Power system risk situation assessment and defense control method

Abstract

The invention discloses an electric power system risk situation assessment and defense control method, which comprises the steps of analyzing a novel electric power system power imbalance risk, and delimiting a power grid safety operation boundary; providing a power grid security situation assessment index, and establishing a power grid frequency security situation assessment model; establishing a power grid day-ahead operation mode optimization and adjustment model by considering the load inertia and the change of the fault impact curve; a power grid online operation risk grading pre-control model is established by considering an intra-day source load exceeding expected fluctuation risk; and performing risk assessment, optimization correction and defense control on the power grid operation mode based on the model. The invention further provides a novel power system power imbalance situation assessment, operation mode optimization control and security risk grading defense method. The method can effectively evaluate the power imbalance risk situation of the power grid, corrects the safety operation domain of the power grid, realizes active defense of the safety risk of the power grid, 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 a power system. Background Art

[0002] With the rapid development of a new type of power system, new energy has gradually become the main installed capacity, and thermal power is changing from the main power source to a regulating and supporting power source, resulting in profound changes in the foundation of the power system. The rapid development of new energy has led to an increasing probability of imbalance risk and a continuous reduction in the system's rotational inertia. The existing power system regulation mode is difficult to support the power balance of the new type of power system, and the frequency security risk of the power grid continues to rise. To improve the "climate resilience, safety resilience, and regulation flexibility" of the power system, the operation control mode of the power grid urgently needs to transform from a passive mode of operating and defending according to a pre-established plan to an active defense mode based on situation assessment and trend analysis.

[0003] The power balance security situation of the power grid involves two aspects: the power balance situation and the frequency stability situation. Among them, the main influencing factors of the power balance situation include aspects such as source-load fluctuations, power source regulation capabilities, and energy storage regulation capabilities, reflecting the real-time source-load balance capabilities of the power system during certain periods. The influencing factors of the frequency stability situation mainly include aspects such as system inertia, fault impact, and frequency regulation capabilities, and its safety constraints involve multiple indicators in the inertia response, transient, and quasi-steady state processes. Existing research has a certain research foundation in the power balance security situation of the power grid. In terms of power balance, evaluation indicators such as peak shaving adequacy and peak shaving capacity ratio have been proposed; in terms of 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, the above indicators are mainly used as evaluation indicators for the local characteristics of the system or safety constraints for the operation mode of the power grid, and it is difficult to reflect the overall safety level of the power grid. In guiding the safe operation of the new type of power system frequency, it is urgent to establish a systematic and comprehensive understanding system of safety situation characteristics, accurately quantify and describe the power grid safety situation, and provide a decision-making basis for the safety correction and active defense control of the power system operation mode.

[0004] There are still two deficiencies in existing research. First, in the method check, only the influence of power inertia is often considered, insufficient consideration is given to the real-time changes of the load model and load inertia, and the risk of system fault impact is not fully taken into account, resulting in insufficient accuracy of frequency security check. Second, the unexpected fluctuations of power sources and loads are not considered. When there is a risk of power imbalance in the established operation plan, how to make online decisions on the operation mode and defense measures of the power grid. It is urgent to propose methods for optimizing and correcting the operation mode and making decisions on fault defense control for different types of power imbalance risks existing in the power grid, so as to improve the frequency security level of the new power system. 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 to improve the technical problems of insufficient risk situation assessment and defense control methods in the existing power system.

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

[0007] Step 1, analyze the power imbalance risk of the new power system and delimit the safe operation boundary of the power grid;

[0008] Step 2, propose power grid security situation assessment indicators and establish a power grid frequency security situation assessment model;

[0009] Step 3, taking into account the changes in load inertia and fault impact curves, establish an optimized adjustment model for the daily operation mode of the power grid;

[0010] Step 4, considering the risk of unexpected fluctuations of power sources and loads during the day, establish an online operation risk classification and pre-control model for the power grid;

[0011] Step 5, based on the above models, conduct risk assessment, optimization and correction, and defense control on the operation mode of the power grid.

[0012] Among them, in Step 1, the whole process of frequency regulation of the new power system includes six safety constraints: steady-state frequency safety constraints CtIPG, CtRPG, transient frequency safety constraints RoCoF, LFoT, FDoQS, and quasi-steady-state frequency safety constraint FRC; the delimitation of the safe operation boundary of the power grid is: CtIPG should be greater than the upward random fluctuation value of the system net load, CtRPG should be greater than the downward random fluctuation value of the system net load, and its critical safety constraint is to meet the flexible regulation demand value of the net load under the confidence level β. The critical safety constraints of RoCoF, LFoT, and FDoQS are established values, and the critical safety constraint of FRC is that the additional power of the system within a certain period after the primary frequency modulation is not less than the system imbalance 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 downward flexibility demand and the total downward flexibility reserve of the system 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 point 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] In the formula: is the FRC margin ratio of the system at time t; F t,SFR , Rn t,SFR are respectively the secondary frequency regulation demand and the total secondary frequency regulation reserve of the system at time t.

[0033] Further, the first-level risk index and the second-level risk index are defined as:

[0034]

[0035] In the formula: are the six safety situation indicators of the system at time t;

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

[0037]

[0038] In the formula: SR t , FR t , TR t are respectively the first-level risk situation, the second-level risk situation, and the total safety situation of the system at time t; χ is the margin ratio when the system is in the critical safety state; when conducting a safety situation assessment for a certain period, if there is a risk sub-index less than 0, the safety situation is defined as -1, and it is determined that the period is in a risk state; if all risk sub-indices are greater than 0, but there is a risk sub-index in the range of 0 to χ then the safety situation is defined as 0, and it is determined that the period is in the critical safety state; if all risk sub-indices are greater than χ , then the safety 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 and adjustment model is as follows:

[0040] S1. Track the grid's day-ahead operating mode, conduct frequency security checks before putting it into operation. Considering the motor load curve and fault impact curve, use the grid frequency security situation assessment model to conduct risk assessment on the grid's day-ahead operating mode. Before the assessment, the power market clearing methods include thermal power unit start-stop, thermal power unit output, system reserve reservation, and the curtailment limits of wind, light, and load. If the grid's day-ahead operating mode is in the non-safe operating domain, optimize and adjust the grid's day-ahead operating mode, and increase energy storage regulation without changing the start-stop status of thermal power units. The corrected grid's day-ahead operating mode includes thermal power unit output, system reserve reservation, the curtailment limits of wind, light, and load, and the energy storage dispatching plan;

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

[0042]

[0043] In the formula: is the sum of the output deviation penalty costs of all units at time t; is the cost coefficient of the output adjustment of unit g; ΔP g,t is the output adjustment amount of unit g at time t; is the total curtailment cost of the system at time t; are the curtailment costs of wind, light, and load shedding of the system at time t respectively; δ w , δ v , δ d are the curtailment cost coefficients of wind, light, and load shedding of the system respectively; P t w , P t v , P t d are the total curtailment amounts of wind, light, and load shedding of the system at time t respectively; is the dispatching cost of the energy storage at time t; C ess is the one-time acquisition cost of the energy storage; P ess,t is the power of the energy storage at time t; S ess is the service life of the energy storage; E ess,t is the capacity of the energy storage at time t; are the total upward and downward flexible reserve costs and primary and secondary frequency modulation reserve costs of the system at time t respectively; X up , X dn , X pfr , X sfr are the upward and downward flexible reserve cost coefficients and primary and secondary frequency modulation reserve cost coefficients of the system respectively; The upward and downward flexibility reserves provided by energy storage at time t, as well as the primary and secondary frequency regulation reserves; T is the dispatching period; ΔT is the dispatching interval.

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

[0045] S1. In the intraday optimal dispatching stage, with a fixed number of hours as the operation mode update period, considering the net load prediction curve, use the power grid frequency security situation assessment model to conduct risk assessment on the established operation mode of the power grid, and formulate online operation risk classification and pre-control measures for the power grid;

[0046] S2. The online operation risk classification and pre-control measures of the power grid include establishing an online operation first-level risk pre-control model and an online operation second-level risk pre-control model for the power grid. The established operation mode of the power grid is preferentially verified through the first-level risk. The first-level risk pre-control measures include optimizing the start-stop and output plans of thermal power units, the energy storage call plan, and the wind-solar load curtailment plan; if there is no first-level risk in the power grid, then conduct a second-level risk verification. The second-level risk pre-control measures include optimizing the start-stop and output plans of thermal power units, the energy storage call plan, and the low-frequency load shedding strategy plan; if both the first-level risk situation and the second-level risk situation of the established operation mode of the power grid are in the safe operation area, then the established operation mode of the power grid can be used to guide the operation of the power grid within the future fixed number of hours.

[0047] Furthermore, the online operation first-level risk pre-control model of the power grid takes the minimum sum of the start-stop and output costs of units, the curtailment costs of new energy and load, the system reserve cost, and the energy storage dispatching cost within the online dispatching period as the optimization objective, and sets the objective function:

[0048]

[0049] In the formula: Δt is the online dispatching period; is the sum of the power generation and start-stop 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-stop cost of unit g at time t.

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

[0051] (1) Power balance constraint:

[0052]

[0053] (2) Thermal power operation constraint:

[0054]

[0055] Where: T on,g and T off,g are the minimum start-up and shut-down times of the unit g respectively; \(t_{on}\) and \(t_{off}\) are the sets of corresponding moments of the unit in the start-up and shut-down 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 and P D,t are the charge and discharge powers of the energy storage at time t respectively; μ C,t and μ D,t are the charge and discharge states of the energy storage at time t respectively; P C,max and P D,max are the maximum charge and discharge power limits of the energy storage respectively; η C and η D are the charge and discharge efficiencies of the energy storage respectively; E ess,max and E ess,min are the maximum and minimum limits of the energy storage capacity respectively; E ess,1 and E ess,T are the initial and final capacities of the energy storage respectively;

[0065] (4) System peak shaving constraints:

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

[0067]

[0068] (5) Frequency security constraint:

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

[0070]

[0071]

[0072] (6) Reserve splitting constraint:

[0073] The upward regulation flexibility reserve, primary frequency regulation reserve, and secondary frequency regulation reserve provided by thermal power and energy storage jointly split the upward regulation capacity of the system;

[0074]

[0075] (7) Power flow security constraint:

[0076]

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

[0078] Furthermore, the secondary risk pre-control model for online operation of the power grid takes the minimum sum of the unit start-stop and output costs, new energy and load curtailment costs, system reserve costs, energy storage dispatch costs, and low-frequency load shedding costs within the online dispatching period as the optimization goal, and sets the objective function:

[0079]

[0080] In the formula: is the low-frequency load shedding cost of the system at time t; δ shd is the low-frequency load shedding penalty coefficient of the system; P t shd is the total low-frequency load shedding amount of the system at time t.

[0081] Furthermore, the secondary risk pre-control model for online operation of the power grid has the following constraint conditions:

[0082] (1) Power balance constraint:

[0083]

[0084] (2) Thermal power operation constraints:

[0085]

[0086] In the formula: T on,g , T off,g are respectively the minimum start-up and shutdown times of unit g; t_on and t_off are respectively the sets of times corresponding to the start-up and shutdown states of the unit.

[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] In the formula: P C,t , P D,t are respectively the charging and discharging powers of the energy storage at time t; μ C,t , μ D,t are respectively the charging and discharging states of the energy storage at time t; P C,max , P D,max are respectively the maximum charging and discharging power limits of the energy storage; η C , η D are respectively the charging and discharging efficiencies of the energy storage; E ess,max , E ess,minare the maximum and minimum limits of the energy storage capacity; E ess,1 and E ess,T are the initial and final energy storage capacities respectively;

[0096] (4) System peak shaving constraint:

[0097] The sum of the upward / downward regulation reserves provided by thermal power and energy storage should be greater than the upward / downward regulation demand of the system;

[0098]

[0099] (5) Frequency security constraint:

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

[0101]

[0102] (6) Reserve splitting constraint:

[0103] The upward regulation flexibility reserve, primary frequency regulation reserve and secondary frequency regulation reserve provided by thermal power and energy storage jointly split the system's upward regulation capacity;

[0104]

[0105] (7) Power flow security constraint:

[0106]

[0107] In the formula: U g and U w and U v and U d and 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] A power system risk situation assessment and defense control method proposed in this application can effectively evaluate the power imbalance risk situation of the power grid, correct the safe operation area of the power grid, achieve active defense against power grid security risks, and has engineering application value. Among them, based on case analysis and verification, the frequency security situation assessment model can comprehensively evaluate the operation risks of the power grid and intuitively represent the power grid security situation; the day-ahead operation mode optimization and adjustment model can effectively correct the day-ahead operation mode of the power market, ensure that the day-ahead operation mode of the power grid is within the safe operation area, and improve the economy of system operation; the online operation risk classification and pre-control model can effectively cope with the frequency security risks under unexpected fluctuations of power sources and loads, and achieve classification and pre-control of power grid online operation risks.

[0110] The frequency security situation assessment model proposed in this application can effectively check the safe operation situation of the power grid and achieve hierarchical assessment and early warning of power grid operation risks; the day-ahead operation mode safety check method proposed in this application can make full use of the adjustable resources of the system and achieve double improvement of system operation economy and security; the power grid operation risk classification and pre-control method proposed in this application can effectively cope with various risks in power grid online operation and achieve hierarchical defense control of different types of risks. The power imbalance risk classification assessment and defense control model proposed in this application is closely combined with engineering practice scenarios, practical and effective, and has obvious advantages over many other risk defense control models, providing new ideas for power grid risk prevention and control. Brief Description of the Drawings

[0111] Figure 1 It is the step flow chart of the method of the present invention;

[0112] Figure 2 It is the schematic diagram of the power grid frequency regulation process of the present invention;

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

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

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

[0116] Figure 6 It is the flow chart for formulating hierarchical pre-control measures of the present invention;

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

[0118] Figure 8 It is the curve graph of the motor load ratio of the present invention;

[0119] Figure 9Fault risk impact curve diagram of the present invention;

[0120] Figure 10 Schematic diagram of the calculated value of the sub - index before optimization of the present invention;

[0121] Figure 11 Schematic diagram of the comprehensive safety situation assessment before optimization of the present invention;

[0122] Figure 12 Safety situation radar chart before optimization of the present invention;

[0123] Figure 13 Schematic diagram of the calculated value of the sub - index after optimization of the present invention;

[0124] Figure 14 Schematic diagram of the comprehensive safety situation assessment after optimization of the present invention;

[0125] Figure 15 Safety situation radar chart after optimization of the present invention;

[0126] Figure 16 Schematic diagram of the comparison of the daily and intraday net load curves of the present invention;

[0127] Figure 17 Schematic diagram of the comparison between the system power balance demand and the adjustable capacity of the present invention;

[0128] Figure 18 Schematic diagram of the comparison between the system frequency regulation demand and the remaining frequency regulation reserve of the present invention;

[0129] Figure 19 Safety situation radar chart before online pre - control of the present invention;

[0130] Figure 20 Safety situation radar chart after online pre - control of the present invention. Detailed implementation manners

[0131] In the description of this application, the meaning of "a plurality" is at least two, for example, two, three, etc., unless otherwise specifically and clearly defined. In all the directional indications (such as up, down, left, right, front, back, top, bottom...) in the embodiments of this application, they are only used to explain the relative position relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will change accordingly. In addition, the terms "comprise" and "have" and any deformation thereof are intended to cover non - exclusive inclusion. 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 further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products or Internet of Things terminals.

[0132] In addition, the mention of "embodiment" in this document means that the specific features, structures, or characteristics described in connection with the embodiment can be included in at least one embodiment of the present application. The occurrence of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0133] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the present application. It should be noted that the numerical values described in the present application should not be fixed values. The numerical values are only example numerical values and should not limit the scope of protection of the present application. The relevant numerical data in the present application can be determined according to the specific situation of the power grid.

[0134] To address the frequency security risks caused by source-load fluctuations and fault impacts, the present invention focuses on the power supply, consumption, and safety issues of the new power system, conducts research from three aspects: security characteristic assessment, system operation control, and active fault defense, analyzes the disturbance types of power grid power imbalance, proposes security assessment indicators covering the entire process of frequency regulation, and establishes a hierarchical quantitative assessment model for the security situation. On this basis, an efficient deduction and analysis decision-making model for the power grid operation situation is constructed, the safety operation margin of the power grid is accurately grasped, the short-cycle operation mode, real-time operation mode, and fault defense strategy of the power grid are optimized, and accurate situation assessment, efficient operation control, and active fault defense are realized to support the safe, stable, and economic operation of the new power system.

[0135] The purpose of the present invention is to propose a method for power system risk situation assessment and defense control to improve the deficiencies of the existing power system risk situation assessment and defense control methods. Based on six security constraint indicators related to power grid frequency fluctuations, the safe operation boundary is delimited, a hierarchical assessment indicator for the active power frequency security risk of the power grid is proposed, and based on this, a power grid security situation assessment model is established, an optimization adjustment model for the daily operation mode is established, and a hierarchical control model for power grid security defense when the source-load fluctuates beyond expectations is established. Furthermore, a method for power imbalance situation assessment, operation mode optimization control, and security risk hierarchical defense of a new power system is proposed.

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

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

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

[0139] As Figure 2 shown, power source and load fluctuations are the system frequency fluctuation risks that occur when the random fluctuations in power sources and loads exceed the flexible regulation ability of the power grid, manifested in two forms: upward fluctuations or downward fluctuations. For large power grids, when the frequency fluctuations caused by power source and load fluctuations are within the range of 50 ± 0.1 Hz, it is considered that the system frequency level is not out of limit. Power source and load fluctuation disturbances may occur throughout the system frequency regulation process, including steady state, transient state, and quasi-steady state, and have the characteristics of long duration and slow frequency fluctuations; fault impact is the risk that when a transient fault occurs in the power grid, due to instantaneous power imbalance, the frequency drops (or rises) rapidly, exceeding the transient frequency safety constraint, and has the characteristics of short duration and fast frequency change.

[0140] In the new power system, these two types of frequency disturbance risks may occur alone or in combination. Considering that high-frequency generator tripping can effectively control the problem of transient frequency increase in the system, generally, the risk of system frequency reduction type is mainly considered.

[0141] As Figure 3As shown in the figure, under the dual disturbances of source-load fluctuations and fault impact risks, the whole process of frequency regulation in a 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 power grid can provide when facing upward random fluctuations in net load; the capacity to reduce power generation is the downward flexible regulation reserve that the power grid can provide when facing downward random fluctuations in net load; the rate of change of frequency is the change rate of the system frequency after the power grid suffers a transient impact; the lowest frequency of transient is the lowest limit of the system frequency drop after the power grid suffers a transient impact; the frequency deviation of quasi-stable state is the deviation between the system frequency and the initial operating frequency after the power grid completes primary frequency modulation; and the frequency recovery capacity is the frequency recovery capacity of the system.

[0142] In Figure 2 - Figure 3 it, f0 represents the initial operating frequency of the power grid, represents the system frequency after the power grid suffers a frequency-increasing disturbance, represents the system frequency after the power grid suffers a frequency-decreasing disturbance, f min represents the lowest system frequency after the power grid suffers a transient disturbance, Δf0 represents the deviation between the quasi-stable state frequency and the initial operating frequency of the power grid, t1 represents the initial moment when the power grid suffers a transient disturbance, t2 represents the moment when the primary frequency modulation of the power grid starts to take effect, t m represents the moment when the power grid frequency reaches the lowest point, t3 represents the initial moment when the power grid enters the quasi-stable state stage, t4 represents the end moment of the power grid frequency modulation response, and t5 represents the end moment when the power grid returns to the steady state stage after suffering a disturbance.

[0143] When the steady-state frequency safety constraints CtIPG and CtRPG are exceeded, the flexible peak regulation capacity of the system is insufficient, and there is a risk of frequency fluctuation; when the transient frequency safety constraints RoCoF, LFoT, and FDoQS are exceeded, the fault frequency support capacity of the system is insufficient, and there is a risk of frequency instability; when the quasi-stable state frequency safety constraint FRC is exceeded, the frequency recovery capacity of the system is insufficient, and there is a risk of long-term low-frequency operation after a fault.

[0144] To ensure the safety of the entire process of system frequency regulation and delimit the frequency safe operating boundary, CtIPG should be greater than the upward random fluctuation value of the system net load, and CtRPG should be greater than the downward random fluctuation value of the system net load. Its critical safety constraint can be expressed as meeting the flexible regulation demand of the net load at a certain confidence level β. In the present invention, the value of β is 95%. The critical safety constraints of RoCoF, LFoT, and FDoQS are generally defined as a certain established value. The critical safety constraint of FRC is that after primary frequency regulation is completed, the system increases power by no less than the system unbalanced power within a certain period of time.

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

[0146] As Figure 4 shown, when all six safety constraints of the system can meet the critical safety constraints, the system operates in the safe operating region. When any index is lower than the critical safety stability demand, there is a frequency safety risk in the system. There are inherent correlations among the steady-state, transient, and quasi-steady-state frequency safety constraints of the system. To explore whether the FRC ability is sufficient, it should be premised on the sufficiency of the steady-state and transient frequency regulation abilities; the transient frequency safety of the system should be premised on the steady-state frequency safety. At the same time, when the frequency regulation ability of the system cannot balance the source-load fluctuation risk and fault impact risk of the system, the regulation ability should be preferentially used to cope with the first-occurring risk of the two.

[0147] Considering that the system should first meet the power balance demand and then further address the frequency safety risk, the present invention defines the steady-state frequency safety risks (CtIPG, CtRPG) as first-level risks and the transient and quasi-steady-state frequency safety risks (RoCoF, LFoT, FDoQS, FRC) as second-level risks. Considering that there is a certain coupling relationship among the six safety constraint indicators, the safety constraints and the economic operation of the system should be considered collaboratively, and the power grid operation mode should be reasonably formulated to ensure that the power grid is in the safe and economic operation region.

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

[0149] To quantitatively evaluate the safe operation situation of the power grid, the first-level risk indicators and second-level risk indicators shown in Figure 4 are respectively defined. Considering that the thermal reserve of the regulating power source needs to meet the peak shaving demand of the system, the margin ratios of CtIPG and CtRPG are defined as the first-level risk indicators; to evaluate the frequency safety level of the power grid when facing the fault impact risk, the margin ratios of RoCoF, LFoT, FDoQS, and FRC are defined as the second-level risk indicators. Specifically as follows:

[0150] (1) CtIPG margin ratio

[0151]

[0152] Wherein: is the CtIPG margin ratio of the system at time t. F t,up , Rn t,up are respectively the upward flexibility demand and the total upward flexibility reserve of the system at time t, and their specific calculation formulas are as follows:

[0153]

[0154] Wherein: is the upward flexibility reserve provided by unit g at time t; is the maximum upward ramp rate of unit g; μ g,t is the unit g start-stop state variable at time t, 1 for start and 0 for stop; P g,max is the unit g maximum technical output; P g,t is the unit g actual output at time t; is the upper limit of the prediction interval of the system's net load at time t under confidence level β; P L,t is the net load power of the system at time t, defined as follows:

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

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

[0157] (2) CtRPG margin ratio

[0158]

[0159] Wherein: is the CtRPG margin ratio of the system at time t; F t,dn , Rn t,dn are respectively the downward flexibility demand and the total downward flexibility reserve of the system at time t, and their specific calculation formulas are as follows:

[0160]

[0161] Wherein: is the downward flexibility reserve provided by unit g at time t; is the maximum downward ramp - up capacity of unit g; P g,min is the minimum technical output of unit g; is the lower limit of the prediction interval of the system's net load at time t under the confidence level β.

[0162] (3) RoCoF margin ratio

[0163]

[0164] In the formula: 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 1Hz / s in the present invention; τ t is the frequency change rate of the system at time t, and its calculation formula is as follows:

[0165]

[0166] In the formula: ΔP t is the power shock suffered by the system at time t; f0 is the initial frequency of the system; ρ t is the system inertia coefficient considering the real - time change of load inertia.

[0167] (4) LFoT margin ratio

[0168]

[0169] In the formula: 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 - point frequency of the system at time t, and its calculation formula is shown in Equation (11):

[0170]

[0171] In the formula: 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] In the formula: is the FDoQS margin ratio of the system at time t; is the safety limit of the quasi - steady - state frequency deviation of the system, which is set to 0.2Hz 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] In the formula: D d is the damping coefficient of the load in the system; is the primary frequency regulation reserve provided by unit g at time t:

[0177]

[0178] In the formula: 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 ability coefficient of the unit; M y (x) is the y-th linear piecewise function of the primary frequency regulation ability of the unit.

[0179] (6) FRC margin ratio

[0180]

[0181] In the formula: is the FRC margin ratio of the system at time t; F t,SFR and Rn t,SFR are the secondary frequency regulation demand and the total secondary frequency regulation reserve of the system at time t respectively, and their specific calculation formulas are as follows:

[0182]

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

[0184]

[0185] For the convenience of aggregating sub-indicators of different levels of risk, the above indicators are defined as:

[0186]

[0187] In the formula: 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] In the formula: SR t, FR t , TR t are the primary risk situation, secondary risk situation, and total security situation of the system at time t, respectively; χ is the margin ratio when the system is in a critical security state. For the convenience of calculation, the present invention takes 0.03. It can be seen from equations (20) to (22) that when evaluating the security situation for a certain time period, if there is a risk sub-index less than 0, the security situation is defined as -1, and it is determined that the time period is in a risk state; if all risk sub-indices are greater than 0, but there is a risk sub-index in the range of 0 to χ , the security situation is defined as 0, and it is determined that the time period is in a critical security state; if all risk sub-indices are greater than χ , the security situation is defined as 1, and it is determined that the time period is in a security state.

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

[0192] The day-ahead operation mode of the power system is determined by the power market decision and requires frequency security verification before being put into operation. The present invention aims to track the day-ahead operation mode formulated by the power market. On the basis of not changing the start-stop state of the units, considering energy storage as the adjustment resource of the system, optimize and adjust the day-ahead operation mode, and the security verification idea is as Figure 5 shown.

[0193] Taking the sum of the penalty cost of unit output deviation, the cost of abandoning limits of new energy and load, the system reserve cost, and the energy storage dispatching cost as the minimum, as the optimization objective, set the objective function:

[0194]

[0195] In the formula: is the sum of the penalty costs of output deviation of all units at time t; is the cost coefficient of the output adjustment of unit g; ΔP g,t is the output adjustment amount of unit g at time t; is the total cost of abandoning limits of the system at time t; are the costs of abandoning wind, abandoning light, and shedding load of the system at time t, respectively; δ w , δ v , δ d are the cost coefficients of abandoning wind, abandoning light, and shedding load of the system, respectively; P t w , P t v , P t d are the total amounts of abandoned wind, abandoned light, and load shedding of the system at time t, respectively; is the dispatching cost of energy storage at time t; C essis the one-time acquisition cost for energy storage; P ess,t is the power of the energy storage at time t; S ess is the service life of the energy storage; E ess,t is the capacity of the energy storage at time t; are respectively the total upward and downward flexible reserve costs and the primary and secondary frequency regulation reserve costs of the system at time t; X up 、X dn 、X pfr 、X sfr are respectively the upward and downward flexible reserve cost coefficients and the primary and secondary frequency regulation reserve cost coefficients of the system; are respectively the upward and downward flexible reserves and the primary and secondary frequency regulation reserves provided by the energy storage at time t; T is the scheduling period, which is taken as 24 h in the present invention; ΔT is the scheduling interval, which is taken as 1 h in the present invention.

[0196] Set the following constraint conditions:

[0197] (1) Power balance constraint:

[0198]

[0199] (2) Thermal power operation constraint:

[0200]

[0201] In the formula: T on,g 、T off,g are respectively the minimum start-up and shutdown times of unit g; t_{on} and t_{off} are respectively the sets of times corresponding to the start-up and shutdown states of the unit.

[0202] (3) Energy storage operation constraint:

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

[0211] (4) System peak shaving constraint:

[0212] The sum of the upward / downward regulation reserves provided by thermal power and energy storage should be greater than the upward / downward regulation demand of the system.

[0213]

[0214] (5) Frequency security constraint:

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

[0216]

[0217] (6) Reserve splitting constraint:

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

[0219]

[0220] (7) Power flow security constraint:

[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 the source and load within the day, establish an online operation risk classification and pre-control model for the power grid;

[0224] In the intraday optimal dispatching stage, with a 4-hour operation mode update cycle, use the evaluation model of this application to evaluate the risk of the established operation mode, and formulate classification and pre-control measures to achieve online active defense control of the power grid frequency safety. The optimization process is as Figure 6 shown. As Figure 6 can be seen, the pre-control measures prioritize the defense of the first-level risks of the power grid. The defense measures include optimizing the start-stop of thermal power units, energy storage call plans, and curtailment plans for wind and light loads; if there are no first-level risks in the power grid, then use the optimization of the start-stop of thermal power units, energy storage call plans, and low-frequency load shedding strategies to defend the second-level risks of the power grid; if both the first-level risk situation and the second-level risk situation of the established operation mode of the power grid are in the safe operation area, the established operation mode can be used to guide the operation of the power grid in the next 4 hours.

[0225] 1. First-level risk pre-control model

[0226] Taking the minimum sum of the start-stop and output costs of units, the curtailment costs of new energy and loads, the system reserve cost, and the energy storage dispatching cost within the online dispatching cycle as the optimization objective, set the objective function:

[0227]

[0228] In the formula: Δt is the online dispatching cycle, and in this invention, it is taken as 4 hours; is the sum of the power generation and start-stop 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-stop cost of unit g at time t.

[0229] Set the constraint conditions to be the same as those set in Step 3, as shown in Equations (28) to (47).

[0230] 2. Second-level risk pre-control model

[0231] Taking the minimum sum of the start-stop and output costs of units, the curtailment costs of new energy and loads, the system reserve cost, the energy storage dispatching cost, and the low-frequency load shedding cost within the online dispatching cycle as the optimization objective, set the objective function:

[0232]

[0233] In the formula: is the low-frequency load shedding cost of the system at time t; δ shd is the low-frequency load shedding penalty coefficient of the system; P t shd is the total low-frequency load shedding amount of the system at time t.

[0234] Set the constraint conditions to be the same as those set in step 3, as shown in equations (28) to (47). However, considering that low-frequency load shedding is equivalent to offsetting the unbalanced power of the system by shedding load, the system frequency safety constraints shown in equations (39) to (42) change as follows:

[0235] (1) Lowest frequency 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 constraint

[0242]

[0243] Step 5: Based on the model established in the above steps, conduct risk assessment, optimization correction, and defensive control on the power grid operation mode.

[0244] Embodiment

[0245] The set example is established by using the improved IEEE 39-node. The example includes 7 thermal power units, 1 aggregated equivalent photovoltaic power plant, 1 aggregated equivalent wind farm, and 1 aggregated equivalent energy storage power station. The prediction curve graphs of new energy and load in the example are as Figure 7 shown, the time-varying characteristic curve graph of load inertia is as Figure 8 shown, and the system transient impact power curve graph is as Figure 8 shown.

[0246] I. Risk assessment of the power grid's day-ahead operation mode

[0247] Based on the frequency safety situation assessment model established in this application, conduct safety verification on the day-ahead operation mode 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 Figure 10 shown, and the total safety situation of the system is as Figure 11 shown. FromFigure 10 - 11 It can be seen that under the current operating mode, the margin ratio of CtRPG is less than 0 in time periods 2, 5, 16, and 21; the margin ratio of FDoQS is less than 0 in time periods 6 - 15, 17, and 22 - 23; the margin ratio of FRC is less than 0 in time periods 3, 6 - 8, 10, and 19 - 20. It can be determined that the system is in a safe state in time periods 1 and 24; in a critical safety state in time periods 4 and 18; in a first-level risk state in time periods 2, 5, 16, and 21; and in a second-level risk state in time periods 3, 6 - 15, 17, 19 - 20, and 22 - 23. Therefore, the operating mode in the corresponding time periods needs to be optimized and adjusted.

[0248] Taking time periods 1, 5, 17, and 18 as examples, the radar chart of the system security situation is as Figure 12 shown. From Figure 12 it can be seen that for all sub-indicators of the system in time period 1, the margin ratio is greater than 3%, and it is in a safe state; for CtRPG in time period 5, the margin ratio is less than 0, and it is in a first-level risk state; for FDoQS in time period 17, the margin ratio is less than 0, and it is in a second-level risk state; for LFoT and FDoQS in time period 18, the margin ratio is greater than 0 and less than 3%, and it is in a critical safety state.

[0249] In summary, it can be known that the frequency security situation assessment model can comprehensively evaluate the grid operation risk and intuitively represent the grid security situation.

[0250] II. Optimization and adjustment of the current operating mode

[0251] Based on the above safety check results and considering the regulation ability of energy storage resources, the current operating mode is corrected for safety.

[0252] 1. Economic comparison

[0253] The dispatching costs before and after the adjustment of the current operating mode are shown in Table 1:

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

[0255]

[0256] As can be seen from Table 1, after the energy storage participates in the regulation, the start-stop operation cost of the system is reduced by 8.79%, the flexibility reserve cost is increased by 0.43%, the frequency modulation reserve cost is increased by 5.31%, the source-load curtailment cost is reduced by 97.3%, and the total dispatching cost is reduced by 5.52%.

[0257] In summary, it can be known that although the optimized operating mode increases the energy storage dispatching operation cost, it relieves the peak shaving and frequency modulation pressure of thermal power, significantly reduces the curtailment of wind and solar new energy, and improves the economic efficiency of system operation.

[0258] 2. Safety comparison

[0259] The six sub - indicators of the security situation assessment after the adjustment of the daily operation mode are as Figure 13 shown, and the overall security situation of the system is as Figure 14 shown. From Figure 13 - 14 it can be seen that after the optimization and adjustment of the daily operation mode, the margin ratios of all sub - indicators are greater than 0. It can be determined that the system is in a critical security state during periods 4, 7, 11, 13 - 14, 17, and 23, and is in a safe state during other periods, and the operation risk of the system has been eliminated.

[0260] Taking periods 1, 5, 17, and 18 as examples, the security situation radar chart of the system after optimization and adjustment is as Figure 15 shown. From Figure 15 it can be seen that after the optimization and adjustment of the daily mode, the margin ratios of all sub - indicators in periods 1, 5, and 18 are greater than 3%, and they are in a safe state; for period 17, the margin ratios of CtRPG, LFoT, and FDoQS are greater than 0 and less than 3%, and it is in a critical security state.

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

[0262] III. Formulation of Online Operation Risk Classification and Pre - control Measures

[0263] During the online operation of the power grid, there is a risk of unexpected fluctuations in the net load curve. At this time, the established daily operation mode is difficult to ensure that the power grid is still in the safe operation domain, and it is necessary to online evaluate the frequency security situation of the power grid and formulate pre - control measures at different levels.

[0264] Using the evaluation model of this application to analyze the change trend chart of the net load prediction curve, with a 4 - hour online dispatching cycle and taking period 6 as the initial online operation time t, the comparative curve of the system security situation when the net load curve changes as Figure 16 shown during period t - t + 4.

[0265] Analyzing the intraday security situation of the power grid, when the net load prediction curve changes significantly, the comparison of the power balance demand and adjustable capacity of the system is as Figure 17 shown. From Figure 17 it can be seen that the adjustable capacity of the system during periods 1 - 2 cannot meet the power balance demand of the system, and first - level risk pre - control measures need to be taken. The adjustable capacity reserved during periods 3 - 4 can meet the power balance demand of the system, and it is necessary to conduct secondary risk verification.

[0266] Considering that the adjustable capacity of the system gives priority to meeting the power balance demand, and the remaining capacity is used to deal with secondary risks, the comparison of the remaining frequency regulation reserve and the system frequency regulation demand during periods 3 - 4 is as Figure 18 shown. From Figure 18It can be seen that the remaining secondary frequency regulation reserve in period 3 of the system cannot meet the secondary frequency regulation demand of the system, and the remaining primary and secondary frequency regulation reserves in period 4 cannot meet the primary and secondary frequency regulation demands of the system. It is necessary to take secondary risk pre-control measures.

[0267] Before taking the pre-control measures, the safety situation radar chart of the system is as Figure 19 shown. It can be Figure 19 seen that the CtIPG margin ratio of the system in periods 1 and 2 is less than 0, being in a first-level risk state; the FRC margin ratio in period 3 is less than 0, being in a second-level risk state; the FDoQS and FRC margin ratios in period 4 are less than 0, being in a second-level risk state. It is necessary to take hierarchical pre-control measures in the corresponding periods.

[0268] The operation of the power grid should first ensure the steady-state safety of the system and then further check the transient safety situation. When there is a risk of power imbalance in the online operation of the power grid, the defense priority of the first-level risk of power grid frequency safety should be higher than that of the second-level risk. Through the above analysis, the following hierarchical pre-control measures for online operation risks can be formulated. The system needs to first ensure power balance in periods 1 and 2 and should take first-level pre-control measures. In periods 3 and 4, when the power balance meets the requirements, the transient safety requirements of the system can be further considered and second-level pre-control measures can be taken. In the future 4h, one thermal power unit was shut down in periods 1-2 of the system, and first-level pre-control measures were taken to maintain the power balance of the system. In periods 3-4, a low-frequency load shedding and load cutting strategy was configured, and second-level pre-control measures were taken to ensure the frequency safety of the system.

[0269] After taking the pre-control measures, the safety situation radar chart of the system is as Figure 20 shown. It can be Figure 20 seen that after the system executes the pre-control measures, the margin ratios of all sub-indicators in each period are greater than 3%, and the system returns from the risk state to the safe operation state. It can be seen from this that the method proposed in this application can effectively cope with the frequency safety risk under the unexpected fluctuations of the power source and load, and realizes the hierarchical pre-control of the online operation risk of the power grid.

[0270] To sum up, the frequency safety situation assessment model proposed in this application can effectively check 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 check method proposed in this application can make full use of the adjustable resources of the system and realize the double improvement of the operation economy and safety of the system; the power grid operation risk hierarchical pre-control method proposed in this application can effectively cope with various risks in the online operation of the power grid and realize the 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 combined with the engineering practice scenario, is practical and effective, and has obvious advantages over many other risk defense control models, providing a new idea for the risk prevention and control of the power grid.

[0271] The basic principles of the present application have been described in conjunction with specific embodiments. However, it should be noted that the advantages, benefits, effects, etc. mentioned in the present application are merely examples and not limitations. It cannot be considered that these advantages, benefits, effects, etc. are essential for each embodiment of the present application. Additionally, the specific details disclosed above are only for illustrative and facilitating understanding purposes, rather than limitations. These details do not limit the present application to necessarily implement using the above specific details. The above description is provided to enable any person skilled in the art to make or use the present application. Various modifications to these aspects are 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 the present application. Therefore, the present application is not intended to be limited to the aspects shown herein, but rather to the broadest scope consistent with the principles and novel features invented herein.

[0272] The above are only the preferred embodiments of the present invention creation, and are not intended to limit the present invention creation. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention creation shall be included within the protection scope of the present invention creation.

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

Claims

1. A method for risk situation 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 power grid security situation assessment indicators and establish a power grid frequency security situation assessment model; Step 3: Considering the changes of load inertia and fault impact curve, establish the optimization adjustment model of the day-ahead operation mode of the power grid; Step 4: Considering the risk of unexpected fluctuations in daily source and load, a risk classification pre-control model for online operation of power grid 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 and pre-control model established in step 4, risk assessment, optimization correction and defense control are performed on the grid operation mode.

2. A power system risk situation assessment and defense control method according to claim 1, characterized in that: In the step 1, the whole frequency regulation process of the novel power system includes six safety constraints: steady-state frequency safety constraints CtIPG, 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, 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 RoCoF, LFoT, and FDoQS are given values, and the critical safety constraint of FRC is that after a frequency regulation is completed, the system's additional power within a period of time 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: 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; (2) CtRPG margin ratio Where: is the CtRPG margin ratio of the system at time t; F t,dn , Rn t,dn are the downward flexibility demand and the total downward flexibility reserve of the system at time t, respectively; The secondary risk indicators include: (1)RoCoF margin ratio 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; (2) LFoT margin ratio Where: is the LFoT margin ratio of the system at time t; Δf m is the maximum deviation limit of the system frequency; is the lowest frequency of the system at time t; (3) FDoQS margin ratio Where: is the FDoQS margin ratio of the system at time t; is the quasi-steady-state frequency deviation safety limit of the system; is the quasi-steady-state frequency deviation of the system at time t; (4) FRC margin ratio 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.

4. A power system risk situation assessment and defense control method according to claim 3, characterized in that: The primary risk indicator and the secondary risk indicator are defined as: Where: are the six security situation indicators of the system at time t; The power grid frequency security situation assessment model is: Where: SR t , FR t ,TR t They are the primary risk situation, secondary risk situation, and overall safety situation of the system at time t; 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 that is 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, the safety situation is defined as 0, and the period is judged to be in a critical safety state; if all risk sub-indicators are greater than χ, the safety situation is defined as 1, and the period is judged to be in a safe state.

5. A power system risk situation assessment and defense control method according to claim 1, characterized in that: 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, perform frequency safety verification before putting it into operation, take into account the motor load curve and fault impact curve, use the power grid frequency safety situation assessment model to conduct risk assessment on the day-ahead operation mode of the power grid, and 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 abandonment limit. If the day-ahead operation mode of the power grid is in the unsafe operation domain, optimize and adjust the day-ahead operation mode of the power grid, and add 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 abandonment limit and the energy storage dispatch plan; S2. The optimization adjustment model for the day-ahead operation mode of the power grid takes the minimum sum of the penalty cost of unit output deviation, the cost of new energy and load abandonment, the system backup cost and the energy storage dispatch cost as the optimization goal, and sets the objective function: 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; They are the total wind curtailment, solar curtailment and load shedding of the system at time t respectively; is the dispatching cost of energy storage at time t; C ess is the one-time purchase cost of energy storage; P ess,t is the power of energy storage 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 reserve costs; X up , X dn , X pfr , X sfr They are the system's upward and downward regulation 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 the energy storage at time t; T is the dispatch period; ΔT is the dispatch interval.

6. A power system risk situation assessment and defense control method according to claim 1, characterized in that: In step 4, the method for establishing the grid online operation risk classification pre-control model is as follows: S1. In the intraday optimization scheduling stage, the operation mode update cycle is fixed in hours, the net load forecast curve is taken into consideration, the power grid frequency security situation assessment model is used to conduct risk assessment on the established operation mode of the power grid, and risk classification and pre-control measures for online operation of the power grid are formulated; S2. The risk classification and prevention measures for online operation of the power grid include establishing a first-level risk prevention model and a second-level risk prevention model for online operation of the power grid. The established operation mode of the power grid shall first pass the first-level risk verification. The first-level risk prevention measures include optimizing the start and stop of thermal power units, energy storage call plan, and wind and solar load abandonment plan. If there is no first-level risk in the power grid, the second-level risk verification shall be passed. The second-level risk prevention measures include optimizing the start and stop of thermal power units, energy storage call plan, and low-frequency load reduction strategy plan. If the first-level risk situation and the second-level risk situation of the established operation mode of the power grid are both in the safe operation domain, the established operation mode of the power grid can be used to guide the operation of the power grid within the fixed number of hours in the future.

7. A power system risk situation assessment and defense control method according to claim 6, characterized in that: The grid online operation first-level risk pre-control model takes the minimum sum of the start-up and shutdown and output costs of the units, the costs of new energy and load abandonment, the system backup costs and the energy storage dispatching costs within the online dispatching cycle as the optimization goal, and sets the objective function: 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.

8. The method for risk assessment and defense control of a power system according to any one of claims 5 or 7, characterized in that: The model has the following constraints: (1) Power balance constraints: (2) Thermal power operation constraints: 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 of the start and stop state of the unit respectively; (3) Energy storage operation constraints: P ess,t =P D,t -P C,t 0≤P C,t ≤μ C,t P C,max 0≤P D,t ≤μ D,t P D,max E ess,t+1 =E ess,t +n C P C,t -P D,t / or D m C,t +m D,t ≤1 AND ess,min ≤E ess,t ≤E ess,max AND ess,1 =And ess,T 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 charging and discharging states of the energy storage at time t; P C,max , P D,max They are the maximum charging and discharging power limits of energy storage respectively; 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; (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 up / down regulation demand of the system; (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: The upward regulation 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; (7) Flow safety constraints: 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.

9. A power system risk situation assessment and defense control method according to claim 6, characterized in that: The grid online operation secondary risk pre-control model takes the minimum sum of the start-up and shutdown and output costs of the units, the costs of new energy and load abandonment, the system backup costs, the energy storage dispatching costs and the low-frequency load reduction costs within the online dispatching cycle as the optimization goal, and sets the objective function: Where: is the low-frequency load reduction cost of the system at time t; shd is the system's low-frequency load reduction penalty coefficient; is the total under-frequency load reduction of the system at time t.

10. A power system risk situation assessment and defense control method according to claim 9, 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: 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 of the start and stop state of the unit respectively; (3) Energy storage operation constraints: P ess,t =P D,t -P C,t 0≤P C,t ≤μ C,t P C,max 0≤P D,t ≤μ D,t P D,max E ess,t+1 =E ess,t +n C P C,t -P D,t / or D m C,t +m D,t ≤1 AND ess,min ≤E ess,t ≤E ess,max AND ess,1 =And ess,T 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 charging and discharging states of the energy storage at time t; P C,max , P D,max They are the maximum charging and discharging power limits of energy storage respectively; 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; (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 up / down regulation demand of the system; (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: The upward regulation 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; (7) Flow safety constraints: 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.

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