Power system stability analysis method based on energy storage converter

Abstract

The invention discloses a power system stability analysis method based on an energy storage converter, and relates to the technical field of power stability analysis. The method comprises the following steps: obtaining operation data of a network following type-network constructing type converter, and constructing a dynamic impedance model of the network following type-network constructing type converter; analyzing according to the dynamic impedance model to obtain a frequency band distribution rule of the dynamic impedance, and analyzing according to the frequency band distribution rule of the dynamic impedance to obtain a frequency band dominant factor; respectively establishing a mapping relation between the voltage and current of the relaxation node and the dynamic impedance of the following network type converter and the structure network type converter; identifying weak links of the power system, and obtaining instability factors of the power system according to the weak links; and combining the frequency band dominant factors, the mapping relation and the instability factors, and performing comprehensive analysis to obtain the stability degree of the power system. According to the method, the accuracy of stability analysis of the power system of the network-to-network converter is improved.

Description

Technical Field

[0001] The present application relates to the technical field of power stability analysis, and in particular to a power system stability analysis method based on energy storage converters. Background Art

[0002] Stability is the basis for the safe operation of power systems. Traditional stability theory originated from the characteristics of synchronous machines. After a century of accumulation and practice, it has become more mature, but it is difficult to adapt to the rapid development of the "double high" power system. According to the latest report of the Institute of Electrical and Electronics Engineers, 70% of the global power outages in ten years are related to the "double high" characteristics. The new power system with the coexistence of grid-type and grid-building converters is becoming more and more mature, and traditional stability theory is difficult to adapt, resulting in inaccurate stability analysis results. Summary of the invention

[0003] The purpose of the present invention is to provide a method for analyzing the stability of a power system based on an energy storage converter to solve the problems raised in the above background technology.

[0004] The present application provides a method for analyzing the stability of a power system based on an energy storage converter, which adopts the following technical solutions:

[0005] Obtaining the operation data of the grid-following-grid-building converter and constructing a dynamic impedance model of the grid-following-grid-building converter;

[0006] According to the dynamic impedance model, the frequency band distribution law of dynamic impedance is obtained, and according to the frequency band distribution law of dynamic impedance, the frequency band dominant factor is obtained;

[0007] The mapping relationship between the relaxed node voltage and current and the dynamic impedance of the grid-following and grid-forming converters is established respectively;

[0008] Identify the weak links of the power system and obtain the instability factors of the power system based on the weak links;

[0009] Combining the dominant factors of the frequency band, mapping relationship and instability factors, a comprehensive analysis is conducted to obtain the stability of the power system.

[0010] Preferably, the step of obtaining the operation data of the grid-following type-grid-building type converter and constructing the dynamic impedance model of the grid-following type-grid-building type converter comprises the following steps:

[0011] Obtaining a system topology diagram of a power system of a grid-following-grid-building converter under stable operating conditions;

[0012] A system model of the power system under stable operation conditions is established and recorded as a stable model, and the state equation of the dynamic model of the grid-following-grid-building converter is extracted based on the stable model;

[0013] Obtain the variation relationship between the equivalent impedance of the inverter and the current, and obtain the Thevenin equivalent circuit and Norton equivalent circuit of the grid-following and grid-forming converters respectively according to the variation relationship;

[0014] Obtain the topology structure and control strategy of the converter, and model the converter according to the topology structure and control strategy to obtain a topology model and a strategy model;

[0015] Obtain the frequency response characteristics of the converter, and combine the topology model and the strategy model to obtain the influence of the frequency response characteristics on the control strategy on the dynamic characteristics;

[0016] The full-condition nonlinear dynamic impedance model of the grid-following-grid-building converter is constructed by combining the state equation, Thevenin equivalent circuit, Norton equivalent circuit and the degree of influence.

[0017] Preferably, the step of obtaining the frequency band distribution law of dynamic impedance according to the dynamic impedance model analysis, and obtaining the frequency band dominant factor according to the frequency band distribution law of dynamic impedance analysis, comprises the following steps:

[0018] Obtain the electromagnetic time scale stability of the power system and establish the impedance model of the entire system based on the electromagnetic time scale stability;

[0019] According to the full-operating nonlinear dynamic impedance model of the grid-following and grid-building converters, the impedance stability analysis method of the protection mapping theory is used, and the complementary space of the electromagnetic time scale stable region of the system stable operation is obtained in combination with the impedance forbidden region judgment basis.

[0020] According to the complementary space, different line impedances are selected to obtain different characteristics of the dynamic impedance of the power system in different frequency bands and form the frequency band distribution law of the dynamic impedance;

[0021] According to the frequency band distribution law of dynamic impedance, the corresponding frequency band dominant factor is found.

[0022] Preferably, the step of establishing the mapping relationship between the relaxation node voltage, current and the dynamic impedance of the grid-following and grid-forming converters respectively comprises the following steps:

[0023] Extract impedance angle data according to the full-operating impedance model of the grid-following and grid-building converters, and determine the stability of the impedance angle according to the impedance angle data;

[0024] Establish the active-reactive power relationship of the power system and obtain the reactive power change curve of the system;

[0025] Combining the stability of the impedance angle and the reactive power variation curve, a correlation curve between the system stability and the stability of the impedance angle is obtained and recorded as a system-impedance curve;

[0026] Find the balance point of the power system and obtain the impedance angle range at the balance point;

[0027] The changing relationship between the active power and reactive power of the power system is obtained, and the mapping relationship between the voltage and current of the relaxation node and the dynamic impedance of the grid-following and grid-forming converters is established according to the changing relationship.

[0028] Preferably, the step of obtaining the change relationship between the active power and reactive power of the power system and establishing a mapping relationship between the relaxed node voltage, current and the dynamic impedance of the grid-following and grid-forming converters according to the change relationship comprises the following steps:

[0029] According to the change relationship, the changes of the inverter output voltage and current are obtained and recorded as a voltage change curve and a current change curve respectively;

[0030] Find the slack nodes of the power system and determine whether the system can return to a stable state based on the impedance angle range and current change curve of the slack nodes;

[0031] If the system can return to a stable state, a mapping relationship between the relaxed node voltage and the dynamic impedance of the grid-following converter is established according to the voltage change curve and the impedance angle range;

[0032] According to the voltage variation curve and the impedance angle range, a mapping relationship between the relaxed node voltage and the dynamic impedance of the grid-forming converter is established;

[0033] A mapping relationship between the relaxation node current and the dynamic impedance of the grid-following converter is established according to the current variation curve and the impedance angle range;

[0034] The mapping relationship between the relaxation node current and the dynamic impedance of the grid-type converter is established according to the current variation curve and the impedance angle range.

[0035] Preferably, the step of identifying the weak links of the power system and obtaining the instability factors of the power system according to the weak links comprises the following steps:

[0036] Obtain sample data of the power system and build a self-evolutionary learning model based on the sample data;

[0037] Identify weak links in power systems based on self-evolving learning models;

[0038] The dominant factor of instability is determined based on the weak link and recorded as the instability factor.

[0039] Preferably, the step of acquiring sample data of the power system and constructing a self-evolutionary learning model according to the sample data comprises the following steps:

[0040] Acquire broadband oscillation data, and extract oscillation samples according to the broadband oscillation data;

[0041] Preprocessing oscillation samples of different frequencies to obtain processed samples, wherein the preprocessing includes data normalization and feature extraction;

[0042] An impedance angle model is constructed according to the processed samples, and impedance angle characteristics are extracted according to the impedance angle model;

[0043] A self-evolving data model is constructed based on the system-impedance curve.

[0044] Preferably, the step of identifying the weak links of the power system according to the self-evolution learning model comprises the following steps:

[0045] Determine whether the system has potential instability risks based on the self-evolving data model;

[0046] If there is a risk of instability in the system, the instability cause set of each link of the power system is obtained;

[0047] Determine the system broadband oscillation instability boundary based on the power system oscillation mechanism, conditions and judgment basis;

[0048] According to the instability boundary, the basic instability cause is determined from the instability cause set, and the link of the power system prone to oscillation is obtained according to the basic instability cause and recorded as the weak link.

[0049] Preferably, the step of determining the dominant instability factor based on the weak link and recording it as the instability factor comprises the following steps:

[0050] According to the transient and stable energy transfer laws of the power system, the voltage and current at the fault point caused by oscillation and instability of the system are analyzed;

[0051] Analyze the stability of each part of the power system based on voltage and current, and filter out the unstable parts based on the stability;

[0052] According to the wide-band oscillation stability criterion of the power system and the three major stability criteria of voltage, frequency and power angle of the traditional power system, the relationship between different influencing factors and the stability of the power system is determined;

[0053] The dominant factor of instability is confirmed based on the stability of the unstable part.

[0054] In summary, the present application includes at least one of the following beneficial technical effects:

[0055] 1. Improve power supply reliability: Grid-following / grid-building converters can improve power supply reliability by optimizing the power supply path and adjusting grid parameters in real time, reducing the time and scope of power outages when faults occur.

[0056] 2. Reduce energy loss: By optimizing power distribution and reducing resistance losses, grid-connected / grid-forming converters can reduce energy losses and improve the energy efficiency of new power systems.

[0057] 3. Increase grid stability: Grid-following / grid-building converters can balance grid load and voltage, improve grid stability, and reduce voltage fluctuations and power imbalance problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a schematic diagram of the specific steps of an embodiment of a method for analyzing power system stability based on an energy storage converter of the present invention. DETAILED DESCRIPTION

[0059] Below is a combination of the embodiments and Figure 1 The present invention is further described in detail, but the embodiments of the present invention are not limited thereto.

[0060] The present invention discloses a method for analyzing the stability of a power system based on an energy storage converter, which specifically comprises the following steps:

[0061] Step S1, obtaining the operation data of the grid-following type-grid-forming type converter, and constructing a dynamic impedance model of the grid-following type-grid-forming type converter.

[0062] Step S2, analyzing the frequency band distribution law of dynamic impedance according to the dynamic impedance model, and analyzing the frequency band distribution law of dynamic impedance to obtain the frequency band dominant factor.

[0063] Step S3, respectively establishing mapping relationships between the voltage and current of the relaxation nodes and the dynamic impedances of the grid-following and grid-forming converters.

[0064] Step S4, identifying weak links of the power system, and obtaining instability factors of the power system according to the weak links.

[0065] Step S5, combining the frequency band dominant factors, mapping relationship and instability factors, and comprehensively analyzing to obtain the stability of the power system.

[0066] In practical applications, stability analysis is one of the important contents of the research on new power systems with grid-connected / grid-forming converters. Stability analysis can deeply understand the operation mechanism and characteristics of new power systems with grid-connected / grid-forming converters by establishing new power system models, analyzing the dynamic response and steady-state characteristics of the system. In addition, stability analysis can also help researchers discover potential problems of new power systems with grid-connected / grid-forming converters, and propose corresponding solutions to ensure the stable operation of the power system. Grid-forming control consists of two parts. The first part is the simulation of the actual synchronous machine, including the dynamic swing equation, active power and phase angle adjustment, voltage droop and virtual impedance simulation. The second part is the internal control of the voltage source converter, including the outer loop voltage and inner loop current control, which is used to control the output voltage to track the reference value given in the first part. The core function of grid-forming control is to achieve synchronization and reference power output according to the power angle relationship, adjust the output voltage amplitude according to the voltage support strategy, thereby controlling the grid connection point voltage output and presenting the PV node in the power grid. The grid-forming control is proposed to deal with the problem that the grid-following control cannot achieve voltage support and synchronization difficulties under weak grid conditions.

[0067] Taking the typical network control strategy virtual synchronous machine as an example, power synchronization includes three parts, as shown in (3-1): virtual inertia J, damping D, and active power droop coefficient K D Power synchronization is to control and adjust the output phase according to the active power difference between the reference and actual output until there is no difference in active power and synchronization is completed. Among them, the reference power simulates the mechanical power of the synchronous machine, and the actual power simulates the electromagnetic power in the synchronous machine. The specific control equation is as follows:

[0068]

[0069] Δω VSG =ω VSG -ω grid (3-2)

[0070]

[0071] P=i od v od +i oq v oq (3-4)

[0072] Where P* is the reference active power, P is the output active power, ω* is the reference frequency, ω VSG is the converter virtual frequency, ω grid is the grid frequency, which can be measured by a phase-locked loop. It is worth noting that the grid-type control synchronization is only achieved by the swing equation (3-1), rather than by a phase-locked loop. o,d / v o,qis the output voltage in the synchronous orthogonal coordinate system, i o,q / i o,d is the output current in the synchronous rectangular coordinate system.

[0073] Voltage control can refer to the synchronous machine voltage control AVR mode to determine the output amplitude as shown in the formula where K v Gain part, reactive power-voltage droop control can also be used such as K q Gain section.

[0074] E=V * +K v (V * -V g )+K q (Q * -Q) (3-5)

[0075] Q=-i o,q v o,d +i o,d v o,q (3-6)

[0076] Where Q* is the reference reactive power, Q is the output reactive power, V* is the reference voltage, V g is the grid voltage.

[0077] The synchronous machine electromotive force E is simulated by equation (3-5) and combined with the virtual impedance, the output voltage reference value can be obtained:

[0078]

[0079] where i o =i od +ji oq is the output current, It is the internal voltage control reference value of the converter.

[0080] The second part is the internal control of the converter. The reference value obtained in the first part controls and adjusts the voltage output of the grid common connection point PCC. The outer loop voltage controller provides a reference for the inner loop current controller. The inner loop current controller controls the converter terminal voltage output v cv . PI controller is used for both voltage and current control, and the control equations are (3-9) and (3-10) respectively.

[0081]

[0082] The voltage PI control parameter is K pv , K iv ; The current PI control parameter is K pc , K ic ; ε dis the integral value of the voltage error; γ d The integrated value of the current error.

[0083] The steps of obtaining the operation data of the grid-following type-grid-building type converter and constructing the dynamic impedance model of the grid-following type-grid-building type converter include the following steps:

[0084] Step S11, obtaining a system topology diagram of a power system of a grid-following type-grid-building type converter under a stable operating condition.

[0085] Step S12, establishing a system model of the power system under stable operating conditions and recording it as a stable model, and extracting the state equation of the dynamic model of the grid-following type-grid-building type converter according to the stable model.

[0086] Step S13, obtaining the variation relationship between the equivalent impedance of the inverter and the current, and obtaining the Thevenin equivalent circuit and the Norton equivalent circuit of the grid-following type and grid-forming type converters respectively according to the variation relationship.

[0087] Step S14, obtaining the topology structure and control strategy of the converter, and modeling according to the topology structure and control strategy of the converter to obtain a topology model and a strategy model.

[0088] Step S15, obtaining the frequency response characteristics of the converter, and combining the topology model and the strategy model to obtain the influence of the frequency response characteristics on the control strategy on the dynamic characteristics.

[0089] Step S16, combining the state equation, the Thevenin equivalent circuit, the Norton equivalent circuit and the influence degree to construct a full-condition nonlinear dynamic impedance model of the grid-following type-grid-building type converter.

[0090] In practical applications, the stability analysis method of impedance technology is to establish an impedance model of the entire system and use the generalized Nyquist curve or the generalized inverse Nyquist curve to determine the stability of the system. First, the dynamic characteristics of the grid-type-grid-forming converter are modeled, including its voltage-current characteristics, voltage-frequency characteristics, current-frequency characteristics, etc. By modeling the transfer function of the converter, its impedance characteristics at different frequencies are analyzed. Considering that the grid-type-grid-forming converter usually adopts advanced control strategies, the construction of the dynamic impedance model needs to consider the impact of its control strategy on the dynamic characteristics, such as current control, voltage control, etc. The relationship between the equivalent impedance of the grid-type-grid-forming converter and the current is studied, and the equivalent model of the inverter is studied and analyzed to obtain the change law of the equivalent impedance of the inverter, and the physical characteristics of the inverter are fully described using the characteristics of negative impedance.

[0091] The steps of obtaining the frequency band distribution law of dynamic impedance according to the dynamic impedance model analysis and obtaining the frequency band dominant factor according to the frequency band distribution law of dynamic impedance analysis include the following steps:

[0092] Step S21, obtaining the electromagnetic time scale stability of the power system, and establishing an impedance model of the entire system according to the electromagnetic time scale stability.

[0093] Step S22, according to the full-operating-condition nonlinear dynamic impedance model of the grid-following-grid-building converter, using the impedance stability analysis method of the protection mapping theory, combined with the impedance forbidden area judgment basis, obtain the complementary space of the electromagnetic time scale stable area for the stable operation of the system.

[0094] Step S23, selecting different line impedances according to the complementary space, obtaining different characteristics of the dynamic impedance of the power system in different frequency bands and forming a frequency band distribution law of the dynamic impedance.

[0095] Step S24, searching and obtaining the corresponding frequency band dominant factor according to the frequency band distribution rule of the dynamic impedance.

[0096] In practical applications, the electromagnetic time-scale stability of the power system based on impedance technology is studied to establish the impedance model of the entire system and use the generalized Nyquist curve or the generalized inverse Nyquist curve to determine the stability of the system. A method of impedance stability analysis based on protection mapping theory is studied, and the complementary space of the electromagnetic time-scale stable region of the system stable operation is obtained through the impedance forbidden region criterion. The stability of the impedance of the power system at different frequencies is studied, and the dynamic impedance response of the power system at low, medium and high frequency bands is studied. The different characteristics of the dynamic impedance of the power system in different frequency bands are studied, and the frequency band distribution law and frequency band dominant factors of dynamic impedance are explored.

[0097] The steps of respectively establishing mapping relationships between the relaxed node voltage and current and the dynamic impedance of the grid-following and grid-forming converters include the following steps:

[0098] Step S31, extracting impedance angle data according to the full-operating impedance model of the grid-following type-grid-building type converter, and determining the stability of the impedance angle according to the impedance angle data.

[0099] Step S32, establishing the active-reactive power relationship of the power system, and obtaining the reactive power variation curve of the system.

[0100] Step S33: combining the stability of the impedance angle and the reactive power variation curve, a correlation curve between the system stability and the stability of the impedance angle is obtained and recorded as a system-impedance curve.

[0101] Step S34, finding the balance point of the power system and obtaining the impedance angle range at the balance point.

[0102] Step S35, obtaining the change relationship between the active power and reactive power of the power system, and establishing a mapping relationship between the relaxed node voltage, current and the dynamic impedance of the grid-following and grid-forming converters according to the change relationship.

[0103] In actual application, the impedance angle stability analysis of the full-operating impedance model of the grid-following and grid-forming converters is carried out, the curve of the reactive power of the system changing with the impedance angle is studied, and the relationship between the system stability and the impedance angle is derived by combining the relationship between current and impedance. The load disturbance analysis of the system at a certain equilibrium point is studied, and the changes in the inverter output voltage and current are obtained according to the relationship between the active power and reactive power of the system. According to the relationship between current and impedance, it is studied whether the system can return to a stable state. The mapping relationship between the relaxed node voltage / current and the dynamic impedance of the grid-following / grid-forming converter is established, the instability evolution law of the new power system is studied, and the instability mechanism of the system is clarified.

[0104] The step of obtaining the change relationship between the active power and reactive power of the power system and establishing the mapping relationship between the voltage and current of the relaxation node and the dynamic impedance of the grid-following and grid-forming converters according to the change relationship includes the following steps:

[0105] Step S351, obtaining the changes of the inverter output voltage and current according to the change relationship and recording them as a voltage change curve and a current change curve respectively.

[0106] Step S352, finding the slack nodes of the power system, and judging whether the system can return to a stable state according to the impedance angle range and current variation curve of the slack nodes.

[0107] Step S353: if the system can return to a stable state, a mapping relationship between the relaxation node voltage and the dynamic impedance of the grid-following converter is established according to the voltage variation curve and the impedance angle range.

[0108] Step S354: establishing a mapping relationship between the relaxation node voltage and the dynamic impedance of the grid-type converter according to the voltage variation curve and the impedance angle range.

[0109] Step S355 , establishing a mapping relationship between the relaxation node current and the dynamic impedance of the grid-following converter according to the current variation curve and the impedance angle range.

[0110] Step S356, establishing a mapping relationship between the relaxation node current and the dynamic impedance of the grid-type converter according to the current variation curve and the impedance angle range.

[0111] The steps of identifying the weak links of the power system and obtaining the instability factors of the power system according to the weak links include the following steps:

[0112] Step S41, obtaining sample data of the power system, and constructing a self-evolution learning model according to the sample data.

[0113] Step S42, identifying weak links of the power system according to the self-evolution learning model.

[0114] Step S43, determining the dominant instability factor based on the weak link and recording it as the instability factor.

[0115] The steps of obtaining sample data of the power system and constructing a self-evolution learning model according to the sample data include the following steps:

[0116] Step S411, obtaining broadband oscillation data, and extracting oscillation samples according to the broadband oscillation data.

[0117] Step S412, preprocessing the oscillation samples of different frequencies to obtain processed samples, wherein the preprocessing includes data normalization and feature extraction.

[0118] Step S413: construct an impedance angle model according to the processed sample, and extract the impedance angle characteristics according to the impedance angle model.

[0119] Step S414: construct a self-evolving data model according to the system-impedance curve.

[0120] In practical applications, how to accurately analyze the modal frequency in the signal based on a period of sampled data is a topic that needs to be studied. The resolution of frequency analysis is closely related to the length of the selected data window. The higher the resolution, the longer the data window is required. On the one hand, a large amount of data is required for calculation, which is not suitable for implementation on the device; on the other hand, the analysis of frequency and amplitude has a large lag, which cannot be used to analyze rapidly changing signals and is not suitable for real-time online dynamic calculations.

[0121] In order to obtain more accurate modal frequencies, a cyclic DFT correction algorithm based on a sliding data window is used to analyze very accurate modal frequencies without losing the transient change trend information of the amplitude. The DFT correction algorithm is used to calculate the modal frequency and modal phasor (i.e., amplitude and phase) for fixed-interval sampling data, which can effectively avoid the influence of frequency leakage.

[0122] Through the actual test system, it was found that within the frequency band where wide-band oscillations occur in the "double-high" power system, the equivalent impedance of the grid-type inverter will change with the change of current.

[0123] In the frequency band of 48-49.4 Hz, the equivalent impedance of the inverter is negative resistance capacitance; when the current changes, the equivalent impedance of the inverter shows that the phase remains basically unchanged within this range, but the amplitude increases with the increase of current. At the same time, through simulation experiments, it is found that the oscillation frequency of the system also appears in the frequency band of 48-49.4 Hz. This result is a subsynchronous oscillation, which is a broadband oscillation phenomenon of the "double high" power system.

[0124] Z=R+jX is the sum of the inverter equivalent output impedance and the line impedance; Z=Z1+Z2, Z1=R1+jX1, Z2=R2+jX2; R1 and X1 are the inverter equivalent output resistance and reactance respectively; R2 and X2 are the resistance and reactance of the line respectively; δ is the angular deviation between the inverter output voltage and the bus voltage.

[0125] The inverter output apparent power S can be expressed as

[0126]

[0127] Where: P is the output active power; Q is the output reactive power.

[0128]

[0129] Where: θ is the phase angle of the sum of the inverter equivalent output impedance and the line impedance Z; R is the sum of the inverter equivalent output resistance and the line resistance; X is the sum of the inverter equivalent output reactance and the line reactance.

[0130] Therefore, the active power and reactive power can be expressed as

[0131]

[0132] In actual systems, since the power angle value is very small

[14] , it is assumed that the power angle is approximately equal to 0, then equation (3-22) can be equivalent to

[0133]

[0134] Due to the existence of the equivalent negative impedance of the inverter, the synthetic impedance angle θ will be expanded from the conventional range [-π / 2,π / 2] to [-π,π].

[0135] The steps of identifying the weak links of the power system according to the self-evolution learning model include the following steps:

[0136] Step S421, judging whether the system has a potential risk of instability according to the self-evolving data model.

[0137] Step S422: If there is a risk of instability in the system, a set of instability causes of each link in the power system is obtained.

[0138] Step S423, determining the system broadband oscillation instability boundary according to the power system oscillation mechanism, conditions and judgment basis.

[0139] Step S424, determining the basic instability cause from the instability cause set according to the instability boundary, obtaining the link of the power system that is prone to oscillation according to the basic instability cause and recording it as the weak link.

[0140] In actual application, a high proportion of new energy and a high proportion of power electronic equipment are connected to the power system, and the system oscillation frequency range is wider. When the system is in a specific working condition or fault disturbance, the wide-band oscillation in the system causes the system to become instable. The principle of identifying the weak links of the new power system is to determine the instability boundary of the system wide-band oscillation according to the system oscillation mechanism, conditions, and criteria, so as to determine whether there is a hidden danger of instability in the system and the cause of the instability, and obtain the link of the system that is prone to oscillation. By analyzing the failure rate, maintenance history, and availability of each key equipment in the power system, the weak links in the system are evaluated. The performance of the system under different working conditions is studied, especially the operation under the conditions of weak links, so as to quantitatively evaluate the weak links of the system.

[0141] The steps of determining the dominant instability factor based on the weak link and recording it as the instability factor include the following steps:

[0142] Step S431, according to the transient and stable energy transfer rules of the power system, analyze and obtain the voltage and current at the fault point caused by the oscillation and instability of the system.

[0143] Step S432, analyzing the stability of each part of the power system according to the voltage and current, and screening out the unstable part according to the stability.

[0144] Step S433, determining the relationship between different influencing factors and the stability of the power system according to the wide-band oscillation stability criterion of the power system and the three major stability criteria of voltage, frequency and power angle of the traditional power system.

[0145] Step S434, determining the dominant factor of instability according to the stability degree of the unstable part.

[0146] In actual application, the factors and stability conditions that affect system stability are studied based on the established wide-band oscillation stability criteria of the "double-high" power system and the three major stability criteria of voltage, frequency, and power angle of the traditional power system. The relationship between different influencing factors and different types of stability is studied, and methods for identifying the main influencing factors of system stability and the types of system instability are designed. Through experimental research on the instability caused by various influencing factors of the system and the analysis of the phenomenon of system instability caused by multiple factors, the dominant factors of instability of the new power system are studied.

[0147] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for analyzing power system stability based on energy storage converter, characterized in that: The following steps are involved: Obtaining the operation data of the grid-following-grid-building converter and constructing a dynamic impedance model of the grid-following-grid-building converter; According to the dynamic impedance model, the frequency band distribution law of the dynamic impedance is obtained, and according to the frequency band distribution law of the dynamic impedance, the frequency band dominant factor is obtained; The mapping relationship between the relaxed node voltage and current and the dynamic impedance of the grid-following and grid-forming converters is established respectively; Identify the weak links of the power system and obtain the instability factors of the power system based on the weak links; Combining the dominant factors of the frequency band, mapping relationship and instability factors, a comprehensive analysis is conducted to obtain the stability of the power system.

2. A method for analyzing power system stability based on energy storage converter according to claim 1, characterized in that: The steps of obtaining the operation data of the grid-following type-grid-building type converter and constructing the dynamic impedance model of the grid-following type-grid-building type converter include the following steps: Obtaining operating conditions of a system topology diagram of a power system of a grid-following-grid-building converter; Establishing a system model of the power system under operating conditions and recording it as a stable model, and extracting a state equation of a dynamic model of a grid-following-grid-building converter according to the stable model; Obtaining the variation relationship between the equivalent impedance of the inverter and the current, and obtaining the Thevenin equivalent circuit and the Norton equivalent circuit of the grid-following type and grid-forming type converters respectively according to the variation relationship; Obtain the topology structure and control strategy of the converter, and model the converter according to the topology structure and control strategy to obtain a topology model and a strategy model; Obtain the frequency response characteristics of the converter, and combine the topology model and the strategy model to obtain the influence of the frequency response characteristics on the control strategy on the dynamic characteristics; The full-condition nonlinear dynamic impedance model of the grid-following-grid-building converter is constructed by combining the state equation, Thevenin equivalent circuit, Norton equivalent circuit and the degree of influence.

3. A method for analyzing power system stability based on energy storage converter according to claim 2, characterized in that: The steps of obtaining the frequency band distribution law of dynamic impedance according to the dynamic impedance model analysis and obtaining the frequency band dominant factor according to the frequency band distribution law of dynamic impedance analysis include the following steps: Obtaining the electromagnetic time scale stability of the power system, and establishing an impedance model of the entire system according to the electromagnetic time scale stability; According to the full-operating nonlinear dynamic impedance model of the grid-following and grid-building converters, the impedance stability analysis method of the protection mapping theory is used, and the complementary space of the electromagnetic time scale stable region of the system stable operation is obtained in combination with the impedance forbidden region judgment basis. According to the complementary space, different line impedances are selected to obtain different characteristics of the dynamic impedance of the power system in different frequency bands and form the frequency band distribution law of the dynamic impedance; According to the frequency band distribution law of dynamic impedance, the corresponding frequency band dominant factor is found.

4. A method for analyzing power system stability based on energy storage converter according to claim 3, characterized in that: The steps of respectively establishing mapping relationships between the relaxed node voltage and current and the dynamic impedances of the grid-following and grid-forming converters include the following steps: Extracting impedance angle data according to the full-operating impedance model of the grid-following-grid-building converter, and determining the stability of the impedance angle according to the impedance angle data; Establish the active-reactive power relationship of the power system and obtain the reactive power change curve of the system; Combining the stability of the impedance angle and the reactive power variation curve, a correlation curve between the system stability and the stability of the impedance angle is obtained and recorded as a system-impedance curve; Finding a balance point of the power system and obtaining an impedance angle range at the balance point; The changing relationship between the active power and reactive power of the power system is obtained, and the mapping relationship between the voltage and current of the relaxation node and the dynamic impedance of the grid-following and grid-forming converters is established according to the changing relationship.

5. A method for analyzing power system stability based on energy storage converter according to claim 4, characterized in that: The steps of obtaining the change relationship between the active power and reactive power of the power system and establishing the mapping relationship between the voltage and current of the relaxation node and the dynamic impedance of the grid-following and grid-forming converters according to the change relationship include the following steps: According to the change relationship, the changes of the inverter output voltage and current are obtained and recorded as a voltage change curve and a current change curve respectively; Finding a slack node of the power system, and judging whether the system can return to a stable state according to the impedance angle range and current change curve of the slack node; If the system can return to a stable state, a mapping relationship between the relaxed node voltage and the dynamic impedance of the grid-following converter is established according to the voltage change curve and the impedance angle range; According to the voltage variation curve and the impedance angle range, a mapping relationship between the relaxed node voltage and the dynamic impedance of the grid-forming converter is established; A mapping relationship between the relaxation node current and the dynamic impedance of the grid-following converter is established according to the current variation curve and the impedance angle range; The mapping relationship between the relaxation node current and the dynamic impedance of the grid-type converter is established according to the current variation curve and the impedance angle range.

6. A method for analyzing power system stability based on energy storage converter according to claim 5, characterized in that: The steps of identifying the weak links of the power system and obtaining the instability factors of the power system according to the weak links include the following steps: Acquire sample data of the power system, and construct a self-evolution learning model according to the sample data; Identify weak links in power systems based on self-evolving learning models; The dominant factor of instability is determined based on the weak link and recorded as the instability factor.

7. A method for analyzing power system stability based on energy storage converter according to claim 6, characterized in that: The steps of obtaining sample data of the power system and constructing a self-evolution learning model according to the sample data include the following steps: Acquiring broadband oscillation data, and extracting oscillation samples according to the broadband oscillation data; Preprocessing oscillation samples of different frequencies to obtain processed samples, wherein the preprocessing includes data normalization and feature extraction; An impedance angle model is constructed according to the processed samples, and impedance angle characteristics are extracted according to the impedance angle model; A self-evolving data model is constructed based on the system-impedance curve.

8. A method for analyzing power system stability based on energy storage converter according to claim 7, characterized in that: The steps of identifying the weak links of the power system according to the self-evolution learning model include the following steps: Determine whether the system has potential instability risks based on the self-evolving data model; If there is a risk of instability in the system, the instability cause set of each link of the power system is obtained; Determine the system broadband oscillation instability boundary based on the power system oscillation mechanism, conditions and judgment basis; According to the instability boundary, the basic instability cause is determined from the instability cause set, and the link of the power system prone to oscillation is obtained according to the basic instability cause and recorded as the weak link.

9. A method for analyzing power system stability based on energy storage converter according to claim 8, characterized in that: The steps of determining the dominant instability factor based on the weak link and recording it as the instability factor include the following steps: According to the transient and stable energy transfer laws of the power system, the voltage and current at the fault point caused by oscillation and instability of the system are analyzed; Analyze the stability of each part of the power system according to the voltage and current, and select the unstable part according to the stability; According to the wide-band oscillation stability criterion of the power system and the three major stability criteria of voltage, frequency and power angle of the traditional power system, the relationship between different influencing factors and the stability of the power system is determined; The dominant factor of instability is confirmed based on the stability of the unstable part.

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