New energy grid-connected system broadband oscillation risk assessment method, system, equipment and medium

Abstract

The invention relates to the technical field of power systems, and discloses a new energy grid-connected system broadband oscillation risk assessment method, system, device and medium, and the method comprises the steps: constructing an impedance external characteristic model of a new energy station, and constructing impedance external characteristic models of an AC power grid of different broadband oscillation risk assessment frequency bands; therefore, different broadband oscillation risk assessment frequency bands are flexibly processed, and the impedance external characteristic model of the new energy station and the impedance external characteristic model of the AC power grid are used to determine the impedance external characteristic curve of the new energy station and the impedance external characteristic curve of the AC power grid. And performing broadband oscillation risk assessment on the new energy grid-connected system by using a comparison result of the impedance external characteristic curve of the new energy station and the impedance external characteristic curve of the alternating current power grid, and fully considering the influence of a topological structure and an operation condition on the broadband oscillation risk. And the broadband oscillation risk assessment accuracy and adaptability of the new energy grid-connected system are improved.

Description

Technical Field

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

[0002] In recent years, new energy represented by offshore wind power and photovoltaic power has experienced explosive growth. It is estimated that by 2030, the total installed capacity of new energy in my country will account for nearly 50%. The AC grid-connected system of new energy stations contains a large number of new energy converters, static var generators (SVG) and other power electronic conversion devices, which interact with high-frequency filter circuits, bus cable / overhead line capacitance to ground and grid impedance, resulting in an increased risk of resonance in the AC grid-connected system of new energy stations.

[0003] In large-scale renewable energy grid-connected projects, when multiple broadband oscillation events occur, it may greatly threaten the stability of the power grid project.

[0004] It can be seen that the risk of broadband oscillation in the power electronic device access system is high, and it has the characteristics of wide resonant frequency band, multiple types and complex mechanism, which seriously threatens the safe and stable operation of grid-connected equipment and power systems. Therefore, it is necessary to carry out the assessment of broadband oscillation risk of new energy grid-connected systems.

[0005] At present, it is difficult to consider various operating conditions of the system in the broadband oscillation risk assessment method for the renewable energy grid-connected system, which easily leads to low accuracy and poor adaptability of the broadband oscillation risk assessment of the renewable energy grid-connected system. Summary of the invention

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

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

[0008] According to a plurality of electrical units of the new energy station, an impedance external characteristic model of each of the electrical units is established;

[0009] According to the impedance external characteristic model and wiring structure of each electrical unit of the new energy station, each electrical unit is connected, and according to the impedance series-parallel relationship of each electrical unit, the impedance external characteristic model of the new energy station corresponding to the wide-band oscillation risk assessment frequency band is obtained;

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

[0011] Determining an impedance external characteristic curve of the new energy station and an impedance external characteristic curve of the AC power grid according to the impedance external characteristic model of the new energy station and the impedance external characteristic model of the AC power grid;

[0012] A broadband oscillation risk assessment is performed on the new energy grid-connected system based on a comparison result of the impedance external characteristic curve of the new energy 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 a plurality of new energy units and a plurality of AC lines, and the plurality of new energy units and the plurality of 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:

[0015] According to different broadband oscillation risk assessment frequency bands, the voltage and current small signal phasors at the common coupling point of a single new energy unit under three-phase symmetrical working conditions are constructed;

[0016] Based on the voltage and current small signal phasors, the AC side admittance matrix is ​​obtained by performing Laplace transform on the control process of the single new energy generator set; wherein the AC side admittance matrix of the sub-supersynchronous frequency band introduces a phase-locked loop control link coefficient matrix affected by the AC side power operation level;

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

[0018] The Bergeron model is used to perform equivalent simulation on the AC line between the two new energy units to obtain the equivalent impedance model of the AC line;

[0019] Based on the connection relationship between the multiple new energy units on the feeder and the AC line, the impedance characteristic model of the single new energy unit and the equivalent impedance model of the AC line are connected in series and parallel to obtain an 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 an 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 an impedance modeling method;

[0022] Using a T-shaped equivalent circuit or a π-shaped equivalent circuit to perform equivalent modeling on the transformer to obtain an impedance external characteristic model of the transformer;

[0023] The impedance external characteristic model of the feeder, the impedance external characteristic model of the reactive compensation device, the impedance external characteristic model of the energy storage unit and the impedance external characteristic model of the transformer are connected in series and parallel to form the impedance external characteristic model of the new energy station.

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

[0025] Determine the outgoing line end of the AC power grid after multi-level lines or transformation by using multiple ideal voltage sources and concentrated parameter impedance;

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

[0027] Preferably, the broadband oscillation risk assessment frequency band is a 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 an operation mode under different power operation levels; the new energy grid-connected system corresponding to the medium and high frequency bands adopts an operation mode under the rated operating power operation level; wherein the operation mode adopts one of the following modes, wherein the operation mode includes:

[0029] Black start, full connection, all reactive compensation devices withdrawn, reactive compensation devices put into operation separately, some new energy generator sets withdrawn, some new energy feeders withdrawn, some AC bus withdrawn, some transformers withdrawn, some reactive compensation devices withdrawn and some energy storage withdrawn.

[0030] Preferably, the performing of broadband 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 station and the impedance external characteristic curve of the AC power grid comprises:

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

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

[0033] If it is determined 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;

[0034] 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.

[0035] In a second aspect, the present invention provides a broadband oscillation risk assessment system for a new energy grid-connected system, which is applied to assess the broadband oscillation risk of the new energy grid-connected system in different broadband oscillation risk assessment frequency bands, wherein the broadband oscillation risk assessment frequency bands include medium and high frequency bands and sub-supersynchronous frequency bands; including:

[0036] An impedance model building module is used to build an impedance external characteristic model of each electrical unit according to multiple electrical units of the new energy station;

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

[0038] A grid-side model building module, used to 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;

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

[0040] The risk assessment module is used to perform a broadband oscillation risk assessment on the new energy grid-connected system based on a comparison result of the impedance external characteristic curve of the new energy 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, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method for assessing the risk of wide-band oscillation of a new energy grid-connected system as described in the first aspect.

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

[0043] It can be seen from the above technical solutions that the present invention constructs an impedance external characteristic model of a new energy station and constructs an impedance external characteristic model of an AC power grid with different broadband oscillation risk assessment frequency bands, thereby realizing flexible processing of different broadband oscillation risk assessment frequency bands. The impedance external characteristic model of the new energy station and the impedance external characteristic model of the AC power grid are used to determine the impedance external characteristic curve of the new energy station and the impedance external characteristic curve of the AC power grid. The broadband oscillation risk of the new energy grid-connected system is assessed by comparing the impedance external characteristic curve of the new energy station with the impedance external characteristic curve of the AC power grid. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

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

[0046] Figure 2 A flow chart of a method for assessing the risk of broadband oscillation in a new energy grid-connected system provided by an embodiment of the present invention;

[0047] Figure 3 This is a typical structure diagram of the AC power grid of the new energy grid-connected system;

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

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

[0050] Figure 6 This is a typical wind turbine topology diagram;

[0051] Figure 7 This is a typical wind turbine control block diagram;

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

[0053] Fig. 9 is the equivalent diagram of the AC line;

[0054] Fig.10 is the equivalent model of the feeder;

[0055] Fig.11 It is the electrical wiring diagram of the reactive power compensation device;

[0056] Fig.12 This is the control architecture diagram of the reactive power compensation device;

[0057] Fig.13 The topological structure diagram of the AC transmission grid-connected system for offshore wind farms;

[0058] Fig.14 , Fig.15 Modeling and verification diagram of impedance of a single wind turbine in the medium and high frequency bands;

[0059] Fig.16 , Fig.17 Modeling and verification diagram for AC submarine cables;

[0060] Fig.18 , Fig.19 It is the high frequency impedance characteristic curve of offshore wind farm;

[0061] Fig. 20 , Fig.21 This is the impedance characteristic curve after considering the impact of the booster station on the new energy station;

[0062] Fig. 22 , Fig.23 The impedance characteristic curve of the offshore wind farm after considering the influence of long-distance AC transmission lines;

[0063] Fig.24 , Fig.25 It is the impedance characteristic curve of the reactive power compensation parallel branch at medium and high frequency;

[0064] Fig.26 , Fig. 27 It is a comparison diagram of impedance characteristic curves of reactive compensation parallel branch and new energy station;

[0065] Fig.28 , Fig.29 The impedance characteristic curve of the new energy station after the reactive power compensation parallel branch is considered for medium and high frequency;

[0066] Fig.30 , Fig.31 It is the impedance characteristic curve of the typical reactive power compensation parallel branch and the new energy station connection mode at medium and high frequency;

[0067] Fig.32 , Fig.33 A comparison chart of the theoretical value of the impedance model of a single wind turbine in the sub-supersynchronous frequency band and the actual frequency scanning value;

[0068] Fig.34 , Fig.35 This is the impedance characteristic curve of a single wind turbine in the sub-supersynchronous frequency band under working condition 1;

[0069] Fig.36 , Fig.37 This is the impedance characteristic curve of a single wind turbine in the sub-supersynchronous frequency band under working condition 2;

[0070] Fig.38 , Fig.39 The AC submarine cable modeling and verification results after Bergeron model equivalence;

[0071] Fig.40 , Fig.41 To consider the super-synchronous frequency band impedance characteristic curve of offshore wind farms after multiple feeders are fed in;

[0072] Fig.42 , Fig.43 The impedance characteristic curve of offshore wind farm in sub-supersynchronous frequency band after considering the influence of offshore voltage rise;

[0073] Fig.44 , Fig.45 The impedance characteristic curve of the sub-supersynchronous frequency band offshore wind farm seen from the onshore grid connection point of the AC submarine cable;

[0074] Fig.46 , Fig.47 is the impedance characteristic curve of the reactive power compensation parallel branch in the sub-supersynchronous frequency band;

[0075] Fig.48 , Fig.49 It is a comparison diagram of impedance characteristic curves of reactive power compensation parallel branch and new energy station in sub-supersynchronous frequency band;

[0076] Fig.50 , Fig.51 The impedance characteristic curve of the new energy station after considering the reactive power compensation parallel branch in the sub-supersynchronous frequency band;

[0077] Fig.52 , Fig.53 The equivalent impedance of the AC grid under working condition 1 is used to evaluate the oscillation risk of the sub-supersynchronous frequency band of the new energy transmission system through the grid connection;

[0078] Fig.54 , Fig.55 The equivalent impedance of the AC grid under working condition 2 is used to evaluate the oscillation risk of the sub-supersynchronous frequency band of the new energy transmission system through the grid connection;

[0079] Fig.56 It is a structural schematic diagram of a broadband oscillation risk assessment system for a new energy grid-connected system;

[0080] Fig.57 The figure is a schematic diagram of the structure of an electronic device. DETAILED DESCRIPTION

[0081] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] The broadband oscillation risk assessment method for a new energy grid-connected system provided in the embodiment of the present application can be applied to Figure 1 In the application environment shown. Among them, each device node of the new energy grid-connected system communicates with the server 102 through the 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 it can be placed on 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 that provides cloud computing services.

[0083] An embodiment of the present application provides a method for assessing the broadband oscillation risk of a new energy grid-connected system, which is applied to assessing the broadband oscillation risk of the new energy grid-connected system in different broadband oscillation risk assessment frequency bands, wherein the broadband oscillation risk assessment frequency bands include medium and high frequency bands and sub-supersynchronous frequency bands.

[0084] Among them, the embodiments of the present application respectively carry out the process of establishing the impedance model of the new energy station side and the AC power grid for the wide-band oscillation risk assessment frequency bands of different new energy grid-connected systems. The wide-band oscillation risk assessment frequency bands include medium and high frequency bands (frequency bands greater than 200Hz) and sub-supersynchronous frequency bands (frequency bands of 1~200Hz).

[0085] At the same time, the embodiment of the present application adaptively adjusts the impedance external characteristic model of the new energy station and the impedance external characteristic model of the AC power grid according to different broadband oscillation risk assessment frequency bands to ensure the accuracy and effectiveness of the impedance model.

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

[0087] Step S1: establishing an impedance external characteristic model of each electrical unit according to multiple electrical units of a new energy station.

[0088] Among them, the new energy grid-connected system is connected to the AC power grid by the new energy station with the PCC (Point of Common Coupling) as the dividing point. Figure 3 As shown in Figure 2, the onshore AC power grid is connected to the power grid after multiple-stage transformation. Considering the two-stage transformer, the ideal voltage source and concentrated parameter impedance can be used to characterize the end of the onshore AC power grid.

[0089] Among them, the electrical unit includes a feeder, a transformer, a reactive compensation device and an energy storage unit. Among them, the feeder contains multiple new energy units and multiple AC lines. Multiple new energy 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 station, and obtain the impedance external characteristic model of the new energy station corresponding to the wide-band 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 station is determined by the impedance external characteristic models of multiple electrical units and the wiring structure and impedance series-parallel relationship between them. The various electrical units in the new energy station, such as feeders, transformers, reactive compensation devices and energy storage units, etc.

[0092] The impedance external characteristic model of each electrical unit is connected according to the wiring structure of each electrical unit of the new energy station, and according to the impedance series-parallel relationship of each electrical unit, the impedance external characteristic model of the new energy station is obtained.

[0093] Step S3: determining 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, the impedance model of the AC grid is established according to the series-parallel relationship of the AC lines, transformers and other primary devices of the AC grid. The AC grid modeling of the new energy grid-connected system needs to consider the outgoing lines of two-stage transformers and above. Considering the part after the two-stage transformer, the ideal voltage source and concentrated parameter impedance can be used to characterize the end of the AC grid. And considering different operating conditions such as full connection of the AC grid, withdrawal of a single device, and withdrawal of a single line, the impedance model of the AC grid under different operating conditions is obtained. Among them, the equivalent impedance of the AC grid will change according to the outgoing line conditions of the AC grid. The impact of changes in the topological structure in the AC grid and changes in the operating conditions on the impedance external characteristic model can also be considered. For example, when there is a ring network structure in the AC grid, these structures need to be equivalently modeled to obtain a more accurate impedance external characteristic model. It should be noted that the impedance model of the AC lines, transformers and other primary devices of the AC grid can refer to the corresponding equipment in the new energy station for impedance modeling.

[0095] In some embodiments, the short circuit ratio equivalent method may also be used to consider the equivalent impedance of the AC power grid in the sub-supersynchronous frequency band, that is, the impedance external characteristic model of the AC power grid is based on the short circuit ratio equivalent method and is constructed according to the equivalent short circuit ratio of the AC power grid.

[0096] For example, assuming that the equivalent short circuit ratio (SCR) of the AC power grid under a certain outgoing line condition is known (if there are multiple infeed renewable energy stations in the AC power grid, the SCR should use the equivalent short circuit ratio of multiple infeed renewable energy stations), the equivalent impedance model of the AC side is as follows:

[0097] (1)

[0098] Where U base , P base are the rated voltage and rated power of the AC 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 station and the impedance external characteristic curve of the AC power grid according to the impedance external characteristic model of the new energy 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 station, the amplitude and phase are obtained, and the impedance external characteristic curve of the new energy station can be drawn. According to the impedance external characteristic model of the AC power grid, a fast Fourier transform is performed to obtain the amplitude and phase, and the impedance external characteristic curve of the AC power grid can be drawn.

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

[0102] It should be noted that the present invention constructs an impedance external characteristic model of a new energy station and constructs an impedance external characteristic model of an AC power grid with different broadband oscillation risk assessment frequency bands, thereby realizing flexible processing of different broadband oscillation risk assessment frequency bands. The impedance external characteristic model of the new energy station and the impedance external characteristic model of the AC power grid are used to determine the impedance external characteristic curve of the new energy station and the impedance external characteristic curve of the AC power grid. The broadband oscillation risk of the new energy grid-connected system is assessed by comparing the impedance external characteristic curve of the new energy station with the impedance external characteristic curve of the AC power grid. 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.

[0103] In some embodiments, a broadband oscillation risk assessment is performed on a new energy grid-connected system based on a comparison result of an impedance external characteristic curve of a new energy station and an impedance external characteristic curve of an AC power grid, including:

[0104] Step S501: According to the impedance external characteristic curve of the new energy station and the impedance external characteristic curve of the AC power grid, determine that the impedance amplitude of the AC power grid in the same broadband oscillation risk assessment frequency band is greater than the frequency interval range of the new energy station.

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

[0106] Step S502: determine 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 station within the frequency range is greater than a preset phase difference threshold.

[0107] Step S503: if it is determined that the phase difference is greater than a 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 determined 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, Figure 4~Figure 5 The positive sequence subsystem and negative sequence subsystem of the renewable energy grid-connected system shown in the figure, where Z Rp ,I Rp Respectively represent the positive sequence impedance of new energy and the equivalent current source; Z Mp、V Mp Respectively represent the positive sequence impedance and equivalent voltage source of the flexible DC converter station; V outp ,I outp Respectively represent the AC bus voltage and current of the new energy station. Rn ,I Rn Respectively represent the negative sequence impedance of new energy and the equivalent current source; Z Rn ,I Rn Respectively represent the negative sequence impedance of new energy and the equivalent current source; Z Mn 、V Mn Respectively represent the negative sequence impedance of the AC power grid and the equivalent voltage source; V outn ,I outn They respectively represent the AC bus voltage and current at the grid connection point of the new energy station.

[0110] Taking the positive sequence subsystem as an example, according to Figure 4 , the voltage V of the AC busbar of the new energy station in the positive sequence subsystem can be solved outp 、Current I outp They are:

[0111] (2)

[0112] (3)

[0113] Assuming that the new energy station and the AC power grid are both in a stable state when operating independently, I Rp 、V Mp Therefore, when the new energy station is interconnected with the AC power grid, the stability of the positive sequence subsystem depends on the term 1 / (1+Z Mp (s) / Z Rp (s)) is stable.

[0114] The system does not meet the stability criterion and oscillates if and only if the following two conditions are met: ① There is Z Mp (s) Impedance amplitude is greater than Z Rp (s) frequency range of impedance amplitude; ② at Z Mp (s) Impedance amplitude is greater than Z Rp (s) The frequency range of impedance amplitude, Z Mp (s) and Z Rp (s) The phase-frequency characteristic curves differ by more than 180°.

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

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

[0117] Step S202: Based on voltage and current small signal phasors, Laplace transform is performed on the control process of a single new energy generator set to obtain an AC side admittance matrix; wherein the AC side admittance matrix of the sub-supersynchronous frequency band introduces a phase-locked loop control link coefficient matrix affected by the AC side power operation level;

[0118] Among them, a single new energy unit takes a wind turbine as an example. In the phase-locked loop control link of a single wind turbine, the input of the coefficient matrix of the voltage variable of the phase-locked loop control link is the AC side voltage, and its output phase θ is greatly affected by the power operation level of the AC side. The phase-locked loop control frequency band is located in the sub-supersynchronous frequency band. The influence of the phase-locked loop 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 phase-locked loop on the impedance characteristics. The sub-supersynchronous impedance characteristics of the wind turbine are affected by the system power level due to the phase-locked loop control. When conducting sub-supersynchronous frequency band oscillation risk assessment, it is necessary to consider the influence of the power level on the sub-supersynchronous impedance characteristics of a single wind turbine (see Table 1 for examples of different power levels of wind turbines).

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

[0120]

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

[0122] Figure 6 In, Z t is the leakage reactance of the commutation transformer, Y c is the admittance of the AC side filter bank, Z f is the passive branch impedance on the AC side, Z G is the AC impedance of a single fan viewed from the high-pressure side, Z g is the AC impedance of a single fan viewed from the low-pressure side, I source It is a controlled current source for simulating the machine-side converter station and other parts.

[0123] Figure 7 In, P in Inject active power into the DC side, u dc , C dc are the DC side voltage and DC side equivalent capacitance, u mabcis the three-phase voltage abc 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, R f , C f They are filter resistor and filter capacitor, L t1 is the leakage inductance of the commutation transformer, k t1 is the commutation ratio. PLL is the phase-locked loop, θ PLL is the phase-locked loop output phase angle, abc / dq represents the Park transformation process, H f is the filtering link, i gdq ,u gdq are the dq axis current and voltage after Park transformation, respectively, including the dq axis current i gd 、i gq and dq axis voltage u gd 、u gq , U dc ref , Q ref are the DC voltage reference value and the AC side common coupling point reactive power reference value, G V , G Q , G I , K d They are respectively the voltage outer loop, the reactive outer loop, the current inner loop PI control link and the decoupling link, dq / abc is the Park inverse transformation link, H D is the system equivalent control link delay, PWM is the modulation process, and the three-phase modulation wave m is generated. abc .

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

[0125] (4)

[0126] In the formula, , are the voltages at frequencies p and p-2 respectively, , They are currents with frequencies p and p-2 respectively.

[0127] The AC side admittance matrix of a single fan can be written as follows:

[0128] (5)

[0129] Where Y 11 , Y22 All are wind turbine self-admittance, Y 12 , Y 21 are fan coupling admittance, Y G (s) represents the fan admittance matrix.

[0130] Among them, the impedance matrix of the fan can be defined according to The impedance matrix can be obtained. The equivalent system model is established by using the state space average method, and the voltage and current small signal phasors, the AC side admittance matrix and the control process are Laplace transformed and linearized. The fan including the AC side passive branch, AC side filter and transformer can be solved from the point of common coupling (PCC) into the AC side admittance matrix, 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 the 2×2 matrices related to the AC side passive branch, the converter transformer leakage inductance and the AC test filter, , G V,i (s) are coefficient matrices related to the DC voltage outer loop voltage and current variables, is the coefficient matrix of the reactive outer loop voltage variable, , is the coefficient matrix of the voltage variable of the phase-locked loop control link, , are the coefficient matrices related to the DC voltage inner loop voltage and current variables, E is a 2×2 unit matrix, It is the coefficient matrix related to the reactive outer loop current variable.

[0133] Among them, for the mid- and high-frequency bands can be ignored, that is is zero, and the AC side admittance matrix can be further simplified. Since the input is the AC side voltage, its output reference phase θ is greatly affected by the AC side power operation level, so it is necessary to Make reservations.

[0134] Step S203, determining the impedance characteristic model of a single new energy generator set according to the AC side admittance matrix;

[0135] Among them, the AC side admittance matrix of the common coupling point is used as the impedance characteristic model of a single wind turbine. In some embodiments, verification is required to provide support for the risk assessment of wide-band oscillation of AC transmission of new energy stations. Considering that the present invention focuses on the impedance characteristics of the model, 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, such as Figure 8 The impedance scanning system structure shown in FIG. 1 , wherein the device to be scanned is a single fan.

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

[0137] 1) When a single wind turbine is in steady-state operation, a disturbance voltage at multiple different measurement frequency points is applied to the AC side of the single wind turbine, and the grid connection point voltage and current data of the AC side of the single wind turbine are obtained;

[0138] Among them, when the device to be scanned maintains stable operation, a small disturbance voltage (or a small disturbance current) with different measurement frequencies is applied to the AC side, and an impedance scanning module is used on the AC side to obtain the voltage and current data of the grid connection point.

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

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

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

[0142] 5) Compare the similarity between the impedance external characteristic curve and the impedance external 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 based on the similarity comparison results;

[0144] 7) If the impedance characteristic model of the single fan is verified to be incorrect, the parameters of the impedance characteristic model of the single fan are updated until the impedance characteristic model of the single fan is verified to be correct.

[0145] When updating the parameters of the impedance characteristic model of a single wind turbine, it is possible to consider updating parameters such as voltage and current small signal phasors, and then re-derive the impedance characteristic model of the single wind turbine.

[0146] Step S204: using the Bergeron model to perform equivalent simulation on the AC line between the two new energy units to obtain an equivalent impedance model of the AC line;

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

[0148] (7)

[0149] Where γ is the propagation constant of the line, ; Z C is the wave impedance, , Z line is the equivalent impedance of the Bergeron model, Y line is the equivalent admittance of the Bergeron model, and the equivalent AC cable length is l 0 , the unit length impedance and admittance are z 0 ,y 0 .

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

[0151] Among them, a feeder line of a wind farm is composed of multiple wind turbines and multiple AC lines connected in series and parallel. The impedance model of a single feeder line of a new energy station is obtained through the series-parallel relationship of the equivalent impedance model of the wind turbine and the collection line.

[0152] Specifically, starting from the head end wind turbine, the wind turbine admittance is connected in parallel with the Bergeron model equivalent admittance, then connected in series with the Bergeron model equivalent impedance, and then connected in parallel with the Bergeron model equivalent admittance to obtain the equivalent impedance viewed from the next wind turbine to the head end. According to the feeder topology structure, that is, the Bergeron model parameters, the equivalent model of the entire feeder can be obtained by series and parallel connection, such as Fig.10 As shown (the process of the present invention is applicable to a single feeder topology including but not limited to Fig.10 ), assuming that the impedance of a single fan is Z Gij , admittance is Y Gij (Each wind turbine can have different power operation levels, control parameters, and control structures). The equivalent impedance of the Bergeron model of the AC submarine cable between wind turbines is Z aij , the equivalent admittance is Y aij .

[0153] according to Fig. 9 The impedance characteristic model of a single feeder can be obtained, which is recorded as:

[0154] (8)

[0155] In which, the impedance at the end of a single feeder is assumed to be Z Fi , then ZFi =1 / Y Eij That is, the impedance of a single feeder. Assuming that the impedance and admittance of a single wind turbine are Z Gij , Y Gij , the equivalent impedance and admittance of the Bergeron model of the jth section of the feeder line are Z aij , Y bij , the equivalent impedance and admittance from the outlet of a fan to the head end is Z pij , Y pij The equivalent impedance and admittance from the Bergeron line head end to the line head end is Z cij , Y cij The equivalent impedance and admittance from the equivalent impedance at the end of the Bergeron line to the beginning of the line are Z hij , Y hij ,according to Fig.10 By modeling the impedance characteristics of a single wind turbine and Bergeron model and the topological structure of a single feeder, the impedance characteristic curve Z of a single feeder can be established through the impedance series-parallel relationship. Fi The impedance characteristic curve of a single feeder can be verified by impedance scanning. Since the types of wind turbines and control parameters on the wind farm feeders are different, and the feeder topology structures are also different, the AC submarine cable modeling and verification results after the Bergeron model is used are given here.

[0156] Step S206: constructing an impedance external characteristic model of the reactive power compensation device by using an impedance modeling method according to the primary structure and control structure of the reactive power compensation device;

[0157] The control process of the reactive power compensation device is used to perform Laplace transformation to obtain the impedance external characteristic model of the reactive power compensation device.

[0158] Among them, in order to establish the branch impedance model of the parallel reactive power compensation device, the electrical wiring diagram and control architecture of the reactive power compensation device are considered. Figure 11~Figure 12 shown.

[0159] in, Fig.11 In the figure, the 35KV high-voltage busbar is connected to the 35KV user switch cabinet, wherein the 35KV user switch cabinet is provided with a circuit breaker QF1, and the circuit breaker QF1 is connected to the outdoor part, wherein the outdoor part includes a switch K1, a circuit breaker QF2 and an inductor L, and the outdoor part is connected to the SVG power cabinet.

[0160] Fig.12 Middle,U A 、i A is the voltage and current of phase A on the AC side, PLL is the phase-locked loop, θ ais the phase-locked loop output phase angle, Delay is the delay, 3s / 2r is the Park transformation process, and the three-phase voltage and current on the AC side are transformed by Park to generate dq axis voltage and current u d 、u q 、i d 、i q , U dca_ref , U dcam They are the DC side voltage reference value and the DC side voltage actual value respectively. After addition and subtraction operations, the d-axis current reference value i is generated through the PI control link. dref ; AC voltage outer loop I s is the AC side current, with a slope coefficient k slope Then generate the ramp voltage U slope , and the AC voltage reference value U ref And the actual value of AC voltage U rms After addition and subtraction operations, the q-axis current reference value i is generated through the PI control link. qref1 ; Reactive power reference value Q in reactive power outer loop ref After addition and subtraction with the actual value of reactive power Q, the q-axis current reference value i is obtained through the PI control link. qref2 . K d is the decoupling link, u dref 、u qref are the dq axis voltage reference values ​​respectively, and 2r / 3s is the Park inverse transformation process to generate the AC voltage reference value u aref 、u bref 、u cref .

[0161] Under typical control, SVG adopts split-phase control in the dq axis coordinate system. First, the virtual dq axis component is constructed. The frequency domain expression of the modulation wave is obtained from the SVG control system by using the harmonic linearization method. The influence of the control link delay and discrete control is further considered. Combined with the primary circuit structure of SVG, the SVG converter impedance and system impedance are obtained as shown in equation (9).

[0162] (9)

[0163] Where, L is the AC side impedance of SVG, G i is the current inner loop controller transfer function, K d is the dq axis decoupling coefficient, G d is the control link delay transfer function, G o is the zero-order holder transfer function, G sv is the voltage feedforward low-pass filter transfer function, R edis the equivalent resistance of SVG, and T is the power frequency period. The impedance characteristic curve of SVG 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: constructing an impedance external characteristic model of the energy storage unit by impedance modeling method according to the primary structure and control structure of the energy storage unit;

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

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

[0167] Step S209, the impedance external characteristic model of the feeder, the impedance external characteristic model of the reactive compensation device, the impedance external characteristic model of the energy storage unit and the impedance external characteristic model of the transformer are connected in series and parallel to form an impedance external characteristic model of the new energy station.

[0168] Among them, according to the determined primary structure, control structure and parameters of the energy storage unit, a model for accurately 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 broadband oscillation risk assessment frequency band is a medium-high frequency band or a sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is:

[0170] Step S301, determining the outgoing line end of the AC power grid after multi-level lines or transformation by using multiple ideal voltage sources and concentrated parameter impedance;

[0171] Among them, by adopting multiple ideal voltage sources and lumped parameter impedances to determine the outgoing line end of the AC power grid after multi-stage lines or transformation, the grid structure, transformer ratio, line impedance and other parameters can be determined according to the electrical wiring diagram of the AC power grid, 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 outgoing line end of the AC power grid after multi-stage lines or transformation.

[0172] Step S302: Starting from the common coupling point between the new energy station and the AC power grid, looking toward the AC power grid to the end of the outgoing line, and obtaining the impedance external characteristic model of the AC power grid according to the series-parallel relationship of the AC line, transformer and other primary devices in the AC power grid.

[0173] In some embodiments, the broadband oscillation risk assessment frequency band is a 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.

[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 connected in series with an equivalent impedance. The 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 station.

[0175] In some embodiments, the new energy grid-connected system corresponding to the sub-supersynchronous frequency band adopts an operation mode under different power operating levels; the new energy grid-connected system corresponding to the medium and high frequency bands adopts an operation mode under the rated operating power operating level; wherein the operation mode adopts one of the following modes, wherein the operation mode includes: black start, full connection, all reactive compensation devices are exited, reactive compensation devices are put into operation alone, some new energy generator sets are exited, some new energy feeders are exited, some AC busbars are exited, some transformers are exited, some reactive compensation devices are exited, and some energy storage is exited.

[0176] Specifically, because the impedance model of power electronic components in the sub-supersynchronous 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 impact on the sub-supersynchronous frequency band oscillation. This method can take into account the dynamic characteristics of the system under different load conditions, so as to more accurately assess the oscillation risk. For example, when the system is at a low power operation level, sub-supersynchronous oscillation may be triggered due to certain specific operating conditions; and when the system is at a high power operation level, the oscillation risk may increase due to power fluctuations and distribution problems. For example: specific power operation levels include: maximum capacitive reactive output of 100% active output, maximum inductive reactive output of 100% active output, 0 reactive output of 100% active output, maximum capacitive reactive output of 10% active output, maximum inductive reactive output of 10% active output, 0 reactive output of 10% active output, etc.

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

[0178] Black start is a special operation mode to restore power supply after a complete power outage. In a renewable energy grid-connected system, black start usually means starting a specific renewable energy generator set or energy storage device without any external power support to gradually restore power to the entire system. When assessing the risk of broadband oscillation, the operation mode of black start is considered in order to analyze the stability and oscillation characteristics of the system under extreme conditions. This helps to formulate more effective emergency measures and oscillation control strategies.

[0179] The fully wired operation mode refers to the operation mode of the new energy grid-connected system when all lines and equipment are connected. In this mode, the structure and parameters of the system are relatively fixed, which facilitates accurate oscillation risk assessment. By simulating the system operation in the fully wired state, the impact of each line and equipment on oscillation can be evaluated, thereby determining the key nodes and weak links.

[0180] The operation modes of all reactive compensation devices exiting and reactive compensation devices being put into operation alone are used to analyze the impact of reactive compensation devices and reactive power on system oscillation. Reactive compensation devices and reactive power have an important impact on the stability and oscillation characteristics of the system. By adjusting the operating state of the reactive compensation device, the oscillation of the system at different reactive power levels can be observed, providing a basis for formulating reactive power control strategies.

[0181] The operation modes of some renewable energy generators being shut down and some renewable energy feeders being shut down are used to analyze the contribution of each part of the renewable energy grid-connected system to the overall oscillation characteristics. By simulating the withdrawal of different parts, the degree of influence of each part on the system oscillation can be evaluated, thereby determining the areas and equipment that need to be focused on.

[0182] The operation modes of partial AC busbar withdrawal, partial transformer withdrawal, partial reactive compensation device withdrawal and partial energy storage withdrawal are used to analyze the oscillation characteristics of the system under different structures. By simulating the withdrawal of these parts, the impact of system structure changes on oscillation can be observed, providing guidance for optimizing system structure and improving stability.

[0183] Among them, in the embodiment of the present application, when evaluating the risk of broadband oscillation in the new energy grid-connected system,

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

[0185] Specifically, the measures to suppress the risk of broadband oscillation in the medium and high frequency bands are:

[0186] If there is a risk of medium- and high-frequency oscillation in the new energy grid-connected system, measures shall be taken to change the impedance of the new energy station or the impedance of the AC power grid. The measures to change the impedance of the new energy station include changing the control structure or parameters of the new energy power generation unit, changing the control structure or parameters of the SVG, changing the primary circuit of the new energy station, installing passive equipment, and installing active equipment; the measures to change the impedance of the AC power grid include restricting specific AC power grid operation modes, installing passive equipment, and installing active equipment.

[0187] The measures to suppress the risk of broadband oscillation in the sub-supersynchronous frequency band are:

[0188] Take measures to change the impedance of the new energy station or the impedance of the AC power grid. The measures to change the impedance of the new energy station include: changing the control structure or parameters of the new energy power generation unit, changing the control structure or parameters of the SVG, changing the primary circuit of the new energy station, installing passive equipment, installing active equipment, limiting the operating power level of the new energy unit or energy storage unit or SVG; measures to change the impedance of the AC power grid include limiting specific AC power grid operation modes.

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

[0190] In this example, the AC grid-connected transmission structure of an offshore wind farm is taken as an example. The topological structure of the AC grid-connected transmission system of an offshore wind farm is as follows: Fig.13 As shown, there are multiple wind turbines P 11 ~P 1n Each wind turbine is equipped with a wind turbine, an inverter and a step-up transformer. The inverter is used to convert the AC power generated by the wind turbine into a form of electrical energy suitable for subsequent transmission. Then, the electrical energy is collected to the collector line through the connecting cable. The resistance of different branches in the collector line is l 11 ~l 1nThese collection lines collect the electric energy of the dispersed wind turbines and send it to the offshore booster station. The booster transformer in the station will increase the voltage of the electric energy. The high-voltage electric energy after the boosting of the offshore booster station is transmitted to the land through the submarine cable to ensure the stable transmission of the electric energy to the land, and then transmitted to the land control center through the submarine cable. Among them, the electric energy transmitted by the submarine cable first enters the converter station after reaching the land. The converter station contains the converter transformer c and the converter transformer p, so as to transform the electric energy to meet the requirements of being connected to the power grid. At the same time, the system is equipped with SVG (Static Var Generator) for reactive power compensation, improving the power factor of the power system, stabilizing the voltage, and ensuring the quality of electric energy. The electric energy processed by the converter station will first pass through the high-voltage reactor, which can limit the short-circuit current and reduce the operating overvoltage. Finally, the electric energy reaches the point of common coupling (PCC), at which point the electric energy generated by offshore wind power is connected to the grid equivalent voltage source and connected to the onshore grid through the grid equivalent impedance, thereby realizing the transmission of offshore wind power to the user end.

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

[0192] The following tests were conducted in the mid- and high-frequency band oscillation risk assessment:

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

[0194] 2) Establish and verify the impedance model of a single feeder: Due to the different types of wind turbines and control parameters on the wind farm feeders, as well as the different feeder topologies, the AC submarine cable modeling and verification results after the Bergeron model is used are given here. Figure 16-17 After the impedance model of a single wind turbine and AC submarine cable is verified, the impedance characteristic curve model of a single feeder can be obtained through the series-parallel relationship of a single feeder topology.

[0195] 3) Impedance characteristic modeling of offshore wind farms: Consider the high-frequency impedance characteristic curve of an offshore wind farm after multiple feeders are fed in, such as Figure 18-19 As shown, where Degree is the phase.

[0196] 4) Considering the impact of the booster station on the impedance of the new energy station, the impedance characteristics of the offshore wind farm are calculated from the high-voltage side of the offshore booster transformer. Figure 20~Figure 21As shown in the figure, offshore boost transformers mainly affect the high-frequency impedance of wind farms. Due to the inductive effect of transformers in the high-frequency band, wind farms mainly exhibit inductive characteristics in the high-frequency band.

[0197] 5) Considering the impact of long-distance AC transmission lines on the impedance of new energy stations, the impedance characteristics of offshore wind farms are calculated from the AC submarine cable onshore grid connection point as follows: Figure 22~Figure 23 It can be seen that due to the influence of the AC submarine cable, the wind farm impedance presents positive damping in a large range of medium and high frequency bands, but the impedance phase angle is around ±90°, and the system damping is weak.

[0198] 6) Considering the impact of SVG and other parallel branches on the impedance of new energy stations, the impedance characteristic curve of the reactive compensation parallel branch under a specific working condition is as follows: Figures 24 and 25 Taking a specific working condition as an example, the impedance characteristics of the offshore wind farm seen from the parallel branch and the grid connection point on the AC submarine cable are compared as shown in Figure 2. Figure 26-27 shown.

[0199] In the medium and high frequency bands, the impedance amplitude of the reactive compensation parallel branch is much larger than the impedance of the new energy station. Therefore, the reactive compensation parallel branch has little effect on the impedance of the wind farm. Considering the impedance characteristics of the new energy station after the reactive compensation parallel branch, Figure 28-29 shown.

[0200] 7) Considering the input of reactive power compensation parallel branch and the connection mode of new energy station, the impedance characteristic curve of new energy station side under the typical reactive power compensation parallel branch input and the connection mode of new energy station is as follows: Figure 30~Figure 31 As shown (taking a certain working condition as an example).

[0201] 8) Oscillation risk assessment of medium and high frequency renewable energy grid-connected transmission system, Figure 30~Figure 31 It can be seen that under working conditions, offshore wind farms all have medium and high frequency negative damping, and the negative damping frequency band is mainly distributed in the range of 1500~4200Hz. Under normal circumstances, a short circuit fault in the AC power grid causes the line to exit (such as N-1, N-2, N-3, etc.), which will make the AC power grid impedance phase angle closer to +90° or -90° in a larger range, thereby 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 AC power grid impedance to change, it will not actively excite medium and high frequency resonance.

[0202] The following tests were performed in the sub-supersynchronous band oscillation risk assessment:

[0203] 1) Taking the rated power as an example, the modeling verification is carried out. The theoretical value of the impedance model of a single wind turbine in the sub-supersynchronous frequency band is compared with the actual frequency scanning value. Figure 32-33As shown, the modeling theoretical values ​​are in good agreement with the actual frequency scanning values, and the established model can be used to evaluate the sub-supersynchronous frequency band oscillation risk.

[0204] Considering the sub-supersynchronous frequency band of a single wind turbine under different power levels, Fig.34 , 35 , 36, and 37 (taking two power levels as examples), it can be seen that the power level has a significant impact on the sub-supersynchronous frequency band impedance of power electronic devices.

[0205] 2) Due to the different types of wind turbines and control parameters on the wind farm feeders, as well as the different feeder topologies, the AC submarine cable modeling and verification results after the Bergeron model is equivalent are given here, such as Figures 38 and 39 After the impedance model of a single wind turbine and AC submarine cable is verified, the impedance characteristic curve model of a single feeder can be obtained through the series-parallel relationship of a single feeder topology.

[0206] 3) Impedance characteristic modeling of offshore wind farms, considering the impedance characteristic curve of the super-synchronous frequency band of offshore wind farms after multiple feeders are fed in, as shown in Figures 40-41 shown.

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

[0208] 5) Considering the impact of long-distance AC transmission lines on the impedance of new energy stations, the impedance characteristics of offshore wind farms are calculated from the AC submarine cable onshore grid connection point as follows: Figures 44 and 45 shown.

[0209] 6) Considering the impact of parallel branches such as SVG on the impedance of new energy stations, the impedance characteristic curve of the reactive compensation parallel branch at a certain power level is as follows: Figures 46 and 47 Taking a specific working condition as an example, the impedance characteristics of the offshore wind farm seen from the parallel branch and the grid connection point on the AC submarine cable are compared as shown in Figure 2. Figures 48 and 49 shown.

[0210] In the sub-supersynchronous frequency band, the impedance amplitude of the reactive power compensation parallel branch is similar to that of the new energy station. Therefore, the reactive power compensation parallel branch has a greater impact on the wind farm impedance. Considering the impedance characteristics of the new energy station after the reactive power compensation parallel branch, Figures 50-51 shown.

[0211] 7) AC grid modeling and sub-supersynchronous frequency band new energy grid-connected transmission system oscillation risk assessment: Use SCR equivalent to establish the equivalent impedance of the AC grid, limit the operating power level of the wind turbine, select the equivalent impedance of the AC grid under two working conditions to evaluate the oscillation risk of the new energy grid-connected transmission system sub-supersynchronous frequency band, and use the impedance analysis method for analysis, such as Fig.52 , 53 , 54, and 55.

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

[0213] Based on the same inventive concept, an embodiment of the present application further provides a new energy grid-connected system broadband oscillation risk assessment system for implementing the above-mentioned new energy grid-connected system broadband oscillation risk assessment method.

[0214] The implementation solution for solving the problem provided by the system is similar to the implementation solution recorded in the above method. Therefore, the specific limitations in one or more embodiments of the wide-band oscillation risk assessment system for new energy grid-connected systems provided below can be referred to the limitations on the wide-band oscillation risk assessment method for new energy grid-connected systems mentioned above and will not be repeated here.

[0215] like Fig.56 As shown, an embodiment of the present invention provides a broadband oscillation risk assessment system for a new energy grid-connected system, comprising:

[0216] The impedance model building module 100 is used to build an impedance external characteristic model of each electrical unit according to multiple electrical units of the new energy station;

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

[0218] A grid-side model building module 300 is used to determine an impedance external characteristic model of an AC power grid corresponding to a broadband oscillation risk assessment frequency band according to different broadband 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 station and the impedance external characteristic curve of the AC power grid according to the impedance external characteristic model of the new energy station and the impedance external characteristic model of the AC power grid;

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

[0221] In some embodiments, the electrical unit includes a feeder, a transformer, a reactive compensation device and an energy storage unit, wherein the feeder includes multiple new energy units and multiple AC lines, and the multiple new energy 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 station is as follows:

[0223] According to different broadband oscillation risk assessment frequency bands, the voltage and current small signal phasors at the common coupling point of a single new energy unit under three-phase symmetrical working conditions are constructed;

[0224] Based on voltage and current small signal phasors, the AC side admittance matrix is ​​obtained by performing Laplace transform on the control process of a single new energy unit; the AC side admittance matrix of the sub-supersynchronous frequency band introduces the 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 unit based on the AC side admittance matrix;

[0226] The Bergeron model is used to perform equivalent simulation on the AC line between the two new energy units to obtain the equivalent impedance model of the AC line;

[0227] Based on the connection relationship between multiple new energy units and AC lines on the feeder, the impedance characteristic model of a single new energy unit and the equivalent impedance model of the AC line are connected in series and parallel 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 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 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 station is constructed by connecting the impedance external characteristic model of the feeder, the impedance external characteristic model of the reactive compensation device, the impedance external characteristic model of the energy storage unit and the impedance external characteristic model of the transformer in series and parallel.

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

[0233] Determine the outgoing line end of the AC power grid after multi-level lines or transformation by using multiple ideal voltage sources and concentrated parameter impedance;

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

[0235] In some embodiments, the broadband oscillation risk assessment frequency band is a 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 an operation mode under different power operating levels; the new energy grid-connected system corresponding to the medium and high frequency bands adopts an operation mode under the rated operating power operating level; wherein the operation mode adopts one of the following modes, wherein the operation mode includes: black start, full connection, all reactive compensation devices are exited, reactive compensation devices are put into operation alone, some new energy generator sets are exited, some new energy feeders are exited, some AC busbars are exited, some transformers are exited, some reactive compensation devices are exited, and some energy storage is exited.

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

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

[0239] Determine 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 station within the frequency range 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 the new energy grid-connected system has a broadband oscillation risk;

[0241] If it is determined 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.

[0242] like Fig.57 As shown, an embodiment of the present application also provides an electronic device, the electronic device 10 includes a memory 20 and a processor 30, the memory 20 stores a computer program, and when the computer program is executed by the processor 30, the processor 30 executes the steps of the above-mentioned new energy grid-connected system wide-band oscillation risk assessment method.

[0243] The embodiment of the present application also provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed, the steps of the above-mentioned method for assessing the risk of broadband oscillation of a new energy grid-connected system 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 above-described system, electronic device and computer storage medium can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

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

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

[0247] In the 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 only schematic. For example, the division of units is only a logical function division. There may be other division methods in actual implementation. 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 mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

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

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

[0250] If the 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 this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for executing all or part of the steps of the method described in each embodiment of the present invention through a computer device (which can be a personal computer, server, or network device, etc.). The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (full name in English: Read-Only Memory, English abbreviation: ROM), random access memory (full name in English: Random Access Memory, English abbreviation: RAM), disk or optical disk and other media 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 the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for assessing broadband oscillation risk of a new energy grid-connected system, which is applied to assessing the broadband oscillation risk of a new energy grid-connected system in different broadband oscillation risk assessment frequency bands, wherein the broadband oscillation risk assessment frequency bands include medium and high frequency bands and sub-supersynchronous frequency bands; characterized in that: The method comprises: According to a plurality of electrical units of the new energy station, an impedance external characteristic model of each of the electrical units is established; According to the impedance external characteristic model and wiring structure of each electrical unit of the new energy station, each electrical unit is connected, and according to the impedance series-parallel relationship of each electrical unit, the impedance external characteristic model of the new energy station corresponding to the wide-band oscillation risk assessment frequency band is obtained; According to different broadband oscillation risk assessment frequency bands, determining an impedance external characteristic model of an AC power grid corresponding to the broadband oscillation risk assessment frequency band; Determining an impedance external characteristic curve of the new energy station and an impedance external characteristic curve of the AC power grid according to the impedance external characteristic model of the new energy station and the impedance external characteristic model of the AC power grid; A broadband oscillation risk assessment is performed on the new energy grid-connected system based on a comparison result of the impedance external characteristic curve of the new energy 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 electrical unit includes a feeder, a transformer, a reactive power compensation device and an energy storage unit, wherein the feeder includes a plurality of new energy generating sets and a plurality of AC lines, and the plurality of new energy generating sets and the plurality of AC lines are connected in series and parallel to form the feeder.

3. The method for assessing the risk of broadband oscillation in a new energy grid-connected system according to claim 2, characterized in that: The process of constructing the impedance external characteristic model of the new energy station is as follows: According to different broadband oscillation risk assessment frequency bands, the voltage and current small signal phasors at the common coupling point of a single new energy unit under three-phase symmetrical working conditions are constructed; Based on the voltage and current small signal phasors, the AC side admittance matrix is ​​obtained by performing Laplace transform on the control process of the single new energy generator set; wherein the AC side admittance matrix of the sub-supersynchronous 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; The Bergeron model is used to perform equivalent simulation on the AC line between the two new energy units to obtain the equivalent impedance model of the AC line; Based on the connection relationship between the multiple new energy units on the feeder and the AC line, the impedance characteristic model of the single new energy unit and the equivalent impedance model of the AC line are connected in series and parallel to obtain an impedance external characteristic model of the feeder; 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 an impedance modeling method; 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 an impedance modeling method; Using a T-shaped equivalent circuit or a π-shaped equivalent circuit to perform equivalent modeling on the transformer to obtain an impedance external characteristic model of the transformer; The impedance external characteristic model of the feeder, the impedance external characteristic model of the reactive compensation device, the impedance external characteristic model of the energy storage unit and the impedance external characteristic model of the transformer are connected in series and parallel to form the impedance external characteristic model of the new energy station.

4. The method for assessing broadband oscillation risk of a new energy grid-connected system according to claim 1, characterized in that: The broadband oscillation risk assessment frequency band is a medium-high frequency band or a sub-supersynchronous frequency band; the construction process of the impedance external characteristic model of the AC power grid is: Determine the outgoing line end of the AC power grid after multi-level lines or transformation by using multiple ideal voltage sources and concentrated parameter impedance; Starting from the common coupling point between the new energy station and the AC power grid, looking towards the AC power grid to the end of the outgoing line, the impedance external characteristic model of the AC power grid is obtained according to the series-parallel relationship between the AC line, the transformer and other primary equipment in the AC power grid.

5. The method for assessing broadband oscillation risk of a new energy grid-connected system according to claim 1, characterized in that: The broadband oscillation risk assessment frequency band is a 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.

6. The method for assessing broadband oscillation risk of a new energy grid-connected system according to claim 1, characterized in that: The new energy grid-connected system corresponding to the sub-supersynchronous frequency band adopts an operation mode under different power operating levels; the new energy grid-connected system corresponding to the medium and high frequency bands adopts an operation mode under the rated operating power operating level; wherein, the operation mode adopts one of the following modes, wherein, the operation mode includes: black start, full connection, all reactive compensation devices are withdrawn, reactive compensation devices are put into operation alone, some new energy generator sets are withdrawn, some new energy feeders are withdrawn, some AC busbars are withdrawn, some transformers are withdrawn, some reactive compensation devices are withdrawn and some energy storage is withdrawn.

7. The method for assessing broadband oscillation risk of a new energy grid-connected system according to claim 1, characterized in that: The performing of broadband 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 station and the impedance external characteristic curve of the AC power grid comprises: According to the impedance external characteristic curve of the new energy station and the impedance external characteristic curve of the AC power grid, determining that the impedance amplitude of the AC power grid in the same wide-band oscillation risk assessment frequency band is greater than the frequency interval range of the new energy station; Determine whether a phase difference between an impedance external characteristic curve of the AC power grid and an impedance external characteristic curve of the new energy station within the frequency range is greater than a preset phase difference threshold; If it is determined 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; 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.

8. A broadband oscillation risk assessment system for a new energy grid-connected system, which is used to assess the broadband oscillation risk of a new energy grid-connected system in different broadband oscillation risk assessment frequency bands, wherein the broadband oscillation risk assessment frequency bands include medium and high frequency bands and sub-supersynchronous frequency bands; characterized in that: include: An impedance model building module is used to build an impedance external characteristic model of each electrical unit according to multiple electrical units of the new energy station; A station model building module is used to connect the electrical units of the new energy station according to the impedance external characteristic model and wiring structure of each electrical unit, and obtain the impedance external characteristic model of the new energy station corresponding to the wide-band oscillation risk assessment frequency band according to the impedance series-parallel relationship of each electrical unit; A grid-side model building module, used to 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; An impedance curve determination module, used to determine the impedance external characteristic curve of the new energy station and the impedance external characteristic curve of the AC power grid according to the impedance external characteristic model of the new energy station and the impedance external characteristic model of the AC power grid; The risk assessment module is used to perform a broadband oscillation risk assessment on the new energy grid-connected system based on a comparison result of the impedance external characteristic curve of the new energy station and the impedance external characteristic curve of the AC power grid.

9. An electronic device, characterized in that: The electronic device includes a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the method for assessing the risk of broadband oscillation of a new energy grid-connected system as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the steps of the method for assessing the risk of broadband oscillation of a new energy grid-connected system are implemented as described in any one of claims 1 to 7.

Images