A method and related device for access evaluation of an active support type flexible DC system

Abstract

This application discloses a method and related apparatus for evaluating the grid connection of an actively supported flexible DC system. The method includes: performing system frequency response analysis on the actively supported flexible DC system under disturbance conditions to construct a frequency response model; calculating frequency, voltage, and damping indices on the frequency response model to obtain evaluation indices; obtaining the response indices of a synchronous generator and a grid-connected inverter of the same capacity as the actively supported flexible DC system under the same disturbance scenario to obtain a first reference index and a second reference index; and performing visual scoring processing on the evaluation indices based on the first and second reference indices to obtain a graphical evaluation result. The embodiments of this application can improve the efficiency of grid system evaluation and can be widely applied in the field of power technology.

Description

Technical Field

[0001] This application relates to the field of power grid technology, and in particular to an active support type flexible DC system access assessment method and related apparatus. Background Technology

[0002] In related technologies, there are methods that use a single indicator to evaluate the access of actively supported flexible DC systems, i.e., using a single frequency curve or a single voltage curve to judge their performance. However, in practical applications, it has been found that using only a single frequency indicator cannot fully characterize its active support capability, making it difficult to form a unified evaluation result for engineering acceptance or scheme comparison, thus affecting the evaluation efficiency of the power grid system.

[0003] In summary, the technical problems existing in the relevant technologies need to be improved. Summary of the Invention

[0004] The main objective of this application is to propose an active support type flexible DC system access assessment method and related apparatus, which can improve the assessment efficiency of the power grid system.

[0005] To achieve the above objectives, one aspect of this application proposes an access evaluation method for an actively supported flexible DC system, the method comprising: Based on the disturbance conditions, the frequency response of the actively supported flexible DC system is analyzed, and a frequency response model is constructed. The frequency response model is used to calculate frequency, voltage, and damping parameters to obtain evaluation indicators. Obtain the response indicators of a synchronous generator and a grid-connected inverter of the same capacity as the actively supported flexible DC system under the same disturbance scenario, and obtain the first reference indicator and the second reference indicator. The evaluation indicators are visually scored based on the first reference indicator and the second reference indicator to obtain graphical evaluation results.

[0006] In some embodiments, the step of performing system frequency response analysis on the actively supported flexible DC system based on disturbance conditions and constructing a frequency response model includes the following steps: The active-supported flexible DC system is constructed based on the generator and inverter. Based on the disturbance conditions, the generator in the actively supported flexible DC system is modeled for governor droop and turbine dynamics, and the inverter is modeled for droop control and virtual synchronous generator control to obtain the frequency response model.

[0007] In some embodiments, calculating frequency, voltage, and damping parameters of the frequency response model to obtain evaluation parameters includes the following steps: Dynamic analysis was performed on the frequency response model to obtain the dynamic transfer function of the generator system; The power system frequency support calculation is performed on the dynamic transfer function of the generator system to obtain the frequency index and the damping index; The voltage minimum point and steady-state voltage offset of the frequency response model are simulated to obtain the voltage index; The evaluation index is obtained based on the frequency index, the damping index, and the voltage index.

[0008] In some embodiments, performing power system frequency support calculations on the generator system dynamic transfer function to obtain the frequency index and the damping index includes the following steps: The dynamic transfer function of the generator system is simplified based on the sensitivity of the frequency response to the governor parameters to obtain the second-order system function; Substituting the active power step disturbance amplitude and the system equivalent inertia parameter into the second-order system function, the time-domain expression of the frequency deviation is calculated. The frequency deviation and the rate of change of frequency are calculated based on the time-domain expression of the frequency deviation, and the frequency index is obtained. The damping index is obtained by calculating the damping coefficient and disturbance recovery time based on the second-order system function.

[0009] In some embodiments, the step of calculating the frequency deviation and the rate of change of frequency based on the time-domain expression of the frequency deviation to obtain the frequency index includes the following steps: Based on the time-domain expression of the frequency deviation, find the position where the frequency derivative is equal to zero, and obtain the time of the lowest frequency point; Substituting the time of the lowest frequency point into the time-domain expression of the frequency deviation and performing a mathematical transformation, the frequency deviation is obtained. The location of the fastest frequency change rate is found based on the time-domain expression of the frequency deviation, and the frequency change rate is obtained. The frequency index is determined based on the frequency deviation and the frequency change rate.

[0010] In some embodiments, the step of calculating the damping coefficient and disturbance recovery time based on the second-order system function to obtain the damping index includes the following steps: The second-order system function is subjected to parameter aggregation processing to obtain the inertial time constant and damping constant; The damping coefficient and disturbance recovery time are calculated based on the inertial time constant and the damping constant to obtain the damping index.

[0011] In some embodiments, the step of visually scoring the evaluation indicators based on the first reference indicator and the second reference indicator to obtain graphical evaluation results includes the following steps: The evaluation index is scored using a dual-benchmark system based on the first reference index and the second reference index to obtain the index score. The index scores are then visualized to obtain the graphical evaluation results.

[0012] To achieve the above objectives, another aspect of this application proposes an access evaluation device for an actively supported flexible DC system, the device comprising: The response analysis module is used to perform system frequency response analysis on the actively supported flexible DC system according to the disturbance conditions, and to construct a frequency response model. The index calculation module is used to calculate the frequency index, voltage index and damping index of the frequency response model to obtain the evaluation index. The reference calculation module is used to obtain the response indicators of synchronous generators and grid-connected inverters of the same capacity as the active-supported flexible DC system under the same disturbance scenario, and to obtain the first reference indicator and the second reference indicator. The access evaluation module is used to perform visual scoring processing on the evaluation indicators based on the first reference indicator and the second reference indicator to obtain graphical evaluation results.

[0013] To achieve the above objectives, another aspect of this application provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described above.

[0014] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer-readable storage medium storing a computer program that, when executed by a processor, implements the methods described above.

[0015] The embodiments of this application include at least the following beneficial effects: This application provides a method and related apparatus for evaluating the access of an actively supported flexible DC system. This scheme calculates evaluation indicators by applying frequency, voltage, and damping indices to a frequency response model, thus incorporating frequency support, voltage support, and damping support into the same evaluation framework. Furthermore, this scheme performs visual scoring processing on the evaluation indicators based on a first and second reference index, obtaining graphical evaluation results. This allows for a quantitative, intuitive, and comparable evaluation of the active support effect of the grid-connected flexible DC system using synchronous machine benchmarks, grid-connected inverter benchmarks, and hexagonal visualization results, thereby improving the evaluation efficiency of the power grid system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an implementation environment provided in the embodiments of this application; Figure 2 This is a flowchart of an active-support flexible DC system access evaluation method provided in an embodiment of this application; Figure 3 This is a single-line diagram of an IEEE 10-machine 39-node system provided in an embodiment of this application; Figure 4 This is a dynamic frequency response curve of the system after disturbance provided in an embodiment of this application; Figure 5 This is a system frequency response model diagram considering VSC provided in the embodiments of this application; Figure 6 This is a frequency variation diagram under a fully synchronous machine provided in an embodiment of this application; Figure 7 This is a diagram showing the maximum deviation rate and maximum frequency change rate of the generator G2 replacement / network flexible DC frequency according to an embodiment of this application; Figure 8 This is a diagram showing the frequency damping coefficient and disturbance recovery time of generator G2 replacement / network flexible DC transmission provided in an embodiment of this application; Figure 9 This is a diagram showing the lowest point and steady-state offset of the frequency voltage of the generator G2 replacement grid flexible DC transmission system provided in this application embodiment; Figure 10 This is a hexagonal subdivision diagram of the grid converter provided in the embodiments of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0018] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various concepts, but unless otherwise stated, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the words “if,” “when,” or “in response to a determination” as used herein may be interpreted as “when…” or “when…” or “in response to a determination.”

[0019] As used in this application, the terms "at least one", "multiple", "each", "any", etc., "at least one" includes one, two or more, "multiple" includes two or more, "each" refers to each of the corresponding multiples, and "any" refers to any one of the multiples.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0021] With the large-scale grid connection of new energy sources such as wind power and photovoltaics, the power system is gradually transforming from a power system dominated by traditional synchronous generators to a new type of power system composed of synchronous generators and power electronic interface power supplies. Traditional synchronous generators, through electromagnetic coupling with the grid via mechanical rotors, naturally possess rotational inertia, primary frequency regulation, excitation voltage regulation, and oscillation damping capabilities. When the system experiences disturbances such as generator tripping, load surges, DC blocking, rapid fluctuations in new energy output, or AC faults, the synchronous generator can release rotor kinetic energy in the early stages of the disturbance to slow down the rate of frequency change; during the primary frequency regulation stage, it can increase or decrease mechanical power through the speed regulation system to improve the frequency minimum point and steady-state frequency deviation; during voltage disturbances, it can provide reactive power support through the excitation system; and during electromechanical transient oscillations, it can suppress oscillation attenuation through damping torque and power system stabilizers.

[0022] However, power electronic equipment such as new energy generating units, energy storage devices, and flexible DC transmission converter stations are typically connected to the grid via converters. Conventional grid-connected control mainly relies on phase-locked loops to detect the voltage phase at the grid connection point and then inject current into the grid according to given active and reactive current commands. These devices essentially function as controlled current sources, with their output voltage phase and frequency dependent on a reference provided by the external grid. When the strength of the external grid decreases, short-circuit capacity declines, and the proportion of synchronous machines decreases, conventional grid-connected power electronic equipment struggles to actively establish voltage and frequency references like synchronous generators, and also finds it difficult to provide equivalent inertia and damping support in the early stages of disturbances.

[0023] Therefore, in large power grids with a high proportion of new energy sources and a high proportion of power electronic equipment connected, the system operation safety faces the following changes: First, the system's equivalent inertia decreases, and the frequency change rate increases in the initial stage of disturbances; second, primary frequency regulation resources are relatively reduced, and the minimum frequency point after disturbances is lowered; third, short-circuit capacity decreases, and voltage becomes more sensitive to reactive power disturbances and fault disturbances; fourth, the contribution of synchronous machine damping decreases, and the system may experience slow recovery of power, frequency, or voltage oscillations after large disturbances.

[0024] The core idea of ​​grid-based flexible DC transmission is to make the converter station behave as a controlled voltage source, rather than simply a current source following the external power grid. Its control structure can simulate the oscillation equation of a synchronous generator through an active-frequency link, simulate excitation voltage regulation characteristics through a reactive-voltage link, and improve the dynamic response after disturbances through methods such as virtual damping, virtual inertia, virtual impedance, or power synchronization control. Virtual synchronous generator control, or VSG control, is one of the important forms of grid-based control. It introduces virtual inertia and virtual damping into the converter control, enabling the power electronic equipment to exhibit dynamic characteristics similar to a synchronous generator under frequency disturbances.

[0025] In related technologies, even comprehensive evaluation methods using radar charts or multiple indicators are mostly used for comprehensive scoring of steady-state power quality, planning schemes, or equipment performance. They struggle to simultaneously evaluate the improvement effects of flexible DC converter stations on voltage minimum points, steady-state voltage deviations, and damping recovery processes. Evaluation results are typically presented in tables, curves, or as single conclusions, lacking intuitiveness.

[0026] For example, simulation evaluation schemes are easily affected by factors such as unit capacity, fault location, disturbance amplitude, system short-circuit capacity, operating mode, and measurement point selection. If the lowest frequency point, lowest voltage point, or recovery time is directly compared under different engineering scenarios, the conclusions drawn may not be due to differences in the active support capability of flexible DC transmission, but rather to differences in system scale, disturbance intensity, or grid conditions.

[0027] In view of this, this application provides an active support type flexible DC system access evaluation method and related apparatus. This scheme is aimed at grid-connected flexible DC, VSG-controlled flexible DC, or other flexible DC converter stations with active support capabilities. Under the same capacity, the same disturbance, the same measurement points, or equivalent comparable operating conditions, it uses synchronous generators of the same capacity, grid-connected inverters, and grid-connected actively supported flexible DC as comparison objects to establish a unified evaluation system for three types of grid characteristics: frequency, voltage, and damping. This application can incorporate frequency support, voltage support, and damping support into the same evaluation framework, and achieve quantitative, intuitive, and comparable evaluation of the active support effect of grid-connected flexible DC through synchronous machine benchmarks, grid-connected inverter benchmarks, and hexagonal visualization results.

[0028] This application provides an active-support flexible DC system access assessment method, relating to the field of power grid technology. This method can be applied to a terminal, a server, or software running on either a terminal or a server. In some embodiments, the terminal can be a smartphone, tablet, laptop, desktop computer, smart speaker, smartwatch, or vehicle-mounted terminal, but is not limited to these. The server can be configured as an independent physical server, a server cluster or distributed system composed of multiple physical servers, or a cloud server providing basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communication, middleware services, domain name services, security services, CDN, and big data and artificial intelligence platforms. The server can also be a node server in a blockchain network. The software can be an application implementing the active-support flexible DC system access assessment method, but is not limited to the above forms.

[0029] This application can be used in a wide variety of general-purpose or special-purpose computer system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics devices, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices. This application can be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. This application can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0030] Figure 1 This is a schematic diagram illustrating the implementation environment of a method provided in an embodiment of this application. (Refer to...) Figure 1 The main hardware and software components of this implementation environment include terminal 101 and server 102, which are communicatively connected. The method can be executed based on the interaction between terminal 101 and server 102. Furthermore, terminal 101 and server 102 can be nodes in a blockchain; this embodiment does not specifically limit this.

[0031] Figure 2 This is an optional flowchart of an active-support flexible DC system access evaluation method provided in an embodiment of this application. Figure 2The method may include, but is not limited to, steps S201 to S204.

[0032] Step S201: Perform system frequency response analysis on the actively supported flexible DC system according to the disturbance conditions, and construct a frequency response model; Step S202: Calculate the frequency index, voltage index, and damping index of the frequency response model to obtain the evaluation index; Step S203: Obtain the response indicators of a synchronous generator and a grid-connected inverter with the same capacity as the active-supported flexible DC system under the same disturbance scenario, and obtain the first reference indicator and the second reference indicator. Step S204: Visualize and score the evaluation indicators based on the first reference indicator and the second reference indicator to obtain graphical evaluation results.

[0033] Steps S201 to S204 of this application embodiment involve setting disturbance conditions for the actively supported flexible DC system, where the disturbance conditions include active power deficit, reactive power deficit, or fault clearing. This application constructs a frequency response model by performing frequency response analysis on the actively supported flexible DC system, and then calculates frequency, voltage, and damping indices from the frequency response model to obtain evaluation indicators. This application establishes a unified evaluation system of six indicators across three aspects—frequency, voltage, and damping—for the comprehensive dynamic support effect evaluation of actively supported flexible DC systems integrated into the large power grid, moving beyond the limitation to evaluating only one type of indicator such as the minimum frequency point, frequency change rate, voltage deviation, or damping ratio. By simultaneously extracting the minimum frequency deviation point, frequency change rate, minimum voltage point, steady-state voltage deviation, damping coefficient or damping ratio, and disturbance recovery time, it can more comprehensively reflect the improvement effect of actively supported flexible DC systems on the frequency security, voltage stability, and oscillation recovery capability of the large power grid. Furthermore, this application uses synchronous generators and grid-connected inverters of the same capacity as benchmarks to perform linear interpolation or extrapolation scoring on six indicators of active support for flexible DC, obtaining graphical evaluation results. Through the hexagonal graphical evaluation results, this application can intuitively display the distribution of support capabilities for active support of flexible DC in six dimensions, enabling engineers to quickly determine the advantages and disadvantages of flexible DC solutions compared to synchronous generators and grid-connected inverters.

[0034] One of the above technical solutions has the following advantages or beneficial effects: The embodiments of this application calculate frequency index, voltage index and damping index and perform graphical evaluation, which can be applied to the evaluation of flexible DC engineering access, control parameter setting, comparison of different grid control schemes and quantitative evaluation of support capabilities in power grid planning and operation.

[0035] In some embodiments, the step of performing system frequency response analysis on the actively supported flexible DC system based on disturbance conditions and constructing a frequency response model includes the following steps: The active-supported flexible DC system is constructed based on the generator and inverter. Based on the disturbance conditions, the generator in the actively supported flexible DC system is modeled for governor droop and turbine dynamics, and the inverter is modeled for droop control and virtual synchronous generator control to obtain the frequency response model.

[0036] In the embodiments of this application, please refer to Figure 3 , Figure 3 This is a single-line diagram of the IEEE 10-machine 39-node system. In this embodiment, a synchronous generator of the same capacity, a grid-connected flexible DC converter station of the same capacity, and a network-connected flexible DC converter station of the same capacity are connected to the same bus. The capacity, inertia constant, and damping coefficient of the synchronous generator are taken from the parameters of the replaced unit or the target grid-connected unit; the grid-connected flexible DC converter station uses phase-locked loop synchronization and current source type active and reactive power control; the network-connected flexible DC converter station uses a control strategy with voltage source external characteristics, such as virtual synchronous generator control, droop control, or matching control. Power system inertia manifests as resistance to changes in system state caused by external disturbances; inertia is the magnitude of inertia. For the trend of system frequency change over time under active power disturbances, please refer to [link to relevant documentation]. Figure 4 The active power response process of the system after disturbance is presented. Therefore, two parameters, the rate of change of frequency (RoCoF) and the frequency deviation (FD), are selected as the evaluation system.

[0037] For a large power grid, there are various types of generating units. However, since thermal power units are still the most widely used, a system frequency response (SFR) model is considered for analysis. The SFR model only considers the primary frequency regulation of thermal power units with reheaters. It cannot characterize the frequency regulation characteristics of other types of units, but it provides a model foundation for covering multiple types of frequency regulation resources. This model can be extended to construct a frequency response model for high-proportion power electronic power systems. Therefore, this scheme constructs an actively supported flexible DC system based on generators and inverters, such as... Figure 5 As shown, this system consists of multiple conventional thermal power generators (subscript g) and generators based on power electronic inverters (subscript c).

[0038] Described by the generator's oscillation equation, Hg and Dg represent the sum of the generator's per-unit inertial time constant and damping constant.

[0039] ; ; in, i ∈ N g It is a collection of traditional synchronous generators. The low-order model proposed in the model is used to model governor droop and turbine dynamics; T gi It is the turbine time constant. R gi and K gi These are their respective droop and mechanical power gain factors, while F gi This represents the fraction of the total power generated by the turbine of the synchronous machine.

[0040] For inverter control schemes, the most popular grid-based control methods are droop control and VSG control. In actual operation, due to the nature of the control methods, these two control methods are similar to the control of a turbine and governor in a generator. When a frequency change is detected, power is provided to support the frequency. Therefore, in Figure 5 The inverter module in the system includes these two control methods, which are T ci It is the time constant of the converter. R ci and K ci They are j ∈ N d The droop and mechanical power gain factor, while H ck and D ck express k ∈ N v The per-unit inertial time constant and damping constant of the inverter.

[0041] Therefore, the embodiments of this application can construct a frequency response model by performing governor droop and turbine dynamic modeling on the generator in the actively supported flexible DC system, and performing droop control and virtual synchronous generator control modeling on the inverter.

[0042] In some embodiments, calculating frequency, voltage, and damping parameters of the frequency response model to obtain evaluation parameters includes the following steps: Dynamic analysis was performed on the frequency response model to obtain the dynamic transfer function of the generator system; The power system frequency support calculation is performed on the dynamic transfer function of the generator system to obtain the frequency index and the damping index; The voltage minimum point and steady-state voltage offset of the frequency response model are simulated to obtain the voltage index; The evaluation index is obtained based on the frequency index, the damping index, and the voltage index.

[0043] In this embodiment, a dynamic analysis is performed on the frequency response model to obtain the dynamic transfer function of the generator system. The expression of the dynamic transfer function of the generator system is as follows: ; In the formula, s This is the Laplace operator, used to represent the dynamic process of a system in the frequency domain; T gi It represents the equivalent time constant of the synchronous generator turbine or governor, used to describe the dynamic lag characteristics of the unit's primary frequency regulation mechanical power response.

[0044] Based on the sensitivity of the frequency response to the governor parameters, the dynamic transfer function of the generator system can be calculated to obtain the frequency index and damping index. The frequency index includes the frequency deviation and the rate of frequency change, while the damping index includes the damping coefficient and the disturbance recovery time.

[0045] For voltage parameters, since the generator model includes a power system stabilizer module, the two voltage parameters, namely the voltage minimum point and the voltage steady-state offset, can be obtained through simulation.

[0046] In some embodiments, performing power system frequency support calculations on the generator system dynamic transfer function to obtain the frequency index and the damping index includes the following steps: The dynamic transfer function of the generator system is simplified based on the sensitivity of the frequency response to the governor parameters to obtain the second-order system function; Substituting the active power step disturbance amplitude and the system equivalent inertia parameter into the second-order system function, the time-domain expression of the frequency deviation is calculated. The frequency deviation and the rate of change of frequency are calculated based on the time-domain expression of the frequency deviation, and the frequency index is obtained. The damping index is obtained by calculating the damping coefficient and disturbance recovery time based on the second-order system function.

[0047] In this embodiment, based on the sensitivity of the frequency response to the governor parameters, the lowest frequency point of the system based on this SFR model has the lowest sensitivity to the governor time constant. Therefore, it is assumed that the time constants of all synchronizers are equal ( T gi= T This is a reasonable simplification. Furthermore, the inverter's time constant... T ci Its time constant is about 2-3 orders of magnitude lower than that of a synchronous motor, which can be considered to be... T gi T ci ≈0. G(s) can now be simplified into a standard second-order system, the expression for which is shown below: ; Among them, the natural oscillation angular frequency ω n Damping ratio ζ The expressions are as follows: ; ; Assume the step disturbance in the electric power is ΔPe(s) = ΔP / s, where ΔP represents the amplitude of the active power step disturbance, and H represents the system's equivalent inertia parameter. Substituting these parameters into the second-order system function, we obtain the time-domain expression for the frequency deviation. ω ( t )≡Δ f ( t This can be deduced as: ; ; in, ω d Indicates the angular frequency of the damped oscillation. This represents the auxiliary phase angle introduced as a result of the inverse Laplace transform.

[0048] In some embodiments, the step of calculating the frequency deviation and the rate of change of frequency based on the time-domain expression of the frequency deviation to obtain the frequency index includes the following steps: Based on the time-domain expression of the frequency deviation, find the position where the frequency derivative is equal to zero, and obtain the time of the lowest frequency point; Substituting the time of the lowest frequency point into the time-domain expression of the frequency deviation and performing a mathematical transformation, the frequency deviation is obtained. The location of the fastest frequency change rate is found based on the time-domain expression of the frequency deviation, and the frequency change rate is obtained. The frequency index is determined based on the frequency deviation and the frequency change rate.

[0049] In this embodiment, by finding the position where the frequency derivative equals zero based on the time-domain expression of the frequency deviation, the time of the lowest frequency can be obtained; that is, the lowest frequency point (t) can be determined by observing the frequency change. m The time of finding the frequency. ω ( t By finding the point where the derivative of is equal to zero, we can obtain the expression for the time of the lowest frequency: ; This application obtains the value of the lowest frequency point, i.e., the frequency deviation, by substituting the time of the lowest frequency point into the time-domain expression of the frequency deviation and performing mathematical transformations. The expression for the frequency deviation is as follows: ; According to the model of the frequency response process, when the maximum frequency change occurs, that is, when only inertia supports the frequency in the initial stage of the disturbance, the rate of frequency change is the fastest and equals the rate of frequency change. The expression for the rate of frequency change is as follows: ; Finally, frequency indices can be obtained based on frequency deviation and frequency change rate. The lowest point of frequency deviation is used to reflect the degree of frequency drop in the system after the disturbance, and the frequency change rate is used to reflect the inertia support capability in the early stage of the disturbance.

[0050] In some embodiments, the step of calculating the damping coefficient and disturbance recovery time based on the second-order system function to obtain the damping index includes the following steps: The second-order system function is subjected to parameter aggregation processing to obtain the inertial time constant and damping constant; The damping coefficient and disturbance recovery time are calculated based on the inertial time constant and the damping constant to obtain the damping index.

[0051] In this embodiment, the parameters of the second-order system function are defined as follows: ; ; ; ; ; The above parameters are obtained based on the superposition principle of linear systems, the per-unit equivalence rule under a unified capacity benchmark, and the parameter aggregation rule of the system frequency response model. Since the effects of each synchronous generator, droop control inverter, and virtual synchronous control inverter on the system frequency dynamics can be superimposed under linearization conditions in the small disturbance frequency response model, the parameters of multiple devices can be converted into equivalent aggregated parameters. The expressions for the inertial time constant and damping constant are shown below: ; ; The damping coefficient and disturbance recovery time can be calculated from the inertial time constant and the damping constant. The expression for the damping coefficient is as follows: ; The expression for the time it takes for a disturbance to recover to 90% of its steady state is shown below: .

[0052] In some embodiments, the step of visually scoring the evaluation indicators based on the first reference indicator and the second reference indicator to obtain graphical evaluation results includes the following steps: The evaluation index is scored using a dual-benchmark system based on the first reference index and the second reference index to obtain the index score. The index scores are then visualized to obtain the graphical evaluation results.

[0053] In this embodiment, the first reference index is a relevant index measured by a synchronous generator under the same disturbance and capacity conditions, and the second reference index is a relevant index measured by a grid-connected inverter under the same disturbance and capacity conditions. Using a synchronous generator as 100 points and a grid-connected inverter as 50 points, linear interpolation or extrapolation is performed to score the six active support indicators of grid-connected flexible DC. Let the calculation results of the m-th evaluation index in the synchronous generator scenario, the grid-connected inverter scenario, and the grid-connected flexible DC scenario be Im,SG, Im,GFL, and Im,GFM, respectively. Where the synchronous generator scenario is used as the 100-point benchmark and the grid-connected inverter scenario as the 50-point benchmark, the score of the grid-connected flexible DC on the m-th index is: ; When Im,GFL=Im,GFM, the grid-type flexible DC score is 50 points; when Im,GFM=Im,SG, the grid-type flexible DC score is 100 points; when the grid-type flexible DC index is better than the synchronous generator benchmark, the score can be extrapolated to be higher than 100 points; when its index is worse than the grid-type inverter benchmark, the score can be extrapolated to be lower than 50 points. Finally, these index scores can be used to create a graphical evaluation result.

[0054] The solutions of this application embodiment will be described in detail and explained below with reference to specific application examples: This application's embodiments can be applied to the field of power grid technology, and are suitable for evaluation scenarios after an actively supported flexible DC system is connected to the power grid. This application's embodiments, through modeling and simulation, verify the inertia time constant and damping coefficient of ten generating units, as shown in the table below (all units are based on a 100MW baseline capacity), as shown in Table 1, Simulation Parameter Table:

[0055] Table 1 Simulation Parameter Table By setting active and reactive power deficits of 800MW / MVar at bus5 of the IEEE 39-node system, comparing the output of generators and flexible DC transmissions, and measuring the frequency and voltage at the grid connection points of the generators and flexible DC transmissions, the parameters for replacing the G2 generator with the same grid-connected flexible DC transmission are... H =3, D =5. Taking all synchronous machines as an example, such as Figure 6 As shown, the same tests were performed on generator G2 in both grid-connected and grid-connected configurations. The simulation results for frequency and damping were obtained as follows. Figure 7 and Figure 8 As shown.

[0056] This application embodiment performs voltage disturbance testing, and the simulation results are as follows: Figure 9 As shown, two voltage parameters are taken when Kq = 31.75pu for the flexible DC transmission, and the lowest voltage point and steady-state offset value are compared. Based on the above six data points, a hexagonal scoring diagram is drawn, with the synchronous generator as 100 points and the grid-connected inverter as 50 points. Linear interpolation or extrapolation is performed on the six active support indicators of the grid-connected flexible DC transmission, and the final result can be plotted as shown below. Figure 10 The assigned graph is shown.

[0057] This application uses a synchronous generator of the same capacity as a 100-point benchmark and a grid-connected inverter of the same capacity as a 50-point benchmark to perform linear interpolation or extrapolation scoring on six indicators of active support for flexible DC. This solves the problem in existing methods where evaluation results cannot be directly compared due to different system capacities, disturbance amplitudes, and operating modes. Through hexagonal graphical evaluation results, this application can intuitively display the distribution of support capabilities of active support for flexible DC in six dimensions, enabling engineers to quickly determine the advantages and disadvantages of flexible DC solutions compared to synchronous generators and grid-connected inverters.

[0058] This application maps six indicator scores onto a hexagonal graph, forming a six-dimensional graphical evaluation result of active support capability. The closer the hexagon is to the synchronous generator reference boundary, the closer the grid-connected flexible DC transmission is to the dynamic support capability of the large power grid in terms of frequency, voltage, and damping. If a certain dimension shrinks significantly, it indicates that there is still insufficient support in that dimension, which can provide a basis for the tuning of flexible DC transmission control parameters, engineering selection, comparison of access schemes, and system operation safety assessment.

[0059] This application embodiment also provides an access assessment device for an actively supported flexible DC system, which can implement the above-described access assessment method for an actively supported flexible DC system. The device includes: The response analysis module is used to perform system frequency response analysis on the actively supported flexible DC system according to the disturbance conditions, and to construct a frequency response model. The index calculation module is used to calculate the frequency index, voltage index and damping index of the frequency response model to obtain the evaluation index. The reference calculation module is used to obtain the response indicators of synchronous generators and grid-connected inverters of the same capacity as the active-supported flexible DC system under the same disturbance scenario, and to obtain the first reference indicator and the second reference indicator. The access evaluation module is used to perform visual scoring processing on the evaluation indicators based on the first reference indicator and the second reference indicator to obtain graphical evaluation results.

[0060] It is understood that the content of the above method embodiments is applicable to the present device embodiments. The specific functions implemented by the present device embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0061] This application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the above-described method. This electronic device can be any smart terminal, including tablet computers, in-vehicle computers, etc.

[0062] It is understood that the content of the above method embodiments is applicable to this device embodiment. The specific functions implemented by this device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0063] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0064] It is understood that the content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0065] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0066] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0067] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0068] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0069] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0070] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0071] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0072] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0073] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0074] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0075] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A method for evaluating the access of an actively supported flexible DC system, characterized in that, The method includes the following steps: Based on the disturbance conditions, the frequency response of the actively supported flexible DC system is analyzed, and a frequency response model is constructed. The frequency response model is used to calculate frequency, voltage, and damping parameters to obtain evaluation indicators. Obtain the response indicators of a synchronous generator and a grid-connected inverter of the same capacity as the actively supported flexible DC system under the same disturbance scenario, and obtain the first reference indicator and the second reference indicator. The evaluation indicators are visually scored based on the first reference indicator and the second reference indicator to obtain graphical evaluation results.

2. The method according to claim 1, characterized in that, The process of analyzing the system frequency response of the actively supported flexible DC system based on disturbance conditions and constructing a frequency response model includes the following steps: The active-supported flexible DC system is constructed based on the generator and inverter. Based on the disturbance conditions, the generator in the actively supported flexible DC system is modeled for governor droop and turbine dynamics, and the inverter is modeled for droop control and virtual synchronous generator control to obtain the frequency response model.

3. The method according to claim 1, characterized in that, The calculation of frequency, voltage, and damping parameters of the frequency response model to obtain evaluation parameters includes the following steps: Dynamic analysis was performed on the frequency response model to obtain the dynamic transfer function of the generator system; The power system frequency support calculation is performed on the dynamic transfer function of the generator system to obtain the frequency index and the damping index; The voltage minimum point and steady-state voltage offset of the frequency response model are simulated to obtain the voltage index; The evaluation index is obtained based on the frequency index, the damping index, and the voltage index.

4. The method according to claim 3, characterized in that, The step of performing power system frequency support calculations on the dynamic transfer function of the generator system to obtain the frequency index and the damping index includes the following steps: The dynamic transfer function of the generator system is simplified based on the sensitivity of the frequency response to the governor parameters to obtain the second-order system function; Substituting the active power step disturbance amplitude and the system equivalent inertia parameter into the second-order system function, the time-domain expression of the frequency deviation is calculated. The frequency deviation and the rate of change of frequency are calculated based on the time-domain expression of the frequency deviation, and the frequency index is obtained. The damping index is obtained by calculating the damping coefficient and disturbance recovery time based on the second-order system function.

5. The method according to claim 3, characterized in that, The process of calculating the frequency deviation and the rate of change of frequency based on the time-domain expression of the frequency deviation to obtain the frequency index includes the following steps: Based on the time-domain expression of the frequency deviation, find the position where the frequency derivative is equal to zero, and obtain the time of the lowest frequency point; Substituting the time of the lowest frequency point into the time-domain expression of the frequency deviation and performing a mathematical transformation, the frequency deviation is obtained. The location of the fastest frequency change rate is found based on the time-domain expression of the frequency deviation, and the frequency change rate is obtained. The frequency index is determined based on the frequency deviation and the frequency change rate.

6. The method according to claim 3, characterized in that, The step of calculating the damping coefficient and disturbance recovery time based on the second-order system function to obtain the damping index includes the following steps: The second-order system function is subjected to parameter aggregation processing to obtain the inertial time constant and damping constant; The damping coefficient and disturbance recovery time are calculated based on the inertial time constant and the damping constant to obtain the damping index.

7. The method according to any one of claims 1 to 6, characterized in that, The step of visually assigning scores to the evaluation indicators based on the first reference indicator and the second reference indicator to obtain graphical evaluation results includes the following steps: The evaluation index is scored using a dual-benchmark system based on the first reference index and the second reference index to obtain the index score. The index scores are then visualized to obtain the graphical evaluation results.

8. An active-support flexible DC system access evaluation device, characterized in that, The device includes: The response analysis module is used to perform system frequency response analysis on the actively supported flexible DC system according to the disturbance conditions, and to construct a frequency response model. The index calculation module is used to calculate the frequency index, voltage index and damping index of the frequency response model to obtain the evaluation index. The reference calculation module is used to obtain the response indicators of synchronous generators and grid-connected inverters of the same capacity as the active-supported flexible DC system under the same disturbance scenario, and to obtain the first reference indicator and the second reference indicator. The access evaluation module is used to perform visual scoring processing on the evaluation indicators based on the first reference indicator and the second reference indicator to obtain graphical evaluation results.

9. An electronic device, characterized in that, The electronic device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the method according to any one of claims 1 to 7.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 1 to 7.

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