coordination index, the supply-demand current adaptation index, and the grid side bearing capacity index of the grid connection adaptability index of the solar photovoltaic power generation system connected to the target grid after normalization, to obtain the grid connection adaptability index of the solar photovoltaic power generation system connected to the target grid.

[0054] The coupling driving index is the dynamic coupling degree of power disturbance under the conditions of voltage and interface conduction, which can be obtained by acquiring the active power value (which can be obtained by a power meter), the output voltage value (which can be obtained by a Hall voltage sensor), and the interface conductivity value (obtained by acquiring the output voltage value and the current value and calculating and analyzing the output current / output voltage value), and comprehensively analyzing the results (i.e., standardizing the results and weighting based on the standardized results).

[0055] The source grid symmetry coordination index is a measure of the symmetry and consistency of three-phase power on the source side (photovoltaic power generation) and the grid side (target grid), which can be obtained by acquiring the source side three-phase current, voltage (acquired by a voltage transformer and a Hall current sensor in turn), and the grid side three-phase current, voltage (acquired by a voltage transformer and a Hall current sensor in turn), and comprehensively analyzing the results (i.e., difference processing for each current in the source side three-phase current and the corresponding phase current in the grid side three-phase current, and the same processing for the source side three-phase voltage and the grid side three-phase voltage, and then standardizing the results), and weighting based on the comprehensive analysis results.

[0056] The supply-demand current adaptation index is the ratio of the output current capacity of the source side (obtained by acquiring the source side three-phase current and performing mean value processing) to the current required by the load on the grid side (obtained by a current transformer).

[0057] The grid side bearing capacity index is the absorption capacity of the grid, which can be obtained by acquiring the grid side three-phase voltage value and performing mean value processing, and the grid side three-phase current value and performing mean value processing, and then multiplying them, i.e., (sqrt(3)) x grid side three-phase current mean x grid side three-phase voltage mean.

[0058] The specific formula for calculating the grid connection adaptability index of the solar photovoltaic power generation system connected to the target grid is as follows: BsY = μ1YwX' + μ2GxP' + μ3WsG' + μ4DqS' + μ5 + μ6, wherein BsY is the grid-connection adaptability index of the solar photovoltaic power generation system when connected to the target power grid, YwX' is the normalized source-grid symmetry coordination index of the solar photovoltaic power generation system when connected to the target power grid, μ1 is the symmetry adjustment coefficient stored in the database, GxP' is the normalized supply-demand current adaptation index of the solar photovoltaic power generation system when connected to the target power grid, μ2 is the adaptation adjustment coefficient stored in the database, WsG' is the normalized grid-side bearing capacity index of the solar photovoltaic power generation system when connected to the target power grid, μ3 is the bearing adjustment coefficient stored in the database, DqS' is the normalized coupling driving index of the solar photovoltaic power generation system when connected to the target power grid, μ4 is the driving adjustment coefficient stored in the database, μ5 is the driving adaptation adjustment coefficient stored in the database, and μ6 is the smoothing adjustment coefficient stored in the database.

[0059] It should be explained that the expression of the Tanh function is e is a natural constant, and in this embodiment example, e is 2.71, and the domain is (-∞, +∞), and the range is (-1, 1).

[0060] In the formula This term is used to adjust the inhibitory effect on grid-connection adaptability under the double impact of disturbance and incoordination.

[0061] μ1, μ2, μ3, μ4, μ5, and μ6 can be obtained by the following steps: based on historical data, the initial influence weight of each variable (source-grid symmetry coordination index, supply-demand current adaptation index, grid-side bearing capacity index, and coupling driving index) on the grid-connection adaptability index is determined through statistical regression analysis, then the value range of the coefficient is adjusted by using the sensitivity analysis method to evaluate the stability and applicability of these parameters on the formula output, next, the weight is further fitted through model optimization (such as multi-objective optimization) to ensure that the formula can accurately reflect the adaptability of actual grid-connection.

[0062] The specific implementation example of calculating the grid-connection adaptability index of the solar photovoltaic power generation system when connected to the target power grid is as follows. The following data are available: the coupling driving index, the source-grid symmetry coordination index, the supply-demand current adaptation index, and the grid-side bearing capacity index of the solar photovoltaic power generation system when connected to the target power grid, as shown in Table 1.

[0063] Table 1: Example of source-grid interaction data of the solar photovoltaic power generation system when connected to the target power grid

[0064]

[0065] The data in Table 1 are normalized to obtain Table 2, and as shown in Table 2. Figure 3

[0066] ​Table 2. Example of normalized source-grid interaction data of the solar photovoltaic power generation system connected to the target power grid

[0067]

[0068] The symmetric adjustment coefficient μ1 stored in the database is about 0.293;

[0069] The adaptive adjustment coefficient μ2 stored in the database is about 0.538;

[0070] The bearing adjustment coefficient μ3 stored in the database is about 0.317;

[0071] The driving adjustment coefficient μ4 stored in the database is about 0.824;

[0072] The driving adaptive adjustment coefficient μ5 stored in the database is about 0.426;

[0073] The smoothing adjustment coefficient μ6 stored in the database is about 0.364;

[0074] Substituting the data in Table 2 and the above adjustment coefficients into the specific formula of the grid-connection adaptability index of the solar photovoltaic power generation system connected to the target power grid, we get:

[0075] The grid-connection adaptability index of the solar photovoltaic power generation system connected to the target power grid is about 0.781.

[0076] In this embodiment, by precisely constructing the grid-connection adaptability index, the degree of adaptation and stability in the dynamic interaction process between the solar photovoltaic power generation system and the target power grid are deeply reflected, and the coupling driving effect of power disturbance, the symmetric coordination of three-phase power on the source side and the grid side, the matching degree of supply and demand current, and the actual power absorption capacity of the power grid are comprehensively considered. Various dynamic and static factors in the source-grid interaction process are quantified from multiple dimensions, thereby improving the sensitivity and accuracy of grid-connection evaluation. In addition, by means of statistical regression analysis, sensitivity analysis, and multi-objective optimization method, the parameter coefficients are dynamically adjusted and optimized, so that the evaluation system continuously adapts to the actual operating conditions, ensuring real-time response to changes in the power grid environment. For example, when the power grid demand load experiences severe fluctuations and other adverse factors, the photovoltaic power generation system can quickly capture subtle adaptation deviations between the source and the grid, and make timely adjustment decisions, thereby avoiding potential safety risks and grid-connection impacts. In this way, the stable operation of the photovoltaic power generation system after grid-connection and the reliability and safety of the overall operation of the power grid are effectively ensured.

[0077] Specifically, the specific steps of the preset grid-connected control measure based on the source-grid collaborative safety index when the solar photovoltaic power generation system is connected to the target power grid are as follows: the source-grid collaborative safety index when the solar photovoltaic power generation system is connected to the target power grid is judged and analyzed with the preset source-grid collaborative safety index threshold; if the source-grid collaborative safety index when the solar photovoltaic power generation system is connected to the target power grid is lower than or equal to the preset source-grid collaborative safety index threshold, the first grid-connected control measure is taken, which can specifically be reducing output power (reducing active power injection into the power grid and reducing impact), enabling reactive power support (supporting the power grid voltage by providing reactive power), limiting power climb rate (controlling the slope of output power rise to avoid instantaneous impact), delaying grid connection access (delaying the synchronization access time to avoid the peak of grid connection point disturbance), for reducing grid disturbance and improving system stability; if the source-grid collaborative safety index when the solar photovoltaic power generation system is connected to the target power grid is higher than the preset source-grid collaborative safety index threshold, the second grid-connected control measure is taken, which can specifically be enabling maximum power output mode (the photovoltaic system performs full power output), optimizing power quality (starting the harmonic suppression function in the photovoltaic inverter to ensure that the output current and voltage waveform meet the power quality standard), to ensure that the photovoltaic system operates efficiently and safely in grid connection and provides stable power output.

[0078] In the embodiment, by setting a clear source-grid collaborative safety index threshold and establishing a corresponding dynamic control mechanism, self-adaptive fine regulation and control between the solar photovoltaic power generation system and the power grid is realized, and the initiative, safety and stability in the grid connection process are significantly improved. This "double mode" dynamic decision mechanism greatly improves the response capability of the photovoltaic power generation system to power grid load fluctuation and external environment changes, thereby achieving a high balance between grid connection safety and power generation efficiency. At the same time, due to the high degree of automation and real-time response characteristics of the whole process, the delay and misjudgment risk caused by manual intervention is reduced, thereby significantly improving the grid connection decision efficiency, ensuring the friendliness of photovoltaic power generation to the power grid, and thereby enhancing the overall operation reliability and safety of the power grid.

[0079] Please refer to Figure 4The embodiment of the present application provides a technical scheme: a grid-connected control system in a solar photovoltaic power generation system, comprising: a data acquisition module, configured to acquire power generation operation data when the solar photovoltaic power generation system is connected to a target grid, including grid equipment operation data, photovoltaic power operation data, and source-grid interaction data; a feature extraction module, configured to perform feature analysis on the power generation operation data when the solar photovoltaic power generation system is connected to the target grid, to obtain a set of grid-connected evaluation indexes when the solar photovoltaic power generation system is connected to the target grid, including a grid equipment stability index, a photovoltaic operation stability index, and a grid-connected adaptability index; a comprehensive analysis module, configured to perform comprehensive analysis on the set of grid-connected evaluation indexes when the solar photovoltaic power generation system is connected to the target grid, to obtain a source-grid collaborative safety index when the solar photovoltaic power generation system is connected to the target grid; and a grid-connected control module, configured to take a preset grid-connected control measure based on the source-grid collaborative safety index when the solar photovoltaic power generation system is connected to the target grid.

[0080] Although preferred embodiments of the application have been described herein, after further studying the drawings and disclosure of this application, those skilled in the art will undoubtedly be able to make additional modifications and variations to these preferred embodiments. Therefore, it is intended that the appended claims be construed as including all such modifications and variations as fall within the scope of the application.

[0081] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application also intends to include these modifications and variations.

Claims

1. A grid connection control method for a solar photovoltaic power generation system, characterized in that, Includes the following steps: Acquire power generation operation data when the solar photovoltaic power generation system is connected to the target power grid, including power grid equipment operation data, photovoltaic power operation data, and source-grid interaction data; The power generation operation data of the solar photovoltaic power generation system when connected to the target power grid are subjected to feature analysis to obtain a set of grid connection evaluation indices, including the grid equipment stability index, photovoltaic operation stability index, and grid connection adaptability index. A comprehensive analysis is then performed to obtain the source-grid coordinated security index when the solar photovoltaic power generation system is connected to the target power grid. Pre-set grid connection control measures are adopted based on the source-grid coordination security index when the solar photovoltaic power generation system is connected to the target power grid; The power grid equipment operation data includes the inverter feedforward steady-state index, the circuit breaker feedforward steady-state index, and the transformer feedforward steady-state index. The specific steps for obtaining the power grid equipment stability index when the solar photovoltaic power generation system is connected to the target power grid are as follows: The inverter feedforward steady-state index, circuit breaker feedforward steady-state index, and transformer feedforward steady-state index are comprehensively analyzed when the solar photovoltaic power generation system is connected to the target power grid to obtain the initial grid equipment stability index and equipment interaction correction index when the solar photovoltaic power generation system is connected to the target power grid. Furthermore, a comprehensive analysis was conducted on the initial grid equipment stability index and equipment interaction correction index when the solar photovoltaic power generation system was connected to the target grid, resulting in the grid equipment stability index when the solar photovoltaic power generation system was connected to the target grid. The photovoltaic power operation data includes the series current dispersion index, the backsheet temperature gradient index, and the photovoltaic power quality index. The specific steps to obtain the photovoltaic operation stability index when the solar photovoltaic power generation system is connected to the target grid are as follows: The solar photovoltaic power generation system is connected to the target power grid. The irradiance, ambient temperature and radiation reflectance values ​​are obtained and combined with the backsheet temperature gradient index. A comprehensive analysis is then performed to obtain the photovoltaic operation correction factor when the solar photovoltaic power generation system is connected to the target power grid. A comprehensive analysis of the photovoltaic operation correction factor, series current dispersion index, and photovoltaic power quality index when the solar photovoltaic power generation system is connected to the target power grid is conducted to obtain the photovoltaic operation stability index when the solar photovoltaic power generation system is connected to the target power grid. The source-grid interaction data includes the coupling drive index, source-grid symmetry coordination index, supply-demand current adaptation index, and grid-side carrying capacity index. The specific steps to obtain the grid-connection adaptability index when the solar photovoltaic power generation system is connected to the target grid are as follows: The coupling drive index, source-grid symmetry coordination index, supply-demand current adaptation index, and grid-side carrying capacity index of the grid-connected adaptability index when the solar photovoltaic power generation system is connected to the target grid are normalized. The coupling drive index, source-grid symmetry coordination index, supply-demand current adaptation index, and grid-side carrying capacity index of the normalized solar photovoltaic power generation system when connected to the target power grid are comprehensively analyzed to obtain the grid connection adaptability index of the solar photovoltaic power generation system when connected to the target power grid.

2. The grid connection control method in a solar photovoltaic power generation system according to claim 1, characterized in that, The specific formula for calculating the source-grid coordinated security index when a solar photovoltaic power generation system is connected to the target power grid is as follows: ; in, , , , The four indices are, in order: source-grid coordination security index, grid equipment stability index, photovoltaic operation stability index, and grid connection adaptability index when the solar photovoltaic power generation system is connected to the target grid. , , The following are, in order, the equipment stability adjustment coefficient, photovoltaic operation adjustment coefficient, and grid connection adaptation adjustment coefficient stored in the database. This refers to the photovoltaic operation smoothing coefficient stored in the database.

3. The grid connection control method in a solar photovoltaic power generation system according to claim 1, characterized in that, The specific steps to obtain the inverter feedforward steady-state index when the solar photovoltaic power generation system is connected to the target power grid are as follows: The inverter current stability index, inverter current harmonic distortion index, inverter voltage harmonic distortion index, inverter resonant impedance index, and inverter temperature value are obtained when the solar photovoltaic power generation system is connected to the target power grid, and then standardized. A comprehensive analysis of the inverter current stability index, inverter current harmonic distortion index, inverter voltage harmonic distortion index, inverter resonant impedance index, and inverter temperature value when the standardized solar photovoltaic power generation system is connected to the target power grid is conducted to obtain the inverter feedforward steady-state index when the solar photovoltaic power generation system is connected to the target power grid.

4. The grid connection control method in a solar photovoltaic power generation system according to claim 1, characterized in that, The specific steps for obtaining the photovoltaic power quality index when a solar photovoltaic power generation system is connected to the target power grid are as follows: Obtain the voltage deviation, current deviation, power deviation, and three-phase balance index when the solar photovoltaic power generation system is connected to the target power grid, and perform standardization processing. Based on a comprehensive analysis of the voltage deviation, current deviation, power deviation, and three-phase balance index of the standardized solar photovoltaic power generation system when connected to the target power grid, the photovoltaic power quality index when the solar photovoltaic power generation system is connected to the target power grid is obtained.

5. The grid connection control method in a solar photovoltaic power generation system according to claim 1, characterized in that, The specific formula for calculating the grid-connected adaptability index when a solar photovoltaic power generation system is connected to the target power grid is as follows: ; in, This is the grid-connectivity index for solar photovoltaic power generation systems when connected to the target power grid. , , , The following are, in order: source-grid symmetry coordination index, supply-demand current adaptation index, grid-side carrying capacity index, and coupling drive index, when a normalized solar photovoltaic power generation system is connected to the target power grid. , , , , , The coefficients stored in the database are, in order: symmetry adjustment coefficient, adaptation adjustment coefficient, load adjustment coefficient, drive adjustment coefficient, drive adaptation adjustment coefficient, and smoothing adjustment coefficient.

6. The grid connection control method in a solar photovoltaic power generation system according to claim 1, characterized in that, The specific steps of grid connection control measures based on the preset source-grid coordinated security index when a solar photovoltaic power generation system is connected to the target power grid are as follows: The source-grid coordination security index when the solar photovoltaic power generation system is connected to the target power grid is compared with the preset source-grid coordination security index threshold for analysis. If the source-grid coordination security index of the solar photovoltaic power generation system is lower than or equal to the preset source-grid coordination security index threshold when it is connected to the target power grid, the first grid connection control measure shall be adopted. If the source-grid coordination security index of the solar photovoltaic power generation system when connected to the target grid is higher than the preset source-grid coordination security index threshold, then a second grid connection control measure will be adopted.

7. A grid connection control system for a solar photovoltaic power generation system, employing the grid connection control method for a solar photovoltaic power generation system according to any one of claims 1-6, characterized in that, include: The data acquisition module is used to acquire power generation operation data when the solar photovoltaic power generation system is connected to the target power grid, including power grid equipment operation data, photovoltaic power operation data, and source-grid interaction data; The feature extraction module is used to perform feature analysis on the power generation operation data of the solar photovoltaic power generation system when it is connected to the target power grid, and obtain the grid connection evaluation index set when the solar photovoltaic power generation system is connected to the target power grid, including the grid equipment stability index, the photovoltaic operation stability index, and the grid connection adaptability index. The comprehensive analysis module is used to comprehensively analyze the grid connection evaluation index set when the solar photovoltaic power generation system is connected to the target power grid, and obtain the source-grid coordination security index when the solar photovoltaic power generation system is connected to the target power grid. The grid connection control module is used to take preset grid connection control measures based on the source-grid coordination security index when the solar photovoltaic power generation system is connected to the target power grid.

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