A method for power system risk situation assessment and defense control

Abstract

The present invention discloses a method for power system risk situation assessment and defense control, comprising the following steps: analyzing the power imbalance risk of a new power system and defining the safe operation boundary of the power grid; proposing a power grid safety situation assessment index and establishing a power grid frequency safety situation assessment model; taking into account the changes in load inertia and fault impact curves, establishing a power grid day-ahead operation mode optimization and adjustment model; considering the risk of unexpected intraday source and load fluctuations, establishing a power grid online operation risk classification and pre-control model; and performing risk assessment, optimization correction and defense control on the power grid operation mode based on the above model. Furthermore, a new power system power imbalance situation assessment, operation mode optimization control and safety risk classification defense method is proposed. This method can effectively assess the power imbalance risk situation of the power grid, correct the safe operation domain of the power grid, and realize active defense of the power grid security risk, and has engineering application value.

Description

Technical Field

[0001] The present invention relates to the field of power systems, and in particular to a method for risk situation assessment and defense control of power systems. Background Art

[0002] With the rapid development of new power systems, renewable energy sources are gradually becoming the majority of installed capacity. Thermal power is shifting from a primary power source to a regulating and supporting power source, and the foundations of the power system are undergoing profound changes. The rapid development of renewable energy is leading to an increasing risk of probabilistic imbalances and a continuous decrease in system rotational inertia. The existing power system regulation model is unable to support the power balance of the new power system, and the frequency security risk of the power grid continues to rise. To enhance the power system's "climate resilience, security resilience, and regulatory flexibility," the power grid's operational control model urgently needs to transition from a passive mode of operation and defense based on established plans to an active defense mode based on situation assessment and trend analysis.

[0003] The power balance security status of a power grid involves both power balance and frequency stability. The main factors influencing the power balance status include source-load fluctuations, power supply regulation capabilities, and energy storage regulation capabilities, reflecting the power system's real-time source-load balance capabilities during certain periods. Frequency stability is primarily influenced by system inertia, fault impact, and frequency regulation capabilities. Its security constraints involve multiple indicators related to inertia response, transients, and quasi-steady-state processes. Existing research has established a solid foundation for power balance security. For power balance, evaluation indicators such as peak shaving adequacy and peak shaving capacity ratio have been proposed. For frequency security, safety constraints such as rate of change of frequency (RoCoF), lowest frequency of transient (LFoT), and frequency deviation of quasi-stable state (FDoQS) have been proposed. However, these indicators are primarily used as evaluation indicators of local system characteristics or as safety constraints for power grid operation, and therefore fail to reflect the overall security level of the power grid. In terms of guiding the safe operation of the frequency of new power systems, it is urgent to establish a systematic and comprehensive security situation characteristic cognition system to accurately and quantitatively characterize the security situation of the power grid and provide a decision-making basis for the safe correction of the power system operation mode and active defense control.

[0004] Existing research still has two shortcomings. First, mode verification often only considers the impact of power source inertia, and insufficient consideration is given to load models and real-time changes in load inertia. The risk of system fault impact is also not fully accounted for, resulting in insufficient frequency safety verification accuracy. Second, it does not consider unexpected fluctuations in sources and loads. When the established operation plan poses a power imbalance risk, how to make online decisions on the grid's operation mode and defense measures. It is urgent to propose operation mode optimization correction and fault defense control decision-making methods for different types of power imbalance risks in the power grid to improve the frequency security level of new power systems. Summary of the Invention

[0005] The purpose of the present invention is to propose a method for risk situation assessment and defense control of a power system, so as to improve the technical problems of insufficient risk situation assessment and defense control methods in existing power systems.

[0006] To solve the above technical problems, the present invention provides a method for power system risk situation assessment and defense control, comprising the following steps:

[0007] Step 1: Analyze the power imbalance risk of the new power system and define the safe operation boundary of the power grid;

[0008] Step 2: Propose grid security situation assessment indicators and establish a grid frequency security situation assessment model;

[0009] Step 3: Considering the changes in load inertia and fault impact curves, establish a grid day-ahead operation mode optimization adjustment model;

[0010] Step 4: Considering the risk of unexpected fluctuations in daily load and source, a risk classification and pre-control model for online power grid operation is established;

[0011] Step 5: Based on the above model, risk assessment, optimization correction and defense control of the power grid operation mode are carried out.

[0012] Among them, in step 1, the entire frequency regulation process of the new power system includes six safety constraints: steady-state frequency safety constraints CtIPG and CtRPG, transient frequency safety constraints RoCoF, LFoT, FDoQS, and quasi-steady-state frequency safety constraints FRC; the definition of the safe operation boundary of the power grid is: the CtIPG should be greater than the random upward fluctuation value of the system net load, the CtRPG should be greater than the random downward fluctuation value of the system net load, and its critical safety constraint is to meet the flexible adjustment demand value of the net load under the confidence level β. The critical safety constraints of the RoCoF, LFoT, and FDoQS are predetermined values, and the critical safety constraint of the FRC is that after a frequency regulation is completed once, the system's additional power within a period of time is not less than the system's unbalanced power.

[0013] In step 2, the power grid security situation assessment indicators include primary risk indicators and secondary risk indicators. The primary risk indicators include:

[0014] (1) CtIPG margin ratio

[0015]

[0016] Where: is the CtIPG margin ratio of the system at time t; F t,up 、Rn t,up are the upward flexibility demand and the total upward flexibility reserve of the system at time t, respectively;

[0017] (2) CtRPG margin ratio

[0018]

[0019] Where: is the CtRPG margin ratio of the system at time t; F t,dn 、Rn t,dn are the system's downward flexibility demand and total downward flexibility reserve at time t, respectively;

[0020] The secondary risk indicators include:

[0021] (1)RoCoF margin ratio

[0022]

[0023] Where: is the RoCoF margin ratio of the system at time t; τ max is the maximum frequency change rate of the system; τ t is the frequency change rate of the system at time t;

[0024] (2) LFoT margin ratio

[0025]

[0026] Where: is the LFoT margin ratio of the system at time t; Δf m is the maximum deviation limit of the system frequency; f t min is the lowest frequency of the system at time t;

[0027] (3) FDoQS margin ratio

[0028]

[0029] Where: is the FDoQS margin ratio of the system at time t; is the quasi-steady-state frequency deviation safety limit of the system; f t ss is the quasi-steady-state frequency deviation of the system at time t;

[0030] (4) FRC margin ratio

[0031]

[0032] Where: is the FRC margin ratio of the system at time t; F t,SFR 、Rn t,SFR are the secondary frequency regulation demand and total secondary frequency regulation reserve of the system at time t respectively.

[0033] Furthermore, the first-level risk indicator and the second-level risk indicator are defined as:

[0034]

[0035] Where: are the six security situation indicators of the system at time t;

[0036] The power grid frequency security situation assessment model is:

[0037]

[0038] Where: SR t , FR t , TR t are the first-level risk situation, second-level risk situation, and overall safety situation of the system at time t respectively; χ is the margin ratio when the system is in a critical safety state; when evaluating the security situation of a certain period, if there is a risk sub-indicator less than 0, the security situation is defined as -1, and the period is judged to be in a risky state; if all risk sub-indicators are greater than 0, but there is a risk sub-indicator between 0 and χ If all risk sub-indicators are greater than χ , then the security situation is defined as 1, and it is determined that the period is in a safe state.

[0039] In step 3, the method for establishing the power grid day-ahead operation mode optimization adjustment model is as follows:

[0040] S1. Track the day-ahead operation mode of the power grid and perform a frequency safety check before putting it into operation. Taking into account the motor load curve and the fault impact curve, the power grid frequency safety situation assessment model is used to conduct a risk assessment of the day-ahead operation mode of the power grid. Before the assessment, the power market clearing mode includes the start and stop of thermal power units, the output of thermal power units, the system reserve reserve, and the wind and solar load curtailment limit. If the day-ahead operation mode of the power grid is in an unsafe operation domain, the day-ahead operation mode of the power grid is optimized and adjusted by adding energy storage adjustment without changing the start and stop status of the thermal power units. The corrected day-ahead operation mode of the power grid includes the output of thermal power units, the system reserve reserve, the wind and solar load curtailment limit, and the energy storage scheduling plan.

[0041] S2. The grid day-ahead operation mode optimization adjustment model takes the sum of unit output deviation penalty cost, new energy and load curtailment cost, system backup cost, and energy storage dispatch cost as the optimization goal, and sets the objective function:

[0042]

[0043] Where: is the sum of the output deviation penalty costs of all units at time t; is the cost coefficient for adjusting the output of unit g; ΔP g,t is the output adjustment of unit g at time t; is the total abandonment cost of the system at time t; are the wind curtailment, solar curtailment and load shedding costs of the system at time t; δ w , δ v , δ d are the system's wind curtailment, solar curtailment and load shedding cost coefficients respectively; P t w 、P t v 、P t d are the total wind curtailment, solar curtailment and load shedding of the system at time t respectively; is the dispatch cost of energy storage at time t; C ess is the one-time purchase cost of energy storage; P ess,t is the energy storage power at time t; S ess is the service life of energy storage; E ess,t is the energy storage capacity at time t; are the total upward and downward flexible reserve costs of the system at time t, as well as the primary and secondary frequency regulation reserve costs; X up 、X dn 、X pfr 、X sfr They are the system's upward and downward flexible reserve cost coefficients and the primary and secondary frequency regulation reserve cost coefficients; They are the upward and downward flexibility reserves and the primary and secondary frequency regulation reserves provided by energy storage at time t; T is the dispatch period; ΔT is the dispatch interval.

[0044] In step 4, the method for establishing the grid online operation risk classification pre-control model is as follows:

[0045] S1. During the intraday optimization scheduling phase, with a fixed number of hours as the operation mode update cycle, taking into account the net load forecast curve, the grid frequency security situation assessment model is used to conduct a risk assessment of the established grid operation mode, and formulates grid online operation risk classification and pre-control measures;

[0046] S2. The grid online operation risk classification and prevention measures include establishing a first-level grid online operation risk prevention model and a second-level grid online operation risk prevention model. The established grid operation mode shall first pass the first-level risk verification. The first-level risk prevention measures include optimizing the start-up and shutdown of thermal power units, energy storage call plans, and wind and solar load curtailment plans. If the grid does not have a first-level risk, it shall pass the second-level risk verification. The second-level risk prevention measures include optimizing the start-up and shutdown of thermal power units, energy storage call plans, and low-frequency load reduction strategy plans. If the first-level risk situation and the second-level risk situation of the established grid operation mode are both in the safe operation domain, the established grid operation mode may be used to guide grid operation within the fixed number of hours in the future.

[0047] Furthermore, the grid online operation first-level risk pre-control model takes the minimization of the sum of unit start-up and shutdown and output costs, new energy and load curtailment costs, system backup costs, and energy storage scheduling costs within the online scheduling cycle as the optimization goal, and sets the objective function:

[0048]

[0049] Where: Δt is the online scheduling period; is the sum of the power generation and start-up and shutdown costs of all units in the system at time t; C g (P g,t ) is the power generation cost of unit g at time t; is the start-up and shutdown cost of unit g at time t.

[0050] Furthermore, the grid day-ahead operation mode optimization and adjustment model and the grid online operation first-level risk pre-control model have the following constraints:

[0051] (1) Power balance constraints:

[0052]

[0053] (2) Thermal power operation constraints:

[0054]

[0055] Where: T on,g 、T off,g are the minimum start and stop time of unit g respectively; t_{on} and t_{off} are the sets of corresponding time points of the unit start and stop states respectively;

[0056] (3) Energy storage operation constraints:

[0057] P ess,t =P D,t -P C,t

[0058] 0≤P C,t ≤μ C,t P C,max

[0059] 0≤P D,t ≤μ D,t P D,max

[0060] E ess,t+1 =E ess,t +η C P C,t -P D,t / η D

[0061] μ C,t +μ D,t ≤1

[0062] E ess,min ≤E ess,t ≤E ess,max

[0063] E ess,1 =E ess,T

[0064] Where: P C,t 、P D,t are the charging and discharging power of the energy storage at time t; μ C,t 、μ D,t are the charge and discharge states of the energy storage at time t; P C,max 、P D,max are the maximum charge and discharge power limits of energy storage; η C ,η D are the charging and discharging efficiency of energy storage; E ess,max 、E ess,min are the maximum and minimum limits of energy storage capacity respectively; E ess,1 、E ess,T are the initial and final capacities of energy storage respectively;

[0065] (4) System peak load constraints:

[0066] The sum of the up / down regulation reserves provided by thermal power and energy storage should be greater than the system's up / down regulation requirements;

[0067]

[0068] (5) Frequency safety constraints:

[0069] The following are the system's frequency minimum point constraint, frequency change rate constraint, quasi-steady-state frequency deviation constraint, and quasi-steady-state frequency recovery constraint:

[0070]

[0071]

[0072] (6) Alternate split constraints:

[0073] Thermal power and energy storage provide upward flexibility reserves, primary frequency regulation reserves, and secondary frequency regulation reserves, which together divide the system's upward regulation capacity.

[0074]

[0075] (7) Current safety constraints:

[0076]

[0077] Where: U g 、U w 、U v 、U d 、U e are the power flow transfer factors of the unit, wind power, photovoltaic, load and energy storage respectively; P br,max is the power transmission limit of the line.

[0078] Furthermore, the grid online operation secondary risk pre-control model takes the minimization of the sum of unit start-up and shutdown and output costs, renewable energy and load curtailment costs, system backup costs, energy storage scheduling costs, and low-frequency load reduction costs within the online scheduling cycle as the optimization goal, and sets the objective function:

[0079]

[0080] Where: is the low-frequency load reduction cost of the system at time t; δ shd is the system's low-frequency load reduction penalty coefficient; P t shd is the total underfrequency load reduction of the system at time t.

[0081] Furthermore, the grid online operation secondary risk pre-control model has the following constraints:

[0082] (1) Power balance constraints:

[0083]

[0084] (2) Thermal power operation constraints:

[0085]

[0086] Where: T on,g 、T off,g are the minimum start and stop time of unit g respectively; t_{on} and t_{off} are the sets of corresponding time points of the unit start and stop states respectively;

[0087] (3) Energy storage operation constraints:

[0088] P ess,t =P D,t -P C,t

[0089] 0≤P C,t ≤μ C,t P C,max

[0090] 0≤P D,t ≤μ D,t P D,max

[0091] E ess,t+1 =E ess,t +η C P C,t -P D,t / η D

[0092] μ C,t +μ D,t ≤1

[0093] E ess,min ≤E ess,t ≤E ess,max

[0094] E ess,1 =E ess,T

[0095] Where: P C,t 、P D,t are the charging and discharging power of the energy storage at time t; μ C,t 、μ D,t are the charge and discharge states of the energy storage at time t; P C,max 、P D,max are the maximum charge and discharge power limits of energy storage; η C ,η D are the charging and discharging efficiency of energy storage; E ess,max 、E ess,minare the maximum and minimum limits of energy storage capacity respectively; E ess,1 、E ess,T are the initial and final capacities of energy storage respectively;

[0096] (4) System peak load constraints:

[0097] The sum of the up / down regulation reserves provided by thermal power and energy storage should be greater than the system's up / down regulation requirements;

[0098]

[0099] (5) Frequency safety constraints:

[0100] The following are the system's frequency minimum point constraint, frequency change rate constraint, quasi-steady-state frequency deviation constraint, and quasi-steady-state frequency recovery constraint:

[0101]

[0102] (6) Alternate split constraints:

[0103] Thermal power and energy storage provide upward flexibility reserves, primary frequency regulation reserves, and secondary frequency regulation reserves, which together divide the system's upward regulation capacity.

[0104]

[0105] (7) Current safety constraints:

[0106]

[0107] Where: U g 、U w 、U v 、U d 、U e are the power flow transfer factors of the unit, wind power, photovoltaic, load and energy storage respectively; P br,max is the power transmission limit of the line.

[0108] Compared with the prior art, the beneficial technical effects of the present invention are:

[0109] The power system risk situation assessment and defense control method proposed in this application can effectively assess the power imbalance risk situation of the power grid, correct the safe operation domain of the power grid, and realize active defense of power grid security risks, which has engineering application value. Among them, based on case analysis and verification, the frequency security situation assessment model can comprehensively assess the operation risk of the power grid and intuitively characterize the power grid security situation; the day-ahead operation mode optimization and adjustment model can effectively correct the power market clearing operation mode, ensure that the day-ahead operation mode of the power grid is in the safe operation domain, and improve the economic efficiency of system operation; the online operation risk hierarchical pre-control model can effectively deal with the frequency security risk under the unexpected fluctuation of source and load, and realize hierarchical pre-control of online power grid operation risk.

[0110] The frequency security situation assessment model proposed in this application can effectively verify the safe operation situation of the power grid and realize the hierarchical assessment and early warning of the power grid operation risks; the day-ahead operation mode safety verification method proposed in this application can make full use of the system's adjustable resources to achieve a dual improvement in the system's economic efficiency and safety; the power grid operation risk hierarchical pre-control method proposed in this application can effectively respond to various risks of online power grid operation and realize hierarchical defense control of different types of risks. The power imbalance risk hierarchical assessment and defense control model proposed in this application is closely integrated with engineering practice scenarios, is practical and effective, has obvious advantages over many other risk defense control models, and provides a new idea for risk prevention and control in the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] Figure 1 is a flow chart of the steps of the method of the present invention;

[0112] Figure 2 Schematic diagram of the grid frequency regulation process of the present invention;

[0113] Figure 3 A schematic diagram of frequency security risks faced by the power grid operation of the present invention;

[0114] Figure 4 This is a schematic diagram of the multi-dimensional indicators of power grid frequency security of the present invention;

[0115] Figure 5 This is a flow chart of the safety check idea of ​​the present invention;

[0116] Figure 6 Develop a flow chart for the hierarchical preventive measures of the present invention;

[0117] Figure 7 This is the wind, light and load prediction curve diagram of the present invention;

[0118] Figure 8 is a motor load ratio curve diagram of the present invention;

[0119] Figure 9is a failure risk impact curve diagram of the present invention;

[0120] Figure 10 This is a schematic diagram of the calculated values ​​of the sub-indicators before optimization of the present invention;

[0121] Figure 11 This is a schematic diagram of comprehensive security situation assessment before optimization of the present invention;

[0122] Figure 12 This is a radar diagram of the security situation before optimization of the present invention;

[0123] Figure 13 This is a schematic diagram of the calculated values ​​of the optimized sub-indicators of the present invention;

[0124] Figure 14 This is a schematic diagram of the comprehensive evaluation of security situation after optimization of the present invention;

[0125] Figure 15 This is the optimized security situation radar map of the present invention;

[0126] Figure 16 This is a schematic diagram of the comparison of the net load curve within the day before the present invention;

[0127] Figure 17 A schematic diagram showing a comparison between the power balance requirement and the adjustable capacity of the system according to the present invention;

[0128] Figure 18 A schematic diagram showing the comparison between the system frequency modulation demand and the remaining frequency modulation reserve of the present invention;

[0129] Figure 19 A radar diagram of the safety situation before online pre-control of the present invention;

[0130] Figure 20 This is a radar chart of the safety situation after online pre-control of the present invention. DETAILED DESCRIPTION

[0131] In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically limited. In the embodiments of the present application, all directional indications (such as up, down, left, right, front, back, top, bottom ...) are only used to explain the relative position relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or Internet of Things terminal that includes a series of steps or units is not limited to the listed steps or units, but optionally also includes steps or units that are not listed, or optionally also includes other steps or units inherent to these processes, methods, products or Internet of Things terminals.

[0132] In addition, references to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0133] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. It should be noted that the numerical values ​​described in this application should not be fixed values. The numerical values ​​are only example values ​​and should not be limited to the scope of protection of this application. The relevant numerical data of this application can be determined according to the specific situation of the power grid.

[0134] To address frequency security risks caused by source-load fluctuations and fault shocks, this paper focuses on the supply, absorption, and safety issues of new power systems. It conducts research from three perspectives: safety characteristic assessment, system operation control, and active fault prevention. It analyzes the types of disturbances that can cause power imbalances in the power grid, proposes safety assessment indicators covering the entire frequency regulation process, and establishes a hierarchical and quantitative assessment model for security status. On this basis, it constructs an efficient deduction and analysis decision-making model for the power grid's operational status, accurately grasps the power grid's safe operating margin, optimizes the power grid's short-cycle and real-time operating modes, and fault prevention strategies, achieving precise situation assessment, efficient operation control, and active fault prevention, supporting the safe, stable, and economical operation of new power systems.

[0135] The purpose of the present invention is to propose a power system risk situation assessment and defense control method to improve the shortcomings of the existing power system risk situation assessment and defense control method, define the safe operation boundary based on six safety constraint indicators related to power grid frequency fluctuations, propose a power grid active frequency safety risk grading assessment indicator, and based on this, establish a power grid security situation assessment model, establish an optimization adjustment model for the day-ahead operation mode, and establish a power grid security defense graded control model when the source and load fluctuate beyond expectations, and then propose a new power system power imbalance situation assessment, operation mode optimization control and safety risk graded defense method.

[0136] like Figure 1 The present invention provides a method for risk assessment and defense control of a power system, as shown in the flowchart of the present application. The specific steps are as follows:

[0137] Step 1: Analyze the power imbalance risk of the new power system and define the safe operation boundary of the power grid;

[0138] A power imbalance disturbance analysis is conducted on the power imbalance risk of the new power system. The new power system has the characteristics of random source and load fluctuations, and its frequency disturbance mode can be divided into two types: steady-state source and load fluctuations and transient fault impacts.

[0139] like Figure 2 As shown, source-load fluctuation is the risk of system frequency fluctuation that occurs when the random fluctuation of source load exceeds the flexible regulation capability of the power grid, and manifests itself in two forms: upward fluctuation or downward fluctuation. For large power grids, when the frequency fluctuation caused by source-load fluctuation is within the range of 50±0.1Hz, the system frequency level is considered to be within the limit. Source-load fluctuation disturbances may occur in the entire process of system frequency regulation, including steady-state, transient and quasi-steady-state, and are characterized by long duration and slow frequency fluctuations. Fault shock is the risk of frequency rapidly dropping (or rising) due to instantaneous power imbalance when a transient fault occurs in the power grid, exceeding the transient frequency safety constraint. It is characterized by short duration and rapid frequency change.

[0140] In new power systems, the two types of frequency disturbance risks can occur independently or in combination. Given that high-frequency generator shedding can effectively control transient increases in system frequency, the primary consideration is to mitigate the risk of system frequency reduction.

[0141] like Figure 3As shown in the figure, under the dual disturbances of source-load fluctuations and fault shock risks, the frequency regulation process of the new power system includes six safety constraints: capacity to increase power generation (CtIPG), capacity to reduce power generation (CtRPG), rate of change of frequency (RoCoF), lowest frequency of transient (LFoT), frequency deviation of quasi-stable state (FDoQS), and frequency recovery capacity (FRC). Among them, the capacity to increase power generation is the upward flexible regulation reserve that the system can provide when the grid faces random upward fluctuations in net load; the capacity to reduce power generation is the downward flexible regulation reserve that the system can provide when the grid faces random downward fluctuations in net load; the frequency change rate is the rate of change of system frequency after the grid suffers a transient shock; the lowest frequency of transient is the minimum limit of the system frequency drop after the grid suffers a transient shock; the quasi-stable frequency deviation is the deviation of the system frequency from the initial operating frequency after the grid completes a frequency regulation; and the frequency recovery capacity is the frequency recovery capacity of the system.

[0142] exist Figure 2-Figure 3 In the equation, f0 represents the initial operating frequency of the power grid. Indicates the system frequency after the power grid suffers a frequency-increasing disturbance. represents the system frequency after the power grid suffers a frequency reduction disturbance, f min represents the lowest frequency of the system after the power grid suffers a transient disturbance, Δf0 represents the deviation between the quasi-steady-state frequency of the power grid and the initial operating frequency, t1 represents the initial moment when the power grid suffers a transient disturbance, t2 represents the moment when the primary frequency regulation of the power grid begins to work, and t m It represents the time when the grid frequency reaches the lowest point, t3 represents the initial time when the grid enters the quasi-steady-state stage, t4 represents the end time of the grid frequency regulation response, and t5 represents the end time when the grid recovers to the steady-state stage after suffering a disturbance.

[0143] When the steady-state frequency safety constraints CtIPG and CtRPG exceed the limit, the system's flexible peak-shaving capability is insufficient and there is a risk of frequency fluctuation; when the transient frequency safety constraints RoCoF, LFoT, and FDoQS exceed the limit, the system's fault frequency support capability is insufficient and there is a risk of frequency instability; when the quasi-steady-state frequency safety constraint FRC exceeds the limit, the system's frequency recovery capability is insufficient and there is a risk of long-term low-frequency operation after a fault.

[0144] To ensure the safety of the entire system frequency regulation process and define the safe frequency operation boundaries, CtIPG should be greater than the random upward fluctuation value of the system net load, and CtRPG should be greater than the random downward fluctuation value of the system net load. Their critical safety constraints can be expressed as meeting the flexible regulation requirements of the net load under a certain confidence level β. In this invention, β is set to 95%. The critical safety constraints of RoCoF, LFoT, and FDoQS are generally defined as certain predetermined values. The critical safety constraint of FRC is that after a frequency regulation is completed, the system's additional power within a certain period of time must be no less than the system's unbalanced power.

[0145] For transient frequency safety constraints RoCoF, LFoT, and FDoQS, their safety levels are affected by multiple factors such as fault impact, power supply inertia, load model, and primary frequency regulation capability. These factors should be fully considered in system safety assessment.

[0146] like Figure 4 As shown, when all six system safety constraints satisfy the critical safety constraint, the system operates in the safe operating domain. When any indicator falls below the critical safety stability requirement, the system faces a frequency safety risk. The system's steady-state, transient, and quasi-steady-state frequency safety constraints are inherently interrelated. The adequacy of FRC capacity should be considered based on the adequacy of steady-state and transient frequency regulation capabilities; the system's transient frequency safety should be based on steady-state frequency safety. Furthermore, when the system's frequency regulation capability cannot address both the source-load fluctuation risk and the fault impact risk, the regulation capability should be prioritized to address the first of these two risks.

[0147] Considering that the system must first meet power balance requirements before further addressing frequency security risks, this paper defines steady-state frequency security risks (CtIPG, CtRPG) as primary risks and transient and quasi-steady-state frequency security risks (RoCoF, LFoT, FDoQS, FRC) as secondary risks. Given the coupled relationship between the six security constraints, the security constraints and system operational economics should be considered in a coordinated manner to rationally formulate grid operation modes and ensure that the grid operates within a safe and economical domain.

[0148] Step 2: Propose grid security situation assessment indicators and establish a grid frequency security situation assessment model;

[0149] In order to quantitatively evaluate the safe operation status of the power grid, Figure 4 The first-level risk indicators and second-level risk indicators shown in are defined separately. Considering that the hot standby power supply needs to meet the peak load demand of the system, the margin ratios of CtIPG and CtRPG are defined as the first-level risk indicators; in order to assess the frequency security level of the power grid when facing the risk of fault impact, the margin ratios of RoCoF, LFoT, FDoQS, and FRC are defined as the second-level risk indicators. The details are as follows:

[0150] (1) CtIPG margin ratio

[0151]

[0152] Where: is the CtIPG margin ratio of the system at time t. t,up 、Rn t,up are the system's upward flexibility demand and the total amount of upward flexibility reserve at time t, respectively. The specific calculation formulas for the two are as follows:

[0153]

[0154] Where: The upward flexibility reserve provided to unit g at time t; is the maximum upward climbing ability of unit g; μ g,t For the crew g The start / stop state variable at time t is 1 when starting and 0 when stopping; g,max For the crew g The maximum technical output of P g,t For the crew g The actual output at time t; is the upper limit of the prediction interval of the net load of the system at time t under the confidence level β; P L,t is the net load power of the system at time t, which is defined as follows:

[0155] P L,t =P d,t -P w,t -P v,t (4)

[0156] Where: P w,t 、P v,t 、P d,t are the wind power, photovoltaic power and load power of the system at time t respectively.

[0157] (2) CtRPG margin ratio

[0158]

[0159] Where: is the CtRPG margin ratio of the system at time t; F t,dn 、Rn t,dn are the system's downward flexibility demand and the total downward flexibility reserve at time t, respectively. The specific calculation formulas for the two are as follows:

[0160]

[0161] Where: The downward flexibility reserve provided to unit g at time t; is the maximum downward climbing ability of unit g; P g,min is the minimum technical output of unit g; It is the lower limit of the prediction interval of the net load of the system at time t under the confidence level β.

[0162] (3)RoCoF margin ratio

[0163]

[0164] Where: is the RoCoF margin ratio of the system at time t; τ max is the maximum frequency change rate of the system, which is set to 1 Hz / s in the present invention; τ t is the frequency change rate of the system at time t, which is calculated as follows:

[0165]

[0166] Where: ΔP t is the power shock suffered by the system at time t; f0 is the initial frequency of the system; ρ t The system inertia coefficient is used to take into account the real-time changes in load inertia.

[0167] (4) LFoT margin ratio

[0168]

[0169] Where: is the LFoT margin ratio of the system at time t; Δf m is the maximum deviation limit of the system frequency, which is set to 0.5Hz in the present invention; f t min is the lowest frequency of the system at time t, and its calculation formula is shown in formula (11):

[0170]

[0171] Where: K g is the static power-frequency characteristic coefficient of unit g; T g is the comprehensive time constant of unit g; k D is the load regulation coefficient of the system.

[0172] (5) FDoQS margin ratio

[0173]

[0174] Where: is the FDoQS margin ratio of the system at time t; is the quasi-steady-state frequency deviation safety limit of the system, which is set to 0.2 Hz in the present invention; f tss is the quasi-steady-state frequency deviation of the system at time t, and its calculation formula is as follows:

[0175]

[0176] Where: D d is the damping coefficient of the load in the system; The primary frequency regulation reserve provided for unit g at time t is:

[0177]

[0178] Where: E g is the kinetic energy of unit g; η t is the motor load ratio of the system at time t; H d is the inertia coefficient of the load; α is the primary frequency regulation capability coefficient of the unit; M y (x) is the yth segment linear piecewise function of the unit’s primary frequency regulation capability.

[0179] (6) FRC margin ratio

[0180]

[0181] Where: is the FRC margin ratio of the system at time t; F t,SFR 、Rn t,SFR are the secondary frequency regulation demand and the total secondary frequency regulation reserve of the system at time t, respectively. The specific calculation formulas for the two are as follows:

[0182]

[0183] Where: The secondary frequency regulation reserve provided by unit g at time t. Considering that the secondary frequency regulation capability of the unit is limited by its own ramp rate and remaining regulation space:

[0184]

[0185] To facilitate the aggregation of sub-indicators of risk at different levels, the above indicators are defined as:

[0186]

[0187] Where: are the six security situation indicators of the system at time t.

[0188] By aggregating the values ​​of each sub-indicator, the power grid security situation assessment index system model is obtained as follows:

[0189]

[0190] Where: SR t, FR t , TR t are the first-level risk situation, second-level risk situation, and total safety situation of the system at time t; χ is the margin ratio when the system is in a critical safety state. For the convenience of calculation, the present invention takes 0.03; From formulas (20) to (22), it can be seen that when evaluating the safety situation of a certain period, if there is a risk sub-indicator less than 0, the safety situation is defined as -1, and the period is judged to be in a risky state; if all risk sub-indicators are greater than 0, but there is a risk sub-indicator between 0 and χ If all risk sub-indicators are greater than χ , then the security situation is defined as 1, and it is determined that the period is in a safe state.

[0191] Step 3: Considering the changes in load inertia and fault impact curves, establish a grid day-ahead operation mode optimization adjustment model;

[0192] The day-ahead operating mode of the power system is determined by the power market, and a frequency safety check is required before it is put into operation. This invention aims to track the day-ahead operating mode determined by the power market. Without changing the start and stop status of the units, it considers energy storage as a regulating resource of the system and optimizes and adjusts the day-ahead operating mode. The safety check idea is as follows: Figure 5 shown.

[0193] The optimization goal is to minimize the sum of the unit output deviation penalty cost, the new energy and load curtailment cost, the system backup cost, and the energy storage dispatch cost. The objective function is set as follows:

[0194]

[0195] Where: is the sum of the output deviation penalty costs of all units at time t; is the cost coefficient for adjusting the output of unit g; ΔP g,t is the output adjustment of unit g at time t; is the total abandonment cost of the system at time t; are the wind curtailment, solar curtailment and load shedding costs of the system at time t; δ w , δ v , δ d are the system's wind curtailment, solar curtailment and load shedding cost coefficients respectively; P t w 、P t v 、P t d are the total wind curtailment, solar curtailment and load shedding of the system at time t respectively; is the dispatch cost of energy storage at time t; C essis the one-time purchase cost of energy storage; P ess,t is the energy storage power at time t; S ess is the service life of energy storage; E ess,t is the energy storage capacity at time t; are the total upward and downward flexible reserve costs of the system at time t, as well as the primary and secondary frequency regulation reserve costs; X up 、X dn 、X pfr 、X sfr They are the system's upward and downward flexible reserve cost coefficients and the primary and secondary frequency regulation reserve cost coefficients; They are respectively the upward and downward flexibility reserves and the primary and secondary frequency regulation reserves provided by the energy storage at time t; T is the scheduling period, which is 24h in the present invention; ΔT is the scheduling interval, which is 1h in the present invention.

[0196] Set the constraints as follows:

[0197] (1) Power balance constraints:

[0198]

[0199] (2) Thermal power operation constraints:

[0200]

[0201] Where: T on,g 、T off,g are the minimum start and stop time of unit g respectively; t_{on} and t_{off} are the sets of corresponding moments of the unit start and stop states respectively.

[0202] (3) Energy storage operation constraints:

[0203] P ess,t =P D,t -P C,t (30)

[0204] 0≤P C,t ≤μ C,t P C,max (31)

[0205] 0≤P D,t ≤μ D,t P D,max (32)

[0206] E ess,t+1 =E ess,t +η C P C,t -P D,t / η D (33)

[0207] μ C,t +μ D,t ≤1 (34)

[0208] E ess,min ≤E ess,t ≤E ess,max (35)

[0209] E ess,1 =E ess,T (36)

[0210] Where: P C,t 、P D,t are the charging and discharging power of the energy storage at time t; μ C,t 、μ D,t are the charge and discharge states of the energy storage at time t; P C,max 、P D,max are the maximum charge and discharge power limits of energy storage; η C ,η D are the charging and discharging efficiency of energy storage; E ess,max 、E ess,min are the maximum and minimum limits of energy storage capacity respectively; E ess,1 、E ess,T are the initial and final capacities of energy storage respectively.

[0211] (4) System peak load constraints:

[0212] The sum of the up / down regulation reserves provided by thermal power and energy storage should be greater than the system's up / down regulation requirements.

[0213]

[0214] (5) Frequency safety constraints:

[0215] Equations (39) to (42) are the system's frequency minimum point constraint, frequency change rate constraint, quasi-steady-state frequency deviation constraint, and quasi-steady-state frequency recovery constraint, respectively.

[0216]

[0217] (6) Alternate split constraints:

[0218] The upward flexibility reserve, primary frequency regulation reserve and secondary frequency regulation reserve provided by thermal power and energy storage jointly divide the system's upward regulation capacity.

[0219]

[0220] (7) Current safety constraints:

[0221]

[0222] Where: Ug 、U w 、U v 、U d 、U e are the power flow transfer factors of the unit, wind power, photovoltaic, load and energy storage respectively; P br,max is the power transmission limit of the line.

[0223] Step 4: Considering the risk of unexpected fluctuations in daily load and source, a risk classification and pre-control model for online power grid operation is established;

[0224] In the intraday optimization scheduling stage, with 4 hours as the operation mode update cycle, the application assessment model is used to conduct risk assessment on the established operation mode, and hierarchical pre-control measures are formulated to achieve online active defense control of grid frequency security, and the optimization process is as follows: Figure 6 As shown. Figure 6 It can be seen that preventive control measures prioritize the defense against the first-level risks of the power grid. The defense measures include optimizing the start and stop of thermal power units, energy storage call plans, and wind and solar load curtailment plans. If there is no first-level risk in the power grid, the optimization of the start and stop of thermal power units, energy storage call plans, and low-frequency load reduction strategies are used to defend against the second-level risks of the power grid. If the first-level and second-level risk situations of the power grid's established operating mode are both in the safe operating domain, the established operating mode can be used to guide the power grid operation in the next 4 hours.

[0225] 1. Level 1 risk prevention model

[0226] The optimization goal is to minimize the sum of the unit start-up and shutdown and output costs, new energy and load curtailment costs, system backup costs, and energy storage scheduling costs within the online scheduling cycle, and the objective function is set as follows:

[0227]

[0228] Where: Δt is the online scheduling period, which is 4h in this invention; is the sum of the power generation and start-up and shutdown costs of all units in the system at time t; C g (P g,t ) is the power generation cost of unit g at time t; is the start-up and shutdown cost of unit g at time t.

[0229] The constraints set are consistent with those set in step 3, see equations (28) to (47).

[0230] 2. Secondary risk prevention model

[0231] The optimization goal is to minimize the sum of the unit start-up and shutdown and output costs, new energy and load curtailment costs, system backup costs, energy storage scheduling costs, and low-frequency load reduction costs within the online scheduling cycle, and the objective function is set as follows:

[0232]

[0233] Where: is the low-frequency load reduction cost of the system at time t; δ shd is the system's low-frequency load reduction penalty coefficient; P t shd is the total underfrequency load reduction of the system at time t.

[0234] The constraints set are consistent with those set in step 3, as shown in equations (28) to (47). However, considering that underfrequency load shedding is equivalent to offsetting the unbalanced power of the system by load shedding, the system frequency security constraints shown in equations (39) to (42) change as follows:

[0235] (1) Frequency minimum point constraint

[0236]

[0237] (2) Frequency change rate constraint

[0238]

[0239] (3) Quasi-steady-state frequency deviation constraint

[0240]

[0241] (4) Quasi-steady-state frequency recovery constraints

[0242]

[0243] Step 5: Based on the model established in the above steps, risk assessment, optimization correction and defense control of the power grid operation mode are carried out.

[0244] Example

[0245] The example is set up using the improved IEEE39 node. The example includes 7 thermal power units, 1 aggregate equivalent photovoltaic power plant, 1 aggregate equivalent wind farm, and 1 aggregate equivalent energy storage power station. The forecast curve of the new energy and load of the example is as follows: Figure 7 As shown in the figure, the time-varying characteristic curve of load inertia is as follows: Figure 8 As shown, the system transient impact power curve is as follows Figure 8 shown.

[0246] 1. Risk Assessment of the Day-Ahead Operation Mode of the Grid

[0247] Based on the frequency safety situation assessment model established in this application, the day-ahead operation mode is safety checked to determine whether it is in the safe operation domain. The six safety situation assessment sub-indicators of the day-ahead operation mode are as follows: Figure 10 As shown in the figure, the overall security situation of the system is as follows Figure 11 As shown. Figure 10-11 It can be seen that under the day-ahead operating mode, the CtRPG margin ratio is less than 0 in periods 2, 5, 16, and 21; the FDoQS margin ratio is less than 0 in periods 6-15, 17, and 22-23; and the FRC margin ratio is less than 0 in periods 3, 6-8, 10, and 19-20. This indicates that the system is in a safe state in periods 1 and 24; in a critical safety state in periods 4 and 18; in a level 1 risk state in periods 2, 5, 16, and 21; and in a level 2 risk state in periods 3, 6-15, 17, 19-20, and 22-23. Optimization and adjustment of the operating mode for these periods are necessary.

[0248] Taking time periods 1, 5, 17, and 18 as examples, the radar chart of the system security situation is as follows: Figure 12 As shown. Figure 12 It can be seen that the margin ratios of all sub-indicators of the system in period 1 are greater than 3%, which means the system is in a safe state; the CtRPG margin ratio in period 5 is less than 0, which means the system is in a level 1 risk state; the FDoQS margin ratio in period 17 is less than 0, which means the system is in a level 2 risk state; and the LFoT and FDoQS margin ratios in period 18 are greater than 0 and less than 3%, which means the system is in a critical safety state.

[0249] In summary, the frequency security situation assessment model can comprehensively evaluate the grid operation risks and intuitively characterize the grid security situation.

[0250] 2. Optimization and Adjustment of the Current Operation Mode

[0251] Based on the above safety verification results, the day-ahead operation mode is safety corrected taking into account the regulation capability of energy storage resources.

[0252] 1. Economic comparison

[0253] The dispatch costs before and after the day-ahead operation mode adjustment are shown in Table 1:

[0254] Table 1 Comparison of scheduling costs before and after adjustment

[0255]

[0256] As shown in Table 1, after energy storage is involved in regulation, the system's start-up and shutdown operating costs are reduced by 8.79%, the flexibility reserve cost increases by 0.43%, the frequency regulation reserve cost increases by 5.31%, the source and load curtailment cost decreases by 97.3%, and the total dispatch cost decreases by 5.52%.

[0257] In summary, although the optimized operation mode increases the energy storage dispatching and operating costs, it alleviates the peak and frequency regulation pressure of thermal power, significantly reduces the curtailment of wind and solar power, and improves the economic efficiency of system operation.

[0258] 2. Security comparison

[0259] The six security situation assessment sub-indicators after the recent adjustment of the operation mode are as follows: Figure 13 As shown in the figure, the overall security situation of the system is as follows Figure 14 As shown. Figure 13-14 It can be seen that after the optimization and adjustment of the operating mode a few days ago, the margin ratios of all sub-indicators are greater than 0. It can be determined that the system is in a critical safety state in time periods 4, 7, 11, 13-14, 17, and 23, and is in a safe state in other time periods. The operating risk of the system has been eliminated.

[0260] Taking time periods 1, 5, 17, and 18 as examples, the security situation radar chart of the system after optimization and adjustment is as follows: Figure 15 As shown. Figure 15 It can be seen that after the optimization and adjustment of the day-ahead method, the margin ratios of all sub-indicators in periods 1, 5, and 18 are greater than 3%, indicating a safe state; the margin ratios of CtRPG, LFoT, and FDoQS in period 17 are greater than 0 and less than 3%, indicating a critical safety state.

[0261] In summary, the day-ahead operation mode optimization and adjustment strategy proposed in this application can effectively correct the electricity market clearing operation mode and ensure that the day-ahead operation mode of the power grid is in a safe operating domain.

[0262] 3. Formulation of risk-grading and preventive control measures for online operations

[0263] During online grid operation, the net load curve is subject to the risk of unexpected fluctuations. In such cases, the established day-ahead operating model cannot guarantee the grid remains within a safe operating range. Therefore, it is necessary to conduct an online assessment of the grid frequency security situation and formulate preventive control measures at different levels.

[0264] The evaluation model of this application is used to analyze the trend of the net load forecast curve. Taking 4 hours as the online scheduling cycle and time period 6 as the initial online operation time t, the net load curve appears as follows in time period t~t+4: Figure 16 The system security situation comparison curve chart shows the changes.

[0265] Analyze the security situation of the power grid during the day. When the net load forecast curve changes significantly, the system's power balance demand and adjustable capacity are compared. Figure 17 As shown. Figure 17 It can be seen that the system's adjustable capacity in time periods 1 to 2 cannot meet the system's power balance needs, and first-level risk prevention measures need to be taken. The adjustable capacity reserved in time periods 3 to 4 can meet the system's power balance needs, and it is necessary to conduct second-level risk verification.

[0266] Considering that the system's adjustable capacity gives priority to meeting the power balance demand, and the remaining capacity is used to deal with secondary risks, the remaining frequency regulation reserve and system frequency regulation demand in periods 3 to 4 are compared. Figure 18 As shown. Figure 18It can be seen that the secondary frequency regulation reserve remaining in the system in time period 3 cannot meet the secondary frequency regulation demand of the system, and the primary and secondary frequency regulation reserves remaining in time period 4 cannot meet the primary and secondary frequency regulation demand of the system. Secondary risk prevention measures need to be taken.

[0267] Before taking preventive measures, the system's security situation radar chart is as follows: Figure 19 As shown. Figure 19 It can be seen that the system's CtIPG margin ratio in time periods 1 and 2 is less than 0, and it is in a level one risk state; the FRC margin ratio in time period 3 is less than 0, and it is in a level two risk state; the FDoQS and FRC margin ratios in time period 4 are less than 0, and it is in a level two risk state, and graded preventive measures need to be taken in the corresponding time periods.

[0268] Grid operation should first ensure the steady-state safety of the system, and then further verify transient safety. When the risk of power imbalance arises during online grid operation, the priority for defending against the first-level grid frequency safety risk should be higher than that of the second-level risk. Based on the above analysis, the following hierarchical preventive measures for online operation risks can be formulated. During time periods 1 and 2, the system must first ensure power balance, and first-level preventive measures should be implemented. During time periods 3 and 4, if power balance meets the requirements, further consideration can be given to the system's transient safety requirements, and second-level preventive measures can be implemented. In the next 4 hours, the system shuts down a thermal power unit during time periods 1 and 2, implementing first-level preventive measures to maintain the system's power balance. During time periods 3 and 4, an underfrequency load shedding strategy is deployed, and second-level preventive measures are implemented to ensure the system's frequency safety.

[0269] After taking preventive measures, the system's security situation radar chart is as follows: Figure 20 As shown. Figure 20 It can be seen that after the system implemented the preventive control measures, the margin ratios of the sub-indicators in all time periods were greater than 3%, and the system returned to a safe operating state from a risky state. Therefore, it can be seen that the method proposed in this application can effectively address frequency security risks caused by unexpected source and load fluctuations, and realize hierarchical preventive control of online power grid operation risks.

[0270] In summary, the frequency security situation assessment model proposed in this application can effectively verify the safe operation situation of the power grid and realize the hierarchical assessment and early warning of the power grid operation risk; the day-ahead operation mode safety verification method proposed in this application can make full use of the system's adjustable resources to achieve a dual improvement in the system's economic efficiency and safety; the power grid operation risk hierarchical pre-control method proposed in this application can effectively respond to various risks of online power grid operation and realize hierarchical defense control of different types of risks. The power imbalance risk hierarchical assessment and defense control model method proposed in this application is closely integrated with engineering practice scenarios, is practical and effective, has obvious advantages over many other risk defense control models, and provides a new idea for risk prevention and control in power grids.

[0271] The basic principles of the present application are described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, effects, etc. mentioned in this application are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. are necessary for each embodiment of the present application. In addition, the specific details disclosed above are only for the purpose of illustration and ease of understanding, and are not limitations. The above details do not limit this application to being implemented by adopting the above specific details. The above description disclosed is provided to enable any person skilled in the art to make or use this application. Various modifications to these aspects will be very obvious to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this application. Therefore, this application is not intended to be limited to the aspects shown herein, but to the widest scope consistent with the principles and novel features of this invention.

[0272] The above is only a preferred embodiment of the invention of this application and is not intended to limit the invention of this application. Any modifications, equivalent replacements, etc. made within the spirit and principles of the invention of this application should be included in the scope of protection of the invention of this application.

[0273] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for risk assessment and defense control of a power system, characterized in that: The following steps are involved: Step 1: Analyze the power imbalance risk of the new power system and define the safe operation boundary of the power grid; Step 2: Propose grid security situation assessment indicators and establish a grid frequency security situation assessment model; Step 3: Considering the changes in load inertia and fault impact curves, establish a grid day-ahead operation mode optimization adjustment model; Step 4: Considering the risk of unexpected fluctuations in daily load and source, a risk classification and pre-control model for online power grid operation is established; Step 5: Based on the grid frequency security situation assessment model established in step 2, the grid day-ahead operation mode optimization and adjustment model established in step 3, and the grid online operation risk classification pre-control model established in step 4, risk assessment, optimization correction, and defense control are performed on the grid operation mode; The power grid frequency security situation assessment model is: Where: 、 、 System The primary risk situation, secondary risk situation, and overall safety situation at all times; For the system Security situation indicators at all times; is the margin ratio when the system is in a critical safety state; When evaluating the security situation for a certain period, if a risk sub-indicator is less than 0, the security situation is defined as -1, and the period is considered to be in a risky state; If all risk sub-indicators are greater than 0, but there is a risk sub-indicator between 0 and If all risk sub-indicators are greater than , then the security situation is defined as 1, and the period is determined to be in a safe state; In step 3, the method for establishing the power grid day-ahead operation mode optimization adjustment model is as follows: S1. Track the day-ahead operation mode of the power grid and perform a frequency safety check before putting it into operation. Taking into account the motor load curve and the fault impact curve, the power grid frequency safety situation assessment model is used to conduct a risk assessment of the day-ahead operation mode of the power grid. Before the assessment, the power market clearing mode includes the start and stop of thermal power units, the output of thermal power units, the system reserve reserve, and the wind and solar load curtailment limit. If the day-ahead operation mode of the power grid is in an unsafe operation domain, the day-ahead operation mode of the power grid is optimized and adjusted by adding energy storage adjustment without changing the start and stop status of the thermal power units. The corrected day-ahead operation mode of the power grid includes the output of thermal power units, the system reserve reserve, the wind and solar load curtailment limit, and the energy storage scheduling plan. S2. The grid day-ahead operation mode optimization adjustment model takes the sum of unit output deviation penalty cost, new energy and load curtailment cost, system backup cost, and energy storage dispatch cost as the optimization goal, and sets the objective function: Where: for The sum of the output deviation penalty costs of all units at the moment; For the crew Cost coefficient for output adjustment; For the crew exist Output adjustment at each moment; For the system Total abandonment cost at the moment; 、 、 They are The system's wind and solar curtailment and load shedding costs at all times; 、 、 are the system's wind curtailment, solar curtailment and load shedding cost coefficients respectively; 、 、 They are The total amount of wind and solar curtailment and load shedding in the system at any given moment; is the dispatch cost of energy storage at time t; The one-time purchase cost of energy storage; is the energy storage power at time t; The service life of the energy storage; is the energy storage capacity at time t; 、 、 、 are the total upward and downward flexible reserve costs and the primary and secondary frequency regulation reserve costs of the system at time t respectively; 、 、 、 They are the system's upward and downward flexible reserve cost coefficients and the primary and secondary frequency regulation reserve cost coefficients; 、 、 、 They are The upward and downward flexibility reserve provided by instant energy storage, as well as the primary and secondary frequency regulation reserve; is the scheduling period; is the scheduling interval; In step 4, the method for establishing the grid online operation risk classification pre-control model is as follows: S1. During the intraday optimization scheduling phase, with a fixed number of hours as the operation mode update cycle, taking into account the net load forecast curve, the grid frequency security situation assessment model is used to conduct a risk assessment of the established grid operation mode, and formulates grid online operation risk classification and pre-control measures; S2. The grid online operation risk classification and prevention measures include establishing a first-level grid online operation risk prevention model and a second-level grid online operation risk prevention model. The established grid operation mode shall first pass the first-level risk verification. The first-level risk prevention measures include optimizing the start-up and shutdown of thermal power units, energy storage call plans, and wind and solar load curtailment plans. If the grid does not have a first-level risk, it shall pass the second-level risk verification. The second-level risk prevention measures include optimizing the start-up and shutdown of thermal power units, energy storage call plans, and low-frequency load reduction strategy plans. If the first-level risk situation and the second-level risk situation of the established grid operation mode are both in the safe operation domain, the established grid operation mode may be used to guide grid operation within the fixed number of hours in the future.

2. A power system risk situation assessment and defense control method according to claim 1, characterized in that: In step 1, the frequency regulation process of the novel power system includes six safety constraints: steady-state frequency safety constraints CtIPG and CtRPG, transient frequency safety constraints RoCoF, LFoT, FDoQS, and quasi-steady-state frequency safety constraints FRC; The safe operation boundary of the power grid is defined as follows: the CtIPG should be greater than the random upward fluctuation value of the system net load, and the CtRPG should be greater than the random downward fluctuation value of the system net load. The critical safety constraint is to meet the net load confidence level. The flexible adjustment demand value under the above conditions is as follows: the critical safety constraints of RoCoF, LFoT and FDoQS are predetermined values; the critical safety constraint of FRC is that the system's additional power within a period of time after a frequency modulation is completed is not less than the system's unbalanced power.

3. A power system risk situation assessment and defense control method according to claim 1, characterized in that: In step 2, the power grid security situation assessment indicators include primary risk indicators and secondary risk indicators, and the primary risk indicators include: (1) CtIPG margin ratio Where: For the system CtIPG margin ratio at the moment; 、 The system is The upward flexibility demand and the total amount of upward flexibility reserve at each moment; (2) CtRPG margin ratio Where: For the system CtRPG margin ratio at the moment; 、 The system is The downward flexibility demand and total downward flexibility reserve at each moment; The secondary risk indicators include: (1)RoCoF margin ratio Where: For the system RoCoF margin ratio at the moment; is the maximum frequency change rate of the system; For the system Frequency change rate at a given moment; (2) LFoT margin ratio Where: For the system LFoT margin ratio at the moment; is the maximum deviation limit of the system frequency; For the system The lowest frequency at the moment; (3) FDoQS margin ratio Where: For the system FDoQS margin ratio at the moment; is the quasi-steady-state frequency deviation safety limit of the system; for Quasi-steady-state frequency deviation of the system at each moment; (4) FRC margin ratio Where: For the system FRC margin ratio at the moment; 、 The system is Secondary frequency regulation demand and total secondary frequency regulation reserve at each moment.

4. A power system risk situation assessment and defense control method according to claim 3, characterized in that: The first-level risk indicator and the second-level risk indicator are defined as: Where: 、 、 、 、 、 For the system Six security posture indicators at all times.

5. A power system risk situation assessment and defense control method according to claim 1, characterized in that: The grid online operation first-level risk pre-control model takes the minimization of the sum of unit start-up and shutdown and output costs, new energy and load curtailment costs, system backup costs, and energy storage scheduling costs within the online scheduling cycle as the optimization goal, and sets the objective function: Where: is the online scheduling period; is the sum of the power generation and start-up and shutdown costs of all units in the system at time t; The unit at time t the cost of electricity generation; The unit at time t start-stop costs.

6. The power system risk situation assessment and defense control method according to any one of claims 1 or 5, characterized in that: The model has the following constraints: (1) Power balance constraints: (2) Thermal power operation constraints: Where: 、 Respectively for units Minimum start and stop time; 、 are the sets of corresponding moments of the unit start and stop states respectively; (3) Energy storage operation constraints: Where: 、 Energy storage t The charging and discharging power at each moment; 、 Energy storage t The charge and discharge status at each moment; 、 are the maximum charge and discharge power limits of energy storage respectively; 、 are the charging and discharging efficiency of energy storage respectively; 、 are the maximum and minimum limits of energy storage capacity respectively; 、 are the initial and final capacities of energy storage respectively; (4) System peak load constraints: The sum of the up / down regulation reserves provided by thermal power and energy storage should be greater than the system's up / down regulation requirements; (5) Frequency safety constraints: The following are the system's frequency minimum point constraint, frequency change rate constraint, quasi-steady-state frequency deviation constraint, and quasi-steady-state frequency recovery constraint: (6) Alternate split constraints: Thermal power and energy storage provide upward flexibility reserves, primary frequency regulation reserves, and secondary frequency regulation reserves, which together divide the system's upward regulation capacity. (7) Current safety constraints: Where: 、 、 、 、 are the power flow transfer factors of the units, wind power, photovoltaic, load and energy storage respectively; is the power transmission limit of the line.

7. A power system risk situation assessment and defense control method according to claim 1, characterized in that: The grid online operation secondary risk pre-control model takes the minimization of the sum of the unit start-up and shutdown and output costs, new energy and load curtailment costs, system backup costs, energy storage scheduling costs, and low-frequency load reduction costs within the online scheduling cycle as the optimization goal, and sets the objective function: Where: for t Low-frequency load shedding costs of the moment system; is the system's low-frequency load reduction penalty coefficient; for The total underfrequency load reduction of the system at that moment.

8. A power system risk situation assessment and defense control method according to claim 7, characterized in that: The grid online operation secondary risk pre-control model has the following constraints: (1) Power balance constraints: (2) Thermal power operation constraints: Where: 、 Respectively for units Minimum start and stop time; 、 are the sets of corresponding moments of the unit start and stop states respectively; (3) Energy storage operation constraints: Where: 、 Energy storage t The charging and discharging power at each moment; 、 Energy storage t The charge and discharge status at each moment; 、 are the maximum charge and discharge power limits of energy storage respectively; 、 are the charging and discharging efficiency of energy storage respectively; 、 are the maximum and minimum limits of energy storage capacity respectively; 、 are the initial and final capacities of energy storage respectively; (4) System peak load constraints: The sum of the up / down regulation reserves provided by thermal power and energy storage should be greater than the system's up / down regulation requirements; (5) Frequency safety constraints: The following are the system's frequency minimum point constraint, frequency change rate constraint, quasi-steady-state frequency deviation constraint, and quasi-steady-state frequency recovery constraint: (6) Alternate split constraints: Thermal power and energy storage provide upward flexibility reserves, primary frequency regulation reserves, and secondary frequency regulation reserves, which together divide the system's upward regulation capacity. (7) Current safety constraints: Where: 、 、 、 、 are the power flow transfer factors of the units, wind power, photovoltaic, load and energy storage respectively; is the power transmission limit of the line.

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