Grid-connected performance test method and system applied to energy storage system, and medium

Abstract

The invention relates to the technical field of grid-connected performance testing and monitoring, in particular to a grid-connected performance testing method and system applied to an energy storage system and a medium, and the method comprises the steps: obtaining the voltage of an energy storage side at each moment after grid connection of the energy storage system, the voltage and current of a power grid side at each moment, and the current of the energy storage side at each moment before grid connection of the energy storage system; determining the wave crest interval difference degree after grid connection of the energy storage system; determining a voltage cooperation index after grid connection of the energy storage system; dividing all moments of the power grid side into time periods; determining a monotone difference index of each time period of the power grid side; determining a waveform difference index after grid connection of the energy storage system in combination with the monotonic difference index; determining a harmonic difference index before and after grid connection of the energy storage system; and determining a performance index of the energy storage system after grid connection in combination with the voltage cooperation index and the waveform difference index, and evaluating the grid connection performance of the energy storage system. According to the invention, the accuracy of the grid-connected performance test of the energy storage system is improved.

Description

Technical Field

[0001] The present application relates to the technical field of grid-connected performance testing, and in particular to a method, system and medium for grid-connected performance testing of energy storage systems. Background Art

[0002] With the development of renewable energy, the importance of energy storage systems in power systems has become increasingly prominent. Energy storage technology can not only balance power supply and demand and improve system reliability, but also promote the consumption of renewable energy. Especially in resources with large fluctuations such as wind and solar energy, energy storage systems can effectively smooth the output power, thereby ensuring a stable supply of electricity. However, in the process of connecting the energy storage system to the power grid, the grid-connected performance of the energy storage system is very important, which is not only related to the safety and reliability of power equipment, but also directly affects the power quality of the power grid. Therefore, it is necessary to test the grid-connected performance of the energy storage system to ensure stable power supply to the power grid.

[0003] However, existing methods for testing the grid-connected performance of energy storage systems mainly focus on evaluating the basic physical properties of energy storage batteries, such as charge and discharge characteristics, internal resistance, and capacity. Although this method helps to understand the working status of energy storage devices, it does not take into account the impact of the interaction between the energy storage system and the power grid on the overall power network. The analysis of the grid-connected performance of energy storage systems is not comprehensive enough, and the test results are not good. Summary of the invention

[0004] In order to solve the above technical problems, a method, system and medium for testing the grid-connected performance of an energy storage system are provided to solve the existing problems.

[0005] The solution to the technical problem of this application is to provide a method, system and medium for testing the grid-connected performance of an energy storage system, including the following steps: In a first aspect, an embodiment of the present application provides a method for testing the grid-connected performance of an energy storage system, the method comprising the following steps: Obtain the voltage at each moment of the energy storage side and the voltage and current at each moment of the grid side after the energy storage system is connected to the grid, as well as the current at each moment of the energy storage side before the energy storage system is connected to the grid; According to the difference distribution between the interval time of adjacent voltage peaks on the energy storage side and the interval time of adjacent voltage peaks on the grid side, the peak interval difference after the energy storage system is connected to the grid is determined; the fluctuation difference of the local voltage in the neighborhood at the same time between the energy storage side and the grid side, as well as the correlation degree of the voltage at all times between the energy storage side and the grid side are analyzed, and the voltage coordination index after the energy storage system is connected to the grid is determined in combination with the peak interval difference; Analyze the changes in the peaks and troughs of the current on the grid side, and divide all the time on the grid side into each time period; determine the monotonic difference index of each time period on the grid side according to the differences in the monotonic changes of the current in different time periods on the grid side, and the differences in the changing trends of the current in different time periods; analyze the degree of fluctuation difference of the current waveform in different time periods on the grid side, and determine the waveform difference index after the energy storage system is connected to the grid in combination with the monotonic difference index; According to the difference in harmonic content of the current between the energy storage side before the energy storage system is connected to the grid and the grid side after the energy storage system is connected to the grid, the harmonic difference index before and after the energy storage system is connected to the grid is determined; combined with the voltage coordination index and the waveform difference index, the performance index of the energy storage system after the grid connection is determined, and the grid-connected performance of the energy storage system is evaluated.

[0006] Preferably, the step of determining the peak interval difference after the energy storage system is connected to the grid includes: Obtain the peak values ​​of the voltage at the energy storage side and the voltage at the grid side at all times respectively; Calculate the interval between the time corresponding to each voltage peak on the energy storage side and the grid side and the time corresponding to the previous voltage peak; The difference between the discreteness of the interval time lengths of all voltage peaks on the energy storage side and the discreteness of the interval time lengths of all voltage peaks on the grid side is taken as the peak interval difference degree.

[0007] Preferably, determining the voltage synergy index of the energy storage system after grid connection includes: Calculate the discrete degree of voltage at each time on the energy storage side and the grid side and multiple times in its neighborhood after the energy storage system is connected to the grid, and use them as the local fluctuation factor at each time on the energy storage side and the local fluctuation factor at each time on the grid side; Calculate the difference between the local fluctuation factor at each moment on the energy storage side and the local fluctuation factor at the same moment on the grid side, record it as the first difference, and take the average of the first difference at all moments as the relative fluctuation difference degree after the energy storage system is connected to the grid; Calculate the correlation coefficient between the voltage at the energy storage side at all times and the voltage at the grid side at all times after the energy storage system is connected to the grid; The sum of the peak interval difference and the relative fluctuation difference is calculated, and the ratio of the correlation coefficient to the sum is used as the voltage synergy index of the energy storage system after grid connection.

[0008] Preferably, dividing all the time periods on the grid side into each time period includes: Calculate the mean value of the current on the grid side at all times after the energy storage system is connected to the grid, and obtain the peaks and troughs of the current on the grid side at all times after the energy storage system is connected to the grid; record the differences between each current peak and each current trough on the grid side and the mean value as the peak convexity of each current peak and the trough concavity of each current trough; Performing threshold segmentation on the peak convexity of all current peaks and the valley concavity of all current valleys on the grid side respectively to obtain a current peak threshold and a current valley threshold; The current peak whose crest convexity is smaller than the current crest threshold is recorded as a normal peak; the current trough whose trough concavity is smaller than the current trough threshold is recorded as a normal trough; The time period between the moment corresponding to the normal wave peak and the moment corresponding to the adjacent normal wave trough is recorded as each time period.

[0009] Preferably, determining the monotonic difference index of each time period on the grid side includes: Calculate the difference between the current at each moment and the previous moment in each period on the grid side, and record it as the differential current at each moment; Calculate the difference between the number of the differential currents greater than or equal to 0 and the number less than 0 in each time period on the grid side, record it as a second difference, and take the ratio of the second difference to the number at all times in the corresponding time period as the monotonic index of each time period on the grid side; Perform linear fitting on the current at all times in each period on the grid side to obtain the absolute value of the slope of the fitting line; Calculate the mean of the difference between the monotonic index of each time period on the grid side and all other time periods, and record it as the first mean; calculate the mean of the difference between the absolute value of the slope of each time period on the grid side and all other time periods, and record it as the second mean; The sum of the first mean value and the second mean value is used as the monotonic difference index of each time period on the grid side.

[0010] Preferably, the step of determining the waveform difference index of the energy storage system after grid connection includes: The absolute value of the differential current at each moment is recorded as the differential absolute current; the average of the distances between the differential absolute current at all moments of each time period on the grid side and all other time periods is recorded as the fluctuation difference degree of each time period on the grid side; Calculate the product of the monotonic difference index and the fluctuation difference, and use the ratio of the product to the monotonic index to obtain the relative difference of the waveform in each period on the grid side; The product of the mean of the relative difference of the waveforms in all time periods on the grid side and the degree of dispersion is taken as the waveform difference index after the energy storage system is connected to the grid.

[0011] Preferably, the harmonic difference index before and after the energy storage system is connected to the grid is determined as follows: Perform frequency domain analysis on the current at all times on the grid side after the energy storage system is connected to the grid, obtain the fundamental amplitude of the fundamental frequency and the harmonic amplitudes of different harmonic frequencies, and use the total harmonic distortion function to obtain the total harmonic distortion rate on the grid side after the connection to the grid; For the current at all times on the energy storage side before the energy storage system is connected to the grid, the total harmonic distortion rate of the energy storage side before the grid connection is obtained using the same method as the total harmonic distortion rate on the grid side; The normalized result of the difference in total harmonic distortion rate between the energy storage side before grid connection and the grid side after grid connection is used as the harmonic difference index before and after grid connection of the energy storage system.

[0012] Preferably, the determining of the performance index of the energy storage system after grid connection and the evaluation of the grid connection performance of the energy storage system include: Calculating a normalized value of the ratio of the voltage synergy index to the waveform difference index, and taking the sum of the normalized value and the harmonic difference index as a performance index of the energy storage system after grid connection; The performance index is normalized. If the normalized performance index is greater than or equal to a preset threshold, the grid-connected performance of the energy storage system is good; otherwise, the grid-connected performance of the energy storage system is poor.

[0013] In a second aspect, the embodiment of the present application further provides a system for testing the grid-connected performance of an energy storage system, the system comprising: The data acquisition module is used to obtain the voltage at each moment of the energy storage side after the energy storage system is connected to the grid, the voltage and current at each moment of the grid side, and the current at each moment of the energy storage side before the energy storage system is connected to the grid; The grid-connected performance analysis module determines the difference in peak intervals after the energy storage system is connected to the grid based on the difference distribution between the intervals of adjacent voltage peaks on the energy storage side and the intervals of adjacent voltage peaks on the grid side; analyzes the difference in local voltage fluctuations in the neighborhood at the same time between the energy storage side and the grid side, as well as the correlation between the voltages at all times on the energy storage side and the grid side, and determines the voltage coordination index of the energy storage system after the grid connection based on the peak interval difference; analyzes the changes in the peaks and troughs of the current on the grid side, and divides all times on the grid side into each time period; and The monotonic change difference of the current in different time periods and the difference of the current change trend in different time periods are used to determine the monotonic difference index of each time period on the grid side; the fluctuation difference degree of the current waveform in different time periods on the grid side is analyzed, and the waveform difference index after the energy storage system is connected to the grid is determined in combination with the monotonic difference index; the harmonic difference index before and after the energy storage system is connected to the grid is determined according to the difference in the harmonic content of the current between the energy storage side before the energy storage system is connected to the grid and the grid side after the energy storage system is connected to the grid; the performance index of the energy storage system after the energy storage system is connected to the grid is determined in combination with the voltage coordination index and the waveform difference index; The grid-connected performance evaluation module is used to evaluate the grid-connected performance of the energy storage system through the performance index of the energy storage system after being connected to the grid.

[0014] In a third aspect, an embodiment of the present application further provides a medium for testing the grid-connected performance of an energy storage system, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the steps of any one of the above-mentioned methods for testing the grid-connected performance of an energy storage system are implemented.

[0015] This application has at least the following beneficial effects: The present application determines the difference in peak intervals after the energy storage system is connected to the grid based on the distribution of the difference between the intervals of adjacent voltage peaks on the energy storage side and the intervals of adjacent voltage peaks on the grid side; analyzes the difference in local voltage fluctuations in the neighborhood at the same time between the energy storage side and the grid side, as well as the degree of correlation between the voltages at all times on the energy storage side and the grid side, and determines the voltage coordination index of the energy storage system after the grid connection in combination with the peak interval difference. The beneficial effect is that the difference in voltage fluctuations between the energy storage side and the grid side is analyzed to reflect the consistency of coordinated changes in the output voltage of the energy storage side and the voltage on the grid side after the energy storage system is connected to the grid, thereby evaluating the voltage regulation capability of the energy storage system after the grid connection, so as to preliminarily reflect the grid connection performance of the energy storage system; analyzes the changes in the peaks and troughs of the current on the grid side, and divides all the times on the grid side into each time period; determines the monotonic difference index of each time period on the grid side based on the difference in the monotonic changes of the current in different time periods on the grid side, and the difference in the current change trend in different time periods; analyzes the fluctuation difference of the current waveform in different time periods on the grid side The degree of grid connection is determined by combining the monotonic difference index to determine the waveform difference index of the energy storage system after grid connection. The beneficial effect is that by analyzing the monotonic changes of the current in different periods on the grid side and the differences in the current waveform changes, the distortion of the current waveform on the grid side after grid connection is explained, thereby reflecting the degree of influence of harmonics on the current on the grid side after the energy storage system is grid-connected, and further reflecting the grid-connected performance of the energy storage system; according to the difference in the harmonic content of the current between the energy storage side before grid connection and the grid side after grid connection, the harmonic difference index before and after grid connection of the energy storage system is determined; combined with the voltage coordination index and the waveform difference index, the performance index of the energy storage system after grid connection is determined, and the grid-connected performance of the energy storage system is evaluated. The beneficial effect is that the difference in the harmonic content carried by the current on the energy storage side and the grid side before and after grid connection of the energy storage system is considered to reflect whether too much harmonic content is introduced into the current after the energy storage system is grid-connected, thereby evaluating the grid-connected performance of the energy storage system; through the performance index, the impact of the grid connection of the energy storage system on the grid side is taken into account, and the accuracy of the grid-connected performance test of the energy storage system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The following is a further detailed description of the grid-connected performance testing method for an energy storage system of the present application in conjunction with the accompanying drawings.

[0017] Figure 1A flowchart of the steps of the method for testing the grid-connected performance of an energy storage system provided in an embodiment of the present application; Figure 2 A flowchart of the steps of a method for obtaining a voltage synergy index of an energy storage system after grid connection provided in an embodiment of the present application; Figure 3 A flowchart of the steps of a method for obtaining a monotonic difference index for each time period on the grid side after the energy storage system is connected to the grid provided in an embodiment of the present application; Figure 4 A block diagram of a grid-connected performance test system for an energy storage system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of this application more clear, the following is a further detailed description of the method, system and medium for testing the grid-connected performance of energy storage systems proposed in this application in combination with the accompanying drawings and implementation examples. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0019] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0020] See also Figure 1 , which shows a flowchart of a method for testing the grid-connected performance of an energy storage system provided by an embodiment of the present application, the method comprising the following steps: Step 1: Obtain the voltage at each moment of the energy storage side and the voltage and current at each moment of the grid side after the energy storage system is connected to the grid, as well as the current at each moment of the energy storage side before the energy storage system is connected to the grid.

[0021] With the rapid advancement of the construction of domestic grid-side energy storage power stations, the capacity of energy storage power stations connected to the grid has increased rapidly. At present, the energy storage system in the grid is mainly electrochemical energy storage, which is mainly composed of battery packs, battery management systems, energy storage inverters, energy management platforms, and electrical equipment such as step-up transformers. Among them, the energy storage inverter is an energy conversion system between the energy storage battery and the AC power grid. The energy storage system is connected to the grid through an energy storage inverter (PCS, also known as a bidirectional energy storage inverter or controller). However, it is impossible to determine whether the grid-connected performance test of the energy storage inverter and the energy storage power station is standardized. Therefore, this embodiment takes the energy storage system and the grid connected to it as the research object and tests the grid-connected performance of the energy storage system.

[0022] By deploying a semi-physical simulation test system in the constructed grid-connected performance test platform, the simulation system is connected to some entities to perform simulation to test the grid-connected performance of the energy storage system. Figure 2As shown, based on the existing RT-LAB simulation system, the energy storage battery model, energy storage PCS controller model and energy storage system model are developed. In combination with the added energy storage power station AG controller, AVC controller, energy storage EMS controller and PCS controller, the energy storage system simulation model is developed to carry out grid-related performance tests of energy storage core components and operation tests of energy storage systems.

[0023] Since the energy storage system is connected to the grid through a power conversion system (PCS), the DC power stored in the energy storage system can be converted into AC power and transmitted to the grid, or the AC power in the grid can be converted into DC power and stored. Therefore, current sensors and voltage sensors are installed at the input end of the energy storage converter connected to the energy storage system and the output end connected to the grid, respectively, to collect the voltage on the energy storage side, the voltage and current on the grid side, and the current before the energy storage system is connected to the grid. The collection time interval is t, and the collection time is T. All the collected data are normalized to obtain the voltage on the energy storage side at each moment after the energy storage system is connected to the grid, the voltage and current on the grid side at each moment, and the current at each moment before the energy storage system is connected to the grid.

[0024] Preferably, in this embodiment, the collection time interval is 1ms, the collection time is 10min, and the maximum and minimum normalization method is used for normalization processing, wherein the maximum and minimum normalization method is a well-known technology and will not be described in detail here. As other implementation methods, the implementer can adopt other methods of the prior art, such as the Z-score normalization method, etc., and this embodiment does not impose any special restrictions on this. Secondly, it should be noted that when collecting the current of the energy storage side before grid connection, the moment when the energy storage system transmits power to the grid, that is, the moment of grid connection, is represented as the grid connection moment, and the current of the energy storage side at all times within 10min before the grid connection moment is collected as the current of the energy storage system before grid connection.

[0025] At this point, the voltage at each moment of the energy storage side after the energy storage system is connected to the grid, the voltage and current at each moment of the grid side, and the current at each moment of the energy storage side before the grid connection are obtained.

[0026] Step 2: Determine the difference in peak intervals after the energy storage system is connected to the grid based on the difference distribution between the intervals of adjacent voltage peaks on the energy storage side and the intervals of adjacent voltage peaks on the grid side; analyze the difference in local voltage fluctuations in the neighborhood at the same time between the energy storage side and the grid side, as well as the correlation between the voltages at all times on the energy storage side and the grid side, and determine the voltage coordination index after the energy storage system is connected to the grid based on the peak interval difference.

[0027] When the energy storage system transmits electricity to the grid, that is, when it is connected to the grid, it is necessary to ensure that the voltage and frequency at both ends of the bidirectional energy storage inverter remain consistent. However, due to the existence of various fluctuation factors within the grid, such as load changes and nonlinear characteristics of electrical equipment, these factors easily introduce harmonic interference, resulting in voltage fluctuations at the output end of the bidirectional energy storage inverter connected to the grid.

[0028] If the energy storage system has good grid-connected performance, can quickly respond to voltage fluctuations on the grid side, and keep the output voltage of the energy storage system synchronized with the voltage on the grid side, it can ensure the effective transmission and seamless connection of electricity to the greatest extent; on the contrary, if the energy storage system has poor grid-connected performance, cannot respond promptly to voltage changes on the grid side, and fails to synchronize with the grid effectively, resulting in a large voltage difference between the two ends of the bidirectional energy storage inverter, it will not only affect the stability of the grid connection and the power supply capacity of the energy storage system, but may even cause grid connection failure. Therefore, by analyzing the difference in voltage between the two ends of the bidirectional energy storage inverter when the energy storage system is connected to the grid, the grid-connected performance of the energy storage system can be preliminarily reflected.

[0029] First, the correlation between the voltage changes at all times on the energy storage side and the grid side after grid connection is analyzed to reflect the possibility of the energy storage system responding quickly to the fluctuations in the grid side voltage. Specifically: Calculate the correlation coefficient between the voltage at the energy storage side at all times and the voltage at the grid side at all times after the energy storage system is connected to the grid; Preferably, in this embodiment, the Pearson correlation coefficient between the voltage at all times on the energy storage side and the voltage at all times on the grid side is calculated, wherein the calculation of the Pearson correlation coefficient is a well-known technique and will not be described in detail herein. As other implementation methods, implementers may adopt other methods of the prior art, such as the Spearman correlation coefficient, cosine similarity, etc., and this embodiment does not impose any special restrictions on this.

[0030] It should be noted that the larger the correlation coefficient is, the stronger the correlation between the voltage changes between the energy storage side and the grid side is, which means that the energy storage system is more likely to respond quickly to fluctuations in the grid side voltage.

[0031] Furthermore, the difference in the peak changes of the voltages on the energy storage side and the grid side after the energy storage system is connected to the grid is analyzed, and the peak interval difference is determined to reflect the stability of power transmission between the energy storage side and the grid side, specifically: Obtain all peaks of the voltage at the energy storage side at all times and the voltage at the grid side at all times after the energy storage system is connected to the grid; Preferably, in this embodiment, an automatic multiscale-based peak detection algorithm (AMPD) is used to obtain the peak, wherein the AMPD peak detection algorithm is a well-known technology and will not be described in detail here. As other implementation methods, the implementer can adopt other methods of the prior art, such as the derivative method, the difference method, etc., and this embodiment does not impose any special restrictions on this.

[0032] Calculate the interval between the time corresponding to each voltage peak on the energy storage side and the time corresponding to the previous voltage peak; Calculate the interval between the time corresponding to each voltage peak on the grid side and the time corresponding to the previous voltage peak; The difference between the discreteness of the intervals of all voltage peaks on the energy storage side and the discreteness of the intervals of all voltage peaks on the grid side is taken as the peak interval difference after the energy storage system is connected to the grid; Preferably, in this embodiment, the degree of dispersion is obtained by calculating the variance of the interval time lengths of all voltage peaks on the energy storage side and the variance of the interval time lengths of all voltage peaks on the energy storage side. As other implementation methods, the implementer may adopt other methods of the prior art, such as standard deviation, coefficient of variation, etc., which are not particularly limited in this embodiment; secondly, the absolute value of the difference between the degree of dispersion of the interval time lengths of all voltage peaks on the energy storage side and the degree of dispersion of the interval time lengths of all voltage peaks on the grid side is taken as the peak interval difference.

[0033] It should be noted that the smaller the difference in peak intervals, the more consistent the time interval distribution of the peak changes of the voltages on the energy storage side and the grid side is, and the better the response of the energy storage system to the voltage on the grid side is.

[0034] Furthermore, the fluctuation of local voltage within the neighborhood at each time is analyzed to determine the local fluctuation factor, which is: Calculate the discrete degree of voltage at each moment on the energy storage side and multiple moments in its neighborhood as the local fluctuation factor at each moment on the energy storage side; Calculate the discrete degree of the voltage at each time on the grid side and multiple times in its neighborhood as the local fluctuation factor at each time on the grid side; Preferably, in this embodiment, the voltage at each moment and 9 moments in its neighborhood are selected. As other implementation methods, the implementer can set it according to the actual situation; secondly, the degree of discreteness is calculated by calculating the coefficient of variation of the voltage at each moment and multiple moments in its neighborhood. The calculation of the coefficient of variation is a well-known technology and will not be repeated here. As other implementation methods, the implementer can adopt other methods of the prior art, such as variance, standard deviation, information entropy, etc., and this embodiment does not impose any special restrictions on this.

[0035] Calculate the difference between the local fluctuation factor at each moment on the energy storage side and the local fluctuation factor at the same moment on the grid side, record it as the first difference, and take the average of the first difference at all moments as the relative fluctuation difference degree after the energy storage system is connected to the grid; Preferably, in this embodiment, the absolute value of the difference between the local fluctuation factor at each moment on the energy storage side and the local fluctuation factor at the same moment on the grid side is calculated.

[0036] It should be noted that the greater the relative fluctuation difference, the more significant the difference in fluctuation amplitude between the voltage on the energy storage side and the voltage on the grid side.

[0037] Further, based on the correlation coefficient, the peak interval difference and the relative fluctuation difference, a voltage coordination index is determined to reflect the coordinated change of the voltage between the energy storage side of the energy storage system and the power grid, specifically: Calculating the sum of the peak interval difference and the relative fluctuation difference, and using the ratio of the correlation coefficient to the sum as the voltage synergy index of the energy storage system after grid connection; Preferably, in this embodiment, the calculation formula of the voltage synergy index of the energy storage system after grid connection is: ,in, is the voltage coordination index after the energy storage system is connected to the grid, is the correlation coefficient, is the relative fluctuation difference of the energy storage system after grid connection, is the peak interval difference after the energy storage system is connected to the grid, is a preset value greater than 0. To avoid the denominator being 0, in this embodiment, The value is 0.01. As other implementation methods, the implementer can set it according to the actual situation.

[0038] It should be noted that the relevant index The larger the relative fluctuation difference B is, the stronger the correlation between the voltage changes between the energy storage side and the grid side is, and the greater the possibility that the energy storage system can quickly respond to changes in grid voltage; the smaller the relative fluctuation difference B is, the smaller the difference in the voltage fluctuation amplitude between the energy storage side and the grid side is, the energy storage system can effectively maintain the stable difference between its grid voltage, and the fluctuation degree between the energy storage voltage and the grid voltage is relatively consistent; the smaller the peak interval difference W is, the energy storage system can stably respond to changes in grid voltage, and its voltage waveform has good synchronization with the grid voltage waveform; therefore, the larger the obtained voltage coordination index A is, the stronger the synchronization and coordination ability of the voltage between the energy storage system and the grid after the energy storage system is connected to the grid, the greater the possibility that the energy storage system can maintain a stable power supply during grid-connected operation, and the stronger the grid-connected performance of the energy storage system.

[0039] Further, the flowchart of the method for obtaining the voltage synergy index of the energy storage system after grid connection provided in the embodiment of the present application is as follows: Figure 2 shown.

[0040] At this point, the voltage synergy index of the energy storage system after grid connection is obtained.

[0041] Step 3, analyzing the changes in the peaks and troughs of the current on the grid side, and dividing all the time on the grid side into each time period; determining the monotonic difference index of each time period on the grid side according to the differences in the monotonic changes of the current in different time periods on the grid side, and the differences in the changing trends of the current in different time periods; analyzing the degree of fluctuation difference of the current waveform in different time periods on the grid side, and combining the monotonic difference index, determining the waveform difference index after the energy storage system is connected to the grid.

[0042] Furthermore, when transmitting electricity to the grid through the energy storage system, not only is the energy storage system required to be able to respond quickly to the voltage changes of the grid, but also the output current and voltage waveforms are required to maintain good quality. When the energy storage system sends the stored electric energy into the grid, it is necessary to convert direct current into alternating current through a bidirectional energy storage inverter. However, the existing control technology cannot achieve an absolutely smooth current waveform output, which will inevitably introduce current harmonics. At this time, if the grid-connected performance of the energy storage system is good and the power conversion control strategy for the inverter is good, the introduced harmonic content will be less, and even harmonic compensation can be performed, thereby improving the power quality. On the contrary, if the energy storage system is applied to the bidirectional energy storage inverter with a poor power conversion control strategy, a large number of harmonics will be introduced, causing serious distortion of the current or voltage waveform and seriously reducing the power quality. Therefore, the grid-connected performance of the energy storage system is further evaluated by analyzing the degree of current waveform distortion and the changes in harmonic content.

[0043] First, analyze the changes in the peaks and troughs of the current at all times on the grid side. Due to the influence of harmonics, a large number of peaks and troughs will appear, so it is necessary to screen the peaks and troughs, specifically: Calculate the mean value of the current on the grid side at all times after the energy storage system is connected to the grid, and obtain the peaks and troughs of the current on the grid side at all times after the energy storage system is connected to the grid; take the difference between each current peak on the grid side and the mean value as the peak convexity of each current peak; take the difference between each current trough on the grid side and the mean value as the trough concavity of each current trough; A threshold segmentation algorithm is used to perform threshold segmentation on the peak convexity of all current peaks on the grid side after the energy storage system is connected to the grid, so as to obtain a current peak threshold; correspondingly, a threshold segmentation is performed on the valley concavity of all current valleys on the grid side after the energy storage system is connected to the grid, so as to obtain a current valley threshold; The current peak whose crest convexity is smaller than the current crest threshold is recorded as a normal peak; the current trough whose trough concavity is smaller than the current trough threshold is recorded as a normal trough; The time period between the moment corresponding to the normal wave peak and the moment corresponding to the adjacent normal wave trough is recorded as each time period; Furthermore, if the grid-connected performance of the energy storage system is good and the output current waveform is not distorted, the current in each period has an obvious monotonic trend, and the monotonicity of the current between different periods is relatively consistent. Therefore, the monotonic change of the current in each period is analyzed to determine the monotonic index, which is: Calculate the difference between the current at each moment and the previous moment in each period on the grid side after the energy storage system is connected to the grid, and record it as the differential current at each moment; The difference between the number of differential currents greater than or equal to 0 and the number of differential currents less than 0 in each period on the grid side after the energy storage system is connected to the grid is recorded as the second difference, and the ratio of the monotonic difference to the number at all times in the corresponding period is used as the monotonic index of each period on the grid side; Preferably, in this embodiment, the calculation formula of the monotonic index of each time period on the grid side after the energy storage system is connected to the grid is: ,in, For the grid side The monotonic index of the time period, For the grid side The number of differential currents greater than or equal to 0 in a time period, For the grid side The number of time periods in which the differential current is less than 0, Grid side The number of all moments in a period; secondly, The second difference.

[0044] It should be noted that The larger the The more obvious the current change trend is within a period, the stronger the monotonicity of the current waveform is. and The closer they are, the The greater the possibility of a completely monotonic trend in a period, the larger the monotonic index is, indicating that the The stronger the monotonicity of the current in a time period, the better the quality of the current waveform.

[0045] Furthermore, the trend change intensity of the current in each period on the grid side is analyzed, and the monotonic difference index is determined by the difference in the monotonic change and trend intensity change of the current in different time periods, which is specifically: Perform linear fitting on the current at all times in each period on the grid side to obtain the absolute value of the slope of the fitting line; Preferably, in this embodiment, the least square method is used for linear fitting, wherein the least square method is a well-known technology and will not be described in detail here.

[0046] Calculate the average value of the difference between the monotonic index in each time period on the grid side and all other time periods after the energy storage system is connected to the grid, and record it as the first mean value; Calculate the average of the differences between the absolute values ​​of the slopes in each time period on the grid side and in all other time periods after the energy storage system is connected to the grid, and record it as the second average; The sum of the first mean value and the second mean value is used as the monotonic difference index of each period on the grid side after the energy storage system is connected to the grid; Preferably, in this embodiment, the average of the absolute values ​​of the difference between the monotonic index in each time period on the grid side and all other time periods after the energy storage system is connected to the grid is calculated; the average of the absolute values ​​of the difference between the absolute values ​​of the slope in each time period on the grid side and all other time periods after the energy storage system is connected to the grid is calculated, which is recorded as the second mean.

[0047] Further, the flowchart of the method for obtaining the monotonic difference index of each time period on the grid side after the energy storage system is connected to the grid provided in the embodiment of the present application is as follows: Figure 3 shown.

[0048] It should be noted that the monotonic difference index reflects the difference in the monotonicity of the current change between each time period and the other time periods. The smaller the monotonic difference index is, the more consistent the monotonicity of the current change between different time periods is.

[0049] Furthermore, if the current waveform is good, the degree of change of the current in different time periods will be relatively consistent. However, considering that the current waveform has both single increase and single decrease change trends, the absolute value of the differential current is taken to analyze the degree of change of the current waveform, and the fluctuation difference is determined by the difference in current changes in different time periods, specifically: Take the absolute value of the differential current at each moment and record it as the differential absolute current at each moment; The average of the distances between the differential absolute currents at all times in each time period on the grid side and all other time periods after the energy storage system is connected to the grid is taken as the fluctuation difference degree of each time period on the grid side after the energy storage system is connected to the grid; Preferably, in this embodiment, the average of the DTW distances between the differential absolute currents at all times in each time period on the grid side and all other time periods after the energy storage system is connected to the grid is taken as the fluctuation difference degree of each time period on the grid side after the energy storage system is connected to the grid.

[0050] It should be noted that if the fluctuation difference is smaller, it means that the differential absolute current in the corresponding time period and the other time periods are more similar in waveform change.

[0051] Further, based on the monotonic difference index, the monotonic index and the fluctuation difference, the waveform relative difference is determined, specifically: Calculating the product of the monotonic difference index and the fluctuation difference, and taking the ratio of the product to the monotonic index as the relative difference of the waveform at each time period on the grid side after the energy storage system is connected to the grid; Preferably, in this embodiment, the calculation formula for the relative difference of the waveform in each period on the grid side after the energy storage system is connected to the grid is: In the formula, After the energy storage system is connected to the grid, the grid side Relative differences in waveforms for different time periods; After the energy storage system is connected to the grid, the grid side Monotonic difference index of time periods; After the energy storage system is connected to the grid, the grid side Monotonic index of the time period; After the energy storage system is connected to the grid, the grid side The volatility difference of each period, To preset a value greater than 0 to avoid the denominator being 0, in this embodiment, The value is 0.01. As other implementation methods, the implementer can set it according to the actual situation.

[0052] It should be noted that the monotonic difference index reflects the difference in the monotonicity of current changes between different time periods. The smaller the monotonic difference index, the more consistent the monotonicity; the fluctuation difference reflects the similarity of the waveform changes of the current between different time periods. The smaller the fluctuation difference, the more consistent the waveform changes; the monotonic index reflects the monotonic changes of the current itself in each time period. The larger the monotonic index, the stronger the monotonic change of the current in the corresponding time period; therefore, the smaller the relative difference of the obtained waveform, the stronger the monotonicity of the current in the corresponding time period, and the more consistent it is with the waveform of the current changes in other time periods.

[0053] Further, based on the relative difference of the waveforms, a waveform difference index is determined to reflect the influence of harmonics on the current on the grid side, specifically: The product of the mean of the relative difference of the waveforms in all time periods on the grid side after the energy storage system is connected to the grid and the degree of dispersion is taken as the waveform difference index after the energy storage system is connected to the grid; Preferably, in this embodiment, the product of the mean and variance of the relative differences of the waveforms in all time periods on the grid side after the energy storage system is connected to the grid is used as the waveform difference index after the energy storage system is connected to the grid. As other implementation methods, the implementer can use other methods of the prior art to measure the degree of discreteness, such as standard deviation, etc. This embodiment does not impose any special restrictions on this.

[0054] It should be noted that the smaller the waveform difference index is, the more consistent the degree of change in the current waveform is between different time periods, which means that the harmonic interference is less affected.

[0055] At this point, the waveform difference index of the energy storage system after grid connection is obtained.

[0056] Step 4: Determine the harmonic difference index of the energy storage system before and after grid connection based on the difference in harmonic content of the current between the energy storage side before grid connection and the grid side after grid connection; determine the performance index of the energy storage system after grid connection by combining the voltage coordination index and the waveform difference index, and evaluate the grid connection performance of the energy storage system.

[0057] Furthermore, the waveform difference index only analyzes the grid-connected performance of the energy storage system based on the changes in the current waveform. However, when the power grid fluctuates, it may also cause changes in the current waveform. Therefore, it is not comprehensive enough to detect the grid-connected performance of the energy storage system only through the changes in the current waveform. By combining the current changes on the energy storage side and the grid side before and after grid connection and analyzing the degree of harmonic distortion of the current, the grid-connected performance of the energy storage system can be further analyzed.

[0058] First, the harmonic distortion rate is determined by performing frequency domain analysis on the current at all times on the grid side to reflect the harmonic content carried by the current on the grid side, specifically: Perform frequency domain analysis on the current at all times on the grid side to obtain the fundamental amplitude of the fundamental frequency and the harmonic amplitudes of different harmonic frequencies; Based on the fundamental amplitude of the fundamental frequency and the harmonic amplitudes of all harmonic frequencies, a total harmonic distortion function (THD) is used to obtain the total harmonic distortion rate on the grid side; Preferably, in this embodiment, a Fourier transform algorithm is used for frequency domain analysis, wherein an integer multiple of the fundamental frequency is set as the harmonic frequency, wherein the fundamental frequency is set to 50 Hz, and the maximum integer multiple is 15, that is, 100 Hz, 150 Hz, 200 Hz, , 750 Hz as the harmonic frequency, the Fourier transform algorithm and the calculation of the total harmonic distortion are well-known technologies and will not be described in detail here.

[0059] For the current at all times on the energy storage side before grid connection, the total harmonic distortion rate of the energy storage side before grid connection is obtained using the same method as the total harmonic distortion rate on the grid side; The normalized result of the difference between the total harmonic distortion rate of the energy storage side before grid connection and the total harmonic distortion rate of the grid side is used as the harmonic difference index before and after grid connection; Preferably, in this embodiment, a sigmoid function is used for normalization processing. As other implementations, implementers may use other methods in the prior art, such as a tanh function, etc. This embodiment does not impose any special restrictions on this.

[0060] It should be noted that the larger the harmonic difference index is, the less harmonics carried by the grid-side current are carried after the energy storage system is connected to the grid, which means that the energy storage system has a better power conversion control strategy for the bidirectional energy storage inverter and has performed harmonic compensation for the current harmonics, and the grid-connected performance of the energy storage system is better; conversely, the smaller the harmonic difference index is, or even a negative number, it means that after the bidirectional energy storage inverter is used for conversion, a large amount of harmonics are introduced into the current on the grid side, causing serious distortion of the current or voltage waveform, and the grid-connected performance of the energy storage system is worse.

[0061] Further, based on the voltage coordination index, the waveform difference index and the harmonic difference index, a performance index of the energy storage system is determined to reflect the grid-connected performance of the energy storage system, specifically: Calculating a normalized value of the ratio of the voltage synergy index to the waveform difference index, and taking the sum of the normalized value and the harmonic difference index as a performance index of the energy storage system after grid connection; It should be noted that the larger the voltage synergy index is, the better the performance of the energy storage system in voltage regulation is, and the stronger its response to voltage changes on the grid side is; the smaller the waveform difference index is, the more consistent the degree of change of the current waveform on the grid side in different periods is, and the smaller the harmonic interference is; the harmonic difference index reflects the change in the harmonic content of the grid current before and after the energy storage system is connected to the grid. The larger the harmonic difference index is, the less harmonics carried by the current on the grid side are reduced after the energy storage system is connected to the grid, and the better the grid-connected performance of the energy storage system is; therefore, the larger the performance index is, the better the grid-connected performance of the energy storage system is.

[0062] Further, based on the performance index, the grid-connected performance of the energy storage system is evaluated, specifically: The performance index is normalized. If the normalized performance index is greater than or equal to the preset threshold, the grid-connected performance of the energy storage system is good, indicating that after being connected to the grid, the energy storage system can not only respond to voltage changes on the grid side in a timely manner, but also further suppress harmonics in the current; if the normalized performance index is less than the preset threshold, the grid-connected performance of the energy storage system is poor.

[0063] Preferably, in this embodiment, the preset threshold value is 0.5. As other implementation modes, the implementer can set it according to the actual situation.

[0064] The present application also provides a system for testing the grid-connected performance of an energy storage system, including: The data acquisition module is used to obtain the voltage at each moment of the energy storage side after the energy storage system is connected to the grid, the voltage and current at each moment of the grid side, and the current at each moment of the energy storage side before the energy storage system is connected to the grid; The grid-connected performance analysis module determines the difference in peak intervals after the energy storage system is connected to the grid based on the difference distribution between the intervals of adjacent voltage peaks on the energy storage side and the intervals of adjacent voltage peaks on the grid side; analyzes the difference in local voltage fluctuations in the neighborhood at the same time between the energy storage side and the grid side, as well as the correlation between the voltages at all times on the energy storage side and the grid side, and determines the voltage coordination index of the energy storage system after the grid connection based on the peak interval difference; analyzes the changes in the peaks and troughs of the current on the grid side, and divides all times on the grid side into each time period; and The monotonic change of the current in different time periods and the difference in the change trend of the current in different time periods are used to determine the monotonic difference index of each time period on the grid side; the fluctuation difference degree of the current waveform in different time periods on the grid side is analyzed, and the waveform difference index after the energy storage system is connected to the grid is determined in combination with the monotonic difference index; the harmonic difference index before and after the energy storage system is connected to the grid is determined according to the difference in the harmonic distortion of the current between the energy storage side before the energy storage system is connected to the grid and the grid side after the energy storage system is connected to the grid; the performance index of the energy storage system after the grid connection is determined in combination with the voltage coordination index and the waveform difference index; The grid-connected performance evaluation module is used to evaluate the grid-connected performance of the energy storage system through the performance index of the energy storage system.

[0065] Further, the block diagram of the system for testing the grid-connected performance of an energy storage system provided in the embodiment of the present application is as follows: Figure 4 shown.

[0066] Based on the same inventive concept as the above method, an embodiment of the present application also provides a medium for testing the grid-connected performance of an energy storage system, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of any one of the above methods for testing the grid-connected performance of an energy storage system are implemented.

[0067] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0068] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the present application. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application without departing from the content of the technical solution of the present application, shall fall within the protection scope of the technical solution of the present application.

Claims

1. A method for testing the grid-connected performance of an energy storage system, characterized in that: The method comprises the following steps: Obtain the voltage at each moment of the energy storage side and the voltage and current at each moment of the grid side after the energy storage system is connected to the grid, as well as the current at each moment of the energy storage side before the energy storage system is connected to the grid; According to the difference distribution between the interval time of adjacent voltage peaks on the energy storage side and the interval time of adjacent voltage peaks on the grid side, the peak interval difference after the energy storage system is connected to the grid is determined; the fluctuation difference of the local voltage in the neighborhood at the same time between the energy storage side and the grid side, as well as the correlation degree of the voltage at all times between the energy storage side and the grid side are analyzed, and the voltage coordination index after the energy storage system is connected to the grid is determined in combination with the peak interval difference; Analyze the changes in the peaks and troughs of the current on the grid side, and divide all the time on the grid side into each time period; determine the monotonic difference index of each time period on the grid side according to the differences in the monotonic changes of the current in different time periods on the grid side, and the differences in the changing trends of the current in different time periods; analyze the degree of fluctuation difference of the current waveform in different time periods on the grid side, and determine the waveform difference index after the energy storage system is connected to the grid in combination with the monotonic difference index; According to the difference in harmonic content of the current between the energy storage side before the energy storage system is connected to the grid and the grid side after the energy storage system is connected to the grid, the harmonic difference index before and after the energy storage system is connected to the grid is determined; combined with the voltage coordination index and the waveform difference index, the performance index of the energy storage system after the grid connection is determined, and the grid-connected performance of the energy storage system is evaluated.

2. The method for testing the grid-connected performance of an energy storage system according to claim 1, characterized in that: Determining the peak interval difference after the energy storage system is connected to the grid includes: Obtain the peak values ​​of the voltage at the energy storage side and the voltage at the grid side at all times respectively; Calculate the interval between the time corresponding to each voltage peak on the energy storage side and the grid side and the time corresponding to the previous voltage peak; The difference between the discreteness of the interval time lengths of all voltage peaks on the energy storage side and the discreteness of the interval time lengths of all voltage peaks on the grid side is taken as the peak interval difference.

3. The method for testing the grid-connected performance of an energy storage system according to claim 1, characterized in that: Determining the voltage coordination index of the energy storage system after grid connection includes: Calculate the discrete degree of voltage at each time on the energy storage side and the grid side and multiple times in its neighborhood after the energy storage system is connected to the grid, and use them as the local fluctuation factor at each time on the energy storage side and the local fluctuation factor at each time on the grid side; Calculate the difference between the local fluctuation factor at each moment on the energy storage side and the local fluctuation factor at the same moment on the grid side, record it as the first difference, and take the average of the first difference at all moments as the relative fluctuation difference degree after the energy storage system is connected to the grid; Calculate the correlation coefficient between the voltage at the energy storage side at all times and the voltage at the grid side at all times after the energy storage system is connected to the grid; The sum of the peak interval difference and the relative fluctuation difference is calculated, and the ratio of the correlation coefficient to the sum is used as the voltage synergy index of the energy storage system after grid connection.

4. The method for testing the grid-connected performance of an energy storage system according to claim 1, characterized in that: The grid-side all time periods are divided into each period, including: Calculate the mean value of the current on the grid side at all times after the energy storage system is connected to the grid, and obtain the peaks and troughs of the current on the grid side at all times after the energy storage system is connected to the grid; record the differences between each current peak and each current trough on the grid side and the mean value as the peak convexity of each current peak and the trough concavity of each current trough; Performing threshold segmentation on the peak convexity of all current peaks and the valley concavity of all current valleys on the grid side respectively to obtain a current peak threshold and a current valley threshold; The current peak whose crest convexity is smaller than the current crest threshold is recorded as a normal peak; the current trough whose trough concavity is smaller than the current trough threshold is recorded as a normal trough; The time period between the moment corresponding to the normal wave peak and the moment corresponding to the adjacent normal wave trough is recorded as each time period.

5. The method for testing the grid-connected performance of an energy storage system according to claim 1, characterized in that: Determining the monotonic difference index of each time period on the grid side includes: Calculate the difference between the current at each moment and the previous moment in each period on the grid side, and record it as the differential current at each moment; Calculate the difference between the number of the differential currents greater than or equal to 0 and the number less than 0 in each time period on the grid side, record it as a second difference, and take the ratio of the second difference to the number at all times in the corresponding time period as the monotonic index of each time period on the grid side; Perform linear fitting on the current at all times in each period on the grid side to obtain the absolute value of the slope of the fitting line; Calculate the mean of the difference between the monotonic index of each time period on the grid side and all other time periods, and record it as the first mean; calculate the mean of the difference between the absolute value of the slope of each time period on the grid side and all other time periods, and record it as the second mean; The sum of the first mean value and the second mean value is used as the monotonic difference index of each time period on the grid side.

6. The method for testing the grid-connected performance of an energy storage system according to claim 5, characterized in that: Determining the waveform difference index after the energy storage system is connected to the grid includes: The absolute value of the differential current at each moment is recorded as the differential absolute current; the average of the distances between the differential absolute current at all moments of each time period on the grid side and all other time periods is recorded as the fluctuation difference degree of each time period on the grid side; Calculate the product of the monotonic difference index and the fluctuation difference, and use the ratio of the product to the monotonic index to obtain the relative difference of the waveform in each period on the grid side; The product of the mean of the relative difference of the waveforms in all time periods on the grid side and the degree of dispersion is taken as the waveform difference index after the energy storage system is connected to the grid.

7. The method for testing the grid-connected performance of an energy storage system according to claim 1, characterized in that: Determining the harmonic difference index before and after the energy storage system is connected to the grid: Perform frequency domain analysis on the current at all times on the grid side after the energy storage system is connected to the grid, obtain the fundamental amplitude of the fundamental frequency and the harmonic amplitudes of different harmonic frequencies, and use the total harmonic distortion function to obtain the total harmonic distortion rate on the grid side after the connection to the grid; For the current at all times on the energy storage side before the energy storage system is connected to the grid, the total harmonic distortion rate of the energy storage side before the grid connection is obtained using the same method as the total harmonic distortion rate on the grid side; The normalized result of the difference in total harmonic distortion rate between the energy storage side before grid connection and the grid side after grid connection is used as the harmonic difference index before and after grid connection of the energy storage system.

8. The method for testing the grid-connected performance of an energy storage system according to claim 1, characterized in that: Determining the performance index of the energy storage system after grid connection and evaluating the grid connection performance of the energy storage system include: Calculating a normalized value of the ratio of the voltage synergy index to the waveform difference index, and taking the sum of the normalized value and the harmonic difference index as a performance index of the energy storage system after grid connection; The performance index is normalized. If the normalized performance index is greater than or equal to a preset threshold, the grid-connected performance of the energy storage system is good; otherwise, the grid-connected performance of the energy storage system is poor.

9. Applied to the energy storage system grid-connected performance test system, characterized in that: The system comprises: The data acquisition module is used to obtain the voltage at each moment of the energy storage side after the energy storage system is connected to the grid, the voltage and current at each moment of the grid side, and the current at each moment of the energy storage side before the energy storage system is connected to the grid; The grid-connected performance analysis module determines the difference in peak intervals after the energy storage system is connected to the grid based on the difference distribution between the intervals of adjacent voltage peaks on the energy storage side and the intervals of adjacent voltage peaks on the grid side; analyzes the difference in local voltage fluctuations in the neighborhood at the same time between the energy storage side and the grid side, as well as the correlation between the voltages at all times on the energy storage side and the grid side, and determines the voltage coordination index of the energy storage system after the grid connection based on the peak interval difference; analyzes the changes in the peaks and troughs of the current on the grid side, and divides all times on the grid side into each time period; and The monotonic change difference of the current in different time periods and the difference of the current change trend in different time periods are used to determine the monotonic difference index of each time period on the grid side; the fluctuation difference degree of the current waveform in different time periods on the grid side is analyzed, and the waveform difference index after the energy storage system is connected to the grid is determined in combination with the monotonic difference index; the harmonic difference index before and after the energy storage system is connected to the grid is determined according to the difference in the harmonic content of the current between the energy storage side before the energy storage system is connected to the grid and the grid side after the energy storage system is connected to the grid; the performance index of the energy storage system after the energy storage system is connected to the grid is determined in combination with the voltage coordination index and the waveform difference index; The grid-connected performance evaluation module is used to evaluate the grid-connected performance of the energy storage system through the performance index of the energy storage system after being connected to the grid.

10. A medium for testing the grid-connected performance of an energy storage system, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the method for testing the grid-connected performance of an energy storage system as described in any one of claims 1 to 8 are implemented.

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