Sub-hyper-synchronous oscillation damping estimation method and device for power electronic interface power grid-connected system

Abstract

The invention relates to the field of power system analysis, and provides a sub-hyper-synchronous oscillation damping estimation method and device for a power electronic interface power grid-connected system, and the method comprises the steps: carrying out the estimation of the sub-hyper-synchronous oscillation damping of the power electronic interface power grid-connected system according to each sampling frequency; calculating an impedance matrix of the power electronic interface power supply under different sampling frequencies; calculating impedance matrixes of other parts of the power grid except the power electronic interface power supply based on the impedance characteristic parameters of the power grid; determining a total impedance matrix according to the impedance matrixes of other parts and the impedance matrix of the power electronic interface power supply; based on the frequency domain response characteristics of the total impedance matrix, determining a preliminary estimation value of the sub-hyper-synchronous oscillation through modal frequency identification; and within the neighborhood range of the preliminary estimation value, generating a damping evaluation index representing the stability of the sub-hyper-synchronous oscillation through fitting estimation. The method does not depend on an internal model of the system, and precise estimation of the sub-hyper-synchronous oscillation damping of the black box system is achieved.

Description

Technical Field

[0001] The present invention relates to the field of power system analysis, and particularly to a method and device for estimating the damping of sub-super synchronous oscillation in a power electronic interface power grid-connected system. Background Art

[0002] With the vigorous development of a high proportion of renewable energy, the degree of power electronics in the system has gradually increased; the adverse interaction between power electronic devices and the network has induced a new type of sub-super synchronous oscillation problem, seriously threatening the safety of the power grid, such as the oscillation of the Static Var Generator (SVG) in the Jingxia South Wind Farm, and the oscillation of the Yitian Photovoltaic in the Tuquan Substation.

[0003] Therefore, many researchers have begun to focus on the mechanism analysis and damping evaluation methods of sub-super synchronous oscillation. Such research is usually carried out based on linearization methods such as eigenvalue analysis method and complex torque coefficient method. The above methods rely on the accurate modeling of the system, otherwise the results may be inaccurate. However, due to commercial factors, confidentiality, etc., it is often difficult to obtain the accurate model and parameters of the power electronic interface power supply, which also hinders the further popularization and use of the above methods.

[0004] In contrast, the method based on the measured impedance-frequency curve stands out with its unique advantage of not relying on modeling. The most common ones are the method based on the impedance matrix norm and the method based on the generalized Nyquist criterion. These two methods can qualitatively judge whether the system is stable based on the impedance information in the full frequency band. Unfortunately, these two methods are difficult to quantitatively evaluate the stability of the system, that is, damping.

[0005] At the same time, some scholars have proposed a method based on the Resistor-Inductor-Capacitor (RLC) aggregation circuit to achieve quantitative estimation of the oscillation damping. Due to the dq-axis coupling characteristics of the power electronic interface power supply, its impedance matrix is a 2×2 dimensional matrix, which also brings difficulties to the aggregation of the model. One approach is to reduce the matrix dimension to a complex number, and then fit the reduced system to an RLC aggregation circuit, which is a second-order system, and calculate its eigenvalues as the eigenvalues of the sub-super synchronous oscillation mode of the system. However, the dimension reduction approach ignores the coupling characteristics of the system, which may lead to great errors in the estimation results. There is also research proposing to aggregate the determinant of the impedance matrix into an RLC circuit, and then calculate its eigenvalues. However, on the one hand, this method has no clear physical meaning as a support, and on the other hand, its accuracy and the iterative convergence speed of fitting also need to be improved.

[0006] In summary, various existing methods for estimating the subsynchronous and supersynchronous oscillation damping are either not widely applicable in practice due to the limitation of the model black box or have problems with limited accuracy. Therefore, there is an urgent need to study an accurate estimation method for the subsynchronous and supersynchronous oscillation damping of a power electronic interface power grid-connected system that is based on measurement information and does not rely on modeling. Summary of the Invention

[0007] The present invention provides a method and device for estimating the subsynchronous and supersynchronous oscillation damping of a power electronic interface power grid-connected system, which solves the problems in the prior art that it cannot be widely applied in practice due to the limitation of the model black box or has limited accuracy, and realizes the accurate estimation of the subsynchronous and supersynchronous oscillation damping of the power electronic interface power grid-connected system.

[0008] The present invention provides a method for estimating the subsynchronous and supersynchronous oscillation damping of a power electronic interface power grid-connected system, including: within the subsynchronous frequency range, performing frequency sampling to obtain the sampling frequency; for each sampling frequency, performing the following operations to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: injecting a disturbance voltage with a frequency of the sampling frequency into the grid connection point of the power electronic interface power supply, and measuring the response current corresponding to the sampling frequency; calculating the impedance matrix of the power electronic interface power supply according to the measured response current; calculating the impedance matrix of other parts of the grid except the power electronic interface power supply based on the impedance characteristic parameters of the grid where the power electronic interface power supply is located; determining the total impedance matrix according to the calculated impedance matrix of other parts and the impedance matrix of the power electronic interface power supply; based on the frequency-domain response characteristics of the total impedance matrix, determining a preliminary estimate value of the subsynchronous and supersynchronous oscillation through modal frequency identification; within the neighborhood range of the preliminary estimate value, generating a damping evaluation index characterizing the subsynchronous and supersynchronous oscillation stability through fitting estimation.

[0009] According to the method for estimating the subsynchronous and supersynchronous oscillation damping of a power electronic interface power grid-connected system provided by the present invention, the injection form of the disturbance voltage includes dual-frequency components in the synchronous rotating coordinate system, and calculating the impedance matrix of the power electronic interface power supply according to the measured response current includes: performing a transformation of the synchronous rotating coordinate system on the measured response current to obtain the current components in the synchronous rotating coordinate system; extracting the components with the same frequency as the disturbance voltage from the current components through fast Fourier transform to obtain the amplitude and phase of the current; calculating the impedance matrix of the power electronic interface power supply at the sampling frequency according to the extracted current amplitude and phase.

[0010] According to the method for estimating the sub-super synchronous oscillation damping of the power electronic interface power grid-connected system provided by the present invention, based on the frequency-domain response characteristics of the total impedance matrix, the preliminary estimated value of the sub-super synchronous oscillation is determined through modal frequency identification, including: calculating the determinant-frequency curve of the total impedance matrix; obtaining the real part of the determinant-frequency curve; and determining the frequency corresponding to the zero crossing of the real part as the preliminary estimated value of the sub-super synchronous oscillation modal frequency.

[0011] According to the method for estimating the sub-super synchronous oscillation damping of the power electronic interface power grid-connected system provided by the present invention, within the neighborhood range of the preliminary estimated value, a damping evaluation index characterizing the stability of the sub-super synchronous oscillation is generated through fitting estimation, including: within the neighborhood of the preliminary estimated value, fitting the determinant-frequency curve into a fitting form matching the physical characteristics of the power grid-connected system of the power electronic interface power supply, and obtaining the result after iterative convergence as the eigenvalue of the sub-super synchronous oscillation mode of the system; calculating the damping ratio of the sub-super synchronous oscillation according to the eigenvalue as the damping evaluation index characterizing the stability of the sub-super synchronous oscillation.

[0012] According to the method for estimating the sub-super synchronous oscillation damping of the power electronic interface power grid-connected system provided by the present invention, the result after iterative convergence obtained by fitting the determinant-frequency curve into a fitting form matching the physical characteristics of the power grid-connected system of the power electronic interface power supply is the eigenvalue of the sub-super synchronous oscillation mode of the system, including: fitting the determinant-frequency curve within the neighborhood of the preliminary estimated value of the sub-super synchronous oscillation modal frequency into the following form: where represents the determinant-frequency curve, ω is the frequency variable, c is a complex number, and its conjugate are also complex numbers. After fitting convergence, the results and are the estimated eigenvalues of the sub-super synchronous oscillation mode.

[0013] The present invention also provides a sub-super synchronous oscillation damping estimation device for a power electronic interface power grid connection system, including: a sampling module configured to perform frequency sampling within the sub-synchronous frequency range to obtain a sampling frequency; a first calculation module configured to, for each sampling frequency, perform the following operations to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: inject a disturbance voltage with a frequency of the sampling frequency into the grid connection point of the power electronic interface power supply, and measure the response current corresponding to the sampling frequency; calculate the impedance matrix of the power electronic interface power supply according to the measured response current; a second calculation module configured to calculate the impedance matrix of other parts of the grid except the power electronic interface power supply based on the impedance characteristic parameters of the grid where the power electronic interface power supply is located; a first determination module configured to determine the total impedance matrix according to the calculated impedance matrix of other parts and the impedance matrix of the power electronic interface power supply; a second determination module configured to determine a preliminary estimate of the sub-super synchronous oscillation based on the frequency domain response characteristics of the total impedance matrix through modal frequency identification; a generation module configured to generate a damping evaluation index characterizing the stability of the sub-super synchronous oscillation through fitting estimation within the neighborhood range of the preliminary estimate.

[0014] According to the sub-super synchronous oscillation damping estimation device for a power electronic interface power grid connection system provided by the present invention, the injection form of the disturbance voltage includes a dual-frequency component in a synchronous rotating coordinate system. The first calculation module is further configured to: perform a transformation of the synchronous rotating coordinate system on the measured response current to obtain the current component in the synchronous rotating coordinate system; extract the component with the same frequency as the disturbance voltage from the current component through fast Fourier transform to obtain the amplitude and phase of the current; calculate the impedance matrix of the power electronic interface power supply at the sampling frequency according to the extracted current amplitude and phase.

[0015] According to the sub-super synchronous oscillation damping estimation device for a power electronic interface power grid connection system provided by the present invention, the second determination module is further configured to: calculate the determinant-frequency curve of the total impedance matrix; obtain the real part of the determinant-frequency curve; determine the frequency corresponding to the zero crossing point of the real part as the preliminary estimate of the sub-super synchronous oscillation modal frequency.

[0016] According to the sub-super synchronous oscillation damping estimation device for a power electronic interface power grid connection system provided by the present invention, the second determination module is further configured to: within the neighborhood of the preliminary estimate, fit the determinant-frequency curve into a fitting form matching the physical characteristics of the grid connection system of the power electronic interface power supply to obtain the result after iterative convergence as the eigenvalue of the sub-super synchronous oscillation mode of the system; calculate the damping ratio of the sub-super synchronous oscillation according to the eigenvalue as the damping evaluation index characterizing the stability of the sub-super synchronous oscillation.

[0017] The second determination module of the sub-supersynchronous oscillation damping estimation device for the power electronic interface power grid connection system provided by the present invention is further configured to: fit the determinant-frequency curve in the neighborhood of the preliminary estimated value of the sub-supersynchronous oscillation mode frequency into the following form: where represents the determinant-frequency curve, ω is the frequency variable, c is a complex number, and its conjugate are also complex numbers. After the fitting converges, the results and are the eigenvalues of the estimated sub-supersynchronous oscillation mode.

[0018] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the sub-supersynchronous oscillation damping estimation method for the power electronic interface power grid connection system as described in any one of the above is implemented.

[0019] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the sub-supersynchronous oscillation damping estimation method for the power electronic interface power grid connection system as described in any one of the above is implemented.

[0020] The present invention also provides a computer program product, including a computer program. When the computer program is executed by a processor, the sub-supersynchronous oscillation damping estimation method for the power electronic interface power grid connection system as described in any one of the above is implemented.

[0021] The sub-supersynchronous oscillation damping estimation method and device for the power electronic interface power grid connection system provided by the present invention do not rely on the accurate modeling of the power electronic interface power source, and only need to obtain its frequency-domain impedance information through measurement. That is, the damping ratio of the sub-supersynchronous oscillation of the system can be accurately estimated in the case of a model black box. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 is a schematic flow chart of the sub-supersynchronous oscillation damping estimation method for the power electronic interface power grid connection system provided by the present invention.

[0024] Figure 2It is a schematic diagram of the grid-connected system of the doubly-fed wind turbine provided by the present invention.

[0025] Figure 3 It is a schematic diagram of the impedance-frequency curve of the real part of the power electronic interface power supply provided by the present invention.

[0026] Figure 4 It is a schematic diagram of the impedance-frequency curve of the imaginary part of the power electronic interface power supply provided by the present invention.

[0027] Figure 5 It is a schematic diagram of the impedance-frequency curve of the real part of other parts of the power grid provided by the present invention.

[0028] Figure 6 It is a schematic diagram of the impedance-frequency curve of the imaginary part of other parts of the power grid provided by the present invention.

[0029] Figure 7 It is a schematic diagram of the impedance-frequency curve of the real part of the total impedance matrix provided by the present invention.

[0030] Figure 8 It is a schematic diagram of the impedance-frequency curve of the imaginary part of the total impedance matrix provided by the present invention.

[0031] Figure 9 It is a schematic diagram of the real part-frequency curve of the system determinant provided by the present invention.

[0032] Figure 10 It is a schematic diagram of the imaginary part-frequency curve of the system determinant provided by the present invention.

[0033] Figure 11 It is a schematic diagram of the structure of the sub-super synchronous oscillation damping estimation device for the power electronic interface power supply grid-connected system provided by the present invention.

[0034] Figure 12 It is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed implementation manners

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention pertains. The "first", "second" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. Similarly, the similar terms such as "a", "an" or "the" do not denote a quantity limitation, but mean that there is at least one. The similar terms such as "comprising" or "including" mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects. The similar terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0037] The following gives a simple explanation of the terms related to the present invention.

[0038] The following Figures 1-12 describes the method and device for estimating the sub-super synchronous oscillation damping of the power electronic interface power grid-connected system of the present invention.

[0039] Figure 1 is a schematic flow chart of the method for estimating the sub-super synchronous oscillation damping of the power electronic interface power grid-connected system provided by the present invention. As Figure 1 shown, the method includes the following: Step 101: In the sub-synchronous frequency range, perform frequency sampling to obtain the sampling frequency.

[0040] In this embodiment, in the sub-synchronous frequency range (2 - 50 Hz), the frequency sampling can be performed based on the sampling rate to obtain the sampling frequency, and the setting of the sampling rate can be adjusted according to actual needs.

[0041] Step 102: For each sampling frequency, perform the following operations to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: Inject a disturbance voltage with a frequency of the sampling frequency into the grid connection point of the power electronic interface power supply, and measure the response current corresponding to the sampling frequency; Calculate the impedance matrix of the power electronic interface power supply according to the measured response current.

[0042] In this embodiment, for the obtained sampling frequencies, the above injection measurement and calculation operations can be respectively performed to obtain the impedance matrix of the power electronic interface power supply at each sampling frequency. See Figure 2, taking the grid-connected system of a doubly-fed induction generator (DFIG) as an example, a disturbance voltage can be injected at the point of common coupling (PCC), the current with the same or similar frequency as the disturbance voltage can be measured, and the impedance matrix of the power electronic interface power supply at this frequency can be calculated; by changing the frequency of the disturbance voltage, repeating the measurement process to obtain the impedance-frequency curve of the power electronic interface power supply. Measure the response current with the same frequency as the disturbance voltage, and perform dq transformation to obtain the current components in the dq coordinate system. It should be noted that the representation of the impedance matrix is not limited to the dq coordinate system, and other coordinate systems can also be selected according to the analysis target and the complexity of the system, etc. In addition, the values of the calculated impedance matrix at each sampling frequency can be plotted as a curve, which is the impedance-frequency curve of the power electronic interface power supply. This curve can intuitively display the impedance characteristics of the power electronic interface power supply at different frequencies, providing a basis for subsequent system stability analysis.

[0043] Step 103: Calculate the impedance matrix of other parts of the power grid except the power electronic interface power supply based on the impedance characteristic parameters of the power grid where the power electronic interface power supply is located.

[0044] In this embodiment, the impedance characteristic parameters of the power grid can include resistance (R), inductance (L), capacitance (C), etc. According to the resistance R, inductance L, and capacitance C information provided by the power grid, the impedance-frequency curve of other parts of the power grid can be obtained.

[0045] Step 104: Determine the total impedance matrix according to the calculated impedance matrix of other parts and the impedance matrix of the power electronic interface power supply.

[0046] In this embodiment, the total impedance-frequency curve of the system can be obtained by adding the impedance of other parts of the power grid and the impedance of the power electronic interface power supply, or other factors can be considered to increase the parameters involved in the calculation.

[0047] Step 105: Based on the frequency-domain response characteristics of the total impedance matrix, determine the preliminary estimate of the sub-supersynchronous oscillation through modal frequency identification.

[0048] In this embodiment, common modal frequency identification methods include the Prony method, the Matrix Pencil Method (MPM), and the method based on DFT curve fitting. The selected identification method can be applied to the real and imaginary parts of the determinant-frequency curve to extract the modal parameters of the sub-supersynchronous oscillation, including frequency, damping ratio, and oscillation amplitude. According to the identification results, the preliminary estimate of the sub-supersynchronous oscillation, that is, the modal frequency, can be determined. As an example, the determinant of the total impedance matrix of the system can be calculated, its real and imaginary parts can be extracted, and the zero-crossing point of its real part is used as the preliminary estimate of the sub-supersynchronous oscillation modal frequency, and at the same time is used as the initial value of the iteration for subsequent fitting.

[0049] Step 106: In the neighborhood range of the preliminary estimated value, generate a damping evaluation index characterizing the stability of the subsynchronous oscillation through fitting estimation.

[0050] In this embodiment, the fitting form matches the physical characteristics of the system. For example, a second-order model is used to fit a second-order system, otherwise errors may occur. The damping evaluation index characterizing the stability of the subsynchronous oscillation may include damping ratio, decay time constant, energy decay rate, etc., which can be selected and calculated according to actual needs.

[0051] The method for estimating the damping of the subsynchronous oscillation of the power electronic interface power grid-connected system provided by the present invention does not rely on the accurate modeling of the power electronic interface power supply, and only needs to obtain its frequency-domain impedance information through measurement. That is, it can accurately estimate the damping ratio of the subsynchronous oscillation of the system under the condition of a model black box.

[0052] In some optional implementation manners, the injection form of the disturbance voltage includes dual-frequency components in the synchronous rotating coordinate system, and calculating the impedance matrix of the power electronic interface power supply according to the measured response current, including: performing a transformation of the synchronous rotating coordinate system on the measured response current to obtain the current components in the synchronous rotating coordinate system; extracting the components with the same frequency as the disturbance voltage from the current components through fast Fourier transform to obtain the amplitude and phase of the current; calculating the impedance matrix of the power electronic interface power supply at the sampling frequency according to the extracted current amplitude and phase.

[0053] As an example, to measure the impedance matrix at a frequency of in the synchronous rotating coordinate system (dq coordinate system), the two groups of injected voltages and can be respectively: where is the synchronous rotating frequency. Taking the example of taking 100π rad / s in a system with a rated frequency of 50 Hz and 120π rad / s in a 60 Hz system; is the amplitude of the injected voltage, and t is the time.

[0054] Then the measured current sequences are respectively and , and after dq transformation, the voltages and the current sequences in the dq coordinate system are obtained.

[0055] After performing a Fast Fourier Transform (FFT), extract the amplitude and phase of the component with a frequency of and represent the instantaneous value sequence in vector form , , , .

[0056] Then, the impedance matrix of the power electronic interface power supply in the dq coordinate system at a frequency of is: where each element in the matrix is a complex number, and here .

[0057] The above operations can be repeated in the sub-synchronous frequency range (2 - 50 Hz). The sampling rate can be selected freely, and the impedance-frequency curve of the power electronic interface power supply is obtained as: Taking the example of repeating the above operations in the sub-synchronous frequency range (2 - 50 Hz) and performing one measurement with a sampling interval set to 0.01 Hz, 4801 * 2 measurements are required. The impedance-frequency curve of the power electronic interface power supply is as shown in Figure 3 and Figure 4 , Figure 3 which shows the variation curves of the real parts of the four impedance components ( Z dd , Z dq , Z qd , Z qq ) of the power electronic interface power supply with respect to frequency (2 - 50 Hz). Figure 4 shows the variation curves of the imaginary parts of the four impedance components ( Z dd , Z dq , Z qd , Z qq ) of the power electronic interface power supply with respect to frequency (2 - 50 Hz).

[0058] In some alternative implementation manners, based on the frequency-domain response characteristics of the total impedance matrix, a preliminary estimate of the sub-supersynchronous oscillation is determined through modal frequency identification, including: calculating the determinant-frequency curve of the total impedance matrix; obtaining the real part of the determinant-frequency curve; and determining the frequency corresponding to the zero-crossing point of the real part as the preliminary estimate of the sub-supersynchronous oscillation modal frequency.

[0059] As an example, based on the resistance R, inductance L, and capacitance C information provided by the power grid, the impedance-frequency curve of other parts of the power grid can be obtained as follows: Taking R = 0.064, L = 0.64, and C = 0.2, all in per-unit values, as an example, the impedance-frequency curve of other parts of the power grid is as shown in Figure 5 and Figure 6 shown below, Figure 5 which shows the variation curves of the real parts of the four impedance components ( Z dd , Z dq , Z qd , Z qq ) of other parts of the power grid with respect to frequency (2 - 50 Hz). Figure 6 which shows the variation curves of the imaginary parts of the four impedance components ( Z dd , Z dq , Z qd , Z qq ) of other parts of the power grid with respect to frequency (2 - 50 Hz).

[0060] Then the total impedance matrix of the system is the sum of the impedance matrix of the power electronic interface power supply and the impedance matrix of other parts of the power grid, which is: The result can be referred to as shown in Figure 7 and Figure 8 shown below, Figure 7 which shows the variation curves of the real parts of the four impedance components ( Z dd , Z dq , Z qd , Z qq ) of the total impedance matrix with respect to frequency (2 - 50 Hz). Figure 8 which shows the variation curves of the imaginary parts of the four impedance components ( Z dd , Z dq , Z qd , Z qq ) of the total impedance matrix with respect to frequency (2 - 50 Hz).

[0061] In some alternative implementations, within the neighborhood of the preliminary estimate value, a damping evaluation index characterizing the stability of sub-supersynchronous oscillation is generated through fitting estimation, including: within the neighborhood of the preliminary estimate value, fitting the determinant-frequency curve into a fitting form that matches the physical characteristics of the grid-connected system of the power electronic interface power supply, and obtaining the result after iterative convergence as the eigenvalue of the sub-supersynchronous oscillation mode of the system; calculating the damping ratio of the sub-supersynchronous oscillation based on the eigenvalue as the damping evaluation index characterizing the stability of the sub-supersynchronous oscillation.

[0062] As an example, to estimate the frequency of the sub-supersynchronous oscillation mode of the system, first, the determinant-frequency curve of the total impedance matrix of the system can be calculated. : Extract its real part and imaginary part, denoted as and respectively. Then, both should have a zero-crossing within the sub-synchronous frequency range. Referring to Figure 9 shows a schematic diagram of the real part-frequency curve of the system determinant, Figure 10 shows a schematic diagram of the imaginary part-frequency curve of the system determinant. Here, the zero-crossing of is denoted as , and it is denoted as the initial estimate value of the sub-supersynchronous oscillation frequency, with the result being 33.0710 Hz.

[0063] Taking the zero-crossing of the real part-frequency curve of the determinant as the preliminary estimate value of the sub-supersynchronous oscillation mode frequency, as the initial value of the iteration for fitting in step s4, it can achieve rapid convergence of the fitting.

[0064] In some alternative implementations, fitting the determinant-frequency curve into a fitting form that matches the physical characteristics of the grid-connected system of the power electronic interface power supply, the result after iterative convergence obtained is the eigenvalue of the sub-supersynchronous oscillation mode of the system, including: fitting the determinant-frequency curve within the neighborhood of the preliminary estimate value of the sub-supersynchronous oscillation mode frequency into the following form: where represents the determinant-frequency curve, ω is the frequency variable, c is a complex number, and its conjugate are also complex numbers. After fitting convergence, the results and are the estimated eigenvalues of the sub-supersynchronous oscillation mode. Based on the proposed fitting form, the eigenvalues of the sub-supersynchronous oscillation mode can be directly estimated without relying on other calculations.

[0065] Its damping ratio can be selected as an index for quantitatively evaluating stability, which is calculated by the following formula: The specific results and their comparison with the exact eigenvalues obtained by linearizing the model are shown in the following table: Table 1 Estimation results of eigenvalues and damping ratios It can be seen that the proposed method does not rely on modeling and still realizes the accurate estimation of the eigenvalues and damping ratios of the sub-supersynchronous oscillation of the power electronic interface power grid-connected system.

[0066] Next, the sub-supersynchronous oscillation damping estimation device for the power electronic interface power grid-connected system provided by the present invention will be described. The sub-supersynchronous oscillation damping estimation device for the power electronic interface power grid-connected system described below can be correspondingly referred to the sub-supersynchronous oscillation damping estimation method for the power electronic interface power grid-connected system described above.

[0067] Figure 11 FIG. is a schematic structural diagram of the sub-supersynchronous oscillation damping estimation device for the power electronic interface power grid-connected system provided by the embodiment of the present application. As Figure 11 shown, it specifically includes: a sampling module 1101 configured to perform frequency sampling within the sub-synchronous frequency range to obtain a sampling frequency; a first calculation module 1102 configured to perform the following operations for each sampling frequency to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: injecting a disturbance voltage with a frequency of the sampling frequency into the grid connection point of the power electronic interface power supply and measuring the response current corresponding to the sampling frequency; calculating the impedance matrix of the power electronic interface power supply according to the measured response current; a second calculation module 1103 configured to calculate the impedance matrix of other parts of the power grid except the power electronic interface power supply based on the impedance characteristic parameters of the power grid where the power electronic interface power supply is located; a first determination module 1104 configured to determine the total impedance matrix according to the calculated impedance matrix of other parts and the impedance matrix of the power electronic interface power supply; a second determination module 1105 configured to determine a preliminary estimated value of the sub-supersynchronous oscillation through modal frequency identification based on the frequency domain response characteristics of the total impedance matrix; a generation module 1106 configured to generate a damping evaluation index characterizing the stability of the sub-supersynchronous oscillation through fitting estimation within the neighborhood range of the preliminary estimated value.

[0068] In some alternative implementation manners, the injection form of the disturbance voltage includes dual-frequency components in a synchronous rotating coordinate system. The first calculation module 1102 is further configured to: perform a transformation of the synchronous rotating coordinate system on the measured response current to obtain current components in the synchronous rotating coordinate system; extract components with the same frequency as the disturbance voltage from the current components through fast Fourier transform to obtain the amplitude and phase of the current; calculate the impedance matrix of the power electronic interface power supply at the sampling frequency according to the extracted current amplitude and phase.

[0069] In some alternative implementation manners, the first determination module 1104 is configured to determine the sub-supersynchronous oscillation based on the frequency-domain response characteristics of the total impedance matrix through modal frequency identification, and is further configured to: calculate the determinant-frequency curve of the total impedance matrix; obtain the real part of the determinant-frequency curve; determine the frequency corresponding to the zero crossing of the real part as the preliminary estimated value of the sub-supersynchronous oscillation modal frequency.

[0070] In some alternative implementation manners, the second determination module 1105 is configured to determine the sub-supersynchronous oscillation based on the frequency-domain response characteristics of the total impedance matrix through modal frequency identification, and is further configured to: within the neighborhood of the preliminary estimated value, fit the determinant-frequency curve into a fitting form that matches the physical characteristics of the grid-connected system of the power electronic interface power supply, and obtain the result after iterative convergence as the eigenvalue of the sub-supersynchronous oscillation mode of the system; calculate the damping ratio of the sub-supersynchronous oscillation according to the eigenvalue as the damping evaluation index characterizing the stability of the sub-supersynchronous oscillation.

[0071] In some alternative implementation manners, the second determination module 1105 is configured to determine the sub-supersynchronous oscillation based on the frequency-domain response characteristics of the total impedance matrix through modal frequency identification, and is further configured to: fit the determinant-frequency curve within the neighborhood of the preliminary estimated value of the sub-supersynchronous oscillation modal frequency into the following form: where represents the determinant-frequency curve, ω is the frequency variable, c is a complex number, and its conjugate are also complex numbers. After the fitting converges, the results and are the estimated eigenvalues of the sub-supersynchronous oscillation mode.

[0072] The device for estimating the damping of sub-supersynchronous oscillation in the grid-connected system of the power electronic interface power supply provided by the present invention does not rely on the accurate modeling of the power electronic interface power supply, and only needs to obtain its frequency-domain impedance information through measurement, that is, it can accurately estimate the damping ratio of the sub-supersynchronous oscillation in the system under the condition of a model black box.

[0073] Figure 12 Illustrates a schematic diagram of the physical structure of an electronic device, such asFigure 12 As shown, the electronic device may include: a processor 1210, a communications interface 1220, a memory 1230, and a communication bus 1240. Among them, the processor 1210, the communications interface 1220, and the memory 1230 complete communication with each other through the communication bus 1240. The processor 1210 may call the logical instructions in the memory 1230 to execute the sub-super-synchronous oscillation damping estimation method for the power electronic interface power grid connection system. The method includes: within the sub-synchronous frequency range, performing frequency sampling to obtain the sampling frequency; for each sampling frequency, performing the following operations to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: injecting a disturbance voltage with a frequency of the sampling frequency into the grid connection point of the power electronic interface power supply, and measuring the response current corresponding to the sampling frequency; calculating the impedance matrix of the power electronic interface power supply according to the measured response current; determining the impedance-frequency curve of the power electronic interface power supply according to the calculated impedance matrix; calculating the impedance matrix of other parts of the power grid except the power electronic interface power supply based on the impedance characteristic parameters of the power grid where the power electronic interface power supply is located; determining the total impedance matrix according to the calculated impedance matrix of other parts and the impedance matrix of the power electronic interface power supply; based on the frequency domain response characteristics of the total impedance matrix, determining a preliminary estimate of the sub-super-synchronous oscillation through modal frequency identification; within the neighborhood range of the preliminary estimate, generating a damping evaluation index characterizing the stability of the sub-super-synchronous oscillation through fitting estimation.

[0074] In addition, when the logical instructions in the above-mentioned memory 1230 are implemented in the form of software functional units and sold or used as an independent product, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0075] On the other hand, the present invention also provides a computer program product, which includes a computer program. The computer program can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the sub-super-synchronous oscillation damping estimation method of the power electronic interface power grid connection system provided by the above-mentioned various methods. The method includes: within the sub-synchronous frequency range, performing frequency sampling to obtain a sampling frequency; for each sampling frequency, performing the following operations to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: injecting a disturbance voltage with a frequency of the sampling frequency into the grid connection point of the power electronic interface power supply, measuring the response current corresponding to the sampling frequency; calculating the impedance matrix of the power electronic interface power supply according to the measured response current; determining the impedance-frequency curve of the power electronic interface power supply according to the calculated impedance matrix; calculating the impedance matrix of other parts of the power grid except the power electronic interface power supply based on the impedance characteristic parameters of the power grid where the power electronic interface power supply is located; determining the total impedance matrix according to the calculated impedance matrix of other parts and the impedance matrix of the power electronic interface power supply; based on the frequency-domain response characteristics of the total impedance matrix, determining a preliminary estimate of the sub-super-synchronous oscillation through modal frequency identification; within the neighborhood range of the preliminary estimate, generating a damping evaluation index characterizing the stability of the sub-super-synchronous oscillation through fitting estimation.

[0076] On another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it realizes the sub-super-synchronous oscillation damping estimation method of the power electronic interface power grid connection system provided by the above-mentioned various methods. The method includes: within the sub-synchronous frequency range, performing frequency sampling to obtain a sampling frequency; for each sampling frequency, performing the following operations to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: injecting a disturbance voltage with a frequency of the sampling frequency into the grid connection point of the power electronic interface power supply, measuring the response current corresponding to the sampling frequency; calculating the impedance matrix of the power electronic interface power supply according to the measured response current; determining the impedance-frequency curve of the power electronic interface power supply according to the calculated impedance matrix; calculating the impedance matrix of other parts of the power grid except the power electronic interface power supply based on the impedance characteristic parameters of the power grid where the power electronic interface power supply is located; determining the total impedance matrix according to the calculated impedance matrix of other parts and the impedance matrix of the power electronic interface power supply; based on the frequency-domain response characteristics of the total impedance matrix, determining a preliminary estimate of the sub-super-synchronous oscillation through modal frequency identification; within the neighborhood range of the preliminary estimate, generating a damping evaluation index characterizing the stability of the sub-super-synchronous oscillation through fitting estimation.

[0077] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative work.

[0078] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for estimating sub-supersynchronous oscillation damping of a power electronic interface power grid-connected system, characterized in that: include: Within the sub-synchronous frequency range, frequency sampling is performed to obtain a sampling frequency; For each sampling frequency, the following operations are performed to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: a disturbance voltage having a frequency of the sampling frequency is injected into the grid connection point of the power electronic interface power supply, and a response current corresponding to the sampling frequency is measured; the impedance matrix of the power electronic interface power supply is calculated according to the measured response current; Calculate the impedance matrix of other parts of the power grid except the power electronic interface power supply based on the impedance characteristic parameters of the power grid where the power electronic interface power supply is located; Determine a total impedance matrix according to the calculated impedance matrices of other parts and the impedance matrix of the power electronic interface power supply; Based on the frequency domain response characteristics of the total impedance matrix, determining a preliminary estimate of the sub-supersynchronous oscillation through modal frequency identification; Within the neighborhood of the preliminary estimated value, a damping evaluation index characterizing the stability of the sub-supersynchronous oscillation is generated by fitting estimation.

2. The sub-supersynchronous oscillation damping estimation method of the power electronic interface power supply grid-connected system according to claim 1, characterized in that: The injection form of the disturbance voltage includes a dual-frequency component in a synchronous rotating coordinate system, and the impedance matrix of the power electronic interface power supply is calculated according to the measured response current, including: Transforming the measured response current in a synchronous rotating coordinate system to obtain a current component in the synchronous rotating coordinate system; Extracting the component with the same frequency as the disturbance voltage from the current component by fast Fourier transform to obtain the amplitude and phase of the current; The impedance matrix of the power electronic interface power supply at the sampling frequency is calculated based on the extracted current amplitude and phase.

3. The sub-supersynchronous oscillation damping estimation method of the power electronic interface power supply grid-connected system according to claim 1, characterized in that: The method of determining a preliminary estimate of a sub-supersynchronous oscillation by modal frequency identification based on the frequency domain response characteristics of the total impedance matrix comprises: Calculating a determinant-frequency curve of the total impedance matrix; Obtaining the real part of the determinant-frequency curve; The frequency corresponding to the zero-crossing point of the real part is determined as a preliminary estimation value of the sub-supersynchronous oscillation mode frequency.

4. The sub-supersynchronous oscillation damping estimation method of the power electronic interface power grid-connected system according to claim 3, characterized in that: The damping evaluation index characterizing the stability of the sub-supersynchronous oscillation is generated by fitting estimation within the neighborhood of the preliminary estimated value, including: In the neighborhood of the preliminary estimated value, the determinant-frequency curve is fitted into a fitting form that matches the physical characteristics of the grid-connected system of the power electronic interface power supply, and a result after iterative convergence is obtained as a characteristic value of the sub-supersynchronous oscillation mode of the system; The damping ratio of the sub-supersynchronous oscillation is calculated according to the characteristic value as a damping evaluation index characterizing the stability of the sub-supersynchronous oscillation.

5. The sub-supersynchronous oscillation damping estimation method of the power electronic interface power supply grid-connected system according to claim 4, characterized in that: The step of fitting the determinant-frequency curve into a fitting form that matches the physical characteristics of the grid-connected system of the power electronic interface power supply, and obtaining the result after iterative convergence as the characteristic value of the sub-supersynchronous oscillation mode of the system, includes: The determinant-frequency curve is fitted in the neighborhood of the preliminary estimate of the sub-supersynchronous oscillation mode frequency to the following form: in, represents the determinant-frequency curve, ω is the frequency variable, c is a complex number, and its conjugate is also a complex number. After the fitting converges, the result is and That is the estimated eigenvalue of the sub-supersynchronous oscillation mode.

6. A sub-supersynchronous oscillation damping estimation device for a power electronic interface power supply grid-connected system, characterized in that: include: The sampling module is configured to perform frequency sampling within a sub-synchronous frequency range to obtain a sampling frequency; The first calculation module is configured to perform the following operations for each sampling frequency to calculate the impedance matrix of the power electronic interface power supply at different sampling frequencies: injecting a disturbance voltage having a frequency of the sampling frequency into a grid connection point of the power electronic interface power supply, and measuring a response current corresponding to the sampling frequency; and calculating the impedance matrix of the power electronic interface power supply according to the measured response current; A second calculation module is configured to calculate an impedance matrix of other parts of the power grid except the power electronic interface power supply based on an impedance characteristic parameter of the power grid where the power electronic interface power supply is located; A first determination module is configured to determine a total impedance matrix according to the calculated impedance matrices of other parts and the impedance matrix of the power electronic interface power supply; A second determination module is configured to determine a preliminary estimate of the sub-supersynchronous oscillation by modal frequency identification based on the frequency domain response characteristics of the total impedance matrix; The generating module is configured to generate a damping evaluation index characterizing the stability of the sub-supersynchronous oscillation by fitting estimation within the neighborhood of the preliminary estimated value.

7. The sub-supersynchronous oscillation damping estimation device of the power electronic interface power supply grid-connected system according to claim 6, characterized in that: The injection form of the disturbance voltage includes a dual-frequency component in a synchronously rotating coordinate system, and the first calculation module is further configured as follows: Transforming the measured response current in a synchronous rotating coordinate system to obtain a current component in the synchronous rotating coordinate system; Extracting the component with the same frequency as the disturbance voltage from the current component by fast Fourier transform to obtain the amplitude and phase of the current; The impedance matrix of the power electronic interface power supply at the sampling frequency is calculated based on the extracted current amplitude and phase.

8. The sub-supersynchronous oscillation damping estimation device of the power electronic interface power supply grid-connected system according to claim 6, characterized in that: The second determining module is further configured to: Calculating a determinant-frequency curve of the total impedance matrix; Obtaining the real part of the determinant-frequency curve; The frequency corresponding to the zero-crossing point of the real part is determined as a preliminary estimation value of the sub-supersynchronous oscillation mode frequency.

9. An electronic device 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 sub-supersynchronous oscillation damping estimation method of the power electronic interface power supply grid-connected system according to any one of claims 1 to 5 is implemented.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the sub-supersynchronous oscillation damping estimation method of the power electronic interface power supply grid-connected system according to any one of claims 1 to 5 is implemented.

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