A Risk Assessment Method, System, Device and Medium for Wide-Frequency Oscillation in a New Energy Grid-Connected System

Abstract

The present invention relates to the technical field of power systems, and discloses a method, system, device and medium for broadband oscillation risk assessment of a new energy grid-connected system. By constructing an impedance external characteristic model of a new energy power station and an impedance external characteristic model of an AC power grid in different broadband oscillation risk assessment frequency bands, flexible processing of different broadband oscillation risk assessment frequency bands can be achieved. The impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid are determined by using the impedance external characteristic model of the new energy power station and the impedance external characteristic model of the AC power grid, and the broadband oscillation risk assessment of the new energy grid-connected system is carried out by using the comparison result of the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid. Moreover, the influence of the topological structure and operating conditions on the broadband oscillation risk is fully considered, improving the accuracy and adaptability of the broadband oscillation risk assessment of the new energy grid-connected system.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular, to a method, system, device and medium for evaluating the broadband oscillation risk of a new energy grid-connected system. Background Art

[0002] In recent years, new energy represented by offshore wind power and photovoltaic has experienced explosive growth. It is estimated that by 2030, the proportion of the total installed capacity of new energy in China will be close to 50%. The AC grid-connected system of new energy power stations contains a large number of power electronic conversion devices such as new energy converters and static var generators (SVG), which interact with high-frequency filter circuits, the shunt capacitance of busbars / cables to ground, and the grid impedance, resulting in an increased resonance risk in the AC transmission and grid-connected system of new energy power stations.

[0003] In large-scale new energy grid-connected projects, when multiple broadband oscillation events occur, it may pose a great threat to the stability of grid projects.

[0004] It can be seen that the risk of broadband oscillation in the system with power electronic devices connected is high, and it has the characteristics of wide resonance frequency band, various types, and complex mechanisms, seriously threatening the safe and stable operation of grid-connected equipment and power systems. Therefore, it is necessary to carry out the evaluation work on the broadband oscillation risk of new energy grid-connected systems.

[0005] Currently, in the methods for evaluating the broadband oscillation risk of new energy grid-connected systems, it is difficult to consider various operating conditions of the system, which easily leads to low accuracy and poor adaptability in the evaluation of the broadband oscillation risk of new energy grid-connected systems. Summary of the Invention

[0006] In view of this, the present invention provides a method, system, device and medium for evaluating the broadband oscillation risk of a new energy grid-connected system, which solves the technical problems that in the methods for evaluating the broadband oscillation risk of new energy grid-connected systems, it is difficult to consider various operating conditions of the system, and it easily leads to low accuracy and poor adaptability in the evaluation of the broadband oscillation risk of new energy grid-connected systems.

[0007] In the present invention, in a first aspect, a method for evaluating the broadband oscillation risk of a new energy grid-connected system is provided, which is applied to evaluate the broadband oscillation risk of a new energy grid-connected system in different broadband oscillation risk assessment frequency bands, and the broadband oscillation risk assessment frequency bands include the medium-high frequency band and the sub-supersynchronous frequency band; the method includes:

[0008] Based on multiple electrical units of a new energy power station, establish an impedance external characteristic model for each of the electrical units;

[0009] According to the impedance external characteristic models and wiring structures of the electrical units of the new energy power station, connect the electrical units, and based on the series-parallel relationship of the impedances of the electrical units, obtain the impedance external characteristic model of the new energy power station corresponding to the wide-frequency oscillation risk assessment frequency band;

[0010] According to different wide-frequency oscillation risk assessment frequency bands, determine the impedance external characteristic model of the AC power grid corresponding to the wide-frequency oscillation risk assessment frequency band;

[0011] According to the impedance external characteristic model of the new energy power station and the impedance external characteristic model of the AC power grid, determine the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid;

[0012] Perform a wide-frequency oscillation risk assessment on the new energy grid-connected system according to the comparison results of the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid.

[0013] Preferably, the electrical unit includes a feeder, a transformer, a reactive power compensation device, and an energy storage unit, wherein the feeder includes multiple new energy generating units and multiple AC lines, and the multiple new energy generating units and the multiple AC lines are connected in series and parallel to form the feeder.

[0014] Preferably, the process of constructing the impedance external characteristic model of the feeder is as follows:

[0015] Construct the voltage and current small-signal phasors at the point of common coupling under three-phase symmetrical conditions for a single new energy generating unit according to different wide-frequency oscillation risk assessment frequency bands;

[0016] Based on the voltage and current small-signal phasors, perform a Laplace transform on the control process of the single new energy generating unit to obtain the AC side admittance matrix; wherein, the AC side admittance matrix in the sub-supersynchronous frequency band introduces a PLL control link coefficient matrix affected by the AC side power operation level;

[0017] Determine the impedance characteristic model of a single new energy generating unit according to the AC side admittance matrix;

[0018] Use the Bergeron model to equivalently simulate the AC line between two new energy generating units to obtain the equivalent impedance model of the AC line;

[0019] Based on the connection relationship between multiple new energy generating units on the feeder and the AC line, connect the impedance characteristic model of the single new energy generating unit and the equivalent impedance model of the AC line in series and parallel to obtain the impedance external characteristic model of the feeder;

[0020] According to the primary structure and control structure of the reactive power compensation device, an impedance external characteristic model of the reactive power compensation device is constructed by the impedance modeling method;

[0021] According to the primary structure and control structure of the energy storage unit, an impedance external characteristic model of the energy storage unit is constructed by the impedance modeling method;

[0022] The transformer is equivalently modeled by using a T-shaped equivalent circuit or a π-shaped equivalent circuit to obtain an impedance external characteristic model of the transformer;

[0023] An impedance external characteristic model of the new energy power station is constituted by connecting the impedance external characteristic models of the feeder, the reactive power compensation device, the energy storage unit, and the transformer through series-parallel relationships.

[0024] Preferably, the broadband oscillation risk assessment frequency band is the medium-high frequency band or the sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is as follows:

[0025] The outlet end of the AC power grid after being stepped down by multiple lines or transformers is determined by using multiple ideal voltage sources and lumped parameter impedances;

[0026] Starting from the point of common coupling between the new energy power station and the AC power grid, looking towards the AC power grid to the outlet end, according to the series-parallel relationships of the AC lines, transformers, and other primary equipment in the AC power grid, an impedance external characteristic model of the AC power grid is obtained.

[0027] Preferably, the broadband oscillation risk assessment frequency band is the sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is: based on the short-circuit ratio equivalent method, it is constructed according to the equivalent short-circuit ratio of the AC power grid.

[0028] Preferably, the new energy grid-connected system corresponding to the sub-supersynchronous frequency band adopts operating modes under different power operating levels; the new energy grid-connected system corresponding to the medium-high frequency band adopts the operating mode at the rated operating power level; among them, the operating mode adopts one of the following methods, and the operating mode includes:

[0029] Black start, full connection, all reactive power compensation devices withdrawn, single reactive power compensation device put in, some new energy generating units withdrawn, some new energy feeders withdrawn, some AC buses withdrawn, some transformers withdrawn, some reactive power compensation devices withdrawn, and some energy storage withdrawn.

[0030] Preferably, the broadband oscillation risk assessment of the new energy grid-connected system according to the comparison result of the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid includes:

[0031] According to the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid, determine the frequency range in which the impedance amplitude of the AC power grid is greater than that of the new energy power station under the same wide-frequency oscillation risk assessment frequency band;

[0032] Judge whether the phase difference between the impedance external characteristic curve of the AC power grid and the impedance external characteristic curve of the new energy power station within the frequency range is greater than a preset phase difference threshold;

[0033] If it is judged that the phase difference is greater than the preset phase difference threshold, it is determined that the new energy grid-connected system has a wide-frequency oscillation risk;

[0034] If it is judged that the phase difference is not greater than the preset phase difference threshold, it is determined that the new energy grid-connected system does not have a wide-frequency oscillation risk.

[0035] In a second aspect, the present invention provides a wide-frequency oscillation risk assessment system for a new energy grid-connected system, which is used to evaluate the wide-frequency oscillation risk of the new energy grid-connected system in different wide-frequency oscillation risk assessment frequency bands. The wide-frequency oscillation risk assessment frequency bands include the medium-high frequency band and the sub-supersynchronous frequency band; it includes:

[0036] An impedance model construction module, configured to establish an impedance external characteristic model for each of the electrical units according to multiple electrical units of the new energy power station;

[0037] A power station model construction module, configured to connect each of the electrical units according to the impedance external characteristic models and the wiring structure of the electrical units of the new energy power station, and obtain an impedance external characteristic model of the new energy power station corresponding to the wide-frequency oscillation risk assessment frequency band according to the impedance series-parallel relationship of each of the electrical units;

[0038] A grid-side model construction module, configured to determine an impedance external characteristic model of the AC power grid corresponding to the wide-frequency oscillation risk assessment frequency band according to different wide-frequency oscillation risk assessment frequency bands;

[0039] An impedance curve determination module, configured to determine an impedance external characteristic curve of the new energy power station and an impedance external characteristic curve of the AC power grid according to the impedance external characteristic model of the new energy power station and the impedance external characteristic model of the AC power grid;

[0040] A risk assessment module, configured to perform a wide-frequency oscillation risk assessment on the new energy grid-connected system according to the comparison result of the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid.

[0041] In a third aspect, the present invention further provides an electronic device, which includes a memory and a processor. A computer program is stored in the memory. When the computer program is executed by the processor, the processor is caused to execute the steps of the new energy grid-connected system broadband oscillation risk assessment method as described in the first aspect.

[0042] In a fourth aspect, the present invention further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed, the steps of the new energy grid-connected system broadband oscillation risk assessment method as described in the first aspect are implemented.

[0043] As can be seen from the above technical solutions, the present invention constructs an impedance external characteristic model of a new energy power station and an impedance external characteristic model of an AC power grid in different broadband oscillation risk assessment frequency bands, so as to flexibly process different broadband oscillation risk assessment frequency bands. The impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid are determined by using the impedance external characteristic model of the new energy power station and the impedance external characteristic model of the AC power grid. The broadband oscillation risk of the new energy grid-connected system is evaluated by using the comparison result of the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid, and the influence of the topological structure and operating conditions on the broadband oscillation risk is fully considered, thereby improving the accuracy and adaptability of the broadband oscillation risk assessment of the new energy grid-connected system. Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only 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.

[0045] Figure 1 The application environment of a new energy grid-connected system broadband oscillation risk assessment method provided by an embodiment of the present invention;

[0046] Figure 2 The flowchart of a new energy grid-connected system broadband oscillation risk assessment method provided by an embodiment of the present invention;

[0047] Figure 3 Schematic diagram of a typical structure of an AC power grid of a new energy grid-connected system;

[0048] Figure 4 Schematic diagram of the positive sequence subsystem of a new energy grid-connected system;

[0049] Figure 5 Schematic diagram of the negative sequence subsystem of a new energy grid-connected system;

[0050] Figure 6 It is a schematic diagram of the topology of a typical wind turbine generator set;

[0051] Figure 7 It is a control block diagram of a typical wind turbine generator set;

[0052] Figure 8 It is a schematic diagram of the structure of an impedance scanning system;

[0053] Figure 9 It is an equivalent diagram of an AC line;

[0054] Figure 10 It is an equivalent model of a feeder;

[0055] Figure 11 It is an electrical wiring diagram of a reactive power compensation device;

[0056] Figure 12 It is a control architecture diagram of a reactive power compensation device;

[0057] Figure 13 It is a topology structure diagram of an AC transmission and grid connection system for an offshore wind farm;

[0058] Figure 14 、 Figure 15 It is a diagram for impedance modeling and verification of a single wind turbine in the medium and high frequency bands;

[0059] Figure 16 、 Figure 17 It is a diagram for modeling and verification of an AC submarine cable;

[0060] Figure 18 、 Figure 19 It is the impedance characteristic curve of an offshore wind farm in the medium and high frequency bands;

[0061] Figure 20 、 Figure 21 It is the impedance characteristic curve considering the influence of the collection and boosting substation on the new energy power station;

[0062] Figure 22 、 Figure 23 It is the impedance characteristic curve of an offshore wind farm considering the influence of a long-distance AC transmission line;

[0063] Figure 24 、 Figure 25 It is the impedance characteristic curve of the reactive power compensation parallel branch in the medium and high frequency bands;

[0064] Figure 26 、 Figure 27 It is a comparison diagram of the impedance characteristic curves of the reactive power compensation parallel branch and the new energy power station;

[0065] Figure 28 、 Figure 29 It is the impedance characteristic curve of the new energy power station considering the reactive power compensation parallel branch in the medium and high frequency bands;

[0066] Figure 30 、 Figure 31 is the impedance characteristic curve under the connection mode of the typical reactive power compensation shunt branch and the new energy power station in the medium and high frequency range;

[0067] Figure 32 、 Figure 33 is the comparison diagram between the theoretical value of the impedance model of a single wind turbine in the sub-supersynchronous frequency band and the actual frequency scan value;

[0068] Figure 34 、 Figure 35 is the impedance characteristic curve of a single wind turbine in the sub-supersynchronous frequency band under Condition 1;

[0069] Figure 36 、 Figure 37 is the impedance characteristic curve of a single wind turbine in the sub-supersynchronous frequency band under Condition 2;

[0070] Figure 38 、 Figure 39 is the modeling and verification result of the AC submarine cable after the Bergeron model is equivalent;

[0071] Figure 40 、 Figure 41 is the impedance characteristic curve of the offshore wind farm in the sub-supersynchronous frequency band considering the feeding of multiple feeders;

[0072] Figure 42 、 Figure 43 is the impedance characteristic curve of the offshore wind farm in the sub-supersynchronous frequency band considering the influence of the offshore booster transformer;

[0073] Figure 44 、 Figure 45 is the impedance characteristic curve of the offshore wind farm in the sub-supersynchronous frequency band seen from the onshore connection point of the AC submarine cable;

[0074] Figure 46 、 Figure 47 is the impedance characteristic curve of the reactive power compensation shunt branch in the sub-supersynchronous frequency band;

[0075] Figure 48 、 Figure 49 is the comparison diagram of the impedance characteristic curves of the reactive power compensation shunt branch and the new energy power station in the sub-supersynchronous frequency band;

[0076] Figure 50 、 Figure 51 is the impedance characteristic curve of the new energy power station considering the reactive power compensation shunt branch in the sub-supersynchronous frequency band;

[0077] Figure 52 、 Figure 53 is the oscillation risk assessment diagram of the equivalent impedance of the AC power grid under Condition 1 for the sub-supersynchronous frequency band of the new energy through the grid connection and transmission system;

[0078] Figure 54 、 Figure 55 It is a diagram for evaluating the oscillation risk of the new energy transmitted through the grid connection system in the sub-super synchronous frequency band by the equivalent impedance of the AC power grid under Condition 2;

[0079] Figure 56 It is a schematic structural diagram of a wide-frequency oscillation risk assessment system for a new energy grid connection system;

[0080] Figure 57 It is a schematic structural diagram of an electronic device. Specific implementation manners

[0081] To enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0082] The wide-frequency oscillation risk assessment method for a new energy grid connection system provided by the embodiments of the present application can be applied to an application environment as Figure 1 shown. Among them, each device node of the new energy grid connection system communicates with the server 102 through a network. The data storage system can store the data that the server 102 needs to process. The data storage system can be integrated on the server 102, or can be placed in the cloud or other network servers. The server 102 can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server providing cloud computing services.

[0083] The embodiments of the present application provide a wide-frequency oscillation risk assessment method for a new energy grid connection system, which is applied to evaluate the wide-frequency oscillation risk of the new energy grid connection system in different wide-frequency oscillation risk assessment frequency bands. The wide-frequency oscillation risk assessment frequency bands include the medium-high frequency band and the sub-super synchronous frequency band.

[0084] Among them, the embodiments of the present application respectively establish the impedance models of the new energy power station side and the AC power grid for different wide-frequency oscillation risk assessment frequency bands of the new energy grid connection system. The wide-frequency oscillation risk assessment frequency bands include the medium-high frequency band (frequency band greater than 200 Hz) and the sub-super synchronous frequency band (1 - 200 Hz frequency band).

[0085] At the same time, the embodiments of the present application adaptively adjust the impedance external characteristic models of the new energy power station and the AC power grid according to different wide-frequency oscillation risk assessment frequency bands to ensure the accuracy and effectiveness of the impedance models.

[0086] As shown in Figure 2 , a broadband oscillation risk assessment method for a new energy grid-connected system provided by an embodiment of the present application is described by taking the server 102 in Figure 1 as an example, and includes the following steps S1 to S5. Among them:

[0087] Step S1: Establish an impedance external characteristic model for each electrical unit according to multiple electrical units of the new energy power station.

[0088] Among them, the new energy grid-connected system is connected to the grid with the PCC (Point of Common Coupling) as the demarcation point between the new energy power station and the AC power grid. As shown in Figure 3 . The onshore AC power grid is stepped down through multiple levels of transformation and then exits. After considering two-level transformers, the end of the onshore AC power grid can be characterized by an ideal voltage source and a lumped parameter impedance.

[0089] Among them, the electrical units include feeders, transformers, reactive power compensation devices, and energy storage units. Among them, the feeder includes multiple new energy generating units and multiple AC lines. The multiple new energy generating units and multiple AC lines are connected in series and parallel to form a feeder.

[0090] Step S2: Connect each electrical unit according to the impedance external characteristic model and wiring structure of each electrical unit of the new energy power station, and obtain the impedance external characteristic model of the new energy power station corresponding to the broadband oscillation risk assessment frequency band according to the impedance series-parallel relationship of each electrical unit.

[0091] Among them, the impedance external characteristic model of the new energy power station is jointly determined by the impedance external characteristic models of multiple electrical units, their wiring structure, and impedance series-parallel relationship. Each electrical unit in the new energy power station, such as feeders, transformers, reactive power compensation devices, and energy storage units, etc.

[0092] Connect the impedance external characteristic models of each electrical unit according to the wiring structure of each electrical unit of the new energy power station, and obtain the impedance external characteristic model of the new energy power station according to the impedance series-parallel relationship of each electrical unit.

[0093] Step S3: Determine the impedance external characteristic model of the AC power grid corresponding to the broadband oscillation risk assessment frequency band according to different broadband oscillation risk assessment frequency bands.

[0094] For the medium and high frequency bands, an impedance model of the AC power grid is established based on the series and parallel relationships of the AC lines, transformers, and other primary equipment in the AC power grid. When modeling the AC power grid of a new energy grid-connected system, the outgoing lines with two-stage voltage transformation or above need to be considered. The part after considering the two-stage transformer can be characterized by an ideal voltage source and lumped parameter impedance to represent the end of the AC power grid. Different operating conditions such as the full connection of the AC power grid, the withdrawal of a single device, and the withdrawal of a single line are considered to obtain the impedance models of the AC power grid under different operating conditions. Among them, the equivalent impedance of the AC power grid will change according to the outgoing line conditions of the AC power grid. The influence of changes in the topological structure and operating conditions in the AC power grid on the impedance external characteristic model can also be considered. For example, when there is a loop network structure in the AC power grid, these structures need to be equivalently modeled to obtain a more accurate impedance external characteristic model. It should be noted that for the impedance models of the AC lines, transformers, and other primary equipment in the AC power grid, the corresponding equipment in the new energy power station can be referred to for impedance modeling.

[0095] In some embodiments, for the sub-supersynchronous frequency band, the equivalent impedance of the AC power grid can also be considered by using the short-circuit ratio equivalent method, that is, the impedance external characteristic model of the AC power grid is constructed based on the short-circuit ratio equivalent method according to the equivalent short-circuit ratio of the AC power grid.

[0096] Exemplarily, assuming that the equivalent short-circuit ratio (short circuit ratio, SCR) of the AC power grid under a certain outgoing line condition is known (if there are multiple new energy power stations with feed-in in the AC power grid, the SCR of the multi-feed-in new energy power station should be selected), the equivalent impedance model on the AC side is as follows:

[0097] (1)

[0098] In the formula, U base , P base are the rated voltage and rated power of the AC power grid respectively. , by taking different frequencies f, the equivalent impedance of the AC power grid in the sub-supersynchronous frequency band can be obtained.

[0099] Step S4: Determine the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid according to the impedance external characteristic model of the new energy power station and the impedance external characteristic model of the AC power grid.

[0100] Among them, according to the impedance external characteristic model of the new energy power station, the amplitude and phase are obtained, and the impedance external characteristic curve of the new energy power station can be drawn. Through fast Fourier transform according to the impedance external characteristic model of the AC power grid, the amplitude and phase are obtained, and the impedance external characteristic curve of the AC power grid can be drawn.

[0101] Step S5: Conduct a broadband oscillation risk assessment for the new energy grid-connected system based on the comparison results of the impedance external characteristic curves of the new energy power station and the AC power grid.

[0102] It should be noted that the present invention constructs an impedance external characteristic model of the new energy power station and an impedance external characteristic model of the AC power grid for different broadband oscillation risk assessment frequency bands, so as to flexibly process different broadband oscillation risk assessment frequency bands. The impedance external characteristic curves of the new energy power station and the AC power grid are determined by using the impedance external characteristic models of the new energy power station and the AC power grid. The broadband oscillation risk assessment of the new energy grid-connected system is carried out by using the comparison results of the impedance external characteristic curves of the new energy power station and the AC power grid. The influence of the topological structure and operating conditions on the broadband oscillation risk is fully considered, which improves the accuracy and adaptability of the broadband oscillation risk assessment of the new energy grid-connected system.

[0103] In some embodiments, conducting a broadband oscillation risk assessment for the new energy grid-connected system based on the comparison results of the impedance external characteristic curves of the new energy power station and the AC power grid includes:

[0104] Step S501: Determine the frequency range where the impedance amplitude of the AC power grid is greater than that of the new energy power station in the same broadband oscillation risk assessment frequency band according to the impedance external characteristic curves of the new energy power station and the AC power grid.

[0105] Among them, in the medium and high frequency bands, determine the phase difference where the impedance amplitude of the AC power grid is greater than that of the new energy power station in the frequency band greater than 200 Hz. In the sub-supersynchronous frequency band, determine the phase difference where the impedance amplitude of the AC power grid is greater than that of the new energy power station in the frequency band of 1 - 200 Hz.

[0106] Step S502: Judge whether the phase difference between the impedance external characteristic curve of the AC power grid and the impedance external characteristic curve of the new energy power station in the frequency range is greater than a preset phase difference threshold.

[0107] Step S503: If it is judged that the phase difference is greater than the preset phase difference threshold, it is determined that the new energy grid-connected system has a broadband oscillation risk;

[0108] Step S504: If it is judged that the phase difference is not greater than the preset phase difference threshold, it is determined that the new energy grid-connected system does not have a broadband oscillation risk.

[0109] Among them, as Figures 4 - 5 shown in the positive sequence subsystem and negative sequence subsystem of the new energy grid-connected system, where Z Rp 、I Rp respectively represent the new energy positive sequence impedance and the equivalent current source; Z Mp, V Mp respectively represent the positive-sequence impedance and equivalent voltage source of the VSC-HVDC converter station; V outp , I outp respectively represent the AC bus voltage and current of the new energy power station. Z Rn , I Rn respectively represent the negative-sequence impedance and equivalent current source of the new energy; Z Rn , I Rn respectively represent the negative-sequence impedance and equivalent current source of the new energy; Z Mn , V Mn respectively represent the negative-sequence impedance and equivalent voltage source of the AC power grid; V outn , I outn respectively represent the AC bus voltage and current at the grid connection point of the new energy power station.

[0110] Taking the positive-sequence subsystem as an example, according to Figure 4 , the voltage V outp and current I outp of the AC bus of the new energy power station in the positive-sequence subsystem can be solved as follows:

[0111] (2)

[0112] (3)

[0113] Assume that both the new energy power station and the AC power grid are in a stable state when operating independently. At this time, I Rp and V Mp are both stable. Therefore, when the new energy power station and the AC power grid are interconnected and operating, the stability of the positive-sequence subsystem depends on whether the term 1 / (1 + Z Mp (s) / Z Rp (s)) in equations (2) and (3) is stable.

[0114] When and only when the following two conditions are met, the system does not meet the stability criterion and oscillations occur: ① There is a frequency range where the magnitude of the impedance Z Mp (s) is greater than the magnitude of the impedance Z Rp (s); ② In the frequency range where the magnitude of the impedance Z Mp (s) is greater than the magnitude of the impedance Z Rp (s), the phase-frequency characteristic curves of Z Mp (s) and Z Rp (s) differ by more than 180°.

[0115] In some embodiments, the process of constructing the impedance external characteristic model of the new energy power station is as follows:

[0116] Step S201: Construct small-signal phasors of voltage and current at the point of common coupling of a single new energy generator set under three-phase symmetrical conditions according to different broadband oscillation risk assessment frequency bands;

[0117] Step S202: Based on the voltage and current small-signal phasors, perform Laplace transform on the control process of a single new energy unit to obtain the AC-side admittance matrix; among them, the AC-side admittance matrix in the sub-super-synchronous frequency band introduces a PLL control link coefficient matrix affected by the AC-side power operation level.

[0118] Among them, taking a single new energy unit as an example of a wind turbine, in the PLL control link of a single wind turbine, the input of the coefficient matrix of the voltage variable in the PLL control link is the AC-side voltage, and the output phase θ is greatly affected by the AC-side power operation level. The PLL control band is located in the sub-super-synchronous frequency band, and the influence of PLL control decays rapidly in the medium and high frequency bands. Therefore, the impedance characteristic curve of the wind turbine in the medium and high frequency bands can ignore the influence of the system power operation level caused by the PLL on the impedance characteristics. However, due to the PLL control effect on the sub-super-synchronous impedance characteristics of the wind turbine, the impedance of the system in the sub-super-synchronous frequency band is affected by the system power level. When evaluating the sub-super-synchronous oscillation risk, it is necessary to consider the influence of the power level on the sub-super-synchronous impedance characteristics of a single wind turbine (examples of different power levels of wind turbines are shown in Table 1).

[0119] Table 1 Examples of operating conditions with different power levels of wind turbines (the operating conditions applicable to the invention include but are not limited to this table)

[0120]

[0121] The typical topology and control block diagram of a wind turbine are as Figure 6 and Figure 7 shown. Due to the frequency coupling effect caused by the dynamic characteristics of the DC bus and the dq-axis asymmetric control of the converter, the system signals need to be described by 2D phasors. By linearizing at the steady-state point, the small-signal phasors of each dynamic quantity can be constructed, and the phasor is composed of the Fourier coefficients of different frequencies of the dynamic quantity.

[0122] Figure 6 In t , Z c is the leakage reactance of the converter transformer, Y f is the admittance of the AC-side filter bank, Z G is the impedance of the AC-side passive branch, Z g is the AC impedance of a single wind turbine seen from the high-voltage side, Z source is the AC impedance of a single wind turbine seen from the low-voltage side, and I source is the controlled current source simulating parts such as the machine-side converter station.

[0123] Figure 7 In in , P in is the active power injected into the DC side, u dc , C dc are the DC-side voltage and the DC-side equivalent capacitance respectively, and u mabcabc three-phase voltages at the fan outlet, L f is the filter inductor, u gabc 、i gabc 、q g are the voltage, current and reactive power at the common coupling point respectively, R f 、C f are the filter resistor and filter capacitor respectively, L t1 is the leakage inductance of the converter transformer, k t1 is the turns ratio of the converter transformer. PLL is the phase-locked loop, θ PLL is the output phase angle of the phase-locked loop, abc / dq represents the Park transformation process, H f is the filter section, i gdq ,u gdq are the dq-axis current and voltage after Park transformation respectively, and contain the dq-axis currents i gd 、i gq and the dq-axis voltages u gd 、u gq ,U dc ref 、Q ref are the DC voltage reference value and the reactive power reference value of the AC-side common coupling point respectively, G V 、G Q 、G I 、K d are the voltage outer loop, reactive power outer loop, current inner loop PI control links and decoupling links respectively, dq / abc is the Park inverse transformation link, H D is the system equivalent control link delay, PWM is the modulation process, generating three-phase modulation wave m abc .

[0124] The small-signal phasors of voltage and current constructed at the fan port are as follows. Since it is for a three-phase symmetric operating condition, any voltage and current phasors at the common coupling point of one phase are taken and denoted as 、 :

[0125] (4)

[0126] In the formula, 、 are the voltages of frequencies p and p - 2 respectively, 、 are the currents of frequencies p and p - 2 respectively.

[0127] The AC-side admittance matrix of a single fan can be written as the following formula:

[0128] (5)

[0129] In the formula, Y 11 、Y22 are all the self-admittance of the wind turbine, Y 12 , Y 21 are all the coupling admittances of the wind turbine, Y G (s) represents the wind turbine admittance matrix.

[0130] Among them, the impedance matrix of the wind turbine can be defined, and the impedance matrix can be obtained according to . By using the state-space average method to establish an equivalent system model, and performing Laplace transform and linearization on the voltage, current small-signal phasors, the AC-side admittance matrix and the control process, the AC-side admittance matrix of the wind turbine considering the passive branch on the AC side, the AC-side filter and the transformer as seen from the point of common coupling (PCC) can be solved, and its specific form is as follows:

[0131] (6)

[0132] In the formula, is the AC-side admittance matrix, s is the Laplace operator, is the system control link delay matrix, Z f (s), Z t (s), Y c (s) are 2×2 matrices related to the passive branch on the AC side, the leakage inductance of the commutation transformer, and the AC-side filter respectively, , G V,i (s) are coefficient matrices related to the DC voltage outer-loop voltage and current variables respectively, is the coefficient matrix related to the reactive power outer-loop voltage variable, , is the coefficient matrix of the voltage variable of the phase-locked loop control link, , are coefficient matrices related to the DC voltage inner-loop voltage and current variables respectively, E is the 2×2 identity matrix, is the coefficient matrix related to the reactive power outer-loop current variable.

[0133] Among them, for the in the medium and high frequency bands can be ignored, that is, is zero, and the AC-side admittance matrix can be further simplified. For the in the sub-super-synchronous frequency band, since the input is the AC-side voltage and its output reference phase θ is greatly affected by the AC-side power operation level, needs to be retained.

[0134] Step S203: Determine the impedance characteristic model of a single new energy unit according to the AC-side admittance matrix;

[0135] Among them, the admittance matrix of the AC side of the common coupling point is used as the impedance characteristic model of a single wind turbine. In some embodiments, it needs to be verified to provide support for the wide-band oscillation risk assessment of the AC transmission of new energy power stations. Considering that the present invention focuses on the external impedance characteristics of the model, therefore, the present invention uses a modeling verification method based on impedance scanning to verify the correctness of the impedance characteristic model of a single wind turbine, as Figure 8 shown in the impedance scanning system structure, where the device to be scanned is a single wind turbine.

[0136] Specifically, the process of verifying the correctness of the impedance characteristic model of a single wind turbine by using the modeling verification method of impedance scanning includes:

[0137] 1) Apply disturbance voltages at multiple different measurement frequency points to the AC side of a single wind turbine under steady-state operation, and obtain the grid connection point voltage data and current data of the AC side of the single wind turbine;

[0138] Among them, under the condition that the device to be scanned operates stably, apply small disturbance voltages (or small disturbance currents) with different measurement frequencies to the AC side, and use an impedance scanning module to obtain grid connection point voltage and current data on the AC side.

[0139] 2) Perform a fast Fourier transform on the grid connection point voltage data and current data to obtain voltage FFT complex variables and current FFT complex variables at multiple different measurement frequency points;

[0140] 3) Determine the impedance complex value according to the voltage FFT complex variables and current FFT complex variables at multiple different measurement frequency points;

[0141] 4) Determine the external impedance characteristic curve of a single wind turbine according to the amplitude and phase of the impedance complex value;

[0142] 5) Compare the similarity between the external impedance characteristic curve and the external impedance characteristic curve determined by the impedance characteristic model of a single wind turbine;

[0143] 6) Verify whether the impedance characteristic model of a single wind turbine is correct according to the similarity comparison result;

[0144] 7) If it is verified that the impedance characteristic model of a single wind turbine is incorrect, update the parameters of the impedance characteristic model of the single wind turbine until it is verified that the impedance characteristic model of the single wind turbine is correct.

[0145] Among them, when updating the parameters of the impedance characteristic model of a single wind turbine, parameters such as voltage and current small-signal phasors can be considered for updating, and then the impedance characteristic model of the single wind turbine is re-derived.

[0146] Step S204: Use the Bergeron model to equivalently simulate the AC line between two new energy units to obtain the equivalent impedance model of the AC line;

[0147] Among them, the equivalent diagram of the AC line is as shown in Figure 9 and the expressions of the equivalent impedance and equivalent admittance of the Bergeron model are as follows:

[0148] (7)

[0149] In the formula, γ is the propagation constant of the line, ; Z C is the wave impedance, , Z line is the equivalent impedance of the Bergeron model, and Y line is the equivalent admittance of the Bergeron model. Assume that the length of the equivalent AC cable is l0, and the impedance and admittance per unit length are z0 and y0 respectively.

[0150] Step S205: Based on the connection relationship between multiple new energy units on the feeder and the AC line, connect the impedance characteristic models of single new energy units and the equivalent impedance models of AC lines in series and parallel to obtain the external impedance characteristic model of the feeder;

[0151] Among them, a feeder of a wind farm is composed of multiple wind turbines and multiple AC lines through series and parallel connections. Through the series and parallel relationship of the equivalent impedance models of the wind turbines and the collection lines, the impedance model of a single feeder of the new energy station is obtained.

[0152] Specifically, starting from the first wind turbine at the head end, the admittance of the wind turbine is connected in parallel with the equivalent admittance of the Bergeron model, then connected in series with the equivalent impedance of the Bergeron model, and then connected in parallel with the equivalent admittance of the Bergeron model to obtain the equivalent impedance looking from the next wind turbine towards the head end. According to the feeder topology structure and the Bergeron model parameters, series and parallel connections can be made to obtain the equivalent model of the entire feeder, as shown in Figure 10 (The process of the present invention is applicable to single feeder topology structures including but not limited to Figure 10 ), assuming that the impedance of a single wind turbine is Z Gij and the admittance is Y Gij (each wind turbine can be a wind turbine with different power operation levels, control parameters, and control structures), and the equivalent impedance of the Bergeron model of the AC submarine cable between wind turbines is Z aij and the equivalent admittance is Y aij .

[0153] According to Figure 9 the impedance characteristic model of a single feeder can be obtained, denoted as:

[0154] (8)

[0155] Among them, assuming that the impedance at the end of a single feeder is Z Fi , then Z Fi = 1 / Y EijThat is the impedance of a single feeder. Assume the impedance and admittance of a single wind turbine are Z Gij and Y Gij , and the equivalent impedance and admittance of the j-th section of the line on the feeder according to the Bergeron model are Z aij and Y bij . The equivalent impedance and admittance looking from the outlet of a certain wind turbine towards the head end are Z pij and Y pij . The equivalent impedance and admittance looking from the equivalent admittance at the head end of the Bergeron line towards the head end of the line are Z cij and Y cij . The equivalent impedance and admittance looking from the equivalent impedance at the end of the Bergeron line towards the head end of the line are Z hij and Y hij . According to Figure 10 , through the impedance characteristics modeling of a single wind turbine and the Bergeron model and the topological structure of a single feeder, and through the series-parallel relationship of impedances, the impedance characteristic curve Z Fi of a single feeder can be established. Through impedance scanning, the verification of the impedance characteristic curve of a single feeder can be realized. Among them, since the types of wind turbines and control parameters on the feeder of the wind farm are different, and at the same time the topological structures of the feeders are not the same, the modeling and verification results of the AC submarine cable after equivalent by the Bergeron model are given here.

[0156] Step S206: According to the primary structure and control structure of the reactive power compensation device, construct the impedance external characteristic model of the reactive power compensation device through the impedance modeling method;

[0157] Use the control process of the reactive power compensation device to perform Laplace transform to obtain the impedance external characteristic model of the reactive power compensation device.

[0158] Among them, to establish the branch impedance model of the shunt reactive power compensation device, consider the electrical wiring diagram and control architecture of the reactive power compensation device as shown in Figures 11 - 12 .

[0159] Among them, Figure 11 , the 35KV high-voltage bus is connected to the 35KV user switch cabinet. Among them, there is a circuit breaker QF1 in the 35KV user switch cabinet. The circuit breaker QF1 is connected to the outdoor part. Among them, the outdoor part includes a switch K1, a circuit breaker QF2, and an inductor L. The outdoor part is also connected to the SVG power cabinet.

[0160] Figure 12 , U A and i A are the AC side phase A voltage and current. The PLL is a phase-locked loop. θ a is the phase angle output by the phase-locked loop. Delay is the time delay. 3s / 2r is the Park transformation process. The three-phase voltage and current on the AC side generate dq-axis voltage and current u d and uq and i d and i q , U dca_ref and U dcam are the DC-side voltage reference value and the actual DC-side voltage respectively. After addition and subtraction operations, the d-axis current reference value i dref is generated through the PI control link; in the AC voltage outer loop, I s is the AC-side current. After passing through the ramp factor k slope , the ramp voltage U slope is generated, which, together with the AC voltage reference value U ref and the actual AC voltage value U rms , generates the q-axis current reference value i qref1 through addition and subtraction operations and then through the PI control link; in the reactive power outer loop, the reactive power reference value Q ref and the actual reactive power value Q generate the q-axis current reference value i qref2 through addition and subtraction operations and then through the PI control link. K d is the decoupling link, u dref and u qref are the dq-axis voltage reference values respectively. 2r / 3s is the Park inverse transformation process, generating the AC voltage reference values u aref , u bref , and u cref .

[0161] Under typical control, the SVG adopts phase-separated control in the dq-axis coordinate system. First, virtual dq-axis components are constructed. Using the harmonic linearization method, the frequency-domain expression of the modulation wave is obtained from the SVG control system. Further considering the influence of the control link delay and discrete control, combined with the primary circuit structure of the SVG, the SVG converter impedance and the system impedance are respectively shown in Equation (9).

[0162] (9)

[0163] In the formula, L is the AC-side impedance of the SVG, G i is the transfer function of the current inner-loop controller, K d is the dq-axis decoupling coefficient, G d is the transfer function of the control link delay, G o is the transfer function of the zero-order hold, G sv is the transfer function of the voltage feedforward low-pass filter, R ed is the equivalent resistance of the SVG, and T is the power frequency period. The SVG impedance characteristic curve is affected by the power operation condition. Considering the influence of different power operation conditions, different SVG impedance characteristic curves are obtained.

[0164] Step S207: Construct an impedance external characteristic model of the energy storage unit through the impedance modeling method according to the primary structure and control structure of the energy storage unit;

[0165] Step S208: Use a T-equivalent circuit or a π-equivalent circuit to perform equivalent modeling on the transformer to obtain the impedance external characteristic model of the transformer;

[0166] Among them, the transformers in the new energy substation include new energy unit transformers and substation main step-up transformers. Taking a two-winding transformer as an example, a T-equivalent circuit or a π-equivalent circuit can be selected.

[0167] Step S209: Connect the impedance external characteristic models of the feeder, the reactive power compensation device, the energy storage unit, and the transformer through series and parallel relationships to form the impedance external characteristic model of the new energy substation.

[0168] Among them, according to the determined primary structure, control structure, and parameters of the energy storage unit, an accurate model for obtaining the impedance external characteristic curve of a single energy storage unit is established through the impedance modeling method and verified based on the electromagnetic transient simulation frequency scanning method.

[0169] In some embodiments, the wide-frequency oscillation risk assessment frequency band is the medium-high frequency band or the sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is as follows:

[0170] Step S301: Determine the outlet end of the AC power grid after multiple-level lines or transformation by using multiple ideal voltage sources and lumped parameter impedances;

[0171] Among them, to determine the outlet end of the AC power grid after multiple-level lines or transformation by using multiple ideal voltage sources and lumped parameter impedances, specifically, according to the electrical wiring diagram of the AC power grid, parameters such as the grid structure, transformer turns ratio, and line impedance are determined, and then based on these parameters, multiple ideal voltage sources and lumped parameter impedances are used to equivalently represent the AC power grid, thereby determining the outlet end of the AC power grid after multiple-level lines or transformation.

[0172] Step S302: Starting from the point of common coupling between the new energy substation and the AC power grid, looking towards the AC power grid to the outlet end, according to the series and parallel relationships of the AC lines, transformers, and other primary equipment in the AC power grid, obtain the impedance external characteristic model of the AC power grid.

[0173] In some embodiments, the wide-frequency oscillation risk assessment frequency band is the sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is: constructed based on the short-circuit ratio equivalent method according to the equivalent short-circuit ratio of the AC power grid.

[0174] Among them, it is constructed according to the equivalent short-circuit ratio of the AC power grid. Specifically, the AC power grid is regarded as an ideal voltage source in series with an equivalent impedance, and this equivalent impedance is the impedance external characteristic of the AC power grid. Among them, the equivalent short-circuit ratio is defined as the ratio of the system short-circuit capacity to the rated capacity of the new energy power station.

[0175] In some embodiments, the new energy grid-connected system corresponding to the sub-super-synchronous frequency band adopts operating modes at different power operation levels; the new energy grid-connected system corresponding to the medium-high frequency band adopts the operating mode at the rated operating condition power level; among them, the operating mode adopts one of the following modes, and the operating mode includes: black start, full connection, all reactive power compensation devices withdrawn, single reactive power compensation device put in, partial new energy generating units withdrawn, partial new energy feeders withdrawn, partial AC buses withdrawn, partial transformers withdrawn, partial reactive power compensation devices withdrawn, and partial energy storage withdrawn.

[0176] Specifically, because the impedance model of power electronic components in the sub-super-synchronous frequency band is affected by the power operation level, the state of the new energy grid-connected system at different power operation levels can be simulated to observe its influence on the sub-super-synchronous frequency band oscillation. This method can take into account the dynamic characteristics of the system under different load conditions, so as to more accurately evaluate the oscillation risk. For example, when the system is at a low power operation level, sub-super-synchronous oscillation may be triggered due to certain specific operating conditions; while when the system is at a high power operation level, the oscillation risk may increase due to power fluctuation and distribution problems. For example: The specific power operation levels include: the maximum capacitive reactive power output at 100% active power output, the maximum inductive reactive power output at 100% active power output, 0 reactive power output at 100% active power output, the maximum capacitive reactive power output at 10% active power output, the maximum inductive reactive power output at 10% active power output, 0 reactive power output at 10% active power output, etc.

[0177] The new energy grid-connected system corresponding to the medium-high frequency band adopts the operating mode at the rated power operation level. The impedance model of the new energy grid-connected system in the medium-high frequency band is not affected by the power operation level. Therefore, in the rated power operation mode, it can ensure that the oscillation risk can be accurately evaluated under various working conditions.

[0178] Black start is a special operating mode for restoring power supply after the system is completely powered off. In the new energy grid-connected system, black start usually means starting through specific new energy generating units or energy storage devices without any external power support, and gradually restoring the power supply of the entire system. When evaluating the wide-frequency oscillation risk, considering the operating mode of black start is to analyze the stability and oscillation characteristics of the system in extreme cases. This helps to formulate more effective emergency measures and oscillation control strategies.

[0179] The full-connection operation mode refers to the operation mode of the new energy grid-connected system when all lines and equipment are in the connected state. In this mode, the structure and parameters of the system are relatively fixed, which is convenient for accurate oscillation risk assessment. By simulating the system operation in the full-connection state, the influence of each line and equipment on oscillation can be evaluated, so as to determine the key nodes and weak links.

[0180] Operation modes such as all reactive power compensation devices being withdrawn and single reactive power compensation device being put into operation are used to analyze the influence of reactive power compensation devices and reactive power on system oscillation. Reactive power compensation devices and reactive power have important influences on the stability and oscillation characteristics of the system. By adjusting the operation state of the reactive power compensation devices, the oscillation conditions of the system at different reactive power levels can be observed, providing a basis for formulating reactive power control strategies.

[0181] Operation modes such as partial new energy generating units being withdrawn and partial new energy feeders being withdrawn are used to analyze the contribution of each part of the new energy grid-connected system to the overall oscillation characteristics. By simulating the withdrawal of different parts, the influence degree of each part on system oscillation can be evaluated, so as to determine the areas and equipment that need to be focused on.

[0182] Operation modes such as partial AC busbars being withdrawn, partial transformers being withdrawn, partial reactive power compensation devices being withdrawn, and partial energy storage being withdrawn are used to analyze the oscillation characteristics of the system under different structures. By simulating the withdrawal of these parts, the influence of system structure changes on oscillation can be observed, providing guidance for optimizing the system structure and improving stability.

[0183] Among them, in the embodiments of this application, when evaluating the wide-frequency oscillation risk of the new energy grid-connected system,

[0184] suppression measures for the new energy grid-connected system corresponding to different wide-frequency oscillation risk assessment frequency bands are proposed until the wide-frequency oscillation risk disappears.

[0185] Specifically: The suppression measures for the wide-frequency oscillation risk in the medium-high frequency band are:

[0186] If the new energy grid-connected system has a medium-high frequency oscillation risk, measures are taken to change the impedance of the new energy station or the AC power grid. Among them, the measures to change the impedance of the new energy station include changing the control structure or parameters of the new energy generating unit, changing the control structure or parameters of the SVG, changing the primary circuit of the new energy station, installing passive devices, and installing active devices; the measures to change the impedance of the AC power grid include restricting specific AC power grid operation modes, installing passive devices, and installing active devices.

[0187] The suppression measures for the wide-frequency oscillation risk in the sub-supersynchronous frequency band are:

[0188] Measures are taken to change the impedance of the new energy power station or the AC power grid. The measures to change the impedance of the new energy power station include: changing the control structure or parameters of the new energy generation unit, changing the control structure or parameters of the SVG, changing the primary circuit of the new energy power station, installing passive devices, installing active devices, and limiting the operating power level of the new energy generator set or energy storage unit or SVG. The measures to change the impedance of the AC power grid include: restricting specific AC power grid operation modes.

[0189] The following is an example calculation of the broadband oscillation risk assessment method for the new energy grid-connected system proposed in combination with the present invention.

[0190] In this example calculation, taking the AC grid-connected transmission structure of an offshore wind farm as an example, the topological structure of the AC grid-connected transmission system of the offshore wind farm is as Figure 13 shown, where multiple wind turbine generators P 11 ~P 1n , and each wind turbine generator is equipped with a wind turbine, a converter, and a step-up transformer. The converter is used to convert the alternating current generated by the wind turbine into an electric energy form suitable for subsequent transmission. Immediately afterwards, the electric energy is collected through connecting cables into the collector line. The resistances of different branches in the collector line are respectively l 11 ~l 1n . These collector lines concentrate the electric energy of the scattered wind turbine generators and send it to the offshore booster station. The step-up transformer in the station will perform voltage boosting processing on the electric energy. The high-voltage electric energy boosted by the offshore booster station is transmitted to the land through the submarine cable to ensure stable transmission of the electric energy to the land, and then transmitted to the onshore centralized control center through the submarine cable. Among them, after the electric energy transmitted by the submarine cable arrives on land, it first enters the converter station. The converter station includes converter transformer c and converter transformer p to transform the electric energy so that it meets the requirements for grid connection. At the same time, the system is equipped with an SVG (Static Var Generator, that is, a static var generator) for reactive power compensation to improve the power factor of the power system, stabilize the voltage, and ensure the power quality. The electric energy processed by the converter station will first pass through a high-voltage reactor, which can limit the short-circuit current and reduce the switching overvoltage, etc. Finally, the electric energy reaches the point of common coupling (PCC). At this point, the electric energy generated by the offshore wind power is connected to the grid equivalent voltage source and accesses the onshore power grid through the grid equivalent impedance, thereby realizing the transmission of offshore wind power to the user side.

[0191] It should be noted that this application is applicable to new energy AC grid-connected transmission systems such as offshore wind power and photovoltaic, and is not limited to Figure 13 the topological structure.

[0192] In the oscillation risk assessment in the medium and high frequency bands, the following tests were carried out:

[0193] 1) Establish the impedance characteristic model of a single wind turbine and verify it: As Figures 14 - 15 shown, the theoretical value of the impedance model of a single wind turbine established in this application is in good agreement with the scanned actual value, and it can be used for the risk assessment of medium and high frequency oscillations.

[0194] 2) Establish the impedance model of a single feeder and verify it: Since the types of wind turbines and control parameters on the feeder of the wind farm are different, and at the same time the feeder topologies are not the same, the modeling and verification results of the AC submarine cable after being equivalent by the Bergeron model are given here, as Figures 16 - 17 shown. After the impedance models of a single wind turbine and the AC submarine cable are verified, the impedance characteristic curve model of a single feeder can be obtained through the series-parallel relationship of the single feeder topology.

[0195] 3) Impedance characteristic modeling of the offshore wind farm: The medium and high frequency impedance characteristic curve of the offshore wind farm considering the feeding of multiple feeders is as Figures 18 - 19 shown, where Degree is the phase.

[0196] 4) Considering the influence of the collection and booster station on the impedance of the new energy power station, looking in from the high-voltage side of the offshore booster transformer, the impedance characteristic of the offshore wind farm is calculated as Figures 20 - 21 shown. The offshore booster transformer mainly affects the high-frequency impedance of the wind farm. Due to the inductive effect of the transformer in the high-frequency band, the wind farm mainly presents an inductive characteristic in the high-frequency band.

[0197] 5) Considering the influence of the long-distance AC transmission line on the impedance of the new energy power station, looking in from the onshore connection point of the AC submarine cable, the impedance characteristic of the offshore wind farm is calculated as Figures 22 - 23 shown. It can be seen that due to the influence of the AC submarine cable, the impedance of the wind farm presents positive damping in a large range in the medium and high frequency bands, but the impedance phase angle is near ±90°, and the system damping is weak.

[0198] 6) Considering the influence of parallel branches such as SVG on the impedance of the new energy power station, the impedance characteristic curve of the reactive power compensation parallel branch under a certain specific working condition is as Figures 24 - 25 shown. Taking a certain specific working condition as an example, the comparison of the impedance characteristics of the parallel branch and the offshore wind farm looking in from the onshore connection point of the AC submarine cable is as Figures 26 - 27 shown.

[0199] In the medium and high frequency bands, the impedance amplitude of the reactive power compensation parallel branch is much larger than that of the new energy power station impedance. Therefore, the reactive power compensation parallel branch has little influence on the impedance of the wind farm. The impedance characteristic of the new energy power station considering the reactive power compensation parallel branch is as Figures 28 - 29 shown.

[0200] 7) Considering the input situation of the reactive power compensation parallel branch and the wiring mode of the new energy power station, the impedance characteristic curve on the new energy power station side under the typical input situation of the reactive power compensation parallel branch and the wiring mode of the new energy power station is as Figures 30 - 31as shown (taking a certain working condition as an example).

[0201] 8) Oscillation risk assessment of medium and high frequency new energy grid-connected transmission system. It can be seen from Figures 30 - 31 that there is medium and high frequency negative damping in the offshore wind farms under the working conditions, and the negative damping frequency band is mainly distributed in the range of 1500 - 4200 Hz. Usually, when a short-circuit fault occurs in the AC power grid and the line exits (such as N-1, N-2, N-3, etc.), the impedance phase angle of the AC power grid will approach +90° or -90° in a larger range, thus increasing the risk of medium and high frequency resonance in the system. However, if it can be ensured that there is no medium and high frequency negative damping in the offshore wind farm, no matter what kind of fault occurs in the AC power grid and causes the change of the AC power grid impedance, the medium and high frequency resonance will not be actively excited.

[0202] In the oscillation risk assessment of the sub-supersynchronous frequency band, the following tests were carried out:

[0203] 1) Taking the rated power condition as an example for modeling verification, the comparison between the theoretical value of the impedance model of a single wind turbine in the sub-supersynchronous frequency band and the actual frequency scan value is as Figures 32 - 33 shown. The theoretical value of the model and the actual frequency scan value are in good agreement, and the established model can be used to evaluate the oscillation risk in the sub-supersynchronous frequency band.

[0204] Considering the sub-supersynchronous frequency band of a single wind turbine under different power levels of working conditions as Figure 34 、 35 、36、37 shown (taking two power levels as an example), it can be seen that the power level has an obvious influence on the impedance of the power electronic device in the sub-supersynchronous frequency band.

[0205] 2) Since the types of wind turbines and control parameters on the feeder of the wind farm are different, and the feeder topology structures are also different, the modeling and verification results of the AC submarine cable after being equivalent by the Bergeron model are given here, as Figures 38 - 39 shown. After the impedance models of a single wind turbine and the AC submarine cable are verified, the impedance characteristic curve model of a single feeder can be obtained through the series-parallel relationship of the topology structure of a single feeder.

[0206] 3) Modeling of the impedance characteristics of the offshore wind farm. Considering the impedance characteristic curve of the offshore wind farm in the sub-supersynchronous frequency band after multiple feeders are fed in as Figures 40 - 41 shown.

[0207] 4) Considering the influence of the collection and booster station on the impedance of the new energy station, looking into from the high-voltage side of the offshore booster transformer, the impedance characteristics of the offshore wind farm are calculated as Figures 42 - 43 shown.

[0208] 5) Considering the influence of the long-distance AC transmission line on the impedance of the new energy station, looking into from the onshore connection point of the AC submarine cable, the impedance characteristics of the offshore wind farm are calculated as Figures 44 - 45 shown.

[0209] 6) Consider the influence of shunt branches such as SVG on the impedance of new - energy power stations. The impedance characteristic curve of the shunt branch for reactive power compensation at a certain power level is as Figures 46 - 47 shown. Taking a specific working condition as an example, the comparison of the impedance characteristics of the shunt branch and the offshore wind farm seen from the grid - connection point on the AC submarine cable is as Figures 48 - 49 shown.

[0210] In the sub - super - synchronous frequency band, the impedance amplitude of the shunt branch for reactive power compensation is similar to that of the new - energy power station. Therefore, the shunt branch for reactive power compensation has a greater impact on the impedance of the wind farm. The impedance characteristic of the new - energy power station considering the shunt branch for reactive power compensation is as Figures 50 - 51 shown.

[0211] 7) AC power grid modeling and oscillation risk assessment of the new - energy grid - connection and transmission system in the sub - super - synchronous frequency band: The equivalent impedance of the AC power grid is established by using the SCR equivalent. The operating power level of the fan is limited. The equivalent impedance of the AC power grid under two certain working conditions is selected to conduct oscillation risk assessment on the sub - super - synchronous frequency band of the new - energy grid - connection and transmission system. The impedance analysis method is used for analysis, as Figure 52 、 53 、54, 55 shown.

[0212] In the frequency range where the amplitude of the AC power grid impedance is greater than that of the offshore wind farm impedance, the impedance phase - angle difference is less than 180°, indicating that the sub - super - synchronous oscillation risk of the system is relatively low.

[0213] Based on the same inventive concept, the embodiment of the present application also provides a new - energy grid - connection system wide - frequency oscillation risk assessment system for implementing the new - energy grid - connection system wide - frequency oscillation risk assessment method involved above.

[0214] The implementation solution provided by this system to solve the problem is similar to the implementation solution recorded in the above - mentioned method. Therefore, the specific limitations in one or more embodiments of the new - energy grid - connection system wide - frequency oscillation risk assessment system provided below can refer to the limitations on the new - energy grid - connection system wide - frequency oscillation risk assessment method in the above text, and will not be elaborated here.

[0215] As Figure 56 shown, the embodiment of the present invention provides a new - energy grid - connection system wide - frequency oscillation risk assessment system, including:

[0216] An impedance model construction module 100, configured to establish an external impedance characteristic model of each electrical unit according to multiple electrical units of the new - energy power station;

[0217] The substation model construction module 200 is used to connect each electrical unit according to the impedance external characteristic model and wiring structure of each electrical unit of the new energy substation, and obtain the impedance external characteristic model of the new energy substation corresponding to the wide-frequency oscillation risk assessment frequency band according to the impedance series-parallel relationship of each electrical unit;

[0218] The grid-side model construction module 300 is used to determine the impedance external characteristic model of the AC power grid corresponding to the wide-frequency oscillation risk assessment frequency band according to different wide-frequency oscillation risk assessment frequency bands;

[0219] The impedance curve determination module 400 is used to determine the impedance external characteristic curve of the new energy substation and the impedance external characteristic curve of the AC power grid according to the impedance external characteristic model of the new energy substation and the impedance external characteristic model of the AC power grid;

[0220] The risk assessment module 500 is used to perform a wide-frequency oscillation risk assessment on the new energy grid-connected system according to the comparison result of the impedance external characteristic curve of the new energy substation and the impedance external characteristic curve of the AC power grid.

[0221] In some embodiments, the electrical units include feeders, transformers, reactive power compensation devices, and energy storage units. Among them, the feeder includes multiple new energy generating units and multiple AC lines, and the multiple new energy generating units and multiple AC lines are connected in series and parallel to form a feeder.

[0222] In some embodiments, the process of constructing the impedance external characteristic model of the new energy substation is as follows:

[0223] Construct the voltage and current small-signal phasors at the point of common coupling under three-phase symmetrical conditions for a single new energy generating unit according to different wide-frequency oscillation risk assessment frequency bands;

[0224] Based on the voltage and current small-signal phasors, obtain the AC-side admittance matrix through Laplace transformation of the control process of a single new energy generating unit; among them, the AC-side admittance matrix in the sub-super-synchronous frequency band introduces a phase-locked loop control link coefficient matrix affected by the AC-side power operation level;

[0225] Determine the impedance characteristic model of a single new energy generating unit according to the AC-side admittance matrix;

[0226] Use the Bergeron model to equivalently simulate the AC line between two new energy generating units to obtain the equivalent impedance model of the AC line;

[0227] Based on the connection relationship of multiple new energy generating units and AC lines on the feeder, perform series-parallel connection on the impedance characteristic model of a single new energy generating unit and the equivalent impedance model of the AC line to obtain the impedance external characteristic model of the feeder;

[0228] According to the primary structure and control structure of the reactive power compensation device, an impedance external characteristic model of the reactive power compensation device is constructed by the impedance modeling method;

[0229] According to the primary structure and control structure of the energy storage unit, an impedance external characteristic model of the energy storage unit is constructed by the impedance modeling method;

[0230] The transformer is equivalently modeled by using a T-shaped equivalent circuit or a π-shaped equivalent circuit to obtain an impedance external characteristic model of the transformer;

[0231] The impedance external characteristic model of the new energy power station is formed by connecting the impedance external characteristic models of the feeder, the reactive power compensation device, the energy storage unit, and the transformer through series-parallel relationships.

[0232] In some embodiments, the wide-frequency oscillation risk assessment frequency band is the medium-high frequency band or the sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is as follows:

[0233] The outlet end of the AC power grid after multi-stage lines or voltage transformation is determined by using multiple ideal voltage sources and lumped parameter impedances;

[0234] Starting from the common coupling point between the new energy power station and the AC power grid, looking towards the AC power grid to the outlet end, according to the series-parallel relationships of the AC lines, transformers, and other primary equipment in the AC power grid, the impedance external characteristic model of the AC power grid is obtained.

[0235] In some embodiments, the wide-frequency oscillation risk assessment frequency band is the sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is: based on the short-circuit ratio equivalent method, it is constructed according to the equivalent short-circuit ratio of the AC power grid.

[0236] In some embodiments, the new energy grid-connected system corresponding to the sub-supersynchronous frequency band adopts the operating modes under different power operating levels; the new energy grid-connected system corresponding to the medium-high frequency band adopts the operating mode under the rated operating power level; among them, the operating mode adopts one of the following methods, and the operating modes include: black start, full connection, all reactive power compensation devices withdrawn, single reactive power compensation device input, partial new energy generating units withdrawn, partial new energy feeders withdrawn, partial AC buses withdrawn, partial transformers withdrawn, partial reactive power compensation devices withdrawn, and partial energy storage withdrawn.

[0237] In some embodiments, the risk assessment module 500 is used for:

[0238] According to the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid, determine the frequency range in which the impedance amplitude of the AC power grid is greater than that of the new energy power station under the same wide-frequency oscillation risk assessment frequency band;

[0239] Determine whether the phase difference between the impedance external characteristic curve of the AC power grid within the frequency range and the impedance external characteristic curve of the new energy power station is greater than a preset phase difference threshold;

[0240] If it is determined that the phase difference is greater than the preset phase difference threshold, it is determined that there is a broadband oscillation risk in the new energy grid-connected system;

[0241] If it is determined that the phase difference is not greater than the preset phase difference threshold, it is determined that there is no broadband oscillation risk in the new energy grid-connected system.

[0242] As Figure 57 shown, an embodiment of the present application further provides an electronic device. The electronic device 10 includes a memory 20 and a processor 30. A computer program is stored in the memory 20. When the computer program is executed by the processor 30, the processor 30 is caused to execute the steps of the broadband oscillation risk assessment method for the new energy grid-connected system as described above.

[0243] An embodiment of the present application further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed, the steps of the broadband oscillation risk assessment method for the new energy grid-connected system as described above are implemented.

[0244] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the systems, electronic devices, and computer storage media described above can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0245] It should be noted that the terms "including" and "having" and any variations thereof in the description and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0246] In several embodiments provided by the present invention, it can be understood that each block in the flowchart or block diagram may represent a module, a program segment, or a part of code. A module, a program segment, or a part of code includes one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in an order different from that marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved.

[0247] In several embodiments provided by the present invention, it should be understood that the disclosed systems, electronic devices, computer storage media, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces. The indirect couplings or communication connections of devices or units can be in electrical, mechanical, or other forms.

[0248] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place, or they can be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0249] In addition, in each embodiment of the present invention, the functional units can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0250] If the above-mentioned integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it 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 all or 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 a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (English full name: Read-Only Memory, English abbreviation: ROM), random access memories (English full name: Random Access Memory, English abbreviation: RAM), magnetic disks, or optical discs that can store program codes.

[0251] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; 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 recorded in the foregoing embodiments, or perform equivalent replacements on 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 various embodiments of the present invention.

Claims

1. A method for evaluating the broadband oscillation risk of a new energy grid-connected system, which is applied to evaluate the broadband oscillation risk of the new energy grid-connected system in different broadband oscillation risk assessment frequency bands, and the broadband oscillation risk assessment frequency bands include the medium-high frequency band and the sub-supersynchronous frequency band; characterized in that, The method includes: Based on multiple electrical units of a new energy power station, establishing impedance external characteristic models for each of the electrical units; the electrical units include feeders, transformers, reactive power compensation devices, and energy storage units, where the feeder includes multiple new energy generating units and multiple AC lines, and the multiple new energy generating units and the multiple AC lines are connected in series and parallel to form the feeder; According to the impedance external characteristic models and wiring structures of the electrical units of the new energy power station, connecting the electrical units, and based on the series and parallel relationships of the impedances of the electrical units, obtaining the impedance external characteristic model of the new energy power station corresponding to the wide - frequency oscillation risk assessment frequency band; The process of constructing the impedance external characteristic model of the new energy power station is as follows: According to different wide - frequency oscillation risk assessment frequency bands, constructing voltage and current small - signal phasors at the point of common coupling under three - phase symmetrical conditions for a single new energy generating unit; Based on the voltage and current small - signal phasors, through Laplace transformation of the control process of the single new energy generating unit, obtaining the AC - side admittance matrix; among them, the AC - side admittance matrix in the sub - super - synchronous frequency band introduces a phase - locked loop control link coefficient matrix affected by the AC - side power operation level; Determining the impedance characteristic model of a single new energy generating unit according to the AC - side admittance matrix; Using the Bergeron model to equivalently simulate the AC line between two new energy generating units to obtain the equivalent impedance model of the AC line; Based on the connection relationship of multiple new energy generating units on the feeder and the equivalent impedance model of the AC line, connecting the impedance characteristic model of the single new energy generating unit and the equivalent impedance model of the AC line in series and parallel to obtain the impedance external characteristic model of the feeder; According to the primary structure and control structure of the reactive power compensation device, constructing the impedance external characteristic model of the reactive power compensation device through impedance modeling; According to the primary structure and control structure of the energy storage unit, constructing the impedance external characteristic model of the energy storage unit through impedance modeling; Using the T - type equivalent circuit or π - type equivalent circuit to equivalently model the transformer to obtain the impedance external characteristic model of the transformer; Connecting the impedance external characteristic model of the feeder, the impedance external characteristic model of the reactive power compensation device, the impedance external characteristic model of the energy storage unit, and the impedance external characteristic model of the transformer through series and parallel relationships to form the impedance external characteristic model of the new energy power station; According to different wide - frequency oscillation risk assessment frequency bands, determining the impedance external characteristic model of the AC power grid corresponding to the wide - frequency oscillation risk assessment frequency band; According to the impedance external characteristic model of the new energy power station and the impedance external characteristic model of the AC power grid, determining the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid; Conducting a wide - frequency oscillation risk assessment on the new energy grid - connected system according to the comparison result of the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid.

2. The broadband oscillation risk assessment method for a new energy grid-connected system according to claim 1, characterized in that The wide - frequency oscillation risk assessment frequency band is the medium - high frequency band or the sub - super - synchronous frequency band; the process of constructing the impedance external characteristic model of the AC power grid is: Determine the end of the outgoing line after the AC power grid passes through multiple levels of lines or transformers by using multiple ideal voltage sources and lumped parameter impedances; Starting from the point of common coupling between the new energy power station and the AC power grid, looking towards the end of the outgoing line of the AC power grid, according to the series-parallel relationship of AC lines, transformers and other primary equipment in the AC power grid, obtain the impedance external characteristic model of the AC power grid.

3. The broadband oscillation risk assessment method for a new energy grid-connected system according to claim 1, wherein The wide-frequency oscillation risk assessment frequency band is the sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is: based on the short-circuit ratio equivalent method, construct according to the equivalent short-circuit ratio of the AC power grid.

4. The broadband oscillation risk assessment method for the new energy grid-connected system according to claim 1, wherein The new energy grid-connected system corresponding to the sub-supersynchronous frequency band adopts the operation mode under different power operation levels; the new energy grid-connected system corresponding to the medium-high frequency band adopts the operation mode under the rated working condition power operation level; among them, the operation mode adopts one of the following methods, and the operation mode includes: black start, full connection, all reactive power compensation devices withdrawn, single reactive power compensation device put in, part of the new energy generating units withdrawn, part of the new energy feeders withdrawn, part of the AC busbars withdrawn, part of the transformers withdrawn, part of the reactive power compensation devices withdrawn and part of the energy storage withdrawn.

5. The method for evaluating the risk of broadband oscillation in a new energy grid-connected system according to claim 1, wherein The wide-frequency oscillation risk assessment of the new energy grid-connected system according to the comparison result of the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid includes: According to the impedance external characteristic curve of the new energy power station and the impedance external characteristic curve of the AC power grid, determine the frequency range in which the impedance amplitude of the AC power grid is greater than that of the new energy power station in the same wide-frequency oscillation risk assessment frequency band; Judge whether the phase difference between the impedance external characteristic curve of the AC power grid and the impedance external characteristic curve of the new energy power station in the frequency range is greater than a preset phase difference threshold; If it is judged that the phase difference is greater than the preset phase difference threshold, it is determined that the new energy grid-connected system has a wide-frequency oscillation risk; If it is judged that the phase difference is not greater than the preset phase difference threshold, it is determined that the new energy grid-connected system does not have a wide-frequency oscillation risk.

6. A broadband oscillation risk assessment system for a new energy grid-connected system, which is applied to assess the broadband oscillation risks of the new energy grid-connected system in different broadband oscillation risk assessment frequency bands, and the broadband oscillation risk assessment frequency bands include the medium-high frequency band and the sub-supersynchronous frequency band; characterized in that, Including: An impedance model construction module, configured to establish an impedance external characteristic model of each of the electrical units according to multiple electrical units of the new energy power station; the electrical units include feeders, transformers, reactive power compensation devices and energy storage units, wherein the feeder includes multiple new energy generating units and multiple AC lines, and the multiple new energy generating units and multiple AC lines are connected in series and parallel to form the feeder; A power station model construction module, configured to connect each of the electrical units according to the impedance external characteristic model and the wiring structure of each of the electrical units of the new energy power station, and obtain the impedance external characteristic model of the new energy power station corresponding to the wide-frequency oscillation risk assessment frequency band according to the impedance series-parallel relationship of each of the electrical units; The construction process of the impedance external characteristic model of the new energy power station is: Construct the voltage and current small-signal phasors at the point of common coupling of a single new energy generating unit under three-phase symmetrical conditions according to different wide-frequency oscillation risk assessment frequency bands; Based on the voltage and current small-signal phasors, by performing Laplace transform on the control process of the single new energy unit, an AC-side admittance matrix is obtained; wherein, the AC-side admittance matrix in the sub-super-synchronous frequency band introduces a phase-locked loop control link coefficient matrix affected by the AC-side power operation level; Determine the impedance characteristic model of a single new energy unit according to the AC-side admittance matrix; Use the Bergeron model to equivalently simulate the AC line between two new energy units to obtain the equivalent impedance model of the AC line; Based on the connection relationship between multiple new energy units on the feeder and the AC line, connect the impedance characteristic model of the single new energy unit and the equivalent impedance model of the AC line in series and parallel to obtain the external impedance characteristic model of the feeder; According to the primary structure and control structure of the reactive power compensation device, construct the external impedance characteristic model of the reactive power compensation device by impedance modeling method; According to the primary structure and control structure of the energy storage unit, construct the external impedance characteristic model of the energy storage unit by impedance modeling method; Use the T-shaped equivalent circuit or π-shaped equivalent circuit to equivalently model the transformer to obtain the external impedance characteristic model of the transformer; The external impedance characteristic model of the new energy substation is formed by connecting the external impedance characteristic model of the feeder, the external impedance characteristic model of the reactive power compensation device, the external impedance characteristic model of the energy storage unit, and the external impedance characteristic model of the transformer through series and parallel relationships; A grid-side model construction module, configured to determine the external impedance characteristic model of the AC power grid corresponding to the wide-frequency oscillation risk assessment frequency band according to different wide-frequency oscillation risk assessment frequency bands; An impedance curve determination module, configured to determine the external impedance characteristic curve of the new energy substation and the external impedance characteristic curve of the AC power grid according to the external impedance characteristic model of the new energy substation and the external impedance characteristic model of the AC power grid; A risk assessment module, configured to perform a wide-frequency oscillation risk assessment on the new energy grid-connected system according to the comparison result of the external impedance characteristic curve of the new energy substation and the external impedance characteristic curve of the AC power grid.

7. An electronic device, characterized in that, The electronic device includes a memory and a processor. When the computer program stored in the memory is executed by the processor, the processor executes the steps of the wide-frequency oscillation risk assessment method for the new energy grid-connected system according to any one of claims 1-5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed, the steps of the wide-frequency oscillation risk assessment method for the new energy grid-connected system according to any one of claims 1-5 are implemented.

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