Frequency safety scheduling method considering standby mutual aid of interconnected power grids

Abstract

The invention discloses a frequency safety scheduling method considering standby mutual aid of an interconnected power grid, which comprises the following steps of: firstly, realizing coordination mutual aid of flexible standby resources and secondary frequency modulation standby resources among regions by delimiting a power imbalance risk operation boundary of the interconnected power grid and dividing an adjusting space of a connecting line; and establishing an active frequency safety day-ahead scheduling model of the interconnected power grid by taking the safe and economic operation cost of the interconnected power grid as a target, and realizing power balance and frequency safety cooperative scheduling of the interconnected power grid. The method can solve the problems of space-time mutual aid of peak and frequency modulation resources of the interconnected power grid and low frequency safety level, can give consideration to the safety and economical efficiency of system operation, effectively resists the risk of power imbalance of the power grid, has important significance and reference value for frequency safety scheduling research of the interconnected power grid, and has engineering application value.

Description

Technical Field

[0001] The present invention relates to a frequency safety dispatching method for a power grid, and in particular to a frequency safety dispatching method considering the backup mutual assistance of interconnected power grids, and belongs to the field of power systems. Background Art

[0002] In recent years, renewable energy has gradually become the main installed capacity of the power system. The randomness and volatility of renewable energy output make it more difficult to balance the power of the system. The replacement of a large number of synchronous units has led to a significant reduction in the system's rotational inertia, a weakening of the frequency regulation capability, and an increasingly prominent problem of frequency safety and stability. In addition, ultra-high voltage direct current (HVDC) has developed rapidly, and regional interconnection and mutual supply through direct current has become a development trend of large power grids. The HVDC connection form causes the rotational inertia of different regions to be isolated from each other, and the overall frequency dynamic response capability of the system is further weakened. How to resist the risk of power imbalance in the power grid and achieve the coordination and mutual assistance of regulation resources in different regions is a key issue facing the safe operation and control of the interconnected power grid.

[0003] The key to the power balance of interconnected power grids is to make full use of the regulation resources at the sending and receiving ends, coordinately deal with the uncertainty of power grid sources and loads, and promote the cross-regional consumption of wind and solar energy. The common optimization idea of ​​interconnected power grid reserve is to evaluate and quantify the risk of source and load abandonment of the system, and deal with multiple uncertain factors in the decision-making process, with the goal of improving the economic benefits of system operation, and realize the joint optimization of power energy and reserve capacity of power grids in different regions. The research on the mutual assistance of frequency regulation resources and frequency safety issues among multiple regions is not sufficient. There is an unclear mechanism of mutual assistance and balance in time and space of interconnected power grids, lack of a coordinated dispatching model for power balance and frequency safety, and insufficient ability to cope with the complex operation mode of coupled and intertwined peak and frequency regulation demands. Summary of the invention

[0004] In order to solve the shortcomings of the above-mentioned technology, the present invention provides a frequency safety dispatching method taking into account the mutual assistance of interconnected power grid reserves, so as to improve the shortcomings of the existing frequency safety dispatching method of interconnected power grids, realize the coordinated mutual assistance of inter-regional flexible reserve and secondary frequency regulation reserve resources, thereby improving the peak-shaving and frequency regulation capabilities and economy of the interconnected power grid, and improving the system's ability to cope with power imbalance risks.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a frequency safety scheduling method taking into account the mutual assistance of interconnected power grid reserves. First, by defining the power imbalance risk operation boundary of the interconnected power grid and dividing the adjustment space of the interconnection line, the coordination and mutual assistance of inter-regional flexible reserve and secondary frequency regulation reserve resources are realized. Then, with the safe and economical operation cost of the interconnected power grid as the goal, an active frequency safety day-ahead scheduling model of the interconnected power grid is established to realize the coordinated scheduling of power balance and frequency safety of the interconnected power grid.

[0006] Preferably, the method is: considering the active frequency disturbance risk of the interconnected power grid, under the dual constraints of safety and economy, by reasonably arranging and adjusting the operation mode of power supply, wind and solar power supply, load, and DC tie line, a safe and economical operation mode of the interconnected power grid is obtained;

[0007] Among them, the active frequency disturbance risk of the interconnected power grid is: in the worst disturbance mode, transient disturbances occur in areas with large transient power shocks;

[0008] Safety constraints include sufficient steady-state flexible peak-shaving capacity, transient system frequency within the limit, sufficient secondary frequency regulation reserve, and operational regulation capacity limit of DC tie lines;

[0009] Economic feasibility requires consideration of the entire dispatch cycle: wind and solar energy abandonment costs, load limit costs, power supply start and stop costs, standby costs, and minimum power generation costs.

[0010] Preferably, taking the superimposed risks faced by the interconnected power grid as disturbance constraints, an operation constraint set including DC tie line safety constraints, active frequency safety constraints, and interconnected power grid safety operation constraints is established;

[0011] Among them, DC tie line safety constraints include: DC tie line power plan value constraint, DC tie line output adjustment rate constraint, DC tie line power unidirectional adjustment constraint, DC tie line power adjustment time constraint, DC tie line power adjustment number constraint, DC tie line mutual assistance capacity constraint;

[0012] Active frequency safety constraints include: steady-state peak load regulation constraints, frequency minimum point constraints, frequency change rate constraints, quasi-steady-state frequency deviation constraints, quasi-steady-state frequency recovery constraints, and unit standby split constraints;

[0013] The safe operation constraints of the interconnected power grid include power balance constraints, power flow safety constraints, and unit operation constraints;

[0014] Two regional power grids A and B based on DC interconnection are defined, where region A is the sending-end power grid and region B is the receiving-end power grid, and regions A and B adopt the same constraints.

[0015] Preferably, the DC tie line safety constraints include:

[0016] a. Constraints on the planned power value of the DC tie line: The power transmitted by the tie line cannot exceed its limit, that is:

[0017] 0≤P DC,t ≤P DC,max (1)

[0018] Where: P DC,maxP is the maximum limit of the power transmitted by the DC interconnection line; DC,t is the power transmitted from region A to region B through the DC interconnection line at time t;

[0019] b. DC tie line output adjustment rate constraint: The power adjustment rate of the tie line cannot exceed its limit, that is:

[0020]

[0021] Where: P DC,t-1 is the power transmitted from region A to region B through the DC tie line at time t-1; ΔP DC,max It is the maximum limit of the upward and downward adjustment rate of the DC tie line; They are the state variables of the DC tie line at time t, which are adjusted upward or downward, and are 1 if adjusted, and 0 if not adjusted;

[0022] c. Constraints on unidirectional adjustment of DC tie line power: The tie line cannot adjust power upward or downward at the same time during the same period, that is:

[0023]

[0024] Preferably, the DC tie line safety constraints further include:

[0025] d. Time constraint for DC tie line power adjustment: After the tie line power is adjusted, it can be maintained for at least one period of time, that is:

[0026]

[0027] Where: T DC The minimum stable time after the DC interconnection line transmission power is adjusted; They are the state variables of the DC tie line upward and downward adjustment at time m, which are 1 for adjustment and 0 for non-adjustment;

[0028] e. Constraints on the number of DC tie line power adjustments: The number of tie line power adjustments cannot exceed the limit, that is:

[0029]

[0030] Where: N DC,max is the maximum number of adjustments of the DC tie line within the dispatching period;

[0031] f. DC tie-line mutual assistance capacity constraints: The flexibility mutual assistance of the tie-line and the secondary frequency mutual assistance need to be subject to the constraints of the tie-line transmission power, power adjustment and maximum transmission capacity at this moment, namely:

[0032] When area A is disturbed:

[0033]

[0034] When area B is disturbed:

[0035]

[0036] Where: They are the upward flexibility reserve and secondary frequency reserve provided by unit i in region A to region B at time t; N are the upward flexibility reserve and secondary frequency reserve provided by unit j in region B to region A at time t; A 、N B are the numbers of thermal power units in area A and area B respectively.

[0037] Preferably, the active frequency safety constraints include:

[0038] a. Steady-state peak load constraint: For a single regional power grid, the sum of its own reserved flexibility reserve and the flexibility reserve obtained from adjacent regions should not be less than its own peak load demand, that is:

[0039]

[0040] Where: They are the upward and downward flexibility demands of region A at time t, which can be obtained through the net load forecast curve under a certain confidence setting; They are the upward flexibility reserve and downward flexibility reserve provided by unit i in region A at time t respectively;

[0041] b. Frequency minimum point constraint: After a single regional power grid suffers a transient shock, the frequency cannot drop too far, that is:

[0042]

[0043] Where: The primary frequency regulation reserve provided for unit i in region A at time t; is the load adjustment factor of area A; is the load power of area A at time t; is the maximum deviation limit of the frequency in area A; is the initial operating frequency of region A; is the transient shock suffered by area A at time t;

[0044] c. Frequency change rate constraint: After a single regional power grid suffers a transient shock, the frequency cannot drop too fast, that is:

[0045]

[0046] Where: is the kinetic energy of unit i in region A; is the start / stop state variable of unit i in region A at time t, with 1 for start and 0 for stop; is the maximum frequency change rate of region A; η A is the proportion of motor load in area A; is the uniform inertia time constant of the motor load in region A.

[0047] Preferably, the active frequency safety constraint further includes:

[0048] d. Quasi-steady-state frequency deviation constraint: Consider the system's long-period low-frequency operation capability limitation, that is:

[0049]

[0050] Where: is the system frequency deviation of region A; is the system frequency deviation limit of area A;

[0051] e. Quasi-steady-state frequency recovery constraint: The sum of the primary frequency regulation reserve and secondary frequency regulation reserve reserved by the units in the region and the secondary frequency regulation reserve obtained from the adjacent regions should not be less than the maximum transient impact suffered by the system, that is:

[0052]

[0053] Where: Secondary frequency regulation reserve provided for unit i in region A at time t; is the maximum transient impact suffered by the interconnected power grid as a whole at time t;

[0054] f. Unit reserve division constraint: For a single unit, the primary frequency regulation reserve, secondary frequency regulation reserve and flexibility reserve reserved in the region, as well as the flexibility reserve and secondary frequency regulation reserve supported to the adjacent region, jointly divide the total hot reserve of the unit, that is:

[0055]

[0056] Preferably, the interconnected power grid safe operation constraints include:

[0057] a. Power balance constraint: The sum of the unit's power generation, new energy grid-connected power and tie-line power should be equal to the load grid-connected power, that is:

[0058]

[0059] Where: are the power of unit i, wind power, photovoltaic power and load in region A at time t, are the total wind curtailment, solar curtailment and load shedding in area A at time t respectively;

[0060] b. Power flow safety constraint: The power flow of the line is calculated using the power flow transfer factor. The power flow of the line should not be greater than the power transmission limit of the line;

[0061]

[0062] Where: They are the power flow transfer factors of unit i, wind power, photovoltaic, load and DC system in region A respectively; is the power transmission limit of the line in area A.

[0063] Preferably, the interconnected power grid safe operation constraints also include:

[0064] c. Unit operation constraints: The units in both regions need to meet the maximum and minimum output constraints, ramp constraints, and start-stop constraints, namely:

[0065]

[0066] Where: are the maximum technical output and minimum technical output of unit i in region A respectively; are the maximum upward and downward climbing capabilities of unit i in region A, respectively; are the minimum start and stop time of unit i in area A; t_{on} A , t_{off} A They are respectively the sets of corresponding times of the start and stop status of the units in area A.

[0067] They are the unit status of area A at the corresponding time of the start and stop status of the unit.

[0068] Preferably, a day-ahead dispatch model for active frequency security of the interconnected power grid is established, that is, the objective function is to minimize the sum of the power generation and start-up and shutdown costs of the units in the region, the costs of new energy and load abandonment, the reserve costs reserved by the units in the region, and the reserve costs for supporting outside the region, that is:

[0069] min(f A +f B ) (twenty two)

[0070] Among them, f A 、f B All of them are as follows:

[0071]

[0072] Where: f A 、f BC is the sum of the power generation and start-up and shutdown costs of the units in regions A and B, the costs of new energy and load abandonment, the reserve costs reserved by the units in the region, and the reserve costs for supporting outside the region; t,g is the sum of the power generation and start-up and shutdown costs of all units in the area at time t; C i (P g,i,t ) is the power generation cost of unit i in the region at time t; C i,t,UD is the start-up and shutdown cost of unit i in the region at time t; C t,w,curt , C t,v,curt , C t,d,curt are the total wind curtailment, solar curtailment and load shedding costs in the region at time t; δ w,curt ,δ v,curt ,δ d,curt are the penalty coefficients for wind abandonment, solar abandonment and load shedding in the area respectively; C t,up , C t,dn are the total upward and downward flexible reserve costs in the region at time t; X g,up , X g,dn are the flexible reserve cost coefficients for the units in the region, respectively; C t,PFR , C t,SFR are the total primary and secondary frequency regulation reserve costs in the area at time t; X g,PFR , X g,SFR are the primary and secondary frequency regulation standby cost coefficients of the units in the area; F sos,i,t,dn is the flexible reserve for the unit i in any region to support another region at time t; T is the dispatching period; C t,curt is the cost of abandoning new energy and load in the area at time t.

[0073] The present invention proposes a coordinated dispatching method that takes into account both the power balance and frequency safety of the interconnected power grid, explains the peak-shaving and frequency regulation process and safety constraints of the interconnected power grid, analyzes the combined mode of steady-state peak-shaving and transient impact disturbance faced by the interconnected power grid, and defines the power imbalance risk operation boundary of the interconnected power grid. By dividing the adjustment space of the interconnection line, the coordination and mutual assistance of inter-regional flexible reserve and secondary frequency regulation reserve resources are achieved. With the goal of safe and economical operation of the interconnected power grid, an active frequency safety day-ahead dispatching model of the interconnected power grid is established to achieve coordinated dispatching of power balance and frequency safety of the interconnected power grid. The dispatching model can solve the problems of temporal and spatial mutual assistance of peak-shaving and frequency regulation resources and low frequency safety level of the interconnected power grid, can take into account the safety and economy of system operation, and effectively resist the power imbalance risk of the power grid. It has important significance and reference value for the study of frequency safety dispatching of the interconnected power grid, and has engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1A schematic diagram of the mutual assistance between the flexible peak-shaving resources and the secondary frequency regulation resources of the DC interconnected power grid of the present invention;

[0075] Figure 2 A frequency dynamic response process diagram of the interconnected power grid of the present invention;

[0076] Figure 3 It is a framework diagram of the safe operation mode of the present invention;

[0077] Figure 4 The prediction curves of new energy and load for the comparative example of the present invention are as follows: (left) wind-solar-load prediction curve for area A; (right) wind-solar-load prediction curve for area B;

[0078] Figure 5 A schematic diagram of the mutual aid quantity of the tie line according to an embodiment of the present invention;

[0079] Figure 6 Schematic diagram of multiple types of spare capacity according to an embodiment of the present invention: (left) multiple types of spare capacity reserved in area A, (right) multiple types of spare capacity reserved in area B;

[0080] Figure 7 Comparison diagrams of reserve amounts in accordance with an embodiment of the present invention: (upper left) comparison diagram of reserve amount for upward adjustment flexibility in area A, (upper right) comparison diagram of reserve amount for upward adjustment flexibility in area B, (lower left) comparison diagram of reserve amount for downward adjustment flexibility in area A, (lower right) comparison diagram of reserve amount for downward adjustment flexibility in area B;

[0081] Figure 8 These are comparison diagrams of the reserve amounts in the embodiments of the present invention: (left) comparison diagram of the reserve amount for frequency modulation in area A once, (right) comparison diagram of the reserve amount for frequency modulation in area B once, and (bottom) comparison diagram of the reserve amount for frequency modulation in area A twice. DETAILED DESCRIPTION

[0082] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0083] The present invention proposes a coordinated dispatching method for the frequency of interconnected power grids that takes into account both flexible peak regulation and safe frequency regulation. Based on the active frequency mutual assistance regulation process of the DC interconnected power grid, the safety constraints and disturbance modes of the entire process of peak regulation and frequency regulation are analyzed. Taking the superimposed risks faced by the interconnected power grid as the disturbance constraint, an idea for obtaining the safe operation mode of active frequency is proposed, and an operation constraint set including DC interconnection line constraints and active frequency safety constraints is established. On this basis, with the goal of safe and economical operation, a coordinated dispatching model of power balance and frequency safety of the DC interconnected power grid is constructed to achieve inter-regional coordination and mutual assistance of regulation resources and improve the level of safe and economical operation of the system. Compared with the traditional dispatching mode, the present invention has obvious advantages.

[0084] The specific steps include:

[0085] 1) Analysis of the active frequency regulation process of interconnected power grid

[0086] Interconnected power grids can achieve regional mutual assistance in regulating resources through tie lines, improve the reliability and flexibility of power supply, and reduce operating costs. Figure 1 As shown, it can realize the mutual assistance of flexible peak-shaving resources and secondary frequency regulation resources within and between regions through the automatic generation control (AGC) system, but it cannot realize the sharing of inertia and primary frequency regulation resources.

[0087] The active frequency regulation process in area A is as follows: Figure 2 As shown, P H Indicates the planned value of the DC interconnection power, ΔP H Indicates the unplanned support power of DC.

[0088] When steady-state flexible peak-shaving demand appears in region A during the period t1-t2, the power shortage causes the system frequency to show a downward trend. Under the regulation of the AGC system, the regulating power supply in region A increases power, while region B provides flexible peak-shaving support through the DC interconnection line, and the two regions jointly maintain the power balance of the system. In the steady-state stage, any region of the interconnected power grid must meet the steady-state peak-shaving demand, that is, the total amount of flexible regulation reserve within the region and flexible regulation support outside the region should not be less than the flexible peak-shaving demand of the region.

[0089] When a transient power shock occurs in region A during the period t3 to t5, since the DC interconnection line cannot be adjusted quickly, region A needs to rely on the system inertia and primary frequency regulation resources in this region to adjust the transient frequency to prevent the frequency from falling too fast or too deep. In the transient stage, when a transient N-1 fault occurs in any region, this region needs to have sufficient inertia backup and primary frequency regulation backup to ensure that the three frequency safety constraint indicators of the lowest frequency of transient (LFoT), rate of change of frequency (RoCoF) and frequency deviation of quasi-stable state (FDoQS) do not exceed the limit.

[0090] When the system completes the primary frequency modulation at time t5, region A enters the quasi-steady-state frequency recovery stage, and the secondary frequency modulation resources of region A and region B work together to restore the frequency of region A to the steady-state initial value. Among them, region B provides flexible peak regulation and secondary frequency modulation support to region A through DC interconnection lines, so its regulation capability is also constrained by DC operation requirements. In the quasi-steady-state stage, the system should have sufficient secondary frequency modulation resources after completing the primary frequency modulation to ensure that the system can be restored to the initial frequency, that is, the total amount of primary frequency modulation standby, secondary frequency modulation standby and secondary frequency modulation support outside the region should not be less than the transient power impact of the region. In addition, the DC interconnection lines have operational constraints in terms of transmission power, regulation rate, regulation time, and number of adjustments, which will also limit the mutual assistance capabilities between regions.

[0091] 2) Disturbance pattern analysis

[0092] The power disturbance of the power grid includes two types: steady-state peak-shaving disturbance and transient impact disturbance. For the interconnected power grid, it should meet the flexible and sufficient requirements and transient N-1 stability constraints. The safe and reliable operation mode must be able to cope with the following types of power disturbance modes: a. A single type of power disturbance occurs in any area; b. Two types of power disturbances occur in any area; c. Power disturbances occur in two areas at the same time, both of which are steady-state peak-shaving disturbances; d. Power disturbances occur in two areas at the same time, which are steady-state peak-shaving disturbances and transient impact disturbances respectively; e. Peak-shaving disturbances occur in two areas at the same time, and transient impact disturbances occur in any area. Among them, the expected disturbance risk of disturbance mode e is the largest, so this mode is used as the active frequency safety constraint condition of the interconnected power grid.

[0093] 3) Acquisition of safe and economical operation modes

[0094] like Figure 3 As shown in the figure, considering the risk of system active frequency disturbance, under the dual constraints of safety and economy, the operation mode of regulating power supply, wind and solar power supply, load and DC interconnection line can be reasonably arranged to obtain a safe and economical operation mode of the interconnected power grid.

[0095] Among them, the disturbance risk of the interconnected power grid should consider the worst disturbance mode, that is, under disturbance mode e, transient disturbances occur in areas with large transient power shocks. Safety constraints mainly include sufficient steady-state flexible peak-shaving capacity, no frequency limit in transient processes, sufficient secondary frequency regulation reserves, and operational regulation capacity limits of DC interconnection lines. Economic requirements mainly consider the cost of wind and solar renewable energy abandonment and load limit, the cost of regulating the start and stop of power sources, the reserve cost, and the minimum power generation cost during the entire dispatch cycle.

[0096] Example

[0097] Two interconnected IEEE39 node systems are used to establish a comparison ratio, defining area A as the sending-end power grid and area B as the receiving-end power grid. Each area contains 7 thermal power units, 1 aggregate equivalent photovoltaic power field, 1 aggregate equivalent wind power field, and 1 DC tie line. The prediction curve of the new energy and load of the comparison ratio is as follows: Figure 4 As shown, area A is connected to 960MW of wind power and 850MW of photovoltaic power, and area B is connected to 620MW of wind power and 520MW of photovoltaic power.

[0098] The scheduling results of the present invention are analyzed as follows:

[0099] The interconnected power grid should meet the flexible and sufficient requirements and the transient N-1 stability constraints. Taking the failure of area A under disturbance mode e as an example, the mutual assistance of the tie line and the multi-type reserve are obtained as follows: Figure 5-6 As shown:

[0100] Depend on Figure 5-6 It can be seen that under the model of the present invention, the upward regulation reserve of area A is divided and decoupled into three parts: flexibility reserve, primary frequency regulation reserve and secondary frequency regulation reserve; the upward regulation reserve of area B is divided and decoupled into two parts: flexibility reserve and primary frequency regulation reserve; and areas A and B can achieve regional mutual assistance of flexibility reserve and secondary frequency regulation reserve through the interconnection line. When the system suffers from power shock and faces power imbalance, the regulation resources in the region can be fully coordinated to deal with the superimposed operation risks.

[0101] Analysis of the advantages of standby mutual aid:

[0102] In order to verify the advantages of the model of the present invention in considering the mutual assistance of multiple types of reserve between regions, two grid operation modes are used to obtain the modes as shown in Table 1 for comparative analysis.

[0103] Table 1 Comparative example settings

[0104]

[0105] The cost composition under different scheduling modes is shown in Table 2:

[0106] Table 2 Comparison of different scheduling modes

[0107]

[0108] As shown in Table 2, compared with the comparative example, the system start-up and shutdown operation cost of the method adopted by the present invention decreased by 10.75%, the flexibility reserve cost decreased by 6.36%, the primary frequency regulation reserve cost decreased by 1.06%, the secondary frequency regulation reserve cost decreased by 5.69%, the abandonment cost decreased by 43.01%, and the total dispatch cost decreased by 10.18%. This is because the comparative example cannot solve the peak-shaving and frequency regulation needs of the system through inter-regional reserve mutual assistance, and can only increase the number of startups to obtain sufficient regulation space, resulting in increased unit start-up and shutdown operation costs, increased reserve reserve costs, and increased wind and solar energy abandonment costs, and the economic efficiency of system operation deteriorates.

[0109] Comparison of the reserve amount under the two operation modes of the scheduling method of the present invention and the comparative example Figure 7 , Figure 8 As shown: the multi-type reserve capacity reserved by the method of the present invention and the comparative example can meet the multi-type reserve requirements of the system in all time periods. The upward adjustment flexibility reserve analysis of area A is as follows: Figure 7 As shown in (upper left), the method of the present invention reduces the reserve by 7.83% compared with the comparative example; the analysis of the upward flexibility reserve of region B is as follows Figure 7 As shown in (upper right), the method of the present invention reduces the reserved area by 13.39% compared with the comparative example; the down-regulation flexibility reserve analysis of region A is shown in Figure 7 As shown in (lower left), the method of the present invention reduces the reserve by 5.11% compared with the comparative example; the downward adjustment flexibility reserve analysis of region B is as follows Figure 7 As shown in (lower right), the method of the present invention reduces the reserved area by 6.57% compared with the comparative example; the primary frequency modulation reserve analysis of area A is as follows Figure 8 As shown in (left), the method of the present invention reduces the reserved space by 1.09% compared with the comparative example. The primary frequency modulation reserve analysis of area B is shown in Figure 8 (right) shows that the method of the present invention reduces the reserved area by 0.78% compared with the comparative example; the secondary frequency modulation reserve analysis of area A is as follows Figure 8 As shown in (below), the method of the present invention reduces the reservation by 6.47% compared with the comparative example. It can be seen that the method of the present invention reduces the multi-type standby reservation compared with the comparative example, saves the standby reservation cost, and improves the economy of system operation under the premise of ensuring the safe operation of the system.

[0110] In summary, the dispatching mode proposed in the present invention can solve the active frequency safety problem caused by insufficient regulation resources, and can realize the accurate characterization of the safe operation boundary of the power grid. The proposed method of dividing the interconnection line regulation space can realize the accurate mutual assistance of inter-regional flexible reserve and secondary frequency regulation reserve resources, and can effectively resist the power imbalance risk of the interconnected power grid. It can take into account the safety of system operation while realizing the improvement of the economic efficiency of system operation, and has obvious advantages over many other dispatching modes.

[0111] The above implementation modes are not limitations of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the scope of the technical solution of the present invention also belong to the protection scope of the present invention.

Claims

1. A frequency security dispatching method considering the mutual assistance of reserve in interconnected power grids, characterized by: Firstly, by defining the power imbalance risk operation boundary of the interconnected power grid and dividing the regulation space of the interconnection line, the coordination and mutual assistance of the flexible reserve and secondary frequency regulation reserve resources between regions can be achieved. Then, with the safe and economical operation cost of the interconnected power grid as the goal, a day-ahead scheduling model of active frequency security of the interconnected power grid is established to realize the coordinated scheduling of power balance and frequency security of the interconnected power grid.

2. The frequency security dispatching method considering the interconnected power grid backup mutual assistance according to claim 1 is characterized by: The method is as follows: considering the active frequency disturbance risk of the interconnected power grid, under the dual constraints of safety and economy, by reasonably arranging and adjusting the operation mode of power supply, wind and solar power supply, load, and DC interconnection line, a safe and economical operation mode of the interconnected power grid is obtained; Among them, the active frequency disturbance risk of the interconnected power grid is: under the worst disturbance mode, transient disturbances occur in areas with large transient power shocks; Safety constraints include sufficient steady-state flexible peak-shaving capacity, transient system frequency within the limit, sufficient secondary frequency regulation reserve, and operational regulation capacity limit of DC tie lines; Economic feasibility requires consideration of the entire dispatching cycle: wind and solar energy abandonment costs, load limit costs, power supply start and stop costs, standby costs, and minimum power generation costs.

3. The frequency safety dispatching method considering the interconnected power grid backup mutual assistance according to claim 2 is characterized by: Taking the superimposed risks faced by the interconnected power grid as disturbance constraints, an operation constraint set including DC tie line safety constraints, active frequency safety constraints, and interconnected power grid safety operation constraints is established; Among them, DC tie line safety constraints include: DC tie line power plan value constraint, DC tie line output adjustment rate constraint, DC tie line power unidirectional adjustment constraint, DC tie line power adjustment time constraint, DC tie line power adjustment number constraint, DC tie line mutual assistance capacity constraint; Active frequency safety constraints include: steady-state peak load regulation constraints, frequency minimum point constraints, frequency change rate constraints, quasi-steady-state frequency deviation constraints, quasi-steady-state frequency recovery constraints, and unit standby split constraints; The safe operation constraints of the interconnected power grid include power balance constraints, power flow safety constraints, and unit operation constraints; Two regional power grids A and B based on DC interconnection are defined, where region A is the sending-end power grid and region B is the receiving-end power grid, and regions A and B adopt the same constraints.

4. The frequency security dispatching method considering the interconnected power grid backup mutual assistance according to claim 3 is characterized by: DC tie line safety constraints include: a. Constraints on the planned power value of the DC tie line: The power transmitted by the tie line cannot exceed its limit, that is: 0≤P DC,t ≤P DC,max (1) Where: P DC,max P is the maximum limit of the power transmitted by the DC interconnection line; DC,t is the power transmitted from region A to region B through the DC interconnection line at time t; b. DC tie line output adjustment rate constraint: The power adjustment rate of the tie line cannot exceed its limit, that is: Where: P DC,t-1 is the power transmitted from region A to region B through the DC tie line at time t-1; ΔP DC,max It is the maximum limit of the upward and downward adjustment rate of the DC tie line; They are the state variables of the DC tie line at time t, which are adjusted upward or downward, and are 1 if adjusted, and 0 if not adjusted; c. Constraints on unidirectional adjustment of DC tie line power: The tie line cannot adjust power upward or downward at the same time during the same period, that is:

5. The frequency security dispatching method considering the interconnected power grid reserve mutual assistance according to claim 4 is characterized in that: DC tie line safety constraints also include: d. Time constraint for DC tie line power adjustment: After the tie line power is adjusted, it can be maintained for at least one period of time, that is: Where: T DC The minimum stable time after the DC interconnection line transmission power is adjusted; They are the state variables of the DC tie line upward and downward adjustment at time m, which are 1 for adjustment and 0 for non-adjustment; e. Constraints on the number of DC tie line power adjustments: The number of tie line power adjustments cannot exceed the limit, that is: Where: N DC,max is the maximum number of adjustments of the DC tie line within the dispatching period; f. DC tie-line mutual assistance capacity constraints: The flexibility mutual assistance of the tie-line and the secondary frequency mutual assistance need to be subject to the constraints of the tie-line transmission power, power adjustment and maximum transmission capacity at this moment, namely: When area A is disturbed: When area B is disturbed: Where: They are the upward flexibility reserve and secondary frequency reserve provided by unit i in region A to region B at time t; N are the upward flexibility reserve and secondary frequency reserve provided by unit j in region B to region A at time t; A 、N B are the numbers of thermal power units in area A and area B respectively.

6. The frequency security dispatching method considering the interconnected power grid backup mutual assistance according to claim 3 is characterized by: Active frequency security constraints include: a. Steady-state peak load constraint: For a single regional power grid, the sum of its own reserved flexibility reserve and the flexibility reserve obtained from adjacent regions should not be less than its own peak load demand, that is: Where: They are the upward and downward flexibility demands of region A at time t, which can be obtained through the net load forecast curve under a certain confidence setting; They are the upward flexibility reserve and downward flexibility reserve provided by unit i in region A at time t respectively; b. Frequency minimum point constraint: After a single regional power grid suffers a transient shock, the frequency cannot drop too far, that is: Where: The primary frequency regulation reserve provided for unit i in region A at time t; is the load adjustment factor of area A; is the load power of area A at time t; is the maximum deviation limit of the frequency in area A; is the initial operating frequency of region A; is the transient shock suffered by area A at time t; c. Frequency change rate constraint: After a single regional power grid suffers a transient shock, the frequency cannot drop too fast, that is: Where: is the kinetic energy of unit i in region A; is the start / stop state variable of unit i in region A at time t, with 1 for start and 0 for stop; is the maximum frequency change rate of region A; η A is the proportion of motor load in area A; is the uniform inertia time constant of the motor load in region A.

7. The frequency safety dispatching method considering the backup mutual assistance of interconnected power grids according to claim 6 is characterized in that: Active frequency security constraints also include: d. Quasi-steady-state frequency deviation constraint: Consider the system's long-period low-frequency operation capability limitation, that is: Where: is the system frequency deviation of region A; is the system frequency deviation limit of area A; e. Quasi-steady-state frequency recovery constraint: The sum of the primary frequency regulation reserve and secondary frequency regulation reserve reserved by the units in the region and the secondary frequency regulation reserve obtained from the adjacent regions should not be less than the maximum transient impact suffered by the system, that is: Where: Secondary frequency regulation reserve provided for unit i in region A at time t; is the maximum transient impact suffered by the interconnected power grid as a whole at time t; f. Unit reserve division constraint: For a single unit, the primary frequency regulation reserve, secondary frequency regulation reserve and flexibility reserve reserved in the region, as well as the flexibility reserve and secondary frequency regulation reserve supported to the adjacent region, jointly divide the total hot reserve of the unit, that is:

8. The frequency security dispatching method considering the interconnected power grid backup mutual assistance according to claim 3 is characterized by: The constraints for safe operation of interconnected power grids include: a. Power balance constraint: The sum of the unit's power generation, new energy grid-connected power and tie-line power should be equal to the load grid-connected power, that is: Where: are the power of unit i, wind power, photovoltaic power and load in region A at time t, are the total wind curtailment, solar curtailment and load shedding in area A at time t respectively; b. Power flow safety constraint: The power flow transfer factor is used to calculate the line power flow. The line power flow should not be greater than the power transmission limit of the line, that is; Where: They are the power flow transfer factors of unit i, wind power, photovoltaic, load and DC system in region A respectively; is the power transmission limit of the line in area A.

9. The frequency safety dispatching method considering the interconnected power grid backup mutual assistance according to claim 8 is characterized in that: The safe operation constraints of the interconnected power grid also include: c. Unit operation constraints: The units in both regions need to meet the maximum and minimum output constraints, ramp constraints, and start-stop constraints, namely: Where: are the maximum technical output and minimum technical output of unit i in region A respectively; are the maximum upward and downward climbing capabilities of unit i in region A, respectively; are the minimum start and stop time of unit i in area A; t_{on} A , t_{off} A are the sets of corresponding times of the start and stop states of the units in area A, They are the unit status of area A at the corresponding time of the start and stop status of the unit.

10. The frequency security dispatching method considering the backup mutual assistance of interconnected power grids according to claim 3 is characterized in that: The active frequency security day-ahead dispatch model of the interconnected power grid is established, that is, the objective function is to minimize the sum of the power generation and start-up and shutdown costs of the units in the region, the costs of new energy and load abandonment, the reserve costs reserved by the units in the region, and the reserve costs supported outside the region, that is: min(f A +f B ) (22) Among them, f A 、f B All of them are as follows: Where: f A 、f B C is the sum of the power generation and start-up and shutdown costs of the units in regions A and B, the costs of new energy and load abandonment, the reserve costs reserved by the units in the region, and the reserve costs for supporting outside the region; t,g is the sum of the power generation and start-up and shutdown costs of all units in the area at time t; C i (P g,i,t ) is the power generation cost of unit i in the region at time t; C i,t,UD is the start-up and shutdown cost of unit i in the region at time t; C t,w,curt , C t,v,curt , C t,d,curt are the total wind curtailment, solar curtailment and load shedding costs in the region at time t; δ w,curt , δ v,curt , δ d,curt are the penalty coefficients for wind abandonment, solar abandonment and load shedding in the area respectively; C t,up , C t,dn are the total upward and downward flexible reserve costs in the region at time t; X g,up , X g,dn are the flexible reserve cost coefficients for the units in the region, respectively; C t,PFR , C t,SFR are the total primary and secondary frequency regulation reserve costs in the area at time t; X g,PFR , X g,SFR are the primary and secondary frequency regulation standby cost coefficients of the units in the area; F sos,i,t,dn is the flexible reserve for the unit i in any region to support another region at time t; T is the dispatching period; C t,curt is the cost of abandoning new energy and load in the area at time t.

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