System-side harmonic impedance estimation method and apparatus

Abstract

The application discloses a system side harmonic impedance estimation method and device, wherein the method comprises the following steps: step A, calculating the multi-order fluctuation energy ratio of the measurement data of a point of common coupling, combining the weak correlation between the fluctuation amounts of the harmonic currents on both sides of the point of common coupling, and selecting the minimum value in the fluctuation energy ratio to estimate the amplitude of the system side harmonic impedance; and step B, calculating the angle of the system side harmonic impedance according to the system side voltage fluctuation energy minimization principle. The application does not require the harmonic current amplitude and the harmonic impedance amplitude of the system side and the user side to satisfy the relationship of "much greater than" or "much smaller than", and the system side harmonic impedance can be relatively accurately estimated even under the condition that the system side harmonic current amplitude and the harmonic impedance amplitude are large or even close to the user side. The application does not strictly constrain the correlation of the harmonic current sources of the system side and the user side, only assumes that the fluctuation amounts of the harmonic currents on both sides are approximately independent, has a wider application range, and has higher estimation accuracy of the harmonic impedance.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, specifically relating to a method and apparatus for estimating system-side harmonic impedance. Background Technology

[0002] As more and more new energy equipment and traditional power electronic equipment are connected to the power grid, the content of harmonics of various frequencies in the power grid increases and the distribution becomes more complex, making the harmonic pollution problem more and more serious. The treatment of harmonic pollution cannot be separated from the accurate calculation of the harmonic impedance on the system side.

[0003] Existing methods for estimating system-side harmonic impedance can be broadly categorized into two types based on whether they actively interfere with power system operation: "interventional methods" and "non-interventional methods." "Interventional methods" estimate system-side harmonic impedance by injecting harmonic currents into the system or generating additional disturbances by switching a branch. While the principle of interventional methods is simple and direct, these methods can disrupt the operation of the power grid and require a certain level of controllability of the power system; therefore, interventional methods have not been widely adopted in practical engineering. "Non-interventional methods" estimate harmonic impedance by analyzing the measured data of harmonic voltage and current at the point of common coupling (PCC). In recent years, scholars both domestically and internationally have conducted extensive research on "non-interventional methods," proposing numerous algorithms for estimating system-side harmonic impedance, including: fluctuation method, stochastic vector covariance method, regression method, independent component analysis (ICA), Bayesian algorithm, maximum likelihood estimation algorithm, support vector machine algorithm, and genetic algorithm.

[0004] The fluctuation method determines the system-side harmonic impedance by utilizing the ratio of harmonic voltage and harmonic current fluctuations at the PCC. This method is simple in principle and easy to implement, but it requires the amplitudes of the system-side harmonic current and impedance to be much smaller than those on the user side. Therefore, the fluctuation method is highly susceptible to interference from background harmonic current fluctuations. Regression-based methods determine the system-side harmonic impedance by establishing regression equations and solving for regression coefficients. These methods are also susceptible to interference from background harmonic current fluctuations. The random vector covariance method estimates the system-side harmonic impedance based on the statistical independence of the harmonic current at the PCC and the system-side harmonic voltage during the observation period. Compared to the fluctuation method, this method is less affected by background harmonic current fluctuations and has improved estimation accuracy. However, this method assumes that the amplitude of the system-side impedance is much smaller than that on the user side. When the amplitudes of the system-side and user-side harmonic impedances do not meet the "much greater than" or "much less than" condition, the error of this method will increase significantly. The ICA method obtains the system-side and user-side harmonic source signals by separating the mixed harmonic signals measured at the PCC, and then calculates the system-side harmonic impedance. ICA-type methods rely on two main assumptions: the harmonic current sources on the system side and the user side are highly independent; and at most one of the harmonic current sources on the system side and the user side follows a Gaussian distribution. In practical engineering, when there are large sinusoidal disturbances in the harmonic current sources on the system side and the user side, the correlation between the harmonic current signals on both sides increases significantly. In addition, the harmonic current signals separated by ICA-type methods are disordered; therefore, in practical applications, ICA-type methods often require additional a priori conditions to determine the attribution of the separated signals. Summary of the Invention

[0005] The technical problem to be solved by the embodiments of the present invention is to provide a method and apparatus for estimating system-side harmonic impedance in order to improve the accuracy of the estimation.

[0006] To address the aforementioned technical problems, this invention provides a method for estimating system-side harmonic impedance, comprising:

[0007] Step A: Calculate the multi-order fluctuation energy ratio of the measurement data at the point of common coupling (PCC). Combined with the weak correlation between the fluctuations of harmonic currents on both sides of the PCC, select the minimum value among the fluctuation energy ratios to estimate the amplitude of the harmonic impedance on the system side.

[0008] Step B: Calculate the angle of the system-side harmonic impedance based on the principle of minimizing system-side voltage fluctuation energy.

[0009] Further, step A specifically includes:

[0010] Step A1: Measure the harmonic voltage and harmonic current at the point of common coupling (PCC).

[0011] Step A2: Calculate the s-order energy ratio of harmonic voltage and harmonic current;

[0012] Step A3: Select the minimum value among the s-order energy ratios and calculate the amplitude of the system-side harmonic impedance.

[0013] Furthermore, step A2 specifically includes:

[0014] The harmonic voltage at point PCC obtained in step A1 Harmonic current Based on the relationship between the harmonic currents and harmonic impedances on both sides of the PCC, calculate the first-order difference components of the harmonic voltage and current at the nth measurement moment. and

[0015] Based on the first-order difference component of the harmonic voltage and current at the nth measurement time and The s-order ripple energy of the harmonic voltage and current signals at PCC is calculated separately.

[0016] Based on the complex ratio between the harmonic current phasors and harmonic impedance amplitudes on both sides of the PCC at N measurement times, the s-order harmonic voltage fluctuation energy and current fluctuation energy are divided to obtain the s-order harmonic energy ratio at the PCC.

[0017] Furthermore, step A3 specifically includes:

[0018] The specific ratio of the s-th harmonic energy at PCC is the system-side harmonic impedance amplitude Z. u The product of the 2s power and the coefficient α(s); defining the dimension of the harmonic energy ratio as the impedance amplitude, we obtain |Z p | 2s and |Z u | The relationship; where α(s) is a univariate function of s;

[0019] Calculate the coefficient α(s), and seek the minimum value of α(s) by changing s. Use the value of α(s) that is closest to 1 to calculate the amplitude of the system-side harmonic impedance.

[0020] Furthermore, step B specifically includes:

[0021] Step B1: Calculate the total energy of harmonic voltage fluctuations on the system side;

[0022] Step B2: Calculate the angle of the system-side harmonic impedance based on the principle of minimizing the total energy of system-side harmonic voltage fluctuations.

[0023] The present invention also provides a system-side harmonic impedance estimation device, comprising:

[0024] The first calculation module is used to calculate the multi-order fluctuation energy ratio of the measurement data of the common coupling point. Combining the weak correlation between the fluctuation of harmonic currents on both sides of the PCC, the minimum value of the fluctuation energy ratio is selected to estimate the amplitude of the harmonic impedance on the system side.

[0025] The second calculation module is used to calculate the angle of the system-side harmonic impedance based on the principle of minimizing the energy of system-side voltage fluctuations.

[0026] Furthermore, the first calculation module is specifically used to: measure the harmonic voltage and harmonic current at the point of common coupling (PCC); calculate the s-order energy ratio of the harmonic voltage and harmonic current; select the minimum value among the s-order energy ratios, and calculate the amplitude of the system-side harmonic impedance.

[0027] Furthermore, the calculation of the s-order energy ratio of harmonic voltage and harmonic current specifically involves:

[0028] Based on the harmonic voltage of the PCC point obtained from the data Harmonic current Based on the relationship between the harmonic currents and harmonic impedances on both sides of the PCC, calculate the first-order difference components of the harmonic voltage and current at the nth measurement moment. and

[0029] Based on the first-order difference component of the harmonic voltage and current at the nth measurement time and The s-order ripple energy of the harmonic voltage and current signals at PCC is calculated separately.

[0030] Based on the complex ratio between the harmonic current phasors and harmonic impedance amplitudes on both sides of the PCC at N measurement times, the s-order harmonic voltage fluctuation energy and current fluctuation energy are divided to obtain the s-order harmonic energy ratio at the PCC.

[0031] Furthermore, the step of selecting the minimum value among the s-order energy ratios and calculating the amplitude of the system-side harmonic impedance specifically involves:

[0032] The ratio of the s-th harmonic energy at PCC is specifically the system-side harmonic impedance amplitude |Z u The product of |2s^2 and the coefficient α(s); defining the dimension of the harmonic energy ratio as the impedance amplitude, we obtain |Z p | 2s and |Z u | The relationship; where α(s) is a univariate function of s;

[0033] Calculate the coefficient α(s), and seek the minimum value of α(s) by changing s. Use the value of α(s) that is closest to 1 to calculate the amplitude of the system-side harmonic impedance.

[0034] Furthermore, the second calculation module is specifically used to: calculate the total energy of system-side harmonic voltage fluctuations; and calculate the angle of system-side harmonic impedance based on the principle of minimizing the total energy of system-side harmonic voltage fluctuations.

[0035] The present invention has the following advantages: It does not require the harmonic current amplitudes and harmonic impedance amplitudes on the system side and user side to satisfy a "much greater than" or "much less than" relationship. Even when the harmonic current amplitude and harmonic impedance amplitude on the system side are large or even close to those on the user side, the system-side harmonic impedance can still be estimated relatively accurately. Furthermore, the present invention does not impose strict constraints on the correlation between the harmonic current sources on the system side and user side, only assuming that the fluctuations of the harmonic currents on both sides are approximately independent. Compared to ICA-type methods that require the assumption of high independence between the harmonic currents on both sides of the PCC, the present invention has a wider range of applications and relatively higher accuracy in estimating harmonic impedance. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart illustrating a system-side harmonic impedance estimation method according to an embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of the Norton equivalent circuit on both sides of the PCC in an embodiment of the present invention.

[0039] Figure 3 This is a schematic diagram of the s-order energy ratio in an embodiment of the present invention. Detailed Implementation

[0040] The following description of the embodiments is taken with reference to the accompanying drawings, which illustrate specific embodiments in which the invention can be implemented.

[0041] Please refer to Figure 1 As shown, Embodiment 1 of the present invention provides a method for estimating system-side harmonic impedance, including:

[0042] Step A: Calculate the multi-order fluctuation energy ratio of the measurement data at the point of common coupling (PCC). Combined with the weak correlation between the fluctuations of harmonic currents on both sides of the PCC, select the minimum value among the fluctuation energy ratios to estimate the amplitude of the harmonic impedance on the system side.

[0043] Step B: Calculate the angle of the system-side harmonic impedance based on the principle of minimizing system-side voltage fluctuation energy.

[0044] Specifically, step A includes:

[0045] Step A1: Measure the harmonic voltage and harmonic current at point PCC;

[0046] Assuming the harmonic detection device collects N sets of harmonic voltages and harmonic currents at the PCC point, that is... Figure 2 In and Among them, the nth harmonic measurement values ​​are respectively and Define the first-order difference components of the harmonic voltage and current at the nth measurement time. and The difference between the harmonic quantities at the nth measurement time and the (n-1)th measurement time is given by the following formula:

[0047]

[0048] Step A2: Calculate the s-order energy ratio of harmonic voltage and harmonic current;

[0049] according to Figure 2 Combining the superposition theorem of circuits, we can obtain and The relationship between the harmonic currents and harmonic impedances on both sides of the PCC is as follows:

[0050]

[0051] Combining formulas (1) and (2) we can and Further written as:

[0052]

[0053] definition and Let be the first-order wave energies of the harmonic voltage signal and current signal at PCC, respectively. Combined with formula (3), and The calculation method is as follows:

[0054]

[0055] Similarly, the s-order ripple energy of the harmonic voltage and current signals at PCC is defined as:

[0056]

[0057] Assume that the complex ratios between the harmonic current phasors and harmonic impedance amplitudes on both sides of the PCC at n measurement times are k(n) and m, respectively, as shown in the following equation:

[0058]

[0059] Combining formula (6), the energy ratio of the s-th harmonic voltage fluctuation and the energy ratio of the current fluctuation in formula (5) are obtained, as shown in the following formula:

[0060]

[0061] Step A3: Select the minimum value among the s-order energy ratios and calculate the amplitude of the system-side harmonic impedance;

[0062] In signal analysis and processing, the autocorrelation function R(x,x) of a signal sequence x(n) and the cross-correlation function R(x,y) of a signal sequence x(n) and a signal sequence y(n) are defined as follows:

[0063]

[0064]

[0065] It is known that when signal sequences x(n) and y(n) are approximately independent, their cross-correlation function R(x,y) is approximately zero. Due to the variations in harmonic currents on the system side and the user side... and They are independent of each other, therefore,

[0066]

[0067] According to formula (10), the ratio of s-th harmonic energy at PCC can be regarded as the amplitude of harmonic impedance on the system side |Z u |2s raised to the power of | and the coefficient α(s). If the dimension of the harmonic energy ratio is defined as the impedance amplitude, then we can obtain |Z p | 2s and |Z u The relationship is as follows:

[0068] |Z p | 2s =α(s)|Z u | 2s (11)

[0069] Where α(s) is a univariate function of s, and can be simplified as follows according to the property shown in formula (3):

[0070]

[0071] in, For combinations,

[0072] Since k and m are generally less than 1 (the amplitude of harmonic current and harmonic impedance on the system side are generally less than those on the user side), the numerator and denominator of α(s) satisfy: Therefore, it can be concluded that:

[0073]

[0074] According to formula (13), by changing s, we can find the minimum value of α(s), that is, the value closest to 1. At this point, the calculated system-side harmonic impedance amplitude is the most accurate, as shown in the following formula:

[0075]

[0076] Step B specifically includes:

[0077] Step B1: Calculate the total energy of harmonic voltage fluctuations on the system side;

[0078] Referring to formula (14), the total energy fluctuation of a certain harmonic voltage on the system side during the entire observation period is Σ. N |ΔV u (n)| 2 It can be calculated using the following formula:

[0079]

[0080] Continue to extract the common factor from the right side of equation (15).

[0081]

[0082] For formula (16) Perform the following square operation on a portion of the sample:

[0083]

[0084] Step B2: Calculate the harmonic impedance angle on the system side based on the principle of minimizing the total energy of harmonic voltage fluctuations on the system side.

[0085] According to formula (17), the background harmonic voltage fluctuation energy on the system side can be seen. With system-side harmonic impedance Z u There is a direct relationship. During power grid operation, efforts are focused on reducing voltage energy loss on the system side, specifically the energy fluctuations of harmonic voltage on the system side. N |ΔV u (n)| 2 The goal is to keep the control within a low range, and this objective is achieved by minimizing the following expression:

[0086]

[0087] in, Represents the angle of vector *.

[0088] To minimize the objective function J, Z shown in equation (18) u Angle The following formula should be satisfied:

[0089]

[0090] It should be noted that the minimum fluctuation energy principle based on formula (19) is "relative minimization" rather than "absolute minimization". That is, the minimization of formula (19) is based on the already determined harmonic impedance amplitude |Z. u Under the premise of | constraining the fluctuation energy ∑ of background harmonic voltage N |ΔV u (n)| 2 Minimum.

[0091] After calculating the amplitude and angle of the system-side harmonic impedance using formulas (14) and (19) respectively, the system-side harmonic impedance can be obtained.

[0092] To better understand the steps and advantages of this invention, a system based on Matlab software was built. Figure 2 The Norton model shown was used for simulation testing to demonstrate the specific implementation of the present invention and verify its effectiveness. Methods 1-5 used in the simulation are: fluctuation method, binary linear regression method, stochastic vector covariance method, fast independent component analysis method, and the method of the present invention, respectively.

[0093] The simulation parameters are set as follows:

[0094] (1) Harmonic current source: User-side harmonic current reference amplitude Set to 30A, during the sampling period, the amplitude... Additional reference amplitude ±10% random disturbance and ±10% Gaussian white noise; user-side and system-side harmonic current reference angles. and The angles were set to 40° and 30° respectively, and a random perturbation of ±5% was added to the angles during the sampling period.

[0095] (2) Harmonic impedance: System-side harmonic impedance Z u Set to a constant value of 5 + j10Ω. User-side harmonic impedance Z c Each simulation test group is set up separately.

[0096] Generate 2000 sets of harmonic voltages using the parameter settings described above. Current phasor The system side harmonic impedance was calculated using five different methods.

[0097] Test 1:

[0098] To investigate the impact of background harmonic current fluctuations on the accuracy of five methods, this group of tests measured the system-side harmonic current amplitude. The reference values ​​are set to 10A, 15A, 20A, and 30A respectively, with an additional random disturbance of ±10% of the reference amplitude and ±10% Gaussian white noise; the user-side harmonic impedance Z c Set it to a constant value of 14 + j22Ω.

[0099] To demonstrate specific embodiments of the present invention, Figure 3 Showing Under different reference values, according to formula (14) |Z u The estimation process of |.

[0100] according to Figure 3 It can be seen that, Under the conditions of reference values ​​of 10A, 15A, 20A, and 30A (as shown below) Figure 3 As shown in (a)-(d), the amplitude of the system-side harmonic impedance |Z| is obtained by the s-order energy ratio method. u The values ​​are 11.35Ω, 11.80Ω, 11.97Ω, and 13.47Ω, respectively, with corresponding average relative errors of 1.54%, 5.58%, 9.07%, and 19.54%. The average relative errors of the harmonic impedance amplitudes calculated by the other four methods are shown in Table 1.

[0101] Table 1. Average relative error of impedance amplitude under different background harmonic current fluctuation conditions.

[0102]

[0103] Based on the obtained system-side harmonic impedance amplitude, the angle of the system-side harmonic impedance is calculated according to the principle of minimizing system-side voltage fluctuation energy, i.e., formula (19), and the average relative error of the present invention and the other four methods is recorded in Table 2.

[0104] Table 2. Average relative error of impedance angle under different background harmonic current fluctuations.

[0105]

[0106]

[0107] As can be seen from Tables 1 and 2, when the system-side harmonic current is much smaller than that on the user side... The accuracy of the five methods is similar, with an average relative error of less than 15%. As the amplitude of the system-side current increases, the background harmonic fluctuation increases accordingly, and the errors of the five methods all increase significantly. However, the error growth rate of method 5 is significantly lower than that of the other methods. When the amplitude of the system-side harmonic current reaches 25A, its error remains below 20%.

[0108] Test 2:

[0109] To compare the impact of the relative magnitudes of harmonic impedances on both sides of the PCC on the five methods, this test was conducted under the condition of a constant system-side current. The amplitude of the user-side harmonic impedance |Z c | Set to 60Ω, 48Ω, 36Ω, 24Ω and 12Ω respectively; impedance angle All angles were set to 50°. Following the steps in Test 1, the average relative errors of the five methods were recorded in Tables 3 and 4.

[0110] Table 3. Average relative error of impedance amplitude under different impedance ratios.

[0111]

[0112] Table 4. Average relative error of impedance amplitude under different impedance ratios.

[0113]

[0114] As can be seen from Tables 3 and 4, as the amplitude of the harmonic impedance on the user side decreases, the errors of methods 1 to 4 all increase to varying degrees. In contrast, the error of method 5 changes more steadily. In particular, when the ratio of the amplitudes of the harmonic impedances on both sides is approximately 1, the estimation accuracy remains at around 5%.

[0115] Corresponding to the system-side harmonic impedance estimation method in Embodiment 1 of the present invention, Embodiment 2 of the present invention provides a system-side harmonic impedance estimation device, comprising:

[0116] The first calculation module is used to calculate the multi-order fluctuation energy ratio of the measurement data of the common coupling point. Combining the weak correlation between the fluctuation of harmonic currents on both sides of the PCC, the minimum value of the fluctuation energy ratio is selected to estimate the amplitude of the harmonic impedance on the system side.

[0117] The second calculation module is used to calculate the angle of the system-side harmonic impedance based on the principle of minimizing the energy of system-side voltage fluctuations.

[0118] Furthermore, the first calculation module is specifically used to: measure the harmonic voltage and harmonic current at the point of common coupling (PCC); calculate the s-order energy ratio of the harmonic voltage and harmonic current; select the minimum value among the s-order energy ratios, and calculate the amplitude of the system-side harmonic impedance.

[0119] Furthermore, the calculation of the s-order energy ratio of harmonic voltage and harmonic current specifically involves:

[0120] Based on the harmonic voltage of the PCC point obtained from the data Harmonic current Based on the relationship between the harmonic currents and harmonic impedances on both sides of the PCC, calculate the first-order difference components of the harmonic voltage and current at the nth measurement moment. and

[0121] Based on the first-order difference component of the harmonic voltage and current at the nth measurement time and The s-order ripple energy of the harmonic voltage and current signals at PCC is calculated separately.

[0122] Based on the complex ratio between the harmonic current phasors and harmonic impedance amplitudes on both sides of the PCC at N measurement times, the s-order harmonic voltage fluctuation energy and current fluctuation energy are divided to obtain the s-order harmonic energy ratio at the PCC.

[0123] Furthermore, the step of selecting the minimum value among the s-order energy ratios and calculating the amplitude of the system-side harmonic impedance specifically involves:

[0124] The ratio of the s-th harmonic energy at PCC is specifically the system-side harmonic impedance amplitude |Z u The product of |2s^2 and the coefficient α(s); defining the dimension of the harmonic energy ratio as the impedance amplitude, we obtain |Z p | 2s and |Z u | The relationship; where α(s) is a univariate function of s;

[0125] Calculate the coefficient α(s), and seek the minimum value of α(s) by changing s. Use the value of α(s) that is closest to 1 to calculate the amplitude of the system-side harmonic impedance.

[0126] Furthermore, the second calculation module is specifically used to: calculate the total energy of system-side harmonic voltage fluctuations; and calculate the angle of system-side harmonic impedance based on the principle of minimizing the total energy of system-side harmonic voltage fluctuations.

[0127] For the working principle and process of this embodiment, please refer to the description of the aforementioned Embodiment 1 of the present invention, which will not be repeated here.

[0128] As can be seen from the above description, compared with the prior art, the beneficial effects of the present invention are as follows: The present invention does not require the harmonic current amplitude and harmonic impedance amplitude on the system side and the user side to satisfy the relationship of "much greater than" or "much less than". When the harmonic current amplitude and harmonic impedance amplitude on the system side are large or even close to those on the user side, the harmonic impedance on the system side can still be estimated relatively accurately. The present invention does not impose strict constraints on the correlation between the harmonic current sources on the system side and the user side, but only assumes that the fluctuation of the harmonic current on both sides is approximately independent. Compared with the ICA-type method, which requires assuming that the harmonic currents on both sides of the PCC are highly independent, the present invention has a wider range of applications and relatively higher accuracy in estimating harmonic impedance.

[0129] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A system-side harmonic impedance estimation method, characterized by, include: Step A: Calculate the multi-order fluctuation energy ratio of the measurement data at the point of common coupling (PCC). Combined with the weak correlation between the fluctuations of harmonic currents on both sides of the PCC, select the minimum value among the fluctuation energy ratios to estimate the amplitude of the harmonic impedance on the system side. Step B: Calculate the angle of the system-side harmonic impedance based on the principle of minimizing system-side voltage fluctuation energy. Step A specifically includes: Step A1: Measure the harmonic voltage and harmonic current at the point of common coupling (PCC). Step A2, calculating the harmonic voltage and harmonic current of s the order energy ratio; Step A3, selecting s The minimum value in the ratio of the order energy is calculated to calculate the amplitude of the system side harmonic impedance.

2. The system-side harmonic impedance estimation method of claim 1, wherein, Step A2 specifically includes: The harmonic voltage at point PCC obtained in step A1 Harmonic current The relationship between the harmonic currents and harmonic impedances on both sides of the PCC is used to calculate the first harmonic current. n The first-order difference components of harmonic voltage and current at each measurement moment and ; According to the first n order differential component of the harmonic voltage and current at the measurement moment and , respectively, the s order fluctuation energy of the harmonic voltage signal and current signal at the PCC is calculated. According to the complex ratio between the harmonic current phasor and the harmonic impedance amplitude on both sides of the PCC at N measurement instants, the s harmonic voltage fluctuation energy and the current fluctuation energy are divided to obtain the s harmonic energy ratio at the PCC.

3. The system-side harmonic impedance estimation method of claim 2, wherein, Step A3 specifically includes: PCC s The ratio of harmonic energy is specifically the system-side harmonic impedance amplitude. 2 s Power and coefficient The product of; defining the dimension of the harmonic energy ratio as impedance amplitude, we obtain and The relationship; among them, For about s A function of one variable; Computing the coefficients and by changing s seeking the minimum of the value closest to 1 for calculating the magnitude of the system-side harmonic impedance.

4. The system-side harmonic impedance estimation method of claim 1, wherein, Step B specifically includes: Step B1: Calculate the total energy of harmonic voltage fluctuations on the system side; Step B2: Calculate the angle of the system-side harmonic impedance based on the principle of minimizing the total energy of system-side harmonic voltage fluctuations.

5. A system-side harmonic impedance estimation device, characterized by comprising: include: The first calculation module is used to calculate the multi-order fluctuation energy ratio of the measurement data of the common coupling point. Combining the weak correlation between the fluctuation of harmonic currents on both sides of the PCC, the minimum value of the fluctuation energy ratio is selected to estimate the amplitude of the harmonic impedance on the system side. The second calculation module is used to calculate the angle of the system-side harmonic impedance based on the principle of minimizing the energy of system-side voltage fluctuations. The first calculation module is specifically used for measuring the harmonic voltage and the harmonic current of the PCC; calculating the harmonic voltage and the harmonic current of the PCC s The ratio of the energy of the harmonic voltage and the harmonic current Selecting s The minimum value in the ratio of the order energy is calculated to calculate the amplitude of the system side harmonic impedance.

6. The system-side harmonic impedance estimation apparatus according to claim 5, wherein The calculation of the harmonic voltage and the harmonic current s The ratio of the energy of the order, specifically: Based on the harmonic voltage of the PCC point collected Harmonic current The relationship between the harmonic currents and harmonic impedances on both sides of the PCC is used to calculate the first harmonic current. n The first-order difference components of harmonic voltage and current at each measurement moment and ; According to the first n The first-order difference components of harmonic voltage and current at each measurement moment and Calculate the harmonic voltage signal and current signal at PCC respectively. s Wave energy; Based on the complex ratio between the harmonic current phasors and harmonic impedance amplitudes on both sides of the PCC at N measurement times, s Dividing the first harmonic voltage fluctuation energy by the current fluctuation energy yields the value at PCC. s The ratio of first harmonic energy.

7. The system-side harmonic impedance estimation device according to claim 6, characterized in that, The selection s The minimum value of the order energy ratio is used to calculate the amplitude of the system-side harmonic impedance. Specifically: PCC s The ratio of harmonic energy is specifically the system-side harmonic impedance amplitude. 2 s Power and coefficient The product of; defining the dimension of the harmonic energy ratio as impedance amplitude, we obtain and The relationship; among them, For about s A function of one variable; Calculate coefficients And by changing s seek The minimum value will The value closest to 1 is used to calculate the amplitude of the system-side harmonic impedance.

8. The system-side harmonic impedance estimation device according to claim 5, characterized in that, The second calculation module is specifically used to: calculate the total energy of system-side harmonic voltage fluctuations; and calculate the angle of system-side harmonic impedance based on the principle of minimizing the total energy of system-side harmonic voltage fluctuations.

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