Spectrum leakage elimination method and system

Abstract

The present invention discloses a method and system for eliminating spectrum leakage, belonging to the technical fields of signal processing and new energy power generation. The elimination method provided by the invention includes harmonic injection and sampling, fast Fourier transform, and calculating the compensation amount by proportional harmonic averaging, and calculating the positive-sequence output impedance and negative-sequence output impedance of the integer frequency at the injection point. Based on the principle of spectrum leakage, this elimination method only requires simple proportional harmonic averaging calculation to eliminate the influence of spectrum leakage caused by non-integer cycle sampling on the impedance measurement value at the swept-frequency harmonic injection frequency when the power grid frequency fluctuates. This method requires less computation, and the swept-frequency results verify the effectiveness of this method.

Description

Technical Field

[0001] The present invention belongs to the technical fields of signal processing and new energy power generation, and particularly relates to a method and system for eliminating spectrum leakage. Background Art

[0002] With the continuous connection of new energy power generation equipment, the stable operation of a high-penetration power system has become a hot issue to be solved urgently. Among them, the interaction between new energy power generation equipment and the power grid has an important impact on the stability of the power system. Therefore, it is necessary to analyze the stability of the grid-connected system. The existing methods for analyzing the stability of grid-connected systems mainly include the state space method and the impedance analysis method, etc. When the internal structure parameters of the inverter system are unknown, the impedance analysis method regards the system as a "black box", obtains the terminal characteristics of the system through frequency sweeping, and then conducts corresponding stability analysis. Due to this characteristic, the impedance analysis method is more applicable to engineering practice and has received extensive attention.

[0003] The doctoral dissertation of Hunan University in 2019, titled "Research on the Broadband Oscillation Mechanism and Suppression Method of New Energy Power Generation Connected to a Weak Grid", developed an impedance measurement device for new energy power generation equipment and realized the measurement of the broadband impedance characteristics of photovoltaic and wind power equipment in new energy power stations. However, this dissertation did not consider the influence of spectrum leakage on the impedance measurement results.

[0004] The article in "Power System Protection and Control", Vol. 10, 2018, pages 96 - 101, titled "Weak Grid Impedance Measurement Algorithm Based on Windowed Fourier Transform". By using the method of windowed Fourier transform to improve the frequency resolution simultaneously, the attenuation speed between the main lobe and the side lobes and between the side lobes is accelerated, and the spectrum leakage is weakened to suppress the over-width of the main lobe caused by windowing. However, increasing the frequency resolution requires increasing the number of sampling points, which improves the requirements for storage space and data processing capabilities.

[0005] The article in "Power Grid Technology", Vol. 3, 2020, pages 1105 - 1113, titled "Power Harmonic Analysis Method Based on Combined Cosine Optimized Window Four-Spectrum Line Interpolation FFT". By using the method of windowed interpolation FFT and obtaining a window function with small side lobe peak level and large side lobe asymptotic attenuation rate based on the genetic algorithm, the spectrum leakage is reduced. However, this algorithm requires a large amount of operations and fails to completely eliminate the influence of spectrum leakage.

[0006] Based on the above literature, the existing technologies have the following deficiencies:

[0007] 1. For the existing impedance frequency sweeping method of new energy power generation equipment, when the grid frequency fluctuates, the influence of non-integer cycle sampling on the output impedance measurement at the frequency to be measured is not considered. It is necessary to study a method for eliminating the influence of spectrum leakage on impedance measurement;

[0008] 2. Existing spectrum leakage suppression methods based on windowed Fourier transform have high requirements for storage space and data processing capabilities. It is necessary to study a method with simple calculation and less storage space occupation.

[0009] 3. Existing multi-spectrum line interpolation methods for suppressing spectrum leakage further reduce the influence of spectrum leakage on the basis of windowed Fourier transform, but have high computational complexity and still cannot completely eliminate the influence of spectrum leakage. Summary of the Invention

[0010] The technical problem to be solved by the present invention is the problem of large amount of calculation and incomplete elimination of the influence of spectrum leakage existing in the prior art. By calculating the proportional harmonic mean of the voltage and current values on both sides of the harmonic injection frequency of impedance sweep only, the influence of spectrum leakage caused by power grid frequency fluctuation on the impedance measurement value is eliminated, thereby improving the accuracy of impedance sweep, facilitating the stability analysis of new energy equipment, and at the same time not requiring excessive calculation and no additional equipment.

[0011] The object of the present invention is achieved as follows. The present invention provides a spectrum leakage elimination method. The grid-connected system applying this method includes a grid-connected inverter and a three-phase power grid. The steps of the elimination method are as follows:

[0012] Harmonics with a frequency of the integer frequency f to be measured are sequentially injected into the point of common coupling, and L terminal voltages U m and L output currents I pcc_r_m_i are collected during the injection process. Here, r is the phase sequence, r = a, b, c, and i is the serial number of the terminal voltage and the output current, i = 1, 2,..., L. Among them, the integer frequency f g_r_m_i to be measured is any N integer frequencies selected from the sweep frequency range H as the integer frequency f m to be measured. The sweep frequency range H, H = [0 Hz, F Hz], where F is the integer corresponding to the maximum integer frequency F Hz in the sweep frequency range H, m = 1, 2,..., N, N < F; m Perform fast Fourier transform on the terminal voltage U

[0013] and the output current I pcc_r_m_i to obtain the frequency-domain terminal voltage U g_r_m_i (k) and the frequency-domain output current I r_m (k), where k is the serial number of the integer frequency within the sweep frequency range H, k = 0, 1,..., F; r_m Extract the positive-sequence voltage component U

[0014] corresponding to the frequency-domain terminal voltage U r_m (k) and the negative-sequence voltage component U p_m (k), and extract the positive-sequence current component I n_m (k) and the negative-sequence current component I r_m(k) corresponding positive-sequence component of current I p_m (k) and negative-sequence component of current I n_m (k);

[0015] Calculate the compensated integer frequency f to be measured through the proportional harmonic mean formula and the integer frequency f to be measured, (f m 、(f m - 1), and (f m + 1) at the positive-sequence component of voltage, negative-sequence component of voltage, positive-sequence component of current, and negative-sequence component of current m Positive-sequence component of voltage U p_m (f m )′, negative-sequence component of voltage U n_m (f m )′, positive-sequence component of current I p_m (f m )′ and negative-sequence component of current I n_m (f m )′;

[0016] Calculate the positive-sequence output impedance Z m (f p ) and negative-sequence output impedance Z m ) at the integer frequency f to be measured. n (f m )

[0017] Preferably, the grid-connected system applying this method further includes a DC-side power supply, a three-phase LC filter, and a three-phase line impedance connected in series in sequence.

[0018] Preferably, the specific process of collecting L terminal voltages U pcc_r_m_i and L output currents I g_r_m_i during the injection process is as follows:

[0019] Inject harmonics with a frequency of f m into the point of common coupling in sequence, each injection lasts for t seconds, and within t seconds, collect the voltages of L points of common coupling and the currents of the three-phase line impedance at equal intervals, and record them as the terminal voltage U pcc_r_m_i and the output current I g_r_m_i .

[0020] Preferably, the injection time t of the harmonics is 1 second, and the maximum integer frequency F is 10000.

[0021] Preferably, the specific transformation process of the frequency-domain terminal voltage U r_m (k) and the frequency-domain output current I r_m (k) is as follows:

[0022] For the terminal voltage U pcc_r_m_i and the output current I g_r_m_iPerform a fast Fourier transform and sweep the frequency to obtain the Fourier-transformed terminal voltage and Fourier-transformed output current corresponding to each integer frequency within the sweep range H, denoted as the frequency-domain terminal voltage U r_m (k) and the frequency-domain output current I r_m (k), and their expressions are respectively:

[0023]

[0024] where j is the imaginary unit.

[0025] Preferably, the expressions for the positive-sequence voltage component U p_m (k), the negative-sequence voltage component U n_m (k), the positive-sequence current component I p_m (k), and the negative-sequence current component I n_m (k) are respectively:

[0026]

[0027] where j is the imaginary unit.

[0028] Preferably, the expression for the proportional harmonic mean formula is:

[0029]

[0030] In the formula, U p_m (f m ) is the positive-sequence voltage component at the integer frequency f m to be measured, U n_m (f m ) is the negative-sequence voltage component at the integer frequency f m to be measured, I p_m (f m ) is the positive-sequence current component at the integer frequency f m to be measured, I n_m (f m ) is the negative-sequence current component at the integer frequency f m to be measured, U p_m (f m - 1) is the positive-sequence voltage component at the integer frequency (f m - 1) to be measured, U n_m (f m - 1) is the negative-sequence voltage component at the integer frequency (f m - 1) to be measured, I p_m (f m - 1) is the positive-sequence current component at the integer frequency (f m - 1) to be measured, I n_m (f m - 1) is the negative-sequence current component at the integer frequency (fm Negative sequence component of current at - 1), U p_m (f m +1) is the positive sequence component of voltage at the measured integer frequency (f m +1), U n_m (f m +1) is the measured integer frequency (f m +1), negative sequence component of voltage, I p_m (f m +1) is the measured integer frequency (f m +1), positive sequence component of current, I n_m (f m +1) is the measured integer frequency (f m +1), negative sequence component of current.

[0031] Preferably, the positive sequence output impedance Z p (f m ) and the negative sequence output impedance Z n (f m ) are calculated as follows:

[0032]

[0033] The present invention also provides a spectrum leakage elimination system, including:

[0034] A DC side power supply, a grid - connected inverter, a three - phase LC filter, a three - phase line impedance, and a three - phase power grid connected in series in sequence;

[0035] A control module for generating a frequency - sweeping range H and obtaining N measured integer frequencies f m ;

[0036] An injection module for injecting harmonics with frequencies of f m to the point of common coupling in sequence;

[0037] A sampling module for collecting the terminal voltage U pcc_r_m_i and the output current I g_r_m_i during the injection process;

[0038] A calculation module for performing fast Fourier transform on the terminal voltage U pcc_r_m_i and the output current I g_r_m_i to obtain the frequency - swept terminal voltage U r_m (k) and the frequency - swept output current I r_m (k);

[0039] An extraction module for extracting the positive sequence component of voltage U r_m (k) and the negative sequence component of voltage U r_m (k) from the frequency - swept terminal voltage U p_m (k) and the frequency - swept output current In_m (k), positive sequence component I of current p_m (k) and negative sequence component I of current n_m calculation module;

[0040] for calculating the positive sequence component U through proportional harmonic averaging p_m (f m )′, negative sequence component U of voltage n_m (f m )′, positive sequence component I of current p_m (f m )′ and negative sequence component I of current n_m (f m )′ calculation module;

[0041] for calculating the positive sequence output impedance Z at the measured integer frequency f m at p (f m ) and negative sequence output impedance Z n (f m ) calculation module;

[0042] and a microprocessor and a memory, each of the modules and the microprocessor is programmed or configured to execute the steps of the spectrum leakage elimination method.

[0043] The present invention also provides a computer-readable storage medium, in which a computer program programmed or configured to execute the spectrum leakage elimination method is stored.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1. The spectrum leakage elimination method described in the present invention, that is, the proportional harmonic averaging elimination method applicable to the impedance sweep frequency spectrum leakage problem, detects the voltage and current on both sides of the measured frequency during the sweep frequency, and performs proportional harmonic averaging calculation, thereby eliminating the influence of spectrum leakage caused by the change of the power grid frequency and improving the impedance sweep accuracy of new energy power generation equipment;

[0046] 2. The present invention only needs simple proportional harmonic averaging calculation to eliminate the influence of spectrum leakage on impedance measurement, requires a small storage space, and does not require high data processing capabilities;

[0047] 3. The spectrum leakage elimination method described in the present invention only improves the existing sweep frequency algorithm, does not require additional equipment, and saves costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is the main circuit structure diagram of the grid-connected system in the embodiment of the present invention.

[0049] Figure 2 The figure is a flow chart of the spectrum leakage elimination method of the present invention.

[0050] Figure 3 The output impedance frequency sweep result and impedance theoretical curve of the grid-connected system when the three-phase grid frequency is 50 Hz under ideal conditions.

[0051] Figure 4 The graph shows the output impedance frequency sweep result and impedance theoretical curve of the grid-connected system when the frequency of the three-phase power grid fluctuates to 50.1 Hz and the method of the present invention is not used.

[0052] Figure 5 The output impedance frequency sweep result and impedance theoretical curve of the grid-connected system using the method of the present invention when the frequency of the three-phase power grid fluctuates to 50.1 Hz. DETAILED DESCRIPTION

[0053] The present embodiment is described in detail below with reference to the accompanying drawings.

[0054] Figure 1 The topology diagram of the grid-connected system used in the present invention includes a DC power supply, a grid-connected inverter, a three-phase LC filter, a three-phase line impedance and a three-phase grid connected in series. Figure 1 In FIG. 1 , Vdc is the voltage of the DC side power supply, 10 is the grid-connected inverter, 20 is the three-phase LC filter, 30 is the three-phase line impedance, and 40 is the three-phase grid.

[0055] Figure 2 This is a flow chart of the spectrum leakage elimination method of the present invention. As can be seen from the figure, the steps of the elimination method are as follows:

[0056] Step 1: Set the frequency sweep range H, H = [0 Hz, F Hz], F is the integer corresponding to the maximum integer frequency F Hz in the frequency sweep range H, and arbitrarily select N integer frequencies in the frequency sweep range H as the integer frequency to be measured f m , m=1, 2,...,N, N<F.

[0057] In this embodiment, F is 10000, that is, in this embodiment, the sweep frequency range = [0 Hz, 10000 Hz].

[0058] Step 2: inject the frequency f into the common coupling point m Harmonics, and collect L terminal voltages U during the injection process pcc_r_m_i and L output current I g_r_m_i , r is the phase sequence, r=a, b, c, i is the sequence number of the terminal voltage and output current, i=1, 2,..., L.

[0059] In this embodiment, the specific injection and collection process is as follows:

[0060] Harmonics with a frequency of f are sequentially injected into the common coupling point m , and each injection lasts for t seconds. During the t seconds, the voltages at L common coupling points and the currents of the three-phase line impedance are collected at equal intervals, and are respectively denoted as the terminal voltage U pcc_r_m_i and the output current I g_r_m_i .

[0061] In this embodiment, t = 1.

[0062] Step 3, perform a fast Fourier transform on the terminal voltage U pcc_r_m_i and the output current I g_r_m _i to obtain the frequency-domain terminal voltage U r_m (k) and the frequency-domain output current I r_m (k), where k is the serial number of the integer frequency within the frequency sweep range H, k = 0, 1,..., F.

[0063] The specific transformation process of the frequency-domain terminal voltage U r_m (k) and the frequency-domain output current I r_m (k) is as follows:

[0064] Perform a fast Fourier transform on the terminal voltage U pcc_r_m_i and the output current I g_r_m_i , and perform frequency sweeping to obtain the Fourier-transformed terminal voltage and the Fourier-transformed output current corresponding to each integer frequency within the frequency sweep range H, which are respectively denoted as the frequency-domain terminal voltage U r_m (k) and the frequency-domain output current I r_m (k), and their expressions are respectively:

[0065]

[0066] where j is the imaginary unit.

[0067] Step 4, extract the positive-sequence voltage component U r_m (k) and the negative-sequence voltage component U p_m (k) corresponding to the frequency-domain terminal voltage U n_m (k), and extract the positive-sequence current component I r_m (k) and the negative-sequence current component I p_m (k) corresponding to the frequency-domain output current I n_m (k).

[0068] The expressions of the positive-sequence voltage component U p_m (k), the negative-sequence voltage component U n_m (k), the positive-sequence current component I p_m (k) and the negative-sequence current component I n_m (k) are respectively:

[0069]

[0070] where j is the imaginary unit.

[0071] Step 5: Calculate the compensated integer frequency f to be measured through the proportional harmonic mean formula m of the positive-sequence voltage component U p_m (f m )′, the negative-sequence voltage component U n_m (f m )′, the positive-sequence current component I p_m (f m )′, and the negative-sequence current component I n_m (f m )′.

[0072] In this embodiment, the expression of the proportional harmonic mean formula is:

[0073]

[0074] In the formula, U p_m (f m ) is the positive-sequence voltage component at the integer frequency f to be measured, U m (f n_m ) is the negative-sequence voltage component at the integer frequency f to be measured, I m (f m ) is the positive-sequence current component at the integer frequency f to be measured, I p_m (f m ) is the negative-sequence current component at the integer frequency f to be measured, U m (f n_m - 1) is the positive-sequence voltage component at the integer frequency (f m - 1) to be measured, U m (f p_m - 1) is the negative-sequence voltage component at the integer frequency (f m - 1) to be measured, I m (f n_m - 1) is the positive-sequence current component at the integer frequency (f m - 1) to be measured, I m - 1) is the negative-sequence current component at the integer frequency (f p_m - 1) to be measured, U m (f m + 1) is the positive-sequence voltage component at the integer frequency (f n_m (f m + 1) to be measured, U m + 1) is the negative-sequence voltage component at the integer frequency (f p_m (f m + 1) to be measured, U m + 1) is the positive-sequence voltage component at the integer frequency (f n_m (f m + 1) to be measured, U mThe negative sequence component of the voltage at (+1), I p_m (f m +1) is the integer frequency to be measured, which is (f m +1), and the positive sequence component of the current at (+1), I n_m (f m +1) is the integer frequency to be measured, which is (f m +1), and the negative sequence component of the current at (+1).

[0075] Step 6: Calculate the positive sequence output impedance Z m at the integer frequency f to be measured p (f m ) and the negative sequence output impedance Z n (f m ).

[0076] In this embodiment, the calculation formulas for the positive sequence output impedance Z p (f m ) and the negative sequence output impedance Z n (f m ) are respectively:

[0077]

[0078] The present invention also provides a spectrum leakage elimination system, including:

[0079] A DC side power supply, a grid-connected inverter, a three-phase LC filter, a three-phase line impedance, and a three-phase power grid connected in series in sequence;

[0080] A control module for generating a frequency sweep range H and obtaining N integer frequencies f m to be measured;

[0081] An injection module for injecting harmonics with frequencies of f m into the point of common coupling in sequence;

[0082] A sampling module for collecting the terminal voltage U pcc_r_m_i and the output current I g_r_m_i during the injection process;

[0083] A calculation module for performing a fast Fourier transform on the terminal voltage U pcc_r_m_i and the output current I g_r_m_i to obtain the frequency-swept terminal voltage U r_m (k) and the frequency-swept output current I r_m (k);

[0084] An extraction module for extracting the positive sequence component U r_m (k) of the voltage and the negative sequence component U r_m (k) of the voltage from the frequency-swept terminal voltage U p_m (k) and the frequency-swept output current I n_m(k), positive sequence component I of current p_m (k) and negative sequence component I of current n_m (k) calculation module;

[0085] Used to calculate the positive sequence component U through the proportional harmonic average formula p_m (f m )′, negative sequence component U of voltage n_m (f m )′, positive sequence component I of current p_m (f m )′ and negative sequence component I of current n_m (f m )′ calculation module;

[0086] Used to calculate the positive sequence output impedance Z at the measured integer frequency f m At p (f m ) and negative sequence output impedance Z n (f m ) calculation module;

[0087] And a microprocessor and a memory, each of the modules and the microprocessor is programmed or configured to execute the steps of the spectrum leakage elimination method.

[0088] The present invention also provides a computer-readable storage medium, in which a computer program programmed or configured to execute the spectrum leakage elimination method is stored.

[0089] In order to prove the beneficial effects of the present invention, the present invention is simulated, and Figure 3 , Figure 4 And Figure 5 are obtained. In the three figures, the abscissa is frequency, and the ordinate is amplitude and phase angle.

[0090] Figure 3 is the swept frequency result of the output impedance of the grid-connected system when the three-phase power grid frequency is 50 Hz under ideal conditions. At this time, no spectrum leakage will occur, and whether the spectrum leakage elimination method proposed by the present invention is adopted does not affect the swept frequency result.

[0091] Figure 4 is the swept frequency result of the output impedance of the grid-connected system when the power grid frequency fluctuates to 50.1 Hz without using the method of the present invention. It can be seen from the figure that there is a large deviation between the swept frequency result of the impedance in the low-frequency band near 50 Hz and the theory. This is the error caused by spectrum leakage due to non-positive periodic sampling of the power grid voltage and current at 50.1 Hz, which seriously affects the swept frequency result of the impedance and further affects the subsequent system stability analysis.

[0092] Figure 5The sweep result of the grid-connected system output impedance when the three-phase power grid frequency fluctuates to 50.1 Hz and the method of the present invention is adopted. Compared with Figure 3 , Figure 4 it can be seen that the spectrum leakage elimination method proposed by the present invention eliminates the influence of spectrum leakage caused by power grid frequency fluctuation on the spectrum at the impedance measurement point.

[0093] Figure 3 , Figure 4 , Figure 5 This can well prove the effectiveness of the method proposed by the present invention.

[0094] The circuit topology structure and elimination method of the present invention above can be regarded as a hardware embodiment of the circuit topology structure alone, or a software embodiment with only the elimination method, or a combination of software and hardware implementation mode of the elimination method based on the circuit topology structure and modules. Moreover, the elimination method part of the present invention can be implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code, and appears in the form of a computer program product; and can be implemented in various computer languages, for example, object-oriented programming language Java and interpreted scripting language JavaScript, etc.

[0095] Furthermore, the embodiments of the present invention are described in combination with flowcharts and / or block diagrams. It should be understood that each process and / or block in the flowcharts and / or block diagrams of the present invention can be implemented by computer program instructions, as well as the combination of processes and / or blocks in the flowcharts and / or block diagrams. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks in the present invention process. These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured product including an instruction device, and the instruction device implements the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks in the present invention process. These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide for implementing the functions specified in Figure 1 one process or multiple processes and / or blocksFigure 1 Steps of the functions specified in one or more boxes.

[0096] Therefore, the above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any changes and modifications made by those of ordinary skill in the art based on the specific embodiments of the present invention and the above circumstances should be regarded as equivalent solutions of this application and should fall within the protection scope of the present invention.

Claims

1. A method for eliminating spectrum leakage, and a grid-connected system applying this method includes a grid-connected inverter and a three-phase power grid, characterized in that, The steps of the elimination method are as follows: Inject harmonics with frequencies of the integer frequencies f to be measured into the common coupling point in sequence m and collect L terminal voltages U pcc_r_m_i and L output currents I g_r_m_i during the injection process, where r is the phase sequence, r = a, b, c, and i is the sequence number of the terminal voltage and the output current, i = 1, 2,..., L. Among them, the integer frequency f to be measured m is any N integer frequencies selected from the frequency sweep range H as the integer frequencies f to be measured m , and the frequency sweep range H, H = [0 Hz, F Hz], where F is the integer corresponding to the maximum integer frequency F Hz in the frequency sweep range H, m = 1, 2,..., N, N < F; The terminal voltage U pcc_r_m_i and the output current I g_r_m_i are subjected to fast Fourier transform to obtain the frequency-domain terminal voltage U r_m (k) and the frequency-domain output current I r_m (k), where k is the serial number of the integer frequency within the frequency-sweeping range H, k = 0, 1,..., F; Extract the voltage positive-sequence component U r_m (k) and the voltage negative-sequence component U p_m (k) corresponding to the voltage U n_m Extract the current positive-sequence component I r_m (k) and the current negative-sequence component I p_m (k) corresponding to the output current I n_m (k); By means of the proportional harmonic average formula and the integer frequency f to be measured m 、(f m - 1), and the positive-sequence voltage component, negative-sequence voltage component, positive-sequence current component, and negative-sequence current component at (f m + 1), calculate the positive-sequence voltage component U m at the integer frequency f to be measured after compensation p_m (f m )′, the negative-sequence voltage component U n_m (f m )′, the positive-sequence current component I p_m (f m )′, and the negative-sequence current component I n_m (f m )′; Calculate the integer frequency f to be measured m Positive-sequence output impedance Z at p (f m ) and negative-sequence output impedance Z n (f m ); The expression of the proportional harmonic mean formula is: Where U p_m (f m ) is the positive-sequence component of the voltage at the integer frequency f m , U n_m (f m ) is the negative-sequence component of the voltage at the integer frequency f m , I p_m (f m ) is the positive-sequence component of the current at the integer frequency f m , I n_m (f m ) is the negative-sequence component of the current at the integer frequency f m , U p_m (f m - 1) is the positive-sequence component of the voltage at the integer frequency (f m - 1), U n_m (f m - 1) is the negative-sequence component of the voltage at the integer frequency (f m - 1), I p_m (f m - 1) is the positive-sequence component of the current at the integer frequency (f m - 1), I n_m (f m - 1) is the negative-sequence component of the current at the integer frequency (f m - 1), U p_m (f m + 1) is the positive-sequence component of the voltage at the integer frequency (f m + 1), U n_m (f m + 1) is the negative-sequence component of the voltage at the integer frequency (f m + 1), I p_m (f m + 1) is the positive-sequence component of the current at the integer frequency (f m + 1), I n_m (f m + 1) is the negative-sequence component of the current at the integer frequency (f m + 1).

2. The method for eliminating spectral leakage according to claim 1, characterized in that The grid-connected system applying this method further includes a DC-side power supply, a three-phase LC filter, and a three-phase line impedance connected in series in sequence.

3. A method for eliminating spectral leakage according to claim 1, characterized in that The specific process of collecting L terminal voltages U pcc_r_m_i and L output currents I g_r_m_i during the injection process is as follows: Harmonics with a frequency of f are sequentially injected into the common coupling point m , and each injection lasts for t seconds. During the t seconds, the voltages at L common coupling points and the currents of the three-phase line impedance are collected at equal intervals, and are respectively denoted as the terminal voltage U pcc_r_m_i and the output current I g_r_m_i .

4. A method for eliminating spectral leakage according to claim 3, characterized in that The time t for injecting harmonics is 1 second, and the maximum integer frequency F is 10,000.

5. A method for eliminating spectral leakage according to claim 1, characterized in that, The voltage U in the frequency domain r_m (k) and the output current I in the frequency domain r_m (k) have the following specific transformation process: The opposite-end voltage U pcc_r_m_i and the output current I g_r_m_i are subjected to fast Fourier transform and frequency sweeping to obtain the Fourier-transformed end voltage and the Fourier-transformed output current corresponding to each integer frequency within the frequency-sweeping range H, which are respectively denoted as the frequency-domain end voltage U r_m (k) and the frequency-domain output current I r_m (k), and their expressions are respectively: Where j is the imaginary unit.

6. A method for eliminating spectral leakage according to claim 1, characterized in that The positive-sequence voltage component U p_m (k), the negative-sequence voltage component U n_m (k), the positive-sequence current component I p_m (k), and the negative-sequence current component I n_m (k) are expressed as follows: Where j is the imaginary unit.

7. A method for eliminating spectral leakage according to claim 1, characterized in that The positive sequence output impedance Z p (f m ) and the negative sequence output impedance Z n (f m ) are calculated as follows:

8. A spectrum leakage elimination system, characterized in that, Including: A DC-side power supply, a grid-connected inverter, a three-phase LC filter, a three-phase line impedance, and a three-phase power grid connected in series in sequence; A control module for generating a sweep range H and obtaining N integer frequencies f to be measured m ; An injection module for sequentially injecting harmonics with a frequency of f m into the common coupling point; Sampling module for collecting terminal voltage U pcc_r_m_i and output current I g_r_m_i during the injection process; For the terminal voltage U pcc_r_m_i and the output current I g_r_m_i to perform a fast Fourier transform to obtain the frequency-domain terminal voltage U r_m (k) and the frequency-domain output current I r_m (k) calculation module; A calculation module for extracting the positive-sequence voltage component U r_m (k) and the positive-sequence output current I r_m (k) from the frequency-domain terminal voltage U p_m , the negative-sequence voltage component U n_m (k), the positive-sequence current component I p_m (k) and the negative-sequence current component I n_m (k); Calculation module for obtaining positive sequence component U by ratio harmonic mean calculation p_m (f m )′, negative sequence voltage component U n_m (f m )′, positive sequence current component I p_m (f m )′ and negative sequence current component I n_m (f m )′ A calculation module for calculating the integer frequency f to be measured m The positive-sequence output impedance Z at p (f m ) and the negative-sequence output impedance Z n (f m ); And a microprocessor and a memory, and each of the above modules and the microprocessor is programmed or configured to execute the steps of the spectrum leakage elimination method described in any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program programmed or configured to execute the spectrum leakage elimination method described in any one of claims 1 to 7.

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